Effects of electroacupuncture on expression of miR-218 and HMGB1/TLR4 signaling pathway in rats with focal cerebral ischemia

To observe the effect of electroacupuncture (EA) on high mobility group box 1 (HMGB1)/toll-like receptor 4 (TLR4) signaling pathway and inflammatory injury in rats with focal cerebral ischemia (FCI), so as to explore its mechanisms underlying amelioration of ischemic stroke.

Male SD rats were randomly divided into sham operation (n=18), model (n=18) and EA (n=18) groups. The FCI model was established according to Longa's method. In the EA group, 24 h after modeling, EA stimulation was applied to "Baihui" (GV20), "Fengfu" (GV16), and "Neiguan" (PC6) and "Xinshu" (BL15) on the left side for 20 min, once a day for 1 week. The neurological deficit severity was evaluated by the modified neurological severity score (mNSS), and the morphological changes of neurons were observed after H.E. staining. The expression of HMGB1 and TLR4 proteins were detected by immunofluorescence staining. The contents of tumor necrosis factor (TNF)-α and interleukin (IL)-6 in the ischemic area tissue of the brain were detected using ELISA. The mRNA expressions of HMGB1 and TLR4 as well as the expression of miR-218 in the ischemic cortex were detected by PCR.

Compared with the sham operation group, the mNSS at 2 h, 48 h and 7 day (d), IL-6 and TNF-α contents, HMGB1 and TLR4 immunoactivity and mRNA expression at 48 h and 7 d were significantly increased (P < 0.01), while miR-218 expression at 48 h and 7 d was obviously downregulated (P < 0.01) in the model group. In comparison with the model group, the mNSS at 7 d, IL-6 and TNF-αcontents, HMGB1 and TLR4 immunoactivity and mRNA expression at 7 d not at 48 h were significantly decreased (P < 0.01, P < 0.05), while the expression of miR-218 at 7 d was apparently up-regulated (P < 0.05) in the EA group. H.E. staining showed that there were signs of neuronal necrosis including blurred outline of the cells, disordered internal structure, dense cytoplasm, shrunk nuclei, etc. in the ischemic area of the brain at 48 h and 7 d in the model group, which was evidently milder on day 7 in the EA group.

EA can reduce the inflammatory injury of brain tissue and improve the neurological impairment in rats with FCI, which may be associated with its effects in inhibiting HMGB1/TLR4 signaling and down-regulating the level of pro-inflammatory cytokines.