Department of Oral Health and Diagnostic Sciences, School of Dental Medicine, University of Connecticut Health Center, Farmington, CT 06030, USA.
Hum Mol Genet. 2011 Mar 1;20(5):948-61. doi: 10.1093/hmg/ddq541. Epub 2010 Dec 13.
Craniometaphyseal dysplasia (CMD) is a rare genetic disorder with hyperostosis of craniofacial bones and widened metaphyses in long bones. Patients often suffer from neurological symptoms due to obstruction of cranial foramina. No proven treatment is available and the pathophysiology is largely unknown. A Phe377 (TTC(1130-1132)) deletion in exon 9 of the pyrophosphate (PPi) transporter ANK leads to CMD-like features in an Ank(KI/KI) mouse model. Here, we investigated the effects of CMD-mutant ANK on mineralization and bone mass at a cellular level. Ank(KI/KI) osteoblast cultures showed decreased mineral deposition. Expression of bone mineralization regulating genes Mmp13, Ocn, Osx and Phex was reduced in Ank(KI/KI) osteoblasts, while the Fgf23 mRNA level was highly elevated in Ank(KI/KI) calvarial and femoral bones. Since ANK is a known PPi transporter, we examined other regulators of Pi/PPi homeostasis Enpp1 and Tnap. Significantly increased ENPP1 activity may compensate for dysfunctional mutant ANK leading to comparable extracellular PPi levels in Ank(+/+) osteoblasts. Similar to Ank(KI/KI) bone marrow-derived macrophage cultures, peripheral blood cultures from CMD patients exhibited reduced osteoclastogenesis. Cell-autonomous effects in Ank(KI/KI) osteoclasts resulted in disrupted actin ring formation and cell fusion. In addition, Ank(KI/KI) osteoblasts failed to adequately support osteoclastogenesis. Increased bone mass could partially be rescued by bone marrow transplants supporting our hypothesis that reduced osteoclastogenesis contributes at least in part to hyperostosis. We conclude that the Phe377del mutation in ANK causes impaired osteoblastogenesis and osteoclastogenesis resulting in hypomineralization and a high bone mass phenotype.
颅骨干骺发育不良（CMD）是一种罕见的遗传性疾病，其特征为颅面骨骨质增生和长骨干骺端增宽。由于颅孔阻塞，患者常伴有神经症状。目前尚无有效的治疗方法，其病理生理学也知之甚少。ANK 焦磷酸盐（PPi）转运蛋白第 9 外显子的 Phe377（TTC(1130-1132))缺失导致 Ank(KI/KI)小鼠模型出现 CMD 样特征。在此，我们研究了 CMD 突变型 ANK 在细胞水平上对矿化和骨量的影响。ANK(KI/KI)成骨细胞培养显示矿化沉积减少。ANK(KI/KI)成骨细胞中骨矿化调节基因 Mmp13、Ocn、Osx 和 Phex 的表达减少，而 Ank(KI/KI)颅骨和股骨中的 Fgf23 mRNA 水平显著升高。由于 ANK 是已知的 PPi 转运蛋白，我们研究了其他 Pi/PPi 稳态调节剂 Enpp1 和 Tnap。显著增加的 ENPP1 活性可能补偿了功能失调的突变型 ANK，导致 Ank(+/+)成骨细胞中类似的细胞外 PPi 水平。与 Ank(KI/KI)骨髓来源的巨噬细胞培养物相似，CMD 患者的外周血培养物表现出破骨细胞生成减少。ANK(KI/KI)破骨细胞中的细胞自主效应导致肌动蛋白环形成和细胞融合受损。此外，ANK(KI/KI)成骨细胞不能充分支持破骨细胞生成。通过骨髓移植部分挽救了骨量增加，这支持了我们的假设，即破骨细胞生成减少至少部分导致了骨质增生。我们得出结论，ANK 中的 Phe377del 突变导致成骨细胞生成和破骨细胞生成受损，导致矿化不足和高骨量表型。
