Effect of electroacupuncture at the ST36 and GB39 acupoints on apoptosis by regulating the p53 signaling pathway in adjuvant arthritis rats

p53 and mouse double minute 2 homolog (MDM2) serve key regulatory roles in the apoptosis of synovial cells. The present study aimed to investigate the effects of electroacupuncture (EA) at the ‘Zusanli’ (ST36) and ‘Xuanzhong’ (GB39) acupoints on apoptosis in an adjuvant arthritis (AA) rat model. A total of 40 male Sprague-Dawley rats were randomly divided into Control, AA, AA + EA and AA + sham EA groups (n=10 rats in each group). Rats in all the groups, with the exception of the control group, were injected with Complete™ Freund's adjuvant into the bilateral hindlimb footpad to establish the AA model. Rats in the AA + EA group were treated with EA at the ST36 and GB39 acupoints. Rats in the AA + sham EA group were treated with percutaneous electrical stimulation at a position of 5 mm away from the ST36 and GB39 acupoints. The arthritis index scores and hindlimb paw volumes of the rats in each group were recorded. Subsequently, pathological changes in the synovial tissue were evaluated by hematoxylin and eosin (H&E) staining, and the apoptotic rate of the synovial cells was detected by TUNEL staining. In addition, the expression levels of the apoptosis-associated proteins, Bax, phorbol-12-myristate-13-acetate-induced protein 1 (Noxa) and p53 upregulated modulator of apoptosis (PUMA), were determined by western blot analysis. The expression of both the gene and protein of p53 and MDM2 in synovial tissue was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis, respectively. The results indicated that the arthritis index scores and hindlimb paw volumes upon EA stimulation were significantly decreased compared with those of the AA group (P<0.05). H&E staining revealed that the synovial inflammation of EA stimulation was significantly decreased compared with the AA group (P<0.05). The TUNEL assay results indicated that the apoptotic rate of synovial cells in the AA + EA group was significantly increased compared with that in the AA group (P<0.05). Furthermore, an increased expression of proapoptotic proteins was confirmed by the increased expression levels of Bax, Noxa and PUMA in the AA + EA group. The results of RT-qPCR and western blot analysis demonstrated that, compared with the AA group, EA stimulation led to a marked increase in p53 (P<0.05) and a significant decrease in MDM2 (P<0.05) gene and protein expression. Taken together, these results demonstrated that EA performed on the ST36 and GB39 acupoints led to a significant amelioration in AA injury of model rats, by regulating the p53 signaling pathway and inducing apoptosis.