Relationship between α7nAChR signaling pathway and regulatory T cells during vagus nerve stimulation-induced reduction of endotoxin-caused acute lung injury in mice

Abstract

Objective To evaluate the relationship between α7 nicotinic acetylcholine receptor (α7nAChR) signaling pathway and regulatory T cells (Tregs) during vagus nerve stimulation-induced reduction of endotoxin-caused acute lung injury (ALI) in mice. Methods Clean-grade healthy male C57BL/6 mice, aged 6-8 weeks, weighing 22-25 g, were divided into 5 groups (n=10 each) using a random number table method: control group (group C), group ALI, vagus nerve stimulation group (group VNS), α-BGT group (group α-BGT) and vagus nerve stimulation plus α-BGT group (group VNS + α-BGT). After successful establishment of the model, the vagus nerve was stimulated for 30 s with a stimulus intensity of 0.5 mA, frequency of 20 Hz, an interval of 5 min, 60 min in total.Sterile normal saline 100 μl was injected into the trachea, and the vagus nerve was only exposed but not stimulated in group C. In group ALI, the ALI model was established, and the vagus nerve was isolated but not stimulated.In group α-BGT, α-BGT 1 μg/kg was intraperitoneally injected, the ALI model was established 1 h later, and the vagus nerve was isolated but not stimulated.In group VNS+ α-BGT, α-BGT 1 μg/kg was intraperitoneally injected, the ALI model was established 1 h later, and the vagus nerve was stimulated at 1 h after the end of establishment.Animals were sacrificed at 72 h after establishing the model, and lungs were removed for determination of lung water content, percentage of Tregs (using flow cytometry), myeloperoxidase (MPO) activity (by colorimetric assay), expression of α7nAChR (by Western blot) and contents of interleukin-10 (IL-10), transforming growth factor-β (TGF-β) and IL-1β (by enzyme-linked immunosorbent assay). Results Compared with group C, the lung water content, MPO activity and IL-1β content were significantly increased in the other four groups, the expression of α7nAChR was significantly down-regulated in ALI, α-BGT and VNS+ α-BGT groups, the percentage of Tregs was significantly increased in group VNS, the IL-10 content was significantly decreased in ALI and α-BGT groups and increased in VNS and VNS+ α-BGT groups, and TGF-β contents were significantly decreased in ALI, α-BGT and VNS+ α-BGT groups and increased in group VNS (P<0.05). Compared with group ALI, the lung water content, MPO activity and IL-1β content were significantly decreased, the expression of α7nAChR was up-regulated, and the percentage of Tregs and contents of IL-10 and TGF-β were increased in group VNS, and the TGF-β content in group α-BGT and contents of IL-10 and TGF-β in group VNS+ α-BGT were significantly increased (P<0.05). Compared with group VNS, the lung water content, MPO activity and IL-1β content were significantly increased, the expression of α7nAChR was down-regulated, and the percentage of Tregs and contents of IL-10 and TGF-β were decreased in α-BGT and VNS+ α-BGT groups (P<0.05). The contents of IL-10 and TGF-β were significantly higher in group VNS+ α-BGT than in group α-BGT (P<0.05). Conclusion Vagus nerve stimulation can activate α7nAChR signaling pathway and raise the percentage of Tregs, thus reducing ALI in mice. Key words: Vagus nerve; Respiratory distress syndrome, adult; T-Lymphocytes, regulatory; Receptors, nicotinic