Insulin-induced vascular endothelial growth factor expression in retina.
OBJECTIVE
Clinical studies have demonstrated that intensive insulin therapy causes a transient worsening of retinopathy. The mechanisms underlying the initial insulin-induced deterioration of retinal status in patients with diabetes remain unknown. Vascular endothelial growth factor (VEGF) is known to be operative in the pathogenesis of diabetic retinopathy. The current study was conducted to characterize the effect of insulin on retinal VEGF gene expression in vitro and in vivo.


METHODS
The effect of insulin on VEGF expression in vivo was examined by in situ hybridization studies of rat retinal VEGF transcripts. To examine the mechanisms by which insulin regulates VEGF expression, human retinal pigment epithelial (RPE) cells were exposed to insulin, and VEGF mRNA levels were quantified with RNase protection assays (RPAs). Conditioned media from insulin-treated RPE cells were assayed for VEGF protein and capillary endothelial cell proliferation. The capacity of insulin to stimulate the VEGF promoter linked to a luciferase reporter gene was characterized in transient transfection assays.


RESULTS
Insulin increased VEGF mRNA levels in the ganglion, inner nuclear, and RPE cell layers. In vitro, insulin increased VEGF mRNA levels in human RPE cells and enhanced VEGF promoter activity without affecting transcript stability. Insulin treatment also increased VEGF protein levels in conditioned RPE cell media in a dose-dependent manner with a median effective concentration of 5 nM. The insulin-conditioned RPE cell media stimulated capillary endothelial cell proliferation, an effect that was completely blocked by anti-VEGF neutralizing antibody.


CONCLUSIONS
Insulin increases VEGF mRNA and secreted protein levels in RPE cells through enhanced transcription of the VEGF gene. Intensive insulin therapy may cause a transient worsening of retinopathy in patients with diabetes through increased retinal VEGF gene expression.
Lu
M
M
Children's Hospital and Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston 02114, USA.
Amano
S
S
Miyamoto
K
K
Garland
R
R
Keough
K
K
Qin
W
W
Adamis
A P
AP
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D016228:Endothelial Growth Factors / Q000235:genetics* / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression; D017403:In Situ Hybridization; D007328:Insulin / Q000494:pharmacology*; D008222:Lymphokines / Q000235:genetics* / Q000378:metabolism; D008297:Male; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D014158:Transcription, Genetic / Q000187:drug effects; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D016228:Endothelial Growth Factors; D007328:Insulin; D008222:Lymphokines; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors