CREB activation affects mesenchymal stem cell migration and differentiation in periodontal tissues due to orthodontic force.

During the orthodontic tooth movement, cells in periodontal ligament could differentiate into osteoblasts to synthesize alveolar bone as well as affect the proliferation, migration and differentiation of mesenchymal stem cells, which also contribute to bone remodeling. However, the mechanism is still largely elusive. Here, we evaluated the expression of CREB at the tension site of mouse periodontal ligament under orthodontic mechanical strain and in the cyclic tension strain treated human periodontal ligament cells. Then, through gain and loss of function analysis, we revealed that CREB in PDLCs promotes SDF-1 and FGF2 secretion, which enhance the migration and osteoblastic differentiation of BMSCs. We further discovered that CREB transcriptionally activates FGF2 and SDF-1 expressions by binding to the promoter regions.In conclusion, this study confirms that CREB is an upregulated gene in periodontal ligament under orthodontic tension strain stimulation and plays an important role in regulating BMSCs' physiological activity in orthodontic tension strain-induced bone formation.

Cyclic Stretch Enhances Osteogenic Differentiation of Human Periodontal Ligament Cells via YAP Activation.

Periodontal remodeling and alveolar bone resorption and formation play essential roles during orthodontic tooth movement (OTM). In the process, human periodontal ligament cells (HPDLCs) sense and respond to orthodontic forces, contributing to the alveolar bone formation. However, the underlying mechanism in this process is not fully elucidated. In the present study, cyclic stress stimulus was applied on HPDLCs to mimic the orthodontic forces during OTM. Our results demonstrated that cyclic stretch promoted the osteogenic differentiation of HPDLCs. Moreover, our data suggested that yes-associated protein (YAP), the Hippo pathway effector, which also involved in mechanical signaling transduction, was activated as we found that the nuclear translocation of YAP was significantly increased in the cyclic stress treated HPDLCs. The mRNA expression of CTGF and CYR61, the target genes of YAP, was also remarkably increased. Furthermore, knockdown of YAP suppressed the cyclic stretch induced osteogenesis in HPDLCs, while overexpression of YAP in HPDLCs enhanced osteogenesis. We also noticed that YAP activities could be suppressed by the ROCK and nonmuscle myosin II inhibitors, Y-27632 and Blebbistatin. The inhibitors also significantly inhibited the cyclic stretch induced osteogenesis in HPDLCs. Finally, in the murine OTM model, our results revealed that YAP was upregulated and nuclearly translocated in the PDLCs at the tension side. In summary, our present study demonstrated that cytoskeleton remodeling induced activation of YAP signaling pathway was crucial for the cyclic stretch-induced osteogenesis of HPDLCs, which might play important roles during OTM.

Wnt5a mediated canonical Wnt signaling pathway activation in orthodontic tooth movement: possible role in the tension force-induced bone formation.

Orthodontic tooth movement (OTM) is associated with bone remodeling mediated by orthodontic mechanical loading. Increasing studies reported that Wnt signaling played crucial roles in mechanical stimuli induced bone remodeling. However, little is known about the involvement of Wnt signaling in orthodontic force-induced bone formation during OTM. In virtue of the OTM mice model as we previously reported, where new bone formation was determined by micro-CT and immunoreactivity of osteocalcin and osterix, we explored the activation of Wnt signaling pathway during OTM. Our results proved the nuclei translocation of ß-catenin, suggesting the activation of canonical Wnt signaling pathway in the periodontal ligament cells (PDLCs) near the alveolar bone at the tension site (TS). Moreover, the immunoreactivity of Wnt5a, but not Wnt3a in PDLCs indicated the activation of canonical Wnt pathway might be mediated by Wnt5a, but not Wnt3a as in most cases. The co-location of Wnt5a and ß-catenin that was evidenced by double labeling immunofluorescence staining further supported the hypothesis. In addition, the high expression of FZD4 and LRP5 in PDLCs at TS of periodontium suggested that the activation of Wnt signaling pathway was mediated by these receptors. The negligible expression of ROR2 also indicated that canonical but not non-canonical Wnt signaling pathway was activated by Wnt5a, since previous studies demonstrated that the activation of canonical/non-canonical Wnt signaling pathway was largely dependent on the receptors. In summary, we here reported that Wnt5a mediated activation of canonical Wnt signaling pathway might contribute to the orthodontic force induced bone remodeling.