Therefore, the question as to whether Sir2 increases lifespan in C. elegans remains unanswered, and further research must be done to elucidate the differences between these studies. Similar to the experiments repeated in worms, when Burnett and colleagues repeated the experiments in flies using the more appropriate transgenic control (tubulin/GAL4+) in both weak and strong expression of the transgene, they did not find an increase in lifespan.

However, they failed to address a previous study which used inducible Sir2 overexpression to extend lifespan. Inhibitors,research,lifescience,medical This study used the appropriate controls and still found a lifespan extension, which was dependent on inducible Sir2 levels.34 Obatoclax Interestingly, in that paper, increasing dSir2 levels ~5-fold as compared to

~3-fold further Inhibitors,research,lifescience,medical extended fly lifespan, indicating that different levels of dSir2 overexpression can differentially increase lifespan. Hence, with conflicting data regarding dSir2-regulated lifespan extension in drosophila, one must wonder exactly which differences are responsible for the apparent discrepancies. Regardless, these studies Inhibitors,research,lifescience,medical emphasize the need for appropriate controls in lifespan experiments, as well as outcrossing to overcome effects of transgene integration. Due to the general confusion regarding the role of sirtuins in worms and flies, the question of whether sirtuins regulate lifespan in mammals was more critical than ever. While there is now a great deal of data on yeast, worms, and flies, which are good research models, they are not similar to mammals and humans. Hence, researchers turned towards mice to investigate whether sirtuins can regulate lifespan Inhibitors,research,lifescience,medical in mammals, thereby completely bypassing the sirtuin debate in lower metazoans. The original results

in mammals were also puzzling. The first sirtuin examined to regulate lifespan in mammals was the most well-known mammalian sirtuin, SIRT1, the closest mammalian homologue to Sir2. However, although moderate overexpression of Inhibitors,research,lifescience,medical SIRT1 protected against age-related diseases such as osteoporosis, glucose intolerance, and metabolic syndrome-related cancers, it did not extend lifespan.35 Thus, MycoClean Mycoplasma Removal Kit either SIRT1 has no role in regulating lifespan; or under the weak expression of the transgene (threefold) SIRT1 has no effect of longevity, and stronger expression of the transgene may be necessary to achieve lifespan extension. In parallel to the research carried out with SIRT1, a separate group examined the role of SIRT6 in regulating lifespan. SIRT6 is a nuclear sirtuin known to be involved in DNA repair, inflammation, and metabolism. It seemed a likely candidate for aging, as the absence of SIRT6 in mice caused a severe aging-like phenotype and early death.36 However, early death is not necessarily indicative of a role in longevity, as developmental or metabolic defects and not premature aging can cause lethal damage.