Sanan D A, Strümpfer A E, van der Westhuyzen D R, Coetzee G A
Eur J Cell Biol. 1985 Jan;36(1):81-90.
Lipoprotein binding and metabolism in actively dividing (sparse) and quiescent (confluent) bovine aortic endothelial cells (EC) were compared quantitatively using 125I-labelled lipoproteins. The amounts of receptor-bound low density lipoproteins (LDL) decreased five- to ten-fold as the cultures progressed from sparse to confluent morphology. High affinity receptor-bound LDL levels were extremely low in confluent EC and accounted for the inability of confluent EC to internalize and degrade significant amounts of LDL. Conversely, the amounts of acetylated LDL (acLDL) bound and degraded via distinct sites increased at least five-fold during EC growth to confluence. LDL binding and metabolism in individual cells was assessed by fluorescence microscopy using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine-labelled lipoproteins or fluorescein-conjugated antibodies. LDL and acLDL bound to the surfaces of sparse EC, at either 4 degrees or 37 degrees C, in a random distribution of fine punctate foci, contrary to a previous report. EC therefore appear to resemble fibroblasts in their distribution of surface LDL receptors. No binding or uptake of LDL was seen in confluent EC. Patterns of acLDL binding and uptake in confluent EC resembled those of LDL in sparse EC. Intracellular LDL and acLDL occurred as perinuclear accumulations of large fluorescent foci in sparse EC. Regeneration experiments were carried out in artificially wounded confluent cultures and renewed LDL receptor activity was shown in actively-dividing cells which had migrated into the "wounded" areas. We conclude that quiescent endothelial cells metabolize little LDL via the LDL-receptor pathway due to a drastically reduced number of receptors in confluent cells. This contrasts with the ability of confluent cells to metabolize relatively large amounts of acLDL via a receptor-mediated mechanism.
使用¹²⁵I标记的脂蛋白对处于活跃分裂（稀疏）和静止（汇合）状态的牛主动脉内皮细胞（EC）中的脂蛋白结合和代谢进行了定量比较。随着培养物从稀疏形态发展到汇合形态，受体结合的低密度脂蛋白（LDL）量减少了五到十倍。在汇合的EC中，高亲和力受体结合的LDL水平极低，这解释了汇合的EC无法内化和降解大量LDL的原因。相反，在EC生长至汇合过程中，通过不同位点结合和降解的乙酰化LDL（acLDL）量至少增加了五倍。使用1,1'-二辛基-3,3,3',3'-四甲基吲哚羰花青标记的脂蛋白或荧光素偶联抗体，通过荧光显微镜评估单个细胞中的LDL结合和代谢。与先前的报道相反，在4℃或37℃下，LDL和acLDL以细点状病灶的随机分布结合在稀疏EC的表面。因此，EC在表面LDL受体的分布上似乎类似于成纤维细胞。在汇合的EC中未观察到LDL的结合或摄取。汇合的EC中acLDL的结合和摄取模式类似于稀疏EC中LDL的模式。在稀疏EC中，细胞内LDL和acLDL以大荧光灶的核周聚集形式出现。在人工损伤的汇合培养物中进行了再生实验，结果显示迁移到“损伤”区域的活跃分裂细胞中LDL受体活性得以恢复。我们得出结论，静止的内皮细胞通过LDL受体途径代谢的LDL很少，这是由于汇合细胞中受体数量急剧减少所致。这与汇合细胞通过受体介导机制代谢相对大量acLDL的能力形成对比。
