Figure 4.

Cathepsin S activates glomerular endothelial cells via protease-activated receptor(PAR)-2. Mouse glomerular endothelial cells were transiently transfected with control siRNA (scrambled) or siRNA specific for PAR-2. Endothelial cell activation with lipopolysaccharide (LPS) or interferon-gamma (IFN-γ) plus different concentrations of Cat-S induced detachment of the cells from the culture dish (A). Flow cytometry of the detached cells identified them to be annexin V/propidium iodide (PI) positive (B). Cells transfected with PAR-2 siRNA or the PAR-2 inhibitory peptide FSLLRY amide lacked this effect. Female MRL-(Fas)lpr mice were intravenously injected with 10 µg of recombinant Cat-S and albuminuria was determined 30 min later (C). Note that the Cat-S-induced albuminuria was entirely blocked by the Cat-S inhibitor RO5459072 or the PAR-2 inhibiting peptide GB83. After 24 h kidneys were harvested for an ultrastructural analysis of glomerular capillaries. Representative images are shown in (D). Note that Cat-S injection induced a massive swelling of the glomerular endothelial cells, with loss of the endothelial fenestrations and obliteration of the vascular lumen. Focal podocyte foot process effacement was also present. In contrast RO5459074 and GB83 completely prevented these abnormalities (scale 2 µm). Data in (C) are expressed as means ± SEM (n = 3 in each group). ***p < 0.001 versus PBS group.