Selectin Catch-bonds Mechanotransduce Integrin Activation and Neutrophil Arrest on Inflamed Endothelium Under Shear Flow

E-selectin extends from the plasma membrane of inflamed endothelium and serves to capture leukocytes from flowing blood via long-lived catch-bonds that support slow leukocyte rolling under shear stress. Its ligands are glycosylated with the tetrasaccharide sialyl Lewis (sLe), which contributes to bond affinity and specificity. E-selectin-mediated rolling transmits signals into neutrophils that trigger activation of high-affinity β-integrins necessary for transition to shear-resistant adhesion and transendothelial migration. Rivipansel is a glycomimetic drug that inhibits E-selectin-mediated vaso-occlusion induced by integrin-dependent sickle-red blood cell-leukocyte adhesion. How Rivipansel antagonizes ligand recognition by E-selectin and blocks outside-in signaling of integrin-mediated neutrophil arrest while maintaining rolling immune-surveillance is unknown. Here, we demonstrate that sLe expressed on human L-selectin is preferentially bound by E-selectin and, on ligation, initiates secretion of MRP8/14 that binds TLR4 to elicit the extension of β-integrin to an intermediate affinity state. Neutrophil rolling over E-selectin at precise shear stress transmits tension and catch-bond formation with L-selectin via sLe, resulting in focal clusters that deliver a distinct signal to upshift β-integrins to a high-affinity state. Rivipansel effectively blocked formation of selectin catch-bonds, revealing a novel mechanotransduction circuit that rapidly converts extended β-integrins to high-affinity shear-resistant bond clusters with intracellular adhesion molecule 1 on inflamed endothelium.