Mechanism and potential contributing factors to temporomandibular joint osteoarthritis

The Role of Sex Hormones in Cartilaginous Tissues: A Scoping Review

Background

The use of sex hormones in the clinic for the management of musculoskeletal conditions is increasingly common. Despite this, the role of sex hormones in various joint tissues such as the intervertebral disc (IVD), temporomandibular joint (TMJ), and articular cartilage remains poorly understood. Here, we employ a database search strategy to critically examine the available literature in this field through a scoping review.

Methods

Using a 4-step protocol, primary research articles pertaining to sex hormones and the IVD, TMJ, or articular cartilage were identified and reviewed by two independent reviewers. ~3900 articles were identified in our initial search, and after review, ~140 were identified to be relevant to our tissues of interest and the effects of sex hormones.

Results

Within all joint tissues investigated here, there were limited investigations on the effects of testosterone. Studies reported here for these tissues indicate that sex hormones are likely beneficial in the context of age-associated joint diseases, but there are important limitations to how this translates to the clinic given that various animal models can display distinct responses to sex hormone exposure. Direct comparisons of sex hormone therapies are limited between biological sexes, but evidence indicates that the molecular responses are likely similar. Current evidence indicates that sex hormone exposure likely has anti-inflammatory effects within joint tissues at the level of gene and protein expression, but the mechanism is unknown.

Conclusion

Sex hormones such as testosterone and estrogen play an important role in inflammatory signaling within joint tissues, which could lead to novel interventions within the clinic for joint degeneration. However, understanding the biological mechanisms of hormones in these distinct tissues, between sexes, and with age is imperative for their proper implementation.

Single monoiodoacetic acid injection reveals toll-like receptor, oestrogen, oxidative stress, and altered energy metabolism as key drivers of temporomandibular joint osteoarthritis in female rats

OBJECTIVES

This study aimed to establish a reproducible and minimally invasive rat model of temporomandibular joint osteoarthritis (TMJ-OA) using intra-articular monoiodoacetic acid (MIA) injection, and to investigate the pathological mechanisms underlying TMJ-OA development, aimed at providing insights for potential clinical treatments.

DESIGN

We compared the effects of single versus multiple MIA injections on body weight, pain behaviour, and condylar pathology in female Sprague-Dawley rats. We longitudinally assessed the progression of TMJ-OA over 5 weeks by evaluating condylar pathology and immunohistochemical staining. We investigated the potential mechanism of MIA-induced TMJ-OA through transcriptome sequencing and polymerase chain reaction validation.

RESULTS

A single MIA injection (0.5 mg) into the joint space effectively induced TMJ-OA in rats and sustained inflammatory reactions and pain without significantly affecting weight. MIA continuously promoted the development of TMJ-OA through the activation of the toll-like receptor pathway, oestrogen metabolism promotion, oxidative stress response enhancement, and energy metabolism alteration in condylar chondrocytes.

CONCLUSION

We have presented a simple and minimally invasive method for modelling TMJ-OA in rats, which can be utilised in animal trials focusing on TMJ-OA treatment strategies. The study also reveals toll-like receptor, oestrogen, oxidative stress, and altered energy metabolism as key drivers of TMJ-OA in female rats.

Fostamatinib alleviates temporomandibular joint osteoarthritis by maintaining cartilage homeostasis through MAPK/NF-κB and AKT/mTOR pathways

Temporomandibular joint osteoarthritis (TMJ OA) is a common degenerative disease characterized by cartilage degeneration. However, the therapeutic strategies aimed to maintain cartilage homeostasis remain unclear. Fostamatinib (Fos) is a potential clinical drug for rheumatoid arthritis (RA) and predicted as target drug for many inflammatory diseases. In this study we investigated the therapeutic effects of Fos for TMJ OA and underlying mechanisms. Interleukin-1β (IL-1β) was used to construct a condylar chondrocyte injury model in vitro and rat TMJ OA models were induced by unilateral anterior crossbite (UAC) in vivo. Subsequently, a series of experiments were performed to assess the therapeutic effects and potential mechanisms of Fos in TMJ OA. Herein, we verified that Fos improved IL-1β-induced decrease in chondrocyte viability and proliferation, as well as inhibited cell apoptosis. Additionally, Fos could alleviate IL-1β-induced inflammation, ECM degradation, and chondrocyte phenotype change through blocking MAPK/NF-κB pathways, as well as promote chondrocyte autophagy by regulating AKT/mTOR pathways. The therapeutic effects of Fos on TMJ OA were further validated through rat UAC model in vivo. Overall, Fos could maintaining cartilage homeostasis through regulating chondrocyte inflammation, ECM degradation, and abnormal cell biological behaviors (apoptosis and autophagy), which made it a promising small molecule drug for TMJ OA early intervention.

How malocclusion interferes with tissue inhibitor of metalloproteinase-1 expression and morphology of the articular cartilage of the mandible in female rats

OBJECTIVE

The purpose of this study was to investigate morphological alterations and tissue inhibitor of metalloproteinase-1 expression in the articular cartilage of the mandible under conditions of experimentally induced malocclusion.

DESIGN

Twenty-four 8-week-old female Wistar rats were used and divided into control and experimental groups with two different treatment periods (2 and 4 weeks). Sagittal malocclusions were orthodontically created, causing mesial movement of the first molars and distalization of the third molars unilaterally and on opposite sides of the arches. Sagittal sections of the articular cartilage of the mandible were subjected to hematoxylin and eosin and immunohistochemistry for tissue inhibitor of metalloproteinase-1. Chi-square and MannWhitney U tests were applied.

RESULTS

Animals treated for 2 and 4 weeks showed morphological alterations in articular cartilage of the mandible. The main findings were thickening of the posterior third, layer derangement, osteoclast activity and osteophyte formation. Among the cellular aspects, the presence of chondrocytes with condensed nuclei and cytoplasm reduction were observed. The enzyme in control animals was observed only in the mature layer. Treated animals showed immunopositive cells in the proliferative and mature layers, and in the 2-week treated group, the posterior third of the cartilage had more immunolabeled cells than control (P=0.0291).

CONCLUSIONS

The occlusal disorder caused morphological changes in articular cartilage of the mandible, probably due to the attempt to adapt to the new condition. Tissue inhibitor of metalloproteinase-1 expression may play a role as an initial modulator in the biological events observed in articular cartilage of the mandible.

Zymosan-Treated SKG Mice: Assessing Effects of Systemic Inflammation on the Temporomandibular Joint

OBJECTIVES

The effects of systemic inflammation on the temporomandibular joint (TMJ) are poorly understood. This study aimed to establish a mouse model to study the effects of systemic inflammation on the TMJ.

MATERIALS AND METHODS

SKG mice, a BALB/c strain with spontaneous onset of rheumatoid arthritis-like symptoms due to a spontaneous point mutation (W163C) in the gene encoding the SH2 domain of ZAP-70, were treated with zymosan (β-1,3-glucan). Synovitis, bone erosion, and cartilage damage in the TMJ were evaluated using established scores for animal models of inflammatory arthritis. Myeloperoxidase-positive areas and numbers of tartrate-resistant acid phosphatase (TRAP)-positive cells were compared between naive and zymosan-treated SKG mice. Correlations between TMJ inflammation scores and clinical scores for extremities were also assessed.

RESULTS

There were significant differences in TMJ inflammation scores, including synovitis, bone erosion, and cartilage damage, between naive and high-dose zymosan-treated mice. There were significant differences in myeloperoxidase-positive areas and numbers of TRAP-positive cells between naive and zymosan-treated mice. There were significant correlations between TMJ inflammation scores and clinical scores for extremities.

CONCLUSIONS

Systemic administration of zymosan efficiently induces TMJ inflammation in SKG mice. Zymosan-treated SKG mice offer a useful tool to investigate the effects of systemic inflammation on the TMJ.

17β-estradiol promotes the progression of temporomandibular joint osteoarthritis by regulating the FTO/IGF2BP1/m6A-NLRC5 axis

BACKGROUND

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative cartilage disease. 17β-estradiol (E2) aggravates the pathological process of TMJOA; however, the mechanisms of its action have not been elucidated. Thus, we investigate the influence of E2 on the cellular biological behaviors of synoviocytes and the molecular mechanisms.

METHODS

Primary fibroblast-like synoviocytes (FLSs) isolated from rats were treated with TNF-α to establish cell model, and phenotypes were evaluated using cell counting kit-8, EdU, Tanswell, enzyme-linked immunosorbent assay, and quantitative real-time PCR (qPCR). The underlying mechanism of E2, FTO-mediated NLRC5 m6A methylation, was assessed using microarray, methylated RNA immunoprecipitation, qPCR, and western blot. Moreover, TMJOA-like rat model was established by intra-articular injection of monosodium iodoacetate (MIA), and bone morphology and pathology were assessed using micro-CT and H&E staining.

RESULTS

The results illustrated that E2 facilitated the proliferation, migration, invasion, and inflammation of TNF-α-treated FLSs. FTO expression was downregulated in TMJOA and was reduced by E2 in FLSs. Knockdown of FTO promoted m6A methylation of NLRC5 and enhanced NLRC5 stability by IGF2BP1 recognition. Moreover, E2 promoted TMJ pathology and condyle remodeling, and increased bone mineral density and trabecular bone volume fraction, which was rescued by NLRC5 knockdown.

CONCLUSION

E2 promoted the progression of TMJOA.

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.

Animal Models of Temporomandibular Joint Osteoarthritis: Classification and Selection

Temporomandibular joint osteoarthritis (TMJOA) is a common degenerative joint disease that can cause severe pain and dysfunction. It has a serious impact on the quality of lives of patients. Since mechanism underlying the pathogenesis of TMJOA is not fully understood, the development of effective tools for early diagnosis and disease-modifying therapies has been hindered. Animal models play a key role in understanding the pathological process of diseases and evaluating new therapeutic interventions. Although some similarities in disease processes between animals and humans are known, no one animal model is sufficient for studying all characteristics of TMJOA, as each model has different translatability to human clinical conditions. For the past 4 decades, TMJOA animal models have been studied by numerous researchers and can be broadly divided into induced, naturally occurring, and genetically modified models. The induced models can be divided into invasive models (intra-articular injection and surgical induction) or non-invasive models (mechanical loading, high-fat diet, and sleep deprivation). Different types of animal models simulate different pathological expressions of TMJOA and have their unique characteristics. Currently, mice, rats, and rabbits are commonly used in the study of TMJOA. This review sought to provide a general description of current experimental models of TMJOA and assist researchers in selecting the most appropriate models for different kinds of research.