Aβ Toxicity Research Articles

The assembly of the Mitochondrial Complex I Assembly complex uncovers a redox pathway coordination

The Mitochondrial Complex I Assembly (MCIA) complex is essential for the biogenesis of respiratory Complex I (CI), the first enzyme in the respiratory chain, which has been linked to Alzheimer’s disease (AD) pathogenesis. However, how MCIA facilitates CI assembly, and how it is linked with AD pathogenesis, is poorly understood. Here we report the structural basis of the complex formation between the MCIA subunits ECSIT and ACAD9. ECSIT binding induces a major conformational change in the FAD-binding loop of ACAD9, releasing the FAD cofactor and converting ACAD9 from a fatty acid β-oxidation (FAO) enzyme to a CI assembly factor. We provide evidence that ECSIT phosphorylation downregulates its association with ACAD9 and is reduced in neuronal cells upon exposure to amyloid-β (Aβ) oligomers. These findings advance our understanding of the MCIA complex assembly and suggest a possible role for ECSIT in the reprogramming of bioenergetic pathways linked to Aβ toxicity, a hallmark of AD.

A delay in vesicle endocytosis by a C-terminal fragment of N-cadherin enhances Aβ synaptotoxicity

Synaptotoxic Aβ oligomers are thought to play a major role in the early pathology of Alzheimer´s disease (AD). However, the molecular mechanisms involved in Aβ-induced synaptic dysfunction and synapse damage remain largely unclear. Previously, Aβ synaptotoxicity has been reported to be enhanced by increased levels of a C-terminal fragment of the synaptic adhesion molecule N-cadherin that is generated by proteolytic shedding of the extracellular domains [1]. To address the molecular mechanisms involved in this process, we have now studied the functional synaptic changes induced by C-terminal fragments (CTF1) of synaptic adhesion proteins. We used synaptophysin-pHluorin (SypHy) fluorescence imaging to monitor synaptic vesicle exo- and endocytosis in cultures of mouse cortical neurons. We increased the levels of C-terminal fragments of synaptic adhesion proteins by pharmacologically inhibiting γ-secretase, which further degrades CTF1 fragments. We found that this intervention caused a delay in synaptic vesicle endocytosis. A similar effect was induced by overexpression of N-cadherin CTF1, but not by overexpression of Neurexin3β CTF1. Based on these observations, we further studied whether directly modulating synaptic vesicle endocytosis enhances Aβ synaptotoxicity. We pharmacologically induced a delayed synaptic vesicle endocytosis by a low concentration of the endocytosis inhibitor dynasore. This treatment enhanced synaptoxicity of Aβ oligomers as indicated by a reduced frequency of miniature postsynaptic currents. In conclusion, we propose that delayed endocytosis results in prolonged exposure of synaptic vesicle membranes to the extracellular space, thus enabling enhanced vesicle membrane binding of Aβ oligomers. This might in turn promote the endocytic uptake of toxic Aβ oligomers and might thus play an important role in intracellular Aβ-mediated synaptotoxicity in AD.

Contextualizing the Role of Osteopontin in the Inflammatory Responses of Alzheimer's Disease.

Alzheimer's disease (AD) is characterized by progressive accumulations of extracellular amyloid-beta (Aβ) aggregates from soluble oligomers to insoluble plaques and hyperphosphorylated intraneuronal tau, also from soluble oligomers to insoluble neurofibrillary tangles (NFTs). Tau and Aβ complexes spread from the entorhinal cortex of the brain to interconnected regions, where they bind pattern recognition receptors on microglia and astroglia to trigger inflammation and neurotoxicity that ultimately lead to neurodegeneration and clinical AD. Systemic inflammation is initiated by Aβ's egress into the circulation, which may be secondary to microglial activation and can confer both destructive and reparative actions. Microglial activation pathways and downstream drivers of Aβ/NFT neurotoxicity, including inflammatory regulators, are primary targets for AD therapy. Osteopontin (OPN), an inflammatory cytokine and biomarker of AD, is implicated in Aβ clearance and toxicity, microglial activation, and inflammation, and is considered to be a potential therapeutic target. Here, using the most relevant works from the literature, we review and contextualize the evidence for a central role of OPN and associated inflammation in AD.

INPP5D modulates TREM2 loss‐of‐function phenotypes in a β‐amyloidosis mouse model

AbstractBackgroundThe genetic associations of TREM2 loss‐of‐function variants with Alzheimer disease (AD) indicate the protective roles of microglia in AD pathogenesis. Functional deficiencies of TREM2 disrupt microglial clustering around amyloid β (Aβ) plaques, impair their transcriptional response to Aβ, and worsen neuritic dystrophy. However, the molecular mechanism underlying these phenotypes remains unclear.MethodsIn this study, we investigated the pathological role of another AD risk gene, INPP5D, encoding a phosphoinositide PI(3,4,5)P3 phosphatase expressed in microglia by crossing Tyrobp knockout, Inpp5d knockout and human mutant APP knockin mice.ResultIn a Tyrobp‐deficient TREM2 loss‐of‐function mouse model, Inpp5d haplodeficiency restored the association of microglia with Aβ plaques, partially restored plaque compaction and astrogliosis, and reduced phosphorylated tau+ dystrophic neurites. RNA‐sequencing of isolated microglia demonstrated that the expression of “disease‐associated microglia” genes is not responsible for these beneficial effects.ConclusionOur results suggest that INPP5D acts downstream of TREM2/TYROBP to regulate the microglial barrier against Aβ toxicity, thereby modulates Aβ‐dependent pathological conversion of tau.

Effects of lithium on phosphatidyinositol‐3‐kinase signaling pathways in triple transgenicanimals of Alzheimer’s disease

AbstractBackgroundAlzheimer’s disease (AD), a severe, progressive and multifactorial disease. Among the altered biological pathways, we have the phosphatidyl inositol 3 kinase (PI3K), an important cell signaling mediator that loses its function as a result of changes in the Tau protein and Aβ toxicity. Our aim is to determine the ontological pathways related to PI3K in 3xTg‐AD animals chronically treated with lithium at therapeutic and subtherapeutic doses. Also determine the unique, statistically significant proteins of the biological pathways in the ontological pathway altered in hippocampal tissue.MethodThe animals' hippocampus (WT and 3xTg‐AD) were divided into three subgroups: Li0 (standard chow); Li1 (ration containing 1.0 g of lithium carbonate/Kg); and Li2 (ration containing 2.0 g of lithium carbonate/Kg). Primary cultures of hippocampal neurons were treated with doses of 0.02; 0. 2 and 2mM. The identified protein pathways will be compared by Gene Ontology, using ClueGO, a Cytoscape software plug‐in. The analyzes for comparison with neurons and subsequent tissue identification will be performed by ‘Benjamini & Hochberg False Discovery Rate’ (p≤0.05 setting) for test correction for ‘biological process’. Ethical committee (1293/09).ResultOur results on PI3K showed enrichment of pathways: response to hormone, cell migration, cellular response to endogenous stimulus, positive regulation of response to stimulus and regulation of catalytic activity.ConclusionInitial results are promising for the pharmacological understanding of lithium as a neuroprotector for Alzheimer’s disease.

Effects of lithium on phosphatidylinositol‐3‐kinase signaling pathways in triple transgenic animals for Alzheimer' disease

AbstractBackgroundAlzheimer’s disease (AD), a severe, progressive and multifactorial disease. Among the altered biological pathways, we have the phosphatidyl inositol 3 kinase (PI3K), an important cell signaling mediator that loses its function as a result of changes in the Tau protein and Aβ toxicity. Our aim is to determine the ontological pathways related to PI3K in 3xTg‐AD animals chronically treated with lithium at therapeutic and subtherapeutic doses. Also determine the unique, statistically significant proteins of the biological pathways in the ontological pathway altered in hippocampal tissue.MethodThe animals' hippocampus (WT and 3xTg‐AD) were divided into three subgroups: Li0 (standard chow); Li1 (ration containing 1.0 g of lithium carbonate/Kg); and Li2 (ration containing 2.0 g of lithium carbonate/Kg). Primary cultures of hippocampal neurons were treated with doses of 0.02; 0. 2 and 2mM. The identified protein pathways will be compared by Gene Ontology, using ClueGO, a Cytoscape software plug‐in. The analyzes for comparison with neurons and subsequent tissue identification will be performed by ‘Benjamini & Hochberg False Discovery Rate’ (p≤0.05 setting) for test correction for ‘biological process’. Ethical committee (1293/09).ResultOur results on PI3K showed enrichment of pathways: response to hormone, cell migration, cellular response to endogenous stimulus, positive regulation of response to stimulus and regulation of catalytic activity.ConclusionInitial results are promising for the pharmacological understanding of lithium as a neuroprotector for Alzheimer’s disease.

Cortical microstructural MRI for detection of early target engagement in AD drug trials: post‐hoc analysis of exploratory outcomes from a Phase 1b safety study for XPro1595 in AD

AbstractBackgroundEvidence in support of the amyloid cascade hypothesis for Alzheimer’s disease (AD) suggests that pathological amyloid‐beta (Aβ) is initially associated with synaptic hyperactivity and accumulates in an activity dependent fashion. These findings are corroborated by longitudinal data from cohort studies with Aβ‐PET imaging, wherein Aβ accumulates first in gray matter (GM) cortices associated with the default‐mode network (DMN) before spreading in a semi‐hierarchical pattern to different neocortical regions as the disease progresses (Mattsson et al. 2019). Mapping brain regions most frequently affected by Aβ pathology at different stages of disease may provide a framework for investigation of new drug entities targeting other components of Aβ toxicity using less invasive imaging modalities. The hypothesis here is that indicators of disease specific, tissue‐level treatment effects should be first detectable in brain regions most frequently affected by active pathology.MethodXPro1595 is a selective, brain penetrant neutralizer of soluble TNF with potent anti‐neuroinflammatory effects recently assessed for safety and pharmacological activity in a small, open‐label phase‐1b dose finding study (NCT03943264) in patients with AD. Clinical trial results for patients (n = 9) with analyzable dMRIs who completed 12‐weeks of treatment with XPro1595 [0.3 mg/kg; n = 3) or (1.0 mg/kg; n = 6)] met criteria for post‐hoc analysis. Exploratory outcomes included the novel cortical diffusivity measurement PerpPD+. PerpPD+ represents the diffusion components perpendicular to cortical GM minicolumns, indicates microscopic disruption when increased, and has proven more sensitive than standard volumetrics to changes in indicators of synaptic function, neuroinflammation and neurodegeneration across the AD continuum.ResultMean MMSE scores at baseline were 23.7 (SD = 2.5) and 15.8 (SD = 7.0) in the low‐dose and high‐dose groups, respectively, indicating varying degrees of severity. Week‐12 results showed decreases in bilateral PerPD+ at the whole brain level and in multiple GM cortices documented in the literature with the highest frequency of early (precuneus, isthmus cingulate, posterior cingulate, insula, and lateral and medial orbitofrontal) and late (lingual, pericalcarine, paracentral, precentral, and postcentral) Aβ accumulation (Figures1‐2).ConclusionCortical diffusivity measurements related to minicolumnar microstructure may provide an opportunity for noninvasive detection of early, disease specific, tissue‐level target engagement in clinical trials for investigational new drugs in AD.

The SMOC1‐matrisomal proteomics network M42 controls brain homeostasis and modulates toxicity in fly Alzheimer’s Disease models

AbstractBackgroundRecent evidence indicates Alzheimer’s disease (AD) has a complex etiology where insults in multiple pathways collude to disrupt neuronal function, yet the molecular changes underlying AD remain poorly understood. To identify changes associated with AD, we previously performed mass‐spectrometry (MS) on post‐mortem brain tissue and identified protein co‐expression networks correlated to AD pathological and clinical traits. The network most strongly correlated with AD pathology (M42) is enriched in components of the matrisome and consists of 32 proteins including multiple signaling pathways, Aß, APOE, and SMOC1, a predicted driver of network behavior. SMOC1 is a key matrisomal protein with conserved roles in modulating TGF‐Beta and wnt signaling during development, yet its role in the adult brain remains unstudied.MethodsWe evaluate the M42 protein network using the powerful genetics of Drosophila melanogaster to determine its role in the brain and uncover links to specific triggers of AD: Amyloid‐Beta (Aβ) and tau. We use a high‐throughput robotic screening platform and video assisted software which enables quantitative assessments of neurological function to identify proteins that modify Aβ‐ or tau‐induced neurodegeneration. We use Mass‐Spectrometry to identify protein changes in the brains of flies harboring homozygous loss‐of‐function mutations in dSMOC1 and genetics, cell biology, and immunofluorescence to characterize dSMOC1 in the fly.ResultsWe identified 13 genes with robust evidence of interactions with either tau or Aβ toxicity including dSMOC1 and multiple signaling components. We focused on dSMOC1, finding that flies homozygous for null mutations (dSMOC1−/−) suffer severely decreased survival upon aging. In the fly brain, dSMOC1 is expressed primarily in glia while the protein is localized around most neuronal cell bodies, consistent with its matrisomal role. Finally, we determined protein changes in the brain of dSMOC1−/− flies and found that ECM/receptor interactions and many metabolic pathways including KREBs/TCA cycle, lipid metabolism, and Oxidative Phosphorylation were perturbed.ConclusionThe M42 protein co‐expression network contains multiple proteins with links to AD. We identified multiple conserved M42 member proteins interacting with specific AD triggers. Together, the genetics and proteomics data support a mechanistic hypothesis where changes in SMOC1 levels disrupt critical signaling pathways leading to disruptions in metabolism affecting survival.

Alzheimer’s disease linked amyloid beta 1‐42 exerts product feedback inhibition on gamma‐secretase impairing downstream signaling cascades

AbstractBackgroundΓ‐secretases are proteolytic switches at the membrane regulating multiple signaling cascades. Their dysfunction, resulting in enhanced generation of longer amyloid β (Aβ) peptides from the amyloid precursor protein (APP), leads to neurodegeneration in the context of Alzheimer’s disease (AD), while their inhibition causes neurodegenerative phenotypes in mice and cognitive worsening in AD patients treated with γ‐secretase inhibitors. The accumulation of Aβ in the brain is the earliest pathological hallmark of AD. Based on the proven affinity of Aβ peptides for γ‐secretases, we hypothesized that elevations in Aβ levels would promote an inhibitory‐feedback mechanism on γ‐secretases and impair downstream cell signaling events.MethodWe conducted rigorous kinetic analyses of γ‐secretase activity in the presence of a series of Aβ and p3 peptides, by quantifying the levels of intracellular domains generated from different γ‐secretase substrates in cell‐free assays. In addition, we determined the effects of these peptides on endogenous γ‐secretase activity in living neurons, using a ratiometric FRET‐based reporter and western blot analysis of the levels of immediate γ‐secretase substrates. Furthermore, we assessed the impact of Aβ and p3 peptides on γ‐secretase‐mediated, p75‐ and TrkA‐dependent downstream signaling via immunostaining for an apoptotic marker: cleaved caspase 3. Finally, we evaluated the impact of Aβ peptides on APP processing in synaptosome fractions derived from mouse brains.ResultOur analyses showed that human Aβ42 inhibited γ‐secretase activity and accordingly caused accumulation of unprocessed γ‐secretase substrates in neuronal cells, i.e. CTFs of APP, p75 and pan‐cadherin. Remarkably, neither murine Aβ42 nor human p3 (17‐42) peptides exerted the inhibition. In TrkA signaling deficient PC12 cells and basal forebrain cholinergic neurons, Aβ1‐42‐mediated inhibition of γ‐secretase led to the accumulation of unprocessed p75‐CTFs and potentiated p75‐dependent cell death, mimicking the effects of γ‐secretase inhibitors.ConclusionWe demonstrate that the pathologically relevant human Aβ1‐42 exerts product feedback inhibition on γ‐secretases, leading to dysregulation of downstream cellular signaling. These findings provide a novel conceptual framework for investigations of Aβ toxicity in the context of γ‐secretase‐dependent homeostatic signaling and raise the possibility that Aβ42‐mediated inactivation of these enzymes contributes to AD development.

ApoE Mimic Peptide COG1410 Reduces Aβ Deposition and Improves Cognitive Function by Inducing the Transformation of A1/A2 Reactive Astrocytes and Increasing the BDNF Concentration in Brain of APP/PS1 Double Transgenic Mice

The main clinical manifestation of Alzheimer's disease is progressive cognitive decline, and its pathological features are β-amyloid (Aβ) deposition, neurofibrillary tangles, synaptic dysfunction and neuron death. Neuroinflammation is an important reason for the occurrence and development of AD, which is mainly manifested by the accumulation of activated microglia and reactive astrocytes. Apolipoprotein E (ApoE) is one of the most important apolipoprotein in the brain, which is related to metabolism, aggregation and toxicity of Aβ. However, the underlying mechanism needs to be further explored. In this study, we studied the effect of ApoE mimetic peptide COG1410 on spatial learning and memory functions, deposition of Aβ in the dentate gyrus (DG) of APP/PS1 transgenic mice, and the different effects of A1 and A2 subtypes of reactive astrocytes. Administration of COG1410 effectively improved performance in spatial learning and memory of APP/PS1 mice, reduced Aβ deposition and significantly reverted the ratio of A1/A2 reactive astrocytes, which could be associated with BDNF/TrkB signaling pathway. On the whole, the present findings suggest new possibility of using apolipoprotein E mimetic peptide to treat AD with potential effectiveness.

Assessing Cannabidiol as a Therapeutic Agent for Preventing and Alleviating Alzheimer's Disease Neurodegeneration.

Alzheimer's disease (AD) is a leading neurodegenerative condition causing cognitive and memory decline. With small-molecule drugs targeting Aβ proving ineffective, alternative targets are urgently needed. Neuroinflammation, which is central to AD's pathology, results in synaptic and neuronal damage, highlighting the importance of addressing inflammation and conserving neuronal integrity. Cannabidiol (CBD), derived from cannabis, is noted for its neuroprotective and anti-inflammatory properties, having shown efficacy in neuropathic pain management for epilepsy. To investigate the therapeutic efficacy of CBD in AD and to elucidate its underlying mechanisms, we aimed to contribute valuable insights for incorporating AD prevention recommendations into future CBD nutritional guidelines. Aβ1-42 was employed for in vivo or in vitro model establishment, CBD treatment was utilized to assess the therapeutic efficacy of CBD, and RNA-seq analysis was conducted to elucidate the underlying therapeutic mechanism. CBD mitigates Aβ-induced cognitive deficits by modulating microglial activity, promoting neurotrophic factor release, and regulating inflammatory genes. The administration of CBD demonstrated a protective effect against Aβ toxicity both in vitro and in vivo, along with an amelioration of cognitive impairment in mice. These findings support the potential inclusion of CBD in future nutritional guidelines for Alzheimer's disease prevention.

Icaritin greatly attenuates β-amyloid-induced toxicity invivo.

The accumulation and deposition of β-amyloid (Aβ) has always been considered a major pathological feature of Alzheimer's disease (AD). The latest and mainstream amyloid cascade hypothesis indicates that all the main pathological changes in AD are attributed to the accumulation of soluble Aβ. However, the exploration of therapeutic drugs for Aβ toxicity has progressed slowly. This study aims to investigate the protective effects of Icaritin on the Aβ-induced Drosophila AD model and its possible mechanism. To identify the effects of Icaritin on AD, we constructed an excellent Drosophila AD model named Aβarc (arctic mutant Aβ42) Drosophila. Climbing ability, flight ability, and longevity were used to evaluate the effects of Icaritin on AD phenotypes. Aβarc was determined by immunostaining and ELISA. To identify the effects of Icaritin on oxidative stress, we performed the detection of ROS, hydrogen peroxide, MDA, SOD, catalase, GST, and Caspase-3. To identify the effects of Icaritin on energy metabolism, we performed the detection of ATP and lactate. Transcriptome analysis and qRT-PCR verifications were used to detect the genes directly involved in oxidative stress and energy metabolism. Mitochondrial structure and function were detected by an electron microscopy assay, a mitochondrial membrane potential assay, and a mitochondrial respiration assay. We discovered that Icaritin almost completely rescues the climbing ability, flight ability, and longevity of Aβarc Drosophila. Aβarc was dramatically reduced by Icaritin treatment. We also found that Icaritin significantly reduces oxidative stress and greatly improves impaired energy metabolism. Importantly, transcriptome analysis and qRT-PCR verifications showed that many key genes, directly involved in oxidative stress and energy metabolism, are restored by Icaritin. Next, we found that Icaritin perfectly restores the integrity of mitochondrial structure and function damaged by Aβarc toxicity. This study suggested that Icaritin is a potential drug to deal with the toxicity of Aβarc, at least partially realized by restoring the mitochondria/oxidative stress/energy metabolism axis, and holds potential for translation to human AD.

Exploration of Lycorine and Copper(II)’s Association with the N-Terminal Domain of Amyloid β

Lycorine (LYC) is an active alkaloid first isolated from Narcissus pseudonarcissus and found in most Amaryllidaceae plants. It belongs to the same family as galantamine, which is the active component of a drug used for the treatment of Alzheimer’s disease. Similarly to galantamine, LYC is able to suppress induced amyloid β (Aβ) toxicity in differentiated SH-SY5Y cell lines and it can weakly interact with the N-terminal region of Aβ via electrostatic interactions. The N-terminal Aβ domain is also involved in Cu(II)/Cu(I) binding and the formed complexes are known to play a key role in ROS production. In this study, the Aβ–LYC interaction in the absence and in the presence of copper ions was investigated by using the N-terminal Aβ peptide encompassing the first 16 residues. NMR analysis showed that Aβ can simultaneously interact with Cu(II) and LYC. The Cu(II) binding mode remains unchanged in the presence of LYC, while LYC association is favored when an Aβ–Cu(II) complex is formed. Moreover, UV-VIS studies revealed the ability of LYC to interfere with the catalytic activities of the Aβ–Cu(II) complexes by reducing the ascorbate consumption monitored at 265 nm.

Hesperidin Methyl Chalcone reduces extracellular Aβ(25-35) peptide aggregation and fibrillation and also protects Neuro 2a cells from Aβ(25-35) induced neuronal dysfunction

In the present study, we evaluated the neuroprotective potential of Hesperidin Methyl Chalcone (HMC) against the neurotoxicity induced by Aβ(25-35) peptide. HMC demonstrated higher free-radical scavenging activity than Hesperidin in initial cell-free studies. Investigations using the fluorescent dye thioflavin T with Aβ(25-35) peptide showed that HMC has the ability to combat extracellular amyloid aggregation by possessing anti-aggregation property against oligomers and by disaggregating mature fibrils. Also, the results of the molecular simulation studies show that HMC ameliorated oligomer formation. Further, the anti-Alzheimer’s property of HMC was investigated in in vitro cell conditions by pre-treating the neuro 2a (N2a) cells with HMC before inducing Aβ(25-35) toxicity. The findings demonstrate that HMC increased cell viability, reduced oxidative stress, prevented macromolecular damage, allayed mitochondrial dysfunction, and exhibited anticholinesterase activity. HMC also reduced Aβ induced neuronal cell death by modulating caspase-3 activity, Bax expression and Bcl2 overexpression, demonstrating that HMC pre-treatment reduced mitochondrial damage and intrinsic apoptosis induced by Aβ(25-35).In silico evaluation against potential AD targets reveal that HMC could be a potent inhibitor of BACE-1, inhibiting the formation of toxic Aβ peptides. Overall, the findings imply that the neuroprotective efficacy of HMC has high prospects for addressing a variety of pathogenic consequences caused by amyloid beta in AD situations and alleviating cognitive impairments.

Two mouse models of Alzheimer’s disease accumulate amyloid at different rates and have distinct Aβ oligomer profiles unaltered by ablation of cellular prion protein

Oligomers formed from monomers of the amyloid β-protein (Aβ) are thought to be central to the pathogenesis of Alzheimer’s disease (AD). Unsurprisingly for a complex disease, current mouse models of AD fail to fully mimic the clinical disease in humans. Moreover, results obtained in a given mouse model are not always reproduced in a different model. Cellular prion protein (PrPC) is now an established receptor for Aβ oligomers. However, studies of the Aβ-PrPC interaction in different mouse models have yielded contradictory results. Here we performed a longitudinal study assessing a range of biochemical and histological features in the commonly used J20 and APP-PS1 mouse models. Our analysis demonstrated that PrPC ablation had no effect on amyloid accumulation or oligomer production. However, we found that APP-PS1 mice had higher levels of oligomers, that these could bind to recombinant PrPC, and were recognised by the OC antibody which distinguishes parallel, in register fibrils. On the other hand, J20 mice had a lower level of Aβ oligomers, which did not interact with PrPC when tested in vitro and were OC-negative. These results suggest the two mouse models produce diverse Aβ assemblies that could interact with different targets, highlighting the necessity to characterise the conformation of the Aβ oligomers concomitantly with the toxic cascade elicited by them. Our results provide an explanation for the apparent contradictory results found in APP-PS1 mice and the J20 mouse line in regards to Aβ toxicity mediated by PrPC.

Cyclization of Peptides Enhances the Inhibitory Activity against Ganglioside-Induced Aβ Fibril Formation.

Alzheimer's disease is a progressive neurodegenerative disease and is the most common cause of dementia. It has been reported that the assembly of amyloid β-protein (Aβ) on the cell membrane is induced by the interaction of the Aβ monomer with gangliosides such as GM1. The ganglioside-bound Aβ (GAβ) complex acts as a seed to promote the toxic assembly of the Aβ fibrils. In a previous study, we found that a GM1 cluster-binding peptide (GCBP) specifically recognizes Aβ-sensitive ganglioside nanoclusters and inhibits the assembly of Aβ on a GM1-containing lipid membrane. In this study, cysteine-substituted double mutants of GCBP were designed and cyclized by intramolecular disulfide bond formation. Affinity assays indicated that one of the cyclic peptides had a higher affinity to a GM1-containing membrane compared to that of GCBP. Furthermore, surface topography analysis indicated that this peptide recognizes GM1 nanoclusters on the lipid membrane. An evaluation of the inhibitory kinetics indicated that the cyclic peptide could inhibit the formation of Aβ fibrils with an IC50 value of 1.2 fM, which is 10,000-fold higher than that of GCBP. The cyclic peptide was also shown to have a clearance effect on Aβ fibrils deposited on the lipid membrane and suppressed the formation of toxic Aβ assemblies. Our results indicate that the cyclic peptide that binds to the Aβ-sensitive ganglioside nanocluster is a potential novel inhibitor of ganglioside-induced Aβ assembly.

Towards the Integrative Theory of Alzheimer's Disease: Linking Molecular Mechanisms of Neurotoxicity, Beta-amyloid Biomarkers, and the Diagnosis.

A major gap in amyloid-centric theories of Alzheimer's disease (AD) is that even though amyloid fibrils per se are not toxic in vitro, the diagnosis of AD clearly correlates with the density of beta-amyloid (Aβ) deposits. Based on our proposed amyloid degradation toxicity hypothesis, we developed a mathematical model explaining this discrepancy. It suggests that cytotoxicity depends on the cellular uptake of soluble Aβ rather than on the presence of amyloid aggregates. The dynamics of soluble beta-amyloid in the cerebrospinal fluid (CSF) and the density of Aβ deposits is described using a system of differential equations. In the model, cytotoxic damage is proportional to the cellular uptake of Aβ, while the probability of an AD diagnosis is defined by the Aβ cytotoxicity accumulated over the duration of the disease. After uptake, Aβ is concentrated intralysosomally, promoting the formation of fibrillation seeds inside cells. These seeds cannot be digested and are either accumulated intracellularly or exocytosed. Aβ starts aggregating on the extracellular seeds and, therefore, decreases in concentration in the interstitial fluid. The dependence of both Aβ toxicity and aggregation on the same process-cellular uptake of Aβ-explains the correlation between AD diagnosis and the density of amyloid aggregates in the brain. We tested the model using clinical data obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI), which included records of beta-amyloid concentration in the cerebrospinal fluid (CSF-Aβ42) and the density of beta-amyloid deposits measured using positron emission tomography (PET). The model predicts the probability of AD diagnosis as a function of CSF-Aβ42 and PET and fits the experimental data at the 95% confidence level. Our study shows that existing clinical data allows for the inference of kinetic parameters describing beta-amyloid turnover and disease progression. Each combination of CSF-Aβ42 and PET values can be used to calculate the individual's cellular uptake rate, the effective disease duration, and the accumulated toxicity. We show that natural limitations on these parameters explain the characteristic distribution of the clinical dataset for these two biomarkers in the population. The resulting mathematical model interprets the positive correlation between the density of Aβ deposits and the probability of an AD diagnosis without assuming any cytotoxicity of the aggregated beta-amyloid. To the best of our knowledge, this model is the first to mechanistically explain the negative correlation between the concentration of Aβ42 in the CSF and the probability of an AD diagnosis. Finally, based on the amyloid degradation toxicity hypothesis and the insights provided by mathematical modeling, we propose new pathophysiology-relevant biomarkers to diagnose and predict AD.

Mitochondrial Complex I and β-Amyloid Peptide Interplay in Alzheimer’s Disease: A Critical Review of New and Old Little Regarded Findings

Alzheimer’s disease (AD) is the most common neurodegenerative disorder and the main cause of dementia which is characterized by a progressive cognitive decline that severely interferes with daily activities of personal life. At a pathological level, it is characterized by the accumulation of abnormal protein structures in the brain—β-amyloid (Aβ) plaques and Tau tangles—which interfere with communication between neurons and lead to their dysfunction and death. In recent years, research on AD has highlighted the critical involvement of mitochondria—the primary energy suppliers for our cells—in the onset and progression of the disease, since mitochondrial bioenergetic deficits precede the beginning of the disease and mitochondria are very sensitive to Aβ toxicity. On the other hand, if it is true that the accumulation of Aβ in the mitochondria leads to mitochondrial malfunctions, it is otherwise proven that mitochondrial dysfunction, through the generation of reactive oxygen species, causes an increase in Aβ production, by initiating a vicious cycle: there is therefore a bidirectional relationship between Aβ aggregation and mitochondrial dysfunction. Here, we focus on the latest news—but also on neglected evidence from the past—concerning the interplay between dysfunctional mitochondrial complex I, oxidative stress, and Aβ, in order to understand how their interplay is implicated in the pathogenesis of the disease.

The Contribution of Hippocampal All-Trans Retinoic Acid (ATRA) Deficiency to Alzheimer's Disease: A Narrative Overview of ATRA-Dependent Gene Expression in Post-Mortem Hippocampal Tissue.

There is accumulating evidence that vitamin A (VA) deficiency contributes to the pathogenesis and progression of Alzheimer's disease (AD). All-trans retinoic acid (ATRA), a metabolite of VA in the brain, serves distinct roles in the human hippocampus. Agonists of retinoic acid receptors (RAR), including ATRA, promote activation of the non-amyloidogenic pathway by enhancing expression of α-secretases, providing a mechanistic basis for delaying/preventing amyloid beta (Aβ) toxicity. However, whether ATRA is actually deficient in the hippocampi of patients with AD is not clear. Here, using a publicly available human transcriptomic dataset, we evaluated the extent to which ATRA-sensitive genes are dysregulated in hippocampal tissue from post-mortem AD brains, relative to age-matched controls. Consistent with ATRA deficiency, we found significant dysregulation of many ATRA-sensitive genes and significant upregulation of RAR co-repressors, supporting the idea of transcriptional repression of ATRA-mediated signaling. Consistent with oxidative stress and neuroinflammation, Nrf2 and NfkB transcripts were upregulated, respectively. Interestingly, transcriptional targets of Nrf2 were not upregulated, accompanied by upregulation of several histone deacetylases. Overall, our investigation of ATRA-sensitive genes in the human hippocampus bolsters the scientific premise of ATRA depletion in AD and that epigenetic factors should be considered and addressed as part of VA supplementation.

GV1001 modulates neuroinflammation and improves memory and behavior through the activation of gonadotropin-releasing hormone receptors in a triple transgenic Alzheimer’s disease mouse model

GV1001 protects neural cells from amyloid-β (Aβ) toxicity and other stressors in in vitro studies and demonstrates clinically beneficial effects in patients with moderate to severe Alzheimer’s disease (AD). Here, we investigated the protective effects and mechanism of action of GV1001 in triple transgenic AD (3xTg-AD) mice. We found that GV1001 improved memory and cognition in middle- and old-aged 3xTg-AD mice. Additionally, it reduced Aβ oligomer and phospho-tau (Ser202 and Thr205) levels in the brain, and mitigated neuroinflammation by promoting a neuroprotective microglial and astrocyte phenotype while diminishing the neurotoxic ones. In vitro, GV1001 bound to gonadotropin releasing hormone receptors (GnRHRs) with high affinity. Levels of cyclic adenosine monophosphate, a direct downstream effector of activated GnRHRs, increased after GV1001 treatment. Furthermore, inhibition of GnRHRs blocked GV1001-induced effects. Thus, GV1001 might improve cognitive and memory functions of 3xTg-AD mice by suppressing neuroinflammation and reducing Aβ oligomers levels and phospho-tau by activating GnRHRs and their downstream signaling pathways.