Overexpression of Bone Sialoprotein Leads to an Uncoupling of Bone Formation and Bone Resorption in Mice
Overexpression of Bone Sialoprotein Leads to an Uncoupling of Bone Formation and Bone Resorption in Mice
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DOI：
10.1359/jbmr.080605
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发表时间：
2008-11-01
影响因子：
6.2
通讯作者：
Chen, Jake
中科院分区：
文献类型：
--
作者：
Valverde, Paloma;Zhang, Jin;Chen, Jake
本研究的目的是确定骨唾液蛋白（BSP）过表达在体内骨代谢的影响，通过使用纯合子转基因小鼠系，组成型过表达小鼠BSP cDNA驱动的巨细胞病毒（CMV）启动子。将CMV-BSP转基因（TG）小鼠和野生型小鼠称重，并测量其长度、BMD和骨小梁体积。测定血清RANKL、骨钙素、骨保护素（OPG）、TRACP 5 b和PTH水平。骨组织形态计量学，von Kossa染色，RT-PCR分析，Western blot，MTS测定，体外矿化测定和TRACP染色也被用于描述该转基因小鼠系的表型。与野生型小鼠相比，成年TG小鼠表现出轻度侏儒症，BMD值较低，骨小梁体积较低。TG小鼠血清中钙水平升高，PTH水平降低，而磷和镁水平在正常范围内。TG小鼠血清中成骨细胞分化标志物水平较低，而标志物水平较高，表明骨细胞活性和骨吸收。H&E染色、TRACP染色和骨组织形态计量学显示，成年TG小鼠的骨更薄，巨大破骨细胞数量更多，而成骨细胞数量在TG小鼠和WT小鼠之间没有显著变化。此外，TG小鼠肥大带的垂直长度略有增加。此外，离体实验表明，过度表达BSP减少成骨细胞的人口和增加骨细胞活性。部分由于其在增强骨细胞活性和减少成骨细胞数量方面的作用，BSP过表达导致骨形成和吸收的解偶联，这反过来又导致小鼠的骨质减少和轻度侏儒症。这些发现有助于开发以高血清BSP水平为特征的代谢性骨病的治疗方法。
The purpose of this study was to determine the effects of bone sialoprotein (BSP) overexpression in bone metabolism in vivo by using a homozygous transgenic mouse line that constitutively overexpresses mouse BSP cDNA driven by the cytomegalovirus (CMV) promoter. CMV-BSP transgenic (TG) mice and wildtype mice were weighed, and their length, BMD, and trabecular bone volume were measured. Serum levels of RANKL, osteocalcin, osteoprotegerin (OPG), TRACP5b, and PTH were determined. Bone histomorphometry, von Kossa staining, RT-PCR analysis, Western blot, MTS assay, in vitro mineralization assay, and TRACP staining were also performed to delineate phenotypes of this transgenic mouse line. Compared with wildtype mice, adult TG mice exhibit mild dwarfism, lower values of BMD, and lower trabecular bone volume. TG mice serum contained increased calcium levels and decreased PTH levels, whereas the levels of phosphorus and magnesium were within normal limits. TG mice serum also exhibited lower levels of osteoblast differentiation markers and higher levels of markers, indicating osteoclastic activity and bone resorption. H&E staining, TRACP staining, and bone histomorphometry showed that adult TG bones were thinner and the number of giant osteoclasts in TG mice was higher, whereas there were no significant alterations in osteoblast numbers between TG mice and WT mice. Furthermore, the vertical length of the hypertrophic zone in TG mice was slightly enlarged. Moreover, ex vivo experiments indicated that overexpression of BSP decreased osteoblast population and increased osteoclastic activity. Partly because of its effects in enhancing osteoclastic activity and decreasing osteoblast population, BSP overexpression leads to an uncoupling of bone formation and resorption, which in turn results in osteopenia and mild dwarfism in mice. These findings are expected to help the development of therapies to metabolic bone diseases characterized by high serum level of BSP.