Glucose transporter GLUT3 in the rat placental barrier: a possible machinery for the transplacental transfer of glucose

Cannabidiol Exposure During Rat Pregnancy Leads to Labyrinth-Specific Vascular Defects in the Placenta and Reduced Fetal Growth

Introduction: Cannabis use is increasing among pregnant people, and cannabidiol (CBD), a constituent of cannabis, is often perceived as "natural" and "safe" as it is non-intoxicating. In utero, cannabis exposure is associated with negative health outcomes, including fetal growth restriction (FGR). The placenta supplies oxygen and nutrients to the fetus, and alterations in placental development can lead to FGR. While there has been some investigation into the effects of Δ9-THC, there has been limited investigation into the impacts of in utero gestational CBD exposure on the placenta. Methods: This study used histological and transcriptomic analysis of embryonic day (E)19.5 rat placentas from vehicle and CBD (3 mg/kg intraperitoneal injection) exposed pregnancies (E6.5-18.5). Results: The study revealed that pups from CBD-exposed pregnancies were 10% smaller, with the placentae displaying a decreased fetal blood space perimeter-to-area ratio. The transcriptomic analysis supported compromised angiogenesis and blood vessel formation with downregulated biological processes, including tube morphogenesis, angiogenesis, blood vessel morphogenesis, blood vessel development and vasculature development. Further, the CBD-exposed placentas displayed changed expression of glucose transporters (decreased GLUT1 and GR expression and increased GLUT3 expression). Transcriptomic analysis further revealed upregulated biological processes associated with metabolism. Finally, histological and transcriptomic analysis revealed altered cell populations within the placenta, specifically to syncytiotrophoblast layer II and endothelial cells. Conclusion: Together these results suggest that the structural changes in CDB-exposed placentae, including the altered expression of nutrient transporters and the changes to the placental fetal vasculature, may underlie the reduced fetal growth.

Maternal hypothyroidism in rats impairs placental nutrient transporter expression, increases labyrinth zone size, and impairs fetal growth

INTRODUCTION

Hypothyroidism during pregnancy is associated with fetal growth restriction (FGR). FGR is commonly caused by placental insufficiency and yet the role of hypothyroidism in placental regulation of fetal growth is unknown. This study aimed to investigate the effects of maternal hypothyroidism on placental nutrient transporter expression, placental morphology, and placental metabolism.

METHODS

Hypothyroidism was induced in female Sprague-Dawley rats by adding methimazole (MMI) to drinking water at moderate (MOD, MMI at 0.005% w/v) and severe (SEV, MMI at 0.02% w/v) doses from one week prior to pregnancy and throughout gestation. Maternal and fetal tissues were collected on embryonic day 20 (E20).

RESULTS

Hypothyroidism reduced fetal weight (PTrt<0.001) despite causing fetal hyperglycaemia (PTrt = 0.016). Placental weight was not affected by hypothyroidism however placental efficiency was reduced (PTrt<0.001), as was the junctional zone (JZ):labyrinth zone (LZ) weight ratio (PTrt = 0.005). LZ glycogen content was increased (PTrt = 0.029) and while mRNA expression of glucose transporters was reduced by hypothyroidism, only GLUT1 protein expression was reduced in male LZs. Maternal hypothyroidism reduced mitochondrial content (PTrt = 0.031), particularly in SEV males relative to CON males (P = 0.004). Protein expression of Complex V (P < 0.001) and Complex III (P = 0.002) of the electron transport chain were also reduced in males. Maternal hypothyroidism reduced LZ (PTrt<0.001) and fetal plasma triglycerides (P = 0.019) while fetal free fatty acids and the expression of LZ lipid transporters was not affected.

DISCUSSION

Overall, maternal hypothyroidism may lead to FGR through reduced maternal T4 availability, changes to placental morphology, altered nutrient transporter expression and sex-specific effects on placental metabolism. Changes to LZ glycogen and triglyceride stores as well as mitochondrial content suggest a metabolic shift from oxidative phosphorylation to anaerobic glycolysis in males. These changes also likely impact fetal substrate availability and therefore fetal growth.

Effects of cyclophosphamide on rat placental development

We examined the morphological effects of cyclophosphamide (CPA) on placental development in pregnant rats. CPA was administered as a single dose to pregnant rats intraperitoneally at 0 mg/kg (the control group), 25 mg/kg on gestation day (GD) 12 (the CPA GD 12-treated group), and 25 mg/kg on GD 14 (the CPA GD 14-treated group). The fetal and placental weight decreased in the CPA-treated groups, complete fetal resorption from GD 17 onwards in the CPA GD 12-treated group, and external malformations in the CPA GD 14-treated group. Histopathologically, CPA induced apoptosis and/or cell proliferation inhibition in each part of the placenta. In the labyrinth zone, syncytiotrophoblasts were selectively reduced, resulting in a small placenta. In the basal zone, the number of spongiotrophoblasts was reduced, resulting in hypoplasia of glycogen cell islands. In addition, a small number of interstitial trophoblasts invaded the metrial gland from the basal zone on GD 15. The severity of these lesions was higher in the CPA GD 12-treated group than in the CPA GD 14-treated group. In the metrial gland, although the number of uterine natural killer cells was reduced, metrial gland development was not affected.

Effects of Stevioside on the Expressions of GLUT 1, GLUT 3, and GLUT 4 Proteins in Diabetic Rat Placenta

The placenta provides maternal-fetal nutrient transport. The primary source of energy for fetus development is glucose and maternal-fetal glucose transport occurs through glucose transporters (GLUTs). Stevioside, a component of Stevia rebaudiana Bertoni, is used for medicinal and commercial purposes. We aim to determine the effects of stevioside on GLUT 1, GLUT 3, and GLUT 4 proteins expressions in diabetic rat placentas. The rats are divided into four groups. A single dose of streptozotocin (STZ) is administered to form the diabetic groups. Pregnant rats receive stevioside to form the stevioside and diabetic + stevioside groups. According to immunohistochemistry results, GLUT 1 protein is found in both the labyrinth and junctional zones. GLUT 3 protein is limited in the labyrinth zone. GLUT 4 protein is detected in trophoblast cells. According to Western blotting results, on the 15th and 20th days of pregnancy, there is no difference in the expression of GLUT 1 protein between groups. On the 20th day of pregnancy, the expression of GLUT 3 protein in the diabetic group is statistically higher compared to the control group. On the 15th day and 20th day of pregnancy, the expression of GLUT 4 protein in the diabetic group is statistically lower compared to the control group. Insulin levels in blood samples derived from rat abdominal aorta are determined by the ELISA method. According to the ELISA results, there is no difference in insulin protein concentration between groups. Stevioside treatment reduces GLUT 1 protein expression under diabetic conditions.

Transplacental transfer of acetaminophen in pregnant rats

Acetaminophen is among the most widely used analgesics; however, the proportion and mechanism of transplacental transfer of unbound acetaminophen with actual pharmacological activity remain unknown. Our hypothesis is that acetaminophen gradually penetrates the blood-placenta barrier to reach the fetus. A multiple microdialysis coupled to liquid chromatography with photodiode array detection method was developed to monitor acetaminophen levels in the maternal blood, placenta, fetus, and amniotic fluid of a pregnant rat and investigate this hypothesis. The pharmacokinetic data indicates that acetaminophen exhibits a nonlinear behavior in the maternal blood within the dosage regimen of 100 and 300 mg/kg. In addition, acetaminophen penetrates the placenta, fetus, and amniotic fluid during treatment. The transplacental transfer ratio represented by the area under the concentration curve (AUC) ratio for the conceptus (the collective term for the fetus, placenta, and amniotic fluid) and maternal blood (AUC_tissue/AUC_blood) was approximately 11-23 % after acetaminophen (100 and 300 mg/kg) administration. However, the transporter of multidrug resistance-associated protein (MRP) inhibitor MK-571 did not significantly change the transplacental transfer ratio. This basic study provides constructive information for the clinical application of acetaminophen in pregnant women.

Metabolic Responses of Dietary Fiber during Heat Stress: Effects on Reproductive Performance and Stress Level of Gestating Sows

Heat stress is an important issue, and the addition of fiber to the diet is an option in modifying intestinal health. This study evaluated the effect of acid detergent fiber (ADF) levels on reproductive performance, intestinal integrity, and metabolism of gestating sows, and its carry-over effect on the lactation period during heat stress. The diets included 4.3% (Low fiber; LF), 5.4% (Medium fiber; MF), and 6.5% (High fiber; HF) ADF. Sows fed the HF diet showed a lower respiratory rate, hair cortisol concentration, and farrowing duration compared with the LF treatment. The HF diet increased the pyruvate, citrate cycle, glyoxylate, dicarboxylate, and thiamine metabolism compared with the MF. The concentration of acetate and total short-chain fatty acids were increased in the sows fed the HF diet. The gene expression of glucose transporter 3 and glucose transporter 4 was increased in the HF treatment. The gene expression of heat shock protein 70 was decreased in the HF treatment. The HF diet during gestation increased feed intake, constipation index, piglet weight, and litter weight compared with the LF. Sows in the LF treatment showed the greatest digestibility of crude protein and the lowest digestibility of ADF. In conclusion, a 6.5% ADF level is recommended for gestating sows during heat stress.

Maternal-fetal outcomes of exercise applied in rats with mild hyperglycemia after embryonic implantation

BACKGROUND

Exercise is commonly recommended to control hyperglycemia, including during pregnancy. We conducted this study to understand the potential benefits and risks of exercise during pregnancy of women with diabetes. Specifically, we evaluated the effects of swimming on a diabetic rat during pregnancy and assayed maternal-fetal parameters.

METHODS

Diabetes was induced in the female newborn from Wistar rats by the streptozotocin administration on first postnatal day. At 110 days of life, after confirm mild symptoms of diabetes, the rats were mated and randomly distributed into four experimental groups (minimum of 13 animals/group): Control (C)-nondiabetic animals without swimming; Control and Exercise (CEx)-nondiabetic animals submitted to swimming; Mild Diabetic (MD)-diabetic animals without swimming; Mild Diabetic and Exercise (MDEx)-diabetic animals submitted to swimming. The swimming program was performed from day 7 to 21 of pregnancy. Maternal parameters were evaluated during the pregnancy period. On day 21 of pregnancy, the rats were sacrificed and maternal and fetal parameters analyzed.

RESULTS

There are no alterations in body weight, food consumption, water intake, and reproductive outcomes among the groups. The swimming program did not normalize maternal glycemia and other biochemical biomarkers. The diabetes and exercise combination increased organ weight. The fetuses born to these exercising diabetic rats had reduced fetal weight and increased skeletal anomalies (mainly incomplete ossification of sternebra).

CONCLUSION

The intense swimming exercise imposed on female rats during pregnancy impaired maternal metabolic repercussions, contributing to intrauterine growth restriction and fetal skeletal anomalies.

Sex-specific effects of leptin administration to pregnant mice on the placentae and the metabolic phenotypes of offspring

Obesity during pregnancy has been shown to increase the risk of metabolic diseases in the offspring. However, the factors within the maternal milieu which affect offspring phenotypes and the underlying mechanisms remain unknown. The adipocyte hormone leptin plays a key role in regulating energy homeostasis and is known to participate in sex‐specific developmental programming. To examine the action of leptin on fetal growth, placental gene expression and postnatal offspring metabolism, we injected C57BL mice with leptin or saline on gestational day 12 and then measured body weights (BWs) of offspring fed on a standard or obesogenic diet, as well as mRNA expression levels of insulin‐like growth factors and glucose and amino acid transporters. Male and female offspring born to leptin‐treated mothers exhibited growth retardation before and a growth surge after weaning. Mature male offspring, but not female offspring, exhibited increased BWs on a standard diet. Leptin administration prevented the development of hyperglycaemia in the obese offspring of both sexes. The placentas of the male and female foetuses differed in size and gene expression, and leptin injection decreased the fetal weights of both sexes, the placental weights of the male foetuses and placental gene expression of the GLUT1 glucose transporter in female foetuses. The data suggest that mid‐pregnancy is an ontogenetic window for the sex‐specific programming effects of leptin, and these effects may be exerted via fetal sex‐specific placental responses to leptin administration.

Interpretation of Fiber Supplementation on Offspring Testicular Development in a Pregnant Sow Model from a Proteomics Perspective

To study the effects of maternal fiber supplementation during pregnancy on the testicular development of male offspring and its possible mechanisms, 36 sows (Landrace × Yorkshire) were allocated to either a control diet (n = 18) or a fiber diet (the control diet supplemented with 22.60 g/kg inulin and 181.60 g/kg cellulosic; n = 18) during pregnancy. The body and testes weight of the offspring, 7-day-old piglets, was recorded. Testes were collected for further analyses. Results showed that the testicular organ index and the number of spermatogonia in single seminiferous tubule were higher in piglets from the fiber group than from the control group (p < 0.05). In addition, a significant increase in the concentration of glucose, lactate, and lipids in the testes was found in the fiber group (p < 0.05). Proteomic analysis suggested that there were notable differences in glucolipid transport and metabolism, oxidation, and male reproduction-related proteins expression between the two groups (p < 0.05). Results revealed that the most enriched signaling pathways in the fiber group testes included starch and sucrose metabolism, fatty acid metabolism, glutathione metabolism, and the renin-angiotensin system. mRNA expression analyzes further confirmed the importance of some signaling pathways in maternal fiber nutrition regulating offspring testicular development. Our results shed new light on the underlying molecular mechanisms of maternal fiber nutrition on offspring testicular development and provided a valuable insight for future explorations of the effect of maternal fiber nutrition on man reproduction.

Early life high-fat diet exposure maintains glucose tolerance and insulin sensitivity with a fatty liver and small brain size in the adult offspring

Diet during pregnancy has long lasting consequences on the offspring, warranting a study on the impact of early exposure to a high fat diet on the adult offspring. We hypothesized that a prenatal n-6 enriched diet will have adverse metabolic outcomes on the adult offspring that may be reversed with a postnatal n-3 enriched diet. To test this hypothesis, we examined the adult offspring from three groups: (1) n-6 group: during gestation and lactation, dams consumed an n-6 polyunsaturated fatty acid enriched diet, (2) n-3 group: gestational n-6 diet was followed by an n-3 enriched diet during lactation, and (3) a control (CD) group that received standard diet throughout gestation and lactation. Offspring from all groups weaned to a control diet ad libitum. Beginning at postnatal day 2 (P < .03) and persisting at 360 days in males (P < .04), an increase in hypothalamic AgRP expression occurred in the n-6 and n-3 groups, with an increase in food intake (P = .01), and the n-3 group displaying lower body (P < .03) and brain (P < .05) weights. At 360 days, the n-6 and n-3 groups remained glucose tolerant and insulin sensitive, with increased phosphorylated-AMP-activated protein kinase (P < .05). n-6 group developed hepatic steatosis with reduced hepatic reflected as higher plasma microRNA-122 (P < .04) that targets pAMPK. We conclude that early life exposure to n-6 and n-3 led to hypothalamic AgRP-related higher food intake, with n-6 culminating in a fatty liver partially mitigated by postnatal n-3. While both diets preserved glucose tolerance and insulin sensitivity, postnatal n-3 displayed detrimental effects on the brain.

Morphology and physiology of rat placenta for toxicological evaluation

The placenta plays a pivotal role in fetal growth, and placental dysfunction and injury are associated with embryo/fetal toxicity. Histological examination of the rat placenta for safety evaluation provides valuable clues to the mechanisms of this toxicity. However, the placenta has specific and complex biological features unlike those of other organs, and placental structure dramatically changes depending on the time during the gestation period. Thus, time-dependent histopathological examination of the rat placenta should be performed based on the understanding of normal developmental changes in morphology and function. The placentas of rats and humans are both anatomically classified as discoid and hemochorial types. However, there are differences between rats and humans in terms of placental histological structure, the fetal-maternal interface, and the function of the yolk sac. Therefore, extrapolation of placental toxicity from rats to humans should be done cautiously in the evaluation of risk factors. This review describes the development, morphology, physiology, and toxicological features of the rat placenta and the differences between the rat and human placenta to enable accurate evaluation of reproductive and developmental toxicity in studies.

Neural Deletion of Glucose Transporter Isoform 3 Creates Distinct Postnatal and Adult Neurobehavioral Phenotypes

We created a neural-specific conditional murine glut3 (Slc2A3) deletion (glut3 ^{flox/flox/nestin-Cre+}) to examine the effect of a lack of Glut3 on neurodevelopment. Compared with age-matched glut3 ^flox/flox = WT and heterozygotes (glut3 ^{flox/+/nestin-Cre+}), we found that a >90% reduction in male and female brain Glut3 occurred by postnatal day 15 (PN15) in glut3 ^{flox/flox/nestin-Cre+} This genetic manipulation caused a diminution in brain weight and cortical thickness at PN15, a reduced number of dendritic spines, and fewer ultrasonic vocalizations. Patch-clamp recordings of cortical pyramidal neurons revealed increased frequency of bicuculline-induced paroxysmal discharges as well as reduced latency, attesting to a functional synaptic and cortical hyperexcitability. Concomitant stunting with lower glucose concentrations despite increased milk intake shortened the lifespan, failing rescue by a ketogenic diet. This led to creating glut3 ^{flox/flox/CaMK2α-Cre+} mice lacking Glut3 in the adult male limbic system. These mice had normal lifespan, displayed reduced IPSCs in cortical pyramidal neurons, less anxiety/fear, and lowered spatial memory and motor abilities but heightened exploratory and social responses. These distinct postnatal and adult phenotypes, based upon whether glut3 gene is globally or restrictively absent, have implications for humans who carry copy number variations and present with neurodevelopmental disorders.SIGNIFICANCE STATEMENT Lack of the key brain-specific glucose transporter 3 gene found in neurons during early postnatal life results in significant stunting, a reduction in dendritic spines found on neuronal processes and brain size, heightened neuronal excitability, along with a shortened lifespan. When occurring in the adult and limited to the limbic system alone, lack of this gene in neurons reduces the fear of spatial exploration and socialization but does not affect the lifespan. These features are distinct heralding differences between postnatal and adult phenotypes based upon whether the same gene is globally or restrictively lacking. These findings have implications for humans who carry copy number variations pertinent to this gene and have been described to present with neurodevelopmental disorders.

Transplacental Nutrient Transport Mechanisms of Intrauterine Growth Restriction in Rodent Models and Humans

Although the causes of intrauterine growth restriction (IUGR) have been intensively investigated, important information is still lacking about the role of the placenta as a link from adverse maternal environment to adverse pregnancy outcomes of IUGR and preterm birth. IUGR is associated with an increased risk of cardiovascular, metabolic, and neurological diseases later in life. Determination of the most important pathways that regulate transplacental transport systems is necessary for identifying marker genes as diagnostic tools and for developing drugs that target the molecular pathways. Besides oxygen, the main nutrients required for appropriate fetal development and growth are glucose, amino acids, and fatty acids. Dysfunction in transplacental transport is caused by impairments in both placental morphology and blood flow, as well as by factors such as alterations in the expression of insulin-like growth factors and changes in the mTOR signaling pathway leading to a change in nutrient transport. Animal models are important tools for systematically studying such complex events. Debate centers on whether the rodent placenta is an appropriate tool for investigating the alterations in the human placenta that result in IUGR. This review provides an overview of the alterations in expression and activity of nutrient transporters and alterations in signaling associated with IUGR and compares these findings in rodents and humans. In general, the data obtained by studies of the various types of rodent and human nutrient transporters are similar. However, direct comparison is complicated by the fact that the results of such studies are controversial even within the same species, making the interpretation of the results challenging. This difficulty could be due to the absence of guidelines of the experimental design and, especially in humans, the use of trophoblast cell culture studies instead of clinical trials. Nonetheless, developing new therapy concepts for IUGR will require the use of animal models for gathering robust data about mechanisms leading to IUGR and for testing the effectiveness and safety of the intervention among pregnant women.

Expression of apoptosis-regulatory genes in the hippocampus of rat neonates born to mothers with diabetes

Diabetes during pregnancy impairs the development of the central nervous system (CNS) and causes cognitive and behavioral abnormalities in offspring. However, the exact mechanism by which the maternal diabetes affects the development of the brain remains to be elucidated. The aim of the present study was to investigate the effects of maternal diabetes in pregnancy on the expression of Bcl-2 and Bax genes and the numerical density of degenerating dark neurons (DNs) in the hippocampus of offspring at the first postnatal two weeks. Wistar female rats were maintained diabetic from a week before pregnancy through parturition and male offspring was sacrificed at P0, P7, and P14. Our findings demonstrated a significant down-regulation in the hippocampal expression of Bcl-2 in the diabetic group newborns (P < 0.05). In contrast, the mRNA expression of Bax was markedly up-regulated in the offspring born to diabetic dams at all of studied time-points (P < 0.05). Moreover, we found a striking increase in the numerical density of DNs in the various subfields of hippocampus of diabetic group pups (P < 0.05). The results of the present study revealed that maternal hyperglycemia during gestational period may result in disturbances in the expression of Bcl-2 and Bax genes as two important genes in neuronal apoptosis regulation and induces the production of DNs in the developing hippocampus of neonatal rats. These disturbances may be a reason for the cognitive, structural, and behavioral anomalies observed in offspring born to diabetic mothers. Furthermore, the control of maternal glycaemia by insulin administration in most cases normalized these negative impacts.

Synaptogenesis in the Cerebellum of Offspring Born to Diabetic Mothers

There is increasing evidence that maternal diabetes mellitus during the pregnancy is associated with a higher risk of neurodevelopmental and neurofunctional anomalies including motor dysfunctions, learning deficits, and behavioral problems in offspring. The cerebellum is a part of the brain that has long been recognized as a center of movement balance and motor coordination. Moreover, recent studies in humans and animals have also implicated the cerebellum in cognitive processing, sensory discrimination, attention, and learning and memory. Synaptogenesis is one of the most crucial events during the development of the central nervous system. Synaptophysin (SYP) is an integral membrane protein of synaptic vesicles and is considered to be a marker for synaptic density and synaptogenesis. Here, we review the manuscripts focusing on the negative impacts of maternal diabetes in pregnancy on the expression or localization of SYP in the developing cerebellar cortex. We believe that the alteration in synaptogenesis or synapse density may be part of the cascade of events through which diabetes in pregnant women affects the newborn's cerebellum.

Altered expression and localization of synaptophysin in developing cerebellar cortex of neonatal rats due to maternal diabetes mellitus

There is sufficient evidence that diabetes during pregnancy is associated with a higher risk of neurodevelopmental anomalies including learning deficits, behavioral problems and motor dysfunctions in the offspring. Synaptophysin (SYP) is an integral membrane protein of synaptic vesicles and is considered as a marker for synaptogenesis and synaptic density. This study aimed to examine the effects of maternal diabetes in pregnancy on the expression and localization of SYP in the developing rat cerebellum. Wistar female rats were maintained diabetic from a week before pregnancy through parturition and male offspring was euthanized at postnatal day (P) 0, 7, and 14. The results revealed a significant down-regulation in the mRNA expression of SYP in the offspring born to diabetic animals at both P7 and P14 (P < 0.05 each). One week after birth, there was a significant reduction in the localization of SYP expression in the external granular (EGL) and in the molecular (ML) layers of neonates born to diabetic animals (P < 0.05 each). We also found a marked decrease in the expression of SYP in all of the cerebellar cortical layers of STZ-D group pups at P14 (P < 0.05 each). Moreover, our results revealed no significant changes in either expression or localization of SYP in insulin-treated group pups when compared with the controls (P ≥ 0.05 each). The present study demonstrated that maternal diabetes has adverse effects on the synaptogenesis in the offspring's cerebellum. Furthermore, the rigid maternal blood glucose control in the most cases normalized these negative impacts.

Stereological study of the effects of maternal diabetes on cerebellar cortex development in rat

Diabetes during pregnancy is associated with the deficits in balance and motor coordination and altered social behaviors in offspring. In the present study, we have investigated the effect of maternal diabetes and insulin treatment on the cerebellar volume and morphogenesis of the cerebellar cortex of rat neonates during the first two postnatal weeks. Sprague Dawley female rats were maintained diabetic from a week before pregnancy through parturition. At the end of pregnancy, the male offspring euthanized on postnatal days (P) 0, 7, and 14. Cavalieri's principle and fractionator methods were used to estimate the cerebellar volume, the thickness and the number of cells in the different layers of the cerebellar cortex. In spite of P0, there was a significant reduction in the cerebellar volume and the thickness of the external granule, molecular, and internal granule layers between the diabetic and the control animals. In diabetic group, the granular and purkinje cell densities were increased at P0. Moreover, the number of granular and purkinje cells in the cerebellum of diabetic neonates was reduced in comparison with the control group at P7 and P14. There were no significant differences in either the volume and thickness or the number of cells in the different layers of the cerebellar cortex between the insulin-treated diabetic group and controls. Our data indicate that diabetes in pregnancy disrupts the morphogenesis of cerebellar cortex. This dysmorphogenesis may be part of the cascade of events through which diabetes during pregnancy affects motor coordination and social behaviors in offspring.

Prenatal Exposure to Sodium Arsenite Alters Placental Glucose 1, 3, and 4 Transporters in Balb/c Mice

Inorganic arsenic (iAs) exposure induces a decrease in glucose type 4 transporter (GLUT4) expression on the adipocyte membrane, which may be related to premature births and low birth weight infants in women exposed to iAs at reproductive age. The aim of this study was to analyze the effect of sodium arsenite (NaAsO2) exposure on GLUT1, GLUT3, and GLUT4 protein expression and on placental morphology. Female Balb/c mice (n = 15) were exposed to 0, 12, and 20 ppm of NaAsO2 in drinking water from 8th to 18th day of gestation. Morphological changes and GLUT1, GLUT3, and GLUT4 expression were evaluated in placentas by immunohistochemical and image analysis and correlated with iAs and arsenical species concentration, which were quantified by atomic absorption spectroscopy. NaAsO2 exposure induced a significant decrease in fetal and placental weight (P < 0.01) and increases in infarctions and vascular congestion. Whereas GLUT1 expression was unchanged in placentas from exposed group, GLUT3 expression was found increased. In contrast, GLUT4 expression was significantly lower (P < 0.05) in placentas from females exposed to 12 ppm. The decrease in placental GLUT4 expression might affect the provision of adequate fetal nutrition and explain the low fetal weight observed in the exposed groups.

Essential role of the ERK/MAPK pathway in blood-placental barrier formation

The mammalian genome contains two ERK/MAP kinase kinase genes, Map2k1 and Map2k2, which encode dual-specificity kinases responsible for ERK activation. Loss of Map2k1 function in mouse causes embryonic lethality due to placental defects, whereas Map2k2 mutants have a normal lifespan. The majority of Map2k1(+/-) Map2k2(+/-) embryos die during gestation from the underdevelopment of the placenta labyrinth, demonstrating that both kinases are involved in placenta formation. Map2k1(+/-) Map2k2(+/-) mutants show reduced vascularization of the labyrinth and defective formation of syncytiotrophoblast layer II (SynT-II) leading to the accumulation of multinucleated trophoblast giant cells (MTGs). To define the cell type-specific contribution of the ERK/MAPK pathway to placenta development, we performed deletions of Map2k1 function in different Map2k1 Map2k2 allelic backgrounds. Loss of MAP kinase kinase activity in pericytes or in allantois-derived tissues worsens the MTG phenotype. These results define the contribution of the ERK/MAPK pathway in specific embryonic and extraembryonic cell populations for normal placentation. Our data also indicate that MTGs could result from the aberrant fusion of SynT-I and -II. Using mouse genetics, we demonstrate that the normal development of SynT-I into a thin layer of multinucleated cells depends on the presence of SynT-II. Lastly, the combined mutations of Map2k1 and Map2k2 alter the expression of several genes involved in cell fate specification, cell fusion and cell polarity. Thus, appropriate ERK/MAPK signaling in defined cell types is required for the proper growth, differentiation and morphogenesis of the placenta.

Prolonged endoplasmic reticulum stress alters placental morphology and causes low birth weight

The role of endoplasmic reticulum (ER) stress in pregnancy remains largely unknown. Pregnant mice were subcutaneously administered tunicamycin (Tun), an ER stressor, as a single dose [0, 50, and 100 μg Tun/kg/body weight (BW)] on gestation days (GDs) 8.5, 12.5, and 15.5. A high incidence (75%) of preterm delivery was observed only in the group treated with Tun 100 μg/kg BW at GD 15.5, indicating that pregnant mice during late gestation are more susceptible to ER stress on preterm delivery. We further examined whether prolonged in utero exposure to ER stress affects fetal development. Pregnant mice were subcutaneously administered a dose of 0, 20, 40, and 60 μg Tun/kg from GD 12.5 to 16.5. Tun treatment decreased the placental and fetal weights in a dose-dependent manner. Histological evaluation showed the formation of a cluster of spongiotrophoblast cells in the labyrinth zone of the placenta of Tun-treated mice. The glycogen content of the fetal liver and placenta from Tun-treated mice was lower than that from control mice. Tun treatment decreased mRNA expression of Slc2a1/glucose transporter 1 (GLUT1), which is a major transporter for glucose, but increased placental mRNA levels of Slc2a3/GLUT3. Moreover, maternal exposure to Tun resulted in a decrease in vascular endothelial growth factor receptor-1 (VEGFR-1), VEGFR-2, and placental growth factor. These results suggest that excessive and exogenous ER stress may induce functional abnormalities in the placenta, at least in part, with altered GLUT and vascular-related gene expression, resulting in low infant birth weight.

Role of monosaccharide transport proteins in carbohydrate assimilation, distribution, metabolism, and homeostasis

The facilitated diffusion of glucose, galactose, fructose, urate, myoinositol, and dehydroascorbicacid in mammals is catalyzed by a family of 14 monosaccharide transport proteins called GLUTs. These transporters may be divided into three classes according to sequence similarity and function/substrate specificity. GLUT1 appears to be highly expressed in glycolytically active cells and has been coopted in vitamin C auxotrophs to maintain the redox state of the blood through transport of dehydroascorbate. Several GLUTs are definitive glucose/galactose transporters, GLUT2 and GLUT5 are physiologically important fructose transporters, GLUT9 appears to be a urate transporter while GLUT13 is a proton/myoinositol cotransporter. The physiologic substrates of some GLUTs remain to be established. The GLUTs are expressed in a tissue specific manner where affinity, specificity, and capacity for substrate transport are paramount for tissue function. Although great strides have been made in characterizing GLUT-catalyzed monosaccharide transport and mapping GLUT membrane topography and determinants of substrate specificity, a unifying model for GLUT structure and function remains elusive. The GLUTs play a major role in carbohydrate homeostasis and the redistribution of sugar-derived carbons among the various organ systems. This is accomplished through a multiplicity of GLUT-dependent glucose sensing and effector mechanisms that regulate monosaccharide ingestion, absorption,distribution, cellular transport and metabolism, and recovery/retention. Glucose transport and metabolism have coevolved in mammals to support cerebral glucose utilization.

Maternal overweight induced by a diet with high content of saturated fat activates placental mTOR and eIF2alpha signaling and increases fetal growth in rats

The mammalian target of rapamycin (mTOR) and the eukaryotic initiation factor 2 (eIF2) signaling pathways control protein synthesis in response to nutrient availability. Moreover, mTOR is a positive regulator of placental nutrient transport and is involved in the regulation of fetal growth. We hypothesized that maternal overweight, induced by a diet with high saturated fat content, i) up-regulates placental mTOR activity and nutrient transport, resulting in fetal overgrowth; ii) inhibits phosphorylation of eIF2 at its alpha subunit (eIF2alpha); and iii) leads to placental inflammation. Albino Wistar female rats were fed a control or high-saturated-fat (HF) diet for 7 wk before mating and during pregnancy. At gestational day 21, the HF diet significantly increased maternal and fetal triglyceride, leptin, and insulin (but not glucose) levels and maternal and fetal weights, and placental weights trended to increase. Phosphorylated 4EBP1 (T37/46 and S65) was significantly higher, and phosphorylated rpS6 (S235/236) tended to increase, in the placentas of dams fed an HF diet, indicating an activation of mTOR complex 1 (mTORC1). Phosphorylation of AMPK and eIF2alpha was reduced in the HF diet group compared to the control. The expression and activity of placental nutrient transporters and lipoprotein lipase (LPL), as well as the activation of inflammatory pathways, were not altered by the maternal diet. We conclude that maternal overweight induced by an HF diet stimulates mTORC1 activity and decreases eIF2alpha phosphorylation in rat placentas. We speculate that these changes may up-regulate protein synthesis and contribute to placental and fetal overgrowth.

The SLC2 (GLUT) family of membrane transporters

GLUT proteins are encoded by the SLC2 genes and are members of the major facilitator superfamily of membrane transporters. Fourteen GLUT proteins are expressed in the human and they are categorized into three classes based on sequence similarity. All GLUTs appear to transport hexoses or polyols when expressed ectopically, but the primary physiological substrates for several of the GLUTs remain uncertain. GLUTs 1-5 are the most thoroughly studied and all have well established roles as glucose and/or fructose transporters in various tissues and cell types. The GLUT proteins are comprised of ∼500 amino acid residues, possess a single N-linked oligosaccharide, and have 12 membrane-spanning domains. In this review we briefly describe the major characteristics of the 14 GLUT family members.

The SLC2 (GLUT) family of membrane transporters

GLUT proteins are encoded by the SLC2 genes and are members of the major facilitator superfamily of membrane transporters. Fourteen GLUT proteins are expressed in the human and they are categorized into three classes based on sequence similarity. All GLUTs appear to transport hexoses or polyols when expressed ectopically, but the primary physiological substrates for several of the GLUTs remain uncertain. GLUTs 1-5 are the most thoroughly studied and all have well established roles as glucose and/or fructose transporters in various tissues and cell types. The GLUT proteins are comprised of ∼500 amino acid residues, possess a single N-linked oligosaccharide, and have 12 membrane-spanning domains. In this review we briefly describe the major characteristics of the 14 GLUT family members.

The SLC2 (GLUT) family of membrane transporters

GLUT proteins are encoded by the SLC2 genes and are members of the major facilitator superfamily of membrane transporters. Fourteen GLUT proteins are expressed in the human and they are categorized into three classes based on sequence similarity. All GLUTs appear to transport hexoses or polyols when expressed ectopically, but the primary physiological substrates for several of the GLUTs remain uncertain. GLUTs 1-5 are the most thoroughly studied and all have well established roles as glucose and/or fructose transporters in various tissues and cell types. The GLUT proteins are comprised of ∼500 amino acid residues, possess a single N-linked oligosaccharide, and have 12 membrane-spanning domains. In this review we briefly describe the major characteristics of the 14 GLUT family members.

The effects of induced type-I diabetes on developmental regulation of insulin & insulin like growth factor-1 (IGF-1) receptors in the cerebellum of rat neonates

Diabetes during pregnancy impairs brain development in offspring, leading to behavioral problems, motor dysfunction and learning deficits. Insulin and insulin-like growth factor-1 (IGF-1) are important regulators of developmental and cognitive functions in the central nervous system. Aim of the present study was to examine the effects of maternal diabetes on insulin receptor (InsR) and IGF-1 receptor (IGF-1R) expression in the developing rat cerebellum. Wistar female rats were maintained diabetic from a week before pregnancy through parturition and male offspring was killed at P0, P7, and P14, an active neurogenesis period in brain development equivalent to the third trimester in human. The expression of InsR and IGF-1R in cerebelli was evaluated using real-time PCR and western blot analysis. We found a significant upregulation of both IGF-1R and InsR transcripts in cerebellum of pups born to diabetic mothers at P0, compared to controls. However, at the same time point, the results of western blot analysis revealed only a slight change in their protein levels. In contrast to InsR, which does not show any difference, there was a markedly reduction in cerebellar expression of IGF-1R mRNA and protein level in the diabetic group of newborns at P7. Moreover, 2 weeks after birth, mRNA expression and protein levels of both InsR and IGF-1R in cerebellum of the diabetic group was significantly downregulated. Compared to controls, we did not find any difference in cerebellar InsR or IGF-1R mRNA and protein levels in the insulin treated group. The present study revealed that diabetes during pregnancy strongly influences the regulation of both InsR and IGF-1R in the developing cerebellum. Furthermore, optimal maternal glycaemia control by insulin administration normalized these effects.

Creb1-Mecp2-(m)CpG complex transactivates postnatal murine neuronal glucose transporter isoform 3 expression

The murine neuronal facilitative glucose transporter isoform 3 (Glut3) is developmentally regulated, peaking in expression at postnatal day (PN)14. In the present study, we characterized a canonical CpG island spanning the 5'-flanking region of the glut3 gene. Methylation-specific PCR and bisulfite sequencing identified methylation of this CpG ((m)CpG) island of the glut3 gene, frequency of methylation increasing 2.5-fold with a 1.6-fold increase in DNA methyl transferase 3a concentrations noted with advancing postnatal age (PN14 vs PN3). 5'-flanking region of glut3-luciferase reporter transient transfection in HT22 hippocampal neurons demonstrated that (m)CpGs inhibit glut3 transcription. Contrary to this biological function, glut3 expression rises synchronously with (m)CpGs in PN14 vs PN3 neurons. Chromatin immunoprecipitation (IP) revealed that methyl-CpG binding protein 2 (Mecp2) bound the glut3-(m)CpGs. Depending on association with specific coregulators, Mecp2, a dual regulator of gene transcription, may repress or activate a downstream gene. Sequential chromatin IP uncovered the glut3-(m)CpGs to bind Mecp2 exponentially upon recruitment of Creb1 rather than histone deacetylase 1. Co-IP and coimmunolocalization confirmed that Creb1 associated with Mecp2 and cotransfection with glut3-(m)CpG in HT22 cells enhanced glut3 transcription. Separate 5-aza-2'-deoxycytidine pretreatment or in combination with trichostatin A reduced (m)CpG and specific small interference RNAs targeting Mecp2 and Creb1 separately or together depleting Mecp2 and/or Creb1 binding of glut3-(m)CpGs reduced glut3 expression in HT22 cells. We conclude that Glut3 is a methylation-sensitive neuronal gene that recruits Mecp2. Recruitment of Creb1-Mecp2 by glut3-(m)CpG contributes towards transactivation, formulating an escape from (m)CpG-induced gene suppression, and thereby promoting developmental neuronal glut3 gene transcription and expression.

Food allergens are transferred intact across the rat blood-placental barrier in vivo

We investigated the mechanism of transplacental macromolecular transport in rats on the nineteenth day of pregnancy using tracers, transmission electron microscopy and immunohistochemistry. The blood-placental barrier of full-term rat placentas was composed of a trilaminar layer of trophoblast cells that separates the fetal capillaries from the maternal blood spaces: a layer of cytotrophoblasts lining the maternal blood space and a bilayer of syncytiotrophoblast surrounding the fetal capillaries. Horseradish peroxidase, intravenously injected into the maternal circulation, was found in the maternal blood spaces, the interspaces between the cytotrophoblasts and the syncytiotrophoblast I, many pits and small vesicles in the syncytiotrophoblast I, vesicles of the syncytiotrophoblast II, fetal connective tissue and fetal capillaries. Intravenously injected ovalbumin was detected in the maternal blood spaces, a trilaminar layer and the fetal capillaries. Neonatal Fc receptor (FcRn), a receptor for IgG, was localized at the maternal side of the blood-placental barrier. These results show that the structure of the rat blood-placental barrier is quite similar to the human blood-placental barrier, and non-specific macromolecules and food allergens may penetrate through the blood-placental barrier of the full-term placenta from the maternal to fetal circulation mediated by FcRn.

Regulation of placental nutrient transport and implications for fetal growth

Fetal macronutrient requirements for oxidative metabolism and growth are met by placental transport of glucose, amino acids, and, to a lesser extent that varies with species, fatty acids. It is becoming possible to relate the maternal–fetal transport kinetics of these molecules in vivo to the expression and distribution of specific transporters among placental cell types and subcellular membrane fractions. This is most true for glucose transport, although apparent inconsistencies among data on the roles and relative importance of the predominant placenta glucose transporters, GLUT-1 and GLUT-3, remain to be resolved. The quantity of macronutrients transferred to the fetus from the maternal bloodstream is greatly influenced by placental metabolism, which results in net consumption of large amounts of glucose and, to a lesser extent, amino acids. The pattern of fetal nutrient supply is also altered considerably by placental conversion of glucose to lactate and, in some species, fructose, and extensive transamination of amino acids. Placental capacity for transport of glucose and amino acids increases with fetal demand as gestation advances through expansion of the exchange surface area and increased expression of specific transport molecules. In late pregnancy, transport capacity is closely related to placental size and can be modified by maternal nutrition. Preliminary evidence suggests that placental expression and function of specific transport proteins are influenced by extracellular concentrations of nutrients and endocrine factors, but, in general, the humoral regulation of placental capacity for nutrient transport is poorly understood. Consequences of normal and abnormal development of placental transport functions for fetal growth, especially during late gestation, and, possibly, for fetal programming of postnatal disorders, are discussed.

Temporal and spatial distribution of murine placental and brain GLUT3-luciferase transgene as a readout of in vivo transcription

To investigate in vivo transcription of the facilitative glucose transporter isoform-GLUT3 gene, we created GLUT3-firefly luciferase transgenic mouse lines that demonstrate tissue-specific [adult: brain > testis ≥ skeletal muscle > placenta; postnatal (PN): skeletal muscle > brain = skin], temporal, and spatial distribution of the reporter gene/enzyme activity that is unique from endogenous GLUT3 mRNA/protein. In this mouse model, luciferase expression/activity serving as a readout of in vivo transcription peaked at 12 days gestation along with proliferating cell nuclear antigen (cell replication) in placenta and embryonic brain preceding peak GLUT3 protein expression at 18-19 days gestation. In contrast, a postnatal increase in brain luciferase mRNA peaked with endogenous GLUT3 mRNA, but after that of NeuroD6 protein (neurogenesis) at PN7. Luciferase activity paralleled GLUT3 protein expression with Na(+)-K(+)-ATPase (membrane expansion) and synaptophysin (synaptogenesis) proteins, peaking at PN14 and lasting until 60 days in the adult. Thus GLUT3 transcription in placenta and embryonic brain coincided with cell proliferation and in postnatal brain with synaptogenesis. Longitudinal noninvasive bioluminescence (BLI) monitoring of in vivo brain GLUT3 transcription reflected cross-sectional ex vivo brain luciferase activity only between PN7 and PN21. Hypoxia/reoxygenation at PN7 revealed transcriptional increase in brain GLUT3 expression reflected by in vivo BLI and ex vivo luciferase activity. These observations collectively support a temporal contribution by transcription toward ensuring adequate tissue-specific, developmental (placenta and embryonic brain), and postnatal hypoxic brain GLUT3 expression.

Evolution of Placental Function in Mammals: The Molecular Basis of Gas and Nutrient Transfer, Hormone Secretion, and Immune Responses

Placenta has a wide range of functions. Some are supported by novel genes that have evolved following gene duplication events while others require acquisition of gene expression by the trophoblast. Although not expressed in the placenta, high-affinity fetal hemoglobins play a key role in placental gas exchange. They evolved following duplications within the beta-globin gene family with convergent evolution occurring in ruminants and primates. In primates there was also an interesting rearrangement of a cassette of genes in relation to an upstream locus control region. Substrate transfer from mother to fetus is maintained by expression of classic sugar and amino acid transporters at the trophoblast microvillous and basal membranes. In contrast, placental peptide hormones have arisen largely by gene duplication, yielding for example chorionic gonadotropins from the luteinizing hormone gene and placental lactogens from the growth hormone and prolactin genes. There has been a remarkable degree of convergent evolution with placental lactogens emerging separately in the ruminant, rodent, and primate lineages and chorionic gonadotropins evolving separately in equids and higher primates. Finally, coevolution in the primate lineage of killer immunoglobulin-like receptors and human leukocyte antigens can be linked to the deep invasion of the uterus by trophoblast that is a characteristic feature of human placentation.

Altered placental development in undernourished rats: role of maternal glucocorticoids

Maternal undernutrition (MUN) during pregnancy may lead to fetal intrauterine growth restriction (IUGR), which itself predisposes to adult risk of obesity, hypertension, and diabetes. IUGR may stem from insufficient maternal nutrient supply or reduced placental nutrient transfer. In addition, a critical role for maternal stress-induced glucocorticoids (GCs) has been suggested to contribute to both IUGR and the ensuing risk of adult metabolic syndrome. While GC-induced fetal organ defects have been examined, there have been few studies on placental responses to MUN-induced maternal stress. Therefore, we hypothesize that 50% MUN associates with increased maternal GC levels and decreased placental HSD11B. This in turn leads to decreased placental and fetal growth, hence the need to investigate nutrient transporters. We measured maternal serum levels of corticosterone, and the placental basal and labyrinth zone expression of glucocorticoid receptor (NR3C1), 11-hydroxysteroid dehydrogenase B 1 (HSD11B-1) predominantly activates cortisone to cortisol and 11-dehydrocorticosterone (11-DHC) to corticosterone, although can sometimes drive the opposing (inactivating reaction), and HSD11B-2 (only inactivates and converts corticosterone to 11-DHC in rodents) in control and MUN rats at embryonic day 20 (E20). Moreover, we evaluated the expression of nutrient transporters for glucose (SLC2A1, SLC2A3) and amino acids (SLC38A1, 2, and 4). Our results show that MUN dams displayed significantly increased plasma corticosterone levels compared to control dams. Further, a reduction in fetal and placental weights was observed in both the mid-horn and proximal-horn positions. Notably, the placental labyrinth zone, the site of feto-maternal exchange, showed decreased expression of HSD11B1-2 in both horns, and increased HSD11B-1 in proximal-horn placentas, but no change in NR3C1. The reduced placental GCs catabolic capacity was accompanied by downregulation of SLC2A3, SLC38A1, and SLC38A2 expression, and by increased SLC38A4 expression, in labyrinth zones from the mid- and proximal-horns. In marked contrast to the labyrinth zone, the basal zone, which is the site of hormone production, did not show significant changes in any of these enzymes or transporters. These results suggest that dysregulation of the labyrinth zone GC "barrier", and more importantly decreased nutrient supply resulting from downregulation of some of the amino acid system A transporters, may contribute to suboptimal fetal growth under MUN.

Fetal overgrowth in the Cdkn1c mouse model of Beckwith-Wiedemann syndrome

Mutations in the imprinted CDKN1C gene are associated with the childhood developmental disorder Beckwith-Wiedemann syndrome (BWS). Multiple mouse models with deficiency of Cdkn1c recapitulate some aspects of BWS but do not exhibit overgrowth of the newborn, a cardinal feature of patients with BWS. In this study, we found that Cdkn1c mutants attained a 20% increase in weight during gestation but experienced a rapid reversal of this positive growth trajectory very late in gestation. We observed a marked effect on placental development concurrently with this loss of growth potential, with the appearance of large thrombotic lesions in the labyrinth zone. The trilaminar trophoblast layer that separates the maternal blood sinusoids from fetal capillaries was disordered with a loss of sinusoidal giant cells, suggesting a role for Cdkn1c in maintaining the integrity of the maternal-fetal interface. Furthermore, the overgrowth of mutant pups decreased in the face of increasing intrauterine competition, identifying a role for Cdkn1c in the allocation of the maternal resources via the placenta. This work explains one difficulty in precisely replicating BWS in this animal model: the differences in reproductive strategies between the multiparous mouse, in which intrauterine competition is high, and humans, in which singleton pregnancies are more common.

Beneficial effects of dietary fibre supplementation of a high-fat diet on fetal development in rats

The objective of the present study was to investigate the effects of the addition of fibre and the antioxidant N-acetylcysteine (NAC) to fat-rich diets on fetal intrauterine development in rats. A total of eighty virgin female Sprague-Dawley rats were fed a control diet, a high-fat diet (HF), a high-fat and high-fibre diet (HFF) or a high-fat NAC diet until day 19·5 of gestation. Maternal HFF consumption resulted in a significantly higher mean fetal number and placental weight than in the other groups (P < 0·05). The HFF diet significantly abrogated HF-induced decreases in maternal serum and placental superoxide anion and hydroxyl radical scavenging capacities (P < 0·05); partially abrogated HF-induced increases in maternal serum and placental malondialdehyde (MDA) and protein carbonyl concentrations (maternal serum MDA and placental protein carbonyl, P < 0·05); resulted in significantly higher fetal liver total superoxide dismutase (SOD), Cu- and Zn-containing SOD and Mn-containing SOD (Mn-SOD) activities than in the HF group (P < 0·05). Furthermore, mRNA expressions of hypoxia-inducible factor 1-α, thioredoxin 2 and Mn-SOD in fetal liver and Mn-SOD in fetal heart and placental GLUT3 in the HFF group were higher than those in the other groups (P < 0·05). The inclusion of dietary fibre in the HF diet was more effective than NAC supplementation in maintaining maternal serum and placental superoxide anion and hydroxyl radical scavenging capacities close to those of the control. These results suggest that maternal fibre intake during pregnancy is beneficial for fetal intrauterine development possibly through the improvement of maternal, placental and fetal antioxidant capacities and placental nutrient transfer capacity.

The cooperative function of nuclear receptor coactivator 1 (NCOA1) and NCOA3 in placental development and embryo survival

Nuclear receptor coactivator 1 [NCOA1/steroid receptor coactivator (SRC)-1] and NCOA3 (SRC-3/AIB1/ACTR) constitute two thirds of the SRC (steroid receptor coactivator) family. Although in vitro experiments have suggested overlapping functions between NCOA1 and NCOA3, their in vivo functional relationship is poorly understood. In this study, NCOA1 and NCOA3 double knockout mice were generated to determine the compensatory roles of NCOA1 and NCOA3 in development. NCOA1(-/-) mice survived normally, whereas most NCOA3(-/-) embryos were viable at embryonic d 13.5 (E13.5). In contrast, the majority of double-knockout (DKO) embryos died by E13.5. NCOA1 and NCOA3 are expressed in the labyrinth, and labyrinths of NCOA1(+/-);NCOA3(-/-) and DKO placentas were small compared with wild-type and single-knockout labyrinths. DKO labyrinths exhibited low densities of maternal blood sinuses and fetal capillaries and displayed fetomaternal blood transfusion. At the interface between maternal and fetal circulations, layer I sinusoidal trophoblast giant cells showed a reduced density of microvilli. Layer III syncytiotrophoblasts appeared to accumulate large lipid droplets and have reduced density and deepened invaginations of the intrasyncytial bays. The endothelial layer in DKO labyrinth showed abnormal morphologies and had large lipid droplets. Furthermore, disruption of NCOA1 and NCOA3 increased labyrinth trophoblast proliferation and their progenitor gene expression but decreased their differentiation gene expression. NCOA1 and NCOA3 deficiencies also affected the expression of several genes for placental morphogenesis including TGFβ-, peroxisome proliferator-activated receptor-β-, and peroxisome proliferator-activated receptor-γ-regulated genes and for glucose transportation including GLUT1 and Cx26. These findings demonstrate that NCOA1 and NCOA3 cooperatively regulate placental morphogenesis and embryo survival.

Adaptations in placental phenotype support fetal growth during undernutrition of pregnant mice

Undernutrition during pregnancy reduces birth weight and programmes adult phenotype with consequences for life expectancy, but its effects on the phenotype of the placenta, responsible for supplying nutrients for fetal growth, remain largely unknown. Using molecular, morphological and functional analyses, placental phenotype was examined in mice during restriction of dietary intake to 80% of control from day 3 of pregnancy. At day 16, undernutrition reduced placental, but not fetal, weight in association with decreased junctional zone volume and placental expression of glucose transporter Slc2a1. At day 19, both placental and fetal weights were reduced in undernourished mice (91% and 87% of control, respectively, P < 0.01), as were the volume and surface area of the labyrinthine zone responsible for placental nutrient transfer (85% and 86%, respectively, P < 0.03). However, unidirectional materno-fetal clearance of tracer glucose was maintained and methyl-aminoisobutyric acid increased 166% (P < 0.005) per gram of undernourished placenta, relative to controls. This was associated with an 18% and 27% increased placental expression of glucose and system A amino acid transporters Slc2a1 and Slc38a2, respectively, at day 19 (P < 0.04). At both ages, undernutrition decreased expression of the placental specific transcript of the Igf2 gene by 35% (P < 0.01), although methylation of its promoter was unaffected. The placenta, therefore, adapts to help maintain fetal growth when its own growth is compromised by maternal undernutrition. Consequently, placental phenotype is responsive to environmental conditions and may help predict the risk of adult disease programmed in utero.

Will the original glucose transporter isoform please stand up!

Monosaccharides enter cells by slow translipid bilayer diffusion by rapid, protein-mediated, cation-dependent cotransport and by rapid, protein-mediated equilibrative transport. This review addresses protein-mediated, equilibrative glucose transport catalyzed by GLUT1, the first equilibrative glucose transporter to be identified, purified, and cloned. GLUT1 is a polytopic, membrane-spanning protein that is one of 13 members of the human equilibrative glucose transport protein family. We review GLUT1 catalytic and ligand-binding properties and interpret these behaviors in the context of several putative mechanisms for protein-mediated transport. We conclude that no single model satisfactorily explains GLUT1 behavior. We then review GLUT1 topology, subunit architecture, and oligomeric structure and examine a new model for sugar transport that combines structural and kinetic analyses to satisfactorily reproduce GLUT1 behavior in human erythrocytes. We next review GLUT1 cell biology and the transcriptional and posttranscriptional regulation of GLUT1 expression in the context of development and in response to glucose perturbations and hypoxia in blood-tissue barriers. Emphasis is placed on transgenic GLUT1 overexpression and null mutant model systems, the latter serving as surrogates for the human GLUT1 deficiency syndrome. Finally, we review the role of GLUT1 in the absence or deficiency of a related isoform, GLUT3, toward establishing the physiological significance of coordination between these two isoforms.

Syncytin-A knockout mice demonstrate the critical role in placentation of a fusogenic, endogenous retrovirus-derived, envelope gene

In most mammalian species, a key process of placenta development is the fusion of trophoblast cells into a highly specialized, multinucleated syncytiotrophoblast layer, through which most of the maternofetal exchanges take place. Little is known about this process, despite the recent identification of 2 pairs of envelope genes of retroviral origin, independently acquired by the human (syncytin-1 and syncytin-2) and mouse (syncytin-A and syncytin-B) genomes, specifically expressed in the placenta, and with in vitro cell-cell fusion activity. By generating knockout mice, we show here that homozygous syncytin-A null mouse embryos die in utero between 11.5 and 13.5 days of gestation. Refined cellular and subcellular analyses of the syncytin-A-deficient placentae disclose specific disruption of the architecture of the syncytiotrophoblast-containing labyrinth, with the trophoblast cells failing to fuse into an interhemal syncytial layer. Lack of syncytin-A-mediated trophoblast cell fusion is associated with cell overexpansion at the expense of fetal blood vessel spaces and with apoptosis, adding to the observed maternofetal interface structural defects to provoke decreased vascularization, inhibition of placental transport, and fetal growth retardation, ultimately resulting in death of the embryo. These results demonstrate that syncytin-A is essential for trophoblast cell differentiation and syncytiotrophoblast morphogenesis during placenta development, and they provide evidence that genes captured from ancestral retroviruses have been pivotal in the acquisition of new, important functions in mammalian evolution.

Altered placental function of 11beta-hydroxysteroid dehydrogenase 2 knockout mice

Fetal glucocorticoid exposure is a key mechanism proposed to underlie prenatal "programming" of adult cardiometabolic and neuropsychiatric disorders. Regulation of fetal glucocorticoid exposure is achieved by the placental glucocorticoid "barrier," which involves glucocorticoid inactivation within the labyrinth zone of the murine placenta by 11beta-hydroxysteroid dehydrogenase 2 (11beta-HSD2). Thus, the absence of placental 11beta-HSD2 may impact on fetal and placental development. The current study investigated transport of amino acids and glucose, key factors required for fetal growth, and vascular development in placentas from 11beta-HSD2(+/+), (+/-), and (-/-) fetuses derived from 11beta-HSD2(+/-) matings. At embryonic d 15 (E15) (term = E19), 11beta-HSD2(-/-) fetal weight was maintained in comparison to 11beta-HSD2(+/+) fetuses. The maintenance of 11beta-HSD2(-/-) fetal weight occurred despite a reduction in placental weight, suggesting that compensatory changes occur in the placenta to maintain function. However, by E18, 11beta-HSD2(-/-) fetal and placental weights were both reduced. Transport studies revealed up-regulation of placental amino acid transport to 11beta-HSD2(-/-) offspring at E15, coinciding with an increase in the expression of the amino acid transporters. Furthermore, at E18, placental glucose transport to 11beta-HSD2(-/-) offspring was markedly reduced, correlating with lower fetal weight and a decrease in glucose transporter 3 expression. Stereological analyses of the labyrinth zone of the placenta revealed that the reduction in placental weight at E18 was associated with restriction of the normal increase in fetal vessel density over the final third of pregnancy. Our data suggest that restriction of fetal growth in 11beta-HSD2(-/-) mice is mediated, at least in part, via altered placental transport of nutrients and reduction in placental vascularization.

Glucose transporter isoform-3 mutations cause early pregnancy loss and fetal growth restriction

Glucose transporter isoform-3 (GLUT3) is the trophoblastic facilitative glucose transporter. To investigate the role of this isoform in embryonic development, we created a novel GLUT3-null mouse and observed arrested early embryonic development and loss at neurulation stage when both alleles were mutated. This loss occurred despite the presence of other related isoforms, particularly GLUT1. In contrast, when a single allele was mutated, despite increased embryonic cell apoptosis, adaptive changes in the subcellular localization of GLUT3 and GLUT1 in the preimplantation embryo led to postimplantation survival. This survival was compromised by decreased GLUT3-mediated transplacental glucose transport, causing late-gestation fetal growth restriction. This yielded young male and female adults demonstrating catch-up growth, with normal basal glucose, insulin, insulin-like growth factor-I and IGF-binding protein-3 concentrations, fat and lean mass, and glucose and insulin tolerance. We conclude that GLUT3 mutations cause a gene dose-dependent early pregnancy loss or late-gestation fetal growth restriction despite the presence of embryonic and placental GLUT1 and a compensatory increase in system A amino acid placental transport. This critical life-sustaining functional role for GLUT3 in embryonic development provides the basis for investigating the existence of human GLUT3 mutations with similar consequences during early pregnancy.

Adaptation of nutrient supply to fetal demand in the mouse involves interaction between the Igf2 gene and placental transporter systems

The mammalian fetus is unique in its dependence during gestation on the supply of maternal nutrients through the placenta. Maternal supply and fetal demand for nutrients need to be fine tuned for healthy growth and development of the fetus along its genetic trajectory. An altered balance between supply and demand can lead to deviations from this trajectory with long-term consequences for health. We have previously shown that in a knockout lacking the imprinted placental-specific Igf2 transcript (P0), growth of the placenta is compromised from early gestation but fetal growth is normal until late gestation, suggesting functional adaptation of the placenta to meet the fetal demands. Here, we show that placental transport of glucose and amino acids are increased in the Igf2 P0(+/-) null and that this up-regulation of transport occurs, at least in part, through increased expression of the transporter genes Slc2a3 and Slc38a4, the imprinted member of the System A amino acid transporter gene family. Decreasing fetal demand genetically by removal of fetal Igf2 abolished up-regulation of both transport systems and reduced placental System A amino acid transport activity and expression of Slc38a2 in late gestation. Our results provide direct evidence that the placenta can respond to fetal demand signals through regulation of expression of specific placental transport systems. Thus, crosstalk between an imprinted growth demand gene (Igf2) and placental supply transporter genes (Slc38a4, Slc38a2, and Slc2a3) may be a component of the genetic control of nutrient supply and demand during mammalian development.