Saturday, December 21, 2024
12/21/2024
PROJECT SUMMARY Obesity is a global epidemic that is associated with excessive central sympathetic outflow to cardiovascular end organs to elevate blood pressure and predispose to hypertension. Accumulating evidence from our laboratory suggests that deficiency of angiotensin-(1-7), a protective hormone of the renin-angiotensin system, provides an important link connecting obesity with sympathetic overactivation and hypertension. Our published observations, combined with preliminary data, support this concept by showing that high fat diet-induced obese mice exhibit circulating angiotensin-(1-7) deficiency, and restoration of this hormone attenuates cardiovascular sympathetic overactivity and hypertension in this model. Our preliminary data expand on these phenotypic findings by providing evidence that angiotensin-(1-7) depressor effects require activation of neural circuits originating in the arcuate nucleus of the hypothalamus (ARC). We show that both systemic and intra-ARC angiotensin-(1-7) lowers blood pressure in mice, with effects prevented by deletion of angiotensin-(1-7) mas receptors in the ARC. We further show that blood pressure lowering effects of angiotensin-(1-7) require activation of specific subpopulations of ARC neurons that are likely proopiomelanocortin (POMC)-expressing, as well as cyclic AMP second messenger systems. We propose that angiotensin-(1-7) selectively activates POMC neurons that release the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). In support of this, we show that: mas receptors are highly localized to GABAergic POMC neurons; and angiotensin-(1-7) increases GABA synthesis enzymes in the ARC without altering POMC gene expression. Based on these data, this proposal will test the central hypothesis that angiotensin-(1-7) activates mas receptors on GABAergic POMC neurons in the ARC to reduce cardiovascular sympathetic outflow and lower blood pressure. Aim 1 will determine if angiotensin-(1-7) selectively increases the excitability of GABAergic ARC POMC neurons using transgenic mouse reporter lines combined with whole cell patch clamp electrophysiology methods. Aim 2 will determine if angiotensin-(1-7) requires mas receptors in ARC POMC neurons to lower blood pressure via GABA release mechanisms using a novel mas receptor conditional knockout mouse model we developed and chemogenetic and pharmacological approaches. Aim 3 will determine if angiotensin-(1-7) decreases sympathetic nerve traffic to cardiovascular organs using sophisticated in vivo isolated nerve recording approaches. These studies will be conducted in male and female mice under control and high fat diet conditions, to determine the impact of sex and obesity on angiotensin-(1-7) activation of this neural circuit. Overall, this proposal will span the cellular to whole animal levels to provide new insight into angiotensin-(1-7) effects on neural circuits controlling sympathetic outflow and blood pressure, and related cellular and neurotransmitter mechanisms. Importantly, these studies have more long-term potential to determine if targeting angiotensin-(1-7) represents a novel approach for the treatment of obesity-related hypertension.
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