Calcium and the physiology of diabetes

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Type 2 diabetes mellitus (T2DM) is a major health concern worldwide, and the prevalence is increasing. Current therapeutics have potentially life-threatening side-effects. A better understanding of the molecular mechanisms underlying T2DM could lead to improved therapy. Calcium (Ca2+) plays a key role in the insulin secretion from pancreatic β cells in the islets of Langerhans. This project focuses on elucidating novel mechanisms underlying altered Ca2+ regulation that contribute to impaired insulin secretion. We show that in a rare genetic disorder intracellular Ca2+ leak via mutant type two ryanodine receptor/calcium release channels (RyR2) in pancreatic β cells is associated with glucose intolerance and decreased insulin secretion. The goal of this project is to use several murine models of T2DM to determine whether the observation that impaired insulin secretion is linked to RyR2-mediated intracellular Ca2+ leak is a generalized phenomenon in diverse models of T2DM. The approach will focus on examining the function of RyR2, a Ca2+ release channel located on the endoplasmic reticulum (ER) of many cell types including pancreatic β cells, in insulin release using biochemical, biophysical and metabolic tests. RyR2 can become leaky either due to genetic mutations or post-translational modifications (chiefly oxidation, nitrosylation and phosphorylation) all of which can impair stable closing of the channel resulting in pathological intracellular Ca2+ leak. The goal is to test the hypothesis that ER Ca2+ “leak” via RyR2 contributes to impaired insulin secretion in T2DM. The rationale is based on our recent finding that patients with leaky mutant RyR2 channels and an inherited form of exercise-induced sudden death (catecholaminergic polymorphic ventricular tachycardia, CPVT) have abnormal glucose tolerance tests (GTT) and reduced insulin levels. Knock-in mice developed in the applicant’s laboratory harboring these CPVT RyR2 mutations have ER Ca2+ leak, abnormal GTT and reduced insulin levels, just like CPVT patients. The aims are: 1 Determine how leaky RyR2 channels cause mitochondrial dysfunction, and reduced insulin release.; 2) Does RyR2 channel dysfunction contribute to impaired insulin secretion in murine models of T2DM? Furthermore we will assess whether pharmacologic treatment with a new class of rycal drugs that fix leaky RyR2 channels, or genetic treatment that fixes leaky RyR2 channels, improves Ca2+ signaling, and insulin secretion in diverse models of T2DM? The goal of the project will be to provide mechanistic links between ER Ca2+ leak, ER stress, mitochondrial dysfunction, reduced insulin secretion and glucose intolerance, and has significant translational implications as leaky RyR2 may represent a novel therapeutic target for the treatment of T2DM.