Shi-Fang Yan

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.

RAGE-dependent signaling in microglia contributes to neuroinflammation, Aβ accumulation, and impaired learning/memory in a mouse model of Alzheimer’s disease

Microglia are critical for amyloid‐β peptide (Aβ)‐mediated neuronal perturbation relevant to Alzheimers disease (AD) pathogenesis. We demonstrate that overexpression of receptor for advanced glycation end products (RAGE) in imbroglio exaggerates neuroinflammation, as evidenced by increased proinflammatory mediator production, Aβ accumulation, impaired learning/memory, and neurotoxicity in an Aβ‐rich environment. Transgenic (Tg) mice expressing human mutant APP (mAPP) in neurons and RAGE in microglia displayed enhanced IL‐1β and TNF‐α production, increased infiltration of microglia and astrocytes, accumulation of Aβ, reduced acetylcholine esterase (AChE) activity, and accelerated deterioration of spatial learning/memory. Notably, introduction of a signal transduction‐defective mutant RAGE (DN‐RAGE) to microglia attenuates deterioration induced by Aβ. These findings indicate that RAGE signaling in microglia contributes to the pathogenesis of an inflammatory response that ultimately impairs neuronal function and directly affects amyloid accumulation. We conclude that blockade of microglial RAGE may have a beneficial effect on Aβ‐mediated neuronal perturbation relevant to AD pathogenesis.—Fang, F., Lue, L.‐F., Yan, S., Xu, H., Luddy, J. S., Chen, D., Walker, D. G., Stern, D. M., Yan, S., Schmidt, A. M., Chen, J. X., Yan, S. S. RAGE‐dependent signaling in microglia contributes to neuroinflammation, Aβ accumulation, and impaired learning/memory in a mouse model of Alzheimers disease. FASEB J. 24, 1043–1055 (2010). www.fasebj.org

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)

Advanced Glycation End Product (AGE)-Receptor for AGE (RAGE) Signaling and Up-regulation of Egr-1 in Hypoxic Macrophages

Receptor for advanced glycation end product (RAGE)-dependent signaling has been implicated in ischemia/reperfusion injury in the heart, lung, liver, and brain. Because macrophages contribute to vascular perturbation and tissue injury in hypoxic settings, we tested the hypothesis that RAGE regulates early growth response-1 (Egr-1) expression in hypoxia-exposed macrophages. Molecular analysis, including silencing of RAGE, or blockade of RAGE with sRAGE (the extracellular ligand-binding domain of RAGE), anti-RAGE IgG, or anti-AGE IgG in THP-1 cells, and genetic deletion of RAGE in peritoneal macrophages, revealed that hypoxia-induced up-regulation of Egr-1 is mediated by RAGE signaling. In addition, the observation of increased cellular release of RAGE ligand AGEs in hypoxic THP-1 cells suggests that recruitment of RAGE in hypoxia is stimulated by rapid production of RAGE ligands in this setting. Finally, we show that mDia-1, previously shown to interact with the RAGE cytoplasmic domain, is essential for hypoxia-stimulated regulation of Egr-1, at least in part through protein kinase C βII, ERK1/2, and c-Jun NH2-terminal kinase signaling triggered by RAGE ligands. Our findings highlight a novel mechanism by which an extracellular signal initiated by RAGE ligand AGEs regulates Egr-1 in a manner requiring mDia-1.

Mice deficient in PKCβ and apolipoprotein E display decreased atherosclerosis

Endothelial activation is a central initiating event in atheroma formation. Evidence from our laboratory and others has demonstrated links between activation of early growth response‐1 (Egr‐1) and atherosclerosis and also has demonstrated that activated protein kinase C (PKC) βII is a critical upstream regulator of Egr‐1 in response to vascular stress. We tested the role of PKCβ in regulating key events linked to atherosclerosis and show that the aortas of apoE–/– mice display an age‐dependent increase in PKCβll antigen in membranous fractions vs. C57BL/6 animals with a ~2‐fold increase at age 6 wk and a ~4.5‐fold increase at age 24 wk. Consistent with important roles for PKCβ in atherosclerosis, a significant decrease in atherosclerotic lesion area was evident in PKCβ–/– apoE–/– vs. apoE–/– mice by ~5‐fold, in parallel with significantly reduced vascular transcripts for Egr‐1 and matrix metalloproteinase (MMP)‐2 antigen and activity vs. apoE–/– mice. Significant reduction in atherosclerosis of ~2‐fold was observed in apoE–/– mice fed ruboxistaurin chow (PKCβ inhibitor) vs. vehicle. In primary murine and human aortic endothelial cells, the PKCβ‐JNK mitogen‐activated protein kinase pathway importantly contributes to oxLDL‐mediated induction of MMP2 expression. Blockade of PKCβ may be beneficial in mitigating endothelial perturbation and atherosclerosis.—Harja, E., Chang, J. S., Lu, Y., Leitges, M., Zou, Y. S., Schmidt, A. M., Yan, S.‐F. Mice deficient in PKC β and apolipoprotein E display decreased atherosclerosis. FASEB J. 23, 1081–1091 (2009)

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.

PKCβ modulates ischemia-reperfusion injury in the heart

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.

Central Role of PKCβ in Neointimal Expansion Triggered by Acute Arterial Injury

We tested the hypothesis that PKC&bgr; contributes to vascular smooth muscle cell (SMC) migration and proliferation; processes central to the pathogenesis of restenosis consequent to vascular injury. Homozygous PKC&bgr; null (−/−) mice or wild-type mice fed the PKC&bgr; inhibitor, ruboxistaurin, displayed significantly decreased neointimal expansion in response to acute femoral artery endothelial denudation injury compared with controls. In vivo and in vitro analyses demonstrated that PKC&bgr;II is critically linked to SMC activation, at least in part via regulation of ERK1/2 MAP kinase and early growth response-1. These data highlight novel roles for PKC&bgr; in the SMC response to acute arterial injury and suggest that blockade of PKC&bgr; may represent a therapeutic strategy to limit restenosis.