Receptors for hyaluronan on corneal endothelial cells.

Previous investigations suggest that the corneal endothelium has specific binding sites for hyaluronan (HYA). In the present study, biochemical and immunological techniques were used to characterize these binding sites and to compare them with the liver endothelial cell (LEC) HYA receptor. Affinity chromatography of solubilised, 125I-labelled corneal endothelial cell surface proteins on immobilised HYA proved that there were molecules that were strongly bound to the polysaccharide. A part of these molecules formed a 100-kDa band when analysed by autoradiography after SDS polyacrylamide electrophoresis (PAGE). A specific antibody against the rat LEC HYA receptor was used for immunohistochemical 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. Hyaluronidase treatment of the tissue sections before receptor staining strikingly increased the specific staining of the corneal endothelial cells (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 unlikely that the corneal endothelial receptor, like its liver endothelial counterpart, is actively involved in receptor-mediated endocytosis. Our studies suggest that CEC carry receptors for HYA that are immunologically similar to the LEC receptors. CEC receptors might act as binding structures increasing the concentration of HYA close to the CEC as a protection of these vulnerable cells from physicochemical damage.

Endogenous hyaluronan in corneal disease.

PURPOSE: Hyaluronan (HA) is a disaccharide polymer capable of binding considerable amounts of water. It is present in trace amounts on the cornea endothelium, and it is not normally found in the epithelium or stroma. A specific histochemical stain was used to test for HA in a wide variety of corneal disorders. METHODS. Eighty-six human corneal tissue specimens were examined histochemically for HA. The material consisted of 84 full-thickness corneal buttons, one epithelium scraping, and one pterygium. Cases were analyzed according to the patient's sex, age, diagnosis, and localization of HA staining. RESULTS: The corneal tissue specimens came from 47 women and 39 men, average age 59 years. Fifty-seven percent of the specimens displayed abnormal HA. HA was visualized in Fuch's dystrophy, keratoconus, infections, regrafts, mechanical and chemical trauma, post-excimer ablations, dystrophies, degenerations, pseudophakic bullous keratopathy, congenital opacities, Stevens-Johnson syndrome, and others. Staining was variously seen in the epithelium, stroma, and endothelium, with intensity of staining ranging from trace amounts to extremely heavy. CONCLUSIONS: Endogenous hyaluronan production is seen in virtually the entire spectrum of corneal disorders. The presence of HA was most often associated with dividing, migrating, or fibroblast-like cells and probably represents a nonspecific tissue response to wounding. Its production is biochemically distinct from that of normally present proteoglycans. The abnormal presence of HA may reduce corneal transparency by disrupting the normal spacing between collagen fibrils, creating focal changes in the index of refraction, and altering the normal flow of solutes through the cornea.

Influence of radial keratotomy on endogenous hyaluronan in cornea and aqueous humour.

BACKGROUND: Hyaluronan is known to appear in corneal wound tissue and is probably involved in the healing process. We measured the changes of endogenous hyaluronan in rabbit cornea and aqueous after radial keratotomy. METHODS: Corneal and aqueous hyaluronan concentrations were measured at different time intervals after radial keratotomies. Hyaluronan was extracted from corneal tissue with two methods employing either pronase or NaCl and measured with a radioimmunoassay. Histochemical staining for hyaluronan was done on the operated eyes. RESULTS: Changes in corneal hyaluronan showed a similar time course with either extraction method. Maximal concentration was reached after 7 to 14 days with a return to normal values in 60 days. Aqueous hyaluronan and proteins were not significantly altered after surgery. Histochemical staining of the corneas demonstrated hyaluronan around the incisions along their entire extent. Blood vessels were absent in the wounds. An increase in elongated fibroblast-like cells was seen in the wound area. CONCLUSIONS: Both quantitatively and histochemically, there is a pronounced increase of corneal hyaluronan in avascular, radial keratomy wounds in the rabbit. The findings suggest a role of hyaluronan in corneal wound healing.