Mutant APP Research Articles

Selective serotonin reuptake inhibitor citalopram ameliorates cognitive decline and protects against amyloid beta-induced mitochondrial dynamics, biogenesis, autophagy, mitophagy and synaptic toxicities in a mouse model of Alzheimer's disease.

In the current study, we investigated the protective role of citalopram against cognitive decline, impaired mitochondrial dynamics, defective mitochondrial biogenesis, defective autophagy, mitophagy and synaptic dysfunction in APP transgenic mouse model of Alzheimer's disease (ad). We treated 12-month-old wild-type (WT) and age-matched transgenic APP mice with citalopram for 2months. Using Morris Water Maze and rotarod tests, quantitative RT-PCR, immunoblotting, biochemical methods and transmission electron microscopy methods, we assessed cognitive behavior, RNA and protein levels of mitochondrial dynamics, biogenesis, autophagy, mitophagy, synaptic, ad-related and neurogenesis genes in wild-type and APP mice treated and untreated with citalopram. Citalopram-treated APP mice relative to citalopram-untreated APP mice exhibited improved cognitive behavior. Increased levels of mRNA associated with mitochondrial fission and ad-related genes; decreased levels of fusion, biogenesis, autophagy, mitophagy, synaptic and neurogenesis genes were found in APP mice relative to WT mice. However, APP mice treated with citalopram compared to citalopram-untreated APP mice revealed reduced levels of the mitochondrial fission and ad-related genes and increased fusion, biogenesis, autophagy, mitophagy, synaptic and neurogenesis genes. Our protein data agree with the mRNA levels. Transmission electron microscopy revealed significantly increased mitochondrial numbers and reduced mitochondrial length in APP mice; these were reversed in citalopram-treated APP mice. Further, Golgi-cox staining analysis revealed reduced dendritic spines in APP mice relative to WT mice. However, citalopram-treated APP mice showed significantly increased dendritic spines, indicating that citalopram enhances spine density, synaptic activity and improved cognitive function in APP mice. These findings suggest that citalopram reduces cognitive decline, Aβ levels and mitochondrial and synaptic toxicities and may have a strong protective role against mutant APP and Aβ-induced injuries in patients with depression, anxiety and ad.

Plaque associated microglia hyper-secrete extracellular vesicles and accelerate tau propagation in a humanized APP mouse model

BackgroundRecent studies suggest that microglia contribute to tau pathology progression in Alzheimer’s disease. Amyloid plaque accumulation transforms microglia, the primary innate immune cells in the brain, into neurodegenerative microglia (MGnD), which exhibit enhanced phagocytosis of plaques, apoptotic neurons and dystrophic neurites containing aggregated and phosphorylated tau (p-tau). It remains unclear how microglia promote disease progression while actively phagocytosing pathological proteins, therefore ameliorating pathology.MethodsAdeno-associated virus expressing P301L tau mutant (AAV-P301L-tau) was stereotaxically injected into the medial entorhinal cortex (MEC) in C57BL/6 (WT) and humanized APP mutant knock-in homozygote (AppNL-G-F) mice at 5 months of age. Mice were fed either chow containing a colony stimulating factor-1 receptor inhibitor (PLX5622) or control chow from 4 to 6 months of age to test the effect of microglia depletion. Animals were tested at 6 months of age for immunofluorescence, biochemistry, and FACS of microglia. In order to monitor microglial extracellular vesicle secretion in vivo, a novel lentiviral EV reporter system was engineered to express mEmerald-CD9 (mE-CD9) specifically in microglia, which was injected into the same region of MEC.ResultsExpressing P301L tau mutant in the MEC induced tau propagation to the granule cell layer of the hippocampal dentate gyrus, which was significantly exacerbated in AppNL-G-F mice compared to WT control mice. Administration of PLX5622 depleted nearly all microglia in mouse brains and dramatically reduced propagation of p-tau in WT and to a greater extent in AppNL-G-F mice, although it increased plaque burden and plaque-associated p-tau+ dystrophic neurites. Plaque-associated MGnD microglia strongly expressed an EV marker, tumor susceptibility gene 101, indicative of heightened synthesis of EVs. Intracortical injection of mE-CD9 lentivirus successfully induced microglia-specific expression of mE-CD9+ EV particles, which were significantly enhanced in Mac2+ MGnD microglia compared to Mac2− homeostatic microglia. Finally, consecutive intracortical injection of mE-CD9 lentivirus and AAV-P301L-tau into AppNL-G-F mice revealed encapsulation of p-tau in microglia-specific mE-CD9+ EVs as determined by super-resolution microscopy and immuno-electron microscopy.DiscussionOur findings suggest that MGnD microglia hyper-secrete p-tau+ EVs while compacting Aβ plaques and clearing NP tau, which we propose as a novel mechanistic link between amyloid plaque deposition and exacerbation of tau propagation in AppNL-G-F mice.

Protective effects of antidepressant citalopram against abnormal APP processing and amyloid beta-induced mitochondrial dynamics, biogenesis, mitophagy and synaptic toxicities in Alzheimer's disease.

The purpose of this study is to study the neuroprotective role of selective serotonin reuptake inhibitor (SSRI), citalopram, against Alzheimer's disease (AD). Multiple SSRIs, including citalopram, are reported to treat patients with depression, anxiety and AD. However, their protective cellular mechanisms have not been studied completely. In the current study, we investigated the protective role of citalopram against impaired mitochondrial dynamics, defective mitochondrial biogenesis, defective mitophagy and synaptic dysfunction in immortalized mouse primary hippocampal cells (HT22) expressing mutant APP (SWI/IND) mutations. Using quantitative RT-PCR, immunoblotting, biochemical methods and transmission electron microscopy methods, we assessed mutant full-length APP/C-terminal fragments and Aβ levels and mRNA and protein levels of mitochondrial dynamics, biogenesis, mitophagy and synaptic genes in mAPP-HT22 cells and mAPP-HT22 cells treated with citalopram. Increased levels of mRNA levels of mitochondrial fission genes, decreased levels of fusion biogenesis, autophagy, mitophagy and synaptic genes were found in mAPP-HT22 cells relative to WT-HT22 cells. However, mAPP-HT22 cells treated with citalopram compared to mAPP-HT22 cells revealed reduced levels of the mitochondrial fission genes, increased fusion, biogenesis, autophagy, mitophagy and synaptic genes. Our protein data agree with mRNA levels. Transmission electron microscopy revealed significantly increased mitochondrial numbers and reduced mitochondrial length in mAPP-HT22 cells; these were reversed in citalopram-treated mAPP-HT22 cells. Cell survival rates were increased in citalopram-treated mAPP-HT22 relative to citalopram-untreated mAPP-HT22. Further, mAPP and C-terminal fragments werealso reduced in citalopram-treated cells. These findings suggest that citalopram reduces mutant APP and Aβ and mitochondrial toxicities and may have a protective role of mutant APP and Aβ-induced injuries in patients with depression, anxiety and AD.

Genetic study of young-onset dementia using targeted gene panel sequencing in Taiwan.

Recent genetic progress allows the molecular diagnosis of young-onset dementia, including Alzheimer's disease (AD) and frontotemporal dementia (FTD). We aimed to identify the mutational and clinical spectra of causal genes in a Taiwanese cohort of young-onset dementia. Ninety-one patients with young-onset dementia and 22 age/gender-matched controls were recruited. Genetic causes were identified by a targeted panel containing 90 causative genes for AD, FTD, and related neurodegenerative disorders. Plasma biomarkers, including total tau, Aβ42, and Aβ40, were assayed. Molecular amyloid and tau PET scans were performed in some patients carrying mutations. Nine of 52 patients (17.3%) with young-onset AD had mutations: 2 (22.2%), 4 (44.5%), 2 (22.2%), and 1 (11.1%) in APP, PSEN1, PSEN2, and TREM2, respectively. Two of 33 patients (6.1%) with young-onset FTD had mutations in MAPT and LRRK2. Three of the 6 patients (50.0%) with possible FTD combined with other neurodegenerative disorders had individual mutations in APP, PSEN2, or MAPT. Patients with PSEN1 mutations had earlier onset of disease than those without mutations (p = .02). Plasma level of total tau was increased and Aβ42 and Aβ40 levels decreased in all groups of dementia patients compared to controls. Our findings provide a genetic spectrum of young-onset dementia in our population.

Impairment of Spike-Timing-Dependent Plasticity at Schaffer Collateral-CA1 Synapses in Adult APP/PS1 Mice Depends on Proximity of Aβ Plaques.

Alzheimer’s disease (AD) is a multifaceted neurodegenerative disorder characterized by progressive and irreversible cognitive decline, with no disease-modifying therapy until today. Spike timing-dependent plasticity (STDP) is a Hebbian form of synaptic plasticity, and a strong candidate to underlie learning and memory at the single neuron level. Although several studies reported impaired long-term potentiation (LTP) in the hippocampus in AD mouse models, the impact of amyloid-β (Aβ) pathology on STDP in the hippocampus is not known. Using whole cell patch clamp recordings in CA1 pyramidal neurons of acute transversal hippocampal slices, we investigated timing-dependent (t-) LTP induced by STDP paradigms at Schaffer collateral (SC)-CA1 synapses in slices of 6-month-old adult APP/PS1 AD model mice. Our results show that t-LTP can be induced even in fully developed adult mice with different and even low repeat STDP paradigms. Further, adult APP/PS1 mice displayed intact t-LTP induced by 1 presynaptic EPSP paired with 4 postsynaptic APs (6× 1:4) or 1 presynaptic EPSP paired with 1 postsynaptic AP (100× 1:1) STDP paradigms when the position of Aβ plaques relative to recorded CA1 neurons in the slice were not considered. However, when Aβ plaques were live stained with the fluorescent dye methoxy-X04, we observed that in CA1 neurons with their somata <200 µm away from the border of the nearest Aβ plaque, t-LTP induced by 6× 1:4 stimulation was significantly impaired, while t-LTP was unaltered in CA1 neurons >200 µm away from plaques. Treatment of APP/PS1 mice with the anti-inflammatory drug fingolimod that we previously showed to alleviate synaptic deficits in this AD mouse model did not rescue the impaired t-LTP. Our data reveal that overexpression of APP and PS1 mutations in AD model mice disrupts t-LTP in an Aβ plaque distance-dependent manner, but cannot be improved by fingolimod (FTY720) that has been shown to rescue conventional LTP in CA1 of APP/PS1 mice.

Regional brain iron associated with deterioration in Alzheimer's disease: A large cohort study and theoretical significance.

This paper is a proposal for an update of the iron hypothesis of Alzheimer's disease (AD), based on large-scale emerging evidence. Iron featured historically early in AD research efforts for its involvement in the amyloid and tau proteinopathies, APP processing, genetics, and one clinical trial, yet iron neurochemistry remains peripheral in mainstream AD research. Much of the effort investigating iron in AD has focused on the potential for iron to provoke the onset of disease, by promoting proteinopathy though increased protein expression, phosphorylation, and aggregation. We provide new evidence from a large post mortem cohort that brain iron levels within the normal range were associated with accelerated ante mortem disease progression in cases with underlying proteinopathic neuropathology. These results corroborate recent findings that argue for an additional downstream role for iron as an effector of neurodegeneration, acting independently of tau or amyloid pathologies. We hypothesize that the level of tissue iron is a trait that dictates the probability of neurodegeneration in AD by ferroptosis, a regulated cell death pathway that is initiated by signals such as glutathione depletion and lipid peroxidation. While clinical biomarkers of ferroptosis are still in discovery, the demonstration of additional ferroptotic correlates (genetic or biomarker derived) of disease progression is required to test this hypothesis. The genes implicated in familial AD are not known to influence ferroptosis, although recent reports on APP mutations and apolipoprotein E allele (APOE) have shown impact on cellular iron retention. Familial AD mutations will need to be tested for their impact on ferroptotic vulnerability. Ultimately, this hypothesis will be substantiated, or otherwise, by a clinical trial of an anti-ferroptotic/iron compound in AD patients. Iron has historically been linked to the amyloid and tau proteinopathies of AD. Tau, APP, and apoE have been implicated in physiological iron homeostasis in the brain. Iron is biochemically the origin of most chemical radicals generated in biochemistry and thus closely associated with the oxidative stress theory of AD. Iron accumulation is also a well-established consequence of aging and inflammation, which are major theories of disease pathogenesis.

Alzheimer's disease: a tale of two diseases?

Sporadic late-onset Alzheimer’s disease (SLOAD) and familial early-onset Alzheimer’s disease (FEOAD) associated with dominant mutations in APP, PSEN1 and PSEN2, are thought to represent a spectrum of the same disorder based on near identical behavioral and histopathological features. Hence, FEOAD transgenic mouse models have been used in past decades as a surrogate to study SLOAD pathogenic mechanisms and as the gold standard to validate drugs used in clinical trials. Unfortunately, such research has yielded little output in terms of therapeutics targeting the disease’s development and progression. In this short review, we interrogate the widely accepted view of one, dimorphic disease through the prism of the Bmi1+/– mouse model and the distinct chromatin signatures observed between SLOAD and FEOAD brains.

&lt;i&gt;In vivo&lt;/i&gt; Evidence That &lt;i&gt;SORL1&lt;/i&gt;, Encoding the Endosomal Recycling Receptor SORLA, Can Function as a Causal Gene in Alzheimer's Disease

The few established causal genes in Alzheimer’s disease (AD), mutations in APP and PSENs, have been functionally characterized using biomarkers, capturing an in vivo profile reflecting the disease’s initial preclinical phase. SORL1, a gene encoding the endosome recycling receptor SORLA, epidemiologically behaves as a causal gene when truncating mutations lead to partial loss of protein function. Here, in an effort to test whether SORL1 can indeed function as an AD causal gene, we used CRISPR-Cas9-based gene editing to develop a novel model of SORL1 haploinsufficiency in Gottingen Minipigs taking advantage of porcine models for biomarker investigations. SORL1 haploinsufficiency in young minipigs was found to phenocopy the preclinical in vivo profile of AD observed with other causal genes, resulting in spinal fluid abnormalities in Ab and tau, with no evident neurodegeneration or amyloid plaque formation. These studies provide functional support that SORL1 is a bona fide causal gene in AD, and when taken together with recent insight on other AD-causal genes, support the idea that dysfunctional endosomal recycling is a dominant pathogenic pathway in the disease.

Abnormal retinal capillary blood flow in autosomal dominant Alzheimer's disease.

IntroductionThis study characterizes retinal capillary blood flow in subjects with autosomal dominant Alzheimer's disease (ADAD)‐causing mutations.MethodsCarriers of PSEN1 or APP mutations were prospectively recruited and split into early‐stage (ES) and late‐stage (LS) groups. Controls were normal subjects and non‐carriers from the at‐risk group. Capillary blood flow was quantified using an optical coherence tomography angiography‐based measure of erythrocyte flux through capillary segments. Statistical analyses were adjusted for correlation between two eyes of the same subject.ResultsES carriers had significantly greater capillary blood flow than controls and LS carriers. ES and LS carriers had significantly greater capillary blood flow heterogeneity than controls. There was no difference between capillary blood flow of LS carriers and controls.DiscussionES ADAD carriers demonstrate increased retinal capillary blood flow and flow heterogeneity compared to controls. These findings support the hypothesis that increased perfusion is a pathophysiologic feature of presymptomatic stages of ADAD.

Leucine Carboxyl Methyltransferase 1 Overexpression Protects Against Cognitive and Electrophysiological Impairments in Tg2576 APP Transgenic Mice.

Background:The serine/threonine protein phosphatase, PP2A, is thought to play a central role in the molecular pathogenesis of Alzheimer’s disease (AD), and the activity and substrate specificity of PP2A is regulated, in part, through methylation and demethylation of its catalytic subunit. Previously, we found that transgenic overexpression of the PP2A methyltransferase, LCMT-1, or the PP2A methylesterase, PME-1, altered the sensitivity of mice to impairments caused by acute exposure to synthetic oligomeric amyloid-β (Aβ).Objective:Here we sought to test the possibility that these molecules also controlled sensitivity to impairments caused by chronically elevated levels of Aβ produced in vivo.Methods:To do this, we examined the effects of transgenic LCMT-1, or PME-1 overexpression on cognitive and electrophysiological impairments caused by chronic overexpression of mutant human APP in Tg2576 mice.Results:We found that LCMT-1 overexpression prevented impairments in short-term spatial memory and synaptic plasticity in Tg2576 mice, without altering APP expression or soluble Aβ levels. While the magnitude of the effects of PME-1 overexpression in Tg2576 mice was small and potentially confounded by the emergence of non-cognitive impairments, Tg2576 mice that overexpressed PME-1 showed a trend toward earlier onset and/or increased severity of cognitive and electrophysiological impairments.Conclusion:These data suggest that the PP2A methyltransferase, LCMT-1, and the PP2A methylesterase, PME-1, may participate in the molecular pathogenesis of AD by regulating sensitivity to the pathogenic effects of chronically elevated levels of Aβ.

Prodromal neuroinflammatory, cholinergic and metabolite dysfunction detected by PET and MRS in the TgF344-AD transgenic rat model of AD: a collaborative multi-modal study.

Mouse models of Alzheimer's disease (AD) are valuable but do not fully recapitulate human AD pathology, such as spontaneous Tau fibril accumulation and neuronal loss, necessitating the development of new AD models. The transgenic (TG) TgF344-AD rat has been reported to develop age-dependent AD features including neuronal loss and neurofibrillary tangles, despite only expressing APP and PSEN1 mutations, suggesting an improved modelling of AD hallmarks. Alterations in neuronal networks as well as learning performance and cognition tasks have been reported in this model, but none have combined a longitudinal, multimodal approach across multiple centres, which mimics the approaches commonly taken in clinical studies. We therefore aimed to further characterise the progression of AD-like pathology and cognition in the TgF344-AD rat from young-adults (6 months (m)) to mid- (12 m) and advanced-stage (18 m, 25 m) of the disease.Methods: TgF344-AD rats and wild-type (WT) littermates were imaged at 6 m, 12 m and 18 m with [18F]DPA-714 (TSPO, neuroinflammation), [18F]Florbetaben (Aβ) and [18F]ASEM (α7-nicotinic acetylcholine receptor) and with magnetic resonance spectroscopy (MRS) and with (S)-[18F]THK5117 (Tau) at 15 and 25 m. Behaviour tests were also performed at 6 m, 12 m and 18 m. Immunohistochemistry (CD11b, GFAP, Aβ, NeuN, NeuroChrom) and Tau (S)-[18F]THK5117 autoradiography, immunohistochemistry and Western blot were also performed.Results: [18F]DPA-714 positron emission tomography (PET) showed an increase in neuroinflammation in TG vs wildtype animals from 12 m in the hippocampus (+11%), and at the advanced-stage AD in the hippocampus (+12%), the thalamus (+11%) and frontal cortex (+14%). This finding coincided with strong increases in brain microgliosis (CD11b) and astrogliosis (GFAP) at these time-points as assessed by immunohistochemistry. In vivo [18F]ASEM PET revealed an age-dependent increase uptake in the striatum and pallidum/nucleus basalis of Meynert in WT only, similar to that observed with this tracer in humans, resulting in TG being significantly lower than WT by 18 m. In vivo [18F]Florbetaben PET scanning detected Aβ accumulation at 18 m, and (S)-[18F]THK5117 PET revealed subsequent Tau accumulation at 25m in hippocampal and cortical regions. Aβ plaques were low but detectable by immunohistochemistry from 6 m, increasing further at 12 and 18 m with Tau-positive neurons adjacent to Aβ plaques at 18 m. NeuroChrom (a pan neuronal marker) immunohistochemistry revealed a loss of neuronal staining at the Aβ plaques locations, while NeuN labelling revealed an age-dependent decrease in hippocampal neuron number in both genotypes. Behavioural assessment using the novel object recognition task revealed that both WT & TgF344-AD animals discriminated the novel from familiar object at 3 m and 6 m of age. However, low levels of exploration observed in both genotypes at later time-points resulted in neither genotype successfully completing the task. Deficits in social interaction were only observed at 3 m in the TgF344-AD animals. By in vivo MRS, we showed a decrease in neuronal marker N-acetyl-aspartate in the hippocampus at 18 m (-18% vs age-matched WT, and -31% vs 6 m TG) and increased Taurine in the cortex of TG (+35% vs age-matched WT, and +55% vs 6 m TG).Conclusions: This multi-centre multi-modal study demonstrates, for the first time, alterations in brain metabolites, cholinergic receptors and neuroinflammation in vivo in this model, validated by robust ex vivo approaches. Our data confirm that, unlike mouse models, the TgF344-AD express Tau pathology that can be detected via PET, albeit later than by ex vivo techniques, and is a useful model to assess and longitudinally monitor early neurotransmission dysfunction and neuroinflammation in AD.

A family‐based genetic study identifies mutations in TLR9 impairing receptor activation: A role for innate immunity in AD pathogenesis

AbstractBackgroundFamily‐based genetic studies in early‐onset Alzheimer disease (EOAD), prompting early gene discoveries, remain powerful for the identification of novel genes in AD. Causal mutations in APP, PSEN1 and PSEN2 explained &lt;10% of EOAD patients, while several EOAD families remained genetically unexplained. We identified a multigenerational Flanders‐Belgian family with autosomal dominant EOAD. DNA, biomaterials and clinical data from two consecutive informative generations were available: 5 AD patients (onset 64.2±13.2 years, range 52‐85) of which 2 with a definite neuropathological diagnosis and 9 unaffected/at‐risk individuals.MethodWhole exome sequencing of 4 patients. Selection of shared rare non‐synonymous variants, validation of co‐segregation with disease and variants frequency assessment using massive parallel‐targeted sequencings (MPS). We used genotyping of STR markers to define haplotypes. Coding regions of candidate genes were sequenced using MPS in a Belgian cohort of 320 EOAD (onset 57.8±5.9y, range 33‐65) and 1166 late‐onset (LO)AD (onset 77.1±6.5y, range 66‐96) patients and a control cohort of 934 persons (inclusion 70.45±9.2y, range 52‐100). Variants pathogenicity was predicted using CADD scores cutoff&gt;20. Evaluation of functional effects by NF‐κB luciferase assay.ResultThree rare variants co‐segregated with AD in the family: CCR3 p.F249Hfs*23 (rs561062190), ZNF589 p.T355M (rs376706270) and TLR9 p.E317D (novel) and are located within a co‐segregating haplotype block of 15.3 cM at ch3p21. Only the TLR9 variant was absent in controls. TLR9 is a DNA‐sensing receptor expressed in immune cells, recognizes unmethylated CpG oligonucleodides and is responsible for innate immune cells activation and mounting acquired responses. The NF‐κB luciferase assay showed that p.E317D, located within the ligand sensor pocket of TLR9, caused a 50% reduction in receptor activation. TLR9 resequencing identified additional rare variants carriers: 7 in EOAD (7/320, 2.19%) and 19 in LOAD (19/1166, 1.63%) patients and 8 in controls (8/934, 0.86%), while TLR9 p.E317D was absent. Of the rare variants, 16 were in patient‐only, 3 in patients and controls and 5 in controls‐only. The NF‐κB luciferase assay indicated reduced TLR9 activation for the novel variants specific to EOAD patients and with a CADD score &gt;20.ConclusionWe discovered TLR9 as candidate gene in AD with a mechanism of loss of receptor activation.

Plasma phospho‐tau in familial Alzheimer’s disease

AbstractBackgroundBlood biomarkers have the potential to advance clinical care and accelerate the development of disease‐modifying treatments. P‐tau181 is a promising blood biomarker, with levels increasing in Alzheimer’s disease (AD) dementia (doi:10.1016/j.jalz.2018.02.013). However, a better understanding of the timing and trajectory of plasma p‐tau181 changes is needed. Therefore, we conducted a longitudinal study in familial AD (FAD).MethodsUsing an in house Single molecule array method, P‐tau181 was measured in 153 plasma samples from 70 individuals from families with PSEN1 or APP mutations (mean ± SD = 2.2 ±1.3 samples/participant;median [IQR] duration of follow up =1.0 (0, 3.7) years). We compared plasma p‐tau181 between symptomatic mutation carriers, presymptomatic carriers, and noncarriers, adjusting for age and sex. We also examined the relationship between plasma p‐tau181 and estimated years to/from symptom onset (EYO), as well as years to/from actual symptom onset (AAO) in a symptomatic subgroup. In addition, we studied associations between plasma p‐tau181 and clinical severity, as well testing for differences in concentration between genetic subgroups (PSEN1 vs APP carriers, PSEN1 pre‐codon 200 vs PSEN1 post‐codon 200 carriers).Results24 of the asymptomatic participants were mutation carriers (mean baseline EYO ‐9.6 years); 27 were noncarriers. Compared with noncarriers, plasma p‐tau181 concentration was higher in symptomatic (p&lt;0.001) and presymptomatic mutation carriers (p&lt;0.001) (Figure 1). Plasma p‐tau181 discriminated symptomatic (AUC 0·93[95% CI 0·84−0·98]) and presymptomatic (AUC 0.86 [95% CI 0·73−0·95]) carriers from noncarriers. Plasma p‐tau181 concentration increased in mutation carriers from 16 years prior to estimated symptom onset (p=0.049) (Figure 2). Plasma p‐tau181 in symptomatic mutation carriers, modelled using AAO, appeared eventually to plateau. Longitudinal p‐tau181 measures demonstrated significant inter‐ and intra‐individual variability, with some participants exhibiting large changes over relatively short time intervals. We did not find a difference in plasma p‐tau181 concentration between APP and PSEN1 carriers, but there was weak evidence (p=0.053) that symptomatic PSEN1 post‐codon 200 carriers had a 54% higher p‐tau181 concentration (95% CI:1% lower, 138% higher) than pre‐codon 200 carriers.ConclusionOur finding that plasma p‐tau181 concentration is increased in presymptomatic and symptomatic FAD suggests its potential utility as an easily accessible biomarker of AD pathology.

IPSC‐derived engineered cerebral organoids (enCORs) as in vitro models of tauopathy

AbstractBackgroundFamilial Alzheimer’s disease (fAD) is caused by mutations in PSEN1, PSEN2 and APP. PSEN1 forms the catalytic core of g‐secretase, a membrane protease which cleaves numerous substrates including APP and Notch. We have previously shown that our panel of fAD patient‐derived iPSCs show altered APP processing and Ab generation. Here we investigated whether mutations led to altered Notch cleavage in neural precursors. We hypothesised that reduced Notch cleavage in fAD lines would promote premature differentiation during iPSC neuronal differentiation and during adult hippocampal neurogenesis.MethodWe generated 2D cortical neurons and 3D cerebral organoids from a panel of 14 donor‐derived iPSC lines (5 controls, 2 APP mutation lines and 7 PSEN1 mutation lines). Neurogenesis was quantified via the proportion of neural precursors versus the number of post‐mitotic neurons at timepoints of neural commitment. In addition, we quantified newly generated neurons in the post‐mortem hippocampus of 3 control brains and 7 brains derived from fAD mutation carriers.ResultWe describe a small, yet reproducible premature differentiation phenotype in lines containing mutations in PSEN1 during in vitro neurogenesis. This is, at least in part, due to reduced Notch signalling; which drives terminal differentiation. These findings are corroborated in independent orthogonal iPSC systems, namely 2D neurogenesis and 3D organoid differentiation. We see describe robust, quantifiable neurogenesis in post‐mortem tissue using b‐III‐tubulin immunohistochemistry. Results are suggestive of mutation‐specific effects and also a premature ageing phenotype in fAD tissue.ConclusionThese findings reveal insights into the functional outcomes of fAD mutations. Mutations in PSEN1, but not APP, alter Notch signalling in neural precursors, which in turn drives premature terminal differentiation. Premature differentiation and mutation‐specific differences both necessitate careful consideration for drug design and patient stratification.

Recessive missense variants in VWA2 increase risk of developing Alzheimer’s disease

AbstractBackgroundAlzheimer’s disease (AD) is the most frequent cause of neurodegenerative dementia and presents at early (age at onset (AAO) ≤65 years, EOAD) or late age (LOAD). Only 5‐10% of EOAD patients are explained by dominant mutations in AD genes, APP, PSEN1 or PSEN2. We aimed at finding recessive mutations in patients that are not genetically explained.MethodsThe Flanders‐Belgian AD cohort (n = 1166) included 170 EOAD (AAO 57.96 ± 6.32 years; range 29‐65) and 996 LOAD (AAO 77.55 ± 6.30 years; range 66‐95) patients. Whole Genome Sequencing (WGS) was provided by Complete Genomics, BGI. The WGS data was searched for recessive variants, altering protein sequences and a minor allele frequencies ≤5%. Gene‐based resequencing was performed using target amplification assays.ResultsWe selected 18 EOAD patients with a well‐documented clinical or pathological diagnosis for WGS analysis. Mean AAO was 56.17 ± 6.90 years (range 37‐65) and 6 patients had pathological confirmed EOAD. One EOAD patient (AAO 64) was homozygous for p.V366M in the gene Von Willebrand Factor A Domain Containing 2 (VWA2). Resequencing of VWA2 in the AD patient cohort identified 1 additional EOAD (AAO 60) and 3 LOAD patients (AAO range 74‐90) with homozygous (p.R69M, p.V366M) or heterozygous (p.V366M/p.L715F) compound variants. Allele sharing analysis of the compound carriers identified common haplotypes flanking p.V366M and p.L715F, suggesting shared ancestors.ConclusionsWe identified 5 AD patients with trans compound variants in VWA2, 2 EOAD patients (2/170; 1.2%) and 3 LOAD patients (3/996; 0.3%). None of the compound carriers had first‐degree relatives with dementia, fitting autosomal recessive inheritance. The observed frequency of compound carriers in the AD patient groups was higher than expected based on the single allele frequencies calculated in our Flemish‐Belgian population. Overall, our genetic results suggest that compound variants in VWA2 might increase risk for AD. VWA2 is likely part of the extracellular exosomes, which are contributing to neuronal interaction and have a role in AD pathology. Genetic replication in independent AD patients cohorts and functional studies will be needed to understand the contribution of the biological function of VWA2 to AD.

Screening for gene mutation in early onset Alzheimer’s disease and frontotemporal dementia: Report from a Serbian tertiary referral center

AbstractBackgroundEarly‐onset dementia (EOD) is conventionally considered to include patients with disease onset before 65 years of age. Alzheimer’s disease (AD) and Frontotemporal dementia (FTD) are two most common forms of degenerative EOD. Our aim was to screen for known gene mutation status in consecutive degenerative EOD patients.MethodTwo hundred and eight consecutive patients diagnosed according to the current clinical criteria for AD and FTD spectrum were recruited from the Neurology Clinic, Clinical Centre of Serbia from 01.04.2012. until 01.04.2017. Patient from AD spectrum were tested for APP, PSEN1, GRN, MAPT and C9ORF72 gene mutation and FTD patients for GRN, MAPT, C9ORF72, VCP, ANG gene mutation.ResultGene mutations were identified in 3.9% of our AD patients: 2.3% patients had mutations in the PSEN1 gene and 1.5% patients in the APP gene. There was no MAPT, GRN and C9ORF72 mutations carriers in our AD cohort. Genetic mutations have been demonstrated in 10.3% of patients with FTD. The most frequent was the hexanucleotide expansion in C9ORF72 (6.4% of all FTD patients), following mutations in GRN, VCP and ANG with the same frequency of (1.3% FTD for each gene). No patient was a MAPT mutation carrier.ConclusionGene mutations were rare causes in our AD cohort. The frequency of carriers was higher in FTD patients‐ mutations were identified in C9ORF72, GRN, VCP and ANG genes. No MAPT mutation carriers were identified in our cohort of patients with degenerative EOD.

White matter hyperintensity increases are a feature of familial AD and are associated with increased brain atrophy

AbstractBackgroundRelatively little is known about how white matter hyperintensity (WMH) changes relate to well‐characterised markers of disease progression such as brain atrophy rates in autosomal dominant familial AD (ADAD). Such analyses may improve models of disease progression and indicate whether WMH accrual and brain atrophy are associated features over the disease course.MethodsWe investigated WMH accrual in the Dominantly Inherited Alzheimer Network (DIAN) cohort. Participants included 72 controls, 95 PSEN1, 7 PSEN2 and 27 APP mutation carriers, with longitudinal multi‐modal imaging. WMH were segmented using a semi‐automated protocol. Brain atrophy rate was calculated using the boundary shift integral (BSI). Three statistical models were used: Model 1 used mixed‐effect linear regression to assess WMH accrual by mutation presence or type, adjusting for evidence of cognitive impairment (symptomatic status as defined using CDR). Model 2 assessed the effect of estimated years to onset (EYO) on WMH accrual. Model 3 estimated correlations between residual rates of change after allowing mean rates of change in WMH and brain volume to depend on proximity to expected onset. All models (1‐3) were allowed to depend upon total intracranial volume.ResultsThe table shows summary statistics and rates of change including annualised rates of WMH accrual and brain atrophy. Results from Model 1 showed differences in WMH accrual between mutation groups after adjustment for symptom status (p&lt;0.001), with APP having higher rates of accrual than all other groups. Model 2 demonstrated WMH increases were associated with EYO in PSEN1 and APP groups (p≤0.001, both tests), with an accelerating rate of accrual observed approaching and passing estimated onset in the PSEN1 and PSEN2 groups (p≤0.005, both tests). Model 3 demonstrated associations between residual rates of change in WMH and brain volume in the PSEN1 (r 0.76, p&lt;0.001) and APP (r 0.55, p=0.03) groups (the figure shows crude rates).ConclusionMutation type has an impact on WMH accrual, with APP mutation carriers in this cohort gaining more WMH over time. WMH changes are an important biomarker in ADAD with burden increasing with EYO. WMH and brain atrophy changes track together across the AD disease course.

Small molecule modulation of the p75 neurotrophin receptor inhibits multiple amyloid beta-induced tau pathologies

Longitudinal preclinical and clinical studies suggest that Aβ drives neurite and synapse degeneration through an array of tau-dependent and independent mechanisms. The intracellular signaling networks regulated by the p75 neurotrophin receptor (p75NTR) substantially overlap with those linked to Aβ and to tau. Here we examine the hypothesis that modulation of p75NTR will suppress the generation of multiple potentially pathogenic tau species and related signaling to protect dendritic spines and processes from Aβ-induced injury. In neurons exposed to oligomeric Aβ in vitro and APP mutant mouse models, modulation of p75NTR signaling using the small-molecule LM11A-31 was found to inhibit Aβ-associated degeneration of neurites and spines; and tau phosphorylation, cleavage, oligomerization and missorting. In line with these effects on tau, LM11A-31 inhibited excess activation of Fyn kinase and its targets, tau and NMDA-NR2B, and decreased Rho kinase signaling changes and downstream aberrant cofilin phosphorylation. In vitro studies with pseudohyperphosphorylated tau and constitutively active RhoA revealed that LM11A-31 likely acts principally upstream of tau phosphorylation, and has effects preventing spine loss both up and downstream of RhoA activation. These findings support the hypothesis that modulation of p75NTR signaling inhibits a broad spectrum of Aβ-triggered, tau-related molecular pathology thereby contributing to synaptic resilience.

Mutational analysis in familial Alzheimer\u2019s disease of Han Chinese in Taiwan with a predominant mutation PSEN1 p.Met146Ile

Mutations in PSEN1, PSEN2, or APP genes are known to be causative for autosomal dominant Alzheimer’s disease (ADAD). While more than 400 mutations were reported worldwide, predominantly PSEN1, over 40 mutations have been reported in Han Chinese and were associated with earlier onset and more affected family members. Between 2002 and 2018, 77 patients in the neurological clinic of Taipei Veterans General Hospital with a history suggestive of ADAD were referred for mutational analysis. We retrospectively collected demographics, initial symptoms, neurological features and inheritance. We identified 16 patients with PSEN1 and 1 with APP mutation. Among the mutations identified, PSEN1 p.Pro117Leu, p.Met146Ile, p.Gly206Asp, p.Gly209Glu, p.Glu280Lys and p.Leu286Val and APP p.Asp678His were known pathogenic mutations; PSEN1 p.His131Arg and p.Arg157Ser were classified as likely pathogenic and variance of unknown significance respectively. The mean age at onset was 46.2 ± 6.2 years in patients with mutation found. PSEN1 p.Met146Ile, occurred in 56.2% (9/16) of patients with PSEN1 mutations, was the most frequent mutation in the cohort. The additional neurological features occurring in 9 PSEN1 p.Met146Ile index patients were similar with the literature. We found patients with genetic diagnoses were more likely to have positive family history, younger age at onset and less brain white matter hyperintensity.

A computer-simulated mechanism of familial Alzheimer’s disease: Mutations enhance thermal dynamics and favor looser substrate-binding to γ-secretase

The 4-subunit intramembrane protease complex γ-secretase cleaves many substrates including fragments of the β-amyloid precursor protein (APP), leading to formation of Aβ peptides, and Notch. Mutations in APP and the catalytic subunit of γ-secretase, presenilin, cause familial Alzheimer’s disease (fAD). Mutations are assumed to change the substrate-binding and cleavage and thereby the Aβ formed. Whereas a wild-type structure of substrate-bound γ-secretase became recently available from cryogenic electron microscopy (6IYC), the structure and dynamics of mutant proteins remain obscure. Here, we studied five prominent mutants of substrate-bound γ-secretase by explicit all-atom molecular dynamics in a phospholipid membrane model at physiological temperature using the experimental structure as template: The presenilin 1 mutants E280A, G384A, A434C, and L435F and the V717I mutant of APP. Our structures and dynamics provide the first atomic detail into how fAD-causing mutations affect substrate binding to γ-secretase. The pathogenic mutations tend to increase the space and variability in the substrate binding site, as seen e.g. from the distance from catalytic aspartate to substrate cleavage sites. We suggest that we have identified the molecular cause of the “imprecise cleavage” that leads to two trimming pathways in γ-secretase, consistent with the FIST model, which may rationalize the experimental Aβ42/Aβ40 ratios as a molecular basis for fAD.