Mutation in Osteoactivin Decreases Bone Formation in Vivo and Osteoblast Differentiation in Vitro
Mutation in Osteoactivin Decreases Bone Formation in Vivo and Osteoblast Differentiation in Vitro
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DOI：
10.1016/j.ajpath.2013.11.031
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发表时间：
2014-03-01
影响因子：
6
通讯作者：
Safadi, Fayez F.
中科院分区：
文献类型：
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作者：
Abdelmagid, Samir M.;Belcher, Joyce Y.;Safadi, Fayez F.
我们之前已经确定骨激活素（OA），由基因编码，作为一个成骨因子，刺激成骨细胞分化在体外。为了阐明OA在成骨过程中的重要性，我们对Gpnmb功能缺失突变的小鼠模型DBA/2J （D2J）的骨骼表型进行了表征。D2J小鼠显微断层扫描显示，与野生型小鼠相比，小梁质量减少[DBA/2J-Gpnmb(+)//SjJ (D2J/Gpnmb)]。血清分析显示，D2J小鼠OA及骨形成标志物碱性磷酸酶和骨钙素降低。与D2J/Gpnmb（+）小鼠相比，D2J小鼠的类骨和矿化表面减少，但成骨细胞数量增加。然后，我们检测了D2J成骨细胞在培养中的分化能力，在培养中，它们的分化和功能下降，表现为碱性磷酸酶活性低和基质矿化。定量RT-PCR分析证实D2J成骨细胞分化标记物表达降低。在体外，与D2J/Gpnmb（+）成骨细胞相比，D2J成骨细胞增殖和存活明显减少。接下来，我们研究突变的OA蛋白是否会诱导D2J成骨细胞内质网应激。D2J成骨细胞内质网应激标志物和内质网超微结构均未发生改变。最后，我们评估了可能改变D2J成骨细胞增殖的潜在机制。有趣的是，tgf - β受体和Smad-2/3磷酸化在D2J成骨细胞中上调，表明OA有助于tgf - β信号传导。这些数据证实了骨关节炎在出生后骨形成中的合成代谢作用。
We have previously identified osteoactivin (OA), encoded by Gprimb, as an osteogenic factor that stimulates osteoblast differentiation in vitro. To elucidate the importance of OA in osteogenesis, we characterized the skeletal phenotype of a mouse model, DBA/2J (D2J) with a loss-of-function mutation in Gpnmb. Micro-tomography of D2J mice showed decreased trabecular mass, compared to that in wild-type mice [DBA/2J-Gpnmb(+)//SjJ (D2J/Gpnmb)]. Serum analysis showed decreases in OA and the bone-formation markers alkaline phosphatase and osteocalcin in D2J mice. Although D2J mice showed decreased osteoid and mineralization surfaces, their osteoblasts were increased in number, compared to D2J/Gpnmb(+) mice. We then examined the ability of D2J osteoblasts to differentiate in culture, where their differentiation and function were decreased, as evidenced by low alkaline phosphatase activity and matrix mineralization. Quantitative RT-PCR analyses confirmed the decreased expression of differentiation markers in D2J osteoblasts. In vitro, D2J osteoblasts proliferated and survived significantly less, compared to D2J/Gpnmb(+) osteoblasts. Next, we investigated whether mutant OA protein induces endoplasmic reticulum stress in D2J osteoblasts. Neither endoplasmic reticulum stress markers nor endoplasmic reticulum ultrastructure were altered in D2J osteoblasts. Finally, we assessed underlying mechanisms that might alter proliferation of D2J osteoblasts. Interestingly, TGF-beta receptors and Smad-2/3 phosphorytation were up-regulated in D2J osteobtasts, suggesting that OA contributes to TGF-beta signaling. These data confirm the anabolic role of OA in postnatal bone formation.