The IRP1-HIF-2α axis coordinates iron and oxygen sensing with erythropoiesis and iron absorption

Isomer of per- and polyfluoroalkyl substances and red blood cell indices in adults: The Isomers of C8 Health Project in China

This study aimed to explore the isomer-specific, sex-specific, and joint associations of PFAS and red blood cell indices. We used data of 1,238 adults from the Isomers of C8 Health Project in China. Associations of PFAS isomers and red blood cell indices were explored using multiple linear regression models, Bayesian Kernel Machine Regression models and subgroup analysis across sex. We found that serum concentration of linear (n-) and branched (Br-) isomers of perfluorooctane sulfonate (PFOS) and perfluorohexanesulfonic acid (PFHxS) were significantly associated with red blood cell indices in single-pollutant models, with stronger associations observed for n-PFHxS than Br-PFHxS, in women than in men. For instance, the estimated percentage change in hemoglobin concentration for n-PFHxS (3.65%; 95% CI: 2.95%, 4.34%) was larger than that for Br-PFHxS (0.96%; 95% CI: 0.52%, 1.40%). The estimated percentage change in red blood cell count for n-PFHxS in women (2.55%; 95% CI: 1.81%, 3.28%) was significantly higher than that in men (0.12%; 95% CI: -1.04%, 1.29%) (Pinter < 0.001). Similarly, sex-specific positive association of PFAS mixture and outcomes was observed. Therefore, the structure, susceptive population, and joint effect of PFAS isomers should be taken into consideration when evaluating the health risk of chemicals.

Ferroptosis in Parkinson's disease -- The iron-related degenerative disease

Parkinson's disease (PD) is a prevalent and advancing age-related neurodegenerative disorder, distinguished by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Iron regional deposit in SNpc is a significant pathological characteristic of PD. Brain iron homeostasis is precisely regulated by iron metabolism related proteins, whereas disorder of these proteins can damage neurons and glial cells in the brain. Additionally, growing studies have reported iron metabolism related proteins are involved in the ferroptosis progression in PD. However, the effect of these proteins in the ferroptosis of PD has not been systematically summarized. This review focuses on the roles of iron metabolism related proteins in the ferroptosis of PD. Finally, we put forward the iron early diagnosis according to the observation of iron deposits in the brain and showed the recent advances in iron chelation therapy in PD.

Iron regulatory protein 2 contributes to antimicrobial immunity by preserving lysosomal function in macrophages

Colorectal cancer and Crohn's disease patients develop pyogenic liver abscesses due to failures of immune cells to fight off bacterial infections. Here, we show that mice lacking iron regulatory protein 2 (Irp2), globally (Irp2-/-) or myeloid cell lineage (Lysozyme 2 promoter-driven, LysM)-specifically (Irp2ΔLysM), are highly susceptible to liver abscesses when the intestinal tissue was injured with dextran sodium sulfate treatment. Further studies demonstrated that Irp2 is required for lysosomal acidification and biogenesis, both of which are crucial for bacterial clearance. In Irp2-deficient liver tissue or macrophages, the nuclear location of transcription factor EB (Tfeb) was remarkably reduced, leading to the downregulation of Tfeb target genes that encode critical components for lysosomal biogenesis. Tfeb mislocalization was reversed by hypoxia-inducible factor 2 inhibitor PT2385 and, independently, through inhibition of lactic acid production. These experimental findings were confirmed clinically in patients with Crohn's disease and through bioinformatic searches in databases from Crohn's disease or ulcerative colitis biopsies showing loss of IRP2 and transcription factor EB (TFEB)-dependent lysosomal gene expression. Overall, our study highlights a mechanism whereby Irp2 supports nuclear translocation of Tfeb and lysosomal function, preserving macrophage antimicrobial activity and protecting the liver against invading bacteria during intestinal inflammation.

Diurnal control of iron responsive element containing mRNAs through iron regulatory proteins IRP1 and IRP2 is mediated by feeding rhythms

BACKGROUND

Cellular iron homeostasis is regulated by iron regulatory proteins (IRP1 and IRP2) that sense iron levels (and other metabolic cues) and modulate mRNA translation or stability via interaction with iron regulatory elements (IREs). IRP2 is viewed as the primary regulator in the liver, yet our previous datasets showing diurnal rhythms for certain IRE-containing mRNAs suggest a nuanced temporal control mechanism. The purpose of this study is to gain insights into the daily regulatory dynamics across IRE-bearing mRNAs, specific IRP involvement, and underlying systemic and cellular rhythmicity cues in mouse liver.

RESULTS

We uncover high-amplitude diurnal oscillations in the regulation of key IRE-containing transcripts in the liver, compatible with maximal IRP activity at the onset of the dark phase. Although IRP2 protein levels also exhibit some diurnal variations and peak at the light-dark transition, ribosome profiling in IRP2-deficient mice reveals that maximal repression of target mRNAs at this timepoint still occurs. We further find that diurnal regulation of IRE-containing mRNAs can continue in the absence of a functional circadian clock as long as feeding is rhythmic.

CONCLUSIONS

Our findings suggest temporally controlled redundancy in IRP activities, with IRP2 mediating regulation of IRE-containing transcripts in the light phase and redundancy, conceivably with IRP1, at dark onset. Moreover, we highlight the significance of feeding-associated signals in driving rhythmicity. Our work highlights the dynamic nature and regulatory complexity in a metabolic pathway that had previously been considered well-understood.

Crosstalk between oxygen signaling and iron metabolism in renal interstitial fibroblasts

To maintain the oxygen supply, the production of red blood cells (erythrocytes) is promoted under low-oxygen conditions (hypoxia). Oxygen is carried by hemoglobin in erythrocytes, in which the majority of the essential element iron in the body is contained. Because iron metabolism is strictly controlled in a semi-closed recycling system to protect cells from oxidative stress caused by iron, hypoxia-inducible erythropoiesis is closely coordinated by regulatory systems that mobilize stored iron for hemoglobin synthesis. The erythroid growth factor erythropoietin (EPO) is mainly secreted by interstitial fibroblasts in the renal cortex, which are known as renal EPO-producing (REP) cells, and promotes erythropoiesis and iron mobilization. Intriguingly, EPO production is strongly induced by hypoxia through iron-dependent pathways in REP cells. Here, we summarize recent studies on the network mechanisms linking hypoxia-inducible EPO production, erythropoiesis and iron metabolism. Additionally, we introduce disease mechanisms related to disorders in the network mediated by REP cell functions. Furthermore, we propose future studies regarding the application of renal cells derived from the urine of kidney disease patients to investigate the molecular pathology of chronic kidney disease and develop precise and personalized medicine for kidney disease.

Iron, Copper, and Selenium: Cancer's Thing for Redox Bling

Cells require micronutrients for numerous basic functions. Among these, iron, copper, and selenium are particularly critical for redox metabolism, and their importance is heightened during oncogene-driven perturbations in cancer. In this review, which particularly focuses on iron, we describe how these micronutrients are carefully chaperoned about the body and made available to tissues, a process that is designed to limit the toxicity of free iron and copper or by-products of selenium metabolism. We delineate perturbations in iron metabolism and iron-dependent proteins that are observed in cancer, and describe the current approaches being used to target iron metabolism and iron-dependent processes.

Contrasting Iron Metabolism in Undifferentiated Versus Differentiated MO3.13 Oligodendrocytes via IL-1β-Induced Iron Regulatory Protein 1

Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by the loss of dopaminergic neurons and the accumulation of iron in the substantia nigra. While iron accumulation and inflammation are implicated in PD pathogenesis, their impact on oligodendrocytes, the brain's myelin-forming cells, remains elusive. This study investigated the influence of interleukin-1β (IL-1β), an elevated proinflammatory cytokine in PD, on iron-related proteins in MO3.13 oligodendrocytes. We found that IL-1β treatment in undifferentiated MO3.13 oligodendrocytes increased iron regulatory protein 1 and transferrin receptor 1 (TfR1) expression while decreasing ferroportin 1 (FPN1) expression. Consequently, iron uptake was enhanced, and iron release was reduced, leading to intracellular iron accumulation. Conversely, IL-1β treatment in differentiated MO3.13 oligodendrocytes exhibited the opposite effect, with decreased TfR1 expression, increased FPN1 expression, and reduced iron uptake. These findings suggest that IL-1β-induced dysregulation of iron metabolism in oligodendrocytes may contribute to the pathological processes observed in PD. IL-1β can increase the iron content in undifferentiated oligodendrocytes, thus facilitating the differentiation of undifferentiated MO3.13 oligodendrocytes. In differentiated oligodendrocytes, IL-1β may facilitate iron release, providing a potential source of iron for neighboring dopaminergic neurons, thereby initiating a cascade of deleterious events. This study provides valuable insights into the intricate interplay between inflammation, abnormal iron accumulation, and oligodendrocyte dysfunction in PD. Targeting the IL-1β-mediated alterations in iron metabolism may hold therapeutic potential for mitigating neurodegeneration and preserving dopaminergic function in PD.

Mechanisms controlling cellular and systemic iron homeostasis

In mammals, hundreds of proteins use iron in a multitude of cellular functions, including vital processes such as mitochondrial respiration, gene regulation and DNA synthesis or repair. Highly orchestrated regulatory systems control cellular and systemic iron fluxes ensuring sufficient iron delivery to target proteins is maintained, while limiting its potentially deleterious effects in iron-mediated oxidative cell damage and ferroptosis. In this Review, we discuss how cells acquire, traffick and export iron and how stored iron is mobilized for iron-sulfur cluster and haem biogenesis. Furthermore, we describe how these cellular processes are fine-tuned by the combination of various sensory and regulatory systems, such as the iron-regulatory protein (IRP)-iron-responsive element (IRE) network, the nuclear receptor co-activator 4 (NCOA4)-mediated ferritinophagy pathway, the prolyl hydroxylase domain (PHD)-hypoxia-inducible factor (HIF) axis or the nuclear factor erythroid 2-related factor 2 (NRF2) regulatory hub. We further describe how these pathways interact with systemic iron homeostasis control through the hepcidin-ferroportin axis to ensure appropriate iron fluxes. This knowledge is key for the identification of novel therapeutic opportunities to prevent diseases of cellular and/or systemic iron mismanagement.

The microbiota and the host organism switch between cooperation and competition based on dietary iron levels

The microbiota significantly impacts digestive epithelium functionality, especially in nutrient processing. Given the importance of iron for both the host and the microbiota, we hypothesized that host-microbiota interactions fluctuate with dietary iron levels. We compared germ-free (GF) and conventional mice (SPF) fed iron-containing (65 mg/Kg) or iron-depleted (<6 mg/Kg) diets. The efficacy of iron privation was validated by iron blood parameters. Ferritin and Dmt1, which represent cellular iron storage and transport respectively, were studied in tissues where they are abundant: the duodenum, liver and lung. When the mice were fed an iron-rich diet, the microbiota increased blood hemoglobin and hepcidin and the intestinal ferritin levels, suggesting that the microbiota helps iron storage. When iron was limiting, the microbiota inhibited the expression of the intestinal Dmt1 transporter, likely via the pathway triggered by Hif-2α. The microbiota assists the host in storing intestinal iron when it is abundant and competes with the host by inhibiting Dmt1 in conditions of iron scarcity. Comparison between duodenum, liver and lung indicates organ-specific responses to microbiota and iron availability. Iron depletion induced temporal changes in microbiota composition and activity, reduced α-diversity of microbiota, and led to Lactobacillaceae becoming particularly more abundant after 60 days of privation. By inoculating GF mice with a simplified bacterial mixture, we show that the iron-depleted host favors the gut fitness of Bifidobacterium longum.

Erythropoietin downregulates red blood cell clearance, increasing transfusion efficacy in severely anemic recipients

Red blood cells (RBC) transfusion is used to alleviate symptoms and prevent complications in anemic patients by restoring oxygen delivery to tissues. RBC transfusion efficacy, that can be measured by a rise in hemoglobin (Hb) concentration, is influenced by donor-, product-, and recipient-related characteristics. In some studies, severe pre-transfusion anemia is associated with a greater than expected Hb increment following transfusion but the biological mechanism underpinning this relationship remains poorly understood. We conducted a prospective study in critically ill patients and quantified Hb increment following one RBC transfusion. In a murine model, we investigated the possibility that, in conjunction with the host erythropoietic response, the persistence of transfused donor RBC is improved to maintain a highest RBC biomass. We confirmed a correlation between a greater Hb increment and a deeper pre-transfusion anemia in a cohort of 17 patients. In the mouse model, Hb increment and post-transfusion recovery were increased in anemic recipients. Post-transfusion RBC recovery was improved in hypoxic mice or those receiving an erythropoiesis-stimulating agent and decreased in those treated with erythropoietin (EPO)-neutralizing antibodies, suggesting that EPO signaling is necessary to observe this effect. Irradiated recipients also showed decreased post-transfusion RBC recovery. The EPO-induced post-transfusion RBC recovery improvement was abrogated in irradiated or in macrophage-depleted recipients, but maintained in splenectomized recipients, suggesting a mechanism requiring erythroid progenitors and macrophages, but which is not spleen-specific. Our study highlights a physiological role of EPO in downregulating post-transfusion RBC clearance, contributing to maintain a vital RBC biomass to rapidly cope with hypoxemia.

Hypoxia-induced signaling in the cardiovascular system: pathogenesis and therapeutic targets

Hypoxia, characterized by reduced oxygen concentration, is a significant stressor that affects the survival of aerobic species and plays a prominent role in cardiovascular diseases. From the research history and milestone events related to hypoxia in cardiovascular development and diseases, The "hypoxia-inducible factors (HIFs) switch" can be observed from both temporal and spatial perspectives, encompassing the occurrence and progression of hypoxia (gradual decline in oxygen concentration), the acute and chronic manifestations of hypoxia, and the geographical characteristics of hypoxia (natural selection at high altitudes). Furthermore, hypoxia signaling pathways are associated with natural rhythms, such as diurnal and hibernation processes. In addition to innate factors and natural selection, it has been found that epigenetics, as a postnatal factor, profoundly influences the hypoxic response and progression within the cardiovascular system. Within this intricate process, interactions between different tissues and organs within the cardiovascular system and other systems in the context of hypoxia signaling pathways have been established. Thus, it is the time to summarize and to construct a multi-level regulatory framework of hypoxia signaling and mechanisms in cardiovascular diseases for developing more therapeutic targets and make reasonable advancements in clinical research, including FDA-approved drugs and ongoing clinical trials, to guide future clinical practice in the field of hypoxia signaling in cardiovascular diseases.

FAM210B is dispensable for erythroid differentiation in adult mice

Iron plays a central role in cellular redox processes, but its ability to adopt multiple oxidation states also enables it to catalyze deleterious reactions. The requirement for iron in erythropoiesis has necessitated the evolution of mechanisms with which to handle the iron required for hemoglobinization. FAM210B was identified as a regulator of mitochondrial iron import and heme synthesis in erythroid cell culture and zebrafish models. In this manuscript, we demonstrate that while FAM210B is required for erythroid differentiation and heme synthesis under standard cell culture conditions, holotransferrin supplementation was sufficient to chemically complement the iron-deficient phenotype. As the biology of FAM210B is complex and context specific, and whole-organism studies on FAM210 proteins have been limited, we sought to unravel the role of FAM210B in erythropoiesis using knockout mice. We were surprised to discover that Fam210b -/- mice were viable and the adults did not have erythropoietic defects in the bone marrow. In contrast to studies in C. elegans, Fam210b -/- mice were also fertile. There were some modest phenotypes, such as a slight increase in lymphocytes and white cell count in Fam210b -/- females, as well as an increase in body weight in Fam210b -/- males. However, our findings suggest that FAM210B may play a more important role in cellular iron homeostasis under iron deficient conditions. Here, we will discuss the cell culture conditions used in iron metabolism studies that can account for the disparate finding on FAM210B function. Moving forward, resolving these discrepancies will be important in identifying novel iron homeostasis genes.

Potential Roles of Metals in the Pathogenesis of Pulmonary and Systemic Hypertension

Pulmonary and systemic hypertension (PH, SH) are characterized by vasoconstriction and vascular remodeling resulting in increased vascular resistance and pulmonary/aortic artery pressures. The chronic stress leads to inflammation, oxidative stress, and infiltration by immune cells. Roles of metals in these diseases, particularly PH are largely unknown. This review first discusses the pathophysiology of PH including vascular oxidative stress, inflammation, and remodeling in PH; mitochondrial dysfunction and metabolic changes in PH; ion channel and its alterations in the pathogenesis of PH as well as PH-associated right ventricular (RV) remodeling and dysfunctions. This review then summarizes metal general features and essentiality for the cardiovascular system and effects of metals on systemic blood pressure. Lastly, this review explores non-essential and essential metals and potential roles of their dyshomeostasis in PH and RV dysfunction. Although it remains early to conclude the role of metals in the pathogenesis of PH, emerging direct and indirect evidence implicates the possible contributions of metal-mediated toxicities in the development of PH. Future research should focus on comprehensive clinical metallomics study in PH patients; mechanistic evaluations to elucidate roles of various metals in PH animal models; and novel therapy clinical trials targeting metals. These important discoveries will significantly advance our understandings of this rare yet fatal disease, PH.

Anti-ferroptotic PRKAA2 serves as a potential diagnostic and prognostic marker for hepatoblastoma

Background

The incidence rate of hepatoblastoma (HB), which is the most prevalent malignant tumour among children, rises each year. According to recent studies, a number of neoplastic disorders and ferroptosis are intimately connected. This study aims to identify key ferroptosis-related genes in HB and explore new directions for the diagnosis and treatment of HB.

Methods

Differentially expressed ferroptosis-related genes were identified using the Gene Expression Omnibus datasets. The functional annotation of candidate genes was evaluated through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Machine learning and receiver operating characteristic (ROC) curves revealed protein kinase AMP-activated catalytic subunit alpha 2 (PRKAA2), tribbles homolog 2 (TRIB2), and liver-type glutaminase (GLS2) as potential diagnostic genes of HB. By using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry, relative expression of PRKAA2 was examined. The effect of PRKAA2 on proliferation, apoptosis, and ferroptosis of HB cells was verified in vitro and in vivo. Fisher's exact test was used to evaluate the clinical significance of PRKAA2 in HB.

Results

The prognostic indicators had a substantial correlation with PRKAA2 expression, which rose dramatically in HB tissues. PRKAA2 promotes proliferation and inhibits ferroptosis in HB cells. PRKAA2 plays a role in ferroptosis by regulating hypoxia-inducible factor 1α (HIF-1α) and transferrin receptor 1 (TFR1).

Conclusions

PRKAA2 functions as a tumor-promoting factor in HB by promoting cell proliferation and prohibiting ferroptosis. Ferroptosis-related genes PRKAA2 is a potential diagnostic and prognostic marker for HB as well as a novel therapeutic target in the future.

A temporal difference in the stabilization of two mRNAs with a 3' iron-responsive element during iron deficiency

The interactions of iron regulatory proteins (IRPs) with mRNAs containing an iron-responsive element (IRE) maintain cellular iron homeostasis and coordinate it with metabolism and possibly cellular behavior. The mRNA encoding transferrin receptor-1 (TFRC, TfR1), which is a major means of iron importation, has five IREs within its 3' UTR, and IRP interactions help maintain cytosolic iron through the protection of the TfR1 mRNA from degradation. An IRE within the 3' UTR of an mRNA splice variant encoding human cell division cycle 14A (CDC14A) has the potential to coordinate the cellular iron status with cellular behavior through a similar IRP-mediated mechanism. However, the stability of the CDC14A splice variant was reported earlier to be unaffected by the cellular iron status, which suggested that the IRE is not functional. We labeled newly synthesized mRNA in HEK293 cells with 5-ethynyl uridine and found that the stability of the CDC14A variant is responsive to iron deprivation, but there are two major differences from the regulation of TfR1 mRNA stability. First, the decay of the CDC14A mRNA does not utilize the Roquin-mediated reaction that acts on the TfR1 mRNA, indicating that there is flexibility in the degradative machinery antagonized by the IRE-IRP interactions. Second, the stabilization of the CDC14A mRNA is delayed relative to the TfR1 mRNA and does not occur until IRP binding activity has been induced. The result is consistent with a hierarchy of IRP interactions in which the maintenance of cellular iron through the stabilization of the TfR1 mRNA is initially prioritized.

A deep dive into future therapies for microcytic anemias and clinical considerations

INTRODUCTION

Microcytic anemias (MA) have frequent or rare etiologies. New discoveries in understanding and treatment of microcytic anemias need to be reviewed.

AREAS COVERED

Microcytic anemias with a focus on most frequent causes and on monogenic diseases that are relevant for understanding biocellular mechanisms of MA. All treatments excepting gene therapy, with a focus on recent advances. Pubmed search with references selected by expert opinion.

EXPERT OPINION

As the genetic and cellular background of dyserythropoiesis will continue to be clarified, collaboration with bioengineering of treatments acting specifically at the protein domain level will continue to provide new therapies in haematology as well as oncology and neurology.

Stimulation of Hepatic Ferritinophagy Mitigates Irp2 Depletion-Induced Anemia

Background: Iron regulatory proteins (IRPs) maintain cellular iron homeostasis. Due to aberrant tissue-iron distribution, Irp2-deficient mice suffer microcytic anemia and neurodegeneration, while iron overload occurs in the liver and intestine. We previously found that Irp2 deficiency-induced Hif2 plays an important role in neurodegeneration. Methods: To test the role of Hif2 in Irp2 deficiency-induced anemia, we used Irp2 global knockout mice. Following Hif2 inhibition, routine blood tests, iron availability in bone marrow, histological assays, and biochemical analysis were performed to assess anemia improvement and tissue iron distribution. Results: We found that Hif2 inhibition improved anemia. The increased iron bioavailability for erythropoiesis was mainly derived from hepatic iron release, and secondly from enhanced intestinal absorption. We further demonstrate that nuclear receptor coactivator 4 (Ncoa4) was upregulated for iron release via the process of ferritinophagy. The released iron was utilized not only for intracellular Fe-S biogenesis but also for erythropoiesis after being exported from the liver to circulation. The hepatic iron export reduced hepcidin expression to further support iron absorption through the hepcidin-ferroportin axis to alleviate intestinal iron overload. Conclusion: Irp2 not only regulates cellular iron homeostasis but also tissue iron distribution by managing the involvement of Hif2-Ncoa4.

Managing the Dual Nature of Iron to Preserve Health

Because of its peculiar redox properties, iron is an essential element in living organisms, being involved in crucial biochemical processes such as oxygen transport, energy production, DNA metabolism, and many others. However, its propensity to accept or donate electrons makes it potentially highly toxic when present in excess and inadequately buffered, as it can generate reactive oxygen species. For this reason, several mechanisms evolved to prevent both iron overload and iron deficiency. At the cellular level, iron regulatory proteins, sensors of intracellular iron levels, and post-transcriptional modifications regulate the expression and translation of genes encoding proteins that modulate the uptake, storage, utilization, and export of iron. At the systemic level, the liver controls body iron levels by producing hepcidin, a peptide hormone that reduces the amount of iron entering the bloodstream by blocking the function of ferroportin, the sole iron exporter in mammals. The regulation of hepcidin occurs through the integration of multiple signals, primarily iron, inflammation and infection, and erythropoiesis. These signals modulate hepcidin levels by accessory proteins such as the hemochromatosis proteins hemojuvelin, HFE, and transferrin receptor 2, the serine protease TMPRSS6, the proinflammatory cytokine IL6, and the erythroid regulator Erythroferrone. The deregulation of the hepcidin/ferroportin axis is the central pathogenic mechanism of diseases characterized by iron overload, such as hemochromatosis and iron-loading anemias, or by iron deficiency, such as IRIDA and anemia of inflammation. Understanding the basic mechanisms involved in the regulation of hepcidin will help in identifying new therapeutic targets to treat these disorders.

Iron Responsiveness to Lysosomal Disruption: A Novel Pathway to Alzheimer's Disease

Familial Alzheimer's disease (fAD) mutations in the amyloid-β protein precursor (AβPP) enhance brain AβPP C-Terminal Fragment (CTF) levels to inhibit lysosomal v-ATPase. Consequent disrupted acidification of the endolysosomal pathway may trigger brain iron deficiencies and mitochondrial dysfunction. The iron responsive element (IRE) in the 5'Untranslated-region of AβPP mRNA should be factored into this cycle where reduced bioavailable Fe-II would decrease IRE-dependent AβPP translation and levels of APP-CTFβ in a cycle to adaptively restore iron homeostasis while increases of transferrin-receptors is evident. In healthy younger individuals, Fe-dependent translational modulation of AβPP is part of the neuroprotective function of sAβPPα with its role in iron transport.

A novel treatment strategy to prevent Parkinson's disease: focus on iron regulatory protein 1 (IRP1)

We propose that neural damage in Parkinson's disease (PD) is due to dysregulation of iron utilization rather than to high iron levels per se. Iron deposits are associated with neuronal cell death in substantia nigra (SN) resulting in PD where high levels of iron in SNs are due to dysregulation of iron utilization. Cytosolic aconitase (ACO1) upon losing an iron-sulfur cluster becomes iron regulatory protein 1 (IRP1). Rotenone increases levels of IRP1 and induces PD in rats. An increase in iron leads to inactivation of IRP1. We propose a novel treatment strategy to prevent PD. Specifically in rats given rotenone by subcutaneous injections, iron, from iron carbonyl from which iron is slowly absorbed, given three times a day by gavage will keep iron levels constant in the gut whereby iron levels and iron utilization systematically can be tightly regulated. Rotenone adversely affects complex 1 iron-sulfur proteins. Iron supplementation will increase iron-sulfur cluster formation switching IRP1 to ACO1. With IRP1 levels kept constantly low, iron utilization will systematically be tightly regulated stopping dysregulation of complex 1 and the neural damage done by rotenone preventing PD.

FAM96A is essential for maintaining organismal energy balance and adipose tissue homeostasis in mice

The iron (Fe) metabolism plays important role in regulating systemic metabolism and obesity development. The Fe inside cells can form iron-sulfur (Fe-S) clusters, which are usually assembled into target proteins with the help of a conserved cluster assembly machinery. Family with sequence similarity 96A (FAM96A; also designated CIAO2A) is a cytosolic Fe-S assembly protein involved in the regulation of cellular Fe homeostasis. However, the biological function of FAM96A in vivo is still incompletely defined. Here, we tested the role of FAM96A in regulating organismal Fe metabolism, which is relevant to obesity and adipose tissue homeostasis. We found that in mice genetically lacking FAM96A globally, intracellular Fe homeostasis was interrupted in both white and brown adipocytes, but the systemic Fe level was normal. FAM96A deficiency led to adipocyte hypertrophy and organismal energy expenditure reduction even under nonobesogenic normal chow diet-fed conditions. Mechanistically, FAM96A deficiency promoted mechanistic target of rapamycin (mTOR) signaling in adipocytes, leading to an elevation of de novo lipogenesis and, therefore, fat mass accumulation. Furthermore, it also caused mitochondrial defects, including defects in mitochondrial number, ultrastructure, redox activity, and metabolic function in brown adipocytes, which are known to be critical for the control of energy balance. Moreover, adipocyte-selective FAM96A knockout partially phenocopied global FAM96A deficiency with adipocyte hypertrophy and organismal energy expenditure defects but the mice were resistant to high-fat diet-induced weight gain. Thus, FAM96A in adipocytes may autonomously act as a critical gatekeeper of organismal energy balance by coupling Fe metabolism to adipose tissue homeostasis.

Host and microbiota derived extracellular vesicles: Crucial players in iron homeostasis

Iron is a double-edged sword. It is vital for all that’s living, yet its deficiency or overload can be fatal. In humans, iron homeostasis is tightly regulated at both cellular and systemic levels. Extracellular vesicles (EVs), now known as major players in cellular communication, potentially play an important role in regulating iron metabolism. The gut microbiota was also recently reported to impact the iron metabolism process and indirectly participate in regulating iron homeostasis, yet there is no proof of whether or not microbiota-derived EVs interfere in this relationship. In this review, we discuss the implication of EVs on iron metabolism and homeostasis. We elaborate on the blooming role of gut microbiota in iron homeostasis while focusing on the possible EVs contribution. We conclude that EVs are extensively involved in the complex iron metabolism process; they carry ferritin and express transferrin receptors. Bone marrow-derived EVs even induce hepcidin expression in β-thalassemia. The gut microbiota, in turn, affects iron homeostasis on the level of iron absorption and possibly macrophage iron recycling, with still no proof of the interference of EVs. This review is the first step toward understanding the multiplex iron metabolism process. Targeting extracellular vesicles and gut microbiota-derived extracellular vesicles will be a huge challenge to treat many diseases related to iron metabolism alteration.

Erythropoietin-driven dynamic proteome adaptations during erythropoiesis prevent iron overload in the developing embryo

Erythropoietin (Epo) ensures survival and proliferation of colony-forming unit erythroid (CFU-E) progenitor cells and their differentiation to hemoglobin-containing mature erythrocytes. A lack of Epo-induced responses causes embryonic lethality, but mechanisms regulating the dynamic communication of cellular alterations to the organismal level remain unresolved. By time-resolved transcriptomics and proteomics, we show that Epo induces in CFU-E cells a gradual transition from proliferation signature proteins to proteins indicative for differentiation, including heme-synthesis enzymes. In the absence of the Epo receptor (EpoR) in embryos, we observe a lack of hemoglobin in CFU-E cells and massive iron overload of the fetal liver pointing to a miscommunication between liver and placenta. A reduction of iron-sulfur cluster-containing proteins involved in oxidative phosphorylation in these embryos leads to a metabolic shift toward glycolysis. This link connecting erythropoiesis with the regulation of iron homeostasis and metabolic reprogramming suggests that balancing these interactions is crucial for protection from iron intoxication and for survival.

Clinical and Molecular Aspects of Iron Metabolism in Failing Myocytes

Heart failure (HF) is a common disease that causes significant limitations on the organism's capacity and, in extreme cases, leads to death. Clinically, iron deficiency (ID) plays an essential role in heart failure by deteriorating the patient's condition and is a prognostic marker indicating poor clinical outcomes. Therefore, in HF patients, supplementation of iron is recommended. However, iron treatment may cause adverse effects by increasing iron-related apoptosis and the production of oxygen radicals, which may cause additional heart damage. Furthermore, many knowledge gaps exist regarding the complex interplay between iron deficiency and heart failure. Here, we describe the current, comprehensive knowledge about the role of the proteins involved in iron metabolism. We will focus on the molecular and clinical aspects of iron deficiency in HF. We believe that summarizing the new advances in the translational and clinical research regarding iron deficiency in heart failure should broaden clinicians' awareness of this comorbidity.

The path from stem cells to red blood cells

As oxygen is essential for energy production in mitochondria, a sufficient amount of oxygen should be continuously delivered to the tissues to maintain life. Therefore, the number of red blood cells which carry the oxygen is considerable, at up to 25 trillion in the body, and 2 million new red blood cells are generated per second.

Genome Editing Targets for Improving Nutrient Use Efficiency and Nutrient Stress Adaptation

In recent years, the development of RNA-guided genome editing (CRISPR-Cas9 technology) has revolutionized plant genome editing. Under nutrient deficiency conditions, different transcription factors and regulatory gene networks work together to maintain nutrient homeostasis. Improvement in the use efficiency of nitrogen (N), phosphorus (P) and potassium (K) is essential to ensure sustainable yield with enhanced quality and tolerance to stresses. This review outlines potential targets suitable for genome editing for understanding and improving nutrient use (NtUE) efficiency and nutrient stress tolerance. The different genome editing strategies for employing crucial negative and positive regulators are also described. Negative regulators of nutrient signalling are the potential targets for genome editing, that may improve nutrient uptake and stress signalling under resource-poor conditions. The promoter engineering by CRISPR/dead (d) Cas9 (dCas9) cytosine and adenine base editing and prime editing is a successful strategy to generate precise changes. CRISPR/dCas9 system also offers the added advantage of exploiting transcriptional activators/repressors for overexpression of genes of interest in a targeted manner. CRISPR activation (CRISPRa) and CRISPR interference (CRISPRi) are variants of CRISPR in which a dCas9 dependent transcription activation or interference is achieved. dCas9-SunTag system can be employed to engineer targeted gene activation and DNA methylation in plants. The development of nutrient use efficient plants through CRISPR-Cas technology will enhance the pace of genetic improvement for nutrient stress tolerance of crops and improve the sustainability of agriculture.

The mutual crosstalk between iron and erythropoiesis

Iron homeostasis and erythropoiesis are strongly interconnected. On one side iron is essential to terminal erythropoiesis for hemoglobin production, on the other erythropoiesis may increase iron absorption through the production of erythroferrone, the erythroid hormone that suppresses hepcidin expression Also erythropoietin production is modulated by iron through the iron regulatory proteins-iron responsive elements that control the hypoxia inducible factor 2-α. The second transferrin receptor, an iron sensor both in the liver and in erythroid cells modulates erythropoietin sensitivity and is a further link between hepcidin and erythropoiesis. When erythropoietin is decreased in iron deficiency the erythropoietin sensitivity is increased because the second transferrin receptor is removed from cell surface. A deranged balance between erythropoiesis and iron/hepcidin may lead to anemia, as in the case of iron deficiency, defective iron uptake and erythroid utilization or subnormal recycling. Defective control of hepcidin production may cause iron deficiency, as in the recessive disorder iron refractory iron deficiency anemia or in anemia of inflammation, or in iron loading anemias, which are characterized by excessive but ineffective erythropoiesis. The elucidation of the mechanisms that regulates iron homeostasis and erythropoiesis is leading to the development of drugs for the benefit of both iron and erythropoiesis disorders.

Endothelin A receptor antagonist attenuated renal iron accumulation in iron overload heme oxygenase-1 knockout mice

Progressive iron accumulation and renal impairment are prominent in both patients and mouse models of sickle cell disease (SCD). Endothelin A receptor (ETA) antagonism prevents this iron accumulation phenotype and reduces renal iron deposition in proximal tubules of SCD mice. To better understand the mechanisms of iron metabolism in the kidney and the role of ETA receptor in iron chelation and transport, we studied renal iron handling in a non-sickle cell iron overload model, heme oxygenase-1 (Hmox-1-/-) knockout mice. We found that Hmox-1-/- mice had elevated plasma endothelin-1 (ET-1), cortical ET-1 mRNA expression, and renal iron content compared to Hmox-1+/+ controls. The ETA receptor antagonist, ambrisentan, attenuated renal iron deposition, without any changes to anemia status in Hmox-1-/- mice. This was accompanied by reduced urinary iron excretion. Finally, ambrisentan had an important iron recycling effect by increasing expression of cellular iron exporter, ferroportin-1 (FPN-1) and circulating total iron levels in Hmox-1-/- mice. These findings suggest the ET-1/ETA signaling pathway contributes to in renal iron trafficking in a murine model of iron overload.

Dysregulation of the sensory and regulatory pathways controlling cellular iron metabolism in unilateral obstructive nephropathy

Chronic kidney disease involves disturbances in iron metabolism including anemia caused by insufficient erythropoietin (EPO) production. However, underlying mechanisms responsible for the dysregulation of cellular iron metabolism are incompletely defined. Using the unilateral ureteral obstruction (UUO) model in Irp1+/+ and Irp1-/- mice, we asked if iron regulatory proteins (IRPs), the central regulators of cellular iron metabolism and suppressors of EPO production, contribute to the etiology of anemia in kidney failure. We identified a significant reduction in IRP protein level and RNA binding activity that associates with a loss of the iron uptake protein transferrin receptor 1 (TfR1), increased expression of the iron storage protein subunits H- and L-ferritin, and a low but overall variable level of stainable iron in the obstructed kidney. This reduction in IRP RNA binding activity and ferritin RNA levels suggests the concomitant rise in ferritin expression and iron content in kidney failure is IRP dependent. In contrast, the reduction in the Epo mRNA level in the obstructed kidney was not rescued by genetic ablation of IRP1, suggesting disruption of normal hypoxia-inducible factor (HIF)-2α regulation. Furthermore, reduced expression of some HIF-α target genes in UUO occurred in the face of increased expression of HIF-α proteins and prolyl hydroxylases 2 and 1, the latter of which is not known to be HIF-α mediated. Our results suggest that the IRP system drives changes in cellular iron metabolism that are associated with kidney failure in UUO but that the impact of IRPs on EPO production is overridden by disrupted hypoxia signaling.NEW & NOTEWORTHY This study demonstrates that iron metabolism and hypoxia signaling are dysregulated in unilateral obstructive nephropathy. Expression of iron regulatory proteins (IRPs), central regulators of cellular iron metabolism, and the iron uptake (transferrin receptor 1) and storage (ferritins) proteins they target is strongly altered. This suggests a role of IRPs in previously observed changes in iron metabolism in progressive renal disease. Hypoxia signaling is disrupted and appeared to dominate the action of IRP1 in controlling erythropoietin expression.

Rethinking IRPs/IRE system in neurodegenerative disorders: Looking beyond iron metabolism

Iron regulatory proteins (IRPs) and iron regulatory element (IRE) systems are well known in the progression of neurodegenerative disorders by regulating iron related proteins. IRPs are also regulated by iron homeostasis. However, an increasing number of studies have suggested a close relationship between the IRPs/IRE system and non-iron-related neurodegenerative disorders. In this paper, we reviewed that the IRPs/IRE system is not only controlled by iron ions, but also regulated by such factors as post-translational modification, oxygen, nitric oxide (NO), heme, interleukin-1 (IL-1), and metal ions. In addition, by regulating the transcription of non-iron related proteins, the IRPs/IRE system functioned in oxidative metabolism, cell cycle regulation, abnormal proteins aggregation, and neuroinflammation. Finally, by emphasizing the multiple regulations of IRPs/IRE system and its potential relationship with non-iron metabolic neurodegenerative disorders, we provided new strategies for disease treatment targeting IRPs/IRE system.

Protective Effects of Hif2 Inhibitor PT-2385 on a Neurological Disorder Induced by Deficiency of Irp2

Iron regulatory protein 2 (IRP2) deficiency in mice and humans causes microcytic anemia and neurodegeneration due to functional cellular iron depletion. Our previous in vitro data have demonstrated that Irp2 depletion upregulates hypoxia-inducible factor subunits Hif1α and Hif2α expression; inhibition of Hif2α rescues Irp2 ablation-induced mitochondrial dysfunction; and inhibition of Hif1α suppresses the overdose production of lactic acid derived from actively aerobic glycolysis. We wonder whether Hif1α and Hif2α are also elevated in vivo and play a similar role in neurological disorder of Irp2^–/– mice. In this study, we confirmed the upregulation of Hif2α, not Hif1α, in tissues, particularly in the central nervous system including the mainly affected cerebellum and spinal cord of Irp2^–/– mice. Consistent with this observation, inhibition of Hif2α by PT-2385, not Hif1α by PX-478, prevented neurodegenerative symptoms, which were proved by Purkinje cell arrangement from the shrunken and irregular to the full and regular array. PT-2385 treatment did not only modulate mitochondrial morphology and quality in vivo but also suppressed glycolysis. Consequently, the shift of energy metabolism from glycolysis to oxidative phosphorylation (OXPHOS) was reversed. Our results indicate that Irp2 depletion-induced Hif2α is, in vivo, in charge of the switch between OXPHOS and glycolysis, suggesting that, for the first time to our knowledge, Hif2α is a clinically potential target in the treatment of IRP2 deficiency-induced neurodegenerative syndrome.

Essential role of systemic iron mobilization and redistribution for adaptive thermogenesis through HIF2-α/hepcidin axis

Iron is an essential biometal, but is toxic if it exists in excess. Therefore, iron content is tightly regulated at cellular and systemic levels to meet metabolic demands but to avoid toxicity. We have recently reported that adaptive thermogenesis, a critical metabolic pathway to maintain whole-body energy homeostasis, is an iron-demanding process for rapid biogenesis of mitochondria. However, little information is available on iron mobilization from storage sites to thermogenic fat. This study aimed to determine the iron-regulatory network that underlies beige adipogenesis. We hypothesized that thermogenic stimulus initiates the signaling interplay between adipocyte iron demands and systemic iron liberation, resulting in iron redistribution into beige fat. To test this hypothesis, we induced reversible activation of beige adipogenesis in C57BL/6 mice by administering a β3-adrenoreceptor agonist CL 316,243 (CL). Our results revealed that CL stimulation induced the iron-regulatory protein-mediated iron import into adipocytes, suppressed hepcidin transcription, and mobilized iron from the spleen. Mechanistically, CL stimulation induced an acute activation of hypoxia-inducible factor 2-α (HIF2-α), erythropoietin production, and splenic erythroid maturation, leading to hepcidin suppression. Disruption of systemic iron homeostasis by pharmacological HIF2-α inhibitor PT2385 or exogenous administration of hepcidin-25 significantly impaired beige fat development. Our findings suggest that securing iron availability via coordinated interplay between renal hypoxia and hepcidin down-regulation is a fundamental mechanism to activate adaptive thermogenesis. It also provides an insight into the effects of adaptive thermogenesis on systemic iron mobilization and redistribution.

Evaluation of candidate reference genes for quantitative real-time PCR analysis in a male rat model of dietary iron deficiency

BACKGROUND

Quantitative real-time polymerase chain reaction (qPCR) is a reliable and efficient method for quantitation of gene expression. Due to the increased use of qPCR in examining nutrient-gene interactions, it is important to examine, develop, and utilize standardized approaches for data analyses and interpretation. A common method used to normalize expression data involves the use of reference genes (RG) to determine relative mRNA abundance. When calculating the relative abundance, the selection of RG can influence experimental results and has the potential to skew data interpretation. Although common RG may be used for normalization, often little consideration is given to the suitability of RG selection for an experimental condition or between various tissue or cell types. In the current study, we examined the stability of gene expression using BestKeeper, comparative delta quantitation cycle, NormFinder, and RefFinder in a variety of tissues obtained from iron-deficient and pair-fed iron-replete rats to determine the optimal selection among ten candidate RG.

RESULTS

Our results suggest that several commonly used RG (e.g., Actb and Gapdh) exhibit less stability compared to other candidate RG (e.g., Rpl19 and Rps29) in both iron-deficient and iron-replete pair-fed conditions. For all evaluated RG, Tfrc expression significantly increased in iron-deficient animal livers compared to the iron-replete pair-fed controls; however, the relative induction varied nearly 4-fold between the most suitable (Rpl19) and least suitable (Gapdh) RG.

CONCLUSION

These results indicate the selection and use of RG should be empirically determined and RG selection may vary across experimental conditions and biological tissues.

Ferroptosis as a mechanism of neurodegeneration in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia, with complex pathophysiology that is not fully understood. While β-amyloid plaque and neurofibrillary tangles define the pathology of the disease, the mechanism of neurodegeneration is uncertain. Ferroptosis is an iron-mediated programmed cell death mechanism characterised by phospholipid peroxidation that has been observed in clinical AD samples. This review will outline the growing molecular and clinical evidence implicating ferroptosis in the pathogenesis of AD, with implications for disease-modifying therapies.

Treatment-resistant schizophrenia: focus on the transsulfuration pathway

Treatment-resistant schizophrenia (TRS) is a severe form of schizophrenia. The severity of illness is positively related to homocysteine levels, with high homocysteine levels due to the low activity of the transsulfuration pathway, which metabolizes homocysteine in synthesizing L-cysteine. Glutathione levels are low in schizophrenia, which indicates shortages of L-cysteine and low activity of the transsulfuration pathway. Hydrogen sulfide (H2S) levels are low in schizophrenia. H2S is synthesized by cystathionine β-synthase and cystathionine γ-lyase, which are the two enzymes in the transsulfuration pathway. Iron-sulfur proteins obtain sulfur from L-cysteine. The oxidative phosphorylation (OXPHOS) pathway has various iron-sulfur proteins. With low levels of L-cysteine, iron-sulfur cluster formation will be dysregulated leading to deficits in OXPHOS in schizophrenia. Molybdenum cofactor (MoCo) synthesis requires sulfur, which is obtained from L-cysteine. With low levels of MoCo synthesis, molybdenum-dependent sulfite oxidase (SUOX) will not be synthesized at appropriate levels. SUOX detoxifies sulfite from sulfur-containing amino acids. If sulfites are not detoxified, there can be sulfite toxicity. The transsulfuration pathway metabolizes selenomethionine, whereby selenium from selenomethionine can be used for selenoprotein synthesis. The low activity of the transsulfuration pathway decreases selenoprotein synthesis. Glutathione peroxidase (GPX), with various GPXs being selenoprotein, is low in schizophrenia. The dysregulations of selenoproteins would lead to oxidant stress, which would increase the methylation of genes and histones leading to epigenetic changes in TRS. An add-on treatment to mainline antipsychotics is proposed for TRS that targets the dysregulations of the transsulfuration pathway and the dysregulations of other pathways stemming from the transsulfuration pathway being dysregulated.

NRF2 and Hypoxia-Inducible Factors: Key Players in the Redox Control of Systemic Iron Homeostasis

Significance: Oxygen metabolism and iron homeostasis are closely linked. Iron facilitates the oxygen-carrying capacity of blood, and its deficiency causes anemia. Conversely, excess free iron is detrimental for stimulating the formation of reactive oxygen species, causing tissue damage. The amount and distribution of iron thus need to be tightly regulated by the liver-expressed hormone hepcidin. This review analyzes the roles of key oxygen-sensing pathways in cellular and systemic regulation of iron homeostasis; specifically, the prolyl hydroxylase domain (PHD)/hypoxia-inducible factor (HIF) and the Kelch-like ECH-associated protein 1/NF-E2 p45-related factor 2 (KEAP1/NRF2) pathways, which mediate tissue adaptation to low and high oxygen, respectively. Recent Advances: In macrophages, NRF2 regulates genes involved in hemoglobin catabolism, iron storage, and iron export. NRF2 was recently identified as the molecular sensor of iron-induced oxidative stress and is responsible for BMP6 expression by liver sinusoidal endothelial cells, which in turn activates hepcidin synthesis by hepatocytes to restore systemic iron levels. Moreover, NRF2 orchestrates the activation of antioxidant defenses that are crucial to protect against iron toxicity. On the contrary, low iron/hypoxia stabilizes renal HIF2a via inactivation of iron-dependent PHD dioxygenases, causing an erythropoietic stimulus that represses hepcidin via an inhibitory effect of erythroferrone on bone morphogenetic proteins. Intestinal HIF2a is also stabilized, increasing the expression of genes involved in dietary iron absorption. Critical Issues: An intimate crosstalk between oxygen-sensing pathways and iron regulatory mechanisms ensures that fluctuations in systemic iron levels are promptly detected and restored. Future Directions: The realization that redox-sensitive transcription factors regulate systemic iron levels suggests novel therapeutic approaches. Antioxid. Redox Signal. 35, 433-452.

Breakthrough Science: Hypoxia-Inducible Factors, Oxygen Sensing, and Disorders of Hematopoiesis

Hypoxia-inducible factors (HIF) were discovered as activators of erythropoietin gene transcription in response to reduced O2 availability. O2-dependent hydroxylation of HIFs on proline and asparagine residues regulates protein stability and transcription activity, respectively. Mutations in genes encoding components of the oxygen sensing pathway cause familial erythrocytosis. Several small molecule inhibitors of HIF prolyl hydroxylases are currently in clinical trials as erythropoiesis stimulating agents. HIFs are overexpressed in bone marrow neoplasms, and the development of HIF inhibitors may improve outcome in these disorders.

The critical roles of iron during the journey from fetus to adolescent: Developmental aspects of iron homeostasis

Iron is indispensable for human life. However, it is also potentially toxic, since it catalyzes the formation of harmful oxidative radicals in unbound form and may facilitate pathogen growth. Therefore, iron homeostasis needs to be tightly regulated. Rapid growth and development require large amounts of iron, while (especially young) children are vulnerable to infections with iron-dependent pathogens due to an immature immune system. Moreover, unbalanced iron status early in life may have effects on the nervous system, immune system and gut microbiota that persist into adulthood. In this narrative review, we assess the critical roles of iron for growth and development and elaborate how the body adapts to physiologically high iron demands during the journey from fetus to adolescent. As a first step towards the development of clinical guidelines for the management of iron disorders in children, we summarize the unmet needs regarding the developmental aspects of iron homeostasis.

Mechanisms of cellular iron sensing, regulation of erythropoiesis and mitochondrial iron utilization

To maintain an adequate iron supply for hemoglobin synthesis and essential metabolic functions while counteracting iron toxicity, humans and other vertebrates have evolved effective mechanisms to conserve and finely regulate iron concentration, storage, and distribution to tissues. At the systemic level, the iron-regulatory hormone hepcidin is secreted by the liver in response to serum iron levels and inflammation. Hepcidin regulates the expression of the sole known mammalian iron exporter, ferroportin, to control dietary absorption, storage and tissue distribution of iron. At the cellular level, iron regulatory proteins 1 and 2 (IRP1 and IRP2) register cytosolic iron concentrations and post-transcriptionally regulate the expression of iron metabolism genes to optimize iron availability for essential cellular processes, including heme biosynthesis and iron-sulfur cluster biogenesis. Genetic malfunctions affecting the iron sensing mechanisms or the main pathways that utilize iron in the cell cause a broad range of human diseases, some of which are characterized by mitochondrial iron accumulation. This review will discuss the mechanisms of systemic and cellular iron sensing with a focus on the main iron utilization pathways in the cell, and on human conditions that arise from compromised function of the regulatory axes that control iron homeostasis.

Iron and erythropoiesis: A mutual alliance

The large amount of iron required for hemoglobin synthesis keeps iron homeostasis and erythropoiesis inter-connected, both iron levels being affected by increased erythropoiesis, and erythropoiesis regulated by serum iron. The connection between these 2 processes is maintained even when erythropoiesis is ineffective. In the last years great advances in the understanding of the mechanisms of this crosstalk have been achieved thanks to the discovery of 2 essential players: hepcidin, the master regulator of iron homeostasis, and erythroferrone, the long sought erythroid regulator. In addition, how circulating transferrin-bound iron contributes to the crosstalk between the 2 systems has started to be unraveled.

CCL17-producing cDC2s are essential in end-stage lupus nephritis and averted by a parasitic infection

Lupus nephritis is a severe organ manifestation in systemic lupus erythematosus leading to kidney failure in a subset of patients. In lupus-prone mice, controlled infection with Plasmodium parasites protects against the progression of autoimmune pathology including lethal glomerulonephritis. Here, we demonstrate that parasite-induced protection was not due to a systemic effect of infection on autoimmunity as previously assumed, but rather to specific alterations in immune cell infiltrates into kidneys and renal draining lymph nodes. Infection of lupus-prone mice with a Plasmodium parasite did not reduce the levels or specificities of autoreactive antibodies, vasculitis, immune complex-induced innate activation, or hypoxia. Instead, infection uniquely reduced kidney-infiltrating CCL17-producing bone marrow-derived type 2 inflammatory dendritic cells (iDC2s). Bone marrow reconstitution experiments revealed that infection with Plasmodium caused alterations in bone marrow cells that hindered the ability of DC2s to infiltrate the kidneys. The essential role for CCL17 in lupus nephritis was confirmed by in vivo depletion with a blocking antibody, which reduced kidney pathology and immune infiltrates, while bypassing the need for parasitic infection. Therefore, infiltration into the kidneys of iDC2s, with the potential to prime local adaptive responses, is an essential regulated event in the transition from manageable glomerulonephritis to lethal tubular injury.

Therapeutic inhibition of HIF-2α reverses polycythemia and pulmonary hypertension in murine models of human diseases

Polycythemia and pulmonary hypertension are 2 human diseases for which better therapies are needed. Upregulation of hypoxia-inducible factor-2α (HIF-2α) and its target genes, erythropoietin (EPO) and endothelin-1, causes polycythemia and pulmonary hypertension in patients with Chuvash polycythemia who are homozygous for the R200W mutation in the von Hippel Lindau (VHL) gene and in a murine mouse model of Chuvash polycythemia that bears the same homozygous VhlR200W mutation. Moreover, the aged VhlR200W mice developed pulmonary fibrosis, most likely due to the increased expression of Cxcl-12, another Hif-2α target. Patients with mutations in iron regulatory protein 1 (IRP1) also develop polycythemia, and Irp1-knockout (Irp1-KO) mice exhibit polycythemia, pulmonary hypertension, and cardiac fibrosis attributable to translational derepression of Hif-2α, and the resultant high expression of the Hif-2α targets EPO, endothelin-1, and Cxcl-12. In this study, we inactivated Hif-2α with the second-generation allosteric HIF-2α inhibitor MK-6482 in VhlR200W, Irp1-KO, and double-mutant VhlR200W;Irp1-KO mice. MK-6482 treatment decreased EPO production and reversed polycythemia in all 3 mouse models. Drug treatment also decreased right ventricular pressure and mitigated pulmonary hypertension in VhlR200W, Irp1-KO, and VhlR200W;Irp1-KO mice to near normal wild-type levels and normalized the movement of the cardiac interventricular septum in VhlR200Wmice. MK-6482 treatment reduced the increased expression of Cxcl-12, which, in association with CXCR4, mediates fibrocyte influx into the lungs, potentially causing pulmonary fibrosis. Our results suggest that oral intake of MK-6482 could represent a new approach to treatment of patients with polycythemia, pulmonary hypertension, pulmonary fibrosis, and complications caused by elevated expression of HIF-2α.

NCOA4 is regulated by HIF and mediates mobilization of murine hepatic iron stores after blood loss

The mechanisms by which phlebotomy promotes the mobilization of hepatic iron stores are not well understood. NCOA4 (nuclear receptor coactivator 4) is a widely expressed intracellular protein previously shown to mediate the autophagic degradation of ferritin. Here, we investigate a local requirement for NCOA4 in the regulation of hepatic iron stores and examine mechanisms of NCOA4 regulation. Hepatocyte-targeted Ncoa4 knockdown in nonphlebotomized mice had only modest effects on hepatic ferritin subunit levels and nonheme iron concentration. After phlebotomy, mice with hepatocyte-targeted Ncoa4 knockdown exhibited anemia and hypoferremia similar to control mice with intact Ncoa4 regulation but showed a markedly impaired ability to lower hepatic ferritin subunit levels and hepatic nonheme iron concentration. This impaired hepatic response was observed even when dietary iron was limited. In both human and murine hepatoma cell lines, treatment with chemicals that stabilize hypoxia inducible factor (HIF), including desferrioxamine, cobalt chloride, and dimethyloxalylglycine, raised NCOA4 messenger RNA. This NCOA4 messenger RNA induction occurred within 3 hours, preceded a rise in NCOA4 protein, and was attenuated in the setting of dual HIF-1α and HIF-2α knockdown. In summary, we show for the first time that NCOA4 plays a local role in facilitating iron mobilization from the liver after blood loss and that HIF regulates NCOA4 expression in cells of hepatic origin. Because the prolyl hydroxylases that regulate HIF stability are oxygen- and iron-dependent enzymes, our findings suggest a novel mechanism by which hypoxia and iron deficiency may modulate NCOA4 expression to impact iron homeostasis.

Preferential uptake of antibody targeted calcium phosphosilicate nanoparticles by metastatic triple negative breast cancer cells in co-cultures of human metastatic breast cancer cells plus bone osteoblasts

Calcium phosphosilicate nanoparticles (CPSNPs) are bioresorbable nanoparticles that can be bioconjugated with targeting molecules and encapsulate active agents and deliver them to tumor cells without causing damage to adjacent healthy tissue. Data obtained in this study demonstrated that an anti-CD71 antibody on CPSNPs targets these nanoparticles and enhances their internalization by triple negative breast cancer cells in-vitro. Caspase 3,7 activation, DNA damage, and fluorescent microscopy confirmed the apoptotic breast cancer response caused by targeted anti-CD71-CPSNPs encapsulated with gemcitabine monophosphate, the active metabolite of the chemotherapeutic gemcitabine used to treat cancers including breast and ovarian. Targeted anti-CD71-CPSNPs encapsulated with the fluorophore, Rhodamine WT, were preferentially internalized by breast cancer cells in co-cultures with osteoblasts. While osteoblasts partially internalized anti-CD71-GemMP-CPSNPs, their cell growth was not affected. These results suggest that CPSNPs may be used as imaging tools and selective drug delivery systems for breast cancer that has metastasized to bone.

Iron control of erythroid microtubule cytoskeleton as a potential target in treatment of iron-restricted anemia

Anemias of chronic disease and inflammation (ACDI) result from restricted iron delivery to erythroid progenitors. The current studies reveal an organellar response in erythroid iron restriction consisting of disassembly of the microtubule cytoskeleton and associated Golgi disruption. Isocitrate supplementation, known to abrogate the erythroid iron restriction response, induces reassembly of microtubules and Golgi in iron deprived progenitors. Ferritin, based on proteomic profiles, regulation by iron and isocitrate, and putative interaction with microtubules, is assessed as a candidate mediator. Knockdown of ferritin heavy chain (FTH1) in iron replete progenitors induces microtubule collapse and erythropoietic blockade; conversely, enforced ferritin expression rescues erythroid differentiation under conditions of iron restriction. Fumarate, a known ferritin inducer, synergizes with isocitrate in reversing molecular and cellular defects of iron restriction and in oral remediation of murine anemia. These findings identify a cytoskeletal component of erythroid iron restriction and demonstrate potential for its therapeutic targeting in ACDI.

Debilitating anemias in chronic diseases can result from deficient iron delivery to red cell precursors. Here, the authors show how this deficiency damages the cytoskeletal framework of progenitor cells and identify a targeted strategy for cytoskeletal repair, leading to anemia correction.

Efficacy and Safety of Daprodustat for Anemia Therapy in Chronic Kidney Disease Patients: A Systematic Review and Meta-Analysis

Objective: Daprodustat is a novel oral agent in treating anemia of chronic kidney disease (CKD), and several clinical trials have been conducted to compare daprodustat with recombinant human erythropoietin (rhEPO) or placebo. Our systematic review aimed to investigate the efficacy and safety of daprodustat for anemia treatment in both dialysis-dependent (DD) and non-dialysis-dependent (NDD) patients.

Methods: Six databases were searched for randomized controlled trials (RCTs) reporting daprodustat vs. rhEPO or placebo for anemia patients in CKD. The outcome indicators were focused on hemoglobin (Hb), ferritin, transferrin saturation (TSAT), total iron-binding capacity (TIBC), vascular endothelial growth factor (VEGF), and serious adverse events (SAEs).

Results: Eight eligible studies with 1,516 participants were included. For both NDD and DD patients, changes in Hb levels from baseline were significantly higher in daprodustat group than that in the placebo (mean difference (MD) = 1.73, [95% confidence interval (CI), 0.34 to 3.12], p = 0.01; MD = 1.88, [95% CI, 0.68 to 3.09], p = 0.002; respectively), and there was no significant difference between daprodustat and rhEPO group (MD = 0.05, [95% CI, −0.49 to 0.59], p = 0.86; MD = 0.12, [95% CI, −0.28 to 0.52], p = 0.55; respectively). The indexes of iron metabolism were improved significantly in the daprodustat group compared to placebo- or rhEPO-treated patients, while there was no similar change in terms of TSAT for DD patients. Furthermore, no trend of increasing plasma VEGF was observed in daprodustat-treated subjects. As for safety, there was no significant difference in the incidence of SAEs between daprodustat and placebo treatment, while the incidence of SAEs in the daprodustat group was significantly lower than that in the rhEPO group.

Conclusion: Daprodustat was efficacious and well tolerated for anemia in both NDD and DD patients in the short term based on current RCTs. And daprodustat may become an effective alternative for treatment of anemia with CKD. Since the application of daprodustat is still under exploration, future researches should consider the limitations of our study to evaluate the value of daprodustat.

Inflaming the Brain with Iron

Iron accumulation and neuroinflammation are pathological conditions found in several neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Iron and inflammation are intertwined in a bidirectional relationship, where iron modifies the inflammatory phenotype of microglia and infiltrating macrophages, and in turn, these cells secrete diffusible mediators that reshape neuronal iron homeostasis and regulate iron entry into the brain. Secreted inflammatory mediators include cytokines and reactive oxygen/nitrogen species (ROS/RNS), notably hepcidin and nitric oxide (·NO). Hepcidin is a small cationic peptide with a central role in regulating systemic iron homeostasis. Also present in the cerebrospinal fluid (CSF), hepcidin can reduce iron export from neurons and decreases iron entry through the blood-brain barrier (BBB) by binding to the iron exporter ferroportin 1 (Fpn1). Likewise, ·NO selectively converts cytosolic aconitase (c-aconitase) into the iron regulatory protein 1 (IRP1), which regulates cellular iron homeostasis through its binding to iron response elements (IRE) located in the mRNAs of iron-related proteins. Nitric oxide-activated IRP1 can impair cellular iron homeostasis during neuroinflammation, triggering iron accumulation, especially in the mitochondria, leading to neuronal death. In this review, we will summarize findings that connect neuroinflammation and iron accumulation, which support their causal association in the neurodegenerative processes observed in AD and PD.

Cell-type-specific insights into iron regulatory processes

Despite its essential role in many biological processes, iron is toxic when in excess due to its propensity to generate reactive oxygen species. To prevent diseases associated with iron deficiency or iron loading, iron homeostasis must be tightly controlled. Intracellular iron content is regulated by the Iron Regulatory Element-Iron Regulatory Protein (IRE-IRP) system, whereas systemic iron availability is adjusted to body iron needs chiefly by the hepcidin-ferroportin (FPN) axis. Here, we aimed to review advances in the field that shed light on cell-type-specific regulatory mechanisms that control or modify systemic and local iron balance, and how shifts in cellular iron levels may affect specialized cell functions.

Differential translational control of 5' IRE-containing mRNA in response to dietary iron deficiency and acute iron overload

Iron regulatory proteins (IRPs) are iron-responsive RNA binding proteins that dictate changes in cellular iron metabolism in animal cells by controlling the fate of mRNAs containing iron responsive elements (IREs). IRPs have broader physiological roles as some targeted mRNAs encode proteins with functions beyond iron metabolism suggesting hierarchical regulation of IRP-targeted mRNAs. We observe that the translational regulation of IRP-targeted mRNAs encoding iron storage (L- and H-ferritins) and export (ferroportin) proteins have different set-points of iron responsiveness compared to that for the TCA cycle enzyme mitochondrial aconitase. The ferritins and ferroportin mRNA were largely translationally repressed in the liver of rats fed a normal diet whereas mitochondrial aconitase mRNA is primarily polysome bound. Consequently, acute iron overload increases polysome association of H- and L-ferritin and ferroportin mRNAs while mitochondrial aconitase mRNA showed little stimulation. Conversely, mitochondrial aconitase mRNA is most responsive in iron deficiency. These differences in regulation were associated with a faster off-rate of IRP1 for the IRE of mitochondrial aconitase in comparison to that of L-ferritin. Thus, hierarchical control of mRNA translation by IRPs involves selective control of cellular functions acting at different states of cellular iron status and that are critical for adaptations to iron deficiency or prevention of iron toxicity.

Impact of bacterial infections on erythropoiesis

INTRODUCTION

The importance of iron is highlighted by the many complex metabolic pathways in which it is involved. A sufficient supply is essential for the effective production of 200 billion erythrocytes daily, a process called erythropoiesis.

AREAS COVERED

During infection, the human body can withhold iron from pathogens, mechanism termed nutritional immunity. The subsequent disturbances in iron homeostasis not only impact on immune function and infection control, but also negatively affect erythropoiesis. The complex interplay between iron, immunity, erythropoiesis and infection control on the molecular and clinical level are highlighted in this review. Diagnostic algorithms for correct interpretation and diagnosis of the iron status in the setting of infection are presented. Therapeutic concepts are discussed regarding effects on anemia correction, but also toward their role on the course of infection.

EXPERT OPINION

In the setting of infection, anemia is often neglected and its impact on the course of diseases is incompletely understood. Clinical expertise can be improved in correct diagnosing of anemia and disturbances of iron homeostasis. Systemic studies are needed to evaluate the impact of specific therapeutic interventions on anemia correction on the course of infection, but also on patients' cardiovascular performance and quality of life.