Hypoglycemia-induced NO in glucose sensing neurons and counterregulation

描述（由申请人提供）：本提案研究反复低血糖对下丘脑腹内侧核（VMN）葡萄糖感应神经元（GSNs）的影响。总体目标是深入了解大脑感知低血糖的细胞信号通路，以及低血糖诱导的这些通路的改变如何导致低血糖相关的自主神经衰竭（HAAF）。本提案中的两个假设直接解决了这些问题。假设一是一氧化氮是中枢葡萄糖感知和低血糖反调节反应启动的必要步骤。然而，复发性胰岛素低血糖期间过量NO的产生会损害随后低血糖导致HAAF的反调节反应。体外和体内技术的结合将在细胞和整个动物水平上验证这一假设。这些实验将研究NO和AMP激活的蛋白激酶之间的正反馈在VMN GSNs的葡萄糖感知和低血糖反调节反应的启动中的作用。假设二：胰岛素诱导的低血糖反应中生理上NO的产生使NO信号通路脱敏，损害葡萄糖感知，导致HAAF的发生。脱敏的机制是NO引起神经元可溶性鸟酰环化酶（NO受体）的s -亚硝基化，使葡萄糖感知神经元对随后的NO产生无反应。这些研究将为反复低血糖重置大脑葡萄糖阈值的方式提供重要信息，从而导致HAAF。这将有助于开发新的、有效的、安全的治疗I型糖尿病及其主要现代并发症低血糖的方法。

DESCRIPTION (provided by applicant): This proposal investigates the effects of recurrent hypoglycemia on glucose sensing neurons (GSNs) in the ventromedial hypothalamic nucleus (VMN). The overall objective is to gain an in depth understanding of the cellular signaling pathways by which hypoglycemia is sensed by the brain and how hypoglycemia induced alterations in these pathways may lead to hypoglycemia- associated autonomic failure (HAAF). The two hypotheses in this proposal directly address these issues. HYPOTHESIS I is that NO is an obligatory step in central glucose sensing and initiation of the counterregulatory response to hypoglycemia. However excess NO production during recurrent insulin-hypoglycemia impairs the counterregulatory response to subsequent hypoglycemia leading to HAAF. A combination of in vitro and in vivo techniques will test this hypothesis at the cellular and whole animal level. These experiments will investigate the role of a positive feedback between NO and AMP activated protein kinase in glucose sensing by VMN GSNs and initiation of the counterregulatory response to hypoglycemia. HYPOTHESIS II is that the supraphysiological NO production in response to insulin-induced hypoglycemia desensitizes the NO signaling pathway, impairing glucose sensing and leading to the developemnt of HAAF. The proposed mechanism for desensitization is that NO causes S-nitrosylation of neuronal soluble guanylyl cyclase (the NO receptor), rendering glucose sensing neurons non-responsive to subsequent NO production. These studies will provide important information regarding the way that recurrent hypoglycemia resets the glucose threshold of the brain, leading to HAAF. This will facilitate the development of new, effective, and safe treatments for Type I diabetes mellitus and its major modern complication, hypoglycemia.