January 2010/ Group leader, Nods-like receptors in infection and immunity (Team 7 at the Center of Infection and Immunity of Lille)
2008/10: Junior tenure scientist – Directeur de recherche première classe - at Institut Pasteur de Lille in the research unit Inserm U801 headed by Pr. M. Simonet;
2005/08: Postdoctoral research fellow then Junior tenure scientist – Chargé de recherché première classe - in the research unit Inserm U795 headed by Pr. P. Desreumaux;
2003/05: Postdoctoral research fellow, University of Michigan, Ann Arbor, USA (Supervisor Pr. G. Nùñez);
1998/02: Ph. D., Inserm U434, Paris, France (Supervisor Pr. G. Thomas);
1997: Master degree, Inserm U347, Kremlin-Bicêtre, France (Supervisor Dr. M. Meunier-Rotival) and Jacques Monod Institute, Paris, France (Supervisor Pr. C. Lamour-Isnard);
1995: Graduate, Tours’ Hospital, Tours, France (Supervisor Dr. S. Briault).
Rationale. The gastrointestinal mucosa enables tolerance towards commensals whereas it promotes a robust antimicrobial response to enteropathogens when they first breach the integrity of the mucosal barrier. While food-borne pathogens remain a major cause of morbidity and mortality worldwide, the intestinal microbiota is also involved in the pathogenesis of several incurable and unpredictive chronic inflammatory diseases, including Crohn’s disease, colorectal cancer and asthma. The molecules involved in this dynamic surveillance machinery still remain an unresolved theme in medicine and biology.
Main achievements. Recent evidence, including work from us, revealed an essential role of NOD2 in anti-bacterial immunity and in the pathogenesis of Crohn’s Disease, a prototypical and incurable form of inflammatory bowel disease that affects millions adults worldwide. NOD2 is a member of the recently identified family of cytosolic NODs-Like Receptors (NLRs), which share similarities with the superfamily of plant disease-resistance proteins. Although some of the NLRs are not fully characterized, these molecules are thought to play an essential role in detecting a diversified set of threats that primarily originate from microorganisms and cell remnants. Biochemical studies revealed that NLRs-mediated signalling recruit and activate downstream effectors such as mitogen-activated protein kinase (MAPK) and transcription factors, including nuclear factor-kappa B.
Our recent studies have focused on the respective roles of NOD2 and NOD1, the NLR molecule closest to NOD2. To gain further insights into the role of NOD2, we first identified MurNAc-L-Ala-D-isoGln (MDP) as the essential microbial structure sensed by NOD2 ex vivo and in vivo. MDP is a structure commonly found in peptidoglycan from both Gram-positive and Gram-negative bacteria. The absence of NOD2 confers increased predisposition to oral, but not systemic, infection by a restricted panel of infectious agents, including Listeria monocytogenes but not Yersinia pseudotuberculosis. Importantly, we found that NOD2 regulates the expression of alpha-defensins produced by Paneth cells in mice. MDP is also a major component of Freund’s complete adjuvant that regulates antigen-specific T-cell responses and antibody production. Our data revealed that MDP-triggered adaptive immunity is abolished in Nod2-deficient animals. Further fundamental work is now required to determine the cellular and molecular basis of the immunomodulatory properties of MDP through NOD2-mediated signalling. Consistent with our data, clinical studies in Crohn’s Disease strongly support our hypothesis by unravelling a deficiency in both alpha- and betta-defensins and an impaired immunological response to MDP by mononuclear cells isolated from peripheral blood.
Similarly to NOD2, we identified that NOD1-dependent signalling is activated in response to the dipeptide g-D-glutamyl-meso-diaminopimelic acid (iE-DAP) or g-D-glutamic-meso-diaminopimelic acid (iQ-DAP). iE-DAP and iQ-DAP represent a signature of bacterial infection in that such motifs are not expressed by eukaryotic cells. Consistently, our data revealed an essential role of NOD1 in limiting infection by both Gram-negative and Gram-positive bacteria in vivo. By using a biochemical and systematic mutational analysis, we identified a general mechanism by which NOD1 and NOD2 detect different structures of the PGN through their leucine-rich repeats. The N-terminal and C-terminal leucine-rich repeats were differentially required in the engagement of NOD2-mediated signalling by MDP. Notably, the residues thought to be involved in the bstrand/bturn of the C-terminal leucine-rich repeats are essential for the MDP-induced NF-kB activation. We also identified specific residues and essential regulatory domains of NOD1 and NOD2 involved in NF-kB activation. Lastly, our data provided a better understanding of the molecular basis of disease susceptibility by revealing that loss-of-function and gain-of-function mutations are predisposing respectively to Crohn’s disease and to Blau syndrome, another granulomatous disorder that affects solely aseptic sites.
More recently, we recently unveiled an unexpected function for the major CD-predisposing NOD2 gene and for the NOD2-related molecule NLRP6 in shaping a protective assembly of gut microbial communities against intestinal inflammation and tumorigenesis, arguing for a need in revisiting dogmas on the quiescent dialogue between the epithelia and commensals.
Research focus. Despite significant progress in the field, the characterization of regulators of innate immunity in the dialogue between the host and the microbiota is currently at the fundamental research stage. Several challenging issues still remain unresolved, however. Notably, it remains to be seen what is the impact(s) of specific components of the microbiota in host defence, tumorigenesis and autoimmunity through NOD2 and NLRP6 ? Which are the regulatory mechanisms accounting for the tissue-restricted phenotype of defective NOD2 and NLRP6 signalling, and particularly so at the level of cells that are lining or patrolling the interface with the luminal digestive environment? In this context, the scientific objectives of our research group aims now at deciphering the role of NOD2 and other NOD2-related molecules, including NLRP6, in the remote control by commensals on either sensitization or protection against intestinal inflammation and tumorigenesis.
Working hypothesis. The overall hypothesis guiding the objectives of the research is that impaired innate immune surveillance of the microbiota at the intestinal barrier level may hasten clinical symptoms through the host’s failure to protect against tissue damage and to drive an optimal immunological response. If this is true, we should be able to identify rational and novel targets with a view to curing inflammatory barrier diseases and/or preventing their natural progression. To this end, several non-exclusive physiopathological hypotheses are tested.
Approaches. We intend to work out the physiological role of NOD2 and other NOD2-related molecules from the whole organism to the molecular level.
The first theme is to determine the biological effect of NOD2 and NLRP6 on the intestinal microbiota and how commensals may affect engagement of NLR-mediated signaling pathway. To achieve this first specific aim, we will therefore combine systematic molecular examination of the gut microbial community and macroarray gene expression analysis.
The second theme aims at elucidating the critical regulatory processes involved in the engagement of NOD2 and NLRP6 activation in intestinal homeostasis, we will therefore determine its respective role within cells that are patrolling or lining the intestinal mucosa in lamina propria leukocytes and in non-hematopoietic cells. To achieve this aim, the project combines the use of high-content siRNA screening, proteomic and relevant cell-based assays using conditional and whole knockout mice models.
Originality. Our global approach will improve not only our understanding of intestinal tolerance, but also of the immunoregulatory properties of the microbiota that constitute major unresolved themes in biology and medicine. Our original proposal might therefore have an impact on unraveling disease pathogenesis and on the worldwide biomedical research by translating into drug development strategies and by manipulating NLR function in vivo for preventing these widespread illnesses.