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Imaging macropinosomes during Shigella infections
Sonja Kühn1, Noelia Lopez-Montero1, Yuen-Yan Chang1
1Department of Cell Biology and Infection, Institut Pasteur, Paris, France.
Abstract:
Macropinocytosis is the uptake of extracellular fluid within vesicles of varying size that takes place during numerous cellular processes in a large variety of cells. A growing number of pathogens, including viruses, parasites, and bacteria are known to induce macropinocytosis during their entry into targeted host cells. We have recently discovered that the human enteroinvasive, bacterial pathogen Shigella causes in situ macropinosome formation during its entry into epithelial cells. These infection-associated macropinosomes are not generated to ingest the bacteria, but are instead involved in Shigella's intracellular niche formation. They make contacts with the phagocytosed shigellae to promote vacuolar membrane rupture and their cytosolic release. Here, we provide an overview of the different imaging approaches that are currently used to analyze macropinocytosis during infectious processes with a focus on Shigella entry. We detail the advantages and disadvantages of genetically encoded reporters as well as chemical probes to trace fluid phase uptake. In addition, we report how such reporters can be combined with ultrastructural approaches for correlative light electron microscopy either in thin sections or within large volumes. The combined imaging techniques introduced here provide a detailed characterization of macropinosomes during bacterial entry, which, apart from Shigella, are relevant for numerous other ones, including Salmonella, Brucella or Mycobacteria.
Insights
Shigella bacteria hijack cellular macropinocytosis (fluid uptake) not for entry, but to create a niche. This process aids their escape into the host cell cytoplasm, crucial for infection.
Area of Science:
- Cell Biology
- Microbiology
- Pathogen-Host Interactions
Background:
- Macropinocytosis is a cellular process for fluid uptake, utilized by various cells.
- Pathogens frequently exploit macropinocytosis for host cell entry and infection progression.
- Shigella, an invasive bacterial pathogen, induces macropinosome formation during epithelial cell invasion.
Purpose of the Study:
- To investigate the role of infection-associated macropinosomes in Shigella pathogenesis.
- To review and detail imaging techniques for analyzing macropinocytosis during pathogen entry.
- To highlight the application of correlative microscopy for studying bacterial-induced macropinosomes.
Main Methods:
- Utilizing genetically encoded reporters and chemical probes to track fluid-phase uptake.
- Employing correlative light and electron microscopy (CLEM) on thin sections and large volumes.
- Analyzing Shigella entry into epithelial cells and subsequent macropinosome dynamics.
Main Results:
- Shigella induces macropinosomes that do not engulf bacteria but are involved in intracellular niche formation.
- These macropinosomes facilitate vacuolar membrane rupture and bacterial release into the host cell cytosol.
- Combined imaging approaches provide detailed characterization of Shigella-induced macropinosomes.
Conclusions:
- Shigella manipulates host macropinocytosis for intracellular niche formation and escape, rather than direct entry.
- Advanced imaging techniques, including CLEM, are essential for dissecting pathogen-induced macropinocytosis.
- The findings are relevant for understanding the invasion mechanisms of other bacterial pathogens like Salmonella, Brucella, and Mycobacteria.
