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Updated: Mar 1, 2026
Detection of Inflammasome Activation and Pyroptotic Cell Death in Murine Bone Marrow-derived Macrophages
Published on: May 21, 2018
The PYRIN domain-only protein POP2 inhibits inflammasome priming and activation
Rojo A Ratsimandresy1, Lan H Chu1,2, Sonal Khare1
1Division of Rheumatology, Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
Abstract:
Inflammasomes are protein platforms linking recognition of microbe, pathogen-associated and damage-associated molecular patterns by cytosolic sensory proteins to caspase-1 activation. Caspase-1 promotes pyroptotic cell death and the maturation and secretion of interleukin (IL)-1β and IL-18, which trigger inflammatory responses to clear infections and initiate wound-healing; however, excessive responses cause inflammatory disease. Inflammasome assembly requires the PYRIN domain (PYD)-containing adaptor ASC, and depends on PYD-PYD interactions. Here we show that the PYD-only protein POP2 inhibits inflammasome assembly by binding to ASC and interfering with the recruitment of ASC to upstream sensors, which prevents caspase-1 activation and cytokine release. POP2 also impairs macrophage priming by inhibiting the activation of non-canonical IκB kinase ɛ and IκBα, and consequently protects from excessive inflammation and acute shock in vivo. Our findings advance our understanding of the complex regulatory mechanisms that maintain a balanced inflammatory response and highlight important differences between individual POP members.
Insights
The PYD-only protein POP2 inhibits inflammasome assembly by blocking ASC adaptor protein interactions, preventing inflammatory caspase-1 activation and cytokine release. This discovery offers new insights into regulating inflammatory responses and preventing disease.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Inflammasomes are crucial protein complexes that activate caspase-1, leading to inflammatory cytokine release and pyroptosis.
- Dysregulated inflammasome activation contributes to various inflammatory diseases.
- Asc (apoptosis-associated speck-like protein containing a CARD) is a key adaptor protein required for inflammasome assembly.
Purpose of the Study:
- To investigate the role of the PYD-only protein POP2 in inflammasome regulation.
- To elucidate the mechanism by which POP2 affects inflammasome assembly and activation.
- To determine the in vivo relevance of POP2 in controlling inflammatory responses.
Main Methods:
- Co-immunoprecipitation assays to study protein-protein interactions between POP2 and ASC.
- Western blotting to assess caspase-1 activation and cytokine secretion.
- In vivo studies using mouse models to evaluate the protective effects of POP2 against acute shock.
Main Results:
- POP2 directly binds to ASC, inhibiting its recruitment to upstream inflammasome sensors.
- POP2 prevents ASC-dependent caspase-1 activation and subsequent release of IL-1β and IL-18.
- POP2 impairs macrophage priming by inhibiting IκB kinase ɛ and IκBα activation.
- POP2 administration protects mice from excessive inflammation and lethal endotoxic shock.
Conclusions:
- POP2 acts as a negative regulator of inflammasome activation by interfering with ASC-PYD interactions.
- POP2 modulates both canonical and non-canonical inflammasome pathways.
- POP2 represents a potential therapeutic target for managing inflammatory diseases caused by inflammasome overactivation.
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