Heart failure (HF) develops at twice the rate in diabetic patients than in nondiabetic patients after myocardial infarction. A number of cardioprotective peptides, including insulin, activate the mammalian target of rapamycin (mTOR). However, the role of mTOR in the heart has not been fully defined because recent reports revealed two mTOR complexes;a rapamycin-sensitive mTOR complex (mTORC1) and a rapamycin- insensitive mTOR complex (mTORC2). To examine the functional consequences of mTOR activation, we generated transgenic mice with cardiac-specific overexpression of wild-type mTOR (mTOR-Tg). We found that the mTOR-Tg mice had preserved cardiac function, less interstitial fibrosis and less left ventricular (LV) dilatation at 4-week after ischemia-reperfusion injury (IRI) than controls. In our preliminary study using two animal models of obesity, db/db mice and high-fat diet induced obese (DIO) mice, we found that activation of cardiac mTORC1 was dramatically decreased in the late stage compared to control hearts, whereas mTORC2 activation was preserved. Hearts from the late stage db/db mice manifest impaired functional recovery after IRI ex vivo, concomitant with a decrease in mTORC1 activation. These data suggest that mTORC1 activation plays a role in cardioprotection after IRI and that loss of mTOR1 activation is involved in the increased vulnerability of the diabetic heart to ischemic injury. Recent papers strongly suggest that mTOR inhibits inflammation by suppressing cytokine production. Since cytokines are also generated in cardiomyocytes, we hypothesize that an enhanced inflammatory reaction due to decreased mTORC1 activation in cardiomyocytes is an important part of diabetic pathogenesis and is likely to account for the high rate of heart failure in diabetic patients. The goal of the current proposal is to understand if, and how, mTOR activation can prevent heart failure in the diabetic heart after IRI. This proposal is based on three hypotheses: 1) that decreased mTOR activation in diabetic hearts increases cardiomyocyte loss in post-IRI, 2) that activating mTOR reduces interstitial fibrosis by suppressing the inflammatory response in post-IRI hearts, and 3) that restoration of mTORC1 activity in diabetic hearts can prevent heart failure following IRI. We will test these hypotheses in the following three aims.
In Aim 1 : To evaluate the role of mTOR complexes in the cardiac response to IRI using genetic mouse models. We will use our mTOR-Tg mice and heterozygous mTOR knockout mice.
In Aim 2 : To examine how mTOR activation affects cell survival and the inflammatory response in in vitro diabetic models. We will examine the effects of manipulating mTOR activation in in vitro cardiomyocyte.
In Aim 3 : To test whether mTOR activation is sufficient to protect the diabetic heart against heart failure post-IRI. We will use two mouse models of diabetes and our mTOR-Tg mice.
In patients with diabetes, heart failure after myocardial infarction develops twice as often as in nondiabetic patients. Although the insulin signaling protein mTOR is known as one potential mediator of metabolism and cell growth in the heart, the role of mTOR in the diabetic heart has not been fully studied. In this proposal, new genetic animal models with cardiac-specific elevation of mTOR protein will be used to explore potential cardioprotective effects of mTOR in a mouse model of diabetes.
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