Microelastic mapping of living endothelial cells exposed to shear stress in relation to three-dimensional distribution of actin filaments.

The surface topography and local elastic moduli of endothelial cells exposed to shear stress were measured using atomic force microscopy. Bovine aortic endothelial cells were exposed to shear stress of 2Pa for 6, 12 or 24h. In addition, a confocal laser-scanning microscope used in conjunction with the atomic force microscope was used to observe the actin filament structure of these endothelial cells to elucidate the relationship between mechanical properties and cytoskeletal structure. The elastic modulus, calculated using the Hertz model, was measured at 50x50 points at 1mum intervals within 40min. For endothelial cells sheared for 6h and 12h, the elastic modulus at the upstream region was found to be higher than that at the downstream region. For endothelial cells sheared for 24h, the elastic modulus at both the upstream and downstream regions increased. Fluorescent images showed thick, elongated actin filaments oriented in the direction of flow at the ventral surface of the cells. In the middle plane of the cells, actin filaments developed around the nucleus, while in the upper plane, short, thick actin filaments were observed but thick stress fibers were not present. The high elastic modulus came from the stress fibers. These results indicate that the higher elastic modulus observed in the upstream and downstream regions of sheared endothelial cells is mainly due to the development of stress fibers at the ventral surface and middle plane of the cell.