Direct cell-cell contact between periodontal ligament fibroblasts and osteoclast precursors synergistically increases the expression of genes related to osteoclastogenesis

Osteogenic differentiation of periodontal ligament fibroblasts inhibits osteoclast formation

One of the deficits of knowledge on bone remodelling, is to what extent cells that are driven towards osteogenic differentiation can contribute to osteoclast formation. The periodontal ligament fibroblast (PdLFs) is an ideal model to study this, since they play a role in osteogenesis, and can also orchestrate osteoclastogenesis.when co-cultured with a source of osteoclast-precursor such as peripheral blood mononuclear cells (PBMCs). Here, the osteogenic differentiation of PdLFs and the effects of this process on the formation of osteoclasts were investigated. PdLFs were obtained from extracted teeth and exposed to osteogenic medium for 0, 7, 14, or 21 out of 21 days. After this 21-day culturing period, the cells were co-cultured with peripheral blood mononuclear cells (PBMCs) for an additional 21 days to study osteoclast formation. Alkaline phosphatase (ALP) activity, calcium concentration, and gene expression of osteogenic markers were assessed at day 21 to evaluate the different stages of osteogenic differentiation. Alizarin red staining and scanning electron microscopy were used to visualise mineralisation. Tartrate-resistant acid phosphatase (TRAcP) activity, TRAcP staining, multinuclearity, the expression of osteoclastogenesis-related genes, and TNF-α and IL-1β protein levels were assessed to evaluate osteoclastogenesis. The osteogenesis assays revealed that PdLFs became more differentiated as they were exposed to osteogenic medium for a longer period of time. Mineralisation by these osteogenic cells increased with the progression of differentiation. Culturing PdLFs in osteogenic medium before co-culturing them with PMBCs led to a significant decrease in osteoclast formation. qPCR revealed significantly lower DCSTAMP expression in cultures that had been supplemented with osteogenic medium. Protein levels of osteoclastogenesis stimulator TNF-α were also lower in these cultures. The present study shows that the osteogenic differentiation of PdLFs reduces the osteoclastogenic potential of these cells. Immature cells of the osteoblastic lineage may facilitate osteoclastogenesis, whereas mature mineralising cells may suppress the formation of osteoclasts. Therefore, mature and immature osteogenic cells may have different roles in maintaining bone homeostasis.

Effects of Improper Mechanical Force on the Production of Sonic Hedgehog, RANKL, and IL-6 in Human Periodontal Ligament Cells In Vitro

Improper mechanical stress may induce side effects during orthodontic treatment. If the roots and alveolar bones are extensively resorbed following excess mechanical stress, unplanned tooth mobility and inflammation can occur. Although multiple factors are believed to contribute to the development of side effects, the cause is still unknown. Sonic hedgehog (Shh), one of the hedgehog signals significantly associated with cell growth and cancer development, promotes osteoclast formation in the jawbone. Shh may be associated with root and bone resorptions during orthodontic treatment. In this study, we investigated the relationships between Shh, RANKL, and IL-6 in human periodontal ligament (hPDL) cells exposed to improper mechanical force. Weights were placed on hPDL cells and human gingival fibroblasts (HGFs) for an optimal orthodontic force group (1.0 g/cm2) and a heavy orthodontic force group (4.0 g/cm2). A group with no orthodontic force was used as a control group. Real-time PCR, SDS-PAGE, and Western blotting were performed to examine the effects of orthodontic forces on the expression of Shh, RANKL, and IL-6 at 2, 4, 6, 8, 12, and 24 h after the addition of pressure. The protein expression of Shh was not clearly induced by orthodontic forces of 1.0 and 4.0 g/cm2 compared with the control in HGFs and hPDL cells. In contrast, RANKL and IL-6 gene and protein expression was significantly induced by 1.0 and 4.0 g/cm2 in hPDL cells for forces lasting 6~24 h. However, neither protein was expressed in HGFs. RANKL and IL-6 expressions in response to orthodontic forces and in the control were clearly inhibited by Shh inhibitor RU-SKI 43. Shh did not directly link to RANKL and IL-6 for root and bone resorptions by orthodontic force but was associated with cell activities to be finally guided by the production of cytokines in hPDL cells.

Multiple effects of dose-related GM-CSF on periodontal resorption in deep-frozen grafted teeth: A reverse study

Autologous tooth grafting is a dental restorative modality based on periodontal ligament healing.Human periodontal ligament stem cells(PDLSCs) are involved in the formation and remodeling of periodontal tissue.Based on previous findings, the proliferation and differentiation of processing cryopreserved periodontal ligament stem cells (PDLSCs) exhibit similarities to those of fresh cells. However, there is evident absorption in the transplanted frozen tooth's roots and bones, with the underlying cause remaining unknown. Granulocyte macrophage colony-stimulating factor(GM-CSF) is named for its produce granulocyte and macrophage precursors from bone marrow precursors, and it also serves as one of the regulatory factors in inflammatory and osteoclast formation. This study aimed to investigate changes in GM-CSF expression in frozen PDLSCs (fhPDLSCs) and evaluate the impact of GM-CSF on PDLSCs with respect to cellular activity and osteogenic ability. The role of GM-CSF in periodontal absorption was further speculated by comparing with IL-1β. The results revealed a significant increase in GM-CSF levels from fhPDLSCs compared to fresh cells, which exhibited an equivalent inflammatory stimulation effect as 1 ng/ml IL-1β. Cell viability also increased with increasing concentrations of GM-CSF; however, the GM-CSF from fhPDLSCs was not sufficient to significantly trigger osteoclastic factors. Considering its interaction with IL-1β and positive feedback mechanism, environments with high doses of GM-CSF derived from fhPDLSCs are more likely to activate osteoclastic responses.Therefore, for frozen tooth replantation, great attention should be paid to anti-inflammation and anti-infection.GM-CSF may serve as a potential therapeutic target for inhibiting periodontal resorption in delayed grafts.

Emerging Oral Nicotine Products and Periodontal Diseases

Oral nicotine pouches are emerging as a new "modern oral" nicotine product. These prefilled pouches contain nicotine, flavorings, and filling agents that dissolve in the mouth. Nicotine can be derived from tobacco leaf or chemical synthesis. Traces of TSNAs and toxic chromium were detected in the pouch products. This raises the concern about general and periodontal health. This review aims to update the current oral nicotine products research relating to periodontal disease and its relevance in periodontal inflammation. Nicotine interacts with host cells and affects inflammatory responses to microbial challenges. It may directly or indirectly deteriorate periodontal tissues by activating nicotinic acetylcholine receptors, repressing PDL fibroblasts cells, increasing cellular ROS and cytokines/chemokines, growth factors, breaking microbiota balance, and dysregulating miRNAs expression. Studies show that appealing flavorings contained in nicotine pouches pose harm to periodontal innate immune responses and increase penetration of nitrosamines. In addition, flavored ONPs increase the risk of dual or poly-tobacco products among young adults, stacking up detrimental effects on the periodontium. Given the recent growth of users, further studies are needed to elucidate the impact of ONPs, even poly-tobacco use, on systemic and periodontal health. Moreover, policymakers should ensure to avoid generating a new wave of nicotine addiction among youths in the U.S.

Dental and Orthopaedic Implant Loosening: Overlap in Gene Expression Regulation

Objectives

Endoprosthetic loosening still plays a major role in orthopaedic and dental surgery and includes various cellular immune processes within peri-implant tissues. Although the dental and orthopaedic processes vary in certain parts, the clinical question arises whether there are common immune regulators of implant loosening. Analyzing the key gene expressions common to both processes reveals the mechanisms of osteoclastogenesis within periprosthetic tissues of orthopaedic and dental origin.

Methods

Donor peripheral blood mononuclear cells (PBMCs) and intraoperatively obtained periprosthetic fibroblast-like cells (PPFs) were (co-)cultured with [± macrophage-colony stimulating factor (MCSF) and Receptor Activator of NF-κB ligand (RANKL)] in transwell and monolayer culture systems and examined for osteoclastogenic regulations [MCSF, RANKL, osteoprotegerin (OPG), and tumor necrosis factor alpha (TNFα)] as well as the ability of bone resorption. Sequencing analysis compared dental and orthopaedic (co-)cultures.

Results

Monolayer co-cultures of both origins expressed high levels of OPG, resulting in inhibition of osteolysis shown by resorption assay on dentin. The high OPG-expression, low RANKL/OPG ratios and a resulting inhibition of osteolysis were displayed by dental and orthopaedic PPFs in monolayer even in the presence of MCSF and RANKL, acting as osteoprotective and immunoregulatory cells. The osteoprotective function was only observed in monolayer cultures of dental and orthopaedic periprosthetic cells and downregulated in the transwell system. In transwell co-cultures of PBMCs/PPFs profound changes of gene expression, with a significant decrease of OPG (20-fold dental versus 100 fold orthopaedic), were identified. Within transwell cultures, which offer more in vivo like conditions, RANKL/OPG ratios displayed similar high levels to the original periprosthetic tissue. For dental and orthopaedic implant loosening, overlapping findings in principal component and heatmap analysis were identified.

Conclusions

Thus, periprosthetic osteoclastogenesis may be a correlating immune process in orthopaedic and dental implant failure leading to comparable reactions with regard to osteoclast formation. The transwell cultures system may provide an in vivo like model for the exploration of orthopaedic and dental implant loosening.

Diabetes Medication Metformin Inhibits Osteoclast Formation and Activity in In Vitro Models for Periodontitis

Diabetes and periodontitis are comorbidities and may share common pathways. Several reports indicate that diabetes medication metformin may be beneficial for the periodontal status of periodontitis patients. Further research using appropriate cell systems of the periodontium, the tissue that surrounds teeth may reveal the possible mechanism. Periodontal ligament fibroblasts anchor teeth in bone and play a role in the onset of both alveolar bone formation and degradation, the latter by inducing osteoclast formation from adherent precursor cells. Therefore, a cell model including this type of cells is ideal to study the influence of metformin on both processes. We hypothesize that metformin will enhance bone formation, as described for osteoblasts, whereas the effects of metformin on osteoclast formation is yet undetermined. Periodontal ligament fibroblasts were cultured in the presence of osteogenic medium and 0.2 or 1 mM metformin. The influence of metformin on osteoclast formation was first studied in PDLF cultures supplemented with peripheral blood leukocytes, containing osteoclast precursors. Finally, the effect of metformin on osteoclast precursors was studied in cultures of CD14⁺ monocytes that were stimulated with M-CSF and receptor activator of Nf-κB ligand (RANKL). No effects of metformin were observed on osteogenesis: not on alkaline phosphatase activity, Alizarin red deposition, nor on the expression of osteogenic markers RUNX-2, Collagen I and Osteonectin. Metformin inhibited osteoclast formation and accordingly downregulated the genes involved in osteoclastogenesis: RANKL, macrophage colony stimulating factor (M-CSF) and osteoclast fusion gene DC-STAMP. Osteoclast formation on both plastic and bone as well as bone resorption was inhibited by metformin in M-CSF and RANKL stimulated monocyte cultures, probably by reduction of RANK expression. The present study unraveling the positive effect of metformin in periodontitis patients at the cellular level, indicates that metformin inhibits osteoclast formation and activity, both when orchestrated by periodontal ligament fibroblasts and in cytokine driven osteoclast formation assays. The results indicate that metformin could have a systemic beneficiary effect on bone by inhibiting osteoclast formation and activity.

Mechanism of alveolar bone destruction in periodontitis - Periodontal bacteria and inflammation

Periodontal disease is an inflammatory disease caused by periodontopathogenic bacteria, which eventually leads to bone tissue (alveolar bone) destruction as inflammation persists. Periodontal tissues have an immune system against the invasion of these bacteria, however, due to the persistent infection by periodontopathogenic bacteria, the host innate and acquired immunity is impaired, and tissue destruction, including bone tissue destruction, occurs. Osteoclasts are essential for bone destruction. Osteoclast progenitor cells derived from hematopoietic stem cells differentiate into osteoclasts. In addition, bone loss occurs when bone resorption by osteoclasts exceeds bone formation by osteoblasts. In inflammatory bone disease, inflammatory cytokines act on osteoblasts and receptor activator of nuclear factor-κB ligand (RANKL)-producing cells, resulting in osteoclast differentiation and activation. In addition to this mechanism, pathogenic factors of periodontal bacteria and mechanical stress activate osteoclasts and destruct alveolar bone in periodontitis. In this review, we focused on the mechanism of osteoclast activation in periodontitis and provide an overview based on the latest findings.

Nox4 Promotes RANKL-Induced Autophagy and Osteoclastogenesis via Activating ROS/PERK/eIF-2α/ATF4 Pathway

Receptor activator of nuclear factor-κB ligand (RANKL) has been found to induce osteoclastogenesis and bone resorption. However, the underlying molecular mechanisms remain unclear. Via conducting a series of biochemical experiments with in vitro cell lines, this study investigated the role and mechanism of NADPH oxidase 4 (Nox4) in RANKL-induced autophagy and osteoclastogenesis. In the current study, we found that RANKL dramatically induced autophagy and osteoclastogenesis, inhibition of autophagy with chloroquine (CQ) markedly attenuates RANKL-induced osteoclastogenesis. Interestingly, we found that the protein level of Nox4 was remarkably upregulated by RANKL treatment. Inhibition of Nox4 by 5-O-methyl quercetin or knockdown of Nox4 with specific shRNA markedly attenuated RANKL-induced autophagy and osteoclastogenesis. Furthermore, we found that Nox4 stimulated the production of nonmitochondrial reactive oxygen species (ROS), activating the critical unfolded protein response (UPR)-related signaling pathway PERK/eIF-2α/ATF4, leading to RANKL-induced autophagy and osteoclastogenesis. Blocking the activation of PERK/eIF-2α/ATF4 signaling pathway either by Nox4 shRNA, ROS scavenger (NAC) or PERK inhibitor (GSK2606414) significantly inhibited autophagy during RANKL-induced osteoclastogenesis. Collectively, this study reveals that Nox4 promotes RANKL-induced autophagy and osteoclastogenesis via activating ROS/PERK/eIF-2α/ATF4 pathway, suggesting that the pathway may be a novel potential therapeutic target for osteoclastogenesis-related disease.

Although Anatomically Micrometers Apart: Human Periodontal Ligament Cells Are Slightly More Active in Bone Remodeling Than Alveolar Bone Derived Cells

The periodontal ligament (PDL) and the alveolar bone are part of the periodontium, a complex structure that supports the teeth. The alveolar bone is continuously remodeled and is greatly affected by several complex oral events, like tooth extraction, orthodontic movement, and periodontitis. Until now, the role of PDL cells in terms of osteogenesis and osteoclastogenesis has been widely studied, whereas surprisingly little is known about the bone remodeling capacity of alveolar bone. Therefore, the purpose of this study was to compare the biological character of human alveolar bone cells and PDL cells in terms of osteogenesis and osteoclastogenesis in vitro. Paired samples of PDL cells and alveolar bone cells from seven patients with compromised general and oral health were collected and cultured. Bone A (early outgrowth) and bone B (late outgrowth) were included. PDL, bone A, bone B cell cultures all had a fibroblast appearance with similar expression pattern of six mesenchymal markers. These cultures were subjected to osteogenesis and osteoclastogenesis assays. For osteoclastogenesis assays, the cells were co-cultured with peripheral blood mononuclear cells, a source for osteoclast precursor cells. The total duration of the experiments was 21 days. Osteogenesis was slightly favored for PDL compared to bone A and B as shown by stronger Alizarin red staining and higher expression of RUNX2 and Collagen I at day 7 and for ALP at day 21. PDL induced approximately two times more osteoclasts than alveolar bone cells. In line with these findings was the higher expression of cell fusion marker DC-STAMP in PDL-PBMC co-cultures compared to bone B at day 21. In conclusion, alveolar bone contains remodeling activity, but to a different extent compared to PDL cells. We showed that human alveolar bone cells can be used as an in vitro model to study bone remodeling.

Biomechanical and biological responses of periodontium in orthodontic tooth movement: up-date in a new decade

Nowadays, orthodontic treatment has become increasingly popular. However, the biological mechanisms of orthodontic tooth movement (OTM) have not been fully elucidated. We were aiming to summarize the evidences regarding the mechanisms of OTM. Firstly, we introduced the research models as a basis for further discussion of mechanisms. Secondly, we proposed a new hypothesis regarding the primary roles of periodontal ligament cells (PDLCs) and osteocytes involved in OTM mechanisms and summarized the biomechanical and biological responses of the periodontium in OTM through four steps, basically in OTM temporal sequences, as follows: (1) Extracellular mechanobiology of periodontium: biological, mechanical, and material changes of acellular components in periodontium under orthodontic forces were introduced. (2) Cell strain: the sensing, transduction, and regulation of mechanical stimuli in PDLCs and osteocytes. (3) Cell activation and differentiation: the activation and differentiation mechanisms of osteoblast and osteoclast, the force-induced sterile inflammation, and the communication networks consisting of sensors and effectors. (4) Tissue remodeling: the remodeling of bone and periodontal ligament (PDL) in the compression side and tension side responding to mechanical stimuli and root resorption. Lastly, we talked about the clinical implications of the updated OTM mechanisms, regarding optimal orthodontic force (OOF), acceleration of OTM, and prevention of root resorption.

Application of specialized pro-resolving mediators in periodontitis and peri-implantitis: a review

Scaling and root planning is a key element in the mechanical therapy used for the eradication of biofilm, which is the major etiological factor for periodontitis and peri‐implantitis. However, periodontitis is also a host mediated disease, therefore, removal of the biofilm without adjunctive therapy may not achieve the desired clinical outcome due to persistent activation of the innate and adaptive immune cells. Most recently, even the resident cells of the periodontium, including periodontal ligament fibroblasts, have been shown to produce several inflammatory factors in response to bacterial challenge. With increased understanding of the pathophysiology of periodontitis, more research is focusing on opposing excessive inflammation with specialized pro‐resolving mediators (SPMs). This review article covers the major limitations of current standards of care for periodontitis and peri‐implantitis, and it highlights recent advances and prospects of SPMs in the context of tissue reconstruction and regeneration. Here, we focus primarily on the role of SPMs in restoring tissue homeostasis after periodontal infection.

Fibroblast-like cells change gene expression of bone remodelling markers in transwell cultures

Introduction

Periprosthetic fibroblast-like cells (PPFs) play an important role in aseptic loosening of arthroplasties. Various studies have examined PPF behavior in monolayer culture systems. However, the periprosthetic tissue is a three-dimensional (3D) mesh, which allows the cells to interact in a multidirectional way. The expression of bone remodeling markers of fibroblast-like cells in a multilayer environment changes significantly versus monolayer cultures without the addition of particles or cytokine stimulation. Gene expression of bone remodeling markers was therefore compared in fibroblast-like cells from different origins and dermal fibroblasts under transwell culture conditions versus monolayer cultures.

Methods

PPFs from periprosthetic tissues (n = 12), osteoarthritic (OA) synovial fibroblast-like cells (SFs) (n = 6), and dermal fibroblasts (DFs) were cultured in monolayer (density 5.5 × 10³/cm²) or multilayer cultures (density 8.5 × 10⁵/cm²) for 10 or 21 days. Cultures were examined via histology, TRAP staining, immunohistochemistry (anti-S100a4), and quantitative real-time PCR.

Results

Fibroblast-like cells (PPFs/SFs) and dermal fibroblasts significantly increased the expression of RANKL and significantly decreased the expression of ALP, COL1A1, and OPG in multilayer cultures. PPFs and SFs in multilayer cultures further showed a higher expression of cathepsin K, MMP-13, and TNF-α. In multilayer PPF cultures, the mRNA level of TRAP was also found to be significantly increased.

Conclusion

The multilayer cultures are able to induce significant expression changes in fibroblast-like cells depending on the nature of cellular origin without the addition of any further stimulus. This system might be a useful tool to get more in vivo like results regarding fibroblast-like cell cultures.

Establishment and validation of an in vitro co-culture model for oral cell lines using human PBMC-derived osteoclasts, osteoblasts, fibroblasts and keratinocytes

Indirect co-culture models with osteoclasts including oral cell lines may be influenced by M-CSF and RANKL in the common cell medium. Therefore, we investigated the viability and proliferation of osteoblasts (OB), fibroblasts (FB) and oral keratinocytes (OK) under stratified medium modification and assessed the differentiation of osteoclasts in each co-culture. The impact of M-CSF and RANKL in the common OC co-culture was assessed for OB, FB and OK via MTT assay via DAPI control. The multinuclearity and function of OC were evaluated by light microscopy, DAPI staining, resorption assay and FACS analysis. The PBMC showed the highest differentiation into OC after an incubation period of 7 days. Furthermore, co-culture with OB enhanced the number of differentiated multinucleated OC in comparison with monoculture, whereas co-culture with OK decreased PBMC multinuclearity and OC differentiation. FB did not influence the number of differentiated OC in a co-culture. RANKL and M-CSF reduction had no impact on OC differentiation in co-culture with FB or OB, whereas this medium modification for OK attenuated PBMC multinuclearity and OC differentiation in all approaches. Supplementation of RANKL and M-CSF can be modified for a co-culture of PBMC with FB or OB without disturbing OC differentiation. Thus, pathogenic processes of bone remodelling involving OB, OC, FB and OK in the oral cavity can be investigated thoroughly.

Vitamin D3 and Dental Mesenchymal Stromal Cells

Vitamin D3 is a hormone involved in the regulation of bone metabolism, mineral homeostasis, and immune response. Almost all dental tissues contain resident mesenchymal stromal cells (MSCs), which are largely similar to bone marrow-derived MSCs. In this narrative review, we summarized the current findings concerning the physiological effects of vitamin D3 on dental MSCs. The existing literature suggests that dental MSCs possess the ability to convert vitamin D3 into 25(OH)D3 and subsequently to the biologically active 1,25(OH)2D3. The vitamin D3 metabolites 25(OH)D3 and 1,25(OH)2D3 stimulate osteogenic differentiation and diminish the inflammatory response of dental MSCs. In addition, 1,25(OH)2D3 influences the immunomodulatory properties of MSCs in different dental tissues. Thus, dental MSCs are both producers and targets of 1,25(OH)2D3 and might regulate the local vitamin D3-dependent processes in an autocrine/paracrine manner. The local vitamin D3 metabolism is assumed to play an essential role in the local physiological processes, but the mechanisms of its regulation in dental MSCs are mostly unknown. The alteration of the local vitamin D3 metabolism may unravel novel therapeutic modalities for the treatment of periodontitis as well as new strategies for dental tissue regeneration.

The effect of lipoxin A4 on E. coli LPS-induced osteoclastogenesis

Objectives

The objective of the present study was to investigate the effect of lipoxin-type A4 (LXA4) on bacterial-induced osteoclastogenesis.

Material and methods

Human periodontal ligament cells (PDLCs) in coculture with osteoclast precursors (RAW264.7 cells) were exposed to bacterial stimulation with lipopolysaccharide (LPS) to induce inflammation. After 24 h, cells were treated to 100 ng/ml of LXA4 and 50 ng/ml of forymul peptide receptor 2 (FPR2/ALX) receptor antagonist (Boc-2). After 5 days, osteoclastic resorptive activity was assessed on calcium phosphate (CaP) synthetic bone substitute. Additionally, osteoclastic differentiation was evaluated using tartrate-resistant acid phosphatase (TRAP) staining, TRAP enzymatic activity assay, and on the expression of osteoclast-specific genes.

Results

We found that stimulation of in the osteoclasts with LPS-stimulated PDLCs induced a significant increase in tartrate-resistant acid phosphatase (TRAP) positive cells, higher resorptive activity, and enhanced expression of specific genes. Meanwhile, LXA4-treatment exhibited strong anti-inflammatory activity, and was able to reverse these inflammatory effects.

Conclusions

We conclude that (1) PDLCs are a potential target for treating bacterial-induced bone resorption in patients with periodontal disease, and (2) LXA4 is a suitable candidate for such therapy.

Clinical relevance

The results prove that lipoxins have a protective role in bacterial-induced periodontal inflammation and alveolar bone resorption, which can be translated into a clinical beneficial alterative treatment.

The Possible Role of Neutrophils in the Induction of Osteoclastogenesis

The ligand of the receptor activator of NF-κB (RANKL) is a key molecule in the formation of osteoclasts, the key cells that cause the disease-associated alveolar bone resorption in periodontitis. We hypothesized that polymorphonuclear leukocytes (PMNs), found as the most prominent cells of inflamed periodontal tissues, could play an important role in providing signals to trigger osteoclastogenesis and thus activating pathological bone resorption in periodontitis. RANKL expression was investigated on circulatory PMNs (cPMNs) and oral PMNs (oPMNs) taken from both controls and periodontitis patients. On average, 2.3% and 2.4% RANKL expression was detected on the cPMNs and oPMNs from periodontitis patients, which did not differ significantly from healthy controls. Since cPMNs may acquire a more osteoclastogenesis-facilitating phenotype while migrating into the inflamed periodontium, we next investigated whether stimulated (with LPS, TNF-α, or IL-6) cPMNs have the capacity to contribute to osteoclastogenesis. Enduring surface expression of RANKL for short-lived cells as cPMNs was achieved by fixating stimulated cPMNs. RANKL expression on stimulated cPMNs, as assessed by flow cytometry and immunohistochemistry, was limited (6.48 ± 0.72%, mean expression ± SEM) after 24 and 48 hours of stimulation with LPS. Likewise, stimulation with TNF-α and IL-6 resulted in limited RANKL expression levels. These limited levels of expression did not induce osteoclastogenesis when cocultured with preosteoclasts for 10 days. We report that, under the aforementioned experimental conditions, neither cPMNs nor oPMNs directly induced osteoclastogenesis. Further elucidation of the key cellular players and immune mediators that stimulate alveolar bone resorption in periodontitis will help to unravel its pathogenesis.

Tunneling nanotubes mediate intercellular communication between endothelial progenitor cells and osteoclast precursors

Tunneling nanotube (TNT)-mediated cell communication play pivotal roles in a series of physiological and pathological processes in multicellular organism. This study was designed to investigate the existence of TNTs between EPCs and osteoclast precursors and evaluate their effects on the differentiation of osteoclast precursors. For these purposes, EPCs and osteoclast precursors (RAW264.7 cells) were stained with different fluorescent dyes before direct co-culture; then, the co-cultured cells were sorted by fluorescence activated cell sorter (FACS), and the differentiation of co-cultured RAW264.7 cells was evaluated. The results showed that the differentiation potential of RAW264.7 cells was significantly inhibited after their co-culture with EPCs. Additionally, the expression of macrophage migration inhibitory factor (MIF) was up-regulated in RAW264.7 cells after co-culture. Moreover, the MIF inhibitor ISO-1 could rescue the formation of TRAP-positive multinuclear osteoclasts and the expression of osteoclastogenesis-associated genes in the co-cultured RAW264.7 cells. The present study demonstrates that EPCs can affect the differentiation of osteoclast precursors through the TNT-like structures formed across these two types of cells and might inform new therapeutic strategies for osteolytic diseases.

Impact of Periprosthetic Fibroblast-Like Cells on Osteoclastogenesis in Co-Culture with Peripheral Blood Mononuclear Cells Varies Depending on Culture System

Co-culture studies investigating the role of periprosthetic fibroblasts (PPFs) in inflammatory osteoclastogenesis reveal contrary results, partly showing an osteoprotective function of fibroblasts and high OPG expression in monolayer. These data disagree with molecular analyses of original periosteolytic tissues. In order to find a more reliable model, PPFs were co-cultivated with peripheral blood mononuclear cells (PBMCs) in a transwell system and compared to conventional monolayer cultures. The gene expression of key regulators of osteoclastogenesis (macrophage colony-stimulating factor (MCSF), receptor activator of NF-κB ligand (RANK-L), osteoprotegerin (OPG), and tumor necrosis factor alpha (TNFα)) as well as the ability of bone resorption were analyzed. In monolayer co-cultures, PPFs executed an osteoprotective function with high OPG-expression, low RANK-L/OPG ratios, and a resulting inhibition of osteolysis even in the presence of MCSF and RANK-L. For transwell co-cultures, profound changes in gene expression, with a more than hundredfold decrease of OPG and a significant upregulation of TNFα were observed. In conclusion, we were able to show that a change of culture conditions towards a transwell system resulted in a considerably more osteoclastogenic gene expression profile, being closer to findings in original periosteolytic tissues. This study therefore presents an interesting approach for a more reliable in vitro model to examine the role of fibroblasts in periprosthetic osteoclastogenesis in the future.

Low‑frequency pulsed electromagnetic field inhibits RANKL‑induced osteoclastic differentiation in RAW264.7 cells by scavenging reactive oxygen species

Bone homeostasis is a dynamic balance maintained by bone formation and resorption. An increase in the number and activity of osteoclasts leads to excessive bone resorption, which in turn results in bone disease, including osteoporosis. Therefore, inhibiting the differentiation and activity of osteoclasts is important for maintaining bone mass. Several studies have revealed that the use of a low-frequency pulsed electromagnetic field (PEMF) is an effective method to treat osteoporosis. However, its exact mechanism remains to be fully clarified. Therefore, the present study was designed to examine the effects that PEMF exerts on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis and intracellular reactive oxygen species (ROS) production in RAW264.7 cells. The viability of cells was determined using a Cell Counting Kit-8 assay, and gene and protein expression were investigated via reverse transcription-quantitative polymerase chain reaction and western blot analyses. Furthermore, microscopy was performed to detect the levels of intracellular ROS and tartrate-resistant acid phosphatase (TRAP). Following the culture of RAW264.7 cells with RANKL (50 ng/ml) for 4 days (3 h/day) under PEMF (75 Hz, 1 mt) exposure, it was observed that PEMF had an inhibitory effect on RANKL-induced osteoclastic differentiation. Multinucleated osteoclast formation, the activity of TRAP and the expression of osteoclastogenesis-associated genes, including cathepsin K, nuclear factor of activated T cells cytoplasmic 1 and TRAP, were significantly reduced by PEMF. Furthermore, PEMF effectively decreased the generation of intracellular ROS during osteoclastic differentiation. In addition, the results demonstrated that ROS are the key factor in osteoclast differentiation and formation. Reducing intracellular ROS with diphenylene-iodonium chloride significantly inhibited RANKL-induced osteoclast differentiation. Taken together, the results of the present study demonstrated that PEMF may inhibit RANKL-induced osteoclastogenesis by scavenging intracellular ROS. These results may provide the groundwork for future PEMF clinical applications in osteoclast-associated bone disease.

Aminothiazoles inhibit osteoclastogenesis and PGE2 production in LPS-stimulated co-cultures of periodontal ligament and RAW 264.7 cells, and RANKL-mediated osteoclastogenesis and bone resorption in PBMCs

Inflammatory mediator prostaglandin E₂ (PGE₂ ) contributes to bone resorption in several inflammatory conditions including periodontitis. The terminal enzyme, microsomal prostaglandin E synthase-1 (mPGES-1) regulating PGE₂ synthesis is a promising therapeutic target to reduce inflammatory bone loss. The aim of this study was to investigate effects of mPGES-1 inhibitors, aminothiazoles TH-848 and TH-644, on PGE₂ production and osteoclastogenesis in co-cultures of periodontal ligament (PDL) and osteoclast progenitor cells RAW 264.7, stimulated by lipopolysaccharide (LPS), and bone resorption in RANKL-mediated peripheral blood mononuclear cells (PBMCs). PDL and RAW 264.7 cells were cultured separately or co-cultured and treated with LPS alone or in combination with aminothiazoles. Multinucleated cells stained positively for tartrate-resistant acid phosphatase (TRAP) were scored as osteoclast-like cells. Levels of PGE₂ , osteoprotegerin (OPG) and interleukin-6, as well as mRNA expression of mPGES-1, OPG and RANKL were analysed in PDL cells. PBMCs were treated with RANKL alone or in combination with aminothiazoles. TRAP-positive multinucleated cells were analysed and bone resorption was measured by the CTX-I assay. Aminothiazoles reduced LPS-stimulated osteoclast-like cell formation both in co-cultures and in RAW 264.7 cells. Additionally, aminothiazoles inhibited PGE₂ production in LPS-stimulated cultures, but did not affect LPS-induced mPGES-1, OPG or RANKL mRNA expression in PDL cells. In PBMCs, inhibitors decreased both osteoclast differentiation and bone resorption. In conclusion, aminothiazoles reduced the formation of osteoclast-like cells and decreased the production of PGE₂ in co-cultures as well as single-cell cultures. Furthermore, these compounds inhibited RANKL-induced bone resorption and differentiation of PBMCs, suggesting these inhibitors for future treatment of inflammatory bone loss such as periodontitis.

The effect of Activin-A on periodontal ligament fibroblasts-mediated osteoclast formation in healthy donors and in patients with fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a genetic disease characterized by heterotopic ossification (HO). The disease is caused by a mutation in the activin receptor type 1 (ACVR1) gene that enhances this receptor's responsiveness to Activin‐A. Binding of Activin‐A to the mutated ACVR1 receptor induces osteogenic differentiation. Whether Activin‐A also affects osteoclast formation in FOP is not known. Therefore we investigated its effect on the osteoclastogenesis‐inducing potential of periodontal ligament fibroblasts (PLF) from teeth of healthy controls and patients with FOP. We used western blot analysis of phosphorylated SMAD3 (pSMAD3) and quantitative polymerase chain reaction to assess the effect of Activin‐A on the PLF. PLF‐induced osteoclast formation and gene expression were studied by coculturing control and FOP PLF with CD14‐positive osteoclast precursor cells from healthy donors. Osteoclast formation was also assessed in control CD14 cultures stimulated by macrophage colony‐stimulating factor (M‐CSF) and receptor activator of nuclear factor kappa‐B ligand (RANK‐L). Although Activin‐A increased activation of the pSMAD3 pathway in both control and FOP PLF, it increased ACVR1, FK binding protein 12 (FKBP12), an inhibitor of DNA binding 1 protein (ID‐1) expression only in FOP PLF. Activin‐A inhibited PLF mediated osteoclast formation albeit only significantly when induced by FOP PLF. In these cocultures, it reduced M‐CSF and dendritic cell‐specific transmembrane protein (DC‐STAMP) expression. Activin‐A also inhibited osteoclast formation in M‐CSF and RANK‐L mediated monocultures of CD14+ cells by inhibiting their proliferation.

This study brings new insight on the role of Activin A in osteoclast formation, which may further add to understanding FOP pathophysiology; in addition to the known Activin‐A‐mediated HO, this study shows that Activin‐A may also inhibit osteoclast formation, thereby further promoting HO formation.

Effect of loaded orthodontic miniscrew implant on compressive stresses in adjacent periodontal ligament

OBJECTIVES

To describe the relationship between the proximity of miniscrew implants (MSIs) to the periodontal ligament (PDL) and stress in the PDL under different load magnitudes and different bone properties.

MATERIALS AND METHODS

Sixteen subject-specific finite element models of the region of the maxillary first molar and second premolar were developed using computed tomography images of four patients. For each patient, an MSI surface model derived from micro-computed tomography was placed at four different distances from the premolar PDL. Finite element analysis was conducted with mesial load on the MSI, increasing from 1 N to 4 N. Peak absolute compression stress (CS) was calculated at each 1 N step. Stepwise multiple regression modeling was conducted to explain compressive stress by proximity, load magnitude, and bone properties.

RESULTS

The multiple regression model explained 83.47% of the variation of CS and included all three factors: proximity, load magnitude, and bone properties. The model expected significant interaction between the bone properties and load magnitude, implying that strong bone properties could be associated with significant increases in CS at small increases in load.

CONCLUSIONS

To ensure the safety of adjacent roots, MSIs should be placed at least 1 mm from the roots. Assessment of alveolar bone properties is recommended when the use of MSI is intended, as some patients may present with strong bone properties and thereby a high risk of MSI-induced root resorption.

Survival, Retention, and Selective Proliferation of Lymphocytes Is Mediated by Gingival Fibroblasts

Periodontitis, a chronic inflammatory disease of the periodontium, is characterized by osteoclast-mediated alveolar bone destruction. Gingival fibroblasts (GFs) present in the bone-lining mucosa have the capacity to activate the formation of osteoclasts, but little is known about which local immune cells (co-)mediate this process. The aim of this study was to investigate the cellular interactions of GFs with immune cells, including the contribution of GFs to osteoclast formation and their possible role in the proliferation of these immune cells. In addition, we investigated the expression of adhesion molecules and the inflammatory cytokines that are evoked by this interaction. GFs were cocultured with peripheral blood mononuclear cells (PBMCs), CD14+ monocytes or peripheral blood lymphocytes (PBLs) for 7, 14, and 21 days. After 21 days, comparable numbers of multinucleated cells (osteoclasts) were found in gingival fibroblast (GF)-PBMC and GF-monocyte cocultures. No osteoclasts were formed in GF-PBL cocultures, indicating that the PBLs present in GF-PBMC cocultures do not contribute to osteoclastogenesis. Persisting mononuclear cells were interacting with osteoclasts in GF-PBMC cocultures. Remarkably, a predominance of CD3+ T cells was immunohistochemically detected in GF cocultures with PBLs and PBMCs for 21 days that frequently interacted with osteoclasts. Significantly more T, B (CD19+), and NK (CD56+CD3-) cells were identified with multicolor flow cytometry in both GF-PBMC and GF-PBL cocultures compared to monocultures without GFs at all time points. GFs retained PBLs independently of the presence of monocytes or osteoclasts over time, showing a stable population of T, B, and NK cells between 7 and 21 days. T helper and cytotoxic T cell subsets remained stable over time in GF cocultures, while the number of Th17 cells fluctuated. Lymphocyte retention is likely mediated by lymphocyte-function-associated antigen-1 (LFA-1) expression, which was significantly higher in GF-PBL cultures compared to GF-monocyte cultures. When assessing inflammatory cytokine expression, high tumor necrosis alpha expression was only observed in the GF-PBMC cultures, indicating that this tripartite presence of GFs, monocytes, and lymphocytes is required for such an induction. Carboxyfluorescein succinimidyl ester-labeling showed that only the CD3+ cells proliferated in presence of GFs. This study demonstrates a novel role for GFs in the survival, retention, and selective proliferation of lymphocytes.

Extracellular Matrix Expression and Production in Fibroblast-Collagen Gels: Towards an In Vitro Model for Ligament Wound Healing

Ligament wound healing involves the proliferation of a dense and disorganized fibrous matrix that slowly remodels into scar tissue at the injury site. This remodeling process does not fully restore the highly aligned collagen network that exists in native tissue, and consequently repaired ligament has decreased strength and durability. In order to identify treatments that stimulate collagen alignment and strengthen ligament repair, there is a need to develop in vitro models to study fibroblast activation during ligament wound healing. The objective of this study was to measure gene expression and matrix protein accumulation in fibroblast-collagen gels that were subjected to different static stress conditions (stress-free, biaxial stress, and uniaxial stress) for three time points (1, 2 or 3 weeks). By comparing our in vitro results to prior in vivo studies, we found that stress-free gels had time-dependent changes in gene expression (col3a1, TnC) corresponding to early scar formation, and biaxial stress gels had protein levels (collagen type III, decorin) corresponding to early scar formation. This is the first study to conduct a targeted evaluation of ligament healing biomarkers in fibroblast-collagen gels, and the results suggest that biomimetic in-vitro models of early scar formation should be initially cultured under biaxial stress conditions.

Osteogenic and osteoclastogenic potential of jaw bone-derived cells-A case study

Though the stem cell properties of tooth-derived periodontal ligament and gingival cells have been widely documented, surprisingly little is known about both the osteogenic and osteoclastogenic differentiation capacities of the more clinically relevant jaw bone-derived cells. These cells could be considered being recruited during bone healing such as after tooth extraction, after placing an implant, or after surgical or traumatic injury. Here, we compared the osteoblast and osteoclastogenesis features of four consecutive bone outgrowths with periodontal ligament and gingiva cells. For osteogenesis assay, cells were cultured in osteogenic medium, whereas in osteoclastogenesis assays, cells were cultured in the presence of human peripheral blood mononuclear cells (PBMCs) as a source of osteoclast precursors. After osteogenic stimulus, all six cell types responded by an increased expression of osteoblast markers RUNX2 and DMP1. Periodontal ligament cells expressed significantly higher levels of RUNX2 compared to all bone outgrowths. Alkaline phosphatase enzyme levels in periodontal ligament cells reached earlier and higher peak expression. Mineral deposits were highest in periodontal ligament, gingiva and the first bone outgrowth. Osteoclastogenesis revealed a stepwise increase of secreted pro-osteoclastogenesis proteins M-CSF, IL-1β, and TNF-α in the last three consecutive bone cultures. OPG mRNA showed the opposite: high expression in periodontal and gingiva cells and the first outgrowth. Osteoclast numbers were similar between the six cultures, both on bone and on plastic. This first study reveals that jaw bone outgrowths contain bone remodelling features that are slightly different from tooth-associated cells.

The Effects of Kaempferol-Inhibited Autophagy on Osteoclast Formation

Kaempferol, a flavonoid compound, is derived from the rhizome of Kaempferia galanga L., which is used in traditional medicine in Asia. Autophagy has pleiotropic functions that are involved in cell growth, survival, nutrient supply under starvation, defense against pathogens, and antigen presentation. There are many studies dealing with the inhibitory effects of natural flavonoids in bone resorption. However, no studies have explained the relationship between the autophagic and inhibitory processes of osteoclastogenesis by natural flavonoids. The present study was undertaken to investigate the inhibitory effects of osteoclastogenesis through the autophagy inhibition process stimulated by kaempferol in murin macrophage (RAW 264.7) cells. The cytotoxic effect of Kaempferol was investigated by MTT assay. The osteoclast differentiation and autophagic process were confirmed via tartrate-resistant acid phosphatase (TRAP) staining, pit formation assay, western blot, and real-time PCR. Kaempferol controlled the expression of autophagy-related factors and in particular, it strongly inhibited the expression of p62/SQSTM1. In the western blot and real time-PCR analysis, when autophagy was suppressed with the application of 3-Methyladenine (3-MA) only, osteoclast and apoptosis related factors were not significantly affected. However, we found that after cells were treated with kaempferol, these factors inhibited autophagy and activated apoptosis. Therefore, we presume that kaempferol-inhibited autophagy activated apoptosis by degradation of p62/SQSTM1. Further study of the p62/SQSTM1 gene as a target in the autophagy mechanism, may help to delineate the potential role of kaempferol in the treatment of bone metabolism disorders.

Interleukin-1β induces human cementoblasts to support osteoclastogenesis

Injury of the periodontium followed by inflammatory response often leads to root resorption. Resorption is accomplished by osteoclasts and their generation may depend on an interaction with the cells in direct contact with the root, the cementoblasts. Our study aimed to investigate the role of human cementoblasts in the formation of osteoclasts and the effect of interleukin (IL)-1β hereupon. Extracted teeth from healthy volunteers were subjected to sequential digestion by type I collagenase and trypsin. The effect of enzymatic digestion on the presence of cells on the root surface was analyzed by histology. Gene expression of primary human cementoblasts (pHCB) was compared with a human cementoblast cell line (HCEM). The pHCBs were analyzed for their expression of IL-1 receptors as well as of receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG). In a co-culture system consisting of osteoclast precursors (blood monocytes) and pHCBs, the formation of osteoclasts and their resorptive activity was assessed by osteo-assay and ivory slices. The cells obtained after a 120 min enzyme digestion expressed the highest level of bone sialoprotein, similar to that of HCEM. This fraction of isolated cells also shared a similar expression pattern of IL-1 receptors (IL1-R1 and IL1-R2). Treatment with IL-1β potently upregulated RANKL expression but not of OPG. pHCBs were shown to induce the formation of functional osteoclasts. This capacity was significantly stimulated by pretreating the pHCBs with IL-1β prior to their co-culture with human blood monocytes. Our study demonstrated that cementoblasts have the capacity to induce osteoclastogenesis, a capacity strongly promoted by IL-1β. These results may explain why osteoclasts can be formed next to the root of teeth.

An investigation into the interaction between tooth root cells and an inflammatory protein sheds light on root degradation following injury. Osteoclast cells digest old bone to release nutrients and recycle bone tissues in a vital process called bone resorption. Cementum, the mineral substance covering tooth roots, is not usually resorbed, but injury to the tissues surrounding roots often triggers inflammation followed by root degradation. To understand this phenomenon better, Ruchanee Salingcarnboriboon Ampornaramveth at Chulalongkorn University in Bangkok, Thailand, and co-workers investigated whether cementum cells can promote the formation of osteoclasts. They found that when cementum cells were treated with interleukin 1 beta, an inflammatory protein expressed at high levels in tissues following injury, levels of another protein needed for osteoclast formation increased. This boosted osteoclast formation around roots, resulting in root resorption

Microtechnologies for Cell Microenvironment Control and Monitoring

A great breadth of questions remains in cellular biology. Some questions cannot be answered using traditional analytical techniques and so demand the development of new tools for research. In the near future, the development of highly integrated microfluidic analytical platforms will enable the acquisition of unknown biological data. These microfluidic systems must allow cell culture under controlled microenvironment and high throughput analysis. For this purpose, the integration of a variable number of newly developed micro- and nano-technologies, which enable control of topography and surface chemistry, soluble factors, mechanical forces and cell–cell contacts, as well as technology for monitoring cell phenotype and genotype with high spatial and temporal resolution will be necessary. These multifunctional devices must be accompanied by appropriate data analysis and management of the expected large datasets generated. The knowledge gained with these platforms has the potential to improve predictive models of the behavior of cells, impacting directly in better therapies for disease treatment. In this review, we give an overview of the microtechnology toolbox available for the design of high throughput microfluidic platforms for cell analysis. We discuss current microtechnologies for cell microenvironment control, different methodologies to create large arrays of cellular systems and finally techniques for monitoring cells in microfluidic devices.

Periodontal and inflammatory bowel diseases: Is there evidence of complex pathogenic interactions?

Periodontal disease and inflammatory bowel disease (IBD) are both chronic inflammatory diseases. Their pathogenesis is mediated by a complex interplay between a dysbiotic microbiota and the host immune-inflammatory response, and both are influenced by genetic and environmental factors. This review aimed to provide an overview of the evidence dealing with a possible pathogenic interaction between periodontal disease and IBD. There seems to be an increased prevalence of periodontal disease in patients with IBD when compared to healthy controls, probably due to changes in the oral microbiota and a higher inflammatory response. Moreover, the induction of periodontitis seems to result in gut dysbiosis and altered gut epithelial cell barrier function, which might contribute to the pathogenesis of IBD. Considering the complexity of both periodontal disease and IBD, it is very challenging to understand the possible pathways involved in their coexistence. In conclusion, this review points to a complex pathogenic interaction between periodontal disease and IBD, in which one disease might alter the composition of the microbiota and increase the inflammatory response related to the other. However, we still need more data derived from human studies to confirm results from murine models. Thus, mechanistic studies are definitely warranted to clarify this possible bidirectional association.

Static compression regulates OPG expression in periodontal ligament cells via the CAMK II pathway

Objective

This study aimed to investigate the potential role of CAMK II pathway in the compression-regulated OPG expression in periodontal ligament cells (PDLCs).

Material and Methods

The PDL tissue model was developed by 3-D culturing human PDLCs in a thin sheet of poly lactic-co-glycolic acid (PLGA) scaffolds, which was subjected to static compression of 25 g/cm² for 3, 6 and 12 h, with or without treatment of KN-93. After that, the expression of OPG, RANKL and NFATC2 was investigated through real-time PCR and western blot analysis.

Results

After static compression, the NFATC2 and RANKL expression was significantly up-regulated, while partially suppressed by KN-93 for 6 and 12 h respectively. The OPG expression was significantly down-regulated by compression in 3 h, started to elevate in 6 h, and significantly up-regulated in 12 h. The up-regulation after 12 h was significantly suppressed by KN-93.

Conclusions

Long-term static compression increases OPG expression in PDLCs, at least partially, via the CAMK II pathway.

RUNX2 Mutation Impairs 1α,25-Dihydroxyvitamin D3 mediated Osteoclastogenesis in Dental Follicle Cells

Cleidocranial dysplasia (CCD), a skeletal disorder characterized by delayed permanent tooth eruption and other dental abnormalities, is caused by heterozygous RUNX2 mutations. As an osteoblast-specific transcription factor, RUNX2 plays a role in bone remodeling, tooth formation and tooth eruption. To investigate the crosstalk between RUNX2 and 1α,25-dihydroxyvitamin D3 (1α,25-(OH)₂D₃) in human dental follicle cells (hDFCs) during osteoclast formation, we established a co-culture system of hDFCs from CCD patient and healthy donors with peripheral blood mononuclear cells (PBMCs). Expression of the osteoclast-associated genes and the number of TRAP⁺ cells were reduced in CCD hDFCs, indicating its suppressed osteoclast-inductive ability, which was reflected by the downregulated RANKL/OPG ratio. In addition, 1α,25-(OH)₂D₃-stimulation elevated the expression of osteoclast-related genes, as well as RANKL mRNA levels and RANKL/OPG ratios in control hDFCs. Conversely, RUNX2 mutation abolished this 1α,25-(OH)₂D₃-induced RANKL gene activation and osteoclast formation in CCD hDFCs. Therefore, RUNX2 haploinsufficiency impairs dental follicle-induced osteoclast formation capacity through RANKL/OPG signaling, which may be partially responsible for delayed permanent tooth eruption in CCD patients. Furthermore, this abnormality was not rescued by 1α,25-(OH)₂D₃ application because 1α,25-(OH)₂D₃-induced RANKL activation in hDFCs is mediated principally via the RUNX2-dependent pathway.

Inflammatory and immune pathways in the pathogenesis of periodontal disease

The pathogenesis of periodontitis involves a complex immune/inflammatory cascade that is initiated by the bacteria of the oral biofilm that forms naturally on the teeth. The susceptibility to periodontitis appears to be determined by the host response; specifically, the magnitude of the inflammatory response and the differential activation of immune pathways. The purpose of this review was to delineate our current knowledge of the host response in periodontitis. The role of innate immunity, the failure of acute inflammation to resolve (thus becoming chronic), the cytokine pathways that regulate the activation of acquired immunity and the cells and products of the immune system are considered. New information relating to regulation of both inflammation and the immune response will be reviewed in the context of susceptibility to, and perhaps control of, periodontitis.

IL-17 regulates the expressions of RANKL and OPG in human periodontal ligament cells via TRAF6/TBK1-JNK/NF-κB pathways

Interleukin-17 (IL-17 or IL-17A), a pleiotropic cytokine produced by T helper (Th) 17 cells, is involved in the pathogenesis of various autoimmune and inflammatory disorders, including periodontitis. Although the ability of pro-inflammation in periodontitis have been widely investigated, the other biological functions of IL-17, including its role in bone remodeling and the underlying molecular mechanism, have not been well clarified. In the present study, IL-17 could significantly enhance the expression of receptor activator for nuclear factor-κB ligand (RANKL) and inhibit the expression of osteoprotegerin (OPG) in human periodontal ligament cells (hPDLCs), the two critical indicators for osteoclastogenesis, suggesting IL-17 may play a destructive role in the pathogenesis of periodontal bone remodeling. Pharmaceutical signal inhibitors targeted at MAPKs, Akt or NF-κB signals, inhibited IL-17-induced RANKL and OPG regulation. Notably, the enhancement of RANKL was significantly blocked by the inhibitors of JNK and NF-κB signals. The upstream signals were further investigated with the small interfering RNA (siRNA). Both TRAF6 and TBK1 were found to be the critically signal molecules for IL-17-dependent RANKL regulation in hPDLCs. These findings may provide comprehensive understanding of the role of IL-17 in the pathogenesis of periodontitis and might also provide a reasonable way for periodontitis therapy. This article is protected by copyright. All rights reserved.

The adaptor protein p62 is involved in RANKL-induced autophagy and osteoclastogenesis

Previous studies have implicated autophagy in osteoclast differentiation. The aim of this study was to investigate the potential role of p62, a characterized adaptor protein for autophagy, in RANKL-induced osteoclastogenesis. Real-time quantitative PCR and western blot analyses were used to evaluate the expression levels of autophagy-related markers during RANKL-induced osteoclastogenesis in mouse macrophage-like RAW264.7 cells. Meanwhile, the potential relationship between p62/LC3 localization and F-actin ring formation was tested using double-labeling immunofluorescence. Then, the expression of p62 in RAW264.7 cells was knocked down using small-interfering RNA (siRNA), followed by detecting its influence on RANKL-induced autophagy activation, osteoclast differentiation, and F-actin ring formation. The data showed that several key autophagy-related markers including p62 were significantly altered during RANKL-induced osteoclast differentiation. In addition, the expression and localization of p62 showed negative correlation with LC3 accumulation and F-actin ring formation, as demonstrated by western blot and immunofluorescence analyses, respectively. Importantly, the knockdown of p62 obviously attenuated RANKL-induced expression of autophagy- and osteoclastogenesis-related genes, formation of TRAP-positive multinuclear cells, accumulation of LC3, as well as formation of F-actin ring. Our study indicates that p62 may play essential roles in RANKL-induced autophagy and osteoclastogenesis, which may help to develop a novel therapeutic strategy against osteoclastogenesis-related diseases.

Intercellular adhesion molecule-1 inhibits osteogenic differentiation of mesenchymal stem cells and impairs bio-scaffold-mediated bone regeneration in vivo

Mesenchymal stem cell (MSC) loaded bio-scaffold transplantation is a promising therapeutic approach for bone regeneration and repair. However, growing evidence shows that pro-inflammatory mediators from injured tissues suppress osteogenic differentiation and impair bone formation. To improve MSC-based bone regeneration, it is important to understand the mechanism of inflammation mediated osteogenic suppression. In the present study, we found that synovial fluid from rheumatoid arthritis patients and pro-inflammatory cytokines including interleukin-1α, interleukin-1β, and tumor necrosis factor α, stimulated intercellular adhesion molecule-1(ICAM-1) expression and impaired osteogenic differentiation of MSCs. Interestingly, overexpression of ICAM-1 in MSCs using a genetic approach also inhibited osteogenesis. In contrast, ICAM-1 knockdown significantly reversed the osteogenic suppression. In addition, after transplanting a traceable MSC-poly(lactic-co-glycolic acid) construct in rat calvarial defects, we found that ICAM-1 suppressed MSC osteogenic differentiation and matrix mineralization in vivo. Mechanistically, we found that ICAM-1 enhances MSC proliferation but causes stem cell marker loss. Furthermore, overexpression of ICAM-1 stably activated the MAPK and NF-κB pathways but suppressed the PI3K/AKT pathway in MSCs. More importantly, specific inhibition of the ERK/MAPK and NF-κB pathways or activation of the PI3K/AKT pathway partially rescued osteogenic differentiation, while inhibition of the p38/MAPK and PI3K/AKT pathway caused more serious osteogenic suppression. In summary, our findings reveal a novel function of ICAM-1 in osteogenesis and suggest a new molecular target to improve bone regeneration and repair in inflammatory microenvironments.

RANK, RANKL and OPG expressions in a permanent molar with a replacement resorption

The aim of this study was to explore the expression of RANK, RANKL and OPG during ankylosis. Structural details and immunohistochemical investigations of the expression of RANK, RANKL and OPG in an extracted secondary retained permanent molar of a 12-year-old girl are reported. Woven and lamellar bones were observed in the thickness of the remodeled dental wall and a tertiary dentin was noticed around the pulp cavity. The resorbing multinucleated cells expressed TRAP and RANK but few of them also expressed RANKL. Both odontoblasts and osteoblasts expressed TRAP and RANK, but the expression of RANKL was limited to osteoblasts. OPG remained undetected. The present case reveals unusual expression of RANKL in the resorbing cells, TRAP and RANK in both osteoblasts and odontoblasts, and a failure of detection of OPG. These proteins could be involved in the pathogenesis of tooth ankylosis.