Synthetic Fragments of Receptor for Advanced Glycation End Products Bind Beta-Amyloid 1-40 and Protect Primary Brain Cells From Beta-Amyloid Toxicity

RAGE induces physiological activation of NADPH oxidase in neurons and astrocytes and neuroprotection

The transmembrane receptor for advanced glycation end products (RAGE) is a signaling receptor for many damage- and pathogen-associated molecules. Activation of RAGE is associated with inflammation and an increase in reactive oxygen species (ROS) production. Although several sources of ROS have been previously suggested, how RAGE induces ROS production is still unclear, considering the multiple targets of pathogen-associated molecules. Here, using acute brain slices and primary co-culture of cortical neurons and astrocytes, we investigated the effects of a range of synthetic peptides corresponding to the fragments of the RAGE V-domain on redox signaling. We found that the synthetic fragment (60-76) of the RAGE V-domain induces activation of ROS production in astrocytes and neurons from the primary co-culture and acute brain slices. This effect occurred through activation of RAGE and could be blocked by a RAGE inhibitor. Activation of RAGE by the synthetic fragment stimulates ROS production in NADPH oxidase (NOX). This RAGE-induced NOX activation produced only minor decreases in glutathione levels and increased the rate of lipid peroxidation, although it also reduced basal and β-amyloid induced cell death in neurons and astrocytes. Thus, specific activation of RAGE induces redox signaling through NOX, which can be a part of a cell protective mechanism.

New insights toward molecular and nanotechnological approaches to antidiabetic agents for Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder affecting a major class of silver citizens. The disorder shares a mutual relationship on account of its cellular and molecular pathophysiology with type-II diabetes mellitus (DM). Chronic DM increases the risk for AD. Emerging evidence recommended that resistance in insulin production develops cognitive dysfunction, which generally leads to AD. Repurposing of antidiabetic drugs can be effective in preventing and treatment of the neurodegenerative disorder. Limitations of antidiabetic drugs restrict the repurposing of the drugs for other disorders. Therefore, nanotechnological intervention plays a significant role in the treatment of neurological disorders. In this review, we discuss the common cellular and molecular pathophysiologies between AD and type-II DM, the relevance of in vivo models of type II DM in the study of AD, and the repurposing of antidiabetic drugs and the nanodelivery systems of antidiabetic drugs against AD.

Differential expression of SLC30A10 and RAGE in mouse pups by early life lead exposure

BACKGROUND

SLC30A10 and RAGE are widely recognized as pivotal regulators of Aβ plaque transport and accumulation. Prior investigations have established a link between early lead exposure and cerebral harm in offspring, attributable to Aβ buildup and amyloid plaque deposition. However, the impact of lead on the protein expression of SLC30A10 and RAGE has yet to be elucidated. This study seeks to confirm the influence of maternal lead exposure during pregnancy, specifically through lead-containing drinking water, on the protein expression of SLC30A10 and RAGE in mice offspring. Furthermore, this research aims to provide further evidence of lead-induced neurotoxicity.

METHODS

Four cohorts of mice were subjected to lead exposure at concentrations of 0 mM, 0.25 mM, 0.5 mM, and 1 mM over a period of 42 uninterrupted days, spanning from pregnancy to the weaning phase. On postnatal day 21, the offspring mice underwent assessments. The levels of lead in the blood, hippocampus, and cerebral cortex were scrutinized, while the mice's cognitive abilities pertaining to learning and memory were probed through the utilization of the Morris water maze. Furthermore, Western blotting and immunofluorescence techniques were employed to analyze the expression levels of SLC30A10 and RAGE in the hippocampus and cerebral cortex.

RESULTS

The findings revealed a significant elevation in lead concentration within the brains and bloodstreams of mice, mirroring the increased lead exposure experienced by their mothers during the designated period (P < 0.05). Notably, in the Morris water maze assessment, the lead-exposed group exhibited noticeably diminished spatial memory compared to the control group (P < 0.05). Both immunofluorescence and Western blot analyses effectively demonstrated the concomitant impact of varying lead exposure levels on the hippocampal and cerebral cortex regions of the offspring. The expression levels of SLC30A10 displayed a negative correlation with lead doses (P < 0.05). Surprisingly, under identical circumstances, the expression of RAGE in the hippocampus and cortex of the offspring exhibited a positive correlation with lead doses (P < 0.05).

CONCLUSION

SLC30A10 potentially exerts distinct influence on exacerbated Aβ accumulation and transportation in contrast to RAGE. Disparities in brain expression of RAGE and SLC30A10 may contribute to the neurotoxic effects induced by lead.

Effect of β-amyloid on blood-brain barrier properties and function

The deposition of beta-amyloid (Aβ) aggregates in the brain, accompanied by impaired cognitive function, is a characteristic feature of Alzheimer's disease (AD). An important role in this process is played by vascular disorders, in particular, a disturbance of the blood-brain barrier (BBB). The BBB controls the entry of Aβ from plasma to the brain via the receptor for advanced glycation end products (RAGE) and the removal of brain-derived Aβ via the low-density lipoprotein receptor-related protein (LRP1). The balance between the input of Aβ to the brain from the periphery and its output is disturbed during AD. Aβ changes the redox-status of BBB cells, which in turn changes the functioning of mitochondria and disrupts the barrier function of endothelial cells by affecting tight junction proteins. Aβ oligomers have the greatest toxic effect on BBB cells, and oligomers are most rapidly transferred by transcytosis from the brain side of the BBB to the blood side. Both the cytotoxic effect of Aβ and the impairment of barrier function are partly due to the interaction of Aβ monomers and oligomers with membrane-bound RAGE. AD therapies based on the disruption of this interaction or the creation of decoys for Aβ are being developed. The question of the transfer of various Aβ isoforms through the BBB is important, since it can influence the development of AD. It is shown that the rate of input of Aβ40 and Aβ42 from the blood into the brain is different. The actual question of the transfer of pathogenic Aβ isoforms with post-translational modifications or mutations through the BBB still remains open.

Impairment of insulin signaling pathway PI3K/Akt/mTOR and insulin resistance induced AGEs on diabetes mellitus and neurodegenerative diseases: a perspective review

Insulin resistance is common in type 2 diabetes mellitus (T2DM), neurodegenerative diseases, cardiovascular diseases, kidney diseases, and polycystic ovary syndrome. Impairment in insulin signaling pathways, such as the PI3K/Akt/mTOR pathway, would lead to insulin resistance. It might induce the synthesis and deposition of advanced glycation end products (AGEs), reactive oxygen species, and reactive nitrogen species, resulting in stress, protein misfolding, protein accumulation, mitochondrial dysfunction, reticulum function, and metabolic syndrome dysregulation, inflammation, and apoptosis. It plays a huge role in various neurodegenerative diseases like Parkinson's disease, Alzheimer's disease, Huntington's disease, and Amyloid lateral sclerosis. In this review, we intend to focus on the possible effect of insulin resistance in the progression of neurodegeneration via the impaired P13K/Akt/mTOR signaling pathway, AGEs, and receptors for AGEs.

Biologically Active Fragment of the Receptor for Advanced Glycation End Products (RAGE) Is Able to Inhibit Oligomerization of the Beta-Amyloid

Abstract

It was found earlier that the synthetic fragment corresponding to the 60–76 sequence of the extracellular domain of the receptor for advanced glycation end products (RAGE) had a protective effect on animal and cellular models of Alzheimer’s disease. It was proposed that this effect was mediated via the interaction of the peptide with beta-amyloid (Aβ), which was one of the RAGE ligands, by inhibiting the formation of toxic Aβ oligomers. The aim of this study was an application of physicochemical methods to an investigation of the ability of the 60–76 peptide to prevent the Aβ40 oligomerization in solution in comparison with the nonprotective 65–76 truncated peptide. The dynamics of the formation of the Aβ40 fibrils in the presence of the peptides was evaluated using thioflavin T. The relative sizes of oligomers were determined by dynamic light scattering. The peptide binding to Aβ40 was examined by fluorescence titration. We demonstrated by the two methods that the peptide corresponding to the 60–76 sequence of RAGE considerably inhibited (by more than 90%) the formation of oligomers and fibrils of Aβ40 distinct from the 65–76 peptide. In addition, we found that the protective effect of the peptides and their ability to inhibit the Aβ40 oligomerization did not correlate with their binding to the monomeric/tetrameric Aβ40. We confirmed in vitro the hypothesis that the protective activity of the synthetic 60–76 fragment of RAGE was associated with its ability to inhibit the Aβ oligomerization.

Dioscin alleviates Alzheimer's disease through regulating RAGE/NOX4 mediated oxidative stress and inflammation

Alzheimer's disease (AD) is a neurodegenerative disease with amyloid beta (Aβ) deposition and intracellular neurofibrillary tangles (NFTs) as its characteristic pathological changes. Ameliorating oxidative stress and inflammation has become a new trend in the prevention and treatment of AD. Dioscin, a natural steroidal saponin which exists in Dioscoreae nipponicae rhizomes, displays various pharmacological activities, but its role in Alzheimer's disease (AD) is still unknown. In the present work, effect of dioscin on AD was evaluated in injured SH-SY5Y cells induced by H₂O₂ and C57BL/6 mice with AD challenged with AlCl₃ combined with D-galactose. Results showed that dioscin obviously increased cell viability and decreased reactive oxygen species (ROS) level in injured SH-SY5Y cells. In vivo, dioscin obviously improved the spatial learning and memory abilities as well as gait and interlimb coordination disorders of mice with AD. Moreover, dioscin distinctly restored the levels of malondialdehyde (MDA), superoxide dismutase (SOD), amyloid beta 42 (Aβ₄₂), acetylcholine (ACh) and acetylcholinesterase (AChE) of mice, and reversed the histopathological changes of brain tissue. Mechanism studies revealed that dioscin markedly down-regulated the expression levels of RAGE and NOX4. Subsequently, dioscin markedly up-regulated the expression levels of Nrf2 and HO-1 related to oxidative stress, and down-regulated the levels of p-NF-κB(p-p65)/NF-κB(p65), AP-1 and inflammatory factors involved in inflammatory pathway. RAGE siRNAs transfection further clarified that the pharmacological activity of dioscin in AD was achieved by regulating RAGE/NOX4 pathway. In conclusion, dioscin showed excellent anti-AD effect by adjusting RAGE/NOX4-mediated oxidative stress and inflammation, which provided the basis for the further research and development against AD.

Advanced Glycosylation End Products Induced Synaptic Deficits and Cognitive Decline Through ROS-JNK-p53/miR-34c/SYT1 Axis in Diabetic Encephalopathy

Background: miR-34c has been found to be implicated in the pathological process of Alzheimer’s disease, diabetes, and its complications. Objective: To investigate the underlying mechanisms of miR-34c in the pathogenesis of diabetic encephalopathy (DE). Methods: Diabetes mellitus rats were developed by incorporating a high-fat diet and streptozotocin injection. Morris water maze test and novel object recognition test were used to assess the cognitive function of rats. Expression of miR-34c were detected by fluorescence in situ hybridization and qRT-PCR. Immunofluorescence and western blot were used to evaluate synaptotagmin 1 (SYT1) and AdipoR2 or other proteins. Golgi staining was performed to investigate dendritic spine density. Results: The increased miR-34c induced by advanced glycation end-products (AGEs) was mediated by ROS-JNK-p53 pathway, but not ROS-Rb-E2F1 pathway, in hippocampus of DE rats or in HT-22 cells. miR-34c negatively regulated the expression of SYT1, but not AdipoR2, in hippocampal neurons. miR-34c inhibitor rescued the AGE-induced decrease in the density of dendritic spines in primary hippocampal neurons. Administration of AM34c by the intranasal delivery increased the hippocampus levels of SYT1 and ameliorated the cognitive function in DE rats. The serum levels of miR-34c were increased in patients with DE comparing with normal controls. Conclusion: These results demonstrated that AGE-induced oxidative stress mediated increase of miR-34c through ROS-JNK-p53 pathway, resulting in synaptic deficits and cognitive decline by targeting SYT1 in DE, and the miR-34c/SYT1 axis could be considered as a novel therapeutic target for DE patients.

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.

Therapeutic Strategies Targeting Amyloid-β Receptors and Transporters in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease that has been recognized as one of the most intractable medical problems with heavy social and economic costs. Amyloid-β (Aβ) has been identified as a major factor that participates in AD progression through its neurotoxic effects. The major mechanism of Aβ-induced neurotoxicity is by interacting with membrane receptors and subsequent triggering of aberrant cellular signaling. Besides, Aβ transporters also plays an important role by affecting Aβ homeostasis. Thus, these Aβ receptors and transporters are potential targets for the development of AD therapies. Here, we summarize the reported therapeutic strategies targeting Aβ receptors and transporters to provide a molecular basis for future rational design of anti-AD agents.

Activation of RAGE leads to the release of glutamate from astrocytes and stimulates calcium signal in neurons

The receptor for advanced glycation end products (RAGE) is a signal receptor first shown to be activated by advanced glycation end products, but also by a variety of signal molecules, including pathological advanced oxidation protein products and β-amyloid. However, most of the RAGE activators have multiple intracellular targets, making it difficult to unravel the exact pathway of RAGE activation. Here, we show that the cell-impermeable RAGE fragment sequence (60-76) of the V-domain of the receptor is able to activate RAGE present on the plasma membrane of neurons and, preferentially, astrocytes. This leads to the exocytosis of vesicular glutamate transporter vesicles and the release of glutamate from astrocytes, which stimulate NMDA and AMPA/kainate receptors, resulting in calcium signals predominantly in neurons. Thus, we show a specific mechanism of RAGE activation by the RAGE fragment and propose a mechanism by which RAGE activation can contribute to the neuronal-astrocytic communication in physiology and pathology.

The Neuroprotective Effect of L-Carnitine against Glyceraldehyde-Induced Metabolic Impairment: Possible Implications in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by progressive cognitive regression and memory loss. Dysfunctions of both glucose metabolism and mitochondrial dynamics have been recognized as the main upstream events of the degenerative processes leading to AD. It has been recently found that correcting cell metabolism by providing alternative substrates can prevent neuronal injury by retaining mitochondrial function and reducing AD marker levels. Here, we induced an AD-like phenotype by using the glycolysis inhibitor glyceraldehyde (GA) and explored whether L-carnitine (4-N-trimethylamino-3-hydroxybutyric acid, LC) could mitigate neuronal damage, both in SH-SY5Y neuroblastoma cells and in rat primary cortical neurons. We have already reported that GA significantly modified AD marker levels; here we demonstrated that GA dramatically compromised cellular bioenergetic status, as revealed by glycolysis and oxygen consumption rate (OCR) evaluation. We found that LC ameliorated cell survival, improved OCR and ATP synthesis, prevented the loss of the mitochondrial membrane potential (Δψ_m) and reduced the formation of reactive oxygen species (ROS). Of note, the beneficial effect of LC did not rely on the glycolytic pathway rescue. Finally, we noticed that LC significantly reduced the increase in pTau levels induced by GA. Overall, these findings suggest that the use of LC can promote cell survival in the setting of the metabolic impairments commonly observed in AD. Our data suggest that LC may act by maintaining mitochondrial function and by reducing the pTau level.

Proteolytic degradation patterns of the receptor for advanced glycation end products peptide fragments correlate with their neuroprotective activity in Alzheimer's disease models

The receptor for advanced glycation end products (RAGE) plays an essential role in Alzheimer's disease (AD). We previously demonstrated that a fragment (60-76) of RAGE improved the memory of olfactory bulbectomized (OBX) and Tg 5 × FAD mice - animal models of AD. The peptide analog (60-76) with protected N- and C-terminal groups was more active than the free peptide in Tg 5 × FAD mice. This study investigated proteolytic cleavage of the RAGE fragment (60-76) and its C- and N-terminally modified analog by blood serum using HPLC and mass spectrometry. The modified peptide was proteolyzed slower than the free peptide. Degrading the protected analog resulted in shortened fragments with memory-enhancing effects, whereas the free peptide yielded inactive fragments. After administering the different peptides to OBX mice, their performance in a spatial memory task revealed that the effective dose of the modified peptide was five times lower than that of the free peptide. HPLC and mass spectrometry analysis of the proteolytic products allowed us to clarify the differences in the neuroprotective activity conferred by administering these two peptides to AD animal models. The current study suggests that the modified RAGE fragment is more promising for the development of anti-AD therapy than its free analog.

NCX1 and EAAC1 transporters are involved in the protective action of glutamate in an in vitro Alzheimer's disease-like model

Increasing evidence suggests that metabolic dysfunctions are at the roots of neurodegenerative disorders such as Alzheimer's disease (AD). In particular, defects in cerebral glucose metabolism, which have been often noted even before the occurrence of clinical symptoms and histopathological lesions, are now regarded as critical contributors to the pathogenesis of AD. Hence, the stimulation of energy metabolism, by enhancing the availability of specific metabolites, might be an alternative way to improve ATP synthesis and to positively affect AD progression. For instance, glutamate may serve as an intermediary metabolite for ATP synthesis through the tricarboxylic acid (TCA) cycle and the oxidative phosphorylation. We have recently shown that two transporters are critical for the anaplerotic use of glutamate: the Na⁺-dependent Excitatory Amino Acids Carrier 1 (EAAC1) and the Na⁺-Ca²⁺ exchanger 1 (NCX1). Therefore, in the present study, we established an AD-like phenotype by perturbing glucose metabolism in both primary rat cortical neurons and retinoic acid (RA)-differentiated SH-SY5Y cells, and we explored the potential of glutamate to halt cell damage by monitoring neurotoxicity, AD markers, ATP synthesis, cytosolic Ca²⁺ levels and EAAC1/NCX1 functional activities. We found that glutamate significantly increased ATP production and cell survival, reduced the increase of AD biomarkers (amyloid β protein and the hyperphosphorylated form of tau protein), and recovered the increase of NCX reverse-mode activity. The RNA silencing of either EAAC1 or NCX1 caused the loss of the beneficial effects of glutamate, suggesting the requirement of a functional interplay between these transporters for glutamate-induced protection. Remarkably, our results indicate, as proof-of-principle, that facilitating the use of alternative fuels, like glutamate, may be an effective approach to overcome deficits in glucose utilization and significantly slow down neuronal degenerative process in AD.

Synthetic fragment (60-76) of RAGE improves brain mitochondria function in olfactory bulbectomized mice

The receptor for advanced glycation end products (RAGE) is considered to contribute to the pathogenesis of Alzheimer's disease (AD), mediating amyloid beta (Aβ) accumulation, mitochondrial damage, and neuroinflammation. Previously, we have synthesized small peptides corresponding to the fragments (60-76) (P1) and (60-62) (P2) of the RAGE extracellular domain, and have shown that administration of P1 fragment but not P2 results in restoration of the spatial memory and decreases the brain Aβ (1-40) level in olfactory bulbectomized (OBX) mice demonstrating main features of Alzheimer's type neurodegeneration. In the present study, we have investigated the supposed mechanism of the therapeutic efficacy of P1 RAGE fragment and compared it to P2 short fragment. We have found that P1 restored activities of the respiratory chain in the Complexes I and IV in both cortical and hippocampal mitochondria of the OBX mice while P2 had no effect. Besides, fluorescein-labeled analog Flu-P1 bound to Aβ (1-40) and Aβ (1-42) with high affinity (K_d in the nanomolar range) whereas Flu-P2 revealed low affinity with tenfold higher K_d value for Aβ (1-40) and did not bind to Aβ (1-42). However, neither of the peptides had a notable impact on inflammation, estimated as mRNA expression of proinflammatory cytokines in the brain tissues of OBX mice. Taken together, our results suggest that direct Aβ-P1 interaction is one of the molecular events mediating the protection of the mitochondria in OBX animals from Aβ toxic effect. The RAGE fragment P1 would be the soluble decoy for Aβs and serve as a promising therapeutic agent against neurodegeneration accompanied by mitochondrial dysfunction.

Progress of RAGE Molecular Imaging in Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by senile plaques (SPs), which are caused by amyloid beta (Aβ) deposition and neurofibrillary tangles (NFTs) of abnormal hyperphosphorylated tau protein. The receptor for advanced glycation end products (RAGE) binds to advanced glycation end products deposited during vascular dysfunction. Alzheimer’s disease may occur when RAGE binds to Aβ and releases reactive oxygen species, further exacerbating Aβ deposition and eventually leading to SPs and NFTs. As it is involved in early AD, RAGE may be considered as a more potent biomarker than Aβ. Positron emission tomography provides valuable information regarding the underlying pathological processes of AD many years before the appearance of clinical symptoms. Thus, to further reveal the role of RAGE in AD pathology and for early diagnosis of AD, a tracer that targets RAGE is needed. In this review, we first describe the early diagnosis of AD and then summarize the interaction between RAGE and Aβ and Tau that is required to induce AD pathology, and finally focus on RAGE-targeting probes, highlighting the potential of RAGE to be used as an effective target. The development of RAGE probes is expected to aid in AD diagnosis and treatment.

Pathological Mechanisms Linking Diabetes Mellitus and Alzheimer's Disease: the Receptor for Advanced Glycation End Products (RAGE)

Diabetes and Alzheimer’s disease (AD) place a significant burden on health care systems in the world and its aging populations. These diseases have long been regarded as separate entities; however, advanced glycation end products (AGEs) and the receptors for AGEs (RAGE) may be a link between diabetes and AD. In our study, mice injected with AGEs through stereotaxic surgery showed significant AD-like features: behavior showed decreased memory; immunofluorescence showed increased phosphorylated tau and APP. These results suggest links between diabetes and AD. Patients with diabetes are at a higher risk of developing AD, and the possible underlying molecular components of this association are now beginning to emerge.