Regulation of Insulin Secretion by G6PC2

描述(申请人提供)：全基因组关联(GWA)研究已将G6PC2基因与人类空腹血糖(FBG)和血红蛋白A1C水平的变化联系起来，这些参数与2型糖尿病和心血管相关死亡的风险都有关。这项应用的总体目标是通过确定G6PC2的功能来建立这些GWA研究的结果。我们的初步数据表明，人的G6PC2基因在胰岛β细胞中选择性地表达，并且G6PC2能降解葡萄糖-6-磷酸(G6P)。基于这些数据，我们的第一个假设是，G6PC2的葡萄糖-6-磷酸酶活性与葡萄糖激酶(GCK)的作用相反，葡萄糖激酶催化葡萄糖转化为G6P。糖酵解通量已被证明决定了葡萄糖刺激的胰岛素分泌的S{0.5}，胰岛领域的现有范例认为GCK单独是β细胞葡萄糖感受器。我们观察的意义在于，他们挑战了这一范式，并表明G6PC2是该传感器的一个基本抑制成分。相反，我们建议GCK/G6PC2无效循环作为β细胞葡萄糖传感器，确定糖酵解通量和GSIS的S{0.5}。更多的初步数据表明，小鼠的G6PC2基因也选择性地在胰岛β细胞中表达，G6PC2也能降解G6P。这表明，使用G6PC2基因敲除(KO)小鼠是研究G6PC2功能的一种创新和合适的工具。小鼠G6PC2基因的缺失会导致空腹血糖水平降低，这与人类GW A研究数据一致。但除此之外，我们还发现G6PC2基因的缺失也会导致运动不耐受，其特征是低血糖和不适当的高GSIS。基于这些数据，我们的第二个假设是，GCK/G6PC2无效循环对于运动中胰岛素分泌的减弱具有重要的生理学意义。胰岛的神经输入在运动过程中被激活，胰岛领域的现有范式认为，这些输入通过超极化β细胞和直接抑制胞吐机制来抑制胰岛素的分泌。我们观察的意义在于，他们挑战了这一范式，并表明G6PC2是运动过程中GSIS被抑制的机制的基本组成部分。与控制空腹血糖和血红蛋白AIC一样，这一主题也具有重要的临床意义，因为运动引起的低血糖是糖尿病患者的一个主要问题，它限制了运动的持续时间，从而限制了运动的有益效果。这项提议的目标是测试我们的两个假设。申请分为两个相匹配的具体目标。目的1从分子水平探讨G6PC2的功能，而目的2探讨GCK/G6PC2无用循环在运动中抑制胰岛素分泌的生理意义。

DESCRIPTION (provided by applicant): Genome wide association (GWA) studies have linked the G6PC2 gene to variations in fasting blood glucose (FBG) and hemoglobin A1C levels in humans, parameters that are associated with both the risk of type 2 diabetes and cardiovascular-associated mortality. The overall objective of this application is to build on the results of these GWA studies by determining the function of G6PC2. Our preliminary data show that the human G6PC2 gene is selectively expressed in pancreatic islet beta cells and that G6PC2 hydrolyzes glucose-6-phosphate (G6P). Based on these data our first hypothesis is that the glucose-6-phosphatase activity of G6PC2 opposes the action of glucokinase (GCK), which catalyses the conversion of glucose to G6P. Glycolytic flux has been shown to determine the S {0.5} of glucose-stimulated insulin secretion (GSIS) and the existing paradigm in the islet field proposes that GCK alone is the beta cell glucose sensor. The significance of our observations is that they challenge this paradigm and suggest that G6PC2 is a fundamental inhibitory component of that sensor. Instead we propose that a GCK/G6PC2 futile cycle acts as the beta cell glucose sensor determining glycolytic flux and the S{0.5} of GSIS. Additional preliminary data show that the mouse G6pc2 gene is also selectively expressed in pancreatic islet beta cells and that G6pc2 also hydrolyzes G6P. This suggests that the use of G6pc2 knockout (KO) mice represents an innovative and appropriate tool to study the function of G6PC2. Deletion of the mouse G6pc2 gene results in reduced FBG levels, consistent with the human GW A study data. But in addition we have found that deletion of the G6pc2 gene also results in exercise intolerance, characterized by hypoglycemia and inappropriately high GSIS. Based on these data our second hypothesis is that the GCK/G6PC2 futile cycle is physiologically important for the attenuation of insulin secretion during exercise. Neural inputs to the islet are activated during exercise and the existing paradigm in the islet field proposes that these inputs inhibit insulin secretion by hyperpolarizing the beta cell and also directly inhibiting the exocytotic machinery. The significance of our observations is that they challenge this paradigm and suggest that G6PC2 is a fundamental component of the machinery through which GSIS is inhibited during exercise. As with the control of FBG and hemoglobin AIC, this topic is also clinically important because exercise induced hypoglycemia is a major problem in individuals with diabetes that limits the duration and hence the beneficial effects of exercise. The goal of this proposal is to test our two hypotheses. The application is divided into two matching Specific Aims. Aim I explores the function of G6pc2 at a molecular level whereas Aim 2 explores the physiological importance of the Gck/G6pc2 futile cycle for the attenuation of insulin secretion during exercise.