Article

Increased NOD2-mediated recognition of N-glycolyl muramyl dipeptide

Department of Medicine, McGill University Health Centre, Montreal, Quebec H3G 1A4, Canada.
Journal of Experimental Medicine (Impact Factor: 13.91). 09/2009; 206(8):1709-16. DOI: 10.1084/jem.20081779
Source: PubMed

ABSTRACT Peptidoglycan-derived muramyl dipeptide (MDP) activates innate immunity via the host sensor NOD2. Although MDP is N-acetylated in most bacteria, mycobacteria and related Actinomycetes convert their MDP to an N-glycolylated form through the action of N-acetyl muramic acid hydroxylase (NamH). We used a combination of bacterial genetics and synthetic chemistry to investigate whether N-glycolylation of MDP alters NOD2-mediated immunity. Upon infecting macrophages with 12 bacteria, tumor necrosis factor (TNF) alpha secretion was NOD2 dependent only with mycobacteria and other Actinomycetes (Nocardia and Rhodococcus). Disruption of namH in Mycobacterium smegmatis obrogated NOD2-mediated TNF secretion, which could be restored upon gene complementation. In mouse macrophages, N-glycolyl MDP was more potent than N-acetyl MDP at activating RIP2, nuclear factor kappaB, c-Jun N-terminal kinase, and proinflammatory cytokine secretion. In mice challenged intraperitoneally with live or killed mycobacteria, NOD2-dependent immune responses depended on the presence of bacterial namH. Finally, N-glycolyl MDP was more efficacious than N-acetyl MDP at inducing ovalbumin-specific T cell immunity in a model of adjuvancy. Our findings indicate that N-glycolyl MDP has a greater NOD2-stimulating activity than N-acetyl MDP, consistent with the historical observation attributing exceptional immunogenic activity to the mycobacterial cell wall.

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    • "PGN consists of glycan chains cross-linked via short peptides (Girardin, Travassos et al. 2003), NOD1 and NOD2 recognise different motifs in this structure: NOD2 recognises the conserved muramyl dipeptide (MDP) motif found in all PGNs (McDonald, Inohara et al. 2005), whereas NOD1 recognises D--glutamyl-meso-DAP dipeptide (iE-DAP), which is present in all Gramnegative , but only some Gram-positive PGNs (Chamaillard, Hashimoto et al. 2003; Benko, Philpott et al. 2008). NOD2 can also recognise viral ssRNA and mycobacterial Nglycolylmuramyl dipeptides (Coulombe, Divangahi et al. 2009; Sabbah, Chang et al. 2009). Thus both NOD1 and NOD2 are involved in the recognition of a variety of pathogenic bacteria including: E. coli, Chlamydia spp, Haemophilus influenza by NOD1, and M. tuberculosis and Streptococcus pneumonia by NOD2 (Kumar, Kawai et al. 2009). "
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    • "Because PGN structures are actively remodeled during bacterial cell growth and division, the constant release of NOD1 and NOD2 ligands from bacteria allows the innate immune system to survey its surrounding for the presence of bacteria. Interestingly, recent studies have identified additional agonists for NOD2, N-glycolyl muramyl dipeptide from mycobacteria (Coulombe et al., 2009) and viral ssRNA (Sabbah et al., 2009) (discussed below) demonstrating that NOD1 and NOD2 initiate innate responses upon recognition of a larger variety of pathogen-derived molecules. The mechanisms by which these agonists cross the host's cell membrane to stimulate NOD1 and NOD2 remain not fully understood . "
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    • "Nonetheless, BCG does generate TNF-α in a NOD2-dependent manner (this report and Coulombe et al., 2009). Of relevance, mycobacteria contain the N-acetyl muramic acid hydroxylase, NamH, which glycosylates MDP causing it to be a more potent stimulator of the immune response via NOD2 suggesting that NOD2 may be more tuned at sensing mycobacterial infections in generating an immune response (Coulombe et al., 2009). "
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