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

Role of advanced glycation end product (AGE)-induced receptor (RAGE) expression in diabetic vascular complications

AIMS

Vascular complications are the major causes of morbidity and mortality in diabetic subjects. Interaction of advanced glycation end products (AGEs) with their receptor (RAGE) induces signal transduction that culminates in vascular complications. Therefore, in the present study we investigated the dependence of RAGE expression on circulating AGEs and evaluated the outcome of AGE-RAGE interaction by the oxidative stress and nature of vascular complications in type 2 diabetes mellitus (T2DM) patients.

METHODS

RAGE expression was determined by quantitative real-time PCR and western blotting, serum AGEs were estimated by ELISA and spectrofluorometry and oxidative stress markers namely protein carbonyl (PCO), advanced oxidation protein products (AOPP) and lipid peroxidation (MDA) were assayed spectrophotometerically in 75 T2DM patients (DM without vascular complication n=25; DM with microvascular complications n=25; DM with macrovascular complications n=25) and 25 healthy controls.

RESULTS

Serum AGE level was significantly higher in diabetic patients having vascular complications as compared to T2DM without complications (p<0.01). RAGE m-RNA expression level in PBMCs assayed by quantitative real time PCR was four times higher in diabetic subjects without vascular complications while DM patients having microvascular and macrovascular complications showed 12 fold and 8 fold higher RAGE m-RNA expression respectively compared to healthy controls. Circulating AGE level showed significant positive correlation with RAGE m-RNA expression and oxidative stress markers.

CONCLUSION

AGE-mediated exacerbation of RAGE expression may contribute to oxidative stress generation that plays a key role in pathogenesis of vascular complications in diabetes.

The proteomics of drusen

The formation of extracellular deposits known as drusen below the macular region of the retina correlates with increased risk of severe visual loss from age-related macular degeneration (AMD). Inflammation and complement dysregulation contribute to AMD progression; however, disease mechanisms remain incompletely defined. Multiple genetic and environmental factors influence AMD pathology, and although immune system processes play a central role, multiple molecular mechanisms appear to be involved. Drusen proteomics, including the analyses of constituent proteins, oxidative protein modifications, and pattern recognition receptors, provide a foundation for deciphering mechanisms of drusen biogenesis and AMD pathology.

Association of RAGE gene polymorphism with vascular complications in Indian type 2 diabetes mellitus patients

AIMS

The study was designed to evaluate the association of -374T/A and -429T/C polymorphism in the promoter region and Gly82Ser polymorphism in exon 3 region of RAGE gene with diabetic vascular complications in Indian population.

METHODS

We screened 603 subjects which includes 176 healthy controls, 140 type 2 diabetes mellitus (T2DM) subjects without any vascular complications (DM), 152 T2DM subjects with microvascular complications (DM-micro) and 135 T2DM subjects with macrovascular complications (DM-macro) for -374T/A, -429T/C and Gly82Ser polymorphisms of RAGE gene. DNA isolated from the enrolled subjects were genotyped by PCR-RFLP. Logistic regression analysis was used to evaluate the association of single nucleotide polymorphisms (SNPs).

RESULTS

The -429 T/C and Gly82Ser RAGE polymorphisms were found to be significantly associated with the development of macrovascular and microvascular complications, respectively, in T2DM subjects while -374A allele showed reduced risk towards the development of macrovascular complications. Further, -429T/C, -374T/A and Gly82Ser haplotype analysis revealed association of CTG haplotype with development of macrovascular complications while haplotype TAG was observed to be significantly protective towards development of macrovascular complications in T2DM subjects (OR=0.617, p=0.0202).

CONCLUSIONS

Our data indicates significant association of RAGE SNPs and haplotypes with vascular complications in North Indian T2DM subjects.

Overexpression of RAGE contributes to cigarette smoke-induced nitric oxide generation in COPD

BACKGROUND

Receptor for advanced glycation end products (RAGE), a multiple-ligands receptor, is implicated in chronic obstructive pulmonary disease (COPD). This study was designed to investigate the potential role of RAGE in nitric oxide (NO) generation, an endogenous marker of nitrosative stress in COPD.

METHODS

Lung tissues from COPD patients were used to describe the relationship between RAGE expression and NO level. RAGE expression was assessed by immunohistochemistry, western blot, and ELISA. Human bronchial epithelial cells (16HBE) were cultured with cigarette smoke extract (CSE). Neutralizing antibody against RAGE was used to detect the role of RAGE in CSE-induced NO generation by 16HBE cells.

RESULTS

Compared with nonsmoker controls, overexpression of RAGE was significantly detected in COPD smokers (p < 0.01), but not healthy smokers and nonsmokers with COPD, which was dominantly expressed at bronchiolar epithelia. Correlation analysis showed that RAGE in COPD smokers was positively related to NO level, smoking status, and lung function decline. In cultured 16HBE cells treated with CSE, soluble RAGE was reduced; however, full-length RAGE was enhanced significantly as the same trend as NO generation. Moreover, increased NO level and NO synthase activity, decreased total glutathione (a major cellular antioxidant), enhanced nuclear translocation of p65 (a key molecule of nuclear factor (NF)-κB) and release of NF-κB-dependent proinflammatory cytokines were all reversed by pretreatment of anti-RAGE antibody.

CONCLUSIONS

These findings suggest that overexpression of RAGE contributes to CS-induced NO generation in COPD with involvement in NF-κB activation.

The receptor for advanced glycation end-products (RAGE) is only present in mammals, and belongs to a family of cell adhesion molecules (CAMs)

The human receptor for advanced glycation endproducts (RAGE) is a multiligand cell surface protein belonging to the immunoglobulin superfamily, and is involved in inflammatory and immune responses. Most importantly, RAGE is considered a receptor for HMGB1 and several S100 proteins, which are Damage-Associated Molecular Pattern molecules (DAMPs) released during tissue damage. In this study we show that the Ager gene coding for RAGE first appeared in mammals, and is closely related to other genes coding for cell adhesion molecules (CAMs) such as ALCAM, BCAM and MCAM that appeared earlier during metazoan evolution. RAGE is expressed at very low levels in most cells, but when expressed at high levels, it mediates cell adhesion to extracellular matrix components and to other cells through homophilic interactions. Our results suggest that RAGE evolved from a family of CAMs, and might still act as an adhesion molecule, in particular in the lung where it is highly expressed or under pathological conditions characterized by an increase of its protein levels.

Early Graft Dysfunction in Living Donor Liver Transplantation and the Small for Size Syndrome

LDLT has arisen as a viable means to reduce waitlist mortality. However, its widespread embrace by the liver transplant community has been met with frustration centered on donor morbidity and small-for-size-syndrome. Focusing on the later entity, we describe the initial recognition of this early graft dysfunction, the theorized pathophysiology and solutions to remedy its emergence.

High-mobility group box 1 inhibits gastric ulcer healing through Toll-like receptor 4 and receptor for advanced glycation end products

High-mobility group box 1 (HMGB1) was initially discovered as a nuclear protein that interacts with DNA as a chromatin-associated non-histone protein to stabilize nucleosomes and to regulate the transcription of many genes in the nucleus. Once leaked or actively secreted into the extracellular environment, HMGB1 activates inflammatory pathways by stimulating multiple receptors, including Toll-like receptor (TLR) 2, TLR4, and receptor for advanced glycation end products (RAGE), leading to tissue injury. Although HMGB1’s ability to induce inflammation has been well documented, no studies have examined the role of HMGB1 in wound healing in the gastrointestinal field. The aim of this study was to evaluate the role of HMGB1 and its receptors in the healing of gastric ulcers. We also investigated which receptor among TLR2, TLR4, or RAGE mediates HMGB1’s effects on ulcer healing. Gastric ulcers were induced by serosal application of acetic acid in mice, and gastric tissues were processed for further evaluation. The induction of ulcer increased the immunohistochemical staining of cytoplasmic HMGB1 and elevated serum HMGB1 levels. Ulcer size, myeloperoxidase (MPO) activity, and the expression of tumor necrosis factor α (TNFα) mRNA peaked on day 4. Intraperitoneal administration of HMGB1 delayed ulcer healing and elevated MPO activity and TNFα expression. In contrast, administration of anti-HMGB1 antibody promoted ulcer healing and reduced MPO activity and TNFα expression. TLR4 and RAGE deficiency enhanced ulcer healing and reduced the level of TNFα, whereas ulcer healing in TLR2 knockout (KO) mice was similar to that in wild-type mice. In TLR4 KO and RAGE KO mice, exogenous HMGB1 did not affect ulcer healing and TNFα expression. Thus, we showed that HMGB1 is a complicating factor in the gastric ulcer healing process, which acts through TLR4 and RAGE to induce excessive inflammatory responses.

Receptor for advanced glycation end products and its involvement in inflammatory diseases

The receptor for advanced glycation end products (RAGE) is a transmembrane receptor of the immunoglobulin superfamily, capable of binding a broad repertoire of ligands. RAGE-ligands interaction induces a series of signal transduction cascades and lead to the activation of transcription factor NF-κB as well as increased expression of cytokines, chemokines, and adhesion molecules. These effects endow RAGE with the role in the signal transduction from pathogen substrates to cell activation during the onset and perpetuation of inflammation. RAGE signaling and downstream pathways have been implicated in a wide spectrum of inflammatory-related pathologic conditions such as arteriosclerosis, Alzheimer's disease, arthritis, acute respiratory failure, and sepsis. Despite the significant progress in other RAGE studies, the functional importance of the receptor in clinical situations and inflammatory diseases still remains to be fully realized. In this review, we will summarize current understandings and lines of evidence on the molecular mechanisms through which RAGE signaling contributes to the pathogenesis of the aforementioned inflammation-associated conditions.

Soluble receptor for advanced glycation end-product levels are related to albuminuria and arterial stiffness in essential hypertension

BACKGROUND AND AIMS

Emerging evidence suggests that the soluble receptor for advanced glycation end-products (sRAGE) is implicated in the development of vascular disease. We investigated the interrelationships of sRAGE with albumin to creatinine ratio (ACR) and arterial stiffness in essential hypertension.

METHODS AND RESULTS

In 309 untreated non-diabetic hypertensives, ACR values were determined as the mean of three non-consecutive morning spot urine samples and aortic stiffness was evaluated on the basis of carotid to femoral pulse wave velocity (c-f PWV). In all subjects, venous blood sampling was performed for the estimation of sRAGE levels. Patients with low (n = 155) compared to those with high sRAGE values (n = 154) had greater 24-h systolic BP (140 ± 8 vs. 134 ± 7 mmHg, p < 0.0001), exhibited higher ACR (36.3 ± 51.6 vs. 17.2 ± 1.2 mg g(-1), p < 0.0001) and c-f PWV (8.3 ± 1.5 vs. 7.8 ± 1.1 m s(-1), p = 0.003), independently of confounding factors. Multiple regression analyses revealed that age, male sex, 24-h systolic BP and sRAGE were the 'independent correlates' of ACR (R(2) = 0.493, p < 0.0001), while age, 24-h systolic BP and sRAGE were the 'independent correlates' of c-f PWV (R(2) = 0.428, p < 0.0001).

CONCLUSION

In hypertensives, decreased sRAGE levels are accompanied by pronounced albuminuria and arterial stiffening. The association of sRAGE with ACR and c-f PWV suggests involvement of sRAGE in the progression of hypertensive vascular damage.

Protein oxidation in aging and the removal of oxidized proteins

Reactive oxygen species (ROS) are generated constantly within cells at low concentrations even under physiological conditions. During aging the levels of ROS can increase due to a limited capacity of antioxidant systems and repair mechanisms. Proteins are among the main targets for oxidants due to their high rate constants for several reactions with ROS and their abundance in biological systems. Protein damage has an important influence on cellular viability since most protein damage is non-repairable, and has deleterious consequences on protein structure and function. In addition, damaged and modified proteins can form cross-links and provide a basis for many senescence-associated alterations and may contribute to a range of human pathologies. Two proteolytic systems are responsible to ensure the maintenance of cellular functions: the proteasomal (UPS) and the lysosomal system. Those degrading systems provide a last line of antioxidative protection, removing irreversible damaged proteins and recycling amino acids for the continuous protein synthesis. But during aging, both systems are affected and their proteolytic activity declines significantly. Here we highlight the recent advantages in the understanding of protein oxidation and the fate of these damaged proteins during aging. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.

Critical role for the advanced glycation end-products receptor in pulmonary arterial hypertension etiology

Background

Pulmonary arterial hypertension (PAH) is a vasculopathy characterized by enhanced pulmonary artery smooth muscle cell (PASMC) proliferation and suppressed apoptosis. This results in both increase in pulmonary arterial pressure and pulmonary vascular resistance. Recent studies have shown the implication of the signal transducer and activator of transcription 3 (STAT3)/bone morphogenetic protein receptor 2 (BMPR2)/peroxisome proliferator‐activated receptor gamma (PPARγ) in PAH. STAT3 activation induces BMPR2 downregulation, decreasing PPARγ, which both contribute to the proproliferative and antiapoptotic phenotype seen in PAH. In chondrocytes, activation of this axis has been attributed to the advanced glycation end‐products receptor (RAGE). As RAGE is one of the most upregulated proteins in PAH patients' lungs and a strong STAT3 activator, we hypothesized that by activating STAT3, RAGE induces BMPR2 and PPARγ downregulation, promoting PAH‐PASMC proliferation and resistance to apoptosis.

Methods and Results

In vitro, using PASMCs isolated from PAH and healthy patients, we demonstrated that RAGE is overexpressed in PAH‐PASMC (6‐fold increase), thus inducing STAT3 activation (from 10% to 40% positive cells) and decrease in BMPR2 and PPARγ levels (>50% decrease). Pharmacological activation of RAGE in control cells by S100A4 recapitulates the PAH phenotype (increasing RAGE by 6‐fold, thus activating STAT3 and decreasing BMPR2 and PPARγ). In both conditions, this phenotype is totally reversed on RAGE inhibition. In vivo, RAGE inhibition in monocrotaline‐ and Sugen‐induced PAH demonstrates therapeutic effects characterized by PA pressure and right ventricular hypertrophy decrease (control rats have an mPAP around 15 mm Hg, PAH rats have an mPAP >40 mm Hg, and with RAGE inhibition, mPAP decreases to 20 and 28 mm Hg, respectively, in MCT and Sugen models). This was associated with significant improvement in lung perfusion and vascular remodeling due to decrease in proliferation (>50% decrease) and BMPR2/PPARγ axis restoration (increased by ≥60%).

Conclusion

We have demonstrated the implications of RAGE in PAH etiology. Thus, RAGE constitutes a new attractive therapeutic target for PAH.

The IKKα-dependent NF-κB p52/RelB noncanonical pathway is essential to sustain a CXCL12 autocrine loop in cells migrating in response to HMGB1

HMGB1 is a chromatin architectural protein that is released by dead or damaged cells at sites of tissue injury. Extracellular HMGB1 functions as a proinflammatory cytokine and chemoattractant for immune effector and progenitor cells. Previously, we have shown that the inhibitor of NF-κB kinase (IKK)β- and IKKα-dependent NF-κB signaling pathways are simultaneously required for cell migration to HMGB1. The IKKβ-dependent canonical pathway is needed to maintain expression of receptor for advanced glycation end products, the ubiquitously expressed receptor for HMGB1, but the target of the IKKα non-canonical pathway was not known. In this study, we show that the IKKα-dependent p52/RelB noncanonical pathway is critical to sustain CXCL12/SDF1 production in order for cells to migrate toward HMGB1. Using both mouse bone marrow-derived macrophages and mouse embryo fibroblasts (MEFs), it was observed that neutralization of CXCL12 by a CXCL12 mAb completely eliminated chemotaxis to HMGB1. In addition, the HMGB1 migration defect of IKKα KO and p52 KO cells could be rescued by adding recombinant CXCL12 to cells. Moreover, p52 KO MEFs stably transduced with a GFP retroviral vector that enforces physiologic expression of CXCL12 also showed near normal migration toward HMGB1. Finally, both AMD3100, a specific antagonist of CXCL12's G protein-coupled receptor CXCR4, and an anti-CXCR4 Ab blocked HMGB1 chemotactic responses. These results indicate that HMGB1-CXCL12 interplay drives cell migration toward HMGB1 by engaging receptors of both chemoattractants. This novel requirement for a second receptor-ligand pair enhances our understanding of the molecular mechanisms regulating HMGB1-dependent cell recruitment to sites of tissue injury.

Modulation of endoplasmic reticulum stress and cardiomyocyte apoptosis by mulberry leaf diet in experimental autoimmune myocarditis rats

Mulberry is commonly used as silkworm diet and an alternative medicine in Japan and China, has recently reported to contain many antioxidative flavanoid compounds and having the free radical scavenging effects. Antioxidants reduce cardiac oxidative stress and attenuate cardiac dysfunction in animals with pacing-induced congestive heart failure. Hence we investigated the cardioprotective effect of mulberry leaf powder in rats with experimental autoimmune myocarditis. Eight-week-old Lewis rats immunized with cardiac myosin were fed with either normal chow or a diet containing 5% mulberry leaf powder and were examined on day 21. ML significantly decreased oxidative stress, myocyte apoptosis, cellular infiltration, cardiac fibrosis, mast cell density, myocardial levels of sarco/endo-plasmic reticulum Ca²⁺ ATPase2, p22^phox, receptor for advanced glycation end products, phospho-p38 mitogen activated protein kinase, phospho-c-Jun NH₂-terminal protein kinase, glucose regulated protein78, caspase12 and osteopontin levels in EAM rats. These results may suggest that mulberry diet can preserve the cardiac function in experimental autoimmune myocarditis by modulating oxidative stress induced MAPK activation and further afford protection against endoplasmic reticulum stress mediated apoptosis.

Human eosinophils express RAGE, produce RAGE ligands, exhibit PKC-delta phosphorylation and enhanced viability in response to the RAGE ligand, S100B

This study tested the hypothesis that human eosinophils produce ligands for the receptor for advanced glycation end-products (RAGE), express RAGE and exhibit RAGE-mediated responses. In examining our microarray data, we identified the presence of RAGE and RAGE ligand (S100A4, S100A6, S100A8, S100A9, S100A11, S100P, HMGB1) transcripts. Expression of eosinophil RAGE mRNA was also compared with a known positive control and further assessed via bioinformatics and sequence analysis of RAGE cDNA. Positive and negative controls were used to identify RAGE, S100A8 and S100A9 protein in human primary eosinophils. Immunoblot assessment of eosinophils treated with cytokines (IL-5 or granulocyte macrophage colony-stimulating factor) indicated an up-regulation of S100A8 and S100A9 production, whereas co-treatment of eosinophils with a RAGE ligand and cytokines displayed a down-regulation in the levels of RAGE. Analysis of eosinophil-conditioned media revealed that eosinophils are capable of releasing RAGE, S100A8 and S100A9. To test the eosinophil response to RAGE activation, the most well-characterized RAGE ligand, S100B, was examined. Treatment of eosinophils with S100B resulted in RAGE-mediated PKC-delta phosphorylation, a 3-fold dose-dependent increase in cell survival and an increase in the level of cellular RAGE. Combined, these studies reveal eosinophil expression of RAGE, RAGE ligands and RAGE-mediated responses. The expression of eosinophil RAGE, soluble RAGE and RAGE ligands may be pivotal to the functions of eosinophils in various human diseases involving RAGE and S100 ligands.

sRAGE in diabetic and non-diabetic critically ill patients: effects of intensive insulin therapy

Introduction

Hyperglycemia represents an independent prognostic factor in critically ill non-diabetic patients but not in those with diabetes. In this context, there is an ongoing debate on the benefit of an intensive insulin therapy, particularly in diabetic patients. We tested the hypothesis that expression of the receptor for advanced glycation end-products (RAGE), an important signal transduction receptor that elicits long-lasting nuclear factor kappa B (NF-κB) activation, may underlie this difference. RAGE expression is regulated by multiple ligands, including high mobility group box-1 (HMGB-1), and is reflected by its released soluble form (sRAGE).

Methods

A predesigned analysis was conducted of prospectively collected samples from 76 hyperglycemic critically ill patients (33 type-2 diabetes, 43 non-diabetes) aged ≥18 years with blood glucose of > 6.1 mmol/L enrolled in a randomized controlled trial comparing intensive insulin therapy with conventional insulin therapy. sRAGE and its ligand HMGB-1 together with IL-6, and soluble thrombomodulin (as markers of inflammation and endothelial cell injury, respectively) were evaluated in ICU, at Days 1, 3, 5 and 7. Plasma samples from 18 healthy subjects were used as controls.

Results

Both diabetic and non-diabetic hyperglycemic patients showed increased plasma sRAGE, HMGB-1 and soluble thrombomodulin levels at the time of admission to ICU. Plasma IL-6 concentration was only increased in non-diabetic patients. Plasma levels of sRAGE were higher in diabetic compared with non-diabetic patients. Intensive insulin therapy resulted in a significant decrease of sRAGE and thrombomodulin at Day 7, in diabetic but not in non-diabetic patients. Circulating sRAGE levels correlated positively with IL-6 and soluble thrombomodulin levels and inversely with HMGB-1. Multivariate regression analysis demonstrated that sRAGE remains independently correlated with HMGB-1 only in diabetic patients. Neither sRAGE nor any inflammatory markers are associated with mortality.

Conclusions

These findings support the hypothesis that sRAGE release, time-course and response to intensive insulin therapy differ between hyperglycemic diabetic and non-diabetic critically ill patients. Whether this difference underlies the dissimilarity in clinical outcome of hyperglycemia in these two conditions warrants further studies.

Differential gene expression pattern of diabetic rat retinas after intravitreal injection of erythropoietin

BACKGROUND

To profile the pattern of gene expression in diabetic rat retinas with or without intravitreal injection of erythropoietin.

DESIGN

By using streptozotocin-induced diabetic rats, after intravitreal injection of erythropoietin, neurosensory retinas were collected to determine the effect of erythropoietin on gene expression.

PARTICIPANTS

Three groups of Sprague-Dawley rats were studied: normal control (15), diabetic rats with saline injection (15) and diabetic rats with intravitreal erythropoietin treatment (15).

METHODS

Diabetes was induced by intra-peritoneal injection of streptozotocin. Intravitreal injection of erythropoietin was performed at the following time points: 0, 30 and 120 days after diabetes onset. Four days after each injection at above-mentioned time points, the retinas were harvested for microarray assay. The real-time PCR was used to evaluate the microarray data.

RESULTS

Genes encoding inflammatory factors, such as interleukin-2 and interleukin-11, which were upregulated in the diabetic retinas, were restored after erythropoietin treatment. Genes encoding pro-apoptotic effectors, like Tnfrsf5, Bid3 and Bcl2l1, were also upregulated in diabetic rats and attenuated in erythropoietin-treated group. In addition, real-time PCR were employed to confirm the changes of the genes Trex2, G1P2, DHX58, RGD1311906 and LOC689064, which have not been reported in diabetic retinopathy.

CONCLUSIONS

Intravitreal erythropoietin treatment is able to normalize the gene expression responsible for pro-apoptotic and inflammatory responses noted in diabetic retinas.

Advanced glycation end products of human β₂ glycoprotein I modulate the maturation and function of DCs

In chronic disorders related to endothelial cell dysfunction, plasma β₂ glycoprotein I (β₂GPI) plays a role as a target antigen of pathogenetic autoimmune responses. However, information is still lacking to clarify why β₂GPI triggers autoimmunity. It is possible that posttranslational modification of the protein, such as nonenzymatic glycosylation, leads to the formation of advanced glycation end products (AGEs). The aim of our study was to explore whether glucose-modified β₂GPI is able to interact and activate monocyte-derived immature dendritic cells (iDCs) from healthy human donors. SDS-PAGE and spectrofluorometric analyses indicated that β₂GPI incubated with glucose was sugar modified, and that this modification likely consisted of AGE formation, resulting in AGE-β₂GPI. AGE-β₂GPI caused phenotypical and functional maturation of iDCs involving the activation of p38 MAPK, ERK, and NF-κB. It also induced on DCs a significant up-regulation of RAGE, the receptor for AGEs. Evidence for RAGE involvement comes from blocking experiments with an anti-RAGE mAb, confocal analysis, and coimmunoprecipitation experiments. AGE-β₂GPI-stimulated DCs had increased allostimulatory ability and primed naive T lymphocytes toward a Th2 polarization. These findings might explain in part the interactive role of β₂GPI, AGEs, and DCs in chronic disorders related to endothelial cell dysfunction.

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.

RAGE: the beneficial and deleterious effects by diverse mechanisms of actions

Receptor for advanced glycation endproducts (RAGE) is a transmembrane protein that belongs to the immunoglobulin superfamily. RAGE is expressed ubiquitously-high in lung and moderate to low in a wide range of cells-in a tightly regulated manner at various stages of development. RAGE is a pattern recognition receptor that binds to multiple ligands, including amphoterin, members of the S100/calgranulin family, the integrin Mac-1, and amyloid β-peptide (Aβ). RAGE-ligand engagement effects the activation of diverse cascades that initiate and stimulate chronic stress pathways and repair, depending on the ligand, environment, and developmental stage. Further, RAGE-ligand interaction and the consequent upregulation of RAGE through a positive feedback loop are often associated with various diseases, including vascular disease, diabetes, cancer, and neurodegenerative disease. It is unknown how RAGE mediates these events, but such phenomena appear to be linked to the inflammatory response. In this review, we summarize the findings on RAGE from published reports and ongoing studies. Also, the implication of RAGE in Alzheimer disease, the most common neurodegenerative disease in the elderly population, will be discussed, with a focus on Aβ-RAGE interactions with regard to signaling pathways and their impact on cellular activity.

Plasminogen activation inhibitor concentrations in bronchoalveolar lavage fluid distinguishes ventilator-associated pneumonia from colonization in mechanically ventilated pediatric patients

OBJECTIVE

To compare the ability of four biomarkers to distinguish between those with ventilator-associated pneumonia (VAP) vs. lower respiratory tract bacterial colonization in mechanically ventilated intensive care unit (ICU) pediatric patients.

DESIGN

Prospective, pilot cohort study.

SETTING

Tertiary care children's hospital, pediatric ICU.

PATIENTS

All pediatric ICU patients mechanically ventilated > 48 hrs were eligible for enrollment between April 2006 to May 2007. Thirty-three patients were consecutively screened and enrolled after institutional consent process.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

VAP was defined by both Centers for Disease and Prevention/National Nosocomial Infections Surveillance criteria and clinician diagnosis; those not meeting the criteria were considered to be colonized. Plasminogen activation inhibitor (PAI-1), soluble triggering receptor expressed on myeloid cells, receptor for advanced glycation end-products, and surfactant protein D levels were measured in bronchoalveolar lavage samples on average within 24 hrs of suspicion for VAP, i.e., a positive screening endotracheal Gram stain. Sixteen patients were diagnosed with VAP and 17 met the criteria for colonization. PAI-1 was associated with VAP independent of age, sex, race, acute lung injury/acute respiratory distress syndrome, Pediatric Risk of Mortality 3 score, pediatric logistic organ dysfunction score, and duration of intubation. The receiver operating characteristics for PAI-1 showed good discrimination with an area under the curve of 0.82. PAI-1 levels of ≥ 2.8 ng/mL had a sensitivity of 81.3%, specificity of 76.5%, and positive likelihood ratio of 3.5. Levels of soluble triggering receptor expressed on myeloid cells, receptor for advanced glycation end-products, and surfactant protein D were not significantly associated with VAP.

CONCLUSIONS

In mechanically ventilated pediatric ICU patients, PAI-1 is independently associated with the diagnosis of VAP. Real-time measurement of PAI-1 levels in bronchoalveolar lavage fluid may be of benefit in the early diagnosis and subsequent treatment of VAP in ICU patients.

S100B attenuates microglia activation in gliomas: possible role of STAT3 pathway

Despite significant infiltration into tumors, the effector function of macrophages (MPs) and microglia (MG) appears to be suppressed in gliomas. Although STAT3 pathway is thought to play a role in this process, the exact mechanism by which gliomas induce STAT3 activation in MPs and MG is not known. Because activation of receptor for advanced glycation end products (RAGE) can induce STAT3, and because gliomas express high levels of S100B, a RAGE ligand, we hypothesized that MP/MG STAT3 activity may be modulated through S100B-RAGE interaction. Exposure of N9 MG and bone marrow-derived monocytes (BMM) to GL261 glioma condition medium (GCM) and low (nM) levels of S100B increased RAGE expression, induced STAT3 and suppressed MG function in vitro. Furthermore, neutralization of S100B in GCM, partially reversed IL-1β suppression in BMM, suggesting that the inhibitory effect of GCM to be in part due to S100B. Finally, blockage of S100B-RAGE interaction inhibited STAT3 activation in N9 MG and in glioma MG/MP in vivo. These findings suggest that the RAGE pathway may play an important role in STAT3 induction in glioma-associated MG/MPs, and that this process may be mediated through S100B.

Implication of the RAGE-EN-RAGE axis in endometriosis

OBJECTIVE

To investigate the involvement of the receptor gene for advanced glycation (RAGE), its ligand EN-RAGE, and COX-2 in endometriosis.

METHODS

The mRNA and protein expression of the corresponding genes were determined from endometriotic cells from 28 study patients and healthy endometrial stromal cells from 20 controls by semiquantitative RT-PCR and Western blot analysis, respectively, using beta-actin as an invariant control.

RESULTS

The expression of COX-2, RAGE, and EN-RAGE was significantly increased, as evidenced by the significantly greater mRNA and protein expression in the cells of the study patients (P<0.001). Previous treatment for endometriosis did not lessen mRNA and protein expression (P<0.001).

CONCLUSION

Our findings strengthen the hypothesis of an underlying inflammation in the pathophysiology of endometriosis and suggest exploring anti-inflammatory therapies as adjunct treatment.

Early release of soluble receptor for advanced glycation endproducts after severe trauma in humans

BACKGROUND

The receptor for advanced glycation endproducts (RAGE) recognizes a variety of ligands that play an important role in the posttraumatic inflammatory response. However, whether soluble RAGE (sRAGE) is released early after trauma hemorrhage in humans and whether such a release is associated with the development of an inflammatory response and coagulopathy is not known and therefore constitutes the aim of this study.

METHODS

One hundred sixty-eight patients were studied as part of a prospective cohort study of severe trauma patients admitted to a single Level I Trauma center. Blood was drawn within 10 minutes of arrival to the emergency department before the administration of any fluid resuscitation. sRAGE, tumor necrosis factor-alpha, interleukin-6, von Willebrand factor, angiopoietin-2, prothrombin time, prothrombin fragments 1 + 2, soluble thrombomodulin, protein C, plasminogen activator inhibitor-1, and d-dimers (fibrin degradation products) were measured using standard techniques. Base deficit was used as a measure of tissue hypoperfusion. Measurements were compared with outcome measures obtained from the electronic medical record and trauma registry.

RESULTS

Plasma levels of sRAGE were increased within 30 minutes after severe trauma in humans and correlated with the severity of injury, early posttraumatic coagulopathy and hyperfibrinolysis, and endothelial cell activation (angiopoietin-1 and complement). Furthermore, we found that there was a significant relationship between plasma levels of sRAGE and the development of acute renal failure. This relationship was not quite significant for patients who developed acute lung injury (p = 0.11), although patients with <26 ventilator-free days had significantly higher plasma levels of sRAGE than those with >26 ventilator-free days. Finally, there was no relationship between plasma levels of sRAGE and mortality rate in trauma patients.

CONCLUSION

The results of this study demonstrate that the release of sRAGE in the bloodstream of trauma patients requires severe injury and is associated with coagulation abnormalities and endothelial cell and complement activation.

sRAGE induces human monocyte survival and differentiation

The receptor for advanced glycation end products (RAGE) is produced either as a transmembrane or soluble form (sRAGE). Substantial evidence supports a role for RAGE and its ligands in disease. sRAGE is reported to be a competitive, negative regulator of membrane RAGE activation, inhibiting ligand binding. However, some reports indicate that sRAGE is associated with inflammatory disease. We sought to define the biological function of sRAGE on inflammatory cell recruitment, survival, and differentiation in vivo and in vitro. To test the in vivo impact of sRAGE, the recombinant protein was intratracheally administered to mice, which demonstrated monocyte- and neutrophil-mediated lung inflammation. We also observed that sRAGE induced human monocyte and neutrophil migration in vitro. Human monocytes treated with sRAGE produced proinflammatory cytokines and chemokines. Our data demonstrated that sRAGE directly bound human monocytes and monocyte-derived macrophages. Binding of sRAGE to monocytes promoted their survival and differentiation to macrophages. Furthermore, sRAGE binding to cells increased during maturation, which was similar in freshly isolated mouse monocytes compared with mature tissue macrophages. Because sRAGE activated cell survival and differentiation, we examined intracellular pathways that were activated by sRAGE. In primary human monocytes and macrophages, sRAGE treatment activated Akt, Erk, and NF-kappaB, and their activation appeared to be critical for cell survival and differentiation. Our data suggest a novel role for sRAGE in monocyte- and neutrophil-mediated inflammation and mononuclear phagocyte survival and differentiation.

Inhibitor of NF-kappa B kinases alpha and beta are both essential for high mobility group box 1-mediated chemotaxis [corrected]

Inhibitor of NF-kappaB kinases beta (IKKbeta) and alpha (IKKalpha) activate distinct NF-kappaB signaling modules. The IKKbeta/canonical NF-kappaB pathway rapidly responds to stress-like conditions, whereas the IKKalpha/noncanonical pathway controls adaptive immunity. Moreover, IKKalpha can attenuate IKKbeta-initiated inflammatory responses. High mobility group box 1 (HMGB1), a chromatin protein, is an extracellular signal of tissue damage-attracting cells in inflammation, tissue regeneration, and scar formation. We show that IKKalpha and IKKbeta are each critically important for HMGB1-elicited chemotaxis of fibroblasts, macrophages, and neutrophils in vitro and neutrophils in vivo. By time-lapse microscopy we dissected different parameters of the HMGB1 migration response and found that IKKalpha and IKKbeta are each essential to polarize cells toward HMGB1 and that each kinase also differentially affects cellular velocity in a time-dependent manner. In addition, HMGB1 modestly induces noncanonical IKKalpha-dependent p52 nuclear translocation and p52/RelB target gene expression. Akin to IKKalpha and IKKbeta, p52 and RelB are also required for HMGB1 chemotaxis, and p52 is essential for cellular orientation toward an HMGB1 gradient. RAGE, a ubiquitously expressed HMGB1 receptor, is required for HMGB1 chemotaxis. Moreover, IKKbeta, but not IKKalpha, is required for HMGB1 to induce RAGE mRNA, suggesting that RAGE is at least one IKKbeta target involved in HMGB1 migration responses, and in accord with these results enforced RAGE expression rescues the HMGB1 migration defect of IKKbeta, but not IKKalpha, null cells. Thus, proinflammatory HMGB1 chemotactic responses mechanistically require the differential collaboration of both IKK-dependent NF-kappaB signaling pathways.

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

Effects of glycation of the model food allergen ovalbumin on antigen uptake and presentation by human dendritic cells

Advanced glycation endproducts (AGEs) of food proteins resulting from the Maillard reaction after cooking or heating may have particular importance in food allergy. The underlying immunological mechanisms are only poorly understood. The aim of the study was to examine the effects of AGE derived from the model food allergen ovalbumin (AGE-OVA) on dendritic cells (DCs), their immunostimulatory capacity and the T-cell response compared with regular OVA. For this purpose, human immature DCs were exposed to fluorescein isothiocyanate (FITC)-labelled AGE-OVA and FITC-labelled regular OVA and uptake was analysed by flow cytometry and fluorescence microscopy. Furthermore, autologous CD4(+) T-cell proliferation and cytokine production induced by mature DCs loaded with AGE-OVA were compared with those induced by mature DCs loaded with OVA. Finally, expression of the receptor for advanced glycation endproducts (RAGE) and activation of the transcription factor nuclear factor (NF)-kappaB by AGE were investigated. Internalization of FITC-AGE-OVA by immature DCs was significantly increased compared with FITC-OVA. Blocking the mannose receptor, macropinocytosis or the scavenger receptor strongly reduced uptake of both FITC-OVA and FITC-AGE-OVA. In a comparison of CD4(+) T cells co-cultured with AGE-OVA-loaded mature DCs versus those co-cultured with OVA-loaded mature DCs, AGE-OVA DCs were found to produce more interleukin (IL)-6 and to induce a stronger T helper type 2 (Th2) and a weaker Th1 cytokine response, while there was no difference in proliferation of CD4(+) T cells. The expression of RAGE was higher on immature DCs compared with mature DCs. AGE-OVA-exposed immature DCs showed a stronger expression of RAGE and activation of the transcription factor NF-kappaB compared with OVA-loaded immature DCs. Our data indicate that AGE-OVA may be more immunogenic/allergenic than regular OVA.

Linking diabetes and atherosclerosis

Cardiovascular diseases are the major causes of morbidity and mortality in people with diabetes. Macroangiopathy in diabetes is manifested by more accelerated and progressive atherosclerosis, which is more widely distributed. The pathogenesis of this accelerated atherosclerosis is multifactorial and includes very complex interactions. Several abnormalities - such as hyperglycemia, dyslipidemia, hypertension, endothelial dysfunction, renin-angiotensin system activation and chronic subclinical inflammation - all appear to play important roles in the development of diabetes-induced atherosclerosis. Treatment of the residual risk, other than glycemia, blood pressure and low-density lipoprotein cholesterol, remains important as the rate of diabetes increases worldwide. A synergistic multifactorial approach against both conventional cardiovascular risk factors and emerging risk factors, such as vasoactive systems, the AGE-RAGE axis, novel proteins, such as TRAIL, and the complement system, as well as oxidative stress and inflammation, may be a promising way to prevent macrovascular disease in diabetes. In this review we focus on the major causes and mechanisms of atherosclerotic disease in patients with diabetes and highlight emerging targets for therapeutic intervention.

S100A8/A9: a Janus-faced molecule in cancer therapy and tumorgenesis

Correlations exist between the abundance of S100 proteins and disease pathologies. Indeed, this is evidenced by the heterodimeric S100 protein complex S100A8/A9 which has been shown to be involved in inflammatory and neoplastic disorders. However, S100A8/A9 appears as a Janus-faced molecule in this context. On the one hand, it is a powerful apoptotic agent produced by immune cells, making it a very fascinating tool in the battle against cancer. It spears the risk to induce auto-immune response and may serve as a lead compound for cancer-selective therapeutics. In contrast, S100A8/A9 expression in cancer cells has also been associated with tumor development, cancer invasion or metastasis. Clearly, there is a dichotomy and future investigations into the role of S100A8/A9 in cancer biology need to consider both sides of the same coin.

Estrogen replacement therapy in diabetic ovariectomized female rats potentiates postischemic leukocyte adhesion in cerebral venules via a RAGE-related process

In this study, we tested the hypothesis that the documented transformation of 17beta-estradiol (E2) from a counterinflammatory hormone in nondiabetic (ND) rats to a proinflammatory agent in rats with diabetes mellitus (DM) is due to an enhanced contribution from the receptor for advanced glycation end products (RAGE). Rhodamine 6G-labeled leukocytes were observed through a closed cranial window in rats. In vivo pial venular leukocyte adherence and infiltration were measured over 10 h reperfusion after transient forebrain ischemia in DM (streptozotocin) versus ND intact, ovariectomized (OVX), and E2-replaced (for 7-10 days) OVX (OVE) females. The role of RAGE was examined in two ways: 1) RAGE knockdown via topical application of RAGE antisense versus missense oligodeoxynucleotide or 2) intracerebroventricular injection of the RAGE decoy inhibitor, soluble RAGE. Among diabetic rats, the lowest levels of cortical RAGE mRNA and immunoreactivity of the RAGE ligand, AGE, were seen in OVX females, with significantly higher levels exhibited in intact and OVE females. However, results from the analysis of cortical RAGE protein only partially tracked those findings. When comparing ND to DM rats, cortical AGE immunoreactivity was significantly lower in OVE and intact females but similar in OVX rats. In DM rats, the level of postischemic leukocyte adhesion and infiltration (highest to lowest) was OVE>intact>>untreated OVX. In NDs, adhesion was highest in the untreated OVX group. Leukocyte extravasation was observed at >6 h postischemia but only in diabetic OVE and intact females and in ND OVX (untreated) rats. Pretreatment with RAGE antisense-oligodeoxynucleotide or soluble RAGE attenuated postischemic leukocyte adhesion and prevented infiltration but only in the diabetic OVE and intact groups. These results indicate that the exacerbation of postischemic leukocyte adhesion by chronic E2 replacement therapy in diabetic OVX females involves a RAGE-related mechanism. Targeting RAGE may restore the neuroprotective effect of E2 replacement therapy in diabetic females.

Para-inflammation in the aging retina

Para-inflammation is a tissue adaptive response to noxious stress or malfunction and has characteristics that are intermediate between basal and inflammatory states (Medzhitov, 2008). The physiological purpose of para-inflammation is to restore tissue functionality and homeostasis. Para-inflammation may become chronic or turn into inflammation if tissue stress or malfunction persists for a sustained period. Chronic para-inflammation contributes to the initiation and progression of many human diseases including obesity, type 2 diabetes, atherosclerosis, and age-related neurodegenerative diseases. Evidence from our studies and the studies of some others suggests that para-inflammation also exists in the aging retina in physiological conditions and might contribute to age-related retinal pathologies. The purpose of this review is to introduce the notion of "para-inflammation" as a state between frank, overt destructive inflammation and the non-inflammatory removal of dead or dying cells by apoptosis, to the retinal community. In diabetes and atherosclerosis, leukocytes particularly monocytes and vascular endothelial cells are constantly under noxious stress due to glycaemic and/or lipidaemic dysregulation. These blood-borne stresses trigger para-inflammatory responses in leukocytes and endothelial cells by up-regulating the expression of adhesion molecules or releasing cytokines/chemokines, which in turn cause abnormal leukocyte-endothelial interactions and ultimately vascular damage. In the aging retina, on the other hand, oxidized lipoproteins and free radicals are considered to be major causes of tissue stress and serve as local triggers for retinal para-inflammation. Microarray analysis has revealed the up-regulation of a large number of inflammatory genes, including genes involved in complement activation and inflammatory cytokine/chemokine production, in the aging retina. Para-inflammatory responses in the neuroretina of aged mice are characterized by microglial activation and subretinal migration, and breakdown of blood-retinal barrier. At the retinal/choroidal interface para-inflammation is manifested by complement activation in Bruch's membrane and RPE cells, and microglia accumulation in subretinal space. With age, para-inflammatory changes have also been observed in the choroidal tissue, evidenced by 1) increased thickness of choroid; 2) increased number of CD45(+)CRIg(+) macrophages; 3) morphological abnormalities in choroidal melanocytes; and 4) fibrosis in choroidal tissue. An increased knowledge of contribution of retinal para-inflammation to various pathological conditions is essential for the better understanding of the pathogenesis of various age-related retinal diseases including diabetic retinopathy, glaucoma and age-related macular degeneration.

Therapies for hyperglycaemia-induced diabetic complications: from animal models to clinical trials

Diabetic complications — the long-term damage to various organ systems — are a great cause of mortality and morbidity in both type 1 and type 2 diabetes. There are currently few therapeutic options to prevent or ameliorate these complications.

High blood glucose levels and the subsequent metabolic consequences of hyperglycaemia are widely considered the primary event that initiates diabetic complications, although there is accumulating evidence that impaired insulin signalling arising from insulin deficiency and insulin resistance may also have a pathogenic role.

Vascular dysfunction is a prominent complication of diabetes that is widely held to underlie damage to organ systems such as the macrovasculature, kidneys, eyes and nerves. Other consequences of diabetes, such as dyslipidaemia and hypertension, are key modifiers of vascular injury and act as accelerators of diabetic complications.

Numerous pathogenic mechanisms, including increased polyol pathway flux and mitochondrial activity, activation of protein kinase C and NADPH oxidase and signalling through the receptor for advanced glycation end products (RAGE) pathway, seem to form a central pathogenic axis that is common to most, if not all, of the complications of diabetes. These disorders all promote excess production of pro-oxidative molecules. Organ-specific mechanisms, such as diminished growth factor support and repair pathway activation, must also be considered.

Few animal models of diabetic complications faithfully reflect the advanced stages of organ pathology seen in humans. Current models can be viewed as potentially illustrating early biochemical and functional disorders of diabetes that ultimately lead to advanced pathology. New animal models are being developed using both a reductionist approach for examining specific gene products of interest and also by combining diverse molecular and physiological risk factors.

Control of blood glucose levels and lipids remains the most meaningful approach for preventing diabetic complications. This strategy is likely to be complemented by a diverse range of more focused therapeutics that have emerged from mechanistic studies in animal models and which are currently in clinical development. Some of these, such as those targeting cardiovascular disease, have the potential to affect several diabetic complications, whereas others focus on intervening in organ-specific pathogenic mechanisms. It is probable that combination therapies aimed at the hyperglycaemia-driven pathogenic axis and also at organ-specific disorders will provide the most effective approach to treating the diverse complications of diabetes.

Long-term diabetes increases the likelihood of developing complications such as macrovascular disease, nephropathy, retinopathy and neuropathy. This Review highlights the range of pathologies that are precipitated by hyperglycaemia and discusses recent developments in preclinical and clinical research for each of these complications.

Long-term diabetes increases the likelihood of developing secondary damage to numerous systems, and these complications represent a substantial cause of morbidity and mortality. Establishing the causes of diabetes remains the key step towards eradicating the disease, but the prevention and amelioration of diabetic complications is equally important for the millions of individuals who already have the disease or are likely to develop it before prophylaxis or a cure become routinely available. In this Review, we focus on four common complications of diabetes, discuss the range of pathologies that are precipitated by hyperglycaemia and highlight emerging targets for therapeutic intervention.

The receptor RAGE: Bridging inflammation and cancer

The receptor for advanced glycation end products (RAGE) is a single transmembrane receptor of the immunoglobulin superfamily that is mainly expressed on immune cells, neurons, activated endothelial and vascular smooth muscle cells, bone forming cells, and a variety of cancer cells. RAGE is a multifunctional receptor that binds a broad repertoire of ligands and mediates responses to cell damage and stress conditions. It activates programs responsible for acute and chronic inflammation, and is implicated in a number of pathological diseases, including diabetic complications, stroke, atheriosclerosis, arthritis, and neurodegenerative disorders. The availability of Rage knockout mice has not only advanced our knowledge on signalling pathways within these pathophysiological conditions, but also on the functional importance of the receptor in processes of cancer. Here, we will summarize molecular mechanisms through which RAGE signalling contributes to the establishment of a pro-tumourigenic microenvironment. Moreover, we will review recent findings that provide genetic evidence for an important role of RAGE in bridging inflammation and cancer.

RAGE (Receptor for Advanced Glycation Endproducts), RAGE ligands, and their role in cancer and inflammation

The Receptor for Advanced Glycation Endproducts [RAGE] is an evolutionarily recent member of the immunoglobulin super-family, encoded in the Class III region of the major histocompatability complex. RAGE is highly expressed only in the lung at readily measurable levels but increases quickly at sites of inflammation, largely on inflammatory and epithelial cells. It is found either as a membrane-bound or soluble protein that is markedly upregulated by stress in epithelial cells, thereby regulating their metabolism and enhancing their central barrier functionality. Activation and upregulation of RAGE by its ligands leads to enhanced survival. Perpetual signaling through RAGE-induced survival pathways in the setting of limited nutrients or oxygenation results in enhanced autophagy, diminished apoptosis, and (with ATP depletion) necrosis. This results in chronic inflammation and in many instances is the setting in which epithelial malignancies arise. RAGE and its isoforms sit in a pivotal role, regulating metabolism, inflammation, and epithelial survival in the setting of stress. Understanding the molecular structure and function of it and its ligands in the setting of inflammation is critically important in understanding the role of this receptor in tumor biology.

Immunostimulatory activity of haptenated proteins

Antigen recognition alone is insufficient for the activation of adaptive immune responses mediated by conventional lymphocytes. Additional signals that indicate the origin of the antigen are also required. These signals are generally provided by the innate immune system upon recognition of conserved microbial structures by a variety of pattern recognition receptors (PRRs). The Toll-like receptors (TLRs) are the best-characterized family of PRRs and control the activation of adaptive immune responses to a variety of immunizations and infections. However, recent studies have questioned the role of TLRs in the induction of antibody responses and, thus, this issue has become controversial. In contrast to earlier studies supporting a role for TLRs in antibody responses, these studies used haptenated antigens rather than native antigens for immunization, but did not consider the potential effect of antigen haptenation on immunogenicity. Here, we show that commonly used haptenated proteins, unlike native proteins, are inherently immunogenic. This immunogenicity is TLR-independent, but the T and B cell responses induced are primarily hapten-specific, rather than protein-specific. Thus, although haptens have immunostimulatory activity, it is distinct from classical adjuvants, which induce immune responses directed at the admixed antigens. Our results thus highlight an unappreciated and unique immunogenicity of haptenated proteins, and provide an experimental explanation for a seeming discrepancy between published results.

C-reactive protein (CRP) up-regulates expression of receptor for advanced glycation end products (RAGE) and its inflammatory ligand EN-RAGE in THP-1 cells: inhibitory effects of atorvastatin

BACKGROUND

Receptor for advanced glycation end products (RAGE) may play an important role in inflammatory processes and endothelial activation. Extracellular newly identified RAGE binding protein (EN-RAGE), natural pro-inflammatory ligand for RAGE. The role of C-reactive protein (CRP) as a mediator in inflammation and atherosclerosis is the subject of recent investigations worldwide. In the present study, we investigated the effect of CRP on RAGE and EN-RAGE gene expression in THP-1 monocytic cell line. MAP kinases (ERK, p38 and JNK) were exploited as possible signaling pathways involved in the signal transduction by CRP. Further, atorvastatin was used as a therapeutic modality for modulation of these genes in the presence of CRP.

MATERIALS AND METHODS

Time and dose-dependent experiments were carried out in the presence of CRP. Specific MAPK pathways inhibitors were used to elucidate the signaling pathways involved. Effect of atorvastatin was also determined in the presence of CRP on the expression of these genes.

RESULTS

Time and dose-dependent experiments revealed that, treatment of THP-1 cells with 100 microg of CRP/ml/10(6) cells for 24 h, augmented the expression of RAGE and EN-RAGE genes by 2.5-3.5 folds and 3.5-4.5 folds respectively. CRP acted via FcgammaRII and utilized ERK, p38 and JNK pathways to transduce signals. Atorvastatin in a dose of 20 muM, was able to attenuate up-regulation of CRP-induced genes (p<0.01) and effects were both dose and time-dependent.

CONCLUSION

Our data strongly suggests that blockade of RAGE-EN-RAGE by statins at an early stage may prevent inflammation in atherosclerosis and counteract the harmful effects mediated by CRP.

RAGE signaling in inflammation and arterial aging

The receptor for advanced glycation end products (RAGE) is a pattern recognition receptor (PRR) that interacts with diverse endogenous ligands. Ligation of RAGE triggers a series of cellular signaling events, including the activation of transcription factor NF-kappaB, leading to the production of pro-inflammatory cytokines, and causing inflammation. While acute inflammation serves to resolve pathogen infection and stresses, which promote tissue repair, persistent inflammation results in maladaptive tissue remodeling and damage. RAGE signaling has been implicated in multiple detrimental human illnesses including diabetes, atherosclerosis, arthritis, and Alzheimer's disease. In addition, prolonged inflammation often serves as the precursor for arterial remodeling that underlies the exponential increase of age-associated arterial diseases. Despite the significant progress and exciting discoveries in RAGE research, little is known on the biochemistry of RAGE and the signaling mechanism of RAGE remains poorly defined. The biological impact of RAGE signaling in clinical situations and aging-associated diseases also remains to be fully realized. This review attempts to provide a comprehensive summary on both recent findings and missing pieces of the RAGE puzzle.

Progressive metaplastic and dysplastic changes in mouse pancreas induced by cyclooxygenase-2 overexpression

Cyclooxygenase-2 (COX-2) overexpression is an established factor linking chronic inflammation with metaplastic and neoplastic change in various tissues. We generated transgenic mice (BK5.COX-2) in which elevation of COX-2 and its effectors trigger a metaplasia-dysplasia sequence in exocrine pancreas. Histologic evaluation revealed a chronic pancreatitis-like state characterized by acinar-to-ductal metaplasia and a well-vascularized fibroinflammatory stroma that develops by 3 months. By 6 to 8 months, strongly dysplastic features suggestive of pancreatic ductal adenocarcinoma emerge in the metaplastic ducts. Increased proliferation, cellular atypia, and loss of normal cell/tissue organization are typical features in transgenic pancreata. Alterations in biomarkers associated with human inflammatory and neoplastic pancreatic disease were detected using immunohistochemistry. The abnormal pancreatic phenotype can be completely prevented by maintaining mice on a diet containing celecoxib, a well-characterized COX-2 inhibitor. Despite the high degree of atypia, only limited evidence of invasion to adjacent tissues was observed, with no evidence of distant metastases. However, cell lines derived from spontaneous lesions are aggressively tumorigenic when injected into syngeneic or nude mice. The progressive nature of the metaplastic/dysplastic changes observed in this model make it a valuable tool for examining the transition from chronic inflammation to neoplasia.

Blockade of receptor for advanced glycation end product attenuates pulmonary reperfusion injury in mice

OBJECTIVE

The receptor for advanced glycation end products (RAGE) is expressed at high levels in the lung, particularly in type 1 alveolar cells, and has been shown to amplify injury triggered by acute stress. Previous studies suggest serum concentrations of soluble RAGE increase during pulmonary reperfusion injury after transplantation. RAGE blockade has been shown to suppress hepatic and cardiac ischemia and reperfusion injury in mice. Thus we tested the hypothesis that RAGE mediates tissue-injury mechanisms in ischemia and reperfusion injury in the lung.

METHODS

C57BL/6 mice were subjected to 30 minutes of pulmonary ischemia by clamping the left hilum, followed by 60 minutes of reperfusion. Lung function was assessed by means of blood gas analysis, and capillary leak was assessed by injecting fluorescein isothiocyanate-labeled albumin and comparing fluorescence in bronchial lavage fluid with that in serum. Histologic analysis of the lung was performed by a pathologist naive to the experimental conditions.

RESULTS

In animals subjected to RAGE blockade, significant increases in Po(2) (108 vs 73 mm Hg, P = .0094) and more than 3-fold decrease in capillary leak Relative Fluorescent Units (RFU, 6.12 vs 1.75; P = .001) were observed. Histologic examination revealed significant injury reduction in soluble RAGE-treated animals versus control animals. RAGE knockout mice exhibited a protected phenotype when exposed to pulmonary ischemia and reperfusion. Additionally, interleukin 8 production and nuclear factor kappaB activation were increased in control mice.

CONCLUSION

Abrogation of RAGE signaling attenuates pulmonary ischemia and reperfusion injury. This study suggests that RAGE might play a central role in pulmonary reperfusion injury and in transplantation and that blockade of RAGE might offer a potential target to abrogate pulmonary reperfusion injury in clinical transplantation.

The role of the amadori product in the complications of diabetes

Strong evidence has emerged in recent years in support of an association between advanced glycation and the complications of diabetes, whereby both glycoxidation products and oxoaldehydes have been implicated. In contrast, except for the fact that skin collagen-linked fructosamine (Amadori product) is a strong predictor of the risk of progression of microvascular disease in humans, Amadori products have not been associated with complications in most animal experiments. Below we develop the hypothesis that glucose-derived advanced glycation end products (AGEs), such as glucosepane, may inflict sustained damage to the extracellular matrix in diabetes and contribute to tissue stiffening and accelerated sclerosis in arteries, kidneys, and other organs as supported by immunochemical studies using a glucosepane antibody. We also hypothesize that many more structures derived from Amadori products with nucleophiles, such as primary amines and thiols, are expected. The selective prevention of Amadori-derived AGEs using deglycating enzymes would be desirable. However, x-ray diffraction studies of Amadoriase I crystals show that the active site of the enzyme is deeply embedded, explaining why this approach is unlikely to succeed in vivo. Preliminary experiments with nucleophiles show that aminoguanidine and other compounds block glucosepane in vitro.

Advanced glycation end products depress function of endothelial progenitor cells via p38 and ERK 1/2 mitogen-activated protein kinase pathways

OBJECTIVE

Advanced glycation end products (AGEs) and endothelial progenitor cells (EPCs) play divergent roles in the process of atherosclerosis. We investigated the effects of AGE-human serum albumin (AGE-HSA) on receptor expression for AGEs (RAGE) and EPCs apoptosis.

METHODS

The human mononuclear cells were obtained by Ficoll density gradient centrifugation and cultured in M199 medium containing rh-VEGF (30 ng/ml), rh-b-FGF(6 ng/ml) and 20% NBCS for 8 days. The adhesive EPCs were sequentially harvested after 24 h synchronization and challenged with AGE-HSA (concentration range from 0 to 300 microg/ml) for 24 h and 200 microg/ml AGE-HSA (time range from 0 to 36 h). EPCs apoptosis and migration were determined, expressions of RAGE, phosphorylated ERK1/2, JNK and p38 mitogen-activated protein kinase (MAPK) of EPCs were quantified by fluorescent quantitation RT-PCR and Western-blot, effect of AGE-HSA on NF-kappaB activtiy was determined by EMSA (electrophoretic mobility shift assay) in the presence and absence of special MAPK pathways pathway inhibitors.

RESULTS

AGE-HSA upregulated the expression of RAGE, this effect could be significantly inhibited by p38 MAPK and ERK MAPK inhibitor, but not by JNK MAPK inhibitor. AGE-HSA also promoted EPCs apoptosis and inhibited EPCs migration and increased NF-kappaB activity, these effects could be significantly attenuated by the anti-RAGE neutralizing antibody as well as by p38 and ERK MAPK inhibitors.

CONCLUSION

AGE-HSA could promote atherosclerosis by upregulating EPCs RAGE expressions and promoting EPCs apoptosis via p38, ERK MAPK pathways, activation of NF-kappaB might also play a role in this process.

A soluble form of the receptor for advanced glycation endproducts (RAGE) is produced by proteolytic cleavage of the membrane-bound form by the sheddase a disintegrin and metalloprotease 10 (ADAM10)

The receptor for advanced glycation endproducts (RAGE) mediates responses to cell danger and stress. When bound by its many ligands (which include advanced glycation endproducts, certain members of the S100/calgranulin family, extracellular high-mobility group box 1, the integrin Mac-1, amyloid beta-peptide and fibrils), RAGE activates programs responsible for acute and chronic inflammation. RAGE is therefore also involved in cancer progression, diabetes, atherosclerosis, and Alzheimer's disease. RAGE has several isoforms deriving from alternative splicing, including a soluble form called endogenous secretory RAGE (esRAGE). We show here that most soluble RAGE, either produced by cell lines or present in human blood, is not recognized by an anti-esRAGE antibody. Cells transfected with the cDNA for full-length RAGE, and thus not expressing esRAGE, produce a form of soluble RAGE, cleaved RAGE (cRAGE) that derives from proteolytic cleavage of the membrane-bound molecules and acts as a decoy receptor. By screening chemical inhibitors and genetically modified mouse embryonic fibroblasts (MEFs), we identify the sheddase ADAM10 as a membrane protease responsible for RAGE cleavage. Binding of its ligand HMGB1 promotes RAGE shedding. Our data do not disprove the interpretation that high levels of soluble forms of RAGE protect against chronic inflammation, but rather suggest that they correlate with high levels of ongoing inflammation.

Acute appendicitis is characterized by a uniform and highly selective pattern of inflammatory gene expression

Acute appendicitis (AA) is the most common life-threatening surgical emergency in pediatrics. To characterize the nature of the inflammatory response in AA, gene expression profiles were generated. We found remarkable uniformity in the genes that were differentially expressed between patients with appendicitis and control groups. Sixty-four probe sets were differentially expressed in samples from patients with both severe and mild appendicitis compared to control samples, and within this group we were able to identify four dominant clusters. Interestingly, expression levels of interleukin (IL)-8 significantly correlated with histologic score, and expression of IL-8 protein was observed within both neutrophils and mononuclear cells by immunohistochemistry, suggesting a possible role in the etiology of appendicitis. Although there was some overlap between genes reported to be differentially expressed in Crohn's disease (CD) and those observed in AA, differential expression of genes involved in interferon responses that characterize CD was not observed.