Effects of interleukin-1β and tumor necrosis factor-α on macrophage inflammatory protein-3α production in synovial fibroblast-like cells from human temporomandibular joints

Potential pathological and molecular mechanisms of temporomandibular joint osteoarthritis

Temporomandibular joint osteoarthritis (TMJ OA) is a progressive degenerative disease of the temporomandibular joint (TMJ). The unclear etiology and mechanisms of TMJ OA bring great difficulties to early diagnosis and effective treatment, causing enormous burdens to patients' life and social economics. In this narrative review, we summarized the main pathological changes of TMJ OA, including inflammatory responses, degeneration of extracellular matrix (ECM), abnormal cell biological behaviors (apoptosis, autophagy, and differentiation) in TMJ tissue, and aberrant angiogenesis. All pathological features are closely linked to each other, forming a vicious cycle in the process of TMJ OA, which results in prolonged disease duration and makes it difficult to cure. Various molecules and signaling pathways are involved in TMJ OA pathogenesis, including nuclear factor kappa-B (NF-κB), mitogen-activated protein kinases (MAPKs), extracellular regulated protein kinases (ERKs) and transforming growth factor (TGF)-β signaling pathways et al. One molecule or pathway can contribute to several pathological changes, and the crosstalk between different molecules and pathways can further lead to a complicated condition TMJ OA. TMJ OA has miscellaneous etiology, complex clinical status, depressed treatment results, and poor prognosis. Therefore, novel in-vivo and in-vitro models, novel medicine, materials, and approaches for therapeutic procedures might be helpful for further investigation of TMJ OA. Furthermore, the role of genetic factors in TMJ OA needs to be elucidated to establish more reasonable and effective clinical strategies for diagnosing and treating TMJ OA.

The Role of TNF-α in the Pathogenesis of Temporomandibular Disorders

Temporomandibular disorder (TMD) is an oral dentofacial disease that is related to multiple factors such as disordered dental occlusion, emotional stress, and immune responses. In the past decades, tumor necrosis factor-alpha (TNF-α), a pleiotropic cytokine, has provided valuable insight into the pathogenesis of TMD, particularly in settings associated with inflammation. It is thought that TNF-α participates in the pathogenesis of TMD by triggering immune responses, deteriorating bone and cartilage, and mediating pain in the temporomandibular joint (TMJ). Initially, TNF-α plays the role of "master regulator" in the complex immune network by increasing or decreasing the production of other inflammatory cytokines. Then, the effects of TNF-α on cells, particularly on chondrocytes and synovial fibroblasts, result in pathologic cartilage degradation in TMD. Additionally, multiple downstream cytokines induced by TNF-α and neuropeptides can regulate central sensitization and inflammatory pain in TMD. Previous studies have also found some therapies target TMD by reducing the production of TNF-α or blocking TNF-α-induced pathways. All this evidence highlights the numerous associations between TNF-α and TMD; however, they are currently not fully understood and further investigations are still required for specific mechanisms and treatments targeting specific pathways. Therefore, in this review, we explored general mechanisms of TNF-α, with a focus on molecules in TNF-α-mediated pathways and their potential roles in TMD treatment. In view of the high clinical prevalence rate of TMD and damage to patients' QOL, this review provides adequate evidence for studying links between inflammation and TMD in further research and investigation.

Neuroimmune interactions in painful TMD: Mechanisms and treatment implications

The underlying mechanisms and treatment of painful temporomandibular disorders (TMDs) are important but understudied topics in craniofacial research. As a group of musculoskeletal diseases, the onset of painful TMD is proved to be a result of disturbance of multiple systems. Recently, emerging evidence has revealed the involvement of neuroimmune interactions in painful TMD. Inflammatory factors play an important role in peripheral sensitization of temporomandibular joint (TMJ), and neurogenic inflammation in turn enhances TMJs dysfunction in TMD. Furthermore, centralized neuroimmune communications contribute to neuron excitability amplification, leading to pain sensitization, and is also responsible for chronic TMD pain and other CNS symptoms. Therapeutics targeting neuroimmune interactions may shed light on new approaches for treating TMD. In this review, we will discuss the role of neuroimmune interactions in the onset of painful TMD from the peripheral and centralized perspectives, and how understanding this mechanism could provide new treatment options. Insights into the neuroimmune interactions within TMJs and painful TMD would broaden the knowledge of mechanisms and treatments of this multifactorial disease.

SP600125, a JNK-Specific Inhibitor, Regulates in vitro Auricular Cartilage Regeneration by Promoting Cell Proliferation and Inhibiting Extracellular Matrix Metabolism

In vitro construction is a major trend involved in cartilage regeneration and repair. Satisfactory in vitro cartilage regeneration depends on a suitable culture system. Current chondrogenic culture systems with a high content of transforming growth factor beta-1 effectively promote cartilaginous extracellular matrix (ECM) production but inhibit chondrocyte survival. As is known, inhibition of the c-Jun N-terminal kinase (JNK) signaling pathway acts in blocking the progression of osteoarthritis by reducing chondrocyte apoptosis and cartilage destruction. However, whether inhibiting JNK signaling resists the inhibitory effect of current chondrogenic medium (CM) on cell survival and affects in vitro auricular cartilage regeneration (including cell proliferation, ECM synthesis, and degradation) has not been investigated. In order to address these issues and optimize the chondrogenic culture system, we generated a three-dimensional in vitro auricular cartilage regeneration model to investigate the effects of SP600125 (a JNK-specific inhibitor) on chondrocyte proliferation and ECM metabolism. SP600125 supplementation efficiently promoted cell proliferation at both cellular and tissue levels and canceled the negative effect of our chondrogenic culture system on cell survival. Moreover, it significantly inhibited ECM degradation by reducing the expressions of tumor necrosis factor-alpha, interleukin-1-beta, and matrix metalloproteinase 13. In addition, SP600125 inhibited ECM synthesis at both cellular and tissue levels, but this could be canceled and even reversed by adding chondrogenic factors; yet this enabled a sufficient number of chondrocytes to be retained at the same time. Thus, SP600125 had a positive effect on in vitro auricular cartilage regeneration in terms of cell proliferation and ECM degradation but a negative effect on ECM synthesis, which could be reversed by adding CM. Therefore, a combination of SP600125 and CM might help in optimizing current chondrogenic culture systems and achieve satisfactory in vitro cartilage regeneration by promoting cell proliferation, reducing ECM degradation, and enhancing ECM synthesis.

YAP1 regulates chondrogenic differentiation of ATDC5 promoted by temporary TNF-α stimulation through AMPK signaling pathway

Local injection of tumor necrosis factor-alpha (TNF-α) at bone fracture sites during the early stage of the inflammatory response is reported to improve fracture repair in a murine model. However, the underlying mechanism is unclear. Endochondral bone formation, a process that is highly related to fracture repair, requires a certain amount of chondrocyte hypertrophy. This study aimed to investigate the effect of TNF-α on the differentiation of murine chondrogenic ATDC5 cells and the underlying mechanism. In this study, improved chondrogenic differentiation of ATDC5 cells was achieved by brief TNF-α stimulation. Moreover, the expression of Yes-associated protein 1 (YAP1) was suppressed after brief TNF-α stimulation. The expressions of inflammatory mediators and chondrogenic and hypertrophic-associated genes in ATDC5 cells triggered by TNF-α were suppressed in the YAP1 overexpression group but enhanced in the YAP1 knockdown group. Mechanistically, TNF-α-induced activation of the 5' AMP-activated protein kinase (AMPK) signaling pathway was regulated by YAP1, as revealed by the phosphorylated-AMPK/AMPK change ratios in the YAP1 overexpression and knockdown groups, respectively. Moreover, the potential for TNF-α to enhance chondrogenic differentiation could be partially reversed with an AMPK inhibitor. Taken together, we demonstrate, for the first time, that YAP1 modulates the ability of TNF-α to enhance chondrocyte differentiation partly through AMPK signaling.

Protective Effect of Genistein on Condylar Cartilage through Downregulating NF-κB Expression in Experimentally Created Osteoarthritis Rats

Temporomandibular joint osteoarthrosis (TMJOA) is characterised by chronic inflammatory changes, with subsequent gradual loss of joint cartilage. NF-κB is a crucial transcription factor in the course of inflammatory and immune responses, which are involved in OA pathology activated by proinflammatory cytokines. Genistein is known to have anti-inflammation and modulation of metabolic pathways through repression of the NF-κB signaling pathway in inflammatory disease. But so far, studies on the effects of genistein on TMJOA are very limited. So, the purpose of this study is to investigate the protective effect of genistein against experimentally induced condylar cartilage degradation through downregulating NF-κB expression in created osteoarthritis rats in vivo. Male SD rats were created as temporomandibular joint osteoarthritis models and administered through oral gavage with low and high dosage genistein (30 mg/kg and 180 mg/kg, respectively) daily for 4 weeks. The morphological changes of the condylar cartilage were studied with HE and Masson staining. The expressions of p65 and inflammatory cytokines (IL-1β and TNFα) were detected using immunohistochemistry and real-time PCR. The results showed that experimentally created osteoarthritis reduced the condylar cartilage thickness of rats and increased the gene expression of cytokines (IL-1β and TNFα) and positive cells of p65. Genistein treatment had positive effects on the condylar cartilage renovation, while high dose genistein treatment had more significant effects on the reversing of OA changes and reduction of the expression of p65 and inflammatory cytokines (IL-1β and TNFα). The results indicated that high dose genistein treatment had obvious therapeutic effects on condyle cartilage damages of OA rats. The mechanism may be that genistein suppresses the NF-κB expression activated by inflammatory cytokines.

Platelet-Released Growth Factors Modulate the Secretion of Cytokines in Synoviocytes under Inflammatory Joint Disease

The etiology and pathogenesis of rheumatoid arthritis (RA) are marked by a complex interplay of various cell populations and is mediated by different signaling pathways. Traditionally, therapies have primarily focused on pain relief, reducing inflammation and the recovery of joint function. More recently, however, researchers have discussed the therapeutic efficacy of autologous platelet-rich plasma (PRP). The main objective of this work is to examine the influences of platelet-released growth factor (PRGF) on human synoviocytes under inflammatory conditions. Additionally, it is checked to which extend treatment with platelet concentrate influences the release of cytokines form synoviocytes. For this purpose, an in vitro RA model was created by stimulating the cells with the TNF-α. The release of cytokines was measured by ELISA. The cytokine gene expression was analyzed by real-time PCR. It has been observed that the stimulation concentration of 10 ng/ml TNF-α resulted in a significantly increased endogenous secretion and gene expression of IL-6 and TNF-α. The anti-inflammatory effect of PRGF could be confirmed through significant reduction of TNF-α and IL-1β. An induced inflammatory condition seems to cause PRGF to inhibit the release of proinflammatory cytokines. Further study is required to understand the exact effect mechanism of PRGF on synoviocytes.

Differential regulation by IFN‑γ on TNF‑α‑induced chemokine expression in synovial fibroblasts from temporomandibular joint

Tumor necrosis factor (TNF)‑α and interferon (IFN)‑γ, are inflammatory cytokines in the synovial fluid of patients with temporomandibular joint disorder (TMD). However, it remains unknown whether they participate in the regulation of various chemokine expression levels associated with TMD. The effects of TNF‑α and IFN‑γ on the expression of several different inflammatory chemokines, including interleukin (IL)‑8, C‑X‑C motif chemokine ligand (CXCL)1, C‑C motif chemokine ligand (CCL)20, CXCL9, CXCL10, and CXCL11 in synovial fibroblasts obtained from the temporomandibular joint (TMJ) were examined. The results demonstrated that TNF‑α increased the mRNA levels of all examined chemokines in synovial fibroblasts obtained from the TMJ. IFN‑γ treatment alone increased the mRNA expression levels of CXCR3 chemokines, including CXCL10, while they were significantly enhanced when administered in combination with TNF‑α compared with either treatment alone. However, the combination of IFN‑γ and TNF‑α resulted in lower mRNA expression levels of IL‑8 and CXCL1 as compared with those induced by TNF‑α alone. The nuclear factor‑κB inhibitor, Bay 11‑7082, decreased the TNF‑α‑mediated expression of IL‑8 and CXCL10 in the absence, and presence of IFN‑γ. In addition, the JAK2 inhibitor, AG490, decreased CXCL10 expression when administered with TNF‑α and IFN‑γ. Finally, the decrease in TNF‑α‑induced IL‑8 caused by IFN‑γ was recovered by AG490. The results of the present study suggest that TNF‑α and IFN‑γ function in a cooperative manner to regulate inflammatory chemokine expression in synovial fibroblasts, which may contribute to the pathological condition of the TMJ.

ERK2 and JNK1 contribute to TNF-α-induced IL-8 expression in synovial fibroblasts

Tumor necrosis factor α (TNF-α) induces the expression and secretion of interleukin 8 (IL-8), which contributes to synovitis in rheumatoid arthritis (RA). To elucidate the mechanism of the onset of RA, we used synovial fibroblasts without autoimmune inflammatory diseases and investigated MAPK signaling pathways in TNF-α-induced IL-8 expression. Synovial fibroblasts isolated from healthy dogs were characterized by flow cytometry, which were positive for the fibroblast markers CD29, CD44, and CD90 but negative for the hematopoietic cell markers CD14, CD34, CD45, and HLA-DR. TNF-α stimulated the secretion and mRNA expression of IL-8 in a time- and dose-dependent manner. ERK and JNK inhibitors attenuated TNF-α-induced IL-8 expression and secretion. TNF-α induced the phosphorylation of ERK1/2 and JNK1/2. TNF-α-induced IL-8 expression was attenuated both in ERK2- and JNK1-knockdown cells. TNF-α-induced ERK1/2 or JNK1/2 was observed in ERK2- or JNK1-knockdown cells, respectively, showing that there is no crosstalk between ERK2 and JNK1 pathways. These observations indicate that the individual activation of ERK2 and JNK1 pathways contributes to TNF-α-induced IL-8 expression in synovial fibroblasts, which appears to be involved in the progress in RA.

Hyperbaric oxygen protects type II collagen in interleukin-1β-induced mandibular condylar chondrocyte via inhibiting the JNK/c-Jun signaling pathway

The aim of this study was to explore the mechanisms of Hyperbaric oxygen (HBO) protective on interleukin-1β (IL-1β) induced rat's mandibular condylar chondrocytes. Chondrocytes were exposure to Hyperbaric oxygen after induced inflammatory by IL-1β. After that, the expression of p-JNK and c-Jun was increased significantly, while the Sox-9 was decreased significantly, Immunofluorescence results showed that the expression of p-JNK and p-c-Jun were decreased while the expression of Sox-9 and COL2 were increased in chondrocytes treated with IL-1β and selective JNK inhibitor. Hyperbaric oxygen might plays similar roles with the JNK-specific inhibitor SP600125, inducing the increase of Sox-9 and COL2 expression. On the whole, IL-1β induced inflammatory in chondrocytes by activating the JNK/c-Jun signaling pathway and down-regulate the expression of Sox-9 and COL2. However, Hyperbaric oxygen can inhibits IL-1β induced inflammatory response in chondrocytes though block the JNK/c-Jun signaling pathway and up-regulate the expression of Sox-9 and COL2.

Carbon nanotubes stimulate synovial inflammation by inducing systemic pro-inflammatory cytokines

Carbon nanotubes (CNTs) have promising applications in a wide range of biomedical fields, including imaging, drug/gene delivery and other therapeutics; however, the biosafety concerns of CNTs should be addressed. To date, many reports have documented the toxicological effects on the cells, tissue or organs that are in direct contact with the tubes; however, there is limited evidence to unravel the secondary toxicity upon CNT treatment. Moreover, more effort is needed to gain a definitive understanding of the adverse outcome pathway (AOP) for CNTs, and a pragmatic framework for risk assessment has not been established yet. In the current study, we aimed to decipher the secondary toxicity to joints under CNT exposure. We demonstrated that carboxylated multi-wall CNTs (MWCNTs-COOH) significantly provoked systemic pro-inflammatory responses, leading to synovial inflammation within knee joints, as evidenced by the infiltration of pro-inflammatory cells in the synovium and meniscus. Mechanistic studies showed that MWCNTs-COOH stimulated pro-inflammatory effects by activating macrophages, and the secreted pro-inflammatory cytokines primed the synoviocytes and chondrocytes, resulting in enhanced production of a large array of enzymes involved in articular cartilage degeneration, including matrix metalloproteinase (MMP) members and cyclooxygenase (COX) members, and increased enzymatic activity of MMPs was demonstrated. Blockade of the cytokines by antibodies significantly attenuated the production of these enzymes. Our current study thus suggests that there is a novel secondary toxicity of CNTs, namely a new AOP to understand the indirect effects of carbon nanotubes: synovial inflammation due to the alteration of the priming state of synoviocytes and chondrocytes under CNT-induced systemic inflammatory conditions.

Gene Expression Profiling of IL-17A-Treated Synovial Fibroblasts from the Human Temporomandibular Joint

Synovial fibroblasts contribute to the inflammatory temporomandibular joint under pathogenic stimuli. Synovial fibroblasts and T cells participate in the perpetuation of joint inflammation in a mutual activation feedback, via secretion of cytokines and chemokines that stimulate each other. IL-17 is an inflammatory cytokine produced primarily by Th17 cells which plays critical role in the pathogenesis of numerous autoimmune and inflammatory diseases. Here, we investigated the roles of IL-17A in temporomandibular joint disorders (TMD) using genome-wide analysis of synovial fibroblasts isolated from patients with TMD. IL-17 receptors were expressed in synovial fibroblasts as assessed using real-time PCR. Microarray analysis indicated that IL-17A treatment of synovial fibroblasts upregulated the expression of IL-6 and chemokines. Real-time PCR analysis showed that the gene expression of IL-6, CXCL1, IL-8, and CCL20 was significantly higher in IL-17A-treated synovial fibroblasts compared to nontreated controls. IL-6 protein production was increased by IL-17A in a time- and a dose-dependent manner. Additionally, IL-17A simulated IL-6 protein production in synovial fibroblasts samples isolated from three patients. Furthermore, signal inhibitor experiments indicated that IL-17-mediated induction of IL-6 was transduced via activation of NFκB and phosphatidylinositol 3-kinase/Akt. These results suggest that IL-17A is associated with the inflammatory progression of TMD.

IL-1β mediating high mobility group box protein-1 expression in condylar chondrocyte during temporomandibular joint inflammation

BACKGROUND

Temporomandibular joint (TMJ) osteoarthritis(OA)characterized with cartilage degen-eration is associated with inflammation. High mobility group box chromosomal protein-1(HMGB-1)is a potent mediator of inflammation and the trigger of OA. The expression of HMGB-1 in TMJ OA was uncovered, but the role of HMGB-1 in TMJ cartilage degeneration is not fully understood. In this study, the regulation of HMGB-1 in TMJ condylar cartilage was revealed.

METHODS

A complete Freund's adjuvant (CFA)-induced TMJ inflammation animal model was employed and the expression of HMGB-1 was detected at 1st, 2nd, and 6th weeks by immunohistochemistry. TMJ condylar chondrocytes were incubated with IL-1β (10 and 40 ng/ml) at 24, 48, and 72 h, and the translocation and protein level of HMGB-1 were evaluated by immunofluorescence and Western blot.

RESULT

Nuclear HMGB-1 staining was predominantly located in chondrocytes of both the fibrosis and proliferative zones in healthy TMJ. 1st week and 2nd week after CFA injection, immunoreaction could be detected in the cytoplasms of HMGB-1-positive cells and cartilage matrix especially in hypertrophic zone. At 6th week after CFA injection, cartilage matrix expression was disappeared and the cytoplasm expression of HMGB-1 was very weak in hypertrophic zone. HMGB-1 was translocated from the nucleus to the cytoplasm at 48 h after incubated with IL-1β (10 ng/ml and 40 ng/ml). The protein level of HMGB-1 was increased after stimulation and had a peak at 48 h.

CONCLUSION

HMGB-1 might be associated with TMJ inflammation and OA. Insight into the role of HMGB-1 in TMJ inflammation is helpful to add the new knowledge into the pathogenesis of TMJ OA.

Dickkopf‑related protein 1 induces angiogenesis by upregulating vascular endothelial growth factor in the synovial fibroblasts of patients with temporomandibular joint disorders

Angiogenesis has an important role in the progression of temporomandibular joint disorders (TMD). The aim of the present study was to explore the association between dickkopf-related protein 1 (DKK-1) and angiogenesis in TMD. The expression levels of DKK-1 and vascular endothelial growth factor (VEGF) were quantified by an ELISA assay of the synovial fluid from patients with TMD. The correlation between DKK-1 and VEGF was analyzed by Pearson correlation test. Synovial fibroblasts were isolated from patients with TMD and were subsequently treated with recombinant human DKK-1, anti-DKK-1 antibody, hypoxia inducible factor-1α (HIF-1α), or small interfering RNA (siRNA). The expression levels of DKK-1, HIF-1α, and VEGF were subsequently quantified. The present study also investigated the effects of DKK-1 on the migration of human umbilical vein endothelial cells (HUVEC). Increased expression levels of DKK-1 were concordant with increased expression levels of VEGF in the synovial fluid from patients with TMD. In the synovial fibroblasts, DKK-1 increased the expression levels of VEGF, and promoted HIF-1α nuclear localization. In addition, DKK-1 induced HUVEC migration, and HIF-1α siRNA inhibited DKK-1-induced cell migration. The results of the present study indicate that DKK-1 is associated with angiogenesis in the synovial fluid of patients with TMD. Furthermore, HIF-1α may be associated with DKK-1-induced HUVEC activation.

Enhanced expression of WD repeat-containing protein 35 via nuclear factor-kappa B activation in bupivacaine-treated Neuro2a cells

The family of WD repeat proteins comprises a large number of proteins and is involved in a wide variety of cellular processes such as signal transduction, cell growth, proliferation, and apoptosis. Bupivacaine is a sodium channel blocker administered for local infiltration, nerve block, epidural, and intrathecal anesthesia. Recently, we reported that bupivacaine induces reactive oxygen species (ROS) generation and p38 mitogen-activated protein kinase (MAPK) activation, resulting in an increase in the expression of WD repeat-containing protein 35 (WDR35) in mouse neuroblastoma Neuro2a cells. It has been shown that ROS activate MAPK through phosphorylation, followed by activation of nuclear factor-kappa B (NF-κB) and activator protein 1 (AP-1). The present study was undertaken to test whether NF-κB and c-Jun/AP-1 are involved in bupivacaine-induced WDR35 expression in Neuro2a cells. Bupivacaine activated both NF-κB and c-Jun in Neuro2a cells. APDC, an NF-κB inhibitor, attenuated the increase in NF-κB activity and WDR35 protein expression in bupivacaine-treated Neuro2a cells. GW9662, a selective peroxisome proliferator-activated receptor-γ antagonist, enhanced the increase in NF-κB activity and WDR35 protein expression in bupivacaine-treated Neuro2a cells. In contrast, c-Jun siRNA did not inhibit the bupivacaine-induced increase in WDR35 mRNA expression. These results indicate that bupivacaine induces the activation of transcription factors NF-κB and c-Jun/AP-1 in Neuro2a cells, while activation of NF-κB is involved in bupivacaine-induced increases in WDR35 expression.