Synergistic Effect of Isoflavones on the BMP-4 Mediated Osteoblastic Differentiation of C2C12 Myoblast

Purpose: Isoflavones are rich in soybean and are known to affect bone formation. This study examined the effects and modes of action of isoflavones on the differentiation of C2C12 myoblasts in the presence of the bone morphogenetic protein (BMP)-4. Materials and Methods: The isoflavones, daidzein, genistein or equol, and/or BMP-4 were added alone or in combination to C2C12 myoblasts. After 72 hours culture, the cells were stained for the early osteoblastic differentiation marker, alkaline phosphatase (ALP). The ALP activity was determined by comparing the color of the stained images as well as by spectrophotometry. The expression profiles of the extracellular matrix (ECM) genes responsible for the extensive remodeling at the cell surface were analyzed using agene expression microarray after treating thesamples with daidzein. Results: ALP staining of BMP-4 or the isoflavones-treated cells showed that BMP-4 increased the activity of ALP in a dose dependent manner, whereas the isoflavones alone did not induced any remarkable increase. However, the ALP activity increased when the cells were treated with BMP-4 and any of the three isoflavones. The macrogen mouse MAC array data showed that the ECM genes, Mmp13 and Mmp3, were up-regulated by daidzein, whereas Col4a2, Col5a1 and Mmp9 were down-regulated. Conclusion: Isoflavones induce osteoblastic differentiation when combined with BMP-4, which is possibly achieved by modulating the expressional levels of various ECM genes.