Mutant Tau knock-in mice display frontotemporal dementia relevant behaviour and histopathology

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Histological and Behavioral Phenotypes of a Novel Mutated APP Knock-In Mouse

Funding sources KP was funded by a donation from Roemex Ltd (Mr. R. Simcox) to BP and GR. The project was in part supported by the Alzheimer’s Research UK (ARUK) Scotland network and by an Alzheimer’s Society project grant (AS-PG-14-039) to BP and GR.Peer reviewedPostprin

Mutant Tau knock-in mice display frontotemporal dementia relevant behaviour and histopathology

Models of Tau pathology related to frontotemporal dementia (FTD) are essential to determine underlying neurodegenerative pathologies and resulting tauopathy relevant behavioural changes. However, existing models are often limited in their translational value due to Tau overexpression, and the frequent occurrence of motor deficits which prevent comprehensive behavioural assessments. In order to address these limitations, a forebrain-specific (CaMKIIα promoter), human mutated Tau (hTauP301L + R406W) knock-in mouse was generated out of the previously characterised PLB1Triple mouse, and named PLB2Tau. After confirmation of an additional hTau species (~60 kDa) in forebrain samples, we identified age-dependent progressive Tau phosphorylation which coincided with the emergence of FTD relevant behavioural traits. In line with the non-cognitive symptomatology of FTD, PLB2Tau mice demonstrated early emerging (~6 months) phenotypes of heightened anxiety in the elevated plus maze, depressive/apathetic behaviour in a sucrose preference test and generally reduced exploratory activity in the absence of motor impairments. Investigations of cognitive performance indicated prominent dysfunctions in semantic memory, as assessed by social transmission of food preference, and in behavioural flexibility during spatial reversal learning in a home cage corner-learning task. Spatial learning was only mildly affected and task-specific, with impairments at 12 months of age in the corner learning but not in the water maze task. Electroencephalographic (EEG) investigations indicated a vigilance-stage specific loss of alpha power during wakefulness at both parietal and prefrontal recording sites, and site-specific EEG changes during non-rapid eye movement sleep (prefrontal) and rapid eye movement sleep (parietal). Further investigation of hippocampal electrophysiology conducted in slice preparations indicated a modest reduction in efficacy of synaptic transmission in the absence of altered synaptic plasticity. Together, our data demonstrate that the transgenic PLB2Tau mouse model presents with a striking behavioural and physiological face validity relevant for FTD, driven by the low level expression of mutant FTD hTau.</p

Abnormal cognition, sleep, eeg and brain metabolism in a novel knock-in alzheimer mouse, plb1

Late-stage neuropathological hallmarks of Alzheimer's disease (AD) are β-amyloid (βA) and hyperphosphorylated tau peptides, aggregated into plaques and tangles, respectively. Corresponding phenotypes have been mimicked in existing transgenic mice, however, the translational value of aggressive over-expression has recently been questioned. As controlled gene expression may offer animal models with better predictive validity, we set out to design a transgenic mouse model that circumvents complications arising from pronuclear injection and massive over-expression, by targeted insertion of human mutated amyloid and tau transgenes, under the forebrain- and neurone-specific CaMKIIα promoter, termed PLB1 Double. Crossing with an existing presenilin 1 line resulted in PLB1 Triple mice. PLB1 Triple mice presented with stable gene expression and age-related pathology of intra-neuronal amyloid and hyperphosphorylated tau in hippocampus and cortex from 6 months onwards. At this early stage, pre-clinical 18FDG PET/CT imaging revealed cortical hypometabolism with increased metabolic activity in basal forebrain and ventral midbrain. Quantitative EEG analyses yielded heightened delta power during wakefulness and REM sleep, and time in wakefulness was already reliably enhanced at 6 months of age. These anomalies were paralleled by impairments in long-term and short-term hippocampal plasticity and preceded cognitive deficits in recognition memory, spatial learning, and sleep fragmentation all emerging at ~12 months. These data suggest that prodromal AD phenotypes can be successfully modelled in transgenic mice devoid of fibrillary plaque or tangle development. PLB1 Triple mice progress from a mild (MCI-like) state to a more comprehensive AD-relevant phenotype, which are accessible using translational tools such as wireless EEG and microPET/CT.</p

Abnormal cognition, sleep, EEG and brain metabolism in a novel knock-in Alzheimer mouse, PLB1

Peer reviewedPublisher PD

New viral and transgenic models of Alzheimer's disease

Mutated human genes associated with human neurodegenerative conditions were used to develop both in vitro and in vivo models to study cellular pathology and disease progression. The in vitro models employed adenoviral vectors for the gene delivery into primary rat hippocampal neurones. Introduction of both APP and Tau transgenes reduced neuronal viability, with the latter leading to accelerated toxicity and faster onset of cell death. Time-lapsing imaging analyses revealed apoptosis-like features for APP-positive neurones, while Tau-positive neuronal death appeared more necrotic. Interestingly, a direct correlation between cell death and protein content in the APP-transduced neurones was not confirmed. A comparison between viral gene delivery and electroporation with the same transgenic constructs confirmed the cellular toxicity of APP and Tau but also showed that with a lower amount of transgene expressing cells per culture dish Tau-induced toxicity was no longer as aggressive as with the viral model. Therefore, electroporation may allow single-cell investigations of functional parameters whereas the large amount of transgene-positive neurones in viral transductions allows faster quantification of cell death. These methods complement each other and thus offer in vitro models suitable for mechanistic studies and drug screening. Accordingly, initial testing of inhibitors of Tau aggregation and amyloid formation were found to ameliorate the transgene-induced damage as proof of principle for our novel in vitro models. Further testing revealed caffeine to be a very promising drug candidate in AD treatment, since it improved viability in both APP and Tau transduced neurones. The transgenic PLB1 mouse knock-in model harbours the same mutated APP and Tau genes as the viral models. A triple transgenic line (PLB1Triple) has been generated with additional mutated presenilin 1 for increased APP processing and accelerated pathology. The mRNA expression of both APP and Tau transgenes was stable over the investigated time (6 and 12 months) with about 2 to 3-fold higher APP over Tau mRNA levels. This expression was specific to the forebrain and negligible in the cerebellum and thus targets a brain region that is vulnerable in AD. The model showed progressive accumulation of AD-linked histopathological features as well as memory- and activity-related symptoms. This low transgene expression in conjunction with a progressive phenotype is advantageous over other aggressive animals models for studying early disease-related pathology.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Age-dependent changes in hippocampal synaptic transmission and plasticity in the PLB1_Triple Alzheimer mouse

Several genetically engineered models exist that mimic aspects of the pathological and cognitive hallmarks of Alzheimer's disease (AD). Here we report on a novel mouse model generated by targeted knock-in of transgenes containing mutated human amyloid precursor protein (APP) and microtubule-associated protein tau genes, inserted into the HPRT locus and controlled by the CaMKIIα regulatory element. These mice were crossed with an asymptomatic presenilin1A246E overexpressing line to generate PLB1 Triple mice. Gene expression analysis and in situ hybridization confirmed stable, forebrain-specific, and gene-dose-dependent transgene expression. Brain tissue harvested from homozygous, heterozygous, and wild-type cohorts aged between 3 and 24 months was analyzed immunohistochemically and electrophysiologically. Homozygous PLB1Triple offspring presented with mostly intracellular cortical and hippocampal human APP/amyloid, first detected reliably at 6 months. Human tau was already uncovered at 3 months (phospho-tau at 6 months) and labeling intensifying progressively with age. Gene-dose dependence was confirmed in age-matched heterozygous females that accumulated less tau and amyloid protein. General excitability of hippocampal neurones was not altered in slices from PLB1Triple mice up to 12 months, but 2-year-old homozygous PLB1Triple mice had smaller synaptically evoked postsynaptic potentials compared with wild types. Synaptic plasticity (paired-pulse depression/facilitation and long-term potentiation) of synaptic CA1 pyramidal cell responses was deficient from 6 months of age. Long-term depression was not affected at any age or in any genotype. Therefore, despite comparatively subtle gene expression and protein build-up, PLB1 Triple mice develop age-dependent progressive phenotypes, suggesting that aggressive protein accumulation is not necessary to reconstruct endophenotypes of AD.</p