Non-invasive Vagus Nerve Stimulation Protects Against Cerebral Ischemia/Reperfusion Injury and Promotes Microglial M2 Polarization Via Interleukin-17A Inhibition.

Microglia play an essential role during cerebral an ischemia/reperfusion (I/R)-related inflammatory process. Because the M2 phenotype of microglia exhibits anti-inflammation activity, it has become a promising target for anti-inflammatory therapy. Vagus nerve stimulation (VNS) reportedly has neuroprotective effects against cerebral I/R injuries via its anti-inflammatory action. The aim of this study was to investigate the ability of non-invasive VNS (nVNS) to alleviate cerebral I/R in mice by promoting microglial M2 polarization. Neurological scoring and cerebral infarct volume assessments were performed 72 h after a middle cerebral artery occlusion (MCAO)-induced stroke. M2 phenotype microglia were identified by immunohistochemistry staining using Arg-1 and Iba-1 antibodies. The protein expressions of Arg-1, IL-17A, IL-10, Bax, and Bcl-2 were detected by Western blot. Apoptotic cells were detected using TUNEL staining. According to our results, nVNS decreased infarct volume, improved neurological outcomes, reduced apoptotic neurons (TUNELNeuN cells), and promoted microglial M2 polarization as indicated by elevated Arg-1 protein expression and increased Arg-1 cells after MCAO. Moreover, nVNS attenuated the increased levels of IL-17A protein expression after MCAO. To test the possible involvement of IL-17A in nVNS-induced neuroprotection and microglial M2 polarization, 1-μg recombinant IL-17A (rIL-17A) was intranasally administered once daily for three consecutive days after reperfusion. We found that the intranasal administration of rIL-17A nullified the nVNS-induced promotion of microglial M2 polarization. Furthermore, rIL-17A administration abolished the neuroprotective effect of nVNS. In conclusion, our study identifies microglial M2 polarization as an important mechanism underlying the nVNS-mediated neuroprotection against cerebral I/R. This effect of nVNS could be attributed to the inhibition of IL-17A expression.