The renin-angiotensin system (RAS) is a major regulator of cardiovascular (CV) and renal function in health and disease. Elevated activity and expression of RAS components in central CV control regions and attenuation of the Hypertension with central lesions or administration of angiotensin-II (Ang-II) antagonists have supported the notion that a hyper-functioning brain RAS may be involved in the pathogenesis of Hypertension in several genetic and experimental models. Until now, the common assumption was that Ang-II served as the main actor of this system. A new member of the RAS, ACE2 (angiotensin converting enzyme type 2) has been identified in organs and tissues related to CV function (e.g. heart, kidney, vessels) and appears to be part of a counter-regulatory pathway buffering the excess of Ang-II. We recently identified the ACE2 protein in brain regions involved in the central regulation of blood pressure (BP) and showed that it is regulated by other components of the RAS. In addition, we recently observed that ACE2 over-expression in the subfornical organ (SFO) dramatically reduces the pressor response to central administration of Ang-II in mice and reduces oxidative stress in cells. These observations added to the role of ACE2 in the generation of biologically active peptides like Ang-(1-7), supply a rationale for further explorations in the brain in the face of normal and pathophysiological states. In this proposal, we hypothesize that central ACE2 plays a major compensatory role during Hypertension;ACE2 over-expression will promote Ang-(1-7) formation and Ang-II degradation, resulting in the reinforcement of compensatory mechanisms and preventing Hypertension and the associated oxidative stress. Taking advantage of our expertise in physiological genomics, a science that studies the physiological consequences of gene manipulation, combined to state of the art recording and analysis of CV function in conscious mice, we propose to investigate the consequences of chronic ACE2 over-expression on the development of neurogenic Hypertension. Using a new genetically-engineered mouse model, with brain-targeted ACE2 over- expression, we will: 1) Establish the functional consequences of brain-targeted ACE2 over-expression in neurogenic hypertension. 2) Identify the role of the SFO and RVLM in the ACE2-mediated reduction of Hypertension in Syn- ACE2 transgenic mice and the molecular consequences of their activation. 3) Determine the effects of ACE2 over-expression on Ang-II and Ang-(1-7) receptors signaling pathways. We believe that this unique model will allow us to determine the physiological role of central ACE2 in- vivo in neurogenic Hypertension. Evidence of a beneficial role of ACE2 in BP regulation could lead to the development of new therapeutics as well as a better utilization of existing therapeutics for the treatment of Hypertension and other CV diseases.

Public Health Relevance

Among cardiovascular diseases, worldwide prevalence estimates for Hypertension may be as much as 1 billion individuals, and approximately 7.1 million deaths per year may be attributable to Hypertension. Using transgenic mice, this application will describe the ability of a new enzyme, ACE2, to prevent the development of Hypertension. If confirmed, ACE2 could become a new target for the treatment of Hypertension and other cardiovascular diseases.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
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Hypertension and Microcirculation Study Section (HM)
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Maric-Bilkan, Christine
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Louisiana State Univ Hsc New Orleans
Schools of Medicine
New Orleans
United States
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Sriramula, Srinivas; Xia, Huijing; Xu, Ping et al. (2015) Brain-targeted angiotensin-converting enzyme 2 overexpression attenuates neurogenic hypertension by inhibiting cyclooxygenase-mediated inflammation. Hypertension 65:577-86
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