Expression of HMGB1 in the periodontal tissue subjected to orthodontic force application by Waldo's method in mice

YAP/WNT5A/FZD4 axis regulates osteogenic differentiation of human periodontal ligament cells under cyclic stretch

OBJECTIVE

To verify the role of YAP/WNT5A/FZD4 axis in stretch-induced osteogenic differentiation of hPDLCs.

BACKGROUND

During orthodontic tooth movement, differentiation of human periodontal ligament cells (hPDLCs) at the tension side of the periodontal ligament mediates new bone formation. WNT5A promotes osteogenesis and its regulator Yes-associated protein (YAP) is responsive to mechanical stimulation in hPDLCs. However, the mechanisms of YAP and WNT5A in alveolar bone remodeling remain unclear.

METHODS

Cyclic stretch was applied to hPDLCs to mimic the orthodontic stretching force. Osteogenic differentiation was determined by alkaline phosphatase (ALP) activity, Alizarin Red staining, qRT-PCR and western blotting. To detect activation of YAP and expression of WNT5A and its receptor Frizzled-4 (FZD4), western blotting, immunofluorescence, qRT-PCR and ELISA were performed. Verteporfin, Lats-IN-1, small interfering RNAs and recombinant protein were used to explore the relationship of YAP, WNT5A and FZD4, and the effect of their relationship on stretch-induced osteogenesis of hPDLCs.

RESULTS

WNT5A, FZD4 and nuclear localization of YAP were upregulated by cyclic stretch. YAP positively regulated WNT5A and FZD4 expression and osteogenic differentiation of hPDLCs under cyclic stretch by YAP inhibition or activation assay. Knockdown of WNT5A and FZD4 attenuated YAP-induced and stretch-induced osteogenic differentiation. Recombinant WNT5A rescued the suppressed osteogenic differentiation by YAP inhibitor in hPDLCs, whereas knockdown of FZD4 weakened the effect of WNT5A and amplified the suppression.

CONCLUSIONS

WNT5A/FZD4 could be positively regulated by YAP and the YAP/WNT5A/FZD4 axis mediated osteogenic differentiation of hPDLCs under cyclic stretch. This study provided further insight into the biological mechanism of orthodontic tooth movement.

Tension force causes cell cycle arrest at G2/M phase in osteocyte-like cell line MLO-Y4

Bone remodelling is the process of bone resorption and formation, necessary to maintain bone structure or for adaptation to new conditions. Mechanical loadings, such as exercise, weight bearing and orthodontic force, play important roles in bone remodelling. During the remodelling process, osteocytes play crucial roles as mechanosensors to regulate osteoblasts and osteoclasts. However, the precise molecular mechanisms by which the mechanical stimuli affect the function of osteocytes remain unclear. In the present study, we analysed viability, cell cycle distribution and gene expression pattern of murine osteocyte-like MLO-Y4 cells exposed to tension force (TF). Cells were subjected to TF with 18% elongation at 6 cycles/min for 24 h using Flexcer Strain Unit (FX-3000). We found that TF stimulation induced cell cycle arrest at G2/M phase but not cell death in MLO-Y4 cells. Differentially expressed genes (DEGs) between TF-stimulated and unstimulated cells were identified by microarray analysis, and a marked increase in glutathione-S-transferase α (GSTA) family gene expression was observed in TF-stimulated cells. Enrichment analysis for the DEGs revealed that Gene Ontology (GO) terms and Kyoto Encyclopedia Genes and Genomes (KEGG) pathways related to the stress response were significantly enriched among the upregulated genes following TF. Consistent with these results, the production of reactive oxygen species (ROS) was elevated in TF-stimulated cells. Activation of the tumour suppressor p53, and upregulation of its downstream target GADD45A, were also observed in the stimulated cells. As GADD45A has been implicated in the promotion of G2/M cell cycle arrest, these observations may suggest that TF stress leads to G2/M arrest at least in part in a p53-dependent manner.

Scleraxis upregulated by transforming growth factor-β1 signaling inhibits tension-induced osteoblast differentiation of priodontal ligament cells via ephrin A2

During tooth movement in orthodontic treatment, bone formation and resorption occur on the tension and compression sides of the alveolar bone, respectively. Although the bone formation activity increases in the periodontal ligament (PDL) on the tension side, the PDL itself is not ossified and maintains its homeostasis, indicating that there are negative regulators of bone formation in the PDL. Our previous report suggested that scleraxis (Scx) has an inhibitory effect on ossification of the PDL on the tension side through the suppression of calcified extracellular matrix formation. However, the molecular biological mechanisms of Scx-modulated inhibition of ossification in the tensioned PDL are not fully understood. The aim of the present study is to clarify the inhibitory role of Scx in osteoblast differentiation of PDL cells and its underlying mechanism. Our in vivo experiment using a mouse experimental tooth movement model showed that Scx expression was increased during early response of the PDL to tensile force. Scx knockdown upregulated expression of alkaline phosphatase, an early osteoblast differentiation marker, in the tensile force-loaded PDL cells in vitro. Transforming growth factor (TGF)-β1-Smad3 signaling in the PDL was activated by tensile force and inhibitors of TGF-β receptor and Smad3 suppressed the tensile force-induced Scx expression in PDL cells. Tensile force induced ephrin A2 (Efna2) expression in the PDL and Efna2 knockdown upregulated alkaline phosphatase expression in PDL cells under tensile force loading. Scx knockdown eliminated the tensile force-induced Efna2 expression in PDL cells. These findings suggest that the TGF-β1-Scx-Efna2 axis is a novel molecular mechanism that negatively regulates the tensile force-induced osteoblast differentiation of PDL cells.

The expression and regulation of Wnt1 in tooth movement-initiated mechanotransduction

INTRODUCTION

The Wnt signaling pathway acts as a key regulator of skeletal development and its homeostasis. However, the potential role of Wnt1 in the mechanotransduction machinery of orthodontic tooth movement-initiated bone remodeling is still unclear. Hence, this study focused on the regulatory dynamics of the Wnt1 expression in both the periodontal ligament (PDL) and osteocytes in vivo and in vitro.

METHODS

The Wnt1 expression in the orthodontically moved maxillary first molar in mice was assessed at 0, 1, and 5 days, on both the compression and tension sides. Primary isolated human PDL (hPDL) fibroblasts, as well as murine long-bone osteocyte-Y4 (MLO-Y4) cells, were exposed to continuous compressive force and static tensile force.

RESULTS

The relative quantification of immunodetection showed that orthodontic tooth movement significantly stimulated the Wnt1 expression in both the PDL and alveolar osteocytes on the tension side on day 5, whereas the expression on the compression side did not change. This increase in the Wnt1 expression, shown in vivo, was also noted after the application of 12% static tensile force in isolated hPDL fibroblasts and 20% in MLO-Y4 cells. In contrast, a compressive force led to the attenuation of the Wnt1 gene expression in both hPDL fibroblasts and MLO-Y4 cells in a force-dependent manner. In the osteocyte-PDL coculture system, recombinant sclerostin attenuated Wnt1 in PDL, whereas the antisclerostin antibody upregulated its gene expression, indicating that mechanically-driven Wnt1 signaling in PDL might be regulated by osteocytic sclerostin.

CONCLUSIONS

Our findings provide that Wnt1 signaling plays a vital role in tooth movement-initiated bone remodeling via innovative mechanotransduction approaches.

Extreme intrusive force affects the expression of c-Fos and matrix metallopeptidase 9 in human dental pulp tissues

This study aimed to investigate the expression of c-Fos and matrix metallopeptidase 9 (MMP-9) in dental pulp of patients receiving orthodontic treatment via wire appliance.Fifteen patients (30 teeth in total) were randomly assigned to five groups: t = 0, t = 1, t = 4, t = 8 and t = 12 (n = 6). The first maxillary premolars of patients in the t = 0 group were extracted without any orthodontic treatment. An intrusive force of 300 g was applied on first maxillary premolars in the other four groups via wire appliances. This force was maintained for 1 week for t = 1 group, 4 weeks for t = 4 group, 8 weeks for t = 8 group, or 12 weeks for t = 12 group, before the teeth were extracted.The expression of c-Fos and MMP-9 in the pulps of each group was analyzed by immunohistochemical staining and real-time PCR. The relationship in the protein expression between c-Fos and MMP-9 in the dental pulp was analyzed by Pearson correlation analysis.Intrusive force of 300 g increased the expression of both c-Fos and MMP-9 in the dental pulp. The protein expression of MMP-9 in the dental pulp was significantly correlated with the expression of c-Fos (P < .001).Extreme intrusive force upregulates c-Fos and MMP-9 expression in the dental pulp. Moreover, protein expression of c-Fos and MMP-9 is significantly correlated under intrusive force.

HMGB1 mediates the development of tendinopathy due to mechanical overloading

Mechanical overloading is a major cause of tendinopathy, but the underlying pathogenesis of tendinopathy is unclear. Here we report that high mobility group box1 (HMGB1) is released to the tendon extracellular matrix and initiates an inflammatory cascade in response to mechanical overloading in a mouse model. Moreover, administration of glycyrrhizin (GL), a naturally occurring triterpene and a specific inhibitor of HMGB1, inhibits the tendon’s inflammatory reactions. Also, while prolonged mechanical overloading in the form of long-term intensive treadmill running induces Achilles tendinopathy in mice, administration of GL completely blocks the tendinopathy development. Additionally, mechanical overloading of tendon cells in vitro induces HMGB1 release to the extracellular milieu, thereby eliciting inflammatory and catabolic responses as marked by increased production of prostaglandin E₂ (PGE₂) and matrix metalloproteinase-3 (MMP-3) in tendon cells. Application of GL abolishes the cellular inflammatory/catabolic responses. Collectively, these findings point to HMGB1 as a key molecule that is responsible for the induction of tendinopathy due to mechanical overloading placed on the tendon.

Expression of biological mediators during orthodontic tooth movement: A systematic review

OBJECTIVES

The aim of the present systematic review was to offer a timeline of the events taking place during orthodontic tooth movement(OTM).

MATERIALS AND METHODS

Electronic databases PubMed, Web of Science and EMBASE were searched up to November 2017. All studies describing the expression of signaling proteins in the periodontal ligament(PDL) of teeth subjected to OTM or describing the expression of signaling proteins in human cells of the periodontal structures subjected to static mechanical loading were considered eligible for inclusion for respectively the in-vivo or the in-vitro part. Risk of bias assessment was conducted according to the validated SYRCLE's RoB tool for animal studies and guideline for assessing quality of in-vitro studies for in-vitro studies.

RESULTS

We retrieved 7583 articles in the initial electronic search, from which 79 and 51 were finally analyzed. From the 139 protein investigated, only the inflammatory proteins interleukin(IL)-1β, cyclooxygenase(COX)-2 and prostaglandin(PG)-E2, osteoblast markers osteocalcin and runt-related transcription factor(RUNX)2, receptor activator of nuclear factor kappa-B ligand(RANKL) and osteoprotegerin(OPG) and extracellular signal-regulated kinases(ERK)1/2 are investigated in 10 or more studies.

CONCLUSION

The investigated proteins were presented in a theoretical model of OTM. We can conclude that the cell activation and differentiation and recruitment of osteoclasts is mediated by osteocytes, osteoblasts and PDL cells, but that the osteogenic differentiation is only seen in stem cell present in the PDL. In addition, the recently discovered Ephrin/Ephs seem to play an role parallel with the thoroughly investigated RANKL/OPG system in mediating bone resorption during OTM.

Effect of corticision on orthodontic tooth movement in a rat model as assessed by RNA sequencing

Corticision is a common technique to accelerate orthodontic tooth movement; however, not much is known about the underlying mechanisms. In this study, we investigated the mechanism of alveolar tissue remodeling after corticision in a rat model of tooth movement (TM) by analyzing the differential transcriptome. A total of 36 male rats were equally divided into TM and TM with corticision (TM+C) groups. Alveolar bone response was examined using micro-computed tomography (micro-CT). Osteoclasts and osteoblasts were quantified on tartrate-resistant acid phosphatase (TRAP) and Goldner's trichrome staining. The transcriptomes of alveolus around the left maxillary first molar were determined on RNA sequencing (RNA-Seq), and the expression of selected differentially expressed genes (DEGs) validated on quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). Immunohistochemical examination of alveolar tissue was performed to examine the expressions of correlative proteins of the selected signaling pathway in the TM and TM+C groups. The ratio of bone volume to total volume (BV/TV), and the trabecular number (Tb.N) were significantly decreased, while the movement distance and the trabecular separation (Tb.Sp) was significantly increased in the TM+C group. However, no significant between-group difference in trabecular thickness (Tb.Th) was observed. On histomorphometric analysis, a significant increase in the number of osteoclasts and increased bone resorption was observed in the TM+C group. A total of 399 DEGs were identified on RNA-SEq. Eleven selected genes were confirmed on qRT-PCR, which included components of the Ras signaling pathway. Four proteins of the Ras signaling pathway showed a higher expression in the TM+C group. Our findings indicate that corticision may speed up orthodontic tooth movement by accelerating osteoclastogenesis mediated via the Ras signaling pathway.

The effect of calcitriol on high mobility group box 1 expression in periodontal ligament cells during orthodontic tooth movement in rats

High mobility group box 1 (HMGB1) is a late inflammatory cytokine that plays an important role in periodontal tissue remodeling during orthodontic tooth movement. Calcitriol (1,25-dihydroxyvitamin D3 [1α,25 (OH)2D3]) is a systemic calcium-regulating hormone shown to downregulate expression of multiple proinflammatory cytokines in human periodontal ligament cells in response to orthodontic force. The purpose of this study was to investigate the effect of 1α,25(OH)2D3 on the expression of HMGB1 in periodontal ligament (PDL) cells during orthodontic tooth movement. Seven-week-old male Wistar rats were used for experimentation. Tooth movement was assessed using a nickel-titanium coil spring to apply mechanical loading to the tooth for 5 days. This was followed by administration of either 1α,25(OH)2D3 or normal saline by gavage every other day for up to 28 days. Immunohistochemistry was used to analyze the expression of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6 and HMGB1. After discontinuation of orthodontic force, expression of the early inflammatory cytokines IL-6 and TNF-α were time-dependently reduced in the 1α,25(OH)2D3 group compared with the control group at each time point. Similarly, expression of HMGB1 was decreased over time in both the 1α,25(OH)2D3 and normal saline groups, and 1α,25(OH)2D3 administration enhanced this decline. These findings indicate that administration of 1α,25(OH)2D3 might provide a favorable microenvironment for orthodontic tooth movement by downregulating expression of HMGB1 in PDL cells.

Altered distribution of HMGB1 in the periodontal ligament of periostin-deficient mice subjected to Waldo's orthodontic tooth movement

Periostin is essential for the integrity and function of the periodontal ligament (PDL), and periostin knockout is related to an enhanced inflammatory status in PDL. High mobility group box 1 (HMGB1), a late inflammatory cytokine, is up-regulated in PDL cells in response to mechanical stress. This study aimed to investigate the effect of periostin deficiency (Pn-/-) on HMGB1 expression in PDL during orthodontic tooth movement. We used 8-week-old male mice homozygous for the disrupted periostin gene and their wild-type (WT) littermates. Tooth movement was performed according to Waldo's method, in which 0.5-mm-thick elastic bands were inserted between the first and second upper molars of anesthetized mice. After 3 days of mechanical loading, mice were fixed by transcardial perfusion of 4% paraformaldehyde in phosphate buffer, and the maxilla was extracted for histochemical analyses. Compared with the WT group, Pn-/- mice showed higher basal expression of HMGB1 in the absence of mechanical loading. Following 3 days of orthodontic tooth movement, the PDL in the compression side of both groups was almost replaced by cell-free hyaline zones, and Pn-/- mice showed a much wider residual PDL than WT mice. In the tension side, the number of HMGB1-positive cells in PDL in both Pn-/- and WT groups increased remarkably without a significant difference between the two groups. Our findings suggest an inhibitory effect of periostin on HMGB1 production by PDL and confirmed the critical role of periostin in integrity of PDL collagen fibrils during orthodontic tooth movement, although mechanical loading is the predominant stimulant of HMGB1 expression relative to periostin deficiency.