Electroacupuncture Alleviates Pain Responses and Inflammation in Collagen-Induced Arthritis Rats via Suppressing the TLR2/4-MyD88-NF-κB Signaling Pathway

Abstract

Background and Purpose. Electroacupuncture (EA) is effective on rheumatoid arthritis (RA), an autoimmune disease, but the mechanisms involved remain poorly understood. This study was designed to investigate the analgesic and anti-inflammatory effects of EA in a chronic inflammatory animal model of collagen-induced arthritis (CIA) and its underlying molecular mechanisms. Experimental Approach. For the male Sprague–Dawley (SD) rats were immunized with bovine type II collagen followed by a booster injection 7 days later. Two weeks after the first immunization, EA stimulation (2/100 Hz, 1 mA, lasting for 30 min/day) was delivered to Zusanli (ST36), and Sanyinjiao (SP6) or OxPAPC (TLR2/TLR4 inhibitor, 1.5 mg/kg) was injected by tail vein for 28 days. After intervention, the analgesic effect was evaluated from the aspect of pain responses including thermal withdrawal latency (TWL) and mechanical withdrawal thresholds (MWT). The anti-inflammatory effect was assessed by paw edema detection, histopathological analysis, and Meso Scale Discovery (MSD) testing of tumor necrosis factor-alpha (TNF-α), interleukin 1 beta (IL-1β), and interleukin 6 (IL-6). The underlying molecular mechanism was analyzed through western blotting and double-immunofluorescence labeling. Results. EA intervention and OxPAPC injection could relieve mechanical allodynia and thermal hyperalgesia caused by CIA. Paw edema and pathological damage of synovium were significantly ameliorated after EA intervention and OxPAPC injection. Furthermore, EA intervention and OxPAPC injection markedly reduced the contents of serum TNF-α, IL-1β, and IL-6, as well as the protein expression levels of synovial TLR2, TLR4, MyD88, and NF-κB p-p65. In particular, the expression of TLR2 and TLR4 on synovial fibroblasts and macrophages in synovium was significantly reduced by EA intervention. Conclusions. Repeated EA stimulation at ST36 and SP6 can effectively relieve joint pain and synovial inflammation caused by RA in CIA rats. The analgesic and anti-inflammatory effect of EA may be closely related to the inhibition of innate immune responses driven by the TLR2/4-MyD88-NF-κB signaling pathway in the synovium.