Microvillous Membrane Research Articles

Adhesion Molecules in Human Trophoblast – A Review. I. Villous Trophoblast

In the placental villus, cells attach to basement membrane via integrin α6β4 and adhere both laterally and apically to their neighbours. The most prominent adhesive specialisation seen using the electron microscope is the desmosome, which connects cytotrophoblast cells (CTB) laterally and also contributes to the attachment of CTB to the overlying syncytium. However, numerous cadherins and other junctional proteins are also present in the corresponding plasma membrane domains, indicating a multiplicity of adhesive interactions. Integrins, tight junction components and cadherins are all found in the syncytial microvillous membrane, perhaps reflecting its ability to form intersyncytial bridges. There is a wide gulf to be filled between molecular anatomy and functional studies, with much to be learned about the role of adhesion molecules in regulating villous epithelial integrity, homeostasis and growth.

Placental protein 13 (galectin-13) has decreased placental expression but increased shedding and maternal serum concentrations in patients presenting with preterm pre-eclampsia and HELLP syndrome

Placental protein 13 (PP13) is a galectin expressed by the syncytiotrophoblast. Women who subsequently develop preterm pre-eclampsia have low first trimester maternal serum PP13 concentrations. This study revealed that third trimester maternal serum PP13 concentration increased with gestational age in normal pregnancies (p < 0.0001), and it was significantly higher in women presenting with preterm pre-eclampsia (p = 0.02) and hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome (p = 0.01) than in preterm controls. Conversely, placental PP13 mRNA (p = 0.03) and protein, as well as cytoplasmic PP13 staining of the syncytiotrophoblast (p < 0.05) was decreased in these pathological pregnancies compared to controls. No differences in placental expression and serum concentrations of PP13 were found at term between patients with pre-eclampsia and control women. In contrast, the immunoreactivity of the syncytiotrophoblast microvillous membrane was stronger in both term and preterm pre-eclampsia and HELLP syndrome than in controls. Moreover, large syncytial cytoplasm protrusions, membrane blebs and shed microparticles strongly stained for PP13 in pre-eclampsia and HELLP syndrome. In conclusion, parallel to its decreased placental expression, an augmented membrane shedding of PP13 contributes to the increased third trimester maternal serum PP13 concentrations in women with preterm pre-eclampsia and HELLP syndrome.

Adenosine receptor A2A expression is higher in placentas of women with preeclampsia

Hypoxia is a potent stimulus for the release of adenosine and angiogenic factors in tissues. Women with preeclampsia show evidence of placental hypoxia and increased concentrations of adenosine in the circulation. It is suggested that activation of adenosine receptors is an adaptive response to reduce hypoxic injury in different tissues. Objective: We tested the hypotheses that the adenosine receptor subtype A2A is expressed in the placenta, expression is altered in preeclamptic pregnancies and under in vitro hypoxic conditions. Methods: Placentas were obtained from primiparous women with uncomplicated pregnancies or preeclampsia. Placental microvillous membranes (MVM) were prepared according to a standard protocol or villous explants were dissected and incubated for 24h at 2% oxygen or under standard conditions (20% oxygen). Western blotting was performed for detection of adenosine A2A receptor and HIF–1α. Data are presented as mean±SEM or fold changes compared to control values. Statistical analyzes were performed with Mann-Whitney or Wilcoxon-signed rank test. Probability values were considered significant at p&lt;0.05. Results: Adenosine receptor subtype A2A is expressed in placental biopsies, villous explants and MVM. The expression was significantly higher in MVM from preeclamptic women (N=5, p=0.04) compared to uncomplicated pregnancies, respectively. In vitro hypoxia increased A2A-R and HIF–1α protein in villous explants (N=4, p=0.06, 0.03). Conclusions: Our results suggest a potential role for adenosine receptors in the pathophysiology of preeclampsia. Further studies will focus on the role of adenosine receptors in the regulation of placental function.

Barium, Tea and Sodium Sensitive Potassium Channels are Present in the Human Placental Syncytiotrophoblast Apical Membrane

The human placental syncytiotrophoblast (hSTB) is a polarized epithelial structure, without paracellular routes, forming the main barrier for materno–fetal exchange. There is ample evidence suggesting the presence of potassium (K +) channels in the placental apical membrane; which could contribute to membrane potential and volume regulation. We have therefore examined the K + currents of isolated apical membranes from human term placenta using electrophysiological methods: reconstitution of ion channels from apical membranes into giant liposomes (single channel recordings, patch clamp method) or their functional transplantation into Xenopus laevis oocytes (total currents recording, voltage clamp method). Single channel recording experiments show the presence of K + channels in the hSTB microvillous membrane sensitive to Tetraethylammonium (TEA) and Barium (Ba +2). Patch current activity was diminished 50% and 70% by 20 mmol/L TEA and 5 mmol/L Ba +2 respectively. The more frequent conductance was approximately 73 pS, however several levels of current were detected suggesting the presence of more than one type of K + channel. In addition, sodium (Na +) sensitivity was detected in the patch current thus, over 10 mmol/L Na + reduced the seal current to 38%. These results were corroborated by the total current experiments where the K + current elicited in injected oocytes with apical purified membrane was blocked by Ba +2 and TEA. The total current was also affected by Na +, becoming larger when a Na +-free solution was used. Our results show the existence of at least two types of Ba +2-sensitive K + channels including a TEA sensitive sub-population, and some of them Na + sensitive K + channels. These channels could be the conductive pathways proposed previously for this cation in placental hSTB. Our novel contribution has been to successfully obtain K + channel recordings in systems suitable for electrophysiological studies of isolated apical membranes.

Distinct Lipid Rafts in Subdomains from Human Placental Apical Syncytiotrophoblast Membranes

We report on the characteristics of raft domains in the apical membrane from human placental syncytiotrophoblast (hSTB), an epithelium responsible for maternal-fetal exchange. Previously, we described two isolated fractions of the hSTB apical membrane: a classical microvillous membrane (MVM) and a light microvillous membrane (LMVM). Detergent-resistant microdomains (DRMs) from MVM and LMVM were prepared with Triton X-100 followed by flotation in a sucrose gradient and tested by Western and dot blot with raft markers (placental alkaline phosphatase, lipid ganglioside, annexin 2) and transferrin receptor as a nonraft marker. DRMs from both fractions showed a consistent peak for these markers, except that the DRMs from MVM had no annexin 2 mark. Cholesterol depletion modified the segregation in both groups of DRMs. Our results show two distinguishable lipid raft subsets from MVM and LMVM. Additionally, we found significant differences between MVM and LMVM in cholesterol content and in expression of cytoskeletal proteins. MVM is enriched in ezrin and beta-actin; in contrast, cholesterol and cytokeratin-7 are more abundant in LMVM. These differences may explain the distinct properties of the lipid raft subtypes.

Maintaining the integrity of trophoblast during growth of the placenta. Focus on “Insulin-like growth factor I and II regulate the life cycle of trophoblast in the developing human placenta”

maternal-fetal exchange of nutrients and respiratory gases occurs across the brush border of the trophoblast lining the intervillous space of the placenta. The trophoblast is syncytial in nature and has a high rate of turnover. Therefore syncytiotrophoblast is continually replenished from an

Placental Expression of α2,6-Linked Sialic Acid is Upregulated in Malaria

In Africa, approximately 25 million pregnant women are at risk of Plasmodium falciparum infection each year, one in four has evidence of placental involvement and up to half of these may be associated with low birth weight outcomes. In infected pregnant women, the placenta is an ideal site for the accumulation of the parasites, and this reduces in extent in subsequent pregnancies. Recent data indicate that terminal α2,3 sialic acid-dependent routes are central to the efficient invasion of erythrocytes with P. falciparum, however, the role in placental malaria of sialylated, or other glycoconjugates, on syncytiotrophoblast has not previously been assessed. Placental biopsies from Zambian women showed the Neu5Ac(α2,6)Gal/GalNAc sequences bound by the lectin from Sambucus nigra (SNA-1) to have greatly increased expression on microvillous membranes in samples with chronic P. falciparum infection showing, by electronic image analysis, a significant trend ( p = 0.002) compared to samples with past or no infection. This suggests a specific placental membrane response to falciparum malaria. Expression of α2,6-linked sialic acid, demonstrated by the binding of SNA-1, has been associated with intercellular repulsion in tissues from patients with cancer, and such repulsion resulting from increased α2,6 sialylation of chorionic villi could influence intervillous placental parasite density. Sialic acid expression should be examined in placental malaria to identify if this is a malaria-specific phenomenon, and to determine its relation to placental inflammation and pregnancy outcomes.

A Role for Tissue Transglutaminase in Stabilization of Membrane-Cytoskeletal Particles Shed from the Human Placenta

Tissue transglutaminase (TGM2; also known as TG2 or tTG) localizes to the syncytial microvillous membrane (MVM) of the human placenta, the primary interface between maternal and fetal tissue. To identify TGM2 substrates in the MVM, membrane vesicles were prepared and labeled with biotinylated acyl donor or acceptor probes. Biotinylated species were selected on an avidin affinity matrix and identified by mass spectrometry of tryptic peptides. The most abundant were cytoskeletal (actin, tubulin, and cytokeratin) and membrane-associated (annexins, integrins, and placental alkaline phosphatase) proteins. During pregnancy, apoptotic particulate material, the end product of the trophoblast life cycle, is shed from the MVM into maternal circulation. Shed material was isolated from primary trophoblast cultures in which syncytial-like masses develop by fusion. A substantial fraction of actin in the particles was in the form of covalent polymeric aggregates, in contrast to cellular actin, which dissociated completely into monomer in SDS-PAGE. When cells were cultured in the presence of transglutaminase inhibitors, actin in the shed particles remained exclusively in monomeric form, and a reduction in trophoblast intercellular fusion and differentiation was observed. These findings suggest that transglutaminase-mediated cross-linking stabilizes the particulate material shed from the placenta.

The PLAC1 protein localizes to membranous compartments in the apical region of the syncytiotrophoblast

PLAC1 is a trophoblast-specific gene that maps to a locus on the X-chromosome important to placental development. We have previously shown that PLAC1 gene expression is linked to trophoblast differentiation. The objective of this study was to define the localization of the PLAC1 polypeptide as a prerequisite to understanding its function. Polyclonal antibodies specific for the putative PLAC1 polypeptide were generated. The subcellular localization of PLAC1 in the trophoblast was examined by immunohistochemical analysis of human placenta complemented by immunoblot analysis of subcellular fractions. Brightfield immunohistochemical analysis of placental tissue indicated that the PLAC1 protein localizes to the differentiated syncytiotrophoblast in the apical region of the cell. Deconvlution immunofluorescence microscopy confirmed localization to the apical region of the syncytiotrophoblast. Its distribution included both intracellular compartments as well as loci in close association with the maternal-facing, microvillous brush border membrane (MVM). These findings were supported by immunoblot analysis of subcellular fractions. A 30 kDa band was associated with the microsomal fraction of placental lysates but not the mitochondrial, nuclear, or soluble fractions, suggesting PLAC1 is targeted to a membrane location. Plasma membranes were obtained from the fetal-facing, basal surface (BM) and the maternal-facing, MVM of the syncytiotrophoblast membrane. PLAC1 immunoreactivity was only detected in membrane fractions derived from the apical MVM consistent with immunohistochemical analyses. These data demonstrate that the PLAC1 protein is restricted primarily to the differentiated trophoblast, localizing to intracellular membranous compartment(s) in the apical region of the syncytiotrophoblast and associated with its apical, microvillous membrane surface.

Gestational and hormonal regulation of human placental lipoprotein lipase

The fetal demand for FFA increases as gestation proceeds, and LPL represents one potential mechanism for increasing placental lipid transport. We examined LPL activity and protein expression in first trimester and term human placenta. The LPL activity was 3-fold higher in term (n = 7; P < 0.05) compared with first trimester (n = 6) placentas. The LPL expression appeared lower in microvillous membrane from first trimester (n = 2) compared with term (n = 2) placentas. We incubated isolated placental villous fragments with a variety of effectors [GW 1929, estradiol, insulin, cortisol, epinephrine, insulin-like growth factor-1 (IGF-1), and tumor necrosis factor-alpha] for 1, 3, and 24 h to investigate potential regulatory mechanisms. Decreased LPL activity was observed after 24 h of incubation with estradiol (1 micro g/ml), insulin, cortisol, and IGF-1 (n = 12; P < 0.05). We observed an increase in LPL activity after 3 h of incubation with estradiol (20 ng/ml) or hyperglycemic medium plus insulin (n = 7; P < 0.05). To conclude, we suggest that the gestational increase in placental LPL activity represents an important mechanism to enhance placental FFA transport in late pregnancy. Hormonal regulation of placental LPL activity by insulin, cortisol, IGF-1, and estradiol may be involved in gestational changes and in alterations in LPL activity in pregnancies complicated by altered fetal growth.

Tissue transglutaminase at the placental microvillous membrane: Implications for pregnancy in celiac disease

Tissue transglutaminase at the placental microvillous membrane: Implications for pregnancy in celiac disease

L-Serine Uptake by Human Placental Microvillous Membrane Vesicles

The human fetus requires more glycine than any other amino acid but placental glycine transfer to the fetus is insufficient to meet fetal demand. l-Serine could represent a major metabolic source of glycine for the human fetus but little is known about the kinetics and physiology of l-serine uptake by the human placenta. We have characterised the amino acid transport systems involved in the uptake of l-serine by the microvillous membrane of the human placental syncytiotrophoblast and compared the uptake rates to those of glycine. l-Serine uptake into microvillous membrane (MVM) vesicles was primarily mediated by system A (MeAIB inhibitable) and system L (BCH inhibitable). Further characterisation using specific substrates of LAT1 and LAT2 found the pattern of l-serine uptake was consistent with that expected for uptake mediated by LAT2. Uptakes were performed with tracer levels of 14C- l-serine, physiological levels of l-serine, or with physiological levels of amino acids. As amino acid concentrations rose, the proportion of uptake by System L decreased while uptake by uncharacterised Na +-independent systems increased. Uptake of l-serine into MVM vesicles had a V max of 2.1 ± 0.4 nmol/mg protein/min, which was significantly higher than for glycine ( V max 1.0 ± 0.2 nmol/mg protein/min). This indicates that MVM vesicles have a higher uptake capacity for l-serine than glycine, despite a greater demand for glycine over serine for fetal protein synthesis. Further studies are now required to define the fate of l-serine taken up by the placenta and its importance for the fetus.

Proteomic Analysis of Apical Microvillous Membranes of Syncytiotrophoblast Cells Reveals A High Degree of Similarity with Lipid Rafts

Brush borders (microvilli) are cell membrane specialized structures that function mainly as high-throughput absortive/secretory areas. It has been well-established that brush borders are particularly rich in membrane lipids characteristic to lipid rafts. Here, we report 57 proteins identified from microvillous membranes (MVM) isolated from human syncytiotrophoblast cells using an experimental method that avoids the use of nonionic detergents. About 60% of the proteins reported here have been described previously as lipid-raft specific. Well-known lipid raft-markers such as Annexin A2 and alkaline phosphatase were identified. Cytoskeleton structural constituents and proteins related with the control and modulation of the cytoskeletal architecture as well as the regulation of the interaction of cytoskeletal constituents with the cell membrane and particularly with lipid raft domains were found (Ezrin, IQGAP1 and 2, EBP50). Other proteins identified include signal transduction molecules, such as Ras-related protein Rab-1B and Rab-7, and ADP-ribosylation factor 1. Several proteins harbor putative post-translational modifications that favor its localization in the lipid-raft environment, such as GPI (alkaline phosphatase and 5'-nucleotidase) and myristoylation (BASP1 and MARCKS). On the whole, this extensive description demonstrates from the protein composition point of view that brush border membranes are indeed highly enriched in lipid raft microdomains.

Endothelial and lipoprotein lipases in human and mouse placenta

Placenta expresses various lipase activities. However, a detailed characterization of the involved genes and proteins is lacking. In this study, we compared the expression of endothelial lipase (EL) and LPL in human term placenta. When placental protein extracts were separated by heparin-Sepharose affinity chromatography, the EL protein eluted as a single peak without detectable phospholipid or triglyceride (TG) lipase activity. The major portion of LPL protein eluted slightly after EL. This peak also had no lipase activity and most likely contained monomeric LPL. Fractions eluting at a higher NaCl concentration contained small amounts of LPL protein (most likely dimeric LPL) and had substantial TG lipase activity. In situ hybridization studies showed EL mRNA expression in syncytiotrophoblasts and endothelial cells and LPL mRNA in syncytiotrophoblasts. In contrast, immunohistochemistry showed EL and LPL protein associated with both cell types. In mouse placentas, lack of LPL expression resulted in increased EL mRNA expression. These results suggest that the cellular expression of EL and LPL in human placenta is different. Nevertheless, the two lipases might have overlapping functions in the mouse placenta. Our data also suggest that the major portions of both proteins are stored in an inactive form in human term placenta.

Isolation and Functional Characterization of a Novel Organic Solute Carrier Protein, hOSCP1

We succeeded in isolating a novel organic solute carrier from a human placenta cDNA library. The isolated cDNA consisted of 1137 base pairs that encoded a 379-amino acid protein, hOSCP1. Northern blot and reverse transcription PCR analyses revealed that the hOSCP1 mRNA is expressed in the placenta and testis and weakly expressed in the thymus and small intestine. When expressed in Xenopus laevis oocytes, hOSCP1 mediated the high affinity transport of p-aminohippurate (PAH) (K(m) = 35.0 +/- 7.5 microm) and tetraethylammonium (K(m) = 62.3 +/- 12.2 microm) in a sodium-independent manner. However, the hOSCP1-expressing oocyte did not mediate the transport of L-carnitine. The transport of PAH by hOSCP1 was sensitive to pH, but the tetraethylammonium was not transported at the high pH examined. hOSCP1 transported prostaglandin E(2), prostaglandin F(2alpha), estrone sulfate, glutarate, L-leucine, L-ascorbic acid, and tetracycline. Thus, hOSCP1 also showed broad substrate specificity. A wide range of structurally unrelated organic compounds inhibited the hOSCP1-mediated PAH uptake. Immunohistochemical analysis revealed that the hOSCP1 protein is localized in the basal membrane of the syncytiotrophoblast in the human placenta. Our results suggest that hOSCP1 is a novel polyspecific organic solute carrier protein responsible for drug clearance from the human placenta.

Functional Analysis of Organic Cation Transporter 3 Expressed in Human Placenta

The aim of this study is to investigate the placental transport mechanism of cationic compounds by comparison of the uptake of an organic cation into human placental basal membrane vesicles (BLMVs) with that into organic cation transporter 3 (OCT3)-expressing cells. Reverse transcription-polymerase chain reaction analysis demonstrated that OCT3 is the only OCT isoform expressed in the human placenta. The function of OCT3 was investigated by measuring the uptake of 1-methyl-4-phenylpyridinium (MPP(+)) into human embryonic kidney (HEK)293 cells stably expressing OCT3 (HEK/OCT3 cells). The OCT3-mediated uptake of MPP(+) was sodium- and chloride-independent and saturable, with a Michaelis constant (K(m)) of 82.5 microM. The OCT3-mediated uptake was inhibited by various cationic drugs in a concentration-dependent manner but not by anionic compounds, such as p-aminohippuric acid and captopril, or a zwitterion, carnitine. Western blotting analysis of membrane vesicles prepared from human term placenta revealed that OCT3 is expressed only in BLMVs but not in microvillous membrane vesicles. The uptake of MPP(+) into BLMVs was membrane potential-dependent and saturable, with a K(m) value of 51.8 muM, which is similar to that in HEK293/OCT3 cells. The inhibitory spectrum of various compounds on MPP(+) uptake by BLMVs was also similar to that in HEK293/OCT3 cells. These results suggest that OCT3 is expressed on the basal membrane of human trophoblast cells and plays an important role in the placental transport of cationic compounds.

Placental amino acid transport systems and fetal growth restriction – A workshop report

Keywords: Placental amino acid transport; Fetal growth restriction; Amino acid transportersINTRODUCTIONTwo circulations perfuse the placental barrier, the maternal oruterine on one side and the fetal or umbilical on the other.This barrier consists of two specific membranes, the maternalfacing, microvillous (MVM) or apical membrane and the fetalfacing or basal membrane (BM). As human gestation advancesthe surface area of the microvillous membrane increases.Though late in pregnancy, this increase is not of comparablerate to the growth rate of the fetus, supporting the concept thatduring later pregnancy the increasing physiological needs ofthe fetus are achieved by multiple functional changes in thetotal placental exchange capacity. One component of thiscapacity is amino acid transport. Both placental membraneshave a range of active energy dependent amino acid transportsystems [1]. These systems act in a coordinated manner totransport amino acids from both circulations into thetrophoblast, as well as out of the trophoblast, into circulation.In addition to surface area, many other factors also influenceoverall activity. Maternal circulating concentrations of aminoacids also play a major role in regulating umbilical uptake,where the transport of any given amino acid from placenta tofetus is considered a function of both its own maternalconcentration and the maternal concentration of inhibitoryamino acids [2]. Additionally, electrical gradients exist over theplacenta, across which transport systems operate, indicative ofthe energy requirement of these systems [3]. It is important toremember that the trophoblast acts not only as a conduit foramino acids between the two circulations, but also has a highmetabolic rate, utilizing amino acids for its own metabolicfunctions, which include hormone and steroid production aswell as waste removal from fetal circulation [4].To understand the overall functional capacity of theplacental barrier, attempts to consider all of the abovecomponents need to be made, especially when investigatinghow adverse situations may impact upon the developmentaland functional capacity of the placenta. Specifically, in thesituation of fetal growth restriction (FGR), there is in vivo andin vitro data to demonstrate significant changes in the placentalsurface area/permeability constants [5], its amino acid trans-port activity in vitro [6e8], and in vivo [9e12]. The FGRplacenta has decreased total villous surface area, indicating thatmorphometric changes in vascularization may contribute to theoverall reduction in placental diffusional transport capacity.Thus, both decreased surface area for diffusional exchange forcompounds such as oxygen and reductions in the number ofspecific nutrient transporters and their activities may contrib-ute to a global reduction in nutrient transport in FGRpregnancies.The purpose of this workshop was to deal with a range ofwork representing aspects of amino acid transport systems,including their locations, their substrates and their activities,from both in vitro and in vivo settings. However, rather thanact as a forum for mini reviews, this workshop was designedfor presenters to put forward experimental inconsistencies insome of these aspects for general discussion and input from thegathered group. The aim, at the end of the workshop, was tohave a consensus of where specific placenta amino acidtransporters may be located, what their substrates and theirindividual activities may be, how they might interact with one

Activity and expression of Na+/H+ exchanger isoforms in the syncytiotrophoblast of the human placenta

The purpose of this study was to compare Na+/H+ exchanger (NHE) activity in the microvillous (MVM) and basal (BM) plasma membrane of the human placental syncytiotrophoblast and to determine the relative contribution of various NHE isoforms to this activity. Uptake of 22Na into isolated MVM vesicles in the presence of a H+ gradient, at initial rate, was four- to fivefold higher than that by BM vesicles (214+/-28 vs. 49+/-9 pmol/mg protein per 30 s, respectively, means+/-SEM, n=8, 6, P<0.001). The 22Na uptake by MVM, but not by BM, was reduced in the absence of a H+ gradient and in the presence of 500 microM amiloride. To determine the contribution of NHE1, NHE2 and NHE3 isoforms to NHE activity in MVM, we investigated the effect of amiloride analogues which show isoform selectivity. HOE 694, an analogue selective for NHE1 at low concentrations, inhibited 22Na uptake with an EC50 of 0.13+/-0.05 microM (n=6), whereas S3226, an analogue selective for NHE3 at low concentrations had an EC50 of 3.01+/-0.85 microM (n=5). To investigate this further, we measured recovery of syncytiotrophoblast intracellular pH (pHi) from an acid load using a H+-selective, fluorescent dye (BCECF) loaded into isolated intact placental fragments. This recovery was blocked in the absence of Na+ and the presence of amiloride (500 microM) and concentrations of HOE 694 and S3226 were comparable to those used in vesicle experiments. Overall these data show that under the conditions used NHE activity in the term placental syncytiotrophoblast is absent from BM. NHE activity in the MVM is attributable predominantly to NHE1.

Tissue Transglutaminase Expression and Activity in Placenta

Tissue transglutaminase (tTG) expression, distribution and activity were examined in human placenta and derived cells. Immunochemical techniques and RT-PCR were used to demonstrate tTG protein and mRNA in stromal cells and trophoblast in first trimester and at term, with higher levels later in pregnancy. Decidual cells also produce tTG. The data were confirmed using primary cultures of trophoblast, fibroblasts and decidual stromal cells. Substrate incorporation studies indicated tTG activity in association with fibroblast extracellular matrix and the syncytial microvillous membrane (MVM), where several target polypeptides could be observed. tTG is a major autoantigen in Coeliac disease (CoD) which is associated with poor pregnancy outcome. tTG at the placental MVM is a plausible target of maternal autoantibody action.

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

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. 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. 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. 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.