Experimental functional shift-induced osteoarthritis-like changes at the TMJ and altered integrin expression in a rat model

A unilateral increase in the occlusal vertical dimension of growing rats results in mandibular deviation

OBJECTIVE

The effects of unilateral increased occlusal vertical dimension (iOVD) on bilateral craniofacial, mandibular and alveolar development in growing rats were investigated via cone-beam computed tomography (CBCT). The role of Wnt/β-catenin signalling in this process was examined.

MATERIALS AND METHODS

Forty-eight female Sprague-Dawley rats were randomly allocated into unilateral iOVD and sham groups. At 2, 4 and 8 weeks, the rats were scanned via CBCT to analyse cranial, maxillary, mandibular and dental morphology. Changes in temporomandibular joint (TMJ) cartilage histology and Wnt/β-catenin signalling were assessed by histochemical and immunohistochemical staining and qRT-PCR.

RESULTS

Dorsal cephalograms revealed that the mandible in the iOVD group tilted approximately 4° to the right. Unilateral iOVD had little effect on cranial and maxillary growth but inhibited mandibular growth (mandibular length and ramal height), especially on the deviated side (DS). Moreover, unilateral iOVD increased the length of the lower incisors and decreased the height of the molars on the DS. Unilateral iOVD induced bilateral osteoarthritis-like changes in the bilateral TMJ condylar cartilage and activated Wnt/β-catenin signalling in the condylar cartilage, especially on the contralateral side (CLS).

CONCLUSION

Occlusion with unilateral iOVD induced mandibular deviation, significantly inhibited mandibular growth and produced compensatory changes in the alveolar bone. In the iOVD group, the mandibular body length and ramal height were greater on the CLS than on the DS. Moreover, the greater β-catenin protein expression in the TMJ condylar cartilage on the CLS than on the DS may account for the difference in asymmetrical mandibular development.

The dynamic progression of temporomandibular joint osteoarthritis-like lesions elicited by mandibular shift in a rat model

BACKGROUND

Temporomandibular joint osteoarthritis (TMJ-OA) presents significant challenges due to its complex etiology, often insidious onset, high incidence, and progressive structural deterioration. While research has explored genetic and molecular factors, treatment outcomes remain suboptimal, emphasizing the need for a deeper understanding of disease progression.

OBJECTIVE

This study employs a specific mandibular shift rat model to explore the dynamic progression of TMJ-OA-like lesions and evaluate the potential for self-repair at different stages, aiming to inform early diagnosis and preventative strategies.

METHODS

Seventy-two female Sprague-Dawley rats were randomized into three groups: a control group (n=24; average weight: 157.23±1.63 g) receiving sham surgery. an experimental group (n=24; average weight: 157.78±1.88 g) subjected to mandibular shift induction, and a removal group (n=24; average weight: 158.11±2.20 g) experiencing mandibular shift for one, two, or four weeks followed by a one-month recovery period (designated as 1w Removal, 2w Removal and 4w Removal, respectively). Histomorphological and molecular analyses were conducted at designated time points.

RESULTS

Rats in the 1-week removal group exhibited substantial recovery in condylar morphology, cartilage thickness, extracellular matrix composition, and expression of OA-related genes. Conversely, the 4-week removal group mirrored the experimental group, indicating limited self-repair capacity at later stages. The 2-week removal group presented with variable outcomes, with some animals showing signs of recovery and others resembling the experimental group, indicating a potential transitional phase in the disease process.

CONCLUSION

Recovery from early-stage TMJ-OA involves eliminating provoking factors such as occlusal interference or reducing joint loading. However, advanced stages exhibit diminished self-repair capabilities, necessitating additional therapeutic interventions. These findings emphasize the importance of early diagnosis and intervention in TMJ-OA management.

Critical signaling molecules in the temporomandibular joint osteoarthritis under different magnitudes of mechanical stimulation

The mechanical stress environment in the temporomandibular joint (TMJ) is constantly changing due to daily mandibular movements. Therefore, TMJ tissues, such as condylar cartilage, the synovial membrane and discs, are influenced by different magnitudes of mechanical stimulation. Moderate mechanical stimulation is beneficial for maintaining homeostasis, whereas abnormal mechanical stimulation leads to degeneration and ultimately contributes to the development of temporomandibular joint osteoarthritis (TMJOA), which involves changes in critical signaling molecules. Under abnormal mechanical stimulation, compensatory molecules may prevent degenerative changes while decompensatory molecules aggravate. In this review, we summarize the critical signaling molecules that are stimulated by moderate or abnormal mechanical loading in TMJ tissues, mainly in condylar cartilage. Furthermore, we classify abnormal mechanical stimulation-induced molecules into compensatory or decompensatory molecules. Our aim is to understand the pathophysiological mechanism of TMJ dysfunction more deeply in the ever-changing mechanical environment, and then provide new ideas for discovering effective diagnostic and therapeutic targets in TMJOA.

Identification of key miRNAs in unilateral mastication-induced disruption of cartilage homeostasis

OBJECTIVE

The present study identified potentially pivotal miRNAs contributing to chondrogenic differentiation in temporomandibular joint suffering abnormal stress.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly divided into control and experimental unilateral mastication (EUM) group. Bone micro-structure parameters was detected by micro-CT, and FGF-1 and MMP-1 expression was examined by immunohistochemistry. Differentially expressed miRNAs of bilateral condyle cartilage were screened via miRNA microarray at 4- and 8-week EUM, then further verified using quantitative reverse-transcription PCR. Over-expression of five differentially expressed miRNAs in chondrocytes was triggered by transfecting miRNA mimics. The expression of MMP-13, Col-II, OPN, and Runx2 was verified by western blotting.

RESULTS

Expressions of FGF-1 and MMP-1 in right condyles gradually increased from 2 to 6 weeks after EUM. A total of 20 differentially expressed miRNAs were regulated by EUM, which related to cell proliferation, invasion, and osteoblast differentiation pathways. The over-expression of miR-148a-3p and miR-1-3p led to down-regulation of Col-II, while MMP-13 and Runx2 were up-regulated by induction of hypotrophic differentiation or IL-1β stimulation. These findings suggested that miR-148a-3p and miR-1-3p promote chondrogenic differentiation.

CONCLUSIONS

Several pivotal miRNAs were found to be related to chondrogenic differentiation, which provides novel insight into pathogenic mechanisms of cartilage homeostasis.

Equine Models of Temporomandibular Joint Osteoarthritis: A Review of Feasibility, Biomarkers, and Molecular Signaling

Osteoarthritis (OA) of the temporomandibular joint (TMJ) occurs spontaneously in humans and various animal species, including horses. In humans, obtaining tissue samples is challenging and clinical symptoms appear late in the disease progression. Therefore, genetically modified, induced, and naturally occurring animal models play a crucial role in understanding the pathogenesis and evaluating potential therapeutic interventions for TMJ OA. Among the naturally occurring models, the equine TMJ OA model is characterized by slow, age-related progression, a wide range of clinical examinations, and imaging modalities that can be performed on horses, as well as easy tissue and synovial fluid collection. The morphological and functional similarities of TMJ structures in both species make the equine model of TMJ OA an excellent opportunity to track disease progression and response to treatment. However, much work remains to be carried out to determine the utility of human TMJ OA biomarkers in horses. Among the main TMJ OA biomarkers, IL-1, IL-6, TGF-β, TNF-α, and PGE2 have been recently investigated in the equine model. However, the majority of biomarkers for cartilage degradation, chondrocyte hypertrophy, angiogenesis, and TMJ overload-as well as any of the main signaling pathways-have not been studied so far. Therefore, it would be advisable to focus further research on equine specimens, considering both mediators and signaling.

Single-cell RNA sequencing reveals neurovascular-osteochondral network crosstalk during temporomandibular joint osteoarthritis: Pilot study in a human condylar cartilage

Purpose

Temporomandibular joint osteoarthritis (TMJ-OA) is one of the most complex temporomandibular disorders, causing pain and dysfunction. The main pathological feature of TMJ-OA is neurovascular invasion from the subchondral bone to the condylar cartilage. This study aimed to discover the cells and genes that play an important role in the neurovascular-osteochondral network crosstalk in human TMJ-OA.

Materials and methods

Condylar cartilages from patient with TMJ-OA were divided into OA group, and others from patients with benign condylar hyperplasia (CH) were used as control for further single-cell RNA-sequencing (scRNA-seq). Hematoxylin and eosin staining were performed. The cells and genes in the condylar cartilage were identified and analyzed by scRNA-seq.

Results

Histological analysis revealed blood vessel invasion and ossification in the TMJ-OA condylar cartilage. The scRNA-seq identified immune cells, endothelial cells, and chondrocytes in the TMJ-OA condylar cartilage. Macrophages, especially M1-like macrophages, contributed to the inflammation, angiogenesis, and innervation. CD31+ endothelial cells contributed to the bone mineralization. The TMJ-OA cartilage chondrocytes highly expressed genes related to inflammation, angiogenesis, innervation, and ossification. The hub genes contributing to these processes in the TMJ-OA chondrocytes included CTGF, FBN1, FN1, EGFR, and ITGA5.

Conclusion

Our study marks the first time scRNA-seq was used to identify the cells and genes in a human TMJ-OA condylar cartilage, and neurovascular-osteochondral network crosstalk during the human TMJ-OA process was demonstrated. Targeting the crosstalk of these processes may be a potential comprehensive and effective therapeutic strategy for human TMJ-OA.

Association of integrin-β2 polymorphism and expression with the risk of rheumatoid arthritis and osteoarthritis in Egyptian patients

BACKGROUND

The genetic architecture of rheumatoid arthritis (RA) and osteoarthritis (OA) are still unclear. Although RA and OA have quite different causes, they share synovial inflammation, risk factors, and some disease-associated genes, including the integrin subunit β2 (ITGB2)/CD18 gene involved in extracellular matrix interactions and immune cell signaling. However, the functional role of ITGB2 genetic variants, its circulating expression pattern, and their clinical usefulness in RA and OA remain unexplored. Our study appraised the association of ITGB2 rs2070946 single nucleotide polymorphism with the vulnerability to RA and OA and its influence on ITGB2 mRNA expression, along with the potential of serum ITGB2 expression in RA and OA diagnosis.

METHODS

This study included 70 RA patients, 70 primary OA patients, and 60 healthy volunteers. Genotyping and gene expression analysis were performed using qPCR. Bioinformatics analysis was employed to construct the protein-protein interaction (PPI) network of ITGB2.

RESULTS

Serum ITGB2 mRNA expression was upregulated in both RA and OA compared to healthy controls. ITGB2 rs2070946 was associated with escalating risk of both diseases. RA patients harboring the rs2070946 CC or TC + CC genotypes had higher serum ITGB2 expression than the TT genotype carriers. Likewise, OA patients having the minor homozygote CC genotype had higher serum ITGB2 expression than those carrying the TT, TC or TT + TC genotypes. Serum ITGB2 expression showed profound diagnostic potential for RA and OA in receiver-operating characteristic analysis. In RA, serum ITGB2 expression positively correlated with rheumatoid factor and disease activity score 28 (DAS28). The ITGB2-PPI network enriched in cell-cell adhesion, ICAM-3 receptor activity, T-cell activation, leukocyte adhesion, complement binding, and NF-κB, tumor necrosis factor, and interleukin signaling pathways.

CONCLUSION

These findings embrace the impact of ITGB2 rs2070946 as a novel genetic biomarker of both RA and OA, which could alter the ITGB2 expression. Serum ITGB2 expression could aid in timely diagnosis of RA and 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.