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Project 29
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Project 29

Winfried Barchet

Cytosolic immune recognition of oxidized DNA forms in bacterial and viral infection

Institute of Clinical Chemistry & Clincal Pharmacology, University Hospital of Bonn

Brief description in German
Die Erkennung von Nukleinsäuren durch Rezeptoren des angeborenen Immunsystems ist entscheidend, um die Antwort auf Virusinfektionen einzuleiten. Diese Rezeptoren können jedoch auch fälschlich von körpereigenen DNA und RNA Molekülen aktiviert werden, was zu Autoimmun-Erkrankungen führen kann.

Wir haben entdeckt, dass DNA nach oxidativer Schädigung nicht mehr durch die 3’ Exonuklease TREX1 abgebaut werden kann, sich im Zytosol ansammelt und so eine deutlich erhöhte Immunaktivierung über den cGAMP synthase (cGAS) / STING Signalweg bewirkt.

Da dieser potentiell gefährliche Mechanismus jedoch in vielen Spezies, einschließlich dem Menschen, evolutionär konserviert ist, verfolgen wir in diesem Projekt die Hypothese, dass er eine wichtige Rolle in physiologischen Abläufen im Immunsystem spielt.

Um ein besseres Verständnis von DNA-abhängigen Entzündungsvorgängen zu erlangen konzentrieren wir uns dabei auf die Evaluation von 4 möglichen Szenarien, in denen DNA Schäden als zusätzliches Kennzeichen für die Pathogendetektion oder als Gefahrensignal fungieren.

Summary
Nucleic acid sensing by innate immune receptors plays a critical role in alerting individual cells, and the immune system to the presence of viruses. On the other hand, erroneous immune activation by self-DNA and RNA promotes autoimmune disease.

We have recently discovered that self-DNA after incurring damage by oxidation becomes highly immune stimulatory, and in this form promotes local inflammation, as well as the emergence of lupus-like skin lesions. We found that oxidized DNA resists degradation by 3’ repair exonuclease 1 (TREX1) and thus remains available in the cytosol to activate the DNA sensor cGAMP synthase (cGAS), which results in a potent type I interferon and pro-inflammatory cytokine response.

Given that humans and mice have conserved this potentially harmful immune mechanism, we hypothesize that potentiated immune recognition of oxidized forms of DNA exerts important functions also in physiological immune processes of pathogen detection and homeostasis.

We envision four scenarios how oxidation damaged DNA may become available for cGAS mediated detection:
i) DNA of viral and bacterial pathogens may be altered by reactive oxygen species (ROS) in lysosomes of phagocytic cells preceding immune detection.
ii) Neutrophils provoked to undergo oxidative burst release oxidized DNA in the form of neutrophil extracellular traps (NETs), which are then taken up by phagocytes either by themselves or together with entrapped pathogens.
iii) Self DNA released from dying cells may act as damage associated molecular pattern (DAMP) to signal immunogenic forms of cell death.
iv) Similarly, oxidation damaged mitochondrial DNA may be released from rupturing mitochondria during necrosis and apoptosis.

The project aims at evaluating the role of oxidized DNA detection in each of these scenarios. Understanding the function of oxidative DNA damage - as an additional label for the immune detection of pathogens, and/or cellular danger signaling - informs on the immune biology of inflammatory processes, and may be employed to improve the immunogenicity of attenuated pathogen vaccines.

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Scenarios of the possible physiological role of preferential immune recognition of oxidized DNA in the cytosol

Phagocytes produce reactive oxygen species (ROS) during the respiratory burst to damage and kill pathogens in their close vicinity or within phagosomes. Oxidative damage may therefore label pathogen derived DNA for immune recognition (I). At sites of infection, neutrophils are known to excrete their genomic DNA to entangle pathogens in neutrophil extracellular traps (NETs). Oxidation damaged NET DNA may serve as endogenous adjuvant to boost the recognition of the associated pathogens (II).  Genomic DNA modified by oxidation may be released and recognized as damage associated molecular pattern (DAMP) to indicate ‘dangerous’ forms of cell death including that of infected cells (III). Mitochondrial membrane integrity breaks down during apoptosis and oxidized mitochondrial DNA is released, which may promote cytosolic immune activation. In addition, viable cells have been shown to expel mitochondrial DNA on contact with pathogens (IV).



 

Project-related publications

Herzner AM, Hagmann CA, Goldeck M, Wolter S, Kübler K, Wittmann S, Gramberg T, Andreeva L, Hopfner KP, Mertens C, Zillinger T, Jin T, Xiao TS, Bartok E, Coch C,Ackermann D, Hornung V, Ludwig J, Barchet W, Hartmann G, Schlee M. Sequence-specific activation of the DNA sensor cGAS by Y-form DNA structures as found in primary HIV-1 cDNA. Nat Immunol. 2015 (10):1025-33.

Junt T, Barchet W. Translating nucleic acid-sensing pathways into therapies. Nat. Rev. Immunol. 2015 15(9):529-44.

Schuberth-Wagner C, Ludwig J, Bruder AK, Herzner AM, Zillinger T, Goldeck M, Schmidt T, Schmid-Burgk JL, Kerber R, Wolter S, Stümpel JP, Roth A, Bartok E, Drosten C, Coch C, Hornung V, Barchet W, Kümmerer BM, Hartmann G, Schlee M. A Conserved Histidine in the RNA Sensor RIG-I Controls Immune Tolerance to N1-2'O-Methylated Self RNA. Immunity 2015 43(1):41-51.

Jaeger M, van der Lee R, Cheng SC, Johnson MD, Kumar V, Ng A, Plantinga TS, Smeekens SP, Oosting M, Wang X, Barchet W, Fitzgerald K, Joosten LA, Perfect JR,  Wijmenga C, van de Veerdonk FL, Huynen MA, Xavier RJ, Kullberg BJ, Netea MG. The RIG-I-like helicase receptor MDA5 (IFIH1) is involved in the host defense against Candida infections. Eur J Clin Microbiol Infect Dis. 2015 34(5):963-74.

Gao P, Zillinger T, Wang W, Ascano M, Dai P, Hartmann G, Tuschl T, Deng L, Barchet W°, Patel DJ°. (2014) Binding-Pocket and Lid-Region Substitutions Render Human STING Sensitive to the Species-Specific Drug DMXAA. Cell Reports 8(6):1668–1676. °co-corresponding authors

Goubau D, Schlee M, Deddouche S, Pruijssers AJ, Zillinger T, Goldeck M, Schuberth C, Van der Veen AG, Fujimura T, Rehwinkel J, Iskarpatyoti JA, Barchet W, Ludwig J, Dermody TS, Hartmann G, Reis E Sousa C. (2014) Antiviral immunity via RIG-I-mediated recognition of RNA bearing 5'-diphosphates. Nature 514(7522):372–375.

Gao P, Ascano M, Wu Y, Barchet W, Gaffney BL, Zillinger T, Serganov AA, Liu Y, Jones RA, Hartmann G, Tuschl T, Patel DW (2013) Cyclic [G(2',5')pA(3“,5”)p] Is the Metazoan Second Messenger Produced by DNA-Activated Cyclic GMP-AMP Synthase. Cell 153:1094–1107

Gao P, Ascano M, Zillinger T, Wang W, Dai P, Serganov AA, Gaffney BL, Shuman S, Jones RA, Deng L, Hartmann G, Barchet W°, Tuschl T°, and Patel DJ° (2013) Structure-Function Analysis of STING Activation by c[G(2',5')pA(3“,5”)p] and Targeting by Antiviral DMXAA. Cell 154:748–762 °co-corresponding authors

Gehrke N, Mertens C, Zillinger T, Wenzel J, Bald T, Zahn, S, Tüting, T, Hartmann G, Barchet W. (2013) Oxidative damage of DNA confers resistance to TREX1 degradation and potentiates STING dependent immune sensing. Immunity 39:482–495

Kübler K, Gehrke N, Riemann S, Böhnert V, Zillinger T, Hartmann E, Pölcher M, Rudlowski C, Kuhn W, Hartmann G, Barchet W. (2010) Targeted activation of RNA helicase retinoic acid-inducible gene-I induces proimmunogenic apoptosis of human ovarian cancer cells. Cancer Research 70: 5293–5304

Kübler K, tho Pesch C, Gehrke N, Riemann S, Daßler J, Coch C, Landsberg J, Wimmenauer V, Pölcher M, Rudlowski C, Tüting T Kuhn W, Hartmann G, Barchet W. (2011) Immunogenic cell death of human ovarian cancer cells induced by cytosolic poly(I:C) leads to myeloid cell maturation and activates NK cells. European Journal of Immunology 41:3028–3039