Ablation of 4E-BP1/2 prevents hyperglycemia-mediated induction of VEGF expression in the rodent retina and in Muller cells in culture.
OBJECTIVE
Vascular endothelial growth factor (VEGF) contributes to diabetic retinopathy, but control of its expression is not well understood. Here, we tested the hypothesis that hyperglycemia mediates induction of VEGF expression in a eukaryotic initiation factor 4E (eIF4E) binding protein (4E-BP) 1 and 2 dependent manner.


METHODS
The retina was harvested from control and type 1 diabetic rats and mice and analyzed for VEGF mRNA and protein expression as well as biomarkers of translational control mechanisms. Similar analyses were performed in Müller cell cultures exposed to hyperglycemic conditions. The effect of 4E-BP1 and 4E-BP2 gene deletion on VEGF expression was examined in mice and in mouse embryo fibroblasts (MEFs).


RESULTS
Whereas VEGF mRNA in the retina remained constant, VEGF expression was increased as early as 2 weeks after the onset of diabetes. Increases in expression of 4E-BP1 protein mirrored those of VEGF and expression of 4E-BP1 mRNA was unchanged. Similar results were observed after 10 h of exposure of cells in culture to hyperglycemic conditions. Importantly, the diabetes-induced increase in VEGF expression was not observed in mice deficient in 4E-BP1 and 4E-BP2, nor in MEFs lacking the two proteins.


CONCLUSIONS
Hyperglycemia induces VEGF expression through cap-independent mRNA translation mediated by increased expression of 4E-BP1. Because the VEGF mRNA contains two internal ribosome entry sites, the increased expression is likely a consequence of ribosome loading at these sites. These findings provide new insights into potential targets for treatment of diabetic retinopathy.
Schrufer
Tabitha L
TL
Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
Antonetti
David A
DA
Sonenberg
Nahum
N
Kimball
Scot R
SR
Gardner
Thomas W
TW
Jefferson
Leonard S
LS
D048868:Adaptor Proteins, Signal Transducing; D000293:Adolescent; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics*; D018797:Cell Cycle Proteins; D002648:Child; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics*; D003930:Diabetic Retinopathy / Q000453:epidemiology; D039561:Eukaryotic Initiation Factor-4E / Q000235:genetics; D039642:Eukaryotic Initiation Factors / Q000235:genetics; D017353:Gene Deletion; D005786:Gene Expression Regulation; D006801:Humans; D006943:Hyperglycemia / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008957:Models, Genetic; D010750:Phosphoproteins / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics*
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C499527:Eif4ebp1 protein, mouse; C499526:Eif4ebp1 protein, rat; C491255:Eif4ebp2 protein, mouse; D039561:Eukaryotic Initiation Factor-4E; D039642:Eukaryotic Initiation Factors; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A