Resolvin D1 attenuates mechanical stretch-induced pulmonary fibrosis via epithelial-mesenchymal transition (EMT).

Mechanical ventilation-induced pulmonary fibrosis plays an important role in the high mortality rate of acute respiratory distress syndrome (ARDS). Resolvin D1 (RvD1) displays potent proresolving activities. Epithelial-mesenchymal transition (EMT) has been proved to be an important pathological feature of lung fibrosis. This study aimed to investigate whether RvD1 can attenuate mechanical ventilation-induced lung fibrosis. Human lung epithelial (BEAS-2B) cells were pretreated with RvD1 for 30 min and exposed to acid for 10 min before being subjected to mechanical stretch for 48 h. C57BL/6 mice were subjected to intratracheal acid aspiration followed by mechanical ventilation 24 h later (peak inspiratory pressure 22 cmH(2)O, positive end-expiratory pressure 2 cmH(2)O, and respiratory rate 120 breaths/min for 2 h). RvD1 was injected into mice for 5 consecutive days after mechanical ventilation. Treatment with RvD1 significantly inhibited mechanical stretch-induced mesenchymal markers (vimentin and alpha-smooth muscle actin) and stimulated epithelial markers (E-cadherin). Tert-butyloxycarbonyl 2 (BOC-2), a lipoxin A4 receptor/formyl peptide receptor 2 (ALX/FPR2) antagonist, is known to inhibit ALX/FPR2 function. BOC-2 could reverse the beneficial effects of RvD1. The antifibrotic effect of RvD1 was associated with the suppression of Smad2/3 phosphorylation. This study demonstrated that mechanical stretch could induce EMT and pulmonary fibrosis and that treatment with RvD1 could attenuate mechanical ventilation-induced lung fibrosis, thus highlighting RvD1 as an effective therapeutic agent against pulmonary fibrosis associated with mechanical ventilation.