TB Research RAHC-Edinburg

Tuberculosis (TB) is one of the leading causes of death all over the world.  My laboratory, located at the UTHSCSA-Regional Academic Health Center in Edinburg, TX, is conducting research to better understand the pathogenic mechanisms of the pathogen, Mycobacterium tuberculosis (Mtb), which causes TB in humans. Additionally, development of genetically engineered vaccines using molecular approaches is also in progress. Following are the research projects that are currently underway in my lab.

1. Role of Msr in the intracellular survival of Mtb. Pathogenic mycobacteria like M. tuberculosis and M. leprae have the ability to survive and replicate within mononuclear phagocytes including macrophages. The intracellular environment is very hostile since macrophages have an impressive battery of antimicrobial responses such as hydrolases, bacterial peptides, and toxic reactive oxygen and nitrogen intermediates (ROI). Elucidation of the mechanism by which intracellular mycobacteria evade macrophage responses, particularly the bacterial factors associated with evasion, is central to the identification of novel vaccine and therapeutic targets. We investigate the role of methionine sulfoxide reductases (Msr) in the pathogenesis of Mtb. Msr are antioxidant repair enzymes which reduce oxidized methionine (Met-O) in proteins to methionine (Met). Since oxidation of methionine in proteins impairs the function of proteins, absence of Msr, particularly MsrA, leads to functional abnormalities in different organisms. We are investigating how absence of Msr affects the intracellular survival of MTB. To address this issue, we have constructed msrA and msrB mutant strains of Mtb and are in the process of studying their survival in macrophages and mice. Our previous study with M. smegmatis revealed that msrA affects the trafficking of ROS generating enzymes like p67phox (component of NADPH oxidase) and iNOS (inducible nitric oxidase synthase) in the phagosomes of infected macrophages. We will use the mutant msr Mtb strains to investigate whether similar phenomenon occurs with this pathogen also.

2. Stress signaling in M. tuberculosis. During the infectious process, Mtb undergoes stress due to variety of stress conditions. Of particular interest is the dormancy stress which results due to deprivation of oxygen and nutrients in the tubercle granulomas. A sigma factor SigF and a two-component system DevS-DevR have been implicated in the dormancy of M. tuberculosis. However, how these regulators receive stress signals remain obscure. We are investigating how SigF receives stress signals. Using protein database searches and protein-protein interaction studies (yeast two-hybrid system), we have identified six new molecules that have putative functions in stress signaling. Further characterization of these molecules in the activation of SigF is underway to better understand the mechanism stress related dormancy in M. tuberculosis.

3. Susceptibility of diabetes patients to TB. Diabetes is a debilitating disease which affects several million people throughout the world. Hispanic and African-American populations are severe targets for the disease and it appears that there is a link between obesity and diabetes. Diabetes patients face several risks and complications and one of the most common risks is infection with Mtb, the causative agent of tuberculosis. As compared to healthy people, diabetic patients face 2-5 times more risk of developing TB. We hypothesize that immune dysfunction in diabetic patients is the reason for this increased risk. Therefore, we are studying the difference in immune responses between the diabetes and healthy subjects to TB antigens for determining what kind of immune dysfunction is making diabetes patients more susceptible to TB.  

4. Development of recombinant vaccines to TB. Attenuated Mycobacterium bovis BCG has long been used as a vaccine against TB, but the use of this vaccine is almost abandoned due to its variable and limited efficacy in different populations. Recent reports indicate that a live Mtb vaccine that has a deletion for the gene coding for fibronectin binding protein A (fpbA), and a subunit vaccine based on the secreted antigenic proteins Ag85B and ESAT-6 of Mtb are very promising against TB. However, they do have some problems. The ∆fbpA live Mtb vaccine has the ability to become virulent after administration, because the genes encoding virulence factors are intact in this strain. This restricts the use of this vaccine in humans. The Ag85B and ESAT-6 based subunit vaccine has problems such as overexpression and purification of these molecules in large quantities, storage in freezers to preserve their antigenicity and injection of the antigens into human beings to produce the desired effects. Therefore, we are conducting research to improve these vaccines using genetic engineering techniques. In order to make the live ∆fbpA Mtb live vaccine into a nonvirulent one, we are in the process of constructing additional gene deletion in ∆fbpA Mtb live vaccine to reduce its virulence. In order to circumvent the problems with Ag85B and ESAT-6 sub unit vaccine, we are genetically engineering recombinant Bacillus subtilis spores to deliver Ag85B and ESAT-6 Mtb antigens.