Characterisation of caveolins from cartilage: expression of caveolin-1,-2 and-3 in chondrocytes and in alginate cell culture of the rat tibia

This study was performed to determine if rat articular chondrocytes express caveolin, the structural protein of caveolae, and to determine differences in the distribution of the caveolin subtypes 1, 2 and 3 in knee joints of newborn and adult rats. All three subtypes of caveolin were detected in adu lt cartilage by immunocytochemical staining. In newborn rats, only caveolin -1 was found in the hyaline cartilage. Caveolin-1, -2 and -3 messenger RNA and protein were also detected in chondrocyte cell cultures. Ultrastructura l investigations of cell culture and cartilage tissue revealed the presence of caveolae at the plasma membrane of chondrocytes. These findings represe nt the first report on the different expression of caveolin isoforms, in pa rticular the expression of the muscle cell-specific caveolin-3 in chondrocy tes. There is evidence that caveolin-2 and -3 are upregulated during growth and development of articular cartilage, suggesting a role for caveolins in chondrocyte differentiation.