[Versatility of differentiated functions of cultured joint chondrocytes. Eventual usefulness in treatment]

The chondrocyte is the unique cell type in articular cartilage. It is responsible for the extracellular matrix production which permits the cartilaginous tissue to compensate the skeletal pressures during movements. The regulation of the different extracellular matrix components (type II collagen and aggrecan) depends on the differentiated state of the chondrocyte. However, in vivo, such as during aging and osteoarthritis, as well as in vitro, in monolayer culture, chondrocytes lose their morphological and biochemical characteristics. This phenomenon has been particularly studied in culture. As soon as at passage 1, there is a gradual shift from the synthesis of type II collagen to type I and III collagens and from the synthesis of large aggregating proteoglycans (aggrecan) to low molecular weight proteoglycans. However, it has been shown that dedifferentiated chondrocytes can reexpress phenotypic markers of the articular chondrocyte. These conditions include tridimensional culture in gels of agarose, collagen and alginate. This can be also obtained after treatment of chondrocytes in monolayer by dihydrocytochalasin B or staurosporine. Although the mechanisms involved in restoration of the differentiated phenotype have not been elucidated yet, it has been shown that the synthesis of specific proteoglycans and type II collagen can be related to a modification of actin architecture. The restoration of the differentiated functions using tridimensional culture of chondrocytes has been used to perform autologous chondrocyte implantation in chondral defects. In the future, the grafts could be improved using chondrocytes treated with stimulating growth factors and synthetically derived matrices.