Human NLRP3 inflammasome activation is Nox1-4 independent

Abstract

The NLRP3 inflammasome can be activated by pathogen-associated molecular patterns or endogenous danger-associated molecular patterns. The activation of the NLRP3 inflammasome results in proteolytic activation and secretion of cytokines of the interleukin-1 (IL-1) family. The precise mode of activation of the NLRP3 inflammasome is still elusive, but has been postulated to be mediated by reactive oxygen species (ROS) generated by an NADPH oxidase. Using primary cells from chronic granulomatous disease (CGD) patients lacking expression of p22 phox , a protein that is required for the function of Nox1-4, we show that cells lacking NADPH oxidase activity are capable of secreting normal amounts of IL-1␤. Thus, we provide evidence that activation of the NLRP3 inflammasome does not depend on ROS generated from an NADPH oxidase. (Blood. 2010;115(26): 5398-5400) IntroductionInflammasomes are specialized intracellular protein complexes responsible for regulating the proteolytic activation of proinflammatory cytokines of the interleukin-1 (IL-1) family. 1 The central components of inflammasomes, the Nod-like receptor (NLR) proteins, act as sensors for exogenous (microbial) or endogenous danger signals. Importantly, inappropriate activation of inflammasomes, due to activating mutations in the NLRs or an excess of danger signals can lead to autoinflammatory disorders such as chronic infantile neurologic cutaneous and articular syndrome, or the more common reactions in gout. 1 The best-studied NLR, NLRP3, forms inflammasomes that mediate the release of IL-1␤ and related cytokines by, for example, macrophages. The NLRP3 inflammasome can be activated by pathogen-associated molecular patterns such as lipopolysaccharide (LPS) or muramyl dipeptide, or endogenous danger-associated molecular patterns such as uric acid. 1 The precise mode of activation of the NLRP3 inflammasome is still elusive, but it has been postulated, in reports by Dostert et al, to be dependent on reactive oxygen species (ROS) generated by an NADPH oxidase. 2,3 In these reports, the authors show an inhibitory effect on IL-1␤ secretion by knockdown of p22 phox , a protein that is part of the catalytic core of several NADPH oxidases.The catalytic core of NADPH oxidases contains a member of the Nox family of proteins. 4 All members of the Nox1-4 subfamily form a heterodimer with the common p22 phox subunit. In the case of Nox2, p22 phox functions as a docking site for the regulatory protein p47 phox , and indirectly for p67 phox , and p40 phox ; the small GTPase Rac binds to p67 phox and serves as a switch for Nox2 activation. 4 For Nox1 and 3, p47 phox and p67 phox homologs are probably involved in this activation. 4 Nox4 is believed not to be regulated by p47 phox and p67 phox or their homologs, and p22 phox is not a conditio sine qua non for its activity but Nox4 activity seems to be clearly enhanced by association with p22 phox4 . The best-studied NADPH oxidase is the phagocyte NADPH oxidase, a microbicidal enzyme that contains Nox2 (gp91 phox ) and p22 phox an...

Phagocyte NADPH Oxidase Restrains the Inflammasome in ANCA-Induced GN

“…32,33 However, this issue remains a matter of debate, because several groups showed that ROS had either no effect or an accelerating effect on inflammasome-mediated IL-1b. [34][35][36] Furthermore, the ROS source and the specific ROS molecule that controls inflammasome activity are not yet characterized. Some investigators favor Phox, 32,34 whereas others implicate alternative sources, such as mitochondria.…”

Adenovirus Membrane Penetration Activates the NLRP3 Inflammasome

“…Although inhibition of ROS production prevents NLRP3 inflammasome activation, the mechanism of ROS production by many NLRP3 stimuli has yet to be fully elucidated. While NADPH oxidase inhibitors, including DPI and apocynin, appear to inhibit NLRP3 activation by many stimuli, including Ad5, genetic approaches have suggested that loss of function of numerous subunits of NADPH oxidase, including gp91 phox , p47 phox , and p22 phox , either enhances or does not affect IL-1␤ release in response to NLRP3 stimuli (33,51). Nonetheless, ROS are known to be produced in response to these NLRP3 stimuli, and NLRP3 activation can be prevented by treatments which prevent ROS production.…”

Molecular mechanisms regulating NLRP3 inflammasome activation

“…9 The TAK1-JNK pathway, which is also modulated by calcium-dependent calcium/calmodulin-dependent protein kinase type II function, is activated through lysosomal rupture and is required for the complete activation of the NLRP3 inflammasome. 9 Although we discuss here common mechanisms, i.e., ROS signaling, 62 K + efflux, 82 and lysosomal destabilization, 55 in terms of NLRP3 inflammasome activation, other pathways, such as purinergic receptor signaling, 104 are being revealed to explain the mechanisms by which diverse stimuli activate the NLRP3 inflammasome complex (Figure 1). …”

“…Several studies demonstrated that caspase-1 activation and IL-1b secretion are not affected, and may even be increased, in phagocyte oxidase-defective monocytes in chronic granulomatous disease. [80][81][82] Moreover, macrophages from NOX2-deficient mice dose not fail in the maturation and secretion of IL-1b in response to various signals, including silica crystals, monosodium urate (MSU), ATP, and deoxyadenylic-deoxythymidylic. 57 In superoxide dismutase 1-deficient macrophages and in vivo, increased superoxide generation inhibits caspase-1 activation and cytokine production.…”