MODULATION OF COMMITMENT, PROLIFERATION, AND DIFFERENTIATION OF CHONDROGENIC CELLS IN DEFINED CULTURE-MEDIUM

The factors regulating the growth and development of mesenchymal precu rsor cells toward chondrogenesis are not well identified. We have deve loped a defined serum-free culture system that allows the proliferatio n of chick embryo chondrogenic cells and their maturation toward hyper trophic chondrocytes. Proliferation is obtained in adhesion in medium supplemented with insulin (Ins), Dexamethasone (Dex), and either basic fibroblast growth factor (FGF-2), platelet derived growth factor bb, epithelial growth factor, or GH; the highest mitogenic response is ind uced by FGF-2 in synergy with Ins. Ins can be substituted by Ins-like growth factor I. When these cells are transferred into suspension cult ure in Ins/Dex and T-3 without growth factor supplement, they undergo the complete chondrogenic development characterized by type X collagen synthesis and cellular hypertrophy. During differentiation, Ins canno t be substituted by Ins-like growth factor I. Chondrogenesis is also e videnced by the formation of hypertrophic cartilage when the medium is supplemented with ascorbic acid. If T-3 is introduced in the prolifer ation phase, the cells fail to differentiate to hypertrophy in suspens ion unless bone morphogenetic protein-2 is added. Assays of ectopic ti ssue formation in nude mice, with cells implanted sc after adsorption on collagen sponge or porous hydroxyapatite ceramics, indicate that ce lls grown in Ins/FGF-2 reform mainly cartilage in vivo, whereas expans ion in Ins/T-3/Dex/FGF-2 leads to the formation of cartilage, bone, an d adipose tissue.