Familial Alzheimer's Disease Mutations Research Articles

Orally Administered Benzofuran Derivative Disaggregated Aβ Plaques and Oligomers in the Brain of 5XFAD Alzheimer Transgenic Mouse.

Amyloid-β (Aβ) aggregated forms are highly associated with the onset of Alzheimer's disease (AD). Aβ abnormally accumulates in the brain and induces neuronal damages and symptoms of AD such as cognitive impairment and memory loss. Since an antibody drug, aducanumab, reduces Aβ aggregates and delays clinical decline, clearance of accumulated Aβ in the brain is accounted as a therapeutic approach to treat AD. In this study, we synthesized 17 benzofuran derivatives that may disaggregate Aβ oligomers and plaques into inert monomers. By a series of Aβ aggregation inhibition and aggregates' disaggregation assays utilizing thioflavin T assays and gel electrophoresis, YB-9, 2-((5-methoxy-3-(4-methoxyphenyl)benzofuran-6-yl)oxy)acetic acid, was selected as the final Aβ-disaggregator candidate. When it was orally administered to the 8-month-old male transgenic mouse model with five familial AD mutations (5XFAD) via drinking water daily for two months, Aβ oligomers and plaques in hippocampus were reduced. Consequently, decreased astrogliosis and rescued synaptic dysfunction were observed in the hippocampus of YB-9-treated 5XFAD mice compared with the untreated transgenic control group.

Synaptic Loss in Alzheimer's Disease: Mechanistic Insights Provided by Two-Photon in vivo Imaging of Transgenic Mouse Models.

Synapse loss is the strongest correlate for cognitive decline in Alzheimer's disease. The mechanisms underlying synapse loss have been extensively investigated using mouse models expressing genes with human familial Alzheimer's disease mutations. In this review, we summarize how multiphoton in vivo imaging has improved our understanding of synapse loss mechanisms associated with excessive amyloid in the living animal brain. We also discuss evidence obtained from these imaging studies for the role of cell-intrinsic calcium dyshomeostasis and cell-extrinsic activities of microglia, which are the immune cells of the brain, in mediating synapse loss.

APOE genotype and sex influence memory and dendritic spine density in an EFAD mouse model of Alzheimer’s disease

AbstractBackgroundWomen carriers of the APOE4 genotype, which is the leading genetic risk factor for late‐onset Alzheimer’s disease (AD), are more likely than women carriers of other APOE genotypes and men of any APOE genotype to develop AD. However, factors underlying the interaction between APOE genotype and sex are not well characterized. The goal of this study was to examine the effects of sex and APOE genotype on memory function and dendritic spine density in a mouse model of AD.MethodsSix month‐old gonadally‐intact male and female transgenic (Tg) mice expressing 5 familial AD mutations (5xFAD+/‐) and human APOE3 +/+ (E3FAD) or APOE4 +/+ (E4FAD) were trained on object recognition (OR) and object placement (OP) tasks designed to test object recognition and spatial memory formation. Memory for previously seen objects or locations was tested 24 or 4 hours later, respectively. Two weeks after the conclusion of behavioral testing, mice were retrained with novel objects, and brains were collected for Golgi staining. Following staining, apical and basal dendritic spines in the dorsal hippocampus (DH) and medial prefrontal cortex (mPFC) were counted and classified by morphological type.ResultsMale E3FAD mice exhibited intact memory for previously seen objects or locations, whereas male E4FADs and female E3FAD or E4FAD mice did not. The density of total, mushroom, and stubby spines on basal CA1 and mPFC dendrites was lower for E4FAD mice of both sexes compared to E3FAD mice. Preliminary data suggest a similar pattern for mPFC apical spine density.ConclusionsThese data suggest that APOE genotype and sex influence object recognition and spatial memory formation, and that APOE4 genotype is associated with reduced density of mature and immature spines in CA1 and the mPFC.

Reduced density of noradrenergic fibers without prominent neuron loss or tau pathology in the locus coeruleus in APP knock‐in mouse models of Aβ amyloidosis

AbstractBackgroundLocus coeruleus (LC) is a nucleus containing the cell bodies of noradrenergic neurons in the brain, and is one of the earliest regions affected by Alzheimer’s disease (AD). Norepinephrine (NE) is critical for cognitive functions as well as anti‐inflammatory and neuroprotective properties, both of which are implicated in AD. LC neurons are among the first to display tau pathology and that significant loss of forebrain noradrenergic projections is evident at prodromal stage of AD, suggesting that abnormality in LC‐NE system initiates the disease pathogenesis. However, mechanisms underlying neurodegeneration in LC‐NE system remain elusive. We have previously reported that AppNL‐G‐F/NL‐G‐F mice, which harbor three familial AD mutations (Swedish, Beyreuther/Iberian, and Arctic) exhibited cognitive deficits and severe neuroinflammation accompanied by massive amyloid‐β (Aβ) pathology. In this study, we asked whether and how LC‐NE system is altered in AppNL‐G‐F/NL‐G‐F mice.MethodTo ask whether AppNL‐G‐F/NL‐G‐F mice exhibit noradrenergic degeneration, we compared the density of norepinephrine transporter (NET)‐positive fibers in the cortex and hippocampus as well as the number of dopamine β‐hydroxylase (DBH)‐positive neurons in the LC between AppNL‐G‐F/NL‐G‐F and wild‐type (WT) C57BL/6J mice at 24 months of age. We also examined whether tau pathology occurs in the LC‐NE system in these mice.ResultHistochemical analyses revealed that 24‐month‐old AppNL‐G‐F/NL‐G‐F mice exhibited significant decreases in the density of NET‐positive fibers in the prefrontal and entorhinal cortices and the hippocampal CA1, the regions associated with learning and memory, compared to WT mice. In contrast, AppNL‐G‐F/NL‐G‐F mice did not display loss of DBH‐positive neurons in the LC even at 24 months of age. Furthermore, AppNL‐G‐F/NL‐G‐F mice did not develop prominent tau pathology either in the nerve terminals or in the cell bodies of LC neurons.ConclusionThis study demonstrates that Aβ pathology is sufficient to reduce the density of noradrenergic fibers independent of neuron loss and tau pathology in the LC. These results also suggest that age‐dependent accumulation of Aβ in the cortex or tau in the LC may additively and independently damage LC neurons from the nerve terminals or from the cell bodies, respectively.

Single nuclear RNA sequencing reveals microglia diversity associated with cognitive resilience in the AD‐BXD mouse model of human Alzheimer’s disease

AbstractBackgroundAn individual’s genetic background plays an important role in governing the risk (or resilience) to developing Alzheimer’s disease (AD) dementia. The goal of this study was to identify the molecular pathways and cell‐types conferring individual differences in cognitive resilience to human familial AD (FAD) mutations that drive high amyloid.MethodA large set of genetically diverse mice harboring familial AD mutations (AD‐BXDs) and their non‐transgenic littermates (Ntg‐BXDs) were tested for short‐ and long‐term memory using contextual fear conditioning at 6m (AD‐BXD n=180, Ntg‐BXD n=174) and 14m (AD‐BXD n=121, Ntg‐BXD n=137). A subset of 14 AD mutation carriers that exhibited extreme resilience (n=7) or susceptibility (n=7) to cognitive decline were selected for hippocampal molecular profiling, along with their Ntg‐BXD littermates, at both 6m and 14m. Data from all hippocampi were aggregated and batch‐corrected using Harmony, and Seurat clustering was employed using the top 2000 variable genes. Known marker genes were used to associate clusters with cell‐types. The fraction of nuclei per sample (cluster composition) and within cell‐type differential gene expression were performed to determine changes in cell quantity and molecular profiles as a function of age, AD mutation carrier status, and resiliency to cognitive decline.ResultThere were no clusters that showed significant change in composition as a function of age. However, AD‐BXD individuals had significantly fewer astrocytes and more microglia than their Ntg‐BXD counterparts. We also found that resilient AD‐BXDs had fewer microglia than susceptible individuals, and the number of microglia at 6m was significantly negatively correlated with cognitive decline in AD‐BXD individuals. Additionally, microglia from resilient individuals showed up‐regulation of mitochondrial respiration and protein translation genes, proposing two pathways that dictate resilience in a microglia‐specific manner.ConclusionOur findings further implicate non‐neuronal cell‐types such as microglia in promoting resilience to cognitive decline in AD, and suggest several pathways by which microglia may be altered in resilient compared to susceptible individuals. We believe that by altering these microglia pathways within susceptible individuals, we can improve how non‐neuronal cells interact with CNS neurons to improve AD cognitive resilience.

Discovering genetic variants contributing to sleep dysfunction in presymptomatic Alzheimer’s mice

AbstractBackgroundDisordered sleep is frequently observed in Alzheimer’s disease patients. Sleep loss is associated with increased Aβ and tau accumulation in both AD patients and model organisms. Furthermore, cognitively intact individuals with impaired sleep are at higher risk for AD. Although individual differences in sleep are known to be highly heritable, little is known of the genetic factors associated with sleep dysfunction in aging and AD and if these contribute to disease development.MethodSleep was assessed at a presymptomatic age (6‐7 months) in a panel of genetically diverse mice carrying familial AD mutations, which better models complex etiology of human AD (AD‐BXDs; Neuner et al 2019). Sleep‐wake activity was measured for five consecutive days using the PiezoSleep tracking system across 25 AD‐BXD strains and their nontransgenic littermates (Ntg‐BXD).ResultAD‐BXD mice slept significantly less during the dark cycle compared to Ntg‐BXDs. Additionally, reduction of sleep was observed during the transition from dark to the light cycle, suggesting disruption of circadian function. Females slept less than males regardless of AD mutation status. We identified a significant quantitative trait locus (QTL) on chromosome 9 associated with total sleep, this region is syntenic with a regions on the human chromosome 11, harboring six sleep‐associated human GWAS SNPs, demonstrating the relevance of this region to human biology. Additionally, we identified a QTL for hourly sleep at ZT14 that mapped to intron 1 of the gene Kirrel3 of chromosome 9 (∼20 mb downstream of the sleep‐QTL). Differential gene expression implicates Kirrel3 as a novel target‐gene for validation.ConclusionWe provide the first evidence that genetic factors interact with AD mutations to influence sleep behavior, and identified two regions causally associated with variation in sleep in the AD‐BXDs. Mouse‐to‐human comparison suggest that both region are relevant to humans, demonstrating the value of the AD‐BXDs as a translational AD model. Future work will leverage genome engineering to correct sleep‐associated variants to test the delay or prevention of cognitive deficits onset apparent in the AD‐BXDs by 14 months of age. These studies may identify novel therapeutic targets to treat AD dementia.

Imbalance of Endocannabinoid/Lysophosphatidylinositol Receptors Marks the Severity of Alzheimer's Disease in a Preclinical Model: A Therapeutic Opportunity.

Simple SummaryAlzheimer’s disease (AD) remains a major challenge for the healthcare system worldwide and, to date, no curative treatment is available. This disease is an irreversible progressive dementia that harms memory and cognitive functions, weakening the ability to carry out tasks by themselves. Among the potential targets for developing innovative therapies for AD, the endocannabinoid system has aroused much interest in the scientific community, since it is involved in multiple processes related to AD pathology. A major challenge to understand the role of the cannabinoid system in AD is to characterize how it contributes to the expression of a specific phenotype, from neuropathology to behavior. In the present study, we addressed this challenge by evaluating the expression of the endocannabinoid system in a transgenic mouse model of AD, bearing five familial AD mutations. Our data suggest that there is an association between the cannabinoid receptors and both the cognitive function and inflammatory response characterizing the disease. Moreover, this association is aggravated by genetic factors. From these data, the expression of endocannabinoid and G protein-coupled 55 receptors (GPR55), and endocannabinoid-related enzymes might be candidate markers for the detection of the severity of this neurodegenerative disease, eventually arising as potential therapeutic targets capable of modifying the course of this incapacitating dementia.Alzheimer’s disease (AD) is the most common form of neurodegeneration and dementia. The endocannabinoid (ECB) system has been proposed as a novel therapeutic target to treat AD. The present study explores the expression of the ECB system, the ECB-related receptor GPR55, and cognitive functions (novel object recognition; NOR) in the 5xFAD (FAD: family Alzheimer’s disease) transgenic mouse model of AD. Experiments were performed on heterozygous (HTZ) and homozygous (HZ) 11 month old mice. Protein expression of ECB system components, neuroinflammation markers, and β-amyloid (Aβ) plaques were analyzed in the hippocampus. According to the NOR test, anxiety-like behavior and memory were altered in both HTZ and HZ 5xFAD mice. Furthermore, both animal groups displayed a reduction of cannabinoid (CB1) receptor expression in the hippocampus, which is related to memory dysfunction. This finding was associated with indirect markers of enhanced ECB production, resulting from the combination of impaired monoacylglycerol lipase (MAGL) degradation and increased diacylglycerol lipase (DAGL) levels, an effect observed in the HZ group. Regarding neuroinflammation, we observed increased levels of CB2 receptors in the HZ group that positively correlate with Aβ’s accumulation. Moreover, HZ 5xFAD mice also exhibited increased expression of the GPR55 receptor. These results highlight the importance of the ECB signaling for the AD pathogenesis development beyond Aβ deposition.

Impact of Cholesterol Concentration and Lipid Phase on Structure and Fluctuation of Amyloid Precursor Protein.

Elevated levels of cellular cholesterol have been identified as one factor contributing to the onset of Alzheimer's disease (AD). Specific interaction between cholesterol and the amyloid precursor protein (APP), investigated via NMR experiments and computational studies, has been proposed to play a critical role in the processing of APP by secretases and the biogenesis of amyloid-β (Aβ) protein. We present all-atom molecular dynamics simulations of the 40-residue congener of the C-terminal domain of APP, C9916-55 (C99), in cholesterol-enriched DMPC lipid bilayers. We investigated the effect of cholesterol concentration on the conformational ensemble of wild-type C99 and C99-cholesterol associations at the low pH of endosomal environments, at which residues E22 and D23 are neutral. C99 was also characterized in liquid ordered domains for Dutch (E22Q) and Iowa (D23N) Familial AD mutants at low pH and for the wild-type sequence using protonation states characteristic of neutral pH. Our results reproduce the equilibrium constant of past NMR characterizations of the C99-cholesterol interaction but are not consistent with the C99-cholesterol binding hypothesis. We find that the lifetimes of both DMPC and cholesterol complexed with C99 display a power-law distribution of residence lifetimes. Longer-lived C99-DMPC and C99-cholesterol complexes are primarily stabilized by salt bridges and hydrogen bonds of lysine amines to phosphate and hydroxyl groups. Nevertheless, specific interfaces for C99-cholesterol association which are not present for DMPC can be identified. Changes to C99-cholesterol interfaces are found to depend on C99 tilt angle and orientation of the juxtamembrane domain of C99 containing residues E22 and D23. These observations support a more nuanced view of the C99-cholesterol interaction than has previously been suggested. We propose that cholesterol modulates the conformation and activity of C99 and other small transmembrane proteins indirectly through induction of the liquid ordered phase and directly through hydrogen bonding. This suggests a critical role for membrane heterogeneity introduced by cholesterol in modulating the structural ensemble of C99 and the production of Aβ.

Evolutionary History of Alzheimer Disease-Causing Protein Family Presenilins with Pathological Implications.

Presenilin proteins make the catalytic component of γ-secretase, a multiprotein transmembrane protease, and are type II transmembrane proteins. Amyloid protein, Notch, and beta catenin are among more than 90 substrates of Presenilins. Mutations in Presenilins lead to defects in proteolytic cleavage of its substrate resulting in some of the most devastating pathological conditions including Alzheimer disease (AD), developmental disorders, and cancer. In addition to catalytic roles, Presenilin protein is also shown to be involved in many non-catalytic roles, i.e., calcium homeostasis, regulation of autophagy, and protein trafficking, etc. These proteolytic proteins are highly conserved and are present in almost all the major eukaryotic groups. Studies, performed on a wide variety of organisms ranging from human to unicellular dictyostelium, have shown the important catalytic and non-catalytic roles of Presenilins. In this study, we infer the evolutionary patterns and history of Presenilins as well as of other γ-secretase proteins. We show that Presenilins are the most ancient of the γ-secretase proteins and that Presenilins may have their origin in the last common ancestor (LCA) of Eukaryotes. We also demonstrate that Presenilin proteins generally lack diversifying selection during the course of their evolution. Through evolutionary trace analysis, we show that Presenilin protein sites that undergo mutations in Familial Alzheimer disease, are highly conserved in metazoans. Finally, we discuss the evolutionary, physiological, and pathological implications of our findings and propose that the evolutionary profile of Presenilins supports the loss of function hypothesis of AD pathogenesis.

How Mutations Perturb γ-Secretase Active Site Studied by Free Energy Simulations.

γ-Secretase is involved in processing of the amyloid precursor protein (APP) and generation of short Aβ peptides that may play a key role in neurodegenerative diseases such as Alzheimer's disease (AD). Several mutations in γ-secretase influence its activity, resulting in early AD onset (Familial AD or FAD mutations). The molecular details of how mutations, not located close to the active site, can affect enzyme activity is not understood. In molecular dynamics simulations of γ-secretase in the absence of substrate (apo), we identified two active site conformational states characterized by a direct contact between catalytic Asp residues (closed state) and an open water-bridged state. In the presence of substrate, only conformations compatible with the open active site geometry are accessible. Systematic free energy simulations on wild type and FAD mutations indicate a free energy difference between closed and open states that is significantly modulated by FAD mutations and correlates with the corresponding experimental activity. For mutations with reduced activity, an increased penalty for open-state transitions was found. Only for two mutations located at the active site a direct perturbation of the open-state geometry was observed that could directly explain the drop of enzyme activity. The simulations suggest that modulation of the closed/open equilibrium and perturbation of the open (active) catalytic geometry are possible mechanisms of how FAD mutations affect γ-secretase activity. The results also offer an explanation for the experimental finding that FAD mutations, although not located at the interface to the substrate, mainly destabilize the enzyme-substrate complex.

The Sound of Silence: Hidden Responses of Neural Circuits to Alzheimer-Linked Mutations

Dysfunctions of cortico-hippocampal circuits represent a hallmark of Alzheimer's disease. In this issue of Neuron, Jun etal. illuminate the spatial coding failures by familial Alzheimer's disease mutations that may underlie the progressive decline in spatial mnemonic processing.

Blood neuro-exosomal synaptic proteins predict Alzheimer's disease at the asymptomatic stage.

IntroductionExosomes are an emerging candidate for biomarkers of Alzheimer's disease (AD). This study investigated whether exosomal synaptic proteins can predict AD at the asymptomatic stage.MethodsWe conducted a two‐stage‐sectional study (discovery stage: AD, 28; amnestic mild cognitive impairment [aMCI], 25; controls, 29; validation stage: AD, 73; aMCI, 71; controls, 72), a study including preclinical AD (160) and controls (160), and a confirmation study in familial AD (mutation carriers: 59; non‐mutation carriers: 62).ResultsThe concentrations of growth associated protein 43 (GAP43), neurogranin, synaptosome associated protein 25 (SNAP25), and synaptotagmin 1 were lower in AD than in controls (P < .001). Exosomal biomarker levels were correlated with those in cerebrospinal fluid (R2 = 0.54–0.70). The combination of exosomal biomarkers detected AD 5 to 7 years before cognitive impairment (area under the curve = 0.87–0.89).DiscussionThis study revealed that exosomal GAP43, neurogranin, SNAP25, and synaptotagmin 1 act as effective biomarkers for prediction of AD 5 to 7 years before cognitive impairment.

Cerebrospinal Fluid YKL-40 and Neurogranin in Familial Alzheimer's Disease: A Pilot Study.

Background:YKL-40 and neurogranin are promising additional cerebrospinal fluid (CSF) biomarkers for Alzheimer’s disease (AD) which reflect different underlying disease mechanisms.Objective:To compare the levels of CSF YKL-40 and neurogranin between asymptomatic carriers of familial AD (FAD) mutations (MC) and non-carriers (NC) from the same families. Another objective was to assess changes in YKL-40 and neurogranin, from the presymptomatic to clinical phase of FAD.Methods:YKL-40 and neurogranin, as well as Aβ42, total tau-protein, and phospho-tau, were measured in the CSF of 14 individuals carrying one of three FAD mutations, APPswe (p.KM670/671NL), APParc (p.E693G), and PSEN1 (p.H163Y), as well as in 17 NC from the same families. Five of the MC developed mild cognitive impairment (MCI) during follow-up.Results:In this pilot study, there was no difference in either CSF YKL-40 or neurogranin when comparing the presymptomatic MC to the NC. YKL-40 correlated positively with expected years to symptom onset and to age in both the MC and the NC, while neurogranin had no correlation to either variable in either of the groups. A subgroup of the participants underwent more than one CSF sampling in which half of the MC developed MCI during follow-up. The longitudinal data showed an increase in YKL-40 levels in the MC as the expected symptom onset approached. Neurogranin remained stable over time in both the MC and the NC.Conclusion:These findings support a positive correlation between progression from presymptomatic to symptomatic AD and levels of CSF YKL-40, but not neurogranin.

Proteomic analysis links alterations of bioenergetics, mitochondria-ER interactions and proteostasis in hippocampal astrocytes from 3xTg-AD mice

The pathogenesis of Alzheimer’s disease (AD), a slowly-developing age-related neurodegenerative disorder, is a result of the action of multiple factors including deregulation of Ca2+ homeostasis, mitochondrial dysfunction, and dysproteostasis. Interaction of these factors in astrocytes, principal homeostatic cells in the central nervous system, is still poorly understood. Here we report that in immortalized hippocampal astrocytes from 3xTg-AD mice (3Tg-iAstro cells) bioenergetics is impaired, including reduced glycolysis and mitochondrial oxygen consumption, and increased production of reactive oxygen species. Shotgun proteomics analysis of mitochondria-ER-enriched fraction showed no alterations in the expression of mitochondrial and OxPhos proteins, while those related to the ER functions and protein synthesis were deregulated. Using ER- and mitochondria-targeted aequorin-based Ca2+ probe we show that, in 3Tg-iAstro cells, ER was overloaded with Ca2+ while Ca2+ uptake by mitochondria upon ATP stimulation was reduced. This was accompanied by the increase in short distance (≈8–10 nm) contact area between mitochondria and ER, upregulation of ER-stress/unfolded protein response genes Atf4, Atf6 and Herp, and reduction of global protein synthesis rate. We suggest that familial AD mutations in 3Tg-iAstro cells induce mitochondria-ER interaction changes that deregulate astrocytic bioenergetics, Ca2+ homeostasis and proteostasis. These factors may interact, creating a pathogenic loop compromising homeostatic and defensive functions of astroglial cells predisposing neurons to dysfunction.

Aging and Progression of Beta-Amyloid Pathology in Alzheimer's Disease Correlates with Microglial Heme-Oxygenase-1 Overexpression.

Neuroinflammation and oxidative stress are being recognized as characteristic hallmarks in many neurodegenerative diseases, especially those that portray proteinopathy, such as Alzheimer’s disease (AD). Heme-oxygenase 1 (HO-1) is an inducible enzyme with antioxidant and anti-inflammatory properties, while microglia are the immune cells in the central nervous system. To elucidate the brain expression profile of microglial HO-1 in aging and AD-progression, we have used the 5xFAD (five familial AD mutations) mouse model of AD and their littermates at different ages (four, eight, 12, and 18 months). Total brain expression of HO-1 was increased with aging and such increase was even higher in 5xFAD animals. In co-localization studies, HO-1 expression was mainly found in microglia vs. other brain cells. The percentage of microglial cells expressing HO-1 and the amount of HO-1 expressed within microglia increased progressively with aging. Furthermore, this upregulation was increased by 2–3-fold in the elder 5xFAD mice. In addition, microglia overexpressing HO-1 was predominately found surrounding beta-amyloid plaques. These results were corroborated using postmortem brain samples from AD patients, where microglial HO-1 was found up-regulated in comparison to brain samples from aged matched non-demented patients. This study demonstrates that microglial HO-1 expression increases with aging and especially with AD progression, highlighting HO-1 as a potential biomarker or therapeutic target for AD.

Presenilin1 familial Alzheimer disease mutants inactivate EFNB1- and BDNF-dependent neuroprotection against excitotoxicity by affecting neuroprotective complexes of N-methyl-d-aspartate receptor.

Excitotoxicity is thought to play key roles in brain neurodegeneration and stroke. Here we show that neuroprotection against excitotoxicity by trophic factors EFNB1 and brain-derived neurotrophic factor (called here factors) requires de novo formation of ‘survival complexes’ which are factor-stimulated complexes of N-methyl-d-aspartate receptor with factor receptor and presenilin 1. Absence of presenilin 1 reduces the formation of survival complexes and abolishes neuroprotection. EPH receptor B2- and N-methyl-d-aspartate receptor-derived peptides designed to disrupt formation of survival complexes also decrease the factor-stimulated neuroprotection. Strikingly, factor-dependent neuroprotection and levels of the de novo factor-stimulated survival complexes decrease dramatically in neurons expressing presenilin 1 familial Alzheimer disease mutants. Mouse neurons and brains expressing presenilin 1 familial Alzheimer disease mutants contain increased amounts of constitutive presenilin 1–N-methyl-d-aspartate receptor complexes unresponsive to factors. Interestingly, the stability of the familial Alzheimer disease presenilin 1–N-methyl-d-aspartate receptor complexes differs from that of wild type complexes and neurons of mutant-expressing brains are more vulnerable to cerebral ischaemia than neurons of wild type brains. Furthermore, N-methyl-d-aspartate receptor-mediated excitatory post-synaptic currents at CA1 synapses are altered by presenilin 1 familial Alzheimer disease mutants. Importantly, high levels of presenilin 1–N-methyl-d-aspartate receptor complexes are also found in post-mortem brains of Alzheimer disease patients expressing presenilin 1 familial Alzheimer disease mutants. Together, our data identify a novel presenilin 1-dependent neuroprotective mechanism against excitotoxicity and indicate a pathway by which presenilin 1 familial Alzheimer disease mutants decrease factor-depended neuroprotection against excitotoxicity and ischaemia in the absence of Alzheimer disease neuropathological hallmarks which may form downstream of neuronal damage. These findings have implications for the pathogenic effects of familial Alzheimer disease mutants and therapeutic strategies.

Mechanisms of γ-Secretase Activation and Substrate Processing.

Amyloid β-peptide, the principal component of characteristic cerebral plaques of Alzheimer’s disease (AD), is produced through intramembrane proteolysis of the amyloid precursor protein (APP) by γ-secretase. Despite the importance in the pathogenesis of AD, the mechanisms of intramembrane proteolysis and substrate processing by γ-secretase remain poorly understood. Here, complementary all-atom simulations using a robust Gaussian accelerated molecular dynamics (GaMD) method and biochemical experiments were combined to investigate substrate processing of wildtype and mutant APP by γ-secretase. The GaMD simulations captured spontaneous activation of γ-secretase, with hydrogen bonded catalytic aspartates and water poised for proteolysis of APP at the ε cleavage site. Furthermore, GaMD simulations revealed that familial AD mutations I45F and T48P enhanced the initial ε cleavage between residues Leu49–Val50, while M51F mutation shifted the ε cleavage site to the amide bond between Thr48–Leu49. Detailed analysis of the GaMD simulations allowed us to identify distinct low-energy conformational states of γ-secretase, different secondary structures of the wildtype and mutant APP substrate, and important active-site subpockets for catalytic function of the enzyme. The simulation findings were highly consistent with experimental analyses of APP proteolytic products using mass spectrometry and Western blotting. Taken together, the GaMD simulations and biochemical experiments have enabled us to elucidate the mechanisms of γ-secretase activation and substrate processing, which should facilitate rational computer-aided drug design targeting this functionally important enzyme.

Amyloid β induces interneuron-specific changes in the hippocampus of APPNL-F mice.

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by cognitive decline and amyloid-beta (Aβ) depositions generated by the proteolysis of amyloid precursor protein (APP) in the brain. In APPNL-F mice, APP gene was humanized and contains two familial AD mutations, and APP–unlike other mouse models of AD–is driven by the endogenous mouse APP promoter. Similar to people without apparent cognitive dysfunction but with heavy Aβ plaque load, we found no significant decline in the working memory of adult APPNL-F mice, but these mice showed decline in the expression of normal anxiety. Using immunohistochemistry and 3D block-face scanning electron microscopy, we found no changes in GABAA receptor positivity and size of somatic and dendritic synapses of hippocampal interneurons. We did not find alterations in the level of expression of perineuronal nets around parvalbumin (PV) interneurons or in the density of PV- or somatostatin-positive hippocampal interneurons. However, in contrast to other investigated cell types, PV interneuron axons were occasionally mildly dystrophic around Aβ plaques, and the synapses of PV-positive axon initial segment (AIS)-targeting interneurons were significantly enlarged. Our results suggest that PV interneurons are highly resistant to amyloidosis in APPNL-F mice and amyloid-induced increase in hippocampal pyramidal cell excitability may be compensated by PV-positive AIS-targeting cells. Mechanisms that make PV neurons more resilient could therefore be exploited in the treatment of AD for mitigating Aβ-related inflammatory effects on neurons.

NitroSynapsin ameliorates hypersynchronous neural network activity in Alzheimer hiPSC models.

Beginning at early stages, human Alzheimer’s disease (AD) brains manifest hyperexcitability, contributing to subsequent extensive synapse loss, which has been linked to cognitive dysfunction. No current therapy for AD is disease-modifying. Part of the problem with AD drug discovery is that transgenic mouse models have been poor predictors of potential human treatment. While it is undoubtedly important to test drugs in these animal models, additional evidence for drug efficacy in a human context might improve our chances of success. Accordingly, in order to test drugs in a human context, we have developed a platform of physiological assays using patch-clamp electrophysiology, calcium imaging, and multielectrode array (MEA) experiments on human (h)iPSC-derived 2D cortical neuronal cultures and 3D cerebral organoids. We compare hiPSCs bearing familial AD mutations vs. their wild-type (WT) isogenic controls in order to characterize the aberrant electrical activity in such a human context. Here, we show that these AD neuronal cultures and organoids manifest increased spontaneous action potentials, slow oscillatory events (~1 Hz), and hypersynchronous network activity. Importantly, the dual-allosteric NMDAR antagonist NitroSynapsin, but not the FDA-approved drug memantine, abrogated this hyperactivity. We propose a novel model of synaptic plasticity in which aberrant neural networks are rebalanced by NitroSynapsin. We propose that hiPSC models may be useful for screening drugs to treat hyperexcitability and related synaptic damage in AD.

Cholinergic-like neurons carrying PSEN1 E280A mutation from familial Alzheimer's disease reveal intraneuronal sAPPβ fragments accumulation, hyperphosphorylation of TAU, oxidative stress, apoptosis and Ca2+ dysregulation: Therapeutic implications.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory loss and cognitive disturbance as a consequence of the loss of cholinergic neurons in the brain, neuritic plaques and hyperphosphorylation of TAU protein. Although the underlying mechanisms leading to these events are unclear, mutations in presenilin 1 (PSEN1), e.g., E280A (PSEN1 E280A), are causative factors for autosomal dominant early-onset familial AD (FAD). Despite advances in the understanding of the physiopathology of AD, there are no efficient therapies to date. Limitations in culturing brain-derived live neurons might explain the limited effectiveness of AD research. Here, we show that mesenchymal stromal (stem) cells (MSCs) can be used to model FAD, providing novel opportunities to study cellular mechanisms and to establish therapeutic strategies. Indeed, we cultured MSCs with the FAD mutation PSEN1 E280A and wild-type (WT) PSEN1 from umbilical cords and characterized the transdifferentiation of these cells into cholinergic-like neurons (ChLNs). PSEN1 E280A ChLNs but not WT PSEN1 ChLNs exhibited increased intracellular soluble amyloid precursor protein (sAPPf) fragments and extracellular Aβ42 peptide and TAU phosphorylation (at residues Ser202/Thr205), recapitulating the molecular pathogenesis of FAD caused by mutant PSEN1. Furthermore, PSEN1 E280A ChLNs presented oxidative stress (OS) as evidenced by the oxidation of DJ-1Cys106-SH into DJ-1Cys106-SO3 and the detection of DCF-positive cells and apoptosis markers such as activated pro-apoptosis proteins p53, c-JUN, PUMA and CASPASE-3 and the concomitant loss of the mitochondrial membrane potential and DNA fragmentation. Additionally, mutant ChLNs displayed Ca2+ flux dysregulation and deficient acetylcholinesterase (AChE) activity compared to control ChLNs. Interestingly, the inhibitor JNK SP600125 almost completely blocked TAU phosphorylation. Our findings demonstrate that FAD MSC-derived cholinergic neurons with the PSEN1 E280A mutation provide important clues for the identification of targetable pathological molecules.