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


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


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


CONCLUSIONS
The insulin-regulatable GLUT4 is expressed in the cytosol of first trimester ST compatible with a role for GLUT4 in placental glucose transport in early pregnancy. The placental expression pattern of GLUT isoforms in early pregnancy is distinct from that later in pregnancy.
Ericsson
A
A
Department of Physiology and Pharmacology, Perinatal Center, Göteborg University, 405 30 Göteborg, Sweden. anette.ericsson@fysiologi.gu.se
Hamark
B
B
Powell
T L
TL
Jansson
T
T
D015153:Blotting, Western; D005260:Female; D005947:Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1; D051274:Glucose Transporter Type 3; D051275:Glucose Transporter Type 4; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology; D009004:Monosaccharide Transport Proteins / Q000235:genetics* / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014327:Trophoblasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D051272:Glucose Transporter Type 1; D051274:Glucose Transporter Type 3; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; C495677:SLC2A1 protein, human; C495687:SLC2A3 protein, human; C495692:SLC2A4 protein, human; D005947:Glucose