Gut microbiota modulates lung fibrosis severity following acute lung injury

Independent reports note the significance of gut microbiota on lung disease severity; however, studies using murine models to define the role of the gut microbiome in pulmonary fibrosis progression are missing. We used the bleomycin murine model to quantify lung fibrosis in C57BL/6J mice housed in germ-free, animal biosafety level 1 (ABSL-1), or animal biosafety level 2 (ABSL-2) environments. Mice housed in gnotobiotic facilities are protected from bleomycin-induced pulmonary fibrosis, while ABSL-1 and ABSL-2 mice develop mild fibrosis and severe lung fibrosis, respectively. Metagenomic analysis of the gut microbiota revealed greater microbial diversity in ABSL-1 compared to ABSL-2 mice, with an increased presence of Lactobacilli and Bifidobacterium in ABSL-1 mice. Flow cytometric analysis of single-cell lung suspensions revealed enhanced IL-6/STAT3 /IL-17A signaling in CD4+ T cells of ABSL-2 mice, compared to ABSL-1 or germ-free mice. Fecal microbiota transplantation (FMT) of low microbial diverse stool (ABSL-2) into germ-free mice before bleomycin administration recapitulated the severe fibrosis phenotype, whereas FMT of ABSL-1 stool induced minimal fibrosis. These findings strongly support a causal role of the gut microbiota in augmenting pulmonary fibrosis severity after acute lung injury.