HIF1A and Airway obstruction: Higher levels of α-SMA and collagen 1 in MRC-5 cells (bronchial fibroblasts) exposed to exosomes derived from CSE-treated HBE cells.In MRC-5 cells, down-regulation of exosomal miR-21 blocked the exosome-induced myofibroblastdifferentiation phenotype as well as the increased and decrease levels of HIF-1α and pVHL respectively.In BLAB/c mice exposed to CS for 8 weeks, down-expression of miR-21 prevented changes inpulmonary function and attenuated inflammationand airway obstruction, restored pVHL expression and decreased HIF-1α levels.