Placental glucose transporter 3 (GLUT3) is up-regulated in human pregnancies complicated by late-onset intrauterine growth restriction

Abstract

Introduction: Transport of glucose from maternal blood across the placental trophoblastic tissue barrier is critical to sustain fetal growth. The mechanism by which GLUTs are regulated in trophoblasts in response to ischemic hypoxia encountered with intrauterine growth restriction (IUGR) has not been suitably investigated.

Objective: To investigate placental expression of GLUT1, GLUT3 and GLUT4 and possible mechanisms of GLUT regulation in idiopathic IUGR.

Methods: We analyzed clinical, biochemical and histological data from placentas collected from women affected by idiopathic full-term IUGR (n = 10) and gestational age-matched healthy controls (n = 10).

Results: We found increased GLUT3 protein expression in the trophoblast (cytotrophoblast greater than syncytiotrophoblast) on the maternal aspect of the placenta in IUGR compared to normal placenta, but no differences in GLUT1 or GLUT4 were found. No differential methylation of the GLUT3 promoter between normal and IUGR placentas was observed. Increased GLUT3 expression was associated with an increased nuclear concentration of HIF-1α, suggesting hypoxia may play a role in the up-regulation of GLUT3.

Discussion: Further studies are needed to elucidate whether increased GLUT3 expression in IUGR is a marker for defective villous maturation or an adaptive response of the trophoblast in response to chronic hypoxia.

Conclusions: Patients with IUGR have increased trophoblast expression of GLUT3, as found under the low-oxygen conditions of the first trimester.

Keywords: GLUT; Glucose; Intrauterine growth restriction; Placenta; Transport.

Published by Elsevier Ltd.

Figures

Fig. 1

(A) Real-time quantitative RT-PCR analysis of placental GLUT1, GLUT3 and GLUT4 expression. IUGR placentas (n=10) are assayed against gestationally age-matched, control placentas (n=10) for the maternal vs. fetal side. Relative quantification of PCR products was based on the Ct value differences between target and the housekeeping gene using the comparative Ct method (Eukaryotic 18s rRNA (Applied Biosystems) was used as an internal control. *P < 0.05. (B) Western blot analysis of GLUT1, GLUT3, and GLUT4 in placental biopsies obtained from women with normal pregnancy (n=10) or pregnancy affected by IUGR, suspected by abnormal prenatal ultrasound (n=10). Protein taken from fetal (F) and maternal (M) sides were loaded on 12% SDS-polyacrylamide gels and transferred onto PVDF membranes. Representative blots are shown. (B, Bottom) Arbitrary densitometric units showing mean of all samples; data are normalized to a control value of 100%, bars indicate SE. *P < 0.05.

Fig. 2

(A) Western blot analysis of HIF-1α in total protein of placental biopsies obtained from the maternal and fetal sides in women with normal pregnancy (n=10), or pregnancy affected by IUGR, suspected by abnormal prenatal ultrasound (n=10), or preeclampsia (n=5). Representative blots are shown. Arbitrary densitometric units showing mean of all samples; data are normalized to a control value of 100%, bars indicate SE. *P

Fig. 3

DNA methylation analysis of placental GLUT3 promoter regions in placental biopsies obtained from the maternal and fetal sides in women with normal pregnancy and pregnancy affected by IUGR. Genomic DNA was processed by pyrosequencing.

Fig. 4

Immunohistochemical localization of GLUT3 and HIF-1α in human placenta. (A) Controls for GLUT3 staining at 600x magnification. GLUT3 staining of human testis; there was no GLUT3 staining in sections where the primary antibody was omitted (A1). Positive control (testis) shows immunoreaction for GLUT3 (brown) in the maturing secondary spermatocytes and sperm (A2). (B) Sections of three different subjects showing normal term placenta (B1-B3) vs. IUGR (slide B4=sample 8, slide B5=sample 10, slide B6=sample 5), stained with GLUT3, staining at 400x magnification. GLUT3 is localized to the cytotrophoblast layer and the syncytiotrophoblast layer to a lesser degree. Arrows indicate immunoreactive syncytium, as determined by their morphology and location relative to the intervillous space. Triangles show underlying cytotrophoblast layer. Scale bars = 50μm (C) GLUT3 positive staining area per squared micrometers was quantified using Dynamiccellcount BZ-HIC software. Digital analysis revealed increased GLUT3 immunopositivity in IUGR as compared to normal placenta. *P