MESENCHYMAL CELL CHONDROGENESIS IS STIMULATED BY BASEMENT-MEMBRANE MATRIX AND INHIBITED BY AGE-ASSOCIATED FACTORS

During development of the embryonic limb, differentiation of mesenchymal progenitor cells into chondrocytes is regulated by cell shape, extracellular matrix, and growth and differentiation factors. In this study, reconstituted basement membrane (Matrigel) prepared from mouse Englebreth-Holm-Swarm tumor tissue was found to stimulate mesenchymal cell chondrogenesis in vitro and the production of cartilage at ectopic sites in athymic mice. The rate of chondrogenesis of mesenchymal cells from chick limb bud was increased four-fold by the addition of 400 mu g/ml Matrigel to the media of micromass cultures, and this activity was not blocked by neutralizing antibodies to transforming growth factor-beta (TGF-beta) or fibroblast growth factor (FGF). Mesenchymal cells cultured on Matrigel, but not laminin or collagen type I or IV, formed spheres of condensed cells which stained with Alcian blue. Chick limb-bud mesenchymal cells suspended in Matrigel prepared from tumors grown in C57 mice aged 3, 12, or 26 months formed disks of hyaline cartilage within 2 weeks with wet weights of 59.1 mg, 35.7 mg, and 21.4mg, indicating that the Matrigel from the old animals was less biologically active. In agreement with the in vivo data, Alcian blue staining of proteoglycan was over two-fold higher in micromass cultures supplemented with the Matrigel from young animals than in cultures treated with the Matrigel from old mice. A high-salt wash preparation of Matrigel from tumors grown in old mice increased the rate of chondrogenesis and cartilage production, suggesting that an inhibitor of chondrogenesis is produced by the old host. Thus, Matrigel contains chondrogenic activity distinct from TGF-beta or FGF. The aged host may produce factors that are inhibitory to mesenchymal cell differentiation and adversely affect cartilage formation and repair.