Development and aging of the articular cartilage of the rabbit knee joint:Distribution of biglycan, decorin, and matrilin-1

We determined the distributions of the small proteoglycans biglycan and dec orin and the glycoprotein matrilin-1 (cartilage matrix protein) during deve lopment and aging of articular cartilage in the rabbit knee joint. Before c avitation, the matrices of the interzone and the adjacent epiphyseal cartil age do not contain biglycan or decorin, but some chondrocytes express their mRNAs. Matrilin-1 is found only in the deeper epiphyseal cartilage. After cavitation, biglycan and decorin are detected in the presumptive articular cartilage, but there is no matrilin-1. All are present in the underlying ep iphyseal cartilage, articular In the neonate, the epiphyseal cartilage is o ssified and the articular cartilage becomes a discrete layer. Biglycan and decorin accumulate in the articular cartilage, but matrilin-1 remains confi ned to the residual epiphyseal cartilage. In the adult, the distributions o f biglycan and decorin are highly variable. Decorin tends to be confined to the central region; matrilin-1 is absent. The findings indicate that the a rticular and epiphyseal cartilages are different from the earliest developm ental stages. The epiphyseal cartilage can be identified by its possession of matrilin-1. Epiphyseal cartilage is removed during development to leave the articular cartilage. The relationships between the distributions of dec orin and matrilin-1 and the fibrillar collagens are discussed.