Pathogenesis of XLH/Hyp: Role of Phex MEPE and FGF23

描述（由申请人提供）：有证据表明激素/酶/细胞外基质蛋白级联可维持全身磷酸盐稳态和矿化。常染色体显性低磷血症佝偻病（ADHR）和x -联低磷血症（XLH）的遗传学研究发现了磷酸化激素FGF23和膜金属蛋白酶PHEX，而肿瘤诱导骨软化症（TIO）的遗传学研究发现了细胞外基质蛋白MEPE。ADHR、XLH和TIO之间的相似性为解释这些疾病中肾磷酸盐消耗和矿化缺陷的共同发病机制提供了一个令人信服的模型基础。在该模型中，循环磷激素FGF23和局部矿化抑制剂MEPE分别引起肾磷消耗和内在矿化异常。我们有数据表明，XLH是由Phex失活突变引起的，该突变导致未知寡肽底物活性改变，进而改变磷酸化因子FGF23和矿化抑制剂MEPE的表达和/或降解。在Aim 1中，我们将使用小鼠遗传学方法在XLH的phex缺陷Hyp小鼠同源物中建立FGF23增加与低磷血症之间的因果关系。在这些研究中，将phex缺陷的Hyp小鼠转移到FGF23零背景中，试图挽救Hyp表型。我们还将通过检测FGF23给药对缺乏特异性纤维母细胞生长因子受体的小鼠的影响，探索FGF23调节肾磷酸盐处理和骨骼矿化的分子机制。在Aim 2中，我们将通过将phex缺乏症转移到MEPE零背景上，研究MEPE在明显的内在矿化缺陷中所起的作用。最后，在Aim 3中，我们将使用互补噬菌体展示和酵母-两种杂交筛选来鉴定生理学上相关的Phex底物、抑制剂和/或相互作用蛋白，这些蛋白允许该酶控制FGF23和MEPE代谢。

DESCRIPTION (provided by applicant): There is evidence for a hormone/enzyme/extracellular matrix protein cascade for maintaining systemic phosphate homeostasis and mineralization. Genetic studies of Autosomal Dominant Hypophosphatemic Rickets (ADHR) and X-linked hypophosphatemia (XLH) identified the phosphaturic hormone FGF23 and the membrane metalloprotease PHEX, while investigations of Tumor Induced Osteomalacia (TIO) discovered the extracellular matrix protein MEPE. Similarities between ADHR, XLH, and TIO provide the basis for a compelling model to explain the common pathogenesis of renal phosphate wasting and defective mineralization in these disorders. In this model, circulating phosphaturic hormone, FGF23, and local inhibitor(s) of mineralization, MEPE, respectively cause renal phosphate wasting and intrinsic mineralization abnormalities. We have data that XLH is caused by inactivating mutations of Phex that leads to altered activity of unidentified oligopeptide substrates that secondarily modify the expression and/or degradation of the phosphaturic factor FGF23 and the mineralization inhibitor MEPE. In Aim 1 we will use mouse genetic approaches to establish a cause-and-effect relationship between increased FGF23 and hypophosphatemia in Phex-deficient Hyp mouse homologue of XLH. In these studies, Phex-deficient Hyp mice will be transferred onto FGF23 null background to attempt rescue of the Hyp phenotype. We will also explore the molecular mechanisms whereby FGF23 regulates renal phosphate handling and skeletal mineralization by examining the effects of FGF23 administration in mice lacking specific fibroblastic growth factor receptors. In Aim 2, we will investigate the role that MEPE plays in the apparent intrinsic mineralization defect by transferring Phex-deficiency onto the MEPE null background. Finally, in Aim 3 we will use complementary phage display and yeast-two hybrid screening to identify physiologically relevant Phex substrates, inhibitors and/or interacting proteins that allow this enzyme to control FGF23 and MEPE metabolism.