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，减少 肝脏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 （纳什）。我们在 NASH 患者中的初步数据表明，两种治疗方法可以缓解过量的 营养应激、热量限制 (CR) 和运动训练 (EX)，改善肝脏组织学。我们最近的 啮齿动物模型研究证实 EX 对肝脏组织学的治疗作用是介导的 通过增加肝线粒体含量和功能。不知道是否有类似的 beneficial effect of such treatment on liver mitochondria occurs in humans.的中心假设 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 生物能量学和改善的肝脏组织学。为了检验这些假设，治疗方案结合了 CR and EX will be used to reduce intrahepatic triacylglycerols (IHTG) in 60 NASH patients.基线 and 9-month liver biopsies in the treated group will be compared to repeat biopsies from 30 patients 正在接受标准的临床管理。我们将完成以下具体目标。 SA1将利用 liver biopsy samples from patients with NASH, and liver samples obtained during bariatric surgery, to 确定患有更晚期肝病的患者是否有肝线粒体，在体外和 ex vivo, exhibit poor energy generation (quality control), biogenesis, and mitophagy; SA2将隔离 9个月后再次检测肝线粒体，以测试IHTG的丧失是否与改善有关 mitochondrial function, biogenesis and quality control as assessed by gene expression, enzyme levels 和脂肪酸氧化。 SA3 will measure whole body glucose and fatty acid flux in subjects under- going active treatment (CR EX) and standard care.措施将在基线时和 9 点后采取 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.总之，这些研究将 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 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作用 influence on the field by determining whether hepatic mitochondrial dysfunction is reversible in humans.

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.