Shuichiro Fukushima’s research while affiliated with Keio University and other places

Morphological remodeling of endothelial cells that was induced by blood flow is considered an adaptive response to a mechanical stimulus. To determine the mechanisms of the response, we examined how shear stress on the surface of the same group of cells changed. The surface geometry of the cells was measured by confocal laser scanning microscopy, and the shear stress distribution on the measured cell surface was determined using the flow field simulated by computational fluid dynamics. When the cells, which were polygonal without alignment at the beginning of the flow exposure, elongated and aligned in the flow direction, the mean shear stress of the cells decreased with time. However, there were some cells whose mean shear stress was increased, and the morphological change of each cell was not always adaptive. The results show the importance of interaction with surrounding cells to the adaptive response as demonstrated in the endothelial layer.

A microscopic velocimetry technique for evaluating the flow field over cultured endothelial cells was developed. Flow around a cell model scaled up by a factor of 100 was visualized by using an optical microscope and was quantified by using particle-tracking velocimetry. Wall shear stress on the model surface was determined from a two-dimensional velocity field interpolated from measured velocity vectors. Accuracy of the velocimetry was verified by measuring the flow over a sinusoidal cell model that had a wall shear stress profile analytically determined with linear perturbation theory. Comparison of the experimental results with the analytical solution revealed that the total error of the measured wall shear stress was 6 percent.

Responses of endothelial cells to shear stress due to blood flow are basically heterogeneous. One of the reasons of the heterogeneity may be variation of the shear stress at individual cell level. In this study, we presented a method of three-dimensional cell shape measurement by confocal laser scanning microscopy, and determination of shear stress distribution on the surface of the cell by particle tracking velocimetry with a scale-up model. Thereby, shear stress distribution on the surface of statically cultured cells and flow-exposed cells was determined. From the results of two examples, it has been shown that the shear stress distribution on a cell had close correlation not only with the surface geometry of the cell but also with that of surrounding cells, and varied from cell to cell. The subcelluar distribution of the shear stress may provide important information to clarify the mechanisms of the mechanotransduction of endothelial cells.

Wall shear stress induced by blood flow affects morphology and physiology of endothelial cells. The specific mechanisms of mechano-biological interactions alternating shapes and functions have not been identified in the cells, because of the lack of a detailed description of microscopic flow near the cell surface. We therefore developed velocimetry using expanded cell model and demonstrated that the microscopic flow depended on three-dimensional cell shape (Fukushima et al., 1997, 1998). Furthermore, we determined wall shear stress distribution on cultured endothelial cells experimentally.

Velocimetry using expanded cell model was developed. It was demonstrated that the microscopic flow depended on three-dimensional cell shape. Further, wall shear stress distribution on cultured endothelial cells was determined experimentally.

Wall shear stress induced by blood flow affects morphology and physiology of endothelial cells. The specific mechanisms alternating shapes and functions have not been identified in endothelial cells, because of the lack of a detailed description of the flow near the cell surface. To clarify the mechanism, an analysis of the flow on subcellular scale is required. We therefore developed velocimetry using expanded cell model (Fukushima et al. 1997). The method, however, needs some improvements in order to discuss wall shear stress distribution on subcellular scale. In this paper we deal with determination of three-dimensional velocity field and wall shear stress distribution and verify the reliability by comparing experimental results with theoretical solution.