The AMPK pathway triggers autophagy during CSF1-induced microglial activation and may be implicated in inducing neuropathic pain.

The development and maintenance of neuropathic pain is now given far more attention in the clinic work. Increasing evidence has shown that colony-stimulating factor 1 (CSF1) is involved in microglial activation and may further induce pain. Here, we observed the signaling events that link the CSF1-induced microglial activated and consequences for pain processing. For the in vitro study, flow cytometry showed the microglial activity was markedly increased after CSF1 stimulation. Western blot showed the increased expression of p-PRKAA1/PRKAA1, p-AMPK/AMPK, p-ULK1/ULK1, p-S6k/S6k and LC3-II/LC3-I. QRT-PCR showed the IL-1, TNF-α and BDNF were simultaneously upregulated in the activated microglia cells, whereas the specific AMPK inhibitor compound C exhibited reverse effects in microglia. Using immunofluorescence staining and electron microscopy, we found CSF1 decreased microglial p62 expression and induced the number of autophagosomes, whereas compound C significantly exhibited the reverse effects. For the in vivo study, compared with the control and AMPK-siRNA transfection, the mice under CSF1 intrathecal injection increased CSF1 receptor and LC3 expressed in the activated spinal microglia. More importantly, qRT-PCR showed CSF1 intrathecal injection substantially upregulated BDNF and c-Fos mRNA expression as well as the ensuing neuropathic pain. Our findings demonstrated that CSF1 induced a significant upregulation of microglial activation via the AMPK signaling pathway and resulted in an increasing microglial autophagic level. An increasing CSF1 level in the central nervous system can mimic and cause pain syndromes by up-regulation of AMPK-depended autophagy, thus offering a new target for the therapy of neuropathic pain.

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Declaration of Competing Interest The authors have no conflicts of interest to declare.