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

摘要 肠道铁吸收失调是铁超载疾病的主要特征。缺氧诱导 因子2 β（HIF 2 β）是在增加的全身性铁需求（即铁 缺乏症、红细胞生成和妊娠）。HIF 2 α调节顶端铁转运机制的表达， 二价金属转运蛋白1（DMT-1）和十二指肠细胞色素B（DcytB），并调节基底外侧铁 不依赖于铁调素的输出转运铁蛋白，铁调素是铁稳态的主要系统调节剂。扰乱 肠HIF 2 α降低铁过载疾病如β-地中海贫血和 遗传性血色病此外，在β-地中海贫血中，肠HIF 2 α的破坏也改善贫血。 这为基于HIF 2 α的β-地中海贫血和遗传性血色素沉着症的治疗奠定了基础， Peloton Therapeutics正在积极研究这一领域。虽然我们的研究结果表明， HIF 2参与肠铁吸收，其在铁吸收中重叠和不同作用背后的潜在机制 缺乏症、β-地中海贫血和遗传性血色病仍不清楚。我们假设， 在全身性hepcidin触发HIF 2 α激活肠上皮细胞，导致铁吸收， 反应，这是铁超载疾病中组织铁积累的关键。我们的长期目标 改善现有的基于HIF 2 α的疗法，并在铁相关疾病中识别新的基于HIF 2 α的疗法。 紊乱这项提案的主要目标是评估HIF 2选择性地抑制肿瘤的确切机制。 调节铁的吸收，并确定是否可以抑制HIF 2 α信号传导和下游介质， 用于限制组织铁过载。我们将通过三个相互关联的具体目标来实现我们的目标。 目的1将确定导致遗传性血色病中HIF 2 α快速激活的机制。我们的数据 提示系统性铁调节剂hepcidin和肠道HIF 2 α之间存在串扰。这一概念将 在新的小鼠模型中进行了测试，使我们能够急性和暂时调节铁调素-铁转运蛋白轴。 目的2将表征导致铁吸收性HIF 2 α应答的精确机制。我们已经确定 母亲对decapentaplegic同源物3（SMAD 3）作为一种新的因素，是必不可少的表达铁， 吸收（但不是糖酵解，血管生成或炎症）HIF 2 α靶基因。我们将详细说明 SMAD 3调节HIF 2 α信号传导的作用和潜在机制。目标3将评估 在系统性铁稳态和铁过载中对HIF 2 α诱导的肠铁蛋白吞噬的需要 紊乱核辅激活因子-4（NCOA-4）是铁蛋白吞噬的主要调节因子，受HIF 2 α直接调节。 在铁缺乏、β-地中海贫血和遗传性血色病中高度诱发。我们会研究 自噬铁蛋白周转在铁吸收中的作用。统称 提出的体内和体外研究将确定HIF 2 α在铁吸收和铁代谢中的基本作用。 并为寻求靶向HIF 2 α的新治疗策略奠定基础。

ABSTRACT Dysregulation of intestinal iron absorption is a primary feature in iron overload disorders. Hypoxia-inducible factor 2 (HIF2) is a critical regulator of iron absorption during increased systemic iron demands (i.e. iron deficiency, erythropoiesis, and pregnancy). HIF2 regulates expression of the apical iron transport machinery, divalent metal transporter 1 (DMT-1) and duodenal cytochrome b (Dcytb), and regulates the basolateral iron exporter ferroportin independent of hepcidin, the master systemic regulator of iron homeostasis. Disrupting intestinal HIF2 decreases tissue iron accumulation in iron overload disorders, such as -thalassemia and heredity hemochromatosis. Moreover, in -thalassemia, disruption of intestinal HIF2 also improves anemia. This has laid the foundation for HIF2-based therapeutics for -thalassemia and heredity hemochromatosis, an area actively being researched by Peloton Therapeutics. Although our results demonstrate a central role for HIF2 in intestinal iron absorption, the underlying mechanisms behind its overlapping and distinct roles in iron deficiency, -thalassemia, and heredity hemochromatosis are still unclear. We hypothesize that a decrease in systemic hepcidin triggers HIF2 activation in intestinal epithelia, leading to an iron-absorptive response, which is critical for tissue iron accumulation in iron overload disorders. Our long-term goals are to improve existing HIF2-based therapies and identify novel HIF2-based therapies in iron-related disorders. The major goal of this proposal is to assess the precise mechanisms by which HIF2 selectively regulates iron absorption and determine if inhibition of HIF2 signaling and downstream mediators can be used to restrict tissue iron overload. We will pursue our objectives through three interconnected Specific Aims. Aim 1 will identify mechanisms leading to rapid activation of HIF2 in hereditary hemochromatosis. Our data suggest a crosstalk between the systemic iron regulator, hepcidin, and intestinal HIF2. This concept will be tested in novel mouse models that allow us to acutely and temporally regulate the hepcidin-ferroportin axis. Aim 2 will characterize precise mechanisms leading to an iron-absorptive HIF2 response. We have identified mothers against decapentaplegic homolog 3 (SMAD3) as a novel factor that is essential for expression of iron- absorptive (but not glycolytic, angiogenic, or inflammatory) HIF2 target genes. We will elucidate the specific role and underlying mechanisms behind SMAD3 regulation of HIF2 signaling. Aim 3 will assess the requirement for HIF2-induced intestinal ferritinophagy in systemic iron homeostasis and iron overload disorders. Nuclear coactivator-4 (NCOA4), the major regulator of ferritinophagy, is directly regulated by HIF2 and is highly induced in iron deficiency, -thalassemia, and heredity hemochromatosis. We will examine the role that autophagic ferritin turnover plays in iron absorption using novel mouse models. Together, the proposed in vivo and in vitro studies will identify fundamental roles of HIF2 in iron absorption and iron overload disorders and lay the foundation for pursuing new therapeutic strategies targeting HIF2.