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Fetomaternal Expression of Glucose Transporters (GLUTs)—Biochemical, Cellular and Clinical Aspects. Nutrients 2022; 14:nu14102025. [PMID: 35631166 PMCID: PMC9146575 DOI: 10.3390/nu14102025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Revised: 04/28/2022] [Accepted: 05/11/2022] [Indexed: 12/10/2022] Open
Abstract
Several types of specialized glucose transporters (GLUTs) provide constant glucose transport from the maternal circulation to the developing fetus through the placental barrier from the early stages of pregnancy. GLUT1 is a prominent protein isoform that regulates placental glucose transfer via glucose-facilitated diffusion. The GLUT1 membrane protein density and permeability of the syncytial basal membrane (BM) are the main factors limiting the rate of glucose diffusion in the fetomaternal compartment in physiological conditions. Besides GLUT1, the GLUT3 and GLUT4 isoforms are widely expressed across the human placenta. Numerous medical conditions and molecules, such as hormones, adipokines, and xenobiotics, alter the GLUT’s mRNA and protein expression. Diabetes upregulates the BM GLUT’s density and promotes fetomaternal glucose transport, leading to excessive fetal growth. However, most studies have found no between-group differences in GLUTs’ placental expression in macrosomic and normal control pregnancies. The fetomaternal GLUTs expression may also be influenced by several other conditions, such as chronic hypoxia, preeclampsia, and intrahepatic cholestasis of pregnancy.
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Wang YN, Ye YX, Guo ZW, Xiong ZL, Sun QS, Zhou D, Jiang SW, Chen H. Inducible knockout of syncytin-a leads to poor placental glucose transport in mice. Placenta 2022; 121:155-163. [PMID: 35349915 DOI: 10.1016/j.placenta.2022.03.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 03/11/2022] [Accepted: 03/14/2022] [Indexed: 02/05/2023]
Abstract
INTRODUCTION Cell-cell fusion of cytotrophoblasts into the syncytiotrophoblast layer is a key process in placental development. Syncytin, an endogenous retroviral envelope protein, is expressed in placental trophoblasts and specifically mediates syncytiotrophoblast layer formation. Syncytin deficiency has been observed in fetal growth-restricted placentas. Abnormal fetal growth, especially fetal growth restriction, is associated with the decreased expression of glucose transporters. Here, we aimed to determine the role of syncytin in fetal growth restriction in placental glucose transport capacity. METHODS To better explore the function of syncytin in fetal growth-restricted placenta, we generated an inducible knockout mouse model of syncytin-a gene. The expression levels of glucose transporters in BeWo cells were measured before and after HERV-W knockdown. RESULTS Syncytin-A disruption was associated with significant abnormalities in placental and fetal development in mice. Syncytin-A destruction causes extensive abnormalities in the maternal-fetal exchange structures in the labyrinth, including an extremely reduced number and dramatically irregular distribution of fetal vessels. Moreover, glucose transporter 1, glucose transporters 3, and connexin 26 expression levels decreased after E14.5. Consistently, low glucose transporter 1, glucose transporter 3, and connexin 26 levels were observed in HERV-W-silenced BeWo cells. DISCUSSION Syncytin-A is crucial for both syncytiotrophoblast layer development and morphogenesis, suggesting that syncytin-A disruption leads to fetal growth restriction associated with abnormalities in the maternal-fetal exchange barrier and decreased glucose transport.
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Affiliation(s)
- Ya-Nan Wang
- Department of Histology and Embryology, Shantou University Medical College, China; Department of Obstetrics and Gynecology, The Second Affiliated Hospital of Shantou University Medical College, China
| | - Yi-Xin Ye
- Department of Histology and Embryology, Shantou University Medical College, China
| | - Ze-Wen Guo
- Department of Obstetrics and Gynecology, Shantou Central Hospital, China
| | - Zhe-Lei Xiong
- Department of Histology and Embryology, Shantou University Medical College, China
| | - Qi-Si Sun
- Department of Histology and Embryology, Shantou University Medical College, China
| | - Da Zhou
- Department of Histology and Embryology, Shantou University Medical College, China
| | - Shi-Wen Jiang
- Center of Reproductive Medicine, The Affiliated Wuxi Maternity and Child Health Care Hospital of Nanjing Medical University, Wuxi, 214123, Jiangsu, China
| | - Haibin Chen
- Department of Histology and Embryology, Shantou University Medical College, China.
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Garcia-Santillan JA, Lazo-de-la-Vega-Monroy ML, Rodriguez-Saldaña GC, Solis-Barbosa MA, Corona-Figueroa MA, Gonzalez-Dominguez MI, Gomez-Zapata HM, Malacara JM, Barbosa-Sabanero G. Placental Nutrient Transporters and Maternal Fatty Acids in SGA, AGA, and LGA Newborns From Mothers With and Without Obesity. Front Cell Dev Biol 2022; 10:822527. [PMID: 35399516 PMCID: PMC8990844 DOI: 10.3389/fcell.2022.822527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 02/25/2022] [Indexed: 12/01/2022] Open
Abstract
Adverse environmental factors in early life result in fetal metabolic programming and increased risk of adult diseases. Birth weight is an indirect marker of the intrauterine environment, modulated by nutrient availability and placental transport capacity. However, studies of placental transporters in idiopathic birth weight alterations and in maternal obesity in relation to neonatal metabolic outcomes are scarce. We aimed to analyze the placental nutrient transporter protein expression in small (SGA, n = 14), adequate (AGA, n = 18), and large (LGA n = 10) gestational age term for newborns from healthy or obese mothers (LGA-OB, n = 9) and their association with maternal fatty acids, metabolic status, placental triglycerides, and neonatal outcomes. The transporter expression was determined by Western blot. The fatty acid profile was evaluated by gas chromatography, and placental triglycerides were quantified by an enzymatic colorimetric method. GLUT1 was higher in LGA and lower in SGA and positively correlated with maternal HbA1c and placental weight (PW). SNAT2 was lower in SGA, while SNAT4 was lower in LGA-OB. FATP1 was lower in SGA and higher in LGA. SNAT4 correlated negatively and FATP1 correlated positively with the PW and birth anthropometry (BA). Placental triglycerides were higher in LGA and LGA-OB and correlated with pregestational BMI, maternal insulin, and BA. Maternal docosahexaenoic acid (DHA) was higher in SGA, specifically in male placentas, correlating negatively with maternal triglycerides, PW, cord glucose, and abdominal perimeter. Palmitic acid (PA) correlated positively with FATP4 and cord insulin, linoleic acid correlated negatively with PA and maternal cholesterol, and arachidonic acid correlated inversely with maternal TG and directly with FATP4. Our study highlights the importance of placental programming in birth weight both in healthy and obese pregnancies.
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Affiliation(s)
| | | | | | - Miguel-Angel Solis-Barbosa
- Medical Sciences Department, Health Sciences Division, University of Guanajuato, Campus Leon, Guanajuato, Mexico
| | | | | | | | - Juan-Manuel Malacara
- Medical Sciences Department, Health Sciences Division, University of Guanajuato, Campus Leon, Guanajuato, Mexico
| | - Gloria Barbosa-Sabanero
- Medical Sciences Department, Health Sciences Division, University of Guanajuato, Campus Leon, Guanajuato, Mexico
- *Correspondence: Gloria Barbosa-Sabanero,
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Illsley NP, Baumann MU. Human placental glucose transport in fetoplacental growth and metabolism. Biochim Biophys Acta Mol Basis Dis 2018; 1866:165359. [PMID: 30593896 DOI: 10.1016/j.bbadis.2018.12.010] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 11/13/2018] [Accepted: 12/06/2018] [Indexed: 02/07/2023]
Abstract
While efficient glucose transport is essential for all cells, in the case of the human placenta, glucose transport requirements are two-fold; provision of glucose for the growing fetus in addition to the supply of glucose required the changing metabolic needs of the placenta itself. The rapidly evolving environment of placental cells over gestation has significant consequences for the development of glucose transport systems. The two-fold transport requirement of the placenta means also that changes in expression will have effects not only for the placenta but also for fetal growth and metabolism. This review will examine the localization, function and evolution of placental glucose transport systems as they are altered with fetal development and the transport and metabolic changes observed in pregnancy pathologies.
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Affiliation(s)
- Nicholas P Illsley
- Center for Abnormal Placentation, Department of Obstetrics and Gynecology, Hackensack University Medical Center, Hackensack, NJ, USA.
| | - Marc U Baumann
- Department of Obstetrics and Gynaecology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
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Sharma A, Davis A, Shekhawat PS. Hypoglycemia in the preterm neonate: etiopathogenesis, diagnosis, management and long-term outcomes. Transl Pediatr 2017; 6:335-348. [PMID: 29184814 PMCID: PMC5682372 DOI: 10.21037/tp.2017.10.06] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Glucose, like oxygen, is of fundamental importance for any living being and it is the major energy source for the fetus and the neonate during gestation. The placenta ensures a steady supply of glucose to the fetus, while birth marks a sudden change in substrate delivery and a major change in metabolism. Hypoglycemia is one of the most common pathologies encountered in the neonatal intensive care unit and affects a wide range of neonates. Preterm, small for gestational age (GA) and intra-uterine growth restricted neonates are especially vulnerable due to their lack of metabolic reserves and associated co-morbidities. Nearly 30-60% of these high-risk infants are hypoglycemic and require immediate intervention. Preterm neonates are uniquely predisposed to developing hypoglycemia and its associated complications due to their limited glycogen and fat stores, inability to generate new glucose using gluconeogenesis pathways, have higher metabolic demands due to a relatively larger brain size, and are unable to mount a counter-regulatory response to hypoglycemia. In this review we will discuss the epidemiology; pathophysiology; clinical presentation; management and neurodevelopmental outcomes in affected infants and summarize evidence to develop a rational and scientific approach to this common problem.
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Affiliation(s)
- Anudeepa Sharma
- Division of Neonatal-Perinatal Medicine, Department of Pediatrics, MetroHealth Medical Center, Case Western Reserve University, Cleveland, Ohio, USA
| | - Ajuah Davis
- Division of Pediatric Endocrinology, Department of Pediatrics, MetroHealth Medical Center, Case Western Reserve University, Cleveland, Ohio, USA
| | - Prem S Shekhawat
- Division of Neonatal-Perinatal Medicine, Department of Pediatrics, MetroHealth Medical Center, Case Western Reserve University, Cleveland, Ohio, USA
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Airley RE, Mobasheri A. Hypoxic regulation of glucose transport, anaerobic metabolism and angiogenesis in cancer: novel pathways and targets for anticancer therapeutics. Chemotherapy 2007; 53:233-56. [PMID: 17595539 DOI: 10.1159/000104457] [Citation(s) in RCA: 244] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2005] [Accepted: 05/09/2006] [Indexed: 12/15/2022]
Abstract
Cancer cells require a steady source of metabolic energy in order to continue their uncontrolled growth and proliferation. Accelerated glycolysis is one of the biochemical characteristics of cancer cells. Recent work indicates that glucose transport and metabolism are essential for the posttreatment survival of tumor cells, leading to poor prognosis. Glycolytic breakdown of glucose is preceded by the transport of glucose across the cell membrane, a rate-limiting process mediated by facilitative glucose transporter proteins belonging to the facilitative glucose transporter/solute carrier GLUT/SLC2A family. Tumors frequently show overexpression of GLUTs, especially the hypoxia-responsive GLUT1 and GLUT3 proteins. There are also studies that have reported associations between GLUT expression and proliferative indices, whilst others suggest that GLUT expression may be of prognostic significance. In this article we revisit Warburg's original hypothesis and review the recent clinical and basic research on the expression of GLUT family members in human cancers and in cell lines derived from human tumors. We also explore the links between hypoxia-induced genes, glucose transporters and angiogenic factors. Hypoxic tumors are significantly more malignant, metastatic, radio- and chemoresistant and have a poor prognosis. With the discovery the oxygen-sensitive transcription factor hypoxia-inducible factor (HIF-1) has come a new understanding of the molecular link between hypoxia and deregulated glucose metabolism. HIF-1 induces a number of genes integral to angiogenesis, e.g. vascular endothelial growth factor (VEGF), a process intimately involved with metastatic spread. This knowledge may enhance existing chemotherapeutic strategies so that treatment can be more rationally applied and personalized for cancer patients.
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Affiliation(s)
- Rachel E Airley
- Department of Developmental and Molecular Biology, Chanin Institute, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY, USA
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Das UG, He J, Ehrhardt RA, Hay WW, Devaskar SU. Time-dependent physiological regulation of ovine placental GLUT-3 glucose transporter protein. Am J Physiol Regul Integr Comp Physiol 2000; 279:R2252-61. [PMID: 11080093 DOI: 10.1152/ajpregu.2000.279.6.r2252] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We immunolocalized the GLUT-3 glucose transporter isoform versus GLUT-1 in the late-gestation epitheliochorial ovine placenta, and we examined the effect of chronic maternal hyperglycemia and hypoglycemia on placental GLUT-3 concentrations. GLUT-3 was limited to the apical surface of the trophoectoderm, whereas GLUT-1 was on the basolateral and apical surfaces of this cell layer and in the epithelial cells lining the placental uterine glands. GLUT-3 concentrations declined at 17-20 days of chronic hyperglycemia (P < 0.05), associated with increased uterine and uteroplacental net glucose uptake rate, but a normal fetal glucose uptake rate was observed. Chronic hypoglycemia did not change GLUT-3 concentrations, although uterine, uteroplacental, and fetal net glucose uptake rates were decreased. Thus maternal hyperglycemia causes a time-dependent decline in the entire placental glucose transporter pool (GLUT-1 and GLUT-3). In contrast, maternal hypoglycemia decreases GLUT-1 but not GLUT-3, resulting in a relatively increased GLUT-3 contribution to the placental glucose transporter pool, which could maintain glucose delivery to the placenta relative to the fetus when maternal glucose is low.
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Affiliation(s)
- U G Das
- Division of Neonatology and Developmental Biology, Department of Pediatrics, University of Pittsburgh, Magee-Womens Research Institute, Pittsburgh, Pennsylvania 15213, USA
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Hay WW. Nutrient-gene interactions during intrauterine life and lactation. Nutrition 2000; 16:226-8. [PMID: 10705079 DOI: 10.1016/s0899-9007(99)00278-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Affiliation(s)
- W W Hay
- University of Colorado Health Sciences Center, Denver 80262, USA
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Holemans K, Aerts L, Van Assche FA. Fetal growth and long-term consequences in animal models of growth retardation. Eur J Obstet Gynecol Reprod Biol 1998; 81:149-56. [PMID: 9989859 DOI: 10.1016/s0301-2115(98)00180-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Perturbations of the maternal environment involve an abnormal intrauterine milieu for the developing fetus. The altered fuel supply (depends on substrate availability, placental transport of nutrients and uteroplacental blood flow) from mother to fetus induces alterations in the development of the fetal endocrine pancreas and adaptations of the fetal metabolism to the altered intrauterine environment, resulting in intrauterine growth retardation. The alterations induced by maternal diabetes or maternal malnutrition (protein-calorie or protein deprivation) have consequences for the offspring, persisting into adulthood and into the next generation.
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Affiliation(s)
- K Holemans
- Department of Obstetrics and Gynecology, Katholieke Universiteit Leuven, U.Z. Gasthuisberg, Belgium
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Das UG, Sadiq HF, Soares MJ, Hay WW, Devaskar SU. Time-dependent physiological regulation of rodent and ovine placental glucose transporter (GLUT-1) protein. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:R339-47. [PMID: 9486290 DOI: 10.1152/ajpregu.1998.274.2.r339] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
To examine the in vivo and in vitro time-dependent effects of glucose on placental glucose transporter (GLUT-1) protein levels, we employed Western blot analysis using placenta from the short-term streptozotocin-induced diabetic pregnancy (STZ-D), uterine artery ligation-intrauterine growth restriction (IUGR) rat models, pregnant sheep exposed to chronic maternal glucose and insulin infusions, and the HRP.1 rat trophoblastic cell line exposed to differing concentrations of glucose. In the rat, 6 days of STZ-D with maternal and fetal hyperglycemia caused no substantive change, whereas 72 h of IUGR with fetal hypoglycemia and ischemic hypoxia resulted in a 50% decline in placental GLUT-1 levels (P < 0.05). In late-gestation ewes, maternal and fetal hyperglycemia caused an initial threefold increase at 48 h (P < 0.05), with a persistent decline between 10 to 21 days, whereas maternal and fetal hypoglycemia led to a 30-50% decline in placental GLUT-1 levels (P < 0.05). Studies in vitro demonstrated no effect of 0 mM, whereas 100 mM glucose caused a 60% decline (P < 0.05; 48 h) in HRP.1 GLUT-1 levels compared with 5 mM of glucose. The added effect of hypoxia on 0 and 100 mM glucose concentrations appeared to increase GLUT-1 concentrations compared with normoxic cells (P < 0.05; 100 mM at 18 h). We conclude that abnormal glucose concentrations alter rodent and ovine placental GLUT-1 levels in a time- and concentration-dependent manner; hypoxia may upregulate this effect. The changes in placental GLUT-1 concentrations may contribute toward the process of altered maternoplacentofetal transport of glucose, thereby regulating placental and fetal growth.
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Affiliation(s)
- U G Das
- Department of Pediatrics, University of Pittsburgh, Magee-Womens Research Institute, Pennsylvania 15213, USA
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Currie MJ, Bassett NS, Gluckman PD. Ovine glucose transporter-1 and -3: cDNA partial sequences and developmental gene expression in the placenta. Placenta 1997; 18:393-401. [PMID: 9250701 DOI: 10.1016/s0143-4004(97)80039-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Transplacental glucose transfer utilizes specific glucose transporter (GLUT) proteins. cDNAs encoding ovine placental GLUT1 and GLUT3 genes were isolated, cloned and sequenced and then used to investigate their developmental regulation in ovine placenta. A cDNA of approximately 2.2 kb was isolated from a Clontech lambda gt10 ovine adult liver cDNA library using a 436-bp rat GLUT1 cDNA probe. Sequence data obtained from this clone (1600 bp) demonstrated 97 per cent homology to nucleotides 477-2079 of bovine GLUT1. The deduced amino acid sequence of the ovine cDNA presented 99 per cent identity to amino acid 103-493 of bovine GLUT1, and 97-98 per cent identity to corresponding regions in human and rat GLUT1 deduced amino acid sequences. Reverse transcription-PCR (RT-PCR) was used to isolate an ovine cDNA fragment from placental total RNA. Forward and reverse primers (16 mer) were designed to amplify a predicted 483-bp fragment between the second transmembrane-spanning domain (M2) and intracellular loop of GLUT3. The deduced 161 amino acid sequence of the ovine cDNA demonstrated 84 and 88 per cent identity with murine and human GLUT3. These cDNAs were used to investigate the ontogeny of placental oGLUT1 and oGLUT3 gene expression by Northern analysis. Total RNA was extracted from ovine placenta at gestational days 45, 60, 90, 120 and 138 (n=6 per time point). Ovine GLUT1 gene expression increased significantly from days 45 to 60 (P<0.05), peaked at around day 120 of gestation, then decreased to about two-thirds of maximal levels by day 138 of gestation (term 147 +/- 2). Ovine GLUT3 gene expression increased throughout gestation with significant increases from days 45 to 60, 60 to 120 and 120 to 138 (P<0.05). This study confirms the presence of both GLUT1 and GLUT3 genes in the ovine placenta and demonstrates ontogenic regulation of gene expression. The difference in temporal gene expression between oGLUT1 and oGLUT3 suggests distinct roles for each transporter during development. The nucleotide sequences reported in this paper have been submitted to the GenBank/EMBL Data Bank under accession numbers U89029 (oGLUT1) and U89030 (oGLUT3).
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Affiliation(s)
- M J Currie
- Research Centre for Developmental Medicine and Biology, Faculty of Medicine and Health Science, University of Auckland, New Zealand
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Abstract
Glucose is one of the most important substances transferred from the maternal blood to the fetal circulation in the placenta, and its transport across the cellular membranes is mediated by glucose transporters. Facilitated-diffusion glucose transporter GLUT1 is abundant in the placental barrier, as is the case in other blood-tissue barriers, where GLUT1 is present at the critical plasma membranes of the barrier cells. In the human placenta, the microvillous apical and the basal plasma membranes of the syncytiotrophoblast are rich in GLUT1, which molecule seems to be responsible for the transcellular transport of glucose across the placental barrier. In the rat placental labyrinth, two layers of syncytiotrophoblasts (termed syncytiotrophoblasts I and II from the maternal side) serve as a barrier. GLUT1 is abundant at the plasma membrane of syncytiotrophoblast I facing the maternal side, and the plasma membrane of syncytiotrophoblast II facing the fetal side. Numerous gap junctions, made of connexin 26, connect syncytiotrophoblasts I and II, comprising a channel for the transfer of glucose between them. GLUT1 in combination with the gap junction, therefore, seems to serve as the structural basis for the transport of glucose across the rat placental barrier.
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Affiliation(s)
- K Takata
- Laboratory of Molecular and Cellular Morphology, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
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Takata K, Hirano H, Kasahara M. Transport of glucose across the blood-tissue barriers. INTERNATIONAL REVIEW OF CYTOLOGY 1997; 172:1-53. [PMID: 9102392 DOI: 10.1016/s0074-7696(08)62357-8] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
In specialized parts of the body, free exchange of substances between blood and tissue cells is hindered by the presence of a barrier cell layer(s). Specialized milieu of the compartments provided by these "blood-tissue barriers" seems to be important for specific functions of the tissue cells guarded by the barriers. In blood-tissue barriers, such as the blood-brain barrier, blood-cerebrospinal fluid barrier, blood-nerve barrier, blood-retinal barrier, blood-aqueous barrier, blood-perilymph barrier, and placental barrier, endothelial or epithelial cells sealed by tight junctions, or a syncytial cell layer(s), serve as a structural basis of the barrier. A selective transport system localized in the cells of the barrier provides substances needed by the cells inside the barrier. GLUT1, an isoform of facilitated-diffusion glucose transporters, is abundant in cells of the barrier. GLUT1 is concentrated at the critical plasma membranes of cells of the barriers and thereby constitutes the major machinery for the transport of glucose across these barriers where transport occurs by a transcellular mechanism. In the barrier composed of double-epithelial layers, such as the epithelium of the ciliary body in the case of the blood-aqueous barrier, gap junctions appear to play an important role in addition to GLUT1 for the transfer of glucose across the barrier.
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Affiliation(s)
- K Takata
- Laboratory of Molecular and Cellular Morphology, Gunma University, Japan
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