Regulation of NLRP3-dependent IL-1b secretion without pyroptosis – IL1PYR

IL-1b is a major pro-inflammatory cytokine participating in host protection against infections but also contributing to a variety of highly prevalent conditions including gout, atherosclerosis, diabetes, neurodegenerations. IL-1b is tightly controlled, as it is produced in the cytosol and requires caspase-1-dependent maturation and unconventional secretion. In response to various cell stress, the caspase-1 protease is activated within inflammasome complexes assembled by cytosolic pattern recognition receptors including NLRP3. Caspase-1 cleaves pro-IL-1b in its mature form and Gasdermin-D (GSDMD). Cleaved GSDMD form pores in the plasma membrane that mediate IL-1b release and pyroptotic inflammatory cell death. IL-1b secretion is therefore generally associated to pyroptosis. However, living cells can secrete IL-1b upon so called “hyperactivation”, as we have recently observed ourselves in macrophages treated with E coli toxin CNF1 or LPS-treated macrophages bearing a NLRP3 mutation associated to auto-inflammation. In these two conditions, post-translational modifications of NLRP3 trigger GSDMD-independent IL-1b secretion, suggesting that hyperactivation may be regulated upstream in the pathway at the level of NLRP3 inflammasome assembly. Importantly, our in vivo data support the physiological relevance of these pathways. The main objective of our project is to provide a better understanding of the regulatory mechanisms controlling, at the level of the NLRP3 inflammasome complex, IL-1b secretion from living cells. We will take advantage of both our two original models developed within our consortium and our complementary expertise to discriminate the upstream signaling pathways as well as NLRP3 molecular and intracellular dynamics leading to hyperactivation vs classical activation. Better understanding of the determinant factors of hyperactivation will be key in identifying novel therapeutical targets against inflammatory diseases.