The receptor for advanced glycation end-products (RAGE) directly binds to ERK by a D-domain-like docking site

Cornuside ameliorates cognitive impairments via RAGE/TXNIP/NF-κB signaling in Aβ1-42 induced Alzheimer's disease mice

Cornuside has been discovered to improve learning and memory in AD mice, however, its underlying mechanism was not fully understood. In the present study, we established an AD mice model by intracerebroventricular injection of Aβ1-42, which were treated with cornuside (3, 10, 30 mg/kg) for 2 weeks. Cornuside significantly ameliorated cognitive function of AD mice in series of behavioral tests, including Morris water maze test, nest building test, novel object recognition test and step-down test. Additionally, cornuside could attenuate neuronal injury, and promote cholinergic synaptic transmission by restoring the level of acetylcholine (ACh) via inhibiting acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), as well as facilitating choline acetyltransferase (ChAT). Furthermore, cornuside inhibited oxidative stress levels amplified as decreased malondialdehyde (MDA), by inhibiting TXNIP expression, improving total anti-oxidative capacity (TAOC), raising activities of superoxide dismutase (SOD) and catalase (CAT). Cornuside also reduced the activation of microglia and astrocytes, decreased the level of proinflammatory factors TNF-α, IL-6, IL-1β, iNOS and COX2 via interfering RAGE-mediated IKK-IκB-NF-κB phosphorylation. Similar anti-oxidative and anti-inflammatory effects were also found in LPS-stimulated BV2 cells via hampering RAGE-mediated TXNIP activation and NF-κB nuclear translocation. Virtual docking revealed that cornuside could interact with the active pocket of RAGE V domain directly. In conclusion, cornuside could bind to the RAGE directly impeding the interaction of Aβ and RAGE, and cut down the expression of TXNIP inhibiting ROS production and oxidative stress, as well as hamper NF-κB p65 mediated the inflammation.

Binding of RAGE and RIPK1 induces cognitive deficits in chronic hyperglycemia-derived neuroinflammation

AIMS

Chronic hyperglycemia-induced inflammation of the hippocampus is an important cause of cognitive deficits in diabetic patients. The receptor for advanced glycation end products (RAGE), which is widely expressed in the hippocampus, is a crucial factor in this inflammation and the associated cognitive deficits. We aimed to reveal the underlying mechanism by which RAGE regulates neuroinflammation in the pathogenesis of diabetes-induced cognitive impairment.

METHODS

We used db/db mice as a model for type 2 diabetes to investigate whether receptor-interacting serine/threonine protein kinase 1 (RIPK1), which is expressed in microglia in the hippocampal region, is a key protein partner for RAGE. GST pull-down assays and AutoDock Vina simulations were performed to identify the key structural domain in RAGE that binds to RIPK1. Western blotting, co-immunoprecipitation (Co-IP), and immunofluorescence (IF) were used to detect the levels of key proteins or interaction between RAGE and RIPK1. Cognitive deficits in the mice were assessed with the Morris water maze (MWM) and new object recognition (NOR) and fear-conditioning tests.

RESULTS

RAGE binds directly to RIPK1 via the amino acid sequence (AAs) 362-367, thereby upregulating phosphorylation of RIPK1, which results in activation of the NLRP3 inflammasome in microglia and ultimately leads to cognitive impairments in db/db mice. We mutated RAGE AAs 362-367 to reverse neuroinflammation in the hippocampus and improve cognitive function, suggesting that RAGE AAs 362-367 is a key structural domain that binds directly to RIPK1. These results also indicate that hyperglycemia-induced inflammation in the hippocampus is dependent on direct binding of RAGE and RIPK1.

CONCLUSION

Direct interaction of RAGE and RIPK1 via AAs 362-367 is an important mechanism for enhanced neuroinflammation in the hyperglycemic environment and is a key node in the development of cognitive deficits in diabetes.

RAGE plays key role in diabetic retinopathy: a review

RAGE is a multiligand receptor for the immunoglobulin superfamily of cell surface molecules and is expressed in Müller cells, vascular endothelial cells, nerve cells and RPE cells of the retina. Diabetic retinopathy (DR) is a multifactorial disease associated with retinal inflammation and vascular abnormalities and is the leading cause of vision loss or impairment in older or working-age adults worldwide. Therapies aimed at reducing the inflammatory response and unnecessary angiogenesis can help slow the progression of DR, which in turn can save patients' vision. To maximize the efficacy and minimize the side effects, treatments that target key players in the pathophysiological process of DR need to be developed. The interaction between RAGE and its ligands is involved in a variety of cytopathological alterations in the retina, including secretion of inflammatory factors, regulation of angiogenesis, oxidative stress, structural and functional changes, and neurodegeneration. In this review, we will summarize the pathologic pathways mediated by RAGE and its ligand interactions and discuss its role in the progression of diabetic retinopathy to explore potential therapeutic targets that are effective and safe for DR.

RAGE Is a Receptor for SARS-CoV-2 N Protein and Mediates N Protein-induced Acute Lung Injury

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein (N-protein) increases early in body fluids during infection and has recently been identified as a direct inducer for lung injury. However, the signal mechanism of N-protein in the lung inflammatory response remains poorly understood. The goal of this study was to determine whether RAGE (receptor for advanced glycation endproducts) participated in N-protein-induced acute lung injury. The binding between N-protein and RAGE was examined via assays for protein-protein interaction. To determine the signaling mechanism in vitro, cells were treated with recombinant N-protein and assayed for the activation of the RAGE/MAPK (mitogen-activated protein kinase)/NF-ĸB pathway. RAGE deficiency mice and antagonist were used to study N-protein-induced acute lung injury in vivo. Binding between N-protein and RAGE was confirmed via flow cytometry-based binding assay, surface plasmon resonance, and ELISA. Pull-down and coimmunoprecipitation assays revealed that N-protein bound RAGE via both N-terminal and C-terminal domains. In vitro, N-protein activated the RAGE-ERK1/2-NF-ĸB signaling pathway and induced a proinflammatory response. RAGE deficiency subdued N-protein-induced proinflammatory signaling and response. In vivo, RAGE was upregulated in the BAL and lung tissue after recombinant N-protein insult. RAGE deficiency and small molecule antagonist partially protected mice from N-protein-induced acute lung injury. Our study demonstrated that RAGE is a receptor for N-protein. RAGE is partially responsible for N-protein-induced acute lung injury and has the potential to become a therapeutic target for treating coronavirus disease.

Receptors for Advanced Glycation End Products (RAGE): Promising Targets Aiming at the Treatment of Neurodegenerative Conditions

Advanced glycation end products (AGEs) are compounds formed after the non-enzymatic addition of reducing sugars to lipids, proteins, and nucleic acids. They are associated with the development of various clinical complications observed in diabetes and cardiovascular diseases, such as retinopathy, nephropathy, diabetic neuropathy, and others. In addition, compelling evidence indicates that these molecules participate in the progression of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Multiple cellular and molecular alterations triggered by AGEs that could alter homeostasis have been identified. One of the main targets for AGE signaling is the receptor for advanced glycation end-products (RAGE). Importantly, this receptor is the target of not only AGEs, but also amyloid β peptides, HMGB1 (high-mobility group box-1), members of the S100 protein family, and glycosaminoglycans. The activation of this receptor induces intracellular signaling cascades that are involved in pathological processes and cell death. Therefore, RAGE represents a key target for pharmacological interventions in neurodegenerative diseases. This review will discuss the various effects of AGEs and RAGE activation in the pathophysiology of neurodegenerative diseases, as well as the currently available pharmacological tools and promising drug candidates.

Role of RAGE and its ligand HMGB1 in the development of COPD

Smoking is a well-established risk factor for chronic obstructive pulmonary disease (COPD). Chronic lung inflammation continues even after smoking cessation and leads to COPD progression. To date, anti-inflammatory therapies are ineffective in improving pulmonary function and COPD symptoms, and new molecular targets are urgently needed to deal with this challenge. The receptor for advanced glycation end-products (RAGE) was shown to be relevant in COPD pathogenesis, since it is both a genetic determinant of low lung function and a determinant of COPD susceptibility. Moreover, RAGE is involved in the physiological response to cigarette smoke exposure. Since innate and acquired immunity plays an essential role in the development of chronic inflammation and emphysema in COPD, here we summarized the roles of RAGE and its ligand HMGB1 in COPD immunity.

Rab31, a receptor of advanced glycation end products (RAGE) interacting protein, inhibits AGE induced pancreatic β-cell apoptosis through the pAKT/BCL2 pathway

Receptor of advanced glycation end products (RAGE) mediates diverse signal transduction following ligand stimulation and plays an important role in diabetes complications and aging associated disease. We have previously verified that advanced glycation end products (AGE) bind to RAGE to cause pancreatic β-cell apoptosis through the mitochondrial pathway. However, the direct interacting protein(s) of RAGE in β cells has never been appreciated. In the present study, we utilized GST pull-down assay combined with mass spectrometry to identify the interacting proteins of the RAGE intracellular domain (C-terminal 43 amino acid of RAGE). Overall four RAGE interacting proteins, including Rab31, were identified with scores over 160. Rab31 was detected in three β-cell lines and confirmed to have interacted with RAGE via co-immunoprecipitation and immunostaining assays. This interaction was further enhanced by glycation-serum (GS) stimulation due to membrane distribution of Rab31 following treatment with GS. We further confirmed that Rab31 promoted RAGE endocytosis and inhibited GS-induced β-cell apoptosis through the pAKT/BCL2 pathway. These findings reveal a new RAGE interaction protein Rab31 that prevents AGE/RAGE-induced pancreatic β-cell apoptosis. Rab31 is therefore a promising therapeutic target for preserving functional β cells under diabetes conditions.

Hypoxia-induced HMGB1 promotes glioma stem cells self-renewal and tumorigenicity via RAGE

Glioma stem cells (GSCs) in the hypoxic niches contribute to tumor initiation, progression, and recurrence in glioblastoma (GBM). Hypoxia induces release of high-mobility group box 1 (HMGB1) from tumor cells, promoting the development of tumor. Here, we report that HMGB1 is overexpressed in human GBM specimens. Hypoxia promotes the expression and secretion of HMGB1 in GSCs. Furthermore, silencing HMGB1 results in the loss of stem cell markers and a reduction in self-renewal ability of GSCs. Additionally, HMGB1 knockdown inhibits the activation of RAGE-dependent ERK1/2 signaling pathway and arrests the cell cycle in GSCs. Consistently, FPS-ZM1, an inhibitor of RAGE, downregulates HMGB1 expression and the phosphorylation of ERK1/2, leading to a reduction in the proliferation of GSCs. In xenograft mice of GBM, HMGB1 knockdown inhibits tumor growth and promotes mouse survival. Collectively, these findings uncover a vital function for HMGB1 in regulating GSC self-renewal potential and tumorigenicity.

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Glioma stem cells overexpress HMGB1 in human glioblastoma

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Hypoxia induces the upregulation and release of HMGB1 in glioma stem cells

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HMGB1 promotes the self-renewal of glioma stem cells via RAGE

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Targeting HMGB1 inhibits the tumorigenesis of glioma stem cells

Therapeutic potential of targeting the receptor for advanced glycation end products (RAGE) by small molecule inhibitors

Receptor for advanced glycation end products (RAGE) is a 45 kDa transmembrane receptor of immunoglobulin family that can bind to various endogenous and exogenous ligands and initiate the inflammatory downstream signaling pathways. RAGE is involved in various disorders including cardiovascular and neurodegenerative diseases, cancer, and diabetes. This review summarizes the structural features of RAGE and its various isoforms along with their pathological effects. Mainly, the article emphasized on the translational significance of antagonizing the interactions of RAGE with its ligands using small molecules reported in the last 5 years and discusses future approaches that could be employed to block the interactions in the treatment of chronic inflammatory ailments. The RAGE inhibitors described in this article could prove as a powerful approach in the management of immune‐inflammatory diseases. A critical review of the literature suggests that there is a dire need to dive deeper into the molecular mechanism of action to resolve critical issues that must be addressed to understand RAGE‐targeting therapy and long‐term blockade of RAGE in human diseases.

A Dual Anti-Inflammatory and Anti-Proliferative 3-Styrylchromone Derivative Synergistically Enhances the Anti-Cancer Effects of DNA-Damaging Agents on Colon Cancer Cells by Targeting HMGB1-RAGE-ERK1/2 Signaling

The current anti-cancer treatments are not enough to eradicate tumors, and therefore, new modalities and strategies are still needed. Most tumors generate an inflammatory tumor microenvironment (TME) and maintain the niche for their development. Because of the critical role of inflammation via high-mobility group box 1 (HMGB1)–receptor for advanced glycation end-products (RAGE) signaling pathway in the TME, a novel compound possessing both anti-cancer and anti-inflammatory activities by suppressing the HMGB1-RAGE axis provides an effective strategy for cancer treatment. A recent work of our group found that some anti-cancer 3-styrylchromones have weak anti-inflammatory activities via the suppression of this axis. In this direction, we searched such anti-cancer molecules possessing potent anti-inflammatory activities and discovered 7-methoxy-3-hydroxy-styrylchromone (C6) having dual suppressive activities. Mechanism-of-action studies revealed that C6 inhibited the increased phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) under the stimulation of HMGB1-RAGE signaling and thereby suppressed cytokine production in macrophage-like RAW264.7 cells. On the other hand, in colorectal cancer HCT116 cells, C6 inhibited the activation of ERK1/2, cyclin-dependent kinase 1, and AKT, down-regulated the protein level of XIAP, and up-regulated pro-apoptotic Bax and caspase-3/7 expression. These alterations are suggested to be involved in the C6-induced suppression of cell cycle/proliferation and initiation of apoptosis in the cancer cells. More importantly, in cancer cells, the treatment of C6 potentiates the anti-cancer effects of DNA-damaging agents. Thus, C6 may be a promising lead for the generation of a novel class of cancer therapeutics.

Receptor for advanced glycation end products aggravates cognitive deficits in type 2 diabetes through binding of C-terminal AAs 2-5 to mitogen-activated protein kinase kinase 3 (MKK3) and facilitation of MEKK3-MKK3-p38 module assembly

In this study, we explored the precise mechanisms underlying the receptor for advanced glycation end products (RAGE)‐mediated neuronal loss and behavioral dysfunction induced by hyperglycemia. We used immunoprecipitation (IP) and GST pull‐down assays to assess the interaction between RAGE and mitogen‐activated protein kinase kinase 3 (MKK3). Then, we investigated the effect of specific mutation of RAGE on plasticity at hippocampal synapses and behavioral deficits in db/db mice through electrophysiological recordings, morphological assays, and behavioral tests. We discovered that RAGE binds MKK3 and that this binding is required for assembly of the MEKK3‐MKK3‐p38 signaling module. Mechanistically, we found that activation of p38 mitogen‐activated protein kinase (MAPK)/NF‐κB signaling depends on mediation of the RAGE‐MKK3 interaction by C‐terminal RAGE (ctRAGE) amino acids (AAs) 2‐5. We found that ctRAGE R2A‐K3A‐R4A‐Q5A mutation suppressed neuronal damage, improved synaptic plasticity, and alleviated behavioral deficits in diabetic mice by disrupting the RAGE‐MKK3 conjugation. High glucose induces direct binding of RAGE and MKK3 via ctRAGE AAs 2‐5, which leads to assembly of the MEKK3‐MKK3‐p38 signaling module and subsequent activation of the p38MAPK/NF‐κB pathway, and ultimately results in diabetic encephalopathy (DE).

Role and Therapeutic Potential of RAGE Signaling in Neurodegeneration

Activation of the receptor for advanced glycation end products (RAGE) has been shown to play an active role in the development of multiple neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis. Although originally identified as a receptor for advanced glycation end products, RAGE is a pattern recognition receptor able to bind multiple ligands. The final outcome of RAGE signaling is defined in a context and cell type specific manner and can exert both neurotoxic and neuroprotective functions. Contributing to the complexity of the RAGE signaling network, different RAGE isoforms with distinctive signaling capabilities have been described. Moreover, multiple RAGE ligands bind other receptors and RAGE antagonism can significantly affect their signaling. Here, we discuss the outcome of celltype specific RAGE signaling in neurodegenerative pathologies. In addition, we will review the different approaches that have been developed to target RAGE signaling and their therapeutic potential. A clear understanding of the outcome of RAGE signaling in a cell type- and disease-specific manner would contribute to advancing the development of new therapies targeting RAGE. The ability to counteract RAGE neurotoxic signaling while preserving its neuroprotective effects would be critical for the success of novel therapies targeting RAGE signaling.

Trimebutine suppresses Toll-like receptor 2/4/7/8/9 signaling pathways in macrophages

Because of the critical roles of Toll-like receptors (TLRs) and receptor for advanced glycation end-products (RAGE) in the pathophysiology of various acute and chronic inflammatory diseases, continuous efforts have been made to discover novel therapeutic inhibitors of TLRs and RAGE to treat inflammatory disorders. A recent study by our group has demonstrated that trimebutine, a spasmolytic drug, suppresses the high mobility group box 1‒RAGE signaling that is associated with triggering proinflammatory signaling pathways in macrophages. Our present work showed that trimebutine suppresses interleukin-6 (IL-6) production in lipopolysaccharide (LPS, a stimulant of TLR4)-stimulated macrophages of RAGE-knockout mice. In addition, trimebutine suppresses the LPS-induced production of various proinflammatory cytokines and chemokines in mouse macrophage-like RAW264.7 cells. Importantly, trimebutine suppresses IL-6 production induced by TLR2-and TLR7/8/9 stimulants. Furthermore, trimebutine greatly reduces mortality in a mouse model of LPS-induced sepsis. Studies exploring the action mechanism of trimebutine revealed that it inhibits the LPS-induced activation of IL-1 receptor-associated kinase 1 (IRAK1), and the subsequent activations of extracellular signal-related kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), and nuclear factor-κB (NF-κB). These findings suggest that trimebutine exerts anti-inflammatory effects on TLR signaling by downregulating IRAK1‒ERK1/2‒JNK pathway and NF-κB activity, thereby indicating the therapeutic potential of trimebutine in inflammatory diseases. Therefore, trimebutine can be a novel anti-inflammatory drug-repositioning candidate and may provide an important scaffold for designing more effective dual anti-inflammatory drugs that target TLR/RAGE signaling.

Role of Advanced Glycation End-Products and Other Ligands for AGE Receptors in Thyroid Cancer Progression

To date, thyroid cancers (TCs) remain a clinical challenge owing to their heterogeneous nature. The etiopathology of TCs is associated not only with genetic mutations or chromosomal rearrangements, but also non-genetic factors, such as oxidative-, nitrosative-, and carbonyl stress-related alterations in tumor environment. These factors, through leading to the activation of intracellular signaling pathways, induce tumor tissue proliferation. Interestingly, the incidence of TCs is often coexistent with various simultaneous mutations. Advanced glycation end-products (AGEs), their precursors and receptors (RAGEs), and other ligands for RAGEs are reported to have significant influence on carcinogenesis and TCs progression, inducing gene mutations, disturbances in histone methylation, and disorders in important carcinogenesis-related pathways, such as PI₃K/AKT/NF-kB, p21/MEK/MPAK, or JAK/STAT, RAS/ERK/p53, which induce synthesis of interleukins, growth factors, and cytokines, thus influencing metastasis, angiogenesis, and cancer proliferation. Precursors of AGE (such as methylglyoxal (MG)) and selected ligands for RAGEs: AS1004, AS1008, and HMGB1 may, in the future, become potential targets for TCs treatment, as low MG concentration is associated with less aggressive anaplastic thyroid cancer, whereas the administration of anti-RAGE antibodies inhibits the progression of papillary thyroid cancer and anaplastic thyroid cancer. This review is aimed at collecting the information on the role of compounds, engaged in glycation process, in the pathogenesis of TCs. Moreover, the utility of these compounds in the diagnosis and treatment of TCs is thoroughly discussed. Understanding the mechanism of action of these compounds on TCs pathogenesis and progression may potentially be the grounds for the development of new treatment strategies, aiming at quality-of-life improvements.

Dietary AGEs as Exogenous Boosters of Inflammation

Most chronic modern non-transmissible diseases seem to begin as the result of low-grade inflammation extending over prolonged periods of time. The importance of diet as a source of many pro-inflammatory compounds that could create and sustain such a low-grade inflammatory state cannot be ignored, particularly since we are constantly exposed to them during the day. The focus of this review is on specific components of the diet associated with inflammation, specifically advanced glycation end products (AGEs) that form during thermal processing of food. AGEs are also generated in the body in normal physiology and are widely recognized as increased in diabetes, but many people are unaware of the potential importance of exogenous AGEs ingested in food. We review experimental models, epidemiologic data, and small clinical trials that suggest an important association between dietary intake of these compounds and development of an inflammatory and pro-oxidative state that is conducive to chronic diseases. We compare dietary intake of AGEs with other widely known dietary patterns, such as the Mediterranean and the Dietary Approaches to Stop Hypertension (DASH) diets, as well as the Dietary Inflammation Index (DII). Finally, we delineate in detail the pathophysiological mechanisms induced by dietary AGEs, both direct (i.e., non-receptor-mediated) and indirect (receptor-mediated).

Molecular Characteristics of RAGE and Advances in Small-Molecule Inhibitors

Receptor for advanced glycation end-products (RAGE) is a member of the immunoglobulin superfamily. RAGE binds and mediates cellular responses to a range of DAMPs (damage-associated molecular pattern molecules), such as AGEs, HMGB1, and S100/calgranulins, and as an innate immune sensor, can recognize microbial PAMPs (pathogen-associated molecular pattern molecules), including bacterial LPS, bacterial DNA, and viral and parasitic proteins. RAGE and its ligands stimulate the activations of diverse pathways, such as p38MAPK, ERK1/2, Cdc42/Rac, and JNK, and trigger cascades of diverse signaling events that are involved in a wide spectrum of diseases, including diabetes mellitus, inflammatory, vascular and neurodegenerative diseases, atherothrombosis, and cancer. Thus, the targeted inhibition of RAGE or its ligands is considered an important strategy for the treatment of cancer and chronic inflammatory diseases.

A 3-styrylchromone converted from trimebutine 3D pharmacophore possesses dual suppressive effects on RAGE and TLR4 signaling pathways

Receptor for advanced glycation end-products (RAGE) and Toll-like receptors (TLRs) are potential therapeutic targets in the treatment of acute and chronic inflammatory diseases. We previously reported that trimebutine, a spasmolytic drug, suppresses RAGE pro-inflammatory signaling pathway in macrophages. The aim of this study was to convert trimebutine to a new small molecule using in silico 3D pharmacophore similarity search, and dissect the mechanistic anti-inflammatory basis. Of note, a unique 3-styrylchromone (3SC), 7-methoxy-3-trimethoxy-SC (7M3TMSC), converted from trimebutine 3D pharmacophore potently suppressed both high mobility group box 1-RAGE and lipopolysaccharide-TLR4 signaling pathways in macrophage-like RAW264.7 cells. More importantly, 7M3TMSC inhibited the phosphorylation of extracellular signaling-regulated kinase 1 and 2 (ERK1/2) and downregulated the production of cytokines, such as interleukin-6. Furthermore, 3D pharmacophore-activity relationship analyses revealed that the hydrogen bond acceptors of the trimethoxy groups in a 3-styryl moiety and the 7-methoxy-group in a chromone moiety in this compound are significant in the dual anti-inflammatory activity. Thus, 7M3TMSC may provide an important scaffold for the development of a new type of anti-inflammatory dual effective drugs targeting RAGE/TLR4-ERK1/2 signaling.

A model of full-length RAGE in complex with S100B

The receptor for advanced glycation end products (RAGE) is an immunoglobulin-type multiligand transmembrane protein expressed in numerous cell types, including the central nervous system cells. RAGE interaction with S100B, released during brain tissue damage, leads to RAGE upregulation and initialization of a spiral proinflammatory associated with different neural disorders. Here, we present the structural characterization of the hetero-oligomeric complex of the full-length RAGE with S100B, obtained by a combination of mass spectrometry-based methods and molecular modeling. We predict that RAGE functions as a tightly packed tetramer exposing a positively charged surface formed by V domains for S100B binding. Based on HDX results we demonstrate an allosteric coupling of the distal extracellular V domains and the transmembrane region, indicating a possible mechanism of signal transmission by RAGE across the membrane. Our model provides an insight into RAGE-ligand interactions, providing a basis for the rational design of the therapeutic modifiers of its activity.

A Unique Anti-Cancer 3-Styrylchromone Suppresses Inflammatory Response via HMGB1-RAGE Signaling

Background: High mobility group box 1 (HMGB1)-receptor for advanced glycation endo-products (RAGE) axis serves as a key player in linking inflammation and carcinogenesis. Recently, papaverine was revealed to suppress the HMGB1-RAGE inflammatory signaling pathway and cancer cell proliferation. Therefore, a dual suppressor targeting this axis is expected to become a new type of therapeutic agent to treat cancer. Methods: Papaverine 3D pharmacophore mimetic compounds were selected by the LigandScout software from our in-house, anti-cancer chemical library and assessed for their anti-inflammatory activities by a HMGB1-RAGE-mediated interleukin-6 production assay using macrophage-like RAW264.7 cells. Molecular-biological analyses, such as Western blotting, were performed to clarify the mechanism of action. Results: A unique 6-methoxy-3-hydroxy-styrylchromone was found to possess potent anti-inflammatory and anti-cancer activities via the suppression of the HMGB1-RAGE-extracellular signal-regulated kinase 1/2 signaling pathway. Furthermore, the 3D pharmacophore-activity relationship analyses revealed that the hydroxyl group at the C4′ position of the benzene ring in a 3-styryl moiety was significant in its dual suppressive effects. Conclusions: These findings indicated that this compound may provide a valuable scaffold for the development of a new type of anti-cancer drug possessing anti-inflammatory activity and as a tool for understanding the link between inflammation and carcinogenesis.

Targeting adaptor protein SLP76 of RAGE as a therapeutic approach for lethal sepsis

Accumulating evidence shows that RAGE has an important function in the pathogenesis of sepsis. However, the mechanisms by which RAGE transduces signals to downstream kinase cascades during septic shock are not clear. Here, we identify SLP76 as a binding partner for the cytosolic tail of RAGE both in vitro and in vivo and demonstrate that SLP76 binds RAGE through its sterile α motif (SAM) to mediate downstream signaling. Genetic deficiency of RAGE or SLP76 reduces AGE-induced phosphorylation of p38 MAPK, ERK1/2 and IKKα/β, as well as cytokine release. Delivery of the SAM domain into macrophages via the TAT cell-penetrating peptide blocks proinflammatory cytokine production. Furthermore, administration of TAT-SAM attenuates inflammatory cytokine release and tissue damage in mice subjected to cecal ligation and puncture (CLP) and protects these mice from the lethality of sepsis. These findings reveal an important function for SLP76 in RAGE-mediated pro-inflammatory signaling and shed light on the development of SLP76-targeted therapeutics for sepsis.

The receptor for advanced glycation end products is a sensor for cell-free heme

Heme's interaction with Toll-like receptor 4 (TLR4) does not fully explain the proinflammatory properties of this hemoglobin-derived molecule during intravascular hemolysis. The receptor for advanced glycation end products (RAGE) shares many features with TLR4 such as common ligands and proinflammatory, prothrombotic, and pro-oxidative signaling pathways, prompting us to study its involvement as a heme sensor. Stable RAGE-heme complexes with micromolar affinity were detected as heme-mediated RAGE oligomerization. The heme-binding site was located in the V domain of RAGE. This interaction was Fe³⁺ -dependent and competitive with carboxymethyllysine, another RAGE ligand. We confirmed a strong basal gene expression of RAGE in mouse lungs. After intraperitoneal heme injection, pulmonary TNF-α, IL1β, and tissue factor gene expression levels increased in WT mice but were significantly lower in their RAGE^-/- littermates. This may be related to the lower activation of ERK1/2 and Akt observed in the lungs of heme-treated, RAGE^-/- mice. Overall, heme binds to RAGE with micromolar affinity and could promote proinflammatory and prothrombotic signaling in vivo, suggesting that this interaction could be implicated in heme-overload conditions.

Endothelial Dysfunction in Diabetes Is Aggravated by Glycated Lipoproteins; Novel Molecular Therapies

Diabetes and its vascular complications affect an increasing number of people. This disease of epidemic proportion nowadays involves abnormalities of large and small blood vessels, all commencing with alterations of the endothelial cell (EC) functions. Cardiovascular diseases are a major cause of death and disability among diabetic patients. In diabetes, EC dysfunction (ECD) is induced by the pathological increase of glucose and by the appearance of advanced glycation end products (AGE) attached to the plasma proteins, including lipoproteins. AGE proteins interact with their specific receptors on EC plasma membrane promoting activation of signaling pathways, resulting in decreased nitric oxide bioavailability, increased intracellular oxidative and inflammatory stress, causing dysfunction and finally apoptosis of EC. Irreversibly glycated lipoproteins (AGE-Lp) were proven to have an important role in accelerating atherosclerosis in diabetes. The aim of the present review is to present up-to-date information connecting hyperglycemia, ECD and two classes of glycated Lp, glycated low-density lipoproteins and glycated high-density lipoproteins, which contribute to the aggravation of diabetes complications. We will highlight the role of dyslipidemia, oxidative and inflammatory stress and epigenetic risk factors, along with the specific mechanisms connecting them, as well as the new promising therapies to alleviate ECD in diabetes.

Circulating soluble receptor for advanced glycation end products and other factors in type 2 diabetes patients with colorectal cancer

BACKGROUND

Recent study showed that individuals with type 2 diabetes have a high risk of developing colorectal cancer (CRC), in which Receptor for Advanced Glycation End Products (RAGE) plays a pivotal role. We conducted a cross-sectional study to examine the relationships of circulating sRAGE, CRC and other clinical factors in type2 diabetes patients.

METHODS

A total of 150 type 2 diabetes patients aged 50 years and older were enrolled, including 50 patients with CRC and 100 patients without CRC. We measured Serum levels of sRAGE and interleukin-6(IL-6) using an enzyme-linked immunosorbent assay (ELISA). In addition, other clinical parameters were also measured during hospitalization.

RESULTS

Type 2 diabetes patients with CRC had higher triglyceride, total cholesterol, IL-6, and circulating sRAGE levels and lower use of medicines than type 2 diabetes patients without CRC. Circulating sRAGE was associated with an increased risk for CRC (OR = 2.289 for each SD increase in sRAGE, 95% CI = 1.037-5.051; P = 0.04) among Type 2 diabetes patients after adjustment for confounders. Furthermore, circulating sRAGE levels among type 2 diabetes patients were positively correlated with triglyceride (r = 0.377, P < 0.001), total cholesterol (r = 0.491, P < 0.001), and low-density lipoprotein cholesterol (LDL-c)(r = 0.330, P < 0.001) levels; the homeostatic model assessment for insulin resistance(HOMA-IR)score (r = 0.194, P = 0.017); and fasting serum insulin (r = 0.167, P = 0.041) and IL-6 (r = 0.311, P < 0.001) concentrations.

CONCLUSIONS

Our results suggested that circulating sRAGE is independently risk factor for CRC, and also closely related to inflammation, dyslipidemia in type 2 diabetes patients.

Circulating Ligands of the Receptor for Advanced Glycation End Products and the Soluble Form of the Receptor Modulate Cardiovascular Cell Apoptosis in Diabetes

We determined whether plasma concentrations of the receptor for advanced glycation end products (RAGE) and the soluble (s) form of RAGE (sRAGE) in healthy individuals and patients with type 2 diabetes (T2D) modulate vascular remodeling. Healthy individuals and patients with T2D were divided into two age groups: young = <35 years old or middle-aged (36-64 years old) and stratified based on normal glucose tolerance (NGT), impaired (IGT), and T2D. Plasma titers of sRAGE, the RAGE ligands, AGEs, S100B, S100A1, S100A6, and the apoptotic marker Fas ligand Fas(L) were measured by enzyme-linked immunosorbent assay (ELISA). The apoptotic potential of the above RAGE ligands and sRAGE were assessed in cultured adult rat aortic smooth muscle cells (ASMC). In NGT individuals, aging increased the circulating levels of AGEs and S100B and decreased sRAGE, S100A1 and S100A6. Middle-aged patients with T2D presented higher levels of circulating S100B, AGEs and FasL, but lower levels of sRAGE, S100A1 and S100A6 than individuals with NGT or IGT. Treatment of ASMC with either AGEs or S100B at concentrations detected in T2D patients increased markers of inflammation and apoptosis. Responses attenuated by concomitant administration of sRAGE. In middle-aged patients with T2D, lower circulating plasma levels of sRAGE may limit decoy and exogenous trapping of deleterious pro-apoptotic/pro-inflammatory RAGE ligands AGEs and S100B, increasing the risk for diabetic complications.

Trimebutine attenuates high mobility group box 1-receptor for advanced glycation end-products inflammatory signaling pathways

We previously identified papaverine as an inhibitor of receptor for advanced glycation end-products (RAGE) and showed its suppressive effect on high mobility group box 1 (HMGB1)-mediated responses to inflammation. Here, we found trimebutine to be a 3D pharmacophore mimetics of papaverine. Trimebutine was revealed to have more potent suppressive effects on HMGB1-induced production of pro-inflammatory cytokines, such as interleukin-6 and tumor necrosis factor-α in macrophage-like RAW264.7 cells and mouse bone marrow primarily differentiated macrophages than did papaverine. However, the inhibitory effect of trimebutine on the interaction of HMGB1 and RAGE was weaker than that of papaverine. Importantly, mechanism-of-action analyses revealed that trimebutine strongly inhibited the activation of RAGE downstream inflammatory signaling pathways, especially the activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2), which are mediator/effector kinases recruited to the intracellular domain of RAGE. Consequently, the activation of Jun amino terminal kinase, which is an important effector kinase for the up-regulation of pro-inflammatory cytokines, was inhibited. Taken together, these results suggest that trimebutine may exert its suppressive effect on the HMGB1-RAGE inflammatory signal pathways by strongly blocking the recruitment of ERK1/2 to the intracellular tail domain of RAGE in addition to its weak inhibition of the extracellular interaction of HMGB1 with RAGE. Thus, trimebutine may provide a unique scaffold for the development of novel dual inhibitors of RAGE for inflammatory diseases.

Involvement of glycated albumin in adipose-derived-stem cell-mediated interleukin 17 secreting T helper cell activation

BACKGROUND

Advanced glycation end products (AGE) are a marker of various diseases including diabetes, in which they participate to vascular damages such as retinopathy, nephropathy and coronaropathy. Besides those vascular complications, AGE are involved in altered metabolism in many tissues, including adipose tissue (AT) where they contribute to reduced glucose uptake and attenuation of insulin sensitivity. AGE are known to contribute to type 1 diabetes (T1D) through promotion of interleukin (IL)-17 secreting T helper (Th17) cells.

AIM

To investigate whether lean adipose-derived stem cells (ASC) could be able to induce IL-17A secretion, with the help of AGE.

METHODS

As we have recently demonstrated that ASC are involved in Th17 cell promotion when they are harvested from obese AT, we used the same co-culture model to measure the impact of glycated human serum albumin (G-HSA) on human lean ASC interacting with blood mononuclear cells. IL-17A and pro-inflammatory cytokine secretion were measured by ELISA. Receptor of AGE (RAGE) together with intercellular adhesion molecule 1 (ICAM-1), human leukocyte Antigen (HLA)-DR, cluster of differentiation (CD) 41, and CD62P surface expressions were measured by cytofluorometry. Anti-RAGE specific monoclonal antibody was added to co-cultures in order to evaluate the role of RAGE in IL-17A production.

RESULTS

Results showed that whereas 1% G-HSA only weakly potentiated the production of IL-17A by T cells interacting with ASC harvested from obese subjects, it markedly increased IL-17A, but also interferon gamma and tumor necrosis factor alpha production in the presence of ASC harvested from lean individuals. This was associated with increased expression of RAGE and HLA-DR molecule by co-cultured cells. Moreover, RAGE blockade experiments demonstrated RAGE specific involvement in lean ASC-mediated Th-17 cell activation. Finally, platelet aggregation and ICAM-1, which are known to be induced by AGE, were not involved in these processes.

CONCLUSION

Thus, our results demonstrated that G-HSA potentiated lean ASC-mediated IL-17A production in AT, suggesting a new mechanism by which AGE could contribute to T1D pathophysiology.

A RAGE-antagonist peptide potentiates polymeric micelle-mediated intracellular delivery of plasmid DNA for acute lung injury gene therapy

Acute lung injury (ALI) is a severe inflammatory lung disease. A high mobility group box-1 (HMGB-1) derived RAGE-antagonist peptide (RAP) was previously developed for anti-inflammatory therapy for ALI. Due to its specific binding to RAGE on the surface of inflammatory cells, the RAP may facilitate polymer-mediated intracellular delivery of plasmid DNA (pDNA) into the inflammatory cells. To evaluate this hypothesis, a pDNA/polymer/RAP ternary-complex was produced and applied for ALI gene therapy. Dexamethasone-conjugated polyamidoamine G2 (PAM-D) was used as a gene carrier, and the adiponectin (APN) gene was employed as a therapeutic gene. First, the ratio of pDNA to PAM-D was optimized in terms of anti-inflammation and low toxicity. Then, the RAP was added to the pDNA/PAM-D complex, producing the pDNA/PAM-D/RAP complex. The transfection efficiency of the luciferase plasmid (pLuc)/PAM-D/RAP reached its maximum at a weight ratio of 1 : 2 : 9. At this weight ratio, pLuc/PAM-D/RAP had a higher transfection efficiency than pLuc/PAM-D or pLuc/RAP. The transfection efficiency of pLuc/PAM-D/RAP decreased due to competition with free RAPs, suggesting the RAGE-mediated endocytosis of the complex. In the LPS-activated ALI mouse models, intratracheal administration of APN plasmid (pAPN)/PAM-D/RAP induced higher APN expression and less pro-inflammatory cytokines in the lungs of ALI animal models than pAPN/PEI25k, pAPN/RAP, and pAPN/PAM-D. Hematoxylin and eosin staining confirmed the higher anti-inflammatory effect of pAPN/PAM-D/RAP than the other complexes in the ALI models. Therefore, RAP-mediated enhanced delivery of pAPN/PAM-D may be useful for the development of a treatment for ALI.

Role of Advanced Glycation End Products in Carcinogenesis and their Therapeutic Implications

Aging is one of the biggest risk factors for the major prevalent diseases such as cardiovascular diseases, neurodegeneration and cancer, but due to the complex and multifactorial nature of the aging process, the molecular mechanisms underlying age-related diseases are not yet fully understood. Research has been intensive in the last years aiming to characterize the pathophysiology of aging and develop therapies to fight age-related diseases. In this context advanced glycation end products (AGEs) have received attention. AGEs, when accumulated in tissues, significantly increase the level of inflammation in the body which has long been associated with the development of cancer. Here we discuss the classical settings promoting AGE formation, as well as reduction strategies, occurrence and relevance of AGEs in cancer tissues and the role of AGE-interaction with the receptor for advanced glycation end products (RAGE) in cancer initiation and progression.

Dynamic oligomerization of hRAGE's transmembrane and cytoplasmic domains within SDS micelles

The human Receptor for Advanced Glycation End Products (hRAGE) is a pattern recognition receptor implicated in inflammation and adhesion. It is involved in both innate and adaptive immunity. Its aberrant signaling is tied to the pathogenesis of diabetic complications, neurodegenerative disorders, and chronic inflammatory responses. Previous structural studies have focused on its extracellular domains with their canonical constant and variable Ig folds, and to a much lesser extent, the intrinsically disorder cytoplasmic domain. No experimental data are reported on the transmembrane domain, which is integral to signaling. We have constructed, expressed and purified the transmembrane domain attached to the cytoplasmic domain of hRAGE in E. coli. Multiple self-associated forms of these domains were observed in vitro. This pattern of mixed oligomers resembled previously reported in vivo forms of the complete receptor. The self-association of these two domains was further characterized using: SDS-PAGE, intrinsic tryptophan fluorescence and heteronuclear NMR spectroscopy. NMR conditions were assessed across time and temperature within micelles. Our data show that the transmembrane and cytoplasmic domains of hRAGE undergo dynamic oligomerizations that can occur in the absence of its extracellular domains or ligand binding. And, such associations are only partially disrupted even with prolonged incubation in strong detergents.

HMGB1/RAGE pro-inflammatory axis promotes vascular endothelial cell apoptosis in limb ischemia/reperfusion injury

OBJECTIVE

High-Mobility Group Box 1 (HMGB1) promotes vascular injuries induced by limb Ischemia and Reperfusion (IR), but the molecular mechanisms are not well understood. This study aimed to investigate the role of Receptor for Advanced-Glycation End products (RAGE) in HMGB1-regulated inflammatory response and vascular injury in limb IR using the rat IR and cellular Hypoxia and Reoxygenation (HR) models.

METHODS

We analyzed the vascular structure and elastic fiber deposition in rat femoral arteries by histological staining. We determined gene expression in vascular tissues and cells by quantitative RT-PCR, Western blotting and immunofluorescence; analyzed the protein levels in rat serum or cell supernatant by ELISA; and assessed protein interaction by co-immunoprecipitation. We used CCK-8 for analyzing cell viability, and assessed apoptosis by Hoechst staining and flow cytometry.

RESULTS

RAGE inhibition by FPS-ZM1 significantly repressed rat vascular injury that was induced by limb IR treatment. HMGB1 and RAGE expression, P38, ERK1/2, P65 and IKBa phosphorylation, as well as HIF-1a, NLRP3, Caspase-1, TNF-a and IL-6 expression and P65 in nucleus, increased in femoral arteries of a rat IR model and HUVEC undergoing HR treatment, whereas all the factors except HMGB1 and RAGE were inhibited by FPS-ZM1 treatment. In addition, we found that HMGB1 binds with RAGE in HUVEC undergoing HR treatment, which was suppressed by FPS-ZM1. Finally, the apoptosis of HUVEC also increased by HR treatment, but repressed under FPS-ZM1 treatment.

CONCLUSION

HMGB1 binds with RAGE to promote vascular inflammation and endothelial cell apoptosis, which mediates vascular injury during acute limb IR.

Inhalable Gene Delivery System Using a Cationic RAGE-Antagonist Peptide for Gene Delivery to Inflammatory Lung Cells

Acute lung injury (ALI) is a severe lung inflammatory disease. In ALI, the receptor for advanced glycation end-products (RAGE) is overexpressed in lung epithelial cells and involved in inflammatory reactions. A previous report showed that a RAGE-antagonist peptide (RAP), from high-mobility group box-1, bound to RAGE and reduced inflammatory reactions. RAP has high levels of positive amino acids, which suggests that RAP may form a complex with plasmid DNA (pDNA) by charge interactions. Because the charge density of RAP is lower than polyethylenimine (25 kDa, PEI25k), it may be able to avoid capture by the negatively charged mucus layer more easily and deliver pDNA into RAGE-positive lung cells of ALI animals by RAGE-mediated endocytosis. To prove this hypothesis, RAP was evaluated as a delivery carrier of adiponectin plasmid (pAPN) in lipopolysaccharide (LPS)-induced ALI animal models. In vitro transfection assays showed that RAP had lower transfection efficiency than PEI25k in L2 lung epithelial cells. However, in vivo administration to ALI animal models by inhalation showed that RAP had higher gene delivery efficiency than PEI25k. Particularly, due to a higher expression of RAGE in lung cells of ALI animals, the gene delivery efficiency of RAP was higher in ALI animals than that in normal animals. Delivery of the pAPN/RAP complex had anti-inflammatory effects, reducing pro-inflammatory cytokines. Hematoxylin and eosin staining confirmed that pAPN/RAP decreased inflammation in ALI models. Therefore, the results suggest that RAP may be useful as a carrier of pDNA into the lungs for ALI gene therapy.

Nitroxidized-Albumin Advanced Glycation End Product and Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease whose major clinical consequence is inflammation of small joints and contiguous structures. Oxidative and nitrosative stress along with increased formation of advanced glycation end products (AGEs) play an important role in the disease process. Generation of reactive species during glycation of proteins further adds to the oxidative and nitrosative stress. Albumin, being the most abundant plasma protein, is frequently targeted by different oxidizing and nitrating agents, including peroxynitrite (OONO-) anion. Albumin is also targeted and modified by dicarbonyl metabolites (glyoxal and methylglyoxal) which are formed in oxidative and non-oxidative processes during the synthesis of AGEs. The endogenously formed OONO- and dicarbonyls may modify plasma albumin including those albumin that have travelled or migrated to synovial cells and caused nitration, oxidation, and glycation. These modifications may produce crosslinks, aggregate in albumin and confer immunogenicity. Simultaneous modification of albumin by OONO- and dicarbonyls may generate nitroxidized-AGE-albumin which may persist in circulation for a longer duration compared to native albumin. Nitroxidized-AGE-albumin level (or serum autoantibodies against nitroxidized- AGE-albumin) along with other pre-clinical features may help predict the likely onset of RA.

Cell-Matrix Interactions and Matricrine Signaling in the Pathogenesis of Vascular Calcification

Vascular calcification is a complex pathological process occurring in patients with atherosclerosis, type 2 diabetes, and chronic kidney disease. The extracellular matrix, via matricrine-receptor signaling plays important roles in the pathogenesis of calcification. Calcification is mediated by osteochondrocytic-like cells that arise from transdifferentiating vascular smooth muscle cells. Recent advances in our understanding of the plasticity of vascular smooth muscle cell and other cells of mesenchymal origin have furthered our understanding of how these cells transdifferentiate into osteochondrocytic-like cells in response to environmental cues. In the present review, we examine the role of the extracellular matrix in the regulation of cell behavior and differentiation in the context of vascular calcification. In pathological calcification, the extracellular matrix not only provides a scaffold for mineral deposition, but also acts as an active signaling entity. In recent years, extracellular matrix components have been shown to influence cellular signaling through matrix receptors such as the discoidin domain receptor family, integrins, and elastin receptors, all of which can modulate osteochondrocytic differentiation and calcification. Changes in extracellular matrix stiffness and composition are detected by these receptors which in turn modulate downstream signaling pathways and cytoskeletal dynamics, which are critical to osteogenic differentiation. This review will focus on recent literature that highlights the role of cell-matrix interactions and how they influence cellular behavior, and osteochondrocytic transdifferentiation in the pathogenesis of cardiovascular calcification.

JNK and ATF4 as two important platforms for tumor necrosis factor-α-stimulated shedding of receptor for advanced glycation end products

Soluble receptor for advanced glycation end products (sRAGE), shed from cell surfaces, is found in human circulation and has been implicated in cardiovascular disease. Its pathophysiological regulation and underlying mechanisms are scarcely understood. In endothelium-specific human RAGE transgenic mice, human sRAGE was detected in circulation, whereas its level was markedly increased after LPS treatment. That increase was preceded by a rapid rise in TNF-α level. Treatment with TNF-α also significantly increased serum sRAGE. In human microvascular endothelial cells or human umbilical vein endothelial cells with RAGE overexpression, TNF-α markedly induced RAGE shedding, which was dependent on MMP9 and ADAM10. TNF-α-stimulated MMP9 expression was completely dependent on JNK activation, with its inhibition partially effective in suppressing TNF-α-induced RAGE shedding. In contrast, TNF-α transiently induced activation transcription factor (ATF)4, a major component in unfolded protein response (UPR), whereas knockdown of ATF4 abrogated TNF-α-stimulated RAGE shedding. Protein levels of the pro and activated forms of ADAM10 were also decreased by ATF4 knockdown, whereas inhibition of other components of UPR, including XBP1 and ATF6, failed to block TNF-α-stimulated RAGE shedding. Although the endoplasmic reticulum stressors thapsigargin and tunicamycin induced markedly and sustained expression of ATF4 and XBP-1, they did not induce RAGE shedding to the same level as TNF-α, suggesting that ATF4 is necessary but not sufficient alone for TNF-α-mediated RAGE shedding. ATF4 inhibition did not affect TNF-α-stimulated MMP9 expression, whereas inhibition of JNK activity did not influence ADAM10 activation. Thus, inflammatory cascades including TNF-α induced RAGE shedding in endothelial cells in vivo and in vitro. JNK and ATF4 may be 2 platforms for regulation of TNF-α-stimulated RAGE shedding.-Miyoshi, A., Koyama, S., Sasagawa-Monden, M., Kadoya, M., Konishi, K., Shoji, T., Inaba, M., Yamamoto, Y., Koyama, H. JNK and ATF4 as two important platforms for tumor necrosis factor-α-stimulated shedding of receptor for advanced glycation end products.

Diaphanous-1 affects the nanoscale clustering and lateral diffusion of receptor for advanced glycation endproducts (RAGE)

The interactions between the cytoplasmic protein diaphanous-1 (Diaph1) and the receptor for advanced glycation endproducts (RAGE) drive the negative consequences of RAGE signaling in several disease processes. Reported in this work is how Diaph1 affects the nanoscale clustering and diffusion of RAGE measured using super-resolution stochastic optical reconstruction microscopy (STORM) and single particle tracking (SPT). Altering the Diaph1 binding site has a different impact on RAGE diffusion compared to when Diaph1 expression is reduced in HEK293 cells. In cells with reduced Diaph1 expression (RAGE-Diaph1^-/-), the average RAGE diffusion coefficient is increased by 35%. RAGE diffusion is known to be influenced by the dynamics of the actin cytoskeleton. Actin labeling shows that a reduced Diaph1 expression leads to cells with reduced filopodia density and length. In contrast, when two RAGE amino acids that interact with Diaph1 are mutated (RAGE_RQ/AA), the average RAGE diffusion coefficient is decreased by 16%. Since RAGE diffusion is slowed when the interaction between Diaph1 and RAGE is disrupted, the interaction of the two proteins results in faster RAGE diffusion. In both RAGE_RQ/AA and RAGE-Diaph1^-/- cells the number and size of RAGE clusters are decreased compared to cells expressing RAGE and native concentrations of Diaph1. This work shows that Diaph1 has a role in affecting RAGE clusters and diffusion.

Phosphorylation of low density lipoprotein receptor-related protein 6 is involved in receptor for advanced glycation end product-mediated β-catenin stabilization in a toluene diisocyanate-induced asthma model

BACKGROUND

We have previously demonstrated that the receptor for advanced glycation end products (RAGE)/β-catenin axis plays a vital role in regulating airway inflammation and airway remodeling in a toluene diisocyanate (TDI)-induced murine asthma model. However, the exact mechanism of β-catenin activation remains unclear. Given that phosphorylation of the low-density lipoprotein receptor-related protein 6 (Lrp6) is a key step in mediating β-catenin stabilization in canonical wnt/β-catenin signaling, we explored the possible relationship between RAGE and Lrp6 in regulating β-catenin stabilization in TDI-induced asthma.

METHODS

In this study, a TDI-induced murine asthma model was generated, and mice were treated with a specific inhibitor of RAGE. In vitro, the human bronchial epithelial cell line 16HBE was treated with TDI-human serum albumin (TDI-HSA). RAGE overexpression or knockdown cells were also constructed and assessed.

RESULTS

The results showed that RAGE inhibition or RAGE knockdown decreased β-catenin nuclear accumulation and the expression of relevant β-catenin targeted genes (VEGF, MMP9, TGF-β1) in the TDI-induced murine asthma model and TDI-HSA-treated 16HBE cells, respectively. Silencing of RAGE reversed the TDI-induced increase in phospho-ERK1/2 (p-ERK) and phospho-Lrp6 (p-Lrp6) in 16HBE cells. Pretreatment with the extracellular signal-regulated kinase (ERK)1/2 inhibitor U0126 suppressed TDI-induced Lrp6 phosphorylation. Furthermore, knockdown of Lrp6 in 16HBE cells decreased β-catenin nuclear translocation and the expression of VEGF, MMP9, and TGF-β1.

CONCLUSION

These data suggested that the RAGE/ERK axis modulates Lrp6 phosphorylation, contributing to β-catenin stabilization in a TDI-induced murine model.

Homeostatic nuclear RAGE-ATM interaction is essential for efficient DNA repair

The integrity of genome is a prerequisite for healthy life. Indeed, defects in DNA repair have been associated with several human diseases, including tissue-fibrosis, neurodegeneration and cancer. Despite decades of extensive research, the spatio-mechanical processes of double-strand break (DSB)-repair, especially the auxiliary factor(s) that can stimulate accurate and timely repair, have remained elusive. Here, we report an ATM-kinase dependent, unforeseen function of the nuclear isoform of the Receptor for Advanced Glycation End-products (nRAGE) in DSB-repair. RAGE is phosphorylated at Serine³⁷⁶ and Serine³⁸⁹ by the ATM kinase and is recruited to the site of DNA-DSBs via an early DNA damage response. nRAGE preferentially co-localized with the MRE11 nuclease subunit of the MRN complex and orchestrates its nucleolytic activity to the ATR kinase signaling. This promotes efficient RPA2^S4-S8 and CHK1^S345 phosphorylation and thereby prevents cellular senescence, IPF and carcinoma formation. Accordingly, loss of RAGE causatively linked to perpetual DSBs signaling, cellular senescence and fibrosis. Importantly, in a mouse model of idiopathic pulmonary fibrosis (RAGE^−/−), reconstitution of RAGE efficiently restored DSB-repair and reversed pathological anomalies. Collectively, this study identifies nRAGE as a master regulator of DSB-repair, the absence of which orchestrates persistent DSB signaling to senescence, tissue-fibrosis and oncogenesis.

Targeting RAGE Signaling in Inflammatory Disease

The receptor for advanced glycation end-products (RAGE) is a multiligand pattern recognition receptor implicated in diverse chronic inflammatory states. RAGE binds and mediates the cellular response to a range of damage-associated molecular pattern molecules (DAMPs) including AGEs, HMGB1, S100s, and DNA. RAGE can also act as an innate immune sensor of microbial pathogen-associated molecular pattern molecules (PAMPs) including bacterial endotoxin, respiratory viruses, and microbial DNA. RAGE is expressed at low levels under normal physiology, but it is highly upregulated under chronic inflammation because of the accumulation of various RAGE ligands. Blocking RAGE signaling in cell and animal models has revealed that targeting RAGE impairs inflammation and progression of diabetic vascular complications, cardiovascular disease (CVD), and cancer progression and metastasis. The clinical relevance of RAGE in inflammatory disease is being demonstrated in emerging clinical trials of novel small-molecule RAGE inhibitors.

Activation of the receptor for advanced glycation end products and consequences on health

Advanced glycation end products (AGE) resulted from a reaction between free amino group of proteins and carbohydrates. This reaction is followed by oxidation and molecular rearrangement. Alternatively AGEs can be produced by glycolysis and oxidation. AGEs bind to a cellular receptor RAGE. RAGE engagement by ligands AGE, β-amyloid peptide, and S100 calgranulin induces a stimulation of NADPH oxidase, reactive oxygen intermediate formation, NFκB activation and gene transcription. This cascade of reaction leads to an inflammatory reaction responsible for alteration of microvessels in the retina and the kidney. Blockade of RAGE by antibodies anti-RAGE, TTP488 (azeliragon), or rRAGE prevents or limits the deleterious effect of AGEs.

High mobility group B1 up-regulates angiogenic and fibrogenic factors in human retinal pigment epithelial ARPE-19 cells

Hypoxia-induced retinal neovascularization plays a central role in the pathogenesis of diabetic retinopathy. This study aimed to investigate whether hypoxia leads to the release of nuclear high mobility group box 1 (HMGB1) peptides from cultured retinal pigment epithelial ARPE-19 cells, to determine the effect of HMGB1 on angiogenic cytokine production and elucidate the involved signaling pathways. A chemical hypoxia mimetic agent, cobalt chloride, induced SIRT1 downregulation, HMGB1 nucleocytoplasmic relocation and extracellular release from ARPE-19 cells, implicating its autocrine function. Resveratrol treatment significantly reduced secretion of HMGB1 from ARPE-19 cells exposed to hypoxia. Cell proliferation and cell cycle analyses demonstrated that exogenous HMGB1 caused significant growth suppression and G1 cell cycle arrest in ARPE-19 cells. Morphological observations showed that HMGB1 enhanced adhesion, but suppressed migration of ARPE-19 cells. More intriguingly, HMGB1 up-regulated expression of angiofibrogenic factors in ARPE-19 cells, including VEGF, bFGF, TGF-β2, and CTGF. Signal profiling characterization indicated that HMGB1 triggered hyperphosphorylation of Akt, p38 MAPK, and NF-κB, but not that of ERK, JNK, and Smad2, whereas inhibition of PI3K, MAPK, or NF-κB significantly attenuated the HMGB1-driven cytokine overproduction in ARPE-19 cells. Functional neutralization with anti-TLR4 and -RAGE antibodies confirmed that both receptors were involved in the cytokine overproduction. In conclusion, chemically-mimicked hypoxia induced nucleocytoplasmic relocation and release of HMGB1 peptides, which in turn up-regulated the production of angiofibrogenic factors in RPE cells, thereby contributing to the pathogenesis of hypoxia-associated diabetic retinopathies. Conversely, blockades of intraocular HMGB1 bioavailability or signal activation may prevent angiofibrogenesis in development of diabetic retinopathy.

Targeted inhibition of RAGE in substantia nigra of rats blocks 6-OHDA-induced dopaminergic denervation

The receptor for advanced glycation endproducts (RAGE) is a pattern-recognition receptor associated with inflammation in most cell types. RAGE up-regulates the expression of proinflammatory mediators and its own expression via activation of NF-kB. Recent works have proposed a role for RAGE in Parkinson's disease (PD). In this study, we used the multimodal blocker of RAGE FPS-ZM1, which has become available recently, to selectively inhibit RAGE in the substantia nigra (SN) of rats intracranially injected with 6-hydroxydopamine (6-OHDA). FPS-ZM1 (40 μg per rat), injected concomitantly with 6-OHDA (10 μg per rat) into the SN, inhibited the increase in RAGE, activation of ERK1/2, Src and nuclear translocation of NF-kB p65 subunit in the SN. RAGE inhibition blocked glial fibrillary acidic protein and Iba-1 upregulation as well as associated astrocyte and microglia activation. Circulating cytokines in serum and CSF were also decreased by FPS-ZM1 injection. The loss of tyrosine hydroxylase and NeuN-positive neurons was significantly inhibited by RAGE blocking. Finally, FPS-ZM1 attenuated locomotory and exploratory deficits induced by 6-OHDA. Our results demonstrate that RAGE is an essential component in the neuroinflammation and dopaminergic denervation induced by 6-OHDA in the SN. Selective inhibition of RAGE may offer perspectives for therapeutic approaches.

Sulodexide prevents activation of the PLA2/COX-2/VEGF inflammatory pathway in human retinal endothelial cells by blocking the effect of AGE/RAGE

Diabetic retinopathy is characterized by the breakdown of endothelial blood-retinal barrier. We tested the hypothesis that sulodexide (SDX), a highly purified glycosaminoglycan composed of 80% iduronylglycosaminoglycan sulfate and 20% dermatan sulfate, protects human retinal endothelial cells (HREC) from high glucose (HG)-induced damage, through the suppression of inflammatory ERK/cPLA2/COX-2/PGE₂ pathway, by blocking the effect of advanced glycation end-products (AGEs). HREC were treated with HG (25mM) or AGEs (glycated-BSA, 2mg/ml) for 48h, with or without SDX (60μg/ml) or aflibercept (AFL, 40μg/ml), a VEGF-trap. SDX protected HREC from HG-induced damage (MTT and LDH release) and preserved their blood-retinal barrier-like properties (Trans Endothelial Electrical Resistance and junction proteins, claudin-5, VE-cadherin and occludin, immunofluorescence and immunoblot) as well as their angiogenic potential (Tube Formation Assay). Both HG and AGEs increased phosphoERK and phospho-cPLA₂, an effect counteracted by SDX and, less efficiently, by AFL. Both HG and exogenous VEGF (80ng/ml) increased PGE₂ release, an effect partially reverted by SDX for HG and by AFL for VEGF. Analysis of NFκB activity revealed that HG increased the abundance of p65 in the nuclear fraction (nuclear translocation), an effect entirely reverted by SDX, but only partially by AFL. SDX, AFL and SDX+AFL protected HREC even when added 24h after HG. These data show that SDX protects HREC from HG damage and suggest that it counteracts the activation of ERK/cPLA2/COX-2/PGE₂ pathway by reducing AGE-related signaling and downstream NFκB activity. This mechanism, partially distinct from VEGF blockade, may contribute to the therapeutic effect of SDX.

All the "RAGE" in lung disease: The receptor for advanced glycation endproducts (RAGE) is a major mediator of pulmonary inflammatory responses

The receptor for advanced glycation endproducts (RAGE) is a pro-inflammatory pattern recognition receptor (PRR) that has been implicated in the pathogenesis of numerous inflammatory diseases. It was discovered in 1992 on endothelial cells and was named for its ability to bind advanced glycation endproducts and promote vascular inflammation in the vessels of patients with diabetes. Further studies revealed that RAGE is most highly expressed in lung tissue and spurred numerous explorations into RAGE's role in the lung. These studies have found that RAGE is an important mediator in allergic airway inflammation (AAI) and asthma, pulmonary fibrosis, lung cancer, chronic obstructive pulmonary disease (COPD), acute lung injury, pneumonia, cystic fibrosis, and bronchopulmonary dysplasia. RAGE has not yet been targeted in the lungs of paediatric or adult clinical populations, but the development of new ways to inhibit RAGE is setting the stage for the emergence of novel therapeutic agents for patients suffering from these pulmonary conditions.

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.

RAGE-TLR Crosstalk Sustains Chronic Inflammation in Neurodegeneration

Chronic inflammatory reactions are consistenly present in neurodegeneration of Alzheimer type and are considered important factors that accelerate progression of the disease. Receptors of innate immunity participate in triggering and driving inflammatory reactions. For example, Toll-like receptors (TLRs) and receptor for advanced glycation end product (RAGE), major receptors of innate immunity, play a central role in perpetuation of inflammation. RAGE activation should be perceived as a primary mechanism which determines self-perpetuated chronic inflammation, and RAGE cooperation with TLRs amplifies inflammatory signaling. In this review, we highlight and discuss that RAGE-TLR crosstalk emerges as an important driving force of chronic inflammation in Alzheimer's disease.

Virtual screening of RAGE inhibitors using molecular docking

Advanced Glycation End products (AGEs) interaction with Receptor for AGEs (RAGE) activates downstream signaling and evokes inflammatory responses in vascular cells. Therefore, it is of interest to design a novel series of molecules with a library of 352 compounds based on natural Isoflavone and Argpyrimidine moities. The compounds screened against the optimized structure of RAGE (PDB code: 3CJJ) using MolDock aided with molecular docking algorithm. This exercise identified compound number 62 with appreciable ADME properties having no toxicity and pharmacophore features. Therefore, compound 62 identified as a RAGE inhibitor is proposed for further validation in the context of Diabetic Retinopathy (DR) and vascular complications.

RAGE and TGF-β1 Cross-Talk Regulate Extracellular Matrix Turnover and Cytokine Synthesis in AGEs Exposed Fibroblast Cells

AGEs accumulation in the skin affects extracellular matrix (ECM) turnover and triggers diabetes associated skin conditions and accelerated skin aging. The receptor of AGEs (RAGE) has an essential contribution to cellular dysfunction driven by chronic inflammatory responses while TGF-β1 is critical in both dermal homeostasis and inflammation. We investigated the contribution of RAGE and TGF-β1 to the modulation of inflammatory response and ECM turnover in AGEs milieu, using a normal fibroblast cell line. RAGE, TGF-β1, collagen I and III gene and protein expression were upregulated after exposure to AGEs-BSA, and MMP-2 was activated. AGEs-RAGE was pivotal in NF-κB dependent collagen I expression and joined with TGF-β1 to stimulate collagen III expression, probably via ERK1/2 signaling. AGEs-RAGE axis induced upregulation of TGF-β1, TNF-α and IL-8 cytokines. TNF-α and IL-8 were subjected to TGF-β1 negative regulation. RAGE’s proinflammatory signaling also antagonized AGEs-TGF-β1 induced fibroblast contraction, suggesting the existence of an inhibitory cross-talk mechanism between TGF-β1 and RAGE signaling. RAGE and TGF-β1 stimulated anti-inflammatory cytokines IL-2 and IL-4 expression. GM-CSF and IL-6 expression appeared to be dependent only on TGF-β1 signaling. Our data also indicated that IFN-γ upregulated in AGEs-BSA milieu in a RAGE and TGF-β1 independent mechanism. Our findings raise the possibility that RAGE and TGF-β1 are both involved in fibrosis development in a complex cross-talk mechanism, while also acting on their own individual targets. This study contributes to the understanding of impaired wound healing associated with diabetes complications.

Small Molecule Inhibition of Ligand-Stimulated RAGE-DIAPH1 Signal Transduction

The receptor for advanced glycation endproducts (RAGE) binds diverse ligands linked to chronic inflammation and disease. NMR spectroscopy and x-ray crystallization studies of the extracellular domains of RAGE indicate that RAGE ligands bind by distinct charge- and hydrophobicity-dependent mechanisms. The cytoplasmic tail (ct) of RAGE is essential for RAGE ligand-mediated signal transduction and consequent modulation of gene expression and cellular properties. RAGE signaling requires interaction of ctRAGE with the intracellular effector, mammalian diaphanous 1 or DIAPH1. We screened a library of 58,000 small molecules and identified 13 small molecule competitive inhibitors of ctRAGE interaction with DIAPH1. These compounds, which exhibit in vitro and in vivo inhibition of RAGE-dependent molecular processes, present attractive molecular scaffolds for the development of therapeutics against RAGE-mediated diseases, such as those linked to diabetic complications, Alzheimer’s disease, and chronic inflammation, and provide support for the feasibility of inhibition of protein-protein interaction (PPI).