High Density Lipoprotein Metabolism Influence of Extracellular Phospholipases

描述(申请人提供)：血浆高密度脂蛋白(高密度脂蛋白)胆固醇及其主要高密度脂蛋白载脂蛋白A-I的水平与动脉粥样硬化性心血管疾病呈负相关。血浆高密度脂蛋白胆固醇和载脂蛋白A-I的水平部分取决于它们的分解代谢速度，但在体内调节它们分解代谢的机制仍然不完全清楚。无论是急性炎症状态，如脓毒症，还是慢性炎症状态，如代谢综合征，都与低水平的高密度脂蛋白胆固醇和载脂蛋白A-I有关，主要是由于分解代谢增加。这个项目的一个主要假设是，细胞外磷脂酶在炎症反应中上调，并通过高密度脂蛋白磷脂的水解来调节全身的高密度脂蛋白代谢。我们克隆并鉴定了脂肪酶基因家族中的一个新成员，我们称之为内皮脂肪酶(EL)。在本项目的当前周期中，我们已经证明了EL在小鼠体内的过度表达会由于分解代谢的增加而导致高密度脂蛋白的显著降低，而在小鼠中抑制EL的抗体会由于分解代谢的减少而导致高密度脂蛋白的增加。在这个相互竞争的更新提案中，我们将集中精力研究EL，以更好地了解它的结构-功能关系，与其他影响高密度脂蛋白的基因的代谢相互作用，与动脉粥样硬化的关系，以及它与人类生理学和病理生理学的关系。具体目的1：研究EL与其高度同源的近亲LPL和HL在脂质和脂蛋白偏好的分子基础上的差异。 具体目的2：验证在肝脏中，EL与HL和SR-BI相互作用影响高密度脂蛋白代谢、选择性摄取胆固醇和反向胆固醇转运的假说。具体目标3：确定慢性肝脏特异性EL表达对小鼠动脉粥样硬化形成的影响。将这些结果与内皮特异性EL表达在动脉粥样硬化中的作用进行比较。检验内皮EL表达影响内皮生理学的假说。 具体目标4：验证这一假设，即在人类炎症条件下，EL增加，并可能导致与这些条件相关的高密度脂蛋白水平降低。最近的一篇社论说：“也许关于内皮脂肪酶最重要的问题是：a)它在人类的高密度脂蛋白代谢中起重要作用吗？b)它在动脉粥样硬化形成中起重要作用吗？”这项建议既解决了这两个问题，也解决了与EL及其对高密度脂蛋白代谢的影响有关的关键结构-功能问题和潜在的基因-基因相互作用。这些研究的结果将为了解EL在高密度脂蛋白代谢和动脉粥样硬化形成中的作用提供重要的新见解。

DESCRIPTION (provided by applicant): Plasma levels of high-density lipoprotein (HDL) cholesterol and its major HDL apolipoprotein, apoA-I, are inversely associated with atherosclerotic cardiovascular disease. Plasma HDL cholesterol and apoA-I levels are determined in part by the rate at which they are catabolized, but the mechanisms that modulate their catabolism in vivo remain incompletely understood. Both acute inflammatory states, such as sepsis, and chronic inflammatory states, such as the metabolic syndrome, are associated with low levels of HDL cholesterol and apoA-I, primarily due to increased catabolism. A major underlying hypothesis of this project has been that extracellular phospholipases are upregulated in response to inflammation and modulate systemic HDL metabolism through hydrolysis of HDL phospholipids. We cloned and characterized a new member of the lipase gene family that we termed endothelial lipase (EL). In the current cycle of this project, we have demonstrated that overexpression of EL in mice causes markedly reduced HDL due to increased catabolism, and antibody inhibition of EL in mice causes increased HDL due to reduced catabolism. In this competing renewal proposal, we will focus our efforts on EL toward achieving a greater understanding of its structure-function relationships, metabolic interactions with other genes that influence HDL, association with atherosclerosis, and its relationship to human physiology and pathophysiology. Specific Aim 1: To investigate the differences between EL and its highly homologous relatives LPL and HL with regard to the molecular basis of the lipid and lipoprotein preferences of EL compared with LPL and HL. Specific Aim 2: To test the hypothesis that in the liver, EL interacts with HL and SR-BI to influence HDL metabolism, selective uptake of cholesterol, and reverse cholesterol transport. Specific Aim 3: To determine the effects of chronic hepatic-specific EL expression on atherogenesis in mice. To compare these results with the effects of endothelial-specific EL expression on atherosclerosis. To test the hypotheses that endothelial EL expression influences endothelial physiology. Specific Aim 4: To test the hypothesis that EL is increased in inflammatory conditions in humans and may contribute to the reduced HDL-C levels associated with these conditions. A recent editorial stated: "Perhaps the most important questions concerning endothelial lipase are: a) does it play an important role in HDL metabolism in humans, and b) does it play a significant role in atherogenesis?" This proposal addresses both of these issues and also addresses key structure-function questions and potential gene-gene interactions with regard to EL and its effects on HDL metabolism. The results of these studies should provide important new insight into the role of EL in HDL metabolism and atherogenesis.