SUNLIVE

Pathogenic mycobacteria have evolved a remarkable ability to evade the immune system and to colonize and survive within the host. Among the key evasion strategies is the capacity of these bacteria to parasitize host macrophages, which represent the major effector cells against intracellular pathogens that can be used as long-term cellular reservoirs. In order to manipulate the macrophage functions to survive and establish infection, mycobacterial pathogens employ a vast panoply of virulence factors, including cell envelope lipids, playing a key role in the modulation of the host innate response. We recently characterized several lipids that are specific to Mycobacterium abscessus (Mabs), acting as virulence factors in macrophage subversion. Mabs is a rapidly growing mycobacterium increasingly acknowledged as a serious non-tuberculous mycobacterial pathogen. It can cause extra-pulmonary infections as well as severe pulmonary disease among otherwise healthy individuals and poses a serious threat to cystic fibrosis patients, where infection correlates with a decline in lung function. Mabs presents distinct smooth (S) and rough (R) colony morphotypes, determined by the presence (S) or absence (R) of cell wall surface associated glycopeptidolipids (GPL). The S variant is thought to be the colonising form and is capable of producing mature biofilms whilst the R variant is impaired in these abilities but forms serpentine cords, a feature which is associated with intense inflammation and hypervirulence. In addition to GPL, we recently characterized a unique lipid entity, a glycosyl diacylated nonadecyl diol (GDND) alcohol, participating in phagosomal membrane damage and in intracellular survival of Mabs in various cellular and animal models. We also identified a yet uncharacterized unique genomic locus related to the GPL locus and absent in M. tuberculosis, encoding putative “GPL-like” lipids, whose disruption leads to strongly impaired intramacrophage growth. Collectively, these observations support the view that complex lipids are potent immuno-modulators, conditioning the pathophysiology and outcome of Mabs infection. We, thus, foresee Mabs as a new training ground for the discovery of new lipids to decipher the structural variability of the mycobacterial lipid repertoire. This will increase our knowledge regarding how lipids benefit mycobacteria to manipulate the host innate and adaptive responses and contribute to Mabs virulence and the pathophysiology of Mabs infections, which are different from M. tuberculosis infections. SUNLIVE is anticipated to 1) Establish the lipidome of the Mabs with a special emphasis on the structural determination of major cell wall lipids; 2) Describe the role of these complex lipids (particularly GDND, GPL, GPL-like) in physiology and immunomodulation and by addressing their biological functions in macrophages thanks to the generation of lipid mutants and purified lipids coupled to beads; 3) Evaluate the role of these lipids in the pathophysiology of Mabs infection in relevant and complementary animal models (zebrafish and “Kramnick” mice). This 3-year project builds on a large set of data already generated by the four teams and the implementation of an integrated approach employing a broad panel of complementary and cutting-edge techniques to characterize new virulence and physiopathological determinants of one of the most drug-resistant and difficult-to-treat mycobacterial species. From an applied perspective, the results obtained may lead to innovative strategies to prevent the development of the severe clinical forms, often fatal in cystic fibrosis patients, and also new insights into the evolution of environmental mycobacteria towards pathogenicity. We anticipate also that the identification of a typical lipid signature will open the path to innovative diagnostic applications against Mabs infection, fitting with the objectives of Axis 3.6 “Immunology, Infectiology and Inflammation”.