Cartilage tissue formation using redifferentiated passaged chondrocytes in vitro.

Articular cartilage has limited ability for repair when damaged by trauma or degenerative disease, such as osteoarthritis, which can result in pain and compromised quality of life. Biological surface replacements developed using tissue engineering methods are a promising approach for cartilage repair, which would avoid the need for total joint replacement with the synthetic implants used currently. A basic requirement of in vitro tissue generation is a supply of sufficient number of cells, which are difficult to acquire from sparsely cellular cartilage tissue. Previously, we have shown that coculture of in vitro-expanded dedifferentiated chondrocytes (P2) with small numbers of primary chondrocytes (P0) induces redifferentiation in passaged (P2) cells. In this study we show that this redifferentiation is not a transient change. After 4 weeks of coculture, the P0 and P2 cells were separated by flow-associated cell sorting, and the redifferentiated P2 (dP2) were cultured alone for a further 4 weeks. The redifferentiated dP2 cells formed thicker cartilage tissue compared to the tissue generated by P2 cells. The newly formed tissue contained type II collagen as demonstrated by immunohistochemical staining and accumulated more proteoglycan per cell than the tissue formed by P2 cells. The dP2 cells also exhibited higher type II collagen and lower type I collagen gene expression than the P2 cells. Interestingly, dP2 cells were able to exert the same effect as P0 cells when cocultured with P2 cells. In conclusion, under proper culture conditions, redifferentiated passaged chondrocytes behave similarly to primary chondrocytes. This coculture system approach can be used to increase the number of differentiated chondrocytes that can be obtained by classical monolayer cell expansion and represents a novel way to acquire sufficient cell numbers for cartilage tissue engineering.