Biomechanics Laboratory, Department of Mechanical Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi, 466-8555, Japan; Micro-Nano Biomechanics Laboratory, Department of Mechanical Systems Engineering, Ibaraki University, Nakanarusawa-cho, Hitachi, Ibaraki, 316-8511, Japan.
Biomechanics Laboratory, Department of Mechanical Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi, 466-8555, Japan.
J Mech Behav Biomed Mater. 2023 Feb;138:105630. doi: 10.1016/j.jmbbm.2022.105630. Epub 2022 Dec 20.
Osteogenic differentiation has been reportedly regulated by various mechanical stresses, including fluid shear stress and tensile and compressive loading. The promotion of osteoblastic differentiation by these mechanical stresses is accompanied by reorganization of the F-actin cytoskeleton, which is deeply involved in intracellular forces and the mechanical environment. However, there is limited information about the effect on the mechanical environment of the intracellular nucleus, such as the mechanical properties of the nucleus and intracellular forces exerted on the nucleus, which have recently been found to be directly involved in various cellular functions. Here, we investigated the changes in the intracellular force applied to the nucleus and the effect on nuclear morphology and mechanical properties during osteogenic differentiation in human osteoblast-like cells (Saos-2). We carried out cell morphological analyses with confocal fluorescence microscopy, nuclear indentation test with atomic force microscopy (AFM), and fluorescence recovery after photobleaching (FRAP) for intranuclear DNA. The results revealed that a significant reorganization of the F-actin cytoskeleton from the nuclear surfaces to the cell periphery occurred in the osteogenic differentiation processes, simultaneously with the reduction of compressive forces to the nucleus. Such changes also facilitated nuclear shrinkage and stiffening, and further intranuclear chromatin compaction. The results indicate that the reduction of the intracellular compressive force due to reorganization of the F-actin cytoskeleton affects the intra- and extra-mechanical environment of the nucleus, and this change may affect gene expression and DNA replication in the osteogenic differentiation process.
成骨分化已被报道受多种机械应力调控，包括流体剪切力、拉伸和压缩负荷。这些机械应力促进成骨细胞分化的同时，伴随着 F-肌动蛋白细胞骨架的重组，它深深地涉及细胞内力和机械环境。然而，关于细胞内核的机械环境的影响，如核的力学性质和作用于核的细胞内力，信息有限，这些性质最近被发现直接参与各种细胞功能。在这里，我们研究了在人成骨样细胞（Saos-2）成骨分化过程中，施加于核的细胞内力的变化及其对核形态和力学性质的影响。我们通过共聚焦荧光显微镜进行细胞形态分析，通过原子力显微镜（AFM）进行核压痕试验，以及核内 DNA 的荧光恢复后光漂白（FRAP）。结果表明，在成骨分化过程中，F-肌动蛋白细胞骨架从核表面到细胞边缘发生了显著的重排，同时对核的压缩力减小。这种变化也促进了核的收缩和变硬，以及进一步的核内染色质浓缩。结果表明，由于 F-肌动蛋白细胞骨架的重组导致细胞内压缩力的减小，影响了核的内外机械环境，这种变化可能影响成骨分化过程中的基因表达和 DNA 复制。
