铁调素(Hepcidin)对细胞铁代谢影响的研究进展

Hepcidin是一种肝脏分泌的富含半胱氨酸的新型抗菌多肽,具有抗细菌和真菌等抗菌肽的特性.近几年的研究证实,Hepcidin在机体铁代谢平衡的调节中起关键作用,因而被人们称为铁调节激素.Hepcidin自肝细胞中合成之后分泌至血液,将体内铁调节的信号传至十二指肠细胞、巨噬细胞、脑细胞、心肌细胞等,通过影响铁转运相关蛋白的表达水平,进而调节机体铁的吸收、储存和转运.     

促红细胞生成素对大鼠机体铁状态及腹腔巨噬细胞铁代谢的影响

网状内皮系统(reticuloendothelial system,RES)在维持机体铁稳态方面起着重要作用．但其调控机制尚不十分清楚．通过皮下注射重组人促红细胞生成素(recombinant human erythropoietin, rHuEPO)引起大鼠红细胞的生成显著增加,改变了血清转铁蛋白饱和度以及机体铁储存状态．利用RT-PCR及Western blot检测发现腹腔巨噬细胞二价金属离子转运蛋白(duodenal divalent metal trans- porter 1,DMT1)的表达显著下降,膜铁转运蛋白1(ferroportin 1,FPN1)的表达显著上升．同时采用~(55)Fe同位素标记示踪法显示腹腔巨噬细胞的铁摄取减少,铁释放量显著增加．研究结果表明在红细胞生成过程中,巨噬细胞摄铁的降低,可能是由于DMT1表达减少所致,巨噬细胞铁释放的增加,可能是由于FPN1表达上升弓J起,肝脏hepcidin在这一调控过程中可能起着重要作用．     

小肠粘膜细胞铁吸收机制

缺铁性贫血和运动性低铁状态在运动员中发生率高于一般人群，运动员补铁效果不理想。寻求有效的补铁措施的关键问题是要阐明小肠粘膜上皮细胞究竟如何吸收铁，然而有关铁吸收的机制一直不清楚。近几年研究发现小肠粘膜上皮细胞存在DMT1、Dcytb、Fp1和Hp等铁转运蛋白TfR-1和TfR-2在隐窝细胞和绒毛细胞基底侧膜具有相对特异性分布。本根据这些发现以及对其转运机制、转运特性和调节机制的研究进展勾画出小肠粘膜上皮细胞铁吸收过程和调节机制模型。     

鳗弧菌质粒编码的铁吸收系统的分子调控

鳗弧菌是鱼类弧菌病的主要病原菌，该菌中质粒编码的铁吸收系统是重要的毒力因子．在铁吸收系统中，铁转运体系以及弧菌素合成基因受到AngR、TAF、Fur、反义RNAs、铁离子以及弧菌素等调控因子的调节，这些调控因子分别在转录或后转录水平参与铁吸收系统的正负调控、     

膜铁转运辅助蛋白研究进展

膜铁转运辅助蛋白（Hp） 是研究性连锁遗传贫血（sla）小鼠时发现的一种新的铁转运相关蛋白．它与铜蓝蛋白（Cp）属同一家族．与Cp不同， Hp是具有一个跨膜结构的完整膜蛋白，主要存在于小肠绒毛的上皮细胞．作为亚铁氧化酶，Hp在铁从肠上皮细胞转运到血液的过程是必需的，该基因突变将造成机体严重的铁缺乏．脑内Hp的发现，为脑铁稳态的调控机制提供了新的认识．文中综述了Hp的发现、结构、表达、调控及其在脑铁代谢中的作用．     

鸡蛋白四苯基双铁卟啉催化氧气氧化乙醇

制备了鸡蛋白固载四苯基双铁卟啉催化剂,用紫外可见光谱(UV-Vis)及傅立叶红外吸收光谱(FT-IR)技术对其进行表征.研究了固载催化剂催化氧气氧化乙醇选择性生成乙醛和乙酸的能力,并对固载催化剂及纯鸡蛋白的催化能力比较.实验结果表明:在最佳反应条件下,鸡蛋白四苯基双铁卟啉催化乙醇氧化的转化率为18.43%,选择性(乙醛+乙酸)是63.5%.在相同条件下,鸡蛋白四苯基双铁卟啉比鸡蛋蛋白的催化活性高.固载的金属卟啉和鸡蛋白中的转铁蛋白共同起催化作用.     

43例妊娠妇女血清贫血检测指标的分析

检测了血清铁（SerumIron）、铁蛋白（Ferritin）和可溶性转铁蛋白受体（Soluble transferrin receptor,sTfe）等指标,并分析了这些指标在诊断妊娠妇女缺铁性贫血中的临床意义。采用免疫分析法和比色法测定43例妊娠24—28周妇女和同期收集的30例健康妇女的血清铁、铁蛋白和可溶性转铁蛋白受体的水平,利用SPSS10．0软件对实验数据进行统计学分析。妊娠组血清铁、可溶性转铁蛋白受体均值较正常对照组无显著差异,铁蛋白均值为19．62±11．52ng／L,明显低于对照组61．14±39．92ng／L（P〈0．05）。按血红蛋白浓度的高低分为4组：1组为Hb〈100g／L,2组为Hb100～110g／L,3组为Hb110—120g／L,4组为Hb〉120s／L。1组只有铁蛋白与对照组有显著差别（P〈0．05）,2组铁蛋白、VitB13和转铁蛋白受体与对照组均有显著差别（P〈0．05）,3组和4组铁蛋白和VitB13与对照组有显著差别（P〈0．05）。在诊断妊娠妇女缺铁性贫血中,铁蛋白是估计人体铁状态的最好参数,可溶性转铁蛋白受体测定在怀孕期间没有显著变化,如有功能性铁缺乏会出现sTfe浓度升高。而血清铁是检测缺铁及铁负荷过多疾病的有效指标,但在一定时期内表现不明显,变化不大。     

两个Caco-2细胞系模型铁生物有效性评价效果研究

研究Caco-2细胞吸收转运模型(模型Ⅰ)和吸收转化模型(模型Ⅱ)对铁生物有效性的评价效果.用不同浓度,pH的硫酸亚铁溶液及稻米分别处理两种模型的Caco-2细胞单层22 h后,测定两种模型细胞铁吸收差异.结果表明Caco-2细胞铁蛋白形成量随铁浓度增加而增加,且模型I高于模型Ⅱ,当铁浓度≥25μmol.L-1时,差异达显著水平(p0.05);细胞铁蛋白形成量和转运铁量均与pH呈负相关,两模型间达到显著相关(p0.05).模型Ⅰ和模型Ⅱ均可用于膳食铁生物有效性评价,高铁浓度时,模型Ⅰ效果优于模型Ⅱ.     

细菌铁蛋白电子光谱和释放铁动力学的新颖特性

棕色固氮菌细菌铁蛋白(Bacterial ferritin of Azotobacter vinelandii,AvBF)分子结构由蛋白壳、铁核和横跨蛋白壳的电子隧道组成.细菌铁蛋白由24个相同类型的亚基组成,其分子量略高于魟鱼肝铁蛋白(Liver ferritin of Dasyatis akajei,DALF).电泳纯的AvBF在可见光谱区内呈现出4个特征吸收峰,波长分别位于414(α峰),525(β峰),555(S峰)和585(未知)nm.经Na2S2O4还原后,其AvBF在紫外可见区内的整体吸收峰强度明显增高.经物理铂金电极还原后,AvBF的α特征吸收峰(414 nm)强度随着控制还原电位降低(-200,-400,-600 mV vs NHE)而增强.动力学研究表明,在弱碱(pH8.0)条件下,AvBF和DALF均以二分之一级反应动力学方式释放铁,均未表现出释放铁速率转换行为,认为AvBF和DALF的释放铁速率和铁蛋白蛋白壳的柔性调节速率处于同步进行状态,使铁蛋白释放铁的过程符合二分之一级反应动力学规律.     

DFO对心肌细胞铁代谢的影响

观察去铁胺(DFO)对原代培养的心肌细胞铁代谢的影响,探讨DFO对心肌细胞铁代谢的影响机制.用原代培养的乳鼠心肌细胞为材料,以不同浓度的DFO孵育细胞,然后检测心肌细胞存活率、搏动频率以及铁转运相关蛋白CP,HP,FP1的表达变化.结果表明:各剂量DFO对心肌细胞存活率无明显影响;心肌细胞搏动频率减慢,停止跳动的细胞数量明显增加,收缩幅度逐渐降低;随着DFO浓度的增加,心肌细胞CP和HP的表达增加而FP1表达减少.由此可以看出,DFO不影响心肌细胞的存活率,但影响细胞的生活状态,也影响心肌细胞内CP,HP和FP1蛋白的表达.     

Evidence for the bilobal nature of diferric rabbit plasma transferrin.

Plasma transferrin is involved in iron transport within the circulatory system of vertebrates, and provides an iron source for haemoglobin synthesis and other metabolic requirements. However, despite extensive studies by spectroscopic, biochemical and physiological techniques, the nature of iron binding and the mechanisms of uptake and release of iron are not fully understood. Plasma transferrins are monomeric glycoproteins with a molecular weight of approximately 80,000 (ref. 2); they have two similar and very strong binding sites for Fe(III), together with two associated anion binding sites. Fragmentation studies on various transferrins have shown that the polypeptide chain is composed of two domains formed from the N-terminal and C-terminal halves of the polypeptide chain. Each domain contains one metal binding site. The marked sequence similarities which exist between the two halves may reflect a doubling of an ancestral structural gene during the phylogenetic development of the protein. Preliminary crystallographic investigations of diferric rabbit plasma transferrin have been reported from this laboratory. We now report initial studies of the X-ray structure determination of dife-ric rabbit plasma transferrin which have led to a 6-A resolution electron density map.     

Structural basis for iron piracy by pathogenic Neisseria

Neisseria are obligate human pathogens causing bacterial meningitis, septicaemia and gonorrhoea. Neisseria require iron for survival and can extract it directly from human transferrin for transport across the outer membrane. The transport system consists of TbpA, an integral outer membrane protein, and TbpB, a co-receptor attached to the cell surface; both proteins are potentially important vaccine and therapeutic targets. Two key questions driving Neisseria research are how human transferrin is specifically targeted, and how the bacteria liberate iron from transferrin at neutral pH. To address these questions, we solved crystal structures of the TbpA-transferrin complex and of the corresponding co-receptor TbpB. We characterized the TbpB-transferrin complex by small-angle X-ray scattering and the TbpA-TbpB-transferrin complex by electron microscopy. Our studies provide a rational basis for the specificity of TbpA for human transferrin, show how TbpA promotes iron release from transferrin, and elucidate how TbpB facilitates this process.     

The type IV mucolipidosis-associated protein TRPML1 is an endolysosomal iron release channel

TRPML1 (mucolipin 1, also known as MCOLN1) is predicted to be an intracellular late endosomal and lysosomal ion channel protein that belongs to the mucolipin subfamily of transient receptor potential (TRP) proteins. Mutations in the human TRPML1 gene cause mucolipidosis type IV disease (ML4). ML4 patients have motor impairment, mental retardation, retinal degeneration and iron-deficiency anaemia. Because aberrant iron metabolism may cause neural and retinal degeneration, it may be a primary cause of ML4 phenotypes. In most mammalian cells, release of iron from endosomes and lysosomes after iron uptake by endocytosis of Fe(3+)-bound transferrin receptors, or after lysosomal degradation of ferritin-iron complexes and autophagic ingestion of iron-containing macromolecules, is the chief source of cellular iron. The divalent metal transporter protein DMT1 (also known as SLC11A2) is the only endosomal Fe(2+) transporter known at present and it is highly expressed in erythroid precursors. Genetic studies, however, suggest the existence of a DMT1-independent endosomal and lysosomal Fe(2+) transport protein. By measuring radiolabelled iron uptake, by monitoring the levels of cytosolic and intralysosomal iron and by directly patch-clamping the late endosomal and lysosomal membrane, here we show that TRPML1 functions as a Fe(2+) permeable channel in late endosomes and lysosomes. ML4 mutations are shown to impair the ability of TRPML1 to permeate Fe(2+) at varying degrees, which correlate well with the disease severity. A comparison of TRPML1(-/- )ML4 and control human skin fibroblasts showed a reduction in cytosolic Fe(2+) levels, an increase in intralysosomal Fe(2+) levels and an accumulation of lipofuscin-like molecules in TRPML1(-/-) cells. We propose that TRPML1 mediates a mechanism by which Fe(2+) is released from late endosomes and lysosomes. Our results indicate that impaired iron transport may contribute to both haematological and degenerative symptoms of ML4 patients.     

A protein on Plasmodium falciparum-infected erythrocytes functions as a transferrin receptor

Several observations suggest that iron is essential for the development of malaria parasites but there is evidence that the parasites in erythrocytes do not obtain iron from haemoglobin. The total haemin level in parasitized erythrocytes does not vary during parasite development, indicating that the iron-containing moiety of haemoglobin is not detectably metabolized. Although parasite proteases can degrade the protein part of haemoglobin in red cells, no parasite enzymes that degrade haemin have been identified. In mammalian cells, haemin is degraded to carbon monoxide and bilirubin by the enzyme haeme oxygenase. This enzyme has not been found in malaria parasites. In fact haemin has been found to be toxic to parasite carbohydrate metabolism. Thus, iron apparently cannot be liberated from haemin and instead is sequestered in infected red cells as haemozoin, the characteristic pigment associated with malarial infection. If iron bound to transferrin is the source of ferric ions for malaria parasites within mature erythrocytes, then the parasite must synthesize its own transferrin receptor and localize it on the surface of the infected cell, because the receptors for transferrin are lost during erythrocyte maturation. Our results here suggest that Plasmodium falciparum synthesizes its own transferrin receptors enabling it to take up iron from transferrin by receptor-mediated endocytosis.     

Transferrin receptor on endothelium of brain capillaries

The blood/brain barrier prevents the passive diffusion of proteins and metabolites from cerebral blood vessels into tissue spaces around neuronal and glial cells. To provide nutrients for these cells, transport mechanisms must exist and indeed have been demonstrated for metabolites. We now show that monoclonal antibodies against rat and human transferrin receptors label blood capillaries in the brain but not in other tissues. In the rat this labelling occurs after injection of antibody into the blood, thus the receptors seem to be accessible at the endothelial surface. It is possible that transferrin receptors are expressed on these cells to allow transport of transferrin (and thus iron) into brain tissues.     

Vesicle-related OsSEC27P enhances H<Superscript>+</Superscript> secretion in the iron deficient transgenic tobacco root

Iron is an essential micronutritional element for plants. In addition to the iron uptake mechanism Strategy I and Strategy II, the vesicle transport process was also found to participate in iron uptake and homeostasis. Herein, a new iron deficiency induced OsSEC27P gene was isolated and investigated in both its localization and its function in transgenic plants. The vesicle-related protein OsSEC27P may play a potential role in enhancing H⁺ secretion in roots under the iron deficiency conditions.     

宿主细胞泛素系统与病毒相互作用的研究

真核细胞中,泛素系统执行对大多数短周期寿命蛋白的选择性降解,且已发现由泛素介导的对蛋白的降解调控在细胞的多种生命过程中起重要作用。病毒侵染宿主细胞后,细胞的泛素系统与一些重要的病毒蛋白相互作用,参与调节病毒的生活周期,如病毒迁移,核酸复制,免疫逃避,出芽等过程。