Ang-2 mRNA and protein increased in the retinal tissues after 8 weeks of diabetes and in high-glucose-treated cells. Intravitreal injection of Ang-2 in rats produced a significant increase in retinal vascular permeability. Ang-2 increased HREC monolayer permeability that was associated with a decrease in VE-cadherin and a change in monolayer morphology. High glucose and Ang-2 produced a significant increase in VE-cadherin phosphorylation. CONCLUSIONS; Ang-2 is upregulated in the retina in an animal model of diabetes, and hyperglycemia induces the expression of Ang-2 in isolated retinal endothelial cells. Increased Ang-2 alters VE-cadherin function, leading to increased vascular permeability. Thus, Ang-2 may play an important role in increased vasopermeability in diabetic retinopathy.

Objective The mechanisms that regulate the physical interaction of pericytes and endothelial cells and the effects of these interactions on interendothelial cell junctions are not well understood. We determined the extent to which vascular pericytes could regulate pericyte-endothelial adhesion and the consequences that this disruption might have on the function of the endothelial barrier. Methods and Results Human retinal microvascular endothelial cells were co-cultured with pericytes, and the effect on the monolayer resistance of endothelial cells and expression of the cell junction molecules N-cadherin and VE-cadherin were measured. The molecules responsible for the effect of pericytes or pericyte conditioned media on the endothelial resistance and cell junction molecules were further analyzed. Our results indicate that pericytes increase the barrier properties of endothelial cell monolayers. This barrier function is maintained through the secretion of pericyte-derived sphingosine 1-phosphate (S1P). S1P aids in maintenance of microvascular stability by up-regulating the expression of N-cadherin and VE-cadherin, and down-regulating the expression of angiopoietin 2. Conclusion Under normal circumstances, the retinal vascular pericytes maintain pericyte-endothelial contacts and vascular barrier function through the secretion of S1P. Alteration of pericyte-derived S1P production may be an important mechanism in the development of diseases characterized by vascular dysfunction and increased permeability.

One of the major complications of diabetes is the alteration of the blood-retinal barrier, leading to retinal edema and consequent vision loss. The aim of this study was to evaluate the role of the urokinase plasminogen activator (uPA)/uPA receptor (uPAR) system in the regulation of retinal vascular permeability. Biochemical, molecular, and histological techniques were used to examine the role of uPA and uPAR in the regulation of retinal vascular permeability in diabetic rats and cultured retinal endothelial cells. The increased retinal vascular permeability in diabetic rats was associated with a decrease in vascular endothelial (VE) -cadherin expression in retinal vessels. Treatment with the uPA/uPAR-inhibiting peptide (A6) was shown to reduce diabetes-induced permeability and the loss of VE-cadherin. The increased permeability of cultured cells in response to advanced glycation end products (AGEs) was significantly inhibited with A6. Treatment of endothelial cells with specific matrix metalloproteinases or AGEs resulted in loss of VE-cadherin from the cell surface, which could be inhibited by A6. uPA/uPAR physically interacts with AGEs/receptor for advanced glycation end products on the cell surface and regulates its activity. uPA and its receptor uPAR play important roles in the alteration of the blood-retinal barrier through proteolytic degradation of VE-cadherin. The ability of A6 to block retinal vascular permeability in diabetes suggests a potential therapeutic approach for the treatment of diabetic macular edema.

Purpose Angiogenesis, or the formation of new retinal blood vessels is a key feature of many proliferative retinal diseases including diabetic retinopathy, retinal vein occlusions, and retinopathy of prematurity. The aim of the present study was to investigate the role of the serine proteinase inhibitor PAI-1 in facilitating retinal angiogenesis. Methods The temporal expression of PAI-1 was examined by real time PCR, western blotting and immunohistochemistry in retinal tissues from mice with oxygen-induced retinopathy. The requirement for PAI-1 in facilitating the retinal angiogenic response in this model was examined by quantitating the angiogenic response using both wildtype and PAI-1 null mice. The mechanism by which PAI-1 mediates angiogenesis was further investigated using isolated human retinal vascular endothelial cells. Results PAI-1 expression is up regulated in the retina of mice with oxygen-induced retinopathy. This coincides with a significant increase in the expression of vitronectin in the retina of the experimental mice. There was significant reduction in the angiogenic response of PAI-1−/− mice as compared to wild type mice. PAI-1 promotes endothelial cell migration in vitro and facilitates migration of cells on a vitronectin substrate by regulating αv integrin cell surface expression. Conclusions These observations suggest a role for PAI-1 during retinal angiogenesis and point to a potential new therapeutic target in the prevention or treatment of retinal neovascularization seen in many ocular diseases.