STING/NF-κB/IL-6-mediated inflammation in microglia contributes to spared nerve injury (SNI)-induced neuropathic pain

Background Innate immune response acts as a first line of host defense against damage and are initiated following the recognition of pathogen-associated molecular patterns (PAMPs). For double-stranded DNA (dsDNA) sensing, interferon gene stimulator (STING) was discovered to be an integral sensor, and could mediate the immune and inflammatory response. However, it is unclear the underlying mechanisms of STING in the development of neuropathic pain. Methods Neuropathic pain model was established by spared nerve injury (SNI). STING agonist DMXAA was introduced into BV-2 cells to assess the inflammatory response in microglia cells. Selective STING antagonist C-176 were administered in the early and late stage following SNI and the mechanical sensitivity and thermal responsiveness were assessed using Von Frey filaments and hot plate tests separately. To investigate the underlying mechanisms, recombinant IL-6 was injected intrathecally and its downstream effectors were examined. The level of dsDNA in the peripheral blood following SNI was assessed using Elisa analysis. STING signaling pathway and its downstream effectors were assessed by qPCR, western blots, Elisa and immunofluorescence staining. Meanwhile, microglia activation and proinflammatory cytokines expression were also assessed in the spinal cord. Results We found dsDNA was significantly increased and STING signaling pathway was activated in dorsal horn microglia following SNI, and our study using BV-2 cells showed that DMXAA significantly activated STING/TANK-binding kinase 1 (TBK1)/nuclear factor-kappa B (NF-κB) pathway, and increased the production of proinflammatory cytokines, as well as phosphorylated the Janus-activated kinase 2/signal transducer activator of transcription 3 (JAK2/STAT3) signal in microglia. Early but not late intrathecal injection of C-176 attenuated SNI-induced pain hypersensitivity, microglia activation, proinflammatory factors and phosphorylated JAK2/STAT3 in the spinal cord dorsal horn. Last, the analgesic effect of C-176 were greatly abolished by recombinant IL-6 following SNI. Conclusions We provided evidence clarifying dsDNA mediated activation of microglial STING signaling pathway, after which promoting expression of proinflammatory cytokines that are required for central sensitization in the spinal cord dorsal horn of SNI model. Further analysis showed that microglial STING/TBK1/NF-κB may contribute to hyperalgesia initiation via IL-6/JAK2/STAT3 signaling. Pharmacological blockade of STING may be a promising target during the initiation of neuropathic pain.