The NLRP1 and CARD8 inflammasomes detect reductive stress

The danger signals that activate the related nucleotide-binding domain leucine-rich repeat pyrin domain-containing 1 (NLRP1) and caspase activation and recruitment domain-containing 8 (CARD8) inflammasomes have not been fully established. We recently reported that the oxidized form of TRX1 binds to NLRP1 and represses inflammasome activation. These findings suggested that intracellular reductive stress, which would reduce oxidized TRX1 and thereby abrogate the NLRP1-TRX1 interaction, is an NLRP1 inflammasome-activating danger signal. 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 both NLRP1 and CARD8, releasing the inflammasome-forming C-terminal fragments from autoinhibition. Overall, this work validates chemical probes that induce reductive stress and establishes reductive stress as a danger signal sensed by both the NLRP1 and CARD8 inflammasomes. [Display omitted] •Radical-trapping antioxidants, including JSH-23, induce reductive stress•JSH-23 accelerates the degradation of the NLRP1- and CARD8-repressive N-terminal fragments•JSH-23 synergizes with DPP8/9 inhibitors to induce NLRP1 and CARD8 inflammasome activation Wang et al. report small molecules that induce intracellular reductive stress. These molecules accelerate the degradation of the NLRP1 and CARD8 N-terminal repressive fragments, thereby potentiating inflammasome activation. These results strongly indicate that NLRP1 and CARD8 detect reductive stress.