Human ApoE4 and Foam Cell Formation

描述(申请人提供)：本项目的总体目标是确定(S)导致经载脂蛋白E4(ApoE4)富集脂蛋白处理的巨噬细胞中胆固醇过度聚集的机制，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)有三个主要等位基因，即52、53和54。与所谓的正常亚型ApoE3相比，54产物ApoE4与动脉粥样硬化性心血管疾病的风险增加有关。载脂蛋白54在非裔美国人中很常见，与其他种族相比，他们的心血管疾病比例很高。郭中茂博士S实验室以前的工作表明，UPR信号转导的真核细胞起始因子21(eIF-21)磷酸化增加是ApoB48/48/ApoE-/-(E&gt；/B48)小鼠脂蛋白处理巨噬细胞胆固醇堆积和泡沫细胞形成的机制。最近，我们发现富含人ApoE4的E&GT；/B48脂蛋白(E4/B48)比同等浓度的富含人ApoE3的E-/B48脂蛋白(E3/B48)在巨噬细胞中诱导更多的胆固醇积聚和增强eIF-21的磷酸化。此外，E4/B48脂蛋白诱导巨噬细胞胆固醇外流转运体--三磷酸腺苷结合盒转运体A1(ABCA1)表达的能力弱于E3/B48脂蛋白。这种转运蛋白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。该项目将检验一种假设，即UPR通路的激活是介导胆固醇外流的转运体表达减少背后的机制，导致E4/B48脂蛋白处理的巨噬细胞中过量的胆固醇积累。我们将通过两个具体目标来检验这一假说。具体目标1将研究E4/B48-脂蛋白对巨噬细胞表达介导胆固醇外流的转运体、胆固醇外流本身和泡沫细胞形成的影响。这一目标将通过测量胆固醇外流转运体(ABCA1、Abcg1和清道夫受体-B1[SR-B1])的表达水平，评估胆固醇外流的程度，并确定巨噬细胞经E4/B48和E3/B48脂蛋白处理后细胞内胆固醇积累的程度来实现。具体目标2将确定UPR信号通路在巨噬细胞表达介导胆固醇外流、胆固醇外流本身和泡沫细胞形成的转运体中所起的作用。普遍定期审议有三条途径。这个项目将重点放在eIF21相关的途径上，因为E4/B48脂蛋白已经被证明激活了它。如果我们的假设是正确的，当这一途径被抑制时，胆固醇外流转运体的表达变化以及由E4/B48脂蛋白诱导的胆固醇外流和积聚将被减弱。 公共卫生相关性：人类载脂蛋白5(Apo5)有三个主要等位基因，即52、53和54，与正常53相比，54亚型与动脉粥样硬化性心血管疾病的风险增加相关。与其他种族相比，非洲裔美国人有更高的54等位基因频率，更容易患上与动脉粥样硬化相关的心血管疾病。通过阐明含ApoE4的脂蛋白在泡沫细胞形成中的作用，泡沫细胞是动脉粥样硬化发展的早期事件，我们将为治疗或预防这种疾病提供策略。

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.