Vagal α7nAChR signaling regulates α7nAChR(+)Sca1(+) cells during lung injury repair

BACKGROUND: The distal airways of the lung and bone marrow are innervated by the vagus nerve. Vagal α7nAChR signaling plays a key role in regulating lung infection and inflammation; however, whether this pathway regulates α7nAChR(+)Sca1(+) cells during lung injury repair remains unknown. We hypothesized that vagal α7nAChR signaling controls α7nAChR(+)Sca1(+) cells, which contribute to the resolution of lung injury. METHODS: Pneumonia was induced by intratracheal challenge with E. coli. The bone marrow mononuclear cells (BM-MNCs) were isolated from the bone marrow of pneumonia mice for immunofluorescence. The bone marrow, blood, BAL, and lung cells were isolated for flow cytometric analysis by labeling with anti-Sca1, VE-cadherin, p-Akt1, or Flk1 antibodies. Immunofluorescence was also used to examine the coexpression of α7nAChR, VE-cadherin, and p-Akt1. Sham, vagotomized, α7nAChR knockout, and Akt1 knockout mice were infected with E. coli to study the regulatory role of vagal α7nAChR signaling and Akt1 in Sca1(+) cells. RESULTS: During pneumonia, BM-MNCs were enriched with α7nAChR(+)Sca1(+) cells, and this cell population proliferated. Transplantation of pneumonia BM-MNCs could mitigate lung injury and increase engraftment in recipient pneumonia lungs. Activation of α7nAChR by its agonist could boost α7nAChR(+)Sca1(+) cells in the bone marrow, peripheral blood, and bronchoalveolar lavage (BAL) in pneumonia. Immunofluorescence revealed that α7nAChR, VE-cadherin, and p-Akt1 were coexpressed in the bone marrow cells. Vagotomy could reduce α7nAChR(+)VE-cadherin(+) and VE-cadherin(+)p-Akt1(+) cells in the bone marrow in pneumonia. Knockout of α7nAChR reduced VE-cadherin(+) cells and p-Akt1(+) cells in the bone marrow. Deletion of Akt1 reduced Sca1(+) cells in the bone marrow and BAL. More importantly, 91.3 ± 4.9% bone marrow and 77.8 ± 4.9% lung α7nAChR(+)Sca1(+)VE-cadherin(+) cells expressed Flk1, which is a key marker of endothelial progenitor cells (EPCs). Vagotomy reduced α7nAChR(+)Sca1(+)VE-cadherin(+)p-Akt1(+) cells in the bone marrow and lung from pneumonia mice. Treatment with cultured EPCs reduced ELW compared to PBS treatment in E. coli pneumonia mice at 48 h. The ELW was further reduced by treatment with EPCs combining with α7nAChR agonist-PHA568487 compared to EPC treatments only. CONCLUSIONS: Vagal α7nAChR signaling regulates α7nAChR(+)Sca1(+)VE-cadherin(+) EPCs via phosphorylation of Akt1 during lung injury repair in pneumonia.