In vitro culture of aberrant basal-like cells from fibrotic lung tissue

Rationale: In idiopathic pulmonary fibrosis (IPF) atypical epithelial cells are present in the alveolar compartment. Their origin and contribution to IPF pathogenesis is unknown. We recently cultured a distinct population of cells, which readily grew from fibrotic lung tissue, but only rarely from non-fibrotic tissue. Here we aimed to characterize these fibrosis-enriched cells and determine transcriptomic differences between cells derived from IPF and patients with other interstitial lung diseases (ILD). Methods: Cells were cultured from peripheral lung tissue of ILD patients and analysed by bulk or single cell RNA sequencing (scRNA-seq), TaqMan-PCR, immunofluorescence (IF), immunoblotting or electron microscopy (EM). Results: scRNA-seq demonstrated an overall homogeneity and epithelial origin of the cells. The majority of cells expressed basal cell markers (Cytokeratin (KRT) 5 and 17, TP63), of which a fraction co-expressed mesenchymal cell markers (VIM, FN1, CDH2), alveolar (SLC34A2, ABCA3, LPCAT1, EMP2, HOPX) and/or secretory epithelial cell markers (SCGB1A1, MUC4). Interestingly, most of the cells showed closest transcriptomic similarity to recently described aberrant basal-like cells. Cells derived from IPF versus other ILD patients revealed significant transcriptomic differences with an up-regulation of fibrosis-associated and a down-regulation of inflammatory pathways in IPF cells. Conclusion: We here confirm the presence of aberrant basal-like cells in fibrotic lung tissue and, importantly, are the first to describe their in vitro characteristics and a way of culturing these cells in vitro. Cultured basal-like cells co-express epithelial and mesenchymal markers, suggesting a partial epithelial to mesenchymal transition (EMT). A subset of cells co-express alveolar, ciliated or secretory epithelial cell markers, possibly indicating differentiation towards these cell linages. Furthermore, cultured basal-like cells display a disease-specific transcriptome, possibly induced by their specific microenvironment. Our findings will contribute to a better understanding of the cells origin and their potential contribution to IPF pathogenesis.