Lipid Metabolism in Fat Cells

描述(申请人提供)：肥胖是一种主要的健康问题，易患2型糖尿病和其他严重疾病。更全面地了解脂肪细胞中脂肪合成是如何调节的，对于指导合理开发治疗肥胖症及其并发症的新方法至关重要。在上一次资助期间，我们证明了中链脂肪酸(辛酸)刺激脂肪细胞中的β-氧化和抑制甘油三酯的合成，模拟了禁食的一些代谢效应。在用肿瘤坏死因子α处理的脂肪细胞中也发现了类似的抗脂作用。我们证明了三种应激源，体内禁食、辛酸和体外肿瘤坏死因子α，诱导了许多相同的细胞反应。其中包括反应性氧化物种(ROS)的生成增加，MAPK和AMP激活的蛋白激酶(AMPK)的激活，以及核转录因子PPARGamma和相关致脂基因的表达减少。根据这些发现，我们计划使用这三种应激源来操纵脂肪细胞中的脂肪生成，以剖析调控机制。我们假设关键信号(ROS或ROS非依赖性)是由于增加的β-氧化而产生的。这些信号分子激活应激反应激酶，从而使PPAR伽马失活，减弱脂肪合成所需基因的表达。为了验证这一假说，我们提出了以下具体目标：(1)确定ROS是否对脂肪生成的调控至关重要；(2)测试β-氧化的变化是否产生导致PPARGamma失活的关键信号；以及(3)确定PPARGamma是否是控制应激诱导的抗脂作用的信号汇聚点，PPARGamma失活的机制是什么，以及哪些代谢基因对应激操作最敏感。每个目标都将通过细胞生物学和分子生物学的综合应用，结合代谢和生化方法，使用培养的小鼠和人类脂肪细胞以及啮齿动物模型来解决。总之，这些研究将为压力诱导脂肪细胞脂肪生成的调控提供新的见解，这是调节能量平衡的潜在重要途径。

DESCRIPTION (provided by applicant): Obesity is a major health problem that predisposes to type 2 diabetes and other serious conditions. A more complete understanding of how fat synthesis is regulated in adipocytes is critical to guide rational development of new approaches for treating obesity and its complications. In the last grant period, we demonstrated that medium-chain fatty acids (octanoate) stimulate beta-oxidation and inhibit triglyceride synthesis in adipocytes, mimicking some of the metabolic effects of fasting. Analogous anti-lipogenic effects have been found in adipocytes treated with TNFalpha. We demonstrated that the three stressors, fasting in vivo, octanoate, and TNFalpha in vitro, induce many of the same cellular responses. These include increased generation of reactive oxidative species (ROS), activation of MAP-kinases (MAPK) and AMP-activated protein kinase (AMPK), and decreased expression of the nuclear transcription factor PPARgamma and associated lipogenic genes. In light of these findings, we plan to use these three stressors to manipulate lipogenesis in adipocytes to dissect mechanisms of regulation. We hypothesize that critical signals (ROS or ROS-independent) are generated as a result of increased beta-oxidation. These signaling molecules activate stress-responsive kinases, which inactivate PPARgamma, attenuating expression of genes necessary for fat synthesis. To test this hypothesis, we propose the following specific aims: (1) to determine whether ROS is crucial for regulation of lipogenesis; (2) to test if changes in beta-oxidation generate critical signals that cause inactivation of PPARgamma; and (3) to determine if PPARgamma is the point at which signals converge that control stress-induced anti-lipogenic effects, what is the mechanism of PPARgamma inactivation, and which metabolic genes are most sensitive to the stress manipulation. Each aim will be addressed with comprehensive and integrated application of cell biology and molecular biology in combination with metabolic and biochemical approaches, using culture murine and human adipocytes as well as rodent models. Together, these studies will provide new insights into the stress-induced regulation of lipogenesis in adipocytes, a potentially important avenue for modulating energy balance.