Intermittent theta burst stimulation regulates microglial polarization through Cry1 to enhance neuroplasticity for stroke recovery

Background: Neuroplasticity is crucial for functional recovery after stroke, with modulation of microglial polarization enhancing this process. Intermittent theta burst stimulation (iTBS), as a neuromodulation technique, can simultaneously generate electric and magnetic fields to act on the central nervous system. Neurons can induce electrochemical signal transduction as excitable cells. Meanwhile, iTBS can regulate microglial inflammatory polarization post-stroke. However, how iTBS exerts its effect on microglia remains unclear. The magnetoreceptive protein Cryptochrome (Cry) can respond to the magnetic effect and is known to regulate macrophage-mediated inflammatory responses. However, whether iTBS modulates microglial polarization through Cry1 is unknown. Objective: To explore the magnetic effects of iTBS on microglial polarization through Cry1, thereby enhancing neuroplasticity and stroke recovery, and also elucidate the role of the Cry1-NF-κB pathway in iTBS-mediated regulation of microglial polarization. Methods: A mouse model was established using photothrombosis (PT), followed by 7-day iTBS intervention. BV2 cells and primary neurons were subjected to oxygen-glucose deprivation/reperfusion (OGD/R) respectively, followed by once-daily iTBS treatment for two days. Brain damage and functional recovery were assessed using Map-2 staining and behavioral tests. RT-PCR, western blot, immunofluorescence and transwell co-culture experiments were employed to evaluate the effects of iTBS on microglial polarization and neuroplasticity. Cry1 knockdown via siRNA transfection was used to explore the Cry1-NF-κB signaling pathway. Results: iTBS ameliorated neuronal damage induced by ischemic injury, reduced pro-inflammatory microglial activation, and promoted anti-inflammatory polarization. Cry1 expression was upregulated in BV2 cells in response to iTBS, while Cry1 knockdown increased CD16 expression, decreased CD206 expression and further alleviate the inhibition of NF-κB activation. In primary neurons, anti-inflammatory microglia induced by iTBS could enhance neuroplasticity. Conclusion: This study demonstrates that post-stroke iTBS promotes neuroplasticity and functional recovery by regulating microglial polarization via the Cry1-NF-κB pathway.