The Lipid Protein Family and Triglyceride Metabolism

项目2的目标是确定脂蛋白家族在甘油三酯代谢中的作用。 我们先前在脂肪肝营养不良突变体中发现脂蛋白-1的突变是脂肪营养不良的原因 并证实脂蛋白-1是脂肪组织发育、肥胖和 小鼠和人类的胰岛素敏感性。最近，Lipin-1的两个不同的分子功能已经被 特色化的。首先，Lipin-1是一种磷脂酸盐磷酸酶-1(PAP1)酶，催化了 甘油三酯的生物合成，并解释了脂肪组织和骨骼肌中所有的PAP1活性。第二, 脂蛋白-1是PPAR-α和PPAR-γ的转录共激活因子 在肝细胞和脂肪细胞中。我们还确认了另外两名利平家族成员和 确定它们具有PAP1活性，并在肝脏(Lipin-2)或骨骼(Lipin-3)有显著表达。 我们假设三种脂蛋白中的每一种在甘油三酯中都有独特的、组织特有的作用 通过它们作为PAP1酶和转录共激活因子的作用来代谢。具体目标是： (1)确定小鼠脂蛋白-1和人脂蛋白-2点突变损伤PAP1的机制 和/或辅助激活功能导致脂肪营养不良和炎症性疾病，马吉德综合征， 分别进行了分析。(2)确定脂肪细胞对Lipin-1辅活化子与PAP1功能的需求 利用遗传和化学方法控制脂类-1活性的分化、生理和新陈代谢。我们 将产生培养的细胞和小鼠，表达“只有辅活化子”的Lipin-1蛋白，并确定 脂肪组织、肝脏、肌肉、神经和生殖中补充脂类-1缺陷的突变体 功能。我们还将描述一种新的成脂化合物的作用机制 项目3增强PAP1活性，并确定其他促脂肪化合物对Lipin-1的影响 辅活化子和PAP1活性。(3)确定Lipin-2和Lipin-3的生理作用。我们将生成 基因敲除小鼠模型，并表征脂类-2在肝脂代谢和炎症中的作用， 脂蛋白-3在骨脂代谢和骨激素产生中的作用 葡萄糖动态平衡。脂蛋白功能的阐明可能会导致新的调节方法 肥胖、胰岛素敏感性和炎症导致肥胖、高脂血症和糖尿病。

The objective of Project 2 is to define the role of the lipin family of proteins in triglyceride metabolism. We previously identified mutations in lipin-1 as the cause of lipodystrophy in the fatty liver dystrophy mutant mouse strain, and established that lipin-1 is a determinant of adipose tissue development, obesity, and insulin sensitivity in mice and humans. Very recently, two distinct molecular functions for lipin-1 have been characterized. First, lipin-1 is a phosphatidate phosphatase-1 (PAP1) enzyme, catalyzing a key step in triglyceride biosynthesis, and accounting for all PAP1 activity in adipose tissue and skeletal muscle. Second, lipin-1 is a transcriptional coactivator of PPAR (peroxisome proliferator-activated receptor)-alpha and PPARgamma in hepatocytes and adipocytes. We have also identified two additional lipin family members and determined that they have PAP1 activity and exhibit prominent expression in liver (lipin-2) or bone (lipin-3). We hypothesize that each of the three lipin proteins has unique, tissue-specific roles in triglyceride metabolism through their actions as PAP1 enzymes and transcriptional coactivators. The Specific Aims are: (1) To determine the mechanisms by which point mutations in mouse lipin-1 and human lipin-2 impair PAP1 and/or coactivator function to cause lipodystrophy and the inflammatory disorder, Majeed syndrome, respectively. (2) To determine the requirement for lipin-1 coactivator versus PAP1 function in adipocyte differentiation, physiology, and metabolism using genetic and chemical manipulation of lipin-1 activity. We will generate cultured cells and mice that express "coactivator only" lipin-1 protein and determine ability of the mutant to complement lipin-1 deficiency in adipose tissue, liver, muscle, nerve, and reproductive function. We will also characterize the mechanism by which a novel adipogenic compound identified in Project 3 enhances PAP1 activity, and determine effects of other proadipogenic compounds on lipin-1 coactivator and PAP1 activity. (3) To establish the physiological roles of lipin-2 and lipin-3. We will generate knockout mouse models and characterize the role of lipin-2 in hepatic lipid metabolism and inflammation, and the role of lipin-3 in bone lipid metabolism and production of bone hormones that modulate systemic glucose homeostasis. The elucidation of lipin protein functions may lead to novel approaches for modulating adiposity, insulin sensitivity and inflammation contributing to obesity, hyperlipidemia, and diabetes.