Caspase-1 activation of IL-1beta and IL-18 are essential for Shigella flexneri-induced inflammation

IL-18 signaling is regulated by caspase 6/8 and IL-18BP in turbot (Scophthalmus maximus)

Interleukin (IL)-18 is synthesized as a precursor that requires intracellular processing to become functionally active. In human, IL-18 is processed by caspase 1 (CASP1). In teleost, the maturation and signal transduction mechanisms of IL-18 are unknown. We identified two IL-18 variants, IL-18a and IL-18b, in turbot. IL-18a, but not IL-18b, was processed by CASP6/8 cleavage. Mature IL-18a bound specifically to IL-18 receptor (IL-18R) α-expressing cells and induced IL-18Rα-IL-18Rβ association. Bacterial infection promoted IL-18a maturation in a manner that required CASP6 activation and correlated with gasdermin E activation. The mature IL-18a induced proinflammatory cytokine expression and enhanced bacterial clearance. IL-18a-mediated immune response was suppressed by IL-18 binding protein (IL-18BP), which functioned as a decoy receptor for IL-18a. IL-18BP also functioned as a pathogen pattern recognition receptor and directly inhibited pathogen infection. Our findings revealed unique mechanism of IL-18 maturation and conserved mechanism of IL-18 signaling and regulation in turbot, and provided new insights into the regulation and function of IL-18 related immune signaling.

Turning Neutrophil Cell Death Deadly in Hypertensive Vascular Disease

Hypertensive vascular disease (HVD) is a major health burden globally and is a comorbidity commonly associated with other metabolic diseases. Many factors are associated with hypertensive vascular disease including obesity, diabetes, smoking, chronic kidney disease, and sterile inflammation. Increasing evidence points to neutrophils as an important component of the chronic inflammatory response in hypertensive vascular disease. Neutrophils are abundant in the circulation and can respond rapidly upon stimulation to deploy an armament of anti-microbial effector functions. One of the outcomes of neutrophil activation is the generation of Neutrophil Extracellular Traps (NETs), a regulated extrusion of chromatin and proteases. While neutrophils and NETs are well described as components of the innate immune response to infection, recent evidence implicates them in HVD. Endothelial cell activation can trigger neutrophil adhesion, activation, and production of NETs promoting vascular dysfunction, vessel remodeling, and loss of resistance. The regulated release of NETs can be controlled by the pore-forming activities of distinct cell death pathways. The best-characterized pathways in this context are apoptosis, pyroptosis, and necroptosis. In this review, we will discuss how inflammatory cell death signaling and NET formation contribute to hypertensive disease. We also examine novel therapeutic approaches to limit NET production and their future potential as therapeutic drugs in cardiovascular disorders.

NLRP3 Inflammasome: A central player in renal pathologies and nephropathy

The cytoplasmic oligomer NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome has been implicated in most inflammatory and autoimmune diseases. Here, we highlight the significance of NLRP3 in diverse renal disorders, demonstrating its activation in macrophages and non-immune tubular epithelial and mesangial cells in response to various stimuli. This activation leads to the release of pro-inflammatory cytokines, contributing to the development of acute kidney injury (AKI), chronic renal injury, or fibrosis. In AKI, NLRP3 inflammasome activation and pyroptotic renal tubular cell death is driven by contrast and chemotherapeutic agents, sepsis, and rhabdomyolysis. Nevertheless, inflammasome is provoked in disorders such as crystal and diabetic nephropathy, obesity-related renal fibrosis, lupus nephritis, and hypertension-induced renal damage that induce chronic kidney injury and/or fibrosis. The mechanisms by which the inflammatory NLRP3/ Apoptosis-associated Speck-like protein containing a Caspase recruitment domain (ASC)/caspase-1/interleukin (IL)-1β & IL-18 pathway can turn on renal fibrosis is also comprehended. This review further outlines the involvement of dopamine and its associated G protein-coupled receptors (GPCRs), including D1-like (D1, D5) and D2-like (D2-D4) subtypes, in regulating this inflammation-linked renal dysfunction pathway. Hence, we identify D-related receptors as promising targets for renal disease management by inhibiting the functionality of the NLRP3 inflammasome.

Research Progress of Pyroptosis in Diabetic Kidney Disease

Pyroptosis, known as one typical mode of programmed cell death, is generally characterized by the cleaved gasdermin family (GSDMs) forming pores in the cell membrane and inducing cell rupture, and the activation of aspartate-specific proteases (caspases) has also been found during this process. Diabetic Kidney Disease (DKD) is caused by the complication of diabetes in the kidney, and the most important kidney's function, Glomerular Filtration Rate (GFR), happens to drop to less than 90% of its usual and even lead to kidney failure in severe cases. The persistent inflammatory state induced by high blood glucose implies the key pathology of DKD, and growing evidence shows that pyroptosis serves as a significant contributor to this chronic immune-mediated inflammatory disorder. Currently, the expanded discovery of GSDMs, pyroptosis, and its association with innate immunity has been more attractive, and overwhelming research is needed to sort out the implication of pyroptosis in DKD pathology. In this review, we comb both classical studies and newly founds on pyroptosis, prick off the novel awakening of pyroptosis in DKD, and center on the significance of pyroptosis in DKD treatment, aiming to provide new research targets and treatment strategies on DKD.

Potentials of Natural Antioxidants in Reducing Inflammation and Oxidative Stress in Chronic Kidney Disease

Chronic kidney disease (CKD) presents a substantial global public health challenge, with high morbidity and mortality. CKD patients often experience dyslipidaemia and poor glycaemic control, further exacerbating inflammation and oxidative stress in the kidney. If left untreated, these metabolic symptoms can progress to end-stage renal disease, necessitating long-term dialysis or kidney transplantation. Alleviating inflammation responses has become the standard approach in CKD management. Medications such as statins, metformin, and GLP-1 agonists, initially developed for treating metabolic dysregulation, demonstrate promising renal therapeutic benefits. The rising popularity of herbal remedies and supplements, perceived as natural antioxidants, has spurred investigations into their potential efficacy. Notably, lactoferrin, Boerhaavia diffusa, Amauroderma rugosum, and Ganoderma lucidum are known for their anti-inflammatory and antioxidant properties and may support kidney function preservation. However, the mechanisms underlying the effectiveness of Western medications and herbal remedies in alleviating inflammation and oxidative stress occurring in renal dysfunction are not completely known. This review aims to provide a comprehensive overview of CKD treatment strategies and renal function preservation and critically discusses the existing literature's limitations whilst offering insight into the potential antioxidant effects of these interventions. This could provide a useful guide for future clinical trials and facilitate the development of effective treatment strategies for kidney functions.

NLRP3 inflammasome and its role in autoimmune diseases: A promising therapeutic target

The NOD-like receptor protein 3 (NLRP3) inflammasome is a protein complex that regulates innate immune responses by activating caspase-1 and the inflammatory cytokines IL-1β and IL-18. Numerous studies have highlighted its crucial role in the pathogenesis and development of inflammatory bowel disease, rheumatoid arthritis, systemic lupus erythematosus, autoimmune thyroid diseases, and other autoimmune diseases. Therefore, investigating the underlying mechanisms of NLRP3 in disease and targeted drug therapies holds clinical significance. This review summarizes the structure, assembly, and activation mechanisms of the NLRP3 inflammasome, focusing on its role and involvement in various autoimmune diseases. This review also identifies studies where the involvement of the NLRP3 inflammasome in the disease mechanism within the same disease appears contradictory, as well as differences in NLRP3-related gene polymorphisms among different ethnic groups. Additionally, the latest therapeutic advances in targeting the NLRP3 inflammasome for autoimmune diseases are outlined, and novel clinical perspectives are discussed. Conclusively, this review provides a consolidated source of information on the NLRP3 inflammasome and may guide future research efforts that have the potential to positively impact patient outcomes.

Inhibition of caspase pathways limits CD4+ T cell loss and restores host anti-retroviral function in HIV-1 infected humanized mice with augmented lymphoid tissue

The study of HIV infection and pathogenicity in physical reservoirs requires a biologically relevant model. The human immune system (HIS) mouse is an established model of HIV infection, but defects in immune tissue reconstitution remain a challenge for examining pathology in tissues. We utilized exogenous injection of the human recombinant FMS-like tyrosine kinase 3 ligand (rFLT-3 L) into the hematopoietic stem cell (HSC) cord blood HIS mouse model to significantly expand the total area of lymph node (LN) and the number of circulating human T cells. The results enabled visualization and quantification of HIV infectivity, CD4 T cell depletion and other measures of pathogenesis in the secondary lymphoid tissues of the spleen and LN. Treatment with the Caspase-1/4 inhibitor VX-765 limited CD4+ T cell loss in the spleen and reduced viral load in both the spleen and axillary LN. In situ hybridization further demonstrated a decrease in viral RNA in both the spleen and LN. Transcriptomic analysis revealed that in vivo inhibition of caspase-1/4 led to an upregulation in host HIV restriction factors including SAMHD1 and APOBEC3A. These findings highlight the use of rFLT-3 L to augment human immune system characteristics in HIS mice to support investigations of HIV pathogenesis and test host directed therapies, though further refinements are needed to further augment LN architecture and cellular populations. The results further provide in vivo evidence of the potential to target inflammasome pathways as an avenue of host-directed therapy to limit immune dysfunction and virus replication in tissue compartments of HIV+ persons.

New insights into Gasdermin D pore formation

Gasdermin D (GSDMD) is a pore-forming protein that perforates the plasma membrane (PM) during pyroptosis, a pro-inflammatory form of cell death, to induce the unconventional secretion of inflammatory cytokines and, ultimately, cell lysis. GSDMD is activated by protease-mediated cleavage of its active N-terminal domain from the autoinhibitory C-terminal domain. Inflammatory caspase-1, -4/5 are the main activators of GSDMD via either the canonical or non-canonical pathways of inflammasome activation, but under certain stimuli, caspase-8 and other proteases can also activate GSDMD. Activated GSDMD can oligomerize and assemble into various nanostructures of different sizes and shapes that perforate cellular membranes, suggesting plasticity in pore formation. Although the exact mechanism of pore formation has not yet been deciphered, cysteine residues are emerging as crucial modulators of the oligomerization process. GSDMD pores and thus the outcome of pyroptosis can be modulated by various regulatory mechanisms. These include availability of activated GSDMD at the PM, control of the number of GSDMD pores by PM repair mechanisms, modulation of the lipid environment and post-translational modifications. Here, we review the latest findings on the mechanisms that induce GSDMD to form membrane pores and how they can be tightly regulated for cell content release and cell fate modulation.

NcRNA Regulated Pyroptosis in Liver Diseases and Traditional Chinese Medicine Intervention: A Narrative Review

Pyroptosis is a novel pro-inflammatory mode of programmed cell death that differs from ferroptosis, necrosis, and apoptosis in terms of its onset and regulatory mechanisms. Pyroptosis is dependent on cysteine aspartate protein hydrolase (caspase)-mediated activation of GSDMD, NLRP3, and the release of pro-inflammatory cytokines, interleukin-1 (IL-1β), and interleukin-18 (IL-18), ultimately leading to cell death. Non-coding RNA (ncRNA) is a type of RNA that does not encode proteins in gene transcription but plays an important regulatory role in other post-transcriptional links. NcRNA mediates pyroptosis by regulating various related pyroptosis factors, which we termed the pyroptosis signaling pathway. Previous researches have manifested that pyroptosis is closely related to the development of liver diseases, and is essential for liver injury, alcoholic fatty liver disease (ALD), non-alcoholic fatty liver disease (NAFLD), liver fibrosis, and liver cancer. In this review, we attempt to address the role of the ncRNA-mediated pyroptosis pathway in the above liver diseases and their pathogenesis in recent years, and briefly outline that TCM (Traditional Chinese Medicine) intervene in liver diseases by modulating ncRNA-mediated pyroptosis, which will provide a strategy to find new therapeutic targets for the prevention and treatment of liver diseases in the future.

The dangerous liaisons in innate immunity involving recombinant proteins and endotoxins: Examples from the literature and the Leptospira field

Endotoxins, also known as lipopolysaccharides (LPS), are essential components of cell walls of diderm bacteria such as Escherichia coli. LPS are microbe-associated molecular patterns that can activate pattern recognition receptors. While trying to investigate the interactions between proteins and host innate immunity, some studies using recombinant proteins expressed in E. coli reported interaction and activation of immune cells. Here, we set out to provide information on endotoxins that are highly toxic to humans and bind to numerous molecules, including recombinant proteins. We begin by outlining the history of the discovery of endotoxins, their receptors and the associated signaling pathways that confer extreme sensitivity to immune cells, acting alone or in synergy with other microbe-associated molecular patterns. We list the various places where endotoxins have been found. Additionally, we warn against the risk of data misinterpretation due to endotoxin contamination in recombinant proteins, which is difficult to estimate with the Limulus amebocyte lysate assay, and cannot be completely neutralized (e.g., treatment with polymyxin B or heating). We further illustrate our point with examples of recombinant heat-shock proteins and viral proteins from severe acute respiratory syndrome coronavirus 2, dengue and HIV, for which endotoxin contamination has eventually been shown to be responsible for the inflammatory roles previously ascribed. We also critically appraised studies on recombinant Leptospira proteins regarding their putative inflammatory roles. Finally, to avoid these issues, we propose alternatives to express recombinant proteins in nonmicrobial systems. Microbiologists wishing to undertake innate immunity studies with their favorite pathogens should be aware of these difficulties.

Rosacea pathogenesis and therapeutics: current treatments and a look at future targets

Rosacea is a chronic inflammatory skin condition associated with a significant health and economic burden from costs and loss of productivity due to seeking medical treatment. The disease encompasses multiple phenotypic manifestations involving a complex and multi-variate pathogenesis. Although the pathophysiology of rosacea is not completely understood, ongoing research is continually elucidating its mechanisms. In this review, current concepts of rosacea pathogenesis will be addressed which involve skin barrier and permeability dysfunction, the innate and adaptive immune systems, and the neurovascular system. More specifically, the cathelicidin pathway, transient potential receptor channels, mast cells, and the NLRP3 inflammasome pathway are various targets of current pharmacologic regimens. Future therapies may seek different mechanisms to act on current treatment targets, like the potential use of JAK/STAT inhibitors in ameliorating skin barrier dysfunction or TLR antagonists in alleviating cathelicidin mediated inflammation. Other potential treatments aim for entirely different molecular targets such as microvesicle particle mediated local and systemic inflammation. Ultimately rosacea is associated with a significant health and economic burden which warrants deeper research into its pathogenesis and resultant new treatment discovery.

Activation of inflammasomes and mechanisms for intracellular recognition of Listeria monocytogenes

The high mortality rate associated with Listeria monocytogenes can be attributed to its ability to invade the body systemically and to activate inflammasomes. Both of these processes are facilitated by expressing a major virulence factor known as listeriolysin O, a 56 kDa pore-forming protein encoded by the hly gene. Listeriolysin O plays a crucial role in the pathogenesis of the bacterium by facilitating the escape of the pathogen from the phagosome into the cytosol. This process is essential for the successful establishment of infection. In addition, listeriolysin O is known as an immunomodulator that activates host signal transduction. In addition to listeriolysin O, Listeria expresses a variety of bacterial ligands, such as lipoteichoic acid, nucleotide, and flagellin, that are recognized by host intracellular pattern-recognition receptors including Nod-like receptors, AIM2-like receptors, and RIG-I-like receptors. This review introduces intracellular recognition of Listeria monocytogenes since recent studies have revealed that the activation of inflammasome exacerbates Gram-positive bacteria infection.

Tanshinone IIA inhibits cardiomyocyte pyroptosis through TLR4/NF-κB p65 pathway after acute myocardial infarction

Background: Tanshinone IIA, derived from Radix Salviae Miltiorrhizae (Salvia miltiorrhiza Bunge), constitutes a significant component of this traditional Chinese medicine. Numerous studies have reported positive outcomes regarding its influence on cardiac function. However, a comprehensive comprehension of the intricate mechanisms responsible for its cardioprotective effects is still lacking. Methods: A rat model of heart failure (HF) induced by acute myocardial infarction (AMI) was established via ligation of the left anterior descending coronary artery. Rats received oral administration of tanshinone IIA (1.5 mg/kg) and captopril (10 mg/kg) for 8 weeks. Cardiac function was assessed through various evaluations. Histological changes in myocardial tissue were observed using staining techniques, including Hematoxylin and Eosin (HE), Masson, and transmission electron microscopy. Tunel staining was used to detect cell apoptosis. Serum levels of NT-pro-BNP, IL-1β, and IL-18 were quantified using enzyme-linked immunosorbent assay (ELISA). Expression levels of TLR4, NF-κB p65, and pyroptosis-related proteins were determined via western blotting (WB). H9C2 cardiomyocytes underwent hypoxia-reoxygenation (H/R) to simulate ischemia-reperfusion (I/R) injury, and cell viability and apoptosis were assessed post treatment with different tanshinone IIA concentrations (0.05 μg/ml, 0.1 μg/ml). ELISA measured IL-1β, IL-18, and LDH expression in the cell supernatant, while WB analysis evaluated TLR4, NF-κB p65, and pyroptosis-related protein levels. NF-κB p65 protein nuclear translocation was observed using laser confocal microscopy. Results: Tanshinone IIA treatment exhibited enhanced cardiac function, mitigated histological cardiac tissue damage, lowered serum levels of NT-pro-BNP, IL-1β, and IL-18, and suppressed myocardial cell apoptosis. Moreover, tanshinone IIA downregulated the expression of TLR4, NF-κB p65, IL-1β, pro-IL-1β, NLRP3, Caspase-1, and GSDMD-N pyroptosis-related proteins in myocardial tissue. Additionally, it bolstered H/R H9C2 cardiomyocyte viability, curbed cardiomyocyte apoptosis, and reduced the levels of TLR4, NF-κB p65, IL-1β, pro-IL-1β, NLRP3, Caspase-1, and GSDMD-N pyroptosis-related proteins in H/R H9C2 cells. Furthermore, it hindered NF-κB p65 protein nuclear translocation. Conclusion: These findings indicate that tanshinone IIA enhances cardiac function and alleviates myocardial injury in HF rats following AMI. Moreover, tanshinone IIA demonstrates potential suppression of cardiomyocyte pyroptosis. These effects likely arise from the inhibition of the TLR4/NF-κB p65 signaling pathway, presenting a promising therapeutic target.

The landscape of pathophysiology guided therapeutic strategies for gout treatment

INTRODUCTION

Gout is a common autoinflammatory disease caused by hyperuricemia with acute and/or chronic inflammation as well as tissue damage. Currently, urate-lowering therapy (ULT) and anti-inflammatory therapy are used as first-line strategies for gout treatment. However, traditional drugs for gout treatment exhibit some unexpected side effects and are not suitable for certain patients due to their comorbidity with other chronic disease.

AREAS COVERED

In this review, we described the pathophysiology of hyperuricemia and monosodium urate (MSU) crystal induced inflammatory response during gout development in depth and comprehensively summarized the advances in the investigation of promising ULT drugs as well as anti-inflammatory drugs that might be safer and more effective for gout treatment.

EXPERT OPINION

New drugs that are developed based on these molecular mechanisms exhibited great efficacy on reduction of disease burden both in vitro and in vivo, implying their potential for clinical application. Moreover, hyperthermia also showed regulation effect on MSU crystals formation and the signaling pathways involved in inflammation.

Self-Adjuvanting Calcium-Phosphate-Coated Microcrystal-Based Vaccines Induce Pyroptosis in Human and Livestock Immune Cells

Successful vaccines require adjuvants able to activate the innate immune system, eliciting antigen-specific immune responses and B-cell-mediated antibody production. However, unwanted secondary effects and the lack of effectiveness of traditional adjuvants has prompted investigation into novel adjuvants in recent years. Protein-coated microcrystals modified with calcium phosphate (CaP-PCMCs) in which vaccine antigens are co-immobilised within amino acid crystals represent one of these promising self-adjuvanting vaccine delivery systems. CaP-PCMCs has been shown to enhance antigen-specific IgG responses in mouse models; however, the exact mechanism of action of these microcrystals is currently unclear. Here, we set out to investigate this mechanism by studying the interaction between CaP-PCMCs and mammalian immune cells in an in vitro system. Incubation of cells with CaP-PCMCs induced rapid pyroptosis of peripheral blood mononuclear cells and monocyte-derived dendritic cells from cattle, sheep and humans, which was accompanied by the release of interleukin-1β and the activation of Caspase-1. We show that this pyroptotic event was cell-CaP-PCMCs contact dependent, and neither soluble calcium nor microcrystals without CaP (soluble PCMCs) induced pyroptosis. Our results corroborate CaP-PCMCs as a promising delivery system for vaccine antigens, showing great potential for subunit vaccines where the enhancement or find tuning of adaptive immunity is required.

Structural Mechanisms of NLRP3 Inflammasome Assembly and Activation

As an important sensor in the innate immune system, NLRP3 detects exogenous pathogenic invasions and endogenous cellular damage and responds by forming the NLRP3 inflammasome, a supramolecular complex that activates caspase-1. The three major components of the NLRP3 inflammasome are NLRP3, which captures the danger signals and recruits downstream molecules; caspase-1, which elicits maturation of the cytokines IL-1β and IL-18 and processing of gasdermin D to mediate cytokine release and pyroptosis; and ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain), which functions as a bridge connecting NLRP3 and caspase-1. In this article, we review the structural information that has been obtained on the NLRP3 inflammasome and its components or subcomplexes, with special focus on the inactive NLRP3 cage, the active NLRP3-NEK7 (NIMA-related kinase 7)-ASC inflammasome disk, and the PYD-PYD and CARD-CARD homotypic filamentous scaffolds of the inflammasome. We further implicate structure-derived mechanisms for the assembly and activation of the NLRP3 inflammasome.

Constitutive secretion of pro-IL-18 allows keratinocytes to initiate inflammation during bacterial infection

Group A Streptococcus (GAS, Streptococcus pyogenes) is a professional human pathogen that commonly infects the skin. Keratinocytes are one of the first cells to contact GAS, and by inducing inflammation, they can initiate the earliest immune responses to pathogen invasion. Here, we characterized the proinflammatory cytokine repertoire produced by primary human keratinocytes and surrogate cell lines commonly used in vitro. Infection induces several cytokines and chemokines, but keratinocytes constitutively secrete IL-18 in a form that is inert (pro-IL-18) and lacks proinflammatory activity. Canonically, IL-18 activation and secretion are coupled through a single proteolytic event that is regulated intracellularly by the inflammasome protease caspase-1 in myeloid cells. The pool of extracellular pro-IL-18 generated by keratinocytes is poised to sense extracellular proteases. It is directly processed into a mature active form by SpeB, a secreted GAS protease that is a critical virulent factor during skin infection. This mechanism contributes to the proinflammatory response against GAS, resulting in T cell activation and the secretion of IFN-γ. Under these conditions, isolates of several other major bacterial pathogens and microbiota of the skin were found to not have significant IL-18-maturing ability. These results suggest keratinocyte-secreted IL-18 is a sentinel that sounds an early alarm that is highly sensitive to GAS, yet tolerant to non-invasive members of the microbiota.

A hierarchy of cell death pathways confers layered resistance to shigellosis in mice

Bacteria of the genus Shigella cause shigellosis, a severe gastrointestinal disease driven by bacterial colonization of colonic intestinal epithelial cells. Vertebrates have evolved programmed cell death pathways that sense invasive enteric pathogens and eliminate their intracellular niche. Previously we reported that genetic removal of one such pathway, the NAIP-NLRC4 inflammasome, is sufficient to convert mice from resistant to susceptible to oral Shigella flexneri challenge (Mitchell et al., 2020). Here, we investigate the protective role of additional cell death pathways during oral mouse Shigella infection. We find that the Caspase-11 inflammasome, which senses Shigella LPS, restricts Shigella colonization of the intestinal epithelium in the absence of NAIP-NLRC4. However, this protection is limited when Shigella expresses OspC3, an effector that antagonizes Caspase-11 activity. TNFα, a cytokine that activates Caspase-8-dependent apoptosis, also provides potent protection from Shigella colonization of the intestinal epithelium when mice lack both NAIP-NLRC4 and Caspase-11. The combined genetic removal of Caspases-1, -11, and -8 renders mice hyper-susceptible to oral Shigella infection. Our findings uncover a layered hierarchy of cell death pathways that limit the ability of an invasive gastrointestinal pathogen to cause disease.

NLRP6 Induces Lung Injury and Inflammation Early in Brucella and Influenza Coinfection

(1) Background: With the resurgence of brucellosis epidemics in China in recent years, the chances of a brucella coinfection with other common respiratory pathogens, such as the influenza virus, have increased dramatically. However, little is known about the pathogenicity or the mechanisms of brucella and influenza coinfections. (2) Methods: To clarify the interventions in the early stages of lung damage due to brucella and influenza coinfections, we evaluated the effect of the coinfection on disease progression and mortality using a coinfection model in WT mice and NLRP6^-/- mice, and we verified the function of NLRP6 in infection and proinflammation. (3) Results: The coinfection induced significant respiratory symptoms, weight loss, and a high mortality rate in WT mice. Influenza in the coinfection group significantly increased brucella proliferation in a synergistic manner. Meanwhile, a histological examination showed severe lung tissue destruction and excessive inflammatory responses in coinfected WT animals, and the expression of NLRP6 and IL-18 was dramatically increased in the lung tissues. Furthermore, NLRP6 deletion attenuated lung injuries and inflammation, a reduced bacterial load, and decreased IL-18 protein expression. (4) Conclusions: Our findings indicated that NLRP6 plays a critical role and might be a promising potential therapeutic target for brucella-influenza coinfections.

Pathogen-driven gene expression patterns lead to a novel approach to the identification of common therapeutic targets

Developing a common medication strategy for disease control and management could be greatly beneficial. Investigating the differences between diseased and healthy states using differentially expressed genes aids in understanding disease pathophysiology and enables the exploration of protein-drug interactions. This study aimed to find the most common genes in diarrhea-causing bacteria such as Salmonella enterica serovar Typhimurium, Campylobacter jejuni, Escherichia coli, Shigella dysenteriae (CESS) to find new drugs. Thus, differential gene expression datasets of CESS were screened through computational algorithms and programming. Subsequently, hub and common genes were prioritized from the analysis of extensive protein-protein interactions. Binding predictions were performed to identify the common potential therapeutic targets of CESS. We identified a total of 827 dysregulated genes that are highly linked to CESS. Notably, no common gene interaction was found among all CESS bacteria, but we identified 3 common genes in both Salmonella-Escherichia and Escherichia-Campylobacter infections. Later, out of 73 protein complexes, molecular simulations confirmed 5 therapeutic candidates from the CESS. We have developed a new pipeline for identifying therapeutic targets for a common medication strategy against CESS. However, further wet-lab validation is needed to confirm their effectiveness.

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.

Dysregulation of neutrophil death in sepsis

Sepsis is a prevalent disease that has alarmingly high mortality rates and, for several survivors, long-term morbidity. The modern definition of sepsis is an aberrant host response to infection followed by a life-threatening organ dysfunction. Sepsis has a complicated pathophysiology and involves multiple immune and non-immune mediators. It is now believed that in the initial stages of sepsis, excessive immune system activation and cascading inflammation are usually accompanied by immunosuppression. During the pathophysiology of severe sepsis, neutrophils are crucial. Recent researches have demonstrated a clear link between the process of neutrophil cell death and the emergence of organ dysfunction in sepsis. During sepsis, spontaneous apoptosis of neutrophils is inhibited and neutrophils may undergo some other types of cell death. In this review, we describe various types of neutrophil cell death, including necrosis, apoptosis, necroptosis, pyroptosis, NETosis, and autophagy, to reveal their known effects in the development and progression of sepsis. However, the exact role and mechanisms of neutrophil cell death in sepsis have not been fully elucidated, and this remains a major challenge for future neutrophil research. We hope that this review will provide hints for researches regarding neutrophil cell death in sepsis and provide insights for clinical practitioners.

Host and Species-Specificities of Pattern Recognition Receptors Upon Infection With Leptospira interrogans

Leptospirosis is a zoonotic infectious disease affecting all vertebrates. It is caused by species of the genus Leptospira, among which are the highly pathogenic L. interrogans. Different mammals can be either resistant or susceptible to the disease which can present a large variety of symptoms. Humans are mostly asymptomatic after infection but can have in some cases symptoms varying from a flu-like syndrome to more severe forms such as Weil's disease, potentially leading to multiorgan failure and death. Similarly, cattle, pigs, and horses can suffer from acute forms of the disease, including morbidity, abortion, and uveitis. On the other hand, mice and rats are resistant to leptospirosis despite chronical colonization of the kidneys, excreting leptospires in urine and contributing to the transmission of the bacteria. To this date, the immune mechanisms that determine the severity of the infection and that confer susceptibility to leptospirosis remain enigmatic. To our interest, differential immune sensing of leptospires through the activation of or escape from pattern recognition receptors (PRRs) by microbe-associated molecular patterns (MAMPs) has recently been described. In this review, we will summarize these findings that suggest that in various hosts, leptospires differentially escape recognition by some Toll-like and NOD-like receptors, including TLR4, TLR5, and NOD1, although TLR2 and NLRP3 responses are conserved independently of the host. Overall, we hypothesize that these innate immune mechanisms could play a role in determining host susceptibility to leptospirosis and suggest a central, yet complex, role for TLR4.

Inflammasome Contribution to the Activation of Th1, Th2, and Th17 Immune Responses

Inflammasomes are cytosolic polyprotein complexes formed in response to various external and internal stimuli, including viral and bacterial antigens. The main product of the inflammasome is active caspase 1 which proteolytically cleaves, releasing functional interleukin-1 beta (IL-1β) and interleukin-18 (IL-18). These cytokines play a central role in shaping immune response to pathogens. In this review, we will focus on the mechanisms of inflammasome activation, as well as their role in development of Th1, Th2, and Th17 lymphocytes. The contribution of cytokines IL-1β, IL-18, and IL-33, products of activated inflammasomes, are summarized. Additionally, the role of cytokines released from tissue cells in promoting differentiation of lymphocyte populations is discussed.

High glucose induced inflammation is inhibited by copper chelation via rescuing mitochondrial fusion protein 2 in retinal pigment epithelial cells

Altered trace element homeostasis is associated with diabetic complications, and studies have shown elevated copper levels in the serum of individuals with type 1 & 2 diabetes. Copper chelation has been shown to be beneficial by preventing or reversing diabetic organ damage and developing as a new treatment strategy for treating diabetic complications. Diabetic retinopathy is the major vision-threatening complication of diabetes. Recent studies have reported copper to be elevated in the serum of patients with diabetic retinopathy. Here in this study, we attempt to unravel the role of copper chelator penicillamine in retinal pigment epithelial cells exposed to high glucose (HG) and copper as a model for diabetic retinopathy. We have found that high glucose by itself and along with copper alters the mitochondrial morphology, reduces the expression of the mitochondrial fusion protein 2 (MFN2), and induces endoplasmic reticulum (ER) stress and inflammation. Copper chelation with penicillamine reduced all these changes in mitochondria, thereby rescuing the cells from mitochondrial damage and inflammation.

Blood cell characterization and transcriptome analysis reveal distinct immune response and host resistance of different ploidy cyprinid fish following Aeromonas hydrophila infection

Aeromonas hydrophila can pose a great threat to survival of freshwater fish. In this study, A. hydrophila infection could decrease blood cell numbers, promote blood cell damage as well as alter the levels of alkaline phosphatase (ALP), lysozyme (LZM), aspartate aminotransferase (AST), total antioxidant capacity (T-AOC), total superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) in immune-related tissues of red crucian carp (RCC, 2 N = 100) and triploid cyprinid fish (3 N fish, 3 N = 150). In addition, the significant alternation of antioxidant status was observed in PBMCs isolated from RCC and 3 N following LPS stimulation. The core differential expression genes (DEGs) involved in apoptosis, immunity, inflammation and cellular signals were co-expressed differentially in RCC and 3 N following A. hydrophila challenge. NOD-like receptor (NLR) signals appeared to play a critical role in A. hydrophila-infected fish. DEGs of NLR signals in RCCah vs RCCctl were enriched in caspase-1-dependent Interleukin-1β (IL-1β) secretion, interferon (IFN) signals as well as cytokine activation, while DEGs of NLR signals in 3Nah vs 3Nctl were enriched in caspase-1-dependent IL-1β secretion and antibacterial autophagy. These results highlighted the differential signal regulation of different ploidy cyprinid fish to cope with bacterial infection.

Regulated cell death: discovery, features and implications for neurodegenerative diseases

Regulated cell death (RCD) is a ubiquitous process in living organisms that is essential for tissue homeostasis or to restore biological balance under stress. Over the decades, various forms of RCD have been reported and are increasingly being found to involve in human pathologies and clinical outcomes. We focus on five high-profile forms of RCD, including apoptosis, pyroptosis, autophagy-dependent cell death, necroptosis and ferroptosis. Cumulative evidence supports that not only they have different features and various pathways, but also there are extensive cross-talks between modes of cell death. As the understanding of RCD pathway in evolution, development, physiology and disease continues to improve. Here we review an updated classification of RCD on the discovery and features of processes. The prominent focus will be placed on key mechanisms of RCD and its critical role in neurodegenerative disease. Video abstract.

Microbiota-Host-Irinotecan Axis: A New Insight Toward Irinotecan Chemotherapy

Irinotecan (CPT11) and its active metabolite ethyl-10-hydroxy-camptothecin (SN38) are broad-spectrum cytotoxic anticancer agents. Both cause cell death in rapidly dividing cells (e.g., cancer cells, epithelial cells, hematopoietic cells) and commensal bacteria. Therefore, CPT11 can induce a series of toxic side-effects, of which the most conspicuous is gastrointestinal toxicity (nausea, vomiting, diarrhea). Studies have shown that the gut microbiota modulates the host response to chemotherapeutic drugs. Targeting the gut microbiota influences the efficacy and toxicity of CPT11 chemotherapy through three key mechanisms: microbial ecocline, catalysis of microbial enzymes, and immunoregulation. This review summarizes and explores how the gut microbiota participates in CPT11 metabolism and mediates host immune dynamics to affect the toxicity and efficacy of CPT11 chemotherapy, thus introducing a new concept that is called "microbiota-host-irinotecan axis". Also, we emphasize the utilization of bacterial β-glucuronidase-specific inhibitor, dietary interventions, probiotics and strain-engineered interventions as emergent microbiota-targeting strategies for the purpose of improving CPT11 chemotherapy efficiency and alleviating toxicity.

Heat stress inhibits TLR4-NF-κB and TLR4-TBK1 signaling pathways in broilers infected with Salmonella Typhimurium

With the global warming, the harm of heat stress (HS) to the breeding industry has become more common, which causes the decline of animal production performance and low immunity. This study aimed to analyze the effect of HS on the intestinal immune function of Salmonella-infected chickens. Fourteen-day-old broilers were divided into the following four groups of eight replicates: control (Control), heat stress (HS), Salmonella Typhimurium (ST), and heat stress + Salmonella Typhimurium (HS+ST). The broilers were subjected to a heat stress of 35 °C from 15 to 28 days of age. Salmonella Typhimurium (ST, 14028, 10⁹ cfu/mL) was inoculated, via oral administration at 29 days of age, into ST and HS+ST group birds. On the 4th day after Salmonella Typhimurium administration, an increase in jejunum IgA levels was observed in chickens infected with Salmonella Typhimurium. Mechanistic regulation of TLR4-NFκB-NLRP3 and TLR4-TBK1 signaling by heat stress was evaluated in Salmonella Typhimurium-infected broilers. Heat stress markedly inhibited the expression of cytokines including TNF-α, IL-6, IL-1β, NLRP3, caspase-1, NF-κB-p65, and p-NF-κB-p65, and the TLR4-TBK1 cytokines IFN-α, IFN-γ, p-IRF3, and p-TBK1 in jejunum of broilers infected with Salmonella Typhimurium. Collectively, our results demonstrate that heat stress can inhibit intestinal immune response by downregulating the expression of TLR4-NFκB-NLRP3 and TLR4-TBK1 signaling pathways in broilers infected with Salmonella Typhimurium.

Pre-existing mycobacterial infection modulates Candida albicans-driven pyroptosis

Active tuberculosis patients are at high risk of coinfection with opportunistic fungal pathogen Candida albicans. However, the molecular mechanisms that orchestrate pathogenesis of Mycobacterium tuberculosis (Mtb)-C. albicans coinfection remain elusive. In the current study, we utilize a mouse model to demonstrate that Mtb promotes a macrophage environment that is conducive for C. albicans survival. Mtb-dependent protein kinase Cζ-WNT signalling axis induces expression of an E3 ubiquitin ligase, constitutive photomorphogenesis protein 1 (COP1). A secondary infection of C. albicans in such Mtb-infected macrophages causes COP1 to mediate the proteasomal degradation of interferon regulatory factor 9 (IRF9), a cardinal factor that we identified to arbitrate an inflammatory programmed cell death, pyroptosis. In vivo experiments mimicking a pre-existing Mtb infection demonstrate that inhibition of pyroptosis in mice results in increased C. albicans burden and aberrant lung tissue architecture, leading to increased host mortality. Together, our study reveals the crucial role of pyroptosis regulation for manifesting a successful C. albicans-Mtb coinfection.

Increased systemic RNA oxidative damage and diagnostic value of RNA oxidative metabolites during Shigella flexneri-induced intestinal infection

BACKGROUND

Shigella flexneri (S. flexneri) is a major pathogen causing acute intestinal infection, but the systematic oxidative damage incurred during the course of infection has not been investigated.

AIM

To investigate the incurred systemic RNA oxidative damage and the diagnostic value of RNA oxidative metabolites during S. flexneri-induced intestinal infection.

METHODS

In this study, a Sprague-Dawley rat model of acute intestinal infection was established by oral gavage with S. flexneri strains. The changes in white blood cells (WBCs) and cytokine levels in blood and the inflammatory response in the colon were investigated. We also detected the RNA and DNA oxidation in urine and tissues.

RESULTS

S. flexneri infection induced an increase in WBCs, C-reactive protein, interleukin (IL)-6, IL-10, IL-1β, IL-4, IL-17a, IL-10, and tumor necrosis factor α (TNF-α) in blood. Of note, a significant increase in urinary 8-oxo-7,8-dihydroguanosine (8-oxo-Gsn), an important marker of total RNA oxidation, was detected after intestinal infection (P = 0.03). The urinary 8-oxo-Gsn level returned to the baseline level after recovery from infection. In addition, the results of a correlation analysis showed that urinary 8-oxo-Gsn was positively correlated with the WBC count and the cytokines IL-6, TNF-α, IL-10, IL-1β, and IL-17α. Further detection of the oxidation in different tissues showed that S. flexneri infection induced RNA oxidative damage in the colon, ileum, liver, spleen, and brain.

CONCLUSION

Acute infection induced by S. flexneri causes increased RNA oxidative damage in various tissues (liver, spleen, and brain) and an increase of 8-oxo-Gsn, a urinary metabolite. Urinary 8-oxo-Gsn may be useful as a biomarker for evaluating the severity and prognosis of infection.

The alarmin interleukin-1α causes preterm birth through the NLRP3 inflammasome

Sterile intra-amniotic inflammation is a clinical condition frequently observed in women with preterm labor and birth, the leading cause of neonatal morbidity and mortality worldwide. Growing evidence suggests that alarmins found in amniotic fluid, such as interleukin (IL)-1α, are central initiators of sterile intra-amniotic inflammation. However, the causal link between elevated intra-amniotic concentrations of IL-1α and preterm birth has yet to be established. Herein, using an animal model of ultrasound-guided intra-amniotic injection of IL-1α, we show that elevated concentrations of IL-1α cause preterm birth and neonatal mortality. Additionally, using immunoblotting techniques and a specific immunoassay, we report that the intra-amniotic administration of IL-1α induces activation of the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome in the fetal membranes, but not in the decidua, as evidenced by a concomitant increase in the protein levels of NLRP3, active caspase-1, and IL-1β. Lastly, using Nlrp3-/- mice, we demonstrate that the deficiency of this inflammasome sensor molecule reduces the rates of preterm birth and neonatal mortality caused by the intra-amniotic injection of IL-1α. Collectively, these results demonstrate a causal link between elevated IL-1α concentrations in the amniotic cavity and preterm birth as well as adverse neonatal outcomes, a pathological process that is mediated by the NLRP3 inflammasome. These findings shed light on the mechanisms underlying sterile intra-amniotic inflammation and provide further evidence that this clinical condition can potentially be treated by targeting the NLRP3 inflammasome.

Pathogenic ubiquitination of GSDMB inhibits NK cell bactericidal functions

Gasdermin B (GSDMB) belongs to a large family of pore-forming cytolysins that execute inflammatory cell death programs. While genetic studies have linked GSDMB polymorphisms to human disease, its function in the immunological response to pathogens remains poorly understood. Here, we report a dynamic host-pathogen conflict between GSDMB and the IpaH7.8 effector protein secreted by enteroinvasive Shigella flexneri. We show that IpaH7.8 ubiquitinates and targets GSDMB for 26S proteasome destruction. This virulence strategy protects Shigella from the bacteriocidic activity of natural killer cells by suppressing granzyme-A-mediated activation of GSDMB. In contrast to the canonical function of most gasdermin family members, GSDMB does not inhibit Shigella by lysing host cells. Rather, it exhibits direct microbiocidal activity through recognition of phospholipids found on Gram-negative bacterial membranes. These findings place GSDMB as a central executioner of intracellular bacterial killing and reveal a mechanism employed by pathogens to counteract this host defense system.

Toxicity and Activity of Ethanolic Leaf Extract of Paullinia pinnata Linn (Sapindaceae) in Shigella flexneri-Induced Diarrhea in Wistar Rats

Herbal products from Paullinia pinnata Linn are widely used in African folk medicine to treat several infectious diseases. Although the extracts from this plant has been shown to possess antimicrobial potential, their activity in infectious diarrhea is less reported. Diarrhea was induced by oral administration of 1.2 × 10⁹ CFU/mL of Shigella flexneri to the rats. The infected rats were treated for 5 days with the doses of 111.42, 222.84, and 445.68 mg/kg of P pinnata. The level of biochemical parameters was assessed and histology of organs examined by 14 days subacute toxicity. S flexneri stool load was considerably reduced after 4 days of treatment with the dose of 445.68 mg/kg, 5 days at the dose of 222.84 mg/kg for the extract, and 2 days with ciprofloxacin. The dose of 111.42 mg/kg appeared efficient after 5 days of treatment. The creatinine level increased at the dose of 445.68 mg/kg in both male and female rats and decrease at the dose of 222.84 mg/mL in female rats while an increase was noted in the male rats. Liver and kidney histology were modified at the dose of 445.68 mg/kg while no change was observed at the doses of 111.42 and 222.84 mg/kg. P pinnata leaf extract is efficient against infectious diarrhea at 111.42 mg/kg without side effect.

The Antisocial Network: Cross Talk Between Cell Death Programs in Host Defense

Nearly all animal cells contain proteins evolved to trigger the destruction of the cell in which they reside. The activation of these proteins occurs via sequential programs, and much effort has been expended in delineating the molecular mechanisms underlying the resulting processes of programmed cell death (PCD). These efforts have led to the definition of apoptosis as a form of nonimmunogenic PCD that is required for normal development and tissue homeostasis, and of pyroptosis and necroptosis as forms of PCD initiated by pathogen infection that are associated with inflammation and immune activation. While this paradigm has served the field well, numerous recent studies have highlighted cross talk between these programs, challenging the idea that apoptosis, pyroptosis, and necroptosis are linear pathways with defined immunological outputs. Here, we discuss the emerging idea of cell death as a signaling network, considering connections between cell death pathways both as we observe them now and in their evolutionary origins. We also discuss the engagement and subversion of cell death pathways by pathogens, as well as the key immunological outcomes of these processes.

Amelioration of diabetes-induced inflammation mediated pyroptosis, sarcopenia, and adverse muscle remodelling by bone morphogenetic protein-7

BACKGROUND

Diabetic myopathy involves hyperglycaemia and inflammation that causes skeletal muscle dysfunction; however, the potential cellular mechanisms that occur between hyperglycaemia and inflammation, which induces sarcopenia, and muscle dysfunction remain unknown. In this study, we investigated hyperglycaemia-induced inflammation mediating high-mobility group box 1 activation, which is involved in a novel form of cell death, pyroptosis, diabetic sarcopenia, atrophy, and adverse muscle remodelling. Furthermore, we investigated the therapeutic potential of bone morphogenetic protein-7 (BMP-7), an osteoporosis drug, to treat pyroptosis, and diabetic muscle myopathy.

METHODS

C57BL6 mice were treated with saline (control), streptozotocin (STZ), or STZ + BMP-7 to generate diabetic muscle myopathy. Diabetes was established by determining the increased levels of glucose. Then, muscle function was examined, and animals were sacrificed. Gastrocnemius muscle or blood samples were analysed for inflammation, pyroptosis, weight loss, muscle atrophy, and adverse structural remodelling of gastrocnemius muscle using histology, enzyme-linked immunosorbent assay, immunohistochemistry, western blotting, and reverse transcription polymerase chain reaction.

RESULTS

A significant (P < 0.05) increase in hyperglycaemia leads to an increase in inflammasome (high-mobility group box 1, toll-like receptor-4, and nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing protein 3) formation in diabetic muscle cells. Further analysis showed an up-regulation of the downstream pyroptotic pathway with significant (P < 0.05) number of positive muscle cells expressing pyroptosis-specific markers [caspase-1, interleukin (IL)-1β, IL-18, and gasdermin-D]. Pyroptotic cell death is involved in further increasing inflammation by releasing pro-inflammatory cytokine IL-6. Structural analysis showed the loss of muscle weight, decreased myofibrillar area, and increased fibrosis leading to muscle dysfunction. Consistent with this finding, BMP-7 attenuated hyperglycaemia (~50%), pyroptosis, inflammation, and diabetic adverse structural modifications as well as improved muscle function.

CONCLUSIONS

In conclusion, we report for the first time that increased hyperglycaemia and inflammation involve cellular pyroptosis that induces significant muscle cell loss and adverse remodelling in diabetic myopathy. We also report that targeting pyroptosis with BMP-7 improves diabetic muscle pathophysiology and muscle function. These findings suggest that BMP-7 could be a potential therapeutic option to treat diabetic myopathy.

VaximmutorDB: A Web-Based Vaccine Immune Factor Database and Its Application for Understanding Vaccine-Induced Immune Mechanisms

Vaccines stimulate various immune factors critical to protective immune responses. However, a comprehensive picture of vaccine-induced immune factors and pathways have not been systematically collected and analyzed. To address this issue, we developed VaximmutorDB, a web-based database system of vaccine immune factors (abbreviated as “vaximmutors”) manually curated from peer-reviewed articles. VaximmutorDB currently stores 1,740 vaccine immune factors from 13 host species (e.g., human, mouse, and pig). These vaximmutors were induced by 154 vaccines for 46 pathogens. Top 10 vaximmutors include three antibodies (IgG, IgG2a and IgG1), Th1 immune factors (IFN-γ and IL-2), Th2 immune factors (IL-4 and IL-6), TNF-α, CASP-1, and TLR8. Many enriched host processes (e.g., stimulatory C-type lectin receptor signaling pathway, SRP-dependent cotranslational protein targeting to membrane) and cellular components (e.g., extracellular exosome, nucleoplasm) by all the vaximmutors were identified. Using influenza as a model, live attenuated and killed inactivated influenza vaccines stimulate many shared pathways such as signaling of many interleukins (including IL-1, IL-4, IL-6, IL-13, IL-20, and IL-27), interferon signaling, MARK1 activation, and neutrophil degranulation. However, they also present their unique response patterns. While live attenuated influenza vaccine FluMist induced significant signal transduction responses, killed inactivated influenza vaccine Fluarix induced significant metabolism of protein responses. Two different Yellow Fever vaccine (YF-Vax) studies resulted in overlapping gene lists; however, they shared more portions of pathways than gene lists. Interestingly, live attenuated YF-Vax simulates significant metabolism of protein responses, which was similar to the pattern induced by killed inactivated Fluarix. A user-friendly web interface was generated to access, browse and search the VaximmutorDB database information. As the first web-based database of vaccine immune factors, VaximmutorDB provides systematical collection, standardization, storage, and analysis of experimentally verified vaccine immune factors, supporting better understanding of protective vaccine immunity.

NAIP-NLRC4-deficient mice are susceptible to shigellosis

Bacteria of the genus Shigella cause shigellosis, a severe gastrointestinal disease that is a major cause of diarrhea-associated mortality in humans. Mice are highly resistant to Shigella and the lack of a tractable physiological model of shigellosis has impeded our understanding of this important human disease. Here, we propose that the differential susceptibility of mice and humans to Shigella is due to mouse-specific activation of the NAIP-NLRC4 inflammasome. We find that NAIP-NLRC4-deficient mice are highly susceptible to oral Shigella infection and recapitulate the clinical features of human shigellosis. Although inflammasomes are generally thought to promote Shigella pathogenesis, we instead demonstrate that intestinal epithelial cell (IEC)-specific NAIP-NLRC4 activity is sufficient to protect mice from shigellosis. In addition to describing a new mouse model of shigellosis, our results suggest that the lack of an inflammasome response in IECs may help explain the susceptibility of humans to shigellosis.

The Role of Inflammation in the Pathogenesis of Preeclampsia

Preeclampsia (PE) affects 5-8% of pregnant women, and it is the major cause of perinatal morbidity and mortality. It is defined as arterial hypertension in women after 20 weeks of gestation which cooccurs with proteinuria (300 mg/d) or as arterial hypertension which is accompanied by one of the following: renal failure, liver dysfunction, hematological or neurological abnormalities, intrauterine growth restriction, or uteroplacental insufficiency. Currently, pathophysiology of preeclampsia poses a considerable challenge for perinatology. Preeclampsia is characterized by excessive and progressive activation of the immune system along with an increase in proinflammatory cytokines and antiangiogenic factors in fetoplacental unit as well as in vascular endothelium in pregnant women. A single, major underlying mechanism of preeclampsia is yet to be identified. This paper discusses the current understanding of the mechanisms which underlie the development of the condition. Some significant factors responsible for PE development include oxidative stress, abnormal concentration and activity in mononuclear phagocytic system, altered levels of angiogenic and antiangiogenic factors, and impaired inflammatory response triggered by inflammasomes. Detailed understanding of pathophysiology of inflammatory process in PE can largely contribute to new, targeted anti-inflammatory therapies that may improve perinatal outcomes in PE patients.

Emerging connectivity of programmed cell death pathways and its physiological implications

The removal of functionally dispensable, infected or potentially neoplastic cells is driven by programmed cell death (PCD) pathways, highlighting their important roles in homeostasis, host defence against pathogens, cancer and a range of other pathologies. Several types of PCD pathways have been described, including apoptosis, necroptosis and pyroptosis; they employ distinct molecular and cellular processes and differ in their outcomes, such as the capacity to trigger inflammatory responses. Recent genetic and biochemical studies have revealed remarkable flexibility in the use of these PCD pathways and indicate a considerable degree of plasticity in their molecular regulation; for example, despite having a primary role in inducing pyroptosis, inflammatory caspases can also induce apoptosis, and conversely, apoptotic stimuli can trigger pyroptosis. Intriguingly, this flexibility is most pronounced in cellular responses to infection, while apoptosis is the dominant cell death process through which organisms prevent the development of cancer. In this Review, we summarize the mechanisms of the different types of PCD and describe the physiological and pathological processes that engage crosstalk between these pathways, focusing on infections and cancer. We discuss the intriguing notion that the different types of PCD could be seen as a single, coordinated cell death system, in which the individual pathways are highly interconnected and can flexibly compensate for one another.

IL-18 and infections: Is there a role for targeted therapies?

Interleukin (IL)-18 is a pro-inflammatory cytokine belonging to the IL-1 family, first identified for its interferon-γ-inducing properties. IL-18 regulates both T helper (Th) 1 and Th2 responses. It acts synergistically with IL-12 in the Th1 paradigm, whereas with IL-2 and without IL-12 it can induce Th2 cytokine production from cluster of differentation (CD)4⁺ T cells, natural killer (NK cells, NKT cells, as well as from Th1 cells. IL-18 also plays a role in the hemophagocytic lymphohistiocytosis, a life-threatening condition characterized by a cytokine storm that can be secondary to infections. IL-18-mediated inflammation was largely studied in animal models of bacterial, viral, parasitic, and fungal infections. These studies highlight the contribution of either IL-18 overproduction by the host or overresponsiveness of the host to IL-18 causing an exaggerated inflammatory burden and leading to tissue injury. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the coronavirus disease 2019 (COVID-19). The damage in the later phase of the disease appears to be driven by a cytokine storm, including interleukin IL-1 family members and secondary cytokines like IL-6. IL-18 may participate in this hyperinflammation, as it was previously found to be able to cause injury in the lung tissue of infected animals. IL-18 blockade has become an appealing therapeutic target and has been tested in some IL-18-mediated rheumatic diseases and infantile-onset macrophage activation syndrome. Given its role in regulating the immune response to infections, IL-18 blockade might represent a therapeutic option for COVID-19, although further studies are warranted to investigate more in detail the exact role of IL-18 in SARS-CoV-2 infection.

Human Amnion Epithelial Cells (AECs) Respond to the FSL-1 Lipopeptide by Engaging the NLRP7 Inflammasome

Context and Objectives: Inflammation is the leading mechanism involved in both physiological and pathological rupture of fetal membranes. Our aim was to obtain a better characterization of the inflammasome-dependent inflammation processes in these tissues, with a particular focus on the nucleotide-binding oligomerization domain (NOD)–like receptor, pyrin domain containing protein 7 (NLRP7) inflammasome.

Methods: The presence of NLRP7 inflammasome actors [NLRP7, apoptosis-associated speck–like protein containing a CARD domain (ASC), and caspase-1] was confirmed by reverse transcriptase–polymerase chain reaction (RT-PCR) in human amnion and choriodecidua at the three trimesters and at term. The protein concentrations were then determined by enzyme-linked immunosorbent assay in term tissues, with or without labor. The presence of Mycoplasma salivarium and Mycoplasma fermentans in human fetal membranes was investigated using a PCR approach. Human amnion epithelial cells (AECs) were treated for 4 or 20 h with fibroblast-stimulating lipopeptide-1 (FSL-1), a M. salivarium–derived ligand. Transcripts and proteins quantity was then measured by RT–quantitative PCR and Western blotting, respectively. NLRP7 and ASC colocalization was confirmed by immunofluorescence. Western blots allowed analysis of pro–caspase-1 and gasdermin D cleavage.

Results: NLRP7, ASC, and caspase-1 transcripts were expressed in both sheets of human fetal membranes during all pregnancy stages, but only ASC protein expression was increased with labor. In addition, M. salivarium and M. fermentans were detected for the first time in human fetal membranes. NLRP7 and caspase-1 transcripts, as well as NLRP7, ASC, and pro–caspase-1 protein levels, were increased in FSL-1–treated AECs. The NLRP7 inflammasome assembled around the nucleus, and pro–caspase-1 and gasdermin D were cleaved into their mature forms after FSL-1 stimulation.

Conclusion: Two new mycoplasmas, M. salivarium and M. fermentans, were identified in human fetal membranes, and a lipopeptide derived from M. salivarium was found to induce NLRP7 inflammasome formation in AECs.

Intra-amniotic inflammation induces preterm birth by activating the NLRP3 inflammasome†

Intra-amniotic inflammation is strongly associated with spontaneous preterm labor and birth, the leading cause of perinatal mortality and morbidity worldwide. Previous studies have suggested a role for the NLRP3 (NLR family pyrin domain-containing protein 3) inflammasome in the mechanisms that lead to preterm labor and birth. However, a causal link between the NLRP3 inflammasome and preterm labor/birth induced by intra-amniotic inflammation has not been established. Herein, using an animal model of lipopolysaccharide-induced intra-amniotic inflammation (IAI), we demonstrated that there was priming of the NLRP3 inflammasome (1) at the transcriptional level, indicated by enhanced mRNA expression of inflammasome-related genes (Nlrp3, Casp1, Il1b); and (2) at the protein level, indicated by greater protein concentrations of NLRP3, in both the fetal membranes and decidua basalis prior to preterm birth. Additionally, we showed that there was canonical activation of the NLRP3 inflammasome in the fetal membranes, but not in the decidua basalis, prior to IAI-induced preterm birth as evidenced by increased protein levels of active caspase-1. Protein concentrations of released IL1β were also increased in both the fetal membranes and decidua basalis, as well as in the amniotic fluid, prior to IAI-induced preterm birth. Finally, using the specific NLRP3 inhibitor, MCC950, we showed that in vivo inhibition of the NLRP3 inflammasome reduced IAI-induced preterm birth and neonatal mortality. Collectively, these results provide a causal link between NLRP3 inflammasome activation and spontaneous preterm labor and birth in the context of intra-amniotic inflammation. We also showed that, by targeting the NLRP3 inflammasome, adverse pregnancy and neonatal outcomes can be significantly reduced.

The Role of Caspase-4 and NLRP1 in MCF7 Cell Pyroptosis Induced by hUCMSC-Secreted Factors

Mesenchymal stem cells (MSCs) are being widely investigated for the development of novel therapeutic approaches for different cancers, including breast cancer, the leading form of cancer in women. Our previous study showed that the factors secreted by human umbilical cord MSCs (hUCMSCs) induced pyroptosis in the breast cancer cell line MCF7 and our RNA sequencing studies revealed an increase in the expression of the pyroptosis-related gene caspase-4 (CASP4) and nucleotide-binding, leucine-rich repeat pyrin domain-containing protein 1 (NLRP1) in pyroptotic MCF7 cells. Cellular pyroptosis can occur via the canonical pathway (involving caspase-1 and NLRP1) or the noncanonical pathway (involving caspase-4). In this study, we first confirmed that the inflammasome complex formed by NLRP1 and ASC is involved in MCF7 cell pyroptosis induced by hUCMSC-CM. Further, we investigated the role of CASP4 and NLRP1 in MCF7 cell pyroptosis induced by hUCMSC-secreted factors using shRNA-mediated transfection of CASP4 or NLRP1 in MCF7 cells. Cytotoxicity analyses revealed that neither CASP4 knockdown nor NLRP1 knockdown could inhibit the hUCMSC-CM-induced pyroptosis in MCF7 cells. Gene and protein expression analysis showed that hUCMSC-CM induced pyroptosis mainly via the canonical pathway in CASP4 knockdown MCF7 cells but mainly via the noncanonical pathway in NLRP1 knockdown MCF7 cells. Our study provides a foundation for further studies aimed at elucidating the precise mechanism underlying hUCMSC-induced pyroptosis in breast cancer cells and aid the identification of potential therapeutic targets for breast cancer.

Staying out or Going in? The Interplay between Type 3 and Type 5 Secretion Systems in Adhesion and Invasion of Enterobacterial Pathogens

Enteric pathogens rely on a variety of toxins, adhesins and other virulence factors to cause infections. Some of the best studied pathogens belong to the Enterobacterales order; these include enteropathogenic and enterohemorrhagic Escherichia coli, Shigella spp., and the enteropathogenic Yersiniae. The pathogenesis of these organisms involves two different secretion systems, a type 3 secretion system (T3SS) and type 5 secretion systems (T5SSs). The T3SS forms a syringe-like structure spanning both bacterial membranes and the host cell plasma membrane that translocates toxic effector proteins into the cytoplasm of the host cell. T5SSs are also known as autotransporters, and they export part of their own polypeptide to the bacterial cell surface where it exerts its function, such as adhesion to host cell receptors. During infection with these enteropathogens, the T3SS and T5SS act in concert to bring about rearrangements of the host cell cytoskeleton, either to invade the cell, confer intracellular motility, evade phagocytosis or produce novel structures to shelter the bacteria. Thus, in these bacteria, not only the T3SS effectors but also T5SS proteins could be considered "cytoskeletoxins" that bring about profound alterations in host cell cytoskeletal dynamics and lead to pathogenic outcomes.

The NAIP/NLRC4 inflammasome in infection and pathology

In this review we give an overview of the NAIP/NLRC4 activation mechanism as well as the described roles of this inflammasome, with a focus on in vivo infection and pathology. After ligand recognition by NAIP sensor proteins the NAIP/NLRC4 inflammasome forms through oligomerization with the NLRC4 adaptor to activate Caspase-1. The activating ligands are intracellular bacterial flagellin or type-3 secretion system components, delivered by pathogens. In vivo experiments indicate a role in macrophages during lung, spleen and liver infection and systemic sepsis like conditions, as well as in intestinal epithelial cells. Upon NAIP/NLRC4 activation in the intestine, epithelial cell extrusion is triggered in addition to the canonical inflammasome outcomes of cytokine cleavage and pyroptosis. Human patients with auto-activating mutations in NLRC4 present with an autoinflammatory syndrome including enterocolitis. Although one of the better understood inflammasomes in terms of mechanism, tissue specific functions of NAIP/NLRC4 are only beginning to be understood.

Inflammasomes: Their Role in Normal and Complicated Pregnancies

Inflammasomes are cytoplasmic multiprotein complexes that coordinate inflammatory responses, including those that take place during pregnancy. Inflammasomes and their downstream mediators caspase-1 and IL-1β are expressed by gestational tissues (e.g., the placenta and chorioamniotic membranes) during normal pregnancy. Yet, only the activation of the NLRP3 inflammasome in the chorioamniotic membranes has been partially implicated in the sterile inflammatory process of term parturition. In vivo and ex vivo studies have consistently shown that the activation of the NLRP3 inflammasome is a mechanism whereby preterm labor and birth occur in the context of microbial- or alarmin-induced inflammation. In the placenta, the activation of the NLRP3 inflammasome is involved in the pathogenesis of preeclampsia and other pregnancy syndromes associated with placental inflammation. This evidence suggests that inhibition of the NLRP3 inflammasome or its downstream mediators may foster the development of novel anti-inflammatory therapies for the prevention or treatment of pregnancy complications.