Journal article

Publication year: 2017

Journal: Frontiers in Immunology

Volume number: 8

ISSN: 1664-3224

Open access status: Gold

DOI Link: https://doi.org/10.3389/fimmu.2017.00842

Publisher: Frontiers Media

Abstract: 

Background: Streptococcus pneumoniae is a major etiologic agent of bacterial pneumonia. Autolysis and antibiotic-mediated lysis of pneumococci induce release of the pore-forming toxin, pneumolysin (PLY), their major virulence factor, which is a prominent cause of acute lung injury. PLY inhibits alveolar liquid clearance and severely compromises alveolar-capillary barrier function, leading to permeability edema associated with pneumonia. As a consequence, alveolar flooding occurs, which can precipitate lethal hypoxemia by impairing gas exchange. The a subunit of the epithelial sodium channel (ENaC) is crucial for promoting Na+ reabsorption across Na+-transporting epithelia. However, it is not known if human lung microvascular endothelial cells (HL-MVEC) also express ENaC-alpha and whether this subunit is involved in the regulation of their barrier function.

Methods: The presence of alpha,beta, and gamma subunits of ENaC and protein phosphorylation status in HL-MVEC were assessed in western blotting. The role of ENaC-alpha in monolayer resistance of HL-MVEC was examined by depletion of this subunit by specific siRNA and by employing the TNF-derived TIP peptide, a specific activator that directly binds to ENaC-alpha.

Results: HL-MVEC express all three subunits of ENaC, as well as acid-sensing ion channel 1a (ASIC1a), which has the capacity to form hybrid non-selective cation channels with ENaC-alpha. Both TIP peptide, which specifically binds to ENaC-alpha, and the specific ASIC1a activator MitTx significantly strengthened barrier function in PLYtreated HL-MVEC. ENaC-alpha depletion significantly increased sensitivity to PLY-induced hyperpermeability and in addition, blunted the protective effect of both the TIP peptide and MitTx, indicating an important role for ENaC-alpha and for hybrid NSC channels in barrier function of HL-MVEC. TIP peptide and MitTx, indicating an important role for ENaC-alpha and for hybrid NSC channels in barrier function of HL-MVEC. TIP peptide blunted PLY-induced phosphorylation of both calmodulin-dependent kinase II (CaMKII) and of its substrate, the actin-binding protein filamin A (FLN-A), requiring the expression of both ENaC-alpha and ASIC1a. Since non-phosphorylated FLN-A promotes ENaC channel open probability and blunts stress fiber formation, modulation of this activity represents an attractive target for the protective actions of ENaC-alpha in both barrier function and liquid clearance.

Conclusion: Our results in cultured endothelial cells demonstrate a previously unrecognized role for ENaC-alpha in strengthening capillary barrier function that may apply to the human lung. Strategies aiming to activate endothelial NSC channels that contain ENaC-alpha should be further investigated as a novel approach to improve barrier function in the capillary endothelium during pneumonia.

Harvard Citation style: Czikora, I., Alli, A., Sridhar, S., Matthay, M., Pillich, H., Hudel, M., et al. (2017) Epithelial Sodium Channnel-α Mediates the Protective Effect of the TNF-Derived TIP Peptide in Pneumolysin-Induced Endothelial Barrier Dysfunction, Frontiers in Immunology, 8, Article 842. https://doi.org/10.3389/fimmu.2017.00842

APA Citation style: Czikora, I., Alli, A., Sridhar, S., Matthay, M., Pillich, H., Hudel, M., Berisha, B., Gorshkov, B., Romero, M., Gonzales, J., Wu, G., Huo, Y., Su, Y., Verin, A., Fulton, D., Chakraborty, T., Eaton, D., & Lucas, R. (2017). Epithelial Sodium Channnel-α Mediates the Protective Effect of the TNF-Derived TIP Peptide in Pneumolysin-Induced Endothelial Barrier Dysfunction. Frontiers in Immunology. 8, Article 842. https://doi.org/10.3389/fimmu.2017.00842