Epigenetic Mapping in Type 2 Diabetes. Glucose-triggered histone modifications in various tissues

Abstract: Epigenetic modifications triggered by high glucose may predispose to diabetes risk by regulating gene expression activity. A growing body of evidence suggests that histone modification which is an essential component of epigenetic mechanism may play an important role in the development of type 2 diabetes (T2D) and its complications. In this thesis, the overarching aim is to map histone modifications triggered by high glucose in various tissues in T2D. In study I and II, we focused on detailed epigenetic regulation mechanisms in thioredoxin-interacting protein (TXNIP) gene which has been previously shown to be strongly linked to glucotoxicity in diabetes. In study I, we investigated epigenetic regulation of TXNIP gene expression induced by hyperglycaemia in kidneys. This study was conducted on a diabetic mouse model, as well as mouse and human kidney cell lines. We found that high glucose induces histone modifications at different histone modification marks including H3K4me1, H3K4me3, H3K9ac, H3K27me3 at TXNIP gene promoter in kidneys following diabetic kidney disease progression. These changes are associated with TXNIP gene transcription, which can be reversed or enhanced by inhibitors to histone acetyltransferase (HAT) or histone deacetylase (HDAC). In study II, we investigated glucose-stimulated TXNIP gene expression regulated by histone acetylation via HAT p300 in pancreatic islets. We created p300 knock-out in a rat pancreatic beta cell line INS1 832/13 by CRISPR/Cas9. Ep300 knock-out leads to decreased histone acetylation in various regions of TXNIP gene, decrease in high glucose-induced TXNIP gene expression, apoptosis and increase in insulin secretion.In study III and IV, we further extended our investigation to genome-wide mapping of glucose-induced histone modification changes in T2D.In study III, we mapped transcriptome and epigenome changes in INS1 832/13 with HAT p300 knock-out created by CRISPR/Cas9. We identified gene expression changes and genome-wide histone acetylation mark H3K9ac modifications mediated by p300 at high glucose. These changes were then overlapped with human islet transcriptome profile, and 62 genes were identified which are highly sensitive to glucose-induced epigenetic changes by histone acetylation. In study IV, we studied genome-wide acetylation changes in peripheral blood mononuclear cells (PBMCs) in atherosclerosis patients with T2D. We found that T2D condition in atherosclerosis leads to H3K9ac enrichment changes in 181 genomic regions. Furthermore, we also discovered an association between the genomic locations of significant H3K9ac changes with genetic variants identified in previous T2D GWAS, including transcription factor 7-like 2 (TCF7L2) rs7903146. Pathways analysis revealed multiple activated pathways involved in immunity.Taken together, the studies in my thesis present exclusive mapping of glucose-induced epigenetic landscape in T2D in pancreatic islets, kidneys and PBMCs; and provide further evidence on epigenetic mechanisms in the development of T2D and its complications.