Al-Haideri M, Goldberg I J, Galeano N F, Gleeson A, Vogel T, Gorecki M, Sturley S L, Deckelbaum R J
Department of Pediatrics, Columbia University, New York, New York 10032, USA.
Biochemistry. 1997 Oct 21;36(42):12766-72. doi: 10.1021/bi9631024.
We explored potential mechanisms of non-low-density lipoprotein (LDL) receptor-mediated uptake of triglyceride-rich particles (TGRP) in the presence of apolipoprotein E (apo E). Human fibroblasts were incubated with model intermediate-density lipoprotein- (IDL-) sized TGRP (10-1000 microg of neutral lipid/mL) containing apo E. The extent of receptor-mediated uptake of TGRP was assessed with (a) an anti-apo E monoclonal antibody, which blocks receptor interaction; (b) incubation with heparin; (c) normal vs LDL receptor-negative fibroblasts; and (d) receptor-associated protein (RAP) to determine the potential contribution of LDL receptor-related protein (LRP). Cell surface heparan sulfate proteoglycan- (HSPG-) mediated uptake was examined with or without the addition of heparinase and heparitinase to cell incubation mixtures. At low particle concentrations (</=100 microg of neutral lipid/mL), almost all apo E-TGRP uptake was via the LDL receptor. At higher particle concentrations, within the physiologic range (>250 microg of neutral lipid/mL), most (>/=60%) particle uptake and internalization was via HSPG-mediated pathways. This HSPG pathway did not involve classical lipoprotein receptors, such as LRP or the LDL receptor. These data suggest that in peripheral tissues, such as the arterial wall, apo E may act in TGRP as a ligand for uptake not only via the LDL receptor and LRP pathways but also via HSPG pathways that are receptor-independent. Thus, at physiologic particle concentrations apo E-TGRP can be bound and internalized in certain cells by relatively low affinity but high capacity HSPG-mediated pathways.
我们探讨了在载脂蛋白E（apo E）存在的情况下，非低密度脂蛋白（LDL）受体介导的富含甘油三酯颗粒（TGRP）摄取的潜在机制。将人成纤维细胞与含有apo E的模型中密度脂蛋白（IDL）大小的TGRP（10 - 1000微克中性脂质/毫升）一起孵育。通过以下方法评估TGRP受体介导的摄取程度：（a）使用阻断受体相互作用的抗apo E单克隆抗体；（b）与肝素一起孵育；（c）正常成纤维细胞与LDL受体阴性成纤维细胞；（d）受体相关蛋白（RAP），以确定低密度脂蛋白受体相关蛋白（LRP）的潜在作用。在细胞孵育混合物中添加或不添加肝素酶和硫酸乙酰肝素酶，检查细胞表面硫酸乙酰肝素蛋白聚糖（HSPG）介导的摄取。在低颗粒浓度（≤100微克中性脂质/毫升）时，几乎所有apo E - TGRP的摄取都是通过LDL受体进行的。在较高颗粒浓度下，即在生理范围内（>250微克中性脂质/毫升），大多数（≥60%）颗粒的摄取和内化是通过HSPG介导的途径。这种HSPG途径不涉及经典的脂蛋白受体，如LRP或LDL受体。这些数据表明，在诸如动脉壁等外周组织中，apo E在TGRP中可能不仅作为通过LDL受体和LRP途径摄取的配体，还作为通过不依赖受体的HSPG途径摄取的配体。因此，在生理颗粒浓度下，apo E - TGRP可以通过相对低亲和力但高容量的HSPG介导途径在某些细胞中结合并内化。
