Role of Mycobacterium tuberculosis nucleoside diphosphate kinase in the pathogenesis of tuberculosis

• Main Author: Sun, Jim
• Language: English
• Published: University of British Columbia 2012
• Online Access: http://hdl.handle.net/2429/42000

Mycobacterium tuberculosis (Mtb) evasion of the host immune response leads to its resilient persistence within the macrophage ultimately triggering active tuberculosis, a deadly infectious disease afflicting millions of people globally. To combat this disease, there is an urgent need to reveal the underlying mechanisms of pathogenesis by understanding how mycobacteria interact with the host macrophage. The work of this thesis contributes to this understanding through the identification of Mtb nucleoside diphosphate kinase (Ndk) as a virulence factor that contributes to pathogenesis by interfering with key host small G-proteins essential for proper function of the innate immune response. Combining biochemical interaction assays with GTPase activation assays, this work demonstrated that Mtb Ndk interacts with host Rab5, Rab7, and Rac1 to inactivate their downstream signaling. The consequence of interfering with Rab5 and Rab7 signaling is a dramatic decrease in phagolysosome fusion of mycobacteria phagosomes, while inactivation of Rac1 led to NADPH oxidase assembly defect causing impaired reactive oxygen species production. Additional studies utilizing mycobacteria strains with knocked down Ndk further demonstrated its contribution to virulence. Indeed, strains with knocked down Ndk were substantially more prone to intracellular killing within the macrophage, which correlated with increased levels of phagolysosome fusion, raised levels of macrophage oxidative burst, and an increase in programmed cell death. Consistent with these findings, in vivo virulence of Mtb with knocked down Ndk was reduced significantly compared to wild type Mtb when monitoring mice survival. Altogether, the work of this thesis demonstrated that Mtb Ndk is a bona fide mycobacterial virulence factor that attenuates host innate immunity.