Hormonal and Molecular Etiology of Skeletal Abnormalities in XLH

XLH 骨骼异常的激素和分子病因学

基本信息

批准号：
9757666
负责人：
Marie Demay
金额：
$ 36.75万
依托单位：
MASSACHUSETTS GENERAL HOSPITAL
依托单位国家：
美国
项目类别：
财政年份：
2017
资助国家：
美国
起止时间：
2017-09-21 至 2022-08-31
项目状态：
已结题

来源：
https://reporter.nih.gov/project-details/9757666
关键词：
Ablation Acute Address Adjuvant Affect Animals Apoptosis Apoptotic Biological Availability Biomechanics Brush Border Cells Child Chondrocytes Chronic Kidney Failure Data Dihydroxycholecalciferols Disease Endopeptidases Epiphysial cartilage Etiology Excretory function Exhibits Familial hypophosphatemic bone disease Fibroblast Growth Factor Receptors Gene Expression Genes Genetic Growth Hormonal Hormones Hour Human Hypercalcemia Hypophosphatemia Impairment In Vitro Incidence Injections Intestines Investigation KDR gene Kidney Knockout Mice MAP2K1 gene MAPK3 gene Mediating Mitochondria Molecular Mus Mutation Nephrocalcinosis Osteomalacia Pathway interactions Patients Phenotype Phosphorylation Process Property Protein Isoforms Receptor Signaling Resistance Rickets Role Secondary Hyperparathyroidism Serum Signal Pathway Signal Transduction Signaling Molecule Supplementation Tubular formation Urine VEGFA gene Vascular Endothelial Growth Factors Vascular calcification Vegf inhibition Vitamin D absorption base bone brush border membrane extracellular gastrointestinal gene induction improved in vivo inhibitor/antagonist inorganic phosphate mouse model novel prevent response screening side effect skeletal skeletal abnormality small molecule small molecule inhibitor therapeutic effectiveness urinary

项目摘要

The investigations in this proposal are directed at identifying the mechanism by which hypophosphatemia leads to rickets, and the molecular basis for the therapeutic effectiveness of 1,25-dihydroxyvitamin D (1,25D) in X-linked hypophosphatemia (XLH). While the combination of phosphate and 1,25D therapy for XLH has been used for the past 4 decades, the molecular basis for the beneficial effects of 1,25D is not fully understood. We have shown that monotherapy with 1,25D in the Hyp mouse model of XLH improves growth, prevents rickets and improves the microarchitectural and biomechanical properties of bone despite doubling the already increased circulating FGF23 levels. Despite this major increase in FGF23, 1,25D treatment significantly decreases urinary phosphate in Hyp mice. Thus, 1,25D has beneficial effects on bone and renal phosphate handling in XLH, in spite of further increasing FGF23. We propose to examine the effects of 1,25D on FGF23 signaling to identify the mechanism by which 1,25D antagonizes the phosphaturic effects of FGF23. Preliminary data suggest that 1,25D causes retention of Npt2a/NHERF1 at renal brush border membranes of Hyp mice by antagonizing FGF23 signaling downstream of FGF23/FGF receptor interactions. Studies will be performed in kidneys, renal tubular cells and brush border membranes of WT and Hyp mice. Hypophosphatemia impairs hypertrophic chondrocyte apoptosis leading to rickets in growing animals and humans, including those with XLH. We have shown that phosphate induction of ERK1/2 phosphorylation is required for activation of the mitochondrial apoptotic pathway in hypertrophic chondrocytes in vitro and in vivo. We have also shown that ablation of A-, B- and C-Raf in chondrocytes abolishes phosphate-induced ERK1/2 phosphorylation, impairs hypertrophic chondrocyte apoptosis and leads to rickets. Raf;MEK1/2;ERK1/2 can be activated by several pathways. We, therefore, undertook a small molecule inhibitor screen to identify the pathway by which phosphate induces ERK1/2 phosphorylation. These studies demonstrated that VEGFR signaling is required for phosphate induced ERK1/2 phosphorylation in primary hypertrophic chondrocytes. The studies proposed will address the hypothesis that phosphate activates VEGFR2 signaling specifically in hypertrophic chondrocytes and will determine whether increased VEGFA release/secretion is required for these effects. They will also address the hypothesis that chondrocyte-specific ablation of VEGFR2 impairs phosphate-mediated hypertrophic chondrocyte apoptosis in vitro and normal growth plate maturation in vivo. The effects of 1,25D on this signaling pathway will be examined to determine how 1,25D prevents rickets in the setting of hypophosphatemia. Thus, the studies proposed will identify the molecular basis for induction of hypertrophic chondrocyte apoptosis by phosphate and will define how 1,25D modulates this process and impairs the phosphaturic effects of FGF23 in the kidney. Our studies will have important implications for the treatment of XLH patients and will identify the mechanism by which phosphate activates signaling pathways.

本提案中的研究旨在确定低磷血症发生的机制导致佝偻病，1,25-二羟基维生素 D (1,25D) 治疗效果的分子基础 X连锁低磷血症（XLH）。虽然磷酸盐和 1,25D 联合治疗 XLH 已过去 4 年来，1,25D 的有益作用的分子基础尚不完全清楚。我们研究表明，在 XLH 的 Hyp 小鼠模型中使用 1,25D 单一疗法可改善生长，预防佝偻病并改善骨骼的微结构和生物力学特性，尽管已经增加了一倍增加循环 FGF23 水平。尽管 FGF23 显着增加，1,25D 治疗仍显着增加降低 Hyp 小鼠的尿磷酸盐。因此，1,25D 对骨和肾磷酸盐具有有益作用尽管 FGF23 进一步增加，但 XLH 中的处理仍然存在。我们建议检查 1,25D 对 FGF23 的影响信号传导以确定 1,25D 拮抗 FGF23 磷酸盐作用的机制。初步数据表明，1,25D 导致 Npt2a/NHERF1 保留在肾刷状缘膜上。 Hyp 小鼠通过拮抗 FGF23/FGF 受体相互作用下游的 FGF23 信号传导。研究将是在 WT 和 Hyp 小鼠的肾脏、肾小管细胞和刷状缘膜中进行。低磷血症会损害肥大软骨细胞凋亡，导致生长动物中的佝偻病人类，包括 XLH 患者。我们已经证明磷酸盐诱导 ERK1/2 磷酸化是体外和体内肥大软骨细胞中线粒体凋亡途径激活所需的。我们还表明，软骨细胞中 A-、B- 和 C-Raf 的消融会消除磷酸盐诱导的 ERK1/2 磷酸化，损害肥大软骨细胞凋亡并导致佝偻病。 Raf;MEK1/2;ERK1/2 可以由多种途径激活。因此，我们进行了小分子抑制剂筛选来识别磷酸盐诱导 ERK1/2 磷酸化的途径。这些研究表明 VEGFR 原代肥大软骨细胞中磷酸盐诱导的 ERK1/2 磷酸化需要信号传导。拟议的研究将解决磷酸盐激活 VEGFR2 信号传导的假设肥大软骨细胞，并将确定是否需要增加 VEGFA 释放/分泌这些影响。他们还将解决以下假设：VEGFR2 的软骨细胞特异性消融会损害磷酸盐介导的体外肥大软骨细胞凋亡和体内正常生长板成熟。将检查 1,25D 对这一信号通路的影响，以确定 1,25D 如何预防佝偻病低磷血症的情况。因此，所提出的研究将确定诱导的分子基础磷酸盐引起的肥大软骨细胞凋亡，并将定义 1,25D 如何调节该过程以及损害肾脏中 FGF23 的磷酸盐作用。我们的研究将对 XLH 患者的治疗并将确定磷酸盐激活信号通路的机制。