Deciphering the molecular basis of memory failure in Alzheimer's disease

Metaplasticity mechanisms restore plasticity and associativity in an animal model of Alzheimer's disease

Dynamic regulation of plasticity thresholds in a neuronal population is critical for the formation of long-term plasticity and memory and is achieved by mechanisms such as metaplasticity. Metaplasticity tunes the synapses to undergo changes that are necessary prerequisites for memory storage under physiological and pathological conditions. Here we discovered that, in amyloid precursor protein (APP)/presenilin-1 (PS1) mice (age 3-4 mo), a prominent mouse model of Alzheimer's disease (AD), late long-term potentiation (LTP; L-LTP) and its associative plasticity mechanisms such as synaptic tagging and capture (STC) were impaired already in presymptomatic mice. Interestingly, late long-term depression (LTD; L-LTD) was not compromised, but the positive associative interaction of LTP and LTD, cross-capture, was altered in these mice. Metaplastic activation of ryanodine receptors (RyRs) in these neurons reestablished L-LTP and STC. We propose that RyR-mediated metaplastic mechanisms can be considered as a possible therapeutic target for counteracting synaptic impairments in the neuronal networks during the early progression of AD.

Altered protein glycosylation predicts Alzheimer's disease and modulates its pathology in disease model Drosophila

The pathological hallmarks of Alzheimer's disease (AD) are pathogenic oligomers and fibrils of misfolded amyloidogenic proteins (e.g., β-amyloid and hyper-phosphorylated tau in AD), which cause progressive loss of neurons in the brain and nervous system. Although deviations from normal protein glycosylation have been documented in AD, their role in disease pathology has been barely explored. Here our analysis of available expression data sets indicates that many glycosylation-related genes are differentially expressed in brains of AD patients compared with healthy controls. The robust differences found enabled us to predict the occurrence of AD with remarkable accuracy in a test cohort and identify a set of key genes whose expression determines this classification. We then studied in vivo the effect of reducing expression of homologs of 6 of these genes in transgenic Drosophila overexpressing human tau, a well-established invertebrate AD model. These experiments have led to the identification of glycosylation genes that may augment or ameliorate tauopathy phenotypes. Our results indicate that OstDelta, l(2)not and beta4GalT7 are tauopathy suppressors, whereas pgnat5 and CG33303 are enhancers, of tauopathy. These results suggest that specific alterations in protein glycosylation may play a causal role in AD etiology.

Design, synthesis, molecular modeling and anticholinesterase activity of benzylidene-benzofuran-3-ones containing cyclic amine side chain

Aim: A series of 2-benzylidene-benzofuran-3-ones were designed from the structures of Ebselen analogs and aurone derivatives and synthesized in good yields. Materials & methods: The target compounds were prepared by the condensation reaction between appropriate benzofuranones with amino alkoxy aldehydes and evaluated as cholinesterase inhibitors by Ellman’s method. Results: The in vitro anti-acetylcholinesterase (AChE)/butyrylcholinesterase activities of the synthesized compounds revealed that 7e (IC50 = 0.045 μM) is the most active compound against AChE. Furthermore, the docking study confirmed the results obtained through in vitro experiments and predicted the possible binding conformation. Conclusion: The anticholinesterase activities of benzylidene-benzofurane-3-ones as aurone analogs revealed that the compounds bearing piperidinylethoxy residue showed better activities against AChE, introducing these compounds for further drug discovery developments.

[Formula: see text]

Role of amyloid β protein receptors in mediating synaptic plasticity

There are few diseases in modern biomedicine that have garnered as much scientific interest and public concern as Alzheimer's disease (AD). The amyloid hypothesis has become the dominant model of AD pathogenesis; however, the details of the hypothesis are changing over time. Recently, given the increasing recognition, subtle effects of amyloid β protein (Aβ) on synaptic efficacy may be critical to AD progression. Synaptic plasticity is the important neurochemical foundation of learning and memory. Recent studies have identified that soluble Aβ oligomers combine with certain receptors to impair synaptic plasticity in AD, which advanced the amyloid hypothesis. The aim of the present review was to summarize the role of Aβ-relevant receptors in regulating synaptic plasticity and their downstream signaling cascades, which may provide novel insights into the understanding of the pathogenesis of AD and the development of therapeutic strategies to slow down the progression of AD-associated memory decline in the early stages.

Neuronal p38α mediates synaptic and cognitive dysfunction in an Alzheimer's mouse model by controlling β-amyloid production

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by a severe and progressive neuronal loss leading to cognitive dysfunctions. Previous reports, based on the use of chemical inhibitors, have connected the stress kinase p38α to neuroinflammation, neuronal death and synaptic dysfunction. To explore the specific role of neuronal p38α signalling in the appearance of pathological symptoms, we have generated mice that combine expression of the 5XFAD transgenes to induce AD symptoms with the downregulation of p38α only in neurons (5XFAD/p38α∆-N). We found that the neuronal-specific deletion of p38α improves the memory loss and long-term potentiation impairment induced by 5XFAD transgenes. Furthermore, 5XFAD/p38α∆-N mice display reduced amyloid-β accumulation, improved neurogenesis, and important changes in brain cytokine expression compared with 5XFAD mice. Our results implicate neuronal p38α signalling in the synaptic plasticity dysfunction and memory impairment observed in 5XFAD mice, by regulating both amyloid-β deposition in the brain and the relay of this accumulation to mount an inflammatory response, which leads to the cognitive deficits.

Resveratrol Attenuates Aβ-Induced Early Hippocampal Neuron Excitability Impairment via Recovery of Function of Potassium Channels

Alzheimer's disease (AD) is an age-related neurodegenerative disease. Amyloid-β (Aβ) is not only the morphological hallmark but also the initiator of the pathology process of AD. As a natural compound found in grapes, resveratrol shows a protective effect on the pathophysiology of AD, but the underlying mechanism is not very clear. This study was to investigate whether resveratrol could attenuate Aβ-induced early impairment in hippocampal neuron excitability and the underlying mechanism. The excitability and voltage-gated potassium currents were examined in rat hippocampal CA1 pyramidal neurons by using whole-cell patch-clamp technique. It was found that Aβ_25-35 increased the excitability of neurons. Resveratrol could reverse the Aβ_25-35-induced increase in the frequency of repetitive firing and the spike half-width of action potential (AP). Moreover, resveratrol can attenuate Aβ_25-35-induced decreases in transient potassium channel (I _A ) and delay rectifier potassium channel (I _K(DR)) of neurons. It was also found that resveratrol could decline the increase of protein kinase A (PKA) and inhibit the activation of PI3K/Akt signaling pathway induced by Aβ_25-35. The results suggest that resveratrol alleviates Aβ_25-35-induced dysfunction in hippocampal CA1 pyramidal neurons via recovery of the function of I _A and I _K(DR) by inhibiting the increase of PKA and the activation of PI3K/Akt signaling pathway.

Inhibition of coactivator-associated arginine methyltransferase 1 modulates dendritic arborization and spine maturation of cultured hippocampal neurons

An improved understanding of the molecular mechanisms in synapse formation provides insight into both learning and memory and the etiology of neurodegenerative disorders. Coactivator-associated arginine methyltransferase 1 (CARM1) is a protein methyltransferase that negatively regulates synaptic gene expression and inhibits neuronal differentiation. Despite its regulatory function in neurons, little is known about the CARM1 cellular location and its role in dendritic maturation and synapse formation. Here, we examined the effects of CARM1 inhibition on dendritic spine and synapse morphology in the rat hippocampus. CARM1 was localized in hippocampal post-synapses, with immunocytochemistry and electron microscopy revealing co-localization of CARM1 with post-synaptic density (PSD)-95 protein, a post-synaptic marker. Specific siRNA-mediated suppression of CARM1 expression resulted in precocious dendritic maturation, with increased spine width and density at sites along dendrites and induction of mushroom-type spines. These changes were accompanied by a striking increase in the cluster size and number of key synaptic proteins, including N-methyl-d-aspartate receptor subunit 2B (NR2B) and PSD-95. Similarly, pharmacological inhibition of CARM1 activity with the CARM1-specific inhibitor AMI-1 significantly increased spine width and mushroom-type spines and also increased the cluster size and number of NR2B and cluster size of PSD-95. These results suggest that CARM1 is a post-synaptic protein that plays roles in dendritic maturation and synaptic formation and that spatiotemporal regulation of CARM1 activity modulates neuronal connectivity and improves synaptic dysfunction.

Centella asiatica attenuates Aβ-induced neurodegenerative spine loss and dendritic simplification

The medicinal plant Centella asiatica has long been used to improve memory and cognitive function. We have previously shown that a water extract from the plant (CAW) is neuroprotective against the deleterious cognitive effects of amyloid-β (Aβ) exposure in a mouse model of Alzheimer's disease, and improves learning and memory in healthy aged mice as well. This study explores the physiological underpinnings of those effects by examining how CAW, as well as chemical compounds found within the extract, modulate synaptic health in Aβ-exposed neurons. Hippocampal neurons from amyloid precursor protein over-expressing Tg2576 mice and their wild-type (WT) littermates were used to investigate the effect of CAW and various compounds found within the extract on Aβ-induced dendritic simplification and synaptic loss. CAW enhanced arborization and spine densities in WT neurons and prevented the diminished outgrowth of dendrites and loss of spines caused by Aβ exposure in Tg2576 neurons. Triterpene compounds present in CAW were found to similarly improve arborization although they did not affect spine density. In contrast caffeoylquinic acid (CQA) compounds from CAW were able to modulate both of these endpoints, although there was specificity as to which CQAs mediated which effect. These data suggest that CAW, and several of the compounds found therein, can improve dendritic arborization and synaptic differentiation in the context of Aβ exposure which may underlie the cognitive improvement observed in response to the extract in vivo. Additionally, since CAW, and its constituent compounds, also improved these endpoints in WT neurons, these results may point to a broader therapeutic utility of the extract beyond Alzheimer's disease.

Plaque formation and the intraneuronal accumulation of β-amyloid in Alzheimer's disease

Amyloid plaques and neurofibrillary tangles (NFTs) in the brain are the neuropathological hallmarks of Alzheimer's disease (AD). Amyloid plaques are composed of β-amyloid peptides (Aβ), while NFTs contain hyperphosphorylated tau proteins. Patients with familial AD who have mutations in the amyloid precursor protein (APP) gene have either increased production of Aβ or generate more aggregation-prone forms of Aβ. The findings of familial AD mutations in the APP gene suggest that Aβ plays a central role in the pathophysiology of AD. Aβ42, composed of 42 amino acid residues, aggregates readily and is considered to form amyloid plaque. However, the processes of plaque formation are still not well known. It is generally thought that Aβ is secreted into the extracellular space and aggregates to form amyloid plaques. Aβ as extracellular aggregates and amyloid plaques are thought to be toxic to the surrounding neurons. The intraneuronal accumulation of Aβ has more recently been demonstrated and is reported to be involved in synaptic dysfunction, cognitive impairment, and the formation of amyloid plaques in AD. We herein provide an overview of the process of the intraneuronal accumulation of Aβ and plaque formation, and discuss its implications for the pathology, early diagnosis, and therapy of AD.

Mechanisms of Alzheimer's Disease Pathogenesis and Prevention: The Brain, Neural Pathology, N-methyl-D-aspartate Receptors, Tau Protein and Other Risk Factors

The characteristic features of Alzheimer’s disease (AD) are the appearance of extracellular amyloid-beta (Aβ) plaques and neurofibrillary tangles in the intracellular environment, neuronal death and the loss of synapses, all of which contribute to cognitive decline in a progressive manner. A number of hypotheses have been advanced to explain AD. Abnormal tau phosphorylation may contribute to the formation of abnormal neurofibrillary structures. Many different structures are susceptible to AD, including the reticular formation, the nuclei in the brain stem (e.g., raphe nucleus), thalamus, hypothalamus, locus ceruleus, amygdala, substantia nigra, striatum, and claustrum. Excitotoxicity results from continuous, low-level activation of N-methyl-D-aspartate (NMDA) receptors. Premature synaptotoxicity, changes in neurotransmitter expression, neurophils loss, accumulation of amyloid β-protein deposits (amyloid/senile plaques), and neuronal loss and brain atrophy are all associated with stages of AD progression. Several recent studies have examined the relationship between Aβ and NMDA receptors. Aβ-induced spine loss is associated with a decrease in glutamate receptors and is dependent upon the calcium-dependent phosphatase calcineurin, which has also been linked to long-term depression.

An Efficient Synthesis of bi-Aryl Pyrimidine Heterocycles: Potential New Drug Candidates to Treat Alzheimer's Disease

A series of 13 novel pyrimidine-based sulfonamides 6a-m were synthesized in short periods of time under microwave conditions in good to excellent yield (54-86%). The chemical structures of these heterocycles consist of a central pyrimidine ring having a phenyl group and pyrimidine groups with sulfonamide motifs. The enzyme inhibitory potential of these compounds was investigated against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) because these enzymes play a crucial role in the treatment of Alzheimer's disease. As compared to the reference compound eserine (IC₅₀  = 0.04 ± 0.0001 μM for AChE and IC₅₀  = 0.85 ± 0.0001 μM for BChE), the IC₅₀ values of the synthesized compounds ranged from 3.73 ± 0.61 μM to 57.36 ± 0.22 μM for AChE and 4.81 ± 0.16 μM to 111.61 ± 0.53 μM for BChE. Among these tested compounds, 6j having a -CH₃ group was found to be the most potent one against both enzymes (AChE, IC₅₀  = 3.73 ± 0.61 μM; BChE, IC₅₀  = 4.81 ± 0.16 μM). Quantitative structure-activity relationship (QSAR) and molecular docking studies of the synthesized compounds were also performed.

High bioavailability curcumin: an anti-inflammatory and neurosupportive bioactive nutrient for neurodegenerative diseases characterized by chronic neuroinflammation

Neuroinflammation is a pathophysiological process present in a number of neurodegenerative disorders, such as Alzheimer's disease, Huntington's disease, Parkinson's disease, stroke, traumatic brain injury including chronic traumatic encephalopathy and other age-related CNS disorders. Although there is still much debate about the initial trigger for some of these neurodegenerative disorders, during the progression of disease, broad range anti-inflammatory drugs including cytokine suppressive anti-inflammatory drugs (CSAIDs) might be promising therapeutic options to limit neuroinflammation and improve the clinical outcome. One of the most promising CSAIDs is curcumin, which modulates the activity of several transcription factors (e.g., STAT, NF-κB, AP-1) and their pro-inflammatory molecular signaling pathways. However, normal curcumin preparations demonstrate low bioavailability in vivo. To increase bioavailability, preparations of high bioavailability curcumin have been introduced to achieve therapeutically relevant concentrations in target tissues. This literature review aims to summarize the pharmacokinetic and toxicity profile of different curcumin formulations.

Cannabinoid Receptor 2 Signaling in Neurodegenerative Disorders: From Pathogenesis to a Promising Therapeutic Target

As a consequence of an increasingly aging population, the number of people affected by neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease and Huntington's disease, is rapidly increasing. Although the etiology of these diseases has not been completely defined, common molecular mechanisms including neuroinflammation, excitotoxicity and mitochondrial dysfunction have been confirmed and can be targeted therapeutically. Moreover, recent studies have shown that endogenous cannabinoid signaling plays a number of modulatory roles throughout the central nervous system (CNS), including the neuroinflammation and neurogenesis. In particular, the up-regulation of type-2 cannabinoid (CB2) receptors has been found in a number of neurodegenerative disorders. Thus, the modulation of CB2 receptor signaling may represent a promising therapeutic target with minimal psychotropic effects that can be used to modulate endocannabinoid-based therapeutic approaches and to reduce neuronal degeneration. For these reasons this review will focus on the CB2 receptor as a promising pharmacological target in a number of neurodegenerative diseases.

Synthesis and Anti-Acetylcholinesterase Activity of N-[(indolyl)ethyl)-coumarin-yloxy)]Alkanamides

Novel coumarin–tryptamine systems attached through a linker were synthesised and evaluated in vitro against acetylcholinesterase by the classical Ellman's test.

Multiregional analysis of global 5-methylcytosine and 5-hydroxymethylcytosine throughout the progression of Alzheimer's disease

Epigenetic modifications to cytosine are known to alter transcriptional states and deregulate gene expression in cancer, embryonic development, and most recently in neurodegeneration. To test the hypothesis that global levels of cytosine modification are altered throughout the progression of Alzheimer's disease, 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) were quantified using gas chromatography/mass spectrometry (GC/MS) and stable labeled internal standards of cytosine, 5-mC, and 5-hmC. Cytosine modifications were quantified in DNA extracted from tissue specimens of four brain regions (cerebellum, inferior parietal lobe, superior and middle temporal gyrus, and hippocampus/parahippocampal gyrus) of cognitively normal control (NC) subjects and subjects with mild cognitive impairment (MCI), preclinical Alzheimer's disease (PCAD), late onset Alzheimer's disease, frontotemporal lobar degeneration (FTLD) and dementia with Lewy bodies (DLB). Repeated measures analyses of the data show significant alterations in 5-mC and 5-hmC in early stages of Alzheimer's disease (PCAD and MCI), as well as FTLD and DLB subjects, across multiple regions of the brain. These data suggest alterations in epigenetic regulation of genes may play an early role in the progression of AD as well as other types of neurodegeneration.

Do anti-amyloid beta protein antibody cross reactivities confound Alzheimer disease research?

Background

Alzheimer disease (AD) research has focussed mainly on the amyloid beta protein (Aβ). However, many Aβ-and P3-type peptides derived from the amyloid precursor protein (APP) and peptides thought to derive from Aβ catabolism share sequence homology. Additionally, conformations can change dependent on aggregation state and solubility leading to significant uncertainty relating to interpretations of immunoreactivity with antibodies raised against Aβ. We review evidence relating to the reactivities of commonly used antibodies including 6F3D, 6E10 and 4G8 and evaluate their reactivity profiles with respect to AD diagnosis and research.

Results

Antibody cross-reactivities between Aβ-type, P3-type and Aβ-catabolic peptides confound interpretations of immunoreactivity. More than one antibody is required to adequately characterise Aβ. The relationships between anti-Aβ immunoreactivity, neuropathology and proposed APP cleavages are unclear.

Conclusions

We find that the concept of Aβ lacks clarity as a specific entity. Anti-Aβ antibody cross-reactivities lead to significant uncertainty in our understanding of the APP proteolytic system and its role in AD with profound implications for current research and therapeutic strategies.

Wnt5a is essential for hippocampal dendritic maintenance and spatial learning and memory in adult mice

Stability of neuronal connectivity is critical for brain functions, and morphological perturbations are associated with neurodegenerative disorders. However, how neuronal morphology is maintained in the adult brain remains poorly understood. Here, we identify Wnt5a, a member of the Wnt family of secreted morphogens, as an essential factor in maintaining dendritic architecture in the adult hippocampus and for related cognitive functions in mice. Wnt5a expression in hippocampal neurons begins postnatally, and its deletion attenuated CaMKII and Rac1 activity, reduced GluN1 glutamate receptor expression, and impaired synaptic plasticity and spatial learning and memory in 3-mo-old mice. With increased age, Wnt5a loss caused progressive attrition of dendrite arbors and spines in Cornu Ammonis (CA)1 pyramidal neurons and exacerbated behavioral defects. Wnt5a functions cell-autonomously to maintain CA1 dendrites, and exogenous Wnt5a expression corrected structural anomalies even at late-adult stages. These findings reveal a maintenance factor in the adult brain, and highlight a trophic pathway that can be targeted to ameliorate dendrite loss in pathological conditions.

Thamnolia vermicularis extract improves learning ability in APP/PS1 transgenic mice by ameliorating both Aβ and Tau pathologies

Considering the complicated pathogenesis of Alzheimer's disease (AD), multi-targets have become a focus in the discovery of drugs for treatment of this disease. In the current work, we established a multi-target strategy for discovering active reagents capable of suppressing both Aβ level and Tau hyperphosphorylation from natural products, and found that the ethanol extract of Thamnolia vermicularis (THA) was able to improve learning ability in APP/PS1 transgenic mice by inhibiting both Aβ levels and Tau hyperphosphorylation. SH-SY5Y and CHO-APP/BACE1 cells and primary astrocytes were used in cell-based assays. APP/PS1 transgenic mice [B6C3-Tg(APPswe, PS1dE9)] were administered THA (300 mg·kg-1·d-1, ig) for 100 d. After the administration was completed, the learning ability of the mice was detected using a Morris water maze (MWM) assay; immunofluorescence staining, Congo red staining and Thioflavine S staining were used to detect the senile plaques in the brains of the mice. ELISA was used to evaluate Aβ and sAPPβ contents, and Western blotting and RT-PCR were used to investigate the relevant signaling pathway regulation in response to THA treatment. In SH-SY5Y cells, THΑ (1, 10, 20 μg/mL) significantly stimulated PI3K/AKT/mTOR and AMPK/raptor/mTOR signaling-mediated autophagy in the promotion of Aβ clearance as both a PI3K inhibitor and an AMPK indirect activator, and restrained Aβ production as a suppressor against PERK/eIF2α-mediated BACE1 expression. Additionally, THA functioned as a GSK3β inhibitor with an IC50 of 1.32±0.85 μg/mL, repressing Tau hyperphosphorylation. Similar effects on Aβ accumulation and Tau hyperphosphorylation were observed in APP/PS1 transgenic mice treated with THA. Furthermore, administration of THA effectively improved the learning ability of APP/PS1 transgenic mice, and markedly reduced the number of senile plaques in their hippocampus and cortex. The results highlight the potential of the natural product THA for the treatment of AD.

Ultra-Early Phase pathologies of Alzheimer's disease and other neurodegenerative diseases

The concept of neurodegenerative diseases and the therapeutics targeting these intractable diseases are changing rapidly. Protein aggregation as the top of pathological cascade is now challenged, and many alternative ideas are proposed. Early molecular pathologies before microscopic detection of diseases protein aggregates, which I propose to call "Ultra-Early Phase pathologies or phase 0 pathologies", are the focus of research that might explain the failures of clinical trials with anti-Aβ antibodies against Alzheimer's disease. In this review article, I summarize the critical issues that should be successfully and consistently answered by a new concept of neurodegeneration. For reevaluating old concepts and reconstructing a new concept of neurodegeneration that will replace the old ones, non-biased comprehensive approaches including proteome combined with systems biology analyses will be a powerful tool. I introduce our recent efforts in this orientation that have reached to the stage of non-clinical proof of concept applicable to clinical trials.

Tranquilizing and Allaying Excitement Needling Method Affects BDNF and SYP Expression in Hippocampus

Sleep disorder is a state of sleep loss caused by various reasons, which leads to a series of changes, such as emotion, learning and memory, and immune function. “Tranquilizing and allaying excitement” was widely used in clinical treatment of insomnia; however, the mechanism was still not very clear. We randomly divided rats into three groups: control group, sleep deprivation group, and acupuncture treatment group. We observed BDNF and SYP expression in hippocampus in these three groups. Both protein contents and mRNA contents of BDNF and SYP were measured by western blot, immunohistochemistry, and RT-PCR analysis. The sleep deprivation model was established using modified multiple platform sleep deprivation method (MMPM). Our study explored the BDNF and SYP abnormality in hippocampus caused by sleep deprivation and “tranquilizing and allaying excitement” intervention regulated the abnormal expression of BDNF and SYP caused by sleep deprivation on the short run and the long run. Our study provided a molecular evidence that “tranquilizing and allaying excitement” treatment in rats with sleep disorder affects learning and memory ability.

Investigating the Neuroprotective Effects of Turmeric Extract: Structural Interactions of β-Amyloid Peptide with Single Curcuminoids

A broad biophysical analysis was performed to investigate the molecular basis of the neuroprotective action of Curcuma longa extracts in Alzheimer's disease. By combining circular dichroism and electron paramagnetic resonance experiments with molecular modeling calculations, the minor components of Curcuma longa extracts, such as demethoxycurcumin (2, DMC), bisdemethoxycurcumin (3, BDMC) and cyclocurcumin (4, CYC), were analyzed in a membrane environment mimicking the phospholipid bilayer. Our study provides the first evidence on the relative role of single curcuminoids interacting with Aβ-peptide. When the CYC and curcumin metabolite tetrahydrocurcumin (5, THC) were inserted into an anionic lipid solution, a significant modification of the Aβ CD curves was detected. These data were implemented by EPR experiments, demonstrating that CYC reaches the inner part of the bilayer, while the other curcuminoids are localized close to the membrane interface. Computational studies provided a model for the curcuminoid-Aβ interaction, highlighting the importance of a constrained "semi-folded" conformation to interact with Aβ analogously to the pattern observed in α-helical coiled-coil peptide structures. This combined approach led to a better understanding of the intriguing in vitro and in vivo activity of curcuminoids as anti-Alzheimer agents, paving a new path for the rational design of optimized druggable analogues.

Silibinin ameliorates Aβ25-35-induced memory deficits in rats by modulating autophagy and attenuating neuroinflammation as well as oxidative stress

Alzheimer's disease (AD) is a progressive, neurodegenerative disease. Accumulating evidence suggests that inflammatory response, oxidative stress and autophagy are involved in amyloid β (Aβ)-induced memory deficits. Silibinin (silybin), a flavonoid derived from the herb milk thistle, is well known for its hepatoprotective activities. In this study, we investigated the neuroprotective effect of silibinin on Aβ_25-35-injected rats. Results demonstrated that silibinin significantly attenuated Aβ_25-35-induced memory deficits in Morris water maze and novel object-recognition tests. Silibinin exerted anxiolytic effect in Aβ_25-35-injected rats as determined in elevated plus maze test. Silibinin attenuated the inflammatory responses, increased glutathione (GSH) levels and decreased malondialdehyde (MDA) levels, and upregulated autophagy levels in the Aβ_25-35-injected rats. In conclusion, silibinin is a potential candidate for AD treatment because of its anti-inflammatory, antioxidant and autophagy regulating activities.

Naphthoquinone-Tryptophan Hybrid Inhibits Aggregation of the Tau-Derived Peptide PHF6 and Reduces Neurotoxicity

Tauopathies, such as Alzheimer's disease (AD), are a group of disorders characterized neuropathologically by intracellular toxic accumulations of abnormal protein aggregates formed by misfolding of the microtubule-associated protein tau. Since protein self-assembly appears to be an initial key step in the pathology of this group of diseases, intervening in this process can be both a prophylactic measure and a means for modifying the course of the disease for therapeutic purposes. We and others have shown that aromatic small molecules can be effective inhibitors of aggregation of various protein assemblies, by binding to the aromatic core in aggregation-prone motifs and preventing their self-assembly. Specifically, we have designed a series of small aromatic naphthoquinone-tryptophan hybrid molecules as candidate aggregation inhibitors of β -sheet based assembly and demonstrated their efficacy toward inhibiting aggregation of the amyloid-β peptide, another culprit of AD, as well as of various other aggregative proteins involved in other protein misfolding diseases. Here we tested whether a leading naphthoquinone-tryptophan hybrid molecule, namely NQTrp, can be repurposed as an inhibitor of the aggregation of the tau protein in vitro and in vivo. We show that the molecule inhibits the in vitro assembly of PHF6, the aggregation-prone fragment of tau protein, reduces hyperphosphorylated tau deposits and ameliorates tauopathy-related behavioral defect in an established transgenic Drosophila model expressing human tau. We suggest that NQTrp, or optimized versions of it, could act as novel disease modifying drugs for AD and other tauopathies.

Palmitoylated APP Forms Dimers, Cleaved by BACE1

A major rate-limiting step for Aβ generation and deposition in Alzheimer's disease brains is BACE1-mediated cleavage (β-cleavage) of the amyloid precursor protein (APP). We previously reported that APP undergoes palmitoylation at two cysteine residues (Cys186 and Cys187) in the E1-ectodomain. 8-10% of total APP is palmitoylated in vitro and in vivo. Palmitoylated APP (palAPP) shows greater preference for β-cleavage than total APP in detergent resistant lipid rafts. Protein palmitoylation is known to promote protein dimerization. Since dimerization of APP at its E1-ectodomain results in elevated BACE1-mediated cleavage of APP, we have now investigated whether palmitoylation of APP affects its dimerization and whether this leads to elevated β-cleavage of the protein. Here we report that over 90% of palAPP is dimerized while only ~20% of total APP forms dimers. PalAPP-dimers are predominantly cis-oriented while total APP dimerizes in both cis- and trans-orientation. PalAPP forms dimers 4.5-times more efficiently than total APP. Overexpression of the palmitoylating enzymes DHHC7 and DHHC21 that increase palAPP levels and Aβ release, also increased APP dimerization in cells. Conversely, inhibition of APP palmitoylation by pharmacological inhibitors reduced APP-dimerization in coimmunoprecipitation and FLIM/FRET assays. Finally, in vitro BACE1-activity assays demonstrate that palmitoylation-dependent dimerization of APP promotes β-cleavage of APP in lipid-rich detergent resistant cell membranes (DRMs), when compared to total APP. Most importantly, generation of sAPPβ-sAPPβ dimers is dependent on APP-palmitoylation while total sAPPβ generation is not. Since BACE1 shows preference for palAPP dimers over total APP, palAPP dimers may serve as novel targets for effective β-cleavage inhibitors of APP as opposed to BACE1 inhibitors.

Microglia-Based Phenotypic Screening Identifies a Novel Inhibitor of Neuroinflammation Effective in Alzheimer's Disease Models

Currently, anti-AD drug discovery using target-based approaches is extremely challenging due to unclear etiology of AD and absence of validated therapeutic protein targets. Neuronal death, regardless of causes, plays a key role in AD progression, and it is directly linked to neuroinflammation. Meanwhile, phenotypic screening is making a resurgence in drug discovery process as an alternative to target-focused approaches. Herein, we employed microglia-based phenotypic screenings to search for small molecules that modulate the release of detrimental proinflammatory cytokines. The identified novel pharmacological inhibitor of neuroinflammation (named GIBH-130) was validated to alter phenotypes of neuroinflammation in AD brains. Notably, this molecule exhibited comparable in vivo efficacy of cognitive impairment relief to donepezil and memantine respectively in both β amyloid-induced and APP/PS1 double transgenic Alzheimer's murine models at a substantially lower dose (0.25 mg/kg). Therefore, GIBH-130 constitutes a unique chemical probe for pathogenesis research and drug development of AD, and it also suggests microglia-based phenotypic screenings that target neuroinflammation as an effective and feasible strategy to identify novel anti-AD agents.

FcγRIIb-SHIP2 axis links Aβ to tau pathology by disrupting phosphoinositide metabolism in Alzheimer's disease model

Amyloid-β (Aβ)-containing extracellular plaques and hyperphosphorylated tau-loaded intracellular neurofibrillary tangles are neuropathological hallmarks of Alzheimer's disease (AD). Although Aβ exerts neuropathogenic activity through tau, the mechanistic link between Aβ and tau pathology remains unknown. Here, we showed that the FcγRIIb-SHIP2 axis is critical in Aβ_1-42-induced tau pathology. Fcgr2b knockout or antagonistic FcγRIIb antibody inhibited Aβ_1-42-induced tau hyperphosphorylation and rescued memory impairments in AD mouse models. FcγRIIb phosphorylation at Tyr273 was found in AD brains, in neuronal cells exposed to Aβ_1-42, and recruited SHIP2 to form a protein complex. Consequently, treatment with Aβ_1-42 increased PtdIns(3,4)P₂ levels from PtdIns(3,4,5)P₃ to mediate tau hyperphosphorylation. Further, we found that targeting SHIP2 expression by lentiviral siRNA in 3xTg-AD mice or pharmacological inhibition of SHIP2 potently rescued tau hyperphosphorylation and memory impairments. Thus, we concluded that the FcγRIIb-SHIP2 axis links Aβ neurotoxicity to tau pathology by dysregulating PtdIns(3,4)P₂ metabolism, providing insight into therapeutic potential against AD.

TREM1 facilitates microglial phagocytosis of amyloid beta

As the most common type of neurodegenerative disease, Alzheimer's disease (AD) is characterized by the accumulation of amyloid-β peptide (Aβ) within the brain. Triggering receptor expressed on myeloid cells (TREM) 1 is an immune receptor expressed by mononuclear phagocytes including monocytes and microglia, coupling with TYRO protein tyrosine kinase binding protein to regulate immune reactions. Emerging evidence indicates that rs6910730^G, an intronic variant of TREM1, is associated with an increased Aβ neuropathology in the brains of elderly subjects, but the underlying mechanisms remain unclear. Here, using two independent cohorts of healthy individuals, we provided evidence that rs6910730^G reduced the ability of human monocytes for Aβ phagocytosis, and this reduction was likely attributed to a decreased monocytic TREM1 expression. By knockdown and overexpression of Trem1 in mouse primary microglia, we showed that TREM1 facilitated microglial phagocytosis of Aβ. In support of this finding, knockdown of Trem1 in the brains of APP/PSEN1 mice increased Aβ_1-42 levels and total amyloid burden, whereas selective overexpression of Trem1 on microglia or activation of Trem1 signaling by an agonistic antibody ameliorated Aβ neuropathology and rescued AD-related spatial cognitive impairments. Altogether, these findings uncover the role of TREM1 in microglial Aβ clearance, and establish TREM1 as a potential therapeutic target for AD.

Neuroprotective Mechanisms Mediated by CDK5 Inhibition

Cyclin-dependent kinase 5 (CDK5) is a proline-directed serine/threonine kinase belonging to the family of cyclin-dependent kinases. In addition to maintaining the neuronal architecture, CDK5 plays an important role in the regulation of synaptic plasticity, neurotransmitter release, neuron migration and neurite outgrowth. Although various reports have shown links between neurodegeneration and deregulation of cyclin-dependent kinases, the specific role of CDK5 inhibition in causing neuroprotection in cases of neuronal insult or in neurodegenerative diseases is not wellunderstood. This article discusses current evidence for the involvement of CDK5 deregulation in neurodegenerative disorders and neurodegeneration associated with stroke through various mechanisms. These include upregulation of cyclin D1 and overactivation of CDK5 mediated neuronal cell death pathways, aberrant hyperphosphorylation of human tau proteins and/or neurofilament proteins, formation of neurofibrillary lesions, excitotoxicity, cytoskeletal disruption, motor neuron death (due to abnormally high levels of CDK5/p25) and colchicine- induced apoptosis in cerebellar granule neurons. A better understanding of the role of CDK5 inhibition in neuroprotective mechanisms will help scientists and researchers to develop selective, safe and efficacious pharmacological inhibitors of CDK5 for therapeutic use against human neurodegenerative disorders, such as Alzheimer's disease, amyotrophic lateral sclerosis and neuronal loss associated with stroke.

Cl-NQTrp Alleviates Tauopathy Symptoms in a Model Organism through the Inhibition of Tau Aggregation-Engendered Toxicity

Alzheimer's disease (AD) is the most abundant tauopathy and is characterized by Aβ-derived plaques and tau-derived tangles, resulting from the unfolding of the corresponding monomeric subunits into ordered β-sheet oligomers and fibrils. Intervening in the toxic aggregation process is a promising therapeutic approach, but, to date, a disease-modifying therapy is neither available for AD nor for other tauopathies. Along these lines, we have previously demonstrated that a small naphthoquinone-tryptophan hybrid, termed NQTrp, is an effective modulator of tauopathy in vitro and in vivo. However, NQTrp is difficult to synthesize and is not very stable. Therefore, we tested whether a more stable and easier-to-synthesize modified version of NQTrp, containing a Cl ion, namely Cl-NQTrp, is also an effective inhibitor of tau aggregation in vitro and in vivo. Cl-NQTrp was previously shown to efficiently inhibit the aggregation of various amyloidogenic proteins and peptides. We demonstrate that Cl-NQTrp inhibits the in vitro assembly of PHF6, the aggregation-prone fragment of tau, and alleviates tauopathy symptoms in a transgenic Drosophila model through the inhibition of tau aggregation-engendered toxicity. These results suggest that Cl-NQTrp could be a unique potential therapeutic for AD since it targets aggregation of both Aβ and tau.

Apolipoprotein E4: A Risk Factor for Successful Cognitive Aging

Apolipoprotein E is a plasma protein that has an important role in transport and metabolism of lipids in serum as well as central nervous system. Among the 3 common alleles, the ε2 allele has the most stable structure followed by ε3 and ε4 in order. There is evidence for a deleterious role of ε4 allele by atherosclerosis and amyloid beta accumulation in brain and body. The presence and gene dose of ε4 allele are risk factors for late-onset Alzheimer's disease. Apolipoprotein E ε4 may have a role in the pathology of amyloid beta and tau and it has a strong relationship with the early onset of late-onset Alzheimer's disease. However, early-onset Alzheimer's disease has a weaker relationship with ε4 allele of apolipoprotein E.

Metformin activation of AMPK-dependent pathways is neuroprotective in human neural stem cells against Amyloid-beta-induced mitochondrial dysfunction

Alzheimer's disease (AD) is the general consequence of dementia and is diagnostic neuropathology by the cumulation of amyloid-beta (Aβ) protein aggregates, which are thought to promote mitochondrial dysfunction processes leading to neurodegeneration. AMP-activated protein kinase (AMPK), a critical regulator of energy homeostasis and a major player in lipid and glucose metabolism, is potentially implied in the mitochondrial deficiency of AD. Metformin, one of the widespread used anti- metabolic disease drugs, use its actions in part by stimulation of AMPK. While the mechanisms of AD are well established, the neuronal roles for AMPK in AD are still not well understood. In the present study, human neural stem cells (hNSCs) exposed to Aβ had significantly reduced cell viability, which correlated with decreased AMPK, neuroprotective genes (Bcl-2 and CREB) and mitochondria associated genes (PGC1α, NRF-1 and Tfam) expressions, as well as increased activation of caspase 3/9 activity and cytosolic cytochrome c. Co-treatment with metformin distinct abolished the Aβ-caused actions in hNSCs. Metformin also significantly rescued hNSCs from Aβ-mediated mitochondrial deficiency (lower D-loop level, mitochondrial mass, maximal respiratory function, COX activity, and mitochondrial membrane potential). Importantly, co-treatment with metformin significantly restored fragmented mitochondria to almost normal morphology in the hNSCs with Aβ. These findings extend our understanding of the central role of AMPK in Aβ-related neuronal impairment. Thus, a better understanding of AMPK might assist in both the recognition of its critical effects and the implementation of new therapeutic strategies in the treatment of AD.

The Effects of Astilbin on Cognitive Impairments in a Transgenic Mouse Model of Alzheimer's Disease

Bioflavonoids are being utilised as neuroprotectants in the treatment of various neurological disorders, including Alzheimer's disease (AD). Astilbin, a bioflavanoid, has been reported to have potent neuroprotective effects, but its preventive effects on amyloid-β (Aβ)-induced, Alzheimer's disease-related, cognitive impairment, and the underlying mechanisms of these effects have not been well characterised. Five-month-old APPswe/PS1dE9 transgenic mice were randomly assigned to a vehicle group and two astilbin (either 20 or 40 mg/kg per day, intraperitoneally) groups. After 8 weeks of treatment, we observed beneficial effects of astilbin (40 mg/kg per day), including lessening learning and memory deficits and reducing plaque burden and Aβ levels. Furthermore, the expressions of both the cAMP responsive element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF) were significantly increased and the disturbance of AKT/GSK-3β signalling pathway was markedly ameliorated in the hippocampus of astilbin-treated (40 mg/kg per day) group. Our data suggest that astilbin might be a potential therapeutic agent against AD.

Yeast Model of Amyloid-β and Tau Aggregation in Alzheimer's Disease

The amyloid-β peptide (Aβ) and the phosphorylated protein tau have been widely implicated in Alzheimer's disease and are the focus of most research. Both agents have been extensively studied in mammalian cell culture and in animal studies, but new research is focusing on yeast models. Yeast are eukaryotes, just like us, and are amenable to effects and expression of Aβ and tau and appear able to 'report' with considerable relevance on the effects of these biomolecules. The use of yeast enables powerful new approaches to understanding how to overcome the effects of Aβ and tau, and such advances could lead to new therapies to prevent the progression of Alzheimer's disease.

Neuronal seipin knockout facilitates Aβ-induced neuroinflammation and neurotoxicity via reduction of PPARγ in hippocampus of mouse

Background

A characteristic phenotype of congenital generalized lipodystrophy 2 (CGL2) that is caused by loss-of-function of seipin gene is mental retardation. Seipin is highly expressed in hippocampal pyramidal cells and astrocytes. Neuronal knockout of seipin in mice (seipin-KO mice) reduces the hippocampal peroxisome proliferator-activated receptor gamma (PPARγ) level without the loss of pyramidal cells. The down-regulation of PPARγ has gained increasing attention in neuroinflammation of Alzheimer’s disease (AD). Thus, the present study focused on exploring the influence of seipin depletion on β-amyloid (Aβ)-induced neuroinflammation and Aβ neurotoxicity.

Methods

Adult male seipin-KO mice were treated with a single intracerebroventricular (i.c.v.) injection of Aβ_25–35 (1.2 nmol/mouse) or Aβ_1–42 (0.1 nmol/mouse), generally a non-neurotoxic dose in wild-type (WT) mice. Spatial cognitive behaviors were assessed by Morris water maze and Y-maze tests, and hippocampal CA1 pyramidal cells and inflammatory responses were examined.

Results

The Aβ_{25–35/1–42} injection in the seipin-KO mice caused approximately 30–35 % death of pyramidal cells and production of Hoechst-positive cells with the impairment of spatial memory. In comparison with the WT mice, the number of astrocytes and microglia in the seipin-KO mice had no significant difference, whereas the levels of IL-6 and TNF-α were slightly increased. Similarly, the Aβ_{25–35/1–42} injection in the seipin-KO mice rather than the WT mice could stimulate the activation of astrocytes or microglia and further elevated the levels of IL-6 and TNF-α. Treatment of the seipin-KO mice with the PPARγ agonist rosiglitazone (rosi) could prevent Aβ_{25–35/1–42}-induced neuroinflammation and neurotoxicity, which was blocked by the PPARγ antagonist GW9962. In the seipin-KO mice, the level of glycogen synthase kinase-3β (GSK3β) phosphorylation at Tyr216 was elevated, while at Ser9, it was reduced compared to the WT mice, which were corrected by the rosi treatment but were unaffected by the Aβ_25–35 injection.

Conclusions

Seipin deficiency in astrocytes increases GSK3β activity and levels of IL-6 and TNF-α through reducing PPARγ, which can facilitate Aβ_{25–35/1–42}-induced neuroinflammation to cause the death of neuronal cells and cognitive deficits.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0598-3) contains supplementary material, which is available to authorized users.

Molecular architecture of Aβ fibrils grown in cerebrospinal fluid solution and in a cell culture model of Aβ plaque formation

OBJECTIVES

The detailed structure of brain-derived Aβ amyloid fibrils is unknown. To approach this issue, we investigate the molecular architecture of Aβ(1-40) fibrils grown in either human cerebrospinal fluid solution, in chemically simple phosphate buffer in vitro or extracted from a cell culture model of Aβ amyloid plaque formation.

METHODS

We have used hydrogen-deuterium exchange (HX) combined with nuclear magnetic resonance, transmission electron microscopy, seeding experiments both in vitro and in cell culture as well as several other spectroscopic measurements to compare the morphology and residue-specific conformation of these different Aβ fibrils.

RESULTS AND CONCLUSIONS

Our data reveal that, despite considerable variations in morphology, the spectroscopic properties and the pattern of slowly exchanging backbone amides are closely similar in the fibrils investigated. This finding implies that a fundamentally conserved molecular architecture of Aβ peptide fold is common to Aβ fibrils.

Ursolic acid attenuates beta-amyloid-induced memory impairment in mice

OBJECTIVE

Increasing evidence demonstrates that oxidative stress and inflammatory are involved in amyloid β (Aβ)-induced memory impairments. Ursolic acid (UA), a triterpenoid compound, has potent anti-inflammatory and antioxidant activities. However, it remains unclear whether UA attenuates Aβ-induced neurotoxicity.

METHOD

The aggregated Aβ25-35 was intracerebroventricularly administered to mice.

RESULTS

We found that UA significantly reversed the Aβ25-35-induced learning and memory deficits. Our results indicated that one of the potential mechanisms of the neuroprotective effect was attenuating the Aβ25-35-induced accumulation of malondialdehyde (MDA) and depletion of glutathione (GSH) in the hippocampus. Furthermore, UA significantly suppressed the upregulation of IL-1β, IL-6, and tumor necrosis-α factor levels in the hippocampus of Aβ25-35-treated mice.

CONCLUSION

These findings suggest that UA prevents memory impairment through amelioration of oxidative stress, inflammatory response and may offer a novel therapeutic strategy for the treatment of Alzheimer's disease.

Cerebrospinal fluid lactate levels and brain [18F]FDG PET hypometabolism within the default mode network in Alzheimer's disease

PURPOSE

It has been suggested that neuronal energy metabolism may be involved in Alzheimer's disease (AD). In this view, the finding of increased cerebrospinal fluid (CSF) lactate levels in AD patients has been considered the result of energetic metabolism dysfunction. Here, we investigated the relationship between neuronal energy metabolism, as measured via CSF lactate levels, and cerebral glucose metabolism, as stated at the 2-deoxy-2-(18F)fluoro-D-glucose positron emission tomography ([18F]FDG PET) in AD patients.

METHODS

AD patients underwent lumbar puncture to measure CSF lactate levels and [18F]FDG PET to assess brain glucose metabolism. CSF and PET data were compared to controls. Since patients were studied at rest, we specifically investigated brain areas active in rest-condition owing to the Default Mode Network (DMN). We correlated the CSF lactate concentrations with the [18F]FDG PET data in brain areas owing to the DMN, using sex, age, disease duration, Mini Mental State Examination, and CSF levels of tau proteins and beta-amyloid as covariates.

RESULTS

AD patients (n = 32) showed a significant increase of CSF lactate levels compared to Control 1 group (n = 28). They also showed brain glucose hypometabolism in the DMN areas compared to Control 2 group (n = 30). Within the AD group we found the significant correlation between increased CSF lactate levels and glucose hypometabolism in Broadman areas (BA) owing to left medial prefrontal cortex (BA10, mPFC), left orbitofrontal cortex (BA11, OFC), and left parahippocampal gyrus (BA 35, PHG).

CONCLUSION

We found high CSF levels of lactate and glucose hypometabolism within the DMN in AD patients. Moreover, we found a relationship linking the increased CSF lactate and the reduced glucose consumption in the left mPFC, OFC and PHG, owing to the anterior hub of DMN. These findings could suggest that neural glucose hypometabolism may affect the DMN efficiency in AD, also proposing the possible role of damaged brain energetic machine in impairing DMN.

The flavonoid baicalein rescues synaptic plasticity and memory deficits in a mouse model of Alzheimer's disease

Increasing evidence suggests that disruptions of synaptic functions correlate with the severity of cognitive deficit in Alzheimer's disease (AD). Our previous study demonstrated that baicalein enhances long-term potentiation (LTP) in acute rat hippocampal slices and improves hippocampus-dependent contextual fear conditioning in rats. Given that baicalein possess various biological activities, especially its effects on synaptic plasticity and cognitive function, we examined the effect of baicalein on synaptic function both in vitro and in vivo in AD model. The effect of baicalein on Aβ42 oligomer impaired LTP was investigated by electrophysiological methods. Baicalein was administered orally via drinking water to the APP/PS1 mice and sex- and age-matched wild-type mice. Treatment started at 5 months of age and mice were assessed for cognition and AD-like pathology at 7-month-old. Cognition was analyzed by Morris water maze test, fear conditioning test, and novel object recognition test. Changes in hippocampal 12/15 Lipoxygenase (12/15LO) and glycogen synthase kinase 3β (GSK3β) activity, Aβ production, tau phosphorylation, synaptic plasticity, and dendritic spine density were evaluated. Baicalein prevented Aβ-induced impairments in hippocampal LTP through activation of serine threonine Kinase (Akt) phosphorylation. Long-term oral administration of baicalein inhibited 12/15LO and GSK3β activity, reduced β-secretase enzyme (BACE1), decreased the concentration of total Aβ, and prevented phosphorylation of tau in APP/PS1 mice. Meanwhile, baicalein restored spine number, synaptic plasticity, and memory deficits. Our results strengthen the potential of the flavonoid baicalein as a novel and promising oral bioactive therapeutic agent that prevents memory deficits in AD.

Progressive Neuronal Pathology and Synaptic Loss Induced by Prediabetes and Type 2 Diabetes in a Mouse Model of Alzheimer's Disease

Age remains the main risk factor for developing Alzheimer's disease (AD) although certain metabolic alterations, including prediabetes and type 2 diabetes (T2D), may also increase this risk. In order to understand this relationship, we have studied an AD-prediabetes mouse model (APP/PS1) with severe hyperinsulinemia induced by long-term high fat diet (HFD), and an AD-T2D model, generated by crossing APP/PS1 and db/db mice (APP/PS1xdb/db). In both, prediabetic and diabetic AD mice, we have analyzed underlying neuronal pathology and synaptic loss. At 26 weeks of age, when both pathologies were clearly established, we observed severe brain atrophy in APP/PS1xdb/db animals as well as cortical thinning, accompanied by increased caspase activity. Reduced senile plaque burden and elevated soluble Aβ40 and 42 levels were observed in AD-T2D mice. Further assessment revealed a significant increase of neurite curvature in prediabetic-AD mice, and this effect was worsened in AD-T2D animals. Synaptic density loss, analyzed by array tomography, revealed a synergistic effect between T2D and AD, whereas an intermediate state was observed, once more, in prediabetic-AD mice. Altogether, our data suggest that early prediabetic hyperinsulinemia may exacerbate AD pathology, and that fully established T2D clearly worsens these effects. Therefore, it is feasible that early detection of prediabetic state and strict metabolic control could slow or delay progression of AD-associated neuropathological features.

Central role for NMDA receptors in redox mediated impairment of synaptic function during aging and Alzheimer's disease

Increased human longevity has magnified the negative impact that aging can have on cognitive integrity of older individuals experiencing some decline in cognitive function. Approximately 30% of the elderly will have cognitive problems that influence their independence. Impaired executive function and memory performance are observed in normal aging and yet can be an early sign of a progressive cognitive impairment of Alzheimer's disease (AD), the most common form of dementia. Brain regions that are vulnerable to aging exhibit the earliest pathology of AD. Senescent synaptic function is observed as a shift in Ca²⁺-dependent synaptic plasticity and similar mechanisms are thought to contribute to the early cognitive deficits associated with AD. In the case of aging, intracellular redox state mediates a shift in Ca²⁺ regulation including N-methyl-d-aspartate (NMDA) receptor hypofunction and increased Ca²⁺ release from intracellular stores to alter synaptic plasticity. AD can interact with these aging processes such that molecules linked to AD, β-amyloid (Aβ) and mutated presenilin 1 (PS1), can also degrade NMDA receptor function, promote Ca²⁺ release from intracellular stores, and may increase oxidative stress. Thus, age is one of the most important predictors of AD and brain aging likely contributes to the onset of AD. The focus of this review article is to provide an update on mechanisms that contribute to the senescent synapse and possible interactions with AD-related molecules, with special emphasis on regulation of NMDA receptors.