Recent Advances in Animal Models, Diagnosis, and Treatment of Temporomandibular Joint Osteoarthritis

N-methyl-D-aspartate Receptor Subunits 2A and 2B Mediate Connexins and Pannexins in the Trigeminal Ganglion Involved in Orofacial Inflammatory Allodynia during Temporomandibular Joint Inflammation

Temporomandibular joint osteoarthritis (TMJOA) is a severe form of temporomandibular joint disorders (TMD), and orofacial inflammatory allodynia is one of its common symptoms which lacks effective treatment. N-methyl-D-aspartate receptor (NMDAR), particularly its subtypes GluN2A and GluN2B, along with gap junctions (GJs), are key players in the mediation of inflammatory pain. However, the precise regulatory mechanisms of GluN2A, GluN2B, and GJs in orofacial inflammatory allodynia during TMJ inflammation still remain unclear. Here, we established the TMJ inflammation model by injecting Complete Freund's adjuvant (CFA) into the TMJ and used Cre/loxp site-specific recombination system to conditionally knock out (CKO) GluN2A and GluN2B in the trigeminal ganglion (TG). Von-frey test results indicated that CFA-induced mechanical allodynia in the TMJ region was relieved in GluN2A and GluN2B deficient mice. In vivo, CFA significantly up-regulated the expression of GluN2A and GluN2B, Gjb1, Gjb2, Gjc2 and Panx3 in the TG, and GluN2A and GluN2B CKO played different roles in mediating the expression of Gjb1, Gjb2, Gjc2 and Panx3. In vitro, NMDA up-regulated the expression of Gjb1, Gjb2, Gjc2 and Panx3 in satellite glial cells (SGCs) as well as promoted the intercellular communication between SGCs, and GluN2A and GluN2B knocking down (KD) altered the expression and function differently. NMDAR regulated Gjb1 and Panx3 through ERK1/2 pathway, and mediated Gjb2 and Gjc2 through MAPK, PKA, and PKC intracellular signaling pathways. These findings shed light on the distinct functions of GluN2A and GluN2B in mediating peripheral sensitization induced by TMJ inflammation in the TG, offering potential therapeutic targets for managing orofacial inflammatory allodynia.

Glutathione peroxidase 4 restrains temporomandibular joint osteoarthritis progression by inhibiting ferroptosis

There are few effective therapeutic strategies for temporomandibular joint osteoarthritis (TMJOA) due to the unclear pathology and mechanisms. We aimed to confirm the roles of GPX4 and ferroptosis in TMJOA progression. ELISA assay was hired to evaluate concentrations of ferroptosis-related markers. The qRT-PCR assay was hired to assess gene mRNA level. Western blot assay and immunohistochemistry were hired to verify the protein level. CCK-8 assay was hired to detect cell viability. Human fibroblast-like synoviocytes (FLSs) were cultured to confirm the effects of GPX4 and indicated inhibitors, and further verified the effects of GPX4 and ferroptosis inhibitors in TMJOA model rats. Markers of ferroptosis including 8-hidroxy-2-deoxyguanosine (8-OHdG) and iron were notably increased in TMJOA tissues and primary OA-FLSs. However, the activity of the antioxidant system including the glutathione peroxidase activity, glutathione (GSH) contents, and glutathione/oxidized glutathione (GSH/GSSG) ratio was notably inhibited in TMJOA tissues, and the primary OA-FLSs. Furthermore, the glutathione peroxidase 4 (GPX4) expression was down-regulated in TMJOA tissues and primary OA-FLSs. Animal and cell experiments have shown that ferroptosis inhibitors notably inhibited ferroptosis and promoted HLS survival as well as up-regulated GPX4 expression. Also, GPX4 knockdown promoted ferroptosis and GPX4 overexpression inhibited ferroptosis. GPX4 also positively regulated cell survival which was the opposite with ferroptosis. In conclusion, GPX4 and ferroptosis regulated the progression of TMJOA. Targeting ferroptosis might be an effective therapeutic strategy for TMJOA patients in the clinic.

Low-frequency pulsed electromagnetic fields alleviate the condylar cartilage degeneration and synovitis at the early stage of temporomandibular joint osteoarthritis

BACKGROUND

Temporomandibular joint osteoarthritis (TMJOA) is characterized by articular cartilage degeneration and progressive synovitis. How to effectively inhibit TMJOA in the early stage has been a hot topic in the biomedical field. As a non-invasive physiotherapy, pulsed electromagnetic field (PEMF) treatment has shown great potential in the treatment of osteoarthritis (OA) in extremity joints.

OBJECTIVE

This study aims to investigate the biological effect of PEMF intervention on TMJ cartilage degeneration and synovium inflammation at the early stage of TMJOA.

METHODS

PEMF (2.0 mT, 15 Hz, 2 h/day) treatment was given to rats in which TMJOA was induced by applying the unilateral anterior crossbite (UAC). Histological and immunohistochemical staining, TUNEL assay, real-time PCR and western blotting assay were performed to detect the changes of the morphology and the expression of pro-inflammatory and degradative factors in condylar cartilage and synovium.

RESULTS

Obvious condylar cartilage degeneration, characterized by decreased cartilage thickness, degraded cartilage extracellular matrix, increased expression of pro-inflammatory and degradative factors (TNF-α, IL-1β, MMP-13, ADAMTS-5, IL-6, MMP-3, MMP-9 and COL-X) and increased chondrocytes death, was observed in UAC group, accompanied by synovium hyperplasia and up-regulation of pro-inflammatory and degradative factors in synovium. PEMF intervention reversed the decreased cartilage thickness at 3 weeks and degraded cartilage extracellular matrix at 6 weeks. Moreover, the up-regulation of pro-inflammatory, degradative and hypertrophyic factors and chondrocytes death in condylar cartilage induced by UAC were inhibited to some extent. In addition, the synovium hyperplasia and the up-regulation of pro-inflammatory and degradative factors in synovium were inhibited at 3 weeks and 6 weeks.

CONCLUSIONS

Appropriate PEMF stimulation can reverse the loss of cartilage extracellular matrix, the chondrocytes death, the increased expression of pro-inflammatory and degradative factors in cartilage, the decreased cartilage thickness and synovium inflammation induced by UAC at the early stage of TMJOA to some extent. PEMF stimulation may be a promising method in clinical TMJOA treatment.

Probing the antinociceptive and therapeutic potential of probiotics in managing temporomandibular joint arthritis

This literature review explored the antinociceptive and therapeutic effects of probiotic therapy (PT) in the treatment of arthritic conditions affecting the temporomandibular joint (TMJ). Indexed databases were searched without time and language restrictions up to and including February 2023, to identify studies addressing the question: "Is PT effective for the management of TMJ arthritis?" The following keywords were used in different combinations with Boolean operators: arthritis, osteoarthritis, pain, probiotic, rheumatoid, temporomandibular disorders, and temporomandibular joint. Original clinical and experimental studies assessing the therapeutic efficacy of PT in the management of osteoarthritis were eligible for inclusion. Letters to the editor, reviews, commentaries, perspectives, and expert opinions were not sought. The structure of the current review was tailored to encapsulate relevant information. A total of 297 relevant studies were identified during the initial literature search, and the full text and reference lists of these studies were scrutinized. To date, the potential role of PT in managing osteoarthritis of the TMJ region remains uninvestigated. No clinical trials in the indexed literature have assessed the efficacy of PT in managing TMJ arthritis; however, this finding does not preclude a potential role of probiotics as antinociceptive and therapeutic agents in susceptible populations.

Loss of Slc39a12 in hippocampal neurons is responsible for anxiety-like behavior caused by temporomandibular joint osteoarthritis

Background

An evident association between mood disorders and TMJ dysfunction has been demonstrated in previous studies. This study observed both the behavioral changes and the pathological changes in hippocampal tissue of rats in an animal model of TMJ-OA by injecting MIA into TMJ.

Methods

Eighteen SD rats were randomly assigned to the NC group and the MIA groups. A TMJ-OA model was established to assess the HWT in the TMJ region, and the rats were subjected to the OFT and EPM. HE, O-fast green staining, qRT-PCR and immunofluorescence were used to detect condylar damage. Serum and hippocampal oxidative stress levels were detected. Functions of genes obtained by RNA-Seq were investigated using H2O2, ZnCl2 and transfection of siRNA on HT22 cells.

Results

Injection of MIA resulted in disorganization of the chondrocyte layer on the condylar surface of rats, with reduced synthesis and increased degradation of the condylar cartilage matrix and reduced HWT. The results of the OFT and EPM showed that the rats in the MIA group developed anxiety-like behavior during the sixth week of MIA injection. Increased Nox4 expression, decreased SOD2 expression, elevated MDA level, and reduced GSH level were detected in serum and hippocampal neurons in the MIA group, with nuclear pyknosis and reduced Nissl bodies observed in neurons. The expression of Slc39a12 in hippocampal neurons of rats in the MIA group decreased. Slc39a12 knockdown in HT22 cells induced increased Nox4 expression, decreased SOD2 expression, increased MDA level, and reduced GSH and intracellular Zn2+. Oxidative stress in HT22 cells after transfection and H2O2 stimulation was reversed when ZnCl2 was added.

Conclusion

Loss of Slc39a12 in hippocampal neurons results in cellular oxidative stress, further leading to neuronal damage. This may potentially explain how TMJ-OA triggers anxiety-like behavior in rats.

A comprehensive patient-specific prediction model for temporomandibular joint osteoarthritis progression

Temporomandibular joint osteoarthritis (TMJ OA) is a prevalent degenerative disease characterized by chronic pain and impaired jaw function. The complexity of TMJ OA has hindered the development of prognostic tools, posing a significant challenge in timely, patient-specific management. Addressing this gap, our research employs a comprehensive, multidimensional approach to advance TMJ OA prognostication. We conducted a prospective study with 106 subjects, 74 of whom were followed up after 2 to 3 y of conservative treatment. Central to our methodology is the development of an innovative, open-source predictive modeling framework, the Ensemble via Hierarchical Predictions through Nested cross-validation tool (EHPN). This framework synergistically integrates 18 feature selection, statistical, and machine learning methods to yield an accuracy of 0.87, with an area under the ROC curve of 0.72 and an F1 score of 0.82. Our study, beyond technical advancements, emphasizes the global impact of TMJ OA, recognizing its unique demographic occurrence. We highlight key factors influencing TMJ OA progression. Using SHAP analysis, we identified personalized prognostic predictors: lower values of headache, lower back pain, restless sleep, condyle high gray level-GL-run emphasis, articular fossa GL nonuniformity, and long-run low GL emphasis; and higher values of superior joint space, mouth opening, saliva Vascular-endothelium-growth-factor, Matrix-metalloproteinase-7, serum Epithelial-neutrophil-activating-peptide, and age indicate recovery likelihood. Our multidimensional and multimodal EHPN tool enhances clinicians' decision-making, offering a transformative translational infrastructure. The EHPN model stands as a significant contribution to precision medicine, offering a paradigm shift in the management of temporomandibular disorders and potentially influencing broader applications in personalized healthcare.

Analysis of joint protein expression profile in anterior disc displacement of TMJ with or without OA

OBJECTIVE

Anterior disc displacement (ADD) is a common clinical issue and may cause osteoarthritis (OA). However, the research of protein changes in synovial fluid as disease development marker and potential treatment clue is still insufficient.

MATERIALS AND METHODS

We conducted the high-resolution mass spectrometry (MS) of synovial fluid collected from 60 patients with normal disk position to ADD and ADD with osteoarthritis (OA). The proteins with significant changes among the 3 groups were analyzed by biological information and further validated by in primary rat condyle chondrocytes and OA animal model.

RESULTS

FGL2, THBS4, TNC, FN1, OMD etc. were significantly increased in ADD without OA (p < 0.05), which reflected the active extracellular matrix and collagen metabolism. FGFR1, FBLN2, GRB2 etc. were significantly increased in ADD with OA group (p < 0.05), which revealed an association with apoptosis and ferroptosis. Proteins such as P4HB, CBLN4, FHL1, VIM continuously increase in the whole disease progress (p < 0.05). Both the in vitro and in vivo results are consistent with protein changes detected in MS profile.

CONCLUSION

This study firstly provides the expression changes of proteins from normal disc condyle relationship toward ADD with OA, which can be selected and studied further as disease progress marker and potential treatment targets.

Anesthetic management of patients with difficult intubation due to temporomandibular joint osteoarthritis: A case report

INTRODUCTION

Temporomandibular joint osteoarthritis (TMJOA) affects 8% to 16% of the global population, yet TMJOA remains relatively underappreciated clinically. To anesthesiologists, who is concerned about patient safety, adequate preoperative evaluation and preparation, as well as individualized anesthetic management of patients, are necessary. Therefore, the anesthesiologist should be alert for difficult airways due to TMJOA, have a full and comprehensive understanding of the disease, and possess the appropriate expertise for difficult airway intubation.

CASE PRESENTATION

A 52-year-old female patient was scheduled for laparoscopic operation of uterine adnexa under general anesthesia. The patient preoperative evaluation showed only 1 finger width of mouth opening, and the computed tomography scan showed bilateral temporomandibular arthritis, which was evident on the right side. Intraoperatively, the expected airway difficulties occurred, and the anesthesiologist opted to use lightwand intubation, which was ultimately successful in 1 pass without any complications.

CONCLUSION

Intubation using a lightwand for patients with difficult intubation due to TMJOA is a very effective intubation modality.

Delivery of dental pulp stem cells by an injectable ROS-responsive hydrogel promotes temporomandibular joint cartilage repair via enhancing anti-apoptosis and regulating microenvironment

Temporomandibular joint (TMJ) cartilage repair poses a considerable clinical challenge, and tissue engineering has emerged as a promising solution. In this study, we developed an injectable reactive oxygen species (ROS)-responsive multifunctional hydrogel (RDGel) to encapsulate dental pulp stem cells (DPSCs/RDGel in short) for the targeted repair of condylar cartilage defect. The DPSCs/RDGel composite exhibited a synergistic effect in the elimination of TMJ OA (osteoarthritis) inflammation via the interaction between the hydrogel component and the DPSCs. We first demonstrated the applicability and biocompatibility of RDGel. RDGel encapsulation could enhance the anti-apoptotic ability of DPSCs by inhibiting P38/P53 mitochondrial apoptotic signal in vitro. We also proved that the utilization of DPSCs/RDGel composite effectively enhanced the expression of TMJOA cartilage matrix and promoted subchondral bone structure in vivo. Subsequently, we observed the synergistic improvement of DPSCs/RDGel composite on the oxidative stress microenvironment of TMJOA and its regulation and promotion of M2 polarization, thereby confirmed that M2 macrophages further promoted the condylar cartilage repair of DPSCs. This is the first time application of DPSCs/RDGel composite for the targeted repair of TMJOA condylar cartilage defects, presenting a novel and promising avenue for cell-based therapy.

Abnormal mechanical stress induced chondrocyte senescence by YAP loss-mediated METTL3 upregulation

OBJECTIVES

Abnormal mechanical stress is the pivotal risk factor of temporomandibular joint osteoarthritis (TMJOA). This study investigated the pathogenic mechanism by which abnormal mechanical stress induced chondrocyte senescence.

MATERIALS AND METHODS

Cellular senescence was investigated in the rodent model of unilateral anterior crossbite and in the chondrocytes subjected to mechanical overloading in vitro. The effects of Yes-associated protein (YAP) in chondrocyte senescence and its correlation with methyltransferase-like 3 (METTL3) and N6 -methyladenosine (m6 A) modification were evaluated. The role of m6 A modification in chondrocyte senescence was determined. The therapeutic effects of m6 A inhibition in TMJOA were investigated.

RESULTS

Senescent chondrocytes were accumulated in the mechanically induced TMJOA lesions in rats and mechanical overloading could trigger chondrocyte senescence in vitro. This mechanical stress-induced cellular senescence was revealed to be mediated by YAP deficiency that promoted METTL3-dependent m6 A modification. Moreover, inhibition of m6 A modification rescued chondrocyte senescence in vitro and in vivo, and suppressed TMJOA progression in rats.

CONCLUSIONS

This study uncovered the underlying mechanism of mechanically induced senescence in TMJOA from the perspective of epitranscriptomics and revealed the therapeutic potential of m6 A inhibition in TMJOA.

IL-37 counteracts inflammatory injury in the temporomandibular joint via the intracellular pathway

Background: The temporomandibular joint is often afflicted by osteoarthritis (TMJOA), causing pain and dysfunction, which is particularly prevalent in the elderly population. IL-37 is effective in avoiding excessive inflammatory damage to the organism. This article investigates the role and mechanism of intracellular IL-37 in TMJOA. Methods: Enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction, Western blotting, Senescence-associated β-galactosidase staining, immunofluorescence, and lentivirus were performed to elucidate the underlying mechanism. Results: The results confirmed that IL-37 in synovial cells decreased with aging. Inflammatory stimulus elevated intracellular IL-37 in synoviocytes, while lentiviral knockdown of IL-37 resulted in more inflammatory factor production. Dynamic changes of IL-37 were observed in the nucleus and supernatant. In addition, Caspease-1 inhibitor hindered intracellular IL-37 maturation, and Smad3 inhibitor caused the loss of nuclear translocation of mature IL-37. Transfection of synovial cells with IL-37-expressing lentivirus resulted in relief not only of synovitis but also of the cartilage damage and inflammation caused by synovitis. Conclusion: This study provides new insights into the intracellular anti-inflammatory mechanism of IL-37. It also confirms that IL-37 decreases with cellular senescence and that increasing intracellular IL-37 can effectively treat synovitis and synovitis-induced inflammatory damage to cartilage.