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女性性类固醇（主要是雌激素（E2））对无机磷（Pi）稳态的调节。无机磷（Pi）是一种重要的矿物元素，在许多重要的生理生化过程中起着重要的作用。临床研究表明，用E2治疗的妇女表现出肾性Pi消耗和低磷酸盐血症。肾和肠在Pi稳态的控制和维持中起重要作用。研究表明，E2刺激Pi在肠道中的吸收;然而，E2对肾脏处理Pi的影响知之甚少。我们的初步研究表明，E2治疗卵巢切除（OVX）大鼠引起尿Pi消耗和低磷血症。这种效应是由IIa型顶端钠依赖性磷酸盐协同转运蛋白（NaPi-IIa）的特异性下调引起的，与食物摄入量和甲状旁腺激素（PTH）水平的变化无关。体外研究表明，这种作用是通过涉及NaPi-IIa的mRNA稳定性的转录后机制介导的。为了充分表征Pi代谢的这种新的调节途径，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。将在雌性OVX大鼠中检查E2对尿Pi排泄、NaPi-IIa转运活性及其膜表达（运输）的影响。将使用涉及PDZK 1和NHERF 1 knout小鼠的体外和体内研究来研究介导这种效应的转导途径。这些研究将补充在体外实验，这将检查表达和运输活性的NaPi-IIa使用近端小管悬浮液，非洲爪蟾卵母细胞和MDCK细胞。目的2：探讨雌二醇（E2）对去卵巢大鼠肾脏Pi处理功能的影响及其分子机制。我们将使用药理学激动剂以及雌激素受体ER基因缺失的小鼠？还是急诊室mRNA稳定性和3 'UTR在E2诱导的NaPi-IIa下调中的作用将使用用NaPi-IIa全长cDNA转染的COS 7细胞来确定。这些研究将使用动物模型以及细胞培养实验。一旦完成，这些研究将为我们提供一个完整的表征E2作为一种新的调节因子的Pi的稳态与一个清晰的了解其对肾脏处理的Pi。我们认为E2可能是一种重要而有效的治疗工具，可以预防高磷血症及其对甲状旁腺功能障碍相关疾病的心血管系统的不良影响。 公共卫生相关性：无机磷（Pi）是一种重要的矿物质，参与身体的多种功能。血液中的Pi水平由雌激素控制，雌激素会增加其在尿液中的排泄。在开雌激素处方时应考虑这种影响，这种激素也可以在血液Pi水平高（高磷血症）时使用。

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).