TB Cell Wall Lipids
Mtb is a rod shaped bacterium with a thick cell wall that contains a large number of complex lipids. The cell wall provides shape to the bacterium and confers resistance to environmental stresses. In addition, the complex lipids found in the outer cell wall are key mediators of the host-pathogen interaction. Mtb devotes an unusually large portion of its genome to fatty acid metabolism, and contains representatives of virtually every known lipid biosynthetic system. The majority of these genes, however, are uncharacterized in Mtb. As the majority of drugs that are effective against Mtb target a few proteins involved in fatty acid/cell wall biosynthesis, we expect that lipid biosynthesis is a potentially fruitful, but largely untapped area for drug development. We use a combination of small molecule inhibitors and bacterial genetics to elucidate pathways for lipid biosynthesis and to attempt to elucidate the function of complex lipids in Mtb.
During infection Mtb is thought to exist along a spectrum of metabolic states, from active replication through a dormant non-replicating state. Mtb metabolism has a significant impact on the efficacy of antibiotics, as slowly replicating or dormant bacteria are very difficult to kill with conventional antibiotics. Macrophage metabolism is also important for the outcome of infection, as shifts in macrophage metabolism affect not only microbicidal mechanisms such as autophagy, but also affect the spectrum of nutrients available to the bacterium. In vivo, Mtb is thought to rely on host lipids and cholesterol as primary carbon sources during infection. We are interested in understanding the intersection between macrophage metabolism and bacterial metabolism, and use a variety of techniques ranging from bacterial and host genetics through metabolomics and proteomics to address these questions.
Mammalian tyrosine and serine/threonine kinases are fundamental regulators of cellular function. We have identified a number of macrophage kinases that support Mtb intracellular replication, either by suppressing macrophage bactericidal responses or by helping promote an environment that is conducive to Mtb growth and persistence. We are interested in understanding the specific role of these kinases during Mtb infection of macrophages, and during in vivo infection using the mouse model of tuberculosis. The fact that many inhibitors of mammalian kinases have been developed for other therapeutic applications facilitates the identification of small molecule inhibitors that can be tested for in vivo efficacy in order to generate candidates for host-targeted therapeutics. In addition, we are using proteomics and phospho-proteomics to elucidate the kinase signaling network that is activated by infection with Mtb, and to identify downstream targets of specific key kinase regulators.