MODULATION OF BLOOD-BRAIN BARRIER NUTRIENT TRANSPORT

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The blood-brain barrier (BBB) GLUT1 glucose transporter is abundant in brain, and localized to the capillary endothelia. In vitro studies of other isoforms of the glucose transporter have demonstrated that rapid up-regulation of glucose transport is achieved through translocation of transporter proteins from intracellular sites to the external cell membrane, i.e., transporter recruitment. Down-regulation is characterized by relocation of the transporters to internal sites. It is proposed to experimentally manipulate BBB glucose transporter in vivo (to confirm that rapid up- or down regulation has been achieved), and then study the localization patterns of the GLUT1 transporter using immunogold electron microscopic methods. A unique feature of BBB endothelia is the apparent asymmetric distribution of GLUT1 transporters; ablumenal membranes have a 3-4 fold greater number of transporters than the lumenal membrane, and relatively short distances (300-500 nm) separate these endothelial surfaces. Because the lumenal capillary membrane is believed to be the site where rate-limitation of BBB glucose transport may occur, we also propose to test the hypothesis that rapid up-and down-regulation in these endothelia may not only involve translocation of cytoplasmic transporter proteins, but also movement from the ablumenal to lumenal membrane across relatively short distances. Using membrane-impermeant agents, site-selective in vivo experimental manipulation of lumenal membrane GLUT1 transporters is planned. It is anticipated that this work will provide insights into the cellular mechanisms of BBB glucose transport, and define transporter responses in anoxia, brain injury, seizures and in brain tumors.