Mechanism of electroacupuncture penetration needling for relieving synovial inflammation of knee osteoarthritis through TLR4/MyD88/NF-κB signal pathway

Abstract

To observe the effects of electroacupuncture (EA) penetration needling on Toll-like receptors 4/myeloid differentiation factor 88/nuclear factor-kappa B (TLR4/MyD88/NF-κB) signaling pathway in rat synovium and the serum-related inflammatory factors, so as to explore the mechanism of EA penetration needling on synovial inflammation in rats with knee osteoarthritis (KOA). SD male rats were randomly divided into sham-operation group, model group, EA+penetration needling group, and conventional EA group, with 16 rats in each group. The rats model was prepared by anterior cruciate ligment transection and these rats were forced to exercise for 8 weeks after operation. After successful modeling, in the EA+penetration needling group, the needles were inserted at "Dubi" (ST35) "Neixiyan" (EX-LE4), and at "Xuehai"(SP10) "Liangqiu"(ST34) on the right hind limb, towards each other, 5-8 mm in depth, respectively. In the conventional EA group, the needles were inserted at ST35 and EX-LE4 on the right hind limb, obliquely, at 30° angle to the skin, 3-5 mm in depth; and were inserted at SP10 and ST34 on the right hind limb perpendicularly, 3-5 mm in depth. In these two groups, electric stimulation was operated with dense-disperse wave, 2 Hz/10 Hz in frequency and 0.5-1.5 mA in intensity, retained for 20 min in each treatment. The treatment was given once daily, 10 days as 1 course of treatment, and 2 courses were required at the interval of 2 days. After the intervention, the knee joint effusion was observed by musculoskeletal ultrasound; the contents of IL-1β, IL-6 and TNF-α in serum were determined by ELISA; the morphological changes in the synovium were observed after H.E. staining; the positive expression of NF-κB p65 in the synovial membrane was detected by immunohistochemical method; the expression levels of TLR4, MyD88, TRAF-6 and NF-κB p65 proteins in the synovial membrane were determined by Western blot. Compared with the sham-operation group, in the model group, the knee joint effusion was obviously increased, the synovial lining cells were distributed irregularly, the cells were disarranged, the pannus was formed largely, and a great number of the inflammatory cells were infiltrated; the contents of serum IL-1β, IL-6 and TNF-α, the positive expression of NF-κB p65, the protein expression levels of TLR4, MyD88, TRAF-6 and NF-κB p65 in the synovial tissue were increased (P<0.05). Compared with the model group, the knee joint effusion was reduced, the synovial lining cells were proliferated, a small number of the inflammatory cells were infiltrated, and the pannus was formed lightly; the contents of serum IL-1β, IL-6 and TNF-α, the positive expression of NF-κB p65, the protein expression levels of TLR4, MyD88, TRAF-6 and NF-κB p65 in the synovial tissue were lower (P<0.05) in the EA+penetration needling group and the conventional EA group. In the conventional EA group, the knee joint effusion was increased, the synovial lining cells were proliferated, the inflammatory cells were infiltrated largely, and the pannus was formed increasingly; the contents of serum IL-1β, IL-6 and TNF-α, and the protein expression levels of TLR4, MyD88 and NF-κB p65 in the synovial tissue were increased when compared with the EA+penetration needling group (P<0.05). The EA+penetration needling can significantly relieve the synovial inflammatory reaction and the knee joint effusion in KOA rats. The mechanism is probably related to down-regulating the downstream inflammatory cascade through inhibiting the transduction of TLR4/MyD88/NF-κB signaling pathway.