Role of hypoxia and interleukin-1β in gene expressions of matrix metalloproteinases in temporomandibular joint disc cells

Immunohistochemical Markers of Temporomandibular Disorders: A Review of the Literature

Temporomandibular disorders (TMD) are a group of internal derangements encompassing dysfunction, displacement, degeneration of the temporomandibular joints and surroundings muscles of mastication, often accompanied by pain. Relationships between TMD and various chemical biomarkers have been examined throughout the years. This paper aims to gather evidence from the literature regarding other biomarkers and presenting them as one systematic review to investigate the potential links between TMD and different biochemical activity. To identify relevant papers, a comprehensive literature search was carried out in MEDLINE/PubMED, EMBASE, Web of Science and a manual search was performed in the International Journal of Oral and Maxillofacial Surgery, Journal of Oral and Maxillofacial surgery, and Journal of Cranio-Maxillo-Facial Surgery. The literature review produced extensive results relating to the biochemical and immunohistochemical markers of TMD. Many enzymes, inflammatory markers, proteoglycans, and hormones were identified and organized in tables, along with a brief description, study design, and conclusion of each study. Through this review, recurring evidence provides confidence in suggesting involvement of certain biomarkers that may be involved in this complex pathogenesis, in addition to pointing to differences in gender prevalence of TMD. However, more organized research on large human samples needs to be conducted to delve deeper into the understanding of how this disease develops and progresses.

General Characteristics, Biomedical and Dental Application, and Usage of Chitosan in the Treatment of Temporomandibular Joint Disorders: A Narrative Review

The aim of this narrative review was to present research investigating chitosan, including its general characteristics, properties, and medical and dental applications, and finally to present the current state of knowledge regarding the efficacy of chitosan in the treatment of temporomandibular disorders (TMDs) based on the literature. The PICO approach was used for the literature search strategy. The PubMed database was analyzed with the following keywords: (“chitosan”[MeSH Terms] OR “chitosan”[All Fields] OR “chitosans”[All Fields] OR “chitosan s”[All Fields] OR “chitosane”[All Fields]) AND (“temporomandibular joint”[MeSH Terms] OR (“tem-poromandibular”[All Fields] AND “joint”[All Fields]) OR “temporomandibular joint”[All Fields] OR (“temporomandibular”[All Fields] AND “joints”[All Fields]) OR “temporo-mandibular joints”[All Fields]). After screening 8 results, 5 studies were included in this review. Chitosan presents many biological properties and therefore it can be widely used in several branches of medicine and dentistry. Chitosan promotes wound healing, helps to control bleeding, and is used in wound dressings, such as sutures and artificial skin. Apart from its antibacterial property, chitosan has many other properties, such as antifungal, mucoadhesive, anti-inflammatory, analgesic, antioxidant, antihyperglycemic, and antitumoral properties. Further clinical studies assessing the efficacy of chitosan in the treatment of TMD are required. According to only one clinical study, chitosan was effective in the treatment of TMD; however, better clinical results were obtained with platelet-rich plasma.

Effect of Sustained Joint Loading on TMJ Disc Nutrient Environment

The temporomandibular joint (TMJ) disc nutrient environment profoundly affects cell energy metabolism, proliferation, and biosynthesis. Due to technical challenges of in vivo measurements, the human TMJ disc extracellular nutrient environment under load, which depends on metabolic rates, solute diffusion, and disc morphometry, remains unknown. Therefore, the study objective was to predict the TMJ disc nutrient environment under loading conditions using combined experimental and computational modeling approaches. Specifically, glucose consumption and lactate production rates of porcine TMJ discs were measured under varying tissue culture conditions (n = 40 discs), and mechanical strain-dependent glucose and lactate diffusivities were measured using a custom diffusion chamber (n = 6 discs). TMJ anatomy and loading area were obtained from magnetic resonance imaging of healthy human volunteers (n = 11, male, 30 ± 9 y). Using experimentally determined nutrient metabolic rates, solute diffusivities, TMJ anatomy, and loading areas, subject-specific finite element (FE) models were developed to predict the 3-dimensional nutrient profiles in unloaded and loaded TMJ discs (unloaded, 0% strain, 20% strain). From the FE models, glucose, lactate, and oxygen concentration ranges for unloaded healthy human TMJ discs were 0.6 to 4.0 mM, 0.9 to 5.0 mM, and 0% to 6%, respectively, with steep gradients in the anterior and posterior bands. Sustained mechanical loading significantly reduced nutrient levels (P < 0.001), with a critical zone in which cells may die representing approximately 13.5% of the total disc volume. In conclusion, this study experimentally determined TMJ disc metabolic rates, solute diffusivities, and disc morphometry, and through subject-specific FE modeling, revealed critical interactions between mechanical loading and nutrient supply and metabolism for the in vivo human TMJ disc. The results suggest that TMJ disc homeostasis may be vulnerable to pathological loading (e.g., clenching, bruxism), which impedes nutrient supply. Given difficulties associated with direct in vivo measurements, this study provides a new approach to systematically investigate homeostatic and degenerative mechanisms associated with the TMJ disc.

[Effect of different oxygen tension on the cytoskeleton remodeling of goat temporomandibular joint disc cells]

Objective The effect of different oxygen tensions on the cytoskeleton remodeling of goat temporomandibular joint (TMJ) disc cells were investigated. Methods Goat TMJ disc cells were cultured under normoxia (21% O₂) and hypoxia (2%, 4%, and 8% O₂). Toluidine blue, picrosirius red, and type Ⅰ collagen immunocytochemical staining were performed to observe the changes in cell phenotype under different oxygen levels. Immunofluorescent staining and real-time reverse transcription-polymerase chain reaction analysis were then performed to identify actin, tubulin, and vimentin in the cultured disc cells. Results TMJ disc cells still displayed fibroblast characteristics under different oxygen levels and their cytoskeletons had regular arrangement. The fluorescence intensities of actin and vimentin were lowest at 4% O₂(P<0.05), whereas that of tubulin was highest at 2% O₂ (P<0.05). No significant difference among the other groups was observed (P>0.05). Actin mRNA levels were considerably decreased at 2% O₂ and 4% O₂ in hypoxic conditions, while actin mRNA expression was highest in 21% O₂. Tubulin mRNA levels considerably increased at 2% O₂, while tubulin mRNA expression was lowest in 8% O₂ (P<0.05). Vimentin mRNA expression was lowest at 4% O₂ and highest at 21% O₂, and significant differences were observed between vimentin mRNA expression levels among these oxygen levels (P<0.05). Conclusion Cytoskeletons were reconstructed in different oxygen tensions, and 2% O₂ may be the optimal oxygen level required to proliferate TMJ disc cells.

MicroRNA221-3p modulates Ets-1 expression in synovial fibroblasts from patients with osteoarthritis of temporomandibular joint

OBJECTIVE

This study aimed to screen differential expression of microRNAs (miRNAs), and investigate function of the specifically selected miRNA in synovial fibroblasts from patients suffering osteoarthritis of temporomandibular joint (TMJOA).

METHODS

MiRNA microarray was used to select differentially expressed miRNAs between TMJOA and normal synovial fibroblasts. The expression of screened miRNA221-3p was quantified using real-time PCR, and its specific target gene was predicted by bioinformatics. After transfection of miRNA221-3p mimics or inhibitor into synovial fibroblasts, the expression of v-Ets avian erythroblastosis virus E26 oncogene homolog 1 (Ets-1) was detected by immunohistochemistry, real-time PCR and Western blot, respectively. Dual luciferase activity was performed to identify the direct regulation of miRNA221-3p on Ets-1. Interlukin-1β (IL-1β) mimics an inflammatory situation.

RESULTS

In TMJOA synovial fibroblasts, eight miRNAs were up-regulated and six miRNAs were down-regulated. MiRNA221-3p was the most down-expressed. A sequence in the 3'-untranslated (3'-UTR) of Ets-1 complementary to the seed sequence of miRNA221-3p. Elevated expression of Ets-1 associated with attenuation of miRNA221-3p. Over-expression of miRNA221-3p suppressed the activity of a reporter construct containing the 3'-UTR of Ets-1 transcript and inhibited the expression of Ets-1 as well as its downstream molecules, matrix metalloproteinase 1 (MMP1) and MMP9 in TMJOA synovial fibroblasts. IL-1β suppressed the expression of miRNA221-3p in both a dose-dependent and time-dependent manner.

CONCLUSION

The reduction of miRNA221-3p in synovial fibroblasts, attributed from abundance of IL-1β in inflamed circumstance, induces Ets-1 up-regulation and then, initiates MMP1 and MMP9 secretion, thereby leading to continuously pathological development in TMJOA.

IL-1β-regulating angiogenic factors expression in perforated temporomandibular disk cells via NF-κB pathway

BACKGROUND

A high density of blood vessels is observed in the perforated disks of temporomandibular joint (TMJ), but the underlying mechanism is unknown. This study aimed to explore the regulation of disk angiogenesis in the perforated disks.

METHODS

Expressions of vascular endothelial growth factor (VEGF), angiogenin-1 (Ang-1), chondromodulin-1 (ChM-1), and thrombospondins-1 (TSP-1) were compared between healthy and perforated TMJ disk cells with or without interleukin-1β (IL-1β) incubation. The tube formation, cell migration, and expressions of matrix-metalloproteinases (MMPs) in human umbilical vein endothelial cell line (HUV-EC-C) were investigated in conditional media of disk cells. Western blot was performed to determine protein level of VEGF, Ang-1, ChM-1 and TSP-1 in IL-1β-induced disk cells cultured by NF-κB- or P38-specific pathway inhibitors, respectively.

RESULTS

Conditional media from perforated disk cells induced more tube formation, cell migration, and MMPs' expression in HUV-EC-C. Expressions of VEGF and Ang-1 were significantly higher, and ChM-1 and TSP-1 were lower in perforated disks compared to healthy disks. The VEGFA concentration was 291.1 ± 36.09 pg/ml in perforated disk cell conditioned media, markedly larger than that in NDCCM (144.9 ± 33.69 pg/ml). IL-1β induced VEGF through NF-κB signaling pathway and Ang-1 through p38 MAPK pathway, while repressed expression of ChM-1 and TSP-1 was through NF-κB pathway. Blockade of each pathway markedly restrained inducing effect of cultural media on HUV-EC-C tube formation and migration.

CONCLUSIONS

Perforated disk cells secreted more angiogenic factors which might induced via NF-κB pathway.

The effects of oxygen level and glucose concentration on the metabolism of porcine TMJ disc cells

OBJECTIVE

To determine the combined effect of oxygen level and glucose concentration on cell viability, ATP production, and matrix synthesis of temporomandibular joint (TMJ) disc cells.

DESIGN

TMJ disc cells were isolated from pigs aged 6-8 months and cultured in a monolayer. Cell cultures were preconditioned for 48 h with 0, 1.5, 5, or 25 mM glucose DMEM under 1%, 5%, 10%, or 21% O2 level, respectively. The cell viability was measured using the WST-1 assay. ATP production was determined using the Luciferin-Luciferase assay. Collagen and proteoglycan synthesis were determined by measuring the incorporation of [2, 3-(3)H] proline and [(35)S] sulfate into the cells, respectively.

RESULTS

TMJ disc cell viability significantly decreased (P < 0.0001) without glucose. With glucose present, decreased oxygen levels significantly increased viability (P < 0.0001), while a decrease in glucose concentration significantly decreased viability (P < 0.0001). With glucose present, decreasing oxygen levels significantly reduced ATP production (P < 0.0001) and matrix synthesis (P < 0.0001). A decreased glucose concentration significantly decreased collagen synthesis (P < 0.0001). The interaction between glucose and oxygen was significant in regards to cell viability (P < 0.0001), ATP production (P = 0.00015), and collagen (P = 0.0002) and proteoglycan synthesis (P < 0.0001).

CONCLUSIONS

Although both glucose and oxygen are important, glucose is the limiting nutrient for TMJ disc cell survival. At low oxygen levels, the production of ATP, collagen, and proteoglycan are severely inhibited. These results suggest that steeper nutrient gradients may exist in the TMJ disc and it may be vulnerable to pathological events that impede nutrient supply.

Effect of mechanical strain on solute diffusion in human TMJ discs: an electrical conductivity study

This study investigated the effect of mechanical strain on solute diffusion in human TMJ discs (mean cadaver age 77.8) using the electrical conductivity method. The electrical conductivity, as well as small ion diffusivity, of male and female TMJ discs was determined under three compressive strains. In the male group, the average disc electrical conductivity (mean ± SD) at 0% strain was 5.14 ± 0.97 mS/cm, decreased to 4.50 ± 0.91 mS/cm (-12.3%) at 10% strain, and 3.93 ± 0.81 mS/cm (-23.5%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.44 ± 0.08, decreased to 0.40 ± 0.08 (-8.9%) at 10% strain, and 0.36 ± 0.08 (-16.7%) at 20% compressive strain. In the female group, the average disc electrical conductivity at 0% strain was 5.84 ± 0.59 mS/cm, decreased to 5.01 ± 0.50 mS/cm (-14.2%) at 10% strain, and 4.33 ± 0.46 mS/cm (-25.8%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.49 ± 0.05, decreased to 0.43 ± 0.04 (-11.3%) at 10% strain, and 0.39 ± 0.04 (-19.9%) at 20% compressive strain. The results indicated that mechanical strain significantly impeded solute diffusion through the disc. This mechanical strain effect was larger in the female than in the male human TMJ disc. This study may provide new insights into TMJ pathophysiology.

Relationship between anisotropic diffusion properties and tissue morphology in porcine TMJ disc

OBJECTIVE

To investigate the relationship between anisotropic solute diffusion properties and tissue morphology in porcine temporomandibular joint (TMJ) discs.

DESIGN

TMJ discs from eleven pigs aged 6-8 months were divided into five regions: anterior, intermediate, posterior, lateral, and medial. The transport properties and tissue morphology were investigated in three orthogonal orientations: anteroposterior (AP), mediolateral (ML), and superoinferior (SI). The anisotropic diffusivity of fluorescein (332 Da) in the right discs was determined by the fluorescence recovery after photobleaching (FRAP) protocols. The tissue morphology in the left discs was quantified by scanning electron microscopy.

RESULTS

The diffusivities of fluorescein in the TMJ disc were significantly anisotropic, except for the anterior region. In the medial, intermediate, and lateral regions, the diffusion along the fiber orientation (i.e., AP direction) was significantly faster than the diffusion in ML and SI directions. In the posterior region, the diffusion along the fiber orientation (i.e., ML direction) was significantly faster than the diffusion in AP and SI directions. The diffusion in the anterior region was mostly isotropic with the lowest degree of diffusion anisotropy, as well as collagen fiber alignment, likely due to the multi-directional fiber arrangement. The anterior region had the highest mean diffusivity [65.6 (49.3-81.8) μm(2)/s] in the disc, likely due to its high water content. The overall average diffusivity of fluorescein across the TMJ disc was 57.0 (43.0-71.0) μm(2)/s.

CONCLUSIONS

The solute diffusion in porcine TMJ discs was strongly anisotropic and inhomogeneous, which associated with tissue structure (i.e., collagen fiber alignment) and composition (e.g., water content).

Effect of mechanical loading on electrical conductivity in porcine TMJ discs

The objective of this study was to examine the impact of mechanical loading on solute transport in porcine temporomandibular joint (TMJ) discs using the electrical conductivity method. The electrical conductivity, as well as ion diffusivity, of TMJ discs was determined under confined compression with 3 strains in 5 disc regions. The average electrical conductivity over the 5 regions (mean ± SD) at 0% strain was 3.10 ± 0.68 mS/cm, decreased to 2.76 ± 0.58 mS/cm (-11.0%) at 10% strain, and 2.38 ± 0.55 mS/cm (-22.2%) at 20% compressive strain. Correspondingly, the average relative ion diffusivity (mean ± SD) at 0% strain was 0.273 ± 0.055, decreased to 0.253 ± 0.048 (-7.3%) at 10% strain, and 0.231 ± 0.048 (-15.4%) at 20% compressive strain. These results indicated that compressive strain impeded solute transport in the TMJ disc. Furthermore, our results showed that the transport properties of TMJ discs were region-dependent. The electrical conductivity and ion diffusivity in the anterior region were significantly higher than in the posterior region. This regional difference is likely due to the significant differences of tissue hydration between these 2 regions. This study provides important insight into the electrical and solute transport behaviors in TMJ discs under mechanical loading and aids in the understanding of TMJ pathophysiology related to tissue nutrition.

Regional cell density distribution and oxygen consumption rates in porcine TMJ discs: an explant study

OBJECTIVE

To determine the regional cell density distribution and basal oxygen consumption rates (based on tissue volume and cell number) of temporomandibular joint (TMJ) discs and further examine the impact of oxygen tension on these rates.

DESIGN

TMJ discs from pigs aged 6-8 months were divided into five regions: anterior, intermediate, posterior, lateral and medial. The cell density was determined using confocal laser scanning microscopy. The change in oxygen tension was recorded while TMJ disc explants were cultured in sealed metabolism chambers. The volume based oxygen consumption rate of explants was determined by theoretical curve-fitting of the recorded oxygen tension data with the Michaelis-Menten equation. The rate on a per-cell basis was calculated based on the cell density measurements and volume based rate measured in another group of discs.

RESULTS

The overall cell density [mean, 95% confidence interval (CI)] was 51.3 (21.3-81.3) × 10(6) cells/mL wet tissue. Along the anteroposterior axis, the anterior band had 25.5% higher cell density than the intermediate zone (P<0.02) and 29.1% higher than the posterior band (P<0.008). Along the mediolateral axes, the medial region had 26.2% higher cell density than the intermediate zone (P<0.04) and 25.4% higher than the lateral region (P<0.045). The overall volume and cell based maximum oxygen consumption rates were 1.44 (0.44-2.44) μmol/mL wet tissue/h and 28.7 (12.2-45.2)nmol/10(6)cells/h, respectively. The central regions (intermediate, lateral, and medial) had significantly higher volume based (P<0.02) and cell based (P<0.005) oxygen consumption rates than the anterior and posterior bands. At high oxygen tension, the oxygen consumption rate remained constant, but dropped as oxygen tension fell below 5%.

CONCLUSIONS

The TMJ disc had higher cell density and oxygen consumption rates than articular cartilage reported in the literature. These results suggest that a steeper oxygen gradient may exist in the TMJ disc and may be vulnerable to pathological events that impede nutrient supply.

Beneficial effects of hyperbaric oxygen on human degenerated intervertebral disk cells via suppression of IL-1β and p38 MAPK signal

Nucleus pulposus cells (NPCs) from degenerating disks produce catabolic and inflammatory factors, including interleukin (IL)-1, nitric oxide (NO), prostaglandin E2 (PGE-2), and matrix metalloproteinaes (MMPs). An imbalance between MMPs and tissue inhibitors of matrix metalloproteinases (TIMPs) has been proposed to exist in the degenerating disk. This study evaluates the effects of hyperbaric oxygen (HBO) on the human degenerated NPCs. NPCs were maintained in alginate bead culture. All hyperoxic cells were exposed to 100% O(2) at 2.5 atmospheres absolute (ATA) in a hyperbaric chamber. p38 MAPK phosphorylation of the NPCs was detected using the phosphor-kinase array kit. RNA was isolated for real-time quantitative polymerase chain reaction (Q-PCR) analysis of aggrecan and type II collagen gene expression. The amounts of IL-1β, NO, PGE-2, MMP-3, and TIMP-1 in the conditioned media were quantified by enzyme-linked immunosorbent assay (ELISA). Our data showed that HBO treatment decreased expression of IL-1β, increased the gene expression of aggrecan and type II collagen, suppressed the phosphorylation of p38 MAPK, decreased NO, PGE-2, and MMP-3, and increased TIMP-1 expression in NPCs as compared with the atmospheric treatment. These results support the hypothesis that IL-1β and the p38 MAPK signal may be responsible for many of the inflammatory and catabolic changes seen in the human disk degeneration, and support our proposal that HBO treatment-induced increase of the anabolic factor (TIMP-1)/catabolic factor (MMP-3) ratio may provide a therapeutic approach to slow the course of intervertebral disk degeneration.

MMP-13 (collagenase 3) localization in human temporomandibular joint discs with internal derangement

The normal articular disc of the human temporomandibular joint (TMJ) consists of regularly arranged collagen fibers and fibroblast-like cells. Disc tissue is subjected to various types of loading. Adaptive remodelling entails microscopic changes in which different types of collagen and non-collagen proteins, as well as matrix metalloproteinases (MMPs), are involved. Collagenase-3 (MMP-13) seems to play a key role. The aim of the study was to evaluate its involvement in TMJ disc histopathology. We studied 10 discs from patients with arthropathy of the TMJ. Paraffin wax-embedded sections were processed for histological and immunohistochemical analysis. A well-characterized mouse monoclonal anti-MMP-13 antibody (anti-collagenase 3) was used. The results showed increased MMP-13 immunoreactivity in TMJ diseased disc tissue was correlated with the severity of the histopathological changes. The more severe the pathological changes, the greater the number of immunolabelled cells detected. Nearly all chondrocyte-like cells were immunopositive, whereas fibroblast-like cells and fibrochondrocytes were more rarely labelled. MMP-13 upregulation in disc tissue from patients with TMJ internal derangement suggests that MMP-13 is involved in disc histopathology, and that disc cells actively participate in the synthesis of extracellular matrix-degrading proteinases.

Interleukin-1beta up-regulates RGS4 through the canonical IKK2/IkappaBalpha/NF-kappaB pathway in rabbit colonic smooth muscle

Initial Ca2+-dependent contraction of the intestinal smooth muscle mediated by G(q)-coupled receptors is attenuated by RGS4 (regulator of G-protein signalling 4). Treatment of colonic muscle cells with IL-1beta (interleukin-1beta) inhibits acetylcholine-stimulated initial contraction through increasing the expression of RGS4. NF-kappaB (nuclear factor kappaB) signalling is the dominant pathway activated by IL-1beta. In the present study we show that RGS4 is a new target gene regulated by IL-1beta/NF-kappaB signalling. Exposure of cultured rabbit colonic muscle cells to IL-1beta induced a rapid increase in RGS4 mRNA expression, which was abolished by pretreatment with a transcription inhibitor, actinomycin D, implying a transcription-dependent mechanism. Existence of the canonical IKK2 [IkappaB (inhibitor of NF-kappaB) kinase 2]/IkappaBalpha pathway of NF-kappaB activation induced by IL-1beta in rabbit colonic muscle cells was validated with multiple approaches, including the induction of reporter luciferase activity and endogenous NF-kappaB-target gene expression, NF-kappaB-DNA binding activity, p65 nuclear translocation, IkappaBalpha degradation and the phosphorylation of IKK2 at Ser(177/181) and p65 at Ser(536). RGS4 up-regulation by IL-1beta was blocked by selective inhibitors of IKK2, IkappaBalpha or NF-kappaB activation, by effective siRNA (small interfering RNA) of IKK2, and in cells expressing either the kinase-inactive IKK2 mutant (K44A) or the phosphorylation-deficient IkappaBalpha mutant (S32A/S36A). An IKK2-specific inhibitor or effective siRNA prevented IL-1beta-induced inhibition of acetylcholine-stimulated PLC-beta (phopsholipase C-beta) activation. These results suggest that the canonical IKK2/IkappaBalpha pathway of NF-kappaB activation mediates the up-regulation of RGS4 expression in response to IL-1beta and contributes to the inhibitory effect of IL-1beta on acetylcholine-stimulated PLC-beta-dependent initial contraction in rabbit colonic smooth muscle.

Acidic extracellular pH increases calcium influx-triggered phospholipase D activity along with acidic sphingomyelinase activation to induce matrix metalloproteinase-9 expression in mouse metastatic melanoma

Acidic extracellular pH is a common feature of tumor tissues. We have reported that culturing cells at acidic pH (5.4-6.5) induced matrix metalloproteinase-9 expression through phospholipase D, extracellular signal regulated kinase 1/2 and p38 mitogen-activated protein kinases and nuclear factor-kappaB. Here, we show that acidic extracellular pH signaling involves both pathways of phospholipase D triggered by Ca2+ influx and acidic sphingomyelinase in mouse B16 melanoma cells. We found that BAPTA-AM [1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl) ester], a chelator of intracellular free calcium, and the voltage dependent Ca2+ channel blockers, mibefradil (for T-type) and nimodipine (for L-type), dose-dependently inhibited acidic extracellular pH-induced matrix metalloproteinase-9 expression. Intracellular free calcium concentration ([Ca2+]i) was transiently elevated by acidic extracellular pH, and this [Ca2+]i elevation was repressed by EGTA and the voltage dependent Ca2+ channel blockers but not by phospholipase C inhibitor, suggesting that acidic extracellular pH increased [Ca2+]i through voltage dependent Ca2+ channel. In contrast, SR33557, an L-type voltage dependent Ca2+ channel blocker and acidic sphingomyelinase inhibitor, attenuated matrix metalloproteinase-9 induction but did not affect calcium influx. We found that acidic sphingomyelinase activity was induced by acidic extracellular pH and that the specific acidic sphingomyelinase inhibitors (perhexiline and desipramine) and siRNA targeting aSMase/smpd1 could inhibit acidic extracellular pH-induced matrix metalloproteinase-9 expression. BAPTA-AM reduced acidic extracellular pH-induced phospholipase D but not acidic sphingomyelinase acitivity. The acidic sphingomyelinase inhibitors did not affect the phosphorylation of extracellular signal regulated kinase 1/2 and p38, but they suppressed nuclear factor-kappaB activity. These data suggest that the calcium influx-triggered phospholipase D and acidic sphingomyelinase pathways of acidic extracellular pH induced matrix metalloproteinase-9 expression, at least in part, through nuclear factor-kappaB activation.

Up-regulation of vascular endothelial growth factor in synovial fibroblasts from human temporomandibular joint by hypoxia

INTRODUCTION

Enhanced expression of vascular endothelial growth factor (VEGF) has been described in patients with internal derangement (ID). Herein, we examined the expression of VEGF in synovial fibroblasts from temporomandibular joint (TMJ) under hypoxia and investigated the regulation of hypoxia-inducible factor-1alpha (HIF-1alpha) involved in the expression of VEGF.

METHODS

Synovial fibroblasts were prepared from human TMJ. These cells were incubated under hypoxia or normoxia for the indicated time periods. VEGF levels in cultured supernatant were measured by an ELISA. VEGF mRNA isoforms and stability were assessed using RT-PCR and Northern blot analysis respectively. HIF-1alpha accumulation was evaluated by Western blotting and immunofluorescence.

RESULTS

VEGF were significantly induced by hypoxia in synovial fibroblasts. In response to hypoxia, VEGF121 and VEGF165 mRNA were both remarkably increased, while there was no change in VEGF mRNA stability. The accumulation and nuclear translocation of HIF-1alpha occurred under hypoxia.

CONCLUSIONS

Hypoxia may mainly induce the expression of VEGF121 and VEGF165 in synovial fibroblasts to promote inflamed angiogenesis of TMJ. HIF-1alpha, which is clearly activated in response to hypoxia, may control the expression of VEGF in synovial fibroblasts from TMJ.