Sclerostin Regulates Release of Bone Mineral by Osteocytes by Induction of Carbonic Anhydrase 2
Sclerostin Regulates Release of Bone Mineral by Osteocytes by Induction of Carbonic Anhydrase 2
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DOI：
10.1002/jbmr.2003
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发表时间：
2013-12-01
影响因子：
6.2
通讯作者：
Atkins, Gerald J.
中科院分区：
文献类型：
--
作者：
Kogawa, Masakazu;Wijenayaka, Asiri R.;Atkins, Gerald J.
骨细胞产物硬化蛋白正在成为骨量的重要旁分泌调节因子。最近有研究表明，骨细胞产生NF-B配体受体激活剂（RANKL）在破骨细胞骨吸收中很重要，我们报道了用硬化蛋白外源性处理骨细胞可以增加RANKL介导的破骨细胞活性。有充分的证据表明，骨细胞本身可以从骨中释放矿物质，这一过程被称为骨细胞溶骨。在目前的研究中，我们研究了人类原代骨细胞样细胞（hOCy）和小鼠MLO-Y4细胞对硬化蛋白刺激的矿物溶解的影响。我们发现硬化蛋白上调了骨细胞中碳酸酐酶2 （CA2/Car2）、组织蛋白酶K （CTSK/ CTSK）和抗酒石酸酸性磷酸酶（ACP5/ ACP5）的表达。由于细胞外基质的酸化是骨中矿物质释放的关键步骤，我们进一步研究了硬化蛋白对CA2的调节。在hOCy和MLO-Y4细胞中，硬化蛋白刺激CA2 mRNA和蛋白的表达。硬化蛋白诱导两种细胞类型的细胞内pH （pHi）降低，细胞外pH （pHo）降低，钙离子从矿化基质中释放。在碳酸酐酶抑制剂乙酰唑胺的共同存在下，这些作用被逆转。MLO-Y4细胞中的Car2-siRNA敲低显著抑制了硬化蛋白降低pHo和从矿化底物中释放钙的能力。在MLO-Y4细胞中，使用siRNA敲低每种可能的硬化蛋白受体Lrp4、Lrp5和Lrp6，抑制了硬化蛋白诱导的Car2、Catk和Acp5 mRNA，以及pHo和钙的释放。与这种导致骨细胞溶解的硬化蛋白活性相一致的是，重组人硬化蛋白在体外处理7天的人小梁骨样品显示出骨细胞腔隙面积增加，这一效应被乙酰唑胺共同添加逆转。这些发现提示了硬化蛋白在骨细胞调节腔周围矿物质中的新作用。(c) 2013年美国骨与矿物研究学会。
The osteocyte product sclerostin is emerging as an important paracrine regulator of bone mass. It has recently been shown that osteocyte production of receptor activator of NF-B ligand (RANKL) is important in osteoclastic bone resorption, and we reported that exogenous treatment of osteocytes with sclerostin can increase RANKL-mediated osteoclast activity. There is good evidence that osteocytes can themselves liberate mineral from bone in a process known as osteocytic osteolysis. In the current study, we investigated sclerostin-stimulated mineral dissolution by human primary osteocyte-like cells (hOCy) and mouse MLO-Y4 cells. We found that sclerostin upregulated osteocyte expression of carbonic anhydrase 2 (CA2/Car2), cathepsin K (CTSK/Ctsk), and tartrate-resistant acid phosphatase (ACP5/Acp5). Because acidification of the extracellular matrix is a critical step in the release of mineral from bone, we further examined the regulation by sclerostin of CA2. Sclerostin stimulated CA2 mRNA and protein expression in hOCy and in MLO-Y4 cells. Sclerostin induced a decrease in intracellular pH (pHi) in both cell types as well as a decrease in extracellular pH (pHo) and the release of calcium ions from mineralized substrate. These effects were reversed in the co-presence of the carbonic anhydrase inhibitor, acetozolamide. Car2-siRNA knockdown in MLO-Y4 cells significantly inhibited the ability of sclerostin to both reduce the pHo and release calcium from a mineralized substrate. Knockdown in MLO-Y4 cells of each of the putative sclerostin receptors, Lrp4, Lrp5 and Lrp6, using siRNA, inhibited the sclerostin induction of Car2, Catk and Acp5 mRNA, as well as pHo and calcium release. Consistent with this activity of sclerostin resulting in osteocytic osteolysis, human trabecular bone samples treated ex vivo with recombinant human sclerostin for 7 days exhibited an increased osteocyte lacunar area, an effect that was reversed by the co-addition of acetozolamide. These findings suggest a new role for sclerostin in the regulation of perilacunar mineral by osteocytes. (c) 2013 American Society for Bone and Mineral Research.