Neutrophil serine proteases degrade endothelial cortactin and promote extravasation.

The adhesive interactions of neutrophils with postcapillary venules during inflammation have been well studied. However, how neutrophils trigger molecular changes in endothelial cells (EC) during their extravasation requires further exploration. The endothelial actin-binding protein cortactin regulates endothelial contacts and neutrophil-endothelial interactions, but the associated mechanisms remain elusive. Hypothesizing that endothelial cortactin dynamics change during inflammation, using super-resolution confocal microscopy of inflamed mouse cremasteric venules and HUVEC, we report that neutrophil interaction with EC induces reduction in EC cortactin levels. This response was specifically mediated by neutrophil serine proteases, including cathepsin G, that were detected inside EC. The observed cortactin degradation was abolished after inhibition of serine proteases or blockade of neutrophil exocytosis. Finally, the endogenous serine protease inhibitor α1-antitrypsin suppressed cortactin degradation in vivo and reduced neutrophil adhesion and extravasation. Collectively, our data unveil a new mechanism by which neutrophils manipulate proteins inside EC to facilitate their extravasation.