Department of Mechanical and Aerospace Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA.
Department of Biomedical Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA.
J Bone Miner Metab. 2020 Mar;38(2):151-160. doi: 10.1007/s00774-019-01042-8. Epub 2019 Sep 6.
Matrix damage sustained by bone tissue is repaired by the concerted action of bone cells. Previous studies have reported extracellular calcium ([Ca]) efflux to originate from regions of bone undergoing diffuse microdamage termed as "diffuse microdamage-induced calcium efflux" (DMICE). DMICE has also been shown to activate and increase intracellular calcium ([Ca]) signaling in osteoblasts via the involvement of voltage-gated calcium channels (VGCC). Past studies have assessed early stage (< 1 h) responses of osteoblasts to DMICE. The current study tested the hypothesis that DMICE has longer-term sustained effect such that it induces anabolic response of osteoblasts.
Osteoblasts derived from mouse calvariae were seeded on devitalized bovine bone wafers. Localized diffuse damage was induced in the vicinity of cells by bending. The response of osteoblasts to DMICE was evaluated by testing gene expression, protein synthesis and mineralized nodule formation.
Cells on damaged bone wafers showed a significant increase in RUNX2 and Osterix expression compared to non-loaded control. Also, RUNX2 and Osterix expression were suppressed significantly when the cells were treated with bepridil, a non-selective VGCC inhibitor, prior to loading. Significantly higher amounts of osteocalcin and mineralized nodules were synthesized by osteoblasts on diffuse damaged bone wafers, while bepridil treatment resulted in a significant decrease in osteocalcin production and mineralized nodule formation.
In conclusion, this study demonstrated that DMICE activates anabolic responses of osteoblasts through activation of VGCC. Future studies of osteoblast response to DMICE in vivo will help to clarify how bone cells repair diffuse microdamage.
骨骼组织受到的基质损伤是由骨细胞协同作用修复的。先前的研究报告称，细胞外钙（[Ca]）外流源自被称为“弥散微损伤诱导钙外流（DMICE）”的弥散微损伤区域。DMICE 还通过电压门控钙通道（VGCC）的参与，激活并增加成骨细胞内钙（[Ca]）信号。过去的研究评估了成骨细胞对 DMICE 的早期（<1 小时）反应。本研究检验了这样一个假设，即 DMICE 具有更长期的持续效应，从而诱导成骨细胞的合成代谢反应。
从老鼠颅骨中分离出的成骨细胞接种在去活牛骨薄片上。通过弯曲在细胞附近诱导局部弥散损伤。通过测试基因表达、蛋白质合成和矿化结节形成来评估成骨细胞对 DMICE 的反应。
与未加载对照相比，受损骨片上的细胞 RUNX2 和 Osterix 表达显著增加。此外，在用非选择性 VGCC 抑制剂贝普立肽处理细胞之前，加载时 RUNX2 和 Osterix 表达显著受到抑制。弥散损伤骨片上的成骨细胞合成了大量的骨钙素和矿化结节，而贝普立肽处理导致骨钙素产生和矿化结节形成显著减少。
总之，本研究表明，DMICE 通过激活 VGCC 激活成骨细胞的合成代谢反应。骨细胞对 DMICE 的体内反应的进一步研究将有助于阐明骨细胞如何修复弥散微损伤。
