Dynamin-related Irgm proteins modulate LPS-induced caspase-4 activation and septic shock

Abstract

ABSTRACT

Inflammation associated with gram-negative bacterial infections is often instigated by the bacterial cell wall component lipopolysaccharide (LPS). LPS-induced inflammation and resulting life-threatening sepsis are mediated by the two distinct LPS receptors TLR4 and caspase-4. Whereas the regulation of TLR4 activation by extracellular and phago-endosomal LPS has been studied in great detail, auxiliary host factors that specifically modulate recognition of cytosolic LPS by caspase-4 are largely unknown. This study identifies dynamin-related membrane remodeling proteins belonging to the family of Immunity related GTPases M clade (IRGM) as negative regulators of caspase-4 activation in macrophages. Phagocytes lacking expression of mouse isoform Irgm2 aberrantly activate caspase-4-dependent inflammatory responses when exposed to extracellular LPS, bacterial outer membrane vesicles or gram-negative bacteria. Consequently, Irgm2-deficient mice display increased susceptibility to caspase-4-mediated septic shock in vivo. This Irgm2 phenotype is partly reversed by the simultaneous genetic deletion of the two additional Irgm paralogs Irgm1 and Irgm3, indicating that dysregulated Irgm isoform expression disrupts intracellular LPS processing pathways that limit LPS availability for caspase-4 activation.

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Published Version (Please cite this version)

10.1101/2020.03.18.997460

Publication Info

Finethy, Ryan, Jacob Dockterman, Miriam Kutsch, Nichole Orench-Rivera, Graham Wallace, Anthony Piro, Sarah Luoma, Arun Haldar, et al. (2020). Dynamin-related Irgm proteins modulate LPS-induced caspase-4 activation and septic shock. 10.1101/2020.03.18.997460 Retrieved from https://hdl.handle.net/10161/26422.

This is constructed from limited available data and may be imprecise. To cite this article, please review & use the official citation provided by the journal.

Scholars@Duke

Kuehn

Margarethe Joanna Kuehn

Associate Professor of Biochemistry

Enterotoxigenic E. coli (ETEC) causes traveler's diarrhea and infant mortality in underdeveloped countries, and Pseudomonas aeruginosa is an opportunistic pathogen for immunocompromised patients. Like all gram negative bacteria studied to date, ETEC and P. aeruginosa produce small outer membrane vesicles that can serve as delivery "bombs" to host tissues. Vesicles contain a subset of outer membrane and soluble periplasmic proteins and lipids. In tissues and sera of infected hosts, vesicles have been observed to bud from the pathogen and come in close contact with epithelial cells. Despite their association with disease, the ability of pathogenic bacteria to distribute an arsenal of virulence factors to the host cells via vesicles remains relatively unexplored.

In our lab, we focus on the genetic, biochemical and functional features of bacterial vesicle production. Using a genetic screen, we have identified genes essential in the vesiculation process, we have identified specific proteins that are enriched in vesicles, and we have identified critical molecules that govern the internalization of vesicles into host cells. Using biochemical analysis of purified vesicles from cell-free culture supernatants, we have found that heat-labile enterotoxin, an important virulence factor of ETEC, is exported from the cells bound to the external surface of vesicles. Presented in this context, it is able to mediate the entry of the entire ETEC vesicle into human colorectal tissue culture cells. We have also discovered that the ability of vesicles to bind to specific cell types depends on their strain of origin: for example, P. aeruginosa vesicles produced by a strain that was cultured from the lungs of a patient with Cystic Fibrosis adhered better to lung than to gut epithelial cells, whereas a strain that was isolated from sera showed no such preference for lung cells. The vesicles stimulate epithelial cells and macrophages to elicit a cytokine response that is distinct from that of LPS (a major component of the vesicles) alone.

These studies will provide new insights into the membrane dynamics of gram-negative bacteria and consequently aid in the identification of new therapeutic targets for important human pathogens.

Taylor

Gregory Alan Taylor

Professor in Medicine

My lab uses mouse genetic modeling and molecular and cellular techniques to study basic biochemical pathways of relevance to aging biology.

I. Aging is often accompanied by increases in inflammation. A major interest of the lab is how perturbations in the regulation of autophagy and mitochondrial dynamics in cells are linked to inflammation. One project in the lab focuses on a family of interferon-gamma and LPS regulated proteins, the Immunity Related GTPases (IRGs). The lab has shown that mice and cells lacking one of these proteins, Irgm1, have excessive inflammatory responses that are accompanied by decreases in autophagy and mitophagy, and altered cellular metabolism. IRG genes in human (IRGM) have been linked to several inflammatory diseases including Crohn’s disease and sepsis. Current work in the lab focuses on their role in those diseases using bacterial and relevant mouse models.

II. Altered expression of the cytokine Transforming Growth Factor beta (TGF-b) has been linked with a number of aging processes, including stem cell and neural function. TGF-b is consequently a therapeutic target for a number of age-related diseases. The lab is studying a novel regulator of TGF-b expression called P311, which drives TGF-b translation. Mice have been created that lack P311 and are being used to address the role of P311 in a number of physiological processes.

Coers

Jorn Coers

Associate Professor in Molecular Genetics and Microbiology

Bacterial infections remain one of the leading causes of morbidity and mortality worldwide. The Coers lab seeks to understand fundamental aspects of the innate immune response to bacterial pathogens as well as the corresponding immune evasion strategies evolved by human pathogens undermining immunity in order to establish infections. Defining innate immunity and microbial counter-immunity pathways on a molecular level will provide roadmaps for the rational design of novel antimicrobial therapies and improved vaccine strategies against pathogens such as the enteric pathogen Shigella or the sexually transmitted pathogen Chlamydia.

In addition to making major inroads in the fields of innate immunity, inflammation and bacterial pathogenesis, our second, but equally important goal, is to train the next generation of scientists in an environment that prioritizes excellence, research integrity, teamwork and inclusiveness. We strive to create an environment of mutual respect, openness, collegiality, integrity and, last but not least, fun, which promotes and awards curiosity and fosters collaborations. We strongly believe that diversity promotes excellence.


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