Mokbel Marcel, Hosseini Kamran, Aland Sebastian, Fischer-Friedrich Elisabeth
Faculty of Informatics/Mathematics, Hochschule für Technik und Wirtschaft, Dresden, Germany.
Cluster of Excellence Physics of Life, Technische Universität Dresden, Dresden, Germany; Biotechnology Center, Technische Universität Dresden, Dresden, Germany.
Biophys J. 2020 Apr 21;118(8):1968-1976. doi: 10.1016/j.bpj.2020.03.002. Epub 2020 Mar 7.
Cell shape changes are vital for many physiological processes such as cell proliferation, cell migration, and morphogenesis. They emerge from an orchestrated interplay of active cellular force generation and passive cellular force response, both crucially influenced by the actin cytoskeleton. To model cellular force response and deformation, cell mechanical models commonly describe the actin cytoskeleton as a contractile isotropic incompressible material. However, in particular at slow frequencies, there is no compelling reason to assume incompressibility because the water content of the cytoskeleton may change. Here, we challenge the assumption of incompressibility by comparing computer simulations of an isotropic actin cortex with tunable Poisson ratio to measured cellular force response. Comparing simulation results and experimental data, we determine the Poisson ratio of the cortex in a frequency-dependent manner. We find that the Poisson ratio of the cortex decreases in the measured frequency regime analogous to trends reported for the Poisson ratio of glassy materials. Our results therefore indicate that actin cortex compression or dilation is possible in response to acting forces at sufficiently fast timescales. This finding has important implications for the parameterization in active gel theories that describe actin cytoskeletal dynamics.
细胞形状变化对于许多生理过程至关重要，如细胞增殖、细胞迁移和形态发生。它们源于主动细胞力产生和被动细胞力响应的协同相互作用，这两者都受到肌动蛋白细胞骨架的关键影响。为了模拟细胞力响应和变形，细胞力学模型通常将肌动蛋白细胞骨架描述为一种收缩性各向同性不可压缩材料。然而，特别是在低频时，没有令人信服的理由假设不可压缩性，因为细胞骨架的含水量可能会发生变化。在这里，我们通过将具有可调泊松比的各向同性肌动蛋白皮质的计算机模拟与测量的细胞力响应进行比较，对不可压缩性假设提出质疑。通过比较模拟结果和实验数据，我们以频率依赖的方式确定皮质的泊松比。我们发现，在测量的频率范围内，皮质的泊松比降低，类似于报道的玻璃态材料泊松比的趋势。因此，我们的结果表明，在足够快的时间尺度上，肌动蛋白皮质可能会因作用力而发生压缩或膨胀。这一发现对于描述肌动蛋白细胞骨架动力学的活性凝胶理论中的参数化具有重要意义。
