Comprehensive decoding of aging pathway: mitochondrial dysfunction as the primary cause of aging leading to sustained collapse of bodily functions hypothesis
Abstract
Aging is a complex, multifactorial process that has eluded a unified explanatory framework. Here, we propose a novel integrative hypothesis positioning mitochondrial dysfunction as the primary driver of aging, orchestrating downstream processes across four regulatory axes—metabolic, inflammatory, hormonal, and epigenetic. This “four-axis model” provides a structured representation of 81 potential combinatorial states, capturing the diversity of aging phenotypes observed in humans. Our framework reconciles existing theories of aging, including cellular senescence, chronic inflammation, metabolic dysregulation, and epigenetic drift, by situating them as downstream manifestations of core mitochondrial decline. Importantly, the model suggests that deviations from balanced axis states can act as initiating events, providing mechanistic insight into the heterogeneity of age-related diseases. By integrating empirical evidence with a systems-level perspective, this hypothesis offers testable predictions and a conceptual foundation for targeted interventions aimed at delaying or mitigating aging. Although primarily theoretical, the model is intended to stimulate experimental exploration and foster a more unified understanding of aging biology.
1 Introduction: Definition of the first cause of aging: decreased mitochondrial functionality
1.1 Limitations of existing decay theories
In the field of life sciences, the mechanism of decline has always been the core and difficulty of research.
Although the mainstream scientific community has proposed various theories of aging, including telomere shortening, genomic instability, epigenetic changes, protein homeostasis imbalance, nutrient sensing imbalance, cell senescence, cell exhaustion, and chronic inflammation, most of these theories focus on specific phenomena or downstream pathways in the aging process and fail to fundamentally define the "first cause" that leads to this series of chain reactions.[1]
These theories describe the different branches of a large tree, but fail to indicate their common root system.For example, the classic theory of mitochondrial decay suggests that the accumulation of mutations in mitochondrial DNA (mtDNA) is the main cause of mitochondrial dysfunction and cellular energy crisis, which in turn drives decay.
However, this theoretical aspect is facing increasing challenges.Studies have shown that the observed decline in mitochondrial respiratory function during aging may not be due to the accumulation of mtDNA mutations, but rather to epigenetic changes in the expression of mitochondrial related genes encoded by nuclear genes.This discovery shakes the foundation of traditional mitochondrial decay theory and suggests deeper regulatory mechanisms at work.
Therefore, a core challenge in the current field of decline research is how to go beyond these isolated, descriptive theoretical frameworks and construct a comprehensive model that can integrate multiple decline markers and elucidate their underlying causal relationships.This article aims to propose a novel approach that defines mitochondrial functional decline as the "first cause" of decline, and systematically analyzes how it ultimately leads to systemic decline in the body through a series of cascading reactions.
1.2 Core argument: Mitochondrial functional decline is the intrinsic driving starting point of aging
The core argument of this article is that mitochondrial dysfunction is the fundamental and intrinsic driving factor behind the entire aging process.This argument does not negate the importance of other mechanisms of decline, but rather reposition them.We believe that mitochondria are not just passive victims of decay, but active initiators.The decline in mitochondrial function, as the starting point of the decay process, activates and amplifies a series of subsequent decay related pathways through its central role as a cellular energy worker and signaling center.This viewpoint has been strongly supported by recent research.For example, a study published in Scienti cReports found that age-related mitochondrial respiratory defects could be completely reversed by reprogramming fibroblasts from elderly individuals into induced pluripotent stem cells (iPSCs), restoring them to levels comparable to fetal fibroblasts.
This shocking result indicates that the decay state of mitochondria is not determined by irreversible mtDNA mutations, but by dynamic and reversible epigenetic regulation.This provides key evidence for our argument that "mitochondrial functional decline is the primary cause": if the decay state of mitochondria can be "reset" by epigenetic reprogramming, then its functional decline must be an upstream and predictable key node in the entire decay chain.Therefore, I consider mitochondrial dysfunction as a "first intrinsic driving factor" that creates necessary pathological conditions for the emergence and development of all subsequent aging characteristics by affecting cellular energy metabolism, redox balance, and signal transduction.
This model defines mitochondrial functional decline as the 'first cause', rather than viewing mtDNA mutations as parallel or alternative drivers of aging. It explicitly states that mtDNA mutations themselves are downstream results of NRF1 mediated damage to mtDNA maintenance function.Therefore, functional decline is not only earlier than structural damage, but also a causal prerequisite for structural damage.
1.3 Definition and scope of mitochondrial functional decline
In order to accurately articulate our theory, a strict definition of 'mitochondrial functional decline' must be provided.In the framework of this article, mitochondrial functional decline refers to a decrease in the ability of mitochondria to perform nuclear biological functions while maintaining normal mitochondrial quantity and macroscopic structure (quality).
This definition is crucial as it shifts our focus from the physical existence (quantity and morphology) of mitochondria to the dynamic efficiency of their biochemical functions.This functional decline is manifested in multiple aspects, including but not limited to: decreased efficiency of oxidative phosphorylation (OXPHOS) leading to reduced ATP production;The imbalance between the production and clearance of reactive oxygen species (ROS) triggers oxidative stress;The ability to participate in key metabolic pathways such as fatty acid beta oxidation, amino acid metabolism, and tricarboxylic acid cycle (TCA cycle) is impaired;And the ability to regulate calcium ion homeostasis decreases.[2]
These subtle functional declines, although not immediately leading to cell death, disrupt the normal physiological rhythm of cells and activate a series of adaptive or pathological signaling pathways.
For example, a slight decrease in energy metabolism activates AMP activated protein kinase (AMPK), while sustained oxidative stress activates transcription factors such as nuclear factor E2 related factor 2 (NRF2).These initial compensatory responses, if present or regulated incorrectly during aging, will shift from protective mechanisms to driving forces that promote aging, thereby closely linking mitochondrial dysfunction as the "first cause" with subsequent aging phenotypes.
Conceptual Analysis
Epigenetic inertia: This hypothesis specifically refers to key genes such as PPAR α, whose expression levels are locked in a stable low-level state that is difficult to recover on their own after inhibition, and is a specific functional disorder pattern in early aging.
Epigenetic disorder: refers to the systematic and global loss of control of epigenetic modifications (such as DNA methylation) across the entire genome during the late stages of aging, caused by a lack of metabolic substrates (such as alpha ketoglutarate AKG).
2 Nuclear regulatory network with decreased mitochondrial functionality
2.1 Interaction between key genes and signaling pathways
The maintenance of mitochondrial function is not determined by a single gene or pathway, but by a complex and interconnected gene regulatory network.
1 The core members of this network include peroxisome proliferator activated receptor alpha (PPAR alpha), AMP activated protein kinase (AMPK), peroxisome proliferator activated receptor gamma co activation factor 1 alpha (PGC-1 alpha), and nuclear factor E2 related factors 1 and 2 (NRF1/NRF2).There are precise positive and negative feedback regulatory loops between these molecules, which together maintain the homeostasis of mitochondrial function.However, during the aging process, the balance of this network is disrupted, leading to a sexual decline in mitochondrial function.Understanding these key nodes and their interactions is the key to deciphering the decay path.
2.1.1 Expression function and role of peroxisome proliferator activated receptor alpha (PPAR alpha) gene.
Peroxisome proliferator activated receptor alpha (PPAR alpha) is a core transcription factor in cellular energy metabolism, whose core function is to coordinate two key metabolic pathways: fatty acid beta oxidation and tricarboxylic acid cycle.In the vast majority of somatic cells, the main role of PPAR α is to dominate the rhythm of the tricarboxylic acid cycle, ensuring that acetyl CoA derived from glucose, amino acids, and fatty acids can be efficiently and orderly oxidized to maintain basal ATP supply.In specific cells such as stem cells, myocardium, and skeletal muscle, PPAR α is endowed with a dual responsibility due to its special requirements for energy sources and efficiency: while regulating the tricarboxylic acid cycle, it directly activates the expression of fatty acid oxidation related genes, enabling cells to flexibly and efficiently utilize fat as the main energy source.
The expression level of PPAR α must be maintained within a precise dynamic equilibrium range. Overexpression or underestimation of PPAR α can disrupt metabolic homeostasis and ultimately lead to the same downstream functional disorders - decreased fatty acid oxidation capacity and increased oxidative stress levels, but the underlying mechanisms are different:
When PPAR α expression is too weak, the direct consequence is a decrease in the driving force of the tricarboxylic acid cycle.This results in the ineffective treatment of acetyl CoA produced by fatty acid degradation and pyruvate produced by glycolysis, leading to the accumulation of FADH2 and NADH upstream in the cycle.This kind of "traffic congestion" not only significantly reduces ATP generation, but also makes the electron transfer chain "useless", and instead leads to an increase in oxidative stress due to an increase in basal reducing pressure.[60]
When PPAR α is overexpressed, especially in non specialized cells, it can excessively drive the tricarboxylic acid cycle.The abnormal increase in circulating flux will force the downstream electron transfer chain to overload, resulting in increased electron leakage and the generation of reactive oxygen species (ROS) such as superoxide, leading to significant oxidative stress.This strong oxidative stress can in turn damage organelles (including mitochondria themselves) and inhibit metabolic enzyme activity, ultimately leading to a secondary decline in overall metabolic functions such as fatty acid oxidation.[59]
Therefore, the function of PPAR α is like a metabolic "master switch", and its precise regulation is crucial for maintaining energy flow, preventing metabolite accumulation, and inhibiting excessive oxidative stress, which is the cornerstone of cellular metabolic health.
2.1.2 Precise regulation and balance of AMPK pathway
AMPK is the "energy sensor" of cells, and its activity is closely related to the intracellular AMP/ATP ratio.When energy is scarce, AMPK is activated by phosphorylating downstream target proteins, initiating a series of catabolic metabolism (such as fatty acid oxidation) and inhibiting synthetic metabolism (such as protein synthesis) to restore energy balance.AMPK plays a crucial role as the "master switch" in the mitochondrial functional regulation network, and precise regulation of its expression level is essential.
This article elaborates on how the human body maintains the "weak expression" state of AMPK through a negative feedback loop, thereby maintaining the function of PPAR α.
The specific pathway is as follows: when the cell energy is fully charged, AMPK activity is lower.
At this point, the mammalian target protein of rapamycin (mTOR) signaling pathway is activated, promoting protein synthesis and cellular biology.[15]
At the same time, an antioxidant network dominated by NRF1/NRF2 is also operating efficiently, maintaining a reduced state within the cell, such as keeping VA in a reduced state.
Maintaining the reduced state of VA can inhibit the activity of AMPK in reverse through mtor [14], keeping it at a lower level, thereby relieving the inhibition of PPAR α and promoting the oxidation of fatty acids.(The molecular mechanism of VA is described in section 8.1.1 below)
However, this balance is extremely fragile.If the expression level of AMPK deviates from this "optimal point", whether it is too high or too low, it will cause damage to mitochondrial function.
When AMPK is overexpressed, it overactivates PGC-1 α, which competes with PPAR α for co activation factors, thereby inhibiting PPAR α expression and leading to a decrease in fatty acid oxidation capacity.[1, 2, 50, 96]
On the contrary, when AMPK expression is too low, it cannot effectively initiate the antioxidant stress response mediated by PGC-1 α, making mitochondria vulnerable to oxidative stress and gradually impaired in function.[1, 2, 50,97 ]
Therefore, maintaining precise balance of AMPK expression is key to ensuring normal mitochondrial function and delaying aging.
2.1.3 Synergistic effect of PGC-1 α - NRF1/NRF2 antioxidant function
PGC-1 α is the "main regulator" of mitochondrial biosynthesis and functional regulation, while NRF1 and NRF2 are key transcription factors downstream of it that perform antioxidant and mitochondrial maintenance functions.PGC-1 α can directly activate the expression of NRF1, which is responsible for regulating the gene expression of nuclear encoded mitochondrial respiratory chain subunits and mitochondrial transcription factor A (TFAM), thereby promoting mitochondrial proliferation and functional maintenance, as well as the expression of glutathione reductase (GSR), which is the rate limiting enzyme catalyzing GSSG → GSH and provides antioxidant support
Meanwhile, overexpression of PGC-1 α and NRF1 accelerates the flux of mitochondrial electron transport chains, which increases the efficiency of ATP production but also increases the risk of electron leakage and ROS production.
In order to cope with this challenge, the cell has evolved an ingenious "free radical promotion" mechanism: the excessive ROS produced by overexpression of PGC-1 α and NRF1 will oxidize and inhibit the Keap1 egg, remove the inhibition of NRF2 from the egg, make it enter the nucleus, and start the expression of a series of antioxidant genes such as caspase synthase synthase, superoxide dismutase, etc.
In this way, PGC-1 α, NRF1, and NRF2 form a synergistic antioxidant network, which can improve mitochondrial productivity and effectively eliminate ROS produced.[4]
However, the balance of this network is also easily disrupted.
When the function of PGC-1 α - NRF1-NRF2 is too strong, although its antioxidant capacity is enhanced, it may excessively inhibit the expression of PPAR α, affecting the utilization of the tricarboxylic acid cycle in cells.[61][59][60][59]
When the function of PGC-1 α - NRF1-NRF2 is too weak, mitochondria will lose effective antioxidant protection and be directly exposed to oxidative stress damage, leading to rapid functional decline [61] [62] [68]. At the same time, the decrease in NRF1 gene expression will also weaken the number of mitochondria.[61]
2.2 The regulatory mechanism of blood oxygen supply function and the core role of mTOR pathway
Mitochondria, as the "energy workers" of cells, cannot function efficiently without the supply of oxygen.
Therefore, the ability of the body to deliver oxygen to tissue cells, known as the oxygen supply function, is a key external factor that determines the functional status of mitochondria.
Oxygen supply is not a simple physical diffusion process, but a precisely regulated biological system, and its nuclear regulatory pathways are also closely related to aging.
Effective blood oxygen supply is the foundation for efficient aerobic respiration in mitochondria, which is a precise physiological system regulated by the mTOR pathway at its core.The activity of the mTOR pathway exhibits a pattern of over strong and over weak expression, both of which affect the regulation mode of blood oxygen supply. Its moderate activity is the key to maintaining the four core elements of blood oxygen supply, namely nitric oxide (NO) level, red blood cell oxygen carrying capacity, quantity, and deformability, working together.
Under physiological conditions, moderate mTOR activity is crucial for maintaining blood oxygen supply: firstly, it supports endothelial cell function and ensures adequate production of nitric oxide (NO).NO is not only a potent vasodilator, but its levels also directly regulate the oxygen release of hemoglobin, thereby affecting the oxygen carrying capacity of red blood cells.Secondly, the mTOR pathway collaborates with erythropoietin (EPO) signaling to support the normal generation of red blood cells and maintain their necessary quantity.
However, this balance is easily disrupted.When the mTOR pathway is overactivated (such as due to overnutrition or chronic inflammation), it will reverse the blood oxygen supply: overactive mTOR can trigger ROS, promote oxidative damage to red blood cell membranes, and reduce their deformability.[99]
On the contrary, when mTOR activity is consistently low, it will simultaneously disrupt multiple upstream processes: on the one hand, it directly leads to a decrease in the synthesis of nitric oxide synthase (NOS), resulting in a decrease in NO levels, which not only causes vasodilation disorders but also weakens its regulation of red blood cell oxygen carrying capacity;On the other hand, it inhibits signaling pathways such as EPO, leading to insufficient red blood cell production and a decrease in quantity.[98]
Ultimately, whether it is excessive activation or long-term inhibition of mTOR, it will lead to insufficient tissue oxygen supply through different pathways, becoming an important external factor driving mitochondrial dysfunction and aging.
Therefore, maintaining moderate activity of the mTOR pathway is the core to ensure efficient operation of the entire blood oxygen supply system, support mitochondrial energy metabolism, and thus delay aging.
2.3.1 The imbalance mechanism of the first cause: epigenetic inertia formed by competitive breakdown of steady-state circuits.This hypothesis suggests that the essence of mitochondrial functional decline (the first cause) is the loss of dynamic balance in the core regulatory circuits that maintain its functional homeostasis.These circuits rely on the self positive feedback maintenance of key molecules and are mutually antagonistic with other circuits.Once external stress persists for too long, the positive feedback loop will be disrupted, and its expression level will be locked in the pathological range, thereby driving the initiation of the first cause [2] [3] [4] [61].
2.3.2.1 Competition of energy metabolism hubs: The trade-off between PPAR α and PGC-1 α
PPAR α and PGC-1 α - NRF1-NRF2 and NRF2-PGC-1 α respectively dominate fatty acid oxidation and antioxidant responses, and the two complement and compete in mitochondrial functional regulation [5] [59].
In an ideal state, the gene expression of PPAR α is self-sustaining through a positive feedback loop: its activation promotes fatty acid oxidation, the production of metabolic intermediates (such as coenzyme A derivatives), and the consumption of NADPH to generate redox signals, which can further stabilize and enhance the expression and activity of PPAR α, forming a steady-state expression range of normal genes [5] [59] [60].
However, when external stress (such as sustained cold or energy deficiency) forces cells to produce non shivering heat, the mitochondrial electron transport chain is over driven, electron leakage increases, and reactive oxygen species (ROS) are explosively produced [2] [18].As compensation, cells urgently upregulate NRF2 to enhance antioxidant defense [4].Continuous high-intensity NRF2 activation competes with PPAR α for limited co activators (such as PGC-1 α) and transcription resources [3] [59] [61], while consuming molecular resources such as NADPH, indirectly weakening the metabolic environment that maintains high PPAR α expression [4] [60].
If this competitive suppression persists for too long, the self-sustaining mechanism of PPAR α will be weakened or even interrupted.Once its expression drops out of the high expression steady state, it will fall into a "weak expression sustained state", forming a competitive inhibition of PPAR α expression with "NRF2-PGC-1 α high expression" that affects the balance [5] [59].
On the contrary, if the AMPK weak expression interval is maintained for too long, an imbalanced state of "high expression of PPAR α - competitively inhibiting the expression of PGC-1 α and suppressing NRF1-NRF2" may occur, which not only exposes mitochondria to oxidative damage, but also leads to a decrease in self quantity due to the decrease in NRF1 expression [2] [5].
The balance of energy perception center: mutual inhibition and self maintenance of AMPK and mTOR
A similar "mutual inhibition self maintenance" mechanism also exists between the energy sensing center AMPK and mTOR [14] [15].
Self maintenance of AMPK: After AMPK activation, it increases the intracellular AMP/ATP ratio by inhibiting mTORC1 activity and promoting catabolism, thereby creating an energy environment conducive to sustained activation and forming positive feedback [14] [56].
Self maintenance of mTOR: After activation, mTORC1 promotes the synthesis of large molecules such as proteins and lipids, reduces the AMP/ATP ratio, and may inhibit upstream activating factors (such as LKB1), creating a synthetic metabolic environment that inhibits AMPK and is conducive to its own stability [15] [38] [39].
The two form a precise bistable switch.Under physiological conditions, they dynamically oscillate based on their energy status to maintain overall balance [14] [15].However, during sustained energy stress or nutrient depletion, one party's self-sustaining mechanism may be overly strengthened, completely suppressing the other party.For example, long-term overnutrition can consolidate the "high expression high activity" homeostasis of mTOR and inhibit AMPK to "low expression low activity", leading to energy sensing failure, autophagy inhibition, and directly promoting mitochondrial mass decline [15] [35] [38].
2.3.4. Description of the optimal state of four gene variable compatibility metabolism, with the central axis model shown in Figure 1.
ATP energy decreases, and AMPK spontaneously increases expression. By increasing PGC-1 α expression, NRF1 expression is directly increased. Overexpression of NRF1 causes electron leakage, leading to increased expression of oxidized KEAP1-NRF2 and oxidation of the antioxidant network function. Under normal antioxidant network conditions, the reduced state of VA will indirectly increase Mtor, thereby reducing the highly expressed AMPK pathway and achieving PPAR α. This promotes energy metabolism and maintenance of necessary downstream metabolites by enhancing the tricarboxylic acid cycle, increasing ATP production. When ATP is too high, Mtor continues to express and inhibit the AMPK pathway until the next cycle of AMPK expression begins again at ATP levels.
In theory, the perfect central axis should be to produce more energy during the tricarboxylic acid cycle, promote mitochondrial regeneration during the PGC-1 α stage, promote cellular mitochondrial regeneration, and regenerate antioxidant function.
But this article infers that in reality, such a central axis is difficult to maintain normal and stable.
For example, just staying up late once can interfere with the operation of the central axis, causing hormonal, blood oxygen microcirculation disorders, oxidative stress, and leading to the imbalance of the central axis.
But at the same time, people's daily diet, such as vegetables containing ferulic acid and antioxidants, can also correct this process, and the entire process presents a dynamic state of change.
2.3.5 Combination state of metabolic homeostasis: theoretical space for multi-path induced mitochondrial functional decline
In sections 2.1.1 to 2.1.3, we thoroughly analyzed the functions and interactions of each node in the core regulatory network of PPAR α, AMPK, PGC-1 α, and mTOR.However, most of the above analyses are based on idealized models of "single node perturbation".
This section aims to reveal a deeper reality: these key factors are not isolated switches, but constitute multiple core circuits with strong self-sustaining capabilities, which are coupled with each other. The combination of their functional states forms a high-dimensional space that determines the fate of cells.
We simplified the expression and activity status of each core factor (AMPK, mTOR, PGC-1 α, PPAR α) into three basic levels: too weak, steady-state, and too strong.Therefore, the total number of combinations composed of these four variables is theoretically 3 to the power of 4, with a total of 81 possible "functional state combinations".
Among these 81 combinations, there is only one combination that represents the perfect internal stability enjoyed in early life - that is, all four cores are in their precise "steady state" range.This state is the only ideal state for optimizing mitochondrial function and achieving clean and efficient energy metabolism, and is the gold standard for delaying the aging process of the body.
And the remaining 80 combinations all constitute potential pathological starting points that trigger the first cause of "mitochondrial functional decline".This vast potential space theoretically lays the molecular foundation for individual differences in the aging process.
It should be emphasized that exogenous signals such as daily diet can shape seemingly contradictory molecular combinations that violate classical theoretical predictions.Traditional linear cognition holds that there are simple inhibitory or activating relationships between these pathways.However, if there is a sustained and strong exogenous signal, this conventional logic can be broken, and the core mechanism lies in the strong "self-sustaining" ability of each pathway, which is sufficient to resist or even cover inhibitory signals from other pathways.
The "metabolic inertia" state of PPAR α: As mentioned earlier, its strong positive feedback loop can form a "metabolic inertia" once it is excessively enhanced by exogenous ligands (such as specific dietary fatty acids), which can reverse suppress the inhibitory signals caused by high AMPK expression, forming an atypical state of "AMPK strong+PPAR α strong".
The "hyperfunction state" of PGC-1 α axis: This hypothesis further emphasizes that the mitochondrial biosynthesis axis dominated by PGC-1 α - NRF1 also has a significant self-sustaining mechanism.When subjected to continuous exercise stimulation or energy challenge, activated PGC-1 α not only promotes mitochondrial production, but its downstream products - newly formed, functionally active mitochondria themselves - continue to produce ATP and alter the cellular energy metabolism landscape (such as increasing NAD+levels and activating SIRT1).
This high-energy, highly reduced internal environment created by its own functional output can further consolidate and enhance the activity and expression of PGC-1 α, forming a self driven positive feedback loop
Once this cycle is excessively enhanced, it can lead to the pathway entering a state of "hyperfunction".In this state, in order to maximize mitochondrial biosynthesis, excessive consumption of cellular biosynthetic resources and co activating factors (such as PGC-1 α itself) may occur, and key pathways such as PPAR α may be continuously competitively inhibited, disrupting the overall balance of the metabolic network and transforming from a "builder" to a "resource predator".
These "double strong structures" or "single pathway dominant" non-equilibrium states, although may exhibit temporary strength in certain aspects such as lipid oxidation or mitochondrial count, are fundamentally deviating from the ideal state and fragile forced equilibrium.Its massive and unbalanced metabolic flow can disrupt the harmony of the entire network by squeezing co activating factors, depleting key metabolic substrates, triggering compensatory inhibition, and ultimately still flowing into the mainstream of mitochondrial dysfunction.
Conclusion: There exists a complex theoretical space in the core metabolic regulatory network consisting of 81 functional state combinations.
Among them, only one is an ideal steady state, while the remaining 80 are potential aging onset points.Exogenous factors determine the unique "entry point" for individuals to enter the aging pathway by shaping specific, even non ideal combinations that violate classical theories, such as "dual strong" or "hegemonic" states driven by their respective maintenance mechanisms.This provides a solid mathematical model and molecular mechanism for the uncertainty of the first cause entrance, and precisely explains why the same aging endpoint originates from vastly different life processes.
3 Cascade reaction of decline: from mitochondrial dysfunction to systemic decline
The decline in mitochondrial functionality, as the "first cause" of decline, is not limited to cellular energy production itself, but spreads like ripples, triggering a series of systematic cascade reactions, constituting the second, third, fourth, and more factors of decline, ultimately manifested as a comprehensive decline in the body's functions.
3.1 Second cause of aging: disorder of glucose and lipid metabolismThe decline in mitochondrial function directly leads to changes in the overall energy metabolism pattern, especially the imbalance in the utilization ratio of sugar and fat, thereby causing disturbances in glucose and lipid metabolism [86, 87].
3.1.1 Decreased lipid metabolism: reduction of free carnitine and accumulation of acylcarnitineMitochondria are the main site of fatty acid beta oxidation, responsible for converting long-chain fatty acids into energy.During this process, free carnitine acts as a "transporter" of fatty acids into the mitochondrial matrix, which is crucial for maintaining fat metabolism [86].
With the decline of mitochondrial function, the level of free carnitine decreases, leading to the obstruction of fatty acid transmembrane transport, and at the same time, acylcarnitine accumulates in large quantities in the cytoplasm [86, 87].
These metabolic intermediates are not only markers of lipid metabolism disorders, but may also interfere with cell membrane function and promote inflammatory responses [87].
In addition, the storage of triglycerides in adipose tissue increases, while the proportion of beneficial fatty acid metabolites (such as unsaturated fatty acids) decreases, further exacerbating metabolic inflammation.
The slow repair and renewal rate of mitochondrial inner membrane phospholipids also affects membrane fluidity and membrane potential, leading to further deterioration of mitochondrial function [87, 88].
3.1.2 Increased sugar metabolism ratio: Accumulation of advanced glycation end products (AGEs) and initiation of inflammationIn normal cells, even when there is sufficient energy, energy is still obtained through the metabolism of ketone bodies. When the efficiency of fat burning decreases, cells become more inclined to obtain energy through glucose oxidative phosphorylation based on metabolic flexibility due to energy needs, resulting in metabolic rigidity and a significant increase in the proportion of sugar metabolism [88, 92].
This metabolic transition has brought serious side effects, namely the accumulation of advanced glycation end products (AGEs) [88].
AGEs are stable covalent adducts formed by non enzymatic reactions between reducing sugars (such as glucose) and free amino groups of proteins, lipids, or nucleic acids.
The accumulation of AGEs can cause various damages to the body:
Protein dysfunction: Collagen and elastin undergo cross-linking after glycosylation, resulting in stiff and fragile skin and vascular walls [88].
Inflammatory response initiation: AGEs can bind to RAGE receptors, activate pro-inflammatory signaling pathways such as NF - κ B, induce the release of inflammatory factors, and maintain a chronic inflammatory state [88, 91].
Oxidative stress intensifies: AGEs generate reactive oxygen species (ROS) during the process, which can induce cells to further produce ROS, forming a vicious cycle [89,90].
Microcirculatory disorders: AGEs accumulate on microvascular endothelial cells, increasing blood viscosity, blocking capillaries, leading to tissue ischemia and hypoxia, and further damaging mitochondrial function [88, 89].
Therefore, the disorder of glucose and lipid metabolism not only reflects changes in energy supply patterns, but also serves as a key bridge connecting mitochondrial dysfunction with chronic inflammation and tissue damage [86-92].
The third cause of decline: GH-IGF-1 axis dysfunction, mitochondrial dysfunction, and metabolic disorders can further affect the hypothalamic pituitary target hormone axis.
The functional decline of the growth hormone (GH) - insulin-like factor-1 (IGF-1) axis is a hallmark event in the aging process.
4.1 Effects of decreased levels of growth hormone (GH) on NRF1 and mitochondrial countGH is not only a key hormone that promotes childhood growth, but also continues to play an important metabolic regulatory role in adulthood [80,81].The decrease in GH levels is closely related to the decline of mitochondrial function [79,81].Firstly, GH is one of the key hormones that promote the expression of NRF1 [81].As the main regulator of mitochondrial biogenesis, the expression level of NRF1 directly determines the number of mitochondria [3,4].When GH levels decrease, the expression of NRF1 also decreases, leading to the inability of cells to maintain sufficient mitochondrial quantity to meet energy requirements. Even if the mass of individual mitochondria is still acceptable, the total energy output still decreases significantly [79,81].This also explains why even supplementing mitochondrial nutrients such as coenzyme Q10 is difficult to completely reverse the decline in energy metabolism during the aging process, as the fundamental problem lies in the reduction of the "number of factories" [79,81].
4.2 Effects of GH-Deiodinase-T4/T3 pathway obstruction on alkaline generation
GH not only affects mitochondrial quantity and function, but also affects metabolism by regulating thyroid hormone activity [80,81].Specifically, GH can promote the activity of type II deiodinase (D2) [82], which is responsible for converting thyroxine (T4) into active triiodothyronine (T3), particularly playing a critical role in peripheral tissues such as liver and skeletal muscle [82].T3 is a core hormone that maintains basal metabolic rate and promotes carnitine synthesis, thereby driving fatty acids into mitochondrial oxidation [82].When GH levels decrease, D2 activity decreases, leading to obstruction of T4 → T3 conversion and a decrease in active T3 levels, thereby inhibiting carnitine production [80,82].
At the same time, elevated levels of glucocorticoids also regulate the activity of type I deiodinase (D1) and type III deiodinase (D3), converting T4 to transtriiodothyronine (rT3), further reducing effective T3 levels [85,82].In conditions of glucose and lipid metabolism disorder or chronic inflammation, inflammatory factors can promote the secretion of glucocorticoids, exacerbate T3 decline, and form a metabolic vicious cycle that overlaps with GH decline [80,82].
The decrease in total carnitine levels hinders the entry of fatty acids into mitochondrial oxidation, exacerbates lipid metabolism disorders, and further affects energy metabolism and mitochondrial function [79,81,82].
4.3 The vicious cycle of decreased ketone metabolism and GH levels
The decrease in GH levels and ketone metabolism together constitute the third cause of aging [79,80,81].GH contributes to fat breakdown and ketone body formation [80,81], and ketone bodies are not only important alternative energy sources, but also maintain mitochondrial function and expression of basic antioxidant genes by activating the AMPK-PGC-1 α - NRF1 pathway [3,4,14].When GH decreases, ketone body production decreases, and this positive regulatory effect weakens accordingly [79,81].
Meanwhile, a decrease in ketone body levels can affect epigenetic homeostasis.Fat breakdown product alpha ketoglutarate (AKG) is an important substrate for histone demethylation, and its decrease may lead to epigenetic silencing of the GH gene itself, further lowering GH levels [6].In addition, a decrease in ketone bodies can weaken their inhibitory effect on histone deacetylase (HDAC), affecting the synthesis of signaling molecules such as ceramides, thereby disrupting cellular metabolism and signal transduction [9,81].
4.4 Switching of metabolic pathways: The energy crisis from oxidative phosphorylation to glycolysis leads to a disruption of glucose and lipid metabolism caused by decreased mitochondrial functionality. One of its core manifestations is a fundamental shift in cellular energy metabolism patterns [79,81].In a healthy and youthful state, cells preferentially break down glucose through efficient mitochondrial oxidative phosphorylation (OXPHOS) to produce sufficient ATP.However, with the significant decrease in NRF1 expression during the aging process (as described in the third factor), the transcriptional synthesis of mitochondrial respiratory chain complex subunits encoded by nuclear genes is hindered, directly leading to a decrease in mitochondrial quantity and functional abnormalities [81,3].The scale reduction and quality decline of this "energy factory" greatly reduce the efficiency of ATP produced by units of glucose through the tricarboxylic acid cycle (TCA cycle) and electron transfer chain [79,3].
To cope with the imminent energy crisis, cells are forced to activate an evolutionarily conservative but inefficient backup plan - tilting towards the glycolytic metabolic pathway [22,3].Glycolysis occurs in the cytoplasm without the involvement of mitochondria, rapidly breaking down glucose into pyruvate and producing 2 molecules of ATP.However, in the context of impaired OXPHOS function, most pyruvate cannot enter mitochondria for further oxidation, but is reduced to lactate in large quantities under the catalysis of lactate dehydrogenase (LDH) [22].
The switching of this metabolic pathway has resulted in two direct catastrophic consequences: firstly, a severe shortage of energy production.The ATP efficiency produced by glycolysis of the same unit of glucose is less than 1/18 of that of OXPHOS, which causes cells to enter a "starvation" state, although glucose levels in the bloodstream may be normal or even high [3,22].Secondly, there is a systematic increase in lactate levels [22].Lactic acid is no longer just a local metabolite during exercise, but has become a systemic metabolic marker as aging progresses [22].The sustained increase in lactate levels in the blood not only exacerbates the acidic load on tissues and interferes with normal physiological functions, but more importantly, it competes with ketone bodies to enter cells through monocarboxylate transporters (MCT) and plays the role of an immune escape promoter in senescent cells (as described in the sixth aspect [8]), directly hindering the immune system's clearance of senescent cells [8].
Therefore, the increase in blood lactate levels is not an isolated metabolic phenomenon, but a key link connecting upstream mitochondrial dysfunction with downstream inflammatory microenvironment formation and stem cell dysfunction [79,3].It marks that the energy metabolism of cells has shifted from the efficient and clean "aerobic combustion" mode to the inefficient and polluting "anaerobic fermentation" mode, and is a concentrated manifestation of systemic aging in the metabolic level of the entire body [3,8].
4.5 Skeletal muscle decline: From muscle loss to systemic inflammation,
skeletal muscle is not only the body's largest protein reserve and energy metabolism organ, but also an important endocrine and immune regulatory tissue [83,84].In the context of GH-IGF-1 axis decline (third cause), the decline in skeletal muscle mass has become a long neglected but crucial pathological link [80,81,83].This hypothesis proposes that Decorin, as a muscle factor directly regulated by GH, plays a pivotal role in this process [83].
4.5.1 GH directly induces Decorin expression and its anti muscle atrophy mechanism
. Research has found that GH can directly induce Decorin expression in skeletal muscle without relying on IGF-1 (mouse model validation) [83].Decorin, as a small molecule leucine rich proteoglycan, plays a crucial role in strongly inhibiting Myostatin, a key factor that negatively regulates muscle growth [83].Myostatin significantly limits muscle mass by inhibiting myoblast differentiation and protein synthesis.Therefore, GH upregulates Decorin and relieves Myostatin's inhibition on muscle growth, which is an important pathway independent of IGF-1 for maintaining skeletal muscle mass [83].
4.5.2 Function loss of skeletal muscle as an anti-inflammatory endocrine organ.
During contraction and metabolism, skeletal muscle can secrete a series of muscle factors with anti-inflammatory and immune regulatory functions, such as IL-6 (manifested as anti-inflammatory during exercise), IL-10, IL-1ra, etc. [84].These factors together form a "muscle derived anti-inflammatory network" that systematically inhibits systemic low-grade inflammation [84].
When GH levels decrease, Decorin expression decreases and Myostatin inhibition is relieved, progressive atrophy of skeletal muscle begins to occur [80,81,83].As muscle mass decreases, the total amount of anti-inflammatory muscle factors secreted by it significantly decreases, leading to insufficient systemic anti-inflammatory signal input [84].
4.5.3 The vicious cycle of muscle loss and uncontrolled inflammation
Muscle atrophy and uncontrolled inflammation form a typical positive feedback vicious cycle:
Muscle loss → reduced anti-inflammatory secretion: The decrease in muscle mass directly leads to a decrease in the secretion of anti-inflammatory factors such as IL-10, weakening the body's buffering capacity against inflammation [84].
Inflammatory factors activate Myostatin: Elevated inflammatory factors in circulation, such as TNF - α and IL-1 β, can further upregulate Myostatin expression and exacerbate muscle breakdown [83,84].
Lipid muscle axis imbalance: Abnormal muscle flow is accompanied by adipose tissue proliferation, and adipose tissue (especially visceral fat) is the main source of pro-inflammatory factors such as leptin and TNF - α.Under this balance, the body's endocrine system shifts from an "anti-inflammatory state" to a "pro-inflammatory state".
Systemic inflammatory storm: After losing the suppression of anti-inflammatory factors from muscle sources, pro-inflammatory signals from aging cells such as SASP and adipose tissue lose balance, and the inflammation glucocorticoid axis (the fifth cause) is overactivated, ultimately leading to sustained elevation of cortisol and causing widespread immune suppression and metabolic disorders [84].
Therefore, the decline of skeletal muscles is not only a loss of muscle function, but also a key link in the collapse of systemic anti-inflammatory defense [83,84].It acts as a direct effector and amplifier downstream of the GH-IGF-1 axis, converting the attenuation of hormone signals into tangible inflammation loss control and body collapse [80,81,83].
4.6. Failure of growth hormone conventional inflammation inhibition pathway.
In young individuals, the GH-JAK2-MAPK-c-Jun-ST6GAL1 axis [100101104] maintains low cellular responsiveness to inflammatory signals in a steady state.Growth hormone (GH) activates the MAPK pathway, promotes moderate phosphorylation of transcription factor c-Jun, and drives sustained expression of ST6GAL1.ST6GAL1, as a sialyltransferase, plays a key role in cell membrane glycosylation modification. Its upregulation can reduce the affinity of membrane receptors for inflammatory ligands (such as TNF - α, IL-6), thereby achieving "feedforward inhibition" of inflammatory signals.This axis constitutes the anti-inflammatory steady-state pathway of GH.
However, as GH secretion decreases during the aging process, the GH-MAPK-c-Jun-ST6GAL1 axis gradually becomes inactive, and the inflammatory response of cells to stress is no longer controlled.At this point, excessive inflammatory factors induce activation of the hypothalamic pituitary adrenal axis (HPA axis), promoting the release of glucocorticoids.Corticosteroids induce MKP-1 expression through their receptor GR, leading to dephosphorylation and temporary inactivation of MAPK family members;However, at the same time, GR itself activates the Ras → Raf → MEK → ERK pathway through Src and PI3K kinase signaling.This pathway cross activates the upstream kinase of JNK, leading to phosphorylation of JNK.Due to the extremely short half-life of MKP-1 protein, it is quickly degraded, while the activation of JNK persists, forming a "sustained activation but uncontrolled JNK state".
Continuously activated JNK enters the nucleus, phosphorylates Ser63 and Ser73 residues of c-Jun, and enhances the transcriptional activity of AP-1 complex formed by c-Jun and c-Fos binding.The AP-1 complex binds to the TPA response element (TRE) of the ST6GAL1 gene promoter, thereby re driving the expression of ST6GAL1.This process forms a compensatory pathway of glucocorticoid-ERK-JNK-c-Jun-ST6GAL1, which temporarily maintains the expression of ST6GAL1 after GH axis collapse to buffer inflammatory responses.[102,103,104]
However, this compensatory pathway is highly stress dependent and unstable, and its sustained activation is often accompanied by oxidative stress and increased energy load, ultimately leading to the formation of an inflammatory maintenance state, known as "chronic low-grade inflammation" of aging tissues.
The fourth cause of aging: collapse of antioxidant network
Mitochondria are the main source of intracellular ROS, and their decreased function inevitably leads to increased oxidative stress [68,69].At the same time, the cell's own antioxidant defense network gradually collapses due to aging, unable to effectively eliminate excessive ROS, leading to accumulated damage [70,71].
5.1 NRF1 and NRF2 functional imbalance and chronic oxidative stress
NRF1 and NRF2 are the core components that maintain the antioxidant network [62, 63, 68, 69].During the aging process, due to factors such as decreased GH levels, NRF1 function continues to decline, leading to a decrease in basal antioxidant capacity [65,70].To compensate, cells tend to overly rely on stress-induced activation of NRF2 [65,71].
One of the downstream target genes of NRF2 is heme oxygenase-1 (HO-1), which releases free iron when decomposing heme [69,70].Continuous activation of NRF2 leads to an increase in intracellular free iron levels, which is a key catalyst for catalyzing the Fenton reaction to generate highly toxic hydroxyl radicals (· OH) [66,67].Therefore, long-term non rhythmic high expression of NRF2 may actually exacerbate oxidative stress, forming a "chronic oxidative stress" state, further damaging mitochondria and other organelles [68,70].
5.2 Vulnerability of Vitamin C, E, and Glutathione Antioxidant Networks
The antioxidant defense of cells is a complex network, in which vitamin C (VC), vitamin E (VE), and glutathione (GSH) are key nodes [68,69,71].This network is extremely fragile and susceptible to chronic oxidative stress breakdown.
Vitamin C (VC): VC is an important water-soluble antioxidant both inside and outside the cell, and its function depends on the cycling between the reduced state (ascorbic acid) and the oxidized state (dehydroascorbic acid) [69].During the aging process, due to the decrease in GSH regeneration dominated by NRF1 and oxidative stress caused by the atypical NRF2 pathway, the proportion of intracellular oxidized VC increases [70].This makes it difficult for exogenous reduced VC to enter cells and exert its effects, while the endogenous antioxidant cycle is also blocked [68,71].
Vitamin E (VE): VE is the main lipid soluble antioxidant that protects cell membranes from lipid peroxidation [68,69].The ratio of oxidation and reduction states of VE is an important signal source.When the proportion of VE oxidation states increases, it indirectly affects SREBP activity by altering membrane lipid peroxidation levels and oxidative stress states, thereby changing the distribution of precursors between cholesterol and coenzyme Q10 in the MVA pathway, indirectly affecting Q10 synthesis, and further affecting mitochondrial function [70,72,73,76,77].
In addition, the state of VE indirectly affects BAX activation by regulating the membrane oxidative environment and ROS signaling, thereby regulating the cell apoptosis threshold. Reduced VE helps maintain the cell repair window, allowing cells to still have repair opportunities under high P53 expression conditions;An increase in the proportion of oxidized VE enhances ROS signaling, making BAX more easily activated, lowering the apoptosis threshold, and promoting cells to more easily enter the aging state [70] [71] [72].
Glutathione (GSH): GSH is the most important antioxidant in cells, and its regeneration depends on NADPH and VC [68,70].During the aging process, the synthesis and circulation of GSH are impaired, leading to a decrease in levels and an inability to effectively neutralize ROS [71].Meanwhile, GSSG (oxidized glutathione) accumulates in the blood and becomes a marker of oxidative stress [69].
5.3 The Core Hub Role of Vitamin C (VC) in the Antioxidant Network
VC is not only an electron donor, but also the core scheduling hub and electronic reserve of the cellular antioxidant defense system [68,69].Its function depends on the precise cascade reaction initiated by the filling of reduced state VC.
When the intracellular environment is in a highly reduced state, the concentration of reduced VC is abundant.At this point, antioxidant resources are optimally allocated: GSH is freed from other antioxidant tasks and more specifically enriched in mitochondria, ensuring the antioxidant needs of this core energy organ [70].
In the cellular antioxidant network, when the proportion of reduced vitamin C (VC) is high, intracellular glutathione (GSH) no longer needs to participate in the regeneration of VC in large quantities, resulting in a "surplus" state of the antioxidant system [68,69,70].At this point, NADPH in the cell can direct more reducing energy resources towards the thioredoxin reductase (Trx) system to maintain the reduced state of key signaling proteins, including PTEN [68,70,71,78].
In the cellular antioxidant network, the redox state of PTEN plays an important regulatory role in downstream signaling pathways.PTEN activation can inhibit PI3K/Akt signaling, thereby reducing mTOR activity [78].The decrease in mTOR activity will release the inhibition of AMPK and increase AMPK activity [14,15].Subsequently, AMPK upregulation activates PGC-1 α through phosphorylation and transcriptional regulation [3,4,59,61], thereby promoting mitochondrial biosynthesis and coenzyme synthesis such as iron sulfur clusters and lipoic acid, providing critical support for mitochondrial function maintenance and energy metabolism.This mechanism reflects the close coupling between the cellular antioxidant system, energy metabolism, and signaling pathways, and reveals the indirect protective effect on mitochondrial function by regulating the reducing state under aging conditions.
Lipoic acid acts as an "electron bridge", mediating the transfer of electrons from VC to GSSG and oxidized VE [68,71].VC has thus become a "strategic electronic reserve", forming a synergistic regeneration loop with lipoic acid, GSH, and VE, significantly enhancing the stability and efficiency of the antioxidant network, and providing a molecular environment for mitochondrial functional remodeling and metabolic homeostasis recovery [68,69,71].
5.3 Association between alanine metabolism and epigenetic disorders
Glycine is one of the precursors for the synthesis of cysteine peptides, and its metabolic pathway is closely related to aging.In the tricarboxylic acid cycle, α - ketoglutaric acid (AKG) can be converted from ammonia to arginine, which in turn produces lysine.Amino acid is an important raw material for the synthesis of serine, and serine is the key to the synthesis of cysteine.
Cysteine binds with arginine to ultimately form cysteine peptide.
Therefore, the AKG alanine serine cysteine peptide pathway constitutes the raw material supply chain for antioxidant defense.During the aging process, due to factors such as a decrease in AKG levels, this supply chain is obstructed, resulting in the inability to synthesize cysteine peptides.
More importantly, AKG is a key substrate for epigenetic demethylation, and a decrease in its level can directly lead to epigenetic disorders, affecting the expression of various key genes including hormones, thereby closely linking metabolic issues with gene regulation.[22][6][7]
6. The fifth cause of aging: immune collapse caused by inflammation and the glucocorticoid axis
The chronic inflammatory state during the aging process is a key factor driving various age-related diseases.This article believes that this inflammatory state stems from the collapse of the immune surveillance system, particularly the loss of iNKT cell function, and the subsequent vicious cycle of inflammation glucocorticoid axis.
6.1 Decreased INKT cell function and depletion of NAD+pool
Inherent natural killer T cells (iNKT cells) are one of the strongest immune cells in the human body capable of clearing senescent cells.
During the aging process, although the level of its activating ligand galactosylceramide did not significantly decrease, the quality and quantity of iNKT cells themselves declined.The core cause lies in the depletion of the NAD+pool.
The proliferation and functional maintenance of iNKT cells depend on the activation of inflammatory cytokines such as IL-6 and TNF - α.Inflammation can upregulate the differentiation cluster 38 (CD38) on the surface of iNKT cells. CD38 generates ADPR and cADPR by consuming NAD+, thereby activating the AMPK pathway and promoting the proliferation and activity of iNKT cells.
This is a compensatory mechanism aimed at enhancing immune function by consuming energy molecules.
However, during the aging process, due to the decline in mitochondrial function, the rate of NAD+regeneration slows down, while the continuous consumption of CD38 rapidly lowers the NAD+pool to the critical point.Once NAD+is depleted, this compensatory pathway becomes ineffective, and the activity of iNKT cells decreases, weakening their ability to clear senescent cells.[8]
6.2 Collapse of the compensatory axis of inflammatory factor-CD38-AMPK
The collapse of the compensatory axis of inflammatory factor-CD38-AMPK is a key node in immune failure.When the NAD+level is acceptable, this axis can maintain the activity of iNKT cells and control the number of senescent cells.But when the NAD+pool reaches the critical point, the immune defense of iNKT cells gradually falls.Aging cells accumulate in large quantities due to their inability to be effectively cleared, and they secrete more senescence related secretory phenotype (SASP) factors, including a large amount of pro-inflammatory factors, further increasing the level of inflammation in the body.This creates a vicious cycle: NAD+depletion → iNKT cell dysfunction → senescent cell accumulation → increased inflammatory levels → more CD38 activation → further depletion of NAD+.[8]
6.3 The inhibitory effects of elevated levels of white alcohols on immunity and metabolism
As the level of inflammation continues to rise, the body compensates by increasing the secretion of glucocorticoids (resveratrol) in order to control excessive inflammatory response.However, high-altitude white alcohols have a widespread inhibitory effect on the body.On the immune side, resveratrol can inhibit the activity and proliferation of immune cells, leading to immune suppression.In terms of metabolism, resveratrol promotes muscle breakdown, increases visceral fat accumulation, and inhibits the function of the GH-IGF-1 axis.In addition, resveratrol can promote the conversion of T4 to inactive transtriiodothyronine (rT3) instead of active T3 by affecting the activity of deiodinase, thereby further reducing the basal metabolic rate.This series of effects collectively led to a new round of accelerated decline, manifested as a further decrease in energy levels, weakened lipolysis function, and intensified skin aging, indicating that the body has entered a new stage of "chronic immune suppression decline".
The Sixth Cause of Aging: Accumulation of Aging Cells and Immune Clearance Disorders
The accumulation of senescent cells is an important cause of tissue dysfunction and the occurrence of age-related diseases.Its accumulation is not only due to the increase in production speed, but also due to the decrease in clearance efficiency.
7.1 The concepts of Silent Senecent Cell Pool and Cell Burst are proposed in this paper to explain the dynamic process of senescent cell accumulation.
Silent library: Not all senescent cells are in an active state and secrete large amounts of SASP genes.Some senescent cells can be "silenced" by ketone bodies.Ketones can inhibit the activity of P53 in senescent cells and subsequently suppress the expression of pro apoptotic protein BAX downstream through Kbhb (β - hydroxybutyrylation) modification.The inhibition of P53 not only inhibits cell apoptosis, but also reduces the expression of its surface immune checkpoint molecules.In this' silent 'state, senescent cells are' accessible 'and' purgeable 'to the immune system, mainly relying on NK cells and T cells for clearance.[9]
Explosion: When the level of ketones in the body decreases (as described in the second cause of aging), the "silent" effect on aging cells is weakened, P53 activity is restored, and cells enter an active stress state again, beginning to secrete SASP factors. This is called "explosion".Explosive senescent cells will consume more energy and ketone bodies, further diluting the level of ketone bodies in the body, leading to more senescent cells bursting and forming a vicious cycle.This is one of the core mechanisms underlying the accumulation of senescent cells.
7.2 Antagonistic effects of ketone bodies and lactate on the fate of senescent cells
Ketones and lactate can both enter cells through MCT (monocarboxylate transporter), playing an antagonistic role in the fate of senescent cells.When ketone bodies dominate, senescent cells tend to be "silenced" and easily cleared by the immune system.
However, when the level of lactate increases (such as mitochondrial dysfunction leading to enhanced anaerobic fermentation), lactate competitively inhibits the entry of ketone bodies into cells.More importantly, after lactate enters senescent cells, it forms a reverse regulation that increases the expression of immune checkpoint molecules, thereby inhibiting immune clearance.Therefore, the intracellular energy metabolism pattern (ketone bodies vs. lactate) directly determines the ultimate fate of senescent cells: whether they are cleared or persist and create inflammation.
3.5.3 P53 and BAX are nuclear molecules that determine the fate of senescent cells in apoptosis and immune escape.
P53 is the "genomic guard" of cells. Upon sensing pressure such as DNA damage, it initiates downstream programs that determine whether cells undergo cycle arrest for repair or initiate apoptosis.
BAX is a downstream target gene of P53 and a key executor of the mitochondrial apoptosis pathway. It forms pores on the outer membrane of mitochondria, leading to the release of cytochrome c and initiating the caspase cascade reaction, ultimately resulting in cell apoptosis.In active senescent cells, P53 expression is elevated, but due to changes in cell membrane permeability and other reasons, BAX cannot effectively form pores, resulting in perforation failure and the inability of cells to undergo smooth apoptosis. Instead, they remain in a state of stress and release SASP factors.In senescent cells silenced by ketone bodies, P53 activity is inhibited and BAX expression decreases accordingly. Although the cells do not die, they no longer release strong "don't eat me" signals, thus creating conditions for immune clearance.
Deep analysis of the 8 key molecular mechanisms
8.1.1 Dual regulatory mechanism of vitamin A (VA)
Vitamin A (VA) plays a complex and crucial role in the regulation of aging, primarily through its two main forms: reduced retinol and oxidized retinoic acid.These two forms activate different signaling pathways, which bidirectionally regulate cell growth and apoptosis, and can be regarded as the "switch" of cell fate.
8.1.2 Reduced VA (retinol) promotes growth through the JAK2-STAT3 mTOR pathway
Reduced vitamin A (retinol) can bind to the membrane receptor STRA6 through plasma retinol binding protein (holo RBP), triggering STRA6 dependent membrane signal transduction rather than passive transport.After binding, this complex can trigger the recruitment and activation of JAK2 in the intracellular region of the receptor, thereby inducing tyrosine phosphorylation and nuclear migration of the STAT family transcription factor STAT5, thereby initiating a set of STAT target gene programs that promote survival and proliferation (such as SOCS3, Bcl xL, Mcl-1, CyclinD1, etc.).In certain cell lines and tumor models, the signal mediated by STRA6 can intersect with the integrin/ILK or IGF-1R → IRS → PI3K → Akt pathway, indirectly activating downstream Akt/PI3K and promoting mTORC1 signaling (p-S6, p70S6K increase, Autophagy index decrease), indicating a functional coupling relationship between STRA6 → JAK2 → STAT and ILK/IGF-1R → PI3K/Akt → mTOR.
It should be emphasized that most direct evidence comes from cell lines or tumor/stem cell models, indicating that STRA6-AK2-STAT is a reliable membrane signaling module, and the activation of mTOR is usually achieved indirectly when crossing the PI3K/Akt or ILK Akt pathways, rather than through direct phosphorylation of mTOR by STRA6.[23][24][25][26]
8.1.3 Oxidative state VA (retinoic acid) promotes apoptosis through the RAR-p53/Bax pathway
When cells are under oxidative stress and have insufficient antioxidant resources, the reduced form of vitamin A (retinol) inside the cell is more easily oxidized to retinoic acid (RA).RA, as an active ligand, enters the nucleus and forms a heterodimer with the retinoic acid receptor (RAR)/RXR. It binds to the retinoic acid response element (RARE) on the target gene, inducing a series of transcriptional programs related to cell cycle arrest and programmed cell death.The RA-RAR signal can upregulate tumor suppressor factors such as p19 ^ ARF (corresponding to p14 ^ ARF in humans), release the inhibition of MDM2, and stabilize and accumulate p53 protein;At the same time, RAR complexes can recruit transcriptional co activators (such as p300/CBP), promote acetylation of p53 and enhance transcriptional activity, thereby promoting the expression of downstream pro apoptotic genes (such as PUMA, NOXA, BAX) of p53.Activated p53 synergizes with upregulated BH3 only protein (PUMA/NOXA) to trigger changes in mitochondrial outer membrane permeability, cytochrome c release, and caspase cascade, thereby initiating mitochondrial pathway mediated apoptosis.Therefore, under oxidative conditions, the molecular chain of RA-RAR → p19 ^ ARF/MDM2 → p53 → PUMA/NOXA/BAX forms a clear apoptotic pathway from nuclear receptor signaling to mitochondrial execution.[27]
8.1.4 Calcium ions and stem cell function
Calcium ions (Ca ² ⁺) are one of the most important second messengers in cells, and their dynamic changes in concentration, namely calcium ion oscillations, play a central role in regulating the proliferation, differentiation, and apoptosis of stem cells.For adult stem cells, precise regulation of calcium signaling is crucial for maintaining self-renewal ability and multipotent differentiation potential ([31]).
8.1.5 Regulation of endoplasmic reticulum calcium ion levels by CD150-IP3 pathway
CD150 (also known as SLAMF1) is a receptor molecule expressed on the surface of hematopoietic stem cells (HSCs) and various immune cells ([28], [29]).Research has shown that CD150 can indirectly affect endoplasmic reticulum (ER) calcium storage and release by regulating inositol triphosphate (IP3) levels ([30]).When CD150 expression is elevated, it promotes the generation of IP3, which binds to the IP3 receptor (IP3R) on the ER membrane, leading to the release of calcium ions into the cytoplasm, thereby reducing ER calcium levels.
ER calcium ions are the main calcium storage reservoir in cells, and their stability is crucial for protein folding, lipid synthesis, and mitochondrial function maintenance.The sustained decrease in ER calcium can disrupt these vital activities and may activate the unfolded protein response (UPR), triggering cellular stress ([28], [30]).
Early differentiation stage
In the early stages of chronic inflammation, CD150 is induced to express, leading to a moderate increase in IP3 levels and a brief but limited release of ER calcium.This calcium signal can serve as a "stress signal" that drives stem cells to undergo symmetric or asymmetric differentiation to replenish damaged cells, manifested as a compensatory regenerative response ([28], [31]).At this stage, the frequency and amplitude of calcium oscillations remain within the acceptable range for stem cells, supporting energy supply and mitochondrial flash activity, providing assurance for maintaining stem cell pluripotency.
Late stage inhibition stageAs chronic inflammation persists, the long-term activation of the CD150-IP3 pathway leads to the continuous emptying of the ER calcium pool.The calcium oscillation mode undergoes fundamental changes, including a sustained reduction in calcium release and an extension of backfill time.Abnormal calcium signaling inhibits mitochondrial flash, which is a critical energy event for resetting the epigenome and maintaining stem cell pluripotency.Ultimately, this disorder leads to a decrease in the self-renewal ability of stem cells, which tends towards symmetrical differentiation, resulting in the production of two offspring cells that both differentiate, leading to exhaustion of the stem cell pool and loss of differentiation potential ([31]).
Regulation of CD150 expression and stem cell functionIn the aging mouse model, CD150 ^ high HSCs exhibit differentiation towards the myeloid lineage and decreased self-renewal ability, while CD150 ^ low HSCs are closer to the functional level of young HSCs.Reducing CD150 ^ high HSCs or inhibiting CD150 expression can improve HSC function, prolong lifespan, and restore stem cell pluripotency in aging mice ([13]).This discovery provides a potential strategy for reversing the decline of stem cell function and further supports the crucial role of the CD150-IP3 Ca ² ⁺ pathway in stem cell aging.
8.1.7 α - Ketoglutarate (AKG) and Glycine Metabolic PathwayAlpha ketoglutarate (AKG) is a key intermediate in the tricarboxylic acid cycle (TCA cycle), while glycine (Gly) is an important amino acid.They not only provide raw materials for energy metabolism and protein synthesis for cells, but also play a core role in epigenetic regulation and antioxidant defense [1, 2, 6].The changes in AKG and glycine levels can directly affect the metabolic status, gene expression, and oxidative stress response ability of cells.
8.1.8 The role of AKG in epigenetic demethylation
AKG is an essential cofactor for various α - ketoglutarate dependent dioxygenases (α - KGDDs), which play a critical role in epigenetic regulation [6].The most important type among them is TET (Ten Eleven Translocation) enzyme, which can catalyze the active demethylation process of DNA.DNA methylation is an important epigenetic modification closely related to gene silencing.By providing AKG, TET enzyme activity is enhanced, thereby removing methyl groups from DNA and reactivating silenced genes [6].
During the aging process, the level of AKG decreases, which weakens the DNA demethylation ability and causes some key genes (such as those regulating growth, metabolism, and antioxidant) to remain silent, thereby accelerating the stability of the aging state [1, 2, 6].Therefore, AKG is an important bridge connecting cellular metabolic status and epigenetic landscape.
8.1.9 Glycine serine cysteine glutathione antioxidant pathway
Glycine is one of the key precursors for the synthesis of glutathione (GSH).GSH is the most important antioxidant in cells, and its synthesis depends on glycine, glutamate, and cysteine.During the aging process, there may be obstacles in the supply chain of antioxidant raw materials [1,2].
Glycine can generate serine through two pathways: one is through the glycolysis intermediate 3-phosphoglycerate, and the other is through the one carbon unit metabolism related serine hydroxymethyltransferase (SHMT) pathway.Serine can then be converted to cysteine, which is the rate limiting precursor for GSH synthesis.Therefore, the metabolic pathway from glycine to serine and then to cysteine constitutes the core link of GSH synthesis [1, 22].When this pathway is blocked due to age-related metabolic disorders, GSH synthesis decreases, cellular antioxidant capacity weakens, and oxidative stress intensifies [1,2].
8.2.1 Regulation of NAD+and SIRT1 by the α - ketobutyric acid (AKB) pathway
Alpha ketobutyrate (AKB) is a product of cysteine metabolism.AKB can effectively increase intracellular NAD+levels through the action of lactate dehydrogenase-1 (LDH-1), which is an essential coenzyme for SIRT1 (deacetylase) [3,4,6,8].
SIRT1 activates PGC-1 α and AMPK through deacetylation, promoting mitochondrial biogenesis and energy metabolism, while enhancing antioxidant defense [3,4].In addition, SIRT1 can activate ACOX1 (fatty acid oxidase) through deacetylation, generate H2O2 signal, and further activate NRF2, thereby forming a positive cycle that promotes mitochondrial health and antioxidant defense [3,4].
When the AKB pathway is blocked, NAD+levels decrease, SIRT1 activity is restricted, PGC-1 α/AMPK/NRF2 signaling is inhibited, mitochondrial function is impaired, antioxidant defense capacity decreases, and aging related energy crisis and oxidative stress are accelerated [1,2,3,6].
8.2.2 Regulation network of triiodothyronine (T3) and protein quality controlTriiodothyronine (T3), as the active form of thyroid hormone, is an important regulator of the body's basal metabolic rate ([34, 37]).Recent studies have shown that T3 plays a central role in cellular protein quality control and forms a critical metabolic quality control cross network with the energy sensing molecule AMPK ([35]).This network not only maintains protein homeostasis, but also participates in regulating mitochondrial function and autophagy processes.
8.2.3 T3 regulates protein homeostasis through FOXO3a-ULK1 autophagy axis
The regulation of protein quality control by T3 is mainly achieved through the activation of transcription factor FOXO3a ([36]).The specific mechanism is as follows:
After upregulating the ubiquitin proteasome system (UPS)
T3 and binding to the nuclear thyroid hormone receptor (TR), it can directly act on the FOXO3a gene promoter, significantly upregulating its transcription level.FOXO3a subsequently promotes the expression of a series of E3 ubiquitin ligases (such as MuRF1, Atrogin-1), labeling misfolded or damaged proteins with "ubiquitin tags" and guiding them into proteasomal degradation ([33,36]).
Activating the autophagy lysosome pathway
FOXO3a is also a key inducer of autophagy.It can upregulate autophagy core genes such as LC3 and ATG12, and release the inhibition of autophagy initiating complex ULK1, thereby initiating cellular autophagy, clearing aggregation proteins and damaged mitochondria ([35,36]).
Therefore, at the physiological T3 level, FOXO3a forms the core pillar that maintains protein homeostasis.With aging (such as a decrease in GH-IGF-1 axis), T3 levels decrease, FOXO3a expression and activity weaken, UPS function and autophagic flux are impaired, leading to increased protein aggregation and cytotoxicity ([33,36]).
8.2.4 Breakage and Quality Control Collapse of T3-AMPK Positive Feedback Loop
There is a precise positive feedback loop between T3 and AMPK ([35, 37]):
T3 activates AMPK by increasing basal metabolic rate, increasing cellular AMP/ATP ratio, and conformational activation of AMPK;In addition, T3 can directly promote AMPK α subunit phosphorylation and enhance its kinase activity ([35]).
Feedback regulation of AMPK on T3
Promote T3 generation: AMPK can phosphorylate and activate type II deiodinase (D2), converting T4 into active T3 and maintaining local T3 levels.
Collaborative downstream signaling: AMPK and T3 can both phosphorylate ULK1, jointly initiate autophagy, and optimize mitochondrial function ([34, 35, 37]).
During the aging process, the decline in upstream mitochondrial function and GH levels lead to the first decrease in T3, weakening AMPK activation;The decrease in AMPK activity in turn inhibits D2 enzyme function, leading to the disruption of the T3-AMPK positive feedback loop.At this point, the UPS and autophagy systems lose sufficient energy and transcriptional support, leading to a sharp decline in protein quality control capabilities and accelerating the disruption of the intracellular environment and the emergence of aging phenotypes ([33-37]).
8.2.4 PTEN Oxidative Deactivation: A Key Molecular Switch for Aging Cell AccumulationIn the cascade reaction of aging, the abnormal accumulation of senescent cells is the core link leading to tissue functional decline and chronic inflammation.This hypothesis proposes that the oxidative inactivation of PTEN protein is a key molecular switch driving this process.It breaks down the inhibition of the mTOR pathway and ultimately blocks the BAX mediated mitochondrial apoptosis pathway, leading cells into an aging stalemate of "inability to survive, inability to seek death" [38-40].
Mechanism explanation: From PTEN oxidation to apoptosis program failure1 The oxidation of PTEN and the release of mTOR pathway.
PTEN, as a key phosphatase, is highly dependent on the reduced state of the thiol group (- SH) in its active center for its activity.During the aging process, the collapse of the upstream antioxidant network (especially the NRF1/2 axis and glutathione system) leads to a sharp increase in intracellular oxidative stress levels.This leads to the oxidation of the thiol group at the PTEN active site, causing it to lose phosphatase activity [38].
One of the core functions of PTEN is to degrade phosphatidylinositol (3,4,5) - triphosphate (PIP3), thereby negatively regulating the PI3K AKT mTOR signaling axis.Once PTEN becomes inactive due to oxidation, its degradation of PIP3 weakens, leading to sustained activation of AKT and subsequent overactivation of the mTORC1 signaling pathway [38,39].
2. mTOR deeply inhibits BAX mediated mitochondrial apoptosis.
The overactivated mTORC1 pathway not only drives abnormal synthesis metabolism, but also strongly suppresses the apoptosis program of cells.Its core function lies in inhibiting the activation and oligomerization of BAX protein [40].
BAX is the core executor of the mitochondrial apoptosis pathway.After receiving pro apoptotic signals such as p53, BAX will migrate from the cytoplasm to the outer membrane of mitochondria and undergo oligomerization, forming pores that lead to the release of cytochrome c, thereby initiating the caspase apoptotic cascade reaction.
However, the active mTORC1 pathway can interfere with this process through various mechanisms:
Indirect inhibition: mTORC1 can promote the synthesis of anti apoptotic proteins (such as Mcl-1, Bcl-2), which can bind to BAX and "trap" it in an inactive state [40].
Direct regulation: The mTOR pathway can affect the phosphorylation status of BAX through downstream targets such as S6K1, directly hindering its translocation to mitochondria and pore formation ability [40].
2 The failure of cell apoptosis and the solidification of aging phenotype
are caused by severe damage signals that should initiate apoptosis (such as irreversible DNA damage). Due to the excessive activation of mTOR, BAX function is inhibited, and the formation of apoptotic pores on the mitochondrial membrane fails.Cytochrome C cannot be effectively released, caspase cascade reaction cannot be initiated, and damaged cells cannot be cleared through normal apoptotic pathways [38-40].So, the cells are forced into an abnormal state of survival - cellular aging.They permanently exit the cell cycle, but their metabolism is abnormally active and they secrete large amounts of SASP factors, becoming "zombie cells" that continuously destroy the tissue microenvironment.
4. Integration and Significance
PTEN oxidation → mTOR activation → BAX inhibition → apoptosis failure "constitutes a key pathway that directly promotes the accumulation of senescent cells [38-40].This positioning also enables the restoration of PTEN function (such as by enhancing the reduction system of thioredoxin) and/or inhibiting overactive mTOR, becoming an important direction for enhancing cell self withering function, slowing down the accumulation rate of senescent cells, and avoiding senescent cell stasis [38-40].
8.2.5 CD38-NAD ⁺ - AMPK axis: a cellular autonomous inflammatory signal reversal mechanismAging is a physiological process that gradually worsens with low-grade chronic inflammation.The initiation, amplification, and loss of control of inflammation have been widely described in various diseases and tissue functional decline [2,3].However, the body has also developed multiple layers of autonomous negative feedback mechanisms aimed at limiting the excessive diffusion of inflammatory signals and maintaining cellular homeostasis.The CD38-NAD ⁺ - AMPK axis has been proposed as the fundamental "inflammatory signal reversal pathway" present in almost all cell types, with its core logic being the active reversal of pro-inflammatory states through metabolism signal coupling [8,41].
Although this axis was first explicitly elucidated in the maintenance of iNKT cell function [8], literature [41] suggests that CD38, as an inflammation sensitive molecule, can be directly induced by classic inflammatory factors such as TNF - α and IL-6, thereby rapidly mediating the regulation of NAD ⁺ levels under inflammatory conditions.This discovery provides direct evidence to explain the link between age-related chronic inflammation and NAD ⁺ baseline depletion.
8.2.5.1 Consumption of NAD ⁺ by CD38 and allosteric activation of AMPK
This pathway is initiated by induction of CD38 expression [41].CD38 is a transmembrane protein with an extracellular enzyme domain exhibiting NAD β - glucanase activity.Under the stimulation of inflammatory factors such as TNF - α and IL-6, CD38 expression is significantly upregulated [41], catalyzing the hydrolysis of NAD ⁺ to produce ADP ribose (ADPR) and cyclic ADP ribose (cADPR) [8].This process leads to a rapid depletion of the cellular NAD ⁺ pool, triggering transient disturbances in the energy response signal.The decrease in NAD ⁺ leads to an increase in the AMP/ATP ratio, and this metabolic crisis signal is captured by the central energy sensor AMPK [14,15].AMPK achieves complete activation by phosphorylating the Thr172 site through the synergistic action of its upstream kinase LKB1 [14].
During this process, cADPR, as a byproduct of CD38, may also participate in the regulation of intracellular calcium homeostasis by modulating calcium signaling, providing a molecular basis for subsequent metabolic inflammatory integration [11].In addition, the activation of AMPK is closely related to the energy status of mitochondria, and can regulate mitochondrial function, ROS levels, and autophagy activity through feedback mechanisms, forming a dual regulation of metabolism and signaling [2,3].This mechanism explains why the CD38-NAD ⁺ - AMPK axis is not only a trigger for inflammation reversal, but also a core hub for maintaining cellular homeostasis.
8.2.5.2 Multidimensional inhibition of NF - κ B transcriptional activity by AMPK
Activated AMPK is the core executor of this reversal pathway, which inhibits the pro-inflammatory transcription factor NF - κ B through multiple mechanisms:
Direct phosphorylation of p65 subunit: AMPK can directly phosphorylate the p65 (RelA) subunit of NF - κ B, such as Ser536 site.This modification not only does not enhance transcriptional activity, but also weakens the binding ability of p65 to DNA reaction elements, promotes its binding to nuclear export proteins, accelerates its extranuclear transport, and directly reduces the transcriptional activity of NF - κ B [8].
Inhibition of IKK complex activity: AMPK activation can indirectly inhibit the I κ B kinase (IKK) complex, reduce the phosphorylation and degradation of I κ B α, anchor NF - κ B more in the cytoplasm, and prevent it from entering the nucleus to initiate inflammatory gene transcription [8].
Synergistic inhibition with SIRT1: Despite the overall decrease in NAD ⁺ levels, AMPK activation can promote NAMPT expression, maintain or rebuild NAD ⁺ supply in local microdomains, thereby supporting the activity of deacetylase SIRT1.SIRT1 deacetylates the p65 Lys310 site and significantly inhibits its transcription ability [8].The synergistic effect of AMPK and SIRT1 forms a "molecular clamp" on NF - κ B activity, achieving strong pro-inflammatory signal reversal.
This multi-layered inhibitory mechanism indicates that the CD38-NAD ⁺ - AMPK axis not only acts as a sensor in metabolic energy sensing, but also plays a "gate" role in molecular regulation of inflammatory signals, providing a reliable mechanism for cells to actively maintain homeostasis.
8.2.5.3 Closed loop feedback and steady-state remodeling of inflammatory signals
The CD38-NAD ⁺ - AMPK axis constructs a self limiting negative feedback loop:
Inflammatory signal ↑ → CD38 ↑ → NAD ⁺↓ → AMPK ↑ → NF - κ B ↓ → Weakened inflammatory signal
The by-products of cADPR may further participate in cell repair, metabolic adaptation, and mitochondrial function regulation by regulating calcium signaling [11].This closed-loop mechanism effectively terminates the malignant spread of inflammation and plays a central role in maintaining cellular metabolism immune homeostasis.
During the aging process, sustained inflammatory stress and baseline depletion of NAD ⁺ weaken the function of this axis, preventing cells from effectively terminating the inflammatory program activated by NF - κ B, leading to chronic low-grade inflammation and accelerating tissue and systemic decline [10,41].Therefore, the CD38-NAD ⁺ - AMPK axis is regarded as the cell's own "inflammatory signal reset program", and the maintenance of its complete function may be key to delaying aging and various aging related diseases.
8.2.6 Gender Differences in Hormone Network Connections Second and Third CausesThis model reveals that sex hormones constitute the key differential physiological background connecting the second and third causes of aging, with the core being the differential regulation of fat distribution, inflammation initiation, and growth hormone axis by male and female hormones, ultimately leading to significant temporal and phenotypic differences in the aging pathway between genders [42].
8.2.6.1 Male pathway: vicious cycle of androgen abdominal fat deposition leptin resistance axis
Under the dominance of male hormones, fat distribution exhibits a typical visceral centripetal aggregation trend [42].When the mitochondrial fatty acid oxidation ability driven by the second factor decreases, the plasma free fatty acids that flood into abdominal fat cannot be effectively cleared, resulting in functional accumulation in the abdominal cavity.This type of accumulated adipose tissue is not an inert energy warehouse, but an active endocrine organ that continuously releases pro-inflammatory factors such as TNF - α and IL-6, initiating local and systemic low-grade inflammation [44] [].
This inflammatory environment performs triple destructive tasks:
Localized lipolysis amplification: Within the abdominal adipose tissue, inflammatory signals activate hormone sensitive lipases, intensifying local lipolysis and producing more free fatty acids that are released into the bloodstream, forming a futile cycle of lipolysis fatty acid overflow re greasing, further pushing up systemic levels of free fatty acids [44] [47].
GH axis inhibition: Elevated plasma free fatty acids themselves and inflammatory factors from their sources jointly act on the hypothalamic arcuate nucleus, directly suppressing the amplitude and frequency of pituitary anterior vein impulse secretion of growth hormone by inhibiting GHRH and stimulating the release of somatostatin (SST).
Subcutaneous lipolysis and cortisol compensation: Circulating inflammatory factors simultaneously induce lipolysis in relatively healthy subcutaneous adipose tissue, which compensates by activating the hypothalamic pituitary adrenal axis and increasing cortisol secretion in an attempt to control uncontrolled inflammation, but cortisol also promotes lipolysis [44] [47] [48] [49].
At the same time, the sustained presence of male hormones continues to strengthen the physiological trend of fat transfer to the abdomen.This process exacerbates systemic aging from two dimensions:
Decreased adiponectin and skin barrier damage: It weakens the total amount and function of subcutaneous adipose tissue, reduces the secretion of adiponectin with beneficial metabolic effects [45], and has a positive promoting effect on the synthesis of ceramides in the stratum corneum of the skin. The decrease in its level directly damages the integrity and moisturizing ability of the skin lipid barrier.
Elevated oxidative stress: The sustained inflammatory burden of abdominal fat, along with the decreased buffering capacity of the subcutaneous layer for inflammatory factors due to fat reduction, collectively amplifies the body's oxidative stress index [44].
A more critical turning point is that excessive transfer and accumulation of adipose tissue in the abdomen can lead to excessive, non rhythmic secretion of leptin [43].At this point, the energy regulation logic of the body underwent a fundamental paradigm shift: from the negative feedback mode of "prototype fat moderate leptin stimulating GH secretion to promote fat oxidation" in a healthy young state, to the leptin resistance mode of "pathological abdominal fat excess leptin inhibiting GH secretion by continuously activating the hypothalamic SOCS3 signal and stimulating SST expression".This hormone network reconstruction, based on the combined background of male hormones and decreased mitochondrial lipid metabolism, accurately links the second and third factors of males into a self driven malignant pathway [42] [43] [44] [45].
8.2.6.2 Female Pathway: Epigenetic Protection of the Growth Hormone Axis by Estrogen
In sharp contrast to the male pathway, women receive effective protection from estrogen during their reproductive age.Estrogen largely shields the GH secretion axis from early lipid metabolism disorders and direct impact of inflammatory factors by maintaining a healthier subcutaneous fat distribution and its inherent anti-inflammatory properties.
Therefore, in the early stages of aging, the connection between the second and third causes in women relies more on a more direct energy crisis signal - the decrease in ATP production rate directly caused by mitochondrial dysfunction, which activates AMPK by increasing the AMP/ATP ratio. Although the latter can indirectly affect mTOR and autophagy in energy perception, it has not yet exerted strong epigenetic silencing pressure on the transcription promoter region of GH genes [46].
This means that in women, the initiation of the third cause is more focused on the global decrease in energy availability, rather than the early and severe systemic upregulation of GH gene epigenetic locking and SST levels mediated by the inflammation leptin axis as in men [46].
Systemic compensation under the principle of survival priority: from co damage of skin and blood vessels to fibrosis fateIn the inflammatory storm of aging, the maintenance of different tissues by the body is not treated equally, but follows a profound principle of "survival first".This hypothesis reveals that when the levels of inflammatory factors systematically increase, their attacks on structural proteins exhibit a cross tissue synchronicity: collagen and elastin in the skin, as well as collagen and elastin in the blood vessel wall, are simultaneously affected and damaged ([50] Li et al., 2023).The former concerns the maintenance of appearance, while the latter directly maintains the fundamental life activity of blood circulation.Faced with this crisis, the human body has activated a sophisticated collaborative response program with survival as its highest goal.
8.2.7.1 Identification of survival crisis and initiation of dual compensation pathwayThe integrity of blood vessels is the bottom line for the survival of life.When inflammatory factors erode the vascular matrix, causing the collagen framework to relax and the elastic network to break, the body recognizes this as the highest level of survival threat.For this reason, it almost synchronously activates two fundamental compensatory pathways:
Emergency anti-inflammatory: By upregulating the secretion of glucocorticoids, the excessive inflammatory response is systematically suppressed, aiming to reduce the sustained attack on vascular (and skin) structural proteins from the source ([50] Li et al., 2023).This is the 'throttling' strategy.
Forced repair: At the same time, significantly increasing the expression level of transforming growth factor - β (TGF - β) strongly drives fibroblasts to synthesize new collagen and elastin (Ren et al., 2023; Kuang et al., 2007), aiming to urgently repair damaged vascular networks and ensure structural support of the circulatory system.This is the 'open source' strategy.
The response mechanism of "one suppression and one rise" forms a protective loop aimed at maintaining vascular function in the short term.
8.2.7.2 The cost of compensation and the vicious cycle of fibrosis
However, under the continuous pressure of aging, this compensatory mechanism aimed at emergency rescue has lost its precise regulation.The highly secreted TGF - β cannot distinguish repair targets, and while attempting to "strengthen" blood vessels, it also indiscriminately acts on fibroblasts throughout the body, including the dermis layer of the skin ([51] Ren et al., 2023; [52] Kuang et al., 2007).This process leads to:
The mandatory repair procedure initiated to save the blood vessels necessary for life, while causing excessive fibrosis and hardening of the skin, manifested as loss of elasticity and deepening wrinkles.
Forming a self reinforcing vicious cycle: inflammation damages blood vessels and skin → the body raises glucocorticoids and TGF - β to protect blood vessels → TGF - β excessive drive leads to skin and multi tissue fibrosis → microcirculation obstruction and hardening of fibrotic tissues → local hypoxia and metabolic disorders → triggering stronger inflammation → further damaging blood vessels and skin matrix.
Therefore, visible fibrosis and wrinkles on the skin, in deep logic, are the direct cost paid by the body to delay the more deadly threat of vascular collapse ([50] Li et al., 2023; [51] Ren et al., 2023; [52] Kuang et al., 2007).This positioning reveals the common driving factors of skin aging and cardiovascular aging at the molecular level, and interprets the "inflammation fibrosis transition" as a typical example of survival instinct initiated but ultimately leading to common decline due to systemic dysfunction.
8.2.8 The Game of NAD ⁺ Level Differentiation and Apoptosis Programs: Pathway Selection of PARP1-AMPK Axis
The determination of cell fate depends on the precise game between its internal energy and signaling pathways.This hypothesis reveals that senescent cells, upon receiving severe DNA damage signals, initiate a severe activation of the PARP1 gene through their intrinsic apoptotic program.As a "molecular sensor" for DNA damage, PARP1's extraordinary activity rapidly depletes the intracellular NAD ⁺ library, aiming to label and initiate repair by synthesizing poly ADP ribose chains [53] [54].
This seemingly repair oriented process indirectly triggers a critical 'backup plan': a sharp decrease in NAD ⁺ triggers a surge in the AMP/ATP ratio, thereby conformationally activating AMPK.The deep strategic purpose of this temporary AMPK activation in the context of apoptosis is to assist the p53 Bax axis in fulfilling its core apoptotic mission - that is, the energy crisis signal provided by AMPK can enhance the activity of p53 and promote the effective oligomerization and "punching" of Bax protein on the mitochondrial membrane, initiating programmed cell clearance and achieving "self termination" of the cell [55].
However, this sophisticated apoptosis preparation program is highly susceptible to disruption in the macroscopic context of aging.The core obstacle comes from the abnormally high expression of the mTOR pathway.The overactive mTORC1 suppresses this apoptotic initiation through the following dual mechanisms [55]:
Indirect blockade: mTORC1 serves as the main switch for protein synthesis, driving the synthesis of anti apoptotic proteins such as Mcl-1 and Bcl-2 in large quantities.These proteins can bind to Bax, firmly imprisoning it and preventing its translocation and oligomerization towards mitochondria.
Direct interference: The downstream signal of mTOR may directly affect the phosphorylation status of Bax, directly hindering its pore formation ability.
Bax perforation failure "means that the apoptosis program carefully laid by the PARP1-NAD ⁺ - AMPK axis is disrupted by mTOR in the final execution stage.The cells failed to undergo apoptosis as expected and instead became trapped in an abnormal survival state, with intracellular NAD ⁺ depleted.
There is a fundamental metabolic pathway fork here: in cells with normal NAD ⁺ levels, incoming ketone bodies (β - hydroxybutyrate, BHB) can smoothly enter mitochondrial metabolism, which increases the AMP/ATP ratio and promotes sustained activation of AMPK [56].Activated AMPK can synergistically enhance the signaling pathway of p53, significantly increasing the sensitivity of cells to internal damage signals and preparing for potential repair or clearance decisions in the future.
However, in senescent cells, this pathway is completely shut down due to depletion of the NAD ⁺ library by PARP1.When ketone bodies enter such cells, they cannot enter the tricarboxylic acid cycle due to the lack of NAD ⁺, a key coenzyme, and thus accumulate abnormally in the cytoplasm [58].The accumulated ketone bodies then enter the epigenetic regulatory pathway and undergo lysine β - hydroxybutyrylation modification, strongly inhibiting the transcriptional activity of p53 [57].
This modification reverses the fate of cells from a stress state of "attempting to initiate apoptosis but failing" to a "silent" state where p53 activity is suppressed and metabolism is stagnant.Therefore, starting from the depletion of NAD ⁺ by PARP1 and continuing until ketone body deposition triggers Kbhbh modification to silence p53, it constitutes a passive stabilization mechanism for senescent cells after the apoptosis program is blocked by mTOR. This is also the complete molecular pathway of the "senescent cell silencing mechanism" in this theory [53-58].
8.3.1 The origin of global epigenetic disorder: from calcium signal breakdown to synthetic metabolic failureThis hypothesis proposes that epigenetic disorders are not isolated events, but rather the inevitable result of the aggregation of upstream key pathological signals.Its startup engine is rooted in the continuous activation of the CD150-IP3 pathway, which triggers the breakdown of calcium oscillation rhythms, combined with the metabolic crisis of decreased levels of alpha ketoglutarate (AKG), collectively triggering the overall failure of the epigenetic maintenance system [1] [2] [6] [7] [28] [31].
8.3.1.1 Upstream Overture: Disruption of Calcium Oscillatory Rhythm and Common Breakthrough of AKG Deficiency in Superficial Maintenance BarrierChronic inflammation induces high expression of CD150, which leads to continuous emptying of the endoplasmic reticulum calcium pool through the action of IP3. This not only depletes calcium reserves, but also alters the dynamic dynamics of calcium ions: the duration of calcium release is shortened, and the filling time is prolonged [28] [31].This disorder directly inhibits the frequency and intensity of mitochondrial flash [2] [3] [4].
Mitochondrial flash, as a brief and high-energy ROS pulse, is a key physiological signal for resetting epigenetic modifications such as acetylation and phosphorylation of local histones, and is the energy basis for maintaining the "plasticity" and "youthfulness" of cellular epigenomes [1] [3] [4].Flash depletion means that the epigenetic landscape loses its driving force for dynamic renewal.
At the same time, the absolute scarcity of AKG, driven by the second and third factors of aging, dealt a fatal blow to the epigenetic maintenance system at the substrate level [6] [7].AKG is an essential cofactor for TET enzyme family DNA demethylases and various histone demethylases [6] [7].The depletion of their levels has left these 'epigenetic erasers' functionally paralyzed.
The dual supply lines of energy signals (mitochondrial flash) and biochemical substrates (AKG) are simultaneously cut off, and cells lose their last resort to maintain epigenetic homeostasis, leading to the outbreak of genome-wide epigenetic disorders [1] [2] [6] [7].
8.3.1.2 Core lesion: Transcriptional blockade of non essential amino acid synthesis caused by epigenetic disordersThe most direct consequence of epigenetic disorders is the complete loss of control over gene expression programs, abnormal silencing of key enzyme genes involved in non essential amino acid synthesis, and the collapse of downstream antioxidant systems.
Glycine metabolic pathway blockade: Glycine synthesis relies on serine hydroxymethyltransferase, and epigenetic disorders can lead to high methylation of its promoter and sustained inhibition of gene expression, blocking the supply chain of glycine serine cysteine glutathione antioxidant raw materials [22].
Paralysis of taurine synthesis pathway: Key enzyme genes such as cysteine dioxygenase and sulfite decarboxylase are silenced, reducing taurine levels, weakening antioxidant stress capacity, and affecting mitochondrial membrane stability [1] [22].
Arginine metabolism imbalance: the expression of arginine metabolism related enzymes (such as argininosuccinate synthase synthase) is abnormal, which affects nitric oxide metabolism and polyamine synthesis, and aggravates vascular endothelial dysfunction and cell regeneration decline [1] [22].
8.3.1.3 Ultimate Disaster: Endogenous Retroviral Release and Autoimmune Attack
After the failure of the epigenetic maintenance system, the disinhibition of endogenous retroviruses (RVs) occurs [10] [11].RVs RNA and virus like proteins form a "viral mimic" in the cytoplasm, which is recognized by the cGAS STING pathway as foreign invasion, triggering type I interferon response and inflammatory cytokine storm [10] [11].
The essence of this process is the body's "autoimmune" clearance of its own cells, with sustained high-level interferon signaling inducing cell aging or apoptosis, further encroaching on depleted transcription and translation resources, and suppressing the possibility of synthetic metabolism and repair [1] [10] [11].
8.2.3 Endogenous retroviral release and CD150 inflammatory self-locking cycle
In the late stage of epigenetic global disorder, the deepest genomic trauma - transcriptional disinhibition of endogenous retroviruses (RVs) - is triggered.These ancient virus remnants integrated into the human genome during the evolutionary process, whose promoter regions were originally tightly "sealed" by DNA high methylation.However, under the combined action of TET enzyme inactivation due to AKG deficiency and abnormal metabolism of methyl donors, the epigenetic seal on the ERK element was largely released.[6]
As a result, there is a significant aggregation of ERK RNA and virus like proteins in the cytoplasm, forming a strong 'viral Mimicry' scenario.This state is recognized by the innate immune system within the cell, particularly the cGAS STING pathway, as viral invasion.The type I interferon response and inflammatory cytokine storm triggered by this are much stronger than conventional chronic inflammation, essentially constituting an "autoimmune" attack by the body on its own cells.
Thus, a self driven and self locked inflammatory cycle is officially formed:
1. ERK release drives inflammation: The transcription and viral analog signals of ERK produce large amounts of type I interferon (such as IFN - α/β) and pro-inflammatory factors (such as TNF - α, IL-6) through pathways such as cGAS STING.
2. Inflammation enhances CD150 expression [28]: These high-intensity inflammatory signals, as the strongest stressor, further strongly and continuously upregulate CD150 expression.As an amplifier and actuator of inflammatory signals, the expression level of CD150 is directly positively correlated with the intensity of inflammation.
3. CD150 exacerbates epigenetic breakdown: High expression of CD150 leads to continuous emptying of the endoplasmic reticulum calcium pool through the IP3 pathway, completely disrupting the rhythm of calcium oscillations.The disordered calcium signal inhibits the energy critical pathway mitochondrial flash that resets the epigenome.
Meanwhile, persistent calcium imbalance itself can directly interfere with the activity of epigenetic modifying enzymes.
4. Epigenetic breakdown leads to more release of rvs: The secondary breakdown of the epigenetic maintenance system (first caused by AKG deficiency and calcium flash inhibition) results in permanent loss of transcriptional control over rvs and other repetitive elements.More RVs are activated and transcribed, releasing stronger viral analog signals.
5. Loop closure and system locking: stronger virus simulation signal → more severe inflammatory storm → higher levels of CD150 expression → more thorough calcium oscillation and epigenetic collapse → wider release of ERK.
This positive feedback loop, consisting of "SERVER release virus simulation inflammation storm CD150 upregulation epigenetic breakdown," is a typical self driven and self amplifying malignant closed loop.It locks the system in a malignant state of high inflammation, high interferon, and complete epigenetic control.[10][11]
The self-locking mechanism of the aging pathway: cascading amplification of interlocking loopsThe aging pathway described in this hypothesis is driven by a series of closely connected and self reinforcing positive feedback loops.These cycles cause the aging process, once initiated, to topple a series of carefully arranged dominoes, with each step's "result" accurately transformed into the next step's "cause", and continuously amplifying the initial signal upstream in reverse, ultimately forming an unbreakable and deteriorating system state.This precise self-locking mechanism is the core driving force that drives the body's functions from initial decline to continuous collapse.
The self-locking mechanism of aging pathway: cascading amplification of interlocking loops
The aging pathway described in this hypothesis is driven by a series of self reinforcing positive feedback loops.This sophisticated self-locking mechanism ensures that once the aging process is initiated, it is like toppling a series of dominoes, with each step's "result" accurately transformed into the next step's "cause", and continuously amplifying the initial signal upstream in reverse, ultimately driving the body's functions from initial decline to continuous collapse.
Step 1: Establishment of Initial Driving Force - Mitochondrial Functional Decline
The aging process is initiated by the fundamental internal driving force of mitochondrial functional decline (the first cause).The core lies in the "epigenetic inertia" of key genes such as PPAR α, which leads to a decrease in oxidative phosphorylation efficiency and an imbalance between ROS production and clearance.This positioning as the initial event of the upstream "first cause" creates the necessary pathological and physiological conditions for all subsequent cascade reactions.
Second loop: Activation of energy metabolism collapse and systemic disorder
As the second cause of aging, glucose and lipid metabolism disorders are directly caused by the first cause.The decreased ability of mitochondrial fatty acid oxidation leads to a decrease in lipid metabolism, resulting in a reduction in free carnitine and accumulation of cytotoxic acylcarnitine;At the same time, energy supply is forced to shift towards glucose oxidative phosphorylation, resulting in an increase in the proportion of sugar metabolism and directly leading to the accumulation of advanced glycation end products (AGEs).
AGEs activate the NF - κ B pathway through their receptor RAGE, initiating chronic mild inflammation.At the same time, the oxidative stress generated during this stage disrupts the homeostasis of vitamin E, and the proportion of its oxidized state increases, competitively inhibiting the synthesis of coenzyme Q10 through the SREBP pathway.At this point, the driving factors of aging have evolved from a simple "mitochondrial dysfunction" to a complex pathological state of "mitochondrial dysfunction+impaired coenzyme Q10 synthesis+chronic mild inflammation".
Key development: The chronic mild inflammation generated during this stage is sufficient as an early signal to induce upregulation of CD150 expression [28].CD150 causes continuous efflux of calcium ions from the endoplasmic reticulum through the IP3 pathway, which initially disrupts the calcium ion oscillation of stem cells.
This results in mild inhibition of self-renewal and asymmetric differentiation of stem cells in the early stages, and the starting point of telomere length in newly generated offspring cells has begun to show a downward trend.This indicates that the regenerative potential of the system is quietly impaired before significant hormonal axis decline.[12][13]
Third Ring: Loss of Control Center and Global Deterioration
The chronic mild inflammation and metabolic disorder environment shaped by the second factor (decreased ketone bodies, accumulation of AGEs) begin to systematically impact the core regulatory hub, leading to the decline of the GH-IGF-1 axis (third factor).The deficiency of AKG caused by the decrease of ketone bodies may trigger epigenetic silencing of the GH gene itself.The decline in GH levels leads to a catastrophic chain reaction:
The downstream key target NRF1 expression is reduced, directly leading to a decrease in mitochondrial count and exacerbating the energy crisis of the first cause at the "hardware" level.
It reduces the conversion ratio of T4 to active T3 by weakening the activity of deiodinase.The deficiency of active T3 not only exacerbates carnitine synthesis disorders (the second cause of reverse deterioration), but also leads to a decline in its ability to regulate protein quality control through the FOXO3a-ULK1 autophagy axis, causing the accumulation of misfolded proteins and protein aggregates.
As a result, the first cross link vicious cycle is declared: metabolic disorders and mild inflammation (the second cause) not only solidify endocrine decline (the third cause), but the decline in the latter's function also exacerbates the decline in antioxidant substrate synthesis caused by CD150 mediated stem cell function inhibition and epigenetic disorder, leading to a decrease in gene expression related to inflammation inhibition, precisely reversing the solidification and exacerbating upstream crises.
At the same time, the release of endogenous retroviruses exacerbates the epigenetic disorder caused by CD150, forming a self reinforcing and self-sustaining trend.
Male specific self-locking mechanism: mandatory suppression of growth hormone by the abdominal fat leptin axis
In the malignant transition from the second cause to the third cause, as described in Section 8.2.7 "Male Pathway", the background of male hormones and the decrease in mitochondrial lipid metabolism jointly drive the transfer of fat to the abdomen and functional stasis.The "androgen abdominal fat accumulation leptin resistance axis" triggered by this process constitutes a powerful self-locking cycle.
Specifically, as mentioned in the previous mechanism, the sustained inflammatory burden and excessive lipolysis of abdominal fat lead to excessive and non rhythmic secretion of leptin.This causes a fundamental paradigm shift in the energy regulation logic of the body: from a negative feedback mode of a healthy state, to a leptin resistance mode of "pathological abdominal fat excess leptin inhibiting GH secretion by continuously activating hypothalamic SOCS3 signaling and stimulating SST expression".
This mechanism transforms the metabolic disorder of the second cause into precise and sustained suppression of the third cause (GH-IGF-1 axis) without any loss, perfectly explaining why the aging process of men often presents a "cliff like" feature earlier, and tightly connects the second and third causes of men into a self driven malignant pathway.
Fourth Ring: Collapse of Defense System and Imbalance of Inflammation Immune Axis
As the GH-IGF-1 axis declines (third cause), NRF1 expression continues to decrease, leading to the collapse of the cell's antioxidant network (fourth cause).
To compensate, cells excessively activate NRF2 non rhythmically, instead exacerbating oxidative stress by increasing free iron levels.The rapidly increasing oxidative stress directly oxidizes and inhibits PTEN protein, thereby releasing the brakes on the mTOR pathway.Overactivation of mTOR can inhibit cellular autophagy.At the same time, depletion of the NAD+pool leads to functional paralysis of iNKT cells, allowing senescent cells to accumulate and secrete large amounts of SASP factors, upgrading mild inflammation to high-intensity inflammation.The compensatory increase of cortisol in the body ultimately transforms into a broad-spectrum immune and metabolic inhibitor, forming a second cross link vicious cycle.
Fifth ring: The steady state of system collapse is locked in
the high inflammation and high cortisol internal environment created by the immune collapse caused by the inflammation glucocorticoid axis (fifth cause). The regeneration and repair processes of various tissues throughout the body are strongly inhibited, and systemic phenotypes such as muscle loss and skin aging begin to emerge.At this point, all the damages in the first four rings - energy crisis, metabolic disorders, hormone decline, oxidative damage, immune suppression - are continuously amplified in this adverse context.The entire body system gradually enters a state of "steady state locking": that is, all internal environmental parameters are maintained at a new equilibrium point of low function, high consumption, and high inflammation, and are interdependent and mutually supportive, jointly resisting the system to return to a young and healthy steady state.
In summary, the essence of this self-locking mechanism lies in weaving five independent "aging factors" into a dynamic, self powered network.From the initial decline in mitochondrial function to the ultimate collapse of systemic function, each step is precisely amplified in reverse, consolidating and intensifying the previous process, ultimately driving the entire life system along a predetermined path, continuously and irreversibly sliding towards decline.Understanding this self-locking mechanism provides a crucial theoretical map for developing systematic anti-aging strategies that can simultaneously interrupt multiple critical processes.
10 Comprehensive and Future Prospects: Potential Targets for Anti Aging Strategies
Pre strategy: From Theory to Practice
Based on the aging pathway model proposed in this article, we can identify a series of potential anti-aging pre targets.These strategies aim to block or reverse mitochondrial functional decline and the cascade reactions it triggers upstream, thereby achieving the goal of systematically delaying aging.
Core metabolic intervention: synergy between high protein ketogenic diet and circadian rhythm
Based on this theory, a powerful intervention strategy is to construct a high protein medium fat extremely low carbohydrate diet structure and precisely coordinate it with the circadian rhythm, with the core being to concentrate the daily main nutrient intake (especially protein) at night.The underlying mechanism of this strategy lies in its clever utilization of the inherent physiological rhythm of the human body to achieve multi-target resetting of the aging cascade: high protein at night synergizes with GH rhythm: the secretion of growth hormone (GH) reaches its peak during deep sleep at night.Consuming proteins rich in lysine and arginine during this period can provide the most critical substrates and signals for the pulsatile secretion of GH, thereby most efficiently combating the third cause of aging (GH-IGF-1 axis decline) and providing strong kinase driving force for upstream restart of NRF1 expression and mitochondrial biosynthesis.
Multi targeted regulation of extremely low carbohydrate intake: Maintaining extremely low carbohydrate intake throughout the day, its core function is to initiate ketone body metabolism: the generated ketone bodies (especially β - hydroxybutyrate) can directly "silence" aging cells through epigenetic modification, inhibit their SASP secretion, and fundamentally reduce the inflammatory storm caused by the sixth cause of aging (accumulation of aging cells).
Relieve the drive of lipid inflammation: extremely low insulin levels can release its sustained activation of Δ -6 desaturase, thereby blocking the upstream conversion of linoleic acid to arachidonic acid and other pro-inflammatory metabolites, accurately cutting off a major key source of lipid inflammation in glucose and lipid metabolism disorders (the second cause).
Metabolic switching of temporal fasting: Long fasting windows during the day, combined with nighttime nutritional supplementation, form a powerful metabolic rhythm.This not only periodically activates AMPK, increases NAD+levels, and stimulates cellular autophagy, but more importantly, it forces the systemic metabolic mode to switch from a pro-inflammatory mode dependent on glucose metabolism to a reparative mode dependent on fatty acid oxidation and ketone body metabolism.
The brilliance of this strategy lies in that it is not simply a nutritional ratio, but a systematic reset plan based on circadian rhythms and metabolic switching, aimed at synchronously resetting the metabolism, hormones, and inflammatory states of aging organisms to a younger state.
Systemic Intervention: From Functional Reshaping to Reverse Tracing
On the basis of completing core metabolic interventions, a collaborative strategy integrating hardware repair, environmental optimization, and immune regulation aims to systematically reverse the physiological environment of aging.The core logic is to forcibly improve the working environment and functional status of mitochondria through external means, and to expect this youthful state to be fixed through mechanisms such as epigenetics, forming a reverse tracing of the upstream "first cause".
Firstly, the hardware foundation repair lays a structural foundation for the recovery of mitochondrial function by jointly supplementing PQQ, coenzyme Q10, and spermidine.The three aspects systematically repair the "engine" itself from three dimensions: promoting mitochondrial biogenesis (increasing quantity), ensuring electron transport chain efficiency (optimizing quality), and activating autophagy (clearing waste), ensuring its hardware potential for efficient operation.
Core: Forced reshaping of functionality and environment
On the basis of hardware support, actively intervene in the function and environment of mitochondria:
Forced increase in blood oxygen supply: While optimizing microcirculation, a medical oxygen concentrator is used to increase and stabilize arterial oxygen partial pressure within the physiological optimal range of 97-160 mmHg.This can directly and quickly alleviate the decrease in ATP production caused by insufficient oxygen supply, and create an efficient working environment for immune cells.
Activate immune surveillance: In a high oxygen environment, the combination of immune enhancers can significantly enhance the clearance efficiency of senescent cells, forming a "three-dimensional encirclement" of senescent cells and reducing the source of inflammation from the root.
Accurate support for antioxidant network: Supplement sufficient vitamin C (VC) as the core electron donor, efficiently maintain the activity of glutathione through the VC lipoic acid regeneration pathway, and provide a stable and low damage internal environment for mitochondrial function restart.
The Deep Philosophy of Intervention: Creating the Possibility of Reverse Tracing
The ultimate goal of this combination strategy of "hardware repair+forced oxygenation+immune activation+antioxidant support" is not conventional "support", but "forced reset".It aims to create a physiological environment for the body that resembles a youthful state in the short term.We speculate that when cells are exposed to this environment for a long time, their metabolism and epigenetic landscape may be reprogrammed.This means that forcibly improving mitochondrial function from downstream may form a powerful reverse signal, backtracking and reshaping the upstream instructions that led to its functional decline, thus opening up a new path for truly touching and reversing the "first cause of aging".
Research hypothesis: To confirm the initiation of the first cause of aging by verifying "structural oxygen deficiency"
In order to validate the hypothesis that mitochondrial dysfunction is the primary cause of aging with minimal cost, we do not need to delve into the complex downstream signaling pathway network, but should directly address the root cause of the problem.
Preliminary theoretical verification - logical chain construction based on recognized knowledge and classical researchThis path aims to construct a complete causal logic chain by linking recognized knowledge from multiple disciplines supported by classical literature.
The logical argument chain and known evidence are as follows:
Red blood cell deformability is a prerequisite for smooth microcirculation
Known evidence: Red blood cells must deform in order to pass through capillaries smaller than their own diameter, which is a fundamental principle of microcirculation physiology.Fedosov et al. revealed through multi-scale modeling that red blood cells rely on highly elastic membrane structures and fluid dynamics to maintain normal fluidity when passing through narrow capillaries [20].Musielak's review of red blood cell deformability measurement techniques further confirms the crucial role of this characteristic in maintaining smooth blood flow [21].
The size of capillaries constitutes physical constraints
Known evidence: The diameter of capillaries in specific areas of the human body, such as the choroid and glomeruli, is indeed 4-6 μ m, while the diameter of red blood cells is about 7-8 μ m. This size difference determines the necessity of red blood cell deformation [20,21].This physical structural difference means that a decrease in the deformability of red blood cells will directly lead to an increase in microcirculatory perfusion resistance.
Reduced deformability of red blood cells leads to microcirculatory disorders and hypoxia
Known evidence: under the pathological conditions such as diabetes and metabolic syndrome, it has been clearly observed that the decrease of erythrocyte deformability is directly related to the stagnation of microcirculation blood flow and the decrease of tissue oxygen partial pressure.Ebenuwa et al. found in clinical research that the deformability of red blood cells in diabetes patients decreased significantly, and was positively correlated with the increase of blood flow viscosity and tissue perfusion limitation [17].At the same time, Williams and others pointed out that oxidative stress and glycosylation reaction related to diabetes can lead to cross-linking of erythrocyte membrane skeleton protein, thus aggravating erythrocyte dysfunction and local hypoxia [16].This establishes a causal relationship between "red blood cell function → microcirculation perfusion → oxygen supply".
Hypoxia selectively and rapidly inhibits mitochondrial function
Known evidence: Numerous cellular biology studies have confirmed that hypoxia can significantly reduce OXPHOS efficiency within minutes to hours by disrupting the chemical gradient of mitochondrial electron transport chains, inhibiting ATP synthase activity, and other mechanisms.Gnaiger et al. found in classic studies that under low oxygen conditions, mitochondrial phosphorylation efficiency decreases and respiratory rate significantly decreases, and this process occurs before structural damage [18].This indicates that hypoxia has a rapid and selective inhibitory effect on mitochondrial function.
Eye socket bruising is a visible indication of microcirculatory disorders
Known evidence: The depth of skin color depends on the oxygenation status of blood flow in capillaries.Stagnation of blood flow and increased deoxyhemoglobin can cause the skin to appear bluish purple, which is a known sign in diagnosis (such as cyanosis).Hartley et al.'s review of "spontaneous periocular bruising" pointed out that thin skin and dense capillaries in the orbital area, abnormal blood flow, or local capillary rupture can all cause persistent cyanosis [19].Therefore, persistent orbital bruising can serve as a reasonable inference for poor local microcirculation and oxygenation status.
Summary of argumentation
Thus, we have completed a logical chain supported by public knowledge and classical research:
red blood cell deformability (known function) → through capillaries (known structural constraints) → affecting microcirculation perfusion and oxygen supply (known pathophysiology) → inhibiting mitochondrial OXPHOS efficiency (known cellular effects).
Eye socket bruising provides a visible and logical clinical anchor point for the initiation of this chain.The pathway of insufficient structural oxygen supply to drive mitochondrial functional decline is highly rational.
However, the existing orbital bruising cannot accurately describe the object, whether it is caused by the Mtor pathway driven nitric oxide, red blood cell count, red blood cell deformation, abnormal red blood cell oxygen carrying symptoms, or by the weak expression of AMPK pathway, weakened ATP energy production, resulting in a comprehensive decrease in cellular dynamics → microcirculatory dysfunction → venous congestion and pigmentation, or the result of other pathways. This verifies the existence of latent hypoxia itself, only demonstrating the necessary antecedents of mitochondrial functional decline, but fails to accurately analyze the mechanism, and further research is needed to follow up.
Actual human verification: Conduct a strict control group experiment based on visible signs of microcirculation disorders such as scleral hypoxia and orbital bruising to demonstrate whether microcirculation disorders can spread throughout multiple parts of the body.
As mentioned earlier, one of the earliest visible indications of microcirculatory stasis caused by decreased deformability of red blood cells appears in the eyeball.The oxygen supply of the eyeball sclera (white eye) mainly depends on its surface capillary network.When microcirculation is obstructed, the scleral tissue will enter a chronic hypoxic state, and the theory of scleral hypoxia is the core mechanism of the accumulation of myopia.
At the same time, the skin around the eye sockets is one of the thinnest in the human body, with an extremely rich and superficial subcutaneous capillary network.Microcirculatory stasis in this area can lead to an increase in the proportion of deoxyhemoglobin in the blood, resulting in dark or patchy bruises on the skin that are purplish green and difficult to fade.This is highly consistent with the pathological signs of "spontaneous periocular bruising" observed in the experimental study in patients with metabolic diseases such as diabetes.
Therefore, persistent orbital bruising and scleral hypoxia together constitute a highly suggestive clinical anchor for significant microcirculation and oxygen supply disorders in the head and face region.
Inference and verification of systemic microcirculatory disorders
According to the logic of this hypothesis, microcirculatory disorders caused by the decline of red blood cell function should not be a local exception, but a systemic phenomenon.Its impact will spread to all organs and tissues that rely on efficient capillary perfusion:
Joint function: Joint cartilage has no direct blood supply, and its nutrition and oxygen rely entirely on the diffusion of synovial fluid.Microcirculatory disorders will lead to a decrease in synovial liquid oxygen partial pressure, causing chondrocytes to be in a hypoxic environment, mitochondrial function to be impaired, and the ability to synthesize and repair extracellular matrix to decrease, thereby accelerating joint degeneration, manifested as decreased mobility, stiffness, and pain.
Nail morphology: The capillary loops of the nail bed are a classic window for observing microcirculation.Insufficient oxygen supply can lead to abnormal morphology of nail bed capillary loops, blood flow stasis, and thus affect the normal growth and keratinization process of nail mother cells, manifested as slow nail growth, loss of luster, longitudinal ridges or thinning and brittleness.
Neurological function: Neurons are the cells with the highest oxygen consumption in the body and are extremely sensitive to hypoxia.Mild disturbances in cerebral microcirculation can lead to insufficient energy supply to cortical neurons, which first manifests as a decrease in the efficiency of higher-order cognitive abilities, such as difficulty concentrating, delayed thinking, decreased short-term memory, and increased mental fatigue.
Validation plan: Systematic microcirculation assessment based on control group
To verify this systematic inference, the following comparative study can be designed:
Select individuals with typical orbital bruising/scleral hypoxia as the experimental group, and select healthy individuals aged 10-18 years and gender matched individuals without such signs as the control group.
Subsequently, multiple site and multi technique microcirculation and functional tests were conducted on the two groups of subjects:
Microscopic examination of nail fold microcirculation: directly observe the morphology, density, and blood flow dynamics of nail bed capillaries, and quantitatively analyze the blood flow velocity and degree of red blood cell aggregation.
Joint near-infrared spectroscopy technology: Non invasive measurement of blood oxygen saturation in tissues around joints to evaluate local oxygenation levels.
Transcutaneous oxygen partial pressure measurement: measuring the oxygen partial pressure diffused through the skin at specific parts of the limb (such as the dorsum pedis), reflecting the oxygen supply status of subcutaneous tissue.
Cognitive Function Scale and Neuroelectrophysiological Examination: Standardized scales are used to evaluate attention and memory function, and combined with event-related potentials to objectively reflect the speed of brain information processing.
Expected results and theoretical value: If the experimental group consistently exhibits more significant microcirculatory disorders and functional decline than the control group on multiple indicators mentioned above, it will strongly prove that "structural oxygen deficiency" is a systemic and fundamental pathophysiological state.This not only provides a systematic evidence chain for "orbital bruising" as an early aging marker, but also verifies the pathway of "microcirculation disorders tissue hypoxia mitochondrial dysfunction" from a spatial dimension, which is a common mechanism driving the parallel decline of multiple system functions in the body. Therefore, the "first cause" hypothesis is placed on an observable and verifiable solid empirical basis, and provides a solid foundation for future epigenetic verification of 80 non steady state pathways leading to aging as the first cause.On the contrary, if eye bruising cannot be found in individuals aged 10-18, and if individuals aged 10-18 only have eye bruising, scleral hypoxia, abnormal nail fold microcirculation, and decreased transcutaneous oxygen pressure measurement, it indicates that the theoretical first cause has been falsified.
If local microcirculatory disorders fail to map systemic microcirculatory disorders, it is entirely due to systemic microcirculatory disorders and an error in the ATP mechanism of systemic cells.
If there is a coexistence of both, such as some people experiencing orbital bruising, scleral hypoxia, abnormal nail fold microcirculation, and decreased transcutaneous oxygen pressure measurement, while others only experience one of them, it can be considered as an unexpected variable caused by differences in human development.
Note: The essence of the first cause is the non steady state decrease in gene expression and ATP levels in most cells throughout the body. The hypoxia model can only prove the existence of this mechanism, rather than the fact that the hypoxia model itself dominates the entire process of the first cause. The entire first cause is like a pendulum. Before humans can clearly recognize it, even if the problem of latent hypoxia is improved, this pendulum will enter another non steady state without authorization, maintaining the state of mitochondrial dysfunction decline. The amplitude and size of this pendulum's swing determine to some extent the strength of promoting aging in the body.
Conclusion: Mitochondrial function serves as the central hub of anti-aging research
In summary, this article systematically elucidates the theoretical framework of mitochondrial dysfunction as the primary cause of decline.I believe that decay is not a passive, random process of accumulated damage, but rather a programmatic process driven by mitochondrial dysfunction, with inherent logic and causal chains.Starting from the decline in mitochondrial function, we have derived a series of interrelated "aging causes" including glucose and lipid metabolism disorders, GH-IGF-1 axis decline, antioxidant network collapse, inflammation glucocorticoid axis imbalance, and accumulation of senescent cells.This model not only integrates various existing decay theories, but also reveals their inherent connections, providing a new perspective for understanding the complexity of decay.
More importantly, this theoretical framework provides direction for anti-aging research and prediction.It tells us that instead of providing targeted treatment for various age-related diseases downstream, it is better to focus our efforts on the upstream and use mitochondrial function as the central hub for systematic prediction.Whether through nutritional supplementation, lifestyle adjustments, or future drugs and gene therapies, the ultimate goal should be to restore and maintain mitochondrial health and efficient function.By breaking the vicious cycle of aging, we may be able to truly achieve "healthy aging", extend the healthy lifespan of humanity, and allow life to maintain vitality and dignity for a longer period of time.
11. Author Introduction: Deduction from "mTOR culprit" to "mitochondrial first cause".
On the occasion of conducting this systematic analysis of aging, the author hopes to share with readers the thought process of the formation of this theory.This is not a sudden inspiration flash, but a scientific research process that has gone through years and continuously explored its origin upstream.
Starting point: Identifying the root cause of "cell zombies". My research began with the observed phenomenon of aging cell accumulation.The SASP factors secreted by these 'zombie cells' are key elements in promoting tissue inflammation and functional decline.At that time, the author clearly recognized that excessive activation of the mTOR pathway was the core root cause of these cells' "survival retention" and clearance barriers.This constitutes the author's' first version 'of the aging model.
First traceability: The breakdown of the antioxidant network. However, the author immediately raised the question: Why did mTOR lose control?The answer points to its upstream regulatory factor PTEN.When PTEN loses its activity due to oxidation, its inhibitory function on mTOR is lost.So, why is PTEN oxidized?This leads the author's research focus to a more upstream event - the overall breakdown of intracellular antioxidant networks.At this point, the focus of the author's research has shifted to the balance between the core transcription factors NRF1 and NRF2.
Secondary traceability: After in-depth research on the antioxidant network, a more fundamental question has emerged: why does NRF1, which dominates basic antioxidant defense, decline first?The chain of evidence points to a decrease in growth hormone (GH) levels.GH is a key signal for maintaining NRF1 expression.The secretion of GH relies on precise pulsatile energy metabolism by hypothalamic pulse generators, which is highly dependent on mitochondrial functions such as coenzyme Q10.At this point, the core of the problem is approaching mitochondria.
Arriving at the source: Mitochondrial functional decline continues to trace upwards along the "decline of pulse energy metabolism", and ultimately all clues converge on one point: the functional decline of mitochondria themselves.Whether it is the insufficient synthesis of CoQ10 or the decreased efficiency of oxidative phosphorylation, it is fundamentally due to the abnormal function of mitochondria as the "energy signal center" of cells.At this point, the author has completed the exploration of the origin: accumulation of aging cells ← excessive activation of mTOR ← oxidation of PTEN ← breakdown of antioxidant networks ← decrease of NRF1 ← decline of GH pulses ← mitochondrial dysfunction. This complete causal chain has convinced the author that mitochondrial dysfunction is not one of the multiple manifestations of aging, but rather the upstream and endogenous "first cause" that triggers the entire aging process.
From the first edition to the current 90th edition: The Development and Unification of Theory. The systematic model you see now can be called the "current edition" of theory.The model starting from mTOR is a precious' first version '.They are not mutually exclusive, but rather an increase in cognitive depth.The 'first edition' accurately elucidates the key events of mid aging, while the 'current edition' reveals the initial cause that triggers the entire chain reaction.
Theoretical limitations and future prospects. Although this article proposes a logically rigorous systematic aging model starting from mitochondrial dysfunction, it must be acknowledged that any theoretical framework has its boundaries in exploration.
The core contribution of this model is to clarify the causal sequence of aging cascade reactions in the spatial dimension, but accurately integrating this static framework with the real dynamic evolution of aging in the temporal dimension remains a major challenge for the future.Specifically, the limitations of this study are mainly reflected in the following aspects: the shortcomings of spatiotemporal transformation: this article clearly explains the logical causal relationship from the first cause to the sixth cause, but this is more of a spatial and logical sequence.In the real time dimension, the occurrence, development, feedback, and deterioration of these events may exhibit high individual differences, organizational specificity, and nonlinear dynamic characteristics.For example, this model has not yet been able to provide an accurate answer: at critical points in an individual's life, such as 25, 34, 45, and 70 years old, which link in the cascade reaction first breaks through the critical point and becomes the main driving force for that age group?
Shortage of a complete dynamic model: In early theoretical constructions (such as the 61st edition model), I initially outlined a dynamic aging map with age ranges as stages.This graph proposes that aging is not a uniform progression of a single factor, but is driven by the depletion of different dominant factors and compensatory mechanisms at different stages:
Incubation period (adolescence): The "first cause" of aging has already been activated, and its early manifestation may be the imbalance of the "eight variables", which can lead to mitochondrial functional decline through multiple pathways, such as inducing latent tissue hypoxia and reducing mitochondrial ATP production.
However, this stage is strongly compensated by extremely strong growth hormones, and the extremely high mitochondrial biosynthesis and quality maintenance capabilities mask functional decline, temporarily preventing the system from collapsing downstream.
Youth period (around 18-25 years old): The growth hormone plateau period ends and begins to decline, and the compensatory advantage of synthetic metabolism weakens.Its support for NRF1 subsequently weakened, and the disruption of glucose and lipid metabolism (the second cause) officially laid the foundation, becoming the dominant feature of this stage.Aging cells tend to accumulate due to activation of the PTEN oxidative Mtor pathway.
During the prime of life (around 25-34 years old), sustained metabolic stress causes the antioxidant compensation mechanism of NRF2 to reach its limit, leading to the collapse of the antioxidant network (the fourth cause), typically characterized by an increase in the proportion of oxidized vitamin E and a reverse inhibition of coenzyme Q10 synthesis, resulting in the first increase in the accumulation rate of senescent cells.At around the age of 34, the metabolic pattern dominated by a systemic increase in lactate levels completely fails to compensate, triggering widespread immune escape of aging cells and forming the first cliff like aging commonly perceived by the public.
Middle age (around 45 years old): Against the backdrop of GH-IGF-1 axis decline (the third cause), coupled with a cliff like drop in sex hormone levels, the final cellular level strategy of the body's long-term dependence on "stem cell quantity compensation diversity" is broken, and tissue repair ability experiences a second cliff.
In old age (around 70 years old), the compensatory mechanism of the inflammation glucocorticoid axis (the fifth cause) ultimately fails, accompanied by the basic depletion of the stem cell pool, and the system falls into a vicious cycle of "inflammatory factors inflammatory factors", leading to a complete collapse.
The current version of the model, due to the pursuit of purity and clarity in logical starting points, has not yet fully integrated this sophisticated, time series based "dominant factor switching" mechanism. Additionally, the 61 version of the time series model is too simplified and has serious issues with rigor, making it unable to be included in the main text.
This results in a lack of sufficient dynamic resolution in explaining why the same person exhibits vastly different aging themes across different age groups in this model.
However, the above limitations precisely indicate the most valuable research direction for the future.I call for future research to focus on creating a 'personalized aging terrain map' - by using large-scale longitudinal data and AI modeling to overlay the spatial logic chain of this model with the timeline of life, in order to predict when, which organization, and which pathway an individual will first lose control of.
Once it is verified that there are different "dominant aging factors" in different age groups, the anti-aging strategy will shift from a "one size fits all" approach to "precise intervention over time": maintaining mitochondrial function in youth, strengthening antioxidant networks in adulthood, and focusing on stem cell and immune surveillance in middle-aged and elderly individuals.This will be the true meaning of 'preventing illness before it occurs'.
I firmly believe that the current version of the model provides the most reliable coordinate system and compass for interpreting the complex dynamic aging landscape of the future.Combining static causality with dynamic timing will ultimately lead us through the fog of aging.
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