Journal Article

Detection of a microbial metabolite by STING regulates inflammasome activation in response to Chlamydia trachomatis infection

Brode, Sven, Gekara, Nelson O., Elder, Matthew J., Bryant, Clare, Tourlomousis, Panagiotis, Clare, Simon, Chee, Ronnie, Goodall, Jane C., Webster, Steve J., Fitzmaurice, Timothy J., Gaston, Hill J. S., Ellis, Lou

2017

Overview

The innate immune system is a critical component of host defence against microbial pathogens, but effective responses require an ability to distinguish between infectious and non-infectious insult to prevent inappropriate inflammation. Using the important obligate intracellular human pathogen Chlamydia trachomatis; an organism that causes significant immunopathology, we sought to determine critical host and pathogen factors that contribute to the induction of inflammasome activation. We assayed inflammasome activation by immunoblotting and ELISA to detect IL-1β processing and LDH release to determine pyroptosis. Using primary murine bone marrow derived macrophages or human monocyte derived dendritic cells, infected with live or attenuated Chlamydia trachomatis we report that the live organism activates both canonical and non-canonical inflammasomes, but only canonical inflammasomes controlled IL-1β processing which preceded pyroptosis. NADPH oxidase deficient macrophages were permissive to Chlamydia trachomatis replication and displayed elevated type-1 interferon and inflammasome activation. Conversely, attenuated, non-replicating Chlamydia trachomatis, primed but did not activate inflammasomes and stimulated reduced type-1 interferon responses. This suggested bacterial replication or metabolism as important factors that determine interferon responses and inflammasome activation. We identified STING but not cGAS as a central mediator of interferon regulated inflammasome activation. Interestingly, exogenous delivery of a Chlamydia trachomatis metabolite and STING ligand-cyclic di-AMP, recovered inflammasome activation to attenuated bacteria in a STING dependent manner thus indicating that a bacterial metabolite is a key factor initiating inflammasome activation through STING, independent of cGAS. These data suggest a potential mechanism of how the innate immune system can distinguish between infectious and non-infectious insult and instigate appropriate immune responses that could be therapeutically targeted.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Activation / AMP / Animals / Apoptosis / Arthritis / Assaying / Attenuation / Bacteria / Bacterial infections / Biology and Life Sciences / Bone marrow / Care and treatment / Cell death / Chlamydia / Chlamydia infections / Chlamydia Infections - immunology / Chlamydia Infections - microbiology / Chlamydia trachomatis / Chlamydia trachomatis - genetics / Chlamydia trachomatis - immunology / Chlamydia trachomatis - physiology / Colleges & universities / Condoms / Critical components / Cyclic AMP - immunology / Dendritic cells / Dendritic Cells - immunology / Dendritic Cells - microbiology / Dosage and administration / Enzyme-linked immunosorbent assay / Female / Health aspects / Humans / Immune response / Immune system / Immunoblotting / Infections / Infectious diseases / Inflammasomes / Inflammasomes - immunology / Inflammation / Innate immunity / Interferon / Interferon Type I - genetics / Interferon Type I - immunology / Interleukin 1 / Interleukin-1beta - genetics / Interleukin-1beta - immunology / Macrophages / Macrophages - immunology / Macrophages - microbiology / Male / Medicine and Health Sciences / Membrane Proteins - genetics / Membrane Proteins - immunology / Metabolism / Metabolites / Mice / Microorganisms / Monocytes / NAD(P)H oxidase / Nucleotidyltransferases - genetics / Nucleotidyltransferases - immunology / Oxidase / Pathogens / Physiological aspects / Proteins / Pyroptosis / Replication / Research and Analysis Methods / Rheumatology / Risk factors / Sexually transmitted diseases / STD / Veterinary medicine