Morinobu Mikihiko, Ishijima Muneaki, Rittling Susan R, Tsuji Kunikazu, Yamamoto Haruyasu, Nifuji Akira, Denhardt David T, Noda Masaki
Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan.
J Bone Miner Res. 2003 Sep;18(9):1706-15. doi: 10.1359/jbmr.2003.18.9.1706.
To clarify the role of OPN in bone formation under mechanical stress, we examined the expression and the function of OPN in bone using an expansion force-induced osteogenesis model. Our results indicated that OPN expression was enhanced during the bone formation and that OPN would be one of the positive factors for the bone formation under mechanical stress.
Bone formation is known to be stimulated by mechanical stress; however, molecules involved in stress-dependent regulation of bone formation have not yet been fully characterized. Extracellular matrix proteins such as osteopontin (OPN) could play a role in mediation of the mechanical stress signal to osteoblasts. However, the function of OPN in bone formation under mechanical force is not known. Therefore, we examined the expression and the role of OPN in bone formation in vivo under tensile mechanical stress.
Sagittal sutures of mice were subjected to expansion mechanical stress by setting orthodontic spring wires, and OPN expression during bone formation within the suture gap was examined.
Expansion of the sutures resulted in bone formation at the edges of the parietal bones within the sagittal suture. Immunohistochemical analysis revealed abundant accumulation of OPN protein in the matrix of newly formed bone on the inner edge of the parietal bone within the mechanically expanded sutures. Osteoblasts forming bone within the suture subjected to tensile stress also exhibited high levels of OPN protein expression. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis indicated that OPN mRNA expression was enhanced in wild-type calvariae subjected to expansion force compared with the control calvariae where dead spring wires were set without expansion stress. In addition, type I collagen mRNA was also expressed in the calvariae under the mechanical stimuli. To understand the function of OPN, sagittal sutures in OPN-deficient mice were subjected the expansion stress, and bone formation within the suture to fill the expanded gap was compared with that observed in wild-type mice. OPN deficiency reduced bone formation at the edge of the parietal bone in contact with the expanded suture gap.
These observations revealed that OPN plays a pivotal role in bone formation under tensile mechanical stress.
为阐明骨桥蛋白（OPN）在机械应力下骨形成中的作用，我们使用扩张力诱导成骨模型研究了OPN在骨中的表达及功能。我们的结果表明，在骨形成过程中OPN表达增强，并且OPN是机械应力下骨形成的积极因素之一。
已知机械应力可刺激骨形成；然而，参与骨形成的应力依赖性调节的分子尚未完全明确。细胞外基质蛋白如骨桥蛋白（OPN）可能在将机械应力信号介导至成骨细胞中发挥作用。然而，OPN在机械力作用下骨形成中的功能尚不清楚。因此，我们研究了在拉伸机械应力下体内OPN在骨形成中的表达及作用。
通过设置正畸弹簧丝对小鼠矢状缝施加扩张机械应力，并检测缝间隙内骨形成过程中OPN的表达。
缝的扩张导致矢状缝内顶骨边缘的骨形成。免疫组织化学分析显示，在机械扩张缝内顶骨内缘新形成骨的基质中，OPN蛋白大量积聚。在承受拉伸应力的缝内形成骨的成骨细胞也表现出高水平的OPN蛋白表达。逆转录聚合酶链反应（RT-PCR）分析表明，与设置无扩张应力的死弹簧丝的对照颅骨相比，受到扩张力的野生型颅骨中OPN mRNA表达增强。此外，在机械刺激下颅骨中也表达I型胶原mRNA。为了解OPN的功能，对OPN缺陷小鼠的矢状缝施加扩张应力，并将缝内填充扩张间隙的骨形成与野生型小鼠中观察到的情况进行比较。OPN缺陷减少了与扩张缝间隙接触的顶骨边缘的骨形成。
这些观察结果表明，OPN在拉伸机械应力下的骨形成中起关键作用。
