Abstract
Purpose:
Since vascular endothelial cells growth factor (VEGF) is key to diabetic macular edema and can be regulated by insulin-like growth factor binding protein 3 (IGFBP-3), we determined the cellular signaling by which IGFBP-3 can reduce VEGF levels in retinal endothelial cells cultured in both normal and high glucose.
Methods:
Primary retinal endothelial cells were cultured in normal (5mM) or high glucose (25mM) with some cells transfected with a mutant IGFBP-3 that does not bind IGF-1. Additional cells were treated with recombinant endothelial nitric oxide synthase (eNOS) or protein kinase C zeta (PKCz) following to transfection with mutant IGFBP-3 to determine the role of eNOS and PKCz in the regulation of VEGF.
Results:
VEGF, eNOS and PKCz are all increased in retinal endothelial cells cultured in high glucose, which were reduced by treatment with mutant IGFBP-3. When cells in high glucose were treated with IGFBP-3 and recombinant eNOS, eNOS significantly increased both the phosphorylation of PKCz and VEGF levels, which were reduced by IGFBP-3 transfection. Similar results were obtained in cells treated with IGFBP-3 and recombinant PKCz.
Conclusions:
These data demonstrate that VEGF is regulated by IGFBP-3 in vascular cells cultured in high glucose. Furthermore, IGFBP-3 significantly reduces eNOS and PKCz to regulate VEGF. Taken together, this study provides a potential novel signaling pathway to allow for development of treatments for macular edema, in addition to the reduction in VEGF. Targeting upstream signaling pathways may also reduce VEGF-initiated responses in retinal endothelial cells.