Regulation of growth differentiation factor 15 expression by intracellular iron

The association between growth differentiation factor-15, erythroferrone, and iron status in thalassemic patients

BACKGROUND

Iron overload can result in grave consequences in thalassemic patients, despite the availability of iron chelators. Therefore, alternative pathways aiming to reduce iron toxicity are currently investigated. Among which, reduction of iron absorption through control of hepcidin production appears to be promising. In this study, we investigated growth differentiation factor-15 (GDF15) and erythroferrone (ERFE) as potential suppressors of hepcidin.

METHODS

This cross-sectional study was conducted on 61 thalassemic patients and 60 healthy controls. The frequency of GDF15 gene polymorphism (rs4808793) (-3148C/G), serum level of GDF15 and erythroferrone were measured and correlated with those of hepcidin and serum ferritin.

RESULTS

The presence of GDF15 gene mutations were significantly higher in the patients' group compared to controls (P value 0.035). Also, thalassemia patients had significantly higher levels of GDF15 and ERFE and lower hepcidin levels than controls (P value < 0.001). Serum hepcidin level showed significantly negative correlations with GDF15, ERFE, reticulocyte count, LDH level, and serum ferritin. Contrarily, it had highly significant positive correlation with hemoglobin.

CONCLUSIONS

High level of GDF15 and/or ERFE may inhibit hepcidin production and increase iron load in patients with thalassemia; therefore, medications that suppress their actions may provide new therapeutic potentials for iron toxicity.

IMPACT

Iron overload continues to be a major contributor to high morbidity and mortality in patients with thalassemia. New strategies together with proper chelation, need to be developed to minimize the effect of iron toxicity. Growth differentiation factor-15 (GDF15) and erythroferrone (ERFE) inhibit hepcidin production and increase iron levels in conditions with ineffective erythropoiesis. Medications that suppress the production or interfere with the action of GDF15 or ERFE may represent new therapeutic potentials for iron toxicity. Prevention of iron toxicity will significantly reduce morbidity and mortality and improve the quality of life of thalassemia patients.

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.

Association of GDF15 levels with body mass index and endocrine status in β-thalassaemia

OBJECTIVE

GDF15 has emerged as a stress-induced hormone, acting on the brain to reduce food intake and body weight while affecting neuroendocrine function. Very high GDF15 levels are found in thalassaemia, where growth, energy balance and neuroendocrine function are impaired. We examined the relationships between GDF15 and anthropometric measures and endocrine status in β-thalassaemia.

DESIGN

Cross sectional study.

PATIENTS

All β-thalassaemia patients attending the thalassaemia unit of Colombo North Teaching Hospital for blood transfusions.

MEASUREMENTS

Anthropometric data, appetite scores, circulating GDF15, IGF, thyroid and reproductive hormone levels in 103 β-thalassaemia patients were obtained.

RESULTS

GDF15 levels were markedly elevated in thalassaemia patients (24.2-fold with β-thalassaemia major compared with healthy controls). Among patients with β-thalassaemia major, the relationship between GDF15 and body mass index (BMI) was curvilinear with all individuals with GDF15 levels above 24,000 pg/mL having a BMI below 20 kg/m2 . After adjustment for BMI, age and Tanner stage, serum IGF1 concentrations correlated negatively with GDF15 in all thalassaemia patients (β = -.027, p = .02). We found a significant positive relationship between GDF15 and gonadotropin (in both sexes) and testosterone (in males).

CONCLUSIONS

GDF15 levels were markedly elevated in patients with β-thalassaemia and its association with BMI is consistent with the known effect of GDF15 to reduce body weight. The inverse association between GDF15 with IGF1 levels may reflect a neuroendocrine impact of GDF15 or an indirect effect via impaired nutritional state. The positive association with testosterone in males and gonadotropins in both sexes, was surprising and should prompt further GDF15 studies on the hypothalamic pituitary gonadal axis.

Changes of biomarkers for erythropoiesis, iron metabolism, and FGF23 by supplementation with roxadustat in patients on hemodialysis

This study aimed to confirm changes in biomarkers of erythropoiesis and iron metabolism and serum fibroblast growth factor 23 (FGF-23) during darbepoetin-α treatment and then switching to the hypoxia-inducible factor prolyl hydroxylase inhibitor roxadustat. A total of 28 patients on hemodialysis who received weekly doses of darbepoetin-α were switched to roxadustat. Biomarkers for erythropoiesis and iron metabolism and intact and C-terminal FGF-23 were measured in blood samples collected before the HD session on days - 7 (darbepoetin-α injection), - 4, and - 2, and days 0 (switch to roxadustat treatment, three times weekly), 3, 5, 7, 14, 21, and 28. Erythropoietin and erythroferrone levels were elevated on day - 4 by darbepoetin-α injection and decreased to baseline levels at day 0. Levels of erythropoietin were not significantly increased by roxadustat supplementation, but erythroferrone levels were continuously elevated, similar to darbepoetin-α treatment. Hepcidin-25 and total iron binding capacity were significantly decreased or increased in patients treated with roxadustat compared with darbepoetin-α. Changes of intact and C-terminal FGF-23 levels were parallel to changes of phosphate levels during roxadustat treatment. However, the actual and percentage changes of intact FGF-23 and C-terminal FGF-23 in patients with low ferritin levels were greater than those in patients with high ferritin levels. Roxadustat might stimulate erythropoiesis by increasing iron usage through hepcidin-25, which was suppressed by erythroferrone in the physiological erythropoietin condition. Changes of intact FGF-23 and C-terminal FGF-23 levels might be affected by roxadustat in patients on hemodialysis, especially those with a low-iron condition.

Hypoxia Triggers the Intravasation of Clustered Circulating Tumor Cells

Circulating tumor cells (CTCs) are shed from solid cancers in the form of single or clustered cells, and the latter display an extraordinary ability to initiate metastasis. Yet, the biological phenomena that trigger the shedding of CTC clusters from a primary cancerous lesion are poorly understood. Here, when dynamically labeling breast cancer cells along cancer progression, we observe that the majority of CTC clusters are undergoing hypoxia, while single CTCs are largely normoxic. Strikingly, we find that vascular endothelial growth factor (VEGF) targeting leads to primary tumor shrinkage, but it increases intra-tumor hypoxia, resulting in a higher CTC cluster shedding rate and metastasis formation. Conversely, pro-angiogenic treatment increases primary tumor size, yet it dramatically suppresses the formation of CTC clusters and metastasis. Thus, intra-tumor hypoxia leads to the formation of clustered CTCs with high metastatic ability, and a pro-angiogenic therapy suppresses metastasis formation through prevention of CTC cluster generation.

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Hypoxia leads to cell-cell junction upregulation and intravasation of CTC clusters

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Hypoxic CTC clusters are highly metastatic compared to normoxic CTCs

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Increase in intra-tumor hypoxia leads to accelerated metastasis

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Treatment with EpB2 reduces hypoxia and prevents CTC cluster formation

The associations between red cell distribution width and plasma proteins in a general population

BACKGROUND

High red cell distribution width (RDW) has been increasingly recognized as a risk factor for cardiovascular diseases (CVDs), but the underlying mechanisms remain unknown. Our aim was to explore the associations between RDW and plasma proteins implicated in the pathogenesis of CVD using a targeted proteomics panel.

METHODS

RDW and 88 plasma proteins were measured in a population-based cohort study (n = 4726), Malmö Diet and Cancer-Cardiovascular Cohort (MDC-CC). A random 2/3 of the cohort was used as discovery sample and remaining 1/3 was used for replication. Multiple linear regression was used to assess the associations between RDW and plasma proteins, with adjustments for age, sex, and other potential confounders. Proteins with Bonferroni-corrected significant associations with RDW in the discovery sub-cohort were validated in the replication cohort.

RESULTS

Thirteen of 88 plasma proteins had significant associations with RDW in the discovery sample, after multivariate adjustments. Eleven of them were also significant in the replication sample, including SIR2-like protein 2 (SIRT2), stem cell factor (SCF, inversely), melusin (ITGB1BP2), growth differentiation factor-15 (GDF-15), matrix metalloproteinase-7 (MMP-7), hepatocyte growth factor (HGF), chitinase-3-like protein 1 (CHI3L1), interleukin-8 (IL-8), CD40 ligand (CD40-L), urokinase plasminogen activator surface receptor (U-PAR) and matrix metalloproteinase-3 (MMP-3).

CONCLUSIONS

Several proteins from this targeted proteomics panel were associated with RDW in this cohort. These proteins could potentially be linked to the increased cardiovascular risk in individuals with high RDW.

Iron Deficiency in Pulmonary Arterial Hypertension: A Deep Dive into the Mechanisms

Pulmonary arterial hypertension (PAH) is a severe cardiovascular disease that is caused by the progressive occlusion of the distal pulmonary arteries, eventually leading to right heart failure and death. Almost 40% of patients with PAH are iron deficient. Although widely studied, the mechanisms linking between PAH and iron deficiency remain unclear. Here we review the mechanisms regulating iron homeostasis and the preclinical and clinical data available on iron deficiency in PAH. Then we discuss the potential implications of iron deficiency on the development and management of PAH.

Association of serum growth differentiation factor-15 with eGFR and hemoglobin in healthy older females

Purpose

Anemia and sarcopenia associated with renal dysfunction caused by cytokine imbalance can contribute to decreased quality of life for older individuals. Growth differentiation factor-15 (GDF-15) is associated with renal dysfunction, although whether it is related to anemia or sarcopenia is unclear. In this study we examined the association of GDF-15 with renal function, hemoglobin and sarcopenia in healthy community-dwelling older females in Japan.

Methods

A total of 66 healthy older community-dwelling females (age: 75.8 ± 6.2 years) were enrolled for this study. Skeletal muscle mass index was determined by bioelectrical impedance analysis. Hand-grip strength and walking speed were also assessed. Serum GDF-15 concentration was determined by enzyme-linked immunosorbent assay and both hemoglobin (Hb) level and estimated glomerular filtration rate (eGFR) were measured.

Results

Serum GDF-15 levels positively correlated with age but negatively correlated with eGFR and walking speed. In multiple regression analysis, eGFR and hemoglobin (Hb) were independent variables to predict serum GDF-15 levels, even after adjusting for age and body mass index (eGFR: β = −0.423, p < 0.001; Hb: β = −0.363, p = 0.004). Serum GDF-15 level was an independent variable to predict eGFR and Hb.

Conclusions

Both Hb and eGFR are predictors for serum GDF-15 concentration in healthy older females. In these community-dwelling older females, renal dysfunction via GDF-15 may be accompanied by anemia, but not sarcopenia.

Biomarkers of iron metabolism in chronic kidney disease

Iron is the most abundant transition metal in the human body and an essential element required for growth and survival. Our understanding of the molecular control of iron metabolism has increased dramatically over the past 20 years due to the discovery of hepcidin, which regulates the uptake of dietary iron and its mobilization from macrophages and hepatic stores. Anemia and iron deficiency are common in chronic kidney disease. The pathogenesis of anemia of chronic kidney disease is multifactorial. Correction of anemia requires two main treatment strategies: increased stimulation of erythropoiesis, and maintenance of an adequate iron supply to the bone marrow. However, there are still many uncertainties in regard to iron metabolism in patients with chronic kidney disease and in renal replacement therapy. The aim of this review was to summarize the current knowledge on iron metabolism in this population, including new biomarkers of iron status. There is an area of uncertainty regarding diagnostic utility of both erythroferrone (ERFE) and hepcidin in end-stage renal disease (ESRD) patients. Higher concentration of hepcidin in oligoanuric patients may reflect decreased renal clearance. Furthermore, the hepcidin-lowering effect of ERFE in ESRD patients treated with erythropoiesis-stimulating agents (ESAs) may be blunted by underlying inflammation and concomitant iron treatment. Thus, future studies should validate the use of ERFE as a biomarker of erythropoiesis and predictor of response to iron and ESA therapy in dialysis-dependent patients.

Hepcidin and GDF-15 are potential biomarkers of iron deficiency anaemia in chronic kidney disease patients in South Africa

BACKGROUND

Anaemia is a common presenting feature among patients with chronic kidney disease (CKD) and it is associated with poor clinical outcomes and quality of life. It is not clear if growth differentiation factor-15 (GDF-15) or hepcidin are useful as early markers of iron deficiency anaemia (IDA) among non-dialysis CKD patients. We therefore evaluated the diagnostic validity of GDF-15 and hepcidin as biomarkers of IDA among non-dialysis CKD patients in Johannesburg, South Africa.

METHOD

An analytic cross-sectional study was conducted among non-dialysis CKD patients (n = 312) and apparently healthy controls (n = 184) from June to December 2016 at an Academic Hospital, in Johannesburg, South Africa. An interviewer administered proforma was used to obtain the socio-biological and clinical characteristics of the participants. 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 absolute and functional iron deficiency anaemia.

RESULTS

About half (50.6%) of the participants were female while the participants' mean age was 49.7 ± 15.8 years. The predictive value of diagnosing absolute IDA among CKD patients using GDF-15 was 74.02% (95% CI: 67.62-80.42%) while the predictive value of diagnosing functional IDA among CKD patients using hepcidin was 70.1% (95% CI: 62.79-77.49%).There was a weak negative correlation between hepcidin levels and GFR (r = - 0.19, p = 0.04) in anaemic CKD patients, and between serum GDF-15 and haemoglobin (r = - 0.34, p = 0.001). Serum ferritin (β = 0.00389, P-value< 0.001), was a predictor of log hepcidin. MCHC (β = - 0.0220, P-value 0.005) and CKD stage (β = 0.4761, P-value < 0.001), race (β = 0.3429, P-value = 0.018) were predictors of log GDF-15. Both GDF-15 (adj OR: 1.0003, 95%CI: 1.0001-1.0005, P = 0.017) and hepcidin (adj OR: 1.003, 95%CI: 1.0004-1.0055, P = 0.023) were associated with iron deficiency anaemia after multiple linear regression modelling.

CONCLUSION

Serum GDF-15 is a potential biomarker of absolute IDA, while hepcidin levels can predict functional IDA among CKD patients.

GDF15: A Hormone Conveying Somatic Distress to the Brain

GDF15 has recently gained scientific and translational prominence with the discovery that its receptor is a GFRAL-RET heterodimer of which GFRAL is expressed solely in the hindbrain. Activation of this receptor results in reduced food intake and loss of body weight and is perceived and recalled by animals as aversive. This information encourages a revised interpretation of the large body of previous research on the protein. GDF15 can be secreted by a wide variety of cell types in response to a broad range of stressors. We propose that central sensing of GDF15 via GFRAL-RET activation results in behaviors that facilitate the reduction of exposure to a noxious stimulus. The human trophoblast appears to have hijacked this signal, producing large amounts of GDF15 from early pregnancy. We speculate that this encourages avoidance of potential teratogens in pregnancy. Circulating GDF15 levels are elevated in a range of human disease states, including various forms of cachexia, and GDF15-GFRAL antagonism is emerging as a therapeutic strategy for anorexia/cachexia syndromes. Metformin elevates circulating GDF15 chronically in humans and the weight loss caused by this drug appears to be dependent on the rise in GDF15. This supports the concept that chronic activation of the GDF15-GFRAL axis has efficacy as an antiobesity agent. In this review, we examine the science of GDF15 since its identification in 1997 with our interpretation of this body of work now being assisted by a clear understanding of its highly selective central site of action.

Hypoxia Induces Growth Differentiation Factor 15 to Promote the Metastasis of Colorectal Cancer via PERK-eIF2α Signaling

Hypoxia plays an essential role in orchestrating Epithelial-mesenchymal transition and promoting metastasis of colorectal cancer. However, the underlying mechanisms are still not well elucidated. Here, we present that hypoxic exposure causes endoplasmic reticulum stress and activates the unfolded protein response pathways, which drives GDF15 expression in colorectal cancer cells. Mechanistically, upregulated CHOP led by activated PERK-eIF2α signaling promotes GDF15 transcription via directly binding to its promoter. Further study implicates that hypoxia-induced GDF15 is required for the EMT and invasion of colorectal cancer cells; enforced expression of GDF15 promotes the mitochondrial oxidation of fatty acids in colorectal cancer cells. Moreover, the abrogation of GDF15 results in smaller xenograft tumors in size and impaired metastasis. GDF15 is expressed much more in tumor tissues of CRC patients and displays positive correlations with CHOP and HIF1α in mRNA levels. Our study demonstrates a novel molecular mechanism underlying hypoxia-promoted metastasis of CRC and provides PERK signaling-regulated GDF15 as a new and promising therapeutic target for clinical treatment and drug discovery.

The Impact of Human Parvovirus B19 Infection on Heart Failure and Anemia with Reference to Iron Metabolism Markers in an Adult Woman

A 35-year-old woman with fever, edema and rash was admitted. Pleural effusion and cardiomegaly were observed. A laboratory analysis revealed anemia with iron deficiency and elevated human parvovirus B19 (B19V) immunoglobulin M. The patient's hepcidin-25 and erythroferrone levels were not elevated compared to those observed later in her clinical course. On the other hand, her growth differentiation factor-15 (GDF-15) levels were elevated. She was diagnosed to have heart failure symptoms and anemia with specific iron metabolism abnormalities due to a B19V infection. After providing supportive treatment, the heart failure symptoms disappeared and her anemia had improved. This case emphasizes the need to include a B19V infection in the differential diagnosis when we encounter cases demonstrating reversible heart failure with anemia.

GDF-15, iron, and inflammation in early chronic kidney disease among elderly patients

PURPOSE

The aim of the study was to assess GDF-15 and iron status in patients in early stages of chronic kidney disease with a particular emphasis on elderly population in association of classic iron status parameters with novel iron homeostasis biomarkers and inflammatory parameters.

METHODS

Serum concentrations of GDF-15, iron (Fe), transferrin saturation, soluble transferrin receptor (sTfR), hepcidin, high-sensitive C-reactive protein (hsCRP), interleukin 6 (IL-6), and hemoglobin were measured in 56 patients ≥65 years of age and in 31 <65 years of age.

RESULTS

In patients ≥65 years, serum concentrations of GDF-15 and hsCRP were significantly higher in comparison with younger group. There was no statistically significant difference in hemoglobin, iron, hepcidin, and sTfR concentration between the two studied groups. In both groups GDF-15 was significantly correlated with hemoglobin, eGFR, hsCRP, and IL-6. GDF-15 was significantly higher in patients with anemia in comparison with their non-anemic counterparts. In multivariate analysis, hemoglobin was found to be a predictor of log GDF-15 (beta value = 0.36, P = 0.006, R (2) = 37 %).

CONCLUSIONS

An intricate interplay between renal function, anemia, and GDF-15 concentrations awaits further studies, as there are few data regarding pathophysiological role of GDF-15 in diabetes, kidney disease, and other comorbidities. Further understanding regarding the signaling pathways of GDF-15 may help to discover next pieces in the exciting puzzle of GDF-15. Finally, as studies dealing with normal level of GDF-15 in the healthy aged are lacking, it is possible that the higher values of GDF-15 values found in the present study represent values of GDF-15 according to age more than CKD levels.

Laboratory use of hepcidin in renal transplant recipients

Hepcidin is a small peptide with a critical role in cellular iron homeostasis, as it regulates utilization of stored iron and antimicrobial defense in inflammation (bacterial and fungal). Since it was isolated in 2000, and especially in the last decade, numerous studies aimed to evaluate the clinical use of plasma and urine hepcidin as a marker of anemia, especially anemia of chronic disease and post-transplant anemia (PTA). Hepcidin regulation is delicately tuned by two inflammatory pathways activated by interleukin-6 (IL-6) and bone morphogenic proteins (BMPs) and iron regulated pathway sensitive to circulating transferin-iron (TR-Fe) complex. BMP-mediated pathway and TR-Fe sensitive pathway seem to be connected by hemojuveline, a BMP co-factor that interacts with transferine receptor 2 (TRF2) in cases of high TR-Fe circulatory concentration. In addition to these regulatory mechanisms other regulators and signaling pathways are being extensively researched.
Hepcidin has been identified as an important contributor to morbidity and mortality in end stage renal disease (ESRD) but no such association has jet been found in case of PTA. However, there is an association between higher doses of erythropoiesis-stimulating agents (ESA) and mortality in the posttransplant period and the assumption that hepcidin might play a role in ESA resistance in PTA. Thus the review’s main goal was to summarize papers published on the association of hepcidin with PTA, give up-to-date information on hepcidin regulation and on potential therapeutics that optimize hepcidin regulation. We also compared the performances of tests for hepcidin determination and reviewed research on immunosuppressants’ (IS) effect on hepcidin concentration.

Growth differentiation factor-15 in children and adolescents with thalassemia intermedia: Relation to subclinical atherosclerosis and pulmonary vasculopathy

BACKGROUND

Heart disease is the leading cause of mortality and one of the main causes of morbidity in β-thalassemia. Growth differentiation factor-15 (GDF-15), a member of the transforming growth factor-β superfamily, is a marker of ineffective erythropoiesis in several anemias.

AIM

To determine GDF-15 levels in children and adolescents with TI and the relation to hemolysis, iron overload and cardiovascular complications.

METHODS

GDF-15 was measured in 35 TI patients without symptoms for heart disease and correlated to echocardiographic parameters and carotid intima media thickness (CIMT).

RESULTS

GDF-15 levels were significantly higher in TI patients compared with controls (p < 0.001). Transfusion dependent patients had higher GDF-15 than non-transfusion dependent patients. TI patients with splenectomy, pulmonary hypertension risk, and heart disease had higher GDF-15 levels than those without. GDF-15 was lower among hydroxyurea-treated patients. Multiple linear regression analysis revealed that transfusion index (p=0.012), serum ferritin (p < 0.001), tricuspid regurgitant jet velocity (p < 0.001), ejection fraction (p=0.01) and CIMT (p=0.007) were independently related to GDF-15. According to ROC curve analysis, the cutoff value of GDF-15 at 1500 pg/mL could differentiate patients with and without heart disease.

CONCLUSION

GDF-15 would identify TI patients at increased risk of pulmonary and cardiovascular complications as well as subclinical atherosclerosis.

Can Serum Gdf-15 be Associated with Functional Iron Deficiency in Hemodialysis Patients?

Functional iron deficiency (FID) incidence is gradually increasing in hemodialysis (HD) patients. Recently, high levels of GDF-15 supressed the iron regulatory protein hepcidin and GDF-15 expression increased in iron-deficient patients. The relationship between FID, GDF-15, and hepcidin is currently unknown. The present study aimed to evaluate the association between GDF-15, hepcidin, and FID in chronic HD patients. Serum GDF-15 and hepcidin concentrations were measured in 105 HD patients and 40 controls. FID is defined as serum ferritin >800 ng/mL, TSAT <25 %, Hb levels <11 g/dL, and reticulocyte haemoglobin content (CHr) <29 pg. Serum GDF-15 and hepcidin levels were increased significantly in HD patients with FID, compared to HD patients without anemia and controls. GDF-15 correlated with ferritin, hepcidin, and CRP in the entire cohort. GDF-15 was related to ferritin and CRP in HD patients with FID. GDF-15 is better diagnostic marker than hepcidin for detection of FID [AUC = 0.982 (0.013) versus AUC = 0.921 (0.027); P = 0.0324]. GDF-15 appears to be a promising tool for detection of FID. High levels of ferritin and CRP correlated with GDF-15. Our results support GDF-15 as a new mediator of FID via hepcidin, chronic inflammation, or unknown pathways.

Deregulation of genes related to iron and mitochondrial metabolism in refractory anemia with ring sideroblasts

The presence of SF3B1 gene mutations is a hallmark of refractory anemia with ring sideroblasts (RARS). However, the mechanisms responsible for iron accumulation that characterize the Myelodysplastic Syndrome with ring sideroblasts (MDS-RS) are not completely understood. In order to gain insight in the molecular basis of MDS-RS, an integrative study of the expression and mutational status of genes related to iron and mitochondrial metabolism was carried out. A total of 231 low-risk MDS patients and 81 controls were studied. Gene expression analysis revealed that iron metabolism and mitochondrial function had the highest number of genes deregulated in RARS patients compared to controls and the refractory cytopenias with unilineage dysplasia (RCUD). Thus mitochondrial transporters SLC25 (SLC25A37 and SLC25A38) and ALAD genes were over-expressed in RARS. Moreover, significant differences were observed between patients with SF3B1 mutations and patients without the mutations. The deregulation of genes involved in iron and mitochondrial metabolism provides new insights in our knowledge of MDS-RS. New variants that could be involved in the pathogenesis of these diseases have been identified.

Iron-chelating and anti-lipid peroxidation properties of 1-(N-acetyl-6-aminohexyl)-3-hydroxy-2-methylpyridin-4-one (CM1) in long-term iron loading β-thalassemic mice

OBJECTIVE

To evaluate the iron-chelating properties and free-radical scavenging activities of 1-(N-acetyl-6-aminohexyl)-3-hydroxy-2-methylpyridin-4-one (CM1) treatment in chronic iron-loaded β-thalassemic (BKO) mice.

METHODS

The BKO mice were fed with a ferrocene-rich diet and were orally administered with CM1 [50 mg/(kg.day)] for 6 months. Blood levels of non-transferrin bound iron, labile plasma iron, ferritin (Ft) and malondialdehyde were determined.

RESULTS

The BKO mice were fed with an iron diet for 8 months which resulted in iron overload. Interestingly, the mice showed a decrease in the non-transferrin bound iron, labile plasma iron and malondialdehyde levels, but not the Ft levels after continuous CM1 treatment.

CONCLUSIONS

CM1 could be an effective oral iron chelator that can reduce iron overload and lipid peroxidation in chronic iron overload β-thalassemic mice.

Molecular liaisons between erythropoiesis and iron metabolism

Although most circulating iron in blood plasma is destined for erythropoiesis, the mechanisms by which erythropoietic demand modulates the iron supply ("erythroid regulators") remain largely unknown. Iron absorption, plasma iron concentrations, and tissue iron distribution are tightly controlled by the liver-produced hormone hepcidin. During the last decade, much progress has been made in elucidating hepcidin regulation by iron and inflammation. This review discusses the less understood mechanisms and mediators of hepcidin suppression in physiologically and pathologically stimulated erythropoiesis.

The WT hemochromatosis protein HFE inhibits CD8⁺ T-lymphocyte activation

MHC class I (MHC I) antigen presentation is a ubiquitous process by which cells present endogenous proteins to CD8(+) T lymphocytes during immune surveillance and response. Hereditary hemochromatosis protein, HFE, is involved in cellular iron uptake but, while structurally homologous to MHC I, is unable to bind peptides. However, increasing evidence suggests a role for HFE in the immune system. Here, we investigated the impact of HFE on CD8(+) T-lymphocyte activation. Using transient HFE transfection assays in a model of APCs, we show that WT HFE (HFEWT ), but not C282Y-mutated HFE, inhibits secretion of MIP-1β from antigen-specific CD8(+) T lymphocytes. HFEWT expression also resulted in major decreases in CD8(+) T-lymphocyte activation as measured by 4-1BB expression. We further demonstrate that inhibition of CD8(+) T-lymphocyte activation was independent of MHC I surface levels, β2-m competition, HFE interaction with transferrin receptor, antigen origin, or epitope affinity. Finally, we identified the α1-2 domains of HFEWT as being responsible for inhibiting CD8(+) T-lymphocyte activation. Our data imply a new role for HFEWT in altering CD8(+) T-lymphocyte reactivity, which could modulate antigen immunogenicity.

The iron cycle in chronic kidney disease (CKD): from genetics and experimental models to CKD patients

Iron is essential for most living organisms but iron excess can be toxic. Cellular and systemic iron balance is therefore tightly controlled. Iron homeostasis is dysregulated in chronic kidney disease (CKD) and contributes to the anemia that is prevalent in this patient population. Iron supplementation is one cornerstone of anemia management in CKD patients, but has not been rigorously studied in large prospective randomized controlled trials. This review highlights important advances from genetic studies and animal models that have provided key insights into the molecular mechanisms governing iron homeostasis and its disturbance in CKD, and summarizes how these findings may yield advances in the care of this patient population.

GDF15-mediated upregulation of ferroportin plays a key role in the development of hyperferritinemia in children with hemophagocytic lymphohistiocytosis

BACKGROUND

Growth differentiation factor 15 (GDF15), a divergent TGFβ superfamily, has recently been implicated in the modulation of iron homeostasis, acting as an upstream negative regulator of hepcidin, the key iron regulatory hormone produced primarily by hepatocytes. However, little is known about possible roles that GDF15 might play in the regulation of iron homeostasis and development of hyperferritinemia in children with hemophagocytic lymphohistiocytosis (HLH).

PROCEDURES

We compared serum GDF15 level and mRNA expressions of GDF15 and key molecules of iron metabolism, and made correlations between their expressions in children with HLH and control children.

RESULTS

Serum GDF15 level was remarkably higher in HLH group than that in controls, with median serum concentration of 1,700 and 260 pg/ml, respectively (P < 0.001). In addition, GDF15 mRNA was significantly upregulated but independent of hypoxia-inducible factor-mediated oxygen signaling pathway. More importantly, GDF15 induction was positively correlated to upregulation of ferroportin, the only cellular iron exporter, and to upregulation of ferritin heavy chain.

CONCLUSIONS

Our study suggests that GDF15 induction helps suppress further activation of macrophages in stressful physiologic states as HLH, and is intimately implicated in the development of hyperferritinemia by modulating the hepcidin-ferroportin axis, resulting in enhanced ferroportin-mediated iron efflux.

Suppression of hepcidin expression and iron overload mediate Salmonella susceptibility in ankyrin 1 ENU-induced mutant

Salmonella, a ubiquitous Gram-negative intracellular bacterium, is a food borne pathogen that infects a broad range of hosts. Infection with Salmonella Typhimurium in mice is a broadly recognized experimental model resembling typhoid fever in humans. Using a N-ethyl-N-nitrosurea (ENU) mutagenesis recessive screen, we report the identification of Ity16 (Immunity to Typhimurium locus 16), a locus responsible for increased susceptibility to infection. The position of Ity16 was refined on chromosome 8 and a nonsense mutation was identified in the ankyrin 1 (Ank1) gene. ANK1 plays an important role in the formation and stabilization of the red cell cytoskeleton. The Ank1^Ity16/Ity16 mutation causes severe hemolytic anemia in uninfected mice resulting in splenomegaly, hyperbilirubinemia, jaundice, extramedullary erythropoiesis and iron overload in liver and kidneys. Ank1^Ity16/Ity16 mutant mice demonstrated low levels of hepcidin (Hamp) expression and significant increases in the expression of the growth differentiation factor 15 (Gdf15), erythropoietin (Epo) and heme oxygenase 1 (Hmox1) exacerbating extramedullary erythropoiesis, tissue iron deposition and splenomegaly. As the infection progresses in Ank1^Ity16/Ity16, the anemia worsens and bacterial load were high in liver and kidneys compared to wild type mice. Heterozygous Ank1^+/Ity16 mice were also more susceptible to Salmonella infection although to a lesser extent than Ank1^Ity16/Ity16 and they did not inherently present anemia and splenomegaly. During infection, iron accumulated in the kidneys of Ank1^+/Ity16 mice where bacterial loads were high compared to littermate controls. The critical role of HAMP in the host response to Salmonella infection was validated by showing increased susceptibility to infection in Hamp-deficient mice and significant survival benefits in Ank1^+/Ity16 heterozygous mice treated with HAMP peptide. This study illustrates that the regulation of Hamp and iron balance are crucial in the host response to Salmonella infection in Ank1 mutants.

Regulation of erythropoiesis by hypoxia-inducible factors

A classic physiologic response to systemic hypoxia is the increase in red blood cell production. Hypoxia-inducible factors (HIFs) orchestrate this response by inducing cell-type specific gene expression changes that result in increased erythropoietin (EPO) production in kidney and liver, in enhanced iron uptake and utilization and in adjustments of the bone marrow microenvironment that facilitate erythroid progenitor maturation and proliferation. In particular HIF-2 has emerged as the transcription factor that regulates EPO synthesis in the kidney and liver and plays a critical role in the regulation of intestinal iron uptake. Its key function in the hypoxic regulation of erythropoiesis is underscored by genetic studies in human populations that live at high-altitude and by mutational analysis of patients with familial erythrocytosis. This review provides a perspective on recent insights into HIF-controlled erythropoiesis and iron metabolism, and examines cell types that have EPO-producing capability. Furthermore, the review summarizes clinical syndromes associated with mutations in the O(2)-sensing pathway and the genetic changes that occur in high altitude natives. The therapeutic potential of pharmacologic HIF activation for the treatment of anemia is discussed.

Hypoxia-inducible factor regulates hepcidin via erythropoietin-induced erythropoiesis

Iron demand in bone marrow increases when erythropoiesis is stimulated by hypoxia via increased erythropoietin (EPO) synthesis in kidney and liver. Hepcidin, a small polypeptide produced by hepatocytes, plays a central role in regulating iron uptake by promoting internalization and degradation of ferroportin, the only known cellular iron exporter. Hypoxia suppresses hepcidin, thereby enhancing intestinal iron uptake and release from internal stores. While HIF, a central mediator of cellular adaptation to hypoxia, directly regulates renal and hepatic EPO synthesis under hypoxia, the molecular basis of hypoxia/HIF-mediated hepcidin suppression in the liver remains unclear. Here, we used a genetic approach to disengage HIF activation from EPO synthesis and found that HIF-mediated suppression of the hepcidin gene (Hamp1) required EPO induction. EPO induction was associated with increased erythropoietic activity and elevated serum levels of growth differentiation factor 15. When erythropoiesis was inhibited pharmacologically, Hamp1 was no longer suppressed despite profound elevations in serum EPO, indicating that EPO by itself is not directly involved in Hamp1 regulation. Taken together, we provide in vivo evidence that Hamp1 suppression by the HIF pathway occurs indirectly through stimulation of EPO-induced erythropoiesis.

The long history of iron in the Universe and in health and disease

BACKGROUND

Not long after the Big Bang, iron began to play a central role in the Universe and soon became mired in the tangle of biochemistry that is the prima essentia of life. Since life's addiction to iron transcends the oxygenation of the Earth's atmosphere, living things must be protected from the potentially dangerous mix of iron and oxygen. The human being possesses grams of this potentially toxic transition metal, which is shuttling through his oxygen-rich humor. Since long before the birth of modern medicine, the blood-vibrant red from a massive abundance of hemoglobin iron-has been a focus for health experts.

SCOPE OF REVIEW

We describe the current understanding of iron metabolism, highlight the many important discoveries that accreted this knowledge, and describe the perils of dysfunctional iron handling.

GENERAL SIGNIFICANCE

Isaac Newton famously penned, "If I have seen further than others, it is by standing upon the shoulders of giants". We hope that this review will inspire future scientists to develop intellectual pursuits by understanding the research and ideas from many remarkable thinkers of the past.

MAJOR CONCLUSIONS

The history of iron research is a long, rich story with early beginnings, and is far from being finished. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Growth differentiation factor 15 in patients with congenital dyserythropoietic anaemia (CDA) type II

Congenital dyserythropoietic anaemias (CDAs) are heterogeneous, hereditary disorders hallmarked by ineffective erythropoiesis and tissue iron overload. Growth differentiation factor 15 (GDF15) was suggested to mediate iron overload in iron-loading anaemias, such as the thalassaemias and CDAI by suppressing hepcidin, the key regulator of iron absorption. Here, we show that serum GDF15 concentrations are elevated in subjects with CDAI and CDAII. Despite similar disease characteristics, CDAI patients present with significantly higher GDF15 concentrations compared to CDAII patients. Hepcidin concentrations are inappropriately low in CDAII patients considering the severe hepatic iron overload associated with this disorder. GDF15 significantly correlates with the degree of anaemia (Hb), the response of erythropoiesis (reticulocyte index) as well as with iron availability in the serum (transferrin saturation). The observation that GDF15 is elevated in CDAII patients is consistent with the proposal that GDF15 is among the erythroid factors down-regulating hepcidin and contributing to iron overload in conditions of dyserythropoiesis.

Modulation of hepcidin production during hypoxia-induced erythropoiesis in humans in vivo: data from the HIGHCARE project

Iron is tightly connected to oxygen homeostasis and erythropoiesis. Our aim was to better understand how hypoxia regulates iron acquisition for erythropoiesis in humans, a topic relevant to common hypoxia-related disorders. Forty-seven healthy volunteers participated in the HIGHCARE project. Blood samples were collected at sea level and after acute and chronic exposure to high altitude (3400-5400 m above sea level). We investigated the modifications in hematocrit, serum iron indices, erythropoietin, markers of erythropoietic activity, interleukin-6, and serum hepcidin. Hepcidin decreased within 40 hours after acute hypoxia exposure (P < .05) at 3400 m, reaching the lowest level at 5400 m (80% reduction). Erythropoietin significantly increased (P < .001) within 16 hours after hypoxia exposure followed by a marked erythropoietic response supported by the increased iron supply. Growth differentiation factor-15 progressively increased during the study period. Serum ferritin showed a very rapid decrease, suggesting the existence of hypoxia-dependent mechanism(s) regulating storage iron mobilization. The strong correlation between serum ferritin and hepcidin at each point during the study indicates that iron itself or the kinetics of iron use in response to hypoxia may signal hepcidin down-regulation. The combined and significant changes in other variables probably contribute to the suppression of hepcidin in this setting.

Iron regulatory proteins: from molecular mechanisms to drug development

Eukaryotic cells require iron for survival but, as an excess of poorly liganded iron can lead to the catalytic production of toxic radicals that can damage cell structures, regulatory mechanisms have been developed to maintain appropriate cell and body iron levels. The interactions of iron responsive elements (IREs) with iron regulatory proteins (IRPs) coordinately regulate the expression of the genes involved in iron uptake, use, storage, and export at the post-transcriptional level, and represent the main regulatory network controlling cell iron homeostasis. IRP1 and IRP2 are similar (but not identical) proteins with partially overlapping and complementary functions, and control cell iron metabolism by binding to IREs (i.e., conserved RNA stem-loops located in the untranslated regions of a dozen mRNAs directly or indirectly related to iron metabolism). The discovery of the presence of IREs in a number of other mRNAs has extended our knowledge of the influence of the IRE/IRP regulatory network to new metabolic pathways, and it has been recently learned that an increasing number of agents and physiopathological conditions impinge on the IRE/IRP system. This review focuses on recent findings concerning the IRP-mediated regulation of iron homeostasis, its alterations in disease, and new research directions to be explored in the near future.

Recent advances in iron metabolism and related disorders

Iron is essential for life, because it is indispensable for several biological reactions such as oxygen transport, DNA synthesis and cell proliferation, but is toxic if present in excess since it causes cellular damage through free radical formation. Either cellular or systemic iron regulation can be disrupted in disorders of iron metabolism. In the past few years, our understanding of iron metabolism and its regulation has dramatically changed. New disorders of iron metabolism have emerged and the role of iron has started to be recognized as a cofactor of other disorders. The study of genetic conditions such as hemochromatosis and iron-refractory-iron-deficiency anemia (IRIDA) has provided crucial insights into the molecular mechanisms controlling iron homeostasis. In the future, these advances may be exploited for a more effective treatment of both genetic and acquired iron disorders.

Ferroportin and erythroid cells: an update

In recent years there have been major advances in our knowledge of the regulation of iron metabolism that have had implications for understanding the pathophysiology of some human disorders like beta-thalassemia and other iron overload diseases. However, little is known about the relationship among ineffective erythropoiesis, the role of iron-regulatory genes, and tissue iron distribution in beta-thalassemia. The principal aim of this paper is an update about the role of Ferroportin during human normal and pathological erythroid differentiation. Particular attention will be given to beta-thalassemia and other diseases with iron overload. Recent discoveries indicate that there is a potential for therapeutic intervention in beta-thalassemia by means of manipulating iron metabolism.

Growth differentiation factor 15 in erythroid health and disease

PURPOSE OF REVIEW

Growth differentiation factor 15 (GDF15) was identified as a hepcidin-suppression factor that is expressed at high levels in patients with ineffective erythropoiesis. This review addresses the regulation, expression and potential functions of GDF15 in the context of erythroid biology.

RECENT FINDINGS

GDF15 expression during late erythroid differentiation was discovered as part of an erythroblast transcriptome project. As GDF15 expression is associated with cellular stress or apoptosis, further investigation of the cytokine was focused upon its involvement in ineffective erythropoiesis. Remarkably high serum levels were detected in patients with thalassemia syndromes, congenital dyserythropoiesis and some acquired sideroblastic anemias. High-level GDF15 expression is not a feature of normal erythropoiesis, or erythroid recovery after bone-marrow transplantation. As GDF15 is a transforming growth factor-beta superfamily member, it was investigated as an effector of ineffective erythropoiesis that suppresses hepcidin expression despite iron overloading.

SUMMARY

In contrast to the low levels of GDF15 expressed during normal erythropoiesis, ineffective erythropoiesis causes high-level expression of GDF15. In patients with thalassemia and related anemias, GDF15 expression may contribute to iron overloading or other features of the disease phenotype.

Expression of growth differentiation factor 15 is not elevated in individuals with iron deficiency secondary to volunteer blood donation

BACKGROUND

Low serum hepcidin levels provide a physiologic response to iron demand in patients with iron deficiency (ID). Based on a discovery of suppressed hepcidin expression by a cytokine named growth differentiation factor 15 (GDF15), it was hypothesized that GDF15 may suppress hepcidin expression in humans with ID due to blood loss.

STUDY DESIGN AND METHODS

To test this hypothesis, GDF15 and hepcidin levels were measured in peripheral blood from subjects with iron-deficient erythropoiesis before and after iron supplementation.

RESULTS

Iron variables and hepcidin levels were significantly suppressed in iron-deficient blood donors compared to healthy volunteers. However, ID was not associated with elevated serum levels of GDF15. Instead, iron-deficient subjects' GDF15 levels were slightly lower than those measured in the control group of subjects (307 +/- 90 and 386 +/- 104 pg/mL, respectively). Additionally, GDF15 levels were not significantly altered by iron repletion.

CONCLUSIONS

ID due to blood loss is not associated with a significant change in serum levels of GDF15.

Iron Loading and Overloading due to Ineffective Erythropoiesis

Erythropoiesis describes the hematopoietic process of cell proliferation and differentiation that results in the production of mature circulating erythrocytes. Adult humans produce 200 billion erythrocytes daily, and approximately 1 billion iron molecules are incorporated into the hemoglobin contained within each erythrocyte. Thus, iron usage for the hemoglobin production is a primary regulator of plasma iron supply and demand. In many anemias, additional sources of iron from diet and tissue stores are needed to meet the erythroid demand. Among a subset of anemias that arise from ineffective erythropoiesis, iron absorption and accumulation in the tissues increases to levels that are in excess of erythropoiesis demand even in the absence of transfusion. The mechanisms responsible for iron overloading due to ineffective erythropoiesis are not fully understood. Based upon data that is currently available, it is proposed in this review that loading and overloading of iron can be regulated by distinct or combined mechanisms associated with erythropoiesis. The concept of erythroid regulation of iron is broadened to include both physiological and pathological hepcidin suppression in cases of ineffective erythropoiesis.

Hypoxic regulation of erythropoiesis and iron metabolism

The kidney is a highly sensitive oxygen sensor and plays a central role in mediating the hypoxic induction of red blood cell production. Efforts to understand the molecular basis of oxygen-regulated erythropoiesis have led to the identification of erythropoietin (EPO), which is essential for normal erythropoiesis and to the purification of hypoxia-inducible factor (HIF), the transcription factor that regulates EPO synthesis and mediates cellular adaptation to hypoxia. Recent insights into the molecular mechanisms that control and integrate cellular and systemic erythropoiesis-promoting hypoxia responses and their potential as a therapeutic target for the treatment of renal anemia are discussed in this review.

Iron homeostasis and its interaction with prolyl hydroxylases

The ability of iron to accept or donate electrons, coupled with the ability of oxygen to act as an electron acceptor, renders both elements essential to normal cellular biology. However, these same chemical properties allow free iron in solution to generate toxic free radicals, particularly in combination with oxygen. Thus, closely interwoven homeostatic mechanisms have evolved to regulate both iron and oxygen concentrations at the systemic and the cellular levels. Systemically, iron levels are regulated through hepcidin-mediated uptake of iron in the duodenum, whereas intracellular free-iron levels are controlled through iron-regulatory proteins (IRPs). Cardiorespiratory changes increase systemic oxygen delivery, whereas at a cellular level, many responses to altered oxygen levels are coordinated by hypoxia-inducible factor (HIF). However, the mechanisms of iron homeostasis also are regulated by oxygen availability, with alterations in both hepcidin and IRP activity. In addition, many genes involved in iron homeostasis are direct targets of HIF. Furthermore, HIF activation is modulated by intracellular iron, through regulation of hydroxylase activity, which requires iron as a cofactor. In addition, HIF-2alpha translation is controlled by IRP activity, providing another level of interdependence between iron and oxygen homeostasis.

Molecular mechanisms of hepcidin regulation: implications for the anemia of CKD

Anemia is prevalent in patients with chronic kidney disease (CKD) and is associated with lower quality of life and higher risk of adverse outcomes, including cardiovascular disease and death. Anemia management in patients with CKD currently revolves around the use of erythropoiesis-stimulating agents and supplemental iron. However, many patients do not respond adequately and/or require high doses of these medications. Furthermore, recent clinical trials have shown that targeting higher hemoglobin levels with conventional therapies leads to increased cardiovascular morbidity and mortality, particularly when higher doses of erythropoiesis-stimulating agents are used and in patients who are poorly responsive to therapy. One explanation for the poor response to conventional therapies in some patients is that these treatments do not fully address the underlying cause of the anemia. In many patients with CKD, as with patients with other chronic inflammatory diseases, poor absorption of dietary iron and the inability to use the body's iron stores contribute to the anemia. Recent research suggests that these abnormalities in iron balance may be caused by increased levels of the key iron regulatory hormone hepcidin. This article reviews the pathogenesis of anemia in CKD, the role and regulation of hepcidin in systemic iron homeostasis and the anemia of CKD, and the potential diagnostic and therapeutic implications of these findings.

Iron chelator-mediated alterations in gene expression: identification of novel iron-regulated molecules that are molecular targets of hypoxia-inducible factor-1 alpha and p53

Iron deficiency affects 500 million people, yet the molecular role of iron in gene expression remains poorly characterized. In addition, the alterations in global gene expression after iron chelation remain unclear and are important to assess for understanding the molecular pathology of iron deficiency and the biological effects of chelators. Considering this, we assessed the effect on whole genome gene expression of two iron chelators (desferrioxamine and 2-hydroxy-1-napthylaldehyde isonicotinoyl hydrazone) that have markedly different permeability properties. Sixteen genes were significantly regulated by both ligands, whereas a further 50 genes were significantly regulated by either compound. Apart from iron-mediated regulation of expression via hypoxia inducible factor-1 alpha, it was noteworthy that the transcription factor p53 was also involved in iron-regulated gene expression. Examining 16 genes regulated by both chelators in normal and neoplastic cells, five genes (APP, GDF15, CITED2, EGR1, and PNRC1) were significantly differentially expressed between the cell types. In view of their functions in tumor suppression, proliferation, and apoptosis, these findings are important for understanding the selective antiproliferative effects of chelators against neoplastic cells. Most of the genes identified have not been described previously to be iron-regulated and are important for understanding the molecular and cellular effects of iron depletion.