Distribution and characterization of sulfated proteoglycans in the human trabecular tissue

The distribution of proteoglycans in the trabecular tissue of human eyes was evaluated histochemically, using Cupromeronic Blue in combination with a series of enzyme digestions and nitrous acid treatment. Within the extracellular matrix of the trabecular meshwork, many Cupromeronic Blue-positive filaments were observed in association with collagen fibrils, basal lamina, a basal lamina-like material and a fine fibrillar-like material. Pretreatment with chondroitinase AC reduced the staining associated with the collagen fibrils, whereas filament staining in this location was completely eliminated by pretreatment with chondroitinase ABC. Nitrous acid treatment eliminated almost all the filament staining associated with the basal lamina and basal lamina-like material. When the tissue was treated with chondroitinase AC, chondroitinase ABC or nitrous acid, filament staining associated with the fine fibrillar-like material was reduced. After a combined treatment with nitrous acid followed by incubation with chondroitinase ABC, all filament staining in the trabecular meshwork was eliminated. These results are consistent with an interpretation that human trabecular tissue contains three distinct types of sulfated proteoglycans, namely chondroitin sulfate, dermatan sulfate and heparan sulfate-type proteoglycans. Proteoglycans containing chondroitin sulfate and dermatan sulfate are present in association with collagen fibrils. Proteoglycans of heparan sulfate-type are associated with the basal lamina and the basal lamina-like material. Chondroitin sulfate, dermatan sulfate and heparan sulfate-type proteoglycans are present in association with the fine fibrillar-like component. The basal lamina, basal lamina-like material and fine fibrillar-like components associated with these negatively charged proteoglycans may be important contributors to aqueous outflow resistance in the juxtacanalicular connective tissue.