NLRP3 inflammasome-dependent HMGB1 release induced by a bacterial pore-forming toxin (136.15)

Abstract

Abstract The NLRP3 inflammasome is a caspase-1-containing complex involved in the maturation of pro-inflammatory cytokines IL-1β and IL-18. NLRP3, independent of its inflammasome functions, also plays a role in a cathepsin B-dependent, caspase-1-independent necrotic cell death process known as pyronecrosis. We have previously shown that the cholesterol-dependent, pore-forming toxin tetanolysin O (TLO) triggers IL-1β release from LPS-primed murine bone marrow-derived macrophages (BMDM) in a NLRP3 inflammasome- and cathepsin B-dependent manner. The work contained herein supports an additional role for TLO in the necrosis of LPS-primed BMDM. Both a low and a high TLO dose induce release of lactate dehydrogenase (LDH) and high mobility group box 1 (HMGB1) and this release is NLRP3-dependent for the low toxin dose. Low dose TLO-induced HMGB1 release is also dependent on the activities of caspase-1 and cathepsin B, suggesting a novel form of cell death that is distinct from caspase-1-independent pyronecrosis. We also observe via fixed cell microscopy that TLO causes HMGB1 to move from the nucleus to the cytoplasm in LPS-primed BMDM and that HMGB1 release is dependent on NLRP3 activity. To our knowledge, this is the first study to visualize HMGB1 localization in cells lacking NLRP3. These results provide information on the regulation of HMGB1 release and could eventually lead to new therapeutic approaches to target HMGB1, which contributes to many inflammatory diseases.