Macrophage endocytosis of high-mobility group box 1 triggers pyroptosis

A brain in flame; do inflammasomes and pyroptosis influence stroke pathology?

Stroke is one of the leading causes of death and disability worldwide. Inflammation plays a key role across the time course of stroke, from onset to the post-injury reparative phase days to months later. Several regulatory molecules are implicated in inflammation, but the most established inflammatory mediator of acute brain injury is the cytokine interleukin-1. Interleukin-1 is regulated by large, macromolecular complexes called inflammasomes, which play a central role in cytokine release and cell death. In this review we highlight recent advances in inflammasome research and propose key roles for inflammasome components in the progression of stroke damage.

Melatonin prevents endothelial cell pyroptosis via regulation of long noncoding RNA MEG3/miR-223/NLRP3 axis

Atherosclerosis (AS) is an inflammatory disease linked to endothelial dysfunction. Melatonin is reported to possess substantial anti-inflammatory properties, which has proven to be effective in AS. Emerging literature suggests that pyroptosis plays a critical role during AS progression. However, whether pyroptosis contributes to endothelial dysfunction and the underlying molecular mechanisms remained unexploited. This study was designed to investigate the antipyroptotic effects of melatonin in atherosclerotic endothelium and to elucidate the potential mechanisms. In this study, high-fat diet (HFD)-treated ApoE^-/- mice were used as an atherosclerotic animal model. We found intragastric administration of melatonin for 12 weeks markedly reduced the atherosclerotic plaque in aorta. Meanwhile, melatonin also attenuated the expression of pyroptosis-related genes, including NLRP3, ASC, cleaved caspase1, NF-κB/GSDMD, GSDMD N-termini, IL-1β, and IL-18 in aortic endothelium of melatonin-treated animals. Consistent antipyroptotic effects were also observed in ox-LDL-treated human aortic endothelial cells (HAECs). We found that lncRNA MEG3 enhanced pyroptosis in HAECs. Moreover, MEG3 acted as an endogenous sponge by sequence complementarity to suppress the function of miR-223 and to increase NLRP3 expression and enhance endothelial cell pyroptosis. Furthermore, knockdown of miR-223 blocked the antipyroptotic actions of melatonin in ox-LDL-treated HAECs. Together, our results suggest that melatonin prevents endothelial cell pyroptosis via MEG3/miR-223/NLRP3 axis in atherosclerosis, and therefore, melatonin replacement might be considered a new strategy for protecting endothelium against pyroptosis, thereby for the treatment of atherosclerosis associated with pyroptosis.

Consumption of pomegranates improves synaptic function in a transgenic mice model of Alzheimer's disease

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder characterized by extracellular plaques containing abnormal Amyloid Beta (Aβ) aggregates, intracellular neurofibrillary tangles containing hyperphosphorylated tau protein, microglia-dominated neuroinflammation, and impairments in synaptic plasticity underlying cognitive deficits. Therapeutic strategies for the treatment of AD are currently limited. In this study, we investigated the effects of dietary supplementation of 4% pomegranate extract to a standard chow diet on neuroinflammation, and synaptic plasticity in APPsw/Tg2576 mice brain. Treatment with a custom mixed diet (pellets) containing 4% pomegranate for 15 months ameliorated the loss of synaptic structure proteins, namely PSD-95, Munc18-1, and SNAP25, synaptophysin, phosphorylation of Calcium/Calmodulin Dependent Protein Kinase IIα (p-CaMKIIα/ CaMKIIα), and phosphorylation of Cyclic AMP-Response Element Binding Protein (pCREB/CREB), inhibited neuroinflammatory activity, and enhanced autophagy, and activation of the phophoinositide-3-kinase-Akt-mammalian target of rapamycin signaling pathway. These neuroprotective effects were associated with reduced β-site cleavage of Amyloid Precursor Protein in APPsw/Tg2576 mice. Therefore, long-term supplementation with pomegranates can attenuate AD pathology by reducing inflammation, and altering APP-dependent processes.

Extracellular HMGB1 as a therapeutic target in inflammatory diseases

INTRODUCTION

High-mobility group box 1 (HMGB1) is a ubiquitous nuclear protein that promotes inflammation when released extracellularly after cellular activation, stress, damage or death. HMGB1 operates as one of the most intriguing molecules in inflammatory disorders via recently elucidated signal and molecular transport mechanisms. Treatments based on antagonists specifically targeting extracellular HMGB1 have generated encouraging results in a wide number of experimental models of infectious and sterile inflammation. Clinical studies are still to come. Areas covered: We here summarize recent advances regarding pathways for extracellular HMGB1 release, receptor usage, and functional consequences of post-translational modifications. The review also addresses results of preclinical HMGB1-targeted therapy studies in multiple inflammatory conditions and outlines the current status of emerging clinical HMGB1-specific antagonists. Expert opinion: Blocking excessive amounts of extracellular HMGB1, particularly the disulfide isoform, offers an attractive clinical opportunity to ameliorate systemic inflammatory diseases. Therapeutic interventions to regulate intracellular HMGB1 biology must still await a deeper understanding of intracellular HMGB1 functions. Future work is needed to create more robust assays to evaluate functional bioactivity of HMGB1 antagonists. Forthcoming clinical studies would also greatly benefit from a development of antibody-based assays to quantify HMGB1 redox isoforms, presently assessed by mass spectrometry methods.

Nitrative DNA damage in cultured macrophages exposed to indium oxide

Objectives:

Indium compounds are used in manufacturing displays of mobile phones and televisions. However, these materials cause interstitial pneumonia in exposed workers. Animal experiments demonstrated that indium compounds caused lung cancer. Chronic inflammation is considered to play a role in lung carcinogenesis and fibrosis induced by particulate matters. 8-Nitroguanine (8-nitroG) is a mutagenic DNA lesion formed during inflammation and may participate in carcinogenesis. To clarify the mechanism of carcinogenesis, we examined 8-nitroG formation in indium-exposed cultured cells.

Methods:

We treated RAW 264.7 mouse macrophages with indium oxide (In₂O₃) nanoparticles (primary diameter: 30-50 nm), and performed fluorescent immunocytochemistry to detect 8-nitroG. The extent of 8-nitroG formation was evaluated by quantitative image analysis. We measured the amount of nitric oxide (NO) in the culture supernatant of In₂O₃-treated cells by the Griess method. We also examined the effects of inhibitors of inducible NO synthase (iNOS) and endocytosis on In₂O₃-induced 8-nitroG formation.

Results:

In₂O₃ significantly increased the intensity of 8-nitroG formation in RAW 264.7 cells in a dose-dependent manner. In₂O₃-induced 8-nitroG formation was observed at 2 h and further increased at 4 h, and the amount of NO released from In₂O₃-exposed cells was significantly increased at 2-4 h compared with the control. 8-NitroG formation was suppressed by 1400W (an iNOS inhibitor), methyl-β-cyclodextrin and monodansylcadaverine (inhibitors of caveolae- and clathrin-mediated endocytosis, respectively).

Conclusions:

These results suggest that endocytosis and NO generation participate in indium-induced 8-nitroG formation. NO released from indium-exposed inflammatory cells may induce DNA damage in adjacent lung epithelial cells and contribute to carcinogenesis.

Intracellular galectin-7 expression in cancer cells results from an autocrine transcriptional mechanism and endocytosis of extracellular galectin-7

The β-galactoside binding protein galectin-7 (gal-7) is constitutively expressed at abnormally high levels in the outside milieu and intracellular compartments of many types of epithelial cancer cells, most notably in aggressive forms of ovarian and breast cancer. It is thus of utmost importance to understand how gal-7 traffics between both intracellular and extracellular compartments to develop novel drugs that target the protumorigenic functions of galectin-7. In the present work, we report that extracellular gal-7 plays a central role in controlling intracellular gal-7 in cells. It does so via two distinct yet complementary mechanisms: firstly by increasing the transcriptional activation of lgals7 gene transcription, and secondly via re-entry into the cells. Increased mRNA levels were dose- and time-dependent and occur in all cell lines tested, including ovarian and breast cancer cell lines. Addition of recombinant gal-7 to MDA-MB-231 transfected with a luciferase reporter vector containing response elements of the lgals7 promoter indicated that increased mRNA level of lgals7 occurs via de novo gene transcription. Re-entry of extracellular gal-7 inside cells was rapid, and reached cytosolic and mitochondrial compartments. Taken together, these findings reveal the existence of a positive self-amplification pathway that regulates intracellular gal-7 expression in breast and ovarian cancer cells.

Ketamine induces hippocampal apoptosis through a mechanism associated with the caspase-1 dependent pyroptosis

Ketamine, a pediatric anesthetic, is widely used in clinical practice. There was growing evidence showing that ketamine can promote neuronal death in developing brains of both humans and animals. In this study, we used in vivo neonatal and juvenile mouse models to induce ketamine-related neurotoxicity in the hippocampus. Active caspase-3 and -9 proteins, which are responsible for the release of cytochrome C, and the mitochondrial translocation of p53, which is associated with mitochondrial apoptosis, were found to be significantly up-regulated in the ketamine-induced hippocampal neurotoxicity. Furthermore, we demonstrated that the levels of pyroptosis-related proteins, including caspase-1 and -11, NOD-like receptor family, pyrin domain containing 3 (NLRP3), and IL-1β and IL-18, significantly increased after multiple doses of ketamine administration. We speculated that ketamine triggered the formation of NLRP3 and caspase-1 complex and its translocation to the mitochondria. In consistent with this, ketamine treatment was found to induce pyroptosis in mouse primary hippocampal neurons, which was characterized by increased pore formation and elevated lactate dehydrogenase release in mitochondria. Silencing caspase-1 with lentivirus-mediated short hairpin RNA (shRNA) significantly decreased the levels of not only pyroptosis-related proteins but also mitochondrial apoptosis-associated proteins in mouse primary hippocampal neurons. We conclude that caspase-1-dependent pyroptosis is an important event which may be an essential pathway involved in the mitochondria-associated apoptosis in ketamine-induced hippocampal neurotoxicity.

The haptoglobin beta subunit sequesters HMGB1 toxicity in sterile and infectious inflammation

BACKGROUND

Extra-corpuscular haemoglobin is an endogenous factor enhancing inflammatory tissue damage, a process counteracted by the haemoglobin-binding plasma protein haptoglobin composed of alpha and beta subunits connected by disulfide bridges. Recent studies established that haptoglobin also binds and sequesters another pro-inflammatory mediator, HMGB1, via triggering CD163 receptor-mediated anti-inflammatory responses involving heme oxygenase-1 expression and IL-10 release. The molecular mechanism underlying haptoglobin-HMGB1 interaction remains poorly elucidated.

METHODS

Haptoglobin β subunits were tested for HMGB1-binding properties, as well as efficacy in animal models of sterile liver injury (induced by intraperitoneal acetaminophen administration) or infectious peritonitis (induced by cecal ligation and puncture, CLP, surgery) using wild-type (C57BL/6) or haptoglobin gene-deficient mice.

RESULTS

Structural-functional analysis demonstrated that the haptoglobin β subunit recapitulates the HMGB1-binding properties of full-length haptoglobin. Similar to HMGB1-haptoglobin complexes, the HMGB1-haptoglobin β complexes also elicited anti-inflammatory effects via CD163-mediated IL-10 release and heme oxygenase-1 expression. Treatment with haptoglobin β protein conferred significant protection in mouse models of polymicrobial sepsis as well as acetaminophen-induced liver injury, two HMGB1-dependent inflammatory conditions.

CONCLUSIONS

Haptoglobin β protein offers a novel therapeutic approach to fight against various inflammatory diseases caused by excessive HMGB1 release.

Gut-liver axis and sterile signals in the development of alcoholic liver disease

BACKGROUND

Innate immunity plays a critical role in the development of alcohol-induced liver inflammation. Understanding the inter-relationship of signals from within and outside of the liver that trigger liver inflammation is pivotal for development of novel therapeutic targets of alcoholic liver disease (ALD).

AIM

The aim of this paper is to review recent advances in the field of alcohol-induced liver inflammation.

METHODS

A detailed literature review was performed using the PubMed database published between January 1980 and December 2016.

RESULTS

We provide an update on the role of intestinal microbiome, metabolome and the gut-liver axis in ALD, discuss the growing body of evidence on the diversity of liver macrophages and their differential contribution to alcohol-induced liver inflammation, and highlight the crucial role of inflammasomes in integration of inflammatory signals in ALD. Studies to date have identified a multitude of new therapeutic targets, some of which are currently being tested in patients with severe alcoholic hepatitis. These treatments aim to strengthen the intestinal barrier, ameliorate liver inflammation and augment hepatocyte regeneration.

CONCLUSION

Given the complexity of inflammation in ALD, multiple pathobiological mechanisms may need to be targeted at the same time as it seems unlikely that there is a single dominant pathogenic pathway in ALD that would be easily targeted using a single target drug approach.

SHORT SUMMARY

Here, we focus on recent advances in immunopathogenesis of alcoholic liver disease (ALD), including gut-liver axis, hepatic macrophage activation, sterile inflammation and synergy between bacterial and sterile signals. We propose a multiple parallel hit model of inflammation in ALD and discuss its implications for clinical trials in alcoholic hepatitis.

Role of scavenger receptors as damage-associated molecular pattern receptors in Toll-like receptor activation

Damage-associated molecular patterns (DAMPs) have been implicated in sterile inflammation in various tissue injuries. High-mobility group box 1 (HMGB1) is a representative DAMP, and has been shown to transmit signals through receptors for advanced glycation end products (RAGEs) and TLRs, including TLR2 and TLR4. HMGB1 does not, however, bind to TLRs with high affinity; therefore, the mechanism of HMGB1-mediated TLR activation remains unclear. In this study, we found that fluorescently labeled HMGB1 was efficiently internalized into macrophages through class A scavenger receptors. Although both M1- and M2-type macrophages internalized HMGB1, only M1-type macrophages secreted cytokines in response to HMGB1. The pan-class A scavenger receptor competitive inhibitor, maleylated bovine serum albumin (M-BSA), inhibited HMGB1 internalization and reduced cytokine production from macrophages in response to HMGB1 but not to LPS. The C-terminal acidic domain of HMGB1 is responsible for scavenger receptor-mediated internalization and cytokine production. HMGB1 and TLR4 co-localized in macrophages, and this interaction was disrupted by M-BSA, suggesting that class A scavenger receptors function as co-receptors of HMGB1 for TLR activation. M-BSA ameliorated LPS-induced sepsis and dextran sulfate sodium (DSS)-induced colitis models in which HMGB1 has been shown to play progressive roles. These data suggest that scavenger receptors function as co-receptors along with TLRs for HMGB1 in M1-type inflammatory macrophages.

Aged Human Stored Red Blood Cell Supernatant Inhibits Macrophage Phagocytosis in an HMGB1 Dependent Manner After Trauma in a Murine Model

Red blood cell transfusions in the setting of trauma are a double-edged sword, as it is a necessary component for life-sustaining treatment in massive hemorrhagic shock, but also associated with increased risk for nosocomial infections and immune suppression. The mechanisms surrounding this immune suppression are unclear. Using supernatant from human packed red blood cell (RBC), we demonstrate that clearance of Escherichia coli by macrophages is inhibited both in vitro and in vivo using a murine model of trauma and hemorrhagic shock. We further explore the mechanism of this inhibition by demonstrating that human-stored RBCs contain soluble high-mobility group box 1 protein (HMGB1) that increases throughout storage. HMGB1 derived from the supernatant of human-stored RBCs was shown to inhibit bacterial clearance, as neutralizing antibodies to HMGB1 restored the ability of macrophages to clear bacteria. These findings demonstrate that extracellular HMGB1 within stored RBCs could be one factor leading to immune suppression following transfusion in the trauma setting.

RAGE deficiency predisposes mice to virus-induced paucigranulocytic asthma

Asthma is a chronic inflammatory disease. Although many patients with asthma develop type-2 dominated eosinophilic inflammation, a number of individuals develop paucigranulocytic asthma, which occurs in the absence of eosinophilia or neutrophilia. The aetiology of paucigranulocytic asthma is unknown. However, both respiratory syncytial virus (RSV) infection and mutations in the receptor for advanced glycation endproducts (RAGE) are risk factors for asthma development. Here, we show that RAGE deficiency impairs anti-viral immunity during an early-life infection with pneumonia virus of mice (PVM; a murine analogue of RSV). The elevated viral load was associated with the release of high mobility group box-1 (HMGB1) which triggered airway smooth muscle remodelling in early-life. Re-infection with PVM in later-life induced many of the cardinal features of asthma in the absence of eosinophilic or neutrophilic inflammation. Anti-HMGB1 mitigated both early-life viral disease and asthma-like features, highlighting HMGB1 as a possible novel therapeutic target.

DOI:http://dx.doi.org/10.7554/eLife.21199.001

Novel involvement of miR-522-3p in high-mobility group box 1-induced prostaglandin reductase 1 expression and reduction of phagocytosis

Resolution of inflammation is important for physiological homeostasis. Chronic inflammatory diseases may be caused by abnormal resolution of inflammation. However, what causes a failure of inflammatory resolution is unclear. Here we investigated the involvement of high mobility group box 1 (HMGB1) protein in the control of inflammatory resolution as an 'anti-resolution factor'. We first confirmed the increased expression of HMGB1 and prostaglandin reductase 1 (PTGR1) in inflammatory conditions and HMGB1-mediated regulation of the expression of PTGR1. The inhibition of phagocytosis by HMGB1 was abrogated by PTGR1 silencing. PTGR1 was a direct target of miR522-3p and its expression was regulated by miRNA-522-3p inhibitor or mimic. Finally, miR-522-3p had an important role in the regulation of PTGR1 expression by HMGB1. The data indicates that HMGB1-miR-522-3p-PTGR1 axis may be involved in the abnormal resolution of inflammation and suggests that this mechanism might be a target for modulation of chronic inflammatory disorder.

Unconventional Pathways of Secretion Contribute to Inflammation

In the conventional pathway of protein secretion, leader sequence-containing proteins leave the cell following processing through the endoplasmic reticulum (ER) and Golgi body. However, leaderless proteins also enter the extracellular space through mechanisms collectively known as unconventional secretion. Unconventionally secreted proteins often have vital roles in cell and organism function such as inflammation. Amongst the best-studied inflammatory unconventionally secreted proteins are interleukin (IL)-1β, IL-1α, IL-33 and high-mobility group box 1 (HMGB1). In this review we discuss the current understanding of the unconventional secretion of these proteins and highlight future areas of research such as the role of nuclear localisation.

Role of the IL-33-ST2 axis in sepsis

Sepsis remains a major clinical problem with high morbidity and mortality. As new inflammatory mediators are characterized, it is important to understand their roles in sepsis. Interleukin 33 (IL-33) is a recently described member of the IL-1 family that is widely expressed in cells of barrier tissues. Upon tissue damage, IL-33 is released as an alarmin and activates various types of cells of both the innate and adaptive immune system through binding to the ST2/IL-1 receptor accessory protein complex. IL-33 has apparent pleiotropic functions in many disease models, with its actions strongly shaped by the local microenvironment. Recent studies have established a role for the IL-33-ST2 axis in the initiation and perpetuation of inflammation during endotoxemia, but its roles in sepsis appear to be organism and model dependent. In this review, we focus on the recent advances in understanding the role of the IL-33/ST2 axis in sepsis.

miRNA-214 Inhibits Cellular Proliferation and Migration in Glioma Cells Targeting Caspase 1 Involved in Pyroptosis

Pyroptosis is a type of proinflammatory programmed cell death mediated by caspase 1 activity and occurs in several types of eukaryotic tumor cells, including gliomas. MicroRNAs (miRNAs), small endogenous noncoding RNAs, have been demonstrated to be advantageous in glioma therapy. However, the question of whether miRNAs regulate pyroptosis in glioma remains unknown. The current study found that caspase 1 expression was substantially increased in both glioma tissues and glioma cell lines, U87 and T98G, while miR-214 expression was significantly downregulated. Luciferase reporter assay recognized caspase 1 as a target gene of miR-214. These findings demonstrate that miR-214 could inhibit cell proliferation and migration through the regulation of pyroptosis intermediated by caspase 1 in glioma U87 and T98G cells and may suggest a novel therapeutic for the intervention of glioma.

Purinergic signalling in autoimmunity: A role for the P2X7R in systemic lupus erythematosus?

Purinergic signalling plays a crucial role in immunity and autoimmunity. Among purinergic receptors, the P2X7 receptor (P2X7R) has an undisputed role as it is expressed to high level by immune cells, triggers cytokine release and modulates immune cell differentiation. In this review, we focus on evidence supporting a possible role of the P2X7R in the pathogenesis of systemic lupus erythematosus (SLE).

C1q and HMGB1 reciprocally regulate human macrophage polarization

A healthy immune system results from a balance of stimulatory and inhibitory pathways that allow effective responses to acute insults, without descending into chronic inflammation. Failed homeostasis is characteristic of autoimmune diseases such as systemic lupus erythematosus. Although HMGB1 induces proinflammatory M1-like macrophage differentiation, we describe a mechanism by which C1q modulates this activity and collaborates with HMGB1 to induce the differentiation of monocytes to anti-inflammatory M2-like macrophages. These anti-inflammatory macrophages are unresponsive to dendritic cell induction factors, effectively removing them from participation in an adaptive immune response. This pathway is mediated through a complex with RAGE and LAIR-1 and depends on relative levels of C1q and HMGB1. Importantly, these data provide insight into a homeostatic mechanism in which C1q and HMGB1 can cooperate to terminate inflammation, and which may be impaired in C1q-deficient patients with autoimmune disease.

Hemorrhagic shock primes for lung vascular endothelial cell pyroptosis: role in pulmonary inflammation following LPS

Hemorrhagic shock (HS) often renders patients more susceptible to lung injury by priming for an exaggerated response to a second infectious stimulus. Acute lung injury (ALI) is a major component of multiple organ dysfunction syndrome following HS and regularly serves as a major cause of patient mortality. The lung vascular endothelium is an active organ that has a central role in the development of ALI through synthesizing and releasing of a number of inflammatory mediators. Cell pyroptosis is a caspase-1-dependent regulated cell death, which features rapid plasma membrane rupture and release of proinflammatory intracellular contents. In this study, we demonstrated an important role of HS in priming for LPS-induced lung endothelial cell (EC) pyroptosis. We showed that LPS through TLR4 activates Nlrp3 (NACHT, LRR, and PYD domains containing protein 3) inflammasome in mouse lung vascular EC, and subsequently induces caspase-1 activation. However, HS induced release of high-mobility group box 1 (HMGB1), which acting through the receptor for advanced glycation end products initiates EC endocytosis of HMGB1, and subsequently triggers a cascade of molecular events, including cathepsin B release from ruptured lysosomes followed by pyroptosome formation and caspase-1 activation. These HS-induced events enhance LPS-induced EC pyroptosis. We further showed that lung vascular EC pyroptosis significantly exaggerates lung inflammation and injury. The present study explores a novel mechanism underlying HS-primed ALI and thus presents a potential therapeutic target for post-HS ALI.

Cell death in the pathogenesis of systemic lupus erythematosus and lupus nephritis

Nephritis is one of the most severe complications of systemic lupus erythematosus (SLE). One key characteristic of lupus nephritis (LN) is the deposition of immune complexes containing nucleic acids and/or proteins binding to nucleic acids and autoantibodies recognizing these molecules. A variety of cell death processes are implicated in the generation and externalization of modified nuclear autoantigens and in the development of LN. Among these processes, apoptosis, primary and secondary necrosis, NETosis, necroptosis, pyroptosis, and autophagy have been proposed to play roles in tissue damage and immune dysregulation. Cell death occurs in healthy individuals during conditions of homeostasis yet autoimmunity does not develop, at least in part, because of rapid clearance of dying cells. In SLE, accelerated cell death combined with a clearance deficiency may lead to the accumulation and externalization of nuclear autoantigens and to autoantibody production. In addition, specific types of cell death may modify autoantigens and alter their immunogenicity. These modified molecules may then become novel targets of the immune system and promote autoimmune responses in predisposed hosts. In this review, we examine various cell death pathways and discuss how enhanced cell death, impaired clearance, and post-translational modifications of proteins could contribute to the development of lupus nephritis.

Cold-inducible RNA-binding protein causes endothelial dysfunction via activation of Nlrp3 inflammasome

Cold-inducible RNA-binding protein (CIRP) is a damage-associated molecular pattern (DAMP) molecule which stimulates proinflammatory cytokine release in hemorrhage and sepsis. Under these medical conditions, disruption of endothelial homeostasis and barrier integrity, typically induced by proinflammatory cytokines, is an important factor contributing to morbidity and mortality. However, the role of CIRP in causing endothelial dysfunction has not been investigated. In this study, we show that intravenous injection of recombinant murine CIRP (rmCIRP) in C57BL/6 mice causes lung injury, evidenced by vascular leakage, edema, increased leukocyte infiltration and cytokine production in the lung tissue. The CIRP-induced lung damage is accompanied with endothelial cell (EC) activation marked by upregulation of cell-surface adhesion molecules E-selectin and ICAM-1. Using in vitro primary mouse lung vascular ECs (MLVECs), we demonstrate that rmCIRP treatment directly increases the ICAM-1 protein expression and activates NAD(P)H oxidase in MLVECs. Importantly, CIRP stimulates the assembly and activation of Nlrp3 inflammasome in MLVECs accompanied with caspase-1 activation, IL-1β release and induction of proinflammatory cell death pyroptosis. Finally, our study demonstrates CIRP-induced EC pyroptosis in the lungs of C57BL/6 mice for the first time. Taken together, the released CIRP in shock can directly activate ECs and induce EC pyroptosis to cause lung injury.

Damage-associated molecular patterns in cancer: a double-edged sword

Damage-associated molecular patterns (DAMPs) are released in response to cell death and stress, and are potent triggers of sterile inflammation. Recent evidence suggests that DAMPs may also have a key role in the development of cancer as well as in the host response to cytotoxic anti-tumor therapy. As such, DAMPs may exert protective functions by alerting the immune system to the presence of dying tumor cells, thereby triggering immunogenic tumor cell death. On the other hand, cell death and release of DAMPs may also trigger chronic inflammation and thereby promote the development or progression of tumors. Here, we will review the contribution of candidate DAMPs and their receptors and discuss the evidence for DAMPs as tumor-promoting and anti-tumor effectors as well as unsolved questions such as DAMP release from non-tumor cells as well as the existence of tumor-specific DAMPs.

Tissue damage negatively regulates LPS-induced macrophage necroptosis

Infection is a common clinical complication following tissue damage resulting from surgery and severe trauma. Studies have suggested that cell pre-activation by antecedent trauma/tissue damage profoundly impacts the response of innate immune cells to a secondary infectious stimulus. Cell necroptosis, a form of regulated inflammatory cell death, is one of the mechanisms that control cell release of inflammatory mediators from important innate immune executive cells such as macrophages (Mφ), which critically regulate the progress of inflammation. In this study, we investigated the mechanism and role of trauma/tissue damage in the regulation of LPS-induced Mφ necroptosis using a mouse model simulating long-bone fracture. We demonstrate that LPS acting through Toll-like receptor (TLR) 4 promotes Mφ necroptosis. However, necroptosis is ameliorated by high-mobility group box 1 (HMGB1) release from damaged tissue. We show that HMGB1 acting through cell surface receptor for advanced glycation end products (RAGE) upregulates caveolin-1 expression, which in turn induces caveolae-mediated TLR4 internalization and desensitization to decrease Mφ necroptosis. We further show that RAGE-MyD88 activation of Cdc42 and subsequent activation of transcription factor Sp1 serves as a mechanism underlying caveolin-1 transcriptional upregulation. These results reveal a previous unidentified protective role of damage-associated molecular pattern (DAMP) molecules in restricting inflammation in response to exogenous pathogen-associated molecular pattern molecules.

Ionizing Radiation Induces HMGB1 Cytoplasmic Translocation and Extracellular Release

OBJECTIVE

A nucleosomal protein, HMGB1, can be secreted by activated immune cells or passively released by dying cells, thereby amplifying rigorous inflammatory responses. In this study we aimed to test the possibility that ionizing radiation similarly induces cytoplasmic HMGB1 translocation and extracellular release.

METHOD

Human skin fibroblast (GM0639) and bronchial epithelial (16HBE) cells and animals (rats) were exposed to X-ray radiation, and HMGB1 translocation and release were assessed by immunocytochemistry and immunoassay, respectively.

RESULTS

At a wide dose range (4.0 - 12.0 Gy), X-ray radiation induced a dramatic cytoplasmic HMGB1 translocation, and triggered a time- and dose-dependent HMGB1 release both in vitro and in vivo. The radiation-mediated HMGB1 release was associated with noticeable chromosomal DNA damage and loss of cell viability.

CONCLUSION

radiation induces HMGB1 cytoplasmic translocation and extracellular release through active secretion and passive leakage processes.

The Role of Cell Death in the Pathogenesis of SLE: Is Pyroptosis the Missing Link?

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by the production of antinuclear antibodies (ANAs) in association with systemic inflammation and organ damage. In addition to genetic factors, a contribution of infection to disease induction has been proposed. In the pathogenesis of lupus, immune complexes of ANAs with nuclear antigens can form and both deposit in the tissue and stimulate cytokine production to intensify inflammation. As such, the extracellular release of nuclear antigens to form pathogenic immune complexes is an important step in the pathway to disease. This release has been considered the consequence of cell death, with apoptotic cells the relevant source of nuclear material. While apoptosis could serve this role, other death forms may act similarly. Among these death forms, pyroptosis, which can be induced by inflammasome activation during infection, has features suggesting involvement in lupus. Thus, unlike apoptosis, pyroptosis is a pro-inflammatory process. Furthermore, pyroptosis leads to the release of intracellular contents including HMGB1 and ATP, both of which can act as DAMPs (death associated molecular patterns) to stimulate further inflammation. Importantly, pyroptosis can lead to the release of intact nuclei, suggesting a relationship to events in the formation of LE cells. While the role of pyroptosis in SLE is hypothetical at this time, further analysis of this death form should provide new insights into lupus pathogenesis and provide the missing link between infection and the initiation of lupus by products of dead and dying cells.

Modulation of P2X4/P2X7/Pannexin-1 sensitivity to extracellular ATP via Ivermectin induces a non-apoptotic and inflammatory form of cancer cell death

Overexpression of P2X7 receptors correlates with tumor growth and metastasis. Yet, release of ATP is associated with immunogenic cancer cell death as well as inflammatory responses caused by necrotic cell death at sites of trauma or ischemia-reperfusion injury. Using an FDA-approved anti-parasitic agent Ivermectin as a prototype agent to allosterically modulate P2X4 receptors, we can switch the balance between the dual pro-survival and cytotoxic functions of purinergic signaling in breast cancer cells. This is mediated through augmented opening of the P2X4/P2X7-gated Pannexin-1 channels that drives a mixed apoptotic and necrotic mode of cell death associated with activation of caspase-1 and is consistent with pyroptosis. We show that cancer cell death is dependent on ATP release and death signals downstream of P2X7 receptors that can be reversed by inhibition of NADPH oxidases-generated ROS, Ca²⁺/Calmodulin-dependent protein kinase II (CaMKII) or mitochondrial permeability transition pore (MPTP). Ivermectin induces autophagy and release of ATP and HMGB1, key mediators of inflammation. Potentiated P2X4/P2X7 signaling can be further linked to the ATP rich tumor microenvironment providing a mechanistic explanation for the tumor selectivity of purinergic receptors modulation and its potential to be used as a platform for integrated cancer immunotherapy.

DAMPs, ageing, and cancer: The 'DAMP Hypothesis'

Ageing is a complex and multifactorial process characterized by the accumulation of many forms of damage at the molecular, cellular, and tissue level with advancing age. Ageing increases the risk of the onset of chronic inflammation-associated diseases such as cancer, diabetes, stroke, and neurodegenerative disease. In particular, ageing and cancer share some common origins and hallmarks such as genomic instability, epigenetic alteration, aberrant telomeres, inflammation and immune injury, reprogrammed metabolism, and degradation system impairment (including within the ubiquitin-proteasome system and the autophagic machinery). Recent advances indicate that damage-associated molecular pattern molecules (DAMPs) such as high mobility group box 1, histones, S100, and heat shock proteins play location-dependent roles inside and outside the cell. These provide interaction platforms at molecular levels linked to common hallmarks of ageing and cancer. They can act as inducers, sensors, and mediators of stress through individual plasma membrane receptors, intracellular recognition receptors (e.g., advanced glycosylation end product-specific receptors, AIM2-like receptors, RIG-I-like receptors, and NOD1-like receptors, and toll-like receptors), or following endocytic uptake. Thus, the DAMP Hypothesis is novel and complements other theories that explain the features of ageing. DAMPs represent ideal biomarkers of ageing and provide an attractive target for interventions in ageing and age-associated diseases.

High Mobility Group Box Protein 1 (HMGB1): The Prototypical Endogenous Danger Molecule

High mobility group box protein 1 (HMGB1) is an evolutionary ancient nuclear protein that exerts divergent biological tasks inside and outside of cells. The functions of HMGB1 depend on location, binding partners and redox states of the molecule. In the nucleus, HMGB1 organizes DNA and nucleosomes and regulates gene transcription. Upon cell activation or injury, nuclear HMGB1 can translocate to the cytoplasm, where it is involved in inflammasome activation and pyroptosis, as well as regulation of the autophagy/apoptosis balance. When actively secreted or passively released into the extracellular milieu, HMGB1 has cytokine, chemokine, neuroimmune and metabolic activities. Thus, HMGB1 plays multiple roles in the pathogenesis of inflammatory diseases and mediates immune responses that range from inflammation and bacterial killing to tissue repair. HMGB1 has been associated with divergent clinical conditions such as sepsis, rheumatoid arthritis and atherosclerosis. HMGB1 initiates and perpetuates immune responses during infectious and sterile inflammation, as the archetypical alarmin and damage-associated molecular pattern (DAMP) molecule. We here describe advances in the understanding of HMGB1 biology with focus on recent findings of its mission as a DAMP in danger sensing and as a therapeutic target in inflammatory diseases.

The interplay between inflammation and metabolism in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by extensive synovitis resulting in erosions of articular cartilage and marginal bone that lead to joint destruction. The autoimmune process in RA depends on the activation of immune cells, which use intracellular kinases to respond to external stimuli such as cytokines, immune complexes, and antigens. An intricate cytokine network participates in inflammation and in perpetuation of disease by positive feedback loops promoting systemic disorder. The widespread systemic effects mediated by pro-inflammatory cytokines in RA impact on metabolism and in particular in lymphocyte metabolism. Moreover, RA pathobiology seems to share some common pathways with atherosclerosis, including endothelial dysfunction that is related to underlying chronic inflammation. The extent of the metabolic changes and the types of metabolites seen may be good markers of cytokine-mediated inflammatory processes in RA. Altered metabolic fingerprints may be useful in predicting the development of RA in patients with early arthritis as well as in the evaluation of the treatment response. Evidence supports the role of metabolomic analysis as a novel and nontargeted approach for identifying potential biomarkers and for improving the clinical and therapeutical management of patients with chronic inflammatory diseases. Here, we review the metabolic changes occurring in the pathogenesis of RA as well as the implication of the metabolic features in the treatment response.

Inflammasome activation and function in liver disease

Inflammation contributes to the pathogenesis of most acute and chronic liver diseases. Inflammasomes are multiprotein complexes that can sense danger signals from damaged cells and pathogens and assemble to mediate caspase-1 activation, which proteolytically activates the cytokines IL-1β and IL-18. In contrast to other inflammatory responses, inflammasome activation uniquely requires two signals to induce inflammation, therefore setting an increased threshold. IL-1β, generated upon caspase-1 activation, provides positive feed-forward stimulation for inflammatory cytokines, thereby amplifying inflammation. Inflammasome activation has been studied in different human and experimental liver diseases and has been identified as a major contributor to hepatocyte damage, immune cell activation and amplification of liver inflammation. In this Review, we discuss the different types of inflammasomes, their activation and biological functions in the context of liver injury and disease progression. Specifically, we focus on the triggers of inflammasome activation in alcoholic steatohepatitis and NASH, chronic HCV infection, ischaemia-reperfusion injury and paracetamol-induced liver injury. The application and translation of these discoveries into therapies promises novel approaches in the treatment of inflammation in liver disease.

Inflammasomes in pancreatic physiology and disease

In this review we summarize the role of inflammasomes in pancreatic physiology and disease with a focus on acute pancreatitis where much recent progress has been made. New findings have identified inducers of and cell specificity of inflammasome component expression in the pancreas, the contribution of inflammasome-regulated effectors to pancreatitis, and metabolic regulation of inflammasome activation, which are strong determinants of injury in pancreatitis. New areas of pancreatic biology will be highlighted in the context of our evolving understanding of gut microbiome- and injury-induced inflammasome priming, pyroptosis, and innate immune-mediated regulation of cell metabolism.

Oxidative stress-mediated HMGB1 biology

High mobility group box 1 (HMGB1) is a widely-expressed and highly-abundant protein that acts as an extracellular signal upon active secretion by immune cells or passive release by dead, dying, and injured cells. Both intracellular and extracellular HMGB1 play pivotal roles in regulation of the cellular response to stress. Targeting the translocation, release, and activity of HMGB1 can limit inflammation and reduce tissue damage during infection and sterile inflammation. Although the mechanisms contributing to HMGB1 biology are still under investigation, it appears that oxidative stress is a central regulator of HMGB1's translocation, release, and activity in inflammation and cell death (e.g., necrosis, apoptosis, autophagic cell death, pyroptosis, and NETosis). Thus, targeting HMGB1 with antioxidant compounds may be an attractive therapeutic strategy for inflammation-associated diseases such as sepsis, ischemia and reperfusion injury, arthritis, diabetes, and cancer.

High systemic levels of the cytokine-inducing HMGB1 isoform secreted in severe macrophage activation syndrome

Macrophage activation syndrome (MAS) is a potentially fatal complication of systemic inflammation. High mobility group box 1 (HMGB1) is a nuclear protein extensively leaked extracellularly during necrotic cell death or actively secreted by natural killer (NK) cells, macrophages and additional cells during infection or sterile injury. Extracellular HMGB1 orchestrates key events in inflammation as a prototypic alarmin. The redox states of its three cysteines render the molecule mutually exclusive functions: fully reduced "all-thiol HMGB1" exerts chemotactic activity; "disulfide HMGB1" has cytokine-inducing, toll-like receptor 4 (TLR4)-mediated effects—while terminally oxidized "sulfonyl HMGB1" lacks inflammatory activity. This study examines the kinetic pattern of systemic HMGB1 isoform expression during therapy in four children with severe MAS. Three of the four patients with underlying systemic rheumatic diseases were treated with biologics and two suffered from triggering herpes virus infections at the onset of MAS. All patients required intensive care unit therapy due to life-threatening illness. Tandem mass-spectrometric analysis revealed dramatically increased systemic levels of the cytokine-inducing HMGB1 isoform during early MAS. Disease control coincided with supplementary etoposide therapy initiated to boost apoptotic cell death, when systemic HMGB1 levels drastically declined and the molecule emerged mainly in its oxidized, noninflammatory isoform. Systemic interferon (IFN)-γ and ferritin peaked concomitantly with HMGB1, whereas interleukin (IL)-18 and monocyte chemotactic protein (MCP)-1 levels developed differently. In conclusion, this work provides new insights in HMGB1 biology, suggesting that the molecule is not merely a biomarker of inflammation, but most likely also contributes to the pathogenesis of MAS. These observations encourage further studies of disulfide HMGB1 antagonists to improve outcome of MAS.

Programmed cell death and its role in inflammation

Cell death plays an important role in the regulation of inflammation and may be the result of inflammation. The maintenance of tissue homeostasis necessitates both the recognition and removal of invading microbial pathogens as well as the clearance of dying cells. In the past few decades, emerging knowledge on cell death and inflammation has enriched our molecular understanding of the signaling pathways that mediate various programs of cell death and multiple types of inflammatory responses. This review provides an overview of the major types of cell death related to inflammation. Modification of cell death pathways is likely to be a logical therapeutic target for inflammatory diseases.

An ongoing search for potential targets and therapies for lethal sepsis

Sepsis, which refers to a systemic inflammatory response syndrome resulting from a microbial infection, represents the leading cause of death in intensive care units. The pathogenesis of sepsis remains poorly understood although it is attributable to dysregulated immune responses orchestrated by innate immune cells that are sequentially released early (e.g., tumor necrosis factor(TNF), interleukin-1(IL-1), and interferon-γ(IFN-γ)) and late (e.g., high mobility group box 1(HMGB1)) pro-inflammatory mediators. As a ubiquitous nuclear protein, HMGB1 can be passively released from pathologically damaged cells, thereby converging infection and injury on commonly dysregulated inflammatory responses. We review evidence that supports extracellular HMGB1 as a late mediator of inflammatory diseases and discuss the potential of several Chinese herbal components as HMGB1-targeting therapies. We propose that it is important to develop strategies for specifically attenuating injury-elicited inflammatory responses without compromising the infection-mediated innate immunity for the clinical management of sepsis and other inflammatory diseases.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Cell death and DAMPs in acute pancreatitis

Cell death and inflammation are key pathologic responses of acute pancreatitis (AP), the leading cause of hospital admissions for gastrointestinal disorders. It is becoming increasingly clear that damage-associated molecular pattern molecules (DAMPs) play an important role in the pathogenesis of AP by linking local tissue damage to systemic inflammation syndrome. Endogenous DAMPs released from dead, dying or injured cells initiate and extend sterile inflammation via specific pattern recognition receptors. Inhibition of the release and activity of DAMPs (for example, high mobility group box 1, DNA, histones and adenosine triphosphate) provides significant protection against experimental AP. Moreover, increased serum levels of DAMPs in patients with AP correlate with disease severity. These findings provide novel insight into the mechanism, diagnosis and management of AP. DAMPs might be an attractive therapeutic target in AP.

MicroRNA-30d regulates cardiomyocyte pyroptosis by directly targeting foxo3a in diabetic cardiomyopathy

Diabetic cardiomyopathy is a common cardiac condition in patients with diabetes mellitus, which can result in cardiac hypertrophy and subsequent heart failure, associated with pyroptosis, the pro-inflammatory programmed cell death. MicroRNAs (miRNAs), small endogenous non-coding RNAs, have been shown to be involved in diabetic cardiomyopathy. However, whether miRNAs regulate pyroptosis in diabetic cardiomyopathy remains unknown. Our study revealed that mir-30d expression was substantially increased in streptozotocin (STZ)-induced diabetic rats and in high-glucose-treated cardiomyocytes as well. Upregulation of mir-30d promoted cardiomyocyte pyroptosis in diabetic cardiomyopathy; conversely, knockdown of mir-30d attenuated it. In an effort to understand the signaling mechanisms underlying the pro-pyroptotic property of mir-30d, we found that forced expression of mir-30d upregulated caspase-1 and pro-inflammatory cytokines IL-1β and IL-18. Moreover, mir-30d directly repressed foxo3a expression and its downstream protein, apoptosis repressor with caspase recruitment domain (ARC). Furthermore, silencing ARC by siRNA mimicked the action of mir-30d: upregulating caspase-1 and inducing pyroptosis. These findings promoted us to propose a new signaling pathway leading to cardiomyocyte pyroptosis under hyperglycemic conditions: mir-30d↑→foxo3a↓→ ARC↓→caspase-1↑→IL-1β, IL-18↑→pyroptosis↑. Therefore, mir-30d may be a promising therapeutic target for the management of diabetic cardiomyopathy.

Involvement of the nuclear high mobility group B1 peptides released from injured hepatocytes in murine hepatic fibrogenesis

This study investigated the pro-fibrogenic role of high mobility group box 1 (HMGB1) peptides in liver fibrogenesis. An animal model of carbon tetrachloride (CCl4)-induced liver fibrosis was used to examine the serum HMGB1 levels and its intrahepatic distribution. The increased serum HMGB1 levels were positively correlated with elevation of transforming growth factor-β1 (TGF-β1) and collagen deposition during fibrogenesis. The cytoplasmic distribution of HMGB1 was noted in the parenchymal hepatocytes of fibrotic livers. In vitro studies confirmed that exposure to hydrogen peroxide and CCl4 induced an intracellular mobilization and extracellular release of nuclear HMGB1 peptides in clone-9 and primary hepatocytes, respectively. An uptake of exogenous HMGB1 by hepatic stellate cells (HSCs) T6 cells indicated a possible paracrine action of hepatocytes on HSCs. Moreover, HMGB1 dose-dependently stimulated HSC proliferation, up-regulated de novo synthesis of collagen type I and α-smooth muscle actin (α-SMA), and triggered Smad2 phosphorylation and its nuclear translocation through a TGF-β1-independent mechanism. Blockade with neutralizing antibodies and gene silencing demonstrated the involvement of the receptor for advanced glycation end-products (RAGE), but not toll-like receptor 4, in cellular uptake of HMGB1 and the HMGB1-mediated Smad2 and ERK1/2 phosphorylation as well as α-SMA up-regulation in HSC-T6 cells. Furthermore, anti-RAGE treatment significantly ameliorated CCl4-induced liver fibrosis. In conclusion, the nuclear HMGB1 peptides released from parenchymal hepatocytes during liver injuries may directly activate HSCs through stimulating HSC proliferation and transformation, eventually leading to the fibrotic changes of livers. Blockade of HMGB1/RAGE signaling cascade may constitute a therapeutic strategy for treatment of liver fibrosis.