Sp1-binding elements in the promoter of RAGE are essential for amphoterin-mediated gene expression in cultured neuroblastoma cells

The receptor for advanced glycation endproducts (RAGE) decreases survival of tumor-bearing mice by enhancing the generation of lung metastasis-associated myeloid-derived suppressor cells

Metastatic cancer has a poor prognosis. Novel pharmacologic targets need to be identified. The receptor for advanced glycation endproducts (RAGE) is a pattern recognition receptor constitutively expressed in the lungs. Absence of overt disease in RAGE null mice suggests that RAGE is unnecessary or redundant in health. We report that RAGE null tumor-bearing mice have reduced lung metastasis and improved survival. Bone marrow chimera studies suggest that hematopoietic cell RAGE is an important contributor to these effects. Deletion of RAGE reduces both the quantity and suppressive activity of tumor-induced MDSC. Protein and mRNA studies suggest that RAGE contributes to the generation and function of MDSC including expression of the alarmins S100A8/A9 and activity of inducible nitric oxide synthase, arginase-1, and NF-κB. These findings demonstrate the important role of RAGE in determining the quantity and function of tumor-associated MDSC and suggest RAGE as a pharmacologic target for patients with metastatic disease.

HMGB1-RAGE, A Useful Partnership in Vital Response?

Introduction: In forensic practice, it is well known that the mechanism and dating of traumatic injuries is one of the primary responsibilities of this specialty. Currently, it is a subject still debated by researchers, and so far, an infallible marker that would objectively support their intravitam/postmortem occurrence has not yet been identified. However, studies have shown that the HMGB1-RAGE axis is rapidly activated after trauma and might be an essential element to help solve the forensic problem of wound dating.

Purpose: To compare the values of HMGB1-RAGE expression occurring in wounds produced intravitally shortly before death and in wounds produced postmortem and to quantify the differences arising between them.

Material and method: For this prospective study, skin fragments were collected from the site of wounds in autopsied cadavers at the County Clinical Service of Forensic Medicine Constanta (SCJML Constanta), wounds produced intravitally and with a maximum survival time of 60 minutes. Postmortem wounds and control fragments from volunteers undergoing surgery for skin tumours were also collected. The main conditions were: chronological documentation of the lesion and absence of neoplastic or inflammatory conditions. Ninety-six autopsy cases between 2021–2022 met the criteria for inclusion in the study. A control fragment accompanied each fragment from the wound. Routine Hematoxylin-Eosin (HE), Perls and Van Gieson Werhoeffstaining, as well as immunohistochemistry with HMGB1 and RAGE markers were performed on each fragment and a score based on staining intensity was determined.

Results: Routine staining was not useful in assessing vitality in segments with survival time up to 30 min. Immunohistochemically, both markers showed increased values compared to control values (p<0.0001) and to lesions produced postmortem. An interesting aspect is the lack of reactivity in the lesion’s margins for both markers.

Conclusions: Although further research is needed, the results of our study support the hypothesis that the HMGB1-RAGE axis is useful in assessing the vital reaction in skin wounds.

Inhibition of the Receptor for Advanced Glycation End Products Enhances the Cytotoxic Effect of Gemcitabine in Murine Pancreatic Tumors

Pancreatic ductal adenocarcinoma (PDAC) remains a very difficult cancer to treat. Recent in vitro and in vivo studies suggest that the activation of the receptor for advanced glycation end products (RAGE) by its ligands stimulates pancreatic cancer cell proliferation and tumor growth. Additional studies show that, in the RAGE ligand, the high mobility group box 1 (HMGB1) protein plays an important role in chemoresistance against the cytotoxic agent gemcitabine by promoting cell survival through increased autophagy. We hypothesized that blocking the RAGE/HMGB1 interaction would enhance the cytotoxic effect of gemcitabine by reducing cell survival and autophagy. Using a preclinical mouse model of PDAC and a monoclonal antibody (IgG 2A11) as a RAGE inhibitor, we demonstrate that RAGE inhibition concurrent with gemcitabine treatment enhanced the cytotoxic effect of gemcitabine. The combination of IgG 2A11 and gemcitabine resulted in decreased autophagy compared to treatment with gemcitabine combined with control antibodies. Notably, we also observed that RAGE inhibition protected against excessive weight loss during treatment with gemcitabine. Our data suggest that the combination of gemcitabine with a RAGE inhibitor could be a promising therapeutic approach for the treatment of pancreatic cancer and needs to be further investigated.

RAGE Up-Regulation Differently Affects Cell Proliferation and Migration in Pancreatic Cancer Cells

The receptor for advanced glycation end products (RAGE) contributes to many cellular aspects of pancreatic cancer including cell proliferation, migration, and survival. Studies have shown that RAGE activation by its ligands promotes pancreatic tumor growth by stimulating both cell proliferation and migration. In this study, we investigated the effect of RAGE up-regulation on the proliferation and migration of the human pancreatic cancer Panc-1 cell-line. We show that moderate overexpression of RAGE in Panc-1 cells results in increased cell proliferation, but decreased cell migration. The observed cellular changes were confirmed to be RAGE-specific and reversible by using RAGE-specific siRNAs and the small molecule RAGE inhibitor FPS-ZM1. At the molecular level, we show that RAGE up-regulation was associated with decreased activity of FAK, Akt, Erk1/2, and NF-κB signaling pathways and greatly reduced levels of α2 and β1 integrin expression, which is in agreement with the observed decreases in cell migration. We also demonstrate that RAGE up-regulation changes the expression of key molecular markers of epithelial-to-mesenchymal transition (EMT). Our results suggest that in the absence of stimulation by external ligands, RAGE up-regulation can differently modulate cell proliferation and migration in pancreatic cancer cells and regulates partly EMT.

Immunological Significance of HMGB1 Post-Translational Modification and Redox Biology

Most extracellular proteins are secreted via the classical endoplasmic reticulum (ER)/Golgi-dependent secretion pathway; however, some proteins, including a few danger-associated molecular patterns (DAMPs), are secreted via non-classical ER/Golgi-independent secretion pathways. The evolutionarily conserved high mobility group box1 (HMGB1) is a ubiquitous nuclear protein that can be released by almost all cell types. HMGB1 lacks signal peptide and utilizes diverse non-canonical secretion mechanisms for its extracellular export. Although the post-translational modifications of HMGB1 were demonstrated, the oxidation of HMGB1 and secretion mechanisms are not highlighted yet. We currently investigated that peroxiredoxins I and II (PrxI/II) induce the intramolecular disulfide bond formation of HMGB1 in the nucleus. Disulfide HMGB1 is preferentially transported out of the nucleus by binding to the nuclear exportin chromosome-region maintenance 1 (CRM1). We determined the kinetics of HMGB1 oxidation in bone marrow-derived macrophage as early as a few minutes after lipopolysaccharide treatment, peaking at 4 h while disulfide HMGB1 accumulation was observed within the cells, starting to secrete in the late time point. We have shown that HMGB1 oxidation status, which is known to determine the biological activity in extracellular HMGB1, is crucial for the secretion of HMGB1 from the nucleus. This review summarizes selected aspects of HMGB1 redox biology relevant to the induction and propagation of inflammatory diseases. We implicate the immunological significance and the need for novel HMGB1 inhibitors through mechanism-based studies.

The effect of high mobility group box-1 protein on cerebral edema, blood-brain barrier, oxidative stress and apoptosis in an experimental traumatic brain injury model

Traumatic brain injury (TBI) is one of the important reason of morbidity and mortality. While the primary injury due to mechanical impact is unavoidable, the secondary injury which is formed as a result of primary injury and thought to occur due to neuroinflammation in the forefront can be prevented and by this way mortality and morbidity can be reduced. High mobility group box-1 (HMGB1) is a protein that triggers the neuroinflammatory process by being released from the nucleus of necrotic tissues after primary injury. The aim of this study is to investigate the effects of HMGB1 on its receptors TLR4 and RAGE, cerebral edema, blood-brain barrier, oxidative stress and apoptosis causing secondary damage in an experimental traumatic brain injury model. Weighing between 280-320 g, 10 to 12 weeks-old, a total of 30 adult male Sprague-Dawley rats were used for the experiments. The rats were randomly assigned to 3 groups: 1) Control, 2) TBI and 3) TBI + ethyl pyruvate group (n = 10 per group). Right parietal cortical contusion was made by using a weight-dropping TBI method. Brain samples were harvested from pericontusional area at 24 h after TBI. HMGB1, TLR4, RAGE, occludin, claudin-5, ZO-1 levels are investigated by western blot analyses and immunohistochemistry examinations. HMGB-1, TLR4 and RAGE expressions increased after TBI. Major tight junction proteins in the blood-brain barrier: occludin, claudin-5 and ZO-1 expressions decreased after TBI. Brain edema increased after TBI. Also, proapoptotic bax and active caspase 3 expressions increased, antiapoptotic bcl-2 levels decreased after TBI. Total oxidant status and oxidative stress increased, total antioxidant status decreased after TBI. HMGB-1 protein plays a key role in the pathophysiology of traumatic brain injury.

High-Mobility Group Box-1 and Liver Disease

High‐mobility group box‐1 (HMGB1) is a ubiquitous protein. While initially thought to be simply an architectural protein due to its DNA‐binding ability, evidence from the last decade suggests that HMGB1 is a key protein participating in the pathogenesis of acute liver injury and chronic liver disease. When it is passively released or actively secreted after injury, HMGB1 acts as a damage‐associated molecular pattern that communicates injury and inflammation to neighboring cells by the receptor for advanced glycation end products or toll‐like receptor 4, among others. In the setting of acute liver injury, HMGB1 participates in ischemia/reperfusion, sepsis, and drug‐induced liver injury. In the context of chronic liver disease, it has been implicated in alcoholic liver disease, liver fibrosis, nonalcoholic steatohepatitis, and hepatocellular carcinoma. Recently, specific posttranslational modifications have been identified that could condition the effects of the protein in the liver. Here, we provide a detailed review of how HMGB1 signaling participates in acute liver injury and chronic liver disease.

All the "RAGE" in lung disease: The receptor for advanced glycation endproducts (RAGE) is a major mediator of pulmonary inflammatory responses

The receptor for advanced glycation endproducts (RAGE) is a pro-inflammatory pattern recognition receptor (PRR) that has been implicated in the pathogenesis of numerous inflammatory diseases. It was discovered in 1992 on endothelial cells and was named for its ability to bind advanced glycation endproducts and promote vascular inflammation in the vessels of patients with diabetes. Further studies revealed that RAGE is most highly expressed in lung tissue and spurred numerous explorations into RAGE's role in the lung. These studies have found that RAGE is an important mediator in allergic airway inflammation (AAI) and asthma, pulmonary fibrosis, lung cancer, chronic obstructive pulmonary disease (COPD), acute lung injury, pneumonia, cystic fibrosis, and bronchopulmonary dysplasia. RAGE has not yet been targeted in the lungs of paediatric or adult clinical populations, but the development of new ways to inhibit RAGE is setting the stage for the emergence of novel therapeutic agents for patients suffering from these pulmonary conditions.

RAGE Enhances TLR Responses through Binding and Internalization of RNA

Nucleic acid recognition is an important mechanism that enables the innate immune system to detect microbial infection and tissue damage. To minimize the recognition of self-derived nucleic acids, all nucleic acid-sensing signaling receptors are sequestered away from the cell surface and are activated in the cytoplasm or in endosomes. Nucleic acid sensing in endosomes relies on members of the TLR family. The receptor for advanced glycation end-products (RAGE) was recently shown to bind DNA at the cell surface, facilitating DNA internalization and subsequent recognition by TLR9. In this article, we show that RAGE binds RNA molecules in a sequence-independent manner and enhances cellular RNA uptake into endosomes. Gain- and loss-of-function studies demonstrate that RAGE increases the sensitivity of all ssRNA-sensing TLRs (TLR7, TLR8, TLR13), suggesting that RAGE is an integral part of the endosomal nucleic acid-sensing system.

Increased Circulating Advanced Oxidation Protein Products and High-Sensitive Troponin T in Cirrhotic Patients with Chronic Hepatitis C: A Preliminary Report

Aim. To investigate the relationship between advanced oxidation protein products (AOPPs) and myocardial injury by comparing the selected biomarker for detecting myocardial injury [high-sensitive troponin T (hs-TnT)] in patients with chronic HCV infection. Methods and Results. Eighty-eight patients with cirrhosis and 40 healthy control subjects were enrolled in the study. Circulating levels of AOPPs-albumin (the ratio of AOPPs to albumin content), hs-TnT, tumor necrosis factor α (TNF-α), and high-sensitivity C-reactive protein (hs-CRP) were assessed. Compared with healthy controls, the cirrhotic patients with chronic HCV infection had higher levels of AOPPs-albumin, which were associated with increased hs-TnT. When the presence of ascites was considered, the plasma levels of AOPPs-albumin were higher, as well as TNF-α. AOPPs-albumin positively correlated with hs-TnT level in all cirrhotic patients with chronic HCV infection and this correlation was stronger in decompensated cirrhotic patients. In multivariate logistic regression analysis, the independent factors associated with the presence of ascites were high AOPPs-albumin levels and elevated hs-TnT levels. Conclusion. The simultaneous monitoring of plasma AOPPs and hs-TnT can be helpful for the alterations in myocardial function control in cirrhotic patients with chronic HCV infection.

Soluble Receptor for Advanced Glycation End-Products Predicts Impaired Alveolar Fluid Clearance in Acute Respiratory Distress Syndrome

RATIONALE

Levels of the soluble form of the receptor for advanced glycation end-products (sRAGE) are elevated during acute respiratory distress syndrome (ARDS) and correlate with severity and prognosis. Alveolar fluid clearance (AFC) is necessary for the resolution of lung edema but is impaired in most patients with ARDS. No reliable marker of this process has been investigated to date.

OBJECTIVES

To verify whether sRAGE could predict AFC during ARDS.

METHODS

Anesthetized CD-1 mice underwent orotracheal instillation of hydrochloric acid. At specified time points, lung injury was assessed by analysis of blood gases, alveolar permeability, lung histology, AFC, and plasma/bronchoalveolar fluid measurements of proinflammatory cytokines and sRAGE. Plasma sRAGE and AFC rates were also prospectively assessed in 30 patients with ARDS.

MEASUREMENTS AND MAIN RESULTS

The rate of AFC was inversely correlated with sRAGE levels in the plasma and the bronchoalveolar fluid of acid-injured mice (Spearman's ρ = -0.73 and -0.69, respectively; P < 10(-3)), and plasma sRAGE correlated with AFC in patients with ARDS (Spearman's ρ = -0.59; P < 10(-3)). Similarly, sRAGE levels were significantly associated with lung injury severity, and decreased over time in mice, whereas AFC was restored and lung injury resolved.

CONCLUSIONS

Our results indicate that sRAGE levels could be a reliable predictor of impaired AFC during ARDS, and should stimulate further studies on the pathophysiologic implications of RAGE axis in the mechanisms leading to edema resolution. Clinical trial registered with www.clinicaltrials.gov (NCT 00811629).

Calycosin Rebalances Advanced Glycation End Products-Induced Glucose Uptake Dysfunction of Hepatocyte In Vitro

Diabetes mellitus (DM) often accompanies liver dysfunction. Astragali Radix is a traditional Chinese herbal medicine that is widely administrated to ameliorate the symptoms of diabetes as well as liver dysfunction, but its acting mechanism is still not yet fully recognized. Advanced glycation end products (AGEs) play a key role in promoting diabetic organ dysfunction. Both hyperglycemia and AGEs can induce insulin resistance, hepatocyte damage and liver dysfunction. We designed this study to explore the effects of the phytoestrogen Calycosin, a major active component of Astragali Radix, on AGEs-induced glucose uptake dysfunction in the hepatocyte cell line and relevant mechanisms. MTT and BrdU methods were applied to evaluate cell viability. 2-NBDG was used to observe glucose uptake by a live cell imaging system. Immunofluorescence method was carried out to investigate GLUT1, GLUT4, and RAGE protein expressions on cell membrane. cAMP content was determined by an EIA method. We found Calycosin concentration-dependently ameliorated AGEs-induced hepatocyte viability damage. AGEs dramatically reduced basal glucose uptake in hepatocytes, and this reduction could be reversed by Calycosin administration. By immunofluorescence detection, we observed that Calycosin could inhibit AGEs-induced GLUT1 expression down-regulation via estrogen receptor (ER). Furthermore, Calycosin decreased AGEs-promoted RAGE and cAMP elevation in hepatocytes. These findings strongly suggest that Calycosin can ameliorate AGEs-promoted glucose uptake dysfunction in hepatocytes; the protection of cell viability and ER-RAGE and GLUT1 pathways play a significant role in this modulation.

HMGB1 in health and disease

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

An overview on HMGB1 inhibitors as potential therapeutic agents in HMGB1-related pathologies

HMGB1 (High-Mobility Group Box-1) is a nuclear protein that acts as an architectural chromatin-binding factor involved in the maintenance of nucleosome structure and regulation of gene transcription. It can be released into the extracellular milieu from immune and non-immune cells in response to various stimuli. Extracellular HMGB1 contributes to the pathogenesis of numerous chronic inflammatory and autoimmune diseases, including sepsis, rheumatoid arthritis, atherosclerosis, chronic kidney disease, systemic lupus erythematosus (SLE), as well as cancer pathogenesis. Interaction of released HMGB1 with the cell-surface receptor for advanced glycation end products (RAGE) is one of the main signaling pathways triggering these diseases. It has been also demonstrated that the inhibition of the HMGB1-RAGE interaction represents a promising approach for the modulation of the inflammatory and tumor-facilitating activity of HMGB1. In this review we describe various approaches recently proposed in the literature to inhibit HMGB1 and the related inflammatory processes, especially focusing on the block of RAGE-HMGB1 signaling. Several strategies are based on molecules which mainly interact with RAGE as competitive antagonists of HMGB1. As an alternative, encouraging results have been obtained with HMGB1-targeting, leading to the identification of compounds that directly bind to HMGB1, ranging from small natural or synthetic molecules, such as glycyrrhizin and gabexate mesilate, to HMGB1-specific antibodies, peptides, proteins as well as bent DNA-based duplexes. Future perspectives are discussed in the light of the overall body of knowledge acquired by a large number of research groups operating in different but related fields.

Inhibition of RAGE signaling through the intracellular delivery of inhibitor peptides by PEI cationization

The receptor for advanced glycation end products (RAGE) is a multi-ligand cell surface receptor and a member of the immunoglobulin superfamily. RAGE is involved in a wide range of inflammatory, degenerative and hyper-proliferative disorders which span over different organs by engaging diverse ligands, including advanced glycation end products, S100 family proteins, high-mobility group protein B1 (HMGB1) and amyloid β. We previously demonstrated that the cytoplasmic domain of RAGE is phosphorylated upon the binding of ligands, enabling the recruitment of two distinct pairs of adaptor proteins, Toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP) and myeloid differentiation protein 88 (MyD88). This engagement allows the activation of downstream effector molecules, and thereby mediates a wide variety of cellular processes, such as inflammatory responses, apoptotic cell death, migration and cell growth. Therefore, inhibition of the binding of TIRAP to RAGE may abrogate intracellular signaling from ligand-activated RAGE. In the present study, we developed inhibitor peptides for RAGE signaling (RAGE-I) by mimicking the phosphorylatable cytosolic domain of RAGE. RAGE-I was efficiently delivered into the cells by polyethylenimine (PEI) cationization. We demonstrated that RAGE-I specifically bound to TIRAP and abrogated the activation of Cdc42 induced by ligand-activated RAGE. Furthermore, we were able to reduce neuronal cell death induced by an excess amount of S100B and to inhibit the migration and invasion of glioma cells in vitro. Our results indicate that RAGE-I provides a powerful tool for therapeutics to block RAGE-mediated multiple signaling.

Advanced oxidation protein products induce cardiomyocyte death via Nox2/Rac1/superoxide-dependent TRAF3IP2/JNK signaling

Advanced oxidation protein products (AOPPs) are formed during chronic oxidative stress as a result of reactions between plasma proteins and chlorinated oxidants. Their levels are elevated during various cardiovascular diseases. Because elevated AOPPs serve as independent risk factors for ischemic heart disease, and cardiomyocyte death is a hallmark of ischemic heart disease, we hypothesized that AOPPs will induce cardiomyocyte death. AOPP-modified mouse serum albumin (AOPP-MSA) induced significant death of neonatal mouse cardiomyocytes that was attenuated by knockdown of the receptor for advanced glycation end products, but not CD36. Notably, TRAF3-interacting protein 2 (TRAF3IP2; also known as CIKS or Act1) knockdown blunted AOPP-induced apoptosis. AOPP-MSA stimulated Nox2/Rac1-dependent superoxide generation, TRAF3IP2 expression, and TRAF3IP2-dependent JNK activation. The superoxide anion generating xanthine/xanthine oxidase system and hydrogen peroxide both induced TRAF3IP2 expression. Further, AOPP-MSA induced mitochondrial Bax translocation and release of cytochrome c into cytoplasm. Moreover, AOPP-MSA suppressed antiapoptotic Bcl-2 and Bcl-xL expression. These effects were reversed by TRAF3IP2 knockdown or forced expression of mutant JNK. Similar to its effects in neonatal cardiomyocytes, AOPP-MSA induced adult cardiomyocyte death in part via TRAF3IP2. These results demonstrate for the first time that AOPPs induce cardiomyocyte death via Nox2/Rac1/superoxide-dependent TRAF3IP2/JNK activation in vitro and suggest that AOPPs may contribute to myocardial injury in vivo. Thus TRAF3IP2 may represent a potential therapeutic target in ischemic heart disease.

Advanced glycation end products (AGE) induce the receptor for AGE in the colonic mucosa of azoxymethane-injected Fischer 344 rats fed with a high-linoleic acid and high-glucose diet

BACKGROUND

Advanced glycation end products (AGE) and the receptor for advanced glycation end products (RAGE) are closely associated with colorectal cancer progression. The association between RAGE and AGE in colon carcinogenesis needs to be clarified.

METHODS

Levels of RAGE and AGE were examined in azoxymethane (AOM)-injected Fischer 344 rats fed a control diet (Group C), a 15 % linoleic acid (LA) diet (Group L), a control diet with 10 % glucose drink (Group G), and a 15 % LA diet with 10 % glucose drink (Group L + G). Group L + G showed the most pronounced increase of body weight, blood sugar, and serum insulin.

RESULTS

The rats in Group L + G showed the most pronounced multiplicity of aberrant crypt foci (ACF) and carcinomas with increased mucosal RAGE and AGE. IEC6 rat intestinal epithelial cells treated with AGE showed increased RAGE expression, which was inhibited by treatment with metformin or losartan. In the AOM-injected rat colon cancer model, the levels of RAGE and AGE, and the multiplicity of ACF and carcinomas, in Group L + G rats were suppressed by treatment with metformin or losartan.

CONCLUSIONS

These results suggest that AGE-RAGE induced by high-LA and high-glucose diets substantially enhances colon cancer development; thus, suppression of AGE-RAGE could be a potential target for colon cancer chemoprevention.

Expression of HMGB1 and RAGE in rat and human brains after traumatic brain injury

BACKGROUND

Increasing evidence suggests that an inflammatory reaction contributes to the secondary brain injury that plays a critical role in the clinical outcome of patients with traumatic brain injury (TBI). Recently, high-mobility group box 1 (HMGB1) has been identified as a key cytokine in the inflammatory reaction and may represent a new target for the treatment of TBI. However, the expression of HMGB1 during this injury process has not yet been studied.

METHODS

In this study, the levels of both HMGB1 and receptor for advanced glycation end products (RAGE) in the rat brain were analyzed by Western blot at different time points after TBI. Immunohistochemistry was also performed to examine the expression pattern of HMGB1 and RAGE in both the rat and the human brain after TBI.

RESULTS

In the rat brain, HMGB1 levels significantly declined below the basal level at 6 hours after TBI and then gradually returned to the basal level 2 days later. RAGE expression increased 6 hours after TBI and reached its peak after 1 day; this level then slowly decreased but remained higher than the sham-injury group until 6 days after TBI. In both rat and human brains, HMGB1 either disappeared or was translocated from the nucleus to the cytoplasm at early stages after TBI and then was localized to the cytoplasm of phagocytic microglia at later stages. RAGE expression increased in the region surrounding the contused area after TBI in both rat and human brains. At later stages, RAGE was mainly expressed in microglia.

CONCLUSION

HMGB1 is involved in both early and later stages after TBI. Targeting HMGB1 signaling may be a promising therapeutic approach for the treatment of TBI.

Macrophage activation by factors released from acetaminophen-injured hepatocytes: potential role of HMGB1

Toxic doses of acetaminophen (AA) cause hepatocellular necrosis. Evidence suggests that activated macrophages contribute to the pathogenic process; however, the factors that activate these cells are unknown. In these studies, we assessed the role of mediators released from AA-injured hepatocytes in macrophage activation. Treatment of macrophages with conditioned medium (CM) collected 24hr after treatment of mouse hepatocytes with 5mM AA (CM-AA) resulted in increased production of reactive oxygen species (ROS). Macrophage expression of heme oxygenase-1 (HO-1) and catalase mRNA was also upregulated by CM-AA, as well as cyclooxygenase (COX)-2 and 12/15-lipoxygenase (LOX). CM-AA also upregulated expression of the proinflammatory chemokines, MIP-1α and MIP-2. The effects of CM-AA on expression of COX-2, MIP-1α and MIP-2 were inhibited by blockade of p44/42 MAP kinase, suggesting a biochemical mechanism mediating macrophage activation. Hepatocytes injured by AA were found to release HMGB1, a potent macrophage activator. This was inhibited by pretreatment of hepatocytes with ethyl pyruvate (EP), which blocks HMGB1 release. EP also blocked CM-AA induced ROS production and antioxidant expression, and reduced expression of COX-2, but not MIP-1α or MIP-2. These findings suggest that HMGB1 released by AA-injured hepatocytes contributes to macrophage activation. This is supported by our observation that expression of the HMGB1 receptor RAGE is upregulated in macrophages in response to CM-AA. These data indicate that AA-injured hepatocytes contribute to the inflammatory environment in the liver through the release of mediators such as HMGB1. Blocking HMGB1/RAGE may be a useful approach to limiting classical macrophage activation and AA-induced hepatotoxicity.

Enterocyte-specific A20 deficiency sensitizes to tumor necrosis factor-induced toxicity and experimental colitis

A20 is a nuclear factor kappaB (NF-kappaB) target gene that encodes a ubiquitin-editing enzyme that is essential for the termination of NF-kappaB activation after tumor necrosis factor (TNF) or microbial product stimulation and for the prevention of TNF-induced apoptosis. Mice lacking A20 succumb to inflammation in several organs, including the intestine, and A20 mutations have been associated with Crohn's disease. However, ablation of NF-kappaB activity, specifically in intestinal epithelial cells (IECs), promotes intestinal inflammation. As A20 deficiency sensitizes cells to TNF-induced apoptosis yet also promotes NF-kappaB activity, it is not clear if A20 deficiency in IECs would exacerbate or ameliorate intestinal inflammation. We generated mice lacking A20 specifically in IECs. These mice did not show spontaneous intestinal inflammation but exhibited increased susceptibility to experimental colitis, and their IECs were hypersensitive to TNF-induced apoptosis. The resulting TNF-driven breakdown of the intestinal barrier permitted commensal bacterial infiltration and led to systemic inflammation. These studies define A20 as a major antiapoptotic protein in the intestinal epithelium and further indicate that defects in A20 might contribute to inflammatory bowel disease in humans.

RAGE: a novel biological and genetic marker for vascular disease

RAGE [receptor for AGEs (advanced glycation end-products)] plays an important role in the development and progression of vascular disease. Studies in cultured cells and small animal models of disease have clearly demonstrated that RAGE is central to the pathogenesis of vascular disease of the macro- and micro-vessels in both the diabetic and non-diabetic state. Emerging results from human clinical studies have revealed that levels of circulating soluble RAGE in the plasma may reflect the presence and/or extent of vascular disease state. Additionally, genetic variants of the RAGE gene (AGER in HUGO nomenclature) have been associated with vascular disease risk. Combining RAGE circulating protein levels and the presence of particular RAGE polymorphisms may be a useful clinical tool for the prediction of individuals at risk for vascular disease. Therapeutic intervention targeted at the RAGE gene may therefore be a useful means of treating pathologies of the vasculature.

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.

Implication of receptor for advanced glycation end product (RAGE) in pulmonary health and pathophysiology

Receptor for advanced glycation end products (RAGE) is a membrane bound receptor and member of the immunoglobulin super family and is normally present in a highly abundant basal level expression in lung. This high expression of RAGE in lung alveolar epithelial type I (ATI) cells is presumably involved in the proliferation and differentiation of pulmonary epithelial cells. However, typically higher than basal level expression of RAGE may indicate the existence of severe pathophysiological condition in lung, e.g. acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). During pulmonary tissue injury an endogenous secretory isoform of RAGE called EsRAGE is noticed at high levels in broncho-alveolar lavage (BAL) and plasma. Recently, a soluble form of RAGE (sRAGE) produced by recombinant gene technology was shown to exhibit a therapeutic potential in experimental animal models. Detailed study of RAGE in the pulmonary tissues will facilitate the understanding of the importance of RAGE signaling in the pulmonary health and pathophysiology.

A peptide inhibitor of the urokinase/urokinase receptor system inhibits alteration of the blood-retinal barrier in diabetes

One of the major complications of diabetes is the alteration of the blood-retinal barrier, leading to retinal edema and consequent vision loss. The aim of this study was to evaluate the role of the urokinase plasminogen activator (uPA)/uPA receptor (uPAR) system in the regulation of retinal vascular permeability. Biochemical, molecular, and histological techniques were used to examine the role of uPA and uPAR in the regulation of retinal vascular permeability in diabetic rats and cultured retinal endothelial cells. The increased retinal vascular permeability in diabetic rats was associated with a decrease in vascular endothelial (VE) -cadherin expression in retinal vessels. Treatment with the uPA/uPAR-inhibiting peptide (A6) was shown to reduce diabetes-induced permeability and the loss of VE-cadherin. The increased permeability of cultured cells in response to advanced glycation end products (AGEs) was significantly inhibited with A6. Treatment of endothelial cells with specific matrix metalloproteinases or AGEs resulted in loss of VE-cadherin from the cell surface, which could be inhibited by A6. uPA/uPAR physically interacts with AGEs/receptor for advanced glycation end products on the cell surface and regulates its activity. uPA and its receptor uPAR play important roles in the alteration of the blood-retinal barrier through proteolytic degradation of VE-cadherin. The ability of A6 to block retinal vascular permeability in diabetes suggests a potential therapeutic approach for the treatment of diabetic macular edema.

Early release of HMGB-1 from neurons after the onset of brain ischemia

The nuclear protein high-mobility group box 1 (HMGB-1) promotes inflammation in sepsis, but little is known about its role in brain ischemia-induced inflammation. We report that HMGB-1 and its receptors, receptor for advanced glycation end products (RAGE), Toll-like receptor 2 (TLR2), and TLR4, were expressed in normal brain and in cultured neurons, endothelia, and glial cells. During middle cerebral artery occlusion (MCAO), in mice, HMGB-1 immunostaining rapidly disappeared from all cells within the striatal ischemic core from 1 h after onset of occlusion. High-mobility group box 1 translocation from nucleus to cytoplasm was observed within the cortical periinfarct regions 2 h after ischemic reperfusion (2 h MCAO). High-mobility group box 1 predominantly translocated to the cytoplasm or disappeared in cells that colabeled with the neuronal marker NeuN. Furthermore, RAGE was robustly expressed in the periinfarct region after MCAO. Cellular release of HMGB-1 was detected by immunoblotting of cerebrospinal fluid as early as 2 h after ischemic reperfusion (2 h MCAO). High-mobility group box 1 released from neurons, in vitro, after glutamate excitotoxicity, maintained biologic activity and induced glial expression of tumor necrosis factor alpha (TNFalpha). Anti-HMGB-1 antibody suppressed TNFalpha upregulation in astrocytes exposed to conditioned media from glutamate-treated neurons. Moreover, TNFalpha and the cytokine intercellular adhesion molecule-1 increased in cultured glia and endothelial cells, respectively, after adding recombinant HMGB-1. In conclusion, HMGB-1 is released early after ischemic injury from neurons and may contribute to the initial stages of the inflammatory response.

G6b-B cell surface inhibitory receptor expression is highly restricted to CD4+ T-cells and induced by interleukin-4–activated STAT6 pathway

The G6b-B gene encodes a novel cell surface receptor of the immunoglobulin superfamily that activates inhibitory signaling pathways by triggering SHP-1/SHP-2 via immunoreceptor tyrosine-based inhibitory motifs (ITIM) in its cytoplasmic domain. We previously identified decreased G6b-B expression in peripheral blood mononuclear cells (PBMC) during acute cellular cardiac allograft rejection. We studied the expression of G6b-B in different human mononuclear cell populations and its regulation. Real-time polymerase chain reaction (PCR) revealed that G6b-B mRNA is higher in CD4+ T cells or monocytes, but is not different between CD25+ CD4+ T cells and CD25- CD4+ T cells. G6b-B mRNA was increased in CD4+ T cells in presence of interleukin-4 in dose- and time-dependent manners. To understand the regulatory mechanism, we analyzed a 1.9-kb 5'-flanking region of the G6b-B translation start site and found a putative cis-acting element for Signal Transducer and Activator of Transcription (STAT)-6. Luciferase-reporter-gene-assay and electrophoretic mobility shift assays identified the STAT6 site as necessary for the induction of G6b-B by IL-4. Our study demonstrates that G6b-B expression is highly restricted to peripheral CD4+ T cells and up-regulated by the IL-4-induced STAT6 pathway, strongly suggesting that G6b-B is involved in regulation of the immune response by CD4+ T cell-mediated and IL-4 induced regulatory mechanisms.

Expression of receptor for advanced glycation end products during rat tongue carcinogenesis by 4-nitroquinoline 1-oxide and effect of a selective cyclooxygenase-2 inhibitor, etodolac

OBJECTIVES

The expression of a receptor for advanced glycation end products (RAGE) in lesions developed during rat tongue carcinogenesis by 4-nitroquinoline 1-oxide (4-NQO) and the effect of a selective cyclooxygenase-2 inhibitor, etodolac, were investigated.

METHODS

The tongue lesions were induced in Fischer 344 rats given 20-30 ppm 4-NQO in their drinking water for 12 weeks and then fed the basal diet containing 150 and 300 ppm of etodolac for 16 weeks, respectively.

RESULTS

The incidence of carcinomas in the 4-NQO-alone group was 100%. Etodolac significantly reduced the incidences of carcinomas to 66.7% (p < 0.05) and 50% (p < 0.01) at doses of 150 and 300 ppm, respectively. RAGE protein was immunohistochemically expressed in dysplastic cells and cancer cells of dysplasias and carcinomas. Etodolac significantly decreased the stainability of RAGE protein in dysplasias (p < 0.02) and carcinomas (p < 0.01). The expression of RAGE mRNA analyzed by RT-PCR was clearly detected in carcinomas developing in the 4-NQO-alone group. In carcinomas developing in the etodolac-treated group, RAGE mRNA expression significantly decreased (p < 0.03).

CONCLUSIONS

These results indicate that RAGE is involved in rat tongue carcinogenesis by 4-NQO and suggest that the chemopreventive effect exerted by etodolac is partly related to the inhibition of RAGE expression.

Diabetes, leukoencephalopathy and rage

Longstanding diabetes mellitus damages kidney, retina, peripheral nerve and blood vessels, but brain is not usually considered a primary target. We describe direct involvement of the brain, particularly white matter, in long-term (9 months) experimental diabetes of mice, not previously modeled, correlating magnetic resonance (MR) imaging with quantitative histological assessment. Leukoencephalopathy and cerebral atrophy, resembling that encountered in diabetic humans, developed in diabetic mice and was accompanied by time-related development of cognitive changes in behavioural testing. Increased RAGE (receptor for advanced glycation end products) expression, a mediator of widespread diabetic complications, increased dramatically at sites of white matter damage in regions of myelination. RAGE expression was also elevated within neurons, astrocytes and microglia in grey matter and within oligodendrocytes in white matter. RAGE null diabetic mice had significantly less neurodegenerative changes when compared to wild-type diabetic mice. Our findings identify a robust and novel model of cerebral, particularly white matter, involvement with diabetes associated with abnormal RAGE signaling.

Diabetic vascular disease: it's all the RAGE

The major consequence of long-term diabetes is the increased incidence of disease of the vasculature. Of the underlying mechanisms leading to disease, the accumulation of advanced glycation end products (AGEs), resulting from the associated hyperglycemia, is the most convincing. Interaction of AGEs with their receptor, RAGE, activates numerous signaling pathways leading to activation of proinflammatory and procoagulatory genes. Studies in rodent models of macro- and microvascular disease have demonstrated that blockade of RAGE can prevent development of disease. These observations highlight RAGE as a therapeutic target for treatment of diabetic vascular disease.

HMGB1: guiding immunity from within

Two of the main challenges that eukaryotic multicellular organisms faced during evolution were to eliminate and replace dying cells and to cope with invading microorganisms. The innate immune system evolved to handle both tasks: to scavenge cellular debris and to form the first line of defence against microbes. In this review, we focus on high mobility group box 1 (HMGB1) protein as a common signal that alerts the innate immune system to excessive or deregulated cell death and to microbial invasion. HMGB1, which is well known nuclear protein, has revealed unexpected facets as an extracellular mediator. The role of HMGB1 as an endogenous molecule that facilitates immune responses and has an important role in tissue homeostasis and disease will be highlighted here.

Monocytes promote natural killer cell interferon gamma production in response to the endogenous danger signal HMGB1

Substantial attention has been paid to the role of the toll-like receptor (TLR) ligands of late and their role in regulating the innate immune response. They serve as exogenous danger signals important in informing and driving the distal adaptive immune response to pathogens. Less clear has been the role of the nominal endogenous danger signals released and recognized in stressed cells following genotoxic or metabolic stress as occurs in progressively growing tumors. HMGB1 (high-mobility group B1) is a nuclear protein well characterized for its ability to modify DNA access to transcriptional proteins that is released from necrotic cells as well as secreted through the endosomal route from hematopoietic cells, serving as a late mediator of sepsis. It interacts with high-affinity RAGE (receptor for advanced glycation end products) and TLR2 receptors. Here we show that HMGB1 enhances interferon gamma release from macrophage (but not dendritic cell)-stimulated NK cells. This is effective only when coupled with other pro-inflammatory cytokines particularly with IL-2 in combination with IL-1 or IL-12. We have used this information to suggest that HMGB1, which also promotes epithelial migration and proliferation, drives repair in the absence or inhibition of other factors but enhances inflammation in their presence. The implications for tumorigenesis and tumor progression are quite important as they may be for other states of chronic inflammation.

Amphoterin as an extracellular regulator of cell motility: from discovery to disease

Amphoterin is a ubiquitous and highly conserved protein previously considered solely as a chromatin-associated, nuclear molecule. Amphoterin is released into the extracellular space by various cell types, and plays an important role in the regulation of cell migration, differentiation, tumorigenesis and inflammation. This paper reviews recent research on the mechanistic background underlying the biology of secreted amphoterin, with an emphasis on the role of amphoterin as an autocrine/paracrine regulator of cell migration.

Cellular Carbonyl Stress Enhances the Expression of Plasminogen Activator Inhibitor-1 in Rat White Adipocytes via Reactive Oxygen Species-dependent Pathway

Carbonyl stress is one of the important mechanisms of tissue damage in vascular complications of diabetes. In the present study, we observed that the plasminogen activator inhibitor-1 (PAI-1) levels in serum and its gene expression in adipose tissue were up-regulated in aged OLETF rats, model animals of obese type 2 diabetes. To study the mechanism of PAI-1 up-regulation, we examined the effect of advanced glycation end products (AGEs) and the product of lipid peroxidation (4-hydroxy-2-nonenal (HNE)), both of which are endogenously generated under carbonyl stress. Stimulation of primary white adipocytes by either AGE or HNE resulted in the elevation of PAI-1 in culture medium and at mRNA levels. The up-regulation of PAI-1 was also observed by incubating the cells in high glucose medium (30 mm, 48 h). The stimulatory effects by AGE or high glucose were inhibited by antioxidant, pyrrolidine dithiocarbamate, and reactive oxygen scavenger, probucol, suggesting a pivotal role of oxidative stress in white adipocytes. We also found that the effect by HNE was inhibited by antioxidant, N-acetylcysteine and that a specific inhibitor of glutathione biosynthesis, l-buthionine-S,R-sulfoximine, augmented the effect of subthreshold effect of HNE. Bioimaging of reactive oxygen species (ROS) by a fluorescent indicator, 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate, revealed ROS production in white adipocytes treated with AGE or HNE. These results suggest that cellular carbonyl stress induced by AGEs or HNE may stimulate PAI-1 synthesis in and release from adipose tissues through ROS formation.

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.

Central role of RAGE-dependent neointimal expansion in arterial restenosis

Cellular proliferation, migration, and expression of extracellular matrix proteins and MMPs contribute to neointimal formation upon vascular injury. Wild-type mice undergoing arterial endothelial denudation displayed striking upregulation of receptor for advanced glycation end products (RAGE) in the injured vessel, particularly in activated smooth muscle cells of the expanding neointima. In parallel, two of RAGE's signal transducing ligands, advanced glycation end products (AGEs) and S100/calgranulins, demonstrated increased deposition/expression in the injured vessel wall. Blockade of RAGE, employing soluble truncated receptor or antibodies, or in homozygous RAGE null mice, resulted in significantly decreased neointimal expansion after arterial injury and decreased smooth muscle cell proliferation, migration, and expression of extracellular matrix proteins. A critical role for smooth muscle cell RAGE signaling was demonstrated in mice bearing a transgene encoding a RAGE cytosolic tail-deletion mutant, specifically in smooth muscle cells, driven by the SM22alpha promoter. Upon arterial injury, neointimal expansion was strikingly suppressed compared with that observed in wild-type littermates. Taken together, these data highlight key roles for RAGE in modulating smooth muscle cell properties after injury and suggest that RAGE is a logical target for suppression of untoward neointimal expansion consequent to arterial injury.

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.

Reduction of the accumulation of advanced glycation end products by ACE inhibition in experimental diabetic nephropathy

The effect of ACE inhibition on the formation of advanced glycation end products (AGEs) and oxidative stress was explored. Streptozocin-induced diabetic animals were randomized to no treatment, the ACE inhibitor ramipril (3 mg/l), or the AGE formation inhibitor aminoguanidine (1 g/l) and followed for 12 weeks. Control groups were followed concurrently. Renal AGE accumulation, as determined by immunohistochemistry and both serum and renal fluorescence, were increased in diabetic animals. This was attenuated by both ramipril and aminoguanidine to a similar degree. Nitrotyrosine, a marker of protein oxidation, also followed a similar pattern. The receptor for AGEs, gene expression of the membrane-bound NADPH oxidase subunit gp91phox, and nuclear transcription factor-kappaB were all increased by diabetes but remained unaffected by either treatment regimen. Two other AGE receptors, AGE R2 and AGE R3, remained unchanged for the duration of the study. The present study has identified a relationship between the renin-angiotensin system and the accumulation of AGEs in experimental diabetic nephropathy that may be linked through oxidative stress

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.

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.

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.