Injecting vascular endothelial growth factor into the temporomandibular joint induces osteoarthritis in mice

Primed IFN-γ-Umbilical Cord Stem Cells Ameliorate Temporomandibular Joint Osteoarthritis

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disorder affecting the temporomandibular joint (TMJ), marked by persistent inflammation and structural damage to the joint. Only symptomatic treatment is available for managing TMJOA. Human umbilical cord mesenchymal stem cells (hUC-MSCs) show potential for treating TMJOA via their immune-modulating actions in the disease area. In addition, stimulation of inflammatory cytokines such as interferon-gamma in hUC-MSCs improves the therapeutic activity of naïve stem cells. Emerging evidence indicates that macrophages play significant roles in regulating joint inflammation through diverse secreted mediators in the pathogenesis of TMJOA. This study was conducted to evaluate the effects of inflammatory cytokine-stimulated hUC-MSCs in repairing TMJOA-induced cartilage lesions and the role of macrophages in the disease. Our in vitro data showed that stimulated hUC-MSCs induce M2 polarization of macrophages and enhance the expression of anti-inflammatory molecules. These effects were subsequently validated in vivo. In a rat model of TMJOA, stimulated hUC-MSCs ameliorated inflammation and increased M2 macrophages ratio. Our results indicate that hUC-MSCs stimulated by inflammatory cytokines modulate the activation of M2 macrophages, thereby shifting the local osteoarthritis microenvironment toward a prochondrogenic state and facilitating cartilage repair in inflammatory conditions. Stimulating hUC-MSCs with inflammatory cytokines could potentially offer an effective therapeutic approach for TMJOA, with macrophages playing a pivotal role in immune modulation.

The Effect of Low-Intensity Pulsed Ultrasound on Temporomandibular Joint Arthritis in Juvenile Rats

Juvenile idiopathic arthritis is an inflammatory disease that can affect the temporomandibular joint (TMJ) and lower jaw growth. Better treatment options are needed, so this study investigated the effect of low-intensity pulsed ultrasound (LIPUS) on TMJ arthritis. Seventy-two 3-week-old male Wistar rats were in vivo microcomputed tomography (micro-CT) scanned and divided into eight groups (n = 9). These groups were Group 1-TMJ arthritis and immediate LIPUS treatment (20 min/day, 4 weeks); Group 2-immediate LIPUS treatment and no TMJ arthritis; Group 3-TMJ arthritis and no LIPUS; Group 4-no TMJ arthritis and no LIPUS; Group 5-TMJ arthritis and LIPUS treatment with a delayed start by 4 weeks; Group 6-Delayed LIPUS and no TMJ arthritis; Group 7-TMJ arthritis and no (delayed) LIPUS; and Group 8-no TMJ arthritis and no (delayed) LIPUS. Ex vivo micro-CT scanning was completed, and samples were prepared for tissue analysis. Synovitis was observed in the TMJ arthritis (collagen-induced arthritis [CIA]) groups, but the severity appeared greater in the groups without LIPUS treatment. Fibrocartilage and hypertrophic cell layer thicknesses in the CIA group without LIPUS treatment were significantly greater (p < 0.05). Proteoglycan staining appeared greater in the LIPUS groups. Immediate LIPUS treatment increased the expression of type II collagen, type X collagen, and transforming growth factor-beta 1 (TGF-β1) immunostaining, and CIA (no LIPUS) increased MMP-13, vascular endothelial growth factor, and interleukin-1 beta (IL-1β) immunostaining. LIPUS treatment prevented growth disturbances observed in the CIA groups (no LIPUS) (p < 0.005). Our results have contributed to the understanding of the uses and limitations of the CIA juvenile rat model and have demonstrated the effects of LIPUS on the TMJ and mandibular growth. This information will help in designing future studies for investigating LIPUS and TMJ arthritis, leading to the development of new treatment options for children with juvenile arthritis in their TMJs.

Efficacy of IFN-γ-Primed Umbilical Cord-Derived Mesenchymal Stem Cells on Temporomandibular Joint Osteoarthritis

BACKGROUND

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease affecting the cartilage and subchondral bone, leading to temporomandibular joint pain and dysfunction. The complex nature of TMJOA warrants effective alternative treatments, and mesenchymal stem cells (MSCs) have shown promise in regenerative therapies. The aim of this study is twofold: firstly, to ascertain the optimal interferon-gamma (IFN-γ)-primed MSC cell line for TMJOA treatment, and secondly, to comprehensively evaluate the therapeutic efficacy of IFN-γ-primed mesenchymal stem cells derived from the human umbilical cord matrix in a rat model of TMJOA.

METHODS

We analyzed changes in the expression of several key genes associated with OA protection in MSC-secreted compounds. Following this, we performed co-culture experiments using a transwell system to predict gene expression changes in primed MSCs in the TMJOA environment. Subsequently, we investigated the efficacy of the selected IFN-γ-primed human umbilical cord matrix-derived MSCs (hUCM-MSCs) for TMJOA treatment in a rat model.

RESULTS

IFN-γ-primed MSCs exhibited enhanced expression of IDO, TSG-6, and FGF-2. Moreover, co-culturing with rat OA chondrocytes induced a decrease in pro-inflammatory and extracellular matrix degradation factors. In the rat TMJOA model, IFN-γ-primed MSCs with elevated IDO1, TSG-6, and FGF2 expression exhibited robust anti-inflammatory and therapeutic capacities, promoting the improvement of the inflammatory environment and cartilage regeneration.

CONCLUSION

These findings underscore the importance of prioritizing the mitigation of the inflammatory milieu in TMJOA treatment and highlight IFN-γ-primed MSCs secreting these three factors as a promising, comprehensive therapeutic strategy.

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.

Endocan Knockdown Down-Regulates the Expression of Angiogenesis-Associated Genes in Il-1ß Activated Chondrocytes

Endocan is a small soluble proteoglycan (PG) known to be involved in inflammation and angiogenesis. Increased endocan expression was found in the synovia of arthritic patients and chondrocytes stimulated with IL-1ß. Considering these findings, we aimed to investigate the effects of endocan knockdown on the modulation of pro-angiogenic molecules expression in a model of IL-1ß-induced inflammation in human articular chondrocytes. Endocan, VEGF-A, MMP-9, MMP-13, and VEGFR-2 expression was measured in both normal and endocan knockdown chondrocytes stimulated with IL-1ß. VEGFR-2 and NF-kB activation were also measured. Results have shown that endocan, VEGF-A, VEGFR-2, MMP-9, and MMP-13 were significantly up-regulated during IL-1ß-induced inflammation; interestingly, the expression of such pro-angiogenic molecules and NF-kB activation were significantly reduced by endocan knockdown. These data support the hypothesis that endocan released by activated chondrocytes may be involved in the mechanisms that stimulate cell migration and invasion, as well as angiogenesis, in the pannus of arthritic joints.

MMP-13, VEGF, and Disease Activity in a Cohort of Rheumatoid Arthritis Patients

Identifying certain serum biomarkers associated with the degree of rheumatoid arthritis (RA) activity can provide us with a more accurate view of the evolution, prognosis, and future quality of life for these patients. Our aim was to analyze the presence and clinical use of matrix metalloproteinase-13 (MMP-13), along with vascular endothelial growth factor (VEGF) and well-known cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6) for patients with RA. We also wanted to identify the possible correlations between MMP-13 and these serological markers, as well as their relationship with disease activity indices, quality of life, and ultrasonographic evaluation. For this purpose, we analyzed serum samples of 34 RA patients and 12 controls. In order to assess serum concentrations for MMP-13, VEGF, TNF-α, and IL-6, we used the enzyme-linked immunosorbent assay (ELISA) technique. Our results concluded that higher levels of MMP-13, VEGF, TNF-α, and IL-6 were present in the serum of RA patients compared to controls, with statistical significance. We furthermore identified moderately positive correlations between VEGF, MMP-13, and disease activity indices, as well as with the ultrasound findings. We also observed that VEGF had the best accuracy (97.80%), for differentiating patients with moderate disease activity. According to the data obtained in our study, that although MMP-13, TNF-α and C-reactive protein (CRP) have the same sensitivity (55.56%), MMP-13 has a better specificity (86.67%) in the diagnosis of patients with DAS28_(4v) CRP values corresponding to moderate disease activity. Thus, MMP-13 can be used as a biomarker that can differentiate patients with moderate or low disease activity. VEGF and MMP-13 can be used as additional parameters, along with TNF-α and IL-6, that can provide the clinician a better picture of the inflammatory process, disease activity, and structural damage in patients with RA. Our data can certainly constitute a start point for future research and extended studies with multicenter involvement, to support the selection of individualized and accurate therapeutic management strategies for our patients.

Beyond mechanical loading: The metabolic contribution of obesity in osteoarthritis unveils novel therapeutic targets

Osteoarthritis (OA) is a prevalent progressive disease that frequently coexists with obesity. For several decades, OA was thought to be the result of ageing and mechanical stress on cartilage. Researchers' perspective has been greatly transformed when cumulative findings emphasized the role of adipose tissue in the diseases. Nowadays, the metabolic effect of obesity on cartilage tissue has become an integral part of obesity research; hoping to discover a disease-modifying drug for OA. Recently, several adipokines have been reported to be associated with OA. Particularly, metrnl (meteorin-like) and retinol-binding protein 4 (RBP4) have been recognized as emerging adipokines that can mediate OA pathogenesis. Accordingly, in this review, we will summarize the latest findings concerned with the metabolic contribution of obesity in OA pathogenesis, with particular emphasis on dyslipidemia, insulin resistance and adipokines. Additionally, we will discuss the most recent adipokines that have been reported to play a role in this context. Careful consideration of these molecular mechanisms interrelated with obesity and OA will undoubtedly unveil new avenues for OA treatment.

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

Temporomandibular joint osteoarthritis (TMJOA) is a gradual degenerative jaw joint condition. Until recent years, TMJOA is still relatively unrecognized and ineffective to be treated. Appropriate animal models with reliable detection methods can help researchers understand the pathophysiology of TMJOA and find therapeutic options. In this study, we summarized common animal models of TMJOA created by chemical, surgical, mechanical, and genetical approaches. The relevant pathological symptoms and induction mechanisms were outlined. In addition, different pathological indicators, furthermore, emerging therapeutic regimens, such as intra-articular drug delivery and tissue engineering-based approaches to treat TMJOA based on these animal models, were summarized and updated. Understanding the physiology and pathogenesis of the TMJOA, together using various ways to diagnose the TMJOA, were elaborated, including imaging techniques, molecular techniques for detecting inflammatory cytokines, histochemical staining, and histomorphometry measures. A more reliable diagnosis will enable the development of new prevention and more effective treatment strategies and thereby improve the quality of life of TMJOA patients. Impact statement Temporomandibular joint osteoarthritis (TMJOA) affects 8 to 16 percent of the population worldwide. However, TMJOA is still relatively unrecognized and ineffective to be treated in the clinic. Appropriate animal models with reliable diagnostic methods can help researchers understand the pathophysiology of TMJOA and find therapeutic options. We herein summarized common animal models of TMJOA and various ways to diagnose the TMJOA. More importantly, emerging therapeutic regimens to treat TMJOA based on these animal models were summarized. With the aid of strategies listed, more effective treatment strategies will be developed and thereby improve the life quality of TMJOA patients.

Netrin-1 Secreted by Human Osteoarthritic Articular Chondrocytes Promotes Angiogenesis in Vitro

OBJECTIVE

Netrin-1 expression in articular cartilage is correlated with osteoarthritic changes. We aimed to investigate the contribution of Netrin-1 secreted by human osteoarthritic articular chondrocytes to angiogenesis process in vitro.

DESIGN

Human articular chondrocytes were extracted from non-osteoarthritic (n = 10) and osteoarthritic (n = 22) joints obtained from surgical specimens and incubated for 24 hours. Medium conditioned by non-osteoarthritic and osteoarthritic articular chondrocytes were collected. Human umbilical vein endothelial cells (HUVEC) were treated with control and conditioned medium and assessed using assays for cell adherence, migration, and tube formation. Netrin-1 expression and secretion was compared between non-osteoarthritic and osteoarthritic chondrocytes by qPCR, Western blot, and ELISA. The role of chondrocyte-secreted Netrin-1 on HUVEC functions was assessed by immunological neutralization using an anti-Netrin-1 monoclonal antibody.

RESULTS

As compared with medium conditioned by non-osteoarthritic chondrocytes, medium conditioned by osteoarthritic chondrocytes permitted tube formation by HUVEC. Both non-osteoarthritic and osteoarthritic chondrocytes expressed Netrin-1 at the RNA and protein levels. At the RNA level, Netrin-1 expression did not differ between non-osteoarthritic and osteoarthritic chondrocytes. At the protein level, Netrin-1 appeared as a full protein of 64 kDa in non-osteoarthritic chondrocytes and as two cleaved proteins of 55 kDa and 64 kDa in osteoarthritic chondrocytes. Immunological neutralization of endogenous Netrin-1 reduced the pro-angiogenic and pro-inflammatory transcriptional profile of HUVEC treated with the medium conditioned by osteoarthritic chondrocytes, as well as their capacities to form tubes.

CONCLUSIONS

Medium conditioned by osteoarthritic chondrocytes permits tube formation by HUVEC in vitro. This permissive effect is mediated by Netrin-1.

Similarities and differences of estrogen in the regulation of temporomandibular joint osteoarthritis and knee osteoarthritis

BACKGROUND

Temporomandibular joint osteoarthritis (TMJOA) and knee osteoarthritis (knee OA) are two kinds of common osteoarthritis (OA) that are characterized by chronic degeneration of soft and hard tissues around joints. Their gender and age differences suggest that there are similarities and differences between the pathogenic mechanisms of TMJOA and knee OA.

OBJECTIVE

To review recent studies on the effect of estrogen on TMJOA and knee OA, and summarize their possible pathogenesis and molecular mechanisms.

SOURCES

Articles up to present reporting the relationship of estrogen and TMJOA or knee OA are included. An extensive electronic search was conducted of databases including PubMed, Web of science core collection.

CONCLUSION

According to epidemiological investigations, TMJOA primarily happens to females of puberty and childbearing age, while knee OA mainly affects postmenopausal women. Epidemiological investigation and experimental research suggest that estrogen may have a different effect on TMJ and on knee. Though estrogen regulates TMJOA and knee OA via estrogen-related receptors (ERR), their pathogenesis and pathway of estrogen regulation are different. To find out the accurate regulation of estrogen on TMJOA and knee OA, specific pathways and molecular mechanisms still need further exploration.

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.

Painful temporomandibular joint overloading induces structural remodeling in the pericellular matrix of that joint's chondrocytes

Mechanical stress to the temporomandibular joint (TMJ) is an important factor in cartilage degeneration, with both clinical and preclinical studies suggesting that repeated TMJ overloading could contribute to pain, inflammation, and/or structural damage in the joint. However, the relationship between pain severity and early signs of cartilage matrix microstructural dysregulation is not understood, limiting the advancement of diagnoses and treatments for temporomandibular joint-osteoarthritis (TMJ-OA). Changes in the pericellular matrix (PCM) surrounding chondrocytes may be early indicators of OA. A rat model of TMJ pain induced by repeated jaw loading (1 h/day for 7 days) was used to compare the extent of PCM modulation for different loading magnitudes with distinct pain profiles (3.5N-persistent pain, 2N-resolving pain, or unloaded controls-no pain) and macrostructural changes previously indicated by Mankin scoring. Expression of PCM structural molecules, collagen VI and aggrecan NITEGE neo-epitope, were evaluated at Day 15 by immunohistochemistry within TMJ fibrocartilage and compared between pain conditions. Pericellular collagen VI levels increased at Day 15 in both the 2N (p = 0.003) and 3.5N (p = 0.042) conditions compared to unloaded controls. PCM width expanded to a similar extent for both loading conditions at Day 15 (2N, p < 0.001; 3.5N, p = 0.002). Neo-epitope expression increased in the 3.5N group over levels in the 2N group (p = 0.041), indicating pericellular changes that were not identified in the same groups by Mankin scoring of the pericellular region. Although remodeling occurs in both pain conditions, the presence of pericellular catabolic neo-epitopes may be involved in the macrostructural changes and behavioral sensitivity observed in persistent TMJ pain.

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.

Tyrosine kinases regulate chondrocyte hypertrophy: promising drug targets for Osteoarthritis

Osteoarthritis (OA) is a major health problem worldwide that affects the joints and causes severe disability. It is characterized by pain and low-grade inflammation. However, the exact pathogenesis remains unknown and the therapeutic options are limited. In OA articular chondrocytes undergo a phenotypic transition becoming hypertrophic, which leads to cartilage damage, aggravating the disease. Therefore, a therapeutic agent inhibiting hypertrophy would be a promising disease-modifying drug. The therapeutic use of tyrosine kinase inhibitors has been mainly focused on oncology, but the Food and Drug Administration (FDA) approval of the Janus kinase inhibitor Tofacitinib in Rheumatoid Arthritis has broadened the applicability of these compounds to other diseases. Interestingly, tyrosine kinases have been associated with chondrocyte hypertrophy. In this review, we discuss the experimental evidence that implicates specific tyrosine kinases in signaling pathways promoting chondrocyte hypertrophy, highlighting their potential as therapeutic targets for OA.

Animal Models of Temporomandibular Disorder

Temporomandibular disorders (TMD) are a group of diseases in the oral and maxillofacial region that can manifest as acute or chronic persistent pain, affecting millions of people worldwide. Although hundreds of studies have explored mechanisms and treatments underlying TMD, multiple pathogenic factors and diverse clinical manifestations make it still poorly managed. Appropriate animal models are helpful to study the pathogenesis of TMD and explore effective treatment measures. At present, due to the high cost of obtaining large animals, rodents and rabbits are often used to prepare TMD animal models. Over the past decade, various animal models have been intensively developed to understand neurobiological and molecular mechanisms of TMD, and seek effective treatments. Although these models cannot carry out all clinical features, they are valuable in revealing the mechanisms of TMD and creating curative access. Currently, there are multitudinous animal models of TMD research. They can be constructed in different means and summarized into four ways according to the various causes and symptoms, including chemical induction (intra-articular injection of ovalbumin, collagenase, formalin, vascular endothelial growth factor, intramuscular injection of complete Freund’s adjuvant, etc.), mechanical stress stimulation (passive mouth opening, change of chewing load), surgical operation (partial disc resection, joint disc perforation) and psychological stress induction. Here, we summarize and discuss different approaches of animal models for determining neurophysiological and mechanical mechanisms of TMD and assess their advantages and limitations, respectively.

Vascular Endothelial Growth Factor Biology and Its Potential as a Therapeutic Target in Rheumatic Diseases

Rheumatic diseases constitute a diversified group of diseases distinguished by arthritis and often involve other organs. The affected individual has low quality of life, productivity even life-threatening in some severe conditions. Moreover, they impose significant economic and social burdens. In recent years, the patient outcome has been improved significantly due to clearer comprehension of the pathology of rheumatic diseases and the effectiveness of "treat to target" therapies. However, the high cost and the adverse effects are the concerns and full remissions are not often observed. One of the main processes that contributes to the pathogenesis of rheumatic diseases is angiogenesis. Vascular endothelial growth factor (VEGF), a central mediator that regulates angiogenesis, has different isoforms and functions in various physiological processes. Increasing evidence suggests an association between the VEGF system and rheumatic diseases. Anti-VEGF and VEGF receptor (VEGFR) therapies have been used to treat several cancers and eye diseases. This review summarizes the current understanding of VEGF biology and its role in the context of rheumatic diseases, the contribution of VEGF bioavailability in the pathogenesis of rheumatic diseases, and the potential implications of therapeutic approaches targeting VEGF for these diseases.

Pathological mechanism of chondrocytes and the surrounding environment during osteoarthritis of temporomandibular joint

Temporomandibular joint (TMJ) osteoarthritis is a common chronic degenerative disease of the TMJ. In order to explore its aetiology and pathological mechanism, many animal models and cell models have been constructed to simulate the pathological process of TMJ osteoarthritis. The main pathological features of TMJ osteoarthritis include chondrocyte death, extracellular matrix (ECM) degradation and subchondral bone remodelling. Chondrocyte apoptosis accelerates the destruction of cartilage. However, autophagy has a protective effect on condylar chondrocytes. Degradation of ECM not only changes the properties of cartilage but also affects the phenotype of chondrocytes. The loss of subchondral bone in the early stages of TMJ osteoarthritis plays an aetiological role in the onset of osteoarthritis. In recent years, increasing evidence has suggested that chondrocyte hypertrophy and endochondral angiogenesis promote TMJ osteoarthritis. Hypertrophic chondrocytes secrete many factors that promote cartilage degeneration. These chondrocytes can further differentiate into osteoblasts and osteocytes and accelerate cartilage ossification. Intrachondral angiogenesis and neoneurogenesis are considered to be important triggers of arthralgia in TMJ osteoarthritis. Many molecular signalling pathways in endochondral osteogenesis are responsible for TMJ osteoarthritis. These latest discoveries in TMJ osteoarthritis have further enhanced the understanding of this disease and contributed to the development of molecular therapies. This paper summarizes recent cognition on the pathogenesis of TMJ osteoarthritis, focusing on the role of chondrocyte hypertrophy degeneration and cartilage angiogenesis.

The role of indoleamine 2,3 dioxygenase 1 in the osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disease and a leading cause of disability. It involves articular cartilage destruction and a whole joint inflammation. In spite of OA pathogenesis is still unclear, new studies on the OA pathophysiological aetiology and immunomodulation therapy continuously achieve significant advances with new concepts. Here, we focus on the indoleamine-2,3-dioxygenase1 (IDO1) activity in the osteoarthritis (OA), which is one of the noticeable enzymes in the synovial fluid of arthritis patients. It was recognized as an essential mediator of autoreactive B and T cell responses in rheumatoid arthritis (RA) and an interesting therapeutic target against RA. However, the role IDO1 plays in the OA pathogenesis hasn't been discussed. The new OA experimental analysis evidenced IDO1 overexpression in the synovial fluid of OA patients, and recent studies reported that IDO1 metabolites were found higher in the OA synovial fluid than RA and spondyloarthropathies (SpA) patients. Moreover, the positive relation of IDO1 metabolites with OA pain and joint stiffness has been confirmed. Thus, the IDO1 plays a pivotal role in the pathogenesis of OA. In this review, the role IDO1 plays in the OA pathogenesis has been deeply discussed. It could be a promising target in the immunotherapy of OA disease.

Intra-articular etanercept attenuates pain and hypoxia from TMJ loading in the rat

Mechanical overloading of the temporomandibular joint (TMJ) and biochemical changes, like inflammation and hypoxia, contribute to cartilage degeneration and pain associated with osteoarthritis (OA). Yet, how overloading contributes to early dysregulation of chondrocytes is not understood, limiting the development of diagnostics and treatments for TMJ OA. Hypoxia-inducible factors (HIF)-1α/2α in chondrocytes were evaluated at Days 8 and 15 in a rat TMJ pain model induced by jaw loading (1 h/day for 7 days) using immunohistochemistry and compared between cases that induce persistent (3.5 N), acute (2 N), or no (0 N) sensitivity. Hypoxia was measured on Day 8 by immunolabeling of the tracer EF5 and 18 F-EF5 PET imaging. To assess the role of tumor necrosis factor (TNF) in painful TMJ loading, intra-articular etanercept was given before loading. Orofacial sensitivity was evaluated during and after loading. Facial grimace, TNF-α, HIF-2α, and hypoxia levels in the TMJ were measured after loading. HIF-2α was elevated (P = .03) after 3.5 N loading at Day 8, but HIF-1α was unchanged. EF5 uptake increased on Day 8 in the 3.5 N group (P < .048) by tissue assay and 18 F-EF5 PET. At Day 8, both HIF-2α (P = .01) and EF5 uptake (P = .005) were correlated with loading magnitude. Etanercept attenuated sensitivity (P < .01) and the facial grimace on Day 7 (P = .01). It also reduced (P < .01) HIF-2α and EF5 uptake on Day 8; but TNF-α levels were not different from controls at that time. Findings suggest that TMJ loading that induces persistent sensitivity upregulates the catabolic factor HIF-2α and reduces oxygen levels in the cartilage, which may be TNF-driven.

MiR-21-5p regulates extracellular matrix degradation and angiogenesis in TMJOA by targeting Spry1

BACKGROUND

Due to the lack of research on the pathological mechanism of temporomandibular joint osteoarthritis (TMJOA), there are few effective treatment measures in the clinic. In recent years, microRNAs (miRs) have been demonstrated to play an important role in the pathogenesis of osteoarthritis (OA) by regulating a variety of target genes, and the latest evidence shows that miR-21-5p is specifically overexpressed in OA. The purpose of this project was to clarify whether miR-21-5p can regulate the TMJOA process by targeting Spry1.

METHODS

TMJOA was induced by a unilateral anterior crossbite (UAC) model, and the effect of miR-21-5p knockout on TMJOA was evaluated by toluidine blue (TB), immunohistochemical (IHC) staining, Western blotting (WB) and RT-qPCR. Primary mouse condylar chondrocytes (MCCs) were isolated, cultured and transfected with a series of mimics, inhibitors, siRNA-Spry1 or cDNA Spry1. WB, RT-qPCR, IHC and TB were used to detect the effect of miR-21-5p and its target gene Spry1 on the expression of MMP-13, VEGF and p-ERK1/2 in TMJOA. The effect of miR-21-5p on angiogenesis was evaluated by chick embryo chorioallantoic membrane (CAM) assay and WB.

RESULTS

In the UAC model, the cartilage thickness and extracellular matrix of miR-21-5p knockout mice were less damaged, and miR-21-5p and UAC model were shown to affect the expression of Spry1, IL-1β, MMP-13, and VEGF. Luciferase experiments confirmed that Spry1 was the direct target of miR-21-5p. The expression levels of Spry1, MMP-13, VEGF and p-ERK1/2 in MCCs transfected with miR-21-5p mimic were higher than those in the inhibitor group. Under the simulated inflammatory environment of IL-1β, the expression levels of MMP-13, VEGF and p-ERK1/2 were positively correlated with miR-21-5p, while Spry1 was negatively correlated with miR-21-5p. Inhibition of miR-21-5p expression and overexpression of Spry1 enhanced the inhibition of MMP-13, VEGF and p-ERK1/2 expression. MiR-21-5p had a significant role in promoting angiogenesis in the chick embryo CAM assay, and this role was clearly mediated by the ERK-MAPK signalling pathway.

CONCLUSION

This study verified that miR-21-5p can promote the process of TMJOA by targeting Spry1, which provides a new direction for future research on the treatment of this disease.

Low-intensity pulsed ultrasound inhibits VEGFA expression in chondrocytes and protects against cartilage degeneration in experimental osteoarthritis

Low-intensity pulsed ultrasound (LIPUS), a noninvasive physical therapy, was recently demonstrated to be an effective treatment for osteoarthritis (OA). Vascular endothelium growth factor A (VEGFA) has been found to be upregulated in the articular cartilage, synovium and subchondral bone of OA patients, leading to cartilage degeneration, synovitis and osteophyte formation. However, the functions and mechanisms of LIPUS in regulating chondrocyte-derived VEGFA expression are still unclear. In this study, we investigated whether LIPUS attenuated OA progression by (a) decreasing the percentage of VEGFA-positive cells in mouse articular cartilage destabilised through medial meniscus surgery and (b) relieving interleukin-1β-induced VEGFA expression in mouse primary chondrocytes. However, this function was negated by a p38 mitogen-activated protein kinase (p38 MAPK) inhibitor. In addition, we found that LIPUS ameliorated VEGFA-mediated disorders in cartilage extracellular matrix metabolism and chondrocyte hypertrophy during OA development. In conclusion, our data indicate a novel effect of LIPUS in regulating the expression of osteoarthritic chondrocyte-derived VEGFA through the suppression of p38 MAPK activity.

The effect of oestrogen on mandibular condylar cartilage via hypoxia-inducible factor-2α during osteoarthritis development

Oestrogen and hypoxia inducible factor-2α (HIF2α) are key regulators in the pathogenesis of osteoarthritis (OA). However, the cellular interaction between oestrogen and HIF2α in articular cartilage during OA process remains unknown. Our previous study has revealed that high-physiological level of oestrogen aggravates the degradation of condylar cartilage in the early stage of temporomandibular joint osteoarthritis (TMJ OA). Here, we hypothesize that HIF2α involves the effect of oestrogen on mandibular condylar cartilage in the progression of TMJ OA. Our experiment in vivo found that the degeneration of condylar cartilage caused by unilateral anterior crossbite (UAC) model, characterized by obvious degenerative morphology, loss of cartilage extracellular matrix, up-regulation of TNF-α, HIF2α and its' down-stream OA-related cytokines (MMP-13, VEGF and Col X), could be alleviated by lack of oestrogen while aggravated by high level of oestrogen in rats. Meanwhile, our in vitro study found that 17β-estradiol stimulation resulted in the loss of extracellular matrix, increased expression of TNF-α, IL-1, HIF2α and its' down-stream OA-related cytokines (MMP-13, VEGF and Col X) in primary condylar chondrocytes via oestrogen receptor beta (ERβ), which could be reversed by ER antagonist, selective estrogen receptor modulators (SERMs) and HIF2α translation inhibitor. Our results reveal that high level of oestrogen can aggravate the degenerative changes of mandibular condylar cartilage, while lack of oestrogen can alleviate it via oestrogen-ERβ-HIF2α pathway during TMJ OA progression.

Estrogen-Related Receptor γ Induces Angiogenesis and Extracellular Matrix Degradation of Temporomandibular Joint Osteoarthritis in Rats

The main causes of cartilage destruction during temporomandibular joint osteoarthritis (TMJOA) are extracellular matrix degradation and angiogenesis, accompanied by an increased level of matrix-degrading enzymes and proangiogenic factors. Interleukin 6 and extracellular signal–regulated kinase (ERK) signaling pathways may play a critical role in these two processes simultaneously, but researchers have not clearly determined the mechanism. We hypothesized that estrogen-related receptor γ (ERRγ) is involved in both cartilage degeneration and angiogenesis in TMJOA. The interactions between ERRγ and the Mmp9 and Vegfa promoter regions were investigated using a chromatin immunoprecipitation (ChIP) assay. A chick embryo chorioallantoic membrane (CAM) assay was performed to investigate the inhibitory effects of U0126 and GSK5182 on angiogenesis. Western blotting, reverse transcription–quantitative PCR (RT-qPCR), immunofluorescence staining, toluidine blue staining, and transfection with cDNAs or small interfering RNAs (siRNAs) were performed on primary mandibular condylar chondrocytes (MCCs). Unilateral anterior crossbite–induced TMJOA models were established in rats, and Western blotting, RT-qPCR, immunohistochemistry, and Safranin O-Fast Green staining were performed to evaluate changes in vivo. ERK1/2 activated matrix metalloproteinase 9 (MMP9) and vascular endothelial growth factor A (VEGFA), which are involved in cartilage destruction, through ERRγ. Based on the ChIP assay results, ERRγ directly activated the transcription of the Mmp9 and Vegfa genes. In chick embryo CAM models, U0126 and GSK5182 significantly inhibited angiogenesis. In conclusion, ERRγ is a downstream transcription factor of ERK1/2, and its upregulation leads to extracellular matrix degradation and angiogenesis in TMJOA. This study identified a common factor between inflammation and vascularization in OA as well as a new therapeutic target for OA: ERRγ.

Abnormal thyroid hormone receptor signaling in osteoarthritic osteoblasts regulates microangiogenesis in subchondral bone

AIMS

Previous study indicated that the increase of local bio-availability of 3'3'5-triiodothyronine (T3) influenced osteoarthritis (OA) initiation. We aimed to investigate the role of thyroid hormone receptors (THRs) signaling in OA osteoblasts.

MATERIALS AND METHODS

THRs expression in OA was detected by immunohistochemistry, immunofluorescence, RT-qPCR and western blotting. These effects on the expression of angiogenesis-related factors were examined after THRα or THRβ knockdown in OA osteoblasts. Fluorescence in situ hybridization was used to confirm the leading receptor for regulating angiogenesis-related factors. Co-culture model was utilized to observe the MMPs expression in chondrocytes after THRα knockdown in osteoblasts. The in vivo effects were also studied after intra-articular injection with THRα siRNA in OA model mice. Micro-CT and immunohistochemistry were employed to evaluate the changes of subchondral bone.

KEY FINDINGS

THRs expression and nuclear translocation were upregulated in human OA osteoblasts. Immunohistochemistry showed that angiogenic activities were increased in OA subchondral bone of human and mice. VEGF, HIF-1α and IGF-1, these THR downstream genes were downregulated after THRα knockdown in OA osteoblasts. Fluorescence in situ hybridization further indicated that THRα signaling mainly regulated VEGF expression. Intra-articular injection with THRα siRNA reduced angiogenic activities in OA model mice subchondral bone and ameliorated cartilage degradation. Micro-CT analysis displayed that the aberrant subchondral bone formation in OA was promoted.

SIGNIFICANCE

The microangiogenesis in subchondral bone may be partly attributed to abnormal THRα signaling in osteoblasts, and local inhibition of the THRα could be a potential target to treat OA.

Therapeutic effect of mesenchymal stem cells derived from human umbilical cord in rabbit temporomandibular joint model of osteoarthritis

Osteoarthritis (OA) is a degenerative condition of the temporomandibular joint (TMJ) characterised by chronic inflammation and damage to joint structures. Because of the complexity of TMJ-OA, only symptomatic treatments are currently available. Recent reports have shown that many of stem cells can exert anti-inflammatory and tissue-regenerating effects. In this study, we investigated the potential cartilage-regenerating and anti-inflammatory effects of human umbilical cord matrix-mesenchymal stem cells (hUCM-MSCs) for the treatment of TMJ-OA. hUCM-MSC lines, isolated from different donors, which showed different activities in vitro. Using a selected cell line, we used different concentrations of hUCM-MSCs to assess therapeutic effects in a rabbit model of monosodium iodoacetate-induced TMJ-OA. Compared with the untreated control group, the potential regenerative result and anti-inflammatory effects of hUCM-MSCs were evident at all the tested concentrations in rabbits with induced TMJ-OA. The median dose of hUCM-MSCs showed the prominent cartilage protective effect and further cartilage regeneration potential. This effect occurred via upregulated expression of growth factors, extracellular matrix markers, and anti-inflammatory cytokines, and reduced expression of pro-inflammatory cytokines. The anti-inflammatory effect of hUCM-MSCs was comparable to that of dexamethasone (DEX). However, only hUCM-MSCs showed potential chondrogenesis effects in this study. In conclusion, our results indicate that hUCM-MSCs may be an effective treatment option for the treatment of TMJ-OA.

Synovial fluid biomarkers associated with osteoarthritis severity reflect macrophage and neutrophil related inflammation

BACKGROUND

To identify a synovial fluid (SF) biomarker profile characteristic of individuals with an inflammatory osteoarthritis (OA) endotype.

METHODS

A total of 48 knees (of 25 participants) were characterized for an extensive array of SF biomarkers quantified by Rules Based Medicine using the high-sensitivity multiplex immunoassay, Myriad Human InflammationMAP® 1.0, which included 47 different cytokines, chemokines, and growth factors related to inflammation. Multivariable regression with generalized estimating equations (GEE) and false discovery rate (FDR) correction was used to assess associations of SF RBM biomarkers with etarfolatide imaging scores reflecting synovial inflammation; radiographic knee OA severity (based on Kellgren-Lawrence (KL) grade, joint space narrowing, and osteophyte scores); knee joint symptoms; and SF biomarkers associated with activated macrophages and knee OA progression including CD14 and CD163 (shed by activated macrophages) and elastase (shed by activated neutrophils).

RESULTS

Significant associations of SF biomarkers meeting FDR < 0.05 included soluble (s)VCAM-1 and MMP-3 with synovial inflammation (FDR-adjusted p = 0.025 and 1.06 × 10^-7); sVCAM-1, sICAM-1, TIMP-1, and VEGF with radiographic OA severity (p = 1.85 × 10^-5 to 3.97 × 10^-4); and VEGF, MMP-3, TIMP-1, sICAM-1, sVCAM-1, and MCP-1 with OA symptoms (p = 2.72 × 10^-5 to 0.050). All these SF biomarkers were highly correlated with macrophage markers CD163 and CD14 in SF (r = 0.43 to 0.90, FDR < 0.05); all but MCP-1 were also highly correlated with neutrophil elastase in SF (r = 0.62 to 0.89, FDR < 0.05).

CONCLUSIONS

A subset of six SF biomarkers was related to synovial inflammation in OA, as well as radiographic and symptom severity. These six OA-related SF biomarkers were specifically linked to indicators of activated macrophages and neutrophils. These results attest to an inflammatory OA endotype that may serve as the basis for therapeutic targeting of a subset of individuals at high risk for knee OA progression.

TRIAL REGISTRATION

Written informed consent was received from participants prior to inclusion in the study; the study was registered at ClinicalTrials.gov ( NCT01237405 ) on November 9, 2010, prior to enrollment of the first participant.

Limiting angiogenesis to modulate scar formation

Angiogenesis, the process of new blood vessel formation from existing blood vessels, is a key aspect of virtually every repair process. During wound healing an extensive, but immature and leaky vascular plexus forms which is subsequently reduced by regression of non-functional vessels. More recent studies indicate that uncontrolled vessel growth or impaired vessel regression as a consequence of an excessive inflammatory response can impair wound healing, resulting in scarring and dysfunction. However, in order to elucidate targetable factors to promote functional tissue regeneration we need to understand the molecular and cellular underpinnings of physiological angiogenesis, ranging from induction to resolution of blood vessels. Especially for avascular tissues (e.g. cornea, tendon, ligament, cartilage, etc.), limiting rather than boosting vessel growth during wound repair potentially is beneficial to restore full tissue function and may result in favourable long-term healing outcomes.

OPG is Required for the Postnatal Maintenance of Condylar Cartilage

Osteoprotegerin (OPG) is one of the protective factors of bony tissue. However, the function of OPG in cartilage tissues remains elusive. The aim of this study is to explore the function of OPG in the postnatal maintenance and the occurring of osteoarthritis (OA) of temporomandibular joint (TMJ) in the rodent models. We found that OPG expressed in the hypertrophic layer of the condylar cartilage and upregulated in the hyperocclusion-induced-TMJ-trauma rat. In the absence of OPG, the cartilage degradation occurred prior to that in WT mice, and the 3-month-old OPG-Knockout (OPG-KO) condyle showed decreased chondrocyte proliferation and increased chondrocyte apoptosis, whereas the number of chondroclasts was comparable to WT condyle. The isolated chondrocytes from the OPG-KO mice also showed impaired survival and promoted chondrogenic differentiation. Furthermore, the hyperocclusion model deteriorated TMJ degradation in the OPG-KO mice. OPG plays a protective role in the condylar chondrocytes' survival, and it is required for the postnatal maintenance of TMJ.

Experimental Methods to Inform Diagnostic Approaches for Painful TMJ Osteoarthritis

Temporomandibular joint (TMJ) osteoarthritis (OA) is a degenerative disease of the joint that can produce persistent orofacial pain as well as functional and structural changes to its bone, cartilage, and ligaments. Despite advances in the clinical utility and reliability of the Diagnostic Criteria for Temporomandibular Disorders, clinical tools inadequately predict which patients will develop chronic TMJ pain and degeneration, limiting clinical management. The challenges of managing and treating TMJ OA are due, in part, to a limited understanding of the mechanisms contributing to the development and maintenance of TMJ pain. OA is initiated by multiple factors, including injury, aging, abnormal joint mechanics, and atypical joint shape, which can produce microtrauma, remodeling of joint tissues, and synovial inflammation. TMJ microtrauma and remodeling can increase expression of cytokines, chemokines, and catabolic factors that damage synovial tissues and can activate free nerve endings in the joint. Although studies have separately investigated inflammation-driven orofacial pain, acute activity of the trigeminal nerve, or TMJ tissue degeneration and/or damage, the temporal mechanistic factors leading to chronic TMJ pain are undefined. Limited understanding of the interaction between degeneration, intra-articular chemical factors, and pain has further restricted the development of targeted, disease-modifying drugs to help patients avoid long-term pain and invasive procedures, like TMJ replacement. A range of animal models captures features of intra-articular inflammation, joint overloading, and tissue damage. Although those models traditionally measure peripheral sensitivity as a surrogate for pain, recent studies recognize the brain's role in integrating, modulating, and interpreting nociceptive inputs in the TMJ, particularly in light of psychosocial influences on TMJ pain. The articular and neural contributors to TMJ pain, imaging modalities with clinical potential to identify TMJ OA early, and future directions for clinical management of TMJ OA are reviewed in the context of evidence in the field.

Tissue Engineering for the Temporomandibular Joint

Tissue engineering potentially offers new treatments for disorders of the temporomandibular joint which frequently afflict patients. Damage or disease in this area adversely affects masticatory function and speaking, reducing patients' quality of life. Effective treatment options for patients suffering from severe temporomandibular joint disorders are in high demand because surgical options are restricted to removal of damaged tissue or complete replacement of the joint with prosthetics. Tissue engineering approaches for the temporomandibular joint are a promising alternative to the limited clinical treatment options. However, tissue engineering is still a developing field and only in its formative years for the temporomandibular joint. This review outlines the anatomical and physiological characteristics of the temporomandibular joint, clinical management of temporomandibular joint disorder, and current perspectives in the tissue engineering approach for the temporomandibular joint disorder. The tissue engineering perspectives have been categorized according to the primary structures of the temporomandibular joint: the disc, the mandibular condyle, and the glenoid fossa. In each section, contemporary approaches in cellularization, growth factor selection, and scaffold fabrication strategies are reviewed in detail along with their achievements and challenges.

Masseter muscle atrophy impairs bone quality of the mandibular condyle but not the alveolar process early after induction

BACKGROUND

Masseter muscle function influences mandibular bone homeostasis. As previously reported, bone resorption markers increased in the mouse mandibular condyle two days after masseter paralysis induced with botulinum toxin type A (BoNTA), followed by local bone loss.

OBJECTIVE

This study aimed to evaluate the bone quality of both the mandibular condyle and alveolar process in the mandible of adult mice during the early stage of a BoNTA-induced masseter muscle atrophy, using a combined 3D histomorphometrics and shape analysis approach.

METHODS

Adult BALB/c mice were divided into an untreated control group and an experimental group; the latter received one single BoNTA injection in the right masseter (BoNTA-right) and saline in the left masseter (Saline-left). 3D bone microstructural changes in the mandibular condyle and alveolar process were determined with high-resolution microtomography. Additionally, landmark-based geometric morphometrics was implemented to assess external shape changes.

RESULTS

After 2 weeks, masseter mass was significantly reduced (P-value <0.001). When compared to Saline-left and untreated condyles, BoNTA-right condyles showed significant bone loss (P-value <0.001) and shape changes. No significant bone loss was observed in the alveolar processes of any of the groups (P-value >0.05).

CONCLUSION

Condyle bone quality deteriorates at an early stage of BoNTA-induced masseter muscle atrophy, and before the alveolar process is affected. Since the observed bone microstructural changes resemble those in human temporomandibular joint degenerative disorders, the clinical safety of BoNTA intervention in the masticatory apparatus remains to be clarified.

Intra-articular injection of hydrogen sulfide decreased the progression of gonarthrosis

Hydrogen sulfide (H₂S) is found in both the plasma and synovial fluid of patients with gonarthrosis. In the present study, we investigated whether intra-articular injection of sodium hydrosulfide (NaSH) (1 mM, 30 μL), a H₂S donor, might affect gonarthrosis in rats. Gonarthrosis was induced surgically in the left knees of rats and left for 6 weeks for the development of disease. Then, intra-articular injections of NaSH or methylprednisolone (1 mg/kg, 30 μL) were administered to rats. Half of each group was sacrificed at the end of the first day and the other half was sacrificed at the end of 4 weeks to evaluate early and later effects of injections on gonarthrosis. The injury induced by anterior cruciate ligament resection and medial meniscectomy in rats caused the development of gonarthrosis. As the duration lengthened after gonarthrosis induction, the progression of the disease continued. According to the modified Mankin Scoring System, intra-articular injection of NaSH histopathologically slowed the progression of gonarthrosis, whereas methylprednisolone was ineffective. In addition, NaSH decreased apoptosis in rat knees with gonarthrosis. Each treatment did not cause injury to healthy knees. Our results lead to the consideration that intra-articular NaSH administration may be effective in the progression of gonarthrosis.

The effect of vascular endothelial growth factor (VEGF) on mouse condylar articular cartilage cultured in vitro

In this study, we explored the direct effect of vascular endothelial growth factor (VEGF) on temporomandibular joint osteoarthritis (TMJ-OA) by analyzing the transformation of mouse condylar cartilage treated in vitro with various concentrations of VEGF. Tissue samples from 126 condyles of four-week-old male C57 mice were randomly divided into 21 groups and treated with VEGF (0 ng/mL, 100 ng/mL, 500 ng/mL, 1 µg/mL, or 2 µg/mL). Furthermore, the samples were treated at different time points (1 d, 2 d, 4 d, and 7 d) and stained with hematoxylin and eosin (HE) and Safranin O and Fast Green stains to observe their morphology. The Mankin score was used to evaluate changes to the condylar cartilage tissues, and immunohistochemistry was performed to observe the expressions of VEGF receptor 2 (VEGFR2), matrix metallopeptidase 9 (MMP9), matrix metallopeptidase 13 (MMP13), and tumor necrosis factor-related activation-induced cytokine (TRANCE). An HE staining analysis revealed that the experimental groups treated with VEGF exhibited the destruction of their condylar cartilage and a proliferation of their hypertrophic cells, in comparison to the control group. Safranin O and Fast Green staining showed that the experimental groups had decreased levels of proteoglycan and degenerative changes in their condylar cartilage. The Mankin score of the samples increased with increasing concentration and treatment time of VEGF, and the differences between the groups were statistically significant (P < 0.05). Immunohistochemistry demonstrated that the expression levels of VEGFR2, MMP9, MMP13, and TRANCE significantly increased in the experimental groups, in comparison to those in the control group, suggesting that VEGF promoted TMJ-OA in mice in vitro.

Grading facial expression is a sensitive means to detect grimace differences in orofacial pain in a rat model

Although pre-clinical models of pain are useful for defining relationships between biological mechanisms and pain, common methods testing peripheral sensitivity do not translate to the human pain experience. Facial grimace scales evaluate affective pain levels in rodent models by capturing and scoring spontaneous facial expression. But, the Rat Grimace Scale (RGS) has not assessed the common disorder of temporomandibular joint (TMJ) pain. A rat model of TMJ pain induced by jaw loading (1 hr/day for 7 days) was used to investigate the time course of RGS scores and compare them between different loading magnitudes with distinct peripheral sensitivity profiles (0N–no sensitivity, 2N–acute sensitivity, 3.5N–persistent sensitivity). In the 3.5N group, RGS is elevated over baseline during the loading period and one day after loading and is correlated with peripheral sensitivity (ρ = −0.48, p = 0.002). However, RGS is not elevated later when that group exhibits peripheral sensitivity and moderate TMJ condylar cartilage degeneration. Acutely, RGS is elevated in the 3.5N loading group over the other loading groups (p < 0.001). These findings suggest that RGS is an effective tool for detecting spontaneous TMJ pain and that spontaneous pain is detectable in rats that develop persistent TMJ sensitivity, but not in rats with acute resolving sensitivity.

The Zonal Architecture of the Mandibular Condyle Requires ADAMTS5

Temporomandibular joint (TMJ) osteoarthritis (TMJOA) disrupts extracellular matrix (ECM) homeostasis, leading to cartilage degradation. Upregulated a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-5 leads to cleavage of its substrate aggrecan (Acan) and is considered a hallmark of TMJOA. However, most research on ADAMTS5-Acan turnover has focused on hyaline cartilage, not fibrocartilage, which comprises the TMJ. The mandibular condylar cartilage (MCC) of the TMJ is organized in zones, and chondrocytes are arranged in axial rows, yet the molecular mechanisms required to generate the MCC zonal architecture have not been elucidated. Here, we test the hypothesis that ADAMTS5 is required for development of the TMJ MCC. Adamts5^+/+ and Adamts5^-/- murine TMJs were harvested at postnatal day 7 (P7), P21, 2 mo, and 6 mo of age; histomorphometrics indicated increased ECM. Immunohistochemistry and Western blots demonstrated the expanded ECM correlated with increased Acan localization in Adamts5^-/- compared to Adamts5^+/+. Cell volume was also decreased in the MCC of Adamts5^-/- due to both a reduction in cell size and less mature hypertrophic chondrocytes. Analysis of chondrogenic maturation markers by quantitative real-time polymerase chain reaction indicated Col2a1, Col10a1, and Sox9 were significantly reduced in Adamts5^-/- MCC compared to that of Adamts5^+/+. The older (6 mo) Adamts5^-/- MCC exhibited changes in chondrogenic cell arrangements, including clustering and chondrogenic atrophy, that correlated with early stages of TMJOA using modified Mankin scoring. These data indicate a potentially novel and critical role of ADAMTS5 for maturation of hypertrophic chondrocytes and establishment of the zonal architecture that, when disrupted, may lead to early onset of TMJOA.

Intraperitoneal injection of thalidomide alleviates early osteoarthritis development by suppressing vascular endothelial growth factor expression in mice

Vascular endothelial growth factor (VEGF) is expressed in articular cartilage and increases in expression levels have been associated with the progression of osteoarthritis (OA). Thalidomide is a drug that has been reported to inhibit angiogenesis and reduce VEGF production by downregulating VEGF expression. The objective of the present study was to determine whether intraperitoneal administration of thalidomide may attenuate early OA development in mice. Male C57BL/6 mice (10‑weeks‑old) were randomly assigned into the destabilization of the medial meniscus (Dmm) with thalidomide treatment (Dmm+Th), Dmm and Sham groups equally. An OA model was induced surgically in Dmm+Th and Dmm groups, and mice of the Dmm+Th group were subsequently treated with an intraperitoneal injection of thalidomide (200 mg/kg/day). At 2 and 4 weeks following surgery, the pathological alterations in cartilage samples were assessed qualitatively by hematoxylin and eosin staining and Safranin O/Fast green staining, and quantitatively by the Osteoarthritis Research Society International scoring system. The mRNA expression levels of matrix metalloproteinase‑13 (MMP‑13) and VEGF were measured by reverse transcription‑quantitative polymerase chain reaction. The protein expression levels of MMP‑13 and VEGF were detected by immunofluorescence and immunohistochemistry, respectively. The production of VEGF in serum was evaluated via an ELISA assay. Pathological scores were significantly higher in the Dmm and the Dmm+Th groups than those in the Sham group; however, the Dmm+Th group exhibited markedly less severe pathological changes compared with the Dmm group. Compared with the Sham group, the mRNA and protein expression levels of VEGF and MMP‑13 in the Dmm and the Dmm+Th groups were significantly increased. The Dmm+Th group exhibited significantly decreased expression levels of VEGF and MMP‑13, as well as significantly decreased serum VEGF concentration compared with the Dmm group. Thus, the results of the present study demonstrated that intraperitoneal administration of thalidomide may alleviate the development of early OA by suppressing VEGF expression in mice and may have potential as a novel therapy for the treatment of OA.

Scaffold-Based Temporomandibular Joint Tissue Regeneration in Experimental Animal Models: A Systematic Review

Reconstruction of degenerated temporomandibular joint (TMJ) structures remains a clinical challenge. Tissue engineering (TE) is a promising alternative to current treatment options, where the TMJ is either left without functional components, or replaced with autogenous, allogeneic, or synthetic grafts. The objective of this systematic review was to answer the focused question: in experimental animal models, does the implantation of biomaterial scaffolds loaded with cells and/or growth factors (GFs) enhance regeneration of the discal or osteochondral TMJ tissues, compared with scaffolds alone, without cells, or GFs? Following PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analysis) guidelines, electronic databases were searched for relevant controlled preclinical in vivo studies. Thirty studies reporting TMJ TE strategies in both small (rodents, rabbits; n = 25) and large animals (dogs, sheep, goats; n = 5) reporting histological and/or radiographic outcomes were included. Twelve studies reported ectopic (subcutaneous) implantation models in rodents, whereas 18 studies reported orthotopic, surgically induced defect models in large animals. On average, studies presented with an unclear-to-high risk of bias. In most studies, mesenchymal stem cells or chondrocytes were used in combination with either natural or synthetic polymer scaffolds, aiming for either TMJ disc or condyle regeneration. In summary, the overall preclinical evidence (ectopic [n = 6] and orthotopic TMJ models [n = 6]) indicate that addition of chondrogenic and/or osteogenic cells to biomaterial scaffolds enhances the potential for TMJ tissue regeneration. Standardization of animal models and quantitative outcome evaluations (biomechanical, biochemical, histomorphometric, and radiographic) in future studies, would allow more reliable comparisons and increase the validity of the results.

Local intra‑articular injection of vascular endothelial growth factor accelerates articular cartilage degeneration in rat osteoarthritis model

In the pathophysiology of osteoarthritis (OA), articular cartilage degeneration exhibits a significant role. Vascular endothelial growth factor (VEGF) is considered to be an effective angiogenic factor and a crucial regulator of articular cartilage degeneration in the development of OA. Therefore, the present study aimed to investigate the underlying influences of exogenous VEGF on articular cartilage degeneration in OA model rat. A total of 24 male Sprague-Dawley rats were randomly allocated into 3 groups. In the normal saline (NS) and VEGF groups, animals received bilateral anterior cruciate ligament (ACL) transection to establish the OA model; at 4 weeks post-surgery, the rats received local intra-articular injections of 100 µl NS or VEGF solution, respectively, every week for 4 weeks. The Control group received neither surgery nor injections. All animals were sacrificed at 12 weeks following surgery. Prominent cartilage degeneration was observed in rats in the NS- and VEGF-injected groups. The extent and the grade of cartilage damage in the VEGF-injected group were notably more severe compared with those in the NS-treated group. Western blotting results demonstrated that the expression levels of aggrecan and type II collagen were significantly reduced in OA model rats that were treated with VEGF. In addition, the expression levels of matrix metalloproteinase (MMP)-3, MMP-9, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs (a disintegrin and metalloproteinase; ADAMTS)-4, −5 and −12, type III collagen and transforming growth factor-β1 were significantly increased following VEGF administration. Results from the present study indicated that VEGF may exhibit a promoting role in the development of OA by destroying articular cartilage matrix.

The Interface of Mechanics and Nociception in Joint Pathophysiology: Insights From the Facet and Temporomandibular Joints

Chronic joint pain is a widespread problem that frequently occurs with aging and trauma. Pain occurs most often in synovial joints, the body's load bearing joints. The mechanical and molecular mechanisms contributing to synovial joint pain are reviewed using two examples, the cervical spinal facet joints and the temporomandibular joint (TMJ). Although much work has focused on the macroscale mechanics of joints in health and disease, the combined influence of tissue mechanics, molecular processes, and nociception in joint pain has only recently become a focus. Trauma and repeated loading can induce structural and biochemical changes in joints, altering their microenvironment and modifying the biomechanics of their constitutive tissues, which themselves are innervated. Peripheral pain sensors can become activated in response to changes in the joint microenvironment and relay pain signals to the spinal cord and brain where pain is processed and perceived. In some cases, pain circuitry is permanently changed, which may be a potential mechanism for sustained joint pain. However, it is most likely that alterations in both the joint microenvironment and the central nervous system (CNS) contribute to chronic pain. As such, the challenge of treating joint pain and degeneration is temporally and spatially complicated. This review summarizes anatomy, physiology, and pathophysiology of these joints and the sensory pain relays. Pain pathways are postulated to be sensitized by many factors, including degeneration and biochemical priming, with effects on thresholds for mechanical injury and/or dysfunction. Initiators of joint pain are discussed in the context of clinical challenges including the diagnosis and treatment of pain.

MicroRNA-29a Counteracts Synovitis in Knee Osteoarthritis Pathogenesis by Targeting VEGF

Synovitis contributes to the development of osteoarthritis (OA) of the knee. MicroRNAs regulate joint microenvironment homeostasis and deterioration. This study was undertaken to characterize the actions of microRNA-29a (miR-29a) to synovial remodeling in OA joints. Synovial specimens isolated from patients with end-stage OA knees showed abundant fibrotic matrix and vessel histopathology concomitant with weak miR-29a expression. In vitro, miR-29a knockdown caused synovial fibroblasts to exhibit high expressions of collagen III, TGF-β1, MMP9, MMP13, and ADAMTS5, whereas miR-29a overexpression diminished these joint-deleterious factors. In collagenase-mediated OA pathogenesis, miR-29a-overexpressing transgenic mice showed minor responses to hyperplasia, macrophage infiltration, fibrosis, hyperangiogenesis, and VEGF expression in synovial lesions. These effects mitigated articular cartilage loss and gait aberrance of injured joints. Intra-articular administration of miR-29a precursor lessened the collagenase aggravation of excessive synovial remodeling reactions and thereby sustained joint tissue integrity. miR-29a lowered VEGF production and angiogenic activities in synovial fibroblasts through targeting the 3′-UTR of VEGF. Taken together, miR-29a deficiency exacerbated synovitis pathogenesis in the end-stage OA knees. miR-29a signaling fends off excessive synovial angiogenesis and fibrosis, which delays joint destruction. This study sheds new light on the protective effects against synovial deterioration and the therapeutic advantage of miR-29a in OA knees.

Identification of the vascular endothelial growth factor signalling pathway by quantitative proteomic analysis of rat condylar cartilage

Angiogenesis mediated by vascular endothelial growth factor (VEGF) is known to play an important role in regulating cartilage remodelling and endochondral ossification. However, the details of how VEGF signalling mechanisms affect condyle remodelling in response to alterations in functional loading remains unclear. To explore this, eighty 16‐day‐old male SD rats were divided into two equal groups which were fed either a soft/powdery diet or a hard diet for 4 weeks; the stiffness of the diet results in alteration of mastication force and hence temporomandibular joint (TMJ) development. We performed a proteomic analysis of rat condylar cartilage using isobaric tags for relative and absolute quantification (iTRAQ) labelling, followed by 2D nano‐high performance liquid chromatography and MALDI‐TOF/time‐of‐flight technology. After protein identification, we used biological information analysis to identify the differentially expressed proteins associated with the VEGF signalling pathway. Among the identified differentially expressed proteins, we found VEGF signalling mainly via the p44/42 MAPK and p38 mitogen‐activated protein kinase (MAPK) pathways in condylar cartilage, including VEGFD, VGFR2, KPCB, KPCT, KPCZ, ARAF, RASN, PLCG2, PLCG1, JUN and M3K12. Furthermore, four representative protein candidates, VEGF, p38 MAPK and p44/42 MAPK/phospho‐p44/42 MAPK, were confirmed by immunohistochemical staining and western blot. Our data suggest that VEGF might play an important role in TMJ development and remodelling in response to alterations in functional loading through the p44/42 MAPK and p38 MAPK signalling pathway. This study provides new clues to the understanding of the signalling mechanism responsible for VEGF production in response to different masticatory functions at the protein level.

Procyanidins Mitigate Osteoarthritis Pathogenesis by, at Least in Part, Suppressing Vascular Endothelial Growth Factor Signaling

Procyanidins are a family of plant metabolites that have been suggested to mitigate osteoarthritis pathogenesis in mice. However, the underlying mechanism is largely unknown. This study aimed to determine whether procyanidins mitigate traumatic injury-induced osteoarthritis (OA) disease progression, and whether procyanidins exert a chondroprotective effect by, at least in part, suppressing vascular endothelial growth factor signaling. Procyanidins (extracts from pine bark), orally administered to mice subjected to surgery for destabilization of the medial meniscus, significantly slowed OA disease progression. Real-time polymerase chain reaction revealed that procyanidin treatment reduced expression of vascular endothelial growth factor and effectors in OA pathogenesis that are regulated by vascular endothelial growth factor. Procyanidin-suppressed vascular endothelial growth factor expression was correlated with reduced phosphorylation of vascular endothelial growth factor receptor 2 in human OA primary chondrocytes. Moreover, components of procyanidins, procyanidin B2 and procyanidin B3 exerted effects similar to those of total procyanidins in mitigating the OA-related gene expression profile in the primary culture of human OA chondrocytes in the presence of vascular endothelial growth factor. Together, these findings suggest procyanidins mitigate OA pathogenesis, which is mediated, at least in part, by suppressing vascular endothelial growth factor signaling.

Inhibition of vascular endothelial growth factor with shRNA in chondrocytes ameliorates osteoarthritis

Osteoarthritis (OA) is a chronic, incurable and destructive joint disease that is characterized by chondrocyte hypertrophy and cartilage degradation. Angiogenesis, mediated by the action of vascular endothelial growth factor (VEGF), is known to be a contributing factor in the pathogenesis of OA. In this study, we use a lentivirus-based approach to investigate whether VEGF knockdown would be beneficial to chondrogenesis and could prevent or slow down OA progression. We first profiled cytokines in human OA cartilage using cytokine antibody arrays. This revealed that as many as 21 angiogenesis-related cytokines were significantly upregulated in severe OA cartilage compared to mild OA samples. Next, we infected chondrocytes with VEGF small hairpin RNA (shRNA) lentivirus (LV-VEGF shRNA) and treated these cells with tumour necrosis factor alpha (TNF-α) to induce hypertrophy. The results showed that inhibition of VEGF not only enhanced chondrogenic differentiation, but also protected chondrocytes from TNF-α-induced hypertrophy. We also found that knockdown of VEGF suppressed TNF-α-induced phosphorylation of ERK1/2 in chondrocytes. Furthermore, using a surgically induced OA rat model, we showed that VEGF inhibition delayed OA progression in animals given intra-articular injection of LV-VEGF shRNA. In conclusion, in this study, we have shown that VEGF knockdown can enhance chondrogenesis and prevent OA progression, thus providing evidence that inhibition of VEGF may be a potential therapeutic approach for OA patients.

KEY MESSAGES

Numerous pro-angiogenic factors are upregulated in severe OA cartilage. Inhibition of VEGF by shRNA protects chondrocytes from TNF-α-induced hypertrophy. Knockdown of VEGF suppresses TNF-α-induced phosphorylation of ERK1/2 in chondrocytes. VEGF inhibition delays OA progression in rat model in vivo. Inhibition of VEGF may be a potential therapeutic approach for OA patients.

Targeting VEGF and Its Receptors for the Treatment of Osteoarthritis and Associated Pain

Increased vascular endothelial growth factor (VEGF) levels are associated with osteoarthritis (OA) progression. Indeed, VEGF appears to be involved in OA-specific pathologies including cartilage degeneration, osteophyte formation, subchondral bone cysts and sclerosis, synovitis, and pain. Moreover, a wide range of studies suggest that inhibition of VEGF signaling reduces OA progression. This review highlights both the potential significance of VEGF in OA pathology and pain, as well as potential benefits of inhibition of VEGF and its receptors as an OA treatment. With the emergence of the clinical use of anti-VEGF therapy outside of OA, both as high-dose systemic treatments and low-dose local treatments, these particular therapies are now more widely understood. Currently, there is no established disease-modifying drug available for patients with OA, which warrants continued study of the inhibition of VEGF signaling in OA, as stand-alone or adjuvant therapy. © 2016 American Society for Bone and Mineral Research.

Upregulation of lncRNA HOTAIR contributes to IL-1β-induced MMP overexpression and chondrocytes apoptosis in temporomandibular joint osteoarthritis

Temporomandibular joint osteoarthritis (TMJ OA) is a common and heterogeneous disease that causes painful and progressive joint degeneration, which restricts daily activities, including talking and chewing. Long noncoding RNAs (lncRNAs) are an important class of genes involved in various physiological and pathological functions, including osteoarthritis (OA).The present study aimed to identify the lncRNAs that are important in TMJ OA and their potential functions. Here, we found that HOTAIR was significantly upregulated in the synovial fluid of TMJ OA patients compared with that of normal controls. Increased HOTAIR was similarly observed in the synovial fluid of TMJ OA rabbits as compared to control rabbits. Furthermore, in interleukin-1β (IL-1β)-induced TMJ OA in vitro model (primary rabbit condylar chondrocytes), the expressions of matrix metalloproteinase (MMP)-1, MMP3, MMP9 and HOTAIR were all dramatically increased. Most importantly, knockdown of HOTAIR in IL-1β-induced TMJ OA in vitro model could not only reverse the IL-1β-stimulated expressions of MMP1, MMP3 and MMP9, but also significantly decrease the apoptosis rate induced by IL-1β in primary rabbit condylar chondrocytes. Our data provides new insight into the mechanisms of chondrocytes destruction in TMJ OA.