The receptor for advanced glycation end products (RAGE) is a cellular binding site for amphoterin. Mediation of neurite outgrowth and co-expression of rage and amphoterin in the developing nervous system

Alzheimer's disease and the Blood-Brain Barrier: Past, Present and Future

Successful prevention and treatment of late-onset Alzheimer’s disease (AD) is a high priority for industrialized societies where the incidence is growing rapidly. Much of the underlying biology leading to AD is unknown, and the more knowledge we gain the more we appreciate the complexities involved. Popular etiologic hypotheses have largely ignored the blood–brain barrier (BBB) as an important factor contributing to the pathologic hallmarks of this most common form of dementia. Evidence identifying BBB dysfunction in AD or patients at risk (i.e., those with mild cognitive impairment) continue to escalate. This review highlights methodological issues facing investigators assessing BBB integrity in living patients while also discussing whether the BBB dysfunction is a cause, effect or epiphenomenon in AD. Rationale for future research pursuits aimed at describing the role of BBB function in AD pathogenesis is also presented.

High-mobility group box 1 (HMGB1) protein at the crossroads between innate and adaptive immunity

Tissue damage occurs often in the life of mammals and is usually repaired. Dying cells are swiftly phagocytosed, but before disappearing, they alert surrounding cells to activate homeostatic programs. They release signals that recruit inflammatory cells to the site of injury, promote cell migration and cell division to replace dead cells, and activate the immune system in anticipation of microbial invasion. Many of these events involve high-mobility group box 1 protein (HMGB1), a nuclear protein that is released passively when necrotic cells lose the integrity of their membranes. HMGB1 behaves as a trigger of inflammation, attracting inflammatory cells, and of tissue repair, recruiting stem cells and promoting their proliferation. Moreover, HMGB1 activates dendritic cells (DCs) and promotes their functional maturation and their response to lymph node chemokines. Activated leukocytes actively secrete HMGB1 in the microenvironment. Thus, HMGB1 acts in an autocrine/paracrine fashion and sustains long-term repair and defense programs. DCs secrete HMGB1 several hours after contact with the first maturation stimulus; HMGB1 secretion is critical for their ability to reach the lymph nodes, to sustain the proliferation of antigen-specific T cells, to prevent their activation-dependent apoptosis, and to promote their polarization towards a T-helper 1 phenotype. These immune responses will also be directed against self-antigens that DCs process at the time of injury and can lead to autoimmunity.

Bench-to-bedside review: The inflammation-perpetuating pattern-recognition receptor RAGE as a therapeutic target in sepsis

Sepsis still represents an important clinical and economic challenge for intensive care units. Severe complications like multi-organ failure with high mortality and the lack of specific diagnostic tools continue to hamper the development of improved therapies for sepsis. Fundamental questions regarding the cellular pathogenesis of experimental and clinical sepsis remain unresolved. According to experimental data, inhibiting macrophage migration inhibitory factor, high-mobility group box protein 1 (HMGB1), and complement factor C5a and inhibiting the TREM-1 (triggering receptor expressed on myeloid cells 1) signaling pathway and apoptosis represent promising new therapeutic options. In addition, we have demonstrated that blocking the signal transduction pathway of receptor of advanced glycation endproducts (RAGE), a new inflammation-perpetuating receptor and a member of the immunglobulin superfamily, increases survival in experimental sepsis. The activation of RAGE by advanced glycation end-products, S100, and HMGB1 initiates nuclear factor kappa B and mitogen-activated protein kinase pathways. Importantly, the survival rate of RAGE knockout mice was more than fourfold that of wild-type mice in a septic shock model of cecal ligation and puncture (CLP). Additionally, the application of soluble RAGE, an extracellular decoy for RAGE ligands, improves survival in mice after CLP, suggesting that RAGE is a central player in perpetuating the innate immune response. Understanding the basic signal transduction events triggered by this multi-ligand receptor may offer new diagnostic and therapeutic options in patients with sepsis.

Elevation of high-mobility group box 1 concentration in asphyxiated neonates

BACKGROUND

In asphyxiated neonates, abnormal proinflammatory cytokine/chemokine production may be induced. High-mobility group box 1 (HMGB-1) protein is a new type of proinflammatory cytokine that induces abnormal inflammatory responses involving proinflammatory cytokine production. However, the physiological significance of HMGB-1 in asphyxia is poorly understood.

OBJECTIVES

We aimed to evaluate whether serum HMGB-1 levels were changed in asphyxia by measuring the serum concentration of HMGB-1 in both asphyxiated and normally delivered neonates at birth.

METHODS

Using enzyme-linked immunosorbent assay, we measured the concentration of HMGB-1 in sera obtained from 53 asphyxiated neonates and 32 normally delivered neonates immediately after birth.

RESULTS

The serum concentrations of HMGB-1 in asphyxiated neonates were significantly higher than those in normally delivered neonates without asphyxia (p = 0.033).

CONCLUSION

We suggest that the elevation of HMGB-1 might be associated with abnormal inflammatory responses involving the excessive production of proinflammatory cytokines in neonates with asphyxia.

Soluble receptor for advanced glycation end products (sRAGE) and endogenous secretory RAGE (esRAGE) in amniotic fluid: modulation by infection and inflammation

OBJECTIVE

The receptor for advanced glycation end products (RAGE) has been proposed to participate in the innate and adaptive immune responses. RAGE can induce production of pro-inflammatory cytokines and chemokines, as well as neutrophil chemotaxis in a manner that may be suppressed or stimulated by soluble, truncated forms of RAGE including the soluble form of RAGE (sRAGE) and endogenous secretory RAGE (esRAGE). The objective of this study was to determine whether intra-amniotic infection/inflammation (IAI) is associated with changes in the amniotic fluid concentration of sRAGE and esRAGE.

STUDY DESIGN

Amniotic fluid (AF) was retrieved from patients in the following groups: 1) mid-trimester (14-18 weeks of gestation; n=68); 2) term not in labor (n=24); 3) term in labor (n=51); 4) preterm labor and intact membranes (n=124); and 5) preterm PROM (n=80). Intra-amniotic infection and inflammation were defined as the presence of a positive amniotic fluid culture for microorganisms and an AF interleukin-6 concentration >or=2.6 ng/mL, respectively. The AF concentration of sRAGE and esRAGE were determined using specific and sensitive ELISAs which measured total immunoreactive sRAGE and esRAGE, respectively. Patients were matched for gestational age at amniocentesis to compare the AF concentration of sRAGE and esRAGE in patients with and without IAI. Non-parametric statistics were used for analysis and a P<0.05 was considered significant.

RESULTS

1) Patients at term not in labor had higher median AF concentrations of sRAGE and esRAGE than those in the mid-trimester (P<0.001 for both comparisons) and those at term in labor (P=0.03 and P=0.04, respectively); 2) patients with preterm labor and intact membranes with intra-amniotic infection/inflammation (IAI) had higher median AF concentrations of sRAGE and esRAGE than those without IAI (P=0.02 and P=0.005, respectively); 3) similarly, patients with preterm PROM with IAI had higher median AF concentrations of sRAGE and esRAGE than those without IAI (P=0.03 and P=0.02, respectively).

CONCLUSION

Intra-amniotic infection/inflammation is associated with increased amniotic fluid concentrations of sRAGE and esRAGE. Changes in the amniotic fluid concentration of sRAGE and esRAGE may represent part of the immune response to intra-amniotic infection/inflammation.

The inflammatory response to cell death

When cells die in vivo, they trigger an inflammatory response. The ensuing hyperemia, leak of plasma proteins, and recruitment of leukocytes serve a number of useful functions in host defense and tissue repair. However, this response can also cause tissue damage and contribute to the pathogenesis of a number of diseases. Given the key role of inflammation in these processes, it is important to understand the underlying mechanisms that drive this response. Injured cells release danger signals that alert the host to cell death. Some of these molecules are recognized by cellular receptors that stimulate the generation of proinflammatory mediators. Other molecules released by dead cells stimulate the generation of mediators from extracellular sources. The resulting mediators then orchestrate the inflammatory response, eliciting its various vascular and cellular components. Dead cells also release danger signals that activate dendritic cells and promote the generation of immune responses to antigens. Here we review what is presently known about the sterile inflammatory response and its underlying mechanisms.

Arguing for the motion: yes, RAGE is a receptor for advanced glycation endproducts

Advanced glycation endproducts (AGEs) are an heterogenous class of compounds formed by diverse stimuli, including hyperglycemia, oxidative stress, inflammation, renal failure, and innate aging. Recent evidence suggests that dietary sources of AGE may contribute to pathology. AGEs impart diverse effects in cells; evidence strongly suggests that crosslinking of proteins by AGEs may irrevocably alter basement membrane integrity and function. In addition, the ability of AGEs to bind to cells and activate signal transduction, thereby affecting broad properties in the cellular milieu, indicates that AGEs are not innocent bystanders in the diseases of AGEing. Here, we present evidence that receptor for AGE (RAGE) is a receptor for AGEs.

Identification, classification, and expression of RAGE gene splice variants

The receptor for advanced glycation end-products (RAGE) is a single-transmembrane, multiligand receptor of the immunoglobulin superfamily. RAGE up-regulation is implicated in numerous pathological states including vascular disease, diabetes, cancer, and neurodegeneration. The understanding of the regulation of RAGE is important in both disease pathogenesis and normal homeostasis. Here, we demonstrate the characterization and identification of human RAGE splice variants by analysis of RAGE cDNA from tissue and cells. We identified a vast range of splice forms that lead to changes in the protein coding region of RAGE, which we have classified according to the Human Gene Nomenclature Committee (HGNC). These resulted in protein changes in the ligand-binding domain of RAGE or the removal of the transmembrane domain and cytosolic tail. Analysis of splice variants for premature termination codons reveals approximately 50% of identified variants are targeted to the nonsense-mediated mRNA decay pathway. Expression analysis revealed the RAGE_v1 variant to be the primary secreted soluble isoform of RAGE. Taken together, identification of functional splice variants of RAGE underscores the biological diversity of the RAGE gene and will aid in the understanding of the gene in the normal and pathological state.

Expression and characterization of recombinant C-terminal biotinylated extracellular domain of human receptor for advanced glycation end products (hsRAGE) in Escherichia coli

The receptor for advanced glycation end products (RAGE) is a multi-ligand receptor involved in the development of diabetic complications. Using an Escherichia coli expression system, we have successfully expressed and purified the C-terminal biotinylated extracellular domain of human RAGE (hsRAGE), which consists of three immunoglobulin-like domains carrying three putative disulfide bonds. Over 90% of hsRAGE was expressed in soluble form in trxB and gor mutant E. coli strain Origami (DE3). Most hsRAGE was biotinylated with a C-terminal AviTag, and stably immobilized onto matrix via streptavidin without any treatment. Immobilized hsRAGE without glycosylation recognized its ligands, such as AGEs. Biotinylated hsRAGE was also able to apply in the detection of AGEs on microtitre wells like antibodies used in enzyme-linked immunoassay. SPR analysis demonstrated that the dissociation constant (K(d)) of RAGE for AGE-BSA was 23.1 nM with the two-state reaction model, and 13.5 nM with the 1:1 binding model, comparable to those of RAGEs on cell surface. These results indicate that biotinylated hsRAGE must be useful not only in analysing RAGE-ligand interactions but also detect AGEs.

RAGE and soluble RAGE: potential therapeutic targets for cardiovascular diseases

Receptor for advanced glycation end-products (RAGE) is known to be involved in microvascular complications in diabetes. RAGE is also profoundly associated with macrovascular complications in diabetes through regulation of atherogenesis, angiogenic response, vascular injury, and inflammatory response. The potential significance of RAGE in the pathogenesis of cardiovascular disease appears not to be confined solely to nondiabetic rather than diabetic conditions. Numerous truncated forms of RAGE have recently been described, and the C-terminally truncated soluble form of RAGE has received much attention. Soluble RAGE consists of several forms, including endogenous secretory RAGE (esRAGE), which is a spliced variant of RAGE, and a shedded form derived from cell-surface RAGE. These heterogeneous forms of soluble RAGE, which carry all of the extracellular domains but are devoid of the transmembrane and intracytoplasmic domains, bind ligands including AGEs and can antagonize RAGE signaling in vitro and in vivo. ELISA systems have been developed to measure plasma esRAGE and total soluble RAGE, and the pathophysiological roles of soluble RAGE have begun to be unveiled clinically. In this review, we summarize recent findings regarding pathophysiological roles in cardiovascular disease of RAGE and soluble RAGE and discuss their potential usefulness as therapeutic targets and biomarkers for the disease.

S100A11, an dual mediator for growth regulation of human keratinocytes

We previously revealed a novel signal pathway involving S100A11 for inhibition of the growth of normal human keratinocytes (NHK) caused by high Ca(++) or transforming growth factor beta. Exposure to either agent resulted in transfer of S100A11 to nuclei, where it induced p21(WAF1). In contrast, S100A11 has been shown to be overexpressed in many human cancers. To address this apparent discrepancy, we analyzed possible new functions of S100A11, and we provide herein evidence that 1) S100A11 is actively secreted by NHK; 2) extracellular S100A11 acts on NHK to enhance the production of epidermal growth factor family proteins, resulting in growth stimulation; 3) receptor for advanced glycation end products, nuclear factor-kappaB, Akt, and cAMP response element-binding protein are involved in the S100A11-triggered signal transduction; and 4) production and secretion of S100A11 are markedly enhanced in human squamous cancer cells. These findings indicate that S100A11 plays a dual role in growth regulation of epithelial cells.

Hypoxia-inducible factor-1 mediates neuronal expression of the receptor for advanced glycation end products following hypoxia/ischemia

Activation of the receptor for advanced glycation endproducts (RAGE) by its multiple ligands can trigger diverse signaling pathways with injurious or pro-survival consequences. In this study, we show that Rage mRNA and protein levels were stimulated in the mouse brain after experimental stroke and systemic hypoxia. In both cases, RAGE expression was primarily associated with neurons. Activation of RAGE-dependent pathway(s) post-ischemia appears to have a neuroprotective role because mice genetically deficient for RAGE exhibited increased infarct size 24 h after injury. Up-regulation of RAGE expression was also observed in primary neurons subjected to hypoxia or oxygen-glucose deprivation, an in vitro model of ischemia. Treatment of neurons with low concentrations of S100B decreased neuronal death after oxygen-glucose deprivation, and this effect was abolished by a neutralizing antibody against RAGE. Conversely, high concentrations of exogenous S100B had a cytotoxic effect that seems to be RAGE-independent. As an important novel finding, we demonstrate that hypoxic stimulation of RAGE expression is mediated by the transcription factor hypoxia-inducible factor-1. This conclusion is supported by the finding that HIF-1alpha down-regulation by Cre-mediated excision drastically decreased RAGE induction by hypoxia or desferrioxamine. In addition, we showed that the mouse RAGE promoter region contains at least one functional HIF-1 binding site, located upstream of the proposed transcription start site. A luciferase reporter construct containing this RAGE promoter fragment was activated by hypoxia, and mutation at the potential HIF-1 binding site decreased hypoxia-dependent promoter activation. Specific binding of HIF-1 to this putative HRE in hypoxic cells was detected by chromatin immunoprecipitation assay.

Cells migrating to sites of tissue damage in response to the danger signal HMGB1 require NF-kappaB activation

Tissue damage is usually followed by healing, as both differentiated and stem cells migrate to replace dead or damaged cells. Mesoangioblasts (vessel-associated stem cells that can repair muscles) and fibroblasts migrate toward soluble factors released by damaged tissue. Two such factors are high mobility group box 1 (HMGB1), a nuclear protein that is released by cells undergoing unscheduled death (necrosis) but not by apoptotic cells, and stromal derived factor (SDF)-1/CXCL12. We find that HMGB1 activates the canonical nuclear factor kappaB (NF-kappaB) pathway via extracellular signal-regulated kinase phosphorylation. NF-kappaB signaling is necessary for chemotaxis toward HMGB1 and SDF-1/CXCL12, but not toward growth factor platelet-derived growth factor, formyl-met-leu-phe (a peptide that mimics bacterial invasion), or the archetypal NF-kappaB-activating signal tumor necrosis factor alpha. In dystrophic mice, mesoangioblasts injected into the general circulation ingress inefficiently into muscles if their NF-kappaB signaling pathway is disabled. These findings suggest that NF-kappaB signaling controls tissue regeneration in addition to early events in inflammation.

Role of Janus kinase/signal transducer and activator of transcription pathway in regulation of expression and inflammation-promoting activity of high mobility group box protein 1 in rat peritoneal macrophages

Signal transduction mechanism in the regulation of high mobility group box protein 1 (HMGB1) has not yet been well elucidated. Our data showed for the first time that Janus kinase-signal transduction and activator of transcription (JAK/STAT) pathway played a major role in the regulation of expression and inflammatory effect of HMGB1. The study was carried out in the following sequence. Firstly, the role of JAK/STAT pathway in the regulation of expression of HMGB1 was examined. After stimulation with 75 ng/mL LPS in vitro, significant increases in HMGB1 expression and prompt activation of JAK/STAT pathway were demonstrated in cultured macrophages. On the other hand, administration of AG490 (specific inhibitor for JAK2), fludarabine (specific inhibitor for STAT1) or rapamycin (specific inhibitor for STAT3) markedly suppressed HMGB1 expression. Secondly, the role of JAK/STAT pathway in the regulation of TNF-alpha expression induced by HMGB1 was examined. When macrophages were stimulated with 10 microg/mL HMGB1 in vitro, significant increases in TNF-alpha expression and prompt activation of JAK/STAT pathway were demonstrated, whereas inhibitors of JAK/STAT pathway significantly suppressed TNF-alpha expression. Taken together, our data strongly indicated that expression and inflammatory effect of HMGB1 could be mediated by JAK/STAT pathway and suggested a possible clinical strategy to control an inflammatory effect of HMGB1 in sepsis.

Alarmins initiate host defense

In response to infection and/or tissue injury, cells of the host innate immune system rapidly produce a variety of structurally distinct mediators (we elect to call alarmins) that not only function as potent effectors of innate defense but also act to alarm the immune system by promoting the recruitment and activation of host leukocytes through interaction with distinct receptors. Alarmins are capable of activating antigen-presenting cells (APCs) and enhancing the development of antigen-specific immune responses. Here, we discuss the characteristics of several alarmins, a variety of potential alarmin candidates and potential implications of alarmins.

Multiple effects of high mobility group box protein 1 in skeletal muscle regeneration

OBJECTIVE

High mobility group box 1 protein (HMGB1) is a cytokine released by necrotic and inflammatory cells in response to injury. We examined the role of HMGB1 in skeletal muscle regeneration after hindlimb ischemia.

METHODS AND RESULTS

Unilateral hindlimb ischemia was induced in mice by femoral artery dissection. HMGB1 levels increased in regenerating skeletal muscle and the blockade of endogenous HMGB1 by the administration of its truncated form, the BoxA, resulted in the reduction of vessel density. In contrast, intramuscular administration of HMGB1 enhanced perfusion and increased the number of regenerating fibers. To separately study the myogenic and the angiogenic effects of HMGB1, in vitro experiments were performed with isolated myoblasts and endothelial cells. Myoblasts were found to express the HMGB1 receptor RAGE and TLR4 which were downregulated during in vitro myogenic differentiation. HMGB1 was extracellularly released by differentiated myoblasts and exerted a chemotactic activity on myogenic cells. This effect was partially dependent on RAGE and was inhibited by BoxA treatment. Finally, HMGB1 stimulated tubular-like structure formation by endothelial cells through the activation of extracellular signal-regulated kinase (ERK) and JNK signal transduction pathways.

CONCLUSIONS

HMGB1 plays a role in skeletal muscle regeneration modulating, in an autocrine-paracrine manner, myoblast and endothelial cell functions.

Microbial pathogen-induced necrotic cell death mediated by the inflammasome components CIAS1/cryopyrin/NLRP3 and ASC

Cryopyrin (CIAS1, NLRP3) and ASC are components of the inflammasome, a multiprotein complex required for caspase-1 activation and cytokine IL-1beta production. CIAS1 mutations underlie autoinflammation characterized by excessive IL-1beta secretion. Disease-associated cryopyrin also causes a program of necrosis-like cell death in macrophages, the mechanistic details of which are unknown. We find that patient monocytes carrying disease-associated CIAS1 mutations exhibit excessive necrosis-like death by a process dependent on ASC and cathepsin B, resulting in spillage of the proinflammatory mediator HMGB1. Shigella flexneri infection also causes cryopyrin-dependent macrophage necrosis with features similar to the death caused by mutant CIAS1. This necrotic death is independent of caspase-1 and IL-1beta, and thus independent of the inflammasome. Furthermore, necrosis of primary macrophages requires the presence of Shigella virulence genes. While similar proteins mediate pathogen-induced cell death in plants, this report identifies cryopyrin as an important host regulator of programmed pathogen-induced necrosis in animals, a process we term pyronecrosis.

Receptor for advanced glycation endproducts and atherosclerosis: From basic mechanisms to clinical implications

The receptor for advanced glycation endproducts (RAGE) is a member of the immunoglobulin superfamily of cell-surface molecules with a diverse repertoire of ligands. In the atherosclerotic milieu, three classes of RAGE ligands, i.e., products of non-enzymatic glycoxidation, S100 proteins and amphoterin, appear to drive receptor-mediated cellular activation and potentially, acceleration of vascular disease. The interaction of RAGE-ligands effectively modulates several steps of atherogenesis, triggering an inflammatory-proliferative process and furthermore, critically contributing to propagation of vascular perturbation, mainly in diabetes. RAGE has a circulating truncated variant isoform, soluble RAGE (sRAGE), corresponding to its extracellular domain only. By competing with cell-surface RAGE for ligand binding, sRAGE may contribute to the removal/neutralization of circulating ligands thus functioning as a decoy. The critical role of RAGE in the chronic vascular inflammation processes highlights this receptor-ligand axis as a possible and attractive candidate for therapeutic intervention to limit vascular damage and its associated clinical disorders.

The high-mobility group box 1 cytokine induces transporter-mediated release of glutamate from glial subcellular particles (gliosomes) prepared from in situ-matured astrocytes

The multifunctional protein high-mobility group box 1 (HMGB1) is expressed in restricted areas of adult brain where it can act as a proinflammatory cytokine. We report here that HMGB1 affects CNS transmission by inducing glutamatergic release from glial (gliosomes) but not neuronal (synaptosomes) resealed subcellular particles isolated from mouse cerebellum and hippocampus. Confocal microscopy showed that gliosomes are enriched with glia-specific proteins such as GFAP and S-100, but not with neuronal proteins such as PSD-95, MAP-2, and beta-tubulin III. Furthermore, gliosomes exhibit labeling neither for integrin-alphaM nor for myelin basic protein, specific for microglia and oligodendrocytes, respectively. The gliosomal fraction contains proteins of the exocytotic machinery coexisting with GFAP. Consistent with ultrastructural analysis, several approximately 30-nm nonclustered vesicles are present in the gliosome cytoplasm. Finally, gliosomes represent functional organelles that actively export glutamate when subjected to releasing stimuli, such as ionomycin or ATP, by mechanisms involving extracellular Ca(2+) and Ca(2+) release from intracellular stores. HMGB1-induced release of the stable glutamate analogue [(3)H]d-aspartate and endogenous glutamate form gliosomes, whereas nerve terminals were insensitive to the protein. The HMGB1-evoked release of glutamate was independent on modifications of cytosolic Ca(2+) concentration, but it was blocked by dl-threo-beta-benzyloxyaspartate, suggesting the involvement of transporter-mediated release mechanisms. Moreover, dihydrokainic acid, a selective inhibitor of glutamate transporter 1 does not block the HMGB1 effect, indicating a role for the glial glutamate-aspartate transporter (GLAST) subtype in this response. HMGB1 bind to gliosomes but not to synaptosomes and can physically interact with GLAST and receptor for advanced glycation end products (RAGE). Taken together, these results suggest that the HMGB1 cytokine could act as a modulator of glutamate homeostasis in adult mammalian brain.

Increased expression of HMGB-1 in the skin lesions of erythema toxicum

At birth, commensal microbes penetrate into the skin of the human newborn, eliciting an acute rash, erythema toxicumn neonatorum. Histologically, the rash is characterized by an upregulation of proinflammatory activity and a local recruitment of immunocytes, including macrophages. High mobility group box chromosomal protein 1, a nuclear and cytosolic protein, is also a pro-inflammatory cytokine released by macrophages in response to microbial stimulation. Here, we reasoned that macrophages but also keratinocytes might upregulate this protein in response to the first colonization and that high mobility group box chromosomal protein 1 might play a role as a proinflammatory mediator in the development and progression of erythema toxicum. Punch biopsy specimens from 1-day-old healthy infants, seven with and four without erythema toxicum were analyzed with indirect immunohistochemistry and two different antihigh mobility group box chromosomal protein 1 antibodies, immunofluorescence, nuclear counterstaining, confocal and immunoelectron imaging. We found relocation of nuclear high mobility group box chromosomal protein 1 into the cytoplasm in keratinocytes and macrophages in erythema toxicum. Cytoplasmatic high mobility group box chromosomal protein 1 was also found in melanocytes and did neither co-locate with lysosomal-associated membrane proteins nor with melanosomes. We speculate that terrestrial adaptation triggers the induction of the endogenous "danger signal" high mobility group box chromosomal protein 1 in the skin of the newborn infant, perhaps in response to the first commensal colonization and that this signal may contribute to alert the immune system and promote a protective immune response.

Short-chain aldehyde-derived ligands for RAGE and their actions on endothelial cells

The formation and accumulation of advanced glycation endproducts (AGE) have been implicated in the development of diabetic vascular complications. Their biological responses are known to be mediated by the receptor for AGE (RAGE). Recently, AGE have been proposed to be derived not only from the classical Maillard reaction but also from other pathways of sugar autoxidation and metabolism. Here, we report the identification of glyceraldehydes (Gcer)- and glycolaldehyde (Gcol)-derived AGE as RAGE ligands and their presence in vivo. The apparent dissociation constants assessed by surface-plasmon resonance (SPR) analysis with purified human RAGE proteins were 360 nM for Gcer-AGE and 1.35 microM for Gcol-AGE. The radiolabeled-ligand binding assay with RAGE-expressing COS-7 cells revealed similar association kinetics. Competitive SPR assay with antibodies specific to the respective AGE fractions demonstrated abundant existence of both Gcer- and Gcol-AGE in RAGE affinity-purified proteins from human sera. The serum contents of Gcer- and Gcol-AGE in a diabetic patient were about twice as high as those in a healthy control. Functionally, Gcer- and Gcol-AGE upregulated the endothelial cell levels of mRNA for vascular endothelial growth factor (VEGF) and the secretion of its protein product into the culture media and DNA synthesis in a dose-dependent manner. Further, these endothelial responses were augmented by RAGE overexpression. The results suggest that RAGE engagement of Gcer- and Gcol-AGE may elicit angiogenesis through the induction of autocrine VEGF, thereby contributing to the development and progression of diabetic angiopathies.

S100B and S100A6 differentially modulate cell survival by interacting with distinct RAGE (receptor for advanced glycation end products) immunoglobulin domains

S100 proteins are EF-hand calcium-binding proteins with various intracellular functions including cell proliferation, differentiation, migration, and apoptosis. Some S100 proteins are also secreted and exert extracellular paracrine and autocrine functions. Experimental results suggest that the receptor for advanced glycation end products (RAGE) plays important roles in mediating S100 protein-induced cellular signaling. Here we compared the interaction of two S100 proteins, S100B and S100A6, with RAGE by in vitro assay and in culture of human SH-SY5Y neuroblastoma cells. Our in vitro binding data showed that S100B and S100A6, although structurally very similar, interact with different RAGE extracellular domains. Our cell assay data demonstrated that S100B and S100A6 differentially modulate cell survival. At micromolar concentration, S100B increased cellular proliferation, whereas at the same concentration, S100A6 triggered apoptosis. Although both S100 proteins induced the formation of reactive oxygen species, S100B recruited phosphatidylinositol 3-kinase/AKT and NF-kappaB, whereas S100A6 activated JNK. More importantly, we showed that S100B and S100A6 modulate cell survival in a RAGE-dependent manner; S100B specifically interacted with the RAGE V and C(1) domains and S100A6 specifically interacted with the C(1) and C(2) RAGE domains. Altogether these results highlight the complexity of S100/RAGE cellular signaling.

The genetic variation of the human HMGB1 gene

High-mobility group box 1 protein (HMGB1) is a nuclear DNA-binding protein, which also functions as a pleiotropic cytokine, implicated in the pathology of several different immune-mediated diseases. The purpose of this study was to examine the HMGB1 gene for putative polymorphisms in 103 healthy Caucasian Danish blood donors. A total of six polymorphisms and four mutations were identified in the HMGB1 gene. Subsequent MatInspector estimation revealed that several polymorphisms might have a potential regulatory impact on HMGB1 transcription. This study has characterized genetic variations in the HMGB1 gene locus, which may have a regulating role in the expression of HMGB1, providing the basis for molecular investigations of the HMGB1 gene in different disease settings.

HMGB1: a signal of necrosis

When tissues are damaged, they usually heal. The cellular responses towards healing require the prior recognition that damage has occurred. High Mobility Group Box 1 protein (HMGB1) is a ubiquitous nuclear protein that is passively released by cells that have died in a traumatic, non-programmed way (necrosis). Several receptors for HMGB1 exist, and upon binding HMGB1 they alert leukocytes to extravasate from the blood into the affected tissue, trigger adaptive immunity and promote the migration and proliferation of cells (including stem cells) to repair the damaged tissue. Significantly, apoptotic cells modify their chromatin so as to bind HMGB1, which is not released. Several cell types (in particular inflammatory cells) when distressed have the ability to secrete HMGB1 actively, via a dedicated pathway, and thus produce a damage signal without dying. Because of its powerful activities, HMGB1 is involved in several disorders, including autoimmune ones.

The HMGB1 acidic tail regulates HMGB1 DNA binding specificity by a unique mechanism

HMGB1 is a conserved chromosomal protein composed of two DNA-binding domains and an acidic C-terminal tail. There were evidences suggesting that the C-terminal tail contributed to the DNA binding specificity of the N-terminal DNA-binding domains. However, the mechanism underlining this observation is largely unknown. Our data first confirmed the previous study with NMR that showed a direct interaction between HMGB1's C-terminal tail and its N-terminal domains. We further demonstrated that this interaction can be competed more efficiently by a DNA with four-way junction structure than by a linear double-stranded DNA. Mutations within the N-terminal region, that disrupt its binding to the C-terminal tail, abolished HMGB1's ability to distinguish the linear DNA and the four-way junction DNA. Those data suggested a unique mechanism designed by nature that utilizes a protein's negatively charged C-terminal tail to enhance its DNA-binding domain's specificity to certain structured DNAs.

RAGE activation by S100P in colon cancer stimulates growth, migration, and cell signaling pathways

PURPOSE

Colon cancer is the third most prevalent cancer in the United States. However, the molecular mechanisms involved in the development and progression of colon cancer are incompletely understood. This study was initiated to explore the potential role of the receptor for advanced glycation end-products and S100P in modulation of key properties of human colon cancer cells.

METHODS

Western blot, reverse transcription-polymerase chain reaction, and quantitative polymerase chain reaction were performed for detection of the receptor for advanced glycation end-products and S100P in colon cancer and matched normal colon. The influence of exogenously added S100P was analyzed on SW480 colon cancer cell line proliferation, migration, phosphorylation of mitogen activated protein kinases, and NFkappaB activation. To identify the mechanisms involved in these responses, coimmunoprecipitation examining the S100P/Receptor for advanced glycation end-products interaction and the effects of receptor for advanced glycation end-products inhibition in this interaction were analyzed.

RESULTS

Although the receptor for advanced glycation end-products was present in normal and malignant colon specimens, only the malignant specimens expressed S100P. Treatment of SW480 cells with S100P increased proliferation and cell migration. Addition of exogenous S100P stimulated both ERK1/2 phosphorylation and NFkappaB activity. The interaction between S100P and the receptor for advanced glycation end-products was demonstrated by coimmunoprecipitation of these molecules from SW480 cells. Antagonism of the receptor for advanced glycation end-products blocked this interaction and the biologic effects of S100P on these cells.

CONCLUSIONS

These data indicate that S100P is expressed at greater levels in colon cancer than matched normal tissue and that S100P stimulates colon cancer cell growth, migration, Erk phosphorylation, and NFkappaB activation in vitro, suggesting that this ligand/receptor pair may be targeted for the development of new therapies.

Endogenous signals released from necrotic cells augment inflammatory responses to bacterial endotoxin

Stressed cells undergoing necrosis release molecules that acts as endogenous danger signals to alert and activate innate immune cells. Both HMGB1 and HSP70 are induced in activated monocytes/macrophages and also are released from stressed or injured cells. We investigated whether HMGB1 and HSP70 released from necrotic monocytes/macrophages, can act as danger signals to mediate proinflammatory cytokine responses to bacterial endotoxin or lipopolysaccharide (LPS). We show that cell lysate, obtained from necrotic cells directly stimulates the proinflammatory cytokine and chemokine responses in human monocyte/macrophage cell line, THP-1, as revealed by the induction of TNF-alpha, IL-6 and IL-8 mRNA expression and protein production. In the presence of LPS, necrotic cell lysate induced a more robust increase in all three proteins. We found that HMGB1 and HSP70 were indeed present in the necrotic cell lysate and were responsible for the significant induction of the proinflammatory cytokine expression, as neutralization with antibodies against both proteins blocked the increase in the cytokine production seen after incubating LPS-stimulated cells with the necrotic cell lysate. We also found that the newly identified triggering receptor expressed on myeloid cells-1 (TREM-1) was involved in mediating the HMGB1- and HSP70-induced cytokine production. Blocking TREM-1 on THP-1 cells with a recombinant chimera prevented the increase in cytokine production, while simultaneous blocking of TLR4 and TREM-1 completely abolished the proinflammatory response, suggesting that TREM-1 synergizes with TLR4 to mediate the effects of such signals from necrotic cells. In addition, blocking HMGB1 or HSP70 simultaneously with TREM-1 did not decrease the cytokine level further, confirming the involvement of TREM-1 in mediating the effect of HMGB1 and HSP70. Although the interaction of HMGB1 and HSP70 with TREM-1 induced I kappa B alpha and p38 expression, both of which are required for the inflammatory cytokine expression, blockade of TREM-1 did not affect I kappa B alpha expression but markedly reduced p38 activation, as revealed by Western blot analysis. Together, these results demonstrate that HMGB1 and HSP70 released from necrotic cells function as endogenous danger signals to augment the proinflammatory responses in monocytes/macrophage and that TREM-1 relays such signals to the cytokine expression cascade. This mechanism may contribute to the amplification and persistence of the inflammatory response to bacterial infection.

Endogenous secretory receptor for advanced glycation endproducts as a novel prognostic marker in chondrosarcoma

BACKGROUND

Chondrosarcoma, the second most frequent primary malignant bone tumor, is classified into 3 grades according to histologic criteria of malignancy. However, a low-grade lesion can be difficult to distinguish from a benign enchondroma, whereas some histologically low-grade lesions may carry a poor prognosis. The receptor for advanced glycation endproducts (RAGE) and its ligand, high-mobility group box-1 (HMGB1), was quantified in enchondromas and chondrosarcomas to determine whether these markers were associated with histological malignancy and prognosis.

METHODS

Enchondromas (n = 20) and typical chondrosarcomas (n = 39) were evaluated for RAGE, endogenous secretory RAGE (esRAGE, a splice variant form), and HMGB1 protein expression by immunohistochemistry including laser confocal microscopy. The content of esRAGE in resected specimens was measured with an enzyme-linked immunosorbent assay. Associations of these molecules with histology and clinical behavior of tumors were analyzed.

RESULTS

Expression of esRAGE and HMGB1 was observed in all specimens. The numbers of cells positive for esRAGE and HMGB1 expression were positively associated with histologic grade. Expression of esRAGE was significantly higher in chondrosarcomas than in enchondromas (P < .001). Tissue esRAGE content was also significantly higher in grade 1 and 2 chondrosarcomas than enchondromas (P = .0255 and P = .008, respectively). High expression of esRAGE in grade 1 chondrosarcoma was associated with subsequent recurrence (P = .0013), lung metastasis (P = .0071), and poor survival (P < .001).

CONCLUSIONS

Assessment of esRAGE expression should aid in diagnostic and prognostic determinations in chondrosarcoma.

The anti-inflammatory effects of heat shock protein 72 involve inhibition of high-mobility-group box 1 release and proinflammatory function in macrophages

High-mobility-group box 1 (HMGB1), a nuclear protein, has recently been identified as an important mediator of local and systemic inflammatory diseases when released into the extracellular milieu. Anti-inflammatory regulation by the stress response is an effective autoprotective mechanism when the host encounters harmful stimuli, but the mechanism of action remains incompletely delineated. In this study, we demonstrate that increases in levels of a major stress-inducible protein, heat shock protein 72 (Hsp72) by gene transfection attenuated LPS- or TNF-alpha-induced HMGB1 cytoplasmic translocation and release. The mechanisms involved inhibition of the chromosome region maintenance 1 (CRM1)-dependent nuclear export pathway. Overexpression of Hsp72 inhibited CRM1 translocation and interaction between HMGB1 and CRM1 in macrophages post-LPS and TNF-alpha treatment. In addition, overexpression of Hsp72 strongly inhibited HMGB1-induced cytokine (TNF-alpha, IL-1beta) expression and release, which correlated closely with: 1) inhibition of the MAP kinases (p38, JNK, and ERK); and 2) inhibition of the NF-kappaB pathway. Taken together, these experiments suggest that the anti-inflammatory activity of Hsp72 is achieved by interfering with both the release and proinflammatory function of HMGB1. Our experimental data provide important insights into the anti-inflammatory mechanisms of heat shock protein protection.

Anti-high mobility group box 1 monoclonal antibody ameliorates brain infarction induced by transient ischemia in rats

The high mobility group box-1 (HMGB1), originally identified as an architectural nuclear protein, exhibits an inflammatory cytokine-like activity in the extracellular space. Here we show that treatment with neutralizing anti-HMGB1 monoclonal antibody (mAb; 200 microg, twice) remarkably ameliorated brain infarction induced by 2-h occlusion of the middle cerebral artery in rats, even when the mAb was administered after the start of reperfusion. Consistent with the 90% reduction in infarct size, the accompanying neurological deficits in locomotor function were significantly improved. Anti-HMGB1 mAb inhibited the increased permeability of the blood-brain barrier, the activation of microglia, the expression of TNF-alpha and iNOS, and suppressed the activity of MMP-9, whereas it had little effect on blood flow. Intracerebroventricular injection of HMGB1 increased the severity of infarction. Immunohistochemical study revealed that HMGB1 immunoreactivity in the cell nuclei decreased or disappeared in the affected areas, suggesting the release of HMGB1 into the extracellular space. These results indicate that HMGB1 plays a critical role in the development of brain infarction through the amplification of plural inflammatory responses in the ischemic region and could be an outstandingly suitable target for the treatment. Intravenous injection of neutralizing anti-HMGB1 mAb provides a novel therapeutic strategy for ischemic stroke.

The novel inflammatory cytokine high mobility group box protein 1 (HMGB1) is expressed by human term placenta

High mobility group box protein 1 (HMGB1) was previously considered a strict nuclear protein, but lately data are accumulating on its extranuclear functions. In addition to its potent proinflammatory capacities, HMGB1 has a prominent role in a number of processes of specific interest for the placenta. Our overall aim was to investigate the expression of HMGB1 in human term placenta and elucidate a potential difference in HMGB1 expression comparing vaginal deliveries with elective Caesarean sections. In addition, placentas from normal pregnancies were compared with placentas from pregnancies complicated by pre-eclampsia. Twenty-five placentas, 12 from normal term pregnancies and 13 from pregnancies complicated by pre-eclampsia were analysed with immunohistochemistry for HMGB1 and its putative receptors; receptor for advanced glycation end-products (RAGE), Toll-like receptor 2 (TLR2) and TLR4. We present the novel finding that in addition to a strong nuclear HMGB1 expression in almost all cells in investigated placentas, an individual variation of cytoplasmic HMGB1 expression was detected in the syncytiotrophoblast covering the peripheral chorionic villi, by cells in the decidua and in amnion. Production of HMGB1 was confirmed by in situ hybridization. Although labour can be described as a controlled inflammatory-like process no differences in HMGB1 expression could be observed comparing active labour and elective Caesarean sections. However, a tendency towards a higher expression of cytoplasmic HMGB1 in the decidua from women with pre-eclampsia was demonstrated. The abundant expression of the receptors RAGE, TLR2 and TLR4 implicates a local capability to respond to HMGB1, although the precise role in the placenta remains to be elucidated.

Receptor for advanced glycation end products (RAGE) is important in the prediction of recurrence in human oral squamous cell carcinoma

AIMS

Receptor for advanced glycation end products (RAGE) has recently been recognized as a cancer-associated protein responsible for cancer progression and metastasis in gastrointestinal cancers. The aim was to examine the role of RAGE in oral squamous cell carcinoma (OSCC).

METHODS AND RESULTS

RAGE expression was examined by immunohistochemistry in 74 OSCC patients and evaluated with a grading based on Allred's score. RAGE expression was compared with clinicopathological parameters including clinical stage, invasive depth, nodal metastasis, disease recurrence and disease-free survival. High-grade expression of RAGE (RAGE-H) was observed in 30 (40.5%) of 74 OSCCs. RAGE-H was associated with depth of invasion (P < 0.0001) and local recurrence (P < 0.0001), but not with histological differentiation, clinical stage or nodal metastasis. Disease-free survival in patients with RAGE-H was significantly worse than in those with low-level RAGE expression. Multivariate analysis showed RAGE-H to be an independent prognostic factor for disease-free survival in OSCC patients (P = 0.0022).

CONCLUSION

RAGE is a relevant factor in predicting disease recurrence and patients' prognosis in OSCC.

Activation of poly(ADP)-ribose polymerase (PARP-1) induces release of the pro-inflammatory mediator HMGB1 from the nucleus

Necrotic cells release inflammatory mediators that activate cytokine production from innate immune cells. One mediator of this activation is high mobility group box 1 protein (HMGB1). HMGB1 is normally a chromatin-associated protein and is sequestered at condensed chromatin during apoptosis. How it is released from chromatin during necrotic cell death is not known. Here we show that after DNA-alkylating damage, the activation of poly(ADP)-ribose polymerase (PARP) regulates the translocation of HMGB1 from the nucleus to the cytosol. This displaced HMGB1 is subject to release if the cell then loses plasma membrane integrity as a result of necrosis. Both full-length HMGB1 and a truncated form of HMGB1 lacking the highly conserved glutamate-rich C-terminal tail can induce macrophage activation and tumor necrosis factor-alpha production. However, displacement of HMGB1 from the nucleus following PARP activation requires the presence of the glutamate-rich C-terminal tail. Although the C-terminal tail is not the sole substrate for PARP modification of HMGB1, it appears to be required to destabilize HMGB1 association with chromatin following PARP-dependent chromatin modifications. These data suggest that PARP-dependent nuclear-to-cytosolic translocation of HMGB1 serves to establish the ability of cells to release this potent inflammatory mediator upon subsequent necrotic death.

Hemorrhagic shock induces NAD(P)H oxidase activation in neutrophils: role of HMGB1-TLR4 signaling

Hemorrhagic shock/resuscitation (HS/R)-induced generation of reactive oxygen species (ROS) plays an important role in posthemorrhage inflammation and tissue injury. We have recently reported that HS/R-activated neutrophils (PMN), through release of ROS, serve an important signaling function in mediating alveolar macrophage priming and lung inflammation. PMN NAD(P)H oxidase has been thought to be an important source of ROS following HS/R. TLR4 sits at the interface of microbial and sterile inflammation by mediating responses to both bacterial endotoxin and multiple endogenous ligands, including high-mobility group box 1 (HMGB1). Recent studies have implicated HMGB1 as an early mediator of inflammation after HS/R and organ ischemia/reperfusion. In the present study, we tested the hypothesis that HS/R activates NAD(P)H oxidase in PMN through HMGB1/TLR4 signaling. We demonstrated that HS/R induced PMN NAD(P)H oxidase activation, in the form of phosphorylation of p47phox subunit of NAD(P)H oxidase, in wild-type mice; this induction was significantly diminished in TLR4-mutant C3H/HeJ mice. HMGB1 levels in lungs, liver, and serum were increased as early as 2 h after HS/R. Neutralizing Ab to HMGB1 prevented HS/R-induced phosphorylation of p47phox in PMN. In addition, in vitro stimulation of PMN with recombinant HMGB1 caused TLR4-dependent activation of NAD(P)H oxidase as well as increased ROS production through both MyD88-IRAK4-p38 MAPK and MyD88-IRAK4-Akt signaling pathways. Thus, PMN NAD(P)H oxidase activation, induced by HS/R and as mediated by HMGB1/TLR4 signaling, is an important mechanism responsible for PMN-mediated inflammation and organ injury after hemorrhage.

The extracellular region of the receptor for advanced glycation end products is composed of two independent structural units

The receptor for advanced glycation end products (RAGE) is an important cell surface receptor being pursued as a therapeutic target because it has been implicated in complications arising from diabetes and chronic inflammatory conditions. RAGE is a single membrane spanning receptor containing a very small approximately 40 residue cytosolic domain and a large extracellular region composed of 3 Ig-like domains. In this study, high level bacterial expression systems and purification protocols were generated for the extracellular region of RAGE (sRAGE) and the five permutations of single and tandem domain constructs to enable biophysical and structural characterization of its tertiary and quaternary structure. The structure and stability of each of these six protein constructs was assayed by biochemical methods including limited proteolysis, dynamic light scattering, CD, and NMR. A homology model of sRAGE was constructed to aid in the interpretation of the experimental data. Our results show that the V and C1 domains are not independent domains, but rather form an integrated structural unit. In contrast, C2 is attached to VC1 by a flexible linker and is fully independent. The interaction with a known RAGE ligand, Ca2+-S100B, was mapped to VC1, with the major contribution from the V domain but clearly defined secondary effects from the C1 domain. The implications of these results are discussed with respect to models for RAGE signaling.

Antibodies against RAGE in sepsis and inflammation: implications for therapy

Many agents have been tried in the hope of providing clinical benefit in sepsis and inflammatory processes. The receptor for advanced glycation end products (RAGE) is involved in inflammation and sepsis, and anti-RAGE antibodies have been studied in models of diabetic complications, chronic inflammation and sepsis. Several characteristics of RAGE make anti-RAGE antibody an attractive treatment possibility. The pathophysiology of sepsis and inflammation is incompletely understood. The complicated nature of these processes may make new techniques, such as computer simulation and genomics, vital in understanding how to target therapies.

Glycotoxins in the diet promote diabetes and diabetic complications

Oxidant stress underlies diabetes and diabetic complications, including cardiovascular, renal, and retinal disease. Advanced glycation end products (AGEs), or glycotoxins, are a significant contributor to oxidant stress in diabetes. The diet is a major, unrecognized source of AGEs. Importantly, reduction of dietary AGEs decreases circulating inflammatory markers in both diabetic patients and prediabetic patients and complications in animal models. This beneficial outcome requires only a 50% decrease in dietary AGEs, making this necessary intervention practical and inexpensive.

High-mobility group box 1 protein plasma concentrations during septic shock

OBJECTIVE

To investigate plasma high-mobility group box 1 protein (HMGB1) concentration and its relationship with organ dysfunction and outcome in septic shock patients.

DESIGN AND SETTING

Prospective, noninterventional study. Medical adult intensive care unit at a university hospital in France.

PATIENTS

42 critically ill patients with septic shock.

METHODS

Arterial blood was drawn within 12 h of admission for the measurement of plasma HMGB1 concentration by ELISA. Repeated sampling was performed on days 3, 7, and 14.

RESULTS

Median HMGB1 concentration was 4.4 ng/ml (IQR 1.2-12.5) at admission, with no difference between survivors and nonsurvivors. A positive correlation was observed between HMGB1 and SOFA score and lactate, and procalcitonin concentrations. There was a progressive but statistically nonsignificant decline in HMGB1 concentration among the survivors, while nonsurvivors showed an increase in HMGB1 level between days 1 and 3. SOFA score and lactate and procalcitonin concentrations did not vary significantly between days 1 and 3. When measured on day 3, HMGB1 discriminated survivors from nonsurvivors with 66% sensitivity and 67% specificity, and concentration greater than 4 ng/ml was associated with an odds ratio of death of 5.5 (95% CI 1.3-23.6).

Receptor for advanced glycation end products (RAGE) in a dash to the rescue: inflammatory signals gone awry in the primal response to stress

The multiligand receptor for advanced glycation end products (RAGE) of the Ig superfamily transduces the biological impact of discrete families of ligands, including advanced glycation end products, certain members of the S100/calgranulin family, high mobility group box-1, Mac-1 (alpha(M)beta(2), CD11b/CD18), and amyloid-beta peptide and beta-sheet fibrils. Although structurally dissimilar, at least at the monomeric level, recent evidence suggests that oligomeric forms of these RAGE ligands may be especially apt to activate the receptor and up-regulate a program of inflammatory and tissue injury-provoking genes. The challenge in probing the biology of RAGE and its impact in acute responses to stress and the potential development of chronic disease is to draw the line between mechanisms that evoke repair versus those that sustain inflammation and tissue damage. In this review, we suggest the concept that the ligands of RAGE comprise a primal program in the acute response to stress. When up-regulated in environments laden with oxidative stress, inflammation, innate aging, or high glucose, as examples, the function of these ligand families may be transformed from ones linked to rapid repair to those that drive chronic disease. Identification of the threshold beyond which ligands of RAGE mediate repair versus injury is a central component in delineating optimal strategies to target RAGE in the clinic.

Masquerader: High Mobility Group Box-1 and Cancer

Since its identification a third of a century ago, the high-mobility group box-1 (HMGB1) protein has been linked to varied diverse cellular processes, including release from necrotic cells and secretion by activated macrophages engulfing apoptotic cells. Initially described as solely chromatin-associated, HMGB1 was additionally discovered in the cytoplasm of several types of cultured mammalian cells 6 years later. In addition to its intracellular role, HMGB1 has been identified extracellularly as a putative leaderless cytokine and differentiation factor. In the years since its discovery, HMGB1 has also been implicated in disease states, including Alzheimer's, sepsis, ischemia-reperfusion, arthritis, and cancer. In cancer, overexpression of HMGB1, particularly in conjunction with its receptor for advanced glycation end products, has been associated with the proliferation and metastasis of many tumor types, including breast, colon, melanoma, and others. This review focuses on current knowledge and speculation on the role of HMGB1 in the development of cancer, metastasis, and potential targets for therapy.

Hypoxia-mediated induction of heme oxygenase type I and carbon monoxide release from astrocytes protects nearby cerebral neurons from hypoxia-mediated apoptosis

To study a putative paracellular protective mechanism of astrocytes for neurons, immunohistochemical analysis was performed in ischemic rat brain, which colocalized with the expression of heme oxygase-1 (HO- 1) in astroglias surrounding dying TUNEL-positive neurons. As an in vitro paradigm for ischemia, cultured astrocytes were exposed to normobaric hypoxia (pO(2) asymptotically equal to 10 torr), which triggered marked increase in the expression of a 33 kDa stress protein, identified as HO-1. Induction of HO-1 message was observed within 4 h of hypoxia and peaked at 12 h, accompanied by an accelerated transcription of HO-1 message. Consistent with the induction of HO-1, a platelet bioassay revealed production of carbon monoxide by reoxygenated astrocytes. The presence of CO in the medium decelerated the hypoxia-mediated apoptotic type of cell death in cultured cerebral neurons via lowering the activity of caspase-3, a key enzyme regulating apoptotic cell death. This protection against apoptosis was likely mediated by CO-mediated increases in intracellular cGMP, because exposure of hypoxic neurons to CO increased intracellular cGMP levels, and addition of cGMP analogue to hypoxic neuronal cultures suppressed caspase-3 activity and promoted neuronal survival. These data describe a potentially important paracellular pathway through which astrocytes may rescue nearby neurons from ischemic death.

Toll-like receptor 9-dependent activation by DNA-containing immune complexes is mediated by HMGB1 and RAGE

Increased concentrations of DNA-containing immune complexes in the serum are associated with systemic autoimmune diseases such as lupus. Stimulation of Toll-like receptor 9 (TLR9) by DNA is important in the activation of plasmacytoid dendritic cells and B cells. Here we show that HMGB1, a nuclear DNA-binding protein released from necrotic cells, was an essential component of DNA-containing immune complexes that stimulated cytokine production through a TLR9-MyD88 pathway involving the multivalent receptor RAGE. Moreover, binding of HMGB1 to class A CpG oligodeoxynucleotides considerably augmented cytokine production by means of TLR9 and RAGE. Our data demonstrate a mechanism by which HMGB1 and RAGE activate plasmacytoid dendritic cells and B cells in response to DNA and contribute to autoimmune pathogenesis.

Lung level of HMBG1 is elevated in response to advanced glycation end product-enriched foodin vivo

High mobility group box protein 1 (HMGB1) is a ubiquitous nuclear protein that can be actively released from the cell in certain conditions thereby mediating cytokine-like function. While nuclear HMGB1 modulates the transcriptional activity of cells, extracellular HMGB1 partially acts via binding to the receptor for advanced glycation end products (RAGE), which is highly expressed in lung tissue. Therefore, we studied the impact of food-derived advanced glycation end products (AGEs), the Maillard reaction products, on the lung expression of HMGB1. Feeding rats with AGE-rich diet, containing either bread crust or coffee beverage, resulted in an upregulation of HMGB1 mRNA and protein especially in those animals receiving bread crust diet. The expression of RAGE was not influenced. Moreover, we revealed a positive correlation between an increased lung AGE level and HMGB1 protein expression in both animal groups receiving either bread crust or coffee extract but not in the control group. In contrast, the ageing-related AGE accumulation was not associated with an increased level of HMGB1 protein in lung tissue from senescent (100 wk) compared to young-adult (24 wk) rats. Our data suggest a physiological role of food- but not ageing-associated AGEs in the regulation of the HMGB1 expression in lung.

HBV pathogenesis in animal models: recent advances on the role of platelets

Hepatitis B virus (HBV) causes acute and chronic necroinflammatory liver diseases and hepatocellular carcinoma (HCC). HBV replicates noncytopathically in the hepatocyte, and most of the liver injury associated with this infection reflects the immune response. While the innate immune response may not contribute significantly to the pathogenesis of liver disease or viral clearance, the adaptive immune response, particularly the cytotoxic T lymphocyte (CTL) response, contributes to both. Recent observations also reveal that antigen-nonspecific inflammatory cells enhance CTL-induced liver pathology and, more surprisingly, that platelets facilitate the intrahepatic accumulation of CTLs, suggesting that the host response to HBV infection is a highly complex but coordinated process. The notion that platelets contribute to liver disease and viral clearance by promoting the recruitment of virus-specific CTLs into the liver is a new concept in viral pathogenesis, which may prove useful to implement treatments of chronic HBV infection in man.

Extracellular hmgb1 functions as an innate immune-mediator implicated in murine cardiac allograft acute rejection

Hmgb1, an evolutionarily conserved chromosomal protein, was recently re-discovered to be an innate immune-mediator contributing to both innate and adaptive immune responses. Here, we show a pivotal role for Hmgb1 in acute allograft rejection in a murine cardiac transplantation model. Extracellular Hmgb1 was found to be a potent stimulator for adaptive immune responses. Hmgb1 can be either passively released from damaged cells after organ harvest and ischemia/reperfusion insults, or actively secreted by allograft infiltrated immune cells. After transplantation, allografts show a significant temporal up-regulation of Hmgb1 expression accompanied by inflammatory infiltration, a consequence of graft destruction. These data suggest the involvement of Hmgb1 in acute allograft rejection. In line with these observations, treatment of recipients with rA-box, a specific blockade for endogenous Hmgb1, significantly prolonged cardiac allograft survival as compared to those recipients treated with either rGST or control vehicle. The enhanced graft survival is associated with reduced allograft expression of TNFalpha, IFNgamma and Hmgb1 and impaired Th1 immune response.

Developmental expression of the receptor for advanced glycation end-products (RAGE) and its response to hyperoxia in the neonatal rat lung

Background

The receptor for advanced glycation end products (mRAGE) is associated with pathology in most tissues, while its soluble form (sRAGE) acts as a decoy receptor. The adult lung is unique in that it expresses high amounts of RAGE under normal conditions while other tissues express low amounts normally and up-regulate RAGE during pathologic processes. We sought to determine the regulation of the soluble and membrane isoforms of RAGE in the developing lung, and its expression under hyperoxic conditions in the neonatal lung.

Results

Fetal (E19), term, 4 day, 8 day and adult rat lung protein and mRNA were analyzed, as well as lungs from neonatal (0–24 hrs) 2 day and 8 day hyperoxic (95% O₂) exposed animals. mRAGE transcripts in the adult rat lung were 23% greater than in neonatal (0–24 hrs) lungs. On the protein level, rat adult mRAGE expression was 2.2-fold higher relative to neonatal mRAGE expression, and adult sRAGE protein expression was 2-fold higher compared to neonatal sRAGE. Fetal, term, 4 day and 8 day old rats had a steady increase in both membrane and sRAGE protein expression evaluated by Western Blot and immunohistochemistry. Newborn rats exposed to chronic hyperoxia showed significantly decreased total RAGE expression compared to room air controls.

Conclusion

Taken together, these data show that rat pulmonary RAGE expression increases with age beginning from birth, and interestingly, this increase is counteracted under hyperoxic conditions. These results support the emerging concept that RAGE plays a novel and homeostatic role in lung physiology.

Mechanisms of Disease: the role of high-mobility group protein 1 in the pathogenesis of inflammatory arthritis

High-mobility group protein 1 (HMG1) is a nonhistone nuclear protein that is a prototype of a dual-function alarmin whose immune activity is dependent upon its cellular location. Inside the cell, HMG1 binds to DNA and has a role in transcriptional regulation. Outside the cell, HMG1 acts as a cytokine and has activities that resemble those of tumor necrosis factor. The cytokine activities of HMG1 become manifest when this protein translocates from the nucleus to the cytoplasm and, eventually, into the external milieu; this translocation occurs during cell activation and cell death. Given its cytokine activity, HMG1 has been implicated in the pathogenesis of a broad range of immune-mediated diseases including arthritis. The role for this protein in arthritis was established by observations of the expression of HMG1 in synovial tissue of patients with rheumatoid arthritis as well as in the joints of animals used to model arthritis. Furthermore, in the mouse model of collagen-induced arthritis, treatment with antibodies to HMG1 or to an inhibitory domain of HMG1 can attenuate joint inflammation and damage. These studies identify a novel pathway in the pathogenesis of inflammatory arthritis, as well as a new target for biologic therapy.