Angiotensin-(1-7) and Hypothalamic control of blood pressure

项目摘要 肥胖是一种全球性流行病，与过度的中枢交感神经流出到心血管系统有关。 终末器官升高血压，易患高血压。收集证据从我们的 实验室提示，缺乏血管紧张素-（1-7），一种保护肾素-血管紧张素系统的激素， 提供了将肥胖与交感神经过度激活和高血压联系起来的重要联系。我们的出版 结合初步数据，观察结果支持这一概念，表明高脂肪饮食引起的肥胖 小鼠表现出循环血管紧张素-（1-7）缺乏，这种激素的恢复减弱了心血管 交感神经过度活跃和高血压。我们的初步数据扩展了这些表型 通过提供证据证明血管紧张素-（1-7）降压效应需要激活神经回路 起源于下丘脑弓状核（ARC）。我们发现，无论是系统性和内ARC 血管紧张素-（1-7）降低小鼠血压，其作用可通过删除血管紧张素-（1-7）mas而阻止 ARC中的受体。我们进一步表明，血管紧张素-（1-7）的降压作用需要 激活可能表达阿黑皮素原（POMC）的ARC神经元的特定亚群， 以及环AMP第二信使系统。我们认为血管紧张素-（1-7）选择性激活 释放抑制性神经递质γ-氨基丁酸（GABA）的POMC神经元。支持 我们发现：mas受体高度定位于GABA能POMC神经元;血管紧张素-（1-7） 增加ARC中的GABA合成酶而不改变POMC基因表达。根据这些数据， 这一提议将检验血管紧张素-（1-7）激活GABA能受体上的mas受体的中心假设 POMC神经元在ARC减少心血管交感神经流出和降低血压。目标1将 确定血管紧张素-（1-7）是否选择性增加GABA能ARC POMC神经元的兴奋性， 转基因小鼠报告细胞系结合全细胞膜片钳电生理学方法。目标2将 确定血管紧张素-（1-7）是否需要ARC POMC神经元中的mas受体来降低血压， 我们开发了一种新的mas受体条件性敲除小鼠模型， 化学遗传学和药理学方法。目标3将确定血管紧张素-（1-7）是否降低 使用复杂的在体分离神经记录的交感神经到心血管器官的交通 接近。这些研究将在控制和高脂肪饮食下的雄性和雌性小鼠中进行 条件下，以确定性别和肥胖对血管紧张素-（1-7）激活这一神经回路的影响。 总的来说，这项提议将跨越细胞到整个动物水平，为血管紧张素-（1-7）提供新的见解。 对控制交感神经流出和血压的神经回路的影响，以及相关的细胞和 神经递质机制重要的是，这些研究有更长期的潜力来确定是否 靶向血管紧张素-（1-7）代表了治疗肥胖相关高血压的新方法。

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.