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The mechanisms of fibrosis onset and development remain to be elucidated. However, it has been reported that mechanical stretch promotes fibrosis in various organs and cells, and may be involved in the pathogenesis of pulmonary fibrosis. We demonstrated that ventilator-induced lung hyperextension stimulation in mice increased the expression of connective tissue growth factor (CTGF), a profibrotic cytokine, in lung tissue. Increased CTGF expression induced by cyclic mechanical stretch (CMS) was also observed in vitro using A549 human alveolar epithelial cells. Pathway analysis revealed that the induction of CTGF expression by CMS involved MEK phosphorylation. Furthermore, early growth response 1 (Egr-1) was identified as a transcription factor associated with CTGF expression. Finally, the antifibrotic drug pirfenidone significantly reduced CTGF expression, MEK phosphorylation, and Egr-1 levels induced by CMS. Thus, our results demonstrated that profibrotic cytokine CTGF induced by CMS may be a therapeutic target of pirfenidone. • Ventilator-induced lung hyperextension stimulation increased CTGF expression. • Induction of CTGF expression by CMS involved MEK phosphorylation. • Egr-1 was identified as a transcription factor associated with CTGF expression. • The antifibrotic drug, pirfenidone, significantly reduced CTGF expression by CMS. [ABSTRACT FROM AUTHOR]

Cyclic mechanical stretching (CMS) of the alveolar epithelium is thought to contribute to alveolar epithelial injury through an increase in oxidative stress. The aim of this study was to investigate the mechanisms of CMS-induced oxidative stress in alveolar epithelial cells (AECs). A549 cells were subjected to CMS, and the levels of 8-isoprostane and 3-nytrotyrosine were measured. Twenty-four hours of CMS induced a significant increase in the levels of 8-isoprostane and 3-nytrotyrosine. Although CMS did not increase the xanthine oxidase activity or the mitochondrial production of reactive oxygen species, it upregulated the expression of nicotine adenine dinucleotide phosphate oxidase (NOX) 2, 4, 5 and DUOX2. The NOX inhibitors DPI and GKT137831 significantly attenuated CMS-induced oxidative stress. Furthermore, the measurement of annexin V/propidium iodide by flow cytometry showed that CMS induced late-phase apoptosis/necrosis, which was also attenuated by both DPI and GKT137831. These data suggest that CMS mainly induces oxidative stress, which may lead to cell injury by activating NOX in AECs. [ABSTRACT FROM AUTHOR]