Sirtuins are NAD-dependent histone deacetylases (HDACs) reported to increase lifespan in yeast, C. elegansand Drosophila, and to mediate effects of dietary restriction (DR) on aging. The role of Sir2 orthologs in animal aging has been tested by over-expression using transgenes, which was found to increase lifespan in C. elegans1,2 and Drosophila3. Gene effects on lifespan can be confounded by genetic background variation4. We verified the impact of Sir2 overexpression on aging, carefully controlling for genetic background and performing tests in multiple laboratories, but saw no effect on lifespan in either organism. InC. elegans, backcrossing to wild type of one long-lived line (LG100) with high level over-expression of
sir-2.1 (ref. 1) abrogated longevity without reducing transgene expression. RNAi of
sir-2.1 reduced transgene-induced over-expression but not longevity. LG100 also exhibited a dye-filling (Dyf) defect which, unlike the transgene, co-segregated with longevity. Backcrossing of a different long-lived line (NL3909) with low level over-expression of
sir-2.1 (ref. 2) also abrogated longevity without reducing transgene-induced over-expression. In Drosophila, over-expression of dSir2 (EP-UAS-dSir2 with the ubiquitously-expressed tubulin-GAL4 driver) extended lifespan relative to wild-type flies, as reported3. However, flies bearing both EP-UAS-dSir2 and tub-GAL4 were not longer lived than genetic controls containing either EP-UAS-dSir2 or tub-GAL4 alone, i.e. increased longevity is not attributable to dSir2 over-expression. Moreover, DR-induced longevity was not dSir2 dependent. Additionally, the HDAC activity of recombinant dSir2 was not activated by resveratrol. These results illustrate the importance of excluding genetic background effects in studies of the impact of individual genes on lifespan. They also suggest that Sir2 over-expression does not increase lifespan in C. elegans or Drosophila, though it remains possible that Sir2 over-expression might increase worm or fly lifespan under other conditions. Nonetheless, these findings raise the possibility that the capacity of Sir2 over-expression to increase lifespan may be restricted to yeast. 1 Nature 410, 227 (2001). 2 Dev Cell 9, 605 (2005).3 PNAS 101, 15998 (2004). 4 Nature 450, 165 (2007).