The overall aim of the project was to identify and characterize host and microbial factors that regulate inflammasome assembly or promote non-canonical functions of inflammasome-derived components. The project has led to several publications in leading scientific journals. We have demonstrated that additional host-derived and microbial-derived effectors can control and modulate microbial sensing by the cytosolic inflammasomes. Specifically, we could unveil that several host- and microbial-derived factors control the induction of the non-canonical inflammasome pathway in response to the Gram-negative component, namely the LPS. More precisely, we found that the non canonical inflammasome is kept under control thanks to the engameent of two host effectors, Irgm2 and Gate16, which limits its deletrious and uncontrolled response (Eren et al., EMBO Rep. 2020). We also determined that, among the large body of microbial ways of triggering the non canonical inflammasome pathway, pathogenic E. coli bacteria produce an hyper active type of outer membrane vesicles (OMVs) that promote a pathological inflammasome-dependent response (David. L et al., Autophagy. 2022). Furthermore, microbial studies also highlighted a surprising process by which P. aeruginosa pathogenic bacteria trigger an exacerbated and lethal infection through the induction of cellular necrosis, a process that we unveiled to require host basal phospholipid peroxidation-induced P. aeruginosa ExoU-dependent activation (Bagayoko and Meunier, FEBS J. 2022) and (Bagayoko et al., PLoS Pathog. 2021).
In another aspect, we deciphered that during SARS-CoV2 infection of airway respiratory cell, responsible of COVID19 disease, an innate immune receptor, namely NLRP1, was able to detect the virulence induced by the SARS-CoV2 protease 3CL (Planes et al., Mol Cell
. 2022). Specifically this sensor behaved as a decoy sensor of the protolytic activity of 3CL protease, which further promoted the formation fo the NRLP1 inflammasome and the death of the infected cell. We also unveiled that the 3CL protease was able to partly counteract this signalling pathway by directly cleaving and inactivating the pyroptosis effector, Gasdermin D. FInally, this work also highlighted that IL-16, a poorly understood and characterized cytokine, was also released upon apoptotic caspase-3-induced epithelial cell pyroptosis during viral infection. Interestingly, this characterization is also linked to a complementary study where we could unveil that neutrophils, critical immune cells, also release IL-16 in an inflammasome-dependent pyroptosis pathway upon P. aeruginosa bacterial infection, hence warranting for a deep charcaterization of the function of IL-16 on the immune response (Santoni et al., PLoS Pathog. 2022), (Santoni, Planes, Meunier Methods Mol Biol. 2022) and in collaboration (Chauhan et al., EMBO Rep. 2022).
Further studies also identified novel microbial, environmental and host signals that specifically regulate the human NLRP1 inflammasome response in various pathological contextes. For instance, we could determine that upon infection with P. aeruginosa bacteria, the human NLRP1 inflammasome is a sensor of the host translation inhibition induced by the P. aeruginosa virulence toxin, ExoA (Pinilla et al., J Exp Med. 2023). We also determined that mutations in the critical pathway involved in teh regulation of the EXOA target, confer resistance to EXOA-induced translation inhibition and subsequent NRLP1 inflammasome response. Related to this, an unexpected finding of this work is that we could detemrine that in non hematopietic cells, the NLRP1 inflammasome is also an innate immune complex that monitor for the intracellular levels of potassium, a critical ionic specie in our body (Rosario, Pinilla et al., Proc Natl Acad Sci U S A. 2024). Beyond this work, these studies required the development of specific human-derived structures, namely organoids, that allowed us to set up novel airway and lung organoids from donors and patients in order to charcaterize their response to infections and the associated signalling pathways involved (Iakobachvili, Leon-Icaza et al., Mol Microbiol. 2022) and (Leon-Icaza et al., PLoS Pathog. 2023).
All in one, the results presented above provide 1/ novel mechanistic insights in the host-driven and microbial-dependent reguation of inflammasome-induced response in macrophages, neutrophils and epithelial cells/organoids, 2/ highlight novel effectors as cell death-derived immune components (IL-16) and 3/ unveil gasdermins as targets of microbial proteases. The generated knowledge aims at serving as scientific ground for future studies but also in the frame of the development of host-targeted therapies.
