Dynamic Regulation of Erythropoietin Gene Expression in Mammals

哺乳动物促红细胞生成素基因表达的动态调控

• 批准号: 7691086
• 负责人: Joseph Anthony Garcia
• 金额: --
• 依托单位: VA NORTH TEXAS HEALTH CARE SYSTEM
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-04-01 至 2012-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7691086
• 关键词: Ablation; Anemia; Attenuated; Binding; Biochemical; Biological; Biological Assay; Bolus Infusion; Brain; Cell Culture Techniques; Cell Line; Cells; Cessation of life; Chronic; Co-Immunoprecipitations; Complex; DNA; Enhancers; Erythrocytes; Erythropoietin; Gene Expression; Genes; Genetic Enhancer Element; Goals; Growth; HIF1A gene; Healthcare; Homeostasis; Hour; Hypertension; Hypoxia; Hypoxia-Responsive Elements; Individual; Kidney; Kidney Diseases; Knockout Mice; Liver; Mammals; Mediating; Messenger RNA; Modeling; Molecular; Molecular Target; Mus; NuRD complex; Oxygen; Pathway interactions; Patients; Pharmacotherapy; Plant Roots; Production; Proteins; Regulation; Repression; Research Personnel; Retina; Reverse Transcriptase Polymerase Chain Reaction; Role; Signal Transduction; Site; Stress; Time; Tissues; Transfection; Veterans; abstracting; bHLH-PAS factor HLF; chromatin immunoprecipitation; cytokine; hepatoma cell; hybrid protein; hypoxia inducible factor 1; in vivo; insight; member; mouse model; novel; overexpression; public health relevance; response; small hairpin RNA; transcription factor

DESCRIPTION (provided by applicant): PROJECT SUMMARY/ABSTRACT Impaired erythropoietin (epo) production is the root cause of anemia in a majority of chronic anemia patients. Over the past century, investigators discovered that the potent inducer of red blood cell mass in response to anemia or systemic hypoxia is circulating epo, a pro-erythrogenic cytokine produced by the kidney. Approximately one-third of chronic anemia patients have normal kidneys, but inappropriately low epo levels. Why is epo expression blunted in these patients? The answer to this question requires first understanding how epo gene expression is regulated in normal individuals. Studies of epo regulation over the past decade have focused on hypoxia signaling. Using hepatoma cell lines producing epo in an oxygen-dependent manner, investigators defined the hypoxia- responsive enhancer region of the epo gene. This in turn led to identification of a cis-acting DNA enhancer element, the Hypoxia Responsive Element (HRE), in the epo enhancer region followed by purification of an HRE-binding oxygen-sensitive transcription factor, Hypoxia Inducible Factor 1 alpha (HIF-11). Investigators initially assumed that HIF-11 regulates endogenous epo gene expression. However, mouse model studies reveal that the second and related HIF member, HIF-21, is critical for in vivo epo gene expression. Our long-term goal is to define the molecular mechanisms regulating mammalian epo expression. Epo synthesis normally increases rapidly with tissue hypoxia, and then returns to baseline within hours. While an essential role of HIF-21 in epo regulation is now recognized, the factors responsible for temporal epo gene expression in vivo, or for abnormal repression of epo gene expression in anemia patients, remain poorly understood. In unpublished Preliminary Studies, we demonstrate novel regulation of epo enhancer function by Early Growth Response (Egr) members, stress-responsive transcription factors whose activity is also altered by hypoxia. We further demonstrate that factors known to repress Egr signaling also repress epo enhancer activity in a HIF-21 dependent manner. We hypothesize that hypoxia initially triggers Egr and HIF-2 activation, leading to synergistic activation of epo gene expression. With continued hypoxia exposure, we propose Egr repressive factors are induced that attenuate epo gene expression. In this proposal, we will define molecular and biochemical mechanisms whereby Egr/HIF-2 signaling regulates epo enhancer activity, and we will define the biological role of Egr/HIF-2 signaling in epo regulation using cell culture and mouse knockout models. Deciphering how Egr/HIF-2 signaling regulates epo enhancer activity will provide mechanistic insights into normal epo regulation and will identify novel molecular targets for modulation of endogenous epo gene expression in chronic anemia patients. PUBLIC HEALTH RELEVANCE: PROJECT NARRATIVE The Potential Impact on Veterans Health Care is identifying specific molecular pathways that can be targeted by novel drug therapies, thereby restoring normal erythropoietin production in a large segment of our veteran patients with chronic anemia.

描述（由申请人提供）： 红细胞生成素（epo）生成受损是大多数慢性贫血患者贫血的根本原因。在过去的世纪里，研究者发现红细胞群对贫血或全身性缺氧反应的有效诱导物是循环epo，一种由肾脏产生的促红细胞生成细胞因子。大约三分之一的慢性贫血患者肾脏正常，但epo水平不适当地低。为什么这些患者的epo表达减弱？要回答这个问题，首先需要了解正常个体中epo基因的表达是如何调节的。 在过去的十年里，epo调节的研究主要集中在缺氧信号上。研究人员利用以氧依赖方式产生epo的肝癌细胞系，确定了epo基因的低氧应答增强子区域。这又导致在epo增强子区域中鉴定出顺式作用DNA增强子元件，缺氧反应元件（HRE），随后纯化HRE结合氧敏感性转录因子，缺氧诱导因子1 α（HIF-11）。研究人员最初认为HIF-11调节内源性epo基因表达。 然而，小鼠模型研究表明，第二个和相关的HIF成员，HIF-21，是体内epo基因表达的关键。 我们的长期目标是确定调节哺乳动物epo表达的分子机制。正常情况下，组织缺氧时Epo合成迅速增加，然后在数小时内恢复到基线水平。虽然现在认识到HIF-21在EPO调节中的重要作用，但对负责体内时间EPO基因表达或贫血患者中EPO基因表达的异常抑制的因素仍然知之甚少。在未发表的初步研究中，我们证明了早期生长反应（EGR）成员，应激反应转录因子的活性也被缺氧改变的EPO增强子功能的新调节。我们进一步证明了已知抑制Egr信号传导的因子也以HIF-21依赖的方式抑制EPO增强子活性。 我们假设缺氧最初触发Egr和HIF-2激活，导致EPO基因表达的协同激活。随着持续缺氧暴露，我们建议Egr抑制因子诱导减弱epo基因表达。在这个提议中，我们将定义Egr/HIF-2信号调节EPO增强子活性的分子和生化机制，我们将使用细胞培养和小鼠敲除模型定义Egr/HIF-2信号在EPO调节中的生物学作用。解读Egr/HIF-2信号如何调节EPO增强子活性将为正常EPO调节提供机制性见解，并将确定用于调节慢性贫血患者内源性EPO基因表达的新分子靶点。 公共卫生相关性： 对退伍军人医疗保健的潜在影响是确定可以通过新型药物治疗靶向的特定分子途径，从而恢复我们的大部分慢性贫血退伍军人患者的正常促红细胞生成素生产。