Caspase-12 modulates NOD signaling and regulates antimicrobial peptide production and mucosal immunity

Area of Science:

• Immunology
• Microbiology
• Cellular Biology

Background:

• Intracellular Nod proteins and Nod-like receptors (NLRs) are crucial for bacterial sensing, inflammation, and pathogen clearance.
• Nod1 and Nod2 signal through Rip2 to activate NF-kappaB, while other NLRs form inflammasomes involving caspase-1.
• The precise mechanisms regulating Nod-Rip2 complex activity and caspase-12's role beyond inflammasomes remain unclear.

Purpose of the Study:

• To investigate the role of caspase-12 in bacterial sensing and innate immunity, independent of caspase-1.
• To elucidate the molecular mechanisms by which caspase-12 modulates the Nod-Rip2 signaling pathway.
• To understand how caspase-12 influences mucosal antimicrobial responses to enteric pathogens.

Main Methods:

• Studied caspase-12's effects on mucosal immunity in bacterial infection models.
• Assessed the production of antimicrobial peptides, cytokines, and chemokines in wild-type and caspase-12-deficient settings.
• Utilized biochemical assays to examine caspase-12 binding to Rip2 and its impact on Traf6 and NF-kappaB activation.

Main Results:

• Caspase-12 deficiency significantly enhanced mucosal antimicrobial peptide, cytokine, and chemokine production against enteric pathogens.
• This enhancement was dependent on bacterial type III secretion systems and the Nod signaling pathway.
• Caspase-12 directly binds to Rip2, displaces Traf6, inhibits its ubiquitin ligase activity, and consequently blunts NF-kappaB activation.

Conclusions:

• Caspase-12 acts as a negative regulator of the innate mucosal antimicrobial response to bacterial infection.
• It dampens immunity by inhibiting the Nod-Rip2-Traf6-NF-kappaB axis, a critical early defense mechanism.
• These findings reveal a novel function for caspase-12 in modulating host defense against bacterial pathogens.