The Neuroprotective Beta Amyloid Hexapeptide Core Reverses Deficits in Synaptic Plasticity in the 5xFAD APP/PS1 Mouse Model

AMPA receptors in Alzheimer disease: Pathological changes and potential therapeutic targets

Alzheimer disease (AD) is a prevalent neurodegenerative disorder that affects synapses and leads to progressive cognitive decline. The role of N-methyl-D-aspartic acid (NMDA) receptors in the pathogenesis of AD is well-established as they contribute to excitotoxicity and neurodegeneration in the pathological process of extrasynaptic glutamate concentration. However, the therapeutic potential of the NMDA receptor antagonist memantine in rescuing synaptic damage is limited. Research indicates that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors also play a significant role in AD. Abnormal transcription, expression, and localization of AMPA receptors lead to synaptic dysfunction and damage, contributing to early cognitive impairment in AD patients. Understanding the impact of AMPA receptors on AD pathogenesis and exploring the potential for the development of AMPA receptor-targeting drugs are crucial. This review aims to consolidate recent research findings on AMPA receptors in AD, elucidate the current state of AMPA receptor research and lay the foundation for future basic research and drug development.

Neuroprotective amyloid β N-terminal peptides differentially alter human α7- and α7β2-nicotinic acetylcholine (nACh) receptor single-channel properties

BACKGROUND AND PURPOSE

Oligomeric amyloid β 1-42 (oAβ1-42) exhibits agonist-like action at human α7- and α7β2-containing nicotinic receptors. The N-terminal amyloid β1-15 fragment (N-Aβ fragment) modulates presynaptic calcium and enhances hippocampal-based synaptic plasticity via α7-containing nicotinic receptors. Further, the N-Aβ fragment and its core sequence, the N-amyloid-beta core hexapeptide (N-Aβcore), protect against oAβ1-42-associated synapto- and neurotoxicity. Here, we investigated how oAβ1-42, the N-Aβ fragment, and the N-Aβcore regulate the single-channel properties of α7- and α7β2-nicotinic receptors.

EXPERIMENTAL APPROACH

Single-channel recordings measured the impact of acetylcholine, oAβ1-42, the N-Aβ fragment, and the N-Aβcore on the unitary properties of human α7- and α7β2-containing nicotinic receptors expressed in nicotinic-null SH-EP1 cells. Molecular dynamics simulations identified potential sites of interaction between the N-Aβ fragment and orthosteric α7+/α7- and α7+/β2- nicotinic receptor binding interfaces.

KEY RESULTS

The N-Aβ fragment and N-Aβcore induced α7- and α7β2-nicotinic receptor single-channel openings. Relative to acetylcholine, oAβ1-42 preferentially enhanced α7β2-nicotinic receptor single-channel open probability and open-dwell times. Co-application with the N-Aβcore neutralized these effects. Further, administration of the N-Aβ fragment alone, or in combination with acetylcholine or oAβ1-42, selectively enhanced α7-nicotinic receptor open probability and open-dwell times (compared to acetylcholine or oAβ1-42).

CONCLUSIONS AND IMPLICATIONS

Amyloid-beta peptides demonstrate functional diversity in regulating α7- and α7β2-nicotinic receptor function, with implications for a wide range of nicotinic receptor-mediated functions in Alzheimer's disease. The effects of these peptides on α7- and/or α7β2-nicotinic receptors revealed complex interactions with these subtypes, providing novel insights into the neuroprotective actions of amyloid β-derived fragments against the toxic effects of oAβ1-42.

Anti-Amyloid Therapies for Alzheimer's Disease and the Amyloid Cascade Hypothesis

Over the past 30 years, the majority of (pre)clinical efforts to find an effective therapy for Alzheimer's disease (AD) focused on clearing the β-amyloid peptide (Aβ) from the brain since, according to the amyloid cascade hypothesis, the peptide was (and it is still considered by many) the pathogenic determinant of this neurodegenerative disorder. However, as reviewed in this article, results from the numerous clinical trials that have tested anti-Aβ therapies to date indicate that this peptide plays a minor role in the pathogenesis of AD. Indeed, even Aducanumab and Lecanemab, the two antibodies recently approved by the FDA for AD therapy, as well as Donanemab showed limited efficacy on cognitive parameters in phase III clinical trials, despite their capability of markedly lowering Aβ brain load. Furthermore, preclinical evidence demonstrates that Aβ possesses several physiological functions, including memory formation, suggesting that AD may in part be due to a loss of function of this peptide. Finally, it is generally accepted that AD could be the result of many molecular dysfunctions, and therefore, if we keep chasing only Aβ, it means that we cannot see the forest for the trees.

Physiological Roles of β-amyloid in Regulating Synaptic Function: Implications for AD Pathophysiology

The physiological functions of endogenous amyloid-β (Aβ), which plays important role in the pathology of Alzheimer's disease (AD), have not been paid enough attention. Here, we review the multiple physiological effects of Aβ, particularly in regulating synaptic transmission, and the possible mechanisms, in order to decipher the real characters of Aβ under both physiological and pathological conditions. Some worthy studies have shown that the deprivation of endogenous Aβ gives rise to synaptic dysfunction and cognitive deficiency, while the moderate elevation of this peptide enhances long term potentiation and leads to neuronal hyperexcitability. In this review, we provide a new view for understanding the role of Aβ in AD pathophysiology from the perspective of physiological meaning.

The neuroprotective N-terminal amyloid-β core hexapeptide reverses reactive gliosis and gliotoxicity in Alzheimer's disease pathology models

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by accumulation of extracellular amyloid beta (Aβ) and intracellular neurofibrillary tangles, leading to chronic activation of astrocytes and microglia and persistent neuroinflammation. Aβ-linked activation of microglia and astrocytes leads to increased intracellular calcium and production of proinflammatory cytokines, impacting the progression of neurodegeneration. An N-terminal Aβ fragment (Aβ_1-15) and a shorter hexapeptide core sequence within the N-Aβ fragment (N-Aβcore: Aβ_10-15) have previously been shown to protect against Aβ-induced mitochondrial dysfunction, oxidative stress and apoptosis in neurons and rescue synaptic and spatial memory deficits in an APP/PSEN1 mouse model. Here, we hypothesized that the N-Aβ fragment and N-Aβcore are protective against Aβ-induced gliotoxicity, promoting a neuroprotective environment and potentially alleviating the characteristically persistent neuroinflammation present in AD.

METHODS

We treated ex vivo organotypic brain slice cultures from an aged familial AD mouse model, 5xFAD, with the N-Aβcore and used immunocytochemistry to assess the impact on astrogliosis and microgliosis and alterations in synaptophysin-positive puncta engulfed by microglia. Isolated neuron/glia cultures, mixed glial cultures or a microglial cell line were treated with oligomeric human Aβ at concentrations mimicking the pathogenic concentrations (μM) observed in AD in the absence or presence of the non-toxic N-terminal Aβ fragments. Resultant changes in synaptic density, gliosis, oxidative stress, mitochondrial dysfunction, apoptosis, and the expression and release of proinflammatory markers were then determined.

RESULTS

We demonstrate that the N-terminal Aβ fragments mitigated the phenotypic switch leading to astrogliosis and microgliosis induced by pathological concentrations of Aβ in mixed glial cultures and organotypic brain slice cultures from the transgenic 5xFAD mouse model, while protecting against Aβ-induced oxidative stress, mitochondrial dysfunction and apoptosis in isolated astrocytes and microglia. Moreover, the addition of the N-Aβcore attenuated the expression and release of proinflammatory mediators in microglial cells activated by Aβ and rescued microglia-mediated loss of synaptic elements induced by pathological levels of Aβ.

CONCLUSIONS

Together, these findings indicate the protective functions of the N-terminal Aβ fragments extend to reactive gliosis and gliotoxicity induced by Aβ, by preventing or reversing glial reactive states indicative of neuroinflammation and synaptic loss central to AD pathogenesis.

The therapeutic potential of the neuroactive peptides of soluble amyloid precursor protein-alpha in Alzheimer's disease and related neurological disorders

Soluble amyloid precursor protein-alpha (sAPPα) is a multi-functional brain-derived protein that has neuroprotective, neurogenic and neurotropic properties. Moreover, it is known to facilitate synaptic function and promote neural repair. These properties suggest sAPPα may be useful as a therapeutic agent for the treatment of neurological diseases characterized by synaptic failure and neuronal loss, such as occurs in Alzheimer's disease, and for neural repair following traumatic brain injury and stroke. However, sAPPα's relatively large size and the difficulty of ongoing delivery of therapeutics to the brain mean this is not currently practicable. Importantly, however, sAPPα is composed of several neuroactive domains that each possess properties that collectively are remarkably similar to those of sAPPα itself. Here, we review the molecular structure of sAPPα and identify the domains that contribute to its overall functionality. Four peptide motifs present as possible targets for therapeutic development. We review their physiochemical and neuroactive properties, both within sAPPα and as isolated peptides, and discuss their potential for future development as multipurpose therapeutic agents for the treatment of Alzheimer's disease and other disorders of neuronal function. Further, we discuss the role of heparin binding sites, found within sAPPα's structure and overlapping with the neuroactive domains, as sites for interactions with effector proteins and synaptic receptors. The potential role of the neuroactive peptides known as Cationic Arginine-Rich Peptides (CARPs) as neuroprotective motifs is also reviewed. Mechanisms of peptide delivery to the brain are briefly discussed. Finally, we summarise the potential benefits and pitfalls of using the isolated peptides, either individually or in combination, for the treatment of neurological diseases.

Best Medicine for Dementia: The Life-Long Defense of the Brain

This review deals with an unwelcome reality about several forms of dementia, including Alzheimer's disease- that these dementias are caused, in part or whole, by the aging of the vasculature. Since the vasculature ages in us all, dementia is our fate, sealed by the realit!ies of the circulation; it is not a disease with a cure pending. Empirically, cognitive impairment before our 7th decade is uncommon and considered early, while a diagnosis in our 11th decade is late but common in that cohort (>40%). Projections from earlier ages suggest that the prevalence of dementia in people surviving into their 12th decade exceeds 80%. We address the question why so few of many interventions known to delay dementia are recognized as therapy; and we try to resolve this few-and-many paradox, identifying opportunities for better treatment, especially pre-diagnosis. The idea of dementia as a fate is resisted, we argue, because it negates the hope of a cure. But the price of that hope is lost opportunity. An approach more in line with the evidence, and more likely to limit suffering, is to understand the damage that accumulates with age in the cerebral vasculature and therefore in the brain, and which eventually gives rise to cognitive symptoms in late life, too often leading to dementia. We argue that hope should be redirected to delaying that damage and with it the onset of cognitive loss; and, for each individual, it should be redirected to a life-long defense of their brain.

Spatial Training Attenuates Long-Term Alzheimer’s Disease-Related Pathogenic Processes in APP/PS1 Mice

Background: Alzheimer’s disease (AD), with cognitive impairment as the main clinical manifestation, is a progressive neurodegenerative disease. The assembly of amyloid-β (Aβ) as senile plaques is one of the most well-known histopathological alterations in AD. Several studies reported that cognitive training reduced Aβ deposition and delayed memory loss. However, the long-term benefits of spatial training and the underlying neurobiological mechanisms have not yet been elucidated. Objective: To explore the long-term effects of spatial training on AD-related pathogenic processes in APP/PS1 mice. Methods: We used Morris water maze (MWM), Open Field, Barnes Maze, western blotting, qPCR, and immunofluorescence. Results: One-month MWM training in APP/PS1 mice at 2.5 months of age could attenuate Aβ deposition and decrease the expression of β-secretase (BACE1) and amyloid-β protein precursor (AβPP) with long-term effects. Simultaneously, regular spatial training increased the expression of synapse-related proteins in the hippocampus. Moreover, MWM training increased adult hippocampal neurogenesis in AD model mice. Nonetheless, cognitive deficits in APP/PS1 transgenic mice at 7 months of age were not attenuated by MWM training at an early stage. Conclusion: Our study demonstrates that MWM training alleviates amyloid plaque burden and adult hippocampal neurogenesis deficits with long-term effects in AD model mice.