CX3CL1/CX3CR1Regulates Nerve Injury-induced Pain Hypersensitivity Through The ERK5Signaling Pathway

Objective:To explore whether CX3CR1contributes to nerve injury-induced spinal microglia activation through the phosphorylation of ERK5, and the role of the spinal microglial CX3CR1/ERK5pathway in the development and maintain of neuropathic pain.Methods:To produce SNL, the L5spinal nerve of male SD rats was isolated and tightly ligated with6-0silk thread. The expression of activated ERK5(p-ERK5) was investigated by immunohistochemistry test. The cell types for the expression of p-ERK5was examined by double-immunoiluorescence histochemical staining. To detect the role of ERK5in neuropathic pain, PWT and PWL was measured with Von Frey hairs and plantar analgesia instrument respectively after intrathecally knockdown of ERK5. For determining the regulating effect of CX3CL1/CX3CR1on activity of microglial ERK5, CX3CR1was blocked by intrathecally injection of anti-rat CX3CR1antibody in SNL rats, and the activity of spinal ERK5was tested; then weather intrathecally knockdown of ERK5can reverse the effect of CX3CL1on pain hypersensitivity and microglia activation was investigated.Results:The expression of p-ERK5-IR cells was significantly increased after SNL as compared to control group. Double-immunoiluorescence histochemical staining revealed extensive co-localization of p-ERK5-IR cells with Ibal (microglial marker), but not with NeuN(neuronal marker) and GFAP(astrocyte marker).The knockdown of the ERK5by the intrathecal injection of antisense oligonucleotides suppressed the activation of the transcription factor NF-κB and the hyperalgesia induced by nerve injury. The blockage of CX3CR1, the receptor of CX3CL1, significantly reduced the level of ERK5activation following SNL. In addition, the antisense knockdown of ERK5reversed the CX3CL1-induced hyperalgesia and spinal microglia activation.Conclusion:(1)CX3CL1/CX3CR1contributes to nerve injury-induced spinal microglia activation through the phosphorylation of ERK5.(2)CX3CL1/CX3CR1participates in the transduction of the nociceptive signaling between neurons and spinal microglia (3) CX3CR1/ERK5signaling pathway may be involved in the modulation of pain signals by regulating NF-κB-dependent gene expression.