Angiotensin-(1-7) and beta adrenergic receptor signaling in aging

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PROJECT SUMMARY Aging is an independent risk factor for developing hypertension and cardiovascular disease. An important hallmark of aging is increased sympathetic nervous system activity, which can decrease vascular β2 adrenergic receptors (β2AR) to reduce nitric oxide (NO)-dependent vasodilation and increase blood pressure. Accumulating evidence from our laboratory suggests that deficiency of angiotensin (Ang)-(1-7), a protective hormone of the renin-angiotensin system, provides an important link to connect aging with sympathetic overactivation and hypertension. In support of this, we have shown that aging mice exhibit circulating Ang-(1-7) deficiency, and chronic restoration of Ang-(1-7) lowers cardiac and vascular sympathetic tone and blood pressure in this model. Our preliminary data translate these findings to show that circulating Ang-(1-7) levels are similarly reduced in older healthy humans, with acute Ang-(1-7) restoration tending to decrease cardiac sympathetic tone and blood pressure and increase endothelial-dependent vasodilation. Importantly, our preliminary data provide evidence that cardioprotective effects of Ang-(1-7) in aging require activation of β2AR- signaling. We show that chronic Ang-(1-7) treatment selectively increases β2AR gene expression in mesenteric vessels from aging mice, and depressor effects of Ang-(1-7) are prevented by β2AR antagonism. Based on these data, this proposal will test the central hypothesis that Ang-(1-7) reduces sympathetic outflow to restore vascular β2AR-NO signaling and lower blood pressure in aging. Aim 1 will determine if acute Ang-(1- 7) infusion decreases sympathetic tone in older healthy humans, and if these effects are associated with increased endothelial-dependent vasodilation and reduced blood pressure. Aim 2 will determine if in vivo Ang- (1-7) treatment increases β2AR-NO signaling pathways in mesenteric arteries from aging mice and endothelial cells from older healthy humans. We will determine potential cellular mechanisms by which Ang-(1-7) interacts with adrenergic-vascular signaling in aging using RNA sequencing to guide future studies. Aim 3 will determine the vascular cell-specific site of action for depressor effects of Ang-(1-7) using genetically modified mouse models with deletion of β2AR in endothelial versus vascular smooth muscle cells. Aim 4 will determine if therapies blocking Ang II activity reduce sympathetic tone and blood pressure by activating endogenous Ang- (1-7) pathways. Overall, this proposal will capitalize on in vivo and in vitro techniques spanning the cellular to preclinical to clinical levels to determine the functional importance of adrenergic-vascular mechanisms to Ang- (1-7) cardiovascular actions in aging. These studies also have the potential to inform on whether Ang-(1-7) represents a novel therapeutic target for age-related cardiovascular disease. These studies logically build upon the PI’s translational background in integrative animal and clinical methods to assess cardiovascular autonomic regulation, will allow her to develop a new skillset in advanced molecular biology methods, and will provide strong mentorship and a research framework to establish an independent and novel area of research.