[Effect of electroacupuncture on pyroptosis of synovial tissues in rats with knee osteoarthritis]

Abstract

Objective: To observe the effect of electroacupuncture (EA) on pyroptosis-related proteins in synovium of knee joint in rats with knee osteoarthritis(KOA), in order to explore its mechanism underlying improvement of KOA.

Methods: Forty male SD rats were randomly divided into control， model, EA and medication groups, with 10 rats in each group. The KOA model was established by injecting 0.2 mL 4% papain solution into the right intra-articular cavity, followed by repeating the injection again on day 4 and 7 after the first injection. After successful modeling, rats of the EA group received EA stimulation of "Neixiyan" (EX-LE4) and "Dubi"(ST35) on the right limb for 15 min, once every day, 6 days per week, for a total of 4 weeks, and those of the medication group received gavage of celecoxib 24 mg/kg, once every day, 6 days per week, for a total of 4 weeks. The severity of dysfunction of the right knee was assessed by using Lequesne's score. Serum interleukin(IL)-1β and IL-18 contents were detected by ELISA. Histopathological changes of the synovium tissue of the right knee joint were observed to give score (synovial pathological score) after H.E. staining. The expression position and intensity of Nod-like receptor pyrin domain 3 (NLRP3) in syno-vial tissue were observed by immunohistochemistry. The expression levels of NLRP3, apoptosis-associated speck-like protein containing card (ASC), Caspase-1, Gasdermin D(GSDMD), IL-1β and IL-18 mRNAs and proteins (including GSDMD-N) in the synovial tissue of the right knee joint were detected by real-time fluorescence quantitative PCR and Western blot, separately.

Results: Compared with the control group, the model group had a significant increase in the Lequesne's score, synovial pathological score, serum IL-1β and IL-18 contents, and the expression levels of NLRP3, ASC, Caspase-1, GSDMD, IL-1β, IL-18 mRNAs and proteins and GSDMD-N protein (P<0.01). Whereas relevant to the model group, both the EA and medication groups had marked lower levels of Lequesne's score and synovial pathological score, serum IL-1β and IL-18 contents, and expression levels of NLRP3, ASC, Caspase-1, IL-1β, IL-18 mRNAs and proteins, GSDMD mRNA and GSDMD-N protein (P<0.01, P<0.05). Comparison between two intervention groups showed that the contents of serum IL-1β and IL-18, and the expression levels of IL-1β mRNA and protein were significantly higher in the EA group than in the medication group (P<0.05, P<0.01). No significant differences were found between the EA and medication groups in the Lequesne's score, synovial pathological score, NLRP3, ASC, Caspase-1 and IL-18 mRNAs and proteins, as well as GSDMD mRNA (P>0.05).

Conclusion: EA can alleviate the inflammatory response of synovial tissues of knee joints in KOA rats, which may be related to its function in down-regulating the expression levels of synovial NLRP3, ASC, Caspase-1, IL-1β and IL-18 mRNAs and proteins, and GSDMD mRNA and GSDMD-N proteins, reducing the occurrence of pyroptosis.

Keywords: Electroacupuncture; Knee osteoarthritis; Pyroptosis; Synovitis.