Flow-Induced Cytoskeletal Changes in Endothelial Cells Growing on Curved Surfaces

Objective: Our purpose was to investigate the effect of the shape of the growth surface (curved versus flat) on flow-induced F-actin organization in endothelial cells. Methods: Human umbilical vein endothelial cells were grown to confluence on curved or flat surfaces. Microchannels (curved surface, 10- to 30-μm radius) or parallel plate flow chambers were perfused (30 minutes to 6 hours) at physiological flow rates (wall shear stress 1 to 10 dyn/cm²). Results: On curved surfaces, the number of central F-actin stress fibers (for cells of equal area) decreased from 4.8 ± 0.3 (mean ± SE, n = 36) (static) to 0.9 ± 0.5 per cell in perfused microchannels. Perfusion with 100 μM histamine prevented this response to flow (5.5 ± 0.8 per cell, n = 12). Stress fibers were initially aligned with the long axis of the microchannel at an angle of 9 ± 0.7° (static). With flow, alignment of the few remaining central F-actin stress fibers with respect to the long axis of the microchannel decreased to 19 ± 4°; this was prevented by perfusion with histamine (5.6 ± 1°). The number of stress fibers per cell, for cells grown on flat surfaces (8.1 ± 0.3, static, n = 36) was significantly greater than for cells on curved surfaces, and did not change with flow (8.1 ± 0.5 per cell, n = 6). On flat surfaces, the stress fiber orientation (with respect to the longitudinal axis of the channel) was 42 ± 1.4° (static) and did not change with flow (38 ± 4.2°). Conclusions: Endothelial cells on curved growth surfaces respond to flow rapidly, with marked changes in F-actin central stress fiber formation. This implicates a tight relationship between cell shape and the environmental substrate, and suggests that the shape of the endothelial cell significantly impacts its ability to respond to its environment.