Microglia inflammatory response contributes to chronic constriction injury-induced neuropathic pain via miR-339/PFKFB3 axis

Purpose: To investigate the effect of miR-339 on neuropathic pain. Methods: A rat neuropathic pain model was established through chronic constriction injury (CCI). Expression of miR-339 in spinal cord was determined 14 days later. Microglial inflammatory response was evaluated using immunofluorescence analysis of ionized calcium binding adaptor molecule 1 (Iba1), while IL-6 and TNF-α were assessed by enzyme-linked immunosorbent assay (ELISA). Pain- associated behavioral effects and microglia-related inflammation were investigated after intrathecal administration of miR-339 agomir into rats post-CCI. The target gene of miR-339 involved in neuropathic pain was evaluated by a luciferase reporter assay. Microglia cells were isolated from rats, then treated with lipopolysaccharide (LPS). The LPS-induced inflammatory response in microglia cells was determined using quantitative reverse transcription PCR analysis of IL-6 and TNF-α. Results: CCI decreased mechanical allodynia and thermal hyperalgesia thresholds, but increased Iba1, IL-6, and TNF-α in rats. MiR-339 was reduced in rat spinal cord after CCI induction while intrathecal injection of miR-339 agomir alleviated CCI-induced changes in mechanical and thermal hyperalgesia in rats, and reversed expression of Iba1, IL-6, and TNF-α. Furthermore, 6-phosphofructo-2- kinase/fructose-2,6-bisphosphatase-3 (PFKFB3) was identified as a miR-339 target gene, and over- expression of miR-339 decreased the expression of PFKFB3, IL-6, and TNF-α in LPS-induced microglia cells. Conclusion: The miR-339/PFKFB3 axis ameliorates CCI-induced neuropathic pain by suppression of microglia inflammatory response, suggesting a novel strategy for neuropathic pain management