Regulation of iron acquisition and storage: consequences for iron-linked disorders

Dietary iron loading negatively affects liver mitochondrial function

Iron is an essential co-factor for several metabolic processes, including mitochondrial respiration, and mitochondria are the major sites of iron-utilization. Cellular iron homeostasis must be tightly regulated, as intracellular iron deficiency can lead to insufficient energy production, whereas iron overload triggers ROS (reactive oxygen species) formation via the Fenton reaction. So far little is known on how iron imbalances affect mitochondrial function in vivo and the impact of the genotype on that, we studied the effects of dietary iron loading on mitochondrial respiratory capacity in liver by comparing two genetically divergent mouse strains, namely C57BL/6N and FVB mice. Both mouse strains differed in their basal iron levels and their metabolic responses to iron loading as determined by expression of iron trafficking proteins (ferritin was increased in livers of animals receiving high iron diet) as well as tissue iron content (2-fold increase, FVB p = 0.0013; C57BL/6N p = 0.0022). Dietary iron exposure caused a significant impairment of mitochondrial oxidative phosphorylation, especially regarding OXPHOS capacity (FVB p = 0.0006; C57BL/6N p = 0.0087) and S-ETS capacity (FVB p = 0.0281; C57BL/6N p = 0.0159). These effects were more pronounced in C57BL/6N than in FVB mice and were paralleled by an iron mediated induction of oxidative stress in mitochondria. The increased susceptibility of C57BL6/N mice to iron loading may be due to reduced expression of anti-oxidant defense mechanisms and altered iron trafficking upon dietary challenge pointing to a role of genetic modifiers for cellular and mitochondrial iron trafficking. Finally, iron-mediated induction of mitochondrial oxidative stress and reduction of oxidative phosphorylation may underlie fatigue in subjects with iron loading diseases.

High levels of iron supplementation prevents neural tube defects in the Fpn1ffe mouse model

BACKGROUND

Periconception maternal nutrition and folate in particular are important factors influencing the incidence of neural tube defects (NTDs). Many but not all NTDs are prevented by folic acid supplementation and there is a pressing need for additional strategies to prevent these birth defects. Other micronutrients such as iron are potential candidates, yet a clear role for iron deficiency in contributing to NTDs is lacking. Our previous studies with the flatiron (ffe) mouse model of Ferroportin1 (Fpn1) deficiency suggest that iron is required for neural tube closure and forebrain development raising the possibility that iron supplementation could prevent NTDs.

METHODS

We determined the effect of periconception iron and/or folic acid supplementation on the penetrance of NTDs in the Fpn1^ffe mouse model. Concurrently, measurements of folate and iron were made to ensure supplementation had the intended effects.

RESULTS

High levels of iron supplementation significantly reduced the incidence of NTDs in Fpn1^ffe mutants. Fpn1 deficiency resulted in reduced folate levels in both pregnant dams and embryos. Yet folic acid supplementation did not prevent NTDs in the Fpn1^ffe model. Similarly, forebrain truncations were rescued with iron. Surprisingly, the high levels of iron supplementation used in this study caused folate deficiency in wild-type dams and embryos.

CONCLUSION

Our results demonstrate that iron supplementation can prevent NTDs and forebrain truncations in the Fpn1^ffe model. Surprisingly, high levels of iron supplementation and iron overload can cause folate deficiency. If iron is essential for neural tube closure, it is possible that iron deficiency might contribute to NTDs. Birth Defects Research 109:81-91, 2017. © 2016 The Authors Birth Defects Research Published by Wiley Periodicals, Inc.

The labile iron pool attenuates peroxynitrite-dependent damage and can no longer be considered solely a pro-oxidative cellular iron source

The ubiquitous cellular labile iron pool (LIP) is often associated with the production of the highly reactive hydroxyl radical, which forms through a redox reaction with hydrogen peroxide. Peroxynitrite is a biologically relevant peroxide produced by the recombination of nitric oxide and superoxide. It is a strong oxidant that may be involved in multiple pathological conditions, but whether and how it interacts with the LIP are unclear. Here, using fluorescence spectroscopy, we investigated the interaction between the LIP and peroxynitrite by monitoring peroxynitrite-dependent accumulation of nitrosated and oxidized fluorescent intracellular indicators. We found that, in murine macrophages, removal of the LIP with membrane-permeable iron chelators sustainably accelerates the peroxynitrite-dependent oxidation and nitrosation of these indicators. These observations could not be reproduced in cell-free assays, indicating that the chelator-enhancing effect on peroxynitrite-dependent modifications of the indicators depended on cell constituents, presumably including LIP, that react with these chelators. Moreover, neither free nor ferrous-complexed chelators stimulated intracellular or extracellular oxidative and nitrosative chemistries. On the basis of these results, LIP appears to be a relevant and competitive cellular target of peroxynitrite or its derived oxidants, and thereby it reduces oxidative processes, an observation that may change the conventional notion that the LIP is simply a cellular source of pro-oxidant iron.

The transferrin receptor: the cellular iron gate

The transferrin receptor (TfR1), which mediates cellular iron uptake through clathrin-dependent endocytosis of iron-loaded transferrin, plays a key role in iron homeostasis. Since the number of TfR1 molecules at the cell surface is the rate-limiting step for iron entry into cells and is essential to prevent iron overload, TfR1 expression is precisely controlled at multiple levels. In this review, we have discussed the latest advances in the molecular regulation of TfR1 expression and we have considered current understanding of TfR1 function beyond its canonical role in providing iron for erythroid precursors and rapidly proliferating cells.

The Aging of Iron Man

Brain iron is tightly regulated by a multitude of proteins to ensure homeostasis. Iron dyshomeostasis has become a molecular signature associated with aging which is accompanied by progressive decline in cognitive processes. A common theme in neurodegenerative diseases where age is the major risk factor, iron dyshomeostasis coincides with neuroinflammation, abnormal protein aggregation, neurodegeneration, and neurobehavioral deficits. There is a great need to determine the mechanisms governing perturbations in iron metabolism, in particular to distinguish between physiological and pathological aging to generate fruitful therapeutic targets for neurodegenerative diseases. The aim of the present review is to focus on the age-related alterations in brain iron metabolism from a cellular and molecular biology perspective, alongside genetics, and neuroimaging aspects in man and rodent models, with respect to normal aging and neurodegeneration. In particular, the relationship between iron dyshomeostasis and neuroinflammation will be evaluated, as well as the effects of systemic iron overload on the brain. Based on the evidence discussed here, we suggest a synergistic use of iron-chelators and anti-inflammatories as putative anti-brain aging therapies to counteract pathological aging in neurodegenerative diseases.

Lysosomal Cholesterol Hydrolysis Couples Efferocytosis to Anti-Inflammatory Oxysterol Production

RATIONALE

Macrophages face a substantial amount of cholesterol after the ingestion of apoptotic cells, and the LIPA (lysosomal acid lipase) has a major role in hydrolyzing cholesteryl esters in the endocytic compartment.

OBJECTIVE

Here, we directly investigated the role of LIPA-mediated clearance of apoptotic cells both in vitro and in vivo.

METHODS AND RESULTS

We show that LIPA inhibition causes a defective efferocytic response because of impaired generation of 25-hydroxycholesterol and 27-hydroxycholesterol. Reduced synthesis of 25-hydroxycholesterol after LIPA inhibition contributed to defective mitochondria-associated membrane leading to mitochondrial oxidative stress-induced NLRP3 (NOD-like receptor family, pyrin domain containing) inflammasome activation and caspase-1-dependent Rac1 (Ras-related C3 botulinum toxin substrate 1) degradation. A secondary event consisting of failure to appropriately activate liver X receptor-mediated pathways led to mitigation of cholesterol efflux and apoptotic cell clearance. In mice, LIPA inhibition caused defective clearance of apoptotic lymphocytes and stressed erythrocytes by hepatic and splenic macrophages, culminating in splenomegaly and splenic iron accumulation under hypercholesterolemia.

CONCLUSIONS

Our findings position lysosomal cholesterol hydrolysis as a critical process that prevents metabolic inflammation by enabling efficient macrophage apoptotic cell clearance.

Unraveling the Burden of Iron in Neurodegeneration: Intersections with Amyloid Beta Peptide Pathology

Iron overload is a hallmark of many neurodegenerative processes such as Alzheimer's, Parkinson's, and Huntington's diseases. Unbound iron accumulated as a consequence of brain aging is highly reactive with water and oxygen and produces reactive oxygen species (ROS) or free radicals. ROS are toxic compounds able to damage cell membranes, DNA, and mitochondria. Which are the mechanisms involved in neuronal iron homeostasis and in neuronal response to iron-induced oxidative stress constitutes a cutting-edge topic in metalloneurobiology. Increasing our knowledge about the underlying mechanisms that operate in iron accumulation and their consequences would shed light on the comprehension of the molecular events that participate in the pathophysiology of the abovementioned neurodegenerative diseases. In this review, current evidences about iron accumulation in the brain, the signaling mechanisms triggered by metal overload, as well as the interaction between amyloid β (Aβ) and iron, will be summarized.

Excited-state intramolecular proton-transfer (ESIPT) based fluorescence sensors and imaging agents

We review recent advances in the design and application of excited-state intramolecular proton-transfer (ESIPT) based fluorescent probes. These sensors and imaging agents (probes) are important in biology, physiology, pharmacology, and environmental science.

Iron Homeostasis Controls Myeloid Blood Cell Differentiation in Drosophila

Iron is an essential divalent ion for aerobic life. Life has evolved to maintain iron homeostasis for normal cellular and physiological functions and therefore imbalances in iron levels exert a wide range of consequences. Responses to iron dysregulation in blood development, however, remain elusive. Here, we found that iron homeostasis is critical for differentiation of Drosophila blood cells in the larval hematopoietic organ, called the lymph gland. Supplementation of an iron chelator, bathophenanthroline disulfate (BPS) results in an excessive differentiation of the crystal cell in the lymph gland. This phenotype is recapitulated by loss of Fer1HCH in the intestine, indicating that reduced levels of systemic iron enhances crystal cell differentiation. Detailed analysis of Fer1HCH-tagged-GFP revealed that Fer1HCH is also expressed in the hematopoietic systems. Lastly, blocking Fer1HCH expression in the mature blood cells showed marked increase in the blood differentiation of both crystal cells and plasmatocytes. Thus, our work suggests a relevance of systemic and local iron homeostasis in blood differentiation, prompting further investigation of molecular mechanisms underlying iron regulation and cell fate determination in the hematopoietic system.

Human calprotectin affects the redox speciation of iron

We report that the metal-sequestering human host-defense protein calprotectin (CP, S100A8/S100A9 oligomer) affects the redox speciation of iron (Fe) in bacterial growth media and buffered aqueous solution. Under aerobic conditions and in the absence of an exogenous reducing agent, CP-Ser (S100A8(C42S)/S100A9(C3S) oligomer) depletes Fe from three different bacterial growth media preparations over a 48 h timeframe (T = 30 °C). The presence of the reducing agent β-mercaptoethanol accelerates this process and allows CP-Ser to deplete Fe over a ≈1 h timeframe. Fe-depletion assays performed with metal-binding-site variants of CP-Ser show that the hexahistidine (His₆) site, which coordinates Fe(ii) with high affinity, is required for Fe depletion. An analysis of Fe redox speciation in buffer containing Fe(iii) citrate performed under aerobic conditions demonstrates that CP-Ser causes a time-dependent increase in the [Fe(ii)]/[Fe(iii)] ratio. Taken together, these results indicate that the hexahistidine site of CP stabilizes Fe(ii) and thereby shifts the redox equilibrium of Fe to the reduced ferrous state under aerobic conditions. We also report that the presence of bacterial metabolites affects the Fe-depleting activity of CP-Ser. Supplementation of bacterial growth media with an Fe(iii)-scavenging siderophore (enterobactin, staphyloferrin B, or desferrioxamine B) attenuates the Fe-depleting activity of CP-Ser. This result indicates that formation of Fe(iii)-siderophore complexes blocks CP-mediated reduction of Fe(iii) and hence the ability of CP to coordinate Fe(ii). In contrast, the presence of pyocyanin (PYO), a redox-cycling phenazine produced by Pseudomonas aeruginosa that reduces Fe(iii) to Fe(ii), accelerates Fe depletion by CP-Ser under aerobic conditions. These findings indicate that the presence of microbial metabolites that contribute to metal homeostasis at the host/pathogen interface can affect the metal-sequestering function of CP.

cAMP signaling regulates DNA hydroxymethylation by augmenting the intracellular labile ferrous iron pool

It is widely accepted that cAMP regulates gene transcription principally by activating the protein kinase A (PKA)-targeted transcription factors. Here, we show that cAMP enhances the generation of 5-hydroxymethylcytosine (5hmC) in multiple cell types. 5hmC is converted from 5-methylcytosine (5mC) by Tet methylcytosine dioxygenases, for which Fe(II) is an essential cofactor. The promotion of 5hmC was mediated by a prompt increase of the intracellular labile Fe(II) pool (LIP). cAMP enhanced the acidification of endosomes for Fe(II) release to the LIP likely through RapGEF2. The effect of cAMP on Fe(II) and 5hmC was confirmed by adenylate cyclase activators, phosphodiesterase inhibitors, and most notably by stimulation of G protein-coupled receptors (GPCR). The transcriptomic changes caused by cAMP occurred in concert with 5hmC elevation in differentially transcribed genes. Collectively, these data show a previously unrecognized regulation of gene transcription by GPCR-cAMP signaling through augmentation of the intracellular labile Fe(II) pool and DNA hydroxymethylation.

Iron-loaded transferrin (Tf) is detrimental whereas iron-free Tf confers protection against brain ischemia by modifying blood Tf saturation and subsequent neuronal damage

Despite transferrin being the main circulating carrier of iron in body fluids, and iron overload conditions being known to worsen stroke outcome through reactive oxygen species (ROS)-induced damage, the contribution of blood transferrin saturation (TSAT) to stroke brain damage is unknown. The objective of this study was to obtain evidence on whether TSAT determines the impact of experimental ischemic stroke on brain damage and whether iron-free transferrin (apotransferrin, ATf)-induced reduction of TSAT is neuroprotective. We found that experimental ischemic stroke promoted an early extravasation of circulating iron-loaded transferrin (holotransferrin, HTf) to the ischemic brain parenchyma. In vitro, HTf was found to boost ROS production and to be harmful to primary neuronal cultures exposed to oxygen and glucose deprivation. In stroked rats, whereas increasing TSAT with exogenous HTf was detrimental, administration of exogenous ATf and the subsequent reduction of TSAT was neuroprotective. Mechanistically, ATf did not prevent extravasation of HTf to the brain parenchyma in rats exposed to ischemic stroke. However, ATf in vitro reduced NMDA-induced neuronal uptake of HTf and also both the NMDA-mediated lipid peroxidation derived 4-HNE and the resulting neuronal death without altering Ca²⁺-calcineurin signaling downstream the NMDA receptor. Removal of transferrin from the culture media or blockade of transferrin receptors reduced neuronal death. Together, our data establish that blood TSAT exerts a critical role in experimental stroke-induced brain damage. In addition, our findings suggest that the protective effect of ATf at the neuronal level resides in preventing NMDA-induced HTf uptake and ROS production, which in turn reduces neuronal damage.

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Blood TSAT is pivotal to determine neuronal fate in rat models of stroke

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During ischemia blood transferrin extravasates and accumulates in ischemic neurons.

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Increasing TSAT with holotransferrin (HTf) is detrimental in rat models of stroke.

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Decreasing TSAT with apotransferrin (ATf) is beneficial in rat models of stroke

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HTf promotes and ATf reduces ROS-, iron- and NMDAR-initiated ischemic neuronal death.

Lactoferrin: A Natural Glycoprotein Involved in Iron and Inflammatory Homeostasis

Human lactoferrin (hLf), an iron-binding multifunctional cationic glycoprotein secreted by exocrine glands and by neutrophils, is a key element of host defenses. HLf and bovine Lf (bLf), possessing high sequence homology and identical functions, inhibit bacterial growth and biofilm dependently from iron binding ability while, independently, bacterial adhesion to and the entry into cells. In infected/inflamed host cells, bLf exerts an anti-inflammatory activity against interleukin-6 (IL-6), thus up-regulating ferroportin (Fpn) and transferrin receptor 1 (TfR1) and down-regulating ferritin (Ftn), pivotal actors of iron and inflammatory homeostasis (IIH). Consequently, bLf inhibits intracellular iron overload, an unsafe condition enhancing in vivo susceptibility to infections, as well as anemia of inflammation (AI), re-establishing IIH. In pregnant women, affected by AI, bLf oral administration decreases IL-6 and increases hematological parameters. This surprising effect is unrelated to iron supplementation by bLf (80 μg instead of 1-2 mg/day), but to its role on IIH. AI is unrelated to the lack of iron, but to iron delocalization: cellular/tissue overload and blood deficiency. BLf cures AI by restoring iron from cells to blood through Fpn up-expression. Indeed, anti-inflammatory activity of oral and intravaginal bLf prevents preterm delivery. Promising bLf treatments can prevent/cure transitory inflammation/anemia/oral pathologies in athletes.

Lactoferrin: A Natural Glycoprotein Involved in Iron and Inflammatory Homeostasis

Human lactoferrin (hLf), an iron-binding multifunctional cationic glycoprotein secreted by exocrine glands and by neutrophils, is a key element of host defenses. HLf and bovine Lf (bLf), possessing high sequence homology and identical functions, inhibit bacterial growth and biofilm dependently from iron binding ability while, independently, bacterial adhesion to and the entry into cells. In infected/inflamed host cells, bLf exerts an anti-inflammatory activity against interleukin-6 (IL-6), thus up-regulating ferroportin (Fpn) and transferrin receptor 1 (TfR1) and down-regulating ferritin (Ftn), pivotal actors of iron and inflammatory homeostasis (IIH). Consequently, bLf inhibits intracellular iron overload, an unsafe condition enhancing in vivo susceptibility to infections, as well as anemia of inflammation (AI), re-establishing IIH. In pregnant women, affected by AI, bLf oral administration decreases IL-6 and increases hematological parameters. This surprising effect is unrelated to iron supplementation by bLf (80 μg instead of 1-2 mg/day), but to its role on IIH. AI is unrelated to the lack of iron, but to iron delocalization: cellular/tissue overload and blood deficiency. BLf cures AI by restoring iron from cells to blood through Fpn up-expression. Indeed, anti-inflammatory activity of oral and intravaginal bLf prevents preterm delivery. Promising bLf treatments can prevent/cure transitory inflammation/anemia/oral pathologies in athletes.

Multifunctional Polymeric Micelles for Combining Chelation and Detection of Iron in Living Cells

Multifunctional self-assembled micelles composed of Pluronics F127 polymer chains are developed and investigated for chelation and selective detection of iron(III) in vitro and in iron-overloaded cells. Tetraphenylethene (TPE) is encapsulated into the micelle core and the iron chelate drug deferoxamine (DFO) is conjugated to micelles to generate a fluorescence quenching detection system termed DFO-TFM for short, where T stands for TPE, F for F127, and M for micelle. The key to the successful formation of this fluorescence quenching system is due to the near-ideal overlap between the absorption spectrum of the DFO:iron(III) complex and fluorescence spectrum of TPE. DFO-TFM can retain the iron-chelation properties of DFO and exhibits negligible cytotoxicity compared to free DFO. Furthermore, this fluorescence "turn-off" system can be utilized to detect the presence of iron and to monitor the chelation process in an iron overload cell model. This study serves as an effective proof-of-concept model for designing future in vivo systems capable of combining the features of iron chelation with iron detection and efforts toward the development of such detection systems are currently underway.

Fat content, fatty acid pattern and iron content in livers of turkeys with hepatic lipidosis

BACKGROUND

The so-called "hepatic lipidosis" in turkeys is an acute progressive disease associated with a high mortality rate in a very short time. Dead animals show a massive fatty degeneration of the liver. The cause is still unclear. Previous findings suggest that there may be parallels to human non-alcoholic fatty liver disease. The object of the study was to examine the changes in the fat contents, the fatty acid composition and the iron content in livers of animals, which have died from hepatic lipidosis.

METHODS

The conspicuous livers (n = 85) were collected from 20 flocks where the phenomenon of massive increased animal losses accompanied by marked macroscopically visible pathological liver steatosis suddenly occurred. For comparison and as a reference, livers (n = 16) of two healthy flocks were taken. Healthy and diseased flocks were fed identical diets concerning official nutrient recommendations and were operating under standardized, comparable conventional conditions.

RESULTS

Compared to livers of healthy animals, in the livers of turkeys died from hepatic lipidosis there were found massively increased fat levels (130 ± 33.2 vs. 324 ± 101 g/kg dry matter-DM). In all fatty livers, different fatty acids concentrations were present in significantly increased concentrations compared to controls (palmitic acid: 104 g/kg DM, +345%; palmitoleic acid: 18.0 g/kg DM, + 570%; oleic acid: 115 g/kg DM, +437%). Fatty acids concentrations relevant for liver metabolism and inflammation were significantly reduced (arachidonic acid: 2.92 g/kg DM, -66.6%; eicosapentaenoic acid: 0.141 g/kg DM, -78.3%; docosahexaenoic acid: 0.227 g/kg DM, -90.4%). The ratio of certain fatty acids to one another between control and case livers changed analogously to liver diseases in humans (e.g.: C18:0/C16:0 - 0.913 against 0.311; C16:1n7/C16:0 - 0.090 against 0.165; C18:1/C18:0 - 0.938 against 4.03). The iron content in the liver tissue also increased massively (271 ± 51.5 vs 712 ± 214 mg/kg DM).

CONCLUSION

The hepatic lipidosis has a massive impact on the lipid content, the lipid composition and the iron content in the liver. The character of the metabolic disorder includes parallels to the non-alcoholic steatohepatitis in humans.

Glutamate Ligation in the Ni(II)- and Co(II)-Responsive Escherichia coli Transcriptional Regulator, RcnR

Escherichia coli RcnR (resistance to cobalt and nickel regulator, EcRcnR) is a metal-responsive repressor of the genes encoding the Ni(II) and Co(II) exporter proteins RcnAB by binding to P_RcnAB. The DNA binding affinity is weakened when the cognate ions Ni(II) and Co(II) bind to EcRcnR in a six-coordinate site that features a (N/O)₅S ligand donor-atom set in distinct sites: while both metal ions are bound by the N terminus, Cys35, and His64, Co(II) is additionally bound by His3. On the other hand, the noncognate Zn(II) and Cu(I) ions feature a lower coordination number, have a solvent-accessible binding site, and coordinate protein ligands that do not include the N-terminal amine. A molecular model of apo-EcRcnR suggested potential roles for Glu34 and Glu63 in binding Ni(II) and Co(II) to EcRcnR. The roles of Glu34 and Glu63 in metal binding, metal selectivity, and function were therefore investigated using a structure/function approach. X-ray absorption spectroscopy was used to assess the structural changes in the Ni(II), Co(II), and Zn(II) binding sites of Glu → Ala and Glu → Cys variants at both positions. The effect of these structural alterations on the regulation of P_rcnA by EcRcnR in response to metal binding was explored using LacZ reporter assays. These combined studies indicate that while Glu63 is a ligand for both metal ions, Glu34 is a ligand for Co(II) but possibly not for Ni(II). The Glu34 variants affect the structure of the cognate metal sites, but they have no effect on the transcriptional response. In contrast, the Glu63 variants affect both the structure and transcriptional response, although they do not completely abolish the function of EcRcnR. The structure of the Zn(II) site is not significantly perturbed by any of the glutamic acid variations. The spectroscopic and functional data obtained on the mutants were used to calculate models of the metal-site structures of EcRcnR bound to Ni(II), Co(II), and Zn(II). The results are interpreted in terms of a switch mechanism, in which a subset of the metal-binding ligands is responsible for the allosteric response required for DNA release.

Iron-Restricted Diet Affects Brain Ferritin Levels, Dopamine Metabolism and Cellular Prion Protein in a Region-Specific Manner

Iron is an essential micronutrient for several physiological functions, including the regulation of dopaminergic neurotransmission. On the other hand, both iron, and dopamine can affect the folding and aggregation of proteins related with neurodegenerative diseases, such as cellular prion protein (PrP^C) and α-synuclein, suggesting that deregulation of iron homeostasis and the consequential disturbance of dopamine metabolism can be a risk factor for conformational diseases. These proteins, in turn, are known to participate in the regulation of iron and dopamine metabolism. In this study, we evaluated the effects of dietary iron restriction on brain ferritin levels, dopamine metabolism, and the expression levels of PrP^C and α-synuclein. To achieve this goal, C57BL/6 mice were fed with iron restricted diet (IR) or with normal diet (CTL) for 1 month. IR reduced iron and ferritin levels in liver. Ferritin reduction was also observed in the hippocampus. However, in the striatum of IR group, ferritin level was increased, suggesting that under iron-deficient condition, each brain area might acquire distinct capacity to store iron. Increased lipid peroxidation was observed only in hippocampus of IR group, where ferritin level was reduced. IR also generated discrete results regarding dopamine metabolism of distinct brain regions: in striatum, the level of dopamine metabolites (DOPAC and HVA) was reduced; in prefrontal cortex, only HVA was increased along with the enhanced MAO-A activity; in hippocampus, no alterations were observed. PrP^C levels were increased only in the striatum of IR group, where ferritin level was also increased. PrP^C is known to play roles in iron uptake. Thus, the increase of PrP^C in striatum of IR group might be related to the increased ferritin level. α-synuclein was not altered in any regions. Abnormal accumulation of ferritin, increased MAO-A activity or lipid peroxidation are molecular features observed in several neurological disorders. Our findings show that nutritional iron deficiency produces these molecular alterations in a region-specific manner and provide new insight into the variety of molecular pathways that can lead to distinct neurological symptoms upon iron deficiency. Thus, adequate iron supplementation is essential for brain health and prevention of neurological diseases.

FBXL5 Inactivation in Mouse Brain Induces Aberrant Proliferation of Neural Stem Progenitor Cells

FBXL5 is the substrate recognition subunit of an SCF-type ubiquitin ligase that serves as a master regulator of iron metabolism in mammalian cells. We previously showed that mice with systemic deficiency of FBXL5 fail to sense intracellular iron levels and die in utero at embryonic day 8.5 (E8.5) as a result of iron overload and subsequent oxidative stress. This early embryonic mortality has thus impeded study of the role of FBXL5 in brain development. We have now generated mice lacking FBXL5 specifically in nestin-expressing neural stem progenitor cells (NSPCs) in the brain. Unexpectedly, the mutant embryos manifested a progressive increase in the number of NSPCs and astroglia in the cerebral cortex. Stabilization of iron regulatory protein 2 (IRP2) as a result of FBXL5 deficiency led to accumulation of ferrous and ferric iron as well as to generation of reactive oxygen species. Pharmacological manipulation suggested that the phenotypes of FBXL5 deficiency are attributable to aberrant activation of mammalian target of rapamycin (mTOR) signaling. Our results thus show that FBXL5 contributes to regulation of NSPC proliferation during mammalian brain development.

Unique high and homogenous surface expression of the transferrin receptor CD71 on murine plasmacytoid dendritic cells in different tissues

Plasmacytoid dendritic cells (pDC) are of increasing interest in cancer vaccine development, but many functions of these highly specialized, multifaceted cells are poorly understood. The transferrin receptor CD71 has also been suggested to function as an antigen uptake receptor on professional antigen-presenting cells. In this study, we employed multiparameter flow cytometry to investigate CD71 expression on various leukocyte subsets, including DC subsets, granulocytes, macrophages, T and B lymphocytes, γδ T cells, and natural killer cells. Cells from various lymphoid and non-lymphoid murine tissues were analyzed using fluorochrome-conjugated monoclonal antibodies. High CD71 expression (90-100%) was observed, uniquely on pDC amongst the leukocyte populations examined, in both lymphoid and non-lymphoid tissues, including other DC subsets. In contrast, CD71 expression on non-tissue pDC, in the bone marrow and peripheral blood, was reduced. The cause and function of this high tissue pDC-selective CD71 expression remain to be examined.

Vitamin D receptor expression and hepcidin levels in the protection or severity of leprosy: a systematic review

Leprosy is a chronic infectious disease whose disequilibrium in the host's genetic, immunological and clinical mechanisms leads to distinct manifestations defining the type of immunological response. This review focuses its attention on the influence of the Vitamin D Receptor and hepcidin expressions that can suggest the protection or severity of leprosy.

Sirtuin 2 regulates cellular iron homeostasis via deacetylation of transcription factor NRF2

SIRT2 is a cytoplasmic sirtuin that plays a role in various cellular processes, including tumorigenesis, metabolism, and inflammation. Since these processes require iron, we hypothesized that SIRT2 directly regulates cellular iron homeostasis. Here, we have demonstrated that SIRT2 depletion results in a decrease in cellular iron levels both in vitro and in vivo. Mechanistically, we determined that SIRT2 maintains cellular iron levels by binding to and deacetylating nuclear factor erythroid-derived 2-related factor 2 (NRF2) on lysines 506 and 508, leading to a reduction in total and nuclear NRF2 levels. The reduction in nuclear NRF2 leads to reduced ferroportin 1 (FPN1) expression, which in turn results in decreased cellular iron export. Finally, we observed that Sirt2 deletion reduced cell viability in response to iron deficiency. Moreover, livers from Sirt2-/- mice had decreased iron levels, while this effect was reversed in Sirt2-/- Nrf2-/- double-KO mice. Taken together, our results uncover a link between sirtuin proteins and direct control over cellular iron homeostasis via regulation of NRF2 deacetylation and stability.

Iron Reduces M1 Macrophage Polarization in RAW264.7 Macrophages Associated with Inhibition of STAT1

Iron metabolism in inflammation has been mostly characterized in macrophages exposed to pathogens or inflammatory conditions. The aim of this study is to investigate the cross-regulatory interactions between M1 macrophage polarization and iron metabolism. Firstly, we characterized the transcription of genes related to iron homeostasis in M1 RAW264.7 macrophages stimulated by IFN-γ. The molecular signature of M1 macrophages showed high levels of iron storage (ferritin), a low level of iron export (ferroportin), and changes of iron regulators (hepcidin and transferrin receptors), which favour iron sequestration in the reticuloendothelial system and are benefit for inflammatory disorders. Then, we evaluated the effect of iron on M1 macrophage polarization. Iron significantly reduced mRNA levels of IL-6, IL-1β, TNF-α, and iNOS produced by IFN-γ-polarized M1 macrophages. Immunofluorescence analysis showed that iron also reduced iNOS production. However, iron did not compromise but enhanced the ability of M1-polarized macrophages to phagocytose FITC-dextran. Moreover, we demonstrated that STAT1 inhibition was required for reduction of iNOS and M1-related cytokines production by the present of iron. Together, these findings indicated that iron decreased polarization of M1 macrophages and inhibited the production of the proinflammatory cytokines. The results expanded our knowledge about the role of iron in macrophage polarization.

Molecular and Cellular Bases of Iron Metabolism in Humans

Iron is a microelement with the most completely studied biological functions. Its wide dissemination in nature and involvement in key metabolic pathways determine the great importance of this metal for uni- and multicellular organisms. The biological role of iron is characterized by its indispensability in cell respiration and various biochemical processes providing normal functioning of cells and organs of the human body. Iron also plays an important role in the generation of free radicals, which under different conditions can be useful or damaging to biomolecules and cells. In the literature, there are many reviews devoted to iron metabolism and its regulation in pro- and eukaryotes. Significant progress has been achieved recently in understanding molecular bases of iron metabolism. The purpose of this review is to systematize available data on mechanisms of iron assimilation, distribution, and elimination from the human body, as well as on its biological importance and on the major iron-containing proteins. The review summarizes recent ideas about iron metabolism. Special attention is paid to mechanisms of iron absorption in the small intestine and to interrelationships of cellular and extracellular pools of this metal in the human body.

Does any drug to treat cancer target mTOR and iron hemostasis in neurodegenerative disorders?

The prevalence of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and Huntington's disease are increased by age. Alleviation of their symptoms and protection of normal neurons against degeneration are the main aspects of the research to establish novel therapeutic strategies. Iron as the one of most important cation not only play important role in the structure of electron transport chain proteins but also has pivotal duties in cellular activities. But disruption in iron hemostasis can make it toxin to neurons which causes lipid peroxidation, DNA damage and etc. In patients with Alzheimer and Parkinson misbalancing in iron homeostasis accelerate neurodegeneration and cause neuroinflmmation. mTOR as the common signaling pathway between cancer and neurodegenerative disorders controls iron uptake and it is in active form in both diseases. Anti-cancer drugs which target mTOR causes iron deficiency and dual effects of mTOR inhibitors can candidate them as a therapeutic strategy to alleviate neurodegeneration/inflammation because of iron overloading.

Iron transport in the kidney: implications for physiology and cadmium nephrotoxicity

The kidney has recently emerged as an organ with a significant role in systemic iron (Fe) homeostasis. Substantial amounts of Fe are filtered by the kidney, which have to be reabsorbed to prevent Fe deficiency. Accordingly Fe transporters and receptors for protein-bound Fe are expressed in the nephron that may also function as entry pathways for toxic metals, such as cadmium (Cd), by way of "ionic and molecular mimicry". Similarities, but also differences in handling of Cd by these transport routes offer rationales for the propensity of the kidney to develop Cd toxicity. This critical review provides a comprehensive update on Fe transport by the kidney and its relevance for physiology and Cd nephrotoxicity. Based on quantitative considerations, we have also estimated the in vivo relevance of the described transport pathways for physiology and toxicology. Under physiological conditions all segments of the kidney tubules are likely to utilize Fe for cellular Fe requiring processes for metabolic purposes and also to contribute to reabsorption of free and bound forms of Fe into the circulation. But Cd entering tubule cells disrupts metabolic pathways and is unable to exit. Furthermore, our quantitative analyses contest established models linking chronic Cd nephrotoxicity to proximal tubular uptake of metallothionein-bound Cd. Hence, Fe transport by the kidney may be beneficial by preventing losses from the body. But increased uptake of Fe or Cd that cannot exit tubule cells may lead to kidney injury, and Fe deficiency may facilitate renal Cd uptake.

Enzymatically Biodegradable Polyrotaxane-Deferoxamine Conjugates for Iron Chelation

Chelation therapy is frequently used to help reduce excess iron in the body, but current chelators such as deferoxamine (DFO) are plagued by short blood circulation times, which necessitates infusions and can cause undesirable toxic side effects in patients. To address these issues, polyrotaxanes (PR) were synthesized by threading α-cyclodextrin (α-CD) onto poly(ethylene glycol) bis(amine) (PEG-BA, MW 3400 g/mol) capped with enzymatically cleavable bulky Z-L phenylalanine (Z-L Phe) moieties. The resulting PR was conjugated to DFO and hydroxypropylated to generate the final polyrotaxane-DFO (hPR-DFO). The iron chelating capability of hPR-DFO was verified by UV-vis absorption spectroscopy and the ability of materials to degrade into smaller CD-conjugated DFO fragments (hCD-DFO) in the presence of the protease was confirmed via gel permeation chromatography. In vitro studies in iron-overloaded macrophages reveal that hPR-DFO can significantly reduce the cytotoxicity of the drug while maintaining its chelation efficacy, and that it is more rapidly endocytosed and trafficked to lysosomes of iron-overloaded cells in comparison to non-iron-overloaded macrophages. In vivo studies indicate that iron-overloaded mice treated with hPR-DFO displayed lower serum ferritin levels (a measure of iron burden in the body) and could eliminate excess iron by both the renal and fecal routes. Moreover, there was no gross evidence of acute toxicological damage to the liver or spleen.

Erythroid cell mitochondria receive endosomal iron by a "kiss-and-run" mechanism

In erythroid cells, more than 90% of transferrin-derived iron enters mitochondria where ferrochelatase inserts Fe²⁺ into protoporphyrin IX. However, the path of iron from endosomes to mitochondrial ferrochelatase remains elusive. The prevailing opinion is that, after its export from endosomes, the redox-active metal spreads into the cytosol and mysteriously finds its way into mitochondria through passive diffusion. In contrast, this study supports the hypothesis that the highly efficient transport of iron toward ferrochelatase in erythroid cells requires a direct interaction between transferrin-endosomes and mitochondria (the "kiss-and-run" hypothesis). Using a novel method (flow sub-cytometry), we analyze lysates of reticulocytes after labeling these organelles with different fluorophores. We have identified a double-labeled population definitively representing endosomes interacting with mitochondria, as demonstrated by confocal microscopy. Moreover, we conclude that this endosome-mitochondrion association is reversible, since a "chase" with unlabeled holotransferrin causes a time-dependent decrease in the size of the double-labeled population. Importantly, the dissociation of endosomes from mitochondria does not occur in the absence of holotransferrin. Additionally, mutated recombinant holotransferrin, that cannot release iron, significantly decreases the uptake of ⁵⁹Fe by reticulocytes and diminishes ⁵⁹Fe incorporation into heme. This suggests that endosomes, which are unable to provide iron to mitochondria, cause a "traffic jam" leading to decreased endocytosis of holotransferrin. Altogether, our results suggest that a molecular mechanism exists to coordinate the iron status of endosomal transferrin with its trafficking. Besides its contribution to the field of iron metabolism, this study provides evidence for a new intracellular trafficking pathway of organelles.

Non-mutagenic Suppression of Enterocyte Ferroportin 1 by Chemical Ribosomal Inactivation via p38 Mitogen-activated Protein Kinase (MAPK)-mediated Regulation: EVIDENCE FOR ENVIRONMENTAL HEMOCHROMATOSIS

Iron transfer across the basolateral membrane of an enterocyte into the circulation is the rate-limiting step in iron absorption and is regulated by various pathophysiological factors. Ferroportin (FPN), the only known mammalian iron exporter, transports iron from the basolateral surface of enterocytes, macrophages, and hepatocytes into the blood. Patients with genetic mutations in FPN or repeated blood transfusion develop hemochromatosis. In this study, non-mutagenic ribosomal inactivation was assessed as an etiological factor of FPN-associated hemochromatosis in enterocytes. Non-mutagenic chemical ribosomal inactivation disrupted iron homeostasis by regulating expression of the iron exporter FPN-1, leading to intracellular accumulation in enterocytes. Mechanistically, a xenobiotic insult stimulated the intracellular sentinel p38 MAPK signaling pathway, which was positively involved in FPN-1 suppression by ribosomal dysfunction. Moreover, ribosomal inactivation-induced iron accumulation in Caenorhabditis elegans as a simplified in vivo model for gut nutrition uptake was dependent on SEK-1, a p38 kinase activator, leading to suppression of FPN-1.1 expression and iron accumulation. In terms of gene regulation, ribosomal stress-activated p38 signaling down-regulated NRF2 and NF-κB, both of which were positive transcriptional regulators of FPN-1 transcription. This study provides molecular evidence for the modulation of iron bioavailability by ribosomal dysfunction as a potent etiological factor of non-mutagenic environmental hemochromatosis in the gut-to-blood axis.

Hepcidin inhibition on the effect of osteogenesis in zebrafish

Iron overload, as a risk factor for osteoporosis, can result in the up-regulation of Hepcidin, and Hepcidin knockout mice display defects in their bone microarchitecture. However, the molecular and genetic mechanisms underlying Hepcidin deficiency-derived bone loss remain unclear. Here, we show that hepcidin knockdown in zebrafish using morpholinos leads to iron overload. Furthermore, a mineralization delay is observed in osteoblast cells in hepcidin morphants, and these defects could be partially restored with microinjection of hepcidin mRNA. Quantitative real-time PCR analyses revealed the osteoblast-specific genes alp, runx2a, runx2b, and sp7 in morphants are down-regulated. Furthermore, we confirmed qRT-PCR results by in situ hybridization and found down-regulated genes related to osteoblast function in hepcidin morphants. Most importantly, we revealed that hepcidin was capable of removing whole-body iron which facilitated larval recovery from the reductions in bone formation and osteogenesis induced by iron overload.

The Endocytic Fate of the Transferrin Receptor Is Regulated by c-Abl Kinase

Clathrin-mediated endocytosis of transferrin (Tf) and its cognate receptor (TfR1) is a central pathway supporting the uptake of trophic iron. It has generally been assumed that this is a constitutive process. However, we have reported that the non-receptor tyrosine kinase, Src, is activated by Tf to facilitate the internalization of the Tf-TfR1 ligand-receptor complex. As an extension of these findings, we have tested whether subsequent trafficking steps might be regulated by additional kinase-dependent cascades, and we observed a significant endocytic block by inhibiting c-Abl kinase by a variety of methods. Importantly, Tf internalization was reduced significantly in all of these cell models and could be restored by re-expression of WT c-Abl. Surprisingly, this attenuated Tf-TfR1 endocytosis was due to a substantial drop in both the surface and total cellular receptor levels. Additional studies with the LDL receptor showed a similar effect. Surprisingly, immunofluorescence microscopy of imatinib-treated cells revealed a marked colocalization of internalized TfR1 with late endosomes/lysosomes, whereas attenuating the lysosome function with several inhibitors reduced this receptor loss. Importantly, inhibition of c-Abl resulted in a striking redistribution of the chaperone Hsc70 from a diffuse cytosolic localization to an association with the TfR1 at the late endosome-lysosome. Pharmacological inhibition of Hsc70 ATPase activity in cultured cells by the drug VER155008 prevents this chaperone-receptor interaction, resulting in an accumulation of the TfR1 in the early endosome. Thus, inhibition of c-Abl minimizes receptor recycling pathways and results in chaperone-dependent trafficking of the TfR1 to the lysosome for degradation. These findings implicate a novel role for c-Abl and Hsc70 as an unexpected regulator of Hsc70-mediated transport of trophic receptor cargo between the early and late endosomal compartments.

Reduction in mitochondrial iron alleviates cardiac damage during injury

Excess cellular iron increases reactive oxygen species (ROS) production and causes cellular damage. Mitochondria are the major site of iron metabolism and ROS production; however, few studies have investigated the role of mitochondrial iron in the development of cardiac disorders, such as ischemic heart disease or cardiomyopathy (CM). We observe increased mitochondrial iron in mice after ischemia/reperfusion (I/R) and in human hearts with ischemic CM, and hypothesize that decreasing mitochondrial iron protects against I/R damage and the development of CM. Reducing mitochondrial iron genetically through cardiac-specific overexpression of a mitochondrial iron export protein or pharmacologically using a mitochondria-permeable iron chelator protects mice against I/R injury. Furthermore, decreasing mitochondrial iron protects the murine hearts in a model of spontaneous CM with mitochondrial iron accumulation. Reduced mitochondrial ROS that is independent of alterations in the electron transport chain's ROS producing capacity contributes to the protective effects. Overall, our findings suggest that mitochondrial iron contributes to cardiac ischemic damage, and may be a novel therapeutic target against ischemic heart disease.

Oxidation-Induced Degradable Nanogels for Iron Chelation

Iron overload can increase cellular oxidative stress levels due to formation of reactive oxygen species (ROS); untreated, it can be extremely destructive to organs and fatal to patients. Since elevated oxidative stress levels are inherent to the condition in such patients, oxidation-induced degradable nanogels for iron chelation were rationally designed by simultaneously polymerizing oxidation-sensitive host-guest crosslinkers between β-cyclodextrin (β-CD) and ferrocene (Fc) and iron chelating moieties composed of deferoxamine (DFO) into the final gel scaffold in reverse emulsion reaction chambers. UV-Vis absorption and atomic absorption spectroscopy (AAS) was used to verify iron chelating capability of nanogels. These materials can degrade into smaller chelating fragments at rates proportional to the level of oxidative stress present. Conjugating DFO reduces the cytotoxicity of the chelator in the macrophage cells. Importantly, the nanogel can effectively reduce cellular ferritin expression in iron overloaded cells and regulate intracellular iron levels at the same time, which is important for maintaining a homeostatic level of this critical metal in cells.

Redox cycling metals: Pedaling their roles in metabolism and their use in the development of novel therapeutics

Essential metals, such as iron and copper, play a critical role in a plethora of cellular processes including cell growth and proliferation. However, concomitantly, excess of these metal ions in the body can have deleterious effects due to their ability to generate cytotoxic reactive oxygen species (ROS). Thus, the human body has evolved a very well-orchestrated metabolic system that keeps tight control on the levels of these metal ions. Considering their very high proliferation rate, cancer cells require a high abundance of these metals compared to their normal counterparts. Interestingly, new anti-cancer agents that take advantage of the sensitivity of cancer cells to metal sequestration and their susceptibility to ROS have been developed. These ligands can avidly bind metal ions to form redox active metal complexes, which lead to generation of cytotoxic ROS. Furthermore, these agents also act as potent metastasis suppressors due to their ability to up-regulate the metastasis suppressor gene, N-myc downstream regulated gene 1. This review discusses the importance of iron and copper in the metabolism and progression of cancer, how they can be exploited to target tumors and the clinical translation of novel anti-cancer chemotherapeutics.

Study on the interaction between Fe3+and fibrinogen and its influence on the polymerization behavior of fibrin networks

The interactions between fibrinogen molecule and Fe³⁺were studied and applied to explicate the polymerization behavior of fibrinogen mediated with Fe³⁺. Overloading Fe³⁺in the fibrinogen solution will accelerate the amorphous aggregation of fibrin.

A high fat diet does not affect the iron bioavailability in Wistar rats fed with chia and increases gene expression of iron metabolism proteins

This study evaluated the effect of chia on the iron bioavailability and gene expression of proteins involved in iron metabolism in animals fed with a high fat diet and a standard diet.

Membrane-anchored ubiquitin ligase complex is required for the turnover of lysosomal membrane proteins

Cells must regulate the abundance and activity of numerous nutrient transporters in different organelle membranes to achieve nutrient homeostasis. As the recycling center and major storage organelle, lysosomes are essential for maintaining nutrient homeostasis. However, very little is known about mechanisms that govern the regulation of its membrane proteins. In this study, we demonstrated that changes of Zn(2+) levels trigger the downregulation of vacuolar Zn(2+) transporters. Low Zn(2+) levels cause the degradation of the influx transporter Cot1, whereas high Zn(2+) levels trigger the degradation of the efflux channel Zrt3. The degradation process depends on the vacuole membrane recycling and degradation pathway. Unexpectedly, we identified a RING domain-containing E3 ligase Tul1 and its interacting proteins in the Dsc complex that are important for the ubiquitination of Cot1 and partial ubiquitination of Zrt3. Our study demonstrated that the Dsc complex can function at the vacuole to regulate the composition and lifetime of vacuolar membrane proteins.

Linking the occurrence of cutaneous opportunistic fungal invaders with elemental concentrations in false killer whale (Pseudorca crassidens) skin

Cetaceans, occupying the top levels in marine food chains, are vulnerable to elevated levels of potentially toxic trace elements, such as aluminium (Al), mercury (Hg) and nickel (Ni). Negative effects associated with these toxic metals include infection by opportunistic microbial invaders. To corroborate the link between the presence of cutaneous fungal invaders and trace element levels, skin samples from 40 stranded false killer whales (FKWs) were analysed using culture techniques and inductively coupled plasma-mass spectroscopy. Twenty-two skin samples yielded 18 clinically relevant fungal species. While evidence for bioaccumulation of Hg in the skin of the FKWs was observed, a strong link was found to exist between the occurrence of opportunistic fungal invaders and higher Al : Se and Al : Zn ratios. This study provides indications that elevated levels of some toxic metals, such as Al, contribute to immunotoxicity rendering FKWs susceptible to colonization by cutaneous opportunistic fungal invaders.

Ferritin Is Required in Multiple Tissues during Drosophila melanogaster Development

In Drosophila melanogaster, iron is stored in the cellular endomembrane system inside a protein cage formed by 24 ferritin subunits of two types (Fer1HCH and Fer2LCH) in a 1:1 stoichiometry. In larvae, ferritin accumulates in the midgut, hemolymph, garland, pericardial cells and in the nervous system. Here we present analyses of embryonic phenotypes for mutations in Fer1HCH, Fer2LCH and in both genes simultaneously. Mutations in either gene or deletion of both genes results in a similar set of cuticular embryonic phenotypes, ranging from non-deposition of cuticle to defects associated with germ band retraction, dorsal closure and head involution. A fraction of ferritin mutants have embryonic nervous systems with ventral nerve cord disruptions, misguided axonal projections and brain malformations. Ferritin mutants die with ectopic apoptotic events. Furthermore, we show that ferritin maternal contribution, which varies reflecting the mother's iron stores, is used in early development. We also evaluated phenotypes arising from the blockage of COPII transport from the endoplasmic reticulum to the Golgi apparatus, feeding the secretory pathway, plus analysis of ectopically expressed and fluorescently marked Fer1HCH and Fer2LCH. Overall, our results are consistent with insect ferritin combining three functions: iron storage, intercellular iron transport, and protection from iron-induced oxidative stress. These functions are required in multiple tissues during Drosophila embryonic development.