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障碍的主要特征。低氧可诱导 因子2()是全身铁需求增加(即铁)时铁吸收的关键调节因子 缺乏、红血球生成和怀孕)。Hif2调控顶端铁运输机制的表达， 二价金属转运蛋白1(DMT-1)和十二指肠细胞色素b(Dcytb)，并调节基侧铁 铁转运蛋白是独立于海普西丁的出口商，海普西丁是铁稳态的主要系统调节器。正在扰乱 肠道HIF2减少铁超载疾病的组织铁积累，如-地中海贫血和 遗传性血色素沉着症。此外，在-地中海贫血中，肠道HIF2的中断也可以改善贫血。 这为基于HIF2治疗地中海贫血和遗传性血色病奠定了基础， 佩洛通治疗公司正在积极研究的一个领域。尽管我们的结果表明， HIF2在肠道铁吸收中的作用及其相互重叠和不同作用的潜在机制 缺乏症、-地中海贫血和遗传性血色素沉着症仍不清楚。我们假设一个减少 在全身性中，海普西丁触发肠上皮细胞HIF2的激活，导致铁吸收 反应，这是铁过载紊乱中组织铁积累的关键。我们的长期目标 是改进现有的基于HIF2的疗法，并在铁相关疾病中发现新的基于HIF2的疗法 精神错乱。这项提案的主要目标是评估hif2选择性的确切机制。 调节铁的吸收，并确定是否可以抑制HIF2信号和下游介质 用来限制组织铁超载。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确定遗传性血色素沉着症中HIF2快速激活的机制。我们的数据 提示全身铁调节剂海普西丁和肠道HIF2之间存在串扰。这一概念将是 在新的小鼠模型中进行了测试，这使得我们能够敏锐地和暂时地调节海普西丁-铁门蛋白轴。 AIM 2将描述导致铁吸收的HIF2反应的精确机制。我们已经确定了 母亲抗十五麻症同源物3(SMAD3)作为一个新的因子，对铁的表达是必不可少的- 可吸收的(但不是糖酵解、血管生成或炎症的)HIF2靶基因。我们将澄清具体的情况 Smad3调控HIF2信号的作用和潜在机制。目标3将评估 全身性铁稳态和铁超载对HIF2诱导的肠道铁蛋白吞噬的要求 精神错乱。核辅活化子4(NCOA4)是噬铁蛋白的主要调节因子，受HIF2直接调控 并在缺铁、地中海贫血和遗传性血色素沉着症中高度诱导。我们将研究 利用新的小鼠模型研究自噬铁蛋白周转在铁吸收中的作用。团结在一起， 建议的体内和体外研究将确定Hif2在铁吸收和铁的基础作用 并为寻求针对HIF2的新治疗策略奠定了基础。

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.