DMP1 Mutations: Defects in Odontogenesis

描述(申请人提供)：牙齿发育需要精确的空间和时间协调程序的细胞生长，分化和矿化。为了寻找正常牙齿形态发生所需的基因，我们使用体内功能丧失和功能获得的方法研究了牙本质基质蛋白1(DMP1)，它是一种在牙髓/成牙本质细胞中高表达的非胶原性基质蛋白。DMP1基因缺失的小鼠表现出严重的牙齿异常，牙髓腔扩大，前牙本质区宽度增加，矿化减少，第三磨牙形成延迟。意识到常染色体隐性遗传性低磷血症(ARHR)患者表现出与Dmp1-KO小鼠非常相似的表型变化，我们最近在这些患者中发现了两个DMP1突变。我们的结论是，这些突变是导致表型与Dmp1-KO小鼠相似的原因，尽管存在微小的差异。在探索DMP1控制牙齿发育的机制时，我们意外地观察到无效牙髓/成牙本质细胞中Osterix的急剧减少。Osterix是一种转录因子，对成骨是必不可少的，但它在牙齿形成中的作用尚不清楚。DMP1在Dmp1-KO牙髓/成牙本质细胞中的靶向性再表达恢复了Osterix的表达，修复了牙齿形成中的缺陷。值得注意的是，我们在Dmp1-KO和Osterix(常规或有条件的)KO小鼠中发现了类似的牙本质异常。因此，我们认为DMP1突变是ARHR患者牙本质缺陷的原因，DMP1在牙齿发育的早期调节Osterix的表达，这在牙齿发育中起着关键作用。为了验证这一假设，我们将通过建立DMP1突变的小鼠模型来研究DMP1突变的分子遗传学和病理生理学。我们还将确定DMP1通过直接作用于细胞核和/或MAPK途径，通过Osterix调控牙齿发育的机制。这些研究的成功完成将有助于1)建立模仿这些人类突变的动物模型；2)了解DMP1通过细胞核内的直接机制和/或MAPK信号转导通过Osterix调控牙齿发育的机制；以及3)鉴定DMP1的生物活性片段(S)，它最终可以用于翻译应用，通过提供与基因变化相对应的治疗方法来造福公众，从而改善牙齿/口腔健康。公共卫生相关性：常染色体隐性遗传性低磷血症(ARHR)患者的表型变化与我们在Dmp1-KO小鼠中观察到的牙本质缺陷非常相似。我们在这些患者中发现的DMP1突变导致了目前研究提案的制定。我们成功完成这些研究将提供牙本质形成的机制细节，并最终将有助于预防牙本质结构缺陷。此外，从这些研究中产生的小鼠模型可以用来将单个基因突变与适当的临床干预相关联。

DESCRIPTION (provided by applicant): Tooth development requires the precise spatial and temporal coordination of programs for cell growth, differentiation, and mineralization. In a search for genes required for normal tooth morphogenesis we have studied Dentin matrix protein1 (DMP1), a non- collagenous matrix protein highly expressed in pulp/odontoblast cells, using in vivo loss- and gain-of-function approaches. Dmp1-null mice display profound tooth abnormalities with enlarged pulp chambers, increased width of the predentin zone, hypomineralization, and delayed 3rd molar formation. Realizing that autosomal recessive hypophosphatemic rickets (ARHR) patients manifest phenotypic changes very similar to those observed in Dmp1-KO mice, we recently discovered two DMP1 mutations in these patients. We have concluded that these mutations are causes of the phenotypes resembling those of Dmp1-KO mice, although minor differences exist. In a search for mechanisms by which DMP1 controls odontogenesis, we unexpectedly observed a sharp reduction of osterix in the null pulp/odontoblasts. Osterix is a transcriptional factor that is essential for osteogenesis but its role in odontogenesis is unknown. Targeted re-expression of DMP1 in Dmp1-KO pulp/odontoblast cells restores osterix expression and rescues the defects in tooth formation. Notably, we found similar dentin abnormalities in Dmp1-KO, and osterix (conventional or conditional) KO mice. Therefore, we propose that DMP1 mutations are the cause of dentin defects in ARHR patients, and that DMP1 regulates osterix expression at an early stage of tooth development, which plays a critical role for odontogenesis. To test this hypothesis we will study the molecular genetics and pathophysiology of DMP1 mutations through creation of a mouse model with DMP1 mutations. We will also determine the mechanisms by which DMP1 modulates odontogenesis through Osterix via direct action at the nucleus and/or MAPK pathways. The successful completion of these studies will lead to 1) generation of an animal model mimicking these human mutations; 2) understanding the mechanism by which DMP1 controls odontogenesis through osterix via a direct mechanism within the nucleus level and/or MAPK signaling; and 3) identification of bioactive fragment(s) of DMP1 which can ultimately be used in translational applications that will benefit the public by providing therapeutic approaches corresponding to genetic alterations, leading to improved dental/oral health. PUBLIC HEALTH RELEVANCE: Patients with autosomal recessive hypophosphatemic rickets (ARHR) patients manifest phenotypic changes very similar to dentin defects we observed in Dmp1-KO mice. Our discovery of DMP1 mutations in these patients led to the formulation of the current research proposal. Our successful completion of these studies will provide mechanistic details about dentin formation, and will ultimately shed light on the prevention of structural defects in dentin. In addition, the mouse models which to be generated from these studies can be used to correlate individual gene mutations with the appropriate clinical intervention.