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Autophagy proteins regulate innate immune responses by inhibiting the release of mitochondrial DNA mediated by the NALP3 inflammasome

Abstract

Autophagy, a cellular process for organelle and protein turnover, regulates innate immune responses. Here we demonstrate that depletion of the autophagic proteins LC3B and beclin 1 enhanced the activation of caspase-1 and secretion of interleukin 1β (IL-1β) and IL-18. Depletion of autophagic proteins promoted the accumulation of dysfunctional mitochondria and cytosolic translocation of mitochondrial DNA (mtDNA) in response to lipopolysaccharide (LPS) and ATP in macrophages. Release of mtDNA into the cytosol depended on the NALP3 inflammasome and mitochondrial reactive oxygen species (ROS). Cytosolic mtDNA contributed to the secretion of IL-1β and IL-18 in response to LPS and ATP. LC3B-deficient mice produced more caspase-1-dependent cytokines in two sepsis models and were susceptible to LPS-induced mortality. Our study suggests that autophagic proteins regulate NALP3-dependent inflammation by preserving mitochondrial integrity.

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Figure 1: Absence of LC3B and heterozygous disruption of beclin 1 enhance caspase-1-dependent cytokine secretion in macrophages.
Figure 2: Depletion of autophagic proteins alters mitochondrial phenotype.
Figure 3: EtBr abolishes caspase-1 activation.
Figure 4: Autophagic protein deficiency promotes mtDNA release into cytosol through increased MPT.
Figure 5: Cytosolic mtDNA is involved in caspase-1 activation.
Figure 6: NALP3 mediates the release of mtDNA.
Figure 7: Deficiency in autophagic proteins augments caspase-1-mediated inflammatory responses in vivo.

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Acknowledgements

We thank B. Levine (University of Texas Southwestern Medical Center) for Becn1+/− mice; and E. Ifedigbo for technical assistance. Supported by National Institutes of Health (HL079904-12, HL08554, HL060234-10 and HL097005 to A.M.K.C., and AI083713 and AI067497 to K.A.F.) and the New England Regional Center of Excellence for Biodefense and Emerging Infectious Diseases (National Institute of Allergy and Infectious Diseases of the National Institutes of Health; AI057159 to V.A.K.R).

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K.N., H.P.K., J.A.H and A.M.K.C conceived of the study with assistance from S.W.R. and K.A.F.; M.R. supervised the generation of LC3B-deficent mice; K.A.F. supervised the generation of AIM-2 deficient mice; K.N., S.J.L. and V.A.K.R did the in vitro experiments; J.A.H., S.J.L. and J.A.E. did the in vivo experiments; H.C.L. did the transmission electron microscopy; M.C. and K.N. did flow cytometry; T.D. analyzed human samples; K.N., J.A.H., A.M.K.C. and S.W.R. wrote the paper; and A.M.K.C supervised the entire project.

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Correspondence to Augustine M K Choi.

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Nakahira, K., Haspel, J., Rathinam, V. et al. Autophagy proteins regulate innate immune responses by inhibiting the release of mitochondrial DNA mediated by the NALP3 inflammasome. Nat Immunol 12, 222–230 (2011). https://doi.org/10.1038/ni.1980

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