Proteases act as sharp scissors that cut protein substrates, modulating protein-protein interactions, creating new bioactive molecules and generating, transducing and amplifying molecular signals. Such critical reactions must be strictly regulated. To date, the molecular mechanisms that silence proteases during diseases are poorly understood.
Inflammasomes are multiprotein signalling hubs that assemble in response to disrupted homeostasis, including metabolic stress and the accumulation of protein aggregates, and provide an activation platform for the cysteine protease caspase-1 (CASP1). Active CASP1 cleaves IL-1 family cytokines (e.g. IL-1b, IL-18) into their bioactive forms and cleaves gasdermin D (GSDMD) to induce cell death. Over the last two decades, most research has defined activation signals for CASP1 and its catalytic function in substrate processing. Little is known about how CASP1 regulates its activity to ensure timely signal inhibition.
Here, we show that autoproteolysis terminates endogenous CASP1 activity in vivo. We generated a knock-in mouse (Casp1.CDL) in which the caspase-1 CARD domain linker (CDL) is mutated to prevent self-cleavage and examined these mice during steady-state and upon major physiological challenges.
In the brain, caspase-1 CDL mutation caused steady-state anxiety-like behaviour, and exacerbated amyloid-induced spatial learning deficits during neurodegeneration. In diet-induced liver disease, caspase-1 CDL mutation accelerated liver steatohepatitis and damage, and importantly, delayed disease resolution during liver healing. Thus, caspase-1 CDL self-cleavage terminates caspase-1 inflammatory programs to maintain steady-state tissue homeostasis, suppress inflammasome-driven diseases, and restore homeostasis after a major challenge to organ function. In revealing when and how CASP1 CDL cleavage occurred is pivotal for our understanding of the molecular mechanism by which this protease is silenced, and we identified caspase-1 as a prime anti-inflammatory drug target