Accumulation and release of iron in polarly and non-polarly cultured trophoblast cells isolated from human term placentas

Differential Iron Status and Trafficking in Blood and Placenta of Anemic and Non-anemic Primigravida Supplemented with Daily and Weekly Iron Folic Acid Tablets

Abstract

The molecular mechanism of iron transfer across placenta in response to maternal anemic status/ iron supplementation is not clear. We hypothesized that maternal iron/ anemia status during early trimesters can be utilized as a biomarker tool to get estimates of placental iron status. Early interventions can be envisaged to maintain optimum placental/ foetal iron levels for healthy pregnancy outcomes. One hundred twenty primigravida were recruited and divided into non-anemic and anemic group on the basis of hemoglobin levels. The groups were randomly allocated to receive daily and weekly iron folic acid (IFA) tablets till six weeks postpartum. Hematological and iron status markers in blood and placenta were studied along with the delivery notes. Weekly IFA supplementation in anemic primigravidas resulted in significantly reduced levels of hematological markers (p < 0.01); whereas non-anemic primigravidas showed lower ferritin and iron levels, and higher soluble transferrin receptor levels (p < 0.05). At baseline, C-reactive protein and cortisol hormone levels were also significantly lower in non-anemic primigravidas (p < 0.05). A significantly decreased placental ferritin expression (p < 0.05); and an increased placental transferrin expression was seen in anemic primigravidas supplemented with weekly IFA tablets. A significant positive correlation was observed between serum and placental ferritin expression in anemic pregnant women (r = 0.80; p < 0.007). Infant weight, gestational length and placental weight were comparable in both the supplementation groups. To conclude, mother's serum iron / anemia status switches the modulation in placental iron transporter expression for delivering the optimum iron to the foetus for healthy pregnancy outcomes.

Trial Registration

Clinical Trial Registry-India: CTRI/2014/10/005135.

CD71+ Erythroid Suppressor Cells Promote Fetomaternal Tolerance through Arginase-2 and PDL-1

Survival of the allogeneic pregnancy depends on the maintenance of immune tolerance to paternal alloantigens at the fetomaternal interface. Multiple localized mechanisms contribute to the fetal evasion from the mother's immune rejection as the fetus is exposed to a wide range of stimulatory substances such as maternal alloantigens, microbes and amniotic fluids. In this article, we demonstrate that CD71⁺ erythroid cells are expanded at the fetomaternal interface and in the periphery during pregnancy in both humans and mice. These cells exhibit immunosuppressive properties, and their abundance is associated with a Th2 skewed immune response, as their depletion results in a proinflammatory immune response at the fetomaternal interface. In addition to their function in suppressing proinflammatory responses in vitro, maternal CD71⁺ erythroid cells inhibit an aggressive allogeneic response directed against the fetus such as reduction in TNF-α and IFN-γ production through arginase-2 activity and PD-1/programmed death ligand-1 (PDL-1) interactions. Their depletion leads to the failure of gestation due to the immunological rejection of the fetus. Similarly, fetal liver CD71⁺ erythroid cells exhibit immunosuppressive activity. Therefore, immunosuppression mediated by CD71⁺ erythroid cells on both sides (mother/fetus) is crucial for fetomaternal tolerance. Thus, our results reveal a previously unappreciated role for CD71⁺ erythroid cells in pregnancy and indicate that these cells mediate homeostatic immunosuppressive/immunoregulatory responses during pregnancy.

Transferrin receptor gene and protein expression and localization in human IUGR and normal term placentas

Iron (Fe) deficiency in pregnancy is associated to low birth weight and premature delivery while in adults it can result in increased blood pressure and cardiovascular disease. Cellular Fe uptake is mediated by the Transferrin Receptor 1 (TFRC), located in the trophoblast membranes. Here, we measured TFRC mRNA expression (Real Time PCR) and TFRC protein expression and localization (Western Blotting and immunohistochemistry) in IUGR compared to control placentas. A total of 50 IUGR and 56 control placentas were studied at the time of elective cesarean section. IUGR was defined by ultrasound in utero, and confirmed by birth weight <10th percentile. Three different severity groups were identified depending on the umbilical artery pulsatility index and fetal heart rate. TFRC mRNA expression was significantly lower in IUGR placentas compared to controls (p < 0.05), and this was confirmed for TFRC protein levels. In both experiments the most severe IUGR group presented lower expression compared to the other groups, and this was also related to umbilical venous oxygen levels. TFRC protein localization in the villous trophoblast did not differ in the groups, and was predominantly present in the syncytiotrophoblast. In conclusion, these are the first observations about TFRC expression in human IUGR placentas, demonstrating its significant decrease in IUGR vs controls. Thus, Fe transport could be limited in IUGR placentas. Further studies are needed to study components of the placental Fe transport system and to clarify the regulation mechanisms involved in TFRC expression, possibly altered in IUGR placentas.

Effects of chronic hypoxia in vivo on the expression of human placental glucose transporters

Birth weight is reduced and the risk of preeclampsia is increased in human high altitude pregnancies. There has been little work to determine whether hypoxia acts directly to reduce fetal growth (e.g. reduced blood flow and oxygen delivery), or via changes in functional capacities such as nutrient transport. We therefore investigated the expression of a primary nutrient transporter, the GLUT1 glucose transporter and two in vitro markers of hypoxia (erythropoietin receptor, EPO-R, and transferrin receptor, TfR) in the syncytial microvillous (MVM) and basal membrane fractions (BMF) of 13 high (3100 m) and 12 low (1600 m) altitude placentas from normal term pregnancies. Birth weight was lower at 3100 m than at 1600 m despite similar gestational age, but none of the infants were clinically designated as fetal growth restriction. EPO-R, TfR and GLUT1 were examined by immunoblotting and maternal circulating erythropoietin and transferrin by ELISA. EPO-R was greater on the MVM (+75%) and BMF (+25%) at 3100 m. TfR was 32% lower on the MVM at 3100 m. GLUT1 was 40% lower in the BMF at 3100 m. Circulating EPO was greater at high altitude, while transferrin was similar, and neither correlated with their membrane receptors. BMF GLUT1 was positively correlated with birth weight at high, but not low altitude. In this in vivo model of chronic placental hypoxia, syncytial EPO-R increased as expected, while nutrient transporters decreased, opposite to what has been observed in vitro. Therefore, hypoxia acts to reduce fetal growth not simply by reducing oxygen delivery, but also by decreasing the density of nutrient transporters.

Transferrin receptor co-localizes and interacts with the hemochromatosis factor (HFE) and the divalent metal transporter-1 (DMT1) in trophoblast cells

Iron uptake and storage are tightly regulated to guarantee sufficient iron for essential cellular processes and to prevent the production of damaging free radicals. The placenta is the entry site for iron, which is delivered to the developing embryo. Iron is taken up by syncytiotrophoblast cells and is transported unidirectionally from mother to fetus against a concentration gradient. Several iron transporters and regulators were recently characterized, including DMT1 and ferroportin/Ireg1 that transport iron through membranes, and HFE that regulates TfR-mediated iron uptake. In this study we demonstrate that in a differentiated choriocarcinoma cell line BeWo, HFE, and TfR are localized mainly in recycling endosomes and a small percentage of these complexes is observed in late endosomes with DMT1 while in trophoblast cells, the level of TfR is significantly lower and it is detected with HFE and DMT1 mainly in late endosomes. Most interestingly, TfR and HFE, as well as TfR and DMT1 interact in placental trophoblast cells. Based on previous and these data we suggest that the level of intracellular iron may regulate both TfR expression (on the post-transcriptional and the post-translational levels) and TfR trafficking/transcytosis in polarized cells.

Influence of gestational age and fetal iron status on IRP activity and iron transporter protein expression in third-trimester human placenta

Placental iron transport during the last trimester of pregnancy determines the iron endowment of the neonate. Iron transport is a function of the major iron transport proteins: transferrin receptor-1 (TfR-1) and ferroportin-1 (FPN-1). The mRNAs for TfR-1 and, potentially, FPN-1 are posttranscriptionally regulated by iron regulatory protein (IRP)-1 and IRP-2. We assessed the effect of gestational age and fetal iron status on IRP-1- and IRP-2-binding activity and on the localization and protein expression of TfR-1 and FPN-1 protein at 24-40 wk of gestation in 21 placentas obtained from iron-sufficient nonanemic mothers. Gestational age had no effect on cord serum ferritin concentration, IRP-2 RNA-binding activity, transporter protein location, and TfR-1 or FPN-1 protein expression. IRP-1 activity remained constant until full term, when it decreased (P = 0.01). Placental ferritin (r = 0.76, P < 0.001) and FPN-1 (r = 0.44, P < 0.05) expression increased with gestational age. Fetal iron status, as indexed by cord serum ferritin concentration, was inversely related to placental IRP-1 (r = -0.66, P < 0.001) and IRP-2 (r = -0.42, P = 0.05) activities. Placental ferritin protein expression correlated better with IRP-1 (r = -0.45, P = 0.04) than with IRP-2 (r = -0.35, P = 0.10) activity. Placental TfR-1 and FPN-1 protein expression was independent of fetal or placental iron status and IRP activities. Iron status had no effect on transport protein localization. We conclude that, toward the end of the third trimester of iron-sufficient human pregnancy, the placenta accumulates ferritin and potentially increases placental-fetal iron delivery through increased FPN-1 expression. IRP-1 may have a more dominant role than IRP-2 activity in regulating ferritin expression.

Neonatal hemochromatosis

Neonatal hemochromatosis is a rare gestational condition in which iron accumulates in the fetal tissues in a distribution like that seen in hereditary hemochromatosis. Extensive liver damage is the dominant clinical feature, with late fetal loss or early neonatal death. NH recurs within sibships at a rate higher than that predicted for simple Mendelian autosomal-recessive inheritance, possibly suggesting the role of a maternal factor. Immunomodulation during pregnancy at risk appears to lessen the severity of disease.

Perinatal aspects of iron metabolism

Iron sufficiency is critical for rapidly developing fetal and neonatal organ systems. The majority of iron in the third trimester fetus and the neonate is found in the red cell mass (as hemoglobin), with lesser amounts in the tissues as storage iron (e.g. ferritin) or functional iron (e.g. myoglobin, cytochromes). Iron is prioritized to hemoglobin synthesis in red cells when iron supply does not meet iron demand. Thus, non-heme tissues such as the skeletal muscle, heart and brain will become iron deficient before signs of iron-deficiency anemia. Gestational conditions that result in lower newborn iron stores include severe maternal iron deficiency, maternal hypertension with intrauterine growth retardation and maternal diabetes mellitus. Stable, very low birthweight premature infants are also at risk for early postnatal iron deficiency because they accrete less iron during gestation, grow more rapidly postnatally, are typically undertreated with enteral iron and receive fewer red cell transfusions. Conversely, iron overload remains a significant concern in multiply transfused sick preterm infants because they have low levels of iron-binding proteins and immature antioxidant systems.

CONCLUSION

The highly variable iron status of preterm infants combined with their risk for iron deficiency and toxicity warrants careful monitoring and support in the newborn and postdischarge periods.

15-Deoxy-delta12,14-prostaglandin J2 induces apoptosis of a thyroid papillary cancer cell line (CG3 cells) through increasing intracellular iron and oxidative stress

Treatment of carcinoma cell lines with 15-deoxy-delta12,14-prostaglandin J2 (15d-PGJ2), a natural ligand of the peroxisome proliferator-activated receptor-gamma, has been reported to induce apoptosis and/or inhibit proliferation. In this study, we investigated the cytotoxic effect and the action mechanisms of 15d-PGJ2 in a thyroid papillary cancer cell line, CG3. The results indicate that 15d-PGJ2 caused cytotoxicity and increased the amount of intracellular reactive oxygen species (ROS) in these cells. Mitochondrial oxidative phosphorylation inhibitors (carbonyl cyanide m-chloro-phenylhydrazone, oligomycin, cyclosporin A and rotenone), NADPH oxidase inhibitor (diphenyleneiodonium), xanthine oxidase inhibitor (allopurinol) and NO synthase inhibitor (N-monomethyl-L-arginine acetate) did not reduce the generation of ROS. However, catalase, N-acetyl-cysteine and the iron chelator desferri-oxamine decreased the intracellular ROS of 15d-PGJ2-treated CG3 cells. Furthermore, 15d-PGJ2 enhanced the accumulation of iron in the CG3 cells. These data suggest that 15d-PGJ2 induces the generation of ROS by enhancing the accumulation of intracellular iron and that the increased oxidative stress may cause apoptosis of CG3 cells.

Identification and localization of divalent metal transporter-1 (DMT-1) in term human placenta

The mechanism by which iron is transported from mother to fetus is incompletely understood. Whereas transferrin receptor (TfR) is responsible for iron uptake from maternal serum by the syncytiotrophoblast, the proteins responsible for intracytoplasmic transport and for delivery to the fetal serum remain unknown. The aim of this study was to determine whether the recently characterized endosomal membrane iron transporter, divalent metal ion transporter-1 (DMT-1), is expressed in human syncytiotrophoblast, and whether its cellular localization would support roles for cytoplasmic and placental-fetal iron transport. Six micron sections of frozen, term human placenta were assessed immunohistochemically using a polyclonal antibody to rat DMT-1 and a monoclonal antibody to human TfR. DMT-1 was found both in the cytoplasm and at the junction of the fetal (basal) membrane and fetal vessels, while TfR was localized predominantly to the maternal (apical) side of the syncytiotrophoblastic membrane. Double staining demonstrated no overlap between the two proteins on the apical membrane and minimal areas of overlap in the cytoplasm. We postulate that the syncytiotrophoblast takes up diferric transferrin from serum via TfR, subsequently incorporating the transferrin : TfR complex via endosomes. Subsequent transport of iron out of the endosome and across the basal membrane to the fetus may occur via DMT-1.