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首页> 外文期刊>Biochemistry >The role of human and mouse hepatic scavenger receptor class B type I (SR-BI) in the selective uptake of low-density lipoprotein-cholesteryl esters
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The role of human and mouse hepatic scavenger receptor class B type I (SR-BI) in the selective uptake of low-density lipoprotein-cholesteryl esters

机译：人类和小鼠I类肝清除剂受体B（SR-BI）在低密度脂蛋白-胆固醇酯选择性摄取中的作用

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摘要

Low-density lipoprotein (LDL)-cholesteryl ester (CE) selective uptake has been demonstrated in nonhepatic cells overexpressing the scavenger receptor class B type I (SR-BI). The role of hepatic SR-BI toward LDL, the main carrier of plasma CE in humans, remains unclear. The aim of this study was to determine if SR-BI, expressed at its normal level, is implicated in LDL-CE selective uptake in human HepG2 hepatoma cells and mouse hepatic cells, to quantify its contribution and to determine if LDL-CE selective uptake is likely to occur in the presence of human HDL. First, antibody blocking experiments were conducted on normal HepG2 cells. SR-BI/BII antiserum inhibited I-125-LDL and I-125-HDL3 binding (10 mug of protein/mL) by 45% (p < 0.05) and CE selective uptake by more than 85% (P < 0.01) for both ligands. Second, HepG2 cells were stably transfected with a eukaryotic vector expressing a 400-bp human SR-BI antisense cDNA fragment. Clone 17 (C17) has a 70% (P < 0.01) reduction in SR-BI expression. In this clone, H-3-CE-LDL and H-3-CE-HDL3 association (10 mug of protein/mL) was 54 +/- 6% and 45 +/- 7% of control values, respectively, while I-125-LDL and I-125-HDL3 protein association was 71 +/- 3% and 58 +/- 5% of controls, resulting in 46% and 55% (p < 0.01) decreases in LDL- and HDL3-CE selective uptake. Normalizing CE selective uptake for SR-BI expression reveals that SR-BI is responsible for 68% and 74% of LDL- and HDL3-CE selective uptake, respectively. Thus, both approaches show that, in HepG2 cells, SR-BI is responsible for 68-85% of CE selective uptake. Other pathways for selective uptake in HepG2 cells do not require CD36, as shown by anti-CD36 antibody blocking experiments, or class A scavenger receptors, as shown by the lack of competition by poly(inosinic acid). However, CD36 is a functional oxidized LDL receptor on HepG2 cells, as shown by antibody blocking experiments. Similar results for CE selective uptake were obtained with primary cultures of hepatic cells from normal (+/+), heterozygous (-/+), and homozygous (-/-) SR-BI knockout mice. Flow cytometry experiments show that SR-BI accounts for 75% of DiI-LDL uptake, the LDL receptor for 14%, and other pathways for 11%. CE selective uptake from LDL and HDL3 is likely to occur in the liver, since unlabeled HDL (total and apoE-free HDL3) and LDL, when added in physiological proportions, only partially competed for LDL- and HDL3-CE selective uptake. In this setting, human hepatic SR-BI may be a crucial molecule in the turnover of both LDL- and HDL3-cholesterol. [References: 77]
机译：低密度脂蛋白（LDL）-胆固醇酯（CE）的选择性摄取已在过表达I型清道夫受体（SR-BI）的非肝细胞中得到证明。肝SR-BI对LDL（人类血浆CE的主要载体）的作用尚不清楚。这项研究的目的是确定以正常水平表达的SR-BI是否与人HepG2肝癌细胞和小鼠肝细胞中LDL-CE的选择性摄取有关，以量化其贡献并确定LDL-CE的选择性摄取可能在人类HDL存在下发生。首先，在正常的HepG2细胞上进行抗体封闭实验。 SR-BI / BII抗血清抑制I-125-LDL和I-125-HDL3结合（10杯蛋白质/毫升）45％（p <0.05）和CE选择性摄取超过85％（P <0.01）两个配体。第二，用表达400bp人SR-BI反义cDNA片段的真核载体稳定转染HepG2细胞。克隆17（C17）的SR-BI表达降低了70％（P <0.01）。在此克隆中，H-3-CE-LDL和H-3-CE-HDL3关联（10杯蛋白质/毫升）分别为对照值的54 +/- 6％和45 +/- 7％。 -125-LDL和I-125-HDL3蛋白质关联为对照组的71 +/- 3％和58 +/- 5％，导致LDL-和HDL3-CE选择性降低46％和55％（p <0.01）摄取。标准化CE对SR-BI表达的选择性摄取表明，SR-BI分别占LDL-和HDL3-CE选择性摄取的68％和74％。因此，这两种方法均表明，在HepG2细胞中，SR-BI导致68-85％的CE选择性摄取。 HepG2细胞中其他选择性摄取途径不需要CD36（如抗CD36抗体阻断实验所示）或A类清道夫受体（如聚肌苷酸缺乏竞争所示）。但是，如抗体阻断实验所示，CD36是HepG2细胞上的一种功能性氧化LDL受体。从正常（+ / +），杂合（-/ +）和纯合（-/-）SR-BI敲除小鼠的肝细胞原代培养物中获得CE选择性摄取的相似结果。流式细胞仪实验表明，SR-BI占DiI-LDL摄取的75％，LDL受体占14％，其他途径占11％。从肝脏中可能会发生LDL和HDL3对CE的选择性摄取，因为按生理比例添加未标记的HDL（完全和无载脂蛋白的HDL3）和LDL只能部分竞争LDL和HDL3-CE的摄取。在这种情况下，人肝SR-BI可能是LDL-和HDL3-胆固醇转换过程中的关键分子。 [参考：77]

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