Ventilator-induced lung injury (VILI) is a common complication in the treatment of respiratory diseases with high morbidity and mortality. ETS-domain containing protein (Elk1) and Matrix metalloproteinase (MMP) 9 are involved in VILI, but the roles have not been fully elucidated. This study examined the mechanisms of the activation of MMP-9 and Elk1 regulating barrier function in VILI in vitro and in vivo. For the in vitro study, Mouse lung epithelial cells (MLE-12) were pre-treated with Elk1 siRNA or MMP-9 siRNA for 48 h prior to cyclic stretch at 20% for 4 h. For the in vivo study, C57BL/6 mice were pre-treated with Elk1 siRNA or MMP-9 siRNA for 72 h prior to 4 h of mechanical ventilation. The expressions of Elk1, MMP-9, Tissue inhibitor of metalloproteinase 1 (TIMP-1), E-cadherin, and occludin were measured by Western blotting. The intracellular distribution of E-cadherin and occludin was shown by immunofluorescence. The degree of pulmonary edema and lung injury were evaluated by Hematoxylin–eosin (HE) staining, lung injury scores, Wet/Dry (W/D) weight ratio, total cell counts, and Evans blue dye. 20% cyclic stretch and high tidal volume increases the expressions of Elk1, MMP-9, and TIMP-1, increases the ratio of MMP-9/TIMP-1, decreases the E-cadherin and occludin level. Elk1 siRNA or MMP-9 siRNA reverses the degradations of E-cadherin, occludin, and the ratio of MMP-9/TIMP-1 caused by cyclic stretch. Elk1 siRNA decreases the MMP-9 level with or not 20% cyclic stretch and high tidal volume. The results demonstrate mechanical stretch damages the tight junctions and aggravates the permeability in VILI, Elk1 plays an important role in affecting the tight junctions and permeability by regulating the balance of MMP-9 and TIMP-1, thus indicating the therapeutic potential of Elk1 to treat VILI.

中文翻译：

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Elk1/MMP-9 轴在呼吸机引起的肺损伤中调节 E-cadherin 和 occludin

呼吸机引起的肺损伤（VILI）是呼吸系统疾病治疗中常见的并发症，发病率和死亡率都很高。含有 ETS 结构域的蛋白质 (Elk1) 和基质金属蛋白酶 (MMP) 9 参与 VILI，但其作用尚未完全阐明。本研究在体外和体内检查了 MMP-9 和 Elk1 在 VILI 中调节屏障功能的激活机制。对于体外研究，小鼠肺上皮细胞 (MLE-12) 用 Elk1 siRNA 或 MMP-9 siRNA 预处理 48 小时，然后以 20% 循环拉伸 4 小时。对于体内研究，C57BL/6 小鼠在机械通气 4 小时之前用 Elk1 siRNA 或 MMP-9 siRNA 预处理 72 小时。免疫印迹法检测Elk1、MMP-9、金属蛋白酶组织抑制剂1（TIMP-1）、E-cadherin和occludin的表达。免疫荧光显示 E-cadherin 和 occludin 的细胞内分布。通过苏木精-伊红 (HE) 染色、肺损伤评分、湿/干 (W/D) 重量比、总细胞计数和伊文思蓝染料评估肺水肿和肺损伤的程度。20%的循环拉伸和高潮气量增加了Elk1、MMP-9和TIMP-1的表达，增加了MMP-9/TIMP-1的比值，降低了E-cadherin和occludin的水平。Elk1 siRNA 或 MMP-9 siRNA 可逆转由循环拉伸引起的 E-cadherin、occludin 和 MMP-9/TIMP-1 比率的降解。Elk1 siRNA 在 20% 循环拉伸和高潮气量的情况下降低 MMP-9 水平。结果表明机械拉伸会破坏紧密连接并加剧 VILI 的渗透性，