TLR-stimulated IRAKM activates caspase-8 inflammasome in microglia and promotes neuroinflammation
Cun-Jin Zhang, … , Richard M. Ransohoff, Xiaoxia Li
Cun-Jin Zhang, … , Richard M. Ransohoff, Xiaoxia Li
Published December 3, 2018; First published October 29, 2018
Citation Information: J Clin Invest. 2018;128(12):5399-5412. https://doi.org/10.1172/JCI121901.
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Categories: Research Article Autoimmunity Inflammation

TLR-stimulated IRAKM activates caspase-8 inflammasome in microglia and promotes neuroinflammation

Abstract

NLRP3 inflammasome plays a critical spatiotemporal role in the pathogenesis of experimental autoimmune encephalomyelitis (EAE). This study reports a mechanistic insight into noncanonical NLRP3 inflammasome activation in microglia for the effector stage of EAE. Microglia-specific deficiency of ASC (apoptosis-associated speck-like protein containing a C-terminal caspase-activation and recruitment [CARD] domain) attenuated T cell expansion and neutrophil recruitment during EAE pathogenesis. Mechanistically, TLR stimulation led to IRAKM–caspase-8–ASC complex formation, resulting in the activation of caspase-8 and IL-1β release in microglia. Noncanonical inflammasome-derived IL-1β produced by microglia in the CNS helped to expand the microglia population in an autocrine manner and amplified the production of inflammatory cytokines/chemokines. Furthermore, active caspase-8 was markedly increased in the microglia in the brain tissue from patients with multiple sclerosis. Taken together, our study suggests that microglia-derived IL-1β via noncanonical caspase-8–dependent inflammasome is necessary for microglia to exert their pathogenic role during CNS inflammation.

Authors

Cun-Jin Zhang, Meiling Jiang, Hao Zhou, Weiwei Liu, Chenhui Wang, Zizhen Kang, Bing Han, Quanri Zhang, Xing Chen, Jianxin Xiao, Amanda Fisher, William J. Kaiser, Masanori A. Murayama, Yoichiro Iwakura, Ji Gao, Julie Carman, Ashok Dongre, George Dubyak, Derek W. Abbott, Fu-Dong Shi, Richard M. Ransohoff, Xiaoxia Li

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Figure 3

IRAKM controls the activity of caspase-8 and IL-1β production in microglia.

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IRAKM controls the activity of caspase-8 and IL-1β production in microgl...
(A–C) Results of immunoblotting with antibodies to the indicated proteins for primary microglia stimulated with LPS (4 hours) plus ATP (30 minutes) and immunoprecipitated with anti–caspase-8 (A), anti-IRAKM (B), or anti-ASC (C). (D) Primary microglia from 6-week-old mice with indicated genotyping were primed with LPS (100 pg/ml) for 4 hours prior to stimulation with 0.5 mM ATP for the indicated times. Cell lysate and supernatants were collected together and immunoblotted with the indicated antibodies. (E) Primary microglia from 6-week-old mice with indicated genotypes was stimulated with LPS (0.1 μg/ml, 4 hours) plus ATP (30 minutes) and stained with caspase-8–FLICA in the last hour, followed by flow analysis of caspase-8 activation (n = 4/group). (F) IL-1β ELISA of cell-free supernatants from adult mice–derived primary microglia treated with LPS (100 pg/ml) for 4 hours and ATP (0.2 mM) for 15 or 30 minutes (n = 4/group). (G) Primary microglia from mice with indicated genotypes was primed with LPS (100 pg/ml) for 4 hours prior to stimulation with 0.2 mM ATP for the indicated times. Cell lysate and supernatants were collected together and immunoblotted with the indicated antibodies. (H–J) Results of immunoblotting with antibodies to the indicated proteins for primary microglia stimulated with LPS (100 pg/ml, 4 hours) plus ATP (30 minutes) and immunoprecipitated with anti-ASC (H) or anti-IRAKM (I and J). Data are representative of 2 independent experiments; mean ± SEM. *P < 0.05 (unpaired 2-tailed Student’s t test).