A Novel Tumor Necrosis Factor-mediated Mechanism of Direct Epithelial Sodium Channel Activation
A Novel Tumor Necrosis Factor-mediated Mechanism of Direct Epithelial Sodium Channel Activation
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DOI：
10.1164/rccm.201405-0833oc
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发表时间：
2014-09-01
影响因子：
24.7
通讯作者：
Lucas, Rudolf
中科院分区：
文献类型：
--
作者：
Czikora, Istvan;Alli, Abdel;Lucas, Rudolf
基本原理：肺泡液体清除率通过 II 型肺泡上皮细胞中顶端表达的上皮钠通道 (ENaC) 和基底外侧定位的 Na+-K+-ATP 酶的 Na+ 摄取来调节。肺部炎症期间这些 Na+ 转运蛋白的功能障碍可能导致肺水肿。 目的：在这项研究中，我们试图确定 TIP 肽（模仿肿瘤坏死因子 (TNF) 的凝集素样结构域）在存在或不存在细菌毒素肺炎球菌溶血素 (PLY) 的情况下刺激同源细胞系统中 Na+ 摄取的精确机制。 方法：我们采用了生物化学、电生理学和分子生物学相结合的体外方法，通过生成三重突变 TNF 敲入小鼠，这些小鼠表达缺乏 Na+ 摄取刺激活性的突变 TNF，评估了 TNF 凝集素样结构域在体内肺泡液体清除中的生理相关性。测量和主要结果：TIP 肽在与通道 a 亚基的羧基末端结构域结合后，直接激活 ENaC，但不激活 Na+-K+-ATP 酶。在 PLY（肺炎球菌诱导的肺水肿介质）存在的情况下，这种结合可稳定 ENaC-PIP2-MARCKS 复合物，这对于通道的开放概率构象是必需的，并通过钝化蛋白激酶 C-α 通路来保留 ENaC-α 蛋白表达。三重突变 TNF 敲入小鼠比野生型小鼠更容易在低剂量气管内 PLY 时出现水肿，这与肺 ENaC-α 亚基表达减少相关。结论：这些结果证明了一种新的 TNF 介导的直接 ENaC 激活机制，并表明 TNF 的凝集素样结构域在炎症期间消除肺泡水肿中的生理作用。
Rationale: Alveolar liquid clearance is regulated by Na+ uptake through the apically expressed epithelial sodium channel (ENaC) and basolaterally localized Na+-K+-ATPase in type II alveolar epithelial cells. Dysfunction of these Na+ transporters during pulmonary inflammation can contribute to pulmonary edema.Objectives: In this study, we sought to determine the precise mechanism by which the TIP peptide, mimicking the lectin-like domain of tumor necrosis factor (TNF), stimulates Na+ uptake in a homologous cell system in the presence or absence of the bacterial toxin pneumolysin (PLY).Methods: We used a combined biochemical, electrophysiological, and molecular biological in vitro approach and assessed the physiological relevance of the lectin-like domain of TNF in alveolar liquid clearance in vivo by generating triple-mutant TNF knock-in mice that express a mutant TNF with deficient Na+ uptake stimulatory activity.Measurements and Main Results: TIP peptide directly activates ENaC, but not the Na+-K+-ATPase, upon binding to the carboxyterminal domain of the a subunit of the channel. In the presence of PLY, a mediator of pneumococcal-induced pulmonary edema, this binding stabilizes the ENaC-PIP2-MARCKS complex, which is necessary for the open probability conformation of the channel and preserves ENaC-alpha protein expression, by means of blunting the protein kinase C-alpha pathway. Triple-mutant TNF knock-in-mice are more prone than wild-type mice to develop edema with low-dose intratracheal PLY, correlating with reduced pulmonary ENaC-alpha subunit expression.Conclusions: These results demonstrate a novel TNF-mediated mechanism of direct ENaC activation and indicate a physiological role for the lectin-like domain of TNF in the resolution of alveolar edema during inflammation.