TRANSFORMING GROWTH FACTOR-BETA-1 STIMULATES TYPE-II COLLAGEN EXPRESSION IN CULTURED PERIOSTEUM-DERIVED CELLS

Chondrogenesis can occur during a bone repair process, which is related to several growth factors. Transforming growth factor beta-1, (TGF-beta-1) downregulates the expression of type II collagen by chondrocytes in vitro, but injection of TGF-beta-1 into the periosteum in vivo increases type II collagen mRNA levels and initiates chondrogenesis. (1) We examined the effect of TGF-beta-1 on collagen gene expression in a bovine periosteum-derived cell culture system to evaluate its direct effect on the periosteum. Cultured cells expressed alkaline phosphatase and collagen pro-alpha-1(I) and pro-alpha-1(II) mRNAs. A low level of type II collagen synthesis was demonstrated by immunoprecipitation. TGF-beta-1 had no effect on periosteal cell proliferation. Expression of collagen pro-alpha-1(I) mRNA did not change with TGF-beta-1 treatment, but alkaline phosphatase mRNA showed a dose-dependent decrease. Expression of collagen pro-alpha-1(II) mRNA was stimulated 2.7-fold by TGF-beta-1. TGF-beta-1 also caused a 2.6-fold increase in type II collagen synthesis by immunoprecipitation. These findings indicate that TGF-beta-1 is an enhancer of the expression of the chondrocyte phenotype of the periosteal cells and suggest that TGF-beta-1 is important in initiating and promoting cartilage formation in vivo.