Changes in the sulfated proteoglycans synthesized by "aging" chondrocytes. II. Organ-cultured vertebral columns

Sulfated proteoglycans synthesized by intact embryonic chick vertebral cartilages maintained in organ culture were characterized by labeling the vertebral chondrocytes with [35S]sulfate. More than 95% of the sulfated macromolecules synthesized by the cartilages are retained in their extracellular matrix. Sucrose velocity sedimentation gradient analyses revealed that the intact cartilages synthesized primarily proteoglycan monomers typical of cartilage and also small amounts of a smaller sized proteoglycan. The continuously varying size distribution of monomers which characterize a population of proteoglycans, could, in part, be attributed to heterogeneity of other chondroitin sulfate chain size. Changes in the proteoglycans synthesized by intact cartilages were analyzed between 6 h and 8 days of organ culture: (i) monomers decreased in molecular size with age in organ culture; (ii) the decrease in monomer size could be partially attributed to a shortening of their chondroitin sulfate chains; (iii) the 6S/4S disaccharide composition of the chondroitin sulfate chains also changed with culture age, from 1.8 to 0.3. This change was shown to be independent of the concomitant decrease in monomer size. These changes are similar to those which occur in proteoglycans synthesized by articular cartilages from chickens of increasing age. This cartilage culture system is likely to be a more useful model for studying changes which accompany aging and/or senescence in cartilage in vivo than the more commonly studied dispersed chondrocyte cultures.