Iron Reutilization Research Articles

Epigenetic modification of a pectin methylesterase gene activates apoplastic iron reutilization in tomato roots.

Iron (Fe) distribution and reutilization are crucial for maintaining Fe homeostasis in plants. Here, we demonstrate that the tomato (Solanum lycopersicum) Colorless nonripening (Cnr) epimutant exhibits increased Fe retention in cell wall pectin due to an increase in pectin methylesterase (PME) activity. This ultimately leads to Fe deficiency responses even under Fe-sufficient conditions when compared to the wild type (WT). Whole-genome bisulfite sequencing revealed that modifications to cell wall-related genes, especially CG hypermethylation in the intron region of PECTIN METHYLESTERASE53 (SlPME53), are involved in the Cnr response to Fe deficiency. When this intron hypermethylation of SlPME53 was artificially induced in WT, we found that elevated SlPME53 expression was accompanied by increased PME activity and increased pectin-Fe retention. The manipulation of SlPME53, either through overexpression in WT or knockdown in Cnr, influenced levels of pectin methylesterification and accumulation of apoplast Fe in roots. Moreover, CG hypermethylation mediated by METHYLTRANSFERASE1 (SlMET1) increased SlPME53 transcript abundance, resulting in greater PME activity and higher Fe retention in cell wall pectin. Therefore, we conclude that the Cnr mutation epigenetically modulates SlPME53 expression by SlMET1-mediated CG hypermethylation, and thus the capacity of the apoplastic Fe pool, creating opportunities for genetic improvement of crop mineral nutrition.

Melatonin Promotes Iron Reactivation and Reutilization in Peach Plants under Iron Deficiency.

The yellowing of leaves due to iron deficiency is a prevalent issue in peach production. Although the capacity of exogenous melatonin (MT) to promote iron uptake in peach plants has been demonstrated, its underlying mechanism remains ambiguous. This investigation was carried out to further study the effects of exogenous MT on the iron absorption and transport mechanisms of peach (Prunus persica) plants under iron-deficient conditions through transcriptome sequencing. Under both iron-deficient and iron-supplied conditions, MT increased the content of photosynthetic pigments in peach leaves and decreased the concentrations of pectin, hemicellulose, cell wall iron, pectin iron, and hemicellulose iron in peach plants to a certain extent. These effects stemmed from the inhibitory effect of MT on the polygalacturonase (PG), cellulase (Cx), phenylalanine ammonia-lyase (PAL), and cinnamoyl-coenzyme A reductase (CCR) activities, as well as the promotional effect of MT on the cinnamic acid-4-hydroxylase (C4H) activity, facilitating the reactivation of cell wall component iron. Additionally, MT increased the ferric-chelate reductase (FCR) activity and the contents of total and active iron in various organs of peach plants under iron-deficient and iron-supplied conditions. Transcriptome analysis revealed that the differentially expressed genes (DEGs) linked to iron metabolism in MT-treated peach plants were primarily enriched in the aminoacyl-tRNA biosynthesis pathway under iron-deficient conditions. Furthermore, MT influenced the expression levels of these DEGs, regulating cell wall metabolism, lignin metabolism, and iron translocation within peach plants. Overall, the application of exogenous MT promotes the reactivation and reutilization of iron in peach plants.

Inhibition of shoot-expressed NRT1.1 improves reutilization of apoplastic iron under iron-deficient conditions.

Iron deficiency is a major constraint for plant growth in calcareous soils. The interplay between NO3 - and Fe nutrition affects plant performance under Fe-deficient conditions. However, how NO3 - negatively regulates Fe nutrition at the molecular level in plants remains elusive. Here, we showed that the key nitrate transporter NRT1.1 in Arabidopsis plants, especially in the shoots, was markedly downregulated at post-translational levels by Fe deficiency. However, loss of NRT1.1 function alleviated Fe deficiency chlorosis, suggesting that downregulation of NRT1.1 by Fe deficiency favors plant tolerance to Fe deficiency. Further analysis showed that although disruption of NRT1.1 did not alter Fe levels in both the shoots and roots, it improved the reutilization of apoplastic Fe in shoots but not in roots. In addition, disruption of NRT1.1 prevented Fe deficiency-induced apoplastic alkalization in shoots by inhibiting apoplastic H+ depletion via NO3 - uptake. In vitro analysis showed that reduced pH facilitates release of cell wall-bound Fe. Thus, foliar spray with an acidic buffer promoted the reutilization of Fe in the leaf apoplast to enhance plant tolerance to Fe deficiency, while the opposite was true for the foliar spray with a neutral buffer. Thus, downregulation of the shoot-part function of NRT1.1 prevents apoplastic alkalization to ensure the reutilization of apoplastic Fe under Fe-deficient conditions. Our findings may provide a basis for elucidating the link between N and Fe nutrition in plants and insight to scrutinize the relevance of shoot-expressed NRT1.1 to the plant response to stress.

Relationship between Down-Regulation of Copper-Related Genes and Decreased Ferroportin Protein Level in the Duodenum of Iron-Deficient Piglets.

In mammals, 2 × 1012 red blood cells (RBCs) are produced every day in the bone marrow to ensure a constant supply of iron to maintain effective erythropoiesis. Impaired iron absorption in the duodenum and inefficient iron reutilization from senescent RBCs by macrophages contribute to the development of anemia. Ferroportin (Fpn), the only known cellular iron exporter, as well as hephaestin (Heph) and ceruloplasmin, two copper-dependent ferroxidases involved in the above-mentioned processes, are key elements of the interaction between copper and iron metabolisms. Crosslinks between these metals have been known for many years, but metabolic effects of one on the other have not been elucidated to date. Neonatal iron deficiency anemia in piglets provides an interesting model for studying this interplay. In duodenal enterocytes of young anemic piglets, we identified iron deposits and demonstrated increased expression of ferritin with a concomitant decline in both Fpn and Heph expression. We postulated that the underlying mechanism involves changes in copper distribution within enterocytes as a result of decreased expression of the copper transporter—Atp7b. Obtained results strongly suggest that regulation of iron absorption within enterocytes is based on the interaction between proteins of copper and iron metabolisms and outcompetes systemic regulation.

Role of heme oxygenase-1 in human placenta on iron supply to fetus

IntroductionTo date, details on how iron is supplied from the mother to the fetus through the placenta have remained unclear. Recently, increasing evidence has shown that heme oxygenase (HO)-1, which is an inducible isoform of the rate-limiting enzyme in the heme degradation pathway, may be involved in the effective reutilization of iron. In this study, we examined the distribution and gene expression of HO-1 in the villous tissue of human placenta at various periods of pregnancy. MethodsUsing the placenta of 38 samples for which consent was obtained, chronological changes in the localization of HO-1 protein were examined by histological examination. RT-PCR was also performed to examine the expression of HO-1, transferrin receptor-1, and ferroportin 1. Ferric iron in the tissues was analyzed by Prussian blue staining. ResultsImmunohistochemical studies showed that HO-1 protein was exclusively expressed in trophoblastic cells throughout gestation. In the miscarriage placenta in the first trimester, ho-1 mRNA levels were significantly higher than normal. Placenta with fetal death (miscarriage) in the first and second trimester indicate significantly higher ratio of ho-1 gene for iron production to the fpn-1 gene for iron excretion than normal. These suggest that the role of HO-1 with various physiological functions is changing throughout pregnancy. DiscussionThese findings suggest that HO-1 in placenta plays an important role in iron supplying system in the second trimester to support fetal development.

Comprehensive reutilization of iron in iron ore tailings: preparation and characterization of magnetic flocculants.

A large number of iron ore tailings (IOTs) are produced in steel industry, posing threat to the environment during its storage and disposal. To effectively reutilize Fe in IOTs, we propose a comprehensive utilization scheme: (1) most Fe in IOTs is extracted by concentrated hydrochloric acid to form FeCl3 flocculants; (2) after separation from the FeCl3 flocculants, a small amount of Fe is absorbed on the residue solids, which is further washed out to synthesize micron Fe3O4 as magnetic seeds. Results show that the as-synthetic FeCl3 flocculants meet the product standard for FeCl3 flocculants in China (GB/T 4482-2018) after a series of treatments including rotary evaporation, neutralization, and dilution and have comparable performance with commercial polyaluminum chloride (PAC) and polyaluminum ferric chloride (PAFC). Moreover, the addition of synthetic superparamagnetic Fe3O4 (as magnetic seeds) doubled the flocculation rate compared with as-synthetic FeCl3 flocculants alone. Finally, the reutilization of Fe in IOTs can create a direct economic value of ¥ 1.27/kg IOTs, and produce 745 g high-silicon residues for further reutilization, which indicates that our comprehensive utilization scheme is of great application potential.

Co-Treatment of Spent Pot-Lining and Red Mud for Carbon Reutilization and Recovery of Iron, Aluminum and Sodium by Reductive Roasting Process

Spent pot-lining (SPL) and red mud (RM) are the two major solid wastes of the aluminum industry. In this study, an innovative method has been proposed for co-treatment of SPL and RM to reuse carbon and recover metal (iron, aluminum and sodium) by a reductive roasting-leaching-magnetic separation process (RRLMS process). Moreover, the transformation behaviors of fluoride, cyanide and sulfur present in these residues were studied. The effects of parameters such as temperature, CaO/SiO2 molar ratio, addition amount of SPL, Na2O/Al2O3 molar ratio and roasting time on the result of the process were investigated. Under optimum conditions, the recovery extents of Al2O3 and Na2O were 83.12 and 91.80 pct, respectively. The corresponding leaching extent and loss of F upon roasting process were 16.03 and 35.27 pct, respectively, and only 29.02 pct of ST in the roasted product was leached. Furthermore, reduction extent of 78.65 pct and a metallization extent of 62.83 pct for iron minerals were achieved. The SPL-RM mixture after treatment was rendered non-hazardous. Finally, wet magnetic separation at 1.2 A current (magnetic field strength of approximately 130 mT) provided 30.83 wt pct concentrate yield with 59.09 wt pct total iron concentration and iron recovery extent of 65.25 pct from the leached residue.

NH4+ facilitates iron reutilization in the cell walls of rice (Oryza sativa) roots under iron-deficiency conditions

NH4+ and NO3− are two major nitrogen sources that differentially affect the uptake and transfer of other nutrients in rice (Oryza sativa), although their effects on Fe remobilization under Fe-starvation conditions are largely unknown. Here, by investigating the rice cultivar ‘Kasalath’ (Kas), which is tolerant of nutrient-deficient soil, we found that NH4+ negatively regulates the hemicellulose 1 content in root cell walls and stimulates the secretion of phenolic compounds from roots under −Fe conditions, thus facilitating the release of cell wall Fe and increasing soluble Fe levels in roots. NH4+ significantly increased the translocation of Fe from root to shoot by upregulating the expression of OsFRDL1 in roots and increasing the Fe content in the xylem. We further found that the higher putrescine content in rice roots under NH4+ conditions led to a higher nitric oxide (NO) content compared with NO3− conditions, and that NO is involved in the NH4+-stimulated cell wall Fe reutilization. The addition of the NO donor sodium nitroprusside significantly reduced the hemicellulose 1 content in cell walls and increased Fe release from cell walls, ultimately increasing the soluble Fe content in rice and alleviating chlorosis under −Fe conditions. Taken together, our findings demonstrate that NH4+ promotes Fe remobilization from the cell wall in rice.

NaCl alleviates iron deficiency through facilitating root cell wall iron reutilization and its translocation to the shoot in Arabidopsis thaliana

The present study was undertaken to investigate the mechanism underlying NaCl-alleviated Fe (iron) deficiency in Arabidopsis thaliana Col-0 (Columbia ecotype). Six-week-old Col-0 with rosettes of similar diameters was grown in full-strength nutrient solution lacking Fe (Fe-deficient) or full-strength nutrient solution (Fe-sufficient) with or without 10 mM NaCl for 7 days. Roots were then harvested for analysis of total Fe content, soluble Fe concentration, and abscisic acid (ABA) content as well as for cell wall and RNA extraction, while shoots were harvested for total Fe content and soluble Fe concentration measurements. The total Fe content and the soluble Fe concentration were higher in roots and shoots of −Fe + NaCl-treated plants than −Fe-treated plants, whereas Fe retention in the cell wall was reduced, suggesting the presence of a cell wall Fe-reutilization mechanism. This conclusion was confirmed by the observation that less hemicelluloses Fe was found in plants under −Fe + NaCl treatment. In addition, associated to the upregulation of genes related to the long-distance transport of Fe, such as FRD3 (FERRIC REDUCTASE DEFECTIVE3), YSL2 (YELLOW STRIPE-LIKE), and NAS1 (NICOTIANAMINE SYNTHASE1) under −Fe + NaCl treatment, more Fe was available in shoots. Furthermore, endogenous ABA is involved in NaCl-alleviated Fe deficiency, as the addition of Flu (fluridone), an inhibitor of ABA biosynthesis, abolished the positive effect of NaCl on Fe deficiency. Under −Fe condition, NaCl not only is involved in the reutilization of cell wall Fe but also participates in the translocation of Fe from root to shoot in Arabidopsis, partially through its effect on ABA contents.

Effects of GlyT1 inhibition on erythropoiesis and iron homeostasis in rats.

Glycine is a key rate-limiting component of heme biosynthesis in erythropoietic cells, where the high intracellular glycine demand is primarily supplied by the glycine transporter 1 (GlyT1). The impact of intracellular glycine restriction after GlyT1 inhibition on hematopoiesis and iron regulation is not well established. We investigated the effects of a potent and selective inhibitor of GlyT1, bitopertin, on erythropoiesis and iron homeostasis in rats. GlyT1 inhibition significantly affected erythroid heme biosynthesis, manifesting as microcytic hypochromic regenerative anemia with a 20% steady-state reduction in hemoglobin. Reduced erythropoietic iron utilization was characterized by down-regulation of the transferrin receptor 1 (TfR1) on reticulocytes and modest increased iron storage in the spleen. Hepatic hepcidin expression was not affected. However, under the condition of reduced heme biosynthesis with reduced iron reutilization and increased storage iron, hepcidin at the lower and higher range of normal showed a striking role in tissue distribution of iron. Rapid formation of iron-positive inclusion bodies (IBs) was observed in circulating reticulocytes, with an ultrastructure of iron-containing polymorphic mitochondrial remnants. IB or mitochondrial iron accumulation was absent in bone marrow erythroblasts. In conclusion, GlyT1 inhibition in rats induced a steady-state microcytic hypochromic regenerative anemia and a species-specific accumulation of uncommitted mitochondrial iron in reticulocytes. Importantly, this glycine-restricted anemia provides no feedback signal for increased systemic iron acquisition and the effects reported are pathogenetically distinct from systemic iron-overload anemias and erythropoietic disorders such as acquired sideroblastic anemia.

Elevation of NO production increases Fe immobilization in the Fe-deficiency roots apoplast by decreasing pectin methylation of cell wall.

Cell wall is the major component of root apoplast which is the main reservoir for iron in roots, while nitric oxide (NO) is involved in regulating the synthesis of cell wall. However, whether such regulation could influence the reutilization of iron stored in root apoplast remains unclear. In this study, we observed that iron deficiency elevated NO level in tomato (Solanum lycopersicum) roots. However, application of S-nitrosoglutathione, a NO donor, significantly enhanced iron retention in root apoplast of iron-deficient plants, accompanied with a decrease of iron level in xylem sap. Consequently, S-nitrosoglutathione treatment increased iron concentration in roots, but decreased it in shoots. The opposite was true for the NO scavenging treatment with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). Interestingly, S-nitrosoglutathione treatment increased pectin methylesterase activity and decreased degree of pectin methylation in root cell wall of both iron-deficient and iron-sufficient plants, which led to an increased iron retention in pectin fraction, thus increasing the binding capacity of iron to the extracted cell wall. Altogether, these results suggested that iron-deficiency-induced elevation of NO increases iron immobilization in root apoplast by decreasing pectin methylation in cell wall.

Assessmet of Labile Plasma Iron and Hepcidin in Patients Who Undergo Hematopoietic Stem Cell Transplantation

Nontransferrin-bound iron (NTBI) has been reported shortly after myeloablative conditioning in patients undergoing hematopoietic stem cell transplantation (HSCT), and it is assumed that the appearance of unbound iron in this nontransfusion setting possibly reflects a major disturbance in body iron distribution, which is related mainly to its underutilization due to erythropoiesis suppression. There is a concern that labile plasma iron (LPI), the most toxic fraction of NTBI that includes the redox-active forms of iron, can be involved in the occurrence of toxicity and other complications commonly observed in the early post-HSCT period. Recently, we demonstrated that LPI levels, albeit normal at baseline measurements, increased substantially 48 hours after the start of conditioning in HSCT patients and remained increased until engraftment, when it returned to normal levels (Acta Haematol 2014;131:222-226). Here we provide a more detailed analysis of iron status in HSCT patients by adding determinations of hepcidin and standard iron parameters along with LPI in 25 adult patients undergoing first autologous HSCT following myeloablative conditioning. All iron parameters were determined before the start of conditioning (baseline), on day 0 (before stem cells infusion) and upon documented engraftment (Table). The fast and substantial increase in LPI levels on day 0, indeed reflected a disruption of iron homeostasis by conditioning, that was accompanied by a response in hepcidin and TfS levels. However, reutilization of iron by a restored erythropoiesis upon engraftment lead to a substantial drop in LPI, but not in hepcidin levels, possibly due to the fact that production of hepcidin by the liver is not only modulated by iron loading and erythropoietic activity, but also inflammation. Ferritin baseline levels were already increased and did not change throughout the study. Considering all determinations (baseline, day 0 and engraftment), hepcidin levels correlated positively with ferritin (r=0,43; p=0,01; Figure Panel A) and TfS (r=0,37; p=0,02; Figure Panel B); and LPI correlated positively with TfS (r=4,3; p=0,002; Figure Panel C), although increased LPI levels were observed with normal TfS levels in some patients. A tendency of correlation between hepcidin and LPI was found considering only baseline and day 0 levels (r=0,30; p=0,05; Figure Panel D). These results indicate that LPI reflected better the changes in iron status caused by cytotoxic chemotherapy in HSCT patients, and could serve as a target in the eventuality of chelation therapy in the early period of HSCT. The other iron parameters were probably influenced by inflammation, even upon engraftment, and would not behave as appropriate surrogate markers for increased LPI levels.*LPI levels <0.5μM are considered normal.† p<0,05 in relation to baseline levels. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Selective VPS34 inhibitor blocks autophagy and uncovers a role for NCOA4 in ferritin degradation and iron homeostasis in vivo.

Cells rely on autophagy to clear misfolded proteins and damaged organelles to maintain cellular homeostasis. In this study we use the new autophagy inhibitor PIK-III to screen for autophagy substrates. PIK-III is a selective inhibitor of VPS34 that binds a unique hydrophobic pocket not present in related kinases such as PI(3)Kα. PIK-III acutely inhibits autophagy and de novo lipidation of LC3, and leads to the stabilization of autophagy substrates. By performing ubiquitin-affinity proteomics on PIK-III-treated cells we identified substrates including NCOA4, which accumulates in ATG7-deficient cells and co-localizes with autolysosomes. NCOA4 directly binds ferritin heavy chain-1 (FTH1) to target the iron-binding ferritin complex with a relative molecular mass of 450,000 to autolysosomes following starvation or iron depletion. Interestingly, Ncoa4(-/-) mice exhibit a profound accumulation of iron in splenic macrophages, which are critical for the reutilization of iron from engulfed red blood cells. Taken together, the results of this study provide a new mechanism for selective autophagy of ferritin and reveal a previously unappreciated role for autophagy and NCOA4 in the control of iron homeostasis in vivo.

Abscisic acid alleviates iron deficiency by promoting root iron reutilization and transport from root to shoot in Arabidopsis

Abscisic acid (ABA) has been demonstrated to be involved in iron (Fe) homeostasis, but the underlying mechanism is largely unknown. Here, we found that Fe deficiency induced ABA accumulation rapidly (within 6 h) in the roots of Arabidopsis. Exogenous ABA at 0.5 μM decreased the amount of root apoplastic Fe bound to pectin and hemicellulose, and increased the shoot Fe content significantly, thus alleviating Fe deficiency-induced chlorosis. Exogenous ABA promoted the secretion of phenolics to release apoplastic Fe and up-regulated the expression of AtNRAMP3 to enhance reutilization of Fe stored in the vacuoles, leading to a higher level of soluble Fe and lower ferric-chelate reductase (FCR) activity in roots. Treatment with ABA also led to increased Fe concentrations in the xylem sap, partially because of the up-regulation of AtFRD3, AtYSL2 and AtNAS1, genes related to long-distance transport of Fe. Exogenous ABA could not alleviate the chlorosis of abi5 mutant resulting from the significantly low expression of AtYSL2 and low transport of Fe from root to shoot. Taken together, our data support the conclusion that ABA is involved in the reutilization and transport of Fe from root to shoot under Fe deficiency conditions in Arabidopsis.

The regulation of iron metabolism in the mononuclear phagocyte system

The daily iron absorption and loss are small and iron metabolism in human is characterized by a limited external exchange and by an efficient reutilization of iron from internal sources. The mononuclear phagocyte system (MPS) plays a key role in recycling iron from hemoglobin of senescent or damaged erythrocytes, which is important in maintaining iron homeostasis. Many iron-related proteins are expressed in the MPS, including heme oxygenase (HO) for heme degradation, the iron importer transferrin receptor 1 (TfR1) and divalent metal transport 1 (DMT1), the iron exporter ferroportin 1 (FPN1) and the iron regulatory hormone hepcidin. Insights into the regulatory mechanisms that control the regulation of iron metabolism proteins in the MPS will deepen our understanding about the molecular mechanism of iron homeostasis and iron-related diseases.

Sanitary landfill leachate treatment using combined solar photo-Fenton and biological oxidation processes at pre-industrial scale

This work proposes a new strategy for the treatment of leachates from sanitary landfills after lagooning pretreatment, using a solar photo-Fenton oxidation process to eliminate the most recalcitrant organic compounds, leading to a biodegradability enhancement of the leachate and promoting its subsequent oxidation in an activated sludge biological reactor. The integrated leachate treatment process was conducted in a pre-industrial plant, incorporating a photocatalytic system with 39.52m2 of compound parabolic collectors (CPCs) and an activated sludge biological reactor, with 3.5m3 capacity, operated under aerated and anoxic conditions. An extensive physico-chemical characterization of the leachate after lagooning was performed during one year, from June 2010 to May 2011, showing its high recalcitrant character mainly associated with the presence of humic substances.The efficiency of the combined treatment was evaluated concerning the leachate characteristics’ variability after lagooning, availability of solar radiation during the year, and different operational process variables, such as the amount of hydrogen peroxide necessary to reach the required COD target value, biodegradability enhancement during the photo-oxidation process, iron reutilization in consecutive oxidation processes, removal of acidic sludge resulting from the acidification process and leachate temperature/average solar power. The elimination of the remaining organic carbon fraction and nitrogen compounds after the pre-oxidation step was also assessed in an activated sludge biological reactor, under aerobic and anoxic conditions, considering the composition variability of photo-treated leachate. Nitrification and denitrification rates were also evaluated.

Nrf2 regulates ferroportin 1-mediated iron efflux and counteracts lipopolysaccharide-induced ferroportin 1 mRNA suppression in macrophages

Iron is an essential element of hemoglobin, and efficient iron recycling from senescent erythrocytes by splenic macrophages is required for erythrocyte hemoglobin synthesis during erythropoiesis. Ferroportin 1 (Fpn1) is the sole iron exporter in mammals, and it also regulates iron reutilization. In this study, we demonstrated genetically that a redox-sensitive transcription factor, Nrf2, regulates Fpn1 mRNA expression in macrophages. Nrf2 activation by several electrophilic compounds commonly resulted in the upregulation of Fpn1 mRNA in bone marrow-derived and peritoneal macrophages obtained from wild-type mice but not from Nrf2 knockout mice. Further, Nrf2 activation enhanced iron release from the J774.1 murine macrophage cell line. Previous studies showed that inflammatory stimuli, such as LPS, downregulates macrophage Fpn1 by transcriptional and hepcidin-mediated post-translational mechanisms leading to iron sequestration by macrophages. We showed that two Nrf2 activators, diethyl maleate and sulforaphane (SFN; a natural Nrf2 activator found in broccoli), restored the LPS-induced suppression of Fpn1 mRNA in human and mouse macrophages, respectively. Furthermore, SFN counteracted the LPS-induced increase of Hepcidin mRNA by an Nrf2-independent mechanism in mouse peritoneal macrophages. These results demonstrate that Nrf2 regulates iron efflux from macrophages through Fpn1 gene transcription and suggest that Nrf2 may control iron metabolism during inflammation.

Hepcidin Is Produced by Lymphoplasmacytic Cells and Is Associated With Anemia in Waldenström's Macroglobulinemia

Waldenström's macroglobulinemia (WM) patients often present with anemia as their primary disease manifestation that may be related to hepcidin, an important regulator of iron homeostasis. We therefore determined hepcidin levels in 53 WM patients, and 20 age-matched healthy patient donors by hepcidin-25 ELISA. Serum hepcidin levels were elevated in WM patients versus healthy patients (P=.04), and correlated with BM disease involvement (P=.004), beta-2-microglobulin levels (P=.029), and inversely with hemoglobin (P=.05). No correlation with serum iron indices was observed, though in patients with high hepcidin levels, increased iron deposition in bone marrow macrophages was observed. Importantly, hepcidin transcripts and protein were produced by primary WM cells. Hepcidin levels correlated with serum IL-6 (P<.001) and C-Reactive Protein (P=.033) levels. The results of this study implicate hepcidin as a contributor to anemia in WM, and suggest that an iron re-utilization defect accompanies hepcidin overproduction leading to its sequestration in WM patients.

Adiponectin-Mediated Heme Oxygenase-1 Induction Protects Against Iron-Induced Liver Injury via a PPARα-Dependent Mechanism

Protective effects of adiponectin (APN; an adipocytokine) were shown against various oxidative challenges; however, its therapeutic implications and the mechanisms underlying hepatic iron overload remain unclear. Herein, we show that the deleterious effects of iron dextran on liver function and iron deposition were significantly reversed by adiponectin gene therapy, which was accompanied by AMP-activated protein kinase (AMPK) phosphorylation and heme oxygenase (HO)-1 induction. Furthermore, AMPK-mediated peroxisome proliferator-activated receptor-α (PPARα) activation by APN was ascribable to HO-1 induction. Additionally, we revealed direct transcriptional regulation of HO-1 by the binding of PPARα to a PPAR-responsive element (PPRE) by various experimental assessments. Interestingly, overexpression of HO-1 in hepatocytes mimicked the protective effect of APN in attenuating iron-mediated injury, whereas it was abolished by SnPP and small interfering HO-1. Furthermore, bilirubin, the end-product of the HO-1 reaction, but not CO, protected hepatocytes from iron dextran-mediated caspase activation. Herein, we demonstrate a novel functional PPRE in the promoter regions of HO-1, and APN-mediated HO-1 induction elicited an antiapoptotic effect and a decrease in iron deposition in hepatocytes subjected to iron challenge.

Heme and non-heme iron transporters in non-polarized and polarized cells

BackgroundHeme and non-heme iron from diet, and recycled iron from hemoglobin are important products of the synthesis of iron-containing molecules. In excess, iron is potentially toxic because it can produce reactive oxygen species through the Fenton reaction. Humans can absorb, transport, store, and recycle iron without an excretory system to remove excess iron. Two candidate heme transporters and two iron transporters have been reported thus far. Heme incorporated into cells is degraded by heme oxygenases (HOs), and the iron product is reutilized by the body. To specify the processes of heme uptake and degradation, and the reutilization of iron, we determined the subcellular localizations of these transporters and HOs.ResultsIn this study, we analyzed the subcellular localizations of 2 isoenzymes of HOs, 4 isoforms of divalent metal transporter 1 (DMT1), and 2 candidate heme transporters--heme carrier protein 1 (HCP1) and heme responsive gene-1 (HRG-1)--in non-polarized and polarized cells. In non-polarized cells, HCP1, HRG-1, and DMT1A-I are located in the plasma membrane. In polarized cells, they show distinct localizations: HCP1 and DMT1A-I are located in the apical membrane, whereas HRG-1 is located in the basolateral membrane and lysosome. 16Leu at DMT1A-I N-terminal cytosolic domain was found to be crucial for plasma membrane localization. HOs are located in smooth endoplasmic reticulum and colocalize with NADPH-cytochrome P450 reductase.ConclusionsHCP1 and DMT1A-I are localized to the apical membrane, and HRG-1 to the basolateral membrane and lysosome. These findings suggest that HCP1 and DMT1A-I have functions in the uptake of dietary heme and non-heme iron. HRG-1 can transport endocytosed heme from the lysosome into the cytosol. These localization studies support a model in which cytosolic heme can be degraded by HOs, and the resulting iron is exported into tissue fluids via the iron transporter ferroportin 1, which is expressed in the basolateral membrane in enterocytes or in the plasma membrane in macrophages. The liberated iron is transported by transferrin and reutilized for hemoglobin synthesis in the erythroid system.