Endogenous Mechanisms of PPAR Modulation

描述（由申请人提供）：过氧化物酶体增殖物激活受体（PPARs）是调节许多关键代谢途径的配体激活转录因子。对PPARs的大部分认识来自合成的PPARs激动剂的研究，包括临床使用的研究。PPARa由降脂贝特类激活，调节脂肪酸代谢。由胰岛素增敏噻唑烷二酮激活的PPARy控制脂肪生成和葡萄糖稳态。PPARa和PPARy激活都可以限制动脉粥样硬化和炎症。这些合成激动剂激活PPAR的数据确立了理解内源性PPAR激活的重要性。最近，我们报道了脂蛋白脂酶（LPL）以特异性和选择性的方式作用于循环脂蛋白以产生PPARalpha配体。该建议侧重于中心假设，即内源性PPAR拮抗作用的直接和间接途径在确定代谢反应中起重要作用。数据提供了三种不同的内源性途径，可能会负调节过氧化物酶体增殖物激活受体的活性。这些机制将通过检查它们对已建立的体外和体内PPAR活化模型的调节来研究。LPL介导的PPARa活化表明结构不同的脂肪酸的不一致的内皮效应可能是由于差异PPARa活化，包括拮抗作用。在目标1中，将在体外和体内研究特定脂肪酸对PPAR的激活和抑制，将ω-3脂肪酸与饱和脂肪酸和反式脂肪酸进行对比。肝核因子4 α（HNF 4 α）是一种脂肪酸激活的重要受体，调节脂质代谢、血栓形成和血糖控制。通过使用我们的LPL/PPARa研究中采用的脂质代谢操作，我们已经确定了HNF 4 α调节的新机制以及PPARalpha和HNF 4 α对脂质代谢途径的不同反应。在目标2中，将探索HNF 4 α和PPAR α之间的这种差异。一个新的，但强大的机制，过氧化物酶体增殖物激活物受体的调节将是存在一个直接的内源性过氧化物酶体增殖物激活物受体拮抗剂。虽然β-胡萝卜素的对称裂解产生RXR核受体的天然配体，但我们已经确定，不对称β-胡萝卜素裂解产生直接拮抗PPAR反应的特定脱胡萝卜素醛。在目的3中，将在体外和体内表征该直接拮抗剂。总之，这些研究整合了生物化学，生物学和体内模型，以更好地了解内源性调节PPAR活性如何决定生物反应。

DESCRIPTION (provided by applicant): Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors regulating many key metabolic pathways. Much of the insight into PPARs derives from studies with synthetic PPAR agonists, including those in clinical use. PPARa, activated by lipid-lowering fibrates, regulates fatty acid metabolism. PPARy, activated by insulin-sensitizing thiazolidinediones, controls adipogenesis and glucose homeostasis. Both PPARa and PPARy activation may limit atherosclerosis and inflammation. This body of data for PPAR activation by synthetic agonists establishes the importance of understanding endogenous PPAR activation. Recently, we reported lipoprotein lipase (LPL) acts on circulating lipoproteins in a specific and selective manner to generate PPARalpha ligands. This proposal focuses on the central hypothesis that direct and indirect pathways for endogenous PPAR antagonism play an important part in determining metabolic responses. Data is provided for three different endogenous pathways that may negatively regulate PPAR activity. These mechanisms will be studied by examining their modulation of well established in vitro and in vivo models of PPAR activation. LPL-mediated PPARa activation suggests the discrepant endothelial effects of structurally diverse fatty acids may be due to differential PPARa activation, including antagonism. In Aim 1, PPAR activation and inhibition by specific fatty acids will be studied in vitro and in vivo, contrasting omega-3 fatty acids to saturated and trans-fatty acids. Hepatic nuclear factor 4 alpha (HNF4alpha) is a poorly understood but critical fatty acidactivated receptor that regulates lipid metabolism, thrombosis, and glucose control. By using the manipulations of lipid metabolism employed in our LPL/PPARa studies, we have identified novel mechanisms of HNF4alpha modulation and divergent responses between PPARalpha and HNF4alpha to pathways of lipid metabolism. In Aim 2, this divergence between HNF4alpha and PPARalpha will be explored. A novel but powerful mechanism for PPAR modulation would be the existence of a direct endogenous PPAR antagonist. While symmetric cleavage of beta carotene generates natural ligands for the RXR nuclear receptor, we have identified that asymmetric beta carotene cleavage produces a specific apocarotenal that directly antagonizes PPAR responses. In Aim 3, this direct antagonist will be characterized in vitro and in vivo. Together, these studies integrate biochemical, biologic, and in vivo models to better understand how endogenous modulation of PPAR activity may determine biologic responses.