Regulation of vascular endothelial growth factor expression by insulin-like growth factor I.
Insulin-like growth factor I (IGF-I) and vascular endothelial growth factor (VEGF) levels are correlated with retinal ischemia-associated intraocular neovascularization in humans. Since VEGF is required for iris and retinal neovascularization in animal models of retinal ischemia, we tested whether IGF-I could act as an indirect angiogenic factor by increasing VEGF gene expression. IGF-I increased retinal pigment epithelial (RPE) cell VEGF mRNA in a concentration-dependent manner with an EC50 of 7 nmol/1 (53.6 ng/ml). RPE and bovine smooth muscle cells exposed to 50 nmol/l (383 ng/m1) IGF-I achieved peak VEGF mRNA expression within 2 h. IGF-I-treated RPE cells increased VEGF protein levels in conditioned media and stimulated capillary endothelial cell proliferation. Blockade of the IGF-I receptor with a neutralizing antibody abrogated the VEGF increases in RPE cells. Further, hypoxia-mediated and IGF-I-mediated increases in VEGF mRNA and protein levels were additive in RPE cells, and the hypoxia-induced VEGF increases were independent of endogenous IGF-I. VEGF promoter activity was enhanced by IGF-I in RPE cells, but VEGF transcript half-life was unaltered. In summary, the supplementation of RPE and smooth muscle cell cultures with IGF-I at 5-100 nmol/l increased VEGF mRNA and secreted protein levels. The VEGF increases in RPE cells occurred primarily through enhanced transcription of the VEGF gene and via the IGF-I receptor. Elevated IGF-I levels may promote neovascularization through increased retinal VEGF gene expression.
Punglia
R S
RS
Laboratory for Surgical Research, Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Lu
M
M
Hsu
J
J
Kuroki
M
M
Tolentino
M J
MJ
Keough
K
K
Levy
A P
AP
Levy
N S
NS
Goldberg
M A
MA
D'Amato
R J
RJ
Adamis
A P
AP
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D015152:Blotting, Northern; D002196:Capillaries; D002455:Cell Division; D015687:Cell Hypoxia; D002461:Cell Line, Transformed; D017077:Culture Media, Conditioned; D016228:Endothelial Growth Factors / Q000096:biosynthesis / Q000235:genetics*; D004730:Endothelium, Vascular / Q000166:cytology; D005786:Gene Expression Regulation; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007700:Kinetics; D008222:Lymphokines / Q000096:biosynthesis / Q000235:genetics*; D051379:Mice; D010857:Pigment Epithelium of Eye / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D000906:Antibodies; D017077:Culture Media, Conditioned; D016228:Endothelial Growth Factors; D008222:Lymphokines; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1