Reactive Oxygen Species-Induced Inhibition of Odontoblastic Differentiation of Mouse Dental Papilla Cells Is Mediated by Downregulation of Importin 7

Tooth dentin is a crucial tooth structure. The biological process of odontoblast differentiation is essential for formation of normal dentin. Accumulation of reactive oxygen species (ROS) leads to oxidative stress, which can influence the differentiation of several cells. As a member of the importin-beta superfamily, importin 7 (IPO7) is essential for nucleocytoplasmic transport and plays an important role in the processes of odontoblast differentiation and oxidative stress. Nevertheless, the association between ROS, IPO7, and odontoblast differentiation in mouse dental papilla cells (mDPCs) and the underlying mechanisms remain to be elucidated. In this study, we confirmed that ROS suppressed odontoblastic differentiation of mDPCs as well as the expression and nucleocytoplasmic shuttle of IPO7 in cells, while overexpression of IPO7 can rescue these effects. ROS resulted in increased phosphorylation of p38 and cytoplasmic aggregation of phosphorylated p38 (p-p38), which was able to be reversed by overexpression of IPO7. p-p38 interacted with IPO7 in mDPCs without hydrogen peroxide (H2O2) treatment, but in the presence of H2O2, the interaction between p-p38 and IPO7 was significantly decreased. Inhibition of IPO7 increased the expression level and nuclear translocation of p53, which are mediated by cytoplasmic aggregation of p-p38. In conclusion, ROS inhibited odontoblastic differentiation of mDPCs, which is mediated by downregulation and damaged nucleocytoplasmic shuttle of IPO7.