HBx modulates iron regulatory protein 1-mediated iron metabolism via reactive oxygen species

Hepatitis B virus X protein (HBx) is involved in viral metabolism and progression of liver disease. Iron metabolism plays a significant role in liver disease. In this report, to elucidate the relationship between iron metabolism and HBx, we established the Huh7 cell lines in which HBx was stably expressed (Huh7-HBx). In Huh7-HBx, we observed that transferrin receptor 1 (TfR1) expression decreased and ferritin heavy chain (FtH) expression increased as well as reactive oxygen species (ROS) level increased. We also found that these modulations were caused by the downregulation of iron regulatory protein 1 (IRP1). Furthermore, the levels of total iron and labile iron pool (LIP) were altered in Huh7-HBx. In addition, antioxidant N-acetylcystein (NaC) increased IRP1 expression by depleting HBx-induced ROS. We also confirmed these alterations of TfR1 and FtH in the primary hepatocytes of HBx transgenic mice and in HepG2.2.15 cells that constitutively replicate the intact HBV genome. In conclusion, these results suggest that HBx modulates iron metabolism via ROS leading to pathological status in liver diseases.     

Skin fibroblasts from pantothenate kinase-associated neurodegeneration patients show altered cellular oxidative status and have defective iron-handling properties

Pantothenate kinase-associated neurodegeneration (PKAN) is a neurodegenerative disease belonging to the group of neurodegeneration with brain iron accumulation disorders. It is characterized by progressive impairments in movement, speech and cognition. The disease is inherited in a recessive manner due to mutations in the Pantothenate Kinase-2 (PANK2) gene that encodes a mitochondrial protein involved in Coenzyme A synthesis. To investigate the link between a PANK2 gene defect and iron accumulation, we analyzed primary skin fibroblasts from three PKAN patients and three unaffected subjects. The oxidative status of the cells and their ability to respond to iron were analyzed in both basal and iron supplementation conditions. In basal conditions, PKAN fibroblasts show an increase in carbonylated proteins and altered expression of antioxidant enzymes with respect to the controls. After iron supplementation, the PKAN fibroblasts had a defective response to the additional iron. Under these conditions, ferritins were up-regulated and Transferrin Receptor 1 (TfR1) was down-regulated to a minor extent in patients compared with the controls. Analysis of iron regulatory proteins (IRPs) reveals that, with respect to the controls, PKAN fibroblasts have a reduced amount of membrane-associated mRNA-bound IRP1, which responds imperfectly to iron. This accounts for the defective expression of ferritin and TfR1 in patients' cells. The inaccurate quantity of these proteins produced a higher bioactive labile iron pool and consequently increased iron-dependent reactive oxygen species formation. Our results suggest that Pank2 deficiency promotes an increased oxidative status that is further enhanced by the addition of iron, potentially causing damage in cells.     

Changes of gene expression of iron regulatory proteins during turpentine oil-induced acute-phase response in the rat

In the present study, turpentine oil was injected in the hind limb muscle of the rat to stimulate an acute-phase response (APR). The changes in the gene expression of cytokines and proteins known to be involved in the iron regulatory pathway were then studied in the liver and in extra-hepatic tissue. In addition to the strong upregulation of interleukin-6 (IL-6) and IL-1 beta observed in the inflamed muscle, an upregulation of the genes for IL1-beta and tumor necrosis factor-alpha, but not IL-6, were detectable in the liver. Hepatic Hepc gene expression increased to a maximum at 6 h after the onset of APR. An upregulation of transferrin, transferrin receptor 1 (TfR1), TfR2, ferritin-H, iron responsive element binding protein-1 (IRP1), IRP2 and divalent metal transporter gene expression was also found. Hemojuvelin (Hjv)-, ferroportin 1-, Dcytb-, hemochromatosis-gene- and hephaestin gene expression was downregulated. Hepcidin (Hepc) gene expression was not only detectable in extra-hepatic tissues such as heart, small intestine, colon, spleen and kidney but it was also upregulated under acute-phase conditions, with the Hjv gene being regulated antagonistically. Fpn-1 gene expression was downregulated significantly in heart, colon and spleen. Most of the genes of the known proteins involved in iron metabolism are expressed not only in the liver but also in extra-hepatic tissues. Under acute-phase conditions, acute-phase cytokines (eg IL-6) may modulate the gene expression of such proteins not only in the liver but also in other organs.     

In vivo role(s) of the iron regulatory proteins (IRP) 1 and 2 in aseptic local inflammation

The maintenance of iron homeostasis is critical as both iron deficiency and iron excess are deleterious. In mammals, iron homeostasis is regulated systemically by the iron-hormone hepcidin, an acute-phase protein secreted by the liver which inhibits iron absorption and recycling. Cellularly, the interaction of iron regulatory proteins (IRP) 1 and 2 with iron-responsive elements controls the expression of target mRNAs encoding proteins of iron acquisition, storage, utilization, and export. These processes critically affect iron levels, which in turn impact on numerous aspects of inflammation. To explore the role of IRP1 and IRP2 in inflammation, IRP-deficient mice, i.e., mice with total and constitutive deficiency of either IRP, were subjected to acute aseptic local inflammation. Turpentine oil injection increases the expression of acute phase proteins in the liver and interleukin 6 levels in the serum of control mice. Both IRP-deficient mouse models mount the same responses, indicating that the treatment was efficient in all animals and that the acute phase response does not require expression of both IRPs. As expected, turpentine oil treatment enhances hepcidin mRNA expression in the liver of wild-type mice, associated with decreased serum iron levels. Importantly, Irp1 ^−/− and Irp2 ^−/− animals, respectively, display quantitatively similar hepcidin mRNA induction and the appropriate reduction of the serum iron values. Our data indicate that the response of Irp1 ^−/− and Irp2 ^−/− mice to acute local inflammation is largely preserved. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

细胞铁代谢变化参与阿司匹林抗氧化作用的调控机制

目的:探讨铁蛋白(Fn)表达及细胞内铁的变化在阿司匹林(AS)抗氧化损伤中的调控作用。方法:ELISA法检测不同浓度AS诱导Fn的表达,以及FeCl₃和去铁胺对AS诱导Fn表达的影响;同时使用RNA-proteinbandshiftassay及RT-PCR检测AS诱导铁蛋白表达过程中铁调节蛋白(IRP)结合活性及IRP₂mRNA水平的变化。结果:0.1mmol/L的AS可诱导内皮细胞Fn表达超过对照25%,随AS剂量的增大诱导Fn表达逐渐增加,二者间有明显的剂量依赖关系。AS诱导Fn表达后能明显增强细胞抗H₂O₂损伤的能力。但去铁胺+AS组细胞Fn表达明显降低,此时IRP的结合活性却为正常的3倍,IRP₂mRNA的表达水平也升高;而FeCl₃+AS组Fn表达明显高于去铁胺组,但IRP的结合活性降低、IRP₂mRNA表达水平下降。结论:阿司匹林通过下调IRP结合活性及IRP₂mRNA水平,导致细胞铁蛋白表达增加而发挥抗氧化损伤的作用。     

线粒体铁蛋白过表达抑制神经肿瘤细胞的增长与细胞铁代谢及细胞周期蛋白表达相关

目的 探讨过表达线粒体铁蛋白（MtFt） 抑制成神经母细胞瘤SH-SY5Y细胞的增殖机制。方法 以过表达MtFt的成神经母细胞瘤细胞MtFt-SY5Y为实验模型,野生型SH-SY5Y和pcDNA3.1-SY5Y（空质粒对照）为实验对照,运用流式细胞术、Western blotting技术等检测了MtFt对SH-SY5Y肿瘤细胞增殖的影响及铁代谢相关蛋白转铁蛋白受体1 （TfR1）,铁蛋白和细胞周期相关蛋白（cyclin）及其依赖性激酶（CDK）、cyclinD1、CDK4、cyclinE、CDK2的表达变化。结果 MtFt过表达通过调节细胞内铁代谢显著抑制了神经肿瘤细胞SH-SY5Y的增殖,与对照组相比,MtFt-SY5Y细胞增殖速度慢了近4倍。MtFt造成了细胞质内铁缺乏, TfR1表达显著上调,而铁蛋白H 亚基（H-ferritin）显著下调。同时 cyclinD1与CDK2蛋白表达显著降低,cyclinE蛋白表达显著上升,CDK4蛋白表达无显著性差异。结论 MtFt过表达能够显著抑制神经肿瘤细胞的生长,其机制可能是通过调节细胞内铁代谢,从而影响细胞周期相关蛋白及其周期蛋白激酶的表达。     

Duodenal HFE expression and hepcidin levels determine body iron homeostasis: modulation by genetic diversity and dietary iron availability

HFE affects the interaction of transferrin bound iron with transferrin receptors (TfR) thereby modulating iron uptake. To study genetically determined differences in HFE expression we examined individual HFE levels in C57BL/Sv129 mice and assessed their relationship to the regulation of iron homeostasis in the duodenum and the liver, and their regulation by diet. We found an up to 14-fold variation in inter-individual expression of HFE mRNA in the duodenum. Mice with high duodenal HFE mRNA expression presented with significantly higher levels of TfR and DMT-1 mRNAs and an increased IRP-1 binding affinity as compared to mice with low HFE levels. Duodenal HFE expression was positively associated with serum iron and liver HFE levels. Dietary iron supplementation decreased HFE in the duodenum but not in the liver. This was paralleled by reduced amounts of DMT-1 and FP-1 in the duodenum while the expression of DMT-1, FP-1, and hepcidin in the liver were increased with dietary iron overload. Duodenal and liver HFE levels are regulated by divergent penetration of as yet unelucidated modifier genes and to a much lesser extent by dietary iron. These measures control duodenal iron transport and liver iron homeostasis by modulating HFE expression either directly or via stimulation of iron sensitive regulatory molecules, such as hepcidin, which then exert their effects on body iron homeostasis.Susanne Ludwiczek and Igor Theurl contributed equally to the work     

Abnormal body iron distribution and erythropoiesis in a novel mouse model with inducible gain of iron regulatory protein (IRP)-1 function

Disorders of iron metabolism account for some of the most common human diseases. Cellular iron homeostasis is maintained by iron regulatory proteins (IRP)-1 and 2 through their binding to cis-regulatory iron-responsive elements (IREs) in target mRNAs. Mouse models with IRP deficiency have yielded valuable insights into iron biology, but the physiological consequences of gain of IRP function in mammalian organisms have remained unexplored. Here, we report the generation of a mouse line allowing conditional expression of a constitutively active IRP1 mutant (IRP1*) using Cre/Lox technology. Systemic activation of the IRP1* transgene from the Rosa26 locus yields viable animals with gain of IRE-binding activity in all the organs analyzed. IRP1* activation alters the expression of IRP target genes and is accompanied by iron loading in the same organs. Furthermore, mice display macrocytic erythropenia with decreased hematocrit and hemoglobin levels as well as impaired erythroid differentiation. Thus, inappropriately high IRP1 activity causes disturbed body iron distribution and erythropoiesis. This new mouse model further highlights the importance of appropriate IRP regulation in central organs of iron metabolism. Moreover, it opens novel avenues to study diseases associated with abnormally high IRP1 activity, such as Parkinson’s disease or Friedreich’s ataxia.     

铁转运相关蛋白在肌萎缩性侧索硬化症转基因鼠脊髓中的表达变化

目的 探讨肌萎缩性侧索硬化症(ALS)转基因鼠脊髓内铁转运相关蛋白表达变化与铁稳态失衡的关联.方法 选取hSOD1G93A转基因鼠(ALS鼠)和同窝野生型鼠(WT鼠),分别于生后70、95和122 d分离脊髓,每时间点每组各9只实验动物.Western blotting检测脊髓组织内铁转运蛋白二价金属转运蛋白-1(DM...     

Up-regulation of divalent metal transporter 1 is involved in 1-methyl-4-phenylpyridinium (MPP(+))-induced apoptosis in MES23.5 cells

Apoptosis has been identified as one of the important mechanisms involved in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Our previous study showed increased iron levels in the substantia nigra as well as loss of dopaminergic neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced PD mouse models. 1-Methyl-4-phenylpyridinium (MPP⁺) is commonly used to establish a cellular model of PD. Although intracellular iron plays a crucial role in MPP⁺-induced apoptosis, the molecular mechanism linking increased iron and MPP⁺-induced neurodegeneration is largely unknown. In the present study, we investigate the involvement of divalent metal transporter 1 (DMT1) that accounts for the ferrous iron transport in MPP⁺-treated MES23.5 cells. In the treated cells, a significant influx of ferrous iron was observed. This resulted in a decreased mitochondrial membrane potential. Additionally, an elevated level of ROS production and activation of caspase-3 were also detected, as well as the subsequent cell apoptosis. These effects could be fully abolished by iron chelator desferal (DFO). Increased DMT1 (−IRE) expression but not DMT1 (+IRE) accounted for the increased iron influx. However, there were no changes for iron regulatory protein 1 (IRP1), despite decreased expression of IRP2. Iron itself had no effect on IRP1 and IRP2 expression. Our data suggest that although DMT1 mRNA contains an iron responsive element, its expression is not totally controlled by this. MPP⁺ could up-regulate the expression of DMT1 (−IRE) in an IRE/IRP-independent manner. Our findings also show that MPP⁺-induced apoptosis in MES23.5 cells involves DMT1-dependent iron influx and mitochondria dysfunction.     

Transferrin Receptors and Selective Iron Deposition in Pancreatic B Cells of Iron-overloaded Rats

Iron overload was produced in Wistar rats by repeated intraperitoneal injections of ferric nitrilotriacetate (Fe³⁺-NTA) for one to six months. Pancreatic tissues from these iron-overloaded rats and untreated controls were examined for insulin (for B cells), glucagon (for A cells), transferrin receptor (TfR), transferrin (Tf) and ferritin (Ft) using immunohistochemical methods, and for iron by histochemical Berlin blue staining. In the islets of iron-overloaded rats, increased Ft staining appeared prior to deposition of Berlin blue-stainable iron, and the staining intensity of Ft and iron was stronger in B cells than in A cells. In the islets of untreated control rats, the staining intensity of TfR was stronger in B cells than in A cells. TfR staining of the islets was weaker in iron-overloaded rats than in the controls. These findings suggest that 1) iron uptake by islet cells in vivo is regulated and mediated by TfR, 2) intracytoplasmic Ft transforms into stainable iron in iron-overloaded rats, and 3) predominance of TfR expression in B cells may result in selective deposition of iron and predispose B cells to damage and diabetes mellitus in iron-overloaded rats. Acta Pathol Jpn 41: 647–652, 1991.     

Differential regulation of iron homeostasis during human macrophage polarized activation

Iron metabolism in inflammation has been mostly characterized in macrophages exposed to pathogens or inflammatory conditions, mimicked by the combined action of LPS and IFN‐γ (M1 polarization). However, macrophages can undergo an alternative type of activation stimulated by Th2 cytokines, and acquire a role in cell growth and tissue repair control (M2 polarization). We characterized the expression of genes related to iron homeostasis in fully differentiated unpolarized (M0), M1 and M2 human macrophages. The molecular signature of the M1 macrophages showed changes in gene expression (ferroportin repression and H ferritin induction) that favour iron sequestration in the reticuloendothelial system, a hallmark of inflammatory disorders, whereas the M2 macrophages had an expression profile (ferroportin upregulation and the downregulation of H ferritin and heme oxygenase) that enhanced iron release. The conditioned media from M2 macrophages promoted cell proliferation more efficiently than those of M1 cells and the effect was blunted by iron chelation. The role of ferroportin‐mediated iron release was demonstrated by the absence of differences from the media of macrophages of a patient with loss of function ferroportin mutation. The distinct regulation of iron homeostasis in M2 macrophages provides insights into their role under pathophysiological conditions.     

Mechanisms underlying T-lymphocyte activation: mitogen initiates and IL-2 amplifies the expression of transferrin receptors via intracellular iron level.

Peripheral blood mononuclear cells (PBM) pulsed with lectin (PHA or Con A for 0.25-3 hr) show a low expression of interleukin-2 and transferrin receptors (IL-2Rs, TfRs) and a mild decline of intracellular ferritin level, compared to control cultures grown in continuous presence of mitogen. Interestingly, lectin-pulsed PBM do not release detectable amounts of IL-2 in the medium. Furthermore, expression of TfRs in these lymphocytes is not inhibited by addition of excess anti-IL-2 neutralizing monoclonal antibody, but is significantly inhibited by treatment with iron salts. These observations suggest that mitogen triggers an IL-2-independent expression of TfRs, at least in part via a decrease of intracellular iron level. Addition of either recombinant IL-2 (rIL-2) or an iron chelator (picolinic acid) to lectin-pulsed PBM induces both a marked enhancement of TfR synthesis and a sharp decline of intracellular ferritin level, which are comparable to the corresponding pattern observed in control cultures. Conversely, addition of iron salts fully inhibits the increase of TfR expression induced by rIL-2. These observations strongly suggest that the enhanced TfR synthesis elicited by rIL-2 is mediated by depletion of a regulatory intracellular iron pool. In line with these studies, greater than 99% purified T lymphocytes stimulated by lectin show a low expression of TfRs, which is markedly enhanced by addition of exogenous rIL-2. Altogether, we postulate that: (i) in resting T lymphocytes the gene encoding TfR is apparently in a 'closed' configuration; (ii) even in the absence of IL-2 activity, a mitogen pulse is sufficient to initiate the expression of TfRs, at least in part via a decline of intracellular iron level; and (iii) TfR synthesis is then largely amplified by IL-2, again via a decrease of the size of a regulatory intracellular iron pool.     

脂多糖对小鼠铁代谢相关基因mRNA水平表达的影响

目的 探讨脂多糖（LPS）对小鼠肝脏和脾脏铁代谢相关基因mRNA水平表达的影响。 方法 10只2月龄雄性小鼠腹腔注射LPS（0.5 μg/g）, 6h后处死并取血液、肝脏和脾脏组织进行血常规测定,使用试剂盒检测血清铁和总铁结合力;使用半定量RT-PCR检测小鼠肝脏和脾脏铁代谢相关基因（HP）、膜铁转运蛋白１(Fpn1)和转铁蛋白受体1(TfR1)以及脾脏白细胞介素-6(IL-6)的mRNA变化。 结果 注射LPS 6h后可造成小鼠脾脏IL-6表达增加,肝脏HP表达增加（P ＜0.05）,肝脏和脾脏Fpn1表达减少,而肝脏TfR1表达亦减少,血清铁下降和适度贫血（Ｐ ＜0.05）。 结论 LPS可通过影响肝脏和脾脏铁相关基因HP、Fpn1和TfR1的mRNA表达而影响血清铁状态。     

Ferroportin-1 is a 'nuclear'-negative acute-phase protein in rat liver: a comparison with other iron-transport proteins

Liver is the central organ of iron metabolism. During acute-phase-response (APR), serum iron concentration rapidly decreases. The current study aimed to compare expression and localization of iron transport protein ferroportin-1 (Fpn-1) and of other iron import proteins after experimental tissue damage induced by injecting turpentine oil in the hind limbs of rats and mice. Serum and spleen iron concentration decreased with an increase in total liver, cytoplasmic and nuclear iron concentration. In liver, mRNA amount of Fpn-1, Fpn-1a, Fpn-1b, HFE, hemojuvelin (HJV) and hephaestin (heph) genes showed a rapid decrease. Hepcidin, divalent metal transporter-1 (DMT-1), transferrin (Tf) and Tf-receptor-1 (TfR1), TfR-2 (TfR2) gene expression was increased. Western blot analysis of liver tissue lysate confirmed the changes observed at mRNA level. In spleen, a rapid decrease in gene expression of Fpn-1, Fpn-1a, Fpn-1b, DMT-1, Tf, TfR1 and TfR2, and an increase in hepcidin was observed. Immunohistochemistry of DMT-1 and TfR2 were mainly detected in the nucleus of rat liver and spleen, whereas TfR1 was clearly localized in the plasma membrane. Fpn-1 was mostly found in the nuclei of liver cells, whereas in spleen, the protein was mainly detected in the cell membrane. Western blot analysis of liver fractions confirmed immunohistochemical results. In livers of wild-type mice, gene expression of Fpn-1, Fpn-1a and Fpn-1b was downregulated, whereas hepcidin gene expression was increased. In contrast, these changes were less pronounced in IL-6ko-mice. Cytokine (IL-6, IL-1b and TNF-a) treatment of rat hepatocytes showed a downregulation of Fpn-1, Fpn-1a and Fpn-1b, and upregulation of hepcidin gene expression. Moreover, western blot analysis of cell lysate of IL-6-treated hepatocytes detected, as expected, an increase of a2-macroglobulin (positive acute-phase protein), whereas albumin (negative acute-phase protein) and Fpn-1 were downregulated. Our results demonstrate that liver behaves as a 'sponge' for iron under acute-phase conditions, and Fpn-1 behaves as a negative acute-phase protein in rat hepatocytes mainly, but not exclusively, because of the effect of IL-6. These changes could explain iron retention in the cytoplasm and in the nucleus of hepatocytes during APR.     

Anthracycline-induced cardiotoxicity

Anthracycline antibiotics are among the most effective and widely used antineoplastic drugs. Their usefulness is limited by a cumulative dose-related cardiotoxicity, whose precise mechanisms are not clear as yet. The principal role is possibly exerted by free oxygen radicals generated by "redox-cycling" of anthracycline molecule and/or by the formation of anthracycline-ferric ion complexes. The iron catalyzes the hydroxyl radical production via Haber-Weiss reaction. The selective toxicity of ANT against cardiomyocytes results from high accumulation of ANT in cardiac tissue, appreciable production of oxygen radicals by mitochondria and relatively poor antioxidant defense systems. Other additional mechanisms of the anthracycline cardiotoxicity have been proposed--calcium overload, histamine release and impairment in autonomic regulation of heart function. The currently used methods for an early identification of anthracycline cardiotoxicity comprise ECG measurement, biochemical markers, functional measurement and morphologic examination. Among a plenty of studied cardioprotective agents only dexrazoxane (ICRF-187) has been approved for clinical use. Its protective effect likely consists in intracellular chelating of iron. However, in high doses dexrazoxane itself may cause myelotoxicity. This fact encourages investigation of new cardioprotectants with lower toxicity. Orally active iron chelators and flavonoids attract more attention. Modification of dosage schedule and synthesis of new anthracycline analogues may represent alternative approaches to mitigate anthracycline cardiotoxicity while preserving antitumour activity.     

山奈酚增强阿霉素在乳腺癌模型中的抗癌作用*

目的：评价山奈酚（KPL）和阿霉素（DOX）在乳腺癌小鼠模型中的联合作用以及预防后者引起的心脏毒性。 方法：采用MTT法检测KPL+DOX（0.1 μmol/L）对乳腺上皮细胞MCF10A、乳腺癌来源的细胞系MCF-7 细胞株 的细胞毒性, 免疫印迹检测MCF-7 细胞中组蛋白去乙酰化酶（HDAC）、DNA 甲基化酶（DNMT）、雌激素受体α （ERα）、caspase-3 蛋白表达情况。采用原位乳腺癌模型评估KPL对DOX 诱导的肿瘤消退和心脏毒性的影响,将 裸鼠根据肿瘤体积分为溶媒处理组、DOX 组、KPL组及DOX+KPL 联合处理组,借助超声心动图监测各组小鼠 的心脏功能,免疫组织化学分析肿瘤组织的病理变化、caspase-3 及聚腺苷二磷酸核糖聚合酶（PARP）的表达情况。 结果：MTT分析表明,KPL+DOX 对MCF10A和MCF-7 细胞的抑制作用高于DOX。与DOX 组相比,KPL+DOX 显著抑制了MCF-7 细胞中HDAC、DNMT 活性,并降低ERα 水平。动物实验表明,KPL+DOX 对MCF-7 肿瘤生 长的抑制作用大于DOX。超声心动图检测显示,KPL+DOX 联合处理可以改善由DOX 引起的心脏毒性、显著降 低了DOX 诱导的MDA 形成和TNF-α、IL-6 炎性细胞因子水平,同时提高了GSH 水平。免疫组织化学分析显示, KPL+DOX 组表现出明显的核凝聚和碎裂,并且caspase-3 和PARP表达水平显著高于其他3 组。结论：KPL作为 一种常见且安全的膳食补充剂,可增强DOX 在癌症治疗中的抗癌活性,同时减少DOX 相关的心脏毒性。