Mitochondrial dysfunction caused by outer membrane vesicles from Gram-negative bacteria activates intrinsic apoptosis...

Area of Science:

• Innate immunity and host-pathogen interactions
• Mitochondrial biology and cellular stress responses
• Inflammasome signaling pathways

Background:

• The innate immune system relies on sensing microbial components to initiate defense mechanisms.
• Mitochondrial function is crucial for cellular immunity, but pathogenic bacteria can disrupt it.
• Outer membrane vesicles (OMVs) are employed by bacteria to deliver toxins and interfere with host cell processes, including mitochondrial activity.

Purpose of the Study:

• To elucidate the response of macrophages to pathogenic bacterial OMVs that target mitochondria.
• To investigate the mechanisms by which mitochondrial dysfunction induced by bacterial toxins leads to immune activation.
• To determine the role of mitochondrial apoptosis and inflammasome activation in the innate immune response to bacterial OMVs.

Main Methods:

• Exposure of macrophages to OMVs from Neisseria gonorrhoeae, uropathogenic Escherichia coli, and Pseudomonas aeruginosa.
• Analysis of mitochondrial apoptosis, inflammasome activation (NLRP3), and host protein synthesis.
• In vitro and in vivo studies to assess the role of mitochondrial apoptosis in interleukin-1β release.

Main Results:

• Macrophage exposure to bacterial OMVs induced mitochondrial apoptosis and NLRP3 inflammasome activation.
• OMVs and toxins causing mitochondrial dysfunction led to host protein synthesis inhibition, MCL-1 depletion, and BAK-dependent apoptosis.
• Caspase-11-mediated pyroptosis, mitochondrial apoptosis, and potassium ion efflux were key events in NLRP3 inflammasome activation.
• In vivo, N. gonorrhoeae OMVs-induced interleukin-1β release was regulated by mitochondrial apoptosis.

Conclusions:

• Macrophages sense infections targeting mitochondria by monitoring mitochondrial health.
• Mitochondrial apoptosis and inflammasome activation are critical innate immune responses to bacterial OMVs.
• These findings reveal a novel mechanism of innate immune sensing and defense against bacterial pathogens.