Comprehensive quantification of modifications of human and mouse myeloperoxidase by LC-MSMS

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic and refractory disease, characterized by necrotizing small to medium vessel vasculitides. AAV constitutes three distinct disorders: microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA) (formerly known as Wegener's granulomatosis), and eosinophilic granulomatosis with polyangiitis (EGPA) (formerly known as Churg-Strauss syndrome). ANCA, a characteristic autoantibody for AAV consists of two major subtypes: one against myeloperoxidase (MPO-ANCA) and the other against leukocyte proteinase 3 (PR3-ANCA). MPO-ANCA is mainly detected in patients with MPA (55-90%) and in those with EGPA (20-40%) and less frequently detected in patients with GPA (20-30%). We hypothesized that an aberrant PTM occurred in neutrophil MPO in patients with MPO-ANCA-positive AAV (MPO-AAV) is involved in the production of MPO-ANCA. To test the hypothesis, SWATH-MS was used to comprehensively quantify PTMs of human MPO purified from neutrophils of MPO-AAV and healthy controls, and PTMs of mouse MPO treated with hydrogen peroxide in vitro.