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

退役的美国武装部队成员患代谢性疾病的风险增加 以 2 型糖尿病 (T2DM) 的患病率为例，估计影响了所有 VHA 的 1/3 患者。 T2DM 病因学的一个关键缺陷是胰岛素无法抑制肝葡萄糖的产生， 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，并且是 主要受线粒体脂肪酸氧化（β-氧化）调节，特别是维持 不同饮食状态下有效的代谢灵活性。以前的工作暗示了机械目标 雷帕霉素 (mTOR) 通过调节 β-氧化作为该过程的介质。然而，我们的 初步工作发现了一个有趣的二分法；抑制 mTOR 会促进脂肪酸的 β-氧化 存在大量可用的饱和脂肪酸底物，但相反，当 不饱和脂肪酸是主要的膳食脂质来源。即不饱和脂肪酸通过β- 在低 mTOR 信号传导的情况下，氧化并不完全。不饱和脂肪酸的β-氧化需要 辅助酶去饱和用作线粒体底物。因为胰岛素的发展 耐药性与代谢灵活性失调有关，我们认为 mTOR 介导的调节 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。 该提案的长期目标是定义一种对发展至关重要的关系 肝脏胰岛素抵抗。这种代谢功能障碍在退伍军人中非常普遍，并且是一个重要的 由于发生与此相关的其他病症的风险增加而导致长期医疗保健问题 疾病，包括非酒精性脂肪肝和肝细胞癌。治疗和预防 选择将显着减轻退伍军人患者的健康负担以及退伍军人健康 与治疗相关的管理费用。我们的总体假设是 mTOR 调节对 膳食脂肪酸通过调节β-氧化辅助酶以及该途径的功能障碍 导致肝脏胰岛素抵抗。我们进行这项研究的理由是了解该途径如何 调节代谢应激下的营养使用将作为确定新治疗目标的一种手段 用于治疗和预防退伍军人的代谢疾病。 我们使用 mTOR 信号传导的药物和基因操作来检验这一假设 原代肝细胞中限速 β-氧化辅助酶 2,4 二炔辅酶 A 还原酶 (DECR1) 和 实验目的小鼠模型将这条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 DECR1 的活性有直接影响 脂肪氧化的功能结果。在目标 2 中，我们随后测试小鼠体内的 β-氧化辅助酶是否存在 使用一种新颖的方法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 DECR1基因敲除小鼠模型。特别是，我们测试了代谢和线粒体对代谢的反应 改变膳食脂肪来源带来的压力。在目标 3 中，我们将肝线粒体重塑作为 维持代谢灵活性的稳态机制和β-氧化辅助的潜在作用 这个过程中需要用到酶。 饮食、遗传和肝脏病理等多种因素都会促进肝脏胰岛素抵抗。由 通过 mTOR 和 β-氧化辅助酶阐明该过程中的中心途径，我们的方法 将带来突破性的发现，从而显着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.