Neuronal waste management: new roles for autophagy genes in the extrusion of protein aggregates and in longevity.

A decline in macroautophagic/autophagic activity with age contributes to the accumulation of damaged molecules and is associated with the impairment of neuronal functions and the onset of age-related diseases, particularly neurodegenerative disorders. To learn about the neuronal-specific roles of autophagy genes in aging, we specifically inhibited autophagy genes pan-neuronally in C. elegans, which leads to unexpected positive impacts on neuronal homeostasis including polyQ aggregate load and organismal lifespan. These improvements are independent of canonical, degradative autophagy in neurons and instead correlate with an increase in the secretion of large, extracellular vesicles, known as exophers. We found that the ATG-16.2 WD40 domain, a conserved domain critical for at least some noncanonical autophagy functions of ATG16L1 in mammalian cells, is required for the increased exopher biogenesis, reduction in polyQ aggregate load, and lifespan extension induced by neuronal inhibition of early-acting autophagy genes. Our study suggests that noncanonical functions of ATG-16.2, and potentially other early-acting autophagy genes, may play a role in neuronal exopher formation and C. elegans aging, extending beyond their canonical degradative functions in the autophagy process.

Autophagy protein ATG-16.2 and its WD40 domain mediate the beneficial effects of inhibiting early-acting autophagy genes in C. elegans neurons.

While autophagy genes are required for lifespan of long-lived animals, their tissue-specific roles in aging remain unclear. Here, we inhibited autophagy genes in Caenorhabditis elegans neurons, and found that knockdown of early-acting autophagy genes, except atg-16.2, increased lifespan, and decreased neuronal PolyQ aggregates, independently of autophagosomal degradation. Neurons can secrete protein aggregates via vesicles called exophers. Inhibiting neuronal early-acting autophagy genes, except atg-16.2, increased exopher formation and exopher events extended lifespan, suggesting exophers promote organismal fitness. Lifespan extension, reduction in PolyQ aggregates and increase in exophers were absent in atg-16.2 null mutants, and restored by full-length ATG-16.2 expression in neurons, but not by ATG-16.2 lacking its WD40 domain, which mediates noncanonical functions in mammalian systems. We discovered a neuronal role for C. elegans ATG-16.2 and its WD40 domain in lifespan, proteostasis and exopher biogenesis. Our findings suggest noncanonical functions for select autophagy genes in both exopher formation and in aging.