Shimizu Natsuo, Fujiwara Kyoko, Mayahara Kotoe, Motoyoshi Mitsuru, Takahashi Tomihisa
Department of Orthodontics, Nihon University School of Dentistry, 1-8-3 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-8310, Japan.
Division of Applied Oral Science, Nihon University Graduate School of Dentistry, 1-8-3 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-8310, Japan.
Heliyon. 2023 Jan 24;9(2):e13236. doi: 10.1016/j.heliyon.2023.e13236. eCollection 2023 Feb.
Bone remodelling is the process of bone resorption and formation, necessary to maintain bone structure or for adaptation to new conditions. Mechanical loadings, such as exercise, weight bearing and orthodontic force, play important roles in bone remodelling. During the remodelling process, osteocytes play crucial roles as mechanosensors to regulate osteoblasts and osteoclasts. However, the precise molecular mechanisms by which the mechanical stimuli affect the function of osteocytes remain unclear. In the present study, we analysed viability, cell cycle distribution and gene expression pattern of murine osteocyte-like MLO-Y4 cells exposed to tension force (TF). Cells were subjected to TF with 18% elongation at 6 cycles/min for 24 h using Flexcer Strain Unit (FX-3000). We found that TF stimulation induced cell cycle arrest at G2/M phase but not cell death in MLO-Y4 cells. Differentially expressed genes (DEGs) between TF-stimulated and unstimulated cells were identified by microarray analysis, and a marked increase in glutathione-S-transferase α (GSTA) family gene expression was observed in TF-stimulated cells. Enrichment analysis for the DEGs revealed that Gene Ontology (GO) terms and Kyoto Encyclopedia Genes and Genomes (KEGG) pathways related to the stress response were significantly enriched among the upregulated genes following TF. Consistent with these results, the production of reactive oxygen species (ROS) was elevated in TF-stimulated cells. Activation of the tumour suppressor p53, and upregulation of its downstream target GADD45A, were also observed in the stimulated cells. As GADD45A has been implicated in the promotion of G2/M cell cycle arrest, these observations may suggest that TF stress leads to G2/M arrest at least in part in a p53-dependent manner.
骨重塑是骨吸收和形成的过程，对于维持骨结构或适应新环境是必要的。机械负荷，如运动、负重和正畸力，在骨重塑中起重要作用。在重塑过程中，骨细胞作为机械传感器在调节成骨细胞和破骨细胞方面发挥关键作用。然而，机械刺激影响骨细胞功能的确切分子机制仍不清楚。在本研究中，我们分析了暴露于张力（TF）的小鼠骨细胞样MLO-Y4细胞的活力、细胞周期分布和基因表达模式。使用Flexcer应变单元（FX-3000）以6个循环/分钟的速度对细胞施加18%伸长的TF，持续24小时。我们发现TF刺激诱导MLO-Y4细胞在G2/M期发生细胞周期阻滞，但未导致细胞死亡。通过微阵列分析鉴定了TF刺激细胞和未刺激细胞之间的差异表达基因（DEG），并且在TF刺激的细胞中观察到谷胱甘肽-S-转移酶α（GSTA）家族基因表达显著增加。对DEG的富集分析表明，与应激反应相关的基因本体（GO）术语和京都基因与基因组百科全书（KEGG）途径在TF后上调的基因中显著富集。与这些结果一致，TF刺激的细胞中活性氧（ROS）的产生增加。在受刺激的细胞中还观察到肿瘤抑制因子p53的激活及其下游靶标GADD45A的上调。由于GADD45A与促进G2/M细胞周期阻滞有关，这些观察结果可能表明TF应激至少部分以p53依赖的方式导致G2/M阻滞。
