The work proposed here seeks to investigate the mechanism by which mammalian macrophages suppress the metabolic checkpoint kinase Mechanistic target of rapamycin (MTOR) to promote immune defenses and counteract anabolic reprogramming by the vacuolar pathogen Legionella pneumophila. MTOR is a universally conserved master switch regulating catabolism to anabolism transition in eukaryotic cells. Vacuolar pathogens rely on host metabolites not only for bacterial replication but also for maintenance of their intracellular niches. The human respiratory pathogen Legionella pneumophila is a prototypical vacuolar pathogen that infects and replicates within mammalian macrophages. We uncovered that Legionella stimulates host membrane biosynthesis to expand its niche by subverting MTOR. However, a host suppression pathway counteracts L. pneumophila-induced MTOR activation by targeting MTOR for ubiquitin-dependent proteolysis. In macrophages, MTOR suppression promotes cell intrinsic (autophagy) and cell extrinsic (inflammation) host defenses. Specifically, pathogenic L. pneumophila expressing the type IVb secretion system (T4bSS) but not the avirulent mutants lacking a functional T4bSS elicited the host MTOR suppression response. Thus, we hypothesize that in mammalian macrophages MTOR functions downstream of homeostatic mechanisms that sense the pathogenic potential of invading microbes to potentiate host defenses. Such mechanisms operate by detecting virulence adaptations encoded by bacterial pathogens (such as specialized secretion systems and secreted toxins), which frequently produce pathogen-specific signatures. In the first aim we will determine the mechanism by which Legionella subverts MTOR function, when the host suppression pathway is inactivated. In the second aim we are going to use biochemical and genetic approaches to determine how the Legionella intracellular niche is controlled by host metabolic regulators.
Our third aim i s to elucidate how the pathogen signature that elicits MTOR suppression is generated. To this end, we will perform a systematic analysis of the Legionella intracellular niche using a variety of imaging approaches to define the early events that trigger MTOR suppression.

Public Health Relevance

Deciphering the molecular interactions between the respiratory bacterial pathogen Legionella pneumophila and cells of the innate immune system will uncover how the host distinguishes virulent from avirulent microbes to initiate appropriate antimicrobial responses. This knowledge provides important insight into how our immune system functions and will ultimately aid in the design of more effective antimicrobial therapies.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI143839-03
Application #
10092094
Study Section
Host Interactions with Bacterial Pathogens Study Section (HIBP)
Program Officer
Pesce, John T
Project Start
2019-02-11
Project End
2024-01-31
Budget Start
2021-02-01
Budget End
2022-01-31
Support Year
3
Fiscal Year
2021
Total Cost
Indirect Cost
Name
Louisiana State University Hsc Shreveport
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
095439774
City
Shreveport
State
LA
Country
United States
Zip Code
71103