Tarnowski B I, Shepherd V L, McLaughlin B J
Department of Anatomy, College of Medicine, University of Tennessee-Memphis.
Invest Ophthalmol Vis Sci. 1988 May;29(5):742-8.
We report here the presence of a mannose-specific receptor on apical membranes of rat retinal pigment epithelial (RPE) cells. For pinocytic studies, 125I-Mannose-BSA (125I-Man-BSA) was incubated with RPE explants from normal (Long Evans) and dystrophic (pigmented RCS) rat retinas. Normal RPE bound 36.1 ng of ligand and, in the presence of mannan competitor, the amount bound was 18.3 ng. In a similar assay, total ligand uptake by dystrophic RPE was 25.9 ng with 9.8 ng specific for mannose recognition. Comparing the amounts of ligand bound, dystrophic RPE recognized 55% of the amount recognized by normal RPE. The presence of the mannose receptor was localized on both normal and dystrophic RPE apical plasma membranes by autoradiographic techniques using 125I-Man-BSA. Normal RPE showed a greater number of silver grains present at the apical cell membrane as compared to dystrophic RPE. Silver grains were significantly reduced when incubation with the ligand was carried out in the presence of a mannan competitor. Further, in phagocytic studies, latex beads coated with mannan were used as phagocytic particles. Normal RPE phagocytized 4.52 mannan-beads per cell profile by a mannose-specific mechanism, whereas dystrophic RPE did not recognize mannan-beads. Our data suggest that RPE cells express surface receptors which recognize both soluble and particulate mannose ligands. The pinocytic and autoradiographic studies suggest that normal RPE binds more soluble ligand than does dystrophic RPE. If the mannose receptors mediate both pinocytosis and phagocytosis, a possible reduction in number of soluble mannose binding sites on the dystrophic RPE may be related to the diminished phagocytic recognition of particulate ligand by the dystrophic RPE.(ABSTRACT TRUNCATED AT 250 WORDS)
我们在此报告大鼠视网膜色素上皮（RPE）细胞顶端膜上存在一种甘露糖特异性受体。在进行胞饮研究时，将125I-甘露糖-牛血清白蛋白（125I-Man-BSA）与来自正常（长 Evans）和营养不良（色素性RCS）大鼠视网膜的RPE外植体一起孵育。正常RPE结合了36.1 ng的配体，在存在甘露聚糖竞争者的情况下，结合量为18.3 ng。在类似的实验中，营养不良的RPE对配体的总摄取量为25.9 ng，其中9.8 ng是特异性识别甘露糖的。比较结合的配体量，营养不良的RPE识别的量是正常RPE识别量的55%。通过使用125I-Man-BSA的放射自显影技术，甘露糖受体定位于正常和营养不良的RPE顶端质膜上。与营养不良的RPE相比，正常RPE在顶端细胞膜上出现的银颗粒数量更多。当在存在甘露聚糖竞争者的情况下与配体孵育时，银颗粒明显减少。此外，在吞噬研究中，用甘露聚糖包被的乳胶珠作为吞噬颗粒。正常RPE通过甘露糖特异性机制每个细胞轮廓吞噬4.52个甘露聚糖珠，而营养不良的RPE不识别甘露聚糖珠。我们的数据表明，RPE细胞表达可识别可溶性和颗粒性甘露糖配体的表面受体。胞饮和放射自显影研究表明，正常RPE比营养不良的RPE结合更多的可溶性配体。如果甘露糖受体介导胞饮和吞噬作用，营养不良的RPE上可溶性甘露糖结合位点数量的可能减少可能与营养不良的RPE对颗粒性配体吞噬识别的减弱有关。（摘要截短至250字）
