The extracellular matrix provides cartilage with its ability to undergo reversible deformation, and thus to cushion the joint during loading. Failure of competent matrix repair during aging or disease causes profound alterations in the biomechanics of cartilage; with progression, this presents clinically as osteoarthritis. The normal composition of the chondrocytic proteoglycans is complex, and changes during aging. Keratan sulfate (KS), virtually absent from fetal proteoglycans, increases to comprise roughly 25% of the glycosaminoglycan composition of mature cartilage. Despite the prominence of KS in aging cartilage, details concerning its role remain obscure. We have developed a human chondrocyte cell line, 105KC, which was derived from a malignant chondrosarcoma and which has continued to synthesize mature-type chondrocytic KS-proteoglycans for more than 4 years. This represents the first system to maintain stable production of keratan sulfate in long term culture and thus provides a unique model of human chondrocyte metabolism. Preliminary data suggest that there is non-random heterogeneity among the KS chains of the high density proteoglycans synthesized by 105KC cells, and thus that there may be regional regulation of KS chain-elongation during proteoglycan biosynthesis. We propose to perform a detailed characterization of the different populations of human skeletal KS, to analyze their substitution patterns onto aggregating proteoglycans, to compare the KS chains derived from the large aggregating proteoglycans with those derived from the small KS-proteoglycans, and to study the effects of physical factors on KS substitution. This will provide previously unavailable structural information regarding human mature chondrocytic proteoglycans, and may yield insight into the role of keratan sulfate in mature and aging cartilage matrix.
