Thioneins are cysteine-rich apoproteins that regulate divalent metal homeostasis by virtue of their metal-chelation properties resulting in the ligand-bound metallothionein state. Previous studies show transient upregulation of the metallothionein (MT) gene cluster as part of a complex transcriptional response to a class of histone H3K27me3 demethylase tool compounds targeting human Fe2+ dependent ketoglutarate oxygenases KDM6A (UTX) and KDM6B (JmjD3). The prototypic bioactive KDM6 inhibitor GSK-J4 induces apoptotic cell death in multiple myeloma cells and corresponding transcriptomic profiles are dominated by metal and integrated stress response (ISR) signatures, also observed in primary human myeloma cells. Here we investigate the hypothesis that metal-chelation by GSK-J4 provides the means for transport and intracellular release of Zn2+ leading to a metallothionein transcriptomic response signature. Live cell imaging of myeloma cells shows transient increases in intracellular free Zn2+ concentrations when exposed to GSK-J4, consistent with a model of inhibitor-mediated metal transport, further supported by direct metal-inhibitor complex formation as determined by MALDI-TOF mass spectrometry and 1H NMR. Comparisons of GSK-J4 and ZnSO4 treatments in the presence or absence of metal chelators show that both treatment conditions induce different transcription factor repertoires with an overlapping MTF1 transcriptional regulation responsible for metallothionein and metal ion transport regulation. The data provide a possible explanation for the observed metal response upon GSK-J4 inhibition however the relationship with the pro-apoptotic ISR mechanism in myeloma cells requires further investigation.

Paramagnetic-rim lesions are a novel diagnostic marker in multiple sclerosis (MS) and are associated with poor prognosis due to their link with chronic inflammation and disease progression. Analyzing 46 postmortem MS cases, researchers found no iron rims in 67 white matter and 85 grey matter spinal cord lesions, despite most being active. In contrast, iron rims appeared in 20.9% of cortical and 80% of subcortical brain lesions, especially in deeper myelin-rich cortical layers. These findings highlight the regional variability of iron accumulation and have important implications for interpreting iron-rims in MS diagnosis, monitoring, and prognostication. ANN NEUROL 2026;99:730-736.

Abstract Iron deficiency during pregnancy remains a global health burden, yet pregnancy-related physiological adaptations complicate the interpretation of iron biomarkers. Modified oral iron regimens are increasingly used to balance iron intake, absorption, and tolerability. This study evaluated the effects of daily, alternate-day, and 3-times-weekly oral iron supplementation on iron status biomarkers in nonanaemic pregnant participants. In the PANDA (Primary prevention of maternal Anemia to avoid preterm Delivery and other Adverse outcomes) dose-finding trial, nonanemic pregnant women were randomized to receive 200 mg of ferrous sulfate daily, on alternate days, or 3-times-weekly. Blood samples were collected at 9 to 13 and 26 to 30 weeks’ gestation (N = 135 participants). Hepcidin and soluble transferrin receptor (sTfR) were measured by enzyme-linked immunosorbent assay, and serum iron, ferritin, transferrin, and C-reactive protein using automated biochemistry. Linear mixed-effects models assessed within- and between-group biomarker changes. Hepcidin, ferritin, and transferrin saturation declined significantly between baseline and follow-up in all groups (P< .001). sTfR increased in the alternate-day (P = .003) and 3-times-weekly groups (P< .001), but not in the daily group (P = .084). Despite supplementation and maintenance of hemoglobin levels, 69% to 72% of women were iron deficient (ferritin <30 μg/L) at 26 to 30 weeks’ gestation. Iron status declined across pregnancy regardless of supplementation regimen, suggesting physiological adaptations may dominate over dosing effects. The absence of a significant rise in sTfR in the daily group suggests that daily dosing best meets the iron demand of pregnancy, though confirmation in larger, adequately powered studies is required. This trial was registered at the UK trial registry as #ISRCTN12911644.

Infection involves the utilization of host nutritional resources by the pathogen. Genetic, experimental, and clinical evidence supports the critical role of iron as a focus for both pathogen attack and host defense. The molecular basis of how mammals regulate iron transport to maintain homeostasis, and in response to infection, has been well characterized since the discovery of the hormone hepcidin. The multiple activities of iron in host innate and adaptive immune cell function have also been studied in increasing depth. Recently these research strands have been converging, showing how host regulation of iron affects not only classical "nutritional immunity" as a defense against pathogens but also influences the development and magnitude of immune responses. These findings are discussed in the context of different types of infectious micro-organisms, against a background of host disease states (including respiratory disorders), and in relation to iron supplementation, vaccination, and pathological immune responses.

Sepsis is a leading cause of death and disability worldwide, so identifying preventable risk factors is important. Iron is essential for immune function and microbial growth, and iron status varies substantially between individuals, across demographics, and is therapeutically modifiable. Here, we review the current understanding of iron status and associated risks of bloodstream infection, sepsis and severe COVID-19 highlighting relevant population-based studies and Mendelian randomisation studies. Both low and high iron status are associated with increased risk of sepsis. Low iron status is associated with sepsis, bloodstream infections and pneumonia. High iron status and mutations affecting hepcidin regulation are linked to increased risk of bloodstream infections, sepsis and COVID-19. Both iron status pathologies and sepsis are global health issues, and the epidemiological studies described indicate they may be linked. More population-scale investigations on iron status, infection and immunity, especially in areas of high iron deficiency and infectious burden are warranted.

Iron is an irreplaceable co-factor for metabolism. Iron deficiency affects >1 billion people and decreased iron availability impairs immunity. Nevertheless, how iron deprivation impacts immune cell function remains poorly characterised. We interrogate how physiologically low iron availability affects CD8+ T cell metabolism and function, using multi-omic and metabolic labelling approaches. Iron limitation does not substantially alter initial post-activation increases in cell size and CD25 upregulation. However, low iron profoundly stalls proliferation (without influencing cell viability), alters histone methylation status, gene expression, and disrupts mitochondrial membrane potential. Glucose and glutamine metabolism in the TCA cycle is limited and partially reverses to a reductive trajectory. Previous studies identified mitochondria-derived aspartate as crucial for proliferation of transformed cells. Despite aberrant TCA cycling, aspartate is increased in stalled iron deficient CD8+ T cells but is not utilised for nucleotide synthesis, likely due to trapping within depolarised mitochondria. Exogenous aspartate markedly rescues expansion and some functions of severely iron-deficient CD8+ T cells. Overall, iron scarcity creates a mitochondrial-located metabolic bottleneck, which is bypassed by supplying inhibited biochemical processes with aspartate. These findings reveal molecular consequences of iron deficiency for CD8+ T cell function, providing mechanistic insight into the basis for immune impairment during iron deficiency.

Iron is crucial for cellular metabolism and cell growth. Nevertheless, in humans, both iron deficiency and disorders of iron overload are widespread. How cellular iron content varies depending upon iron availability, and how this influences cell function is poorly characterised. We developed a method to quantify metals in hundreds of cells per minute via single-cell inductively-coupled plasma mass spectrometry (sc-ICP-MS), and used this to explore iron usage by immune cells. Activated murine T-cells exposed to a 625-fold titration of extracellular iron maintained close homeostatic control, with iron content varying by ∼20%. However, these variations strongly correlated with activation characteristics and proliferation. Running sc-ICP-MS downstream of flow cytometric sorting showed that murine T-cells and B-cells ex vivo exhibit similar mean and heterogeneity of cellular iron while splenic macrophages contain twice as much iron and more heterogeneous iron content. Finally, activated human B-cells contain ∼10-fold more iron per cell than murine B-cells. We suggest that mechanisms of iron homeostasis impart particular ranges or set-points of iron content to different cell types and activation states, and that small changes in iron content have large effects on cell behaviour. Our methodological advance and consequent findings suggest new approaches to studying the biology of metals. ### Competing Interest Statement The authors have declared no competing interest. Tabulated data accompanying the intercalation and murine lymphocyte experiments are included in the supplementary data at the end of this manuscript. Please contact the corresponding author for further information about the data presented in this manuscript. Medical Research Council, https://ror.org/03x94j517, MCU_12010/10

Red blood cell development from erythroid progenitors requires profound reshaping of metabolism and gene expression. How these transcriptional and metabolic alterations are coupled is unclear. Nprl3 (an inhibitor of mTORC1) has remained in synteny with the α-globin genes for >500 million years, and harbours most of the a-globin enhancers. However, whether Nprl3 serves an erythroid role is unknown. We found that while haematopoietic progenitors require basal Nprl3 expression, erythroid Nprl3 expression is further boosted by the α-globin enhancers. This lineage-specific upregulation is required for sufficient erythropoiesis. Loss of Nprl3 affects erythroblast metabolism via elevating mTORC1 signalling, suppressing autophagy and disrupting glycolysis. Broadly consistent with these murine findings, human NPRL3-knockout erythroid progenitors produce fewer enucleated cells and demonstrate dysregulated mTORC1 signalling in response to nutrient availability and erythropoietin. Therefore, we propose that the anciently conserved linkage of NprI3, α-globin and their associated enhancers has coupled metabolic and developmental control of erythropoiesis.

α-globin’s genomic next-door neighbor, Nprl3, contains 4 of the 5 α-globin enhancers. Nprl3 negatively regulates mTORC1, a master controller of cell metabolism. Nprl3, α-globin, and the α-globin enhancers have been colocated for >500 million years. However, the function of this genomic linkage is unknown.Using a mouse in which the Nprl3 promoter is deleted (with no effect on the α-globin enhancers), we showed that Nprl3 is required for optimal erythropoiesis in fetal liver and bone marrow. On embryonic day 13.5 (E13.5) in the fetal liver, Nprl3−/− erythroid cells failed to develop beyond the proerythroblast stage. Metabolite profiling, RNA-Seq and proteomics showed that Nprl3−/− erythroblasts have overactivated mTORC1 signaling, overcharged glycolysis, and suppressed autophagy. Competitive bone marrow-fetal liver chimeras indicated a hematopoietic-intrinsic Nprl3 requirement for erythropoiesis. To study human erythropoiesis, we induced NPRL3-knockout by RNP-editing primary CD34+ cells. Edited progenitors produced fewer enucleated erythroid cells and exhibited defective mTORC1 signaling responses to fluctuating iron, amino acid, and erythropoietin (EPO) availability. Nprl3 tunes the metabolism of developing erythroid cells to their nutritional environment.Nprl3 expression is highly elevated in erythroid cells. We showed that this is due to the interaction between the Nprl3 promoter and α-globin enhancers. We eliminated interactions (in cis) between Nprl3 and the enhancers, while maintaining enhancer control of α-globin. Remarkably, our approach resulted in erythropoietic impairment reminiscent of the Nprl3−/− genotype (with E13.5 erythroid development inhibited at the same stage of differentiation). Therefore, the ancient transcriptional hub of Nprl3, α-globin, and their enhancers supports the erythroid-specific upregulation of Nprl3 and coordinates metabolic control with red blood cell development.

BACKGROUND & AIMS:Pathogenic variants in the cellular iron exporter ferroportin (SLC40A1) cause hepatic and splenic iron overload. Low to normal transferrin saturation (TSAT) and iron accumulation in Kupffer cells with high splenic iron distinguish ferroportin disease (FD) from SLC40A1-related hemochromatosis (SLC40A1-HC), which are both caused by variants in SLC40A1. The aim of our study was to describe pathogenic mutations in SLC40A1, phenotypic variability in affected patients and compare outcomes with HFE-related hemochromatosis (HFE-HC). METHODS:The international EASL non-HFE hemochromatosis patient registry prospectively collected clinical, radiological, biochemical, and genetic data for 95 patients with SLC40A1 variants from six centers. Additionally, 363 patients were identified by a systematic literature review. As a comparator, 603 patients diagnosed with HFE-HC were included. RESULTS:The FD phenotype presented in 65.5% of affected individuals. Patients with FD were younger at diagnosis and more often female than those with SLC40A1-HC. SLC40A1 variants were associated with higher hepatic and splenic iron concentrations compared to the HFE-HC group. Variability in phenotypic presentation was high among patients with SLC40A1 variants, and a genotype-to-phenotype correlation could only explain a small proportion of this variation. Variants that directly affect the metal binding site in ferroportin more likely presented with high TSAT. Patients with the SLC40A1-HC phenotype (TSAT >45%) had a higher risk of fibrosis. Life expectancy was similar between patients with SLC40A1 variants and matched patients with HFE-HC. Most individuals with SLC40A1 variants (73.2%) received regular phlebotomies, which were not associated with differences in life expectancy. CONCLUSIONS:Mutations in SLC40A1 cause a highly variable disease spectrum with hepatic and splenic iron overload. Fibrosis risk is higher in patients with elevated TSAT. IMPACT AND IMPLICATIONS:Clinical management of individuals with SLC40A1 variants has largely been extrapolated from HFE-related hemochromatosis despite fundamental pathophysiological differences. Our study provides detailed phenotypic characterization that supports diagnosis and distinction of these rare iron overload disorders. Long-term follow-up shows preserved life expectancy, unaffected by phlebotomy, underscoring the need to critically assess phlebotomy on an individualized basis. Patients with SLC40A1-related hemochromatosis (transferrin saturation >45%) had a higher prevalence of chronic liver disease than those with ferroportin disease, suggesting that elevated transferrin saturation and hepatic iron drive disease progression, which can guide risk stratification and clinical decision making. CLINICAL TRIAL NUMBER:Not applicable.

Iron is a cofactor for hundreds of enzymes and biochemical processes that support cellular metabolism across the kingdoms of life. Because of this, the host and pathogen compete for iron as a vital resource. Moreover, research has shown that iron acquisition and iron trafficking have substantial effects on the immune system. This is especially important because iron-related disorders — both deficiency and overload — are common worldwide. In this Review, we describe how immune cells acquire and use iron, which branches of the immune system are most affected by iron and how changes in iron availability can affect infectious diseases, autoinflammatory disorders and antitumour immunity. We also discuss key unanswered questions and potential therapeutic opportunities to manipulate immunity by controlling iron trafficking. Iron is crucial for cellular metabolism, but its availability varies greatly within and between individuals and populations. This Review highlights how iron regulates innate and adaptive cellular and humoral responses affecting protection against infections, tumours and autoimmunity.

Herpesviruses modulate immune control to secure lifelong infection. The mechanisms Human Cytomegalovirus (HCMV) employs in this regard can reveal unanticipated aspects of cellular signaling involved in antiviral immunity. Here, we describe a novel relationship between the TGF-β family cytokine BMP9 and HCMV infection. We identify a cross-talk between BMP9-induced and IFN receptor-mediated signaling, showing that BMP9 boosts the transcriptional response to and antiviral activity of IFNβ, thereby enhancing viral restriction. We also show that BMP9 is secreted by human fibroblasts upon HCMV infection. However, HCMV infection impairs BMP9-induced enhancement of the IFNβ response, indicating that this signaling role of BMP9 is actively targeted by HCMV. Indeed, transmembrane proteins US18 and US20, which downregulate type I BMP receptors, are necessary and sufficient to cause inhibition of BMP9-mediated boosting of the antiviral response to IFNβ. HCMV lacking US18 and US20 is more sensitive to IFNβ. Thus, HCMV has a mutually antagonistic relationship with BMP9, which extends the growing body of evidence that BMP signaling is an underappreciated modulator of innate immunity in response to viral infection.

Persistent symptoms following SARS-CoV-2 infection are increasingly reported, although the drivers of post-acute sequelae (PASC) of COVID-19 are unclear. Here we assessed 214 individuals infected with SARS-CoV-2, with varying disease severity, for one year from COVID-19 symptom onset to determine the early correlates of PASC. A multivariate signature detected beyond two weeks of disease, encompassing unresolving inflammation, anemia, low serum iron, altered iron-homeostasis gene expression and emerging stress erythropoiesis; differentiated those who reported PASC months later, irrespective of COVID-19 severity. A whole-blood heme-metabolism signature, enriched in hospitalized patients at month 1–3 post onset, coincided with pronounced iron-deficient reticulocytosis. Lymphopenia and low numbers of dendritic cells persisted in those with PASC, and single-cell analysis reported iron maldistribution, suggesting monocyte iron loading and increased iron demand in proliferating lymphocytes. Thus, defects in iron homeostasis, dysregulated erythropoiesis and immune dysfunction due to COVID-19 possibly contribute to inefficient oxygen transport, inflammatory disequilibrium and persisting symptomatology, and may be therapeutically tractable.

Iron deficiency is globally prevalent, causing an array of developmental, haematological, immunological, neurological, and cardiometabolic impairments, and is associated with symptoms ranging from chronic fatigue to hair loss. Within cells, iron is utilised in a variety of ways by hundreds of different proteins. Here, we review links between molecular activities regulated by iron and the pathophysiological effects of iron deficiency. We identify specific enzyme groups, biochemical pathways, cellular functions, and cell lineages that are particularly iron dependent. We provide examples of how iron deprivation influences multiple key systems and tissues, including immunity, hormone synthesis, and cholesterol metabolism. We propose that greater mechanistic understanding of how cellular iron influences physiological processes may lead to new therapeutic opportunities across a range of diseases.

Vaccines can prevent infectious diseases, but their efficacy varies, and factors impacting vaccine effectiveness remain unclear. Iron deficiency is the most common nutrient deficiency, affecting > 2 billion individuals. It is particularly common in areas with high infectious disease burden and in groups that are routinely vaccinated, such as infants, pregnant women, and the elderly. Recent evidence suggests that iron deficiency and low serum iron (hypoferremia) not only cause anemia but also may impair adaptive immunity and vaccine efficacy. A report of human immunodeficiency caused by defective iron transport underscored the necessity of iron for adaptive immune responses and spurred research in this area. Suf fi cient iron is essential for optimal production of plasmablasts and IgG responses by human B-cells in vitro and in vivo. The increased metabolism of activated lymphocytes depends on the high-iron acquisition, and hypoferremia, especially when occurring during lymphocyte expansion, adversely affects multiple facets of adaptive immunity, and may lead to prolonged inhibition of T-cell memory. In mice, hypoferremia suppresses the adaptive immune response to in fi uenza infection, resulting in more severe pulmonary disease. In African infants, anemia and/or iron de fi ciency at the time of vaccination predict decreased response to diphtheria, pertussis, and pneumococcal vaccines, and response to measles vaccine may be increased by iron supplementation. In this review, we examine the emerging evidence that iron de fi ciency may limit adaptive immunity and vaccine responses. We discuss the molecular mechanisms and evidence from animal and human studies, highlight important unknowns, and propose a framework of key research questions to better understand iron-vaccine interactions.

Iron is arguably the most important nutrient in the ongoing battle between hosts and bacteria. Recently in Nature, a unique iron storage organelle, the ferrosome, was discovered in the human pathogen Clostridioides difficile.1 But what is the role of ferrosomes and how do they affect bacterial behavior and infection?