PTH Regulation of Renal Phosphate Homeostasis

PTH 对肾磷酸盐稳态的调节

• 批准号: 8374995
• 负责人: HARALD W. JUEPPNER
• 金额: $ 38.31万
• 依托单位: MASSACHUSETTS GENERAL HOSPITAL
• 依托单位国家: 美国
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-08-01 至 2013-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8374995
• 关键词: Actins; Affect; Apical; Calcinosis; Calcium; Cell Line; Cell model; Cells; Chronic Kidney Failure; Complex; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cytoskeleton; Data; Diet; Disease; Down-Regulation; Endocytosis; Excretory function; Familial hypophosphatemic bone disease; Genes; Goals; Homeostasis; Hormonal; Hormones; Human; Hydrolysis; Hypoparathyroidism; In Vitro; Inherited; Inositol Phosphates; Investigation; Kidney; Knockout Mice; LLC-PK1 Cells; Lateral; Lead; Link; Mediating; Membrane; Modeling; Mouse Strains; Mus; Mutation; Parathyroid Hormone Receptor; Parathyroid gland; Pathway interactions; Patients; Phosphorylation; Process; Property; Proteins; Proximal Kidney Tubules; Pseudohypoparathyroidism; RNA Interference; Regulation; Resistance; Role; Secondary Hyperparathyroidism; Signal Pathway; Signal Transduction; Solubility; Stream; Surface; Tubular formation; apical membrane; base; basolateral membrane; brush border membrane; calcium metabolism; ezrin; feeding; hormone analog; hormone regulation; hypercalciuria; improved; in vivo; inorganic phosphate; insight; knock-down; member; mutant; novel; protein crosslink; receptor; scaffold; sodium phosphate; sodium-hydrogen exchanger regulatory factor; symporter; tool; urinary

PTH-dependent regulation of renal phosphate homeostasis remains incompletely understood. PTH downregulates the activity of two kidney-specific sodium-phosphate co-transporters, NPT2a and NPT2c. NPT2a handles 70-80% of phosphate reabsorption and it is regulated through PTH-dependent mechanisms that involve cAMP/PKA signaling down-stream of the PTH/PTHrP receptor (PTHR1). Consistent with such an important role of the Gs_/cAMP/PKA pathway in renal phosphate handling, patients affected by some forms of pseudohypoparathyroidism (PHP) develop PTH-resistant hyperphosphatemia because of impaired Gs_ expression or function. NPT2c appears to be regulated through PLC/PKC-signaling mediated by the PTHR1. NPT2c handles only 20-30% of renal phosphate reabsorption, yet inactivating homozygous/compound heterozygous mutations lead to hereditary hypophosphatemic rickets with hypercalciuria (HHRH), an autosomal recessive disorder. NPT2a and NPT2c thus are likely to have non-redundant roles in renal phosphate homeostasis. The PTHR1 is expressed at the baso-lateral membrane (BLM) of renal proximal tubular cells where it regulates NPT2a via the cAMP/PKA pathway; it is, however, unknown whether IP3/PKC-dependent signaling of PTHR1 at the BLM is involved in the regulation of NPT2a and/or NPT2c expression. At the brush-border membrane (BBM), the PTHR1 appears to activate only cAMP/PKAindependent signaling pathways, and evidence from our preliminary studies suggest that these actions regulate NPT2c expression. To elucidate the mechanisms underlying the PTH-dependent regulation of NPT2a and NPT2c, we propose to use mice expressing a PTHR1 mutant that is deficient in PLC-signaling, mice that are "null" for NPT2a, and mice that lack Gs_ expression in the proximal renal tubules (Aim I). Furthermore, we will use genetically-modified proximal tubular LLC-PK1 cells that show PTH-dependent down-regulation of phosphate transport when expressing the PTHR1, in combination with either NPT2a or NPT2c (Aims II and III). Our novel LLC-PK1 cell model will be manipulated to express different wild-type and mutant proteins and treated with PTH and signal-selective PTH analogs applied to either apical or baso-lateral surfaces, thus presenting a valuable tool for our investigations. We predict that the combination of these in vivo and in vitro approaches will provide important new insights into the regulation of phosphate homeostasis and are likely to lead to improved treatment options for human disorders associated with impaired renal phosphate excretion, including hypoparathyroidism, tumoral calcinosis, PHP, and particularly, chronic kidney disease.

肾磷酸稳态的PTH依赖性调节尚未完全理解。 pth下调 两个肾脏特异性磷酸钠共转运蛋白NPT2A和NPT2C的活性。 NPT2A 处理70-80％的磷酸盐重吸收，并通过PTH依赖机制来调节它 涉及PTH/PTHRP受体（PTHR1）的CAMP/PKA信号下游。与这样的 GS_/CAMP/PKA途径在肾脏磷酸盐处理中的重要作用，受某些形式影响的患者 假型甲状腺功能减退症（PHP）由于GS_的受损而出现耐PTH的高磷酸血症 表达或功能。 NPT2C似乎是通过PTHR1介导的PLC/PKC信号来调节的。 NPT2C仅处理20-30％的肾磷酸重吸收，但纯合/化合物却失活 杂合突变导致遗传性下磷酸rick鼠，高钙尿（HHRH），一个 常染色体隐性疾病。因此，NPT2A和NPT2C可能在肾脏中具有非冗余作用 磷酸盐稳态。 PTHR1在肾脏近端的基本外侧膜（BLM）上表达 管状细胞通过CAMP/PKA途径调节NPT2A；但是，尚不清楚是否 BLM处PTHR1的IP3/PKC依赖性信号与NPT2A和/或NPT2C的调节有关 表达。在刷膜膜（BBM），PTHR1似乎仅激活CAMP/PKAIN依赖性 信号通路和我们初步研究的证据表明这些动作调节 NPT2C表达。阐明NPT2A和PTH依赖性调节的机制 NPT2C，我们建议使用表达不足PLC信号的PTHR1突变体的小鼠， NPT2A的“ null”，以及在近端肾小管中缺乏GS_表达的小鼠（AIM I）。此外，我们 将使用遗传改性的近端管状LLC-PK1细胞，这些细胞显示PTH依赖性下调 表达PTHR1时的磷酸盐转运，与NPT2A或NPT2C结合使用（AIMS II和 iii）。我们的新型LLC-PK1细胞模型将被操纵以表达不同的野生型和突变蛋白 并用应用于顶端或基本外侧表面的PTH和信号选择性的PTH类似物处理，从而 为我们的调查提供了宝贵的工具。我们预测这些体内和体外的结合 方法将为调节磷酸盐稳态的调节提供重要的新见解，并可能 导致改善与肾脏磷酸盐排泄受损相关的人类疾病的治疗选择， 包括甲状腺功能低下，肿瘤钙化，PHP，尤其是慢性肾脏疾病。