DEDIFFERENTIATED CHONDROCYTES CULTURED IN ALGINATE BEADS - RESTORATION OF THE DIFFERENTIATED PHENOTYPE AND OF THE METABOLIC RESPONSES TO INTERLEUKIN-1-BETA

Chondrocytes cultivated in monolayer rapidly divide and lose their mor phological and biochemical characteristics, whereas they maintain thei r phenotype for long periods of time when they are cultivated in algin ate beads. Because cartilage has a low cellularity and is difficult to obtain in targe quantities, the number of available cells often becom es a limiting factor in studies of chondrocyte biology. Therefore, we explored the possibility of restoring the differentiated properties of chondrocytes by cultivating them in alginate beads after two multipli cation passages in monolayer. This resulted in the reexpression of the two main markers of differentiated chondrocytes: Aggrecan and type II collagen gene expression was strongly reinduced from day 4 after algi nate inclusion and paralleled protein expression. However, 2 weeks wer e necessary for total suppression of type I and III collagen synthesis , indicators of a modulated phenotype. Interleukin-1 beta, a cytokine that is present in the synovial fluid of rheumatoid arthritis patients , induces many metabolic changes on the chondrocyte biology. Compared with cells in primary culture, the production of nitric oxide and 92-k Da gelatinase in response to interleukin-1 beta was impaired in cells at passage 2 in monolayer but was fully recovered after their culture in alginate beads for 2 weeks. This suggests that the effects of inter leukin-1 beta on cartilage depend on the differentiation state of chon drocytes. This makes the culture in alginate beads a relevant model fo r the study of chondrocyte biology in the presence of interleukin-1 be ta and other mediators of cartilage destruction in rheumatoid arthriti s and osteoarthrosis. (C) 1998 Wiley-Liss, Inc.