DIFFERENTIAL-EFFECTS OF TRANSFORMING GROWTH-FACTORS BETA-1, BETA-2, BETA-3 AND BETA-5 ON CHONDROGENESIS IN MOUSE LIMB BUD MESENCHYMAL CELLS

The present study was performed to determine whether mammalian TGF-bet a isoforms and Xenopus TGF-beta 5 elicit a differential chondrogenic r esponse on mesenchymal cells during mouse limb development, Results sh owed that TGF-beta isoforms produced a distinct chondrogenic pattern d epending on embryonic stage. When they were applied to 5 day micromass cultures of limb mesenchymal cells from embryonic stages 19, 20 and 2 1, a differential response to all four TGF-beta isoforms assayed was o bserved, By stage 19 the cells formed a uniform sheet of cartilage cel ls; by stage 20, mesenchymal cells were more responsive to TGF-beta 1 and TGF-beta 5 than at stages 19 and 21, showing an entire cell layer of chondrogenic cells with higher accumulation of extracellular matrix . The diminished effect of TGF-beta 2 and TGF-beta 3 at stages 20 and 21 was accompanied by a nodular pattern of chondrogenic cells rather t han by a uniform sheet, as seen at stage 19. At stage 20 TGF-beta 1 an d TGF-beta 5 enhanced the expression of sulfated proteoglycans, type I I collagen, cartilage link protein and alkaline phosphatase activity. In contrast, TGF-beta 2 and TGF-beta 3 caused less expression in the s ame parameters, Only a transient exposure to TGF-beta isoforms at days 1 and 2 of culture stimulate chondrogenesis, indicating that TGF-beta isoforms could regulate chondrogenesis at early stages of chondrocyte differentiation, However, when TGF-beta isoforms were applied to low density cultures of mesenchymal cells, chondrogenesis was enhanced onl y by 25%, suggesting that TGF-beta isoforms enhanced cartilage differe ntiation to higher levels in micromass cultures than in situations in which little or no chondrogenic differentiation normally occurs.