The brain-type glucose transporter mRNA is specifically expressed at the blood-brain barrier

Abstract

The brain-type glucose transporter (bGT) is assumed to be distributed among neurons and glial cells, but to be particularly enriched in brain microvascular endothelium, which makes up the bloodbrain barrier (BBB) in vivo. However, in the course of the present studies it was found that the bGT is specifically expressed at the BBB in brain. The relative abundance of bGT and actin (used as a control) mRNAs were measured in bovine brain, brain capillaries, and capillary-depleted brain. Northern blot analysis showed that the bGT 2.9 Kb mRNA was increased 21-fold in brain capillaries as compared to total brain, and it was not detected in capillary-depleted brain even after overexposure of the film. This study demonstrates that i) the bGT is specifically expressed at the BBB in brain, ii) the bGT transcript in total brain represents only dilution of the capillary or BBB glucose transporter transcript, and iii) as yet unidentified glucose transporters are likely expressed in neurons and in glial cells.