An analysis of collagen synthesized by a Swarm rat chondrosarcoma cell line in monolayer culture

Chondrocytes lose their differentiated phenotype with time in monolayer culture and eventually become fibroblast-like. This is accompanied by a change in collagen synthesis from cartilage specific type II collagen to non-specific type I collagen. A cell line that maintained a polygonal to spherical morphology for more than 7 years in monolayer culture was established from the Swarm rat chondrosarcoma tumor. This cell line proliferates with a doubling time of 21 hours.; Biochemical analysis of the collagen synthesized by this cell line identified only cartilage specific type II, type IX and type XI collagens. This indicates that this is a chondrocyte cell line which maintains its differentiated phenotype in serial monolayer culture. Type II collagen is the major collagen produced at 44%. Elevated levels of the minor cartilage collagens, type IX and type XI were produced at 36% and 20% respectively. No proteoglycan forms of type IX collagen were detected. The majority of the collagen was present in the cell layer.; The total proteoglycan levels were 8 times higher than the total collagen levels on a mass basis during the first five days in culture and about 85% of the proteoglycans accumulated in the cell layer.; Although large quantities of collagen were detected in the cell layer, ultrastructural observations of the extracellular matrix of the cell line by electron microscopy showed a near absence of collagen fibrils. Co-cultures of the cell line in direct contact with normal embryonic chick chondrocytes also showed an inhibition of the collagen fibrillar network visible by electron microscopy around the normal chondrocytes.; Culture of the cell line and the co-cultures in the presence of hyaluronidase for 2 weeks to reduce the accumulated proteoglycan content in the matrix, resulted in a three fold reduction in matrix volume and an increase in the number of fibrils in the matrix of the cell line and around the chick chondrocytes as detected by electron microscopy. This implicates the high proteoglycan production by this cell line as one of the factors which inhibit collagen fibril formation in these cultures.