Human Articular Chondrocytes Cultured in Alginate Beads Maintain Their Gene Expression

The culture of articular chondrocytes in alginate beads offers several advantages over culture in monolayer. When bovine chondrocytes are suspended in alginate, they retained their phenotype over prolonged periods of time (8 months or longer). Earlier studies of chondrocytes cultured in alginate concentrated on collagen and proteoglycan synthesis; however, gene expression has not been investigated for this system. The purposes of the present study were to use human chondrocytes to: (a) modify the in situ hybridization procedure for the alginate beads in order to examine the mRNA expression of alpha 1 (II) procollagen, aggrecan, and two matrix metalloproteinases (MMP-3 and MMP-8) thought to be involved in the cartilage matrix degradation; and (b) compare expression in chondrocytes cultured in the alginate beads with that in chondrocytes of intact human cartilage. The results of this study show that aggrecan, MMP-3 and MMP-8 are continuously expressed during 8 months of culture. The alpha 1 (II) procollagen gene is expressed only during the first two months of culture and after three months its expression is undetectable. Type II collagen is synthesized and deposited in cell-associated and further-removed matrix compartments. These data support the culture of human chondrocytes in alginate beads in order to study factors that may modulate collagen synthesis and turnover.