3). These results suggest that KRG prevents Dex-induced apoptosis in MC3T3-E1 cells in a dose-dependent manner. Apoptosis is a regulated cellular suicide mechanism that was characterized by nuclear condensation, cell shrinkage, and DNA fragmentation. The increase in MC3T3-E1 cell viability upon treatment with both KRG and Dex suggests that KRG modulates the expression of cell death-related INCB018424 manufacturer genes. Caspases, a family of cysteine proteases, are the central regulators of apoptosis. To examine the possibility that the expression of these proteins may be modulated, expression levels of both proapoptotic genes (caspase-3, -6, -7, and -9) and antiapoptotic genes (BCL-2, IAPs, and XIPA) were confirmed by

quantitative real-time PCR. The treatment of MC3T3-E1 cells with 100μM Dex for 48 h increased the mRNA levels of caspases, whereas cells exposed to Dex and KRG decreased the mRNA levels of caspase-3 and caspase-9 ( Fig. 4). However, Dex failed to repress the expression of antiapoptotic genes (BCL-2, IAPs, and XIPA). In fact, Dex significantly upregulated the expression of Bcl-XL, IAP-2, and XIAP ( Fig. 5). Therefore, Dex EGFR phosphorylation may induce apoptosis by upregulating proapoptotic gene expression. To survey the molecular mechanism by which KRG exerts its antiapoptotic effects, activation of the MAPK/AKT signaling pathway was examined. MC3T3-E1 cells were incubated with 100μM Dex in the presence

or absence of KRG (1 mg/mL) for 24 h. The JNK, p38, and AKT activation states were reviewed by Western blot analysis. When cells were exposed to 100μM Dex, the

JNK phosphorylation level increased significantly compared to that of the control, whereas it decreased significantly when treated with both Dex and KRG. Given that AKT activation protects cells from cell apoptosis and cell death, we also investigated whether KRG could induce AKT phosphorylation in Dex-exposed MC3T3-E1 cells or not. When cells were exposed to 100μM Dex, AKT phosphorylation decreased significantly 4-Aminobutyrate aminotransferase compared to that of the control, whereas it increased significantly when cells were treated with both Dex and KRG (Fig. 6). To determine the effects of KRG on the expression of osteogenic gene markers and ALP activity, cells were treated with various concentrations of KRG and Dex in osteogenic differentiation conditions for 5 d and 7 d. Osteoblastic differentiation was assessed by using quantitative real-time PCR, by measuring the mRNA expression levels of ALP, bone morphogenic proteins (BMPs), osteopontin (OPN), RUNX2, and osteocalcin (OCN). DEX-treated cells showed decreased ALP activity, but in cells treated with Dex and KRG (30 μg/mL and 60 μg/mL; Fig. 7A) this activity was increased significantly. Based on quantitative real-time PCR, cells treated with 100μM Dex exhibited decreased mRNA expression levels of ALP, OCN, OPN, RUNX2, BMP-2, -6, -7, and -9, whereas these expression levels increased in cells treated with both Dex and KRG (Fig.