Effect of age on orthodontic tooth movement in mice.

Background/purpose: The number of middle-aged and elderly orthodontic patients is increasing due to changes in age composition. It is important to investigate the detailed mechanisms of bone remodeling in orthodontic tooth movement (OTM) in the elderly. However, there are few reports on the mechanism of tooth movement in the elderly. The purpose of the present study was to analyze OTM and osteoclastogenesis in aged mice and to elucidate the mechanism. Materials and methods: It has been reported that tumor necrosis factor (TNF)-α plays an important role in osteoclast formation and OTM. First, 8-week-old and 78-week-old male C57BL/6J mice were subcutaneously injected with TNF-α into the calvaiae, and micro-CT, tartrate-resistant acid phosphatase (TRAP) staining, and real-time PCR were performed to evaluate osteoclast formation and bone resorption. Furthermore, osteoclastogenesis by TNF-α and receptor activator of nuclear factor-kappa B ligand (RANKL) using bone marrow cells was evaluated in vitro. Finally, a nickel-titanium closed-coil spring was attached, mesial movement of the maxillary left first molar was performed, and tooth movement distance and osteoclast formation were evaluated. Results: Compared to 8-week-old mice, 78-week-old mice had decreased TNF-α-induced bone resorption, osteoclastogenesis, and TRAP and cathepsin K expression in the calvariae. In vitro osteoclast formation also decreased in 78-week-old mice. Furthermore, tooth movement distance and osteoclastogenesis were reduced. Conclusion: OTM decreased in aged mice, which was shown to be caused by a decrease in osteoclastogenesis. Therefore, it was suggested that it is necessary to keep in mind that tooth movement may be suppressed when treating elderly patients.

(D-Ala2)GIP Inhibits Inflammatory Bone Resorption by Suppressing TNF-α and RANKL Expression and Directly Impeding Osteoclast Formation.

Glucose-insulinotropic polypeptide (GIP) is an incretin hormone that induces insulin secretion and decreases blood glucose levels. In addition, it has been reported to suppress osteoclast formation. Native GIP is rapidly degraded by dipeptidyl peptidase-4 (DPP-4). (D-Ala2)GIP is a newly developed GIP analog that demonstrates enhanced resistance to DPP-4. This study aimed to evaluate the influence of (D-Ala2)GIP on osteoclast formation and bone resorption during lipopolysaccharide (LPS)-induced inflammation in vivo and in vitro. In vivo, mice received supracalvarial injections of LPS with or without (D-Ala2)GIP for 5 days. Osteoclast formation and bone resorption were evaluated, and TNF-α and RANKL expression were measured. In vitro, the influence of (D-Ala2)GIP on RANKL- and TNF-α-induced osteoclastogenesis, LPS-triggered TNF-α expression in macrophages, and RANKL expression in osteoblasts were examined. Compared to the LPS-only group, calvariae co-administered LPS and (D-Ala2)GIP led to less osteoclast formation, lower bone resorption, and decreased TNF-α and RANKL expression. (D-Ala2)GIP inhibited osteoclastogenesis induced by RANKL and TNF-α and downregulated TNF-α expression in macrophages and RANKL expression in osteoblasts in vitro. Furthermore, (D-Ala2)GIP suppressed the MAPK signaling pathway. The results suggest that (D-Ala2)GIP dampened LPS-triggered osteoclast formation and bone resorption in vivo by reducing TNF-α and RANKL expression and directly inhibiting osteoclastogenesis.

Generating Bone Marrow Chimeric Mouse Using GPR120 Deficient Mouse for the Study of DHA Inhibitory Effect on Osteoclast Formation and Bone Resorption.

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that exerts physiological effects via G protein-coupled receptor 120 (GPR120). In our previous studies, we figured out the inhibitory effects of DHA on TNF-α (Tumor necrosis factor-α)-induced osteoclastogenesis via GPR120 in vivo. Moreover, DHA directly suppressed RANKL expression in osteoblasts via GPR120 in vitro. In this study, we generated bone marrow chimeric mice using GPR120 deficient mice (GPR120-KO) to study the inhibitory effects of DHA on bone resorption and osteoclast formation. Bone marrow cells of wild-type (WT) or GPR120-KO mice were transplanted into irradiated recipient mice, which were WT or GPR120 deficient mice. The resulting chimeric mice contained stromal cells from the recipient and bone marrow cells, including osteoclast precursors, from the donor. These chimeric mice were used to perform a series of histological and microfocus computed tomography (micro-CT) analyses after TNF-α injection for induction of osteoclast formation with or without DHA. Osteoclast number and bone resorption were found to be significantly increased in chimeric mice, which did not express GPR120 in stromal cells, compared to chimeric mice, which expressed GPR120 in stromal cells. DHA was also found to suppress specific signaling pathways. We summarized that DHA suppressed TNF-α-induced stromal-dependent osteoclast formation and bone resorption via GPR120.

Three-dimensional morphologic analysis of the maxillary alveolar bone after anterior tooth retraction with temporary anchorage devices.

OBJECTIVES: To investigate three-dimensional (3D) morphologic changes in the alveolar bone around the maxillary central incisors of patients who underwent premolar extraction and subsequent anterior tooth retraction using temporary anchorage devices (TADs). MATERIALS AND METHODS: The subjects consisted of 16 patients with bimaxillary protrusion. The maxillary anterior teeth were retracted using sliding or loop mechanics and TADs for anchorage reinforcement. Cephalograms and computed tomography scans taken pretreatment and posttreatment were registered with respect to the palatal structures. The movement of the maxillary central incisors and morphologic changes in the anterior alveolar bone were evaluated quantitatively. RESULTS: Displacement in the palatal direction was observed in the alveolar bone around the incisors and the interdental septum. The displacement and bone remodeling/tooth movement ratio were larger on the labial side than the palatal side, and decreased progressively from the crest to apex level. The bone thickness was significantly increased on the labial side and decreased on the palatal side. CONCLUSIONS: Regional differences exist in morphologic changes of the alveolar bone during anterior tooth retraction using TADs. Attention should be paid to the crest region of the palatal alveolar bone because of its small original thickness and low remodeling activity.

Azilsartan inhibits inflammation-triggered bone resorption and osteoclastogenesis in vivo via suppression of TNF-α expression in macrophages.

Introduction: Hypertension is a major risk factor for cardiovascular disease (CVD) and is associated with increased bone loss due to excessive activity of the local renin-angiotensin system (RAS). Angiotensinogen/Angiotensin (ANG) II/Angiotensin II type 1 receptor (AT1R) axis is considered as the core axis regulating RAS activity. Azilsartan is an FDA-approved selective AT1R antagonist that is used to treat hypertension. This study aimed to determine whether azilsartan affects formation of osteoclast, resorption of bone, and the expression of cytokines linked with osteoclastogenesis during lipopolysaccharide (LPS)-triggered inflammation in vivo. Methods: In vivo, following a 5-day supracalvarial injection of LPS or tumor necrosis factor-alpha (TNF-α) with or without azilsartan, the proportion of bone resorption and the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells, which are identified as osteoclasts on mice calvariae were counted. The mRNA expression levels of TRAP, cathepsin K, receptor activator of NF-κB ligand (RANKL), and TNF-α were also evaluated. In vitro, the effect of azilsartan (0, 0.01, 0.1, 1, and 10 µM) on RANKL and TNF-α-triggered osteoclastogenesis were investigated. Also, whether azilsartan restrains LPS-triggered TNF-α mRNA and protein expression in macrophages and RANKL expression in osteoblasts were assessed. Furthermore, western blotting for analysis of mitogen-activated protein kinases (MAPKs) signaling was conducted. Results: Azilsartan-treated calvariae exhibited significantly lower bone resorption and osteoclastogenesis than those treated with LPS alone. In vivo, LPS with azilsartan administration resulted in lower levels of receptor activator of RANKL and TNF-α mRNA expression than LPS administration alone. Nevertheless, azilsartan did not show inhibitory effect on RANKL- and TNF-α-triggered osteoclastogenesis in vitro. Compared to macrophages treated with LPS, TNF-α mRNA and protein levels were lower in macrophages treated by LPS with azilsartan. In contrast, RANKL mRNA and protein expression levels in osteoblasts were the same in cells co-treated with azilsartan and LPS and those exposed to LPS only. Furthermore, azilsartan suppressed LPS-triggered MAPKs signaling pathway in macrophages. After 5-day supracalvarial injection, there is no difference between TNF-α injection group and TNF-α with azilsartan injection group. Conclusion: These findings imply that azilsartan prevents LPS-triggered TNF-α production in macrophages, which in turn prevents LPS-Triggered osteoclast formation and bone resorption in vivo.

CD40-CD40 ligand interaction between periodontal ligament cells and cementoblasts enhances periodontal tissue remodeling in response to mechanical stress.

OBJECTIVE: We analyzed the localization and expression of Cluster of differentiation 40 ligand (CD40L) in murine periodontal tissue applied with the orthodontic force to determine the CD40L-expressing cells under mechanical stress. Furthermore, we investigated whether CD40-CD40L interaction played an important role in transducing mechanical stress between periodontal ligament (PDL) cells and cementoblasts and remodeling the periodontal tissue for its homeostasis. BACKGROUND: PDL is a complex tissue that contains heterogeneous cell populations and is constantly exposed to mechanical stress, such as occlusal force. CD40 is expressed on PDL cells and upregulated under mechanical stress. However, whether its ligand, CD40L, is upregulated in periodontal tissue in response to mechanical stress, and which functions the CD40-CD40L interaction induces by converting the force to biological functions between the cement-PDL complex, are not fully understood. METHODS: The orthodontic treatment was applied to the first molars at the left side of the upper maxillae of mice using a nickel-titanium closed-coil spring. Immunohistochemistry was performed to analyze the localization of CD40L in the periodontal tissue under the orthodontic force. Human cementoblasts (HCEM) and human PDL cells were stretched in vitro and analyzed CD40L and CD40 protein expression using flow cytometry. A GFP-expressing CD40L plasmid vector was transfected into HCEM (CD40L-HCEM). CD40L-HCEM was co-cultured with human PDL cells with higher alkaline phosphatase (ALP) activity (hPDS) or lower ALP (hPDF). After co-culturing, cell viability and proliferation were analyzed by propidium iodide (PI) staining and bromodeoxyuridine (BrdU) assay. Furthermore, the mRNA expression of cytodifferentiation- and extracellular matrix (ECM)-related genes was analyzed by real-time PCR. RESULTS: Immunohistochemistry demonstrated that CD40L was induced on the cells present at the cementum surface in periodontal tissue at the tension side under the orthodontic treatment in mice. The flow cytometry showed that the in vitro-stretching force upregulated CD40L protein expression on HCEM and CD40 protein expression on human PDL cells. Co-culturing CD40L-HCEM with hPDF enhanced cell viability and proliferation but did not alter the gene expression related to cytodifferentiation and ECM. In contrast, co-culturing CD40L-HCEM with hPDS upregulated cytodifferentiation- and ECM-related genes but did not affect cell viability and proliferation. CONCLUSION: We revealed that in response to a stretching force, CD40L expression was induced on cementoblasts. CD40L on cementoblasts may interact with CD40 on heterogeneous PDL cells at the necessary time and location, inducing cell viability, proliferation, and cytodifferentiation, maintaining periodontal tissue remodeling and homeostasis.

Fermented Rice Bran Supplementation Inhibits LPS-Induced Osteoclast Formation and Bone Resorption in Mice.

Fermented rice bran (FRB) is known to have numerous beneficial bioactivities, amongst which is its anti-inflammatory properties when used as a supplement. To determine its effects, we examined osteoclastogenesis and bone resorption caused by injections of lipopolysaccharide (LPS), using mice with and without FRB supplementation. The results were favorable: those that received FRB showed reduced osteoclast numbers and bone resorption compared to those with the control diet. Notably, receptor activator of NF-κB ligand (RANKL) and tumor necrosis factor-α (TNF-α) mRNA levels were shown to be lower in the LPS-treated animals with FRB supplementation. FRB's inhibitory effect on RANKL- and TNF-α-induced osteoclastogenesis was further confirmed in vitro. In culture, macrophages exhibited decreased TNF-α mRNA levels when treated with FRB extract and LPS versus treatment with LPS alone, but there was no significant change in RANKL levels in osteoblasts. We can conclude that FRB supplementation dampens the effect of LPS-induced osteoclastogenesis and bone resorption by controlling TNF-α expression in macrophages and the direct inhibition of osteoclast formation.

The osteocyte and its osteoclastogenic potential.

The skeleton is an organ of dual functionality; on the one hand, it provides protection and structural competence. On the other hand, it participates extensively in coordinating homeostasis globally given that it is a mineral and hormonal reservoir. Bone is the only tissue in the body that goes through strategically consistent bouts of bone resorption to ensure its integrity and organismal survival in a temporally and spatially coordinated process, known as bone remodeling. Bone remodeling is directly enacted by three skeletal cell types, osteoclasts, osteoblasts, and osteocytes; these cells represent the acting force in a basic multicellular unit and ensure bone health maintenance. The osteocyte is an excellent mechanosensory cell and has been positioned as the choreographer of bone remodeling. It is, therefore, not surprising that a holistic grasp of the osteocyte entity in the bone is warranted. This review discusses osteocytogenesis and associated molecular and morphological changes and describes the osteocytic lacunocanalicular network (LCN) and its organization. We highlight new knowledge obtained from transcriptomic analyses of osteocytes and discuss the regulatory role of osteocytes in promoting osteoclastogenesis with an emphasis on the case of osteoclastogenesis in anosteocytic bones. We arrive at the conclusion that osteocytes exhibit several redundant means through which osteoclast formation can be initiated. However, whether osteocytes are true "orchestrators of bone remodeling" cannot be verified from the animal models used to study osteocyte biology in vivo. Results from studying osteocyte biology using current animal models should come with the caveat that these models are not osteocyte-specific, and conclusions from these studies should be interpreted cautiously.

Craniofacial Characteristics and Orthodontic Treatment of Diamond Blackfan Syndrome: Two Case Reports.

Diamond Blackfan anemia (DBA) is a chronic congenital form of erythrocytic hypoplasia in which erythroid precursor cell levels are low. DBA reflects ribosomal dysfunction and is accompanied by hematopoietic cell apoptosis, anemia, and various somatic symptoms. We report the characteristic symptoms of the craniofacial region and the orthodontic treatments of two DBA cases. Case 1 was a 12-year-old female. The typical physical and facial characteristics of DBA were lacking. On initial examination, she exhibited a skeletal Class II jaw and end to end molar relationships and a large overjet. An edgewise appliance was placed after extraction of the first maxillary premolars. After 3 years and 11 months, an appropriate overjet and overbite, rigid intercuspation, and an acceptable profile were evident without any clinical adverse effects. Case 2 was a 13-year-old female. She exhibited a skeletal Class I jaw relationship, a spaced dental arch, the maxillofacial dysplasia characteristic of Binder syndrome, hypoplasia of the right mandibular condyle, and labial protrusions of the maxillary and mandibular incisors. We placed an edgewise appliance and after 1 year and 7 months, the occlusion was optimal in the absence of any adverse effects. Our two DBA cases exhibited a broad spectrum of physical and dentofacial symptoms. Patients with DBA are often prescribed combined steroid/bisphosphonate therapies. Both agents are likely to affect alveolar bone remodeling after tooth extraction and orthodontic tooth movement. Careful consideration of medication with reference to various dentofacial characteristics is necessary.

Titanium nanotopography induces osteocyte lacunar-canalicular networks to strengthen osseointegration.

Osteocyte network architecture is closely associated with bone turnover. The cellular mechanosensing system regulates osteocyte dendrite formation by enhancing focal adhesion. Therefore, titanium surface nanotopography might affect osteocyte network architecture and improve the peri-implant bone tissue quality, leading to strengthened osseointegration of bone-anchored implants. We aimed to investigate the effects of titanium nanosurfaces on the development of osteocyte lacunar-canalicular networks and osseointegration of dental implants. Alkaline etching created titanium nanosurfaces with anisotropically patterned dense nanospikes, superhydrophilicity, and hydroxyl groups. MLO-Y4 mouse osteocyte-like cells cultured on titanium nanosurfaces developed neuron-like dendrites with increased focal adhesion assembly and gap junctions. Maturation was promoted in osteocytes cultured on titanium nanosurfaces compared to cells cultured on machined or acid-etched micro-roughened titanium surfaces. Osteocytes cultured in type I three-dimensional collagen gels for seven days on nano-roughened titanium surfaces displayed well-developed interconnectivity with highly developed dendrites and gap junctions compared to the poor interconnectivity observed on the other titanium surfaces. Even if superhydrophilicity and hydroxyl groups were maintained, the loss of anisotropy-patterned nanospikes reduced expression of gap junction in osteocytes cultured on alkaline-etched titanium nanosurfaces. Four weeks after placing the titanium nanosurface implants in the upper jawbone of wild-type rats, osteocytes with numerous dendrites were found directly attached to the implant surface, forming well-developed lacunar-canalicular networks around the nano-roughened titanium implants. The osseointegration strength of the nano-roughened titanium implants was significantly higher than that of the micro-roughened titanium implants. These data indicate that titanium nanosurfaces promote osteocyte lacunar-canalicular network development via nanotopographical cues and strengthen osseointegration. STATEMENT OF SIGNIFICANCE: The clinical stability of bone-anchoring implant devices is influenced by the bone quality. The osteocyte network potentially affects bone quality and is established by the three-dimensional (3D) connection of neuron-like dendrites of well-matured osteocytes within the bone matrix. No biomaterials are known to regulate formation of the osteocyte network. The present study provides the first demonstration that titanium nanosurfaces with nanospikes created by alkali-etching treatment enhance the 3D formation of osteocyte networks by promoting osteocyte dendrite formation and maturation by nanotopographic cues, leading to strengthened osseointegration of titanium implants. Osteocytes attached to the titanium nanosurfaces via numerous cellular projections. The success of osteocyte regulation by nanotechnology paves the way for development of epoch-making technologies to control bone quality.

Effects of anti-mouse RANKL antibody on orthodontic tooth movement in mice.

Background/purpose: Orthodontic tooth movement is achieved by alveolar bone remodeling, and therefore the balance of bone resorption and formation is important. Receptor activator of nuclear factor-κB ligand (RANKL) plays a crucial role in bone resorption. We previously reported that tumor necrosis factor-α (TNF-α) is also important in bone resorption during tooth movement. In this study, we focused on bone and root resorption during orthodontic tooth movement in mice using anti-mouse RANKL antibody (anti-mRANKL ab). Materials and methods: Anti-mRANKL ab was administered intraperitoneally to mice that subsequently underwent orthodontic tooth movement. After 10 days, tissues around the moved teeth were histologically evaluated. To confirm the effects of anti-mRANKL ab on TNF-α induced bone resorption, TNF-α was administered with and without anti-mRANKL ab into the supracalvaria and the sutures of the calvaria were histologically evaluated. Results: Orthodontic tooth movement was suppressed in mice treated with anti-mRANKL ab. Root resorption was observed after orthodontic tooth movement, but not in mice treated with anti-mRANKL ab. In the calvarial experiment, the number of TRAP-positive cells in the calvarial sutures was lower in mice administered TNF-α with anti-mRANKL ab than in mice administered TNF-α alone. Conclusion: Our findings suggest that anti-mRANKL ab suppressed orthodontic tooth movement. This needs to be considered when orthodontic tooth movement is required in patients using anti-RANKL antibody.

Enhancement of orthodontic tooth movement and root resorption in ovariectomized mice.

Background/purpose: As the number of patients with osteoporosis requiring orthodontic treatment is increasing with the aging of society, it is necessary to evaluate the relations between bone metabolism in old age and orthodontic tooth movement (OTM). However, the effects of changes in bone metabolism due to osteoporosis on OTM and root resorption are still unclear. Therefore, we investigated the effects of OTM and root resorption in a mouse ovariectomy (OVX)-induced osteoporosis model. Materials and methods: Eight-week-old female wild-type mice underwent OVX or sham surgery (Sham) as controls. One month after treatment, a nickel titanium coil spring was used to apply a mesial force to the maxillary left first molars of OVX or Sham mice for 12 days. The distance between the maxillary first molar and the second molar changed due to OTM and osteoclast formation was evaluated. The odontoclast formation and root resorption along the root surface of the distobuccal root of the first molar was also evaluated by histological analysis and scanning electron microscopy. Results: Distance of tooth movement and osteoclast formation were significantly increased in OVX mice compared to Sham controls. Furthermore, root resorption in the mesial surface of the distal molars induced by orthodontic force was significantly increased in OVX mice. Conclusion: The amount of OTM was significantly increased, and the accompanying root resorption was also increased in OVX mice. Therefore, attention should be paid to the risk of root resorption associated with orthodontic treatment in patients with osteoporosis.

Salt-Sensitive Hypertension Induces Osteoclastogenesis and Bone Resorption via Upregulation of Angiotensin II Type 1 Receptor Expression in Osteoblasts.

Hypertension is a chronic-low grade inflammatory disease, which is known to be associated with increased bone loss. Excessive activity of the local renin-angiotensin system (RAS) in bone leads to increased bone resorption. As inflammatory cytokines may activate RAS components, we hypothesized that the elevated proinflammatory cytokine levels in hypertension activate bone RAS and thus lead to increased bone resorption. To investigate whether salt-sensitive hypertension (SSHTN) induces osteoclastogenesis and bone resorption, we generated a model of SSHTN in C57BL/6J mice by post-N ω-nitro-l-arginine methyl ester hydrochloride (l-NAME) high-salt challenge. SSHTN led to the reduction of distal femur trabecular number and bone volume fraction, while trabecular separation of femoral bone showed a significant increase, with no change in cortical thickness. Histomorphometric examination showed a significant reduction in trabecular bone volume fraction with an increased number of multinucleated tartrate-resistant acid phosphatase (TRAP)-positive cells and increased osteoclast surface fraction in the trabecular distal femur of hypertensive mice. Furthermore, analysis of gene expression in bone tissue revealed that TRAP and RANKL/OPG mRNA were highly expressed in hypertensive mice. TNF-α and angiotensin II type 1 receptor (AGTR1) mRNA and protein expression were also upregulated in SSHTN mice. These observations suggested that TNF-α may have an effect on AGTR1 expression leading to osteoclast activation. However, TNF-α stimulation did not promote AGTR1 mRNA expression in osteoclast precursors in culture, while TNF-α increased AGTR1 mRNA expression in osteoblast culture by activation of downstream p38. Angiotensin II was also shown to increase TNF-α-induced RANKL/OPG mRNA expression in primary osteoblast culture and osteoclastogenesis in a TNF-α-primed osteoblast and osteoclast precursor co-culture system. In addition, local injection of lipopolysaccharide into the supracalvariae of SSHTN mice markedly promoted osteoclast and bone resorption. In conclusion, mice with SSHTN show increased osteoclastogenesis and bone resorption due mainly to increased TNF-α and partly to the upregulation of AGTR1 in osteoblasts.

Micro-Osteoperforations Induce TNF-α Expression and Accelerate Orthodontic Tooth Movement via TNF-α-Responsive Stromal Cells.

Micro-osteoperforations (MOPs) have been reported to accelerate orthodontic tooth movement (OTM), and tumor necrosis factor (TNF)-α has been reported to play a crucial role in OTM. In this report, the influence of MOPs during OTM was analyzed. We evaluated the expression of TNF-α with and without MOPs by RT-PCR analysis. A Ni-Ti closed coil spring was fixed between the maxillary left first molar and the incisors as an OTM mouse model to move the first molar in the mesial direction. MOPs were prepared on the lingual side and mesial side of the upper first molars. Furthermore, to investigate the target cell of TNF-α for osteoclast formation during OTM with MOPs in vivo, we created four types of chimeric mice in which bone marrow of wild-type (WT) or TNF receptor 1- and 2-deficient mice (KO) was transplanted into lethally irradiated WT or KO mice. The results showed that MOPs increased TNF-α expression, the distance of tooth movement and osteoclast formation significantly. Furthermore, mice with TNF-α-responsive stromal cells showed a significant increase in tooth movement and number of osteoclasts by MOPs. We conclude that MOPs increase TNF-α expression, and tooth movement is dependent on TNF-α-responsive stromal cells.

Role of the Interaction of Tumor Necrosis Factor-α and Tumor Necrosis Factor Receptors 1 and 2 in Bone-Related Cells.

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine expressed by macrophages, monocytes, and T cells, and its expression is triggered by the immune system in response to pathogens and their products, such as endotoxins. TNF-α plays an important role in host defense by inducing inflammatory reactions such as phagocytes and cytocidal systems activation. TNF-α also plays an important role in bone metabolism and is associated with inflammatory bone diseases. TNF-α binds to two cell surface receptors, the 55kDa TNF receptor-1 (TNFR1) and the 75kDa TNF receptor-2 (TNFR2). Bone is in a constant state of turnover; it is continuously degraded and built via the process of bone remodeling, which results from the regulated balance between bone-resorbing osteoclasts, bone-forming osteoblasts, and the mechanosensory cell type osteocytes. Precise interactions between these cells maintain skeletal homeostasis. Studies have shown that TNF-α affects bone-related cells via TNFRs. Signaling through either receptor results in different outcomes in different cell types as well as in the same cell type. This review summarizes and discusses current research on the TNF-α and TNFR interaction and its role in bone-related cells.

C­X­C receptor 7 agonist acts as a C­X­C motif chemokine ligand 12 inhibitor to ameliorate osteoclastogenesis and bone resorption.

The C­X­C receptor (CXCR) 7 agonist, VUF11207, is a chemical compound that binds specifically to CXCR7, and negatively regulates C­X­C motif chemokine ligand 12 (CXCL12) and CXCR4­induced cellular events. Lipopolysaccharide (LPS) can induce inflammatory cytokines and pathological bone loss. LPS also induces expression of CXCL12, enhancing sensitivity to receptor activator of NF­κB ligand (RANKL) and tumor necrosis factor­α (TNF­α) in vivo. RANKL and TNF­α induce the differentiation of osteoclasts into osteoclast precursors and bone resorption. The current study was performed to examine the effects of a CXCR7 agonist on osteoclastogenesis and bone resorption induced by LPS in vivo. In addition, the mechanisms underlying these in vivo effects were investigated by in vitro experiments. Eight­week­old male C57BL/6J mice were subcutaneously injected over the calvariae with LPS alone or LPS and CXCR7 agonist. After sacrifice, the number of osteoclasts and the bone resorption area were measured. In vitro experiments were performed to investigate the effects of CXCL12 and CXCR7 agonist on osteoclastogenesis induced by RANKL and TNF­α. Mice injected with LPS and CXCR7 agonist showed significantly reduced osteoclastogenesis and bone resorption compared with mice injected with LPS alone. Moreover, the CXCR7 agonist inhibited CXCL12 enhancement of RANKL­ and TNF­α­induced osteoclastogenesis in vitro. Thus, CXCR7 agonist inhibited LPS­induced osteoclast­associated cytokines, such as RANKL and TNF­α, as well as RANKL­ and TNF­α­induced osteoclastogenesis in vitro by modulating CXCL12­mediated enhancement of osteoclastogenesis. In conclusion, CXCR7 agonist reduced CXCL12­mediated osteoclastogenesis and bone resorption.

Tumor necrosis factor-α enhances the expression of vascular endothelial growth factor in a mouse orthodontic tooth movement model.

BACKGROUND/PURPOSE: Tooth movement that is achieved using orthodontic mechanical principles relies on bone resorption which takes place on the compression side via osteoclasts. Tumor necrosis factor-α (TNF-α) has been known to affect osteoclast formation in orthodontic tooth movement (OTM). Vascular endothelial growth factor (VEGF), which is one of the mediators of angiogenesis, also plays an important role in OTM by inducing vascular permeability and chemotaxis of osteoclast precursors. Therefore, the purpose of this research was to evaluate the effect of TNF-α on VEGF expression during OTM. MATERIALS AND METHODS: In order to demonstrate the effect of TNF-α on VEGF expression during OTM, a nickel titanium closed coil spring was fixed to the upper left first molar and the alveolar bone beneath the upper incisors of both wild type (WT) and TNF receptors (TNFRs) deficient mice resulting in a mesial movement of the molar for 12 days. The maxilla was removed for histological analysis and real-time RCR analysis of VEGF expression. RESULTS: Immunohistochemical analysis revealed that there were fewer VEGF-positive cells in the periodontal membrane on the mesial side of the distobuccal root in TNFRs-deficient mice than that in WT mice during the OTM for 12 days. Furthermore, expression of VEGF mRNA is lower level in TNFRs-deficient mice than that in WT mice. CONCLUSION: Our results indicate that TNF-α plays an important role in VEGF expression during tooth movement.

Docosahexaenoic acid inhibits TNF-α-induced osteoclast formation and orthodontic tooth movement through GPR120.

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that has a range of positive impacts on human health, including anti-inflammatory effects and inhibition of osteoclast formation via G-protein-coupled receptor 120 (GPR120). Orthodontic force was reported to induce tumor necrosis factor-α (TNF-α) expression, which activates osteoclast differentiation during orthodontic tooth movement (OTM). The aim of this study was to investigate the influence of DHA on TNF-α-induced osteoclast formation and OTM in vivo. We examined osteoclast formation and bone resorption within the calvaria of both wild-type (WT) and GPR120-deficient (GPR120-KO) mice injected with phosphate-buffered saline (PBS), TNF-α, TNF-α and DHA, or DHA. DHA inhibited TNF-α-induced osteoclast formation and bone resorption in WT mice but had no effect in GPR120-KO mice. OTM experiments were performed in mouse strains with or without regular injection of DHA, and the effects of DHA on osteoclast formation in the alveolar bones during OTM were examined. DHA also suppressed OTM in WT but not GPR120-KO mice. Our data showed that DHA suppresses TNF-α-induced osteoclastogenesis and bone resorption via GPR120. TNF-α has considerable significance in OTM, and therefore, DHA may also inhibit TNF-α-induced osteoclast formation and bone resorption in OTM.

Effect of TNF-α on osteocyte RANKL expression during orthodontic tooth movement.

BACKGROUND/PURPOSE: Orthodontic tooth movement (OTM) is facilitated by two events; bone resorption on the compression side and bone formation on the tension side simultaneously termed bone remodeling. Osteocytes play a critical role in bone remodeling during OTM, as they have been described as the critical source of nuclear factor-κB ligand (RANKL) necessary for bone remodeling during OTM. Tumor necrosis factor (TNF)-α is a cytokine that acts by amplifying RANKL expression in osteocytes. In this study, we evaluated the effects of TNF-α on RANKL expression in osteocyte during OTM. MATERIALS AND METHODS: We assessed whether TNF-α influenced RANKL expression in osteocyte during orthodontic tooth movement by using wild-type (WT) and TNF receptor I and II deficient (TNFRsKO) mice. A Nickel-titanium closed coil spring was attached to the maxillary alveolar bone near the incisors and the upper left first molar, and the first molars were moved mesially in WT and TNFRsKO mice. After OTM, the number of RANKL-positive osteocytes in the alveolar bone was evaluated by immunohistochemistry. RESULTS: The number of RANKL-positive osteocyte in the alveolar bone significantly increased in WT mice than in TNFRsKO mice after OTM. CONCLUSION: The results indicate that TNF-α induces the expression of RANKL in osteocyte during OTM.

Effects of Incretin-Related Diabetes Drugs on Bone Formation and Bone Resorption.

Patients with type 2 diabetes have an increased risk of fracture compared to the general population. Glucose absorption is accelerated by incretin hormones, which induce insulin secretion from the pancreas. The level of the incretin hormone, glucagon-like peptide-1 (GLP-1), shows an immediate postprandial increase, and the circulating level of intact GLP-1 is reduced rapidly by dipeptidyl peptidase-4 (DPP-4)-mediated inactivation. Therefore, GLP-1 receptor agonists and DPP-4 inhibitors are effective in the treatment of type 2 diabetes. However, these incretin-related diabetic agents have been reported to affect bone metabolism, including bone formation and resorption. These agents enhance the expression of bone markers, and have been applied to improve bone quality and bone density. In addition, they have been reported to suppress chronic inflammation and reduce the levels of inflammatory cytokine expression. Previously, we reported that these incretin-related agents inhibited both the expression of inflammatory cytokines and inflammation-induced bone resorption. This review presents an overview of current knowledge regarding the effects of incretin-related diabetes drugs on osteoblast differentiation and bone formation as well as osteoclast differentiation and bone resorption. The mechanisms by which incretin-related diabetes drugs regulate bone formation and bone resorption are also discussed.