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Author Notes:

Correspondence: Rudolf Lucas, rlucas@augusta.edu; Istvan Czikora, iczikora@augusta.edu

Conception or design of the work: IC, AAA, MM, DF, TC, DE, and RL; acquisition, analysis, or interpretation of data: IC, SS, BG, HP, MH, BB, MR, and JG: drafting the work: IC and RL; revising it critically for important intellectual content: AAA, MR, GW, YH, YS, AV, DF, and DE.

All authors approved the final version of the manuscript and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

The authors thank Dr. Wemmie, University of Iowa, for the kind gift of anti-ASIC1a antibodies and Dr. Hummler-Beermann, University of Lausanne, for helpful discussions.

No conflicts of interest, financial or otherwise, are declared by the authors.

The reviewer, SH, declared a past coauthorship with one of the authors, TC, to the handling Editor, who ensured that the process met the standards of a fair and objective review.

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Research Funding:

This work was supported by PO1 grant HL101902 from the NHLBI (to AV and DF) and in part by K01 DK099617 (to AAA), Extramural Success Award from the Vice President for Research at Augusta University (to RL), AHA Scientist Development Grant 17SDG33680024 (to IC), as well as by SFB grant TR-84 “Innate Immunity of the Lung” from the German Research Foundation (DFG) (to HP and TC).

The work was also supported by ADA grant #1-16-IBS-196 (to RL, AV, and DF) and NHLBI grant HL51856 (to MAM). RL is a Mercator Fellow of the DFG.

Keywords:

  • Science & Technology
  • Life Sciences & Biomedicine
  • Immunology
  • epithelial sodium channel
  • non-selective cation channel
  • TNF
  • pneumonia
  • pneumolysin
  • endothelial barrier function
  • LECTIN-LIKE DOMAIN
  • NECROSIS-FACTOR-ALPHA
  • ACUTE LUNG INJURY
  • SENSING ION CHANNELS
  • KINASE-C-ALPHA
  • VASCULAR ENDOTHELIUM
  • EDEMA REABSORPTION
  • ENAC ACTIVITY
  • IN-VITRO
  • CELLS

Epithelial Sodium Channnel-alpha Mediates the Protective Effect of the TNF-Derived TIP Peptide in Pneumolysin-Induced Endothelial Barrier Dysfunction

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Journal Title:

Frontiers in Immunology

Volume:

Volume 8

Publisher:

, Pages 842-842

Type of Work:

Article | Final Publisher PDF

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-α and whether this subunit is involved in the regulation of their barrier function. Methods: The presence of α, β, and γ subunits of ENaC and protein phosphorylation status in HL-MVEC were assessed in western blotting. The role of ENaC-α 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-α. 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-α. Both TIP peptide, which specifically binds to ENaC-α, and the specific ASIC1a activator MitTx significantly strengthened barrier function in PLY-treated HL-MVEC. ENaC-α 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-α 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-α 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-α in both barrier function and liquid clearance. Conclusion: Our results in cultured endothelial cells demonstrate a previously unrecognized role for ENaC-α in strengthening capillary barrier function that may apply to the human lung. Strategies aiming to activate endothelial NSC channels that contain ENaC-α should be further investigated as a novel approach to improve barrier function in the capillary endothelium during pneumonia.

Copyright information:

© 2017 Czikora, Alli, Sridhar, Matthay, Pillich, Hudel, Berisha, Gorshkov, Romero, Gonzales, Wu, Huo, Su, Verin, Fulton, Chakraborty, Eaton and Lucas.

This is an Open Access work distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/).
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