Differential activation of the inflammasome by caspase-1 adaptors ASC and Ipaf

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Initiator caspases are regulated by specific adaptors like FADD and Apaf-1.
• The inflammasome complex, containing adaptors like ASC, Ipaf, and RIP2, activates caspase-1 (interleukin-1 converting enzyme).

Purpose of the Study:

• To investigate the roles of ASC, Ipaf, and RIP2 adaptors in inflammasome function.
• To elucidate the specific contributions of these adaptors to caspase-1 activation and downstream inflammatory responses.

Main Methods:

• Utilized gene-deficient macrophages (ASC-, Ipaf-, RIP2-null) and mice.
• Stimulated macrophages with extracellular ATP, toll-like receptor (TLR) agonists, and intracellular pathogens (Salmonella typhimurium).
• Assessed caspase-1 activation, IL-1beta and IL-18 maturation, endotoxic shock resistance, and pathogen-induced cell death.

Main Results:

• ASC deficiency abrogated extracellular ATP-driven caspase-1 activation, IL-1beta/IL-18 maturation, and endotoxic shock.
• ASC-null macrophages showed severely impaired caspase-1 activation in response to S. typhimurium.
• Ipaf deficiency impaired caspase-1 activation by S. typhimurium but not by TLR plus ATP stimulation.
• RIP2 deficiency did not compromise caspase-1 activation.
• Macrophage cell death triggered by caspase-1-engaging stimuli was abolished in ASC- or Ipaf-deficient cells.

Conclusions:

• ASC is essential for inflammasome-mediated caspase-1 activation, crucial for inflammatory cytokine maturation and host defense.
• Ipaf acts as a specific pathway for inflammasome activation by intracellular pathogens.
• A significant link exists between inflammasome-mediated inflammation and cell death pathways, mediated by ASC and Ipaf.