P36 CATHEPSIN-S INHIBITION HAS A DUAL THERAPEUTIC EFFECT ON THE SYSTEMIC AND PERIPHERAL PATHOMECHANISMS OF LUPUS NEPHRITIS

Abstract

The lysosomal cysteine protease cathepsin (Cat)-S processes the invariant chain-MHC II complex inside antigen- presenting cells as a central pathomechanism of autoimmune diseases. In addition, activated myeloid cells release Cat-S and was recently described to activate protease-activated receptor (PAR)-2 in extracellular compartments (Kumar S, et al JASN 2015). We hypothesized that in lupus nephritis Cat-S blockade can target both pathomechanisms and can elicit synergistic therapeutic effects disease outcomes. Female MRL-Fas(lpr) mice with spontaneous autoimmune tissue injury were treated with different doses of the oral Cat-S antagonist RO5459072 or mycophenolate mofetil (MMF) or vehicle from week 11 or 15 to 19 of age. To evaluate the Cat-S induced micro-vascular damage, female MRL-Fas(lpr) mice were injected with recombinant Cat-S with or without concomintant Cat-S or PAR2 blockade and urine albumin levels were measured at different time intervals. In-vitro studies with PAR2 expressing endothelial cells were used to confirm the Cat-S induced endothelial activation and dysfunction. Cat-S blockade dose-dependently protected aberrant systemic autoimmunity, by reducing the plasma cytokine levels, activation myeloid cells and lymphocytes, and hypergammaglobulinemia. Especially IgG auto-antibodies were suppressed. Of note while (MHC-II-independent) IgM antibodies were not affected by Cat-S blockade but strongly suppressed by MMF. Cat-S blockade dose-dependently suppressed immune complex glomerulonephritis together with a profound and early effect on proteinuria, which was not shared by MMF. In fact, intravenous Cat-S injection induced severe glomerular endothelial cell injury and albuminuria, which was entirely prevented by Cat-S or PAR2 blockade. In-vitro studies confirm that Cat-S induces endothelial cell activation and injury via PAR-2. PAR2 silencing in endothelial cells using siRNA significantly protected the endothelial injury in-vitro. Therapeutic Cat-S blockade suppresses synergistic systemic and peripheral pathomechanisms of autoimmune tissue injury, hence, Cat-S is a promising therapeutic in autoimmune diseases.