Jul 2026· Journal of Immunology· Vol 215· 0 citations
TL;DR
The mechanism by which MARCO facilitates LPS clearance to limit activation of the non-canonical inflammasome is defined, which shows that activation of the non-canonical inflammasome is preceded by a priming step by which type I interferon (IFN) suppresses MARCO expression on TRMs to allow for optimal recognition of LPS and activation of caspase-11.
Abstract
Cytosolic sensing of bacterial lipopolysaccharide (LPS) is mediated by caspase-11 (caspase-4/5 in humans), which triggers non-canonical inflammasome activation. This leads to gasdermin D cleavage, pyroptosis, and release of pro-inflammatory cytokines. Severe gram-negative bacterial infections cause endotoxic septic shock, with systemic inflammation, organ failure, and potential death. Bacterial derived LPS gains access to the cytosol through extracellular vesicles and CD14 receptor mediated endocytosis. However, how this process is controlled during infection to maintain homeostasis is unknown.
We performed an unbiased proteomic screen with biotinylated LPS and identified MARCO as an LPS-binding protein by mass spectrometry. Using macrophages from transgenic mice, we defined the mechanism by which MARCO facilitates LPS clearance to limit activation of the non-canonical inflammasome.
MARCO is a scavenger receptor expressed on tissue resident macrophages (TRMs) and is known to promote clearance of pathogens and apoptotic debris. However, there is a lack of genetic studies and a paucity in our understanding of the functional role MARCO plays in innate immunity and how MARCO expression is regulated on TRMs. Here, we show that activation of the non-canonical inflammasome is preceded by a priming step by which type I interferon (IFN) suppresses MARCO expression on TRMs to allow for optimal recognition of LPS and activation of caspase-11. Remarkably, the metabolite itaconate and transcription factor NRF2 mediate MARCO expression. IFN signaling inhibits NRF2 stabilization, reducing surface MARCO levels. In vivo, MARCO-deficient mice show increased sensitivity to LPS-induced septic shock due to enhanced caspase-11 and non-canonical inflammasome activation.
IFN-mediated suppression of MARCO expression is a previously unknown innate checkpoint that facilitates the recognition of LPS by caspase-11, activation of the non-canonical inflammasome, and progression of septic shock.
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Innate Immune Responses and Host Defense: Molecular Mechanisms (INM)
Severe infections often cause life-threatening inflammation, multi-organ failure, and death. During infection, pathogens carry multiple pathogen-associated molecular patterns (PAMPs) such as LPS, flagellin, nucleic acids, and lipoproteins which activate more than one pattern-recognition receptor (PRR). These PRRs trigger cytokine secretion and inflammatory cell death to control pathogen load; however, a dysregulated immune response can lead to excessive inflammation and lethality. While earlier studies have primarily focused on single PAMP responses, cells in vivo are exposed to multiple microbial ligands simultaneously.
Primary bone marrow-derived macrophages (BMDMs) were stimulated with PAMPs, and real-time imaging of cell death was performed using the IncuCyte system. Microarray analysis was conducted to examine differential gene expression.
We found that specific PAMP combinations induce lytic cell death, while other combinations do not. Toll-like receptors (TLRs) and their adaptor molecules, MyD88 and TRIF, functioned as upstream regulators that activated inflammatory cell death. In addition, signaling through the interferon-α/β receptor (IFNAR) and interferon regulatory factor 1 (IRF1) was essential for the induction of inflammatory cell death. We also performed microarray analysis to understand the upregulated and downregulated genes in PAMP combinations compared with the untreated control. Through this analysis, we identified significant differences in specific molecules, and we performed genetic, functional validation to show that these molecules directly modulated the induction of inflammatory cell death.
These findings identify key mediators of lytic cell death and suggest that targeting these pathways can be used to mitigate inflammation and lethality during infections.
This research was supported by NIH grants AI101935, AI124346, AI160179, AR056296, and CA253095 and the American Lebanese Syrian Associated Charities to Dr. Kanneganti.
Innate Immune Responses and Host Defense: Molecular Mechanisms (INM)
Balamurugan Sundaram, T. Kanneganti· Journal of Immunology· 0 citations
Deletion of MEX3B inhibited caspase-4 and gasdermin D activation, pyroptosis, and secretion of inflammasome-dependent inflammatory cytokines in human cell lines and murine primary macrophages and suggested that MEX3B is a pan-inflammasome regulator targeting inflammatory caspases.
Peng-Hua Wang, Jason G. Cahoon, Duo-Meng Yang et al.· Journal of Immunology· 0 citations
The non-canonical inflammasome is a protein complex involved in bacterial infections, and its activation leads to excessive inflammatory responses during sepsis. The precise regulation of the non-canonical inflammasome in the body remains unclear. Here, we found that some chemicals that chelate zinc ions positively regulated the activation of the non-canonical inflammasome. These chemicals acted by inhibiting the activity of dipeptidyl peptidase 3 (DPP3). DPP3 cleaved phosphatidylethanolamine binding protein 1 (PEBP1) to generate an N-terminal fragment, which could bind to caspase-4/11 and inhibit the response intensity of the non-canonical inflammasome. PEBP1 N terminus appeared in the serum of mice and patients with sepsis. DPP3-deficient mice exhibited stronger inflammatory cytokine responses and had poor survival in the LPS-induced sepsis model. Promoting the activity of DPP3 effectively constrained the response intensity of sepsis in mice and increased their survival. Our findings provide a perspective for understanding the molecular regulatory process of the non-canonical inflammasome in sepsis.
Meng-Qian Li, Jia-Jia Zheng, Chun Kong et al.· Cell Chemical Biology· 0 citations
Pathogens, tissue damage, and cellular stress are detected by innate immune sensor molecules to drive inflammatory signaling and cell death. Mutations in the sensor NLRP1 are associated with inflammatory disease, but the regulation of this sensor is not well understood. Here, we find that LPS, a TLR4 ligand and canonical activator of innate immunity, inhibits NLRP1-mediated caspase activation, IL-18 release, and inflammatory cell death, PANoptosis. This inhibition requires TRIF but not MyD88, implicating TRIF-dependent TLR signaling. IRF3 is also required, suggesting an essential role for type I IFN signaling. Indeed, IFN-β production or treatment with exogenous IFN-α or IFN-β inhibits NLRP1-dependent PANoptosis in mouse bone marrow-derived macrophages and human macrophages and monocytes. Mechanistically, Nlrp1b/NLRP1 expression is significantly reduced in LPS- or type I IFN-treated cells. Overall, our study identifies a TLR4-TRIF-IRF3 signaling axis that induces type I IFNs to negatively regulate NLRP1 transcription, thereby blocking NLRP1-driven, caspase-1/caspase-8/RIPK3-dependent PANoptosis. These findings suggest type I IFNs as a potential therapeutic strategy for NLRP1-driven inflammatory diseases.
B. Sharma, Harisankeerth Mummareddy, S. Chadchan et al.· EMBO Reports· 1 citation
The findings suggest that disulfide stress contributes to NLRP3 inflammasome activation and pyroptosis triggered by BLPs in leukemia cells, the first report linking disulfidptosis-associated disulfide stress to innate immune signaling.
S. Hosojima, Sheng-Hui Zhi, Yamato Tanabe et al.· Cell Death & Disease· 0 citations
BACKGROUND
Sepsis is associated with an extremely high global mortality rate, primarily due to the lack of effective therapeutic strategies for clearing bacteria from infected tissues. However, the underlying mechanisms by which methylsulfonylmethane (MSM) protects mice against lethal doses of MRSA infection remain incompletely understood.
METHODS
RNA sequencing was used to identify transcriptional differences of peritoneal macrophages (PMs). Immunofluorescence, Western blotting, and RT-qPCR were used to assess target protein and RNA levels. Molecular docking, flow cytometry, and pharmacological inhibitors and agonists were employed to characterize MSM targets, cellular functions, and pathway involvement.
RESULTS
MSM significantly enhanced macrophage phagocytic activity without altering cell counts in vivo during MRSA infection. Notably, phagocytic molecule mRNA levels were significantly higher in whole blood from sepsis survivors than non-survivors, linking phagocytic capacity to sepsis outcomes. Transcriptomic analysis revealed MSM upregulated genes involved in phagosomes, JAK-STAT signaling, lysosomes, and GTPase-related functions in macrophages. RT-qPCR confirmed increased phagosome/lysosome marker expression, while immunofluorescence showed MSM induced LAMP1+ late endosome formation. Mechanistically, MSM is predicted to interact with PIK3CB, thereby activating PIP3 signaling and subsequently inducing iNOS expression and nitric oxide (NO) production in CD11b+F4/80+ macrophages. The PI3K/mTOR inhibitor dactolisib blocked MSM-induced PIP3 accumulation and iNOS expression, validating the PI3K-PIP3 pathway's critical role. MSM-stimulated NO production was confirmed to mediate intracellular MRSA killing.
CONCLUSIONS
MSM alleviates lethal MRSA infection by enhancing macrophage phagocytosis and promoting NO production to eliminate intracellular bacteria. These findings position MSM as a promising therapeutic agent against drug-resistant bacterial infections, offering a novel strategy for managing sepsis.
Haoru Liu, Wan-Qi Tang, Hongsheng Zheng et al.· Life Science· 0 citations
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