AIM2 and NLRP3 inflammasomes activate both apoptotic and pyroptotic death pathways via ASC

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Inflammasomes are protein complexes that initiate inflammatory responses and cell death.
• AIM2 and NLRP3 are key inflammasome sensors activated by infection or cell damage.
• Caspase-1 activation by inflammasomes leads to pyroptosis, a form of lytic cell death.

Purpose of the Study:

• To investigate the role of AIM2 and NLRP3 inflammasomes in activating caspases beyond caspase-1.
• To determine the mechanisms by which inflammasomes induce both apoptotic and pyroptotic cell death.
• To elucidate the involvement of caspase-8 in AIM2 and NLRP3 inflammasome-mediated cell death pathways.

Main Methods:

• Utilized gene knockdown techniques to assess the necessity of specific caspases.
• Investigated inflammasome activation by varying concentrations of transfected cytosolic DNA.
• Examined the localization and binding of procaspase-8 to ASC inflammasome complexes.

Main Results:

• AIM2 and NLRP3 inflammasomes activate both caspase-8 and caspase-1.
• The balance between apoptosis and pyroptosis is dependent on DNA concentration, with pyroptosis dominating at higher concentrations.
• Caspase-8 is the apical caspase in AIM2- and NLRP3-dependent apoptosis, with minimal reliance on caspase-9.
• Procaspase-8 directly binds to the ASC pyrin domain within inflammasome specks.

Conclusions:

• The AIM2 and NLRP3 inflammasomes can induce both apoptotic and pyroptotic cell death pathways.
• Caspase-8 is a crucial component of these inflammasome pathways, acting as an apical caspase.
• The findings expand the known functions of inflammasomes and their relevance to caspase-1-deficient cells.