Staphylococcal β-Toxin Modulates Human Aortic Endothelial Cell and Platelet Function through Sphingomyelinase and Biofilm Ligase Activities.
Staphylococcus aureuscauses many infections, such as skin and soft tissue, pneumonia, osteomyelitis, and infective endocarditis (IE). IE is an endovascular infection of native and prosthetic valves and the lining of the heart; it is characterized by the formation of cauliflower-like "vegetations" composed of fibrin, platelets, other host factors, bacteria, and bacterial products. β-Toxin is anS. aureusvirulence factor that contributes to the microorganism's ability to cause IE. This cytolysin has two enzymatic activities: sphingomyelinase (SMase) and biofilm ligase. Although both activities have functions in a rabbit model of IE, the mechanism(s) by which β-toxin directly affects human cells and is involved in the infectious process has not been elucidated. Here, we compared thein vitroeffects of purified recombinant wild-type β-toxin, SMase-deficient β-toxin (H289N), and biofilm ligase-deficient β-toxin (H162A and/or D163A) on human aortic endothelial cells (HAECs) and platelets. β-Toxin was cytotoxic to HAECs and inhibited the production of interleukin 8 (IL-8) from these cells by both SMase and biofilm ligase activities. β-Toxin altered HAEC surface expression of CD40 and vascular cell adhesion molecule 1 (VCAM-1). HAECs treated with β-toxin displayed granular membrane morphology not seen in treatment with the SMase-deficient mutant. The altered morphology resulted in two possibly separable activities, cell rounding and redistribution of cell membranes into granules, which were not the result of endosome production from the Golgi apparatus or lysosomes. β-Toxin directly aggregated rabbit platelets via SMase activity.IMPORTANCEEach year there are up to 100,000 cases of infective endocarditis (IE) in the United States.S. aureusis the most common pathogen in patients with health care-associated IE and the leading cause of community-associated IE in the developed world. Multiple clonal group strains as defined by the Centers for Disease Control and Prevention, particularly USA200 and other clones encoding β-toxin, are highly associated with IE. Considering the strong association and established contribution of β-toxin in animal models of IE, determining how β-toxin directly affects human cell types, including endothelial cells and platelets, is important. In this study, we demonstrate that β-toxin functions to modulate endothelial cells and platelets by both toxin sphingomyelinase and biofilm ligase activities. Our data suggest that these activities modulate inflammation and increase infection severity.
Department of Microbiology, University of Iowa Carver College of Medicine, Iowa City, Iowa, USA.
Alfa
A
Herrera
Department of Microbiology, University of Iowa Carver College of Medicine, Iowa City, Iowa, USA.
Katarina
K
Kulhankova
Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa, USA.
Vijay K
VK
Sonkar
Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa, USA.
Sanjana
S
Dayal
Department of Microbiology, University of Iowa Carver College of Medicine, Iowa City, Iowa, USA.
Aloysius J
AJ
Klingelhutz
Department of Microbiology, University of Iowa Carver College of Medicine, Iowa City, Iowa, USA.
Wilmara
W
Salgado-Pabón
Department of Microbiology, University of Iowa Carver College of Medicine, Iowa City, Iowa, USA Patrick-schlievert@uiowa.edu.
Patrick M
PM
Schlievert
D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development; D001792:Blood Platelets / Q000187:drug effects*; D019013:CD40 Antigens / Q000032:analysis; D002462:Cell Membrane / Q000187:drug effects / Q000648:ultrastructure; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000737:chemistry / Q000187:drug effects*; D006460:Hemolysin Proteins / Q000235:genetics / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D006801:Humans; D008025:Ligases / Q000378:metabolism*; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000235:genetics / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000472:pathogenicity*; D019010:Vascular Cell Adhesion Molecule-1 / Q000032:analysis
D001427:Bacterial Toxins; D019013:CD40 Antigens; D006460:Hemolysin Proteins; D050505:Mutant Proteins; D011994:Recombinant Proteins; D019010:Vascular Cell Adhesion Molecule-1; D013108:Sphingomyelin Phosphodiesterase; C029878:hlb protein, Staphylococcus aureus; D008025:Ligases
Staphylococcus aureus; beta-toxin; biofilm ligase; endothelial cells; sphingomyelinase