Division of Histology, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, 061-0293, Japan.
Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan.
Histochem Cell Biol. 2024 Nov 26;163(1):11. doi: 10.1007/s00418-024-02337-2.
Bmi1 is a polycomb protein localized in stem cells and maintains their stemness. This protein is also reported to regulate the expression of various differentiation genes. In this study, to analyze the role of Bmi1 during dentinogenesis, we examined the immunohistochemical localization of Bmi1 during rat tooth development as well as after cavity preparation. Bmi1 localization was hardly detected in the dental mesenchyme at the bud and cap stages. After the bell stage, however, this protein became detectable in preodontoblasts and early odontoblasts just beginning dentin matrix secretion. As dentin formation progressed, Bmi1 immunoreactivity in the odontoblasts decreased in intensity. After cavity preparation, cells lining the dentin and some pulp cells under the cavity were immunopositive for Bmi1 at 4 days. Odontoblast-like cells forming reparative dentin were immunopositive for Bmi1 at 1 week, whereas their immunoreactivity was not detected after 8 weeks. We further analyzed the function of Bmi1 using KN-3 cells, a dental mesenchymal cell line. Overexpression of Bmi1 in KN-3 cells promoted mineralized tissue formation. In contrast, siRNA knockdown of Bmi1 in KN-3 cells reduced alkaline phosphatase activity and the expression of odontoblast differentiation marker genes such as Runx2, osterix, and osteocalcin. Additionally, KN-3 cells transfected with siRNA against Bmi1 showed reduced nuclear transition of β-catenin and expression of phosphorylated-Smad1/5/8. Taken together, these findings suggest that Bmi1 was localized in the odontoblast-lineage cells in their early differentiation stages. Bmi1 might positively regulate their differentiation by accelerating Wnt and BMP signaling pathways.
BMI1 是一种多梳蛋白，定位于干细胞中，维持其干细胞特性。该蛋白还被报道调节各种分化基因的表达。在这项研究中，为了分析 BMI1 在牙本质发生过程中的作用，我们检查了 BMI1 在大鼠牙齿发育过程中的免疫组织化学定位，以及在龋备后的定位。在芽和帽期，牙间质中几乎检测不到 BMI1 的定位。然而，在钟状期后，该蛋白在前期成牙本质细胞和刚开始分泌牙本质基质的早期成牙本质细胞中可检测到。随着牙本质的形成，成牙本质细胞中的 BMI1 免疫反应性强度降低。龋备后 4 天，牙本质表面的细胞和腔下的一些牙髓细胞呈 BMI1 免疫阳性。在 1 周时，形成修复性牙本质的成牙本质细胞样细胞呈 BMI1 免疫阳性，而在 8 周后则未检测到其免疫反应性。我们使用牙间质细胞系 KN-3 细胞进一步分析了 BMI1 的功能。在 KN-3 细胞中过表达 BMI1 促进了矿化组织的形成。相反，在 KN-3 细胞中 siRNA 敲低 BMI1 降低了碱性磷酸酶活性和牙本质分化标记基因如 Runx2、osterix 和骨钙素的表达。此外，用针对 BMI1 的 siRNA 转染的 KN-3 细胞显示 β-catenin 的核转位和磷酸化-Smad1/5/8 的表达减少。总之，这些发现表明，BMI1 定位于早期分化阶段的成牙本质细胞谱系细胞中。BMI1 可能通过加速 Wnt 和 BMP 信号通路来正向调节它们的分化。
