Marsico Lung Institute, University of North Carolina Cystic Fibrosis Center, School of Medicine, The University of North Carolina at Chapel Hill , Chapel Hill, North Carolina.
Parion Sciences, Incorporated, Durham, North Carolina.
Am J Physiol Lung Cell Mol Physiol. 2018 Feb 1;314(2):L318-L331. doi: 10.1152/ajplung.00382.2017. Epub 2017 Oct 26.
The epithelial Na channel (ENaC) regulates airway surface hydration. In mouse airways, ENaC is composed of three subunits, α, β, and γ, which are differentially expressed (α > β > γ). Airway-targeted overexpression of the β subunit results in Na hyperabsorption, causing airway surface dehydration, hyperconcentrated mucus with delayed clearance, lung inflammation, and perinatal mortality. Notably, mice overexpressing the α- or γ-subunit do not exhibit airway Na hyperabsorption or lung pathology. To test whether overexpression of multiple ENaC subunits produced Na transport and disease severity exceeding that of βENaC-Tg mice, we generated double (αβ, αγ, βγ) and triple (αβγ) transgenic mice and characterized their lung phenotypes. Double αγENaC-Tg mice were indistinguishable from WT littermates. In contrast, double βγENaC-Tg mice exhibited airway Na absorption greater than that of βENaC-Tg mice, which was paralleled by worse survival, decreased mucociliary clearance, and more severe lung pathology. Double αβENaC-Tg mice exhibited Na transport rates comparable to those of βENaC-Tg littermates. However, αβENaC-Tg mice had poorer survival and developed severe parenchymal consolidation. In situ hybridization (RNAscope) analysis revealed both alveolar and airway αENaC-Tg overexpression. Triple αβγENaC-Tg mice were born in Mendelian proportions but died within the first day of life, and the small sample size prevented analyses of cause(s) of death. Cumulatively, these results indicate that overexpression of βENaC is rate limiting for generation of pathological airway surface dehydration. Notably, airway co-overexpression of β- and γENaC had additive effects on Na transport and disease severity, suggesting dose dependency of these two variables.
上皮钠离子通道 (ENaC) 调节气道表面的水合作用。在小鼠气道中，ENaC 由三个亚基组成，α、β和γ，它们的表达不同（α＞β＞γ）。气道靶向过表达β亚基导致 Na 过度吸收，引起气道表面脱水、黏液浓缩且清除延迟、肺部炎症和围产期死亡率增加。值得注意的是，过表达α或γ亚基的小鼠不会出现气道 Na 过度吸收或肺部病变。为了测试过表达多种 ENaC 亚基是否会产生超过βENaC-Tg 小鼠的 Na 转运和疾病严重程度，我们生成了双（αβ、 αγ、βγ）和三（αβγ）转基因小鼠，并对其肺部表型进行了表征。双 αγENaC-Tg 小鼠与 WT 同窝仔鼠没有区别。相比之下，双 βγENaC-Tg 小鼠的气道 Na 吸收大于βENaC-Tg 小鼠，这与生存率降低、黏液纤毛清除率降低和更严重的肺部病变相一致。双 αβENaC-Tg 小鼠的 Na 转运率与βENaC-Tg 同窝仔鼠相当。然而，αβENaC-Tg 小鼠的生存率较低，并出现严重的实质性肺实变。原位杂交（RNAscope）分析显示，肺泡和气道均过表达αENaC-Tg。三 αβγENaC-Tg 小鼠按孟德尔比例出生，但在出生后的第一天内死亡，由于样本量小，无法分析死亡原因。综合这些结果表明，βENaC 的过表达是产生病理性气道表面脱水的限速因素。值得注意的是，气道共过表达β-和 γENaC 对 Na 转运和疾病严重程度有相加作用，表明这两个变量存在剂量依赖性。
