Novel Aspects of Hepatic Mitochondrial Amino Acid Metabolism

项目摘要/摘要 肝脏产生葡萄糖是一个重要的生理过程。肝脏葡萄糖产生的作用 在调节饥饿期间正常血糖中的重要作用，为骨骼肌提供葡萄糖 在运动过程中，并导致糖尿病的高血糖。糖异生，转换的过程 碳在丙酮酸、乳酸或氨基酸中转化为新的葡萄糖，在葡萄糖中起着重要作用 由肝脏产生。糖异生需要丙酮酸或氨基酸在 非通透性线粒体内膜(IMM)及其后续的酶代谢 定位于线粒体基质。申请人实验室最近的研究表明， 线粒体丙酮酸载体(MPC)复合体在糖尿病糖异生中的重要作用 丙酮酸/乳酸。然而，这些研究也表明，丙酮酸-丙氨酸循环作为一种 MPC活性受损时的代偿机制。此外，虽然像丙氨酸这样的氨基酸 被认为是糖异生的重要底物，关于它们的代谢的许多细节是 缺乏。拟议研究的意义在于，我们将剖析 在禁食、运动和糖尿病中调节这些过程。我们假设转录因子 ATF4将调节丙氨酸转氨酶2(ALT2)的表达，该酶将在 在调节丙氨酸刺激的糖尿病肝脏糖异生中的重要作用(特定目标1)。我们也 假设ALT2缺乏对葡萄糖产生的影响将因伴随而增强 失去MPC活性以干扰丙氨酸和丙酮酸的糖异生。(具体目标2)。我们也 提出第三个具有显著科学进步潜力的探索性目标。丙氨酸的转运 丙氨酸需要通过载体介导法穿过不透水的IMM 糖异生作用。然而，调解这一过程的承运人的身份从未确定。 我们推测酵母Avt5和它的哺乳动物同系物Slc38a10作为线粒体 丙氨酸载体和这些蛋白质是线粒体丙氨酸代谢所必需的(具体目标3)。我们 相信拟议的研究将为我们理解肝脏提供显著的科学进步 氨基酸代谢，到目前为止还没有得到充分的研究。此外，这些研究将提供 洞察这些代谢途径对肝脏糖异生的影响并可能影响 开发治疗糖尿病的新药。

Project Summary/Abstract The production of glucose by the liver is a vital physiological process. Hepatic glucose production plays an important role in regulating normoglycemia during starvation, providing skeletal muscle with glucose during exercise, and contributing to hyperglycemia of diabetes. Gluconeogenesis, the process of converting the carbon in pyruvate, lactate, or amino acids into new glucose, plays an important role in glucose production by the liver. Gluconeogenesis requires the transport of pyruvate or amino acids across the impermeable inner mitochondrial membrane (IMM) and subsequent metabolism by enzymes exclusively localized to the mitochondrial matrix. Recent work from the laboratory of the applicant has demonstrated an important role for the mitochondrial pyruvate carrier (MPC) complex in gluconeogenesis from pyruvate/lactate. However, these studies also suggested an important role for pyruvate-alanine cycling as a compensatory mechanism when MPC activity was impaired. In addition, while amino acids like alanine are believed to be an important substrate for gluconeogenesis, many details regarding their metabolism are lacking. The significance of the proposed studies is that we will dissect the molecular mechanisms that mediate these processes in fasting, exercise, and diabetes. We hypothesize that the transcription factor ATF4 will regulate the expression of alanine transaminase 2 (ALT2) and that this enzyme will play an important role in regulating alanine-stimulated gluconeogenesis in diabetic liver (Specific Aim 1). We also hypothesize that that the effects of ALT2 deficiency on glucose production will be enhanced by concomitant loss of MPC activity to disrupt gluconeogenesis from both alanine and pyruvate. (Specific Aim 2). We also propose a third, exploratory Aim that has the potential for marked scientific advance. The transport of alanine across the impermeable IMM by a carrier-mediated process is required for alanine to be used for gluconeogenesis. However, the identity of the carrier that mediates this process has never been determined. We hypothesize that the yeast Avt5 and its mammalian homolog Slc38a10 serve as the mitochondrial alanine carrier and that these proteins are required for mitochondrial alanine metabolism (Specific Aim 3). We believe that the proposed studies will provide marked scientific advance towards our understanding of hepatic amino acid metabolism, which has been understudied to this point. In addition, these studies will provide insight into the effects of these metabolic pathways on hepatic gluconeogenesis and could impact pharmaceutical development of new drugs to treat diabetes.