Distinct regulatory pathways controlling NLRP3 inflammasome in infectious and non-infectious diseases

The proper response of immune cells to pathogenic cues is tightly regulated by elaborate mechanisms to control their onset, intensity and termination. Inflammasomes are large multimolecular complexes responsible for the activation of the inflammatory caspases-1, -4, and -5. These in turn regulate the production of cytokines and induction of pyroptosis upon encountering pathogenic microorganisms or danger signals by the host cells. Inflammasomes are equipped with checkpoints that prevent inappropriate activation and maintain homeostasis. Yet the (dys)regulation of the involved intracellular pathways during episodes of immunosuppression has not been closely examined. Using PBMCs, CD14+ monocytes and plasma derived from patients with sepsis and acute-on-chronic liver failure, we uncovered that, unlike CASP1 and CASP5, CASP4 expression was strongly suppressed and inversely correlated with organ damage markers. Intriguingly, CASP4 downregulation during immunosuppression correlated with impaired interferon-signaling as reflected by downregulation of interferon regulatory factors 1 and 2. These data demonstrate that regulation of caspases differs during systemic inflammation and provides a mechanistic insight into how the NLRP3 inflammasome pathways intersect for maintaining a balanced inflammatory response in disease. A second part of the thesis deals with how the NLRP3 inflammasome is regulated by the CNPY3 chaperone. CNPY3 is known to chaperone and regulate the trafficking of multiple TLRs. Using THP-1 CNPY3-/- macrophages and macrophages derived from a patient with loss-of-function CNPY3 variant, we found that CNPY3 is required for full-blown NLRP3-dependent activation of caspase-1. Mechanistically, CNPY3 is required to recruit caspase-1 into ASC-inflammasome complex upon NLRP3 activation. This work reveals a TLR-independent role of CNPY3 in NLRP3 inflammasome activation, underlining a more complex, dedicated role of CNPY3 to the inflammatory response than anticipated.