Suzuki Nobumitsu, Yoshimura Yoshitaka, Deyama Yoshiaki, Suzuki Kuniaki, Kitagawa Yoshimasa
Department of Oral Diagnosis and Oral Medicine, Hokkaido University Graduate School of Dental Medicine, Sapporo 060-8586, Japan.
Int J Mol Med. 2008 Mar;21(3):291-6.
Although it is known that mechanical stress to osteoblast and periodontal ligament cells suppresses osteoclast differentiation, little is known about the direct effect of mechanical stress on osteoclast differentiation. In this study, we examined the role of mechanical stress on osteoclast differentiation using murine pre-osteoclastic RAW264.7 cells treated with receptor activator of nuclear factor-kappaB ligand (RANKL). RAW cells were cultured with RANKL, and mechanical stress was applied for a given period. We counted the number of osteoclast cells which were tartrate-resistant acid phosphatase (TRAP)-positive and multinucleated (2 nuclei or more), and measured mRNA by RT-PCR. There was a decrease in the number of osteoclasts under mechanical stress compared with the number under no mechanical stress. The number of nuclei per osteoclast also decreased compared to the number of nuclei per osteoclast cultured with the application of mechanical stress. As the cells were cultured for a period of 1-7 days and/or for different periods of mechanical stress application, osteoclast differentiation decreased with mechanical stress and increased after removing mechanical stress. Expression of mRNA for the osteoclast-specific genes, TRAP, matrix metalloproteinase-9, cathepsin-K and calcitonin receptor, decreased with mechanical stress and was associated with the number of osteoclasts. Inducible nitric oxide synthase mRNA which inhibits osteoclast differentiation, increased with mechanical stress. In spite of the decrease in osteoclast number with mechanical stress, nuclear factor of activated T cell cytoplasmic 1 (NFATc1) and NFATc2 mRNA expression increased with mechanical stress. These findings indicate that mechanical stress directly suppresses osteoclast differentiation and increases NFATc1 and NFATc2 suggesting delayed differentiation.
尽管已知对成骨细胞和牙周膜细胞施加机械应力会抑制破骨细胞分化，但关于机械应力对破骨细胞分化的直接影响却知之甚少。在本研究中，我们使用经核因子-κB受体活化因子配体（RANKL）处理的小鼠破骨前体细胞RAW264.7，研究了机械应力在破骨细胞分化中的作用。将RAW细胞与RANKL一起培养，并在给定时间段施加机械应力。我们对耐酒石酸酸性磷酸酶（TRAP）阳性且多核（2个核或更多）的破骨细胞数量进行计数，并通过逆转录聚合酶链反应（RT-PCR）测量mRNA。与无机械应力条件下的破骨细胞数量相比，机械应力下破骨细胞数量减少。与施加机械应力培养的破骨细胞的核数量相比，每个破骨细胞的核数量也减少。随着细胞培养1至7天和/或施加不同时间段的机械应力，破骨细胞分化随机械应力而降低，去除机械应力后则增加。破骨细胞特异性基因TRAP、基质金属蛋白酶-9、组织蛋白酶-K和降钙素受体的mRNA表达随机械应力而降低，并与破骨细胞数量相关。抑制破骨细胞分化的诱导型一氧化氮合酶mRNA随机械应力增加。尽管机械应力使破骨细胞数量减少，但活化T细胞核因子细胞质1（NFATc1）和NFATc2的mRNA表达却随机械应力增加。这些发现表明，机械应力直接抑制破骨细胞分化，并增加NFATc1和NFATc2，提示分化延迟。
