Mesenchymal-Epithelial Interactome Analysis Reveals Essential Factors Required for Fibroblast-Free Alveolosphere Formation

Lung epithelial cells and fibroblasts are key cell populations in lung development. Fibroblasts support type 2 alveolar epithelial cells (AEC2) in the developing and mature lung. However, fibroblast-AEC2 interactions have not been clearly described. We addressed this in the present study by time course serial analysis of gene expression sequencing (SAGE-seq) of epithelial cells and fibroblasts of developing and mature murine lungs. We identified lung fibroblast-epithelial interactions that potentially regulate alveologenesis and are mediated by fibroblast-expressed ligands and epithelial cell surface receptors. In the epithelial-fibroblast co-culture alveolosphere formation assay, single intervention against fibroblast-expressed ligand or associated signaling cascades promoted or inhibited alveolosphere growth. Adding the ligand-associated molecules fibroblast growth factor 7 and Notch ligand and inhibitors of bone morphogenetic protein 4, transforming growth factor β, and glycogen synthase kinase-3β to the culture medium enabled fibroblast-free alveolosphere formation. The results revealed the essential factors regulating fibroblast-AEC2 interactions.