• Weijia Chen and Zhijun Lu.
• Department of Anesthesiology, Ruijin Hospital Luwan Branch, Shanghai Jiaotong University Medical School, No.149, Chongqing Nan Road, Shanghai, 200020, China.
• Neurochem. Res. 2017 Feb 1; 42 (2): 634-643.

AbstractMicroglia, rapidly activated following peripheral nerve injury (PNI), accumulate within the spinal cord and adopt inflammation that contributes to development and maintenance of neuropathic pain. Microglia express functional Toll-like receptors (TLRs), which play pivotal roles in regulating inflammatory processes. However, little is known about the role of TLR3 in regulating neuropathic pain after PNI. Here TLR3 expression and autophagy activation was assayed in dorsal root ganglions and in microglia following PNI by using realtime PCR, western blot and immunohistochemistry. The role of TLR3/autophagy signaling in regulating tactile allodynia was evaluated by assaying paw mechanical withdrawal threshold and cold allodynia after intrathecal administration of Poly (I:C) and 3-methyladenine (3-MA). We found that L5 spinal nerve ligation (SNL) induces the expression of TLR3 in dorsal root ganglions and in primary rat microglia at the mRNA and protein level. Meanwhile, L5 SNL results in an increased activation of autophagy, which contributes to microglial activation and subsequent inflammatory response. Intrathecal administration of Poly (I:C), a TLR3 agonist, significantly increases the activation of microglial autophagy, whereas TLR3 knockdown markedly inhibits L5 SNL-induced microglial autophagy. Poly (I:C) treatment promotes the expression of proinflammatory mediators, whereas 3-MA (a specific inhibitor of autophagy) suppresses Poly (I:C)-induced secretion of proinflammatory cytokines. Autophagy inhibition further inhibits TLR3-mediated mechanical and cold hypersensitivity following SNL. These results suggest that inhibition of TLR3/autophagy signaling contributes to alleviate neurophathic pain triggered by SNL.

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