Cellular localization of glucose transporter messenger RNA in human placenta

High levels of expression of the glucose transporter (GLUT) isoforms 1 and 3 have been demonstrated in the human placenta by Northern blotting. However, the cellular localization of placental GLUT mRNA has not been described. Furthermore, recent preliminary kinetic data indicate that GLUT 2 might be present in syncytiotrophoblast. Human placental tissue from preterm (16-22 weeks) and term pregnancies was collected for identification and localization of glucose transporter mRNA. Following paraffin embedding, sections were cut and in situ hybridization was performed with fluorescein-labelled cRNA. In addition, immunoblotting and immunocytochemistry were carried out using an anti-GLUT 2 antibody. GLUT 1 mRNA was highly expressed in syncytiotrophoblast cells at term. GLUT 1 expression was much less abundant in non-syncytial cells. In contrast, GLUT 3 mRNA was present in lower amounts and more evenly distributed between syncytial and other placental cells. GLUT 1 mRNA was also highly abundant in preterm syncytiotrophoblast. The cellular distributions of GLUT 1 and GLUT 3 mRNA in the preterm placentas were similar to those in term tissue. With regard to GLUT 1, these findings correlate well with cellular localization and gestational development of GLUT 1 protein. No GLUT 2 protein was detected. It is concluded that GLUT 1 is the main isoform involved in transplacental glucose transport in the human.