Circulating microRNA expression profile: a novel potential predictor for chronic nervous lesions

The mechanisms of chronic neuropathic pain are not clear. Serum microRNAs (miRNAs) might show a special feature for chronic nervous lesions. However, little is known about the changes in circulating miRNAs for the neuropathic pain. Therefore, changes in the circulating miRNAs expression profile for the neuropathic pain were investigated. Serum was collected from rats before and after spinal nerve ligation (SNL) surgery, and a microarray analysis was performed to determine the changes in miRNA expression profile. The expression of inflammatory cytokines in serum from the same individuals, including interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and monocyte chemotactic protein-1 (MCP-1), was also measured. The results showed that the expression levels of IL-6, TNF-alpha, and MCP-1 were significantly elevated in SNL rats which were significantly correlated with pain levels. Nine miRNAs with significantly different expression levels before and after SNL surgery were identified by microarray analysis, which were further validated by quantitative real-time polymerase chain reaction analyses. Compared with naive rats without SNL surgery, the expression of five miRNAs (hsa-miR-221, hsa-miR-34c, hsa-miR-21, hsa-miR-30a-5p, and hsa-miR-206) in the serum of rats after SNL surgery was decreased and four miRNAs (hsa-miR-31-5p, hsa-miR-133b, hsa-miR-22, and hsa-miRPlus-A1087) were increased, suggesting that miRNA changes may involve in the regulation of neuropathic pain. TargetScan was used to predict mRNA targets for these miRNAs, and the results showed that the transcripts with multiple predicted target sites belonged to neurologically important pathways. Bioinformatics analysis revealed that several target genes are related to the activation of cell signaling associated with nervous lesions. In this study, the changes to miRNA profiles in serum under neuropathic pain conditions were shown for the first time, suggesting that circulating miRNAs profile in serum is a potential predictor for neuropathic pain.