The Role of Hepatocyte ABCA1 in Lipid Mobilization and Transport

描述（由申请人提供）：ATP结合盒转运蛋白A1（ABCA 1）从细胞中流出磷脂（PL）和游离胆固醇（FC），形成新生高密度脂蛋白（nHDL）。由于ABCA 1在大多数细胞中不稳定表达，我们产生了肝细胞特异性ABCA 1 KO（HSKO）小鼠，以研究肝细胞ABCA 1在脂质动员、转运和代谢中的作用。我们发现，肝细胞ABCA 1调节VLDL、LDL和HDL的产生和分解，使肝细胞ABCA 1成为影响冠心病的所有三种主要血浆脂蛋白类别中脂质转运的关键调节剂 (CHD)发展在初步研究中，我们发现肝细胞ABCA 1还调节肝脏胰岛素和炎症信号传导，这表明肝细胞ABCA 1的功能虽然尚未完全阐明，但比促进大量细胞胆固醇输出和nHDL形成更复杂。 本次更新的目的是确定肝细胞ABCA 1在HSKO小鼠和人类的液体动员和运输中的作用。在具体目标1中，我们将研究肝细胞ABCA 1表达在肝脏胰岛素信号传导、炎症和脂肪生成中的作用。 将在普通饲料和高脂肪喂养的WT和HSKO小鼠中测定代谢表型、血浆VLDL代谢、肝脏脂质合成、肝脏胰岛素受体信号传导和肝脏质膜脂质组成。在具体目标2中，将检查肝脏ABCA 1表达对从血浆HDL到粪便的胆固醇通量的作用。我们将在HSKO与WT小鼠中研究HDL FC和CE相对于apoA-I的血浆衰减、肝脏摄取、再分泌到血浆中以及胆汁和粪便排泄。在具体目标3中，将探索膳食多不饱和脂肪相对于饱和脂肪和单不饱和脂肪降低人肝脏、肠和脂肪组织中ABCA 1表达的程度。 将确定组织ABCA 1 RNA和蛋白质表达、血浆HDL胆固醇浓度、颗粒数量和大小以及血浆HDL FC流出能力作为膳食脂肪饱和度的函数之间的相互关系。在具体目标4中，我们将确定非洲裔美国人（AA）特有的罕见编码ABCA 1序列变体（欧洲裔美国人中不存在，EA）是否影响脂质流出以及血浆HDL胆固醇浓度，颗粒数量和大小以及血浆HDL流出潜力。这些测量结果与冠状动脉钙化斑块评分（CHD的一种测量方法）之间的相关性将被检查。

DESCRIPTION (provided by applicant): ATP binding cassette transporter A1 (ABCA1) effluxes phospholipid (PL) and free cholesterol (FC) from cells, forming nascent high density lipoproteins (nHDL). Because ABCA1 is variably expressed in most cells, we generated hepatocyte-specific ABCA1 KO (HSKO) mice to study the role of hepatocyte ABCA1 in lipid mobilization, transport, and metabolism. We found that hepatocyte ABCA1 regulates the production and catabolism of VLDL, LDL, and HDL, making hepatocyte ABCA1 a key modulator of lipid transport in all three major plasma lipoprotein classes that affect coronary heart disease (CHD) development. In preliminary studies, we found that hepatocyte ABCA1 also regulates hepatic insulin and inflammatory signaling, suggesting the function of hepatocyte ABCA1, while not fully elucidated, is more complex than facilitating bulk cellular cholesterol export and nHDL formation. The goal of this renewal is to determine the role of hepatocyte ABCA1 in liid mobilization and transport in HSKO mice and humans. In specific aim 1, we will examine the role of hepatocyte ABCA1 expression in hepatic insulin signaling, inflammation, and lipogenesis. Metabolic phenotype, plasma VLDL metabolism, hepatic lipid synthesis, hepatic insulin receptor signaling, and hepatic plasma membrane lipid composition will be determined in chow and high fat-fed WT and HSKO mice. In specific aim 2, the role of hepatic ABCA1 expression on cholesterol flux from plasma HDL to feces will be examined. We will investigate the plasma decay, hepatic uptake, re-secretion into plasma, and biliary and fecal excretion of HDL FC and CE, relative to apoA-I, in HSKO vs. WT mice. In specific aim 3, the extent to which dietary polyunsaturated (poly) fat, relative to saturated (sat) and monounsaturated (mono) fat, reduces ABCA1 expression in human liver, intestine and adipose tissue will be explored. Interrelationships among tissue ABCA1 RNA and protein expression, plasma HDL cholesterol concentration, particle number and size, and plasma HDL FC efflux capacity as a function of dietary fat saturation will be determined. In specific aim 4, we will determine whether rare coding ABCA1 sequence variants unique to African Americans (AA) (absent in European Americans, EA) affect lipid efflux as well as plasma HDL cholesterol concentration, particle number and size, and plasma HDL efflux potential. Associations between these measurements and coronary artery calcified plaque score, a measure of CHD, will be examined.