Inflammasomes in infection and inflammation

C9 regulates the complement-mediated cell lysis in association with CD59 to resist bacterial infection in a primary animal

Complement component 9 (C9), as an essential component of terminal membrane attack complex of complement system, plays an important role in innate immune defense. However, the function and regulatory mechanism of C9 in the antimicrobial immune response of teleost fish remain unclear. In this study, the open reading frame of Nile tilapia (Oreochromis niloticus) C9 (OnC9) gene was amplified. The mRNA and protein expression of OnC9 were significantly changed upon infection with Streptococcus agalactiae and Aeromonas hydrophila in vivo and in vitro. Upon bacterial challenge, the OnC9 knockdown could lead to rapid proliferation of the pathogenic bacteria, ultimately resulting in tilapia death. However, the phenotype was rescued by re-injection of OnC9, which restored the healthy status of the knockdown tilapia. Further, the OnC9 was an essential component in complement-mediated cell lysis and associated with OnCD59 to regulate the efficiency of lysis. Overall, this study indicates that OnC9 is involved in host defense against bacterial infection, and provides a valuable reference for further exploration of the molecular regulatory mechanism of C9 in innate immune defense in a primary animal.

Cornus officinalis Seed Extract Inhibits AIM2-Inflammasome Activation and Attenuates Imiquimod-Induced Psoriasis-like Skin Inflammation

The AIM2 inflammasome is an innate immune system component that defends against cytosolic bacteria and DNA viruses, but its aberrant activation can lead to the progression of various inflammatory diseases, including psoriasis. However, there have been few reports of specific inhibitors of AIM2 inflammasome activation. In this study, we aimed to investigate the inhibitory activity of ethanolic extracts of seeds of Cornus officinalis (CO), a herb and food plant used in traditional medicine, on AIM2-inflammasome activation. We found that CO inhibited the release of IL-1β induced by dsDNA in both BMDMs and HaCaT cells, but that it showed no effect on the release of IL-1β induced by NLRP3 inflammasome triggers, such as nigericin and silica, or the NLRC4 inflammasome trigger flagellin. Furthermore, we demonstrated that CO inhibited the cleavage of caspase-1, an inflammasome activation marker, and an upstream event, the translocation and speck formation of ASC. In addition, further experiments and mechanistic investigations revealed that CO can inhibit AIM2 speck formation induced by dsDNA in AIM2-overexpressing HEK293T cells. To verify the correlation in vivo, we investigated the efficacy of CO in an imiquimod (IMQ)-induced psoriasis model, which has reported associations with the AIM2 inflammasome. We found that topical application of CO alleviated psoriasis-like symptoms, such as erythema, scaling, and epidermal thickening, in a dose-dependent manner. Moreover, CO also significantly decreased IMQ-induced expression of AIM2 inflammasome components, including AIM2, ASC, and caspase-1, and led to the elevation of serum IL-17A. In conclusion, our results suggest that CO may be a valuable candidate for the discovery of AIM2 inhibitors and the regulation of AIM2-related diseases.

Sleep and Healthy Aging Research on Depression (SHARE-D) randomized controlled trial: Protocol overview of an experimental model of depression with insomnia, inflammation, and affect mechanisms in older adults

Depression, one of the most common diseases in older adults, carries significant risk for morbidity and mortality. Because of the burgeoning population of older adults, the enormous burden of late-life depression, and the limited efficacy of current antidepressants in older adults, biologically plausible models that translate into selective depression prevention strategies are needed. Insomnia predicts depression recurrence and is a modifiable target to prevent incident and recurrent depression in older adults. Yet, it is not known how insomnia gets converted into biological- and affective risk for depression, which is critical for identification of molecular targets for pharmacologic interventions, and for refinement of insomnia treatments that target affective responding to improve efficacy. Sleep disturbance activates inflammatory signaling and primes immune responses to subsequent inflammatory challenge. In turn, inflammatory challenge induces depressive symptoms, which correlate with activation of brain regions implicated in depression. This study hypothesizes that insomnia serves as a vulnerability factor for inflammation-related depression; older adults with insomnia will show heightened inflammatory- and affective responding to inflammatory challenge as compared to those without insomnia. To test this hypothesis, this protocol paper describes a placebo-controlled, randomized, double-blind study of low dose endotoxin in older adults (n = 160; 60-80 y) with insomnia vs. comparison controls without insomnia. The aims of this study are to examine differences in depressive symptoms, measures of negative affective responding, and measures of positive affective responding as a function of insomnia and inflammatory challenge. If the hypotheses are confirmed, older adults with two "hits", insomnia and inflammatory activation, would represent a high risk group to be prioritized for monitoring and for depression prevention efforts using treatments that target insomnia or inflammation. Moreover, this study will inform the development of mechanism-based treatments that target affect responses in addition to sleep behaviors, and which might also be coupled with efforts to reduce inflammation to optimize efficacy of depression prevention.

Complement C3 Regulates Inflammatory Response and Monocyte/Macrophage Phagocytosis of Streptococcus agalactiae in a Teleost Fish

The complement system is composed of a complex protein network and is pivotal to innate immunity. Complement 3 (C3) is a critical protein in the complement cascade and participates in complement activation and immune defense. In this study, C3 from Nile tilapia (Oreochromis niloticus) was cloned and its function in resisting pathogen infection was characterized. The full length of OnC3 open reading frame is 4974 bp, encoding 1657 aa, and the predicted protein mass weight is 185.93 kDa. The OnC3 amino acid sequence contains macroglobulin domains. The expression pattern of OnC3 mRNA in the tissues of healthy fish was detected, with the highest in the liver and the lowest in the muscle. After challenged with Streptococcus agalactiae and Aeromonas hydrophila, the expression of OnC3 mRNA was significantly up-regulated in the liver, spleen, and head kidney. Further, the recombinant OnC3 protein alleviated the inflammatory response and pathological damage of tissues after infected with S. agalactiae. Moreover, the OnC3 promoted the phagocytosis of monocytes/macrophages to S. agalactiae. The data obtained in this study provide a theoretical reference for in-depth understanding of C3 in host defense against bacterial infection and the immunomodulatory roles in teleost fish.

Research Progress of Pyroptosis in Alzheimer’s Disease

Alzheimer’s disease (AD) is a disease characterized by insidious and progressive neurodegeneration, with clinical syndromes of memory and visuospatial skills damage. The pathogenic mechanism of AD is complex in which neural inflammation and neuron death play important roles. Pyroptosis, an inflammatory programmed cell death, has been reported to be involved in neuron death. Pyroptosis is executed by the protein family of gasdermins which punch pores on plasma membrane when activated by the upstream signals including the activation of NLRP3 and caspases, and subsequently triggers the inflammatory cascades featured by the release of interleukin (IL) -1β and IL-18. Herein, we summarized the current research on the roles of neuron pyroptosis in AD, aiming to provide a comprehensive view of the molecular mechanisms underlying AD pathogenesis and potential therapeutic targets for AD.

Mannose-Binding Lectin Possesses Agglutination Activity and Promotes Opsonophagocytosis of Macrophages with Calreticulin Interaction in an Early Vertebrate

The innate immune system is an ancient defense system in the process of biological evolution, which can quickly and efficiently resist pathogen infection. In mammals, mannose-binding lectin (MBL) is a key molecule in the innate immune and plays an essential role in the first line of host defense against pathogenic bacteria. However, the evolutionary origins and ancient roles of immune defense of MBL and its mechanism in clearance of microbial pathogens are still unclear, especially in early vertebrates. In this study, Oreochromis niloticus MBL (OnMBL) was successfully isolated and purified from the serum of Nile tilapia (O. niloticus). The OnMBL was able to bind and agglutinate with two important pathogens of tilapia, Streptococcus agalactiae and Aeromonas hydrophila Interestingly, the OnMBL was able to significantly inhibit the proliferation of pathogenic bacteria and reduce the inflammatory response. Upon bacterial challenge, the downregulation of OnMBL expression by RNA interference could lead to rapid proliferation of the pathogenic bacteria, ultimately resulting in tilapia death. However, the phenotype was rescued by reinjection of the OnMBL, which restored the healthy status of the knockdown tilapia. Moreover, a mechanistic analysis revealed that the OnMBL could clear pathogenic bacteria by collaborating with cell-surface calreticulin to facilitate phagocytosis in a complement activation-independent manner. To our knowledge, these results provide the first evidence on the antibacterial response mechanism of MBL performing evolutionary conserved function to promote opsonophagocytosis of macrophages in early vertebrates and reveals new insights into the understanding of the evolutionary origins and ancient roles basis of the C-type lectins in the innate immune defense.

Targeting the NLRP3 Inflammasome in Severe COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a member of the genus Betacoronavirus within the family Coronaviridae. It is an enveloped single-stranded positive-sense RNA virus. Since December of 2019, a global expansion of the infection has occurred with widespread dissemination of coronavirus disease 2019 (COVID-19). COVID-19 often manifests as only mild cold-like symptomatology, but severe disease with complications occurs in 15% of cases. Respiratory failure occurs in severe disease that can be accompanied by a systemic inflammatory reaction characterized by inflammatory cytokine release. In severe cases, fatality is caused by the rapid development of severe lung injury characteristic of acute respiratory distress syndrome (ARDS). Although ARDS is a complication of SARS-CoV-2 infection, it is not viral replication or infection that causes tissue injury; rather, it is the result of dysregulated hyperinflammation in response to viral infection. This pathology is characterized by intense, rapid stimulation of the innate immune response that triggers activation of the Nod-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome pathway and release of its products including the proinflammatory cytokines IL-6 and IL-1β. Here we review the literature that describes the pathogenesis of severe COVID-19 and NLRP3 activation and describe an important role in targeting this pathway for the treatment of severe COVID-19.

Diverse therapeutic efficacies and more diverse mechanisms of nicotinamide

BACKGROUND

Nicotinamide (NAM) is a form of vitamin B3 that, when administered at near-gram doses, has been shown or suggested to be therapeutically effective against many diseases and conditions. The target conditions are incredibly diverse ranging from skin disorders such as bullous pemphigoid to schizophrenia and depression and even AIDS. Similar diversity is expected for the underlying mechanisms. In a large portion of the conditions, NAM conversion to nicotinamide adenine dinucleotide (NAD⁺) may be a major factor in its efficacy. The augmentation of cellular NAD⁺ level not only modulates mitochondrial production of ATP and superoxide, but also activates many enzymes. Activated sirtuin proteins, a family of NAD⁺-dependent deacetylases, play important roles in many of NAM's effects such as an increase in mitochondrial quality and cell viability countering neuronal damages and metabolic diseases. Meanwhile, certain observed effects are mediated by NAM itself. However, our understanding on the mechanisms of NAM's effects is limited to those involving certain key proteins and may even be inaccurate in some proposed cases.

AIM OF REVIEW

This review details the conditions that NAM has been shown to or is expected to effectively treat in humans and animals and evaluates the proposed underlying molecular mechanisms, with the intention of promoting wider, safe therapeutic application of NAM.

KEY SCIENTIFIC CONCEPTS OF REVIEW

NAM, by itself or through altering metabolic balance of NAD⁺ and tryptophan, modulates mitochondrial function and activities of many molecules and thereby positively affects cell viability and metabolic functions. And, NAM administration appears to be quite safe with limited possibility of side effects which are related to NAM's metabolites.

Activation of Pyroptotic Cell Death Pathways in Cancer: An Alternative Therapeutic Approach

Cancer can be considered the result of a series of genetic variations that lead to a normal cell being transformed into a malignant one while avoiding cell death-atypical characteristics of tumor development. Although a large number of genomics and epigenetic alterations have been identified in cells undergoing apoptotic, autophagic or necrotic cell death, the treatment of cancer remains thought-provoking. Pyroptosis is differentiated from other types of programmed cell death and is mainly activated by Caspase-1. To initiate pyroptosis, cells receive specific "death" messages, produce cytokines, swell, burst, and ultimately die. The deficiency of Caspase-1 expression may lead to inflammation-mediated tumor progression. Hence, the molecular mechanisms for the Caspase-1 activation in tumor tissues are yet to be exploited extensively. This review aims to summarise the latest discoveries about pyroptosis and its new exciting role in inducing cancer cell death.

Caspases are key regulators of inflammatory and innate immune responses mediated by TLR3 in vivo

Understanding the key regulators which impact the innate immune response during initial phases of tissue injury, can advance the use of therapeutic approaches which aim at attenuating inflammation and organ damage. Recognition of microbial components by TLRs, initiates the transcription of innate immune signal pathways, that induce the expression of key inflammatory mediators: cytokines, chemokines and adhesion molecules. Beside regulating apoptotic cell death, recent studies have revealed distinct roles for caspases in the optimal production of inflammatory cytokines and host defense against injurious infections. Whether caspases can play an immune regulatory role in vivo has not been sufficiently investigated. This study aims to explore whether the pan caspase inhibitor z-VAD-fmk can control inflammation and cytokine production subsequent to challenging the innate immunity of the exocrine secretory tissues in vivo. Submandibular glands (SMGs) of the C57BL/6 mice were challenged with the TLR3 stimulant: polyinosinic-polycytidylic acid (poly (I:C)). Results obtained from the current study provide evidence that caspases can control immune responses downstream of TLR3 ligation. The present work proposes a novel mechanism that can prevent overactivation of the innate immunity, which typically leads to fatal immune disorders.

[Effects of allogeneic hematopoietic stem cell transplantation in combination with infusion of endothelial progenitor cells on bone marrow inflammatory injury]

Objective: To explore effects of allogeneic hematopoietic stem cell transplantation (HSCT) in combination with infusion of endothelial progenitor cells (EPC) on bone marrow inflammatory injury. Methods: 6-8 weeks BALB/c (H-2K(d)) mice after lethal dose of irradiation (TBI) were subjected to allogeneic bone marrow transplantation (BMT group) or co-transplantation of EPC (EPC group) . Samples of bone marrow cells of mice in each group on days 7,14,21,28 after transplantation were obtained to detect EPC cultural and cell chimeric rates by flow cytometer. Mice were sacrificed on days 7, 14, 21 and 28 post HSCT to analyze bone marrow pathology by H&E staining, the infiltration of macrophages and neutrophils by Western blot, validation expression levels of inflammatory complexes nlrp1、nlrp6 and its downstream molecules casepase-1 by Q-PCR and Western blot. Results: Cell chimeric rate on day 7 after transplantation in EPC group[ (91.65±2.77) %] was significantly higher than in BMT group[ (83.69±1.26) %]. Alleviated osteomyelitis injury and inflammatory cell infiltration in EPC group were observed when compared with BMT mice. Also significant reductions of the levels of nlrp1、nlrp6、casepase-1 transcription complexes in EPC mice were noted when compared with BMT ones. Conclusion: Co-transplantation of HSC and EPC could alleviate inflammatory cell infiltration and activation of the complex to promote the repair of bone marrow.

Stress-Induced NLRP3 Inflammasome in Human Diseases

Stress is a complex event that induces disturbances to physiological and psychological homeostasis, and it may have a detrimental impact on certain brain and physiological functions. In the last years, a dual role of the stress effect has been studied in order to elucidate the molecular mechanism by which can induce physiological symptoms after psychological stress exposition and vice versa. In this sense, inflammation has been proposed as an important starring. And in the same line, the inflammasome complex has emerged to give responses because of its role of stress sensor. The implication of the same complex, NLRP3 inflammasome, in different diseases such as cardiovascular, neurodegenerative, psychiatric, and metabolic diseases opens a door to develop new therapeutic perspectives.

Control of Methicillin-Resistant Staphylococcus aureus Pneumonia Utilizing TLR2 Agonist Pam3CSK4

The spread of methicillin-resistant Staphylococcus aureus (MRSA) is a critical health issue that has drawn greater attention to the potential use of immunotherapy. Toll-like receptor 2 (TLR2), a pattern recognition receptor, is an essential component in host innate defense system against S. aureus infection. However, little is known about the innate immune response, specifically TLR2 activation, against MRSA infection. Here, we evaluate the protective effect and the mechanism of MRSA murine pneumonia after pretreatment with Pam3CSK4, a TLR2 agonist. We found that the MRSA-pneumonia mouse model, pretreated with Pam3CSK4, had reduced bacteria and mortality in comparison to control mice. As well, lower protein and mRNA levels of TNF-α, IL-1β and IL-6 were observed in lungs and bronchus of the Pam3CSK4 pretreatment group. Conversely, expression of anti-inflammatory cytokine IL-10, but not TGF-β, increased in Pam3CSK4-pretreated mice. Our additional studies showed that CXCL-2 and CXCL1, which are necessary for neutrophil recruitment, were less evident in the Pam3CSK4-pretreated group compared to control group, whereas the expression of Fcγ receptors (FcγⅠ/Ⅲ) and complement receptors (CR1/3) increased in murine lungs. Furthermore, we found that increased survival and improved bacterial clearance were not a result of higher levels of neutrophil infiltration, but rather a result of enhanced phagocytosis and bactericidal activity of neutrophils in vitro and in vivo as well as increased robust oxidative activity and release of lactoferrin. Our cumulative findings suggest that Pam3CSK4 could be a novel immunotherapeutic candidate against MRSA pneumonia.

Aggregatibacter actinomycetemcomitans: virulence of its leukotoxin and association with aggressive periodontitis

Periodontitis is an infection-induced inflammatory disease that causes loss of the tooth supporting tissues. Much focus has been put on comparison of the microbial biofilm in the healthy periodontium with the diseased one. The information arising from such studies is limited due to difficulties to compare the microbial composition in these two completely different ecological niches. A few longitudinal studies have contributed with information that makes it possible to predict which individuals who might have an increased risk of developing aggressive forms of periodontitis, and the predictors are either microbial or/and host-derived factors. The most conspicuous condition that is associated with disease risk is the presence of Aggregatibacter actinomycetemcomitans at the individual level. This Gram-negative bacterium has a great genetic variation with a number of virulence factors. In this review we focus in particular on the leukotoxin that, based on resent knowledge, might be one of the most important virulence factors of A. actinomycetemcomitans.

Is the CARD8 rs2043211 polymorphism associated with susceptibility to Crohn's disease? A meta-analysis

Many studies have reported the association between the CARD8 gene polymorphism rs2043211 and the susceptibility to Crohn's disease (CD), but the results have remained quite contradictory. Therefore, the aim of the meta-analysis was to explore whether the CARD8 rs2043211 polymorphism has an effect on CD risk. We performed a systematic literature search for related articles published up to July 2014 in multiple databases. Six eligible articles containing eight studies were selected. Odds ratios (ORs) as well as their corresponding 95% confidence intervals (CIs) were used to estimate the association between the CARD8 polymorphism and CD risk in different genotypic models. Heterogeneity analysis was also performed and publication bias was taken into account. Subgroup analyses were conducted according to different ethnicities, as well as different types of CD. In the pooled analyses, no statistical significant association was found between the CARD8 polymorphism and CD risk in the overall population or Caucasian subgroup in the additive model (overall population: OR = 0.93, 95% CI = 0.87-1.01; Caucasian: OR = 0.93, 95% CI = 0.83-1.05). However, subgroup analysis based on different CD types showed a significant association between the CARD8 polymorphism and CD risk in the additive model (ileal CD: OR = 0.83, 95% CI = 0.70-0.98; stenotic or fistulizing CD: OR = 0.81, 95% CI = 0.72-0.92). Our results indicated that CD may involve different types of pathogenesis and have variable clinical manifestations. In patients with ileal, stenotic or fistulizing CD, the mutant-type rs2043211 polymorphism may generate a potentially protective effect.

Drosophila anti-nematode and antibacterial immune regulators revealed by RNA-Seq

Background

Drosophila melanogaster activates a variety of immune responses against microbial infections. However, information on the Drosophila immune response to entomopathogenic nematode infections is currently limited. The nematode Heterorhabditis bacteriophora is an insect parasite that forms a mutualistic relationship with the gram-negative bacteria Photorhabdus luminescens. Following infection, the nematodes release the bacteria that quickly multiply within the insect and produce several toxins that eventually kill the host. Although we currently know that the insect immune system interacts with Photorhabdus, information on interaction with the nematode vector is scarce.

Results

Here we have used next generation RNA-sequencing to analyze the transcriptional profile of wild-type adult flies infected by axenic Heterorhabditis nematodes (lacking Photorhabdus bacteria), symbiotic Heterorhabditis nematodes (carrying Photorhabdus bacteria), and Photorhabdus bacteria alone. We have obtained approximately 54 million reads from the different infection treatments. Bioinformatic analysis shows that infection with Photorhabdus alters the transcription of a large number of Drosophila genes involved in translational repression as well in response to stress. However, Heterorhabditis infection alters the transcription of several genes that participate in lipidhomeostasis and metabolism, stress responses, DNA/protein sythesis and neuronal functions. We have also identified genes in the fly with potential roles in nematode recognition, anti-nematode activity and nociception.

Conclusions

These findings provide fundamental information on the molecular events that take place in Drosophila upon infection with the two pathogens, either separately or together. Such large-scale transcriptomic analyses set the stage for future functional studies aimed at identifying the exact role of key factors in the Drosophila immune response against nematode-bacteria complexes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1690-2) contains supplementary material, which is available to authorized users.

Expression of the lipopolysaccharide biosynthesis gene lpxD affects biofilm formation of Pseudomonas aeruginosa

Bacterial biofilms are an important cause of nosocomial infections. Microorganisms such as Pseudomonas aeruginosa colonize biotic and abiotic surfaces leading to chronic infections that are difficult to eradicate. To characterize novel genes involved in biofilm formation, we identified the lpxD gene from a transposon-mutant library of P. aeruginosa. This gene encodes a glucosamine-N acyltransferase, which is important for lipopolysaccharide biosynthesis. Our results showed that a loss-of-expression mutant of lpxD was defective for biofilm formation on biotic and abiotic surfaces. Additionally, this mutant strain exhibited significantly decreased bacterial attachment to cultured airway epithelial cells, as well as increased bacterial cytotoxicity toward airway cells. However, consistent with a defect in lipid A structure, airway cells incubated with the lpxD mutant or with mutant lipid A extracts exhibited decreased IL-8 production and necrosis, respectively. Overall, our data indicate that manipulating lpxD expression may influence P. aeruginosa's ability to establish biofilm infections.

Imaging of Chlamydia and host cell metabolism

ABSTRACT: 

Chlamydial infections cause a wide range of acute and chronic diseases. Chlamydia trachomatis is the most common sexually transmitted bacterium while Chlamydia pneumoniae causes infections of the upper and lower respiratory tract. Chlamydia are obligate, intracellular bacteria with a biphasic developmental cycle that involves unique metabolic changes. Aside from entering an actively replicating state, Chlamydia may also implement persistent infections depending on different microenvironmental factors. In addition, changes in local oxygen availability and the composition of surrounding host microbiota are suggested to affect chlamydial growth and metabolism. Both bacteria and host cells endure characteristic metabolic changes during infection. Technical developments in recent years enable us to separately characterize chlamydial and host cell metabolism in living cells. This article focuses on novel approaches to analyze chlamydial metabolism such as NAD(P)H fluorescence lifetime imaging by two-photon microscopy. In addition, we provide an overview regarding promising future possibilities to further elucidate host–pathogen metabolic interactions.

Role of the cathelicidin-related antimicrobial peptide in inflammation and mortality in a mouse model of bacterial meningitis

Antimicrobial peptides (AP) are important components of the innate immune system, yet little is known about their expression and function in the brain. Our previous work revealed upregulated gene expression of cathelicidin-related AP (CRAMP) following bacterial meningitis in primary rat glial cells as well as bactericidal activity against frequent meningitis-causing bacteria. However, the effect of cathelicidin expression on the progression of inflammation and mortality in bacterial meningitis remains unknown. Therefore, we used CRAMP-deficient mice to investigate the effect of CRAMP on bacterial growth, inflammatory responses and mortality in meningitis. Meningitis was induced by intracerebral injection of type 3 Streptococcus pneumoniae. The degree of inflammation was analyzed in various brain regions by means of immunohistochemistry and real-time RT-PCR. CRAMP deficiency led to a higher mortality rate that was associated with increased bacterial titers in the cerebellum, blood and spleen as well as decreased meningeal neutrophil infiltration. CRAMP-deficient mice displayed a higher degree of glial cell activation that was accompanied by a more pronounced proinflammatory response. Taken together, this work provides insight into the important role of CRAMP as part of the innate immune defense against pathogens in bacterial CNS infections.

Porcine reproductive and respiratory syndrome virus activates inflammasomes of porcine alveolar macrophages via its small envelope protein E

Porcine reproductive and respiratory syndrome virus (PRRSV) infection results in extensive tissue inflammation and damage, which are believed to be responsible for increased susceptibility to secondary infection and even for death. However, its pathogenic mechanisms are not fully understood. To explore the mechanism underlying the PRRSV-induced tissue inflammation and damage, we investigated whether PRRSV activates porcine alveolar macrophage (PAM) inflammasomes which mediate por-IL-1β maturation/release and subsequently induce tissue inflammation and injury. Our results showed that PRRSV and its small envelope protein E significantly increased IL-1β release from LPS-primed PAMs; however, only PRRSV not protein E significantly increased IL-1β release from no-LPS-primed PAMs, which indicates PRRSV can activate inflammasomes of PAMs by its encoded protein E. These results provide a molecular basis for the pathogenic mechanism of PRRSV on inducing extensive tissue inflammation and damage, and suggest that the inflammasome may provide a potential therapeutic target for PRRS prevention and treatment.

Caspase-1 and IL-1β processing in a teleost fish

Interleukine-1β (IL-1β) is the most studied pro-inflammatory cytokine, playing a central role in the generation of systemic and local responses to infection, injury, and immunological challenges. In mammals, IL-1β is synthesized as an inactive 31 kDa precursor that is cleaved by caspase-1 generating a 17.5 kDa secreted active mature form. The caspase-1 cleavage site strictly conserved in all mammalian IL-1β sequences is absent in IL-1β sequences reported for non-mammalian vertebrates. Recently, fish caspase-1 orthologues have been identified in sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata) but very little is known regarding their processing and activity. In this work it is shown that sea bass caspase-1 auto-processing is similar to that of the human enzyme, resulting in active p24/p10 and p20/p10 heterodimers. Moreover, the presence of alternatively spliced variants of caspase-1 in sea bass is reported. The existence of caspase-1 isoforms in fish and in mammals suggests that they have been evolutionarily maintained and therefore are likely to play a regulatory role in the inflammatory response, as shown for other caspases. Finally, it is shown that sea bass and avian IL-1β are specifically cleaved by caspase-1 at different but phylogenetically conserved aspartates, distinct from the cleavage site of mammalian IL-1β.

Inflammasome activation in bovine monocytes by extracellular ATP does not require the purinergic receptor P2X7

Extracellular adenosine triphosphate (ATP) is a second signal for the assembly of the NLR family, pyrin domain-containing 3 (NLRP3) inflammasome, which form a framework to activate caspase 1, leading to the processing and secretion of the pro-inflammatory cytokine interleukin-1β (IL-1β). The aim of the present study was to investigate the role of the ATP-gated ion channel subtype P2X7 receptor in the inflammasome activation of bovine monocytes. ATP-induced inflammasome assembly in bovine monocytes was shown by caspase-1 activation and the release of IL-1β by LPS/ATP-stimulated bovine cells. The IL-1β release depended on potassium efflux but was independent of reactive oxygen generation of bovine monocytes. Unlike in the human system, a P2X7 receptor antagonist did not block the ATP-induced release of IL-1β of LPS-primed bovine cells. P2X7 mediated pore formation was observed in subsets of bovine T lymphocytes (CD4+>CD8+) but not in monocytes. In addition, ATP and 2-MeSATP but not the high affinity P2X7 agonist BzATP induced calcium influx in bovine monocytes. The data indicate that ROS generation plays no role in the ATP-induced activation of inflammasome in bovine monocytes and that P2X7-mediated pore formation is not necessary for the release of Interleukin-1β.

Molecular and functional properties of P2X receptors--recent progress and persisting challenges

ATP-gated P2X receptors are trimeric ion channels that assemble as homo- or heteromers from seven cloned subunits. Transcripts and/or proteins of P2X subunits have been found in most, if not all, mammalian tissues and are being discovered in an increasing number of non-vertebrates. Both the first crystal structure of a P2X receptor and the generation of knockout (KO) mice for five of the seven cloned subtypes greatly advanced our understanding of their molecular and physiological function and their validation as drug targets. This review summarizes the current understanding of the structure and function of P2X receptors and gives an update on recent developments in the search for P2X subtype-selective ligands. It also provides an overview about the current knowledge of the regulation and modulation of P2X receptors on the cellular level and finally on their physiological roles as inferred from studies on KO mice.

Activation of an NLRP3 inflammasome restricts Mycobacterium kansasii infection

Mycobacterium kansasii has emerged as an important nontuberculous mycobacterium pathogen, whose incidence and prevalence have been increasing in the last decade. M. kansasii can cause pulmonary tuberculosis clinically and radiographically indistinguishable from that caused by Mycobacterium tuberculosis infection. Unlike the widely-studied M. tuberculosis, little is known about the innate immune response against M. kansasii infection. Although inflammasome activation plays an important role in host defense against bacterial infection, its role against atypical mycobacteria remains poorly understood. In this report, the role of inflammasome activity in THP-1 macrophages against M. kansasii infection was studied. Results indicated that viable, but not heat-killed, M. kansasii induced caspase-1-dependent IL-1β secretion in macrophages. The underlying mechanism was found to be through activation of an inflammasome containing the NLR (Nod-like receptor) family member NLRP3 and the adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD). Further, potassium efflux, lysosomal acidification, ROS production and cathepsin B release played a role in M. kansasii-induced inflammasome activation. Finally, the secreted IL-1β derived from caspase-1 activation was shown to restrict intracellular M. kansasii. These findings demonstrate a biological role for the NLRP3 inflammasome in host defense against M. kansasii.

Cellular inhibitors of apoptosis proteins cIAP1 and cIAP2 are required for efficient caspase-1 activation by the inflammasome

Pathogen and danger recognition by the inflammasome activates inflammatory caspases that mediate inflammation and cell death. The cellular inhibitor of apoptosis proteins (cIAPs) function in apoptosis and innate immunity, but their role in modulating the inflammasome and the inflammatory caspases is unknown. Here we report that the cIAPs are critical effectors of the inflammasome and are required for efficient caspase-1 activation. cIAP1, cIAP2, and the adaptor protein TRAF2 interacted with caspase-1-containing complexes and mediated the activating nondegradative K63-linked polyubiquitination of caspase-1. Deficiency in cIAP1 (encoded by Birc2) or cIAP2 (Birc3) impaired caspase-1 activation after spontaneous or agonist-induced inflammasome assembly, and Birc2(-/-) or Birc3(-/-) mice or mice administered with an IAP antagonist had a dampened response to inflammasome agonists and were resistant to peritonitis. Our results describe a role for the cIAPs in innate immunity and further demonstrate the evolutionary conservation between cell death and inflammation mechanisms.

Caspase-4 is required for activation of inflammasomes

IL-1β and IL-18 are crucial regulators of inflammation and immunity. Both cytokines are initially expressed as inactive precursors, which require processing by the protease caspase-1 for biological activity. Caspase-1 itself is activated in different innate immune complexes called inflammasomes. In addition, caspase-1 activity regulates unconventional protein secretion of many other proteins involved in inflammation and repair. Human caspase-4 is a poorly characterized member of the caspase family, which is supposed to be involved in endoplasmic reticulum stress-induced apoptosis. However, its gene is located on the same locus as the caspase-1 gene, which raises the possibility that caspase-4 plays a role in inflammation. In this study, we show that caspase-4 expression is required for UVB-induced activation of proIL-1β and for unconventional protein secretion by skin-derived keratinocytes. These processes require expression of the nucleotide-binding domain leucine-rich repeat containing, Pyrin domain containing-3 inflammasome, and caspase-4 physically interacts with its central molecule caspase-1. As the active site of caspase-4 is required for activation of caspase-1, the latter most likely represents a substrate of caspase-4. Caspase-4 expression is also essential for efficient nucleotide-binding domain leucine-rich repeat containing, Pyrin domain containing-3 and for absent in melanoma 2 inflammasome-dependent proIL-1β activation in macrophages. These results demonstrate an important role of caspase-4 in inflammation and innate immunity through activation of caspase-1. Therefore, caspase-4 represents a novel target for the treatment of (auto)inflammatory diseases.

Reducing or increasing β-cell apoptosis without inflammation does not affect diabetes initiation in neonatal NOD mice

The presentation of islet antigens in the pancreatic LNs (PLNs) of mice is a developmentally regulated process. It has been hypothesized that, during physiological tissue remodeling, a wave of neonatal β-cell apoptosis may initiate diabetes in autoimmune-prone strains of mice. If true, increasing or decreasing physiological β-cell apoptosis in neonatal NOD mice should alter the time-course of antigen presentation in the PLNs. We used transgenic over-expression of either an anti-apoptotic protein (Bcl-2) or a toxic transgene (rat insulin promoter-Kb) in mouse β cells to reduce or increase neonatal β-cell apoptosis, respectively. Neither intervention affected the timing of antigen presentation in the PLNs or the initiation of islet infiltration. This suggests that under physiological conditions and in the absence of inflammation, neonatal β-cell apoptosis in NOD mice is not the trigger for antigen presentation in the draining LNs.

A delicate dance: host response to mycobacteria

Mycobacterium tuberculosis is an enormously successful human pathogen that can infect its host for decades without causing clinical disease, only to reactivate when host immunity is compromised. A normal immune response thus contains bacterial spread without inducing sterilizing immunity, therefore benefitting both host and pathogen. Recent work has begun to outline the complexity of this host-pathogen interaction and to reveal how the homeostatic balance between the two is achieved. This review focuses on two significant aspects of this delicate dance: the host's initial innate response and the mature granuloma that later contains the pathogen. Here, we review the fine balance of inflammatory events triggered or controlled by both the host and bacteria and implications for the survival of each.

Inflammasome signaling at the heart of central nervous system pathology

Neuroinflammation is a complex innate response of neural tissue against harmful effects of diverse stimuli viz., pathogens, damaged cells and irritants within the Central Nervous System (CNS). Studies show that multiple inflammatory mediators including cytokines, chemokines and prostaglandins are elevated in the Cerebrospinal Fluid (CSF) and in post-mortem brain tissues of patients with history of neuroinflammatory conditions as well as neurodegenerative disorders like Alzheimer's disease, Parkinson's disease and Multiple Sclerosis. The innate immunity mediators in the brain, namely microglia and astrocytes, express certain Pattern Recognition Receptors (PRRs), which are always on 'high-alert' for pathogens or other inflammatory triggers and participate in the assembly and activation of the inflammasome. The inflammasome orchestrates the activation of the precursors of proinflammatory caspases, which in turn, cleave the precursor forms of interleukin-1beta, IL-18 and IL-33 into their active forms; the secretion of which leads to a potent inflammatory response, and/or influences the release of toxins from glial and endothelial cells. Altered expression of inflammasome mediators can either promote or inhibit neurodegenerative processes. Therefore, modulating the inflammasome machinery seems a better combat strategy than summarily suppressing all inflammation in most neuroinflammatory conditions. In the current review we have surveyed the identified triggers and pathways of inflammasome activation and the following events which ultimately accomplish the innate inflammatory response in the CNS, with a goal to provide an analytical insight into disease pathogenesis that might provide cues for devising novel therapeutic strategies.

Mechanisms of uric acid crystal-mediated autoinflammation

Gout is an arthritis characterized by elevated uric acid in the bloodstream. In this condition, crystals of uric acid are formed and accumulate in the synovial fluids. Crystal deposition leads to acute inflammation, which is associated with the spontaneous resolution of the disease. Recent studies have led to significant advances in the understanding of the basic biology of crystal-mediated inflammation. Uric acid has been identified as a danger signal that triggers a cytosolic sensor, the inflammasome. This signaling platform is required for the activation of interleukin-1, a cytokine that is critical to the initiation of acute inflammation in gout. Importantly, both molecular and pathological evidence support the notion that gout is a prototypical member of the growing family of autoinflammatory diseases. This review discusses the role of the inflammasome in gout and the emerging new therapeutic strategies aimed at controlling inflammation in crystal arthritis.

Control of intestinal homeostasis, colitis, and colitis-associated colorectal cancer by the inflammatory caspases

Inflammatory caspases are essential effectors of inflammation and cell death. Here, we investigated their roles in colitis and colorectal cancer and report a bimodal regulation of intestinal homeostasis, inflammation and tumorigenesis by caspases-1 and -12. Casp1(-/-) mice exhibited defects in mucosal tissue repair and succumbed rapidly after dextran sulfate sodium administration. This phenotype was rescued by administration of exogenous interleukin-18 and was partially reproduced in mice deficient in the inflammasome adaptor ASC. Casp12(-/-) mice, in which the inflammasome is derepressed, were resistant to acute colitis and showed signs of enhanced repair. Together with their increased inflammatory response, the enhanced repair response of Casp12(-/-) mice rendered them more susceptible to colorectal cancer induced by azoxymethane (AOM)+DSS. Taken together, our results indicate that the inflammatory caspases are critical in the induction of inflammation in the gut after injury, which is necessary for tissue repair and maintenance of immune tolerance.

Pulsed dye laser-induced inflammatory response and extracellular matrix turnover in rat vocal folds and vocal fold fibroblasts

BACKGROUND AND OBJECTIVES

Disruption of the vocal fold extracellular matrix (ECM) can induce a profound and refractory dysphonia. Pulsed dye laser (PDL) irradiation has shown early promise as a treatment modality for disordered ECM in patients with chronic vocal fold scar; however, there are limited data addressing the mechanism by which this laser energy might induce cellular and extracellular changes in vocal fold tissues. In this study, we examined the inflammatory and ECM modulating effects of PDL irradiation on normal vocal fold tissues and cultured vocal fold fibroblasts (VFFs).

STUDY DESIGN/MATERIALS AND METHODS

We evaluated the effects of 585 nm PDL irradiation on inflammatory cytokine and collagen/collagenase gene transcription in normal rat vocal folds in vivo (3-168 hours following delivery of approximately 39.46 J/cm(2) fluence) and VFFs in vitro (3-72 hours following delivery of 4.82 or 9.64 J/cm(2) fluence). We also examined morphological vocal fold tissue changes 3 hours, 1 week, and 1 month post-irradiation.

RESULTS

PDL irradiation altered inflammatory cytokine and procollagen/collagenase expression at the transcript level, both in vitro and in vivo. Additionally, PDL irradiation induced an inflammatory repair process in vivo that was completed by 1 month with preservation of normal tissue morphology.

CONCLUSIONS

PDL irradiation can modulate ECM turnover in phenotypically normal vocal folds. Additional work is required to determine if these findings extend to disordered ECM, such as is seen in vocal fold scar. Lasers Surg. Med. 41:585-594, 2009. (c) 2009 Wiley-Liss, Inc.

Mycobacterium tuberculosis protein ESAT-6 is a potent activator of the NLRP3/ASC inflammasome

Interleukin-1beta (IL-1beta) represents one of the most important mediators of inflammation and host responses to infection. Mycobacterium tuberculosis (Mtb), the causative agent of human tuberculosis, induces IL-1beta secretion at the site of infection, but the underlying mechanism(s) are poorly understood. In this work we show that Mtb infection of macrophages stimulates caspase-1 activity and promotes the secretion of IL-1beta. This stimulation requires live intracellular bacteria expressing a functional ESX-1 secretion system. ESAT-6, an ESX-1 substrate implicated in membrane damage, is both necessary and sufficient for caspase-1 activation and IL-1beta secretion. ESAT-6 promotes the access of other immunostimulatory agents such as AG85 into the macrophage cytosol, indicating that this protein may contribute to caspase-1 activation largely by perturbing host cell membranes. Using a high-throughput shRNA-based screen we found that numerous NOD-like receptors (NLRs) and CARD domain-containing proteins (CARDs) were important for IL-1beta secretion upon Mtb infection. Most importantly, NLRP3, ASC and caspase-1 form an infection-inducible inflammasome complex that is essential for IL-1beta secretion. In summary, we show that recognition of Mtb infection by the NLRP3 inflammasome requires the activity of the bacterial virulence factor ESAT-6, and the subsequent IL-1beta response is regulated by a number of NLR/CARD proteins.

Anthrax lethal toxin induced lysosomal membrane permeabilization and cytosolic cathepsin release is Nlrp1b/Nalp1b-dependent

NOD-like receptors (NLRs) are a group of cytoplasmic molecules that recognize microbial invasion or 'danger signals'. Activation of NLRs can induce rapid caspase-1 dependent cell death termed pyroptosis, or a caspase-1 independent cell death termed pyronecrosis. Bacillus anthracis lethal toxin (LT), is recognized by a subset of alleles of the NLR protein Nlrp1b, resulting in pyroptotic cell death of macrophages and dendritic cells. Here we show that LT induces lysosomal membrane permeabilization (LMP). The presentation of LMP requires expression of an LT-responsive allele of Nlrp1b, and is blocked by proteasome inhibitors and heat shock, both of which prevent LT-mediated pyroptosis. Further the lysosomal protease cathepsin B is released into the cell cytosol and cathepsin inhibitors block LT-mediated cell death. These data reveal a role for lysosomal membrane permeabilization in the cellular response to bacterial pathogens and demonstrate a shared requirement for cytosolic relocalization of cathepsins in pyroptosis and pyronecrosis.

Endoplasmic reticulum stress, inflammation, and perinatal brain damage

Inflammation seems to play a role in the pathogenesis of perinatal brain damage in fetuses/infants born much before term. We raise the possibility that noninflammatory phenomena induce endoplasmic reticulum stress, which, in turn, leads to the unfolded protein response, which is followed by apoptosis-promoting processes and inflammation. Perhaps by these events, noninflammatory stimuli lead to perinatal brain damage.