The Role Of The Vagus Nerve In Preventing Acute Lung Injury: Uncovering the Gut-Lung Axis

Introduction: We have previously shown that vagal nerve stimulation (VNS) has a protective effect against gut epithelial barrier breakdown following injury. We have also shown that VNS prevents acute lung injury from developing 24 hours after burn insult. However, the connection between gut protection and prevention of acute lung injury has yet to be investigated. We hypothesized that taking away the VNS protection to the gut mucosal barrier by performing an abdominal vagotomy (AV), acute lung injury would occur as in animals that do not undergo VNS. Methods: Abdominal vagotomy and VNS were performed prior to 30% TBSA burn in male Balb/c mice and compared to sham, VNS/burn, and burn alone groups. Lung injury was assessed by histology, myeloperoxidase (MPO) and ICAM-1 immunostaining at 24 hours after burn. MPO enzymatic assay and lung IL-8 levels (ELISA) were measured. Lung phospho-IκBα immunoblots were performed to correlate with NF-κB activation measured with bioluminescence by photon emission analysis (IVIS Lumina Xenogen). This bioluminescent measurement was performed using engineered NF-κB-luc transgenic animals. Results: At 6 hours post burn, an increase in phosphorylation of both NF-κB p65, via bioluminescence, and IkBα by immunoblot, were observed. The figure demonstrates increased NF-κB activation in the lung evidenced by increased red color in the image. VNS blunted NF-κB activation in animals with intact abdominal vagus nerves, whereas AV eliminated such protection. Acute lung injury defined by significant pulmonary edema, intra-alveolar hemorrhage, and hyaline membrane formation was present in burn and AV animals but not in sham or VNS-treated animals. Neutrophil infiltration in the lung measured by MPO positive staining cells was increased in burn and AV animals compared to VNS-treated and sham animals. MPO enzymatic assay, ICAM-1 expression on pulmonary endothelium, and IL-8 levels in lung tissue were increased in AV and burn animals. Conclusions: Prevention of acute lung injury by VNS is dependent on the protective effects at the gut epithelial barrier. These results established the importance of the gut-lung axis after injury in the genesis of acute lung injury.