Modern Clinical Mycobacterium tuberculosis Strains Leverage Type I IFN Pathway for a Proinflammatory Response in the Host.

Host phagocytes respond to infections by innate defense mechanisms through metabolic shuffling to restrict the invading pathogen. However, this very plasticity of the host provides an ideal platform for pathogen-mediated manipulation. In the human (THP1/THP1 dual/PBMC-derived monocyte-derived macrophages) and mouse (RAW264.7 and C57BL/6 bone marrow-derived) macrophage models of Mycobacterium tuberculosis infection, we have identified an important strategy employed by clinical lineages in regulating the host immune-metabolism axis. We show greater transit via the macrophage phagosomal compartments by Mycobacterium tuberculosis strains of lineage: M. tuberculosis lineage 3 is associated with an ability to elicit a strong and early type I IFN response dependent on DNA (in contrast with the protracted response to lineage: M. tuberculosis lineage 1). This augmented IFN signaling supported a positive regulatory loop for the enhanced expression of IL-6 consequent to an increase in the expression of 25-hydroxycholesterol in macrophages. This amplification of the macrophage innate response-metabolic axis incumbent on a heightened and early type I IFN signaling portrays yet another novel aspect of improved intracellular survival of clinical M. tuberculosis strains.

The MmpS6-MmpL6 Operon Is an Oxidative Stress Response System Providing Selective Advantage to Mycobacterium tuberculosis in Stress.

Background: The stress response adaptability of Mycobacterium tuberculosis (Mtb) is still unresolved. In this study, we ascribe an important function to the MmpS6-MmpL6 (M6) operon in Mtb stress management. Methods: By using a novel promoter probe in a high-throughput unbiased screen, we identified several quinones as potent inducers of the M6 operon in addition to triclosan. Results: Triclosan and plumbagin effectively altered the intracellular redox potential in Mtb suggestive of oxidative stress in bacteria. Presence of the functional M6 operon correlated with an enhanced ability of clinical strains to survive in the presence of triclosan. Conclusions: Similar to the addition of a powerful reactive oxygen species-quenching agent such as N-acetyl cysteine in the medium, introduction of the complete M6 operon was sufficient to increase tolerance of the M6- strains to triclosan and plumbagin by effectively ablating the change in intracellular redox potential of Mtb, signifying the importance of this operon in oxidative stress survival in mycobacteria.

The antidepressant sertraline provides a novel host directed therapy module for augmenting TB therapy.

A prolonged therapy, primarily responsible for development of drug resistance by Mycobacterium tuberculosis (Mtb), obligates any new TB regimen to not only reduce treatment duration but also escape pathogen resistance mechanisms. With the aim of harnessing the host response in providing support to existing regimens, we used sertraline (SRT) to stunt the pro-pathogenic type I IFN response of macrophages to infection. While SRT alone could only arrest bacterial growth, it effectively escalated the bactericidal activities of Isoniazid (H) and Rifampicin (R) in macrophages. This strengthening of antibiotic potencies by SRT was more evident in conditions of ineffective control by these frontline TB drug, against tolerant strains or dormant Mtb. SRT, could significantly combine with standard TB drugs to enhance early pathogen clearance from tissues of mice infected with either drug sensitive/tolerant strains of Mtb. Further, we demonstrate an enhanced protection in acute TB infection of the highly susceptible C3HeB/FeJ mice with the combination therapy signifying the use of SRT as a potent adjunct to standard TB therapeutic regimens against bacterial populations of diverse physiology. This study advocates a novel host directed adjunct therapy regimen for TB with a clinically approved antidepressant to achieve quicker and greater control of infection.

The mitochondrial gene-CMPK2 functions as a rheostat for macrophage homeostasis.

In addition to their role in cellular energy production, mitochondria are increasingly recognized as regulators of the innate immune response of phagocytes. Here, we demonstrate that altering expression levels of the mitochondria-associated enzyme, cytidine monophosphate kinase 2 (CMPK2), disrupts mitochondrial physiology and significantly deregulates the resting immune homeostasis of macrophages. Both CMPK2 silenced and constitutively overexpressing macrophage lines portray mitochondrial stress with marked depolarization of their membrane potential, enhanced reactive oxygen species (ROS), and disturbed architecture culminating in the enhanced expression of the pro-inflammatory genes IL1ß, TNFα, and IL8. Interestingly, the long-term modulation of CMPK2 expression resulted in an increased glycolytic flux of macrophages akin to the altered physiological state of activated M1 macrophages. While infection-induced inflammation for restricting pathogens is regulated, our observation of a total dysregulation of basal inflammation by bidirectional alteration of CMPK2 expression only highlights the critical role of this gene in mitochondria-mediated control of inflammation.

Phospholipid homeostasis, membrane tenacity and survival of Mtb in lipid rich conditions is determined by MmpL11 function.

The mycobacterial cell wall is a chemically complex array of molecular entities that dictate the pathogenesis of Mycobacterium tuberculosis. Biosynthesis and maintenance of this dynamic entity in mycobacterial physiology is still poorly understood. Here we demonstrate a requirement for M. tuberculosis MmpL11 in the maintenance of the cell wall architecture and stability in response to surface stress. In the presence of a detergent like Tyloxapol, a mmpL11 deletion mutant suffered from a severe growth attenuation as a result of altered membrane polarity, permeability and severe architectural damages. This mutant failed to tolerate permissible concentrations of cis-fatty acids suggesting its increased sensitivity to surface stress, evident as smaller colonies of the mutant outgrown from lipid rich macrophage cultures. Additionally, loss of MmpL11 led to an altered cellular fatty acid flux in the mutant: reduced incorporation into membrane cardiolipin was associated with an increased flux into the cellular triglyceride pool. This increase in storage lipids like triacyl glycerol (TAG) was associated with the altered metabolic state of higher dormancy-associated gene expression and decreased sensitivity to frontline TB drugs. This study provides a detailed mechanistic insight into the function of mmpL11 in stress adaptation of mycobacteria.