Ketone Body Metabolism and Integrated Metabolic Homeostasis

 描述(申请人提供)：与肥胖流行密切相关，非酒精性脂肪性肝病(NAFLD)谱系的疾病，包括非酒精性脂肪性肝炎(NASH)，在美国所有成年人中的患病率接近30%。非酒精性脂肪肝极大地增加了患2型糖尿病和心血管疾病的风险，其自然病史受到基因组和环境输入的严重影响，这些输入仍然不完全清楚。特别是，控制脂肪氧化“处置”的线粒体新陈代谢的作用只有部分特征。线粒体酮体生成(酮发生)通常被认为是一种被动的代谢溢出管道，当碳水化合物和胰岛素供应不足时，β氧化产物通过该管道。 已知的反馈包括Krebs(三羧酸，TCA)循环、葡萄糖产生和脂肪代谢。相反，我们的初步数据表明，(I)肝生酮能力直接影响肝脏的这些代谢途径，即使在碳水化合物丰富的喂养状态下也是如此；(Ii)与1型糖尿病不同，NAFLD/NASH和胰岛素抵抗是酮生作用相对不足的状态，以及(Iii)遗传性生酮不足本身容易导致肝脏脂肪变性增加、肝细胞损伤和血糖升高。总之，我们的初步数据支持以下中心假设：(I)酮体生成不是一条被动的溢出途径，而是肝脏和整体生理动态平衡的动态节点，以及(Ii)谨慎的生酮增强可以缓解NAFLD/NASH和肝糖代谢紊乱，这将通过两个特定的目标进行测试。在目标1中，我们将演示肝酮生成调节肝脏代谢稳态和线粒体功能的机制。我们将使用生酮不足的小鼠模型、高分辨率核磁共振(核磁共振)光谱和高效液相色谱与高质量精确度质谱仪(LC/MS)引导的代谢组学相结合的方法，对接受稳定同位素标记代谢燃料治疗的小鼠进行研究。靶向和非靶向的计算代谢组学和脂类组学方法将被用来全面量化生物化学空间，通过这个空间，酮类生成调节整合的细胞器代谢动态平衡。遗传和药物刺激将揭示肝细胞代谢、线粒体功能和NAFLD/NASH发病机制之间的联系。在目标2中，我们将证明增加肝酮体生成量可以改善NAFLD的发病机制和肝脏糖代谢紊乱。决定命运的生酮线粒体酶3-羟甲基戊二酰辅酶A合成酶的野生型或结构性高活性突变版本将在体内脂肪肝损伤的小鼠模型中表达。不同的肝酮生成对肝脏损伤和炎症、脂肪酸氧化、从头脂肪生成和葡萄糖产生的影响将通过核磁共振光谱、全面的LC/MS代谢组学和系统生理学方法来量化。

 DESCRIPTION (provided by applicant): Tightly linked to the obesity epidemic, disorders along the nonalcoholic fatty liver disease (NAFLD) spectrum, including nonalcoholic steatohepatitis (NASH), occur with nearly 30% prevalence among all adults in the United States. NAFLD dramatically increases the risks of developing type 2 diabetes and cardiovascular disease, and its natural history is heavily influenced by genomic and environmental inputs that are still incompletely understood. In particular, the role of mitochondrial metabolism, which governs the oxidative `disposal' of fats, has only been partially characterized. Mitochondrial ketone body generation (ketogenesis) is generally viewed as a passive metabolic overflow conduit through which products of β-oxidation pass when carbohydrates and insulin are in short supply, with little known feedback on interwoven pathways including the Krebs (tricarboxylic acid, TCA) cycle, glucose production, and lipid metabolism. On the contrary, our preliminary data indicate that (i) hepatic ketogenic capacity directly influences these metabolic pathways in liver, even in the carbohydrate-laden fed state; (ii) in contradistinction to type 1 diabetes, NAFLD/NASH and insulin resistance are states in which ketogenesis is relatively underutilized, and (iii) geneticaly-induced ketogenic insufficiency alone predisposes to increased hepatic steatosis, hepatocellular injury, and glycemia. Together our preliminary data support the central hypotheses that (i) ketogenesis is not a passive overflow pathway but rather a dynamic node in hepatic and integrated physiological homeostasis, and (ii) prudent ketogenic augmentation can mitigate NAFLD/NASH and disordered hepatic glucose metabolism, which will be tested through two Specific Aims. In Aim 1, we will demonstrate the mechanisms by which hepatic ketogenesis governs hepatic metabolic homeostasis and mitochondrial function. We will use mouse models of ketogenic insufficiency, high resolution nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography coupled to high mass accuracy mass spectrometry (LC/MS)-guided metabolomics in mice treated with stable isotopically-labeled metabolic fuels. Targeted and untargeted computational metabolomics and lipidomics approaches will be leveraged to comprehensively quantify the biochemical space through which ketogenesis regulates integrated organelle metabolic homeostasis. Genetic and pharmacological provocations will reveal mechanistic connections among hepatocyte metabolism, mitochondrial function, and NAFLD/NASH pathogenesis. In Aim 2, we will demonstrate that increasing hepatic ketogenesis ameliorates NAFLD pathogenesis and disordered hepatic glucose metabolism. Wild-type or constitutively hyperactive mutated versions of the fate-committing ketogenic mitochondrial enzyme 3-hydroxymethylglutaryl-CoA synthase will be expressed in mouse models of fatty liver injury in vivo. The effects of varying hepatic ketogenesis on hepatic injury and inflammation, fatty acid oxidation, de novo lipogenesis, and glucose production will be quantified by NMR spectroscopy, comprehensive LC/MS metabolomics, and systems physiological approaches.