Nutrient Overload, Insulin Resistance, and Hepatic Mitochondrial Dysfunction

摘要 来自动物研究的有力证据和来自人类成像研究的间接数据表明， 肝线粒体活性是非酒精性脂肪性肝炎病理生理学的关键事件 （NASH）。我们在NASH患者中的初步数据表明，两种治疗方法， 营养应激、热量限制（CR）和运动训练（EX）改善肝组织学。我们最近 在啮齿动物模型中的研究证实EX对肝组织学的治疗作用是通过 通过增加肝线粒体含量和功能。目前尚不清楚是否有类似的 这种治疗对人类肝脏线粒体的有益效果。的中心假设 这个项目是营养超载导致肝线粒体功能障碍，一个关键的调解人， 因此，我们认为，这种超负荷的改善将导致更高的线粒体代谢效率。 生物能量学和改善的肝脏组织学。为了验证这些假设，一种治疗方案， CR和EX将用于减少60例NASH患者的肝内三酰甘油（IHTG）。基线 治疗组9个月的肝活检将与30例患者的重复活检进行比较 接受标准临床管理。我们将完成以下具体目标。SA 1将利用 来自NASH患者的肝活检样品和在减肥手术期间获得的肝样品， 确定患有更晚期肝病的患者是否具有肝线粒体，在体外， 离体，表现出较差的能量产生（质量控制）、生物发生和线粒体自噬; SA 2将分离 9个月后再次检测肝线粒体，以检测IHTG的丢失是否与改善的 通过基因表达、酶水平和生物合成来评估线粒体功能、生物合成和质量控制 和脂肪酸氧化。SA 3将测量以下受试者的全身葡萄糖和脂肪酸通量- 积极治疗（CR+EX）和标准治疗。将在基线和9点后进行测量 个月，数学建模用于定量周边营养物的处置和减少， 肝脏营养负荷，比较其对线粒体功能，纤维化的影响，并通过活组织检查- 使用组织学评估确定NASH活性评分。总之，这些研究将 通过发现1）过量的机制， 营养应激导致肝线粒体功能降低; 2） 线粒体活性和NASH的组织学特征。重要的是，这项工作将发挥持续的 通过确定人类肝脏线粒体功能障碍是否可逆来研究对该领域的影响。

Abstract Strong evidence from animal studies and indirect data from human imaging studies, implicate reduced liver mitochondrial activity as a key event in the pathophysiology of nonalcoholic steatohepatitis (NASH). Our preliminary data in NASH patients demonstrate that two treatments that relieve excess nutrient stress, caloric restriction (CR) and exercise training (EX), improve liver histology. Our recent studies in a rodent model established that the therapeutic effect of EX on liver histology is mediated through increases in both hepatic mitochondrial content and function. It is unknown whether a similar beneficial effect of such treatment on liver mitochondria occurs in humans. The central hypotheses of this project is that nutrient overload results in hepatic mitochondrial dysfunction, a key mediator of NASH pathology, and that amelioration of this overload will result in greater efficiency of mitochondrial bioenergetics and improved liver histology. To test these hypotheses, a treatment regimen combining CR and EX will be used to reduce intrahepatic triacylglycerols (IHTG) in 60 NASH patients. Baseline and 9-month liver biopsies in the treated group will be compared to repeat biopsies from 30 patients undergoing standard clinical management. We will complete the following specific aims. SA1 will utilize liver biopsy samples from patients with NASH, and liver samples obtained during bariatric surgery, to determine whether patients with more advanced liver disease have liver mitochondria that, in vitro and ex vivo, exhibit poor energy generation (quality control), biogenesis, and mitophagy; SA2 will isolate hepatic mitochondria again after 9-months to test whether loss of IHTG is associated with improved mitochondrial function, biogenesis and quality control as assessed by gene expression, enzyme levels and fatty acid oxidation. SA3 will measure whole body glucose and fatty acid flux in subjects under- going active treatment (CR+EX) and standard care. Measures will be made at baseline and after 9 months, and mathematical modeling used to quantitate peripheral nutrient disposal and the reduction in liver nutrient burden to compare its influence on mitochondrial function, fibrosis, and by the biopsy- determined NASH activity score using histological assessment. In summary, these studies will significantly advance the field of NAFLD through discoveries of 1) the mechanisms by which excess nutrient stress contributes to reduced hepatic mitochondrial function and 2) the relationships between mitochondrial activity and the histologic features of NASH. Importantly, this work will exert a sustained influence on the field by determining whether hepatic mitochondrial dysfunction is reversible in humans.