Regulatory role of iron transport in stress and ineffective erythropoiesis

摘要 我们的实验室旨在详细了解铁的运输如何影响红细胞生成，以及 红外线将铁的需求传递给肝脏。用于红细胞生成的铁是由铁运输的 转运蛋白(Tf)和红系前体对铁的摄取需要Tf-Fe与转铁蛋白受体结合 1(TfR1)。反过来，红系前体部分通过分泌因子来调节铁的代谢，如 最近发现的红铁酮(ERFe)，它抑制荷尔蒙海普西丁，一个关键的饮食抑制剂 铁的吸收，从老化的红细胞中回收，以及从铁储存中动员。Erfe在中增加 应激(即去血野生型小鼠)和无效红细胞生成(即β-地中海贫血)模型 老鼠)。此外，红系前体表达铁和血红素输出蛋白，其功能仍然 不清楚。我们发现外源性无铁转铁蛋白可改善β-地中海贫血患者无效的红细胞生成。 小鼠(Li等人，Nat Med，2010)，导致ERFe降低，海普西丁增加，以及相对全身铁 缺乏症。我们假设外源性转铁蛋白对β-地中海贫血小鼠的有益作用是 后果不止于直言不讳的铁限制。具体地说，我们的初步数据表明，TF 通过对TfR1的影响发挥作用，通过对膜TfR1和铁的影响影响去核 通过减少Erfe表达间接代谢和通过减少可溶性TfR1直接代谢。此外， 令人惊讶的是，尽管相对缺铁，TfR1+/-小鼠的海普西丁表达并未受到抑制 红细胞生成和Erfe表达增加。因此，我们假设 外源性Tf对无效红细胞生成的影响是TfR1表达减少或改变的结果 TfR1来自红系前体的贩运。在这里，我们建议详细定义Tf如何变化 浓度、铁摄取和外排以及TfR1在红细胞内的运输影响红细胞生成和红系 海普西丁调节。在提出的三个具体目标中，我们将1)评估Tf和TfR1在 铁限制和无效的红细胞生成；2)检测TfR1作为海普西丁调节因子的意义； 3)阐明Tf和TfR1对红系前体细胞和肝细胞铁外流的影响。铁 红系运输和红系调节铁代谢是康复过程中的中心原则 应激性红细胞生成，在无效的红细胞生成中调节失调。因此，成功地完成了这些 阐明Tf和TfR1在这些途径中的作用的研究对血液学领域非常有意义。 深入了解红血球生成受到干扰的人类疾病的病理生理学 铁代谢的最新知识，并为进一步探索红系调节增加了新的范式 海普西丁。最后，成功完成这些研究，审问应激和 无效的红细胞生成(对PAS-13-031有反应)将促进使用转铁蛋白的临床试验的发展 患有β-地中海贫血和可能的其他铁负荷贫血的患者。

ABSTRACT Our laboratory aims to understand in detail how iron transport influences erythropoiesis and how the erythron communicates iron requirements to the liver. Iron for erythropoiesis is transported by the iron transporter transferrin (Tf) and iron uptake by erythroid precursors requires Tf-Fe binding to transferrin receptor 1 (TfR1). In turn, erythroid precursors regulate iron metabolism in part by secreting factors, such as the recently identified erythroferrone (ERFE), which suppresses the hormone hepcidin, a key inhibitor of dietary iron absorption, recycling from senescent RBCs, and mobilization from iron stores. ERFE is increased in models of both stress (i.e. phlebotomized wild type mice) and ineffective erythropoiesis (i.e. β-thalassemic mice). Furthermore, erythroid precursors express iron and heme export proteins, the function of which remains unclear. We have shown that exogenous iron-free Tf ameliorates ineffective erythropoiesis in β-thalassemic mice (Li et al., Nat Med, 2010), resulting in decreased ERFE, increased hepcidin, and relative systemic iron deficiency. We hypothesize that the beneficial effect of exogenous Tf in β-thalassemic mice is a consequence of more than frank iron restriction. Specifically, our preliminary data suggests that Tf functions via an effect on TfR1, influencing enucleation through effects on membrane TfR1 as well as iron metabolism indirectly by decreasing Erfe expression and directly by decreasing soluble TfR1. Furthermore, surprisingly, hepcidin expression is not suppressed in TfR1+/- mice, despite relative iron deficient erythropoiesis and increased ERFE expression. Thus, we hypothesize that the beneficial effect of exogenous Tf on ineffective erythropoiesis is a consequence of reduced TfR1 expression or altered TfR1 trafficking from erythroid precursors. Here we propose to define in detail how changes in Tf concentration, iron uptake and efflux, and TfR1 trafficking in the erythron influence erythropoiesis and erythroid hepcidin regulation. In the proposed three specific aims, we will 1) assess the regulatory role of Tf and TfR1 in iron restricted and ineffective erythropoiesis; 2) examine the significance of TfR1 as a regulator of hepcidin; and 3) elucidate the effect of Tf and TfR1 on iron efflux from erythroid precursors and hepatocytes. Iron transport for erythropoiesis and erythroid regulation of iron metabolism are central tenets in recovery during stress erythropoiesis and are dysregulated in ineffective erythropoiesis. Thus, successful completion of these studies elucidating the role of Tf and TfR1 in these pathways is of great interest to the hematology field, provides insight into the pathophysiology of human diseases in which erythropoiesis is disturbed, extends current knowledge in iron metabolism, and adds new paradigms for further exploring erythroid regulation of hepcidin. Lastly, the successful completion of these studies interrogating mechanisms involved in stress and ineffective erythropoiesis (responsive to PAS-13-031) will facilitate the development of clinical trials using Tf in patients with β-thalassemia and possibly other iron-loading anemias.