Receptor for advanced glycation end products plays a more important role in cellular survival than in neurite outgrowth during retinoic acid-induced differentiation of neuroblastoma cells

Phosphatidylserine in the Nervous System: Cytoplasmic Regulator of the AKT and PKC Signaling Pathways and Extracellular "Eat-Me" Signal in Microglial Phagocytosis

Phosphatidylserine (PtdSer) is an important anionic phospholipid found in eukaryotic cells and has been proven to serve as a beneficial factor in the treatment of neurodegenerative diseases. PtdSer resides in the inner leaflet of the plasma membrane, where it is involved in regulating the AKT and PKC signaling pathways; however, it becomes exposed to the extracellular leaflet during neurodevelopmental processes and neurodegenerative diseases, participating in microglia-mediated synaptic and neuronal phagocytosis. In this paper, we review several characteristics of PtdSer, including the synthesis and translocation of PtdSer, the functions of cytoplasmic and exposed PtdSer, and different PtdSer-detection materials used to further understand the role of PtdSer in the nervous system.

RAGE Inhibitors for Targeted Therapy of Cancer: A Comprehensive Review

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin family that is overexpressed in several cancers. RAGE is highly expressed in the lung, and its expression increases proportionally at the site of inflammation. This receptor can bind a variety of ligands, including advanced glycation end products, high mobility group box 1, S100 proteins, adhesion molecules, complement components, advanced lipoxidation end products, lipopolysaccharides, and other molecules that mediate cellular responses related to acute and chronic inflammation. RAGE serves as an important node for the initiation and stimulation of cell stress and growth signaling mechanisms that promote carcinogenesis, tumor propagation, and metastatic potential. In this review, we discuss different aspects of RAGE and its prominent ligands implicated in cancer pathogenesis and describe current findings that provide insights into the significant role played by RAGE in cancer. Cancer development can be hindered by inhibiting the interaction of RAGE with its ligands, and this could provide an effective strategy for cancer treatment.

In Vitro Methodologies to Study the Role of Advanced Glycation End Products (AGEs) in Neurodegeneration

Advanced glycation end products (AGEs) can be present in food or be endogenously produced in biological systems. Their formation has been associated with chronic neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis. The implication of AGEs in neurodegeneration is related to their ability to bind to AGE-specific receptors and the ability of their precursors to induce the so-called “dicarbonyl stress”, resulting in cross-linking and protein damage. However, the mode of action underlying their role in neurodegeneration remains unclear. While some research has been carried out in observational clinical studies, further in vitro studies may help elucidate these underlying modes of action. This review presents and discusses in vitro methodologies used in research on the potential role of AGEs in neuroinflammation and neurodegeneration. The overview reveals the main concepts linking AGEs to neurodegeneration, the current findings, and the available and advisable in vitro models to study their role. Moreover, the major questions regarding the role of AGEs in neurodegenerative diseases and the challenges and discrepancies in the research field are discussed.

Proof that the high molecular weight immunophilin FKBP52 mediates the in vivo neuroregenerative effect of the macrolide FK506

The immunosuppressant drug FK506 (or tacrolimus) is a macrolide that binds selectively to immunophilins belonging to the FK506-binding protein (FKBP) subfamily, which are abundantly expressed proteins in neurons of the peripheral and central nervous systems. Interestingly, it has been reported that FK506 increases neurite outgrowth in cell cultures, implying a potential impact in putative treatments of neurodegenerative disorders and injuries of the nervous system. Nonetheless, the mechanism of action of this compound is poorly understood and remains to be elucidated, with the only certainty that its neurotrophic effect is independent of its primary immunosuppressant activity. In this study it is demonstrated that FK506 shows efficient neurotrophic action in vitro and profound effects on the recovery of locomotor activity, behavioural features, and erectile function of mice that underwent surgical spinal cord injury. The recovery of the locomotor activity was studied in knock-out mice for either immunophilin, FKBP51 or FKBP52. The experimental evidence demonstrates that the neurotrophic actions of FK506 are the consequence of its binding to FKBP52, whereas FK506 interaction with the close-related partner immunophilin FKBP51 antagonises the function of FKBP52. Importantly, our study also demonstrates that other immunophilins do not replace FKBP52. It is concluded that the final biological response is the resulting outcome of the drug binding to both immunophilins, FKBP51 and FKBP52, the latter being the one that commands the dominant neurotrophic action in vivo.

Regulation of Neurogenesis in Mouse Brain by HMGB1

The High Mobility Group Box 1 (HMGB1) is the most abundant nuclear nonhistone protein that is involved in transcription regulation. In addition, HMGB1 has previously been found as an extracellularly acting protein enhancing neurite outgrowth in cultured neurons. Although HMGB1 is widely expressed in the developing central nervous system of vertebrates and invertebrates, its function in the developing mouse brain is poorly understood. Here, we have analyzed developmental defects of the HMGB1 null mouse forebrain, and further examined our findings in ex vivo brain cell cultures. We find that HMGB1 is required for the proliferation and differentiation of neuronal stem cells/progenitor cells. Enhanced apoptosis is also found in the neuronal cells lacking HMGB1. Moreover, HMGB1 depletion disrupts Wnt/β-catenin signaling and the expression of transcription factors in the developing cortex, including Foxg1, Tbr2, Emx2, and Lhx6. Finally, HMGB1 null mice display aberrant expression of CXCL12/CXCR4 and reduced RAGE signaling. In conclusion, HMGB1 plays a critical role in mammalian neurogenesis and brain development.

Role and Mechanisms of RAGE-Ligand Complexes and RAGE-Inhibitors in Cancer Progression

Interactions of the receptor for advanced glycation end product (RAGE) and its ligands in the context of their role in diabetes mellitus, inflammation, and carcinogenesis have been extensively investigated. This review focuses on the role of RAGE-ligands and anti-RAGE drugs capable of controlling cancer progression. Different studies have demonstrated interaction of RAGE with a diverse range of acidic (negatively charged) ligands such as advanced glycation end products (AGEs), high-mobility group box1 (HMGB1), and S100s, and their importance to cancer progression. Some RAGE-ligands displayed effects on anti- and pro-apoptotic proteins through upregulation of the phosphatidylinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR), mitogen-activated protein kinases (MAPKs), matrix metalloproteinases (MMPs), vascular endothelial growth factor (VEGF), and nuclear factor kappa B (NF-κB) pathways, while downregulating p53 in cancer progression. In addition, RAGE may undergo ligand-driven multimodal dimerization or oligomerization mediated through self-association of some of its subunits. We conclude our review by proposing possible future lines of study that could result in control of cancer progression through RAGE inhibition.

Action of HMGB1 on miR-221/222 cluster in neuroblastoma cell lines

microRNA (miR/miRNA) are small non-coding RNAs that control gene expression at the post-transcriptional level by targeting mRNAs. Aberrant expression of miRNAs is often observed in different types of cancer. Specific miRNAs function as tumor suppressors or oncogenes and interfere with various aspects of carcinogenesis, including differentiation, proliferation and invasion. Upregulation of miRNAs 221 and 222 has been shown to induce a malignant phenotype in numerous human cancers via inhibition of phosphatase and tensin homolog (PTEN) expression. Neuroblastoma is the most common extracranial solid malignancy in children, which is characterized by cellular heterogeneity that corresponds to different clinical outcomes. The different cellular phenotypes are associated with different gene mutations and miRs that control genetic and epigenetic factors. For this reason miRs are considered a potential therapeutic target in neuroblastoma. The aim of the present study was to investigate the mechanisms by which extracellular high mobility group box 1 (HMGB1) promotes cell growth in neuroblastoma. SK-N-BE(2) and SH-SY5Y neuroblastoma derived cell lines were transfected with the antisense oligonucleotides, anti-miR-221 and -222, followed by treatment with HMGB1 to investigate the expression of the oncosuppressor PTEN. In this study, it was demonstrated that HMGB1, which is released by damaged cells and tumor cells, upregulates miR-221/222 oncogenic clusters in the two human neuroblastoma derived cell lines. The results revealed that the oncogenic cluster miRs 221/222 were more highly expressed by the most undifferentiated cell line [SK-N-BE(2)] compared with the the less tumorigenic cell line (SH-SY5Y) and that exogenous HMGB1 increases this expression. In addition, HMGB1 modulates PTEN expression via miR-221/222, as demonstrated by transiently blocking miR-221/222 with anti-sense oligonucleotides. These results may lead to the development of novel therapeutic strategies for neuroblastoma.

RAGE Expression and ROS Generation in Neurons: Differentiation versus Damage

RAGE is a multiligand receptor able to bind advanced glycation end-products (AGEs), amphoterin, calgranulins, and amyloid-beta peptides, identified in many tissues and cells, including neurons. RAGE stimulation induces the generation of reactive oxygen species (ROS) mainly through the activity of NADPH oxidases. In neuronal cells, RAGE-induced ROS generation is able to favor cell survival and differentiation or to induce death through the imbalance of redox state. The dual nature of RAGE signaling in neurons depends not only on the intensity of RAGE activation but also on the ability of RAGE-bearing cells to adapt to ROS generation. In this review we highlight these aspects of RAGE signaling regulation in neuronal cells.

Advanced glycation end products are mitogenic signals and trigger cell cycle reentry of neurons in Alzheimer's disease brain

Neurons that reenter the cell cycle die rather than divide, a phenomenon that is associated with neurodegeneration in Alzheimer's disease (AD). Reexpression of cell-cycle related genes in differentiated neurons in AD might be rooted in aberrant mitogenic signaling. Because microglia and astroglia proliferate in the vicinity of amyloid plaques, it is likely that plaque components or factors secreted from plaque-activated glia induce neuronal mitogenic signaling. Advanced glycation end products (AGEs), protein-bound oxidation products of sugar, might be one of those mitogenic compounds. Cyclin D1 positive neurons are colocalized with AGEs or directly surrounded by extracellular AGE deposits in AD brain. However, a direct proof of DNA replication in these cells has been missing. Here, we report by using fluorescent in situ hybridization that consistent with the expression of cell cycle proteins, hyperploid neuronal cells are in colocalization with AGE staining in AD brains but not in nondemented controls. To complement human data, we used apolipoprotein E-deficient mice as model of neurodegeneration and showed that increased oxidative stress caused an intensified neuronal deposition of AGEs, being accompanied by an activation of the MAPK cascade via RAGE. This cascade, in turn, induced the expression of cyclin D1 and DNA replication. In addition, reduction of oxidative stress by application of α-lipoic acid decreased AGE accumulations, and this decrease was accompanied by a reduction in cell cycle reentry and a more euploid neuronal genome.

Chronic neuroinflammation in Alzheimer's disease: new perspectives on animal models and promising candidate drugs

Chronic neuroinflammation is now considered one of the major factors in the pathogenesis of Alzheimer's disease (AD). However, the most widely used transgenic AD models (overexpressing mutated forms of amyloid precursor protein, presenilin, and/or tau) do not demonstrate the degree of inflammation, neurodegeneration (particularly of the cholinergic system), and cognitive decline that is comparable with the human disease. Hence a more suitable animal model is needed to more closely mimic the resulting cognitive decline and memory loss in humans in order to investigate the effects of neuroinflammation on neurodegeneration. One of these models is the glial fibrillary acidic protein-interleukin 6 (GFAP-IL6) mouse, in which chronic neuroinflammation triggered constitutive expression of the cytokine interleukin-6 (IL-6) in astrocytes. These transgenic mice show substantial and progressive neurodegeneration as well as a decline in motor skills and cognitive function, starting from 6 months of age. This animal model could serve as an excellent tool for drug discovery and validation in vivo. In this review, we have also selected three potential anti-inflammatory drugs, curcumin, apigenin, and tenilsetam, as candidate drugs, which could be tested in this model.

Role for DNA damage signaling in pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is associated with sustained inflammation known to promote DNA damage. Despite these unfavorable environmental conditions, PAH pulmonary arterial smooth muscle cells (PASMCs) exhibit, in contrast to healthy PASMCs, a pro-proliferative and anti-apoptotic phenotype, sustained in time by the activation of miR-204, nuclear factor of activated T cells, and hypoxia-inducible factor 1-α. We hypothesized that PAH-PASMCs have increased the activation of poly(ADP-ribose) polymerase-1 (PARP-1), a critical enzyme implicated in DNA repair, allowing proliferation despite the presence of DNA-damaging insults, eventually leading to PAH.

METHODS AND RESULTS

Human PAH distal pulmonary arteries and cultured PAH-PASMCs exhibit increased DNA damage markers (53BP1 and γ-H2AX) and an overexpression of PARP-1 (immunoblot and activity assay), in comparison with healthy tissues/cells. Healthy PASMCs treated with a clinically relevant dose of tumor necrosis factor-α harbored a similar phenotype, suggesting that inflammation induces DNA damage and PARP-1 activation in PAH. We also showed that PARP-1 activation accounts for miR-204 downregulation (quantitative reverse transcription polymerase chain reaction) and the subsequent activation of the transcription factors nuclear factor of activated T cells and hypoxia-inducible factor 1-α in PAH-PASMCs, previously shown to be critical for PAH in several models. These effects resulted in PASMC proliferation (Ki67, proliferating cell nuclear antigen, and WST1 assays) and resistance to apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labeling and Annexin V assays). In vivo, the clinically available PARP inhibitor ABT-888 reversed PAH in 2 experimental rat models (Sugen/hypoxia and monocrotaline).

CONCLUSIONS

These results show for the first time that the DNA damage/PARP-1 signaling pathway is important for PAH development and provide a new therapeutic target for this deadly disease with high translational potential.

Receptor for Advanced Glycation Endproducts is upregulated in temporal lobe epilepsy and contributes to experimental seizures

Toll-like receptor 4 (TLR4) activation in neuron and astrocytes by High Mobility Group Box 1 (HMGB1) protein is a key mechanism of seizure generation. HMGB1 also activates the Receptor for Advanced Glycation Endproducts (RAGE), but it was unknown whether RAGE activation contributes to seizures or to HMGB1 proictogenic effects. We found that acute EEG seizures induced by 7ng intrahippocampal kainic acid (KA) were significantly reduced in Rage-/- mice relative to wild type (Wt) mice. The proictogenic effect of HMGB1 was decreased in Rage-/- mice, but less so, than in Tlr4-/- mice. In a mouse mesial temporal lobe epilepsy (mTLE) model, status epilepticus induced by 200ng intrahippocampal KA and the onset of the spontaneous epileptic activity were similar in Rage-/-, Tlr4-/- and Wt mice. However, the number of hippocampal paroxysmal episodes and their duration were both decreased in epileptic Rage-/- and Tlr4-/- mice vs Wt mice. All strains of epileptic mice displayed similar cognitive deficits in the novel object recognition test vs the corresponding control mice. CA1 neuronal cell loss was increased in epileptic Rage-/- vs epileptic Wt mice, while granule cell dispersion and doublecortin (DCX)-positive neurons were similarly affected. Notably, DCX neurons were preserved in epileptic Tlr4-/- mice. We did not find compensatory changes in HMGB1-related inflammatory signaling nor in glutamate receptor subunits in Rage-/- and Tlr4-/- naïve mice, except for ~20% NR2B subunit reduction in Rage-/- mice. RAGE was induced in neurons, astrocytes and microvessels in human and experimental mTLE hippocampi. We conclude that RAGE contributes to hyperexcitability underlying acute and chronic seizures, as well as to the proictogenic effects of HMGB1. RAGE and TLR4 play different roles in the neuropathologic sequelae developing after status epilepticus. These findings reveal new molecular mechanisms underlying seizures, cell loss and neurogenesis which involve inflammatory pathways upregulated in human epilepsy.

The Complexity of Sporadic Alzheimer's Disease Pathogenesis: The Role of RAGE as Therapeutic Target to Promote Neuroprotection by Inhibiting Neurovascular Dysfunction

Alzheimer's disease (AD) is the most common cause of dementia. Amyloid plaques and neurofibrillary tangles are prominent pathological features of AD. Aging and age-dependent oxidative stress are the major nongenetic risk factors for AD. The beta-amyloid peptide (Aβ), the major component of plaques, and advanced glycation end products (AGEs) are key activators of plaque-associated cellular dysfunction. Aβ and AGEs bind to the receptor for AGEs (RAGE), which transmits the signal from RAGE via redox-sensitive pathways to nuclear factor kappa-B (NF-κB). RAGE-mediated signaling is an important contributor to neurodegeneration in AD. We will summarize the current knowledge and ongoing studies on RAGE function in AD. We will also present evidence for a novel pathway induced by RAGE in AD, which leads to the expression of thioredoxin interacting protein (TXNIP), providing further evidence that pharmacological inhibition of RAGE will promote neuroprotection by blocking neurovascular dysfunction in AD.

Vitamin A (retinol) up-regulates the receptor for advanced glycation endproducts (RAGE) through p38 and Akt oxidant-dependent activation

Retinol (vitamin A) is believed to exert preventive/protective effects against malignant, neurodegenerative and cardiovascular diseases by acting as an antioxidant. However, later clinical and experimental data show a pro-oxidant action of retinol and other retinoids at specific conditions. The receptor for advanced glycation endproducts (RAGE) is a pattern recognition receptor, being activated by different ligands such as S100 proteins, HMGB1 (amphoterin), β-amyloid peptide and advanced glycation endproducts (AGE). RAGE activation influences a wide range of pathological conditions such as diabetes, pro-inflammatory states and neurodegenerative processes. Here, we investigated the involvement of different mitogen-activated protein kinases (MAPK: ERK1/2, p38 and JNK), PKC, PKA and Akt in the up-regulation of RAGE by retinol. As previously reported, we observed that the increase in RAGE immunocontent by retinol is reversed by antioxidant co-treatment, indicating the involvement of oxidative stress in this process. Furthermore, the p38 inhibitor SB203580 and the Akt inhibitor LY294002 also decreased the effect of retinol on RAGE levels, suggesting the involvement of these protein kinases in such effect. Both p38 and Akt phosphorylation were increased by treatment with pro-oxidant concentrations of retinol, and the antioxidant co-treatment blocked this effect, indicating that activation of p38 and Akt during retinol treatment is dependent on reactive species production. The 2',7'-dichlorohydrofluorescein diacetate (DCFH) assay also indicated that retinol treatment enhances cellular reactive species production. Altogether, these data indicate that RAGE up-regulation by retinol is mediated by the free radical-dependent activation of p38 and Akt.

Soluble RAGE: therapy and biomarker in unraveling the RAGE axis in chronic disease and aging

The multi-ligand Receptor for Advanced Glycation Endproducts (RAGE) is implicated in the pathogenesis and progression of chronic diseases such as diabetes and immune/inflammatory disorders. Recent studies are uncovering the precise mechanisms by which distinct RAGE ligands bind the extracellular (soluble) domain of the receptor at the V-, C1- and/or C2-immunoglobulin like domains. Experiments using soluble RAGE in animals as a ligand decoy have illustrated largely beneficial effects in reducing vascular and inflammatory stress and, thereby, preventing long-term tissue damage in models of diabetes and immune/inflammatory disorders. Measurement of soluble RAGE levels in the human, both "total" soluble RAGE and a splice variant-derived product known as endogenous secretory or esRAGE, holds promise for the identification of potential therapeutic targets and/or biomarkers of RAGE activity in disease. In this article, we review the evidence from the rodent to the human implicating RAGE in the diverse disease states in which its ligands accumulate.

Expression of receptor for advanced glycation end products (RAGE) is related to prognosis in patients with esophageal squamous cell carcinoma

The receptor for advanced glycation end products (RAGE), known as a multiligand receptor for certain stress-associated factors, has been considered to affect the characteristic differences of various cancer cells. We analyzed the expression and clinicopathological significance of RAGE in esophageal squamous cell carcinoma. We investigated immunohistochemically the relationship between RAGE expression and clinicopathological factors, including prognosis, in surgical specimens of primary tumors in 216 patients with esophageal squamous cell carcinoma. Prognostic factors were examined by univariate and multivariate analyses (Cox proportional hazard regression model). The positive expression rate of RAGE was 50%. RAGE expression was negatively correlated with depth of invasion and venous invasion. Moreover, tumors with positive RAGE expression exhibited better prognosis than those with negative RAGE expression (5-year survival, 52% vs. 32%, respectively). Multivariate analysis indicated that the positive expression of RAGE was an independent prognostic factor, along with tumor depth and nodal metastasis. Our findings suggest that loss of RAGE expression may play an important role in the progression of esophageal squamous cell carcinoma. Evaluation of the expression of RAGE could be useful for determining the tumor properties, including those associated with prognosis, in patients with esophageal squamous cell carcinoma.

Inflammation and the redox-sensitive AGE-RAGE pathway as a therapeutic target in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia. Neuritic amyloid plaques and concomitant chronic inflammation are prominent pathological features of AD. beta-amyloid peptide (Abeta), the major component of plaques, and advanced glycation end products (AGEs), post-translational protein modifications, are key activators of plaque-associated inflammation. Abeta, AGEs, S100b, and amphoterin bind to the receptor for AGEs (RAGE), which transmits the signal from RAGE via redox-sensitive pathways to nuclear factor kappa-B (NF-kappaB)-regulated cytokines. RAGE-mediated inflammation caused by glial cells and subsequent changes in neuronal glucose metabolism are likely to be important contributors to neurodegeneration in AD. As long as the neuronal damage is reversible, drugs interfering with the Abeta and AGE-RAGE pathways might be interesting novel therapeutics for the treatment of AD.

Receptor for advanced glycation end products (RAGE) mediates neuronal differentiation and neurite outgrowth

The receptor for advanced glycation end products (RAGE) plays a crucial role in several disease processes, such as diabetes, inflammation, and neurodegeneration. In this article we report multiple roles of RAGE in neuronal differentiation and neurite outgrowth. In retinoic-induced P19 embryonic carcinoma stem cells, silencing the expression of RAGE by RNA interference (RNAi) blocked differentiation of the P19 cells into neuronal cells and enhanced the formation of vimentin-positive fibroblast-like cells. RAGE knockdown inhibited retinoic acid-induced activation and blocked nuclear translocation of NF-kappaB, suggesting RAGE regulates activation of NF-kappaB. RAGE was also shown to be involved in survival of P19 cells during retinoic acid differentiation. Additionally, knockdown of RAGE strongly inhibited neurite outgrowth in retinoic acid-differentiated P19 cells, indicating that RAGE is required for neurite outgrowth of differentiated P19 cells. Retinoic acid-treated P19 cells activated GTPases, Rac1, and Cdc42. This activation of the GTPases was inhibited in RAGE-knockdown cells. In primary cerebellar granule neurons, the knockdown of RAGE also inhibited neurite outgrowth. In these cells, overexpression of dominant-negative forms of Rac1 and Cdc42 inhibited neurite outgrowth, whereas overexpression of constitutively active forms of Rac1 and Cdc42 in RAGE-deficient neurons restored neurite outgrowth, indicating that RAGE mediated neurite outgrowth through the Rac1/Cdc42 pathway. This is the first report on the role of RAGE in cell lines and primary neurons, as determined by RNAi knockdown.

Site-specific blockade of RAGE-Vd prevents amyloid-beta oligomer neurotoxicity

In the genesis of Alzheimer's disease (AD), converging lines of evidence suggest that amyloid-beta peptide (Abeta) triggers a pathogenic cascade leading to neuronal loss. It was long assumed that Abeta had to be assembled into extracellular amyloid fibrils or aggregates to exert its cytotoxic effects. Over the past decade, characterization of soluble oligomeric Abeta species in the brains of AD patients and in transgenic models has raised the possibility that different conformations of Abeta may contribute to AD pathology via different mechanisms. The receptor for advanced glycation end products (RAGE), a member of the Ig superfamily, is a cellular binding site for Abeta. Here, we investigate the role of RAGE in apoptosis induced by distinct well characterized Abeta conformations: Abeta oligomers (AbetaOs), Abeta fibrils (AbetaFs), and Abeta aggregates (AbetaAs). In our in vitro system, treatment with polyclonal anti-RAGE antibodies significantly improves SHSY-5Y cell and neuronal survival exposed to either AbetaOs or AbetaAs but does not affect AbetaF toxicity. Interestingly, using site-specific antibodies, we demonstrate that targeting of the V(d) domain of RAGE attenuates AbetaO-induced toxicity in both SHSY-5Y cells and rat cortical neurons, whereas inhibition of AbetaA-induced apoptosis requires the neutralization of the C(1d) domain of the receptor. Thus, our data indicate that distinct regions of RAGE are involved in Abeta-induced cellular and neuronal toxicity with respect to the Abeta aggregation state, and they suggest the blockage of particular sites of the receptor as a potential therapeutic strategy to attenuate neuronal death.

A novel function of the receptor for advanced glycation end-products (RAGE) in association with tumorigenesis and tumor differentiation of HCC

Background

The expression of the receptor for advanced glycation end products (RAGE) has an impact on the mechanisms giving rise to characteristic features of various cancer cells. The purpose of this study was to elucidate the clinicopathological relevance of the level of RAGE expression in patients with hepatocellular carcinoma (HCC) and to explore the effect of RAGE expression on the characteristic features of HCC.

Methods

The expression of RAGE was assessed in paired cancer and noncancerous tissues with HCC, using reverse-transcription polymerase chain reaction (RT-PCR), and immunohistochemistry. The quantitative RT-PCR data were analyzed in association with the clinicopathological factors of the patients with HCC. In in vitro experiments, the survival of RAGE-transfected Cos7 and mock-transfected Cos7 cells was compared under hypoxic conditions. In addition, after reducing RAGE levels in RAGE-transfected Cos7 cells by siRNA, similar experiments were performed.

Results

The expression of RAGE mRNA was lower in normal liver than in hepatitis and highest in HCC. Furthermore, in HCC, it was high in well- and moderately differentiated tumors but declined as tumors dedifferentiated to poorly differentiated HCC. Furthermore, HCC lines resistant to hypoxia were found to have higher levels of RAGE expression, and RAGE transfectant also showed significantly prolonged survival under hypoxia.

Conclusions

Our results suggest that HCC during the early stage of tumorigenesis with less blood supply may acquire resistance to stringent hypoxic milieu by hypoxia-induced RAGE expression.

Protective effect of (-)-epigallocatechin gallate against advanced glycation endproducts-induced injury in neuronal cells

Advanced glycation endproducts (AGEs) are believed to be secondary factors in the selective neuronal injury associated with several neurodegenerative disorders. In this study, we investigated the protective effects of (-)-epigallocatechin gallate (EGCG), a major monomer of green tea polyphenols, against AGEs-induced damage in neuron cells. The results showed that EGCG treatment protected against glyceraldehyde-derived AGE-induced neurotoxicity, which is associated with an increase in intracellular reactive oxygen species, as well as against decreases in intracellular catalase (CAT) and superoxide dismutase (SOD) activities. EGCG treatment also decreased malondialdehyde and carbonyl levels, and AGEs formation. Treatment with 10 muM EGCG upregulated SOD and CAT levels, whereas glutathione peroxidase activity was reduced. Furthermore, 5 muM EGCG was found to down-regulate the mRNA level of the AGE receptor (RAGE) in neuronal cells up to 2.5 fold, as determined by real time PCR. The results demonstrated that EGCG may exhibit protective effects against AGEs-induced injury in neuronal cells through its antioxidative properties, as well as by interfering with AGEs-RAGE interaction mediated pathways, suggesting a beneficial role for this tea catechin against neurodegenerative diseases.

The high-mobility group box 1 cytokine induces transporter-mediated release of glutamate from glial subcellular particles (gliosomes) prepared from in situ-matured astrocytes

The multifunctional protein high-mobility group box 1 (HMGB1) is expressed in restricted areas of adult brain where it can act as a proinflammatory cytokine. We report here that HMGB1 affects CNS transmission by inducing glutamatergic release from glial (gliosomes) but not neuronal (synaptosomes) resealed subcellular particles isolated from mouse cerebellum and hippocampus. Confocal microscopy showed that gliosomes are enriched with glia-specific proteins such as GFAP and S-100, but not with neuronal proteins such as PSD-95, MAP-2, and beta-tubulin III. Furthermore, gliosomes exhibit labeling neither for integrin-alphaM nor for myelin basic protein, specific for microglia and oligodendrocytes, respectively. The gliosomal fraction contains proteins of the exocytotic machinery coexisting with GFAP. Consistent with ultrastructural analysis, several approximately 30-nm nonclustered vesicles are present in the gliosome cytoplasm. Finally, gliosomes represent functional organelles that actively export glutamate when subjected to releasing stimuli, such as ionomycin or ATP, by mechanisms involving extracellular Ca(2+) and Ca(2+) release from intracellular stores. HMGB1-induced release of the stable glutamate analogue [(3)H]d-aspartate and endogenous glutamate form gliosomes, whereas nerve terminals were insensitive to the protein. The HMGB1-evoked release of glutamate was independent on modifications of cytosolic Ca(2+) concentration, but it was blocked by dl-threo-beta-benzyloxyaspartate, suggesting the involvement of transporter-mediated release mechanisms. Moreover, dihydrokainic acid, a selective inhibitor of glutamate transporter 1 does not block the HMGB1 effect, indicating a role for the glial glutamate-aspartate transporter (GLAST) subtype in this response. HMGB1 bind to gliosomes but not to synaptosomes and can physically interact with GLAST and receptor for advanced glycation end products (RAGE). Taken together, these results suggest that the HMGB1 cytokine could act as a modulator of glutamate homeostasis in adult mammalian brain.

S100B and S100A6 differentially modulate cell survival by interacting with distinct RAGE (receptor for advanced glycation end products) immunoglobulin domains

S100 proteins are EF-hand calcium-binding proteins with various intracellular functions including cell proliferation, differentiation, migration, and apoptosis. Some S100 proteins are also secreted and exert extracellular paracrine and autocrine functions. Experimental results suggest that the receptor for advanced glycation end products (RAGE) plays important roles in mediating S100 protein-induced cellular signaling. Here we compared the interaction of two S100 proteins, S100B and S100A6, with RAGE by in vitro assay and in culture of human SH-SY5Y neuroblastoma cells. Our in vitro binding data showed that S100B and S100A6, although structurally very similar, interact with different RAGE extracellular domains. Our cell assay data demonstrated that S100B and S100A6 differentially modulate cell survival. At micromolar concentration, S100B increased cellular proliferation, whereas at the same concentration, S100A6 triggered apoptosis. Although both S100 proteins induced the formation of reactive oxygen species, S100B recruited phosphatidylinositol 3-kinase/AKT and NF-kappaB, whereas S100A6 activated JNK. More importantly, we showed that S100B and S100A6 modulate cell survival in a RAGE-dependent manner; S100B specifically interacted with the RAGE V and C(1) domains and S100A6 specifically interacted with the C(1) and C(2) RAGE domains. Altogether these results highlight the complexity of S100/RAGE cellular signaling.

Cell cycle related signaling in neuro2a cells proceeds via the receptor for advanced glycation end products

Re-expression of cell cycle related genes such as cyclin-dependent kinases (cdk), cyclins, or cdk inhibitors in differentiated neurons in Alzheimer's disease (AD) is rooted in aberrant mitogenic signaling. Since microglia and astroglia proliferate in the vicinity of amyloid plaques, it is likely that plaque components or factors secreted from plaque-activated glia induce mitogenic signaling in neurons. Mitogenic compounds might be S100B, overexpressed by activated astrocytes, or advanced glycation end products (AGEs), a component of plaques. Both S100B and AGEs may interact with the multiligand receptor for AGEs (RAGE) and trigger for the activation of the p42/44 mitogen-activated protein kinase (p42/44 MAPK), whether they also count for cell cycle related signaling in neurons remains unresolved. By immunohistochemical staining, we confirmed that cyclin D(1) positive neurons are surrounded by AGE deposits, demonstrating the potential relevance in vivo. For exploring the mitogenic signal cascade, we used Neuro2a cells overexpressing human full-length RAGE (FL-RAGE) or the cytosolic deletion mutant (Delta-RAGE). In both cell lines, S100B and AGEs induced the production of reactive oxygen species but not in a RAGE-dependent manner. By contrast, in FL-RAGE cells but not in Delta-RAGE cells S100B and AGEs activate p42/44 MAPK, augment cyclin D(1)/cdk4 protein and RNA levels and the transition into the S-phase. Moreover, in FL-RAGE cells, decreased protein levels of the cdk inhibitor p16 were observed, and the p42/44 MAPK inhibitor UO126 prevented AGE and S100B stimulated cyclin D(1) expression and hindered cells to enter the S-phase. Our results demonstrate that S100B and AGE may serve as mitogenic sources for the stimulation of neurons to progress through the cell cycle whereby signaling proceeds via RAGE --> p42/44 MAPK --> cyclin D(1)/cdk4.

HMGB1 is a bone-active cytokine

High mobility group box 1 (HMGB1) is a chromatin protein that acts as an immunomodulatory cytokine upon active release from myeloid cells. HMGB1 is also an alarmin, an endogenous molecule released by dying cells that acts to initiate tissue repair. We have previously reported that osteoclasts and osteoblasts release HMGB1 and release by the latter is regulated by parathyroid hormone (PTH), an agent of bone remodeling. A recent study suggests that HMGB1 acts as a chemotactic agent to osteoclasts and osteoblasts during endochondral ossification. To explore the potential impact of HMGB1 in the bone microenvironment and its mechanism of release by osseous cells, we characterized the effects of recombinant protein (rHMGB1) on multiple murine bone cell preparations that together exhibit the various cell phenotypes present in bone. We also inquired whether apoptotic bone cells release HMGB1. rHMGB1 enhanced the RANKL/OPG steady state mRNA ratio and dramatically augmented the release of tumor necrosis factor-alpha (TNFalpha) and interleukin-6 (IL6) in osteoblastogenic bone marrow stromal cell (BMSC) cultures but not in the calvarial-derived MC3T3-E1 cells. Interestingly, rHMGB1 promoted GSK-3beta phosphorylation in MC3T3-E1 cells but not in BMSCs. Apoptotic bone cells released HMGB1, including MLO-Y4 osteocyte-like cells. MLO-Y4 release of HMGB1 was coincident with caspase-3 cleavage. Furthermore, the anti-apoptotic action of PTH on MC3T3-E1 cells correlated with the observed decrease in HMGB1 release. Our data suggest that apoptotic bone cells release HMGB1, that within the marrow HMGB1 is a bone resorption signal, and that intramembraneous and endochondral osteoblasts exhibit differential responses to this cytokine.

Carbohydrate mimics promote functional recovery after peripheral nerve repair

OBJECTIVE

The outcome of peripheral nerve repair is often unsatisfactory, and efficient therapies are not available. We tested the therapeutic potential of functional mimics of the human natural killer cell glycan (3-sulfoglucuronyl beta1-3 galactoside) (HNK-1) epitope, a carbohydrate indicated to favor specificity of motor reinnervation in mice.

METHODS

We applied a linear HNK-1 mimic peptide, scrambled peptide, or vehicle substances in polyethylene cuffs used to reconstruct the severed femoral nerves of adult mice. We used video-based motion analysis and morphological and tracing techniques to monitor the outcome of nerve repair.

RESULTS

After glycomimetic application, quadriceps muscle function recovered to 93% of normal within 3 months. Restoration of function was less complete (71-76%) in control groups. Better functional recovery was associated with larger motoneuron somata, better axonal myelination in the quadriceps nerve, and enhanced precision of target reinnervation. Lesion-induced death of motoneurons was reduced by 20 to 25%. The glycomimetic enhanced survival and neurite outgrowth of both mouse and human motoneurons in vitro by 30 to 75%. Application of a novel cyclic glycomimetic also enhanced functional recovery in vivo.

INTERPRETATION

The improved outcome of nerve repair after glycomimetic application may be attributed to neurotrophic effects. Our results hold promise for therapeutic use in humans.

SRY-box containing gene 11 (Sox11) transcription factor is required for neuron survival and neurite growth

The transcription factor Sox11 is expressed at high levels in developing sensory neurons and injured adult neurons but little is known about its transcriptional targets and function. In this study we examined the role of Sox11 using Neuro2a neuroblastoma cells and cultured mouse dorsal root ganglia (DRG) neurons. Results show Sox11 has an essential role in regulation of neuron survival and neurite outgrowth in Neuro2a cells and primary sensory neurons. Neuro2a cells increase expression of Sox11 as they differentiate in culture. Following addition of 20 microM retinoic acid (RA), a stimulus for differentiation that enhances neurite growth and differentiation, Sox11 level rises. RNAi-mediated knockdown of Sox11 in RA-differentiated Neuro2a cells caused a decrease in neurite growth and an increase in the percent of apoptotic cells. RNA expression analysis showed that Sox11 knockdown modulated the level of mRNAs encoding several genes related to cell survival and death. Further validation in the Neuro2a model showed Sox11 knockdown increased expression of the pro-apoptotic gene BNIP3 (BclII interacting protein 1 NIP3) and decreased expression of the anti-apoptotic gene TANK (TNF receptor-associated factor family member-associated NFkappaB activator). Cultured primary DRG neurons also express Sox11 and treatment with Sox11 small interfering RNA (siRNA) caused a significant decrease in neurite growth and branching and a decrease in mRNA encoding actin-related protein complex 3 (Arpc3), an actin organizing protein that may be involved in axon growth. The percent of apoptotic neurons also increased in cultures of DRG neurons treated with Sox11 siRNA. Similar to Neuro2a cells, a decrease in TANK gene expression occurred, suggesting at least some overlap in Sox11 transcriptional targets in Neuro2a and DRG neurons. These data are consistent with a central role for Sox11 in regulating events that promote neurite growth and neuron survival.

Stimulation of excitatory amino acid release from adult mouse brain glia subcellular particles by high mobility group box 1 protein

The multifunctional protein high mobility group box 1 (HMGB1) is expressed in hippocampus and cerebellum of adult mouse brain. Our aim was to determine whether HMGB1 affects glutamatergic transmission by monitoring neurotransmitter release from glial (gliosomes) and neuronal (synaptosomes) re-sealed subcellular particles isolated from cerebellum and hippocampus. HMGB1 induced release of the glutamate analogue [(3)H]d-aspartate form gliosomes in a concentration-dependent manner, whereas nerve terminals were insensitive to the protein. The HMGB1-evoked release of [(3)H]d-aspartate was independent of modifications of cytosolic Ca(2+) , but it was blocked by dl-threo-beta-benzyloxyaspartate (dl-TBOA), an inhibitor of glutamate transporters. HMGB1 also stimulated the release of endogenous glutamate in a Ca(2+)-independent and dl-TBOA-sensitive manner. These findings suggest the involvement of carrier-mediated release. Moreover, dihydrokainic acid, a selective inhibitor of glutamate transporter 1 (GLT1), does not block the effect of HMGB1, indicating a role for the glial glutamate-aspartate transporter (GLAST) subtype in this response. We also demonstrate that HMGB1/glial particles association is promoted by Ca(2+). Furthermore, although HMGB1 can physically interact with GLAST and the receptor for advanced glycation end products (RAGE), only its binding with RAGE is promoted by Ca(2+). These results suggest that the HMGB1 cytokine could act as a modulator of glutamate homeostasis in adult mammal brain.

S100B protects LAN-5 neuroblastoma cells against Abeta amyloid-induced neurotoxicity via RAGE engagement at low doses but increases Abeta amyloid neurotoxicity at high doses

At the concentrations normally found in the brain extracellular space the glial-derived protein, S100B, protects neurons against neurotoxic agents by interacting with the receptor for advanced glycation end products (RAGE). It is known that at relatively high concentrations S100B is neurotoxic causing neuronal death via excessive stimulation of RAGE. S100B is detected within senile plaques in Alzheimer's disease, where its role is unknown. The present study was undertaken to evaluate a putative neuroprotective role of S100B against Abeta amyloid-induced neurotoxicity. We treated LAN-5 neuroblastoma cultures with toxic amounts of Abeta25-35 amyloid peptide. Our results show that at nanomolar concentrations S100B protects cells against Abeta-mediated cytotoxicity, as assessed by 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and terminal deoxynucleotidyl transferase-mediated dUTP-fluorescein isothiocyanate nick end-labeling (TUNEL) experiments, by countering the Abeta-mediated decrease in the expression of the anti-apoptotic factor Bcl-2. This effect depends on S100B binding to RAGE because S100B is unable to contrast Abeta-mediated neurotoxicity in neurons overexpressing a signaling-deficient RAGE mutant lacking the cytosolic and transducing domain. Our data suggest that at nanomolar doses S100B counteracts Abeta peptide neurotoxicity in a RAGE-mediated manner. However, at micromolar doses S100B is toxic to LAN-5 cells and its toxicity adds to that of the Abeta peptide, suggesting that additional molecular mechanisms may be involved in the neurotoxic process.

Advanced glycation end products induce death of retinal neurons via activation of nitric oxide synthase

The purpose of this study was to determine whether advanced glycation end products (AGEs) are neurotoxic for cultured retinal neurons consisting mainly of amacrine cells, and to determine whether endogenous nitric oxide (NO) is involved in the toxicity. Cultured retinal neurons obtained from fetal Wistar rats (gestational age 19 days) were maintained in culture for 10 days, and then exposed to different concentrations of AGEs (0.02, 0.1, and 0.5 mg ml(-1)) in cultured media for different lengths of time. Both trypan blue exclusion and TUNEL assay were used to determine whether AGEs were neurotoxic, and NG-nitro-L-arginine methyl ester (L-NAME, 500 microM), a nitric oxide synthase (NOS) inhibitor, was used to determine whether NO was involved. Immunohistochemical analyses were performed to determine whether specific receptors of AGEs (RAGE) are present on cultured retinal neurons; caspase-3 was activated, and 3-nitrotyrosine was expressed on neurons treated with AGEs. Nitrite levels were measured in the supernatants of the media where neurons were incubated with AGEs. AGEs induced cell death in a time- and dose-dependent manner. TUNEL-positive cells and immunoreactivity to cleaved caspase-3 were enhanced on neurons following exposure to AGEs. L-NAME significantly suppressed the AGEs-induced neurotoxicity as assessed by both trypan blue exclusion and TUNEL assays. Activation of NOS was suggested by enhanced immunoreactivity to 3-nitrotyrosine on neurons and increased nitrite levels in the media incubated with AGEs. These results indicate that AGEs are neurotoxic to retinal neurons in culture through the activation of NOS. Apoptotic pathways may be in part involved in the death of the neurons.

Apoptotic killing of fibroblasts by matrix-bound advanced glycation endproducts

The extracellular matrix accumulates biologically active advanced glycation endproducts such as carboxymethyl-lysine (CML). Alikhani et al. recently reported that CML-rich collagen, representing an artifically aged matrix protein, induces apoptosis in vivo and in fibroblasts. This observation may have profound implications for the biology of cell-matrix interactions during aging.

Overexpression of receptor of advanced glycation end products hypersensitizes cells for amyloid beta peptide-induced cell death

Receptor of advanced glycation end products (RAGE) was identified as one of the receptors for amyloid beta peptide (Abeta). There is evidence for controversial functions of RAGE such as a mediator of cell death or differentiation. In this report, we demonstrate that RAGE mediates Abeta toxicity. Transient transfection of RAGE already induced cell death. For further analysis, stable clones of hemagglutinin (HA)-tagged RAGE were selected. Analysis of cellular localization of HA-tagged RAGE protein revealed, in addition to the expected cell surface expression, a novel intracellular localization. Stable RAGE-expressing cells were hypersensitive to nanomolar amounts of Abeta. Only cells expressing RAGE at the cell surface showed hypersensitivity to Abeta.

HMGB1 is a potent trigger of arthritis

Rheumatoid arthritis is a chronic inflammatory disease characterized by synovial inflammation and structural damage of joints. Although the cause of rheumatoid arthritis (RA) remains unknown, the excessive production of proinflammatory cytokines such as tumour necrosis factor (TNF) and interleukin-1 (IL-1) by intra-articular macrophages occupies a critical pathogenic role in the development and progression of the disease. High mobility group box chromosomal protein 1 (HMGB1) is a recently identified mediator of interest in human and experimental arthritides. HMGB1 can either be actively secreted from macrophages or passively released from necrotic cells of all kinds. Activated macrophages and unprogrammed cell death caused by ischaemia or activated complement are all prominent features of chronic arthritis, contributing to the persistent synovial inflammation. HMGB1 is cytoplasmically and extracellularly overexpressed in inflammatory synovial tissue in human RA as well as experimental collagen-induced arthritis. Elevated levels of HMGB1 are also present in synovial fluid samples from RA patients. Synovial tissue from rats with experimental arthritis exhibits aberrant deposition of HMGB1 preceding the onset of clinical signs of arthritis, and the expression becomes prominent after the onset of clinical disease. The synovial levels of HMGB1 are comparable with those of TNF and IL-1beta at the peak of manifest disease. HMGB1-targeted intervention with either neutralizing antibodies or the antagonistic A box domain of HMGB1 ameliorates collagen-induced arthritis both in mice and rats, and inhibits the local overexpression of IL-1beta in the joints. It is thus conceivable that therapeutic HMGB1 blockade may contribute to future treatment of human chronic arthritis.

Involvement of Toll-like Receptors 2 and 4 in Cellular Activation by High Mobility Group Box 1 Protein

High mobility group box 1 (HMGB1) protein, originally described as a DNA-binding protein that stabilizes nucleosomes and facilitates transcription, can also be released extracellularly during acute inflammatory responses. Exposure of neutrophils, monocytes, or macrophages to HMGB1 results in increased nuclear translocation of NF-kappaB and enhanced expression of proinflammatory cytokines. Although the receptor for advanced glycation end products (RAGE) has been shown to interact with HMGB1, other putative HMGB1 receptors are known to exist but have not been characterized. In the present experiments, we explored the role of RAGE, Toll-like receptor (TLR) 2, and TLR 4, as well as associated kinases, in HMGB1-induced cellular activation. Culture of neutrophils or macrophages with HMGB1 produced activation of NF-kappaB through TLR 4-independent mechanisms. Unlike lipopolysaccharide (LPS), which primarily increased the activity of IKKbeta, HMGB1 exposure resulted in activation of both IKKalpha and IKKbeta. Kinases and scaffolding proteins downstream of TLR 2 and TLR 4, but not TLR/interleukin-1 receptor (IL-1R)-independent kinases such as tumor necrosis factor receptor-associated factor 2, were involved in the enhancement of NF-kappaB-dependent transcription by HMGB1. Transfections with dominant negative constructs demonstrated that TLR 2 and TLR 4 were both involved in HMGB1-induced activation of NF-kappaB. In contrast, RAGE played only a minor role in macrophage activation by HMGB1. Interactions of HMGB1 with TLR 2 and TLR 4 may provide an explanation for the ability of HMGB1 to generate inflammatory responses that are similar to those initiated by LPS.

Cancer prevention and therapy: strategies and problems

During the next years, molecular diagnostic science and the pharmaceutical industry will face increasing demand for personalized medicine. Therapeutic treatments should be tailored to the needs of individual patient. Patients will inquire for information about potential tumor detection at an early stage when disease can be more likely to be arrested or cured with specific regimens of drug therapy. To respond to this demand, science and industry need to modulate therapeutic approaches to the continuous development of cancer. Now more than ever, it is necessary to fill the knowledge hiatus between the "beginning" and the "end" of cancer development, i.e we need to critically analyze the extensive multi-step process of cancer development that still remains poorly understood.

Neurotoxic mechanisms caused by the Alzheimer's disease-linked Swedish amyloid precursor protein mutation: oxidative stress, caspases, and the JNK pathway

Autosomal dominant forms of familial Alzheimer's disease (FAD) are caused by mutations of the amyloid precursor protein (APP) gene and by mutations of the genes encoding for presenilin 1 or presenilin 2. Simultaneously, evidence is provided that increased oxidative stress might play a crucial role in the rapid progression of the Swedish FAD. Here we investigated the effect of the Swedish double mutation (K670M/N671L) in the beta-amyloid precursor protein on oxidative stress-induced cell death mechanisms in PC12 cells. Western blot analysis and cleavage studies of caspase substrates revealed an elevated activity of the executor caspase 3 after treatment with hydrogen peroxide in cells containing the Swedish APP mutation. This elevated activity is the result of the enhanced activation of both intrinsic and extrinsic apoptosis pathways, including activation of caspase 2 and caspase 8. Furthermore, we observed an enhanced activation of JNK pathway and an attenuation of apoptosis by SP600125, a JNK inhibitor, through protection of mitochondrial dysfunction and reduction of caspase 9 activity. Our findings provide evidence that the massive neurodegeneration in early age of FAD patients could be a result of an increased vulnerability of neurons through activation of different apoptotic pathways as a consequence of elevated levels of oxidative stress.

Microglial activation induces cell death, inhibits neurite outgrowth and causes neurite retraction of differentiated neuroblastoma cells

Activation of glial cells has been proposed to contribute to neuronal dysfunction and neuronal cell death in Alzheimer's disease. In this study, we attempt to determine some of the effects of secreted factors from activated murine N-11 microglia on viability and morphology of neurons using the differentiated neuroblastoma cell line Neuro2a. Microglia were activated either by lipopolysaccharide (LPS), bacterial cell wall proteoglycans, or advanced glycation endproducts (AGEs), protein-bound sugar oxidation products. At high LPS or AGE concentrations, conditioned medium from microglia caused neuronal cell death in a dose-dependent manner. At sublethal LPS or AGE concentrations, conditioned media inhibited retinoic acid-induced neurite outgrowth and stimulated retraction of already extended neurites. Among the many possible secreted factors, the contribution of NO or NO metabolites in the cytotoxicity of conditioned medium was investigated. Cell death and changes in neurite morphology were partly reduced when NO production was inhibited by nitric oxide synthase inhibitors. The results suggest that even in the absence of significant cell death, inflammatory processes, which are partly transmitted via NO metabolites, may affect intrinsic functions of neurons such as neurite extension that are essential components of neuronal morphology and thus may contribute to degenerative changes in Alzheimer's disease.

Intracellular and extracellular roles of S100 proteins

S100, a multigenic family of non-ubiquitous Ca(2+)-modulated proteins of the EF-hand type expressed in vertebrates exclusively, has been implicated in intracellular and extracellular regulatory activities. Members of this protein family have been shown to interact with several effector proteins within cells thereby regulating enzyme activities, the dynamics of cytoskeleton constituents, cell growth and differentiation, and Ca(2+) homeostasis. Structural information indicates that most of S100 proteins exist in the form of antiparallelly packed homodimers (in some cases heterodimers), capable of functionally crossbridging two homologous or heterologous target proteins in a Ca(2+)-dependent (and, in some instances, Ca(2+)-independent) manner. In addition, extracellular roles have been described for several S100 members, although secretion (via an unknown mechanism) has been documented for a few of them. Extracellular S100 proteins have been shown to exert regulatory effects on inflammatory cells, neurons, astrocytes, microglia, and endothelial and epithelial cells, and a cell surface receptor, RAGE, has been identified as a potential S100A12 and S100B receptor transducing the effects of these two proteins on inflammatory cells and neurons. Other cell surface molecules with ability to interact with S100 members have been identified, suggesting that RAGE might not be a universal S100 protein receptor and/or that a single S100 protein might interact with more than one receptor. Collectively, these data indicate that members of the S100 protein family are multifunctional proteins implicated in the regulation of a variety of cellular activities.

RAGE is expressed in pyramidal cells of the hippocampus following moderate hypoxic-ischemic brain injury in rats

The receptor for advanced glycation end products (RAGE) is a multi-ligand member of the immunoglobulin superfamily of cell surface molecules. The RAGE-ligand interaction has a putative role in a range of chronic disorders and is also known to contribute to both inflammatory/degenerative processes as well as regeneration in peripheral nerve injury. We have investigated the expression of RAGE in the moderate hypoxic-ischemic (HI) rat brain injury model in order to determine if this receptor is involved in the cellular perturbation mediated by ischemic stress. RAGE mRNA levels were detected by in situ hybridization using a DIG-labelled 48 mer oligonucleotide probe. Results showed a high level of expression of RAGE mRNA in the CA1/2 pyramidal cell layer of the hippocampus on the lesioned side of the brain 72 h after a moderate hypoxic-ischemic insult. RAGE was not expressed on the control side of the hippocampus. The RAGE-positive cells had a unique morphology, being angular in shape and atrophied with a condensed cell nucleus. They were NeuN-positive and were identified as dying cells by staining with thionin/acid fuchsin. A subset of cells was positive for cleaved Caspase-3, a marker for apoptosis. Together these data show that RAGE is expressed in dying neurons and suggest that RAGE may have a role in neuronal cell death mediated by ischemic stress. Identification of the ligand for RAGE in the ischemic brain may lead to a better understanding of RAGE-mediated cellular dysfunction in the CNS.

Receptor for advanced glycation end products (RAGE) signaling induces CREB-dependent chromogranin expression during neuronal differentiation

Receptor for advanced glycation end products (RAGE) mediates neurite outgrowth and cell migration upon stimulation with its ligand, amphoterin. We show here that RAGE-dependent changes in cell morphology are associated with proliferation arrest and changes in gene expression in neuroblastoma cells. Chromogranin B, a component of secretory vesicles in endocrine cells and neurons, was found to be up-regulated by RAGE signaling during differentiation of neuroblastoma cells along with the two other members of the chromogranin family, chromogranin A and secretogranin II. Ligation of RAGE by amphoterin lead to rapid phosphorylation and nuclear localization of cyclic AMP response element-binding protein (CREB), a major regulator of chromogranin expression. Furthermore, inhibition of ERK1/2-Rsk2-dependent CREB phosphorylation efficiently inhibited up-regulation of chromogranin gene expression upon RAGE activation. To further study the effects of RAGE and amphoterin on cellular differentiation, we stimulated embryonic stem cells expressing RAGE or a signaling-deficient mutant of RAGE with amphoterin. Amphoterin was found to promote RAGE-dependent neuronal differentiation of embryonic stem cells characterized by up-regulation of neuronal markers light neurofilament protein and beta-III-tubulin, activation of CREB, and increased expression of chromogranins A and B. These data suggest that RAGE signaling is capable of driving neuronal differentiation involving CREB activation and induction of chromogranin expression.

Oligomeric and fibrillar species of amyloid-beta peptides differentially affect neuronal viability

Genetic evidence predicts a causative role for amyloid-beta (A beta) in Alzheimer's disease. Recent debate has focused on whether fibrils (amyloid) or soluble oligomers of A beta are the active species that contribute to neurodegeneration and dementia. We developed two aggregation protocols for the consistent production of stable oligomeric or fibrillar preparations of A beta-(1-42). Here we report that oligomers inhibit neuronal viability 10-fold more than fibrils and approximately 40-fold more than unaggregated peptide, with oligomeric A beta-(1-42)-induced inhibition significant at 10 nm. Under A beta-(1-42) oligomer- and fibril-forming conditions, A beta-(1-40) remains predominantly as unassembled monomer and had significantly less effect on neuronal viability than preparations of A beta-(1-42). We applied the aggregation protocols developed for wild type A beta-(1-42) to A beta-(1-42) with the Dutch (E22Q) or Arctic (E22G) mutations. Oligomeric preparations of the mutations exhibited extensive protofibril and fibril formation, respectively, but were not consistently different from wild type A beta-(1-42) in terms of inhibition of neuronal viability. However, fibrillar preparations of the mutants appeared larger and induced significantly more inhibition of neuronal viability than wild type A beta-(1-42) fibril preparations. These data demonstrate that protocols developed to produce oligomeric and fibrillar A beta-(1-42) are useful in distinguishing the structural and functional differences between A beta-(1-42) and A beta-(1-40) and genetic mutations of A beta-(1-42).