Investigating the effects of FoxO transcriptional activity on metabolic homeostasis

Abstract

As with many other age-related pathologies, metabolic disorders entail lifelong treatment producing economic and social burdens in ageing populations. Therefore, improving the study of metabolic disorder and associated treatments is essential to healthy ageing. FoxO transcription factors modulate the expression of key metabolic factors. Previous work focusses on FoxO targets that are controlled by FoxO binding directly to DNA. Recently, studies have highlighted the importance of recruiting FoxO to regulatory gene regions via protein-protein interactions. However, most interactions required FoxO binding to DNA to modulate gene expression. Therefore, there is still little information available regarding the interactions and effects of FoxO on gene expression independent of its DNA-binding abilities. The overall aim of this thesis was to use Drosophila melanogaster as a model system to gain more in-depth knowledge of FoxO activity, particularly its DNA-binding independent activity, to allow for the identification of new and potentially more effective therapeutic targets for treating metabolic disorder. In this thesis, previously unpublished Drosophila FoxO mutants with a canonical DNA-binding domain mutation were verified for appropriate regulation and loss of DNA-binding ability. Phenotypic analysis of FoxO-dependent physiological responses in these mutants identified growth and starvation survival as potential DNA-binding independent processes. Subsequent RNA-sequencing identified genes that were also modulated in a DNA-binding independent manner. Transcription factor binding motif analysis of these differentially expressed genes identified Hp1b and Sin3a as potential comodulators of these genes alongside FoxO. Analysis of publicly available RNA sequencing and chromatin immunoprecipitation-sequencing datasets found significant overlaps between Hp1b and Sin3a regulated genes and genes that were modulated in a FoxO-dependent DNA-binding independent manner. Thus, Hp1b and Sin3a represent candidate co-factors for modulating metabolism-related genes in conjunction with FoxO. Overall, key discoveries involving FoxO’s DNA-binding independent activity including specific metabolism-related phenotypes, genes, and binding partners have been made. Ultimately, more in-depth research on the identified co-regulators will facilitate the identification of potential therapeutic targets for treating metabolic disorder without targeting FoxO directly, preventing severe side effects seen with FoxO-targeted treatments.