Department of Mechanical Systems Engineering, Tokyo Metropolitan University, Hachioji, Tokyo, Japan; Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California Berkeley, Berkeley, CA, USA.
Department of Mechanical Systems Engineering, Tokyo Metropolitan University, Hachioji, Tokyo, Japan.
J Biomech. 2021 Apr 15;119:110292. doi: 10.1016/j.jbiomech.2021.110292. Epub 2021 Feb 14.
Nuclear deformation caused by mechanical stimuli has been suggested to significantly impact various cellular activities, such as gene expression, protein synthesis and mechanotransduction. To understand how nuclear deformation regulates cellular behaviors, the details of intranuclear strain distribution caused by mechanical stimuli as well as intranuclear mechanical properties are required. Here, we examine local mechanical strains within the nucleus in a living cell subjected to substrate stretching and estimate the local nuclear mechanical properties. A HeLa cell in a PDMS chamber was subjected to a 10% step-strain by using a custom-made uni-axial stretching device. Local displacements and the distribution of the equivalent strain within the nucleus were obtained from fluorescence images of the nucleus before and after the application of stretching. The intranuclear strain showed heterogeneous distribution, and higher strain regions were observed not only at the center, but also periphery of the nucleus. We examined the role of the chromatin condensation level and actin cytoskeleton by treating cells with Trichostatin A and Cytochalasin D, respectively. Interestingly, these treatments did not cause significant changes in the intranuclear strain distribution. Referring to the experimental results, we reproduced the nuclear strain distribution in a finite element model to estimate relative distribution of Young's modulus within the nucleus, and observed substantially lower Young's modulus levels in the peripheral regions of the nucleus relative to those found in the central regions of the nucleus. We reveal heterogeneous strain distribution within the nucleus in a living cell subjected to substrate stretching, and the results provide insights into the importance of heterogeneity of intranuclear mechanical properties.
机械刺激引起的核变形被认为会显著影响各种细胞活动，如基因表达、蛋白质合成和力转导。为了了解核变形如何调节细胞行为，需要了解机械刺激引起的核内应变分布的细节以及核内的力学性质。在这里，我们研究了活细胞中细胞核内的局部力学应变，这些细胞受到基底拉伸的影响，并估计了局部核的力学性质。在使用定制的单轴拉伸装置对 PDMS 室中的 HeLa 细胞施加 10%的阶跃应变后，我们从拉伸前后细胞核的荧光图像中获得了细胞核内的局部位移和等效应变分布。核内应变表现出不均匀的分布，不仅在核的中心，而且在核的外围也观察到了较高的应变区域。我们通过分别用 Trichostatin A 和 Cytochalasin D 处理细胞来研究染色质凝聚水平和肌动蛋白细胞骨架的作用。有趣的是，这些处理并没有导致核内应变分布的显著变化。根据实验结果，我们在有限元模型中再现了核应变分布，以估计核内杨氏模量的相对分布，并且观察到核的外围区域的杨氏模量水平明显低于核的中心区域的杨氏模量水平。我们揭示了活细胞在基底拉伸下细胞核内的不均匀应变分布，结果为核内力学性质的异质性的重要性提供了线索。
