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Updated: Sep 22, 2025
Evaluation of Caspase Activation to Assess Innate Immune Cell Death
Published on: January 20, 2023
GSDMEa-mediated pyroptosis is bi-directionally regulated by caspase and required for effective bacterial clearance in
Hang Xu1,2,3, Shuai Jiang4,5,6, Chao Yu1,2,3
1CAS and Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology; CAS Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China.
Abstract:
Gasdermin (GSDM) is a family of pore-forming proteins that, after cleavage by caspase (CASP), induce a type of programmed necrotic cell death called pyroptosis. Gasdermin E (GSDME) is the only pyroptosis-inducing member of the GSDM family existing in teleost. To date, the regulation and function of teleost GSDME in response to bacterial infection remain elusive. In this study, we observed activation of GSDME, as well as multiple CASPs, in turbot Scophthalmus maximus during the infection of the bacterial pathogen Vibrio harveyi. Turbot has two GSDME orthologs named SmGSDMEa and SmGSDMEb. We found that SmGSDMEa was specifically cleaved by turbot CASP (SmCASP) 3/7 and SmCASP6, which produced two different N-terminal (NT) fragments. Only the NT fragment produced by SmCASP3/7 cleavage was able to induce pyroptosis. Ectopically expressed SmCASP3/7 activated SmGSDMEa, resulting in pyroptotic cell death. In contrast, SmCASP6 inactivated SmGSDMEa by destructive cleavage of the NT domain, thus nullifying the activation effect of SmCASP3/7. Unlike SmGSDMEa, SmGSDMEb was cleaved by SmCASP8 and unable to induce cell death. V. harveyi infection dramatically promoted the production and activation of SmGSDMEa, but not SmGSDMEb, and caused pyroptosis in turbot. Interference with SmCASP3/7 activity significantly enhanced the invasiveness and lethality of V. harveyi in a turbot infection model. Together, these results revealed a previously unrecognized bi-directional regulation mode of GSDME-mediated pyroptosis, and a functional difference between teleost GSDMEa and GSDMEb in the immune defense against bacterial infection.
Insights
Gasdermin E (GSDME) in turbot exhibits bi-directional regulation during bacterial infection. Caspase-3/7 activates GSDME for pyroptosis, while Caspase-6 inactivates it, crucial for fish immunity.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Gasdermin (GSDM) proteins form pores and induce pyroptosis upon caspase cleavage.
- Gasdermin E (GSDME) is the sole pyroptosis-inducing GSDM in teleosts, with its regulation and function in bacterial infections being largely unknown.
- Turbot (Scophthalmus maximus) is a commercially important fish species susceptible to bacterial pathogens.
Purpose of the Study:
- To investigate the regulation and function of teleost GSDME in response to bacterial infection.
- To elucidate the roles of different turbot GSDME orthologs (SmGSDMEa and SmGSDMEb) and caspases in pyroptosis.
- To understand the contribution of GSDME-mediated pyroptosis to turbot immunity against Vibrio harveyi.
Main Methods:
- Observation of GSDME and caspase activation in turbot infected with Vibrio harveyi.
- Analysis of SmGSDMEa and SmGSDMEb cleavage by specific turbot caspases (SmCASP3/7, SmCASP6, SmCASP8).
- Ectopic expression studies to assess pyroptosis induction by SmCASP3/7 and SmGSDMEa.
- Interference with SmCASP3/7 activity in a turbot infection model.
Main Results:
- Turbot possesses two GSDME orthologs, SmGSDMEa and SmGSDMEb, with distinct cleavage patterns and functions.
- SmGSDMEa is activated by SmCASP3/7 to induce pyroptosis, but inactivated by SmCASP6.
- SmGSDMEb is cleaved by SmCASP8 and does not induce cell death; its activation is not promoted by V. harveyi infection.
- V. harveyi infection activates SmGSDMEa, leading to pyroptosis in turbot.
- Inhibiting SmCASP3/7 activity increased V. harveyi invasiveness and lethality in turbot.
Conclusions:
- A novel bi-directional regulation of GSDME-mediated pyroptosis is revealed, involving both activation and inactivation pathways.
- Teleost GSDMEa and GSDMEb exhibit functional divergence in immune defense against bacterial pathogens.
- SmGSDMEa-mediated pyroptosis plays a critical role in turbot's innate immune response against Vibrio harveyi infection.
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