Advanced glycation end products induce glomerular endothelial cell hyperpermeability by upregulating matrix metalloproteinase activity

The present study aimed to investigate the effects of advanced glycation end-products (AGEs) on the permeability of glomerular endothelial cells (GEnCs) and determine whether enhanced permeability was due to degradation of tight junction (TJ) complexes by matrix metalloproteinases (MMPs). Cultured monolayers of GEnCs were exposed to AGEs at different doses and treatment durations in the presence or absence of the organic MMP-2/9 inhibitor (2R)-2-((4-biphenyl sulfony-l)amino)-3-phenylproprionic acid) (BiPs). Expression of the TJ proteins occludin and claudin-5 was determined by western blot analysis and immunofluorescence, while the permeability of the GEnCs was measured using transendothelial electrical resistance and by diffusion of 4 kDa fluorescein isothiocyanate (FITC)-dextran. The activities of MMP-2 and MMP-9 were assayed using gelatin zymography. The results indicated that AGE-treated cultures significantly reduced occludin and claudin-5 immunoreactivity. Similarly, the surface expression of these proteins was significantly reduced and rows of TJs which normally connect endothelial cells became discontinuous or fractured following AGE exposure. Disruption of TJs was accompanied by significantly reduced transendothelial resistance and hyperpermeability to FITC-dextran. Treatment with AGEs evoked a dose- and time-dependent upregulation of MMP-2 and MMP-9. However, co-administration of AGEs and BiPS, an inhibitor of MMP-2/MMP-9, inhibited the downregulation of occludin and claudin-5, with a concomitant reversal of GEnC monolayer hyperpermeability. In conclusion, AGEs promoted glomerular hyperpermeability in vitro by the MMP-mediated disruption of TJs. Chronic elevation of endothelial cell AGEs in diabetes mellitus may contribute to glomerular hyperpermeability by inducing the overexpression of MMPs, which degrade TJs, leading to proteinuria.