Synthesis and Turnover of Proteoglycans by Human and Bovine Adult Articular Chondrocytes Cultured in Alginate Beads

Human and bovine adult articular chondrocytes cultured in alginate beads or agarose gel retain their spherical shape and typical chondrocytic appearance for at least 5 weeks. Aggrecan is always the major population of proteoglycans (PGs) synthesized; its size varies depending upon the age of the cartilage from which the cells are derived but it is not influenced by the culture system used. Studies of human chondrocytes cultured in alginate showed that the majority of the newly-synthesized aggrecan molecules are rapidly incorporated into aggregates which can be extracted from the gel in their native form. About one-third of the aggregates formed during a 4-hour period of incubation in the presence of [35S]-sulfate are packed at high concentration in the cell-associated matrix; the remainder is present in areas of the gel further removed from the cells. Aggrecan appears to be turned over more slowly by human than by bovine cells in both culture systems; in both species, the rate of turnover is slower in alginate than in agarose. Decorin is also synthesized in small amounts but it is rapidly lost from the agarose or alginate gel.