Periodic Reporting for period 3 - ENTRAPMENT (Septins: from bacterial entrapment to cellular immunity)
Berichtszeitraum: 2022-04-01 bis 2023-09-30
What is the problem/issue being addressed?
The intracellular bacterium Shigella flexneri is an exceptional model pathogen to address key issues in biology, including how bacteria can move inside host cells and escape the immune system. The cytoskeleton has recently emerged to occupy a central role in innate immunity by promoting bacterial sensing and executing antibacterial functions. We discovered that host cells employ septins, a poorly understood component of the cytoskeleton, to restrict the actin-based motility of Shigella and target them for destruction by autophagy, an important mechanism of innate immune defence. However, the processes underlying septin cage assembly, and the breadth of roles for septins in bacterial infection control, remain to be established. We developed zebrafish (Danio rerio) infection models to study the cell biology of Shigella infection in vivo, and to discover new roles for septins in host defence against bacterial infection. This approach has enabled a cutting-edge platform for in vivo studies both at the single cell and whole animal level, and provides unprecedented opportunities to follow cytoskeleton dynamics and innate immunity at a resolution that cannot be achieved using any other animal model.
Why is it important for society?
The results generated from this research program will provide fundamental advances in understanding septin biology and cellular immunity. They could also suggest the development of new strategies aimed at combating infectious diseases, and possibly other human diseases in which septins have been implicated (including neoplasia and neurodegenerative conditions).
What are the overall objectives?
As the foundation for this research program our overall objectives are to exploit the novelty of septin biology and its direct link to host defence. Using Shigella we will: (1) Discover new roles for the cytoskeleton in host defence against bacterial infection, and (2) Investigate the role of septin-mediated host defence mechanisms in vivo using zebrafish models of infection.
The intracellular bacterium Shigella flexneri is an exceptional model pathogen to address key issues in biology, including how bacteria can move inside host cells and escape the immune system. The cytoskeleton has recently emerged to occupy a central role in innate immunity by promoting bacterial sensing and executing antibacterial functions. We discovered that host cells employ septins, a poorly understood component of the cytoskeleton, to restrict the actin-based motility of Shigella and target them for destruction by autophagy, an important mechanism of innate immune defence. However, the processes underlying septin cage assembly, and the breadth of roles for septins in bacterial infection control, remain to be established. We developed zebrafish (Danio rerio) infection models to study the cell biology of Shigella infection in vivo, and to discover new roles for septins in host defence against bacterial infection. This approach has enabled a cutting-edge platform for in vivo studies both at the single cell and whole animal level, and provides unprecedented opportunities to follow cytoskeleton dynamics and innate immunity at a resolution that cannot be achieved using any other animal model.
Why is it important for society?
The results generated from this research program will provide fundamental advances in understanding septin biology and cellular immunity. They could also suggest the development of new strategies aimed at combating infectious diseases, and possibly other human diseases in which septins have been implicated (including neoplasia and neurodegenerative conditions).
What are the overall objectives?
As the foundation for this research program our overall objectives are to exploit the novelty of septin biology and its direct link to host defence. Using Shigella we will: (1) Discover new roles for the cytoskeleton in host defence against bacterial infection, and (2) Investigate the role of septin-mediated host defence mechanisms in vivo using zebrafish models of infection.
Cell-autonomous immunity, the ability of a host cell to eliminate an invasive infectious agent, is a first line of host defence against microbial pathogens (Lopez-Jimenez and Mostowy, Nat Commun 2021). Recent studies of host-pathogen interactions have shown that components of the host cell cytoskeleton are important for cell-autonomous immunity, yet the structural processes and proteins involved are only beginning to emerge. We discovered that host cells can prevent the actin-based motility of Shigella (a Gram-negative enteroinvasive bacterial pathogen) by compartmentalizing bacteria targeted to autophagy inside ‘septin cages’, a novel mechanism of host defence that restricts bacterial dissemination (Van Ngo and Mostowy, J Cell Sci 2019; Robertin and Mostowy, Cell Microbiol 2020). We showed that septins, poorly characterized cytoskeleton components are recruited with autophagy proteins to cytosolic bacteria and counteract actin tail formation. A comprehensive understanding of autophagy-cytoskeleton interactions will have important consequences for the understanding of both bacterial pathophysiology and its control, as well as normal cell physiology. We recently pioneered a ‘bottom up’ cellular microbiology approach to study cell-autonomous immunity and discovered a fundamental link between bacterial cell biology and the assembly of septin cages around Shigella (Lobato-Marquez et al, Nat Commun 2021). This has been a transformative approach to studying cell-autonomous immunity and represents a milestone in the development of septin-mediated therapies.
Shigella causes ~160 million illness episodes per year. To explore the innate immune response to Shigella, several infection models have been useful, helping to discover key roles for NOD-like receptors (NLRs), neutrophil extracellular traps (NETs), bacterial autophagy, guanylate binding proteins (GBPs) and inflammasomes in host defence. However, mammalian models remain poorly suited to image the cell biology of Shigella infection in vivo. By contrast, the natural translucency of zebrafish (Danio rerio) larvae enables non-invasive in vivo imaging of individual cells and microbe-leukocyte interactions at high resolution throughout the organism (Gomes and Mostowy, Trends Microbiol 2020). Remarkably, the major pathogenic events that lead to shigellosis in humans (macrophage cell death, invasion and multiplication within epithelial cells, cell-to-cell spread, inflammatory destruction of the host epithelium) are faithfully reproduced in our zebrafish model of Shigella infection. We can exploit these results to examine the biogenesis, architecture, coordination and resolution of the innate immune response to Shigella spatio-temporally in vivo. Significantly, we were first to use zebrafish infection to explore the evolution and pathogenesis of Shigella species in vivo (Torraca et al, PLOS Pathog 2019; Torraca et al, Trends Microbiol 2020). We have also innovated new zebrafish infection models to visualise bacterial cell biology in vivo (Mickiewicz et al, Nat Commun 2019), investigate Toxoplasma – leukocyte interactions in vivo (Yoshida et al, Dis Model Mech 2019; Yakimovich et al, mSphere 2020), study interbacterial competition mediated by the Type 7 Secretion System (T7SS) (Ulhuq et al, PNAS 2020) and interrogate mycobacterial infection in vivo using confocal Raman spectroscopic imaging (Høgset et al, Nat Commun 2020).
Shigella causes ~160 million illness episodes per year. To explore the innate immune response to Shigella, several infection models have been useful, helping to discover key roles for NOD-like receptors (NLRs), neutrophil extracellular traps (NETs), bacterial autophagy, guanylate binding proteins (GBPs) and inflammasomes in host defence. However, mammalian models remain poorly suited to image the cell biology of Shigella infection in vivo. By contrast, the natural translucency of zebrafish (Danio rerio) larvae enables non-invasive in vivo imaging of individual cells and microbe-leukocyte interactions at high resolution throughout the organism (Gomes and Mostowy, Trends Microbiol 2020). Remarkably, the major pathogenic events that lead to shigellosis in humans (macrophage cell death, invasion and multiplication within epithelial cells, cell-to-cell spread, inflammatory destruction of the host epithelium) are faithfully reproduced in our zebrafish model of Shigella infection. We can exploit these results to examine the biogenesis, architecture, coordination and resolution of the innate immune response to Shigella spatio-temporally in vivo. Significantly, we were first to use zebrafish infection to explore the evolution and pathogenesis of Shigella species in vivo (Torraca et al, PLOS Pathog 2019; Torraca et al, Trends Microbiol 2020). We have also innovated new zebrafish infection models to visualise bacterial cell biology in vivo (Mickiewicz et al, Nat Commun 2019), investigate Toxoplasma – leukocyte interactions in vivo (Yoshida et al, Dis Model Mech 2019; Yakimovich et al, mSphere 2020), study interbacterial competition mediated by the Type 7 Secretion System (T7SS) (Ulhuq et al, PNAS 2020) and interrogate mycobacterial infection in vivo using confocal Raman spectroscopic imaging (Høgset et al, Nat Commun 2020).
I discovered that infected host cells can prevent the actin-based motility of Shigella flexneri, a Gram-negative enteroinvasive pathogen, by compartmentalizing bacteria inside ‘septin cages’ for targeting to autophagy, revealing the first cellular mechanism that counteracts actin-based motility (Van Ngo and Mostowy, J Cell Sci 2019; Robertin and Mostowy, Cell Microbiol 2020). From this I hypothesized that understanding the role of septins, a poorly characterized component of the cytoskeleton, will provide insights into bacterial infection and cell-autonomous immunity. This research direction was the foundation for my first independent research group at Imperial College London (2012-2017). In recognition of my achievements I was recruited in 2018 to the London School of Hygiene & Tropical Medicine as Professor of Cellular Microbiology, where I am supported by an ERC Consolidator Grant (2019-2024) to exploit septin biology for Shigella infection control.
We recently pioneered a ‘bottom up’ cellular microbiology approach to study cell-autonomous immunity and discovered a fundamental link between bacterial cell biology and the assembly of septin cages around Shigella (Lobato-Marquez et al, Nat Commun 2021). A major issue is now to fully decipher the underlying molecular and cellular events, and to validate these events analyzed in vitro during bacterial infection in vivo using relevant animal models. Significantly, my lab previously developed zebrafish as a new model to study the cell biology of Shigella infection in vivo (Gomes and Mostowy, Trends Microbiol 2020). We were the first research group to investigate bacterial autophagy using zebrafish, and our infection models have recently enabled unprecedented opportunities to follow bacterial interactions with cellular immunity at a resolution that cannot be achieved using any other animal model (eg Torraca et al, PLOS Pathog 2019; Mickiewicz et al, Nat Commun 2019; Ulhuq et al, PNAS 2020; Høgset et al, Nat Commun 2020).
We are now in the unique position to study novel research avenues at the cutting edge of infection and cell biology. The results generated from this research program can be expected to provide fundamental advances in cell-autonomous immunity. A second major aim of this research program is to make sense of the molecular and cellular events analyzed in vitro (autophagy, septin caging, bacterial cell biology) during bacterial infection in vivo in the context of an entire organism (zebrafish, mouse, human). Completion of these objectives will provide insights into the mechanisms required for the control of infection and will develop new animal models to study clinically relevant science.
We recently pioneered a ‘bottom up’ cellular microbiology approach to study cell-autonomous immunity and discovered a fundamental link between bacterial cell biology and the assembly of septin cages around Shigella (Lobato-Marquez et al, Nat Commun 2021). A major issue is now to fully decipher the underlying molecular and cellular events, and to validate these events analyzed in vitro during bacterial infection in vivo using relevant animal models. Significantly, my lab previously developed zebrafish as a new model to study the cell biology of Shigella infection in vivo (Gomes and Mostowy, Trends Microbiol 2020). We were the first research group to investigate bacterial autophagy using zebrafish, and our infection models have recently enabled unprecedented opportunities to follow bacterial interactions with cellular immunity at a resolution that cannot be achieved using any other animal model (eg Torraca et al, PLOS Pathog 2019; Mickiewicz et al, Nat Commun 2019; Ulhuq et al, PNAS 2020; Høgset et al, Nat Commun 2020).
We are now in the unique position to study novel research avenues at the cutting edge of infection and cell biology. The results generated from this research program can be expected to provide fundamental advances in cell-autonomous immunity. A second major aim of this research program is to make sense of the molecular and cellular events analyzed in vitro (autophagy, septin caging, bacterial cell biology) during bacterial infection in vivo in the context of an entire organism (zebrafish, mouse, human). Completion of these objectives will provide insights into the mechanisms required for the control of infection and will develop new animal models to study clinically relevant science.