Scara5 is a ferritin receptor mediating non-transferrin iron delivery

Targeting iron metabolism in drug discovery and delivery

Iron fulfils a central role in many essential biochemical processes in human physiology; thus, proper processing of iron is crucial. Although iron metabolism is subject to relatively strict physiological control, numerous disorders, such as cancer and neurodegenerative diseases, have recently been linked to deregulated iron homeostasis. Consequently, iron metabolism constitutes a promising and largely unexploited therapeutic target for the development of new pharmacological treatments for these diseases. Several iron metabolism-targeted therapies are already under clinical evaluation for haematological disorders, and these and newly developed therapeutic agents are likely to have substantial benefit in the clinical management of iron metabolism-associated diseases, for which few efficacious treatments are currently available.

A Red Carpet for Iron Metabolism

200 billion red blood cells (RBCs) are produced every day, requiring more than 2 × 10¹⁵ iron atoms every second to maintain adequate erythropoiesis. These numbers translate into 20 mL of blood being produced each day, containing 6 g of hemoglobin and 20 mg of iron. These impressive numbers illustrate why the making and breaking of RBCs is at the heart of iron physiology, providing an ideal context to discuss recent progress in understanding the systemic and cellular mechanisms that underlie the regulation of iron homeostasis and its disorders.

SCARA5 plays a critical role in the progression and metastasis of breast cancer by inactivating the ERK1/2, STAT3, and AKT signaling pathways

Scavenger receptor class A member 5 (SCARA5) is a candidate anti-oncogene in several malignancies. However, whether SCARA5 is a suppressor gene in breast cancer and its role in breast cancer cell growth and metastasis remain to be determined. Here, we investigated the biological functions of SCARA5 in the progression and metastasis of breast cancer and explored the underlying mechanisms. A total of 65 breast cancer patients and three cell lines (ZR-75-30, MCF-7, and MDA-MB-231) were analyzed in the study. RT-qPCR, western blotting, and immunohistochemistry were used to detect mRNA and protein expression, and lymphatic vessel density (LVD) and microvessel density (MVD). MTT, colony formation, TUNEL assays, invasion assays and Transwell assays, and flow cytometric analyses were used to evaluate the effect of SCARA5 on breast cancer cells. SCARA5 was significantly downregulated in breast cancer tissues and cells and significantly correlated with tumor size, histological grade, lymph node metastasis, pTNM stage, VEGF-A, VEGF-C, LVD, and MVD. SCARA5 overexpression significantly suppressed cell proliferation, colony formation, invasion, and migration, and induced G0/G1 arrest and apoptosis of ZR-75-30 cells. SCARA5 decreased the phosphorylation of ERK1/2, AKT, and STAT3, and downregulated downstream signaling effectors, including MMP-2, 3, and 9, VEGF-A, VEGF-C, Bax, Cyclin B1, Cyclin D1, and Cyclin E1, and upregulated E-cadherin, Bcl-2, and caspase 3. SCARA5 is associated with multiple signaling pathways and plays a critical role in the progression and metastasis of breast cancer. The present results provide the first evidence that SCARA5 inhibits lymphangiogenesis by downregulating VEGF-C, thereby inhibiting breast cancer lymphatic metastasis.

Loss of Dynamin 2 GTPase function results in microcytic anaemia

In a dominant mouse ethylnitrosurea mutagenesis screen for genes regulating erythropoiesis, we identified a pedigree with a novel microcytic hypochromia caused by a V235G missense mutation in Dynamin 2 (Dnm2). Mutations in Dnm2, a GTPase, are highly disease-specific and have been implicated in four forms of human diseases: centronuclear myopathy, Charcot-Marie Tooth neuropathy and, more recently, T-cell leukaemia and Hereditary Spastic Paraplegia, but red cell abnormalities have not been reported to date. The V235G mutation lies within a crucial GTP nucleotide-binding pocket of Dnm2, and resulted in defective GTPase activity and incompatibility with life in the homozygous state. Dnm2 is an essential mediator of clathrin-mediated endocytosis, which is required for the uptake of transferrin (Tf) into red cells for incorporation of haem. Accordingly, we observed significantly reduced Tf uptake by Dnm2^+/V235G cells, which led to impaired endosome formation. Despite these deficiencies, surprisingly all iron studies were unchanged, suggesting an unexplained alternative mechanism underlies microcytic anaemia in Dnm2^+/V235G mice. This study provides the first in vivo evidence for the requirements of Dnm2 in normal erythropoiesis.

X-ray Structure of the Carboplatin-Loaded Apo-Ferritin Nanocage

The second-generation Pt anticancer agent carboplatin (CBDCA) was encapsulated within the apo horse spleen ferritin (AFt) nanocage, and the X-ray structure of the drug-loaded protein was refined at 1.49 Å resolution. Two Pt binding sites, different from the one observed in the cisplatin-encapsulated AFt, were identified in Ft subunits by inspection of anomalous electron density maps at two wavelengths and difference Fourier electron density maps, which provide the necessary sensitivity to discriminate between Pt from CBDCA and Cd ions that are present in the crystallization conditions. Pt centers coordinate to the NE2 atom of His49 and to the NE2 atom of His132, both on the inner surface of the Ft nanocage.

Adipocyte Metabolic Pathways Regulated by Diet Control the Female Germline Stem Cell Lineage in Drosophila melanogaster

Nutrients affect adult stem cells through complex mechanisms involving multiple organs. Adipocytes are highly sensitive to diet and have key metabolic roles, and obesity increases the risk for many cancers. How diet-regulated adipocyte metabolic pathways influence normal stem cell lineages, however, remains unclear. Drosophila melanogaster has highly conserved adipocyte metabolism and a well-characterized female germline stem cell (GSC) lineage response to diet. Here, we conducted an isobaric tags for relative and absolute quantification (iTRAQ) proteomic analysis to identify diet-regulated adipocyte metabolic pathways that control the female GSC lineage. On a rich (relative to poor) diet, adipocyte Hexokinase-C and metabolic enzymes involved in pyruvate/acetyl-CoA production are upregulated, promoting a shift of glucose metabolism toward macromolecule biosynthesis. Adipocyte-specific knockdown shows that these enzymes support early GSC progeny survival. Further, enzymes catalyzing fatty acid oxidation and phosphatidylethanolamine synthesis in adipocytes promote GSC maintenance, whereas lipid and iron transport from adipocytes controls vitellogenesis and GSC number, respectively. These results show a functional relationship between specific metabolic pathways in adipocytes and distinct processes in the GSC lineage, suggesting the adipocyte metabolism-stem cell link as an important area of investigation in other stem cell systems.

"Pumping iron"-how macrophages handle iron at the systemic, microenvironmental, and cellular levels

Macrophages reside in virtually every organ. First arising during embryogenesis, macrophages replenish themselves in the adult through a combination of self-renewal and influx of bone marrow-derived monocytes. As large phagocytic cells, macrophages participate in innate immunity while contributing to tissue-specific homeostatic functions. Among the key metabolic tasks are senescent red blood cell recycling, free heme detoxification, and provision of iron for de novo hemoglobin synthesis. While this systemic mechanism involves the shuttling of iron between spleen, liver, and bone marrow through the concerted function of defined macrophage populations, similar circuits appear to exist within the microenvironment of other organs. The high turnover of iron is the prerequisite for continuous erythropoiesis and tissue integrity but challenges macrophages’ ability to maintain cellular iron homeostasis and immune function.

This review provides a brief overview of systemic, microenvironmental, and cellular aspects of macrophage iron handling with a focus on exciting and unresolved questions in the field.

Targeting Iron Homeostasis in Acute Kidney Injury

Iron is an essential metal involved in several major cellular processes required to maintain life. Because of iron's ability to cause oxidative damage, its transport, metabolism, and storage is strictly controlled in the body, especially in the small intestine, liver, and kidney. Iron plays a major role in acute kidney injury and has been a target for therapeutic intervention. However, the therapies that have been effective in animal models of acute kidney injury have not been successful in human beings. Targeting iron trafficking via ferritin, ferroportin, or hepcidin may offer new insights. This review focuses on the biology of iron, particularly in the kidney, and its implications in acute kidney injury.

"Silent" Amino Acid Residues at Key Subunit Interfaces Regulate the Geometry of Protein Nanocages

Rendering the geometry of protein-based assemblies controllable remains challenging. Protein shell-like nanocages represent particularly interesting targets for designed assembly. Here, we introduce an engineering strategy-key subunit interface redesign (KSIR)-that alters a natural subunit-subunit interface by selective deletion of a small number of "silent" amino acid residues (no participation in interfacial interactions) into one that triggers the generation of a non-native protein cage. We have applied KSIR to construct a non-native 48-mer nanocage from its native 24-mer recombinant human H-chain ferritin (rHuHF). This protein is a heteropolymer composed of equal numbers of two different subunits which are derived from one polypeptide. This strategy has allowed the study of conversion between protein nanocages with different geometries by re-engineering key subunit interfaces and the demonstration of the important role of the above-mentioned specific residues in providing geometric specificity for protein assembly.

Disposal of iron by a mutant form of lipocalin 2

Iron overload damages many organs. Unfortunately, therapeutic iron chelators also have undesired toxicity and may deliver iron to microbes. Here we show that a mutant form (K3Cys) of endogenous lipocalin 2 (LCN2) is filtered by the kidney but can bypass sites of megalin-dependent recapture, resulting in urinary excretion. Because K3Cys maintains recognition of its cognate ligand, the iron siderophore enterochelin, this protein can capture and transport iron even in the acidic conditions of urine. Mutant LCN2 strips iron from transferrin and citrate, and delivers it into the urine. In addition, it removes iron from iron overloaded mice, including models of acquired (iron-dextran or stored red blood cells) and primary (Hfe^−/−) iron overload. In each case, the mutants reduce redox activity typical of non-transferrin-bound iron. In summary, we present a non-toxic strategy for iron chelation and urinary elimination, based on manipulating an endogenous protein:siderophore:iron clearance pathway.

Iron overload can be either hereditary or acquired via transfusions, and current treatments include the use of iron chelators that have adverse effects in some patients. Here the authors modify siderocalin to enhance iron excretion in urine, and demonstrate therapeutic efficacy in iron overload mouse models.

MEIS3 is repressed in A549 lung epithelial cells by deoxynivalenol and the repression contributes to the deleterious effect

Deoxynivalenol (DON) is an important Fusarium toxin of concern for food safety. The inhalation of powder contaminated with DON is possible and may cause lung toxicity. In this study, we analyzed the gene expression profile of A549 cells treated for 24 hr with 0.2 µg/mL DON by microarray analysis. In total, 16 genes and 5 noncoding RNAs were significantly affected by DON treatment. The repression of B3GALT4, MEIS3, AK7, SEMA3A, KCNMB4, and SCARA5 was confirmed by quantitative PCR. We investigated the DON toxicity on A549 cells that exogenously expressed these 6 genes. The result indicated that A549 cells that transiently expressed MEIS3 were tolerant to the deleterious effects of DON. Our data show that DON affected the expression of genes with various functions, and suggest that the repression of MEIS3 plays roles in the deleterious effect of DON in A549 lung epithelial cells.

The placenta: the forgotten essential organ of iron transport

Optimal iron nutrition in utero is essential for development of the fetus and helps establish birth iron stores adequate to sustain growth in early infancy. In species with hemochorial placentas, such as humans and rodents, iron in the maternal circulation is transferred to the fetus by directly contacting placental syncytiotrophoblasts. Early kinetic studies provided valuable data on the initial uptake of maternal transferrin, an iron-binding protein, by the placenta. However, the remaining steps of iron trafficking across syncytiotrophoblasts and through the fetal endothelium into the fetal blood remain poorly characterized. Over the last 20 years, identification of transmembrane iron transporters and the iron regulatory hormone hepcidin has greatly expanded the knowledge of cellular iron transport and its regulation by systemic iron status. In addition, emerging human and animal data demonstrating comprised fetal iron stores in severe maternal iron deficiency challenge the classic dogma of exclusive fetal control over the transfer process and indicate that maternal and local signals may play a role in regulating this process. This review compiles current data on the kinetic, molecular, and regulatory aspects of placental iron transport and considers new questions and knowledge gaps raised by these advances.

Brain Iron Metabolism Dysfunction in Parkinson's Disease

Dysfunction of iron metabolism, which includes its uptake, storage, and release, plays a key role in neurodegenerative disorders, including Parkinson's disease (PD), Alzheimer's disease, and Huntington's disease. Understanding how iron accumulates in the substantia nigra (SN) and why it specifically targets dopaminergic (DAergic) neurons is particularly warranted for PD, as this knowledge may provide new therapeutic avenues for a more targeted neurotherapeutic strategy for this disease. In this review, we begin with a brief introduction describing brain iron metabolism and its regulation. We then provide a detailed description of how iron accumulates specifically in the SN and why DAergic neurons are especially vulnerable to iron in PD. Furthermore, we focus on the possible mechanisms involved in iron-induced cell death of DAergic neurons in the SN. Finally, we present evidence in support that iron chelation represents a plausable therapeutic strategy for PD.

Functionalized protein nanocages as a platform of targeted therapy and immunodetection

To improve the therapeutic/diagnostic potentials of drugs and/or imaging contrast agents, various targeted delivery systems are actively being developed. Especially protein nanocages, hollow and highly symmetrical nanometer-sized cage structures that are self-assembled from multiple protein subunits, are emerging as powerful targeted delivery tools. Their natural abundance, biocompatibility, low toxicity, well defined size and high symmetry are a few of the favorable characteristics which render protein nanocages as near ideal carriers for pharmaceuticals and/or imaging probes. This review aims to highlight current progress in the development and application of protein nanocages in targeted drug delivery approaches with an emphasis on the use of antibodies as targeting motifs to achieve high selectivity toward specific targets.

H-Ferritin Is Preferentially Incorporated by Human Erythroid Cells through Transferrin Receptor 1 in a Threshold-Dependent Manner

Ferritin is an iron-storage protein composed of different ratios of 24 light (L) and heavy (H) subunits. The serum level of ferritin is a clinical marker of the body's iron level. Transferrin receptor (TFR)1 is the receptor not only for transferrin but also for H-ferritin, but how it binds two different ligands and the blood cell types that preferentially incorporate H-ferritin remain unknown. To address these questions, we investigated hematopoietic cell-specific ferritin uptake by flow cytometry. Alexa Fluor 488-labeled H-ferritin was preferentially incorporated by erythroid cells among various hematopoietic cell lines examined, and was almost exclusively incorporated by bone marrow erythroblasts among human primary hematopoietic cells of various lineages. H-ferritin uptake by erythroid cells was strongly inhibited by unlabeled H-ferritin but was only partially inhibited by a large excess of holo-transferrin. On the other hand, internalization of labeled holo-transferrin by these cells was not inhibited by H-ferritin. Chinese hamster ovary cells lacking functional endogenous TFR1 but expressing human TFR1 with a mutated RGD sequence, which is required for transferrin binding, efficiently incorporated H-ferritin, indicating that TFR1 has distinct binding sites for H-ferritin and holo-transferrin. H-ferritin uptake by these cells required a threshold level of cell surface TFR1 expression, whereas there was no threshold for holo-transferrin uptake. The requirement for a threshold level of TFR1 expression can explain why among primary human hematopoietic cells, only erythroblasts efficiently take up H-ferritin.

Metabolic Catastrophe in Mice Lacking Transferrin Receptor in Muscle

Transferrin receptor (Tfr1) is ubiquitously expressed, but its roles in non-hematopoietic cells are incompletely understood. We used a tissue-specific conditional knockout strategy to ask whether skeletal muscle required Tfr1 for iron uptake. We found that iron assimilation via Tfr1 was critical for skeletal muscle metabolism, and that iron deficiency in muscle led to dramatic changes, not only in muscle, but also in adipose tissue and liver. Inactivation of Tfr1 incapacitated normal energy production in muscle, leading to growth arrest and a muted attempt to switch to fatty acid β oxidation, using up fat stores. Starvation signals stimulated gluconeogenesis in the liver, but amino acid substrates became limiting and hypoglycemia ensued. Surprisingly, the liver was also iron deficient, and production of the iron regulatory hormone hepcidin was depressed. Our observations reveal a complex interaction between iron homeostasis and metabolism that has implications for metabolic and iron disorders.

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Transferrin receptor 1 is required for iron assimilation by skeletal muscle

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Selective inactivation of transferrin receptor 1 in muscle causes severe, systemic metabolic derangement

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Isolated muscle iron deficiency leads to changes in iron homeostasis in the liver

Cytoprotective effects of ferritin on doxorubicin-induced breast cancer cell death

Ferritin is a major iron storage protein and essential for iron homeostasis. It has a wide range of functions in the body including iron delivery, immunosuppression, angiogenesis, and cell proliferation. Ferritin is overexpressed in many cancer cells, but its precise role in cancer is unclear. In the present study, we examined the functional roles of ferritin in protecting the MCF-7 breast cancer cell line against treatment with the chemotherapeutic agent doxorubicin. The effects of ferritin (human liver ferritin) and doxorubicin on the human MCF-7 breast cancer cell line were evaluated using the cell viability assay. The impact of decreasing ferritin light chain (FTL) and ferritin heavy chain (FTH) expression on doxorubicin sensitivity was assessed using siRNA. Reactive oxygen species (ROS) was also measured using the fluorescence probe CM-H2DCFDA. The mechanism of modulated chemosensitivity was evaluated by western blot analysis. Ferritin treatment activated MCF-7 cell proliferation in a concentration- and time-dependent manner. While treatment with doxorubicin alone significantly increased intracelullar ROS production, the addition of ferritin decreased this ROS formation, thereby reducing doxorubicin‑induced MCF-7 cell death. The inhibition of FTL and FTH by siRNA sensitized cells to doxorubicin. Treatment with doxorubicin alone significantly induced the cell cycle‑dependent kinase inhibitor protein p21, whereas ferritin reduced p21 expression. Thus, ferritin plays a critical role in protecting MCF-7 cells against the chemotherapeutic drug doxorubicin. A targeted reduction of ferritin may be a useful strategy for overcoming chemoresistance in breast cancer.

Hypoxia-Induced Iron Accumulation in Oligodendrocytes Mediates Apoptosis by Eliciting Endoplasmic Reticulum Stress

This study was aimed at evaluating the role of increased iron accumulation in oligodendrocytes and its role in their apoptosis in the periventricular white matter damage (PWMD) following a hypoxic injury to the neonatal brain. In response to hypoxia, in the PWM, there was increased expression of proteins involved in iron acquisition, such as iron regulatory proteins (IRP1, IRP2) and transferrin receptor in oligodendrocytes. Consistent with this, following a hypoxic exposure, there was increased accumulation of iron in primary cultured oligodendrocytes. The increased concentration of iron within hypoxic oligodendrocytes was found to elicit ryanodine receptor (RyR) expression, and the expression of endoplasmic reticulum (ER) stress markers such as binding-immunoglobulin protein (BiP) and inositol-requiring enzyme (IRE)-1α. Associated with ER stress, there was reduced adenosine triphosphate (ATP) levels within hypoxic oligodendrocytes. However, treatment with deferoxamine reduced the increased expression of RyR, BiP, and IRE-1α and increased ATP levels in hypoxic oligodendrocytes. Parallel to ER stress there was enhanced reactive oxygen species production within mitochondria of hypoxic oligodendrocytes, which was attenuated when these cells were treated with deferoxamine. At the ultrastructural level, hypoxic oligodendrocytes frequently showed dilated ER and disrupted mitochondria, which became less evident in those treated with deferoxamine. Associated with these subcellular changes, the apoptosis of hypoxic oligodendrocytes was evident with an increase in p53 and caspase-3 expression, which was attenuated when these cells were treated with deferoxamine. Thus, the present study emphasizes that the excess iron accumulated within oligodendrocytes in hypoxic PWM could result in their death by eliciting ER stress and mitochondrial disruption.

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.

Apoferritin applications in nanomedicine

Nanomedicine as a continuously evolving discipline is still looking for a structure with perfect properties that is usable as a multifunctional transporter. Great potential is attributed to synthetic materials such as fullerenes, porous hollow silica nanoparticles and single-wall nanotubes, among others. However, materials that are natural to the human body are more acceptable by the organism, and thus become an attractive approach in this field of research. Ferritins are proteins that naturally occur in most living organisms throughout evolution and may be a possible transporter choice. Numerous applications have demonstrated the possibilities of iron-free ferritins, called apoferritins, serving as platforms for various nanomedical purposes This article summarizes the advantages and disadvantages of these proteins and discusses their practical applications and future perspectives.

Scavenger Receptors: Emerging Roles in Cancer Biology and Immunology

Scavenger receptors constitute a large family of evolutionally conserved protein molecules that are structurally and functionally diverse. Although scavenger receptors were originally identified based on their capacity to scavenge modified lipoproteins, these molecules have been shown to recognize and bind to a broad spectrum of ligands, including modified and unmodified host-derived molecules or microbial components. As a major subset of innate pattern recognition receptors, scavenger receptors are mainly expressed on myeloid cells and function in a wide range of biological processes, such as endocytosis, adhesion, lipid transport, antigen presentation, and pathogen clearance. In addition to playing a crucial role in maintenance of host homeostasis, scavenger receptors have been implicated in the pathogenesis of a number of diseases, e.g., atherosclerosis, neurodegeneration, or metabolic disorders. Emerging evidence has begun to reveal these receptor molecules as important regulators of tumor behavior and host immune responses to cancer. This review summarizes our current understanding on the newly identified, distinct functions of scavenger receptors in cancer biology and immunology. The potential of scavenger receptors as diagnostic biomarkers and novel targets for therapeutic interventions to treat malignancies is also highlighted.

Scavenger receptor structure and function in health and disease

Scavenger receptors (SRs) are a ‘superfamily’ of membrane-bound receptors that were initially thought to bind and internalize modified low-density lipoprotein (LDL), though it is currently known to bind to a variety of ligands including endogenous proteins and pathogens. New family of SRs and their properties have been identified in recent years, and have now been classified into 10 eukaryote families, defined as Classes A-J. These receptors are classified according to their sequences, although in each class they are further classified based in the variations of the sequence. Their ability to bind a range of ligands is reflected on the biological functions such as clearance of modified lipoproteins and pathogens. SR members regulate pathophysiological states including atherosclerosis, pathogen infections, immune surveillance, and cancer. Here, we review our current understanding of SR structure and function implicated in health and disease.

Oxidative stress and the homeodynamics of iron metabolism

Iron and oxygen share a delicate partnership since both are indispensable for survival, but if the partnership becomes inadequate, this may rapidly terminate life. Virtually all cell components are directly or indirectly affected by cellular iron metabolism, which represents a complex, redox-based machinery that is controlled by, and essential to, metabolic requirements. Under conditions of increased oxidative stress—i.e., enhanced formation of reactive oxygen species (ROS)—however, this machinery may turn into a potential threat, the continued requirement for iron promoting adverse reactions such as the iron/H2O2-based formation of hydroxyl radicals, which exacerbate the initial pro-oxidant condition. This review will discuss the multifaceted homeodynamics of cellular iron management under normal conditions as well as in the context of oxidative stress.

Macrophages and iron trafficking at the birth and death of red cells

Macrophages play a critical role in iron homeostasis via their intimate association with developing and dying red cells. Central nurse macrophages promote erythropoiesis in the erythroblastic island niche. These macrophages make physical contact with erythroblasts, enabling signaling and the transfer of growth factors and possibly nutrients to the cells in their care. Human mature red cells have a lifespan of 120 days before they become senescent and again come into contact with macrophages. Phagocytosis of red blood cells is the main source of iron flux in the body, because heme must be recycled from approximately 270 billion hemoglobin molecules in each red cell, and roughly 2 million senescent red cells are recycled each second. Here we will review pathways for iron trafficking found at the macrophage-erythroid axis, with a focus on possible roles for the transport of heme in toto.

Targeting ferritin receptors for the selective delivery of imaging and therapeutic agents to breast cancer cells

In this work the selective uptake of native horse spleen ferritin and apoferritin loaded with MRI contrast agents has been assessed in human breast cancer cells (MCF-7 and MDA-MB-231). The higher expression of L-ferritin receptors (SCARA5) led to an enhanced uptake in MCF-7 as shown in T2 and T1 weighted MR images, respectively. The high efficiency of ferritin internalization in MCF-7 has been exploited for the simultaneous delivery of curcumin, a natural therapeutic molecule endowed with antineoplastic and anti-inflammatory action, and the MRI contrast agent Gd-HPDO3A. This theranostic system is able to treat selectively breast cancer cells over-expressing ferritin receptors. By entrapping in apoferritin both Gd-HPDO3A and curcumin, it was possible to deliver a therapeutic dose of 167 μg ml(-1) (as calculated by MRI) of this natural drug to MCF-7 cells, thus obtaining a significant reduction of cell proliferation.

Macrophages and iron trafficking at the birth and death of red cells

Macrophages play a critical role in iron homeostasis via their intimate association with developing and dying red cells. Central nurse macrophages promote erythropoiesis in the erythroblastic island niche. These macrophages make physical contact with erythroblasts, enabling signaling and the transfer of growth factors and possibly nutrients to the cells in their care. Human mature red cells have a lifespan of 120 days before they become senescent and again come into contact with macrophages. Phagocytosis of red blood cells is the main source of iron flux in the body, because heme must be recycled from approximately 270 billion hemoglobin molecules in each red cell, and roughly 2 million senescent red cells are recycled each second. Here we will review pathways for iron trafficking found at the macrophage-erythroid axis, with a focus on possible roles for the transport of heme in toto.

Detection of quantitative trait loci for mineral content of Nelore longissimus dorsi muscle

Background

Beef cattle require dietary minerals for optimal health, production and reproduction. Concentrations of minerals in tissues are at least partly genetically determined. Mapping genomic regions that affect the mineral content of bovine longissimus dorsi muscle can contribute to the identification of genes that control mineral balance, transportation, absorption and excretion and that could be associated to metabolic disorders.

Methods

We applied a genome-wide association strategy and genotyped 373 Nelore steers from 34 half-sib families with the Illumina BovineHD BeadChip. Genome-wide association analysis was performed for mineral content of longissimus dorsi muscle using a Bayesian approach implemented in the GenSel software.

Results

Muscle mineral content in Bos indicus cattle was moderately heritable, with estimates ranging from 0.29 to 0.36. Our results suggest that variation in mineral content is influenced by numerous small-effect QTL (quantitative trait loci) but a large-effect QTL that explained 6.5% of the additive genetic variance in iron content was detected at 72 Mb on bovine chromosome 12. Most of the candidate genes present in the QTL regions for mineral content were involved in signal transduction, signaling pathways via integral (also called intrinsic) membrane proteins, transcription regulation or metal ion binding.

Conclusions

This study identified QTL and candidate genes that affect the mineral content of skeletal muscle. Our findings provide the first step towards understanding the molecular basis of mineral balance in bovine muscle and can also serve as a basis for the study of mineral balance in other organisms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-014-0083-3) contains supplementary material, which is available to authorized users.

Elevation in multiple serum inflammatory biomarkers predicts survival of pancreatic cancer patients with inoperable disease

PURPOSE

Cancer-associated inflammation plays a driver role in pancreatic tumor development and progression. Moreover, recent studies have implicated the inflammatory tumor microenvironment in modulating therapy response and inducing resistance. The aim of this study is to investigate the prognostic and predictive value of the inflammatory biomarkers serum ferritin and C-reactive protein (CRP) in advanced pancreatic cancer patients.

METHODS

We measured pretreatment serum ferritin and CRP levels in 159 patients with inoperable pancreatic cancer participating in a phase III trial.

RESULTS

Serum ferritin and CRP levels were examined for correlations with overall survival using Kaplan-Meier analysis. When analyzed on a categorical basis, patients with higher ferritin (>median) or CRP (>25th percentile) had shorter overall survival. Moreover, the two biomarkers were not correlated suggesting independent mechanisms of production and release. However, when patients were evaluated by their ferritin and CRP levels, only patients with elevation in both inflammatory biomarkers showed a significant decrease in overall survival.

CONCLUSIONS

Serum ferritin and CRP are independent prognostic factors for shorter survival in patients with inoperable pancreatic tumors. Moreover, the evaluation of patients based on both biomarkers suggested that their prognostic value, although independent, reflected the broader state of cancer-associated inflammation. Thus, serum ferritin and CRP should be further explored as clinical biomarkers.

Serum ferritin is an important inflammatory disease marker, as it is mainly a leakage product from damaged cells

"Serum ferritin" presents a paradox, as the iron storage protein ferritin is not synthesised in serum yet is to be found there. Serum ferritin is also a well known inflammatory marker, but it is unclear whether serum ferritin reflects or causes inflammation, or whether it is involved in an inflammatory cycle. We argue here that serum ferritin arises from damaged cells, and is thus a marker of cellular damage. The protein in serum ferritin is considered benign, but it has lost (i.e. dumped) most of its normal complement of iron which when unliganded is highly toxic. The facts that serum ferritin levels can correlate with both disease and with body iron stores are thus expected on simple chemical kinetic grounds. Serum ferritin levels also correlate with other phenotypic readouts such as erythrocyte morphology. Overall, this systems approach serves to explain a number of apparent paradoxes of serum ferritin, including (i) why it correlates with biomarkers of cell damage, (ii) why it correlates with biomarkers of hydroxyl radical formation (and oxidative stress) and (iii) therefore why it correlates with the presence and/or severity of numerous diseases. This leads to suggestions for how one might exploit the corollaries of the recognition that serum ferritin levels mainly represent a consequence of cell stress and damage.

Kinetics of iron import into developing mouse organs determined by a pup-swapping method

The kinetics of dietary iron import into various organs of mice were evaluated using a novel pup-swapping approach. Newborn pups whose bodies primarily contained (56)Fe or (57)Fe were swapped at birth such that each nursed on milk containing the opposite isotope. A pup from each litter was euthanized weekly over a 7-week period. Blood plasma was obtained, and organs were isolated typically after flushing with Ringer's buffer. (56)Fe and (57)Fe concentrations were determined for organs and plasma; organ volumes were also determined. Mössbauer spectra of equivalent (57)Fe-enriched samples were used to quantify residual blood in organs; this fraction was excluded from later analysis. Rates of import into brain, spleen, heart, and kidneys were highest during the first 2 weeks of life. In contrast, half of iron in the newborn liver exited during that time, and influx peaked later. Two mathematical models were developed to analyze the import kinetics. The only model that simulated the data adequately assumed that an iron-containing species enters the plasma and converts into a second species and that both are independently imported into organs. Consistent with this, liquid chromatography with an on-line ICP-MS detector revealed numerous iron species in plasma besides transferrin. Model fitting required that the first species, assigned to non-transferrin-bound iron, imports faster into organs than the second, assigned to transferrin-bound-iron. Non-transferrin-bound iron rather than transferrin-bound-iron appears to play the dominant role in importing iron into organs during early development of healthy mice.

L-ferritin binding to scara5: a new iron traffic pathway potentially implicated in retinopathy

Iron is essential in the retina because the heme-containing enzyme guanylate cyclase modulates phototransduction in rods and cones. Transferrin endocytosis is the classical pathway for obtaining iron from the blood circulation in the retina. However, the iron storage protein ferritin has been also recently proposed as an iron carrier. In this study, the presence of Scara5 and its binding to L-ferritin was investigated in the retina. Our results showed that Scara5, the specific receptor for L-ferritin, was expressed in mouse and human retinas in many cell types, including endothelial cells. Furthermore, we showed that intravenously injected ferritin crossed the blood retinal barrier through L-ferritin binding to Scara5 in endothelial cells. Thus, suggesting the existence of a new pathway for iron delivery and trafficking in the retina. In a murine model of photoreceptor degeneration, Scara5 was downregulated, pointing out this receptor as a potential player implicated in retinopathy and also as a possible therapeutic target.

'Ride on the ferrous wheel'--the cycle of iron in macrophages in health and disease

Iron homeostasis and macrophage biology are closely interconnected. On the one hand, iron exerts multiple effects on macrophage polarization and functionality. On the other hand, macrophages are central for mammalian iron homeostasis. The phagocytosis of senescent erythrocytes and their degradation by macrophages enable efficient recycling of iron and the maintenance of systemic iron balance. Macrophages express multiple molecules and proteins for the acquisition and utilization of iron and many of these pathways are affected by inflammatory signals. Of note, iron availability within macrophages has significant effects on immune effector functions and metabolic pathways within these cells. This review summarizes the physiological and pathophysiological aspects of macrophage iron metabolism and highlights its relevant consequences on immune function and in common diseases such as infection and atherosclerosis.

Iron-rich ferritin in the hypoxia-tolerant rodent Spalax ehrenbergi: a naturally-occurring biomarker confirms the internalization and pathways of intracellular macromolecules

The discovery of pits/caveolae in the plasmalemma advanced the study of macromolecule internalization. "Transcytosis" describes the transport of macromolecular cargo from one front of a polarized cell to the other within membrane-bounded carrier(s), via endocytosis, intracellular trafficking and exocytosis. Clathrin-mediated transcytosis is used extensively by epithelial cells, while caveolae-mediated transcytosis mostly occurs in endothelial cells. The internalization pathways were monitored by various markers, including radioisotopes, nanoparticles, enzymes, immunostains, and fluorophores. We describe an internalization pathway identified using a naturally-occurring biomarker, in vivo assembled ferritin, containing electron-dense iron cores. Iron, an essential trace metal for most living species and iron homeostasis, is crucial for cellular life. Ferritin is a ubiquitous and highly conserved archeoprotein whose main function is to store a reserve iron supply inside the cytoplasm in a non-toxic form. Ferritin is present in all organisms which have a metabolic requirement for iron and in even in organisms whose taxonomic rank is very low. The newborns of the blind mole, Spalax ehrenbergi, are born and live in a hypoxic environment and have significant iron overload in their liver and heart, but their iron metabolism has not been previously studied. These newborns, which are evolutionarily adapted to fluctuations in the environmental oxygen, have a unique ability to sequester transplacental iron and store it in ferritin without any signs of iron toxicity. Using the ferrihydrite cores of ferritin, we were able to monitor the ferritin internalization from portals of its entry into the cytosol of hepatocytes and cardiomyocytes and into the lysosomes.

NET gains and losses: the role of changing nuclear envelope proteomes in genome regulation

In recent years, our view of the nucleus has changed considerably with an increased awareness of the roles dynamic higher order chromatin structure and nuclear organization play in nuclear function. More recently, proteomics approaches have identified differential expression of nuclear lamina and nuclear envelope transmembrane (NET) proteins. Many NETs have been implicated in a range of developmental disorders as well as cell-type specific biological processes, including genome organization and nuclear morphology. While further studies are needed, it is clear that the differential nuclear envelope proteome contributes to cell-type specific nuclear identity and functions. This review discusses the importance of proteome diversity at the nuclear periphery and highlights the putative roles of NET proteins, with a focus on nuclear architecture.

The high-molecular-weight kininogen domain 5 is an intrinsically unstructured protein and its interaction with ferritin is metal mediated

High-molecular-weight kininogen domain 5 (HK5) is an angiogenic modulator that is capable of inhibiting endothelial cell proliferation, migration, adhesion, and tube formation. Ferritin can bind to a histidine-glycine-lysine-rich region within HK5 and block its antiangiogenic effects. However, the molecular intricacies of this interaction are not well understood. Analysis of the structure of HK5 using circular dichroism and nuclear magnetic resonance [(1) H, (15) N]-heteronuclear single quantum coherence determined that HK5 is an intrinsically unstructured protein, consistent with secondary structure predictions. Equilibrium binding studies using fluorescence anisotropy were used to study the interaction between ferritin and HK5. The interaction between the two proteins is mediated by metal ions such as Co(2+) , Cd(2+) , and Fe(2+) . This metal-mediated interaction works independently of the loaded ferrihydrite core of ferritin and is demonstrated to be a surface interaction. Ferritin H and L bind to HK5 with similar affinity in the presence of metals. The ferritin interaction with HK5 is the first biological function shown to occur on the surface of ferritin using its surface-bound metals.

Iron acquisition in Bacillus cereus: the roles of IlsA and bacillibactin in exogenous ferritin iron mobilization

In host-pathogen interactions, the struggle for iron may have major consequences on the outcome of the disease. To overcome the low solubility and bio-availability of iron, bacteria have evolved multiple systems to acquire iron from various sources such as heme, hemoglobin and ferritin. The molecular basis of iron acquisition from heme and hemoglobin have been extensively studied; however, very little is known about iron acquisition from host ferritin, a 24-mer nanocage protein able to store thousands of iron atoms within its cavity. In the human opportunistic pathogen Bacillus cereus, a surface protein named IlsA (Iron-regulated leucine rich surface protein type A) binds heme, hemoglobin and ferritin in vitro and is involved in virulence. Here, we demonstrate that IlsA acts as a ferritin receptor causing ferritin aggregation on the bacterial surface. Isothermal titration calorimetry data indicate that IlsA binds several types of ferritins through direct interaction with the shell subunits. UV-vis kinetic data show a significant enhancement of iron release from ferritin in the presence of IlsA indicating for the first time that a bacterial protein might alter the stability of the ferritin iron core. Disruption of the siderophore bacillibactin production drastically reduces the ability of B. cereus to utilize ferritin for growth and results in attenuated bacterial virulence in insects. We propose a new model of iron acquisition in B. cereus that involves the binding of IlsA to host ferritin followed by siderophore assisted iron uptake. Our results highlight a possible interplay between a surface protein and a siderophore and provide new insights into host adaptation of B. cereus and general bacterial pathogenesis.

Iron homeostasis is important for all living organisms; too much iron confers cell toxicity, and too little iron results in reduced cell fitness. While crucial for many cellular processes in both man and pathogens, a battle for this essential nutrient erupts during infection between the host and the invading bacteria. Iron is principally stored in ferritin, a large molecule able to bind several thousand iron ions. Although host ferritins represent a mine of iron for pathogens, studies of the mechanisms involved in its acquisition by bacteria are scarce. In the human opportunistic pathogen Bacillus cereus, the surface protein IlsA is able to bind several host iron sources in vitro. In this study, we show that IlsA acts as a ferritin receptor and enhances iron release from the ferritin through direct interaction with each ferritin subunit. Moreover, we demonstrate that the siderophore bacillibactin, a small secreted iron chelator, is essential for ferritin iron acquisition and takes part in B. cereus virulence. We propose a new iron acquisition model that provides new insights into bacterial host adaptation.

Iron homeostasis in the liver

Iron is an essential nutrient that is tightly regulated. A principal function of the liver is the regulation of iron homeostasis. The liver senses changes in systemic iron requirements and can regulate iron concentrations in a robust and rapid manner. The last 10 years have led to the discovery of several regulatory mechanisms in the liver that control the production of iron regulatory genes, storage capacity, and iron mobilization. Dysregulation of these functions leads to an imbalance of iron, which is the primary cause of iron-related disorders. Anemia and iron overload are two of the most prevalent disorders worldwide and affect over a billion people. Several mutations in liver-derived genes have been identified, demonstrating the central role of the liver in iron homeostasis. During conditions of excess iron, the liver increases iron storage and protects other tissues, namely, the heart and pancreas from iron-induced cellular damage. However, a chronic increase in liver iron stores results in excess reactive oxygen species production and liver injury. Excess liver iron is one of the major mechanisms leading to increased steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma.

Suppression of SCARA5 by Snail1 is essential for EMT-associated cell migration of A549 cells

Accumulating evidence indicates that epithelial-to-mesenchymal transition (EMT) might be a key event for cancer progression. The upregulation of Snail1, one of the most extensively studied EMT regulators, has been implicated in cancer metastasis, but the underlying mechanisms remain unclear. This study aims to identify that Snail1 targets regulating EMT-associated cancer cell migration. Human lung carcinoma A549 cells were treated with transforming growth factor beta 1 (TGF-β1), and EMT-associated phenotypic and functional alterations were monitored. TGF-β1 induced typical EMT-like morphological changes, ‘cadherin switching' and cell migration in A549 cells. TGF-β1 stimulation induced rapid and persistent upregulation of Snail1. Moreover, Snail1 upregulation was required for EMT-associated cell migration. Several metastasis suppressors with putative Snail1-binding sites in their promoters were dramatically repressed in A549 cells during TGF-β1-induced EMT. Gain- and loss-of Snail1 function experiments demonstrated that scavenger receptor class A member 5 (SCARA5) was negatively regulated by Snail1. Importantly, SCARA5 downregulation was essential for EMT-induced migration in A549 cells. The chromatin immunoprecipitation assay revealed that Snail1 could bind to the E-box elements in SCARA5 promoter, implying that SCARA5 is a direct Snail1 target modulating cancer cell mobility during EMT. In addition, we showed that DNA methyltransferase 1 was physically associated with Snail1 to silence SCARA5 expression with an unidentified DNA methylation-independent mechanism, suggesting the complexity of Snail1-mediated epigenetic regulation. Collectively, our data demonstrated that EMT-regulator Snail1 suppresses the expression of SCARA5 to promote cancer progression, highlighting the possibility to target Snail1 and SCARA5 for cancer treatment.

The hyperferritinemic syndrome: macrophage activation syndrome, Still's disease, septic shock and catastrophic antiphospholipid syndrome

BACKGROUND

Over the last few years, accumulating data have implicated a role for ferritin as a signaling molecule and direct mediator of the immune system. Hyperferritinemia is associated with a multitude of clinical conditions and with worse prognosis in critically ill patients.

DISCUSSION

There are four uncommon medical conditions characterized by high levels of ferritin, namely the macrophage activation syndrome (MAS), adult onset Still's disease (AOSD), catastrophic antiphospholipid syndrome (cAPS) and septic shock, that share a similar clinical and laboratory features, and also respond to similar treatments, suggesting a common pathogenic mechanism. Ferritin is known to be a pro-inflammatory mediator inducing expression of pro-inflammatory molecules, yet it has opposing actions as a pro-inflammatory and as an immunosuppressant. We propose that the exceptionally high ferritin levels observed in these uncommon clinical conditions are not just the product of the inflammation but rather may contribute to the development of a cytokine storm.

SUMMARY

Here we review and compare four clinical conditions and the role of ferritin as an immunomodulator. We would like to propose including these four conditions under a common syndrome entity termed "Hyperferritinemic Syndrome".

The significance of ferritin in cancer: anti-oxidation, inflammation and tumorigenesis

The iron storage protein ferritin has been continuously studied for over 70years and its function as the primary iron storage protein in cells is well established. Although the intracellular functions of ferritin are for the most part well-characterized, the significance of serum (extracellular) ferritin in human biology is poorly understood. Recently, several lines of evidence have demonstrated that ferritin is a multi-functional protein with possible roles in proliferation, angiogenesis, immunosuppression, and iron delivery. In the context of cancer, ferritin is detected at higher levels in the sera of many cancer patients, and the higher levels correlate with aggressive disease and poor clinical outcome. Furthermore, ferritin is highly expressed in tumor-associated macrophages which have been recently recognized as having critical roles in tumor progression and therapy resistance. These characteristics suggest ferritin could be an attractive target for cancer therapy because its down-regulation could disrupt the supportive tumor microenvironment, kill cancer cells, and increase sensitivity to chemotherapy. In this review, we provide an overview of the current knowledge on the function and regulation of ferritin. Moreover, we examine the literature on ferritin's contributions to tumor progression and therapy resistance, in addition to its therapeutic potential.

Iron absorption in Drosophila melanogaster

The way in which Drosophila melanogaster acquires iron from the diet remains poorly understood despite iron absorption being of vital significance for larval growth. To describe the process of organismal iron absorption, consideration needs to be given to cellular iron import, storage, export and how intestinal epithelial cells sense and respond to iron availability. Here we review studies on the Divalent Metal Transporter-1 homolog Malvolio (iron import), the recent discovery that Multicopper Oxidase-1 has ferroxidase activity (iron export) and the role of ferritin in the process of iron acquisition (iron storage). We also describe what is known about iron regulation in insect cells. We then draw upon knowledge from mammalian iron homeostasis to identify candidate genes in flies. Questions arise from the lack of conservation in Drosophila for key mammalian players, such as ferroportin, hepcidin and all the components of the hemochromatosis-related pathway. Drosophila and other insects also lack erythropoiesis. Thus, systemic iron regulation is likely to be conveyed by different signaling pathways and tissue requirements. The significance of regulating intestinal iron uptake is inferred from reports linking Drosophila developmental, immune, heat-shock and behavioral responses to iron sequestration.

Human ferritin for tumor detection and therapy

Ferritin, a major iron storage protein found in most living organisms, is composed of a 24-subunit protein cage with a hollow interior cavity. Serum ferritin serves as a critical marker to detect total body iron status. However, recent research reveals a number of novel functions of ferritin besides iron storage; for example, a ferritin receptor, transferrin receptor 1 (TfR1), has been identified and serum ferritin levels are found to be elevated in tumors. A particular new finding is that magnetoferritin nanoparticles, biomimetically synthesized using H-chain ferritin to form a 24-subunit cage with an iron oxide core, possess intrinsic dual functionality, the protein shell specifically targeting tumors and the iron oxide core catalyzing peroxidase substrates to produce a color reaction allowing visualization of tumor tissues. Here we attempt to summarize current research on ferritin, particularly newly identified functions related to tumors, in order to address current challenges and highlight future directions.