Receptor-Mediated Endocytosis of Low-Density Lipoprotein by Cultured Human Glomerular Cells

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Abstract
Lipoproteins might be involved in the pathogenesis of glomerular damage. Uptake of low-density lipoprotein (LDL) by cultured human glomerular cells has been studied using LDL, labelled with the fluorescent probe 1,1''-dioctadecyl-3,3,3''3''-tetramethyl-indocarbocyanine perchlorate (diI). Cells have been characterised using phase-contrast microscopy, monoclonal antibodies and lectins. Differentiated glomerular epithelial cells, epthelial-like cells and mesangial cells all took up diI-LDL. Uptake was specific for LDL, of high affinity and inhibited by excess unlabelled LDL, heparin and preloading the cells with cholesterol. Binding of diI-LDL to the cell surface was restricted to discrete areas which were arranged in linear arrays on mesangial cells. Endocytosis of surface-bound diI-LDL occurred within 3 min and breakdown of internalised diI-LDL within 30 min. These results indicate that cultured human glomerular cells take up LDL by receptor-mediated enodcytosis.