Aerobic fitness, mitochondrial dysfunction, and fatty liver disease

描述（由申请人提供）：非酒精性脂肪性肝病（NAFLD）可进展为包括非酒精性脂肪性肝炎、肝硬化和肝细胞癌。NAFLD还与肝胰岛素抵抗的发展有关，肝胰岛素抵抗是2型糖尿病发展的主要因素。最近的临床数据表明，低有氧健身的患者对NAFLD发展的易感性增加。此外，来自我们研究小组和其他人的证据表明，肝脏线粒体功能障碍是NAFLD和肝脏胰岛素抵抗发展的主要特征。我们的初步证据表明，肝脏线粒体功能障碍（线粒体含量低和脂肪酸氧化减少（FAOX））是低有氧健身与NAFLD和肝脏胰岛素抵抗易感性增加之间的联系。然而，这些因素与线粒体功能障碍导致NAFLD的潜在机制之间的联系仍然未知。为了解开这些联系，我们将研究两种新的大鼠品系[高或低能力跑步者（HCR/LCR）]，由于双向发散选择性育种，它们具有30%不同的内在有氧健身水平。与高fit-HCR肝脏相比，低fit-LCR大鼠在年轻时显示线粒体含量和脂肪酸氧化（FAOX）和NAFLD减少，并且肝损伤显著更大。因此，高fit-HCR和低fit-LCR菌株为研究有氧健身对肝脏代谢的作用提供了新的实验平台。该建议的中心假设是，由于线粒体功能障碍，低有氧健身导致NAFLD和肝脏胰岛素抵抗的风险增加。具体目的如下：目的1）测试低fit-LCR大鼠是否对脂质诱导的NAFLD和NASH具有增加的易感性，以及这是否可以通过增加线粒体含量或FAOX来预防。目的2）检测低fit-LCR大鼠是否存在线粒体功能障碍或非酒精性脂肪性肝病（NAFLD）引起的肝脏胰岛素抵抗和肝脏葡萄糖输出失调。目标1和目标2都将利用饮食高脂肪体内研究和脂质过载体外研究（原代肝细胞）来检查低有氧适应性LCR和高有氧适应性HCR动物对NAFLD和胰岛素抵抗的易感性。此外，还将采用体外胰岛素信号转导和体内高胰岛素-正葡萄糖钳夹方法研究肝脏胰岛素抵抗。我们还将评估LCR肝脏或原代肝细胞中过氧化物酶体增殖物γ共激活物1 α（PGC-1，刺激线粒体生物发生）或肉毒碱棕榈酰转移酶-1（CPT-1，增强现有线粒体中的FAOX）的腺病毒过表达是否可以保护免受脂质诱导的NAFLD并改善肝脏胰岛素敏感性。这项研究的结果将提供有氧健身，肝线粒体功能和NAFLD之间的联系更大的机械理解。结果还将确定增加的肝线粒体含量或增加的肝脂肪酸氧化是否是预防NAFLD或肝胰岛素抵抗的有效治疗靶点。

DESCRIPTION (provided by applicant): Non-alcoholic fatty liver disease (NAFLD) can progress to include nonalcoholic steatohepatitis, cirrhosis, and hepatocellular carcinoma. NAFLD is also implicated in the development of hepatic insulin resistance, a primary player in the development of type 2 diabetes. Recent clinical data demonstrates that patients with low aerobic fitness have increased susceptibility for the development of NAFLD. In addition, evidence from our research group and others has implicated hepatic mitochondrial dysfunction as a primary feature in the development of both NAFLD and hepatic insulin resistance. Our preliminary evidence implicates hepatic mitochondrial dysfunction (low mitochondrial content and reduced fatty acid oxidation (FAOX) as the link between low aerobic fitness and increased susceptibility for both NAFLD and hepatic insulin resistance. However, the links between these factors and the underlying mechanism(s) by which mitochondrial dysfunction leads to NAFLD remain unknown. To unravel these links, we will study two novel strains of rats [high or low capacity runners (HCR/LCR)] with 30% different intrinsic aerobic fitness levels due to two-way divergent selective breeding. The low fit-LCR rat displays reduced mitochondrial content and fatty acid oxidation (FAOX) and NAFLD at a young age and significantly greater hepatic injury compared to the high fit-HCR livers. Thus, the high fit-HCR and low fit-LCR strains provide a novel experimental platform to study the role of aerobic fitness on liver metabolism. The central hypothesis of this proposal is that low aerobic fitness leads to increased risk of NAFLD and hepatic insulin resistance because of mitochondrial dysfunction. The specific aims are the following: Aim 1) to test if the low fit-LCR rats have increased susceptibility to lipid induced NAFLD and NASH, and if this can be prevented by increasing either mitochondrial content or FAOX. Aim 2) to test if the low fit-LCR rats have hepatic insulin resistance and dysregulated hepatic glucose output due to mitochondrial dysfunction or due to NAFLD. Both Aim 1 and Aim 2 will utilize dietary high fat in-vivo studies and lipid overload in-vitro studies (primary hepatocytes) to examine susceptibility for NAFLD and insulin resistance in low aerobically fit LCR and high aerobically fit HCR animals. In addition, hepatic insulin resistance will be studied with in-vitro insulin signaling and in-vivo hyperinsulinemic-euglycemic clamp methods. We will also evaluate if adenoviral overexpression of peroxisome proliferator gamma co-activator 1 alpha (PGC-1, to stimulate mitochondrial biogenesis) or carnitine palmitoyltransferase-1 (CPT-1, to enhance FAOX in existing mitochondria) in LCR livers or primary hepatocytes can protect against lipid induced NAFLD and improve hepatic insulin sensitivity. The outcomes of this study will provide a greater mechanistic understanding of the links between aerobic fitness, hepatic mitochondrial function, and NAFLD. The outcomes will also if determine if increased hepatic mitochondrial content or increased hepatic fatty acid oxidation are effective therapeutic targets to prevent NAFLD or hepatic insulin resistance.