Measurement of mechanical properties of cells based on their internal structures

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Relationship linking mechanical properties of cells and their cytoskeletons are important in mechanotransduction. In this study, we measured quasi-static tensile properties and stress relaxation responses mainly of smooth muscle cells (SMCs) freshly isolated from aortic walls (FSMCs) and those cultured following isolation (CSMCs) with micro tensile testers to know the effects of the disruption of actin filaments (AF) or microtubules (MT). Their 3D microstructures were observed with a cell rotation system. Following results were obtained:1. FSMCs were stiffer in their longitudinal direction in which AFs align, and the stiffness of CSMCs decreased by 60% following AF disruption, indicating that AFs play dominant roles in their tensile properties.2. Stress relaxation response of CSMCs could be expressed with the combination of fast exponential decay with a time constant of〜1 min and slow decay with a time constant of 〜1 h, and the AF disruption caused significant change in the slow decay.3. We established a method to stretch cells maintaining their shape on substrate and found that the stiffness of CSMCs decreased by 70 and 30% following AF and MT disruption, respectively. MTs may play significant roles in the tensile properties of SMCs.4. We successfully observed with the cell rotation system that AFs aligned helically in the FSMCs and that nucleus of CSMCs buckled when the cells were detached from substrate and shrank.5. Local stiffness measured with an atomic force microscope increased following MT disruption in CSMCs. Whole-cell stiffness of cultured fibroblasts did not change following MT disruption, but decreased significantly by〜75% following AF disruption.These results indicate that not only AFs but also MTs have significant effects on cell mechanical properties, but the degree of contribution of MTs depends on the cell types and mode of deformation.