Identification of the intracellular location and mechanisms of NOD1-dependent inflammatory responses.  — ASN Events
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  2. Concurrent Symposia 8 Metabolic homeostasis and autophagy
  3. Identification of the intracellular location and mechanisms of NOD1-dependent inflammatory responses. 

Identification of the intracellular location and mechanisms of NOD1-dependent inflammatory responses.  (#93)

Aaron Irving 1 , Hitomi Mimuro 2 , Thomas Kufer 3 , Camden Lo 4 , Lorinda Turner 5 , Belinda Thomas 5 , John Bertin 6 , Ivo Boneca 7 , Chihiro Sasakawa 8 , Dana Philpott 9 , Richard Ferrero 5 , Maria Kaparakis-Liaskos 5
  1. Centre for Cancer Research, MIMR-PHI Institute of Medical Research, Clayton, Victoria, Australia
  2. Division of Bacteriology, Department of Infectious Diseases Control, International Research Center for Infectious Diseases, Institute of Medical Science, The University of Tokyo, Tokyo, Japan
  3. Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, Cologne, Germany
  4. Monash Micro Imaging, Clayton, Victoria, Australia
  5. Centre for Innate Immunity and Infectious Diseases, MIMR-PHI Institute of Medical Research, Clayton, Victoria, Australia
  6. GlaxoSmithKline, Collegeville, USA
  7. Institut Pasteur, Paris, France
  8. Division of Bacterial Infection Biology, Institute of Medical Science, The University of Tokyo, Tokyo, Japan
  9. Department of Immunology, University of Toronto, Toronto, Canada

Aims: Nucleotide oligomerization domain 1 (NOD1) is an intracellular host receptor that senses microbial pathogens by detecting a conserved structure of Gram negative bacterial peptidoglycan (PG). Detection of peptidoglycan by NOD1 ultimately results in a pro-inflammatory cytokine response. However, to date, the intracellular location and the mechanisms whereby NOD1 detects peptidoglycan resulting in the development of pro-inflammatory cytokine responses and autophagy are unknown.

Methods: We used peptidoglycan-containing bacterial outer membrane vesicles (PG-OMVs) as a tool to elucidate the intracellular location of NOD1 and the mechanisms of NOD1-dependent responses that result in cytokine production and autophagy.

Results: Upon entry into host epithelial cells, PG-OMVs from mucosal pathogens induced NOD1-dependent autophagy and IL-8 responses. Fluorescent labelling of peptidoglycan contained within bacterial OMVs revealed that upon entry into host cells, peptidoglycan migrated to early endosomes where it interacted with NOD1 and the NOD1-adaptor protein RIP-2, facilitating the development of an inflammatory response from this location. We showed that migration of PG-OMVs to early endosomes occurred in a NOD1 dependent manner, identifying a previously unknown role for NOD1 in the intracellular migration of peptidoglycan. Most importantly, using fluorescent lifetime imaging microscopy (FLIM)-fluorescence energy transfer (FRET), we were able to show for the first time the direct interaction between bacterial peptidoglycan and NOD1 within host cells. Finally, we found that the NOD1 adaptor protein RIP-2 is essential for the development of NOD1-dependent autophagy and IL-8 production in response to PG-OMVs. 

Conclusions: This study reveals for the first time the intracellular location and the early recognition events required for the detection of Gram negative bacterial pathogens by NOD1. Moreover, this study is the first to visualise a direct interaction between bacterial peptidoglycan and NOD1. These findings will significantly expand our limited knowledge of the contribution of NOD1 in Gram negative bacterial pathogenesis, innate immunity and inflammatory disorders.

  1. Irving A. et.al., Cell Host and Microbe (2014) 15 (5), 623-635