Fibroblast Growth Factor 23 (FGF23) and It's Receptors

描述（由申请人提供）：这份NIH指导的职业发展奖提案描述了一个为期五年的培训计划，旨在发展医师科学家的学术生涯，并促进其向独立研究者的过渡。为了实现这些目标，候选人和她的导师制定了一个综合计划，包括创新的科学理念，基础科学研究领域的高级培训和详细的职业发展计划。本研究将重点阐明FGF23通过降低近端小管中磷酸盐转运蛋白的表达而导致肾脏磷酸盐重吸收减少。此外，FGF23减少近端小管中1,25维生素D的合成。负责FGF23这些不同作用的受体是未知的。众所周知，FGF家族成员与四种被指定为FGFR1-4的成纤维细胞生长因子受体（fgfr）结合。FGFR1， FGFR3和FGFR4存在于近端小管中，其中大部分磷被重吸收。最近一项使用无FGFR小鼠的体内研究表明，FGFR1是主要受体，FGFR4在调节近端小管中的磷酸盐转运蛋白中起次要作用，但在这些无FGFR小鼠中，基线磷酸盐稳态保持正常。该研究表明，个体FGFR-/-小鼠和FGFR1-/- fgfr4 -/-双突变小鼠在基线时存在代偿机制，基线时血清磷酸盐水平较高，对FGF23具有抗性。为了验证这一假设，将产生和表征FGFR1-/- fgfr4 -/-小鼠，并检查FGF23的作用。对1,25维生素D的调节似乎不同于对磷酸钠共转运体的调节，在单个FGFR缺失小鼠中，暴露于药理学剂量的FGF23后，血清中1,25维生素D水平显着降低。为了研究1,25维生素D的调节，研究人员将检测FGFR缺失小鼠的不同组合FGF23对血清1,25维生素D水平的影响。该研究还假设，FGF23作用的重要辅助因子Klotho可以作为一种独立的磷酸盐调节激素，并与FGFR相互作用以调节磷酸盐稳态。为了验证这一假设，将在各种FGFR缺失小鼠中研究Klotho对磷酸盐稳态的影响。在人类中，高FGF23水平会导致磷酸盐稳态紊乱，导致低磷血症和低维生素D水平，导致佝偻病、骨折和生长不良。高水平的FGF23也与慢性肾脏疾病患者死亡风险增加有关。鉴定FGF23的受体将有助于了解FGF23的作用机制，并为设计新的治疗方法来预防FGF23的影响提供基础。

DESCRIPTION (provided by applicant): This NIH mentored Career Development Award proposal describes a five year training program for the development of an academic career of a physician scientist and to facilitate the transition to an independent investigator. To accomplish these goals, the candidate and her mentors have developed an integrated plan including innovative scientific ideas, advanced training in the field of basic science research and a detailed career development plan. This research will focus on elucidating FGF23 causes decreased phosphate reabsorption from the kidney by decreasing the expression of phosphate transporter in the proximal tubule. In addition, FGF23 decreases synthesis of 1,25 vitamin D in the proximal tubule. The receptors responsible for these different actions of FGF23 are unknown. It is known that the FGF family members bind to four fibroblast growth factor receptors (FGFRs) designated as FGFR1-4. FGFR1, FGFR3 and FGFR4 are present in the proximal tubule where the majority of phosphorus is reabsorbed. A recent in vivo study using FGFR null mice indicates that FGFR1 is the predominant receptor with FGFR4 playing a minor role in regulating the phosphate transporters in the proximal tubule, but baseline phosphate homeostasis remains normal in these FGFR null mice. This grant proposes that compensatory mechanisms exist at baseline in individual FGFR-/- mice and FGFR1-/-FGFR4-/- double mutant mice will have high serum phosphate levels at baseline and have resistance to FGF23. To test this hypothesis, FGFR1-/-FGFR4-/- mice will be generated and characterized, and the effects of FGF23 will be examined. Regulation of 1,25 vitamin D appears to be different from the regulation of sodium phosphate cotransporters with individual FGFR null mice showing significant decrease in the serum levels of 1,25 vitamin D on exposure to pharmacological doses of FGF23. To study the regulation of 1,25 vitamin D, different combinations of FGFR null mice will be examined for the effects of FGF23 on serum levels of 1,25 vitamin D. This grant also hypothesizes that Klotho, an essential co-factor for the actions of FGF23 can act as an independent phosphate regulating hormone, and it interacts with FGFRs to regulate phosphate homeostasis. To test this hypothesis, the effects of Klotho on phosphate homoeostasis will be studied in the various FGFR null mice. In humans, high FGF23 levels result in disturbances in phosphate homeostasis with hypophosphatemia and low 1,25 Vitamin D levels resulting in rickets, bone fractures and poor growth. High levels of FGF23 have also been associated with increased risk of mortality in patients with chronic kidney disease. Identifying the receptors for FGF23 will provide insights in to the mechanisms of actions of FGF23 and provide foundation for designing novel therapies to prevent the effects of FGF23. PUBLIC HEALTH RELEVANCE: Patients with high levels of FGF23 have rickets, poor growth, and increased risk of fractures, and lack curative therapy. The current therapy results in kidney stones and progressive renal injury. The identification of specific receptors for FGF23 will help in designing specific receptor antagonists and thus provide curative treatment.