MAPK mediates Hsp25 signaling in incisor development.
ABSTRACT Rodent incisors are continuously growing teeth that include all stages of amelogenesis. Understanding amelogenesis requires investigations of the genes and their gene products control the ameloblast phenotype. One of the mechanisms related to tooth differentiation is mitogen-activated protein kinase (MAPK) signaling. The extracellular-signal regulated kinase (ERK)/mitogen-activated protein kinase kinase (MEK) cascade is associated with mechanisms that control the cell cycle and cell survival. However, the roles of cascades in incisor development remain to be determined. In this study, we investigated incisor development and growth in the mouse based on MAPK signaling. Moreover, heat-shock protein (Hsp)-25 is well known to be a useful marker of odontoblast differentiation. We used anisomycin (a protein-synthesis inhibitor that activates MAPKs) and U0126 (a MAPK inhibitor that blocks ERK1/2 phosphorylation) to examine the role of MAPKs in Hsp25 signaling in the development of the mouse incisor. We performed immunohistochemistry and in vitro culture using incisor tooth germ, and found that phospho-ERK (pERK), pMEK, and Hsp25 localized in developing incisor ameloblasts and anisomycin failed to produce incisor development. In addition, Western blotting results showed that anisomycin stimulated the phosphorylation of ERK, MEK, and Hsp25, and that some of these proteins were blocked by the U0126. These findings suggest that MAPK signals play important roles in incisor formation, differentiation, and development by mediating Hsp25 signaling.
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ABSTRACT: Inorganic phosphate (Pi) is required in many biological processes, including signaling cascades, skeletal development, tooth mineralization, and nucleic acid synthesis. Recently, we showed that Pi transport in osteoblasts, mediated by Slc20a1, a member of the type III sodium-dependent phosphate transporter family, is indispensable for osteoid mineralization in rapidly growing rat bone. In addition, we found that bone mineral density decreased slightly with dysfunction of Pi homeostasis in aged transgenic rats overexpressing mouse Slc20a1 (Slc20a1-Tg). Bone and tooth share certain common molecular features, and thus, we focused on tooth development in Slc20a1-Tg mandibular incisors in order to determine the role of Slc20a1 in tooth mineralization. Around the time of weaning, there were no significant differences in serologic parameters between wild-type and Slc20a1-Tg rats. However, histological analysis showed that Slc20a1-Tg ameloblasts formed clusters in the papillary layer during the maturation stage as early as 4 weeks of age. These pathologies became more severe with age and included the formation of cyst-like or multilayer ameloblast structures, accompanied by a chalky white appearance with abnormal attrition and fracture. Hyperphosphatemia was also observed in aging Slc20a1-Tg rats. Micro-computed tomography and electron probe microanalysis revealed impairments in enamel, such as delayed mineralization and hypomineralization. Our results suggest that enamel formation is sensitive to imbalances in Pit1-mediated cellular function as seen in bone, although these processes are under the control of systemic Pi homeostasis.Calcified Tissue International 06/2011; 89(3):192-202. · 2.50 Impact Factor
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ABSTRACT: To investigate dental pulp healing after tooth replantation in rats using nestin as an odontoblastic marker for immunohistochemical analysis. Twenty-five maxillary right first molars from 25 female Sprague-Dawley rats, aged 4 weeks post-natally, were extracted and immediately repositioned in the original socket within 5 s. Five rats each were later killed on days 3, 5 and weeks 1, 2 and 4. The maxillae were removed en bloc and the tissue samples containing the maxillary right first molars were decalcified, sectioned, mounted and stained with anti-nestin antibody to be observed under a light microscope. At 3 days after replantation, there was a localized inflammatory reaction, but pulp revascularization and healing had begun in the root area. At 5 days after replantation, odontoblast-like cells were observed. Reparative dentine deposition was observed beneath the pulp-dentine border from 1 week after replantation, and gradually increased until 2 weeks after replantation. The presence of odontoblast-like cells and the formation of reparative dentine continued from the first week throughout the experimental period. At week four, deposition of osteodentine and cementum-like tissues were observed. Pulpal mineralization after replantation initially occurred via the deposition of reparative dentine, followed by the deposition of osteodentine and cementum-like tissues in rat teeth.International Endodontic Journal 02/2012; 45(7):652-9. · 2.05 Impact Factor
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ABSTRACT: The selection of a suitable scaffold material is important for dentin tissue regeneration, as the characteristics of biomaterials can potentially influence cell proliferation and differentiation. We compared the effects of different scaffolds on dentin regeneration based on dental pulp stem cells (DPSCs) and investigated the regulatory mechanisms of odontogenic differentiation of DPSCs by these scaffolds. Five different scaffolds were tested: demineralized dentin matrix (DDM), ceramic bovine bone (CBB), small intestinal submucosa (SIS), poly-L-lactate-co-glycolate, and collagen-chondroitin sulfate-hyaluronic acid. DPSCs cultured on DDM and CBB exhibited higher levels of alkaline phosphatase (ALP) activity and mRNA expression of bone sialoprotein, osteocalcin, dentin sialophosphoprotein (DSPP), and dentin matrix protein-1 (DMP-1) than those cultured on the other three scaffolds. Further, the phosphorylation levels of mitogen-activated protein kinase (MAPK) ERK1/2 and p38 in DPSCs cultured on DDM and CBB were also significantly enhanced compared with the other three scaffolds, and their inhibitors significantly inhibited odontogenic differentiation as assessed by ALP activity and mRNA expression of DSPP and DMP-1. The implantation experiment confirmed these results and showed a large amount of regular-shaped dentin-pulp complex tissues, including dentin, predentin, and odontoblasts only in the DDM and CBB groups. The results indicated that natural mineralized scaffolds (DDM and CBB) have potential as attractive scaffolds for dentin tissue-engineering-promoted odontogenic differentiation of DPSCs through the MAPK signaling pathway.Tissue Engineering Part A 11/2011; 18(7-8):677-91. · 4.64 Impact Factor