Signaling by mechanical strain involves transcriptional regulation of proinflammatory genes in human periodontal ligament cells in vitro

Intermittent compressive force regulates matrix metalloproteinases and tissue inhibitors of metalloproteinases expression in human periodontal ligament cells

OBJECTIVE

This study aims to evaluate the effects of intermittent compressive force (ICF) on the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) by human periodontal ligament cells (hPDLCs).

DESIGN

hPDLCs were subjected to ICF with a magnitude of 1.5 g/cm2 and loaded for 24 h. mRNA and protein expression of several MMPs and TIMPs were assessed using RT-PCR and ELISA analyses. An inhibitor of TGF-β (SB431542) was used to assess a possible role of TGF-β in the expression of MMPs and TIMPs under ICF.

RESULTS

mRNA and protein analyses showed that ICF significantly induced expression of TIMP1 and TIMP3, but decreased expression of MMP1. Incubation with the TGF-β inhibitor and applied to ICF showed a downregulation of TIMP3, but expression of MMP1 was not affected.

CONCLUSION

ICF is likely to affect ECM homeostasis by hPDLCs by regulating the expression of MMP1 and TIMPs. Moreover, TGF-β1 regulated expression of TIMP3. These findings suggest ICF may decrease the degradation of ECM and may thus be essential for maintaining PDL homeostasis.

Regulation and mechanistic insights into tensile strain in mesenchymal stem cell osteogenic differentiation

Bone marrow mesenchymal stem cells (BMSCs) are integral to bone remodeling and homeostasis, as they are capable of differentiating into osteogenic and adipogenic lineages. This differentiation is substantially influenced by mechanosensitivity, particularly to tensile strain, which is a prevalent mechanical stimulus known to enhance osteogenic differentiation. This review specifically examines the effects of various cyclic tensile stress (CTS) conditions on BMSC osteogenesis. It delves into the effects of different loading devices, magnitudes, frequencies, elongation levels, dimensionalities, and coculture conditions, providing a comparative analysis that aids identification of the most conducive parameters for the osteogenic differentiation of BMSCs. Subsequently, this review delineates the signaling pathways activated by CTS, such as Wnt/β-catenin, BMP, Notch, MAPK, PI3K/Akt, and Hedgehog, which are instrumental in mediating the osteogenic differentiation of BMSCs. Through a detailed examination of these pathways, this study elucidates the intricate mechanisms whereby tensile strain promotes osteogenic differentiation, offering valuable guidance for optimizing therapeutic strategies aimed at enhancing bone regeneration.

Under pressure-mechanisms and risk factors for orthodontically induced inflammatory root resorption: a systematic review

BACKGROUND

The application of orthodontic forces causes root resorption of variable severity with potentially severe clinical ramifications.

OBJECTIVE

To systematically review reports on the pathophysiological mechanisms of orthodontically induced inflammatory root resorption (OIIRR) and the associated risk factors based on in vitro, experimental, and in vivo studies.

SEARCH METHODS

We undertook an electronic search of four databases and a separate hand-search.

SELECTION CRITERIA

Studies reporting on the effect of orthodontic forces with/without the addition of potential risk factors on OIIRR, including (1) gene expression in in-vitro studies, the incidence root resorption in (2) animal studies, and (3) human studies.

DATA COLLECTION AND ANALYSIS

Potential hits underwent a two-step selection, data extraction, quality assessment, and systematic appraisal performed by duplicate examiners.

RESULTS

One hundred and eighteen articles met the eligibility criteria. Studies varied considerably in methodology, reporting of results, and variable risk of bias judgements.In summary, the variable evidence identified supports the notion that the application of orthodontic forces leads to (1) characteristic alterations of molecular expression profiles in vitro, (2) an increased rate of OIIRR in animal models, as well as (3) in human studies. Importantly, the additional presence of risk factors such as malocclusion, previous trauma, and medications like corticosteroids increased the severity of OIIRR, whilst other factors decreased its severity, including oral contraceptives, baicalin, and high caffeine.

CONCLUSIONS

Based on the systematically reviewed evidence, OIIRR seems to be an inevitable consequence of the application of orthodontic forces-with different risk factors modifying its severity. Our review has identified several molecular mechanisms that can help explain this link between orthodontic forces and OIIRR. Nevertheless, it must be noted that the available eligible literature was in part significantly confounded by bias and was characterized by substantial methodological heterogeneity, suggesting that the results of this systematic review should be interpreted with caution.

REGISTRATION

PROSPERO (CRD42021243431).

Cytokine expression in gingival crevicular fluid around teeth opposing dental implants and 3-unit fixed partial dentures in a cross-sectional study

OBJECTIVE

This study aimed to study the cytokines in gingival crevicular fluid (GCF) of the teeth opposing to dental implants and 3-unit fixed partial dentures (FPDs).

MATERIALS AND METHODS

A total of 74 participants were recruited for this cross-sectional study. Based on the status of lower first molars, the participants were divided into dental implants group and 3-unit FPDs group. Social index and oral hygiene were recorded. Occlusal loading was evaluated with a T-scan. GCF was sampled from the upper first molar and assessed with a commercial cytokine assay kit.

RESULTS

Forty three dental implants patients and 31 3-unit FPDs patients received all of the clinical and laboratory evaluation. The dental implants group had a higher occlusion force distribution on first molars region. IL-10, IL-17, RANK had a higher mean in dental implants group and was associated with occlusion force of first molar. There was a weakly association between IL-10 and dental implants in the binary logistic regression analyses.

CONCLUSIONS

In this study, the teeth opposing implants have a higher level of cytokines in the GCF than teeth opposing to 3-unit FPDs in periodontal healthy participants because of the poor osseoperception of dental implants. IL-10 might reflect a higher occlusion force in dental implants region.

CLINICAL RELEVANCE

This study provided that different tooth restoration methods could influence the periodontal status of the contact teeth.

3D Electrospun Polycaprolactone Scaffolds to Assess Human Periodontal Ligament Cells Mechanobiological Behaviour

While periodontal ligament cells are sensitive to their 3D biomechanical environment, only a few 3D in vitro models have been used to investigate the periodontal cells mechanobiological behavior. The objective of the current study was to assess the capability of a 3D fibrous scaffold to transmit a mechanical loading to the periodontal ligament cells. Three-dimensional fibrous polycaprolactone (PCL) scaffolds were synthetized through electrospinning. Scaffolds seeded with human periodontal cells (10³ mL^-1) were subjected to static (n = 9) or to a sinusoidal axial compressive loading in an in-house bioreactor (n = 9). At the end of the culture, the dynamic loading seemed to have an influence on the cells' morphology, with a lower number of visible cells on the scaffolds surface and a lower expression of actin filament. Furthermore, the dynamic loading presented a tendency to decrease the Alkaline Phosphatase activity and the production of Interleukin-6 while these two biomolecular markers were increased after 21 days of static culture. Together, these results showed that load transmission is occurring in the 3D electrospun PCL fibrous scaffolds, suggesting that it can be used to better understand the periodontal ligament cells mechanobiology. The current study shows a relevant way to investigate periodontal mechanobiology using 3D fibrous scaffolds.

The different irradiation parameters of carbon dioxide laser effects on periodontal ligament cells

Background

Materials and methods

Results

Conclusion

Immunomodulatory Activities of Periodontal Ligament Stem Cells in Orthodontic Forces-Induced Inflammatory Processes: Current Views and Future Perspectives

Orthodontic tooth movement (OTM) is induced by applying active mechanical forces, causing a local non-infectious inflammatory response in the periodontal ligament (PDL). As a prerequisite for OTM, the inflammation status is associated with increased levels of various cytokines and involves the interaction between immune cells and periodontal ligament stem cells (hPDLSCs). It is well established that hPDLSCs respond to orthodontic forces in several ways, such as by secreting multiple inflammatory factors. Another essential feature of hPDLSCs is their immunomodulatory activities, which are executed through cytokine (e.g., TNF-α and IL-1β)-induced production of various soluble immunomediators (e.g., indoleamine-2,3-dioxygenase-1, tumor necrosis factor-inducible gene 6 protein, prostaglandin E₂) and direct cell-to-cell contact (e.g., programmed cell death ligand 1, programmed cell death ligand 2). It is well known that these immunomodulatory abilities are essential for local periodontal tissue homeostasis and regeneration. So far, only a handful of studies provides first hints that hPDLSCs change immunological processes during OTM via their immunomodulatory activities. These studies demonstrate the pro-inflammatory aspect of immunomodulation by hPDLSCs. However, no studies exist which investigate cytokine and cell-to-cell contact mediated immunomodulatory activities of hPDLSCs. In this perspective article, we will discuss the potential role of the immunomodulatory potential of hPDLSCs in establishing and resolving the OTM-associated non-infectious inflammation and hence its potential impact on periodontal tissue homeostasis during OTM.

Effect of Different Parameters of In Vitro Static Tensile Strain on Human Periodontal Ligament Cells Simulating the Tension Side of Orthodontic Tooth Movement

This study aimed to investigate the effects of different magnitudes and durations of static tensile strain on human periodontal ligament cells (hPDLCs), focusing on osteogenesis, mechanosensing and inflammation. Static tensile strain magnitudes of 0%, 3%, 6%, 10%, 15% and 20% were applied to hPDLCs for 1, 2 and 3 days. Cell viability was confirmed via live/dead cell staining. Reference genes were tested by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and assessed. The expressions of TNFRSF11B, ALPL, RUNX2, BGLAP, SP7, FOS, IL6, PTGS2, TNF, IL1B, IL8, IL10 and PGE2 were analyzed by RT-qPCR and/or enzyme-linked immunosorbent assay (ELISA). ALPL and RUNX2 both peaked after 1 day, reaching their maximum at 3%, whereas BGLAP peaked after 3 days with its maximum at 10%. SP7 peaked after 1 day at 6%, 10% and 15%. FOS peaked after 3 days with its maximum at 3%, 6% and 15%. The expressions of IL6 and PTGS2 both peaked after 1 day, with their minimum at 10%. PGE2 peaked after 1 day (maximum at 20%). The ELISA of IL6 peaked after 3 days, with the minimum at 10%. In summary, the lower magnitudes promoted osteogenesis and caused less inflammation, while the higher magnitudes inhibited osteogenesis and enhanced inflammation. Among all magnitudes, 10% generally caused a lower level of inflammation with a higher level of osteogenesis.

Role of chaperone-assisted selective autophagy (CASA) in mechanical stress protection of periodontal ligament cells

Objective

The periodontal ligament (PDL) is exposed to constant mechanical forces potentiated by orthodontic tooth movement (OTM). The aim of our study was to investigate the involvement of chaperone-assisted selective autophagy (CASA) in mechanosensing and cellular adaption to forces in the PDL.

Materials and methods

Human PDL cells were loaded with 2.5, 5, and 10% of static mechanical strain for 24 h in vitro. Untreated cells served as controls. Gene expression of HSPA8, HSPB8, BAG3, STUB1, SYNPO2 was investigated via RT-qPCR (Quantitative reverse transcription PCR). Western blot evidenced protein expression of these molecules and of Filamin A. In vivo analyses of CASA were performed via immunohistochemistry on teeth with and without OTM.

Results

CASA machinery genes were inherently expressed in PDL cells and exhibited transcriptional induction upon mechanical strain. Protein analyses underlined these findings, even though modulation upon force exertion also demonstrated a decrease for some molecules and loading strengths. In vivo results evidenced again the uniform upregulation of HSPA8, HSPB8, BAG3, STUB1, SYNPO2 and Filamin A in teeth with OTM compared to controls. Experiments generally evidenced a pronounced variability in the expression between donors both on the gene and protein level.

Conclusions

Our study is the first to identify both the expression and functional relevance of CASA in the PDL. The data reflect its probable central role in adequate adaption to forces exerted by OTM and in mechanical stress protection of cells. Deeper knowledge of the CASA pathway will allow better assessment of predisposing factors regarding side effects during mechanical force application that can be used in orthodontic practice.

Effect of Tension on Human Periodontal Ligament Cells: Systematic Review and Network Analysis

Orthodontic tooth movement is based on the remodeling of tooth-surrounding tissues in response to mechanical stimuli. During this process, human periodontal ligament cells (hPDLCs) play a central role in mechanosensing and mechanotransduction. Various in vitro models have been introduced to investigate the effect of tension on hPDLCs. They provide a valuable body of knowledge on how tension influences relevant genes, proteins, and metabolites. However, no systematic review summarizing these findings has been conducted so far. Aim of this systematic review was to identify all related in vitro studies reporting tension application on hPDLCs and summarize their findings regarding force parameters, including magnitude, frequency and duration. Expression data of genes, proteins, and metabolites was extracted and summarized. Studies' risk of bias was assessed using tailored risk of bias tools. Signaling pathways were identified by protein-protein interaction (PPI) networks using STRING and GeneAnalytics. According to our results, Flexcell Strain Unit^® and other silicone-plate or elastic membrane-based apparatuses were mainly adopted. Frequencies of 0.1 and 0.5 Hz were predominantly applied for dynamic equibiaxial and uniaxial tension, respectively. Magnitudes of 10 and 12% were mostly employed for dynamic tension and 2.5% for static tension. The 10 most commonly investigated genes, proteins and metabolites identified, were mainly involved in osteogenesis, osteoclastogenesis or inflammation. Gene-set enrichment analysis and PPI networks gave deeper insight into the involved signaling pathways. This review represents a brief summary of the massive body of knowledge in this field, and will also provide suggestions for future researches on this topic.

mRNA and long non-coding RNA expression profiling of human periodontal ligament cells under tension loading

Objective

This study explored the expression profiles of messenger RNAs (mRNAs) and long non-coding RNAs (lncRNAs) in human periodontal ligament (PDL) cells subjected to tensile loading.

Methods

PDL cells were isolated from the teeth of five healthy individuals, cultured and then exposed to tensile loading. RNA sequencing was performed to explore the mRNA and lncRNA expression profiles with or without tensile loading. Differential expression, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were conducted to reveal enriched biological functions and signal transduction pathways. Quantitative polymerase chain reaction (qPCR) was performed to validate the expression of specific mRNAs and lncRNAs associated with the enriched pathways.

Results

Tensile loading significantly enhanced the osteogenic potential of PDL cells. Overall, 1438 mRNAs (860 up- and 578 down-regulated) and 195 lncRNAs (107 up- and 88 down-regulated) were differentially expressed (adjusted P-value <0.05) in the tensile loading group versus the control group. GO and KEGG analyses of the differentially expressed genes indicated significant enrichment in osteogenesis-related biological processes and intracellular signal transduction pathways (e.g. the PI3K–Akt pathway), respectively. The qPCR analysis validated the expression levels of five selected mRNAs (EGFR, FGF5, VEGFA, HIF1A, and FOXO1) and three selected lncRNAs (CYTOR, MIR22HG, and SNHG3).

Limitation

Further studies are warranted to validate the mechanisms regulating tension-induced bone remodelling in PDL cells and potential regulation by the identified lncRNAs.

Conclusion

The notably altered mRNA and lncRNA expression profiles in PDL cells under tensile loading enhance our mechanistic understanding of tension-induced osteogenesis.

Cyclic tensile strain affects the response of human periodontal ligament stromal cells to tumor necrosis factor-α

Objectives

Orthodontic treatment in adult patients predisposed to mild or severe periodontal disease is challenging for orthodontists. Orthodontic malpractice or hyper-occlusal forces may aggravate periodontitis-induced destruction of periodontal tissues, but the specific mechanism remains unknown. In the present study, the combined effect of mechanical stress and tumor necrosis factor (TNF)-α on the inflammatory response in human periodontal ligament stromal cells (hPDLSCs) was investigated.

Materials and methods

hPDLSCs from 5 healthy donors were treated with TNF-α and/or subjected to cyclic tensile strain (CTS) of 6% or 12% elongation with 0.1 Hz for 6- and 24 h. The gene expression of interleukin (IL)-6, IL-8 and cell adhesion molecules VCAM and ICAM was analyzed by qPCR. The protein levels of IL-6 and IL-8 in conditioned media was measured by ELISA. The surface expression of VCAM-1 and ICAM-1 was quantified by immunostaining followed by flow cytometry analysis.

Results

TNF-α-induced IL-6 gene and protein expression was inhibited by CTS, whereas TNF-α-induced IL-8 expression was decreased at mRNA expression level but enhanced at the protein level in a magnitude-dependent manner. CTS downregulated the gene expression of VCAM-1 and ICAM-1 under TNF-α stimulation, but the downregulation of the surface expression analyzed by flow cytometry was observed chiefly for VCAM-1.

Conclusions

Our findings show that mechanical force differentially regulates TNF-α-induced expression of inflammatory mediators and adhesion molecules at the early stage of force application. The effect of cyclic tensile strain is complex and could be either anti-inflammatory or pro-inflammatory depending on the type of pro-inflammatory mediators and force magnitude.

Clinical relevance

Orthodontic forces regulate the inflammatory mediators of periodontitis. The underlying mechanism may have significant implications for future strategies of combined periodontal and orthodontic treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-021-04039-8.

MMPs and TIMPs Expression Levels in the Periodontal Ligament during Orthodontic Tooth Movement: A Systematic Review of In Vitro and In Vivo Studies

Background: During orthodontic tooth movement (OTM), applied orthodontic forces cause an extensive remodeling of the extracellular matrix (ECM) in the periodontal ligament (PDL). This is mainly orchestrated by different types of matrix metalloproteinases (MMPs) and their tissue inhibitors of matrix metalloproteinases (TIMPs), which are both secreted by periodontal ligament (PDL) fibroblasts. Multiple in vitro and in vivo studies already investigated the influence of applied orthodontic forces on the expression of MMPs and TIMPs. The aim of this systematic review was to explore the expression levels of MMPs and TIMPs during OTM and the influence of specific orthodontic force-related parameters. Methods: Electronic article search was performed on PubMed and Web of Science until 31 January 2021. Screenings of titles, abstracts and full texts were performed according to PRISMA, whereas eligibility criteria were defined for in vitro and in vivo studies, respectively, according to the PICO schema. Risk of bias assessment for in vitro studies was verified by specific methodological and reporting criteria. For in vivo studies, risk of bias assessment was adapted from the Joanna Briggs Institute Critical Appraisal Checklist for analytical cross-sectional study. Results: Electronic article search identified 3266 records, from which 28 in vitro and 12 in vivo studies were included. The studies showed that orthodontic forces mainly caused increased MMPs and TIMPs expression levels, whereas the exact effect may depend on various intervention and sample parameters and subject characteristics. Conclusion: This systematic review revealed that orthodontic forces induce a significant effect on MMPs and TIMPs in the PDL. This connection may contribute to the controlled depletion and formation of the PDLs' ECM at the compression and tension site, respectively, and finally to the highly regulated OTM.

Interleukin-1β Induced Matrix Metalloproteinase Expression in Human Periodontal Ligament-Derived Mesenchymal Stromal Cells under In Vitro Simulated Static Orthodontic Forces

The periodontal ligament (PDL) responds to applied orthodontic forces by extracellular matrix (ECM) remodeling, in which human periodontal ligament-derived mesenchymal stromal cells (hPDL-MSCs) are largely involved by producing matrix metalloproteinases (MMPs) and their local inhibitors (TIMPs). Apart from orthodontic forces, the synthesis of MMPs and TIMPs is influenced by the aseptic inflammation occurring during orthodontic treatment. Interleukin (IL)-1β is one of the most abundant inflammatory mediators in this process and crucially affects the expression of MMPs and TIMPs in the presence of cyclic low-magnitude orthodontic tensile forces. In this study we aimed to investigate, for the first time, how IL-1β induced expression of MMPs, TIMPs and how IL-1β in hPDL-MSCs was changed after applying in vitro low-magnitude orthodontic tensile strains in a static application mode. Hence, primary hPDL-MSCs were stimulated with IL-1β in combination with static tensile strains (STS) with 6% elongation. After 6- and 24 h, MMP-1, MMP-2, TIMP-1 and IL-1β expression levels were measured. STS alone had no influence on the basal expression of investigated target genes, whereas IL-1β caused increased expression of these genes. In combination, they increased the gene and protein expression of MMP-1 and the gene expression of MMP-2 after 24 h. After 6 h, STS reduced IL-1β-induced MMP-1 synthesis and MMP-2 gene expression. IL-1β-induced TIMP-1 gene expression was decreased by STS after 6- and 24-h. At both time points, the IL-1β-induced gene expression of IL-1β was increased. Additionally, this study showed that fetal bovine serum (FBS) caused an overall suppression of IL-1β-induced expression of MMP-1, MMP-2 and TIMP-1. Further, it caused lower or opposite effects of STS on IL-1β-induced expression. These observations suggest that low-magnitude orthodontic tensile strains may favor a more inflammatory and destructive response of hPDL-MSCs when using a static application form and that this response is highly influenced by the presence of FBS in vitro.

Mechanisms involved in regulation of periodontal ligament cell production of pro-inflammatory cytokines: Implications in periodontitis

It is well recognized that human periodontal ligament cells (PDL cells) may represent local immune cells of the periodontal tissues. However, it is unclear whether they represent “true” immune cells, since they can produce pro‐inflammatory cytokines not only after stimulation with bacterial lipopolysaccharides but also in response to other stimuli such as mechanical stress. Stimulation with bacterial lipopolysaccharides strongly enhances PDL cell production of pro‐inflammatory cytokines through activation of toll‐like receptors and NF‐κB signaling. Less information is available regarding putative modulators of cytokine production and their mechanisms of action in PDL cells. The anti‐inflammatory glucocorticoid dexamethasone reduces lipopolysaccharide‐induced PDL cell production of cytokines. Recent observations show that vitamin D and the antimicrobial peptide LL‐37 antagonize lipopolysaccharide‐stimulated PDL cell production of pro‐inflammatory cytokines. Secretory leukocyte protease inhibitor is endogenously expressed by PDL cells, and this protein negatively regulates PDL cell‐evoked cytokine production. More information and knowledge about the regulation of PDL cell production of cytokines may clarify the role of PDL cells in oral innate immunity and their importance in periodontitis.

Compressive force strengthened the pro-inflammatory effect of zoledronic acid on il-1ß stimulated human periodontal fibroblasts

OBJECTIVES

The number of patients in dentistry taking bisphosphonates (BP) increases every year. There are only little data about the influence of biomechanical stress due to orthodontic treatment and periodontal inflammation in BP patients. This study focused on the effects of the induced inflammation by IL-1ß in compressed human periodontal ligament fibroblasts (HPdLF) exposed to the nitrogen-containing BP zoledronate in vitro.

MATERIALS AND METHODS

HPdLF were incubated with 5 μmol/l zoledronate and 10 ng/ml IL-1ß for 48 h. In the last 3 h, cells were exposed to a compressive, centrifugal force of 34.9 g/cm². Cell viability was analyzed directly after the compressive force by MTT assay. Gene expression of COX-2 and IL-6 was investigated using quantitative qRT-PCR. PGE-2 and IL-6 protein secretion were measured via ELISA.

RESULTS

The cell viability of HPdLF was not affected. Without inflammatory pre-stimulation, COX-2 expression was increased by compression and zoledronate. IL-6 expression was increased under compression. On secretion level, the combination of compression and zoledronate induced a slightly increase of IL-6 secretion. In contrast, inflammatory pre-stimulation strengthened the compressive upregulation of COX-2, as well as induced a higher PGE-2 secretion. Further addition of zoledronate to pre-stimulated cells additionally strengthened the compression-induced upregulation of COX-2 and IL-6 expression as well as protein secretion compared to all other groups.

CONCLUSIONS

Biomechanical stress might trigger a pro-inflammatory potential of BP further enhanced in the presence of an inflammatory pre-stimulation.

CLINICAL RELEVANCE

To prevent excessive host inflammatory responses, occlusal overloading and mechanical stress due to orthodontic treatment should be avoided in BP patients with untreated periodontitis.

Global gene expression profile of periodontal ligament cells submitted to mechanical loading: A systematic review

OBJECTIVE

To evaluate the evidence reporting gene expression array data of human in vitro cultured periodontal ligament cells (PDLCs) submitted to static mechanical loading compared to a control group.

DESIGN

Systematic searches were performed in MEDLINE/PubMed, Scopus, Web of Science, Virtual Health Library, The Cochrane Library and the System for Information on Grey Literature in Europe up to June 2019. A narrative synthesis was performed to summarize differentially expressed genes (DEGs). These were grouped according to the culture method (2D or 3D), force type (compression or tension) and observation time. Additionally, gene ontology (GO) analysis was performed using the Database for Annotation Visualization and Integrated Discovery. The risk of bias (RoB) and certainty of evidence (CoE) were assessed using a modified CONSORT checklist and the GRADE tool, respectively.

RESULTS

Of eight studies included (all rated as having moderate RoB), only two provided the complete list of DEGs and four studies performed GO, gene network or pathways analysis. "Cell proliferation", "cell-cell signaling", "response to hypoxia and to mechanical stimulus" were among the significantly enriched biological processes in 3D-cultured compressed PDLCs (moderate CoE); while "collagen catabolic process", "extracellular matrix organization" and "cell proliferation" were associated with DEGs of 3D-cultured PDLCs submitted to tension (very low CoE). Biological processes significantly enriched in 2D-cultured PDLCs under compression were "extracellular matrix organization", "canonical glycolysis" and "glycolytic process" (very low CoE).

CONCLUSION

Genes such as NR4A2, NR4A3, NAMPT, PGK1, and REDD1 are suggested as novel biomarkers for orthodontic tooth movement. Limited amount of evidence on the complete gene expression profile and the high heterogeneity in methodologies make it impossible to obtain definite conclusions. New studies following standardized and well-designed in vitro model and reporting complete gene expression datasets are needed.

Bench-to-bedside strategies for osteoporotic fracture: From osteoimmunology to mechanosensation

Osteoporosis is characterized by a decrease in bone mass and strength, rendering people prone to osteoporotic fractures caused by low-energy forces. The primary treatment strategy for osteoporotic fractures is surgery; however, the compromised and comminuted bones in osteoporotic fracture sites are not conducive to optimum reduction and rigid fixation. In addition, these patients always exhibit accompanying aging-related disorders, including high inflammatory status, decreased mechanical loading and abnormal skeletal metabolism, which are disadvantages for fracture healing around sites that have undergone orthopedic procedures. Since the incidence of osteoporosis is expected to increase worldwide, orthopedic surgeons should pay more attention to comprehensive strategies for improving the poor prognosis of osteoporotic fractures. Herein, we highlight the molecular basis of osteoimmunology and bone mechanosensation in different healing phases of elderly osteoporotic fractures, guiding perioperative management to alleviate the unfavorable effects of insufficient mechanical loading, high inflammatory levels and pathogen infection. The well-informed pharmacologic and surgical intervention, including treatment with anti-inflammatory drugs and sufficient application of antibiotics, as well as bench-to-bedside strategies for bone augmentation and hardware selection, should be made according to a comprehensive understanding of bone biomechanical properties in addition to the remodeling status of osteoporotic bones, which is necessary for creating proper biological and mechanical environments for bone union and remodeling. Multidisciplinary collaboration will facilitate the improvement of overall osteoporotic care and reduction of secondary fracture incidence.

Combating osteoporosis and obesity with exercise: leveraging cell mechanosensitivity

Osteoporosis, a condition of skeletal decline that undermines quality of life, is treated with pharmacological interventions that are associated with poor adherence and adverse effects. Complicating efforts to improve clinical outcomes, the incidence of obesity is increasing, predisposing the population to a range of musculoskeletal complications and metabolic disorders. Pharmacological management of obesity has yet to deliver notable reductions in weight and debilitating complications are rarely avoided. By contrast, exercise shows promise as a non-invasive and non-pharmacological method of regulating both osteoporosis and obesity. The principal components of exercise - mechanical signals - promote bone and muscle anabolism while limiting formation and expansion of fat mass. Mechanical regulation of bone and marrow fat might be achieved by regulating functions of differentiated cells in the skeletal tissue while biasing lineage selection of their common progenitors - mesenchymal stem cells. An inverse relationship between adipocyte versus osteoblast fate selection from stem cells is implicated in clinical conditions such as childhood obesity and increased marrow adiposity in type 2 diabetes mellitus, as well as contributing to skeletal frailty. Understanding how exercise-induced mechanical signals can be used to improve bone quality while decreasing fat mass and metabolic dysfunction should lead to new strategies to treat chronic diseases such as osteoporosis and obesity.

Influence of clodronate and compressive force on IL-1ß-stimulated human periodontal ligament fibroblasts

OBJECTIVES

The aim of this study was to investigate in vitro the effect of clodronate on interleukin-1ß (IL-1ß)-stimulated human periodontal ligament fibroblasts (HPdLFs) with the focus on inflammatory factors of orthodontic tooth movement with and without compressive force.

MATERIALS AND METHODS

HPdLFs were incubated with 5 μM clodronate and 10 ng/mL IL-1ß. After 48 h, cells were exposed to 3 h of compressive force using a centrifuge. The gene expression of cyclooxygenase-2 (COX-2), interleukin-6 (IL-6), matrix metalloproteinase 8 (MMP-8), and the tissue inhibitor of MMP (TIMP-1) was analyzed using RT-PCR. Prostaglandin E2 (PGE-2), IL-6, and TIMP-1 protein syntheses were quantified via ELISA.

RESULTS

Compressive force and IL-1ß induced an overexpression of COX-2 gene expression (61.8-fold; p < 0.05 compared with control), diminished by clodronate (41.1-fold; p < 0.05 compared with control). Clodronate slowed down the compression and IL-1ß induced IL-6 gene expression (161-fold vs. 85.6-fold; p < 0.05 compared with control). TNF-α was only slightly affected without statistical significance. Clodronate reduced IL-1ß-stimulated MMP-8 expression with and without compressive force. TIMP-1 on gene and protein level was downregulated in all groups. Analyzing the MMP-8/TIMP-1 ratio, the highest ratio was detected in IL-1ß-stimulated HPdLFs with compressive force (21.2-fold; p < 0.05 compared with control). Clodronate diminished IL-1ß-induced upregulation of MMP-8/TIMP-1 ratio with (11.5-fold; p < 0.05 compared with control) and without (12.5-fold; p < 0.05 compared with control) compressive force.

CONCLUSION

Our study demonstrates a slightly anti-inflammatory effect by clodronate under compressive force in vitro. Additionally, the periodontal remodeling presented by the MMP-8/TIMP-1 ratio seems to be diminished by clodronate.

CLINICAL RELEVANCE

Reduction of pro-inflammatory factors and reduction of periodontal remodeling might explain reduced orthodontic tooth movement under clodronate intake.

Heat shock protein 70 dampens the inflammatory response of human PDL cells to mechanical loading in vitro

BACKGROUND AND OBJECTIVE

Previously, we demonstrated an inflammatory response of human PDL (hPDL) cells to mechanical loading. The cellular reaction was dampened by heat pre-treatment suggesting a protective role for heat shock proteins (HSP) during stress-induced ischemia. Here we explored if HSP70, which has already been documented in the pressure zone of tooth movement, might be regulatorily involved in the attenuation of the inflammatory response.

MATERIALS AND METHODS

Fifth passage hPDL cells were mechanically loaded in the presence of the HSP70 inhibitor VER155008. Cell morphology, HSP70 expression, viability, IL-6 and IL-8 expression were determined by means of microscopy, realtime-PCR and ELISA. The conditioned medium of mechanically loaded and pre-treated hPDL cells was used to culture monocytes to identify a potential impact on adhesion and osteoclastic differentiation capacity.

RESULTS

Mechanical cell stress resulted in a significant increase of pro-inflammatory parameters. HSP70 inhibition led to a further enhancement of cytokine expression. The conditioned medium of mechanically loaded hPDL cells significantly increased monocyte adhesion and differentiation along the osteoclastic pathway. VER155008 pronounced this effect significantly.

CONCLUSION

The results indicate a regulatory role for HSP70 in the control of the inflammatory hPDL cell response to mechanical loading and identify HSP70 as a target in the attempt to attenuate tissue damage during orthodontic tooth movement. Furthermore, the present findings point to the risk of increased periodontal destruction when medication targeting HSP70 is applied for severe medical conditions during orthodontic tooth movement.

Cyclic tensile force stimulates BMP9 synthesis and in vitro mineralization by human periodontal ligament cells

Periodontal ligament (PDL) cells are mechanosensitive and have the potential to differentiate into osteoblast-like cells under the influence of cyclic tensile force (CTF). CTF modulates the expression of regulatory proteins including bone morphogenetic proteins (BMPs), which are essential for the homeostasis of the periodontium. Among the BMPs, BMP9 is one of the most potent osteogenic BMPs. It is yet unknown whether CTF affects the expression of BMP9 and mineralization. Here, we demonstrated that continuously applied CTF for only the first 6 hr stimulated the synthesis of BMP9 and induced mineral deposition within 14 days by human PDL cells. Stimulation of BMP9 expression depended on ATP and P2Y ₁ receptors. Apyrase, an ecto-ATPase, inhibited CTF-mediated ATP-induced BMP9 expression. The addition of ATP increased the expression of BMP9. Loss of function experiments using suramin (a broad-spectrum P2Y antagonist), MRS2179 (a specific P2Y ₁ receptor antagonist), MRS 2365 (a specific P2Y ₁ agonist), U-73122 (a phospholipase C [PLC] inhibitor), and thapsigargin (enhancer of intracytosolic calcium) revealed the participation of P2Y ₁ in regulating the expression of BMP9. This was mediated by an increased level of intracellular Ca ²⁺ through the PLC pathway. A neutralizing anti-BMP9 antibody decreased mineral deposition, which was stimulated by CTF for almost 45% indicating a role of BMP9 in an in vitro mineralization. Collectively, our findings suggest an essential modulatory role of CTF in the homeostasis and regeneration of the periodontium.

Low-Magnitude Forces for Bone Modeling and Remodeling in Dentofacial Orthopedics

PURPOSE OF REVIEW

To examine the evidence in support of light continuous forces for enhancing bone adaptation (modeling and remodeling) in orthodontics and dentofacial orthopedics.

RECENT FINDINGS

Clinical evidence suggests that light continuous orthodontic force can achieve physiologic expansion of the maxillary arch, but the long-term stability and the biological effects of the procedure are unclear. Compared to conventional orthodontic appliances that deliver heavy interrupted forces for tooth movement, the application of low-magnitude forces in animal models leads to anabolic modeling and remodeling of the alveolar bone in the path of orthodontic tooth movement. This results in dental translation and expansion of the alveolar process. Light continuous forces are preferable to heavy forces for more physiologic dentofacial orthopedics. The interaction of low-magnitude loads with soft tissue posture achieves therapeutic adaptation of the craniofacial skeleton. The increasing emphasis on genomic medicine and personalized treatment planning should focus on low-magnitude loads in orthodontics and dentofacial orthopedics.

Resveratrol suppresses the alveolar bone resorption induced by artificial trauma from occlusion in mice

OBJECTIVE

Besides inflammatory bone loss, trauma from occlusion (TO)-induced alveolar bone loss increases the risk of future tooth loss. We have shown that resveratrol, a polyphenol, possesses anti-inflammatory characteristics and a suppressive effect on osteoclastogenesis. Therefore, we investigated the effects of resveratrol on TO-induced bone loss in mice.

MATERIAL AND METHODS

Trauma from occlusion was induced by overlaying composite resin onto the maxillary first molar of C57BL/6 mice. TO-induced mice were administered either resveratrol or vehicle for 15 days from 5 days before TO induction. The mice administered vehicle only served as controls. The effect of resveratrol on bone resorption was assessed histologically. Gene expression in gingival and periodontal ligament tissues was analyzed. In vitro effect of resveratrol on the differentiation of RAW 264.7 cells and bone marrow-derived macrophages into osteoclastic cells was analyzed.

RESULTS

Resveratrol administration significantly decreased the bone loss and suppressed the elevated expression of osteoclastogenesis-related gene in periodontal ligament tissue by TO. Resveratrol treatment also suppressed the differentiation of both RAW 264.7 cells and bone marrow-derived macrophages into osteoclastic cells.

CONCLUSION

Resveratrol administration suppressed the TO-induced alveolar bone loss by suppressing osteoclast differentiation, suggesting that resveratrol is effective in preventing both inflammation and mechanical stress-induced alveolar bone resorption.

Cyclic stretch-induced the cytoskeleton rearrangement and gene expression of cytoskeletal regulators in human periodontal ligament cells

OBJECTIVE

This study aimed to explore the mechanism of the stretch-induced cell realignment and cytoskeletal rearrangement by identifying several mechanoresponsive genes related to cytoskeletal regulators in human PDL cells.

MATERIAL AND METHODS

After the cells were stretched by 1, 10 and 20% strains for 0.5, 1, 2, 4, 6, 12 or 24 h, the changes of the morphology and content of microfilaments were recorded and calculated. Meanwhile, the expression of 84 key genes encoding cytoskeletal regulators after 6 and 24 h stretches with 20% strain was detected by using real-time PCR array. Western blot was applied to identify the protein expression level of several cytoskeletal regulators encoded by these differentially expressed genes.

RESULTS

The confocal fluorescent staining results confirmed that stretch-induced realignment of cells and rearrangement of microfilaments. Among the 84 genes screened, one gene was up-regulated while two genes were down-regulated after 6 h stretch. Meanwhile, three genes were up-regulated while two genes were down-regulated after 24 h stretch. These genes displaying differential expression included genes regulating polymerization/depolymerization of microfilaments (CDC42EP2, FNBP1L, NCK2, PIKFYVE, WASL), polymerization/depolymerization of microtubules (STMN1), interacting between microfilaments and microtubules (MACF1), as well as a phosphatase (PPP1R12B). Among the proteins encoded by these genes, the protein expression level of Cdc42 effector protein-2 (encoded by CDC42EP2) and Stathmin-1 (encoded by STMN1) was down-regulated, while the protein expression level of N-WASP (encoded by WASL) was up-regulated.

CONCLUSION

The present study confirmed the cyclic stretch-induced cellular realignment and rearrangement of microfilaments in the human PDL cells and indicated several force-sensitive genes with regard to cytoskeletal regulators.

Mechanical loading increases pro-inflammatory effects of nitrogen-containing bisphosphonate in human periodontal fibroblasts

OBJECTIVES

There is increasing evidence that inflammation and biomechanical loading can influence the effects of bisphosphonates (BP). The aim of this study was to investigate the influence of tensile strain application combined with IL-1ß and clodronate or zoledronate on human periodontal ligament fibroblasts (HPdLF) in vitro.

MATERIALS AND METHODS

HPdLF were cultured with 10 nM IL-1ß and 5 μM clodronate or zoledronate for 48 h. Cells were applied to cyclic tensile strain (CTS; 3% elongation) for 12 h in vitro. Cell number was analyzed directly after CTS by MTT assay. Gene expression of receptor activator of cyclooxygenase-2 (COX-2) was investigated using real-time PCR. MMP-8, TIMP-1, and PGE2 were measured by ELISA. Statistics were performed with SPSS (ANOVA, p < 0.05).

RESULTS

Zoledronate reduced the cell number of HPdLF (60.3 vs. 100%), which was significant when combined with IL-1ß. Combined with 3% CTS, this effect was voided and cell number increased over the level of the control cells. IL-1ß led to a 10-fold increase of COX-2 gene expression. Combined with CTS and zoledronate, this increase was enhanced to a gene expression 70-fold that of control cells with related PGE2 synthesis. Clodronate neither reduce the cell number nor enhanced the COX-2 gene expression. CTS increased MMP-8 protein synthesis. Combined with BP, this increase was voided. TIMP-1 protein synthesis was increased at all conditions under CTS.

CONCLUSIONS

Mechanical loading might activate cell metabolism and abolish BP- and inflammation-induced reduction of viability. Combination of mechanical loading, inflammation, and nitrogen-containing bisphosphonates can cause pro-inflammatory effects.

CLINICAL RELEVANCE

Periodontal inflammation should be treated initially before BP intake to prevent decreased cell viability of the periodontium and increased inflammation, which might be enhanced by the addition of mastication forces.

MicroRNA-195-5p Regulates Osteogenic Differentiation of Periodontal Ligament Cells Under Mechanical Loading

Osteogenic differentiation and bone formation are tightly regulated by several factors, including microRNAs (miRNAs). However, miRNA expression patterns and function during mechanical loading-induced osteogenic differentiation of human periodontal ligament cells (PDLCs) remain unclear. Here, we investigated the differential expression of miRNA-195-5p in the periodontal tissues of mice under orthodontic mechanical loading and in primary human PDLCs exposed to a simulated tension strain. The miR-195-5p was observed to be down-regulated and negatively correlated with osteogenic differentiation. Overexpression of miR-195-5p significantly inhibited PDLC differentiation under cyclic tension strain (CTS), whereas the functional inhibition of miR-195-5p yielded an opposite effect. Further experiments confirmed that WNT family member 3A (WNT3A), fibroblast growth factor 2 (FGF2), and bone morphogenetic protein receptor-1A (BMPR1A), proteins important for osteogenic activity and stability, were direct targets of miR-195-5p. Mechanical loading increased the WNT3A, FGF2, and BMPR1A protein levels, while miR-195-5p inhibited WNT3A, FGF2, and BMPR1A protein expression. WNT, FGF, and BMP signaling were involved in osteogenic differentiation of PDLCs under CTS. Further study confirmed that reintroduction of WNT3A and BMPR1A can rescue the inhibition of miR-195-5p on osteogenic differentiation of PDLCs. Our findings are the first to demonstrate that miR-195-5p is a mechanosensitive gene that plays an important role in mechanical loading-induced osteogenic differentiation and bone formation.

Novel device for application of continuous mechanical tensile strain to mammalian cells

During orthodontic tooth movement, the periodontal ligament (PDL) is exposed to continuous mechanical strain. However, many researchers have applied cyclic tensile strain, not continuous tensile strain, to PDL cells in vitro because there has been no adequate device to apply continuous tensile strain to cultured cells. In this study, we contrived a novel device designed to apply continuous tensile strain to cells in culture. The continuous tensile strain was applied to human immortalized periodontal ligament cell line (HPL cells) and the cytoskeletal structures of HPL cells were examined by immunohistochemistry. The expression of both inflammatory and osteogenic markers was also examined by real-time reverse transcription polymerase chain reaction. The osteogenic protein, Osteopontin (OPN), was also detected by western blot analysis. The actin filaments of HPL cells showed uniform arrangement under continuous tensile strain. The continuous tensile strain increased the expression of inflammatory genes such as IL-1β, IL-6, COX-2 and TNF-α, and osteogenic genes such as RUNX2 and OPN in HPL cells. It also elevated the expression of OPN protein in HPL cells. These results suggest that our new simple device is useful for exploring the responses to continuous tensile strain applied to the cells.

Summary: Continuous tensile strain from the device changed the cell morphology and increased the expression of inflammatory and osteogenic gene. These effects were similar to those in the PDL during orthodontic tooth movement.

Low-level laser therapy stimulates bone metabolism and inhibits root resorption during tooth movement in a rodent model

This study evaluated the biological effects of low-level laser therapy (LLLT) on bone remodeling, tooth displacement and root resorption, occurred during the orthodontic tooth movement. Upper first molars of a total of sixty-eight male rats were subjected to orthodontic tooth movement and euthanized on days 3, 6, 9, 14 and 21 days and divided as negative control, control and LLLT group. Tooth displacement and histomorphometric analysis were performed in all animals; scanning electron microscopy analysis was done on days 3, 6 and 9, as well as the immunohistochemistry analysis of RANKL/OPG and TRAP markers. Volumetric changes in alveolar bone were analyzed using MicroCT images on days 14 and 21. LLLT influenced bone resorption by increasing the number of TRAP-positive osteoclasts and the RANKL expression at the compression side. This resulted in less alveolar bone and hyalinization areas on days 6, 9 and 14. LLLT also induced less bone volume and density, facilitating significant acceleration of tooth movement and potential reduction in root resorption besides stimulating bone formation at the tension side by enhancing OPG expression, increasing trabecular thickness and bone volume on day 21. Taken together, our results indicate that LLLT can stimulate bone remodeling reducing root resorption in a rat model. LLLT improves tooth movement via bone formation and bone resorption in a rat model.

Impact of mechanical stretch on the cell behaviors of bone and surrounding tissues

Mechanical loading is recognized to play an important role in regulating the behaviors of cells in bone and surrounding tissues in vivo. Many in vitro studies have been conducted to determine the effects of mechanical loading on individual cell types of the tissues. In this review, we focus specifically on the use of the Flexercell system as a tool for studying cellular responses to mechanical stretch. We assess the literature describing the impact of mechanical stretch on different cell types from bone, muscle, tendon, ligament, and cartilage, describing individual cell phenotype responses. In addition, we review evidence regarding the mechanotransduction pathways that are activated to potentiate these phenotype responses in different cell populations.

Biomechanical loading modulates proinflammatory and bone resorptive mediators in bacterial-stimulated PDL cells

The present study aimed to evaluate in vitro whether biomechanical loading modulates proinflammatory and bone remodeling mediators production by periodontal ligament (PDL) cells in the presence of bacterial challenge. Cells were seeded on BioFlex culture plates and exposed to Fusobacterium nucleatum ATCC 25586 and/or cyclic tensile strain (CTS) of low (CTSL) and high (CTSH) magnitudes for 1 and 3 days. Synthesis of cyclooxygenase-2 (COX2) and prostaglandin E2 (PGE2) was evaluated by ELISA. Gene expression and protein secretion of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-B ligand (RANKL) were evaluated by quantitative RT-PCR and ELISA, respectively. F. nucleatum increased the production of COX2 and PGE2, which was further increased by CTS. F. nucleatum-induced increase of PGE2 synthesis was significantly (P < 0.05) increased when CTSH was applied at 1 and 3 days. In addition, CTSH inhibited the F. nucleatum-induced upregulation of OPG at 1 and 3 days, thereby increasing the RANKL/OPG ratio. OPG and RANKL mRNA results correlated with the protein results. In summary, our findings provide original evidence that CTS can enhance bacterial-induced syntheses of molecules associated with inflammation and bone resorption by PDL cells. Therefore, biomechanical, such as orthodontic or occlusal, loading may enhance the bacterial-induced inflammation and destruction in periodontitis.

Mechanosignaling in bone health, trauma and inflammation

SIGNIFICANCE

Mechanosignaling is vital for maintaining the structural integrity of bone under physiologic conditions. These signals activate and suppress multiple signaling cascades regulating bone formation and resorption. Understanding these pathways is of prime importance to exploit their therapeutic potential in disorders associated with bone loss due to disuse, trauma, or disruption of homeostatic mechanisms.

RECENT ADVANCES

In the case of cells of the bone, an impressive amount of data has been generated that provides evidence of a complex mechanism by which mechanical signals can maintain or disrupt cellular homeostasis by driving transcriptional regulation of growth factors, matrix proteins and inflammatory mediators in health and inflammation. Mechanical signals act on cells in a magnitude dependent manner to induce bone deposition or resorption. During health, physiological levels of these signals are essential for maintaining bone strength and architecture, whereas during inflammation, similar signals can curb inflammation by suppressing the nuclear factor kappa B (NF-κB) signaling cascade, while upregulating matrix synthesis via mothers against decapentaplegic homolog and/or Wnt signaling cascades. Contrarily, excessive mechanical forces can induce inflammation via activation of the NF-κB signaling cascade.

CRITICAL ISSUES

Given the osteogenic potential of mechanical signals, it is imperative to exploit their therapeutic efficacy for the treatment of bone disorders. Here we review select signaling pathways and mediators stimulated by mechanical signals to modulate the strength and integrity of the bone.

FUTURE DIRECTIONS

Understanding the mechanisms of mechanotransduction and its effects on bone lay the groundwork for development of nonpharmacologic mechanostimulatory approaches for osteodegenerative diseases and optimal bone health.

Cyclic tensile stress during physiological occlusal force enhances osteogenic differentiation of human periodontal ligament cells via ERK1/2-Elk1 MAPK pathway

Physiological occlusal force constitutively exists in the oral environment and is important for periodontal homeostasis and remodeling. Cyclic tensile stress (CTS) triggers the biological response of periodontal ligament (PDL). However, a few reports have studied the correlation between CTS during physiological occlusal force and PDL cell activities such as osteogenic differentiation. In the present study, human PDL cells (hPDLCs) were subjected to 10% elongation CTS loading at 0.5 Hz for 24 h, which represents the physiological conditions of occlusal force. Gene expression microarray was used to investigate the mechano-induced differential gene profile and pathway analysis in vitro. The osteogenic relative factors, that is, SPP1, RUNX2, and SP7, were assessed by real-time PCR and Western blot. The involvement of mitogen-activated protein kinase (MAPK) signaling pathways was investigated by Western blot with a specific inhibitor. The expressions of SPP1, RUNX2, SP7, p-ERK1/2, and p-Elk1 were up-regulated after 10% CTS exposure. However, these up-regulated expressions were prevented by ERK1/2 inhibitor U0126 in the physiological occlusal force-applied hPDLCs. These results showed that 10% CTS could enhance osteogenic differentiation of hPDLCs via ERK1/2-Elk1 MAPK pathway, indicating that CTS during physiological occlusal force is a potent agent for PDL remodeling.

Vocal exercise may attenuate acute vocal fold inflammation

OBJECTIVES/HYPOTHESES

The objective was to assess the utility of selected "resonant voice" (RV) exercises for the reduction of acute vocal fold inflammation. The hypothesis was that relatively large-amplitude, low-impact vocal fold exercises associated with RV would reduce inflammation more than spontaneous speech (SS) and possibly more than voice rest.

STUDY DESIGN

The study design was prospective, randomized, and double blind.

METHODS

Nine vocally healthy adults underwent a 1-hour vocal loading procedure, followed by randomization to a SS condition, vocal rest condition, or RV exercise condition. Treatments were monitored in clinic for 4 hours and continued extraclinically until the next morning. At baseline (BL), immediately after loading, after the 4-hour in-clinic treatment, and 24 hours post-BL, secretions were suctioned from the vocal folds bilaterally and submitted to enzyme-linked immunosorbent assay to estimate concentrations of key markers of tissue injury and inflammation: interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor α, matrix metalloproteinase (MMP)-8, and IL-10.

RESULTS

Complete data sets were obtained for three markers--IL-1β, IL-6, and MMP-8--for one subject in each treatment condition. For these markers, results were poorest at 24-hour follow-up in the SS condition, sharply improved in the voice rest condition, and was the best in the RV condition. Average results for all markers and responsive subjects with normal BL mediator concentrations revealed an almost identical pattern.

CONCLUSIONS

Some forms of tissue mobilization may be useful to attenuate acute vocal fold inflammation.

Involvement of JNK-AP-1 and ERK-NF-κB signaling in tension-stimulated expression of Type I collagen and MMP-1 in human periodontal ligament fibroblasts

Type I collagen (COL I) and matrix metalloproteinase-1 (MMP-1) are the predominant matrix proteins in the extracellular matrix of the human periodontal ligament (PDL). The expression of these proteins in PDL fibroblasts (PLF) is sensitive to physiological and mechanical stress and is critical for PDL remodeling accompanied by alveolar bone remodeling. This study examined how dose tensile force regulates the expression of COL I and MMP-1 and explored the possible roles of mitogen-activated protein kinases (MAPKs) and transcription factors, such as activator protein-1 (AP-1) and nuclear factor-κB (NF-κB). Tensile force stimulated the mRNA expression of COL I and MMP-1 in the cells and also activated MAPKs including extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK), and p38 MAPK. A pharmacological inhibitor of ERK or JNK prevented the expression of matrix genes and the nuclear translocation of c-Jun proteins in the force-applied PLF. The knockdown of c-Jun by transfecting the cells with its antisense oligonucleotides reduced the force-induced increase in matrix gene expression. In particular, the ERK inhibitor but not JNK or p38 MAPK inhibitor attenuated the force-mediated stimulation of NF-κB-DNA binding and MMP-1 expression. Overall, these results highlight the mechanotransduction pathways involved in matrix gene expression in PLF, where the tension-stimulated expression of COL I and MMP-1 is controlled by the ERK/JNK-AP-1 and ERK-NF-κB signaling pathways.

MAPKs, activator protein-1 and nuclear factor-κB mediate production of interleukin-1β-stimulated cytokines, prostaglandin E₂ and MMP-1 in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Determination of the interleukin-1 (IL-1) signaling cascades that lead to the production of various inflammatory mediators and catabolic factors may clarify attractive targets for therapeutic intervention for periodontitis. We comprehensively assessed the involvement of MAPKs, activator protein-1 (AP-1) and nuclear factor-κB (NF-κB) in IL-1β-induced production of interleukin-6 (IL-6), interleukin-8 (IL-8), prostaglandin E(2) (PGE(2) ) and MMP-1 in human periodontal ligament cells.

MATERIAL AND METHODS

Human periodontal ligament cells were pretreated with an inhibitor for each of the MAPKs or NF-κB and subsequently treated with IL-1β. Following treatment, phosphorylation of three types of MAPK (ERK, p38 MAPK and c-Jun N-terminal kinase), IκB kinase (IKK) α/β/γ and IκB-α, as well as the DNA binding activity of AP-1 and NF-κB and the production of IL-6, IL-8, PGE(2) and MMP-1, were determined by western blotting, a gel mobility shift assay and ELISA, respectively.

RESULTS

The three MAPKs, simultaneously activated by IL-1β, mediated the subsequent DNA binding of AP-1 at various magnitudes, while IKKα/β/γ, IκB-α and NF-κB were also involved in the IL-1 signaling cascade. Furthermore, IL-1β stimulated the production of IL-6, IL-8, PGE(2) and MMP-1 via activation of the three MAPKs and NF-κB, because inhibitors of these significantly suppressed the IL-1β-stimulated production of these factors.

CONCLUSION

Our results strongly suggest that MAPK, AP-1 and NF-κB mediate the IL-1β-stimulated synthesis of IL-6, IL-8, PGE(2) and MMP-1 in human periodontal ligament cells. Therefore, inhibition of activation of MAPK, AP-1 and/or NF-κB may lead to therapeutic effects on progression of periodontitis.

Analysis of gene expression profile of periodontal ligament cells subjected to cyclic compressive force

Cyclic compressive force is an important mechanical stimulus on periodontal ligament (PDL). The differential expression of genes in PDL cells is thought to be involved in the remodeling of periodontal tissues subjected to mechanical stress. However, little is known about differentially expressed genes in PDL cells under cyclic compressive force. In our study, human PDL cells were subjected to 4000 μ strain compressive stress loading at 0.5 Hz for 2 h. The effect of mechanical stress on PDL cells proliferation was observed by flow cytometry. Microarray analysis was used to investigate the mechano-induced differential gene profile in PDL cells. Differential expression was confirmed by quantitative real-time polymerase chain reaction (RT-PCR) analysis on genes of interest and explored at two more force loading times (6 h, 12 h). After mechanical loading, cell proliferation was repressed. The microarray data showed that 217 out of 35,000 genes were differentially expressed; among the 217 genes, 207 were up-regulated whereas 10 were down-regulated (p < 0.05). Gene ontology analysis suggested that majority of differentially expressed genes were located in the nucleus and functioned as transcription factors involved in a variety of biological processes. Five genes of interest (IL6, IL8, ETS1, KLF10, and DLC1) were found to be closely related to negative regulation of cell proliferation. The PCR results showed increased expression after 2 h loading, then a decline with extended loading time. The signaling pathways involved were also identified. These findings expand understanding of molecular regulation in the mechano-response of PDL cells.

Upregulation of MMP-13 and TIMP-1 expression in response to mechanical strain in MC3T3-E1 osteoblastic cells

BACKGROUND

Mechanical strain plays a significant role in the regulation of bone matrix turnover, which is mediated in part by matrix metalloproteinase (MMP)-13 and tissue inhibitors of matrix metalloproteinase (TIMP)-1. However, little is known about the correlation between mechanical strain and osteoblastic cell activities, including extracellular matrix (ECM) metabolism. Herein, we determined the effect of different magnitudes of cyclic tensile strain (0%, 6%, 12%, and 18%) on MMP-13 and TIMP-1 mRNA and protein expression in MC3T3-E1 osteoblasts. Furthermore, we employed specific inhibitors to examine the role of distinct signal transduction pathways known to mediate cellular responses to mechanical strain.

RESULTS

We identified a magnitude-dependent increase in MMP-13 and TIMP-1 mRNA and protein levels in response to mechanical strains corresponding to 6%, 12%, and 18% elongation. The strain-induced increases in MMP-13 and TIMP-1 mRNA expression were inhibited by PD098059 and cycloheximide, respectively.

CONCLUSIONS

Our results suggest a mechanism for the regulation of bone matrix metabolism mediated by the differential expression of MMP-13 and TIMP-1 in response to increasing magnitudes of mechanical strain.

Effects of raised-intensity phonation on inflammatory mediator gene expression in normal rabbit vocal fold

OBJECTIVE

To investigate the hypothesis that a transient episode of raised-intensity phonation causes a significant increase in vocal fold inflammatory messenger RNA (mRNA) expression in vivo.

STUDY DESIGN

Prospective animal study.

SETTING

Laboratory.

SUBJECTS AND METHODS

Ten New Zealand White breeder rabbits received 30 minutes of experimentally induced modal or raised-intensity phonation, followed by a 30-minute recovery period. A separate group of five rabbits served as sham controls. Real-time polymerase chain reaction was performed to investigate the mRNA expression of interleukin 1beta (IL-1beta), transforming growth factor beta-1 (TGFbeta1), and cyclooxygenase-2 (COX-2). Separate one-way analysis of variance (ANOVA) tests were used to investigate differences in gene expression across groups, with an appropriate alpha correction of 0.016 to control for type I error. Significant main effects were further examined using Fisher's least significant difference.

RESULTS

ANOVA revealed that there were differences for IL-1beta, TGFbeta1, and COX-2 between sham control, modal phonation, and raised-intensity phonation (P 0.0001). Pairwise comparisons revealed that the expression of IL-1beta, COX-2, and TGFbeta1 increased significantly during raised-intensity phonation, compared to modal phonation and sham control (P 0.0001).

CONCLUSION

Results provided support for the hypothesis that a transient episode of raised-intensity phonation causes a significant increase in vocal fold inflammatory mRNA expression. Future studies will investigate the signal transduction pathways and mechanisms regulating the vocal fold inflammatory response. The long-term goal of these studies is to advance understanding of the molecular and cellular events underlying phonation-related tissue alterations.

Mechanisms of tooth eruption and orthodontic tooth movement

Teeth move through alveolar bone, whether through the normal process of tooth eruption or by strains generated by orthodontic appliances. Both eruption and orthodontics accomplish this feat through similar fundamental biological processes, osteoclastogenesis and osteogenesis, but there are differences that make their mechanisms unique. A better appreciation of the molecular and cellular events that regulate osteoclastogenesis and osteogenesis in eruption and orthodontics is not only central to our understanding of how these processes occur, but also is needed for ultimate development of the means to control them. Possible future studies in these areas are also discussed, with particular emphasis on translation of fundamental knowledge to improve dental treatments.