BCFA Metabolism and the Regulation of Energy Balance

项目摘要 针对棕色脂肪组织（BAT）功能来增加能量消耗是一种有吸引力的策略 治疗肥胖和相关的2型糖尿病。BAT和相关的米色脂肪表达解偶联蛋白1 （UCP 1），一种线粒体膜蛋白，将呼吸与ATP合成解偶联，并促进 产热作用奇怪的是，UCP 1缺失小鼠只有在维持热中性时才肥胖，这表明 生热的替代机制的存在。根据这一概念，几个UCP 1- 在棕色和米色脂肪细胞中已经鉴定出独立的消耗ATP的无效循环。但 这些途径对调节全身能量代谢的相对贡献仍不清楚。 我们的初步研究表明，过氧化物酶体，专门用于脂质代谢的细胞器， 基于支链过氧化物酶体代谢的脂肪组织产热的替代机制 脂肪酸（BCFA）。过氧化物酶体占总细胞耗氧量的20%。过氧化物酶 与线粒体氧消耗不同，呼吸与ATP合成无关，而是产生热量。 单甲基（mm）BCFA是通过从头脂肪生成合成的，使用衍生自以下的前体： 支链氨基酸（BCAA）。我们的研究结果表明，冷处理增加了基因表达， 产热脂肪中mmBCFA合成和β-氧化的相关因子。产热刺激促进 BCFA合成蛋白易位至过氧化物酶体，BCFA β-氧化位点。BCFA上调 β-氧化提高褐色脂肪细胞的细胞内温度，并增加耗氧率 在WT和UCP 1 KO棕色脂肪细胞中。总之，这些结果使我们假设过氧化物酶体是 参与以BCFA无效过程为特征的UCP 1独立产热机制 合成和β-氧化。由于脂肪酸的从头合成是一个高能量需求的过程， 过氧化物酶体β-氧化与ATP的产生无关，我们进一步假设这种无效的循环促进了 负能量平衡，导致防止肥胖和胰岛素抵抗。为了验证这个假设， 我们提出两个具体目标。第一个目标将使用生物化学，细胞培养为基础，并在体内的方法， 过氧化物酶体参与了BCFA代谢的无效过程。第二个目标将使用功能丧失， BCFA β-氧化的功能获得性小鼠模型，以研究其在产热和全身能量中的作用 新陈代谢.

PROJECT SUMMARY Targeting brown adipose tissue (BAT) function to increase energy expenditure represents an attractive strategy to treat obesity and the associated type 2 diabetes. BAT and the related beige fat express uncoupling protein 1 (UCP1), a mitochondrial membrane protein that uncouples respiration from ATP synthesis and promotes thermogenesis. Paradoxically, UCP1 null mice are only obese when maintained at thermoneutrality, suggesting the existence of alternative mechanisms of thermogenesis. Consistent with this notion, several UCP1- independent ATP-consuming futile cycles have been identified in brown and beige adipocytes. However, the relative contribution of these pathways to the regulation of whole-body energy metabolism remains unclear. Our preliminary studies suggest that peroxisomes, organelles specialized for lipid metabolism, are involved in an alternative mechanism of adipose tissue thermogenesis based on peroxisomal metabolism of branched chain fatty acids (BCFA). Peroxisomes account for up to 20% of total cellular oxygen consumption. Peroxisomal respiration, unlike mitochondrial oxygen consumption, is not linked to ATP synthesis and instead generates heat. Monomethyl (mm) BCFA are synthesized via de novo lipogenesis using a precursor derived from catabolism of branched chain amino acids (BCAA). Our results reveal that cold treatment increases the gene expression of factors involved in mmBCFA synthesis and beta-oxidation in thermogenic fat. A thermogenic stimulus promotes translocation of BCFA synthetic proteins to peroxisomes, the site of BCFA beta-oxidation. Upregulation of BCFA beta oxidation raises the intracellular temperature in brown adipocytes and increases oxygen consumption rate in WT and UCP1 KO brown adipocytes. Together, these results lead us to hypothesize that peroxisomes are involved in a UCP1-independent mechanism of thermogenesis characterized by a futile process of BCFA synthesis and beta-oxidation. Since de novo synthesis of fatty acids is a highly energy-demanding process and peroxisomal beta-oxidation is not linked to ATP production, we further hypothesize that this futile cycle promotes negative energy balance, leading to protection against obesity and insulin resistance. To test this hypothesis, we propose two specific aims. The first aim will use biochemical, cell culture-based, and in vivo approaches to implicate peroxisomes in a futile process of BCFA metabolism. The second aim will use loss-of-function and gain-of-function mouse models of BCFA beta-oxidation to study its role in thermogenesis and whole-body energy metabolism.