Abstract Rationale ARDS involves the death of type I alveolar epithelial cells, which are then repopulated by a progenitor population that is a subset of type II alveolar epithelial cells. Alveolar epithelial cells are in continuous contact with alveolar macrophages, but the mechanistic role of the interactions between these cells are undefined. Connexin-43 (Cx43) is a hemichannel that, when connected on adjoining cells, forms a gap junction, and is expressed by both alveolar macrophages and epithelial cells. We hypothesized that alveolar macrophages protect against ARDS through Cx43-mediated communication with alveolar epithelial progenitors. Materials and Methods We generated mice with deletion of core-binding factor-β in the myeloid compartment (LysM-Cre+/-, CBFβ-fl/fl) that lack alveolar macrophages, mice with Cx43 deletion on CD11c-expressing cells (CD11c-Cre+/-, Cx43-fl/fl), and mice with Cx43 deleted on alveolar epithelial progenitor cells (Tfc2l1-Cre+/-, Cx43-fl/fl). We used intra-tracheal bleomycin administration to induce acute lung injury and pulse oximetry, histology, bronchoalveolar lavage fluid analysis, and soluble collagen content were used to determine lung inflammation, injury, and fibrosis. Lung immune cell components and epithelial cells were tested by flow cytometry. Alveolar were isolated using Siglec-F beads, and transferred intranasally to recipient mice. PKH26 was intranasally administered to mice one day before bleomycin for labeling resident alveolar macrophages. Results In comparison to littermate controls, mice with alveolar macrophage deficiency were healthy at baseline but developed progressively hypoxia and mortality in the first week after bleomycin administration, with higher BAL albumin content and lung leukocyte infiltration, but no difference in fibrosis. In mice with selective deletion of Cx43 on CD11c+ cells, bleomycin challenge resulted in a similar predisposition to lung injury and reduced survival of resident alveolar macrophages. Furthermore, the susceptibility of mice with alveolar macrophage deficiency to lung injury was rescued with transfer of wildtype, but not Cx43-deficient, alveolar macrophages. Lastly, selective ablation of Cx43 on alveolar epithelial progenitor cells resulted in similarly more severe lung damage after bleomycin challenge. In addition, these mice had a dramatic reduction in both the number of type I alveolar epithelial cells and resident alveolar macrophages as compared with in littermate controls. Conclusions Our study identifies the critical role of Cx43-mediated crosstalk between alveolar macrophages and alveolar epithelial progenitor cells in protection against ARDS. This abstract is funded by: NIH R01AI135128 and R01HL169974
Qu et al. (Fri,) studied this question.