Liraglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist, restores hyperglycemic conditions in patients with type 2 diabetes and has recently shown promising anti-inflammatory properties. In this study, we explored its potential to suppress osteoclast formation and bone loss triggered by lipopolysaccharide (LPS), an inflammatory agent. In animal models, the co-administration of liraglutide with LPS on the calvaria regions in mice markedly reduced osteoclast numbers and bone resorption areas relative to treatment with LPS alone. Furthermore, the expression levels of receptor activators of the NF-κB ligand (RANKL) and tumor necrosis factor (TNF)-α mRNA were notably lower in the group receiving liraglutide and LPS compared to treatment with LPS alone. Moreover, in vitro tests revealed that liraglutide has no direct inhibitory effect on RANKL-induced osteoclastogenesis and TNF-α-induced osteoclastogenesis. In addition, liraglutide had no direct inhibitory effect on LPS-stimulated RANKL expression in osteoblasts. Moreover, liraglutide effectively suppressed TNF-α mRNA expression in macrophages stimulated by LPS. These findings suggest that liraglutide prevents inflammatory bone destruction not by targeting osteoclast formation directly but by inhibiting the production of TNF-α within macrophages.

Osteocytes regulate bone remodeling by interacting with osteoblasts and osteoclasts. Hypoxia influences osteocyte function and has been linked to increased osteoclastogenesis in pathological conditions such as orthodontic tooth movement (OTM) and bone metabolic diseases; however, the molecular mechanisms underlying these effects remain unclear. This study aimed to identify hypoxia-responsive genes in osteocytes and investigate their effects on osteoclastogenesis. Transcriptome analysis of murine long bone osteocyte-Y4 (MLO-Y4) osteocytes cultured under hypoxia (2% O2) revealed that lipocalin-2 (Lcn2) was the most significantly upregulated gene. Real-time RT-PCR confirmed increased Lcn2 expression and an elevated Rankl/osteoprotegerin (Opg) ratio. Primary osteocytes were purified from DMP1-Topaz mice showed same hypoxic response. Functional analysis demonstrated that Lcn2 did not directly affect osteoclast precursors. However, it enhanced osteoclastogenesis via osteocytes in co-culture experiments. Western blot analysis demonstrated that LCN2 activated the MAPK signaling pathway in osteocytes. Furthermore, immunohistochemical analysis of hypoxic osteocytes on the compression side of OTM exhibited increased LCN2 expression. These findings suggest that LCN2 is upregulated in osteocytes under hypoxia and promotes osteoclastogenesis by increasing RANKL expression. This study provides new insights into the molecular mechanisms of bone resorption under hypoxic conditions and suggests Lcn2 as a potential therapeutic target for bone metabolic diseases.

Orthodontic tooth movement (OTM), a complex biological process driven by orchestrated bone remodeling, involves osteoclastic bone resorption and osteoblastic bone formation in response to mechanical force. Traditionally, OTM-related cell death has been discussed in terms of apoptosis and necrosis. However, recent advances in cell death research have revealed various forms of regulated cell death (RCD) beyond these conventional categories. This review summarizes the current understanding of the diverse RCD pathways and their roles in various cell populations during OTM. It delineates the involvement of distinct RCD mechanisms, including apoptosis, autophagy, pyroptosis, ferroptosis, and necroptosis. On the compression side, these RCD pathways in periodontal ligament (PDL) cells, cementoblasts, cementocytes, and bone-related cells actively drive inflammatory responses, promote bone resorption, and contribute to root resorption. Conversely, on the tension side, specific RCD pathways, notably autophagy in the PDL and osteocytes, play crucial roles in promoting osteogenesis and tissue repair. Collectively, cell death is not merely a passive elimination of cells but actively functions as a critical switch for alveolar bone remodeling during OTM. Understanding these multifaceted RCD mechanisms provides novel insights into the biological regulation of tooth movement and identifies potential therapeutic targets for enhancing tooth movement efficiency and mitigating adverse effects.

Glucose-dependent insulinotropic polypeptide (GIP) was the first incretin hormone identified, best known for promoting glucose-stimulated insulin secretion. Increasing evidence has expanded its physiological relevance beyond glucose metabolism, revealing a significant role for GIP in the gut-bone axis. In vitro studies demonstrate that GIP inhibits osteoclast differentiation and activity while promoting osteoblastic bone formation. Findings from genetic animal models and human variant analyses further support the essential role of endogenous GIP signaling in maintaining bone mass and quality. Exogenous administration of GIP suppresses the bone-resorption marker C-terminal telopeptide of type I collagen (CTX) and increases the bone-formation marker procollagen type I N-terminal propeptide (P1NP) in healthy individuals, reflecting an acute shift toward reduced bone resorption and enhanced bone formation. Moreover, GIP confers protection against bone deterioration in multiple pathological conditions, including postmenopausal osteoporosis, inflammatory bone loss, obesity, and diabetes, etc., suggesting therapeutic potential beyond physiological contexts. Recent evidence also shows that GIP attenuates orthodontic tooth movement by limiting mechanically induced osteoclast activity, highlighting its broader skeletal actions. In this review, we summarize recent advances regarding the role of GIP in bone metabolism, integrating evidence from cellular studies, animal models and human investigations, and discuss future directions for GIP-based interventions.

Post-transcriptional gene regulation is central to maintaining cellular homeostasis. Among its mechanisms, alternative splicing (AS) fine-tunes cellular adaptation to stress. This study employed an approach combining RNA splicing analysis with RNA-binding protein (RBP) motif enrichment in primary osteocytes cultured in high-glucose conditions. Our analysis identified the RBP human antigen R (HuR) as a top candidate associated with AS regulation. Loss of HuR reshaped the transcriptome through gene expression and splicing changes, converging on two major pathways: stress response and translational control. Functional validation revealed that HuR depletion heightened oxidative stress, impaired mitochondrial function, and rewired key translational signals, while preserving global protein output. Mechanistically, we identified TXNIP mRNA-protein uncoupling following HuR knockdown (KD), characterized by elevated mRNA but reduced protein expression. Collectively, these findings support HuR’s role as a key post-transcriptional regulator of osteocyte metabolic adaptation under high-glucose stress, with potential implications for hyperglycemic bone fragility.

OBJECTIVE:Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are significant environmental pollutants, raising growing concerns about their potential impact on human health, particularly oral health. This study aimed to investigate the combined effects of these pollutants on periodontitis (PD) - a prevalent chronic inflammatory disease affecting tooth-supporting structures. METHODS:This study utilized the National Health and Nutrition Examination Survey data to examine interactions between HMs, PAHs, and PD. A comprehensive analytical approach included survey-weighted multivariate logistic regression to evaluate individual pollutant exposures, restricted cubic splines to assess dose-response relationships, and advanced models such as Weighted Quantile Sum regression, Quantile G-Computation (qgcomp), and Bayesian Kernel Machine Regression to analyse joint pollutant effects. RESULTS:Findings revealed significant associations between high levels of certain blood HMs - particularly cadmium (Cd) and lead (Pb) - and increased PD risk. Elevated urinary levels of PAH metabolites were similarly linked to higher risk. Importantly, the study highlights that risk is substantially amplified by the synergistic effects of combined HMs and PAHs exposure. Weighted Quantile Sum, qgcomp, and Bayesian Kernel Machine Regression consistently demonstrated that simultaneous exposures lead to a notably higher PD risk, suggesting that traditional single-pollutant assessments may underestimate health risks. CONCLUSION:This study provides robust evidence that exposure to both individual and combined HMs and PAHs significantly elevates PD risk. These findings underscore the importance of considering cumulative and interactive pollutant effects in public health risk assessments.

Background/Objective: Osteocytes are the most abundant cell type in the skeleton, with key endocrine functions, particularly in regulating osteoblast and osteoclast activity to maintain bone quality. Angiotensin II (Ang II), a critical component of the renin–angiotensin–aldosterone system, is well-known for its role in vasoconstriction during hypertension. Beyond its cardiovascular functions, Ang II participates in various biological processes, including bone metabolism. While its influence on osteoblast proliferation, differentiation, and osteoclastogenesis has been documented, its effects on osteocytes remain unexplored. This study hypothesized that Ang II enhances the osteoclastogenic activity of osteocytes. Methods: Mouse calvariae were cultured ex vivo in an Ang II-containing medium, analyzed via immunohistochemistry, and evaluated for osteoclastogenic gene expression through real-time PCR. Western blotting was employed to assess protein levels and signaling pathway activation in the MLO-Y4 osteocytic cell line in vitro. Results: Ang II significantly increased the expression of receptor activator of nuclear factor κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). These effects were abrogated by azilsartan, a blocker targeting Ang II type 1 receptors (AT1R). p38 and ERK1/2 in the MAPK pathway were also activated by Ang II. Conclusions: Ang II enhances osteocyte-mediated osteoclastogenesis via AT1R activation, highlighting its potential as a therapeutic target for bone diseases.

Tumor necrosis factor-alpha (TNF-α) is a significant cytokine that regulates bone resorption under inflammatory conditions. However, its mechanism of action in osteocytes remains unclear. In this study, highly purified osteocytes were isolated from dentin matrix protein 1 (DMP1)-Topaz mice using cell sorter. RNA sequencing (RNA-seq) revealed that TNF-α stimulation increased C-X-C motif chemokine ligand 10 (CXCL10) gene expression in osteocytes. Although CXCL10 did not affect osteoclast differentiation in vitro, it enhanced the migration of osteoclast precursors. Additionally, in the transwell co-culture system, TNF-α induced the migration of osteoclast precursors. However, this effect was attenuated by a CXCL10-neutralizing antibody. In vivo, mice were administered supracalvarial injections of TNF-α with or without the CXCL10-neutralizing antibody for 5 days. The percentage of CXCL10-positive osteocytes increased after TNF-α administration. Additionally, osteoclast formation and bone resorption were assessed. CXCL10-neutralizing antibody-treated calvariae exhibited a significantly lower number of osteoclasts and bone resorption than those treated with TNF-α alone. These results indicated that TNF-α-induced CXCL10, which affects the migration of osteocyte-derived osteoclast precursors, may enhance TNF-α-triggered osteoclast formation and bone resorption in vivo.

This case report describes the three-dimensional (3D) craniofacial morphology of a patient with severe facial asymmetry caused by unilateral coronal synostosis. The patient was an 11-year-and-3-month-old girl at the time of the first examination. Facial photographs revealed upper facial deviation toward the right (affected) side and lower facial deviation toward the left (non-affected) side. The nasal bridge was bent toward the non-affected side, and the external canthus on the affected side was retracted superolaterally. The midline of the lower dentition deviated toward the non-affected side. Molar relationships were Class III on the affected side and Class I on the non-affected side. A virtual fusion model of the skull and dentition was reconstructed and analyzed using a 3D coordinate system. The model demonstrated absence of the right coronal and sphenofrontal sutures, deviation of the nasal pyramid and vomer toward the affected side, and anterior displacement of the petrous bone. Unlike typical facial symmetry cases, this case exhibited a prominently anterior glenoid fossa and reduced mandibular body length on the affected side. These findings demonstrate the complex craniofacial morphology associated with unilateral coronal synostosis and highlight the role of the coronal suture in maintaining facial symmetry and the mandible's adaptive growth in response to glenoid fossa asymmetry.

A challenge in orthodontic treatment is the long time taken to move teeth, which extends the long treatment period. Accordingly, various treatment protocols and orthodontic materials have been developed to shorten the orthodontic treatment period. However, controlling biological reactions is considered necessary to further shorten this treatment period. Orthodontic force results in compression of the periodontal ligament in the direction of tooth movement, resulting in various reactions in the periodontal ligament that induce osteoclast development, alveolar bone absorption, and teeth movement. The aforementioned reactions include immune reactions. Cytokines are substances responsible for intercellular communication and are involved in various physiological actions, including immune and inflammatory reactions. They cause various cellular responses, including cell proliferation, differentiation, cell death, and functional expression. Various cytokines are involved in biological reactions during orthodontic tooth movement (OTM). It is important to understand the role of cytokines during OTM in order to elucidate their biological response. This review discusses the role of cytokines during OTM.

The incretin hormone glucose-dependent insulinotropic polypeptide (GIP) promotes insulin secretion, lowers blood glucose levels, and is increasingly linked to bone remodeling. Native GIP is quickly inactivated by the enzyme dipeptidyl peptidase-4 (DPP-4), whereas (D-Ala2)GIP is a novel GIP analog engineered to resist DPP-4 degradation. Tumor necrosis factor-alpha (TNF-α), a key proinflammatory cytokine, promotes osteoclastogenesis and is notably upregulated during orthodontic tooth movement (OTM). This study aimed to evaluate the effects of (D-Ala2)GIP on TNF-α-induced osteoclast formation and bone resorption in vivo, as well as on OTM and related root resorption. Mice received daily supracalvarial injections of TNF-α with or without (D-Ala2)GIP for 5 days. The (D-Ala2)GIP-treated group showed significantly reduced osteoclast formation, bone resorption, and expression of osteoclastic markers TRAP and cathepsin K, compared to the group that received TNF-α alone. OTM was induced in mice by applying a nickel-titanium closed-coil spring, and mice were treated with either phosphate-buffered saline (PBS) or (D-Ala2)GIP every 2 days. After 12 days, the (D-Ala2)GIP-treated group showed significantly reduced tooth movement and fewer osteoclasts and odontoclasts on the compression side compared to the PBS control. These findings suggest that (D-Ala2)GIP inhibits OTM, potentially by suppressing TNF-α-driven osteoclastogenesis and bone resorption.

Background/purpose Orthodontic tooth movement (OTM) is a critical aspect of dental treatment that requires the precise control of bone remodeling processes. Hypertension (HTN) can affect the effectiveness of OTM. Salt-sensitive hypertension (SSHTN) is of particular concern due to its detrimental effects on bone health, potentially altering orthodontic outcomes. This study aimed to investigate the effects of SSHTN on OTM using a mouse model. Materials and methods Male mice were divided into a normal and an SSHTN group. The SSHTN model was generated by administering N(ω)-nitro-l-arginine methyl ester (l-NAME) followed by a high-salt diet. The OTM was performed using a nickel-titanium (Ni-Ti) closed-coil spring, and the tooth movement was measured after 12 days. Silicone imprinting was used to estimate the OTM distance. Osteoclast activity was assessed using tartrate-resistant acid phosphatase (TRAP) staining of decalcified maxillary sections. Results SSHTN mice exhibited significantly increased tooth movement compared to normal mice. This enhanced movement was associated with more osteoclasts in the SSHTN group than in the control group. These findings suggest that SSHTN increases OTM levels by promoting bone resorption. Conclusion SSHTN significantly affected OTM by enhancing osteoclast activity and increasing tooth movement. These results underscore the importance of considering hypertensive conditions in orthodontic treatment planning as they may require adjustments in force application to prevent potential adverse effects.

Orthodontic tooth movement (OTM) has been described as a bone remodeling process mediated by the expression of various inflammatory cytokines, including tumor necrosis factor-α (TNF-α). Necroptosis is a form of regulated cell death that is mainly induced by TNF-α, leading to the release of damage-associated molecular patterns (DAMPs) that cause inflammation. However, the role of osteocyte necroptosis in regulating osteoclastogenesis during OTM remains unclear. Here, we investigated the effects of osteocyte necroptosis on osteoclastogenesis in a mouse model of OTM. In wild-type mice, osteocyte death was remarkably increased on day 6 after OTM. Transmission electron microscopy identified apoptotic osteocytes, necrotic osteocytes, and empty lacunae based on morphological characteristics. TNF receptor type 1- and 2-deficient (TNFRsKO) mice showed a reduction in osteocyte death on day 6 after OTM. Immunofluorescence staining detected necroptosis markers in osteocytes on the compression side in wild-type OTM mice, whereas such osteocytes were almost undetectable in TNFRsKO OTM mice. Furthermore, the conditioned medium from primary osteocytes undergoing necroptosis significantly enhanced osteoclastogenesis. These findings suggest that TNF-α-induced osteocyte necroptosis enhances osteoclastogenesis and alveolar bone resorption on the compression side during OTM, involving the release of inflammatory factors including DAMPs.

Background/purpose:Orthodontic treatment is one of the most demanding procedures available for both patients and clinicians. The challenges stem from the extended duration to achieve desired results, often necessitating surgical interventions, such as micro-osteoperforations (MOPs). This study aimed to investigate the biological effects and extent of changes resulting from these interventions. Specifically, we evaluated the degree of root resorption during orthodontic tooth movement accelerated by MOPs. Materials and methods:We assessed the tooth movement rates and root resorption in eight-to ten-week-old male mice. A nickel-titanium (Ni-Ti) closed-coil spring was applied between the maxillary left first molar and maxillary incisors. In the MOPs group, micro-perforations were made on the mesial and palatal surfaces of the left maxillary first molar. Odontoclast formation and root resorption were assessed using histological analysis and scanning electron microscopy. Results:Tooth movement was greater in the MOPs group. Odontoclast formation was remarkably higher in this group than in the orthodontic tooth movement (OTM) group. Additionally, more extensive root resorption was observed on the mesial surface of the distobuccal root of the left maxillary first molar. Conclusion:Root resorption significantly increased in mice with MOPs. These findings highlight the need to carefully consider the risk of root resorption in patients undergoing MOPs during orthodontic treatment.

Post-transcriptional gene regulation is central to maintaining cellular homeostasis, among its mechanism alternative splicing (AS) fine-tunes cellular adaptation to stress. In this study we employed an approach combining RNA splicing analysis to define RNA binding protein (RBP) motif enrichment around alternatively spliced exons in primary osteocytes cultured in high glucose conditions (HG). We identified the RBP human antigen R (HuR) as a top candidate regulator of AS. Loss of HuR reshaped the transcriptome through widespread changes in gene expression and splicing, converging on two major pathways: stress response and translational control. Functional validation of splicing revealed that HuR depletion heightened oxidative stress sensitivity and compromised cell viability under HG by stabilizing and upregulating TXNIP, a thioredoxin inhibitor. HuR knockdown also impaired mitochondrial mass and function and disrupted key translational signals, despite preserving global protein output. These findings establish HuR as a central post-transcriptional regulator of osteocyte survival and metabolic adaptation under high glucose stress, with potential implications for hyperglycemic bone fragility. ### Competing Interest Statement The authors have declared no competing interest. Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, to AM Japan Science and Technology Agency, https://ror.org/00097mb19, JPMJSP2114 to ZF

Bone remodeling is maintained through the coordinated actions of osteoblasts, osteoclasts, and osteocytes, among which osteocytes serve as major regulators of osteoclast-mediated bone resorption through the receptor activator of the nuclear factor-κB ligand (RANKL)-osteoprotegerin (OPG) signaling axis. While molecular signals regulating osteocytic RANKL-OPG expression are fairly understood, how post-transcriptional mechanisms impact osteocyte function remains poorly defined. HuR (human antigen R) encoded by Elavl1 (embryonic lethal abnormal vision-like 1), a ubiquitously expressed RNA-binding protein, is known for stabilizing AU-rich element-containing transcripts involved in inflammatory and stress responses; however, its role in osteocyte-derived bone resorption is unknown. In this study, we examined the effect of HuR loss on osteocyte-osteoclastogenesis. Short hairpin RNA (shRNA)-mediated HuR knockdown in MLO-Y4 osteocyte-like cells resulted in a significant increase in OPG mRNA and its protein expression, whereas RANKL levels remained unchanged, leading to a significantly reduced RANKL/OPG ratio. Both co-culture and conditioned-medium assays demonstrated that HuR-deficient osteocytes produced a markedly diminished osteoclastogenic environment. Actinomycin D chase experiments showed no alteration in OPG mRNA decay kinetics, and RNA immunoprecipitation (RIP)-PCR failed to detect HuR-OPG interactions, indicating that HuR regulates OPG expression through indirect mechanisms rather than mRNA binding. These findings identify HuR as an indirect regulator of osteocyte-derived OPG expression that impacts osteoclast differentiation and reveal a previously unrecognized mechanism by which HuR contributes to bone remodeling.

Osteocytes are central regulators of skeletal homeostasis, yet how their transcriptome and proteome jointly adapt to metabolic stress is unclear. Here, we combined RNA–sequencing with label-free quantitative proteomics in MLO–Y4 osteocytic cells exposed to hyperglycemic levels of glucose, to interrogate RNA–protein coupling at baseline and under hyperglycemic stress. Transcriptionally, high glucose and mannitol elicited overlapping osmoadaptive transcriptional programs indicative of metabolic remodeling, whereas high glucose alone induced mitochondrial and oxidative phosphorylation downregulation alongside selective activation of bone anabolic and inflammatory pathways. RNA–protein integration revealed moderate coupling at baseline, indicating that mRNA levels capture only part of the proteomic output. High glucose reorganized RNA–protein relationship, sorting genes into four patterns of matched or opposing RNA–protein responses. The four groups were enriched in distinct biological pathways that shaped cellular response to stress exposing significant post–transcriptional and translational control under high glucose levels. These data indicate that osteocytes adapt to stress through program–specific RNA–protein interactions in which post–transcriptional regulation of protein translation reshapes the proteome beyond what is predicted by mRNA levels. ### Competing Interest Statement The authors have declared no competing interest. Japan Society for the Promotion of Science, https://ror.org/00hhkn466, #25K20447

Orthodontic tooth movement (OTM) is a biologically orchestrated process involving the dynamic interplay of mechanical force, inflammatory signaling, and bone remodeling. Osteocytes, the most abundant cells within the bone matrix, serve as mechanosensitive regulators that transduce mechanical cues into biochemical signals in response to orthodontic force. This review delineates the multifaceted role of osteocytes in facilitating bone resorption required for OTM. The role of osteocytes is examined in inflammation, mechanical adaptation, and cell death. Additionally, we discuss the evidence on how aging alters osteocyte function, with senescence-associated changes disrupting mechanosensory networks and attenuating bone remodeling. Finally, the possibility that osteocytes themselves undergo morphological adaptation during force application is explored. This structural plasticity may impact individual variability in orthodontic outcomes. Advancing our understanding of osteocyte signaling in OTM holds significant promise for optimizing treatment outcomes across diverse patient populations.

Osteoclastogenesis—the activation and differentiation of osteoclasts—is one of the pivotal processes of bone remodeling and is regulated by RANKL/RANK signaling, the decoy function of osteoprotegerin (OPG), and a cascade of pro- and anti-inflammatory cytokines. The disruption of this balance leads to pathological bone loss in diseases such as osteoporosis and rheumatoid arthritis. FFAR4 (Free Fatty Acid Receptor 4), a G protein-coupled receptor for long-chain omega-3 fatty acids, has been confirmed as a key mediator of metabolic and anti-inflammatory effects. This review focuses on how FFAR4 acts as the selective receptor for the omega-3 fatty acid docosahexaenoic acid (DHA). It activates two divergent signaling pathways. The Gαq-dependent cascade facilitates intracellular calcium mobilization and ERK1/2 activation. Meanwhile, β-arrestin-2 recruitment inhibits NF-κB. These collective actions reshape the cytokine environment. In macrophages, DHA–FFAR4 signaling lowers the levels of TNF-α, interleukin-6 (IL-6), and IL-1β while increasing IL-10 secretion. Consequently, the activation of NFATc1 and NF-κB p65 is profoundly suppressed under TNF-α or RANKL stimulation. Additionally, DHA modulates the RANKL/OPG axis in osteoblastic cells by suppressing RANKL expression, thereby reducing osteoclast differentiation in an inflammatory mouse model.