RUNX2 promotes fibrosis via an alveolar-to-pathological fibroblast transition

A hallmark of pulmonary fibrosis is the aberrant activation of lung fibroblasts into pathological fibroblasts that produce excessive extracellular matrix^1-3. Thus, the identification of key regulators that promote the generation of pathological fibroblasts can inform the development of effective countermeasures against disease progression. Here we use two mouse models of pulmonary fibrosis to show that LEPR⁺ fibroblasts that arise during alveologenesis include SCUBE2⁺ alveolar fibroblasts as a major constituent. These alveolar fibroblasts in turn contribute substantially to CTHRC1⁺POSTN⁺ pathological fibroblasts. Genetic ablation of POSTN⁺ pathological fibroblasts attenuates fibrosis. Comprehensive analyses of scRNA-seq and scATAC-seq data reveal that RUNX2 is a key regulator of the expression of fibrotic genes. Consistently, conditional deletion of Runx2 with Lepr^creERT2 or Scube2^creERT2 reduces the generation of pathological fibroblasts, extracellular matrix deposition and pulmonary fibrosis. Therefore, LEPR⁺ cells that include SCUBE2⁺ alveolar fibroblasts are a key source of pathological fibroblasts, and targeting Runx2 provides a potential treatment option for pulmonary fibrosis.