High expression of the Glut1 glucose transporter in human brain hemangioblastoma endothelium

The principal glucose transporter at the blood-brain barrier is Glut1, and GLUT1 expression is downregulated in high grade gliomas. In the present study, glucose transporter expression was studied in surgically resected hemangioblastoma tissue. Light microscopic immunochemistry indicated the high expression of the Glut1 glucose transporter isoform throughout the central vascular endothelium of this tissue. Glial fibrillary acidic protein (GFAP) was observed only at the tumor border, with no GFAP immunoreactivity in stromal cells, pericytes or endothelia in the central tumor regions. It is generally believed that more Glut1 is found in erythrocytes than any other cell, but quantitative electron microscopic immunogold analyses of Glut1-immunoreactive sites per micron of capillary membrane showed the Glut1 density in tumor endothelial membranes glucose transporter was 2-3-fold higher than in human red cells. In the same tissue samples, qualitative immunogold electron microscopy of human serum albumin indicated that this protein (MW 65,000) moved freely from the vascular space into pericapillary regions, confirming the leaky barrier characteristics of the hemangioblastoma. These studies show that Glut1 expression may be high in endothelia that are highly permeable and devoid of astroglial contacts. Thus, human cerebral hemangioblastomas may provide a novel system for studying the induction of Glut1 in the blood-brain barrier.