A multiplex analysis for profiling the expression of candidate microRNAs (miRNAs), which are small noncoding RNAs that function as key post-transcriptional regulators, may lead to a better understanding of the complex machinery of neuropathic pain. In the present study, we performed a miRNA array analysis using tissues of the dorsal root ganglion (DRG), a primary site for pain processing, obtained from mice with partial sciatic nerve ligation. Among 1135 total miRNAs, 26 miRNAs showed up-regulation (more than 2-fold change) and only 4 miRNAs showed down-regulation (less than 0.5-fold change) in the DRG of nerve-ligated mice. In a RT-qPCR assay, the levels of miR-21, miR-431, and miR-511-3p were significantly increased on the ipsilateral side of the DRG from 3 to 7 days after sciatic nerve ligation. These elevations were almost absent in IL-6 knockout mice. Furthermore, the expression level of miR-21, but not those of miR-431 or miR511-3p, was significantly increased in exosomes extracted from blood of nerve-ligated mice. These findings suggest that the increased expression of IL-6-regulated miR-21, miR-431, and miR-511-3p in the DRG and increased exosomal miR-21 extracted from blood after sciatic nerve ligation may play at least a partial role in neuropathic pain.
Sciatic nerve ligation induces the increase in the expression of miR-21 in the DRG and blood exosomes via IL-6 signaling pathway. Therefore, miR-21 could be a diagnostic biomarker for the neuropathic pain.