The pathogenesis of cardiac dysfunction in diabetes is partially understood. Our goal is to determine the mechanisms by which reduced insulin signaling in cardiomyocytes and vascular endothelium contributes to the pathogenesis of diabetic cardiomyopathy. Our overall hypotheses are: (1) In diabetes, deficient or reduced insulin signaling in cardiomyocytes leads to an initial defect in glucose/pyruvate oxidation, and a secondary increase in fatty acid oxidation that leads to increased production of reactive oxygen species (ROS) that ultimately causes progressive mitochondrial injury. Increased fatty acid delivery to insulin resistant cardiomyocytes during diabetes will accelerate mitochondrial dysfunction. (2) In the heart the (acute and chronic) regulation of cardiac muscle substrate metabolism by insulin involves paracrine interactions between cardiomyocytes and other cells in the heart such as endothelial cells. Thus, impaired insulin signaling in these cells and in cardiomyocytes both contribute to altered cardiac metabolism and function. The consequences of these defects will be exaggerated when cardiac energy requirements are increased such as during left ventricular hypertrophy.
Aim 1 : will determine the mechanisms by which chronic deficiency of insulin signaling in cardiomyocytes impairs mitochondrial oxidative capacity and predisposes the heart to lipotoxic injury. Studies will be performed in mice with constitutive and inducible deletion of insulin signaling in cardiomyocytes. We will determine the mechanisms for changes in PDH activity, the mechanisms that lead to increased fatty acid utilization in these models and the role of increased ROS generation in precipitating mitochondrial dysfunction and lipotoxic cardiomyopathy.
Aim 2 : will determine the mechanisms by which non-myocyte cells in the heart modulate cardiomyocyte metabolism. We will determine if loss of insulin signaling in these compartments will accelerate or exacerbate the metabolic and functional impairment in hearts that lack insulin signaling in cardiomyocytes by studying hearts deprived of insulin signaling in endothelial cells and cardiomyocytes under basal conditions and following pressure overload hypertrophy. The role of nitric oxide in the paracrine regulation of myocardial metabolism by insulin will be determined. These studies will shed important insight into the regulation of cardiac function and metabolism by insulin and the role of impaired insulin signaling in the pathogenesis of diabetic cardiomyopathy. ? ?
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