A novel heterodimeric cysteine protease is required for interleukin-1 beta processing in monocytes

Bibliometric evaluation of publications on inflammasomes in atherosclerosis from 2002 to 2022

Background

Inflammasomes have emerged as an important and promising area of investigation in atherosclerosis. This field, however, lacks bibliometric studies. To help understand how basic and clinical research on inflammasomes in atherosclerosis will develop in the future, we used bibliometric analysis to visualize hotspots and trends.

Methods

Studies related to inflammasomes in atherosclerosis were collected from the Web of Science Core Collection database. Each study was analyzed bibliometrically and visually. CiteSpace and VOSviewer software were used to generate knowledge maps.

Results

A total of 894 articles were identified. Sixty-two countries and 338 institutions led by China and the United States contributed to these publications. The leading research institutions were Harvard Medical School and Columbia University. Circulation was the most frequently cited journal in this field. Among the 475 authors determined, Eicke Latz authored the most studies, and Peter Duewell has been cocited the most. NLRP3 inflammasome, NF-kappa B, macrophage and oxidative stress are the most commonly used keywords.

Conclusion

There has been a blooming of research on inflammasomes in atherosclerosis during the last two decades. Future studies will likely explore the molecular mechanism of inflammasomes in cell death. More compellingly, researchers may further delve into the potential clinical value of affecting pathological changes in atherosclerosis by modulating the initial transcription immune response and intracellular multiprotein assembly process of the NLRP3 inflammasome. Our research will be helpful to scholars focusing on inflammation-a much-needed breakthrough in the pathophysiological alterations of atherosclerosis-with a novel perspective.

Methods to Measure NLR Oligomerization I: Size Exclusion Chromatography, Co-immunoprecipitation, and Cross-Linking

Protein oligomerization is a common principle of regulating cellular responses. Oligomerization of NLRs is essential for the formation of NLR signaling platforms and can be detected by several biochemical techniques. Some of these biochemical methods can be combined with functional assays, such as caspase-1 activity assay. Size exclusion chromatography (SEC) allows separation of native protein lysates into different sized complexes by FPLC for follow-up analysis. Using co-immunoprecipitation (co-IP), combined with SEC or on its own, enables subsequent antibody-based purification of NLR complexes and associated proteins, which can then be analyzed by immunoblot and/or subjected to functional caspase-1 activity assay. Native gel electrophoresis also allows detection of the NLR oligomerization state by immunoblot. Chemical cross-linking covalently joins two or more molecules, thus capturing the oligomeric state with high sensitivity and stability. ASC oligomerization has been successfully used as readout for NLR/ALR inflammasome activation in response to various PAMPs and DAMPs in human and mouse macrophages and THP-1 cells. Here, we provide a detailed description of the methods used for NLRP7 oligomerization in response to infection with Staphylococcus aureus (S. aureus) in primary human macrophages, co-immunoprecipitation, and immunoblot analysis of NLRP7 and NLRP3 inflammasome complexes as well as caspase-1 activity assays. Also, ASC oligomerization is shown in response to dsDNA, LPS/ATP, and LPS/nigericin in mouse bone marrow-derived macrophages (BMDMs) and/or THP-1 cells or human primary macrophages.

New Insights of Early Brain Injury after Subarachnoid Hemorrhage: A Focus on the Caspase Family

Spontaneous subarachnoid hemorrhage (SAH), primarily caused by ruptured intracranial aneurysms, remains a prominent clinical challenge with a high rate of mortality and morbidity worldwide. Accumulating clinical trials aiming at the prevention of cerebral vasospasm (CVS) have failed to improve the clinical outcome of patients with SAH. Therefore, a growing number of studies have shifted focus to the pathophysiological changes that occur during the periods of early brain injury (EBI). New pharmacological agents aiming to alleviate EBI have become a promising direction to improve outcomes after SAH. Caspases belong to a family of cysteine proteases with diverse functions involved in maintaining metabolism, autophagy, tissue differentiation, regeneration, and neural development. Increasing evidence shows that caspases play a critical role in brain pathology after SAH. Therefore, caspase regulation could be a potential target for SAH treatment. Herein, we provide an overview pertaining to the current knowledge on the role of caspases in EBI after SAH, and we discuss the promising therapeutic value of caspase-related agents after SAH.

The role of interleukin-1 in perinatal inflammation and its impact on transitional circulation

Preterm birth is defined as delivery at <37 weeks of gestational age (GA) and exposes 15 million infants worldwide to serious early life diseases. Lowering the age of viability to 22 weeks GA entailed provision of intensive care to a greater number of extremely premature infants. Moreover, improved survival, especially at extremes of prematurity, comes with a rising incidence of early life diseases with short- and long-term sequelae. The transition from fetal to neonatal circulation is a substantial and complex physiologic adaptation, which normally happens rapidly and in an orderly sequence. Maternal chorioamnionitis or fetal growth restriction (FGR) are two common causes of preterm birth that are associated with impaired circulatory transition. Among many cytokines contributing to the pathogenesis of chorioamnionitis-related perinatal inflammatory diseases, the potent pro-inflammatory interleukin (IL)-1 has been shown to play a central role. The effects of utero-placental insufficiency-related FGR and in-utero hypoxia may also be mediated, in part, via the inflammatory cascade. In preclinical studies, blocking such inflammation, early and effectively, holds great promise for improving the transition of circulation. In this mini-review, we outline the mechanistic pathways leading to abnormalities in transitional circulation in chorioamnionitis and FGR. In addition, we explore the therapeutic potential of targeting IL-1 and its influence on perinatal transition in the context of chorioamnionitis and FGR.

The CARD8 inflammasome in HIV infection

The biggest challenge to immune control of HIV infection is the rapid within-host viral evolution, which allows selection of viral variants that escape from T cell and antibody recognition. Thus, it is impossible to clear HIV infection without targeting "immutable" components of the virus. Unlike the adaptive immune system that recognizes cognate epitopes, the CARD8 inflammasome senses the essential enzymatic activity of the HIV-1 protease, which is immutable for the virus. Hence, all subtypes of HIV clinical isolates can be recognized by CARD8. In HIV-infected cells, the viral protease is expressed as a subunit of the viral Gag-Pol polyprotein and remains functionally inactive prior to viral budding. A class of anti-HIV drugs, the non-nucleoside reverse transcriptase inhibitors (NNRTIs), can promote Gag-pol dimerization and subsequent premature intracellular activation of the viral protease. NNRTI treatment triggers CARD8 inflammasome activation, which leads to pyroptosis of HIV-infected CD4⁺ T cells and macrophages. Targeting the CARD8 inflammasome can be a potent and broadly effective strategy for HIV eradication.

The NLRP1 inflammasome in skin diseases

Healthy human skin is constantly exposed to sterile and microbial agents. The skin immune system plays an important role in immune surveillance between tolerance and immune activation. This is mainly mediated by neutrophils, macrophages and most importantly lymphocytes. Keratinocytes, which form the outer skin barrier (epidermis) are also critical for cutaneous homeostasis. Being a non-professional immune cell, recognition of danger signals in keratinocytes is mediated by innate immune receptors (pattern recognition receptors, PRR). While Toll-like receptors are located on the cell membrane or the endosomes, nucleotide-binding domain and leucine-rich repeat containing gene family receptors (NLR) are intracellular PRRs. Some of these, once activated, trigger the formation of inflammasomes. Inflammasomes are multiprotein complexes and serve as platforms that mediate the release of innate cytokines after successful recognition, thereby attracting immune cells. Moreover, they mediate the pro-inflammatory cell death pyroptosis. Best characterized is the NLRP3 inflammasome. The function of inflammasomes differs significantly between different cell types (keratinocytes versus immune cells) and between different species (human versus mouse). In recent years, great progress has been made in deciphering the activation mechanisms. Dysregulation of inflammasomes can lead to diseases with varying degrees of severity. Here we focus on the structure, function, and associated pathologies of the NLRP1 inflammasome, which is the most relevant inflammasome in keratinocytes.

Myeloid cell-derived proteases produce a proinflammatory form of IL-37 that signals via IL-36 receptor engagement

Interleukin-1 (IL-1) family cytokines are key barrier cytokines that are typically expressed as inactive, or partially active, precursors that require proteolysis within their amino termini for activation. IL-37 is an enigmatic member of the IL-1 family that has been proposed to be activated by caspase-1 and to exert anti-inflammatory activity through engagement of the IL-18R and SIGIRR. However, here we show that the longest IL-37 isoform, IL-37b, exhibits robust proinflammatory activity upon amino-terminal proteolysis by neutrophil elastase or cathepsin S. In sharp contrast, caspase-1 failed to process or activate IL-37 at concentrations that robustly activated its canonical substrate, IL-1β. IL-37 and IL-36 exhibit high structural homology, and, consistent with this, a K53-truncated form of IL-37, mimicking the cathepsin S-processed form of this cytokine, was found to exert its proinflammatory effects via IL-36 receptor engagement and produced an inflammatory signature practically identical to IL-36. Administration of K53-truncated IL-37b intraperitoneally into wild-type mice also elicited an inflammatory response that was attenuated in IL-36R^-/- animals. These data demonstrate that, in common with other IL-1 family members, mature IL-37 can also elicit proinflammatory effects upon processing by specific proteases.

Molecular Characteristics of Cell Pyroptosis and Its Inhibitors: A Review of Activation, Regulation, and Inhibitors

Pyroptosis is an active and ordered form of programmed cell death. The signaling pathways of pyroptosis are mainly divided into canonical pathways mediated by caspase-1 and noncanonical pathways mediated by caspase-11. Cell pyroptosis is characterized by the activation of inflammatory caspases (mainly caspase-1, 4, 5, 11) and cleavage of various members of the Gasdermin family to form membrane perforation components, leading to cell membrane rupture, inflammatory mediators release, and cell death. Moderate pyroptosis is an innate immune response that fights against infection and plays an important role in the occurrence and development of the normal function of the immune system. However, excessive pyroptosis occurs and leads to immune disorders in many pathological conditions. Based on canonical pathways, research on pyroptosis regulation has demonstrated several pyroptotic inhibitors, including small-molecule drugs, natural products, and formulations of traditional Chinese medicines. In this paper, we review the characteristics and molecular mechanisms of pyroptosis, summarize inhibitors of pyroptosis, and propound that herbal medicines should be a focus on the research and development for pyroptosis blockers.

The NLRP3 inflammasome: regulation by metabolic signals

Macrophages undergo profound metabolic reprogramming upon sensing infectious and sterile stimuli. This metabolic shift supports and regulates essential innate immune functions, including activation of the NLRP3 inflammasome. Within distinct metabolic networks, key enzymes play pivotal roles to control flux restraining detrimental inflammasome signaling. However, depending on the metabolic cues, specific enzymes and metabolites result in inflammasome activation outcomes which contrast other metabolic steps in the pathway. We posit that understanding which metabolic steps commit to discrete inflammasome fates will broaden our understanding of metabolic checkpoints to maintain homeostasis and offer better therapeutic options in human disease.

Dysregulated inflammasome activity in intestinal inflammation - Insights from patients with very early onset IBD

Inflammatory bowel disease (IBD) is a multifactorial disorder triggered by imbalances of the microbiome and immune dysregulations in genetically susceptible individuals. Several mouse and human studies have demonstrated that multimeric inflammasomes are critical regulators of host defense and gut homeostasis by modulating immune responses to pathogen- or damage-associated molecular patterns. In the context of IBD, excessive production of pro-inflammatory Interleukin-1β has been detected in patient-derived intestinal tissues and correlated with the disease severity or failure to respond to anti-tumor necrosis factor therapy. Correspondingly, genome-wide association studies have suggested that single nucleotide polymorphisms in inflammasome components might be associated with risk of IBD development. The relevance of inflammasomes in controlling human intestinal homeostasis has been further exemplified by the discovery of very early onset IBD (VEO-IBD) patients with monogenic defects affecting different molecules in the complex regulatory network of inflammasome activity. This review provides an overview of known causative monogenic entities of VEO-IBD associated with altered inflammasome activity. A better understanding of the molecular mechanisms controlling inflammasomes in monogenic VEO-IBD may open novel therapeutic avenues for rare and common inflammatory diseases.

Involvement of the p38 MAPK-NLRC4-Caspase-1 Pathway in Ionizing Radiation-Enhanced Macrophage IL-1β Production

Macrophages are abundant immune cells in the tumor microenvironment and are crucial in regulating tumor malignancy. We previously reported that ionizing radiation (IR) increases the production of interleukin (IL)-1β in lipopolysaccharide (LPS)-treated macrophages, contributing to the malignancy of colorectal cancer cells; however, the mechanism remained unclear. Here, we show that IR increases the activity of cysteine-aspartate-specific protease 1 (caspase-1), which is regulated by the inflammasome, and cleaves premature IL-1β to mature IL-1β in RAW264.7 macrophages. Irradiated RAW264.7 cells showed increased expression of NLRC4 inflammasome, which controls the activity of caspase-1 and IL-1β production. Silencing of NLRC4 using RNA interference inhibited the IR-induced increase in IL-1β production. Activation of the inflammasome can be regulated by mitogen-activated protein kinase (MAPK)s in macrophages. In RAW264.7 cells, IR increased the phosphorylation of p38 MAPK but not extracellular signal-regulated kinase and c-Jun N-terminal kinase. Moreover, a selective inhibitor of p38 MAPK inhibited LPS-induced IL-1β production and NLRC4 inflammasome expression in irradiated RAW264.7 macrophages. Our results indicate that IR-induced activation of the p38 MAPK-NLRC4-caspase-1 activation pathway in macrophages increases IL-1β production in response to LPS.

PANoptosis: A Unique Innate Immune Inflammatory Cell Death Modality

Innate immunity is the first response to protect against pathogens and cellular insults. Pattern recognition receptors sense pathogen- and damage-associated molecular patterns and induce an innate immune response characterized by inflammation and programmed cell death (PCD). In-depth characterization of innate immune PCD pathways has highlighted significant cross-talk. Recent advances led to the identification of a unique inflammatory PCD modality called PANoptosis, which is regulated by multifaceted PANoptosome complexes that are assembled by integrating components from other PCD pathways. The totality of biological effects observed in PANoptosis cannot be accounted for by any other PCD pathway alone. In this review, we briefly describe mechanisms of innate immune cell death, including molecular mechanisms of PANoptosis activation and regulation. We also highlight the PANoptosomes identified to date and provide an overview of the implications of PANoptosis in disease and therapeutic targeting. Improved understanding of innate immune-mediated cell death, PANoptosis, is critical to inform the next generation of treatment strategies.

A Possible Causal Involvement of Neuroinflammatory, Purinergic P2X7 Receptors in Psychiatric Disorders

P2X7 receptors (Rs) are prominent members of the P2XR family, which after binding ATP, open non-selective cationic channels, thereby allowing the transmembrane passage of Na+, Ca²⁺, and K+. Long-lasting and repetitive stimulation of the receptor by its agonist leads to the formation of large membrane pores permeable for organic cations of up to 900 Da molecular size. These pores are believed to play a role in apoptosis and inflammation. P2X7Rs are located primarily at peripheral macrophages and microglial cells, the resident macrophages of the CNS. The coactivation of toll-like receptors 4 (TLR4) by lipopolysaccharide, a constituent of the cell membrane of gram-negative bacteria, and the P2X7R by ATP leads to the generation and release of the proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α. Together with the microglial release of chemokines, reactive oxygen and nitrogen species, proteases, and excitotoxic glutamate, these cytokines result in neurodegeneration. P2X7Rs were found not only to amplify various neurodegenerative illnesses, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis, but also to participate in a range of psychiatric diseases, such as major depression, bipolar disorder, schizophrenia, and autism spectrum disorder. Based on the prevention/reversal of neuroinflammation, pharmacological antagonists of P2X7Rs and their genetic deletion in animal experiments counteract these deleterious psychiatric conditions. Hence, brain penetrant P2X7R antagonists are potential therapeutics for psychiatric diseases, although the available evidence still needs to be extended and validated by further clinical data.

A microfluidic Braille valve platform for on-demand production, combinatorial screening and sorting of chemically distinct droplets

Droplet microfluidics is a powerful tool for a variety of biological applications including single-cell genetics, antibody discovery and directed evolution. All these applications make use of genetic libraries, illustrating the difficulty of generating chemically distinct droplets for screening applications. This protocol describes our Braille Display valving platform for on-demand generation of droplets with different chemical contents (16 different reagents and combinations thereof), as well as sorting droplets with different chemical properties, on the basis of fluorescence signals. The Braille Display platform is compact, versatile and cost efficient (only ~US$1,000 on top of a standard droplet microfluidics setup). The procedure includes manufacturing of microfluidic chips, assembly of custom hardware, co-encapsulation of cells and drugs into droplets, fluorescence detection of readout signals and data analysis using shared, freely available LabVIEW and Python packages. As a first application, we demonstrate the complete workflow for screening cancer cell drug sensitivities toward 74 conditions. Furthermore, we describe here an assay enabling the normalization of the observed drug sensitivity to the number of cancer cells per droplet, which additionally increases the robustness of the system. As a second application, we also demonstrate the sorting of droplets according to enzymatic activity. The drug screening application can be completed within 2 d; droplet sorting takes ~1 d; and all preparatory steps for manufacturing molds, chips and setting up the Braille controller can be accomplished within 1 week.

The Inflammasomes Adaptor Protein PYCARD Is a Potential Pyroptosis Biomarker Related to Immune Response and Prognosis in Clear Cell Renal Cell Carcinoma

Simple Summary

Inflammation has been recognized as one of the hallmarks of cancers. PYCARD, the adaptor protein of inflammasomes, plays an important role in pyroptosis and apoptosis. However, the function of PYCARD remains unclear in human cancers. Here, we systematically performed a comprehensive analysis of PYCARD expression and its relationship with immunotherapy response and prognosis. We found significant differences in PYCARD expression between tumor and normal tissue, particularly in clear cell renal cell carcinoma. We also found that PYCARD was an unfavorable prognostic factor and was confirmed by external validation cohorts. Exploration of the profound mechanisms of PYCARD might help to identify new therapeutic targets and improve the efficacy of immunotherapy.

Abstract

PYCARD is a protein engaged in inflammation, pyroptosis, and apoptosis. However, the function of PYCARD in human cancers remains unclear. The objective of our study was to explore PYCARD expression and prognostic value in human cancers. Public databases were used to assess PYCARD expression and prognostic value. The TISIDB database was used to explore the associations between PYCARD expression and different immune subtypes. The correlations between PYCARD expression and ICP genes, MMR genes, MSI, and TMB were also investigated. The immunotherapy response was assessed using the TIDE database. Single-cell RNA databases evaluated the PYCARD expression of immune cells. External datasets and immunohistochemical staining were conducted to validate PYCARD expression and prognostic value. The results showed that PYCARD expression varied in several cancers and was associated with prognosis, immune-related genes, published biomarkers, and immunotherapy response. Of note, PYCARD expression was upregulated in renal cancers with high diagnostic ability. Upregulation of PYCARD was correlated with worse prognosis in KIRC and external validation cohorts. In conclusion, PYCARD demonstrated strong correlations with prognosis, immune response, and disease progression in pan-cancer analysis. In ccRCC, PYCARD might serve as a biomarker for diagnosis and therapeutic target-boosting immunotherapy response.

A pyroptosis-associated signature plays a role in prognosis prediction in clear cell renal cell carcinoma

Background

Approximately 90% of renal malignancies are RCCs (renal cell carcinomas), and the primary subtype in histology is ccRCC (clear cell RCC). In recent years, pyroptosis has been considered a kind of inflammation-related programmed cell death that participates in the invasion, metastasis, and proliferation of tumour cells, thereby influencing tumour prognosis. Nonetheless, the expression level of pyroptosis-associated genes in RCCs and their relationship with prognosis remain obscure.

Results

In our research, 44 regulators of pyroptosis that were differentially expressed between normal kidney and ccRCC tissues were identified. ccRCC cases were categorized into 2 subgroups according to prognostic-related DEGs (differentially expressed genes), and there was a significant difference in OS (overall survival) between them. The prognostic value of pyroptosis-associated genes was assessed as a signature based on a cohort from TCGA (The Cancer Genome Atlas). Following Cox regression with DEGs and LASSO (least absolute shrinkage and selection operator), a 6-gene signature was established, and all ccRCC cases in the cohort from TCGA were categorized into an LR (low-risk) or HR (high-risk) group (P < 0.001). In combination with clinical features, risk scores were considered a predictive factor of OS in ccRCC. KEGG (Kyoto Encyclopedia of Genes and Genomes) and GO (Gene Ontology) analyses suggest increased immunity and enrichment of genes related to immunity in the HR group.

Conclusions

Our findings indicate that genes related to pyroptosis have an important role in tumour immunity and may be used to predict the prognosis of ccRCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01339-0.

Characterization of IMG Microglial Cell Line as a Valuable In Vitro Tool for NLRP3 Inflammasome Studies

Microglial cells constantly surveil the cerebral microenvironment and become activated following injury and disease to mediate inflammatory responses. The nucleotide-binding oligomerization domain-, leucine-rich repeat-, and pyrin domain-containing 3 (NLRP3) inflammasome, which is abundantly expressed in microglial cells, plays a key role in these responses as well as in the development of many neurological disorders. Microglial cell lines are a valuable tool to study the causes and possible treatments for neurological diseases which are linked to inflammation. Here, we investigated whether the mouse microglial cell line IMG is suitable to study NLRP3 inflammasome by incubating cells with different concentrations of NLRP3 inflammasome priming and activating agents lipopolysaccharide (LPS) and ATP, respectively, and applying short (4 h) or long (24 h) LPS incubation times. After short LPS incubation, the mRNA levels of most pro-inflammatory and NLRP3 inflammasome-associated genes were more upregulated than after long incubation. Moreover, the combination of higher LPS and ATP concentrations with short incubation time resulted in greater levels of active forms of caspase-1 and interleukin-1 beta (IL-1β) proteins than low LPS and ATP concentrations or long incubation time. We also demonstrated that treatment with NLRP3 inflammasome inhibitor glibenclamide suppressed NLRP3 inflammasome activation in IMG cells, as illustrated by the downregulation of gasdermin D N-fragment and mature caspase-1 and IL-1β protein levels. In addition, we conducted similar experiments with primary microglial cells and BV-2 cell line to determine the similarities and differences in their responses. Overall, our results indicate that IMG cell line could be a valuable tool for NLRP3 inflammasome studies. In IMG cells, 4-h incubation with lipopolysaccharide (LPS) induces a stronger upregulation of NLRP3 inflammasome-associated pro-inflammatory genes compared to 24-h incubation. NLRP3 inflammasome is robustly activated only after the addition of 3 mM of ATP following short LPS incubation time.

NLRP3 inflammasome: The rising star in cardiovascular diseases

Cardiovascular diseases (CVDs) are the prevalent cause of mortality around the world. Activation of inflammasome contributes to the pathological progression of cardiovascular diseases, including atherosclerosis, abdominal aortic aneurysm, myocardial infarction, dilated cardiomyopathy, diabetic cardiomyopathy, heart failure, and calcific aortic valve disease. The nucleotide oligomerization domain-, leucine-rich repeat-, and pyrin domain-containing protein 3 (NLRP3) inflammasome plays a critical role in the innate immune response, requiring priming and activation signals to provoke the inflammation. Evidence shows that NLRP3 inflammasome not only boosts the cleavage and release of IL-1 family cytokines, but also leads to a distinct cell programmed death: pyroptosis. The significance of NLRP3 inflammasome in the CVDs-related inflammation has been extensively explored. In this review, we summarized current understandings of the function of NLRP3 inflammasome in CVDs and discussed possible therapeutic options targeting the NLRP3 inflammasome.

Pyroptosis in development, inflammation and disease

In the early 2000s, caspase-1, an important molecule that has been shown to be involved in the regulation of inflammation, cell survival and diseases, was given a new function: regulating a new mode of cell death that was later defined as pyroptosis. Since then, the inflammasome, the inflammatory caspases (caspase-4/5/11) and their substrate gasdermins (gasdermin A, B, C, D, E and DFNB59) has also been reported to be involved in the pyroptotic pathway, and this pathway is closely related to the development of various diseases. In addition, important apoptotic effectors caspase-3/8 and granzymes have also been reported to b involved in the induction of pyroptosis. In our article, we summarize findings that help define the roles of inflammasomes, inflammatory caspases, gasdermins, and other mediators of pyroptosis, and how they determine cell fate and regulate disease progression.

Pyroptosis and Its Role in the Modulation of Cancer Progression and Antitumor Immunity

Pyroptosis is a type of programmed cell death (PCD) accompanied by an inflammatory reaction and the rupture of a membrane. Pyroptosis is divided into a canonical pathway triggered by caspase-1, and a non-canonical pathway independent of caspase-1. More and more pyroptosis-related participants, pathways, and regulatory mechanisms have been exploited in recent years. Pyroptosis plays crucial roles in the initiation, progression, and metastasis of cancer and it affects the immunotherapeutic outcome by influencing immune cell infiltration as well. Extensive studies are required to elucidate the molecular mechanisms between pyroptosis and cancer. In this review, we introduce the discovery history of pyroptosis, delineate the signaling pathways of pyroptosis, and then make comparisons between pyroptosis and other types of PCD. Finally, we provide an overview of pyroptosis in different cancer types. With the progression in the field of pyroptosis, new therapeutic targets and strategies can be explored to combat cancer.

OxLDL induces the release of IL-1β from primed human endothelial and smooth muscle cells via different caspase -1-dependent mechanisms

Atherosclerosis is characterised by abnormal lipid and cell accumulation within arterial layers that leads to disturbed blood flow. Modified cholesterol forms such as oxidised low-density lipoprotein (oxLDL) enter cells altering their phenotype, triggering over-exuberant repair and arterial occlusion, myocardial infarction or stroke. We hypothesised that oxLDL enters vascular wall cells and induces interleukin-1β (IL-1β) secretion, potentially via a caspase-1/NLRP3 mechanism. Human coronary artery endothelial cells (HCAEC) and smooth muscle cells (HCASMC), isolated from different donors, were cultured and stimulated (primed) with pro-inflammatory cytokines TNFα and IL-1α (10 ng/mL each, for 48 h), followed by incubation with human oxLDL (10-50 ug/mL) for up to 6 h. Inhibitors of caspase-1 (YVAD), NLRP3 (MCC950) and gasdermin D (disulfiram) were added 1 h before oxLDL. Cell lysates and culture supernatants were collected and analysed for IL-1β using ELISA. Microscopy imaging showed oxLDL entered stimulated cells and formed particles. OxLDL at 20 and 50 ug/mL induced the maximum release of IL-1β from stimulated HCASMCs and HCAECs, respectively, compared to control. Inhibition of either NLRP3, caspase-1 or gasdermin D significantly reduced the release of IL-1β (4-fold, P < 0.0001; 14-fold, P < 0.0001, 1.5-fold, P < 0.0003, respectively) in HCAEC. In contrast, in HCASMCs, only caspase-1 inhibition reduced the release of IL-1β (2.1-fold, P < 0.0001). HCAECs and HCASMCs elicited the release of IL-1β in response to the same stimulus via different mechanisms. In HCAECs, released IL-1β potentially exits via a GSDMD-induced membrane pore. These data suggest that caspase-1 or gasdermin D inhibition is likely to be effective vessel wall cell-specific strategies for the reduction of atherosclerosis.

Extracellular pH sensing by plant cell-surface peptide-receptor complexes

The extracellular pH is a vital regulator of various biological processes in plants. However, how plants perceive extracellular pH remains obscure. Here, we report that plant cell-surface peptide-receptor complexes can function as extracellular pH sensors. We found that pattern-triggered immunity (PTI) dramatically alkalinizes the acidic extracellular pH in root apical meristem (RAM) region, which is essential for root meristem growth factor 1 (RGF1)-mediated RAM growth. The extracellular alkalinization progressively inhibits the acidic-dependent interaction between RGF1 and its receptors (RGFRs) through the pH sensor sulfotyrosine. Conversely, extracellular alkalinization promotes the alkaline-dependent binding of plant elicitor peptides (Peps) to its receptors (PEPRs) through the pH sensor Glu/Asp, thereby promoting immunity. A domain swap between RGFR and PEPR switches the pH dependency of RAM growth. Thus, our results reveal a mechanism of extracellular pH sensing by plant peptide-receptor complexes and provide insights into the extracellular pH-mediated regulation of growth and immunity in the RAM.

Revisiting the origin of interleukin 1 in anamniotes and sub-functionalization of interleukin 1 in amniotes

The cytokine interleukin 1 (IL-1) is an evolutionary innovation of vertebrates. Fish and amphibian have one IL1 gene, while mammals have two copies of IL1, IL1A and IL1B, with distinct expression patterns and differences in their proteolytic activation. Our current understanding of the evolutionary history of IL-1 is mainly based on phylogenetic analysis, but this approach provides no information on potentially different functions of IL-1 homologues, and it remains unclear which biological activities identified for IL-1α and IL-1β in mammals are present in lower vertebrates. Here, we use in vitro and in vivo experimental models to examine the expression patterns and cleavage of IL-1 proteins from various species. We found that IL-1 in the teleost medaka shares the transcriptional patterns of mammalian IL-1α, and its processing also resembles that of mammalian IL-1α, which is sensitive to cysteine protease inhibitors specific for the calpain and cathepsin families. By contrast, IL-1 proteins in reptiles also include biological properties of IL-1β. Therefore, we propose that the duplication of the ancestral IL1 gene led to the segregation of expression patterns and protein processing that characterizes the two extant forms of IL-1 in mammals.

Immunogenic Cell Death and Role of Nanomaterials Serving as Therapeutic Vaccine for Personalized Cancer Immunotherapy

Immunogenic cell death (ICD) is a rapidly growing research area representing one of the emerging therapeutic strategies of cancer immunotherapy. ICD is an umbrella term covering several cell death modalities including apoptosis, necroptosis, ferroptosis and pyroptosis, and is the product of a balanced combination of adjuvanticity (damage-associated molecular patterns and chemokines/cytokines) and antigenicity (tumor associated antigens). Only a limited number of anti-cancer therapies are available to induce ICD in experimental cancer therapies and even much less is available for clinical use. To overcome this limitation, nanomaterials can be used to increase the immunogenicity of cancer cells killed by anti-cancer therapy, which in themselves are not necessarily immunogenic. In this review, we outline the current state of knowledge of ICD modalities and discuss achievements in using nanomaterials to increase the immunogenicity of dying cancer cells. The emerging trends in modulating the immunogenicity of dying cancer cells in experimental and translational cancer therapies and the challenges facing them are described. In conclusion, nanomaterials are expected to drive further progress in their use to increase efficacy of anti-cancer therapy based on ICD induction and in the future, it is necessary to validate these strategies in clinical settings, which will be a challenging research area.

Pathway of Cell Death and Its Role in Virus Infection

The global pandemic of SARS-CoV-2 in the past 2 years has aroused great attention to infectious diseases, and emerging virus outbreaks have brought huge challenges to the global health system. Viruses are specific pathogens that completely rely on host cells for their own survival and disease transmission. At present, a growing number of studies have proved that inducing the death of virus-infected cells can prevent the spread of virus and promote disease recovery. Therefore, many ways to induce the death of infected cells are considered to be beneficial to host immunity. Cell death is a basic biological phenomenon. Programmed cell death (PCD), as an important part of the host's innate immune response, provides effective protection against virus transmission. Pyroptosis, apoptosis, and necroptosis are the most commonly studied pathways of PCD. Recent studies have found that three pathways of cell death can be activated during virus infection. More and more studies have shown the existence of extensive connections between PCDs, and this complex relationship is defined as PANoptosis, an inflammatory PCD pathway regulated by the PANoptosome complex, whose characteristics cannot be explained by any of the three PCD pathways. During viral infection, PANoptosis can promote inflammatory response by inducing the production of inflammatory cytokines and cell death to exert an antiviral mechanism. This article reviews the various effects of cell death pathways during viral infection and provides new ideas for clinical antiviral therapy and related immunotherapy.

Diverse Control Mechanisms of the Interleukin-1 Cytokine Family

The majority of interleukin-1 (IL-1) family cytokines lack amino terminal secretion signals or transmembrane domains for secretion along the conventional biosynthetic pathway. Yet, these factors must be translocated from the cytoplasm across the plasma membrane into the extracellular space in order to regulate inflammation. Recent work has identified an array of mechanisms by which IL-1 family cytokines can be released into the extracellular space, with supramolecular organizing centers known as inflammasomes serving as dominant drivers of this process. In this review, we discuss current knowledge of the mechanisms of IL-1 family cytokine synthesis, processing, and release from cells. Using this knowledge, we propose a model whereby host metabolic state dictates the route of IL-1β secretion, with implications for microbial infection and sterile inflammation.

IL-1 family cytokines serve as 'activity recognition receptors' for aberrant protease activity indicative of danger

Members of the extended IL-1 cytokine family play key roles as instigators of inflammation in numerous infectious and sterile injury contexts and are highly enriched at barrier surfaces such as the skin, lungs and intestinal mucosa. Because IL-1 family cytokines do not possess conventional ER-golgi trafficking and secretory signals, these cytokines are typically released into the extracellular space due to tissue damage resulting in necrosis, or pathogen detection resulting in pyroptosis. The latter feature, in combination with other factors, suggests that IL-1 family cytokines serve as canonical damage-associated molecular patterns (DAMPs), which instigate inflammation in response to tissue damage. However, IL-1 family cytokines also require a proteolytic activation step and diverse intracellular, extracellular and non-self proteases have been identified that are capable of processing and activating members of this family. This suggests that IL-1 family members function as sentinels for aberrant protease activity, which is frequently associated with infection or tissue damage. Here, we overview the diversity of proteases implicated in the activation of IL-1 family cytokines and suggest that this ancient cytokine family may have evolved to complement 'pattern recognition receptors', by serving as 'activity recognition receptors' enabling the detection of aberrant enzyme activity indicative of 'danger'.

EV-Mediated Chemoresistance in the Tumor Microenvironment: Is NF-κB a Player?

Drug resistance is a major impediment to patient survival and remains the primary cause of unsuccessful cancer therapy. Drug resistance occurs in many tumors and is frequently induced by chemotherapy which triggers a defensive response both in cancerous and cancer-associated cells that constitute the tumor microenvironment (TME). Cell to cell communication within the TME is often mediated by extracellular vesicles (EVs) which carry specific tumor-promoting factors able to activate survival pathways and immune escape mechanisms, thus sustaining tumor progression and therapy resistance. NF-κB has been recognized as a crucial player in this context. NF-κB activation is involved in EVs release and EVs, in turn, can trigger NF-κB pathway activation in specific contexts, based on secreting cytotype and their specific delivered cargo. In this review, we discuss the role of NF-κB/EVs interplay that sustain chemoresistance in the TME by focusing on the molecular mechanisms that underlie inflammation, EVs release, and acquired drug resistance.

Gasdermins in Innate Host Defense Against Entamoeba histolytica and Other Protozoan Parasites

Gasdermins (GSDMs) are a group of proteins that are cleaved by inflammatory caspases to induce pore formation in the plasma membrane to cause membrane permeabilization and lytic cell death or pyroptosis. All GSDMs share a conserved structure, containing a cytotoxic N-terminal (NT) pore-forming domain and a C-terminal (CT) repressor domain. Entamoeba histolytica (Eh) in contact with macrophages, triggers outside-in signaling to activate inflammatory caspase-4/1 via the noncanonical and canonical pathway to promote cleavage of gasdermin D (GSDMD). Cleavage of GSDMD removes the auto-inhibition that masks the active pore-forming NT domain in the full-length protein by interactions with GSDM-CT. The cleaved NT-GSDMD monomers then oligomerize to form pores in the plasma membrane to facilitate the release of IL-1β and IL-18 with a measured amount of pyroptosis. Pyroptosis is an effective way to counteract intracellular parasites, which exploit replicative niche to avoid killing. To date, most GSDMs have been verified to perform pore-forming activity and GSDMD-induced pyroptosis is rapidly emerging as a mechanism of anti-microbial host defence. Here, we review our comprehensive and current knowledge on the expression, activation, biological functions, and regulation of GSDMD cleavage with emphases on physiological scenario and related dysfunctions of each GSDM member as executioner of cell death, cytokine secretion and inflammation against Eh and other protozoan parasitic infections.

Pro- and anti-inflammatory bioactive lipids imbalance contributes to the pathobiology of autoimmune diseases

Autoimmune diseases are driven by T_H17 cells that secrete pro-inflammatory cytokines, especially IL-17. Under normal physiological conditions, autoreactive T cells are suppressed by TGF-β and IL-10 secreted by microglia and dendritic cells. When this balance is upset due to injury, infection and other causes, leukocyte recruitment and macrophage activation occurs resulting in secretion of pro-inflammatory IL-6, TNF-α, IL-17 and PGE2, LTs (leukotrienes) accompanied by a deficiency of anti-inflammatory LXA4, resolvins, protecting, and maresins. PGE2 facilitates T_H1 cell differentiation and promotes immune-mediated inflammation through T_H17 expansion. There is evidence to suggest that autoimmune diseases can be suppressed by anti-inflammatory bioactive lipids LXA4, resolvins, protecting, and maresins. These results imply that systemic and/or local application of LXA4, resolvins, protecting, and maresins and administration of their precursors AA/EPA/DHA could form a potential therapeutic approach in the prevention and treatment of autoimmune diseases.

Trifolirhizin regulates the balance of Th17/Treg cells and inflammation in the ulcerative colitis mice through inhibiting the TXNIP-mediated activation of NLRP3 inflammasome

Ulcerative colitis (UC) is a chronic and recurrent autoimmune disease, characterized by recurrence and remission of mucosal inflammation. Although the understanding of the pathogenesis of UC has been improved, effective therapeutic drugs are required for treating patients with UC. In current work, the mouse model of colitis was established. Trifolirhizin was demonstrated to improve symptom in dextran sulfate sodium (DSS)-induced colitis mice. The body weight of mice was elevated, while the disease activity index (DAI) was reduced. Moreover, Trifolirhizin was involved in inhibition of inflammation and regulation of Th17/Treg cell balance in DSS-induced colitis mice. Further, the activation NLRP3 inflammasome was suppressed by Trifolirhizin in DSS-induced colitis mice. Trifolirhizin was also identified to regulate AMPK-TXNIP pathway. The Trifolirhizin-mediated anti-inflammatory effect was inhibited by suppressing AMPK in DSS-induced UC mice. In summary, the research suggested that administration of Trifolirhizin significantly improved the symptoms and the pathological damage in DSS-induced UC mice. Trifolirhizin regulated the balance of Th17/Treg cells and inflammation in the UC mice through inhibiting the TXNIP-mediated activation of NLRP3 inflammasome. This article is protected by copyright. All rights reserved.

Phosphatidylserine externalization by apoptotic cells is dispensable for specific recognition leading to innate apoptotic immune responses

Surface determinants newly expressed by apoptotic cells that are involved in triggering potent immunosuppressive responses, referred to as “innate apoptotic immunity (IAI)” have not been characterized fully. It is widely assumed, often implicitly, that phosphatidylserine, a phospholipid normally cloistered in the inner leaflet of cells and externalized specifically during apoptosis, is involved in triggering IAI, just as it plays an essential role in the phagocytic recognition of apoptotic cells. It is notable, however, that the triggering of IAI in responder cells is not dependent on the engulfment of apoptotic cells by those responders. Contact between the responder and the apoptotic target, on the other hand, is necessary to elicit IAI. Previously, we demonstrated that exposure of protease-sensitive determinants on the apoptotic cell surface are essential for initiating IAI responses; exposed glycolytic enzyme molecules were implicated in particular. Here, we report our analysis of the involvement of externalized phosphatidylserine in triggering IAI. To analyze the role of phosphatidylserine, we employed a panel of target cells that either externalized phosphatidylserine constitutively, independently of apoptosis, or did not, as well as their WT parental cells that externalized the phospholipid in an apoptosis-dependent manner. We found that the externalization of phosphatidylserine, which can be fully uncoupled from apoptosis, is neither sufficient nor necessary to trigger the profound immunomodulatory effects of IAI. These results reinforce the view that apoptotic immunomodulation and phagocytosis are dissociable and further underscore the significance of protein determinants localized to the cell surface during apoptosis in triggering innate apoptotic immunity.

Adult kidney explants is a physiologic model for studying diabetic nephropathy

Inflammatory processes play a central role in the pathogenesis of diabetic nephropathy (DN) in the early stages of the disease. In vitro approach using cell lines help to understand the mechanisms involves and allow the molecular and biochemical processes. Adult kidney (AK) explants remain an essential instrument for advancing our understanding of the molecular and cellular regulation of signalling pathways from an organotipic view with physiological system interaction integrated. AK explants from T1DM animal model (BB rat) are obtained by slicing central kidney area preserving the organ's cytoarchitecture and reproduce the classical events detected during the DN in an in vivo model such as inflammation, epithelial-mesenchymal transition (EMT) processes by the modulation of a-SMA and e-Cadherin among others which have been determined by qRT-PCR, western-blot and immunohistochemistry. In this regard, AK explants reproduce the signalling pathways involve in DN progression (proinflammatory NFkB and inflammasome complex). This work demonstrates AK explants is a physiological experimental approach for studying the development and progression of DN. Furthermore, the inflammatory processes in AK explants under a diabetic environment and/or BB rats could be modulated by potential treatments for DN.

Ars moriendi: Proteases as sculptors of cellular suicide

The Ars moriendi, which translates to "The Art of Dying," encompasses two Latin texts that gave advice on how to die well and without fear according to the Christian precepts of the late Middle Ages. Given that ten to hundred billion cells die in our bodies every day, it is obvious that the concept of a well and orderly ("regulated") death is also paramount at the cellular level. In apoptosis, as the most well-studied form of regulated cell death, proteases of the caspase family are the central mediators. However, caspases are not the only proteases that act as sculptors of cellular suicide, and therefore, we here provide an overview of the impact of proteases in apoptosis and other forms of regulated cell death.

The Pseudomonas aeruginosa Type III Secretion System Exoenzyme Effector ExoU Induces Mitochondrial Damage in a Murine Bone Marrow-Derived Macrophage Infection Model

Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that causes nosocomial pneumonia, urinary tract infections, and bacteremia. A hallmark of P. aeruginosa pathogenesis is disruption of host cell function by the type III secretion system (T3SS) and its cognate exoenzyme effectors. The T3SS effector ExoU is phospholipase A2 (PLA2) that targets the host cell plasmalemmal membrane to induce cytolysis and is an important virulence factor that mediates immune avoidance. In addition, ExoU has been shown to subvert the host inflammatory response in a noncytolytic manner. In primary bone marrow-derived macrophages (BMDMs), P. aeruginosa infection is sensed by the nucleotide-binding domain containing leucine-rich repeats-like receptor 4 (NLRC4) inflammasome, which triggers caspase-1 activation and inflammation. ExoU transiently inhibits NLRC4 inflammasome-mediated activation of caspase-1 and its downstream target, interleukin 1β (IL-1β), to suppress activation of inflammation. In the present study, we sought to identify additional noncytolytic virulence functions for ExoU and discovered an unexpected association between ExoU, host mitochondria, and NLRC4. We show that infection of BMDMs with P. aeruginosa strains expressing ExoU elicited mitochondrial oxidative stress. In addition, mitochondria and mitochondrion-associated membrane fractions enriched from infected cells exhibited evidence of autophagy activation, indicative of damage. The observation that ExoU elicited mitochondrial stress and damage suggested that ExoU may also associate with mitochondria during infection. Indeed, ExoU phospholipase A2 enzymatic activity was present in enriched mitochondria and mitochondrion-associated membrane fractions isolated from P. aeruginosa-infected BMDMs. Intriguingly, enriched mitochondria and mitochondrion-associated membrane fractions isolated from infected Nlrc4 homozygous knockout BMDMs displayed significantly lower levels of ExoU enzyme activity, suggesting that NLRC4 plays a role in the ExoU-mitochondrion association. These observations prompted us to assay enriched mitochondria and mitochondrion-associated membrane fractions for NLRC4, caspase-1, and IL-1β. NLRC4 and pro-caspase-1 were detected in enriched mitochondria and mitochondrion-associated membrane fractions isolated from noninfected BMDMs, and active caspase-1 and active IL-1β were detected in response to P. aeruginosa infection. Interestingly, ExoU inhibited mitochondrion-associated caspase-1 and IL-1β activation. The implications of ExoU-mediated effects on mitochondria and the NLRC4 inflammasome during P. aeruginosa infection are discussed.

The colonic pathogen Entamoeba histolytica activates caspase-4/1 that cleaves the pore-forming protein gasdermin D to regulate IL-1β secretion

A hallmark of Entamoeba histolytica (Eh) invasion in the gut is acute inflammation dominated by the secretion of pro-inflammatory cytokines TNF-α and IL-1β. This is initiated when Eh in contact with macrophages in the lamina propria activates caspase-1 by recruiting the NLRP3 inflammasome complex in a Gal-lectin and EhCP-A5-dependent manner resulting in the maturation and secretion of IL-1β and IL-18. Here, we interrogated the requirements and mechanisms for Eh-induced caspase-4/1 activation in the cleavage of gasdermin D (GSDMD) to regulate bioactive IL-1β release in the absence of cell death in human macrophages. Unlike caspase-1, caspase-4 activation occurred as early as 10 min that was dependent on Eh Gal-lectin and EhCP-A5 binding to macrophages. By utilizing CRISPR-Cas9 gene edited CASP4/1, NLRP3 KO and ASC-def cells, caspase-4 activation was found to be independent of the canonical NLRP3 inflammasomes. In CRISPR-Cas9 gene edited CASP1 macrophages, caspase-4 activation was significantly up regulated that enhanced the enzymatic cleavage of GSDMD at the same cleavage site as caspase-1 to induce GSDMD pore formation and sustained bioactive IL-1β secretion. Eh-induced IL-1β secretion was independent of pyroptosis as revealed by pharmacological blockade of GSDMD pore formation and in CRISPR-Cas9 gene edited GSDMD KO macrophages. This was in marked contrast to the potent positive control, lipopolysaccharide + Nigericin that induced high expression of predominantly caspase-1 that efficiently cleaved GSDMD with high IL-1β secretion/release associated with massive cell pyroptosis. These results reveal that Eh triggered “hyperactivated macrophages” allowed caspase-4 dependent cleavage of GSDMD and IL-1β secretion to occur in the absence of pyroptosis that may play an important role in disease pathogenesis.

A unique feature of Entamoeba histolytica (Eh) infection is the capability to cause symptoms in only a limited subset of individuals. This occurs when Eh breaches intestinal innate host defences and comes in contact with the colonic epithelium and immune cells in the lamina propria to elicit a pro-inflammatory response critical in disease pathogenesis. Macrophages are considered among the first responders that Eh comes in direct contact with to activate caspase-1 by initiating the assembly of the NLRP3 inflammasome complex in a Gal-lectin and EhCP-A5-dependent manner, resulting in processing and release of IL-1β. In this study, we showed that inflammatory caspase-4 was activated earlier than caspase-1 when Eh contacts macrophages independent of the NLRP3 inflammasome complex. More importantly, Eh-induced caspase-4 was essential in regulating bioactive IL-1β secretion in the absence of cell death (pyroptosis) that was induced primarily by the activation of caspase-1. Mechanistically, we reveal that Eh-induced caspase-4 activation was critically important in regulating a measured amount of gasdermin D (GSDMD) cleavage resulting in GSDMD pore formation that facilitated sustained IL-1β secretion from macrophages. This was in marked contrast to LPS + Nigericin stimulated macrophages that robustly activated casapase-1 via the NLRP3 inflammasome that resulted in almost complete cleavage of GSDMD with pore-forming proteins that caused massive pyroptosis. Our study provides new insights on how Eh in contact with macrophages fine tune macrophage responses via the activation of caspase-4/1 to allow the cell to regulate IL-1β release by keeping the cells alive. We believe this mechanism of activating macrophages (termed hyperactivation) is a critically overlooked response in the biology of Eh that may play a major role in disease pathogenesis and host defence.

TRIMs: Generalists Regulating the NLRP3 Inflammasome Signaling Pathway

Inflammation is a double-edged sword. The moderate inflammatory response is a fundamental defense mechanism produced by the body's resistance to dangerous stimuli and a repair process of the body itself. Increasing studies have confirmed that the overactivation of the inflammasome is involved in the occurrence and development of inflammatory diseases. Strictly controlling the overactivation of the inflammasome and preventing excessive inflammatory response have always been the research focus on inflammatory diseases. However, the endogenous regulatory mechanism of inflammasome is not completely clear. The tripartite motif (TRIM) protein is one of the members of E3 ligases in the process of ubiquitination. The universality and importance of the functions of TRIM members are recognized, including the regulation of inflammatory response. This article will focus on research on the relationship between TRIMs and NLRP3 Inflammasome, which may help us make some references for future related research and the discovery of treatment methods.

Mechanistic Insights into Gasdermin Pore Formation and Regulation in Pyroptosis

The gasdermin family is a newly identified class of pore-forming proteins that play as the executioners of pyroptosis, a lytic pro-inflammatory type of cell death triggered by sensing cytosolic infections and danger signals. Upon activation, the gasdermin N-terminal domain translocates to the cell membrane to form pores, which allow the release of proinflammatory cytokines and alarmins, and cause cell lysis. Many structural studies have been conducted in the past few years to investigate the mechanisms of gasdermin proteins in the activation and pore formation. Here, we review these high-resolution structures and highlight the mechanistic insights into the gasdermin activation and regulation that are provided.

Coronaviruses Nsp5 Antagonizes Porcine Gasdermin D-Mediated Pyroptosis by Cleaving Pore-Forming p30 Fragment

Coronaviruses (CoVs) are a family of RNA viruses that typically cause respiratory, enteric, and hepatic diseases in animals and humans. Here, we use porcine epidemic diarrhea virus (PEDV) as a model of CoVs to illustrate the reciprocal regulation between CoV infection and pyroptosis. For the first time, we elucidate the molecular mechanism of porcine gasdermin D (pGSDMD)-mediated pyroptosis and demonstrate that amino acids R238, T239, and F240 within pGSDMD-p30 are critical for pyroptosis. Furthermore, 3C-like protease Nsp5 from SARS-CoV-2, MERS-CoV, PDCoV, and PEDV can cleave pGSDMD at the Q193-G194 junction to produce two fragments unable to trigger pyroptosis. The two cleaved fragments could not inhibit PEDV replication. In addition, Nsp5 from SARS-CoV-2 and MERS-CoV also cleave human GSDMD (hGSDMD). Therefore, we provide clear evidence that PEDV may utilize the Nsp5-GSDMD pathway to inhibit pyroptosis and, thus, facilitate viral replication during the initial period, suggesting an important strategy for the coronaviruses to sustain their infection. IMPORTANCE Recently, GSDMD has been reported as a key executioner for pyroptosis. This study first demonstrates the molecular mechanism of pGSDMD-mediated pyroptosis and that the pGSDMD-mediated pyroptosis protects host cells against PEDV infection. Notably, PEDV employs its Nsp5 to directly cleave pGSDMD in favor of its replication. We found that Nsp5 proteins from other coronaviruses, such as porcine deltacoronavirus, severe acute respiratory syndrome coronavirus 2, and Middle East respiratory syndrome coronavirus, also had the protease activity to cleave human and porcine GSDMD. Thus, we provide clear evidence that the coronaviruses might utilize Nsp5 to inhibit the host pyroptotic cell death and facilitate their replication during the initial period, an important strategy for their sustaining infection. We suppose that GSDMD is an appealing target for the design of anticoronavirus therapies.

ExoU Induces Lung Endothelial Cell Damage and Activates Pro-Inflammatory Caspase-1 during Pseudomonas aeruginosa Infection

The Gram-negative, opportunistic pathogen Pseudomonas aeruginosa utilizes a type III secretion system to inject exoenzyme effectors into a target host cell. Of the four best-studied exoenzymes, ExoU causes rapid cell damage and death. ExoU is a phospholipase A₂ (PLA₂) that hydrolyses host cell membranes, and P. aeruginosa strains expressing ExoU are associated with poor outcomes in critically ill patients with pneumonia. While the effects of ExoU on lung epithelial and immune cells are well studied, a role for ExoU in disrupting lung endothelial cell function has only recently emerged. Lung endothelial cells maintain a barrier to fluid and protein flux into tissue and airspaces and regulate inflammation. Herein, we describe a pulmonary microvascular endothelial cell (PMVEC) culture infection model to examine the effects of ExoU. Using characterized P. aeruginosa strains and primary clinical isolates, we show that strains expressing ExoU disrupt PMVEC barrier function by causing substantial PMVEC damage and lysis, in a PLA₂-dependent manner. In addition, we show that strains expressing ExoU activate the pro-inflammatory caspase-1, in a PLA₂-dependent manner. Considering the important roles for mitochondria and oxidative stress in regulating inflammatory responses, we next examined the effects of ExoU on reactive oxygen species production. Infection of PMVECs with P. aeruginosa strains expressing ExoU triggered a robust oxidative stress compared to strains expressing other exoenzyme effectors. We also provide evidence that, intriguingly, ExoU PLA₂ activity was detectable in mitochondria and mitochondria-associated membrane fractions isolated from P. aeruginosa-infected PMVECs. Interestingly, ExoU-mediated activation of caspase-1 was partially inhibited by reactive oxygen species scavengers. Together, these data suggest ExoU exerts pleiotropic effects on PMVEC function during P. aeruginosa infection that may inhibit endothelial barrier and inflammatory functions.

The role of Cl- and K+ efflux in NLRP3 inflammasome and innate immune response activation

Inflammation is part of innate immunity and is a natural response of the body to bacteria, virus, any other pathogen infections, or to damaged tissues. However, too much inflammation or chronic inflammation contributes to a wide variety of diseases such as inflammatory bowel disease, cancer, type 2 diabetes, heart disease, or autoimmune disease such as rheumatoid arthritis. Recent studies underscored the critical role of K⁺ and Cl^- efflux in the activation of the inflammasome. The NLRP3 inflammasome is a multiprotein complex that mediates the production of the proinflammatory cytokines IL-1β and IL-18 and initiates the inflammatory cell death or pyroptosis. The NLRP3 inflammasome can be activated by multiple stimuli such as extracellular ATP, microbial toxins, ROS, mitochondria DNA or particulate matter. Although the precise mechanisms of NLRP3 activation and regulation by these diverse agonists remain unclear, multiple reports indicate that all NLRP3 agonists ultimately lead to a drop in intracellular concentration of potassium (K⁺ efflux) and chloride (Cl^- efflux). The WNK-SPAK/OSR1-[N]KCC pathway plays a critical role maintaining K⁺ and Cl^- ions concentration in the cell. Recent advances indicate that the WNK-SPAK-[N]KCC pathway play a role in the activation of the innate immune response. This review highlights recent discoveries detailing how ion transport regulates innate immune cell response to inflammatory stimuli.

Cytokines and Inflammation in Meniere Disease

Meniere disease (MD) is a rare set of conditions associated with the accumulation of endolymph in the cochlear duct and the vestibular labyrinth with a decrease of endocochlear potential. It is considered a chronic inflammatory disorder of the inner ear with a multifactorial origin. The clinical syndrome includes several groups of patients with a core phenotype: sensorineural hearing loss, episodes of vertigo, and tinnitus with a non-predictable course. Genetic factors and the innate immune response seem to play a central role in the pathophysiology of the condition. Autoimmune MD should be diagnosed if a patient fulfills the diagnostic criteria for MD and one of the following autoimmune disorders: autoimmune thyroid disease, psoriasis, autoimmune arthritis, ankylosing spondylitis, or systemic lupus erythematosus. We summarize the evidence to support autoimmune MD as an endophenotype in bilateral MD associated with the allelic variant rs4947296 and nuclear factor-kappa B (NF-κB)-mediated inflammation, the role of cytokines (particularly interleukin-1β and tumor necrosis factor-α) in defining a subset of patients with autoinflammation, and the potential role of cytokines as biomarkers to distinguish between patients with MD and vestibular migraine. Finally, we also introduce a list of potential drugs that could regulate the immune response in MD with potential for repurposing in clinical trials.

Pyroptosis: A Developing Foreland of Ovarian Cancer Treatment

Ovarian cancer (OVCA) has the second highest mortality among all gynecological cancers worldwide due to its complexity and difficulty in early-stage diagnosis and a lack of targeted therapy. Modern strategies of OVCA treatment involve debulking surgery combined with chemotherapy. Nonetheless, the current treatment is far from satisfactory sometimes and therefore the demand for novel therapeutic measures needs to be settled. Pyroptosis is a notable form of programmed cell death characterized by influx of sodium with water, swelling of cells, and finally osmotic lysis, which is distinctive from numerous classes of programmed cell death. So far, four major pathways underlying mechanisms of pyroptosis have been identified and pyroptosis is indicated to be connected with a variety of disorders including cancerous diseases. Interestingly enough, pyroptosis plays an important role in ovarian cancer with regard to long non-coding RNAs and several regulatory molecules, as is shown by previously published reports. In this review, we summarized major pathways of pyroptosis and the current research foundations of pyroptosis and ovarian cancer, anticipating enriching the thoughts for the treatment of ovarian cancer. What is more, some problems yet unsolved in this field were also raised to hopefully propose several potential threads of OVCA treatment and research directions in future.

Role of Interleukin-1 in the pathogenesis of colorectal cancer: A brief look at anakinra therapy

Colorectal cancer (CRC) is known as one of the deadliest and most common cancers globally and causes nearly one million cancer deaths yearly. Like many malignancies, the immune system and its components play a crucial role in the pathogenesis of CRC. As multifunction mediators of the immune system, cytokines are involved in several inflammatory and anti-inflammatory responses. Interleukin-1 (IL-1) belongs to a family of 11 members and is involved in inflammatory responses. Beyond its biological role as a mediator of innate immune responses, it is also seen in chronic stress and inflammation and numerous pathological states. The role of IL-1 in malignancies can also be very significant because it has recently been shown that this cytokine can also be secreted from tumor cells and induce the recruitment of myeloid-derived immunosuppressive cells. As a result, the tumor microenvironment (TME) is affected and, despite being inflammatory, causes the onset and progression of tumor cells. Since surgery and chemotherapy are the first choices to treat patients with cancer, especially CRC, it is usually not well-prognosed, particularly in patients with metastatic lesions CRC. Therefore, targeted therapy may prolong the overall survival of CRC patients. Furthermore, evidence shows that anakinra has had satisfactory results in treating CRC. Therefore, this review summarized the role of IL-1 in the pathogenesis of CRC as well as immunotherapy based on inhibition of this cytokine in this type of cancer.

The IFN-inducible GTPase IRGB10 regulates viral replication and inflammasome activation during influenza A virus infection in mice

The upregulation of interferon (IFN)-inducible GTPases in response to pathogenic insults is vital to host defense against many bacterial, fungal, and viral pathogens. Several IFN-inducible GTPases play key roles in mediating inflammasome activation and providing host protection after bacterial or fungal infections, though their role in inflammasome activation after viral infection is less clear. Among the IFN-inducible GTPases, the expression of immunity-related GTPases (IRGs) varies widely across species for unknown reasons. Here, we report that IRGB10, but not IRGM1, IRGM2, or IRGM3, is required for NLRP3 inflammasome activation in response to influenza A virus (IAV) infection in mice. While IRGB10 functions to release inflammasome ligands in the context of bacterial and fungal infections, we found that IRGB10 facilitates endosomal maturation and nuclear translocation of IAV, thereby regulating viral replication. Corresponding with our in vitro results, we found that Irgb10^-/- mice were more resistant to IAV-induced mortality than WT mice. The results of our study demonstrate a detrimental role of IRGB10 in host immunity in response to IAV and a novel function of IRGB10, but not IRGMs, in promoting viral translocation into the nucleus.

Focus on the Mechanisms and Functions of Pyroptosis, Inflammasomes, and Inflammatory Caspases in Infectious Diseases

Eukaryotic cells can initiate several distinct self-destruction mechanisms to display essential roles for the homeostasis maintenance, development, and survival of an organism. Pyroptosis, a key response mode in innate immunity, also referred to as caspase-1-dependent proinflammatory programmed necrotic cell death activated by human caspase-1/4/5, or mouse caspase-1/11, plays indispensable roles in response to cytoplasmic insults and immune defense against infectious diseases. These inflammatory caspases are employed by the host to eliminate pathogen infections such as bacteria, viruses, protozoans, and fungi. Gasdermin D requires to be cleaved and activated by these inflammatory caspases to trigger the pyroptosis process. Physiological rupture of cells results in the release of proinflammatory cytokines, the alarmins IL-1β and IL-18, symbolizing the inflammatory potential of pyroptosis. Moreover, long noncoding RNAs play direct or indirect roles in the upstream of the pyroptosis trigger pathway. Here, we review in detail recently acquired insights into the central roles of inflammatory caspases, inflammasomes, and pyroptosis, as well as the crosstalk between pyroptosis and long noncoding RNAs in mediating infection immunity and pathogen clearance.