Lipolytic Mechanisms of PPAR Activation

PPAR 激活的脂肪分解机制

• 批准号: 6722735
• 负责人: JORGE PLUTZKY
• 金额: $ 41.69万
• 依托单位: BRIGHAM AND WOMEN'S HOSPITAL
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-01-01 至 2007-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6722735
• 关键词: biological signal transduction; genetically modified animals; human tissue; laboratory mouse; lipolysis; lipoprotein lipase; northern blottings; peroxisome proliferator activated receptor; receptor expression; triacylglycerol lipase; very low density lipoprotein

DESCRIPTION (provided by applicant): Peroxisome Proliferator-Activated Receptors (PPARs) are ligand-activated nuclear receptors central to the transcriptional regulation of adipogenesis, glucose control and lipid metabolism. More recent work establishes PPAR expression and effects in the vasculature, including endothelial cells (EC). Despite these advances, major unresolved issues persist. One central unanswered question in the PPAR field is the nature of endogenous PPAR ligands, which might recapitulate the effects of synthetic PPAR agonists, or how such natural mediators are produced under physiologic conditions. Similarly, despite extensive studies implicating PPARs in lipid biology, little data exists regarding the links between pathways of lipid metabolism and subsequent PPAR activation. Such insight could have major implications for metabolic disorders and atherosclerosis. Data is presented establishing lipoprotein lipase (LPL), the central enzyme in triglyceride-rich lipoprotein metabolism, as an endogenous mechanism for PPARalpha activation. In vitro and in vivo evidence, using both gain of function (LPL overexpression) and loss of function (PPARalpha-deficiency) models, support this claim. LPL-mediated PPAR-alpha activation is independent of LPL's known non-enzymatic effects and is selective as to PPAR (PPARalpha>>PPARdelta> PPARgamma), lipoprotein substrate (VLDL>>LDL>HDL), and lipase- absent with other fatty acid-releasing lipases tested. Furthermore, monoacylglycerol (MAG), a LPL-specific product, is identified as a novel PPARalpha activator contributing to these LPL responses. Our central hypothesis is that lipolysis is a major pathway for endogenous PPAR activation, with distal effects determined by the varying nature of lipoprotein substrate, lipase, and targeted PPAR. This proposal outlines experiments to define lipolytic mechanisms for PPAR activation across these same parameters. Unique contributors to LPL-mediated PPARalpha activation, as suggested by preliminary data, will be studied, including MAG as a little studied signaling molecule and mechanisms of ligand delivery. Key lipolytic variables of lipoprotein substrate and other tiglyceride lipases will be examined in terms of their PPARalpha, -delta, and -gamma effects. These studies include measures of lipolytic PPAR responses on available well-characterized VLDL and plasma samples from both mice and humans. The existence of genetic LPL variants in mouse models and in humans, which have a range of LPL activity, will be utilized in vitro and in vivo to determine how graded LPL function alters well-established PPAR responses. These LPL models include the otherwise lethal LPL-deficient mice rescued by transient LPL expression. Through these programmatic efforts, insight will be gained into lipolysis as a mechanism for selective endogenous PPAR activation, and its distal transcriptional effects.

描述（由申请人提供）：过氧化物酶体分解物激活受体（PPARs）是配体激活的核受体，对脂肪形成、葡萄糖控制和脂质代谢的转录调节至关重要。最近的工作建立了血管系统，包括内皮细胞（EC）中的PPAR表达和作用。尽管取得了这些进展，但重大的未决问题依然存在。在PPAR领域的一个中心未回答的问题是内源性的PPAR配体的性质，这可能概括的合成的PPAR激动剂的作用，或如何在生理条件下产生这样的天然介质。类似地，尽管大量研究表明PPARs参与脂质生物学，但关于脂质代谢途径与随后的PPARs活化之间的联系的数据很少。这样的见解可能对代谢紊乱和动脉粥样硬化有重大意义。 提供的数据确立了脂蛋白脂肪酶（LPL）（富含甘油三酯的脂蛋白代谢中的中心酶）作为PPARalpha激活的内源性机制。使用功能获得（LPL过表达）和功能丧失（PPARalpha缺乏）模型的体外和体内证据支持这一主张。LPL介导的PPAR-a活化不依赖于LPL已知的非酶促作用，并且对PPAR（PPARalpha>>PPARdelta> PPARgamma）、脂蛋白底物（VLDL>>LDL>HDL）和脂肪酶是选择性的-在测试的其它释放脂肪酸的脂肪酶中不存在。此外，单酰基甘油（MAG），LPL特异性产品，被确定为一种新的PPARalpha激活剂有助于这些LPL的反应。我们的中心假设是脂解是内源性PPAR激活的主要途径，远端效应由脂蛋白底物、脂肪酶和靶向PPAR的不同性质决定。该提案概述了在这些相同参数下定义PPAR激活的脂解机制的实验。如初步数据所示，将研究LPL介导的PPARalpha活化的独特贡献者，包括MAG作为很少研究的信号分子和配体递送机制。脂蛋白底物和其他甘油三酯脂肪酶的关键脂解变量将在其PPARalpha，-δ和-γ效应方面进行检查。这些研究包括对来自小鼠和人的可用的充分表征的VLDL和血浆样品的脂解PPAR反应的测量。在小鼠模型和人类中存在的遗传LPL变体，具有一系列LPL活性，将在体外和体内用于确定分级LPL功能如何改变完善的PPAR反应。这些LPL模型包括通过瞬时LPL表达拯救的另外致死的LPL缺陷小鼠。通过这些程序性的努力，将深入了解脂解作为选择性内源性过氧化物酶体增殖物激活体的机制，及其远端转录效应。