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

项目摘要/摘要 NHANES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非常紧密 与控制静息代谢率(RMR)的途径交织在一起。长期肥胖，心血管疾病- 刺激自主神经反应和血压反应保持不变，但RMR逐渐控制 脱敏(称为“RMR适应”的过程)。RMR适应被认为有助于抵抗 身体要保持减肥，而身体有恢复体重的倾向。因此，有一个批判性的 尚未满足的需要了解协调控制血压和血压的基本下丘脑神经回路 在健康条件下的RMR，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，大脑中的RAS系统通过多个动作对血压控制做出贡献 大脑区域，我们的团队最近发现，下丘脑弓状核内的RAS (ARC)在RMR的控制中发挥了关键作用。尤其是血管紧张素II(Ang)1A型受体(AT1a) 在ARC的神经元中，表达AgRP是控制RMR所必需的，而不是血液所必需的 对瘦素、血管紧张素和其他刺激作出反应的压力。因此，本提案的目的是澄清 AT1a受体用来控制RMR的AgRP神经元内的分子信号通路。 初步数据表明，在瘦状态下，(I)只有一部分AgRP神经元表达AT1a，(Ii)这些AT1a 通过Gi第二信使发出信号，以及(Iii)这种信号导致细胞抑制，最终解除抑制 黑素皮质素在自主神经前靶区的信号转导，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中AT1a表达的AgRP神经元亚群自发地 出现“G蛋白信号转换”，并开始与GQ偶联，而不是GI第二信使，结果是 血管紧张素转换酶对这些细胞的刺激作用。因此，我们提出一般假设：(I)在精益生产中 AT1a表达AgRP神经元在RMR调控中起重要作用，AT1a通过Gi， 但(Ii)在饮食诱导肥胖后，AT1a第二信使的改变从Gi级联到Gs级联 细胞是RMR适应发展的原因。目标1将定义AT1a的“正常”信号级联 在瘦肉动物的AgRP神经元中，虽然目标2将剖析G蛋白信号的机制贡献 在这些细胞的切换中，RMR适应的发展。这些研究将利用一系列新的 转基因动物模型、病毒传递方法、尖端心脏代谢表型方法，以及 化学发生学方法。该项目的完成将大大增加对RMR的基本了解 控制和适应生物学，并提供了第一次体内评价的病理生理学意义 在心脏代谢生理学中，G蛋白信号在单个细胞类型的Ang受体下游切换。

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.