Hoffman, E. T. | bioRxiv Science

bioRxiv2026

Inflammatory Fibroblasts Promote Repair After Injury Through Epithelial Proliferation

Fibroblast heterogeneity after lung injury is a well observed phenomenon made highly relevant by the widespread application of single cell RNA-sequencing. The characterization of homeostatic and injury associated states has led to the identification of a population of fibroblasts that emerge during inflammation and express cytokines that may potentially amplify the inflammatory circuit. However, whether these cells actively contribute to inflammation or serve an alternative function within the broader injury-repair cascade remains unclear. By integrating several robust murine lung injury data sets we establish the persistence of the inflammatory fibroblast across multiple injury models and identify a role for these cells in lung repair after injury through effects on alveolar epithelial proliferation. We validate this observation in-vivo using a genetic model of spontaneous lung fibrosis and in-vitro with mixed alveolar organoid cultures of various homeostatic and injury associated fibroblasts wherein we identify a mesenchymal-epithelial BMP signaling axis as a key driver of the AT2 cell injury repair response. Finally, we present supporting evidence from human disease, reinforcing the relevance of this fibroblast subset in pathological settings. These findings extend critical observations made prior to the single-cell era and contribute to our evolving understanding of fibroblast heterogeneity as a key feature of lung repair.

molecular 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↗