13:40 - 15:10
Workshop 5, “Genetic disorders in cytokines and inflammation”
Room: ANA Crowne Plaza “Ohtori” Room C
Workshop Session
Chair/s:
Koji Yasutomo, Warren Leonard
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XIAP deficiency results in excess NLRP3 inflammasome activation and cell death as a consequence of TLR-MyD88 induced cIAP1-TRAF2 degradation
Kate Lawlor1, 2, Rebecca Feltham1, 2, Monica Yabal3, Stephanie Conos1, 2, Kaiwen Chen4, Tan Nguyen1, 2, Cathrine Hall1, Simon Chatfield1, 2, Damian D'Silva1, Kenneth Pang5, Kate Schroder4, John Silke1, 2, David Vaux1, 2, Philipp Jost3, James Vince1, 2
1Walter and Eliza Hall Institute of Medical Research, Parkville, Australia, 2Department of Medical Biology, The University of Melbourne, Parkville, Australia, 3III. Medical Department for Hematology and Oncology, Klinikum rechts der Isar, Technische Universitat Munchen, Munchen, Germany, 4Institute for Molecular Bioscience and Centre for Inflammation and Disease Research, The University of Queensland, St Lucia, Australia, 5Department of Paediatrics, University of Melbourne, Parkville, Australia

Introduction: X-linked Inhibitor of Apoptosis (XIAP) deficiency predisposes people to the pathogen-associated autoinflammatory-like syndrome, hemophagocytic lymphohistiocytosis. Consistent with XIAP mutant patient cytokine profiling, Toll-like Receptor (TLR) ligation drives excess activation of IL-1β and IL-18 in IAP-deficient mice. Upon XIAP loss, the activation of IL-1β results from RIPK3 and caspase-8-induced NLRP3 inflammasome formation, and also direct IL-1β processing by caspase-8. However, how XIAP deficiency specifically triggers these inflammatory signals remains unclear.

Methods: Wildtype (WT) and Xiap-/-, cIAP1LysMcreXiap-/-, Trif-/-, MyD88-/-, IFNAR1-/- Tnfr2-/-, Tnfr1-/-, Xiap-/-Tnfr2-/- bone marrow derived macrophages and dendritic cells were stimulated with TLR ligands (LPS, Pam3Cys, Poly I:C, CpG), IAP antagonists, IFNβ and neutralising anti-TNFR1 or TNFR2 antibodies, as indicated. At specified times cytokine production was assayed by ELISA and cell death measured by propidium iodide uptake and flow cytometric analysis. In parallel, IAP levels, NLRP3 and caspase activity was measured by immmunoblot. WT and mutant mice were challenged with LPS and serum cytokines measured.

Results: We found that TLR-MyD88 engagement causes the degradation of cIAP1, and its adaptor, TRAF2, by inducing TNF Receptor 2 (TNFR2) signaling. Moreover, in the absence of XIAP enhanced TLR-induced cIAP1 degradation promotes excess NLRP3 inflammasome activity and cell death in vitro and in vivo. Consistent with this, deletion of TNFR2 in XIAP-deficient myeloid cells prevented TLR-induced cIAP1-TRAF2 degradation, limited cell death and prevented NLRP3 activation and, notably, these blunted responses in Xiap-/-Tnfr2-/- cells were reversed by IAP antagonist targeting of cIAP1. We also show that TLR-TRIF induced IFNβ counterbalances TLR-MyD88 signaling by impeding cIAP1 loss and consequent cell death.

Conclusion: These data reveal how XIAP and cIAP1 cooperate to prevent RIPK3 activation of the inflammasome and cell death, and help explain why XIAP-deficient patients can exhibit symptoms reminiscent of patients with activating inflammasome mutations.

Reference:
Mo-WS5-5
Session:
Workshop 5, “Genetic disorders in cytokines and inflammation”
Presenter/s:
Kate Lawlor
Presentation type:
Oral Presentation
Room:
ANA Crowne Plaza “Ohtori” Room C
Chair/s:
Koji Yasutomo, Warren Leonard
Date:
Monday, 30 October 2017
Time:
14:40 - 14:50
Session times:
13:40 - 15:10
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