Cluster for Craniofacial Development and Regeneration Research, Institute of Oral Biosciences, Chonbuk National University School of Dentistry, Jeonju 54896, South Korea.
Cluster for Craniofacial Development and Regeneration Research, Institute of Oral Biosciences, Chonbuk National University School of Dentistry, Jeonju 54896, South Korea.
Bone. 2019 Aug;125:8-15. doi: 10.1016/j.bone.2019.05.001. Epub 2019 May 4.
During cementum formation, the key roles of osterix (Osx) and inorganic pyrophosphate (PPi), mainly controlled by nucleotide pyrophosphatase 1 (Npp1; encoded by the Enpp1 gene) and progressive ankylosis protein (Ank), have been demonstrated by animal models displaying altered cementum formation. In this study, we analyzed the relationship of Osx and local PPi during cementum formation using compound mutant mice with their wildtype and corresponding single gene mutants. Importantly, functional defects in PPi regulation led to the induction of Osx expression at the cervical cementum as demonstrated by Enpp1 mutant mice and cementoblasts with the retroviral transduction of small hairpin RNA for Enpp1 or Ank. Conversely, cementoblasts exposed to inorganic PPi or with the enforced expression of Enpp1 or Ank reduced Osx expression in a concentration-dependent manner. Furthermore, the loss of Osx induced the higher expression of Npp1 and Ank at the apical region of the developing tooth root as observed in Osx-deficient mice. The activity of PPi-generating ectoenzymes (nucleoside triphosphate pyrophosphohydrolase, NTPPPHase) and the level of extracellular PPi were significantly increased in Osx-knockdown cementoblasts. However, the formation of ectopic cervical cementum was not completely diminished by inactivation of Osx in Enpp1 mutant mice. In addition, fibroblast growth factor (FGF) receptor 1 (Fgfr1) was strongly localized in cementoblasts lining the acellular cementum and involved in the inhibitory regulation of matrix accumulation and further mineralization by supporting PPi production. Taken together, these results suggest that local PPi suppresses matrix accumulation and further mineralization through an antagonistic interaction with Osx under the synergistic influence of FGF signaling during cementum formation.
在牙骨质形成过程中，动物模型显示牙骨质形成改变，表明骨形成蛋白（Osx）和无机焦磷酸盐（PPi）发挥关键作用，主要受核苷酸焦磷酸酶 1（Npp1；由 Enpp1 基因编码）和进行性强直蛋白（Ank）调控。在这项研究中，我们使用复合突变小鼠及其野生型和相应的单基因突变小鼠分析了牙骨质形成过程中 Osx 和局部 PPi 的关系。重要的是，PPi 调节功能缺陷导致 Enpp1 突变小鼠和转染 Enpp1 或 Ank 短发夹 RNA 的成牙骨质细胞中颈牙骨质 Osx 表达诱导。相反，无机 PPi 处理或过表达 Enpp1 或 Ank 的成牙骨质细胞以浓度依赖性方式降低 Osx 表达。此外，如在 Osx 缺陷小鼠中观察到的，Osx 缺失诱导发育中牙根根尖区域 Npp1 和 Ank 的更高表达。在 Osx 敲低的成牙骨质细胞中，产生 PPi 的胞外酶（核苷三磷酸磷酸水解酶，NTPPPHase）活性和细胞外 PPi 水平显著增加。然而，在 Enpp1 突变小鼠中，Osx 的失活并没有完全消除异位颈牙骨质的形成。此外，成纤维细胞生长因子（FGF）受体 1（Fgfr1）强烈定位于无细胞牙骨质衬里的成牙骨质细胞中，并通过支持 PPi 产生参与对基质积累和进一步矿化的抑制调节。总之，这些结果表明，局部 PPi 通过在 FGF 信号协同作用下与 Osx 产生拮抗相互作用，抑制基质积累和进一步矿化。
