The Inflammasome Drives GSDMD-Independent Secondary Pyroptosis and IL-1 Release in the Absence of Caspase-1 Protease Activity

How Pyroptosis Contributes to Inflammation and Fibroblast-Macrophage Cross-Talk in Rheumatoid Arthritis

About thirty years ago, a new form of pro-inflammatory lytic cell death was observed and termed pyroptosis. Only in 2015, gasdermins were defined as molecules that create pores at the plasma membrane and drive pyroptosis. Today, we know that gasdermin-mediated death is an important antimicrobial defence mechanism in bacteria, yeast and mammals as it destroys the intracellular niche for pathogen replication. However, excessive and uncontrolled cell death also contributes to immunopathology in several chronic inflammatory diseases, including arthritis. In this review, we discuss recent findings where pyroptosis contributes to tissue damage and inflammation with a main focus on injury-induced and autoimmune arthritis. We also review novel functions and regulatory mechanisms of the pyroptotic executors gasdermins. Finally, we discuss possible models of how pyroptosis may contribute to the cross-talk between fibroblast and macrophages, and also how this cross-talk may regulate inflammation by modulating inflammasome activation and pyroptosis induction.

ManNAc protects against podocyte pyroptosis via inhibiting mitochondrial damage and ROS/NLRP3 signaling pathway in diabetic kidney injury model

Podocyte pyroptosis is an inflammatory form of cell death associated with Diabetic nephropathy (DN). It is reported that hyposialylated Angiopoietin-like-4 (Angptl4) secreted by glomerular podocytes plays an important role in the formation of proteinuria. Previous study indicated that supplementation of sialic acid precursor N-acetylmannosamine (ManNAc) could inhibit podocyte apoptosis and actin cytoskeleton rearrangement. Nevertheless, whether ManNAc could improve diabetic kidney damage by inhibiting podocyte pyroptosis remains unclear. This study aimed to explore the effect of ManNAc therapy on alleviating diabetic renal injury and podocyte pyroptosis, and its possible mechanism was also figured out. The male 8-week-old C57BL/6 mice were divided into three groups: control group, Streptozocin (STZ)-induced DN group, and ManNAc treated diabetic group. Then, the changes in renal function, renal histopathology, podocyte pyroptosis, reactive oxygen species (ROS), and mitochondrial dysfunction were measured. Herein, we observed that the upregulated expression of Angptl4 was involved in podocyte injury. ManNAc treatment ameliorated podocyte ultrastructure, renal function, and renal histopathology in STZ-induced DN mice. In addition, ManNAc administration attenuated podocyte cell death and suppressed the activation of Nucleotide leukin-rich polypeptide 3 (NLRP3), caspase-1, and interleukin-1β (IL-1β), and the cleavage of gasdermin-D (GSDMD). Moreover, ManNAc inhibited ROS production and restored mitochondrial morphology in vivo and vitro. Further, ManNAc administration significantly alleviated podocyte pyroptosis through inhibiting ROS/NLRP3 signaling pathway. Therefore, these results elucidated that the upregulated expression of Angptl4 was involved in podocyte injury and ManNAc treatment protected against podocyte pyroptosis via inhibiting mitochondrial injury and ROS/NLRP3 signaling pathway in DN mice.

Mesenchymal stem cells inhibited the apoptosis of alveolar epithelial cells caused by ARDS through CXCL12/CXCR4 axis

Mesenchymal stem cells (MSCs) have a wide range of anti-inflammatory and immunomodulatory effects and have been observed to have potential therapeutic potential in the clinical treatment of various diseases. We pretreated lung cancer cells A549 with tumor necrosis factor (TNF-α), knocked down the key chemokine receptor CXCR4 on MSCs using lentivirus, and induced acute respiratory distress syndrome (ARDS) mouse model using lipopolysaccharide (LPS) and CXCL12 expression in vivo by adeno-associated virus (AAV-rh10) infection in mice. By co-culturing the MSCs with A549 and in vivo experiments, we observed the effects of MSCs on cell biological functions after inflammatory stimulation, oxidative stress, and the amelioration of lung injury in ARDS mice. TNF-α inhibited A549 proliferation and promoted apoptosis, scorch death-related factor activity, and oxidative stress factor were increased and CXCL12 levels in the cell supernatant were decreased. The co-culture of MSCs was able to increase cell activity and decrease oxidative stress factor levels, and this effect was not present after the knockdown of CXCR4 in MSCs. In vivo transplantation of MSCs significantly attenuated lung injury in ARDS, inhibited serum pro-inflammatory factors in mice, and down-regulated expression of apoptotic and focal factors in lung tissues while blocking CXCR4 or CXCL12 lost the repairing effect of MSCs on ARDS lung tissues. After the co-culture of MSC and lung cancer cells, the expression of CXCR4 on the surface of lung cancer cells was significantly increased, and more CXCR4 and CXCL12 acted together to activate more pro-survival pathways and inhibit apoptosis induced by TNF-α.

Application of Regulatory Cell Death in Cancer: Based on Targeted Therapy and Immunotherapy

The development of cancer treatment methods is constantly changing. For common cancers, our treatment methods are still based on conventional treatment methods, such as chemotherapy, radiotherapy, and targeted drug therapy. Nevertheless, the emergence of tumor resistance has a negative impact on treatment. Regulated cell death is a gene-regulated mode of programmed cell death. After receiving specific signal transduction, cells change their physical and chemical properties and the extracellular microenvironment, resulting in structural destruction and decomposition. As research accumulates, we now know that by precisely inducing specific cell death patterns, we can treat cancer with less collateral damage than other treatments. Many newly discovered types of RCD are thought to be useful for cancer treatment. However, some experimental results suggest that some RCDs are not sensitive to cancer cell death, and some may even promote cancer progression. This review summarizes the discovered types of RCDs, reviews their clinical efficacy in cancer treatment, explores their anticancer mechanisms, and discusses the feasibility of some newly discovered RCDs for cancer treatment in combination with the immune and tumor microenvironment.

A Cycle of Inflammatory Adipocyte Death and Regeneration in Murine Adipose Tissue

Adipose tissue (AT) expands by a combination of two fundamental cellular mechanisms: hypertrophic growth of existing adipocytes or through generation of new adipocytes, also known as hyperplastic growth. Multiple lines of evidence suggest a limited capacity for hyperplastic growth of AT in adulthood and that adipocyte number is relatively stable, even with fluctuations in AT mass. If the adipocyte number is stable in adulthood, despite well-documented birth and death of adipocytes, then this would suggest that birth may be coupled to death in a regenerative cycle. To test this hypothesis, we examined the dynamics of birth of new fat cells in relationship to adipocyte death by using high-fidelity stable isotope tracer methods in C57Bl6 mice. We discovered birth of new adipocytes at higher frequency in histological proximity to dead adipocytes. In diet-induced obesity, adipogenesis surged after an adipocyte death peak beyond 8 weeks of high-fat feeding. Through transcriptional analyses of AT and fractionated adipocytes, we found that the dominant cell death signals were inflammasome related. Proinflammatory signals were particularly evident in hypertrophied adipocytes or with deletion of a constitutive oxygen sensor and inhibitor of hypoxia-inducible factor, Egln1. We leveraged the potential role for the inflammasome in adipocyte death to test the adipocyte death-birth hypothesis, finding that caspase 1 loss of function attenuated adipocyte death and birth in murine visceral AT. These data collectively point to a regenerative cycle of adipocyte death and birth as a driver of adipogenesis in adult murine AT.

Integrative Analysis of a Pyroptosis-Related Signature of Clinical and Biological Value in Multiple Myeloma

Purpose

Pyroptosis is an inflammation-based programmed cell death that holds great potential as a novel cancer therapeutic target in patients with multiple myeloma (MM). However, thus far, the function of pyroptosis-related genes (PRGs) in MM and their prognostic relevance remains undetermined.

Methods

The model was established by the LASSO analysis, based on the Gene Expression Omnibus (GEO) dabatase, and its efficacy was verified using two external datasets. The model’s predictive ability was assessed by the Kaplan-Meier survival and time-dependent receiver operating characteristic (ROC) curves. Finally, a nomogram was established for clinical application. We also confirmed the validity of our model using specimens and in vitro experiments.

Results

We established an 11-PRG signature profile, and verified its efficacy using two validation cohorts (VCs). In both cohorts, patients were separated into two subpopulations, according to their median risk scores (RS). Our analysis revealed that high-risk (HR) patients experienced considerably lower overall survival (OS), compared to the low-risk (LR) patients. Using functional enrichment and immune infiltration analyses, we demonstrated that the immunologic status was strongly related to RS. Furthermore, using a pyroptosis inhibitor Q-VD-OPh, we revealed that MM cell proliferation and progression was drastically suppressed and the doxorubicin (DOX)-induced apoptosis was reversed.

Conclusion

Based on our analysis, pyroptosis not only serves as a measure of MM treatment efficiency and patient prognosis, but is also a possible target for anti-MM therapy.

Crosstalk Between Pyroptosis and Apoptosis in Hepatitis C Virus-induced Cell Death

Extensive inflammation in the liver is known to contribute to the pathogenesis of hepatitis C virus (HCV) infection. Apoptosis has, for a long time, been known to act as a mechanism of hepatocyte death, but our previous research also identified inflammasome-mediated pyroptosis in infected and uninfected bystander cells as an additional mechanism of HCV-induced cytopathicity. The purpose of this study was to investigate the mechanism of HCV-induced cell death and to determine the timing and relative contributions of apoptosis and pyroptosis during HCV infection. In a model employing a cell culture-adapted strain of JFH-1 HCV and Huh-7.5 hepatocyte-like cells, we found that pyroptosis occurred earlier than did apoptosis during infection. CRISPR knockout of NLRP3 resulted in decreased caspase-1 activation, but not complete elimination, indicating multiple sensors are likely involved in HCV-induced pyroptosis. Knockout of gasdermin-D resulted in increased activation of apoptosis-related caspase-3, suggesting potential crosstalk between the two cell death pathways. An unexpected decrease in activated caspase-1 levels was observed when caspase-3 was knocked out, implying that caspase-3 may have a role in the initiation of pyroptosis, at least in the context of HCV infection. Lower viral titres in culture fluids and increased ratios of intracellular to extracellular levels of infectious virus were observed in knockout versus wild-type Huh-7.5 cells, suggesting that HCV may induce programmed cell death in order to enhance virus release from infected cells. These results contribute to the understanding of HCV pathogenesis and add to the increasing volume of literature suggesting various programmed cell death pathways are not mutually exclusive.

Nucleotide receptors mediate protection against neonatal sepsis and meningitis caused by alpha-hemolysin expressing Escherichia coli K1

Neonatal meningitis-associated Escherichia coli (NMEC) is among the leading causes of bacterial meningitis and sepsis in newborn infants. Several virulence factors have been identified as common among NMEC, and have been shown to play an important role in the development of bacteremia and/or meningitis. However, there is significant variability in virulence factor expression between NMEC isolates, and relatively little research has been done to assess the impact of variable virulence factor expression on immune cell activation and the outcome of infection. Here, we investigated the role of NMEC strain-dependent P2X receptor (P2XR) signaling on the outcome of infection in neonatal mice. We found that alpha-hemolysin (HlyA)-expressing NMEC (HlyA⁺ ) induced robust P2XR-dependent macrophage cell death in vitro, while HlyA^- NMEC did not. P2XR-dependent cell death was inflammasome independent, suggesting an uncoupling of P2XR and inflammasome activation in the context of NMEC infection. In vivo inhibition of P2XRs was associated with increased mortality in neonatal mice infected with HlyA⁺ NMEC, but had no effect on the survival of neonatal mice infected with HlyA^- NMEC. Furthermore, we found that P2XR-dependent protection against HlyA⁺ NMEC in vivo required macrophages, but not neutrophils or NLRP3. Taken together, these data suggest that HlyA⁺ NMEC activates P2XRs which in turn confers macrophage-dependent protection against infection in neonates. In addition, our findings indicate that strain-dependent virulence factor expression should be taken into account when studying the immune response to NMEC.

Innate Sensors Trigger Regulated Cell Death to Combat Intracellular Infection

Intracellular pathogens pose a significant threat to animals. In defense, innate immune sensors attempt to detect these pathogens using pattern recognition receptors that either directly detect microbial molecules or indirectly detect their pathogenic activity. These sensors trigger different forms of regulated cell death, including pyroptosis, apoptosis, and necroptosis, which eliminate the infected host cell niche while simultaneously promoting beneficial immune responses. These defenses force intracellular pathogens to evolve strategies to minimize or completely evade the sensors. In this review, we discuss recent advances in our understanding of the cytosolic pattern recognition receptors that drive cell death, including NLRP1, NLRP3, NLRP6, NLRP9, NLRC4, AIM2, IFI16, and ZBP1. Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The pyroptosis-related gene signature predicts prognosis and indicates immune activity in hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) remains one of the most common malignant tumors with poor survival. Pyroptosis is a kind of programmed cell death that can regulate the proliferation, invasion, and metastasis of tumor cells. However, the expression levels of pyroptosis-related genes (PRGs) in HCC and their relationship with prognosis are still unclear.

Methods

Our study identified 35 PRGs through bioinformatics analysis that were differentially expressed between tumor samples and nontumor samples. According to these differentially expressed genes, HCC patients could be divided into two groups, cluster 1 and cluster 2. The least absolute shrinkage and selection operator (LASSO) Cox regression method was performed to construct a 10-gene signature that classified HCC patients in the cancer genome atlas (TCGA) database into low-risk and high-risk groups.

Results

The results showed that the survival rate of HCC patients in the low-risk group was significantly higher than that in the high-risk group (p < 0.001). The validation cohort, the Gene Expression Omnibus (GEO) cohort, was divided into two risk groups based on the median risk score calculated by the TCGA cohort. The overall survival (OS) of the low-risk group was significantly better than that of the high-risk group (p = 0.007). Univariate and multivariate Cox regression analyses revealed that the risk score was an independent factor in predicting OS in HCC patients. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses showed that immune-related high-risk groups were rich in genes and had reduced immune status.

Conclusions

PRGs play a significant role in tumor immunity and have the potential capability to predict the prognosis of HCC patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00445-0.

Network modeling-based identification of the switching targets between pyroptosis and secondary pyroptosis

The newly identified cell death type, pyroptosis plays crucial roles in various diseases. Most recently, mounting evidence accumulates that pyroptotic signaling is highly correlated with coronavirus disease 2019 (COVID-19). Thus, understanding the induction of the pyroptotic signaling and dissecting the detail molecular control mechanisms are urgently needed. Based on recent experimental studies, a core regulatory model of the pyroptotic signaling is constructed to investigate the intricate crosstalk dynamics between the two cell death types, i.e., pyroptosis and secondary pyroptosis. The model well reproduces the experimental observations under different conditions. Sensitivity analysis determines that only the expression level of caspase-1 or GSDMD has the potential to individually change death modes. The decrease of caspase-1 or GSDMD level switches cell death from pyroptosis to secondary pyroptosis. Besides, eight biochemical reactions are identified that can efficiently switch death modes. While from the viewpoint of bifurcation analysis, the expression level of caspase-3 is further identified and twelve biochemical reactions are obtained. The coexistence of pyroptosis and secondary pyroptosis is predicted to be observed not only within the bistable range, but also within proper monostable range, presenting two potential different control mechanisms. Combined with the landscape theory, we further explore the stochastic dynamic and global stability of the pyroptotic system, accurately quantifying how each component mediates the individual occurrence probability of pyroptosis and secondary pyroptosis. Overall, this study sheds new light on the intricate crosstalk of the pyroptotic signaling and uncovers the regulatory mechanisms of various stable state transitions, providing potential clues to guide the development for prevention and treatment of pyroptosis-related diseases.

Benzimidazoles induce concurrent apoptosis and pyroptosis of human glioblastoma cells via arresting cell cycle

Glioblastoma multiforme (GBM) is the most malignant and lethal primary brain tumor in adults accounting for about 50% of all gliomas. The only treatment available for GBM is the drug temozolomide, which unfortunately has frequent drug resistance issue. By analyzing the hub genes of GBM via weighted gene co-expression network analysis (WGCNA) of the cancer genome atlas (TCGA) dataset, and using the connectivity map (CMAP) platform for drug repurposing, we found that multiple azole compounds had potential anti-GBM activity. When their anti-GBM activity was examined, however, only three benzimidazole compounds, i.e. flubendazole, mebendazole and fenbendazole, potently and dose-dependently inhibited proliferation of U87 and U251 cells with IC₅₀ values below 0.26 μM. Benzimidazoles (0.125-0.5 μM) dose-dependently suppressed DNA synthesis, cell migration and invasion, and regulated the expression of key epithelial-mesenchymal transition (EMT) markers in U87 and U251 cells. Benzimidazoles treatment also dose-dependently induced the GBM cell cycle arrest at the G₂/M phase via the P53/P21/cyclin B1 pathway. Furthermore, the drugs triggered pyroptosis of GBM cells through the NF-κB/NLRP3/GSDMD pathway, and might also concurrently induced mitochondria-dependent apoptosis. In a nude mouse U87 cell xenograft model, administration of flubendazole (12.5, 25, and 50 mg · kg^-1 · d^-1, i.p, for 3 weeks) dose-dependently suppressed the tumor growth without obvious adverse effects. Taken together, our results demonstrated that benzimidazoles might be promising candidates for the treatment of GBM.

GSDMD-mediated pyroptosis: a critical mechanism of diabetic nephropathy

Pyroptosis is a recently identified mechanism of programmed cell death related to Caspase-1 that triggers a series of inflammatory reactions by releasing several proinflammatory factors such as IL-1β and IL-18. The process is characterised by the rupture of cell membranes and the release of cell contents through the mediation of gasdermin (GSDM) proteins. GSDMD is an important member of the GSDM family and plays a critical role in the two pathways of pyroptosis. Diabetic nephropathy (DN) is a microvascular complication of diabetes and a major cause of end-stage renal disease. Recently, it was revealed that GSDMD-mediated pyroptosis plays an important role in the occurrence and development of DN. In this review, we focus on two types of kidney cells, tubular epithelial cells and renal podocytes, to illustrate the mechanism of pyroptosis in DN and provide new ideas for the prevention, early diagnosis and molecular therapy of DN.

Pathway network of pyroptosis and its potential inhibitors in acute kidney injury

Acute kidney injury (AKI) is a worldwide problem, and there is no effective drug to eliminate AKI. The death of renal cells is an important pathological basis of intrinsic AKI. At present, targeted therapy for TEC death is a research hotspot in AKI therapy. There are many ways of cell death involved in the occurrence and development of AKI, such as apoptosis, necrosis, ferroptosis, and pyroptosis. This article mainly focuses on the role of pyroptosis in AKI. The assembly and activation of NLRP3 inflammasome is a key event in the occurrence of pyroptosis, which is affected by many factors, such as the activation of the NF-κB signaling pathway, mitochondrial instability and excessive endoplasmic reticulum (ER) stress. The activation of NLRP3 inflammasome can trigger its downstream inflammatory cytokines, which will lead to pyroptosis and eventually induce AKI. In this paper, we reviewed the possible mechanism of pyroptosis in AKI and the potential effective inhibitors of various key targets in this process. It may provide potential therapeutic targets for novel intrinsic AKI therapies based on pyroptosis, so as to develop better therapeutic strategies.

Identification of an ASC oligomerization inhibitor for the treatment of inflammatory diseases

The ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD)) protein is an scaffold component of different inflammasomes, intracellular multiprotein platforms of the innate immune system that are activated in response to pathogens or intracellular damage. The formation of ASC specks, initiated by different inflammasome receptors, promotes the recruitment and activation of procaspase-1, thereby triggering pyroptotic inflammatory cell death and pro-inflammatory cytokine release. Here we describe MM01 as the first-in-class small-molecule inhibitor of ASC that interferes with ASC speck formation. MM01 inhibition of ASC oligomerization prevents activation of procaspase-1 in vitro and inhibits the activation of different ASC-dependent inflammasomes in cell lines and primary cultures. Furthermore, MM01 inhibits inflammation in vivo in a mouse model of inflammasome-induced peritonitis. Overall, we highlight MM01 as a novel broad-spectrum inflammasome inhibitor for the potential treatment of multifactorial diseases involving the dysregulation of multiple inflammasomes.

NLRP3/caspase-1/GSDMD-mediated pyroptosis exerts a crucial role in astrocyte pathological injury in mouse model of depression

Emerging evidence suggests that astrocyte loss is one of the most important pathological features in the hippocampus of patients with major depressive disorder (MDD) and depressive mice. Pyroptosis is a recently discovered form of programmed cell death depending on Caspase-gasdermin D (Casp-GSDMD), which is involved in multiple neuropsychiatric diseases. However, the involvement of pyroptosis in the onset of MDD and glial pathological injury remains obscure. Here, we observed that depressive mice showed astrocytic pyroptosis, which was responsible for astrocyte loss, and selective serotonin reuptake inhibitor (SSRI) treatment could attenuate the pyroptosis induced by the chronic mild stress (CMS) model. Genetic KO of GSDMD, Casp-1, and astrocytic NOD-like receptor protein 3 (NLRP3) inflammasome in mice alleviated depression-like behaviors and inhibited the pyroptosis-associated protein expression. In contrast, overexpression of astrocytic GSDMD-N-terminal domain (GSDMD-N) in the hippocampus could abolish the improvement of behavioral alterations in GSDMD-deficient mice. This work illustrates that targeting the NLRP3/Casp-1/GSDMD-mediated pyroptosis may provide potential therapeutic benefits to stress-related astrocyte loss in the pathogenesis of depression.

The Versatile Gasdermin Family: Their Function and Roles in Diseases

The gasdermin (GSDM) family, a novel group of structure-related proteins, consists of GSDMA, GSDMB, GSDMC, GSDMD, GSDME/DNFA5, and PVJK/GSDMF. GSDMs possess a C-terminal repressor domain, cytotoxic N-terminal domain, and flexible linker domain (except for GSDMF). The GSDM-NT domain can be cleaved and released to form large oligomeric pores in the membrane that facilitate pyroptosis. The emerging roles of GSDMs include the regulation of various physiological and pathological processes, such as cell differentiation, coagulation, inflammation, and tumorigenesis. Here, we introduce the basic structure, activation, and expression patterns of GSDMs, summarize their biological and pathological functions, and explore their regulatory mechanisms in health and disease. This review provides a reference for the development of GSDM-targeted drugs to treat various inflammatory and tissue damage-related conditions.

Inhibition of the NLRP3/IL-1β axis protects against sepsis-induced cardiomyopathy

BACKGROUND

Septic cardiomyopathy worsens the prognosis of critically ill patients. Clinical data suggest that interleukin-1β (IL-1β), activated by the NLRP3 inflammasome, compromises cardiac function. Whether or not deleting Nlrp3 would prevent cardiac atrophy and improve diastolic cardiac function in sepsis was unclear. Here, we investigated the role of NLRP3/IL-1β in sepsis-induced cardiomyopathy and cardiac atrophy.

METHODS

Male Nlrp3 knockout (KO) and wild-type (WT) mice were exposed to polymicrobial sepsis by caecal ligation and puncture (CLP) surgery (KO, n = 27; WT, n = 33) to induce septic cardiomyopathy. Sham-treated mice served as controls (KO, n = 11; WT, n = 16). Heart weights and morphology, echocardiography and analyses of gene and protein expression were used to evaluate septic cardiomyopathy and cardiac atrophy. IL-1β effects on primary and immortalized cardiomyocytes were investigated by morphological and molecular analyses. IonOptix and real-time deformability cytometry (RT-DC) analysis were used to investigate functional and mechanical effects of IL-1β on cardiomyocytes.

RESULTS

Heart morphology and echocardiography revealed preserved systolic (stroke volume: WT sham vs. WT CLP: 33.1 ± 7.2 μL vs. 24.6 ± 8.7 μL, P < 0.05; KO sham vs. KO CLP: 28.3 ± 8.1 μL vs. 29.9 ± 9.9 μL, n.s.; P < 0.05 vs. WT CLP) and diastolic (peak E wave velocity: WT sham vs. WT CLP: 750 ± 132 vs. 522 ± 200 mm/s, P < 0.001; KO sham vs. KO CLP: 709 ± 152 vs. 639 ± 165 mm/s, n.s.; P < 0.05 vs. WT CLP) cardiac function and attenuated cardiac (heart weight-tibia length ratio: WT CLP vs. WT sham: -26.6%, P < 0.05; KO CLP vs. KO sham: -3.3%, n.s.; P < 0.05 vs. WT CLP) and cardiomyocyte atrophy in KO mice during sepsis. IonOptix measurements showed that IL-1β decreased contractility (cell shortening: IL-1β: -15.4 ± 2.3%, P < 0.001 vs. vehicle, IL-1RA: -6.1 ± 3.3%, P < 0.05 vs. IL-1β) and relaxation of adult rat ventricular cardiomyocytes (time-to-50% relengthening: IL-1β: 2071 ± 225 ms, P < 0.001 vs. vehicle, IL-1RA: 564 ± 247 ms, P < 0.001 vs. IL-1β), which was attenuated by an IL-1 receptor antagonist (IL-1RA). RT-DC analysis indicated that IL-1β reduced cardiomyocyte size (P < 0.001) and deformation (P < 0.05). RNA sequencing showed that genes involved in NF-κB signalling, autophagy and lysosomal protein degradation were enriched in hearts of septic WT but not in septic KO mice. Western blotting and qPCR disclosed that IL-1β activated NF-κB and its target genes, caused atrophy and decreased myosin protein in myocytes, which was accompanied by an increased autophagy gene expression. These effects were attenuated by IL-1RA.

CONCLUSIONS

IL-1β causes atrophy, impairs contractility and relaxation and decreases deformation of cardiomyocytes. Because NLRP3/IL-1β pathway inhibition attenuates cardiac atrophy and cardiomyopathy in sepsis, it could be useful to prevent septic cardiomyopathy.

Jinwujiangu Capsule Treats Fibroblast-Like Synoviocytes of Rheumatoid Arthritis by Inhibiting Pyroptosis via the NLRP3/CAPSES/GSDMD Pathway

Jinwujiangu capsule (JWJGC) is a traditional Chinese medicine formula used to treat rheumatoid arthritis (RA). However, whether its mechanism is associated with pyroptosis remains unclear. In this study, the ability of JWJGC to inhibit the growth of fibroblast-like synoviocytes of RA (RA-FLS) through pyroptosis was evaluated. The cells isolated from patients with RA were identified by hematoxylin and eosin (H&E) staining, immunohistochemistry, and flow cytometry. After RA-FLS were treated with different concentrations of JWJGC-containing serum, the cell proliferation inhibition rate, expression of caspase-1/3/4/5, NOD-like receptor protein 3 (NLRP3), gasdermin-D (GSDMD), and apoptosis-associated speck-like protein containing a CARD (ASC), concentrations of interleukin-1β (IL-1β) and interleukin-18 (IL-18), the activity of lactic dehydrogenase (LDH), and pyroptosis were evaluated. The results showed that JWJGC increased the proliferative inhibition rate, decreased the expression of caspase-1/3/4/5, GSDMD, NLRP3, and ASC, suppressed the expression of IL-1β and IL-18, induced the activity of LDH, and downregulated the number of double-positive FITC anti-caspase-1 and PI. Generally, our findings suggest that JWJGC can regulate NLRP3/CAPSES/GSDMD in treating RA-FLS through pyroptosis.

FOXM1-activated SIRT4 inhibits NF-κB signaling and NLRP3 inflammasome to alleviate kidney injury and podocyte pyroptosis in diabetic nephropathy

Forkhead box M1 (FOXM1) has been reported to play a protective role against acute kidney injury by driving tubular regeneration. This study aims to probe the function of FOXM1 in diabetic nephropathy (DN) and the molecules involved. FOXM1 was poorly expressed in DN-diseased kidney tissues. A murine model of DN was established, and podocytes cells (MPC5) were treated with high-glucose (HG) for in vitro studies. FOXM1 overexpression improved kidney function and reduced pathological changes in mice, and it increased the expression of the podocyte marker Nephrin in kidney tissues. In vitro, FOXM1 increased viability and reduced pyroptosis of the HG-treated MPC5 cells, and it elevated the expression of the podocyte marker Nephrin whereas reduced the expression of pyroptosis-related NLRP3 inflammasome and cleaved caspase 1. FOXM1 bound to the promoter of sirtuin 4 (SIRT4) to induce transcriptional activation. Downregulation of SIRT4 blocked the protective roles of FOXM1 both in vivo and in vitro. Phosphorylation of nuclear factor-kappa B (NF-κB) in HG-treated cells was suppressed by FOXM1 but restored after SIRT4 inhibition. In conclusion, this study suggested that FOXM1 transcriptionally activates SIRT4 and inhibits NF-κB signaling and the NLRP3 inflammasome to alleviate kidney injury and podocyte pyroptosis in DN.

Gasdermin D Is a Novel Prognostic Biomarker and Relates to TMZ Response in Glioblastoma

The gasdermin (GSDM) family act as executioners during pyroptosis. However, its expression and biological role in glioma remain to be determined. This study carried out gene expression from six public datasets. Westerns blots and immunohistochemistry (IHC) staining were employed to examine GSDM expression in glioma in an in-house cohort. Kaplan-Meier and Cox regression analyses were performed to evaluate the prognostic role of GSDMs in glioma. Association between gene expression and immune infiltration was assessed by IHC and immunofluorescence (IF) staining of tissue sections. TMZ-induced pyroptosis was assessed by observation of morphological changes, WB and ELISA detection. Only GSDMD expression was upregulated in glioma compared with nontumor brain tissues both in the public datasets and in-house cohort. High GSDMD expression was significantly associated with WHO grade IV, IDH 1/2 wild-type and mesenchymal subtypes. Besides, high GSDMD expression was associated with shorter overall survival and could be used as an independent risk factor for poor outcomes in LGG and GBM. GO enrichment analysis and IHC validation revealed that GSDMD expression might participate in regulating macrophage infiltration and polarization. TMZ treatment induced the pyroptosis in GBM cells and GSDMD expression increased with after treating with TMZ in a time-dependent manner. Moreover, knocking down GSDMD obviously decreased IL-1β expression and reduced TMZ-induced pyroptosis in in vitro. GSDMD was a novel prognostic biomarker, as well as TMZ-treatment response marker in glioma.

Tyrosine phosphorylation of NLRP3 by the Src family kinase Lyn suppresses the activity of the NLRP3 inflammasome

[Figure: see text].

NLRC4 inflammasome-dependent cell death occurs by a complementary series of three death pathways and determines lethality in mice

Inflammasome is an innate immune defense mechanism, but its overactivation can lead to host death. Here, we show that cell death dictates mouse death caused by NLRC4 inflammasome overactivation. To execute NLRC4-dependent cell death, three death pathways complement each other in a specific order: Pyroptosis pathway requiring caspase-1 and GSDMD is the default path; impairment of it initiates ASC-mediated caspase-8–dependent apoptosis; when these two pathways are blocked, caspase-1 triggers intrinsic apoptotic pathway. Blocking one or two of these death pathways inhibits induction of various cytokines and lipid mediators, but mice still succumb, and only genetic deletions that block all death paths prevent NLRC4-mediated cell death, tissue damage, and mice death. In addition, infection of nonpropagative Salmonella-caused mice death is attenuated by blocking these death pathways. Thus, to reduce the lethality of infection-related diseases, preventing cell death might be necessary when propagation of infected pathogen was controlled by other means.

The miR-223-3p Regulates Pyroptosis Through NLRP3-Caspase 1-GSDMD Signal Axis in Periodontitis

Salivary exosomes contain various components and may play important roles in oral diseases. The purpose of this study was to verify the possible function of miR-223-3p from salivary exosomes in periodontitis. We isolated the salivary exosomes and found that the miR-223-3p content of salivary exosomes from periodontitis was less than the healthy control. Furthermore, we performed dual-luciferase reporter assay and real-time PCR to verify that (NOD)-like receptor (NLR) pyrin domain-containing 3 (NLRP3) was the target of miR-223-3p. When we knocked down the miR-223-3p expression in THP-1-derived macrophages, the expression of NLRP3 and the downstream inflammatory mediators interleukin-1β (IL-1β) and IL-6 were upregulated. By using integrated bioinformatics analysis, we found that pyroptosis and cytokine secretion participated in inflammatory gingival tissues. In addition, NLRP3, and the pyroptosis executioner, gasdermin D (GSDMD) was highly active in inflammatory gingival tissues compared with healthy controls by western blotting and immunohistochemistry. In summary, we speculated that miR-223-3p in salivary exosomes might regulate GSDMD-mediated pyroptosis by targeting NLRP3 in periodontitis. Detection of miR-223-3p expression in salivary exosomes could be used as an important non-invasive method to diagnose and evaluate the severity of periodontitis.

Mafenide derivatives inhibit neuroinflammation in Alzheimer's disease by regulating pyroptosis

The main mechanism of pyroptosis is Caspase‐1–mediated GSDMD cleavage, and GSDMD is also the executive protein of pyroptosis. Our previous study has shown that mafenide can inhibit pyroptosis by inhibiting the GSDMD‐Asp275 site to suppress cleavage. In this study, sulfonamide was used as the parent nucleus structure to synthesize sulfa‐4 and sulfa‐20. Screening of drug activity in the pyroptosis model of BV2 and iBMDM cell lines revealed the efficacy of five compounds were superior to mafenide, which exerted a better inhibitory effect on the occurrence of pyroptosis. For in vivo assay, Sulfa‐4 and Sulfa‐22 were intervened in the neuroinflammation APP/PS1 mice. As a result, the administration of Sulfa‐4 and Sulfa‐22 could significantly inhibit the activation of microglia, decrease the expression of inflammatory factors in the central nervous system and simultaneously suppress the production of p30‐GSDMD as well as the expression of upstream NLRP3 inflammasome and Caspase‐1 protein. Immunoprecipitation and Biotin‐labelled assay confirmed the targeted binding relationship of Sulfa‐4 and Sulfa‐22 with GSDMD protein in the iBMDM model in vitro. In this study, we investigated a new type inhibitor of GSDMD cleavage, which exerted a good inhibitory effect on pyroptosis and provided new references for the development of inflammatory drugs in the future.

N-salicyloyl tryptamine derivatives as potential therapeutic agents for Alzheimer's disease with neuroprotective effects

Alzheimer's disease (AD) has become a serious threat to the developed nations with burgeoning patients and annual costs on health care system in modern society. Neuroinflammation, as one of the specific biochemical factors in the progress of neurodegeneration diseases, performs a crucial role in the pathogenesis and development of AD. Therefore, it is of great significance to develop effective anti-neuroinflammatory strategies for the treatment of AD. N-salicyloyl tryptamine derivatives were previously reported and demonstrated that possessed great potential anti-neuroinflammatory effects and favorable blood-brain barrier (BBB) permeation. Herein, a series of novel N-salicyloyl tryptamine derivatives were synthesized and their anti-AD potential was evaluated both in vitro and in vivo. Among them, L7 performed well anti-neuroinflammatory effects and excellent neuroprotective effects, as well as little toxicity. To lucubrate its potential for the treatment of AD, behavior tests including morris water maze (MWM), eight-arm radial maze, open field test and novel object recognition (NOR) test were carried out and the results showed that L7 could remarkably improve Aβ-induced cognitive impairment. Moreover, the mechanism of action of L7 on improving Aβ-induced AD was preliminarily investigated, and the results uncovered that the neuroprotective effects of L7 was might exerte via intervening Aβ-induced pyroptosis through NLRP3-caspase-1-GSDMD axis and ameliorating neuronal apoptosis by mitochondrial apoptosis pathway. Besides, the distribution of Aβ plaques in brain tissues were detected by immunohistochemical (IHC) assay and the results indicated that L7 could significantly attenuate the deposition of Aβ plaques in the brain.

N-acetyl-L-tryptophan attenuates hepatic ischemia-reperfusion injury via regulating TLR4/NLRP3 signaling pathway in rats

The aim of this study was to investigate the changes of TLR4/NLRP3 signal during hepatic ischemia-reperfusion injury (HIRI) and to verify whether N-acetyl-L-tryptophan (L-NAT) protected hepatocytes by regulating the activation of TLR4/NLRP3 signal. We have established the rat HIRI model and H₂O₂-induced cell damage model to simulate ischemia-reperfusion injury and detect the corresponding indicators. Compared with the sham group, Suzuki score and the level of serum ALT increased after HIRI, accompanied by an increased expression of NLRP3, ASC, Caspase-1, IL-1β, TLR4, and NF-κB. While L-NAT pretreatment reversed the above-mentioned changes. Compared with the control group, cells in the H₂O₂ treated group became smaller in cell volume and round in shape with unclear boundaries. Similar to the phenotypes in vivo, H₂O₂ treatment also induced significant increase in expression of pyroptosis-related proteins (NLRP3, ASC, Caspase-1 and IL-1β) and inflammatory factors (TLR4 and NF-κB). While L-NAT pretreatment attenuated injuries caused by H₂O₂. In conclusion, the present findings demonstrate that L-NAT alleviates HIRI by regulating activation of NLRP3 inflammasome, which may be related to the TLR4/NF-κB signaling pathway.

Inhibition of NLRP3 inflammasome activation and pyroptosis with the ethyl acetate fraction of Bungeanum ameliorated cognitive dysfunction in aged mice

Zanthoxylum bungeanum Maxim (Rutaceae), a medicinal herb and foodstuff, has previously been demonstrated as useful for the potential prevention of age-related cognitive dysfunction. However, the mechanisms and material basis remain elusively understood. The prevention of cognitive impairment by four fractions of Z. bungeanum was evaluated in d-galactose-induced aging mice, including petroleum ether (PE), methylene chloride (DCM), ethyl acetate (EA), and n-butanol (N-BAI). The results showed that mice treated with EA and N-BAI had significantly alleviated d-galactose-induced memory deficit. In addition, EA could clearly protect neurons from cell death, alleviate oxidative damage and inhibit the activation of microglia in aging mice. Our data also showed that the activation of the NLRP3 inflammasome, the expression of pyroptosis-related proteins, and the release of IL-1β and IL-18 could be remarkably inhibited by the EA fraction in aging mice and LPS/ATP-induced BV-2 microglial cells. Besides, the chemical composition of an active EA fraction was qualitatively analyzed by using HPLC-MS/MS. Thirty-four compounds were tentatively identified based on their retention times, accurate mass, and MS/MS spectra. Moreover, eighteen reference compounds were analyzed by HPLC-MS/MS and their contents of EA were determined. The work demonstrated that the ethyl acetate fraction of Bungeanum ameliorated cognitive deficits, and its effects may be related to ameliorating oxidative stress and suppressing the NLRP3 inflammasome pathway and GSDMD-mediated pyroptosis in aging mice.

Gasdermin E-mediated programmed cell death: An unpaved path to tumor suppression

Hearing loss-associated protein gasdermin E (GSDME), an effector of secondary necrosis, has been identified in a new pathway of programmed cell death (PCD). GSDME epigenetic silencing and mutations resulting in loss-of-function have been reported in cancer tissues. Additionally, GSDME upregulation inhibits tumor proliferation as well as colony forming ability, and reduces the incidence of lymphatic metastasis, demonstrating that GSDME may act as a tumor suppressor. Here, we have focused on the molecular mechanisms of GSDME-mediated PCD, and tried to reveal the crosstalk between this cell death pathway and apoptosis, autophagy, GSDMD-mediated pyroptosis. Moreover, we concluded the anti-cancer activity of GSDME include forming permeable membranes, and triggering anti-cancer immunity. Thus, GSDME was potential to be a novel target for cancer prevention and treatment.

Identification of the pyroptosis‑related prognostic gene signature and the associated regulation axis in lung adenocarcinoma

Lung adenocarcinoma (LUAD) remains the most common deadly disease and has a poor prognosis. Pyroptosis could regulate tumour cell proliferation, invasion, and metastasis, thereby affecting the prognosis of cancer patients. However, the role of pyroptosis-related genes (PRGs) in LUAD remains unclear. In our study, comprehensive bioinformatics analysis was performed to construct a prognostic gene model and ceRNA network. The correlations between PRGs and tumour-immune infiltration, tumour mutation burden, and microsatellite instability were evaluated using Pearson’s correlation analysis. A total of 23 PRGs were upregulated or downregulated in LUAD. The genetic mutation variation landscape of PRG in LUAD was also summarised. Functional enrichment analysis revealed that these 33 PRGs were mainly involved in pyroptosis, the NOD-like receptor signalling pathway, and the Toll-like receptor signalling pathway. Prognosis analysis indicated a poor survival rate in LUAD patients with low expression of NLRP7, NLRP1, NLRP2, and NOD1 and high CASP6 expression. A prognostic PRG model constructed using the above five prognostic genes could predict the overall survival of LUAD patients with medium-to-high accuracy. Significant correlation was observed between prognostic PRGs and immune-cell infiltration, tumour mutation burden, and microsatellite instability. A ceRNA network was constructed to identify a lncRNA KCNQ1OT1/miR-335-5p/NLRP1/NLRP7 regulatory axis in LUAD. In conclusion, we performed a comprehensive bioinformatics analysis and identified a prognostic PRG signature containing five genes (NLRP7, NLRP1, NLRP2, NOD1, and CASP6) for LUAD patients. Our results also identified a lncRNA KCNQ1OT1/miR-335-5p/NLRP1/NLRP7 regulatory axis, which may also play an important role in the progression of LUAD. Further study needs to be conducted to verify this result.

Jiangzhi Ligan Decoction Inhibits GSDMD-Mediated Canonical/Noncanonical Pyroptosis Pathways and Alleviates High-Fat Diet-Induced Nonalcoholic Fatty Liver Disease

Increasing evidence suggests that gasdermin D (GSDMD) mediated pyroptosis signaling pathways play a vital role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Jiangzhi Ligan Decoction (JZLGD) has been verified to prevent NAFLD, but its specific mechanism has not been determined. In this study, an NAFLD model was established in Sprague-Dawley rats by a high-fat diet (HFD). After 12 weeks, JZLGD was orally administered once a day for 6 additional weeks. We investigated the effects of JZLGD on NAFLD rats and determined the GSDMD pathway-associated proteins to explore whether such effects were associated with pyroptosis. Our data show that JZLGD significantly reduced the liver index; improved serum lipid levels, liver function parameters, and lipid droplet content; and relieved NAFLD. We further found that the serum levels of the proinflammatory factors interleukin-1β (IL-1β), IL-18, tumor necrosis factor-α, and IL-6 were obviously decreased in the JZLGD group. HFD rats treated with GSDMD exhibited NLRP3, caspase-1, lipopolysaccharide (LPS), and caspase-11 activation; however, these effects were blunted by JZLGD treatment. Taken together, JZLGD may exert hepatoprotective effects against NAFLD in a rat HFD model by regulating GSDMD-mediated canonical/noncanonical pyroptosis pathways.

Pro-inflammatory effects of human apatite crystals extracted from patients suffering from calcific tendinopathy

BACKGROUND

Calcific tendonitis of the rotator cuff is due to carbonated apatite deposits in the shoulder tendons. During the evolution of the disease, an acute inflammatory episode may occur leading to the disappearance of the calcification. Although hydroxyapatite crystal-induced inflammation has been previously studied with synthetic crystals, no data are available with calcifications extracted from patients suffering from calcific tendinopathy. The objective of the study was to explore the inflammatory properties of human calcifications and the pathways involved.

METHODS

Human calcifications and synthetic hydroxyapatite were used in vitro to stimulate human monocytes and macrophages, the human myeloid cell line THP-1, and human tenocytes. The release of IL-1β, IL-6, and IL-8 by cells was quantified by ELISA. The gene expression of pro- and anti-inflammatory cytokines was evaluated by quantitative PCR. NF-kB activation and NLRP3 involvement were assessed in THP-1 cells using a NF-kB inhibitor and a caspase-1 inhibitor. The inflammatory properties were then assessed in vivo using a mouse air pouch model.

RESULTS

Human calcifications were able to induce a significant release of IL-1β when incubated with monocytes, macrophages, and THP-1 only if they were first primed with LPS (monocytes and macrophages) or PMA (THP-1). Stimulation of THP-1 by human calcifications led to similar levels of IL-1β when compared to synthetic hydroxyapatite although these levels were significantly inferior in monocytes and macrophages. The patient's crystals enhanced mRNA expression of pro-IL-1β, as well as IL-18, NF-kB, and TGFβ when IL-6 and TNFα expression were not. IL-1β production was reduced by the inhibition of caspase-1 indicating the role of NLRP3 inflammasome. In vivo, injection of human calcifications or synthetic hydroxyapatite in the air pouch led to a significant increase in membrane thickness although significant overexpression of IL-1β was only observed for synthetic hydroxyapatite.

CONCLUSIONS

As synthetic hydroxyapatite, human calcifications were able to induce an inflammatory response resulting in the production of IL-1β after NF-kB activation and through NLRP3 inflammasome. In some experiments, IL-1β induction was lower with human calcifications compared to synthetic apatite. Differences in size, shape, and protein content may explain this observation.

Targeting RIP Kinases in Chronic Inflammatory Disease

Chronic inflammatory disorders are characterised by aberrant and exaggerated inflammatory immune cell responses. Modes of extrinsic cell death, apoptosis and necroptosis, have now been shown to be potent drivers of deleterious inflammation, and mutations in core repressors of these pathways underlie many autoinflammatory disorders. The receptor-interacting protein (RIP) kinases, RIPK1 and RIPK3, are integral players in extrinsic cell death signalling by regulating the production of pro-inflammatory cytokines, such as tumour necrosis factor (TNF), and coordinating the activation of the NOD-like receptor protein 3 (NLRP3) inflammasome, which underpin pathological inflammation in numerous chronic inflammatory disorders. In this review, we firstly give an overview of the inflammatory cell death pathways regulated by RIPK1 and RIPK3. We then discuss how dysregulated signalling along these pathways can contribute to chronic inflammatory disorders of the joints, skin, and gastrointestinal tract, and discuss the emerging evidence for targeting these RIP kinases in the clinic.

Advanced research on the regulated necrosis mechanism in myocardial ischemia-reperfusion injury

Myocardial ischemia-reperfusion injury is an important factor that seriously affects the prognosis of patients with myocardial infarction. It can cause myocardial stun, no-reflow phenomenon, reperfusion arrhythmia, and even irreversible cardiomyocyte death. Regulated necrosis is a newly discovered type of regulatory cell death that is different from apoptosis, including necroptosis, pyrolysis, iron death and other forms. Regulated necrosis plays an important role in myocardial infarction, heart failure and other cardiovascular diseases, as well as myocardial ischemia-reperfusion injury and other pathophysiological processes, and is expected to become a new target for intervention in this type of disease.

Emerging mechanisms of immunocoagulation in sepsis and septic shock

Sepsis and septic shock driven by microbial infections are still among the most challenging health problems, causing 11 million deaths worldwide every year. How does the host's response to pathogen infections effectively restore homeostasis instead of precipitating pathogenic and potentially fatal feedforward reactions? Recently, there have been significant new advances in our understanding of the interface between mammalian immunity and coagulation ('immunocoagulation') and its impact on sepsis. In particular, the release and activation of F3 (the main initiator of coagulation) from and on myeloid or epithelial cells is facilitated by activating inflammasomes and consequent gasdermin D (GSDMD)-mediated pyroptosis, coupled to signaling via high mobility group box 1 (HMGB1), stimulator of interferon response CGAMP interactor 1 (STING1), or sequestosome 1 (SQSTM1). Pharmacological modulation of the immunocoagulation pathways emerge as novel and potential therapeutic strategies for sepsis.

Chaihu-Longgu-Muli Decoction exerts an antiepileptic effect in rats by improving pyroptosis in hippocampal neurons

ETHNOPHARMACOLOGICAL RELEVANCE

Chaihu-Longgu-Muli Decoction (CLMD) is a classic prescription created by Zhong-jing Zhang, a famous ancient Chinese medical scientist, to harmonize uncontrollable body activities and calm the minds. Now Traditional Chinese Medicine (TCM) physicians often apply it to treat psychiatric diseases such as epilepsy.

AIM OF THE STUDY

This study investigated the mechanism of the effect of Chaihu-Longgu-Muli Decoction (CLMD) on hippocampal neurons pyroptosis in rats with Temporal Lobe Epilepsy (TLE).

MATERIALS AND METHODS

The lithium chloride-pilocarpine-induced TLE rat model was established. The behavioral testing was performed and, the expression of IL-1β and TNF-α in serum was detected by ELISA, qRT-PCR was used to detect the mRNA expression of NLRP3, Caspase-1, IL-1β and TNF-α in hippocampus. The expression of NLRP3 and Caspase-1 in hippocampal dentate gyrus was detected by immunofluorescence assay.

RESULTS

CLMD could significantly suppress the frequency and duration time of epileptic seizures, reduce the expression of NLRP3, Caspase-1 TNF-α and IL-1β.

CONCLUSIONS

CLMD exerted an obvious antiepileptic effect by improving pyroptosis in hippocampal neurons of TLE rats.

Gasdermin E permits interleukin-1 beta release in distinct sublytic and pyroptotic phases

Cellular inflammasome activation causes caspase-1 cleavage of the pore-forming protein gasdermin D (GSDMD) with subsequent pyroptotic cell death and cytokine release. Here, we clarify the ambiguous role of the related family member gasdermin E (GSDME) in this process. Inflammasome stimulation in GSDMD-deficient cells led to apoptotic caspase cleavage of GSDME. Endogenous GSDME activation permitted sublytic, continuous interleukin-1β (IL-1β) release and membrane leakage, even in GSDMD-sufficient cells, whereas ectopic expression led to pyroptosis with GSDME oligomerization and complete liberation of IL-1β akin to GSDMD pyroptosis. We find that NLRP3 and NLRP1 inflammasomes ultimately rely concurrently on both gasdermins for IL-1β processing and release separately from their ability to induce cell lysis. Our study thus identifies GSDME as a conduit for IL-1β release independent of its ability to cause cell death.

Pyroptosis executive protein GSDMD as a biomarker for diagnosis and identification of Alzheimer's disease

OBJECTIVE

This study was mainly conducted to explore the expression changes of GSDMD and conventional markers (including T-Tau, Tau181p, and Aβ_1-42 ) in the cerebrospinal fluid among patients with Alzheimer's disease (AD) and vascular dementia (VD), followed by determination of role of GSDMD in diagnosing and identifying AD and VD.

METHODS

In this study, 60 patients with VD, 60 patients with AD, and 50 healthy controls were enrolled. Lumbar puncture was performed to collect cerebrospinal fluid samples. Patients with VD and patients with AD were evaluated using the Mini-Mental State Examination (MMSE) scale, Montreal Cognitive Assessment (MoCA) scale, Clinical Dementia Rating (CDR) scale, Activity of Daily Living (ADL) scale, and Neuropsychiatric Inventory (NPI) questionnaire, aiming to determine the behavioral ability of patients. ELISA kit was purchased to determine the levels of GSDMD, T-Tau, Tau181p, and Aβ_1-42 in cerebrospinal fluid, and the expression of inflammatory factors, IL-1β and IL-6, was also detected.

RESULTS

(1) The levels of GSDMD, T-Tau, and Tau181p in the cerebrospinal fluid were higher in patients with AD than those of patients with VD and healthy controls, while the levels of Aβ_1-42 in the cerebrospinal fluid were lower in patients with AD than that in healthy controls and patients with VD. (2) GSDMD had good diagnostic accuracy in AD. Additionally, GSDMD, T-Tau, Tau181p, and Aβ_1-42 had good discrimination accuracy in distinguishing AD and VD. (3) The expression levels of inflammatory factors (IL-1β and IL-6) in cerebrospinal fluid were higher in patients with AD than those of healthy controls and patients with VD, which were positively correlated with GSDMD expression.

CONCLUSION

The expression of GSDMD was increased in patients with AD, which could be used as a biomarker for AD diagnosis and identification from VD.

Inflammasomes and adaptive immune responses

A fundamental concept in immunology is that the innate immune system initiates or instructs downstream adaptive immune responses. Inflammasomes are central players in innate immunity to pathogens, but how inflammasomes shape adaptive immunity is complex and relatively poorly understood. Here we highlight recent work on the interplay between inflammasomes and adaptive immunity. We address how inflammasome-dependent release of cytokines and antigen activates, shapes or even inhibits adaptive immune responses. We consider how distinct tissue or cellular contexts may alter the effects of inflammasome activation on adaptive immunity and how this contributes to beneficial or detrimental outcomes in infectious diseases, cancer and autoimmunity. We aspire to provide a framework for thinking about inflammasomes and their connection to the adaptive immune response.

Non-canonical Caspase-1 Signaling Drives RIP2-Dependent and TNF-α-Mediated Inflammation In Vivo

Pro-inflammatory caspase-1 is a key player in innate immunity. Caspase-1 processes interleukin (IL)-1β and IL-18 to their mature forms and triggers pyroptosis. These caspase-1 functions are linked to its enzymatic activity. However, loss-of-function missense mutations in CASP1 do not prevent autoinflammation in patients, despite decreased IL-1β production. In vitro data suggest that enzymatically inactive caspase-1 drives inflammation via enhanced nuclear factor κB (NF-κB) activation, independent of IL-1β processing. Here, we report two mouse models of enzymatically inactive caspase-1-C284A, demonstrating the relevance of this pathway in vivo. In contrast to Casp1^-/- mice, caspase-1-C284A mice show pronounced hypothermia and increased levels of the pro-inflammatory cytokines tumor necrosis factor alpha (TNF-α) and IL-6 when challenged with lipopolysaccharide (LPS). Caspase-1-C284A signaling is RIP2 dependent and mediated by TNF-α but independent of the NLRP3 inflammasome. LPS-stimulated whole blood from patients carrying loss-of-function missense mutations in CASP1 secretes higher amounts of TNF-α. Taken together, these results reveal non-canonical caspase-1 signaling in vivo.

Guidelines for Regulated Cell Death Assays: A Systematic Summary, A Categorical Comparison, A Prospective

Over the past few years, the field of regulated cell death continues to expand and novel mechanisms that orchestrate multiple regulated cell death pathways are being unveiled. Meanwhile, researchers are focused on targeting these regulated pathways which are closely associated with various diseases for diagnosis, treatment, and prognosis. However, the complexity of the mechanisms and the difficulties of distinguishing among various regulated types of cell death make it harder to carry out the work and delay its progression. Here, we provide a systematic guideline for the fundamental detection and distinction of the major regulated cell death pathways following morphological, biochemical, and functional perspectives. Moreover, a comprehensive evaluation of different assay methods is critically reviewed, helping researchers to make a reliable selection from among the cell death assays. Also, we highlight the recent events that have demonstrated some novel regulated cell death processes, including newly reported biomarkers (e.g., non-coding RNA, exosomes, and proteins) and detection techniques.

Cadmium and molybdenum co-induce pyroptosis via ROS/PTEN/PI3K/AKT axis in duck renal tubular epithelial cells

Cadmium (Cd) and excess molybdenum (Mo) are harmful to animals, but the combined nephrotoxic mechanism of Cd and Mo in duck remains poorly elucidated. To assess joint effects of Cd and Mo on pyroptosis via ROS/PTEN/PI3K/AKT axis in duck renal tubular epithelial cells, cells were cultured with 3CdSO₄·8H₂O (4.0 μM), (NH₄)₆Mo₇O₂₄·4H₂O (500.0 μM), MCC950 (10.0 μM), BHA (100.0 μM) and combination of Cd and Mo or Cd, Mo and MCC950 or Cd, Mo and BHA for 12 h, and the joint cytotoxicity was explored. The results manifested that toxicity of non-equitoxic binary mixtures of Mo and Cd exhibited synergic interaction. Mo or/and Cd elevated ROS level, PTEN mRNA and protein levels, and decreased PI3K, AKT and p-AKT expression levels. Simultaneously, Mo or/and Cd upregulated ASC, NLRP3, NEK7, Caspase-1, GSDMA, GSDME, IL-18 and IL-1β mRNA levels and Caspase-1 p20, NLRP3, ASC, GSDMD protein levels, increased the percentage of pyroptotic cells, LDH, NO, IL-18 and IL-1β releases as well as relative conductivity. Moreover, NLRP3 inhibitor MCC950 and ROS scavenger BHA could ameliorate the above changed factors induced by Mo and Cd co-exposure. Collectively, our results reveal that combination of Mo and Cd synergistically cause oxidative stress and trigger pyroptosis via ROS/PTEN/PI3K/AKT axis in duck tubular epithelial cells.

Role of pyroptosis in spinal cord injury and its therapeutic implications

BACKGROUND

Currently, spinal cord injury (SCI) is a pathological incident that triggers several neuropathological conditions, leading to the initiation of neuronal damage with several pro-inflammatory mediators' release. However, pyroptosis is recognized as a new programmed cell death mechanism regulated by the stimulation of caspase-1 and/or caspase-11/-4/-5 signaling pathways with a series of inflammatory responses.

AIM

Our current review concisely summarizes the potential role of pyroptosis-regulated programmed cell death in SCI, according to several molecular and pathophysiological mechanisms. This review also highlights the targeting of pyroptosis signaling pathways and inflammasome components and its therapeutic implications for the treatment of SCI.

KEY SCIENTIFIC CONCEPTS

Multiple pieces of evidence have illustrated that pyroptosis plays significant roles in cell swelling, plasma membrane lysis, chromatin fragmentation and intracellular pro-inflammatory factors including IL-18 and IL-1β release. In addition, pyroptosis is directly mediated by the recently discovered family of pore-forming protein known as GSDMD. Current investigations have documented that pyroptosis-regulated cell death plays a critical role in the pathogenesis of multiple neurological disorders as well as SCI. Our narrative article suggests that inhibiting the pyroptosis-regulated cell death and inflammasome components could be a promising therapeutic approach for the treatment of SCI in the near future.

Streptococcus pyogenes M1T1 Variants Induce an Inflammatory Neutrophil Phenotype Including Activation of Inflammatory Caspases

Invasive infections due to group A Streptococcus (GAS) advance rapidly causing tissue degradation and unregulated inflammation. Neutrophils are the primary immune cells that respond to GAS. The neutrophil response to GAS was characterised in response to two M1T1 isolates; 5448 and animal passaged variant 5448AP. Co-incubation of neutrophils with 5448AP resulted in proliferation of GAS and lowered the production of reactive oxygen species when compared with 5448. Infection with both strains invoked neutrophil death, however apoptosis was reduced in response to 5448AP. Both strains induced neutrophil caspase-1 and caspase-4 expression in vitro, with inflammatory caspase activation detected in vitro and in vivo. GAS infections involving strains such as 5448AP that promote an inflammatory neutrophil phenotype may contribute to increased inflammation yet ineffective bacterial eradication, contributing to the severity of invasive GAS infections.

Fueling the Fire: Inflammatory Forms of Cell Death and Implications for Cancer Immunotherapy

Unleashing the immune system with immune checkpoint inhibitors (ICI) has significantly improved overall survival for subsets of patients with stage III/IV cancer. However, many tumors are nonresponsive to ICIs, in part due to a lack of tumor-infiltrating lymphocytes (TIL). Converting these immune "cold" tumors to "hot" tumors that are thus more likely to respond to ICIs is a major obstacle for cancer treatment. Triggering inflammatory forms of cell death, such as necroptosis and pyroptosis, may alter the tumor immune microenvironment and the influx of TILs. We present an emerging view that promoting tumor-localized necroptosis and pyroptosis may ultimately enhance responses to ICI. SIGNIFICANCE: Many tumor types respond poorly to ICIs or respond but subsequently acquire resistance. Effective therapies for ICI-nonresponsive tumors are lacking and should be guided by evidence from preclinical studies. Promoting inflammatory cell death mechanisms within the tumor may alter the local immune microenvironment toward an ICI-responsive state.

The intricate biophysical puzzle of caspase-1 activation

This review takes a closer look at the structural components of the molecules involved in the processes leading to caspase-1 activation. Interleukins 1β and 18 (IL-1β, IL-18) are well-known proinflammatory cytokines that are produced following cleavage of their respective precursor proteins by the cysteine protease caspase-1. Active caspase-1 is the final step of the NLRP3 inflammasome, a three-protein intracellular complex involved in inflammation and induction of pyroptosis (a proinflammatory cell-death process). NLRP3 activators facilitate assembly of the inflammasome complex and subsequent activation of caspase-1 by autoproteolysis. However, the definitive structural components of active caspase-1 are still unclear and new data add to the complexity of this process. This review outlines the historical and recent findings that provide supporting evidence for the structural aspects of caspase-1 autoproteolysis and activation.

Gasdermin D restricts Burkholderia cenocepacia infection in vitro and in vivo

Burkholderia cenocepacia (B. cenocepacia) is an opportunistic bacterium; causing severe life threatening systemic infections in immunocompromised individuals including cystic fibrosis patients. The lack of gasdermin D (GSDMD) protects mice against endotoxin lipopolysaccharide (LPS) shock. On the other hand, GSDMD promotes mice survival in response to certain bacterial infections. However, the role of GSDMD during B. cenocepacia infection is not yet determined. Our in vitro study shows that GSDMD restricts B. cenocepacia replication within macrophages independent of its role in cell death through promoting mitochondrial reactive oxygen species (mROS) production. mROS is known to stimulate autophagy, hence, the inhibition of mROS or the absence of GSDMD during B. cenocepacia infections reduces autophagy which plays a critical role in the restriction of the pathogen. GSDMD promotes inflammation in response to B. cenocepacia through mediating the release of inflammasome dependent cytokine (IL-1β) and an independent one (CXCL1) (KC). Additionally, different B. cenocepacia secretory systems (T3SS, T4SS, and T6SS) contribute to inflammasome activation together with bacterial survival within macrophages. In vivo study confirmed the in vitro findings and showed that GSDMD restricts B. cenocepacia infection and dissemination and stimulates autophagy in response to B. cenocepacia. Nevertheless, GSDMD promotes lung inflammation and necrosis in response to B. cenocepacia without altering mice survival. This study describes the double-edged functions of GSDMD in response to B. cenocepacia infection and shows the importance of GSDMD-mediated mROS in restriction of B. cenocepacia.

Mini-Review: GSDME-Mediated Pyroptosis in Diabetic Nephropathy

Pyroptosis is a recently identified type of lytic programmed cell death, in which pores form in the plasma membrane, and cells swell, rupture, and then release their contents, including inflammatory cytokines. Molecular studies indicated that pyroptosis may occur via a gasdermin D (GSDMD) and caspase-1 (Casp1) -dependent classical pathway, a GSDMD and Casp11/4/5-dependent non-classical pathway, or a gasdermin E (GSDME) and Casp3-dependent pathway. Studies of animal models and humans indicated that pyroptosis can exacerbate several complications of diabetes, including diabetic nephropathy (DN), a serious microvascular complication of diabetes. Many studies investigated the mechanism mediating the renoprotective effect of GSDMD regulation in the kidneys of patients and animal models with diabetes. As a newly discovered regulatory mechanism, GSDME and Casp3-dependent pyroptotic pathway in the progression of DN has also attracted people's attention. Z-DEVD-FMK, an inhibitor of Casp3, ameliorates albuminuria, improves renal function, and reduces tubulointerstitial fibrosis in diabetic mice, and these effects are associated with the inhibition of GSDME. Studies of HK-2 cells indicated that the molecular and histological features of secondary necrosis were present following glucose stimulation due to GSDME cleavage, such as cell swelling, and release of cellular contents. Therefore, therapies targeting Casp3/GSDME-dependent pyroptosis have potential for treatment of DN. A novel nephroprotective strategy that employs GSDME-derived peptides which are directed against Casp3-induced cell death may be a key breakthrough. This mini-review describes the discovery and history of research in this pyroptosis pathway and reviews the function of proteins in the gasdermin family, with a focus on the role of GSDME-mediated pyroptosis in DN. Many studies have investigated the impact of GSDME-mediated pyroptosis in kidney diseases, and these studies used multiple interventions, in vitro models, and in vivo models. We expect that further research on the function of GDSME in DN may provide valuable insights that may help to improve treatments for this disease.

Effect and mechanism of phospholipid scramblase 4 (PLSCR4) on lipopolysaccharide (LPS)-induced injury to human pulmonary microvascular endothelial cells

Background

Previous experiments revealed phospholipid scramblase 4 (PLSCR4) mRNA to be significantly increased in a lipopolysaccharide (LPS)-induced acute respiratory distress syndrome (ARDS) model of human pulmonary microvascular endothelial cells (HPMECs); however, the effect of PLSCR4 and its mechanism have not been reported to date. The PLSCR family is thought to mediate the transmembrane movement of phospholipids (PS), and has been found to be involved in pyroptosis through combing with gasdermin D (GSDMD). We therefore speculated that PLSCR4 may contribute to cell death via pyroptosis.

Methods

To investigate the effect and mechanism of PLSCR4 in ARDS, we constructed an in vitro model of LPS-induced ARDS in HPMECs transfected with PLSCR4 small interfering RNA (siRNA) or scramble siRNA (sc siRNA). After 4 h of LPS stimulation, western blotting, immunoprecipitation, enzyme-linked immunosorbent assay (ELISA), tracer flux assays, and fluorescence assays were used to study the relationship between PLSCR4 and pyroptosis with regards to their impact on ARDS. We also established an ARDS mouse model which was pretreated with a liquid complex of PLSCR4 siRNA/sc siRNA-lipofectamine 2000 through the fundus venous plexus. Finally, we used DNA pull-down and protein profiling to study the potential transcription factor of PLSCR4.

Results

It was found that when the expression of PLSCR4 was elevated, the concentration of interleukin 1 beta (IL-1β) and IL-18 decreased, along with barrier damage (P<0.05). Furthermore, HPMEC injury was reduced with more distribution of PS and N-terminal cleavage product (GSDMD-NT) of GSDMD on the external side of cell membrane. However, the pyroptosis-relevant proteins of GSDMD and caspase-1 were not obviously changed (P<0.05); we further found that when PLSCR4 was depressed, the lung injury was aggravated in the mice. In the DNA pull-down assay, P62280 remarkably increased, which suggested that P62280 might be the transcription factor for PLSCR4.

Conclusions

PLSCR4 alleviated pyroptosis by transporting PS to the outside of the membrane, blocking the formation of pyroptosis pores composed of GSDMD. Moreover, P62280 might be the transcription factor of PLSCR4. These insults may provide useful insights into the clinical treatment of ARDS.

Dioscin Improves Pyroptosis in LPS-Induced Mice Mastitis by Activating AMPK/Nrf2 and Inhibiting the NF-κB Signaling Pathway

Dioscin, a natural steroid saponin, has been shown to have anti-inflammatory effects, but its protective mechanism against mastitis is still unknown. NLRP3 inflammasome and pyroptosis play important roles in the pathogenesis of many inflammatory diseases, including mastitis. The purpose of this study was to explore the effect of dioscin on lipopolysaccharide- (LPS-) induced mastitis in vivo and in vitro and its mechanism of action. In vivo experiments, dioscin can reduce the inflammatory lesions and neutrophil motility in mammary tissue. Moreover, dioscin also can reduce the production of proinflammatory factors such as interleukin-1 beta (IL-1β) and inhibit the activation of NLRP3 inflammasome in LPS-induced mice mastitis. In vitro experiments, the results showed that dioscin inhibited the inflammatory response and the activation of NLRP3 inflammasome, but the survival rate of mouse mammary epithelial cells (mMECs) induced by LPS+ATP is increased. Subsequently, the experiment convinces that dioscin can reduce LPS+ATP-induced mMEC pyroptosis by adding Ac-DEVD-CHO (a caspase-3 inhibitor). Further mechanistic studies demonstrate that dioscin can activate AMPK/Nrf2 to inhibit NLRP3/GSDMD-induced mMEC pyroptosis. In summary, this paper reveals a novel function of dioscin on mMEC pyroptosis and provides a new potential therapy of dioscin for the treatment and prevention of mastitis.