Differences in the cellular uptake and intracellular itineraries of amyloid beta proteins 40 and 42: ramifications for the Alzheimer's drug discovery

Tracking mitochondrial Cu(I) fluctuations through a ratiometric fluorescent probe in AD model cells: Towards understanding how AβOs induce mitochondrial Cu(I) dyshomeostasis

Mitochondrial copper signaling pathway plays a role in Alzheimer's disease (AD), especially in relevant Amyloid-β oligomers (AβOs) neurotoxicity and mitochondrial dysfunction. Clarifying the relationship between mitochondrial copper homeostasis and both of mitochondrial dysfunction and AβOs neurotoxicity is important for understanding AD pathogenesis. Herein, we designed and synthesized a ratiometric fluorescent probe CHC-NS4 for Cu(I). CHC-NS4 possesses excellent ratiometric response, high selectivity to Cu(I) and specific ability to target mitochondria. Under mitochondrial dysfunction induced by oligomycin, mitochondrial Cu(I) levels gradually increased, which may be related to inhibition of ATP7A-mediated Cu(I) exportation and/or high expression of COX. On this basis, CHC-NS4 was further utilized to visualize the fluctuations of mitochondrial Cu(I) levels during progression of AD model cells induced by AβOs. It was found that mitochondrial Cu(I) levels were gradually elevated during the AD progression, which depended on not only AβOs concentration but also incubation time. Moreover, endocytosis maybe served as a prime pathway mode for mitochondrial Cu(I) dyshomeostasis induced by AβOs during AD progression. These results have provided a novel inspiration into mitochondrial copper biology in AD pathogenesis.

Clathrin mediated endocytosis in Alzheimer's disease: cell type specific involvement in amyloid beta pathology

This review provides a comprehensive examination of the role of clathrin-mediated endocytosis (CME) in Alzheimer's disease (AD) pathogenesis, emphasizing its impact across various cellular contexts beyond neuronal dysfunction. In neurons, dysregulated CME contributes to synaptic dysfunction, amyloid beta (Aβ) processing, and Tau pathology, highlighting its involvement in early AD pathogenesis. Furthermore, CME alterations extend to non-neuronal cell types, including astrocytes and microglia, which play crucial roles in Aβ clearance and neuroinflammation. Dysregulated CME in these cells underscores its broader implications in AD pathophysiology. Despite significant progress, further research is needed to elucidate the precise mechanisms underlying CME dysregulation in AD and its therapeutic implications. Overall, understanding the complex interplay between CME and AD across diverse cell types holds promise for identifying novel therapeutic targets and interventions.

On the Inadequacy of the Current Transgenic Animal Models of Alzheimer's Disease: The Path Forward

For at least two reasons, the current transgenic animal models of Alzheimer's disease (AD) appear to be patently inadequate. They may be useful in many respects, the AD models; however, they are not. First, they are incapable of developing the full spectrum of the AD pathology. Second, they respond spectacularly well to drugs that are completely ineffective in the treatment of symptomatic AD. These observations indicate that both the transgenic animal models and the drugs faithfully reflect the theory that guided the design and development of both, the amyloid cascade hypothesis (ACH), and that both are inadequate because their underlying theory is. This conclusion necessitated the formulation of a new, all-encompassing theory of conventional AD-the ACH2.0. The two principal attributes of the ACH2.0 are the following. One, in conventional AD, the agent that causes the disease and drives its pathology is the intraneuronal amyloid-β (iAβ) produced in two distinctly different pathways. Two, following the commencement of AD, the bulk of Aβ is generated independently of Aβ protein precursor (AβPP) and is retained inside the neuron as iAβ. Within the framework of the ACH2.0, AβPP-derived iAβ accumulates physiologically in a lifelong process. It cannot reach levels required to support the progression of AD; it does, however, cause the disease. Indeed, conventional AD occurs if and when the levels of AβPP-derived iAβ cross the critical threshold, elicit the neuronal integrated stress response (ISR), and trigger the activation of the AβPP-independent iAβ generation pathway; the disease commences only when this pathway is operational. The iAβ produced in this pathway reaches levels sufficient to drive the AD pathology; it also propagates its own production and thus sustains the activity of the pathway and perpetuates its operation. The present study analyzes the reason underlying the evident inadequacy of the current transgenic animal models of AD. It concludes that they model, in fact, not Alzheimer's disease but rather the effects of the neuronal ISR sustained by AβPP-derived iAβ, that this is due to the lack of the operational AβPP-independent iAβ production pathway, and that this mechanism must be incorporated into any successful AD model faithfully emulating the disease. The study dissects the plausible molecular mechanisms of the AβPP-independent iAβ production and the pathways leading to their activation, and introduces the concept of conventional versus unconventional Alzheimer's disease. It also proposes the path forward, posits the principles of design of productive transgenic animal models of the disease, and describes the molecular details of their construction.

Next Generation Therapeutic Strategy for Treatment and Prevention of Alzheimer's Disease and Aging-Associated Cognitive Decline: Transient, Once-in-a-Lifetime-Only Depletion of Intraneuronal Aβ (iAβ) by Its Targeted Degradation via Augmentation of Intra-iAβ-Cleaving Activities of BACE1 and/or BACE2

Although the long-standing Amyloid Cascade Hypothesis (ACH) has been largely discredited, its main attribute, the centrality of amyloid-beta (Aβ) in Alzheimer's disease (AD), remains the cornerstone of any potential interpretation of the disease: All known AD-causing mutations, without a single exception, affect, in one way or another, Aβ. The ACH2.0, a recently introduced theory of AD, preserves this attribute but otherwise differs fundamentally from the ACH. It posits that AD is a two-stage disorder where both stages are driven by intraneuronal (rather than extracellular) Aβ (iAβ) albeit of two distinctly different origins. The first asymptomatic stage is the decades-long accumulation of Aβ protein precursor (AβPP)-derived iAβ to the critical threshold. This triggers the activation of the self-sustaining AβPP-independent iAβ production pathway and the commencement of the second, symptomatic AD stage. Importantly, Aβ produced independently of AβPP is retained intraneuronally. It drives the AD pathology and perpetuates the operation of the pathway; continuous cycles of the iAβ-stimulated propagation of its own AβPP-independent production constitute an engine that drives AD, the AD Engine. It appears that the dynamics of AβPP-derived iAβ accumulation is the determining factor that either drives Aging-Associated Cognitive Decline (AACD) and triggers AD or confers the resistance to both. Within the ACH2.0 framework, the ACH-based drugs, designed to lower levels of extracellular Aβ, could be applicable in the prevention of AD and treatment of AACD because they reduce the rate of accumulation of AβPP-derived iAβ. The present study analyzes their utility and concludes that it is severely limited. Indeed, their short-term employment is ineffective, their long-term engagement is highly problematic, their implementation at the symptomatic stages of AD is futile, and their evaluation in conventional clinical trials for the prevention of AD is impractical at best, impossible at worst, and misleading in between. In contrast, the ACH2.0-guided Next Generation Therapeutic Strategy for the treatment and prevention of both AD and AACD, namely the depletion of iAβ via its transient, short-duration, targeted degradation by the novel ACH2.0-based drugs, has none of the shortcomings of the ACH-based drugs. It is potentially highly effective, easily evaluable in clinical trials, and opens up the possibility of once-in-a-lifetime-only therapeutic intervention for prevention and treatment of both conditions. It also identifies two plausible ACH2.0-based drugs: activators of physiologically occurring intra-iAβ-cleaving capabilities of BACE1 and/or BACE2.

Amyloid-Beta Peptides 40 and 42 Employ Distinct Molecular Pathways for Cell Entry and Intracellular Transit at the Blood-Brain Barrier Endothelium

The blood-brain barrier (BBB) plays a critical role in maintaining the equilibrium between amyloid beta (Aβ) levels in blood and the brain by regulating Aβ transport. Our previous publications demonstrated that BBB trafficking of Aβ42 and Aβ40 is distinct and is disrupted under various pathophysiological conditions. However, the intracellular mechanisms that allow BBB endothelium to differentially handle Aβ40 and Aβ42 have not been clearly elucidated. In this study, we identified mechanisms of Aβ endocytosis in polarized human cerebral microvascular endothelial cell monolayers. Our studies demonstrated that Aβ peptides with fluorescent label (F-Aβ) were internalized by BBB endothelial cells via energy, dynamin, and actin-dependent endocytosis. Interestingly, endocytosis of F-Aβ40 but not F-Aβ42 was substantially reduced by clathrin inhibition, whereas F-Aβ42 but not F-Aβ40 endocytosis was reduced by half after inhibiting the caveolae-mediated pathway. Following endocytosis, both isoforms were sorted by the endo-lysosomal system. Although Aβ42 was shown to accumulate more in the lysosomes, which could lead to its higher degradation and/or aggregation at lower lysosomal pH, Aβ40 demonstrated robust accumulation in recycling endosomes, which may facilitate its exocytosis by the endothelial cells. These results provide a mechanistic insight into the selective ability of BBB endothelium to transport Aβ40 versus Aβ42. This knowledge contributes to the understanding of molecular pathways underlying Aβ accumulation in the BBB endothelium and associated BBB dysfunction. Moreover, it allows us to establish mechanistic rationale for altered Aβ40:Aβ42 ratios and anomalous amyloid deposition in the cerebral vasculature as well as brain parenchyma during Alzheimer's disease progression. SIGNIFICANCE STATEMENT: Differential interaction of Aβ40 and Aβ42 isoforms with the blood-brain barrier (BBB) endothelium may contribute to perturbation in Aβ42:Aβ40 ratio, which is associated with Alzheimer's disease (AD) progression and severity. The current study identified distinct molecular pathways by which Aβ40 and Aβ42 are trafficked at the BBB, which regulates equilibrium between blood and brain Aβ levels. These findings provide molecular insights into mechanisms that engender BBB dysfunction and promote Aβ accumulation in AD brain.

The novel function of bexarotene for neurological diseases

Bexarotene, a retinoid X receptor (RXR) agonist, is approved by FDA to treat cutaneous T-cell lymphoma. However, it has also demonstrated promising therapeutic potential for neurological diseases such as stroke, traumatic brain injury, Parkinson's disease, and particularly Alzheimer's disease(AD). In AD, bexarotene inhibits the production and aggregation of amyloid β (Aβ), activates Liver X Receptor/RXR heterodimers to increase lipidated apolipoprotein E to remove Aβ, mitigates the negative impact of Aβ, regulates neuroinflammation, and ultimately improves cognitive function. For other neurological diseases, its mechanisms of action include inhibiting inflammatory responses, up-regulating microglial phagocytosis, and reducing misfolded protein aggregation, all of which aid in alleviating neurological damage. Here, we briefly discuss the characteristics, applications, and adverse effects of bexarotene, summarize its pharmacological mechanisms and therapeutic results in various neurological diseases, and elaborate on the problems encountered in preclinical research, with the aim of providing help for the further application of bexarotene in central nervous system diseases.

Principles of Design of Clinical Trials for Prevention and Treatment of Alzheimer's Disease and Aging-Associated Cognitive Decline in the ACH2.0 Perspective: Potential Outcomes, Challenges, and Solutions

With the Amyloid Cascade Hypothesis (ACH) largely discredited, the ACH2.0 theory of Alzheimer's disease (AD) has been recently introduced. Within the framework of the ACH2.0, AD is triggered by amyloid-β protein precursor (AβPP)-derived intraneuronal Aβ (iAβ) and is driven by iAβ produced in the AβPP-independent pathway and retained intraneuronally. In this paradigm, the depletion of extracellular Aβ or suppression of Aβ production by AβPP proteolysis, the two sources of AβPP-derived iAβ, would be futile in symptomatic AD, due to its reliance on iAβ generated independently of AβPP, but effective in preventing AD and treating Aging-Associated Cognitive Decline (AACD) driven, in the ACH2.0 framework, by AβPP-derived iAβ. The observed effect of lecanemab and donanemab, interpreted in the ACH2.0 perspective, supports this notion and mandates AD-preventive clinical trials. Such trials are currently in progress. They are likely, however, to fail or to yield deceptive results if conducted conventionally. The present study considers concepts of design of clinical trials of lecanemab, donanemab, or any other drug, targeting the influx of AβPP-derived iAβ, in prevention of AD and treatment of AACD. It analyzes possible outcomes and explains why selection of high-risk asymptomatic participants seems reasonable but is not. It argues that outcomes of such AD preventive trials could be grossly misleading, discusses inevitable potential problems, and proposes feasible solutions. It advocates the initial evaluation of this type of drugs in clinical trials for treatment of AACD. Whereas AD protective trials of these drugs are potentially of an impractical length, AACD clinical trials are expected to yield unequivocal results within a relatively short duration. Moreover, success of the latter, in addition to its intrinsic value, would constitute a proof of concept for the former. Furthermore, this study introduces concepts of the active versus passive iAβ depletion, contends that targeted degradation of iAβ is the best therapeutic strategy for both prevention and treatment of AD and AACD, proposes potential iAβ-degrading drugs, and describes their feasible and unambiguous evaluation in clinical trials.

The Amyloid Cascade Hypothesis 2.0 for Alzheimer's Disease and Aging-Associated Cognitive Decline: From Molecular Basis to Effective Therapy

With the long-standing amyloid cascade hypothesis (ACH) largely discredited, there is an acute need for a new all-encompassing interpretation of Alzheimer's disease (AD). Whereas such a recently proposed theory of AD is designated ACH2.0, its commonality with the ACH is limited to the recognition of the centrality of amyloid-β (Aβ) in the disease, necessitated by the observation that all AD-causing mutations affect, in one way or another, Aβ. Yet, even this narrow commonality is superficial since AD-causing Aβ of the ACH differs distinctly from that specified in the ACH2.0: Whereas in the former, the disease is caused by secreted extracellular Aβ, in the latter, it is triggered by Aβ-protein-precursor (AβPP)-derived intraneuronal Aβ (iAβ) and driven by iAβ generated independently of AβPP. The ACH2.0 envisions AD as a two-stage disorder. The first, asymptomatic stage is a decades-long accumulation of AβPP-derived iAβ, which occurs via internalization of secreted Aβ and through intracellular retention of a fraction of Aβ produced by AβPP proteolysis. When AβPP-derived iAβ reaches critical levels, it activates a self-perpetuating AβPP-independent production of iAβ that drives the second, devastating AD stage, a cascade that includes tau pathology and culminates in neuronal loss. The present study analyzes the dynamics of iAβ accumulation in health and disease and concludes that it is the prime factor driving both AD and aging-associated cognitive decline (AACD). It discusses mechanisms potentially involved in AβPP-independent generation of iAβ, provides mechanistic interpretations for all principal aspects of AD and AACD including the protective effect of the Icelandic AβPP mutation, the early onset of FAD and the sequential manifestation of AD pathology in defined regions of the affected brain, and explains why current mouse AD models are neither adequate nor suitable. It posits that while drugs affecting the accumulation of AβPP-derived iAβ can be effective only protectively for AD, the targeted degradation of iAβ is the best therapeutic strategy for both prevention and effective treatment of AD and AACD. It also proposes potential iAβ-degrading drugs.

Effect of Lecanemab in Early Alzheimer's Disease: Mechanistic Interpretation in the Amyloid Cascade Hypothesis 2.0 Perspective

In clinical trials, lecanemab showed statistically significant yet marginal slowdown of Alzheimer's disease (AD)-associated cognitive decline. This could be due to its sub-optimal design and/or deployment; alternatively, its limited efficiency could be intrinsic. Distinguishing between the two is of great importance considering the acute need of efficient AD therapy and tremendous resources being invested in its pursuit. The present study analyzes the mode of operation of lecanemab within the framework of recently proposed Amyloid Cascade Hypothesis 2.0 and concludes that the second is correct. It suggests that substantial improvement of the efficiency of lecanemab in symptomatic AD is unlikely and proposes the alternative therapeutic strategy.

Electrostatic assembly of gold nanoparticle and metal-organic framework nanoparticles attenuates amyloid β aggregate-mediated neurotoxicity

The deposition of amyloid β (Aβ) is a conventional pathological hallmark of Alzheimer's disease (AD). Consequently, the inhibition of Aβ aggregation combined with the disaggregation of Aβ fibrils is an important therapeutic method for AD treatment. In this study, a gold nanoparticle-decorated porous metal organic framework MIL-101(Fe) (AuNPs@PEG@MIL-101) was created as an Aβ inhibitor. The high positively charged MIL-101 induced a high number of Aβ₄₀ to be absorbed or aggregated on the surface of nanoparticles. In addition, AuNPs improved the surface property of MIL-101, causing it to uniformly bind Aβ monomers and Aβ fibrils. Thus, this framework can efficiently suppress extracellular Aβ monomer fibrillation and disrupt the preformed Aβ fibers. AuNPs@PEG@MIL-101 also decreases intracellular Aβ₄₀ aggregation and the amount of Aβ₄₀ immobilized on the cell membrane, thus protecting PC12 cells from Aβ₄₀-induced microtubular defects and cell membrane damage. In summary, AuNPs@PEG@MIL-101 shows great potential for application in AD therapy.

The Amyloid Cascade Hypothesis 2.0: Generalization of the Concept

Recently, we proposed the Amyloid Cascade Hypothesis 2.0 (ACH2.0), a reformulation of the ACH. In the former, in contrast to the latter, Alzheimer's disease (AD) is driven by intraneuronal amyloid-β (iAβ) and occurs in two stages. In the first, relatively benign stage, Aβ protein precursor (AβPP)-derived iAβ activates, upon reaching a critical threshold, the AβPP-independent iAβ-generating pathway, triggering a devastating second stage resulting in neuronal death. While the ACH2.0 remains aligned with the ACH premise that Aβ is toxic, the toxicity is exerted because of intra- rather than extracellular Aβ. In this framework, a once-in-a-lifetime-only iAβ depletion treatment via transient activation of BACE1 and/or BACE2 (exploiting their Aβ-cleaving activities) or by any means appears to be the best therapeutic strategy for AD. Whereas the notion of differentially derived iAβ being the principal moving force at both AD stages is both plausible and elegant, a possibility remains that the second AD stage is enabled by an AβPP-derived iAβ-activated self-sustaining mechanism producing a yet undefined deleterious "substance X" (sX) which anchors the second AD stage. The present study generalizes the ACH2.0 by incorporating this possibility and shows that, in this scenario, the iAβ depletion therapy may be ineffective at symptomatic AD stages but fully retains its preventive potential for both AD and the aging-associated cognitive decline, which is defined in the ACH2.0 framework as the extended first stage of AD.

Oxidative Stress and Natural Antioxidants: Back and Forth in the Neurological Mechanisms of Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the progressive degeneration of neuronal cells. With the increase in aged population, there is a prevalence of irreversible neurodegenerative changes, causing a significant mental, social, and economic burden globally. The factors contributing to AD are multidimensional, highly complex, and not completely understood. However, it is widely known that aging, neuroinflammation, and excessive production of reactive oxygen species (ROS), along with other free radicals, substantially contribute to oxidative stress and cell death, which are inextricably linked. While oxidative stress is undeniably important in AD, limiting free radicals and ROS levels is an intriguing and potential strategy for deferring the process of neurodegeneration and alleviating associated symptoms. Therapeutic compounds from natural sources have recently become increasingly accepted and have been effectively studied for AD treatment. These phytocompounds are widely available and a multitude of holistic therapeutic efficiencies for treating AD owing to their antioxidant, anti-inflammatory, and biological activities. Some of these compounds also function by stimulating cholinergic neurotransmission, facilitating the suppression of beta-site amyloid precursor protein-cleaving enzyme 1, α-synuclein, and monoamine oxidase proteins, and deterring the occurrence of AD. Additionally, various phenolic, flavonoid, and terpenoid phytocompounds have been extensively described as potential palliative agents for AD progression. Preclinical studies have shown their involvement in modulating the cellular redox balance and minimizing ROS formation, displaying them as antioxidant agents with neuroprotective abilities. This review emphasizes the mechanistic role of natural products in the treatment of AD and discusses the various pathological hypotheses proposed for AD.

AP2S1 regulates APP degradation through late endosome-lysosome fusion in cells and APP/PS1 mice

AP2S1 is the sigma 2 subunit of adaptor protein 2 (AP2) that is essential for endocytosis. In this study, we investigated the potential role of AP2S1 in intracellular processing of amyloid precursor protein (APP), which contributes to the pathogenesis of Alzheimer disease (AD) by generating the toxic β-amyloid peptide (Aβ). We found that knockdown or overexpression of AP2S1 decreased or increased the protein levels of APP and Aβ in cells stably expressing human full-length APP695, respectively. This effect was unrelated to endocytosis but involved lysosomal degradation. Morphological studies revealed that silencing of AP2S1 promoted the translocalization of APP from RAB9-positive late endosomes (LE) to LAMP1-positive lysosomes, which was paralleled by the enhanced LE-lysosome fusion. In support, silencing of vacuolar protein sorting-associated protein 41 (VPS41) that is implicated in LE-lyso fusion prevented AP2S1-mediated regulation of APP degradation and translocalization. In APP/PS1 mice, an animal model of AD, AAV-mediated delivery of AP2S1 shRNA in the hippocampus significantly reduced the protein levels of APP and Aβ, with the concomitant APP translocalization, LE-lyso fusion and the improved cognitive functions. Taken together, these data uncover a LE-lyso fusion mechanism in APP degradation and suggest a novel role for AP2S1 in the pathophysiology of AD.

The Amyloid Cascade Hypothesis 2.0: On the Possibility of Once-in-a-Lifetime-Only Treatment for Prevention of Alzheimer’s Disease and for Its Potential Cure at Symptomatic Stages

We posit that Alzheimer’s disease (AD) is driven by amyloid-β (Aβ) generated in the amyloid-β protein precursor (AβPP) independent pathway activated by AβPP-derived Aβ accumulated intraneuronally in a life-long process. This interpretation constitutes the Amyloid Cascade Hypothesis 2.0 (ACH2.0). It defines a tandem intraneuronal-Aβ (iAβ)-anchored cascade occurrence: intraneuronally-accumulated, AβPP-derived iAβ triggers relatively benign cascade that activates the AβPP-independent iAβ-generating pathway, which, in turn, initiates the second, devastating cascade that includes tau pathology and leads to neuronal loss. The entire output of the AβPP-independent iAβ-generating pathway is retained intraneuronally and perpetuates the pathway’s operation. This process constitutes a self-propagating, autonomous engine that drives AD and ultimately kills its host cells. Once activated, the AD Engine is self-reliant and independent from Aβ production in the AβPP proteolytic pathway; operation of the former renders the latter irrelevant to the progression of AD and brands its manipulation for therapeutic purposes, such as BACE (beta-site AβPP-cleaving enzyme) inhibition, as futile. In the proposed AD paradigm, the only valid direct therapeutic strategy is targeting the engine’s components, and the most effective feasible approach appears to be the activation of BACE1 and/or of its homolog BACE2, with the aim of exploiting their Aβ-cleaving activities. Such treatment would collapse the iAβ population and ‘reset’ its levels below those required for the operation of the AD Engine. Any sufficiently selective iAβ-depleting treatment would be equally effective. Remarkably, this approach opens the possibility of a short-duration, once-in-a-lifetime-only or very infrequent, preventive or curative therapy for AD; this therapy would be also effective for prevention and treatment of the ‘common’ pervasive aging-associated cognitive decline. The ACH2.0 clarifies all ACH-unresolved inconsistencies, explains the widespread ‘resilience to AD’ phenomenon, predicts occurrences of a category of AD-afflicted individuals without excessive Aβ plaque load and of a novel type of familial insusceptibility to AD; it also predicts the lifespan-dependent inevitability of AD in humans if untreated preventively. The article details strategy and methodology to generate an adequate AD model and validate the hypothesis; the proposed AD model may also serve as a research and drug development platform.

Amentoflavone Promotes Cellular Uptake and Degradation of Amyloid-Beta in Neuronal Cells

Deposition of fibrillar forms of amyloid β-protein (Aβ) is commonly found in patients with Alzheimer's disease (AD) associated with cognitive decline. Impaired clearance of Aβ species is thought to be a major cause of late-onset sporadic AD. Aβ secreted into the extracellular milieu can be cleared from the brain through multiple pathways, including cellular uptake in neuronal and non-neuronal cells. Recent studies have showed that the naturally-occurring polyphenol amentoflavone (AMF) exerts anti-amyloidogenic effects. However, its effects on metabolism and cellular clearance of Aβ remain to be tested. In the present study, we demonstrated that AMF significantly increased the cellular uptake of both Aβ_1-40 and Aβ_1-42, but not inverted Aβ_42-1 in mouse neuronal N2a cells. Though AMF promoted internalization of cytotoxic Aβ_1-42, it significantly reduced cell death in our assay condition. Our data further revealed that the internalized Aβ is translocated to lysosomes and undergoes enzymatic degradation. The saturable kinetic of Aβ uptake and our pharmacologic experiments showed the involvement of receptor-mediated endocytosis, in part, through the class A scavenger receptors as a possible mechanism of action of AMF. Taken together, our findings indicate that AMF can lower the levels of extracellular Aβ by increasing their cellular uptake and clearance, suggesting the therapeutic potential of AMF for the treatment of AD.

Optical Nanosensor for Intracellular and Intracranial Detection of Amyloid-Beta

Amyloid-beta (Aβ) deposition occurs in the early stages of Alzheimer's disease (AD), but the early detection of Aβ is a persistent challenge. Herein, we engineered a near-infrared optical nanosensor capable of detecting Aβ intracellularly in live cells and intracranially in vivo. The sensor is composed of single-walled carbon nanotubes functionalized with Aβ wherein Aβ-Aβ interactions drive the response. We found that the Aβ nanosensors selectively responded to Aβ via solvatochromic modulation of the near-infrared emission of the nanotube. The sensor tracked Aβ accumulation in live cells and, upon intracranial administration in a genetic model of AD, signaled distinct responses in aged mice. This technology enables the interrogation of molecular mechanisms underlying Aβ neurotoxicity in the development of AD in living systems.

Amyloid Beta Is Internalized via Macropinocytosis, an HSPG- and Lipid Raft-Dependent and Rac1-Mediated Process

Intracellular amyloid β peptide (Aβ) accumulation has drawn attention in relation to the pathophysiology of Alzheimer’s disease in addition to its extracellular deposition as senile plaque. Cellular uptake of extracellular Aβ is one of the possible mechanisms by which intracellular Aβ deposits form. Given the relevance of Aβ inside cells, it is important to understand the mechanism by which it is taken up by them. In this study, we elucidated that Neuro2A and SH-SY5Y cells internalize specifically oligomerized Aβ in a time- and dose-dependent manner. The depletion of plasma membrane cholesterol with methyl-β-cyclodextrin or treatment with trypsin diminished the internalization of oAβ, suggesting that the oAβ uptake might be both a lipid raft-dependent and heparan sulfate proteoglycan-mediated process. Treatment with a macropinocytosis inhibitor (ethylisopropyl amiloride and wortmannin) also drastically reduced the uptake of oligomer-Aβ (oAβ). oAβ-treated cells exhibited an increase in Rac1 activity, indicating that macropinocytosis induced by oAβ is regulated by these small GTPases. These findings suggest that macropinocytosis is a major endocytic route through which oAβ42 enters cells.

Circadian control of heparan sulfate levels times phagocytosis of amyloid beta aggregates

Alzheimer's Disease (AD) is a neuroinflammatory disease characterized partly by the inability to clear, and subsequent build-up, of amyloid-beta (Aβ). AD has a bi-directional relationship with circadian disruption (CD) with sleep disturbances starting years before disease onset. However, the molecular mechanism underlying the relationship of CD and AD has not been elucidated. Myeloid-based phagocytosis, a key component in the metabolism of Aβ, is circadianly-regulated, presenting a potential link between CD and AD. In this work, we revealed that the phagocytosis of Aβ42 undergoes a daily circadian oscillation. We found the circadian timing of global heparan sulfate proteoglycan (HSPG) biosynthesis was the molecular timer for the clock-controlled phagocytosis of Aβ and that both HSPG binding and aggregation may play a role in this oscillation. These data highlight that circadian regulation in immune cells may play a role in the intricate relationship between the circadian clock and AD.

Semimechanistic Population Pharmacokinetic Modeling to Investigate Amyloid Beta Trafficking and Accumulation at the BBB Endothelium

Elevated exposure to toxic amyloid beta (Aβ) peptides and consequent blood-brain barrier (BBB) dysfunction are believed to promote vasculopathy in Alzheimer's disease (AD). However, the accumulation kinetics of different Aβ isoforms within the BBB endothelium and how it drives BBB dysfunction are not clearly characterized. Using single positron emission computed tomography (SPECT)-computed tomography (CT) dynamic imaging coupled with population pharmacokinetic modeling, we investigated the accumulation kinetics of Aβ40 and Aβ42 in the BBB endothelium. Brain clearance was quantified after intracerebral administration of ¹²⁵I-Aβ, and BBB-mediated transport was shown to account for 54% of ¹²⁵I-Aβ40 total clearance. A brain influx study demonstrated lower values of both maximal rate (V_max) and Michaelis constant (K_m) for ¹²⁵I-Aβ42 compared to ¹²⁵I-Aβ40. Validated by a transcytosis study in polarized human BBB endothelial cell (hCMEC/D3) monolayers, model simulations demonstrated impaired exocytosis was responsible for inefficient permeability and enhanced accumulation of Aβ42 in the BBB endothelium. Further, both isoforms were shown to disrupt the exocytosis machinery of BBB endothelial cells so that a vicious cycle could be generated. The validated model was able to capture changes in Aβ steady-state levels in plasma as well as the brain during AD progression and allowed us to predict the kinetics of Aβ accumulation in the BBB endothelium.

Uptake of Aβ by OATPs might be a new pathophysiological mechanism of Alzheimer disease

BACKGROUND

The accumulation of neurotoxic amyloid-beta (Aβ) in the brain is a characteristic of Alzheimer's disease (AD), at the same time, it is possible alterations of liver function could affect brain Aβ levels through changes in blood Aβ concentration. Over the last decade, a number of reports have shown that P-glycoprotein (encoded by ABC1B1) actively mediates the efflux transport of Aβ peptides. However, the mechanism by which Aβ peptides enter the cells is not clear. In the preliminary study, we found that the protein expression of organic anion transporting Polypeptide 1a4 (OATP1B1) in the liver tissue of mice with AD was significantly higher than that in the normal mice. In contrast, the protein expression of Oatp1a4 in the brain significantly decreased in mice with AD. OATP1B1, an important drug transporter might be related to the pathophysiology of AD.

RESULTS

In this study, we established an OATP1B1-GFP-HEK293T cell model to confirm the OATP1B1 mediated transport of Aβ_1-42. Compared to the control group of GFP-HEK293Tcells, the uptake of Aβ_1-42 protein in the OATP1B1-GFP-HEK293T group increased significantly with the increase in concentration of Aβ_1-42, and also increased significantly with an increase in the duration of incubation. Similar results were observed in the flow cytometry experiment, and the uptake of Aβ_1-42in HEK293T-OATP1B1 cells was almost twice that in the control group. These results indicate that OATPs may act as an important "carrier" for the transport of Aβ1-42 from the blood to the tissues, including liver and brain.

CONCLUSIONS

This is a novel and interesting finding and OATP1B1 can be investigated as a new treatment target for AD.

Multifunctional Gold Nanoparticle-Conjugated Cellulose Nanoonions Alleviate Aβ42 Fibrillation-Induced Toxicity via Regulation of Oxidative Stress and Ion Homeostasis

Inhibition of hen egg white lysozyme (HEWL) and Aβ42 fibrillation have been established as the main models for the treatment of systemic lysozyme amyloidosis and Alzheimer's disease (AD), respectively. Several antiamyloidogenic nanomaterials have been developed over the period; however, their intracellular mechanism of action is still not well understood. In this context, plant-based, gold-conjugated, injectable, hydrophilic cellulose nanoonions (CNOs), viz., DH-CNO (∼60 ± 5 nm) and LC-CNO (∼55 ± 12 nm), were developed from their respective hydrophobic cellulose nanocrystals (DH-CNC and LC-CNC) using a single-step chemical template-mediated process. This unique nanocellulose architecture was chemically and morphologically characterized by various spectroscopic and microscopic techniques. Further, the different biophysical studies documented marked the inhibition/disintegration potential of gold-conjugated LC-CNO against HEWL and Aβ42 peptide aggregation. It was further observed that inhibition of protein fibrillation could be achieved within ∼10 min when the same materials were used under photoirradiation conditions. In vitro protein aggregation studies using HEK293 cells suggested that gold-conjugated LC-CNO could effectively reduce the cellular toxicity via regulation of oxidative stress and ion homeostasis. The outcome of the present study will help in designing cellulose-based novel functional nanochaperones against various neurodegenerative diseases.

Distinct Uptake Kinetics of Alzheimer Disease Amyloid-β 40 and 42 at the Blood-Brain Barrier Endothelium

Blood-brain barrier (BBB) endothelial cells lining the cerebral microvasculature maintain dynamic equilibrium between soluble amyloid-β (Aβ) levels in the brain and plasma. The BBB dysfunction prevalent in Alzheimer disease contributes to the dysregulation of plasma and brain Aβ and leads to the perturbation of the ratio between Aβ42 and Aβ40, the two most prevalent Aβ isoforms in patients with Alzheimer disease. We hypothesize that BBB endothelium distinguishes between Aβ40 and Aβ42, distinctly modulates their trafficking kinetics between plasma and brain, and thereby contributes to the maintenance of healthy Aβ42/Aβ40 ratios. To test this hypothesis, we investigated Aβ40 and Aβ42 trafficking kinetics in hCMEC/D3 monolayers (human BBB cell culture model) in vitro as well as in mice in vivo. Although the rates of uptake of fluorescein-labeled Aβ40 and Aβ42 (F-Aβ40 and F-Aβ42) were not significantly different on the abluminal side, the luminal uptake rate of F-Aβ42 was substantially higher than F-Aβ40. Since higher plasma Aβ levels were shown to aggravate BBB dysfunction and trigger cerebrovascular disease, we systematically investigated the dynamic interactions of luminal [¹²⁵I]Aβ peptides and their trafficking kinetics at BBB using single-photon emission computed tomography/computed tomography imaging in mice. Quantitative modeling of the dynamic imaging data thus obtained showed that the rate of uptake of toxic [¹²⁵I]Aβ42 and its subsequent BBB transcytosis is significantly higher than [¹²⁵I]Aβ40. It is likely that the molecular mechanisms underlying these kinetic differences are differentially affected in Alzheimer and cerebrovascular diseases, impact plasma and brain levels of Aβ40 and Aβ42, engender shifts in the Aβ42/Aβ40 ratio, and unleash downstream toxic effects. SIGNIFICANCE STATEMENT: Dissecting the binding and uptake kinetics of Aβ40 and Aβ42 at the BBB endothelium will facilitate the estimation of Aβ40 versus Aβ42 exposure to the BBB endothelium and allow assessment of the risk of BBB dysfunction by monitoring Aβ42 and Aβ40 levels in plasma. This knowledge, in turn, will aid in elucidating the role of these predominant Aβ isoforms in aggravating BBB dysfunction and cerebrovascular disease.

Deciphering the roles of caveolin in neurodegenerative diseases: The good, the bad and the importance of context

Neurodegenerative diseases (NDDs), which contribute to progressive and irreversible impairments of both the structure and function of the nervous system, pose a substantial socioeconomic burden on society. Mitochondrial dysfunction, oxidative stress, membrane damage, DNA damage, and abnormal protein degradation pathways play pivotal roles in the etiology of NDDs. Recently, growing evidence has demonstrated that caveolins are important in the pathology of NDDs due to their cellular functions in signal transduction, endocytosis, transcytosis, cholesterol transport, and lipid homeostasis. Given the significance of caveolins, here we review the literature to clarify their molecular mechanisms and roles in NDDs. We first briefly introduce the general background on caveolins. Next, we focus on the various important functions of caveolins in the brain. Finally, we emphasize recent progress regarding caveolins, especially Cav-1, which exert both benefit and unfavorable effects in NDDs such as AD and PD. Collectively, the data presented here should advance the investigation of caveolins for the future development of innovative strategies for the treatment of NDDs.

Soy flavonoids prevent cognitive deficits induced by intra-gastrointestinal administration of beta-amyloid

BACKGROUND

In Alzheimer's diseases, beta-amyloid may act as prion-like protein and migrate from the gastrointestinal tract towards the brain. Soy flavonoids have been identified as neuroprotective against cognitive loss in human. Diet with soy flavonoids may be used to slow down the progression of Alzheimer's diseases.

METHODS AND RESULTS

We performed in-vitro tissue culture experiments using myenteric plexus longitudinal muscle layers isolated from the ileum and colon of ICR mice. Beta-amyloid can be taken up into myenteric neurons and induce neuron degeneration, which is protected by flavonoids compounds, including daidzein, genistein, glycitein and luteolin. We also administered oligomeric beta-amyloid (1-42) (total dose: 8 μg) into the gastrointestinal walls of ICR mice and conducted memory tests and gastrointestinal function assessments after 6 and 12 months. Mice treated with beta-amyloid exhibited minor learning deficits in a T-maze memory test at 6 months and significant memory impairment in a novel object recognition task at 12 months. These impairments were prevented by soy flavonoids. Tracking studies performed using fluorescently tagged beta-amyloid found that, beta-amyloid injected at the stomach can aggregate within the layer of myenteric neurons and migrate to the jejunum or via the vagus nerves to the brain after 1 month. Reductions in the gastrointestinal tissue weight and the spontaneous ileal contraction frequency were also observed at 6 and 12 months, respectively.

CONCLUSION

Our findings indicate that beta-amyloid can migrate from the gastrointestinal tract to the brain to induce cognitive impairments. Furthermore, chronic soy flavonoids in drinking water have protective actions.

Potentiation of NMDA-Mediated Responses by Amyloid-β Peptide 1-40 in Rat Sympathetic Preganglionic Neurons

The abnormal accumulation of amyloid-β peptides (Aβ) is one of the main characteristics of Alzheimer's disease (AD). Cerebro- and cardiovascular diseases may be the risk factors for developing AD. The effect of Aβ on central sympathetic control of cardiovascular function remains unclear. The present study examines the acute effects of Aβ oligomers on the function of NMDA receptors, a subtype of ionotropic glutamate receptors, in rat sympathetic preganglionic neurons (SPNs). In the in vitro electrophysiological study, Aβ1-40 but not Aβ1-42 applied by superfusion for 5 min significantly potentiated NMDA-induced depolarizations in SPNs of neonatal rat spinal cord slice preparation. Application of Aβ1-40 had little effects on AMPA-induced depolarizations or GABA-induced hyperpolarizations. Treatment with a selective protein kinase C (PKC) inhibitor applied together with Aβ1-40 blocked the augmentation by Aβ1-40 of NMDA-induced depolarizations. Western blot analysis showed an increase in the levels of phosphoserine 896, selectively regulated by PKC, without significant changes in phosphoserine 897 on GluN1 subunits in lateral horn areas of spinal cord slices following treatment with Aβ1-40. In the in vivo study, intrathecal injection of Aβ1-40 (0.2 nmol) potentiated the pressor effects induced by NMDA (2 nmol) injected intrathecally in urethane-anesthetized rats. These results suggest that different fragments of Aβ may have differential effects on the NMDA receptor function and the selective augmentation of NMDA receptor function by Aβ1-40 may involve PKC-dependent mechanisms in sympathetic preganglionic neurons.

Alzheimer's Disease is Driven by Intraneuronally Retained Beta-Amyloid Produced in the AD-Specific, βAPP-Independent Pathway: Current Perspective and Experimental Models for Tomorrow

A view of the origin and progression of Alzheimer's disease, AD, prevailing until now and formalized as the Amyloid Cascade Hypothesis theory, maintains that the disease is initiated by overproduction of beta-amyloid, Aβ, which is generated solely by the Aβ precursor protein, βAPP, proteolytic pathway and secreted from the cell. Consequent extracellular accumulation of Aβ triggers a cascade of molecular and cellular events leading to neurodegeneration that starts early in life, progresses as one prolonged process, builds up for decades, and culminates in symptomatic manifestations of the disease late in life. In this paradigm, a time window for commencement of therapeutic intervention is small and accessible only early in life. The outlook introduced in the present study is fundamentally different. It posits that the βAPP proteolytic/secretory pathway of Aβ production causes AD in humans no more than it does in either short- or long-lived non-human mammals that share this pathway with humans, accumulate beta-amyloid as they age, but do not develop the disease. Alzheimer's disease, according to this outlook, is driven by an additional powerful AD-specific pathway of Aβ production that operates in affected humans, is completely independent of the βAPP precursor, and is not available in non-human mammals. The role of the βAPP proteolytic pathway in the disease in humans is activation of this additional AD-specific Aβ production pathway. This occurs through accumulation of intracellular Aβ, primarily via ApoE-assisted cellular uptake of secreted beta-amyloid, but also through retention of a fraction of Aβ produced in the βAPP proteolytic pathway. With time, accumulated intracellular Aβ triggers mitochondrial dysfunction. In turn, cellular stresses associated with mitochondrial dysfunction, including ER stress, activate a second, AD-specific, Aβ production pathway: Asymmetric RNA-dependent βAPP mRNA amplification; animal βAPP mRNA is ineligible for this process. In this pathway, every conventionally produced βAPP mRNA molecule serves potentially as a template for production of severely 5'-truncated mRNA encoding not the βAPP but its C99 fragment (hence "asymmetric"), the immediate precursor of Aβ. Thus produced, N-terminal signal peptide-lacking C99 is processed not in the secretory pathway on the plasma membrane, but at the intracellular membrane sites, apparently in a neuron-specific manner. The resulting Aβ is, therefore, not secreted but is retained intraneuronally and accumulates rapidly within the cell. Increased levels of intracellular Aβ augment mitochondrial dysfunction, which, in turn, sustains the activity of the βAPP mRNA amplification pathway. These self-propagating mutual Aβ overproduction/mitochondrial dysfunction feedback cycles constitute a formidable two-stroke engine, an engine that drives Alzheimer's disease. The present outlook envisions Alzheimer's disorder as a two-stage disease. The first stage is a slow process of intracellular beta-amyloid accumulation. It results neither in significant neurodegenerative damage, nor in manifestation of the disease. The second stage commences with the activation of the βAPP mRNA amplification pathway shortly before symptomatic onset of the disease, sharply increases the rate of Aβ generation and the extent of its intraneuronal accumulation, produces significant damages, triggers AD symptoms, and is fast. In this paradigm, the time window of therapeutic intervention is wide open, and preventive treatment can be initiated any time, even late in life, prior to commencement of the second stage of the disease. Moreover, there are good reasons to believe that with a drug blocking the βAPP mRNA amplification pathway, it would be possible not only to preempt the disease but also to stop and to reverse it even when early AD symptoms have already manifested. There are numerous experimental models of AD, all based on a notion of the exceptionality of βAPP proteolytic/secretory pathway in Aβ production in the disease. However, with no drug even remotely effective in Alzheimer's disease, a long list of candidate drugs that succeeded remarkably in animal models, yet failed utterly in human clinical trials of potential AD drugs, attests to the inadequacy of currently employed AD models. The concept of a renewable supply of beta-amyloid, produced in the βAPP mRNA amplification pathway and retained intraneuronally in Alzheimer's disease, explains spectacular failures of both BACE inhibition and Aβ-immunotherapy in human clinical trials. This concept also forms the basis of a new generation of animal and cell-based experimental models of AD, described in the present study. These models incorporate Aβ- or C99-encoding mRNA amplification pathways of Aβ production, as well as intracellular retention of their product, and can support not only further investigation of molecular mechanisms of AD but also screening for and testing of candidate drugs aimed at therapeutic targets suggested by the present study.

Preparation and in vitro evaluation of multi-target-directed selenium-chondroitin sulfate nanoparticles in protecting against the Alzheimer's disease

The purpose of this study was to ascertain the effect of selenium-chondroitin sulfate nanoparticles (CS@Se) on multi-target-directed therapy for the treatment of Alzheimer's disease (AD). CS@Se nanoparticles were successfully synthesized, and their therapeutic effects were studied in in vitro AD models. CS@Se effectively inhibited amyloid-β (Aβ) aggregation and protected SH-SY5Y cells from Aβ_1-42-induced cytotoxicity. Moreover, CS@Se significantly decreased okadaic acid-induced actin cytoskeleton instability in SH-SY5Y cells. In addition, CS@Se decreased the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and increased the levels of glutathione peroxidase (GSH-Px). The Western blot results indicated that CS@Se attenuated the hyperphosphorylation of tau (Ser396/Ser404) by regulating the expression of GSK-3β. In summary, this study demonstrated that CS@Se could inhibit the aggregation of Aβ, reduce damage to the cytoskeleton, mitigate oxidative stress and attenuate the hyperphosphorylation of tau protein. CS@Se might be a potent multi-functional agent for the treatment of AD and thus warrants further research and evaluation.

Blocking Inflammasome Activation Caused by β-Amyloid Peptide (Aβ) and Islet Amyloid Polypeptide (IAPP) through an IAPP Mimic

Inflammation in the brain and pancreas is linked to cell degeneration and pathogenesis of both Alzheimer's disease (AD) and type 2 diabetes (T2D). Inflammatory cascades in both tissues are triggered by the uptake of β-amyloid peptide (Aβ) or islet amyloid polypeptide (IAPP) aggregates by microglial cells (AD) or macrophages (T2D) and their insufficient lysosomal degradation. This results in lysosomal damage, caspase-1/NLRP3 inflammasome activation and release of interleukin-1β (IL-1β), a key proinflammatory cytokine in both diseases. Here we show that the inflammatory processes mediated by Aβ and IAPP aggregates in microglial cells and macrophages are blocked by IAPP-GI, a nonamyloidogenic IAPP mimic, which forms high-affinity soluble and nonfibrillar hetero-oligomers with both polypeptides. In contrast to fibrillar Aβ aggregates, nonfibrillar Aβ/IAPP-GI or Aβ/IAPP hetero-oligomers become rapidly internalized by microglial cells and targeted to lysosomes where Aβ is fully degraded. Internalization occurs via IAPP receptor-mediated endocytosis. Moreover, in contrast to IAPP aggregates, IAPP/IAPP-GI hetero-oligomers become rapidly internalized and degraded in the lysosomal compartments of macrophages. Our findings uncover a previously unknown function for the IAPP/Aβ cross-amyloid interaction and suggest that conversion of Aβ or IAPP into lysosome-targeted and easily degradable hetero-oligomers by heteroassociation with IAPP mimics could become a promising approach to specifically prevent amyloid-mediated inflammation in AD, T2D, or both diseases.

Propagation of Protein Aggregation in Neurodegenerative Diseases

Most common neurodegenerative diseases feature deposition of protein amyloids and degeneration of brain networks. Amyloids are ordered protein assemblies that can act as templates for their own replication through monomer addition. Evidence suggests that this characteristic may underlie the progression of pathology in neurodegenerative diseases. Many different amyloid proteins, including Aβ, tau, and α-synuclein, exhibit properties similar to those of infectious prion protein in experimental systems: discrete and self-replicating amyloid structures, transcellular propagation of aggregation, and transmissible neuropathology. This review discusses the contribution of prion phenomena and transcellular propagation to the progression of pathology in common neurodegenerative diseases such as Alzheimer's and Parkinson's. It reviews fundamental events such as cell entry, amplification, and transcellular movement. It also discusses amyloid strains, which produce distinct patterns of neuropathology and spread through the nervous system. These concepts may impact the development of new diagnostic and therapeutic strategies.

Reduced Extracellular Matrix Stiffness Prompts SH-SY5Y Cell Softening and Actin Turnover To Selectively Increase Aβ(1-42) Endocytosis

Alzheimer's disease (AD), the most common neurodegenerative disorder, is characterized by the extracellular deposition of dense amyloid beta plaques. Emerging evidence suggests that the production of these plaques is initiated by the intracellular uptake and lysosomal preconcentration of the amyloid-beta (Aβ) peptide. All previous endocytosis studies assess Aβ uptake with cells plated on traditional tissue culture plastic; however, brain tissue is distinctly soft with a low-kPa stiffness. Use of an ultrastiff plastic/glass substrate prompts a mechanosensitive response (increased cell spreading, cell stiffness, and membrane tension) that potentially distorts a cell's endocytic behavior from that observed in vivo or in a more physiologically relevant mechanical environment. Our studies demonstrate substrate stiffness significantly modifies the behavior of undifferentiated SH-SY5Y neuroblastoma, where cells plated on soft (∼1 kPa) substrates display a rounded morphology, decreased actin polymerization, reduced adhesion (decreased β₁ integrin expression), and reduced cell stiffness compared to cells plated on tissue culture plastic. Moreover, these neuroblastoma on softer substrates display a preferential increase in the uptake of the Aβ(1-42) compared to Aβ(1-40), while both isoforms display a clear stiffness-dependent increase of uptake relative to cells plated on plastic. Considering the brain is a soft tissue that continues to soften with age, this mechanosensitive endocytosis of Aβ has significant implications for understanding age-related neurodegeneration and the mechanism behind Aβ uptake and fibril production. Overall, identifying these physical factors that contribute to the pathology of AD may offer novel avenues of therapeutic intervention.

News from Mars: Two-Tier Paradox, Intracellular PCR, Chimeric Junction Shift, Dark Matter mRNA and Other Remarkable Features of Mammalian RNA-Dependent mRNA Amplification. Implications for Alzheimer's Disease, RNA-Based Vaccines and mRNA Therapeutics

Molecular Biology, a branch of science established to examine the flow of information from "letters" encrypted into DNA structure to functional proteins, was initially defined by a concept of DNA-to-RNA-to-Protein information movement, a notion termed the Central Dogma of Molecular Biology. RNA-dependent mRNA amplification, a novel mode of eukaryotic protein-encoding RNA-to-RNA-to-Protein genomic information transfer, constitutes the extension of the Central Dogma in the context of mammalian cells. It was shown to occur in cellular circumstances requiring exceptionally high levels of production of specific polypeptides, e.g. globin chains during erythroid differentiation or defined secreted proteins in the context of extracellular matrix deposition. Its potency is reflected in the observed cellular levels of the resulting amplified mRNA product: At the peak of the erythroid differentiation, for example, the amount of globin mRNA produced in the amplification pathway is about 1500-fold higher than the amount of its conventionally generated counterpart in the same cells. The cellular enzymatic machinery at the core of this process, RNA-dependent RNA polymerase activity (RdRp), albeit in a non-conventional form, was shown to be constitutively and ubiquitously present, and RNA-dependent RNA synthesis (RdRs) appeared to regularly occur, in mammalian cells. Under most circumstances, the mammalian RdRp activity produces only short antisense RNA transcripts. Generation of complete antisense RNA transcripts and amplification of mRNA molecules require the activation of inducible components of the mammalian RdRp complex. The mechanism of such activation is not clear. The present article suggests that it is triggered by a variety of cellular stresses and occurs in the context of stress responses in general and within the framework of the integrated stress response (ISR) in particular. In this process, various cellular stresses activate, in a stress type-specific manner, defined members of the mammalian translation initiation factor 2α, eIF2α, kinase family: PKR, GCN2, PERK and HRI. Any of these kinases, in an activated form, phosphorylates eIF2α. This results in suppression of global cellular protein synthesis but also in activation of expression of select group of transcription factors including ATF4, ATF5 and CHOP. These transcription factors either function as inducible components of the RdRp complex or enable their expression. The assembly of the competent RdRp complex activates mammalian RNA-dependent mRNA amplification, which appears to be a two-tier process. Tier One is a "chimeric" pathway, named so because it results in an amplified chimeric mRNA molecule containing a fragment of the antisense RNA strand at its 5' terminus. Tier Two further amplifies one of the two RNA end products of the chimeric pathway and constitutes the physiologically occurring intracellular polymerase chain reaction, iPCR. Depending on the structure of the initial mRNA amplification progenitor, the chimeric pathway, Tier One, may result in multiple outcomes including chimeric mRNA that produces either a polypeptide identical to the original, conventional mRNA progenitor-encoded protein or only its C-terminal fragment, CTF. The chimeric RNA end product of Tier One may also produce a polypeptide that is non-contiguously encoded in the genome, activate translation from an open reading frame, which is "silent" in a conventionally transcribed mRNA, or initiate an abortive translation. In sharp contrast, regardless of the outcome of Tier One, the mRNA end product of Tier Two of mammalian mRNA amplification, the iPCR pathway, always produces a polypeptide identical to a conventional mRNA progenitor-encoded protein. This discordance is referred to as the Two-Tier Paradox and discussed in detail in the present article. On the other hand, both Tiers are similar in that they result in heavily modified mRNA molecules resistant to reverse transcription, undetectable by reverse transcription-based methods of sequencing and therefore constituting a proverbial "Dark Matter" mRNA, despite being highly ubiquitous. It appears that in addition to their other functions, the modifications of the amplified mRNA render it compatible, unlike the bulk of cellular mRNA, with phosphorylated eIF2α in translation, implying that in addition to being extraordinarily abundant due to the method of its generation, amplified mRNA is also preferentially translated under the ISR conditions, thus augmenting the efficiency of the amplification process. The vital importance of powerful mechanisms of amplification of protein-encoding genomic information in normal physiology is self-evident. Their malfunctions or misuse appear to be associated with two types of abnormalities, the deficiency of a protein normally produced by these mechanisms and the mRNA amplification-mediated overproduction of a protein normally not generated by such a process. Certain classes of beta-thalassemia exemplify the first type, whereas the second type is represented by overproduction of beta-amyloid in Alzheimer's disease. Moreover, the proposed mechanism of Alzheimer's disease allows a crucial and verifiable prediction, namely that the disease-causing intraneuronally retained variant of beta-amyloid differs from that produced conventionally by βAPP proteolysis in that it contains the additional methionine or acetylated methionine at its N-terminus. Because of its extraordinary evidential value as a natural reporter of the mRNA amplification pathway, this feature, if proven, would, arguably, constitute the proverbial Holy Grail not only for Alzheimer's disease but also for the mammalian RNA-dependent mRNA amplification field in general. Both examples are discussed in detail in the present article, which summarizes and systematizes our current understanding of the field and describes two categories of reporter constructs, one for the chimeric Tier of mRNA amplification, another for the iPCR pathway; both reporter types are essential for elucidating underlying molecular mechanisms. It also suggests, in light of the recently demonstrated feasibility of RNA-based vaccines, that the targeted intracellular amplification of exogenously introduced amplification-eligible antigen-encoding mRNAs via the induced or naturally occurring RNA-dependent mRNA amplification pathway could be of substantial benefit in triggering a fast and potent immune response and instrumental in the development of future vaccines. Similar approaches can also be effective in achieving efficient and sustained expression of exogenous mRNA in mRNA therapeutics.

Alzheimer's Disease Prevention and Treatment: Case for Optimism

A paradigm shift is under way in the Alzheimer's field. A view of Alzheimer's disease, AD, prevailing until now, the old paradigm, maintains that it is initiated and driven by the overproduction and extracellular accumulation of beta-amyloid, Aβ; a peptide assumed to be derived, both in health and disease, solely by proteolysis of its large precursor, βAPP. In AD, according to this view, Aβ overproduction-associated neurodegeneration begins early, accumulates throughout the lifespan, and manifests symptomatically late in life. A number of drugs, designed within the framework of exceptionality of the βAPP proteolytic/secretory pathway in Aβ production in Alzheimer's disease, achieved spectacular successes in treatment, even the reversal, of AD symptoms in animal models. Without exception, they all exhibited equally spectacular failures in human clinical trials. This paradigm provides few causes for optimism with regard to prevention and treatment of AD. In its context, the disease is considered untreatable in the symptomatic phase; even prodromal cases are assumed too advanced for treatment because Aβ-triggered damages have been accumulating for preceding decades, presumably starting in the early twenties and, to be effective, this is when therapeutic intervention should commence and continue for life. The new paradigm does not dispute the seminal role of Aβ in AD but posits that beta-amyloid produced in the βAPP proteolytic/secretory pathway causes AD in humans no more than it does in non-human mammals that share this pathway with humans, accumulate Aβ as they age, but do not develop the disease. Alzheimer's disease, according to this outlook, is driven by the AD-specific pathway of Aβ production, independent of βAPP and absent in animals. Its activation, late in life, occurs through accumulation, via both cellular uptake of secreted Aβ and neuronal retention of a fraction of beta-amyloid produced in the βAPP proteolytic pathway, of intraneuronal Aβ, which triggers mitochondrial dysfunction. Cellular stresses associated with mitochondrial dysfunction, or, probably, the integrated stress response, ISR, elicited by it, activate an AD-specific Aβ production pathway. In it, every conventionally produced βAPP mRNA molecule potentially serves repeatedly as a template for production of severely 5'-truncated mRNA encoding C99 fragment of βAPP, the immediate precursor of Aβ that is processed in a non-secretory pathway, apparently in a neuron-specific manner. The resulting intraneuronally retained Aβ augments mitochondrial dysfunction, which, in turn, sustains the activity of the βAPP mRNA amplification pathway. These self-propagating Aβ overproduction/mitochondrial dysfunction mutual feedback cycles constitute the engine that drives AD and ultimately triggers neuronal death. In this paradigm, preventive treatment can be initiated any time prior to commencement of βAPP mRNA amplification. Moreover, there are good reasons to believe that with a drug blocking the amplification pathway, it would be possible not only to preempt the disease but also stop and reverse it even when early AD symptoms are already manifested. Thus, the new paradigm introduces a novel theory of Alzheimer's disease. It explains the observed discordances, determines defined therapeutic targets, provides blueprints for a new generation of conceptually distinct AD models and specifies design of a reporter for the mRNA amplification pathway. Most importantly, it offers detailed guidance and tangible hope for prevention of the disease and its treatment at the early symptomatic stages.

Preparation, characterisation and in vitro and in vivo evaluation of CD44-targeted chondroitin sulphate-conjugated doxorubicin PLGA nanoparticles

The purpose of this study was to ascertain the effect of chondroitin sulphate-modified doxorubicin (Dox) nanoparticles on enhancing the tumour-targeting effect and tumour growth inhibition effect of doxorubicin both in vitro and in vivo. The chondroitin sulphate-doxorubicin conjugate and its poly(lactic-co-glycolic acid) (PLGA) nanoparticles (CS-Dox-PLGA) were successfully synthesised, and then characterized by Fourier-transform infrared spectroscopy (FTIR), proton magnetic resonance (¹HNMR), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), transmission electron microscope (TEM), zeta potential and laser light scattering. Taking advantage of the enhanced permeability and CD44-mediated endocytosis, CS-Dox-PLGA showed excellent capacity for penetrating the peripheral tumour barrier and into the nucleus of tumour cells. The CS-Dox-PLGA cellular uptake was improved and exhibited a significantly higher level of cytotoxicity in U251 cells. After intravenous administration, the CS-Dox-PLGA showed good pharmacokinetic properties and excellent U251-induced tumour inhibition with low cardiac toxicity. Therefore, CS-Dox-PLGA with low cardiac toxicity and good anti-tumour ability might be a better choice for Dox in clinical practice.

High-density lipoprotein mimetic peptide 4F mitigates amyloid-β-induced inhibition of apolipoprotein E secretion and lipidation in primary astrocytes and microglia

The apolipoprotein E (apoE) ε4 allele is the primary genetic risk factor for late-onset Alzheimer's disease (AD). ApoE in the brain is produced primarily by astrocytes; once secreted from these cells, apoE binds lipids and forms high-density lipoprotein (HDL)-like particles. Accumulation of amyloid-β protein (Aβ) in the brain is a key hallmark of AD, and is thought to initiate a pathogenic cascade leading to neurodegeneration and dementia. The level and lipidation state of apoE affect Aβ aggregation and clearance pathways. Elevated levels of plasma HDL are associated with lower risk and severity of AD; the underlying mechanisms, however, have not been fully elucidated. This study was designed to investigate the impact of an HDL mimetic peptide, 4F, on the secretion and lipidation of apoE. We found that 4F significantly increases apoE secretion and lipidation in primary human astrocytes as well as in primary mouse astrocytes and microglia. Aggregated Aβ inhibits glial apoE secretion and lipidation, causing accumulation of intracellular apoE, an effect that is counteracted by co-treatment with 4F. Pharmacological and gene editing approaches show that 4F mediates its effects partially through the secretory pathway from the endoplasmic reticulum to the Golgi apparatus and requires the lipid transporter ATP-binding cassette transporter A1. We conclude that the HDL mimetic peptide 4F promotes glial apoE secretion and lipidation and mitigates the detrimental effects of Aβ on proper cellular trafficking and functionality of apoE. These findings suggest that treatment with such an HDL mimetic peptide may provide therapeutic benefit in AD. Read the Editorial Highlight for this article on page 580.

Insulin differentially affects the distribution kinetics of amyloid beta 40 and 42 in plasma and brain

Impaired brain clearance of amyloid-beta peptides (Aβ) 40 and 42 across the blood-brain barrier (BBB) is believed to be one of the pathways responsible for Alzheimer's disease (AD) pathogenesis. Hyperinsulinemia prevalent in type II diabetes was shown to damage cerebral vasculature and increase Aβ accumulation in AD brain. However, there is no clarity on how aberrations in peripheral insulin levels affect Aβ accumulation in the brain. This study describes, for the first time, an intricate relation between plasma insulin and Aβ transport at the BBB. Upon peripheral insulin administration in wild-type mice: the plasma clearance of Aβ40 increased, but Aβ42 clearance reduced; the plasma-to-brain influx of Aβ40 increased, and that of Aβ42 reduced; and the clearance of intracerebrally injected Aβ40 decreased, whereas Aβ42 clearance increased. In hCMEC/D3 monolayers (in vitro BBB model) exposed to insulin, the luminal uptake and luminal-to-abluminal permeability of Aβ40 increased and that of Aβ42 reduced; the abluminal-to-luminal permeability of Aβ40 decreased, whereas Aβ42 permeability increased. Moreover, Aβ cellular trafficking machinery was altered. In summary, Aβ40 and Aβ42 demonstrated distinct distribution kinetics in plasma and brain compartments, and insulin differentially modulated their distribution. Cerebrovascular disease and metabolic disorders may disrupt this intricate homeostasis and aggravate AD pathology.

Interactions of amyloid-β peptides on lipid bilayer studied by single molecule imaging and tracking

The amyloid-β peptides (Aβ40 and Aβ42) feature prominently in the synaptic dysfunction and neuronal loss associated with Alzheimer's disease (AD). This has been proposed to be due either to interactions between Aβ and cell surface receptors affecting cell signaling, or to the formation of calcium-permeable channels in the membrane that disrupt calcium homeostasis. In both mechanisms the cell membrane is the primary cellular structure with which Aβ interacts. Aβ concentrations in human bodily fluids are very low (pM-nM) rendering studies of the size, composition, cellular binding sites and mechanism of action of the oligomers formed in vivo very challenging. Most studies, therefore, have utilized Aβ oligomers prepared at micromolar peptide concentrations, where Aβ forms oligomeric species which possess easily observable cell toxicity. Such toxicity has not been observed when nM concentrations of peptide are used in the experiment highlighting the importance of employing physiologically relevant peptide concentrations for the results to be of biological significance. In this paper single-molecule microscopy was used to monitor Aβ oligomer formation and diffusion on a supported lipid bilayer at nanomolar peptide concentrations. Aβ monomers, the dominant species in solution, tightly associate with the membrane and are highly mobile whereas trimers and higher-order oligomers are largely immobile. Aβ dimers exist in a mixture of mobile and immobile states. Oligomer growth on the membrane is more rapid for Aβ40 than for the more amyloidogenic Aβ42 but is largely inhibited for a 1:1 Aβ40:Aβ42 mixture. The mechanism underlying these Aβ40-Aβ42 interactions may feature in Alzheimer's pathology.

Oxidative Stress, Synaptic Dysfunction, and Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder without a cure. Most AD cases are sporadic where age represents the greatest risk factor. Lack of understanding of the disease mechanism hinders the development of efficacious therapeutic approaches. The loss of synapses in the affected brain regions correlates best with cognitive impairment in AD patients and has been considered as the early mechanism that precedes neuronal loss. Oxidative stress has been recognized as a contributing factor in aging and in the progression of multiple neurodegenerative diseases including AD. Increased production of reactive oxygen species (ROS) associated with age- and disease-dependent loss of mitochondrial function, altered metal homeostasis, and reduced antioxidant defense directly affect synaptic activity and neurotransmission in neurons leading to cognitive dysfunction. In addition, molecular targets affected by ROS include nuclear and mitochondrial DNA, lipids, proteins, calcium homeostasis, mitochondrial dynamics and function, cellular architecture, receptor trafficking and endocytosis, and energy homeostasis. Abnormal cellular metabolism in turn could affect the production and accumulation of amyloid-β (Aβ) and hyperphosphorylated Tau protein, which independently could exacerbate mitochondrial dysfunction and ROS production, thereby contributing to a vicious cycle. While mounting evidence implicates ROS in the AD etiology, clinical trials with antioxidant therapies have not produced consistent results. In this review, we will discuss the role of oxidative stress in synaptic dysfunction in AD, innovative therapeutic strategies evolved based on a better understanding of the complexity of molecular mechanisms of AD, and the dual role ROS play in health and disease.

Endocytic uptake of monomeric amyloid-β peptides is clathrin- and dynamin-independent and results in selective accumulation of Aβ(1-42) compared to Aβ(1-40)

Intraneuronal accumulation of amyloid-β (Aβ) peptides represent an early pathological feature in Alzheimer’s disease. We have therefore utilized flow cytometry and confocal microscopy in combination with endocytosis inhibition to explore the internalisation efficiency and uptake mechanisms of Aβ(1–40) and Aβ(1–42) monomers in cultured SH-SY5Y cells. We find that both variants are constitutively internalised via endocytosis and that their uptake is proportional to cellular endocytic rate. Moreover, SH-SY5Y cells internalise consistently twice the amount of Aβ(1–42) compared to Aβ(1–40); an imaging-based quantification showed that cells treated with 1 µM peptide for 8 h contained 800,000 peptides of Aβ(1–42) and 400,000 of Aβ(1–40). Both variants co-localised to >90% with lysosomes or other acidic compartments. Dynasore and chlorpromazine endocytosis inhibitors were both found to reduce uptake, particularly of Aβ(1–42). Overexpression of the C-terminal of the clathrin-binding domain of AP180, dynamin2 K44A, or Arf6 Q67L did however not reduce uptake of the Aβ variants. By contrast, perturbation of actin polymerisation and inhibition of macropinocytosis reduced Aβ(1–40) and Aβ(1–42) uptake considerably. This study clarifies mechanisms of Aβ(1–40) and Aβ(1–42) uptake, pinpoints differences between the two variants and highlights a common and putative role of macropinocytosis in the early accumulation of intraneuronal Aβ in AD.

Amyloid-β(1-42) Aggregation Initiates Its Cellular Uptake and Cytotoxicity

The accumulation of amyloid β peptide(1-42) (Aβ(1-42)) in extracellular plaques is one of the pathological hallmarks of Alzheimer disease (AD). Several studies have suggested that cellular reuptake of Aβ(1-42) may be a crucial step in its cytotoxicity, but the uptake mechanism is not yet understood. Aβ may be present in an aggregated form prior to cellular uptake. Alternatively, monomeric peptide may enter the endocytic pathway and conditions in the endocytic compartments may induce the aggregation process. Our study aims to answer the question whether aggregate formation is a prerequisite or a consequence of Aβ endocytosis. We visualized aggregate formation of fluorescently labeled Aβ(1-42) and tracked its internalization by human neuroblastoma cells and neurons. β-Sheet-rich Aβ(1-42) aggregates entered the cells at low nanomolar concentration of Aβ(1-42). In contrast, monomer uptake faced a concentration threshold and occurred only at concentrations and time scales that allowed Aβ(1-42) aggregates to form. By uncoupling membrane binding from internalization, we found that Aβ(1-42) monomers bound rapidly to the plasma membrane and formed aggregates there. These structures were subsequently taken up and accumulated in endocytic vesicles. This process correlated with metabolic inhibition. Our data therefore imply that the formation of β-sheet-rich aggregates is a prerequisite for Aβ(1-42) uptake and cytotoxicity.

Penetratin Peptide-Functionalized Gold Nanostars: Enhanced BBB Permeability and NIR Photothermal Treatment of Alzheimer's Disease Using Ultralow Irradiance

The structural changes of amyloid-beta (Aβ) from nontoxic monomers into neurotoxic aggregates are implicated with pathogenesis of Alzheimer's disease (AD). Over the past decades, weak disaggregation ability and low permeability to the blood-brain barrier (BBB) may be the main obstacles for major Aβ aggregation blockers. Here, we synthesized penetratin (Pen) peptide loaded poly(ethylene glycol) (PEG)-stabilized gold nanostars (AuNS) modified with ruthenium complex (Ru@Pen@PEG-AuNS), and Ru(II) complex as luminescent probes for tracking drug delivery. We revealed that Ru@Pen@PEG-AuNS could obviously inhibit the formation of Aβ fibrils as well as dissociate preformed fibrous Aβ under the irradiation of near-infrared (NIR) due to the NIR absorption characteristic of AuNS. More importantly, this novel design could be applied in medicine as an appropriate nanovehicle, being highly biocompatible and hemocompatible. In addition, Ru@Pen@PEG-AuNS had excellent neuroprotective effect on the Aβ-induced cellular toxicity by applying NIR irradiation. Meanwhile, Pen peptide could effectively improve the delivery of nanoparticles to the brain in vitro and in vivo, which overcame the major limitation of Aβ aggregation blockers. These consequences illustrated that the enhanced BBB permeability and efficient photothermolysis of Ru@Pen@PEG-AuNS are promising agents in AD therapy.

Cell Biology of Prions and Prionoids: A Status Report

The coalescence of proteins into highly ordered aggregates is a hallmark of protein misfolding disorders (PMDs), which, when affecting the central nervous system, lead to progressive neurodegeneration. Although the chemical identity and the topology of each culprit protein are unique, the principles governing aggregation and propagation are strikingly stereotypical. It is now clear that such protein aggregates can spread from cell to cell and eventually affect entire organ systems - similarly to prion diseases. However, because most aggregates are not found to transmit between individuals, they are not infectious sensu strictiori. Therefore, they are not identical to prions and we prefer to define them as 'prionoids'. Here we review recent advances in understanding the toxicity of protein aggregation affecting the brain.

Sialic acid (SA)-modified selenium nanoparticles coated with a high blood-brain barrier permeability peptide-B6 peptide for potential use in Alzheimer's disease

The blood-brain barrier (BBB) is a formidable gatekeeper toward exogenous substances, playing an important role in brain homeostasis and maintaining a healthy microenvironment for complex neuronal activities. However, it also greatly hinders drug permeability into the brain and limits the management of brain diseases. The development of new drugs that show improved transport across the BBB represents a promising strategy for Alzheimer's disease (AD) intervention. Whereas, previous study of receptor-mediated endogenous BBB transport systems has focused on a strategy of using transferrin to facilitate brain drug delivery system, a system that still suffers from limitations including synthesis procedure, stability and immunological response. In the present study, we synthetised sialic acid (SA)-modified selenium (Se) nanoparticles conjugated with an alternative peptide-B6 peptide (B6-SA-SeNPs, a synthetic selenoprotein analogue), which shows high permeability across the BBB and has the potential to serve as a novel nanomedicine for disease modification in AD. Laser-scanning confocal microscopy, flow cytometry analysis and inductively coupled plasma-atomic emission spectroscopy ICP-AES revealed high cellular uptake of B6-SA-SeNPs by cerebral endothelial cells (bEnd.3). The transport efficiency of B6-SA-SeNPs was evaluated in a Transwell experiment based on in vitro BBB model. It provided direct evidence for B6-SA-SeNPs crossing the BBB and being absorbed by PC12 cells. Moreover, inhibitory effects of B6-SA-SeNPs on amyloid-β peptide (Aβ) fibrillation could be demonstrated in PC12 cells and bEnd3 cells. B6-SA-SeNPs could not only effectively inhibit Aβ aggregation but could disaggregate preformed Aβ fibrils into non-toxic amorphous oligomers. These results suggested that B6-SA-SeNPs may provide a promising platform, particularly for the application of nanoparticles in the treatment of brain diseases.

STATEMENT OF SIGNIFICANCE

Alzheimer's disease (AD) is the world's most common form of dementia characterized by intracellular neurofibrillary tangles in the brain. Over the past decades, the blood-brain barrier (BBB) limits access of therapeutic or diagnostic agents into the brain, which greatly hinders the development of new drugs for treating AD. In this work, we evaluated the efficiency of B6-SA-SeNPs across BBB and investigated the interactions between B6-SA-SeNPs and amyloid-β peptide (Aβ). We confirm that B6-SA-SeNPs could provide a promising platform because of its high brain delivery efficiency, anti-amyloid properties and anti-oxidant properties, which may serve as a novel nanomedicine for the application in the treatment of brain diseases.

Aβ42 and Aβ40: similarities and differences

The abnormal accumulation of amyloid-β (Aβ) peptide in the brain is one of the most important hallmarks of Alzheimer's disease. Aβ is an aggregation-prone and toxic polypeptide with 39-43 residues, derived from the amyloid precursor protein proteolysis process. According to the amyloid hypothesis, abnormal accumulation of Aβ in the brain is the primary influence driving Alzheimer's disease pathologies. Among all kinds of Aβ isoforms, Aβ40 and Aβ42 are believed to be the most important ones. Although these two kinds of Aβ differ only in two amino acid residues, recent studies show that they differ significantly in their metabolism, physiological functions, toxicities, and aggregation mechanism. In this review, we mainly summarize the similarities and differences between Aβ42 and Aβ40, recent studies on selective inhibitors as well as probes will also be mentioned.

Choroid plexus dysfunction impairs beta-amyloid clearance in a triple transgenic mouse model of Alzheimer's disease

Compromised secretory function of choroid plexus (CP) and defective cerebrospinal fluid (CSF) production, along with accumulation of beta-amyloid (Aβ) peptides at the blood-CSF barrier (BCSFB), contribute to complications of Alzheimer’s disease (AD). The AD triple transgenic mouse model (3xTg-AD) at 16 month-old mimics critical hallmarks of the human disease: β-amyloid (Aβ) plaques and neurofibrillary tangles (NFT) with a temporal- and regional- specific profile. Currently, little is known about transport and metabolic responses by CP to the disrupted homeostasis of CNS Aβ in AD. This study analyzed the effects of highly-expressed AD-linked human transgenes (APP, PS1 and tau) on lateral ventricle CP function. Confocal imaging and immunohistochemistry revealed an increase only of Aβ42 isoform in epithelial cytosol and in stroma surrounding choroidal capillaries; this buildup may reflect insufficient clearance transport from CSF to blood. Still, there was increased expression, presumably compensatory, of the choroidal Aβ transporters: the low density lipoprotein receptor-related protein 1 (LRP1) and the receptor for advanced glycation end product (RAGE). A thickening of the epithelial basal membrane and greater collagen-IV deposition occurred around capillaries in CP, probably curtailing solute exchanges. Moreover, there was attenuated expression of epithelial aquaporin-1 and transthyretin (TTR) protein compared to Non-Tg mice. Collectively these findings indicate CP dysfunction hypothetically linked to increasing Aβ burden resulting in less efficient ion transport, concurrently with reduced production of CSF (less sink action on brain Aβ) and diminished secretion of TTR (less neuroprotection against cortical Aβ toxicity). The putative effects of a disabled CP-CSF system on CNS functions are discussed in the context of AD.

Sequence-dependent internalization of aggregating peptides

Recently, a number of aggregation disease polypeptides have been shown to spread from cell to cell, thereby displaying prionoid behavior. Studying aggregate internalization, however, is often hampered by the complex kinetics of the aggregation process, resulting in the concomitant uptake of aggregates of different sizes by competing mechanisms, which makes it difficult to isolate pathway-specific responses to aggregates. We designed synthetic aggregating peptides bearing different aggregation propensities with the aim of producing modes of uptake that are sufficiently distinct to differentially analyze the cellular response to internalization. We found that small acidic aggregates (≤500 nm in diameter) were taken up by nonspecific endocytosis as part of the fluid phase and traveled through the endosomal compartment to lysosomes. By contrast, bigger basic aggregates (>1 μm) were taken up through a mechanism dependent on cytoskeletal reorganization and membrane remodeling with the morphological hallmarks of phagocytosis. Importantly, the properties of these aggregates determined not only the mechanism of internalization but also the involvement of the proteostatic machinery (the assembly of interconnected networks that control the biogenesis, folding, trafficking, and degradation of proteins) in the process; whereas the internalization of small acidic aggregates is HSF1-independent, the uptake of larger basic aggregates was HSF1-dependent, requiring Hsp70. Our results show that the biophysical properties of aggregates determine both their mechanism of internalization and proteostatic response. It remains to be seen whether these differences in cellular response contribute to the particular role of specific aggregated proteins in disease.

Mechanisms of U87 astrocytoma cell uptake and trafficking of monomeric versus protofibril Alzheimer's disease amyloid-β proteins

A significant hallmark of Alzheimer’s disease is the formation of senile plaques in the brain due to the unbalanced levels of amyloid-beta (Aβ). However, although how Aβ is produced from amyloid precursor proteins is well understood, little is known regarding the clearance and metabolism of various Aβ aggregates from the brain. Similarly, little is known regarding how astrocytes internalize and degrade Aβ, although astrocytes are known to play an important role in plaque maintenance and Aβ clearance. The objective of this study is to investigate the cellular mechanisms that mediate the internalization of soluble monomeric versus oligomeric Aβ by astrocytes. We used a combination of laser confocal microscopy and genetic and pharmacological experiments to dissect the internalization of sAβ42 and oAβ42 and their postendocytic transport by U87 human brain astrocytoma cell line. Both Aβ42 species were internalized by U87 cells through fluid phase macropinocytosis, which required dynamin 2. Depleting LDL receptor-related protein 1 (LRP1) decreased sAβ42 uptake more significantly than that of oAβ42. We finally show that both Aβ42 species were rapidly transported to lysosomes through an endolytic pathway and subjected to proteolysis after internalization, which had no significant toxic effects to the U87 cells under relatively low concentrations. We propose that macropinocytic sAβ42 and oAβ42 uptake and their subsequent proteolytic degradation in astroglial cells is a significant mechanism underlying Aβ clearance from the extracellular milieu. Understanding the molecular events involved in astrocytic Aβ internalization may identify potential therapeutic targets for Alzheimer’s disease.

Epigallocatechin-3-gallate (EGCG)-stabilized selenium nanoparticles coated with Tet-1 peptide to reduce amyloid-β aggregation and cytotoxicity

Alzheimer's disease (AD), the most common neurodegenerative disease, is caused by an accumulation of amyloid-β (Aβ) plaque deposits in the brains. Evidence is increasingly showing that epigallocatechin-3-gallate (EGCG) can partly protect cells from Aβ-mediated neurotoxicity by inhibiting Aβ aggregation. In order to better understand the process of Aβ aggregation and amyloid fibril disaggregation and reduce the cytotoxicity of EGCG at high doses, we attached EGCG onto the surface of selenium nanoparticles (EGCG@Se). Given the low delivery efficiency of EGCG@Se to the targeted cells and the involvement of selenoprotein in antioxidation and neuroprotection, which are the key factors for preventing the onset and progression of AD, we synthesized EGCG-stabilized selenium nanoparticles coated with Tet-1 peptide (Tet-1-EGCG@Se, a synthetic selenoprotein analogue), considering the affinity of Tet-1 peptide to neurons. We revealed that Tet-1-EGCG@Se can effectively inhibit Aβ fibrillation and disaggregate preformed Aβ fibrils into nontoxic aggregates. In addition, we found that both EGCG@Se and Tet-1-EGCG@Se can label Aβ fibrils with a high affinity, and Tet-1 peptides can significantly enhance the cellular uptake of Tet-1-EGCG@Se in PC12 cells rather than in NIH/3T3 cells.