Increasing attention in the research community is being given to age-related dysfunction of microglia in the brain as a contribution to loss of cognitive function and onset and progression of neurodegenerative conditions. Microglia are innate immune cells analogous to macrophages elsewhere in the body, responsible not just for defense against pathogens, but also maintenance of neural tissue and supporting the function of neural networks. With age a growing population of microglia become senescent or otherwise inflammatory and disruptive to normal function of brain tissue. Given that established methods exist to either selectively destroy senescent microglia or completely clear the microglial population to allow it to reconsitute itself over a period of weeks, it seems that there should be more in the way of efforts to bring these approaches to the clinic than are actually taking place.
Microglial senescence has emerged as a potentially important aging-related mechanism in Alzheimer's disease (AD), shaped in part by epigenetic reprogramming and closely coupled to immunometabolic dysfunction. While microglia initially mount adaptive responses to amyloid-beta (Aβ), tau, and tissue stress, persistent exposure to chronic neurodegenerative cues may drive subsets of microglia toward senescence-like states characterized by altered chromatin regulation, transcriptional remodeling, stable cell-cycle arrest, and a sustained senescence-associated secretory phenotype (SASP). These changes are accompanied by impaired phagocytosis, lysosomal and autophagic dysfunction, mitochondrial stress, and disrupted lipid handling, collectively weakening homeostatic surveillance and promoting a neurotoxic microenvironment. In turn, senescence-associated microglial dysfunction may contribute to amyloid and tau pathology, synaptic injury, neurovascular unit impairment, and chronic neuroinflammation across the AD continuum.
In this review, we synthesize current evidence on the phenotypic and molecular features of senescent microglia, with particular emphasis on epigenetic and transcriptional reprogramming as an organizing framework linking aging, immune dysregulation, and metabolic vulnerability. We further discuss how senescent microglia relate to other disease-associated microglial states, and we highlight unresolved questions regarding causality, biomarker specificity, and the distinction between chronic activation and true senescence in human AD. Finally, we evaluate emerging therapeutic approaches - including senolytic strategies, microglial depletion-repopulation paradigms, and metabolic or epigenetic interventions - and discuss their opportunities, limitations, and translational challenges.
Link: https://doi.org/10.1016/j.exger.2026.113177
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