Hypoglycemia-induced NO in glucose sensing neurons and counterregulation

描述(申请人提供)：本研究旨在研究反复低血糖对下丘脑腹内侧核(VMN)葡萄糖感觉神经元(GSN)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如何改变可能导致低血糖相关的自主神经衰竭(HAF)。该提案中的两个假设直接解决了这些问题。假设I认为，NO是中枢葡萄糖感应和启动对低血糖的逆调节反应的必需步骤。然而，在反复发生的胰岛素低血糖期间过量的NO产生会损害对随后的低血糖的反调节反应，从而导致HAAF。体外和体内技术的结合将在细胞和整个动物水平上检验这一假说。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的血糖感知中的作用以及对低血糖的反调节反应的启动。假说II认为，胰岛素诱导的低血糖引起的超生理性NO的产生使NO信号通路变得不敏感，损害了对葡萄糖的感知，从而导致了HAAF的发生。提出的脱敏机制是，NO引起神经元可溶性鸟苷酸环化酶(NO受体)的S亚硝化，使葡萄糖感受型神经元对随后产生的NO没有反应。这些研究将提供有关反复低血糖重置大脑葡萄糖阈值，从而导致HAAF的重要信息。这将促进针对I型糖尿病及其主要现代并发症低血糖的新的、有效和安全的治疗方法的开发。

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.