Pigment epithelium-derived factor downregulates vascular endothelial growth factor (VEGF) expression and inhibits VEGF–VEGF receptor 2 binding in diabetic retinopathy

Abstract

It has been shown that the balance between vascular endothelial growth factor (VEGF), a major angiogenic stimulator, and pigment epithelium-derived factor (PEDF), a potent angiogenic inhibitor, is critical for the regulation of vascular permeability and angiogenesis. However, the regulation of the balance is largely unclear. The present study demonstrated that there is a reciprocal interaction between VEGF and PEDF in the retina. PEDF significantly decreased VEGF expression in both retinal capillary endothelial cells (RCEC) and Mü ller cells. This PEDF effect was confirmed in the retina of rats with oxygen-induced retinopathy. Silencing of the PEDF gene by siRNA in Mü ller cells resulted in a significant upregulation of VEGF expression at both the RNA and protein levels, suggesting that PEDF is an endogenous negative regulator of VEGF. The further study of the mechanism showed that PEDF inhibited hypoxia-induced increases in VEGF promoter activity, HIF-1 nuclear translocation and mitogen activated protein kinase phosphorylation. These results suggest that PEDF inhibits VEGF expression at the transcriptional level. In addition, PEDF effectively inhibited VEGF binding to RCEC. Moreover, in vitro receptor-binding assay demonstrated that PEDF competed with VEGF for binding to VEGF receptor 2, which may represent a new mechanism for PEDF activity. On the other hand, VEGF significantly downregulated PEDF expression in RCEC, but not in retinal Mü ller cells, suggesting a VEGF receptormediated process. These results suggest that the reciprocal regulation between VEGF and PEDF may play a role in angiogenic control. The decrease in PEDF levels in the retina is at least partially responsible for the increase in VEGF expression and subsequent vascular leakage and neovascularization in diabetes.

Vascular endothelial growth factor in eye disease

“…Clinical trials in patients with diabetic macular edema have shown beneficial effects of anti-VEGF agents in reducing retinal vascular permeability as assessed by fluorescein angiography and decreasing macular edema as shown by optical coherence tomography (Avery et al, 2006;Haritoglou et al, 2006;Jorge et al, 2006;Starita et al, 2007). Recent data indicate that intravitreal injections of PEDF can also reduce vascular hyper-permeability in diabetic rats by a process associated with decreased levels of a variety of inflammatory mediators, including VEGF, VEGFR-2, MCP-1, TNF-α and ICAM-1 (Zhang et al, 2006a(Zhang et al, , 2006b). Studies of the mechanisms by which VEGF induces the vascular permeability increase indicate that multiple pathways are involved.…”

“…Evidence from cell culture and in vivo models of neovascularization provides support that PEDF may be an endogenous negative regulator of VEGF expression and also may interfere with VEGF binding to VEGF receptor 2 (Zhang et al, 2006b). In retinal endothelial cells, VEGF downregulated PEDF (Zhang et al, 2006b).…”

“…Evidence from cell culture and in vivo models of neovascularization provides support that PEDF may be an endogenous negative regulator of VEGF expression and also may interfere with VEGF binding to VEGF receptor 2 (Zhang et al, 2006b). In retinal endothelial cells, VEGF downregulated PEDF (Zhang et al, 2006b). There is also evidence that variability in oxygen-induced angiogenic responses in different strains of mice and rats is related to differences in VEGF and PEDF expression, VEGF lower and PEDF higher in the less angiogenic strains (Chan et al, 2005;Gao et al, 2001).…”

Neurovascular Protection by Targeting Early Blood–Brain Barrier Disruption with Neurotrophic Factors after Ischemia–Reperfusion in Rats

“…To enable this environment, we strategized an early intervention with the non-inhibitory member of the serine protease inhibitor (SERPIN), pigment epithelium-derived factor (PEDF) by considering its anti-inflammatory, anti-oxidant and inhibitory properties on the VEGF-NADPH oxidase pathway among others followed by another exposure to the potent mitogen epidermal growth factor (EGF). 8,9 As a first step toward such a combined therapeutic approach, we investigated the properties of each of these peptides separately on a rodent model of ischemia-reperfusion (I/R) injury. This model exhibits a biphasic course of BBB permeability changes over time and the NTF treatment was initiated and confined to the initial phase of the altered BBB permeability.…”

Role of matrix metalloproteinase-2 and -9 in the development of diabetic retinopathy

“…To initiate retinal angiogenesis, the delicate balance between proangiogenic and antiangiogenic factors is likely to be shifted, such that mitogenic factors are enhanced and/or inhibitory factors are decreased. In the retina of a diabetic rodent, the antiangiogenic factor, pigment epithelium-derived factor mRNA, and protein expression are reduced and upregulate the angiogenic factor (VEGF) [97][98][99]. The increased levels of MMP-2 and -9 are often found in angiogenesis [100,101].…”