The Synthesis of Collagen and Glycosaminoglycans by Dedifferentiated Chondroblasts in Culture

Marked changes occur in the morphology of chick chondroblasts grown for 5 days in F-10 medium containing either 5-bromo-2'-deoxyuridine or embryo extract. The cells lose the characteristic polygonal morphology and assume a flattened 'fibroblastic' appearance. To determine whether the morphological changes reflect a biochemical transformation toward frank fibroblasts, changes in collagen and glycosaminoglycan synthesis were examined in these 'dedifferentiated' cells. Growth in either medium did not significantly affect the total amount of collagen synthesized. However, the subunit composition of the collagen chains was different. Freshly isolated cartilage trunks or control chondroblast cultures synthesized only α1 subunits (suggesting exclusive synthesis of α1(ll)₃-type collagen), whereas dedifferentiated cultures synthesized both α1 and, in addition, some α2 subunits (suggesting synthesis of fibroblasttype α1(l)₂α2-type collagen). Incorporation of labelled glucosamine in F-10 medium showed that the major glycosaminoglycan synthesized by either cartilage trunks or chondroblast monolayers is chondroitin sulphate; little, if any, hyaluronic acid could be detected. With growth in embryo extract (EE) glucosamine was incorporated equally into chondroitin sulphate and hyaluronic acid, whereas in BUdR, chondroitin sulphate synthesis was completely inhibited. Distinct biochemical differences were therefore found for both collagen and glycosaminoglycan synthesis during growth in either BUdR or EE. Such changes were not identical but both demonstrate changes in synthetic programme tending to approach that of frank fibroblasts.