Host/Pathogen Interactions
In the tug of war between microbes and their hosts, the manipulation of eukaryotic signalling pathways by bacterial effector proteins plays a crucial role in virulence. Our research focuses on Coxiella burnetii and Brucella, two intravacuolar bacterial pathogens that evolved specific strategies to evade host cell recognition and develop stealthy, chronic infections.
Towards a systems biology approach to host/pathogen interactions
In recent years, the effective identification of bacterial virulence determinants and the study of their diverse mechanisms of action represented a real technical challenge for which the available laboratory techniques are often not suited. Technological advances towards laboratory automation have encouraged the development of high-throughput and high-content screens (HTS and HCS respectively) that revolutionised our approach to scientific questions. Our team has been designing new functional assays for the large-scale identification and characterisation of host/pathogen interactions. Since then, we have set up multi-parametric phenotypic screening approaches aiming at a comprehensive study of the cell biology of intracellular bacterial pathogens.
Cell biology of infection
The development of an intracellular replicative niche is a fundamental step in the pathogenesis of intravacuolar bacterial pathogens and involves reprogramming multiple host membrane trafficking pathways. If on the one hand, Brucella diverts the tight-fitting BCVs (Brucella-containing vacuoles) from the endocytic maturation pathway to escape lysosomal degradation, Coxiella subverts membrane traffic to provide membranes and nutrients for the development of a large, lysosomal-like CCV (Coxiella-containing vacuole). The radical differences between these bacterial replicative compartments make Coxiella and Brucella excellent models to investigate how bacteria differentially manipulate host cell functions. Following our recent advances on the role of autophagy and lipid metabolism in the development of CCVs, we explore how Rab GTPases and lipid metabolism differentially contribute to the development of these two radically different replicative compartments. Subversion of host cell functions relies on the translocation of bacterial effector proteins by specialised secretion systems. Genome analysis using state-of-the-art bioinformatics tools effectively predicts genes encoding candidate T4SS substrates in C. burnetii and Brucella spp. Combined with transcriptomics analysis on both bacteria in the course of infection, these data will allow us to shed light on the arsenal used by these microbes to manipulate host cell functions to protect infected cells from apoptosis, prevent inflammasome activation and suppress the innate immune response. The role of candidate Coxiella and Brucella virulence determinants will be assessed using the techniques already available in our teams and taking advantage of transposon mutant libraries and/or targeted mutants.
Transcriptional regulation
Advances in Next-Gen sequencing techniques allow nowadays to trace the transcriptional landscape of bacterial infections. On the microbial side, this allows pinpointing virulence genes involved in the adaptation of bacteria to the host environment and the manipulation of host cell functions. On the host side, transcriptional profiling highlights specific signalling pathways activated upon infection and, using specific bacterial mutants, how these are suppressed or enhanced during infections. Using dual RNA-Seq, we investigate candidate virulence determinants in Coxiella and Brucella, and we use gene set enrichment analysis to characterise the host cell response to these microbes. The characteristic profiles of Coxiella– and Brucella-infected cells will be compared to identify shared signalling pathways that might be used as targets for the development of antimicrobials. In recent years, Next-Gen Seq also highlighted an emerging role of the non-coding genome in the regulation of eukaryotic and prokaryotic functions and how these can play an important role in host/pathogen interactions. Accordingly, several intergenic mutations in Coxiella result in severe intracellular growth defects.
Stress response
Infections represent a stress signal for both the host cell and the pathogen. On the one hand, eukaryotic cells respond to pathogens invasion and intracellular replication by triggering many response pathways, some of which are pathogen-specific, which collectively aim at clearing the infection. On the microbial side, upon host cell invasion, bacteria are exposed to a radically different environment as compared to the extracellular milieu. Coxiella and Brucella represent an excellent model to investigate the stress response associated with infections in this context. Both are stealth pathogens, capable of repressing cellular stress response using translocated effector proteins. Moreover, pH variations are sensed by both pathogens to trigger a transcriptional response. Coxiella seeks a hostile environment for optimal replication, whereas Brucella actively escapes lysosomal compartments by modifying the composition of its replicative niche. We have recently observed that Coxiella infections elicit a stress response in infected cells which, similarly to abiotic stress, may lead to the expression of long non-coding RNAs that serves as platforms to transiently sequesters proteins in the nucleus. Also, we observed that bacterial effector proteins might interfere with this mechanism. 
2017 
En bref
Organisme(s) modèle(s)
Coxiella burnetii
Brucella spp
Processus biologique étudié
Interactions hôte/pathogène
Techniques utilisées
- Criblage phénotypique multi-paramétrique
- Biologie des systèmes
- Protéomique
- Transcriptomique
Applications médicales
- Identification de cibles potentielles pour le développement des molécules anti-infectieuses
Financements
