Complement pathway amplifies caspase-11-dependent cell death and endotoxin-induced sepsis severity

Area of Science:

• Immunology
• Molecular Biology
• Complement System

Background:

• Sepsis mortality is linked to cell death and proinflammatory mediators.
• Caspase-11-dependent cell death exacerbates sepsis pathology and reduces survival.
• Host cell priming via TLR4 and interferon receptors induces caspase-11 expression, while cytosolic LPS directly activates it.

Purpose of the Study:

• To identify novel mediators of caspase-11-dependent cell death using a genome-wide CRISPR-Cas9 screen.
• To elucidate the role of identified mediators in sepsis pathogenesis and outcome.

Main Methods:

• Conducted a CRISPR-Cas9 genome-wide screen to identify genes regulating caspase-11-dependent cell death.
• Investigated the function of carboxypeptidase B1 (Cpb1) in caspase-11 expression and activation.
• Analyzed the Cpb1-C3-C3aR pathway's role in innate immune signaling and sepsis severity in mouse models.
• Examined C3aR and caspase-11 orthologue expression in human macrophages and sepsis patient data.

Main Results:

• Identified carboxypeptidase B1 (Cpb1) as essential for caspase-11 gene expression and subsequent cell death.
• Demonstrated that Cpb1 modifies C3, leading to C3aR activation and modulation of innate immune signaling.
• The Cpb1-C3-C3aR pathway amplifies MAPK activity downstream of TLR4 and Ifnar, inducing caspase-11 expression and mediating sepsis severity.
• C3aR is required for caspase-11 orthologue upregulation in human macrophages, and C3aR1/caspase-5 are highly expressed in severe sepsis patients.

Conclusions:

• The complement-related peptidase Cpb1 and the Cpb1-C3-C3aR pathway represent a novel mechanism in sepsis.
• This pathway amplifies inflammatory signaling, drives caspase-11-dependent cell death, and contributes to sepsis severity.
• Findings suggest the Cpb1-C3-C3aR-caspase-11 axis is a critical player in human sepsis, offering potential therapeutic targets.