Receptor for Advanced Glycation End Products (RAGE) in Type 1 Diabetes Pathogenesis

The receptor for advanced glycation end products (RAGE) is a novel protein increasingly studied in the pathogenesis of type 1 diabetes (T1D). RAGE is expressed by several immune cell types, including T cells, antigen-presenting cells, endothelial cells, and the endocrine cells of the pancreatic islets. RAGE binds various ligands including advanced glycation end products (AGEs), high-mobility group box protein 1 (HMGB1), S100 proteins, β-amyloid, β-sheet fibrils, and lipopolysaccharide. AGEs are a particularly interesting ligand because their exogenous introduction into the body can be accelerated by the consumption of AGE-rich processed foods. This review will detail RAGE isoforms and its ligands and discuss how RAGE binding on the aforementioned cells could be linked to T1D pathogenesis.     

Advanced glycation end products and their receptors co-localise in rat organs susceptible to diabetic microvascular injury

Summary Advanced glycation end products (AGEs) are believed to play an important role in the development of diabetic complications. AGEs are increased in experimental diabetes and treatment with the inhibitor of advanced glycation end products, aminoguanidine, has been shown to attenuate the level of these products in tissues undergoing complications. Recently, an AGE-binding protein has been isolated from bovine lung endothelial cells and termed the receptor for advanced glycated end products (RAGE). The present study sought to determine the distribution of AGE and RAGE in tissues susceptible to the long-term complications of diabetes including the kidney, eye, nerve, arteries as well as in a tissue resistant to such complications, the lung. Using polyclonal antisera both AGE and RAGE were found to co-localize in the renal glomerulus. AGE staining was clearly increased with age and was further increased by diabetes. Aminoguanidine treatment reduced AGE accumulation in the kidney. Co-localisation of AGE and RAGE was demonstrated in the inner plexiform layer and the inner limiting membrane of the retina and in nerve bundles from mesenteric arteries. In the aorta, both AGE and RAGE were found in the intima, media and adventitia. Medial staining was increased in diabetes and was reduced by aminoguanidine treatment. A similar pattern was observed for RAGE in the aorta. In the lung, RAGE was found widely distributed throughout the lung whereas the distribution of AGE staining was more limited, primarily localising to macrophages. The co-localisation of AGEs and RAGE in sites of diabetic microvascular injury suggests that this ligand-receptor interaction may represent an important mechanism in the genesis of diabetic complications. [Diabetologia (1997) 40: 619–628] Received: 16 October 1996 and in final revised form: 17 February 1997     

Plasma glycation adducts and various RAGE isoforms are intricately associated with oxidative stress and inflammatory markers in type 2 diabetes patients with vascular complications

BackgroundThe secondary vascular complications in diabetes mellitus (DM) are contributed by acute as well as inflammatory responses which get activated due to interaction between glycation adducts and respective receptors.AimThe present work was performed to understand the relationship between Advanced glycation end products (AGEs)-receptor for advanced glycation end products (RAGE) interaction with oxidative stress and inflammation in vascular complications.MethodsFor the present work we recruited 103 controls, 200 patients with type 2 DM, and 200 patients with Diabetic complications. Different Plasma glycation adducts (fructosamine, carbonyls, AGEs, β-amyloid content, free amino groups, and free thiol groups); RAGE isoforms, level of antioxidant such as glutathione, catalase activity, nitric oxide level, total antioxidant capacity, and superoxide dismutase activity, as well as oxidative markers, and expression of Nε-carboxymethyl-lysine (CML), different isoforms of RAGE, NF-κB, and inflammatory markers were analyzed.ResultsGlycation adducts were higher in DM patients and more elevated in nephropathy patients where free amino groups and thiol groups lowered as compared to controls. sRAGE levels and expression were increased mainly in nephropathy. CML expression was higher in nephropathy patients. The antioxidant profile indicates a reduced level of different antioxidants while increased lipid peroxidation and intracellular ROS generation in DM and much higher in nephropathy patients. Expression of membrane RAGE, NF-κB, and inflammatory markers showed a remarkably increased level in DM patients with nephropathy.ConclusionThis work provides the first evidence of four different RAGE isoforms in diabetes and in complications. The glycation via the activation of RAGE, oxidative stress, and resultant inflammation plays a crucial role in the development of diabetic complications.     

晚期糖基化终末产物及其受体在原发性高血压中的作用机制

近年来研究发现晚期糖基化终末产物（advanced glycation end products,AGEs）在原发性高血压的发生、发展过程中起着一定的病理作用,AGEs主要通过直接修饰蛋白、结合受体RAGE并激活信号转导通路两条作用途径来发挥效应。此外AGEs—RAGE还与肾素-血管紧张素系统、氧化应激三者构成正反馈环路,共同参与了原发性高血压的进程。相信随着对AGEs—RAGE作剧机制及药物干预的进一步研究,抗AGEs的治疗策略将有望成为防治高血压及其并发症的新方向。     

Protein glycation: a firm link to endothelial cell dysfunction

The advanced glycation end products (AGEs) are a heterogeneous class of molecules, including the following main subgroups: bis(lysyl)imidazolium cross-links, hydroimidazolones, 3-deoxyglucosone derivatives, and monolysyl adducts. AGEs are increased in diabetes, renal failure, and aging. Microvascular lesions correlate with the accumulation of AGEs, as demonstrated in diabetic retinopathy or renal glomerulosclerosis. On endothelial cells, ligation of receptor for AGE (RAGE) by AGEs induces the expression of cell adhesion molecules, tissue factor, cytokines such as interleukin-6, and monocyte chemoattractant protein-1. A chief means by which AGEs via RAGE exert their effects is by generation of reactive oxygen species, at least in part via stimulation of NADPH oxidase. Diabetes-associated vascular dysfunction in vivo can be prevented by blockade of RAGE. Thus, agents that limit AGE formation, increase the catabolism of these species, or antagonize their binding to RAGE may provide new targets for vascular protection in diabetes.     

Serum levels of soluble form of receptor for advanced glycation end products (sRAGE) are positively associated with circulating AGEs and soluble form of VCAM-1 in patients with type 2 diabetes

We have recently found that soluble form of receptor for advanced glycation end products (sRAGE) levels are positively associated with inflammatory biomarkers and the presence of coronary artery disease (CAD) in type 2 diabetic patients. Since advanced glycation end products (AGEs) up-regulate RAGE expression and endogenous sRAGE could be generated from the cleavage of cell surface RAGE, it is conceivable that sRAGE is positively associated with circulating AGEs levels in diabetes. In this study, we examined whether sRAGE were correlated to circulating levels of AGEs and soluble forms of vascular cell adhesion molecule-1 (sVCAM-1) and intercellular adhesion molecule-1 (sICAM-1) in patients with type 2 diabetes. Eighty-two Japanese type 2 diabetic patients underwent a complete history and physical examination, determination of blood chemistries, sRAGE, AGEs, sVCAM-1 and sICAM-1. Multiple regression analysis revealed that serum levels of AGEs and sVCAM-1 were independently correlated with sRAGE. This study demonstrated that serum levels of sRAGE were positively associated with circulating AGEs and sVCAM-1 levels in type 2 diabetic patients. Our present observations suggest sRAGE level may be elevated in response to circulating AGEs, thus being a novel marker of vascular injury in patients with type 2 diabetes.     

Receptor for advanced glycation end products (RAGE) in vascular and inflammatory diseases

Historically, the receptor for advanced glycation end products (RAGE) was thought to exclusively play an important role under hyperglycemic conditions. However, more and more evidence suggests that RAGE in fact is an inflammation perpetuating multi-ligand receptor and participates actively in various vascular and inflammatory diseases even in normoglycaemic conditions. Various ligands include advanced glycation end products (AGEs), S100 proteins and amphoterins etc. Besides full-length RAGE, numerous truncated forms of the receptor have also been described including the well-characterized soluble RAGE (sRAGE). sRAGE has an ability to act as a decoy to avoid interaction of RAGE with its pro-inflammatory ligands. Ligand engagement of RAGE activates multiple signaling pathways and also forms a positive feedback loop for its own enhanced expression. This review will discuss the role of multi-ligand receptor i.e. RAGE in context to various vascular diseases, which have a pathophysiologically important inflammatory component in normoglycaemic conditions.     

替米沙坦对人血管内皮细胞炎性反应的影响及其相关机制

目的探讨替米沙坦对晚期糖基化终末产物(AGEs)诱导人脐静脉内皮细胞(HUVECs)炎性反应的影响及与过氧化物酶体增殖物激活受体γ(PPARγ)的关系。方法酶消化法获取HUVECs。实验分8组:BSA组;AGEs组;以不同浓度替米沙坦刺激细胞30 min,再加AGEs,依次为TM 1组(1 nmol/L)、TM 2组(10 nmol/L)、TM 3组(100 nmol/L)、TM 4组(1000 nmol/L);GW9662组:GW9662预先刺激细胞30 min后,加替米沙坦和AGEs;15d-PGJ_2组:15d-PGJ_2预先刺激细胞30 min后,加AGEs。各组均刺激细胞24 h。采用RT-PCR法检测PPARγ、AGEs受体(RAGE)和单核细胞趋化蛋白1(MCP-1)mRNA的表达;荧光探针2,7-二氯二氢荧光素乙酰乙酸检测细胞内活性氧的变化。结果替米沙坦呈浓度依赖性抑制AGEs诱导的MCP-1 mRNA表达。与AGEs组比较,TM 4组和15d-PGJ_2组PPARγ mRNA水平明显升高,RAGE mRNA和MCP-1 mRNA水平明显下降,活性氧荧光信号强度明显减弱。与TM 4组比较,GW9662组PPARγ mRNA的表达水平明显下降,RAGE mRNA和MCP-1 mRNA的表达水平明显升高,活性氧荧光信号强度明显增强。结论替米沙坦可抑制AGEs诱导的HUVECs炎性反应;替米沙坦可能通过激活PPARγ抑制HUVECs炎性反应。     

Glycation and cardiovascular disease in diabetes: A perspective on the concept of metabolic memory

Epidemiological studies have suggested that cumulative diabetic exposure, namely prolonged exposure to chronic hyperglycemia, contributes to the increased risk of cardiovascular disease (CVD) in diabetes. The formation and accumulation of advanced glycation end‐products (AGEs) have been known to progress under hyperglycemic conditions. Because AGEs‐modified collagens are hardly degraded and remain in diabetic vessels, kidneys and the heart for a long time, even after glycemic control has been achieved, AGEs could become a marker reflecting cumulative diabetic exposure. Furthermore, there is a growing body of evidence that an interaction between AGEs and the receptor for AGEs (RAGE) plays a role in the pathogenesis of CVD. In addition, AGEs induce the expression of RAGE, thus leading to sustained activation of the AGEs–RAGE axis in diabetes. Herein we review the pathological role of the AGEs–RAGE axis in CVD, focusing particularly on the phenomenon of metabolic memory, and discuss the potential clinical usefulness of measuring circulating and tissue levels of AGEs accumulation to evaluate diabetic macrovascular complications.     

高级糖基化终末产物的合成及其与疾病的关系

高级糖基化终末产物(advanced glycation end products,AGEs)是由蛋白或者脂质暴露于还原糖中而形成的一组复杂且具有异质性的物质.该物质可通过内源性或外源性途径形成,大体可分为6种.AGEs可在不同种类的细胞内累积,影响细胞内及细胞外的结构和功能,同时它还可以通过和细胞表面的受体作用,通过信号传导,引发一系列的病理生理过程.AGEs沉积在细胞内,影响细胞功能,导致糖尿病血管并发症的发生.AGEs还与各种肿瘤的生物学特性相关,它可以修饰热休克蛋白27或者与AGEs受体相结合来影响肿瘤细胞的生长和浸润.AGEs的抑制物,如OPB-9195,可抑制这一系列病理生理过程.     

AGE-RAGE系统在糖尿病视网膜病变中的作用

糖尿病视网膜病变(DR)的发病机制至今尚未完全阐明。晚期糖基化终末产物(AGEs)的形成参与糖尿病视网膜病变的发生、发展,它们能与AGEs受体(RAGE)相互作用,并通过一系列分子机制导致视网膜周细胞缺失,诱发炎性反应以及新生血管的形成。因此,抑制AGEs形成或阻断AGEs与其受体相互作用可能延缓糖尿病视网膜病变的发生、发展。本文就AGEs形成、AGE-RAGE系统在DR中的作用和DR的药物治疗等作一综述。     

Wnt/β-catenin信号通路介导糖基化终未产物对大鼠骨髓间充质干细胞成骨分化的影响

目的探讨糖基化终末产物(advanced glycation end products,AGEs)对体外培养SD大鼠骨髓间充质干细胞(bone marrow mesenchymal stem cells,BMSCs)增生及成骨分化的影响及可能机制.方法采用全骨髓法分离培养4周龄SD大鼠的BMSCs.将BMSCs随机分为成骨诱导液、BSA组、AGEs3组,Western blot法检测AGEs对BMSCs成骨分化过程中β-catenin、OSX、RUNX2、RAGE(AGE受体)蛋白表达量的影响,茜素红染色观察AGEs对BMSCs成骨分化过程中矿化的影响.抑制RAGE后实时荧光定量聚合酶链反应(real-time fluo-rescence quantitative polymerase chain reaction,RT-PCR)及Western blot法再次测定上述指标水平.结果0.2 g/L AGEs作用于体外培养SD大鼠BMSCs,上调RAGE蛋白表达(0.88±0.04),β-catenin、OSX、RUNX2蛋白表达降低(分别为0.21±0.02,0.25±0.03和0.21±0.01,P<0.05).RAGE中和抗体阻断RAGE作用后,AGE+RAGE中和抗体组RAGE蛋白表达下调(0.30±0.03),β-catenin、OSX、RUNX2蛋白表达增高(0.90±0.02,0.84±0.03和0.88±0.02,P<0.05).结论AGEs通过Wnt/β-catenin信号通路抑制BMSCs成骨分化.     

Low Levels of Serum Soluble Receptors for Advanced Glycation End Products,Biomarkers for Disease State: Myth or Reality

Advanced glycation end products (AGEs) interact with the receptor for AGEs (RAGE) on the membrane and induce deleterious effects via activation of nuclear factor kappa-B, and increased oxidative stress and inflammatory mediators. AGEs also combine with circulating soluble receptors (endogenous secretory RAGE [esRAGE] and soluble receptor for RAGE [sRAGE]) and sequester RAGE ligands and act as a cytoprotective agent. esRAGE is secreted from the cells and is a spliced variant of RAGE. The sRAGE on the other hand is proteolytically cleaved from cell surface receptor via matrix metalloproteinase (MMPs). sRAGE is elevated in type 1 and type 2 diabetes and in patients with decreased renal function. Serum levels of sRAGE are reduced in diseases including coronary artery disease, atherosclerosis, essential hypertension, chronic obstructive lung disease, heart failure, and hypercholesterolemia. Serum levels of AGEs are elevated in patients with coronary artery disease and atherosclerosis. However, the increases in serum AGEs are very high in patients with diabetes and renal disease. There is a positive correlation between serum levels of AGEs and RAGE and sRAGE. The elevated levels of sRAGE in patients with diabetes and impaired renal function may be due to increased levels of MMPs. AGEs increase in the expression and production of MMPs, which would increase the cleavage of sRAGE from cell surface. In conclusion, low level of serum sRAGE is a good biomarker for disease other than diabetes and renal disease. A unified formula that takes into consideration of AGEs, sRAGE, and esRAGE such as AGE/sRAGE or AGEs/esRAGE would be better biomarker than sRAGE or esRAGE for all AGE-RAGE–associated diseases including diabetes and renal disease.     

晚期糖基化终末产物受体在心血管疾病中的研究进展

晚期糖基化终末产物受体(RAGE)属于细胞表面免疫球蛋白超家族中的一员,广泛表达于人体内皮细胞、平滑肌细胞、系膜细胞、心肌细胞、单核巨噬细胞和神经元细胞等。RAGE不仅参与炎症反应,还与糖尿病慢性并发症的发生、发展,类风湿性关节炎,肿瘤的侵袭和转移,阿尔茨海默病,慢性肾病等有关。现主要论述其在心血管疾病中的作用。     

Advanced Glycation End Products and Receptor–Oxidative Stress System in Diabetic Vascular Complications

Reducing sugars can react non‐enzymatically with amino groups of protein to form Amadori products. These early glycation products undergo further complex reactions, such as rearrangement, dehydration, and condensation, to become irreversibly cross‐linked, heterogeneous fluorescent derivatives, termed advanced glycation end products (AGEs). The formation and accumulation of AGEs have been known to progress at an accelerated rate in patients with diabetes mellitus, thus being involved in the development and progression of diabetic micro‐ and macroangiopathy. Indeed, there is accumulating evidence that an interaction between an AGE and its receptor (RAGE) generates oxidative stress and subsequently evokes vascular inflammation and thrombosis, thereby playing a central role in diabetic vascular complications. In this paper, we review the pathophysiological role of AGE‐RAGE–oxidative stress system and its therapeutic interventions in diabetic micro‐ and macroangiopathy.     

Olmesartan blocks advanced glycation end products (AGEs)-induced angiogenesis in vitro by suppressing receptor for AGEs (RAGE) expression

We have previously shown that advanced glycation end products (AGEs)-their receptor (RAGE) interaction elicits angiogenesis through autocrine production of vascular endothelial growth factor (VEGF), thus suggesting the active involvement of the AGEs-RAGE system in proliferative diabetic retinopathy (PDR). Since the crosstalk between the AGEs-RAGE and the renin-angiotensin system has also been proposed in the pathogenesis of PDR, we investigated here whether olmesartan, an angiotensin II type 1 receptor blocker, inhibited the AGEs-elicited angiogenesis in vitro by suppressing the NF-kappaB-mediated RAGE expression. Olmesartan significantly inhibited the AGEs-induced NF-kappaB promoter activity and RAGE gene expression in cultured microvascular endothelial cells (ECs). Further, olmesartan was found to block the AGEs-induced up-regulation of VEGF mRNA levels and consequent increase in DNA synthesis in ECs. These results demonstrated for the first time that olmesartan inhibited the AGEs signaling to angiogenesis by suppressing RAGE expression in ECs. Our present study suggests that blockade of the renin-angiotensin system by olmesartan may play a protective role against PDR by attenuating the deleterious effects of AGEs via down-regulation of RAGE.     

Advanced glycation end products: role in pathology of diabetic cardiomyopathy

Increasing evidence demonstrates that advanced glycation end products (AGEs) play a pivotal role in the development and progression of diabetic heart failure, although there are numerous other factors that mediate the disease response. AGEs are generated intra- and extracellularly as a result of chronic hyperglycemia. Then, following the interaction with receptors for advanced glycation end products (RAGEs), a series of events leading to vascular and myocardial damage are elicited and sustained, which include oxidative stress, increased inflammation, and enhanced extracellular matrix accumulation resulting in diastolic and systolic dysfunction. Whereas targeting glycemic control and treating additional risk factors, such as obesity, dyslipidemia, and hypertension, are mandatory to reduce chronic complications and prolong life expectancy in diabetic patients, drug therapy tailored to reducing the deleterious effects of the AGE–RAGE interactions is being actively investigated and showing signs of promise in treating diabetic cardiomyopathy and associated heart failure. This review shall discuss the formation of AGEs in diabetic heart tissue, potential targets of glycation in the myocardium, and underlying mechanisms that lead to diabetic cardiomyopathy and heart failure along with the use of AGE inhibitors and breakers in mitigating myocardial injury.