Enhancement of glucose transport by vascular endothelial growth factor in retinal endothelial cells

PURPOSE. To investigate effects of vascular endothelial growth factor (VEGF) on glucose transport and GLUT1 glucose transporter expression in primary bovine retinal endothelial cell (BREC) cultures. METHODS. Glucose transport in control and VEGF-treated BREC cultures was determined by measurement of [C-14]-3-O-methylglucose (3MG) uptake. GLUT1 protein and mRNA was determined by Western and Northern blot analyses, respectively. Protein kinase C (PKC) activity was measured in control and VEGF-treated cultures, and glucose transport was determined with and without prior PKC depletion and PKC inhibition. RESULTS. Dose-dependent increases in 3MG uptake were seen in the VEGF-treated cultures, with an increase of 69% after a 24-hour exposure to 50 ng/ml VEGF (P < 0.001). Total cellular GLUT1 mRNA or protein, however, was unchanged. Western blot analysis of plasma membrane fractions revealed a 75% increase in plasma membrane GLUT1 in VEGF-treated cultures (P = 0.02), suggesting that the VEGF-stimulated increase in glucose transport was due to a translocation of GLUT1 to the cell membrane. VEGF stimulated a 90% increase in PK activity in membrane fractions from cultures treated with VEGF, and VEGF-stimulated enhancement of glucose transport was abolished by cellular PKC depletion and by general and PKC beta inhibition. CONCLUSIONS. The present study demonstrates VEGF-mediated enhancement of retinal endothelial cell glucose transport and suggests that this increase is due to PKC beta-mediated translocation of cytosolic GLUT1 to the plasma membrane surface. Upregulation of retinal endothelial cell glucose transport by various factors associated with the development of retinopathy may be responsible for the metabolic derangements observed in the diabetic inner blood-retinal barrier in vivo.