High Demand For Iron Research Articles

Novel approaches targeting ferroptosis in treatment of glioma.

Glioma is a malignant brain tumor with a high mortality rate; hence novel treatment approaches are being explored to improve patient outcomes. Ferroptosis, a newly described form of regulated cell death, is emerging as a potential therapeutic target in glioma. Ferroptosis is characterized by the accumulation of lipid peroxides due to a loss of intracellular antioxidant systems represented by the depletion of glutathione and decreased activity of glutathione peroxidase 4 (GPX4). Since glioma cells have a high demand for iron and lipid metabolism, modulation of ferroptosis may represent a promising therapeutic approach for this malignancy. Recent studies indicate that ferroptosis inducers like erastin and RSL3 display potent anticancer activity in a glioma model. In addition, therapeutic strategies, including GPX4 targeting, lipid metabolism modulation, inhibition of amino acid transporters, and ferroptosis targeting natural compounds, have shown positive results in preclinical studies. This review will provide an overview of the functions of ferroptosis in glioma and its potential as a suitable target for glioma therapy.

Effect of Eculizumab on Iron Metabolism in Transfusion-independent Patients With Paroxysmal Nocturnal Hemoglobinuria

Effect of Eculizumab on Iron Metabolism in Transfusion-independent Patients With Paroxysmal Nocturnal Hemoglobinuria

Excessive Erythrocytosis Is Not Associated With Altered Iron Homeostasis in Men From the World's Highest City.

Excessive Erythrocytosis Is Not Associated With Altered Iron Homeostasis in Men From the World's Highest City.

Prevalence of iron-deficiency anemia in pregnant women with various thalassemia genotypes: Thoughts on iron supplementation in pregnant women with thalassemia genes.

There are limited studies on iron-deficiency anemia (IDA) in carriers of various thalassemia genotypes. However, for pregnant women (PW) with high iron demand, ignoring the phenomenon of carrying the thalassemia genes combined with IDA may lead to adverse pregnancy outcomes. The hematological phenotype indexes of 15,051 PW who received a prenatal diagnosis of thalassemia in our hospital were analyzed, and the plasma ferritin (PF) of 714 anemic pregnant women (APW) was determined. The results showed that 87.43% of APW without thalassemia suffered from IDA. Among APW with various thalassemia genotypes, we found that 40.00∼77.78% of subjects with α-thalassemia silent genotypes [αCS (or QS)α/αα (40.00%), -α3.7(or 4.2)/αα (57.65%), and αWSα/αα (77.78%)] and 18.18∼84.21% of subjects with α-thalassemia minor genotypes [αCS (or QS)α/-α3.7(or 4.2) (18.18%), -α3.7(or 4.2)/-α3.7(or 4.2) (40.00%), αα/-SEA (44.55%), and αWSα/-α3.7(or 4.2) (84.21%)] developed IDA, while in subjects with α-thalassemia intermedia genotypes, only αWSα/-SEA was associated with IDA, with an incidence of 16.67%. However, the incidence of IDA in APW with common β-thalassemia minor genotypes (βCD17(A>T)/β, βCD41/42 (-TTCT)/β, βCD71/72(+A)/β, βIVS-II-654(C>T)/β, and β-28(A>G)/β) was less than 10.85%. In addition, the APW with β-thalassemia minor had a higher PF level than the APW without thalassemia. Our study is the first to reveal differences in the prevalence of IDA among PW with various thalassemia genotypes, indicating that the possibility of IDA should be fully considered when managing PW with α-thalassemia silent or minor genotypes in high-risk areas, and that iron supplementation should be monitored dynamically for PW with β-thalassemia minor genotypes.

Genomic and transcriptomic characterization revealed key adaptive mechanisms of Marinobacter hydrocarbonoclasticus NI9 for proliferation and degradation of jet fuel

Marinobacter hydrocarbonoclasticus NI9 has the ability to degrade short-chain alkanes (n-C6 to n-C8), which provides a competitive advantage over other microorganisms. Therefore, we sequenced NI9's genome and analyzed its transcriptome using RNAseq when growing in jet fuel. The genome (3.98 Mb) has at least two alkane monooxygenase genes that are differentially expressed with monooxygenase FH712_RS17105 being highly induced compared to monooxygenase FH712_RS06210. FH712_RS17105 is clustered in an operon with a long-chain-fatty-acid--CoA ligase, an aldehyde dehydrogenase family protein, and rubredoxin. The entire gene cluster was induced along with several dioxygenase and cytochrome P450 genes. Genome analyses further revealed aupA and aupB genes encoding proteins involved in the uptake of micelle-solubilized alkanes. M. hydrocarbonoclasticus NI9 cells achieved fuel tolerance through the activation of efflux pumps and blockage of the efflux pumps with an efflux pump inhibitor significantly reduced NI9 growth in fuel. We identified a fuel-inducible RND-efflux pump, which is an orthologue of the P. aeruginosa MexB. M. hydrocarbonoclasticus NI9 also induced ABC iron transport mechanisms suggesting that there is a high demand for iron during fuel degradation. The results collectively suggest that M. hydrocarbonoclasticus NI9 employ similar adaptive mechanisms to those in P. aeruginosa to proliferate in hydrocarbon-containing environments.

Proteomic Analysis of Methanococcus voltae Grown in the Presence of Mineral and Nonmineral Sources of Iron and Sulfur.

ABSTRACTIron sulfur (Fe-S) proteins are essential and ubiquitous across all domains of life, yet the mechanisms underpinning assimilation of iron (Fe) and sulfur (S) and biogenesis of Fe-S clusters are poorly understood. This is particularly true for anaerobic methanogenic archaea, which are known to employ more Fe-S proteins than other prokaryotes. Here, we utilized a deep proteomics analysis of Methanococcus voltae A3 cultured in the presence of either synthetic pyrite (FeS2) or aqueous forms of ferrous iron and sulfide to elucidate physiological responses to growth on mineral or nonmineral sources of Fe and S. The liquid chromatography-mass spectrometry (LCMS) shotgun proteomics analysis included 77% of the predicted proteome. Through a comparative analysis of intra- and extracellular proteomes, candidate proteins associated with FeS2 reductive dissolution, Fe and S acquisition, and the subsequent transport, trafficking, and storage of Fe and S were identified. The proteomic response shows a large and balanced change, suggesting that M. voltae makes physiological adjustments involving a range of biochemical processes based on the available nutrient source. Among the proteins differentially regulated were members of core methanogenesis, oxidoreductases, membrane proteins putatively involved in transport, Fe-S binding ferredoxin and radical S-adenosylmethionine proteins, ribosomal proteins, and intracellular proteins involved in Fe-S cluster assembly and storage. This work improves our understanding of ancient biogeochemical processes and can support efforts in biomining of minerals.IMPORTANCE Clusters of iron and sulfur are key components of the active sites of enzymes that facilitate microbial conversion of light or electrical energy into chemical bonds. The proteins responsible for transporting iron and sulfur into cells and assembling these elements into metal clusters are not well understood. Using a microorganism that has an unusually high demand for iron and sulfur, we conducted a global investigation of cellular proteins and how they change based on the mineral forms of iron and sulfur. Understanding this process will answer questions about life on early earth and has application in biomining and sustainable sources of energy.

Transcriptomic Analysis of the Molecular Response Mechanism of Microcystis aeruginosa to Iron Limitation Stress

Iron is an essential micronutrient for cyanobacteria. It is involved in physiological activities such as photosynthesis, respiration, and the synthesis of pigments. The impact of iron limitation on planktonic algae growth occurs in surface oceans globally, as well as in freshwater ecosystems. However, the molecular and physiological effects and response mechanism of cyanobacteria under iron-limited conditions have not been reported in detail. In this study, the effects of iron limitation on the cell density, chlorophyll content, and photosynthetic activity of Microcystis aeruginosa were determined, and transcriptome sequencing was undertaken. In a severely iron-deficient environment, the cell density and chlorophyll-a content of M. aeruginosa were significantly lower than in the iron-rich group (a 55.42% and 83.51% reduction, respectively). Similarly, the photosynthetic efficiency of M. aeruginosa was also inhibited by iron deficiency, and the maximum photochemical efficiency (Fv/Fm) of the severe iron deficiency group was only 66.72% of the control group. The transcriptome results showed that to cope with the iron-deficient environment, most genes involved in iron absorption and transport in M. aeruginosa were up-regulated. In particular, the fur and perR genes that regulate the iron uptake regulatory protein (Fur) were both up-regulated. Due to the high demand for iron in the photosynthetic electron transport chain of M. aeruginosa, most photosynthesis-related genes were down-regulated, for example, petJ, which regulates iron-containing cytochrome c6. In contrast, most of the genes related to glycolysis and respiration were up-regulated. These changes in gene expression may be a survival strategy for M. aeruginosa to cope with a long-term iron-deficient environment. This study provides insights into the molecular response mechanism of M. aeruginosa under iron limitation stress.

Examining Pathways of Iron and Sulfur Acquisition, Trafficking, Deployment, and Storage in Mineral-Grown Methanogen Cells.

ABSTRACTMethanogens have a high demand for iron (Fe) and sulfur (S); however, little is known of how they acquire, deploy, and store these elements and how this, in turn, affects their physiology. Methanogens were recently shown to reduce pyrite (FeS2), generating aqueous iron sulfide (FeSaq) clusters that are likely assimilated as a source of Fe and S. Here, we compared the phenotypes of Methanococcus voltae grown with FeS2 or ferrous iron [Fe(II)] and sulfide (HS−). FeS2-grown cells are 33% smaller yet have 193% more Fe than Fe(II)/HS−-grown cells. Whole-cell electron paramagnetic resonance revealed similar distributions of paramagnetic Fe, although FeS2-grown cells showed a broad spectral feature attributed to intracellular thioferrate-like nanoparticles. Differential proteomic analyses showed similar expression of core methanogenesis enzymes, indicating that Fe and S source does not substantively alter the energy metabolism of cells. However, a homolog of the Fe(II) transporter FeoB and its putative transcriptional regulator DtxR were up-expressed in FeS2-grown cells, suggesting that cells sense Fe(II) limitation. Two homologs of IssA, a protein putatively involved in coordinating thioferrate nanoparticles, were also up-expressed in FeS2-grown cells. We interpret these data to indicate that, in FeS2-grown cells, DtxR cannot sense Fe(II) and therefore cannot downregulate FeoB. We suggest this is due to the transport of Fe(II) complexed with sulfide (FeSaq), leading to excess Fe that is sequestered by IssA as a thioferrate-like species. This model provides a framework for the design of targeted experiments aimed at further characterizing Fe acquisition and homeostasis in M. voltae and other methanogens.IMPORTANCE FeS2 is the most abundant sulfide mineral in the Earth’s crust and is common in environments inhabited by methanogenic archaea. FeS2 can be reduced by methanogens, yielding aqueous FeSaq clusters that are thought to be a source of Fe and S. Here, we show that growth of Methanococcus voltae on FeS2 results in smaller cell size and higher Fe content per cell, with Fe likely stored intracellularly as thioferrate-like nanoparticles. Fe(II) transporters and storage proteins were upregulated in FeS2-grown cells. These responses are interpreted to result from cells incorrectly sensing Fe(II) limitation due to assimilation of Fe(II) as FeSaq. These findings have implications for our understanding of how Fe/S availability influences methanogen physiology and the biogeochemical cycling of these elements.

Genome-Wide CRISPR/Cas9-Mediated Loss-of-Function Screening in Human Erythroleukemic Cells Identifies Novel Cellular Components Involved in Iron and Heme Trafficking

To meet the high demand for iron during erythropoiesis, erythroid precursors utilize efficient yet tightly regulated mechanisms of iron trafficking. Transferrin-bound iron (TBI), the major cellular iron source for erythroid cells under physiological conditions, is taken up through the transferrin receptor (TfR) by endocytosis. Non-transferrin bound iron (NTBI), which exists in the circulation under conditions of iron overload, is also utilized by erythroid cells and its uncontrolled uptake by erythroid precursors presumably results in ineffective erythropoiesis (IE). The majority of iron acquired by erythroid cells is incorporated into heme in the mitochondria. Cellular trafficking of heme is indispensable for erythropoiesis and many other essential biological processes. Comprehensive elucidation of molecular pathways governing and regulating cellular iron acquisition and heme trafficking is required to better understand physiological and pathological processes affecting erythropoiesis. In this study, we employed a functional approach to identify cellular components involved in TBI and NTBI uptake and heme trafficking in human erythroid cells. We performed genome-wide loss-of-function screens using the CRISPR-Cas9 system in K562 erythroleukemic cells, which can utilize either TBI or NTBI as an essential iron source for proliferation and can be differentiated into erythroid cells by hemin. In addition to genes that are known to be involved in the studied processes, our approach revealed novel candidates whose roles in iron uptake, heme trafficking and erythroid differentiation were validated using targeted confirmatory approaches. Our screen on iron uptake identified 25 genes potentially involved in TBI acquisition in addition to 18 NTBI uptake candidate genes. The transferrin receptor (TfR1) was one of the top TBI uptake candidates indicating that our approach effectively revealed mechanistically relevant components in the process. Unsurprisingly, several components of the endocytic pathway were shown potentially indispensable for transferrin acquisition. We identified a role for the vacuolar-type H+ - ATPase (V-ATPase) assembly factor CCDC115 in TBI uptake and validated this role by generating individual CCDC115 deficient K562 cells. Our study on heme trafficking revealed several candidate genes relevant to cellular heme uptake, heme-induced differentiation and heme export. Pathway analysis indicates a major role for clathrin-mediated endocytosis and vesicle acidification in heme acquisition by K562 cells. Interestingly, we demonstrated that CCDC115, which was also identified as a significant heme uptake candidate, is indispensable for heme-induced hemoglobinization. We further identified components involved in heme detoxification including two ATP-binding cassette (ABC) transporters that could play a critical unrevealed role in mitochondrial and cellular heme export. Our work demonstrates the strength of functional genomics in studying the various mechanisms affecting erythropoiesis. DisclosuresFraenkel:Sanofi: Employment, Other: Sanofi had no role in funding or influencing this study.

Ferroportin 3 is a dual-targeted mitochondrial/chloroplast iron exporter necessary for iron homeostasis in Arabidopsis.

Mitochondria and chloroplasts are organelles with high iron demand that are particularly susceptible to iron-induced oxidative stress. Despite the necessity of strict iron regulation in these organelles, much remains unknown about mitochondrial and chloroplast iron transport in plants. Here, we propose that Arabidopsis ferroportin3 (FPN3) is an iron exporter that is dual-targeted to mitochondria and chloroplasts. FPN3 is expressed in shoots, regardless of iron conditions, but its transcripts accumulate under iron deficiency in roots. fpn3 mutants cannot grow as well as the wild type under iron-deficient conditions and their shoot iron levels are lower compared with the wild type. Analyses of iron homeostasis gene expression in fpn3 mutants and inductively coupled plasma mass spectrometry (ICP-MS) measurements show that iron levels in the mitochondria and chloroplasts are increased relative to the wild type, consistent with the proposed role of FPN3 as a mitochondrial/plastid iron exporter. In iron-deficient fpn3 mutants, abnormal mitochondrial ultrastructure was observed, whereas chloroplast ultrastructure was not affected, implying that FPN3 plays a critical role in the mitochondria. Overall, our study suggests that FPN3 is essential for optimal iron homeostasis.

Pathways of Iron and Sulfur Acquisition, Cofactor Assembly, Destination, and Storage in Diverse Archaeal Methanogens and Alkanotrophs.

ABSTRACTArchaeal methanogens, methanotrophs, and alkanotrophs have a high demand for iron (Fe) and sulfur (S); however, little is known of how they acquire, traffic, deploy, and store these elements. Here, we examined the distribution of homologs of proteins mediating key steps in Fe/S metabolism in model microorganisms, including iron(II) sensing/uptake (FeoAB), sulfide extraction from cysteine (SufS), and the biosynthesis of iron-sulfur [Fe-S] clusters (SufBCDE), siroheme (Pch2 dehydrogenase), protoheme (AhbABCD), cytochrome c (Cyt c) (CcmCF), and iron storage/detoxification (Bfr, FtrA, and IssA), among 326 publicly available, complete or metagenome-assembled genomes of archaeal methanogens/methanotrophs/alkanotrophs. The results indicate several prevalent but nonuniversal features, including FeoB, SufBC, and the biosynthetic apparatus for the basic tetrapyrrole scaffold, as well as its siroheme (and F430) derivatives. However, several early-diverging genomes lacked SufS and pathways to synthesize and deploy heme. Genomes encoding complete versus incomplete heme biosynthetic pathways exhibited equivalent prevalences of [Fe-S] cluster binding proteins, suggesting an expansion of catalytic capabilities rather than substitution of heme for [Fe-S] in the former group. Several strains with heme binding proteins lacked heme biosynthesis capabilities, while other strains with siroheme biosynthesis capability lacked homologs of known siroheme binding proteins, indicating heme auxotrophy and unknown siroheme biochemistry, respectively. While ferritin proteins involved in ferric oxide storage were widespread, those involved in storing Fe as thioferrate were unevenly distributed. Collectively, the results suggest that differences in the mechanisms of Fe and S acquisition, deployment, and storage have accompanied the diversification of methanogens/methanotrophs/alkanotrophs, possibly in response to differential availability of these elements as these organisms evolved.IMPORTANCE Archaeal methanogens, methanotrophs, and alkanotrophs, argued to be among the most ancient forms of life, have a high demand for iron (Fe) and sulfur (S) for cofactor biosynthesis, among other uses. Here, using comparative bioinformatic approaches applied to 326 genomes, we show that major differences in Fe/S acquisition, trafficking, deployment, and storage exist in this group. Variation in these characters was generally congruent with the phylogenetic placement of these genomes, indicating that variation in Fe/S usage and deployment has contributed to the diversification and ecology of these organisms. However, incongruency was observed among the distribution of cofactor biosynthesis pathways and known protein destinations for those cofactors, suggesting auxotrophy or yet-to-be-discovered pathways for cofactor biosynthesis.

Low sediment redox promotes cyanobacteria blooms across a trophic range: implications for management

Molot LA, Schiff SL, Venkiteswaran JJ, Baulch HM, Higgins SN, Zastepa A, Verschoor MJ, Walters D. 2021. Low sediment redox promotes cyanobacteria blooms across a trophic range: implications for management. Lake Reserv Manage. 37:120–142. Field observations and experimental manipulations with different oxidizing agents including nitrate demonstrate that high sediment redox prevents cyanobacteria blooms in eutrophic freshwaters. Conversely, low sediment redox caused by depletion of dissolved oxygen and nitrate allows blooms to form. This explains why bloom risk increases with phosphorus levels: Higher productivity increases the spatial and temporal extent of low sediment redox. The intermediate link between low redox and cyanobacteria blooms appears to be internal loading of ferrous iron (Fe2+) from reduced sediments with diffusion to depths accessible to migrating cyanobacteria, providing a source for their high iron demand. Regardless of whether Fe2+ release is the intermediate link, the concept of “low sediment redox as promoter” has major potential to improve bloom management if managers consider the impact of their nutrient management choices, nutrient targets, and in-lake methods on sediment redox. Phosphorus input targets can be adjusted as climate change alters the extent of anoxia, and short-term bloom prediction models that incorporate the sediment redox concept could predict onset of blooms earlier than current models that depend on detection of photosynthetic pigments associated with blooms.

A unique porin meditates iron‐selective transport through cyanobacterial outer membranes

Cyanobacteria are globally important primary producers and nitrogen fixers with high iron demands. Low ambient dissolved iron concentrations in many aquatic environments mean that these organisms must maintain sufficient and selective transport of iron into the cell. However, the nature of iron transport pathways through the cyanobacterial outer membrane remains obscure. Here we present multiple lines of experimental evidence that collectively support the existence of a novel class of substrate-selective iron porin, Slr1908, in the outer membrane of the cyanobacterium Synechocystis sp. PCC 6803. Elemental composition analysis and short-term iron uptake assays with mutants in Slr1908 reveal that this protein is primarily involved in inorganic iron uptake and contributes less to the accumulation of other metals. Homologues of Slr1908 are widely distributed in both freshwater and marine cyanobacteria, most notably in unicellular marine diazotrophs. Complementary experiments with a homologue of Slr1908 in Synechococcus sp. PCC 7002 restored the phenotype of Synechocystis knockdown mutants, showing that this siderophore producing species also possesses a porin with a similar function in Fe transport. The involvement of a substrate-selective porins in iron uptake may allow cyanobacteria to tightly control iron flux into the cell, particularly in environments where iron concentrations fluctuate.

Endocytosis, signal transduction and proteolytic cleaving of human holotransferrin in Entamoeba histolytica

Amoebiasis is a parasitic infection of the human large intestine caused by Entamoeba histolytica; this disease mainly affects people from developing countries. To survive, this primitive protozoan has a high demand for iron, and it uses host iron proteins upon invasion. Transferrin (Tf) is a plasma iron-binding protein that transports and delivers iron to all cells. Iron-loaded Tf (holoTf) in humans can support the proliferation of amoebae in vitro by binding to an amoebic TfR (EhTfR), and amoebae endocytose it inside clathrin-coated vesicles. In this study, it was found that EhTfR phosphorylation is required for human holoTf endocytosis by E. histolytica. Once this complex is endocytosed, human holoTf could be degraded with a nutritional purpose by cysteine proteases. HoloTf endocytosis initiates the activation of the mitogen-activated protein kinases (MAPKs) and focal adhesion kinase (FAK) pathways, which induce cell proliferation with phosphoinositide 3-kinase (PI-3 K) and Ca2+ involvement. In the first minutes after holoTf is endocytosed, several proteins are phosphorylated including transketolase, enolase, L-myo-inositol-1-phosphate synthase and phosphoglucomutase, which control carbohydrate metabolism, and heat shock protein-70. The study of these proteins and their signal transduction pathways could be useful for developing future therapies.

The Medicago truncatula Vacuolar iron Transporter-Like proteins VTL4 and VTL8 deliver iron to symbiotic bacteria at different stages of the infection process.

Summary The symbiotic relationship between legumes and rhizobium bacteria in root nodules has a high demand for iron, and questions remain regarding which transporters are involved. Here, we characterize two nodule‐specific Vacuolar iron Transporter‐Like (VTL) proteins in Medicago truncatula.Localization of fluorescent fusion proteins and mutant studies were carried out to correlate with existing RNA‐seq data showing differential expression of VTL4 and VTL8 during early and late infection, respectively.The vtl4 insertion lines showed decreased nitrogen fixation capacity associated with more immature nodules and less elongated bacteroids. A mutant line lacking the tandemly‐arranged VTL4–VTL8 genes, named 13U, was unable to develop functional nodules and failed to fix nitrogen, which was almost fully restored by expression of VTL8 alone. Using a newly developed lux reporter to monitor iron status of the bacteroids, a moderate decrease in luminescence signal was observed in vtl4 mutant nodules and a strong decrease in 13U nodules. Iron transport capability of VTL4 and VTL8 was shown by yeast complementation.These data indicate that VTL8, the closest homologue of SEN1 in Lotus japonicus, is the main route for delivering iron to symbiotic rhizobia. We propose that a failure in iron protein maturation leads to early senescence of the bacteroids.

In vitro assessment of the cytotoxicity of Gallium(III) complexes with Isoniazid-Derived Hydrazones: Effects on clonogenic survival of HCT-116 cells

Cancer cells have high iron demand to mediate their rapid proliferation. Aiming to obtain cytotoxic compounds with potential iron metabolism disturbance in malignant cells, [Ga(HAPIH)(APIH)](NO3)2⋅2H2O (1) and [Ga(HPAmIH)(PAmIH)](NO3)2⋅2H2O (2) were synthesized with the iron chelators 2-acetylpyridine- and 2-pyridineformamide isonicotinoyl hydrazone (HAPIH and HPAmIH, respectively) and gallium(III), an iron(III) mimetic. The hydrazones and their gallium(III) complexes were assayed for their action against HL-60 (leukemia), MCF-7 (breast cancer), HCT-116 (colorectal carcinoma) and PC3 (prostate cancer) tumor cell lines, as well as non-malignant Human Embryonic Kidney293 (HEK-293) cells. HAPIH and its complex 1 were the most cytotoxic compounds, with HCT-116 being the most susceptible line (IC50 = 1.6 μM for HAPIH and 0.4 μM for complex 1). Moreover, the compounds proved to be at least 25-fold less toxic to HEK-293 than to the tumor cells. According to clonogenic survival assays, the relative number of colonies formed by HCT-116 cells was reduced by around 95% after pretreatment with HAPIH and 1 at their IC90 concentrations (18 μM and 4 μM, respectively). Both compounds were also able to inhibit the cell cycle and increased the subdiploid DNA content of HCT-116 after 24 h treatment, which suggests they possess a pro-apoptotic potential.

The Importance of Iron Status for Young Children in Low- and Middle-Income Countries: A Narrative Review.

Early childhood is characterised by high physiological iron demand to support processes including blood volume expansion, brain development and tissue growth. Iron is also required for other essential functions including the generation of effective immune responses. Adequate iron status is therefore a prerequisite for optimal child development, yet nutritional iron deficiency and inflammation-related iron restriction are widespread amongst young children in low- and middle-income countries (LMICs), meaning iron demands are frequently not met. Consequently, therapeutic iron interventions are commonly recommended. However, iron also influences infection pathogenesis: iron deficiency reduces the risk of malaria, while therapeutic iron may increase susceptibility to malaria, respiratory and gastrointestinal infections, besides reshaping the intestinal microbiome. This means caution should be employed in administering iron interventions to young children in LMIC settings with high infection burdens. In this narrative review, we first examine demand and supply of iron during early childhood, in relation to the molecular understanding of systemic iron control. We then evaluate the importance of iron for distinct aspects of physiology and development, particularly focusing on young LMIC children. We finally discuss the implications and potential for interventions aimed at improving iron status whilst minimising infection-related risks in such settings. Optimal iron intervention strategies will likely need to be individually or setting-specifically adapted according to iron deficiency, inflammation status and infection risk, while maximising iron bioavailability and considering the trade-offs between benefits and risks for different aspects of physiology. The effectiveness of alternative approaches not centred around nutritional iron interventions for children should also be thoroughly evaluated: these include direct targeting of common causes of infection/inflammation, and maternal iron administration during pregnancy.

MiR-148a regulates expression of the transferrin receptor 1 in hepatocellular carcinoma

Transferrin receptor 1 (TFR1) is a transmembrane glycoprotein that allows for transferrin-bound iron uptake in mammalian cells. It is overexpressed in various cancers to satisfy the high iron demand of fast proliferating cells. Here we show that in hepatocellular carcinoma (HCC) TFR1 expression is regulated by miR-148a. Within the TFR1 3′UTR we identified and experimentally validated two evolutionarily conserved miRNA response elements (MREs) for miR-148/152 family members, including miR-148a. Interestingly, analyses of RNA sequencing data from patients with liver hepatocellular carcinoma (LIHC) revealed a significant inverse correlation of TFR1 mRNA levels and miR-148a. In addition, TFR1 mRNA levels were significantly increased in the tumor compared to matched normal healthy tissue, while miR-148a levels are decreased. Functional analysis demonstrated post-transcriptional regulation of TFR1 by miR-148a in HCC cells as well as decreased HCC cell proliferation upon either miR-148a overexpression or TFR1 knockdown. We hypothesize that decreased expression of miR-148a in HCC may elevate transferrin-bound iron uptake, increasing cellular iron levels and cell proliferation.

On Demand Recruitment of Macrophages Is Required for Erythroid Niche Formation during Stress Erythropoiesis in the Bone Marrow

Every second more than 2 million new erythrocytes are released from the bone marrow of human adults, highlighting the tremendous turn-over of these cells. In parallel to hematopoietic stem cell niches, the last stages of erythropoiesis take place in specialized bone marrow niches, termed ‘erythroid niches’. Concretely, the erythroid niche is composed of a ‘central macrophage’ which is surrounded by erythroid progenitor cells. Regardless of steady-state or stress erythropoiesis, iron availability is, beside erythropoietin, a key factor determining erythroid output and red blood cell quality, as reflected by hemoglobin content of these cells. It is well established that systemic iron availability for erythropoiesis, in the form of iron saturated transferrin (Tf), is mainly maintained via a recycling process of senescent red blood cells, which takes place in macrophages of the reticuloendothelial system. Yet, it is still a matter of debate if also central macrophages are involved in iron supply for red blood cell development in a more direct way due to their close proximity to developing red blood cells. Using a myeloid-specific knockout mouse strain, lacking the solely known iron exporter ferroportin (Fpn; Fpnfl/flLysMCre+/+ mice) and specific reporter mice (ROSA26tdTomatofl/fl Cx3cr1CreERT2 mice), we examined the connection between iron metabolism, erythropoiesis and central macrophages.Analysis of Fpnfl/flLysMCre+/+ animals at steady state revealed microcytic anemia, higher tissue iron loading, reduced hepatic hepcidin expression and distorted erythroid precursor population distribution in the bone marrow with no significant chances in Tf saturation (Tf-Sat). The latter is giving a first hint, that local bone marrow Fpn expression on macrophages may be important for iron supply for erythropoiesis. Strikingly, further work up via flow cytometry demonstrated that disturbances seen in bone marrow erythropoiesis were accompanied by nearby loss of resident bone marrow macrophages (defined as CD11blo, F4/80pos, MerTKpos). In parallel, a CD11bhi, F4/80pos, MerTKpos population came into existence, suggesting that these cells may compensate for the loss of ‘canonical’ central macrophages.Attempting to explain these intriguing results, we sought to investigate differentiation pathways and turnover of bone marrow central macrophages. First, we used the ROSA26tdTomatofl/fl Cx3cr1CreERT2 monocyte-specific reporter mice and techniques of transient monocyte labelling in utero and in adult phlebotomized animals to determine the origin of central macrophages. We could show that those cells undergo constant replenishment by circulating monocytes. Notably, the rate of this process got markedly increased upon recovery from blood loss and concomitant expansion of the central macrophage population. Second, by administration of a CCR2/CCR5 inhibitor (cenicriviroc), diminishing monocyte egress from the bone marrow and tissue infiltration, we could demonstrate decreased reticulocyte count during stress erythropoiesis, thus strengthening the direct impact of macrophages to support effective erythroid output.Next, effects of stress-induced erythropoiesis were investigated in Fpnfl/flLysMCre+/+ compared to Fpnfl/flLysMCre-/- mice. Amelioration of anemia after phlebotomy was extended, microcytosis was more pronounced and reticulocyte egress was diminished but prolonged. Of interest, Fpnfl/flLysMCre+/+ mice on a diet containing an 8-times higher iron content during phlebotomy, thus transiently increasing Tf-Sat, recovered from anemia wildtype-like. These results indicate that stress erythropoiesis with a high iron demand depends, under normal iron availability, in part on central macrophages and their nursing function to overcome the increased demand of iron.Ongoing experiments aim to identify how recruited bone marrow macrophages, i.e. central macrophages, contribute to erythropoiesis during stress - if central macrophages directly supply developing erythroid cells with iron in a Tf-free fashion or, if they are suppliers of additional growth factors that work synergistically with the Tf-bound iron to drive hemoglobin production. In summary our data clearly show that macrophages need to be recruited to the bone marrow for effective erythroid output during stress erythropoiesis. DisclosuresWeiss:Kymab Ltd.: Consultancy. Theurl:Kymab Ltd.: Consultancy, Research Funding.

Mineral iron utilization by natural and cultured Trichodesmium and associated bacteria

AbstractThe high iron (Fe) demands of Trichodesmium, a keystone nitrogen‐fixing cyanobacterium, are often met by dust deposition at the ocean surface. Following up on our findings of unique dust capturing and processing by Trichodesmium, we explored the ability of natural Trichodesmium colonies from the Gulf of Aqaba and Fe‐limited laboratory culture (IMS101) to obtain Fe from the mineral ferrihydrite and compete with their epibiotic bacteria for this Fe source. To study this complex system, we carefully optimized a radiotracer method ensuring complete removal of external ferrihydrite and efficient separation of bacteria from the colonies. Trichodesmium‐only uptake rates of natural colonies were 5–50 times faster than those of laboratory culture, suggesting that natural colonies acquire ferrihydrite at a greater efficiency. In some days, total uptake rates of natural colonies exceeded dissolved Fe release from ferrihydrite, indicating that the colonies enhance the mineral dissolution rate. Furthermore, uptake rates of bacteria associated with natural colonies were faster than those of bacteria associated with the culture, implying that the bacteria benefit from the Trichodesmium‐enhanced mineral dissolution. At the cellular level, surface area normalized uptake rates of bacteria always exceeded those of cultured Trichodesmium, but in natural populations, the dominance shifted between Trichodesmium and bacteria on different days. At the community level, when accounting for the total bacteria and Trichodesmium cells, Trichodesmium dominated Fe uptake in both cultured and natural colonies. Overall, our findings suggest that natural Trichodesmium colonies are exceptionally adapted for accessing mineral Fe and maintaining a sustainable relationship with their associated bacteria.