HYDROLYSIS OR CYCLIZATION OF ATP: REGULATING CHOLESTEROL UTILIZATION IN MYCOBACTERIUM TUBERCULOSIS
Tuberculosis remains a major cause of human morbidity and mortality, and is caused by infection with the bacterium Mycobacterium tuberculosis. For thousands of years, M. tuberculosis has adapted virulence strategies that allow it to survive in humans, its sole natural host. After transmission by aerosol infection, M. tuberculosis provokes a complex series of interactions with the host immune system, allowing the bacterium to establish a persistent niche inside immune cells located within granuloma lesions at infection sites. The bacterium routinely survives for months or years within an individual host, eventually provoking pathology that leads to transmission and compromises lung function. The worldwide burden of M. tuberculosis infection is enormous, despite the existence of antibiotic regimens to treat this disease. Current antibiotic regimens for eliminating drug-sensitive M. tuberculosis are hampered by their length, and regimens for drug-resistant M. tuberculosis are relatively ineffective and riddled with side effects. One approach to develop improved antibiotic targets is to better understand the metabolic pathways that support M. tuberculosis survival and persistence during chronic infection and in the face of antibiotic pressures. Over the last decade, lipid utilization has been identified as a central pathway that contributes to M. tuberculosis survival and persistence under these conditions. However, mechanisms that can be leveraged to generate chemical inhibitors of lipid utilization in M. tuberculosis are poorly understood, and there are no antibiotics of this class represented yet in a clinical setting. Here we have explored two mechanisms through which ATP lies at the center of lipid utilization in M. tuberculosis. We demonstrate the necessity of ATP hydrolysis to drive fatty acid and cholesterol import into M. tuberculosis, and identify differences in regulation of these two transport pathways. Examining promising chemical inhibitors of M. tuberculosis growth that were previously identified by a novel high-throughput screening technique, we characterize new compounds that inhibit cholesterol utilization in M. tuberculosis by upregulating the cyclization of ATP to form cyclic-AMP (cAMP). These represent a significant advance because the compounds show promising safety and pharmacokinetic profiles, and are the first M. tuberculosis-directed cholesterol utilization inhibitors suitable for testing in animal models. These compounds represent an unusual mechanism of action for an antimicrobial, in which activating excessive synthesis of a second-messenger disrupts pathogen fitness during infection. The compounds also initiated our efforts to characterize the unexpected link between cAMP signaling and cholesterol utilization in M. tuberculosis, in which the function of cAMP signaling in pathogenesis is generally not well characterized. Lastly, we have begun to examine whether these compounds have secondary effects on the host cell immune response, as cAMP is well-known for modulating immune cell phenotypes and Mtb is poised to secrete excess cAMP into the host cell when this pathway is chemically activated.
adenylyl cyclase; cholesterol; cyclic AMP; Mycobacterium tuberculosis
VanderVen, Brian C.
Hollopeter, Gunther; Leifer, Cynthia Anne; Song, Jeongmin
Biomedical and Biological Sciences
Ph. D., Biomedical and Biological Sciences
Doctor of Philosophy
Attribution 4.0 International
dissertation or thesis
Except where otherwise noted, this item's license is described as Attribution 4.0 International