A protective role for inflammasome activation following injury

Cytosolic nucleic acid sensing as driver of critical illness: mechanisms and advances in therapy

Nucleic acids from both self- and non-self-sources act as vital danger signals that trigger immune responses. Critical illnesses such as acute respiratory distress syndrome, sepsis, trauma and ischemia lead to the aberrant cytosolic accumulation and massive release of nucleic acids that are detected by antiviral innate immune receptors in the endosome or cytosol. Activation of receptors for deoxyribonucleic acids and ribonucleic acids triggers inflammation, a major contributor to morbidity and mortality in critically ill patients. In the past decade, there has been growing recognition of the therapeutic potential of targeting nucleic acid sensing in critical care. This review summarizes current knowledge of nucleic acid sensing in acute respiratory distress syndrome, sepsis, trauma and ischemia. Given the extensive research on nucleic acid sensing in common pathological conditions like cancer, autoimmune disorders, metabolic disorders and aging, we provide a comprehensive summary of nucleic acid sensing beyond critical illness to offer insights that may inform its role in critical conditions. Additionally, we discuss potential therapeutic strategies that specifically target nucleic acid sensing. By examining nucleic acid sources, sensor activation and function, as well as the impact of regulating these pathways across various acute diseases, we highlight the driving role of nucleic acid sensing in critical illness.

The NLRP3 inflammasome in burns: a novel potential therapeutic target

Burns are an underestimated serious injury negatively impacting survivors physically, psychologically and economically, and thus are a considerable public health burden. Despite significant advancements in burn treatment, many burns still do not heal or develop serious complications/sequelae. The nucleotide-binding oligomerization domain-like receptors (NLRs) family pyrin domain-containing 3 (NLRP3) inflammasome is a critical regulator of wound healing, including burn wound healing. A better understanding of the pathophysiological mechanism underlying the healing of burn wounds may help find optimal therapeutic targets to promote the healing of burn wounds, reduce complications/sequelae following burn, and maximize the restoration of structure and function of burn skin. This review aimed to summarize current understanding of the roles and regulatory mechanisms of the NLRP3 inflammasome in burn wound healing, as well as the preclinical studies of the involvement of NLRP3 inhibitors in burn treatment, highlighting the potential application of NLRP3-targeted therapy in burn wounds.

Systemic immune response of burns from the acute to chronic phase

Immune responses that occur following burn injury comprise a series of reactions that are activated in response to damaged autologous tissues, followed by removal of damaged tissues and foreign pathogens such as invading bacteria, and tissue repair. These immune responses are considered to be programmed in living organisms. Developments of modern medicine have led to the saving of burned patients who could not be cured previously; however, the programmed response is no longer able to keep up, and various problems have arisen. This paper describes the mechanism of immune response specific to burn injury and the emerging concept of persistent inflammation, immunosuppression, and catabolism syndrome.

Role of Inflammasomes in Keloids and Hypertrophic Scars-Lessons Learned from Chronic Diabetic Wounds and Skin Fibrosis

Keloids and hypertrophic scars are pathological cutaneous scars. They arise from excessive wound healing, which induces chronic dermal inflammation and results in overwhelming fibroblast production of extracellular matrix. Their etiology is unclear. Inflammasomes are multiprotein complexes that are important in proinflammatory innate-immune system responses. We asked whether inflammasomes participate in pathological scarring by examining the literature on scarring, diabetic wounds (also characterized by chronic inflammation), and systemic sclerosis (also marked by fibrosis). Pathological scars are predominantly populated by anti-inflammatory M2 macrophages and recent literature hints that this could be driven by non-canonical inflammasome signaling. Diabetic-wound healing associates with inflammasome activation in immune (macrophages) and non-immune (keratinocytes) cells. Fibrotic conditions associate with inflammasome activation and inflammasome-induced transition of epithelial cells/endothelial cells/macrophages into myofibroblasts that deposit excessive extracellular matrix. Studies suggest that mechanical stimuli activate inflammasomes via the cytoskeleton and that mechanotransduction-inflammasome crosstalk is involved in fibrosis. Further research should examine (i) the roles that various inflammasome types in macrophages, (myo)fibroblasts, and other cell types play in keloid development and (ii) how mechanical stimuli interact with inflammasomes and thereby drive scar growth. Such research is likely to significantly advance our understanding of pathological scarring and aid the development of new therapeutic strategies.

SARS-CoV-2 non-structural protein 6 triggers NLRP3-dependent pyroptosis by targeting ATP6AP1

A recent mutation analysis suggested that Non-Structural Protein 6 (NSP6) of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a key determinant of the viral pathogenicity. Here, by transcriptome analysis, we demonstrated that the inflammasome-related NOD-like receptor signaling was activated in SARS-CoV-2-infected lung epithelial cells and Coronavirus Disease 2019 (COVID-19) patients' lung tissues. The induction of inflammasomes/pyroptosis in patients with severe COVID-19 was confirmed by serological markers. Overexpression of NSP6 triggered NLRP3/ASC-dependent caspase-1 activation, interleukin-1β/18 maturation, and pyroptosis of lung epithelial cells. Upstream, NSP6 impaired lysosome acidification to inhibit autophagic flux, whose restoration by 1α,25-dihydroxyvitamin D₃, metformin or polydatin abrogated NSP6-induced pyroptosis. NSP6 directly interacted with ATP6AP1, a vacuolar ATPase proton pump component, and inhibited its cleavage-mediated activation. L37F NSP6 variant, which was associated with asymptomatic COVID-19, exhibited reduced binding to ATP6AP1 and weakened ability to impair lysosome acidification to induce pyroptosis. Consistently, infection of cultured lung epithelial cells with live SARS-CoV-2 resulted in autophagic flux stagnation, inflammasome activation, and pyroptosis. Overall, this work supports that NSP6 of SARS-CoV-2 could induce inflammatory cell death in lung epithelial cells, through which pharmacological rectification of autophagic flux might be therapeutically exploited.

Sequential Changes of NLRP3 Inflammasome Activation in Sepsis and its Relationship With Death

INTRODUCTION

Inflammasomes are recognized as key components of the innate immune response in sepsis. We aimed to describe the transcriptional expression of nucleotide-binding domain, leucine-rich repeat-containing receptor, pyrin domain-containing-3 (NLRP3), and serum interleukin-1β (IL-1 β) in critically ill patients, their changes over the first week and their prognostic value in septic patients.

METHODS

Prospective study including patients with sepsis based on Sepsis-3 definitions and a control group of critically ill patients without sepsis. We measured the circulating levels of IL-1β as well as the transcriptional expression of NLRP3 at admission and on days 3 and 7. Caspase-1 and caspase-3 activation was analyzed in a matched cohort of patients with septic shock (four dead and four survivors).

RESULTS

Fifty-five septic patients and 11 non-septic patients were studied. Levels on day 0 and 3 of IL-1 β and NLRP3 inflammasome expression were significantly higher in patients with sepsis than in controls. NLRP3 was significantly higher in septic patients who survived at day 7 without significant difference between survivors and non-survivors at baseline and on day 3. In survivors, an increased caspase-1 protein expression with reduced expression caspase-3 was observed with the opposite pattern in those who died.

CONCLUSIONS

NLRP3 is activated in critically ill patients but this up-regulation is more intense in patients with sepsis. In sepsis, a sustained NLRP3 activation during the first week is protective and sepsis. An increased caspase-1 protein expression with reduced expression caspase-3 is the pattern observed in septic shock patients who survive.

NLRP3 deficiency did not attenuate NASH development under high fat calorie diet plus high fructose and glucose in drinking water

NOD-like receptor protein 3 (NLRP3) promotes the inflammatory response during progression of nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH). This study aimed to further delineate the role of NLRP3 in NASH development by abolishing its expression in mice. A high-fat and calorie diet plus high fructose and glucose in drinking water (HFCD-HF/G) was used to establish NASH in both wild-type (WT) and NLRP3 knock-out (KO) mice. Hepatocellular injury, hepatic steatosis and fibrosis, as well as inflammatory response and insulin resistance in the liver and epidydimal white adipose tissue (eWAT) were determined. Elevated body weight, liver weight and serum alanine transaminase level, increased hepatic triglyceride accumulation and collagen deposition, and worsened systemic insulin resistance were observed in Nlrp3-/- mice compared to WT mice under HFCD-HF/G feeding. Upregulated hepatic transcription of tumor necrosis factor-α (TNF-α) and monocyte chemotactic protein-1 (MCP-1), and enhanced infiltration of inducible nitric oxide synthase-positive (iNOS+) M1 macrophages were also documented in HFCD-HF/G-fed Nlrp3-/- mice in comparison to HFCD-HF/G-fed WT mice. Moreover, transcription of TNF-α and MCP-1 and infiltration of iNOS+ M1 macrophages were increased in the liver of Nlrp3-/- mice under control diet. NLRP3 deficiency did not attenuate, but instead aggravated NASH development under HFCD-HF/G feeding. The worsened extent of NASH might be attributed to enhanced hepatic MCP-1 expression and M1 macrophage infiltration in Nlrp3-/- mice. Our study points to additional caution when NLRP3 blockade is considered as a therapeutic strategy in the treatment of human NASH.

Bone Marrow-Derived Mononuclear Cell Transplantation Can Reduce Systemic Inflammation and Endothelial Glycocalyx Damage in Sepsis

ABSTRACT

Bone marrow-derived mononuclear cells (BMMNCs) secrete anti-inflammatory mediators that protect against acute inflammation. Current evidence suggests that BMMNC transplantation can reduce acute tissue injury caused by systemic inflammation and lung dysfunction. This study evaluated the role of BMMNCs in reducing systemic inflammatory responses to vascular endothelial injury in sepsis. Bone marrow cells were harvested from the tibias and femurs of 12-week-old male Wistar rats; BMMNCs were separated by density centrifugation. Additional rats underwent cecal ligation and puncture (CLP) or similar sham surgery. BMMNCs were injected intravenously 30 min after CLP. The Sham and CLP Control groups were administered PBS. The 7-day survival rate improved markedly in the CLP-BMMNC group compared with that in the Control group. BMMNCs markedly suppressed the serum levels of pro-inflammatory mediators such as tumor necrosis factor-alpha, interleukin-6, and histone H3 at 3, 6, and 12 h after CLP. In the CLP-BMMNC group, the serum levels of syndecan-1, the main component of the vascular endothelial glycocalyx layer, were notably lower than those in the Control group 6 h after CLP. Histological analysis revealed improvement of morphological damages in the CLP-BMMNC group. Ultrastructural analysis revealed that the glycocalyx structure was maintained and the continuity of the vascular endothelial glycocalyx layer was preserved in the BMMNC group, compared with the case for the Control group at 6 and 12 h. Therefore, BMMNC transplantation may provide reduced systemic inflammation and endothelial glycocalyx damage, dramatically improving the survival of rats. These findings provide insights into formulating potential therapeutic strategies against sepsis.

NLRP3 Inflammasome in Inflammation and Metabolism: Identifying Novel Roles in Postburn Adipose Dysfunction

Inflammasomes are multiprotein complexes that respond to pathogen or host associated damage markers, leading to caspase-1 maturation and processing of pro-inflammatory cytokines. Initially, inflammasomes were implicated primarily in inflammatory and infectious conditions. However, increasing evidence demonstrates broader roles beyond inflammation, including regulation of adipose tissue metabolism after burns. Here, we conducted a search for articles on PubMed, Web of Science, Embase, Scopus, and UpToDate with applied search strategies including a combination of "burns," "trauma," "(NLRP3) inflammasome," "metabolic conditions," "white adipose tissue," "macrophages," "browning," and "lipolysis" and included papers from 2000 to 2020. We discuss unexpected roles for NLRP3, the most characterized inflammasome to date, as a key metabolic driver in a variety of conditions. In particular, we highlight the function of NLRP3 inflammasome in burn trauma, which is characterized by both hyperinflammation and hypermetabolism. We identify a critical part for NLRP3 activation in macrophage dynamics and delineate a novel role in postburn white adipose tissue remodeling, a pathological response associated with hypermetabolism and poor clinical outcomes. Mechanistically, how inflammation and inflammasome activation is linked to postburn hypermetabolism is a novel concept to contemplate, and herein we provide evidence of an immunometabolic crosstalk between adipocytes and infiltrating macrophages.

Impact of oral resuscitation on circulating and splenic leukocytes after burns

BACKGROUND

Hemodynamic aberrations after severe burns are treated with aggressive intravenous (IV) fluid resuscitation however, oral resuscitation has been proposed in resource poor scenarios. Previously we have shown that animals receiving oral fluid following burns were able to recover kidney function. However, immune function such as circulating and splenic immune cell populations after oral or intravenous fluid administration was not examined. Herein, we perform a follow up analysis of splenic tissue and plasma from the previous animal study to examine the splenic response following these resuscitation strategies after burn injury.

METHODS

Eighteen anesthetized Yorkshire swine receiving 40%TBSA contact burns were randomized to receive either: (1) no fluids (Fluid Restricted; negative control), (2) 70 mL/kg/d Oral Rehydration Salt solution (Oral), or (3) 2 mL/kg/%TBSA/d of lactated Ringer's solution IV. Blood was drawn for blood cell analysis, and CT scans were performed before and 48 h post-burn, at which point spleens were harvested for histological, Western blot, and RT-PCR analyses.

RESULTS

Splenic artery diameter decreased by -0.97 ± 0.14 mm in fluid-restricted animals, while IV led to an increase of 0.68 ± 0.30 mm. No significant differences were detected in white and red pulp. IV fluids reduced the population of splenic monocytes (CD163; P = 0.001) and neutrophils (MPO protein; P = 0.13), as well as cytokines IL-8 (P = 0.003), IFN-γ (P = 0.11) and TNFα (P = 0.05). Additionally, withholding IV fluids consistently decreased the expression of FoxP3, CCR6, and IL17β in spleen, suggesting a shift in T-cell phenotype with IV resuscitation.

CONCLUSIONS

The route of fluid administration has a minor influence on the changes in circulating and splenic leukocytes post-burn in the acute phase. Further research is needed to help guide resuscitation approaches using immunologic markers of splenic function following burns.

Cytokines in Inflammatory Disease

This review aims to briefly discuss a short list of a broad variety of inflammatory cytokines. Numerous studies have implicated that inflammatory cytokines exert important effects with regard to various inflammatory diseases, yet the reports on their specific roles are not always consistent. They can be used as biomarkers to indicate or monitor disease or its progress, and also may serve as clinically applicable parameters for therapies. Yet, their precise role is not always clearly defined. Thus, in this review, we focus on the existing literature dealing with the biology of cytokines interleukin (IL)-6, IL-1, IL-33, tumor necrosis factor-alpha (TNF-α), IL-10, and IL-8. We will briefly focus on the correlations and role of these inflammatory mediators in the genesis of inflammatory impacts (e.g., shock, trauma, immune dysregulation, osteoporosis, and/or critical illness).

NLRP3 inflammasome mediates white adipose tissue browning after burn

A hallmark after burn is the stress and inflammatory-induced hypermetabolic response. Recently, we and others found that browning of white adipose tissue (WAT) is a critical component of this complex detrimental response. Although browning and inflammation have been independently delineated to occur after injury, their interaction is currently not well defined. One of the master regulators of inflammation and adipose tissue remodeling after burns is nucleotide-binding and oligomerization domain, leucine rich repeat and pyrin domain containing 3 (NLRP3) inflammasome. The aim of this this study was to determine whether NLRP3 modulates and activates WAT browning after burn. To obtain molecular and mechanistic insights, we used an NLRP3 knockout (NLRP3^-/-) murine burn model. We demonstrated that genetic deletion of NLRP3 promoted persistent and augmented browning in adipocytes, evidenced by increased gene expression of peroxisome proliferator-activated receptor γ and CIDEA at 3 days (5.74 vs. 0.29, P < 0.05; 26.0 vs. 0.71, P < 0.05) and uncoupling protein 1 (UCP1) and PGC1α at 7 days (7,406 vs. 3,894, P < 0.05; 20.6 vs. 2.52, P < 0.01) and enhanced UCP1 staining and multilocularity. Additionally, the main regulator of postburn WAT browning, IL-6, was elevated in the plasma acutely after burn in NLRP3^-/- compared with wild-type counterparts (478.9 vs. 67.1 pg/mL, P < 0.05 at 3 days). These results suggest that NLRP3 has antibrowning effects and that blocking NLRP3 increases thermogenesis and augments browning via increased levels of IL-6. Our findings provide insights into targeting innate inflammatory systems for regulation of adaptive thermogenesis, a critical response after burns and other hypermetabolic conditions.

Whole blood assay as a model for in vitro evaluation of inflammasome activation and subsequent caspase-mediated interleukin-1 beta release

Processing of pro-interleukin (IL)-1β and IL-18 is regulated by multiprotein complexes, known as inflammasomes. Inflammasome activation results in generation of bioactive IL-1β and IL-18, which can exert potent pro-inflammatory effects. Our aim was to develop a whole blood-based assay to study the inflammasome in vitro and that also can be used as an assay in clinical studies. We show whole blood is a suitable milieu to study inflammasome activation in primary human monocytes. We demonstrated that unprocessed human blood cells can be stimulated to activate the inflammasome by the addition of adenosine 5'-triphosphate (ATP) within a narrow timeframe following lipopolysaccharide (LPS) priming. Stimulation with LPS resulted in IL-1β release; however, addition of ATP is necessary for "full-blown" inflammasome stimulation resulting in high IL-1β and IL-18 release. Intracellular cytokine staining demonstrated monocytes are the major producers of IL-1β in human whole blood cultures, and this was associated with activation of caspase-1/4/5, as detected by a fluorescently labelled caspase-1/4/5 probe. By applying caspase inhibitors, we show that both the canonical inflammasome pathway (via caspase-1) as well as the non-canonical inflammasome pathway (via caspases-4 and 5) can be studied using this whole blood-based model.

Inflammasome activation in Kupffer cells confers a protective response in nonalcoholic steatohepatitis through pigment epithelium-derived factor expression

Hepatocellular death or ballooning distinguishes the transition of simple steatosis to irreversible nonalcoholic steatohepatitis (NASH). However, the molecular mechanism of hepatocellular apoptosis in NASH is largely unclear, and discovery of endogenous mediators that could prevent or inhibit cell death is thereby critical in intercepting NASH progression. Here, we identified pigment epithelium-derived factor (PEDF), a secreted, moonlighting hepatokine as 1 hepatoprotective agent in mice with diet-induced NASH. Hepatic PEDF expression is induced by IL-1β, which is derived from inflammasome activation in liver-resident Kupffer cells, an effect that is negatively regulated by TNF-α and predominantly secreted by monocyte-derived, recruited, hepatic macrophages. Mechanistically, reciprocal and opposing roles for IL-1β and TNF-α in PEDF expression are mediated by differential activation of NF-κB. Although augmented TNF-α production leads to temporal reduction of PEDF expression in NASH, PEDF conversely abrogates TNF-α-mediated hepatocyte death by modulating the extrinsic apoptosis pathway. Thus, our study highlights PEDF as a functionally important hepatokine in NASH progression by linking inflammasome activation and hepatocellular death.-Adak, M., Das, D., Niyogi, S., Nagalakshmi, C., Ray, D., Chakrabarti, P. Inflammasome activation in Kupffer cells confers a protective response in nonalcoholic steatohepatitis through pigment epithelium-derived factor expression.

Comparative Analysis of the Regulatory T Cells Dynamics in Peripheral Blood in Human and Porcine Polytrauma

Background

Severely injured patients experience substantial immunological stress in the aftermath of traumatic insult, which often results in systemic immune dysregulation. Regulatory T cells (Treg) play a key role in the suppression of the immune response and in the maintenance of immunological homeostasis. Little is known about their presence and dynamics in blood after trauma, and nothing is known about Treg in the porcine polytrauma model. Here, we assessed different subsets of Treg in trauma patients (TP) and compared those to either healthy volunteers (HV) or data from porcine polytrauma.

Methods

Peripheral blood was withdrawn from 20 TP with injury severity score (ISS) ≥16 at the admittance to the emergency department (ED), and subsequently on day 1 and at day 3. Ten HV were included as controls (ctrl). The porcine polytrauma model consisted of a femur fracture, liver laceration, lung contusion, and hemorrhagic shock resulting in an ISS of 27. After polytrauma, the animals underwent resuscitation and surgical fracture fixation. Blood samples were withdrawn before and immediately after trauma, 24 and 72 h later. Different subsets of Treg, CD4+CD25+, CD4+CD25+FoxP3+, CD4+CD25+CD127-, and CD4+CD25+CD127-FoxP3+ were characterized by flow cytometry.

Results

Absolute cell counts of leukocytes were significantly increasing after trauma, and again decreasing in the follow-up in human and porcine samples. The proportion of human Treg in the peripheral blood of TP admitted to the ED was lower when compared to HV. Their numbers did not recover until 72 h after trauma. Comparable data were found for all subsets. The situation in the porcine trauma model was comparable with the clinical data. In porcine peripheral blood before trauma, we could identify Treg with the typical immunophenotype (CD4+CD25+CD127-), which were virtually absent immediately after trauma. Similar to the human situation, most of these cells expressed FoxP3, as assessed by intracellular FACS stain.

Conclusion

Despite minor percental differences in the recovery of Treg populations after trauma, our findings show a comparable decrease of Treg early after polytrauma, and strengthen the immunological significance of the porcine polytrauma model. Furthermore, the Treg subpopulation CD4+CD25+CD127- was characterized in porcine samples.

Schistosome-Induced Fibrotic Disease: The Role of Hepatic Stellate Cells

Hepatic fibrosis is a common pathology in various liver diseases. Hepatic stellate cells (HSCs) are the main cell type responsible for collagen deposition and fibrosis formation in the liver. Schistosomiasis is characterised by granulomatous fibrosis around parasite eggs trapped within the liver and other host tissues. This response is facilitated by the recruitment of immune cells and the activation of HSCs. The interactions between HSCs and schistosome eggs are complex and diverse, and a better understanding of these interactions could lead to improved resolution of fibrotic liver disease, including that associated with schistosomiasis. Here, we discuss recent advances in HSC biology and the role of HSCs in hepatic schistosomiasis.

Caspase-1-dependent pyroptosis of peripheral blood mononuclear cells predicts the development of sepsis in severe trauma patients: A prospective observational study

Pyroptosis plays a pivotal role in sepsis and septic shock in animal studies. However, its clinical significance in pathological conditions has not been well elucidated. This study aimed to evaluate the correlation between the percentage of pyroptotic peripheral blood mononuclear cells (PBMCs) and the clinical index and to investigate the relationship between PBMCs pyroptosis and the development of sepsis in trauma patients.This prospective study was conducted from October 2016 to May 2017 in a comprehensive trauma center. Sixty trauma patients and 10 healthy controls were enrolled. Peripheral blood samples were collected from the patients within 24 hours after injury. The percentages of pyroptotic and apoptotic PBMCs were measured using flow cytometry, and plasma levels of cytokines were evaluated using flow cytometric analysis with a human inflammation 13-plex panel.Trauma patients who developed sepsis had higher percentages of pyroptotic and apoptotic PBMCs at admission. Patients who developed sepsis (n = 33) had higher interleukin (IL)-6, IL-18, and monocyte chemotactic protein-1 (MCP-1) concentrations at admission than patients (n = 27) who did not develop sepsis. The percentage of PBMCs pyroptosis was significantly correlated with injury severity score (ISS), acute physiology and chronic health evaluation (APACHE) II score, IL-10, IL-18, and MCP-1 levels in trauma patients. PBMCs pyroptosis is a better biomarker in predicting the development of sepsis after trauma.This study indicates that the percentage of pyroptotic PBMCs increases during the early phase of trauma and that this increase is significantly correlated with the severity and state of inflammation in trauma patients. PBMCs pyroptosis is a potential marker for predicting the development of sepsis after trauma.

NOD-like receptor(s) and host immune responses with Pseudomonas aeruginosa infection

INTRODUCTION

Molecular mechanisms underlying the interactions between Pseudomonas aeruginosa, the common opportunistic pathogen in cystic fibrosis individuals, and host induce a number of marked inflammatory responses and associate with complex therapeutic problems due to bacterial resistance to antibiotics in chronic stage of infection.

METHODS

Pseudomonas aeruginosa is recognized by number of pattern recognition receptors (PRRs); NOD-like receptors (NLRs) are a class of PRRs, which can recognize a variety of endogenous and exogenous ligands, thereby playing a critical role in innate immunity.

RESULTS

NLR activation initiates forming of a multi-protein complex called inflammasome that induces activation of caspase-1 and resulted in cleavage of pro-inflammatory cytokines interleukin (IL)-1β and IL-18. When the IL-1β is secreted excessively, this causes tissue damage and extensive inflammatory responses that are potentially hazardous for the host.

CONCLUSIONS

Recent evidence has laid out inflammasome-forming NLR far beyond inflammation. This review summarizes current knowledge regarding the various roles played by different NLRs and associated down-signals, either in recognition of P. aeruginosa or may be associated with such bacterial pathogen infection, which may relate to for the complexity of lung diseases caused by P. aeruginosa.

Activation of NLRP3 inflammasomes in mouse hepatic stellate cells during Schistosoma J. infection

The major pathological changes during Schistosoma J. infection are characterized by granulomatous inflammation in the liver, a cellular immune response to schistosomal egg antigens. The molecular mechanisms initiating or promoting this schistosomal granulomatous inflammation remain poorly understood. In the present study, we first demonstrated that in mice infected with Schistosoma J. for 6 weeks exhibited increased levels of IL-1β in liver, a major product of NLRP3 inflammasomes and collagen deposition around the eosinophilic granuloma with Schistosoma J. eggs, which was substantially attenuated by caspase-1 inhibitor, YVAD. This activation of the NLRP3 inflammasome occurred in hepatic stellate cells (HSCs), as shown by a marked increase in co-localization of IL-1β with HSCs marker, desmin. Using isolated, cultured mouse HSCs, we further explored the mechanisms by which soluble egg antigen (SEA) from Schistosoma J. activates NLRP3 inflammasomes. SEA induced the formation and activation of NLRP3 inflammasomes, which was associated with both redox regulation and lysosomal dysfunction, but not with potassium channel activation. These results suggest that NLRP3 inflammasome activation in HSCs may serve as an early mechanism to turn on the inflammatory response and thereby instigate liver fibrosis during Schistosoma J. infection.

Traumatic Injury

Traumatic injury as one of the world's most relevant but neglected health concerns results in modulated inflammasome activity, which is closely linked to the development of post-injury complications. Cytokine-producing capacity of cells is important for the appropriate immune response to trauma and requires not only synthesis and transcription of inflammasome components but also their activation. Unfortunately, the precise role of inflammasome in trauma is still largely unknown. However, in the following chapter, we provide an overview on the best described inflammasomes in the various settings of trauma, introducing the recent findings on the up-to-date best described NLRP inflammasomes and underlying cytokines in the inflammatory response to trauma.

[Caspase-1 regulates autoinflammation in rheumatic diseases]

Caspase-1 is an integral regulator of the innate immune system. Its core functions are the processing and secretion of the proinflammatory cytokines interleukin 1β (IL-1 beta) and IL-18 and the initiation of proinflammatory cell death, which is referred to as pyroptosis. Activation of caspase-1 plays a pivotal role during immune defense mechanisms against infections by the innate immune system. Dysregulated activation of caspase-1 has been recognized to be involved in the pathophysiology of a constantly increasing number of inflammatory diseases. This article gives an overview of the regulation and function of caspase-1 and its involvement in monogenic, polygenic and/or polyetiological rheumatic diseases.

Caspase-1 Activation Protects Lung Endothelial Barrier Function during Infection-Induced Stress

Dysregulated activation of the inflammasome-caspase-1-IL-1β axis elicits damaging hyperinflammation during critical illnesses, such as pneumonia and sepsis. However, in critical illness models of Salmonella infection, burn, or shock, caspase-1 inhibition worsens outcomes. These paradoxical effects suggest that caspase-1 drives novel protective responses. Whether the protective effects of caspase-1 activation involve canonical immune cell and/or nonimmune cell responses is unknown. The objective of this study was to test the hypothesis that, in addition to its recognized proinflammatory function, caspase-1 initiates protective stress responses in nonimmune cells. In vivo, lung epithelial and endothelial barrier function and inflammation were assessed in mice infected with Pseudomonas aeruginosa in the presence or absence of a caspase-1 inhibitor. Lung endothelial barrier function was assessed ex vivo in isolated, perfused rat lungs infected with P. aeruginosa in the presence or absence of a caspase-1 inhibitor. Endothelial barrier function during P. aeruginosa infection was assessed in vitro in cultured rat wild-type pulmonary microvascular endothelial cells (PMVECs) or recombinant PMVECs engineered to decrease caspase-1 expression. We demonstrated in vivo that caspase-1 inhibition in P. aeruginosa-infected mice ameliorated hyperinflammation, but, counterintuitively, increased pulmonary edema. Ex vivo, caspase-1 inhibition increased pulmonary permeability in P. aeruginosa-infected isolated rat lungs. To uncouple caspase-1 from its canonical inflammatory role, we used cultured rat PMVECs in vitro and discovered that genetic knockdown of caspase-1 accelerated P. aeruginosa-induced barrier disruption. In conclusion, caspase-1 is a sentinel stress-response regulator that initiates proinflammatory responses and also initiates novel response(s) to protect PMVEC barrier function during pneumonia.

3,4-Methylenedioxy-β-Nitrostyrene Ameliorates Experimental Burn Wound Progression by Inhibiting the NLRP3 Inflammasome Activation

BACKGROUND

Burn wound progression remains a challenging problem in the clinic. Secondary tissue damage caused by unlimited inflammatory response is considered to be one of the key factors contributing to this clinical problem. Nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome has recently been found to play important roles in immune activation and the inflammatory response after burn/trauma. This experimental study aims (1) to observe the expression and distribution of NLRP3 inflammasome in burn wounds of a rat burn model and (2) to study whether inhibiting the NLRP3 inflammasome activation would ameliorate burn wound progression.

METHODS

A deep second-degree burn was inflicted on the backs of Wistar rats. The expression of NLRP3 inflammasome components and interleukin-1β were determined by Western blot and coimmunoprecipitation. The distribution of NLRP3 inflammasome was assessed by immunohistochemical staining and double-labeling immunofluorescence. Neutrophil infiltration, wound perfusion, burn depth, and wound healing time were assessed.

RESULTS

Burn induced remarkable NLRP3 inflammasome activation and cleavage of interleukin-1β. The NLRP3 inflammasome was observed mainly in macrophages of the zone of stasis. 3,4-Methylenedioxy-β-nitrostyrene significantly inhibited NLRP3 inflammasome activation and inflammatory cytokine production in burn wounds. Consequently, neutrophil infiltration was reduced, wound perfusion was restored, burn wound progression was ameliorated, and wound healing was accelerated.

CONCLUSIONS

In this study, the authors demonstrated that burn induced NLRP3 inflammasome activation and inflammatory response in wounds, which may be associated with burn wound progression. Treatment with 3,4-methylenedioxy-β-nitrostyrene inhibited NLRP3 inflammasome activation, ameliorated burn wound progression, and promoted wound healing.

Intervention with a caspase-1 inhibitor reduces obesity-associated hyperinsulinemia, non-alcoholic steatohepatitis and hepatic fibrosis in LDLR-/-.Leiden mice

Background/Objectives:

Non-alcoholic steatohepatitis (NASH) is a serious liver condition, closely associated with obesity and insulin resistance. Recent studies have suggested an important role for inflammasome/caspase-1 in the development of NASH, but the potential therapeutic value of caspase-1 inhibition remains unclear. Therefore, we aimed to investigate the effects of caspase-1 inhibition in the ongoing disease process, to mimic the clinical setting.

Subjects/Methods:

To investigate effects of caspase-1 inhibition under therapeutic conditions, male LDLR−/−.Leiden mice were fed a high-fat diet (HFD) for 9 weeks to induce a pre-diabetic state before start of treatment. Mice were then continued on HFD for another 12 weeks, without (HFD) or with (HFD-YVAD) treatment with the caspase-1 inhibitor Ac-YVAD-cmk (40 mg kg⁻¹ per day).

Results:

Nine weeks of HFD feeding resulted in an obese phenotype, with obesity-associated hypertriglyceridemia, hypercholesterolemia, hyperglycemia and hyperinsulinemia. Treatment with Ac-YVAD-cmk did not affect further body weight gain or dyslipidemia, but did attenuate further progression of insulin resistance. Histopathological analysis of livers clearly demonstrated prevention of NASH development in HFD-YVAD mice: livers were less steatotic and neutrophil infiltration was strongly reduced. In addition, caspase-1 inhibition had a profound effect on hepatic fibrosis, as assessed by histological quantification of collagen staining and gene expression analysis of fibrosis-associated genes Col1a1, Acta2 and Tnfa.

Conclusions:

Intervention with a caspase-1 inhibitor attenuated the development of NASH, liver fibrosis and insulin resistance. Our data support the importance of inflammasome/caspase-1 in the development of NASH and demonstrate that therapeutic intervention in the already ongoing disease process is feasible.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

Anti-inflammatory Activity of Saxifragin via Inhibition of NF-κB Involves Caspase-1 Activation

Saxifragin, the 5-glucoside of the flavonoid quercetin, is found in plants and insects. It has been reported that saxifragin has peroxynitrite-scavenging effects. However, the mechanism of anti-inflammatory effects of saxifragin has not yet been clearly identified. In this study, we investigated the anti-inflammatory effects of saxifragin in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages and animal models of inflammation. We found that saxifragin suppressed the production of nitric oxide (NO) and prostaglandin E2 (PGE2) in LPS-activated RAW 264.7 macrophages by suppressing the level of protein and mRNA expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), respectively. Furthermore, saxifragin inhibited mRNA expression of pro-inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β. We studied the inhibitory effects of saxifragin on the nuclear translocation of nuclear factor (NF)-κB, activation of caspase-1, and phosphorylation of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Furthermore, pretreatment with saxifragin increased the survival rate of mice with LPS-induced septic death. Collectively, these findings suggest that saxifragin exerts anti-inflammatory activity by inhibiting NF-κB, caspase-1, and mitogen-activated protein kinase (MAPK) activation.

Caspase-1: an integral regulator of innate immunity

Caspase-1 is a unique cysteine protease playing central roles in innate immunity. Pathogens, stress, and damage signals induce activation of caspase-1, typically mediated by proximity-induced autoproteolysis in multimeric protein complexes called the inflammasome. Active caspase-1 induces secretion of pro-inflammatory cytokines and mediates pyroptosis, a programmed pro-inflammatory cell death, thereby initiating an immune response finally leading to pathogen clearance. Excessive activation of caspase-1 is the underlying cause for rare diseases such as periodic fever syndromes, and more common disorders, including atherosclerosis, type 2 diabetes, and gout. Beside these well-known pro-inflammatory functions, active caspase-1 also has anti-inflammatory and protective functions contributing to cell survival, reduced inflammatory cytokine signaling, and improved outcomes in mouse models of burn injury or trauma and shock. Furthermore, naturally occurring procaspase-1 variants with reduced or abrogated enzymatic activity mediate enhanced inflammatory signaling and have been associated to autoinflammatory symptoms. Here, we review functions of caspase-1 focusing on anti-inflammatory signaling pathways and discuss the role of enzymatically inactive caspase-1 as disease-promoting factors in autoinflammatory diseases. Moreover, we illustrate differential requirements for autoproteolysis and enzymatic activity in caspase-1 functions.

Molecular activation of the NLRP3 Inflammasome in fibrosis: common threads linking divergent fibrogenic diseases

SIGNIFICANCE

Over the past 10 years, there has been a plethora of investigations centering on the NLRP3 inflammasome and its role in fibrosis and other disease pathologies. To date, the signaling pathways from the inflammasome to myofibroblast differentiation and chronic collagen synthesis have not been fully elucidated, and many questions are left to be answered.

RECENT ADVANCES

Recent studies have demonstrated the significant and critical role of reactive oxygen species (ROS) and calcium signaling in the assembly of the inflammasome, and this may result in autocrine signaling maintaining the myofibroblast phenotype, leading to fibrotic disease.

CRITICAL ISSUES

Traditionally, myofibroblasts under tight regulation aid in wound healing and then, once the wound has closed, undergo apoptosis and the collagen in the wound remodels. During fibrosis, however, the myofibroblast maintains an activated state via a chronically activated inflammasome, leading to the continual synthesis of collagens and other extracellular matrix proteins that result in damage to the tissue or organ. The mechanism that is driving this abnormality has not been fully elucidated.

FUTURE DIRECTIONS

However, studies have been conducted to suggest that modulating the calcium or the ROS axis may be of therapeutic value in regulating inflammasome activation. A number of novel drugs are currently being developed that may prove beneficial to patients suffering from fibrotic diseases.

Radiation exposure induces inflammasome pathway activation in immune cells

Radiation exposure induces cell and tissue damage, causing local and systemic inflammatory responses. Because the inflammasome pathway is triggered by cell death and danger-associated molecular patterns, we hypothesized that the inflammasome may signal acute and chronic immune responses to radiation. Using a mouse radiation model, we show that radiation induces a dose-dependent increase in inflammasome activation in macrophages, dendritic cells, NK cells, T cells, and B cells as judged by cleaved caspase-1 detection in cells. Time course analysis showed the appearance of cleaved caspase-1 in cells by day 1 and sustained expression until day 7 after radiation. Also, cells showing inflammasome activation coexpressed the cell surface apoptosis marker annexin V. The role of caspase-1 as a trigger for hematopoietic cell losses after radiation was studied in caspase-1(-/-) mice. We found less radiation-induced cell apoptosis and immune cell loss in caspase-1(-/-) mice than in control mice. Next, we tested whether uric acid might mediate inflammasome activation in cells by treating mice with allopurinol and discovered that allopurinol treatment completely blocked caspase-1 activation in cells. Finally, we demonstrate that radiation-induced caspase-1 activation occurs by a Nod-like receptor family protein 3-independent mechanism because radiation-exposed Nlrp3(-/-) mice showed caspase-1 activation profiles that were indistinguishable from those of wild-type mice. In summary, our data demonstrate that inflammasome activation occurs in many immune cell types following radiation exposure and that allopurinol prevented radiation-induced inflammasome activation. These results suggest that targeting the inflammasome may help control radiation-induced inflammation.

Activation of NLRP3 and AIM2 inflammasomes in Kupffer cells in hepatic ischemia/reperfusion

Inflammasome activation by danger signals in ischemia/reperfusion (I/R) injury is responsible for the sterile inflammatory response. Signals triggering formation and activation of the inflammasome involve the generation of oxidative stress. The aim of this study was to examine the molecular mechanisms of inflammasome activation and the involvement of reactive oxygen species in hepatic I/R. I/R induced the formation of nucleotide-binding domain leucine-rich repeat containing family pyrin domain containing 3 (NLRP3) and absent in melanoma 2 (AIM2) inflammasomes and the subsequent serum release of interleukin 1β. Pannexin-1 inhibitor and anti-cathepsin B antibody attenuated I/R-induced inflammasome activation and hepatic injury. The expression of the thioredoxin-interacting protein gene and the interaction between NLRP3 and the thioredoxin-interacting protein increased after I/R. Treatment with the antioxidant N-acetylcysteine significantly attenuated protein conversion of interleukin 1β after hepatic I/R. Moreover, pannexin-1 protein expression and cathepsin B release were strongly attenuated by N-acetylcysteine. The depletion of Kupffer cells with gadolinium chloride markedly decreased NLRP3 and AIM2 inflammasome expression and activation of their signaling pathways, and also reduced the level of caspase-1 protein in F4/80-positive cells. Our findings suggest that reactive-oxygen-species-mediated activation of NLRP3 and AIM2 inflammasomes leads to I/R-induced inflammatory responses in which Kupffer cells play a crucial role.

Burn plus lipopolysaccharide augments endoplasmic reticulum stress and NLRP3 inflammasome activation and reduces PGC-1α in liver

Extensively burned patients often suffer from sepsis (especially caused by Pseudomonas aeruginosa), which may prolong metabolic derangement, contribute to multiple organ failure, and increase mortality. The molecular and cellular mechanisms of such infection-related metabolic derangement and organ dysfunction are unclear. We have previously shown that severely burned patients have significant and persisting hepatic endoplasmic reticulum (ER) stress. We hypothesized that ER stress and the unfolded protein response correlate with NOD-like receptor, pyrin domain containing 3 (NLRP3) inflammasome activation in burn. These may trigger profound metabolic changes in the liver, which form the pathological basis of liver damage and liver dysfunction after burn injury. A two-hit rat model was established by a 60% total body surface area scald burn and intraperitoneal injection of P. aeruginosa-derived lipopolysaccharide (LPS) 3 days after burn. One day later, animals were killed, and liver tissue samples were collected for gene expression and protein analysis of NLRP3 inflammasome activation, ER stress, and glucose and lipid metabolism. Liver damage was assessed by plasma markers (alanine aminotransferase and aspartate aminotransferase) and liver immunohistochemical analysis. Our results showed that burn injury and LPS injection induced inflammasome activation in liver and augmented hepatic ER stress and liver damage. Although there was an increased metabolic demand after burn, hepatic NLRP3 inflammasome activation corresponded to inhibition of PGC-1α (peroxisome proliferator-activated receptor γ-coactivator 1α) and its upstream regulators protein kinase A catalyst unit, AMP-activated protein kinase α, and sirtuin-1 may provide a mechanism for the enhanced metabolic derangement after major burn injury plus sepsis. In conclusion, burn + LPS augments inflammasome activation and ER stress in liver, which in turn contribute to postburn metabolic derangement.

Wound infections and healing: are they contributing factors for carcinogenesis?

The link between inflammation and tumourisation has long been considered as a key event in clinical cancer development. Inflammation and inflammatory diseases can be caused by many factors including infectious agents, altered genetics and various degrees of injuries from simple cuts to traumatic wounds, such as those suffered in battlefield. Improved management of all wound types is critical in protecting affected individuals against the development of tumourisation cues, which may potentially lead to cancer development. There have been numerous studies on the mechanism of inflammation-induced tumourisation. Thus, in this mini review, we summarised evidence demonstrating the potential link between infectious agents and their moonlight proteins, wounding, trauma, overactive repair mechanisms, and carcinogenesis.

Human procaspase-1 variants with decreased enzymatic activity are associated with febrile episodes and may contribute to inflammation via RIP2 and NF-κB signaling

The proinflammatory enzyme caspase-1 plays an important role in the innate immune system and is involved in a variety of inflammatory conditions. Rare naturally occurring human variants of the caspase-1 gene (CASP1) lead to different protein expression and structure and to decreased or absent enzymatic activity. Paradoxically, a significant number of patients with such variants suffer from febrile episodes despite decreased IL-1β production and secretion. In this study, we investigate how variant (pro)caspase-1 can possibly contribute to inflammation. In a transfection model, such variant procaspase-1 binds receptor interacting protein kinase 2 (RIP2) via Caspase activation and recruitment domain (CARD)/CARD interaction and thereby activates NF-κB, whereas wild-type procaspase-1 reduces intracellular RIP2 levels by enzymatic cleavage and release into the supernatant. We approach the protein interactions by coimmunoprecipitation and confocal microscopy and show that NF-κB activation is inhibited by anti-RIP2-short hairpin RNA and by the expression of a RIP2 CARD-only protein. In conclusion, variant procaspase-1 binds RIP2 and thereby activates NF-κB. This pathway could possibly contribute to proinflammatory signaling.

Immune response to traumatic injury: harmony and discordance of immune system homeostasis

Trauma remains one of the leading causes of death worldwide. Traumatic injury disrupts immune system homeostasis and may predispose patients to opportunistic infections and inflammatory complications. Prevention of multiple organ dysfunction syndrome due to septic complications following severe trauma is a challenging problem. Following severe injury, the immune system usually tends toward a pro-inflammatory phenotype and then changes to a counter-inflammatory phenotype. This immune system homeostasis is believed to be a protective response based on the balance between the innate and adaptive immune systems. We reported that injury activates inflammasomes and primes Toll-like receptors. The primed innate immune system is prepared for a rapid and strong antimicrobial immune defense. However, trauma can also develop the "two-hit" response phenotype. We also reported that injury augments regulatory T cell activity, which can control the "two-hit" response phenotype in trauma. We discuss the current idea that traumatic injury induces a unique type of innate and adaptive immune response that may be triggered by damage-associated molecular pattern molecules, which are a combination of endogenous danger signal molecules that include alarmins and pathogen-associated molecular pattern molecules.

Involvement of inflammasome activation in lipopolysaccharide-induced mice depressive-like behaviors

AIMS

The NLRP3 inflammasome is a cytoplasmic multiprotein complex of the innate immune system that regulates the cleavage of interleukin-1β and interleukin-18 precursors. It can detect a wide range of danger signals and trigger a series of immune-inflammatory reactions. There were plenty of studies indicating that activation of the immune system played pivotal roles in depression. However, the underlying mechanisms of immune-depression interactions remained elusive and there was no report about the involvement of inflammasome activation in depression.

METHODS

We established an acute depression mouse model with lipopolysaccharide to explore the involvement of inflammasome activation in depression.

RESULTS

The lipopolysaccharide-treated mice displayed depressive-like behaviors and pro-inflammatory cytokine interleukin-1β protein and mRNA levels significantly increased. The NLRP3 inflammasome mRNA expression level also significantly elevated in depressed mice brain. Pretreatment with the NLRP3 inflammasome inhibitor Ac-YVAD-CMK significantly abrogated the depressive-like behaviors induced by lipopolysaccharide.

CONCLUSION

These data suggest for the first time that the NLRP3 inflammasome is involved in lipopolysaccharide-induced mice depressive-like behaviors. The NLRP3 inflammasome may be a central mediator between immune activation and depression, which raises the possibility that it may be a more specific target for the depression treatments in the near future.

Deficient Candida-specific T-helper 17 response during sepsis

Patients with sepsis in the intensive care unit (ICU) are prone to develop Candida infections. Here, we investigated Candida-induced T-helper 17 (Th17) responses during experimental human endotoxemia and in patients with sepsis admitted to the ICU. Peripheral blood mononuclear cells were stimulated with Candida albicans. The Th17 response was significantly lower during endotoxemia, compared with baseline. Patients with gram-negative sepsis had a significantly lower Th17 response as compared to healthy controls. These data demonstrate that the Th17 response is deficient during endotoxin-related systemic inflammation, which likely represents an important risk factor for increased susceptibility to develop Candida infection in patients with sepsis.

Inflection points in sepsis biology: from local defense to systemic organ injury

Sepsis and septic shock lead to considerable morbidity and mortality in developed and developing countries. Despite advances in understanding the innate immune events that lead to septic shock, molecular therapies based on these advances have failed to improve sepsis mortality. The clinical failure of laboratory-derived therapies may be, in part, due to the pleiotropic consequences of the acute inflammatory response, which is the focus of this review. A brisk response to infecting organism is essential for pathogen containment and eradication. However, systemic spread of inflammation beyond a single focus leads to organ injury and higher mortality. The primary goal of this article is to discuss recent animal- and human-based scientific advances in understanding the host response to infection and to highlight how these defense mechanisms can be locally beneficial but systemically detrimental. There are other factors that determine the severity of sepsis that are beyond the scope of this review, including the virulence of the pathogen and regulation by Toll-like receptors. Specifically, this review focuses on how the effector mechanisms of platelets, mast cells, neutrophil extracellular traps (NETs), and the endothelium participate in combating local infections yet can induce organ injury during systemic infection.

Trauma equals danger--damage control by the immune system

Traumatic injuries induce a complex host response that disrupts immune system homeostasis and predisposes patients to opportunistic infections and inflammatory complications. The response to injuries varies considerably by type and severity, as well as by individual variables, such as age, sex, and genetics. These variables make studying the impact of trauma on the immune system challenging. Nevertheless, advances have been made in understanding how injuries influence immune system function as well as the immune cells and pathways involved in regulating the response to injuries. This review provides an overview of current knowledge about how traumatic injuries affect immune system phenotype and function. We discuss the current ideas that traumatic injuries induce a unique type of a response that may be triggered by a combination of endogenous danger signals, including alarmins, DAMPs, self-antigens, and cytokines. Additionally, we review and propose strategies for redirecting injury responses to help restore immune system homeostasis.

NLRC4 inflammasomes in dendritic cells regulate noncognate effector function by memory CD8⁺ T cells

Memory T cells exert antigen-independent effector functions, but how these responses are regulated is unclear. We discovered an in vivo link between flagellin-induced NLRC4 inflammasome activation in splenic dendritic cells (DCs) and host protective interferon-γ (IFN-γ) secretion by noncognate memory CD8(+) T cells, which could be activated by Salmonella enterica serovar Typhimurium, Yersinia pseudotuberculosis and Pseudomonas aeruginosa. We show that CD8α(+) DCs were particularly efficient at sensing bacterial flagellin through NLRC4 inflammasomes. Although this activation released interleukin 18 (IL-18) and IL-1β, only IL-18 was required for IFN-γ production by memory CD8(+) T cells. Conversely, only the release of IL-1β, but not IL-18, depended on priming signals mediated by Toll-like receptors. These findings provide a comprehensive mechanistic framework for the regulation of noncognate memory T cell responses during bacterial immunity.