Flow-induced strain focusing in the endothelial cytoskeleton

Displacement or deformation of the endothelial cell cytoskeleton by hemodynamic shear stress may reflect redistribution of intracellular force to molecular signaling complexes that initiate adaptive mechanisms. In these studies, cytoskeletal movement in response to onset of shear stress was measured in endothelial cells expressing GFP-vimentin or GFP-actin. High-resolution optical sectioning fluorescence microscopy and quantitative image processing revealed increased intermediate filament displacement with height in the cell and in downstream regions of the cytoplasm. The Lagrangian strain tensor demonstrated highly localized deformation near the coverslip. Variability in principal strain orientation increased significantly after onset of shear stress. In contrast to the spatially heterogeneous distribution of displacement and strain in the intermediate filament network, onset of shear stress induced rapid extension of actin ruffles in the upstream direction, and lamellipodia along downstream edges of the cell were often retracted. This directional response often subsided within 10-15 min and occurred in cells in confluent but not subconfluent monolayers. In addition, microfilaments in central regions of the cytoplasm were often displaced by flow onset. These data suggest that endothelial cells sense changes in shear stress and rapidly mobilize an active cytoskeletal response that may contribute to initiation of adaptive mechanotransduction networks.