Ehrt Lab Research

We are interested in the pathogenesis of tuberculosis and investigate the interactions of Mycobacterium tuberculosis (Mtb) with its host in multiple areas:

Intracellular survival strategies

To better understand the molecular basis for the ability of Mtb to survive within macrophages and resist host defense mechanisms we identify and characterize mutants that are susceptible to stresses encountered by the pathogen during persistence within its host (1–4). The analysis of the molecular mechanisms underlying the loss of stress resistance and loss of virulence of these mutants can help better understand the intracellular environment encountered by Mtb and reveal how the pathogen resists host defense mechanisms.

Latent Mtb infection

Tuberculosis (TB) chemotherapy often fails to sterilize Mtb, resulting in individuals at risk of relapse TB. Taking advantage of conditional gene expression systems (5–7), we have, together with Dirk’s group, developed models of latent infection in mice (8). Investigating the mechanisms required by Mtb to persist during chronic (3, 9, 10) and latent TB in mice can identify points of vulnerability, which could be targeted to kill populations that escape current chemotherapy in people with latent Mtb infection. These models are also being used to investigate the host immune components that control dormant Mtb and uncover mechanisms of control or disease progression in TB.

Metabolic adaptation and nutrient acquisition in vivo

Metabolic adaptations to the nutritional environments encountered within the host have been a major focus of the analysis of Mtb-host interactions and are relevant to the identification and evaluation of new TB drug targets. We apply genetic, biochemical and - in close collaboration with Kyu Rhee - metabolomic approaches to investigate the metabolic pathways that Mtb requires to establish and maintain chronic infections (11–15). During infection, the host suppresses mycobacterial replication and dissemination by enclosing bacteria within phagosomes, thereby reducing access to nutrients. We are implementing genetic strategies to identify nutrient acquisition pathways in Mtb during infection.

TB vaccines

Vaccination with Mycobacterium bovis BCG can induce protection against the worst forms of TB in children but fails to prevent pulmonary TB in adolescents and adults. In collaboration with Dirk, Eric Rubin and Sarah Fortune at Harvard Medical School, Joanne Flynn at the University of Pittsburgh and Bob Seder at the NIH, we use genetic strategies to generate improved TB vaccines. We pursue different strategies building on BCG and we are testing if virulent Mtb could be converted into a safe and protective vaccine strain.

References

1. O. H. Vandal, L. M. Pierini, D. Schnappinger, C. F. Nathan, S. Ehrt, A membrane protein preserves intrabacterial pH in intraphagosomal Mycobacterium tuberculosis. Nat Med. 14, 849–854 (2008).

2. H. Botella, J. Vaubourgeix, M. H. Lee, N. Song, W. Xu, H. Makinoshima, M. S. Glickman, S. Ehrt, Mycobacterium tuberculosis protease MarP activates a peptidoglycan hydrolase during acid stress. Embo J. 36, 536–548 (2017).

3. R. Wang, K. Kreutzfeldt, H. Botella, J. Vaubourgeix, D. Schnappinger, S. Ehrt, Persistent Mycobacterium tuberculosis infection in mice requires PerM for successful cell division. Elife. 8, e49570 (2019).

4. A. Gouzy, C. Healy, K. A. Black, K. Y. Rhee, S. Ehrt, Growth of Mycobacterium tuberculosis at acidic pH depends on lipid assimilation and is accompanied by reduced GAPDH activity. Proc National Acad Sci. 118, e2024571118 (2021).

5. S. Ehrt, X. V. Guo, C. M. Hickey, M. Ryou, M. Monteleone, L. W. Riley, D. Schnappinger, Controlling gene expression in mycobacteria with anhydrotetracycline and Tet repressor. Nucleic Acids Res. 33, e21–e21 (2005).

6. J.-H. Kim, K. M. O’Brien, R. Sharma, H. I. M. Boshoff, G. Rehren, S. Chakraborty, J. B. Wallach, M. Monteleone, D. J. Wilson, C. C. Aldrich, C. E. Barry, K. Y. Rhee, S. Ehrt, D. Schnappinger, A genetic strategy to identify targets for the development of drugs that prevent bacterial persistence. Proc National Acad Sci. 110, 19095–19100 (2013).

7. K. Lin, K. M. O’Brien, C. Trujillo, R. Wang, J. B. Wallach, D. Schnappinger, S. Ehrt, Mycobacterium tuberculosis Thioredoxin Reductase Is Essential for Thiol Redox Homeostasis but Plays a Minor Role in Antioxidant Defense. Plos Pathog. 12, e1005675 (2016).

8. H. Su, K. Lin, D. Tiwari, C. Healy, C. Trujillo, Y. Liu, T. R. Ioerger, D. Schnappinger, S. Ehrt, Genetic models of latent tuberculosis in mice reveal differential influence of adaptive immunity. J Exp Med. 218, e20210332 (2021).

9. N. Goodsmith, X. V. Guo, O. H. Vandal, J. Vaubourgeix, R. Wang, H. Botella, S. Song, K. Bhatt, A. Liba, P. Salgame, D. Schnappinger, S. Ehrt, Disruption of an M. tuberculosis Membrane Protein Causes a Magnesium-dependent Cell Division Defect and Failure to Persist in Mice. Plos Pathog. 11, e1004645 (2015).

10. C. Healy, A. Gouzy, S. Ehrt, Peptidoglycan Hydrolases RipA and Ami1 Are Critical for Replication and Persistence of Mycobacterium tuberculosis in the Host. Mbio. 11, e03315-19 (2020).

11. J. Marrero, K. Y. Rhee, D. Schnappinger, K. Pethe, S. Ehrt, Gluconeogenic carbon flow of tricarboxylic acid cycle intermediates is critical for Mycobacterium tuberculosis to establish and maintain infection. Proc National Acad Sci. 107, 9819–9824 (2010).

12. U. Ganapathy, J. Marrero, S. Calhoun, H. Eoh, L. P. S. de Carvalho, K. Rhee, S. Ehrt, Two enzymes with redundant fructose bisphosphatase activity sustain gluconeogenesis and virulence in Mycobacterium tuberculosis. Nat Commun. 6, 7912 (2015).

13. S. Puckett, C. Trujillo, Z. Wang, H. Eoh, T. R. Ioerger, I. Krieger, J. Sacchettini, D. Schnappinger, K. Y. Rhee, S. Ehrt, Glyoxylate detoxification is an essential function of malate synthase required for carbon assimilation in Mycobacterium tuberculosis. Proc National Acad Sci. 114, E2225–E2232 (2017).

14. N. Ruecker, R. Jansen, C. Trujillo, S. Puckett, P. Jayachandran, G. G. Piroli, N. Frizzell, H. Molina, K. Y. Rhee, S. Ehrt, Fumarase Deficiency Causes Protein and Metabolite Succination and Intoxicates Mycobacterium tuberculosis. Cell Chem Biol. 24, 306–315 (2017).

15. K. A. Black, L. Duan, L. Mandyoli, B. P. Selbach, W. Xu, S. Ehrt, J. C. Sacchettini, K. Y. Rhee, Metabolic bifunctionality of Rv0812 couples folate and peptidoglycan biosynthesis in Mycobacterium tuberculosis. J Exp Med. 218, e20191957 (2021).