Spatiotemporal analysis of flow-induced intermediate filament displacementin living endothelial cells

The distribution of hemodynamic shear stress throughout the arterial tree i s transduced by the endothelium into local cellular responses that regulate vasoactivity, vessel wall remodeling, and atherogenesis, Although the exac t mechanisms of mechanotransduction remain unknown, the endothelial cytoske leton has been implicated in transmitting extracellular force to cytoplasmi c sites of signal generation via connections to the lumenal, intercellular, and basal surfaces. Direct observation of intermediate filament (IF) displ acement in cells expressing green fluorescent protein-vimentin has suggeste d that cytoskeletal mechanics are rapidly altered by the onset of fluid she ar stress. Here, restored images from time-lapse optical sectioning fluores cence microscopy were analyzed as a four-dimensional intensity distribution function that represented IF positions. A displacement index, related to t he product moment correlation coefficient as a function of time and subcell ular spatial location, demonstrated patterns of IF displacement within endo thelial cells in a confluent monolayer, Flow onset induced a significant in crease in IF displacement above the nucleus compared with that measured nea r the coverslip surface, and displacement downstream from the nucleus was l arger than in upstream areas. Furthermore, coordinated displacement of IF n ear the edges of adjacent cells suggested the existence of mechanical conti nuity between cells. Thus, quantitative analysis of the spatiotemporal patt erns of flow-induced IF displacement suggests redistribution of intracellul ar force in response to alterations in hemodynamic shear stress acting at t he lumenal surface.