Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Ontario, Canada.
Institute of Physiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Am J Physiol Lung Cell Mol Physiol. 2021 Apr 1;320(4):L486-L497. doi: 10.1152/ajplung.00461.2020. Epub 2021 Jan 13.
The constant transport of ions across the alveolar epithelial barrier regulates alveolar fluid homeostasis. Dysregulation or inhibition of Na transport causes fluid accumulation in the distal airspaces resulting in impaired gas exchange and respiratory failure. Previous studies have primarily focused on the critical role of amiloride-sensitive epithelial sodium channel (ENaC) in alveolar fluid clearance (AFC), yet activation of ENaC failed to attenuate pulmonary edema in clinical trials. Since 40% of AFC is amiloride-insensitive, Na channels/transporters other than ENaC such as Na-coupled neutral amino acid transporters (SNATs) may provide novel therapeutic targets. Here, we identified a key role for SNAT2 () in AFC and pulmonary edema resolution. In isolated perfused mouse and rat lungs, pharmacological inhibition of SNATs by HgCl and α-methylaminoisobutyric acid (MeAIB) impaired AFC. Quantitative RT-PCR identified SNAT2 as the highest expressed System A transporter in pulmonary epithelial cells. Pharmacological inhibition or siRNA-mediated knockdown of SNAT2 reduced transport of l-alanine across pulmonary epithelial cells. Homozygous mice were subviable and died shortly after birth with severe cyanosis. Isolated lungs of mice developed higher wet-to-dry weight ratios (W/D) as compared to wild type (WT) in response to hydrostatic stress. Similarly, W/D ratios were increased in mice as compared to controls in an acid-induced lung injury model. Our results identify SNAT2 as a functional transporter for Na and neutral amino acids in pulmonary epithelial cells with a relevant role in AFC and the resolution of lung edema. Activation of SNAT2 may provide a new therapeutic strategy to counteract and/or reverse pulmonary edema
离子在肺泡上皮屏障中的持续转运调节肺泡液的动态平衡。钠离子转运的失调或抑制会导致远端气腔中的液体积累，从而导致气体交换受损和呼吸衰竭。先前的研究主要集中在阿米洛利敏感的上皮钠离子通道（ENaC）在肺泡液清除（AFC）中的关键作用上，但在临床试验中，ENaC 的激活未能减轻肺水肿。由于 40%的 AFC 对阿米洛利不敏感，除 ENaC 以外的钠离子通道/转运体，如钠离子偶联的中性氨基酸转运体（SNATs），可能提供新的治疗靶点。在这里，我们确定了 SNAT2（）在 AFC 和肺水肿消退中的关键作用。在分离的灌注小鼠和大鼠肺中，HgCl 和 α-甲基氨基异丁酸（MeAIB）对 SNATs 的药理学抑制损害了 AFC。定量 RT-PCR 确定 SNAT2 是肺上皮细胞中表达最高的系统 A 转运体。SNAT2 的药理学抑制或 siRNA 介导的敲低减少了肺上皮细胞中 l-丙氨酸的转运。杂合子 小鼠在出生后不久就因严重发绀而无法存活，并且很快死亡。与野生型（WT）相比，在静水压力下， 小鼠的肺湿重/干重比（W/D）升高。在酸诱导的肺损伤模型中， 小鼠的 W/D 比值也比对照升高。我们的研究结果确定 SNAT2 是肺上皮细胞中钠离子和中性氨基酸的功能性转运体，在 AFC 和肺水肿消退中具有重要作用。SNAT2 的激活可能为对抗和/或逆转肺水肿提供新的治疗策略。
