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Activity of uncleaved caspase-8 controls anti-bacterial immune defense and TLR-induced cytokine production independent of cell death

ABSTRACT: Caspases regulate cell death programs in response to environmental stresses, including infection and inflammation, and are therefore critical for the proper operation of the mammalian immune system. Caspase-8 is necessary for optimal production of inflammatory cytokines and host defense against infection by multiple pathogens including Yersinia, but whether this is due to death of infected cells or an intrinsic role of caspase-8 in TLR-induced gene expression is unknown. Caspase-8 activation at death signaling complexes results in its autoprocessing and subsequent cleavage and activation of its downstream apoptotic targets. Whether caspase-8 activity is also important for inflammatory gene expression during bacterial infection has not been investigated. Here, we report that caspase-8 plays an essential cell-intrinsic role in innate inflammatory cytokine production in vivo during Yersinia infection. Unexpectedly, we found that caspase-8 enzymatic activity regulates gene expression in response to bacterial infection as well as TLR signaling independently of apoptosis. Using newly-generated mice in which caspase-8 autoprocessing is ablated (Casp8DA/DA), we now demonstrate that caspase-8 enzymatic activity, but not autoprocessing, mediates induction of inflammatory cytokines by bacterial infection and a wide variety of TLR stimuli. Because unprocessed caspase-8 functions in an enzymatic complex with its homolog cFLIP, our findings implicate the caspase-8/cFLIP heterodimer in control of inflammatory cytokines during microbial infection, and provide new insight into regulation of antibacterial immune defense.

ORGANISM(S): Mus musculus

PROVIDER: GSE86922 | GEO | 2016/09/15

SECONDARY ACCESSION(S): PRJNA343025

REPOSITORIES: GEO

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Project description:COVID-19 has rapidly circulated around the globe and caused significant morbidity and mortality. The disease is characterized by excessive production of pro-inflammatory cytokines and acute lung damage and patient mortality. Although initial cytokine cascades may be beneficial to the host for clearing the virus, enhanced production of pro-inflammatory cytokines and increasing levels in the systemic circulation, referred to as cytokine storm, can promote tissue damage by inducing inflammatory cell death in both infected and bystander cells. Of the multiple inflammatory cytokines produced by innate immune cells during SARS-CoV-2 infection, we found that the combination of TNF-α and IFN-γ specifically induced cell death characterized by GSDME¬–mediated pyroptosis, caspase-8–mediated apoptosis, and MLKL–mediated necroptosis. Cells deficient in both RIPK3 and caspase-8 or RIPK3 and FADD were resistant to this cell death. However, deletion of pyroptosis, apoptosis, or necroptosis individually was not sufficient to protect against cell death. Mechanistically, the STAT1/IRF1 axis activated by TNF-α and IFN-γ co-treatment induced iNOS for the production of nitric oxide. Pharmacological and genetic deletion of this pathway inhibited pyroptosis, apoptosis, and necroptosis in macrophages. Moreover, inhibition of inflammatory cell death protected mice from TNF-α and IFN-γ–induced lethal cytokine shock that mirrors the pathological symptoms of COVID-19. To determine the physiological relevance of protection, we neutralized both TNF-α and IFN-γ in multiple disease models associated with cytokine storm and found that this treatment provided substantial protection against not only SARS-CoV-2 infection, but also sepsis, hemophagocytic lymphohistiocytosis, and cytokine shock models. Collectively, our findings reveal that blocking the COVID-19 cytokine-mediated inflammatory cell death signaling pathway identified in this study may benefit patients with COVID-19 or other cytokine storm-driven syndromes by limiting inflammation and tissue damage. Additionally, these results open new avenues for the treatment of other infectious and autoinflammatory diseases and cancer where TNF-α and IFN-γ synergism play key pathological roles.

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Activity of uncleaved caspase-8 controls anti-bacterial immune defense and TLR-induced cytokine production independent of cell death

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