8-bromo-cyclicAMP stimulates glucose transporter-1 expression in a human choriocarcinoma cell line

Fetomaternal Expression of Glucose Transporters (GLUTs)—Biochemical, Cellular and Clinical Aspects

Several types of specialized glucose transporters (GLUTs) provide constant glucose transport from the maternal circulation to the developing fetus through the placental barrier from the early stages of pregnancy. GLUT1 is a prominent protein isoform that regulates placental glucose transfer via glucose-facilitated diffusion. The GLUT1 membrane protein density and permeability of the syncytial basal membrane (BM) are the main factors limiting the rate of glucose diffusion in the fetomaternal compartment in physiological conditions. Besides GLUT1, the GLUT3 and GLUT4 isoforms are widely expressed across the human placenta. Numerous medical conditions and molecules, such as hormones, adipokines, and xenobiotics, alter the GLUT’s mRNA and protein expression. Diabetes upregulates the BM GLUT’s density and promotes fetomaternal glucose transport, leading to excessive fetal growth. However, most studies have found no between-group differences in GLUTs’ placental expression in macrosomic and normal control pregnancies. The fetomaternal GLUTs expression may also be influenced by several other conditions, such as chronic hypoxia, preeclampsia, and intrahepatic cholestasis of pregnancy.

Role of Placental Glucose Transporters in Determining Fetal Growth

Maternal nutrient availability and its transport through the placenta are crucial for fetal development. Nutrients are transported to the fetus via specific transporters present on the microvillous (MVM) and basal membrane (BM) of the placenta. Glucose is the most abundant nutrient transferred to the fetus and plays a key role in the fetal growth and development. The transfer of glucose across the human placenta is directly proportional to maternal glucose concentrations, and is mediated by glucose transporter family proteins (GLUTs). Maternal glucose concentration influences expression and activity of GLUTs in the MVM (glucose uptake) and BM (glucose delivery). Alteration in the number and function of these transporters may affect the growth and body composition of the fetus. The thin-fat phenotype of the Indian baby (low ponderal index, high adiposity) is proposed as a harbinger of future metabolic risk. We propose that placental function mediated through nutrient transporters contributes to the phenotype of the baby, specifically that glucose transporters will influence neonatal fat. This review discusses the role of various glucose transporters in the placenta in determining fetal growth and body composition, in light of the above hypothesis.

Susceptibility of Broiler Chickens to Deoxynivalenol Exposure via Artificial or Natural Dietary Contamination

Simple Summary

This study evaluated the effect of diets artificially or naturally contaminated with 4000 μg/kg deoxyvalenol (DON) on the intestinal integrity and nutrient absorption of broiler chickens. Young broiler chickens (14 days old) were more sensitive to DON than older birds (28 days old), and negative impacts were observed when diets were naturally contaminated with DON. Aside from the decrease in the villus height of the jejunum in young broilers, their capacity to absorb peptides was decreased, as shown by the down-regulation of a peptide transporter. However, this effect was compensated in older broilers by an increase in the expression of carbohydrate transporter.

Abstract

Multi-mycotoxin contamination of poultry diets is a recurrent problem, even if the mycotoxins levels are below EU recommendations. Deoxynivalenol (DON) is one of the main studied mycotoxins due to its risks to animal production and health. When evaluating the effects of DON, one must consider that under practical conditions diets will not be contaminated solely with this mycotoxin. In the present study, broiler chickens were fed diets with negligible mycotoxin levels or with naturally or artificially contaminated diets containing approximately 4000 μg/kg DON. Birds were sampled at D14 and D28. Naturally-contaminated diets caused the most harm to the birds, especially the young ones, which presented decreased jejunal villus height and increased lesions, down-regulation of a peptide transporter. At D28 broiler chickens seemed to have adapted to the dietary conditions, when no differences were observed in villus morphometry, together with up-regulation of a carbohydrate transporter. However, intestinal lesions remained present in these older birds.

Glucose transporter 1 is important for the glycolytic metabolism of human endometrial stromal cells in hypoxic environment

Aim

The study aimed to elucidate the glycolytic metabolism of human endometrial stromal cells (hESCs) in hypoxic environment.

Main methods

The hESCs were cultured in hypoxic environment, and their metabolic pathways were analyzed using metabolomics. We assessed glucose uptake using 2-deoxyglucose (2-DG) assay. The expression of glucose transporters (GLUTs) required for glucose uptake was determined using real-time quantitative polymerase chain reaction (qPCR) and western blotting. Furthermore, we knocked down GLUT1 and examined the uptake of 2-DG.

Key findings

Under hypoxia, glucose-6-phosphate, fructose-6-phosphate, and fructose-1,6-diphosphate were significantly elevated in hESCs (P < 0.05). This finding indicated enhancement in glycolysis. The volume of glucose uptake increased significantly under hypoxia (P < 0.05). Hypoxia simultaneously induced the expression of GLUT1 and GLUT3 mRNA (P < 0.05) and attenuated the expression of GLUT8 (P < 0.05). Glucose uptake was significantly inhibited upon knockdown of GLUT1 (P < 0.0001).

Significance

These results demonstrated a very important role of glucose transport under hypoxia. Also, hESCs utilize glycolysis to adapt to hypoxic conditions that could occur in menstrual and implantation period. These findings pave the way to study implantation failure and tumors originating from the endometrium.

Expression of placental glucose transporter proteins in pregnancies complicated by fetal growth disorders

During pregnancy fetal growth disorders, including fetal macrosomia and fetal growth restriction (FGR) are associated with numerous maternal-fetal complications, as well as due to the adverse effect of the intrauterine environment lead to an increased morbidity in adult life. Accumulating evidence suggests that occurrence of fetal macrosomia or FGR, may be associated with alterations in the transfer of nutrients across the placenta, in particular of glucose. The placental expression and activity of specific GLUT transporters are the main regulatory factors in the process of maternal-fetal glucose exchange. This review article summarizes the results of previous studies on the expression of GLUT transporters in the placenta, concentrating on human pregnancies complicated by intrauterine fetal growth disorders. Characteristics of each transporter protein found in the placenta is presented, alterations in the location and expression of GLUT isoforms observed in individual placental compartments are described, and the factors regulating the expression of selected GLUT proteins are examined. Based on the above data, the potential function of each GLUT isoform in the maternal-fetal glucose transfer is determined. Further on, a detailed analysis of changes in the expression of glucose transporters in pregnancies complicated by fetal growth disorders is given, and significance of these modifications for the pathogenesis of fetal macrosomia and FGR is discussed. In the final part novel interventional approaches that might reduce the risk associated with abnormalities of intrauterine fetal growth through modifications of placental GLUT-mediated glucose transfer are explored.

Hypoxia increases glucose transporter 1 expression in bovine corpus luteum at the early luteal stage

A major role of the corpus luteum (CL) is to produce progesterone (P4). The CL has immature vasculature shortly after ovulation, suggesting it exists under hypoxic conditions. Hypoxia-inducible factor-1 (HIF1) induces the expression of glucose transporter 1 (GLUT1). To clarify the physiological roles of GLUT1 in bovine CL, we examined GLUT1 mRNA expression in the CL under hypoxic conditions by quantitative RT-PCR. We also measured the effects of glucose (0-25 mM) and GLUT1 inhibitors (cytochalasin B, STF-31) on P4 production in bovine luteal cells. GLUT1 mRNA expression in bovine CL was higher at the early luteal stage compared to the other later stages. Hypoxia (3% O₂) increased GLUT1 mRNA expression in early luteal cells, but not in mid luteal cells. Glucose (0-25 mM) increased P4 production in early luteal cells, but not in mid luteal cells. Both GLUT1 inhibitors decreased P4 production in early and mid luteal cells. Overall, the results suggest that GLUT1 (possibly induced by hypoxic conditions in the early CL) plays a role in the establishment and development of bovine CL, especially in supporting luteal P4 synthesis at the early luteal stage.

CREB1 regulates glucose transport of glioma cell line U87 by targeting GLUT1

Glioma is stemmed from the glial cells in the brain, which is accounted for about 45% of all intracranial tumors. The characteristic of glioma is invasive growth, as well as there is no obvious boundary between normal brain tissue and glioma tissue, so it is difficult to resect completely with worst prognosis. The metabolism of glioma is following the Warburg effect. Previous researches have shown that GLUT1, as a glucose transporter carrier, affected the Warburg effect, but the molecular mechanism is not very clear. CREB1 (cAMP responsive element-binding protein1) is involved in various biological processes, and relevant studies confirmed that CREB1 protein regulated the expression of GLUT1, thus mediating glucose transport in cells. Our experiments mainly reveal that the CREB1 could affect glucose transport in glioma cells by regulating the expression of GLUT1, which controlled the metabolism of glioma and affected the progression of glioma.

p45 NF-E2 regulates syncytiotrophoblast differentiation by post-translational GCM1 modifications in human intrauterine growth restriction

Placental insufficiency jeopardizes prenatal development, potentially leading to intrauterine growth restriction (IUGR) and stillbirth. Surviving fetuses are at an increased risk for chronic diseases later in life. IUGR is closely linked with altered trophoblast and placental differentiation. However, due to a paucity of mechanistic insights, suitable biomarkers and specific therapies for IUGR are lacking. The transcription factor p45 NF-E2 (nuclear factor erythroid derived 2) has been recently found to regulate trophoblast differentiation in mice. The absence of p45 NF-E2 in trophoblast cells causes IUGR and placental insufficiency in mice, but mechanistic insights are incomplete and the relevance of p45 NF-E2 for human syncytiotrophoblast differentiation remains unknown. Here we show that p45 NF-E2 negatively regulates human syncytiotrophoblast differentiation and is associated with IUGR in humans. Expression of p45 NF-E2 is reduced in human placentae complicated with IUGR compared with healthy controls. Reduced p45 NF-E2 expression is associated with increased syncytiotrophoblast differentiation, enhanced glial cells missing-1 (GCM1) acetylation and GCM1 desumoylation in IUGR placentae. Induction of syncytiotrophoblast differentiation in BeWo and primary villous trophoblast cells with 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP) reduces p45 NF-E2 expression. Of note, p45 NF-E2 knockdown is sufficient to increase syncytiotrophoblast differentiation and GCM1 expression. Loss of p45 NF-E2 using either approach resulted in CBP-mediated GCM1 acetylation and SENP-mediated GCM1 desumoylation, demonstrating that p45 NF-E2 regulates post-translational modifications of GCM1. Functionally, reduced p45 NF-E2 expression is associated with increased cell death and caspase-3 activation in vitro and in placental tissues samples. Overexpression of p45 NF-E2 is sufficient to repress GCM1 expression, acetylation and desumoylation, even in 8-Br-cAMP exposed BeWo cells. These results suggest that p45 NF-E2 negatively regulates differentiation and apoptosis activation of human syncytiotrophoblast by modulating GCM1 acetylation and sumoylation. These studies identify a new pathomechanism related to IUGR in humans and thus provide new impetus for future studies aiming to identify new biomarkers and/or therapies of IUGR.

Placental glucose transporter 3 (GLUT3) is up-regulated in human pregnancies complicated by late-onset intrauterine growth restriction

INTRODUCTION

Transport of glucose from maternal blood across the placental trophoblastic tissue barrier is critical to sustain fetal growth. The mechanism by which GLUTs are regulated in trophoblasts in response to ischemic hypoxia encountered with intrauterine growth restriction (IUGR) has not been suitably investigated.

OBJECTIVE

To investigate placental expression of GLUT1, GLUT3 and GLUT4 and possible mechanisms of GLUT regulation in idiopathic IUGR.

METHODS

We analyzed clinical, biochemical and histological data from placentas collected from women affected by idiopathic full-term IUGR (n = 10) and gestational age-matched healthy controls (n = 10).

RESULTS

We found increased GLUT3 protein expression in the trophoblast (cytotrophoblast greater than syncytiotrophoblast) on the maternal aspect of the placenta in IUGR compared to normal placenta, but no differences in GLUT1 or GLUT4 were found. No differential methylation of the GLUT3 promoter between normal and IUGR placentas was observed. Increased GLUT3 expression was associated with an increased nuclear concentration of HIF-1α, suggesting hypoxia may play a role in the up-regulation of GLUT3.

DISCUSSION

Further studies are needed to elucidate whether increased GLUT3 expression in IUGR is a marker for defective villous maturation or an adaptive response of the trophoblast in response to chronic hypoxia.

CONCLUSIONS

Patients with IUGR have increased trophoblast expression of GLUT3, as found under the low-oxygen conditions of the first trimester.

PKA and cAMP stimulate proliferation of mouse embryonic stem cells by elevating GLUT1 expression mediated by the NF-κB and CREB/CBP signaling pathways

BACKGROUND

Regulation of glucose transporter (GLUT) expression and activity plays a vital role in the supply of glucose to embryonic stem (ES) cells.

METHODS

To observe the effect of 6-phenyl cyclic monophosphate (cAMP) on glucose uptake and cell proliferation, 2-deoxyglucose (2-DG) uptake, immunohistochemistry, Western blotting, and immunoprecipitation were carried out.

RESULTS

Among GLUT isoforms in mouse ES cells, GLUT1 was predominantly expressed and 6-phenyl cAMP increased GLUT mRNA levels. Among cAMP agonists, 6-phenyl cAMP increased 2-DG uptake more than that of 8-p-chlorophenylthio-2'-O-methyl-cAMP. 6-Phenyl cAMP increased GLUT1 expression and translocation from the cytosol to the plasma membrane. 6-Phenyl cAMP increased 2-DG uptake in a time- and concentration-dependent manner due to an increase in V(max) but not K(m). 6-Phenyl cAMP increased phosphorylation of nuclear factor-κB (NF-κB) and cAMP response element binding (CREB) and expression of the CREB protein (CBP) and transducer of regulated CREB activity 2 (TORC2) in sequence. 6-Phenyl cAMP induced complex formation of NF-κB/CREB/CBP/TORC2, which are involved in the increase of gluconeogenic enzyme expression. 6-Phenyl cAMP also increased cell cycle regulatory protein expression levels, the proportion of S-phase cells, and proto-oncogene expression via protein kinase A (PKA)-dependent NF-κB signaling. Finally, GLUT1 siRNA blocked the 6-phenyl cAMP-induced increase in ES cell proliferation. We conclude that PKA stimulated the complex formation of CREB/CBP/TORC2 via NF-κB, which induced effective coordination of glucose uptake as well as proliferation in ES cells.

GENERAL SIGNIFICANCE

6-Phenyl cAMP-induced PKA activation modified the proliferation, which may be beneficial for expanding ES cell use to cell therapy.

Differential regulation of glucose transporters mediated by CRH receptor type 1 and type 2 in human placental trophoblasts

Glucose transport across the placenta is mediated by glucose transporters (GLUT), which is critical for normal development and survival of the fetus. Regulatory mechanisms of GLUT in placenta have not been elucidated. Placental CRH has been implicated to play a key role in the control of fetal growth and development. We hypothesized that CRH, produced locally in placenta, could act to modulate GLUT in placenta. To investigate this, we obtained human placentas from uncomplicated term pregnancies and isolated and cultured trophoblast cells. GLUT1 and GLUT3 expressions in placenta were determined, and effects of CRH on GLUT1 and GLUT3 were examined. GLUT1 and GLUT3 were identified in placental villous syncytiotrophoblasts and the endothelium of vessels. Treatment of cultured placental trophoblasts with CRH resulted in an increase in GLUT1 expression while a decrease in GLUT3 expression in a dose-dependent manner. Cells treated with either CRH antibody or nonselective CRH receptor (CRH-R) antagonist astressin showed a decrease in GLUT1 and an increase in GLUT3 expression. CRH-R1 antagonist antalarmin decreased GLUT1 expression while increased GLUT3 expression. CRH-R2 antagonist astressin2b increased the expression of both GLUT1 and GLUT3. Knockdown of CRH-R1 decreased GLUT1 expression while increased GLUT3 expression. CRH-R2 knockdown caused an increase in both GLUT1 and GLUT3 expression. Our data suggest that, in placenta, CRH produced locally regulates GLUT1 and GLUT3 expression, CRHR1 and CRHR2-mediated differential regulation of GLUT1 and GLUT3 expression. Placental CRH may regulate the growth of fetus and placenta by modulating the expression of GLUT in placenta during pregnancy.

Glucose transporter 3 (GLUT3) protein expression in human placenta across gestation

Conflicting information regarding expression of GLUT3 protein in the human placenta has been reported and the localization and pattern of expression of GLUT3 protein across gestation has not been clearly defined. The objective of this study was characterization of syncytial GLUT3 protein expression across gestation. We hypothesized that GLUT3 protein is present in the syncytial microvillous membrane and that its expression decreases over gestation. GLUT3 protein was measured in samples from a range of gestational ages (first to third trimester), with human brain and human bowel used as a positive and negative control respectively. As an additional measure of specificity, we transfected BeWo choriocarcinoma cells, a trophoblast cell line expressing GLUT3, with siRNA directed against GLUT3 and analyzed expression by Western blotting. GLUT3 was detected in the syncytiotrophoblast at all gestational ages by immunohistochemistry. Using Western blotting GLUT3 was detected as an integral membrane protein at a molecular weight of ∼50 kDa in microvillous membranes from all trimesters but not in syncytial basal membranes. The identity of the primary antibody target was confirmed by demonstrating that expression of the immunoblotting signal in GLUT3 siRNA-treated BeWo was decreased to 18 ± 6% (mean ± SEM) of that seen in cells transfected with a non-targeting siRNA. GLUT3 expression in microvillous membranes detected by Western blot decreased through the trimesters such that expression in the second trimester (wks 14-26) was 48 ± 7% of that in the first trimester and by the third trimester (wks 31-40) only 34 ± 10% of first trimester expression. In addition, glucose uptake into BeWo cells treated with GLUT3 siRNA was reduced to 60% of that measured in cells treated with the non-targeting siRNA. This suggests that GLUT3-mediated uptake comprises approximately 50% of glucose uptake into BeWo cells. These results confirm the hypothesis that GLUT3 is present in the syncytial microvillous membrane early in gestation and decreases thereafter, supporting the idea that GLUT3 is of greater importance for glucose uptake early in gestation.

Possible role of the exchange protein directly activated by cyclic AMP (Epac) in the cyclic AMP-dependent functional differentiation and syncytialization of human placental BeWo cells

BACKGROUND

The mononuclear villous cytotrophoblast (CTB) differentiates and fuses to the multinucleated syncytiotrophoblast (STB), which produces hCG and progesterone. cAMP-mediated intracellular pathways are involved in the process of endocrine differentiation and fusion (syncytialization). The exchange protein directly activated by cAMP (Epac) is a mediator of cAMP signaling. We examined the differential roles of Epac and protein kinase A (PKA) signaling in the cell fusion and differentiation of trophoblast-derived BeWo cells.

METHODS

Epac1 and Epac2 were localized in human placental tissue (n = 9) by immunohistochemistry. The PKA-selective cAMP analog (N(6)-phenyl-cAMP, Phe) or Epac-selective cAMP analog (CPT) was tested for effects on hCG and progesterone production, and syncytialization in BeWo cells. The effect of knockdown of Epac or its downstream target molecule (Rap1) on syncytialization was evaluated.

RESULTS

Epac1 and Epac2 proteins were expressed in villous CTB, STB, stroma, blood vessels and extravillous CTB of the placenta. Phe increased the expression of hCG alpha/beta mRNA and secretion of hCG protein in BeWo cells (P < 0.01 versus control). CPT-stimulated production of hCG (P < 0.05), albeit to a lesser extent than Phe. Progesterone production was also enhanced by Phe or CPT (P < 0.01 and P < 0.05, respectively). CPT or a stable cAMP analog (dibutyryl-cAMP: Db) increased the number of syncytialized BeWo cells (P < 0.01), whereas Phe did not stimulate fusion. CPT- or Db-induced syncytialization was observed, even in the presence of a PKA inhibitor. Knockdown of Epac1 or Rap1 repressed the Db-, CPT- or forskolin-induced cell fusion.

CONCLUSIONS

The Epac signaling pathway may be associated with the cAMP-mediated functional differentiation and syncytialization of human trophoblasts.

Variants in ADCY5 and near CCNL1 are associated with fetal growth and birth weight

To identify genetic variants associated with birth weight, we meta-analyzed six genome-wide association (GWA) studies (n = 10,623 Europeans from pregnancy/birth cohorts) and followed up two lead signals in 13 replication studies (n = 27,591). rs900400 near LEKR1 and CCNL1 (P = 2 x 10(-35)) and rs9883204 in ADCY5 (P = 7 x 10(-15)) were robustly associated with birth weight. Correlated SNPs in ADCY5 were recently implicated in regulation of glucose levels and susceptibility to type 2 diabetes, providing evidence that the well-described association between lower birth weight and subsequent type 2 diabetes has a genetic component, distinct from the proposed role of programming by maternal nutrition. Using data from both SNPs, we found that the 9% of Europeans carrying four birth weight-lowering alleles were, on average, 113 g (95% CI 89-137 g) lighter at birth than the 24% with zero or one alleles (P(trend) = 7 x 10(-30)). The impact on birth weight is similar to that of a mother smoking 4-5 cigarettes per day in the third trimester of pregnancy.

Metal transcription factor-1 is involved in hypoxia-dependent regulation of placenta growth factor in trophoblast-derived cells

Placenta growth factor (PlGF) is a placental angiogenic factor. Metal-responsive transcription factor (MTF)-1 was reported to take part in the hypoxic induction of PlGF in RAS-transformed mouse fibroblasts. We contrarily showed that PlGF mRNA and protein levels decreased under hypoxia in a choriocarcinoma BeWo cell line derived from trophoblast. In this report, we examined whether hypoxia-dependent regulation of the PlGF gene in these cells also depends on MTF-1. We analyzed the effect of hypoxia on MTF-1 expression, and it was revealed to be decreased. Moreover, MTF-1 small interfering RNA treatment decreased PlGF mRNA level. To investigate the transcription of PlGF under hypoxia, we cloned promoter region of the human PlGF. Promoter deletion analysis suggested that triple repeats of metal-responsive element located between -511 and -468 bp in the promoter are important for the hypoxic regulation of PlGF. Treatment with MTF-1 small interfering RNA resulted in the significant decreased luciferase activity in PlGF reporter constructs. Chromatin immunoprecipitation showed the binding of the MTF-1 protein to the promoter region. We examined MTF-1 immunoreactivity in trophoblasts of term placental tissue from patients with normal pregnancies and preeclampsia, which represents a condition of placental hypoxia. Immunoreactivity of the MTF-1 protein was decreased in placentas from pregnant women with preeclampsia when compared with those from normal pregnant women. Taken together, these findings suggest that MTF-1 is involved in hypoxia-dependent regulation of PlGF in trophoblast-derived cells.

The facilitative glucose transporter GLUT3: 20 years of distinction

Glucose metabolism is vital to most mammalian cells, and the passage of glucose across cell membranes is facilitated by a family of integral membrane transporter proteins, the GLUTs. There are currently 14 members of the SLC2 family of GLUTs, several of which have been the focus of this series of reviews. The subject of the present review is GLUT3, which, as implied by its name, was the third glucose transporter to be cloned (Kayano T, Fukumoto H, Eddy RL, Fan YS, Byers MG, Shows TB, Bell GI. J Biol Chem 263: 15245-15248, 1988) and was originally designated as the neuronal GLUT. The overriding question that drove the early work on GLUT3 was why would neurons need a separate glucose transporter isoform? What is it about GLUT3 that specifically suits the needs of the highly metabolic and oxidative neuron with its high glucose demand? More recently, GLUT3 has been studied in other cell types with quite specific requirements for glucose, including sperm, preimplantation embryos, circulating white blood cells, and an array of carcinoma cell lines. The last are sufficiently varied and numerous to warrant a review of their own and will not be discussed here. However, for each of these cases, the same questions apply. Thus, the objective of this review is to discuss the properties and tissue and cellular localization of GLUT3 as well as the features of expression, function, and regulation that distinguish it from the rest of its family and make it uniquely suited as the mediator of glucose delivery to these specific cells.

Regulation of placental growth hormone secretion in a human trophoblast model--the effects of hormones and adipokines

Placental growth hormone (PGH) is secreted from the human placental syncytiotrophoblast into the maternal circulation. PGH levels in pregnant women correlate with the birth weight of their offspring. We hypothesized that metabolic regulators may alter PGH secretion. BeWo cells as human trophoblast models were treated for 24, 48, and 72 h with insulin, insulin-like growth factor (IGF)-1, cortisol, ghrelin, leptin and visfatin. Cyclic-adenosinmonophosphate treatment served as positive control. PGH concentrations in culture media were measured. Insulin reduced (p < 0.008; analysis of variance) PGH secretion from BeWo cells after 72 h. No effect was found when treating cells with IGF-1. Cortisol reduced PGH secretion after 48 h (p < 0.00118; analysis of variance) and 72 h (p < 0.015). Leptin and ghrelin both suppressed (p < 0.027 and p < 0.017, paired t test) whereas visfatin increased (p < 0.014, paired t test) PGH secretion at 72 h. Cyclic adenosinmonophosphate increased (p < 0.003) PGH secretion at 72 h. Our results indicate that in vitro PGH secretion by BeWo cells is regulated by hormonal factors and adipokines. We speculate on the existence of a maternal-placental regulatory loop, in which elevated insulin and leptin levels might down-regulate PGH secretion.

Regulation of GLUT3 and glucose uptake by the cAMP signalling pathway in the breast cancer cell line ZR-75

Increased glucose uptake as a principal energy source is a requirement for the continued survival of tumour cells. Facilitative glucose transporter-1 (GLUT1) and -3 (GLUT3) have been previously shown to be present and regulated in breast cancer cells and are associated with poor patient prognosis. In cancer cells, the cAMP secondary messenger pathway is known to potentiate described glucose transporter activators and regulate cell fate. However, no regulation of the glucose transporters in breast cancer cells by cAMP has previously been examined. Herein, we determined in the well-characterized breast cancer cell line ZR-75, if the cAMP analogue 8-br-cAMP was capable of regulating GLUT1 and GLUT3 expression and thus glucose uptake. We demonstrated that 8-br-cAMP transiently up-regulates GLUT3 mRNA levels. The use of actinomycin-D and the cloning of 1,200 bp upstream of the human GLUT3 promoter demonstrated that this regulation was transcriptional. Immunocytochemistry and Western blotting confirmed that the increase in mRNA was reflected by an increase in protein levels. No notable regulation of GLUT1 in the presence of 8-br-cAMP was detected. Finally, we determined using the non-metabolizable glucose analogue 2-DOG if this up-regulation in GLUT3 increased glucose uptake. We observed the presence of two uptake components, one corresponding to the Km of GLUT1/4 and the other to GLUT3. A doubling in the uptake velocity was observed only at the Km corresponding to GLUT3. In conclusion, we demonstrate and characterize for the first time, an up-regulation of GLUT3 mRNA, protein and glucose uptake by the cAMP pathway in breast cancer cells.

Involvement of RelA-associated inhibitor in regulation of trophoblast differentiation via interaction with transcriptional factor specificity protein-1

Glucose transporter-1 (GLUT1), one of the key functional indicators of placental differentiation, has an important role in placental glucose transport. We previously showed that the protein levels of GLUT1 and nuclear transcription factor specificity protein-1 (Sp1) in rat choriocarcinoma cells (Rcho-1 cells) decreased during the differentiation of these cells to giant cells. We also showed that Sp1 was involved in the regulation of GLUT1 gene expression during this process. RelA-associated inhibitor (RAI) is an inhibitor of nuclear factor-kappaB that was identified by a yeast two-hybrid screen and is preferably expressed in human placenta and heart. RAI was also found to interact with Sp1 and exert an inhibitory effect against the DNA-binding activity of Sp1. We first show here that RAI mRNA expression increased as gestation proceeded and that RAI was localized mainly in the syncytiotrophoblast throughout pregnancy. The chloramphenicol acetyltransferase activity assay in Rcho-1 cells revealed that cotransfection of RAI expression vector resulted in decreased activity of the rat GLUT1 promoter but not in that of a mutated rat GLUT1 promoter lacking the Sp1 binding site. Furthermore, the protein level of RAI increased during differentiation. In addition, transfection of RAI expression vector promoted the morphological differentiation of Rcho-1 cells, and RAI knockdown using RAI-specific small interfering RNA reveals inhibitory effects on the morphological differentiation, as assessed by photomicroscopy. Taken together, these findings suggest that RAI may be involved in the regulation of trophoblast differentiation via interaction with Sp1.

Hepatitis B virus translocates across a trophoblastic barrier

Mother-infant transmission of hepatitis B virus (HBV) accounts for up to 30% of worldwide chronic infections. The mechanism and high-risk period of HBV transmission from mother to infant are unknown. Although largely prevented by neonatal vaccination, significant transmission continues to occur in high-risk populations. It is unclear whether HBV can traverse an intact epithelial barrier to infect a new host. Transplacental transmission of a number of viruses relies on transcytotic pathways across placental cells. We wished to determine whether infectious HBV can traverse a polarized trophoblast monolayer. We used a human placenta-derived cell line, BeWo, cultured on membranes as polarized monolayers, to model the maternal-fetal barrier. We assessed the effects of placental maturity and maternal immunoglobulin on viral transport. Intracellular viral trafficking pathways were investigated by confocal microscopy. Free HBV (and infectious duck hepatitis B virus) transcytosed across trophoblastic cells at a rate of 5% in 30 min. Viral transport occurred in microtubule-dependent endosomal vesicles. Additionally, confocal microscopy showed that the internalized virus traverses a monensin-sensitive endosomal compartment. Differentiation of the cytotrophoblasts to syncytiotrophoblasts resulted in a 25% reduction in viral transcytosis, suggesting that placental maturity may protect the fetus. Virus translocation was also reduced in the presence of HBV immunoglobulin. We show for the first time that transcytosis of infectious hepadnavirus can occur across a trophoblastic barrier early in gestation, with the risk of transmission being reduced by placental maturity and specific maternal antibody. This study suggests a mechanism by which mother-infant transmission may occur.

Hypoxic upregulation of glucose transporters in BeWo choriocarcinoma cells is mediated by hypoxia-inducible factor-1

Placental hypoxia has been implicated in pregnancy pathologies, including fetal growth restriction and preeclampsia; however, the mechanism by which the trophoblast cell responds to hypoxia has not been adequately explored. Glucose transport, a process crucial to fetoplacental growth, is upregulated by hypoxia in a number of cell types. We investigated the effects of hypoxia on the regulation of trophoblast glucose transporter (GLUT) expression and activity in BeWo choriocarcinoma cells, a trophoblast cell model, and human placental villous tissue explants. GLUT1 expression in BeWo cells was upregulated by the hypoxia-inducing chemical agents desferroxamine and cobalt chloride. Reductions in oxygen tension resulted in dose-dependent increases in GLUT1 and GLUT3 expression. Exposure of cells to hypoxic conditions also resulted in an increase in transepithelial glucose transport. A role for hypoxia-inducible factor (HIF)-1 was suggested by the increase in HIF-1alpha as a result of hypoxia and by the increase in GLUT1 expression following treatment of BeWo with MG-132, a proteasomal inhibitor that increases HIF-1 levels. The function of HIF-1 was confirmed in experiments where the hypoxic upregulation of GLUT1 and GLUT3 was inhibited by antisense HIF-1alpha. In contrast to BeWo cells, hypoxia produced minimal increases in GLUT1 expression in explants; however, treatment with MG-132 did upregulate syncytial basal membrane GLUT1. Our results show that GLUTs are upregulated by hypoxia via a HIF-1-mediated pathway in trophoblast cells and suggest that the GLUT response to hypoxia in vivo will be determined not only by low oxygen tension but also by other factors that modulate HIF-1 levels.

Multiple signalling pathways involved in beta2-adrenoceptor-mediated glucose uptake in rat skeletal muscle cells

1. Beta-adrenoceptor (AR) agonists increase 2-deoxy-[3H]-D-glucose uptake (GU) via beta2-AR in rat L6 cells. The beta-AR agonists, zinterol (beta2-AR) and (-)-isoprenaline, increased cAMP accumulation in a concentration-dependent manner (pEC50=9.1+/-0.02 and 7.8+/-0.02). Cholera toxin (% max increase 141.8+/-2.5) and the cAMP analogues, 8-bromo-cAMP (8Br-cAMP) and dibutyryl cAMP (dbcAMP), also increased GU (196.8+/-13.5 and 196.4+/-17.3%). 2. The adenylate cyclase inhibitor, 2',5'-dideoxyadenosine (50 microM), significantly reduced cAMP accumulation to zinterol (100 nM) (109.7+35.0 to 21.6+4.5 pmol well(-1)), or forskolin (10 microM) (230.1+/-58.0 to 107.2+/-26.3 pmol well(-1)), and partially inhibited zinterol-stimulated GU (217+/-26.3 to 176.1+/-20.4%). The protein kinase A (PKA) inhibitor, 4-cyano-3-methylisoquinoline (100 nM), did not inhibit zinterol-stimulated GU. The PDE4 inhibitor, rolipram (10 microM), increased cAMP accumulation to zinterol or forskolin, and sensitised the GU response to zinterol, indicating a stimulatory role of cAMP in GU. 3. cAMP accumulation studies indicated that the beta2-AR was desensitised by prolonged stimulation with zinterol, but not forskolin, whereas GU responses to zinterol increased with time, suggesting that receptor desensitisation may be involved in GU. Receptor desensitisation was not reversed by inhibition of PKA or Gi. 4. PTX pretreatment (100 ng ml(-1)) inhibited insulin or zinterol-stimulated but not 8Br-cAMP or dbcAMP-stimulated GU. The PI3K inhibitor, LY294002 (1 microM), inhibited insulin- (174.9+/-5.9 to 142.7+/-2.7%) and zinterol- (166.9+/-7.6 to 141.1+/-8.1%) but not 8 Br-cAMP-stimulated GU. In contrast to insulin, zinterol did not cause phosphorylation of Akt. 5. The results suggest that GU in L6 cells involves three mechanisms: (1) an insulin-dependent pathway involving PI3K, (2) a beta2-AR-mediated pathway involving both cAMP and PI3K, and (3) a receptor-independent pathway suggested by cAMP analogues that increase GU independently of PI3K. PKA appears to negatively regulate beta2-AR-mediated GU.

Do glucose transporters have other roles in addition to placental glucose transport during early pregnancy?

Human placenta regulates the transport of maternal molecules to the fetus. It is known that glucose transport occurs via glucose transporters (GLUTs) in the feto-placental unit. Data on the expression of GLUTs during implantation are very scarce. Moreover, the question of how the decidual leukocytes obtain the energy for their activation during implantation mechanism is still under investigation. We studied the distributions of GLUT1, GLUT3, and GLUT4 in tissue sections of first trimester pregnancies the human maternal-fetal interface. GLUT1 was present in apical microvilli of the syncytiotrophoblast, in cytotrophoblast, and in vascular patterns of the villous core, whereas GLUT3 was localized in cytotrophoblasts of placental villi and in some fetal endothelial cells. Moreover, the proliferating cells of the proximal cell columns were also immunopositive for GLUT1 and GLUT3. We did not observe any positive immunoreactivity for GLUT4 in placental and decidual tissues. Essentially, GLUT3 and also to some extent GLUT1 was present in maternal leukocytes and platelets. In conclusion, our results suggest that the glucose taken up via GLUT1 and GLUT3 from the maternal circulation might not only be needed for placental functions but also for successful implantation by trophoblast invasion, proliferation and also by having a role to support energy for maternal leukocytes.

Glucose transporter isoform 4 is expressed in the syncytiotrophoblast of first trimester human placenta

BACKGROUND

Placental glucose transport mechanisms in early pregnancy are poorly understood. The aims of this study were to investigate the expression of glucose transporter (GLUT) isoforms 1, 3 and 4 in first trimester villous tissue, to assess the effects of insulin on glucose uptake and compare them with term.

METHODS

The expression of GLUT isoforms was investigated using immunohistochemistry, Western blot and reverse transcription (RT)-PCR in trophoblast tissue from terminations at 6-13 weeks gestation and term. The effects of insulin (300 ng/ml, 1 h) on glucose uptake were studied in villous fragments.

RESULTS

In the first trimester, GLUT1 and GLUT3 were present in the microvillous membrane and the cytotrophoblast, and GLUT4 in perinuclear membranes in the cytosol of the syncytiotrophoblast (ST). GLUT4 protein (48 kDa) and mRNA were identified in trophoblast homogenates. Whereas GLUT1 was expressed abundantly in term placenta, the expression of GLUT3 and 4 was markedly lower at term compared with first trimester. Insulin increased glucose uptake by 182% (n=6, P<0.05) in first trimester fragments, but not in term fragments.

CONCLUSIONS

The insulin-regulatable GLUT4 is expressed in the cytosol of first trimester ST compatible with a role for GLUT4 in placental glucose transport in early pregnancy. The placental expression pattern of GLUT isoforms in early pregnancy is distinct from that later in pregnancy.

Neurobarrier coupling in the brain: a partner of neurovascular and neurometabolic coupling?

Neurovascular and neurometabolic coupling help the brain to maintain an appropriate energy flow to the neural tissue under conditions of increased neuronal activity. Both coupling phenomena provide us, in addition, with two macroscopically measurable parameters, blood flow and intermediate metabolite fluxes, that are used to dynamically image the functioning brain. The main energy substrate for the brain is glucose, which is metabolized by glycolysis and oxidative breakdown in both astrocytes and neurons. Neuronal activation triggers increased glucose consumption and glucose demand, with new glucose being brought in by stimulated blood flow and glucose transport over the blood-brain barrier. Glucose is shuttled over the barrier by the GLUT-1 transporter, which, like all transporter proteins, has a ceiling above which no further stimulation of the transport is possible. Blood-brain barrier glucose transport is generally accepted as a nonrate-limiting step but to prevent it from becoming rate-limiting under conditions of neuronal activation, it might be necessary for the transport parameters to be adapted to the increased glucose demand. It is proposed that the blood-brain barrier glucose transport parameters are dynamically adapted to the increased glucose needs of the neural tissue after activation according to a neurobarrier coupling scheme. This review presents neurobarrier coupling within the current knowledge on neurovascular and neurometabolic coupling, and considers arguments and evidence in support of this hypothesis.

Hormonal regulation of glucose and system A amino acid transport in first trimester placental villous fragments

Alterations in placental nutrient transfer have been implicated in fetal growth abnormalities. In pregnancies complicated by diabetes and accelerated fetal growth, upregulations of glucose transporter 1 (GLUT1) and amino acid transporter system A have been shown in the syncytiotrophoblast of term placenta. In contrast, intrauterine growth restriction is associated with a downregulation of placental system A transporters. However, underlying mechanisms of transporter regulation are poorly understood, particularly in early pregnancy. In this study, hormonal regulation of placental glucose and system A transporters was investigated. The uptake of 3-O-[methyl-(14)C]-d-glucose was studied in villous fragments isolated from first trimester (6-13 wk of gestation) and term human placenta. Villous fragments were incubated in buffer containing insulin, leptin, cortisol, growth hormone (GH), prolactin, IGF-I, or under hypo/hyperglycemic conditions for 1 h. Subsequently, 3-O-[methyl-(14)C]-D-glucose uptake was measured with and without phloretin for 70 s in first trimester tissue and 20 s in term tissue. Methylaminoisobutyric uptake was measured with and without Na+ for 20 min. Glucose uptake was unaltered by hormones or hypo/hyperglycemia. GH decreased system A activity by 31% in first trimester (P < 0.05). The uptake of glucose was 50% higher in term compared with first trimester fragments and increased markedly between 6 and 13 wk of gestation (P < 0.05). We conclude that placental glucose transporter activity is not regulated by short exposures to the hormones or glucose concentrations tested. In contrast to term placental villous fragments, system A activity was not regulated by insulin or leptin in first trimester but was downregulated by GH.

Characterization of an organic anion transport system in a placental cell line

Transporters within the placenta play a crucial role in the distribution of nutrients and xenobiotics across the maternal-fetal interface. An organic anion transport system was identified on the apical membrane of the rat placenta cell line HRP-1, a model for the placenta barrier. The apical uptake of 3H-labeled organic anion estrone sulfate in HRP-1 cells was saturable (Km = 4.67 microM), temperature and Na+ dependent, Li+ tolerant, and pH sensitive. The substrate specificity of the transport system includes various steroid sulfates, such as beta-estradiol 3,17-disulfate, 17 beta-estradiol 3-sulfate, and dehydroepiandrosterone 3-sulfate (DHEAS) but does not include taurocholate, p-aminohippuric acid (PAH), and tetraethylammonium. Preincubation of HRP-1 cells with 8-bromo-cAMP (a cAMP analog) and forskolin (an adenylyl cyclase activator) acutely stimulated the apical transport activity. This stimulation was further enhanced in the presence of IBMX (a phosphodiesterase inhibitor). Together these data show that the apical membrane of HRP-1 cells expresses an organic anion transport system that is regulated by cellular cAMP levels. This transport system appears to be different from the known taurocholate-transporting organic anion-transporting polypeptides and PAH-transporting organic anion transporters, both of which also mediate the transport of estrone sulfate and DHEAS.

Peroxisome proliferator-activated receptor gamma thiazolidinedione agonists increase glucose metabolism in astrocytes

Activation of peroxisome proliferator-activated receptors (PPARs) can regulate brain physiology and provide protection in models of neurological disease; however, neither their exact targets nor mechanisms of action in brain are known. In many cells, PPAR gamma agonists increase glucose uptake and metabolism. Because astrocytes store glucose and provide lactate to neurons on demand, we tested effects of PPAR gamma agonists on astroglial glucose metabolism. Incubation of cortical astrocytes with the PPAR gamma thiazolidinedione (TZD) agonist pioglitazone (Pio) significantly increased glucose consumption in a time- and dose-dependent manner, with maximal increase of 36% observed after 4 h in 30 microm Pio. Pio increased 2-deoxy-glucose uptake because of increased flux through the type 1 glucose transporter. However, at this time point Pio did not increase type 1 glucose transporter expression, nor were its effects blocked by transcriptional or translational inhibitors. Pio also increased astrocyte lactate production as soon as 3 h after incubation. These effects were replicated by other TZDs; however, the order of efficacy (troglitazone > pioglitazone > rosiglitazone) suggests that effects were not mediated via PPAR gamma activation. TZDs increased astrocyte cAMP levels, and their glucose modifying effects were reduced by protein kinase A inhibitors. TZDs inhibited state III respiration in isolated brain mitochondria, whereas in astrocytes they caused mitochondrial membrane hyperpolarization. Pio protected astrocytes against hypoglycemia-induced cell death. Finally, glucose uptake was modified in brain sections prepared from Pio-fed rats. These results demonstrate that TZDs modify astrocyte metabolism and mitochondrial function, which could be beneficial in neurological conditions where glucose availability is reduced.

Immunolocalization of glucose transporter 1 and 3 in the placenta: application to cytodiagnosis of Papanicolaou smear

A positive immunostaining for glucose transporter 1 (GLUT1) was exclusively localized in microvilli on the free surface of syncytiotrophoblasts in the placenta. An enhanced immunoreaction for glucose transporter 3 (GLUT3) was elicited in the cell membrane of intermediate trophoblasts and cytotrophoblasts. Neither GLUT1 nor GLUT3 was positive in decidual cells and epithelial components from cervical dysplasia and carcinoma in situ. Cervicovaginal smears from six pregnant women containing atypical cells of unknown origin were subjected to immunocytochemical testing with antibodies against GLUT1 and GLUT3. Atypical cells in smears from two pregnant women were found to be positive for GLUT3 while no specific immunoreaction for GLUT1 was elicited, indicating their origin from either intermediate trophoblasts or cytotrophoblasts. Through the use of antibodies against vimentin and cytokeratin 17, GLUT3-negative atypical cells were further sorted into decidual cells and epithelial components from cervical dysplasia, respectively.

Expression and regulation of 4F2hc and hLAT1 in human trophoblasts

The neutral amino acid transport system L is a sodium-independent transport system in human placenta and choriocarcinoma cells. Recently, it was found that the heterodimer composed of hLAT1 (a light-chain protein) and 4F2 heavy chain (4F2hc), a type II transmembrane glycoprotein, is responsible for system L amino acid transport. We found that the mRNAs of 4F2hc and hLAT1 were expressed in the human placenta and a human choriocarcinoma cell line. The levels of the 4F2hc and hLAT1 proteins in the human placenta increased at full term compared with those at midtrimester. Immunohistochemical data showed that these proteins were localized mainly in the placental apical membrane. Data from leucine uptake experiments, Northern blot analysis, and immunoblot analysis showed that this transport system was partially regulated by protein kinase C and calcium ionophore in the human choriocarcinoma cell line. Our results suggest that the heterodimer of 4F2hc and hLAT1 may play an important role in placental amino acid transport system L.

Placental corticotrophin-releasing hormone, local effects and fetomaternal endocrinology

The human placenta produces corticotrophin-releasing hormone (CRH) in exponentially increasing amounts during pregnancy with peak levels during labour. CRH in human pregnancy appears to be involved in many aspects of pregnancy including placental bloodflow, placental prostaglandin production, myornetrial function, fetal pituitary and adrenal function and the maternal stress axis. Since fetal cortisol levels are associated with pulmonary development and maturity, placental CRH may have an indirect role in fetal development.Although the precise role of placental CRH in the regulation of gestational length and timing of parturition is unclear it appears to be involved in a placental clock. While glucocorticoids inhibit hypothalamic CRH production they stimulate CRH gene expression in the placenta.This difference may allow the fetal and maternal stress axes to influence this placental clock.Maternal CRH levels are elevated in many pathological conditions of pregnancy where fetal well-being is compromised, and in these situations it may act to maintain a stable intrauterine environment. Therefore, CRH appears to link placental function, maternal well-being, fetal well-being and fetal development to the duration of gestation and the timing of parturition.

Involvement of nuclear transcription factor Sp1 in regulating glucose transporter-1 gene expression during rat trophoblast differentiation

Glucose transporter-1 (GLUT1) is important in placental glucose transport. However, the mechanism of regulation of placental GLUT1 expression remains to be elucidated. We show here that the level of GLUT1 protein in rat choriocarcinoma cells (Rcho-1) decreased during differentiation. To analyze the regulatory mechanism of rat GLUT1 (rGLUT1) gene expression, we transfected rGLUT1 promoter-chloramphenicol acetyltransferase constructs into Rcho-1 cells. Deletion analysis of the rGLUT1 promoter suggested that the region -76/-53 bp was essential for basal transcriptional activity. Electrophoretic mobility shift assays showed that transcription factors Sp1 and Sp3 bound two GC boxes in the region -99/-33 bp of the rGLUT1 promoter. Mutation analysis of the Sp1 binding sites revealed that the promoter-proximal site located between -76 and -53 bp was essential for basal rGLUT1 promoter activity. Furthermore, the decreased level of GLUT1 may result from a decreased level of Sp1 during differentiation. These findings suggest that Sp1 is involved in the regulation of rGLUT1 gene expression during rat trophoblast differentiation.