The role of the mitochondrial GTP cycle in insulin secretion

描述(由申请人提供)：�细胞不能分泌足够的胰岛素是糖尿病发展的关键。这项资助的长期目标是阐明线粒体GTP(MtGTP)循环中�细胞葡萄糖传感的细胞机制。这笔赠款建立在我们最近的研究基础上，该研究表明，mtGTP作为葡萄糖代谢的传感器，由TCA循环通过GTP特有的琥珀酰辅酶A合成酶(SCS-GTP)直接合成的关键作用。MtGTP被困在线粒体内，必须通过依赖于GTP的线粒体亚型磷酸烯醇式丙酮酸羧基激酶(PEPCK-M)将无性代谢产物转化为PEP，然后将信号传递到细胞质。因此，了解这一重要信号的机制及其在体内胰岛素分泌正常生理中的作用是这项研究的重点。具体地说，它将通过以下方式评估mtGTP循环的作用：1)使用两个新产生的具有�细胞特异性诱导表达的小鼠品系来研究mtGTP合成对体内胰岛素分泌的影响；2)表征由PEPCK-M和SCS-GTP形成的复合体的功能相互作用；以及3)使用一系列分子短路和泄漏来评估mtGTP周期的每个组成部分在胰岛素分泌中的作用。基于所有三个目标的强有力的初步数据，支持线粒体GTP循环在调节葡萄糖刺激的胰岛素分泌中的重要作用，预计这些研究的结果将导致对胰腺�细胞功能的重要的新范式的转变，这将导致合理开发用于增加胰岛素分泌或防止�细胞衰竭的新的治疗靶点。

DESCRIPTION (provided by applicant): Failure of �-cells to secrete adequate insulin is essential for the development of diabetes mellitus. The long- term objectives of this grant are to elucidate the cellular mechanisms of �-cell glucose sensing by the mitochondrial GTP (mtGTP) cycle. This grant builds on our recent studies demonstrating a key role for mtGTP directly synthesized by the TCA cycle by the GTP-specific isoform of the enzyme succinyl CoA synthetase (SCS-GTP) as a sensor of glucose metabolism. The mtGTP is trapped within the mitochondria and must convert anaplerotic metabolites into PEP by the GTP-dependent mitochondrial isoform of phosphoenolpyruvate carboxykinase (PEPCK-M) that then transmits the signal to the cytosol. Therefore, understanding the mechanism of this important signal and its role in the normal physiology of insulin secretion in vivo is the focus of this grant. Specifically it will assess the role of the mtGTP cycle by: 1) using two newly generated strains of mice with the inducible �-cell specific expression of SCS-GTP or SCS-ATP to study the impact of mtGTP synthesis on insulin secretion in vivo, 2) characterize the functional interaction of a complex formed by PEPCK-M and SCS-GTP, and 3) using a series of molecular short-circuits and leaks to assess the role of each of the components of the mtGTP cycle in insulin secretion. Based on strong preliminary data for all three aims that support an essential role for the mtGTP cycle in the regulation of glucose-stimulated insulin secretion, it is anticipated that the results of these studies will lead to important new paradigm shifting insights into the function of pancreatic �-cells that will lead to the rational development of novel therapeutic targets for either augmenting insulin secretion or preventing �-cell failure.