Programming of lifespan by insulin/IGF-like signalling in Drosophila.

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The proportion of older individuals is steadily increasing in our societies. Since age is the main risk factor for a number of debilitating, chronic diseases, this demographic change is resulting in ever-increasing human and socioeconomic costs. Understanding the biology of ageing is a key research priority because it has the potential to provide us with means to maintain health into old age. Early-life nutrition can impact subsequent health in older humans. While the existence of this phenomenon is supported by a wealth of epidemiological evidence and corroborated by direct experimentation in mammals, the mechanistic links between early nutritional environment and age-related phenotypes remain unclear. We have recently used the fruit fly Drosophila melanogaster to elucidate the mechanisms whereby the diet consumed by young adults influences their subsequent ageing. We found that a relatively short exposure to a diet rich in sugar activates insulin/IGF-like signalling (IIS) inhibiting the transcription factor dFOXO to programme adult lifespan, curtailing subsequent survival despite a dietary improvement. IIS pathway is present in all animals. It signals the animal's nutritional status to fine-tune its physiology. The importance of the IIS pathway is manifest in the role it plays in ageing: inhibition of IIS activity promotes longevity in all animals tested. At the same time, the pathway is a important determinant of human metabolic health. Our preliminary data show that modulating this pathway directly, independently of a dietary intervention, in early adulthood in Drosophila is sufficient to programme subsequent lifespan. Animal responses to nutrition are complex, simultaneously mediated by several signalling pathways in response to relative and absolute amounts of multiple dietary components. To start tackling this complexity, we propose to examine directly the molecular mechanisms whereby modulation of IIS in early adult life can shape subsequent longevity in Drosophila. This will provide us with a simpler, more tractable experimental system, focused on a single, relevant, nutrient-signalling pathway. In turn, the findings will start building a coherent and comprehensive picture of how early-life nutrition affects ageing. Our recent findings show that short-term modulation of IIS activity in just the fat body of the fly (equivalent to mammalian adipose and liver) is sufficient to change the animal's subsequent longevity. We will determine if there are other organs from which the long-term effects on ageing can be elicited. We will also determine which effectors of the pathway play a role. Work by us and others has revealed the most-likely mechanism for the long-term effects of IIS modulation on animal physiology: IIS activity appears able to change chromatin, which is the packaging of the animal's genetic material, with long-term consequences for gene expression. We will determine the impact of IIS modulation on chromatin structure and long-term gene expression in the relevant adult tissues.We and other groups have established that several enzymes capable of modifying or re-organising chromatin are engaged by the IIS pathway. We will examine whether any of these genes are mediating the long-term effects of IIS activity.In summary, the project will elucidate how relatively short-term changes in the levels of IIS can cause long-term effects in an adult animal, in vivo. This will help us understand how early-life nutrition can have an impact on human ageing. This knowledge, in the long-term, has the potential to provide us with means to ensure human health and wellbeing throughout the life course.