FGF23 induction in phosphate-responsive single cells

抽象的。无机磷是细胞内信号、DNA-RNA骨架的形成所必需的， 以三磷酸腺苷的形式储存和生产能量，以及维持矿化的骨骼。然而， 哺乳动物适应磷酸盐变化影响激素产生和骨骼的机制 成矿作用目前尚不清楚。这项提案试图确定与传输有关的生物成分 调节磷酸盐中的关键激素成纤维细胞生长因子-23(FGF23)浓度的信号 动态平衡。FGF23需要其共同受体αKlotho的表达才能使血磷正常化 促进肾脏磷酸盐排泄和减少1，25(OH)2维生素D(1，25D)抑制 肠道对磷酸盐的吸收。在哺乳动物的肌肉骨骼系统中，太少的磷会导致 严重的骨骼畸形，包括软骨病和软骨病，牙齿异常(脓肿)和 骨折/假性骨折。我们已经证明这些表现出现在常染色体显性遗传中。 低磷血症(ADHR)，常染色体隐性遗传性低磷血症(ARHR，由DMP1引起的1型 基因突变，以及FAM20c突变导致的3型)和X-连锁低磷血症(XLH；小鼠模型Hyp)。 高磷血症性家族性肿瘤钙质沉着症(Hftc)可导致磷滞留， 以严重的组织和血管钙化为特征。我们和其他人证明了异质性损失 在FGF23自身的功能突变中，GALNT3和KLOTHO是导致iFGF23低和高的原因 这些患者的血磷水平。FGF23是在成骨细胞和骨细胞中产生的，并对 完整生物活性FGF23(IFGF23)的血磷浓度增加是剂量依赖性的 几小时和几天，与必要的转录活动一致。此外，人类受试者经历了 随着时间的推移，磷酸盐负荷也显著增加了循环中的FGF23。最后，VDR缺陷小鼠 有低水平的血清磷酸盐和FGF23，但当被放置在富含磷酸盐的饮食血清时 IFGF23水平升高，表明磷酸盐可以独立于1，25D增加FGF23。高血清 磷酸盐导致血管和大脑矿化，导致心血管疾病，这是主要原因 慢性肾脏疾病(CKD)的死亡人数。这是一个关键的结果，因为升高的FGF23是独立的 与慢性肾脏病患者死亡率增加6倍相关。因此，我们的中心假设是： 胞外磷酸引起成骨细胞和骨细胞转录重编程以控制FGF23 制作。这一探索性方案中的研究将利用单细胞对细胞因子变化的反应 并以一种公正的方式使用FGF23作为“分子标签”。我们期待着调查结果 从这项工作开始阐明在正常条件下和在 代谢性骨病。

Abstract. Inorganic phosphate is necessary for intracellular signaling, the formation of DNA-RNA backbones, energy storage and production in the form of ATP, as well as maintaining a mineralized skeleton. However, the mechanisms by which mammals adapt to changes in phosphate to affect hormone production and bone mineralization are currently unknown. This proposal seeks to identify biocomponents involved in transmitting signals to modulate blood concentrations of Fibroblast growth factor-23 (FGF23), the key hormone in phosphate homeostasis. FGF23 requires the expression of its co-receptor αKlotho to normalize blood phosphate by promoting phosphate excretion from the kidney and reducing 1,25(OH)2 vitamin D (1,25D) to suppress phosphate absorption in the intestine. In the mammalian musculoskeletal system, too little phosphate results in severe skeletal deformities including rickets and osteomalacia, dental abnormalities (abscesses) and fractures/pseudofractures. We have shown these manifestations arise in autosomal dominant hypophosphatemic rickets (ADHR), autosomal recessive hypophosphatemic rickets (ARHR, type 1 due to DMP1 mutations, and type 3 due to FAM20c mutations), and X-linked hypophosphatemia (XLH; mouse model Hyp). Phosphate retention can result from the disorder hyperphosphatemic familial tumoral calcinosis (hfTC), characterized by severe tissue and vascular calcifications. We and others demonstrated that heterogeneous loss of function mutations in FGF23 itself, GALNT3, and KLOTHO are responsible for low iFGF23 and the elevated serum phosphate in these patients. FGF23 is produced in bone osteoblasts and osteocytes, and in response to increased blood phosphate concentrations intact bioactive FGF23 (‘iFGF23’) is dose-dependently secreted over hours and days, consistent with necessary transcriptional activity. Further, human subjects that undergo phosphate loading also have significant increases in circulating FGF23 over days. Finally, VDR-deficient mice have low serum levels of phosphate and FGF23, but when placed on a phosphate-rich ‘‘rescue’’ diet serum iFGF23 levels are elevated, indicating that phosphate can increase FGF23 independently of 1,25D. High serum phosphate leads to mineralization of blood vessels and brain, causing cardiovascular disease, the primary cause of death in chronic kidney disease (CKD). This is a critical outcome, as elevated FGF23 is independently associated with a >6-fold increased odds for CKD patient mortality. Thus, our central hypothesis is: changes in extracellular phosphate cause transcriptional reprogramming in osteoblasts and osteocytes to control FGF23 production. The studies in this exploratory proposal will take advantage of single-cell responses to changes of blood phosphate in vivo and use FGF23 as a ‘molecular tag’ in an unbiased manner. We expect the findings from this work to begin to elucidate novel mechanisms controlling FGF23 under normal conditions and during metabolic bone diseases.