Control of iron absorption by intestinal HIF2 in iron and hematological disorders

描述(申请人提供)：铁超载是遗传性血色素沉着症和β-地中海贫血患者死亡和发病的主要原因。需要新的方法来预防和治疗这些疾病。肠道对铁的高吸收是导致组织铁超载的重要机制，抑制肠道铁吸收是一个潜在的靶点。低氧诱导因子(HIF)是由α亚基(HIF1-α或HIF2-α)和β亚基(芳烃核转运体(ARNT))组成的异源二聚体转录因子。利用遗传的小鼠模型和HIF信号转导的细胞系，我们已经证明肠道HIF2-α是铁吸收的关键调节因子。最近，我们证明了HIF2-α(而不是HIF1-α)是调节肠道铁吸收基因所需的中心转录因子，并且在遗传性血色素沉着症和β-地中海贫血的小鼠模型中显著增加。此外，肠道特异的HIF-α过度表达的小鼠会出现自发的铁超载。基于这些观察，我们推测，肠道HIF2-α诱导的铁吸收在铁超载和血液系统疾病的发病机制中起关键作用，并为治疗提供了一个新的靶点。拟议研究的长期目标是阐明HIF2-α如何调节肠道铁吸收的确切机制，以推动可用于治疗血色素沉着症和β-地中海贫血的治疗方案的开发。我们将通过四个相互关联的具体目标来实现我们的目标。目的1将确定在铁超载和血液疾病期间肠道HIF2-α被激活的机制。这将在肠道来源的细胞系和遗传性血色素沉着症、中间β地中海贫血和库利氏贫血(重度β地中海贫血)的HFe-/-、Hbbth3/+和Hbbth3/th3模型中分别进行检测。目的探讨HIF2-α激活铁吸收基因的分子机制。这将通过启动子分析进行检验，重点放在HIF2-α铁吸收靶基因上。这一目标还将通过对遗传性血色素沉着症和β-地中海贫血小鼠模型的十二指肠组织进行全基因组启动子结合研究，识别HIF2-α的新靶基因。AIMS 3和4将确定HIF2-α在血色素沉着症和β-地中海贫血小鼠模型组织铁超载进展中的需求。这将在HFe-/-、Hbbth3/+和Hbbth3/th3小鼠模型中进行检查，这些模型包含肠道中HIF2-α的条件性干扰。这些研究的成功完成将增加我们对肠道铁吸收是如何调节的理解，并为寻求铁超载和血液系统疾病患者的新治疗策略奠定基础。

DESCRIPTION (provided by applicant): Iron overload is the main cause of mortality and morbidity in patients with hereditary hemochromatosis and beta-thalassemia. There is a need for new approaches to prevent and treat these diseases. Intestinal hyperabsorption of iron is a critical mechanism leading to tissue iron overload, and inhibiting intestinal iron absorption presents a potential target. Hypoxia-inducible factors (HIFs) are heterodimeric transcription factors consisting of an alpha-subunit (HIF1-alpha or HIF2-alpha) and beta-subunit (aryl hydrocarbon nuclear translocator (ARNT). Using genetic mouse models and cell lines of HIF signaling, we have shown that intestinal HIF2-alpha is a critical regulator of iron absorption. More recently we demonstrate that HIF2-alpha (but not HIF1-alpha) is the central transcription factor required for regulating intestinal iron absorptive genes and is robustly increased in mouse models of hereditary hemochromatosis and beta-thalassemia. Moreover, intestine-specific HIF-alpha overexpressing mice develop spontaneous iron overload. Based on these observations, we hypothesize that intestinal HIF2-alpha-induced iron absorption is critical in the pathogenesis of iron overload and hematological disorders and presents a novel target for therapy. The long-term objectives of the proposed studies are to elucidate precise mechanisms of how HIF2-alpha regulates intestinal iron absorption as an impetus to the development of therapeutic regimens that can be used to treat hemochromatosis and beta-thalassemia. We will pursue our objectives through four interconnected Specific Aims. Aim 1 will determine mechanisms by which intestinal HIF2-alpha is activated during iron overload and hematological disorders. This will be examined in intestinal-derived cell lines and Hfe-/-, Hbbth3/+, and Hbbth3/th3 models of hereditary hemochromatosis, beta-thalassemia intermedia, and Cooley's anemia (beta-thalassemia major), respectively. Aim 2 will assess the molecular mechanisms of iron absorptive gene activation by HIF2-alpha. This will be examined by promoter analysis with a focus on HIF2-alpha iron absorptive target genes. This Aim will also identify novel target genes of HIF2-alpha using genome-wide promoter binding studies in duodenal tissues from mouse models of hereditary hemochromatosis and beta-thalassemia. Aims 3 and 4 will determine the requirement for HIF2-alpha in the progression of tissue iron overload in mouse models of hemochromatosis and beta-thalassemia. This will be examined in Hfe-/-, Hbbth3/+, and Hbbth3/th3 mouse models that contain a conditional disruption of HIF2-alpha in the intestine. Successful completion of these studies will increase our understanding of how intestinal iron absorption is regulated, and lays the foundation for pursuing new therapeutic strategies in patients with iron overload and hematological disorders.