Novel Aspects of the Cardiac Renin-Angiotensin System

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DESCRIPTION (provided by applicant): The renin angiotensin system (RAS) has a central role in cardiovascular homeostasis and development of renal, vascular, and cardiac pathologies. The effects of angiotensin II (Ang II) are primarily mediated by binding to AT1 receptor in an endocrine and/or autocrine/paracrine manner. We and others have recently identified a novel, intracrine or intracellular, mode of Ang II-mediated actions that do not require Ang II-AT1 interaction. We reported that cardiac myocytes synthesize high levels of Ang II intracellularly, which redistributes to cytoplasm and nucleus, without affecting extracellular levels, in high glucose conditions. Intracellular Ang II (iAng II) synthesis in high glucose conditions is chymase, not angiotensin converting enzyme (ACE) dependent. Intracellular synthesis of Ang II is completely blocked by a renin inhibitor. We have also observed activation of the intracellular RAS in cardiac fibroblasts. Significantly, iAng II levels, cardiac myocyte apoptosis, oxidative stress, and cardiac fibrosis are markedly increased in the heart of diabetic rats, which are normalized by renin inhibition, not by ACE or AT1 inhibition. These observations suggest a significant role of iAng II in diabetic cardiomyopathy, with the implications that AT1 receptor antagonists and ACE inhibitors would be ineffective in blocking iAng II effects. The cellular mechanisms that lead to intracellular expression of RAS components and Ang II synthesis, in high glucose conditions, and the mechanism of iAng II actions are not known. We have reported that iAng II causes cardiac hypertrophy; however, the relative significance of iAng II versus extracellular Ang II in pathophysiological conditions is not known. In this proposal, we will test the hypothesis that metabolic changes, induced by high glucose, result in intracellular synthesis of Ang II, which has a significant role in development of diabetic cardiomyopathy, through interaction with novel intracellular proteins. We will use cardiac myocytes and fibroblasts, both neonatal and adult, to identify hyperglycemia-induced cellular events, such as the hexosamine biosynthesis pathway, protein O-glycosylation and oxidative stress, on regulation of the intracellular RAS, by pharmacological and genetic approaches. We will identify and characterize novel iAng II interacting proteins, using affinity binding and mass spectrometry approaches. AT1 receptor deficient mice will be utilized to determine the specific role of iAng II in diabetic cardiac dysfunction. The proposed studies will identify novel mechanisms of Ang II actions in the heart and provide for new strategies in clinical interventions for diabetic cardiomyopathy. PUBLIC HEALTH RELEVANCE: This research will focus on the development of novel strategies for the treatment of patients with diabetes. Blockade of the intracellular renin-angiotensin system, may provide substantial benefit for the prevention/treatment of diabetic cardiomyopathy, compared to standard therapy with angiotensin receptor blockers and angiotensin converting enzyme inhibitors.