Glucagon Regulation of Hepatic Mitochondrial Activity and Glucose Metabolism by InsP3R-1

非酒精性脂肪性肝病(NAFLD)影响着全球约25%的人口，是肝脏胰岛素抵抗和2型糖尿病(T2D)发病机制中的关键因素。NAFLD是非酒精性脂肪性肝炎(NASH)和肝细胞癌的易感因素，也是心血管疾病的独立危险因素。然而，目前还没有批准的治疗NAFLD的方法。为了解决这一未得到满足的需求，我们计划在体内研究胰升糖素改变肝脏线粒体脂肪氧化和肝脏回流的细胞和分子机制，以及三磷酸肌醇受体-1(InsP3R-1)在介导这些作用中的潜在作用。这些问题将由一个成熟的跨学科研究团队来解决，该团队将使用我们最近开发的最先进的核磁共振波谱(NMR)-气相色谱-质谱仪(GC-MS)方法，首次在清醒的肝脏特异性InsP3R-1基因敲除小鼠中评估肝脏线粒体脂肪酸氧化、肝脏葡萄糖氧化和肝丙酮酸羧化酶通量的活体速率。这些方法将被应用于以下特定目的：1)研究InsP3R-1在介导胰高血糖素促进肝脏线粒体氧化和肝糖异生中的作用。2)研究IP3R-I在介导运动诱导的肝脏线粒体脂肪氧化增加和NAFLD及NAFLD相关的肝脏胰岛素抵抗减轻中的作用。3)检测胰升糖素对IP3R-I的慢性刺激是否会增加肝脏线粒体氧化，逆转NAFLD和NAFLD相关的肝脏胰岛素抵抗。综上所述，本次拨款申请中提出的研究旨在从机制上全面了解高血糖素对体内肝脏线粒体脂肪氧化和肝丙酮酸羧化酶通量的影响，以及InsP3R-I在介导高血糖素对肝脏线粒体功能影响中的作用。此外，预计这些研究结果将为新型胰升糖素激动剂逆转NAFLD和肝脏胰岛素抵抗的机制提供重要的新见解，并有可能将InsP3R-I确定为治疗NAFLD/NASH和T2D的新治疗靶点。

Non-alcoholic fatty liver disease (NAFLD) affects ~25% of the world’s population and is a key factor in the pathogenesis of hepatic insulin resistance and type 2 diabetes (T2D). NAFLD is a predisposing factor for nonalcoholic steatohepatitis (NASH) and hepatocellular cancer and an independent risk factor for cardiovascular disease. However, there are currently no approved therapies to treat NAFLD. In order to address this unmet need, we plan to examine the cellular and molecular mechanisms by which glucagon alters hepatic mitochondrial fatty oxidation and hepatic anaplerotic fluxes in vivo and the potential role of the Inositol Triphosphate Receptor-1 (InsP3R-1) in mediating these effects. These questions will be addressed by a well-established team of interdisciplinary investigators using state-of-the-art nuclear magnetic resonance spectroscopy (NMR)-gas chromatographic-mass spectrometry (GC-MS) methodologies that we have recently developed to assess in vivo rates of hepatic mitochondrial fatty acid oxidation, hepatic glucose oxidation, and hepatic pyruvate carboxylase flux for the first time in awake liver-specific InsP3R-1 knockout mice. These methods will be applied to address the following Specific Aims: 1) To examine the role of InsP3R-1 in mediating glucagon’s effect to promote hepatic mitochondrial oxidation and hepatic gluconeogenesis. 2) To examine the role of IP3R-I in mediating exercise-induced increases in hepatic mitochondrial fat oxidation and reductions in NAFLD and NAFLD-associated hepatic insulin resistance. 3) To examine whether chronic stimulation of IP3R-I by glucagon will increase hepatic mitochondrial oxidation and reverse NAFLD and NAFLD-associated hepatic insulin resistance. Taken together, the studies proposed in this grant application are designed to generate a comprehensive mechanistic understanding of the impact of glucagon on hepatic mitochondrial fat oxidation and hepatic pyruvate carboxylase flux in vivo and on the role of InsP3R-I in mediating glucagon’s effects on hepatic mitochondrial function. Furthermore, it is anticipated that the results of these studies will provide important new insights into the mechanism by which novel glucagon agonists might reverse NAFLD and hepatic insulin resistance as well as potentially identify InsP3R-I as a novel therapeutic target for the treatment of NAFLD/NASH and T2D.