Autophagy, an evolutionarily conserved cytoplasmic degradation system, has been implicated as a convergent mechanism in various longevity pathways. Autophagic activity decreases with age in several organisms, but the underlying mechanism is unclear. Here, we show that the expression of Rubicon, a negative regulator of autophagy, increases in aged worm, fly and mouse tissues at transcript and/or protein levels, suggesting that an age-dependent increase in Rubicon impairs autophagy over time, and thereby curtails animal healthspan. Consistent with this idea, knockdown of Rubicon extends worm and fly lifespan and ameliorates several age-associated phenotypes. Tissue-specific experiments reveal that Rubicon knockdown in neurons has the greatest effect on lifespan. Rubicon knockout mice exhibits reductions in interstitial fibrosis in kidney and reduced α-synuclein accumulation in the brain. Rubicon is suppressed in several long-lived worms and calorie restricted mice. Taken together, our results suggest that suppression of autophagic activity by Rubicon is one of signatures of aging.
Introduction
Macroautophagy (hereafter, autophagy) is an evolutionarily conserved intracellular membrane trafficking process in which double-membrane structures called autophagosomes sequester cytoplasmic materials and fuse with lysosomes, where their contents are degraded. Initially, autophagy was described as a bulk degradation system, but it has become clear that autophagy also selectively targets aggregated proteins, lipids, damaged organelles, and invading bacteria. By driving the degradation of a wide range of targets, autophagy maintains cellular homeostasis; consequently, dysfunction in autophagy has been implicated in many human diseases, including cancer, neurodegeneration, and metabolic disorders.
Recent evidence has shown that autophagy is also involved in animal aging. Autophagic activity decreases with age in many species1,2,3,4. Studies using several model organisms including C. elegans led to the discovery of several conserved longevity pathways, including mild reduction of insulin/IGF-1 signalling, calorie restriction, germline removal, reduced mitochondrial respiration and reduced TOR signalling. Importantly, all of these interventions activate autophagy and extend animal lifespan in a manner that depends on active autophagy, suggesting that autophagy is one of convergent mechanisms of many longevity pathways5,6,7,8,9. Moreover, overexpression of ATG5 in mice or neuronal Atg8 or Atg1 in Drosophila extends lifespan4,10,11, although it remains unclear why simple overexpression of genes involved in autophagosome formation would activate autophagy. More recently, a knock-in gain-of-function point mutation in Beclin-1 which disrupt beclin1-BCL2 interaction and constitutively activates autophagy has been shown to extend lifespan in both female and male mice12. Although these accumulating evidences further manifest the positive correlation between activation of autophagy and longevity13, yet our knowledge of the molecular mechanism by which autophagic activity declines with age is still limited14.
Although many autophagy related genes are positive regulators of autophagy, we and others previously identified one of few negative regulators of autophagy, Rubicon (Run domain Beclin-1 interacting and cysteine-rich containing protein), as a Beclin 1 interacting protein. Especially, Rubicon inhibits autophagosome-lysosome fusion process as well as endocytic trafficking through binding to PI3K (class III phosphatidylinositol-3 kinase) complex15,16. Recently, we have found that Rubicon level is increased in association of autophagy impairment in livers of mice fed a high-fat diet, recapitulating NAFLD (nonalcoholic fatty liver disease)17. Hepatocyte specific Rubicon knockout mice displays significant improvement of liver steatosis and autophagy, indicating upregulation of Rubicon plays a pathogenic role in NAFLD17. Since the prevalence of NAFLD increases with age18,19, we decided to examine the relationship between Rubicon and aging. In the current study, we found that Rubicon is increased in worm, fly and mouse tissues. Reduction of Rubicon extends lifespan in worm and female fly and ameliorates age-associated phenotype in worm, fly, and mouse tissues. These results suggest that increase of Rubicon could be evolutionally conserved one of causes for age-dependent autophagy impairment.
Source: https://www.nature.c...467-019-08729-6
