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      Mitochondrial DNA in innate immune responses and inflammatory pathology

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      Nature Reviews Immunology

      Springer Nature

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          Abstract

          Mitochondrial DNA (mtDNA) can engage multiple pattern-recognition receptors to trigger pro-inflammatory and type I interferon responses. This Review provides an overview of how these responses are activated by summarizing the unique features of mtDNA and how it is exposed during cellular stress.

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          Most cited references 116

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          Circulating Mitochondrial DAMPs Cause Inflammatory Responses to Injury

          Injury causes a systemic inflammatory response syndrome (SIRS) clinically much like sepsis 1. Microbial pathogen-associated molecular patterns (PAMPs) activate innate immunocytes through pattern recognition receptors 2. Similarly, cellular injury can release endogenous damage-associated molecular patterns (DAMPs) that activate innate immunity 3. Mitochondria are evolutionary endosymbionts that were derived from bacteria 4 and so might bear bacterial molecular motifs. We show here that injury releases mitochondrial DAMPs (MTD) into the circulation with functionally important immune consequences. MTD include formyl peptides and mitochondrial DNA. These activate human neutrophils (PMN) through formyl peptide receptor-1 and TLR9 respectively. MTD promote PMN Ca2+ flux and phosphorylation of MAP kinases, thus leading to PMN migration and degranulation in vitro and in vivo. Circulating MTD can elicit neutrophil-mediated organ injury. Cellular disruption by trauma releases mitochondrial DAMPs with evolutionarily conserved similarities to bacterial PAMPs into the circulation. These can then signal through identical innate immune pathways to create a sepsis-like state. The release of such mitochondrial ‘enemies within’ by cellular injury is a key link between trauma, inflammation and SIRS.
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            Autophagy proteins regulate innate immune response by inhibiting NALP3 inflammasome-mediated mitochondrial DNA release

            Autophagy, a cellular process for organelle and protein turnover, regulates innate immune responses. We demonstrate that depletion of autophagic proteins microtubule associated protein-1 light chain 3B (LC3B) and Beclin 1 enhances caspase-1 activation and secretion of interleukin-1β and interleukin-18. Autophagic protein depletion promoted 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 ROS. Cytosolic mtDNA contributed to IL-1β and IL-18 secretion 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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              Type I interferons in infectious disease.

              Type I interferons (IFNs) have diverse effects on innate and adaptive immune cells during infection with viruses, bacteria, parasites and fungi, directly and/or indirectly through the induction of other mediators. Type I IFNs are important for host defence against viruses. However, recently, they have been shown to cause immunopathology in some acute viral infections, such as influenza virus infection. Conversely, they can lead to immunosuppression during chronic viral infections, such as lymphocytic choriomeningitis virus infection. During bacterial infections, low levels of type I IFNs may be required at an early stage, to initiate cell-mediated immune responses. High concentrations of type I IFNs may block B cell responses or lead to the production of immunosuppressive molecules, and such concentrations also reduce the responsiveness of macrophages to activation by IFNγ, as has been shown for infections with Listeria monocytogenes and Mycobacterium tuberculosis. Recent studies in experimental models of tuberculosis have demonstrated that prostaglandin E2 and interleukin-1 inhibit type I IFN expression and its downstream effects, demonstrating that a cross-regulatory network of cytokines operates during infectious diseases to provide protection with minimum damage to the host.
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                Author and article information

                Journal
                Nature Reviews Immunology
                Nat Rev Immunol
                Springer Nature
                1474-1733
                1474-1741
                April 10 2017
                April 10 2017
                :
                :
                Article
                10.1038/nri.2017.21
                28393922
                © 2017
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