A novel 90-kDa protein named periostin, which is preferentially expressed in the periosteum and the periodontal ligament (PDL), may play a role in bone metabolism and remodeling. However, the precise role of periostin in the PDL remains unclear. Therefore, we examined the expression of periostin mRNA during experimental tooth movement. Experimental tooth movement was achieved in 7-week-old male Sprague-Dawley rats. In control specimens without tooth movement, the expression of periostin mRNA was uniformly observed in the PDL surrounding the mesial and distal roots of the upper molars and was weak in the PDL of the root furcation area. The periostin mRNA-expressing cells were mainly fibroblastic cells in the PDL and osteoblastic cells on the alveolar bone surfaces. The divergent expression of periostin mRNA in the PDL began to be observed at 3 h and continued up to 96 h after tooth movement. The maximum changes, which showed stronger staining in the pressure sites than in the tension sites, were observed at 24 h. The expression of periostin mRNA in the PDL 168 h after tooth movement exhibited a similar distribution to that of the control specimens. These results suggest that periostin is one of the local contributing factors in bone and periodontal tissue remodeling following mechanical stress during experimental tooth movement.

Apert syndrome is an autosomal dominant disease characterized by craniosynostosis and bony syndactyly associated with point mutations (S252W and P253R) in the fibroblast growth factor receptor (FGFR) 2 that cause FGFR2 activation. Here we investigated the role of the S252W mutation of FGFR2 on osteoblastic differentiation. Osteoblastic cells derived from digital bone in two Apert patients with the S252W mutation showed more prominent alkaline phosphatase activity, osteocalcin and osteopontin mRNA expression, and mineralized nodule formation compared with the control osteoblastic cells derived from two independent non-syndromic polydactyly patients. Stable clones of the human MG63 osteosarcoma cells (MG63-Ap and MG63-IIIc) overexpressing a splice variant form of FGFR2 with or without the S252W mutation (FGFR2IIIcS252W and FGFR2IIIc) showed a higher RUNX2 mRNA expression than parental MG63 cells. Furthermore MG63-Ap exhibited a higher osteopontin mRNA expression than did MG63-IIIc. The enhanced osteoblastic marker gene expression and mineralized nodule formation of the MG63-Ap was inhibited by the conditioned medium from the COS-1 cells overexpressing the soluble FGFR2IIIcS252W. Furthermore the FGF2-induced osteogenic response in the mouse calvarial organ culture system was blocked by the soluble FGFR2IIIcS252W. These results show that the S252W mutation in the FGFR2 gene enhances the osteoblast phenotype in human osteoblasts and that a soluble FGFR2 with the S252W mutation controls osteoblast differentiation induced by the S252W mutation through a dominant negative effect on FGFR2 signaling in Apert syndrome.Apert syndrome is an autosomal dominantly inherited syndrome characterized by craniosynostosis, which results in skull deformity, and symmetric bony syndactyly of the hands and feet. Its prevalence is ϳ15.5/1,000,000 newborns (1) and accounts for about 4.5% of all cases of craniosynostosis (2). Mutations of the human fibroblast growth factor receptors (FGFRs) 1 have been identified to be the cause of a number of craniosynostosis syndromes such as Crouzon, Pfeiffer, JacksonWeiss, Apert, Beare-Stevenson, and Muenke syndromes (3-8).With rare exceptions, Apert syndrome is caused by one of the two missense mutations of the FGFR2 gene involving an amino acid substitution, S252W or P253R, in the linker region between the second and third extracellular Ig domains (4, 9, 10). S252W results from a C755G missense mutation and is more common than P253R caused by C758G in Apert patients (11), and each mutation shows differential effects on the phenotype of syndactyly and cleft palate in this syndrome (12, 13). Most of the Apert patients are sporadic cases and are exclusively affected by mutations arising in the paternal germ line (14). Apert mutation in the FGFR2 gene serves as a gain-offunction mutation by decreasing the dissociation rate of FGFs from FGFR2 (15, 16) as well as by evoking the liganddependent receptor activation. In addition to the retained ligand dependence for the receptor activation, the loss of ligand ...

Extensive histological study revealed the impairment of bone remodeling caused by mechanical stress in OPN knockout mice in a tooth movement system. Analysis of OPN promoter transgenic mice showed the mechanical stress response element(s) in the 5.5-kb upstream region. These results were also obtained with the primary cultured cells.Introduction: Mechanical loading system changes the bone architecture through the stimulation of bone remodeling by the action of a numbers of molecules. Among them, we showed that osteopontin (OPN) plays an important role in response to mechanical loading in rats with an experimental system for tooth movement. The results indicate the important role of OPN in bone remodeling. However, the molecular mechanism of OPN expression in response to mechanical stress is unknown. Materials and Methods: OPN knockout mice and transgenic mice carrying green fluorescent protein (GFP) in the control of the OPN promoter were used for analysis. Orthodontic closed coil springs were bonded to the maxillary first molars and incisors for the experimental tooth movement. Spatial expression of GFP and OPN was detected by in situ hybridization. Results: In contrast to wildtype mice, a smaller number of TRACP + cells was detected in OPN knockout mice after treatment. In GFP-OPN5.5 mice, OPN and GFP mRNA-expressing cells were detected in bone cells after treatment, and the localization of GFP was consistent with that of endogenous OPN. An increase in the co-expression of GFP and OPN was detected when primary cultured osteoblastic cells derived from the transgenic mice were exposed to strain or pressure force. Significant increase in the number of OPN + osteocyte was detected in the pressure side at 48 h after treatment. At 72 h, increase in the number of TRACP + cells was detected predominantly in the pressure side. Conclusions: Bone remodeling in response to mechanical stress was suppressed in OPN knockout mice. These results indicate the critical role of OPN in the process of bone remodeling. The analysis of GFP expression in the promoter transgenic mice indicated the presence of an in vivo mechanical stress response element in the 5.5-kb upstream region of the OPN gene.

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The mechanical force generated during tooth movement creates compressed and cell-free areas in the periodontal membrane. The way in which periodontal ligament cells disappear at the compressed area during tooth movement remains unclear. In the present study we examined whether periodontal ligament cells undergo apoptosis by mechanical stress during tooth movement using the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick-end-labelling method (TUNEL). TUNEL-positive stainings of periodontal ligament cells began to appear at the compressed areas 12 h after tooth movement, and the number of those cells reached maximum at 24 h after tooth movement. Thereafter TUNEL-positive cells disappeared at 48 h, and direct and undermining bone resorption began at the same area 72 h after tooth movement. These results showed that compressed periodontal ligament cells were eliminated by apoptosis in the early phase of tooth movement.

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