MOLECULAR REGULATION OF THE BLOOD-BRAIN-BARRIER GLUT1 GLUCOSE-TRANSPORTER BY BRAIN-DERIVED FACTORS

Glucose is the crucial metabolic fluid for the brain, and the transpor t of this nutrient from blood to brain is limited by the blood-brain b arrier (BBB) GLUT1 glucose transporter. The activity of this transport er is altered in different pathophysiological conditions including Alz heimer's disease. The expression of the BBB-GLUT1 gene is directed by brain trophic factors, and the brain-derived peptide preparation Cereb rolysin(C) (C1, EBEWE, Austria), used in the treatment of Alzheimer's disease, increases the BBB-GLUT1 mRNA stability and the expression of the BBB-GLUT1 gene. In the present investigation, C1 markedly increase d (p < 0.001) the expression of a BBB-GLUT1 reporter gene, named clone 753, that contains an important regulatory cis-ac ting element involv ed in the stabilization of this transcript in brain endothelial cultur ed cells (ECL). In experiments with a reporter gene lacking this regul atory element, C1 produced only a minimal fraction of the effect obser ved with clone 753. UV-cross linking/PAGE experiments showed that the GLUT1 transcript reacts with ECL cytosolic proteins to form a RNA/prot ein complex of similar to 80 kDa. The abundance of this cis/trans acti ng complex was found to be increased in C1-treated cells. Overall, dat a presented here demonstrate that i) Cl increases the expression of a BBB-GLUT1-luciferase reporter gene containing a region of the 3'-untra nslated region of BBB-GLUT1 mRNA with important regulatory cis-acting elements involved in the stabilization of this transcript, and ii) the increased expression of this BBB-GLUT1 reporter gene was associated w ith augmented abundance of a transacting factor that binds to the cis- acting element described in (i), suggesting that this association may be involved in the stabilization of GLUT1 mRNA induced by C1.