Cytoskeletal response of microvessel endothelial cells to an applied stress force at the submicrometer scale studied by atomic force microscopy.

Cytoskeleton fibers form an intricate three-dimensional network to provide structure and function to microvessel endothelial cells. During accommodation to blood flowing, stress fiber bundles become more prominent and align with the direction of blood flow. This network either mechanically resists the applied shear stress (lateral force) or, if deformed, is dynamically remodeled back to a preferred architecture. However, the detailed response of these stress fiber bundles to applied lateral force at submicrometer scales are as yet poorly understood. In our in vitro study, the tip, topography probe in lateral force microscopy of atomic force microscopy, acted as a tool for exerting quantitative vertical and lateral force on the filaments of the cytoskeleton. Moreover, the authors developed a formula to calculate the value of lateral force exerted on every point of the filaments. The results show that cytoskeleton fibers of healthy tight junctions in rat cerebral microvessel endothelial cells formed a cross-type network, and were reinforced and elongated in the direction of scanning under lateral force of 15-42 nN. Under peroxidation (H(2)O(2) of 300 micromol/L), the cytoskeleton remodeled at intercellular junctions, and changed over the meshwork structures into a dense bundle, that redistributed the stress. Once mechanical forces were exerted on an area, the cells shrank and lost morphologic tight junctions. It would be useful in our understanding of certain pathological processes, such as cerebral ischemia/reperfusion injury, which maybe caused by biomechanical forces and which are overlooked in current disease models.