• Zhou Lv, Yan Wang, Yu-Jian Liu, Yan-Fei Mao, Wen-Wen Dong, Zhong-Nuo Ding, Guang-Xun Meng, Lai Jiang, and Xiao-Yan Zhu.
• Department of Anesthesiology and Surgical Intensive Care Unit, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
• Crit. Care Med. 2018 Jan 1; 46 (1): e49-e58.

ObjectivesMechanical ventilation can induce lung fibrosis. This study aimed to investigate whether ventilator-induced lung fibrosis was associated with endothelial-mesenchymal transition and to uncover the underlying mechanisms.DesignRandomized, controlled animal study and cell culture study.SettingUniversity research laboratory.SubjectsAdult male Institute of Cancer Research, NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) knockout and wild-type mice. Primary cultured mouse lung vascular endothelial cells.InterventionsInstitute of Cancer Research, NLRP3 knockout and wild-type mice were subjected to mechanical ventilation (20 mL/kg) for 2 hours. Mouse lung vascular endothelial cells were subjected to cyclic stretch for 24 hours.Measurements And Main ResultsMice subjected to mechanical ventilation exhibited increases in collagen deposition, hydroxyproline and type I collagen contents, and transforming growth factor-β1 in lung tissues. Ventilation-induced lung fibrosis was associated with increased expression of mesenchymal markers (α smooth muscle actin and vimentin), as well as decreased expression of endothelial markers (vascular endothelial-cadherin and CD31). Double immunofluorescence staining showed the colocalization of CD31/α smooth muscle actin, CD31/vimentin, and CD31/fibroblast-specific protein-1 in lung tissues, indicating endothelial-mesenchymal transition formation. Mechanical ventilation also induced NLRP3 inflammasome activation in lung tissues. In vitro direct mechanical stretch of primary mouse lung vascular endothelial cells resulted in similar NLRP3 activation and endothelial-mesenchymal transition formation, which were prevented by NLRP3 knockdown. Furthermore, mechanical stretch-induced endothelial-mesenchymal transition and pulmonary fibrosis were ameliorated in NLRP3-deficient mice as compared to wild-type littermates.ConclusionsMechanical stretch may promote endothelial-mesenchymal transition and pulmonary fibrosis through a NLRP3-dependent pathway. The inhibition of endothelial-mesenchymal transition by NLRP3 inactivation may be a viable therapeutic strategy against pulmonary fibrosis associated with mechanical ventilation.

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