Faculty Bibliography

The Receptor for Advanced Glycation End-products (RAGE) is a complex, multi-ligand signaling system implicated in the pathogenesis of diabetes, cardiovascular disease and various cancers. RAGE undergoes extensive alternative splicing to produce a variety of transcripts with diverse functions, including soluble antagonists and variants with altered ligand binding domains. Studies focused on the major soluble variant (RAGEv1/esRAGE) have revealed this to function by binding RAGE-ligands and preventing activation of RAGE signaling in vascular and tumor cells. Furthermore, measurement of this variant in human serum has revealed that RAGEv1/esRAGE levels may represent a novel biomarker for RAGE-ligand related pathogenic states. Understanding the full plethora of RAGE alternative splicing and its regulation is central to elucidating the role of RAGE in biology and disease

The receptor for advanced glycation endproducts (RAGE) was first described as a signal transduction receptor for advanced glycation endproducts (AGEs), the products of nonenzymatic glycation and oxidation of proteins and lipids that accumulate in diabetes and in inflammatory foci. The discovery that RAGE was a receptor for inflammatory S100/calgranulins and high mobility group box 1 (HMGB1) set the stage for linking RAGE to both the consequences and causes of types 1 and 2 diabetes. Recent discoveries regarding the structure of RAGE as well as novel intracellular binding partner interactions advance our understanding of the mechanisms by which RAGE evokes pathological consequences and underscore strategies by which antagonism of RAGE in the clinic may be realized. Finally, recent data tracking RAGE in the clinic suggest that levels of soluble RAGEs and polymorphisms in the gene encoding RAGE may hold promise for the identification of patients who are vulnerable to the complications of diabetes and/or are receptive to therapeutic interventions designed to prevent and reverse the damage inflicted by chronic hyperglycemia, irrespective of its etiology

BACKGROUND: Recent evidence suggests that storage-induced alterations of the red blood cell (RBC) are associated with adverse consequences in susceptible hosts. As RBCs have been shown to form advanced glycation end products (AGEs) after increased oxidative stress and under pathologic conditions, we examined whether stored RBCs undergo modification with the specific AGE N-(carboxymethyl)lysine (N(epsilon) -CML) during standard blood banking conditions. STUDY DESIGN AND METHODS: Purified, fresh RBCs from volunteers were compared to stored RBCs (35-42 days old) obtained from the blood bank. N(epsilon) -CML formation was quantified using a competitive enzyme-linked immunosorbent assay. The receptor for advanced glycation end products (RAGE) was detected in human pulmonary microvascular endothelial cells (HMVEC-L) by real-time polymerase chain reaction, Western blotting, and flow cytometry. Intracellular reactive oxygen species (ROS) generation was measured by the use of 5-(and 6-)chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester-based assays. RESULTS: Stored RBCs showed increased surface N(epsilon) -CML formation when compared with fresh RBCs. HMVEC-L showed detectable surface RAGE expression constitutively. When compared to fresh RBCs, stored RBCs triggered increased intracellular ROS generation in both human umbilical vein endothelial cells and HMVEC-L. RBC-induced endothelial ROS generation was attenuated in the presence of soluble RAGE or RAGE blocking antibody. CONCLUSIONS: The formation of the AGE N(epsilon) -CML on the surface of stored RBCs is one functional consequence of the storage lesion. AGE-RAGE interactions may be one mechanism by which transfused RBCs cause endothelial cell damage.

OBJECTIVE: A link between periodontal infections and an increased risk for vascular disease has been demonstrated. Porphyromonas gingivalis, a major periodontal pathogen, localizes in human atherosclerotic plaques, accelerates atherosclerosis in animal models and modulates vascular cell function. The receptor for advanced glycation endproducts (RAGE) regulates vascular inflammation and atherogenesis. We hypothesized that RAGE is involved in P. gingivalis's contribution to pro-atherogenic responses in vascular endothelial cells. METHODS AND RESULTS: Murine aortic endothelial cells (MAEC) were isolated from wild-type C57BL/6 or RAGE-/- mice and were infected with P. gingivalis strain 381. P. gingivalis 381 infection significantly enhanced expression of RAGE in wild-type MAEC. Levels of pro-atherogenic advanced glycation endproducts (AGEs) and monocyte chemoattractant protein 1 (MCP-1) were significantly increased in wild-type MAEC following P. gingivalis 381 infection, but were unaffected in MAEC from RAGE-/- mice or in MAEC infected with DPG3, a fimbriae-deficient mutant of P. gingivalis 381. Consistent with a role for oxidative stress and an AGE-dependent activation of RAGE in this setting, both antioxidant treatment and AGE blockade significantly suppressed RAGE gene expression and RAGE and MCP-1 protein levels in P. gingivalis 381-infected human aortic endothelial cells (HAEC). CONCLUSION: The present findings implicate for the first time the AGE-RAGE axis in the amplification of pro-atherogenic responses triggered by P. gingivalis in vascular endothelial cells.

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.

Receptor for advanced glycation end products (RAGE) and its ligands are overexpressed in multiple cancers. RAGE has been implicated in tumorigenesis and metastasis, but little is known of the mechanisms involved. In this study, we define a specific functional role for an alternate splice variant termed RAGE splice variant 1 (RAGEv1), which encodes a soluble endogenous form of the receptor that inhibits tumorigenesis. RAGEv1 was downregulated in lung, prostate, and brain tumors relative to control matched tissues. Overexpressing RAGEv1 in tumor cells altered RAGE ligand stimulation of several novel classes of genes that are critical in tumorigenesis and metastasis. Additionally, RAGEv1 inhibited tumor formation, cell invasion, and angiogenesis induced by RAGE ligand signaling. Analysis of signal transduction pathways underlying these effects revealed marked suppression of c-jun-NH(2)-kinase (JNK) pathway signaling, and JNK inhibition suppressed signaling through the RAGE pathway. Tumors expressing RAGEv1 were significantly smaller than wild-type tumors and displayed prominently reduced activation of JNK. Our results identify RAGEv1 as a novel suppressor, the study of which may offer new cancer therapeutic directions.

OBJECTIVE: The receptor for advanced glycation end products mediates a variety of inflammatory responses. Soluble receptor for advanced glycation end products has been suggested to function as a decoy abrogating cellular activation. High-mobility group box 1 is a high-affinity binding ligand for the receptor for advanced glycation end products with cytokine activities and plays a role in sepsis. DESIGN: Controlled, in vivo laboratory study. SETTING: Research laboratory of a health sciences university. SUBJECTS: C57BL/6 mice. INTERVENTIONS: Peritonitis was induced by intraperitoneal injection of Escherichia coli. Mice received soluble receptor for advanced glycation end products or anti-high-mobility group box 1 immunoglobulin G, or the appropriate control treatment. MEASUREMENTS AND MAIN RESULTS: Soluble receptor for advanced glycation end products-treated mice demonstrated an enhanced bacterial dissemination to liver and lungs, accompanied by increased hepatocellular injury and exaggerated systemic cytokine release, 20 hrs after intraperitoneal administration of Escherichia coli. Soluble receptor for advanced glycation end products administration in healthy, uninfected mice did not induce an immune response. Remarkably, lung inflammation was unaffected. Furthermore, high-mobility group box 1 release was enhanced during peritonitis and anti-high-mobility group box 1 treatment was associated with higher bacterial loads in liver and lungs. CONCLUSIONS: These data are the first to suggest that receptor for advanced glycation end products ligands, including high-mobility group box 1, limit bacterial dissemination during Gram-negative sepsis.

The multiligand receptor of the immunoglobulin superfamily, receptor for advanced glycation endproducts (RAGE), is a signal transduction receptor that binds advanced glycation endproducts, certain members of the S100/calgranulin family of proteins, high mobility group box 1 (HMGB1), advanced oxidation protein products, and amyloid (beta-sheet fibrils). Initial studies investigating the role of RAGE in renal dysfunction focused on diabetes. However, RAGE also has roles in the pathogenesis of renal disorders that are not associated with diabetes, such as obesity-related glomerulopathy, doxorubicin-induced nephropathy, hypertensive nephropathy, lupus nephritis, renal amyloidosis, and ischemic renal injuries. Experiments that have employed transgenic mouse models, pharmacological blockade of RAGE, or genetic deletion or modification of RAGE indicate that modulation of RAGE expression or function affects the functional and pathological properties of these nephropathies. Accumulating evidence links RAGE to the pathogenesis of nephropathies, indicating that antagonism of RAGE might be a strategy for the treatment of chronic kidney disease.