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 blotti ng. 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 t issue from preterm (16-22 weeks) and term pregnancies was collected fo r identification and localization of glucose transporter mRNA. Followi ng 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 antibod y. GLUT 1 mRNA was highly expressed in syncytiotrophoblast cells at te rm. GLUT 1 expression was much less abundant in non-syncytial cells. I n contrast, GLUT 3 mRNA was present in lower amounts and more evenly d istributed between syncytial and other placental cells. GLUT 1 mRNA wa s also highly abundant in preterm syncytiotrophoblast. The cellular di stributions of GLUT 1 and GLUT 3 mRNA in the preterm placentas were si milar to those in term tissue. With regard to GLUT 1, these findings c orrelate well with cellular localization and gestational development o f GLUT 1 protein. No GLUT 2 protein was detected. It is concluded that GLUT 1 is the main isoform involved in transplacental glucose transpo rt in the human.