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D. Navaratna, G. Menicucci, P.G. McGuire, A. Das; Proteolytic Degradation of VE–Cadherin Leads to Alteration of the Blood–Retinal Barrier in Diabetes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):949.
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© ARVO (1962-2015); The Authors (2016-present)
Increased vaso–permeability due to alteration of the blood–retinal barrier (BRB) is one of the foremost complications in early non–proliferative diabetic retinopathy. The aim of the present study was to determine if diabetes alters the cellular expression and distribution of the adherens junction protein, VE–cadherin in microvascular endothelial cells, and if this alteration is mediated through increased proteinase activity.
The streptozotocin–induced diabetic Brown Norway rats (2 weeks old) were examined for increased retinal vascular permeability by the Evans Blue technique, and VE–cadherin levels in the retinas were measured by conventional RT–PCR. The distribution of VE–cadherin in retinal vessels was qualitatively determined by immunohistochemistry and confocal microscopy. To ascertain if the expression of MMPs and monolayer permeability of cells is altered by one of the reactive metabolites of diabetes, AGE (advanced glycation end–products), we treated bovine retinal microvascular endothelial cells in culture with AGE–BSA (2 µM). Also, the effect of AGE–BSA on the distribution of VE–cadherin between cell borders was examined by immunocytochemistry. We used a MMP 2/9 inhibitor with AGE–BSA in an in vitro FITC–dextran monolayer permeability assay to determine if AGE action was specifically mediated through MMPs.
The retinal vascular permeability was increased by three–fold in diabetic rats at 2 weeks, and the VE–cadherin mRNA expression in retinas was downregulated. Treatment of retinal endothelial cells with AGE–BSA led to loss of cell contacts, disruption of lateral junctions and a reduction of VE–cadherin staining on the cell surface. This was accompanied by a 2–fold increase in monolayer permeability upon AGE stimulation. The MMP–inhibitor was able to successfully abolish the action of AGE–BSA on altered VE–cadherin distribution, and restore permeability back to near control levels. A separate in vitro experiment showed that MMP–2 is able to cleave VE–cadherin in cell extracts and on the surface of intact cells possibly leading to subsequent internalization.
These observations suggest a possible mechanism by which AGE contributes to BRB breakdown through proteolytic degradation of VE–cadherin. This further establishes the role of extracellular proteinases in macular edema seen in diabetic retinopathy, suggesting the use of proteinase inhibitors as possible therapeutic agents.
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