Ectodomain shedding of the receptor for advanced glycation end products: a novel therapeutic target for Alzheimer's disease

The role of sRAGE in cardiovascular diseases

Advanced glycation end products (AGEs), by-products of glucose metabolism, have been linked to the emergence of cardiovascular disorders (CVD). AGEs can cause tissue damage in four different ways: (1) by altering protein function, (2) by crosslinking proteins, which makes tissue stiffer, (3) by causing the generation of free radicals, and (4) by activating an inflammatory response after binding particular AGE receptors, such as the receptor for advanced glycation end products (RAGE). It is suggested that the soluble form of RAGE (sRAGE) blocks ligand-mediated pro-inflammatory and oxidant activities by serving as a decoy. Therefore, several studies have investigated the possible anti-inflammatory and anti-oxidant characteristics of sRAGE, which may help lower the risk of CVD. According to the results of various studies, the relationship between circulating sRAGE, cRAGE, and esRAGE and CVD is inconsistent. To establish the potential function of sRAGE as a therapeutic target in the treatment of cardiovascular illnesses, additional studies are required to better understand the relationship between sRAGE and CVD. In this review, we explored the potential function of sRAGE in different CVD, highlighting unanswered concerns and outlining the possibilities for further investigation.

Impact of Gut Microbiome Manipulation in 5xFAD Mice on Alzheimer's Disease-Like Pathology

The gut brain axis seems to modulate various psychiatric and neurological disorders such as Alzheimer's disease (AD). Growing evidence has led to the assumption that the gut microbiome might contribute to or even present the nucleus of origin for these diseases. In this regard, modifiers of the microbial composition might provide attractive new therapeutics. Aim of our study was to elucidate the effect of a rigorously changed gut microbiome on pathological hallmarks of AD. 5xFAD model mice were treated by antibiotics or probiotics (L. acidophilus and L. rhamnosus) for 14 weeks. Pathogenesis was measured by nest building capability and plaque deposition. The gut microbiome was affected as expected: antibiotics significantly reduced viable commensals, while probiotics transiently increased Lactobacillaceae. Nesting score, however, was only improved in antibiotics-treated mice. These animals additionally displayed reduced plaque load in the hippocampus. While various physiological parameters were not affected, blood sugar was reduced and serum glucagon level significantly elevated in the antibiotics-treated animals together with a reduction in the receptor for advanced glycation end products RAGE-the inward transporter of Aβ peptides of the brain. Assumedly, the beneficial effect of the antibiotics was based on their anti-diabetic potential.

Plasma angiogenesis and oxidative stress markers in patients with diabetic retinopathy

Background: Neovascularization in the retina and hyperglycaemia-induced oxidative stress are implicated in the pathogenesis of diabetic retinopathy (DR). In this study, we hypothesized that the plasma angiogenic and oxidative stress markers associated with these derangements could aid in the screening of diabetic patients who are at an increased risk of developing retinopathy.Methods: This study included normal (n = 148), type2 diabetes without retinopathy (DNR; n = 148), proliferative DR (PDR; n = 74) and non-PDR (NPDR; n = 148) subjects. Plasma concentrations of vascular endothelial growth factor-A (VEGF-A), hypoxia-inducible factor-1α (HIF-1α), matrix metalloproteinase-9 (MMP-9), pigment epithelium-derived factor (PEDF), nitric oxide (NO), soluble receptors for advanced glycation end products (sRAGE), malondialdehyde (MDA) and protein thiols were estimated.Results: A statistically significant increase was observed in the plasma concentrations of pro-angiogenic factors and markers of oxidative stress in both retinopathy groups. By contrast, the concentrations of anti-angiogenic factors and antioxidants were decreased significantly in these groups. Receiver operating characteristic analysis indicated that the plasma thresholds of HIF-1α and PEDF can be suitable markers in case of NPDR. However, in PDR, HIF-1α, NO, MMP-9 and PEDF showed high sensitivity and specificity.Conclusions: The factors associated with hypoxia, matrix degradation and angiogenic inhibition play a crucial role in predicting DR.

Plasma amyloid beta level changes in aged mice with cognitive dysfunction following sevoflurane exposure

INTRODUCTION

Previous studies have stated that cognitive impairment induced by anesthetics was associated with amyloid beta (Aβ). However, few researchers have investigated the transport of Aβ inside and outside of the brain.

AIM

We attempted to probe the effects of sevoflurane on cognitive functions, the plasma Aβ, and transporters of Aβ in aged mice. The receptor for advanced glycation end-products (RAGE) is an Aβ influx protein, and Low-density lipoprotein receptor-related protein-1 (LRP-1) is an Aβ efflux protein.

METHODS

Aged mice were divided into the control group and the sevoflurane group. The mice were exposed to 100% oxygen or 2.5% sevoflurane for 2 h. The abilities of spatial learning and memory in mice were tested using the Morris water maze. Aβ concentrations of plasma were measured with enzyme-linked immunosorbent assay kits. The RAGE and LRP-1 gene levels in the brain were assessed with quantitative polymerase chain reaction, and the protein levels were determined by western blot analysis. The locations of RAGE in the brain were confirmed via immunofluorescence.

RESULTS

In the sevoflurane group mice, the escape latency was increased on the 5th day of training, and the time spent in the target quadrant was decreased on the 7th day after anesthesia. Sevoflurane reduced the concentration of plasma Aβ1-40. In addition, sevoflurane increased both gene and protein levels of RAGE in the brain, and increased RAGE proteins co-localized with the hippocampal vascular endothelial cells.

CONCLUSION

RAGE over-expression in the hippocampal vascular endothelial cells possibly resulted in the excessive transport of the plasma Aβ1-40 into the brain after treatment with sevoflurane, which was associated with sevoflurane-induced cognitive dysfunction in aged mice.

Role of Blood-Brain Barrier in Alzheimer's Disease

The blood-brain barrier (BBB) is involved in the pathogenesis of Alzheimer's disease (AD). BBB is a highly selective semipermeable structural and chemical barrier which ensures a stable internal environment of the brain and prevents foreign objects invading the brain tissue. BBB dysfunction induces the failure of Aβ transport from brain to the peripheral circulation across the BBB. Especially, decreased levels of LRP-1 (low density lipoprotein receptor-related protein 1) and increased levels of RAGE (receptor for advanced glycation endproducts) at the BBB can cause the failure of Aβ transport. The pathogenesis of AD is related to the BBB structural components, including pericytes, astrocytes, vascular endothelial cells, and tight junctions. BBB dysfunction will trigger neuroinflammation and oxidative stress, then enhance the activity of β-secretase and γ-secretase, and finally promote Aβ generation. A progressive accumulation of Aβ in brain and BBB dysfunction may become a feedback loop that gives rise to cognitive impairment and the onset of dementia. The correlation between BBB dysfunction and tau pathology has been well-reported. Therefore, regulating BBB function may be a new therapeutic target for treating AD.

Influence of ADAM10 Polymorphisms on Plasma Level of Soluble Receptor for Advanced Glycation End Products and The Association With Alzheimer's Disease Risk

To determine the role of A disintegrin and metalloproteinase 10 (ADAM10) in genetic susceptibility to Alzheimer's disease (AD) in a representative Chinese sample, we genotyped 362 AD patients and 370 healthy controls for the rs514049A/C and rs653765C/T polymorphisms in the ADAM10 promoter using the SNaPshot technique. We also examined the potential impact of these polymorphisms on the plasma level of soluble receptor for advanced glycation end products (sRAGE), a decoy receptor whose reduction has been associated with a higher risk of AD. Additionally, a meta-analysis was performed using the present study and the largest GWAS from the International Genomics of Alzheimer's Project (IGAP). No significant differences were found in the distributions of genotypes or alleles between AD patients and control subjects. However, age-at-onset stratification analysis revealed that there were significant differences in the genotypes (P = 0.015) and alleles (P = 0.006) of the rs653765 SNP. Furthermore, patients with the rs653765 CC genotype showed a lower ADAM10 level and a faster cognitive deterioration than those in patients with the CT/TT genotype in late-onset AD (LOAD), and the rs653765 CC polymorphism was able to regulate the production of the ADAM10 substrate sRAGE. In contrast, the rs514049 polymorphism was not statistically associated with AD. In the meta-analysis, we observed that both rs514049 (A allele vs. C allele, P = 0.002) and rs653765 (C allele vs. T allele, P = 0.004) were associated with AD risk. The present study indicated that the rs653765 polymorphism might be associated with the risk and development of LOAD; in particular, the risk genotype, CC, may decrease the expression of ADAM10, influencing the plasma levels of sRAGE, and thus may be correlated with the clinical progression of AD.

Targeting the Receptor for Advanced Glycation Endproducts (RAGE): A Medicinal Chemistry Perspective

The receptor for advanced glycation endproducts (RAGE) is an ubiquitous, transmembrane, immunoglobulin-like receptor that exists in multiple isoforms and binds to a diverse range of endogenous extracellular ligands and intracellular effectors. Ligand binding at the extracellular domain of RAGE initiates a complex intracellular signaling cascade, resulting in the production of reactive oxygen species (ROS), immunoinflammatory effects, cellular proliferation, or apoptosis with concomitant upregulation of RAGE itself. To date, research has mainly focused on the correlation between RAGE activity and pathological conditions, such as cancer, diabetes, cardiovascular diseases, and neurodegeneration. Because RAGE plays a role in many pathological disorders, it has become an attractive target for the development of inhibitors at the extracellular and intracellular domains. This review describes the role of endogenous RAGE ligands/effectors in normo- and pathophysiological processes, summarizes the current status of exogenous small-molecule inhibitors of RAGE and concludes by identifying key strategies for future therapeutic intervention.

Plasma levels of soluble receptor for advanced glycation end products in Alzheimer's disease

BACKGROUND

A decreased plasma level of soluble form of the receptor for advanced glycation end products (sRAGE) in patients with Alzheimer's disease (AD) has been reported. However, no evidence has shown whether the sRAGE plasma level of AD patients may differentiate from other types of dementia.

METHODS

Our study assessed sRAGE concentrations in the following 121 individuals in Chongqing area: 36 patients with AD, 12 with vascular dementia (VaD), 14 with mixed dementia (MD), 24 with other dementia (OD) including Parkinson's disease dementia, frontotemporal dementia, paralytic dementia and 35 cognitively normal controls. The total plasma level of sRAGE was determined using sandwich ELISA method.

RESULTS

sRAGE concentration in AD is significantly decreased compared with healthy controls. However, the receiver operating characteristic curve analysis of sRAGE between the AD and the control shows a low diagnostic accuracy.

CONCLUSIONS

Our results demonstrate that sRAGE may assist the diagnosis of AD from normal individuals, but cannot differentiate AD from VaD, MD or OD.

Receptor for advanced glycation endproduct modulators: a new therapeutic target in Alzheimer's disease

INTRODUCTION

Reduction in the deposition of amyloid β (Aβ) has been the primary target for Alzheimer's disease (AD) therapeutics recently, but in clinical trials this approach has generally been unsuccessful. A common feature of AD pathology is a complex inflammatory component that could be a target for treatment. One feature of this inflammation has been the involvement of the receptor for advanced glycation endproducts (RAGE), whose ligands include advanced glycation-endproduct-modified proteins as well as lipids and Aβ, which are found at elevated levels in AD brains.

AREAS COVERED

In this article, the authors describe the key features of RAGE and how it could have a role in AD pathogenesis. They also summarize experimental animal and clinical data that demonstrate the therapeutic effect of RAGE inhibition and consider what these findings mean for human disease.

EXPERT OPINION

RAGE has multiple ligands, including Aβ, that are increased in AD brains. Inhibiting RAGE-ligand interactions without activating receptor signaling can reduce multiple pathological pathways relevant for AD. Several RAGE inhibitors and modulators are now being tested as therapeutics for AD. Recent Phase II studies have established the good safety and tolerability of TTP448 with some evidence of positive benefit at lower dose. This suggests that further studies are required.

Pyrazole-5-carboxamides, novel inhibitors of receptor for advanced glycation end products (RAGE)

In an effort to develop novel inhibitors of receptor for advanced glycation end products (RAGE) for the treatment of Alzheimer's disease, a series of pyrazole-5-carboxamides were designed, synthesized and biologically evaluated. Analyses of the extensive structure-activity relationship (SAR) led us to identify a 4-fluorophenoxy analog (40) that exhibited improved in vitro RAGE inhibitory activity and more favorable aqueous solubility than the parent 2-aminopyrimidine, 1. Surface plasmon resonance (SPR) and molecular docking study strongly supported the RAGE inhibitory activity of pyrazole-5-carboxamides. The brain Aβ-lowering effect of 40 is also described.

Mesenchymal stem cells protects hyperoxia-induced lung injury in newborn rats via inhibiting receptor for advanced glycation end-products/nuclear factor κB signaling

Bone marrow-derived mesenchymal stem cells (BMSCs) have been shown recently to ameliorate hyperoxia-induced lung injury, but the underlying mechanism remains unclear. This study aimed to determine whether BMSCs attenuate hyperoxia-induced lung injury by down-modulating the inflammatory RAGE/NF-κB (receptor for advanced glycation end-products/nuclear factor-κB) signaling. Thirty Sprague-Dawley newborn rats were randomly divided into three groups ( n = 10): sham control (C); hyperoxia-induced acute lung injury (ALI) (B) and ALI with BMSCs transplantation (A). Rats were sacrificed at three-day post-transplantation. RAGE and NF-κB expression in lung tissue was detected by reverse transcription polymerase chain reaction, Western blot and immunohistochemistry analysis. The levels of tumor necrosis factor α (TNF-α) and RAGE in bronchoalveolar lavage fluid (BALF) and in serum were detected by enzyme-linked immunosorbent assay. The lung damage was evaluated by histological examination. The results showed that RAGE and TNF-α concentrations in BALF were significantly lower in Group A than in Group B. Moreover, RAGE and NF-κB expression in lung tissue at mRNA and protein concentrations was significantly lower in Group A than in Group B. The lung damage score was significantly lower in Group A than in Group B. These data demonstrate that hyperoxia induces the inflammation and causes damage in the lung but BMSC transplantation could alleviate hyperoxia-induced lung injury by inhibiting the inflammatory process mediated by RAGE/NF-κB signaling.

Amyloid beta accumulation in HIV-1-infected brain: The role of the blood brain barrier

In recent years, we face an increase in the aging of the HIV-1-infected population, which is not only due to effective antiretroviral therapy but also to new infections among older people. Even with the use of the antiretroviral therapy, HIV-associated neurocognitive disorders represent an increasing problem as the HIV-1-infected population ages. Increased amyloid beta (Aβ) deposition is characteristic of HIV-1-infected brains, and it has been hypothesized that brain vascular dysfunction contributes to this phenomenon, with a critical role suggested for the blood-brain barrier in brain Aβ homeostasis. This review will describe the mechanisms by which the blood-brain barrier may contribute to brain Aβ accumulation, and our findings in the context of HIV-1 infection will be discussed.

An advanced glycation end product (AGE)-receptor for AGEs (RAGE) axis restores adipogenic potential of senescent preadipocytes through modulation of p53 protein function

The impaired adipogenic potential of senescent preadipocytes is a hallmark of adipose aging and aging-related adipose dysfunction. Although advanced glycation end products (AGEs) derived from both foods and endogenous nonenzymatic glycation and AGE-associated signaling pathways are known to play a key role in aging and its related diseases, the role of AGEs in adipose aging remains elusive. We show a novel pro-adipogenic function of AGEs in replicative senescent preadipocytes and mouse embryonic fibroblasts, as well as primary preadipocytes isolated from aged mice. Using glycated bovine serum albumin (BSA) as a model protein of AGEs, we found that glycated BSA restores the impaired adipogenic potential of senescent preadipocytes in vitro and ex vivo. However, glycated BSA showed no effect on adipogenesis in nonsenescent preadipocytes. The AGE-induced receptor for AGE (RAGE) expression is required for the pro-adipogenic function of AGEs in senescent preadipocytes. RAGE is required for impairment of p53 expression and p53 function in regulating p21 expression in senescent preadipocytes. We also observed a direct binding between RAGE and p53 in senescent preadipocytes. Taken together, our findings reveal a novel pro-adipogenic function of the AGE-RAGE axis in p53-regulated adipogenesis of senescent preadipocytes, providing new insights into aging-dependent adiposity by diet-driven and/or endogenous glycated proteins.

Synthesis and structure-activity relationships of tri-substituted thiazoles as RAGE antagonists for the treatment of Alzheimer's disease

A series of thiazole derivatives were designed, and prepared to develop RAGE antagonist for the treatment of Alzheimer's disease (AD). SAR studies were performed to optimize inhibitory activity on Aβ-RAGE binding. SAR studies showed that introducing an amino group at part A was essential for inhibitory activity on Aβ-RAGE binding. Compounds selected from Aβ-RAGE binding screening displayed inhibitory activity on Aβ transport across BBB. They also showed inhibitory activity against Aβ-induced NF-κB activation. These results indicated that our derivatives had a potential as therapeutic agent for the treatment of AD.

Is There Inflammatory Synergy in Type II Diabetes Mellitus and Alzheimer's Disease?

Metabolic dysregulation, including abnormal glucose utilization and insulin resistance or deficiency, occurs at an early stage of AD independent of type II diabetes mellitus (T2DM). Thus, AD has been considered as type 3 diabetes. T2DM is a risk factor for AD; the coexistence of these two diseases in a society with an increasing mean age is a significant issue. Recently, research has focused on shared molecular mechanisms in these two diseases with the goal of determining whether treating T2DM can lessen the severity of AD. The progress in this field lends strong support to several mechanisms that could affect these two diseases, including insulin resistance and signaling, vascular injuries, inflammation, and the receptor for advanced glycation endproducts and their ligands. In this paper, we focus on inflammation-based mechanisms in both diseases and discuss potential synergism in these mechanisms when these two diseases coexist in the same patient.

Elevated serum levels of advanced glycation end products and their monocyte receptors in patients with type 2 diabetes

BACKGROUND AND AIMS

Animal experiments showed that interaction between advanced glycation end products (AGE) and their receptors (RAGE) play an important role in the pathogenesis of diabetic complications. Soluble RAGE (sRAGE) can function as a decoy for RAGE ligands. The present study aimed to examine the levels of AGEs, RAGE and sRAGE in patients with type 2 diabetes (T2D).

METHODS

RAGE gene expression was determined by real-time PCR in 50 patients with T2D (27 men, mean age 52 ± 7.7 years) and 50 age-matched controls without T2D. Serum AGEs and sRAGEs were assayed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Serum level of AGEs was increased in patients with T2D (10.35 ± 2.27 μg/mL vs.7.69 ± 0.56 μg/mL, p <0.05). sRAGE was decreased in patients with T2D (573.6 ± 172.5 pg/mL vs. 603.4 ± 120.8 pg/mL p <0.01). RAGE gene expression was higher in T2D than in controls (p <0.01). There was an association between monocyte RAGE and serum levels of AGEs in both T2D patients (r = 0.29, p = 0.03) and controls (r = 0.31, p = 0.02). Serum AGEs correlated with homeostasis model assessment of insulin resistance (HOMA-IR) in both patients with T2D (r = 0.322, p = 0.004) and controls (r = 0.281, p = 0.003).

CONCLUSIONS

Serum AGEs and monocyte RAGE expression are increased in patients with T2D, whereas serum sRAGE is decreased. Pharmacological intervention on serum AGEs and sRAGE may be a potential therapy for diabetes.

A gain-of-glycosylation mutation associated with myoclonus-dystonia syndrome affects trafficking and processing of mouse ε-sarcoglycan in the late secretory pathway

Missense mutations in the SGCE gene encoding ε-sarcoglycan account for approximately 15% of SGCE-positive cases of myoclonus-dystonia syndrome (MDS) in humans. In this study, we show that while the majority of MDS-associated missense mutants modeled with a murine ε-sarcoglycan cDNA are substrates for endoplasmic reticulum-associated degradation, one mutant, M68T (analogous to human c.275T>C, p.M92T), located in the Ig-like domain of ε-sarcoglycan, results in a gain-of-glycosylation mutation producing a protein that is targeted to the plasma membrane, albeit at reduced levels compared to wild-type ε-sarcoglycan. Removal of the ectopic N-linked glycan failed to restore efficient plasma membrane targeting of M68T demonstrating that the substitution rather than the glycan was responsible for the trafficking defect of this mutant. M68T also colocalized with CD63-positive vesicles in the endosomal-lysosomal system and was found to be more susceptible to lysosomal proteolysis than wild-type ε-sarcoglycan. Finally, we demonstrate impaired ectodomain shedding of M68T, a process that occurs physiologically for ε-sarcoglycan resulting in the lysosomal trafficking of the intracellular C-terminal domain of the protein. Our findings show that functional analysis of rare missense mutations can provide a mechanistic insight into the pathogenesis of MDS and the physiological role of ε-sarcoglycan.

Total soluble and endogenous secretory receptor for advanced glycation end products as predictive biomarkers of coronary heart disease risk in patients with type 2 diabetes: an analysis from the CARDS trial

OBJECTIVE

Circulating levels of soluble receptor for advanced glycation end products (sRAGE) likely comprise both a secreted isoform (esRAGE) and wild-type RAGE cleaved from the cell membrane. Both sRAGE and esRAGE have been proposed as biomarkers of cardiovascular disease (CVD), but prospective data are limited. We examined the relationship of sRAGE and esRAGE to incident coronary heart disease (CHD) and stroke in type 2 diabetic patients followed for 3.9 years in a trial of atorvastatin: the Collaborative Atorvastatin Diabetes Study (CARDS).

RESEARCH DESIGN AND METHODS

We used a nested case-control design sampling all incident cases of CVD with available plasma and randomly selecting three control subjects, who were free of CVD throughout follow-up, per case. Analysis was by Cox regression with adjustment for treatment allocation and relevant covariates.

RESULTS

sRAGE and esRAGE were strongly correlated (ρ = 0.88) and were both higher in those with lower BMI (P < 0.001), higher adiponectin (P < 0.001), lower estimated glomerular filtration rate (P = 0.009), and white ethnicity (P < 0.001). Both sRAGE and esRAGE were associated with incident CHD events, independently of treatment allocation and the above factors; hazard ratio (HR) = 1.74 (95% CI 1.25-2.41; P = 0.002) for a doubling of the sRAGE level; HR = 1.45 (1.11-1.89; P = 0.006) for a doubling of the esRAGE level. There was no significant association with stroke; HR for sRAGE = 0.66 (0.38-1.14). Atorvastatin, 10 mg daily, did not alter sRAGE.

CONCLUSIONS

Higher levels of sRAGE and esRAGE are associated with incident CHD but not stroke in type 2 diabetes.

The functional -374T/A polymorphism of the receptor for advanced glycation end products may modulate Crohn's disease

The receptor for advanced glycation end products (RAGE) is involved in innate immune mechanisms. Polymorphisms of the RAGE gene have been described as a factor amplifying inflammation in susceptible patients, but the association with Crohn's disease (CD) is not known. The coding RAGE polymorphism G82S (rs2070600) and two promoter polymorphisms, -374T/A (rs1800624) and -429T/C (rs1800625), were studied in two samples from Germany and the United States consisting of 421 and 317 CD patients and 549 and 218 controls, respectively. To test the functional relevance, additional data on serum soluble RAGE (sRAGE), tissue RNA, and protein levels were collected and immunohistochemical stainings of bowel tissue of CD patients and healthy controls as well as models of experimental (dextran sodium sulfate-induced) colitis in RAGE knockout and wild-type mice were performed. The -374T/A RAGE promotor single nucleotide polymorphism (SNP) was negatively associated with CD (odds ratio = 0.708, 95% confidence interval = 0.535-0.938, P = 0.016) and with stenosis (OR = 0.627, P = 0.04) in the German sample. Transmission disequilibrium testing confirmed an undertransmission of the -374A allele. Serum sRAGE levels were higher in patients in complete remission of the -374AA/TA group (1,975 ± 299 pg/ml; -374TT group: 1,310 ± 153 pg/ml SE, P < 0.05) and showed a trend toward decreased levels in CD patients with active disease compared with CD patients in remission. Further in vitro and in vivo studies indicated that an increase of sRAGE ameliorates inflammation. The -429T/C and the G82S polymorphism were not associated with CD. The -374T/A RAGE polymorphism leading to facilitated RAGE gene transcription may to some degree protect from developing a stricturing subphenotype of CD, most likely by increasing levels of sRAGE, which neutralizes proinflammatory mediators.

RAGE: the beneficial and deleterious effects by diverse mechanisms of actions

Receptor for advanced glycation endproducts (RAGE) is a transmembrane protein that belongs to the immunoglobulin superfamily. RAGE is expressed ubiquitously-high in lung and moderate to low in a wide range of cells-in a tightly regulated manner at various stages of development. RAGE is a pattern recognition receptor that binds to multiple ligands, including amphoterin, members of the S100/calgranulin family, the integrin Mac-1, and amyloid β-peptide (Aβ). RAGE-ligand engagement effects the activation of diverse cascades that initiate and stimulate chronic stress pathways and repair, depending on the ligand, environment, and developmental stage. Further, RAGE-ligand interaction and the consequent upregulation of RAGE through a positive feedback loop are often associated with various diseases, including vascular disease, diabetes, cancer, and neurodegenerative disease. It is unknown how RAGE mediates these events, but such phenomena appear to be linked to the inflammatory response. In this review, we summarize the findings on RAGE from published reports and ongoing studies. Also, the implication of RAGE in Alzheimer disease, the most common neurodegenerative disease in the elderly population, will be discussed, with a focus on Aβ-RAGE interactions with regard to signaling pathways and their impact on cellular activity.

Enhanced expression of receptor for advanced glycation end-products is associated with low circulating soluble isoforms of the receptor in Type 2 diabetes

The sRAGE [soluble RAGE (receptor for advanced glycation end-products)] lack the transmembrane and cytoplasmic domain of the full-length receptor and can function as a decoy for RAGE ligands. Recent evidence suggests that sRAGE may be a potential biomarker of RAGE-mediated pathology. The present study aimed to examine the relationship between RAGE expression in peripheral blood monocytes and circulating sRAGE and esRAGE (endogenous sRAGE, a splice variant of sRAGE) in Type 2 diabetes. Protein expression of RAGE and esRAGE in monocyte cell lysate was determined by Western blot in 53 diabetic patients and 52 controls. Monocyte cell-surface-bound full-length RAGE expression was measured using flow cytometry. Serum sRAGE, esRAGE and AGE (advanced glycation end products) were assayed by ELISA. The mean HbA1c (glycated haemoglobin) of the diabetic patients was 9.74% and serum AGEs was increased. Monocyte full-length RAGE expression was significantly higher in diabetic patients whereas esRAGE expression was reduced, and serum AGEs concentration was an independent determinant of monocyte cell surface full-length RAGE expression. Serum levels of sRAGE [573.3 (375.7-754.3) compared with 608.1 (405.3-940.8) pg/ml, P<0.05] and esRAGE [241.8 (154.6-356.6) compared with 286.5 (202.6-390.0) pg/ml, P<0.05; values are medians (interquartile range)] were decreased. There was an inverse association between monocyte RAGE expression and log(serum sRAGE) (r=-0.34, P=0.01) but not with esRAGE. In conclusion, despite an increase in full-length RAGE expression, esRAGE expression was down-regulated in the diabetic patients, and serum sRAGE and esRAGE was also reduced. Hence increased full-length RAGE levels are not associated with a similar increase in sRAGE isoforms levels.

Shedding; towards a new paradigm of syndecan function in cancer

Syndecans, cell surface heparansulfate proteoglycans, have been proposed to act as cell surface receptors and/or coreceptors to play critical roles in multiple cellular functions. However, recent reports suggest that the function of syndecans can be further extended through shedding, a cleavage of extracellular domain. Shedding constitutes an additional level for controlling the function of syndecans, providing a means to attenuate and/or regulate amplitude and duration of syndecan signals by modulating the activity of syndecans as cell surface receptors. Whether these remaining cleavage products are still capable of functioning as cell surface receptors to efficiently transduce signals inside of cells is not clear. However, shedding transforms cell surface receptor syndecans into soluble forms, which, like growth factors, may act as novel ligands to induce cellular responses by association with other cell surface receptors. It is becoming interestingly evident that shed syndecans also contribute significantly to syndecan functions in cancer biology. This review presents current knowledge about syndecan shedding and its functional significance, particularly in the context of cancer.