Gaining New Insights Into Regulation of Systemic Iron Homeostasis.

铁是红细胞生成所必需的。精确控制肝激素hepcidin（体内的中央铁调节剂）对调节全身铁稳态至关重要，以维持铁需求和供应之间的平衡。铁或炎症刺激Hepcidin的表达，并导致铁输出通道的降解和内化。然后，铁不能在肠道中被吸收，而被困在铁储备中，如肝细胞和巨噬细胞。hepcidin的诱导引起慢性疾病贫血（ACD）。hepcidin的相对或绝对缺乏会导致铁超载，也称为血色素沉着症。这两种疾病都非常普遍，对患者的健康造成严重影响。因此，第一个提案和这个更新提案的总体目标是增加我们对系统性铁调节的了解，以便能够开发出由hepcidin调节不平衡引起的疾病的治疗方法。抑制骨形态发生蛋白（BMP）信号通路是通过炎症降低hepcidin表达的一种方法，可治疗小鼠ACD。此外，BMP受体缺乏的小鼠存在hepcidin缺乏和铁超载。在第一项资助中，研究了对ACD发病机制至关重要的BMP受体，在体外确定了BMP I型受体ALK2-和ALK3依赖的铁调节所需的蛋白质-蛋白质相互作用，并表征了ALK2和ALK3在调节肝脏铁代谢和铁过载中的作用。我们的数据表明，hepcidin的诱导不仅依赖于BMP受体，还依赖于其他调节蛋白，如BMP I型受体ALK3在体外与铁调节蛋白HFE和TfR2相互作用。因此，蛋白质-蛋白质相互作用将在体内进行研究，这是续期拨款提案的具体目标1。在有或没有肝细胞特异性Alk3缺乏症的小鼠中使用腺相关病毒进行基因过表达将用于证明相关的相互作用及其在体内的功能。在特定目标2中，建立的小鼠铁过载模型的小鼠铁过载将通过小动物MRI成像来确定器官水平的铁积累，以及µXRF和LS-MCPM来确定单细胞水平的铁积累。在特定的目的3中，我们将研究小鼠心脏铁过载经历缺血/再灌注损伤，经主动脉延长或暴露于心脏毒性药物，以了解铁依赖性心肌病的病理生理发展和治疗疾病。这项续期资助将使我们对系统铁稳态的调节有新的见解，这将对研究界和所有照顾因铁调节系统失衡引起的疾病患者的医生产生重大影响。

Iron is required for erythropoiesis. Precise control of the hepatic hormone hepcidin, the central iron regulator in the body, is important for regulation of systemic iron homeostasis in order to maintain a balance between iron demand and supply. Hepcidin expression is stimulated by iron or inflammation, and leads to degradation and internalization of the iron export channel. Then, iron cannot be absorbed in the intestine, and remains trapped in the iron stores, such as hepatocytes and macrophages. An induction of hepcidin causes the anemia of chronic disease (ACD). A relative or absolute deficiency of hepcidin causes iron overload, also called hemochromatosis. Both diseases are highly prevalent and do have a severe impact on patient`s health. Therefore, the overall goal of the first proposal and of this renewal proposal is to increase our knowledge in systemic iron regulation in order to be able to develop treatments for diseases caused by imbalances of hepcidin regulation. A way to decrease hepcidin expression by inflammation is inhibition of the bone morphogenetic protein (BMP) signaling pathway, which cures ACD in mice. In addition, mice with a deficiency of a BMP receptor present with hepcidin deficiency and iron overload.In the first grant, the BMP receptor critical for the pathogenesis of ACD was investigated, the protein-protein interactions required for BMP type I receptors ALK2- and ALK3-dependent iron regulation were determined in vitro and the role of ALK2 and ALK3 in regulation of hepatic iron metabolism and iron overload were characterized. Our data indicate that hepcidin induction relies not only on BMP receptors but also on other regulatory proteins, as the BMP type I receptor ALK3 interacts with the iron regulatory proteins HFE and TfR2 in vitro. Therefore, protein-protein interactions will be investigated in vivo in specific aim 1 of the renewal grant proposal. Gene overexpression using adeno-associated viruses in mice with and without hepatocyte-specific Alk3 deficiency will be used to proof relevant interactions and their functions in vivo. In specific aim 2, murine iron overload of the established murine iron overload models will be imaged by small animal MRI to determine iron accumulation at organ level as well as µXRF and LS-MCPM to determine iron accumulation at single cell level. In specific aim 3 we will investigate murine cardiac iron overload undergoing either ischemia/reperfusion injury, transaortic elongation or exposed to cardiotoxic drugs in order to learn about the pathophysiologic development of iron-dependent cardiomyopathy and to treat the disease.The renewal grant will enable us to gain novel insights into regulation of systemic iron homeostasis, which will be of high impact to the research society and all the physicians caring for patients with diseases caused by imbalances of the iron regulatory system.