Department of Biomedical Sciences, Texas A&M University College of Dentistry, Dallas, TX, United States of America.
Department of Stomatology, the 2nd Affiliated Hospital of Harbin Medical University, Harbin, Heilongjiang, China.
PLoS One. 2018 Apr 19;13(4):e0195854. doi: 10.1371/journal.pone.0195854. eCollection 2018.
Mutations in the dentin sialophosphoprotein (DSPP) gene cause dentinogenesis imperfecta. After synthesis, DSPP is proteolytically processed into NH2- and COOH-terminal fragments. The NH2-terminal fragment of DSPP is highly glycosylated but not phosphorylated, whereas the COOH-terminal fragment (named "dentin phosphoprotein" or "DPP") is highly phosphorylated but not glycosylated. These two fragments are believed to perform distinct roles in dentin formation. To analyze the functions of DPP in dentinogenesis, we created "Dspp-/-;DPP Tg mice", which expressed transgenic DPP driven by a Type I collagen promoter but lacked the endogenous Dspp gene. We characterized the dentin of the Dspp-/-;DPP Tg mice using X-ray radiography, histology, scanning electron microscopy, double fluorochrome labeling, immunohistochemistry and in situ hybridization. Micro-computed tomography analyses revealed that at postnatal 6 months, the transgenic expression of DPP increased the dentin thickness of the Dspp-null mice by 97.1% and restored the dentin material density by 29.5%. Histological analyses showed that the Dspp-null mice manifested an abnormal widening of the predentin while the predentin in Dspp-/-;DPP Tg mice was narrower than in the Dspp-null mice. Scanning electron microscopy analyses showed that the dentinal tubules in the Dspp-/-;DPP Tg mice were better organized than in the Dspp-null mice. The double fluorochrome labeling analyses demonstrated that the dentin mineral deposition rate in the Dspp-/-;DPP Tg mice was significantly improved compared to that in the Dspp-null mice. These findings indicate that the transgenic expression of DPP partially rescued the dentin defects of the DSPP-null mice, suggesting that DPP may promote dentin formation and that the coordinated actions between DPP and the NH2-terminal fragment of DSPP may be necessary for dentinogenesis.
DSPP 基因突变会导致牙本质生成不全。DSPP 合成后，会被蛋白水解酶加工成氨基端和羧基端片段。DSPP 的氨基端片段高度糖基化但不磷酸化，而羧基端片段（称为“牙本质磷蛋白”或“DPP”）高度磷酸化但不糖基化。这两个片段被认为在牙本质形成中发挥不同的作用。为了分析 DPP 在牙本质生成中的作用，我们创建了“Dspp-/-;DPP Tg 小鼠”，这些小鼠表达由 I 型胶原启动子驱动的转基因 DPP，但缺乏内源性 Dspp 基因。我们使用 X 射线射线照相、组织学、扫描电子显微镜、双荧光标记、免疫组织化学和原位杂交技术对 Dspp-/-;DPP Tg 小鼠的牙本质进行了表征。微计算机断层扫描分析显示，在出生后 6 个月时，DPP 的转基因表达使 Dspp 缺失小鼠的牙本质厚度增加了 97.1%，并使牙本质物质密度恢复了 29.5%。组织学分析表明，Dspp 缺失小鼠表现出前牙髓异常增宽，而 Dspp-/-;DPP Tg 小鼠的前牙髓比 Dspp 缺失小鼠的前牙髓更窄。扫描电子显微镜分析表明，Dspp-/-;DPP Tg 小鼠的牙本质小管排列更整齐。双荧光标记分析表明，与 Dspp 缺失小鼠相比，Dspp-/-;DPP Tg 小鼠的牙本质矿化沉积率显著提高。这些发现表明，DPP 的转基因表达部分挽救了 DSPP 缺失小鼠的牙本质缺陷，表明 DPP 可能促进牙本质形成，并且 DPP 和 DSPP 的氨基端片段之间的协调作用可能是牙本质生成所必需的。
