miR-21 in EVs from pulmonary epithelial cells promotes myofibroblast differentiation via glycolysis in arsenic-induced pulmonary fibrosis

As an environmental toxicant, arsenic causes damage to various organs and systems of the body and has attracted worldwide attention. It is well-known that exposure to arsenic can induce pulmonary fibrosis, but the molecular mechanisms are elusive. Glycolysis is involved in the process of various diseases, including pulmonary fibrosis. Extracellular vehicles (EVs) are mediators of cell communication through transporting miRNAs. The potential of miRNAs in EVs as liquid biopsy biomarkers for various diseases has been reported, and they have been applied in clinical diagnoses. In the present investigation, we focused on the roles and mechanisms of miR-21 in EVs on arsenic-induced glycolysis and pulmonary fibrosis through experiments with human populations, experimental animals, and cells. The results for arsenicosis populations showed that the serum levels of hydroxyproline, lactate, and EVs-miRNAs were elevated and that EVs-miR-21 levels were positively related to the levels of hydroxyproline and lactate. For mice, chronic exposure to arsenite led to high levels of miR-21, AKT activation, elevated glycolysis, and pulmonary fibrosis; however, these effects were blocked by the depletion of miR-21 in miR-21 knockout (miR-21KO) mice. After MRC-5 cells were co-cultured with arsenite-treated HBE cells, the levels of miR-21, AKT activation, glycolysis, and myofibroblast differentiation were enhanced, effects that were blocked by reducing miR-21 and by inhibiting the EVs in HBE cells. The down-regulation of PTEN in MRC-5 cells and primary lung fibroblasts (PLFs) reversed the blocking effect of inhibiting miR-21 in HBE cells. Thus, miR-21 down-regulates PTEN and promotes glycolysis via activating AKT, which is associated with arsenite-induced myofibroblast differentiation and pulmonary fibrosis. Our results provide a new approach for the construction of clinical diagnosis technology based on analysis of the mechanism of arsenite-induced pulmonary fibrosis.