mTOR-Mediated Desaturation of Fatty Acids in Hepatic Insulin Resistance.

美国武装部队退役人员患代谢性疾病的风险增加， 例如2型糖尿病（T2 DM）的患病率影响了估计1/3的VHA 患者2型糖尿病病因学的一个关键缺陷是胰岛素不能抑制肝脏葡萄糖的产生， 或肝脏胰岛素抵抗。肝脏脂质代谢的改变先于肝脏胰岛素抵抗， 主要由线粒体脂肪酸氧化（β-氧化）调节，特别是维持 不同膳食状态下的有效代谢灵活性。以前的工作已经暗示了 雷帕霉素（mTOR）通过调节β-氧化作为这一过程的介体。但我们的 初步工作发现了一个有趣的二分法;当mTOR抑制时， 饱和脂肪酸底物普遍存在，但相反，当 不饱和脂肪酸是主要的膳食脂质来源。也就是说，不饱和脂肪酸被β- 在低mTOR信号传导的情况下氧化不完全。不饱和脂肪酸的β-氧化需要 辅助酶去饱和以用作线粒体底物。因为胰岛素的发展 耐药与代谢灵活性失调有关，我们认为mTOR介导的这种调节 这一过程是维持肝脏胰岛素敏感性和预防代谢性疾病的关键。 本提案的长期目标是确定一种关系， 肝胰岛素抵抗这种代谢功能障碍在退伍军人中非常普遍， 由于与此相关的其他疾病的风险增加， 疾病，包括非酒精性脂肪肝和肝细胞癌。治疗和预防 选择将大大减少退伍军人患者的健康负担以及退伍军人健康 与治疗相关的行政费用。我们的总体假设是，mTOR调节了对 膳食脂肪酸对β-氧化辅助酶调节及其功能障碍 导致肝脏胰岛素抵抗。我们进行这项研究的基本原理是， 调节代谢应激下的营养素使用将作为定义新的治疗靶点的手段， 用于治疗和预防退伍军人的代谢性疾病。 我们使用mTOR信号的药物和遗传操纵以及 原代肝细胞中的限速β-氧化辅助酶2，4-二壬基-CoA还原酶（DECR 1）， 实验目的中的小鼠模型将该途径与线粒体能量功能联系起来， 新陈代谢.在目标1中，我们测试mTOR信号传导是否对DECR 1的活性具有直接影响， 脂肪氧化的功能结果。在目的2中，我们然后测试小鼠中的β-氧化辅助酶是否 在代谢应激下肝脏胰岛素信号传导的发展中发挥重要作用， DECR 1敲除小鼠模型。特别是，我们测试了代谢和线粒体对代谢的反应， 改变饮食中脂肪来源的压力。在目标3中，我们将肝线粒体的重塑作为一种 维持代谢灵活性的稳态机制和β-氧化辅助物的潜在作用 酶在这个过程中 肝脏胰岛素抵抗由多种因素促进，包括饮食、遗传和肝脏病理。通过 通过mTOR和β-氧化辅助酶阐明了该过程中的中心途径，我们的方法 将导致突破性的发现，这将大大加强健康研究，以帮助我们的退伍军人。

Discharged members of the US Armed Services are at an increased risk of metabolic disease which is exemplified by the prevalence of type 2 diabetes mellitus (T2DM) affecting an estimated 1/3 of all VHA patients. A key defect in the etiology of T2DM is the inability of insulin to suppress hepatic glucose production, or hepatic insulin resistance. Alterations in hepatic lipid metabolism precede hepatic insulin resistance and are regulated largely by mitochondrial fatty acid oxidation (β-oxidation) and, in particular, the ability to maintain effective metabolic flexibility under different dietary states. Previous work has implicated mechanistic target of rapamycin (mTOR) as a mediator of this process through the regulation of β-oxidation. However, our preliminary work found an interesting dichotomy; inhibition of mTOR promotes β-oxidation of fatty acids when there is a prevalence of saturated fatty acids substrates available but in contrast impairs β-oxidation when unsaturated fatty acids are the primary dietary lipid sources. That is, unsaturated fatty acid catabolism by β- oxidation is not complete in the context of low mTOR singaling. β-oxidation of unsaturated fatty acids requires accessory enzymes to desaturate for use as mitochondrial substrates. Because the development of insulin resistance is linked to dysregulation in metabolic flexibility, we propose that mTOR-mediated regulation of this process is a key to maintaining hepatic insulin sensitivity and preventing metabolic disease. The long-term goal of this proposal is define a relationship that could be central to the development of hepatic insulin resistance. This metabolic dysfunction is highly prevalent among Veterans and is a significant long-term healthcare issue due to increased risk of developing additional pathologies associated with this condition, including non-alcoholic fatty liver disease and hepatocellular carcinoma. Treatment and prevention options will significantly reduce the health burden of Veteran patients as well as Veterans Health Administration costs associated with treatment. Our overall hypothesis is that mTOR regulates the response to dietary fatty acids through its regulation of β-oxidation accessory enzymes and that dysfunction in this pathway leads to hepatic insulin resistance. Our rationale for this study is that understanding how this pathway regulates nutrient usage under metabolic stress will serve as a means to define new therapeutic targets to be utilized for treatment and prevention of metabolic disease in Veterans. We test this hypothesis using both pharmaceutical and genetic manipulation of mTOR signaling and the rate limiting β-oxidation accessory enzyme 2,4 Dieonyl-CoA reductase (DECR1) in primary hepatocytes and mouse models in experimental aims that link this pathway with mitochondrial energetic function and metabolism. In aim 1, we test whether mTOR signaling has direct impact on the activity of DECR1 with a functional outcome on fat oxidation. In aim 2, we then test whether β-oxidation accessory enzymes in mice play a significant role in the development of hepatic insulin signaling under metabolic stress using a novel DECR1 knockout mouse model. In particular, we test the metabolic and mitochondrial response to metabolic stress from changing dietary sources of fat. In aim 3, we address remodeling of the hepatic mitochondria as a homeostatic mechanism to maintain metabolic flexibility and the potential role of β-oxidation accessory enzymes in this process. Hepatic insulin resistance is promoted by several factors including diet, genetics and liver pathology. By clarifying a central pathway in the process through mTOR and β-oxidation accessory enzymes, our approach will lead to breakthrough discoveries that will significantly enhance health research to help our Veterans.