| Summary: | Ageing is the major risk factor for all age-related diseases such as cancer, diabetes, cardiovascular disorders, and neurodegenerative diseases. Moreover, the rate of ageing is controlled, at least to some extent, by genetic pathways and biochemical processes conserved in evolution. With age, there is a general loss of histones, global and local change in DNA methylation and an imbalance of activating and repressive histone modifications. The use of Drosophila melanogaster as a model to study ageing is well established and posses many advantages, such as a rich genetic toolbox. Therefore, I investigated whether and how chromatin status is associated with ageing in Drosophila, in specific through histone lysine methylation. In order to do so, I carried out an RNAi screen of many of the most relevant histone lysine methyltransferases and demethylases in flies. From this screen, I identified five longevity genes that, when downregulated by RNAi, can extend the lifespan. Thus, I successfully established a link between these specific chromatin modifiers with epigenetic changes and lifespan in Drosophila. Moreover, among these five genes, I further characterized two, Lsd1 an H3K4me1/me2 demethylase and Set1, and an H3K4me2/me3 methyltransferase. In addition, I examined the long-lived flies for resistance to stresses such as starvation and oxidative stress, and measured their health through fecundity assays. Furthermore, I observed by western blotting that there was no change in global H3K4 methylation levels in long-lived Lsd1 heterozygous flies, nor in long-lived flies in which Set1 has been downregulated (~60%) in the intestine/gut fat body, suggesting that lifespan extension might result as a consequence from changes in specific loci and/or alterations in non-histone targets. Insulin/IGF-1 signalling (IIS), mTOR and RAS-ERK-ETS are highly evolutionary conserved longevity pathways in which many of the anti-ageing interventions converge. By ascertaining the levels of known markers of these pathways by western blotting in different tissues, I found that Lsd1 and Set1 longevity do not converge on the IIS, mTOR, or Ras-Erk-ETS pathways. Therefore, downregulation of Lsd1 and Set1 constitute a novel anti-ageing intervention in Drosophila, which could be combined with inhibitors of the aforementioned pathways for a more pronounced lifespan extension. Finally, I tested whether any relationship was discernible between the lifespan extension mediated by Lsd1 and Set1 and genomic integrity. Interestingly, downregulation of Lsd1 and Set1 exhibited increased bleomycin resistance. Therefore, lifespan extension that results from downregulation of Lsd1 and Set1 might arise from changes in specific loci and/or alterations in non-histone targets, which might play a part in the DNA damage response triggered by double-strand breaks.
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