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. 2017 Dec 19;21(12):3427-3444.
doi: 10.1016/j.celrep.2017.11.088.

V体育官网入口 - Caspase-1 Engagement and TLR-Induced c-FLIP Expression Suppress ASC/Caspase-8-Dependent Apoptosis by Inflammasome Sensors NLRP1b and NLRC4

Nina Van Opdenbosch  1 , Hanne Van Gorp  1 , Maarten Verdonckt  1 , Pedro H V Saavedra  1 , Nathalia M de Vasconcelos  1 , Amanda Gonçalves  2 , Lieselotte Vande Walle  1 , Dieter Demon  1 , Magdalena Matusiak  1 , Filip Van Hauwermeiren  1 , Jinke D'Hont  3 , Tino Hochepied  3 , Stefan Krautwald  4 , Thirumala-Devi Kanneganti  5 , Mohamed Lamkanfi  6
Affiliations

Caspase-1 Engagement and TLR-Induced c-FLIP Expression Suppress ASC/Caspase-8-Dependent Apoptosis by Inflammasome Sensors NLRP1b and NLRC4

Nina Van Opdenbosch et al. Cell Rep. .

Abstract

The caspase activation and recruitment domain (CARD)-based inflammasome sensors NLRP1b and NLRC4 induce caspase-1-dependent pyroptosis independent of the inflammasome adaptor ASC. Here, we show that NLRP1b and NLRC4 trigger caspase-8-mediated apoptosis as an alternative cell death program in caspase-1-/- macrophages and intestinal epithelial organoids (IECs). The caspase-8 adaptor FADD was recruited to ASC specks, which served as cytosolic platforms for caspase-8 activation and NLRP1b/NLRC4-induced apoptosis. We further found that caspase-1 protease activity dominated over scaffolding functions in suppressing caspase-8 activation and induction of apoptosis of macrophages and IECs. Moreover, TLR-induced c-FLIP expression inhibited caspase-8-mediated apoptosis downstream of ASC speck assembly, but did not affect pyroptosis induction by NLRP1b and NLRC4. Moreover, unlike during pyroptosis, NLRP1b- and NLRC4-elicited apoptosis retained alarmins and the inflammasome-matured cytokines interleukin 1β (IL-1β) and IL-18 intracellularly VSports手机版. This work identifies critical mechanisms regulating apoptosis induction by the inflammasome sensors NLRP1b and NLRC4 and suggests converting pyroptosis into apoptosis as a paradigm for suppressing inflammation. .

Keywords: ASC; NLRC4; NLRP1; apoptosis; caspase-1; caspase-8; cell death; inflammasome; inflammation; pyroptosis V体育安卓版. .

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Graphical abstract
Figure 1
Figure 1
LeTx Triggers Caspase-8 Activation and Apoptosis in Caspase-1-Deficient Macrophages (A–D) B6Nlrp1b+ and B6Nlrp1b+C1−/−C11−/− BMDMs were treated with LeTx for 3 hr before supernatants were analyzed for LDH activity (A), bright-field images were acquired (B), and cells were stained for annexin V and PI followed by FACS analysis (C) and quanitification of annexin V-positive cells (D). (E and H) Wild-type and caspase-1/11-deficient BALB/c BMDMs were stimulated with LeTx for 3 hr and then microscopically analyzed (E), and lysates were immunoblotted for caspase-1 and caspase-8 (H). (F and G) BMDM lysates of the indicated genotypes were immunoblotted for RIPK3 and RIPK1 (F) and caspase- 1 and caspase-8 (G) following LeTx-treatment for the indicated durations. (I–K) z-IETD-fmk-pretreated B6Nlrp1b+C1−/−C11−/− BMDMs were stimulated with LeTx for 3 hr before lysates were immunoblotted for caspase-8 (I). Cells were analyzed by FACS (J) and annexin V-positive cells (K) were quantified in parallel. (L and M) BMDMs were incubated with TAT-CrmA for 10 min, followed by LeTx for 3 hr, before lysates were immunoblotted for caspase-1 and caspase-8 (L), and bright-field images were acquired (M). All scale bars are set at 20 μm. All data are representative of results from three independent experiments. Data are shown as mean ± SD from a single representative experiment of at least three independent experiments, with each condition performed in triplicate.
Figure 2
Figure 2
NLRP1b and ASC Are Required for LeTx-Induced Caspase-8 Activation and Apoptosis (A and B) BMDMs were treated with LeTx for the indicated durations before lysates were immunoblotted for caspase-8 and caspase-3 (A). Bright-field images were taken 3 hr after LeTx stimulation (scale bar, 20 μm) (B). (C and D) BMDMs were stimulated with PA and LF or the catalytic LFE687C mutant before lysates were immunoblotted for caspase11 and caspase-8 (C), and bright-field images were acquired (scale bar, 20 μm) (D). (E) BMDMs were treated with MG132 followed by LeTx before lysates were immunoblotted for caspase-1 and caspase-8. (F–H) Crosslinked ASC oligomers were isolated from BMDMs following LeTx stimulation, and lysates were immunoblotted for ASC (F). (G and H) ASC specks were quantified over multiple representative confocal micrographs depicting DAPI (blue), caspase-8 (green), and ASC (red) staining (scale bar, 10 μm) (G). Representative images are shown (H). (I–K) BMDMs of the indicated genotypes were stimulated with LeTx before lysates were immunoblotted for caspase-1 and caspase-8 and ASC (I). Confocal images were acquired for DAPI (blue), caspase-8 (green), and ASC (red) (scale bar, 10 μm) (J), and bright-field images were taken (scale bar, 20 μm) (K). All results are representative of at least three independent experiments, and data are shown as mean ± SD from a single representative experiment.
Figure 3
Figure 3
NAIP5/NLRC4-Induced Apoptosis Is Dependent on ASC and Caspase-8 (A and B) Recombinant flagellin was transfected in BMDMs using SLO before bright-field images were acquired (scale bar, 20 μm) (A) and lysates were immunoblotted for caspase-1 and caspase-8 and ASC (B). (C) BMDMs were treated with FlaTox, and confocal micrographs for DAPI (blue), FADD (green), and ASC (red) were taken (scale bar, 10 μm). (D and E) BMDMs of the indicated genotypes were infected with S. Typhimurium (50 MOI). Lysates were collected 2 hr post-infection and immunoblotted for caspases 1 and 8 and RIPK3 (D), and cell death was quantified by tracking SYTOX Green incorporation over time (E). Data are shown as mean ± SD from a single representative experiment, with each condition performed in duplicate. (F and G) Primary intestinal epithelial cell (IEC) organoids of the indicated genotypes were stimulated with FlaTox and quantified for PI staining over a 16 hr time window (scale bar, 100 μm). Representative images are shown (F). Observed PI intensity was normalized to organoid surface (G). All data are representative of results from three independent experiments.
Figure 4
Figure 4
Caspase-1 Protease and Scaffolding Functions Contribute to Suppression of ASC- and Caspase-8-Dependent Apoptosis (A–E) BMDMs of the indicated genotypes were either primed or not primed with LPS for 3 hr and subsequently stimulated with FlaTox for another 2 hr. Lysates were immunoblotted for caspase-1, caspase-3, and caspase-8, IL-1β; and IL-18 (A and D). The levels of IL-1β (B) and IL-18 (C) were determined in culture supernatants, and bright-field micrographs were taken 2 hr post-stimulation (scale bar, 20 μm) (E). Data are shown as mean ± SD from a single representative experiment of three independent experiments, with each condition performed in triplicate. (F) FlaTox-treated C1−/−and C1C284A/C284A BMDMs were incubated with CellEvent Caspase-3/7 Green and followed in time by IncuCyte technology. Data are shown as mean ± SD from a single representative experiment of three independent experiments, with each condition performed in duplicate. (G and H) Primary intestinal epithelial organoids of the indicated genotypes were stimulated with FlaTox and followed during 16 hr for PI incorporation (scale bar, 100 μm) (G). Quantification was performed on PI intensity normalized to the surface of the organoid (H). All data are representative of results from at least three independent experiments.
Figure 5
Figure 5
Cytokines and Alarmins Are Not Released during NLRP1b- and NLRC4-Mediated Apoptosis (A–C) BMDMs of the indicated genotypes were stimulated as depicted. Supernatants were analyzed for IL-1β (A) and IL-18 (B), and lysates were immunoblotted for IL-1β and IL-18 (C). (D and E) BMDMs of the indicated genotypes were stimulated as depicted, and supernatants were analyzed for IL-1β (D) and IL-18 (E) by Luminex assay. (F) B6Nlrp1b+ and B6Nlrp1b+C1−/−C11−/− BMDMs were stimulated with LeTx, and culture supernatants were immunoblotted for HMGB1 and albumin. (G) LPS-primed or unprimed B6Nlrp1b+ and B6Nlrp1b+C1−/−C11−/− BMDMs were stimulated with LeTx. The supernatant was analyzed for IL-1α (G). Data are shown as mean ± SD from a single representative experiment of three experiments, with each condition performed in triplicate. (H–M) BMDMs from B6, NLRC4−/−, ASC−/−, and C1−/−C11−/− mice were left unprimed (H, J, and L) or primed (I, K, and M) with LPS for 3 hr and subsequently infected with S. typhimurium (MOI 50). The supernatant was used to determine the levels of IL-1β (H and I), IL-18 (J and K), and IL-1α (L and M) by Luminex. Data are shown as mean ± SD from a single representative experiment of three experiments, with each condition performed in triplicate.
Figure 6
Figure 6
TLR-Induced Upregulation of c-FLIP Expression Inhibits LeTx-Induced Caspase-8 Activation Downstream of ASC Speck Formation (A and B) BMDMs of the indicated genotypes were stimulated as depicted, lysates were immunoblotted for caspase-1 and caspase-8 (A), and bright-field micrographs were taken (scale bar, 20 μm) (B). (C) Where indicated, B6Nlrp1b+C1−/−C11−/− BMDMs were pretreated with cycloheximide (CHX) prior to stimulation with LPS and LeTx for 3 hr, and lysates were immunoblotted for caspase-8. (D) BMDMs of the indicated genotypes were primed with Pam3CSK4 or poly(I:C) before treatment with LeTx for 3 hr. Lysates were immunoblotted for caspase-1 and caspase-8. (E–G) B6Nlrp1b+ and B6Nlrp1b+C1−/−C11−/− BMDMs were stimulated as indicated before confocal micrographs of DAPI (blue), caspase-8 (green), and ASC (red) staining were taken (scale bar, 10 μm) (E), and ASC specks were quantified over multiple representative confocal micrographs (F). Crosslinked ASC oligomers were isolated, and lysates were immunoblotted for ASC (G). (H) B6Nlrp1b+C1−/−C11−/− BMDMs were stimulated as indicated, and lysates were immunoblotted for c-FLIP and β-actin. (I) Lysates B6Nlrp1b+C1−/−C11−/− BMDMs were immunoblotted for the indicated proteins. (J–L) Pam3CSK4-stimulated B6Nlrp1b+C1−/−C11−/− BMDMs were transfected with scrambled and c-FLIP siRNAs before lysates were probed for c-FLIP and β-actin expression (J). Pam3CSK4-stimulated BMDMs were treated as depicted before lysates were immunoblotted for caspase-8 (K), and analyzed for DEVD-amc conversion (L). Data are shown as mean ± SD from a single representative experiment of at least three experiments.
Figure 7
Figure 7
NLRC4-Induced Apoptosis Is Inhibited by LPS Priming (A) Naive and LPS-primed B6Nlrp1b+C1−/−C11−/− BMDMs were infected with S. Typhimurium (50 MOI) for 2 hr before lysates were immunoblotted for c-FLIP and β-actin. (B) BMDMs of the indicated genotypes were treated as depicted before lysates were immunoblotted for caspase-1 and caspase-8. (C) B6Nlrp1b+C1−/−C11−/− BMDMs were transfected with scrambled control and c-FLIP-targeting siRNAs before stimulation with Pam3CSK4 (Pam) and SLO-mediated cytosolic delivery of recombinant flagellin. Lysates were immunoblotted for caspase-8. (D–G) BMDMs of the indicated genotypes were left unprimed (●) or primed with LPS (▪) for 3 hr before infection with S. Typhimurium (50 MOI). Supernatants were analyzed for LDH activity (dash line), and annexin V/PI staining (full line) was performed by FACS. Data are shown as mean from a single representative experiment out of two independent experiments, with each condition performed in triplicate. (H) Schematic representation of cell death signaling by the CARD-based inflammasome sensors NLRP1b and NLRC4. Engagement of NLRP1b or NLRC4 leads to caspase-1 maturation and induction of pyroptosis with release of alarmins and inflammatory cytokines, resulting in inflammation. In the absence of caspase-1, ASC specks serve as cytosolic platforms for efficient caspase-8 activation, which drives apoptosis characterized by the absence of alarmin and inflammatory cytokine release. TLR-mediated c-FLIP upregulation potently impedes caspase-8-dependent apoptosis but not pyroptosis.
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