Role of non-genomic regulation of mitochondrial trifunctional protein in NAFLD

非酒精性脂肪性肝病（NAFLD）的特征是肝脏中脂肪沉积增加， 进展为炎症、肝细胞癌和肝功能衰竭。NAFLD与2型密切相关 糖尿病和肥胖症。它仍然是一个重大的公共卫生问题，在其 治疗令人不安的是，NAFLD似乎在军队和退伍军人中更常见， 与美国大众。因此，努力了解有助于 NAFLD将为我们的退伍军人群体开发治疗方案提供有价值的见解。 线粒体功能障碍在NAFLD的发生发展中起着至关重要的作用，然而，关于线粒体功能障碍如何发生却知之甚少。 治疗线粒体功能障碍并挽救相关的NAFLD。线粒体三功能蛋白 是线粒体脂肪酸氧化（FAO）的主要酶复合物，由4个α和4个β亚基组成 携带三种酶活性，分解线粒体中的脂肪酸。一个关键的未解之谜是 MTP的调节是否调节NAFLD。在报道的MTP缺陷小鼠模型中， 缺陷杂合子（MTP+/-）发展线粒体功能障碍并且易患NAFLD。 在这种小鼠模型中确定涉及调节MTP的机制对于理解 线粒体在NAFLD发生和挽救中的作用。本申请中的假设是， 增加MTP复合物的组装增加了其稳定性，这导致改善了 线粒体脂肪酸氧化（FAO）和NAFLD的拯救。本申请中的建议是， NAD+依赖性SIRT 3和三碘甲状腺原氨酸（T3）激素通过非基因组途径改善MTP稳定性 通过增强MTP复合物组装的机制。初步数据有力地支持了 假说.首先，线粒体FAO，MTP和SIRT 3水平在从肝脏中获得的肝脏样品中降低。 患有NAFLD的人类受试者。第二，MTP+/-小鼠中SIRT 3的过表达减少了 与对照组相比，MTP增加了线粒体FAO，减少了脂肪变性和炎症标志物。 肝脏第三，在培养细胞中的体外研究表明，MTP的稳定性和其水平增加， T3治疗。为了验证这一假设，我们将使用从退伍军人患者获得的人类肝脏样本。 群体和MTP小鼠模型进行离体、体内和体外研究， 具体目的：1）明确肝MTP-α、SIRT 3、线粒体FAO与肝纤维化的关系 和疾病严重程度。2)以确定潜在的 通过小鼠中SIRT 3过表达增加MTP水平的机制。3)为了测试T3是否挽救NAFLD， 在MTP小鼠模型中，以及它是否通过增加MTP稳定性来改善肝线粒体FAO 通过与线粒体缩短的甲状腺受体相互作用。这是第一次研究监管 通过SIRT 3和T3的MTP，以及如何影响线粒体FAO和NAFLD。该提案涉及关键 未回答的问题和知识差距，在该领域的影响，在我们的退伍军人的重大健康问题 人口确定SIRT 3和T3调节MTP的机制将具有重要意义 并将为未来发现NAFLD的新疗法带来希望，NAFLD是一种越来越常见的疾病， 治疗选择有限的退伍军人。

Nonalcoholic fatty liver disease (NAFLD) is characterized by increased deposition of fat in the liver that may progress to inflammation, hepatocellular carcinoma, and liver failure. NAFLD is closely linked to type 2 diabetes mellitus and obesity. It remains a major public health problem with little progress made on its treatment. Disturbingly, NAFLD appears to be more common in the military and Veteran population compared with the general US population. Thus, efforts to understand the underlying mechanisms that contribute to NAFLD will provide valuable insight into developing therapeutic options for our Veteran population. Mitochondrial dysfunction plays a crucial role in the development of NAFLD, however, little is known about how to treat mitochondrial dysfunction and rescue the associated NAFLD. Mitochondrial trifunctional protein (MTP) is the major enzymatic complex in mitochondrial fatty acid oxidation (FAO) that consists of 4 α and 4β subunits carrying three enzymatic activities breaks down fatty acids in the mitochondria. A key unanswered question is whether regulation of MTP modulates NAFLD. In a reported mouse model with an MTP defect, mice heterozygous for the defect (MTP+/-) develop mitochondrial dysfunction and are susceptible to NAFLD. Determining the mechanisms involved in regulating MTP in this mouse model is critical to the understanding of the role of mitochondria in development and rescue of NAFLD. The hypothesis in this application is that increasing the assembly of the MTP complex increases its stability, which leads to improvement in mitochondrial fatty acid oxidation (FAO) and rescue of NAFLD. The proposal in this application is that both the NAD+-dependent SIRT3 and the triiodothyronine (T3) hormone improve MTP stability by nongenomic mechanisms through enhancement of the MTP complex assembly. The preliminary data strongly support the hypothesis. First, mitochondrial FAO, MTP and SIRT3 levels were reduced in liver samples obtained from human subjects with NAFLD. Second, overexpression of SIRT3 in the MTP+/- mice reduced the acetylation of MTP compared to controls, increased mitochondrial FAO, and reduced steatosis and inflammatory markers in the liver. Third, in vitro studies in cultured cells demonstrate that MTP stability and its levels were increased by T3 treatment. To examine this hypothesis, we will use human liver samples obtained from a Veteran patient population and the MTP mouse model to conduct ex vivo, in vivo, and in vitro studies towards the following specific aims: 1) To define the relationship between hepatic MTP-α levels, SIRT3 levels, mitochondrial FAO and disease severity in human liver samples obtained from Veteran population. 2) To determine the underlying mechanisms of increased MTP levels by SIRT3 overexpression in mice. 3) To test whether T3 rescues NAFLD in the MTP mouse model and whether it improves hepatic mitochondrial FAO by increasing MTP stability through interaction with mitochondrial shortened thyroid receptors. This is the first study to examine regulation of MTP by SIRT3 and T3, and how that impacts mitochondrial FAO and NAFLD. This proposal addresses key unanswered questions and knowledge gaps in the field that impact a significant health problem in our Veteran population. Identifying the mechanisms by which SIRT3 and T3 regulate MTP will have important implications and will hold promise for future discovery of novel treatments for NAFLD, an increasingly common disease in Veterans with limited therapeutic options.