ATP Release from Human Airway Epithelial Cells Exposed to Staphylococcus aureus Alpha-Toxin

Abstract

Airway epithelial cells reduce cytosolic ATP content in response to treatment with S. aureus alpha-toxin (hemolysin A, Hla). This study was undertaken to investigate whether this is due to attenuated ATP generation or to release of ATP from the cytosol and extracellular ATP degradation by ecto-enzymes. Exposure of cells to rHla did result in mitochondrial calcium uptake and a moderate decline in mitochondrial membrane potential, indicating that ATP regeneration may have been attenuated. In addition, ATP may have left the cells through transmembrane pores formed by the toxin or through endogenous release channels (e.g., pannexins) activated by cellular stress imposed on the cells by toxin exposure. Exposure of cells to an alpha-toxin mutant (H35L), which attaches to the host cell membrane but does not form transmembrane pores, did not induce ATP release from the cells. The Hla-mediated ATP-release was completely blocked by IB201, a cyclodextrin-inhibitor of the alpha-toxin pore, but was not at all affected by inhibitors of pannexin channels. These results indicate that, while exposure of cells to rHla may somewhat reduce ATP production and cellular ATP content, a portion of the remaining ATP is released to the extracellular space and degraded by ecto-enzymes. The release of ATP from the cells may occur directly through the transmembrane pores formed by alpha-toxin.

Staphylococcus aureusα-toxin induces acid sphingomyelinase release from a human endothelial cell line

“…Murine endothelia have been shown to degrade tight junctions upon challenge with staphylococcal α-toxin thereby leading to lung edema in vivo (Seeger et al, 1990;Bartlett et al, 2008;Becker et al, 2018). We here treated bEnd.3 endothelial cells with staphylococcal αtoxin and investigated phosphorylation of p38 MAPK, which has been previously shown to be activated by α-toxin in epithelial cells (Eiffler et al, 2016). Ten to twenty minutes after addition of the toxin we observed an increase in phospho-p38 (Fig.…”

Impact of Bacterial Toxins in the Lungs

“…Like LLO and PLY, Hla fosters transmembrane influx of Ca 2+ , which ultimately leads to the development of pulmonary edema [12,20]. Binding of Hla to ADAM10 causes activation and upregulation of its metalloprotease activity leading to the pathologic cleavage of its substrates, including epithelial E-cadherin and vascular endothelial (VE)-cadherin, with concomitant loss of barrier function [70][71][72][73][74][75][76]. Moreover, Hla has the ability to disrupt endothelial-cell TJs through activating acid sphingomyelinase and release of ceramide [69].…”

“…Alveolar epithelial cells represent sensitive targets to an Hla assault [73], since the pore-forming toxin impairs the alveolar-capillary barrier of the lung in a rat model of S. aureus-induced pneumonia [74,75], upon inducing alterations in cell shape and by promoting formation of paracellular gaps in human airway epithelial cells [75,76]. Hla pore formation in bronchial epithelium causes the release of cytosolic ATP to the extracellular space [76,77], which increases ciliary beat frequency in tracheal cells via both P2X and P2Y receptors [78]. Hla, moreover, induces mucus secretion in goblet cells [79,80] and fosters Interleukin 6 (IL-6) secretion by small human airway epithelial cells [81].…”

Das alpha‐Toxin von Staphylococcus aureus

“…Die schon lange gehegte Vermutung, dass die Hla‐Pore in Atemwegsepithelzellen auch für kleine organische Moleküle wie ATP durchlässig ist, konnte in jüngerer Zeit experimentell belegt werden . Das extrazelluläre ATP könnte als Gefahrensignal ( danger signal ) dienen , denn es bindet an ▸ purinerge Rezeptoren in der apikalen Zellmembran benachbarter Atemwegsepithelzellen und löst dort gegen die Bakterien gerichtete Abwehrreaktionen aus (zusätzliche Sekretion von Salz, Wasser und Schleimstoffen, Verstärkung des Zilienschlags etc.).…”