A Novel Neural Mechanism that Mediates the Therapeutic Effects of Metformin

二甲双胍是最常用的一线抗糖尿病药物。二甲双胍已被广泛接受， 主要通过减少肝脏中的葡萄糖输出来降低血糖，并且在较小程度上通过增加 外周葡萄糖摄取然而，二甲双胍如何做到这一点仍然存在争议和争论。 大脑已经（重新）成为全身葡萄糖代谢的重要调节器。中枢神经 已知中枢神经系统（CNS）调节外周组织中的葡萄糖输出和葡萄糖摄取，从而 改变全身葡萄糖平衡。我们以前发现，大脑或大脑中的小GTIPRAP 1， 下丘脑强烈地影响葡萄糖平衡而不影响能量平衡。值得注意的是，我们 进一步揭示了前脑特异性Rap 1缺陷小鼠对二甲双胍的选择性耐药， 降糖作用，但保留对其他类别的抗糖尿病药物的敏感性。本初步 这一发现表明，一个以前完全未被认识到的中枢神经系统过程可能导致抗- 二甲双胍的糖尿病机制。阐明二甲双胍降低血液中 我们将检验二甲双胍通过抑制Rap 1发挥中枢作用降低高血糖的假设 在下丘脑腹内侧核（VMH）中，这是一个公认的血糖控制部位。这一假设 是根据我们令人兴奋的，坚实的初步数据，通过遗传，解剖，药理学， 和电生理学研究，这是第一次在这里提出。以下三个具体目标 将致力于测试我们的假设：1）使用最先进的体内方法，如血糖正常 钳和稳定同位素示踪技术，我们将研究二甲双胍在大脑中的确切作用 调节全身葡萄糖代谢，2）使用体内GCaMP和化学遗传学工具，我们将 确定VMH SF 1神经元对二甲双胍治疗作用的重要性;以及3） 目标3中的实验将使用功能丧失和功能获得研究来最终确定 Rap 1在VMH中的作用与二甲双胍的抗糖尿病作用有关。总之，这些目标将揭示一个全新的 二甲双胍的作用部位和分子机制。这项提案将揭开一个长期猜测的 解释二甲双胍如何通过建立一种以前未知的 二甲双胍、大脑（VMH）和小GTdR Rap 1之间的联系。最后，结果是 可能为2型糖尿病的病理生理学和治疗发现开辟新的领域。

Metformin is the most prescribed first-line anti-diabetic drug. It has been widely accepted that metformin lowers blood glucose primarily by reducing glucose output in the liver, and to a lesser extent by increasing peripheral glucose uptake. However, exactly how metformin can do so remains controversial and debated. The brain has (re)emerged as an important regulator of whole-body glucose metabolism. The central nervous system (CNS) is known to regulate glucose output and glucose uptake in the peripheral tissues, thereby changing whole-body glucose balance. We previously found that the small GTPase Rap1 in the brain or in the hypothalamus strongly influences glucose balance without affecting energy balance. Remarkably, we have further revealed that forebrain-specific Rap1 deficient mice are selectively resistant to metformin's glucose-lowering action, but retain sensitivity to other classes of anti-diabetic drugs. This preliminary discovery suggests a previously completely unrecognized CNS process potentially accounting for the anti- diabetic mechanism of metformin. To elucidate the neural mechanisms by which metformin lowers blood glucose, we will test the hypothesis that metformin acts centrally to lower hyperglycemia via inhibition of Rap1 in the ventromedial hypothalamic nucleus (VMH), a well-established site for glycemic control. This hypothesis is formulated on the basis of our exciting, solid preliminary data through genetic, anatomical, pharmacological and electrophysiology studies, which are for the first time presented here. The following three Specific Aims will be addressed to test our hypothesis: 1) using state-of-the-art in vivo methodologies such as euglycemic clamp and stable-isotope tracer techniques, we will investigate exactly how metformin in the brain regulates systemic glucose metabolism, 2) using in vivo GCaMP and chemogenetic tools, we will establish the importance of VMH SF1 neurons for the therapeutic action of metformin; and 3) experiments in Aim 3 will use loss-of-function and gain-of-function studies to conclusively determine the role of Rap1 in the VMH for metformin's anti-diabetic action. Together, these Aims will uncover an entirely novel site(s) and molecular mechanism(s) of action of metformin. This proposal will uncover a long-speculated mechanism explaining how metformin exerts its anti-diabetic actions by establishing a previously unknown connection between metformin, the brain (VMH) and the small GTPase Rap1. Lastly, the outcomes are thus likely to open a new area of pathophysiological and therapeutic discovery of type 2 diabetes.