Cholesterol Ester Hydrolysis and cholesterol efflux

描述（由申请方提供）：存在胆固醇酯负载的巨噬泡沫细胞是动脉粥样硬化病变的最显著特征之一。细胞外受体介导的游离胆固醇（FC）流出是清除细胞胆固醇的主要机制，在预防泡沫细胞形成和动脉粥样硬化病变发展中至关重要。然而，为了发生外排，FC必须首先通过中性胆固醇酯水解酶（CEH）介导的水解从储存的胆固醇酯（CE）中释放出来，这一步骤越来越多地被认为是FC外排的限速步骤。PI已克隆并表征了人巨噬细胞CEH，并证明CEH过表达后细胞CE动员增加，并通过调节细胞CE水解确定CEH在动脉粥样硬化形成中的作用是上一个资助周期的重点。人巨噬细胞CEH在动脉粥样硬化易感性LDLR-/-小鼠中的巨噬细胞特异性转基因表达不仅导致饮食诱导的动脉粥样硬化和主动脉病变的胆固醇含量显著降低，而且还减少了病变坏死。我们的机制研究表明，增强CEH介导的CE在巨噬细胞中的水解增强了胆固醇从巨噬细胞到肝脏的流量，以最终消除为胆汁酸进入胆汁和粪便，提供了直接证据，即增强的CEH介导的细胞内CE水解具有抗动脉粥样硬化作用。目前的建议的总体目标是扩大我们的工作，在调节巨噬细胞的脂质负荷的CEH在三个关键领域的作用：描绘增强巨噬细胞CEH表达对现有的动脉粥样硬化病变的进展的影响，以确定CEH介导的巨噬细胞脂质负荷减少的全身效应，并获得最终的证据，缺乏CEH将动脉粥样硬化。因此，该建议的中心假设是：巨噬细胞CEH水平决定细胞内CE蓄积，从而影响动脉粥样硬化病变的发展以及与动脉壁相关巨噬细胞泡沫细胞的脂质负荷相关的全身畸变。提出了以下三个具体目的：目的1：确定巨噬细胞特异性CEH表达在降低LDLR-/-小鼠中现有动脉粥样硬化病变进展中的作用;目的2：确定CEH介导的LDLR-/-CEHTg小鼠中巨噬细胞胆固醇负荷降低的全身效应，并描述潜在机制;目的3：通过巨噬细胞特异性靶向破坏小鼠CEH获得体内概念验证，并确定其对细胞内CE代谢和动脉粥样硬化的影响。巨噬细胞泡沫细胞的形成是动脉粥样硬化形成的初始事件之一。HDL介导的未酯化或游离胆固醇（FC）从这些泡沫细胞中储存的胆固醇酯（CE）中流出是清除细胞内胆固醇和泡沫细胞消退的主要机制。广泛的早期研究表明，在易患动脉粥样硬化的动物物种中，巨噬细胞胆固醇酯代谢发生畸变。此外，这些研究还确定了中性胆固醇酯水解酶（CEH）催化的细胞内胆固醇酯水解作为胆固醇流出过程中的限制步骤。在该项目的最后一个资助周期中，我们证明了巨噬细胞CEH在调节细胞CE水平，增强FC流出，从而减弱LDLR-/-小鼠中饮食诱导的动脉粥样硬化中的作用。拟议的研究将建立在这一基础上，并建立CEH不仅在预防现有斑块进展，而且在改善全身炎症和胰岛素敏感性方面的作用，因为减少巨噬细胞脂质负荷。考虑到动脉粥样硬化和冠状动脉疾病的患病率，肥胖和胰岛素抵抗是主要的危险因素，目前的研究结果可能具有重要的临床意义。

DESCRIPTION (provided by applicant): Presence of cholesteryl ester-laden macrophage foam cells is one of the most prominent characteristics of an atherosclerotic lesion. Extracellular acceptor-mediated free cholesterol (FC) efflux is the primary mechanism for the removal of cellular cholesterol and is critical in preventing foam cell formation and atherosclerotic lesion development. However, in order for efflux to occur, FC must first be released from stored cholesteryl esters (CE) by hydrolysis mediated by neutral cholesteryl ester hydrolase (CEH) and this step is increasingly being recognized as the rate-limiting step in FC efflux. The PI has cloned and characterized the human macrophage CEH and demonstrated increased cellular CE mobilization after CEH over-expression and establishing the role of CEH in atherogenesis by regulating cellular CE hydrolysis was the focus during the last funding cycle. Macrophage-specific transgenic expression of human macrophage CEH in athero-susceptible LDLR-/- mice not only led to a significant reduction in diet-induced atherosclerosis and cholesterol content of the aortic lesions but also reduced lesion necrosis. Our mechanistic studies showed that enhancing CEH-mediated hydrolysis of CE in macrophages enhanced the flux of cholesterol from macrophages to liver for the final elimination as bile acids into bile and feces providing direct evidence that enhanced CEH-mediated intracellular CE hydrolysis is anti-atherogenic. The overall objective of the current proposal is to expand on our work on the role of CEH in regulating macrophage lipid burden in three critical areas: to delineate the effect of enhancing macrophage CEH expression on progression of existing atherosclerotic lesions; to determine the systemic effects of CEH-mediated reduction in macrophage lipid burden and to obtain the final proof that lack of CEH will be atherogenic. Therefore, it is the central hypothesis of this proposal that: Macrophage CEH levels determine intracellular CE accumulation and thereby influence atherosclerotic lesion development as well as systemic aberrations associated with lipid burden of artery wall associated macrophage foam cells. The following three specific Aims are proposed: Aim 1: To determine the role of macrophage-specific CEH expression in reducing the progression of existing atherosclerotic lesions in LDLR-/- mice; Aim 2: To determine the systemic effects of CEH-mediated reduction in Macrophage cholesterol burden in LDLR-/-CEHTg mice and delineate the underlying mechanisms and Aim 3: To obtain in vivo proof of concept by macrophage-specific targeted disruption of CEH in mice and to determine its effect on intracellular CE metabolism and atherosclerosis. Formation of macrophage foam cells is one of the initial events in atherogenesis. HDL- mediated efflux of unesterified or free cholesterol (FC) from the stored cholesteryl esters (CE) in these foam cells is the primary mechanism for removal of intracellular cholesterol and foam cell regression. Extensive earlier research has indicated aberrations in macrophage cholesterol ester metabolism in animal species susceptible to atherosclerosis. Further, these studies have also identified intracellular cholesterol ester hydrolysis catalyzed by neutral cholesteryl ester hydrolase (CEH) as a limiting step in the process of cholesterol efflux. During the last funding cycle of this project we demonstrated the role of macrophage CEH in regulating cellular CE levels, enhancing FC efflux and thereby attenuating diet-induced atherosclerosis in LDLR-/- mice. The proposed studies will build on this foundation and establish the role of CEH in not only preventing progression of existing plaque but in improving systemic inflammation and insulin sensitivity as a result of decreasing macrophage lipid burden. Given the prevalence of atherosclerosis and coronary artery disease with obesity and insulin resistance as major risk factors, the current findings are likely to have important clinical relevance.