Emergence of fibrotic pericytes and their transcriptional regulation in pulmonary fibrosis.

Multiple cell types have been implicated in pathogenesis of pulmonary fibrosis with pericytes emerging as a new focus due to their role in promoting fibrotic remodeling. Fibrotic environment changes normal pericyte functions, but transcriptional programs regulating pericyte transition towards fibrotic state remain unclear. Utilizing single cell RNA-sequencing of human pulmonary fibrotic lungs and mouse genetic models, we identified a unique cluster of fibrosis-associated pericytes which was not present in normal lungs and exhibited a distinctive transcriptional signature indicating transition of normal pericytes to a fibrotic state. FOXF1 was identified as one of the transcription factors decreased in fibrotic pericytes. Pericyte-specific deletion of Foxf1 increased severity of pulmonary fibrosis in bleomycin mouse model as demonstrated by reduced survival, impaired lung functions, increased body weight loss and increased fibrotic remodeling. Pericyte-specific overexpression of Foxf1 attenuated pulmonary fibrosis, reversed fibrotic changes and improved survival outcomes. Based on single cell RNA-sequencing and chromatin immunoprecipitation sequencing, FOXF1 transcriptionally regulates an extensive pericyte signaling network critical for pulmonary fibrosis. In vitro, FOXF1 transcriptionally activated ID3 which inhibited fibroblast activation through decreased secretion of IL8 and CXCL1 by pericytes. Altogether, FOXF1 prevents transition of pericytes to a fibrotic state, suggesting new therapeutic opportunities for treatment of pulmonary fibrosis.