Exosomal miRNA Let-7 from Menstrual Blood-Derived Endometrial Stem Cells Alleviates Pulmonary Fibrosis through Regulating Mitochondrial DNA Damage

Idiopathic pulmonary fibrosis (IPF) is a prototype of chronic, progressive, and fibrotic lung disease with high morbidity and high mortality. Menstrual blood-derived stem cells (MenSCs) have proven to be an attractive tool for the treatment of acute lung injury and fibrosis-related diseases through immunosuppression and antifibrosis. However, whether MenSC-derived exosomes have the similar function on pulmonary fibrosis remains unclear. In the present study, exosomes secreted from MenSCs (MenSCs-Exo) were verified by transmission electron microscope (TEM), nanoparticle tracking analyzer (NTA), and western blotting. And MenSC-Exo addition significantly improved BLM-induced lung fibrosis and alveolar epithelial cell damage in mice, mainly reflected in BLM-mediated enhancement of the fibrosis score, blue collagen deposition, dry/wet gravity ratio, hydroxyproline and malondialdehyde levels, and downregulation of glutathione peroxidase, which were all robustly reversed by MenSC-Exo management. Additionally, BLM- and TGF-beta 1-evoked cellular reactive oxygen species (ROS), mitochondrial DNA (mtDNA) damage, and cell apoptosis were rescued by MenSCs-Exo in vivo and in vitro. Further study indicated that the MenSCs-Exo could transport miRNA Let-7 into recipient alveolar epithelial cells. Let-7 inhibitor administration significantly blocked the exosome-mediated improvement role on lung fibrosis in mice. Mechanistically, Let-7 was able to regulate the expression of lectin-like oxidized low-density lipoprotein receptor-1 (LOX1) through binding to its 3 '-UTR region. Forced expression of LOX1 promoted the expression of apoptosis-related protein and mtDNA damage markers via regulating NLRP3 which was also confirmed in BLM model mice under the combination therapy of the exosome and Let-7 inhibitor. Collectively, this study demonstrates that exosomal Let-7 from MenSCs remits pulmonary fibrosis through regulating ROS, mtDNA damage, and NLRP3 inflammasome activation. This provides a new approach of exocytosis on the treatment of fibrotic lung disease.