Cortical Tension of Cells: From Apical Membrane Patches to Patterned Cells

During their lifetime, cells and tissues have to deal with a variety of mechanical challenges. Shear forces exist inside of vessels, bones have to carry the weight of organisms and connective tissues are generally deformed on a regular basis. The elasticity moduli of human tissues differ by orders of magnitude depending on the tissue type, and the successful homeostasis of elasticity is required for proper function. Cellular mechanics can be described in different ways. Here, indentation studies on apical membranes on living MDCKII cells as well as on isolated apical membrane sheets, originating also from Madin-Darbey Canine Kidney (MDCKII) cells, are presented. Preparation of apical cortices is performed using porous substrates with holes of 1.2 m diameter that are open on both sides. These studies will provide evidence that an intact mechanical cortex can be obtained and behave mechanically similar to living cells, as addition of crosslinking agents like glutaraldehyde will stiffen the patches while treatment with PronaseE will soften them. These results suggest that only a thin layer of cells determines their mechanical response to indentation. Further indentation experiments on an epithelial cell layers show a Correlations of surface mechanical properties of cells with their projected area. To investigate this correlation, micropatterned substrates were created, providing small but precisely shaped islands of extracellular matrix proteins with a non-adhesive surrounding on standard culture dishes’ glass surfaces. Cells in different shapes and areas are used in nanoindentation experiments, creating reliable maps of surface mechanical parameters. The indentation data was analysed by both, a continuum model resulting in Young’s moduli and a tension model yielding a prestress and a compressibility modulus. Characteristic differences were found depending on the geometrical condition of the cells and are discussed here, resembling a possible mechanism for cells to recognize their shape