Regulation of inflammasomes by autophagy Tatsuya Saitoh, PhD, Shizuo Akira, MD, PhD  Journal of Allergy and Clinical Immunology  Volume 138, Issue 1, Pages 28-36 (July 2016) DOI: 10.1016/j.jaci.2016.05.009 Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 1 Autophagy. The isolation membrane appears after exposure to stressors. The ER-mitochondria contact site is a membrane source for the isolation membrane. The isolation membrane elongates and engulfs cytosolic constituents to form the autophagosome, which fuses with lysosomes to form the autolysosome, resulting in degradation of the engulfed constituents. Autophagy promotes reuse of cellular components, turnover of old organelles, and elimination of unfavorable materials, thus playing a vital role in maintenance of cellular homeostasis and disease prevention. ATG proteins drive membrane trafficking necessary for the generation of isolation membrane and autophagosomes. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 2 Autophagy eliminates damaged organelles. Membranes of damaged phagosomes containing bacteria or crystals and damaged mitochondria are ubiquitinated and targeted by adaptor proteins, such as p62, NDP52, and optineurin. β-Galactose chains within the damaged phagosome are recognized by cytosolic galectin-8, which binds to the adaptor protein NDP52. Adaptor proteins recruit ATG proteins to generate autophagosomes in the proximity of the damaged organelle, which engulf and eliminate damaged organelles after fusion with lysosomes. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 3 Autophagy suppresses TLR4-dependent production of IL-1β and IL-18. TLR4 detects LPS, triggers the myeloid differentiation primary response gene–88 (MyD88)–dependent signaling pathway to activate the transcription factor nuclear factor κB (NF-κB), and promotes pro–IL-1β expression. A, TLR4 hardly induces production of IL-1β and IL-18 in autophagy-competent normal macrophages because autophagy suppresses the TRIF-dependent signaling pathway, leading to ROS generation. B, TIR-domain-containing adapter-inducing interferon-β (TRIF)-mediated ROS production is greatly enhanced in autophagy-deficient macrophages, which lack ATG16L1 expression. Thus autophagy deficiency enhances LPS-induced production of IL-1β and IL-18. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 4 Crohn disease–associated ATG16L1 is susceptible to protease degradation. The Crohn disease–associated ATG16L1 variant (T300A), but not wild-type ATG16L1, is processed by caspase-3 and caspase-7. When cells are exposed to severe stress, these caspases induce processing of ATG16L1 (T300A) and make it unstable, resulting in loss of autophagy activity. Autophagy deficiency causes massive inflammation, leading to development of colitis. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 5 Autophagy suppresses NLRP3 inflammasome activation. Stimulatory particles, such as monosodium urate and cholesterol crystals, cause phagosomal rupture, resulting in mitochondrial damage. ATP released from dying cells stimulates P2X7R and causes mitochondrial damage, which in turn releases ROS, causing activation of the NLRP3 inflammasome. Mitochondrial damage also causes release of mitochondrial DNA (mtDNA) to activate the NLRP3 inflammasome. Parkin, an E3 ubiquitin ligase, induces ubiquitination of a set of proteins expressed on damaged mitochondria. Autophagy selectively eliminates damaged mitochondria after sensing ubiquitinated proteins by adaptor protein p62. Autophagy suppresses activation of the NLRP3 inflammasome by eliminating damaged mitochondria, which prevents excess production of ROS and mtDNA. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 6 NOD2-dependent autophagy suppresses influenza virus–induced activation of the NLRP3 inflammasome. Influenza virus infection causes mitochondrial damage, causing ROS production, which results in NLRP3 inflammasome activation. Autophagy eliminates damaged mitochondria to prevent excess ROS production and subsequent activation of the NLRP3 inflammasome. However, influenza virus also induces autophagy by stimulating NOD2. NOD2 deficiency causes impaired autophagy induction, resulting in massive pulmonary inflammation during influenza virus infection. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 7 Autophagy suppresses noncanonical inflammasome activation. Gram-negative bacteria stimulate TLR4 through LPS and induce expression of guanylate-binding proteins (GBPs), caspase-11, pro–IL-1α, and pro–IL-1β in mouse macrophages. Gram-negative bacteria also induce phagosomal rupture, causing leakage of LPS into the cytosol, which then stimulates the caspase-11–driven noncanonical pathway of inflammasome activation. This leads to induction of pyroptosis and production of IL-1α and IL-1β. Autophagy eliminates damaged phagosomes to prevent aberrant activation of the NLRP3 inflammasome. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 8 Autophagy suppresses the inflammatory response by eliminating ASC and IL-1β. Ubiquitinated ASC is targeted by adaptor protein p62 and is recruited to the autophagosome. IL-1β is detected in the LC3-positive cytosolic compartment. The autophagosome engulfs these substrates and eliminates them after fusion with the lysosome. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 9 Autophagy mediates IL-1β secretion under starved conditions. Under starved conditions, the ATG protein ATG5 is involved in secretion of IL-1β induced by nigericin, an inducer of the NLRP3 inflammasome. Golgi reassembly stacking protein (GRASP) and RAB8A are also involved in IL-1β secretion. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 10 Autophagy deficiency causes inflammasome-related inflammatory disorders. Autophagy deficiency caused by gene disruption results in accumulation of damaged organelles, ASC, and IL-1β after exposure to various stressors, such as microbes and stimulatory metabolites. Thus autophagy deficiency induces aberrant activation of the inflammasomes and subsequent production of IL-1β and IL-18, leading to development of inflammatory disorders. Journal of Allergy and Clinical Immunology 2016 138, 28-36DOI: (10.1016/j.jaci.2016.05.009) Copyright © 2016 American Academy of Allergy, Asthma & Immunology Terms and Conditions