Cardiac remodeling includes changes to both cardiomyocytes and cardiac fibroblasts as well as vascular smooth muscle cells (VSMCs) and perivascular fibroblasts of intracoronary arteries which occur in response to injury to the heart concomitant with hypertension, myocardial infarction, or aging. These alterations, due to both hemodynamic and humoral factors such as angiotensin II (Ang II) and endothelin (Et-1), result in left ventricular hypertrophy, coronary artery thickening as well as perivascular and interstitial fibrosis. Angiotensin- (1-7) [Ang-(1-7)] is an anti-proliferative and anti-fibrotic peptide which opposes the mitogenic, pro-fibrotic effects of various mitogens and hormones including Ang II. During the current funding cycle of Project 2, we showed that Ang-(1-7) inhibits the growth of cardiac myocytes through activation of the G protein-coupled receptor mas and inhibition of the phosphorylation/activation of the mitogen-activated protein (MAP) kinases ERK1 and ERK2. The heptapeptide reduces proliferation and decreases collagen synthesis in cardiac fibroblasts, concomitant with up-regulation of the MAP kinase phosphatase DUSP1 and down-regulation of cyclooxygenase-2 (COX-2) and prostaglandin E synthase (PGES-1). Ang-(1-7) also increases DUSP1 in VSMCs, to attenuate ERK1/ERK2 activities, inhibit VSMC growth, and reduce vascular hypertrophy and perivascular fibrosis. Based upon these observations, the hypothesis of this project is that Ang-(1-7) counterregulates the effects of Ang II by up-regulating the MAP kinase phosphatase DUSP1 to prevent hypertrophy and reduce fibrosis. Preliminary studies show that administration of Ang-(1-7) to normotensive rats chronically treated with Ang II causes a pressure-independent reduction in the interstitial and perivascular fibrosis and coronary artery hypertrophy associated with cardiac remodeling. We will use this model to identify the molecular mechanisms by which Ang-(1-7) inhibits cell growth and fibrosis, using a combination of molecular biology, proteonomic and immunocytochemical techniques. The role of the protein phosphatase DUSP1 in hypertrophy and fibrosis will be studied in normotensive rats transfected with lentivirus containing shRNAs to the MAP kinase phosphatase DUSP1 to reduce or ablate the enzyme in vivo and attenuate the response to Ang-(1-7) treatment. The role of Ang-(1-7) in preventing the Ang ll-mediated inflammatory response by reducing cyclooxygenase 2 (COX-2) activity or prostaglandin synthase activities to alter the ratio of proliferative to anti-proliferative prostanoids will be determined in vitro and in vivo, in cultured cells and tissues from rats treated with angiotensin peptides. Finally, hypertensive rats of the mRen2.Lewis congenic strain, normotensive rats with ischemia/reperfusion injury and aged rats with progressive heart disease will be treated with Ang-(1-7), in preclinical studies to demonstrate the efficacy of Ang-(1-7) in reducing cardiac hypertrophy and fibrosis. Ang-(1-7) may represent a novel targeted therapeutic treatment for cardiac pathologies associated with high blood pressure, myocardial infarction, and aging.
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