Measurement of mechanical properties of cells based on their internal structures

细胞的力学性能与其细胞骨架之间的关系在机械转导中具有重要意义。为了解肌动蛋白细丝(AF)或微管(MT)断裂对血管内皮细胞的影响，本研究用微张力仪测定了新分离的主动脉壁(FSMC)和分离后培养的SMC(CSMC)的准静态拉伸特性和应力松弛反应。用细胞旋转系统观察了它们的三维显微结构。结果表明：1.房颤后，FSMCs在与AFS对齐的纵向上硬度增加，硬度下降60%，说明AFS在CSMCs的拉伸性能中起主导作用。CSMCs的应力松弛反应可表现为时间常数为~1min的快速指数衰减和时间常数为~1h的慢衰减的组合，而房颤的破坏使慢衰减发生显著变化。我们建立了一种在基质上保持细胞形状的拉伸方法，发现房颤和MT破坏后，CSMCs的硬度分别下降了70%和30%。MTS可能在SMCs的拉伸性能中起重要作用。利用细胞旋转系统，我们成功地观察到AFS在FSMCs中螺旋排列，当细胞从底物和碎片中分离出来时，CSMCs的细胞核发生弯曲。用原子力显微镜测量的局部硬度随着MT的破坏而增加。体外培养的成纤维细胞的全细胞硬度在MT损伤后无明显变化，但在AF损伤后显著降低~75%。这些结果表明，不仅AFS对细胞力学性能有显著影响，MTS对细胞力学性能的影响程度取决于细胞类型和变形方式。

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.