The NLRP1 and CARD8 inflammasomes detect reductive stress

The danger signals that activate the NLRP1 and CARD8 inflammasomes have not been fully established. We recently discovered that cytosolic peptide accumulation activates these inflammasomes. In addition, we found that the oxidized form of TRX1 binds to and represses NLRP1, suggesting that NLRP1 also detects a lack of reactive oxygen species, or reductive stress. However, no agents that induce reductive stress were known to test this premise. Here, we identify and characterize several radical-trapping antioxidants, including JSH-23, that induce reductive stress. We show that these compounds accelerate the proteasome-mediated degradation of the repressive N-terminal fragments of NLRP1 and CARD8, releasing the inflammasome-forming C-terminal fragments from autoinhibition. Moreover, we found that reductive stress and peptide accumulation together trigger much more intense inflammasome activation than either signal alone. Overall, this work validates chemical probes that induce reductive stress, and establishes reductive stress alongside peptide accumulation as the key inflammasome-activating danger signals.