Regulation of Hepatic Macronutrient Metabolism by Mitochondrial Citrate Transport

项目摘要 在2型糖尿病（T2 D）期间，与肝脏脂质蓄积密切相关的胰岛素敏感性丧失增加了慢性高血糖症的潜在危险。此外，T2 D期间肝脏新生脂肪生成（DNL）增加被认为会导致胰岛素抵抗和非酒精性脂肪性肝病（NAFLD）。因此，识别直接调节肝DNL和肝再生的机制对于理解T2 D病理生理学和治疗机会可能具有独特价值。胞质柠檬酸盐被认为是肝脏代谢的主要调节剂，通过调节糖酵解和代谢产物的生成以及为DNL提供底物和还原力。柠檬酸盐在线粒体中产生，并且需要特定的转运蛋白，线粒体柠檬酸盐载体（CiC），以到达胞质溶胶。因此，预测CiC占据连接肝线粒体代谢、DNL、葡萄糖和还原驱动的中心代谢节点。然而，令人惊讶的是，CiC在正常和T2 D状态下调节肝DNL和肝新生的作用在体内仍然很少得到解决。本申请的总体目标是了解肝脏CiC如何促进基础代谢和T2 D病理生理学。这将通过追求两个特定目标来解决：1）确定肝脏CiC功能如何在T2 D状态下调节肝脏DNL;和2）确定肝脏CiC功能如何在T2 D状态下促成高血糖症。目的1中的实验将测试以下假设：在T2 D状态期间破坏体内肝CiC活性通过减少柠檬酸盐作为碳源的供应和减少可用于脂肪链延长的NAPDH来降低DNL。目标2中的实验将测试以下假设：在T2 D状态期间破坏体内肝CiC活性通过减弱肝胰岛素抵抗、使肝葡萄糖代谢远离肝异生向糖酵解转变以及降低NAFLD进展的小鼠相关性来降低高血糖症。总的来说，拟议的研究将测试CiC在体内的基本调节作用，并提供关于线粒体柠檬酸盐输出的单一代谢步骤如何有助于增加肝脏DNL和肝异生的核心T2 D特征的新的机制信息。这项研究意义重大，因为成功完成将独特地推进对T2 D病理生理学的基本理解。这项研究是创新的，因为它将利用新的体内CiC破坏和代谢组学追踪模型来测试CiC在T2 D中连接线粒体代谢、DNL和新生儿的作用。

PROJECT SUMMARY During type 2 diabetes (T2D), loss of insulin sensitivity strongly associated with hepatic lipid accumulation increases gluconeogenesis underlying chronic hyperglycemia. Furthermore, increased hepatic de novo lipogenesis (DNL) during T2D is thought to drive insulin resistance and non-alcoholic fatty liver disease (NAFLD). Thus, identifying mechanisms directly modulating both hepatic DNL and gluconeogenesis could be uniquely valuable for understanding T2D pathophysiology and therapeutic opportunity. Cytosolic citrate is believed to be a master regulator of hepatic metabolism by reciprocally regulating glycolysis and gluconeogenesis and by supplying substrate and reducing power for DNL. Citrate is produced in the mitochondria and requires a specific transporter, the mitochondrial citrate carrier (CiC), to reach the cytosol. Thus, the CiC is predicted to occupy a central metabolic node linking hepatic mitochondrial metabolism, DNL, glucose, and reductive drive. Yet, surprisingly, the role of the CiC modulating hepatic DNL and gluconeogenesis in normal and T2D states remains sparsely addressed in vivo. The overall goal of this application is to understand how the hepatic CiC contributes to fundamental metabolism and T2D pathophysiology. This will be addressed by pursuing two specific aims: 1) Determine how hepatic CiC function regulates hepatic DNL in T2D states; and 2) Determine how hepatic CiC function contributes to hyperglycemia in T2D states. Experiments in aim 1 will test the hypothesis that disrupting hepatic CiC activity in vivo during T2D states decreases DNL, by decreasing supply of citrate as a carbon source and decreasing NAPDH available for fatty chain elongation. Experiments in aim 2 will test the hypothesis that disrupting hepatic CiC activity in vivo during T2D states decreases hyperglycemia by attenuating liver insulin resistance, shifting hepatic glucose metabolism towards glycolysis away from gluconeogenesis, and decreasing mouse correlates of NAFLD progression. Overall, the proposed investigation will test the fundamental regulatory role of the CiC in vivo and provide novel, mechanistic information on how the single metabolic step of mitochondrial citrate export contributes to the core T2D features of increased hepatic DNL and gluconeogenesis. This research is significant because successful completion will uniquely advance fundamental understanding of T2D pathophysiology. This research is innovative because it will utilize novel in vivo CiC disruption and metabolomic tracing models to test the role of the CiC role linking mitochondrial metabolism, DNL, and gluconeogenesis in T2D.