Renal Medullary HIF Prolyl Hydroxylases and Salt Sensitivity of Blood Pressure

描述（由申请人提供）：缺氧诱导因子（HIF）-1 α是一种转录因子，在肾髓质中高度表达，并调节该肾区域的许多抗高血压基因，如血红素加氧酶-1、环氧合酶-2和一氧化氮合酶-2。脯氨酰羟化酶结构域蛋白-2（PHD 2）是促进肾髓质中HIF-1 α降解的主要酶。在上一个资助期，我们证明高盐摄入降低了肾髓质中PHD 2 mRNA水平，从而诱导HIF-1 α介导的抗高血压基因激活。这种PHD 2/HIF-1 α介导的肾髓质分子适应对于肾脏在高盐摄入下清除额外的Na+负荷和维持正常血压是重要的。问题仍然存在：高盐摄入如何减少PHD 2 mRNA？我们的初步研究表明，高盐饮食促进了肾髓质中PHD 2 mRNA的降解，而microRNA miR-429可能是高盐诱导的PHD 2 mRNA降解增强的上游介质：1）在靶向PHD 2 mRNA的microRNA中，高盐摄入增加了肾髓质中miR-429的水平; 2）miR-429显示靶向PHD 2 mRNA 3 '-UTR; 3）miR-429在体外和体内降低PHD 2 mRNA水平。此外，miR-429抑制剂阻断了高盐诱导的肾髓质中PHD 2 mRNA的减少，并在正常大鼠中产生盐敏感性高血压。我们还检测到Dahl盐敏感性高血压（SS）大鼠肾髓质中miR-429的损伤。基于这些初步数据，我们假设miR-429调节PHD 2/HIF-1 α介导的肾髓质中抗高血压基因的激活有助于肾盐适应，并参与肾Na+处理和血压的控制。为了验证这一假设，我们将首先确定慢性肾脏对高盐摄入的适应是否与miR-429的增加有关，miR-429降低了PHD 2水平并激活了正常大鼠肾髓质中HIF-1 α介导的抗高血压基因的转录。然后，我们将确定抑制miR-429功能以防止PHD 2减少并减少肾髓质中HIF-1 α介导的抗高血压基因的激活是否会减弱压力性尿钠排泄并损害肾Na+处理，从而导致正常大鼠的盐敏感性高血压。最后，我们将确定Dahl SS大鼠的盐敏感性高血压是否与肾脏髓质中与PHD 2/HIF-1 α通路相关的miR-429介导的分子适应功能障碍相关，并研究在该高血压模型中导致肾脏髓质miR-429缺乏的机制。这些研究将揭示一种新的介导肾脏适应高盐摄入的分子机制，并为盐敏感性高血压的发病机制提供新的见解。

DESCRIPTION (provided by applicant): Hypoxia inducible factor (HIF)-1alpha is a transcriptional factor that is highly expressed in the renal medulla and regulates many anti-hypertensive genes, such as heme oxygenase-1, cyclooxygenase-2 and nitric oxide synthase-2, in this kidney region. Prolyl hydroxylase domain-containing protein-2 (PHD2) is the major enzyme to promote the degradation of HIF-1alpha in the renal medulla. In the last funding period, we proved that high salt intake reduced PHD2 mRNA levels in the renal medulla, which consequently induced HIF-1alpha-mediated activation of anti-hypertensive genes. This PHD2/HIF-1alpha-mediated molecular adaptation in the renal medulla is important for the kidneys to remove extra Na+ loading and maintain normal blood pressure under high salt intake. The question remains: how does high salt intake reduce PHD2 mRNA? Our preliminary studies showed that high salt diet enhanced the degradation of PHD2 mRNA in the renal medulla and that microRNA miR-429 was probably the upstream mediator for high salt-induced enhancement of PHD2 mRNA decay: 1) among the microRNAs that target PHD2 mRNA, miR-429 levels were increased by high salt intake in the renal medulla; 2) miR-429 was shown to target PHD2 mRNA 3'-UTR; 3) miR-429 reduced PHD2 mRNA levels in vitro and in vivo. Moreover, miR-429 inhibitor blocked the high salt- induced decrease in PHD2 mRNA in the renal medulla and produced salt sensitive hypertension in normal rats. We also detected impairment in miR-429 in the renal medulla in Dahl salt-sensitive hypertensive (SS) rats. Based on these preliminary data, we hypothesize that miR-429 regulation of PHD2/HIF-1alpha-mediated activation of anti-hypertensive genes in the renal medulla contributes to renal salt adaptation and participates in the controls of renal Na+ handling and blood pressure. To test this hypothesis, we will first determine whether chronic renal adaptation to high salt intake is associated with an increase in miR-429, which decreases PHD2 levels and activates HIF-1alpha-mediated transcriptions of anti-hypertensive genes in the renal medulla in normal rats. We will then determine whether inhibition of miR-429 function to prevent PHD2 reduction and to diminish HIF-1alpha-mediated activation of anti-hypertensive genes in the renal medulla will blunt pressure natriuresis and impair renal Na+ handling, leading to salt sensitive hypertension in normal rats. Finally, we will determine whether salt-sensitive hypertension in Dahl SS rats is associated with the dysfunction in miR-429- mediated molecular adaptation related to PHD2/HIF-1alpha-pathway in the renal medulla and also investigate the mechanisms that cause the deficiency of renal medullary miR-429 in this hypertensive model. The proposed studies will reveal a novel molecular mechanism mediating renal adaptation to high salt intake and provide new insights into the pathogenesis of salt-sensitive hypertension.