Mechanical Strength and Structural Basis ofβ2 Integrin to Mediate Neutrophil Accumulation on Liver Sinusoidal Endothelial Cells:A Study Using Atomic Force Microscopy and Molecular Dynamics Simulations

Neutrophil(PMN)accumulation on liver sinusoidal endothelial cells(LSECs)is crucial to pathogen clearance and tissue damage in the liver sinusoids and controlled by a series of adhesion molecules expressed on the surface of PMNs and LSECs.The role of lymphocyte function-associated antigen-1(LFA-1)and macrophage-1 antigen(Mac-1)in this process is still contentious.Here we compared the dynamic force spectra of the binding ofβ2 integrin to intercellular adhesion molecule-1(ICAM-1)on LSECs using atomic force microscopy(AFM)and performed free and steered molecular dynamics(MD)simulations to analyze their structural bases of LFA-1-or Mac-1-I-domain and ICAM-1-D1 or D3 pair in their force spectra.Our AFM data suggest that the mechanical strength of LFA-1-ICAM-1 bond is significantly stronger than that of Mac-1-ICAM-1 bond,implying a dominate role for LFA-1 to mediate PMN adhesion under shear flow.MD simulations indicated that spontaneous dissociation of Mac-1-I-domain vs.ICAMD3-domain is slower with the stronger interaction energy than that for LFA-1 I-domain vs.ICAM-D1-domain and that the rupture force for Mac-1 is lower than that for LFA-1,which are in qualitative agreement with the above experimental observations.These data indicate that the biomechanical features of LFA-1 and Mac-1 to mediate PMN adhesion on LSECs in vitro are similar with those in other tissues like cerebrovascular endothelium,while Mac-1-mediated PMN recruitment in liver sinusoids may stem from the slow blood flow in vivo.These findings further the understandings of PMN recruitment under shear flow in liver sinusoids.