Human ApoE4 and Foam Cell Formation

描述（由申请人提供）：该项目的总体目标是确定载脂蛋白E4 （ApoE4）富集脂蛋白处理巨噬细胞导致过量胆固醇积累的机制，并阐明未折叠蛋白反应（UPR）在这一过程中的作用。人类载脂蛋白5 （Apo5）主要有三种等位基因，即52,53和54。与ApoE3（所谓的正常亚型）相比，54的产物ApoE4与动脉粥样硬化性心血管疾病的风险增加有关。Apo54在非裔美国人中普遍存在，与其他种族相比，他们患心血管疾病的比例更高。郭中mao博士的实验室先前的研究表明，真核起始因子21 （eIF-21）磷酸化的增加（UPR的一种信号）是巨噬细胞中胆固醇积累和泡沫细胞形成的机制，巨噬细胞使用来自ApoB48/48/ApoE-/- (E b> /B48)小鼠的脂蛋白处理。最近，我们发现富含人ApoE4的E- >/B48脂蛋白（E4/B48）在巨噬细胞中诱导的胆固醇积累和eIF-21磷酸化比同样浓度的富含人ApoE3的E-/B48脂蛋白（E3/B48）更大。此外，E4/B48脂蛋白在巨噬细胞中诱导胆固醇外排转运蛋白atp结合盒转运蛋白A1 （ABCA1）表达的能力不如E3/B48脂蛋白。这种转运体的缺乏与广泛的泡沫细胞形成和严重的动脉粥样硬化有关。本项目将验证UPR通路的激活是介导胆固醇外溢的转运蛋白表达减少的机制，从而导致E4/B48脂蛋白处理巨噬细胞过量胆固醇的积累。为了验证这一假设，将实施两个具体目标。特异性目的1将研究E4/ b48脂蛋白对巨噬细胞中介导胆固醇外排的转运蛋白表达、胆固醇外排本身以及泡沫细胞形成的影响。通过测量胆固醇外排转运体（ABCA1、ABCG1和清运受体b1 [SR-B1]）的表达水平，评估胆固醇外排程度，并确定巨噬细胞在E4/B48和E3/B48脂蛋白处理后细胞胆固醇积累的程度，可以实现这一目标。特异性Aim 2将确定UPR信号通路在巨噬细胞介导胆固醇外排的转运蛋白表达、胆固醇外排本身和泡沫细胞形成中的作用。普遍定期审议有三种途径。该项目将重点关注eif21相关途径，因为E4/B48脂蛋白已被证明可以激活它。如果我们的假设是正确的，那么E4/B48脂蛋白诱导的胆固醇外排转运蛋白的表达变化以及胆固醇外排和积累将在该途径被抑制后减弱。

DESCRIPTION (provided by applicant): The overall goal of this project is to determine the mechanism(s) leading to excess cholesterol accumulation in macrophages treated with apolipoprotein E4 (ApoE4)-enriched lipoproteins, and to elucidate the role of unfolded protein response (UPR) in this process. There are three major human alleles of apolipoprotein 5 (Apo5), i.e., 52, 53, and 54. The 54 product, ApoE4, is associated with increased risk of atherosclerotic cardiovascular disease compared to ApoE3, the so-called normal isoform. Apo54 is prevalent in African-Americans, for whom cardiovascular disease is disproportionally high compared to other ethnic groups. Previous work in Dr. ZhongMao Guo"s laboratory demonstrated that increased eukaryotic initiation factor 21 (eIF-21) phosphorylation, a signaling of UPR, is a mechanism underlying cholesterol accumulation and foam cell formation in macrophages treated with lipoproteins derived from ApoB48/48/ApoE-/- (E>/B48) mice. Recently, we found that E>/B48 lipoproteins enriched with human ApoE4 (E4/B48) induce greater cholesterol accumulation and enhanced eIF-21 phosphorylation in macrophages than an equal concentration of E-/B48 lipoproteins enriched with the same amount of human ApoE3 (E3/B48). In addition, E4/B48 lipoproteins are less able than E3/B48 lipoproteins to induce the expression of the cholesterol efflux transporter, ATP-binding cassette transporter A1 (ABCA1), in macrophages. Deficiency of this transporter is associated with widespread foam cell formation and severe atherosclerosis. This project will test the hypothesis that activation of UPR pathways is a mechanism behind the reduction in transporter expression mediating cholesterol efflux, leading to accumulation of excess cholesterol in macrophages treated with E4/B48 lipoproteins. Two specific aims will be carried out to test this hypothesis. Specific Aim 1 will study the effect of E4/B48-lipoproteins on macrophage expression of transporters mediating cholesterol efflux, cholesterol efflux itself, and foam cell formation. This aim will be accomplished by measuring the expression levels of cholesterol efflux transporters (ABCA1, ABCG1, and scavenger receptor-B1 [SR-B1]), evaluating the degree of cholesterol efflux, and determining the extent of cellular cholesterol accumulation after macrophages are treated with E4/B48 and E3/B48 lipoproteins. Specific Aim 2 will determine the role that UPR signaling pathways play in macrophage expression of transporters mediating cholesterol efflux, cholesterol efflux itself, and foam cell formation. There are three UPR pathways. This project will focus on the eIF21-associated pathway because E4/B48 lipoproteins have been shown to activate it. If our hypothesis is correct, changes in expression of cholesterol efflux transporters, and cholesterol efflux and accumulation induced by E4/B48 lipoproteins will be attenuated when this pathway is inhibited. PUBLIC HEALTH RELEVANCE: There are three major human alleles of apolipoprotein 5 (Apo5), i.e., 52, 53, and 54, and the 54 isoform is associated with increased risk of atherosclerotic cardiovascular disease compared to the normal 53. African-Americans have higher 54 allelic frequency and are more prone to cardiovascular diseases related to atherosclerosis compared to other ethnic groups. By elucidating the role that ApoE4-containing lipoproteins play in the formation of foam cells, an early event in the development of atherosclerosis, we will provide strategies for treatment or prevention of this disease.