bioRxiv2021
Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis (TB) and is a major cause of human morbidity and mortality. Crucially, Mtb can persist and replicate within host macrophages (M[FE]) and subvert multiple antimicrobial defense mechanisms. How this is achieved is incompletely understood. Previously, we reported that lipids shed by persistent mycobacteria inhibit NPC1, the lysosomal protein deficient in most cases of the rare, inherited lysosomal storage disorder Niemann-Pick disease type C (NPC). Inhibition of NPC1 leads to a drop in lysosomal calcium levels blocking phagosome-lysosome fusion and thereby leads to mycobacterial persistence. Studies of mycobacterial lineages have identified events during mycobacterial evolution that result in the acquisition of persistence. We speculated that the production of specific cell wall lipid(s) capable of inhibiting NPC1 activities could have been a critical step in the evolution of pathogenicity. In this study, we have therefore investigated whether lipid extracts from clinical Mtb strains representative of multiple Mtb lineages, members of the Mtb complex (MTBC) and selected non-tubercular mycobacteria (NTM) inhibit the NPC pathway. We have found that the ability to inhibit the NPC pathway was present in all clinical isolates studied from Mtb lineages 1, 2 and 4. We also found that lipids from MTBC member, Mycobacterium bovis and the NTM, Mycobacterium abscessus and Mycobacterium avium also inhibited the NPC pathway. However, when lipids were assayed from Mycobacterium canettii (M. canettii), a smooth tubercle mycobacterium, which is considered to resemble the common ancestor of the MTBC no inhibition of the NPC1 pathway was detected. We therefore conclude that the evolution of mycobacterial cell wall lipids that inhibit the NPC pathway evolved early and post divergence from M. canettii related mycobacteria and NPC1 inhibition significantly contributes to the ability of these pathogens to persist and cause disease. Authors summaryMycobacterium tuberculosis (Mtb) actively modifies the hostile intracellular environment of host cells to create a niche in which it can persist and replicate. How this is accomplished is incompletely understood. We previously reported an unexpected phenotypic similarity between cells infected with pathogenic mycobacteria and those of the rare, neurodegenerative lysosomal storage disorder, Niemann-Pick disease type C (NPC). Mechanistically, we showed that pathogenic mycobacteria shed lipids that inhibit NCP1, the lysosomal membrane protein that is dysfunctional in NPC and thereby establish conditions that favour their survival. In this study, we have investigated the phylogenetic distribution of lipids that inhibit NPC1. We have screened lipid extracts from multiple clinical mycobacterial isolates representing different Mtb lineages, other members of the Mtb complex and non-tuberculous mycobacteria for their ability to induce NPC phenotypes. We detected activity in all of the groups tested, but not from Mycobacterium canettii, which is believed to resemble the ancestral species. These data indicate that targeting of NPC1 to achieve intracellular persistence evolved early in the evolution of the Mtb complex, but after divergence from the presumed ancestral species.