Sclerostin Promotes Bone Remodeling in the Process of Tooth Movement

Physiological cell bioprinting density in human bone-derived cell-laden scaffolds enhances matrix mineralization rate and stiffness under dynamic loading

Human organotypic bone models are an emerging technology that replicate bone physiology and mechanobiology for comprehensive in vitro experimentation over prolonged periods of time. Recently, we introduced a mineralized bone model based on 3D bioprinted cell-laden alginate-gelatin-graphene oxide hydrogels cultured under dynamic loading using commercially available human mesenchymal stem cells. In the present study, we created cell-laden scaffolds from primary human osteoblasts isolated from surgical waste material and investigated the effects of a previously reported optimal cell printing density (5 × 106 cells/mL bioink) vs. a higher physiological cell density (10 × 106 cells/mL bioink). We studied mineral formation, scaffold stiffness, and cell morphology over a 10-week period to determine culture conditions for primary human bone cells in this microenvironment. For analysis, the human bone-derived cell-laden scaffolds underwent multiscale assessment at specific timepoints. High cell viability was observed in both groups after bioprinting (>90%) and after 2 weeks of daily mechanical loading (>85%). Bioprinting at a higher cell density resulted in faster mineral formation rates, higher mineral densities and remarkably a 10-fold increase in stiffness compared to a modest 2-fold increase in the lower printing density group. In addition, physiological cell bioprinting densities positively impacted cell spreading and formation of dendritic interconnections. We conclude that our methodology of processing patient-specific human bone cells, subsequent biofabrication and dynamic culturing reliably affords mineralized cell-laden scaffolds. In the future, in vitro systems based on patient-derived cells could be applied to study the individual phenotype of bone disorders such as osteogenesis imperfecta and aid clinical decision making.

The effect of light compressive and tensile mechanical forces on SOST and POSTN expressions in human periodontal ligament cells: an in vitro study

Periodontal ligament (PDL) cells play an important role in mechanosensing and secretion of signaling molecules during bone remodeling. However, the regulatory mechanism is unknown. The aim of the present study is to investigate the expression pattern of periostin and sclerostin in response to orthodontic forces in periodontal ligament cells in vitro. PDL cells were isolated from extracted teeth and treated with compressive forces of 25 gr/cm2 or equiaxial tension forces at frequency 1 Hz for 0, 24, 48, and 72 h. qRT-PCR was applied to evaluate the gene expressions. The secretion of sclerostin and periostin was assessed using ELISA. DAPI staining was used to evaluate apoptosis. The expression of sclerostin elevated significantly at protein and gene levels under compression forces after 24 h, while the application of tensile forces induced the expression of periostin and its upstream regulator RUNX2 (p < 0.05). Gene expression up-regulation was significant for POSTN and RUNX2 after 48 and 72 h tensile forces. Also, the gene expression of sclerostin reduced in a time-dependent manner after application of tensile force. The compression forces enhanced apoptosis to 7.5 ± 3.5% and induced gene expression of apoptotic markers of CASP9, and BCL2 within 72 h of exposure. Periostin and sclerostin play an important role in orthodontic loads and their expressions are affected oppositely by compressive and tensile forces that might be suggested as a biomarker for assessment of bone remodeling during orthodontic treatment.

Dynamic changes in transcriptome during orthodontic tooth movement

OBJECTIVES

The objective of this study was to determine global changes in gene expression with next generation sequencing (NGS) in order to assess the biological effects of orthodontic tooth movement (OTM) on alveolar bone in a rat model.

MATERIALS AND METHODS

Thirty-five Wistar rats (age 14 weeks) were used in the study. The OTM was performed using closed coil Nickel-Titanium spring to apply a mesial force on maxillary first molars of 8-10 g. Three hours, 1, 3, 7 and 14 days after the placement of the appliance, rats were killed at each time point respectively. The alveolar bone, around left maxillary first molar, were excised on compression side. The samples were immediately frozen in liquid nitrogen for subsequent RNA extraction. Total RNA samples were prepared for mRNA sequencing using the Illumina kit. RNA-Seq reads were aligned to the rat genomes using the STAR Aligner and bioinformatic analysis was performed.

RESULTS

A total of 18 192 genes were determined. Day 1 has the highest number of differentially expressed genes (DEGs) observed with more upregulated than downregulated genes. A total of 2719 DEGs were identified to use as input for the algorithm. Six distinct clusters of temporal patterns were observed representing proteins that were differentially regulated indicating different expression kinetics. Principal component analysis (PCA) showed distinct clustering by time points and days 3, 7 and 14 share similar gene expression pattern.

CONCLUSIONS

Distinct gene expression pattern was observed at different time points studied. Hypoxia, inflammation and bone remodelling pathways are major mechanisms behind OTM.

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.

Role of noncoding RNAs in orthodontic tooth movement: new insights into periodontium remodeling

Orthodontic tooth movement (OTM) is biologically based on the spatiotemporal remodeling process in periodontium, the mechanisms of which remain obscure. Noncoding RNAs (ncRNAs), especially microRNAs and long noncoding RNAs, play a pivotal role in maintaining periodontal homeostasis at the transcriptional, post-transcriptional, and epigenetic levels. Under force stimuli, mechanosensitive ncRNAs with altered expression levels transduce mechanical load to modulate intracellular genes. These ncRNAs regulate the biomechanical responses of periodontium in the catabolic, anabolic, and coupling phases throughout OTM. To achieve this, down or upregulated ncRNAs actively participate in cell proliferation, differentiation, autophagy, inflammatory, immune, and neurovascular responses. This review highlights the regulatory mechanism of fine-tuning ncRNAs in periodontium remodeling during OTM, laying the foundation for safe, precise, and personalized orthodontic treatment.

The Effect of IFT80 Deficiency in Osteocytes on Orthodontic Loading-Induced and Physiologic Bone Remodeling: In Vivo Study

Osteocytes are the main mechanosensory cells during orthodontic and physiologic bone remodeling. However, the question of how osteocytes transmit mechanical stimuli to biological responses remains largely unanswered. Intraflagellar transport (IFT) proteins are important for the formation and function of cilia, which are proposed to be mechanical sensors in osteocytes. In particular, IFT80 is highly expressed in mouse skulls and essential for ciliogenesis. This study aims to investigate the short- and long-term effects of IFT80 deletion in osteocytes on orthodontic bone remodeling and physiological bone remodeling in response to masticatory force. We examined 10-week-old experimental DMP1 CRE+.IFT80f/f and littermate control DMP1 CRE-.IFT80f/f mice. After 5 and 12 days of orthodontic force loading, the orthodontic tooth movement distance and bone parameters were evaluated using microCT. Osteoclast formation was assessed using TRAP-stained paraffin sections. The expression of sclerostin and RANKL was examined using immunofluorescence stain. We found that the deletion of IFT80 in osteocytes did not significantly impact either orthodontic or physiologic bone remodeling, as demonstrated by similar OTM distances, osteoclast numbers, bone volume fractions (bone volume/total volume), bone mineral densities, and the expressions of sclerostin and RANKL. Our findings suggest that there are other possible mechanosensory systems in osteocytes and anatomic limitations to cilia deflection in osteocytes in vivo.

Sclerostin is a promising therapeutic target for oral inflammation and regenerative dentistry

Sclerostin is the protein product of the SOST gene and is known for its inhibitory effects on bone formation. The monoclonal antibody against sclerostin has been approved as a novel treatment method for osteoporosis. Oral health is one of the essential aspects of general human health. Hereditary bone dysplasia syndrome caused by sclerostin deficiency is often accompanied by some dental malformations, inspiring the therapeutic exploration of sclerostin in the oral and dental fields. Recent studies have found that sclerostin is expressed in several functional cell types in oral tissues, and the expression level of sclerostin is altered in pathological conditions. Sclerostin not only exerts similar negative outcomes on the formation of alveolar bone and bone-like tissues, including dentin and cementum, but also participates in the development of oral inflammatory diseases such as periodontitis, pulpitis, and peri-implantitis. This review aims to highlight related research progress of sclerostin in oral cavity, propose necessary further research in this field, and discuss its potential as a therapeutic target for dental indications and regenerative dentistry.

Sclerostin in Periodontal Ligament: Homeostatic Regulator in Biophysical Force-Induced Tooth Movement

AIM

This study elucidates the role of sclerostin in periodontal ligament (PDL) as a homeostatic regulator in biophysical force-induced tooth movement (BFTM).

MATERIALS AND METHODS

BFTM was performed in rats, followed by microarray, immunofluorescence, in situ hybridization, and real-time PCR for detection and identification of the molecules. The periodontal space was analyzed via micro-computed tomography. Effects on osteoclastogenesis and bone resorption were evaluated in mouse bone marrow-derived cells. In vitro human PDL cells were subjected to biophysical forces.

RESULTS

In the absence of BFTM, sclerostin was hardly detected in the periodontium except the PDL and alveolar bone in the furcation region and apex of the molar roots. However, sclerostin was upregulated in the PDL in vivo by adaptable force, which induced typical transfiguration without changes in periodontal space as well as in vitro PDL cells under compression and tension. In contrast, the sclerostin level was unaffected by heavy force, which caused severe degeneration of the PDL and narrowed periodontal space. Sclerostin inhibited osteoclastogenesis and bone resorption, which corroborates the accelerated tooth movement by the heavy force.

CONCLUSIONS

Sclerostin in PDL may be a key homeostatic molecule in the periodontium and a biological target for the therapeutic modulation of BFTM. This article is protected by copyright. All rights reserved.

The c-Myc Oncogene Maintains Corneal Epithelial Architecture at Homeostasis, Modulates p63 Expression, and Enhances Proliferation During Tissue Repair

Purpose

The transcription factor c-Myc (Myc) plays central regulatory roles in both self-renewal and differentiation of progenitors of multiple cell lineages. Here, we address its function in corneal epithelium (CE) maintenance and repair.

Methods

Myc ablation in the limbal–corneal epithelium was achieved by crossing a floxed Myc mouse allele (Myc^fl/fl) with a mouse line expressing the Cre recombinase gene under the keratin (Krt) 14 promoter. CE stratification and protein localization were assessed by histology of paraffin and plastic sections and by immunohistochemistry of frozen sections, respectively. Protein levels and gene expression were determined by western blot and real-time quantitative PCR, respectively. CE wound closure was tracked by fluorescein staining.

Results

At birth, mutant mice appeared indistinguishable from control littermates; however, their rates of postnatal weight gain were 67% lower than those of controls. After weaning, mutants also exhibited spontaneous skin ulcerations, predominantly in the tail and lower lip, and died 45 to 60 days after birth. The mutant CE displayed an increase in stratal thickness, increased levels of Krt12 in superficial cells, and decreased exfoliation rates. Accordingly, the absence of Myc perturbed protein and mRNA levels of genes modulating differentiation and proliferation processes, including ΔNp63β, Ets1, and two Notch target genes, Hey1 and Maml1. Furthermore, Myc promoted CE wound closure and wound-induced hyperproliferation.

Conclusions

Myc regulates the balance among CE stratification, differentiation, and surface exfoliation and promotes the transition to the hyperproliferative state during wound healing. Its effect on this balance may be exerted through the control of multiple regulators of cell fate, including isoforms of tumor protein p63.

Sclerostin regulation: a promising therapy for periodontitis by modulating alveolar bone

Periodontitis is one of the most prevalent epidemics affecting human health and life recently, and exploration of the pathogenesis and treatment of periodontitis has been valued by scholars. In recent years, sclerostin, a new factor on bone resorption and reconstruction caused by inflammation and mechanical stimulation, has been a research hotspot. This article summarizes the researches on sclerostin in periodontitis development in recent years. Among them, sclerostin has been shown to be a critical negative regulator of bone formation, thereby inhibiting bone remodeling in periodontitis development, and is closely associated with tooth movement. Besides, evidence indicates that the removal of sclerostin seems to reasonably protect the alveolar bone from resorption. Regulation of sclerostin expression is a novel, promising treatment for periodontitis and addresses several complications seen with traditional therapies; accordingly, many drugs with similar mechanisms have emerged. Moreover, the application prospect of sclerostin in periodontal therapy combined with orthodontic treatment is another promising approach. There are also a lot of drugs that regulate sclerostin. Anti-sclerostin antibody (Scl-Ab) is the most direct one that inhibits bone resorption caused by sclerostin. At present, drugs that inhibit the expression of sclerostin have been applied to the treatment of diseases such as multiple myeloma and osteoporosis. Therefore, the application of sclerostin in the oral field is just around the corner, which provides a new therapeutic bone regulation strategy in oral and general health.

Mechanistic Insight into Orthodontic Tooth Movement Based on Animal Studies: A Critical Review

Alveolar bone remodeling in orthodontic tooth movement (OTM) is a highly regulated process that coordinates bone resorption by osteoclasts and new bone formation by osteoblasts. Mechanisms involved in OTM include mechano-sensing, sterile inflammation-mediated osteoclastogenesis on the compression side and tensile force-induced osteogenesis on the tension side. Several intracellular signaling pathways and mechanosensors including the cilia and ion channels transduce mechanical force into biochemical signals that stimulate formation of osteoclasts or osteoblasts. To date, many studies were performed in vitro or using human gingival crevicular fluid samples. Thus, the use of transgenic animals is very helpful in examining a cause and effect relationship. Key cell types that participate in mediating the response to OTM include periodontal ligament fibroblasts, mesenchymal stem cells, osteoblasts, osteocytes, and osteoclasts. Intercellular signals that stimulate cellular processes needed for orthodontic tooth movement include receptor activator of nuclear factor-κB ligand (RANKL), tumor necrosis factor-α (TNF-α), dickkopf Wnt signaling pathway inhibitor 1 (DKK1), sclerostin, transforming growth factor beta (TGF-β), and bone morphogenetic proteins (BMPs). In this review, we critically summarize the current OTM studies using transgenic animal models in order to provide mechanistic insight into the cellular events and the molecular regulation of OTM.

Establishment of in vitro three-dimensional cementocyte differentiation scaffolds to study orthodontic root resorption

Orthodontic-induced root resorption is a severe side effect that can lead to tooth root shortening and loss. Compressive force induces tissue stress in the cementum that covers the tooth root, which is associated with activation of bone metabolism and cementum resorption. To investigate the role of cementocytes in mechanotransduction and osteoclast differentiation, the present study established an in vitro three-dimensional (3D) model replicating cellular cementum and observed the effects of static compression on the cellular behavior of the cementocytes. Cell Counting Kit-8 assay, alkaline phosphatase staining and dentin matrix protein 1 quantification were used to evaluate the cementocyte differentiation in the 3D scaffolds. Cellular viability under static compression was evaluated using live/dead staining, and expression of mineral metabolism-related genes were analyzed via reverse transcription-quantitative PCR. The results suggested that the cementocytes maintained their phenotype and increased the expression of osteoprotegerin (OPG), receptor activator of NF-κB ligand (RANKL) and sclerostin (SOST) in the 3D model compared with cells cultured in two dimensions. Compression force increased cell death and induced osteoclastic differentiation via the upregulation of SOST and RANKL/OPG ratio, and the downregulation of osteocalcin. The effect of compression showed a force magnitude-dependent pattern. The present study established an in vitro model of cellular cementum to study the biology of cementocytes. The results indicated that cementocytes are sensitive to mechanical loading and may serve potential roles in the metabolic regulation of minerals during orthodontic root resorption. These findings provide a novel tool to study biological processes in the field of orthodontics and expand knowledge of the biological function of cementocytes.

Gli1+ Periodontium Stem Cells Are Regulated by Osteocytes and Occlusal Force

Teeth are attached to alveolar bone by the periodontal ligament (PDL), which contains stem cells supporting tissue turnover. Here, we identified Gli1+ cells in adult mouse molar PDL as multi-potential stem cells (PDLSCs) giving rise to PDL, alveolar bone, and cementum. They support periodontium tissue turnover and injury repair. Gli1+ PDLSCs are surrounding the neurovascular bundle and more enriched in the apical region. Canonical Wnt signaling is essential for their activation. Alveolar bone osteocytes negatively regulate Gli1+ PDLSCs activity through sclerostin, a Wnt inhibitor. Blockage of sclerostin accelerates the PDLSCs lineage contribution rate in vivo. Sclerostin expression is modulated by physiological occlusal force. Removal of occlusal force upregulates sclerostin and inhibits PDLSCs activation. In summary, Gli1+ cells are the multipotential PDLSCs in vivo. Osteocytes provide negative feedback to PDLSCs and inhibit their activities through sclerostin. Physiological occlusal force indirectly regulates PDLSCs activities by fine-tuning this feedback loop.

Osteocyte TSC1 promotes sclerostin secretion to restrain osteogenesis in mice

Osteocytes secrete the glycoprotein sclerostin to inhibit bone formation by osteoblasts, but how sclerostin production is regulated in osteocytes remains unclear. Here, we show that tuberous sclerosis complex 1 (TSC1) in osteocytes promotes sclerostin secretion through inhibition of mechanistic target of rapamycin complex 1 (mTORC1) and downregulation of Sirt1. We generated mice with DMP1-Cre-directed Tsc1 gene deletion (Tsc1 CKO) to constitutively activate mTORC1 in osteocytes. Although osteocyte TSC1 disruption increased RANKL expression and osteoclast formation, it markedly reduced sclerostin production in bone, resulting in severe osteosclerosis with enhanced bone formation in mice. Knockdown of TSC1 activated mTORC1 and decreased sclerostin, while rapamycin inhibited mTORC1 and increased sclerostin mRNA and protein expression levels in MLO-Y4 osteocyte-like cells. Furthermore, mechanical loading activated mTORC1 and prevented sclerostin expression in osteocytes. Mechanistically, TSC1 promotes sclerostin production and prevents osteogenesis through inhibition of mTORC1 and downregulation of Sirt1, a repressor of the sclerostin gene Sost. Our findings reveal a role of TSC1/mTORC1 signalling in the regulation of osteocyte sclerostin secretion and bone formation in response to mechanical loading in vitro. Targeting TSC1 represents a potential strategy to increase osteogenesis and prevent bone loss-related diseases.

Suppression of tooth movement-induced sclerostin expression using β-adrenergic receptor blockers

OBJECTIVE

Regulation of bone metabolism by the sympathetic nervous system has recently been clarified. Tooth movement is increased by increased bone metabolic turnover due to sympathetic activation. This study aimed to compare the effects of the β-adrenergic receptor (β-AR) blockers atenolol (β1-AR blocker), butoxamine (β2-AR blocker) and propranolol (non-selective β-AR blocker) on tooth movement in spontaneously hypertensive rats (SHR) with sympathicotonia.

MATERIALS AND METHODS

Spontaneously hypertensive rats were divided into the following four groups: an SHR control group and groups treated with 0.1 mg/kg atenolol, 1 mg/kg butoxamine or 1 mg/kg propranolol (n = 6 rats/group). Atenolol, butoxamine or propranolol was administered daily to each treatment group, and orthodontic force was applied using a closed-coil spring. Finally, immunohistochemical analysis was performed for receptor activator of nuclear factor kappa-B ligand (RANKL) and sclerostin (SOST).

RESULTS

Atenolol, butoxamine and propranolol inhibited tooth movement and increased maxillary alveolar bone volume. Histological analysis revealed that these β-AR blockers decreased osteoclast activity on the compression side. Furthermore, immunohistochemical analysis revealed that atenolol, butoxamine and propranolol decreased the number of RANKL- and SOST-positive osteocytes on the compression side.

CONCLUSIONS

β-AR blockers decreased tooth movement and downregulated SOST in osteocytes, accompanied by increasing alveolar bone resorption.

Three-Dimensional Co-culture of Primary Human Osteocytes and Mature Human Osteoclasts in Collagen Gels

Osteoclasts are pivotal cells for bone remodeling and their activity is coordinated by osteocytes that reside inside the bone matrix. In vitro co-cultures of osteocytes and osteoclasts are therefore advantageous to analyze the crosstalk between these cell species. In this study, primary osteocytes were isolated from human bone in a multistep isolation process and embedded into three-dimensional collagen gels. Mature human osteoclasts were generated by differentiation of human peripheral blood mononuclear cells (PBMCs). Different surfaces were tested for osteoclast formation: suspension dishes, collagen gels, and normal tissue culture polystyrene. After detachment from the surfaces, osteoclasts showed typical morphology and gene expression of osteoclast markers. Osteoclasts that were differentiated on collagen exhibited the highest osteoclast marker expression. Cocultivation of mature osteoclasts with osteocytes was performed in a transwell system, with osteocytes, embedded in collagen gels at the apical side and osteoclasts on the basal side of a porous polyethylen terephtalate membrane, which allowed the separate gene expression analysis for osteocytes and osteoclasts. After 7 days of co-culture both cell species showed their typical morphology, which is multinucleated giant cells for osteoclasts and star-shaped cells with dendritic extensions for osteocytes. Furthermore, osteoclast markers tartrate-resistant acid phosphatase, carbonic anhydrase II, and cathepsin K were detected both on gene expression and protein level in single and co-cultures. Osteocytes showed gene expression of typical osteocyte markers E11, sclerostin, dentin matrix protein 1, osteocalcin, and receptor activator of nuclear factor-κ ligand both in single and co-culture. Impact statement This study is the first to establish an in vitro bone model that contains both primary human osteocytes and primary human osteoclasts. Previous studies applied rodent osteocyte cell lines to examine the influence of osteocytes on osteoclast function. This model mimics the clinical situation better since osteocytes are postmitotic cells whose function might be different in primary state compared with a proliferating cell line. Furthermore, the co-culture model can be the basis for in vitro triple culture models involving osteoblasts as the third bone cell species.

Effects of occlusal forces on the peri-implant-bone interface stability

The occlusal forces and their influence on the initiation of peri-implant bone loss or their relationship with peri-implantitis have created discussion during the past 30 years given the discrepancies observed in clinical, animal, and finite element analysis studies. Beyond these contradictions, in the case of an osseointegrated implant, the occlusal forces can influence the implant-bone interface and the cells responsible for the bone remodeling in different ways that may result in the maintenance or loss of the osseointegration. This comprehensive review focuses on the information available about the forces transmitted through the implant-crown system to the implant-bone interface and the mechano-transduction phenomena responsible for the bone cells' behavior and their interactions. Knowledge of the basic molecular biology of the peri-implant bone would help clinicians to understand the complex phenomenon of occlusal forces and their effects on the implant-bone interface, and would allow better control of the negative effects of mechanical stresses, leading to therapy with fewer risks and complications.

Murine iPSC-derived microglia and macrophage cell culture models recapitulate distinct phenotypical and functional properties of classical and alternative neuro-immune polarisation

The establishment and validation of reliable induced pluripotent stem cell (iPSC)-derived in vitro models to study microglia and monocyte/macrophage immune function holds great potential for fundamental and translational neuro-immunology research. In this study, we first demonstrate that ramified CX₃CR1⁺ iPSC-microglia (cultured within a neural environment) and round-shaped CX₃CR1^- iPSC-macrophages can easily be differentiated from newly established murine CX₃CR1^eGFP/+CCR2^RFP/+ iPSC lines. Furthermore, we show that obtained murine iPSC-microglia and iPSC-macrophages are distinct cell populations, even though iPSC-macrophages may upregulate CX₃CR1 expression when cultured within a neural environment. Next, we characterized the phenotypical and functional properties of murine iPSC-microglia and iPSC-macrophages following classical and alternative immune polarisation. While iPSC-macrophages could easily be triggered to adopt a classically-activated or alternatively-activated phenotype following, respectively, lipopolysaccharide + interferon γ or interleukin 13 (IL13) stimulation, iPSC-microglia and iPSC-macrophages cultured within a neural environment displayed a more moderate activation profile as characterised by the absence of MHCII expression upon classical immune polarisation and the absence of Ym1 expression upon alternative immune polarisation. Finally, extending our preceding in vivo studies, this striking phenotypical divergence was also observed for resident microglia and infiltrating monocytes within highly inflammatory cortical lesions in CX₃CR1^eGFP/+CCR2^RFP/+ mice subjected to middle cerebral arterial occlusion (MCAO) stroke and following IL13-mediated therapeutic intervention thereon. In conclusion, our study demonstrates that the applied murine iPSC-microglia and iPSC-macrophage culture models are able to recapitulate in vivo microglia and monocyte/macrophage ontogeny and corresponding phenotypical/functional properties upon classical and alternative immune polarisation, and therefore represent a valuable in vitro platform to further study and modulate microglia and (infiltrating) monocyte immune responses under neuro-inflammatory conditions within a neural environment.

Impact of pharmacologic inhibition of tooth movement on periodontal and tooth root tissues during orthodontic force application

OBJECTIVE

The goal of this study was to investigate potential negative sequelae of orthodontic force application ±delivery of an osteoclast inhibitor, recombinant osteoprotegerin protein (OPG-Fc), on periodontal tissues.

SETTING AND SAMPLE POPULATION

Sprague Dawley rats from a commercial supplier were investigated in a laboratory setting.

MATERIALS AND METHODS

Rats were randomly divided into four groups (n = 7 each): one group with no orthodontic appliances and injected once prior to the experimental period with empty polymer microspheres, one group with orthodontic appliances and injected once with empty microspheres, one group with orthodontic appliances and injected once with polymer microspheres containing 1 mg/kg of OPG-Fc, and one group with orthodontic appliances and injected with non-encapsulated 5 mg/kg of OPG-Fc every 3 days during the experimental period. The animals were euthanized after 28 days of tooth movement for histomorphometric analyses.

RESULTS

Root resorption, PDL area and widths were similar in animals without appliances and animals with appliances plus high-dose OPG-Fc. PDL blood vessels were compressed and decreased in number in all animals that received orthodontic appliances, regardless of OPG-Fc. Hyalinization was significantly increased only in animals with orthodontic appliances plus multiple injections of 5 mg/kg non-encapsulated OPG-Fc when compared to animals without appliances.

CONCLUSIONS

Results of this study indicate that while pharmacological modulation of tooth movement through osteoclast inhibition is feasible when delivered in a locally controlled low-dose manner, high-dose levels that completely prevent tooth movement through bone may decrease local blood flow and increase the incidence of hyalinization.

Effect of TNF-α-Induced Sclerostin on Osteocytes during Orthodontic Tooth Movement

Osteocytes are abundant cells in bone, which contribute to bone maintenance. Osteocytes express receptor activator of nuclear factor kappa-B ligand (RANKL) and regulate osteoclast formation. Orthodontic tooth movement (OTM) occurs by osteoclast resorption of alveolar bone. Osteocyte-derived RANKL is critical in bone resorption during OTM. Additionally, tumor necrosis factor-α (TNF-α) is important in osteoclastogenesis during OTM. Sclerostin has been reported to enhance RANKL expression in the MLO-Y4 osteocyte-like cell line. This study investigated the effect of TNF-α on sclerostin expression in osteocytes during OTM. In vitro analysis of primary osteocytes, which were isolated from DMP1-Topaz mice by sorting the Topaz variant of GFP-positive cells, revealed that SOST mRNA expression was increased when osteocytes were cultured with TNF-α and that RANKL mRNA expression was increased when osteocytes were cultured with sclerostin. Moreover, the number of TRAP-positive cells was increased in osteocytes and osteoclast precursors cocultured with sclerostin. In vivo analysis of mouse calvariae that had been subcutaneously injected with phosphate-buffered saline (PBS) or TNF-α revealed that the number of TRAP-positive cells and the percentage of sclerostin-positive osteocytes were higher in the TNF-α group than in the PBS group. Furthermore, the level of SOST mRNA was increased by TNF-α. As an OTM model, a Ni-Ti closed-coil spring connecting the upper incisors and upper-left first molar was placed to move the first molar to the mesial direction in wild-type (WT) mice and TNF receptor 1- and 2-deficient (TNFRsKO) mice. After 6 days of OTM, the percentage of sclerostin-positive osteocytes on the compression side of the first molar in TNFRsKO mice was lower than that in WT mice. In this study, TNF-α increased sclerostin expression in osteocytes, and sclerostin enhanced RANKL expression in osteocytes. Thus, TNF-α may play an important role in sclerostin expression in osteocytes and enhance osteoclast formation during OTM.

Sclerostin injection enhances orthodontic tooth movement in rats

OBJECTIVE

It was aimed to investigate the in vivo effects of local injection of sclerostin protein on orthodontic tooth movement.

DESIGN

A total of 48 rats underwent orthodontic mesialization of the maxillary first molars on both sides. Local injection was given at the compression side in the alveolar bone on both maxillary sides, with sclerostin protein carried by hydrogel on one side, and the same volume of normal saline carried by hydrogel on the other side serving as the control. After two weeks, the tooth movement amount and effects on the periodontium were assessed through micro-computed tomography (μCT) analysis, tartrate-resistant acid phosphatase (TRAP) staining and immunohistochemistry (IHC) analysis.

RESULTS

After two weeks of intervention, tooth movement was significantly greater in the 4 μg/kg and 20 μg/kg sclerostin injection groups, compared to the control. Analysis of the furcation area of the maxillary first molar showed that the 20 μg/kg group had significantly decreased BV/TV. At the compression side, the number of TRAP-positive osteoclasts was significantly increased in 20 μg/kg group compared to the control. The expression of RANKL was statistically higher in all the sclerostin groups, while the expression of OPG was statistically lower in the 4 μg/kg and 20 μg/kg groups, compared to the control. At the tension side, the expression of RUNX2 and COL-1 was statistically higher in the 20 μg/kg group compared to the control.

CONCLUSIONS

Local injection of sclerostin protein in the alveolar bone at the compression side accelerates OTM in rats by promoting osteoclastogenesis.

Mechanical Loading Differentially Affects Osteocytes in Fibulae from Lactating Mice Compared to Osteocytes in Virgin Mice: Possible Role for Lacuna Size

Hormonal changes during lactation are associated with profound changes in bone cell biology, such as osteocytic osteolysis, resulting in larger lacunae. Larger lacuna shape theoretically enhances the transmission of mechanical signals to osteocytes. We aimed to provide experimental evidence supporting this theory by comparing the mechanoresponse of osteocytes in the bone of lactating mice, which have enlarged lacunae due to osteocytic osteolysis, with the response of osteocytes in bone from age-matched virgin mice. The osteocyte mechanoresponse was measured in excised fibulae that were cultured in hormone-free medium for 24 h and cyclically loaded for 10 min (sinusoidal compressive load, 3000 µε, 5 Hz) by quantifying loading-related changes in Sost mRNA expression (qPCR) and sclerostin and β-catenin protein expression (immunohistochemistry). Loading decreased Sost expression by ~ threefold in fibulae of lactating mice. The loading-induced decrease in sclerostin protein expression by osteocytes was larger in lactating mice (55% decrease ± 14 (± SD), n = 8) than virgin mice (33% decrease ± 15, n = 7). Mechanical loading upregulated β-catenin expression in osteocytes in lactating mice by 3.5-fold (± 0.2, n = 6) which is significantly (p < 0.01) higher than the 1.6-fold increase in β-catenin expression by osteocytes in fibulae from virgin mice (± 0.12, n = 4). These results suggest that osteocytes in fibulae from lactating mice with large lacunae may respond stronger to mechanical loading than those from virgin mice. This could indicate that osteocytes residing in larger lacuna show a stronger response to mechanical loading.

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

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Role of Osteocyte-PDL Crosstalk in Tooth Movement via SOST/Sclerostin

Sclerostin (Scl) negatively regulates bone formation and favors bone resorption. Osteocytes, the cells responsible for mechanosensing, are known as the primary source of Scl and are a key regulator of bone remodeling through the induction of receptor activator of NF-κB ligand (RANKL). However, the spatiotemporal patterns of Scl in response to mechanical stimuli and their regulatory mechanisms remain unknown. We investigated the regulatory dynamics of the SOST/Scl expression generated by orthodontic tooth movement (OTM) in vivo and in vitro. In 8-wk-old male mice, coil springs were used to move the first molar mesially for 0, 1, 5, or 10 d. A regional histogram and the distribution patterns of the Scl expression showed that the Scl expression in the alveolar bone was increased on the compression side and peaked on day 5, with a gradual increase in the degree of significance. On day 10, the expression around the periodontal ligament (PDL)-alveolar bone boundary returned to the control level. Conversely, the expression of Scl on the tension side was only significantly decreased on day 1. Compressive force biphasically modulated the SOST/Scl expression in the isolated human PDL and thereby upregulated osteocytic SOST via paracrine activation in an osteocyte-PDL co-culture system designed to mimic OTM. This system did not affect the RANKL or OPG expression in osteocytes, suggesting that the bone resorption pathways are acted upon in a PDL-dependent and osteocyte-independent manner through RANKL/OPG signaling. Moreover, sclerostin neutralizing antibody significantly attenuated the upregulation of SOST that was induced by compressive force. In conclusion, our results provide evidence to support that factors secreted by the PDL, including SOST/Scl, control alveolar bone remodeling through osteocytic SOST/Scl in OTM.

[SOST knockdown promotes differentiation of osteoblasts MG63 and mesenchymal stem cells C3H10 in an in vitro model of bone metastasis of breast cancer]

OBJECTIVE

To investigate whether SOST is involved in breast cancer MDA-MB-231 cells-induced suppression of differentiation of osteoblast MG63 cells and mesenchymal stem C3H10 cells.

METHODS

SOST-specific small interfering RNA (siRNA) was transfected into breast cancer MDA-MB-231 cells, and the interfering efficiency was verified by RT-PCR. The supernatants were collected from MDA-MB-231 cells in routine culture, cells transfected with SOST siRNA via adenovirus, and cells transfected with empty adenoviral vectors and added in MG63 or C3H10 cell cultures. The changes in the expressions of OPG, OCN, OPN and IBSP in MG63 and C3H10 cells were detected using quantitative real-time PCR, and ALP activity was detected with ALP reading and ALP staining with the cells cultured in routine culture medium and cells in osteogenic induction medium as the negative and positive controls.

RESULTS

The adenovirus Ad-siSOST effectively knocked down the expression of SOST in MDA-MB-231 cells. MG63 cells and C3H10 cells cultured in osteogenic medium showed significantly upregulated expressions of the osteoblast markers OPG, OPN, OCN and IBSP (P<0.01), while co-culture with the supernatant of MDA-MB-231 cells obviously reduced the expressions of the osteoblast markers (P<0.01); the expression of the markers increased again in MG63 and C3H10 cells after treatment with the supernatant of MDA-MB-231 cells transfected with ad-siSOST (P<0.01). ALP activity in MG63 and C3H10 cells exhibited a similar pattern of variations in response to the treatments (P<0.01).

CONCLUSION

In the in vitro model of bone metastasis of breast cancer, the differentiation of MG63 or C3H10 cells is suppressed, which can be partly reversed by knocking down the expression of SOST in the bone metastasis microenvironment.