Endogenously expressed apolipoprotein E has different effects on cell lipid metabolism as compared to exogenous apolipoprotein E carried on triglyceride-rich particles
Endogenously expressed apolipoprotein E has different effects on cell lipid metabolism as compared to exogenous apolipoprotein E carried on triglyceride-rich particles
复制标题
DOI：
10.1021/bi992294a
复制
发表时间：
2000-04-25
期刊：
影响因子：
2.9
通讯作者：
Deckelbaum, RJ
中科院分区：
文献类型：
--
作者：
Ho, YY;Al-Haideri, M;Deckelbaum, RJ
载脂蛋白E （apoE）对模型富甘油三酯颗粒（TGRP）增加甘油三酯（TG）的利用和胆固醇吞噬物（CE）的水解，独立于其增强颗粒摄取的作用。我们质疑，在生理浓度下，与外源性apoE相比，内源性表达的apoE是否对细胞脂质代谢有相似的影响。不表达apoE的J774巨噬细胞通过转染人apoE3 cDNA表达构建体（E+）或对照载体（E-）来表达内源性apoE。比较外源性apoE的影响；和内源性apoE对TGRP摄取的影响，细胞与h -3-胆固醇醚标记的TGRP相关的apoE孵育或不孵育。外源性apoE增强了E-和E+细胞对TGRP的摄取。E（-）细胞对TGRP的摄取明显高于E+细胞。抑制细胞蛋白多糖合成的氯酸钠显著降低了E-和E+细胞对TGRP摄取的差异，表明内源性载脂蛋白蛋白多糖相互作用导致了两种细胞类型之间摄取的差异。在E-和E+细胞中，LDL受体、LDL受体相关蛋白或清道夫受体对颗粒的摄取相似，这表明内源性apoE表达对内吞途径没有普遍影响。外源性apoE携带TGRP刺激两种细胞的TG利用和CE水解。然而，内源性apoE表达不影响TG利用和CE水解。综上所述，巨噬细胞表达apoE对TGRP代谢的影响与外源性apoE有很大不同。本研究的荧光显微镜结果显示，外源性apoE和内源性apoE被限制在不同的细胞区室中，这支持了一种假设，即与内源性细胞表达的apoE相比，这些差异是由不同的细胞内运输途径引起的，然后是外源性apoE与TGRP结合。
Apolipoprotein E (apoE) on model triglyceride-rich particles (TGRP) increases triglyceride (TG) utilization and cholesteryl eater (CE) hydrolysis, independent of its effect on enhancing particle uptake. We questioned whether, under physiological concentrations, endogenously expressed apoE has similar effects on cellular lipid metabolism as compared to exogenous apoE. J774 macrophages, which do not express apoE, were engineered to express endogenous apoE by transfection of human apoE3 cDNA expression constructs (E+) or control vectors (E-) into the cells. To compare the effects of exogenous apoE; and endogenous apoE on TGRP uptake, cells were incubated with or without apoE associated with H-3-cholesteryl ether-labeled TGRP. Exogenous apoE enhanced TGRP uptake in both E- and E+ cells. E(-)cells displayed significantly higher TGRP uptake than E+ cells. Sodium chlorate, which inhibits cell proteoglycan synthesis, markedly diminished differences in TGRP uptake between E- and E+ cells, suggesting that endogenous apoE-proteoglycan interaction contributes to differences in uptake between the two cell types. Particle uptake by the LDL receptor, by the LDL receptor related protein, or by scavenger receptors were similar between E- and E+ cells indicating that endogenous apoE expression does not have a general effect on endocytic pathways. Exogenous apoE carried on TGRP stimulated TG utilization and CE hydrolysis in both cell types. However, TG utilization and CE hydrolysis were not affected by endogenous apoE expression. In conclusion, macrophage expression of apoE has very different effects on TGRP metabolism than exogenously supplied apoE. The fluorescence microscopy results in this study showing that exogenous apoE and endogenous apoE were confined in separate cellular compartments support the hypothesis that these differences resulted from distinct intracellular trafficking pathways followed by exogenous apoE bound to TGRP as compared to endogenous cell-expressed apoE.