Letter | Published:

TLR signalling augments macrophage bactericidal activity through mitochondrial ROS

Nature volume 472, pages 476480 (28 April 2011) | Download Citation

Abstract

Reactive oxygen species (ROS) are essential components of the innate immune response against intracellular bacteria and it is thought that professional phagocytes generate ROS primarily via the phagosomal NADPH oxidase machinery1. However, recent studies have suggested that mitochondrial ROS (mROS) also contribute to mouse macrophage bactericidal activity, although the mechanisms linking innate immune signalling to mitochondria for mROS generation remain unclear2,3,4. Here we demonstrate that engagement of a subset of Toll-like receptors (TLR1, TLR2 and TLR4) results in the recruitment of mitochondria to macrophage phagosomes and augments mROS production. This response involves translocation of a TLR signalling adaptor, tumour necrosis factor receptor-associated factor 6 (TRAF6), to mitochondria, where it engages the protein ECSIT (evolutionarily conserved signalling intermediate in Toll pathways), which is implicated in mitochondrial respiratory chain assembly5. Interaction with TRAF6 leads to ECSIT ubiquitination and enrichment at the mitochondrial periphery, resulting in increased mitochondrial and cellular ROS generation. ECSIT- and TRAF6-depleted macrophages have decreased levels of TLR-induced ROS and are significantly impaired in their ability to kill intracellular bacteria. Additionally, reducing macrophage mROS levels by expressing catalase in mitochondria results in defective bacterial killing, confirming the role of mROS in bactericidal activity. These results reveal a novel pathway linking innate immune signalling to mitochondria, implicate mROS as an important component of antibacterial responses and further establish mitochondria as hubs for innate immune signalling.

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Acknowledgements

We would like to thank C. Schindler, B. Reizis and L. Ciaccia for comments on the manuscript. We also thank P. Rabinovitch for MCAT mice, J. Cotney for technical assistance, Z. Zhang for animal maintenance and M. Graham and K. Zichichi for assistance with immuno-electron microscopy. This work was supported by NIH grants to S.G. (R37-AI33443) and G.S.S. (NS-056206).

Author information

Author notes

    • Igor E. Brodsky

    Present address: Department of Pathobiology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, Pennsylvania 19104, USA.

Affiliations

  1. Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA

    • A. Phillip West
    •  & Igor E. Brodsky
  2. Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520, USA

    • Christoph Rahner
  3. Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06520, USA

    • Dong Kyun Woo
    •  & Gerald S. Shadel
  4. Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA

    • Hediye Erdjument-Bromage
    •  & Paul Tempst
  5. Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA

    • Matthew C. Walsh
    •  & Yongwon Choi
  6. Department of Microbiology and Immunology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA

    • Sankar Ghosh

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Contributions

A.P.W. designed and performed experiments and wrote the paper; I.E.B. generated GFP-expressing Salmonella, helped to design and perform bacterial challenge experiments and edited the paper; C.R. assisted with immuno-electron microscopy; D.K.W. provided MCAT tissues for generating BMDMs; H.E.B. and P.T. performed mass spectrometry analysis; M.C.W. and Y.C. provided reagents and technical advice for experiments involving Traf6-knockout cells; G.S.S. designed experiments and edited the paper; S.G. designed experiments and wrote the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Sankar Ghosh.

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    Supplementary Information

    This file contains Supplementary Figures 1-15 with legends and Supplementary Table 1.

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DOI

https://doi.org/10.1038/nature09973

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