Molecular mechanisms of zymosan-induced inflammasome activation in macrophages

Area of Science:

• Immunology
• Cell Biology
• Metabolic pathways

Background:

• Zymosan, derived from Saccharomyces cerevisiae, is a potent immunomodulator used to study inflammatory responses.
• The release of the pro-inflammatory cytokine IL-1β by macrophages is critical for combating fungal infections but its precise regulation is unclear.

Purpose of the Study:

• To elucidate the intracellular mechanisms governing zymosan-induced release of active IL-1β in peritoneal macrophages.
• To investigate the role of metabolic changes in zymosan-mediated inflammasome activation.

Main Methods:

• Macrophages were stimulated with zymosan.
• Intracellular signaling pathways including TLR2/MyD88 and Dectin-1 were analyzed.
• Changes in intracellular potassium ion concentration and ATP levels were measured.
• The role of the NLRP3 inflammasome components (ASC, caspase-1) was assessed.
• Glycolytic flux was manipulated to observe effects on ATP and inflammasome activation.

Main Results:

• Zymosan initiates pro-IL-1β formation via TLR2/MyD88, with Dectin-1 amplifying its conversion to active IL-1β.
• Active IL-1β release depends on NLRP3, ASC, and caspase-1, triggered by decreased intracellular potassium.
• Caspase-1 activation by zymosan does not require phagocytosis but correlates with a rapid drop in intracellular ATP.
• Disrupting glycolytic flux exacerbates ATP reduction and amplifies caspase-1 and IL-1β activation.

Conclusions:

• Zymosan recognition by macrophages induces metabolic dysfunction characterized by decreased intracellular ATP.
• This ATP depletion is directly linked to the activation of the NLRP3 inflammasome, leading to IL-1β release.
• The findings reveal a novel link between fungal-induced metabolic changes and inflammatory signaling in macrophages.