PhD in Cellular Biology and host-pathogen interactions

Description of the thesis topic:

“Role of extracellular vesicles in host-pathogen interactions and virulence of Mycobacterium tuberculosis”

Tuberculosis is one of the 10 leading causes of death in the world (WHO, 2018) (1). The etiological agent, Mycobacterium tuberculosis (Mtb), infects alveolar macrophages and establishes a chronic infection in humans through its ability to adapt to intracellular conditions and host immune responses (2). A better understanding of the host-pathogen interactions of this infection is necessary for the development of more effective means of control. Every living cell releases extracellular vesicles (EV) that shuttle diverse molecules (lipids, proteins, nucleic acids) and play important roles in intercellular communication, regulation of immune responses or bacterial virulence (3). Similarly, infected cells as well as the bacillus release EV during Mtb infection. If the host-pathogen interaction of this infection is essentially studied at the direct interface between the 2 organisms, the diffusion of bacterial and eukaryotic factors within EV most likely contribute significantly to these interactions at the infection site and beyond (4, 5). However, the characterization of the composition and immunomodulatory properties of these EV remains largely incomplete.

In this context, the aim of this project is to better characterize the interactions of these vesicles with the preferred target of Mtb: the macrophages. Their capacity to regulate the inflammatory and microbicide properties of macrophages. In particular, we will study the capacity of EV to activate and induce cytokine production and autophagy, via their interaction with innate immunity receptors or Pattern Recognition Receptors (PRRs), such as Toll Like Receptors (TLRs) or C-type lectins. Their intracellular trafficking, which conditions their immunomodulatory properties, will be analysed by super-resolution microscopy. The vesicles released in presence of mycobacteria of variable virulence will be studied comparatively in these different assays. In order to decipher the molecular basis of their immunomodulatory properties, we will undertake to characterize their content in PRR ligands using omic-type methods, among others.
Given their relevance for the study of host-pathogen interactions, a better characterization of EV will provide important insights into Mtb pathogenesis.

Methods: cell and mycobacterial culture, vesicle purification (density gradient, exclusion chromatography), TEM and super-resolution microscopy, activation assays of reporter and functional bioassay on primary cells, flow cytometry, Western blot, ELISA, mass spectrometry.

References: (1) WHO. Global Tuberculosis Report 2020. https://www.who.int/tb/. (2) Ernst J. D. Mechanisms of M. tuberculosis Immune Evasion as Challenges to TB Vaccine Design. Cell Host Microbe 2018, 24(1):34-42. (3) Robbins PD, Morelli AE. Regulation of immune responses by extracellular vesicles. Nat Rev Immunol. 2014, 14(3):195-208. (4) Prados-Rosales R, et al. Mycobacteria release active membrane vesicles that modulate immune responses in a TLR2-dependent manner in mice. J Clin Invest. 2011, 121(4):1471-83. (5) Layre E. Trafficking of Mycobacterium tuberculosis Envelope Components and Release Within Extracellular Vesicles: Host-Pathogen Interactions Beyond the Wall. Front Immunol. 2020, 11:1230.

Work Context

This project will be carried out in the team "Immunomodulation by lipids and mycobacterial glycoconjugates" led by Dr. J. Nigou, in the "Tuberculosis and Infection Biology" department of the Institute of Pharmacology and Structural Biology (IPBS, joint research unit CNRS-Paul Sabatier University, Toulouse, France). The student will work under the supervision of Drs. Emilie Layre (CR, CNRS) and Jérome Nigou (DR, CNRS). The IPBS offers a stimulating research environment and benefits from several state-of-the-art facilities on site, including proteomics and mass spectrometry, macromolecular crystallography, liquid and solid state NMR, high resolution imaging of tissues and cells imaging of tissues and cells, flow cytometry and cell sorting in standard in standard or level 3 security laboratories and animal facilities.
The IPBS is located on the main campus of the University Toulouse III-Paul Sabatier. which offers multidisciplinary education in the fields of science health, engineering and technology, and is developing one of the most important scientific research centers in France. Founded in 1996, the IPBS is today composed of 16 internationally recognized research groups, which bring together more than 250 scientists, including numerous post-doctoral fellows and national and international PhD students.