Galectin-3 promotes non-canonical inflammasome activation through binding to glycans on LPS intracellularly

Abstract

Abstract In response to infection, pyroptosis is a typical inflammatory form of cell death. Even though the various stimuli have been well elucidated in the regulation of host immune responses through caspase-1, the mechanism of caspase-4/5/11 is not defined. Lipopolysaccharides (LPS) from Gram-negative bacteria have been shown to induce non-canonical inflammasome activation by binding to caspase-4/5/11 through its lipid A moiety intracellularly and causing oligomerization and activation. Galectin-3, belonging to a beta-galactoside-binding protein family, can bind to LPSs from different Gram-negative bacteria, which are composed of beta-galactoside-containing polysaccharide chains. Galectin-3 is known to self-associate upon binding to multivalent glycans through its non-lectin domain. Therefore, we hypothesized that galectin-3 can cross-link LPS and form an ordered array of galectin-3-LPS complex, and consequently, amplify LPS-induced caspase-4/5/11 oligomerization and activation. To test this hypothesis, we transferred LPSs intracellularly by liposome-mediated transfection into galectin-3−/− bone marrow-derived macrophages (BMDMs) and wild-type cells. We noted galectin-3 deficiency resulted in a lower level of LPS-induced pyroptosis. Co-immunoprecipitation confirmed the interaction between galectin-3 and caspase-11 in RAW264.7 cells after LPS intracellular delivery. In a cell-free system, we showed that galectin-3 facilitated the assembly of LPS-induced caspase-4 oligomerization and activation. In conclusion, galectin-3 is a novel host factor in the induction of higher degree of caspase-4/5/11 oligomerization and activation through LPS binding, resulting in more intense pyroptosis.