Thoralf Wendt

A mechanism converting psychosocial stress into mononuclear cell activation

Little is known about the mechanisms converting psychosocial stress into cellular dysfunction. Various genes, up-regulated in atherosclerosis but also by psychosocial stress, are controlled by the transcription factor nuclear factor κB (NF-κB). Therefore, NF-κB is a good candidate to convert psychosocial stress into cellular activation. Volunteers were subjected to a brief laboratory stress test and NF-κB activity was determined in peripheral blood mononuclear cells (PBMC), as a window into the body and because PBMC play a role in diseases such as atherosclerosis. In 17 of 19 volunteers, NF-κB was rapidly induced during stress exposure, in parallel with elevated levels of catecholamines and cortisol, and returned to basal levels within 60 min. To model this response, mice transgenic for a strictly NF-κB-controlled β-globin transgene were stressed by immobilization. Immobilization resulted in increased β-globin expression, which could be reduced in the presence of the α1-adrenergic inhibitor prazosin. To define the role of adrenergic stimulation in the up-regulation of NF-κB, THP-1 cells were induced with physiological amounts of catecholamines for 10 min. Only noradrenaline resulted in a dose- and time-dependent induction of NF-κB and NF-κB-dependent gene expression, which depended on pertussis-toxin-sensitive G protein-mediated phosphophatidylinositol 3-kinase, Ras/Raf, and mitogen-activated protein kinase activation. Induction was reduced by α1- and β-adrenergic inhibitors. Thus, noradrenaline-dependent adrenergic stimulation results in activation of NF-κB in vitro and in vivo. Activation of NF-κB represents a downstream effector for the neuroendocrine response to stressful psychosocial events and links changes in the activity of the neuroendocrine axis to the cellular response.

RAGE drives the development of glomerulosclerosis and implicates podocyte activation in the pathogenesis of diabetic nephropathy.

Diabetic nephropathy ensues from events involving earliest changes in the glomeruli and podocytes, followed by accumulation of extracellular matrix in the mesangium. Postulated mechanisms include roles for vascular endothelial growth factor (VEGF), produced by podocytes and contributing to enhanced excretion of urinary albumin and recruitment/activation of inflammatory cells, and transforming growth factor-beta (TGF-beta), elicited largely from mesangial cells and driving production of extracellular matrix. RAGE, a receptor for advanced glycation endproducts (AGEs) and S100/calgranulins, displays enhanced expression in podocytes of genetically diabetic db/db mice by age 13 weeks. RAGE-bearing podocytes express high levels of VEGF by this time, in parallel with enhanced recruitment of mononuclear phagocytes to the glomeruli; events prevented by blockade of RAGE. By age 27 weeks, soluble RAGE-treated db/db mice displayed diminished albuminuria and glomerulosclerosis, and improved renal function. Diabetic homozygous RAGE null mice failed to develop significantly increased mesangial matrix expansion or thickening of the glomerular basement membrane. We propose that activation of RAGE contributes to expression of VEGF and enhanced attraction/activation of inflammatory cells in the diabetic glomerulus, thereby setting the stage for mesangial activation and TGF-beta production; processes which converge to cause albuminuria and glomerulosclerosis.

RAGE Blockade Stabilizes Established Atherosclerosis in Diabetic Apolipoprotein E–Null Mice

Background—Previous studies suggested that blockade of RAGE in diabetic apolipoprotein (apo) E–null mice suppressed early acceleration of atherosclerosis. A critical test of the potential applicability of RAGE blockade to clinical settings was its ability to impact established vascular disease. In this study, we tested the hypothesis that RAGE contributed to lesion progression in established atherosclerosis in diabetic apoE-null mice. Methods and Results—Male apoE-null mice, age 6 weeks, were rendered diabetic with streptozotocin or treated with citrate buffer. At age 14 weeks, certain mice were killed or treated with once-daily murine soluble RAGE or albumin; all mice were killed at age 20 weeks. Compared with diabetic mice at age 14 weeks, albumin-treated animals displayed increased atherosclerotic lesion area and complexity. In diabetic mice treated with sRAGE from age 14 to 20 weeks, lesion area and complexity were significantly reduced and not statistically different from those observed in diabetic mice at age 14 weeks. In parallel, decreased parameters of inflammation and mononuclear phagocyte and smooth muscle cell activation were observed. Conclusions—RAGE contributes not only to accelerated lesion formation in diabetic apoE-null mice but also to lesion progression. Blockade of RAGE may be a novel strategy to stabilize atherosclerosis and vascular inflammation in established diabetes.

RAGE is a multiligand receptor of the immunoglobulin superfamily: Implications for homeostasis and chronic disease

Abstract: Receptor for AGE (RAGE) is a member of the immunoglobulin superfamily that engages distinct classes of ligands. The biology of RAGE is driven by the settings in which these ligands accumulate, such as diabetes, inflammation, neurodegenerative disorders and tumors. In this review, we discuss the context of each of these classes of ligands, including advance glycation endproducts, amyloid β peptide and the family of β sheet fibrils, S100/calgranulins and amphoterin. Implications for the role of these ligands interacting with RAGE in homeostasis and disease will be considered.

Receptor for Advanced Glycation End Products Mediates Inflammation and Enhanced Expression of Tissue Factor in Vasculature of Diabetic Apolipoprotein E–Null Mice

Abstract—Advanced glycation end products (AGEs) and their cell surface receptor, RAGE, have been implicated in the pathogenesis of diabetic complications. Here, we studied the role of RAGE and expression of its proinflammatory ligands, EN-RAGEs (S100/calgranulins), in inflammatory events mediating cellular activation in diabetic tissue. Apolipoprotein E– null mice were rendered diabetic with streptozotocin at 6 weeks of age. Compared with nondiabetic aortas and kidneys, diabetic aortas and kidneys displayed increased expression of RAGE, EN-RAGEs, and 2 key markers of vascular inflammation, vascular cell adhesion molecule (VCAM)-1 and tissue factor. Administration of soluble RAGE, the extracellular domain of the receptor, or vehicle to diabetic mice for 6 weeks suppressed levels of VCAM-1 and tissue factor in the aorta, in parallel with decreased expression of RAGE and EN-RAGEs. Diabetic kidney demonstrated increased numbers of EN-RAGE–expressing inflammatory cells infiltrating the glomerulus and enhanced mRNA for transforming growth factor-&bgr;, fibronectin, and &agr; 1 (IV) collagen. In mice treated with soluble RAGE, the numbers of infiltrating inflammatory cells and mRNA levels for these glomerular cytokines and components of extracellular matrix were decreased. These data suggest that activation of RAGE primes cells targeted for perturbation in diabetic tissues by the induction of proinflammatory mediators.

Glucose, Glycation, and RAGE: Implications for Amplification of Cellular Dysfunction in Diabetic Nephropathy

Receptor for advanced glycation endproducts (RAGE) is a multi-ligand member of the immunoglobulin superfamily of cell surface molecules. Driven by rapid accumulation and expression of key ligands such as advanced glycation endproducts (AGE) and S100/calgranulins in diabetic tissues, upregulation and activation of RAGE magnifies cellular perturbation in tissues affected by hyperglycemia, such as the large blood vessels and the kidney. In the diabetic glomerulus, RAGE is expressed principally by glomerular visceral epithelial cells (podocytes). Blockade of RAGE in the hyperglycemic db/db mouse suppresses functional and structural alterations in the kidney, in the absence of alterations in blood glucose. Recent studies in homozygous RAGE null mice support a key role for RAGE in glomerular perturbation in diabetes. Importantly, beyond diabetes, studies in other settings of glomerulopathies support a critical RAGE-dependent pathway in podocytes linked to albuminuria, mesangial expansion, and glomerular sclerosis. A new paradigm is proposed in glomerular injury, and it is suggested that blockade of the RAGE axis may provide a novel means to prevent irreparable glomerular injury in diabetes and other sclerosing glomerulopathies.

RAGE axis: Animal models and novel insights into the vascular complications of diabetes

Receptor for AGE (RAGE) is a multi-ligand member of the immunoglobulin superfamily of cell surface molecules. Engagement of RAGE by its signal transduction ligands evokes inflammatory cell infiltration and activation in the vessel wall. In diabetes, when fueled by oxidant stress, hyperglycemia, and superimposed stresses such as hyperlipidemia or acute balloon/endothelial denuding arterial injury, the ligand–RAGE axis amplifies vascular stress and accelerates atherosclerosis and neointimal expansion. In this brief synopsis, we review the use of rodent models to test these concepts. Taken together, our findings support the premise that RAGE is an amplification step in vascular inflammation and acceleration of atherosclerosis. Future studies must rigorously test the potential impact of RAGE blockade in human subjects; such trials are on the horizon.

RAGE modulates peripheral nerve regeneration via recruitment of both inflammatory and axonal outgrowth pathways

Axotomy of peripheral nerve stimulates events in multiple cell types that initiate a limited inflammatory response to axonal degeneration and simultaneous outgrowth of neurites into the distal segments after injury. We found that pharmacological blockade of RAGE impaired peripheral nerve regeneration in mice subjected to RAGE blockade and acute crush of the sciatic nerve. As our studies revealed that RAGE was expressed in axons and in infiltrating mononuclear phagocytes upon injury, we tested the role of RAGE in these distinct cell types on nerve regeneration. Transgenic mice expressing signal transduction‐deficient RAGE in mononuclear phagocytes or peripheral neurons were generated and subjected to unilateral crush injury to the sciatic nerve. Transgenic mice displayed decreased functional and morphological recovery compared with littermate controls, as assessed by motor and sensory conduction velocities;and myelinated fiber density. In double transgenic mice expressing signal transduction deficient RAGE in both mononuclear phagocytes and peripheral neurons, regeneration was even further impaired, suggesting the critical interplay between RAGE‐modulated inflammation and neurite outgrowth in nerve repair. These findings suggest that RAGE signaling in inflammatory cells and peripheral neurons plays an important role in plasticity of the peripheral nervous system.—Rong, L. L., Yan, S.‐F., Wendt, T., Hans, D., Pachydaki, S., Bucciarelli, L. G., Adebayo, A., Qu, W., Lu, Y., Kostov, K., Lalla, E., Yan, S. D., Gooch, C., Szabolcs, M., Trojaborg, W., Hays, A. P.,Schmidt, A. M. RAGE modulates peripheral nerve regeneration via recruitment of both inflammatory and axonal outgrowth pathways. FASEB J. 18, 1818–1825 (2004)

RAGE and its ligands: a lasting memory in diabetic complications?

The complications of diabetes are myriad and represent a rising cause of morbidity and mortality, particularly in the Western world. The update of the Diabetes Control and Clinical Trials Group/Epidemiology of Diabetes Interventions and Complications Research Group (DCCT/EDIC) suggested that previous strict control of hyperglycaemia was associated with reduced carotid atherosclerosis compared to conventional treatment, even after levels of glycosylated haemoglobin between the two treatment groups became indistinguishable. These intriguing findings prompt the key question, why does the blood vessel ‘remember’? This review focuses on the hypothesis that the ligand/RAGE axis contributes importantly to glycaemic ‘memory’. Studies in rodent models of diabetes suggest that blockade or genetic modification of RAGE suppress diabetes-associated progression of atherosclerosis, exaggerated neointimal expansion consequent to acute arterial injury, and cardiac dysfunction. We propose that therapeutic RAGE blockade will intercept maladaptive diabetes-associated memory in the vessel wall and provide cardiovascular protection in diabetes.

AGE-RAGE: eine Hypothese oder ein Mechanismus?

Zusammenfassung.Kürzlich konnte ein Zusammenhang zwischen der Hyperglykämie und der akzelerierten Atherosklerose im Rahmen des Diabetes mellitus hergestellt werden. Einen möglichen pathogenetischen Mechanismus der akzelerierten Atherosklerose stellt die AGE-RAGE-Interaktion dar. Die Hyperglykämie führt durch nichtenzymatische Glykierung zur Entstehung von AGEs (advanced glycation endproducts). AGEs, aber auch andere Liganden wie S100/Calgranulin und Amphoterin, vermitteln rezeptorunabhängige und rezeptorabhängige (z.B. via RAGE-Interaktion) Effekte. Die RAGE-Liganden-Interaktion führt zu einer vermehrten Aktivierung von NF-κB, eine vermehrte Expression von Zytokinen, Chemokinen und Adhäsionsmolekülen und induziert oxidativen Stress. Tierexperimentelle Daten belegen die Relevanz der Liganden-RAGE-Interaktion für die akzelerierte Atherosklerose und die vermehrte Neointimabildung im Rahmen eines Diabetes mellitus. Erste Analysen atherosklerotischer Läsionen von Diabetikern unterstützen ebenfalls eine pathogenetische Rolle der Liganden-RAGE-Interaktion für die Atherosklerose. Neue experimentelle Daten belegen, dass auf der einen Seite AGEs mit weiteren Rezeptoren (außer RAGE), auf der anderen Seite RAGE mit diversen Liganden interagiert. Weitere Untersuchungen zur Charakterisierung der Liganden-RAGE-Interaktion werden das erforderliche Grundlagenwissen zur Entwicklung innovativer Therapieansätze der akzelerierten Atherosklerose beim Diabetes mellitus bereitstellen.Abstract.A causal relation between hyperglycemia and accelerated atherosclerosis has been recently suggested. The AGE-RAGE interaction is a potential mechanism underlying the accelerated atherosclerosis. Hyperglycemia causes via nonenzymatic glycation the formation of AGEs (advanced glycation endproducts). AGEs as well as other ligands like S100/Calgranulin and Amphoterin mediate receptor-independent and -dependent (via the interaction with RAGE) effects. The ligand-RAGE-interaction results in an activation of NF-κB, increased expression of cytokines, chemokines, and adhesion molecules and induces oxidative stress. A relevant role of the ligand-RAGE-interaction has been demonstrated in in vivo studies, both for the accelerated atherosclerosis and increased neointima formation in diabetes mellitus. Recent data analysing atherosclerotic lesions of diabetic patients provide further evidence for the pathogenetic role of the RAGE-ligand-interaction. In addition, new experimental data established that AGEs interact with other receptors than RAGE, while RAGE interacts with a diverse group of ligands. Thus, further studies are needed for the characterization of the ligand-RAGE-interaction. These studies will provide a rationale for the development of new therapeutic approaches for accelerated atherosclerosis in diabetes mellitus.