Mechanisms of hepcidin effects in the anemia of chronic disease

描述（由申请人提供）： 慢性病性贫血（ACD）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，伴有低血清铁浓度，尽管有足够的网状内皮铁储备。ACD通常被认为是由与炎症的细胞因子介导物相关的病理过程的组合引起的。然而，铁代谢改变在ACD诊断中的重要性使许多研究者认为这一特征是该综合征的主要病理生理机制。铁调素是一种抗菌蛋白，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，其表达由白细胞介素（IL）-6诱导，并由肿瘤坏死因子（TNF）下调。铁调素的特异性铁调节功能，以及在具有铁调素基因表达异常的患者和转基因动物中观察到的贫血综合征（下文讨论），已经使许多人认为它是解开“ACD之谜“的关键。 ACD的发病机制涉及三个主要过程。红细胞存活时间的轻微缩短会导致骨髓产生少量红细胞。由于红细胞生成受损和网状内皮系统铁储备动员受损，骨髓不能充分响应这种需求。铁调素在ACD铁异常中的潜在作用得到了现有数据的有力支持。然而，铁的变化并不是ACD的唯一异常特征。如果铁调素是导致ACD的主要因素，那么它也应该有助于在该综合征中观察到的红细胞生成受损。 铁调素有助于ACD中红细胞生成受损的假设将通过以下具体目标来解决：1.铁调素对红系细胞集落形成影响的测定及相关机制的研究。这将包括A.，铁调素对红细胞生成的作用是直接作用的还是需要辅助细胞; B.，Epo浓度在铁调素对红细胞生成的作用中的作用; C.，凋亡/抗增殖在铁调素对红细胞生成的抑制作用中的作用; D.，细胞因子对铁调素/红细胞生成关系的影响; E.，铁对铁调素对CFU-E集落形成的作用的贡献; F.，膜铁转运蛋白（FPN）和变体FPN在铁调素对CFU-E的作用中的作用;和G.，Epo和炎性细胞因子对红系细胞中FPN变体表达的影响。2.铁调素和细胞因子在骨髓巨噬细胞铁转运中相互作用的测定。铁调素通过下调铁输出蛋白FPN抑制铁从骨髓巨噬细胞中排出。将确定炎性细胞因子增强或减弱这种作用的能力，以及对变体FPN.3表达的任何影响。铁调素对体外诱导的Epo产生的影响的测定，以及相关机制的描述。这将包括A.，确定和定量铁调素对肝和肾模型中Epo蛋白诱导的作用，以及这些作用的时程;和B.，确定炎性细胞因子在调节这些作用中的作用; C.，铁的可用性在这些效应中的作用;和D.，确定铁调素对Epo转录的影响，以及参与这些影响的机制。4. rhEpo对体外铁调素合成的影响。在这个目标中，我们将确定A.，Epo对HepG 2以及B.，这些作用受TNF、IL-1和IL-6调节的程度。与VA使命的相关性：拟议的研究可能会提高对ACD机制的理解，并导致更有效的治疗。 公共卫生相关性： 贫血是慢性病患者发病率和死亡率的主要原因，而慢性病贫血（ACD）是这种贫血的主要病因。这种疾病通常表现为低增殖性贫血，伴有低血清铁浓度，尽管有足够的网状内皮铁储备。ACD在VA人群中非常普遍。在ACD中，红细胞存活的轻微缩短产生了对骨髓产生红细胞的小幅增加的需求。由于红细胞生成受损和网状内皮系统铁储备动员受损，骨髓不能充分响应这种需求。铁调素在ACD铁异常中的潜在作用得到了现有数据的有力支持。如果铁调素是导致ACD的主要因素，那么它也应该有助于在该综合征中观察到的红细胞生成受损。拟议的研究可能会提高对ACD机制的理解，从而获得更有效的治疗。

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.