Inhibition of mTOR decreases insoluble protein burden by reducing translation in C. elegans

Aging animals accumulate insoluble protein as a consequence of a decline of proteostatic maintenance with age. In Caenorhabditis elegans, for instance, levels of detergent-insoluble protein increase with age. In longer-lived strains of C. elegans, this accumulation occurs more slowly, implying a link to lifespan determination. We further explored this link, and found that detergent-insoluble protein accumulates more rapidly at higher temperatures, a condition where lifespan is short. We employed a C. elegans strain carrying a GFP transcriptional reporter under the control of a heat shock (hsp-16.2) promoter to investigate the dynamics of proteostatic failure in individual nematodes. We found that early, sporadic activation of hsp-16.2 was predictive of shorter remaining lifespan in individual nematodes. Exposure to rapamycin, resulting in reduced mTOR signaling, delayed spurious expression, extended lifespan, and delayed accumulation of insoluble protein, suggesting that targets downstream of the mTOR pathway regulate the accumulation of insoluble protein. We specifically explored ribosomal S6 kinase (rsks-1) as one such candidate and found that RNAi against rsks-1 also resulted in less age-dependent accumulation of insoluble protein and extended lifespan. Our results demonstrate that inhibition of protein translation via reduced mTOR signaling resulted in slower accumulation of insoluble protein, delayed proteostatic crisis and extended lifespan in C. elegans.