IκBε deficiency accelerates disease development in chronic lymphocytic leukemia.

The NFKBIE gene, which encodes the NF-κB inhibitor IκBε, is mutated in 3-7% of patients with chronic lymphocytic leukemia (CLL). The most recurrent alteration is a 4-bp frameshift deletion associated with NF-κB activation in leukemic B cells and poor clinical outcome. To study the functional consequences of NFKBIE gene inactivation, both in vitro and in vivo, we engineered CLL B cells and CLL-prone mice to stably down-regulate NFKBIE expression and investigated its role in controlling NF-κB activity and disease expansion. We found that IκBε loss leads to NF-κB pathway activation and promotes both migration and proliferation of CLL cells in a dose-dependent manner. Importantly, NFKBIE inactivation was sufficient to induce a more rapid expansion of the CLL clone in lymphoid organs and contributed to the development of an aggressive disease with a shortened survival in both xenografts and genetically modified mice. IκBε deficiency was associated with an alteration of the MAPK pathway, also confirmed by RNA-sequencing in NFKBIE-mutated patient samples, and resistance to the BTK inhibitor ibrutinib. In summary, our work underscores the multimodal relevance of the NF-κB pathway in CLL and paves the way to translate these findings into novel therapeutic options.

Bone marrow Tfr2 deletion improves the therapeutic efficacy of the activin-receptor ligand trap RAP-536 in ß-thalassemic mice.

ß-thalassemia is a disorder characterized by anemia, ineffective erythropoiesis (IE), and iron overload, whose treatment still requires improvement. The activin receptor-ligand trap Luspatercept, a novel therapeutic option for ß-thalassemia, stimulates erythroid differentiation inhibiting the transforming growth factor ß pathway. However, its exact mechanism of action and the possible connection with erythropoietin (Epo), the erythropoiesis governing cytokine, remain to be clarified. Moreover, Luspatercept does not correct all the features of the disease, calling for the identification of strategies that enhance its efficacy. Transferrin receptor 2 (TFR2) regulates systemic iron homeostasis in the liver and modulates the response to Epo of erythroid cells, thus balancing red blood cells production with iron availability. Stimulating Epo signaling, hematopoietic Tfr2 deletion ameliorates anemia and IE in Hbbth3/+ thalassemic mice. To investigate whether hematopoietic Tfr2 inactivation improves the efficacy of Luspatercept, we treated Hbbth3/+ mice with or without hematopoietic Tfr2 (Tfr2BMKO/Hbbth3/+) with RAP-536, the murine analog of Luspatercept. As expected, both hematopoietic Tfr2 deletion and RAP-536 significantly ameliorate IE and anemia, and the combined approach has an additive effect. Since RAP-536 has comparable efficacy in both Hbbth3/+ and Tfr2BMKO/Hbbth3/+ animals, we propose that the drug promotes erythroid differentiation independently of TFR2 and EPO stimulation. Notably, the lack of Tfr2, but not RAP-536, can also attenuate iron-overload and related complications. Overall, our results shed further light on the mechanism of action of Luspatercept and suggest that strategies aimed at inhibiting hematopoietic TFR2 might improve the therapeutic efficacy of activin receptor-ligand traps.

Iron Induces Cell Death and Strengthens the Efficacy of Antiandrogen Therapy in Prostate Cancer Models.

PURPOSE: In search of novel strategies to improve the outcome of advanced prostate cancer, we considered that prostate cancer cells rearrange iron homeostasis, favoring iron uptake and proliferation. We exploited this adaptation by exposing prostate cancer preclinical models to high-dose iron to induce toxicity and disrupt adaptation to androgen starvation. EXPERIMENTAL DESIGN: We analyzed markers of cell viability and mechanisms underlying iron toxicity in androgen receptor-positive VCaP and LNCaP, castration-resistant DU-145 and PC-3, and murine TRAMP-C2 cells treated with iron and/or the antiandrogen bicalutamide. We validated the results in vivo in VCaP and PC-3 xenografts and in TRAMP-C2 injected mice treated with iron and/or bicalutamide. RESULTS: Iron was toxic for all prostate cancer cells. In particular, VCaP, LNCaP, and TRAMP-C2 were highly iron sensitive. Toxicity was mediated by oxidative stress, which primarily affected lipids, promoting ferroptosis. In highly sensitive cells, iron additionally caused protein damage. High-basal iron content and oxidative status defined high iron sensitivity. Bicalutamide-iron combination exacerbated oxidative damage and cell death, triggering protein oxidation also in poorly iron-sensitive DU-145 and PC-3 cells.In vivo, iron reduced tumor growth in TRAMP-C2 and VCaP mice. In PC-3 xenografts, bicalutamide-iron combination caused protein oxidation and successfully impaired tumor expansion while single compounds were ineffective. Macrophages influenced body iron distribution but did not limit the iron effect on tumor expansion. CONCLUSIONS: Our models allow us to dissect the direct iron effect on cancer cells. We demonstrate the proof of principle that iron toxicity inhibits prostate cancer cell proliferation, proposing a novel tool to strengthen antiandrogen treatment efficacy.

Iron Causes Lipid Oxidation and Inhibits Proteasome Function in Multiple Myeloma Cells: A Proof of Concept for Novel Combination Therapies.

Adaptation to import iron for proliferation makes cancer cells potentially sensitive to iron toxicity. Iron loading impairs multiple myeloma (MM) cell proliferation and increases the efficacy of the proteasome inhibitor bortezomib. Here, we defined the mechanisms of iron toxicity in MM.1S, U266, H929, and OPM-2 MM cell lines, and validated this strategy in preclinical studies using Vk*MYC mice as MM model. High-dose ferric ammonium citrate triggered cell death in all cell lines tested, increasing malondialdehyde levels, the by-product of lipid peroxidation and index of ferroptosis. In addition, iron exposure caused dose-dependent accumulation of polyubiquitinated proteins in highly iron-sensitive MM.1S and H929 cells, suggesting that proteasome workload contributes to iron sensitivity. Accordingly, high iron concentrations inhibited the proteasomal chymotrypsin-like activity of 26S particles and of MM cellular extracts in vitro. In all MM cells, bortezomib-iron combination induced persistent lipid damage, exacerbated bortezomib-induced polyubiquitinated proteins accumulation, and triggered cell death more efficiently than individual treatments. In Vk*MYC mice, addition of iron dextran or ferric carboxymaltose to the bortezomib-melphalan-prednisone (VMP) regimen increased the therapeutic response and prolonged remission without causing evident toxicity. We conclude that iron loading interferes both with redox and protein homeostasis, a property that can be exploited to design novel combination strategies including iron supplementation, to increase the efficacy of current MM therapies.

Limiting hepatic Bmp-Smad signaling by matriptase-2 is required for erythropoietin-mediated hepcidin suppression in mice.

Hepcidin, the main regulator of iron homeostasis, is repressed when erythropoiesis is acutely stimulated by erythropoietin (EPO) to favor iron supply to maturing erythroblasts. Erythroferrone (ERFE) has been identified as the erythroid regulator that inhibits hepcidin in stress erythropoiesis. A powerful hepcidin inhibitor is the serine protease matriptase-2, encoded by TMPRSS6, whose mutations cause iron refractory iron deficiency anemia. Because this condition has inappropriately elevated hepcidin in the presence of high EPO levels, a role is suggested for matriptase-2 in EPO-mediated hepcidin repression. To investigate the relationship between EPO/ERFE and matriptase-2, we show that EPO injection induces Erfe messenger RNA expression but does not suppress hepcidin in Tmprss6 knockout (KO) mice. Similarly, wild-type (WT) animals, in which the bone morphogenetic protein-mothers against decapentaplegic homolog (Bmp-Smad) pathway is upregulated by iron treatment, fail to suppress hepcidin in response to EPO. To further investigate whether the high level of Bmp-Smad signaling of Tmprss6 KO mice counteracts hepcidin suppression by EPO, we generated double KO Bmp6-Tmprss6 KO mice. Despite having Bmp-Smad signaling and hepcidin levels that are similar to WT mice under basal conditions, double KO mice do not suppress hepcidin in response to EPO. However, pharmacologic downstream inhibition of the Bmp-Smad pathway by dorsomorphin, which targets the BMP receptors, improves the hepcidin responsiveness to EPO in Tmprss6 KO mice. We concluded that the function of matriptase-2 is dominant over that of ERFE and is essential in facilitating hepcidin suppression by attenuating the BMP-SMAD signaling.

Bmp6 expression in murine liver non parenchymal cells: a mechanism to control their high iron exporter activity and protect hepatocytes from iron overload?

Bmp6 is the main activator of hepcidin, the liver hormone that negatively regulates plasma iron influx by degrading the sole iron exporter ferroportin in enterocytes and macrophages. Bmp6 expression is modulated by iron but the molecular mechanisms are unknown. Although hepcidin is expressed almost exclusively by hepatocytes (HCs), Bmp6 is produced also by non-parenchymal cells (NPCs), mainly sinusoidal endothelial cells (LSECs). To investigate the regulation of Bmp6 in HCs and NPCs, liver cells were isolated from adult wild type mice whose diet was modified in iron content in acute or chronic manner and in disease models of iron deficiency (Tmprss6 KO mouse) and overload (Hjv KO mouse). With manipulation of dietary iron in wild-type mice, Bmp6 and Tfr1 expression in both HCs and NPCs was inversely related, as expected. When hepcidin expression is abnormal in murine models of iron overload (Hjv KO mice) and deficiency (Tmprss6 KO mice), Bmp6 expression in NPCs was not related to Tfr1. Despite the low Bmp6 in NPCs from Tmprss6 KO mice, Tfr1 mRNA was also low. Conversely, despite body iron overload and high expression of Bmp6 in NPCs from Hjv KO mice, Tfr1 mRNA and protein were increased. However, in the same cells ferritin L was only slightly increased, but the iron content was not, suggesting that Bmp6 in these cells reflects the high intracellular iron import and export. We propose that NPCs, sensing the iron flux, not only increase hepcidin through Bmp6 with a paracrine mechanism to control systemic iron homeostasis but, controlling hepcidin, they regulate their own ferroportin, inducing iron retention or release and further modulating Bmp6 production in an autocrine manner. This mechanism, that contributes to protect HC from iron loading or deficiency, is lost in disease models of hepcidin production.

Erythroblast apoptosis and microenvironmental iron restriction trigger anemia in the VK*MYC model of multiple myeloma.

Multiple myeloma is a malignant disorder characterized by bone marrow proliferation of plasma cells and by overproduction of monoclonal immunoglobulin detectable in the sera (M-spike). Anemia is a common complication of multiple myeloma, but the underlying pathophysiological mechanisms have not been completely elucidated. We aimed to identify the different determinants of anemia using the Vk*MYC mouse, which spontaneously develops an indolent bone marrow localized disease with aging. Affected Vk*MYC mice develop a mild normochromic normocytic anemia. We excluded the possibility that anemia results from defective erythropoietin production, inflammation or increased hepcidin expression. Mature erythroid precursors are reduced in Vk*MYC bone marrow compared with wild-type. Malignant plasma cells express the apoptogenic receptor Fas ligand and, accordingly, active caspase 8 is detected in maturing erythroblasts. Systemic iron homeostasis is not compromised in Vk*MYC animals, but high expression of the iron importer CD71 by bone marrow plasma cells and iron accumulation in bone marrow macrophages suggest that iron competition takes place in the local multiple myeloma microenvironment, which might contribute to anemia. In conclusion, the mild anemia of the Vk*MYC model is mainly related to the local effect of the bone marrow malignant clone in the absence of an overt inflammatory status. We suggest that this reproduces the initial events triggering anemia in patients.

Identification of TMPRSS6 cleavage sites of hemojuvelin.

Hemojuvelin (HJV), the coreceptor of the BMP-SMAD pathway that up-regulates hepcidin transcription, is a repulsive guidance molecule (RGMc) which undergoes a complex intracellular processing. Following autoproteolysis, it is exported to the cell surface both as a full-length and a heterodimeric protein. In vitro membrane HJV (m-HJV) is cleaved by the transmembrane serine protease TMPRSS6 to attenuate signalling and to inhibit hepcidin expression. In this study, we investigated the number and position of HJV cleavage sites by mutagenizing arginine residues (R), potential TMPRSS6 targets, to alanine (A). We analysed translation and membrane expression of HJV R mutants and the pattern of fragments they release in the culture media in the presence of TMPRSS6. Abnormal fragments were observed for mutants at arginine 121, 176, 218, 288 and 326. Considering that all variants, except HJV(R121A) , lack autoproteolytic activity and some (HJV(R176A) and HJV(R288A) ) are expressed at reduced levels on cell surface, we identified the fragments originating from either full-length or heterodimeric proteins and defined the residues 121 and 326 as the TMPRSS6 cleavage sites in both isoforms. Using the N-terminal FLAG-tagged HJV, we showed that residue 121 is critical also in the rearrangement of the N-terminal heterodimeric HJV. Exploiting the recently reported RGMb crystallographic structure, we generated a model of HJV that was used as input structure for all-atoms molecular dynamics simulation in explicit solvent. As assessed by in silico studies, we concluded that some arginines in the von Willebrand domain appear TMPRSS6 insensitive, likely because of partial protein structure destabilization.

Iron uptake in quiescent and inflammation-activated astrocytes: a potentially neuroprotective control of iron burden.

Astrocytes play a crucial role in proper iron handling within the central nervous system. This competence can be fundamental, particularly during neuroinflammation, and neurodegenerative processes, where an increase in iron content can favor oxidative stress, thereby worsening disease progression. Under these pathological conditions, astrocytes undergo a process of activation that confers them either a beneficial or a detrimental role on neuronal survival. Our work investigates the mechanisms of iron entry in cultures of quiescent and activated hippocampal astrocytes. Our data confirm that the main source of iron is the non-transferrin-bound iron (NTBI) and show the involvement of two different routes for its entry: the resident transient receptor potential (TRP) channels in quiescent astrocytes and the de novo expressed divalent metal transporter 1 (DMT1) in activated astrocytes, which accounts for a potentiation of iron entry. Overall, our data suggest that at rest, but even more after activation, astrocytes have the potential to buffer the excess of iron, thereby protecting neurons from iron overload. These findings further extend our understanding of the protective role of astrocytes under the conditions of iron-mediated oxidative stress observed in several neurodegenerative conditions.

Iron increases the susceptibility of multiple myeloma cells to bortezomib.

Multiple myeloma is a malignant still incurable plasma cell disorder. Pharmacological treatment based on proteasome inhibition has improved patient outcome; however, bortezomib-resistance remains a major clinical problem. Inhibition of proteasome functionality affects cellular iron homeostasis and iron is a potent inducer of reactive oxygen species and cell death, unless safely stored in ferritin. We explored the potential role of iron in bortezomib-resistance. We analyzed iron proteins, oxidative status and cell viability in 7 multiple myeloma cell lines and in plasma cells from 5 patients. Cells were treated with increasing bortezomib concentrations with or without iron supplementation. We reduced ferritin levels by both shRNA technology and by drug-induced iron starvation. Multiple myeloma cell lines are characterized by distinct ferritin levels, which directly correlate with bortezomib resistance. We observed that iron supplementation upon bortezomib promotes protein oxidation and cell death, and that iron toxicity inversely correlates with basal ferritin levels. Bortezomib prevents ferritin upregulation in response to iron, thus limiting the ability to buffer reactive oxygen species. Consequently, reduction of basal ferritin levels increases both bortezomib sensitivity and iron toxicity. In patients' cells, we confirmed that bortezomib prevents ferritin increase, that iron supplementation upon bortezomib increases cell death and that ferritin reduction overcomes bortezomib resistance. Bortezomib affects iron homeostasis, sensitizing cells to oxidative damage. Modulation of iron status is a strategy worth exploring to improve the efficacy of proteasome inhibition therapies.

Skin fibroblasts from pantothenate kinase-associated neurodegeneration patients show altered cellular oxidative status and have defective iron-handling properties.

Pantothenate kinase-associated neurodegeneration (PKAN) is a neurodegenerative disease belonging to the group of neurodegeneration with brain iron accumulation disorders. It is characterized by progressive impairments in movement, speech and cognition. The disease is inherited in a recessive manner due to mutations in the Pantothenate Kinase-2 (PANK2) gene that encodes a mitochondrial protein involved in Coenzyme A synthesis. To investigate the link between a PANK2 gene defect and iron accumulation, we analyzed primary skin fibroblasts from three PKAN patients and three unaffected subjects. The oxidative status of the cells and their ability to respond to iron were analyzed in both basal and iron supplementation conditions. In basal conditions, PKAN fibroblasts show an increase in carbonylated proteins and altered expression of antioxidant enzymes with respect to the controls. After iron supplementation, the PKAN fibroblasts had a defective response to the additional iron. Under these conditions, ferritins were up-regulated and Transferrin Receptor 1 (TfR1) was down-regulated to a minor extent in patients compared with the controls. Analysis of iron regulatory proteins (IRPs) reveals that, with respect to the controls, PKAN fibroblasts have a reduced amount of membrane-associated mRNA-bound IRP1, which responds imperfectly to iron. This accounts for the defective expression of ferritin and TfR1 in patients' cells. The inaccurate quantity of these proteins produced a higher bioactive labile iron pool and consequently increased iron-dependent reactive oxygen species formation. Our results suggest that Pank2 deficiency promotes an increased oxidative status that is further enhanced by the addition of iron, potentially causing damage in cells.

Ceruloplasmin oxidation, a feature of Parkinson's disease CSF, inhibits ferroxidase activity and promotes cellular iron retention.

Parkinson's disease is a neurodegenerative disorder characterized by oxidative stress and CNS iron deposition. Ceruloplasmin is an extracellular ferroxidase that regulates cellular iron loading and export, and hence protects tissues from oxidative damage. Using two-dimensional electrophoresis, we investigated ceruloplasmin patterns in the CSF of human Parkinson's disease patients. Parkinson's disease ceruloplasmin profiles proved more acidic than those found in healthy controls and in other human neurological diseases (peripheral neuropathies, amyotrophic lateral sclerosis, and Alzheimer's disease); degrees of acidity correlated with patients' pathological grading. Applying an unsupervised pattern recognition procedure to the two-dimensional electrophoresis images, we identified representative pathological clusters. In vitro oxidation of CSF in two-dimensional electrophoresis generated a ceruloplasmin shift resembling that observed in Parkinson's disease and co-occurred with an increase in protein carbonylation. Likewise, increased protein carbonylation was observed in Parkinson's disease CSF, and the same modification was directly identified in these samples on ceruloplasmin. These results indicate that ceruloplasmin oxidation contributes to pattern modification in Parkinson's disease. From the functional point of view, ceruloplasmin oxidation caused a decrease in ferroxidase activity, which in turn promotes intracellular iron retention in neuronal cell lines as well as in primary neurons, which are more sensitive to iron accumulation. Accordingly, the presence of oxidized ceruloplasmin in Parkinson's disease CSF might be used as a marker for oxidative damage and might provide new insights into the underlying pathological mechanisms.

Over-expression of mitochondrial ferritin affects the JAK2/STAT5 pathway in K562 cells and causes mitochondrial iron accumulation.

BACKGROUND: Mitochondrial ferritin is a nuclear encoded iron-storage protein localized in mitochondria. It has anti-oxidant properties related to its ferroxidase activity, and it is able to sequester iron avidly into the organelle. The protein has a tissue-specific pattern of expression and is also highly expressed in sideroblasts of patients affected by hereditary sideroblastic anemia and by refractory anemia with ringed sideroblasts. The present study examined whether mitochondrial ferritin has a role in the pathogenesis of these diseases. DESIGN AND METHODS: We analyzed the effect of mitochondrial ferritin over-expression on the JAK2/STAT5 pathway, on iron metabolism and on heme synthesis in erythroleukemic cell lines. Furthermore its effect on apoptosis was evaluated on human erythroid progenitors. RESULTS: Data revealed that a high level of mitochondrial ferritin reduced reactive oxygen species and Stat5 phosphorylation while promoting mitochondrial iron loading and cytosolic iron starvation. The decline of Stat5 phosphorylation induced a decrease of the level of anti-apoptotic Bcl-xL transcript compared to that in control cells; however, transferrin receptor 1 transcript increased due to the activation of the iron responsive element/iron regulatory protein machinery. Also, high expression of mitochondrial ferritin increased apoptosis, limited heme synthesis and promoted the formation of Perls-positive granules, identified by electron microscopy as iron granules in mitochondria. CONCLUSIONS: Our results provide evidence suggesting that Stat5-dependent transcriptional regulation is displaced by strong cytosolic iron starvation status induced by mitochondrial ferritin. The protein interferes with JAK2/STAT5 pathways and with the mechanism of mitochondrial iron accumulation.

Polarization dictates iron handling by inflammatory and alternatively activated macrophages.

BACKGROUND: Macrophages play a key role in iron homeostasis. In peripheral tissues, they are known to polarize into classically activated (or M1) macrophages and alternatively activated (or M2) macrophages. Little is known on whether the polarization program influences the ability of macrophages to store or recycle iron and the molecular machinery involved in the processes. DESIGN AND METHODS: Inflammatory/M1 and alternatively activated/M2 macrophages were propagated in vitro from mouse bone-marrow precursors and polarized in the presence of recombinant interferon-γ or interleukin-4. We characterized and compared their ability to handle radioactive iron, the characteristics of the intracellular iron pools and the expression of molecules involved in internalization, storage and export of the metal. Moreover we verified the influence of iron on the relative ability of polarized macrophages to activate antigen-specific T cells. RESULTS: M1 macrophages have low iron regulatory protein 1 and 2 binding activity, express high levels of ferritin H, low levels of transferrin receptor 1 and internalize--albeit with low efficiency -iron only when its extracellular concentration is high. In contrast, M2 macrophages have high iron regulatory protein binding activity, express low levels of ferritin H and high levels of transferrin receptor 1. M2 macrophages have a larger intracellular labile iron pool, effectively take up and spontaneously release iron at low concentrations and have limited storage ability. Iron export correlates with the expression of ferroportin, which is higher in M2 macrophages. M1 and M2 cells activate antigen-specific, MHC class II-restricted T cells. In the absence of the metal, only M1 macrophages are effective. CONCLUSIONS: Cytokines that drive macrophage polarization ultimately control iron handling, leading to the differentiation of macrophages into a subset which has a relatively sealed intracellular iron content (M1) or into a subset endowed with the ability to recycle the metal (M2).

Pantothenate kinase-2 (Pank2) silencing causes cell growth reduction, cell-specific ferroportin upregulation and iron deregulation.

Pantothenate kinase 2 (Pank2) is a mitochondrial enzyme that catalyses the first regulatory step of Coenzyme A synthesis and that is responsible for a genetic movement disorder named Pank-associated neurodegeneration (PKAN). This is characterized by abnormal iron accumulation in the brain, particularly in the globus pallidus. We downregulated Pank2 in some cell lines by using specific siRNAs to study its effect on iron homeostasis. In HeLa cells this caused a reduction of cell proliferation and of aconitase activity, signs of cytosolic iron deficiency without mitochondrial iron deposition, and a 12-fold induction of ferroportin mRNA. Pank2 silencing caused a strong induction of ferroportin mRNA also in hepatoma HepG2, a modest one in neuroblastoma SH-SY5Y and none in glioma U373 cells. A reduction of cell growth was observed in all these cell types. The strong Pank2-mediated alteration of ferroportin expression in some cell types might alter iron transfer to the brain and be connected with brain iron accumulation.

Oxidative stress and cell death in cells expressing L-ferritin variants causing neuroferritinopathy.

Neuroferritinopathies are dominantly inherited movement disorders associated with nucleotide insertions in the L-ferritin gene that modify the protein's C-terminus. The insertions alter physical and functional properties of the ferritins, causing an imbalance in brain iron homeostasis. We describe the effects produced by the over-expression in HeLa and neuroblastoma SH-SY5Y cells of two pathogenic L-ferritin variants, 460InsA and 498InsTC. Both peptides co-assembled with endogenous ferritins, producing molecules with reduced iron incorporation capacity, acting in a dominant negative manner. The cells showed an increase in cell death and a decrease in proteasomal activity. The formation of iron-ferritin aggregates became evident after 10 days of variant expression and was not associated with increased cell death. The addition of iron chelators or antioxidants restored proteasomal activity and reduced aggregate formation. The data indicate that cellular iron imbalance and oxidative damage are primary causes of cell death, while aggregate formation is a secondary effect.

Mitochondrial ferritin limits oxidative damage regulating mitochondrial iron availability: hypothesis for a protective role in Friedreich ataxia.

Mitochondrial ferritin (FtMt) is a nuclear-encoded iron-sequestering protein that specifically localizes in mitochondria. In mice it is highly expressed in cells characterized by high-energy consumption, while is undetectable in iron storage tissues like liver and spleen. FtMt expression in mammalian cells was shown to cause a shift of iron from cytosol to mitochondria, and in yeast it rescued the defects associated with frataxin deficiency. To study the role of FtMt in oxidative damage, we analyzed the effect of its expression in HeLa cells after incubation with H(2)O(2) and Antimycin A, and after a long-term growth in glucose-free media that enhances mitochondrial respiratory activity. FtMt reduced the level of reactive oxygen species (ROS), increased the level of adenosine 5'triphosphate and the activity of mitochondrial Fe-S enzymes, and had a positive effect on cell viability. Furthermore, FtMt expression reduces the size of cytosolic and mitochondrial labile iron pools. In cells grown in glucose-free media, FtMt level was reduced owing to faster degradation rate, however it still protected the activity of mitochondrial Fe-S enzymes without affecting the cytosolic iron status. In addition, FtMt expression in fibroblasts from Friedreich ataxia (FRDA) patients prevented the formation of ROS and partially rescued the impaired activity of mitochondrial Fe-S enzymes, caused by frataxin deficiency. These results indicate that the primary function of FtMt involves the control of ROS formation through the regulation of mitochondrial iron availability. They are consistent with the expression pattern of FtMt observed in mouse tissues, suggesting a FtMt protective role in cells characterized by defective iron homeostasis and respiration, such as in FRDA.

The human counterpart of zebrafish shiraz shows sideroblastic-like microcytic anemia and iron overload.

Inherited microcytic-hypochromic anemias in rodents and zebrafish suggest the existence of corresponding human disorders. The zebrafish mutant shiraz has severe anemia and is embryonically lethal because of glutaredoxin 5 (GRLX5) deletion, insufficient biogenesis of mitochondrial iron-sulfur (Fe/S) clusters, and deregulated iron-regulatory protein 1 (IRP1) activity. This leads to stabilization of transferrin receptor 1 (TfR) RNA, repression of ferritin, and ALA-synthase 2 (ALAS2) translation with impaired heme synthesis. We report the first case of GLRX5 deficiency in a middle-aged anemic male with iron overload and a low number of ringed sideroblasts. Anemia was worsened by blood transfusions but partially reversed by iron chelation. The patient had a homozygous (c.294A>G) mutation that interferes with intron 1 splicing and drastically reduces GLRX5 RNA. As in shiraz, aconitase and H-ferritin levels were low and TfR level was high in the patient's cells, compatible with increased IRP1 binding. Based on the biochemical and clinical phenotype, we hypothesize that IRP2, less degraded by low heme, contributes to the repression of the erythroblasts ferritin and ALAS2, increasing mitochondrial iron. Iron chelation, redistributing iron to the cytosol, might relieve IRP2 excess, improving heme synthesis and anemia. GLRX5 function is highly conserved, but at variance with zebrafish, its defect in humans leads to anemia and iron overload.

Characterization of the l-ferritin variant 460InsA responsible of a hereditary ferritinopathy disorder.

Hereditary ferritinopathies are dominant inherited movement disorders associated with extensive alterations of the l-ferritin C-terminus peptide caused by nucleotide insertions in l-ferritin gene (FTL). We describe the characterization of the most common variant, produced by the 460InsA mutations and here named Ln1. The recombinant Ln1 assembled into 24-mer ferritin shells with low efficiency, however, it was able to form heteropolymers that showed a reduced capacity to incorporate iron in vitro. The Ln1 expressed in HeLa cells formed hybrid ferritins, with the endogenous H and L chains, and caused an iron excess phenotype. Ferritin inactivation and faster degradation in Ln1 transfectants concurred in increasing iron availability, which was probably responsible for the higher sensitivity to H(2)O(2) toxicity and higher level of oxidized proteins. The findings suggest that the pathogenic effects of Ln1 expression are more likely due to deregulation of cellular iron homeostasis rather than to protein conformational problems.

Iron regulatory proteins 1 and 2 in human monocytes, macrophages and duodenum: expression and regulation in hereditary hemochromatosis and iron deficiency.

BACKGROUND AND OBJECTIVES: The functions of the iron regulatory proteins (IRP1 and IRP2), which control cellular iron homeostasis are similar but not identical. As an inappropriate up-regulation of total IRP activity has been found in the duodenum and monocytes of patients with hereditary hemochromatosis (HH), we investigated the respective roles of IRP1 and IRP2 in these settings. DESIGN AND METHODS: Specific antibodies were used in RNA-supershift, immunoblotting and immunohistochemistry assays to evaluate IRP1 and IRP2 separately in monocytes, macrophages and duodenum of control subjects, and patients with HH or iron-deficiency anemia. RESULTS: The activity of both IRP1 and IRP2 and the levels of IRP2 were: (i) higher in monocytes and macrophages of HH patients than in those of control subjects; (ii) increased in the duodenal samples of the patients with HH and iron-deficiency anemia. IRP2 levels increased when monocytes differentiated to macrophages. Under all of the examined conditions, IRP2 was induced to a greater extent. In the duodenum of HH and anemic patients, IRP1 was shifted from the aconitase form (present in controls) to the apoform, whereas the IRP1 in monocytes/macrophages was always in the apoform, in both the patients and controls. The RNA-bound fraction of IRP1 was small in all of the samples. Both IRP were expressed more in the villi than in the crypts of the duodenum, with no differences in localization or expression between the patients and controls. INTERPRETATION AND CONCLUSIONS: These findings of the first extensive investigation of the comparative expression of the two IRP in human tissues and blood cells indicate that IRP2 is the major regulator of intracellular iron homeostasis in humans.