FGF23 induction in phosphate-responsive single cells

抽象的。无机磷酸盐对于细胞内信号传导、DNA-RNA骨架的形成、 以ATP的形式储存和生产能量，以及维持矿化的骨骼。但 哺乳动物适应磷酸盐变化以影响激素产生和骨骼的机制 矿化目前尚不清楚。该提案旨在确定参与传播的生物成分 调节成纤维细胞生长因子-23（FGF 23）血液浓度的信号，FGF 23是磷酸盐中的关键激素。 体内平衡FGF 23需要其共受体αKlotho的表达，以通过以下方式使血磷正常化： 促进磷酸盐从肾脏排泄并减少1，25（OH）2维生素D（1，25 D），以抑制 磷酸盐在肠道中的吸收。在哺乳动物的肌肉骨骼系统中，磷酸盐过少会导致 严重的骨骼畸形，包括佝偻病和骨软化症，牙齿畸形（牙齿畸形）， 骨折/假骨折。我们已经证明这些表现出现在常染色体显性遗传 低磷血症性佝偻病（ADHR）、常染色体隐性低磷血症性佝偻病（ARHR，1型，由于DMP 1 突变和FAM 20 c突变导致的3型）和X连锁低磷酸盐血症（XLH;小鼠模型Hyp）。 磷酸盐潴留可由高磷酸盐血症家族性肿瘤性钙质沉着症（hfTC）引起， 其特征在于严重的组织和血管钙化。我们和其他人证明， FGF 23本身、GALNT 3和KLOTHO的功能突变导致iFGF 23水平降低和iFGF 23水平升高。 这些患者的血清磷。FGF 23在骨成骨细胞和骨细胞中产生，并且响应于 增加的血磷酸盐浓度使完整的生物活性FGF 23（“iFGF 23”）以剂量依赖性方式分泌， 小时和天，与必要的转录活性一致。此外，经历了 磷酸盐负荷也使循环FGF 23在数天内显著增加。最后，VDR缺陷小鼠 血清磷酸盐和FGF 23水平较低，但当被置于富含磷酸盐的“救援”饮食血清中时， iFGF 23水平升高，表明磷酸盐可以独立于1，25 D增加FGF 23。高血清 磷酸盐导致血管和大脑的矿化，引起心血管疾病，主要原因是 慢性肾脏病（CKD）的死亡率。这是一个关键的结果，因为升高的FGF 23是独立的。 与CKD患者死亡率增加>6倍相关。因此，我们的中心假设是： 细胞外磷酸盐引起成骨细胞和骨细胞中的转录重编程以控制FGF 23 生产这项探索性建议中的研究将利用单细胞对细胞周期变化的反应， 在体内测定血磷酸盐，并以无偏的方式使用FGF 23作为“分子标签”。我们希望调查结果 从这项工作开始开始阐明在正常条件下和在生长过程中控制FGF 23的新机制。 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.