Normal and dystrophic rat retinal pigment epithelia display different sensitivities to plant lectins

Previous studies showed that cultured retinal pigment epithelial (RPE) cells from the Royal College of Surgeons (RCS) rat incorporate 50% less fucose into a number of cell-surface glycoproteins compared with controls. The cause of reduced fucose incorporation may be a generalized defect in glycoprotein processing in the RCS rat RPE. This hypothesis has been further explored by comparing the relative sensitivities of normal and dystrophic rat RPE to the toxicity of plant lectins of various specificities. Freshly isolated RPE cells from normal and dystrophic rats were cultured in the presence of increasing concentrations of lectin. For each lectin, the concentration at which less than 10% of the cells survived was determined. These tests showed that the dystrophic RPE cells were more sensitive to lectins that bound to core sugar moieties such as mannose and N-acetylglucosamine; normal RPE cells were more sensitive to lectins which bound to the more terminally located sugars, galactose and N-acetylgalactosamine. Overall, the results suggest that decreased incorporation of fucose into the RCS RPE may be due to failure of the dystrophic RPE to add either N-acetylgalactosamine or galactose (to which fucose is subsequently added) to oligosaccharide structures.