Mycobacterium tuberculosis infection suppresses the expression of host genes involved in lysosomal targeting in the macrophage

Mycobacterial modulation of phagosome maturation in infected cells is a widely studied area in host-pathogen interactions, yet there is still no definitive understanding of all the mechanisms involved. Infection with M. tuberculosis (M.tb) is well known for a resultant modulation of gene expression of the host cell. This study identified and investigated three macrophage genes suppressed during M.tb infection, involved in lysosomal trafficking pathways: RILP, OSBPL1a and RIN2, with the hypothesis that M.tb infection actively suppresses the expression in order to disrupt phagolysosome fusion resulting in pathogen survival. Two approaches were taken, the first, co-localisation studies using constructed cell lines over-expressing RILP, OSBPL1a and RIN2. The second approach was to analyse host cell gene expression in response to M.tb mutants known to be trafficked to the lysosome. Fluorescence microscopy co-location studies in RIN2 over-expressing transfected macrophage cell lines exhibited differential trafficking of M.tb. Gene expression of M.tb in response to RILP, RIN2 and OSBPL1a over-expression revealed changes to notable genes associated with exposure to the phagosomal environment. Finally, macrophage infections with M.tb mutants known to be trafficked to the lysosome, revealed that a moaC1 mutant was unable to suppress the expression of RILP and OSBPL1a, indicating an active role in M.tb survival by blocking phago-lysosomal maturation. The intention of this study was to gain a better understanding of the mechanisms by which M.tb evades lysosomal destruction to aid in devising potential new host-directed and pathogen-directed strategies for treatment and prevention of the disease, tuberculosis.