Characterizing the Role of Complement in the Caspase-11-Dependent Inflammasome

Inflammatory caspases are a critical component of innate immunity and play a crucial role in host defense against invading pathogens. Caspase-11 is an important mediator of the host cell response to Gram-negative bacterial... [ view full abstract ]

Inflammatory caspases are a critical component of innate immunity and play a crucial role in host defense against invading pathogens. Caspase-11 is an important mediator of the host cell response to Gram-negative bacterial pathogens and sepsis. Stimulation of toll-like receptor 4 by bacterial lipopolysaccharide (LPS) induces the expression of caspase-11. Upon detection and binding of cytosolic LPS, caspase-11 is activated, which leads to an inflammatory form of cell death known as pyroptosis. Despite the important role of caspase-11-dependent cell death during LPS-induced inflammation, not much is known about this cell death pathway. A CRISPR-Cas9 genome-wide genetic screen in macrophages was performed to uncover novel mediators of caspase-11-dependent cell death. This screen revealed carboxypeptidase B1 (Cpb1) may be working through complement to amplify expression of caspase-11 and other pro-inflammatory genes during LPS stimulation. CRISPR knockouts of complement proteins C3 and C3aR were stimulated in culture by purified LPS and bacteria to examine pro-inflammatory gene expression and cell death. Relative cell death and inflammatory gene expression were found to be reduced in C3-/- and C3aR-/- macrophages after LPS stimulation, affirming the possibility of complement amplification in caspase-11 cell death, and potentially unveiling a new relationship between two important innate immune pathways.