Staphylococcus aureus Alpha-Toxin Disrupts Endothelial-Cell Tight Junctions via Acid Sphingomyelinase and Ceramide

Abstract

() infections are among the most common and severe infections, garnering notoriety in an era of increasing resistance to antibiotics. It is therefore important to define molecular mechanisms by which this pathogen attacks host cells. Here, we demonstrate that alpha-toxin, one of the major toxins of , induces activation of acid sphingomyelinase and concomitant release of ceramide in endothelial cells treated with the toxin. Activation of acid sphingomyelinase by alpha-toxin is mediated via ADAM10. Infection experiments employing alpha-toxin-deficient and the corresponding wild-type strain reveal that activation of acid sphingomyelinase in endothelial cells requires alpha-toxin expression by the pathogen. Activation of acid sphingomyelinase is linked to degradation of tight junctions in endothelial cells , which is blocked by pharmacological inhibition of acid sphingomyelinase. Most importantly, alpha-toxin induces severe degradation of tight junctions in the lung and causes lung edema, which is prevented by genetic deficiency of acid sphingomyelinase. These data indicate a novel and important role of the acid sphingomyelinase/ceramide system for the endothelial response to toxins and provide a molecular link between alpha-toxin and the degradation of tight junctions. The data also suggest that inhibition of acid sphingomyelinase may provide a novel treatment option to prevent lung edema caused by alpha-toxin.

Untargeted lipidomic analysis to broadly characterize the effects of pathogenic and non-pathogenic staphylococci on mammalian lipids

“…This is also in contrast to pathogenic S . aureus that express beta-hemolysin, a sphingomyelinase C[ 25 ], to hydrolyze sphingomyelin to compromise endothelial integrity[ 76 ]. The absence of sphingomyelin degradation in our experiment suggests that S .…”

Impact of Bacterial Toxins in the Lungs

“…Hla is a small β-barrel archetypal pore-forming toxin with a molecular mass of 34 kDa expressed by most strains of S. aureus as a water-soluble monomer [12,65]. Hla contributes to the pathogenesis of ventilator-associated pneumonia [64,66,67] through forming pores, manipulating structural and functional properties of alveolar epithelium, capillary endothelium, and AMs, and provoking inflammatory mediator release [67][68][69][70]. Pore formation occurs upon binding of Hla to its receptor A Disintegrin and Metalloprotease 10 (ADAM-10) in the target cell membrane, which induces oligomerization, self-assembly, and the generation of a lipid-bilayer mushroom-shaped hexameric/heptameric channel [67].…”

“…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]. Ceramide produced by acid sphingomyelinase is associated with PAF-induced pulmonary edema [72].…”

Sphingolipid metabolism in the pathophysiology and treatment of Alzheimer’s disease

“…The loss of barrier integrity was accompanied by an increase in monocyte migration across the endothelial cells after exposure to ceramide [143]. Interestingly, the inhibition of A-SMase activity prevented the degradation of zonula occludens 1 and 2, and occludin, proteins important for in tight junctions, indicating an important role for A-SMase/ceramide in tight junction regulation [204].…”

“…A-SMase and ceramide have been studied in relation to BBB function. Brain endothelial cells stimulated with an inflammatory stimulus showed increased A-SMase activity and concomitant ceramide production, which resulted in the disruption of tight junction proteins [204]. Exposure of brain endothelial cells to C2:0 ceramide induced a decrease in barrier resistance, which is indicative for barrier integrity.…”