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

Involvement of Toll-like Receptors 2 and 4 in Cellular Activation by High Mobility Group Box 1 Protein

High mobility group box 1 (HMGB1) protein, originally described as a DNA-binding protein that stabilizes nucleosomes and facilitates transcription, can also be released extracellularly during acute inflammatory responses. Exposure of neutrophils, monocytes, or macrophages to HMGB1 results in increased nuclear translocation of NF-kappaB and enhanced expression of proinflammatory cytokines. Although the receptor for advanced glycation end products (RAGE) has been shown to interact with HMGB1, other putative HMGB1 receptors are known to exist but have not been characterized. In the present experiments, we explored the role of RAGE, Toll-like receptor (TLR) 2, and TLR 4, as well as associated kinases, in HMGB1-induced cellular activation. Culture of neutrophils or macrophages with HMGB1 produced activation of NF-kappaB through TLR 4-independent mechanisms. Unlike lipopolysaccharide (LPS), which primarily increased the activity of IKKbeta, HMGB1 exposure resulted in activation of both IKKalpha and IKKbeta. Kinases and scaffolding proteins downstream of TLR 2 and TLR 4, but not TLR/interleukin-1 receptor (IL-1R)-independent kinases such as tumor necrosis factor receptor-associated factor 2, were involved in the enhancement of NF-kappaB-dependent transcription by HMGB1. Transfections with dominant negative constructs demonstrated that TLR 2 and TLR 4 were both involved in HMGB1-induced activation of NF-kappaB. In contrast, RAGE played only a minor role in macrophage activation by HMGB1. Interactions of HMGB1 with TLR 2 and TLR 4 may provide an explanation for the ability of HMGB1 to generate inflammatory responses that are similar to those initiated by LPS.

Extracellular HMGB1, a signal of tissue damage, induces mesoangioblast migration and proliferation

High mobility group box 1 (HMGB1) is an abundant chromatin protein that acts as a cytokine when released in the extracellular milieu by necrotic and inflammatory cells. Here, we show that extracellular HMGB1 and its receptor for advanced glycation end products (RAGE) induce both migration and proliferation of vessel-associated stem cells (mesoangioblasts), and thus may play a role in muscle tissue regeneration. In vitro, HMGB1 induces migration and proliferation of both adult and embryonic mesoangioblasts, and disrupts the barrier function of endothelial monolayers. In living mice, mesoangioblasts injected into the femoral artery migrate close to HMGB1-loaded heparin-Sepharose beads implanted in healthy muscle, but are unresponsive to control beads. Interestingly, alpha-sarcoglycan null dystrophic muscle contains elevated levels of HMGB1; however, mesoangioblasts migrate into dystrophic muscle even if their RAGE receptor is disabled. This implies that the HMGB1-RAGE interaction is sufficient, but not necessary, for mesoangioblast homing; a different pathway might coexist. Although the role of endogenous HMGB1 in the reconstruction of dystrophic muscle remains to be clarified, injected HMGB1 may be used to promote tissue regeneration.

[Role of the innate immune response in sepsis]

The innate immune system succeeds against the majority of infections before the adaptive immune system is activated. New findings contribute to a better understanding of the pathophysiology of sepsis and lead to the development of new therapeutic strategies. The innate immune system, being responsible for the first response to infections, can trigger adaptive immune responses in case the initial response is ineffective. Both arms of the immune system interact with each other, mainly via cell-cell-interactions but also by soluble factors, such as cytokines and chemokines. Two sub-populations of helper T-cells direct both balanced activation and inhibition of the two arms of the immune systems using specific patterns of cytokine release. Results obtained in new animal models of sepsis, taking a progressive growth of bacteria into account, have implied that existing knowledge has to be reanalyzed. The idea of sepsis as a mere "over-reaction to inflammation" has to be abandoned. Various so-called pattern recognition receptors (e.g. toll-like receptors, TLRs, NOD proteins) are located intracellularly or in the plasma membrane of innate immune cells and recognize certain patterns expressed exclusively by extracellular pathogens. Upon receptor engagement, intracellular signaling pathways lead to cellular activation, followed by release of various cytokines and anti-microbial substances. During the course of sepsis a cytokine shift towards increasing immune suppression occurs. The innate immune system also contributes to the migration of leukocytes in inflammed tissue, involving chemokines and adhesion molecules. Leukocytes also secrete the tissue factor leading to formation of thrombin. The environment in sepsis can cause disseminated intravascular coagulation (DIC), but at the same time thrombin triggers the release of chemokines and adhesion molecules through endothelial cells, which represents a positive feedback mechanism for innate immune responses. New therapeutic strategies for sepsis try to establish a well-balanced immune response. Intervention is accomplished through inhibition of inflammatory cytokines, their receptors or through activation of immunostimulatory responses.

S100B causes apoptosis in a myoblast cell line in a RAGE-independent manner

S100B, a Ca(2+)-modulated protein with both intracellular and extracellular regulatory roles, is most abundant in astrocytes, is expressed in various amounts in several non-nervous cells and is also found in normal serum. Astrocytes secrete S100B, and extracellular S100B exerts trophic and toxic effects on neurons depending on its concentration, in part by interacting with the receptor for advanced glycation end products (RAGE). The presence of S100B in normal serum and elevation of its serum concentration in several non-nervous pathological conditions suggest that S100B-expressing cells outside the brain might release the protein and S100B might affect non-nervous cells. Recently we reported that at picomolar to nanomolar doses S100B inhibits rat L6 myoblast differentiation via inactivation of p38 kinase in a RAGE-independent manner. We show here that at >or=5 nM in the absence of and at >100 nM in the presence of serum S100B causes myoblast apoptosis via stimulation of reactive oxygen species (ROS) production and inhibition of the pro-survival kinase, extracellular signal-regulated kinase (ERK)1/2, again in a RAGE-independent manner. Together with our previous data, the present results suggest that S100B might participate in the regulation of muscle development and regeneration by two independent mechanism, i.e., by inhibiting crucial steps of the myogenic program at the physiological levels found in serum and by causing elevation of ROS production and myoblast apoptosis following accumulation in serum and/or muscle extracellular space. Our data also suggest that RAGE has no role in the transduction of S100B effects on myoblasts, implying that S100B can interact with more than one receptor to affect its target cells.

Blockade of receptor for advanced glycation endproducts: a new target for therapeutic intervention in diabetic complications and inflammatory disorders

The glycation and oxidation of proteins/lipids leads to the generation of a new class of biologically active moieties, the advanced glycation endproducts (AGEs). Recent studies have elucidated that carboxymethyllysine (CML) adducts of proteins/lipids are a highly prevalent AGE in vivo. CML-modified adducts are signal transduction ligands of the receptor for AGE (RAGE), a member of the immunoglobulin superfamily. Importantly, CML-modified adducts accumulate in diverse settings. In addition to enhanced formation in settings of high glucose, these adducts form in inflammatory milieu. Studies performed both in vitro and in vivo have suggested that the proinflammatory/tissue destructive consequences of RAGE activation in the diabetic/inflamed environment may be markedly attenuated by blockade of the ligand-RAGE axis. Here, we will summarize the known consequences of RAGE activation in the tissues and highlight novel areas for therapeutic intervention in these disease states.

Molecular characterization of the canine HMGB1

Due to the close similarities of numerous canine diseases to their human counterparts, the dog could join the mouse as the species of choice to unravel the genetic background of complex diseases as e.g. cancer and metabolic diseases. Accordingly, the role of the dog as a model for therapeutic approaches is strongly increasing. However, prerequisite for such studies is the characterization of the corresponding canine genes. Recently, the human high mobility group protein B1 (HMGB1) has attracted considerable interest of oncologists because of what is called its "double life". Besides its function as an architectural transcription factor HMGB1 can also be secreted by certain cells and then acts as a ligand for the receptor for advanced glycation end products (RAGE). The binding of HMGB1 to RAGE can activate key cell signaling pathways, such as p38(MAPK), JNK, and p42/p44(MAPK) emphasizing the important role of HMGB1 in inflammation and tumor metastasis. These results make HMGB1 a very interesting target for therapeutic studies done in model organisms like the dog. In this study we characterized the molecular structure of the canine HMGB1 gene on genomic and cDNA levels, its predicted protein, the gene locus and a basic expression pattern.

High mobility group 1 B-box mediates activation of human endothelium

OBJECTIVES

Severe sepsis and septic shock is a consequence of a generalized inflammatory systemic response because of an invasive infection that may result in acute organ dysfunction. Mortality is high despite access to modern intensive care units. The nuclear DNA binding protein high mobility group 1 (HMGB1) protein has recently been suggested to act as a late mediator of septic shock via its function as a macrophage-derived pro-inflammatory cytokine (J Exp Med 2000; 192: 565, Science1999; 285: 248). We investigated the pro-inflammatory activities of the A-box and the B-box of HMGB1 on human umbilical venular endothelial cells (HUVEC).

DESIGN

The HUVEC obtained from healthy donors were used for experiments. Recombinant human full-length HMGB1, A-box and B-box were cloned by polymerase chain reaction (PCR) amplification from a human brain quick-clone cDNA. The activation of HUVEC was studied regarding (i) upregulation of adhesion molecules, (ii) the release of cytokines and chemokines, (iii) the adhesion of neutrophils to HUVEC, (iv) the activation of signalling transduction pathways and (v) the involvement of the receptor for advanced glycation end-products (RAGE).

RESULTS

The full-length protein and the B-box of HMGB1 dose-dependently activate HUVEC to upregulate adhesion molecules such as ICAM-1, VCAM-1 and E-selectin and to release IL-8 and G-CSF. The activation of HUVEC could be inhibited to 50% by antibodies directed towards the RAGE. HMGB1-mediated HUVEC stimulation resulted in phosphorylation of the ELK-1 signal transduction protein and a nuclear translocation of p65 plus c-Rel, suggesting that HMGB1 signalling is regulated in endothelial cells through NF-kappaB.

CONCLUSIONS

The HMGB1 acts as a potent pro-inflammatory cytokine on HUVEC and the activity is mainly mediated through the B-box of the protein. HMGB1 may be a key factor mediating part of the pro-inflammatory response occurring in septic shock and severe inflammation.

Physiological significance of apoptosis during animal virus infection

Apoptosis has been considered to be a host defense mechanism against viral infection in multicellular organisms. This is based on the findings that apoptogenic mutants of insect viruses cannot grow because infected host cells die by apoptosis. This suggests that the apoptotic response of host cells has a deleterious effect on virus infection. Thus, apoptosis is an important host defense mechanism that is capable of inhibiting viral replication during infection. However, in vitro studies indicated that apoptosis alone does not provide the same protection against viral infection in animal cells as it does in the insect cells. Still, most animal viruses have acquired a strategy to overcome host cell apoptosis. In addition, a varying degree of necrosis usually accompanies apoptosis, suggesting a possible contribution of necrosis to the host reactions against virus. To understand the physiological significance of apoptosis during animal virus infection, we have characterized viral growth and the cellular responses against virus infection in a wide variety of virus-cell interaction systems. Mainly based on our own works, we discuss the nature of apoptosis in the animal virus infection and verify its role as a host defense mechanism against virus infection.

The receptor for advanced glycation end-products (RAGE) directly binds to ERK by a D-domain-like docking site

The receptor for advanced glycation end-products (RAGE)-mediated cellular activation through the mitogen-activated protein kinase (MAPK) cascade, activation of NF-kappaB and Rho family small G-proteins, cdc42/Rac, is implicated in the pathogenesis of inflammatory disorders and tumor growth/metastasis. However, the precise molecular mechanisms for the initiation of cell signaling by RAGE remain to be elucidated. In this study, proteins which directly bind to the cytoplasmic C-terminus of RAGE were purified from rat lung extracts using an affinity chromatography technique and identified to be extracellular signal-regulated protein kinase-1 and -2 (ERK-1/2). Their interactions were confirmed by immunoprecipitation of ERK-1/2 from RAGE-expressing HT1080 cell extracts with anti-RAGE antibody. Furthermore, the augmentation of kinase activity of RAGE-bound ERK upon the stimulation of cells with amphoterin was demonstrated by determining the phosphorylation level of myelin basic protein, an ERK substrate. In vitro binding studies using a series of C-terminal deletion mutants of human RAGE revealed the importance of the membrane-proximal cytoplasmic region of RAGE for the direct ERK-RAGE interaction. This region contained a sequence similar to the D-domain, a ERK docking site which is conserved in some ERK substrates including MAPK-interacting kinase-1/2, mitogen- and stress-activated protein kinase-1, and ribosomal S6 kinase. These data suggest that ERK may play a role in RAGE signaling through direct interaction with RAGE.

Regulation of expression of sulfoglucuronyl carbohydrate (HNK-1), Amphoterin and RAGE in retinoic acid-differentiated P19 embryonal carcinoma cells

HNK-1 antibody reactive sulfoglucuronyl carbohydrate (SGC) and SSEA-1 antibody reactive Lewis X (Lex) epitope are expressed on several glycolipids, glycoproteins, and proteoglycans of the nervous system and have been implicated in cell-cell recognition, neurite outgrowth, and/or neuronal migration during development. Interaction of SGC with its binding protein Amphoterin and interaction of Amphoterin with a cell-signaling molecule, receptor for advance glycation end product (RAGE) have been suggested to regulate neurite outgrowth and neuronal migration. The regulation of expression of SGC, Lex, Amphoterin, and RAGE was studied in embryonal carcinoma P19 cells after treatment with retinoic acid (RA). The untreated proliferating P19 cells strongly expressed the Lex epitope, which was mostly due to Lex-glycoproteins. P19 cells, when differentiated into neuron-like cells by RA, did not express the Lex epitope, but expressed increasing levels of SGC, with time in culture. Quantitative biochemical analyses showed that in the P19 cells after RA treatment, the amount of SGC-glycoproteins increased at a significantly higher level than sulfoglucuronyl glycolipid-1 (SGGL-1). The increase in the levels of SGGL-1 was due to 16-fold upregulation in the activity of lactosylceramide: N-acetylglucosaminyl-transferase (Lc3 synthase), which synthesizes the key intermediate lactotriosylceramide (Lc3Cer), for lacto- and neolacto-glycolipids. The large increase in the activity of Lc3 synthase appeared to regulate the levels of other neolacto glycolipids, such as Lc3Cer, nLc4Cer, nLc6Cer, disialosyl-nLc4Cer (LD1), and Lex-glycolipids. Strong upregulation of glucuronyl-transferase and modest twofold enhancement in the activity of the glucuronyl-sulfotransferase, which catalyze the final steps in the SGC synthesis, also would account for the large increase in the synthesis SGC-glycoproteins. RA also upregulated the synthesis of Amphoterin and RAGE in P19 cells. SGC, RAGE, and Amphoterin were co-localized in the RA-differentiated neurons. The initiation of neurite outgrowth along with co-ordinated upregulation of Amphoterin, RAGE, SGC-glycoproteins, and SGGLs in RA-treated P19 cells support the hypothesis that these molecules are involved in the neuronal process formation.

Successful treatment of collagen-induced arthritis in mice and rats by targeting extracellular high mobility group box chromosomal protein 1 activity

OBJECTIVE

Extracellular high mobility group box chromosomal protein 1 (HMGB-1) is a recently identified, endogenous, potent tumor necrosis factor- and interleukin-1 (IL-1)-inducing protein detectable in inflamed synovia in both human and experimental disease. In the present study, we examined clinical effects in collagen-induced arthritis (CIA) using therapeutic administration of neutralizing HMGB-1 antibodies or truncated HMGB-1-derived A-box protein, a specific, competitive antagonist of HMGB-1.

METHODS

CIA was induced in DBA/1j mice or dark agouti rats, and animals were examined daily for signs of arthritis. Treatment with polyclonal anti-HMGB-1 antibodies or the A-box protein was initiated at the onset of disease and was administered intraperitoneally twice daily for 7 days. Animals were killed 8 days after initiation of therapy, and immunohistochemical analysis of synovial tissue specimens was performed.

RESULTS

Systemic administration of anti-HMGB-1 antibodies or A-box protein significantly reduced the mean arthritis score, the disease-induced weight loss, and the histologic severity of arthritis. Beneficial effects were observed in both mice and rats. Immunohistochemical analysis revealed pronounced synovial IL-1beta expression and articular cartilage destruction in vehicle-treated mice. Both these features were significantly less manifested in animals treated with anti-HMGB-1 antibodies or A-box protein.

CONCLUSION

Counteracting extracellular HMGB-1 with either neutralizing antibodies or a specific HMGB-1 antagonist may offer a new method for the successful treatment of arthritis. Inflammation and tissue destruction were suppressed in CIA after HMGB-1 blockade.

High mobility group box-1 as a therapeutic target downstream of tumor necrosis factor

The discovery of tumor necrosis factor (TNF) as a necessary and sufficient mediator of systemic inflammation started a new field of research to rationally modulate cytokine responses to therapeutic advantage. However, the early kinetics of the TNF response during infection defined an extremely narrow window of opportunity during which anti-TNF therapeutics are efficacious, hampering clinical development for severe sepsis. Because death from severe sepsis often occurs as a late phenomenon, we began a search began for putative "late" mediators that could be targeted after the onset of infection. We have now identified high mobility group box-1 (HMGB1) as a late mediator of endotoxemia and sepsis. HMGB1 is released by activated macrophages, induces the release of other proinflammatory mediators, and mediates lethality when overexpressed. Administration of anti-HMGB1 antibodies inhibit systemic inflammation, even in established cases, because HMGB1 activity is elevated at significantly later time points than TNF or interleukin-1. It will now be important to determine whether this wider window of activity can be translated into therapeutic advantage for human inflammatory disease.

Glia as a putative target for antidepressant treatments

BACKGROUND

Since the early 1950s, various molecular mechanisms have been invoked to explain how antidepressants work. The most recent suggests that pharmacologically stimulated adult neurogenesis might be involved. Surprisingly, in the adult brain, an important source of new neurons and possibly mediators of neurogenesis appears to be glia, i.e., astrocytes. We have recently shown that protracted administration of the antidepressant fluoxetine to adult rats upregulated the astrocytic protein S100beta content and increased neurogenesis in the hippocampus.

METHODS

Rats were treated with fluoxetine for 21 days; before sacrifice bromodeoxyuridine (BrdU) was injected to label the proliferating cells. Immunofluorescence was used to identify proliferating BrdU-positive cells, and cells immunopositive for S100beta and its receptor receptor for advanced glycation end products (RAGE).

RESULTS

Typically, S100beta-positive cells were observed in the vicinity of BrdU-positive cells. On the other hand, we observed colocalization of RAGE receptors and BrdU immunoreactivities, suggesting that some proliferating cells express these receptors for S100beta. RAGE expression by neuronal cells or neuronal precursors and its activation by S100beta may promote their survival.

LIMITATIONS

The anatomical localization of hippocampal S100beta, its receptor RAGE, and BrdU-positive cells that we describe in this study is only indicative of a putative role for glia in antidepressant-stimulated neurogenesis. Functional in vitro and in vivo studies are needed to directly investigate this role; quantitative assays and time-course studies are also warranted.

CONCLUSION

We propose that a better understanding of glia functioning could establish its role as a target for novel antidepressant treatments.

High mobility group box chromosomal protein 1, a DNA binding cytokine, induces arthritis

OBJECTIVE

To examine the potential role of high mobility group box chromosomal protein 1 (HMGB-1) in the pathogenesis of arthritis.

METHODS

Mice were injected intraarticularly with 1 microg or 5 microg of HMGB-1. Joints were dissected on days 4, 7, and 28 after injection and were evaluated histopathologically and immunohistochemically. To investigate the importance of different white blood cell populations for the development of arthritis, in vivo cell depletion procedures were performed. In addition, spleen cells were cultured in the presence of HMGB-1, and nuclear factor kappaB (NF-kappaB) activation was detected by electrophoretic mobility shift assay.

RESULTS

Injection of recombinant HMGB-1 (rHMGB-1) into different mouse strains resulted in an overall frequency of arthritis in 80% of the animals. The inflammation was characterized by mild to moderate synovitis and lasted for at least 28 days. The majority of cells found in the inflamed synovium were Mac-1+ macrophages, whereas only a few CD4+ lymphocytes were detected. Pannus formation was observed in some cases 7 and 28 days after HMGB-1 injection. No significant differences were found with respect to incidence and severity of arthritis between mice depleted of monocytes, granulocytes, or lacking T/B lymphocytes. However, combined removal of monocytes and neutrophils resulted in a 43% lower incidence of arthritis. Mice rendered deficient in the interleukin-1 (IL-1) receptor did not develop inflammation upon challenge with HMGB-1. In vitro data corroborate this finding, showing that rHMGB-1 activated NF-kappaB, a major pathway leading to IL-1 production.

CONCLUSION

Our results indicate that HMGB-1 is not a mere expression of inflammatory responses, but on its own, it triggers joint inflammation by activating macrophages and inducing production of IL-1 via NF-kappaB activation.

Differential effects between amphoterin and advanced glycation end products on colon cancer cells

Amphoterin is 1 ligand of the receptor for advanced glycation end products (RAGE). We studied expression of amphoterin and RAGE mRNA and proteins in colorectal carcinoma cells and investigated their associations with the invasive activities of cells exposed to advanced glycation end products (AGE). Expression of RAGE and amphoterin was examined in 4 colorectal carcinoma cell lines. All cell lines expressed both RAGE and amphoterin. The effects of RAGE and amphoterin on cell growth (MTT assay), migration (wound healing assay) and invasion (in vitro invasion assay) were tested by treatment of cells with RAGE and amphoterin antisense S-oligodeoxynucleotides (ODNs). Cell growth, migration and invasion were inhibited significantly in Colo320 and WiDr carcinoma cells treated with RAGE and amphoterin antisense S-ODNs compared with sense-treated cells. Differences in ligand activity between amphoterin and AGE were examined with AGE-bovine serum albumin (BSA). AGE-BSA decreased cell growth, migration and invasion of amphoterin antisense S-ODN-treated Colo320 and WiDr cells compared with those of cells treated with Colo320 conditioned medium. Phosphorylation of extracellular signal-regulated kinase-1/2, Rac1 and AKT and production of matrix metalloproteinase 9 were increased to a greater degree by amphoterin than by AGE-BSA. In contrast, production of inducible nitric oxide synthase and nuclear factor-kappaBp65 were increased to a greater degree by AGE-BSA than by amphoterin.

Glucose, glycation, and RAGE: implications for amplification of cellular dysfunction in diabetic nephropathy

Receptor for advanced glycation endproducts (RAGE) is a multi-ligand member of the immunoglobulin superfamily of cell surface molecules. Driven by rapid accumulation and expression of key ligands such as advanced glycation endproducts (AGE) and S100/calgranulins in diabetic tissues, upregulation and activation of RAGE magnifies cellular perturbation in tissues affected by hyperglycemia, such as the large blood vessels and the kidney. In the diabetic glomerulus, RAGE is expressed principally by glomerular visceral epithelial cells (podocytes). Blockade of RAGE in the hyperglycemic db/db mouse suppresses functional and structural alterations in the kidney, in the absence of alterations in blood glucose. Recent studies in homozygous RAGE null mice support a key role for RAGE in glomerular perturbation in diabetes. Importantly, beyond diabetes, studies in other settings of glomerulopathies support a critical RAGE-dependent pathway in podocytes linked to albuminuria, mesangial expansion, and glomerular sclerosis. A new paradigm is proposed in glomerular injury, and it is suggested that blockade of the RAGE axis may provide a novel means to prevent irreparable glomerular injury in diabetes and other sclerosing glomerulopathies.

S100B in brain damage and neurodegeneration

S100B is a calcium-binding peptide produced mainly by astrocytes that exert paracrine and autocrine effects on neurons and glia. Some knowledge has been acquired from in vitro and in vivo animal experiments to understand S100B's roles in cellular energy metabolism, cytoskeleton modification, cell proliferation, and differentiation. Also, insights have been gained regarding the interaction between S100B and the cerebral immune system, and the regulation of S100B activity through serotonergic transmission. Secreted glial S100B exerts trophic or toxic effects depending on its concentration. At nanomolar concentrations, S100B stimulates neurite outgrowth and enhances survival of neurons during development. In contrast, micromolar levels of extracellular S100B in vitro stimulate the expression of proinflammatory cytokines and induce apoptosis. In animal studies, changes in the cerebral concentration of S100B cause behavioral disturbances and cognitive deficits. In humans, increased S100B has been detected with various clinical conditions. Brain trauma and ischemia is associated with increased S100B concentrations, probably due to the destruction of astrocytes. In neurodegenerative, inflammatory and psychiatric diseases, increased S100B levels may be caused by secreted S100B or release from damaged astrocytes. This review summarizes published findings on S100B regarding human brain damage and neurodegeneration. Findings from in vitro and in vivo animal experiments relevant for human neurodegenerative diseases and brain damage are reviewed together with the results of studies on traumatic, ischemic, and inflammatory brain damage as well as neurodegenerative and psychiatric disorders. Methodological problems are discussed and perspectives for future research are outlined.

Inflammation-promoting activity of HMGB1 on human microvascular endothelial cells

Systemic inflammation because of sepsis results in endothelial cell activation and microvascular injury. High-mobility group protein-1 (HMGB1), a novel inflammatory molecule, is a late mediator of endotoxin shock and is present in the blood of septic patients. The receptor for advanced glycation end products (RAGE) is expressed on endothelium and is a receptor for HMGB1. Here we examine the effects of HMGB1 on human endothelial cell function. Recombinant human HMGB1 (rhHMGB1) was cloned and expressed in Escherichia coli and incubated with human microvascular endothelium. rhHMGB1 caused a dose- and time-dependent increase in the expression of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and RAGE. rhHMGB1 induced the secretion of tumor necrosis factor-alpha (TNFalpha), interleukin 8 (IL-8), monocyte chemotactic protein-1 (MCP-1), plasminogen activator inhibitor 1 (PAI-1), and tissue plasminogen activator (tPA) (P <.01). rhHMGB1 stimulation resulted in transient phosphorylation of mitogen-activated protein (MAP) kinases, extracellular signal-related kinase (ERK), Jun N-terminal kinase (JNK), and p38, and in nuclear translocation of transcription factors NF-kappaB and Sp1. These effects are partially mediated by TNFalpha autocrine stimulation, as anti-TNFalpha antibodies significantly decrease chemokine and adhesion molecule responses (P </=.002). Thus, rhHMGB1 elicits proinflammatory responses on endothelial cells and may contribute to alterations in endothelial cell function in human inflammation.

IFN-gamma induces high mobility group box 1 protein release partly through a TNF-dependent mechanism

We recently discovered that a ubiquitous protein, high mobility group box 1 protein (HMGB1), is released by activated macrophages, and functions as a late mediator of lethal systemic inflammation. To elucidate mechanisms underlying the regulation of HMGB1 release, we examined the roles of other cytokines in induction of HMGB1 release in macrophage cell cultures. Macrophage migration inhibitory factor, macrophage-inflammatory protein 1beta, and IL-6 each failed to significantly induce the release of HMGB1 even at supraphysiological levels (up to 200 ng/ml). IFN-gamma, an immunoregulatory cytokine known to mediate the innate immune response, dose-dependently induced the release of HMGB1, TNF, and NO, but not other cytokines such as IL-1alpha, IL-1beta, or IL-6. Pharmacological suppression of TNF activity with neutralizing Abs, or genetic disruption of TNF expression (TNF knockout) partially (50-60%) inhibited IFN-gamma-mediated HMGB1 release. AG490, a specific inhibitor for Janus kinase 2 of the IFN-gamma signaling pathway, dose-dependently attenuated IFN-gamma-induced HMGB1 release. These data suggest that IFN-gamma plays an important role in the regulation of HMGB1 release through a TNF- and Janus kinase 2-dependent mechanism.

Activation of gene expression in human neutrophils by high mobility group box 1 protein

High mobility group box 1 (HMGB1) protein, a DNA binding protein that stabilizes nucleosomes and facilitates transcription, was recently identified as a late mediator of endotoxin lethality. High serum HMGB1 levels in patients with sepsis are associated with increased mortality, and administration of HMGB1 produces acute inflammation in animal models of lung injury and endotoxemia. Neutrophils occupy a critical role in mediating the development of endotoxemia-associated acute lung injury, but previously it was not known whether HMGB1 could influence neutrophil activation. In the present experiments, we demonstrate that HMGB1 increases the nuclear translocation of NF-kappaB and enhances the expression of proinflammatory cytokines in human neutrophils. These proinflammatory effects of HMGB1 in neutrophils appear to involve the p38 MAPK, phosphatidylinositol 3-kinase/Akt, and ERK1/2 pathways. The mechanisms of HMGB1-induced neutrophil activation are distinct from endotoxin-induced signals, because HMGB1 leads to a different profile of gene expression, pattern of cytokine expression, and kinetics of p38 activation compared with LPS. These findings indicate that HMGB1 is an effective stimulus of neutrophil activation that can contribute to development of a proinflammatory phenotype in diseases characterized by excessively high levels of HMGB1.

RAGE is expressed in pyramidal cells of the hippocampus following moderate hypoxic-ischemic brain injury in rats

The receptor for advanced glycation end products (RAGE) is a multi-ligand member of the immunoglobulin superfamily of cell surface molecules. The RAGE-ligand interaction has a putative role in a range of chronic disorders and is also known to contribute to both inflammatory/degenerative processes as well as regeneration in peripheral nerve injury. We have investigated the expression of RAGE in the moderate hypoxic-ischemic (HI) rat brain injury model in order to determine if this receptor is involved in the cellular perturbation mediated by ischemic stress. RAGE mRNA levels were detected by in situ hybridization using a DIG-labelled 48 mer oligonucleotide probe. Results showed a high level of expression of RAGE mRNA in the CA1/2 pyramidal cell layer of the hippocampus on the lesioned side of the brain 72 h after a moderate hypoxic-ischemic insult. RAGE was not expressed on the control side of the hippocampus. The RAGE-positive cells had a unique morphology, being angular in shape and atrophied with a condensed cell nucleus. They were NeuN-positive and were identified as dying cells by staining with thionin/acid fuchsin. A subset of cells was positive for cleaved Caspase-3, a marker for apoptosis. Together these data show that RAGE is expressed in dying neurons and suggest that RAGE may have a role in neuronal cell death mediated by ischemic stress. Identification of the ligand for RAGE in the ischemic brain may lead to a better understanding of RAGE-mediated cellular dysfunction in the CNS.

Novel splice variants of the receptor for advanced glycation end-products expressed in human vascular endothelial cells and pericytes, and their putative roles in diabetes-induced vascular injury

The binding of advanced glycation end-products (AGE) to the receptor for AGE (RAGE) is known to deteriorate various cell functions and is implicated in the pathogenesis of diabetic vascular complications. In the present study, we show that the cellular constituents of small vessels, endothelial cells (EC) and pericytes express novel splice variants of RAGE mRNA coding for the isoforms that lack the N-terminal V-type immunoglobulin-like domain (N-truncated) or the C-terminal transmembrane domain (C-truncated), as well as the known full-length mRNA. The ratio of the expression of the three variants was different between EC and pericytes; the content of the C-truncated form was highest in EC, whereas the full-length form was the most abundant in pericytes. Transfection experiments with COS-7 cells demonstrated that those variant mRNAs were translated into proteins as deduced; C-truncated RAGE was efficiently secreted into the culture media, and N-truncated RAGE was located mainly on the plasma membrane. The three isoforms were also detected in primary cultured human EC and pericytes. Further, full-length and C-truncated forms of RAGE bound to an AGE-conjugated column, whereas N-truncated RAGE did not. The AGE induction of extracellular-signal-related kinase phosphorylation and vascular endothelial growth factor in EC and of the growth and cord-like structure formation of EC was abolished completely by C-truncated RAGE, indicating that this endogenous secretory receptor (endogenous secretory RAGE) is cytoprotective against AGE. The results may contribute to our understanding of the molecular basis for the diversity of cellular responses to AGE and for individual variations in the susceptibility to diabetic vascular complications.

Suppression of experimental autoimmune encephalomyelitis by selective blockade of encephalitogenic T-cell infiltration of the central nervous system

Multiple sclerosis (MS) is a devastating neuroinflammatory disorder of the central nervous system (CNS) in which T cells that are reactive with major components of myelin sheaths have a central role. The receptor for advanced glycation end products (RAGE) is present on T cells, mononuclear phagocytes and endothelium. Its pro-inflammatory ligands, S100-calgranulins, are upregulated in MS and in the related rodent model, experimental autoimmune encephalomyelitis (EAE). Blockade of RAGE suppressed EAE when disease was induced by myelin basic protein (MBP) peptide or encephalitogenic T cells, or when EAE occurred spontaneously in T-cell receptor (TCR)-transgenic mice devoid of endogenous TCR-alpha and TCR-beta chains. Inhibition of RAGE markedly decreased infiltration of the CNS by immune and inflammatory cells. Transgenic mice with targeted overexpression of dominant-negative RAGE in CD4+ T cells were resistant to MBP-induced EAE. These data reinforce the importance of RAGE-ligand interactions in modulating properties of CD4+ T cells that infiltrate the CNS.

HMGB1, an architectural chromatin protein and extracellular signalling factor, has a spatially and temporally restricted expression pattern in mouse brain

HMGB1 is an abundant chromatin component, so far considered ubiquitous. HMGB1 also has an extracellular signalling role: when passively released by necrotic cells, it triggers inflammation; moreover, it can be actively secreted by myeloid cells, neurons and neuronal cancer cells. We show here that HMGB1 protein is undetectable in most cells in adult mouse brain, and is present in a subset of brain cells during development, with a very complex temporal, spatial and subcellular expression pattern. HMGB1 is expressed in the cortical plate of E14.5 embryos, predominantly in the nucleus, although roughly 1% of cells show a cytoplasmic localization as well. In E16 embryos, HMGB1 is nuclearly expressed in scattered cells apparently moving from the ventricular zone to the cortical plate. HMGB1 expression is strongly down-regulated at later developmental stages; in adult mice significant expression is maintained only in areas of continuing neurogenesis. Finally, HMGB1 subcellular localization changes during retinoic acid induced differentiation of P19 neuroblastoma cells.

Role of high mobility group protein-1 (HMG1) in amyloid-beta homeostasis

In Alzheimer's disease (AD), fibrillar amyloid-beta (Abeta) peptides form senile plaques associated with activated microglia. Recent studies have indicated that microglial Abeta clearance is facilitated by several activators such as transforming growth factor-beta1 (TGF-beta1). The relationship between microglia and Abeta formation and deposition is still unclear. In the present study, high mobility group protein-1 (HMG1) inhibited the microglial uptake of Abeta (1-42) in the presence and absence of TGF-beta1. In addition, HMG1 bound to Abeta (1-42) and stabilized the oligomerization. In AD brains, protein levels of HMG1 were significantly increased in both the cytosolic and particulate fractions, and HMG1 and Abeta were colocalized in senile plaques associated with microglia. These results suggest that HMG1 may regulate the homeostasis of extracellular Abeta (1-42) and Abeta oligomerization.

Glycation in diabetic neuropathy: characteristics, consequences, causes, and therapeutic options

Glycation is the nonenzymatic reaction of glucose, alpha-oxoaldehydes, and other saccharide derivatives with proteins, nucleotides, and lipids. Early glycation adducts (fructosamines) and advanced glycation adducts (AGEs) are formed. "Glycoxidation" is a term used for glycation processes involving oxidation. Sural, peroneal, and saphenous nerves of human diabetic subjects contained AGEs in the perineurium, endothelial cells, and pericytes of endoneurial microvessels and in myelinated and unmyelinated fibres localized to irregular aggregates in the cytoplasm and interstitial collagen and basement membranes. Pentosidine content was increased in cytoskeletal and myelin protein extracts of the sural nerve of human subjects and cytoskeletal proteins of the sciatic nerve of streptozotocin-induced diabetic rats. AGEs in the sciatic nerve of diabetic rats were decreased by islet transplantation. Improved glycemic control of diabetic patients may be expected to decrease protein glycation in the nerve. Protein glycation may decrease cytoskeletal assembly, induce protein aggregation, and provide ligands for cells surface receptors. The receptor for advanced glycation and products (RAGE) was expressed in peripheral neurons. It is probable that high intracellular glucose concentration is an important trigger for increased glycation, leading to increased formation of methylglyoxal, glyoxal, and 3-deoxyglucosone that glycate proteins to form AGEs intracellularly and extracellularly. Oxidative stress enhances these processes and is, in turn, enhanced by AGE/RAGE interactions. An established therapeutic strategy to prevent glycation is the use of alpha-oxoaldehyde scavengers. Available therapeutic options for trial are high-dose nicotinamide and thiamine therapies to prevent methylglyoxal formation. Future possible therapeutic strategies are RAGE antagonists and inducers of the enzymatic antiglycation defense. More research is required to understand the role of glycation in the development of diabetic neuropathy.

[Possible participation of advanced glycation endproducts and their receptor system in the development of diabetic vascular complications]

Diabetes causes vascular injuries in various organs and tissues, among which the lesions in retina and kidney are called retinopathy and nephropathy, respectively. As the number of diabetic patients is increasing in Japan, the population with the vascular complications is also elevating. For preventing diabetic complications, it is necessary to develop new drugs that target for key molecules in the development of this disease and useful animal models for the evaluation of their therapeutic potentials. We have focused on the non-enzymatic glycation reaction under prolonged hyperglycemia, which results in the formation and accumulation of advanced glycation endproducts (AGE). The interaction of AGE with the receptor for AGE (RAGE) has been implicated in the development of the vascular complications. AGE elicited vascular cell changes typical of diabetes, including angiogenic and thrombogenic responses of endothelial cells (EC), and a decrease in pericytes, the hallmarks of diabetic retinopathy. Our recent in vivo study revealed that transgenic mice overexpressing human RAGE in vascular EC developed advanced nephropathy when they were made diabetic. This mouse is thus regarded as a useful animal model of diabetic vascular disease. These results suggest that the AGE-RAGE system plays an active role in the development of diabetic vasculopathy and is a promising target in the prophylaxis and therapy of this disease. Recently, we identified three RAGE variants: novel C-terminally and N-terminally truncated forms and the known full-length form. The C-terminally truncated variant was found to be a soluble form and actually detected in human sera, and it was found to have neutralizing activities against AGE-induced EC injury. The endogenous soluble decoy against the AGE-RAGE system may contribute to the individual resistance to the development of diabetic vascular complications. The stimulation of secretion of this protein can be a new means for the prevention of chronic vascular disease in diabetes.

Receptor for advanced glycation endproducts: a multiligand receptor magnifying cell stress in diverse pathologic settings

Receptor for Advanced Glycation Endproducts (RAGE) is a member of the immunoglobulin superfamily of cell surface molecules capable of interacting with a broad spectrum of ligands, including advanced glycation endproducts (AGEs), amyloid fibrils, S100/calgranulins and amphoterin. The biology of RAGE is dictated by the accumulation of these ligands at pathologic sites, leading to upregulation of the receptor and sustained RAGE-dependent cell activation eventuating in cellular dysfunction. Although RAGE is not central to the initial pathogenesis of disorders in which it ultimately appears to be involved, such as diabetes, amyloidoses, inflammatory conditions and tumors (each of these conditions leading to accumulation of RAGE ligands), the receptor functions as a progression factor driving cellular dysfunction and exaggerating the host response towards tissue destruction, rather than restitution of homeostasis. These observations suggest that RAGE might represent a therapeutic target in a diverse group of seemingly unrelated disorders linked only by a multiligand receptor with an unusually wide and diverse repertoire of ligands, namely, RAGE.

Receptor for advanced glycation end products (RAGE) signaling induces CREB-dependent chromogranin expression during neuronal differentiation

Receptor for advanced glycation end products (RAGE) mediates neurite outgrowth and cell migration upon stimulation with its ligand, amphoterin. We show here that RAGE-dependent changes in cell morphology are associated with proliferation arrest and changes in gene expression in neuroblastoma cells. Chromogranin B, a component of secretory vesicles in endocrine cells and neurons, was found to be up-regulated by RAGE signaling during differentiation of neuroblastoma cells along with the two other members of the chromogranin family, chromogranin A and secretogranin II. Ligation of RAGE by amphoterin lead to rapid phosphorylation and nuclear localization of cyclic AMP response element-binding protein (CREB), a major regulator of chromogranin expression. Furthermore, inhibition of ERK1/2-Rsk2-dependent CREB phosphorylation efficiently inhibited up-regulation of chromogranin gene expression upon RAGE activation. To further study the effects of RAGE and amphoterin on cellular differentiation, we stimulated embryonic stem cells expressing RAGE or a signaling-deficient mutant of RAGE with amphoterin. Amphoterin was found to promote RAGE-dependent neuronal differentiation of embryonic stem cells characterized by up-regulation of neuronal markers light neurofilament protein and beta-III-tubulin, activation of CREB, and increased expression of chromogranins A and B. These data suggest that RAGE signaling is capable of driving neuronal differentiation involving CREB activation and induction of chromogranin expression.

High mobility group box chromosomal protein 1: a novel proinflammatory mediator in synovitis

OBJECTIVE

High mobility group box chromosomal protein 1 (HMGB-1) is a ubiquitous chromatin component expressed in nucleated mammalian cells. It has recently and unexpectedly been demonstrated that stimulated live mononuclear phagocytes secrete HMGB-1, which then acts as a potent factor that causes inflammation and protease activation. Macrophages play pivotal roles in the pathogenesis of arthritis. The aim of this study was to determine whether synovial macrophage expression of HMGB-1 is altered in human and experimental synovitis.

METHODS

Intraarticular tissue specimens were obtained from healthy Lewis rats, Lewis rats with Mycobacterium tuberculosis-induced adjuvant arthritis, and from patients with rheumatoid arthritis (RA). Specimens were immunohistochemically stained for cellular HMGB-1. Extracellular HMGB-1 levels were assessed in synovial fluid samples from RA patients by Western blotting.

RESULTS

Immunostaining of specimens from normal rats showed that HMGB-1 was primarily confined to the nucleus of synoviocytes and chondrocytes, with occasional cytoplasmic staining and no extracellular matrix deposition. In contrast, inflammatory synovial tissue from rats with experimental arthritis as well as from humans with RA showed a distinctly different HMGB-1 staining pattern. Nuclear HMGB-1 expression was accompanied by a cytoplasmic staining in many mononuclear cells, with a macrophage-like appearance and an extracellular matrix deposition. Analysis of synovial fluid samples from RA patients further confirmed the extracellular presence of HMGB-1; 14 of 15 samples had HMGB-1 concentrations of 1.8-10.4 microg/ml.

CONCLUSION

The proinflammatory mediator HMGB-1 was abundantly expressed as a nuclear, cytoplasmic, and extracellular component in synovial tissues from RA patients and from rats with experimental arthritis. These findings suggest a pathogenetic role for HMGB-1 in synovitis and indicate a new potential therapeutic target molecule.

At the crossroads of necrosis and apoptosis: signaling to multiple cellular targets by HMGB1

Cells can die through two mechanisms: necrosis and apoptosis. Necrosis occurs in response to stimuli that cause cellular damage and result in the release of intracellular proteins, which stimulate the inflammatory response. Necrosis is associated with tissue damage and organ deterioration. Apoptosis is a programmed cell death during which the cellular membrane remains intact, but activated enzymes destroy the cell from within. Bustin discusses how the mobility of the nuclear protein high mobility group B1 (HMGB1) may be a key signal for determining whether certain cells undergo necrotic or apoptotic death. Necrosis may result when HMGB1 is released from the cells and stimulates the inflammatory response. HMGB1 appears to have extracellular signaling functions, such as stimulation of cell motility and tumor metastasis and activation of the cytokine signaling pathways. Through its action on the cytokine signaling targets, HMGB1 may be an important therapeutic target for diseases of cytokine excess, including septic shock.

HMGB1 B box increases the permeability of Caco-2 enterocytic monolayers and impairs intestinal barrier function in mice

BACKGROUND & AIMS

High mobility group (HMG) B1 is a nonhistone nuclear protein that was recently identified as a late-acting mediator of lipopolysaccharide-induced lethality in mice. The proinflammatory actions of HMGB1 have been localized to a region of the molecule called the B box.

METHODS

To determine whether HMGB1 or B box are capable of causing derangements in intestinal barrier function, we incubated cultured Caco-2 human enterocytic monolayers with recombinant human HMGB1 or a 74-residue truncated form of the protein consisting of the B box domain.

RESULTS

Both HMGB1 and B box increased the permeability of Caco-2 monolayers to fluorescein isothiocyanate-labeled dextran (FD4) in a time- and dose-dependent fashion. The increase in permeability was reversible following removal of the recombinant protein. Exposure of Caco-2 cells to B box resulted in increased expression of inducible nitric oxide synthase messenger RNA and increased production of NO. When we used various pharmacologic strategies to inhibit NO production or scavenge NO or peroxynitrite (ONOO(-)), we abrogated B box-induced hyperpermeability. Administration of B box to wild-type mice increased both ileal mucosal permeability to FD4 and bacterial translocation to mesenteric lymph nodes. These effects were not observed in inducible nitric oxide synthase knockout mice.

CONCLUSIONS

These data support the view that HMGB1 and B box are capable of causing alterations in gut barrier function via a mechanism that depends on the formation of NO and ONOO(-).

Release of chromatin protein HMGB1 by necrotic cells triggers inflammation

High mobility group 1 (HMGB1) protein is both a nuclear factor and a secreted protein. In the cell nucleus it acts as an architectural chromatin-binding factor that bends DNA and promotes protein assembly on specific DNA targets. Outside the cell, it binds with high affinity to RAGE (the receptor for advanced glycation end products) and is a potent mediator of inflammation. HMGB1 is secreted by activated monocytes and macrophages, and is passively released by necrotic or damaged cells. Here we report that Hmgb1(-/-) necrotic cells have a greatly reduced ability to promote inflammation, which proves that the release of HMGB1 can signal the demise of a cell to its neighbours. Apoptotic cells do not release HMGB1 even after undergoing secondary necrosis and partial autolysis, and thus fail to promote inflammation even if not cleared promptly by phagocytic cells. In apoptotic cells, HMGB1 is bound firmly to chromatin because of generalized underacetylation of histone and is released in the extracellular medium (promoting inflammation) if chromatin deacetylation is prevented. Thus, cells undergoing apoptosis are programmed to withhold the signal that is broadcast by cells that have been damaged or killed by trauma.

Transmission of cell stress from endoplasmic reticulum to mitochondria: enhanced expression of Lon protease

The rat homologue of a mitochondrial ATP-dependent protease Lon was cloned from cultured astrocytes exposed to hypoxia. Expression of Lon was enhanced in vitro by hypoxia or ER stress, and in vivo by brain ischemia. These observations suggested that changes in nuclear gene expression (Lon) triggered by ER stress had the potential to impact important mitochondrial processes such as assembly and/or degradation of cytochrome c oxidase (COX). In fact, steady-state levels of nuclear-encoded COX IV and V were reduced, and mitochondrial-encoded subunit II was rapidly degraded under ER stress. Treatment of cells with cycloheximide caused a similar imbalance in the accumulation of COX subunits, and enhanced mRNA for Lon and Yme1, the latter another mitochondrial ATP-dependent protease. Furthermore, induction of Lon or GRP75/mtHSP70 by ER stress was inhibited in PERK (-/-) cells. Transfection studies revealed that overexpression of wild-type or proteolytically inactive Lon promoted assembly of COX II into a COX I-containing complex, and partially prevented mitochondrial dysfunction caused by brefeldin A or hypoxia. These observations demonstrated that suppression of protein synthesis due to ER stress has a complex effect on the synthesis of mitochondrial-associated proteins, both COX subunits and ATP-dependent proteases and/or chaperones contributing to assembly of the COX complex.

A fragment of the HMGN2 protein homes to the nuclei of tumor cells and tumor endothelial cells in vivo

We used a screening procedure to identify protein domains from phage-displayed cDNA libraries that bind both to bone marrow endothelial progenitor cells and tumor vasculature. Screening phage for binding of progenitor cell-enriched bone marrow cells in vitro, and for homing to HL-60 human leukemia cell xenograft tumors in vivo, yielded a cDNA fragment that encodes an N-terminal fragment of human high mobility group protein 2 (HMGN2, formerly HMG-17). Upon i.v. injection, phage displaying this HMGN2 fragment homed to HL-60 and MDA-MB-435 tumors. Testing of subfragments localized the full binding activity to a 31-aa peptide (F3) in the HMGN2 sequence. Fluorescein-labeled F3 peptide bound to and was internalized by HL-60 cells and human MDA-MB-435 breast cancer cells, appearing initially in the cytoplasm and then in the nuclei of these cells. Fluorescent F3 accumulated in HL-60 and MDA-MB-435 tumors after an i.v. injection, appearing in the nuclei of tumor endothelial cells and tumor cells. Thus, F3 can carry a payload (phage, fluorescein) to a tumor and into the cell nuclei in the tumor. This peptide may be suitable for targeting cytotoxic drugs and gene therapy vectors into tumors.

Stimulation of erythroleukaemia cell differentiation by extracellular high-mobility group-box protein 1 is independent of the receptor for advanced glycation end-products

In several cell types the binding of extracellular high-mobility group-box protein 1 (HMGB1) with the receptor for advanced glycation end-products (RAGE) induces cytoskeletal reorganization and cell motility. To establish whether RAGE is also involved in murine erythroleukaemia (MEL) cell differentiation stimulated by HMGB1, we have demonstrated that these cells express a 51 kDa protein identified as RAGE, and then we have produced stable transfectants overexpressing wild-type (wt) RAGE or a dominant negative (dn) RAGE mutant lacking the cytoplasmic domain to analyse the differentiation process in these cells. Several experimental findings indicated that RAGE was not involved in the MEL cell differentiation programme. This was also supported by the identical stimulatory effect exerted by HMGB1 on both wt- or dn-RAGE transfectants. We have also observed that HMGB1 binds a 65 kDa protein on the surface of MEL cells, supporting the hypothesis that alternative targets of HMGB1 are expressed on the MEL cell membrane and may be involved as mediators of its signalling.

RAGE and arthritis: the G82S polymorphism amplifies the inflammatory response

The receptor for advanced glycation end products (RAGE) and its proinflammatory S100/calgranulin ligands are enriched in joints of subjects with rheumatoid arthritis (RA) and amplify the immune/inflammatory response. In a model of inflammatory arthritis, blockade of RAGE in mice immunized and challenged with bovine type II collagen suppressed clinical and histologic evidence of arthritis, in parallel with diminished levels of TNF-alpha, IL-6, and matrix metalloproteinases (MMP) 3, 9 and 13 in affected tissues. Allelic variation within key domains of RAGE may influence these proinflammatory mechanisms, thereby predisposing individuals to heightened inflammatory responses. A polymorphism of the RAGE gene within the ligand-binding domain of the receptor has been identified, consisting of a glycine to serine change at position 82. Cells bearing the RAGE 82S allele displayed enhanced binding and cytokine/MMP generation following ligation by a prototypic S100/calgranulin compared with cells expressing the RAGE 82G allele. In human subjects, a case-control study demonstrated an increased prevalence of the 82S allele in patients with RA compared with control subjects. These data suggest that RAGE 82S upregulates the inflammatory response upon engagement of S100/calgranulins, and, thereby, may contribute to enhanced proinflammatory mechanisms in immune/inflammatory diseases.

Relationship between sprouting axons, proteoglycans and glial cells following unilateral nigrostriatal axotomy in the adult rat

Proteoglycans may modulate axon growth in the intact and injured adult mammalian CNS. Here we investigate the distribution and time course of deposition of a range of proteoglycans between 4 and 14 days following unilateral axotomy of the nigrostriatal tract in anaesthetised adult rats. Immunolabelling using a variety of antibodies was used to examine the response of heparan sulphate proteoglycans, chondroitin sulphate proteoglycans and keratan sulphate proteoglycans. We observed that many proteoglycans became abundant between 1 and 2 weeks post-axotomy. Heparan sulphate proteoglycans were predominantly found within the lesion core (populated by blood vessels, amoeboid macrophages and meningeal fibroblasts) whereas chondroitin sulphate proteoglycans and keratan sulphate proteoglycans were predominantly found in the lesion surround (populated by reactive astrocytes, activated microglia and adult precursor cells). Immunolabelling indicated that cut dopaminergic nigral axons sprouted prolifically within the lesion core but rarely grew into the lesion surround. We conclude that sprouting of cut dopaminergic nigral axons may be supported by heparan sulphate proteoglycans but restricted by chondroitin sulphate proteoglycans and keratan sulphate proteoglycans.

Cellular oxidant stress and advanced glycation endproducts of albumin: caveats of the dichlorofluorescein assay

In order to understand the mechanism by which advanced glycation endproducts (AGEs) elicit oxidative stress, macrophage-like RAW264.7 cells were exposed to various AGE-albumins, and oxidant stress was estimated from the fluorescence of oxidized dichlorofluorescein using the microtiter plate assay. Strongest fluorescence was observed with methylglyoxal modified albumin (MGO-BSA) compared with native albumin. Similar effects that were prevented by arginine coincubation were seen with phenylglyoxal-BSA. MGO-BSA had increased affinity for Cu(2+) and Ca(2+), but was conformationally similar to native albumin. Surprisingly, the mere addition of unmodified albumin to cells suppressed the fluorescence of oxidized DCF. While, several site-directed mutants of human serum albumin (HSA), including C34S and recombinant domains II and III retained fluorescence suppressing activity, proteolytic digests, recombinant domain I, and several nonalbumin proteins failed to suppress. Kinetic and ANS binding studies suggested albumin quenches DCF fluorescence by binding to hydrophobic pockets in domains II and III and that MGO-BSA is less hydrophobic than BSA. Finally, BSA also prevented H(2)O(2) catalyzed DCF fluorescence more potently than MGO-BSA. These studies reveal important caveats of the widely used dichlorofluorescein assay and suggest methods other than the microtiter plate assay are needed to accurately assess cellular oxidant stress in presence of native or modified albumin.

Receptor for advanced glycation end products plays a more important role in cellular survival than in neurite outgrowth during retinoic acid-induced differentiation of neuroblastoma cells

The receptor for advanced glycation end products (RAGE), a member of the immunoglobulin superfamily, is known to interact with amphoterin. This interaction has been proposed to play a role in neurite outgrowth and process elongation during neurodifferentiation. However, there is as yet no direct evidence of the relevance of this pathway to neurodifferentiation under physiological conditions. In this study we have investigated a possible role of RAGE and amphoterin in the retinoic acid-induced differentiation of neuroblastoma cells. The functional inactivation of RAGE by dominant negative and antisense strategies showed that RAGE is not required for process outgrowth or differentiation, although overexpression of RAGE accelerates the elongation of neuritic processes. Using the antisense strategy, amphoterin was shown to be essential for process outgrowth and differentiation, suggesting that amphoterin may interact with other molecules to exert its effect in this context. Interestingly, the survival of the neuroblastoma cells treated with retinoic acid was partly dependent on the expression of RAGE, and inhibition of RAGE function partially blocked the increase in anti-apoptotic protein Bcl-2 following retinoic acid treatment. Based on these results we propose that a combination therapy using RAGE blockers and retinoic acid may prove as a useful approach for chemotherapy for the treatment of neuroblastoma.

Expression of receptors for advanced glycation end-products (RAGE) is closely associated with the invasive and metastatic activity of gastric cancer

The receptor for advanced glycation end-products (RAGE) is a newly recognized factor regulating cancer cell invasion and metastasis. This study investigated the expression of RAGE in gastric carcinomas and its association with invasion and metastasis. Of eight gastric cancer cell lines examined, seven constitutively expressed RAGE messenger ribonucleic acid (mRNA), MKN45 being the exception. RAGE protein expression of MKN28 cells treated with RAGE antisense S-oligodeoxynucleotide was nine times less than that of sense S-oligodeoxynucleotide-treated cells. Growth of cells under RAGE antisense S-oligodeoxynucleotide treatment was not different from that seen under sense S-oligodeoxynucleotide treatment in MKN28 (a cell line producing high levels of RAGE) and MKN45 (a non-RAGE-expressing cell line). RAGE antisense S-oligodeoxynucleotide treatment suppressed the invasive activity of RAGE-positive MKN28 cells, as estimated by in vitro invasion assay. The number of MKN28 cells invading the type IV collagen-coated membrane under RAGE antisense S-oligodeoxynucleotide treatment was significantly lower than under RAGE sense S-oligodeoxynucleotide treatment (p<0.0001). In contrast, antisense and sense S-oligodeoxynucleotide-treated RAGE-negative MKN45 cells showed no difference. A wound-healing assay showed that no RAGE antisense S-oligodeoxynucleotide-treated MKN28 cells migrated into the scraped area, whereas sense S-oligodeoxynucleotide-treated cells showed many budding nests in the scraped area. Immunohistochemistry of gastric carcinoma tissue showed that 62 (65%) of the 96 cases examined were RAGE-positive and that poorly differentiated adenocarcinomas preferentially expressed RAGE protein (38/42, 90%) (p<0.0001). Strong RAGE immunoreactivity was also correlated with depth of invasion and lymph node metastasis (p<0.0001). RAGE-positive cancer cells tended to be distributed at the invasive front of primary tumours and were detected in all metastatic foci in lymph nodes. In contrast, a major RAGE ligand, amphoterin, was expressed in 82 (85%) of the 96 cases, regardless of histological type and disease progression. RAGE expression appears to be closely associated with invasion and metastasis in gastric cancer.

Dual roles for HMGB1: DNA binding and cytokine

Effective therapies against overwhelming Gram-negative bacteremia, or sepsis, have eluded successful development. The discovery that tumor necrosis factor (TNF), a host-derived inflammatory mediator, was both necessary and sufficient to recapitulate Gram-negative sepsis raised cautious optimism for developing a targeted therapeutic. However, the rapid kinetics of the TNF response to infection defined an extremely narrow window of opportunity during which anti-TNF therapeutics could be successfully administered. HMGB1 was previously studied as a DNA-binding protein involved in DNA replication, repair, and transcription; and as a membrane-associated protein that mediates neurite outgrowth. A decade-long search has culminated in our identification of HMGB1 as a late mediator of endotoxemia. HMGB1 is released by macrophages upon exposure to endotoxin, activates many other pro-inflammatory mediators, and is lethal to otherwise healthy animals. Elevated levels of HMGB1 are observed in the serum of patients with sepsis, and the highest levels were found in those patients that died. The delayed kinetics of HMGB1 release indicate that it may be useful to target this toxic cytokine in the development of future therapies.