Diabetes-Induced Superoxide Anion and Breakdown of the Blood-Retinal Barrier: Role of the VEGF/uPAR Pathway

Abstract

Diabetes-induced breakdown of the blood-retinal barrier (BRB) has been linked to hyperglycemia-induced expression of vascular endothelial growth factor (VEGF) and is likely mediated by an increase in oxidative stress. We have shown that VEGF increases permeability of retinal endothelial cells (REC) by inducing expression of urokinase plasminogen activator receptor (uPAR). The purpose of this study was to define the role of superoxide anion in VEGF/uPAR expression and BRB breakdown in diabetes. Studies were performed in streptozotocin diabetic rats and mice and high glucose (HG) treated REC. The superoxide dismutase (SOD) mimetic tempol blocked diabetes-induced permeability and uPAR expression in rats and the cell permeable SOD inhibited HG-induced expression of uPAR and VEGF in REC. Inhibiting VEGFR blocked HG-induced expression of VEGF and uPAR and GSK-3β phosphorylation in REC. HG caused β-catenin translocation from the plasma membrane into the cytosol and nucleus. Treatment with HG-conditioned media increased REC paracellular permeability that was blocked by anti-uPA or anti-uPAR antibodies. Moreover, deletion of uPAR blocked diabetes-induced BRB breakdown and activation of MMP-9 in mice. Together, these data indicate that diabetes-induced oxidative stress triggers BRB breakdown by a mechanism involving uPAR expression through VEGF-induced activation of the GSK3β/β-catenin signaling pathway.

Impact of altered glycaemia on blood-brain barrier endothelium: an in vitro study using the hCMEC/D3 cell line

“…In addition, our findings are also supported by previous studies performed in brain [24,41] and retinal ECs [42]. Notably, our results have shown significant differences in endothelial response to hypo or hyperglycemic conditions which manifested through differential release of VEGF when ECs were cultured with or without abluminal astrocytes (Figure 3).…”

Thrombosis and Hemorrhage in Diabetic Retinopathy: A Perspective from an Inflammatory Standpoint

“…In addition, activation of the uPA/uPAR pathway also contributes to increased retinal vascular permeability in diabetic rats through proteolytic disruption of VE-cadherin. 38 El-Remessy et al 37 have also reported increased matrix metalloproteinase MMP-9 activity downstream of uPA/uPAR signaling in diabetic mice retina which leads to ECM disruption in retinal vessels. Absence of uPAR in uPAR À/À mice results in blockade of diabetes-induced increase in retinal vascular permeability and MMP-9 activity.…”

“…10,35 Urokinase plasminogen activator (uPA), a component of the fibrinolytic system, is increased in epiretinal membranes obtain from patients with PDR 36 and retinal uPA receptor (uPAR) expression is increased in diabetic rats. 37 Upon activation, uPA converts plasminogen to plasmin, which mediates fibrinolysis and can activate matrix metalloproteinases. In addition, activation of the uPA/uPAR pathway also contributes to increased retinal vascular permeability in diabetic rats through proteolytic disruption of VE-cadherin.…”

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

“…In this context, rod-derived cone viability factor injected into the eye of the P23H transgenic rat model of RP preserved the vision by increasing cone survival and function (Yang et al, 2009). Clinical trials with encapsulated ARPE-19 cells secreting CNTF into the vitreous of patients with RP and AMD showed evidence of photoreceptor protection and/or improved visual acuity (Birch et al, 2013;Emerich and Thanos, 2008;Sieving et al, 2006;Talcott et al, 2011;Zhang et al, 2011).…”