Effects of transforming growth factor-beta 1 on murine clonal osteoblastic cells (MC3T3-E1)

Transforming growth factor (TGF)-beta family is considered to be an important local factor that greatly regulates bone metabolism. However, the effects of this polypeptide on osteoblasts have been divergent under various experimental conditions. Moreover, three forms of TGF-beta have been recently described. Therefore, we reexamined the effects of TGF-beta 1 on clonal murine osteoblastic MC3T3-E1 cells. TGF-beta 1 dose- and time-dependently depressed alkaline phosphatase activity in the cells supported by low concentration of serum. On the contrary, in the same range of concentrations, TGF-beta 1 stimulated DNA synthesis in the cells. These effects of TGF-beta 1 were observed in the cells cultured in the media without or with a high concentration of serum. These effects of TGF-beta 1 are not mediated by endogenous production of prostaglandin, since the basal level of prostaglandin E2 was very low and rather inhibited by TGF-beta 1; and, further, indomethacin did not modify the effects of TGF-beta 1 on the cells under the present conditions. Furthermore, TGF-beta 1 greatly stimulated not only type I but also type III collagen production. Hydroxyurea completely blocked the stimulation of DNA synthesis by TGF-beta 1, but partially inhibited the collagen synthesis, suggesting that the TGF-beta 1-stimulated collagen synthesis is at least in part linked to the proliferation. However, the stimulation of collagen synthesis by TGF-beta 1 was greater than that of DNA synthesis, and further, the amount of hydroxyproline in the cell was evidently augmented by TGF-beta 1. Our data presented here thus suggest that TGF-beta 1 may act on preosteoblasts to increase the number of osteoblasts and the amount of bone organic matrix.