RECEPTORS FOR HYALURONAN ON CORNEAL ENDOTHELIAL-CELLS

Previous investigations suggest that the corneal endothelium has speci fic binding sites for hyaluronan (HYA). In the present study, biochemi cal and immunological techniques were used to characterize these bindi ng sites and to compare them with the liver endothelial cell (LEC) HYA receptor. Affinity chromatography of solubilised, I-125-labelled corn eal endothelial cell surface proteins on immobilised HYA proved that t here were molecules that were strongly bound to the polysaccharide. A part of these molecules formed a 100-kDa band when analysed by autorad iography after SDS polyacrylamide electrophoresis (PAGE). A specific a ntibody against the rat LEC HYA receptor was used for immunohistochemi cal studies of monkey and human corneas. There was a specific staining of the corneal endothelium of both species, and hyaluronan treatment before isolation of the human eyes reduced the staining intensity. Hya luronidase treatment of the tissue sections before receptor staining s trikingly increased the specific staining of the corneal endothelial c ells (CEC). Immunoblotting of human corneal proteins, separated by SDS -PAGE, showed staining at 200, 150-160 and 55 kDa. Uptake experiments of tritiated HYA in cultured monkey CEC showed only a slight increase in cell associated radioactivity over 2-6 hr. The results make it unli kely that the corneal endothelial receptor, like its liver endothelial counterpart, is actively involved in receptor-mediated endocytosis. O ur studies suggest that CEC carry receptors for HYA that are immunolog ically similar to the LEC receptors. CEC receptors might act as bindin g structures increasing the concentration of HYA close to the CEC as a protection of these vulnerable cells from physicochemical damage.