Divalent Metal Transporter 1 Expression Research Articles

The effect of lead exposure on brain iron homeostasis and the expression of DMT1/FP1 in the brain in developing and aged rats

The relation between lead (Pb) and iron (Fe) becomes increasingly concerned because they are both divalent metals that are absorbed by the same intestinal mechanism, and Pb exposure and Fe deficiency in the developmental brain, as well as Fe overload in the aged brain, can cause cognitive deficits. However, the interaction between Pb exposure and Fe status in the brain has not been established. Therefore, in the current study, we examined the effects of maternal ingestion of Pb in drinking water during gestation and lactation on the Fe status and the expression of divalent metal transporter 1 (DMT1) and ferroportin 1 (FP1) in the brain of offspring. The offspring were followed through old age, with measurements taken at postnatal week 3 (PNW3), 41 (PNW41) and 70 (PNW70). Pb exposure increases the Fe content in the old-aged rats’ brain, which might be not subjected to DMT1 mediating, but may be associated with the decrease expression of FP1. Furthermore, the effect of Pb on FP1 expression is regulated at transcriptional and posttranscriptional levels. The perturbation in Fe homeostasis may contribute to the neurotoxicology consequences induced by Pb exposure, and FP1 may play a role in Pb-induced Fe cumulation in the brain.

Divalent Metal Transporter 1 Regulates Iron-Mediated ROS and Pancreatic β Cell Fate in Response to Cytokines

Reactive oxygen species (ROS) contribute to target-cell damage in inflammatory and iron-overload diseases. Little is known about iron transport regulation during inflammatory attack. Through a combination of invitro and invivo studies, we show that the proinflammatory cytokine IL-1β induces divalent metal transporter 1 (DMT1) expression correlating with increased β cell iron content and ROS production. Iron chelation and siRNA and genetic knockdown of DMT1 expression reduce cytokine-induced ROS formation and cell death. Glucose-stimulated insulin secretion in the absence of cytokines in Dmt1 knockout islets is defective, highlighting a physiological role of iron and ROS in the regulation of insulin secretion. Dmt1 knockout mice are protected against multiple low-dose streptozotocin and high-fat diet-induced glucose intolerance, models of type1 and type 2 diabetes, respectively. Thus, β cells become prone to ROS-mediated inflammatory damage via aberrant cellular iron metabolism,a finding with potential general cellular implications.

AVIAN IRON STORAGE DISEASE: VARIATIONS ON A COMMON THEME?

Many frugivorous avian species kept in captivity develop iron storage disease (ISD) as indicated by high concentrations of hepatic iron and hemosiderin deposits in hepatocytes or phagocytes. In several susceptible species fed diets containing moderate levels of iron, ISD develops because of an inability to match rates of iron absorption to tissue needs. Evidence suggests that the pathophysiologic basis of excess iron absorption is due to high levels of expression of divalent metal transporter-1 that transports iron into enterocytes in the proximal intestine, and ferroportin that exports iron to the circulation. The regulatory basis for this inability to sufficiently down-regulate iron absorption is unknown, but disruptions in the hepcidin-ferroportin axis are likely candidates based on recent research in humans and laboratory rodents. It is likely that ISD-susceptible avian species evolved on foods that were very low in bioavailable iron, so there was strong selection pressure for the efficient capture of the small amount of dietary iron but low selection pressure for preventing iron toxicities. Thus, the transporters and regulatory networks for iron absorption seem to be heavily skewed toward iron storage even when food items that are high in iron are consumed. Infections, trauma and neoplasias that trigger an acute phase response may exacerbate ISD in susceptible species and may be the primary cause in species that are normally resistant to ISD (i.e., those that are normally able to shut down intestinal iron absorption when iron stores are replete). The evolutionary basis that resulted in some avian species to be susceptible to ISD (e.g., dietary cause) seems to differ from many inherited ISD disorders in humans that are thought to have evolved to bolster protection against infectious diseases. However the evolutionary basis of ISD in other mammalian species might be more similar to that in ISD-susceptible avian species.

Late-onset Parkinsonism in NF B/c-Rel-deficient mice

Activation of the nuclear factor κB/c-Rel can increase neuronal resilience to pathological noxae by regulating the expression of pro-survival manganese superoxide dismutase (MnSOD, now known as SOD2) and Bcl-xL genes. We show here that c-Rel-deficient (c-rel−/−) mice developed a Parkinson’s disease-like neuropathology with ageing. At 18 months of age, c-rel−/− mice exhibited a significant loss of dopaminergic neurons in the substantia nigra pars compacta, as assessed by tyrosine hydroxylase-immunoreactivity and Nissl staining. Nigral degeneration was accompanied by a significant loss of dopaminergic terminals and a significant reduction of dopamine and homovanillic acid levels in the striatum. Mice deficient of the c-Rel factor exhibited a marked immunoreactivity for fibrillary α-synuclein in the substantia nigra pars compacta as well as increased expression of divalent metal transporter 1 (DMT1) and iron staining in both the substantia nigra pars compacta and striatum. Aged c-rel−/− mouse brain were characterized by increased microglial reactivity in the basal ganglia, but no astrocytic reaction. In addition, c-rel−/− mice showed age-dependent deficits in locomotor and total activity and various gait-related deficits during a catwalk analysis that were reminiscent of bradykinesia and muscle rigidity. Both locomotor and gait-related deficits recovered in c-rel−/− mice treated with l-3,4-dihydroxyphenylalanine. These data suggest that c-Rel may act as a regulator of the substantia nigra pars compacta resilience to ageing and that aged c-rel−/− mice may be a suitable model of Parkinson’s disease.

Ferroportin-1 is a ‘nuclear'-negative acute-phase protein in rat liver: a comparison with other iron-transport proteins

Liver is the central organ of iron metabolism. During acute-phase-response (APR), serum iron concentration rapidly decreases. The current study aimed to compare expression and localization of iron transport protein ferroportin-1 (Fpn-1) and of other iron import proteins after experimental tissue damage induced by injecting turpentine oil in the hind limbs of rats and mice. Serum and spleen iron concentration decreased with an increase in total liver, cytoplasmic and nuclear iron concentration. In liver, mRNA amount of Fpn-1, Fpn-1a, Fpn-1b, HFE, hemojuvelin (HJV) and hephaestin (heph) genes showed a rapid decrease. Hepcidin, divalent metal transporter-1 (DMT-1), transferrin (Tf) and Tf-receptor-1 (TfR1), TfR-2 (TfR2) gene expression was increased. Western blot analysis of liver tissue lysate confirmed the changes observed at mRNA level. In spleen, a rapid decrease in gene expression of Fpn-1, Fpn-1a, Fpn-1b, DMT-1, Tf, TfR1 and TfR2, and an increase in hepcidin was observed. Immunohistochemistry of DMT-1 and TfR2 were mainly detected in the nucleus of rat liver and spleen, whereas TfR1 was clearly localized in the plasma membrane. Fpn-1 was mostly found in the nuclei of liver cells, whereas in spleen, the protein was mainly detected in the cell membrane. Western blot analysis of liver fractions confirmed immunohistochemical results. In livers of wild-type mice, gene expression of Fpn-1, Fpn-1a and Fpn-1b was downregulated, whereas hepcidin gene expression was increased. In contrast, these changes were less pronounced in IL-6ko-mice. Cytokine (IL-6, IL-1β and TNF-α) treatment of rat hepatocytes showed a downregulation of Fpn-1, Fpn-1a and Fpn-1b, and upregulation of hepcidin gene expression. Moreover, western blot analysis of cell lysate of IL-6-treated hepatocytes detected, as expected, an increase of α2-macroglobulin (positive acute-phase protein), whereas albumin (negative acute-phase protein) and Fpn-1 were downregulated. Our results demonstrate that liver behaves as a ‘sponge' for iron under acute-phase conditions, and Fpn-1 behaves as a negative acute-phase protein in rat hepatocytes mainly, but not exclusively, because of the effect of IL-6. These changes could explain iron retention in the cytoplasm and in the nucleus of hepatocytes during APR.

EGCG protects against 6‐OHDA induced neurotoxicity in a cell culture model

Disruption of iron metabolism may involve in the progression of Parkinson's disease. Our objective was to test whether the protective effect of (−)‐epigallocatechin‐3‐gallate (EGCG) against 6‐hydroxydopamine (6‐OHDA) induced neurotoxicity was by regulating iron homeostasis in N27 cells. EGCG pretreatment significantly protected against 6‐OHDA‐induced neurotoxicity (MTT, SYTOX Green and Caspase‐3 activity assays). EGCG with 6OHDA treatment significantly increased (p<0.0001) TH+ cell count (3.1‐fold) and neurite length (12.5‐fold) compared with 6‐OHDA alone in primary mesencephalic neurons. 6‐OHDA treatment significantly (p<0.05) increased divalent metal transporter‐1 (DMT1), hepcidin, transferrin receptor‐2 (TfR2), H‐ferritin and decreased ferroportin‐1 (Fpn1), TfR1 mRNA expressions. The protein expressions of DMT1, hepcidin and Fpn1 matched with the gene expression data. However, EGCG significantly reversed the effect of 6‐OHDA on above genes and proteins expression. The increased ~2‐fold (p<0.001) 55Fe cell uptake with 6‐OHDA and normalization with EGCG pretreatment confirmed iron burden associated with neurotoxicity and protection by EGCG. In conclusion, EGCG protected against 6‐OHDA induced neurotoxicity by regulating genes and proteins involved in brain iron homeostasis. However, further studies are warranted to determine the mechanism of that regulation.Grant Funding Source : Nutrition Wellness and Research Center

Relative contribution of CTR1 and DMT1 in copper transport by the blood–CSF barrier: Implication in manganese-induced neurotoxicity

The homeostasis of copper (Cu) in the cerebrospinal fluid (CSF) is partially regulated by the Cu transporter-1 (CTR1) and divalent metal transporter-1 (DMT1) at the blood–CSF barrier (BCB) in the choroid plexus. Data from human and animal studies suggest an increased Cu concentration in blood, CSF, and brains following in vivo manganese (Mn) exposure. This study was designed to investigate the relative role of CTR1 and DMT1 in Cu transport under normal or Mn-exposed conditions using an immortalized choroidal Z310 cell line. Mn exposure in vitro resulted in an increased cellular 64Cu uptake and the up-regulation of both CTR1 and DMT1. Knocking down CTR1 by siRNA counteracted the Mn-induced increase of 64Cu uptake, while knocking down DMT1 siRNA resulted in an increased cellular 64Cu uptake in Mn-exposed cells. To distinguish the roles of CTR1 and DMT1 in Cu transport, the Z310 cell-based tetracycline (Tet)-inducible CTR1 and DMT1 expression cell lines were developed, namely iZCTR1 and iZDMT1 cells, respectively. In iZCTR1 cells, Tet induction led to a robust increase (25 fold) of 64Cu uptake with the time course corresponding to the increased CTR1. Induction of DMT1 by Tet in iZDMT1 cells, however, resulted in only a slight increase of 64Cu uptake in contrast to a substantial increase in DMT1 mRNA and protein expression. These data indicate that CTR1, but not DMT1, plays an essential role in transporting Cu by the BCB in the choroid plexus. Mn-induced cellular overload of Cu at the BCB is due, primarily, to Mn-induced over-expression of CTR1.

DMT1 (IRE) expression in intestinal and erythroid cells is regulated by peripheral benzodiazepine receptor-associated protein 7

The divalent metal transporter 1 (DMT1) is essential for cellular uptake of iron, mediating iron absorption across the duodenal brush border membrane. We have previously shown that with iron feeding DMT1 in the brush border membrane undergoes endocytosis into the subapical compartment of enterocytes. To understand the mechanisms of iron-induced endocytosis of DMT1, we used the yeast two-hybrid system to find proteins that interact with DMT1 and isolated from a rat duodenal cDNA library a protein that interacts specifically with the IRE containing isoform of DMT1 {DMT1 [iron-responsive element (IRE)]}. The protein (Genbank AY336075) is 97.5% identical with peripheral benzodiazepine receptor-associated protein 7 (PAP7), a protein that interacts with the peripheral benzodiazepine receptor. PAP7 is ubiquitously expressed in the rat and in multiple cell lines with consensus sequences including a nuclear localization signal and a Golgi dynamic domain. PAP7, expressed on the brush border of rat duodenum, copurified with DMT1 in brush border membrane vesicles, and following iron feeding, was internalized in parallel with the internalization of DMT1. To determine if PAP7 plays a role in cellular iron metabolism, we downregulated PAP7 expression in K562 cells with small interfering RNA. Following the decrease in PAP7 protein, DMT1 (IRE) protein but not mRNA was significantly downregulated but without effect on DMT1 (non-IRE), transferin (Tf)R1, or ferritin expression. Lowered levels of PAP7 resulted also in decreased cell proliferation and G(1) cell cycle arrest. These data are consistent with PAP7 interacting with DMT1 (IRE) and regulating DMT1 (IRE) expression in K562 cells by modulating expression of DMT1 (IRE) protein.

Studies on Predictors of Non-Response of Patients with Hepatitis C Virus (HCV) Infection following Multiple Interferon-Based Treatments

Statement of Purpose, Innovation or Hypothesis: Studies documented hepatic iron deposition in HCV infected implicated in the non-response to therapy. The mechanism remains elusive. This study was a retrospective review in conjunction with assessing the serum expression of divalent metal transporter 1 (DMT1) in patients with hepatitis C virus infection by immuno dot blotting.Methods and Materials: The patients were outpatients in Brookdale Hospital with chronic hepatitis C infection enrolled in single or multiple Interferon-based therapeutic trials during 1997- 2007. Non-response was defined when patients did not achieve a sustained virology response and /or had active viremia at 72 weeks. The antibodies used in this study were rabbit polyclonal sera been raised against putative extracellular loops of DMT1 through Sigma-Genosys Company. The sequence of the synthetic peptides used for immunization and their location within the primary amino acid sequences were KPSQSQVLKGMTVP (anti-DMT1 [174-187] and VFAEAFFGKTNEQVVE (anti DMT1 [260-275]. The detection of reactivity of antibodies to serum antigens was used by immuno dot blotting method.Results: There were total 93 outpatients with mean age of 46.5 years (range 28-65). There were 3 groups in this study: Response single trial group (R), Non-Response Single trial (NRS) group and Non-Response Multiple trials (NRM) group. There were significant difference in AA race, BMI (P<0.0001), baseline viral load (P<0.005 and p<0.0001) and the reactivity of anti-DMT1 dot blotting (P<0.005 and p < 0.0001) between R group with NRS group and NRM group, respectively.Interpretation, Conclusion or Significance: The NRS is the predictor of non-response to multiple treatments. The data suggests, but does not prove, that the reactivity of anti-DMT1 antibodies to the serum of hepatitis C virus infected patients may be one of the predictors for anti-viral responses.

Manganese source affects manganese transport and gene expression of divalent metal transporter 1 in the small intestine of broilers

In the present study, two experiments were conducted to investigate the effect of Mn source on Mn transport and the expression of a Mn transporter, divalent metal transporter 1 (DMT1), in the small intestine of broilers. In Expt 1, in situ ligated duodenal loops from Mn-deficient chicks (29-d-old) were perfused with solutions containing 0-8.74 mmol Mn/l from either MnSO4, or one of two organic chelates of Mn and amino acids with moderate (OM) or strong (OS) chelation strength (Q(f)) up to 30 min. In Expt 2, Mn-deficient intact broilers (14-d-old) were fed a control diet (12.45 mg Mn/kg) or the control diet supplemented with 100 mg Mn/kg as one of all Mn sources for 14 d. The uptake kinetics of Mn from different Mn sources in the ligated duodenal loops followed a saturable process as determined by regression analysis of concentration-dependent uptake rates. The maximum transport rate (Jmax) and K(m) values, and DMT1 mRNA levels in the ligated duodenal loops were higher (P < 0.01) for OM and OS than for MnSO4. DMT1 mRNA levels were much higher (P < 0.01) in the duodenum than in the jejunum and ileum. Both DMT1 mRNA levels in the duodenum and plasma Mn contents from the hepatic portal vein of intact chicks on day 14 post-feeding increased (P < 0.05) in the following order: control < MnSO4 < OM < OS. These results indicated that organic Mn sources with stronger Q(f) showed higher Mn transport and absorption, and DMT1 might be involved in the regulation of organic Mn transport in the proximal small intestine of broilers.

Expression of divalent metal transporter 1 in primary hippocampal neurons: reconsidering its role in non‐transferrin‐bound iron influx

The divalent metal transporter 1 (DMT1) is the best characterized Fe²⁺ transporter involved in cellular iron uptake in mammals. Four possible isoforms have been identified as a result of alternative promoter (DMT1-1A and DMT1-1B) and alternative splicing involving the C-terminus and producing transcripts with or without an iron responsive element [DMT1-IRE⁺ and DMT1-IRE⁻, respectively]. Despite the general importance of DMT1 in controlling iron homeostasis, the distribution and the role of the transporter in the CNS is still controversial. In this study, we characterize the expression of DMT1 in hippocampal neurons and astrocytes. We found that the main isoform endogenously expressed is DMT1-1B/IRE⁺, which shows cytoplasmic distribution, colocalization with late endosome/lysosome markers and iron regulation, as expected from the presence of an iron responsive element. Our results also show that DMT1-1B/IRE⁺ isoform does not sustain iron entry, even after its neuronal over-expression. Overall, our results argue against a physiological role of the endogenous DMT1 in neuronal iron uptake but do not exclude that, under pathological conditions, the expression of other DMT1 isoforms might contribute to iron overload.

Iron, Copper, and Zinc Transport: Inhibition of Divalent Metal Transporter 1 (DMT1) and Human Copper Transporter 1 (hCTR1) by shRNA

Iron (Fe), copper (Cu), and zinc (Zn) fulfill various essential biological functions and are vital for all living organisms. They play important roles in oxygen transport, cell growth and differentiation, neurotransmitter synthesis, myelination, and synaptic transmission. Because of their role in many critical functions, they are commonly used in food fortification and supplementation strategies globally. To determine the involvement of divalent metal transporter 1 (DMT1) and human copper transporter 1 (hCTR1) on Fe, Cu, and Zn uptake, Caco-2 cells were transfected with four different shRNA plasmids to selectively inhibit DMT1 or hCTR1 transporter expression. Fe and Cu uptake and total Zn content measurements were performed in shRNA-DMT1 and shRNA-hCTR1 cells. Both shRNA-DMT1 and shRNA-hCTR1 cells had lower apical Fe uptake (a decrease of 51% and 41%, respectively), Cu uptake (a decrease of 25.8% and 38.5%, respectively), and Zn content (a decrease of 23.1% and 22.7%, respectively) compared to control cells. These results confirm that DMT1 is involved in active transport of Fe, Cu, and Zn although Zn showed a different relative capacity. These results also show that hCTR1 is able to transport Fe and Zn.

Divalent Metal Transporter 1 Expression and Regulation in Human Placenta

Divalent metal transporter 1 (DMT1) is likely responsible for the release of iron from endosomes to the cytoplasm in placental syncytiotrophoblasts (STB). To determine the localization and the regulation of DMT1 expression by iron directly in placenta, the expression of DMT1 in human term placental tissues and BeWo cells (human placental choriocarcinoma cell line) was detected and the change in expression in response to different iron treatments on BeWo cells was observed. DMT1 was shown to be most prominent near the maternal side in human term placenta and predominantly in the cytoplasm of BeWo cells. BeWo cells were treated with desferrioxamine (DFO) and human holotransferrin (hTf-2Fe) and it was found that both DMT1 mRNA and protein increased significantly with DFO treatment and decreased with hTf-2Fe treatment. Further, DMT1 mRNA responded more significantly to treatments if it possessed an iron-responsive element than mRNA without this element. This study indicated that DMT1 is likely involved in endosomal iron transport in placental STB and placental DMT1 + IRE expression was primarily regulated by the IRE/IRP mechanism.

Hepcidin directly inhibits transferrin receptor 1 expression in astrocytes via a cyclic AMP‐protein kinase a pathway

Hepcidin, an iron-regulatory hormone, plays a central role in iron homeostasis in peripheral tissues. The widespread distribution of hepcidin in the brain implies that the hormone may be essential for brain iron homeostasis. Here, we investigated the effects of hepcidin on the expression of iron uptake proteins, including transferrin receptor 1 (TfR1) and divalent metal transporter1 (DMT1) and the release protein ferroportin1 (Fpn1) in the cultured astrocytes. The effects of hepcidin on iron uptake, including transferrin-bound iron (Tf-Fe) and non-transferrin-bound iron (NTBI), and iron release were also studied. Our results demonstrated that astrocytes, when treated with hepcidin peptide or infected with hepcidin expression adenovirus (ad-hepcidin), showed a significant ability in reducing iron uptake (both Tf-Fe and NTBI), and iron release, which were accompanied by decreased expressions of TfR1, DMT1, and Fpn1. Moreover, we found that the effect of hepcidin in reducing TfR1 expression, which is dependent on the cyclic AMP-protein kinase A pathway, was the primary and dominant event. In conclusion, our results demonstrated that hepcidin controlled iron uptake and release by regulating expression of iron transport proteins. The findings also implied the existence of a novel hepcidin-receptor on the membrane of astrocytes.

Divalent metal transporter 1 is a hypoxia‐inducible gene

Our recent study revealed a high correlation between the expression of hypoxia-inducible factor-1 (HIF-1) alpha and divalent metal transporter 1 (DMT1) in HepG2 cells treated with chemical or physical hypoxia. We therefore speculated that DMT1 might be one of the target genes of HIF-1. Here, we characterized the DMT1 exon1B promoter region and identified a functional hypoxia response element (HRE, 5'-TCAGTACCTAACGTGGCGCCACGGC-3') harboring a binding site for HIF-1. We demonstrated that hypoxia-dependent activation of a luciferase reporter gene in transfected HepG2 cells is mediated by a fragment of human DMT1 exon1B promoter containing the putative HRE sequence. We also showed that the HIF-1 binding site (HBS) is in DMT1 exon1B promoter with the core sequence of HRE (5'-ACGTG-3') at -327 to -323 relative to the transcription start site of the human DMT1 exon1B gene. The mutation of this sequence prevented stimulation of luciferase activity. Electrophoretic mobility shift assays revealed that the HRE sequence found in the DMT1 gene promoter was bound by HIF-1. In addition, we provide evidence that hypoxia could significantly increase ferrous uptake, while the silencing of total DMT1 by RNA interference down-regulates DMT1 expression and ferrous uptake in HepG2 cells. We conclude that DMT1 is a hypoxia-inducible gene.

Does Hepatic Hepcidin Play an Important Role in Exercise-Associated Anemia in Rats?

Some athletes are diagnosed as suffering from sports anemia because of iron deficiency, but the regulatory mechanism remains poorly understood. It is reported that hepcidin may provide a way to illuminate the regulatory mechanism of exercise-associated anemia. Here the authors investigate the hepcidin-involved iron absorption in exercise-associated anemia. Twelve male Wistar rats (300 ± 10 g) were randomly divided into 2 groups, 6 in a control group (CG) and 6 in an exercise group (EG, 5 wk treadmill exercise of different intensities with progressive loading). Serum samples were analyzed for circulating levels of IL-6 by means of enzyme-linked immunosorbent assay (ELISA). The expression of hepatic hepcidin mRNA was examined by real-time polymerase chain reaction analysis. The protein levels of divalent metal transporter 1 (DMT1), ferroportin1 (FPN1), and heme-carrier protein 1 (HCP1) of duodenum epithelium were examined by Western blot. The results showed that the amount of iron and ferritin in serum were lower in EG than in CG (p < .05). The levels of IL-6 and white blood cells were greater in EG than in CG (p < .01). The expression of DMT1, HCP1, and FPN1 was significantly lower in EG than in CG (p < .01). The mRNA expressions of hepatic hepcidin and hemojuvelin in skeletal muscle were remarkably higher in EG than in CG. The data indicated that inflammation was induced by strenuous exercise, and as a result, the transcriptional level of the hepatic hepcidin gene was increased, which further inhibited the expression of iron-absorption proteins and led to exercise-associated anemia.

Intestinal DMT1 Cotransporter Is Down-regulated by Hepcidin via Proteasome Internalization and Degradation

The mechanism by which hepcidin regulates iron export from macrophages has been well established and is believed to involve degradation of ferroportin. However, in the small intestine, hepcidin's mechanisms of action are not known. We studied human polarized intestinal (Caco-2/TC7) cells and mouse duodenal segments, ex vivo, to investigate the molecular mechanisms by which hepcidin down-regulates intestinal transepithelial iron transport. Iron transport was analyzed using ⁵⁵FeNTA. Expression of Divalent Metal Transporter 1 (DMT1) and ferroportin was evaluated by reverse-transcription quantitative polymerase chain reaction and immunoblotting. Videomicroscopy analysis was performed on live cells that expressed either DMT1 or ferroportin fused to green fluorescent protein. In Caco-2/TC7 cells, physiologic doses of hepcidin (50-1000 nmol/L) inhibited transport of ⁵⁵Fe in a dose-dependent manner; a half-maximum effect was observed at 75-100 nmol/L. However, 200 nmol/L hepcidin induced a significant decrease in DMT1 protein expression but no change in ferroportin protein levels, unlike macrophages. This result was confirmed ex vivo in isolated duodenal segments: 200 nmol/L hepcidin induced a significant reduction in iron transport and DMT1 protein levels but no change in ferroportin levels. In Caco-2/TC7 cells, the effect of hepcidin on the DMT1 protein level was completely abolished in the presence of a proteasome inhibitor (MG-132); DMT1 ubiquitination was induced by the addition of hepcidin. An acute increase in hepcidin concentration reduces intestinal iron absorption through ubiquitin-dependent proteasome degradation of DMT1.

Cross-resistance of cadmium-resistant cells to manganese is associated with reduced accumulation of both cadmium and manganese

The mechanism of cellular entry of cadmium remains unclear. We have previously established cadmium-resistant cells from mouse embryonic cells of metallothionein (MT)-null mice, and demonstrated that the down-regulation of a zinc transporter, Zrt/Irt-related protein (ZIP) 8, was responsible for the reduced cadmium incorporation into cells. In the present study, we developed cadmium-resistant cells (A +70 and B +70) from mouse embryonic cells of MT-expressing wild-type mice. The LC 50 values of CdCl 2 for A +70 and B +70 cells were about 200 μM while that of the parental cells was 30 μM. We found that the cadmium resistance of these cells was conferred not only by enhanced expression of MT, but also by a decrease in cadmium accumulation. Since the uptake rates of cadmium into A +70 and B +70 cells were lowered, we determined the expression levels of the metal transporters and channels potentially involved in the cellular uptake of cadmium. We found a down-regulation of multiple transport systems, including ZIP8, divalent metal transporter 1 (DMT1), and α 1 subunits of L-type (Ca V1.2) and T-type (Ca V3.1) voltage-dependent calcium channels, in A +70 and B +70 cells. Furthermore, A +70 and B +70 cells exhibited cross-resistance to cytotoxicity of MnCl 2, probably due to a marked decrease in manganese uptake in these cells. These results suggest that the suppressed expression of ZIP8 and DMT1, which are known to have affinities for both cadmium and manganese, may be responsible for the reduction in the uptake, and consequently the cytotoxicity, of cadmium and manganese in A +70 and B +70 cells.

Calcium and Iron Absorption - Mechanisms and Public Health Relevance

Studies on human subjects have shown that calcium (Ca) can inhibit iron (Fe) absorption, regardless of whether it is given as Ca salts or in dairy products. This has caused concern as increased Ca intake commonly is recommended for children and women, the same populations that are at risk of Fe deficiency. However, a thorough review of studies on humans in which Ca intake was substantially increased for long periods shows no changes in hematological measures or indicators of iron status. Thus, the inhibitory effect may be of short duration and there also may be compensatory mechanisms. The interaction between Ca and Fe may be a lumenal event, affecting Fe uptake through DMT1 (divalent metal transporter 1) at the apical membrane. However, it is also possible that inhibition occurs during Fe transfer into circulation, suggesting roles for the serosal exporter ferroportin (FPN) and hephaestin. We explored these possibilities in human intestinal Caco-2 cells cultured in monolayers. Iron transport ((59)Fe) and expression of DMT1, FPN, and hephaestin were assessed after 1.5 and 4 hours with 0 or 100 µM CaCl(2.) Although Ca did not affect Fe uptake or DMT1 expression at 1.5 hours, FPN abundance at the basolateral membrane decreased, resulting in increased cellular Fe retention and decreased Fe efflux. After 4 hours, DMT1 and FPN expression increased and there was increased FPN at the membrane, suggesting a rebound effect. Thus, the effect of Ca on Fe absorption may be of short duration and adaptation may occur with time. This may explain why studies on long-term Ca supplementation of different groups fail to show any adverse effects on Fe status.

Hypoxia regulates the ferrous iron uptake and reactive oxygen species level via divalent metal transporter 1 (DMT1) Exon1B by hypoxia‐inducible factor‐1

Hypoxia has been shown to increase the expression of a variety of proteins involved in iron homeostasis, including ceruloplasmin, transferrin, and transferring receptor. Divalent metal transporter 1 (DMT1) is a transmembrane protein that is important in divalent metal ion transport, in particular iron. Although previous studies have provided that DMT1 exon1A is regulated by hypoxia, little is known about the relationship between DMT1 exon1B and hypoxia. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor which is stabilized when mammalian cells are subjected to hypoxia. In this study, we have identified a functional hypoxia-response element (HRE) at position of -327 to -323 (-ACGTG-) in DMT1 exon1B promoter using a combination of bioinformatics and biological approaches. Both the total cellular iron and ferrous uptake increased after hypoxia, decreased after DMT1 RNA interference. Reactive oxygen species (ROS) were also changed by +iron responsive element (IRE) DMT1 exon1B overexpression. These findings implicated DMT1 exon1B was a target gene for HIF-1. Hypoxia might affect cellular iron uptake through regulating the expression of DMT1. When iron was present in excess, cells might be damaged by the ROS production.