Re-expression of differentiated proteoglycan phenotype by dedifferentiatedhuman chondrocytes during culture in alginate beads

The proteoglycans (PGs) synthesised by normal human articular chondrocytes and a chondrocyte cell line cultured in monolayer and alginate beads were c ompared. Chondrocytes became dedifferentiated after serial subcultures in m onolayer, exhibited a fibroblastic morphology and synthesised a large propo rtion of lower molecular weight, dermatan sulphate containing PGs. When tra nsferred into alginate beads, the cells quickly regained their spherical sh ape and actively incorporated [H-3]thymidine and [S-35]sulphate during 70 d ays of culture. This resulted in a continuous increase in their DNA content and a rapid deposition of PGs for the first 25 days of culture, which then remained stable. Immediately after dedifferentiated chondrocytes were enca psulated into alginate beads, they began to synthesise a population of PGs with normal monomer size and an increased ability to form aggregates. The m onomer size of newly synthesised PGs remained unchanged during extended per iods of culture, but their ability to form aggregates and the ratios of cho ndroitin-6-sulphate to chondroitin-4-sulphate in their glycosaminoglycan ch ains gradually increased for the first 25 days before reaching normal value s. Parallel experiments with HCS-2/8 cells, derived from a human chondrosar coma, showed that they followed a similar pattern of development in alginat e culture. The ability of their newly synthesised PGs to form aggregates in creased with time and their sulphation pattern also gradually became normal . These results showed that culture in alginate promoted redifferentiation of dedifferentiated articular chondrocytes and assisted differentiation of HCS-2/8 chondrocytes. However, complete redifferentiation took a period of several weeks, after which synthesis of normal aggregating PGs was maintain ed. (C) 1998 Elsevier Science B.V. All rights reserved.