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Overexpression of sirtuins (NAD(+)-dependent protein deacetylases) has been reported to increase lifespan in budding yeast (Saccharomyces cerevisiae), Caenorhabditis elegans and Drosophila melanogaster. Studies of the effects of genes on ageing are vulnerable to confounding effects of genetic background. Here we re-examined the reported effects of sirtuin overexpression on ageing and found that standardization of genetic background and the 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 overexpression abrogated the longevity increase, but did not abrogate sir-2.1 overexpression. Instead, longevity co-segregated with a second-site mutation affecting sensory neurons. Outcrossing of a line with low-copy-number sir-2.1 overexpression also abrogated longevity. A Drosophila strain with ubiquitous overexpression of dSir2 using the UAS-GAL4 system was long-lived relative to wild-type controls, as previously reported, but was not long-lived relative to the appropriate transgenic controls, and nor was a new line with stronger overexpression of dSir2. These findings underscore the importance of controlling for genetic background and for the mutagenic effects of transgene insertions in studies of genetic effects on lifespan. The life-extending effect of dietary restriction on ageing in Drosophila has also been reported to be dSir2 dependent. We found that dietary restriction 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 of sirtuins on lifespan in C. elegans and Drosophila., (© 2011 Macmillan Publishers Limited. All rights reserved)

Mammals possess multiple insulin-like growth factor (IGF) binding proteins (IGFBPs), and related proteins, that modulate the activity of insulin/IGF signalling (IIS), a conserved neuroendocrine signalling pathway that affects animal lifespan. Here, we examine if increased levels of an IGFBP-like protein can extend lifespan, using Drosophila as the model organism. We demonstrate that Imaginal morphogenesis protein-Late 2 (IMP-L2), a secreted protein and the fly homologue of the human IGFBP7 tumour suppressor, is capable of binding at least two of the seven Drosophila insulin-like peptides (DILPs), namely native DILP2 and DILP5 as present in the adult fly. Increased expression of Imp-L2 results in phenotypic changes in the adult consistent with down-regulation of IIS, including accumulation of eIF-4E binding protein mRNA, increase in storage lipids, reduced fecundity and enhanced oxidative stress resistance. Increased Imp-L2 results in up-regulation of dilp2, dilp3 and dilp5 mRNA, revealing a feedback circuit that is mediated via the fly gut and/or fat body. Importantly, over-expression of Imp-L2, ubiquitous or restricted to DILP-producing cells or gut and fat body, extends lifespan. This enhanced longevity can also be observed upon adult-onset induction of Imp-L2, indicating it is not attributable to developmental changes. Our findings point to the possibility that an IGFBP or a related protein, such as IGFBP7, plays a role in mammalian aging.

The insulin/IGF-like signalling (IIS) pathway has diverse functions in all multicellular organisms, including determination of lifespan. The seven insulin-like peptides (DILPs) in Drosophila are expressed in a stage- and tissue-specific manner. Partial ablation of the median neurosecretory cells (mNSCs) in the brain, which produce three DILPs, extends lifespan, reduces fecundity, alters lipid and carbohydrate metabolism and increases oxidative stress resistance. To determine if reduced expression of DILPs is causal in these effects, and to investigate possible functional diversification and redundancy between DILPs, we used RNA interference to lower specifically the transcript and protein levels of dilp2, the most highly expressed of the mNSC-derived DILPs. We found that DILP2 was limiting only for the increased whole-body trehalose content associated with mNSC-ablation. We observed a compensatory increase in dilp3 and 5 mRNA upon dilp2 knock down. By manipulation of dfoxo and dInR, we showed that the increase in dilp3 is regulated via autocrine insulin signaling in the mNSCs. Our study demonstrates that, despite the correlation between reduced dilp2 mRNA levels and lifespan-extension often observed, DILP2 reduction is not sufficient to extend lifespan. Nor is the increased trehalose storage associated with reduced IIS sufficient to extend lifespan. To understand the normal regulation of expression of the dilps and any functional diversification between them will require independent control of the expression of different dilps.