Immunolocalization of glucose transporter 1 and 3 in the placenta: application to cytodiagnosis of Papanicolaou smear

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

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.

Temporal and spatial distribution of murine placental and brain GLUT3-luciferase transgene as a readout of in vivo transcription

To investigate in vivo transcription of the facilitative glucose transporter isoform-GLUT3 gene, we created GLUT3-firefly luciferase transgenic mouse lines that demonstrate tissue-specific [adult: brain > testis ≥ skeletal muscle > placenta; postnatal (PN): skeletal muscle > brain = skin], temporal, and spatial distribution of the reporter gene/enzyme activity that is unique from endogenous GLUT3 mRNA/protein. In this mouse model, luciferase expression/activity serving as a readout of in vivo transcription peaked at 12 days gestation along with proliferating cell nuclear antigen (cell replication) in placenta and embryonic brain preceding peak GLUT3 protein expression at 18-19 days gestation. In contrast, a postnatal increase in brain luciferase mRNA peaked with endogenous GLUT3 mRNA, but after that of NeuroD6 protein (neurogenesis) at PN7. Luciferase activity paralleled GLUT3 protein expression with Na(+)-K(+)-ATPase (membrane expansion) and synaptophysin (synaptogenesis) proteins, peaking at PN14 and lasting until 60 days in the adult. Thus GLUT3 transcription in placenta and embryonic brain coincided with cell proliferation and in postnatal brain with synaptogenesis. Longitudinal noninvasive bioluminescence (BLI) monitoring of in vivo brain GLUT3 transcription reflected cross-sectional ex vivo brain luciferase activity only between PN7 and PN21. Hypoxia/reoxygenation at PN7 revealed transcriptional increase in brain GLUT3 expression reflected by in vivo BLI and ex vivo luciferase activity. These observations collectively support a temporal contribution by transcription toward ensuring adequate tissue-specific, developmental (placenta and embryonic brain), and postnatal hypoxic brain GLUT3 expression.

Cervical neoplasia in pregnancy. Part 1: screening and management of preinvasive disease

Cervical cancer screening is an essential component of prenatal care. The diagnosis and management of cervical intraepithelial neoplasia (CIN) during pregnancy are challenging, and sufficient information does not exist to allow for a definitive evidence-based approach. The American Society for Colposcopy and Cervical Pathology has recently published guidelines regarding the evaluation of abnormal Papanicolaou tests and the treatment of CIN in this setting. Many techniques traditionally recommended in the evaluation of abnormal cervical cytology and the treatment of CIN in the nonpregnant woman, such as colposcopy, cervical biopsy, and electrosurgical excision, can be applied to the pregnant patient with important exceptions. The vascular cervix associated with the gravid condition and the risk of premature pregnancy loss mandates deviation from existing consensus guidelines in screening for cervical cancer in pregnancy and treating associated CIN. In the present review, current guidelines regarding cervical cancer screening are reviewed, and data from studies of pregnant populations are summarized.

GLUT1 and GLUT8 in endometrium and endometrial adenocarcinoma

Glucose is provided to cells by a family of glucose transport facilitators known as GLUTs. These transporters are expressed in a tissue specific manner and are overexpressed in many primary tumors of these tissues. Regulation of glucose transport facilitator expression has been demonstrated in endometrial tissue and endometrial adenocarcinoma. The following experiments were conducted to quantify and localize the expression of GLUT1 and GLUT8 in benign endometrium and compare this expression to endometrial cancer. Endometrial tissue samples were obtained from random hysterectomy specimens of patients with benign indications for surgery and endometrial cancer. Immunoblot and immunolocatization studies were performed using GLUT1 and GLUT8 specific antisera. Endometrial samples from 65 women who had undergone hysterectomy were examined (n=38 benign, n=27 malignant). A 44 and a 35.4 kDa immunoreacive species was demonstrated in endometrium and endometrial cancer for GLUT1 and GLUT8, respectively. Upregulation of GLUT1 expression was demonstrated with increasing grade of tumors (P<0.002). GLUT8 expression was increased in all tumor subtypes compared to atrophic endometrium (P<0.001). Apical localization by GLUT1 and GLUT8 was demonstrated in endometrial glands. GLUT1 and GLUT8 demonstrated diffuse intracellular localization in the cancer subtypes. GLUT1 and GLUT8 are expressed in both human endometrium and endometrial cancer. There appears to be a step-wise progression in GLUT1 and GLUT8 expression as tumor histopathology worsens. GLUT1 and GLUT8 may be important markers in tumor differentiation, as well as providing energy to rapidly dividing tumor cells.