Expression of β1 Integrins by Cultured Articular Chondrocytes and in Osteoarthritic Cartilage

Expression of beta 1 integrins was studied in vitro as articular chondrocytes reestablished a matrix in culture and in situ in a nonhuman primate model of osteoarthritis in order to investigate a potential role for integrins in mediating cell-extracellular matrix interactions in cartilage. Chondrocytes were found to express alpha 1 beta 1, alpha 3 beta 1, and alpha 5 beta 1 integrins both in vitro and in situ. Cell surface expression of beta 1 integrins increased as chondrocytes were maintained in cultured from 3 to 7 days. Increased beta 1 integrin expression was also observed in osteoarthritic cartilage compared with normal cartilage. The greatest relative increase in both systems was noted for the alpha 1 beta 1 integrin. The increase in chondrocyte beta 1 integrin expression in vitro was noted in both monolayer and alginate cultures and occurred prior to detectable changes in the differentiated phenotype of the chondrocyte. Disruption of the cytoskeleton with the drug dihydrocytochalasin B inhibited the cell culture induced increase in integrin expression, while treatment of cultured cells with TGF-beta resulted in increased expression of the alpha 5 beta 1 integrin. The modulation of beta 1 integrin expression noted in vitro and in situ indicates that chondrocytes are capable of regulated expression of beta 1 integrins and suggests that beta 1 integrins may play an important role in mediating chondrocyte-extracellular matrix interactions in cartilage.