Defining the roles of Orai3 channel in cardiomyocytes and cardiomyopathy.

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Abstract Dilated cardiomyopathy (DCM) is a severe condition, often idiopathic, that results in ventricular enlargement and progressive systolic dysfunction. While usually treated with a combination of medications or using implantable devices, cardiac transplantation is typically the ultimate treatment for DCM. The precise mechanisms leading to ventricular dilatation and dysfunction are not well understood. However, during the last few years, attention has focused on abnormalities of contractile and structural myocardial proteins and disorders of cardiac energy metabolism. We identified Orai3, a Ca2+-selective ion channel and a member of the store-operated Ca2+ channels (SOCC), as a critical proactive factor required for maintenance of postnatal cardiac function. The goal of this proposal is to investigate the roles of Orai3-mediated Ca2+ entry and associated molecular mechanisms in cardiomyocytes. To pursue our goal, we have generated several lines of cardiomyocyte-specific Orai3 knockout (Orai3cKO) mice. While constitutive Orai3cKO mice are fertile and viable, they nevertheless develop DCM that closely resembles many of the anatomical, pathophysiological, and clinical features of human DCM culminating in heart failure (HF) and premature death. We discovered through our preliminary research that Orai3-deficient cardiomyocytes exhibited loss of myofiber integrity and ultrastructural abnormalities associated with severe dysregulation of mitochondrial proteins involved in oxidative metabolism and autophagy. Our preliminary data strongly indicate that the Orai3 channel is an essential regulator of cardiac muscle function, and the data provide evidence linking Orai3-mediated Ca2+ signaling to sarcomere cell integrity and bioenergetics balance. We hypothesize that Orai3-mediated Ca2+ entry activates genetic programs through Ca2+ sensitive pathways that promote survival of post-natal cardiomyocytes. We plan to test our hypothesis by pursuing the following Specific Aims: Aim 1: To characterize the DCM phenotype following loss of Orai3 expression in the adult myocardium; Aim 2: To elucidate mechanisms by which Orai3 loss leads to cardiac function deterioration and DCM by analyzing inducible Orai3cKO mice; and Aim 3: To test the hypothesis that Orai3-mediated Ca2+ entry regulates mitochondrial metabolism. This work will lead to discovery of the molecular mechanisms by which Orai3 regulates heart function; identification of Orai as a novel mediator of DCM; and potential identification of new strategies aimed at reversing or delaying the metabolic and functional derangements seen in HF.