INSULAGE · Understanding the interplay of insulin/IGF signalling with endocrine hormones in ageing

Final Activity Report Summary - INSULAGE (Understanding the interplay of insulin/IGF signalling with endocrine hormones in ageing)

Insulin / insulin-like growth factor (IGF) signalling (IIS) is a fundamental pathway controlling body growth and development, glucose and fat homeostasis and ageing. Our scientific aim was to understand the molecular basis of ageing process using drosophila melanogaster, the fruit fly, which showed evolutionarily conserved IIS resembling that of mammals. Recent scientific evidence indicates that IIS reduction extends lifespan, while activation of IIS is necessary for cell survival and healthy juvenile growth. Reduction of IIS can cause insulin resistance and increase risks of age-related cardiovascular diseases and obesity. Reduction of IIS shows both advantageous and disadvantageous effects on human ageing. This is also true of IIS in drosophila, where severe IIS reduction is deleterious for adult survival, whereas subtle reduction is related to the extent of adult lifespan. This suggested that precise alterations of signalling activity might determine the lifespan or that the tissue and time specific functions might be important. In order to identify tissue and chronological specificity of IIS required for slowing the fly ageing process, a comprehensive analysis of the drosophila insulin receptor CHICO (dInR-CHICO) cascade regulating tissue and body growth, developmental time, fecundity and lifespan was performed via genetic manipulations. Ubiquitous overexpression of a dominant negative form of the single fly insulin receptor dInR (dInRDN) gave rise to an inhibitory effect on the endogenous receptor and produced moderate dwarfism, infertility, two-day delay of juvenile development and massive extension of lifespan. The median lifespan was around 84 days compared with 60 days in controls. In addition to this, protein kinase B (Akt/PKB) phosphorylation was inhibited in these long-lived flies. In contrast, overexpression of CHICO ribonucleic acid interference (chiRNAi) produced normal or shortened lifespan, smaller body size and lower fecundity. A further analysis examined the role of IIS in the pre-adult period on lifespan using a tubulin promoter GeneSwitch Gal4 system (tub-GS), through administration of various concentration of RU486, ranging from 2 to 100 µM, with high concentration of RU486, between 50 and 100 µM, and demonstrated that mortality in early life was increased. In contrast, chiRNAi driven by tub-GS constantly showed subtle, however significant, extension of lifespan with moderate dwarfism. The result suggested that CHICO possessed some specific function in ageing and, on that subtle reduction of body size, affected the ageing process via reducing fecundity. Moreover, we analysed adult tissue specificity via overexpressing the dInRDN with tissue-specific GS drivers. Neural-specific inhibition of the receptor antagonist did not extend lifespan, while abdominal fat tissue specific inhibition resulted in increased lifespan, which demonstrated that the fat tissue was an IIS target. We also found that lifespan extension by dInRDN required 400 µM of RU486 instead of the 200 µM which were normally administrated to obtain dFOXO-dependent longevity. This suggested that lifespan extension showed a critical threshold in determining lifespan. In summary, the project successfully determined IIS chronological specificity in order to demonstrate the ageing process and that the abdominal fat tissue was actually a specific tissue. As ligands of the receptor were expressed in the brain, the brain-adipocyte endocrine axis of the IIS would thus become an important signalling circuit for ageing research.

Data: CORDIS, © European Union