Mitochondrial sirtuins sir-2.2 and sir-2.3 regulate lifespan in C. elegans

Mitochondrial sirtuins regulate metabolism and are emerging drug targets for metabolic and age-related diseases such as cancer, diabetes, and neurodegeneration. Yet, the extent of their functions remains unclear. Here, we uncover a physiological role for the Caenorhabditis elegans mitochondrial sirtuins, sir-2.2 and sir-2.3, in lifespan regulation. Using genetic alleles with deletions that destroy catalytic activity, we demonstrate that sir-2.2 and sir-2.3 mutants live an average of 25% longer than controls when fed the normal lab diet of live E. coli OP50. While decreased consumption of food is a known mechanism for lifespan extension, we did not find evidence of reduced pharyngeal pumping. Interestingly, lifespan extension effected by loss of sir-2.2 or sir-2.3 is sensitive to the diet. The lifespan extension of the sir-2.2 mutants is eliminated and that of sir-2.3 mutants is attenuated when the animals are fed the E. coli strain HT115, which is typically used for RNAi experiments. We used growth ability of the food source and a virulent pathogenic strain to ask if differences in pathogenicity are related to the mechanisms for lifespan extension. sir-2.3 deletion results in lifespan extension in all conditions. However, removing the ability of the food source to grow eliminated the sir-2-mediated effect. We also examine the response of the mutants to oxidative stress, and our results suggest that a hormetic response contributes to lifespan extension in both mutants. Our data suggest that sir-2.2 and sir-2.3 use overlapping yet distinct mechanisms for regulating lifespan.