Non-canonical Inflammasome Research Articles

Evolutionary dynamics of pro-inflammatory caspases in primates and rodents.

Caspase-1 and related proteases are key players in inflammation and innate immunity. Here, we characterize the evolutionary history of caspase-1 and its close relatives across 19 primates and 21 rodents, focusing on differences that may cause discrepancies between humans and animal studies. While caspase-1 has been retained in all these taxa, other members of the caspase-1 subfamily (caspase-4, -5, -11, -12, and CARD16, 17, and 18) each have unique evolutionary trajectories. Caspase-4 is found across simian primates, whereas we identified multiple pseudogenization and gene loss events in caspase-5, caspase-11, and the CARDs. Because caspases-4 and -11 are both key players in the non-canonical inflammasome pathway, we expected that these proteins would be likely to evolve rapidly. Instead, we found that these two proteins are largely conserved, whereas caspase-4's close paralog, caspase-5, showed significant indications of positive selection, as did primate caspase-1. Caspase-12 is a non-functional pseudogene in humans. We find this extends across most primates, although many rodents and some primates retain an intact, and likely functional, caspase-12. In mouse laboratory lines, we found that 50% of common strains carry non-synonymous variants that may impact the functions of caspase-11 and -12, and therefore recommend specific strains to be used (and avoided). Finally, unlike rodents, primate caspases have undergone repeated rounds of gene conversion, duplication, and loss leading to a highly dynamic pro-inflammatory caspase repertoire. Thus we uncovered many differences in the evolution of primate and rodent pro-inflammatory caspases, and discuss the potential implications of this history for caspase gene functions.

Molecular mechanisms of emerging inflammasome complexes and their activation and signaling in inflammation and pyroptosis.

Inflammasomes are multi-protein complexes that assemble within the cytoplasm of mammalian cells in response to pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs), driving the secretion of the pro-inflammatory cytokines IL-1β and IL-18, and pyroptosis. The best-characterized inflammasome complexes are the NLRP3, NAIP-NLRC4, NLRP1, AIM2, and Pyrin canonical caspase-1-containing inflammasomes, and the caspase-11 non-canonical inflammasome. Newer inflammasome sensor proteins have been identified, including NLRP6, NLRP7, NLRP9, NLRP10, NLRP11, NLRP12, CARD8, and MxA. These inflammasome sensors can sense PAMPs from bacteria, viruses and protozoa, or DAMPs in the form of mitochondrial damage, ROS, stress and heme. The mechanisms of action, physiological relevance, consequences in human diseases, and avenues for therapeutic intervention for these novel inflammasomes are beginning to be realized. Here, we discuss these emerging inflammasome complexes and their putative activation mechanisms, molecular and signaling pathways, and physiological roles in health and disease.

Role of caspase-11 non-canonical inflammasomes in retinal ischemia/reperfusion injury

BackgroundRetinal ischemia/reperfusion (IR) injury is a common pathological process in many ophthalmic diseases. Interleukin-1β (IL-1β) is an important inflammatory factor involved in the pathology of retinal IR injury, but the mechanism by which IL-1β is regulated in such injury remains unclear. Caspase-11 non-canonical inflammasomes can regulate the synthesis and secretion of IL-1β, but its role in retinal IR injury has not been elucidated. This study aimed to evaluate the role of caspase-11 non-canonical inflammasomes in retinal IR injury.MethodsRetinal IR injury was induced in C57BL/6J mice by increasing the intraocular pressure to 110 mmHg for 60 min. The post-injury changes in retinal morphology and function and in IL-1β expression were compared between caspase-11 gene knockout (caspase-11−/−) mice and wild-type (WT) mice. Morphological and functional changes were evaluated using hematoxylin–eosin staining and retinal whole mount staining and using electroretinography (ERG), respectively. IL-1β expression in the retina was measured using enzyme-linked immunosorbent assay (ELISA). The levels of caspase-11-related protein were measured using western blot analysis. The location of caspase-11 in the retina was determined via immunofluorescence staining. Mouse type I astrocytes C8-D1A cells were used to validate the effects of caspase-11 simulation via hypoxia in vitro. Small-interfering RNA targeting caspase-11 was constructed. Cell viability was evaluated using the MTT assay. IL-1β expression in supernatant and cell lysate was measured using ELISA. The levels of caspase-11-related protein were measured using western blot analysis.ResultsRetinal ganglion cell death and retinal edema were more ameliorated, and the ERG b-wave amplitude was better after retinal IR injury in caspase-11−/− mice than in WT mice. Further, caspase-11−/− mice showed lower protein expressions of IL-1β, cleaved caspase-1, and gasdermin D (GSDMD) in the retina after retinal IR injury. Caspase-11 protein was expressed in retinal glial cells, and caspase-11 knockdown played a protective role against hypoxia in C8-D1A cells. The expression levels of IL-1β, cleaved caspase-1, and GSDMD were inhibited after hypoxia in the si-caspase-11 constructed cells.ConclusionsRetinal IR injury activates caspase-11 non-canonical inflammasomes in glial cells of the retina. This results in increased protein levels of GSDMD and IL-1β and leads to damage in the inner layer of the retina.

Neisseria meningitidis activates pyroptotic pathways in a mouse model of meningitis: role of a two-partner secretion system.

There is evidence that in infected cells in vitro the meningococcal HrpA/HrpB two-partner secretion system (TPS) mediates the exit of bacteria from the internalization vacuole and the docking of bacteria to the dynein motor resulting in the induction of pyroptosis. In this study we set out to study the role of the HrpA/HrpB TPS in establishing meningitis and activating pyroptotic pathways in an animal model of meningitis using a reference serogroup C meningococcal strain, 93/4286, and an isogenic hrpB knockout mutant, 93/4286ΩhrpB. Survival experiments confirmed the role of HrpA/HrpB TPS in the invasive meningococcal disease. In fact, the ability of the hrpB mutant to replicate in brain and spread systemically was impaired in mice infected with hrpB mutant. Furthermore, western blot analysis of brain samples during the infection demonstrated that: i. N. meningitidis activated canonical and non-canonical inflammasome pyroptosis pathways in the mouse brain; ii. the activation of caspase-11, caspase-1, and gasdermin-D was markedly reduced in the hrpB mutant; iii. the increase in the amount of IL-1β and IL-18, which are an important end point of pyroptosis, occurs in the brains of mice infected with the wild-type strain 93/4286 and is strongly reduced in those infected with 93/4286ΩhrpB. In particular, the activation of caspase 11, which is triggered by cytosolic lipopolysaccharide, indicates that during meningococcal infection pyroptosis is induced by intracellular infection after the exit of the bacteria from the internalizing vacuole, a process that is hindered in the hrpB mutant. Overall, these results confirm, in an animal model, that the HrpA/HrpB TPS plays a role in the induction of pyroptosis and suggest a pivotal involvement of pyroptosis in invasive meningococcal disease, paving the way for the use of pyroptosis inhibitors in the adjuvant therapy of the disease.

Immunomodulatory Effects and Regulatory Mechanisms of (R)-6-HITC, an Isothiocyanate from Wasabi (Eutrema japonicum), in an Ex Vivo Mouse Model of LPS-Induced Inflammation.

The present study aimed to investigate the effects of (R)-(-)-1-isothiocyanato-6-(methylsulfinyl)-hexane [(R)-6-HITC], the major isothiocyanate present in wasabi, in an ex vivo model of inflammation using lipopolysaccharide-stimulated murine peritoneal macrophages. (R)-6-HITC improved the immune response and mitigated oxidative stress, which involved suppression of reactive oxygen species, nitric oxide, and pro-inflammatory cytokines (IL-1β, IL-6, IL-17, IL-18, and TNF-α) production and downregulation of pro-inflammatory enzymes such as inducible nitric oxide synthase, COX-2, and mPGES-1. In addition, (R)-6-HITC was able to activate the Nrf2/HO-1 axis while simultaneously inhibiting key signaling pathways, including JAK2/STAT3, mitogen-activated protein kinases, and canonical and noncanonical inflammasome pathways, orchestrating its potent immunomodulatory effects. Collectively, these findings demonstrate the potential of (R)-6-HITC as a promising nutraceutical for the management of immuno-inflammatory diseases and justify the need for further in vivo validation studies.

Plexin C1 influences immune response to intracellular LPS and survival in murine sepsis

BackgroundIntracellular sensing of lipopolysaccharide (LPS) is essential for the immune response against gram-negative bacteria and results in activation of caspase-11 and pyroptotic cell death with fatal consequences in sepsis. We found the neuronal guidance receptor plexin C1 (PLXNC1) influences the intracellular response to LPS.MethodsWe employed a murine model of sepsis via cecal ligation and binding (CLP), using PLXNC1-/- mice and littermate controls, and additionally transfected murine bone-marrow-derived macrophages (BMDMs) from both genotypes with LPS to achieve activation of the noncanonical inflammasome ex vivo. Additionally, we transfected the PLXNC1 ligand SL4c-d in vivo and ex vivo to examine its effect on intracellular LPS response.ResultsWe found the neuronal guidance receptor PLXNC1 dampens the intracellular response to LPS by interacting with adenylate cyclase 4 (ADCY4) and protein kinase A activity, which in turn diminishes caspase-11 expression. The absence of PLXNC1 results in excessive inflammation marked by increased cytokine release, increased secondary organ injury and reduced sepsis survival in a murine sepsis model induced by CLP. Notably, administration of SL4c-d—peptide ligand of PLXNC1—reduces the inflammatory response during CLP-induced sepsis and improves survival.ConclusionsThese results elucidate a previously unknown mechanism for PLXNC1 suppressing excessive noncanonical inflammasome activity and offer a new potential target for treatment of sepsis with its detrimental effects.

Characterization of Turbo, a TLR Ligand-based Adjuvant for Glycoconjugate Vaccines.

Many bacterial polysaccharide vaccines, including the typhoid Vi polysaccharide (ViPS) and tetravalent meningococcal polysaccharide conjugate (MCV4) vaccines, do not incorporate adjuvants and are not highly immunogenic, particularly in infants. I found that endotoxin, a TLR4 ligand in ViPS, contributes to the immunogenicity of typhoid vaccines. Because endotoxin is pyrogenic, and its levels are highly variable in vaccines, I developed monophosphoryl lipid A, a nontoxic TLR4 ligand-based adjuvant named Turbo. Admixing Turbo with ViPS and MCV4 vaccines improved their immunogenicity across all ages and eliminated booster requirement. To understand the characteristics of this adjuvanticity, I compared Turbo with alum. Unlike alum, which polarizes the response toward the IgG1 isotype, Turbo promoted Ab class switching to all IgG isotypes with affinity maturation; the magnitude of this IgG response is durable and accompanied by the presence of long-lived plasma cells in the mouse bone marrow. In striking contrast with the pathways employed by alum, Turbo adjuvanticity is independent of NLPR3, pyroptotic cell death effector Gasdermin D, and canonical and noncanonical inflammasome activation mediated by Caspase-1 and Caspase-11, respectively. Turbo adjuvanticity is primarily dependent on the MyD88 axis and is lost in mice deficient in costimulatory molecules CD86 and CD40, indicating that Turbo adjuvanticity includes activation of these pathways. Because Turbo formulations containing either monophosphoryl lipid A or TLR2 ligands, Pam2CysSerLys4, and Pam3CysSerLys4 help generate Ab response of all IgG isotypes, as an adjuvant Turbo can improve the immunogenicity of glycoconjugate vaccines against a wide range of bacterial pathogens whose elimination requires appropriate IgG isotypes.

Can We Exploit Inflammasomes for Host-Directed Therapy in the Fight against Mycobacterium tuberculosis Infection?

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tb), is a major global health issue, with around 10 million new cases annually. Advances in TB immunology have improved our understanding of host signaling pathways, leading to innovative therapeutic strategies. Inflammasomes, protein complexes organized by cytosolic pattern recognition receptors (PRRs), play a crucial role in the immune response to M. tb by activating caspase 1, which matures proinflammatory cytokines IL1β and IL18. While inflammation is necessary to fight infection, excessive or dysregulated inflammation can cause tissue damage, highlighting the need for precise inflammasome regulation. Drug-resistant TB strains have spurred research into adjunctive host-directed therapies (HDTs) that target inflammasome pathways to control inflammation. Canonical and non-canonical inflammasome pathways can trigger excessive inflammation, leading to immune system exhaustion and M. tb spread. Novel HDT interventions can leverage precision medicine by tailoring treatments to individual inflammasome responses. Studies show that medicinal plant derivatives like silybin, andrographolide, and micheliolide and small molecules such as OLT1177, INF39, CY-09, JJ002, Ac-YVAD-cmk, TAK-242, and MCC950 can modulate inflammasome activation. Molecular tools like gene silencing and knockouts may also be used for severe TB cases. This review explores these strategies as potential adjunctive HDTs in fighting TB.

Ribonuclease inhibitor 1 emerges as a potential biomarker and modulates inflammation and iron homeostasis in sepsis

Sepsis, marked by organ dysfunction, necessitates reliable biomarkers. Ribonuclease inhibitor 1 (RNH1), a ribonuclease (RNase) inhibitor, emerged as a potential biomarker for acute kidney injury and mortality in thoracoabdominal aortic aneurysm patients. Our study investigates RNH1 dynamics in sepsis, its links to mortality and organ dysfunction, and the interplay with RNase 1 and RNase 5. Furthermore, we explore RNH1 as a therapeutic target in sepsis-related processes like inflammation, non-canonical inflammasome activation, and iron homeostasis. We showed that RNH1 levels are significantly higher in deceased patients compared to sepsis survivors and correlate with creatine kinase, aspartate and alanine transaminase, bilirubin, serum creatinine and RNase 5, but not RNase 1. RNH1 mitigated LPS-induced TNFα and RNase 5 secretion, and relative mRNA expression of ferroptosis-associated genes HMOX1, FTH1 and HAMP in PBMCs. Monocytes were identified as the predominant type of LPS-positive PBMCs. Exogenous RNH1 attenuated LPS-induced CASP5 expression, while increasing IL-1β secretion in PBMCs and THP-1 macrophages. As RNH1 has contradictory effects on inflammation and non-canonical inflammasome activation, its use as a therapeutic agent is limited. However, RNH1 levels may play a central role in iron homeostasis during sepsis, supporting our clinical observations. Hence, RNH1 shows promise as biomarkers for renal and hepatic dysfunction and hepatocyte injury, and may be useful in predicting the outcome of septic patients.

A Synthetic Small Molecule, LGM2605: A Promising Modulator of Increased Pro-Inflammatory Cytokine and Osteoclast Differentiation by Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin.

Our research explores the interplay between Aggregatibacter actinomycetemcomitans (Aa) cytolethal distending toxin (Cdt) and the host's inflammatory response in molar/incisor pattern periodontitis (MIPP). Cdt disrupts phosphatidylinositol-3,4,5-triphosphate (PIP3) signaling, influencing cytokine expression through canonical and non-canonical inflammasome activation as well as nuclear factor-κB (NF-κB) activation, leading to inflammation in MIPP. THP-1 differentiated macrophages (TDMs) exposed to Cdt exhibited an upregulation of pro-inflammatory genes and subsequent cytokine release. We analyzed the ability of a small molecule therapeutic, LGM2605, known for its anti-inflammatory properties, to reduce pro-inflammatory gene expression and cytokine release in Cdt-exposed and Aa-inoculated TDMs. LGM2605's mechanism of action involves inhibiting NF-κB while activating the Nrf2-transcription factor and antioxidants. Herein, we show that this small molecule therapeutic mitigates Cdt-induced pro-inflammatory cytokine expression and secretion. Our study also further defines Cdt's impact on osteoclast differentiation and maturation in MIPP. Cdt promotes increased TRAP+ cells, indicating heightened osteoclast differentiation, specific to Cdt's phosphatase activity. Cathepsin K levels rise during this process, reflecting changes in TRAP distribution between control and Cdt-treated cells. Exploring LGM2605's effect on Cdt-induced osteoclast differentiation and maturation, we found TRAP+ cells significantly reduced with LGM2605 treatment compared to Cdt alone. Upon LGM2605 treatment, immunocytochemistry revealed a decreased TRAP intensity and number of multinucleated cells. Moreover, immunoblotting showed reduced TRAP and cathepsin K levels, suggesting LGM2605's potential to curb osteoclast differentiation and maturation by modulating inflammatory cytokines, possibly involving Nrf2 activation. In summary, our research reveals the intricate connections between Cdt, pro-inflammatory cytokines, and osteoclast differentiation, offering novel therapeutic possibilities for managing these conditions.

2, 6-dimethoxy-1, 4-benzoquinone alleviates septic shock in mice by inhibiting NLRP3 inflammasome activation

To investigate the mechanism of 2, 6-dimethoxy-1, 4-benzoquinone (DMQ), an active ingredients in fermented wheat germ extract, for inhibiting NLRP3 inflammasome activation and alleviating septic shock in mice. Cultured murine bone marrow-derived macrophages (BMDM) stimulated with lipopolysaccharide (LPS) were treated with DMQ, followed by treatment with Nigericin, ATP, and MSU for activating the canonical NLRP3 inflammasome; the noncanonical NLRP3 inflammasome was activated by intracellular transfection of LPS, and AIM2 inflammasome was activated using Poly A: T.In human monocytic THP-1 cells, the effect of Nigericin on inflammasome activation products was examined using Western blotting and ELISA.Co-immunoprecipitation was performed to explore the mechanism of DMQ-induced blocking of NLRP3 inflammasome activation.In a male C57BL/6J mouse model of LPS-induced septic shock treated with 20 and 40 mg/kg DMQ, the levels of IL-1β and TNF-α in the serum and peritoneal lavage fluid were determined using ELISA, and the survival time of the mice within 36 h was observed. Treatment with DMQ effectively inhibited LPS-induced activation of canonical NLRP3 inflammasome in mouse BMDM and human THP-1 cells and also inhibited non-canonical NLRP3 inflammasome activation in mouse BMDM, but produced no significant effect on AIM2 inflammasome activation.DMQ significantly blocked the binding between ASC and NLRP3.In the mouse models of septic shock, DMQ treatment significantly reduced the levels of IL-1β in the serum and peritoneal fluid and obviously prolonged survival time of the mice. DMQ can effectively block ASC-NLRP3 interaction to inhibit NLRP3 inflammasome activation and alleviate LPSinduced septic shock in mice.

Microglia Caspase11 non-canonical inflammasome drives fever.

Animals exhibit physiological changes designed to eliminate the perceived danger, provoking similar symptoms of fever. However, a high-grade fever indicates poor clinical outcomes. Caspase11 (Casp11) is involved in many inflammatory diseases. Whether Casp11 leads to fever remains unclear. In this study, we investigate the role of the preoptic area of the hypothalamus (PO/AH) microglia Casp11 in fever. We perform experiments using a rat model of LPS-induced fever. We measure body temperature and explore the functions of peripheral macrophages and PO/AH microglia in fever signaling by ELISA, immunohistochemistry, immunofluorescence, flow cytometry, macrophage depletion, protein blotting, and RNA-seq. Then, the effects of macrophages on microglia in a hyperthermic environment are observed invitro. Finally, adeno-associated viruses are used to knockdown or overexpress microglia Casp11 in PO/AH to determine the role of Casp11 in fever. We find peripheral macrophages and PO/AH microglia play important roles in the process of fever, which is proved by macrophage and microglia depletion. By RNA-seq analysis, we find Casp11 expression in PO/AH is significantly increased during fever. Co-culture and conditioned-culture simulate the induction of microglia Casp11 activation by macrophages in a non-contact manner. Microglia Casp11 knockdown decreases body temperature, pyrogenic factors, and inflammasome, and vice versa. We report that Casp11 drives fever. Mechanistically, peripheral macrophages transmit immune signals via cytokines to microglia in PO/AH, which activate the Casp11 non-canonical inflammasome. Our findings identify a novel player, the microglia Casp11, in the control of fever, providing an explanation for the transmission and amplification of fever immune signaling.

Oxidative photocatalysis on membranes triggers non-canonical pyroptosis

Intracellular membranes composing organelles of eukaryotes include membrane proteins playing crucial roles in physiological functions. However, a comprehensive understanding of the cellular responses triggered by intracellular membrane-focused oxidative stress remains elusive. Herein, we report an amphiphilic photocatalyst localised in intracellular membranes to damage membrane proteins oxidatively, resulting in non-canonical pyroptosis. Our developed photocatalysis generates hydroxyl radicals and hydrogen peroxides via water oxidation, which is accelerated under hypoxia. Single-molecule magnetic tweezers reveal that photocatalysis-induced oxidation markedly destabilised membrane protein folding. In cell environment, label-free quantification reveals that oxidative damage occurs primarily in membrane proteins related to protein quality control, thereby aggravating mitochondrial and endoplasmic reticulum stress and inducing lytic cell death. Notably, the photocatalysis activates non-canonical inflammasome caspases, resulting in gasdermin D cleavage to its pore-forming fragment and subsequent pyroptosis. These findings suggest that the oxidation of intracellular membrane proteins triggers non-canonical pyroptosis.

Abstract 1115: Novel Mechanism For Extrahepatic Inflammation In Progressive Familial Intrahepatic Cholestasis 1

Background: Human mutations in ATP8b1, a member of the P4-type ATPase family, cause Progressive Familial Intrahepatic Cholestasis I (PFIC1). PFIC1 patients often show extrahepatic inflammatory manifestations such as atherosclerosis, pancreatitis, and hearing loss. Even after liver transplantation, which rescues PFIC1 hepatic symptoms, the extrahepatic inflammatory symptoms persist. The mechanism of how ATP8b1 regulates inflammation is not clear. Pyroptosis executor Gasdermin D (GsdmD) plays a major role in promoting inflammation. GsdmD can be cleaved via a caspase-1/Nlrp3 dependent canonical inflammasome pathway, or a caspase-11 (in mice) or caspase-4/5 (in humans) dependent non-canonical inflammasome pathway. Goal: To decipher the mechanism for ATP8b1-mediated regulation of inflammasome activity in immune cells. Methods & Results: We employed Crispr-Cas9 generated homozygous ATP8b1 knockout human monocytes/macrophages to determine the status of inflammasome activity. Human monocytes/macrophages lacking ATP8b1 released significantly more IL-1β upon exposure to LPS (1μg/ml) + Nigericin (5 mM) vs. control cells (mean±SD, N=3-6, p<0.0001 by t-test.) Interestingly, ATP8b1 -/- cells showed GsdmD cleavage with LPS priming alone without a secondary signal, and markedly increased IL-1β release vs. WT cells (N=3-6, mean±SD, p<0.001). Mechanistically, LPS gained cytoplasmic access in ATP8b1 -/- immune cells, leading to cleavage of GsdmD in an NLRP3-independent, and caspase 4/5 dependent non-canonical inflammasome. The ATP8b1 -/- immune cells showed impaired lysosomal acidification, though the lysosomal number and lysosomal membrane integrity were not compromised. ATP8b1 -/- immune cells showed defects in inflammasome-resolving pathways such as phagocytosis and efferocytosis. Atomic force microscopy of ATP8b1 -/- cells showed a reduced order state of the plasma membrane with Young’s modulus of elasticity for THP-1 ATP8b1 -/- (Ey= 296±10.42 Pa) vs. WT macrophages (Ey =680±25.27 Pa, N =30, mean±SD, p<0.0001). Conclusions: ATP8b1 negatively regulates GsdmD cleavage via a non-canonical inflammasome pathway. GsdmD may serve as a therapeutic target for resolving inflammation in PFIC1 patients.

Caspase-5: Structure, Pro-Inflammatory Activity and Evolution.

Caspase-5 is a protease that induces inflammation in response to lipopolysaccharide (LPS), a component of the cell envelope of Gram-negative bacteria. The expression level of the CASP5 gene is very low in the basal state, but strongly increases in the presence of LPS. Intracellular LPS binds to the caspase activation and recruitment domain (CARD) of caspase-5, leading to the formation of a non-canonical inflammasome. Subsequently, the catalytic domain of caspase-5 cleaves gasdermin D and thereby facilitates the formation of cell membrane pores through which pro-inflammatory cytokines of the interleukin-1 family are released. Caspase-4 is also able to form a non-canonical inflammasome upon binding to LPS, but its expression is less dependent on LPS than the expression of caspase-5. Caspase-4 and caspase-5 have evolved via the duplication of a single ancestral gene in a subclade of primates, including humans. Notably, the main biomedical model species, the mouse, has only one ortholog, namely caspase-11. Here, we review the structural features and the mechanisms of regulation that are important for the pro-inflammatory roles of caspase-5. We summarize the interspecies differences and the evolution of pro-inflammatory caspases in mammals and discuss the potential roles of caspase-5 in the defense against Gram-negative bacteria and in sepsis.

Adipose triglyceride lipase suppresses noncanonical inflammasome by hydrolyzing LPS.

Intracellular recognition of lipopolysaccharide (LPS) by mouse caspase-11 or human caspase-4 is a vital event for the activation of the noncanonical inflammasome. Whether negative regulators are involved in intracellular LPS sensing is still elusive. Here we show that adipose triglyceride lipase (ATGL) is a negative regulator of the noncanonical inflammasome. Through screening for genes participating in the noncanonical inflammasome, ATGL is identified as a negative player for intracellular LPS signaling. ATGL binds LPS and catalyzes the removal of the acylated side chains that contain ester bonds. LPS with under-acylated side chains no longer activates the inflammatory caspases. Cells with ATGL deficiency exhibit enhanced immune responses when encountering intracellular LPS, including an elevated secretion of interleukin-1β, decreased cell viability and increased cell cytotoxicity. Moreover, ATGL-deficient mice show exacerbated responses to endotoxin challenges. Our results uncover that ATGL degrades cytosolic LPS to suppress noncanonical inflammasome activation.

NAD+ prevents septic shock-induced death by non-canonical inflammasome blockade and IL-10 cytokine production in macrophages.

Septic shock is characterized by an excessive inflammatory response depicted in a cytokine storm that results from invasive bacterial, fungi, protozoa, and viral infections. Non-canonical inflammasome activation is crucial in the development of septic shock promoting pyroptosis and proinflammatory cytokine production via caspase-11 and gasdermin D (GSDMD). Here, we show that NAD+ treatment protected mice toward bacterial and lipopolysaccharide (LPS)-induced endotoxic shock by blocking the non-canonical inflammasome specifically. NAD+ administration impeded systemic IL-1β and IL-18 production and GSDMD-mediated pyroptosis of macrophages via the IFN-β/STAT-1 signaling machinery. More importantly, NAD+ administration not only improved casp-11 KO (knockout) survival but rendered wild type (WT) mice completely resistant to septic shock via the IL-10 signaling pathway that was independent from the non-canonical inflammasome. Here, we delineated a two-sided effect of NAD+ blocking septic shock through a specific inhibition of the non-canonical inflammasome and promoting immune homeostasis via IL-10, underscoring its unique therapeutic potential.

NAD+ prevents septic shock-induced death by non-canonical inflammasome blockade and IL-10 cytokine production in macrophages

Septic shock is characterized by an excessive inflammatory response depicted in a cytokine storm that results from invasive bacterial, fungi, protozoa, and viral infections. Non-canonical inflammasome activation is crucial in the development of septic shock promoting pyroptosis and proinflammatory cytokine production via caspase-11 and gasdermin D (GSDMD). Here, we show that NAD+ treatment protected mice toward bacterial and lipopolysaccharide (LPS)-induced endotoxic shock by blocking the non-canonical inflammasome specifically. NAD+ administration impeded systemic IL-1β and IL-18 production and GSDMD-mediated pyroptosis of macrophages via the IFN-β/STAT-1 signaling machinery. More importantly, NAD+ administration not only improved casp-11 KO (knockout) survival but rendered wild type (WT) mice completely resistant to septic shock via the IL-10 signaling pathway that was independent from the non-canonical inflammasome. Here, we delineated a two-sided effect of NAD+ blocking septic shock through a specific inhibition of the non-canonical inflammasome and promoting immune homeostasis via IL-10, underscoring its unique therapeutic potential.

Mechanistic insights from inflammasome structures.

Inflammasomes are supramolecular complexes that form in the cytosol in response to pathogen-associated and damage-associated stimuli, as well as other danger signals that perturb cellular homoeostasis, resulting in host defence responses in the form of cytokine release and programmed cell death (pyroptosis). Inflammasome activity is closely associated with numerous human disorders, including rare genetic syndromes of autoinflammation, cardiovascular diseases, neurodegeneration and cancer. In recent years, a range of inflammasome components and their functions have been discovered, contributing to our knowledge of the overall machinery. Here, we review the latest advances in inflammasome biology from the perspective of structural and mechanistic studies. We focus on the most well-studied components of the canonical inflammasome - NAIP-NLRC4, NLRP3, NLRP1, CARD8 and caspase-1 - as well as caspase-4, caspase-5 and caspase-11 of the noncanonical inflammasome, and the inflammasome effectors GSDMD and NINJ1. These structural studies reveal important insights into how inflammasomes are assembled and regulated, and how they elicit the release of IL-1 family cytokines and induce membrane rupture in pyroptosis.

Roles of the Caspase-11 Non-Canonical Inflammasome in Rheumatic Diseases.

Inflammasomes are intracellular multiprotein complexes that activate inflammatory signaling pathways. Inflammasomes comprise two major classes: canonical inflammasomes, which were discovered first and are activated in response to a variety of pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs), and non-canonical inflammasomes, which were discovered recently and are only activated in response to intracellular lipopolysaccharide (LPS). Although a larger number of studies have successfully demonstrated that canonical inflammasomes, particularly the NLRP3 inflammasome, play roles in various rheumatic diseases, including rheumatoid arthritis (RA), infectious arthritis (IR), gouty arthritis (GA), osteoarthritis (OA), systemic lupus erythematosus (SLE), psoriatic arthritis (PA), ankylosing spondylitis (AS), and Sjögren's syndrome (SjS), the regulatory roles of non-canonical inflammasomes, such as mouse caspase-11 and human caspase-4 non-canonical inflammasomes, in these diseases are still largely unknown. Interestingly, an increasing number of studies have reported possible roles for non-canonical inflammasomes in the pathogenesis of various mouse models of rheumatic disease. This review comprehensively summarizes and discusses recent emerging studies demonstrating the regulatory roles of non-canonical inflammasomes, particularly focusing on the caspase-11 non-canonical inflammasome, in the pathogenesis and progression of various types of rheumatic diseases and provides new insights into strategies for developing potential therapeutics to prevent and treat rheumatic diseases as well as associated diseases by targeting non-canonical inflammasomes.