Rebamipide Attenuates Mandibular Condylar Degeneration in a Murine Model of TMJ-OA by Mediating a Chondroprotective Effect and by Downregulating RANKL-Mediated Osteoclastogenesis

Posttraumatic hyperalgesia and associated peripheral sensitization after temporomandibular joint injury in mice

ABSTRACT

Temporomandibular disorder (TMD) is the most prevalent painful condition in the craniofacial area. Recent studies have suggested that external or intrinsic trauma to the temporomandibular joint (TMJ) is associated with the onset of painful TMD in patients. Here, we investigated the effects of TMJ trauma through forced-mouth opening (FMO) in mice to determine pain behaviors and peripheral sensitization of trigeminal nociceptors in both sexes. Forced-mouth opening increased mechanical pain as assessed by the von Frey test, with spontaneous pain-like behaviors assessed using the mouse grimace scale and anxiety-like behaviors assessed using the open-field test. Changes in pain-like behaviors were not different between male and female mice. However, in vivo GCaMP Ca2+ imaging of intact trigeminal ganglia (TG) showed modality- and sex-dependent changes. Forced-mouth opening increased spontaneous Ca2+ responses and mechanical hypersensitivity of TG neurons compared to the sham group, which was more pronounced in male mice. Forced-mouth opening also increased Ca2+ responses evoked by cold, heat, and capsaicin stimuli, which was not different between the sexes. In retrogradely labeled trigeminal TMJ afferents, FMO induced an increase in small-sized neuronal proportions with increased colocalization with calcitonin gene-related peptides and transient receptor potential vanilloid subtype 1, which was modestly sex dependent. These results suggest that TMJ injury leads to persistent posttraumatic hyperalgesia associated with peripheral sensitization of trigeminal nociceptors with distinct sex dependency.

Targeting G6PD to mitigate cartilage inflammation in TMJOA: The NOX4-ROS-MAPK axis as a therapeutic avenue

Chondrocytes, known for their metabolic adaptability in response to varying stimuli, play a significant role in osteoarthritis (OA) progression. Glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway, has recently been found to upregulate in OA chondrocyte. However, the exact role of G6PD in temporomandibular joint osteoarthritis (TMJOA) and its effect on chondrocyte function remains unclear. In present study, we induced OA-like conditions in the rat temporomandibular joint via occlusal disharmony (OD), noting a marked increase in G6PD expression in the condylar cartilage. Our data show that G6PD knockdown in mandibular condylar chondrocytes (MCCs) reduces the expression of catabolic enzymes (e.g., MMP3, MMP13) and inflammatory cytokines (e.g., IL6) induced by IL-1β. G6PD knockdown also mitigates IL-1β-induced upregulation of ERK, JNK, and p38 phosphorylation and reduces reactive oxygen species (ROS) levels by decreasing the nicotinamide adenine dinucleotide phosphate (NADPH) and NADPH oxidases 4 (NOX4) mRNA expression. In summary, G6PD appears to regulate the inflammatory state of condylar chondrocytes via the NOX-ROS-MAPK axis, highlighting its potential as a therapeutic target for TMJOA.

Forced mouth opening induces post-traumatic hyperalgesia and associated peripheral sensitization after temporomandibular joints injury in mice

Temporomandibular disorder (TMD) is the most prevalent painful condition in the craniofacial area. The pathophysiology of TMD is not fully understood, and it is necessary to understand pathophysiology underlying painful TMD conditions to develop more effective treatment methods. Recent studies suggested that external or intrinsic trauma to TMJ is associated with chronic TMD in patients. Here, we investigated the effects of the TMJ trauma through forced-mouth opening (FMO) in mice to determine pain behaviors and peripheral sensitization of trigeminal nociceptors. FMO increased mechanical hyperalgesia assessed by von Frey test, spontaneous pain-like behaviors assessed by mouse grimace scale, and anxiety-like behaviors assessed by open-field test. In vivo GCaMP Ca 2+ imaging of intact trigeminal ganglia (TG) showed increased spontaneous Ca 2+ activity and mechanical hypersensitivity of TG neurons in the FMO compared to the sham group. Ca 2+ responses evoked by cold, heat, and capsaicin stimuli were also increased. FMO-induced hyperalgesia and neuronal hyperactivities were not sex dependent. TG neurons sensitized following FMO were primarily small to medium-sized nociceptive afferents. Consistently, most TMJ afferents in the TG were small-sized peptidergic neurons expressing calcitonin gene-related peptides, whereas nonpeptidergic TMJ afferents were relatively low. FMO-induced intraneural inflammation in the surrounding tissues of the TMJ indicates potentially novel mechanisms of peripheral sensitization following TMJ injury. These results suggest that the TMJ injury leads to persistent post-traumatic hyperalgesia associated with peripheral sensitization of trigeminal nociceptors.

The degeneration-pain relationship in the temporomandibular joint: Current understandings and rodent models

Temporomandibular disorders (TMD) represent a group of musculoskeletal conditions involving the temporomandibular joints (TMJ), the masticatory muscles and associated structures. Painful TMD are highly prevalent and conditions afflict 4% of US adults annually. TMD include heterogenous musculoskeletal pain conditions, such as myalgia, arthralgia, and myofascial pain. A subpopulations of TMD patients show structural changes in TMJ, including disc displacement or degenerative joint diseases (DJD). DJD is a slowly progressing, degenerative disease of the TMJ characterized by cartilage degradation and subchondral bone remodeling. Patients with DJD often develop pain (TMJ osteoarthritis; TMJ OA), but do not always have pain (TMJ osteoarthrosis). Therefore, pain symptoms are not always associated with altered TMJ structures, which suggests that a causal relationship between TMJ degeneration and pain is unclear. Multiple animal models have been developed for determining altered joint structure and pain phenotypes in response to various TMJ injuries. Rodent models of TMJOA and pain include injections to induce inflammation or cartilage destruction, sustained opening of the oral cavity, surgical resection of the articular disc, transgenic approaches to knockout or overexpress key genes, and an integrative approach with superimposed emotional stress or comorbidities. In rodents, TMJ pain and degeneration occur during partially overlapping time periods in these models, which suggests that common biological factors may mediate TMJ pain and degeneration over different time courses. While substances such as intra-articular pro-inflammatory cytokines commonly cause pain and joint degeneration, it remains unclear whether pain or nociceptive activities are causally associated with structural degeneration of TMJ and whether structural degeneration of TMJ is necessary for producing persistent pain. A thorough understanding of the determining factors of pain-structure relationships of TMJ during the onset, progression, and chronification by adopting novel approaches and models should improve the ability to simultaneously treat TMJ pain and TMJ degeneration.

Wnt/β-catenin signaling pathway is activated in the progress of mandibular condylar cartilage degeneration and subchondral bone loss induced by overloaded functional orthopedic force (OFOF)

Objective

To explore the role of Wnt/β-catenin signaling pathway in the pathogenesis and progression of temporomandibular joint osteoarthritis (TMJ OA) caused by overloaded force.

Materials and methods

We generated a rat model of forward mandibular extension device to induce TMJ OA by overloaded force. Condylar cartilage samples were collected at 2wk, 4wk, and 8wk after appliances were installed. Changes of the condylar cartilage and subchondral bone were evaluated by hematoxylin and eosin (HE), Safranin O and Fast Green staining (SO&FG), micro-CT, tartrate resistant acid phosphatase (TRAP) staining. The expression levels of β-catenin, COL-2, MMP3 and sclerostin (SOST) were detected by immunohistochemistry (IHC) and PCR.

Results

HE, SO&FG, micro-CT, OARSI and Mankin scores showed that the condyle cartilage layer was significantly thinner and proteoglycan loss in the overloded group. TRAP staining exhibited that the number of positive osteoclasts increased and OPG level decreased in the overload group. IHC, PCR showed that the expression of COL2 and SOST decreased, while MMP3 and β-catenin increased in the overload group.

Conclusion

Wnt/β-catenin signaling pathway is activated in the progress of mandibular condylar cartilage degeneration and subchondral bone loss induced by overloaded functional orthopedic force (OFOF)

Role of osteoclast differentiation in the occurrence of osteoarthritis of temporomandibular joint

OBJECTIVES

This study aimed to explore the role of osteoclast differentiation in the occurrence of temporomandibular joint osteoarthritis (TMJOA).

METHODS

A mouse TMJOA model was constructed. Micro-CT was used to observe the changes in condylar bone during the development of TMJOA. Hematoxylin-eosin (HE) staining was used to observe the histological structure changes of the condyle of TMJOA mice. Tartrate resistant acid phosphatase (TRAP) staining was used to observe the presence of osteoclasts in TMJOA joint tissue. The synovial fluid of patients with TMJ-OA was collected to determine the effect on osteoclast differentiation.

RESULTS

Micro-CT revealed that the condyle of the TMJOA group had the most obvious damage in the second and third weeks, and the shape of the condyles also changed in a beak-like manner. HE staining showed that the condyle cartilage and subchondral bone structure of TMJOA mice were disordered in the second week. TRAP tissue staining showed that the number of osteoclasts of the TMJOA group obviously increased in the second week. Results of cell experiments showed that the number of osteoclast differentiation significantly increased after stimulation of synovial fluid from TMJOA patients, and the cell volume increased.

CONCLUSIONS

TMJOA animal models and TMJOA patient synovial cell experiments could induce osteoclast differentiation, indicating that osteoclast differentiation plays an important role in TMJOA occurrence.

Roles for B[a]P and FICZ in subchondral bone metabolism and experimental temporomandibular joint osteoarthritis via the AhR/Cyp1a1 signaling axis

Bone loss due to smoking represents a major risk factor for fractures and bone osteoporosis. Signaling through the aryl hydrocarbon receptor (AhR) and its ligands contributes to both bone homeostasis and inflammatory diseases. It remains unclear whether the same AhR signaling axis affects the temporomandibular joint (TMJ). The aim of this study was to investigate possible mechanisms which mediate bone loss in the TMJ due to smoking. In particular, whether benzo[a]pyrene (B[a]P), a carcinogen of tobacco smoke, induces expression of the AhR target gene, Cyp1a1, in mandibular condyles. Possible functions of an endogenous ligand of FICZ, were also investigated in a TMJ-osteoarthritis (OA) mouse model. B[a]P was administered orally to wild-type and AhR-/- mice and bone metabolism was subsequently examined. TMJ-OA was induced in wild-type mice with forceful opening of the mouth. Therapeutic functions of FICZ were detected with μCT and histology. Exposure to B[a]P accelerated bone loss in the mandibular subchondral bone. This bone loss manifested with osteoclastic bone resorption and upregulated expression of Cyp1a1 in an AhR-dependent manner. In a mouse model of TMJ-OA, FICZ exhibited a dose-dependent rescue of mandibular subchondral bone loss by repressing osteoclast activity. Meanwhile, in vitro, pre-treatment with FICZ reduced RANKL-mediated osteoclastogenesis. B[a]P regulates mandibular subchondral bone metabolism via the Cyp1a1. The AhR ligand, FICZ, can prevent TMJ-OA by regulating osteoclast differentiation.

The Antioxidant Resveratrol Protects against Chondrocyte Apoptosis by Regulating the COX-2/NF-κB Pathway in Created Temporomandibular Osteoarthritis

Temporomandibular joint osteoarthritis (TMJOA) is characterized by chronic inflammatory degradation of mandibular condylar cartilage (MCC). Studies have found a positive correlation between inflammation and cyclooxygenase- (COX-) 2 in OA pathology. NF-κB is a crucial transcription factor of inflammatory and immune responses in the cause of TMJOA pathology. Resveratrol (RES) plays a critical role in antioxidation and anti-inflammation. But, studies on the effects of RES on TMJOA are very limited. So, the purpose of this study is to investigate the antioxidant and protective effects of RES against MCC degradation through downregulating COX-2/NF-κB expression. In vitro studies, the MCC cells were divided into three groups: the NC group, OA group, and RES group. The optimum dose of RES (10 μM) was determined. The TMJOA model of mice was created by injection of collagenase. And mice were injected with RES (100 μg/10 μl) 3 times one week for 4 weeks in the RES group. The expressions of COX-2, P65, MMP1, MMP13, COL2, and ACAN were measured by RT-PCR. Morphological changes of MCC were studied with HE staining. The results showed that inflammation could induce MCC degradation in vitro and vivo, while RES could reverse the degradation. Meanwhile, RES could downregulate COX-2/NF-κB/MMP expression and increase cartilage markers in vitro and vivo studies. The results indicated that RES treatment had antioxidant effects against chondrocyte apoptosis by downregulating the COX-2/NF-κB pathway in created TMJOA.

Understanding Early-Stage Posttraumatic Osteoarthritis for Future Prospects of Diagnosis: from Knee to Temporomandibular Joint

PURPOSE OF REVIEW

Many mechanical load-bearing joints of the body are prone to posttraumatic osteoarthritis (PTOA), including the knee joint and temporomandibular joint (TMJ). Early detection of PTOA can be beneficial in prevention or alleviating further progression of the disease.

RECENT FINDINGS

Various mouse models, similar to those used in development of novel diagnosis strategies for early stages of OA, have been proposed to study early PTOA. While many studies have focused on OA and PTOA in the knee joint, early diagnostic methods for OA and PTOA of the TMJ are still not well established. Previously, we showed that fluorescent near-infrared imaging can diagnose inflammation and cartilage damage in mouse models of knee PTOA. Here we propose that the same approach can be used for early diagnosis of TMJ-PTOA. In this review, we present a brief overview of PTOA, application of relevant mouse models, current imaging methods available to examine TMJ-PTOA, and the prospects of near-infrared optical imaging to diagnose early-stage TMJ-OA.

The immunoregulatory role of p21 in the development of the temporomandibular joint-osteoarthritis

Objective

We aimed to identify the immunoregulatory role of the cyclin‐dependent kinase inhibitor p21 in the homeostasis of mandibular condylar cartilage affected by mechanical stress.

Materials and methods

Ten C57BL/6 wild‐type (WT) and ten p21^−/− mice aged 8 weeks were divided into the untreated and treated groups. In the treated groups, mechanical stress was applied to the temporomandibular joint (TMJ) through forced mouth opening for 3 hr/day for 7 days. The dissected TMJs were assessed using micro‐CT, histology, and immunohistochemistry.

Results

Treated p21^−/− condyles with mechanical stress revealed more severe subchondral bone destruction, with thinner cartilage layers and smaller proteoglycan area relative to treated WT condyles; untreated WT and p21^−/− condyles had smoother surfaces. Immunohistochemistry revealed significant increases in the numbers of caspase‐3, interleukin‐1β, matrix metalloprotease (MMP)‐9, and MMP‐13 positive cells, and few aggrecan positive cells, in treated p21^−/− than in treated WT samples. Moreover, the number of TUNEL positive cells markedly increased in p21^−/− condyles affected by mechanical stress.

Conclusions

Our findings indicate that p21 in chondrocytes contributes to regulate matrix synthesis via the control ofm aggrecan and MMP‐13 expression under mechanical stress. Thus, p21 might regulate the pathogenesis of osteoarthritis in the TMJ.

Knockout of miR-21-5p alleviates cartilage matrix degradation by targeting Gdf5 in temporomandibular joint osteoarthritis

AIMS

The study aimed to determine whether the microRNA miR21-5p (MiR21) mediates temporomandibular joint osteoarthritis (TMJ-OA) by targeting growth differentiation factor 5 (Gdf5).

METHODS

TMJ-OA was induced in MiR21 knockout (KO) mice and wild-type (WT) mice by a unilateral anterior crossbite (UAC) procedure. Mouse tissues exhibited histopathological changes, as assessed by: Safranin O, toluidine blue, and immunohistochemistry staining; western blotting (WB); and quantitative real-time polymerase chain reaction (RT-qPCR). Mouse condylar chondrocytes were transfected with a series of MiR21 mimic, MiR21 inhibitor, Gdf5 siRNA (si-GDF5), and flag-GDF5 constructs. The effects of MiR-21 and Gdf5 on the expression of OA related molecules were evaluated by immunofluorescence, alcian blue staining, WB, and RT-qPCR.

RESULTS

UAC altered the histological structure and extracellular matrix content of cartilage in the temporomandibular joint (TMJ), and KO of MiR21 alleviated this effect (p < 0.05). Upregulation of MiR21 influenced the expression of TMJ-OA related molecules in mandibular condylar chondrocytes via targeting Gdf5 (p < 0.05). Gdf5 overexpression significantly decreased matrix metalloproteinase 13 (MMP13) expression (p < 0.05) and reversed the effects of MiR21 (p < 0.05).

CONCLUSION

MiR21, which acts as a critical regulator of Gdf5 in chondrocytes, regulates TMJ-OA related molecules and is involved in cartilage matrix degradation, contributing to the progression of TMJ-OA. Cite this article: Bone Joint Res 2020;9(10):689-700.

Effectiveness of low-intensity pulsed ultrasound on osteoarthritis of the temporomandibular joint: A review

Loading is indispensable for the growth, development, and maintenance of joint tissues, including mandibular condylar cartilage, but excessive loading or reduced host adaptive capacity can considerably damage the temporomandibular joint (TMJ), leading to temporomandibular joint osteoarthritis (TMJ-OA). TMJ-OA, associated with other pathological conditions and aging processes, is a highly degenerative disease affecting the articular cartilage. Many treatment modalities for TMJ-OA have been developed. Traditional clinical treatment includes mainly nonsurgical options, such as occlusal splints. However, non-invasive therapy does not achieve joint tissue repair and regeneration. Growing evidence suggests that low-intensity pulsed ultrasound (LIPUS) accelerates bone fracture healing and regeneration, as well as having extraordinary effects in terms of soft tissue repair and regeneration. The latter have received much attention, and various studies have been performed to evaluate the potential role of LIPUS in tissue regeneration including that applied to articular cartilage. The present article provides an overview of the status of LIPUS stimulation used to prevent the onset and progression of TMJ-OA and enhance the tissue regeneration of mandibular condylar cartilage. The etiology and management of TMJ-OA are explained briefly, animal models of TMJ-OA are described, and the effectiveness of LIPUS on cell metabolism and tissue regeneration in the TMJ is discussed.

Factors secreted from dental pulp stem cells show multifaceted benefits for treating experimental temporomandibular joint osteoarthritis

OBJECTIVE

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease characterized by progressive cartilage degeneration, abnormal bone remodeling, and chronic pain. In this study, we aimed to investigate effective therapies to reverse or suppress TMJOA progression.

DESIGN

To this end, we performed intravenous administration of serum free conditioned media from human exfoliated deciduous teeth stem cells (SHED-CM) into a mechanical-stress induced murine TMJOA model.

RESULTS

SHED-CM administration markedly suppressed temporal muscle inflammation, and improved bone integrity and surface smoothness of the destroyed condylar cartilage. Moreover, SHED-CM treatment decreased the number of IL-1β, iNOS, and MMP-13 expressing chondrocytes, whereas it specifically increased PCNA-positive cells in the multipotent polymorphic cell layer. Notably, the numbers of TdT-mediated dUTP nick end labeling (TUNEL)-positive apoptotic chondrocytes in the SHED-CM treated condyles were significantly lower than in those treated with DMEM, whereas the proteoglycan positive area was restored to a level similar to that of the sham treated group, demonstrating that SHED-CM treatment regenerated the mechanical-stress injured condylar cartilage and subchondral bone. Secretome analysis revealed that SHED-CM contained multiple therapeutic factors that act in osteochondral regeneration.

CONCLUSIONS

Our data demonstrated that SHED-CM treatment promoted the regeneration and repair of mechanical-stress induced mouse TMJOA. Our observations suggest that SHED-CM has potential to be a potent tissue-regenerating therapeutic agent for patients with severe TMJOA.

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.

Potential Role of Rebamipide in Osteoclast Differentiation and Mandibular Condylar Cartilage Homeostasis

Background:

Temporomandibular joint osteoarthritis (TMJ-OA) is a degenerative disease that involves changes in subchondral bone and progressive degradation of cartilage. Currently, rebamipide, a gastroprotective drug, is administered to protect gastric mucosa and accelerate ulcer healing.

Objectives:

Recent studies have shown that rebamipide also attenuates cartilage degeneration by suppressing oxidative damage and inducing homeostasis of the extracellular matrix of articular chondrocytes. Regarding the latter, reduced expression of cathepsin K, NFATc1, c-Src, and integrin β3, and increased expression of nuclear factor-kappa B, have been found to be mediated by the transcription factor, receptor activator of nuclear factor kappa-B ligand (RANKL).

Methods:

Treatment with rebamipide was also found to activate, mitogen-activated protein kinases such as p38, ERK, and JNK to reduce osteoclast differentiation. Taken together, these results strongly indicate that rebamipide mediates inhibitory effects on cartilage degradation and osteoclastogenesis in TMJ-OA.

Results and Conclusion:

Here, we highlight recent evidence regarding the potential for rebamipide to affect osteoclast differentiation and TMJ-OA pathogenesis. We also discuss the potential role of rebamipide to serve as a new strategy for the treatment of TMJ-OA.

Curcumin inhibits osteoclastogenic potential in PBMCs from rheumatoid arthritis patients via the suppression of MAPK/RANK/c-Fos/NFATc1 signaling pathways

The aim of the present study was to determine the effects of curcumin on the osteoclastogenic potential of peripheral blood mononuclear cells (PBMCs) obtained from patients with rheumatoid arthritis (RA), and to investigate the underlying molecular mechanisms. PBMCs from patients with RA (n=12) and healthy controls (n=10) were cultured to assess osteoclastogenic potential. The number of tartrate-resistant acid phosphatase-positive osteoclasts differentiated from PBMCs isolated from patients with RA was significantly increased compared with that of the healthy controls. In addition, the osteoclast number in patients with RA was correlated with the clinical indicators, Sharp score (r=0.810; P=0.001) and lumbar T-score (r=−0.685; P=0.014). Furthermore, the resorption area was increased in the RA group compared with the healthy controls. The mRNA and protein expression levels in PBMC-derived osteoclasts treated with curcumin were measured by reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. Curcumin inhibited the osteoclastogenic potential of PBMCs, potentially by suppressing activation of extracellular signal-regulated kinases 1 and 2, p38 and c-Jun N-terminal kinase, and inhibiting receptor activator of nuclear factor κB (RANK), c-Fos and nuclear factor of activated T cells (NFATc1) expression. The results of the present study demonstrated that curcumin may inhibit the osteoclastogenic potential of PBMCs from patients with RA through the suppression of the mitogen-activated protein kinase/RANK/c-Fos/NFATc1 signaling pathways, and that curcumin may be a potential novel therapeutic agent for the treatment of bone deterioration in inflammatory diseases such as RA.