Nociceptive behavioural assessments in mouse models of temporomandibular joint disorders

Multi-class segmentation of temporomandibular joint using ensemble deep learning

Temporomandibular joint disorders are prevalent causes of orofacial discomfort. Diagnosis predominantly relies on assessing the configuration and positions of temporomandibular joint components in magnetic resonance images. The complex anatomy of the temporomandibular joint, coupled with the variability in magnetic resonance image quality, often hinders an accurate diagnosis. To surmount this challenge, we developed deep learning models tailored to the automatic segmentation of temporomandibular joint components, including the temporal bone, disc, and condyle. These models underwent rigorous training and validation utilizing a dataset of 3693 magnetic resonance images from 542 patients. Upon evaluation, our ensemble model, which combines five individual models, yielded average Dice similarity coefficients of 0.867, 0.733, 0.904, and 0.952 for the temporal bone, disc, condyle, and background class during internal testing. In the external validation, the average Dice similarity coefficients values for the temporal bone, disc, condyle, and background were 0.720, 0.604, 0.800, and 0.869, respectively. When applied in a clinical setting, these artificial intelligence-augmented tools enhanced the diagnostic accuracy of physicians, especially when discerning between temporomandibular joint anterior disc displacement and osteoarthritis. In essence, automated temporomandibular joint segmentation by our deep learning approach, stands as a promising aid in refining temporomandibular joint disorders diagnosis and treatment strategies.

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.

Liproxstatin-1 alleviates cartilage degradation by inhibiting chondrocyte ferroptosis in the temporomandibular joint

BGROUND INFORMATION

Ferroptosis contributes to temporomandibular joint osteoarthritis (TMJOA) lesion development and is still poorly understood.

RESULTS

In this study, we used different TMJOA animal models to examine whether ferroptosis was related to disease onset in TMJOA induced by monosodium iodoacetate (MIA), IL-1β, occlusion disorder (OD), and unilateral anterior crossbite (UAC). Immunohistochemical staining and Western blot analysis were used to detect ferroptosis- and cartilage degradation-related protein expression. Our results revealed reduced levels of the ferroptosis-related protein GPX4 in the cartilage layer, but the levels of ACSL4 and P53 were increased in the condyle. Injection of the ferroptosis inhibitor liproxstatin-1 (Lip-1) effectively decreased ACSL4, P53 and TRF expression. In vitro, IL-1β reduced cartilage extracellular matrix expression in mandibular condylar chondrocytes (MCCs). Lip-1 maintained the morphology and function of mitochondria and ameliorated the exacerbation of lipid peroxidation and reactive oxygen species (ROS) production induced by IL-1β.

CONCLUSION

These results suggest that chondrocyte ferroptosis plays an important role in the development and progression of TMJOA.

SIGNIFICANCE

Inhibiting condylar chondrocyte ferroptosis could be a promising therapeutic strategy for TMJOA.

Assessment of orofacial nociceptive behaviors of mice with the sheltering tube method: Oxaliplatin-induced mechanical and cold allodynia in orofacial regions

Preclinical studies on pathological pain rely on the von Frey test to examine changes in mechanical thresholds and the acetone spray test to determine alterations in cold sensitivity in rodents. These tests are typically conducted on rodent hindpaws, where animals with pathological pain show reliable nocifensive responses to von Frey filaments and acetone drops applied to the hindpaws. Pathological pain in orofacial regions is also an important clinical problem and has been investigated with rodents. However, performing the von Frey and acetone spray tests in the orofacial region has been challenging, largely due to the high mobility of the head of testing animals. To solve this problem, we implemented a sheltering tube method to assess orofacial nociception in mice. In experiments, mice were sheltered in elevated tubes, where they were well accommodated because the tubes provided safe shelters for mice. Examiners could reliably apply mechanical stimuli with von Frey filament, cold stimuli with acetone spray, and light stimuli with a laser beam to the orofacial regions. We validated this method in Nav1.8-ChR2 mice treated with oxaliplatin that induced peripheral neuropathy. Using the von Frey test, orofacial response frequencies and nociceptive response scores were significantly increased in Nav1.8-ChR2 mice treated with oxaliplatin. In the acetone spray test, the duration of orofacial responses was significantly prolonged in oxaliplatin-treated mice. The response frequencies to laser light stimulation were significantly increased in Nav1.8-ChR2 mice treated with oxaliplatin. Our sheltering tube method allows us to reliably perform the von Frey, acetone spray, and optogenetic tests in orofacial regions to investigate orofacial pain.

An analysis of the relationship between dietary pattern changes and temporomandibular joint inflammation in diabetic rats

Background

The temporomandibular joint (TMJ) is the most commonly used joint in the human body. Recent studies have shown pathologic relationships between inflammation, diabetes, and musculoskeletal disorders (MSDs). Chewing disorder is a significant sign of dysfunction in the masticatory system. This study investigated dietary pattern changes in response to TMJ inflammation in diabetic rats.

Methods

This experimental study was carried out on 30 male rats. The rats were fed concentrated 20-mg dietary tablets. Complete Freund's adjuvant (CFA) was used to induce TMJ inflammation and streptozotocin (STZ) was used to induce diabetes. The animals were randomly divided into three groups (n=10), including group I (CFA+STZ), group II (healthy rats+CFA), and group III (healthy rats, no injection). Parameters such as overall food intake, food intake duration, food intake frequency, and the interval between meals were recorded in a checklist and analyzed by Mann-Whitney and Kruskal-Wallis tests (P<0.05).

Results

The results showed no significant difference between groups in overall food intake and food intake frequency on days 0 and 1, but this difference was significant from day 2 to day 7. Regarding the time and end of food intake, there was a significant difference between the three groups from day 1 to day 7, but this difference was not significant on day zero.

Conclusion

Dietary pattern changes were similar in the diabetic TMJ inflammation and TMJ inflammation groups. These changes can be used as a behavioral marker for TMJ inflammation in rats.

A Novel Burn / Synovectomy Mouse Model for Temporomandibular Joint Osteoarthritis

Temporomandibular Disorders (TMDs) is present in 33% of the U.S. population. Currently available animal models do not faithfully simulate the native disease progression of TMJ OA. The initiation of TMJ OA requires both local trauma and systemic inflammation. In this study, we present a novel mouse model which reproduces these two conditions. This is achieved by a procedure involving both synovectomy (local trauma) and a distant burn injury (systemic inflammation). Its efficacy at inducing TMJ OA was assessed with histomorphology and radiographic evaluation at 1,3, and 9 weeks after the procedure. We found that burn/synovectomy mice demonstrated significantly more degenerative changes in TMJ than uninjured control mice or synovotomy mice. The observed histology in burn/synoectomy mice mimicked native TMJ OA disease progression in a faithful manner. This animal model is invaluable in future research of the mechanism and risk factors of TMJ OA.

Assessing Orofacial Pain Behaviors in Animal Models: A Review

Orofacial pain refers to pain occurring in the head and face, which is highly prevalent and represents a challenge to clinicians, but its underlying mechanisms are not fully understood, and more studies using animal models are urgently needed. Currently, there are different assessment methods for analyzing orofacial pain behaviors in animal models. In order to minimize the number of animals used and maximize animal welfare, selecting appropriate assessment methods can avoid repeated testing and improve the reliability and accuracy of research data. Here, we summarize different methods for assessing spontaneous pain, evoked pain, and relevant accompanying dysfunction, and discuss their advantages and disadvantages. While the behaviors of orofacial pain in rodents are not exactly equivalent to the symptoms displayed in patients with orofacial pain, animal models and pain behavioral assessments have advanced our understanding of the pathogenesis of such pain.

Chemokine Regulation in Temporomandibular Joint Disease: A Comprehensive Review

Temporomandibular joint disorders (TMDs) are conditions that affect the muscles of mastication and joints that connect the mandible to the base of the skull. Although TMJ disorders are associated with symptoms, the causes are not well proven. Chemokines play an important role in the pathogenesis of TMJ disease by promoting chemotaxis inflammatory cells to destroy the joint synovium, cartilage, subchondral bone, and other structures. Therefore, enhancing our understanding of chemokines is critical for developing appropriate treatment of TMJ. In this review, we discuss chemokines including MCP-1, MIP-1α, MIP-3a, RANTES, IL-8, SDF-1, and fractalkine that are known to be involved in TMJ diseases. In addition, we present novel findings that CCL2 is involved in β-catenin-mediated TMJ osteoarthritis (OA) and potential molecular targets for the development of effective therapies. The effects of common inflammatory factors, IL-1β and TNF-α, on chemotaxis are also described. In conclusion, this review aims to provide a theoretical basis for future chemokine-targeted therapies for TMJ OA.

The neurobiology of pain and facial movements in rodents: Clinical applications and current research

One of the most controversial aspects of the use of animals in science is the production of pain. Pain is a central ethical concern. The activation of neural pathways involved in the pain response has physiological, endocrine, and behavioral consequences, that can affect both the health and welfare of the animals, as well as the validity of research. The strategy to prevent these consequences requires understanding of the nociception process, pain itself, and how assessment can be performed using validated, non-invasive methods. The study of facial expressions related to pain has undergone considerable study with the finding that certain movements of the facial muscles (called facial action units) are associated with the presence and intensity of pain. This review, focused on rodents, discusses the neurobiology of facial expressions, clinical applications, and current research designed to better understand pain and the nociceptive pathway as a strategy for implementing refinement in biomedical research.

Current understanding of osteoarthritis pathogenesis and relevant new approaches

Osteoarthritis (OA) is the most common degenerative joint disease that causes painful swelling and permanent damage to the joints in the body. The molecular mechanisms of OA are currently unknown. OA is a heterogeneous disease that affects the entire joint, and multiple tissues are altered during OA development. To better understand the pathological mechanisms of OA, new approaches, methods, and techniques need to be used to understand OA pathogenesis. In this review, we first focus on the epigenetic regulation of OA, with a particular focus on DNA methylation, histone modification, and microRNA regulation, followed by a summary of several key mediators in OA-associated pain. We then introduce several innovative techniques that have been and will continue to be used in the fields of OA and OA-associated pain, such as CRISPR, scRNA sequencing, and lineage tracing. Next, we discuss the timely updates concerning cell death regulation in OA pathology, including pyroptosis, ferroptosis, and autophagy, as well as their individual roles in OA and potential molecular targets in treating OA. Finally, our review highlights new directions on the role of the synovial lymphatic system in OA. An improved understanding of OA pathogenesis will aid in the development of more specific and effective therapeutic interventions for OA.

A novel approach to establishing a temporomandibular joint fibrocartilage cell line

Background/purpose

The temporomandibular joint (TMJ) is a bi-arthrodial joint that is composed of the temporal bone glenoid fossa and the condylar head of the mandible both having fibrocartilaginous articular surfaces. Functional overloading of the TMJ is the main cause of TMJ osteoarthritis (TMJ OA) disease. The aim of this study was to establish immortalized TMJ fibrocartilage cell clones to provide enough cells to adequately investigate the molecular mechanisms studies of TMJ OA.

Materials and methods

We have isolated temporomandibular condyle chondrocytes from adult Sprague Dawley rat. The cells were cultured and immortalized by treating with Y-27632, a well-characterized inhibitor of Rho-Associated Kinase (ROCK). Clones were characterized on the basis of cell morphology and analyses of marker gene expression through 45 passages.

Results

Cells from the condylar fibrocartilage of the TMJ were successfully immortalized by ROCK inhibitor, retaining a consistent cuboidal cell morphology and the expression of several cell markers of polymorphic cell fate. In addition, they retained phenotype features similar to the primary parental TMJ fibrocartilage cells when the cells were challenged with different cytokines and growth factors.

Conclusion

These studies establish a novel immortalized cell line through ROCK inhibitor Y-27632, that retains the polymorphic phenotype of primary cell lines from TMJ fibrocartilage chondrocyte cell through a high number of passages, serving as a valuable preclinical resource for mechanistic in vitro assessment of TMJ health, disease, and regeneration.

Antisense Oligonucleotide-Based Therapy on miR-181a-5p Alleviates Cartilage Degradation of Temporomandibular Joint Osteoarthritis via Promoting SIRT1

Temporomandibular joint osteoarthritis (TMJOA) condylar cartilage degeneration and abnormal subchondral bone pathological remodeling induce pain and joint dysfunction, and cartilage degeneration is considered irreversible. Very few therapeutic approaches are administrated in practice. Nucleotides have demonstrated considerable potential as a next-generation medication, and they have been applied in several models of osteoarthritis. There is a need to establish an effective protocol for TMJOA gene therapy. In the current study unilateral anterior crossbite (UAC) surgery was used to simulate mechanical stress-induced TMJOA in mice. Degeneration of condylar cartilage and destruction of subchondral bone were observed in damaged joints, and miR-181a-5p was elevated in chondrocytes. Intra-articular injection of miR-181a-5p antisense oligonucleotide (ASO) could reduce the cartilage damage and alleviate UAC-induced TMJOA progression, but it did not restore injured subchondral bone. Mechanically, miR-181a-5p evidently targeted the 3’ untranslated region of Sirt1 directly, resulting in inhibition of silent information regulator 1 expression and promoting apoptosis by elevating p53-dependent signaling, indicating that miR181a-5p ASO promoted chondrocyte survival. The present study suggests that ASO-based gene therapy may be an effective TMJOA treatment.

Preclinical models of deep craniofacial nociception and temporomandibular disorder pain

Chronic pain in temporomandibular disorder (TMD) is a common health problem. Cumulating evidence indicates that the etiology of TMD pain is complex with multifactorial experience that could hamper the developments of treatments. Preclinical research is a resource to understand the mechanism for TMD pain, whereas limitations are present as a disease-specific model. It is difficult to incorporate multiple risk factors associated with the etiology that could increase pain responses into a single animal. This article introduces several rodent models which are often employed in the preclinical studies and discusses their validities for TMD pain after the elucidations of the neural mechanisms based on the clinical reports. First, rodent models were classified into two groups with or without inflammation in the deep craniofacial tissues. Next, the characteristics of each model and the procedures to identify deep craniofacial pain were discussed. Emphasis was directed on the findings of the effects of chronic psychological stress, a major risk factor for chronic pain, on the deep craniofacial nociception. Preclinical models have provided clinically relevant information, which could contribute to better understand the basis for TMD pain, while efforts are still required to bridge the gap between animal and human studies.