Faculty Bibliography

OBJECTIVE: Subjects with diabetes experience an increased risk of myocardial infarction and cardiac failure compared with nondiabetic age-matched individuals. The receptor for advanced glycation end products (RAGE) is upregulated in diabetic tissues. In this study, we tested the hypothesis that RAGE affected ischemia/reperfusion (I/R) injury in the diabetic myocardium. In diabetic rat hearts, expression of RAGE and its ligands was enhanced and localized particularly to both endothelial cells and mononuclear phagocytes. RESEARCH DESIGN AND METHODS: To specifically dissect the impact of RAGE, homozygous RAGE-null mice and transgenic (Tg) mice expressing cytoplasmic domain-deleted RAGE (DN RAGE), in which RAGE-dependent signal transduction was deficient in endothelial cells or mononuclear phagocytes, were rendered diabetic with streptozotocin. Isolated perfused hearts were subjected to I/R. RESULTS: Diabetic RAGE-null mice were significantly protected from the adverse impact of I/R injury in the heart, as indicated by decreased release of LDH and lower glycoxidation products carboxymethyl-lysine (CML) and pentosidine, improved functional recovery, and increased ATP. In diabetic Tg mice expressing DN RAGE in endothelial cells or mononuclear phagocytes, markers of ischemic injury and CML were significantly reduced, and levels of ATP were increased in heart tissue compared with littermate diabetic controls. Furthermore, key markers of apoptosis, caspase-3 activity and cytochrome c release, were reduced in the hearts of diabetic RAGE-modified mice compared with wild-type diabetic littermates in I/R. CONCLUSIONS: These findings demonstrate novel and key roles for RAGE in I/R injury in the diabetic heart

In the kidney, the receptor for advanced glycation end products (RAGE) is principally expressed in the podocyte at low levels, but is upregulated in both human and mouse glomerular diseases. Because podocyte injury is central to proteinuric states, such as the nephrotic syndrome, the murine adriamycin nephrosis model was used to explore the role of RAGE in podocyte damage. In this model, administration of the anthracycline antibiotic adriamycin provokes severe podocyte stress and glomerulosclerosis. In contrast to wild-type animals, adriamycin-treated RAGE-null mice were significantly protected from effacement of the podocyte foot processes, albuminuria, and glomerulosclerosis. Administration of adriamycin induced rapid generation of RAGE ligands, and treatment with soluble RAGE protected against podocyte injury and glomerulosclerosis. In vitro, incubation of RAGE-expressing murine podocytes with adriamycin stimulated AGE formation, and treatment with RAGE ligands rapidly activated nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, via p44/p42 MAP kinase signaling, and upregulated pro-fibrotic growth factors. These data suggest that RAGE may contribute to the pathogenesis of podocyte injury in sclerosing glomerulopathies such as focal segmental glomerulosclerosis

Many important biochemical mechanisms are activated in the presence of high levels of glucose, which occur in diabetes. Elevated levels of glucose accelerate the formation of advanced glycation end-products (AGEs). Via their chief signaling receptor-the AGE-specific receptor (commonly abbreviated as RAGE)-AGEs generate reactive oxygen species and activate inflammatory signaling cascades. Consequently, AGEs have key roles in the pathogenesis of diabetic complications. Two discoveries have advanced our knowledge of the roles of RAGE in inflammation. First, this receptor has multiple ligands and binds not only AGEs but also proinflammatory, calcium-binding S100 proteins (also known as calgranulins) and nuclear high mobility group protein box-1. Second, RAGE is expressed on T lymphocytes, monocytes and macrophages; RAGE expression on T lymphocytes is essential for effective priming of immune responses in vivo. In this Review, we chronicle roles for RAGE in the pathogenesis of diabetic complications and develop the hypothesis that, in addition to RAGE's central role in the inflammatory response, it is critically linked to the pathogenesis of types 1 and 2 diabetes

The receptor for advanced glycation end-products (RAGE) has been implicated in the pathogenesis of ischemia-reperfusion (I/R) injury in the isolated perfused heart. To test the hypothesis that RAGE-dependent mechanisms modulated responses to I/R in a murine model of transient occlusion and reperfusion of the left anterior descending coronary artery (LAD), we subjected male homozygous RAGE(-/-) mice and their wild-type age-matched littermates to 30 min of occlusion of the LAD followed by reperfusion. At 48 h of reperfusion, hematoxylin and eosin staining revealed significantly larger infarct size in wild-type versus RAGE(-/-) mice. Contractile function, as evaluated by echocardiography 48 h after reperfusion, revealed that fractional shortening was significantly higher in RAGE(-/-) versus wild-type mice. Plasma levels of creatine kinase were markedly decreased in RAGE(-/-) versus wild-type animals. Integral to the impact of RAGE deletion on diminished myocardial damage after infarction was significantly decreased apoptosis in the heart, as assessed by TUNEL staining, release of cytochrome c, and caspase-3 activity. Experiments investigating the impact of RAGE on early signaling pathways influencing myocardial ischemic injury revealed attenuation of JNK and STAT5 phosphorylation in RAGE(-/-) mouse hearts versus robust activation observed in wild-type mice upon ischemia and reperfusion. Solidifying the link to RAGE, these experiments revealed that infarction stimulated the rapid production of advanced glycation end-products in the heart. Thus, we tested the effect of ligand decoy soluble RAGE (sRAGE). Administration of sRAGE protected the myocardium from ischemic damage, similar to the effects observed in RAGE(-/-) mouse hearts. Taken together, these data implicate RAGE and its ligands in the pathogenesis of I/R injury and identify JNK and STAT signal transduction as central downstream effector pathways of the ligand-RAGE axis in the heart subjected to I/R injury

Protein kinase C-betaII (PKCbetaII) is an important modulator of cellular stress responses. To test the hypothesis that PKCbetaII modulates the response to myocardial ischemia-reperfusion (I/R) injury, we subjected mice to occlusion and reperfusion of the left anterior descending coronary artery. Homozygous PKCbeta-null (PKCbeta(-/-)) and wild-type mice fed the PKCbeta inhibitor ruboxistaurin displayed significantly decreased infarct size and enhanced recovery of left ventricular (LV) function and reduced markers of cellular necrosis and serum creatine phosphokinase and lactate dehydrogenase levels compared with wild-type or vehicle-treated animals after 30 min of ischemia followed by 48 h of reperfusion. Our studies revealed that membrane translocation of PKCbetaII in LV tissue was sustained after I/R and that gene deletion or pharmacological blockade of PKCbeta protected ischemic myocardium. Homozygous deletion of PKCbeta significantly diminished phosphorylation of c-Jun NH(2)-terminal mitogen-activated protein kinase and expression of activated caspase-3 in LV tissue of mice subjected to I/R. These data implicate PKCbeta in I/R-mediated myocardial injury, at least in part via phosphorylation of JNK, and suggest that blockade of PKCbeta may represent a potent strategy to protect the vulnerable myocardium

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. Multiple studies have elucidated that ligand-RAGE interaction on cells, such as monocytes, macrophages, and endothelial cells, mediates cellular migration and upregulation of proinflammatory and prothrombotic molecules. In addition, recent studies reveal definitive rules for RAGE in effective T lymphocyte priming in vivo. RAGE ligand AGEs may be formed in diverse settings; although AGEs are especially generated in hyperglycemia, their production in settings characterized by oxidative stress and inflammation suggests that these species, in part via RAGE, may contribute to the pathogenesis of atherosclerosis. In murine models of atherosclerosis, vascular inflammation is a key factor and one which is augmented, in parallel with even further increases in RAGE ligands, in diabetic macrovessels. The findings that antagonism and genetic disruption of RAGE in atherosclerosis-susceptible mice strikingly reduces vascular inflammation and atherosclerotic lesion area and complexity link RAGE intimately to these processes and suggest that RAGE is a logical target for therapeutic intervention in aberrant inflammatory mechanisms and in atherosclerosis

Endothelial dysfunction is a key triggering event in atherosclerosis. Following the entry of lipoproteins into the vessel wall, their rapid modification results in the generation of advanced glycation endproduct epitopes and subsequent infiltration of inflammatory cells. These inflammatory cells release receptor for advanced glycation endproduct (RAGE) ligands, specifically S100/calgranulins and high-mobility group box 1, which sustain vascular injury. Here, we demonstrate critical roles for RAGE and its ligands in vascular inflammation, endothelial dysfunction, and atherosclerotic plaque development in a mouse model of atherosclerosis, apoE-/- mice. Experiments in primary aortic endothelial cells isolated from mice and in cultured human aortic endothelial cells revealed the central role of JNK signaling in transducing the impact of RAGE ligands on inflammation. These data highlight unifying mechanisms whereby endothelial RAGE and its ligands mediate vascular and inflammatory stresses that culminate in atherosclerosis in the vulnerable vessel wall

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

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