The AIM2 inflammasome is critical for innate immunity to Francisella tularensis

Correlation between double-stranded DNA and acute urticaria

BACKGROUND

Acute urticaria is a prevalent inflammatory dermatosis characterized by fulminant wheals, often accompanied by severe pruritis. It may also cause nausea, vomiting, and abdominal pain. Numerous studies have substantiated the pivotal involvement of double-stranded DNA (dsDNA) in autoimmunity. However, the role of dsDNA in the pathogenesis of acute urticaria is unclear.

METHODS

We measured serum dsDNA levels in patients and controls. The relationship between dsDNA levels and environmental exposures (temperature, ultraviolet [UV] index, and season) was investigated by correlating disease onset dates with archived meteorological data. Finally, we used quantitative PCR to determine the expressions of genes encoding dsDNA receptors, single-stranded RNA (ssRNA) receptors, exosome formation, and type I interferon in the peripheral blood of patients and controls.

RESULTS

Serum dsDNA levels were significantly higher in patients with acute urticaria compared with controls (mean values 1.38 and 0.94 ng/ml, respectively, P < 0.001). dsDNA levels were higher in patients exposed to higher environmental temperatures and UV indices and were higher during the summer months. We also found that the expressions of genes encoding dsDNA receptors, ssRNA receptors, absent in melanoma factor 2 (AIM2)-related inflammatory factors, and interferon alpha were up-regulated in patients.

CONCLUSIONS

We demonstrated that serum dsDNA levels are elevated in acute urticaria and are influenced by climatic factors such as temperature, ultraviolet index, and season. We also found that elevated dsDNA promotes the expression of AIM2-related factors and type I interferons. This study generates new hypotheses regarding the pathogenesis of acute urticaria and suggests novel therapeutic targets.

Immune System of Dental Pulp in Inflamed and Normal Tissue

Teeth are vulnerable to structural compromise, primarily attributed to carious lesions, in which microorganisms originating from the oral cavity deteriorate the mineralized structures of enamel and dentin, subsequently infiltrating the underlying soft connective tissue, known as the dental pulp. Nonetheless, dental pulp possesses the necessary capabilities to detect and defend against bacteria and their by-products, using a variety of intricate defense mechanisms. The pulp houses specialized cells known as odontoblasts, which encounter harmful substances produced by oral bacteria. These cells identify pathogens at an early stage and commence the immune system response. As bacteria approach the pulp, various cell types within the pulp, such as different immune cells, stem cells, fibroblasts, as well as neuronal and vascular networks, contribute a range of defense mechanisms. Therefore, the immune system is present in the healthy pulp to restrain the initial spread of pathogens, and then in the inflamed pulp, it prepares the conditions for necrosis or regeneration, so inflammatory response mechanisms play a critical role in maintaining tissue homeostasis. This review aims to consolidate the existing literature on the immune system in dental pulp, encompassing current knowledge on this topic that explains the diverse mechanisms of recognition and defense against pathogens exhibited by dental pulp cells, elucidates the mechanisms of innate and adaptive immunity in inflamed pulp, and highlights the difference between inflamed and normal pulp tissue.

The roles of AIM2 in neurodegenerative diseases: insights and therapeutic implications

AIM2, a cytosolic innate immune receptor, has the capability to recognize double-stranded DNA (dsDNA). This paper delineates the structural features of AIM2 and its mechanisms of activation, emphasizing its capacity to detect cytosolic DNA and initiate inflammasome assembly. Additionally, we explore the diverse functions of AIM2 in different cells. Insights into AIM2-mediated neuroinflammation provide a foundation for investigating novel therapeutic strategies targeting AIM2 signaling pathways. Furthermore, we present a comprehensive review of the roles of AIM2 in neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Finally, we discuss its therapeutic implications. In conclusion, a profound understanding of AIM2 in neurodegenerative diseases may facilitate the development of effective interventions to mitigate neuronal damage and slow disease progression.

Unanticipated Loss of Inflammasomes in Birds

Inflammasomes are multiprotein complexes that form in response to ligands originating from pathogens as well as alterations of normal cell physiology caused by infection or tissue damage. These structures engage a robust inflammatory immune response that eradicates environmental microbes before they cause disease, and slow the growth of bona fide pathogens. Despite their undeniable utility in immunity, inflammasomes are radically reduced in birds. Perhaps most surprising is that, within all birds, NLRP3 is retained, while its signaling adapter ASC is lost, suggesting that NLRP3 signals via a novel unknown adapter. Crocodilian reptiles and turtles, which share a more recent common ancestor with birds, retain many of the lost inflammasome components, indicating that the deletion of inflammasomes occurred after birds diverged from crocodiles. Some bird lineages have even more extensive inflammasome loss, with songbirds continuing to pare down their inflammasomes until only NLRP3 and CARD8 remain. Remarkably, songbirds have lost caspase-1 but retain the downstream targets of caspase-1: IL-1β, IL-18, and the YVAD-linker encoding gasdermin A. This suggests that inflammasomes can signal through alternative proteases to activate cytokine maturation and pyroptosis in songbirds. These observations may reveal new contexts of activation that may be relevant to mammalian inflammasomes and may suggest new avenues of research to uncover the enigmatic nature of the poorly understood NLRP3 inflammasome.

Absent in Melanoma 2 Mediates Inflammasome Signaling Activation against Clostridium perfringens Infection

Absent in melanoma 2 (AIM2), a key component of the IFI20X/IFI16 (PYHIN) protein family, is characterized as a DNA sensor to detect cytosolic bacteria and DNA viruses. However, little is known about its immunological role during pathogenic Clostridium perfringens (C. perfringens) infection, an extracellular bacterial pathogen. In a pathogenic C. perfringens gas gangrene model, Aim2-/- mice are more susceptible to pathogenic C. perfringens soft tissue infection, revealing the importance of AIM2 in host protection. Notably, Aim2 deficiency leads to a defect in bacterial killing and clearance. Our in vivo and in vitro findings further establish that inflammasome signaling is impaired in the absence of Aim2 in response to pathogenic C. perfringens. Mechanistically, inflammasome signaling downstream of active AIM2 promotes pathogen control. Importantly, pathogenic C. perfringens-derived genomic DNA triggers inflammasome signaling activation in an AIM2-dependent manner. Thus, these observations uncover a central role for AIM2 in host defense and triggering innate immunity to combat pathogenic C. perfringens infections.

Strategies of bacterial detection by inflammasomes

Mammalian innate immunity is regulated by pattern-recognition receptors (PRRs) and guard proteins, which use distinct strategies to detect infections. PRRs detect bacterial molecules directly, whereas guards detect host cell manipulations by microbial virulence factors. Despite sensing infection through different mechanisms, both classes of innate immune sensors can activate the inflammasome, an immune complex that can mediate cell death and inflammation. Inflammasome-mediated immune responses are crucial for host defense against many bacterial pathogens and prevent invasion by non-pathogenic organisms. In this review, we discuss the mechanisms by which inflammasomes are stimulated by PRRs and guards during bacterial infection, and the strategies used by virulent bacteria to evade inflammasome-mediated immunity.

AIM2 participates in house dust mite (HDM)-induced epithelial dysfunctions and ovalbumin (OVA)-induced allergic asthma in infant mice

Objective: Allergen sensitization and high rates of concomitant allergic diseases are characteristic of severe pediatric asthma. The present study was aimed to explore the mechanism of allergic asthma via bioinformatics and experiment investigation. Methods: The GSE27011 dataset contained the expression profiles of normal and pediatric asthma white blood cells was downloaded for analyzing the different expression genes and function enrichment. The allergic asthma model in infant mice was established by ovalbumin (OVA) stimulation. The cellular model was established by house dust mite (HDM)-stimulation in human bronchial epithelial cells. The absent in melanoma 2 (AIM2) knockdown was achieved by intranasal lentivirus injection or cell infection. The bronchoalveolar lavage fluid (BALF) was collected for cell counting and ELISA assessment of cytokines. Lung tissues were collected for HE staining and immunohistochemical (IHC) staining. Real-time PCR and immunoblotting were used for the determination of key gene expressions in mouse and cell models. Results: upregulation of AIM2 gene expression was observed in pediatric asthma patients based on GSE27011 and OVA-induced infant mouse allergic asthma model. AIM2 knockdown ameliorated OVA caused elevation in airway hyper-responsiveness (AHR), elevation in cell quantities (eosinophils, neutrophils, lymphocytes), and levels of cytokines (IL-4, IL-13, TNF-α, and OVA-specific IgE) in BALF. Moreover, AIM2 knockdown relieved OVA-caused histopathological alterations in mouse lungs, up-regulation of AIM2 levels, and NOD1 and receptor-interacting protein 2 (RIP2) protein levels, as well as p65 phosphorylation. In the cell model, AIM2 knockdown partially ameliorated HDM-induced epithelial dysfunctions by promoting cell viability, down-regulating inflammatory cytokines levels, and decreasing the protein levels of AIM2, NOD1, RIP2, and phosphorylated p65. Conclusion: AIM2 participates in HDM-induced epithelial dysfunctions and OVA-induced allergic asthma progression. AIM2 could be a promising target for pediatric allergic asthma treatment regimens, which warrants further in vivo investigations.

Pervasive loss of regulated necrotic cell death genes in elephants, hyraxes, and sea cows (Paenungualta)

Gene loss can promote phenotypic differences between species, for example, if a gene constrains phenotypic variation in a trait, its loss allows for the evolution of a greater range of variation or even new phenotypes. Here, we explore the contribution of gene loss to the evolution of large bodies and augmented cancer resistance in elephants. We used genomes from 17 Afrotherian and Xenarthran species to identify lost genes, i.e., genes that have pseudogenized or been completely lost, and Dollo parsimony to reconstruct the evolutionary history of gene loss across species. We unexpectedly discovered a burst of gene losses in the Afrotherian stem lineage and found that the loss of genes with functions in regulated necrotic cell death modes was pervasive in elephants, hyraxes, and sea cows (Paenungulata). Among the lost genes are MLKL and RIPK3, which mediate necroptosis, and sensors that activate inflammasomes to induce pyroptosis, including AIM2, MEFV, NLRC4, NLRP1, and NLRP6. These data suggest that the mechanisms that regulate necrosis and pyroptosis are either extremely derived or potentially lost in these lineages, which may contribute to the repeated evolution of large bodies and cancer resistance in Paenungulates as well as susceptibility to pathogen infection.

Dual proteomics of infected macrophages reveal bacterial and host players involved in the Francisella intracellular life cycle and cell to cell dissemination by merocytophagy

Bacterial pathogens adapt and replicate within host cells, while host cells develop mechanisms to eliminate them. Using a dual proteomic approach, we characterized the intra-macrophage proteome of the facultative intracellular pathogen, Francisella novicida. More than 900 Francisella proteins were identified in infected macrophages after a 10-h infection. Biotin biosynthesis-related proteins were upregulated, emphasizing the role of biotin-associated genes in Francisella replication. Conversely, proteins encoded by the Francisella pathogenicity island (FPI) were downregulated, supporting the importance of the F. tularensis Type VI Secretion System for vacuole escape, not cytosolic replication. In the host cell, over 300 proteins showed differential expression among the 6200 identified during infection. The most upregulated host protein was cis-aconitate decarboxylase IRG1, known for itaconate production with antimicrobial properties in Francisella. Surprisingly, disrupting IRG1 expression did not impact Francisella's intracellular life cycle, suggesting redundancy with other immune proteins or inclusion in larger complexes. Over-representation analysis highlighted cell-cell contact and actin polymerization in macrophage deregulated proteins. Using flow cytometry and live cell imaging, we demonstrated that merocytophagy involves diverse cell-to-cell contacts and actin polymerization-dependent processes. These findings lay the groundwork for further exploration of merocytophagy and its molecular mechanisms in future research.Data are available via ProteomeXchange with identifier PXD035145.

Advances in the mechanism of inflammasomes activation in herpes virus infection

Herpesviruses, prevalent DNA viruses with a double-stranded structure, establish enduring infections and play a part in various diseases. Despite their deployment of multiple tactics to evade the immune system, both localized and systemic inflammatory responses are triggered by the innate immune system's recognition of them. Recent progress has offered more profound understandings of the mechanisms behind the activation of the innate immune system by herpesviruses, specifically through inflammatory signaling. This process encompasses the initiation of an intracellular nucleoprotein complex, the inflammasome associated with inflammation.Following activation, proinflammatory cytokines such as IL-1β and IL-18 are released by the inflammasome, concurrently instigating a programmed pathway for cell death. Despite the structural resemblances between herpesviruses, the distinctive methods of inflammatory activation and the ensuing outcomes in diseases linked to the virus exhibit variations.The objective of this review is to emphasize both the similarities and differences in the mechanisms of inflammatory activation among herpesviruses, elucidating their significance in diseases resulting from these viral infections.Additionally, it identifies areas requiring further research to comprehensively grasp the impact of this crucial innate immune signaling pathway on the pathogenesis of these prevalent viruses.

A Variety of Mouse PYHIN Proteins Restrict Murine and Human Retroviruses

PYHIN proteins are only found in mammals and play key roles in the defense against bacterial and viral pathogens. The corresponding gene locus shows variable deletion and expansion ranging from 0 genes in bats, over 1 in cows, and 4 in humans to a maximum of 13 in mice. While initially thought to act as cytosolic immune sensors that recognize foreign DNA, increasing evidence suggests that PYHIN proteins also inhibit viral pathogens by more direct mechanisms. Here, we examined the ability of all 13 murine PYHIN proteins to inhibit HIV-1 and murine leukemia virus (MLV). We show that overexpression of p203, p204, p205, p208, p209, p210, p211, and p212 strongly inhibits production of infectious HIV-1; p202, p207, and p213 had no significant effects, while p206 and p214 showed intermediate phenotypes. The inhibitory effects on infectious HIV-1 production correlated significantly with the suppression of reporter gene expression by a proviral Moloney MLV-eGFP construct and HIV-1 and Friend MLV LTR luciferase reporter constructs. Altogether, our data show that the antiretroviral activity of PYHIN proteins is conserved between men and mice and further support the key role of nuclear PYHIN proteins in innate antiviral immunity.

Mammalian Target of Rapamycin Complex 1 Activation in Macrophages Contributes to Persistent Lung Inflammation following Respiratory Tract Viral Infection

Respiratory tract virus infections cause millions of hospitalizations worldwide each year. Severe infections lead to lung damage that coincides with persistent inflammation and a lengthy repair period. Vaccination and antiviral therapy help to mitigate severe infections before or during the acute stage of disease, but there are currently limited specific treatment options available to individuals experiencing the long-term sequelae of respiratory viral infection. Herein, C57BL/6 mice were infected with influenza A/PR/8/34 as a model for severe viral lung infection and allowed to recover for 21 days. Mice were treated with rapamycin, a well-characterized mammalian target of rapamycin complex 1 (mTORC1) inhibitor, on days 12 to 20 after infection, a time period after viral clearance. Persistent inflammation following severe influenza infection in mice was primarily driven by macrophages and T cells. Uniform manifold approximation and projection analysis of flow cytometry data revealed that lung macrophages had high activation of mTORC1, an energy-sensing kinase involved in inflammatory immune cell effector functions. Rapamycin treatment reduced lung inflammation and the frequency of exudate macrophages, T cells, and B cells in the lung, while not impacting epithelial progenitor cells or adaptive immune memory. These data highlight mTORC1's role in sustaining persistent inflammation following clearance of a viral respiratory pathogen and suggest a possible intervention for post-viral chronic lung inflammation.

Mitochondrial damage and clearance in retinal pigment epithelial cells

Age-related macular degeneration (AMD) is a devastating eye disease that causes permanent vision loss in the central part of the retina, known as the macula. Patients with such severe visual loss face a reduced quality of life and are at a 1.5 times greater risk of death compared to the general population. Currently, there is no cure for or effective treatment for dry AMD. There are several mechanisms thought to underlie the disease, for example, ageing-associated chronic oxidative stress, mitochondrial damage, harmful protein aggregation and inflammation. As a way of gaining a better understanding of the molecular mechanisms behind AMD and thus developing new therapies, we have created a peroxisome proliferator-activated receptor gamma coactivator 1-alpha and nuclear factor erythroid 2-related factor 2 (PGC1α/NFE2L2) double-knockout (dKO) mouse model that mimics many of the clinical features of dry AMD, including elevated levels of oxidative stress markers, damaged mitochondria, accumulating lysosomal lipofuscin and extracellular drusen-like structures in retinal pigment epithelial cells (RPE). In addition, a human RPE cell-based model was established to examine the impact of non-functional intracellular clearance systems on inflammasome activation. In this study, we found that there was a disturbance in the autolysosomal machinery responsible for clearing mitochondria in the RPE cells of one-year-old PGC1α/NFE2L2-deficient mice. The confocal immunohistochemical analysis revealed an increase in autophagosome marker microtubule-associated proteins 1A/1B light chain 3B (LC3B) as well as multiple mitophagy markers such as PTE-induced putative kinase 1 (PINK1) and E3 ubiquitin ligase (PARKIN), along with signs of damaged mitochondria. However, no increase in autolysosome formation was detected, nor was there a colocalization of the lysosomal marker LAMP2 or the mitochondrial marker, ATP synthase β. There was an upregulation of late autolysosomal fusion Ras-related protein (Rab7) in the perinuclear space of RPE cells, together with autofluorescent aggregates. Additionally, we observed an increase in the numbers of Toll-like receptors 3 and 9, while those of NOD-like receptor 3 were decreased in PGC1α/NFE2L2 dKO retinal specimens compared to wild-type animals. There was a trend towards increased complement component C5a and increased involvement of the serine protease enzyme, thrombin, in enhancing the terminal pathway producing C5a, independent of C3. The levels of primary acute phase C-reactive protein and receptor for advanced glycation end products were also increased in the PGC1α/NFE2L2 dKO retina. Furthermore, selective proteasome inhibition with epoxomicin promoted both nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondrial-mediated oxidative stress, leading to the release of mitochondrial DNA to the cytosol, resulting in potassium efflux-dependent activation of the absent in melanoma 2 (AIM2) inflammasome and the subsequent secretion of interleukin-1β in ARPE-19 cells. In conclusion, the data suggest that there is at least a relative decrease in mitophagy, increases in the amounts of C5 and thrombin and decreased C3 levels in this dry AMD-like model. Moreover, selective proteasome inhibition evoked mitochondrial damage and AIM2 inflammasome activation in ARPE-19 cells.

New insights into nucleic acid sensor AIM2: The potential benefit in targeted therapy for cancer

The AIM2 inflammasome represents a multifaceted oligomeric protein complex within the innate immune system, with the capacity to perceive double-stranded DNA (dsDNA) and engage in diverse physiological reactions and disease contexts, including cancer. While originally conceived as a discerning DNA sensor, AIM2 has demonstrated its capability to discern various nucleic acid variations, encompassing RNA and DNA-RNA hybrids. Through its interaction with nucleic acids, AIM2 orchestrates the assembly of a complex involving multiple proteins, aptly named the AIM2 inflammasome, which facilitates the enzymatic cleavage of proinflammatory cytokines, namely pro-IL-1β and pro-IL-18. This process, in turn, underpins its pivotal biological role. In this review, we provide a systematic summary and discussion of the latest advancements in AIM2 sensing various types of nucleic acids. Additionally, we discuss the modulation of AIM2 activation, which can cause cell death, including pyroptosis, apoptosis, and autophagic cell death. Finally, we fully illustrate the evidence for the dual role of AIM2 in different cancer types, including both anti-tumorigenic and pro-tumorigenic functions. Considering the above information, we uncover the therapeutic promise of modulating the AIM2 inflammasome in cancer treatment.

Cell death

Cell death supports morphogenesis during development and homeostasis after birth by removing damaged or obsolete cells. It also curtails the spread of pathogens by eliminating infected cells. Cell death can be induced by the genetically programmed suicide mechanisms of apoptosis, necroptosis, and pyroptosis, or it can be a consequence of dysregulated metabolism, as in ferroptosis. Here, we review the signaling mechanisms underlying each cell-death pathway, discuss how impaired or excessive activation of the distinct cell-death processes can promote disease, and highlight existing and potential therapies for redressing imbalances in cell death in cancer and other diseases.

Nanomaterial-induced pyroptosis: a cell type-specific perspective

This review presents the advancements in nanomaterial (NM)-induced pyroptosis in specific types of cells. We elucidate the relevance of pyroptosis and delineate its mechanisms and classifications. We also retrospectively analyze pyroptosis induced by various NMs in a broad spectrum of non-tumorous cellular environments to highlight the multifunctionality of NMs in modulating cell death pathways. We identify key knowledge gaps in current research and propose potential areas for future exploration. This review emphasizes the need to focus on less-studied areas, including the pathways and mechanisms of NM-triggered pyroptosis in non-tumor-specific cell types, the interplay between biological and environmental factors, and the interactions between NMs and cells. This review aims to encourage further investigations into the complex interplay between NMs and pyroptosis, thereby providing a basis for developing safer and more effective nanomedical therapeutic applications.

The role of inflammasomes in human diseases and their potential as therapeutic targets

Inflammasomes are large protein complexes that play a major role in sensing inflammatory signals and triggering the innate immune response. Each inflammasome complex has three major components: an upstream sensor molecule that is connected to a downstream effector protein such as caspase-1 through the adapter protein ASC. Inflammasome formation typically occurs in response to infectious agents or cellular damage. The active inflammasome then triggers caspase-1 activation, followed by the secretion of pro-inflammatory cytokines and pyroptotic cell death. Aberrant inflammasome activation and activity contribute to the development of diabetes, cancer, and several cardiovascular and neurodegenerative disorders. As a result, recent research has increasingly focused on investigating the mechanisms that regulate inflammasome assembly and activation, as well as the potential of targeting inflammasomes to treat various diseases. Multiple clinical trials are currently underway to evaluate the therapeutic potential of several distinct inflammasome-targeting therapies. Therefore, understanding how different inflammasomes contribute to disease pathology may have significant implications for developing novel therapeutic strategies. In this article, we provide a summary of the biological and pathological roles of inflammasomes in health and disease. We also highlight key evidence that suggests targeting inflammasomes could be a novel strategy for developing new disease-modifying therapies that may be effective in several conditions.

Characterization of Inflammasomes and Their Regulation in the Red Fox

BACKGROUND

Inflammasomes recognize endogenous and exogenous danger signals, and subsequently induce the secretion of IL-1β. Studying inflammasomes in the red fox (Vulpes vulpes) is crucial for wildlife veterinary medicine, as it can help control inflammatory diseases in foxes.

METHODS

We investigated the activation and intracellular mechanisms of three inflammasomes (NLRP3, AIM2, and NLRC4) in fox peripheral blood mononuclear cells (PBMCs), using established triggers and inhibitors derived from humans and mice.

RESULTS

Fox PBMCs exhibited normal activation and induction of IL-1β secretion in response to representative inflammasome triggers (ATP and nigericin for NLRP3, dsDNA for AIM2, flagellin for NLRC4). Additionally, PBMCs showed normal IL-1β secretion when inoculated with inflammasome-activating bacteria. In inhibitors of the inflammasome signaling pathway, fox inflammasome activation was compared with mouse inflammasomes. MCC950, a selective NLRP3 inhibitor, suppressed the secretion of dsDNA- and flagellin-mediated IL-1β in foxes, unlike mice.

CONCLUSIONS

These findings suggest that NLRP3 may have a common role in dsDNA- and flagellin-mediated inflammasome activation in the red fox. It implies that this fox inflammasome biology can be applied to the treatment of inflammasome-mediated diseases in the red fox.

Pathogenicity and virulence of Francisella tularensis

Tularaemia is a zoonotic disease caused by the Gram-negative bacterium, Francisella tularensis. Depending on its entry route into the organism, F. tularensis causes different diseases, ranging from life-threatening pneumonia to less severe ulceroglandular tularaemia. Various strains with different geographical distributions exhibit different levels of virulence. F. tularensis is an intracellular bacterium that replicates primarily in the cytosol of the phagocytes. The main virulence attribute of F. tularensis is the type 6 secretion system (T6SS) and its effectors that promote escape from the phagosome. In addition, F. tularensis has evolved a peculiar envelope that allows it to escape detection by the immune system. In this review, we cover tularaemia, different Francisella strains, and their pathogenicity. We particularly emphasize the intracellular life cycle, associated virulence factors, and metabolic adaptations. Finally, we present how F. tularensis largely escapes immune detection to be one of the most infectious and lethal bacterial pathogens.

PANoptosis in cancer, the triangle of cell death

BACKGROUND

PANoptosis is a novel form of programmed cell death (PCD) found in 2019 that is regulated by the PANoptosome. PANoptosis combines essential features of pyroptosis, apoptosis, and necroptosis, forming a "death triangle" of cells. While apoptosis, pyroptosis, and necroptosis have been extensively studied for their roles in human inflammatory diseases and many other clinical conditions, historically they were considered as independent processes. However, emerging evidence indicates that these PCDs exhibit cross talk and interactions, resulting in the development of the concept of PANoptosis.

METHODS

In this review, we offer a concise summary of the fundamental mechanisms of apoptosis, pyroptosis, and necroptosis. We subsequently introduce the notion of PANoptosis and detail the assembly mechanism of the PANoptosome complex which is responsible for inducing cell death. We also describe some regulatory networks of PANoptosis.

RESULTS

PANoptosis now has been associated with various human diseases including cancer. Although the exact function of PANoptosis in each tumor is not fully understood, it represents a prospective avenue for cancer therapy, offering promise for advancements in cancer therapy.

CONCLUSIONS

In the future, in-depth study of PANoptosis will continue to help us in understanding the fundamental processes underlying cell death and provide scientific support for cancer research.

PINK1-mediated mitophagy induction protects against preeclampsia by decreasing ROS and trophoblast pyroptosis

INTRODUCTION

Preeclampsia (PE) is a multisystemic disorder attributed to the excessive presentation of placenta-derived immunoinflammatory factors. PTEN-induced putative kinase 1 (PINK1)-mediated mitophagy participates in the development and persistence of the inflammation. We hypothesized that dysregulated mitophagy might be involved in the pathogenesis of PE by promoting the activation of trophoblast pyroptosis that augment inflammation.

METHODS

The morphology of mitochondrial in placenta were observed by transmission electron microscopy. The localization of PINK1 in the placenta was determined by immunohistochemistry. The expression levels of PINK1, PARKIN, LC3B, and SQSTM1 and pyroptosis-related molecules were compared between normal pregnancies and PE. We used hypoxia/reoxygenation (H/R) to stimulate the trophoblast hypoxia environment. HTR-8/SVneo cells were transfected with PINK1 plasmid and si-PINK1, respectively, and then were treated with H/R, to determine whether PINK1 regulated ROS and HTR-8/Svneo pyroptosis. Finally, ROS production was inhibited by MitoTEMPO to observe whether the pro-pyroptosis effect of PINK1 knockdown is alleviated.

RESULTS

Swollen mitochondrial were accumulated in the PE placentae. PINK1 is localized on villus trophoblast (VTs) and extravillous trophoblast (EVTs). PINK1-mediated mitophagy was abolished in the PE placenta, while the levels of pyroptosis were induced. H/R stimulation aggravated the downregulation of mitophagy and the up-regulation of pyroptosis. Overexpression of PINK1 mitigated H/R-induced upregulation of ROS and pyroptosis while silencing PINK1 did the opposite. Reducing ROS production can effectively resist the pro-pyroptosis effect of PINK1 knockdown.

DISCUSSION

This study demonstrated that PINK1-mediated mitophagy might played a protective role in PE by reducing ROS and trophoblast pyroptosis.

Progress in understanding the role of cGAS-STING pathway associated with programmed cell death in intervertebral disc degeneration

Nucleus pulposus (NP) inflammatory response can induce intervertebral disc degeneration (IVDD) by causing anabolic and catabolic disequilibrium of the extracellular matrix (ECM). This process is accompanied by the production of endogenous DNAs, then detectable by the DNA sensor cyclic GMP-AMP synthase (cGAS). cGAS recognizes these DNAs and activates the downstream adaptor protein, a stimulator of interferon genes (STING), initiating a cascade of inflammation responses through various cytokines. This evidence implies a crucial role of the cGAS-STING signaling pathway in IVDD. Additionally, it is suggested that this pathway could modulate IVDD progression by regulating apoptosis, autophagy, and pyroptosis. However, a detailed understanding of the role of cGAS-STING pathway in IVDD is still lacking. This review provides a comprehensive summary of recent advances in our understanding of the role of the cGAS-STING pathway in modulating inflammatory response in IVDD. We delve into the connection between the cGAS-STING axis and apoptosis, autophagy, and pyroptosis in IVDD. Furthermore, we discuss the therapeutic potential of targeting the cGAS-STING signaling pathway in IVDD treatment. Overall, this review aims to provide a foundation for future directions in IVDD treatment strategies.

Modified activities of macrophages' deubiquitinating enzymes after Francisella infection

Francisella tularensis influences several host molecular/signaling pathways during infection. Ubiquitination and deubiquitination are among the most important regulatory mechanisms and respectively occur through attachment or removal of the ubiquitin molecule. The process is necessary not only to mark molecules for degradation, but also, for example, to the activation of signaling pathways leading to pro-inflammatory host response. Many intracellular pathogens, including Francisella tularensis, have evolved mechanisms of modifying such host immune responses to escape degradation. Here, we describe that F. tularensis interferes with the host's ubiquitination system. We show increased total activity of deubiquitinating enzymes (DUBs) in human macrophages after infection, while confirm reduced enzymatic activities of two specific DUBs (USP10 and UCH-L5), and demonstrate increased activity of USP25. We further reveal the enrichment of these three enzymes in exosomes derived from F. tularensis-infected cells. The obtained results show the regulatory effect on ubiquitination mechanism in macrophages during F. tularensis infection.

Potential roles of inflammasomes in the pathophysiology of Psoriasis: A comprehensive review

Psoriasis is an inflammatory skin disease whose pathophysiology is attributed to both innate and adaptive immune cells and molecules. Despite the crucial roles of the immune system in psoriasis, it cannot be categorized as an autoimmune disease because of the lack of main signs of autoimmunity, such as specific antibodies, well-defined antigens, and autoimmune genetic risk factors. The presence of some cellular and molecular properties, such as the presence of neutrophils in skin lesions and the activation of the innate immune system, attributes psoriasis to a group of diseases called autoinflammatory disorders. Autoinflammatory diseases refer to a group of inherited disorders whose main manifestations are recurrent fever, a high level of acute-phase reactant, and a tendency for inflammation of the skin, joints, and other organs like the nervous system. In most autoinflammatory disorders, it has been seen that complexes of the high-molecular-weight protein named inflammasomes have significant roles. The inflammasome complex usually is formed and activated in the stimulated immune cell cytoplasm, and its activation consequently leads to inflammatory events such as producing of active caspase-1, mature interleukin-1β (IL-1β), and IL-18 and can cause an inflammatory programmed cell death called pyroptosis. Since the identification of inflammasomes, it has been shown that there are close links between them and hereditary and acquired autoinflammatory diseases like psoriasis. In this review, we aim to focus on well-defined inflammasome and their role in the pathophysiology of psoriasis.

In Vitro Evaluation of Apoptosis, Inflammation, Angiogenesis, and Neuroprotection Gene Expression in Retinal Pigmented Epithelial Cell Treated with Interferon α-2b

Angiogenesis, retinal neuropathy, and inflammation are the main molecular features of diabetic retinopathy (DR) and should be taken into consideration for potential treatment approaches. Retinal pigmented epithelial (RPE) cells play a major role in DR progression. This study evaluated the in vitro effect of interferon (IFN) α-2b on the expression of genes involved in apoptosis, inflammation, neuroprotection, and angiogenesis in RPE cells. RPE cells were cocultured with IFN α-2b at 2 doses (500 and 1,000 IU) and treatment periods (24 and 48 h). The quantitative relative expression of genes (BCL-2, BAX, BDNF, VEGF, and IL-1b) was evaluated in the treated versus control cells through real-time polymerase chain reaction (PCR). The result of this study demonstrated that IFN treatment at 1,000 IU (48 h) led to significant upregulation of BCL-2, BAX, BDNF, and IL-1b; however, the BCL-2/BAX ratio was not statistically altered from 1:1, in any of the treatment patterns. We also showed that VEGF expression was downregulated in RPE cells treated with 500 IU for 24 h. It can be concluded that IFN α-2b was safe (BCL-2/BAX ∼1:1) and enhanced neuroprotection at 1,000 IU (48 h); however-at the same time-IFN α-2b induced inflammation in RPE cells. Moreover, the antiangiogenic effect of IFN α-2b was solely observed in RPE cells treated with 500 IU (24 h). It seems that IFN α-2b in lower doses and short duration exerts antiangiogenic effects and in higher doses and longer duration has neuroprotective and inflammatory effects. Hence, appropriate concentration and duration of treatment, according to the type and stage of the disease, should be considered to achieve success in IFN therapy.

A 360° view of the inflammasome: Mechanisms of activation, cell death, and diseases

Inflammasomes are critical sentinels of the innate immune system that respond to threats to the host through recognition of distinct molecules, known as pathogen- or damage-associated molecular patterns (PAMPs/DAMPs), or disruptions of cellular homeostasis, referred to as homeostasis-altering molecular processes (HAMPs) or effector-triggered immunity (ETI). Several distinct proteins nucleate inflammasomes, including NLRP1, CARD8, NLRP3, NLRP6, NLRC4/NAIP, AIM2, pyrin, and caspases-4/-5/-11. This diverse array of sensors strengthens the inflammasome response through redundancy and plasticity. Here, we present an overview of these pathways, outlining the mechanisms of inflammasome formation, subcellular regulation, and pyroptosis, and discuss the wide-reaching effects of inflammasomes in human disease.

Comparative analysis of absent in melanoma 2-inflammasome activation in Francisella tularensis and Francisella novicida

Francisella tularensis is a highly virulent Gram-negative bacterium that causes the fatal zoonotic disease tularemia. The mechanisms and signaling pathways leading to the absent in melanoma 2 (Aim2) inflammasome activation have been elegantly elucidated using Francisella novicida as a model. Although not pathogenic for humans, F. novicida can cause tularemia in mice, and the inflammatory response it triggers is the polar opposite to that observed in mice infected with F. tularensis strains. This study aimed to understand the mechanisms of Aim2 inflammasome activation in F. tularensis-infected macrophages. The results reveal that macrophages infected with the F. tularensis live vaccine strain (LVS) induce lower levels of Aim2-dependent IL-1β than those infected with F. novicida. The suppression/weak activation of Aim2 in F. tularensis LVS-infected macrophages is due to the suppression of the cGAS-STING DNA-sensing pathway. Furthermore, the introduction of exogenous F. tularensis LVS DNA into the cytosol of the F. tularensis LVS-infected macrophages, alone or in conjunction with a priming signal, failed to restore IL-1β levels similar to those observed for F. novicida-infected macrophages. These results indicated that, in addition to the bacterial DNA, DNA from some other sources, specifically from the damaged mitochondria, might contribute to the robust Aim2-dependent IL-1β levels observed in F. novicida-infected macrophages. The results indicate that F. tularensis LVS induces mitophagy that may potentially prevent the leakage of mitochondrial DNA and the subsequent activation of the Aim2 inflammasome. Collectively, this study demonstrates that the mechanisms of Aim2 inflammasome activation established for F. novicida are not operative in F. tularensis.

Filament assembly underpins the double-stranded DNA specificity of AIM2-like receptors

Upon sensing cytosolic- and/or viral double-stranded (ds)DNA, absent-in-melanoma-2 (AIM2)-like-receptors (ALRs) assemble into filamentous signaling platforms to initiate inflammatory responses. The versatile yet critical roles of ALRs in host innate defense are increasingly appreciated; however, the mechanisms by which AIM2 and its related IFI16 specifically recognize dsDNA over other nucleic acids remain poorly understood (i.e. single-stranded (ss)DNA, dsRNA, ssRNA and DNA:RNA hybrid). Here, we find that although AIM2 can interact with various nucleic acids, it preferentially binds to and assembles filaments faster on dsDNA in a duplex length-dependent manner. Moreover, AIM2 oligomers assembled on nucleic acids other than dsDNA not only display less ordered filamentous structures, but also fail to induce the polymerization of downstream ASC. Likewise, although showing broader nucleic acid selectivity than AIM2, IFI16 binds to and oligomerizes most readily on dsDNA in a duplex length-dependent manner. Nevertheless, IFI16 fails to form filaments on single-stranded nucleic acids and does not accelerate the polymerization of ASC regardless of bound nucleic acids. Together, we reveal that filament assembly is integral to nucleic acid distinction by ALRs.

AIM2 sensors mediate immunity to Plasmodium infection in hepatocytes

Malaria, caused by Plasmodium parasites is a severe disease affecting millions of people around the world. Plasmodium undergoes obligatory development and replication in the hepatocytes, before initiating the life-threatening blood-stage of malaria. Although the natural immune responses impeding Plasmodium infection and development in the liver are key to controlling clinical malaria and transmission, those remain relatively unknown. Here we demonstrate that the DNA of Plasmodium parasites is sensed by cytosolic AIM2 (absent in melanoma 2) receptors in the infected hepatocytes, resulting in Caspase-1 activation. Remarkably, Caspase-1 was observed to undergo unconventional proteolytic processing in hepatocytes, resulting in the activation of the membrane pore-forming protein, Gasdermin D, but not inflammasome-associated proinflammatory cytokines. Nevertheless, this resulted in the elimination of Plasmodium-infected hepatocytes and the control of malaria infection in the liver. Our study uncovers a pathway of natural immunity critical for the control of malaria in the liver.

Deciphering the Role of Pyroptosis Impact on Cardiovascular Diseases

Pyroptosis has become a noteworthy area of focus in recent years due to its association with inflammatory diseases. Pyroptosis is a type of programmed cell death accompanied by an inflammatory response, and the discovery of the gasdermin family has expanded the study of pyroptosis. The primary characteristics of pyroptosis include cell expansion, membrane penetration, and the ejection of cell contents. In healthy physiology, pyroptosis is an essential part of the host's defence against pathogen infection. Excessive Pyroptosis, however, can lead to unchecked and persistent inflammatory responses, including the emergence of inflammatory diseases. More precisely, gasdermin family members have a role in the creation of membrane holes during pyroptosis, which leads to cell lysis. It is also related to how pro-inflammatory intracellular substances, including IL-1, IL-18, and High mobility group box 1 (HMGB1), are used. Two different signalling pathways, one of which is regulated by caspase-1 and the other by caspase-4/5/11, are the primary causes of pyroptosis. Cardiovascular diseases are often associated with cell death and acute or chronic inflammation, making this area of research particularly relevant. In this review, we first systematically summarize recent findings related to Pyroptosis, exploring its characteristics and the signalling pathway mechanisms, as well as various treatment strategies based on its modulation that has emerged from the studies. Some of these strategies are currently undergoing clinical trials. Additionally, the article elaborates on the scientific evidence indicating the role of Pyroptosis in various cardiovascular diseases. As a whole, this should shed insight into future paths and present innovative ideas for employing Pyroptosis as a strong disease-fighting weapon.

Inflammasome-Independent Roles of NLR and ALR Family Members

Pattern recognition receptors, including members of the NLR and ALR families, are essential for recognition of both pathogen- and host-derived danger signals. Several members of these families, including NLRP1, NLRP3, NLRC4, and AIM2, are capable of forming multiprotein complexes, called inflammasomes, that result in the activation of pro-inflammatory caspase-1. However, in addition to the formation of inflammasomes, a number of these family members exert inflammasome-independent functions. Here, we will discuss inflammasome-independent functions of NLRC4, NLRP12, and AIM2 and examine their roles in regulating innate and adaptive immune processes.

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.

Interactions between gut microbes and NLRP3 inflammasome in the gut-brain axis

The role of the gut-brain axis in maintaining the brain's and gut's homeostasis has been gradually recognized in recent years. The connection between the gut and the brain takes center stage. In this scenario, the nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome promotes inflammatory cell recruitment. It plays a crucial role in coordinating host physiology and immunity. Recent evidence shows how vital the gut-brain axis is for maintaining brain and gut homeostasis. However, more research is needed to determine the precise causal link between changed gut microbiota structure and NLRP3 activation in pathogenic circumstances. This review examines the connection between gut microbiota and the NLRP3 inflammasome. We describe how both dynamically vary in clinical cases and the external factors affecting both. Finally, we suggest that the crosstalk between the gut microbiota and NLRP3 is involved in signaling in the gut-brain axis, which may be a potential pathological mechanism for CNS diseases and intestinal disorders.

Canonical Inflammasomes

The innate immune response represents the first line of host defense, and it is able to detect pathogen- and damage-associated molecular patterns (PAMPs and DAMPs, respectively) through a variety of pattern recognition receptors (PRRs). Among these PRRs, certain cytosolic receptors of the NLRs family (specifically NLRP1, NLRP3, NLRC4, and NAIP) or those containing at least a pyrin domain (PYD) such as pyrin and AIM2, activate the multimeric complex known as inflammasome, and its effector enzyme caspase-1. The caspase-1 induces the proteolytic maturation of the pro-inflammatory cytokines IL-1ß and IL-18, as well as the pore-forming protein gasdermin D (GSDMD). GSDMD is responsible for the release of the two cytokines and the induction of lytic and inflammatory cell death known as pyroptosis. Each inflammasome receptor detects specific stimuli, either directly or indirectly, thereby enhancing the cell's ability to sense infections or homeostatic disturbances. In this chapter, we present the activation mechanism of the so-called "canonical" inflammasomes.

Aeromonas hydrophila inhibits autophagy triggering cytosolic translocation of mtDNA which activates the pro-apoptotic caspase-1/IL-1β-nitric oxide axis in headkidney macrophages

The molecular mechanisms underlying Aeromonas hydrophila-pathogenesis are not well understood. Using head kidney macrophages (HKM) of Clarias gariepinus, we previously reported the role of ER-stress in A. hydrophila-induced pathogenesis. Here, we report that PI3K/PLC-induced cytosolic-Ca²⁺ imbalance induces the expression of pro-apoptotic ER-stress marker, CHOP in A. hydrophila-infected HKM. CHOP promotes HKM apoptosis by inhibiting AKT activation and enhancing JNK signaling. Elevated mitochondrial ROS (mtROS) was recorded which declined significantly by ameliorating ER-stress and in the presence of ER-Ca²⁺ release modulators (2-APB and dantrolene) and mitochondrial-Ca²⁺ uptake inhibitor, Ru360, together suggesting the role of ER-mitochondrial Ca²⁺ dynamics in mtROS generation. Inhibiting mtROS production reduced HKM death implicating the pro-apoptotic role of mtROS in A. hydrophila-pathogenesis. The expression of autophagic proteins (LC3B, beclin-1, and atg 5) was suppressed in the infected HKM. Our results with autophagy-inducer rapamycin demonstrated that impaired autophagy favored the cytosolic accumulation of mitochondrial DNA (mtDNA) and the process depended on mtROS levels. Enhanced caspase-1 activity and IL-1β production was detected and transfection studies coupled with pharmacological inhibitors implicated mtROS/mtDNA axis to be crucial for activating the caspase-1/IL-1β cascade in infected HKM. RNAi studies further suggested the involvement of IL-1β in generating pro-apoptotic NO in A. hydrophila-infected HKM. Our study suggests a novel role of ER-mitochondria cross-talk in regulating A. hydrophila pathogenesis. Based on our observations, we conclude that A. hydrophila induces ER-stress and inhibits mitophagy resulting in mitochondrial dysfunction which leads to mtROS production and translocation of mtDNA into cytosol triggering the activation of caspase-1/IL-1β-mediated NO production, culminating in HKM apoptosis.

Discovery of bakuchiol as an AIM2 inflammasome activator and cause of hepatotoxicity

ETHNOPHARMACOLOGICAL RELEVANCE

Psoralea corylifolia (P. corylifolia Linn.) is a traditional Chinese medicinal plant that exhibits significant aphrodisiac, diuretic, and anti-rheumatic effects. However, it has been reported to cause hepatic injury, but the precise mechanisms remain unclear.

AIM OF THE STUDY

To evaluate the safety and risk of P. corylifolia and to elucidate the underlying mechanisms of drug-induced liver injury.

MATERIALS AND METHODS

Western blotting, enzyme-linked immunosorbent assay (ELISA), immunofluorescence, quantitative polymerase chain reaction (Q-PCR), and flow cytometry were used to explore the effect of bakuchiol (Bak), one of the most abundant and biologically active components of P. corylifolia, on the AIM2 inflammasome activation and the underlying mechanism. Furthermore, we used the lipopolysaccharides (LPS)-induced drug-induced liver injury (DILI) susceptible mice model to study the Bak-mediated hepatotoxicity.

RESULTS

Bak induced the maturation of caspase-1 P20, and significantly increased the expression of IL-1β and TNF-α (P < 0.0001) compared with the control group. Moreover, compared to the Bak group, knockdown of AIM2 inhibited Bak-induced caspase-1 maturation and significantly decreased the production of IL-1β and TNF-α, but knockout of NLRP3 had no effect. Mechanistically, Bak-induced AIM2 inflammasome activation is involved in mitochondrial damage, mitochondrial DNA (mtDNA) release, and subsequent recognition of cytosolic mtDNA. Our in vivo data showed that co-exposure to LPS and non-hepatotoxic doses of Bak significantly increased the levels of ALT, AST, IL-1β, TNF-α, and IL-18, indicating that Bak can induce severe liver inflammation (P < 0.005).

CONCLUSIONS

The result shows that Bak activates the AIM2 inflammasome by inducing mitochondrial damage to release mtDNA, and subsequently binds to the AIM2 receptor, indicating that Bak may be a risk factor for P. corylifolia-induced hepatic injury.

GSDMD drives canonical inflammasome-induced neutrophil pyroptosis and is dispensable for NETosis

Neutrophils are the most prevalent immune cells in circulation, but the repertoire of canonical inflammasomes in neutrophils and their respective involvement in neutrophil IL-1β secretion and neutrophil cell death remain unclear. Here, we show that neutrophil-targeted expression of the disease-associated gain-of-function Nlrp3^A350V mutant suffices for systemic autoinflammatory disease and tissue pathology in vivo. We confirm the activity of the canonical NLRP3 and NLRC4 inflammasomes in neutrophils, and further show that the NLRP1b, Pyrin and AIM2 inflammasomes also promote maturation and secretion of interleukin (IL)-1β in cultured bone marrow neutrophils. Notably, all tested canonical inflammasomes promote GSDMD cleavage in neutrophils, and canonical inflammasome-induced pyroptosis and secretion of mature IL-1β are blunted in GSDMD-knockout neutrophils. In contrast, GSDMD is dispensable for PMA-induced NETosis. We also show that Salmonella Typhimurium-induced pyroptosis is markedly increased in Nox2/Gp91^Phox -deficient neutrophils that lack NADPH oxidase activity and are defective in PMA-induced NETosis. In conclusion, we establish the canonical inflammasome repertoire in neutrophils and identify differential roles for GSDMD and the NADPH complex in canonical inflammasome-induced neutrophil pyroptosis and mitogen-induced NETosis, respectively.

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.

Calycosin represses AIM2 inflammasome-mediated inflammation and pyroptosis to attenuate monosodium urate-induced gouty arthritis through NF-κB and p62-Keap1 pathways

Gouty arthritis is an inflammatory disease induced by monosodium urate (MSU), and is closely related to the activation of inflammasomes. Calycosin plays an anti-inflammatory role in arthritis. This study explored the mechanism of Calycosin in MSU-induced gouty arthritis. MSU-induced gouty arthritis mouse models with or without treatment of Calycosin were established, and physiological and pathological indicators were determined. Similarly, peripheral blood mononuclear cells (PBMCs) and THP-1 macrophages were used in vitro. Lactate dehydrogenase (LDH) was tested. The degree of centrifugal infiltration was detected by immunofluorescence. ELISA and quantitative reverse-transcription polymerase chain reaction were conducted to determine the levels of inflammatory factors. Immunohistochemistry, immunofluorescence, and flow cytometry were utilized to detect the content of caspase-1. Protein expressions of NF-κB-, p62-Keap1 pathway-, and pyroptosis-related factors were examined by western blot. In MSU-induced mouse models, calycosin increased mechanical hyperalgesia but decreased the swelling index of the mouse knee joint in a time-dependent manner. MSU treatment increased inflammatory cells and LysM-eGFP⁺ neutrophils recruitment in vivo, and promoted the LDH content in vitro, and meanwhile, calycosin reversed the aforementioned effects of MSU. In addition, calycosin repressed the release of inflammatory factors, promoted p62 level and diminished the levels of AIM2, caspase-1, ASC, IL-1β, Keap1, Cleaved GSDMD, and Cleaved caspase-1 and phosphorylation of p65 and IκBα in MSU-induced mouse or cell models. Furthermore, AIM2 silencing also inhibited MSU-induced inflammation and pyroptosis. Collectively, calycosin may inhibit AIM2 inflammasomes-mediated inflammation and pyroptosis through NF-κB and p62-Keap1 pathways, ultimately playing a protective role in gouty arthritis.

Role of pyroptosis in inflammation and cancer

Pyroptosis is a form of programmed cell death mediated by gasdermin and is a product of continuous cell expansion until the cytomembrane ruptures, resulting in the release of cellular contents that can activate strong inflammatory and immune responses. Pyroptosis, an innate immune response, can be triggered by the activation of inflammasomes by various influencing factors. Activation of these inflammasomes can induce the maturation of caspase-1 or caspase-4/5/11, both of which cleave gasdermin D to release its N-terminal domain, which can bind membrane lipids and perforate the cell membrane. Here, we review the latest advancements in research on the mechanisms of pyroptosis, newly discovered influencing factors, antitumoral properties, and applications in various diseases. Moreover, this review also provides updates on potential targeted therapies for inflammation and cancers, methods for clinical prevention, and finally challenges and future directions in the field.

Klebsiella pneumoniae hijacks the Toll-IL-1R protein SARM1 in a type I IFN-dependent manner to antagonize host immunity

Many bacterial pathogens antagonize host defense responses by translocating effector proteins into cells. It remains an open question how those pathogens not encoding effectors counteract anti-bacterial immunity. Here, we show that Klebsiella pneumoniae exploits the evolutionary conserved innate protein SARM1 to regulate negatively MyD88- and TRIF-governed inflammation, and the activation of the MAP kinases ERK and JNK. SARM1 is required for Klebsiella induction of interleukin-10 (IL-10) by fine-tuning the p38-type I interferon (IFN) axis. SARM1 inhibits the activation of Klebsiella-induced absent in melanoma 2 inflammasome to limit IL-1β production, suppressing further inflammation. Klebsiella exploits type I IFNs to induce SARM1 in a capsule and lipopolysaccharide O-polysaccharide-dependent manner via the TLR4-TRAM-TRIF-IRF3-IFNAR1 pathway. Absence of SARM1 reduces the intracellular survival of K. pneumoniae in macrophages, whereas sarm1-deficient mice control the infection. Altogether, our results illustrate an anti-immunology strategy deployed by a human pathogen. SARM1 inhibition will show a beneficial effect to treat Klebsiella infections.

Host-pathogen protein-nucleic acid interactions: A comprehensive review

Recognition of pathogen-derived nucleic acids by host cells is an effective host strategy to detect pathogenic invasion and trigger immune responses. In the context of pathogen-specific pharmacology, there is a growing interest in mapping the interactions between pathogen-derived nucleic acids and host proteins. Insight into the principles of the structural and immunological mechanisms underlying such interactions and their roles in host defense is necessary to guide therapeutic intervention. Here, we discuss the newest advances in studies of molecular interactions involving pathogen nucleic acids and host factors, including their drug design, molecular structure and specific patterns. We observed that two groups of nucleic acid recognizing molecules, Toll-like receptors (TLRs) and the cytoplasmic retinoic acid-inducible gene (RIG)-I-like receptors (RLRs) form the backbone of host responses to pathogen nucleic acids, with additional support provided by absent in melanoma 2 (AIM2) and DNA-dependent activator of Interferons (IFNs)-regulatory factors (DAI) like cytosolic activity. We review the structural, immunological, and other biological aspects of these representative groups of molecules, especially in terms of their target specificity and affinity and challenges in leveraging host-pathogen protein-nucleic acid interactions (HP-PNI) in drug discovery.

Therapeutic effect of NLRP3 inhibition on hearing loss induced by systemic inflammation in a CAPS-associated mouse model

Background

Cryopyrin-associated periodic syndrome (CAPS) is an inherited autoinflammatory disease caused by a gain-of-function mutation in NLRP3. Although CAPS patients frequently suffer from sensorineural hearing loss, it remains unclear whether CAPS-associated mutation in NLRP3 is associated with the progression of hearing loss.

Methods

We generated a mice with conditional expression of CAPS-associated NLRP3 mutant (D301N) in cochlea-resident CX3CR1 macrophages and examined the susceptibility of CAPS mice to inflammation-mediated hearing loss in a local and systemic inflammation context.

Findings

Upon lipopolysaccharide (LPS) injection into middle ear cavity, NLRP3 mutant mice exhibited severe cochlear inflammation, inflammasome activation and hearing loss. However, this middle ear injection model induced a considerable hearing loss in control mice and inevitably caused an inflammation-independent hearing loss possibly due to ear tissue damages by injection procedure. Subsequently, we optimized a systemic LPS injection model, which induced a significant hearing loss in NLRP3 mutant mice but not in control mice. Peripheral inflammation induced by a repetitive low dose of LPS injection caused a blood-labyrinth barrier disruption, macrophage infiltration into cochlea and cochlear inflammasome activation in an NLRP3-dependent manner. Interestingly, both cochlea-infiltrating and -resident macrophages contribute to peripheral inflammation-mediated hearing loss of CAPS mice. Furthermore, NLRP3-specific inhibitor, MCC950, as well as an interleukin-1 receptor antagonist significantly alleviated systemic LPS-induced hearing loss and inflammatory phenotypes in NLRP3 mutant mice.

Interpretation

Our findings reveal that CAPS-associated NLRP3 mutation is critical for peripheral inflammation-induced hearing loss in our CAPS mice model, and an NLRP3-specific inhibitor can be used to treat inflammation-mediated sensorineural hearing loss.

Funding

National Research Foundation of Korea Grant funded by the Korean Government and the Team Science Award of Yonsei University College of Medicine.

Pathogen-selective killing by guanylate-binding proteins as a molecular mechanism leading to inflammasome signaling

Inflammasomes are cytosolic signaling complexes capable of sensing microbial ligands to trigger inflammation and cell death responses. Here, we show that guanylate-binding proteins (GBPs) mediate pathogen-selective inflammasome activation. We show that mouse GBP1 and GBP3 are specifically required for inflammasome activation during infection with the cytosolic bacterium Francisella novicida. We show that the selectivity of mouse GBP1 and GBP3 derives from a region within the N-terminal domain containing charged and hydrophobic amino acids, which binds to and facilitates direct killing of F. novicida and Neisseria meningitidis, but not other bacteria or mammalian cells. This pathogen-selective recognition by this region of mouse GBP1 and GBP3 leads to pathogen membrane rupture and release of intracellular content for inflammasome sensing. Our results imply that GBPs discriminate between pathogens, confer activation of innate immunity, and provide a host-inspired roadmap for the design of synthetic antimicrobial peptides that may be of use against emerging and re-emerging pathogens.

Guanylate-binding proteins (GBP) have a function in inflammasome formation and pathogen defence. Here the authors show that these GBP proteins are able to kill certain bacteria and promote selective inflammasome activation and that this is mediated by specific GBP protein regions.

Identification of a Novel Pyroptosis-Related Gene Signature Indicative of Disease Prognosis and Treatment Response in Skin Cutaneous Melanoma

Purpose

Pyroptosis plays an important role in the occurrence and progression of many tumors; however, the specific mechanisms involved remain unknown. Here, we construct a pyroptosis-related gene signature that can be used to predict survival prognosis of skin cutaneous melanoma (SKCM) and provide guidance for clinical treatment.

Methods

By integrating data from the two databases from the GTEx and TCGA, differentially expressed genes (DEGs) from normal tissues and skin cutaneous tumor tissues were identified. The main signaling pathways and function enrichment of these differential genes were determined. Univariate and multivariate COX regression analysis, and risk score analysis were used to construct a signature to assess its predictive value for overall survival. The mRNA expression of these five genes in melanoma cells was determined by quantitative polymerase chain reaction (qPCR). The pRRophetic algorithm was used to estimate the half-maximal inhibitory concentration (IC50) of chemotherapy drugs in SKCM patients. The expression of multiple immune checkpoint genes also was evaluated.

Results

Sixteen DEGs associated with pyroptosis in SKCM and normal skin tissues were identified. Of these, 12 pyroptosis-related DEGs were associated with the prognosis of SKCM. A five-gene signature (GSDMA, GSDMC, IL-18, NLRP6, and AIM2) model was constructed. Patients were divided into high-risk and low-risk groups using the risk scores. Of these, the high-risk group had a worse survival prognosis. There are significant differences in the predicted sensitivity of the high-risk and low-risk groups to chemotherapeutic drugs. In addition, compared with the high-risk group, the low-risk group showed higher expression of PD-1, PDL-1, CTLA-4, LAG-3, and VSIR.

Conclusion

In this study, we constructed a novel prognostic pyroptosis-related gene-signature for SKCM. These genes showed good predictive value for patient prognosis and could provide guidance for better treatment of SKCM patients.

Detecting DNA: An Overview of DNA Recognition by Inflammasomes and Protection against Bacterial Respiratory Infections

The innate immune system plays a key role in modulating host immune defense during bacterial disease. Upon sensing pathogen-associated molecular patterns (PAMPs), the multi-protein complex known as the inflammasome serves a protective role against bacteria burden through facilitating pathogen clearance and bacteria lysis. This can occur through two mechanisms: (1) the cleavage of pro-inflammatory cytokines IL-1β/IL-18 and (2) the initiation of inflammatory cell death termed pyroptosis. In recent literature, AIM2-like Receptor (ALR) and Nod-like Receptor (NLR) inflammasome activation has been implicated in host protection following recognition of bacterial DNA. Here, we review current literature synthesizing mechanisms of DNA recognition by inflammasomes during bacterial respiratory disease. This process can occur through direct sensing of DNA or indirectly by sensing pathogen-associated intracellular changes. Additionally, DNA recognition may be assisted through inflammasome–inflammasome interactions, specifically non-canonical inflammasome activation of NLRP3, and crosstalk with the interferon-inducible DNA sensors Stimulator of Interferon Genes (STING) and Z-DNA Binding Protein-1 (ZBP1). Ultimately, bacterial DNA sensing by inflammasomes is highly protective during respiratory disease, emphasizing the importance of inflammasome involvement in the respiratory tract.

Salicornia herbacea Aqueous Extracts Regulate NLRP3 Inflammasome Activation in Macrophages and Trophoblasts

Salicornia herbacea L. (Chenopodiaceae), an edible salt marsh plant with anti-inflammatory effects, was examined in macrophages and trophoblasts whether it modulates NLRP3 inflammasome activity. Pretreatment and delayed treatment of S. herbacea extract (SHE) in bone marrow-derived macrophages (BMDMs) reduced the activity of NLRP3 inflammasome induced by lipopolysaccharide (LPS) and adenosine triphosphate stimulation and downregulated interleukin (IL)-1β production. SHE also inhibited pyroptotic cell death, the adaptor molecule apoptosis-associated speck-like protein containing a CARD (ASC), oligomerization, and speck by NLRP3 inflammasome activity in BMDM. Similarly, SHE decreased the mRNA expression of NLRP3, ASC, IL-1β, and IL-6 in the LPS-stimulated human trophoblast cell line, Swan 71 cells. In addition, SHE inhibited the production of IL-6 and IL-1β and decreased the expression of cyclooxygenase-2 and prostaglandin E2 in stimulated Swan 71 cells. Finally, 3,5-dicaffeoylquinic acid (3,5-DCQA), one of the components of S. herbacea, inhibited IL-1β produced by NLRP3 inflammasome activity. In conclusion, SHE downregulated the activity of the NLRP3 inflammasome in macrophages and trophoblasts.

Fas/CD95 Signaling Pathway in Damage-Associated Molecular Pattern (DAMP)-Sensing Receptors

Study of the initial steps of the CD95-mediated signaling pathways is a field of intense research and a long list of actors has been described in the literature. Nonetheless, the dynamism of protein-protein interactions (PPIs) occurring in the presence or absence of its natural ligand, CD95L, and the cellular distribution where these PPIs take place render it difficult to predict what will be the cellular outcome associated with the receptor engagement. Accordingly, CD95 stimulation can trigger apoptosis, necroptosis, pyroptosis, or pro-inflammatory signaling pathways such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and phosphatidylinositol-3-kinase (PI3K). Recent data suggest that CD95 can also activate pattern recognition receptors (PRRs) known to sense damage-associated molecular patterns (DAMPs) such as DNA debris and dead cells. This activation might contribute to the pro-inflammatory role of CD95 and favor cancer development or severity of chronic inflammatory and auto-immune disorders. Herein, we discuss some of the molecular links that might connect the CD95 signaling to DAMP sensors.