dc.description.abstract | In this study, human dental pulp stem cells, hDPSC, cultured in regular culture medium (CM) or osteogenesis medium (OM) were treated direct current stimulation to discuss the effect of electrical stimulation on cell cycle and osteogenesis. The calcium deposition and cell number assay demonstrated that the mineralization of electrical stimulation treated group was improved 1.5 to 2 folds compared to the control group, however, it also reduced cell amounts. To investigate whether the reduction of cell under electrical stimulation resulted from cell cycle arrest, cell growth curve and two-step cell cycle analysis were performed. The results suggested that cell growth was retarded by electrical stimulation, and cells were arrested at G2/M and G1 when they were cultured in CM and OM, respectively. Therefore, we applied Western blotting to analyze proteins relative to cell cycle and signal transduction. In CM condition, p21 and p53 were up-regulated, suggesting cell cycle was arrested by electrical stimulation. Phosphorylation levels of Rb and Cyclin E were both increased, indicating cells were accelerated to leave from G1. The up-regulation of Cyclin A2 and down-regulation of Cyclin B1 suggested that cells were arrested at G2 stage. Therefore, we further analyzed Wee1 and phosphorylation of CDK1, the regulated protein in the checkpoint between G2 and M stages. The results demonstrated that Wee1 was up-regulated to increase the phosphorylation of CDK1, which eventually caused G2 stage arrest. In the OM condition, p21 was also unregulated. In addition, phosphorylation of Rb as well as the down regulations of Cyclin D1, Cyclin E1, CDK4, and CDK6 all supported that cell treated electrical stimulation in OM were arrested in G1 stage. Finally, the gene regulation of Smad proteins results demonstrated that Smad3 and Smad1/5 were both highly phosphorylated and the Smad4 was also up-regulated. These results indicated that electrical stimulation can accelerate Smad-mediated signal transduction, which not only improved osteogenesis but also up-regulated p21 to arrest cell cycle. | en_US |