Experimental and clinical data support the concept of a diabetic cardiomyopathy, but the pathogenesis of diabetic cardiomyopathy is unclear. The Beta Arrestins are well known as important regulators of receptor signaling, including beta adrenergic signaling. The Beta Arrestins are actually part of a larger Arrestin Superfamily of proteins with likely structural similarity;in mammals, the related proteins called the Alpha Arrestins include Thioredoxin-Interacting Protein (Txnip) and five other Alpha Arrestin proteins. Compared with the Beta Arrestins, relatively little is known about the Alpha Arrestins. Txnip was initially identified as a protein that stably binds to thioredoxin and inhibits thioredoxin's reducing activity. In addition to potential thioredoxin inhibition, Txnip plays an important role in metabolism, and high glucose levels strongly induce Txnip expression in many cell types in vitro and in vivo. Increased Txnip expression resulting from high glucose can reduce thioredoxin activity, and thus Txnip may contribute to oxidative stress. Txnip overexpression also suppresses growth and promotes apoptosis, and recent studies indicate that hyperglycemia promotes apoptosis specifically through induction of Txnip. Here we present preliminary data demonstrating that Txnip is induced in myocardium by hyperglycemia, including in the myocardium of human and animal diabetic hearts. We show that Txnip can regulate redox state through an intermolecular disulfide bond with thioredoxin, supporting the concept that induction of Txnip by hyperglycemia may promote oxidative stress. We also present data that the Alpha Arrestins may function through non-redox mechanisms that include regulation of PPAR-gamma activation. Because Txnip can regulate cardiac function in vivo, this leads to our central hypothesis that Alpha Arrestins play a role in myocardial function, including in diabetic cardiomyopathy.
Our Aims are:
Aim 1 : To test the hypothesis that Txnip, one of the genes most robustly induced by glucose and a regulator of cardiac function in vivo, plays an important role in diabetic cardiomyopathy, using inducible, cardiac-specific deletion of Txnip in both Type I and Type II models of diabetes.
Aim 2 : To test the hypothesis that Txnip regulates post-ischemic cardiac function and redox state in diabetes through a specific intermolecular disulfide bond with thioredoxin, using a "knock-in" mutation of a critical Txnip cysteine.
Aim 3 : To explore non-redox mechanisms by which the Alpha Arrestin proteins regulate cardiomyocyte function. At the end of this project, we will have established the role of a candidate protein, Txnip, for mediating myocardial oxidative stress and altered cardiac function in the setting of diabetes. Furthermore, we will have new insight on the roles of Alpha Arrestin proteins in the myocardium.
Heart muscle function is worse in patients with diabetes compared to non-diabetic patients. Because heart failure and diabetes are both increasing in the United States, this diabetes-induced dysfunction of heart muscle may become a major cause of death. This project addresses the role of a specific set of proteins that may participate in heart dysfunction in diabetes.
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