TNF­α increases inflammatory factor expression in synovial fibroblasts through the toll­like receptor­3­mediated ERK/AKT signaling pathway in a mouse model of rheumatoid arthritis.

ABSTRACT

Osteoarthritis is a type of joint disease that may lead to other joint diseases. Previous research has demonstrated that tumor necrosis factor (TNF)­α is associated with osteoarthritis activity and pathology. The possible mechanisms of the TNF­α­mediated signaling pathway have not been clearly elaborated in synovial fibroblasts. The present study aimed to investigate the potential mechanisms of TNF­α in a mouse model of iodoacetate­induced osteoarthritis. Reverse transcription­quantitative polymerase chain reaction, ELISA, western blotting and immunohistochemistry were performed to evaluate the role of TNF­α in the progression of osteoarthritis. The results revealed that the serum levels of TNF­α, interleukin (IL)­1ß, IL­4 and IL­6 were significantly upregulated in a mouse model of iodoacetate­induced osteoarthritis compared with healthy mice (P<0.01). TNF­α, IL­1ß, IL­4 and IL­6 mRNA and protein levels were also significantly upregulated in synovial fibroblasts in the experimental mice (P<0.01). It was demonstrated that TNF­α increased pro­inflammation factors matrix metalloproteinase (MMP)­3, MMP­9, nuclear factor (NF)­κB and receptor activator of NF­κB ligand (RANKL) in synovial fibroblasts. It was also observed that the toll­like receptor (TLR)­3 was significantly upregulated and extracellular signal­regulated kinase (ERK) and protein kinase B (AKT) were significantly downregulated in synovial fibroblasts in osteoarthritis mice (P<0.01). An in vitro assay demonstrated that TNF­α inhibitor decreased mRNA and protein levels of IL­1ß, IL­4 and IL­6 in synovial fibroblasts. The knockdown of TLR­3 abolished the TNF­α upregulated mRNA and protein levels of IL­1ß, IL­4 and IL­6 in synovial fibroblasts. In addition, the knockdown of TLR­3 also reversed TNF­α­upregulated ERK and AKT expression in synovial fibroblasts. In vivo assays demonstrated that TNF­α inhibitor significantly decreased the deposition of IL­1ß, IL­4 and IL­6 as well as bone destruction and significantly increased the body weight and osteoarthritis score for osteoarthritic mice (P<0.01). TNF­α inhibitor decreased TLR­3 and significantly increased the expression and phosphorylation of ERK and AKT in articular cartilage (P<0.01). In conclusion the results of the present study indicate that TNF­α serves an essential role in synovial fibroblasts in osteoarthritis, suggesting that inhibition of TNF­α may decrease inflammation via the TLR­3­mediated ERK/AKT signaling pathway in a mouse model of monosodium iodoacetate­induced osteoarthritis.