Interaction PGL /lectins and modulation of the host immune response by mycobacterial pathogens – PGLECT

In this project, four well-qualified teams from the CNRS, INRA and Institut Pasteur, with common interest in mycobacterial disease control, propose to combine their complementary and multidisciplinary strengths i) to establish the contribution of mycobacterial lipids to host immune suppression, ii) to identify the molecular targets and mechanisms of action of these lipids, iii) to perform structure-function studies and unravel the structural basis of their roles in virulence.
To achieve this ambitious goal, we will develop a novel strategy based on the reprogrammation of a biosynthesis pathway in a bacterial model to make it synthesize various species-specific lipids and to allow us to compare the activity of the various lipids in the context of a similar and relevant mycobacterial cell envelope. We will couple this strategy with a synthetic chemistry approach, in which various lipid domains will be chemically synthesized. These microbial (recombinant strains) and molecular (synthetic molecules) tools will be used i) to study the interaction of lipids with host cell molecules, ii) to analyze the signaling pathways targeted by these lipids in phagocytes; iii) to characterize the impact of these lipids on the generation of immune responses.

project on going

In addition to advance our understanding of the pathogenesis of major human diseases, we are expecting this work to open new avenues for vaccine development and therapy against mycobacterial infections.

project on going

Tuberculosis, leprosy and Buruli ulcer consitute challenges to global public health, causing death, suffering, economic losses and poverty. These human diseases are caused by bacteria from the Mycobacterium genus, namely Mycobacterium tuberculosis, M. leprae and M. ulcerans. Their impact on public health is staggering: one third of the world’s population is infected with M. tuberculosis; mycobacterial diseases kill more adults than AIDS, malaria and all other tropical diseases combined. Although chemotherapy to fight mycobacterial infections and a vaccine, M. bovis BCG, against TB exist, these therapeutic tools have failed to control mycobacterial diseases. Crucially, novel vaccines and new drugs are urgently needed to achieve effective and sustainable control of mycobacterial infections. We must improve our basic knowledge of the biology of mycobacteria and of the factors important for the pathogenesis and their mechanisms of action, in order to design novel approaches to anti-mycobacterial vaccination and therapy.
The hallmark of mycobacterial pathogens is their ability to persist for decades in the infected hosts. This feature is closely associated with the pathogen’s capacity to delay and suppress the adaptive immune responses. Among the virulence factors suspected to play a role in the host immunomodulation are the phenolic glycolipids (PGL), which are only produced by a limited number of mycobacterial species, and notably by all the major human pathogens. These molecules display a similar lipid core and species-specific saccharidic domains. In vitro, these PGL exhibit activities that may account for the incapacity of the infected hosts to mount protective immune responses and to clear the infection. However, the demonstration of the role of these molecules in vivo and the molecular mechanisms involved remain to be elucidated.

In this project, four well-qualified teams from the CNRS, INRA and Institut Pasteur, with common interest in mycobacterial disease control, propose to combine their complementary and multidisciplinary strengths to:
- establish the contribution of mycobacterial PGL to host immune suppression,
- identify the molecular targets and mechanisms of action of PGL
- perform structure-function studies and unravel the structural basis of PGL roles in virulence.

To achieve this ambitious goal, we will develop a novel strategy based on the reprogrammation of a biosynthesis pathway in M. bovis BCG to make it synthesize various species-specific PGL. This highly innovative approach will allow us to compare ex vivo and in vivo the activity of various PGL in the context of a similar and relevant mycobacterial cell envelope. A proof of concept of the methodology has already been obtained through the construction of a recombinant BCG strain expressing the PGL-1 of M. leprae. Using this tool, we were able to demonstrate that bacterial production of PGL-1 endows BCG with an increased capacity to exploit the complement receptor CR3 for silent invasion of host phagocytes, suggesting that CR3-mediating pathways are deviated by PGL-1. To gain further insight into the structural basis of PGL activity, we propose to couple our reprogrammation strategy with a synthetic chemistry approach, in which the various species specific domains of PGL will be linked to functional groups. These microbial (recombinant BCG strains) and molecular (synthetic molecules) tools will be used i) to study the interaction of PGL with CR3 and to search for other cellular partners of these glycolipids; ii) to analyze the signaling pathways targeted by PGL in macrophages and dendritic cells; iii) to characterize the impact of PGL production on the generation of immune responses against model antigens in the mouse model.

In addition to advance our understanding of the pathogenesis of major human diseases, we are expecting this work to open new avenues for vaccine development and therapy against mycobacterial infections.