The role of DMP1 in FGF23-induced hypophosphatemia

项目总结 成纤维细胞生长因子23(FGF23)是一种由骨产生的磷酸激素。低磷血症性软骨病 X连锁低磷血症和常染色体隐性遗传性低磷血症性软骨病 (ARHR)与FGF23过多、骨骼生长受损和导致衰弱的骨软化症有关 骨痛和骨折。注射FGF23抗体提高血磷的新疗法 促黄体生成素水平可促进骨骼生长和矿化。然而，还需要进一步的研究来确定 这一策略在长期和其他与FGF23过量相关的疾病中是有效的，包括ARHR。 XLH和ARHR I型分别是由PI调节基因同源失活突变引起的 协同作用调节FGF23的内肽酶X连锁(PHEX)和牙本质基质蛋白(DMP1) 制作。在这个项目的初步数据中，我们显示(1)FGF23过多和低磷血症 (2)过量的FGF23和甲状旁腺激素并不是唯一的 (3)DMP1直接刺激肾脏对PI的重吸收；(4)PHEX和DMP1 在发生PI重吸收的肾小管上皮细胞中表达，以及(5)肾脏PHEX的丧失导致 尽管DMP1水平升高，FGF23水平降低，但仍有磷酸尿和骨丢失。这个项目的目标是 探讨DMP1缺乏所致低磷血症的发病机制。 在目标1中，我们将确定成纤维细胞生长因子23过量和低磷血症对受损的骨矿化的贡献。 在患有ARHR的小鼠中。我们将使用正常和高膳食PI，以及野生-FGF23的基因缺失- TYPE(WT)和Dmp1KO评估小鼠和原代培养小鼠骨和矿物质代谢的改变 随着时间的推移，成骨细胞。在目标2中，我们将通过拮抗来确定DMP1在刺激PI重吸收中的作用 FGF23-FGFR1在肾脏中的信号传导。我们将使用正常和高膳食PI，并遗传 WT小鼠和Dmp1基因过表达动物中FGF23的过表达或FGFR1的缺失 (Dmp1Tg)。我们将评估骨骼和矿物质代谢，PI的摄取和排泄，肾功能和FGFR1 在FGF23和DMP1水平升高的情况下，肾脏中的激活。最后，在目标3中，我们将调查 肾脏DMP1缺乏症在ARHR和XLH病理生理机制中的作用 Dmp1TG和Dmp1KO之间以及WT、Hyp和Dmp1TG供体和受体小鼠之间的移植。我们 将确定是否需要肾脏表达的DMP1来完全纠正ARHR小鼠的低磷血症， 如果肾脏PHEX功能的丧失足以导致高磷尿症和骨丢失，尽管升高 DMP1和低FGF23水平。这将演示PHEX和DMP1之间的关键功能交互作用 肾脏。这些创新目标得到了西北大学一个富有成效的协作团队的支持 将进一步加深我们对DMP1、FGF23和PI功能的理解，最终有助于小说的开发 改善与PI平衡改变相关疾病的结果的治疗。

PROJECT SUMMARY Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone produced by bone. Hypophosphatemic rickets disorders, such as X-linked hypophosphatemia (XLH) and autosomal recessive hypophosphatemic rickets (ARHR), are associated with FGF23 excess, impaired skeletal growth and osteomalacia leading to debilitating bone pain and fractures. New therapy consisting in FGF23 antibody injections to increase serum phosphate (Pi) levels in XLH improves bone growth and mineralization. However, further studies are needed to determine if this strategy is efficacious in the long term and in other diseases associated with FGF23 excess, including ARHR. XLH and ARHR type I are respectively caused by inactivating mutations of Pi regulating gene with homologies to endopeptidase X-linked (PHEX) and dentin matrix protein (DMP1) that work in concert to regulate FGF23 production. In preliminary data for this project, we show that (1) FGF23 excess and hypophosphatemia contribute to the bone defects in mice with ARHR, (2) excess FGF23 and parathryroid hormone are not solely responsible for renal Pi wasting, (3) DMP1 directly stimulates Pi reabsorption in the kidney, (4) PHEX and DMP1 are expressed in renal tubular cells where Pi reabsorption occurs, and (5) loss of kidney PHEX induces phosphaturia and bone loss despite increased DMP1 and low FGF23 levels. The goal of this project is to investigate the pathogenesis of hypophosphatemia induced by DMP1 deficiency. In Aim 1, we will define the contribution of FGF23 excess and hypophosphatemia to impaired bone mineralization in mice with ARHR. We will use normal and high dietary Pi administration, and genetic deletion of Fgf23 in wild- type (WT) and Dmp1KO to assess modifications of bone and mineral metabolism in mice and cultured primary osteoblasts over time. In Aim 2, we will establish the role of DMP1 in stimulating Pi reabsorption by antagonizing FGF23-FGFR1 signaling in the kidney. We will use normal and high dietary Pi administration, and genetic overexpression of Fgf23 or deletion of Fgfr1, in WT mice and in animals with genetic overexpression of Dmp1 (Dmp1TG). We will assess bone and mineral metabolism, Pi intake and excretion, kidney function and FGFR1 activation in the kidney, in presence of elevated FGF23 and DMP1 levels. Finally, in Aim 3, we will investigate the contribution of kidney DMP1 deficiency to the pathophysiology of ARHR and XLH by performing kidney transplants between Dmp1TG and Dmp1KO and between WT, Hyp and Dmp1TG donor and recipient mice. We will establish whether kidney-expressed DMP1 is required to fully correct hypophosphatemia in mice with ARHR, and if loss of kidney PHEX function is sufficient to induce hyperphosphaturia and bone loss despite elevated DMP1 and low FGF23 levels. This will demonstrate a key functional interaction between PHEX and DMP1 in the kidney. These innovative aims are supported by a productive collaborative team at Northwestern University that will further develop our understanding of DMP1, FGF23 and Pi function, and ultimately help to develop novel therapies to improve outcomes in diseases associated with altered Pi balance.