Hoyle, C. | bioRxiv Science

bioRxiv2021

NLRP3 activation in response to disrupted endocytic traffic

Inflammation driven by the NLRP3 inflammasome is coordinated through multiple signaling pathways and with a poorly defined regulation by sub-cellular organelles. Here, we tested the hypothesis that NLRP3 senses disrupted endosome trafficking to trigger inflammasome formation and inflammatory cytokine secretion. NLRP3-activating stimuli disrupted endosome trafficking and triggered localization of NLRP3 to vesicles positive for endosome markers and the inositol lipid PtdIns4P. Chemical disruption of endosome trafficking sensitized macrophages to the NLRP3 activator imiquimod driving enhanced inflammasome activation and cytokine secretion. Together these data suggest that NLRP3 is capable of sensing disruptions in the trafficking of endosomal cargoes, and that this may explain in part the spatial activation of the NLRP3 inflammasome complex. These data highlight new mechanisms amenable for the therapeutic targeting of NLRP3. One-Sentence SummaryNLRP3 senses disruptions in endosome trafficking to trigger the formation of an inflammasome complex and initiate an inflammatory response.

immunology↗

bioRxiv2021

Itaconate and fumarate derivatives exert a dual inhibitory effect on canonical NLRP3 activation in macrophages and microglia

The NLRP3 inflammasome is a multi-protein complex that regulates the protease caspase-1 and subsequent interleukin (IL)-1{beta} release from cells of the innate immune system, or microglia in the brain, in response to infection or injury. Derivatives of the metabolites itaconate and fumarate, dimethyl itaconate (DMI), 4-octyl itaconate (4OI) and dimethyl fumarate (DMF), limit both expression of IL-1{beta}, and IL-1{beta} release following NLRP3 inflammasome activation. However, the direct effects of these metabolite derivatives on NLRP3 inflammasome responses in macrophages and microglia require further investigation. Using murine bone marrow-derived macrophages, mixed glia and organotypic hippocampal slice cultures (OHSCs), we demonstrate that DMI and 4OI pre-treatment limited IL-1{beta}, IL-6 and tumor necrosis factor production in response to lipopolysaccharide (LPS) priming, as well as inhibiting subsequent NLRP3 inflammasome activation. DMI, 4OI, DMF and monomethyl fumarate (MMF), another fumarate derivative, also directly inhibited biochemical markers of NLRP3 activation in LPS-primed macrophages, mixed glia and OHSCs, including ASC speck formation, caspase-1 activation, gasdermin D cleavage and IL-1{beta} release. Finally, DMF, an approved treatment for multiple sclerosis, as well as DMI, 4OI and MMF, inhibited NLRP3 activation in macrophages in response to the phospholipid lysophosphatidylcholine, which is used to induce demyelination, suggesting a possible mechanism of action for DMF in multiple sclerosis through NLRP3 inhibition. Together, these findings reveal the importance of immunometabolic regulation for both the priming and activation steps of NLRP3 activation in macrophages and microglia. Furthermore, we highlight itaconate and fumarate derivatives as a potential therapeutic option in NLRP3-driven diseases, including in the brain. Summary statementWe show that itaconate and fumarate derivatives inhibit both the priming and activation steps of NLRP3 inflammasome responses in macrophages and microglia, revealing the importance of immunometabolic NLRP3 regulation.

immunology↗