High Doses of Dexamethasone Induce Endoplasmic Reticulum Stress-Mediated Apoptosis by Promoting Calcium Ion Influx-Dependent CHOP Expression in Osteoblasts
Abstract Background: The molecular mechanisms by which dexamethasone (Dex) induces apoptosis in osteoblasts remain unclear.Materials and Methods: MC3T3-E1 cells were treated with 0, 10-8, 10-6, and 10-4 M Dex for 24 h. The expression of ATF6, and phosphorylated PERK and IRE1, cell apoptosis, and the activity of caspase-12 and caspase-3 were measured. The expression of CHOP and the rate of influx of calcium ions were also measured in cells treated with 0 and 10-4 M Dex for 24 h. The effect of 2-APB treatment was assessed in cells treated with 0 or 10-4 M Dex.Results: The levels of ATF6 and phosphorylated PERK and IRE1 increased in a dose-dependent manner in MC3T3-E1 cells treated with 10-8, 10-6, and 10-4 M Dex, compared to in cells treated with 0 M Dex (P <0.05). Cells treated with 10-6 and 10-4 M Dex had significantly increased cell apoptosis rates and caspase-12 and caspase-3 activity compared to the control (P <0.05). Cells treated with 10-4 M Dex had significantly increased levels of CHOP and calcium ion influx rates compared to in the control (P <0.05). Combined treatment with 10-4 M Dex and 2-APB abrogated the observed increases in cell apoptosis and the activity of caspase-12 and caspase-3 (P>0.05). Conclusion: High doses of Dex induce endoplasmic reticulum stress-mediated apoptosis by promoting calcium ion influx-dependent expression of CHOP, and the activation of caspase-12 and caspase-3 in osteoblasts. Combined treatment with 2-APB protects the cells from the effects of Dex, preventing endoplasmic reticulum stress-mediated apoptosis.