Mechanical Strength and Structural Basis of β2 Integrin to Mediate Neutrophil Accumulation on Liver Sinusoidal Endothelial Cells: A Study Using Atomic Force Microscopy and Molecular Dynamics Simulations

Abstract

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 of β2 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.