Regulation Of Inorganic Phosphorus (Pi) Metabolism By Estrogen

描述（由申请人提供）：本提案的长期目标是研究雌性类固醇，主要是雌激素（E2）对无机磷（Pi）稳态的调节。无机磷（Pi）是多种重要生理生化过程所必需的重要矿物质。临床研究表明，接受E2治疗的女性表现出肾Pi消耗和低磷血症。肾和肠在Pi稳态的控制和维持中都起着重要作用。研究表明E2刺激肠道对π的吸收；然而，E2对肾处理Pi的影响尚不清楚。我们的初步研究表明，E2治疗卵巢切除（OVX）大鼠引起尿Pi浪费和低磷血症。这种效应是由IIa型根尖钠依赖性磷酸盐共转运蛋白（NaPi-IIa）的特异性下调引起的，独立于食物摄入量和甲状旁腺激素（PTH）水平的变化。体外研究表明，这种作用是通过涉及NaPi-IIa mRNA稳定性的转录后机制介导的。为了充分表征这一新的Pi代谢调控途径，我们建议进行以下两个特定目的中描述的实验。目的1：表征E2对肾脏处理Pi的快速非基因组效应。E2对雌性OVX大鼠尿Pi排泄、NaPi-IIa运输活性及其膜表达（运输）的影响将被检测。介导这种效应的转导途径将通过PDZK1和NHERF1 knout小鼠的体内和体外研究进行研究。这些研究将辅以体外实验，利用近端小管悬浮液、非洲爪蟾卵母细胞和MDCK细胞检测NaPi-IIa的表达和运输活性。目的2：确定E2对OVX雌性大鼠肾Pi处理慢性影响的分子机制和转导途径。我们将使用药物激动剂以及雌激素受体基因缺失的小鼠？还是呃?。mRNA稳定性和3'UTR在E2诱导的NaPi-IIa下调中的作用将通过转染NaPi-IIa全长cDNA的COS7细胞来确定。这些研究将使用动物模型和细胞培养实验。一旦完成，这些研究将为我们提供E2作为Pi稳态新调控因子的完整表征，并清楚地了解其对肾脏处理Pi的影响。我们认为E2可能是一种重要而有效的治疗工具，可以预防甲状旁腺功能障碍相关的高磷血症及其对心血管系统的不良影响。

DESCRIPTION (provided by applicant): The long-term objective of this proposal is to study the regulation of inorganic phosphorus (Pi) homeostasis by female sex steroids, mainly Estrogen (E2). Inorganic phosphorus (Pi) is an important mineral that is essential to various important physiological and biochemical processes. Clinical studies have shown that women treated with E2 exhibited renal Pi wasting and hypophosphatemia. Both kidney and intestine play an important role in the control and maintenance of Pi homeostasis. Studies have shown that E2 stimulates Pi absorption in the intestine; however, the effect of E2 on renal handling of Pi is poorly understood. Our preliminary studies showed that E2 treatment of ovariectomized (OVX) rat caused urinary Pi wasting and hypophosphatemia. This effect resulted from a specific downregulation of type IIa apical sodium-dependent phosphate cotransporter (NaPi-IIa), independently of changes in food intake and parathyroid hormone (PTH) levels. In vitro studies indicated that this effect is mediated through a posttranscriptional mechanism involving the mRNA stability of NaPi-IIa. To fully characterize this new regulatory pathway of Pi metabolism, we propose to perform the experiments described in the following two Specific Aims. Aim 1: Characterize the rapid, non-genomic effect of E2 on Pi handling by the kidney. The effects of E2 on urinary Pi excretion, NaPi-IIa transport activity, and its membrane expression (trafficking) will be examined in female OVX rats. The transduction pathways mediating this effect will be investigated using both in vitro and in vivo studies involving PDZK1 and NHERF1 knout mice. These studies will be complemented with in vitro experiments, which will examine the expression and transport activity of NaPi-IIa using proximal tubule suspensions, Xenopus Laevis oocytes and MDCK cells. Aim 2: Determine the molecular mechanisms and transduction pathways mediating the chronic effect of E2 on renal Pi handling in OVX female rats. We will use the pharmacological agonists as well as mice with genetic deletion of estrogen receptors ER? or ER?. The role of mRNA stability and 3'UTR in E2- induced downregulation of NaPi-IIa will be determined using COS7 cells transfected with NaPi-IIa full- length cDNA. These studies will use both animal models as well as cell culture experiments. Once completed, these studies will provide us with a full characterization of E2 as a novel regulatory factor of Pi homeostasis with a clear understanding of its effects on renal handling of Pi. We propose that E2 could be an important and efficient therapeutic tool that can prevent hyperphosphatemia and its adverse effects on cardiovascular system in conditions associated with parathyroid gland dysfunction. PUBLIC HEALTH RELEVANCE: Inorganic phosphorus (Pi) is an important mineral involved in several functions of the body. The blood level of Pi is controlled by estrogen, which increases its excretion in the urine. This effect should be considered when prescribing estrogen, and this hormone can also be used when blood level of Pi is high (hyperphosphatemia).