Identification of erythroferrone as an erythroid regulator of iron metabolism

Cellular and animal models for the investigation of β-thalassemia

β-Thalassemia is a genetic form of anemia due to mutations in the β-globin gene, that leads to ineffective and extramedullary erythropoiesis, abnormal red blood cells and secondary iron-overload. The severity of the disease ranges from mild to lethal anemia based on the residual levels of globins production. Despite being a monogenic disorder, the pathophysiology of β-thalassemia is multifactorial, with different players contributing to the severity of anemia and secondary complications. As a result, the identification of effective therapeutic strategies is complex, and the treatment of patients is still suboptimal. For these reasons, several models have been developed in the last decades to provide experimental tools for the study of the disease, including erythroid cell lines, cultures of primary erythroid cells and transgenic animals. Years of research enabled the optimization of these models and led to decipher the mechanisms responsible for globins deregulation and ineffective erythropoiesis in thalassemia, to unravel the role of iron homeostasis in the disease and to identify and validate novel therapeutic targets and agents. Examples of successful outcomes of these analyses include iron restricting agents, currently tested in the clinics, several gene therapy vectors, one of which was recently approved for the treatment of most severe patients, and a promising gene editing strategy, that has been shown to be effective in a clinical trial. This review provides an overview of the available models, discusses pros and cons, and the key findings obtained from their study.

Iron chelation improves ineffective erythropoiesis and iron overload in myelodysplastic syndrome mice

Myelodysplastic syndrome (MDS) is a heterogeneous group of bone marrow stem cell disorders characterized by ineffective hematopoiesis and cytopenias, most commonly anemia. Red cell transfusion therapy for anemia in MDS results in iron overload, correlating with reduced overall survival. Whether the treatment of iron overload benefits MDS patients remains controversial. We evaluate underlying iron-related pathophysiology and the effect of iron chelation using deferiprone on erythropoiesis in NUP98-HOXD13 transgenic mice, a highly penetrant well-established MDS mouse model. Our results characterize an iron overload phenotype with aberrant erythropoiesis in these mice which was reversed by deferiprone-treatment. Serum erythropoietin levels decreased while erythroblast erythropoietin receptor expression increased in deferiprone-treated MDS mice. We demonstrate, for the first time, normalized expression of the iron chaperones Pcbp1 and Ncoa4 and increased ferritin stores in late-stage erythroblasts from deferiprone-treated MDS mice, evidence of aberrant iron trafficking in MDS erythroblasts. Importantly, erythroblast ferritin is increased in response to deferiprone, correlating with decreased erythroblast ROS. Finally, we confirmed increased expression of genes involved in iron uptake, sensing, and trafficking in stem and progenitor cells from MDS patients. Taken together, our findings provide evidence that erythroblast-specific iron metabolism is a novel potential therapeutic target to reverse ineffective erythropoiesis in MDS.

FK506 bypasses the effect of erythroferrone in cancer cachexia skeletal muscle atrophy

Skeletal muscle atrophy is a hallmark of cachexia, a wasting condition typical of chronic pathologies, that still represents an unmet medical need. Bone morphogenetic protein (BMP)-Smad1/5/8 signaling alterations are emerging drivers of muscle catabolism, hence, characterizing these perturbations is pivotal to develop therapeutic approaches. We identified two promoters of "BMP resistance" in cancer cachexia, specifically the BMP scavenger erythroferrone (ERFE) and the intracellular inhibitor FKBP12. ERFE is upregulated in cachectic cancer patients' muscle biopsies and in murine cachexia models, where its expression is driven by STAT3. Moreover, the knock down of Erfe or Fkbp12 reduces muscle wasting in cachectic mice. To bypass the BMP resistance mediated by ERFE and release the brake on the signaling, we targeted FKBP12 with low-dose FK506. FK506 restores BMP-Smad1/5/8 signaling, rescuing myotube atrophy by inducing protein synthesis. In cachectic tumor-bearing mice, FK506 prevents muscle and body weight loss and protects from neuromuscular junction alteration, suggesting therapeutic potential for targeting the ERFE-FKBP12 axis.

Biomarkers of erythropoiesis response to intravenous iron in a crossover pilot study in unexplained anemia of the elderly

Anemia is common in older adults, but often unexplained. Previously, we conducted a randomized, controlled trial of intravenous (IV) iron sucrose to study its impact on the 6-minute walk test and hemoglobin in older adults with unexplained anemia and ferritin levels of 20-200 ng/mL. In this report, we present for the first time the response of hemoglobin, as well as the dynamic response of biomarkers of erythropoiesis and iron indices, in a pooled analysis of the initially IV iron-treated group of 9 subjects and the subsequently IV iron treated 10 subjects from the delayed treatment group. We hypothesized that there would be a reproducible hemoglobin response from IV iron, and that iron indices and erythropoietic markers would reflect appropriate iron loading and reduced erythropoietic stress. To investigate the biochemical response of anemia to IV iron, we studied the dynamics of soluble transferrin receptor (STfR), hepcidin, erythropoietin (EPO), and iron indices over 12 weeks after treatment. In total, all 19 treated subjects were evaluable: 9 from initial treatment and 10 after cross-over. Hemoglobin rose from 11.0 to 11.7 g/dL, 12 weeks after initiating IV iron treatment of 1000 mg divided weekly over 5 weeks. We found early changes of iron loading after 1-2 IV iron dose: serum iron increased by 184 mcg/dL from a baseline of 66 mcg/dL, ferritin by 184 ng/mL from 68 ng/mL, and hepcidin by 7.49 ng/mL from 19.2 ng/mL, while STfR and serum EPO declined by 0.55 mg/L and 3.5 mU/mL from 19.2 ng/mL and 14 mU/mL, respectively. The erythroid response and evidence of enhanced iron trafficking are consistent with the hypothesis that IV iron overcomes iron deficient or iron-restricted erythropoiesis. These data provide new insight that iron-restricted erythropoiesis is a potential and targetable mechanism for patients diagnosed with unexplained anemia of the elderly and offers support for larger prospective trials of IV iron among anemic older adults of low to normal ferritin.

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.

Characterization of erythroferrone structural domains relevant to its iron-regulatory function

Iron delivery to the plasma is closely coupled to erythropoiesis, the production of red blood cells, as this process consumes most of the circulating plasma iron. In response to hemorrhage and other erythropoietic stresses, increased erythropoietin stimulates the production of the hormone erythroferrone (ERFE) by erythrocyte precursors (erythroblasts) developing in erythropoietic tissues. ERFE acts on the liver to inhibit bone morphogenetic protein (BMP) signaling and thereby decrease hepcidin production. Decreased circulating hepcidin concentrations then allow the release of iron from stores and increase iron absorption from the diet. Guided by evolutionary analysis and Alphafold2 protein complex modeling, we used targeted ERFE mutations, deletions, and synthetic ERFE segments together with cell-based bioassays and surface plasmon resonance to probe the structural features required for bioactivity and BMP binding. We define the ERFE active domain and multiple structural features that act together to entrap BMP ligands. In particular, the hydrophobic helical segment 81 to 86 and specifically the highly conserved tryptophan W82 in the N-terminal region are essential for ERFE bioactivity and Alphafold2 modeling places W82 between two tryptophans in its ligands BMP2, BMP6, and the BMP2/6 heterodimer, an interaction similar to those that bind BMPs to their cognate receptors. Finally, we identify the cationic region 96-107 and the globular TNFα-like domain 186-354 as structural determinants of ERFE multimerization that increase the avidity of ERFE for BMP ligands. Collectively, our results provide further insight into the ERFE-mediated inhibition of BMP signaling in response to erythropoietic stress.

Iron metabolism abnormalities in autoimmune hemolytic anemia and Jianpishengxue keli can ameliorate hemolysis and improve iron metabolism in AIHA mouse models

OBJECTIVE

Autoimmune hemolytic anemia (AIHA) is rare heterogeneous disorder characterized by red blood cell (RBC) destruction via auto-antibodies, and after RBC is destroyed, proinflammatory danger-associated molecular patterns including extracellular hemoglobin, heme, and iron which causing cell injury. And oxidative stress represents one of the most significant effects of chronic hemolysis. Jianpishengxue keli can improve the symptoms of anemia patients with kidney disease and tumors and are beneficial in promoting recovery from chronic inflammation. Therefore, it is presumed that Jianpishengxue keli can improve the symptoms of AIHA. We aimed to investigate iron metabolism in AIHA and effects of Jianpishengxue keli on AIHA murine model.

METHODS

Nineteen hemolytic episode AIHA patients, 10 remission patients and 10 healthy controls (HCs) were enrolled in this study. Serum hepcidin, ferritin and other related indicators of iron metabolism were measured. Mouse models of AIHA were established and received high, medium, or low doses of Jianpishengxue keli by gavage daily for 14 and 28 days respectively. The level of RBCs, Hb, bilirubin, LDH, hepcidin, and the expression level of hepcidin mRNA, and hepatic ferroportin 1(FPN1) protein were evaluated.

RESULTS

Serum hepcidin in hemolytic episode AIHA patients and remission patients were significantly higher than that in HCs (p = 0.0083 and p = 0.0473, respectively). Serum ferritin in hemolytic AIHA patients was significantly higher than that in HCs (p = 0.008). Serum transferrin saturation levels are increased in patients with AIHA[ (57.21 ± 8.96) %]. EPO in hemolytic group was higher than that in healthy control (p＜0.05). In AIHA mouse models, IBIL decreased after 14 days of high dose drug intervention. After 28 days, TBIL and IBIL both significantly decreased in all dose groups and LDH significantly decreased in the medium-and high-dose groups. Body weight improved, and the level of RBCs, Hb and hepcidin in the high-dose group returned to normal. After 14 and 28 days of intervention, hepatic hepcidin mRNA in all dose group significantly decreased. Hepatic FPN1 protein which were significantly lower in the AIHA mouse models, increased in all dose groups after drug intervention for 28 days.

CONCLUSION

Iron metabolism abnormalities exists in AIHA patients and Jianpishengxue keli can ameliorate hemolysis and improve iron metabolism in AIHA mouse models.KEY MESSAGESIron metabolism abnormalities exists in hemolytic episode AIHA patients. Hepcidin and ferritin levels significantly elevated and also correlated with the severity of AIHA patients. Jianpishengxue keli can ameliorate hemolysis and prompt the recovery of AIHA.

Low Serum Hepcidin Levels in Patients with Ulcerative Colitis - Implications for Treatment of Co-existent Iron-Deficiency Anemia

Ulcerative colitis (UC) is often associated with anemia. Hepcidin, the central regulator of iron homeostasis, is known to be induced by inflammation and suppressed by anemia. It is not clear how hepcidin is affected in those with UC, when both inflammation and anemia may co-exist.Such knowledge may hold implications for treatment. Hematological and iron-related parameters, C-reactive protein (CRP), growth differentiation factor 15 (GDF-15) and erythroferrone (ERFE) (erythroid regulators of hepcidin) levels were estimated in blood from those with UC and in control subjects. Values for hematological and iron-related parameters showed evidence of iron-deficiency and resultant anemia, in patients with UC. The presence of UC was significantly associated with inflammation. Serum levels of ERFE, but not of GDF-15, were significantly higher in patients with UC than in control patients, while hepcidin levels were significantly lower. Serum hepcidin concentrations in patients with UC correlated positively with serum iron, ferritin and GDF-15, and negatively with serum ERFE. The iron status and serum hepcidin levels in UC patients with co-existent anemia were significantly lower and serum ERFE values significantly higher than in those with UC without anemia. The effect of anemia on hepcidin predominated over that of inflammation in patients with UC, resulting in suppressed hepcidin levels. This effect is possibly mediated through erythroferrone. We suggest that a serum hepcidin-guided approach may be useful to guide use of oral iron supplements to treat co-existent iron-deficiency anemia in patients with UC and other chronic inflammatory diseases.

[Diagnosis and treatment of iron overload]

Etiological investigation of hyperferritinemia includes a full clinical examination, with the measurement of waist circumference, and simple biological tests including transferrin saturation. The classification between hyperferritinemia without iron overload (inflammation, excessive alcohol intake, cytolysis, L-ferritin mutation) or with iron overload is then relatively easy. Dysmetabolic iron overload syndrome is the most common iron overload disease and is defined by an unexplained serum ferritin level elevation associated with various metabolic syndrome criteria and mild hepatic iron content increase assessed by magnetic resonance imaging. Bloodlettings are often poorly tolerated without clear benefit. Type 1 genetic hemochromatosis (homozygous C282Y mutation on the HFE gene) leads to iron accumulation through an increase of dietary iron absorption due to hypohepcidinemia. More than 95% of hemochromatosis are type 1 hemochromatosis but the phenotypic expression is highly variable. Elastography is recommended to identify advanced hepatic fibrosis when serum ferritin exceeds 1000μg/L. Life expectancy is normal when bloodlettings are started early. Ferroportin gene mutation is an autosomal dominant disease with generally moderate iron overload. Chelators are used in iron overload associated with anaemia (myelodysplastic syndromes or transfusion-dependent thalassemia). Chelation is initiated when hepatic iron content exceeds 120μmol/g. Deferasirox is often used as first-line therapy, but deferiprone may be of interest despite haematological toxicity (neutropenia). Deferoxamine (parenteral route) is the treatment of choice for severe iron overload or emergency conditions.

Iron Supplements Concomitant within Hypoxia-Inducible Factor Prolyl Hydroxylase Domain Inhibitors in the Treatment of Chronic Kidney Disease Anemia

Background

Anemia is a common and important complication in patients with chronic kidney disease (CKD). Accordingly, the current treatment is based on erythropoiesis-stimulating agents (ESAs) and iron. Hypoxia-inducible factor (HIF) prolyl hydroxylase domain inhibitors (HIF-PHIs) have been developed to treat renal anemia through a novel mechanism. HIF-PHIs increase erythropoietin at physiologic blood concentrations and also improve the supply of hematopoietic iron. Iron is the main component of hemoglobin, and ensuring efficient iron metabolism is essential in the treatment of anemia.

Summary

HIF-PHIs may have advantages in improving iron utilization and mobilization compared to ESAs. Most HIF-PHI trials revealed a significant decline of hepcidin, increase in transferrin level and total iron binding capacity in patients. From a clinical point of view, improvements in iron metabolism should translate into reductions in iron supplementation. There are differences in the iron treatment regimentation currently used, so it is important to evaluate and timely iron supplementation across studies.

Key Messages

This review summarizes the mechanism of HIF-PHIs on improved iron metabolism and the route of iron usage in the trials for dialysis-dependent CKD and non-dialysis CKD. And this review also makes an interpretation of the clinical practice guidelines in China and recommendation by Asia Pacific Society of Nephrology.

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.

BMP5 contributes to hepcidin regulation and systemic iron homeostasis in mice

Hepcidin is the master regulator of systemic iron homeostasis. The bone morphogenetic protein (BMP) signaling pathway is a critical regulator of hepcidin expression in response to iron and erythropoietic drive. Although endothelial-derived BMP6 and BMP2 ligands have key functional roles as endogenous hepcidin regulators, both iron and erythropoietic drives still regulate hepcidin in mice lacking either or both ligands. Here, we used mice with an inactivating Bmp5 mutation (Bmp5se), either alone or together with a global or endothelial Bmp6 knockout, to investigate the functional role of BMP5 in hepcidin and systemic iron homeostasis regulation. We showed that Bmp5se-mutant mice exhibit hepcidin deficiency at age 10 days, blunted hepcidin induction in response to oral iron gavage, and mild liver iron loading when fed on a low- or high-iron diet. Loss of 1 or 2 functional Bmp5 alleles also leads to increased iron loading in Bmp6-heterozygous mice and more profound hemochromatosis in global or endothelial Bmp6-knockout mice. Moreover, double Bmp5- and Bmp6-mutant mice fail to induce hepcidin in response to long-term dietary iron loading. Finally, erythroferrone binds directly to BMP5 and inhibits BMP5 induction of hepcidin in vitro. Although erythropoietin suppresses hepcidin in Bmp5se-mutant mice, it fails to suppress hepcidin in double Bmp5- and Bmp6-mutant males. Together, these data demonstrate that BMP5 plays a functional role in hepcidin and iron homeostasis regulation, particularly under conditions in which BMP6 is limited.

Anemia status of infants and young children aged six to thirty-six months in Ma'anshan City: A retrospective study

BACKGROUND

Anemia in infants and young children can have long-term effects on cognitive and physical development. In Ma'anshan City, China, there has been growing concern about the prevalence of anemia among children aged 6 to 36 mo. Understanding the factors influencing this condition is crucial for targeted interventions and improving overall child health in the region.

AIM

To analyze the anemia status and influencing factors of infants and young children aged 6 to 36 mo in Ma'anshan City, China. Providing scientific evidence for reducing the incidence of anemia and improving the health level of children in this age group.

METHODS

The study encompassed 37698 infants and young children, aged from 6 to 36 mo, who underwent health examinations at the Ma'anshan Maternal and Child Health Hospital from January 2018 to October 2022 were included in the study. Basic information, physical examination, and hemoglobin detection data were collected. Descriptive analysis was used to analyze the prevalence of anemia in children in the region, and univariate analysis was used to analyze the influencing factors of anemia.

RESULTS

The mean hemoglobin level of infants and young children aged 9 to 36 mo increased with age, and the anemia detection rate decreased with age. The anemia detection rate in rural infants aged 6, 9, and 12 mo was higher than that in urban infants. Although the anemia detection rate was higher in 6-mo-old boys than girls, it was higher in 24-mo-old girls than boys. There were statistically significant differences in the anemia detection rates among 9-mo-old and 12-mo-old infants with different nutritional statuses (emaciation, overweight, obese, and normal). Moreover, there were no statistically significant differences in anemia detection rates among infants and young children with different nutritional statuses at other ages. Besides, the anemia detection rates in obese infants aged 9 and 12 mo were higher than those in normal and overweight infants, with statistically significant differences. Finally, there were no statistically significant differences in the anemia detection rates between emaciation infants and those with other nutritional statuses.

CONCLUSION

The anemia situation among infants and young children aged 6 to 36 mo in Ma'anshan City, China, is relatively prominent and influenced by various factors. Our result shown that attention should be paid to the anemic infant and young child population, with strengthened education and targeted prevention and dietary guidance to help them establish good living habits, improve nutritional status, and reduce the occurrence of anemia to improve children's health levels.

Leveraging inter-individual transcriptional correlation structure to infer discrete signaling mechanisms across metabolic tissues

Inter-organ communication is a vital process to maintain physiologic homeostasis, and its dysregulation contributes to many human diseases. Beginning with the discovery of insulin over a century ago, characterization of molecules responsible for signal between tissues has required careful and elegant experimentation where these observations have been integral to deciphering physiology and disease. Given that circulating bioactive factors are stable in serum, occur naturally, and are easily assayed from blood, they present obvious focal molecules for therapeutic intervention and biomarker development. For example, physiologic dissection of the actions of soluble proteins such as proprotein convertase subtilisin/kexin type 9 (PCSK9) and glucagon-like peptide 1 (GLP1) have yielded among the most promising therapeutics to treat cardiovascular disease and obesity, respectively1–4. A major obstacle in the characterization of such soluble factors is that defining their tissues and pathways of action requires extensive experimental testing in cells and animal models. Recently, studies have shown that secreted proteins mediating inter-tissue signaling could be identified by “brute-force” surveys of all genes within RNA-sequencing measures across tissues within a population5–9. Expanding on this intuition, we reasoned that parallel strategies could be used to understand how individual genes mediate signaling across metabolic tissues through correlative analyses of gene variation between individuals. Thus, comparison of quantitative levels of gene expression relationships between organs in a population could aid in understanding cross-organ signaling. Here, we surveyed gene-gene correlation structure across 18 metabolic tissues in 310 human individuals and 7 tissues in 103 diverse strains of mice fed a normal chow or HFHS diet. Variation of genes such asFGF21, ADIPOQ, GCGandIL6showed enrichments which recapitulate experimental observations. Further, similar analyses were applied to explore both within-tissue signaling mechanisms (liverPCSK9) as well as genes encoding enzymes producing metabolites (adiposePNPLA2), where inter-individual correlation structure aligned with known roles for these critical metabolic pathways. Examination of sex hormone receptor correlations in mice highlighted the difference of tissue-specific variation in relationships with metabolic traits. We refer to this resource asGene-DerivedCorrelationsAcrossTissues (GD-CAT) where all tools and data are built into a web portal enabling users to perform these analyses without a single line of code (gdcat.org). This resource enables querying of any gene in any tissue to find correlated patterns of genes, cell types, pathways and network architectures across metabolic organs.

Novel potential therapeutics to modify iron metabolism and red cell synthesis in diseases associated with defective erythropoiesis

Under normal conditions, iron metabolism is carefully regulated to sustain normal cellular functions and the production of hemoglobin in erythroid cells. Perturbation to the erythropoiesis-iron metabolism axis can result in iron imbalances and cause anemia or organ toxicity. Various congenital and acquired diseases associated with abnormal red cell production are characterized by aberrant iron absorption. Several recent studies have shown that improvements in red blood cell production also ameliorate iron metabolism and vice versa. Many therapeutics are now under development with the potential to improve a variety of hematologic diseases, from β-thalassemia and iron-refractory iron deficiency anemia to anemia of inflammation and polycythemia vera. This review summarizes selected mechanisms related to red cell production and iron metabolism and describes potential therapeutics and their current uses. We also consider the potential application of the discussed therapeutics on various diseases, alone or in combination. The vast repertoire of drugs under development offers new opportunities to improve the clinical care of patients suffering from congenital or acquired red blood cell disorders with limited or no treatment options.

Alterations of erythropoiesis in Covid-19 patients: prevalence of positive Coombs tests and iron metabolism

Background

For more than 2 years medical practice has been dealing with the Covid-19 pandemic. Atypical symptoms, such as frostbites and acrosyndromes, have appeared, and autoimmune anemias (some of which with cold agglutinins) have been described.

Objectives

We planned to study the prevalence of positive direct Coombs tests (DCTs) and hemolytic autoimmune anemia in patients infected with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and its correlation with complications, and then investigate the impact of the infection on iron metabolism.

Design

This is an observational, cross-sectional, single-center, exploratory study.

Methods

We obtained Coombs tests in a population of 179 infected patients at the CHU of Liège. We then studied iron metabolism in some of these patients, by measuring serum ferritin, erythropoietin (EPO), erythroferrone and hepcidin.

Results

We did not identify any case of autoimmune hemolysis. However, there was a 20.3% prevalence of positive DCT, mainly with IgG (91.7%). These patients, compared to DCT-negative patients, were not only more anemic and transfused, but also required more transfers to intensive care units and had longer hospital stays and mechanical ventilation. The pattern of anemia was consistent with the anemia of inflammation, showing elevated hepcidin and ferritin levels, while EPO and erythroferrone values were lower than expected at this degree of anemia. Erythroferrone was higher and Hb was lower in DCT-positive patients. Finally, we identified a correlation between iron parameters and complicated forms of infection.

Conclusion

Covid-19 patients suffered from inflammatory anemia with more severe forms of infection correlated to positive DCT status. This could potentially be of interest for future clinical practice.

A Decrease in Maternal Iron Levels Is the Predominant Factor Suppressing Hepcidin during Pregnancy in Mice

In order to supply adequate iron during pregnancy, the levels of the iron regulatory hormone hepcidin in the maternal circulation are suppressed, thereby increasing dietary iron absorption and storage iron release. Whether this decrease in maternal hepcidin is caused by changes in factors known to regulate hepcidin expression, or by other unidentified pregnancy factors, is not known. To investigate this, we examined iron parameters during pregnancy in mice. We observed that hepatic iron stores and transferrin saturation, both established regulators of hepcidin production, were decreased in mid and late pregnancy in normal and iron loaded dams, indicating an increase in iron utilization. This can be explained by a significant increase in maternal erythropoiesis, a known suppressor of hepcidin production, by mid-pregnancy, as indicated by an elevation in circulating erythropoietin and an increase in spleen size and splenic iron uptake. Iron utilization increased further in late pregnancy due to elevated fetal iron demand. By increasing maternal iron levels in late gestation, we were able to stimulate the expression of the gene encoding hepcidin, suggesting that the iron status of the mother is the predominant factor influencing hepcidin levels during pregnancy. Our data indicate that pregnancy-induced hepcidin suppression likely occurs because of reductions in maternal iron reserves due to increased iron requirements, which predominantly reflect stimulated erythropoiesis in mid-gestation and increased fetal iron requirements in late gestation, and that there is no need to invoke other factors, including novel pregnancy factor(s), to explain these changes.

How I treat non-transfusion-dependent β-thalassemia

The intricate interplay of anemia and iron overload under the pathophysiological umbrella of ineffective erythropoiesis in non-transfusion-dependent β-thalassemia (NTDT) results in a complex variety of clinical phenotypes that are challenging to diagnose and manage. In this article, we use a clinical framework rooted in pathophysiology to present 4 common scenarios of patients with NTDT. Starting from practical considerations in the diagnosis of NTDT, we delineate our strategy for the longitudinal care of patients who exhibit different constellations of symptoms and complications. We highlight the use of transfusion therapy and novel agents, such as luspatercept, in the patient with anemia-related complications. We also describe our approach to chelation therapy in the patient with iron overload. Although tackling every specific complication of NTDT is beyond the scope of this article, we touch on the management of the various morbidities and multisystem manifestations of the disease.

Clinical Significance of Erythroferrone and Bone Morphogenetic Protein-6 in Patients with Anemia in the Course of Inflammatory Bowel Disease

In recent years, a steady increase in the incidence of inflammatory bowel diseases (IBD) has been observed with anemia as their most common extraintestinal symptom. Erythroferrone and Bone Morphogenetic Protein 6 (BMP-6) are recently identified cytokines involved in the process of increased erythropoiesis in anemia of various pathomechanisms. The aim of this study was to analyze the concentration of erythroferrone and BMP-6 in IBD patients in relation to clinical and laboratory data. The study comprised 148 patients: 118 with IBD, including 73 (61.85%) diagnosed with anemia (42 with Crohn's disease (CD) (66.7%) and 31 (56.4%) with ulcerative colitis (UC)) and 30 as a control group. The erythroferrone concentration was significantly higher in IBD patients with anemia (p = 0.009) and higher in UC patients both with and without anemia (p = 0.018), compared to the control group. In CD, no similar difference was observed between patients with and without anemia. Regarding BMP-6, higher levels were found in CD patients with anemia compared to the control group (p = 0.021). The positive correlation between BMP-6 and iron concentration in UC was also noticed. In conclusion, we confirm an increase in erythroferrone concentration in the entire group of IBD patients with anemia, while BMP-6 levels were higher only in anemic CD patients. Due to the clinical importance of anemia in IBD, this problem is worth further analysis and research projects.

Bone marrow sinusoidal endothelial cells are a site of Fgf23 upregulation in a mouse model of iron deficiency anemia

Iron deficiency is a potent stimulator of fibroblast growth factor 23 (FGF23), a hormonal regulator of phosphate and vitamin D metabolism, that is classically thought to be produced by bone-embedded osteocytes. Here, we show that iron-deficient transmembrane serine protease 6 knockout (Tmprss6-/-) mice exhibit elevated circulating FGF23 and Fgf23 messenger RNA (mRNA) upregulation in the bone marrow (BM) but not the cortical bone. To clarify sites of Fgf23 promoter activity in Tmprss6-/- mice, we introduced a heterozygous enhanced green fluorescent protein (eGFP) reporter allele at the endogenous Fgf23 locus. Heterozygous Fgf23 disruption did not alter the severity of systemic iron deficiency or anemia in the Tmprss6-/- mice. Tmprss6-/-Fgf23+/eGFP mice showed green fluorescence in the vascular regions of BM sections and showed a subset of BM endothelial cells that were GFPbright by flow cytometry. Mining of transcriptomic data sets from mice with normal iron balance revealed higher Fgf23 mRNA in BM sinusoidal endothelial cells (BM-SECs) than that in other BM endothelial cell populations. Anti-GFP immunohistochemistry of fixed BM sections from Tmprss6-/-Fgf23+/eGFP mice revealed GFP expression in BM-SECs, which was more intense than in nonanemic controls. In addition, in mice with intact Tmprss6 alleles, Fgf23-eGFP reporter expression increased in BM-SECs following large-volume phlebotomy and also following erythropoietin treatment both ex vivo and in vivo. Collectively, our results identified BM-SECs as a novel site for Fgf23 upregulation in both acute and chronic anemia. Given the elevated serum erythropoietin in both anemic models, our findings raise the possibility that erythropoietin may act directly on BM-SECs to promote FGF23 production during anemia.

Oral Iron Absorption of Ferric Citrate Hydrate and Hepcidin-25 in Hemodialysis Patients: A Prospective, Multicenter, Observational Riona-Oral Iron Absorption Trial

Oral ferric citrate hydrate (FCH) is effective for iron deficiencies in hemodialysis patients; however, how iron balance in the body affects iron absorption in the intestinal tract remains unclear. This prospective observational study (Riona-Oral Iron Absorption Trial, R-OIAT, UMIN 000031406) was conducted at 42 hemodialysis centers in Japan, wherein 268 hemodialysis patients without inflammation were enrolled and treated with a fixed amount of FCH for 6 months. We assessed the predictive value of hepcidin-25 for iron absorption and iron shift between ferritin (FTN) and red blood cells (RBCs) following FCH therapy. Serum iron changes at 2 h (ΔFe2h) after FCH ingestion were evaluated as iron absorption. The primary outcome was the quantitative delineation of iron variables with respect to ΔFe2h, and the secondary outcome was the description of the predictors of the body's iron balance. Generalized estimating equations (GEEs) were used to identify the determinants of iron absorption during each phase of FCH treatment. ΔFe2h increased when hepcidin-25 and TSAT decreased (-0.459, -0.643 to -0.276, p = 0.000; -0.648, -1.099 to -0.197, p = 0.005, respectively) in GEEs. FTN increased when RBCs decreased (-1.392, -1.749 to -1.035, p = 0.000) and hepcidin-25 increased (0.297, 0.239 to 0.355, p = 0.000). Limiting erythropoiesis to maintain hemoglobin levels induces RBC reduction in hemodialysis patients, resulting in increased hepcidin-25 and FTN levels. Hepcidin-25 production may prompt an iron shift from RBC iron to FTN iron, inhibiting iron absorption even with continued FCH intake.

Lactate modulates iron metabolism by binding soluble adenylyl cyclase

Overproduction of lactate (LA) can occur during exercise and in many diseases such as cancers. Individuals with hyperlactatemia often display anemia, decreased serum iron, and elevated hepcidin, a key regulator of iron metabolism. However, it is unknown whether and how LA regulates hepcidin expression. Here, we show LA binds to soluble adenylyl cyclase (sAC) in normal hepatocytes and affects systemic iron homeostasis in mice by increasing hepcidin expression. Comprehensive in vitro, in vivo, and in silico experiments show that the LA-sAC interaction raises cyclic adenosine monophosphate (cAMP) levels, which activates the PKA-Smad1/5/8 signaling pathway to increase hepcidin transcription. We verified this regulatory axis in wild-type mice and in mice with disordered iron homeostasis. LA also regulates hepcidin in humans at rest and subjected to extensive exercise that produce elevated LA. Our study links hyperlactatemia to iron deficiency, offering a mechanistic explanation for anemias seen in athletes and patients with lactic acidosis.

Characterization of erythroferrone oligomerization and its impact on BMP antagonism

Hepcidin, a peptide hormone that negatively regulates iron metabolism, is expressed by bone morphogenetic protein (BMP) signaling. Erythroferrone (ERFE) is an extracellular protein that binds and inhibits BMP ligands, thus positively regulating iron import by indirectly suppressing hepcidin. This allows for rapid erythrocyte regeneration after blood loss. ERFE belongs to the C1Q/TNF related protein (CTRP) family and is suggested to adopt multiple oligomeric forms: a trimer, a hexamer, and a high molecular weight species. The molecular basis for how ERFE binds BMP ligands and how the different oligomeric states impact BMP inhibition are poorly understood. In this study, we demonstrated that ERFE activity is dependent on the presence of stable dimeric or trimeric ERFE, and that larger species are dispensable for BMP inhibition. Additionally, we used an in-silico approach to identify a helix, termed the ligand binding domain (LBD), that was predicted to bind BMPs and occlude the type I receptor pocket. We provide evidence that the LBD is crucial for activity through luciferase assays and surface plasmon resonance (SPR) analysis. Our findings provide new insight into how ERFE oligomerization impacts BMP inhibition, while identifying critical molecular features of ERFE essential for binding BMP ligands.

Normal range and predictors of serum erythroferrone in infants

BACKGROUND

Erythroferrone (ERFE) has been identified as a hepcidin-regulating hormone synthetized by erythroblasts correlating to the erythropoietic activity and the needs for iron substrate in bone marrow of adults. The present study aimed to assess the ERFE serum concentrations and its predictors in infants.

METHODS

ERFE was explored at 4 time points during the first year of life in 45 healthy, breastfed, normal birth weight (NBW) infants, and 136 marginally low birth weight infants (LBW, 2000-2500 g) receiving iron (N = 58) or placebo (N = 78) between 6 weeks and 6 months of age.

RESULTS

ERFE concentrations were low at birth, increasing gradually during the first year of life. In NBW infants, reference ranges (5th to 95th percentile) were at 6 weeks <0.005-0.99 ng/mL and at 12 months <0.005-33.7 ng/mL. ERFE was higher in LBW infants at 6 weeks but lower at 12 months compared to NBW and minimally affected by iron supplementation among LBW infants. Correlations of ERFE with erythropoietic and iron status markers were weak and inconsistent.

CONCLUSIONS

The role of ERFE in the crosstalk of erythropoiesis and iron homeostasis remains unclear in infants and further studies on ERFE in infants and older children are warranted within the framework of the erythropoietin-ERFE-hepcidin axis.

IMPACT

Normal range of erythroferrone in healthy infants is described for the first time. Erythroferrone in infants lacks correlation to iron status and markers of erythropoiesis. The findings indicate differences in infant regulation of iron homeostasis as compared to adults. The findings point to a need to study infant erythropoiesis separately from its adult counterpart. The findings may have clinical impact on management strategies of iron-loading anemia in infancy.

How I treat anemia with red blood cell transfusion and iron

Severe anemia is commonly treated with red blood cell transfusion. Clinical trials have demonstrated that a restrictive transfusion strategy of 7 to 8 g/dL is as safe as a liberal transfusion strategy of 9 to 10 g/dL in many clinical settings. Evidence is lacking for subgroups of patients, including those with preexisting coronary artery disease, acute myocardial infarction, congestive heart failure, and myelodysplastic neoplasms. We present 3 clinical vignettes that highlight the clinical challenges in caring for patients with coronary artery disease with gastrointestinal bleeding, congestive heart failure, or myelodysplastic neoplasms. We emphasize that transfusion practice should be guided by patient symptoms and preferences in conjunction with the patient's hemoglobin concentration. Along with the transfusion decision, evaluation and management of the etiology of the anemia is essential. Iron-restricted erythropoiesis is a common cause of anemia severe enough to be considered for red blood cell transfusion but diagnosis and management of absolute iron deficiency anemia, the anemia of inflammation with functional iron deficiency, or their combination may be problematic. Intravenous iron therapy is generally the treatment of choice for absolute iron deficiency in patients with complex medical disorders, with or without coexisting functional iron deficiency.

GDF-15 and hepcidin as a therapeutic target for anemia in chronic kidney disease

BACKGROUND

Anaemia is a common presenting feature among patients with chronic kidney disease (CKD) and associated with poor clinical outcomes. We evaluated the diagnostic validity of growth differentiation factor-15 (GDF-15) and hepcidin as it is not clear if they are useful as a biomarkers of anaemia among non-dialysis CKD egyptian patients.

METHOD

An analytical cross-sectional study was conducted among non-dialysis CKD patients (n = 60) and apparently healthy controls (n = 28) at Minia University maternity & children Hospital. Serum levels of GDF-15 and hepcidin were determined. Predictive logistic regression models were built and post estimation receiver operator characteristics were determined to evaluate diagnostic validity of hepcidin and GDF-15 for iron deficiency anaemia.

RESULTS

Hepcidin and GDF-15 are significantly higher in cases than control p value (0.047 < 0.0001) respectively. The predictive value of diagnosing anaemia among CKD patients using hepcidin and GDF-15 was 72.0%, 70.0%. There was a weak negative correlation between hepcidin levels and glomerular filtration rate GFR (r = -.175, p = 0.105) in CKD patients, and significant correlation between serum GDF-15 and haemoglobin (r = -0.897, p < 0.0001), ferritin (r = 0.489, P < 0.000), Iron (r = -0.314, P = 0.002), CRP (r = 0.409, P < 0.0001).

CONCLUSION

Hepcidin and GDF-15 is a potential biomarker for predicting anaemia connected with inflammation among CKD Egyptian patients.

Iron Homeostasis During Pregnancy: Maternal, Placental, and Fetal Regulatory Mechanisms

Pregnancy entails a large negative balance of iron, an essential micronutrient. During pregnancy, iron requirements increase substantially to support both maternal red blood cell expansion and the development of the placenta and fetus. As insufficient iron has long been linked to adverse pregnancy outcomes, universal iron supplementation is common practice before and during pregnancy. However, in high-resource countries with iron fortification of staple foods and increased red meat consumption, the effects of too much iron supplementation during pregnancy have become a concern because iron excess has also been linked to adverse pregnancy outcomes. In this review, we address physiologic iron homeostasis of the mother, placenta, and fetus and discuss perturbations in iron homeostasis that result in pathological pregnancy. As many mechanistic regulatory systems have been deduced from animal models, we also discuss the principles learned from these models and how these may apply to human pregnancy.

Normal and dysregulated crosstalk between iron metabolism and erythropoiesis

Erythroblasts possess unique characteristics as they undergo differentiation from hematopoietic stem cells. During terminal erythropoiesis, these cells incorporate large amounts of iron in order to generate hemoglobin and ultimately undergo enucleation to become mature red blood cells, ultimately delivering oxygen in the circulation. Thus, erythropoiesis is a finely tuned, multifaceted process requiring numerous properly timed physiological events to maintain efficient production of 2 million red blood cells per second in steady state. Iron is required for normal functioning in all human cells, the erythropoietic compartment consuming the majority in light of the high iron requirements for hemoglobin synthesis. Recent evidence regarding the crosstalk between erythropoiesis and iron metabolism sheds light on the regulation of iron availability by erythroblasts and the consequences of insufficient as well as excess iron on erythroid lineage proliferation and differentiation. In addition, significant progress has been made in our understanding of dysregulated iron metabolism in various congenital and acquired malignant and non-malignant diseases. Finally, we report several actual as well as theoretical opportunities for translating the recently acquired robust mechanistic understanding of iron metabolism regulation to improve management of patients with disordered erythropoiesis, such as anemia of chronic inflammation, β-thalassemia, polycythemia vera, and myelodysplastic syndromes.

Myonectin protects against skeletal muscle dysfunction in male mice through activation of AMPK/PGC1α pathway

To maintain and restore skeletal muscle mass and function is essential for healthy aging. We have found that myonectin acts as a cardioprotective myokine. Here, we investigate the effect of myonectin on skeletal muscle atrophy in various male mouse models of muscle dysfunction. Disruption of myonectin exacerbates skeletal muscle atrophy in age-associated, sciatic denervation-induced or dexamethasone (DEX)-induced muscle atrophy models. Myonectin deficiency also contributes to exacerbated mitochondrial dysfunction and reduces expression of mitochondrial biogenesis-associated genes including PGC1α in denervated muscle. Myonectin supplementation attenuates denervation-induced muscle atrophy via activation of AMPK. Myonectin also reverses DEX-induced atrophy of cultured myotubes through the AMPK/PGC1α signaling. Furthermore, myonectin treatment suppresses muscle atrophy in senescence-accelerated mouse prone (SAMP) 8 mouse model of accelerated aging or mdx mouse model of Duchenne muscular dystrophy. These data indicate that myonectin can ameliorate skeletal muscle dysfunction through AMPK/PGC1α-dependent mechanisms, suggesting that myonectin could represent a therapeutic target of muscle atrophy.

Erythroferrone exacerbates iron overload and ineffective extramedullary erythropoiesis in a mouse model of β-thalassemia

β-thalassemia is characterized by chronic hepcidin suppression and iron overload, even in patients who have not undergone transfusion. The HbbTh3/+ (Th3/+) mouse model of nontransfusion-dependent β-thalassemia (NTDBT) partially recapitulates the human phenotype but lacks chronic hepcidin suppression, progressive iron accumulation into adulthood, or the interindividual variation of the rate of iron loading observed in patients. Erythroferrone (ERFE) is an erythroid regulator that suppresses hepcidin during increased erythropoiesis. ERFE concentrations in the sera of patients with NTDBT correlate negatively with hepcidin levels but vary over a broad range, possibly explaining the variability of iron overload in patients. To analyze the effect of high ERFE concentrations on hepcidin and iron overload in NTDBT, we crossed Th3/+ mice with erythroid ERFE-overexpressing transgenic mice. Th3/ERFE-transgenic mice suffered high perinatal mortality, but embryos at E18.5 showed similar viability, appearance, and anemia effects as Th3/+ mice. Compared with Th3/+ littermates, adult Th3/ERFE mice had similarly severe anemia but manifested greater suppression of serum hepcidin and increased iron accumulation in the liver, kidney, and spleen. The Th3/ERFE mice had much higher concentrations of serum ERFE than either parental strain, a finding attributable to both a higher number of erythroblasts and higher production of ERFE by each erythroblast.Th3/+ and Th3/ERFE mice had similar red blood cell count and shortened erythrocyte lifespan, but Th3/ERFE mice had an increased number of erythroid precursors in their larger spleens, indicative of aggravated ineffective extramedullary erythropoiesis. Thus, high ERFE concentrations increase the severity of nontransfusional iron overload and ineffective erythropoiesis in thalassemic mice but do not substantially affect anemia or hemolysis.

Fetal factors disrupt placental and maternal iron homeostasis in murine β-thalassemia

Pregnancy rates in β-thalassemia are increasing but the risk of complications is higher; thus, better understanding of maternal and fetal iron homeostasis in this disorder is needed. HbbTh3/+ (Th3/+) mice model human β-thalassemia. Both the murine and human diseases are characterized by low hepcidin, high iron absorption, and tissue iron overload, with concurrent anemia. We hypothesized that disordered iron metabolism in pregnant Th3/+ mice would negatively affect their unborn offspring. The experimental design included these groups: wild-type (WT) dams carrying WT fetuses (WT1); WT dams carrying WT and Th3/+ fetuses (WT2); Th3/+ dams carrying WT and Th3/+ fetuses (Th3/+); and age-matched, nonpregnant adult females. Serum hepcidin was low, and mobilization of splenic and hepatic storage iron was enhanced in all 3 groups of experimental dams. Intestinal 59Fe absorption was lower in Th3/+ dams (as compared with WT1/2 dams) but splenic 59Fe uptake was higher. Th3/+ dams had hyperferremia, which led to fetal and placenta iron loading, fetal growth restriction, and placentomegaly. Notably, Th3/+ dams loaded Th3/+ and WT fetuses, with the latter situation more closely mirroring human circumstances when mothers with thalassemia have relatively unaffected (thalassemia trait) offspring. Iron-related oxidative stress likely contributed to fetal growth impairment; enhanced placental erythropoiesis is a probable cause of placental enlargement. Moreover, high fetal liver iron transactivated Hamp; fetal hepcidin downregulated placental ferroportin expression, limiting placental iron flux and thus mitigating fetal iron loading. Whether gestational iron loading occurs in human thalassemic pregnancy, when blood transfusion can further elevate serum iron, is worth consideration.

Comparative effectiveness and acceptability of HIF prolyl-hydroxylase inhibitors versus for anemia patients with chronic kidney disease undergoing dialysis: a systematic review and network meta-analysis

Background: The comparative benefits and acceptability of HIF-PHIs for treating anemia have not been well researched to date. We sought to compare the effectiveness of 6 HIF-PHIs and 3 ESAs for the treatment of renal anemia patients undergoing dialysis. Data sources: Cochrane Central Register of Controlled Trials, PubMed, Embase, Cochrane Library, MEDLINE, Web of Science, and clinicaltrials.gov databases. Results: Twenty-five RCTs (involving 17,204 participants) were included, all of which were designed to achieve target Hb levels by adjusting thee dose of HIF-PHIs. Regarding the efficacy in achieving target Hb levels, no significant differences were found between HIF-PHIs and ESAs in Hb response at the dose-adjusted designed RCTs selected for comparison. Intervention with roxadustat showed a significantly lower risk of RBC transfusion than rhEPO, with an OR and 95% CI of 0.76 (0.56-0.93). Roxadustat and vadadustat had higher risks of increasing the discontinuation rate than ESAs; the former had ORs and 95% CIs of 1.58 (95% CI: 1.21-2.06) for rhEPO, 1.66 (1.16-2.38) for DPO (darbepoetin alfa), and 1.76 (1.70-4.49) for MPG-EPO, and the latter had ORs and 95% CIs of 1.71 (1.09-2.67) for rhEPO, 1.79 (1.29-2.49) for DPO, and 2.97 (1.62-5.46) for MPG-EPO. No differences were observed in the AEs and SAEs among patients who received the studied drugs. Results of a meta-analysis of gastrointestinal disorders among AEs revealed that vadadustat was less effect on causing diarrea than DPO, with an OR of 0.97 (95% CI, 0.9-0.99). Included HIF-PHIs, were proven to be more effective than ESAs in reducing hepcidin levels and increasing TIBC and serum iron level with OR of -0.17 (95% CI, -0.21 to -0.12), OR of 0.79 (95% CI, 0.63-0.95), and OR of 0.39 (95% CI, 0.33-0.45), respectively. Conclusion: HIF-PHIs and ESAs have their characteristics and advantages in treating anemia undergoing dialysis. With the selected dose-adjusted mode, some HIF-PHIs appeared to be a potential treatment for DD-CKD patients when ompared with rhEPO, due to its effectiveness in decreasing the risk of RBC transfusion rate or regulating iron or lipid metabolism while achieving target Hb levels. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=306511; Identifier: CRD42022306511.

Bone-derived C-terminal FGF23 cleaved peptides increase iron availability in acute inflammation

Inflammation leads to functional iron deficiency by increasing the expression of the hepatic iron regulatory peptide hepcidin. Inflammation also stimulates fibroblast growth factor 23 (FGF23) production by increasing both Fgf23 transcription and FGF23 cleavage, which paradoxically leads to excess in C-terminal FGF23 peptides (Cter-FGF23), rather than intact FGF23 (iFGF23) hormone. We determined that the major source of Cter-FGF23 is osteocytes and investigated whether Cter-FGF23 peptides play a direct role in the regulation of hepcidin and iron metabolism in response to acute inflammation. Mice harboring an osteocyte-specific deletion of Fgf23 showed a ∼90% reduction in Cter-FGF23 levels during acute inflammation. Reduction in Cter-FGF23 led to a further decrease in circulating iron in inflamed mice owing to excessive hepcidin production. We observed similar results in mice showing impaired FGF23 cleavage owing to osteocyte-specific deletion of Furin. We next showed that Cter-FGF23 peptides bind members of the bone morphogenetic protein (BMP) family, BMP2 and BMP9, which are established inducers of hepcidin. Coadministration of Cter-FGF23 and BMP2 or BMP9 prevented the increase in Hamp messenger RNA and circulating hepcidin levels induced by BMP2/9, resulting in normal serum iron levels. Finally, injection of Cter-FGF23 in inflamed Fgf23KO mice and genetic overexpression of Cter-Fgf23 in wild type mice also resulted in lower hepcidin and higher circulating iron levels. In conclusion, during inflammation, bone is the major source of Cter-FGF23 secretion, and independently of iFGF23, Cter-FGF23 reduces BMP-induced hepcidin secretion in the liver.

Iron, glucose and fat metabolism and obesity: an intertwined relationship

A bidirectional relationship exists between adipose tissue metabolism and iron regulation. Total body fat, fat distribution and exercise influence iron status and components of the iron-regulatory pathway, including hepcidin and erythroferrone. Conversely, whole body and tissue iron stores associate with fat mass and distribution and glucose and lipid metabolism in adipose tissue, liver, and muscle. Manipulation of the iron-regulatory proteins erythroferrone and erythropoietin affects glucose and lipid metabolism. Several lines of evidence suggest that iron accumulation and metabolism may play a role in the development of metabolic diseases including obesity, type 2 diabetes, hyperlipidaemia and non-alcoholic fatty liver disease. In this review we summarise the current understanding of the relationship between iron homoeostasis and metabolic disease.

A single approach to targeting transferrin receptor 2 corrects iron and erythropoietic defects in murine models of anemia of inflammation and chronic kidney disease

Anemia is a common complication of systemic inflammation. Proinflammatory cytokines both decrease erythroblast sensitivity to erythropoietin (EPO) and increase the levels of the hepatic hormone hepcidin, sequestering iron in stores and causing functional iron deficiency. Anemia of chronic kidney disease (CKD) is a peculiar form of anemia of inflammation, characterized by impaired EPO production paralleling progressive kidney damage. Traditional therapy based on increased EPO (often in combination with iron) may have off-target effects due to EPO interaction with its non-erythroid receptors. Transferrin Receptor 2 (Tfr2) is a mediator of the iron-erythropoiesis crosstalk. Its deletion in the liver hampers hepcidin production, increasing iron absorption, whereas its deletion in the hematopoietic compartment increases erythroid EPO sensitivity and red blood cell production. Here, we show that selective hematopoietic Tfr2 deletion ameliorates anemia in mice with sterile inflammation in the presence of normal kidney function, promoting EPO responsiveness and erythropoiesis without increasing serum EPO levels. In mice with CKD, characterized by absolute rather than functional iron deficiency, Tfr2 hematopoietic deletion had a similar effect on erythropoiesis but anemia improvement was transient because of limited iron availability. Also, increasing iron levels by downregulating only hepatic Tfr2 had a minor effect on anemia. However, simultaneous deletion of hematopoietic and hepatic Tfr2, stimulating erythropoiesis and increased iron supply, was sufficient to ameliorate anemia for the entire protocol. Thus, our results suggest that combined targeting of hematopoietic and hepatic Tfr2 may be a therapeutic option to balance erythropoiesis stimulation and iron increase, without affecting EPO levels.

Placental Erythroferrone and Erythropoietin mRNA Expression is not Associated with Maternal or Neonatal Iron Status in Adolescents Carrying Singletons and Adult Women Carrying Multiples

BACKGROUND

The iron regulatory hormones erythroferrone (ERFE), erythropoietin (EPO), and hepcidin, and the cargo receptor nuclear receptor coactivator 4 (NCOA4) are expressed in the placenta. However, determinants of placental expression of these proteins and their associations with maternal or neonatal iron status are unknown.

OBJECTIVES

To characterize expression of placental ERFE, EPO, and NCOA4 mRNA in placentae from newborns at increased risk of iron deficiency and to evaluate these in relation to maternal and neonatal iron status and regulatory hormones.

METHODS

Placentae were collected from 114 neonates born to adolescents carrying singletons (14-18 y) and 110 neonates born to 54 adults (20-46 y) carrying multiples. Placental EPO, ERFE, and NCOA4 mRNA expression were measured by RT-qPCR and compared with maternal and neonatal iron status indicators (SF, sTfR, total body iron, serum iron) and hormones.

RESULTS

Placental ERFE, EPO, and NCOA4 mRNA were detected in all placentae delivered between 25 and 42 wk of gestation. Relationships between placental ERFE and EPO differed by cohort. In the multiples cohort, placental EPO and ERFE were positively correlated (P = 0.004), but only a positive trend (P = 0.08) was evident in the adolescents. Placental EPO and ERFE were not associated with maternal or neonatal iron status markers or hormones in either cohort. Placental NCOA4 was not associated with placental EPO or ERFE in either cohort but was negatively associated with maternal SF (P = 0.03) in the multiples cohort and positively associated with neonatal sTfR (P = 0.009) in the adolescents.

CONCLUSIONS

The human placenta expresses ERFE, EPO, and NCOA4 mRNA as early as 25 wk of gestation. Placental expression of ERFE and EPO transcripts was not associated with maternal or neonatal iron status. Greater placental NCOA4 transcript expression was evident in women and newborns with poor iron status (lower SF and higher sTfR, respectively). Further research is needed to characterize the roles of these proteins in the human placenta.

TRIAL REGISTRATION NUMBER

These clinical trials were registered at clinicaltrials.gov as NCT01019902 (https://clinicaltrials.gov/ct2/show/NCT01019902) and NCT01582802 (https://clinicaltrials.gov/ct2/show/NCT01582802).

Chronic intermittent hypobaric hypoxia improves iron metabolism disorders via the IL-6/JAK2/STAT3 and Epo/STAT5/ERFE signaling pathways in metabolic syndrome rats

AIM

Our previous study demonstrated that chronic intermittent hypobaric hypoxia (CIHH) improved iron metabolism disorder in obese rats through the downregulation of hepcidin. This study aimed to observe the molecular mechanism of CIHH in improving iron metabolism disorders, especially by Janus kinase/signal transducer and activation of the transcription (JAK/STAT) signaling pathway in metabolic syndrome (MS) rats.

METHODS

Six-week-old male Sprague-Dawley rats were randomly divided into four groups: CON, CIHH (subjected to hypobaric hypoxia simulating 5000-m altitude for 28 days, 6 h daily), MS (induced by high fat diet and fructose water), and MS+CIHH. The serum levels of glucose, lipid metabolism, iron metabolism, interleukin-6 (IL-6), erythropoietin (Epo) and hepcidin were measured. The protein expressions of JAK2, STAT3, STAT5, bone morphogenetic protein 6 (BMP6), small mothers against decapentaplegic 1 (SMAD1) and hepcidin were examined. The mRNA expressions of erythroferrone (ERFE) and hepcidin were analyzed.

RESULTS

The MS rats displayed obesity, hyperglycemia, hyperlipidemia, iron metabolism disorder, increased IL-6 and hepcidin serum levels, upregulation of JAK2/STAT3 signaling pathway, decreased Epo serum levels, downregulation of STAT5/ERFE signaling pathway in spleen, upregulation of BMP/SMAD signaling pathway in liver, and increased hepcidin mRNA and protein expression compared to CON rats. All the aforementioned abnormalities in MS rats were ameliorated in MS + CIHH rats.

CONCLUSIONS

CIHH improved iron metabolism disorders, possibly by inhibiting IL-6/JAK2/STAT3 and activating Epo/STAT5/ERFE signaling pathway, thus downregulating hepcidin in MS rats.

Iron homeostasis governs erythroid phenotype in polycythemia vera

Polycythemia vera (PV) is a myeloproliferative neoplasm driven by activating mutations in JAK2 that result in unrestrained erythrocyte production, increasing patients' hematocrit and hemoglobin concentrations, placing them at risk of life-threatening thrombotic events. Our genome-wide association study of 440 PV cases and 403 351 controls using UK Biobank data showed that single nucleotide polymorphisms in HFE known to cause hemochromatosis are highly associated with PV diagnosis, linking iron regulation to PV. Analysis of the FinnGen dataset independently confirmed overrepresentation of homozygous HFE variants in patients with PV. HFE influences the expression of hepcidin, the master regulator of systemic iron homeostasis. Through genetic dissection of mouse models of PV, we show that the PV erythroid phenotype is directly linked to hepcidin expression: endogenous hepcidin upregulation alleviates erythroid disease whereas hepcidin ablation worsens it. Furthermore, we demonstrate that in PV, hepcidin is not regulated by expanded erythropoiesis but is likely governed by inflammatory cytokines signaling via GP130-coupled receptors. These findings have important implications for understanding the pathophysiology of PV and offer new therapeutic strategies for this disease.

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.

The Role of Fractalkine in the Regulation of Endometrial Iron Metabolism in Iron Deficiency

Iron is a crucial element in the human body. Endometrial iron metabolism is implicated in endometrium receptivity and embryo implantation. Disturbances of the maternal as well as the endometrial iron homeostasis, such as iron deficiency, can contribute to the reduced development of the fetus and could cause an increased risk of adverse pregnancy outcomes. Fractalkine is a unique chemokine that plays a role in the communication between the mother and the fetus. It has been demonstrated that FKN is involved in the development of endometrial receptivity and embryo implantation, and it functions as a regulator of iron metabolism. In the present study, we examined the effect of FKN on the iron metabolism of HEC-1A endometrial cells in a state of iron deficiency mediated by desferrioxamine treatment. Based on the findings, FKN enhances the expression of iron metabolism-related genes in iron deficiency and modifies the iron uptake via transferrin receptor 1 and divalent metal transporter-1, and iron release via ferroportin. FKN can activate the release of iron from heme-containing proteins by elevating the level of heme oxygenase-1, contributing to the redistribution of intracellular iron content. It was revealed that the endometrium cells express both mitoferrin-1 and 2 and that their levels are not dependent on the iron availability of the cells. FKN may also contribute to maintaining mitochondrial iron homeostasis. FKN can improve the deteriorating effect of iron deficiency in HEC-1A endometrium cells, which may contribute to the development of receptivity and/or provide iron delivery towards the embryo.

Ferroptotic mechanisms and therapeutic targeting of iron metabolism and lipid peroxidation in the kidney

Ferroptosis is a mechanism of regulated necrotic cell death characterized by iron-dependent, lipid peroxidation-driven membrane destruction that can be inhibited by glutathione peroxidase 4. Morphologically, it is characterized by cellular, organelle and cytoplasmic swelling and the loss of plasma membrane integrity, with the release of intracellular components. Ferroptosis is triggered in cells with dysregulated iron and thiol redox metabolism, whereby the initial robust but selective accumulation of hydroperoxy polyunsaturated fatty acid-containing phospholipids is further propagated through enzymatic and non-enzymatic secondary mechanisms, leading to formation of oxidatively truncated electrophilic species and their adducts with proteins. Thus, ferroptosis is dependent on the convergence of iron, thiol and lipid metabolic pathways. The kidney is particularly susceptible to redox imbalance. A growing body of evidence has linked ferroptosis to acute kidney injury in the context of diverse stimuli, such as ischaemia-reperfusion, sepsis or toxins, and to chronic kidney disease, suggesting that ferroptosis may represent a novel therapeutic target for kidney disease. However, further work is needed to address gaps in our understanding of the triggers, execution and spreading mechanisms of ferroptosis.

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.

Iron Deficiency and Iron Deficiency Anemia: Potential Risk Factors in Bone Loss

Iron is one of the essential mineral elements for the human body and this nutrient deficiency is a worldwide public health problem. Iron is essential in oxygen transport, participates in many enzyme systems in the body, and is an important trace element in maintaining basic cellular life activities. Iron also plays an important role in collagen synthesis and vitamin D metabolism. Therefore, decrease in intracellular iron can lead to disturbance in the activity and function of osteoblasts and osteoclasts, resulting in imbalance in bone homeostasis and ultimately bone loss. Indeed, iron deficiency, with or without anemia, leads to osteopenia or osteoporosis, which has been revealed by numerous clinical observations and animal studies. This review presents current knowledge on iron metabolism under iron deficiency states and the diagnosis and prevention of iron deficiency and iron deficiency anemia (IDA). With emphasis, studies related to iron deficiency and bone loss are discussed, and the potential mechanisms of iron deficiency leading to bone loss are analyzed. Finally, several measures to promote complete recovery and prevention of iron deficiency are listed to improve quality of life, including bone health.

Serum Levels of Myonectin Are Lower in Adults with Metabolic Syndrome and Are Negatively Correlated with Android Fat Mass

Myonectin has shown beneficial effects on lipid regulation in murine models; therefore, it may have implications in the pathophysiology of metabolic syndrome (MS). We evaluated the relationship between serum myonectin and serum lipids, global and regional fat mass, intramuscular lipid content, and insulin resistance (IR) in adults with metabolic risk factors. This was a cross-sectional study in sedentary adults who were diagnosed with MS or without MS (NMS). Serum myonectin was quantified by enzyme-linked immunosorbent assay, lipid profile by conventional techniques, and free fatty acids (FFA) by gas chromatography. Body composition was assessed by dual-energy X-ray absorptiometry and intramuscular lipid content through proton nuclear magnetic resonance spectroscopy in the right vastus lateralis muscle. IR was estimated with the homeostatic model assessment (HOMA-IR). The MS (n = 61) and NMS (n = 29) groups were comparable in age (median (interquartile range): 51.0 (46.0-56.0) vs. 53.0 (45.5-57.5) years, p > 0.05) and sex (70.5% men vs. 72.4% women). MS subjects had lower serum levels of myonectin than NMS subjects (1.08 (0.87-1.35) vs. 1.09 (0.93-4.05) ng·mL^-1, p < 0.05). Multiple linear regression models adjusted for age, sex, fat mass index and lean mass index showed that serum myonectin was negatively correlated with the android/gynoid fat mass ratio (R² = 0.48, p < 0.01), but not with the lipid profile, FFA, intramuscular lipid content or HOMA-IR. In conclusion, serum myonectin is lower in subjects with MS. Myonectin negatively correlates with a component relevant to the pathophysiology of MS, such as the android/gynoid fat mass ratio, but not with other components such as FFA, intramuscular fat or IR.

The hepatokine FGL1 regulates hepcidin and iron metabolism during the recovery from hemorrhage-induced anemia in mice

As a functional component of erythrocyte hemoglobin, iron is essential for oxygen delivery to all tissues in the body. The liver-derived peptide hepcidin is the master regulator of iron homeostasis. During anemia, the erythroid hormone erythroferrone regulates hepcidin synthesis to ensure adequate supply of iron to the bone marrow for red blood cells production. However, mounting evidence suggested that another factor may exert a similar function. We identified the hepatokine FGL1 as a previously undescribed suppressor of hepcidin that is induced in the liver in response to hypoxia during the recovery from anemia and in thalassemic mice. We demonstrated that FGL1 is a potent suppressor of hepcidin in vitro and in vivo . Deletion of Fgl1 in mice results in a blunted repression of hepcidin after bleeding. FGL1 exerts its activity by direct binding to BMP6, thereby inhibiting the canonical BMP-SMAD signaling cascade that controls hepcidin transcription.

Key points

1/ FGL1 regulates iron metabolism during the recovery from anemia. 2/ FGL1 is an antagonist of the BMP/SMAD signaling pathway.

TMPRSS6 as a Therapeutic Target for Disorders of Erythropoiesis and Iron Homeostasis

TMPRSS6 is a serine protease highly expressed in the liver. Its role in iron regulation was first reported in 2008 when mutations in TMPRSS6 were shown to be the cause of iron-refractory iron deficiency anemia (IRIDA) in humans and in mouse models. TMPRSS6 functions as a negative regulator of the expression of the systemic iron-regulatory hormone hepcidin. Over the last decade and a half, growing understanding of TMPRSS6 biology and mechanism of action has enabled development of new therapeutic approaches for patients with diseases of erythropoiesis and iron homeostasis.ClinicalTrials.gov identifier NCT03165864.

Pathogenic Mechanisms in Thalassemia II: Iron Overload

Iron overload remains a lethal complication of β-thalassemia and other anemias caused by ineffective erythropoiesis. This review discusses the pathogenetic mechanisms of iron overload in thalassemia, at organismal, cellular, and molecular levels.

Hepcidin and its multiple partners: Complex regulation of iron metabolism in health and disease

The peptide hormone hepcidin is central to the regulation of iron metabolism, influencing the movement of iron into the circulation and determining total body iron stores. Its effect on a cellular level involves binding ferroportin, the main iron export protein, preventing iron egress and leading to iron sequestration within ferroportin-expressing cells. Hepcidin expression is enhanced by iron loading and inflammation and suppressed by erythropoietic stimulation. Aberrantly increased hepcidin leads to systemic iron deficiency and/or iron restricted erythropoiesis as occurs in anemia of chronic inflammation. Furthermore, insufficiently elevated hepcidin occurs in multiple diseases associated with iron overload such as hereditary hemochromatosis and iron loading anemias. Abnormal iron metabolism as a consequence of hepcidin dysregulation is an underlying factor resulting in pathophysiology of multiple diseases and several agents aimed at manipulating this pathway have been designed, with some already in clinical trials. In this chapter, we assess the complex regulation of hepcidin, delineate the many binding partners involved in its regulation, and present an update on the development of hepcidin agonists and antagonists in various clinical scenarios.