MicroRNA-375 prevents TGF-β-dependent transdifferentiation of lung fibroblasts via the MAP2K6/P38 pathway

Transdifferentiation of lung fibroblasts to myofibroblasts is a crucial pathophysiological process in pulmonary fibrosis. MicroRNA-375 (miR-375) was initially identified as a tumor-suppressive factor, and its expression was negatively associated with the severity of lung cancer; however, its role and potential mechanism in myofibroblast transdifferentiation and pulmonary fibrosis remain unclear. In the present study, human lung fibroblasts were stimulated with transforming growth factor-β (TGF-β) to induce myofibroblast transdifferentiation. A mimic and inhibitor of miR-375, and their negative controls, were used to overexpress or suppress miR-375 in lung fibroblasts, respectively. The mRNA expression levels of fibrotic markers, and protein expression of α-smooth muscle actin and periostin, were subsequently detected by reverse transcription-quantitative PCR and western blotting, to assess myofibroblast transdifferentiation. miR-375 was markedly upregulated in human lung fibroblasts after TGF-β stimulation. The miR-375 mimic alleviated, whereas the miR-375 inhibitor aggravated TGF-β-dependent transdifferentiation of lung fibroblasts. Mechanistically, miR-375 prevented myofibroblast transdifferentiation and collagen synthesis by blocking the P38 mitogen-activated protein kinases (P38) pathway, and P38 suppression abrogated the deleterious effect of the miR-375 inhibitor on myofibroblast transdifferentiation. Furthermore, the present study revealed that mitogen-activated protein kinase kinase 6 was involved in P38 inactivation by miR-375. In conclusion, miR-375 was implicated in modulating TGF-β-dependent transdifferentiation of lung fibroblasts, and targeting miR-375 expression may help to develop therapeutic approaches for treating pulmonary fibrosis.