Hypoxia Downregulates Expression and Activity of Epithelial Sodium Channels in Rat Alveolar Epithelial Cells

To maintain alveolar air spaces relatively fluid free, the alveolar epithelium appears capable of vectorial transport of water and solutes. Active transepithelial transport of sodium by alveolar epithelial cell monolayers has previously been demonstrated, indicating that alveolar pneumocytes must possess ion transport mechanisms by which sodium can enter the cells apically for subsequent extrusion via Na(+)-K(+)-adenosinetriphosphatase activity at the basolateral surface. In this study, sodium entry mechanisms were investigated by directly measuring 22Na uptake into rat alveolar epithelial cells grown in primary culture. Cells exhibited increasing 22Na uptake with time over a 30-min interval. Total sodium uptake was compared in the presence and absence of several sodium transport inhibitors. Uptake was inhibited by the sodium channel blockers amiloride and benzamil but was not affected by two amiloride analogues (bromohexamethylene amiloride and dimethylamiloride) with diminished specificity for blocking sodium channels and enhanced specificity for inhibiting the Na(+)-H+ antiporter. Uptake was also unaffected by the chloride transport inhibitor bumetanide or by the absence of glucose. These data suggest that sodium uptake occurs primarily via sodium channel and that Na(+)-H+ antiport, Na(+)-K(+)-2Cl- cotransport, and Na(+)-glucose cotransport do not contribute significantly to sodium uptake under these experimental conditions. The presence of sodium channels in the alveolar epithelial cell membrane may provide the major entry mechanism by which sodium enters these cells for subsequent active extrusion, thereby effecting net salt and water reabsorption from the alveolar spaces.

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Fibrinolysis influences SARS-CoV-2 infection in ciliated cells

10.1101/2021.01.07.425801 ◽

2021 ◽

Author(s):

Yapeng Hou ◽

Yan Ding ◽

Hongguang Nie ◽

Hong-Long Ji

Keyword(s):

Epithelial Cells ◽

Single Cell ◽

Protein S ◽

Alveolar Epithelial Cells ◽

Virus Infectivity ◽

Epithelial Sodium Channels ◽

Alveolar Epithelial ◽

Relative Expression Level ◽

Rapid Spread ◽

Ciliated Epithelial Cells

Rapid spread of COVID-19 has caused an unprecedented pandemic worldwide, and an inserted furin site in SARS-CoV-2 spike protein (S) may account for increased transmissibility. Plasmin, and other host proteases, may cleave the furin site of SARS-CoV-2 S protein and γ subunits of epithelial sodium channels (γ ENaC), resulting in an increment in virus infectivity and channel activity. As for the importance of ENaC in the regulation of airway surface and alveolar fluid homeostasis, whether SARS-CoV-2 will share and strengthen the cleavage network with ENaC proteins at the single-cell level is urgently worthy of consideration. To address this issue, we analyzed single-cell RNA sequence (scRNA-seq) datasets, and found the PLAU (encoding urokinase plasminogen activator), SCNN1G (γENaC), and ACE2 (SARS-CoV-2 receptor) were co-expressed in alveolar epithelial, basal, club, and ciliated epithelial cells. The relative expression level of PLAU, TMPRSS2, and ACE2 were significantly upregulated in severe COVID-19 patients and SARS-CoV-2 infected cell lines using Seurat and DESeq2 R packages. Moreover, the increments in PLAU, FURIN, TMPRSS2, and ACE2 were predominately observed in different epithelial cells and leukocytes. Accordingly, SARS-CoV-2 may share and strengthen the ENaC fibrinolytic proteases network in ACE2 positive airway and alveolar epithelial cells, which may expedite virus infusion into the susceptible cells and bring about ENaC associated edematous respiratory condition. Keywords: SARS-CoV-2; plasmin; ENaC; COVID-19; furin

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Dexamethasone inhibits the action of TNF on ENaC expression and activity

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00511.2005 ◽

2006 ◽

Vol 291 (6) ◽

pp. L1220-L1231 ◽

Cited By ~ 25

Author(s):

André Dagenais ◽

Rosalie Fréchette ◽

Marie-Eve Clermont ◽

Chantal Massé ◽

Anik Privé ◽

...

Keyword(s):

Epithelial Cells ◽

Mrna Expression ◽

Promoter Activity ◽

Potential Role ◽

Inhibitory Effect ◽

Alveolar Epithelial Cells ◽

Normal Range ◽

Alveolar Epithelial ◽

Expression And Activity

We have reported that TNF, a proinflammatory cytokine present in several lung pathologies, decreases the expression and activity of the epithelial Na+channel (ENaC) by ∼70% in alveolar epithelial cells. Because dexamethasone has been shown to upregulate ENaC mRNA expression and is well known to downregulate proinflammatory genes, we tested if it could alleviate the effect of TNF on ENaC expression and activity. In cotreatment with TNF, we found that dexamethasone reversed the inhibitory effect of TNF and upregulated α, β, and γENaC mRNA expression. When the cells were pretreated for 24 h with TNF before cotreatment, dexamethasone was still able to increase αENaC mRNA expression to 1.8-fold above control values. However, in these conditions, β and γENaC mRNA expression was reduced to 47% and 14%, respectively. The potential role of TNF and dexamethasone on αENaC promoter activity was tested in A549 alveolar epithelial cells. TNF decreased luciferase (Luc) expression by ∼25% in these cells, indicating that the strong diminution of αENaC mRNA must be related to posttranscriptional events. Dexamethasone raised Luc expression by fivefold in the cells and augmented promoter activity by 2.77-fold in cotreatment with TNF. In addition to its effect on αENaC gene expression, dexamethasone was able to maintain amiloride-sensitive current as well as the liquid clearance abilities of TNF-treated cells within the normal range. All these results suggest that dexamethasone alleviates the downregulation of ENaC expression and activity in TNF-treated alveolar epithelial cells.

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