Inflammasomes alert the mammalian immune system to the presence of infection and tissue damage. These cytosolic protein complexes detect danger signals or microbial products released by a wide variety of intracellular pathogens. In the case of bacterial pathogens, a number of prokaryotic signatures are recognized including the major cell-wall constituent of most Gram-negative species, lipopolysaccharide (LPS). Detection of LPS inside host cells activates a ?non-canonical? inflammasome pathway where caspase-11 (Caspases 4 and 5 in humans) act as upstream sensors to stimulate inflammasome complex assembly and processing of the pore-forming protein, Gasdermin D (Gsdmd), further downstream. Gsdmd pores release protective cytokines and contribute to a lytic form of cell death termed pyroptosis that may help eliminated infected host cells. How these sequential events are co-ordinated and the host factors involved remains a major question in the field of innate immunity and host defense. Here, we focus on members of a new 65-73kDa immune GTPase family termed Guanylate- Binding Proteins (GBPs) that control distinct steps in the non-canonical pathway. Preliminary results suggest Gbp2 may target cytosolic bacteria to help liberate LPS for caspase-11 detection whereas Gbp3 acts further downstream to regulate Gsdmd trafficking to the plasma membrane. GBPs thus offer a unique opportunity to understand how this sequential hierarchy unfolds.
In Aim 1, we will test the respective contributions of Gbp2 and Gbp3 to immunity against Gram-negative Salmonella typhimurium (Stm) infection via the non-canonical inflammasome in vitro and in vivo. CRISPR-Cas9 deleted human and mouse cells as well as newly-created Gbp2-/-, Gbp3-/- and GbpDchr.3H1 mice will be infected with Stm variants designed to interfere with GBP recruitment or responsiveness to LPS. Thereafter, we will dissect the molecular mechanisms enlisted by these GBPs to confer their intracellular functions as part of Aim 2. Here gene-deficient macrophages complemented with GBP mutants with distinct biochemical lesions will reveal how GBPs direct the inflammasome core machinery to LPS- positive bacteria or control downstream events such as Gsdmd trafficking and assembly on the plasma membrane. Cell-free studies will also attempt to reconstitute the GBP ?coatomer? on the bacterial outer membrane that serves as a platform for inflammasome assembly. Collectively, our proposal examines a new set of host factors that act at different stages within the non-canonical signaling cascade as part of a unique functional hierarchy, helping choreograph these events with major implications for the treatment of sepsis and Gram-negative bacterial infections.

Public Health Relevance

. Inflammasomes are protein assemblies inside host cells that detect the presence of microbial pathogens including Gram-negative bacteria to alert the immune response. This proposal focuses on a new group of host immune proteins - the Guanylate Binding Proteins (GBPs) ? that tailor the ?non-canonical? inflammasome response specifically against Gram-negative bacteria such as Salmonella that are a major cause of food-borne gastroenteritis and blood-borne sepsis in U.S. intensive care units. Our efforts will uncover how GBPs control the ?non-canonical? inflammasome that provides a conceptual framework for therapies aimed at treating life- threatening Gram-negative infections and sepsis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI108834-07
Application #
10083168
Study Section
Immunity and Host Defense (IHD)
Program Officer
Liu, Qian
Project Start
2014-09-19
Project End
2024-12-31
Budget Start
2021-01-01
Budget End
2021-12-31
Support Year
7
Fiscal Year
2021
Total Cost
Indirect Cost
Name
Yale University
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
043207562
City
New Haven
State
CT
Country
United States
Zip Code
06520
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Gaudet, Ryan G; Bradfield, Clinton J; MacMicking, John D (2016) Evolution of Cell-Autonomous Effector Mechanisms in Macrophages versus Non-Immune Cells. Microbiol Spectr 4: