MATRIX ACCUMULATION AND RETENTION IN EMBRYONIC CARTILAGE AND IN-VITROCHONDROGENESIS

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 hyaluro nan hexasaccharides for native hyaluronan during matrix assembly, accu mulation and retention in embryonic cartilage was studied. Chondrocyte s released from explants with collagenase P retained pericellular matr ices, but chondrocytes appeared ''matrix-free'' when released from hex asaccharide-treated explants. Decreased safranin O staining was also o bserved in the hexasaccharide-treated explants. This loss of proteogly can retention was demonstrated quantitatively in the cartilage extract s and recovered in the media. The continual presence of hexasaccharide s in micromass cultures resulted in decreased proteoglycan deposition. Increased proteoglycan retention, indicative of matrix repair, occurr ed following hexasaccharide wash-out. Thus, native hyaluronan-chondroc yte interactions are important for the assembly and maintenance of car tilage matrix.