Targeting sKlotho-FGF23 Interactions to Improve Pathological Phosphate Handling in CKD

项目摘要/摘要：研究受干扰矿物质引起的疾病的分子病因学 新陈代谢有助于确定磷酸盐稳态的新循环调节因子。我们 通过定位克隆方法分离出成纤维细胞生长因子 23 (FGF23) 基因 导致常染色体显性低磷血症性佝偻病 (ADHR)，其特征为 继发于肾磷酸盐消耗、佝偻病/骨软化症和骨折的低磷血症。 FGF23 共受体 α-Klotho (KL) 与典型 FGF 受体 (FGFR) 形成异聚复合物，是 正常磷酸代谢所需。 KL 功能丧失这一事实强调了这一点 突变导致终末器官 FGF23 抵抗，并导致 ADHR 表型相互紊乱， 高磷血症家族性肿瘤性钙质沉着症（hfTC）。类似地，慢性肾病患者 慢性肾病 (CKD) 表明由于功能性肾质量损失而导致 FGF23 反应性受损，并且 Klotho 表达减少，导致血清磷酸盐浓度增加，并进一步增加 FGF23 生产。 KL 表达为膜结合蛋白 (‘mKL’)，介导 FGF23 依赖性 靶组织中的信号传导，以及源自蛋白水解酶的主要循环物种 mKL 在其邻近细胞外膜结构域内裂解，衍生出可溶形式或“sKL”。虽然 最近对 FGF23-sKL-FGFR1 三重晶体结构的解决揭示了对静态 sKL-FGF23 的深入了解 相互作用，mKL 与 sKL 在控制 FGF23 和矿物质方面的生物功能的完整范围 由于缺乏适当的体内模型，代谢仍不清楚。我们对小鼠的初步研究 基因减少的 sKL 表达显示出响应膳食磷酸盐的异常 FGF23 产生 挑战。与全局 KL-KO 小鼠不同，该模型具有寿命长的优点，可以延长 研究，为深入了解慢性病中 FGF23 生物活性的调节提供了新的机会 条件。总的来说，我们的结果支持识别特定 sKL-FGF23 相互作用的机制目标 磷酸盐代谢的控制，以及测试 sKL 作为治疗中的转化靶点 人类失调。本提案要检验的中心假设是：需要 Klotho 的 sKL 形式 用于正常 FGF23 介导的磷酸盐处理，并且在肾脏疾病期间具有保护作用。我们期望我们的 使用尖端的体内和体外技术进行研究，以提供新颖的转化见解 深入了解磷酸盐代谢的基础生物学，以及罕见和常见的改变的综合征 Klotho 和 FGF23 表达。

Project Summary/Abstract: Investigating the molecular etiology of disorders caused by disturbed mineral metabolism has been instrumental in identifying new circulating regulators of phosphate homeostasis. We identified Fibroblast growth factor-23 (FGF23) in a positional cloning approach to isolate the gene responsible for autosomal dominant hypophosphatemic rickets (ADHR), characterized by hypophosphatemia secondary to renal phosphate wasting, rickets/osteomalacia, and fracture. The FGF23 co-receptor alpha-Klotho (KL), acting in a heteromeric complex with a canonical FGF receptor (FGFR), is required for normal phosphate metabolism. This is emphasized by the fact that KL loss of function mutations lead to end-organ FGF23 resistance, and cause the phenotypic reciprocal disorder to ADHR, hyperphosphatemic familial tumoral calcinosis (hfTC). In a similar manner, patients with chronic kidney disease (CKD) demonstrate impaired FGF23-responsiveness due to a loss of functional kidney mass and reduced Klotho expression, leading to increased serum phosphate concentrations and further increases in FGF23 production. KL is expressed as a membrane-bound protein (`mKL') that mediates FGF23-dependent signaling in target tissues, as well as a major circulating species that originates from the proteolytic cleavage of mKL within its juxta-extracellular membrane domain to derive a soluble form or `sKL'. Although the recent solving of the FGF23-sKL-FGFR1 triple crystal structure revealed insight into static sKL-FGF23 interactions, the complete scope of mKL versus sKL biological functions in the control of FGF23 and mineral metabolism remains unclear due to a lack of appropriate in vivo models. Our initial studies in mice with genetically reduced sKL expression showed aberrant FGF23 production in response to dietary phosphate challenges. Unlike global KL-KO mice, this model has the advantage of a lifespan that allows extended studies, providing new opportunities to gain critical insight into the regulation of FGF23 bioactivity in chronic conditions. Collectively, our results support mechanistic aims to identify specific sKL-FGF23 interactions in the control of phosphate metabolism, as well as to test sKL as a translational target in the treatment of human disorders. The central hypothesis to be tested in this proposal is: the sKL form of Klotho is required for normal FGF23-mediated phosphate handling and is protective during renal disease. We expect our studies using dovetailed, cutting-edge in vivo and in vitro techniques to provide novel, translational insight into the basic biology of phosphate metabolism, as well as into both rare and common syndromes of altered Klotho and FGF23 expression.