RUNX2 promotes pulmonary fibrosis through the conversion of alveolar fibroblasts into pathological fibroblasts

A hallmark of pulmonary fibrosis is aberrant activation of lung fibroblasts into pathological fibroblasts producing excessive extracellular matrix (ECM). Thus, identification of key regulator(s) driving the generation of pathological fibroblasts can inform effective countermeasures against disease progression. In this study, we show that Leptin Receptor (Lepr)+ fibroblasts arising during alveologenesis include Signal Peptide-CUB-EGF Domain-containing Protein 2 (Scube2)+ alveolar fibroblasts as a major constituent significantly contributing to collagen triple helix repeat containing 1 (Cthrc1)+ Periostin (Postn)+ pathological fibroblasts in two mouse models of pulmonary fibrosis. Genetic ablation of the Postn+ pathological fibroblasts attenuates fibrosis. Comprehensive analysis of single cell RNA sequencing (scRNA-seq) and single cell Assay for Transposase-Accessible Chromatin sequencing (scATAC-seq) reveal Runt related transcription factor 2 (RUNX2) as a key regulator of fibrotic genes. Consistently, conditional deletion of Runx2 with Lepr-CreERT2 or Scube2-CreERT2 reduces the generation of pathological fibroblasts, ECM deposition, and pulmonary fibrosis. Therefore, Lepr+ derived fibroblasts which include Scube2+ alveolar fibroblasts are a key source of pathological fibroblasts, and targeting Runx2 provides a potential treatment option for pulmonary fibrosis. Single cell ATAC-seq from sorted adult lung mesenchymal cells (Epcam-CD31-CD45-) of saline control and Bleomycin (BLM) treated mice. Bleomycin sample are from wild type B6 male, single dose bleo (1.0U/kg). Control sample are from wild type B6 male. Lungs are harvested at Day 14 post administration.