Matrix accumulation and retention in embryonic cartilage and in vitro chondrogenesis

Since hyaluronan anchors the proteoglycan-rich pericellular matrix to chondrocytes, hyaluronan-cell interactions may direct cartilage matrix assembly. To test this hypothesis, the competitive binding of hyaluronan hexasaccharides for native hyaluronan during matrix assembly, accumulation and retention in embryonic cartilage was studied. Chondrocytes released from explants with collagenase P retained pericellular matrices, but chondrocytes appeared ''matrix-free'' when released from hexasaccharide-treated explants. Decreased safranin O staining was also observed in the hexasaccharide-treated explants. This loss of proteoglycan retention was demonstrated quantitatively in the cartilage extracts and recovered in the media. The continual presence of hexasaccharides in micromass cultures resulted in decreased proteoglycan deposition. Increased proteoglycan retention, indicative of matrix repair, occurred following hexasaccharide wash-out. Thus, native hyaluronan-chondrocyte interactions are important for the assembly and maintenance of cartilage matrix.