Hypoxia-inducible Factor Expression Is Related to Apoptosis and Cartilage Degradation in Temporomandibular Joint Osteoarthritis

Background: It remains unclear whether hypoxic conditions affect apoptosis and contribute to degradation of cartilaginous tissues in osteoarthritis (OA) lesions. In this study, we hypothesized that hypoxic conditions induced the accumulation of hypoxia-inducible factor (HIF) and activated apoptosis to contribute to OA cartilage degeneration in vivo.Methods: Malocclusion stress was applied for 2 weeks, 4 weeks and 8 weeks to induce an OA-like lesion animal model (OD) in rats. Histological analysis was performed by H&E staining and safranin O/fast green staining. The expression levels of protein in condylar cartilage were examined by immunostaining to evaluate cartilage degeneration.Results: We found apparent histological phenotypes associated with degeneration in the occlusion disorder stress (OD) group. The OD group at 4 weeks and 8 weeks had obviously reduced expression of Acan and Col II in cartilage. In contrast, the OD groups had higher levels of Col X, ADAMTS5 and MMP13 in the condylar cartilage than the control group. Moreover, the OD group cartilage had prominent degenerative changes with reduced levels of HIF1α and increased levels of HIF2α and the apoptosis factor Caspase3 in condylar cartilage at 8 weeks.Occlusion disorder stress results in cartilage degeneration. HIF1α and HIF2α are involved in temporomandibular joint (TMJ) cartilage homeostasis by regulating chondrocyte apoptosis, which contributes to TMJ cartilage degeneration. Conclusion: Thus, abnormal hypoxic conditions inducing opposite expression patterns of HIF1α and HIF2α could be involved in the pathogenesis of condylar cartilage degeneration. HIF2α may provide a potential negative feedback mechanism for HIF1α during cartilage damage.

The Attenuating Effect of Low-Intensity Pulsed Ultrasound on Hypoxia-Induced Rat Chondrocyte Damage in TMJ Osteoarthritis Based on TMT Labeling Quantitative Proteomic Analysis

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease with a complex and multifactorial etiology. An increased intrajoint pressure or weakened penetration can exacerbate the hypoxic state of the condylar cartilage microenvironment. Our group previously simulated the hypoxic environment of TMJOA in vitro. Low-intensity pulsed ultrasound (LIPUS) stimulation attenuates chondrocyte matrix degradation via a hypoxia-inducible factor (HIF) pathway-associated mechanism, but the mode of action of LIPUS is currently poorly understood. Moreover, most recent studies investigated the pathological mechanisms of osteoarthritis, but no biomarkers have been established for assessing the therapeutic effect of LIPUS on TMJOA with high specificity, which results in a lack of guidance regarding clinical application. Here, tandem mass tag (TMT)-based quantitative proteomic technology was used to comprehensively screen the molecular targets and pathways affected by the action of LIPUS on chondrocytes under hypoxic conditions. A bioinformatic analysis identified 902 and 131 differentially expressed proteins (DEPs) in the <1% oxygen treatment group compared with the control group and in the <1% oxygen + LIPUS stimulation group compared with the <1% oxygen treatment group, respectively. The DEPs were analyzed by gene ontology (GO), KEGG pathway and protein-protein interaction (PPI) network analyses. By acting on extracellular matrix (ECM)-associated proteins, LIPUS increases energy production and activates the FAK signaling pathway to regulate cell biological behaviors. DEPs of interest were selected to verify the reliability of the proteomic results. In addition, this experiment demonstrated that LIPUS could upregulate chondrogenic factors (such as Sox9, Collagen Ⅱ and Aggrecan) and increase the mucin sulfate content. Moreover, LIPUS reduced the hydrolytic degradation of the ECM by decreasing the MMP3/TIMP1 ratio and vascularization by downregulating VEGF. Interestingly, LIPUS improved the migration ability of chondrocytes. In summary, LIPUS can regulate complex biological processes in chondrocytes under hypoxic conditions and alter the expression of many functional proteins, which results in reductions in hypoxia-induced chondrocyte damage. ECM proteins such as thrombospondin4, thrombospondin1, IL1RL1, and tissue inhibitors of metalloproteinase 1 play a central role and can be used as specific biomarkers determining the efficacy of LIPUS and viable clinical therapeutic targets of TMJOA.

Involvement of an FTO gene polymorphism in the temporomandibular joint osteoarthritis

Objectives The FTO gene has been reported as an obesity-associated gene and is also considered a risk gene for osteoarthritis (OA). However, its exact function is unclear, and there is conflicting evidence on the involvement of FTO polymorphisms in OA via obesity. The purpose of this study was to determine the effects of FTO polymorphism rs8044769 alleles on OA in the temporomandibular joint (TMJ), which is minimally affected by body weight. Materials and methods A total of 324 TMJs (113 with OA and 211 without OA, serving as controls) from 162 Japanese patients with temporomandibular disorders and undergoing MRI examination were analyzed. Genotyping was conducted, and multivariate analysis was performed after adjusting for the effects of age, sex, body mass index, and TMJ disc abnormalities. Results Mean age, BMI, and sex did not differ between the TMJs with OA and the TMJs without OA, but a significant difference was found for positional and dynamic disc abnormalities (P < 0.05). The allele frequency of FTO polymorphisms also differed significantly between the TMJs with OA and the TMJs without OA (P = 0.011). Moreover, logistic regression analysis showed no significant association between BMI (P = 0.581) and the occurrence of TMJOA but also indicated that the CC allele of rs8044769 is a risk factor for TMJOA (P = 0.040). Conclusions Our results show that rs8044769 in the FTO gene might be involved in TMJOA. Clinical relevance The present study provides a basis for a deeper understanding of the mechanism underlying degenerative skeletal diseases and the more effective selection and development of treatment strategies based on the patients’ genetic characteristics.

Therapeutic application of 3B-PEG injectable hydrogel/Nell-1 composite system to temporomandibular joint osteoarthritis

Objective: This study aims to construct a composite system of the tri-block polyethylene glycol injectable hydrogel (3B-PEG IH) and Neural epithelial growth factor-like Protein 1 (Nell-1), and to analyze its therapeutic effect on temporomandibular joint osteoarthritis (TMJOA)。 Methods: Sol-gel transition temperature was measured via inverting test. The viscoelastic modulus curves was measured by Rheometer. Degradation and controlled release profiles of 3B-PEG IH were drawn by incubated in PBS. In vivo gel retention and biocompatibility were completed subcutaneously on the back of rats. After primary chondrocytes were extracted and identified, the cell viability in 3B-PEG IH was measured. Evaluation of gene expression in hydrogel was performed by real-time polymerase chain reaction. TMJOA rabbits were established by intraarticular injection of type II collagenase. Six weeks after composite systems being injected, gross morphological score, micro-CT and histological staining and grading were evaluated. Results: different types of 3B-PEG IH all reached a stable gel state at 37°C and could support the three-dimensional growth of chondrocytes, but poly(lactide-co-caprolactone)-block-poly(ethyleneglycol)-block-poly(lactide-co-caprolactone)(PLCL-PEG-PLCL) hydrogel had a wider gelation temperature range and better hydrolytic stability for about 4 weeks. Its controlled release curve is closest to the zero-order release kinetics. In vitro, PLCL-PEG-PLCL/Nell-1 could promote the chondrogenic expression and reduce the inflammatory expression. In vivo, TMJOA rabbits were mainly characterized by the disorder of cartilage structure and the destruction of subchondral bone. However, PLCL-PEG-PLCL/Nell-1 could reverse the destruction of the subchondral trabecula, restore the fibrous and proliferative layers of the surface, and reduce the irregular hyperplasia of fibrocartilage layer. Conclusion: By comparing the properties of different 3B-PEG IH, 20wt% PLCL-PEG-PLCL hydrogel was selected as the most appropriate material. PLCL-PEG-PLCL/Nell-1 composite could reverse osteochondral damage caused by TMJOA, Nfatc1-Runx3 signaling pathway may play a role in it. This study may provide a novel, minimally-invasive therapeutic strategy for clinical treatment of TMJOA.

No Effects of Intra-Articular Injections of Sodium Hyaluronate, Corticosteroids, Platelet-Rich Plasma on Temporomandibular Joint Osteoarthritis: a Systematic Review and Network Meta-analysis of Randomized Controlled Trials

Background Intra-articular injections of corticosteroids (CCS), hyaluronic acid (HA), and platelet-rich plasma (PRP) have often been used for temporomandibular joint osteoarthritis (TMJ OA). However, there is no guideline for the choice of pharmacological injections. The aim of this network meta-analysis (NMA) is to compare the efficacy of different intra-articular injectable treatments on TMJ OA. Methods Studies were identified from PubMed, Embase and Cochrane Central with date up to December 2020. Randomized Controlled Trials (RCTs) included were the studies of patients with TMJ OA who had intra-articular treatment with CCS, HA, PRP, placebo and follow-up assessing TMJ function in target outcome variables. The primary outcome was temporomandibular joint pain (VAS). The secondary outcomes were maximal mouth opening (mm), and lateral movement to the affected side (mm). Results Nine RCTs involving 316 patients were included. For primary pain outcome, no significance was detected when CCS, HA and PRP were compared with placebo by both short- (3-6 months) and long-term (>12 months) follow-up. In addition, these injectables did not significantly outperform placebo by evaluating secondary functional outcomes (maximal mouth opening and lateral movement) with the same follow-up. Subgroup analyses showed that the effect of CCS on subgroups with more than 70% women was statistically less effective compared with placebo. Conclusion Evidence suggested that intra-articular pharmacological injections of CCS, HA, and PRP had no effect on improving TMJ pain and functional outcomes compared with placebo injection. Trial registration This study is registered with PROSPERO, number CRD42021270914.