S. aureus-serine protease-like protein B (SplB) activates PAR2 and induces endothelial barrier dysfunction

Staphylococcus aureus (S. aureus) is a major cause of life-threatening systemic infection in humans. To cause blood stream infections such as sepsis and endocarditis, the bacteria must overcome the host″s endothelial barrier. The serine protease-like proteins (Spls) of S. aureus are known to contribute to pneumonia and allergic airway inflammation in animal models, but their role in endothelial damage is unknown. Here we demonstrate that SplB induces proinflammatory cytokine release in primary human vascular endothelial cells (HUVECs) in vitro. Mechanistically, we show that SplB selectively cleaves and activates human proteinase-activated receptor-2 (PAR2), and induces biased signaling via β-arrestin-1 and -2 and activates NF-κβ. This activation did not trigger Gαq/11-mediated calcium release nor ERK phosphorylation. Inhibition of PAR2 in HUVECs reduced the SplB-mediated cytokine release. Intravital microscopy of cremaster muscles in mice demonstrated that administration of SplB causes microvascular leakage. Neutralization of SplB with a monoclonal antibody retained the endothelial barrier. This study identifies PAR2 as a receptor and substrate for SplB and highlights its role in mediating endothelial damage.