Fibroblasts-derived extracellular vesicles contain SFRP1 and mediate pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a lethal and chronic lung disease characterized by aberrant intercellular communication, increased extracellular matrix (ECM) deposition, and destruction of functional lung tissue. Extracellular vesicles (EVs) accumulate within the lung in IPF, but their cargo and biological effects remain unclear. Here, we provide the entire the proteome of EV and non-EV fraction during pulmonary fibrosis, and functionally characterize their contribution to fibrosis. EVs were isolated by differential ultracentrifugation of bronchoalveolar lavage fluid (BALF) collected from mice challenged with bleomycin (or PBS as control) or culture supernatants from primary mouse lung fibroblasts. EVs were characterized by nanoparticle tracking analysis, Western Blotting, and quantitative mass spectrometry to define their proteome. EVs accumulation peaked at 14 days post-bleomycin instillation and correlated with decreased lung function. Label-free proteomics identified 107 proteins specific to fibrotic BALF-EVs. This signature was associated with wound healing, extracellular matrix organization, and cell motility. BALF-EVs from fibrotic lungs promoted fibrogenesis, including induction of ECM proteins in precision cut lung slices ex vivo and impaired alveolar epithelial cell stem cell function. Deconvolution using single cell RNA sequencing datasets revealed that fibroblasts are the major cellular source of BALF-EVs. EVs from fibroblasts were significantly enriched in Secreted Frizzled Related Protein 1 (SFRP1). In the lungs of patients with IPF, SFRP1 was significantly increased in mesenchymal cells. Sfrp1 deficiency reduced the ability of fibroblast-derived EVs to potentiate bleomycin-induced lung fibrosis in vivo and led to a reduction in fibrosis marker gene expression. In sum, EVs carry specific protein cargos, such as SFRP1, to contribute to organ remodeling during fibrosis. Our data identified EVs transporting SFRP1 as a potential therapeutic target for IPF.