Measurement and finite element modeling of the force balance in the vertical section of adhering vascular endothelial cells

Previous studies on the intracellular force balance that forms the adherent cell structure have paid much attention to the mechanical behavior of cells seen in the horizontal project plane. By contrast, there are only few quantitative considerations on that in the vertical plane. Particularly, the contribution of the nucleus to the bearing of the vertical cell structure remains unclear. Here, we investigated the determinant of the vertical cell morphology from experimental and numerical approaches. The effect of cytoskeleton-affecting agents on the vascular endothelial cell height, as a measure of the vertical force balance, was examined by atomic force microscope indentation, demonstrating that actin depolymerization caused an increase in cell height. In contrast, disruption of microtubules lowered the cell height, whereas their stabilization elevated the cell plasma membrane. Time-lapse microscopy showed that intracellular vesicles moved radially outward after the microtubule disruption, together with an enlargement of the nuclear area in the project plane, that is probably associated with the decrease in cell height. Finite element analyses employing a 3D model were carried out to interpret the experimental results and examine potent parameters (such as prestress, elastic modulus, and Poisson’s ratio) that affect vertical cell morphology. How the prestress in subcellular components influences cells subjected to extracellular tensile forces was also examined. These results indicate that the nuclear/cytoplasmic mechanical properties and degrees of prestress determine the vertical section structure of adhering cells.