M2 macrophage-derived exosomal miR-350-5p facilitates pulmonary fibrosis through targeting Smad7 in lung fibroblasts and alveolar epithelial cells

Pulmonary fibrosis (PF) is a chronic and progressive lung disease, in which sustained alveolar epithelial damage and abnormal fibroblast proliferation and activation into myofibroblasts play a key role. M2-type macrophages and exosomes have been reported to participate in pulmonary fibrosis pathological development. In this study, exosomes were successfully extracted and identified from M0- and M2-type macrophages derived from the RAW264.7 mouse monocyte-macrophage cell line and mouse bone marrow–derived primary macrophages. In vivo experiments on the pulmonary fibrosis mouse model revealed that M2-exosomes administration notably exacerbated pulmonary fibrosis progression compared with M0- administration. In vitro studies demonstrated that M2-derived exosomes significantly facilitated fibroblast activation and alveolar epithelial cell mesenchymal transition. Comprehensive miRNA sequencing of M0- and M2-derived exosomes, and functional assays further confirmed that M2-type macrophage-derived exosomal miR-350-5p could be delivered into mouse fibroblasts and alveolar epithelial cells; inhibiting miR-350-5p in M2-type macrophages partially improves fibroblast activation and epithelial-mesenchymal transition (EMT) in vitro. Moreover, treatment with exosomes from miR-350-5p-inhibited M2 macrophages significantly attenuated pulmonary fibrosis and collagen deposition in vivo. Mechanistically, exosomal miR-350-5p directly targets and suppresses Smad7 in lung fibroblasts and alveolar epithelial cells, thereby amplifying TGF-β/Smad signaling and promoting fibrotic cellular phenotypes. In conclusion, the present study revealed the pro-fibrotic effect of exosomal miR-350-5p derived from M2 macrophages on pulmonary fibrosis development, particularly through its interaction with Smad7 in pulmonary fibroblasts and alveolar epithelium, emphasizing the potential of the miR-350-5p/Smad7 axis as therapeutic targets for lung fibrosis treatment.