Obesity-induced sympathoexcitation: role of brain insulin

 描述(申请人提供)：肥胖是一种迅速升级的流行病，在美国，它在医疗保健方面的支出比任何其他疾病都要多，每年总计超过1000亿美元。一个严重的心血管后果是高血压，部分原因是肌肉和肾脏的交感神经活动(SNA)增加。然而，其机制尚未确定。与之前对瘦素的研究一样，我们最近的数据表明，肥胖显著放大了大脑胰岛素的交感兴奋效应，这表明胰岛素可能发挥着比之前认识到的更大的作用。我们的主要目标是确定这种致敏的细胞-分子机制，目前尚不清楚。我们认为肥胖使胰岛素在控制下丘脑弓状核(ArcN)的SNA中的作用部位变得敏感。一些间接证据表明，这种敏化是由ArcN血管紧张素II(AngII)AT1R激活增加所介导的。首先，肥胖的人类和饮食诱导肥胖(DIO)的大鼠血浆血管紧张素转换酶水平升高。第二，全身性血管紧张素受体阻滞剂可阻止SNA的急剧升高和胰岛素的慢性高血压作用。第三，DIO大鼠的高血压可以通过全身性阻断肾素-血管紧张素系统(RAS)而逆转，而用RAS阻滞剂治疗肥胖者会降低SNA。最后，ArcN表达AT1aR，向ArcN内微量注射AngII可增加MAP和SNA。因此，我们假设肥胖引起的血管紧张素Ⅱ的增加放大了ArcN胰岛素增加SNA的作用。我们选择了DIO的啮齿动物模型来检验这一假设，因为它与人类的情况非常相似。我们将使用互补的方法，包括脑内选择性抑制剂的纳米注射和多个交感神经活性变化的测量，显微解剖的下丘脑组织的Western/qPCR分析，以及已鉴定的ArcN神经元的电生理记录和免疫细胞化学，系统地剖析神经肽Y中InsR和AT1R的相互依赖关系，以及ArcN中的前阿片黑素皮质素神经元，以提高基础SNA。这一核心信息与DREADDS技术相结合，并使用病毒载体在肥胖和瘦大鼠的ArcN中慢性敲除InsR或AT1R，将使我们能够确定这些神经调节剂作为交感兴奋贡献者的作用，最终导致肥胖受试者的高血压发展和最终器官损害。

 DESCRIPTION (provided by applicant): Obesity is a rapidly escalating epidemic that accounts for more health care expenditures in the US than any other medical condition, amounting to over $100 billion per year. One severe cardiovascular consequence is hypertension, due in part to increased sympathetic nerve activity (SNA) to muscle and the kidneys. However, the mechanisms have not been identified. In parallel to previous studies with leptin, our recent data indicate that obesity markedly amplifies the sympathoexcitatory effects of brain insulin, suggesting that insulin may play a greater role than previously appreciated. Our major goal is to identify the cellular-molecular mechanisms of this sensitization, which are currently unknown. We propose that obesity sensitizes insulin's site of action in the control of SNA, the hypothalamic arcuate nucleus (ArcN). Several lines of indirect evidence suggest that this sensitization is mediated by increased ArcN angiotensin II (AngII) AT1R activation. First, plasma AngII levels are increased in obese humans and rats with diet-induced obesity (DIO). Second, systemic AngII blockade prevents the acute increases in SNA and the chronic hypertensive actions of insulin. Third, hypertension in DIO rats is reversed by systemic blockade of the renin-angiotensin system (RAS), and treatment of obese humans with blockers of the RAS decreases SNA. Finally, the ArcN expresses AT1aR, and microinjection of AngII into the ArcN increases MAP and SNA. Therefore, we hypothesize that obesity-induced increases in AngII amplify the actions of ArcN insulin to increase SNA. We have chosen rodent models of DIO to test this hypothesis, because of broad similarities to the human condition. We will use complementary approaches, including brain nanoinjection of selective inhibitors and the measurement of the changes in activity of multiple sympathetic nerves, Western/qPCR analysis of microdissected hypothalamic tissue, and electrophysiologic recordings and immunocytochemistry of identified ArcN neurons to systematically dissect the interdependency of InsR and AT1R in Neuropeptide Y and pro-opiomelanocortin neurons in the ArcN to elevate basal SNA. This core information coupled with DREADDs technology and the use of viral vectors to chronically knockdown InsR or AT1R in the ArcN of obese and lean rats will allow us to establish the role of these neuromodulators as contributors to sympathoexcitation and ultimately to hypertension development and end organ damage in obese subjects.