Identification Of Novel Mechanisms Of Glucolipotoxicity In Type 2 Diabetes.

Abstract

Type 2 Diabetes, a metabolic disorder associated with chronic hyperglycaemia and hyperlipidaemia, is characterised by an impairment of insulin secretion and production and β-cell death. This β-cell dysfunction is determined by different factors, among which inflammatory processes, characterised by increased expression of pro-inflammatory cytokines and chemokines. Although some molecular mechanisms have been proposed to be involved in this β-cell dysfunction, they fail to explain the whole process. In this thesis, a combined approach of microarray, RNAseq, RT-qPCR and western blot will be used to elucidate the pathways affected under glucolipotoxicity, in order to discover novel molecules involved in the pathogenesis of T2D. We found that INS-1 cells exposed to 27 mM glucose, 200 μM oleic acid, 200 μM palmitic acid, show an overexpression of CD40, a TNF receptor involved in inflammation (more than 300% p<0.01), both at RNA and protein level. These data were validated in cultured human islets (p<0.05) and in islets of mice fed a high fat diet (p<0.05). We showed also that siRNA downregulation of CD40 is associated with increase in insulin secretion (p<0.05), revealing a potential new role of this receptor in β-cells. In addition, RNAseq analysis revealed a wide list of molecules differentially expressed in glucolipotoxicity, in particular molecules involved in inflammation, insulin/IGF pathway, fatty acids-cholesterol metabolism and biosynthesis. We focused our attention on potential novel targets, including the thyroid pathway, unknown microRNAs and novel genes, in order to discover new pathways involved in the impairment of insulin secretion in T2D. This work will open the way to future studies aiming to characterise these molecules and to understand their role in the insulin secretion process. Interesting candidates can then be used in the future as potential targets for the development of new and specific therapeutic strategies.