Characterization and therapeutic targeting of neutrophil serine proteases in ANCA vasculitis

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Anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitides (AAV) are necrotizing small-vessel inflammatory diseases that can affect every organ, frequently manifesting in the kidneys as necrotizing crescentic glomerulonephritis with rapidly-progressive renal failure. ANCA bind to either proteinase 3 (PR3) or myeloperoxidase (MPO) on the surface of neutrophils and monocytes that exclusively express these autoantigens. ANCA activate these cells that adhere to and damage the endothelium leading to systemic vasculitis. We characterized several injury mechanisms some of which involve enzymatically active neutrophil serine proteases (NSPs). The NSP family consist of PR3, human neutrophil elastase (HNE) and cathepsin G (CatG) and low-abundant NSP4. PR3 is a unique NSP for it provides the major ANCA antigen. NSPs are generated from inactive zymogen proforms by cathepsin C (CatC) that removes an N-terminal dipeptide. Loss-of-function mutations in CatC prevents NSP maturation and leads to zymogen degradation. Pharmacological CatC inhibitors have the potential to abrogate NSP maturation thereby eliminating NSP proteins and proteolytic activity. Thus, pharmacological CatC inhibition provides possibly a novel treatment strategy in AAV. With this proposal, we will (i) systematically characterize NSP proteins and proteolytical activity in human and murine neutrophils and monocytes, (ii) target NSPs by pharmacological CatC inhibition to characterize NSP-mediated damage mechanisms using stem cell differentiation models and endothelial cells, and (iii) test the hypothesis that pharmacological CatC inhibition protects from ANCA-induced vasculitis using murine AAV disease models. Our findings will improve understanding ANCA-induced disease mechanisms that link NSPs to vasculitis. In addition, the study could encourage clinical trials exploring pharmacological CatC inhibition as a new treatment for AAV.