Neuronal-specific iron deficiency dysregulates mammalian target of rapamycin signaling during hippocampal development in nonanemic genetic mouse models

Biomarkers of Brain Dysfunction in Perinatal Iron Deficiency

Iron deficiency in the fetal and neonatal period (perinatal iron deficiency) bodes poorly for neurodevelopment. Given its common occurrence and the negative impact on brain development, a screening and treatment strategy that is focused on optimizing brain development in perinatal iron deficiency is necessary. Pediatric societies currently recommend a universal iron supplementation strategy for full-term and preterm infants that does not consider individual variation in body iron status and thus could lead to undertreatment or overtreatment. Moreover, the focus is on hematological normalcy and not optimal brain development. Several serum iron indices and hematological parameters in the perinatal period are associated with a risk of abnormal neurodevelopment, suggesting their potential use as biomarkers for screening and monitoring treatment in infants at risk for perinatal iron deficiency. A biomarker-based screening and treatment strategy that is focused on optimizing brain development will likely improve outcomes in perinatal iron deficiency.

Role of iron in host-microbiota interaction and its effects on intestinal mucosal growth and immune plasticity in a piglet model

Iron is an essential trace element for both the host and resident microbes in the gut. In this study, iron was administered orally and parenterally to anemic piglets to investigate the role of iron in host-microbiota interaction and its effects on intestinal mucosal growth and immune plasticity. We found that oral iron administration easily increased the abundance of Proteobacteria and Escherichia-Shigella, and decreased the abundance of Lactobacillus in the ileum. Furthermore, similar bacterial changes, namely an increase in Proteobacteria, Escherichia-Shigella, and Fusobacterium and a reduction in the Christensenellaceae_R-7_group, were observed in the colon of both iron-supplemented groups. Spearman's correlation analysis indicated that the changed Fusobacterium, Fusobacteria and Proteobacteria in the colon were positively correlated with hemoglobin, colon and spleen iron levels. Nevertheless, it was found that activated mTOR1 signaling, improved villous height and crypt depth in the ileum, enhanced immune communication, and increased protein expression of IL-22 and IL-10 in the colon of both iron-supplemented groups. In conclusion, the benefits of improved host iron outweigh the risks of altered gut microbiota for intestinal mucosal growth and immune regulation in treating iron deficiency anemia.

Brain Iron Metabolism, Redox Balance and Neurological Diseases

The incidence of neurological diseases, such as Parkinson's disease, Alzheimer's disease and stroke, is increasing. An increasing number of studies have correlated these diseases with brain iron overload and the resulting oxidative damage. Brain iron deficiency has also been closely linked to neurodevelopment. These neurological disorders seriously affect the physical and mental health of patients and bring heavy economic burdens to families and society. Therefore, it is important to maintain brain iron homeostasis and to understand the mechanism of brain iron disorders affecting reactive oxygen species (ROS) balance, resulting in neural damage, cell death and, ultimately, leading to the development of disease. Evidence has shown that many therapies targeting brain iron and ROS imbalances have good preventive and therapeutic effects on neurological diseases. This review highlights the molecular mechanisms, pathogenesis and treatment strategies of brain iron metabolism disorders in neurological diseases.

Glial Cell Metabolic Profile Upon Iron Deficiency: Oligodendroglial and Astroglial Casualties of Bioenergetic Adjustments

Iron deficiency (ID) represents one of the most prevalent nutritional deficits, affecting almost two billion people worldwide. Gestational iron deprivation induces hypomyelination due to oligodendroglial maturation deficiencies and is thus a useful experimental model to analyze oligodendrocyte (OLG) requirements to progress to a mature myelinating state. A previous proteomic study in the adult ID brain by our group demonstrated a pattern of dysregulated proteins involved in the tricarboxylic acid cycle and mitochondrial dysfunction. The aim of the present report was to assess bioenergetics metabolism in primary cultures of OLGs and astrocytes (ASTs) from control and ID newborns, on the hypothesis that the regulation of cell metabolism correlates with cell maturation. Oxygen consumption and extracellular acidification rates were measured using a Seahorse extracellular flux analyzer. ID OLGs and ASTs both exhibited decreased spare respiratory capacity, which indicates that ID effectively induces mitochondrial dysfunction. A decrease in glycogen granules was observed in ID ASTs, and an increase in ROS production was detected in ID OLGs. Immunolabeling of structural proteins showed that mitochondrial number and size were increased in ID OLGs, while an increased number of smaller mitochondria was observed in ID ASTs. These results reflect an unfavorable bioenergetic scenario in which ID OLGs fail to progress to a myelinating state, and indicate that the regulation of cell metabolism may impact cell fate decisions and maturation.

Sex-Specific Effects of Early-Life Iron Deficiency and Prenatal Choline Treatment on Adult Rat Hippocampal Transcriptome

Background: Fetal-neonatal iron deficiency (ID) causes long-term neurocognitive and affective dysfunctions. Clinical and preclinical studies have shown that early-life ID produces sex-specific effects. However, little is known about the molecular mechanisms underlying these early-life ID-induced sex-specific effects on neural gene regulation. Objective: To illustrate sex-specific transcriptome alterations in adult rat hippocampus induced by fetal-neonatal ID and prenatal choline treatment. Methods: Pregnant rats were fed an iron-deficient (4 mg/kg Fe) or iron-sufficient (200 mg/kg Fe) diet from gestational day (G) 2 to postnatal day (P) 7 with or without choline supplementation (5 g/kg choline) from G11–18. Hippocampi were collected from P65 offspring of both sexes and analyzed for changes in gene expression. Results: Both early-life ID and choline treatment induced transcriptional changes in adult female and male rat hippocampi. Both sexes showed ID-induced alterations in gene networks leading to enhanced neuroinflammation. In females, ID-induced changes indicated enhanced activity of oxidative phosphorylation and fatty acid metabolism, which were contrary to the ID effects in males. Prenatal choline supplementation induced the most robust changes in gene expression, particularly in iron-deficient animals where it partially rescued ID-induced dysregulation. Choline supplementation also altered hippocampal transcriptome in iron-sufficient rats with indications for both beneficial and adverse effects. Conclusions: This study provided unbiased global assessments of gene expression regulated by iron and choline in a sex-specific manner, with greater effects in female than male rats. Our new findings highlight potential sex-specific gene networks regulated by iron and choline for further investigation.

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.

Perinatal iron deficiency as an early risk factor for schizophrenia

Growing evidence indicates that a suboptimal intrauterine environment confers risk for schizophrenia. The developmental model of schizophrenia posits that aberrant brain growth during early brain development and adolescence may interact to contribute to this psychiatric disease in adulthood. Although a variety of factors may perturb the environment of the developing fetus and predispose for schizophrenia later, a common mechanism has yet to be elucidated. Micronutrient deficiencies during the perinatal period are known to induce potent effects on brain development by altering neurodevelopmental processes. Iron is an important candidate nutrient to consider because of its role in energy metabolism, monoamine synthesis, synaptogenesis, myelination, and the high prevalence of iron deficiency (ID) in the mother-infant dyad. Understanding the current state of science regarding perinatal ID as an early risk factor for schizophrenia is imperative to inform empirical work investigating the etiology of schizophrenia and develop prevention and intervention programs. In this narrative review, we focus on perinatal ID as a common mechanism underlying the fetal programming of schizophrenia. First, we review the neural aberrations associated with perinatal ID that indicate risk for schizophrenia in adulthood, including disruptions in dopaminergic neurotransmission, hippocampal-dependent learning and memory, and sensorimotor gating. Second, we review the pathophysiology of perinatal ID as a function of maternal ID during pregnancy and use epidemiological and cohort studies to link perinatal ID with risk of schizophrenia. Finally, we review potential confounding phenotypes, including nonanemic causes of perinatal brain ID and future risk of schizophrenia.

Prenatal Iron Deficiency and Choline Supplementation Interact to Epigenetically Regulate Jarid1b and Bdnf in the Rat Hippocampus into Adulthood

Early-life iron deficiency (ID) causes long-term neurocognitive impairments and gene dysregulation that can be partially mitigated by prenatal choline supplementation. The long-term gene dysregulation is hypothesized to underlie cognitive dysfunction. However, mechanisms by which iron and choline mediate long-term gene dysregulation remain unknown. In the present study, using a well-established rat model of fetal-neonatal ID, we demonstrated that ID downregulated hippocampal expression of the gene encoding JmjC-ARID domain-containing protein 1B (JARID1B), an iron-dependent histone H3K4 demethylase, associated with a higher histone deacetylase 1 (HDAC1) enrichment and a lower enrichment of acetylated histone H3K9 (H3K9ac) and phosphorylated cAMP response element-binding protein (pCREB). Likewise, ID reduced transcriptional capacity of the gene encoding brain-derived neurotrophic factor (BDNF), a target of JARID1B, associated with repressive histone modifications such as lower H3K9ac and pCREB enrichments at the Bdnf promoters in the adult rat hippocampus. Prenatal choline supplementation did not prevent the ID-induced chromatin modifications at these loci but induced long-lasting repressive chromatin modifications in the iron-sufficient adult rats. Collectively, these findings demonstrated that the iron-dependent epigenetic mechanism mediated by JARID1B accounted for long-term Bdnf dysregulation by early-life ID. Choline supplementation utilized a separate mechanism to rescue the effect of ID on neural gene regulation. The negative epigenetic effects of choline supplementation in the iron-sufficient rat hippocampus necessitate additional investigations prior to its use as an adjunctive therapeutic agent.

Early-Life Iron Deficiency Anemia Programs the Hippocampal Epigenomic Landscape

Iron deficiency (ID) anemia is the foremost micronutrient deficiency worldwide, affecting around 40% of pregnant women and young children. ID during the prenatal and early postnatal periods has a pronounced effect on neurodevelopment, resulting in long-term effects such as cognitive impairment and increased risk for neuropsychiatric disorders. Treatment of ID has been complicated as it does not always resolve the long-lasting neurodevelopmental deficits. In animal models, developmental ID results in abnormal hippocampal structure and function associated with dysregulation of genes involved in neurotransmission and synaptic plasticity. Dysregulation of these genes is a likely proximate cause of the life-long deficits that follow developmental ID. However, a direct functional link between iron and gene dysregulation has yet to be elucidated. Iron-dependent epigenetic modifications are one mechanism by which ID could alter gene expression across the lifespan. The jumonji and AT-rich interaction domain-containing (JARID) protein and the Ten-Eleven Translocation (TET) proteins are two families of iron-dependent epigenetic modifiers that play critical roles during neural development by establishing proper gene regulation during critical periods of brain development. Therefore, JARIDs and TETs can contribute to the iron-mediated epigenetic mechanisms by which early-life ID directly causes stable changes in gene regulation across the life span.

Autophagy as a Target for Drug Development Of Skin Infection Caused by Mycobacteria

Pathogenic mycobacteria species may subvert the innate immune mechanisms and can modulate the activation of cells that cause disease in the skin. Cutaneous mycobacterial infection may present different clinical presentations and it is associated with stigma, deformity, and disability. The understanding of the immunopathogenic mechanisms related to mycobacterial infection in human skin is of pivotal importance to identify targets for new therapeutic strategies. The occurrence of reactional episodes and relapse in leprosy patients, the emergence of resistant mycobacteria strains, and the absence of effective drugs to treat mycobacterial cutaneous infection increased the interest in the development of therapies based on repurposed drugs against mycobacteria. The mechanism of action of many of these therapies evaluated is linked to the activation of autophagy. Autophagy is an evolutionary conserved lysosomal degradation pathway that has been associated with the control of the mycobacterial bacillary load. Here, we review the role of autophagy in the pathogenesis of cutaneous mycobacterial infection and discuss the perspectives of autophagy as a target for drug development and repurposing against cutaneous mycobacterial infection.

Effects of PI3K/AKT/mTOR pathway regulation of HIF-1α on Lanthanum-induced neurotoxicity in rats

This study examined the effects of the AKT/mTOR/HIF-1α signaling pathway on learning and memory in offspring rats induced by lanthanum from neuroethology and molecular biology perspectives. 32 pregnant adult Wistar rats were divided into four groups randomly: control group (NC), 0.25%, 0.5% and 1.0% LaCl3 groups (n = 8). All rats were poisoned through free drinking from day 0 of pregnancy to postnatal day 21 (suckling period). All offspring rats were poisoned through free drinking from delactation to postnatal day 48. Offspring rats aged 49-days-old were used as sampling objects to construct an LaCl3 poisoning model of offspring rats. Changes in hippocampal neurons, apoptosis of hippocampal neurons, learning and memory abilities of LaCl3-poisoned animals were measured by Nissl staining, TUNEL method and the shuttle box test, respectively. Expressions of PI3K, AKT, and mTOR, HIF-1α, and VEGF in the hippocampus were tested by qPCR and Western blot. Distributions of PI3K and p-AKT in hippocampal neurons were observed through the immunohistochemical method. With increasing LaCl3 dose, lightning strike time and active avoidance incubation period of offspring rats in the different LaCl3 groups were significantly prolonged. The Nissl body positive neurons of hippocampal neurons gradually declined while apoptosis in cells increased. The expressions of both mRNA (PI3K, AKT, mTOR, HIF-1α, VEGF) and proteins (PI3K, p-AKT, p-mTOR, HIF-1α, VEGF) in the hippocampus of the LaCl3 groups were significantly lower than those of NC group (p < 0.05). LaCl3 poisoning can induce developmental injuries in hippocampal neurons and can increase cell apoptosis. As a result, learning and memory abilities of offspring rats, as well as the expressions of PI3K/AKT/mTOR, are decreased, thus inhibiting activation of HIF-1α and influencing the expression of the downstream VEGF gene.

Sex differences in adult social, cognitive, and affective behavioral deficits following neonatal phlebotomy-induced anemia in mice

INTRODUCTION

Anemia is common in prematurely born infants due to blood loss resulting from frequent phlebotomies and may contribute to their neurobehavioral deficits. Preclinical models of phlebotomy-induced anemia (PIA) have revealed metabolic and genomic changes in multiple brain structures of young mice, yet the impact of neonatal PIA on early-life and adult behavior has not been assessed.

METHODS

The present study employed a range of behavioral measures in phlebotomized anemic neonatal mice to investigate short- and long-term neurodevelopmental effects. PIA from postnatal (P) days 3 to 14 caused sex-specific changes in social behavior, novelty preference, and anxiety at P17 that persisted into adulthood.

RESULTS

Our preclinical model suggests that PIA may contribute to acute and long-term behavioral and affective deficits and warrants further substantiation of the observed behavioral phenomena in larger samples.

CONCLUSIONS

We conclude that this model is a useful tool for beginning to better understand the lasting effect that early-life PIA might have on the developing brain. The differential impact of PIA on male and female subjects warrants further exploration for the development of appropriately targeted interventions.

Iron Nutrition, Erythrocytes, and Erythropoietin in the NICU: Erythropoietic and Neuroprotective Effects

Prematurity, maternal diabetes, maternal smoking, being medically underserved, and small size for gestational age are common characteristics of neonates in the NICU and can predispose them to develop congenital iron deficiency. Iron is critical for organ development. In the fetus and newborn, iron is prioritized for red blood cell production, sometimes at the expense of other tissues, including the brain. It is critical to optimize iron levels in newborns to support erythropoiesis, growth, and brain development. Available studies support improved neurodevelopmental outcomes with either iron supplementation or delayed umbilical cord clamping at birth. Erythropoietic doses of erythropoietin/erythrocyte-stimulating agents may also improve neurocognitive outcomes. However, the literature on the effect of liberal red blood cell transfusions on long-term neurodevelopment is mixed. Understanding age-specific normal values and monitoring of iron indices can help individualize and optimize the iron status of patients in the NICU.

Iron Deficiency Reprograms Phosphorylation Signaling and Reduces O-GlcNAc Pathways in Neuronal Cells

Micronutrient sensing is critical for cellular growth and differentiation. Deficiencies in essential nutrients such as iron strongly affect neuronal cell development and may lead to defects in neuronal function that cannot be remedied by subsequent iron supplementation. To understand the adaptive intracellular responses to iron deficiency in neuronal cells, we developed and utilized a Stable Isotopic Labeling of Amino acids in Cell culture (SILAC)-based quantitative phosphoproteomics workflow. Our integrated approach was designed to comprehensively elucidate the changes in phosphorylation signaling under both acute and chronic iron-deficient cell models. In addition, we analyzed the differential cellular responses between iron deficiency and hypoxia (oxygen-deprived) in neuronal cells. Our analysis identified nearly 16,000 phosphorylation sites in HT-22 cells, a hippocampal-derived neuronal cell line, more than ten percent of which showed at least 2-fold changes in response to either hypoxia or acute/chronic iron deficiency. Bioinformatic analysis revealed that iron deficiency altered key metabolic and epigenetic pathways including the phosphorylation of proteins involved in iron sequestration, glutamate metabolism, and histone methylation. In particular, iron deficiency increased glutamine-fructose-6-phosphate transaminase (GFPT1) phosphorylation, which is a key enzyme in the glucosamine biosynthesis pathway and a target of 5' AMP-activated protein kinase (AMPK), leading to reduced GFPT1 enzymatic activity and consequently lower global O-GlcNAc modification in neuronal cells. Taken together, our analysis of the phosphoproteome dynamics in response to iron and oxygen deprivation demonstrated an adaptive cellular response by mounting post-translational modifications that are critical for intracellular signaling and epigenetic programming in neuronal cells.

Vitamin D - A host directed autophagy mediated therapy for tuberculosis

According to the WHO report 2019, Tuberculosis (TB) is an ancient disease of humanity that is curable. TB has caused significant morbidity and mortality even in 2018. The etiological agent of TB, Mycobacterium tuberculosis (MTB) exploits its virulence factors to escape from host immunity and therapeutic drugs. Host Directed Therapy (HDT) is an adjunctive therapy where repurposed drugs, small molecules, vitamins, cytokines, and monoclonal antibodies are used to overcome the pathogen exploited pathways in the host. One of the HDTs, i.e. induction of autophagy is a highly regulated intracellular self-degradative process in which pathogens are sequestered in double-layered autophagosomes and targeted to the lysosome for degradation. Apart from the pathogen clearance, autophagy involves the release of nutrients during starvation, removal of damaged organelles and aggregated proteins, antigen presentation, tumor suppression, and anti-aging mechanisms. Xenophagy is a type of selective autophagy against microbes induced by ubiquitin receptors (p62/SQSTM1, NDP52, NBR1, OPTN, Parkin and Smurf proteins) after pathogen recognition. ULK1/2, Beclin-1, ATG5-ATG12-ATG16 L and LC-II-PE complexes along with two nutrient-sensing protein complexes, mTOR and AMPK activate autophagy mechanisms to limit infection. Pattern Recognition Receptors (PRRs) such as TLR2, recognize lipopolysaccharide (LPS) of MTB and triggers vitamin D₃ activating enzymes. Activated vitamin D₃ induces the synthesis of antimicrobial peptide, LL-37, which further enhances xenophagy. Apart from vitamin D, few micronutrients such as zinc and iron also regulate autophagy. In this review, we discuss current knowledge, advances and perspectives of autophagy against TB.

The Effects of Early-Life Iron Deficiency on Brain Energy Metabolism

Iron deficiency (ID) is one of the most prevalent nutritional deficiencies in the world. Iron deficiency in the late fetal and newborn period causes abnormal cognitive performance and emotional regulation, which can persist into adulthood despite iron repletion. Potential mechanisms contributing to these impairments include deficits in brain energy metabolism, neurotransmission, and myelination. Here, we comprehensively review the existing data that demonstrate diminished brain energetic capacity as a mechanistic driver of impaired neurobehavioral development due to early-life (fetal-neonatal) ID. We further discuss a novel hypothesis that permanent metabolic reprogramming, which occurs during the period of ID, leads to chronically impaired neuronal energetics and mitochondrial capacity in adulthood, thus limiting adult neuroplasticity and neurobehavioral function. We conclude that early-life ID impairs energy metabolism in a brain region- and age-dependent manner, with particularly strong evidence for hippocampal neurons. Additional studies, focusing on other brain regions and cell types, are needed.

A genome-wide transcriptional study reveals that iron deficiency inhibits the yeast TORC1 pathway

Iron is an essential micronutrient that participates as a cofactor in a broad range of metabolic processes including mitochondrial respiration, DNA replication, protein translation and lipid biosynthesis. Adaptation to iron deficiency requires the global reorganization of cellular metabolism directed to optimize iron utilization. The budding yeast Saccharomyces cerevisiae has been widely used to characterize the responses of eukaryotic microorganisms to iron depletion. In this report, we used a genomic approach to investigate the contribution of transcription rates to the modulation of mRNA levels during adaptation of yeast cells to iron starvation. We reveal that a decrease in the activity of all RNA polymerases contributes to the down-regulation of many mRNAs, tRNAs and rRNAs. Opposite to the general expression pattern, many genes including components of the iron deficiency response, the mitochondrial retrograde pathway and the general stress response display a remarkable increase in both transcription rates and mRNA levels upon iron limitation, whereas genes encoding ribosomal proteins or implicated in ribosome biogenesis exhibit a pronounced fall. This expression profile is consistent with an activation of the environmental stress response. The phosphorylation stage of multiple regulatory factors strongly suggests that the conserved nutrient signaling pathway TORC1 is inhibited during the progress of iron deficiency. These results suggest an intricate crosstalk between iron metabolism and the TORC1 pathway that should be considered in many disorders.

Effects of maternal exposure to nonylphenol on learning and memory in offspring involve inhibition of BDNF-PI3K/Akt signaling

Nonylphenol (NP), a global environmental pollutant, has been found to result in impairments of neurodevelopment. However, effects of maternal exposure to NP on learning and memory and the potential mechanisms are largely unexplored. Thus, we treated dams with NP during gestation and lactation to study its effect on learning and memory in offspring. Morris water maze (MWM) task and the electrophysiological recording in the hippocampus were conducted in pups. We also investigated the activation of BDNF-PI3K/Akt signaling and the expression of its target protein PSD-95 in offspring hippocampus, which are curial for the synaptic plasticity and learning and memory. The results showed that maternal exposure to NP led to poor performance in MWM task and especially impairments of long-term potentiation (LTP), although the termination of NP exposure was at the end of lactation. Meanwhile, maternal exposure to NP also decreased the activation of BDNF-PI3K/Akt signaling and the protein level of PSD-95. Taken together, our results support the hypothesis that maternal exposure to NP during gestation and lactation causes damages to learning and memory. In addition, suppressed activation of the BDNF-PI3K/Akt signaling may contribute to these impairments caused by maternal exposure to NP.

Biomarkers of Nutrition for Development (BOND)-Iron Review

This is the fifth in the series of reviews developed as part of the Biomarkers of Nutrition for Development (BOND) program. The BOND Iron Expert Panel (I-EP) reviewed the extant knowledge regarding iron biology, public health implications, and the relative usefulness of currently available biomarkers of iron status from deficiency to overload. Approaches to assessing intake, including bioavailability, are also covered. The report also covers technical and laboratory considerations for the use of available biomarkers of iron status, and concludes with a description of research priorities along with a brief discussion of new biomarkers with potential for use across the spectrum of activities related to the study of iron in human health.The I-EP concluded that current iron biomarkers are reliable for accurately assessing many aspects of iron nutrition. However, a clear distinction is made between the relative strengths of biomarkers to assess hematological consequences of iron deficiency versus other putative functional outcomes, particularly the relationship between maternal and fetal iron status during pregnancy, birth outcomes, and infant cognitive, motor and emotional development. The I-EP also highlighted the importance of considering the confounding effects of inflammation and infection on the interpretation of iron biomarker results, as well as the impact of life stage. Finally, alternative approaches to the evaluation of the risk for nutritional iron overload at the population level are presented, because the currently designated upper limits for the biomarker generally employed (serum ferritin) may not differentiate between true iron overload and the effects of subclinical inflammation.

Neonatal mouse hippocampus: phlebotomy-induced anemia diminishes and treatment with erythropoietin partially rescues mammalian target of rapamycin signaling

BackgroundPhlebotomy-induced anemia (PIA) is common in premature infants and affects neurodevelopment. PIA alters hippocampal metabolism in neonatal mice through tissue hypoxia and iron deficiency. The mammalian target of rapamycin (mTOR) pathway senses the status of critical metabolites (e.g., oxygen, iron), thereby regulating hippocampal growth and function. We determined the effect of PIA and recombinant human erythropoietin (rHuEpo) treatment on mTOR signaling and expression of genes related to mTOR pathway functions.MethodsMice receiving an iron-supplemented diet were phlebotomized from postnatal day (P)3 to a target hematocrit of <25% by P7. Half were maintained at <25% until P14; half received rHuEpo from P7 to increase the hematocrit to 25-28%. Hippocampal phosphorylated to total protein ratios of four key mTOR pathway proteins were measured by western blotting at P14 and compared with non-phlebotomized, non-anemic control mice. mRNA levels of genes regulated by mTOR were measured by quantitative PCR.ResultsPIA suppressed phosphorylation of all mTOR proteins. rHuEpo restored AMP-activated protein kinase (AMPK) and AKT status, and partially rescued the mTOR output protein S6K. PIA and rHuEpo treatment also altered the expression of genes regulated by S6K.ConclusionPIA compromises and rHuEpo treatment partially rescues a pathway regulating neuronal DNA transcription, protein translation, and structural complexity.

The Effects of Prenatal Iron Deficiency and Risperidone Treatment on the Rat Frontal Cortex: A Proteomic Analysis

Prenatal iron deficiency (pID) has been described to increase the risk for neurodevelopmental disorders such as autism and schizophrenia; however, the precise molecular mechanisms are still unknown. Here, we utilized high-throughput MS to examine the proteomic effects of pID in adulthood on the rat frontal cortex area (FCA). In addition, the FCA proteome was examined in adulthood following risperidone treatment in adolescence to see if these effects could be prevented. We identified 1501 proteins of which 100 were significantly differentially expressed in the FCA at postnatal day 90. Pathway analysis of proteins affected by pID revealed changes in metabolic processes, including the tricyclic acid cycle, mitochondrial dysfunction, and P13K/Akt signaling. Interestingly, most of these protein changes were not present in the adult pID offspring who received risperidone in adolescence. Considering the link between pID and several neurodevelopmental disorders such as autism and schizophrenia these presented results bring new perspectives to understand the role of iron in metabolic pathways and provide novel biomarkers for future studies of pID.

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

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

Iron is prioritized to red blood cells over the brain in phlebotomized anemic newborn lambs

BACKGROUND

Critically ill preterm and term neonates are at high risk for negative iron balance due to phlebotomy that occurs with frequent laboratory monitoring, and the high iron demand of rapid growth. Understanding the prioritization of iron between red blood cells (RBCs) and brain is important given iron's role in neurodevelopment.

METHODS

Ten neonatal twin lamb pairs (n = 20) underwent regular phlebotomy for 11 d. Lambs were randomized to receive no iron or i.v. daily iron supplementation from 1 to 5 mg/kg. Serum hemoglobin concentration and reticulocyte count were assayed, iron balance calculated, and iron content of RBCs, liver, brain, muscle, and heart measured at autopsy.

RESULTS

Among phlebotomized lambs: (i) liver iron concentration was directly related to net iron balance (r = 0.87; P < 0.001) and (ii) brain iron concentration was reduced as a function of net iron balance (r = 0.63) only after liver iron was depleted. In animals with negative iron balance, total RBC iron was maintained while brain iron concentration decreased as a percentage of the iron present in RBCs (r = -0.70; P < 0.01) and as a function of reticulocyte count (r = -0.63; P < 0.05).

CONCLUSION

Phlebotomy-induced negative iron balance limits iron availability to the developing brain.

Prenatal Choline Supplementation Diminishes Early-Life Iron Deficiency-Induced Reprogramming of Molecular Networks Associated with Behavioral Abnormalities in the Adult Rat Hippocampus

BACKGROUND

Early-life iron deficiency is a common nutrient deficiency worldwide. Maternal iron deficiency increases the risk of schizophrenia and autism in the offspring. Postnatal iron deficiency in young children results in cognitive and socioemotional abnormalities in adulthood despite iron treatment. The rat model of diet-induced fetal-neonatal iron deficiency recapitulates the observed neurobehavioral deficits.

OBJECTIVES

We sought to establish molecular underpinnings for the persistent psychopathologic effects of early-life iron deficiency by determining whether it permanently reprograms the hippocampal transcriptome. We also assessed the effects of maternal dietary choline supplementation on the offspring's hippocampal transcriptome to identify pathways through which choline mitigates the emergence of long-term cognitive deficits.

METHODS

Male rat pups were made iron deficient (ID) by providing pregnant and nursing dams an ID diet (4 g Fe/kg) from gestational day (G) 2 through postnatal day (PND) 7 and an iron-sufficient (IS) diet (200 g Fe/kg) thereafter. Control pups were provided IS diet throughout. Choline (5 g/kg) was given to half the pregnant dams in each group from G11 to G18. PND65 hippocampal transcriptomes were assayed by next generation sequencing (NGS) and analyzed with the use of knowledge-based Ingenuity Pathway Analysis. Real-time polymerase chain reaction was performed to validate a subset of altered genes.

RESULTS

Formerly ID rats had altered hippocampal expression of 619 from >10,000 gene loci sequenced by NGS, many of which map onto molecular networks implicated in psychological disorders, including anxiety, autism, and schizophrenia. There were significant interactions between iron status and prenatal choline treatment in influencing gene expression. Choline supplementation reduced the effects of iron deficiency, including those on gene networks associated with autism and schizophrenia.

CONCLUSIONS

Fetal-neonatal iron deficiency reprograms molecular networks associated with the pathogenesis of neurologic and psychological disorders in adult rats. The positive response to prenatal choline represents a potential adjunctive therapeutic supplement to the high-risk group.

Fetal and neonatal iron deficiency but not copper deficiency increases vascular complexity in the developing rat brain

OBJECTIVES

Anemia caused by nutritional deficiencies, such as iron and copper deficiencies, is a global health problem. Iron and copper deficiencies have their most profound effect on the developing fetus/infant, leading to brain development deficits and poor cognitive outcomes. Tissue iron depletion or chronic anemia can induce cellular hypoxic signaling. In mice, chronic hypoxia induces a compensatory increase in brain blood vessel outgrowth. We hypothesized that developmental anemia, due to iron or copper deficiencies, induces angiogenesis/vasculogenesis in the neonatal brain.

METHODS

To test our hypothesis, three independent experiments were performed where pregnant rats were fed iron- or copper-deficient diets from gestational day 2 through mid-lactation. Effects on the neonatal brain vasculature were determined using quantitative real-time polymerase chain reaction to assess mRNA levels of angiogenesis/vasculogenesis-associated genes and GLUT1 immunohistochemistry to assess brain blood vessel density and complexity.

RESULTS

Iron deficiency, but not copper deficiency, increased mRNA expression of brain endothelial cell- and angiogenesis/vasculogenesis-associated genes (i.e. Glut1, Vwf, Vegfa, Ang2, Cxcl12, and Flk1) in the neonatal brain, suggesting increased cerebrovascular density. Iron deficiency also increased hippocampal and cerebral cortical blood vessel branching by 62 and 78%, respectively.

DISCUSSION

This study demonstrates increased blood vessel complexity in the neonatal iron-deficient brain, which is likely due to elevated angiogenic/vasculogenic signaling. At least initially, this is probably an adaptive response to maintain metabolic substrate homeostasis in the developing iron-deficient brain. However, this may also contribute to long-term neurodevelopmental deficits.

A critical role for mTORC1 in erythropoiesis and anemia

Red blood cells (RBC) must coordinate their rate of growth and proliferation with the availability of nutrients, such as iron, but the signaling mechanisms that link the nutritional state to RBC growth are incompletely understood. We performed a screen for cell types that have high levels of signaling through mTORC1, a protein kinase that couples nutrient availability to cell growth. This screen revealed that reticulocytes show high levels of phosphorylated ribosomal protein S6, a downstream target of mTORC1. We found that mTORC1 activity in RBCs is regulated by dietary iron and that genetic activation or inhibition of mTORC1 results in macrocytic or microcytic anemia, respectively. Finally, ATP competitive mTOR inhibitors reduced RBC proliferation and were lethal after treatment with phenylhydrazine, an inducer of hemolysis. These results identify the mTORC1 pathway as a critical regulator of RBC growth and proliferation and establish that perturbations in this pathway result in anemia.

DOI:http://dx.doi.org/10.7554/eLife.01913.001

To multiply and grow, cells need to create more of the molecules—such as proteins—that make up their structure. This only happens if the cell has a good supply of the nutrients used to build the proteins.

Red blood cells are particularly sensitive to the supply of nutrients, especially iron, which is a key component of the hemoglobin molecules that enable the cells to transport oxygen around the body. A lack of iron can lead to a shortage of red blood cells and a condition called anemia. People with mild forms of anemia may feel tired or weak, but more severe forms of anemia can cause heart problems and even death.

A protein called mTOR forms part of a protein complex that helps alert the cells of many different organisms to the presence of nutrients. mTOR can add phosphate groups to ribosomes—the molecular machines that translate molecules of mRNA to build proteins. In 2012, researchers developed a technique called Phospho-Trap that can isolate these phosphorylated ribosomes from cells. Cells with an activated mTOR complex express more mTOR protein and in turn have more ribosomes that are modified. Examining the mRNA molecules associated with these ribosomes can reveal which proteins are produced in greater amounts in these cells.

Previous experiments using Phospho-Trap found the proteins that make up hemoglobin in unexpectedly high amounts in the mouse brain. Now, Knight et al.—and other researchers involved in the 2012 work—have established that the hemoglobin was not coming from the brain cells but from immature red blood cells circulating within the brain. These immature blood cells were found to have a highly active mTOR complex that promotes the production of hemoglobin and new blood cells.

Using genetic techniques in mice, Knight et al. found that the mTOR complex can cause anemia if it is underactive or overactive. Underactive mTOR complexes cause a type of anemia that produces small red blood cells and is usually triggered by a lack of iron. This made sense because mTOR is known to regulate both protein production and cell size. Boosting the activity of the mTOR complex leads to a type of anemia in which the cells are much larger than normal, and which is normally associated with inadequate amounts of folate and B12 vitamins.

When Knight et al. gave mice a drug that inhibits the mTOR protein, the mice developed anemia that resolved when the treatment stopped. However, mice that were given the mTOR inhibitor at the same time as a drug that destroys red blood cells, all died within days. Clinical trials are currently testing mTOR inhibitors as a possible cancer treatment; however, a common side effect of chemotherapy is that it stops new red blood cells being produced. Knight et al. suggest that the red blood cells of patients in these clinical trials must be closely monitored before deciding whether to continue the treatment further.

DOI:http://dx.doi.org/10.7554/eLife.01913.002

Gestational iron deficiency differentially alters the structure and function of white and gray matter brain regions of developing rats

Gestational iron deficiency (ID) has been associated with a wide variety of central nervous system (CNS) impairments in developing offspring. However, a focus on singular regions has impeded an understanding of the CNS-wide effects of this micronutrient deficiency. Because the developing brain requires iron during specific phases of growth in a region-specific manner, we hypothesized that maternal iron deprivation would lead to region-specific impairments in the CNS of offspring. Female rats were fed an iron control (Fe+) or iron-deficient (Fe-) diet containing 240 or 6 μg/g iron during gestation and lactation. The corpus callosum (CC), hippocampus, and cortex of the offspring were analyzed at postnatal day 21 (P21) and/or P40 using structural and functional measures. In the CC at P40, ID was associated with reduced peak amplitudes of compound action potentials specific to myelinated axons, in which diameters were reduced by ∼20% compared with Fe+ controls. In the hippocampus, ID was associated with a 25% reduction in basal dendritic length of pyramidal neurons at P21, whereas branching complexity was unaffected. We also identified a shift toward increased proximal branching of apical dendrites in ID without an effect on overall length compared with Fe+ controls. ID also affected cortical neurons, but unlike the hippocampus, both apical and basal dendrites displayed a uniform decrease in branching complexity, with no significant effect on overall length. These deficits culminated in significantly poorer performance of P40 Fe- offspring in the novel object recognition task. Collectively, these results demonstrate that non-anemic gestational ID has a significant and region-specific impact on neuronal development and may provide a framework for understanding and recognizing the presentation of clinical symptoms of ID.

Is low iron status a risk factor for neural tube defects?

BACKGROUND

Folic acid supplements can protect against neural tube defects (NTDs). Low folate and low vitamin B12 status may be maternal risk factors for having an NTD affected pregnancy. However, not all NTDs are preventable by having an adequate folate/ B12 status and other potentially modifiable factors may be involved. Folate and vitamin B12 status have important links to iron metabolism. Animal studies support an association between poor iron status and NTDs, but human data are scarce. We examined the relevance of low iron status in a nested NTD case-control study of women within a pregnant population-based cohort.

METHODS

Pregnant women were recruited between 1986 and 1990, when vitamin or iron supplementation in early pregnancy was rare. Blood samples, taken at an average of 14 weeks gestation, were used to measure ferritin and hemoglobin in 64 women during an NTD affected pregnancy and 207 women with unaffected pregnancies.

RESULTS

No significant differences in maternal ferritin or hemoglobin concentrations were observed between NTD affected and nonaffected pregnancies (case median ferritin 16.9 µg/L and hemoglobin 12.4 g/dl versus 15.4 µg/L and 12.3g/dl in controls). As reported previously, red cell folate and vitamin B12 concentrations were significantly lower in cases. Furthermore, there was no significant association of iron status with type of NTD lesion (anencephaly or spina bifida).

CONCLUSION

We conclude that low maternal iron status during early pregnancy is not an independent risk factor for NTDs. Adding iron to folic acid for periconceptional use may improve iron status but is not likely to prevent NTDs.

Mammalian target of rapamycin coordinates iron metabolism with iron-sulfur cluster assembly enzyme and tristetraprolin

Both iron deficiency and excess are relatively common health concerns. Maintaining the body's levels of iron within precise boundaries is critical for cell functions. However, the difference between iron deficiency and overload is often a question of a scant few milligrams of iron. The mammalian target of rapamycin (mTOR), an atypical Ser/Thr protein kinase, is attracting significant amounts of interest due to its recently described role in iron homeostasis. Despite extensive study, a complete understanding of mTOR function has remained elusive. mTOR can form two multiprotein complexes that consist of mTOR complex 1 (mTORC1) and mTOR complex 2. Recent advances clearly demonstrate that mTORC1 can phosphorylate iron-sulfur cluster assembly enzyme ISCU and affect iron-sulfur clusters assembly. Moreover, mTOR is reported to control iron metabolism through modulation of tristetraprolin expression. It is now well appreciated that the hormonal hepcidin-ferroportin system and the cellular iron-responsive element/iron-regulatory protein regulatory network play important regulatory roles for systemic iron metabolism. Sustained ISCU protein levels enhanced by mTORC1 can inhibit iron-responsive element and iron-regulatory protein binding activities. In this study, hepcidin gene and protein expression in the livers of tristetraprolin knockout mice were dramatically reduced. Here, we highlight and summarize the current understanding of how mTOR pathways serve to modulate iron metabolism and homeostasis as the third iron-regulatory system.

Early-life iron deficiency anemia alters the development and long-term expression of parvalbumin and perineuronal nets in the rat hippocampus

Early-life iron deficiency anemia (IDA) alters the expression of critical genes involved in neuronal dendritic structural plasticity of the hippocampus, thus contributing to delayed maturation of electrophysiology, and learning and memory behavior in rats. Structural maturity in multiple cortical regions is characterized by the appearance of parvalbumin-positive (PV(+)) GABAergic interneurons and perineuronal nets (PNNs). Appearance of PV(+) interneurons and PNNs can serve as cellular markers for the beginning and end of a critical developmental period, respectively. During this period, the system progresses from an immature yet highly plastic condition, to a more mature and efficient state that is however less flexible and may exhibit poorer potential for recovery from injury. To test if fetal-neonatal IDA alters parvalbumin (PV) mRNA expression, protein levels, and the number of PV(+) interneurons and PNNs in the male rat hippocampus, pregnant dams were given an iron-deficient (ID) diet (3 mg iron/kg chow) from gestational day 2 to postnatal day (P) 7 and then placed on an iron-sufficient (IS) diet (198 mg/kg) for the remainder of the experiment. On this regimen, formerly ID animals become fully iron-replete by P56. Minimal levels of PV (mRNA and protein), PV(+) interneurons, and PNNs were found in IS and ID P7 rats. By P15, and continuing through P30 and P65, ID rats had reduced PV mRNA expression and protein levels compared to IS controls. While there were no differences in the number of PV(+) neurons at either P30 or P65, the percentage of PV(+) cells surrounded by PNNs was slightly greater in ID rats as compared to IS controls. The lower levels of these acknowledged critical period biomarkers in the ID group are consistent with studies that demonstrate later maturation of the acutely ID hippocampus and lower plasticity in the adult formerly ID hippocampus. The findings provide additional potential cellular bases for previously described electrophysiologic and behavioral abnormalities found during and following early-life IDA.