Signaling of Neutrophil Recruitment is Mechanotransduced Via High Affinity LFA-1

Résumé du livre

Neutrophil adhesion to the inflamed endothelium is in part mediated by LFA-1 (CD11a/CD18) that recognizes its ligand ICAM-1. It is known that ICAM-1 rapidly forms homodimers and this conformation supports stable bonds with high affinity LFA-1 on the PMN under shear flow. We hypothesize that shear stress on these homodimeric bonds acts as a gate keeping mechanism to activate an intracellular signaling cascade involving calcium flux and cytoskeletal protein recruitment that together mediates firm neutrophil adhesion. Employing vascular mimetic microfluidic channels and real time fluorescence microscopy we observed the sequence of signaling events once neutrophils were arrested, while varying LFA-1 and ICAM-1 affinity and valence states. The presence of tensile force on LFA-1/ICAM-1 bonds was required for firm adhesion and signaling. Calcium flux through CRAC was crucial for adhesion strengthening even in the presence of LFA-1 bond formation. Kindlin-3 and Talin-1 were found to associate at the contact site upstream and downstream of Orai1 calcium release activated channel (CRAC) mediated calcium flux, respectively. Moreover, the efficient recruitment of PMN at high shear stress on microfluidic flow channels and into an acute skin wound required expression of Orai1 CRAC. In summary, integrin mediated outside-in signaling is dependent on shear force, the affinity of LFA-1 and valence of ICAM-1 which together elicit the assembly of a macromolecular complex that provides a key navigational step in the transition from PMN arrest to a migratory phenotype.