Conditional Alpl Ablation Phenocopies Dental Defects of Hypophosphatasia
Conditional Alpl Ablation Phenocopies Dental Defects of Hypophosphatasia
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DOI：
10.1177/0022034516663633
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发表时间：
2017-01-01
影响因子：
7.6
通讯作者：
Millan, J. L.
中科院分区：
文献类型：
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作者：
Foster, B. L.;Kuss, P.;Millan, J. L.
ALPL的功能缺失突变导致低磷酸酶症（HPP），这是一种先天性代谢缺陷，可导致骨骼和牙齿矿化缺陷。ALPL编码组织非特异性碱性磷酸酶，这是一种在骨骼、牙齿、肝脏和肾脏中表达的酶，可水解矿化抑制剂无机焦磷酸盐。由于Alpl缺失小鼠在断奶前死亡，我们的目标是通过工程化floxed Alpl等位基因来产生寿命延长的迟发型HPP小鼠模型，从而在与Cre重组酶转基因小鼠杂交时允许条件性基因消除（条件性敲除[cKO]）。作者假设，成骨细胞和选定的牙细胞（Col 1a 1-cKO）中Alpl的靶向缺失或软骨细胞、成骨细胞和颅面间充质（Prx 1-cKO）中Alpl的靶向缺失将表型复制迟发型HPP的骨骼和牙齿表现。Col 1a 1-cKO和Prx 1-cKO小鼠存活且具有生育能力，它们没有表现出严重婴儿HPP的Alpl-/-模型的癫痫发作特征。两种cKO模型均具有正常的出生后体重，但与野生型小鼠相比，在8至12周时显著降低。与对照组相比，两种cKO模型在24周时的血浆碱性磷酸酶降低约75%。放射学检查显示cKO小鼠存在严重的骨骼缺陷，包括佝偻病变化、长骨矿化不足、变形和骨折体征。显微计算机断层扫描证实了皮质骨和松质骨的定量差异，包括皮质厚度和矿物质密度降低。Col 1a 1-cKO小鼠表现出典型的HPP牙槽病体征，包括短磨牙根伴牙本质薄、缺乏脱细胞牙骨质和牙槽骨中类骨质积聚。Prx 1-cKO小鼠表现出相同的牙周缺损阵列，但其磨牙牙本质受影响较小。在24周时，两种cKO模型均表现出牙槽骨高度降低和破骨细胞样细胞数量增加4倍，与HPP相关的牙周病一致。这些新的迟发性HPP模型可以为长期的骨骼和牙齿表现提供信息，并将为进一步研究病因和治疗干预提供必要的工具。
Loss-of-function mutations in ALPL result in hypophosphatasia (HPP), an inborn error of metabolism that causes defective skeletal and dental mineralization. ALPL encodes tissue-nonspecific alkaline phosphatase, an enzyme expressed in bone, teeth, liver, and kidney that hydrolyzes the mineralization inhibitor inorganic pyrophosphate. As Alpl-null mice die before weaning, we aimed to generate mouse models of late-onset HPP with extended life spans by engineering a floxed Alpl allele, allowing for conditional gene ablation (conditional knockout [cKO]) when crossed with Cre recombinase transgenic mice. The authors hypothesized that targeted deletion of Alpl in osteoblasts and selected dental cells (Col1a1-cKO) or deletion in chondrocytes, osteoblasts, and craniofacial mesenchyme (Prx1-cKO) would phenocopy skeletal and dental manifestations of late-onset HPP. Col1a1-cKO and Prx1-cKO mice were viable and fertile, and they did not manifest the epileptic seizures characteristic of the Alpl-/-model of severe infantile HPP. Both cKO models featured normal postnatal body weight but significant reduction as compared with wild type mice by 8 to 12 wk. Plasma alkaline phosphatase for both cKO models at 24 wk was reduced by approximately 75% as compared with controls. Radiography revealed profound skeletal defects in cKO mice, including rachitic changes, hypomineralized long bones, deformations, and signs of fractures. Microcomputed tomography confirmed quantitative differences in cortical and trabecular bone, including decreased cortical thickness and mineral density. Col1a1-cKO mice exhibited classic signs of HPP dentoalveolar disease, including short molar roots with thin dentin, lack of acellular cementum, and osteoid accumulation in alveolar bone. Prx1-cKO mice exhibited the same array of periodontal defects but featured less affected molar dentin. Both cKO models exhibited reduced alveolar bone height and 4-fold increased numbers of osteoclast-like cells versus wild type at 24 wk, consistent with HPP-associated periodontal disease. These novel models of late-onset HPP can inform on long-term skeletal and dental manifestations and will provide essential tools to further studies of etiopathologies and therapeutic interventions.