The role of host-derived lipids in Mycobacterium tuberculosis infection

The bacteria Mycobacterium tuberculosis is a global killer causing over a million deaths from tuberculosis (TB) every year. It is therefore a major burden to human health. To reduce the deadly impact of TB, we need a better understanding of the strategies used by M. tuberculosis to adapt its metabolism in order to survive in the variable environments encountered in the human host; this will help us design better ways to treat and control TB.

All cells need to respond to environmental changes such as acidic pH, a condition encountered within the stomach as well as the macrophages that engulf mycobacteria. Responses to acid have been studied extensively in bacteria such as Escherichia coli, Vibrio cholerae, and Helicobacter pylori, that all encounter the extremely acidic pH (pH 2-3) of the stomach.

In contrast, there is little information on how bacterial pathogens that can live inside human cells, like M. tuberculosis, survive and replicate within acid vacuoles inside cells like macrophages. The pH of the macrophage compartment in which M. tuberculosis resides ranges from pH 6.2 to 4.5, depending on the activation state of the macrophage. We can study how bacteria respond to and survive changes in pH in culture flasks in the laboratory, as well as in cultured macrophages to identify bacterial factors that help them survive.

Changing M. tuberculosis metabolism is one way to survive changes in the environment and interfering with these processes presents an attractive method for treating TB. We have identified an enzyme cAMP-dependant-lysine acetyl transferase (Rv0998, KATmt) involved in acid survival, and based on our preliminary data we hypothesize that KATmt plays a key role in the metabolic adaptation of M. tuberculosis to intracellular life a key part of M. tuberculosis pathogenesis.

To address this hypothesis, we propose to study the role of KATmt in rewiring the metabolism of M. tuberculosis at a whole cell level. To achieve this goal our objectives are to:

1. Use genetic mutants of M. tuberculosis KATmt to identify the metabolic pathways KATmt and how this is regulated. Identify substrates for KATmt activity, which may represent new and attractive drug targets.

2. Use bioenergetics and metabolomics to determine the role KATmt plays in host macrophage metabolome remodelling. M. tuberculosis manipulates its host cell to generate a more favourable environment for its survival and replication, and understanding how it does this is key to finding new interventions.

3. We will compare how the KATmt mutant behave in the mouse model of TB, compared to the parental and complemented strains, looking for changes in bacterial survival and changes in host lipids associated with infection.

In this way, we will elucidate the mechanisms by which KATmt mediates the resistance of M. tuberculosis to the acidic stress encountered during infection not only by altering its own metabolism, but also by manipulating host macrophage lipid metabolism Overall, this will identify and validate key pathways in M. tuberculosis pathogenesis, opening up new avenues for small molecule interventions.