Bmi1 plays an important role in dentin and mandible homeostasis by maintaining redox balance.

To explore whether polycomb repressor Bmi1 plays an important role in dentin and mandible development homeostasis by maintaining redox balance, 3-week-old Bmi1 gene knockout (Bmi1) mice were treated with the antioxidant N-acetylcysteine (NAC) for 2 weeks in their drinking water and phenotypes of the tooth and mandibles were compared with vehicle-treated Bmi1 mice and wild-type mice by radiograph, histochemistry and immunohistochemistry. Alterations of oxidative stress, DNA damage, cell proliferation and cell cycle-related parameters were also examined in mandibles. Results showed that the tooth volume and the dentin sialoprotein immunopositive areas, the cortical thickness, alveolar bone volume, osteoblast number and activity, and mRNA expression levels of Runx2, alkaline phosphatase and type I collagen were all reduced significantly in Bmi1 mice compared with their wild-type littermates, whereas these parameters were increased significantly in NAC-treated Bmi1 mice compared with vehicle-Bmi1 mice, although they were not normalized. The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were reduced, DNA damage markers including γ-H2AX and 8-oxoguanine levels were increased, the number of Ki67 positive cells was decreased, whereas protein expression levels of p16, p19, p21, p27 and p53 were up-regulated in mandibles from Bmi1 mice compared with those from wild-type mice; alterations of these antioxidative enzyme activities, DNA damage markers, cell proliferation and cell cycle-related parameters were all partially rescued by the treatment with antioxidant NAC in Bmi1 deficient mice. These results demonstrated that Bmi1 deficiency resulted in defects in dentin and alveolar bone formation, while the treatment with antioxidant could improve these defects obviously. Therefore, our results indicate that Bmi1 plays an important role in stimulating dentin formation and alveolar bone formation by maintaining redox homeostasis, preventing DNA damage and inhibiting cyclin-dependent kinase inhibitors.