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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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 4

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

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IRAKM controls the activity of caspase-8 and IL-1β production in microgl...
(A and B) Targeting vector design for generation of a mouse strain with Irak3 exon 3 flanked by loxp sites (A), and Western blot analysis of IRAKM expression in FACS-sorted microglia from indicated mice (B). (C) Mean clinical score for EAE in WT→Cx3cr1creIrakmfl/+ (IRAKMWT, n = 5) and WT→Cx3cr1creIrakmfl/fl (IRAKMΔmicroglia, n = 7) bone marrow chimera mice induced by active immunization with MOG35–55. (D) Absolute numbers of immune cell infiltration as well as resident microglia determined at the peak of disease in brains of EAE mice by flow cytometry (n = 3/group). (E) H&E and Luxol Fast Blue staining of lumbar spinal cords harvested at the peak of disease. Scale bars: 200 μm. (F) Flow cytometry analysis of caspase-8 activation in microglia of EAE mice at peak disease (n = 4). (G) Primary microglia of EAE brains were isolated and cultured for 24 hours ex vivo. Cell-free supernatant was collected for IL-1β ELISA (n = 4). Data are representative of 2 independent experiments; mean ± SEM. *P < 0.05, **P < 0.01 (unpaired 2-tailed Student’s t test). EAE clinical score by 2-way ANOVA.