Exosome-Derived <i>microRNA</i>-<i>22</i> Ameliorates Pulmonary Fibrosis by Regulating Fibroblast-to-Myofibroblast Differentiation <i>in Vitro</i> and <i>in Vivo</i>

BACKGROUND: Although aberrant proliferation and activation of lung fibroblasts are implicated in the initiation and progression of idiopathic pulmonary fibrosis (IPF), the underlying mechanisms are not well characterized. Numerous microRNAs (miRNAs) have been implicated in this process; however, miRNAs derived from exosomes and the relevance of such miRNAs to fibroblast-to-myofibroblast differentiation are not well understood. In this study, we attempted to identify exosome-derived miRNAs relevant to fibrosis development. METHODS: Using miRNA array analysis, we profiled exosome-derived miRNA expression in sera of C57BL/6 mice exhibiting bleomycin-induced pulmonary fibrosis. After validating a selected miRNA by quantitative reverse-transcription polymerase chain reaction, its effect on fibroblast-to-myofibroblast differentiation was investigated in human lung fibroblasts. Furthermore, we determined the role of the selected miRNA in an in vivo model of pulmonary fibrosis. RESULTS: MiRNA array analysis revealed that miR-22 expression was increased by up to 2 fold on day 7 after bleomycin treatment compared with that in vehicle-treated mice. In vitro, miR-22 transfection suppressed TGF-β1-induced α-SMA expression. This was mediated via inhibition of the ERK1/2 pathway. Baseline α-SMA expression was increased upon miR-22 inhibitor transfection. Furthermore, miR-22 negatively regulated connective tissue growth factor expression in the presence of TGF-β1. In vivo, administration of a miR-22 mimic on day 10 after bleomycin challenge ameliorated pulmonary fibrosis lesions accompanied by decreased α-SMA expression in the model mice. CONCLUSIONS: Exosomal miR-22 modulates fibroblast-to-myofibroblast differentiation. The present findings warrant further study, which could shed light on miR-22 as a novel therapeutic target in IPF.