Receptor For Advanced Glycation Endproducts Ligands Research Articles

Soluble RAGE: Therapy and biomarker in unraveling the RAGE axis in chronic disease and aging

The multi-ligand Receptor for Advanced Glycation Endproducts (RAGE) is implicated in the pathogenesis and progression of chronic diseases such as diabetes and immune/inflammatory disorders. Recent studies are uncovering the precise mechanisms by which distinct RAGE ligands bind the extracellular (soluble) domain of the receptor at the V-, C1- and/or C2-immunoglobulin like domains. Experiments using soluble RAGE in animals as a ligand decoy have illustrated largely beneficial effects in reducing vascular and inflammatory stress and, thereby, preventing long-term tissue damage in models of diabetes and immune/inflammatory disorders. Measurement of soluble RAGE levels in the human, both “total” soluble RAGE and a splice variant-derived product known as endogenous secretory or esRAGE, holds promise for the identification of potential therapeutic targets and/or biomarkers of RAGE activity in disease. In this article, we review the evidence from the rodent to the human implicating RAGE in the diverse disease states in which its ligands accumulate.

Abstract 5672: Deletion of Bone Marrow Derived Receptor for Advanced Glycation End-products (RAGE) Does Not Attenuate Plaque Formation but Inhibits Plaque Progression in a Mouse Model of Advanced Atherosclerosis

Background and Hypothesis: The multiligand receptor for advanced glycation end products (RAGE) of the immunoglobulin superfamily is expressed on multiple cell types implicated in the immune-inflammatory response and in atherosclerosis. We sought to determine the role that bone marrow derived RAGE plays in different stages of atherosclerotic lesion development in apolipoprotein E deficient (apoE −/− ) mice. Methods and Results: 7 and 23 week apoE −/− mice were lethally irradiated and given bone marrow from RAGE null (RAGE −/− //apoE −/− ) or RAGE −/−/ /apoE −/− mice to create double knock out chimeras. After 16 weeks on a standard chow diet the mice were sacrificed and atherosclerotic lesion development was evaluated. Plaques in the aortic root of the young mice showed no significant difference in maximum plaque size (217 470±17 480 μ m 2 for the RAGE −/− //apoE −/− mice compared to 244 764±45 840 μ m 2 ) whereas plaques from the older innominate artery of Rage −/− /apoE −/− mice had significantly smaller maximum plaque area compared to the Rage −/−/ apoE −/− mice (83 384±17 981 μ m 2 compared to 136 041±13604 μ m 2 , p<.05) as well as reduced average necrotic core area (35 582±4 797 μ m 2 compared to 55 604±6 523 μ m 2 , p<.05). Reduced plaque size and more stable plaque morphology was associated with significant decreases in the expression of important atherogenic mediators including VCAM-1, ICAM-1, and MCP-1. Accumulation of the RAGE ligand HMGB-1 was also significantly reduced within the lesions of the Rage −/− /apoE −/− mice. Conclusions: This study demonstrates that bone marrow derived RAGE is an important factor in the progression of atherosclerotic plaque development by causing increased expression of pro-atherosclerotic mediators. It provides evidence that RAGE could be a potential target for clinical treatment of advanced atherosclerosis.

The receptor for advanced glycation end products (RAGE) sustains autophagy and limits apoptosis, promoting pancreatic tumor cell survival.

Activation of the induced receptor for advanced glycation endproducts (RAGE) leads to initiation of NF-κB and MAP kinase signaling pathways resulting in propagation and perpetuation of inflammation. RAGE knock out animals are less susceptible to acute inflammation and carcinogen induced tumor development. We have reported that most forms of tumor cell death result in release of the RAGE ligand, HMGB1. We now report a novel role for RAGE in the tumor cell response to stress. Targeted knockdown of RAGE in the tumor cell, leads to increased apoptosis, diminished autophagy and decreased tumor cell survival . In contrast, overexpression of RAGE is associated with enhanced autophagy, diminished apoptosis and greater tumor cell viability. RAGE limits apoptosis through a p53 dependent mitochondrial pathway. Moreover, RAGE-sustained autophagy is associated with decreased phosphorylation of mTOR and increased Beclin-1/VPS34 autophagosome formation. These findings demonstrate that the inflammatory receptor RAGE plays a heretofore unrecognized role in the tumor cell response to stress. Furthermore, these studies establish a direct link between inflammatory mediators in the tumor microenvironment and resistance to programmed cell death. Our data suggest that targeted inhibition of RAGE or its ligands may serve as novel targets to enhance current cancer therapies.

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.

Advanced glycation end products regulate extracellular matrix protein and protease expression by human glomerular mesangial cells

Advanced glycation end products (AGEs) may play a role in the pathogenesis of diabetic nephropathy, by modulating extracellular matrix turnover. AGEs are known to activate specific membrane receptors, including the receptor for AGE (RAGE). In the present study, we analyzed the various receptors for AGEs expressed by human mesangial cells and we studied the effects of glycated albumin and of carboxymethyl lysine on matrix protein and remodelling enzyme synthesis. Membrane RAGE expression was confirmed by FACS analysis. Microarray methods, RT-PCR, and Northern blot analysis were used to detect and confirm specific gene induction. Zymographic analysis and ELISA were used to measure the induction of tPA and PAI-1. We show herein that cultured human mesangial cells express AGE receptor type 1, type 2 and type 3 and RAGE. AGEs (200 microg/ml) induced at least a 2-fold increase in mRNA for 10 genes involved in ECM remodelling, including tPA, PAI-1 and TIMP-3. The increase in tPA synthesis was confirmed by fibrin zymography. The stimulation of PAI-1 synthesis was confirmed by ELISA. AGEs increased PAI-1 mRNA through a signalling pathway involving reactive oxygen species, the MAP kinases ERK-1/ERK-2 and the nuclear transcription factor NF-kappaB, but not AP-1. Carboxymethyl lysine (CML, 5 microM), which is a RAGE ligand, also stimulated PAI-1 synthesis by mesangial cells. In addition, a blocking anti-RAGE antibody partially inhibited the AGE-stimulated gene expression and decreased the PAI-1 accumulation induced by AGEs and by CML. Inhibition of AGE receptors or neutralization of the protease inhibitors TIMP-3 and PAI-1 could represent an important new therapeutic strategy for diabetic nephropathy.

The receptor for advanced glycation endproducts (RAGE) and cardiovascular disease

Recent and compelling investigation has expanded our view of the biological settings in which the products of nonenzymatic glycation and oxidation of proteins and lipids - the advanced glycation endproducts (AGEs) - form and accumulate. Beyond diabetes, natural ageing and renal failure, AGEs form in inflammation, oxidative stress and in ischaemia-reperfusion. The chief signal transduction receptor for AGEs - the receptor for AGEs (RAGE) - is a multiligand-binding member of the immunoglobulin superfamily. In addition to AGEs, RAGE binds certain members of the S100/calgranulin family, high-mobility group box 1 (HMGB1), and beta-amyloid peptide and beta-sheet fibrils. Recent studies demonstrate beneficial effects of RAGE antagonism and genetic deletion in rodent models of atherosclerosis and ischaemia-reperfusion injury in the heart and great vessels. Experimental evidence is accruing that RAGE ligand generation and release during ischaemia-reperfusion may signal through RAGE, thus suggesting that antagonism of this receptor might provide a novel form of therapeutic intervention in heart disease. However, it is plausible that innate, tissue-regenerative roles for these RAGE ligands may also impact the failing heart - perhaps through RAGE and/or distinct receptors. In this review, we focus on RAGE and the consequences of its activation in the cardiovasculature.

Receptor for AGE (RAGE) and its ligands—cast into leading roles in diabetes and the inflammatory response

The actors in the pathogenesis of diabetes and its complications are many and multifaceted. The effects of elevated levels of glucose are myriad; among these is the generation of advanced glycation end products (AGEs), the products of nonenzymatic glycoxidation of proteins and lipids. The finding that AGEs stimulate signal transduction cascades through the multiligand receptor RAGE unveiled novel insights into diabetes and its complications. Inextricably woven into AGE-RAGE interactions in diabetes is the engagement of the innate and adaptive immune responses. Although glucose may be the triggering stimulus to draw RAGE into diabetes pathology, consequent cellular stress results in release of proinflammatory RAGE ligands S100/calgranulins and HMGB1. We predict that once RAGE is engaged in the diabetic tissue, a vicious cycle of ligand-RAGE perturbation ensues, leading to chronic tissue injury and suppression of repair mechanisms. Targeting RAGE may be a beneficial strategy in diabetes, its complications, and untoward inflammatory responses.

In Skeletal Muscle Advanced Glycation End Products (AGEs) Inhibit Insulin Action and Induce the Formation of Multimolecular Complexes Including the Receptor for AGEs

Chronic hyperglycemia promotes insulin resistance at least in part by increasing the formation of advanced glycation end products (AGEs). We have previously shown that in L6 myotubes human glycated albumin (HGA) induces insulin resistance by activating protein kinase Calpha (PKCalpha). Here we show that HGA-induced PKCalpha activation is mediated by Src. Coprecipitation experiments showed that Src interacts with both the receptor for AGE (RAGE) and PKCalpha in HGA-treated L6 cells. A direct interaction of PKCalpha with Src and insulin receptor substrate-1 (IRS-1) has also been detected. In addition, silencing of IRS-1 expression abolished HGA-induced RAGE-PKCalpha co-precipitation. AGEs were able to induce insulin resistance also in vivo, as insulin tolerance tests revealed a significant impairment of insulin sensitivity in C57/BL6 mice fed a high AGEs diet (HAD). In tibialis muscle of HAD-fed mice, insulin-induced glucose uptake and protein kinase B phosphorylation were reduced. This was paralleled by a 2.5-fold increase in PKCalpha activity. Similarly to in vitro observations, Src phosphorylation was increased in tibialis muscle of HAD-fed mice, and co-precipitation experiments showed that Src interacts with both RAGE and PKCalpha. These results indicate that AGEs impairment of insulin action in the muscle might be mediated by the formation of a multimolecular complex including RAGE/IRS-1/Src and PKCalpha.

Abstract 3645: RAGE Impairs Angiogenesis Consequent to Femoral Artery Ligation in Diabetic Mice

The Receptor for Advanced Glycation Endproducts (RAGE) is implicated in the pathogenesis of diabetic complications. Previous studies illustrated that blockade/genetic deletion of RAGE prevented aberrant neointimal expansion in atherosclerosis and carotid artery balloon injury. Here, we tested the hypothesis that RAGE would contribute to impaired revascularization in the setting of acute femoral artery (FA) ligation, especially in diabetes. Wild type (WT) and RAGE −/− mice were rendered diabetic (D) with streptozotocin (stz); non-diabetic (ND) cohorts were treated with buffer alone. RAGE antigen (Western blotting) was upregulated ≈2.1 fold in the ipsilateral muscle tissue of animals subjected to arterial ligation beginning on day 3 and persisting through 28 days post-operatively; confocal microscopy localized RAGE expression to cells expressing CD31 (EC) and SM actin (SMC). A key proinflammatory RAGE ligand, S100B, was highly upregulated (Western blot) in the ipsilateral muscle tissue from day 1 through 14 after ligation and localized to cells expressing CD45 (inflammatory) and vascular cells (expressing CD31 and SMA). To test the role of RAGE in FA ligation, ND and D mice were subjected to surgery; immediately after surgery, animals received either RAGE ligand-binding decoy soluble RAGE (sRAGE), 200 μg, i/p per day for 7 days) or vehicle, PBS. In D mice, administration of sRAGE resulted in improved blood flow ratios on days 3 and 7 after FA ligation vs. vehicle ( p <0.01). To dissect the particular role of RAGE, we tested homozygous RAGE null mice. Both ND and D RAGE −/− mice displayed improved blood flow ratios (laser Doppler) on days 28 after FA ligation compared to ND and D WT mice ( p <0.05 & p <0.01). Immunohistochemistry staining with CD31 on ipsilateral muscle tissue demonstrated significantly increased microvessel density in D RAGE −/− mice on days 28 after FA ligation compared to D WT mice ( p <0.001). Together, these data link the ligand/RAGE axis to impaired vascular responses consequent to severe tissue ischemia in the peripheral vasculature, particularly in diabetes.

Stopping the Primal RAGE Reaction in Myocardial Infarction

The report of Andrassy and colleagues1 in the current issue of Circulation adds to the growing body of evidence that the receptor for advanced glycation end products (RAGE) and its ligands, particularly high mobility group box-1 (HMGB1), are central mediators of ischemia/reperfusion (I/R) injury in the heart.1–4 A major cause of injury, especially in the reperfusion phase, is the influx of inflammatory cells into the stressed heart. Andrassy and colleagues show that infiltrating leukocytes express proinflammatory HMGB1 and that HMGB1 plays fundamental roles in injury responses in the I/R heart. In homeostasis, HMGB1 is largely a nuclear protein. In stress conditions, HMGB1 may be released from injured cells, particularly on necrosis. The chief receptor for HMGB1, RAGE, is expressed in multiple cell types in the I/R heart, such as inflammatory cells, and also in cardiomyocytes and vascular cells (endothelial cells and smooth muscle cells).2 Although HMGB1 may interact with distinct receptors beyond RAGE (for example, toll receptors),5 the current study of Andrassy and colleagues reveals major roles for RAGE in transducing the effects of HMGB1 in the heart, as administration of recombinant HMGB1 or antagonists of this molecule had significant proinjury effects in the wild-type mouse heart, but no additive effects were noted in mice devoid of RAGE. The biology of RAGE, however, is complex and extends beyond HMGB1 in the injured heart. Article p 3216 In addition to HMGB1, other ligands of RAGE likely play pivotal roles in the response to ischemia or I/R in the heart. For example, rapid generation of pre–advanced glycation end products (AGE) species (methylglyoxal) and AGEs in transient occlusion/reperfusion of the LAD coronary artery has been illustrated.2 In hypoxia, in both the murine heart and in isolated primary murine endothelial cells, AGE-immunoreactive species are central mediators of regulation of …

RAGE: developmental expression and positive feedback regulation by Egr-1 during cigarette smoke exposure in pulmonary epithelial cells

The receptor for advanced glycation end-products (RAGE) is a member of the immunoglobin superfamily of multiligand receptors. Following ligand binding, mechanisms associated with host defense, tissue remodeling, and inflammation are activated. RAGE is highly expressed in pulmonary epithelium transitioning from alveolar type (AT) II to ATI cells and is upregulated in the presence of ligand; however, the regulation and function of RAGE during development are less clear. Herein, immunohistochemistry demonstrated a temporal-spatial pattern of RAGE expression in pulmonary epithelial cells from embryonic day 17.5 to postnatal day 10. Cotransfection experiments revealed that the mouse RAGE promoter was activated by early growth response gene 1 (Egr-1) and inhibited by thyroid transcription factor-1 (TTF-1) via interaction with specific regulatory elements. A rat ATI cell line (R3/1) with endogenous RAGE expression also differentially regulated RAGE when transfected with TTF-1 or Egr-1. Because Egr-1 is markedly induced in pulmonary epithelial cells exposed to cigarette smoke extract (CSE; Reynolds PR, Hoidal JR. Am J Respir Cell Mol Biol 35: 314-319, 2006.), we sought to investigate RAGE induction by CSE. Employing RT-PCR and Western blotting, RAGE and common ligands (amphoterin and S100A12) were upregulated in epithelial (R3/1 and A549) and macrophage (RAW) cell lines following exposure to CSE. Immunostaining for RAGE in cells similarly exposed and in lungs from mice exposed to cigarette smoke for 6 mo revealed elevated RAGE expression in pulmonary epithelium. After the addition of glyoxylated BSA, an advanced glycation end-product that binds RAGE, real-time RT-PCR detected a 200-fold increase in Egr-1. These results indicate that Egr-1 regulates RAGE expression during development and the likelihood of positive feedback involving Egr-1 and RAGE in cigarette smoke-related disease.

Calcium-regulated intramembrane proteolysis of the RAGE receptor

The receptor for advanced glycation endproducts (RAGE) interacts with several ligands and is involved in various human diseases. RAGE_v1 or sRAGE, a RAGE splice variant, is secreted and contributes to the removal of RAGE ligands. Because RAGE blockade by specific antibodies directed against RAGE extracellular domains and the use of sRAGE have been proven to be beneficial in the context of pathological settings, both RAGE and sRAGE are considered as therapeutic target. Here, we show that sRAGE is also produced through regulated intramembrane proteolysis of the RAGE receptor, which is catalyzed by ADAM10 and the γ-secretase and that calcium is an essential regulator of RAGE processing. Furthermore, RAGE intracellular domain localizes both in the cytoplasm and the nucleus and induces apoptosis when expressed in cells. These findings reveal new aspects of RAGE regulation and signaling and also provide a new interaction between RAGE and human pathologies.

RAGE and RAGE Ligands in Cancer

The receptor for advanced glycation end-products (RAGE) is a multifunctional receptor with multiple ligands that is known to play a key role in several diseases, including diabetes, arthritis, and Alzheimer's disease. Recent evidence indicates that this receptor also has an important role in cancer. RAGE ligands, which include the S100/calgranulins and high-mobility group box 1 (HMGB1) ligands, are expressed and secreted by cancer cells and are associated with increased metastasis and poorer outcomes in a wide variety of tumors. These ligands can interact in an autocrine manner to directly activate cancer cells and stimulate proliferation, invasion, chemoresistance, and metastasis. RAGE ligands derived from cancer cells can also influence a variety of important cell types within the tumor microenvironment, including fibroblasts, leukocytes, and vascular cells, leading to increased fibrosis, inflammation, and angiogenesis. Several of the cells in the tumor microenvironment also produce RAGE ligands. Most of the cancer-promoting effects of RAGE ligands are the result of their interaction with RAGE. However, these ligands also often have separate intracellular roles, and some may interact with other extracellular targets, so it is not currently possible to assign all of their effects to RAGE activation. Despite these complications, the bulk of the evidence supports the premise that the ligand-RAGE axis is an important target for therapeutic intervention in cancer.

Hypoxia-inducible Factor-1 Mediates Neuronal Expression of the Receptor for Advanced Glycation End Products following Hypoxia/Ischemia

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

RAGE in Diabetic Nephropathy

As is diabetes itself, diabetic angiopathy is a multi-factorial disease. Advanced glycation endproducts (AGE) cause vascular cell derangement characteristic of diabetes, and this is mainly mediated by their interaction with receptor for AGE (RAGE). When made diabetic, RAGE-overexpressing transgenic mice exhibited exacerbation of the indices of nephropathy, and this was prevented by the inhibition of AGE formation. On the other hand, RAGE-deficient animals showed amelioration of diabetic nephropathy. Accordingly, AGE and RAGE should be regarded as environmental and cellular accounts and as a potential therapeutic target for diabetic nephropathy. In effect, substances that inhibit the formation of AGE, break preformed AGE, change metabolic flows away from glycation, antagonize RAGE, and capture RAGE ligands have been proven as effective remedies against this life-threatening disease.

Receptor for AGE (RAGE): Weaving Tangled Webs Within the Inflammatory Response

The family of RAGE ligands, including Advanced Glycation Endproducts (AGEs), S100/calgranulins, High Mobility Group Box-1 (HMGB1) and amyloid beta peptide (Abeta) and beta-sheet fibrils are highly enriched in immune and inflammatory foci. In parallel, upregulation of Receptor for AGE (RAGE) is noted in diverse forms of inflammation and autoimmunity, based on experiments examining human tissues as well as animal models. Indeed, prior to the demonstration that S100/calgranulins were signal transduction ligands of RAGE, these molecules were considered "biomarkers" of disease and disease activity in disorders such as colitis and arthritis. Premiere roles for RAGE in advancing cellular migration implicate this receptor in targeting immune cells to vulnerable foci. Once engaged, ligand-RAGE interaction in inflammatory and vascular cells amplifies upregulation of inflammatory cytokines, adhesion molecules and matrix metalloproteinases (MMPs). Discerning the primal versus chronic injury-provoking roles for this ligand-receptor interaction is a challenge in delineating the functions of the ligand/RAGE axis. As RAGE is expressed by many of the key cell types linked integrally to the immune response, we propose that the sites and time course of ligand-RAGE stimulation determine the phenotype produced by this axis. Ultimately, drawing the fine line between antagonism versus stimulation of the receptor in health and disease will depend on the full characterization of RAGE in repair versus injury.

Receptor for Advanced Glycation Endproducts (RAGE): A Formidable Force in the Pathogenesis of the Cardiovascular Complications of Diabetes & Aging

Unifying mechanisms for the consequences of aging and chronic diabetes are coming to light with the identification that common to both settings is the production and accumulation of the largely irreversible Advanced Glycation Endproducts (AGEs). AGEs impart multiple consequences in the tissues; a key means by which they exert maladaptive effects is via their interaction with and activation of their chief cell surface receptor, Receptor for AGE or RAGE. Although the time course, rate and extent of AGE generation and accumulation in diabetes and aging may be distinct, unifying outcomes of the ligand-RAGE interaction in the vasculature and heart are linked to upregulation of inflammatory and tissue-destructive mechanisms. Consistent with these concepts, administration of the ligand-binding decoy of RAGE, soluble or sRAGE, suppresses early initiation and progression of atherosclerosis in diabetic mice; suppresses exaggerated neointimal expansion consequent to arterial injury; and mitigates the adverse impact of ischemia/reperfusion injury in the heart. Importantly, the RAGE ligand repertoire upregulated in these settings is not limited to AGEs. The key finding that RAGE was a multi-ligand receptor unified the concept that in diabetes and aging, innate and adaptive inflammatory mechanisms contribute to the pathogenesis of tissue injury. We conclude that antagonism of RAGE may reflect a novel and therapeutically logical and safe target in cardiovascular stress induced by aging and chronic diabetes.

The role of the receptor for advanced glycation end-products in lung fibrosis

The pathogenesis of pulmonary fibrosis remains unclear. The receptor for advanced glycation end-products (RAGE) is a multi-ligand receptor known to be involved in the process of fibrotic change in several organs, such as peritoneal fibrosis and kidney fibrosis. The aim of this study was to examine the contribution of RAGE during the acute inflammation and chronic fibrotic phases of lung injury induced by intratracheal instillation of bleomycin in mice. Bleomycin-induced lung fibrosis was evaluated in wild-type and RAGE-deficient (RAGE-/-) mice. Bleomycin administration to wild-type mice caused an initial pneumonitis that evolved into fibrosis. While RAGE-/- mice developed a similar early inflammatory response, the mice were largely protected from the late fibrotic effects of bleomycin. The protection afforded by RAGE deficiency was accompanied by reduced pulmonary levels of the potent RAGE-inducible profibrotic cytokines transforming growth factor (TGF)-beta and PDGF. In addition, bleomycin administration induced high mobility group box 1 (HMGB-1) production, one of the ligands of RAGE, from inflammatory cells that accumulated within the air space. Coculture with HMGB-1 induced epithelial-mesenchymal transition (EMT) in alveolar type II epithelial cells from wild-type mice. However, alveolar type II epithelial cells derived from RAGE-/- mice did not respond to HMGB-1 treatment, such that the RAGE/HMGB-1 axis may play an important role in EMT. Also, bleomycin administration induced profibrotic cytokines TGF-beta and PDGF only in wild-type mouse lungs. Our results suggested that RAGE contributes to bleomycin-induced lung fibrosis through EMT and profibrotic cytokine production. Thus, RAGE may be a new therapeutic target for pulmonary fibrosis.

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

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

Endogenous Secretory Receptor for Advanced Glycation Endproducts Levels Are Correlated With Serum Pentosidine and CML in Patients With Type 1 Diabetes

Advanced glycation end products (AGEs) and receptor for AGE (RAGE)-mediated mechanism has been implicated in the pathogenesis of the vascular derangements.1–3 Yonekura et al recently identified a novel splice variant of RAGE that would serve as a decoy receptor, and named it endogenous secretory RAGE (esRAGE).4 esRAGE is secreted from expresser cells exemplified by vascular endothelial cells and is able to captures RAGE ligands extracellularly, thereby protecting cells from AGE-induced injury.4 Recently, we reported that type 1 diabetic patients with high serum esRAGE levels were resistant to developing early retinal complications than those with low esRAGE levels.5 Moreover, plasma esRAGE is found to be a novel biomarker and a potential protective factor in metabolic syndrome and atherosclerosis.6 It is thus expected that esRAGE plays a protective role in the development of diabetic vascular complications. The balance or imbalance between RAGE ligand and esRAGE levels may be a …