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NLRP3 activation induces ASC-dependent programmed necrotic cell death, which leads to neutrophilic inflammation.

ABSTRACT: NLR family pyrin domain containing 3 (NLRP3) is a cytoplasmic pattern recognition receptor that regulates innate immune responses by forming a protein complex, the inflammasome. It leads to production of proinflammatory cytokine productions such as interleukin 1? (IL-1?). We and others demonstrated that an induction of activated NLRP3 also induced cell death. However, little is known about the characteristics and mechanisms of the cell death and its involvement in the pathogenesis of inflammatory conditions. In this study, we established cell lines in which NLRP3 was induced by doxycycline using a tetracycline-inducible expression (Tet-on) system. Using this system, the expression of NLRP3 mutants in cryopyrin-associated periodic syndrome (CAPS) patients was sufficient for the induction of necrotic cell death without lipopolysaccharide stimulation or generation of mature IL-1?. We also found that CA074-Me, a cathepsin B inhibitor, blocked cell death before oligomerization of apoptosis-associated speck-like protein containing a CARD (ASC), whereas Z-VAD-fmk, a pan-caspase inhibitor, blocked the cell death after the oligomerization. Silencing of the ASC gene (Pycard) by small hairpin RNA treatment inhibited the NLRP3 mutant-induced cell death, but silencing of the caspase-1 gene (Casp1) did not. Taken together, these results indicated that ASC was indispensable for NLRP3-mediated programmed necrotic cell death, and that this type of cell death was distinct from 'pyroptosis', which requires caspase-1. Finally, we demonstrated in an in vivo model that the programmed necrotic cell death induced by activated NLRP3 could cause neutrophil infiltration, indicating a possible role of cell death in neutrophil infiltration of skin lesions in CAPS patients.

SUBMITTER: Satoh T

PROVIDER: S-EPMC3674376 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature

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NLRP3 activation induces ASC-dependent programmed necrotic cell death, which leads to neutrophilic inflammation.

Satoh T T Kambe N N Matsue H H

Cell death & disease 20130523

NLR family pyrin domain containing 3 (NLRP3) is a cytoplasmic pattern recognition receptor that regulates innate immune responses by forming a protein complex, the inflammasome. It leads to production of proinflammatory cytokine productions such as interleukin 1β (IL-1β). We and others demonstrated that an induction of activated NLRP3 also induced cell death. However, little is known about the characteristics and mechanisms of the cell death and its involvement in the pathogenesis of inflammator ...[more]

PMID: 23703389

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Project description:The incidence of chronic liver disease is constantly increasing, owing to the obesity epidemic. However, the causes and mechanisms of inflammation-mediated liver damage remain poorly understood. Endoplasmic reticulum (ER) stress is an initiator of cell death and inflammatory mechanisms. Although obesity induces ER stress, the interplay between hepatic ER stress, NLRP3 inflammasome activation and hepatocyte death signaling has not yet been explored during the etiology of chronic liver diseases. Steatosis is a common disorder affecting obese patients; moreover, 25% of these patients develop steatohepatitis with an inherent risk for progression to hepatocarcinoma. Increased plasma LPS levels have been detected in the serum of patients with steatohepatitis. We hypothesized that, as a consequence of increased plasma LPS, ER stress could be induced and lead to NLRP3 inflammasome activation and hepatocyte death associated with steatohepatitis progression. In livers from obese mice, administration of LPS or tunicamycin results in IRE1? and PERK activation, leading to the overexpression of CHOP. This, in turn, activates the NLRP3 inflammasome, subsequently initiating hepatocyte pyroptosis (caspase-1, -11, interleukin-1? secretion) and apoptosis (caspase-3, BH3-only proteins). In contrast, the LPS challenge is blocked by the ER stress inhibitor TUDCA, resulting in: CHOP downregulation, reduced caspase-1, caspase-11, caspase-3 activities, lowered interleukin-1? secretion and rescue from cell death. The central role of CHOP in mediating the activation of proinflammatory caspases and cell death was characterized by performing knockdown experiments in primary mouse hepatocytes. Finally, the analysis of human steatohepatitis liver biopsies showed a correlation between the upregulation of inflammasome and ER stress markers, as well as liver injury. We demonstrate here that ER stress leads to hepatic NLRP3 inflammasome pyroptotic death, thus contributing as a novel mechanism of inflammation-mediated liver injury in chronic liver diseases. Inhibition of ER-dependent inflammasome activation and cell death pathways may represent a potential therapeutic approach in chronic liver diseases.

Project description:The endoplasmic reticulum stress sensor, the unfolded protein response (UPR), regulates intracellular protein homeostasis. While transient activation of the reactive UPR by unfolded protein is protective, prolonged and sustained activation of the reactive UPR triggers CHOP-mediated apoptosis. In the recently characterized, evolutionarily conserved anticipatory UPR, mitogenic hormones and other effectors pre-activate the UPR; how strong and sustained activation of the anticipatory UPR induces cell death was unknown. To characterize this cell death pathway, we used BHPI, a small molecule that activates the anticipatory UPR through estrogen receptor ? (ER?) and induces death of ER?+ cancer cells. We show that sustained activation of the anticipatory UPR by BHPI kills cells by inducing depletion of intracellular ATP, resulting in classical necrosis phenotypes, including plasma membrane disruption and leakage of intracellular contents. Unlike reactive UPR activation, BHPI-induced hyperactivation of the anticipatory UPR does not induce apoptosis or sustained autophagy. BHPI does not induce CHOP protein or PARP cleavage, and two pan-caspase inhibitors, or Bcl2 overexpression, have no effect on BHPI-induced cell death. Moreover, BHPI does not increase expression of autophagy markers, or work through recently identified programmed-necrosis pathways, such as necroptosis. Opening of endoplasmic reticulum IP3R calcium channels stimulates cell swelling, cPLA2 activation, and arachidonic acid release. Notably, cPLA2 activation requires ATP depletion. Importantly, blocking rapid cell swelling or production of arachidonic acid does not prevent necrotic cell death. Rapid cell death is upstream of PERK activation and protein synthesis inhibition, and results from strong and sustained activation of early steps in the anticipatory UPR. Supporting a central role for ATP depletion, reversing ATP depletion blocks rapid cell death, and the onset of necrotic cell death is correlated with ATP depletion. Necrotic cell death initiated by strong and sustained activation of the anticipatory UPR is a newly discovered role of the UPR.

Dataset Information

NLRP3 activation induces ASC-dependent programmed necrotic cell death, which leads to neutrophilic inflammation.

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NLRP3 activation induces ASC-dependent programmed necrotic cell death, which leads to neutrophilic inflammation.

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