Department of Internal Medicine, Justus Liebig University, Universities of Giessen and Marburg Lung Center (UGMLC), Member of the German Center for Lung Research (DZL), 35392 Giessen, Germany.
The Cardio-Pulmonary Institute (CPI), 35392 Giessen, Germany.
Int J Mol Sci. 2020 Feb 21;21(4):1467. doi: 10.3390/ijms21041467.
Alveolar edema, impaired alveolar fluid clearance, and elevated CO levels (hypercapnia) are hallmarks of the acute respiratory distress syndrome (ARDS). This study investigated how hypercapnia affects maturation of the Na,K-ATPase (NKA), a key membrane transporter, and a cell adhesion molecule involved in the resolution of alveolar edema in the endoplasmic reticulum (ER). Exposure of human alveolar epithelial cells to elevated CO concentrations caused a significant retention of NKA-β in the ER and, thus, decreased levels of the transporter in the Golgi apparatus. These effects were associated with a marked reduction of the plasma membrane (PM) abundance of the NKA-α/β complex as well as a decreased total and ouabain-sensitive ATPase activity. Furthermore, our study revealed that the ER-retained NKA-β subunits were only partially assembled with NKA α-subunits, which suggests that hypercapnia modifies the ER folding environment. Moreover, we observed that elevated CO levels decreased intracellular ATP production and increased ER protein and, particularly, NKA-β oxidation. Treatment with α-ketoglutaric acid (α-KG), which is a metabolite that has been shown to increase ATP levels and rescue mitochondrial function in hypercapnia-exposed cells, attenuated the deleterious effects of elevated CO concentrations and restored NKA PM abundance and function. Taken together, our findings provide new insights into the regulation of NKA in alveolar epithelial cells by elevated CO levels, which may lead to the development of new therapeutic approaches for patients with ARDS and hypercapnia.
肺泡水肿、肺泡液体清除受损和二氧化碳水平升高（高碳酸血症）是急性呼吸窘迫综合征（ARDS）的标志。本研究探讨了高碳酸血症如何影响 Na，K-ATPase（NKA）的成熟，NKA 是一种关键的膜转运体，也是参与内质网（ER）中肺泡水肿消退的细胞黏附分子。将人肺泡上皮细胞暴露于高浓度的 CO 中会导致 NKA-β 在 ER 中大量滞留，从而降低高尔基体内转运体的水平。这些效应与 NKA-α/β 复合物的质膜（PM）丰度显著降低以及总和哇巴因敏感的 ATP 酶活性降低有关。此外，我们的研究表明，ER 中滞留的 NKA-β 亚基仅与 NKA α 亚基部分组装，这表明高碳酸血症改变了 ER 折叠环境。此外，我们观察到，升高的 CO 水平会降低细胞内 ATP 的产生并增加 ER 蛋白，尤其是 NKA-β 的氧化。用α-酮戊二酸（α-KG）处理，α-KG 是一种已被证明可增加高碳酸血症暴露细胞中 ATP 水平并挽救线粒体功能的代谢物，可减轻高浓度 CO 的有害影响，并恢复 NKA PM 的丰度和功能。总之，我们的研究结果为高碳酸血症对肺泡上皮细胞中 NKA 的调节提供了新的见解，这可能为 ARDS 和高碳酸血症患者的治疗提供新的方法。
