SYNTHESIS OF CORNEAL KERATAN SULFATE PROTEOGLYCANS BY BOVINE KERATOCYTES IN-VITRO

Keratan sulfate proteoglycans (KSPGs) are the major proteoglycans of t he cornea and are secreted by keratocytes in the corneal stroma. Previ ous studies have been able to show only transient secretion of KSPG in cell culture, In this study, cultures of bovine keratocytes were foun d to secrete the three previously characterized KSPG proteins into cul ture medium, Reactivity with monoclonal antibody 122 demonstrated subs titution of these proteins with keratan sulfate chains. KSPG constitut ed 15% of the proteoglycan metabolically labeled with [S-35]sulfate in keratocyte culture medium. This labeled KSPG contained keratan sulfat e chains of 4700 Da compared to 21,000 Da for bovine corneal keratan s ulfate. Labeled keratan sulfate from cultures contained nonsulfated, m onosulfated, and disulfated disaccharides that were released by digest ion with endo-beta-galactosidase or keratanase II, Nonsulfated disacch arides were relatively more abundant in keratan sulfate from culture t han in corneal keratan sulfate, These results show that cultured bovin e keratocytes maintain the ability to express all three of the known K SPG proteins, modified with keratan sulfate chains and sulfated on bot h N-acetylglucosamine and galactose moieties. KSPG made in vitro diffe rs from that found in vivo in the length and sulfation of its keratan sulfate chains, The availability of cell cultures secreting corneal ke ratan sulfate proteoglycans provides an opportunity to examine biosynt hesis and control of this important class of molecules.