Ultra-Large von Willebrand Factor Fibers Mediate Luminal Staphylococcus Aureus Adhesion to an Intact Endothelial Cell Layer under Shear Stress
Background—During pathogenesis of infective endocarditis S. aureus adherence often occurs without identifiable pre-existing heart disease. However, molecular mechanisms mediating initial bacterial adhesion to morphologically intact endocardium are largely unknown.
Methods and Results—Perfusion of activated human endothelial cells with fluorescent bacteria under high shear rate conditions revealed 95% attachment of the S. aureus by ultra-large von Willebrand factor (ULVWF). Flow experiments with VWF deletion mutants and heparin indicate a contribution of the A-type domains of VWF to bacterial binding. In this context analyses of different bacterial deletion mutants suggest the involvement of wall teichoic acid but not of staphylococcal protein A. Presence of inactivated platelets and serum increased significantly ULVWF-mediated bacterial adherence. ADAMTS13 caused a dose-dependent reduction of bacterial binding and a reduced length of ULVWF, but single cocci were still tethered by ULVWF at physiological levels of ADAMTS13. To further prove the role of VWF in vivo, we compared wild type mice with VWF knock-out mice. Binding of fluorescent bacteria was followed in TNFα stimulated tissue by intravital microscopy applying the dorsal skinfold chamber model. In comparison to wild type mice (n=6) we found less bacteria in postcapillary (60±6 vs. 32±5 bacteria) and collecting venules (48±5 vs. 18±4 bacteria, P<0.05) of VWF knock-out mice (n=5).
Conclusions—Our data provide first evidence that ULVWF contribute to the initial pathogenic step of S. aureus-induced endocarditis in patients with an apparently intact endothelium. An intervention reducing the ULVWF formation with heparin or ADAMTS13 suggests novel therapeutic options to prevent infective endocarditis.
- Received February 14, 2013.
- Revision received May 7, 2013.
- Accepted May 14, 2013.