Mechanisms of hepcidin effects in the anemia of chronic disease

描述(由申请人提供)： 慢性病贫血是医学实践中最常见的临床综合征之一。这种疾病通常表现为低增殖性贫血，并伴有低血清铁浓度，尽管网状内皮铁储备充足。ACD通常被认为是多种病理过程共同作用的结果，这些病理过程可能与炎症的细胞因子介质有关。然而，铁代谢改变在ACD中的诊断重要性使许多研究人员认为这一特征代表了这种综合征的主要病理生理机制。海普西丁是一种抗菌蛋白，它在肝脏中产生，在血液中循环，并在尿液中排泄。它是一种II型急性时相蛋白，由白细胞介素6(IL-6)诱导表达，受肿瘤坏死因子(TNF)下调。海普西丁特殊的铁调节功能，以及在患者和带有海普西丁基因表达异常的转基因动物中观察到的贫血综合征(如下所述)，使许多人认为它是解开“ACD之谜”的关键。ACD的发病过程主要涉及三个过程。红细胞存活时间的略微缩短会导致骨髓对红细胞产量的小幅增加。由于红细胞生成受损和网状内皮系统铁储存动员受损，骨髓不能对这一需求做出充分反应。现有数据有力地支持了海普西丁在ACD铁异常中的潜在作用。然而，铁的改变并不是ACD唯一的异常特征。如果海普西丁是ACD的主要致病因素，那么它也应该是导致这种综合征中红细胞生成受损的原因。海普西丁导致ACD患者红细胞生成受损的假说将通过以下具体目标得到解决：1.测定海普西丁对红系集落形成的影响，并探讨其机制。这将包括：A.，海普西丁对红细胞生成的影响是直接作用的，还是需要辅助细胞；B.EPO浓度在海普西丁对红细胞生成的影响中的作用；C.，凋亡/抗增殖在海普西丁抑制红细胞生成作用中的作用；D.，细胞因子对海普西丁/红细胞生成关系的影响；E.铁对海普西丁对CFU-E集落形成的影响；F.，门静脉铁蛋白(FPN)及其变体FPN在海普西丁对CFU-E的影响中的作用；以及G.EPO和炎性细胞因子对红系细胞中FPN变体表达的影响。2.骨髓巨噬细胞铁转运中海普西丁与细胞因子相互作用的测定海普西丁通过下调铁输出蛋白FPN来抑制骨髓巨噬细胞中铁的外流。将确定炎性细胞因子增强或减弱这种影响的能力，以及对变异型FPN.3表达的任何影响。测定海普西丁对体外诱导的EPO产生的影响，并对相关机制进行描述。这将包括：A.测定和量化海普西丁在肝脏和肾脏模型中诱导EPO蛋白的作用，以及这些作用的时间进程；B.确定炎症细胞因子在调节这些作用中的作用；C.铁的可获得性在这些作用中的作用；以及D.测定海普西丁对EPO转录的影响，以及这些影响所涉及的机制。4.重组人Epo体外对海普西丁产生的影响在这一目标中，我们将确定A，EPO对HepG2产生海普西丁的影响，以及B，这些影响被肿瘤坏死因子，白介素1和白介素6调节的程度。与退伍军人管理局任务的相关性：拟议的研究可能有助于加深对ACD机制的理解，并导致更有效的治疗。 公共卫生相关性： 贫血是导致慢性病患者发病率和死亡率的主要因素，而慢性病贫血(ACD)是导致这种贫血的主要原因。这种疾病通常表现为低增殖性贫血，并伴有低血清铁浓度，尽管网状内皮铁储备充足。退伍军人病症在退伍军人中非常普遍。在ACD中，红细胞存活时间的轻微缩短会导致骨髓对红细胞产量的小幅增加。由于红细胞生成受损和网状内皮系统铁储存动员受损，骨髓不能对这一需求做出充分反应。现有数据有力地支持了海普西丁在ACD铁异常中的潜在作用。如果海普西丁是ACD的主要致病因素，那么它也应该对观察到的这种综合征中的红细胞生成受损起作用。拟议的研究可能有助于加深对ACD机制的了解，从而产生更有效的治疗方法。

DESCRIPTION (provided by applicant): The anemia of chronic disease (ACD) is one of the most common clinical syndromes encountered in the practice of medicine. This disorder typically manifests itself as a hypoproliferative anemia accompanied by a low serum iron concentration despite adequate reticuloendothelial iron stores. ACD has generally been considered to result from a combination of pathologic processes which can be linked to the cytokine mediators of inflammation. However, the diagnostic importance of altered iron metabolism in ACD has led many investigators to consider that this feature denotes the dominant pathophysiologic mechanism of this syndrome. Hepcidin is an antibacterial protein which is produced in the liver, circulates in the blood, and is excreted in the urine. It is a type II acute phase protein, the expression of which is induced by interleukin (IL)-6, and down-regulated by tumor necrosis factor (TNF). The specific iron regulatory functions of hepcidin, as well as the anemia syndromes observed in patients and transgenic animals with abnormalities of hepcidin gene expression (discussed below), have led many to consider that it is the key to unlocking "the mysteries of ACD ". Three major processes are involved in the pathogenesis of ACD. A slight shortening of red cell survival creates a demand for a small increase in red cell production by the bone marrow. The marrow cannot respond adequately to this demand due to impaired erythropoiesis and impaired mobilization of reticuloendothelial system iron stores. A potential role for hepcidin in the iron anomalies of ACD is strongly supported by available data. However, iron changes are not the sole abnormality characteristic of ACD. If hepcidin is the major factor responsible for ACD, then it should also contribute to the impaired erythropoiesis observed in this syndrome. The hypothesis that hepcidin contributes to impaired erythropoiesis in ACD will be addressed through the following specific aims: 1. Determination of hepcidin effects on erythroid colony formation, and investigation of the mechanisms involved. This will include A., whether the effects of hepcidin on erythropoiesis are direct-acting, or require an accessory cell; B., the role of Epo concentration in hepcidin effects on erythropoiesis; C., the role of apoptosis/anti-proliferation in inhibitory effects of hepcidin on erythropoiesis; D., the effects of cytokines on the hepcidin/erythropoiesis relationship; E., the contributions of iron to hepcidin effects on CFU-E colony formation; F., the role of ferroportin (FPN) and variant FPN in hepcidin effects on CFU-E; and G., effects of Epo and inflammatory cytokines on FPN variant expression in erythroid cells. 2. Determination of the interactions of hepcidin and cytokines in bone marrow macrophage iron transport. Hepcidin inhibits egress of iron from bone marrow macrophages by downregulation of the iron export protein FPN. The ability of inflammatory cytokines to enhance or diminish this effect will be determined, as well as any effects on the expression of variant FPN.3. Determination of hepcidin effects on induced Epo production in vitro, and delineation of involved mechanisms. This will include A., determination and quantification of the effects of hepcidin on the induction of Epo protein in hepatic and renal models, and of the time-course of these effects; and B., determination of the roles of inflammatory cytokines in modulating these effects; C., the role of iron availability in these effects; and D., determination of the effects of hepcidin on Epo transcription, and the mechanism involved in these effects. 4. Effects of rhEpo on hepcidin production in vitro. In this Aim, we will determine A., the effects of Epo on hepcidin production by HepG2, as well as B., the extent to which these effects are modulated by TNF, IL-1, and IL-6. Relevance to VA mission: The proposed studies can potentially lead to an enhanced understanding of the mechanisms of ACD, and lead to more effective therapy. PUBLIC HEALTH RELEVANCE: Anemia is a major contributor to morbidity and mortality in chronically ill patients, and the anemia of chronic disease (ACD) is the major etiology of this anemia. This disorder typically manifests itself as a hypoproliferative anemia accompanied by a low serum iron concentration despite adequate reticuloendothelial iron stores. ACD is highly prevalent in the VA population. In ACD, a slight shortening of red cell survival creates a demand for a small increase in red cell production by the bone marrow. The marrow cannot respond adequately to this demand due to impaired erythropoiesis and impaired mobilization of reticuloendothelial system iron stores. A potential role for hepcidin in the iron anomalies of ACD is strongly supported by available data. If hepcidin is the major factor responsible for ACD, then it should also contribute to the impaired erythropoiesis observed in this syndrome. The proposed studies can potentially lead to an enhanced understanding of the mechanisms of ACD, and therefore to more effective therapy.