Absence of effects of Sir2 overexpression on lifespan in C. elegans and Drosophila

Abstract

Over-expression of sirtuins (NAD+-dependent protein deacetylases) has been reported to increase lifespan in budding yeast, Caenorhabditis elegans and Drosophila melanogaster1-3. Studies of gene effects on ageing are vulnerable to confounding effects of genetic background4. We re-examined the reported effects of sirtuin over-expression on ageing and found that standardisation of genetic background and use of appropriate controls abolished the apparent effects in both C. elegans and Drosophila. In C. elegans, outcrossing of a line with high level sir-2.1 over-expression1 abrogated the longevity increase, but not sir-2.1 over-expression. Instead, longevity co-segregated with a second-site mutation affecting sensory neurons. Outcrossing of a line with low copy number sir-2.1 over-expression2 also abrogated longevity. A Drosophila strain with ubiquitous over-expression of dSir2 using the UAS-GAL4 system was long-lived relative to wild-type controls, as previously reported3, but not relative to the appropriate transgenic controls, and nor was a new line with stronger over-expression of dSir2. These findings underscore the importance of controlling for genetic background and the mutagenic effects of transgene insertions in studies of genetic effects on lifespan. The life extending effect of dietary restriction (DR) on ageing in Drosophila has also been reported to be dSir2 dependent3. We found that DR increased fly lifespan independently of dSir2. Our findings do not rule out a role for sirtuins in determination of metazoan lifespan, but they do cast doubt on the robustness of the previously reported effects on lifespan in C. elegans and Drosophila.

Specific protein homeostatic functions of small heat‐shock proteins increase lifespan

“…The ey‐GAL4 driver, which is traditionally used for eye‐specific expression, also induces expression in the rest of the body ( flyatlas http://www.flyatlas.org). To properly evaluate the effects of single gene overexpression on lifespan, we backcrossed all lines over w 1118 males for six generations (Burnett et al ., 2011). This led to loss of expression of the transgenes in some lines (Fig.…”

Autophagy and ageing: Insights from invertebrate model organisms

“…Similarly, although a Drosophila strain with ubiquitous overexpression of dSir2 mediated by a tubulin-GAL4 driver was long-lived relative to wild-type controls, as previously reported , it was not long-lived relative to appropriate transgenic controls. These findings imply that the effects of dSir2 overexpression on lifespan in flies could reflect heterosis in the vicinity of the transgene inserts or a mutagenic effect of transgene insertion (Burnett et al, 2011).…”

“…Reduced dSir2 activity prevents lifespan extension by caloric restriction or mutations in rpd3 (another deacetylase gene), known to increase lifespan by acting within a pathway related to caloric restriction Rogina et al, 2002). However, a recent study questions the conserved role of dSir2 in mediating lifespan extension in response to dietary restriction (Burnett et al, 2011).…”

CCAR‐1 is a negative regulator of the heat‐shock response in Caenorhabditis elegans

“…SIRT1‐regulated processes are also conserved in the worm and are mediated by SIR‐2.1. Worms expressing extra copies of sir‐2.1 exhibit increased longevity (Burnett et al, 2011; Rizki et al, 2011; Tissenbaum & Guarente, 2001; Viswanathan & Guarente, 2011). Also, enhancing sir‐2.1 activity through caloric restriction enhances the transcription of hsp‐70 (Raynes, Leckey, Nguyen, & Westerheide, 2012).…”