Microtubule-Mediated NLRP3 Inflammasome Activation Is Independent of Microtubule-Associated Innate Immune Factor GEF-H1 in Murine Macrophages

Abstract

Inflammasomes are intracellular multiple protein complexes that mount innate immune responses to tissue damage and invading pathogens. Their excessive activation is crucial in the development and pathogenesis of inflammatory disorders. Microtubules have been reported to provide the platform for mediating the assembly and activation of NLRP3 inflammasome. Recently, we have identified the microtubule-associated immune molecule guanine nucleotide exchange factor-H1 (GEF-H1) that is crucial in coupling microtubule dynamics to the initiation of microtubule-mediated immune responses. However, whether GEF-H1 also controls the activation of other immune receptors that require microtubules is still undefined. Here we employed GEF-H1-deficient mouse bone marrow-derived macrophages (BMDMs) to interrogate the impact of GEF-H1 on the activation of NLRP3 inflammasome. NLRP3 but not NLRC4 or AIM2 inflammasome-mediated IL-1β production was dependent on dynamic microtubule network in wild-type (WT) BMDMs. However, GEF-H1 deficiency did not affect NLRP3-driven IL-1β maturation and secretion in macrophages. Moreover, α-tubulin acetylation and mitochondria aggregations were comparable between WT and GEF-H1-deficient BMDMs in response to NLRP3 inducers. Further, GEF-H1 was not required for NLRP3-mediated immune defense against Salmonella typhimurium infection. Collectively, these findings suggest that the microtubule-associated immune modulator GEF-H1 is dispensable for microtubule-mediated NLRP3 activation and host defense in mouse macrophages.

Inflammasome activation in neutrophils of patients with severe COVID-19

“…Caspase-1 is known to have many substrates such as the cytoskeleton and nuclear envelop components that need to disassemble for NETosis to proceed 20 , and early caspase-1 activation could facilitate these processes. Notably MTs, a major component of cytoskeletal systems, that are involved in the regulation and distribution of several cell organelles, are important for NET release 34,35 . The formation of speck preceding MT disassembly may be because microtubule transport is needed for ASC protein assembly at the inflammasome 23,24,36 .…”

A detailed Molecular Network Map and Model of the NLRP3 Inflammasome

“…In the (casp8-/-) model presented here, where NLRP3 activation absolutely depends on NEK7 [78], we assume that NLRP3 would need to reach the centrosome, where NEK7 is reported to be localised [126], in order to be activated. Consistent with this hypothesis, NLRP3 activation has been found to depend on microtubule-based transport to bring NLRP3 to the centrosome and NEK7 [127]. It is worth stressing that caspase-8 is known to be recruited to and activated by CL [128], pointing to a possible mechanistic role of caspase-8 in NLRP3 activation as well as a potential difference of the NLRP3 activation by CL and PI(4)P. However, the mechanistic role of caspase-8 in NLRP3 activation remains uncertain [129], and there is evidence for a role for microtubule transport also of mitochondria in NLRP3 activation [130].…”

“…This localises the Signal 2-sensing to this region, and PI(4)P binding is the only regulatory feature that has been mapped to this region, strongly suggesting that this is the critical regulatory input. Second, PI(4)P binding is in itself not enough [31], and NLRP3 release from its resting position on PI(4)P-containing Golgi membranes is necessary for activation [16], as is microtubule-based transport [127]. However, some membrane dispersing toxins (shown for monensin) do not result in NLRP3 activation [140], showing that also dispersal is insufficient for activation, suggesting that either PI(4)P accumulation or microtubule transport is regulated.…”

Downregulation of Three Novel miRNAs in the Lymph Nodes of Sheep Immunized With the Brucella suis Strain 2 Vaccine

“…Complement C4 is one of the chief constituents of innate immunity for immediate recognition and elimination of invading microbes, and plays an essential role in the functions of both classical and lectin complement pathways ( 47 ). ARHGEF2 encodes the microtubule-associated immune molecule guanine nucleotide exchange factor-H1 (GEF-H1), which is crucial in coupling microtubule dynamics to the initiation of microtubule-mediated immune responses ( 48 ). Microfibril-associated glycoprotein 4 (MFAP4), a pattern recognition-like molecule with a fibrinogen-like domain (FBG), has the ability to recognize and agglutinate pathogens, playing an essential role in host innate immune defense ( 49 , 50 ).…”