The classical NLRP3 inflammasome controls FADD unconventional secretion through microvesicle shedding

Abstract

Fas-associated death domain (FADD) is a key adaptor molecule involved in numerous physiological processes including cell death, proliferation, innate immunity and inflammation. Therefore, changes in FADD expression have dramatic cellular consequences. In mice and humans, FADD regulation can occur through protein secretion. However, the molecular mechanisms accounting for human FADD secretion were still unknown. Here we report that canonical, non-canonical, but not alternative, NLRP3 inflammasome activation in human monocytes/macrophages induced FADD secretion. NLRP3 inflammasome activation by the bacterial toxin nigericin led to the proinflammatory interleukin-1β (IL-1β) release and to the induction of cell death by pyroptosis. However, we showed that FADD secretion could occur in absence of increased IL-1β release and pyroptosis and, reciprocally, that IL-1β release and pyroptosis could occur in absence of FADD secretion. Especially, FADD, but not IL-1β, secretion following NLRP3 inflammasome activation required extracellular glucose. Thus, FADD secretion was an active process distinct from unspecific release of proteins during pyroptosis. This FADD secretion process required K + efflux, NLRP3 sensor, ASC adaptor and CASPASE-1 molecule. Moreover, we identified FADD as a leaderless protein unconventionally secreted through microvesicle shedding, but not exosome release. Finally, we established human soluble FADD as a new marker of joint inflammation in gout and rheumatoid arthritis, two rheumatic diseases involving the NLRP3 inflammasome. Whether soluble FADD could be an actor in these diseases remains to be determined. Nevertheless, our results advance our understanding of the mechanisms contributing to the regulation of the FADD protein expression in human cells.

Priming Is Dispensable for NLRP3 Inflammasome Activation in Human Monocytes In Vitro

“…Caspase-1 has a broad range of substrate specificity and its activation by the inflammasome regulate cellular responses beyond those attributed to IL-1β and IL-18 activation ( 58 ). These include the release of alarmins such as HMGB1 and ASC via pyroptosis ( 13 ), FADD (Fas-Associated Death Domain) release via microvesicle shedding ( 59 ) or the degradation of UBE2L3 (E2 ubiquitin-conjugating enzyme L3) involved in NF-κB activation and pro-IL-1β turnover ( 27 ). We have shown that UBE2L3 degradation occurs in the absence of TLR-priming, as does FADD release ( 59 ), indicating the ability of active caspase-1 to cleave the same substrates independently of its priming state.…”

“…These include the release of alarmins such as HMGB1 and ASC via pyroptosis ( 13 ), FADD (Fas-Associated Death Domain) release via microvesicle shedding ( 59 ) or the degradation of UBE2L3 (E2 ubiquitin-conjugating enzyme L3) involved in NF-κB activation and pro-IL-1β turnover ( 27 ). We have shown that UBE2L3 degradation occurs in the absence of TLR-priming, as does FADD release ( 59 ), indicating the ability of active caspase-1 to cleave the same substrates independently of its priming state. This suggests that inflammasome activation can contribute to the amplification of the inflammatory response by mechanisms other than IL-18 signaling in an unprimed setting.…”

Ibudilast Attenuates Folic Acid–Induced Acute Kidney Injury by Blocking Pyroptosis Through TLR4-Mediated NF-κB and MAPK Signaling Pathways

“…Pyroptosis not only contributes to infectious diseases (Zhang et al, 2018) but also participates in sterile inflammatory diseases, including gout, diabetes, asbestosis, and metabolic syndrome, which might further induce kidney injury (Gaidt et al, 2016;Chen et al, 2018;Hughes and O'Neill 2018;Mouasni et al, 2019). Increasing evidence has shown that programmed cell death, including pyroptosis, rather than apoptosis, plays an essential role in the pathological progression of various types of AKI (Hughes and O'Neill 2018;Mouasni et al, 2019). Activation of the NLRP3 inflammasome was reported to be the key mediator of I/R-induced renal injuries (Yang et al, 2014;Wang L. et al, 2019).…”

The Potential Role of Inflammation in Modulating Endogenous Hippocampal Neurogenesis After Spinal Cord Injury

“…NK and its constituent, 12/15-lipoxygenase, responsible for destroying and phagocytizing viral particles, are significantly downregulated even several years after SCI (Campagnolo et al, 2008;Uderhardt et al, 2012). NLRP3 inflammasomes and associated proinflammatory pathways are further activated, followed by dysfunctional autophagosomes increasing the presence of bacterial LPS (Mouasni et al, 2019) while the prevalence of infections increases (Evans et al, 2008;Tofte et al, 2017). This predicament creates a simultaneous increase in inflammatory cytokine production and infection rate.…”