Molecular Regulators of Mitochondria in Diabetic Cardiomyopathy

Diabetes is at epidemic proportions, with 300 million people worldwide projected to have diabetes by 2025. Heart disease is the cause of death in 80% of diabetic patients. Heart disease related to diabetes is triggered by alteration in fatty acid metabolism, hyperinsulinemia, and hyperglycemia and involves complex changes in signaling and metabolism that may be regulated at multiple levels: 1) altered membrane ultrastructure and signaling;; 2) altered mitochondrial function and dynamics. As such, the mitochondria and membrane could be defined as integrative control points in the heart to adapt to diabetic stress and offer novel therapeutic targets. A metabolic, molecular regulator that integrates membrane and mitochondrial signaling has not been identified. Over the last 7 years of funding, this VA Merit proposal has studied caveolin biology in the setting of diabetes, and then kinase regulation in the setting of ischemia-­reperfusion injury. Building upon our findings, this renewal will merge these two ideas to propose a novel metabolic, molecular regulator of cardiac function critical to diabetic cardiomyopathy. Signaling molecules exist as dynamic, spatially organized multi-­protein complexes in lipid-­rich microdomains of the plasma membrane continuously forming and dissociating under basal or stimulated conditions. Caveolae are cholesterol and sphingolipid-­enriched structures that form microscopically distinct flask-­like invaginations of the plasma membrane. Our laboratory and others have shown that the caveolar structural proteins, caveolins, act as scaffolding molecules to aid in localization and regulation of receptors and signaling molecules to facilitate coordinated, precise, and rapid regulation of cell function. Recent evidence suggests that caveolins may exist outside of caveolae and may regulate signaling and membrane dynamics in distinct organelles. Little information exists regarding protein kinase A (PKA) localization and functionality in caveolae. Preliminary data suggest that caveolae regulate cellular cAMP. PKA signaling components are also localized to subcellular compartment where Cav-­3 localizes to and are enriched in subsarcolemmal mitochondria though little is known in the setting of diabetes. We hypothesize that, caveolin and PKA may, therefore, be a novel dyad integrating membrane and mitochondria signaling to maintain cellular and physiological homeostasis in the diabetic heart. The following specific hypotheses and aims are proposed: Aim 1: We hypothesize that mitochondria degrade when exposed to diabetic insults and that mitochondrial localized Cav-­3/PKA will sense cardiac metabolic load, tightly couple electron transport, limit generation of varied reactive species, and maintain mitochondrial structure and function. To test this hypothesis, we will determine the role of Cav-­3/PKA in mitochondrial function and structure and the therapeutic potential of mitochondrial-­targeted gene transfer in the progression of diabetes-­induced cardiac dysfunction. Aim 2: We hypothesize that plasma membranes degrade with diabetic insults, are less capable of healing and maintaining coupled insulin receptor signaling, and that membrane-­localized Cav-­3/PKA will regulate these processes to maintain normal membrane integrity. To test this hypothesis, we will determine the role of Cav-­ 3/PKA in membrane repair and signaling.