Development of Diabetic Cardiomyopathy in GLUT4 +/- Mice

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DESCRIPTION: (Scanned from the applicant's abstract) Mice with a single knockout allele of GLUT4(+/-) on a low fat diet develop type II diabetes including hyperinsulinemia, hyperglycemia, hyperleptinemia, mild hypertension, cardiomyopathy and liver steatosis with age. These pathologies occur independent of obesity, dyslipidemia, pancreatic failure and hepatic insulin resistance. We propose to conduct the first in vivo longitudinal study which examines critical molecular/metabolic/energetic alterations leading to diabetic cardiomyopathy. This addresses the important interplay between whole body metabolism and circulating factors that regulate cellular processes which result in end organ pathology. The central hypothesis is global reduction of GLUT4 expression and/or function leads to alterations in cardiac insulin action, glucose metabolism and energetics mediated by reductions in the activity of PPARgamma and Akt/PKB which result in altered contractile function and diabetic cardiomyopathy. Altered substrate use with increased reliance upon fatty acid metabolism is associated with increased oxidative stress and mitochondrial uncoupling that result in diminished energy reserves. Insulin sensitizer treatment with BRL49653, a thiazolidinedione (TZD) that activates PPARg, will improve whole body glucose homeostasis and cardiac function through alterations in AktJPKB activity, substrate usage and expression of uncoupling protein (UCP) and glucose transporter (GLUT) genes/proteins. These studies will provide unique insight into molecular, metabolic, and morphologic alterations in GLUT4+/- hearts as mice progress to diabetes that should facilitate development of therapeutics to prevent and/or minimize diabetic cardiomyopathy in humans. To accomplish these goals we have four specific aims. Each aim will identify alterations in insulin action through Akt/PKB, GLUT4- and GLUTx1 translocation, substrate partitioning/trafficking, and GLUT and UCP2/3 gene/protein expression in hearts of GLUT4+/- and control mice. Molecular and cellular analyses will be correlated with morphologic and hemodynamic changes in heart and alterations in whole body glucose homeostasis and circulating serum factors (e.g. leptin, insulin, T3/T4, glucose, free fatty acids) as mice progress from normal (N/N) to prediabetic (N/H) to overt diabetic (H/H) phenotypes. Effects of short term treatment with the TZD BRL49653 (PPARg agonist) on these parameters will be defined before significant alterations in body weight or adiposity can be measured. The latter studies will determine the mechanism of action of TZDs in the heart and may reveal novel therapeutic targets and applications.