Shear stress induces spatial reorganization of the endothelial cell cytoskeleton

Abstract

The morphology of endothelial cells in vivo depends on the local hemodynamic forces. Cells are polygonal and randomly oriented in areas of low shear stress, but they are elongated and aligned in the direction of fluid flow in regions of high shear stress. Endothelial cells in vitro also have a polygonal shape, but the application of shear stress orients and elongates the cells in the direction of fluid flow. The corresponding spatial reorganization of the cytoskeleton in response to the applied hemodynamic forces is unknown. In this study, we determined the spatial reorganization of the cytoskeleton throughout the volume of cultured bovine aortic endothelial cells after the cells had been exposed to a physiological level of shear stress for 0, 1.5, 3, 6, 12, or 24 h. The response of the monolayer to shear stress was not monotonic; it had three distinct phases. The first phase occurred within 3 h. The cells elongated and had more stress fibers, thicker intercellular junctions, and more apical microfilaments. After 6 h of exposure, the monolayer entered the second phase, where the cells exhibited characteristics of motility. The cells lost their dense peripheral bands and had more of their microtubule organizing centers and nuclei located in the upstream region of the cell. The third phase began after 12 h of exposure and was characterized by elongated cells oriented in the direction of fluid flow. The stress fibers in these cells were thicker and longer, and the heights of the intercellular junctions and microfilaments were increased. These results suggest that endothelial cells initially respond to shear stress by enhancing their attachments to the substrate and neighboring cells. The cells then demonstrate characteristics of motility as they realign. The cells eventually thicken their intercellular junctions and increase the amount of apical microfilaments. The time course of rearrangement can be described as a constrained motility that produces a new cytoskeletal organization that alters how the forces produced by fluid flow act on the cell and how the forces are transmitted to the cell interior and substrate.

Finite-Element Stress Analysis of a Multicomponent Model of Sheared and Focally-Adhered Endothelial Cells

“…20 However, it has been shown here that a continuum approach to cell mechanics can reproduce heterogeneous response in cells consistent with what is reported in the literature, suggesting that the cytoskeletal structures and other organelles are sufficiently inter-connected and pore sizes are small enough (~50 nm) for the cytoplasm to be approximated by continuum theory. However, interconnections of stiff filaments and compressive elements may play a role in altering the transmission of stress within the cell.…”

“…Thus the present model provides quantitative predictions of early, rapid, shear-induced deformations (which are important in the earliest mechanotransduction events). Larger force-induced displacements of cytoplasmic components 20,23 observed on the order of minutes to hours after shearimposition may be better explained by models which include structural remodeling, plastic deformation, or cytoskeletal force generation.…”

Characterisation of glucose transporters in the intact coronary artery endothelium in rats: GLUT-2 upregulated by long-term hyperglycaemia

“…Endothelial cells were distinguished from other cells of the vascular wall using morphological criteria and specific markers. The nuclei of endothelial cells are oriented parallel to the lumen due to the shear stress produced by blood flow [23], whereas smooth muscle cell nuclei are oriented perpendicularly. This is reflected in the fusiform shape of the DAPI-labelled nuclei and in their orientation, parallel to the long axis of the vessel, as shown in Fig.…”

Assembly and Reorientation of Stress Fibers Drives Morphological Changes to Endothelial Cells Exposed to Shear Stress

“…Adaptation to shear involves a high degree of co-alignment of microfilaments, focal adhesion complexes, and microtubules. 41 Because cytoskeletal and adhesive structures display considerable stochastic behavior, 42,43 their continuous, active reorganization may offset an incessant, entropy-driven drift toward randomized orientation of cell structures and, ultimately, cell morphology.…”