Biomechanics Laboratory, Department of Mechanical Engineering, Nagoya Institute of Technology, Omohi College, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan.
Biomechanics Laboratory, Department of Mechanical Engineering, Nagoya Institute of Technology, Omohi College, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan.
J Biomech. 2014 Apr 11;47(6):1422-9. doi: 10.1016/j.jbiomech.2014.01.042. Epub 2014 Jan 31.
Actin stress fibers (SFs) generate intercellular tension and play important roles in cellular mechanotransduction processes and the regulation of various cellular functions. We recently found, in vascular smooth muscle cells (SMCs) cultured on a substrate, that the apical SFs running across the top surface of the nucleus have a mechanical connection with the cell nucleus and that their internal tension is transmitted directly to the nucleus. However, the effects of the connecting conditions and binding forces between SFs and the nucleus on force transmission processes are unclear at this stage. Here, we estimated the mechanical connection between apical SFs and the nucleus in SMCs, taking into account differences in the contractility of individual SFs, using experimental and numerical approaches. First, we classified apical SFs in SMCs according to their morphological characteristics: one subset appeared pressed onto the apical surface of the nucleus (pressed SFs), and the other appeared to be smoothly attached to the nuclear surface (attached SFs). We then dissected these SFs by laser irradiation to release the pretension, observed the dynamic behavior of the dissected SFs and the nucleus, and estimated the pretension of the SFs and the connection strength between the SFs and the nucleus by using a simple viscoelastic model. We found that pressed SFs generated greater contractile force and were more firmly connected to the nuclear surface than were attached SFs. We also observed line-like concentration of the nuclear membrane protein nesprin 1 and perinuclear DNA that was significantly located along the pressed SFs. These results indicate that the internal tension of pressed SFs is transmitted to the nucleus more efficiently than that of attached SFs, and that pressed SFs have significant roles in the regulation of the nuclear morphology and rearrangement of intranuclear DNA.
肌动蛋白应力纤维（SFs）产生细胞间张力，在细胞力学转导过程和各种细胞功能的调节中发挥重要作用。我们最近发现，在培养于基底上的血管平滑肌细胞（SMCs）中，横跨核顶表面延伸的顶端 SFs 与细胞核具有机械连接，并且它们的内部张力直接传递到细胞核。然而，在现阶段，SFs 和细胞核之间的连接条件和结合力对力传递过程的影响尚不清楚。在这里，我们通过实验和数值方法，考虑到单个 SFs 的收缩性差异，估计了 SMCs 中顶端 SFs 与细胞核之间的机械连接。首先，我们根据形态特征对顶端 SFs 进行分类：一部分呈压在核顶表面（受压 SFs），另一部分则呈平滑附着在核表面（附着 SFs）。然后，我们通过激光照射将这些 SFs 分离以释放预张力，观察分离后的 SFs 和细胞核的动态行为，并使用简单的粘弹性模型估计 SFs 的预张力和 SFs 与细胞核之间的连接强度。我们发现，受压 SFs 产生的收缩力更大，与核表面的连接也更牢固，而附着 SFs 则相反。我们还观察到核膜蛋白 nesprin 1 和核周 DNA 的线状聚集，这些聚集物明显沿着受压 SFs 分布。这些结果表明，受压 SFs 的内部张力比附着 SFs 更有效地传递到细胞核，并且受压 SFs 在调节核形态和核内 DNA 的重排方面具有重要作用。
