Gaining New Insights Into Regulation of Systemic Iron Homeostasis.

铁是红细胞生成所必需的。精确控制肝脏激素海普西丁是体内铁的中枢调节因子，对于调节全身铁平衡以维持铁的供需平衡非常重要。海普西丁的表达受到铁或炎症的刺激，并导致铁输出通道的降解和内化。然后，铁不能被肠道吸收，而被困在铁的储存中，如肝细胞和巨噬细胞。海普西丁的诱导会导致慢性病贫血(ACD)。海普西丁的相对或绝对缺乏会导致铁负荷过重，也称为血色素沉着症。这两种疾病都是高度流行的，确实对患者的健康造成了严重影响。因此，第一个方案和这个更新方案的总体目标是增加我们对全身铁调节的了解，以便能够开发出治疗由海普西丁调节失衡引起的疾病的方法。通过炎症降低海普西丁表达的一种方法是抑制骨形态发生蛋白(BMP)信号通路，该信号通路可治愈小鼠的ACD。在第一项研究中，研究了ACD发病机制中关键的BMP受体，在体外测定了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，并研究了ALK2和ALK3在调节肝脏铁代谢和铁负荷中的作用。我们的数据表明，海普西丁的诱导不仅依赖于BMP受体，还依赖于其他调节蛋白，因为BMP I型受体ALK3在体外与铁调节蛋白HFE和TfR2相互作用。因此，将在续期赠款提案的特定目标1中在体内研究蛋白质-蛋白质相互作用。利用腺相关病毒在患有和不患有肝细胞特异性Alk3缺乏症的小鼠中的基因过度表达将被用来证明相关的相互作用及其在体内的功能。在具体目标2中，建立的小鼠铁超载模型将通过小动物MRI成像来确定器官水平的铁积累，以及微X射线荧光和LS-MCPM来确定单细胞水平的铁积累。在具体目标3中，我们将研究小鼠心脏铁超载经历缺血/再灌注损伤、经主动脉延长或暴露于心脏毒性药物，以了解铁依赖型心肌病的病理生理发展并治疗该疾病。续期拨款将使我们能够对全身铁稳态的调节获得新的见解，这将对研究学会和所有护理铁调节系统失衡引起的疾病的医生产生很大影响。

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.