Mycobacterium tuberculosis Exploits Focal Adhesion Kinase to Induce Necrotic Cell Death and Inhibit Reactive Oxygen Species Production

Tuberculosis is a deadly, contagious respiratory disease that is caused by the pathogenic bacterium Mycobacterium tuberculosis (Mtb). Mtb is adept at manipulating and evading host immunity by hijacking alveolar macrophages, the first line of defense against inhaled pathogens, by regulating the mode and timing of host cell death. It is established that Mtb infection actively blocks apoptosis and instead induces necrotic-like modes of cell death to promote disease progression. This survival strategy shields the bacteria from destruction by the immune system and antibiotics while allowing for the spread of bacteria at opportunistic times. As such, it is critical to understand how Mtb interacts with host macrophages to manipulate the mode of cell death. Herein, we demonstrate that Mtb infection triggers a time-dependent reduction in the expression of focal adhesion kinase (FAK) in human macrophages. Using pharmacological perturbations, we show that inhibition of FAK (FAKi) triggers an increase in a necrotic form of cell death during Mtb infection. In contrast, genetic overexpression of FAK (FAK⁺) completely blocked macrophage cell death during Mtb infection. Using specific inhibitors of necrotic cell death, we show that FAK-mediated cell death during Mtb infection occurs in a RIPK1-depedent, and to a lesser extent, RIPK3-MLKL-dependent mechanism. Consistent with these findings, FAKi results in uncontrolled replication of Mtb, whereas FAK⁺ reduces the intracellular survival of Mtb in macrophages. In addition, we demonstrate that enhanced control of intracellular Mtb replication by FAK⁺ macrophages is a result of increased production of antibacterial reactive oxygen species (ROS) as inhibitors of ROS production restored Mtb burden in FAK⁺ macrophages to same levels as in wild-type cells. Collectively, our data establishes FAK as an important host protective response during Mtb infection to block necrotic cell death and induce ROS production, which are required to restrict the survival of Mtb.

[6]-Gingerol exhibits potent anti-mycobacterial and immunomodulatory activity against tuberculosis

The currently available anti-tuberculosis treatment (ATT) comprises exclusively of anti-bacterial drugs, is very lengthy, has adverse side effects on the host and leads to the generation of drug-resistant variants. Therefore, a combination therapy directed against the pathogen and the host is required to counter tuberculosis (TB). Here we demonstrate that [6]-Gingerol, one of the most potent and pharmacologically active ingredients of ginger restricted mycobacterial growth inside the lungs, spleen and liver of mice infected with Mycobacterium tuberculosis (Mtb). The spleen of [6]-Gingerol treated mice displayed increased expression of pro-inflammatory cytokines and enhanced Th1/Th17 responses confirming the immunomodulatory action of [6]-Gingerol. Finally, [6]-Gingerol displayed an excellent potential as an adjunct drug, along with front line anti-TB drug isoniazid. Interestingly, [6]-Gingerol displayed stark anti-tubercular activity against dormant/starved bacilli and drug-resistant variants of Mtb. Taken together, these results indicate strong prospects of [6]-Gingerol as an adjunct anti-mycobacterial and immunomodulatory drug for the treatment of drug-susceptible and drug-resistant strains of TB.