Apoptotic caspases suppress mtDNA-induced STING-mediated type I IFN production

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Activated caspases are key to intrinsic apoptosis but not essential for cell death in vivo.
• Dying cells can trigger immune responses, suggesting caspases may have immune-modulatory roles.

Purpose of the Study:

• To investigate the role of the caspase cascade in suppressing immune responses during Bak/Bax-mediated apoptosis.
• To determine if caspases prevent type I interferon production by dying cells.

Main Methods:

• Utilized pharmacological caspase inhibition and genetic deletion of caspase pathway components (caspase-9, Apaf-1, caspase-3/7).
• Assessed mitochondrial DNA release and cGAS/STING-dependent DNA sensing pathway activation.
• Measured interferon-beta (IFN-β) production in vitro and in vivo.
• Evaluated hematopoietic stem cell function in the presence of Bak/Bax-mediated apoptosis.

Main Results:

• The caspase cascade suppresses type I interferon production in cells undergoing Bak/Bax-mediated apoptosis.
• Caspase inhibition or deletion leads to IFN-β secretion by dying cells.
• In vivo, this IFN-β elevation causes hematopoietic stem cell dysfunction.
• Loss of Bak and Bax corrects the stem cell dysfunction.

Conclusions:

• The apoptotic caspase cascade renders mitochondrial apoptosis immunologically silent.
• Caspase activity is crucial for preventing inflammatory responses initiated by dying cells.
• This mechanism protects vital cell populations, like hematopoietic stem cells, from immune-mediated damage.