Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease with the cessation of matrix anabolism and aggravation of inflammation, which results in severe pain and impaired joint function. However, the mechanisms are not well understood. Circular RNAs (circRNAs) are reported to have various biological functions and participate in the development, diagnosis, prognosis, and treatment of different diseases. This study aimed to investigate the roles and mechanisms of circ-slain2 in TMJOA. We first established TMJOA mouse models and found circ-slain2 was lowly expressed in the cartilage of TMJOA through sequencing data. We observed that circ-slain2 is predominantly localized in the cytoplasm and downregulated in mouse condylar chondrocytes (mCCs) treated with tumor necrosis factor α (TNFα) and interferon γ (IFNγ). Micro-computed tomography and histological examination showed that intra-articular injection of circ-slain2 overexpressing adeno-associated virus could alleviate cartilage catabolism and synovial inflammation to relieve TMJOA in vivo. In addition, elevated circ-slain2 also showed anticatabolic and anti-inflammatory effects on IFNγ- and TNFα-stimulated mouse condylar chondrocytes (mCCs). Functional enrichment analysis indicated that protein processing in endoplasmic reticulum (ER) was associated with TMJOA, and further functional experiments confirmed that circ-slain2 could suppress ER stress in OA mCCs. RNA binding protein immunoprecipitation assay revealed an overt interaction between activating transcription factor 6 (ATF6) and circ-slain2. Inhibition of the expression of both ATF6 and circ-slain2 resulted in dilation of the ER and enhanced the expression of ER stress markers, whose ER stress level was higher than inhibition of ATF6 but lower than knockdown of circ-slain2 expression. Collectively, our research demonstrated that circ-slain2 could regulate ATF6 to relieve ER stress, reducing temporomandibular joint cartilage degradation and synovial inflammation. These findings provide prospects for developing novel osteoarthritis therapies based on circ-slain2 by focusing on reducing the inflammation of synovium and the imbalance between matrix synthesis and degradation.

中文翻译：

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Circ-Slain2 减轻软骨退化和 TMJOA 炎症。

颞下颌关节骨关节炎（TMJOA）是一种退行性疾病，伴随基质合成代谢停止和炎症加重，导致剧烈疼痛和关节功能受损。然而，其机制尚不清楚。据报道，环状RNA（circRNA）具有多种生物学功能，参与不同疾病的发生、诊断、预后和治疗。本研究旨在探讨circ-slain2在TMJOA中的作用和机制。我们首先建立了TMJOA小鼠模型，通过测序数据发现circ-slain2在TMJOA软骨中低表达。我们观察到 circ-slain2 主要位于细胞质中，并在用肿瘤坏死因子 α (TNFα) 和干扰素 γ (IFNγ) 处理的小鼠髁软骨细胞 (mCC) 中下调。显微计算机断层扫描和组织学检查表明，关节内注射circ-slain2过表达腺相关病毒可以减轻软骨分解代谢和滑膜炎症，从而缓解体内TMJOA。此外，升高的 circ-slain2 还对 IFNγ 和 TNFα 刺激的小鼠髁软骨细胞 (mCC) 表现出抗分解代谢和抗炎作用。功能富集分析表明内质网（ER）中的蛋白质加工与TMJOA相关，进一步的功能实验证实circ-slain2可以抑制OA mCC中的ER应激。RNA 结合蛋白免疫沉淀测定揭示了激活转录因子 6 (ATF6) 和 circ-slain2 之间明显的相互作用。抑制ATF6和circ-slain2的表达会导致内质网扩张，并增强内质网应激标记物的表达，其内质网应激水平高于抑制ATF6，但低于敲除circ-slain2表达。总的来说，我们的研究表明 circ-slain2 可以调节 ATF6 以缓解 ER 应激，减少颞下颌关节软骨退化和滑膜炎症。这些发现为开发基于 circ-slain2 的新型骨关节炎疗法提供了前景，重点是减少滑膜炎症和基质合成与降解之间的不平衡。