Ginsenoside Rh2(S) induces differentiation and mineralization of MC3T3-E1 cells through activation of the PKD/AMPK signaling pathways.

As part of our search for biologically active anti-osteoporotic agents that enhance differentiation and mineralization of osteoblastic MC3T3-E1 cells, we identified the ginsenoside Rh2(S). Mostly known to exhibit beneficial effects in cancer prevention and metabolic diseases, Rh2(S) is one of the most active ginsenosides. Here, we show that Rh2(S) stimulates osteoblastic differentiation and mineralization, manifested by the up-regulation of differentiation markers (alkaline phosphatase and osteogenic genes) and von Kossa/Alizarin Red staining, respectively. Rh2(S) also activated protein kinase D (PKD) and AMP-activated protein kinase (AMPK) in a time- and concentration-dependent manner, and Rh2(S)-induced differentiation and mineralization of osteoblastic cells were significantly abolished in the presence of specific inhibitors; Go6976 for PKD and Ara-A for AMPK. Furthermore, Go6976 suppressed Rh2(S)-mediated activation of AMPK, indicating that PKD may be an upstream signal for AMPK in Rh2(S)-induced differentiation and mineralization of MC3T3-E1 cells. Taken together, these results indicate that Rh2(S) induces the differentiation and mineralization of MC3T3-E1 cells through activation of PKD/AMPK signaling pathways. These findings provide a molecular basis for the osteogenic effect of Rh2(S).