Circ-USP9X interacts with EIF4A3 to promote endothelial cell pyroptosis by regulating GSDMD stability in atherosclerosis.

Endothelial pyroptosis is a pathological mechanism of atherosclerosis (AS). Circular RNAs (circRNAs) are vital in AS progression by regulating endothelial cell functions. The study aimed to explore whether circ-USP9× regulated pyroptosis of endothelial cell to involve in AS development and the molecular mechanism. Pyroptosis was determined using lactate dehydrogenase (LDH) assay, enzyme linked immunosorbent assay (ELISA), flow cytometry, propidium iodide (PI) staining assay, and western blot. The mechanism of circ-USP9× was determined using RNA pull-down and RNA binding protein immunoprecipitation (RIP) assays. Results showed that circ-USP9× was upregulated in AS and oxidized low-density lipoprotein (ox-LDL)-treated human umbilical vein endothelial cells (HUVECs). Knockdown of circ-USP9× suppressed ox-LDL induced pyroptosis of HUVECs. Mechanically, circ-USP9× could bind to EIF4A3 in the cytoplasm. Moreover, EIF4A3 was bound to GSDMD and further affects GSDMD stability. Overexpression of EIF4A3 rescued cell pyroptosis induced by circ-USP9× depletion. In short, circ-USP9× interacted with EIF4A3 to enhance GSDMD stability, thus further promoting ox-LDL-induced pyroptosis of HUVECs. These findings suggested that circ-USP9× participates in AS progression and may be a potential therapeutic target for AS.

[Effects of electroacupuncture on NLRP3 inflammasome and pyroptosis protein GSDMD in uterine tissue in rats with primary dysmenorrhea].

OBJECTIVE: To observe the effects of electroacupuncture (EA) on NLRP3 inflammasome and its downstream protein gastermin D (GSDMD) in rats with primary dysmenorrhea (PDM), and to explore the potential mechanism of EA on the treatment of PDM. METHODS: Forty healthy female SD rats without pregnancy were randomly divided into a control group, a model group, an EA group and an ibuprofen group, 10 rats in each group. PDM model was prepared by injection of estradiol benzoate and oxytocin. Except the control group, the rats in each group were subcutaneously injected with estradiol benzoate for 10 days, and oxytocin was injected on the 11th day. The rats in the EA group were intervened with EA (dense wave, frequency of 50 Hz) at "Guanyuan" (CV 4) and "Sanyinjiao" (SP 6) at the same time of modeling, once a day, 20 min each time, for 10 consecutive days. The rats in the ibuprofen group were treated with 0.8 mL of ibuprofen by gavage (concentration of ibuprofen solution was 1.25 mg/mL) for 10 consecutive days. After modeling, the writhing reaction was observed. After intervention, the HE staining method was used to observe the histological morphology of uterus and evaluate the pathological damage score of uterus; ELISA method was used to detect the serum levels of prostaglandin E2 (PGE2) and prostaglandin F2α (PGF2α); Western blot method was used to detect the protein expression of NLRP3, apoptosis related spot like protein (ASC), caspase-1, GSDMD, GSDMD-N and inflammatory factors (interleukin [IL]-1ß, IL-18) in uterine tissue. RESULTS: In the model group, a large number of vacuolar degeneration and death of endometrial epithelial cells, spiral arterioles congestion in lamina propria and neutrophil infiltration were observed. In the EA group, there was a small amount of vacuolar degeneration and death of endometrial epithelial cells, a small amount of spiral arterioles congestion in the lamina propria, and a small amount of neutrophils infiltration. In the ibuprofen group, there was very small number of degeneration and death of endometrial epithelial cells, and no obvious arterial congestion was found in lamina propria, and neutrophil infiltration was occasionally seen. Compared with the control group, in the model group the number of writhing was increased (P<0.01), the writhing reaction score and serum level of PGF2α and PGF2α/PGE2 value were increased (P<0.01), the level of PGE2 was decreased (P<0.01). Compared with the model group, in the EA group and the ibuprofen group the number of writhing were decreased (P<0.05), the latency of writhing was prolonged (P<0.01), the writhing reaction scores and serum levels of PGF2α and PGF2α/PGE2 values were decreased (P<0.05, P<0.01), the levels of PGE2 were increased (P<0.01). Compared with the control group, the protein expression of NLRP3, ASC, caspase-1, GSDMD, GSDMD-N, IL-1ß and IL-18 in the uterine tissues of rats was increased in the model group (P<0.01). Compared with the model group, the protein expression of NLRP3, ASC, caspase-1, GSDMD, GSDMD-N, IL-1ß and IL-18 in the uterine tissues of rats was decreased in the EA group and the ibuprofen group (P<0.01, P<0.05). There was no significant difference between the EA group and the ibuprofen group in the above indexes (P>0.05). CONCLUSION: EA could alleviate pain and uterine tissue injury in rats with PDM. The mechanism may be related to the inhibition of the activation of NLRP3 inflammasome in rat uterine tissues, thereby inhibiting pyroptosis and its inflammatory factors release.

Pyroptosis and degenerative diseases of the elderly.

Pyroptosis is a recently described mechanism of programmed cell death mediated by proteins of the gasdermin family. Widely recognized signaling cascades include the classical, non-classical, caspase-3-dependent gasdermin E and caspase-8-dependent gasdermin D pathways. Additional pyroptotic pathways have been subsequently reported. With the rising prevalence of advanced age, the role of pyroptosis in the degenerative diseases of the elderly has attracted increased research attention. This article reviews the primary mechanisms of pyroptosis and summarizes progress in the research of degenerative diseases of the elderly such as presbycusis, age-related macular degeneration, Alzheimer's disease, intervertebral disc degeneration, and osteoarthritis.

Oxidized mitochondrial DNA induces gasdermin D oligomerization in systemic lupus erythematosus.

Although extracellular DNA is known to form immune complexes (ICs) with autoantibodies in systemic lupus erythematosus (SLE), the mechanisms leading to the release of DNA from cells remain poorly characterized. Here, we show that the pore-forming protein, gasdermin D (GSDMD), is required for nuclear DNA and mitochondrial DNA (mtDNA) release from neutrophils and lytic cell death following ex vivo stimulation with serum from patients with SLE and IFN-γ. Mechanistically, the activation of FcγR downregulated Serpinb1 following ex vivo stimulation with serum from patients with SLE, leading to spontaneous activation of both caspase-1/caspase-11 and cleavage of GSDMD into GSDMD-N. Furthermore, mtDNA oxidization promoted GSDMD-N oligomerization and cell death. In addition, GSDMD, but not peptidyl arginine deiminase 4 is necessary for extracellular mtDNA release from low-density granulocytes from SLE patients or healthy human neutrophils following incubation with ICs. Using the pristane-induced lupus model, we show that disease severity is significantly reduced in mice with neutrophil-specific Gsdmd deficiency or following treatment with the GSDMD inhibitor, disulfiram. Altogether, our study highlights an important role for oxidized mtDNA in inducing GSDMD oligomerization and pore formation. These findings also suggest that GSDMD might represent a possible therapeutic target in SLE.

Reconstitution of human pyroptotic cell death in Saccharomyces cerevisiae.

Pyroptosis is a lytic form of programmed cell death induced by the activation of gasdermins. The precise mechanism of gasdermin activation by upstream proteases remains incompletely understood. Here, we reconstituted human pyroptotic cell death in yeast by inducible expression of caspases and gasdermins. Functional interactions were reflected by the detection of cleaved gasdermin-D (GSDMD) and gasdermin-E (GSDME), plasma membrane permeabilization, and reduced growth and proliferative potential. Following overexpression of human caspases-1, -4, -5, and -8, GSDMD was cleaved. Similarly, active caspase-3 induced proteolytic cleavage of co-expressed GSDME. Caspase-mediated cleavage of GSDMD or GSDME liberated the ~ 30 kDa cytotoxic N-terminal fragments of these proteins, permeabilized the plasma membrane and compromised yeast growth and proliferation potential. Interestingly, the observation of yeast lethality mediated by co-expression of caspases-1 or -2 with GSDME signified functional cooperation between these proteins in yeast. The small molecule pan-caspase inhibitor Q-VD-OPh reduced caspase-mediated yeast toxicity, allowing us to expand the utility of this yeast model to investigate the activation of gasdermins by caspases that would otherwise be highly lethal to yeast. These yeast biological models provide handy platforms to study pyroptotic cell death and to screen for and characterize potential necroptotic inhibitors.

Eugenol Alleviates TGEV-Induced Intestinal Injury via Suppressing ROS/NLRP3/GSDMD-Dependent Pyroptosis.

Transmissible gastroenteritis virus (TGEV), a coronavirus, is one of the main causative agents of diarrhea in piglets and significantly impacts the global swine industry. Pyroptosis is involved in the pathogenesis of coronavirus, but its role in TGEV-induced intestinal injury has yet to be fully elucidated. Eugenol, an essential plant oil, plays a vital role in antiviral innate immune responses. We demonstrate the preventive effect of eugenol on TGEV infection. Eugenol alleviates TGEV-induced intestinal epithelial cell pyroptosis and reduces intestinal injury in TGEV-infected piglets. Mechanistically, eugenol reduces the activation of NLRP3 inflammasome, thereby inhibiting TGEV-induced intestinal epithelial cell pyroptosis. In addition, eugenol scavenges TGEV-induced reactive oxygen species (ROS) increase, which in turn prevents TGEV-induced NLRP3 inflammasome activation and pyroptosis. Overall, eugenol protects the intestine by reducing TGEV-induced pyroptosis through inhibition of NLRP3 inflammasome activation, which may be mediated through intracellular ROS levels. These findings propose that eugenol may be an effective strategy to prevent TGEV infection.

FAM21 is critical for TLR2/CLEC4E-mediated dendritic cell function against Candida albicans.

FAM21 (family with sequence similarity 21) is a component of the Wiskott-Aldrich syndrome protein and SCAR homologue (WASH) protein complex that mediates actin polymerization at endosomal membranes to facilitate sorting of cargo-containing vesicles out of endosomes. To study the function of FAM21 in vivo, we generated conditional knockout (cKO) mice in the C57BL/6 background in which FAM21 was specifically knocked out of CD11c-positive dendritic cells. BMDCs from those mice displayed enlarged early endosomes, and altered cell migration and morphology relative to WT cells. FAM21-cKO cells were less competent in phagocytosis and protein antigen presentation in vitro, though peptide antigen presentation was not affected. More importantly, we identified the TLR2/CLEC4E signaling pathway as being down-regulated in FAM21-cKO BMDCs when challenged with its specific ligand Candida albicans Moreover, FAM21-cKO mice were more susceptible to C. albicans infection than WT mice. Reconstitution of WT BMDCs in FAM21-cKO mice rescued them from lethal C. albicans infection. Thus, our study highlights the importance of FAM21 in a host immune response against a significant pathogen.

Protein engineering reveals that gasdermin A preferentially targets mitochondrial membranes over the plasma membrane during pyroptosis.

When activated, gasdermin family members are thought to be pore-forming proteins that cause lytic cell death. Despite this, numerous studies have suggested that the threshold for lytic cell death is dependent on which gasdermin family member is activated. Determination of the propensity of various gasdermin family members to cause pyroptosis has been handicapped by the fact that for many of them, the mechanisms and timing of their activation are uncertain. In this article, we exploit the recently discovered exosite-mediated recognition of gasdermin D (GSDMD) by the inflammatory caspases to develop a system that activates gasdermin family members in an efficient and equivalent manner. We leverage this system to show that upon activation, GSDMD and gasdermin A (GSDMA) exhibit differential subcellular localization, differential plasma membrane permeabilization, and differential lytic cell death. While GSDMD localizes rapidly to both the plasma membrane and organelle membranes, GSDMA preferentially localizes to the mitochondria with delayed and diminished accumulation at the plasma membrane. As a consequence of this differential kinetics of subcellular localization, N-terminal GSDMA results in early mitochondrial dysfunction relative to plasma membrane permeabilization. This study thus challenges the assumption that gasdermin family members effect cell death through identical mechanisms and establishes that their activation in their respective tissues of expression likely results in different immunological outcomes.

Eugenol Alleviates TGEV-Induced Intestinal Injury via Suppressing ROS/NLRP3/GSDMD-Dependent Pyroptosis.

Transmissible gastroenteritis virus (TGEV), a coronavirus, is one of the main causative agents of diarrhea in piglets and significantly impacts the global swine industry. Pyroptosis is involved in the pathogenesis of coronavirus, but its role in TGEV-induced intestinal injury has yet to be fully elucidated. Eugenol, an essential plant oil, plays a vital role in antiviral innate immune responses. We demonstrate the preventive effect of eugenol on TGEV infection. Eugenol alleviates TGEV-induced intestinal epithelial cell pyroptosis and reduces intestinal injury in TGEV-infected piglets. Mechanistically, eugenol reduces the activation of NLRP3 inflammasome, thereby inhibiting TGEV-induced intestinal epithelial cell pyroptosis. In addition, eugenol scavenges TGEV-induced reactive oxygen species (ROS) increase, which in turn prevents TGEV-induced NLRP3 inflammasome activation and pyroptosis. Overall, eugenol protects the intestine by reducing TGEV-induced pyroptosis through inhibition of NLRP3 inflammasome activation, which may be mediated through intracellular ROS levels. These findings propose that eugenol may be an effective strategy to prevent TGEV infection.

Non-canonical inflammasome activation mediates the adjuvanticity of nanoparticles.

The non-canonical inflammasome sensor caspase-11 and gasdermin D (GSDMD) drive inflammation and pyroptosis, a type of immunogenic cell death that favors cell-mediated immunity (CMI) in cancer, infection, and autoimmunity. Here we show that caspase-11 and GSDMD are required for CD8+ and Th1 responses induced by nanoparticulate vaccine adjuvants. We demonstrate that nanoparticle-induced reactive oxygen species (ROS) are size dependent and essential for CMI, and we identify 50- to 60-nm nanoparticles as optimal inducers of ROS, GSDMD activation, and Th1 and CD8+ responses. We reveal a division of labor for IL-1 and IL-18, where IL-1 supports Th1 and IL-18 promotes CD8+ responses. Exploiting size as a key attribute, we demonstrate that biodegradable poly-lactic co-glycolic acid nanoparticles are potent CMI-inducing adjuvants. Our work implicates ROS and the non-canonical inflammasome in the mode of action of polymeric nanoparticulate adjuvants and establishes adjuvant size as a key design principle for vaccines against cancer and intracellular pathogens.

GSDMD deficiency ameliorates hyperoxia-induced BPD and ROP in neonatal mice.

Bronchopulmonary dysplasia (BPD) and retinopathy of prematurity (ROP) are among the most common morbidities affecting extremely premature infants who receive oxygen therapy. Many clinical studies indicate that BPD is associated with advanced ROP. However, the mechanistic link between hyperoxia, BPD, and ROP remains to be explored. Gasdermin D (GSDMD) is a key executor of inflammasome-induced pyroptosis and inflammation. Inhibition of GSDMD has been shown to attenuate hyperoxia-induced BPD and brain injury in neonatal mice. The objective of this study was to further define the mechanistic roles of GSDMD in the pathogenesis of hyperoxia-induced BPD and ROP in mouse models. Here we show that global GSDMD knockout (GSDMD-KO) protects against hyperoxia-induced BPD by reducing macrophage infiltration, improving alveolarization and vascular development, and decreasing cell death. In addition, GSDMD deficiency prevented hyperoxia-induced ROP by reducing vasoobliteration and neovascularization, improving thinning of multiple retinal tissue layers, and decreasing microglial activation. RNA sequencing analyses of lungs and retinas showed that similar genes, including those from inflammatory, cell death, tissue remodeling, and tissue and vascular developmental signaling pathways, were induced by hyperoxia and impacted by GSDMD-KO in both models. These data highlight the importance of GSDMD in the pathogenesis of BPD and ROP and suggest that targeting GSDMD may be beneficial in preventing and treating BPD and ROP in premature infants.

Putting the p(hosphor) in pyroptosis.

A recent study in Science found Mycobacterium tuberculosis inhibits pyroptosis of the host cell by secreting a phosphatase (PtpB). PtpB targets the plasma membrane to dephosphorylate PI4P and PI(4,5)P2, inhibiting recruitment of the pore-forming gasdermin D N-terminal fragment. Pyroptosis inhibition contributes to virulence, as ptpB-deficient Mtb is attenuated in mice.

Ceramide induces pyroptosis through TXNIP/NLRP3/GSDMD pathway in HUVECs.

BACKGROUND: Pyroptosis of endothelial cells is a new cause of endothelial dysfunction in multiple diseases. Ceramide acts as a potential bioactive mediator of inflammation and increases vascular endothelial permeability in many diseases, whether it can aggravate vascular endothelial injury by inducing cell pyroptosis remains unknown. This study was established to explore the effects of C8-ceramide (C8-Cer) on human umbilical vein vascular endothelial cells (HUVECs) and its possible underlying mechanism. METHODS: HUVECs were exposed to various concentrations of C8-Cer for 12 h, 24 h, 48 h. The cell survival rate was measured using the cell counting kit-8 assay. Western blotting and Real-time polymerase chain reaction (RT-PCR) were used to detect the pyroptosis-releated protein and mRNA expressions, respectively. Caspase-1 activity assay was used to detect caspase-1 activity. Hoechst 33342/propidium iodide double staining and flow cytometry were adopted to measure positive staining of cells. Lactate dehydrogenase release assay and enzyme-linked immunosorbent assay were adopted to measure leakage of cellular contents. FITC method was used to detect the permeability of endothelial cells. ROS fluorescence intensity were detected by flow cytometry. RESULTS: The viability of HUVECs decreased gradually with the increase in ceramide concentration and time. Ceramide upregulated the expression of thioredoxin interacting protein (TXNIP), NLRP3, GSDMD, GSDMD-NT, caspase-1 and Casp1 p20 at the protein and mRNA level in a dose-dependent manner. It also enhanced the PI uptake in HUVECs and upregulated caspase-1 activity. Moreover, it promoted the release of lactate dehydrogenase, interleukin-1ß, and interleukin-18. Meanwhile, we found that ceramide led to increased vascular permeability. The inhibitor of NLRP3 inflammasome assembly, MCC950, was able to disrupt the aforementioned positive loop, thus alleviating vascular endothelial cell damage. Interestingly, inhibition of TXNIP either chemically using verapamil or genetically using small interfering RNA (siRNA) can effectively inhibit ceramide-induced pyroptosis and improved cell permeability. In addition, ceramide stimulated reactive oxygen species (ROS) generation. The pretreatment of antioxidant N-acetylcysteine (NAC), ROS scavenger, blocked the expression of pyroptosis markers induced by C8-cer in HUVECs. CONCLUSION: The current study demonstrated that C8-Cer could aggravate vascular endothelial cell damage and increased cell permeability by inducing cell pyroptosis. The results documented that the ROS-dependent TXNIP/NLRP3/GSDMD signalling pathway plays an essential role in the ceramide-induced pyroptosis in HUVECs.

Disulfiram attenuates hypoxia-induced pulmonary hypertension by inhibiting GSDMD cleavage and pyroptosis in HPASMCs.

BACKGROUND: Pulmonary hypertension (PH) is characterized by progressive pulmonary arterial remodelling, associated with different severities of inflammation and altered immune processes. Disulfiram eliminates the formation of N-gasdermin D (GSDMD) plasma membrane pores to prevent pyroptosis. Pyroptosis is a form of lytic cell death characterized by inflammasome activation and proinflammatory cytokine release that acts in the development of PH. We sought to investigate whether disulfiram could alleviate hypoxia-induced PH by inhibiting pyroptosis. METHODS: To investigate whether disulfiram alleviates the progression of pulmonary hypertension, rodents were exposed to chronic hypoxia (10% oxygen, 4 weeks) to induce PH. The severity of PH was assessed by measuring right ventricular systolic pressure, mean pulmonary artery pressure, and the degree of right ventricular hypertrophy. Western blotting was used to measure proteins associated with the pyroptosis pathway, and ELISA was performed to measure the secretion of IL-18 and IL-1ß, both of which are the primary methods for assessing pyroptosis. RESULTS: IL-18 and IL-1ß concentrations were higher in patients with PH than in normal controls. Disulfiram suppressed the progression of PH in mice and rats through the alleviation of pulmonary arterial remodelling. Pyroptosis-related proteins and the inflammasome were activated in rodent models of PH. Disulfiram inhibited the processing of GSDMD into N-GSDMD and attenuated the secretion of IL-1ß and IL18. In vivo experiments showed that disulfiram also inhibited lytic death in HPASMCs. CONCLUSIONS: Disulfiram treatment reduces PH progression through suppressing vascular remodelling by inhibiting GSDMD cleavage and pyroptosis. It might become a novel therapeutic option for the treatment of PH.

Neutrophil inflammasomes sense the subcellular delivery route of translocated bacterial effectors and toxins.

In neutrophils, caspase-11 cleaves gasdermin D (GSDMD), causing pyroptosis to clear cytosol-invasive bacteria. In contrast, caspase-1 also cleaves GSDMD but seems to not cause pyroptosis. Here, we show that this pyroptosis-resistant caspase-1 activation is specifically programmed by the site of translocation of the detected microbial virulence factors. We find that pyrin and NLRC4 agonists do not trigger pyroptosis in neutrophils when they access the cytosol from endosomal compartment. In contrast, when the same ligands penetrate through the plasma membrane, they cause pyroptosis. Consistently, pyrin detects extracellular Yersinia pseudotuberculosis ΔyopM in neutrophils, driving caspase-1-GSDMD pyroptosis. This pyroptotic response drives PAD4-dependent H3 citrullination and results in extrusion of neutrophil extracellular traps (NETs). Our data indicate that caspase-1, GSDMD, or PAD4 deficiency renders mice more susceptible to Y. pseudotuberculosis ΔyopM infection. Therefore, neutrophils induce pyroptosis in response to caspase-1-activating inflammasomes triggered by extracellular bacterial pathogens, but after they phagocytose pathogens, they are programmed to forego pyroptosis.

Trimethylamine oxide induces pyroptosis of vascular endothelial cells through ALDH2/ROS/NLRP3/GSDMD pathway. / 氧化三甲胺通过ALDH2/ROS/NLRP3/GSDMDé€šè·¯è¯±å¯¼è¡€ç®¡å† çš®ç»†èƒžç„¦äº¡ï¼ˆè‹±æ–‡ï¼‰.

OBJECTIVES: Trimethylamine oxide (TMAO) is a metabolite of intestinal flora and is known to promote the progression of atherosclerotic plaques. However, how TMAO works, including its effect on vascular endothelial cells, is not fully understood. This study aims to explore the biological role of TMAO in human umbilical vein endothelial cells (HUVECs) and the underlying mechanism. METHODS: Cell pyroptosis and the loss of plasma membrane integrity were induced under TMAO stimulation in HUVECs. The plasma membrane integrity of the cells was measured by Hoechst 33342/propidium iodide (PI) staining and lactate dehydrogenase leakage assay, and the changes in cell morphology were observed by atomic force microscope. The expression of proteins related to pyroptosis was determined by Western blotting or immunofluorescence. Mitochondrial acetaldehyde dehydrogenase 2 (ALDH2) activity in HUVECs was measured by the ALDH2 activity assay kit, and the level of reactive oxygen species (ROS) was detected by fluorescent probe DCFH-DA. RESULTS: TMAO induced pyroptotic cell death, manifesting by the presence of propidium iodide-positive cells, the leakage of lactate dehydrogenase, the production of N-terminal gasdermin D (GSDMD-N), and the formation of plasma membrane pores. Moreover, TMAO induced elevated expression of inflammasome components, nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), and caspase-1 in cells. TMAO significantly inhibited ALDH2 activity and increased intracellular ROS production. However, the activation of ALDH2 by pharmacological manipulation attenuated TMAO-induced inflammasome activation and GSDMD-N production. CONCLUSIONS: TMAO induces pyroptosis of vascular endothelial cells through the ALDH2/ROS/NLRP3/GSDMD signaling pathway, which may be a potential therapeutic target for improving the treatment of atherosclerosis.

The Gasdermin D N-terminal fragment acts as a negative feedback system to inhibit inflammasome-mediated activation of Caspase-1/11.

Inflammatory pathways usually utilize negative feedback regulatory systems to prevent tissue damage arising from excessive inflammatory response. Whether such negative feedback mechanisms exist in inflammasome activation remains unknown. Gasdermin D (GSDMD) is the pyroptosis executioner of downstream inflammasome signaling. Here, we found that GSDMD, after its cleavage by caspase-1/11, utilizes its RFWK motif in the N-terminal ß1-ß2 loop to inhibit the activation of caspase-1/11 and downstream inflammation in a negative feedback manner. Furthermore, an RFWK motif-based peptide inhibitor can inhibit caspase-1/11 activation and its downstream substrates GSDMD and interleukin-1ß cleavage, as well as lipopolysaccharide-induced sepsis in mice. Collectively, these findings provide a demonstration of the N-terminal fragment of GSDMD as a negative feedback regulator controlling inflammasome activation and a detailed delineation of the underlying inhibitory mechanism.

Enhancer decommissioning by MLL4 ablation elicits dsRNA-interferon signaling and GSDMD-mediated pyroptosis to potentiate anti-tumor immunity.

Enhancer deregulation is a well-established pro-tumorigenic mechanism but whether it plays a regulatory role in tumor immunity is largely unknown. Here, we demonstrate that tumor cell ablation of mixed-lineage leukemia 3 and 4 (MLL3 and MLL4, also known as KMT2C and KMT2D, respectively), two enhancer-associated histone H3 lysine 4 (H3K4) mono-methyltransferases, increases tumor immunogenicity and promotes anti-tumor T cell response. Mechanistically, MLL4 ablation attenuates the expression of RNA-induced silencing complex (RISC) and DNA methyltransferases through decommissioning enhancers/super-enhancers, which consequently lead to transcriptional reactivation of the double-stranded RNA (dsRNA)-interferon response and gasdermin D (GSDMD)-mediated pyroptosis, respectively. More importantly, we reveal that both the dsRNA-interferon signaling and GSDMD-mediated pyroptosis are of critical importance to the increased anti-tumor immunity and improved immunotherapeutic efficacy in MLL4-ablated tumors. Thus, our findings establish tumor cell enhancers as an additional layer of immune evasion mechanisms and suggest the potential of targeting enhancers or their upstream and/or downstream molecular pathways to overcome immunotherapeutic resistance in cancer patients.

Structure-Guided Approach to Discover Tuberosin as a Potent Activator of Pyruvate Kinase M2, Targeting Cancer Therapy.

Metabolic reprogramming is a key attribute of cancer progression. An altered expression of pyruvate kinase M2 (PKM2), a phosphotyrosine-binding protein is observed in many human cancers. PKM2 plays a vital role in metabolic reprogramming, transcription and cell cycle progression and thus is deliberated as an attractive target in anticancer drug development. The expression of PKM2 is essential for aerobic glycolysis and cell proliferation, especially in cancer cells, facilitating selective targeting of PKM2 in cell metabolism for cancer therapeutics. We have screened a virtual library of phytochemicals from the IMPPAT (Indian Medicinal Plants, Phytochemistry and Therapeutics) database of Indian medicinal plants to identify potential activators of PKM2. The initial screening was carried out for the physicochemical properties of the compounds, and then structure-based molecular docking was performed to select compounds based on their binding affinity towards PKM2. Subsequently, the ADMET (absorption, distribution, metabolism, excretion and toxicity) properties, PAINS (Pan-assay interference compounds) patterns, and PASS evaluation were carried out to find more potent hits against PKM2. Here, Tuberosin was identified from the screening process bearing appreciable binding affinity toward the PKM2-binding pocket and showed a worthy set of drug-like properties. Finally, molecular dynamics simulation for 100 ns was performed, which showed decent stability of the protein-ligand complex and relatival conformational dynamics throughout the trajectory. The study suggests that modulating PKM2 with natural compounds is an attractive approach in treating human malignancy after required validation.

Sublytic gasdermin-D pores captured in atomistic molecular simulations.

Gasdermin-D (GSDMD) is the ultimate effector of pyroptosis, a form of programmed cell death associated with pathogen invasion and inflammation. After proteolytic cleavage by caspases, the GSDMD N-terminal domain (GSDMDNT) assembles on the inner leaflet of the plasma membrane and induces the formation of membrane pores. We use atomistic molecular dynamics simulations to study GSDMDNT monomers, oligomers, and rings in an asymmetric plasma membrane mimetic. We identify distinct interaction motifs of GSDMDNT with phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) and phosphatidylserine (PS) headgroups and describe their conformational dependence. Oligomers are stabilized by shared lipid binding sites between neighboring monomers acting akin to double-sided tape. We show that already small GSDMDNT oligomers support stable, water-filled, and ion-conducting membrane pores bounded by curled beta-sheets. In large-scale simulations, we resolve the process of pore formation from GSDMDNT arcs and lipid efflux from partial rings. We find that high-order GSDMDNT oligomers can crack under the line tension of 86 pN created by an open membrane edge to form the slit pores or closed GSDMDNT rings seen in atomic force microscopy experiments. Our simulations provide a detailed view of key steps in GSDMDNT-induced plasma membrane pore formation, including sublytic pores that explain nonselective ion flux during early pyroptosis.