Generation of aggregated beta-amyloid in the rat hippocampus impairs synaptic transmission and plasticity and causes memory deficits

Teucrium Polium ameliorates amyloid β-induced brain network disorders in rats: electrophysiological and behavioral studies

Synaptic failure in specific cholinergic networks in rat brains has been implicated in amyloid β-induced neurodegeneration. Teucrium polium is a promising candidate for drug development against Alzheimer's disease (AD) and similar disorders. However, the protective effect of Teucrium polium against amyloid β-induced impairment of short-term synaptic plasticity is still poorly understood. In this study, we used in vivo extracellular single-unit recordings to investigate the preventive efficacy of Teucrium polium on Aβ(25-35)-induced aberrant neuronal activity in the hippocampus and basolateral amygdala of rats, in response to high-frequency stimulation of the cholinergic nucleus basalis magnocellularis (NBM). After 12 weeks of intracerebroventricular administration of Aβ(25-35), alterations such as decreased excitatory responses and increased inhibitory synaptic activity were observed in the NBM-hippocampus and NBM-basolateral amygdala cholinergic circuits. Treatment with Teucrium polium improved the balance of excitatory and inhibitory responses by modulating synaptic transmission strength and restoring short-term plasticity. Acute injection of a therapeutic dose of Teucrium temporarily inhibited spiking activity in single NBM neurons. Open field tests revealed that amyloid-injected rats displayed anxiety and reduced exploratory drive. Treatment with Teucrium polium improved these behaviors, reducing anxiety and increasing exploration. Teucrium polium mitigated amyloid β-induced alterations in cholinergic circuits by enhancing the adaptive capacity of short-term synaptic plasticity. These findings suggest that Teucrium polium could serve as a preventive strategy to delay the progression of cholinergic neurodegeneration.

Distinct Aggregation Behavior of N-Terminally Truncated Aβ4-42 Over Aβ1-42 in the Presence of Zn(II)

The deposition of amyloid-β (Aβ) aggregates and metal ions within senile plaques is a hallmark of Alzheimer's disease (AD). Among the modifications observed in Aβ peptides, N-terminal truncation at Phe4, yielding Aβ4-x, is highly prevalent in AD-affected brains and significantly alters Aβ's metal-binding and aggregation profiles. Despite the abundance of Zn(II) in senile plaques, its impact on the aggregation and toxicity of Aβ4-x remains unexplored. Here, we report the distinct aggregation behavior of N-terminally truncated Aβ, specifically Aβ4-42, in the absence and presence of either Zn(II), Aβ seeds, or both, and compare it to that of full-length Aβ1-42. Our findings reveal notable differences in the aggregation profiles of Aβ4-42 and Aβ1-42, largely influenced by their different Zn(II)-binding properties. These results provide insights into the mechanisms underlying the distinct aggregation behavior of truncated and full-length Aβ in the presence of Zn(II), contributing to a deeper understanding of AD pathology.

Protein aggregation and its affecting mechanisms in neurodegenerative diseases

Protein aggregation serves as a critical pathological marker in a spectrum of neurodegenerative diseases (NDs), including the formation of amyloid β (Aβ) and Tau neurofibrillary tangles in Alzheimer's disease, as well as α-Synuclein (α-Syn) aggregates in Parkinson's disease, Parkinson's disease-related dementia (PDD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). A significant proportion of patients with amyotrophic lateral sclerosis (ALS) exhibit TDP-43 aggregates. Moreover, a confluence of brain protein pathologies, such as Aβ, Tau, α-Syn, and TDP-43, has been identified in individual NDs cases, highlighting the intricate interplay among these proteins that is garnering heightened scrutiny. Importantly, protein aggregation is modulated by an array of factors, with burgeoning evidence suggesting that it frequently results from perturbations in protein homeostasis, influenced by the cellular membrane milieu, metal ion concentrations, post-translational modifications, and genetic mutations. This review delves into the pathological underpinnings of protein aggregation across various NDs and elucidates the intercommunication among disparate proteins within the same disease context. Additionally, we examine the pathogenic mechanisms by which diverse factors impinge upon protein aggregation, offering fresh perspectives for the future therapeutic intervention of NDs.

Altering plasma lipids and liver enzyme activities via hippocampal injections of hen Lysozyme amyloid aggregates in an Alzheimer's disease mouse model: Insights into the therapeutic role of Bis (Indolyl) phenylmethane

Alzheimer's disease (AD) is a prevalent form of dementia in the elderly. There is currently no effective treatment available for this disease. Diagnosis of AD typically relies on clinical manifestations and specific biomarkers. The present study investigated the impact of inducing Alzheimer's disease (AD) in mice through the injection of lysozyme amyloids formed in the presence or absence of Bis (Indolyl) phenylmethane (BIPM) on alterations in plasma lipid profiles and liver enzyme activities. 24 adult Wistar rats were divided into control, Scopolamine, Lysozyme, BIPM groups and the blood samples were obtained from the groups for biochemical analysis. The findings of the study revealed significant changes in the plasma lipid profiles and liver enzyme markers of the Lysozyme group compared to the control group. The Lysozyme group exhibited elevated triglycerides (n = 6, P < 0.02) and LDL levels (n = 6, P < 0.02), reduced HDL (n = 6, P < 0.05) and cholesterol levels (n = 6, P < 0.02), and altered serum glutamic oxaloacetic transaminase (SGOT) level (n = 6, P < 0.05) compared to controls. While the level of serum glutamic pyruvic transaminase (SGPT) did not change significantly compared to the control. BIPM groups showed no significant changes in lipid or enzyme levels compared to controls. Overall, our research has shown that BIPM has the ability to modify the structure of HEWL aggregates, thereby improving the detrimental effects associated with AD caused by these aggregates. Analyzing lipid profiles and liver enzyme markers presents a promising avenue for targeted therapeutic approaches. These alterations observed in the plasma may potentially serve as candidate biomarkers for diagnosing this disease.

A novel mouse model for N-terminal truncated Aβ2-x generation through meprin β overexpression in astrocytes

Neurotoxic amyloid-β (Aβ) peptides cause neurodegeneration in Alzheimer's disease (AD) patients' brains. They are released upon proteolytic processing of the amyloid precursor protein (APP) extracellularly at the β-secretase site and intramembranously at the γ-secretase site. Several AD mouse models were developed to conduct respective research in vivo. Most of these classical models overexpress human APP with mutations driving AD-associated pathogenic APP processing. However, the resulting pattern of Aβ species in the mouse brains differs from those observed in AD patients' brains. Particularly mutations proximal to the β-secretase cleavage site (e.g., the so-called Swedish APP (APPswe) fostering Aβ1-x formation) lead to artificial Aβ production, as N-terminally truncated Aβ peptides are hardly present in these mouse brains. Meprin β is an alternative β-secretase upregulated in brains of AD patients and capable of generating N-terminally truncated Aβ2-x peptides. Therefore, we aimed to generate a mouse model for the production of so far underestimated Aβ2-x peptides by conditionally overexpressing meprin β in astrocytes. We chose astrocytes as meprin β was detected in this cell type in close proximity to Aβ plaques in AD patients' brains. The meprin β-overexpressing mice showed elevated amyloidogenic APP processing detected with a newly generated neo-epitope-specific antibody. Furthermore, we observed elevated Aβ production from endogenous APP as well as AD-related behavior changes (hyperlocomotion and deficits in spatial memory). The novel mouse model as well as the established tools and methods will be helpful to further characterize APP cleavage and the impact of different Aβ species in future studies.

Evolving therapeutic interventions for the management and treatment of Alzheimer's disease

Alzheimer's Disease (AD) patients experience diverse symptoms, including memory loss, cognitive impairment, behavioral abnormalities, mood changes, and mental issues. The fundamental objective of this review is to discuss novel therapeutic approaches, with special emphasis on recently approved marketed formulations for the treatment of AD, especially Aducanumab, the first FDA approved moiety that surpasses the blood-brain barrier (BBB) and reduces amyloid plaques in the brain, thereby reducing associated cognitive decline. However, it is still in the phase IV trial and is to be completed by 2030. Other drugs such as lecanemab are also under clinical trial and has recently been approved by the FDA and is also discussed here. In this review, we also focus on active and passive immunotherapy for AD as well as several vaccines, such as amyloid-beta epitope-based vaccines, amyloid-beta DNA vaccines, and stem cell therapy for AD, which are in clinical trials. Furthermore, ongoing pre-clinical trials associated with AD and other novel strategies such as curcumin-loaded nanoparticles, Crispr/ cas9, precision medicine, as well as some emerging therapies like anti-sense therapy are also highlighted. Additionally, we discuss some off-labeled drugs like non-steroidal anti-inflammatory drugs (NSAID), anti-diabetic drugs, and lithium, which can manage symptoms of AD and different non-pharmacological approaches are also covered which can help to manage AD. In summary, we have tried to cover all the therapeutic interventions which are available for the treatment and management of AD under sections approved, clinical phase, pre-clinical phase or futuristic interventions, off-labelled drugs, and non-pharmacological interventions for AD, offering positive findings and well as challenges that remain.

Deleterious and protective effects of epothilone-D alone and in the context of amyloid β- and tau-induced alterations

Amyloid-β (Aβ) and hyperphosphorylated tau (P-tau) are Alzheimer's disease (AD) biomarkers that interact in a complex manner to induce most of the cognitive and brain alterations observed in this disease. Since the neuronal cytoskeleton is a common downstream pathological target of tau and Aβ, which mostly lead to augmented microtubule instability, the administration of microtubule stabilizing agents (MSAs) can protect against their pathological actions. However, the effectiveness of MSAs is still uncertain due to their state-dependent negative effects; thus, evaluating their specific actions in different pathological or physiological conditions is required. We evaluated whether epothilone-D (Epo-D), a clinically used MSA, rescues from the functional and behavioral alterations produced by intracerebroventricular injection of Aβ, the presence of P-tau, or their combination in rTg4510 mice. We also explored the side effects of Epo-D. To do so, we evaluated hippocampal-dependent spatial memory with the Hebb-Williams maze, hippocampal CA1 integrity and the intrinsic and synaptic properties of CA1 pyramidal neurons with the patch-clamp technique. Aβ and P-tau mildly impaired memory retrieval, but produced contrasting effects on intrinsic excitability. When Aβ and P-tau were combined, the alterations in excitability and spatial reversal learning (i.e., cognitive flexibility) were exacerbated. Interestingly, Epo-D prevented most of the impairments induced Aβ and P-tau alone and combined. However, Epo-D also exhibited some side effects depending on the prevailing pathological or physiological condition, which should be considered in future preclinical and translational studies. Although we did not perform extensive histopathological evaluations or measured microtubule stability, our findings show that MSAs can rescue the consequences of AD-like conditions but otherwise be harmful if administered at a prodromal stage of the disease.

Evidence of disturbed insulin signaling in animal models of Alzheimer's disease

Since glucose reuptake by neurons is mostly independent of insulin, it has been an intriguing question whether insulin has or not any roles in the brain. Consequently, the identification of insulin receptors in the central nervous system has fueled investigations of insulin functions in the brain. It is also already known that insulin can influence glucose reuptake by neurons, mostly during activities that have the highest energy demand. The identification of high density of insulin receptors in the hippocampus also suggests that insulin may present important roles related to memory. In this context, studies have reported worse performance in cognitive tests among diabetic patients. In addition, alterations in the regulation of central insulin pathways have been observed in the brains of Alzheimer's disease (AD) patients. In fact, some authors have proposed AD as a third type of diabetes and recently, our group proposed insulin resistance as a common link between different AD hypotheses. Therefore, in the present narrative review, we intend to revise and gather the evidence of disturbed insulin signaling in experimental animal models of AD.

ACSS2-dependent histone acetylation improves cognition in mouse model of Alzheimer's disease

BACKGROUND

Nuclear acetyl-CoA pools govern histone acetylation that controls synaptic plasticity and contributes to cognitive deterioration in patients with Alzheimer's disease (AD). Nuclear acetyl-CoA pools are generated partially from local acetate that is metabolized by acetyl-CoA synthetase 2 (ACSS2). However, the underlying mechanism of histone acetylation dysregulation in AD remains poorly understood.

METHODS

We detected ACSS2 expression and histone acetylation levels in the brains of AD patients and 5 × FAD mice. When we altered ACSS2 expression by injecting adeno-associated virus into the dorsal hippocampus of 5 × FAD mice and replenished ACSS2 substrate (acetate), we observed changes in cognitive function by Morris water maze. We next performed RNA-seq, ChIP-qPCR, and electrophysiology to study molecular mechanism underlying ACSS2-mediated spatial learning and memory in 5 × FAD mice.

RESULTS

We reported that ACSS2 expression and histone acetylation (H3K9, H4K12) were reduced in the hippocampus and prefrontal cortex of 5 × FAD mice. Reduced ACSS2 levels were also observed in the temporal cortex of AD patients. 5 × FAD mice exhibited a low enrichment of acetylated histones on the promoters of NMDARs and AMPARs, together with impaired basal and activity-dependent synaptic plasticity, all of which were rescued by ACSS2 upregulation. Moreover, acetate replenishment enhanced ac-H3K9 and ac-H4K12 in 5 × FAD mice, leading to an increase of NMDARs and AMPARs and a restoration of synaptic plasticity and cognitive function in an ACSS2-dependent manner.

CONCLUSION

ACSS2 is a key molecular switch of cognitive impairment and that targeting ACSS2 or acetate administration may serve as a novel therapeutic strategy for the treatment of intermediate or advanced AD. Nuclear acetyl-CoA pools are generated partly from local acetate that is metabolized by acetyl-CoA synthetase 2 (ACSS2). Model depicts that ACSS2 expression is downregulated in the brains of 5×FAD model mice and AD patients. Of note, ACSS2 downregulation mediates a reduction in ionotropic glutamate receptor expression through histone acetylation, which exacerbates synaptic plasticity impairment in AD. These deficits can be rescued by ACSS2 upregulation or acetate supplementation (GTA, an FDA-approved food additive), which may serve as a promising therapeutic strategy for AD treatment.

The Interaction Between NF-κB and Estrogen in Alzheimer's Disease

Post-menopausal women are at a higher risk of developing Alzheimer's disease (AD) than males. The higher rates of AD in women are associated with the sharp decline in the estrogen levels after menopause. Estrogen has been shown to downregulate inflammatory cytokines in the central nervous system (CNS), which has a neuroprotective role against neurodegenerative diseases including AD. Sustained neuroinflammation is associated with neurodegeneration and contributes to AD. Nuclear factor kappa-B (NF-κB) is a transcription factor involved with the modulation of inflammation and interacts with estrogen to influence the progression of AD. Application of 17β-estradiol (E2) has been shown to inhibit NF-κB, thereby reducing transcription of NF-κB target genes. Despite accumulating evidence showing that estrogens have beneficial effects in pre-clinical AD studies, there are mixed results with hormone replacement therapy in clinical trials. Furthering our understanding of how NF-κB interacts with estrogen and alters the progression of neurodegenerative disorders including AD, should be beneficial and result in the development of novel therapeutics.

Microglia-Astrocyte Communication in Alzheimer's Disease

Microglia and astrocytes are regarded as active participants in the central nervous system under various neuropathological conditions, including Alzheimer's disease (AD). Both microglia and astrocyte activation have been reported to occur with a spatially and temporarily distinct pattern. Acting as a double-edged sword, glia-mediated neuroinflammation may be both detrimental and beneficial to the brain. In a variety of neuropathologies, microglia are activated before astrocytes, which facilitates astrocyte activation. Yet reactive astrocytes can also prevent the activation of adjacent microglia in addition to helping them become activated. Studies describe changes in the genetic profile as well as cellular and molecular responses of these two types of glial cells that contribute to dysfunctional immune crosstalk in AD. In this paper, we construct current knowledge of microglia-astrocyte communication, highlighting the multifaceted functions of microglia and astrocytes and their role in AD. A thorough comprehension of microglia-astrocyte communication could hasten the creation of novel AD treatment approaches.

Oligomeropathies, inflammation and prion protein binding

The central role of oligomers, small soluble aggregates of misfolded proteins, in the pathogenesis of neurodegenerative disorders is recognized in numerous experimental conditions and is compatible with clinical evidence. To underline this concept, some years ago we coined the term oligomeropathies to define the common mechanism of action of protein misfolding diseases like Alzheimer, Parkinson or prion diseases. Using simple experimental conditions, with direct application of synthetic β amyloid or α-synuclein oligomers intraventricularly at micromolar concentrations, we could detect differences and similarities in the biological consequences. The two oligomer species affected cognitive behavior, neuronal dysfunction and cerebral inflammatory reactions with distinct mechanisms. In these experimental conditions the proposed mediatory role of cellular prion protein in oligomer activities was not confirmed. Together with oligomers, inflammation at different levels can be important early in neurodegenerative disorders; both β amyloid and α-synuclein oligomers induce inflammation and its control strongly affects neuronal dysfunction. This review summarizes our studies with β-amyloid or α-synuclein oligomers, also considering the potential curative role of doxycycline, a well-known antibiotic with anti-amyloidogenic and anti-inflammatory activities. These actions are analyzed in terms of the therapeutic prospects.

Urokinase-Type Plasminogen Activator Triggers Wingless/Int1-Independent Phosphorylation of the Low-Density Lipoprotein Receptor-Related Protein-6 in Cerebral Cortical Neurons

BACKGROUND

Urokinase-type plasminogen activator (uPA) is a serine proteinase found in excitatory synapses located in the II/III and V cortical layers. The synaptic release of uPA promotes the formation of synaptic contacts and the repair of synapses damaged by various forms of injury, and its abundance is decreased in the synapse of Alzheimer's disease (AD) patients. Inactivation of the Wingless/Int1 (Wnt)-β-catenin pathway plays a central role in the pathogenesis of AD. Soluble amyloid-β (Aβ) prevents the phosphorylation of the low-density lipoprotein receptor-related protein-6 (LRP6), and the resultant inactivation of the Wnt-β-catenin pathway prompts the amyloidogenic processing of the amyloid-β protein precursor (AβPP) and causes synaptic loss.

OBJECTIVE

To study the role of neuronal uPA in the pathogenesis of AD.

METHODS

We used in vitro cultures of murine cerebral cortical neurons, a murine neuroblastoma cell line transfected with the APP-695 Swedish mutation (N2asw), and mice deficient on either plasminogen, or uPA, or its receptor (uPAR).

RESULTS

We show that uPA activates the Wnt-β-catenin pathway in cerebral cortical neurons by triggering the phosphorylation of LRP6 via a plasmin-independent mechanism that does not require binding of Wnt ligands (Wnts). Our data indicate that uPA-induced activation of the Wnt-β-catenin pathway protects the synapse from the harmful effects of soluble Aβ and prevents the amyloidogenic processing of AβPP by inhibiting the expression of β-secretase 1 (BACE1) and the ensuing generation of Aβ 40 and Aβ 42 peptides.

CONCLUSION

uPA protects the synapse and antagonizes the inhibitory effect of soluble Aβ on the Wnt-β-catenin pathway by providing an alternative pathway for LRP6 phosphorylation and β-catenin stabilization.

Targeting the alternative oxidase (AOX) for human health and food security, a pharmaceutical and agrochemical target or a rescue mechanism?

Some of the most threatening human diseases are due to a blockage of the mitochondrial electron transport chain (ETC). In a variety of plants, fungi, and prokaryotes, there is a naturally evolved mechanism for such threats to viability, namely a bypassing of the blocked portion of the ETC by alternative enzymes of the respiratory chain. One such enzyme is the alternative oxidase (AOX). When AOX is expressed, it enables its host to survive life-threatening conditions or, as in parasites, to evade host defenses. In vertebrates, this mechanism has been lost during evolution. However, we and others have shown that transfer of AOX into the genome of the fruit fly and mouse results in a catalytically engaged AOX. This implies that not only is the AOX a promising target for combating human or agricultural pathogens but also a novel approach to elucidate disease mechanisms or, in several cases, potentially a therapeutic cure for human diseases. In this review, we highlight the varying functions of AOX in their natural hosts and upon xenotopic expression, and discuss the resulting need to develop species-specific AOX inhibitors.

The comprehensive mechanistic insight into the effects of vitamin D on dementia – a review

Purpose

This paper aims to depict the mechanistic role of vitamin D on dementia prevention, relief of the severity and the complication of the disease. All papers indexed in scientific databases, including Scopus, Elsevier, PubMed, Embase and Google Scholar between 2000 and 2021 were extracted and discussed. To present the mechanistic role of vitamin D in declining the severity of dementia, keywords including dementia, vitamin D, oxidative stress, inflammation, amyloid beta-Peptides were used.

Design/methodology/approach

Dementia is a prevalent cognitive disorder worldwide, especially in elderly people, which is accompanied by serious disabilities. Besides genetic, biological and lifestyle factors are involved in the incidence of dementia. An unhealthy diet along with micronutrient deficiencies are among modifiable factors. Vitamin D is one of the important micronutrients in brain health. Besides the involvement in gene expression, bone mineralization, apoptosis, inflammation, skeletal maturation, neurotropic action and hemostasis of phosphate and calcium, vitamin D also exerts neuroprotective effects via genomic and non-genomic pathways.

Findings

Vitamin D up-regulates the expression of various genes involved in dementia incidence via various mechanisms. Decreasing oxidative stress and the neuro-inflammatory cytokines levels, regulation of the expression of alternated Proteins including Tau and Amyloid-ß, calcium homeostasis in the central nervous system and also vascular are considered main mechanisms.

Originality/value

Considering the importance of diet in preventing dementia, adherence to a healthy diet that provides essential nutrients to brain function seems to be urgent. Controlling serum levels of vitamin D periodically and providing vitamin D by related sources or supplements, if there is a deficiency, is recommended. Future studies are needed to clarify other related mechanisms.

A unifying framework for amyloid-mediated membrane damage: The lipid-chaperone hypothesis

Over the past thirty years, researchers have highlighted the role played by a class of proteins or polypeptides that forms pathogenic amyloid aggregates in vivo, including i) the amyloid Aβ peptide, which is known to form senile plaques in Alzheimer's disease; ii) α-synuclein, responsible for Lewy body formation in Parkinson's disease and iii) IAPP, which is the protein component of type 2 diabetes-associated islet amyloids. These proteins, known as intrinsically disordered proteins (IDPs), are present as highly dynamic conformational ensembles. IDPs can partially (mis) fold into (dys) functional conformations and accumulate as amyloid aggregates upon interaction with other cytosolic partners such as proteins or lipid membranes. In addition, an increasing number of reports link the toxicity of amyloid proteins to their harmful effects on membrane integrity. Still, the molecular mechanism underlying the amyloidogenic proteins transfer from the aqueous environment to the hydrocarbon core of the membrane is poorly understood. This review starts with a historical overview of the toxicity models of amyloidogenic proteins to contextualize the more recent lipid-chaperone hypothesis. Then, we report the early molecular-level events in the aggregation and ion-channel pore formation of Aβ, IAPP, and α-synuclein interacting with model membranes, emphasizing the complexity of these processes due to their different spatial-temporal resolutions. Next, we underline the need for a combined experimental and computational approach, focusing on the strengths and weaknesses of the most commonly used techniques. Finally, the last two chapters highlight the crucial role of lipid-protein complexes as molecular switches among ion-channel-like formation, detergent-like, and fibril formation mechanisms and their implication in fighting amyloidogenic diseases.

Alzheimer's pathology causes impaired inhibitory connections and reactivation of spatial codes during spatial navigation

Synapse loss and altered synaptic strength are thought to underlie cognitive impairment in Alzheimer’s disease (AD) by disrupting neural activity essential for memory. While synaptic dysfunction in AD has been well characterized in anesthetized animals and in vitro, it remains unknown how synaptic transmission is altered during behavior. By measuring synaptic efficacy as mice navigate in a virtual reality task, we find deficits in interneuron connection strength onto pyramidal cells in hippocampal CA1 in the 5XFAD mouse model of AD. These inhibitory synaptic deficits are most pronounced during sharp-wave ripples, network oscillations important for memory that require inhibition. Indeed, 5XFAD mice exhibit fewer and shorter sharp-wave ripples with impaired place cell reactivation. By showing inhibitory synaptic dysfunction in 5XFAD mice during spatial navigation behavior and suggesting a synaptic mechanism underlying deficits in network activity essential for memory, this work bridges the gap between synaptic and neural activity deficits in AD.

Prince et al. find impaired inhibitory synapses, sharp-wave ripples, and place cell reactivation during behavior in a mouse model of Alzheimer’s disease. These results link synaptic deficits in Alzheimer’s disease to dysfunction of neural activity essential for memory.

Spearmint Extract Containing Rosmarinic Acid Suppresses Amyloid Fibril Formation of Proteins Associated with Dementia

Neurological dementias such as Alzheimer's disease and Lewy body dementia are thought to be caused in part by the formation and deposition of characteristic insoluble fibrils of polypeptides such as amyloid beta (Aβ), Tau, and/or α-synuclein (αSyn). In this context, it is critical to suppress and remove such aggregates in order to prevent and/or delay the progression of dementia in these ailments. In this report, we investigated the effects of spearmint extract (SME) and rosmarinic acid (RA; the major component of SME) on the amyloid fibril formation reactions of αSyn, Aβ, and Tau proteins in vitro. SME or RA was added to soluble samples of each protein and the formation of fibrils was monitored by thioflavin T (ThioT) binding assays and transmission electron microscopy (TEM). We also evaluated whether preformed amyloid fibrils could be dissolved by the addition of RA. Our results reveal for the first time that SME and RA both suppress amyloid fibril formation, and that RA could disassemble preformed fibrils of αSyn, Aβ, and Tau into non-toxic species. Our results suggest that SME and RA may potentially suppress amyloid fibrils implicated in the progression of Alzheimer's disease and Lewy body dementia in vivo, as well.

Design and synthesis of novel pyrazolo[3,4-d]pyrimidin-4-one bearing quinoline scaffold as potent dual PDE5 inhibitors and apoptotic inducers for cancer therapy

PDE5 targeting represents a new and promising strategy for apoptosis induction and inhibition of tumor cell growth due to its over-expression in diverse types of human carcinomas. Accordingly, we report the synthesis of series of pyrazolo[3,4-d]pyrimidin-4-one carrying quinoline moiety (11a-r) with potential dual PDE5 inhibition and apoptotic induction for cancer treatment. These hybrids were structurally elucidated and characterized with variant spectroscopic techniques as ¹H NMR, ¹³C NMR and elemental analysis. The assessment of their anticancer activities has been declared. All the rationalized compounds 11a-r have been selected for their cytotoxic activity screening by NCI against 60 cell lines. Compounds 11a, 11b, 11j and 11k were the most active hybrids. Among all, compound 11j was further selected for five dose tesing and it displayed outstanding activity with strong antitumor activity against the nine tumor subpanels tested with selectivity ratios ranging from 0.019 to 8.3 at the GI₅₀ level. Further, the most active targets 11a, b, j and k were screened for their PDE5 inhibitory activity, compound 11j (with IC₅₀ 1.57 nM) exhibited the most potent PDE5 inhibitory activity. Moreover, compound 11j is also showed moderate EGFR inhibition with IC₅₀ of 5.827 ± 0.46 µM, but significantly inhibited the Wnt/β-catenin pathway with IC₅₀1286.96 ± 12.37 ng/mL. In addition, compound 11j induced the intrinsic apoptotic mitochondrial pathway in HepG2 cells as evidenced by the lower expression levels of the anti-apoptotic Bcl-2 protein, and the higher expression of the pro-apoptotic protein Bax, p53, cytochrome c and the up-regulated active caspase-9 and caspase-3 levels. All results confirmed by western blotting assay. Compound 11j exhibit pre G1 apoptosis and cell cycle arrest at G2/M phase. In conclusion, hybridization of quinoline moiety with the privileged pyrazolo[3,4-d]pyrimidinon-4-one structure resulted in highly potent anticancer agent, 11j, which deserves more study, in particular, in vivo and clinical investiagtions, and it is expected that these results would be applied for more drug discovery process.

Neuroprotective Potential of Curcumin-Loaded Nanostructured Lipid Carrier in an Animal Model of Alzheimer's Disease: Behavioral and Biochemical Evidence

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases and is caused by accumulation of amyloid-β (Aβ) peptide and is associated with neurological abnormalities in learning and memory. The protective role of curcumin on nerve cells, along with a potent antioxidant and free radical scavenging activity, has been widely studied. However, its low bioavailability and limited transport ability across the blood-brain barrier are two major drawbacks of its application in the treatment of different neurodegenerative diseases. The present study was designed to improve the effectiveness of curcumin in the treatment of Aβ-induced cognitive deficiencies in a rat model of AD by loading it into nanostructured lipid carriers (NLCs). The accumulation rate of curcumin (505.76±38.4 ng/g-1 h) in rat brain, as well as its serum levels, were significantly increased by using curcumin-loaded NLCs. The effective role of NLCs for brain delivery of curcumin was confirmed by reduced oxidative stress parameters (ROS formation, lipid peroxidation, and ADP/ATP ratio) in the hippocampal tissue and improvement of spatial memory. Also, histopathological studies revealed the potential of Cur-NLCs in decreasing the hallmarks of Aβ in AD in the animal model. The result of studying the neuroprotective potential of Cur-NLC in both pre-treatment and treatment modes showed that loading curcumin in NLCs is an effective strategy for increasing curcumin delivery to the brain and reducing Aβ-induced neurological abnormalities and memory defects and that it can be the basis for further studies in the area of AD prevention and treatment.

Impairments of Synaptic Plasticity Induction Threshold and Network Oscillatory Activity in the Hippocampus Underlie Memory Deficits in a Non-Transgenic Mouse Model of Amyloidosis

In early Alzheimer disease (AD) models synaptic failures and upstreaming aberrant patterns of network synchronous activity result in hippocampal-dependent memory deficits. In such initial stage, soluble forms of Amyloid-β (Aβ) peptides have been shown to play a causal role. Among different Aβ species, Aβ_25-35 has been identified as the biologically active fragment, as induces major neuropathological signs related to early AD stages. Consequently, it has been extensively used to acutely explore the pathophysiological events related with neuronal dysfunction induced by soluble Aβ forms. However, the synaptic mechanisms underlying its toxic effects on hippocampal-dependent memory remain unresolved. Here, in an in vivo model of amyloidosis generated by intracerebroventricular injections of Aβ_25-35 we studied the synaptic dysfunction mechanisms underlying hippocampal cognitive deficits. At the synaptic level, long-term potentiation (LTP) of synaptic excitation and inhibition was induced in CA1 region by high frequency simulation (HFS) applied to Schaffer collaterals. Aβ_25-35 was found to alter metaplastic mechanisms of plasticity, facilitating long-term depression (LTD) of both types of LTP. In addition, aberrant synchronization of hippocampal network activity was found while at the behavioral level, deficits in hippocampal-dependent habituation and recognition memories emerged. Together, our results provide a substrate for synaptic disruption mechanism underlying hippocampal cognitive deficits present in Aβ_25-35 amyloidosis model.

Synaptic Elimination in Neurological Disorders

Synapses are well known as the main structures responsible for transmitting information through the release and recognition of neurotransmitters by pre- and post-synaptic neurons. These structures are widely formed and eliminated throughout the whole lifespan via processes termed synaptogenesis and synaptic pruning, respectively. Whilst the first pro-cess is needed for ensuring proper connectivity between brain regions and also with the periphery, the second phenomenon is important for their refinement by eliminating weaker and unnecessary synapses and, at the same time, maintaining and fa-voring the stronger ones, thus ensuring proper synaptic transmission. It is well-known that synaptic elimination is modulated by neuronal activity. However, only recently the role of the classical complement cascade in promoting this phenomenon has been demonstrated. Specifically, microglial cells recognize activated complement component 3 (C3) bound to synapses tar-geted for elimination, triggering their engulfment. As this is a highly relevant process for adequate neuronal functioning, dis-ruptions or exacerbations in synaptic pruning could lead to severe circuitry alterations that could underlie neuropathological alterations typical of neurological and neuropsychiatric disorders. In this review, we focus on discussing the possible in-volvement of excessive synaptic elimination in Alzheimer’s disease, as it has already been reported dendritic spine loss in post-synaptic neurons, increased association of complement proteins with its synapses and, hence, augmented microglia-mediated pruning in animal models of this disorder. In addition, we briefly discuss how this phenomenon could be related to other neurological disorders, including multiple sclerosis and schizophrenia.

Dissociation of somatostatin and parvalbumin interneurons circuit dysfunctions underlying hippocampal theta and gamma oscillations impaired by amyloid β oligomers in vivo

Accumulation of amyloid β oligomers (AβO) in Alzheimer’s disease (AD) impairs hippocampal theta and gamma oscillations. These oscillations are important in memory functions and depend on distinct subtypes of hippocampal interneurons such as somatostatin-positive (SST) and parvalbumin-positive (PV) interneurons. Here, we investigated whether AβO causes dysfunctions in SST and PV interneurons by optogenetically manipulating them during theta and gamma oscillations in vivo in AβO-injected SST-Cre or PV-Cre mice. Hippocampal in vivo multi-electrode recordings revealed that optogenetic activation of channelrhodopsin-2 (ChR2)-expressing SST and PV interneurons in AβO-injected mice selectively restored AβO-induced reduction of the peak power of theta and gamma oscillations, respectively, and resynchronized CA1 pyramidal cell (PC) spikes. Moreover, SST and PV interneuron spike phases were resynchronized relative to theta and gamma oscillations, respectively. Whole-cell voltage-clamp recordings in CA1 PC in ex vivo hippocampal slices from AβO-injected mice revealed that optogenetic activation of SST and PV interneurons enhanced spontaneous inhibitory postsynaptic currents (IPSCs) selectively at theta and gamma frequencies, respectively. Furthermore, analyses of the stimulus–response curve, paired-pulse ratio, and short-term plasticity of SST and PV interneuron-evoked IPSCs ex vivo showed that AβO increased the initial GABA release probability to depress SST/PV interneuron’s inhibitory input to CA1 PC selectively at theta and gamma frequencies, respectively. Our results reveal frequency-specific and interneuron subtype-specific presynaptic dysfunctions of SST and PV interneurons’ input to CA1 PC as the synaptic mechanisms underlying AβO-induced impairments of hippocampal network oscillations and identify them as potential therapeutic targets for restoring hippocampal network oscillations in early AD.

Probing the Nongeneralized Amyloid Inhibitory Mechanism of Hydrophobic Chaperone

Increasing prevalence of protein misfolding disorders urges the search for effective therapies. Although several antiaggregation molecules have been identified, their molecular process of aggregation and clinical trials are underway. The present study is focused on the mechanism through which phenyl butyrate (PB), a chemical chaperone, triggers inhibition of human serum albumin (HSA) fibrillation. Turbidity and Rayleigh light scattering (RLS) measurements reveal the marked presence of aggregates in HSA that were confirmed as amyloid fibrils by thioflavin T (ThT) and Congo red (CR) and were subsequently inhibited by PB in a dose dependent manner. ThT fluorescence kinetics reveals a decrease in the apparent rate constant, K_app, in the presence of PB without triggering a lag phase in HSA suggesting PB's interference with the elongation phase. Dynamic light scattering (DLS) results display a reduction in the aggregate size in the presence of PB. Isothermal titration calorimetry (ITC) data reveals strong binding of PB at site II both at 25 °C (K_b ≈ 1.94 × 10⁵ M^-1) and 65 °C (K_b ≈ 2.90 × 10⁴ M^-1), mediated by hydrogen bonding. Overall, our finding establishes that PB stabilizes partially unfolded HSA molecules through hydrogen bonding, thereby preventing establishment of hydrogen bonds between them and hindering their progression into amyloid fibrils. This is in contrast to its chaperone effect manifested with other proteins.

Neuroprotective Effect of New Nanochelating-Based Nano Complex, ALZc3, Against Aβ (1-42)-Induced Toxicity in Rat: a Comparison with Memantine

PURPOSE

The current drugs for Alzheimer's disease (AD) are only used to slow or delay the progression of the pathology. So using a novel technology is a necessity to synthesize more effective medications to control this most common cause of dementia. In this study, using nanochelating technology, ALZc3 was synthesized and its therapeutic effects were evaluated in comparison with memantine on a well-known rat model of AD, which is based on Amyloid-βeta (Aβ) injection into the brain.

MATERIALS AND METHODS

Aβ (1-42) was injected bilaterally into the CA1 area of the hippocampus of male rats and then animals were treated daily by oral administration of Alz-C3, memantine or their vehicles. Activities of antioxidant enzymes catalase and superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA) levels, as well as Bax/Bcl-2 ratio, caspase-3 activation, and TNF-α expression were evaluated 7 days after Aβ injection. Finally, learning and memory of the rats were assessed by Morris water maze test.

RESULTS

ALZc3 and memantine improved memory impairment and antioxidant activity and reduced TNF-α expression, caspase-3 activity and Bax/Bcl-2 ratio in the rat's hippocampus. The results showed a superiority of ALZC3 compared to memantine in reducing caspase-3, increasing CAT activity in Aβ (1-42)-injected groups and improving apoptosis factor in healthy mice.

CONCLUSION

These results indicated that ALZc3 could significantly prevent the memory impairment and Aβ (1-42) toxicity. Thus, ALZc3 could be a promising novel anti-AD agent.

Human Neural Stem Cells Reinforce Hippocampal Synaptic Network and Rescue Cognitive Deficits in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is characterized by memory impairments in its earliest clinical phase. The synaptic loss and dysfunction leading to failures of synaptic networks in AD brain directly cause cognitive deficits of patient. However, it remains unclear whether the synaptic networks in AD brain could be repaired. In this study, we generated functional human induced neural progenitor/stem cells (iNPCs) that had been transplanted into the hippocampus of immunodeficient wild-type and AD mice. The grafted human iNPCs efficiently differentiated into neurons that displayed long-term survival, progressively acquired mature membrane properties, formed graft-host synaptic connections with mouse neurons and functionally integrated into local synaptic circuits, which eventually reinforced and repaired the neural networks of host hippocampus. Consequently, AD mice with human iNPCs exhibited enhanced synaptic plasticity and improved cognitive abilities. Together, our results suggest that restoring synaptic failures by stem cells might provide new directions for the development of novel treatments for human AD.

Cytotoxic species in amyloid-associated diseases: Oligomers or mature fibrils

Amyloid diseases especially, Alzheimer's disease (AD), is characterized by an imbalance between the production and clearance of amyloid-β (Aβ) species. Amyloidogenic proteins or peptides can transform structurally from monomers into β-stranded fibrils via multiple oligomeric states. Among various amyloid species, structured oligomers are proposed to be more toxic than fibrils; however, the identification of amyloid oligomers has been challenging due to their heterogeneous and metastable nature. Multiple techniques have recently helped in better understanding of oligomer's assembly details and structural properties. Moreover, some progress on elucidating the mechanisms of oligomer-triggered toxicity has been made. Based on the collection of current findings, there is growing consensus that control of toxic amyloid oligomers could be a valid approach to regulate amyloid-associated toxicity, which could advance development of new diagnostics and therapeutics for amyloid-related diseases. In this review, we have described the recent scenario of amyloid diseases with a great deal of information about the recent understanding of oligomers' assembly, structural properties, and toxicity. Also comprehensive details have been provided to differentiate the degree of toxicity associated with prefibrillar aggregates.

BACE1 inhibitors: Current status and future directions in treating Alzheimer's disease

Alzheimer's disease (AD) is an irreversible, progressive neurodegenerative brain disorder with no current cure. One of the important therapeutic approaches of AD is the inhibition of β-site APP cleaving enzyme-1 (BACE1), which is involved in the rate-limiting step of the cleavage process of the amyloid precursor protein (APP) leading to the generation of the neurotoxic amyloid β (Aβ) protein after the γ-secretase completes its function. The produced insoluble Aβ aggregates lead to plaques deposition and neurodegeneration. BACE1 is, therefore, one of the attractive targets for the treatment of AD. This approach led to the development of potent BACE1 inhibitors, many of which were advanced to late stages in clinical trials. Nonetheless, the high failure rate of lead drug candidates targeting BACE1 brought to the forefront the need for finding new targets to uncover the mystery behind AD. In this review, we aim to discuss the most promising classes of BACE1 inhibitors with a description and analysis of their pharmacodynamic and pharmacokinetic parameters, with more focus on the lead drug candidates that reached late stages of clinical trials, such as MK8931, AZD-3293, JNJ-54861911, E2609, and CNP520. In addition, the manuscript discusses the safety concerns and insignificant physiological effects, which were highlighted for the most successful BACE1 inhibitors. Furthermore, the review demonstrates with increasing evidence that despite tremendous efforts and promising results conceived with BACE1 inhibitors, the latest studies suggest that their clinical use for treating Alzheimer's disease should be reconsidered. Finally, the review sheds light on alternative therapeutic options for targeting AD.

Exploring the influence of brilliant blue G on amyloid fibril formation of lysozyme

Evidence suggests that amyloid fibril mitigation/inhibition is considered a promising approach toward treating amyloid diseases. In this work, we first examined how amyloid fibrillogenesis of lysozyme was affected by BBG, a safe triphenylmethane compound with nice blood-brain-barrier-permeability, and found that shorter fibrillar species were formed in the lysozyme samples treated with BBG. Next, alterations in the features including the secondary as well as tertiary structure, extent of aggregation, and molecular distribution of lysozyme triggered by the addition of BBG were examined by various spectroscopic techniques, right-angle light scattering, dynamic light scattering, and SDS-PAGE. In addition, we have investigated how BBG affected the lysozyme fibril-induced cytotoxicity in SH-SY5Y cells. We found that a large quantity of shorter fibrillar species and more lysozyme monomers were present in the samples treated with BBG. Also, the addition of BBG rescued SH-SY5Y cells from cell death induced by amyloid fibrils of lysozyme. Finally, information about the binding sites and interacting forces involved in the BBG-lysozyme interaction was further explored using synchronous fluorescence and molecular docking approaches. Molecular docking results revealed that, apart from the hydrophobic interaction(s), hydrogen bonding, electrostatic interactions, and van der Waal forces may also be involved in the binding interaction.

Extracellular Zn2+-independently attenuated LTP by human amyloid β1-40 and rat amyloid β1-42

Human amyloid-β_1-40 (Aβ_1-40) and rat Aβ_1-42 have lower affinity for extracellular Zn²⁺ than human Aβ_1-42. Here we report extracellular Zn²⁺-independent attenuation of dentate gyrus long-term potentiation (LTP) by human Aβ_1-40 and rat Aβ_1-42. On the basis of the data that dentate gyrus LTP is extracellular Zn²⁺-dependently attenuated after local injection of human Aβ_1-42 (25 pmol, 1 μl) into the dentate gyrus, which increases intracellular Zn²⁺ in the dentate gyrus, the toxicity of human Aβ_1-40 and rat Aβ_1-42 was compared in the in vivo system with human Aβ_1-42. Dentate gyrus LTP was attenuated after injection of human Aβ_1-40 and rat Aβ_1-42 (25 pmol, 1 μl) into the dentate gyrus, which did not increase intracellular Zn²⁺ in the dentate gyrus. The attenuated LTP was not rescued by co-injection of CaEDTA, an extracellular Zn²⁺ chelator. The present study suggests that human Aβ_1-40 and rat Aβ_1-42 affect cognitive activity via extracellular Zn²⁺-independent mechanism at low micromolar concentration.

Protective role of Apelin-13 on amyloid β25-35-induced memory deficit; Involvement of autophagy and apoptosis process

Alzheimer's disease (AD) by progressive neurodegenerative pattern is associated with autophagy stress which is suggested as a potential cause of amyloid β (Aβ) aggregation and neural loss. Apelin-13, a neuropeptide with modulatory effect on autophagy, has been shown the beneficial effects on neural cell injuries. We investigated the effect of Apelin-13 on Aβ-induced memory deficit as well as autophagy and apoptosis processes. We performed bilateral intra-CA1 injection of Aβ25-35 alone or in combination with Apelin-13. Spatial reference and working memory was evaluated using the Morris water maze (MWM) and Y-maze tests. Hippocampus was harvested on 2, 5, 10 and 21 days after Aβ injection. The light chain 3 (LC3II/I) ratio, histone deacetylase 6 (HDAC6) level, Caspase-3 cleavage, and mTOR phosphorylation were assessed using western blot technique. Intra-CA1 injection of Aβ caused impairment of working and spatial memory. We observed higher LC3II/I ratio, cleaved caspase-3 and lower HDAC6, and p-mTOR/mTOR ratio in Aβ-treated animals. Apelin-13 provided significant protection against the destructive effects of Aβ on working and spatial memory. Apelin-13 prevented the increase of LC3II/I ratio and cleaved caspase-3 on days 10 and 21 after injection of Aβ. It also limited the Aβ-induced reduction in HDAC6 expression. This implies that Apelin-13 has suppressed both autophagy and apoptosis. Our findings suggested that the neuroprotection of Apelin-13 may be in part related to autophagy and apoptosis inhibition via the mTOR signaling pathway. Apelin-13 may be a promising approach to improve memory impairment and potentially pave the way for new therapeutic plans in AD.

Translational inhibition of α-synuclein by Posiphen normalizes distal colon motility in transgenic Parkinson mice

Parkinson disease (PD) is a neurodegenerative disease with motor as well as non-motor symptoms, including gastrointestinal dysfunction. In humans, these precede the motor symptoms by decades. Previously developed and characterized transgenic mice expressing the mutant human α-synuclein gene (SNCA) (either A53T or A30P), but not the endogenous mouse Snca, serve as models for familial PD. These animals demonstrate both robust abnormalities in enteric nervous system (ENS) function as well as synuclein-immunoreactive aggregates in ENS ganglia by 3 months of age, recapitulating early gastrointestinal abnormalities seen before the gait impairment characteristics of human and murine PD. Posiphen is a translational inhibitor of α-synuclein that targets the 5' untranslated region (UTR) of SNCA mRNA and could be a potential drug for the treatment of PD. However, its efficacy in ameliorating symptoms of PD has not yet been evaluated. Here, we used these transgenic mouse models to investigate the efficacy of Posiphen in reversing the gastrointestinal dysfunction. We show that Posiphen normalizes the colonic motility of both transgenic mouse models, although it did not affect the Whole Gut Transit Time (WGTT). Pharmacokinetics studies revealed that Posiphen is more abundant in the brain than in blood, in agreement with its lipophilicity, and the main metabolite is N⁸-NorPosiphen, a molecule with similar properties as Posiphen. The brain Posiphen levels necessary to effect optimal function were calculated and compared with efficacious brain levels from previous studies, showing that a 2-3 mM concentration of Posiphen and metabolites is sufficient for functional efficacy. Finally, 10 mg/kg Posiphen reduced α-synuclein levels in the gut of hSNCA^A53T mice treated for twenty-one weeks, while 50 and 65 mg/kg Posiphen reduced α-synuclein levels in the brain of hSNCA^A53T mice treated for twenty-one days. In conclusion, this is the first study showing the preclinical efficacy of Posiphen in normalizing the colonic motility in mouse models of gastrointestinal dysfunction in early PD. This result is in agreement with the ability of Posiphen to reach the nervous system, and its mechanism of action, the translational inhibition of α-synuclein expression. These significant findings support further development of Posiphen as a drug for the treatment of PD.

Amyloid Oligomers, Protofibrils and Fibrils

Amyloid diseases are of major concern all over the world due to a number of factors including: (i) aging population, (ii) increasing life span and (iii) lack of effective pharmacotherapy options. The past decade has seen intense research in discovering disease-modifying multi-targeting small molecules as therapeutic options. In recent years, targeting the amyloid cascade has emerged as an attractive strategy to discover novel neurotherapeutics. Formation of amyloid species, with different degrees of solubility and neurotoxicity is associated with the gradual decline in cognition leading to dementia/cell dysfunction. Here, in this chapter, we have described the recent scenario of amyloid diseases with a great deal of information about the structural features of oligomers, protofibrils and fibrils. Also, comprehensive details have been provided to differentiate the degree of toxicity associated with prefibrillar aggregates. Moreover, a review of the technologies that aid characterisation of oligomer, protofibrils and fibrils as well as various inhibition strategies to overcome protein fibrillation are also discussed.

Amyloid toxicity in Alzheimer's disease

A major feature of Alzheimer's disease (AD) pathology is the plaque composed of aggregated amyloid-β (Aβ) peptide. Although these plaques may have harmful properties, there is much evidence to implicate soluble oligomeric Aβ as the primary noxious form. Aβ oligomers can be generated both extracellularly and intracellularly. Aβ is toxic to neurons in a myriad of ways. It can cause pore formation resulting in the leakage of ions, disruption of cellular calcium balance, and loss of membrane potential. It can promote apoptosis, cause synaptic loss, and disrupt the cytoskeleton. Current treatments for AD are limited and palliative. Much research and effort is being devoted to reducing Aβ production as an approach to slowing or preventing the development of AD. Aβ formation results from the amyloidogenic cleavage of human amyloid precursor protein (APP). Reconfiguring this process to disfavor amyloid generation might be possible through the reduction of APP or inhibition of enzymes that convert the precursor protein to amyloid.

Amyloid-Beta and Phosphorylated Tau Accumulations Cause Abnormalities at Synapses of Alzheimer's disease Neurons

Amyloid-beta (Aβ) and hyperphosphorylated tau are hallmark lesions of Alzheimer's disease (AD). However, the loss of synapses and dysfunctions of neurotransmission are more directly tied to disease severity. The role of these lesions in the pathoetiological progression of the disease remains contested. Biochemical, cellular, molecular, and pathological studies provided several lines of evidence and improved our understanding of how Aβ and hyperphosphorylated tau accumulation may directly harm synapses and alter neurotransmission. In vitro evidence suggests that Aβ and hyperphosphorylated tau have both direct and indirect cytotoxic effects that affect neurotransmission, axonal transport, signaling cascades, organelle function, and immune response in ways that lead to synaptic loss and dysfunctions in neurotransmitter release. Observations in preclinical models and autopsy studies support these findings, suggesting that while the pathoetiology of positive lesions remains elusive, their removal may reduce disease severity and progression. The purpose of this article is to highlight the need for further investigation of the role of tau in disease progression and its interactions with Aβ and neurotransmitters alike.

Environmental enrichment and exercise are better than social enrichment to reduce memory deficits in amyloid beta neurotoxicity

Recently, nongenetic animal models to study the onset and development of Alzheimer's disease (AD) have appeared, such as the intrahippocampal infusion of peptides present in Alzheimer amyloid plaques [i.e., amyloid-β (Aβ)]. Nonpharmacological approaches to AD treatment also have been advanced recently, which involve combinations of behavioral interventions whose specific effects are often difficult to determine. Here we isolate the neuroprotective effects of three of these interventions-environmental enrichment (EE), anaerobic physical exercise (AnPE), and social enrichment (SE)-on Aβ-induced oxidative stress and on impairments in learning and memory induced by Aβ. Wistar rats were submitted to 8 wk of EE, AnPE, or SE, followed by Aβ infusion in the dorsal hippocampus. Short-term memory (STM) and long-term memory (LTM) of object recognition (OR) and social recognition (SR) were evaluated. Biochemical assays determined hippocampal oxidative status: reactive oxygen species, lipid peroxidation by thiobarbituric acid reactive substance (TBARS) test, and total antioxidant capacity by ferric reducing/antioxidant power (FRAP), as well as acetylcholinesterase activity. Aβ infusion resulted in memory deficits and hippocampal oxidative damage. EE and AnPE prevented all memory deficits (STM and LTM of OR and SR) and lipid peroxidation (i.e., TBARS). SE prevented only the SR memory deficits and the decrease of total antioxidant capacity decrease (i.e., FRAP). Traditionally, findings obtained with EE protocols do not allow discrimination of the roles of the three individual factors involved. Here we demonstrate that EE and physical exercise have better neuroprotective effects than SE in memory deficits related to Aβ neurotoxicity in the AD model tested.

Synaptic plasticity modulation by circulating peptides and metaplasticity: Involvement in Alzheimer's disease

Synaptic plasticity is a cellular process involved in learning and memory whose alteration in its two main forms (Long Term Depression (LTD) and Long Term Potentiation (LTP)), is observed in most brain pathologies, including neurodegenerative disorders such as Alzheimer's disease (AD). In humans, AD is associated at the cellular level with neuropathological lesions composed of extracellular deposits of β-amyloid (Aβ) protein aggregates and intracellular neurofibrillary tangles, cellular loss, neuroinflammation and a general brain homeostasis dysregulation. Thus, a dramatic synaptic environment perturbation is observed in AD patients, involving changes in brain neuropeptides, cytokines, growth factors or chemokines concentration and diffusion. Studies performed in animal models demonstrate that these circulating peptides strongly affect synaptic functions and in particular synaptic plasticity. Besides this neuromodulatory action of circulating peptides, other synaptic plasticity regulation mechanisms such as metaplasticity are altered in AD animal models. Here, we will review new insights into the study of synaptic plasticity regulatory/modulatory mechanisms which could influence the process of synaptic plasticity in the context of AD with a particular attention to the role of metaplasticity and peptide dependent neuromodulation.

Prion-Like Characteristics of Polyglutamine-Containing Proteins

Transmissible spongiform encephalopathies are infectious neurodegenerative diseases caused by the conversion of prion protein (PrP) into a self-replicating conformation that spreads via templated conversion of natively folded PrP molecules within or between cells. Recent studies provide compelling evidence that prion-like behavior is a general property of most protein aggregates associated with neurodegenerative diseases. Many of these disorders are associated with spontaneous protein aggregation, but genetic mutations can increase the aggregation propensity of specific proteins, including expansion of polyglutamine (polyQ) tracts, which is causative of nine inherited neurodegenerative diseases. Aggregates formed by polyQ-expanded huntingtin (Htt) in Huntington's disease can transfer between cells and seed the aggregation of cytoplasmic wild-type Htt in a prion-like manner. Additionally, prion-like properties of glutamine-rich proteins underlie nonpathological processes in yeast and higher eukaryotes. Here, we review current evidence supporting prion-like characteristics of polyQ and glutamine-rich proteins.

Seed-induced acceleration of amyloid-β mediated neurotoxicity in vivo

Seeded propagation of amyloid-beta (Aβ) pathology is suggested to contribute to the progression of Alzheimer's disease. Local overproduction of aggregation-prone Aβ variants could explain the focal initiation of a seeding cascade that subsequently triggers widespread pathology. Several animal models support this seeding concept by demonstrating accelerated Aβ deposition following inoculation with Aβ-containing homogenates, however its role in progressive neurodegeneration remains unclear. Here, we present a non-invasive approach to study Aβ seeding processes in vivo using Drosophila models. We show that small amounts of aggregation-competent Aβ₄₂ seeds, generated in selected neuronal clusters, can induce the deposition of the pan-neuronally expressed and otherwise soluble Aβ₄₀. Moreover, our models visualize the accelerated formation and propagation of amyloid pathology throughout the brain, which correlates with severe neurotoxicity. Taken together, these in vivo models provide mechanistic insights into disease-related processes and represent versatile genetic tools to determine novel modifiers of the Aβ seeding cascade.Seeding of amyloid beta from one brain region to another is thought to contribute to the progression of Alzheimer's disease, although to date most studies have depended on inoculation of animals with exogenous amyloid. Here the authors describe a genetic seed and target system in Drosophila which may be useful for the mechanistic study of seeding of amyloid in vivo.

Differential Membrane Toxicity of Amyloid-β Fragments by Pore Forming Mechanisms

A major characteristic of Alzheimer's disease (AD) is the presence of amyloid-β peptide (Aβ) oligomers and aggregates in the brain. It is known that Aβ oligomers interact with the neuronal membrane and induce perforations that cause an influx of calcium ions and enhance the release of synaptic vesicles leading to a delayed synaptic failure by vesicle depletion. To better understand the mechanism by which Aβ exerts its effect on the plasma membrane, we evaluated three Aβ fragments derived from different regions of Aβ(1-42); Aβ(1-28) from the N-terminal region, Aβ(25-35) from the central region, and Aβ(17-42) from the C-terminal region. The neuronal activities of these fragments were examined with patch clamp, immunofluorescence, transmission electron microscopy, aggregation assays, calcium imaging, and MTT reduction assays. The present results indicate that the fragment Aβ(1-28) contributes to aggregation, an increase in intracellular calcium and synaptotoxicity, but is not involved in membrane perforation; Aβ(25-35) is important for membrane perforation, calcium increase, and synaptotoxicity; and Aβ(17-42) induced mitochondrial toxicity similar to the full length Aβ(1-42), but was unable to induce membrane perforation and calcium increase, supporting the idea that it is less toxic in the non-amyloidogenic pathway.

G-CSF-mobilized Bone Marrow Mesenchymal Stem Cells Replenish Neural Lineages in Alzheimer's Disease Mice via CXCR4/SDF-1 Chemotaxis

Recent studies reported granulocyte colony-stimulating factor (G-CSF) treatment can improve the cognitive function of Alzheimer's disease (AD) mice, and the mobilized hematopoietic stem cells (HSCs) or bone marrow mesenchymal stem cells (BM-MSCs) are proposed to be involved in this recovery effect. However, the exact role of mobilized HSC/BM-MSC in G-CSF-based therapeutic effects is still unknown. Here, we report that C-X-C chemokine receptor type 4 (CXCR4)/stromal cell-derived factor 1 (SDF-1) chemotaxis was a key mediator in G-CSF-based therapeutic effects, which was involved in the recruitment of repair-competent cells. Furthermore, we found both mobilized HSCs and BM-MSCs were able to infiltrate into the brain, but only BM-MSCs replenished the neural lineage cells and contributed to neurogenesis in the brains of AD mice. Together, our data show that mobilized BM-MSCs are involved in the replenishment of neural lineages following G-CSF treatment via CXCR4/SDF-1 chemotaxis and further support the potential use of BM-MSCs for further autogenically therapeutic applications.

Alzheimer's disease like pathology induced six weeks after aggregated amyloid-beta injection in rats: increased oxidative stress and impaired long-term memory with anxiety-like behavior

OBJECTIVES

Amyloid-beta (Aβ) peptide deposition into insoluble plaques is a pathological hallmark of Alzheimer's disease (AD), but soluble oligomeric Aβ is considered to be more potent and has been hypothesized to directly impair learning and memory. Also, evidences from some clinical studies indicated that Aβ oligomer formation is the major cause for early AD onset. However, the biochemical mechanism involved in the oligomer-induced toxicity is not very well addressed. So, thise present study was undertaken to study the effects of single intracerebroventricular (icv) injection of protofibrillar Aβ 1-42 on the behavioral and biochemical profile in rats.

METHODS

Rats were divided into two groups (n = 8 per group): (1) sham control group and (2) Aβ 1-42 injected group. A single dose of protofibrillar Aβ 1-42 (5 ul) through icv injection was bilaterally administered into the dorsal hippocampus, while sham control animals were administered with 5 µl of vehicle.

RESULTS

The results demonstrated that the protofibrillar Aβ significantly inhibited long-term memory retention and increased anxiety levels as shown by the behavioral studies. The amyloid deposits were present inside the brain even six weeks after injection as confirmed by thioflavin-T staining and the neurodegeneration induced by these deposits was confirmed by Nissl's staining in hippocampal and cortical regions. The amyloid aggregates induced reactive oxygen species (ROS) production, acetylcholinesterase activity, nitrite levels, lipid peroxidation, and inhibited antioxidant enzyme activity in hippocampus, cortex, and striatum regions of rat brain after six weeks.

DISCUSSION

The present study indicated that protofibrillar Aβ 1-42 injection altered long term memory, induced anxiety-like behavior and also developed Alzheimer's disease like pathology in rats.

Designer Self-Assemble Peptides Maximize the Therapeutic Benefits of Neural Stem Cell Transplantation for Alzheimer's Disease via Enhancing Neuron Differentiation and Paracrine Action

The neuropathological hallmarks of Alzheimer's disease (AD) include the presence of extracellular amyloid-β peptide (Aβ) in the form of amyloid plaques and neuronal loss. Neural stem cell (NSC) is being scrutinized as a promising cell replacement therapy for various neurodegenerative diseases. However, the unfavorable niche at the site of degenerative disease is hostile to the survival and differentiation of transplanted cells. Here, we undertook in vitro and in vivo works to examine whether a designer self-assemble peptide (DSP), which contains one functional domain Tyr-Ile-Gly-Ser-Arg (YIGSR) derived from laminin, promotes the survival and neuronal differentiation of NSC and behavioral improvement. We found that DSP could undergo spontaneous assembly into well-ordered nanofibers, and it not only facilitated the cell viability in normal culture condition, but also decreased the number of apoptotic cells induced by Aβ in vitro. NSC seeded in DSP showed much more neuronal differentiation than that seeded in self-assemble peptide (SP) or alone. In the AD model, NSC transplantation in DSP-treated AD rats demonstrated much more obvious cognitive rescue with restoration of learning/memory function compared with NSC transplantation in SP, NSC alone, or DSP alone treated ones. Interestingly, DSP enhanced the survival and neuronal differentiation of transplanted NSC. Apoptosis levels in the CA1 region and Aβ level in the hippocampus were significantly decreased in the group of NSC transplantation in DSP. Moreover, synaptic function, indicated by the expression of pre-synaptic protein synapsin-1, was restored and the secretion of anti-inflammatory and neurotrophic factors were increased, such as IL-10, brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), and insulin-like growth factor 1 (IGF-1), while the expression of pro-inflammatory factors were decreased, such as TNF-α and IL-1β. These data firstly unveiled that the biomaterial DSP can maximize the therapeutic benefits of NSC transplantation for AD through improving the survival and differentiation of transplanted stem cells and promoting the effects of neuroprotection, anti-neuroinflammatory and paracrine action. Our results may have important clinical implications for the design of future NSC-based strategies using the biomaterials for various neurodegenerative diseases including AD.

Glutamate protects neuromuscular junctions from deleterious effects of β-amyloid peptide and conversely: an in vitro study in a nerve-muscle coculture

Murine models of Alzheimer's disease with elevated levels of amyloid-β (Aβ) peptide present motor axon defects and neuronal death. Aβ1-42 accumulation is observed in motor neurons and spinal cords of sporadic and familial cases of amyotrophic lateral sclerosis (ALS). Motor neurons are highly susceptible to glutamate, which has a role in ALS neuronal degeneration. The current study investigates the link between Aβ and glutamate in this neurodegenerative process. Primary rat nerve and human muscle cocultures were intoxicated with glutamate or Aβ. Neuromuscular junction (NMJ) mean size and neurite length were evaluated. The role of N-methyl-D-aspartate receptor (NMDAR) was investigated by using MK801. Glutamate and Aβ production were evaluated in culture supernatant. The current study shows that NMJs are highly sensitive to Aβ peptide, that the toxic pathway involves glutamate and NMDAR, and that glutamate and Aβ act in an interlinked manner. Some motor diseases (e.g., ALS), therefore, could be considered from a new point of view related to these balance disturbances.

Nuclear translocation uncovers the amyloid peptide Aβ42 as a regulator of gene transcription

Although soluble species of the amyloid-β peptide Aβ42 correlate with disease symptoms in Alzheimer disease, little is known about the biological activities of amyloid-β (Aβ). Here, we show that Aβ peptides varying in lengths from 38 to 43 amino acids are internalized by cultured neuroblastoma cells and can be found in the nucleus. By three independent methods, we demonstrate direct detection of nuclear Aβ42 as follows: (i) biochemical analysis of nuclear fractions; (ii) detection of biotin-labeled Aβ in living cells by confocal laser scanning microscopy; and (iii) transmission electron microscopy of Aβ in cultured cells, as well as brain tissue of wild-type and transgenic APPPS1 mice (overexpression of amyloid precursor protein and presenilin 1 with Swedish and L166P mutations, respectively). Also, this study details a novel role for Aβ42 in nuclear signaling, distinct from the amyloid precursor protein intracellular domain. Chromatin immunoprecipitation showed that Aβ42 specifically interacts as a repressor of gene transcription with LRP1 and KAI1 promoters. By quantitative RT-PCR, we confirmed that mRNA levels of the examined candidate genes were exclusively decreased by the potentially neurotoxic Aβ42 wild-type peptide. Shorter peptides (Aβ38 or Aβ40) and other longer peptides (nontoxic Aβ42 G33A substitution or Aβ43) did not affect mRNA levels. Overall, our data indicate that the nuclear translocation of Aβ42 impacts gene regulation, and deleterious effects of Aβ42 in Alzheimer disease pathogenesis may be influenced by altering the expression profiles of disease-modifying genes.

Sleep deficits in mild cognitive impairment are related to increased levels of plasma amyloid-β and cortical thinning

Evidence suggests that amyloid-beta (Aβ) depositions parallel sleep deficits in Alzheimer's disease (AD). However, it remains unknown whether impaired sleep and changes in plasma Aβ levels are related in amnestic mild cognitive impairment (aMCI) subjects, and whether both markers are further associated with cortical thinning in canonical AD regions. To jointly address this issue, we investigated relationships between changes in physiological sleep and plasma Aβ concentrations in 21 healthy old (HO) adults and 21 aMCI subjects, and further assessed whether these two factors were associated with cortical loss in each group. aMCI, but not HO subjects, showed significant relationships between disrupted slow-wave sleep (SWS) and increased plasma levels of Aβ42. We also found that shortened rapid-eye movement (REM) sleep in aMCI correlated with thinning of the posterior cingulate, precuneus, and postcentral gyrus; whereas higher levels of Aβ40 and Aβ42 accounted for grey matter (GM) loss of posterior cingulate and entorhinal cortex, respectively. These results support preliminary relationships between Aβ burden and altered sleep physiology observed in animal models of AD amyloidosis, and provide precise cortical correlates of these changes in older adults with aMCI. Taken together, these findings open new research avenues on the combined role of sleep, peripheral Aβ levels and cortical integrity in tracking the progression from normal aging to early neurodegeneration.