Dherwani, R. | bioRxiv Science

bioRxiv2025

Stc1-expressing myofibroblasts are a developmentally distinct lineage cleared through intrinsic apoptosis in the neonatal lung

Lung myofibroblasts are necessary for early postnatal alveolar growth and develop again during pathological fibrosis. Determining the unique contributions of multiple myofibroblast lineages to development and disease is hampered by a lack of genetic tools to distinguish between them. In this study, we generated a Stc1CreERT2 mouse line that faithfully labels the developmentally transient secondary crest myofibroblasts (SCMF) and distinguishes SCMFs from alveolar duct myofibroblasts (DMF) and smooth muscle. SCMF populations expand by clonal proliferation of Stc1-expressing progenitors and contract by apoptosis. We deleted the intrinsic apoptosis effectors Bax and Bak1 in the Stc1-lineage, which prevented SCMF clearance during alveologenesis. Single-cell RNA-seq revealed that residual Stc1-lineage cells lacking Bax and Bak1 lose myofibroblast identity but express a combination of SCMF and DMF marker genes. Embryonic lineage tracing identified that SCMFs and DMFs have distinct progenitor populations with unique niches, and genetic activation of developmentally important signaling pathways could not interconvert these lineages. These findings establish Stc1-lineage SCMFs as a discrete population, developmentally divergent from DMFs, and define their life cycle in isolation from other myofibroblast lineages.

developmental biology↗

bioRxiv2024

Aberrant Transitional Alveolar Epithelial Cells Promote Pathogenic Activation of Lung Fibroblasts in Preclinical Fibrosis Modeling

Pulmonary fibrosis (PF) is a chronic progressive lung disease histopathologically characterized by fibrotic remodeling and the presence of pathological epithelial and mesenchymal cell populations in the distal lung parenchyma. Within the epithelial compartment, a subset of alveolar type 2 cells (AT2s) enter and persist in an aberrant transitional state. Whether and how these aberrant transitional cells participate in lung fibrosis is not known. To address this, we exploited the SftpcC121G mouse model, where we previously demonstrated that chronic expression of a PF-associated point mutation (C121G) in the AT2-specific surfactant protein C (Sftpc) gene results in spontaneous and progressive fibrosis driven by intrinsic AT2 dysfunction. We utilized single cell RNA sequencing to demonstrate the emergence of pathologic epithelial and mesenchymal cells in the SftpcC121G murine lung fibrosis model, including aberrant transitional alveolar epithelial cells as well as transitional and fibrotic fibroblasts. Aberrant transitional alveolar epithelial cells share similar transcriptional profiles to human aberrant basaloid cells, including the upregulation of profibrotic gene markers (Fn1, Ctgf, Tgfb2, Pdgfb, Spp1), and develop a unique interactome with pathogenic lung fibroblasts. We developed a method to reliably flow sort aberrant transitional alveolar epithelial cells, and we highlight their ability to cause fibrotic activation of fibroblasts in ex vivo organoid assays and using conditioned supernatant, suggesting a profibrotic secretome. We conclude that aberrant transitional alveolar epithelial cells actively contribute to fibrotic lung remodeling through pathogenic activation of alveolar fibroblasts.

cell biology↗