Cullen P, Cignarella A, Brennhausen B, Mohr S, Assmann G, von Eckardstein A
Institut für Arterioskleroseforschung, Westfälische Wilhelms-Universität, 48149 Münster, Germany.
J Clin Invest. 1998 Apr 15;101(8):1670-7. doi: 10.1172/JCI119887.
In this study, we investigated the impact of the common apoE polymorphism on apoE metabolism and cholesterol homeostasis in monocyte-derived macrophages isolated from E2/2, E3/3, and E4/4 subjects. Unloaded cells of all genotypes contained similar amounts of free cholesterol, cholesteryl ester, and apoE mRNA. E3/3 cells secreted 77 and 30% more apoE than E2/2 or E4/4 cells, respectively. Pulse-chase studies confirmed that the apoE secretion rate was greatest in E3/3 and least in E2/2 cells and showed that a portion of apoE2, but not apoE3 or apoE4, was degraded intracellularly. Surface binding of apoE was greatest in E4/4 cells, as revealed by heparinase treatment. On cholesterol loading with acetylated LDL, apoE mRNA levels and protein secretion rose most in E4/4 and least in E2/2 cells. Cholesterol and cholesteryl ester content, however, rose most in E2/2 and least in E3/3 cells. Incubations with 3H-cholesterol-labeled acetylated LDL revealed that E2/2 cells were most efficient at secreting cholesterol. The greatest reuptake of 3H-cholesterol-rich particles was from E4/4 macrophage- conditioned media. Thus, E2/2 macrophages, despite a low apoE secretion rate, are protected from cholesterol storage by apoE-mediated cholesterol efflux. In E3/3 macrophages, cholesterol accumulation is lessened by a high basal apoE secretion rate. E4/4 macrophages secrete the most apoE but lack effective net cholesterol efflux due to enhanced surface binding and reuptake of cholesterol-rich particles.
在本研究中，我们调查了常见的载脂蛋白E（apoE）基因多态性对从E2/2、E3/3和E4/4受试者分离的单核细胞衍生巨噬细胞中apoE代谢及胆固醇稳态的影响。所有基因型的未负载细胞所含游离胆固醇、胆固醇酯和apoE mRNA的量相似。E3/3细胞分泌的apoE分别比E2/2或E4/4细胞多77%和30%。脉冲追踪研究证实，apoE分泌率在E3/3细胞中最高，在E2/2细胞中最低，并表明apoE2的一部分而非apoE3或apoE4在细胞内被降解。如用肝素酶处理所示，apoE的表面结合在E4/4细胞中最强。在用乙酰化低密度脂蛋白（LDL）加载胆固醇时，apoE mRNA水平和蛋白质分泌在E4/4细胞中上升最多，在E2/2细胞中上升最少。然而，胆固醇和胆固醇酯含量在E2/2细胞中上升最多，在E3/3细胞中上升最少。用3H-胆固醇标记的乙酰化LDL孵育显示，E2/2细胞在分泌胆固醇方面最有效。富含3H-胆固醇颗粒的最大再摄取来自E4/4巨噬细胞条件培养基。因此，E2/2巨噬细胞尽管apoE分泌率低，但通过apoE介导的胆固醇流出可免受胆固醇储存的影响。在E3/3巨噬细胞中，高基础apoE分泌率减少了胆固醇积累。E4/4巨噬细胞分泌的apoE最多，但由于增强的表面结合和富含胆固醇颗粒的再摄取而缺乏有效的净胆固醇流出。
