CHONDROCYTES SYNTHESIZE TYPE-I COLLAGEN AND ACCUMULATE THE PROTEIN INTHE MATRIX DURING DEVELOPMENT OF RAT TIBIAL ARTICULAR-CARTILAGE

The present study was designed to investigate whether or not chondrocy tes in articular cartilage express type I collagen in vivo under physi ological conditions. Expressions of the gene and the phenotype of type I collagen were examined in rat tibial articular cartilage in the kne e joint during development. Knee joints of Wistar rats at 1, 5, and 11 weeks postnatal were fixed in 4% paraformaldehyde with or without 0.5 % glutaraldehyde and decalcified in 10% EDTA. After the specimens were embedded in paraffin and serial sections made adjacent sections were processed for immunohistochemistry and in situ hybridization for type I collagen. The epiphysis of the tibia was composed of cartilage in we ek-1 rats. Formation of articular cartilage was in progress in week 5 as endochondral ossification proceeded and was completed in week 11. A nti-type I collagen antibody: stained only the superficial area of the epiphysis in week 1 but the immunoreactivity was expanded into the de eper region of the articular cartilage with development in weeks 5 and 11. Hybridization signals for pro-alpha 1 (I) collagen were seen in s ome of chondrocytes in the epiphysis of the week-1 tibia. The most int ense signals were identified in chondrocytes in week 5 and the signals appeared weaker in week 11, The present study demonstrated that chond rocytes synthesize type I collagen and accumulate the protein in the m atrix during development of the articular cartilage.