Phagocyte NADPH Oxidase Restrains the Inflammasome in ANCA-Induced GN

Abstract

ANCA-activated phagocytes cause vasculitis and necrotizing crescentic GN (NCGN). ANCA-induced phagocyte NADPH oxidase (Phox) may contribute by generating tissue-damaging reactive oxygen species. We tested an alternative hypothesis, in which Phox restrains inflammation by downregulating caspase-1, thereby reducing IL-1b generation and limiting NCGN. In an antimyeloperoxidase (anti-MPO) antibody-mediated disease model, mice transplanted with either gp91 phox -deficient or p47 phox -deficient bone marrow showed accelerated disease with increased crescents, necrosis, glomerular monocytes, and renal IL-1b levels compared with mice transplanted with wild-type bone marrow. IL-1b receptor blockade abrogated aggravated NCGN in gp91 phox -deficient mice. In vitro, challenge with anti-MPO antibody strongly enhanced caspase-1 activity and IL-1b generation in gp91 phox -deficient and p47 phox -deficient monocytes compared with wild-type monocytes. This enhanced IL-1b generation was abrogated when caspase-1 was blocked. ANCA-induced superoxide and IL-1b generation were inversely related in human monocytes. Furthermore, transplantation of gp91 phox /caspase-1 double-deficient bone marrow rescued the accelerated NCGN phenotype in gp91 phox bone marrow-deficient mice. These results suggest that Phox-generated reactive oxygen species downregulate caspase-1, thereby keeping the inflammasome in check and limiting ANCA-induced inflammation. IL-1 receptor blockade may provide a promising strategy in NCGN, whereas our data question the benefit of antioxidants.

Of Inflammasomes and Alarmins: IL-1β and IL-1α in Kidney Disease

“…30 A20-driven ubiquitination of NLRP3, PYRIN domain-only protein POP1-dependent inhibition of inflammasome assembly, or reactive oxygen species-driven suppression of caspase-1 are just three such regulatory mechanisms. [31][32][33] Figure 2. Inflammasome activation in dendritic cells and macrophages involves numerous elements.…”

Neutrophils in animal models of autoimmune disease

“…A monoclonal anti-PR3 ANCA antibody model has been used in isolated rat lungs to show that activation of the neutrophil NADPH oxidase is a major mediator of tissue injury [49]. However, in the anti-MPO antibody-mediated disease model, Schreiber et al have recently reported just the opposite – mice genetically deficient in NADPH oxidase activity (either Nox2 or p47 phox deficient animals) actually developed more severe vasculitis and glomerulonephritis following challenge with anti-MPO serum [50]. These authors found that the NADPH oxidase-deficient neutrophils over produced IL-1β following anti-MPO antibody challenge and that IL-1β-receptor blockade protected recipient mice from severe glomerulonephritis following anti-MPO challenge.…”

Neutrophil serine proteases exert proteolytic activity on endothelial cells

“…47 Assessment of PR3-specific proteolytic activity by FRET PR3-specific proteolytic activity was measured in cell lysates using the FRET substrate 2-Abz-VAD-norV-ADYQ-EDA-Dnp (Biosynthan, Berlin, Germany) prepared as described previously. 48 In brief, 10 μg of EC cell lysate in 150 μl of buffer (100 mmol/l HEPES, 500 mmol/l NaCl, pH 7.2) was incubated with 3 μL of 2 mmol/l FRET substrate.…”