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

项目摘要/摘要：研究矿物质扰动引起疾病的分子病因学 新陈代谢在确定新的磷酸盐稳态循环调节剂方面起到了重要作用。我们 利用定位克隆技术分离成纤维细胞生长因子-23(FGF23) 负责常染色体显性遗传性低磷血症性软骨病(ADHR)，特征为 继发于肾脏磷酸盐消耗、软骨病/软骨病和骨折的低磷血症。FGF23 共受体α-Klotho(KL)与典型的成纤维细胞生长因子受体(FGFR)形成异构体复合体，是 是正常的磷酸盐代谢所必需的。这一点在以下事实中得到了强调：KL功能丧失 突变导致终末器官FGF23耐药，并导致ADHR的表型相互紊乱。 高磷血症性家族性肿瘤钙质沉着症(HfTC)。以类似的方式，慢性肾脏病患者 疾病(CKD)表现为FGF23反应性受损，原因是肾功能肿块和 Klotho表达减少，导致血清磷浓度增加，并进一步增加 FGF23生产。KL以膜结合蛋白(‘mKL’)的形式表达，介导FGF23依赖 靶组织中的信号，以及起源于蛋白水解物的主要循环物种 MKL在其邻胞外膜结构域内裂解，得到一种可溶的形式或‘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的洞察 MKL和SKL在FGF23和矿物质调控中的完整生物学功能相互作用 由于缺乏合适的体内模型，新陈代谢尚不清楚。我们在小鼠身上进行的初步研究 基因降低的SKL表达显示FGF23的产生异常对膳食磷酸盐的反应 挑战。与全球KL-KO小鼠不同，该模型具有寿命延长的优势 研究，提供了新的机会，以获得关键洞察力的FGF23生物活性的调节在慢性 条件。总的来说，我们的结果支持确定特定SKL-FGF23相互作用的机制目标 控制磷酸盐代谢，以及测试SKL作为翻译靶点在治疗 人类疾病。这项提议中要检验的中心假设是：Klotho的SKL形式是必需的 用于正常的FGF23介导的磷酸盐处理，在肾脏疾病期间具有保护作用。我们期待我们的 使用吻合的体内和体外尖端技术提供新的翻译见解的研究 磷酸盐代谢的基础生物学，以及罕见和常见的变态综合征 Klotho和FGF23的表达。

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.