The role of the mitochondrial GTP cycle in insulin secretion

说明（由申请人提供）：β细胞不能分泌足够的胰岛素是糖尿病发展的关键。该基金的长期目标是阐明线粒体GTP（mtGTP）循环对β细胞葡萄糖感知的细胞机制.这项资助建立在我们最近的研究基础上，这些研究证明了由TCA循环直接合成的mtGTP作为葡萄糖代谢传感器的关键作用，所述TCA循环是由琥珀酰辅酶A合成酶（SCS-GTP）的GTP特异性亚型合成的。mtGTP被捕获在线粒体内，并且必须通过磷酸烯醇丙酮酸羧激酶（PEPCK-M）的GTP依赖性线粒体同种型将回补代谢物转化为PEP，然后将信号传递到胞质溶胶。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本基金的重点。具体而言，它将通过以下方式评估中期增长计划周期的作用：1）利用两种新产生的具有可诱导的β细胞特异性表达SCS-GTP或SCS-ATP的小鼠品系，研究体内mtGTP合成对胰岛素分泌的影响，2）表征PEPCK-M和SCS-GTP形成的复合物的功能相互作用，以及3）使用一系列分子短路和泄漏来评估mtGTP循环的每个组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mtGTP循环在葡萄糖刺激的胰岛素分泌调节中的重要作用，预计这些研究的结果将导致对胰腺β细胞功能的重要新范式转变，这将导致合理开发新的治疗靶点，用于增加胰岛素分泌或预防β细胞衰竭。

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.