Endoplasmic reticulum stress triggered autophagy and regulated the phenotype transformation of rheumatoid arthritis synovial fibroblasts via the IRE1/JNK pathway

BACKGROUND: Previous studies have indicated that endoplasmic reticulum (ER) stress may actively promote the pathogenesis of rheumatoid arthritis (RA) by evoking autophagy. However, the underlying mechanism remains largely unknown. This study aimed to explore the mechanism of the ER stress-autophagy pathway in regulating the phenotype transformation of rheumatoid arthritis synovial fibroblasts (RASFs). METHODS: Synovial tissue was obtained from RA and osteoarthritis (OA) patients during joint replacement surgery. ER stress/autophagy signature markers were examined in synovial tissue by real-time quantitative polymerase chain reaction (RT-PCR), western blot, and immunohistochemistry. Phenotype transformation of RASFs, including increased cell proliferation and invasion capability, was measured by CCK-8 assay and transwell invasion assay. Signaling pathways were further investigated and inositol requiring enzyme 1 (IRE1) was down-regulated in RASFs by transfecting specific short hairpin RNA-ERN1 (shRNA-ERN1) carried by lentiviral vectors. RESULTS: The expression of ER stress/autophagy pathway-associated proteins, including GRP78, IRE1, protein kinase R-like endoplasmic reticulum kinase (PERK), and LC3, was significantly increased in RA synovium compared with OA synovium. After stimulation with tumor necrosis factor alpha (TNF-α) in vitro, the proliferation and invasion ability of RASFs were upregulated, while this phenomenon could be inhibited by 4-PBA (ER stress inhibitor) or 3-MA (autophagy inhibitor). The expression of IRE1 and p-JNK in particular, occurred in an obviously time-dependent manner after stimulation with TNF-α. Moreover, the proliferation and invasion of RASFs were inhibited after transfection with sh-RNA-ERN1 to downregulate IRE1 expression. CONCLUSIONS: ER stress triggered autophagy via the IRE1/JNK pathway to regulate the phenotype transformation of RASFs, indicating an important role of the ER stress-autophagy pathway in the pathological process of synovitis in RA.