Ketone Body Metabolism and Integrated Metabolic Homeostasis

非酒精性脂肪性肝病（NAFLD），包括非酒精性脂肪性肝炎（NASH）是最常见的 西方国家肝病的原因。人类NAFLD的严重程度与全身胰岛素相关 耐药性; 2型糖尿病的风险;并驱动下游并发症，包括心血管疾病， 肝硬化、需要肝移植和肝癌。随着NAFLD的进展， 功能障碍成为显著特征，并且人NAFLD表现出进行性生酮缺陷。 肝细胞生酮产生酮体乙酰乙酸酯（AcAc）和D-β-羟基丁酸酯（D-βOHB）， 它们是脂肪不完全氧化的产物。生酮作用的测量通常被用作 肝脂肪氧化，但这些措施未能充分报告肝脂肪氧化，因为生酮是盲目的， 三羧酸（TCA）循环中的脂肪完全氧化，这也随NAFLD的过程而变化。 在上一个资助周期中产生的已发表和未发表的观察结果表明， 提供重要的反馈，协调整个肝细胞的能量供应和需求。当老鼠的基因 被编程为缺乏所有生酮，肝脏通过增加TCA循环流量进行补偿，但 易患高脂肪饮食诱导的纤维化，这是NASH中最能预测不良结局的特征。 相反，当小鼠被遗传编程为仅产生AcAc而不产生D-βOHB时[通过敲除 NAD+/NADH D-βOHB脱氢酶（BDH 1）]，肝脏通过减少TCA循环流量进行补偿， 防止高脂肪饮食引起的纤维化。这些发现揭示了能量与 肝脏中的供需可能对如何考虑代谢药物靶点产生深远影响 在NAFLD。此外，最近的观察表明，肝细胞来源的AcAc通过以下途径保护免于纤维化： 邻近巨噬细胞的氧化。因此，该提议的中心假设是肝酮 代谢通过（a）调节肝细胞能量供应/需求平衡来调节肝纤维化， (b)AcAc在肝巨噬细胞线粒体中的代谢。这一假设将通过两个测试 具体目标。首先，为了揭示BDH 1在NASH相关肝损伤中的作用，缺乏BDH 1的小鼠选择性地在NASH相关肝损伤中表达BDH 1。 将使用基于示踪剂的质谱法、核磁共振和 线粒体生物能量学研究，共同支持碳，电子， 质子和氧通量，以构建线粒体效率和NAFLD样之间的关系 发病机制在第二个目标中，基于示踪剂和通量的方法将量化酮体的影响 NASH样发病机制中肝细胞和邻近巨噬细胞之间的交换，使用缺乏 琥珀酰-CoA：3-氧代酸-CoA转移酶（SCOT），其是巨噬细胞中AcAc氧化所需的。 总之，拟议的实验将确定机制，通过它酮代谢可以利用 保护肝脏免受NAFLD损伤的恶化，这是一个明显未满足的需求，对公共卫生的影响不断升级。

Nonalcoholic fatty liver disease (NAFLD), including nonalcoholic steatohepatitis (NASH) is the most common cause of liver disease in Western countries. The severity of NAFLD in humans correlates with systemic insulin resistance; risk of type 2 diabetes; and drives downstream complications, including cardiovascular disease, cirrhosis, need for liver transplantation, and liver cancer. As NAFLD progresses, mitochondrial oxidative dysfunction becomes a prominent feature, and human NAFLD exhibits progressive ketogenic deficits. Hepatocyte ketogenesis produces the ketone bodies acetoacetate (AcAc) and D-β-hydroxybutyrate (D-βOHB), which are products of incomplete fat oxidation. Measurements of ketogenesis are often used as a proxy for hepatic fat oxidation, but these measures fail to fully report hepatic fat oxidation, because ketogenesis is blind to complete fat oxidation in the tricarboxylic acid (TCA) cycle, which also varies over the course of NAFLD. Published and unpublished observations generated during the previous funding cycle suggest that ketogenesis provides vital feedback coordinating overall hepatocyte energy supply and demand. When mice are genetically programmed to be devoid of all ketogenesis, the liver compensates by increasing TCA cycle flux, but is predisposed to high fat diet-induced fibrosis, the feature most predictive of adverse outcomes in NASH. Conversely, when mice are genetically programmed to produce only AcAc, but not D-βOHB [via knockout of NAD+/NADH D-βOHB dehydrogenase (BDH1)], the liver compensates by decreasing TCA cycle flux, and is protected from high fat diet-induced fibrosis. These findings reveal unexpected relationships between energy supply and demand in liver that may have profound impact on how metabolic drug targets should be considered in NAFLD. Moreover, recent observations indicate that hepatocyte derived AcAc protects against fibrosis through oxidation in neighboring macrophages. Therefore, the central hypothesis of this proposal is that liver ketone metabolism modulates hepatic fibrogenesis through (a) tuning hepatocyte energy supply/demand balance and (b) metabolism of AcAc in the mitochondria of liver macrophages. This hypothesis will be tested through two Specific Aims. First, to reveal the role of BDH1 in NASH-relevant liver injury, mice lacking BDH1 selectively in hepatocytes will be interrogated using tracer-based mass spectrometry, nuclear magnetic resonance, and mitochondrial bioenergetics studies, together supporting sophisticated quantifications of carbon, electron, proton, and oxygen fluxes to construct relationships between mitochondrial efficiency and NAFLD-like pathogenesis. In the Second Aim, tracer and flux-based approaches will quantify the effects of ketone body exchange between hepatocytes and neighboring macrophages in NASH-like pathogenesis, using mice that lack succinyl-CoA:3-oxoacid-CoA transferase (SCOT), which is required for AcAc oxidation in macrophages. Together, the proposed experiments will define mechanisms through which ketone metabolism can be leveraged to protect the liver from worsening NAFLD injury, a clear unmet need with escalating public health implications.