Roles of 3D traction forces in migration and focal adhesion dynamics of bovine aortic endothelial cells

Mechanical forces play an important role in the regulation of physiological responses which affect cell structure and function, including local changes of adhesion sites and cytoskeletons, and alterations in cell motility, proliferation and survival. The traction forces exerted by an adherent cell on the substrate have been studied with traction force microscopy techniques. However, only two dimensional (2D) traction forces tangential to the substrate have been considered in the previous studies although forces are generally three-dimensional (3D) in nature. I have developed a novel technique to measure 3D traction forces, including the normal forces as well as tangential forces, exerted by cultured bovine aortic endothelial cells (BAECs) based on the image processing techniques and finite element method (FEM). Using this method, it has been demonstrated that not only tangential but also normal traction forces are related to the BAEC on the substrate. Upward normal traction force is shown at the edge of the BAEC while downward normal traction force is dominant under the nucleus. Combined with green fluorescent protein (GFP) technique to visualize the focal adhesion (FA) molecules including focal adhesion kinase (FAK) and paxillin, it has been demonstrated that 3D traction force is related to the FA dynamics of BAECs. It has been shown in migrating cells that upward normal traction force is related to the dynamic FAs (FAs that traverse a long distance or undergo turnover), and that downward normal traction force is related to the stable FAs (FAs do not change their position and size). This 3D traction force microscopy technique applied to BAECs and other types of cells provides a new way of assessing the full range of biomechanical dynamics of cells in conjunction with their biochemical activities and can contribute to the understanding of cellular functions in health and diseas