tACS suppresses M1 polarization of microglia after spinal cord injury through the cGMP-PKG signaling pathway

Background Strategies for repairing spinal cord injury (SCI) emphasize blocking the shift of microglia to the pro-inflammatory M1 phenotype, lowering neuroinflammation, and fostering neuronal survival. The cGMP-PKG pathway modulates immune cell function by decreasing the secretion of pro-inflammatory elements such as IL-1β and TNF and boosting the levels of the anti-inflammatory element IL-10, thereby alleviating inflammatory responses. Additionally, transcranial alternating current stimulation (tACS) at specific frequencies may indirectly regulate immune cell activity and inflammatory cytokine secretion by modulating the autonomic nervous system, thereby demonstrating anti-inflammatory potential. Objective To assess how tACS influences microglial polarization following SCI and investigate the underlying molecular mechanisms. Methods Proteomics sequencing, Western blotting, ELISA, Nissl staining, hematoxylin and eosin (HE) staining, real-time quantitative PCR (qPCR), immunofluorescence, live/dead staining and other experimental techniques were employed. Furthermore, an in vivo rat model was used to determine the effect of tACS on the recovery of motor function following injury. Results The polarization of glial cells towards the M1 proinflammatory phenotype was partially suppressed by tACS, thereby alleviating neuroinflammation and improving neuronal survival to promote functional recovery after SCI. Mechanistic studies revealed that tACS modulates the conversion of the glial inflammatory phenotype by initiating the cGMP-PKG signaling pathway, thereby offering neuroprotective and anti-inflammatory effects. Conclusion The activity of the cGMP-PKG signaling pathway is upregulated by tACS, thereby modulating microglial polarization, suppressing neuroinflammation and protecting neurons from inflammatory injury. As a non-invasive neuromodulation technique, tACS holds potential as a therapeutic approach for SCI.