Pharmacological Cathepsin C Inactivation Eliminates Proteinase 3, the Antigen in Autoimmune Vasculitis

Abstract

Membrane‐bound proteinase 3 (PR3) is the main target antigen of anti‐neutrophil cytoplasmic autoantibodies (ANCA) in granulomatosis with polyangiitis (GPA), a systemic small‐vessel vasculitis. Binding of ANCA to membrane PR3 triggers neutrophil activation with the secretion of enzymatically active PR3 and additional granule proteins, thereby contributing to vascular damage. PR3 and related neutrophil serine proteases (NSP) are activated from proforms by the lysosomal cysteine protease cathepsin C (CatC) during neutrophil maturation. We hypothesized that pharmacological inhibition of CatC provides an effective measure to reduce intracellular and membrane‐bound PR3 and has therefore implications as a novel therapeutic approach in GPA. We first studied PR3 in neutrophils from 21 patients with Papillon‐Lefèvre syndrome (PLS), a genetic form of CatC deficiency. PLS neutrophil lysates showed a largely reduced, but still detectable (0.5–4%) PR3 activity when compared to healthy control cells. The PR3 membrane expression on activated PLS neutrophils was diminished by approximately 80% as shown by flow cytometry. We then explored the effect of a potent cell permeable nitrile CatC inhibitor on PR3 expression in normal neutrophils using a CD34+ hematopoietic stem cell model. Human CD34+ hematopoietic stem cells were treated with a CatC inhibitor during neutrophil differentiation over 10 days. We observed complete abrogation of membrane PR3, cellular PR3 protein and proteolytic PR3 activity whereas neutrophil differentiation was not compromised. Our data suggest that pharmacological CatC inhibition could provide an attractive novel treatment strategy for PR3‐ANCA associated autoimmune vasculitis that should be explored further.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.