Costa Kevin D, Sim Alan J, Yin Frank C-P
Department of Biomedical Engineering, Columbia University, New York, NY, USA.
J Biomech Eng. 2006 Apr;128(2):176-84. doi: 10.1115/1.2165690.
Detailed measurements of cell material properties are required for understanding how cells respond to their mechanical environment. Atomic force microscopy (AFM) is an increasingly popular measurement technique that uniquely combines subcellular mechanical testing with high-resolution imaging. However, the standard method of analyzing AFM indentation data is based on a simplified "Hertz" theory that requires unrealistic assumptions about cell indentation experiments. The objective of this study was to utilize an alternative "pointwise modulus" approach, that relaxes several of these assumptions, to examine subcellular mechanics of cultured human aortic endothelial cells (HAECs). Data from indentations in 2- to 5-microm square regions of cytoplasm reveal at least two mechanically distinct populations of cellular material. Indentations colocalized with prominent linear structures in AFM images exhibited depth-dependent variation of the apparent pointwise elastic modulus that was not observed at adjacent locations devoid of such structures. The average pointwise modulus at an arbitrary indentation depth of 200 nm was 5.6+/-3.5 kPa and 1.5+/-0.76 kPa (mean+/-SD, n=7) for these two material populations, respectively. The linear structures in AFM images were identified by fluorescence microscopy as bundles of f-actin, or stress fibers. After treatment with 4 microM cytochalasin B, HAECs behaved like a homogeneous linear elastic material with an apparent modulus of 0.89+/-0.46 kPa. These findings reveal complex mechanical behavior specifically associated with actin stress fibers that is not accurately described using the standard Hertz analysis, and may impact how HAECs interact with their mechanical environment.
为了理解细胞如何对其力学环境做出反应，需要对细胞材料特性进行详细测量。原子力显微镜（AFM）是一种越来越受欢迎的测量技术，它独特地将亚细胞力学测试与高分辨率成像结合在一起。然而，分析AFM压痕数据的标准方法基于一种简化的“赫兹”理论，该理论对细胞压痕实验做出了不切实际的假设。本研究的目的是利用一种替代的“逐点模量”方法，该方法放宽了其中的一些假设，以研究培养的人主动脉内皮细胞（HAECs）的亚细胞力学。来自细胞质2至5微米见方区域压痕的数据显示，细胞材料至少有两个力学上不同的群体。在AFM图像中与突出的线性结构共定位的压痕显示出表观逐点弹性模量随深度的变化，而在没有此类结构的相邻位置未观察到这种变化。对于这两个材料群体，在任意压痕深度200纳米处的平均逐点模量分别为5.6±3.5千帕和1.5±0.76千帕（平均值±标准差，n = 7）。AFM图像中的线性结构通过荧光显微镜鉴定为f-肌动蛋白束或应力纤维。用4 microM细胞松弛素B处理后，HAECs表现得像一种均匀的线性弹性材料，表观模量为0.89±0.46千帕。这些发现揭示了与肌动蛋白应力纤维特异性相关的复杂力学行为，使用标准的赫兹分析无法准确描述，并且可能会影响HAECs与其力学环境的相互作用。
