Abstract Introduction Idiopathic Pulmonary Fibrosis (IPF) is an age-related, chronic, progressive lung disorder mediated by an interaction between environmental exposures and an individual’s genetic risk. Shortened telomeres are found in Idiopathic Pulmonary Fibrosis (IPF) lung epithelial cells and are hypothesized to be molecular drivers of the disease. Rationale To study the contribution of telomere dysfunction to IPF, we previously developed a mouse model with type II alveolar epithelial (AT2) cell telomere dysfunction, which causes spontaneous lung fibrosis in mice. This study examines how the lung remodels in mice with AT2 cell telomere dysfunction in response to injury and whether it leads to non-resolving fibrosis. Methods Wild Type (WT) controls and Telomere Repeat-binding Factor 1 (TRF1) floxed mice which are Surfactant Protein C (SPC)-cre driven were used for experiments. TRF1 was conditionally deleted in SPC expressing AT2 cells. Mice were oropharyngeally administered normal saline or low dose bleomycin (bleo) (0.625 U/Kg) 2 weeks after initiation of weekly tamoxifen injections, which were continued for 2 months following bleomycin instillation. Mice were classified into 3 groups: WT control, WT-Bleo and TRF1-Bleo. For single cell RNA-sequencing (scRNA-seq), whole lung single cell suspension was prepared, and all live cells were analyzed. Results Non-resolving fibrosis was achieved by the combination of telomere dysfunction and low dose bleomycin administration. Histology demonstrated lung remodeling with significantly elevated hydroxyproline levels in TRF1-Bleo compared to WT-Bleo where fibrosis resolved. scRNA-seq demonstrated cellular heterogeneity in immune, epithelial and fibroblast populations. A ∼6-fold lower AT2 and 4-fold higher basal cell proportions was observed in epithelial cells of TRF1-Bleo group compared to WT-Bleo and TRF1 controls. Immunofluorescence staining confirmed enrichment and proliferation of Krt5+ basal cells in fibrotic areas compared to TRF1 controls. The emergence of two distinct pathologic basal cell clusters was observed in epithelial cells. A Krt15+ progenitor basal cell cluster that co-expressed collagen binding protein Abi3bp was enriched in TRF1-Bleo. A second basal cell cluster expressed Trp63+Krt14+ and Trp63+Krt14- populations and exclusively present in TRF1-Bleo likely attempting to regenerate the epithelium. Conclusions A combination approach of telomere dysfunction with bleomycin injury resulted in non-resolving fibrosis. Many of these additional elements of remodeling are present in IPF lungs. Krt15+ and Krt14+ progenitor basal cells identified in this model are both present in IPF and may contribute to the progression of idiopathic lung fibrosis. This abstract is funded by: NIH R01HL139897 (P.J.W.) and an investigator-initiated grant from Sanofi
Naikawadi et al. (Fri,) studied this question.