miR-185-5p alleviates CCI-induced neuropathic pain by repressing NLRP3 inflammasome through dual targeting MyD88 and CXCR4

MicroRNAs (miRNAs) are important modulators in the evolvement and progression of neuropathic pain (NP). According to reports, miR-185-5p contributes to various diseases and inflammatory responses. However, it is not clear whether miR-185-5p mediates neuroinflammation and NP following chronic constrictive injury (CCI). The CCI model was constructed in rats to induce NP. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were employed to evaluate pain threshold in CCI rats. The expression of miR-185-5p, GFAP, Iba1, Caspase-3-positive cells, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL)-labeled apoptotic neurons, inflammatory mediators, including interleukin (IL)-6, IL-1 beta and tumor necrosis factor-alpha (TNF-alpha) in lumbar portion (L4-L6) of CCI rats were determined. Furthermore, the targets of miR185-5p were predicted by the Starbase, and the binding association between miR-185-5p and MyD88, miR-1855p and CXCR4 was verified by the dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. As shown by the data, miR-185-5p was distinctly reduced in L4-L6 spinal cord tissues of rats after CCI. Up-regulating miR-185-5p alleviated mechanical and thermal hyperalgesia, inactivated microglia and astrocytes accumulation, and abated the contents of IL-1 beta, IL-6 and TNF-alpha in L4-L6 spinal cord tissues of CCI rats. Bioinformatics analysis suggested that MyD88 and CXCR4 were potential target genes of miR-185-5p. Increasing miR-185-5p expression notably impeded the expression of MyD88, CXCR4 and NLRP3 inflammasome in BV2 microglia, while attenuating miR-185-5p expression exerted the opposite effects. Notably, down-regulating MyD88 and CXCR4 significantly enhanced the miR-185-5p-mediated anti-inflammatory effects, and reversed miR-185-5p inhibitor mediated proinflammatory effects. Additionally, up-regulating miR-185-5p repressed BV2-induced neuronal apoptosis and increased neuronal viability. In conclusion, this study suggested that miR-185-5p chokes CCIinduced NP and neuroinflammation by targeting MyD88 and CXCR4, indicating that miR-186-5p is an underlying therapeutic target for NP.