title: Expression and functional characterisation of System L amino acid transporters in the human term placenta.
abstract: BACKGROUND
  System L transporters LAT1 (SLC7A5) and LAT2 (SLC7A8) mediate the uptake of large, neutral amino acids in the human placenta. Many System L substrates are essential amino acids, thus representing crucial nutrients for the growing fetus. Both LAT isoforms are expressed in the human placenta, but the relative contribution of LAT1 and LAT2 to placental System L transport and their subcellular localisation are not well established. Moreover, the influence of maternal body mass index (BMI) on placental System L amino acid transport is poorly understood. Therefore the aims of this study were to determine: i) the relative contribution of the LAT isoforms to System L transport activity in primary human trophoblast (PHT) cells isolated from term placenta; ii) the subcellular localisation of LAT transporters in human placenta; and iii) placental expression and activity of System L transporters in response to maternal overweight/obesity.
  
  
  METHODS
  System L mediated leucine uptake was measured in PHT cells after treatment with si-RNA targeting LAT1 and/or LAT2. The localisation of LAT isoforms was studied in isolated microvillous plasma membranes (MVM) and basal membranes (BM) by Western blot analysis. Results were confirmed by immunohistochemistry in sections of human term placenta. Expression and activity System L transporters was measured in isolated MVM from women with varying pre-pregnancy BMI.
  
  
  RESULTS
  Both LAT1 and LAT2 isoforms contribute to System L transport activity in primary trophoblast cells from human term placenta. LAT1 and LAT2 transporters are highly expressed in the MVM of the syncytiotrophoblast layer at term. LAT2 is also localised in the basal membrane and in endothelial cells lining the fetal capillaries. Measurements in isolated MVM vesicles indicate that System L transporter expression and activity is not influenced by maternal BMI.
  
  
  CONCLUSIONS
  LAT1 and LAT2 are present and functional in the syncytiotrophoblast MVM, whereas LAT2 is also expressed in the BM and in the fetal capillary endothelium. In contrast to placental System A and beta amino acid transporters, MVM System L activity is unaffected by maternal overweight/obesity.
authors.affiliation: Department of Obstetrics and Gynaecology, University of Cambridge, Cambridge, UK. fg327@medschl.cam.ac.uk.
authors.forename: Francesca
authors.initials: F
authors.lastname: Gaccioli
authors.affiliation: Division of Basic Reproductive Sciences, Department of Obstetrics and Gynaecology, University of Colorado Denver Anschutz Medical Campus, Aurora, Denver, CO, USA. irving.aye@ucdenver.edu.
authors.forename: Irving L M H
authors.initials: IL
authors.lastname: Aye
authors.affiliation: Institute of Biomedicine, The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden. sara.roos@gu.se.
authors.forename: Sara
authors.initials: S
authors.lastname: Roos
authors.affiliation: Department of Obstetrics and Gynaecology, University of Cambridge, Cambridge, UK. sml60@medschl.cam.ac.uk.
authors.forename: Susanne
authors.initials: S
authors.lastname: Lager
authors.affiliation: Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center, San Antonio, TX, USA. vaninram@yahoo.com.
authors.forename: Vanessa I
authors.initials: VI
authors.lastname: Ramirez
authors.affiliation: Division of Bio-System Pharmacology, Department of Pharmacology, Osaka University Graduate School of Medicine, Osaka, Japan. ykanai@pharma1.med.osaka-u.ac.jp.
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Kanai
authors.affiliation: Section of Neonatology, Department of Pediatrics, University of Colorado Denver Anschutz Medical Campus, Aurora, Denver, CO, USA. theresa.powell@ucdenver.edu.
authors.forename: Theresa L
authors.initials: TL
authors.lastname: Powell
authors.affiliation: Division of Basic Reproductive Sciences, Department of Obstetrics and Gynaecology, University of Colorado Denver Anschutz Medical Campus, Aurora, Denver, CO, USA. thomas.jansson@ucdenver.edu.
authors.forename: Thomas
authors.initials: T
authors.lastname: Jansson
mesh_terms: D000328:Adult; D027062:Amino Acid Transport System L / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D009765:Obesity / Q000235:genetics / Q000378:metabolism; D050177:Overweight / Q000235:genetics / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D047929:Term Birth / Q000378:metabolism; D014327:Trophoblasts / Q000378:metabolism*
chemical_list: D027062:Amino Acid Transport System L