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 代谢在鉴定磷酸盐体内平衡的新循环调节剂中起作用。我们 通过定位克隆方法分离基因，鉴定成纤维细胞生长因子-23（FGF23 常染色体显性遗传性低磷酸盐血症性佝偻病（ADHR），特征为 继发于肾性磷酸盐消耗、佝偻病/骨软化和骨折的低磷酸盐血症。FGF23 辅助受体α-Klotho（KL）与典型FGF受体（FGFR）以异聚复合物形式起作用， 正常的磷酸盐代谢所需。这是强调的事实，KL功能丧失 突变导致终末器官FGF 23抗性，并导致ADHR表型相互失调， 家族性肿瘤性钙质沉着症（hfTC）。类似地，慢性肾病患者 慢性肾脏病（CKD）患者由于功能性肾脏质量的丧失而表现出受损的FGF 23-反应性， Klotho表达减少，导致血清磷酸盐浓度增加， FGF23生产。KL表达为膜结合蛋白（"mKL"），其介导FGF23依赖性 在靶组织中的信号传导，以及来源于蛋白水解的主要循环种类， mKL在其近胞外膜结构域内裂解以衍生可溶形式或"sKL"。虽然 最近对FGF 23-sKL-FGFR 1三重晶体结构的解析揭示了对静态sKL-FGF 23的深入了解， 通过相互作用，mKL相对于sKL在控制FGF 23和矿物质代谢中的生物学功能的完整范围被确定。 由于缺乏适当的体内模型，代谢仍然不清楚。我们在小鼠中的初步研究 sKL基因表达的降低显示了FGF23的异常产生， 挑战与全球KL-KO小鼠不同，该模型具有寿命延长的优点， 研究，提供了新的机会，以获得关键的洞察力，调节FGF23的生物活性，在慢性 条件总的来说，我们的研究结果支持了确定特定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 人类疾病本提案中要检验的中心假设是：需要Klotho的sKL形式 用于正常的FGF23介导的磷酸盐处理，并在肾脏疾病期间具有保护作用。我们期望我们 研究采用了尖端的体内和体外技术，以提供新的、转化的见解 磷酸盐代谢的基础生物学，以及改变的罕见和常见综合征， 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.