Electroacupuncture inhibits TLR4/NF-κB signaling in the dorsal root ganglion of rats with spared nerve injury

Objective: Neuropathic pain can be provoked by high mobility group box 1 (HMGB1) activation of toll-like receptor (TLR)4/nuclear factor (NF)-κB signaling in the dorsal root ganglion (DRG). Electroacupuncture (EA) has been reported to effectively alleviate neuropathic pain with few side effects, but its precise mechanism of action remains unknown. The aim of this study was to explore whether 2 Hz EA stimulation suppresses TLR4/NF-κB signaling in the DRG following spared nerve injury (SNI) in a rat model. Methods: In this experiment, SNI rats were given 2 Hz EA once every other day for a total of 21 days. Paw withdrawal threshold (PWT) was measured to assess SNI-induced mechanical hypersensitivity, and western blotting and immunofluorescence staining were used to determine the levels of pain-related signaling molecules and pro-inflammatory mediators in the DRG. Results: SNI up-regulated HMGB1, TLR4, myeloid differentiation factor-88 adaptor protein (MyD88) and NF-κB p65 protein expression in the DRG. In addition, immunofluorescence staining demonstrated that SNI induced higher levels of TLR4 and MyD88 in the DRG. We also demonstrated co-localization of TLR4 and MyD88 with both calcitonin gene-related peptide (CGRP) and isolectin GS-IB4 in the DRG of SNI rats, respectively. Meanwhile, 2 Hz EA stimulation effectively reversed the elevations of HMGB1, TLR4, MyD88 and NF-κB p65 induced by SNI in the DRG, which was coupled with amelioration of SNI-induced mechanical hypersensitivity. Conclusions: The results of this study suggested that inhibition of the TLR4/NF-κB signaling pathway in the DRG by 2 Hz EA might be exploited as a therapeutic option for neuropathic pain.