Osteoimmunology in Periodontitis and Orthodontic Tooth Movement

Quercetin through miR-147-5p/Clip3 axis reducing Th17 cell differentiation to alleviate periodontitis

Background

Quercetin (QU) plays an important role in treating periodontitis; however, the mechanism through which microRNAs regulate Th17 cell differentiation has not been determined.

Methods

QU was administered intragastrically to periodontitis rats once a day for one month. The morphology of alveolar bone was observed by micro-CT, gingival tissue structure was observed by HE staining, IL-6, TNF-α, IL-17A, RORγt, FOXP3 and IL-10 were detected by immunohistochemical staining, and Th17 and Treg cells in the peripheral blood were detected by flow cytometry. CD4+T cells were induced to differentiate into Th17 cells in vitro. Cell viability was determined by CCK8, and IL-17A and RORγt were detected by qPCR. Th17 cells were detected by flow cytometry, microRNA sequencing and bioinformatics analysis were used to screen key microRNAs, the phenotypic changes of Th17 cells were observed after overexpressed microRNAs via mimics. TargetScan database, in situ hybridization, and dual-luciferase reporter experiment were used to predict and prove target genes of microRNAs. The phenotype of Th17 cells was observed after overexpression of microRNA and target gene.

Results

Compared with periodontitis group, the distance from cementoenamel junction(CEJ) to alveolar bone(AB) was decreased, the structure of gingival papilla was improved, IL-6, TNF-α, IL-17, and RORγt were downregulated, FOXP3 and IL-10 were upregulated, the proportion of Th17 decreased and Treg increased in peripheral blood after QU treatment. Compared with Th17 cell group, mRNA levels of IL-17A and RORγt were decreased, and proportion of Th17 cells was significantly lower in the coculture group. MiR-147-5p was low in control group, upregulated in Th17 cell group, and downregulated after QU intervention, it's eight bases were inversely related to 3'UTR of Clip3, miR-147-5p with Clip3 were co-located in cells of periodontal tissue. Compared with those in Th17-mimicsNC + QU cells, the mRNA levels of RORγt and IL-17A upregulated, and proportion of Th17 cells increased in Th17-miR-147-5p + QU cells. The miR-147-5p mimics inhibited the luciferase activity of the WT Clip3 3'UTR but had no effect on the Mut Clip3 3'UTR. Clip3 was significantly downregulated after the overexpression of miR-147-5p. Mimics transfected with miR-147-5p reversed the decrease in the proportion of Th17 cells induced by QU, while the overexpression of Clip3 antagonized the effect of miR-147-5p and further reduced the proportion of Th17 cells. Moreover, the overexpression of miR-147-5p reversed the decreases in the mRNA levels of IL-17 and RORγt induced by QU treatment, while pcDNA3.1 Clip3 treatment further decreased the mRNA levels of IL-17 and RORγt.

Conclusion

QU reducing inflammatory response and promoting alveolar bone injury and repair, which closely relative to inhibit the differentiation of CD4+T cells into Th17 cells by downregulating miR-147-5p to promote the activation of Clip3.

FoxO1-modulated macrophage polarization regulates osteogenesis via PPAR-γ signaling

Periodontitis, a common chronic inflammatory disease, epitomizes a significant impairment in the host immune system and an imbalance of bone metabolism. Macrophage polarization, a dynamic process dictated by the microenvironment, intricately contributes to the interplay between the immune system and bone remodeling, namely the osteoimmune system. Forkhead box protein O1 (FoxO1) has been shown to play a dramatic role in mediating oxidative stress, bone mass, as well as cellular metabolism. Nevertheless, the function and underlying mechanisms of FoxO1 in regulating macrophage polarization-mediated osteogenesis in periodontitis remain to be further elucidated. Here, we found that FoxO1 expression was closely linked to periodontitis, accompanied by aggravated inflammation. Notably, FoxO1 knockdown skewed macrophage polarization from M1 to the antiinflammatory M2 phenotype under inflammatory conditions, which rescued the impaired osteogenic potential. Mechanistically, we revealed that the enhancement of the transcription of peroxisome proliferator-activated receptor (PPAR) signaling in FoxO1-knockdown macrophages. In agreement with this contention, GW9662, a specific inhibitor of PPAR-γ signaling, greatly aggravated macrophage polarization from M2 to the M1 phenotype and attenuated osteogenic potential under inflammatory conditions. Additionally, PPAR-γ signaling agonist rosiglitazone (RSG) was applied to address ligature-induced periodontitis with attenuated inflammation. Our data lend conceptual credence to the function of FoxO1 in mediating macrophage polarization-regulated osteogenesis which serves as a novel therapeutic target for periodontitis.

CircHIPK3 regulates cementoblast differentiation via the miR-10b-5p/DOHH/NF-κB axis

BACKGROUND

Intact cementum is vital for tooth stability and health. Cementoblasts, which line the root surface, are responsible for cementum formation. Recent evidence suggests that circular RNAs (circRNAs) are involved in various cellular functions and may have clinical applications. Although circHIPK3 has been shown to participate in osteogenesis, its role in cementoblast differentiation and mineralization is not well understood.

METHODS

The ring structure of circHIPK3 was confirmed using Sanger sequencing and an actinomycin D assay. Subcellular localization of circHIPK3 was assessed using a nucleus-cytoplasm separation assay. RT-qPCR was employed to analyze circHIPK3 expression during cementoblast differentiation and following TNF-α treatment. In vivo, periapical lesions were induced in mouse mandibular first molars to mimic an inflammatory environment, and circHIPK3 expression was evaluated. The interaction of the circHIPK3/miR-10b-5p/DOHH axis was explored through RNA pull-down assays, bioinformatics analysis, and dual-luciferase reporter assays. The effects on cementoblast differentiation and mineralization were assessed by measuring osteogenic markers, alkaline phosphatase (ALP) activity, ALP staining, and alizarin red S staining.

RESULTS

CircHIPK3 was predominantly located in the cytoplasm of cementoblasts, and its expression was significantly upregulated during cementoblast differentiation. Knockdown of circHIPK3 inhibited cementoblast differentiation and mineralization, whereas its overexpression promoted these processes. Mechanistically, circHIPK3 upregulated DOHH expression by sponging miR-10b-5p, thereby enhancing cementoblast differentiation and mineralization. The NF-κB pathway was found to act downstream of the circHIPK3/miR-10b-5p/DOHH axis in these processes. Additionally, circHIPK3 expression was significantly downregulated in inflammatory environments both in vitro and in vivo. Forced overexpression of circHIPK3 mitigated the inhibitory effects of TNF-α on cementoblast differentiation and mineralization.

CONCLUSION

CircHIPK3 acts as a positive regulator of cementoblast differentiation and mineralization through the miR-10b-5p/DOHH/NF-κB axis, playing a crucial role in both normal and pathological cementogenesis.

Ubiquitin C-terminal hydrolase L1 activation in periodontal ligament cells mediates orthodontic tooth movement via the MAPK signaling pathway

PURPOSE

Periodontal ligament cells (PDLCs) play a significant role in orthodontic force induced bone remodeling. However, the molecular mechanisms by which PDLCs respond to mechanical stimuli and influence osteoclastic activities remain unclear. This study aims to investigate the role of UCHL1, a key deubiquitinating enzyme involved in protein degradation and cellular responses, in force-treated PDLCs during orthodontic tooth movement (OTM).

MATERIALS AND METHODS

In this study, we conducted in vivo and in vitro experiments using human PDLCs and a rat model of OTM. Mechanical stress was applied to PDLCs, and UCHL1 expression was analyzed through quantitative real-time polymerase chain reaction (qPCR), Western blot, and immunofluorescence staining. UCHL1 knockdown was achieved using siRNA, and its effects on osteoclast differentiation were assessed. The role of the MAPK/ERK pathway was investigated using the MEK-specific inhibitor U0126. An animal model of OTM was established, and the impact of UCHL1 inhibitor-LDN57444 on OTM and osteoclastic activity was evaluated through micro-CT analysis, histological staining, and immunohistochemistry.

RESULTS

Mechanical force induced UCHL1 expression in PDLCs during OTM. UCHL1 knockdown downregulated the RANKL/OPG ratio in PDLCs, affecting osteoclast differentiation. LDN57444 inhibited OTM and osteoclastic activity. UCHL1 activation correlated with ERK1/2 phosphorylation in force-treated PDLCs.

CONCLUSIONS

Mechanical force mediated UCHL1 activation in PDLCs promotes osteoclast differentiation via the ERK1/2 signaling pathway during OTM.

Extracellular Vesicles from Compression-Loaded Cementoblasts Promote the Tissue Repair Function of Macrophages

Treatment strategies for hard tissue defects aim to establish a mineralized microenvironment that facilitates tissue remodeling. As a mineralized tissue, cementum shares a similar structure with bone and exhibits an excellent capacity to resist resorption under compression. Macrophages are crucial for mineralized remodeling; however, their functional alterations in the microenvironment of cementum remain poorly understood. Therefore, this study explores the mechanisms by which cementum resists resorption under compression and the regulatory roles of cementoblasts in macrophage functions. As a result, extracellular vesicles from compression-loaded cementoblasts (Comp-EVs) promote macrophage M2 polarization and enhance the clearance of apoptotic cells (efferocytosis) by 2- to 3-fold. Local injection of Comp-EVs relieves cementum destruction in mouse root resorption model by activating the tissue repair function of macrophages. Moreover, Comp-EV-loaded hydrogels achieve significant bone healing in calvarial bone defect. Unexpectedly, under compression, EV secretion in cementoblasts is reduced by half. RNA-Seq analysis and verification reveal that Rab35 expression decreases by 60% under compression, thereby hampering the release of EVs. Rab35 overexpression is proposed as a modification of cementoblasts to boost the yield of Comp-EVs. Collectively, Comp-EVs activate the repair function of macrophages, which will be a potential therapeutic strategy for hard tissue repair and regeneration.

Mesenchymal stem cells and their extracellular vesicles in bone and joint diseases: targeting the NLRP3 inflammasome

The nucleotide-binding oligomerization domain-like-receptor family pyrin domain-containing 3 (NLRP3) inflammasome is a cytosolic multi-subunit protein complex, and recent studies have demonstrated the vital role of the NLRP3 inflammasome in the pathological and physiological conditions, which cleaves gasdermin D to induce inflammatory cell death called pyroptosis and mediates the release of interleukin-1 beta and interleukin-18 in response to microbial infection or cellular injury. Over-activation of the NLRP3 inflammasome is associated with the pathogenesis of many disorders affecting bone and joints, including gouty arthritis, osteoarthritis, rheumatoid arthritis, osteoporosis, and periodontitis. Moreover, mesenchymal stem cells (MSCs) have been discovered to facilitate the inhibition of NLRP3 and maybe ideal for treating bone and joint diseases. In this review, we implicate the structure and activation of the NLRP3 inflammasome along with the detail on the involvement of NLRP3 inflammasome in bone and joint diseases pathology. In addition, we focused on MSCs and MSC-extracellular vesicles targeting NLRP3 inflammasomes in bone and joint diseases. Finally, the existing problems and future direction are also discussed.

The Role of Bone and Root Resorption on the Biomechanical Behavior of Mandibular Anterior Teeth Subjected to Orthodontic Forces: A Finite Element Approach

AIMS

This study was conducted to systematically evaluate the biomechanical impact of varying degrees of root and bone resorption resulting from periodontitis and orthodontic tooth movement (OTM) on the mandibular anterior teeth. The objective was to determine whether these distinct resorption patterns exert a specific influence on tooth displacement and strain patterns.

METHODS

A finite element (FE) model of an idealized anterior mandible from the first premolar in the third to the fourth quadrant was developed without bone or root resorption and a constant periodontal ligament (PDL) thickness of 0.2 mm. Variations included three root resorption levels (0%, 20%, 50%) and three bone resorption types (circular 50%, circular 80%, vestibular 80%). Models ranged from 200,000 to 440,000 elements and 55,000 to 130,000 nodes. Orthodontic forces, namely root torque (5 Nmm), intrusion (0.2 N), and distalization (0.5 N) were applied for subsequent crown displacement and PDL strain analysis.

RESULTS

A total of 180 simulations were performed. Simulations showed that displacement was similar across different bone resorption conditions, irrespective of modeled root resorptions. Circumferential bone resorption increased tooth displacement, regardless of root resorption status. Vestibular bone resorption exhibited less increase in tooth displacement. However, when accompanied by root resorption, the combination exacerbated tooth displacement. Strains in the PDL clearly increased with a circumferential bone resorption of 80%.

CONCLUSIONS

This study highlights the critical role of bone resorption in tooth displacement during OTM, particularly the challenges associated with circumferential resorption. Clinicians must consider both bone and root resorption for personalized medicine treatment of patients with severe periodontitis, in favor of low-force application strategies to optimize outcomes and minimize complications linked to excessive tooth displacement.

Periodontal Ligament Cell Apoptosis Activates Lepr+ Osteoprogenitors in Orthodontics

Alveolar bone (AB) remodeling, including formation and absorption, is the foundation of orthodontic tooth movement (OTM). However, the sources and mechanisms underlying new bone formation remain unclear. Therefore, we aimed to understand the potential mechanism of bone formation during OTM, focusing on the leptin receptor+ (Lepr+) osteogenitors and periodontal ligament cells (PDLCs). We demonstrated that Lepr+ cells activated by force-induced PDLC apoptosis served as distinct osteoprogenitors during orthodontic bone regeneration. We investigated bone formation both in vivo and in vitro. Single-cell RNA sequencing analysis and lineage tracing demonstrated that Lepr represents a subcluster of stem cells that are activated and differentiate into osteoblasts during OTM. Targeted ablation of Lepr+ cells in a mouse model disrupted orthodontic force-guided bone regeneration. Furthermore, apoptosis and sequential fluorescent labeling assays revealed that the apoptosis of PDLCs preceded new bone deposition. We found that PDL stem cell-derived apoptotic vesicles activated Lepr+ cells in vitro. Following apoptosis inhibition, orthodontic force-activated osteoprogenitors and osteogenesis were significantly downregulated. Notably, we found that bone formation occurred on the compression side during OTM; this has been first reported here. To conclude, we found a potential mechanism of bone formation during OTM that may provide new insights into AB regeneration.

Exploring the role of innate lymphoid cells in the periodontium: insights into immunological dynamics during orthodontic tooth movement

Background

The periodontal ligament (PDL) experiences considerable mechanical stresses between teeth and bone, vital for tissue adaptation, especially in orthodontic tooth movement (OTM). While recent research emphasizes the role of innate lymphoid cells (ILCs) in regulating sterile inflammation, their involvement in periodontal tissues during OTM remains largely unexplored.

Methods

In this study, PDL tissues from orthodontic patients (n = 8) were examined using flow cytometry to detect ILC subtypes. Transwell co-culture systems were used to expose PDL cells to mechanical strain, followed by measuring migration and ratios of sorted ILC subtypes. Statistical analyses were conducted using paired Student's t-test, Kruskal-Wallis test, Dunn's post-test and one-way/two-way ANOVA with Tukey's post-test (p≤ 0.05; **, p≤ 0.01; ***, p≤ 0.001).

Results

Our findings demonstrate a significant increase in CD127+ CD161+ ILC frequencies in PDL tissues during OTM, indicating ILC involvement in sterile inflammation induced by orthodontic forces. Co-culture assays show directed migration of ILC subsets towards PDL cells and substantial proliferation and expansion of ILCs.

Conclusions

This study is the first to comprehensively investigate the role of ILCs in sterile inflammation during OTM, revealing their presence and distribution within PDL tissues' innate immune response in vivo, and exploring their migratory and proliferative behavior in vitro. The results suggest a crosstalk between ILCs and PDL cells, potentially influencing the inflammatory response and tissue remodeling processes associated with OTM.

An update on periodontal inflammation and bone loss

Periodontal disease is a chronic inflammatory condition that affects the supporting structures of the teeth, including the periodontal ligament and alveolar bone. Periodontal disease is due to an immune response that stimulates gingivitis and periodontitis, and its systemic consequences. This immune response is triggered by bacteria and may be modulated by environmental conditions such as smoking or systemic disease. Recent advances in single cell RNA-seq (scRNA-seq) and in vivo animal studies have provided new insight into the immune response triggered by bacteria that causes periodontitis and gingivitis. Dysbiosis, which constitutes a change in the bacterial composition of the microbiome, is a key factor in the initiation and progression of periodontitis. The host immune response to dysbiosis involves the activation of various cell types, including keratinocytes, stromal cells, neutrophils, monocytes/macrophages, dendritic cells and several lymphocyte subsets, which release pro-inflammatory cytokines and chemokines. Periodontal disease has been implicated in contributing to the pathogenesis of several systemic conditions, including diabetes, rheumatoid arthritis, cardiovascular disease and Alzheimer's disease. Understanding the complex interplay between the oral microbiome and the host immune response is critical for the development of new therapeutic strategies for the prevention and treatment of periodontitis and its systemic consequences.

Alveolar morphometry in young adults with and without agenesis of the upper lateral incisor: A retrospective study

INTRODUCTION

We aimed to compare alveolar morphometry in young adults with agenesis of the upper lateral incisor versus the side without agenesis and versus matched controls.

MATERIAL AND METHODS

In this observational retrospective study, cone beam computed tomography scans were obtained of 36 upper hemiarches from young adults aged 15 to 30 years. The hemiarches were distributed into three groups: group 1: 12 upper hemiarches presenting agenesis of the upper lateral incisor; group 2: 12 upper hemiarches from the opposite side without agenesis of the upper lateral incisor (control group 1); and group 3: 12 upper hemiarches without agenesis of the upper lateral incisor matched for age and sex with respect to the affected group (control group 2). A trained and calibrated investigator performed all the alveolar measurements at two different times, including sagittal, coronal and axial slices of each hemiarch. Paired Student's t-tests, Chi-square and repeated measures ANOVA with Bonferroni correction were used, (P<0.05).

RESULTS

Apical mesial evaluation of group 1 (4.22±1.19mm) was significantly lower (P<0.001) than that of groups 2 (6.72±1.17mm) and 3 (7.58±1.67mm). Apical distal evaluation also showed differences (P<0.001) among the three groups, with the dimension being smaller in group 1 with agenesis (4.53±1.14mm), followed by group 2 without agenesis (6.23±1.55mm) and the healthy control group 3 (7.73±1.71mm).

CONCLUSIONS

Lateral incisor agenesis significantly reduces the alveolar dimensions of the affected area. In cases of unilateral agenesis, the unaffected side also shows sequelae, with decreased dimensions compared to cases without agenesis. This condition should be taken into account when making therapeutic decisions regarding rehabilitation with implants or canine replacement.

Effect of fence tray matching care on excess adhesive and bracket placement accuracy for orthodontic bonding: an in vitro study

OBJECTIVE

This study aimed to evaluate the effect of fence tray matching care (FTMC) in bracket bonding by measuring excess adhesive, as well as linear and angular deviations, and by comparing it with the half-wrapped tray (HWT).

MATERIALS AND METHODS

An intraoral scanner was used to acquire data on the maxillary dental arch of a patient with periodontitis.Furthermore, 20 maxillary dental arch models were 3D printed. Using 3Shape, PlastyCAD software, and 3D printing technology, 10 FTMC (method I) and HWT (method II) were obtained. By preoperative preparation, intraoperative coordination, and postoperative measurement, the brackets were transferred from the trays to the 3D-printed maxillary dental arch models. Additionally, the bracket's excess adhesive as well as linear and angular deviations were measured, and the differences between the two methods were analyzed.

RESULTS

Excess adhesive was observed in both methods, with FTMC showing less adhesive (P< 0.001), with a statistical difference. Furthermore, HWT's vertical, tip and torque, which was significantly greater than FTMC (P< 0.05), with no statistical difference among other respects. The study data of incisors, canines, and premolars, showed that the premolars had more adhesive residue and were more likely to have linear and angular deviations.

CONCLUSIONS

The FTMC had higher bracket bonding effect in comparison to HWT, and the adhesive residue, linear and angular deviations are smaller. The fence tray offers an intuitive view of the precise bonding of the bracket, and can remove excess adhesive to prevent white spot lesions via care, providing a different bonding method for clinical applications.

Smoking and osteoimmunology: Understanding the interplay between bone metabolism and immune homeostasis

Smoking continues to pose a global threat to morbidity and mortality in populations. The detrimental impact of smoking on health and disease includes bone destruction and immune disruption in various diseases. Osteoimmunology, which explores the communication between bone metabolism and immune homeostasis, aims to reveal the interaction between the osteoimmune systems in disease development. Smoking impairs the differentiation of mesenchymal stem cells and osteoblasts in bone formation while promoting osteoclast differentiation in bone resorption. Furthermore, smoking stimulates the Th17 response to increase inflammatory and osteoclastogenic cytokines that promote the receptor activator of NF-κB ligand (RANKL) signaling in osteoclasts, thus exacerbating bone destruction in periodontitis and rheumatoid arthritis. The pro-inflammatory role of smoking is also evident in delayed bone fracture healing and osteoarthritis development. The osteoimmunological therapies are promising in treating periodontitis and rheumatoid arthritis, but further research is still required to block the smoking-induced aggravation in these diseases.

Translational potential

This review summarizes the adverse effect of smoking on mesenchymal stem cells, osteoblasts, and osteoclasts and elucidates the smoking-induced exacerbation of periodontitis, rheumatoid arthritis, bone fracture healing, and osteoarthritis from an osteoimmune perspective. We also propose the therapeutic potential of osteoimmunological therapies for bone destruction aggravated by smoking.

A whole-course-repair system based on ROS/glucose stimuli-responsive EGCG release and tunable mechanical property for efficient treatment of chronic periodontitis in diabetic rats

Elevated glucose levels, multiple pro-inflammatory cytokines and the generation of excessive reactive oxygen species (ROS) are pivotal characteristics within the microenvironments of chronic periodontitis with diabetes mellitus (CPDM). Control of inflammation and modulation of immune system are required in the initial phase of CPDM treatment, while late severe periodontitis requires a suitable scaffold to promote osteogenesis, rebuild periodontal tissue and reduce alveolar bone resorption. Herein, a whole-course-repair system is introduced by an injectable hydrogel using phenylboronic acid functionalized oxidized sodium alginate (OSA-PBA) and carboxymethyl chitosan (CMC). Epigallocatechin-3-gallate (EGCG) was loaded to simultaneously adjust the mechanical property of the OSA-PBA/CMC + EGCG hydrogel (OPCE). This hydrogel has distinctive adaptability, injectability, and ROS/glucose-triggered release of EGCG, making it an ideal drug delivery carrier. As expected, OPCE hydrogel shows favourable antioxidant and anti-inflammatory properties, along with a regulatory influence on the phenotypic transition of macrophages, providing a favourable immune microenvironment. Apart from that, it provides a favourable mechanical support for osteoblast/osteoclast differentiation regulation at the late proliferation stage of periodontal regeneration. The practical therapeutic effects of OPCE hydrogels were also confirmed when applied for treating periodontitis in diabetic rats. In summary, OPCE hydrogel may be a promising whole-course-repair system for the treatment of CPDM.

Single-cell transcriptome analysis reveals periodontal ligament fibroblast heterogeneity with distinct IL-1β and RANKL expression in periodontitis

Periodontitis (PD) is an inflammatory disease with alveolar bone destruction by osteoclasts (OCs). In PD, both inflammation and OC activation are significantly influenced by periodontal ligament fibroblasts (PDL-Fib). Yet, whether PDL-Fib has heterogeneity and whether distinct PDL-Fib subsets have specific functions have not been investigated. In this study, we discovered the complexity of PDL-Fib in PD, utilizing single-cell RNA sequencing data from human PD patients. We identified distinct subpopulations of PDL-Fib: one expressing interleukin-1 beta (IL-1β) and another expressing the receptor activator of nuclear factor-kappa B ligand (RANKL), both crucial in OC differentiation and bone resorption. In periodontal tissues of mice with PD, active IL-1β, cleaved caspase 1, and nucleotide-binding oligomerization domain-like receptor 3 (NLPR3) were significantly elevated, implicating the NLRP3 inflammasome in IL-1β production. Upon stimulation of PDL-Fib with LPS from Porphyromonas gingivalis (pg), the most well-characterized periodontal bacteria, a more rapid increase in IL-1β, followed by RANKL induction, was observed. IL-1β and tumor necrosis factor alpha (TNF-α), another LPS-responsive cytokine, effectively increased RANKL in PDL-Fib, suggesting an indirect effect of pgLPS through IL-1β and TNF-α on RANKL induction. Immunohistological analyses of mouse periodontal tissues also showed markedly elevated levels of IL-1β and RANKL upon PD induction and displayed separate locations of IL-1β-expressing PDL-Fib and RANKL-expressing PDL-Fib in PD. The heterogenic feature of fibroblasts expressing IL-1β and RANKL was also mirrored in our combined cross-tissue single-cell RNA sequencing datasets analysis. In summary, our study elucidates the heterogeneity of PDL-Fib, highlighting distinct functional groups for producing RANKL and IL-1β, which collectively promote OC generation and bone destruction in PD.

CD97 inhibits osteoclast differentiation via Rap1a/ERK pathway under compression

Acceleration of tooth movement during orthodontic treatment is challenging, with osteoclast-mediated bone resorption on the compressive side being the rate-limiting step. Recent studies have demonstrated that mechanoreceptors on the surface of monocytes/macrophages, especially adhesion G protein-coupled receptors (aGPCRs), play important roles in force sensing. However, its role in the regulation of osteoclast differentiation remains unclear. Herein, through single-cell analysis, we revealed that CD97, a novel mechanosensitive aGPCR, was expressed in macrophages. Compression upregulated CD97 expression and inhibited osteoclast differentiation; while knockdown of CD97 partially rescued osteoclast differentiation. It suggests that CD97 may be an important mechanosensitive receptor during osteoclast differentiation. RNA sequencing analysis showed that the Rap1a/ERK signalling pathway mediates the effects of CD97 on osteoclast differentiation under compression. Consistently, we clarified that administration of the Rap1a inhibitor GGTI298 increased osteoclast activity, thereby accelerating tooth movement. In conclusion, our results indicate that CD97 suppresses osteoclast differentiation through the Rap1a/ERK signalling pathway under orthodontic compressive force.

The interleukin-6 signal regulates orthodontic tooth movement and pain

Orthodontic tooth movement (OTM) is accomplished by controlling the mechanical loading onto the bone around the roots of target teeth. The precise orthodontic force induces osteoclastic bone resorption on the compression side and osteoblastic bone formation on the tension side of the alveolar bone. Orthodontic intervention causes inflammation in the periodontal ligament (PDL), which manifests as acute pain. Because inflammation is deeply connected to bone remodeling, it has been indicated that the inflammation after orthodontic intervention affects both the movement of teeth and generation of pain. However, the precise mechanisms underlying the immune regulation of OTM and the related pain are not well elucidated. Here, we found from the search of a public database that the interleukin (IL)-6 family of cytokines are highly expressed in the PDL by mechanical loading. The IL-6 signal was activated in the PDL after orthodontic intervention. The signal promoted OTM by inducing osteoclastic bone resorption. IL-6 was found to increase the number of osteoclasts by suppressing apoptosis and increasing their responsiveness to macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). Furthermore, IL-6 signal was shown to elicit orthodontic pain by inducing neuroinflammation in the trigeminal ganglion (TG). Taken together, it was demonstrated that the IL-6 signal regulates tooth movement and pain during orthodontic treatment. It was also indicated that local blockade of the IL-6 signal is a promising therapeutic option in orthodontic treatment, targeting both tooth movement and pain.

MicroRNA-155 targets SOCS1 to inhibit osteoclast differentiation during orthodontic tooth movement

BACKGROUND

MicroRNA-155 (miR-155) is a multifunctional miRNA whose expression is known to be involved in a range of physiological and pathological processes. Its association with several oral diseases has been established. However, the specific role of miR-155 in orthodontic tooth movement remains unclear. In this study, we investigated the impact of miR-155 on osteoclast differentiation and orthodontic tooth movement models, aiming to explore the underlying mechanisms.

METHODS

In this experiment, we utilized various agents including miR-155 mimic, miR-155 inhibitor, as well as non-specific sequences (NC mimic & NC inhibitor) to treat murine BMMNCs. Subsequently, osteoclast induction (OC) was carried out to examine the changes in the differentiation ability of monocytes under different conditions. To assess these changes, we employed RT-PCR, Western blotting, and TRAP staining techniques. For the orthodontic tooth movement model in mice, the subjects were divided into two groups: the NaCl group (injected with saline solution) and the miR-155 inhibitor group (injected with AntagomiR-155). We observed the impact of orthodontic tooth movement using stereoscopic microscopy, micro-CT, and HE staining. Furthermore, we performed RT-PCR and Western blotting analyses on the tissues surrounding the moving teeth. Additionally, we employed TargetScan to predict potential target genes of miR-155.

RESULTS

During osteoclast induction of BMMNCs, the expression of miR-155 exhibited an inverse correlation with osteoclast-related markers. Overexpression of miR-155 led to a decrease in osteoclast-related indexes, whereas underexpression of miR-155 increased those indexes. In the mouse orthodontic tooth movement model, the rate of tooth movement was enhanced following injection of the miR-155 inhibitor, leading to heightened osteoclast activity. TargetScan analysis identified SOCS1 as a target gene of miR-155.

CONCLUSIONS

Our results suggest that miR-155 functions as an inhibitor of osteoclast differentiation, and it appears to regulate osteoclasts during orthodontic tooth movement. The regulatory mechanism of miR-155 in this process involves the targeting of SOCS1.

Mechanisms of Osteoclastogenesis in Orthodontic Tooth Movement and Orthodontically Induced Tooth Root Resorption

Orthodontic tooth movement (OTM) is achieved by the simultaneous activation of bone resorption by osteoclasts and bone formation by osteoblasts. When orthodontic forces are applied, osteoclast-mediated bone resorption occurs in the alveolar bone on the compression side, creating space for tooth movement. Therefore, controlling osteoclastogenesis is the fundamental tenet of orthodontic treatment. Orthodontic forces are sensed by osteoblast lineage cells such as periodontal ligament (PDL) cells and osteocytes. Of several cytokines produced by these cells, the most important cytokine promoting osteoclastogenesis is the receptor activator of nuclear factor-κB ligand (RANKL), which is mainly supplied by osteoblasts. Additionally, osteocytes embedded within the bone matrix, T lymphocytes in inflammatory conditions, and PDL cells produce RANKL. Besides RANKL, inflammatory cytokines, such as interleukin-1, tumor necrosis factor-α, and prostaglandin E2 promote osteoclastogenesis under OTM. On the downside, excessive osteoclastogenesis activation triggers orthodontically-induced external root resorption (ERR) through pro-osteoclastic inflammatory cytokines. Therefore, understanding the mechanisms of osteoclastogenesis during OTM is essential in reducing the adverse effects of orthodontic treatment. Here, we review the current concepts of the mechanisms underlying osteoclastogenesis in OTM and orthodontically induced ERR.

Synergy of Regenerative Periodontal Surgery and Orthodontics Improves Quality of Life of Patients with Stage IV Periodontitis: 24-Month Outcomes of a Multicenter RCT

In stage IV periodontitis patients with pathologic tooth migration (PTM), interdisciplinary treatment includes regenerative periodontal surgery (RPS) with an application of biomaterials and orthodontic therapy (OT) to restore function, esthetics and thereby quality of life (QoL). In a 24-month randomized trial we explored the synergy between regenerative medicine and biomechanical force application. The following methods were used: Forty-three patients had been randomized to a combined treatment comprising RPS and subsequent OT starting either 4 weeks (early OT) or 6 months (late OT) post-operatively. Clinical periodontal parameters and oral health-related QoL (GOHAI) were recorded up to 24 months. We obtained the following results: Mean clinical attachment gain (∆CAL ± SD) was significantly higher with early OT (5.96 ± 2.1 mm) versus late OT (4.65 ± 1.76 mm) (p = 0.034). Pocket closure (PPD ≤ 4 mm) was obtained in 91% of defects with early OT compared to 90% with late OT. GOHAI-scores decreased significantly from 26.1 ± 7.5 to 9.6 ± 4.7 (early OT) and 25.1 ± 7.1 to 12.7 ± 5.6 (late OT). Inconclusion, teeth severely compromised by intrabony defects and PTM can be treated successfully by RPS followed by early OT with the advantage of an overall reduced treatment time. As a result of the combined periodontal-orthodontic therapy, the oral health-related QoL of patients was significantly improved. Early stimulation of wound healing with orthodontic forces had a favorable impact on the outcomes of regenerative periodontal surgery.