Decorin Prevents Retinal Pigment Epithelial Barrier Breakdown Under Diabetic Conditions by Suppressing p38 MAPK Activation.

PURPOSE: The purpose of this study was to determine the effect of decorin on the barrier function of human retinal pigment epithelial (RPE) cells under high-glucose (HG) plus hypoxia conditions.

METHODS: Human RPE (ARPE-19) cells were cultured for 18 days in normal glucose (5.5 mM) or HG (25 mM) medium. In addition, to mimic the hypoxic impact which occurs in diabetic retinopathy, cells were treated with 100 μM CoCl2 during the last 2 days of the experiment. Decorin, 100 nM, was applied 1 hour before CoCl2 was added. Retinal pigment epithelial barrier function was evaluated by measuring transepithelial electrical resistance (TER) and apical-basolateral permeability of fluorescein isothiocyanate (FITC)-dextran. The content and distribution of tight junction proteins (claudin-1, occludin, and zonula occludens-1 [ZO-1]) were examined by Western blotting and immunofluorescence. p38 mitogen-activated protein kinase (MAPK) phosphorylation was evaluated by Western blotting, and small interfering RNA transfection to p38 MAPK was also performed in ARPE-19 monolayers.

RESULTS: High-glucose plus hypoxia significantly increased FITC-dextran permeability, paralleled by decreased TER. Decorin reversed both of these effects. High-glucose plus hypoxia-induced reduction and disorganization of occludin and ZO-1 were also reversed by decorin. Decorin prevented the activation of p38 MAPK induced by hypoxia. Silence of p38 MAPK by RNA interference also inhibited the breakdown of ARPE-19 cell monolayer induced by HG plus hypoxia.

CONCLUSIONS: Retinal pigment epithelial barrier disruption induced by HG plus hypoxia was prevented by decorin through suppression of p38 MAPK activation, which could present a new therapeutic strategy for inhibition of diabetic macular edema.