Distinct changes in endosomal composition promote NLRP3 inflammasome activation

Abstract

Inflammasome complexes are pivotal in the innate immune response. The NLR family pyrin domain containing protein 3 (NLRP3) inflammasome is activated in response to a broad variety of cellular stressors. However, a primary and converging sensing mechanism by the NLRP3 receptor initiating inflammasome assembly remains ill defined. Here, we demonstrate that NLRP3 inflammasome activators primarily converge on disruption of endoplasmic reticulum–endosome membrane contact sites (EECS). This defect causes endosomal accumulation of phosphatidylinositol 4-phosphate (PI4P) and a consequent impairment of endosome-to-trans-Golgi network trafficking (ETT), necessary steps for endosomal recruitment of NLRP3 and subsequent inflammasome activation. Lowering endosomal PI4P levels prevents endosomal association of NLRP3 and inhibits inflammasome activation. Disruption of EECS or ETT is sufficient to enhance endosomal PI4P levels, to recruit NLRP3 to endosomes and to potentiate NLRP3 inflammasome activation. Mice with defects in ETT in the myeloid compartment are more susceptible to lipopolysaccharide-induced sepsis. Our study thus identifies a distinct cellular mechanism leading to endosomal NLRP3 recruitment and inflammasome activation.

Disruptions in endocytic traffic contribute to the activation of the NLRP3 inflammasome

“…These data suggest that NLRP3 can localize to multiple endolysosomal membranes upon stimulation, consistent with a previous report of colocalization of TGN38, EEA1, and NLRP3-GFP in nigericintreated HeLa cells (5). Furthermore, as presented in a related study, activated NLRP3 localizes to RAB5-positive endosomes after stimulation (26).…”

“…Furthermore, NLRP3 can interact with PI4P through a conserved polybasic motif (5), and endosomal membranes contain this lipid (28). A related study reports NLRP3 recruitment to PI4P-containing endosomes (26). PI4P seems likely to be important for NLRP3 membrane recruitment but may not be the only factor.…”

“…A related study showed that knocking out proteins involved in endosome-to-TGN retrograde trafficking such as ADP ribosylation factor–related protein 1 (ARFRP1) and SYS1 in THP1 cells enhanced NLRP3 inflammasome activation. It was also reported that the endosome-to-TGN retrograde trafficking inhibitor Retro-2 ( 25 ) enhances NLRP3 inflammasome activation in THP1 cells ( 26 ). We therefore tested whether Retro-2 could potentiate NLRP3 inflammasome activation in our experiments as further evidence of disrupted endosome trafficking contributing to inflammasome activation.…”

Pyroptosis in neutrophils: Multimodal integration of inflammasome and regulated cell death signaling pathways

“…This likely reflects effects of polymorphonuclear architecture to favor formation of multiple specks adjacent to individual lobes of the atypical nucleus. Recent studies in macrophages have also demonstrated that the initial formation of NLRP3 oligomers is seeded at discrete endosomal loci 194,195 . As discussed in Section 5.1, neutrophils containing activated NLRP3 inflammasomes are particularly resistant to pyroptosis 31,33,51,57 with delayed lysis in only a small percentage of cells 75 .…”

Cathepsin B in programmed cell death machinery: mechanisms of execution and regulatory pathways

“…For example, (1) CatB involves in the activation of NFκB, which is responsible for the transcriptional regulation of NLRP3 and IL-1β; (2) Mitochondrial ROS is one of the key factors for NLRP3 activation, and we have reported that leaked CatB in the cytosol could induce mitochondrial ROS production [ 12 ]; (3) NLRP3 inflammasome was reported to be activated on the dispersed trans-Golgi network where CatB has the chance to interact with NLRP3 inflammasome [ 22 , 23 ]. (4) A new finding suggested that the vesicles to which NLRP3 is recruited are of endosomal origin [ 24 ]. It is reasonable to assume that CatB may activate NLRP3 inflammasome in the endosomes.…”