Angiotensin receptor G protein signal switching in AgRP neurons in cardiometabolic control

项目总结/摘要 NHANES的数据显示，47.3%的美国人患有高血压，71.3%的人超重， 这些群体之间有很强的重叠性。控制血压的下丘脑通路 与控制静息代谢率（RMR）的途径交织在一起。如果长期肥胖，心血管- 刺激自主神经反应和血压反应保持不变，但RMR控制进行性 脱敏（称为“RMR适应”的过程）。RMR适应被认为有助于抵抗 身体保持体重减轻，以及身体恢复质量的倾向。因此，有一个关键的 未满足的需要是了解协调控制血压的基本下丘脑神经回路， RMR在健康条件下，以及这个系统如何在肥胖期间选择性地脱敏。肾素-血管紧张素 众所周知，脑内的RAS系统（RAS）通过多个神经元的作用来促进血压控制。 我们的团队最近发现，下丘脑弓状核内的RAS (ARC)在RMR的控制中起着关键作用。特别地，血管紧张素II（ANG）1A型受体（AT 1A） 在ARC的神经元中，表达Agouti相关肽（AgRP）是控制RMR所必需的，而不是血液 压力响应瘦素，ANG和其他刺激。因此，本提案的目的是澄清 AgRP神经元内被AT 1A受体利用来控制RMR的分子信号传导途径。 初步数据表明，在精益状态下，（i）只有一个子集的AgRP神经元表达AT 1A，（ii）这些AT 1A （iii）这种信号传导引起细胞的抑制，最终解除抑制 黑皮质素信号传导在前自主靶区域，从而增加RMR。令人兴奋的是，我们发现 在长时间高脂喂养后，ARC的一个AT 1A表达AgRP神经元亚群自发地 表现出“G蛋白信号转换”，并且开始与Gq而不是Gi第二信使偶联，这导致 ANG对这些细胞的刺激作用。因此，我们提出了一般假设，（i）在精益 所述AT 1A-表达AgRP神经元重要地参与RMR控制，且AT 1A通过Gi， 但（ii）在饮食诱导的肥胖后，这些患者中AT 1A第二信使级联反应从Gi到Gs的改变， 细胞是RMR适应发展的原因。目的1将定义AT 1A的“正常”信号级联 在瘦动物的AgRP神经元中，而目标2将剖析G蛋白信号的机制贡献 在RMR适应的发展中这些细胞的转换。这些研究将利用一系列新颖的 转基因动物模型、病毒递送方法、尖端的心脏代谢表型分析方法，以及 化学遗传学方法该项目的完成将大大增加对RMR的基本理解 控制和适应生物学，并提供了第一个在体内评估的病理生理意义， 心脏代谢生理学中单个细胞类型中ANG受体下游的G蛋白信号转换。

Project Summary / Abstract NHANES data indicate that 47.3% of Americans have high blood pressure (hypertension), 71.3% are overweight, and there is strong overlap between these groups. Hypothalamic pathways controlling blood pressure are tightly intertwined with pathways controlling resting metabolic rate (RMR). With prolonged obesity, cardiovascular- stimulating autonomic responses and blood pressure responses remain intact, but RMR control progressively desensitizes (a process termed “RMR adaptation”). RMR adaptation is thought to contribute to the resistance of the body to maintaining weight loss, and the propensity of the body to regain mass. Thus, there is a critically unmet need to understand the basic hypothalamic neurocircuitry that coordinately controls blood pressure and RMR in healthy conditions, and how this system selectively desensitizes during obesity. The renin-angiotensin system (RAS) within the brain is well known to contribute to blood pressure control through actions in multiple brain regions, and our team recently discovered that the RAS within the arcuate nucleus of the hypothalamus (ARC) is critically involved in the control of RMR. In particular, the angiotensin II (ANG) type 1A receptor (AT1A) in neurons of the ARC that express Agouti-related peptide (AgRP) are required for control of RMR but not blood pressure in response to leptin, ANG, and other stimuli. The objective of the current proposal is therefore to clarify the molecular signaling pathways within AgRP neurons that are utilized by the AT1A receptor to control RMR. Preliminary data indicate that in the lean state, (i) only a subset of AgRP neurons express AT1A, (ii) these AT1A signal via a Gi second messenger, and (iii) such signaling causes inhibition of the cell, ultimately to disinhibit melanocortin signaling in pre-autonomic target regions and thus increase RMR. Excitingly, we have discovered that following prolonged high fat feeding, a subset of AT1A-expressing AgRP neurons of the ARC spontaneously exhibit “G protein signal switching” and begin to couple to Gq instead of Gi second-messengers, which results in stimulatory effects of ANG on these cells. We therefore propose the general hypotheses that (i) in the lean state, AT1A-expressing AgRP neurons are importantly involved in RMR control, and that AT1A signals via Gi, but that (ii) after diet-induced obesity, the alteration in AT1A second-messenger cascade from Gi to Gs in these cells is causal for the development of RMR adaptation. Aim 1 will define the ‘normal’ signaling cascade of AT1A in AgRP neurons in lean animals, while Aim 2 will dissect the mechanistic contribution of G protein signal switching in these cells in the development of RMR adaptation. These studies will utilize an array of novel transgenic animal models, viral delivery methods, cutting-edge cardiometabolic phenotyping approaches, and chemogenetic methods. Completion of the project will greatly increase fundamental understanding of RMR control and adaptation biology, and provide the first in vivo evaluation of the pathophysiological significance of G protein signal switching downstream of ANG receptors in a single cell type in cardiometabolic physiology.