At the time of diagnosis, a patient with Type 2 Diabetes Mellitus (T2DM) is estimated to have lost nearly 50% of his or her 2 cell function. Moreover, large prospective studies like the UKPDS, demonstrate that islet function declines continuously throughout the course of this disease. The long-range objective of this applicant is to define the biochemical and epigenetic pathways that govern gene expression and cellular function in the pancreatic 2 cell in order to identify key sites of dysregulation in the pathological state of T2DM. Insulin release from the 2 cell occurs through a Ca2+ dependent mechanism that couples cellular depolarization with intracellular Ca2+ influx from voltage-gated Ca2+ channels, and insulin granule exocytosis. The maintenance of intracellular calcium homeostasis is dependent on adequate sarco-endoplasmic reticulum Ca2+ ATPAse (SERCA) gene expression, protein levels, and protein activity. Preliminary and published studies show that islets from diabetic mice manifest striking changes in SERCA mRNA and protein levels. Further, data from the cardiovascular literature suggests that SERCA is highly susceptible to nitration, oxidation, and degradation under inflammatory conditions. The hypothesis underlying this proposal is that the hyperglycemic and cytokine enriched milieu of diabetes leads to dual insults that alter SERCA2 gene expression and protein activity, which have profound downstream effects on islet calcium homeostasis and islet secretory function. To test this hypothesis, two specific aims are proposed.
In Aim 1, the transcriptional regulation of the SERCA2 gene in Type 2 diabetes will be characterized. Experiments will be performed to identify transcriptional cofactors for SERCA2 gene transactivation and to define the epigenetic pathways that govern SERCA2 expression in the islet.
In Aim 2, the post-translational regulation of SERCA2 activity in T2DM will be systematically characterized through experiments designed to correlate the development of irreversible inactivating post- translational modifications of SERCA2 protein with endoplasmic reticulum Ca2+ levels and islet secretory function.
Type 2 diabetes mellitus is a disorder of glucose homeostasis caused by a combination of insulin resistance and progressive dysfunction of the insulin producing 2 cells of the pancreas. The incidence of Type 2 diabetes mellitus is increasing dramatically in our society. The research proposed in this application will improve our understanding of the pathogenesis of Type 2 diabetes and inform the development of new treatment strategies for this disease that focus on the preservation of 2 cell function.
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