Abstract
Mycobacterium tuberculosis (Mtb) has evolved protective and detoxification mechanisms to maintain cytoplasmic redox balance in response to exogenous oxidative stress encountered inside host phagocytes. In contrast, little is known about the dynamic response of this pathogen to endogenous oxidative stress generated within Mtb. Using a noninvasive and specific biosensor of cytoplasmic redox state of Mtb, we for first time discovered a surprisingly high sensitivity of this pathogen to perturbation in redox homeostasis induced by elevated endogenous reactive oxygen species (ROS). We synthesized a series of hydroquinone-based small molecule ROS generators and found that ATD-3169 permeated mycobacteria to reliably enhance endogenous ROS including superoxide radicals. When Mtb strains including multidrug-resistant (MDR) and extensively drug-resistant (XDR) patient isolates were exposed to this compound, a dose-dependent, long-lasting, and irreversible oxidative shift in intramycobacterial redox potential was detected. Dynamic redox potential measurements revealed that Mtb had diminished capacity to restore cytoplasmic redox balance in comparison with Mycobacterium smegmatis (Msm), a fast growing nonpathogenic mycobacterial species. Accordingly, Mtb strains were extremely susceptible to inhibition by ATD-3169 but not Msm, suggesting a functional linkage between dynamic redox changes and survival. Microarray analysis showed major realignment of pathways involved in redox homeostasis, central metabolism, DNA repair, and cell wall lipid biosynthesis in response to ATD-3169, all consistent with enhanced endogenous ROS contributing to lethality induced by this compound. This work provides empirical evidence that the cytoplasmic redox poise of Mtb is uniquely sensitive to manipulation in steady-state endogenous ROS levels, thus revealing the importance of targeting intramycobacterial redox metabolism for controlling TB infection.
Highlights
Reactive oxygen species (ROS) and reactive nitrogen species (RNS) produced by the host enzymes are critical for controlling Mycobacterium tuberculosis, the causative agent of tuberculosis [1,2,3]
Animal models, and macrophages clearly indicate that exogenous oxidants such as O2À produced by a phagocytic respiratory burst are critical components of host defense against bacterial infection [3,4,5]
While Mycobacterium tuberculosis (Mtb)'s ability to resist host-generated redox stress is widely studied, to the best of our knowledge how mycobacteria respond to a specific increase in endogenous O2À level has not been characterized to date
Summary
Reactive oxygen species (ROS) and reactive nitrogen species (RNS) produced by the host enzymes are critical for controlling Mycobacterium tuberculosis, the causative agent of tuberculosis [1,2,3]. Both clinical observations in patients suffering from chronic granulomatous disease and recent experimental studies in zebra fish indicate a major role of superoxide (O2À). Generated by NOX2 in neutrophil-mediated containment of mycobacterial infection in vivo [4,5] These studies suggest a beneficial role of host-generated ROS and RNS in limiting survival of Mtb during infection.
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