Pulmonary fibroblast subsets demonstrate differentially enriched signaling pathways during fibrosis resolution and repair.

The lungs have a remarkable capacity to undergo homoeostatic repair and regeneration after injury, which often occurs in patients with acute respiratory distress syndrome (ARDS) and in the single-dose bleomycin mouse model. Fibroblasts are critical mediators of fibrotic disease and RNA sequencing has identified significant heterogeneity within pulmonary fibroblast populations. However, the contribution of distinct fibroblast subsets to the repair process has been understudied compared with their role in fibrosis initiation and progression. Therefore, we sought to define the transcriptional landscape of 3 phenotypically defined fibroblast subsets that occupy discrete spatial locations in naive lungs. Using TdTomato-lineage tracing approaches, we identified and interrogated collagen1a1+ (Col1a1) fibroblasts, perilipin 2+ (Plin2) alveolar fibroblasts, and α-smooth muscle actin+ (Acta2) myofibroblasts during fibrosis development and resolution after single-dose bleomycin. Quantification of fibroblast numbers showed that all 3 subsets expanded during fibrosis and contracted toward naive levels with resolution. Principal component and gene set enrichment analyses indicate that each subset underwent major transcriptomic shifts during fibrosis development, converging on a similar profibrotic transcriptional profile. However, during resolution, Plin2+ and Acta2+ fibroblasts reverted toward a prefibrotic transcriptional state, whereas Col1a1+ fibroblasts acquired a distinct program that suggests an active role in mediating the repair processes.