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UBC Theses and Dissertations

Exploring the function and regulation of histone H3 lysine 4 trimethylation in mature beta cells Vanderkruk, Benjamin Geoffrey Keith


Aims: Insufficient insulin release by β-cells is the primary etiology in type 2 diabetes and coincides with impaired expression of genes essential for β-cell function, but drivers of gene expression dysregulation are not well resolved. Alterations to the genome-wide enrichment and organization of chromatin post-translational modifications may promote gene expression dysregulation. Here, I investigate the role of H3K4me3 in mature β-cells and how its organization in chromatin is linked to the unique β-cell gene transcriptome in health and diabetes. I further test how its enrichment is altered by external challenges in the form of type 2 diabetes-like stresses or perturbation of one carbon metabolism. Methods: To study the functional importance of H3K4me3 in mature β-cells, we depleted H3K4me3 in β-cells of mature mice using an inducible Dpy30 deletion model under control of the Pdx1 or Ins1 promoter and performed a panel of metabolic, transcriptomic, and epigenetic tests. We compared H3K4me3 enrichment patterns with gene expression changes that occur in islets in a mouse model of type 2 diabetes and in human type 2 diabetes. We then examined the metabolic and transcriptomic consequences of folic acid restriction in mouse islets. Results: H3K4me3 contributes to gene expression in mature β-cells. H3K4me3 contributes to H3K27ac levels and, in the absence of H3K4me3, promoter-associated H3K4me1 is partially sufficient to maintain expression. H3K4me3 peak breadth is correlated with gene expression dysregulation in type 2 diabetes in mice and humans. Using a genetic mouse model to impair the methyltransferase activity of trithorax group complexes, we find that reduction of H3K4me3 reduces insulin production and glucose-responsiveness and increases transcriptional entropy. H3K4me3 in mouse β-cells is particularly required for the expression of genes that are dysregulated in a mouse model of type 2 diabetes. While locus-specific alterations are observed, global enrichment of H3K4me3 in islets is robust against external disruption of glucose homeostasis and one-carbon metabolism. Conclusions/interpretation: Overall, this thesis shows that H3K4me3 contributes to expression of genes essential for β-cell identity and function in mature β-cells and implicates dysregulation of H3K4me3 as a factor contributing to β-cell dysfunction in type 2 diabetes by altering gene expression patterns.

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