Glucose-Mediated Remodeling of Cardiac DNA Methylation

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Despite overall reductions in heart disease, the increased risk of developing heart failure has remained 2-fold greater among people with diabetes. Evidence from our laboratory and others has identified that fluctuations in glucose level and uptake directly contributes to cardiovascular disease (CVD) by modifying proteins, DNA, and gene expression. In the case of glucose, clinical studies have shown that following tight glycemic control, susceptibility to disease progression is sustained years or even decades in a process termed “glycemic memory”. A long-term goal of our laboratory is to understand the role of glucose in the formation of glycemic memory and determine if these changes alter disease progression. Recently the mechanism of epigenetic regulation, which consists of modifications of the histone proteins that help package DNA and direct modifications of the DNA (e.g. methylation), is linked to glycemic memory. A critical barrier in determining the molecular mechanisms has been the ability to place the marks in the intact heart to test disease susceptibility. Two novel advances have taken place over the last 2-5 years that place the glucose-mediated protein post-translational modification, O-GlcNAcylation, at the forefront of this quest. Specifically, O- GlcNAcylation is part of the histone code. Secondly, the proteins that regulate O-GlcNAcylation interact with the proteins that tailor DNA methylation, providing a second link between glucose and epigenetics. The objective of the current proposal is to determine the mechanism by which fluctuations in glucose alter DNA methylation and how these changes alter gene expression and cardiac function. As diabetes and heart failure are diseases with strong metabolic components, we will focus on how glucose-mediated epigenetic changes alter metabolism and energetics in acquired heart disease. We have developed two novel mouse models to test this hypothesis. The first builds upon our model of inducible cardiomyocyte-specific expression of the glucose transporter, GLUT4, and the second is a new model of cardiomyocyte O-GlcNAc regulation. Thus uniquely allowing us to directly test the role that cardiomyocyte glucose delivery and GlcNAcylation have on CVD. Our preliminary data define persistent DNA methylation changes that increase susceptibility to pressure- overload hypertrophy. In this proposal we will: determine the mechanism of altered DNA methylation (Aim 1), determine if these epigenetic modifications alter contractile and metabolic dysfunction in response to a common diabetic co-morbidity of hypertension (Aim 2), and determine if O-GlcNAc alone is sufficient to increase disease susceptibility (Aim 3). Collectively, the completion of these studies will provide fundamental insights into the mechanistic basis for glucose in the regulation of cardiac gene expression contributing to the development of diabetic CVD.