Cathepsin D: an Mφ‐derived factor mediating increased endothelial cell permeability with implications for alteration of the blood‐retinal barrier in diabetic retinopathy

Abstract

Inflammation plays an important role in the pathogenesis of diabetic retinopathy (DR). We have previously reported increased monocyte (Mono) trafficking into the retinas of diabetic animals. In this study, we have examined the effect of activated Monos on retinal endothelial cells (ECs). The U937 Mf-conditioned medium (CM) significantly decreased the transendothelial resistance of EC monolayers as measured by electric cellsubstrate impedance sensing (P = 0.007). The CM was fractioned, and the effective fraction (30-100 kDa) was analyzed by liquid chromatography-mass spectrometry, and cathepsin D (CD) was identified as a major secreted product. Immunoprecipitated CD resulted in decreased resistance in ECs (P = 0.006). The specificity of CD in mediating alterations of the EC barrier was confirmed using small interfering RNA. The decreased resistance correlated with a significantly increased gap between ECs. CD altered the Ras homolog gene family, member A/Rho-associated kinase pathway with increased stress actin filament formation in the EC layer. Increased CD levels were found in the retinas of diabetic mice (3-fold) and serum samples of patients with diabetic macular edema (1.6-fold) measured by Western blot and ELISA. These findings suggest an important role for Mf-derived

Cathepsin D plays a role in endothelial–pericyte interactions during alteration of the blood–retinal barrier in diabetic retinopathy

“…We have previously shown that the addition of M6P with CD stabilizes endothelial resistance (12). In the current study, we have shown the direct interaction of the ligand and the receptor using an ELISA‐based method (Fig.…”

“…In our previous study, we reported the effect of the macrophage‐derived factor, CD, on the mediation of increased endothelial cell permeability in the retinas of diabetic mice (12). Here, we have demonstrated the effect of pro‐CD on the endothelial–pericyte interaction via the modulation of PDGFRβ, N‐Cad, and Ang2.…”

“…Previous studies have demonstrated that cadherins are targeted by extracellular and cytoplasmic proteases, including metalloproteinases, elastase, and cathepsin G (10, 11), that could lead to the down‐regulation of cell–cell adhesion. In an earlier study, we showed that the macrophage‐derived factor, cathepsin D (CD), an aspartyl protease, increases endothelial cell permeability by disrupting the endothelial junctional barrier via increased Rho/ROCK‐dependent cell contractility (12). Of importance, CD protein is increased in the retinas of diabetic mice and serum of patients with diabetic macular edema (12).…”

“…In an earlier study, we showed that the macrophage‐derived factor, cathepsin D (CD), an aspartyl protease, increases endothelial cell permeability by disrupting the endothelial junctional barrier via increased Rho/ROCK‐dependent cell contractility (12). Of importance, CD protein is increased in the retinas of diabetic mice and serum of patients with diabetic macular edema (12). Thus, CD may play an important role in the alteration of the BRB in diabetic retinopathy, and it can be used as a therapeutic target in the management of diabetic macular edema.…”

ROCK inhibitors in ocular disease

“…Monickaraj et al [72] reported that patients suffering from manifest diabetic macular edema, a consequence of diabetic retinopathy, had elevated cathepsin D levels in their serum. The protease caused mechanical disruption of the endothelial barrier through increased RhoA-ROCK-dependent contractility in human retinal endothelial cells.…”