Regulation of glucose transporters during development of the retinal pigment epithelium

The retinal pigment epithelium (RPE) separates the outer retina from its bl ood supply. To satisfy the retina's large requirement for glucose, the RPE expresses high levels of glucose transporters. In most rat cells, the trans porter GLUT3 provides a basal level of transport, but the expression of GLU T1 can be regulated. The opposite is true in chicken (P. Wagstaff, H.Y. Kan g, D. Mylott, P.J. Robbins, M.K. White, Characterization of the avian GLUT1 glucose transporter: differential regulation of GLUT1 and GLUT3 in chicken embryo fibroblasts, Mel. Biol. Cell 6 (1995) 1575-1589). We examined chick RPE to determine which isoform is regulated during development, and if the neural retina regulates GLUT expression. By RT-PCR, RPE expressed GLUT1 an d GLUT3, but not GLUT2. Only the level of GLUT1 increased between E5 and E1 8. A corresponding increase in GLUT1 protein was observed by immunoblotting . Most of the increase occurred between E14 and E18, which corresponds to t he late stage of tight junction development. A culture model of development was used to examine the intermediate phase, which extends from E7 to E14. While medium conditioned by the neural retina decreased paracellular diffus ion across the tight junctions, it increased diffusion through the glucose transporters. Unlike mammals, chick upregulates different isoforms in quies cent RPE and proliferating fibroblasts. Further, the upregulation of glucos e transport is coordinated with the development of tight junctions in the b lood-retinal barrier. (C) 2000 Elsevier Science B.V. All rights reserved.