Transforming growth factor β1 stimulates type II collagen expression in cultured periosteum-derived cells

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Abstract
Chondrogenesis can occur during a bone repair process, which is related to several growth factors. Transforming growth factor β1, (TGF-β1,) downregulates the expression of type II collagen by chondrocytes in vitro, but injection of TGF-β1, into the periosteum in vivo increases type II collagen mRNA levels and initiates chondrogenesis.(1) We examined the effect of TGF-β1, 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 proα1,(I) and proα1(II) mRNAs. A low level of type II collagen synthesis was demonstrated by immunoprecipitation. TGF-β1, had no effect on periosteal cell proliferation. Expression of collagen proα1(I) mRNA did not change with TGF-β1, treatment, but alkaline phosphatase mRNA showed a dose-dependent decrease. Expression of collagen proα1(II) mRNA was stimulated 2.7-fold by TGF-β1. TGF-β1, also caused a 2.6-fold increase in type II collagen synthesis by immunoprecipitation. These findings indicate that TGF-β1 is an enhancer of the expression of the chondrocyte phenotype of the periosteal cells and suggest that TGF-β1, is important in initiating and promoting cartilage formation in vivo.