Mechanisms and consequences of inflammasome activation

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Abstract

Inflammation is the response of the body to injury or threats. Immune cells such as macrophages have a crucial role in controlling and regulating this process. The potent pro-inflammatory cytokines interleukin (IL)-1beta and IL-18 are synthesized by macrophages as inactive precursors which activation follows a unique mechanism involving the activation of caspase-1 by assembly of a macromolecular complex called the inflammasome. However, the assembly of the inflammasome is a double-edged sword. Although inflammasome activation is necessary for a normal inflammatory response, its malfunction can trigger and contribute to inflammatory disorders such as gout, arthritis or cryopirin-associated periodic syndromes (CAPS). The fine regulation of this mechanism and the cell death associated with it is key for the outcome of the inflammatory process. In this thesis we tackle three aspects of the mechanisms and consequences of inflammasome activation. First we studied the role of the deubiquitinases USP7 and USP47 in inflammasome activation. We showed how USP7 and USP47 activity is increased upon danger signals and how that is necessary for the assembly of the inflammasome. We also pointed how their inhibition dampens the deubiquitination of ASC using a BRET2 assay. Second we examined how the activity of IL-18 is controlled by the release of IL-18BP during inflammasome activation. We showed how IL-18BP release increased upon membrane permeabilization and pyroptosis. This release happens in other types of lytic cell (necrosis and necroptosis) death but not in apoptosis. Finally, we showed that this IL-18BP acute release dampens IL-18 signalling and IFN gamma production by PBMCs. These results demonstrate a novel mechanism by which lytic cell death could dampen IL-18-driven inflammation and highlights a key role for IL-18BP in inflammasome related diseases. Finally we studied the role of inflammasome in lung epithelial cells as a model to investigate lung infections. We found that lung epithelial cells lack NLRP3 inflammasome activity and components, but express caspase-4 and caspase-8 which could have a role in the release of IL-1 family of cytokines. To conclude we showed how lung epithelial release IL-18 upon Aspergillus fumigatus infection. Overall, this thesis enhances our understanding of the mechanisms that control IL-1beta and IL-18 activity by regulating inflammasome activation and by understanding the consequences of its activation.

Keyword(s)

Deubiquitinase; IL-1; IL-18; IL-18BP; Inflammasome; Inflammation; USP47; USP7

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