Lysosome repositioning as an autophagy escape mechanism by Mycobacterium tuberuculosis Beijing strain
Autophagy is a conserved lysosomal-dependent cellular degradation process shown to play a key role in immune defense against Mycobacterium tuberculosis inside host macrophages. Induction of autophagy enhances mycobacterial phagosome acquisition of lysosomal hydrolases, resulting in the destruction of intracellular M. tuberculosis reference strain H37Rv and strains belonging to the East African Indian genotype. However, our previous study showed that strains belonging to the hypervirulent M. tuberculosis Beijing genotype have a special ability to resist autophagic killing but the mechanism involved remains unclear. In this study, we carried out whole transcriptome analyses of host macrophages infected with the autophagy resistant Beijing strain compared to that of H37Rv. Our results identified several genes that are differentially regulated in the Beijing strain-infected host cells including those function in the lysosome positioning pathway. Host macrophages depleted of Kxd1 and Pleckhm2, two proteins in this pathway, can now enhance the lysosomal hydrolase acquisition into the Beijing phagosomes and restrict the bacterial survival upon autophagy induction. High-content image analysis showed an increase in lysosome numbers at the cell periphery in host cells infected with the autophagy resistant Beijing strain in a Pleckhm2-dependent manner. Taken together, these data indicated that the M. tuberculosis Beijing strain escapes autophagic elimination by upregulating the lysosome positioning pathway resulting in an increase in lysosome relocation toward the cell periphery and therefore sparing the mycobacteria from autophagic restriction. Our work thus identified new strategy employed by M. tuberculosis to evade autophagy which may provide potential new targets for drug discovery against tuberculosis Overall design: Raw264.7 macrophages were uninfected or infected with either the autophagy-sensitive reference strain H37Rv or autophagy-resistant Beijing strain for 2 hr. Cells were then uninduced or induced to undergo autophagy by stravation for 2 hr. Total RNAs were then collected and subjected to RNA-Seq analyses.