Proteolytic Degradation of VE-Cadherin Alters the Blood-Retinal Barrier in Diabetes

Abstract

OBJECTIVE-Increased vascular permeability due to alteration of the blood-retinal barrier (BRB) is one of the major complications in early diabetes. The aim of the present study was to determine whether diabetes alters the cellular expression and distribution of the adherens junction protein vascular endothelial (VE)-cadherin in retinal endothelial cells and if this alteration is mediated by proteinase activity.RESEARCH DESIGN AND METHODS-Diabetes was induced in Brown Norway rats using streptozotocin, and retinal vascular permeability was measured by the Evans blue technique. The expression of matrix metalloproteinases (MMPs) and VE-cadherin was examined in isolated retinal vessels or cultured endothelial cells in response to diabetes and advanced glycation end products (AGEs). The cleavage of VE-cadherin from the endothelial cell surface was monitored by Western blotting following MMP or AGE treatment.RESULTS-Retinal vascular permeability was significantly increased in rats following 2 weeks of diabetes coincident with a decrease of VE-cadherin expression. This increased vascular permeability could be inhibited with an MMP inhibitor. Treatment of endothelial cells with AGE-BSA led to a reduction of VE-cadherin staining on the cell surface and increased permeability, which was MMP mediated. Treatment of cells with specific MMPs or AGEs resulted in cleavage of VE-cadherin from the cell surface. T he normal permeability of the retinal microvasculature is tightly controlled by a series of complex interactions between adjacent endothelial cells and by additional interactions between the endothelial cells and other cell types in the retina, including vascular pericytes, astrocytes, and Mü ller glial cells (1). These interactions form the structural basis of the inner blood-retinal barrier (BRB), which facilitates normal functioning of the neural retina. Disruption of these interactions is anticipated to lead to a compromise of the barrier function, resulting in leakage of plasma constituents into the surrounding retinal tissues and retinal edema. The alteration of the BRB followed by retinal edema are key early events in the pathogenesis of diabetic retinopathy, and macular edema is the leading cause of vision loss in diabetic patients. CONCLUSIONS-TheseEndothelial cells of the retinal microvasculature contribute to the function of the BRB through the formation of specialized intercellular junctions including adherens and tight junctions. The cadherin family of proteins, of which there are more than 80 members, is a primary component of the adherens junctions (2). The vascular endothelial (VE)-cadherin mediates calcium-dependent homophilic adhesion between endothelial cells. In addition, VE-cadherin functions as a plasma membrane attachment site for the cytoskeleton through its interactions with the cytoplasmic proteins ␤-and ␥-catenin (3-5). In addition to contributing to the mechanical attachment of cells, VEcadherin also plays a role in the regulation of a variety of endothelial cell behaviors including motility, m...

Ablation of MMP9 Gene Ameliorates Paracellular Permeability and Fibrinogen–Amyloid Beta Complex Formation during Hyperhomocysteinemia

“…The role of MMP9 activity in regulation of VE-cadherin has been shown previously. 48 We also have shown that expression of VE-cadherin in mouse pial vessels is lower in the absence of MMP9 activity. 29 Thus, our results confirm a strong involvement of MMP9 activity in regulation of EC JPs and the resultant cerebrovascular permeability to proteins via paracellular transport pathway.…”

Melatonin inhibits IL1β-induced MMP9 expression and activity in human umbilical vein endothelial cells by suppressing NF-κB activation

“…Endothelial MMP2, which is activated by breast cancer cell adhesion to VE cells, could degrade interendothelial junctional protein VE-cadherin and promote cancer cell transendothelial migration (Shen et al 2010). Moreover, oxidants, inflammatory cytokines, and pharmacological agents can spur the activation of MMPs to destroy the adherens junctional protein VE-cadherin and the tight junctional protein occludin (Alexander & Elrod 2002, Navaratna et al 2007. Our pervious study suggested that IL1b increased the permeability of HUVECs monolayer by damaging adherens junctions and enlarging the junctions cleft width (Yuan et al 2011).…”

“…The main tight junction proteins are occludin, claudins, and ZO-1 (Thanabalasundaram et al 2010). Therefore, to maintain and regulate the endothelium barrier function it is possible to involve the integrity of the adherens junctional protein VE-cadherin and the tight junctional protein occludin (Navaratna et al 2007, Rangasamy et al 2011. The integrity of junctional proteins between adjacent endothelial cells essentially indicates the extent of permeability of the endothelial cell barrier.…”

Truncated netrin-1 contributes to pathological vascular permeability in diabetic retinopathy

“…39 and Figure 5A), we sought to determine whether netrin-1 could be a substrate for collagenases. MMP-9 is a collagenase that is induced in DR and has documented roles in vascular permeability (40) (Figure 6A). We therefore incubated full-length netrin-1 with MMP-9 at 37°C and monitored fragmentation at different time points (30 and 60 min) by Western blot analysis.…”