Department of Prosthodontics and Periodontics, Campinas State University, Piracicaba, São Paulo, Brazil.
J Periodontol. 2012 May;83(5):653-63. doi: 10.1902/jop.2011.110310. Epub 2011 Oct 20.
Mutations in the liver/bone/kidney alkaline phosphatase (ALPL) gene in hypophosphatasia (HPP) reduce the function of tissue non-specific alkaline phosphatase (ALP), resulting in increased pyrophosphate (PP(i)) and a severe deficiency in acellular cementum. We hypothesize that exogenous phosphate (P(i)) would rescue the in vitro mineralization capacity of periodontal ligament (PDL) cells harvested from HPP-diagnosed patients, by correcting the P(i)/PP(i) ratio and modulating expression of genes involved with P(i)/PP(i) metabolism.
Ex vivo and in vitro analyses were used to identify mechanisms involved in HPP-associated PDL/tooth root deficiencies. Constitutive expression of PP(i)-associated genes was contrasted in PDL versus pulp tissues obtained from healthy individuals. Primary PDL cell cultures from patients with HPP (monozygotic twin males) were established to assay ALP activity, in vitro mineralization, and gene expression. Exogenous P(i) was provided to correct the P(i)/PP(i) ratio.
PDL tissues obtained from healthy individuals featured higher basal expression of key PP(i) regulators, genes ALPL, progressive ankylosis protein (ANKH), and ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), versus paired pulp tissues. A novel ALPL mutation was identified in the twin patients with HPP enrolled in this study. Compared to controls, HPP-PDL cells exhibited significantly reduced ALP and mineralizing capacity, which were rescued by addition of 1 mM P(i). Dysregulated expression of PP(i) regulatory genes ALPL, ANKH, and ENPP1 was also corrected by adding P(i), although other matrix markers evaluated in our study remained downregulated.
These findings underscore the importance of controlling the P(i)/PP(i) ratio toward development of a functional periodontal apparatus and support P(i)/PP(i) imbalance as the etiology of HPP-associated cementum defects.
成骨不全症（HPP）中肝脏/骨骼/肾脏碱性磷酸酶（ALPL）基因突变降低组织非特异性碱性磷酸酶（ALP）的功能，导致焦磷酸（PP(i)）增加和无细胞牙骨质严重缺乏。我们假设通过纠正 Pi/PP(i) 比值并调节参与 Pi/PP(i) 代谢的基因表达，外源性磷酸盐（Pi）可以挽救从 HPP 诊断的患者中获得的牙周韧带（PDL）细胞的体外矿化能力。
使用离体和体外分析来鉴定与 HPP 相关的 PDL/牙根缺陷相关的机制。在从健康个体获得的 PDL 与牙髓组织中对比 PP(i)相关基因的组成型表达。从患有 HPP（同卵双胞胎男性）的患者中建立原代 PDL 细胞培养物以测定 ALP 活性、体外矿化和基因表达。提供外源性 Pi 以纠正 Pi/PP(i) 比值。
与配对牙髓组织相比，从健康个体获得的 PDL 组织中关键 PP(i)调节剂基因、ALPL、进行性骨化蛋白（ANKH）和核苷酸外切酶/磷酸二酯酶 1（ENPP1）的基础表达更高。在本研究中纳入的患有 HPP 的双胞胎患者中发现了一种新的 ALPL 突变。与对照组相比，HPP-PDL 细胞的 ALP 和矿化能力显著降低，通过添加 1 mM Pi 可得到挽救。添加 Pi 还纠正了 PP(i)调节基因 ALPL、ANKH 和 ENPP1 的失调表达，尽管我们在研究中评估的其他基质标记物仍下调。
这些发现强调了控制 Pi/PP(i) 比值对功能性牙周器械发育的重要性，并支持 Pi/PP(i) 失衡是 HPP 相关牙骨质缺陷的病因。
