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Concept: Tau protein

382

In recent years consumption of canola oil has increased due to lower cost compared with olive oil and the perception that it shares its health benefits. However, no data are available on the effect of canola oil intake on Alzheimer’s disease (AD) pathogenesis. Herein, we investigated the effect of chronic daily consumption of canola oil on the phenotype of a mouse model of AD that develops both plaques and tangles (3xTg). To this end mice received either regular chow or a chow diet supplemented with canola oil for 6 months. At this time point we found that chronic exposure to the canola-rich diet resulted in a significant increase in body weight and impairments in their working memory together with decrease levels of post-synaptic density protein-95, a marker of synaptic integrity, and an increase in the ratio of insoluble Aβ 42/40. No significant changes were observed in tau phosphorylation and neuroinflammation. Taken together, our findings do not support a beneficial effect of chronic canola oil consumption on two important aspects of AD pathophysiology which includes memory impairments as well as synaptic integrity. While more studies are needed, our data do not justify the current trend aimed at replacing olive oil with canola oil.

Concepts: Alzheimer's disease, Neuron, Fatty acid, Neurology, Ratio, Semantic memory, Tau protein, Alois Alzheimer

174

Filamentous inclusions made of hyperphosphorylated tau are characteristic of numerous human neurodegenerative diseases, including Alzheimer’s disease, tangle-only dementia, Pick disease, argyrophilic grain disease (AGD), progressive supranuclear palsy, and corticobasal degeneration. In Alzheimer’s disease and AGD, it has been shown that filamentous tau appears to spread in a stereotypic manner as the disease progresses. We previously demonstrated that the injection of brain extracts from human mutant P301S tau-expressing transgenic mice into the brains of mice transgenic for wild-type human tau (line ALZ17) resulted in the assembly of wild-type human tau into filaments and the spreading of tau inclusions from the injection sites to anatomically connected brain regions. Here we injected brain extracts from humans who had died with various tauopathies into the hippocampus and cerebral cortex of ALZ17 mice. Argyrophilic tau inclusions formed in all cases and following the injection of the corresponding brain extracts, we recapitulated the hallmark lesions of AGD, PSP and CBD. Similar inclusions also formed after intracerebral injection of brain homogenates from human tauopathies into nontransgenic mice. Moreover, the induced formation of tau aggregates could be propagated between mouse brains. These findings suggest that once tau aggregates have formed in discrete brain areas, they become self-propagating and spread in a prion-like manner.

Concepts: Alzheimer's disease, Brain, Cerebral cortex, Neurodegenerative disorders, Dementia, Progressive supranuclear palsy, Tau protein, Tauopathy

46

Reduced bone mineral density (BMD) and its clinical sequelae, osteoporosis, occur at a much greater rate the rate in patients with Alzheimer’s disease (AD), often emerging early in the disease before significant cognitive decline is seen. Reduced BMD translates to increased bone fracture risk, decreased quality of life, and increased mortality for AD patients. However, the mechanism responsible for this observation is unclear. We hypothesize that bone loss is an additional component of an AD prodrome, changes that emerge prior to dementia and are mediated by dysfunction of the central serotonergic pathways. We characterized the skeletal phenotype of htau mice that express human forms of the microtubule-associated protein tau that become pathologically hyperphosphorylated in AD. Using radiographic densitometry, we measured BMD in female and male htau mice from 2-6 months of age-time-points prior to the presence of significant tauopathy in the hippocampal/entorhinal regions characteristic of this model. We found a significantly reduced BMD phenotype in htau mice that was most pronounced in males. Using western blotting and immunofluorescence, we showed overall reduced tryptophan hydroxylase (TPH) protein in htau brainstem and a 70% reduction in TPH-positive cells in the dorsal raphe nucleus (DRN)-a pivotal structure in the regulation of the adult skeleton. Elevations of hyperphosphorylated tau (ptau) proteins were also measured in brainstem, and co-labeled immunofluorescence studies showed presence of ptau in TPH-positive cells of the DRN as early as 4 months of age in htau mice. Together, these findings demonstrate that reduced BMD occurs earlier than overt degeneration in a tau-based AD model and that pathological changes in the tau phosphorylation occur in the serotonin-producing neurons of the brainstem raphe in these mice. This illuminates a need to define a mechanistic relationship between bone loss and serotonergic deficits in early AD.

Concepts: Alzheimer's disease, Osteoporosis, Gene, Bone density, Skeletal system, Serotonin, Skeleton, Tau protein

46

A central question in Alzheimer’s Disease (AD) is whether the neuritic plaque is necessary and sufficient for the development of tau pathology. Hyperphosphorylation of tau is found within dystrophic neurites surrounding β-amyloid deposits in AD mouse models but the pathological conversion of tau is absent. Likewise, expression of a human tau repeat domain in mice is insufficient to drive the pathological conversion of tau. Here we developed an Aβ-amyloidosis mouse model that expresses the human tau repeat domain and show that in these mice, the neuritic plaque facilitates the pathological conversion of wild-type tau. We show that this tau fragment seeds the neuritic plaque-dependent pathological conversion of wild-type tau that spreads from the cortex and hippocampus to the brain stem. These results establish that in addition to the neuritic plaque, a second determinant is required to drive the conversion of wild-type tau.

Concepts: Alzheimer's disease, Neuron, Gene, Brain, Semantic memory, Mice, Necessary and sufficient condition, Tau protein

28

The main objective of the present study was to establish whether the mixed σ1/muscarinic ligand ANAVEX2-73, shown to be neuroprotective in AD models in vivo (Villard et al, 2011) and currently in clinical phase I/IIa, could have the ability to reduce the appearance of hyperphosphorylated Tau and Aβ1-42 in the Aβ25-35 mouse model of AD. We therefore first confirmed that Aβ25-35 injection induced hyperphosphorylation of Tau protein, by showing that it rapidly decreased Akt activity and activated GSK-3β in the mouse hippocampus. Second, we showed that the kinase activation, and resulting Tau alteration, directly contributed to the amyloid toxicity, since co-administration of the selective GSK-3β inhibitor Tibpo blocked both Tau phosphorylation and Aβ25-35-induced memory impairments. Third, we analyzed the ANAVEX2-73 effect on Tau phosphorylation and activation of the related kinase pathways (Akt and GSK-3β). And fourth, we also addressed the impact of the drug on Aβ25-35-induced Aβ1-42 seeding and observed that the compound significantly blocked the increase in Aβ1-42 and C99 levels in the hippocampus, suggesting that it may alleviate amyloid load in AD models. The comparison with PRE-084, a selective and reference σ1 receptor agonist, and xanomeline, a muscarinic ligand presenting similar profile as ANAVEX2-73 on M1 and M2 subtypes, confirmed that both muscarinic and σ1 targets are involved in the ANAVEX2-73 effects. The drug, acting synergistically on both targets, but with moderate affinity, presents a promising pharmacological profile.Neuropsychopharmacology accepted article preview online, 14 March 2013; doi:10.1038/npp.2013.70.

Concepts: Alzheimer's disease, Pharmacology, Signal transduction, Receptor, Receptor antagonist, Agonist, Inverse agonist, Tau protein

28

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder characterized by progressive memory deficits and other cognitive disturbances. Neuropathologically, AD is characterized by the progressive loss of basal forebrain cholinergic neurons that innervate the hippocampus and cortex and the abnormal extracellular accumulation of amyloid-β and intracellular tau protein. Current research on AD is focused on the mechanisms underlying the abnormal oligomerization, fibrillation, and accumulation of the amyloid-β and tau proteins, mechanisms that may alter the dynamics of this accumulation and on experimental therapeutics approaches aimed at the clearance of the abnormally folded proteins and other potentially neuroprotective interventions. This review will summarize the main areas of investigation in AD and present ways forward for future work.

Concepts: Alzheimer's disease, Brain, Neurology, Acetylcholine, Tau protein, Basal forebrain, Tauopathy, Proteopathy

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To evaluate18F-AV-1451 tau-PET binding among microtubule-associated protein tau (MAPT) mutation carriers.

Concepts: Proteins, Molecular biology, Tau protein

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The accumulation of amyloidogenic proteins is a pathological hallmark of neurodegenerative disorders. The aberrant accumulation of the microtubule associating protein tau (MAPT, tau) into toxic oligomers and amyloid deposits is a primary pathology in tauopathies, the most common of which is Alzheimer’s disease (AD). Intrinsically disordered proteins, like tau, are enriched with proline residues that regulate both secondary structure and aggregation propensity. The orientation of proline residues is regulated by cis/trans peptidyl-prolyl isomerases (PPIases). Here we show that cyclophilin 40 (CyP40), a PPIase, dissolves tau amyloids in vitro. Additionally, CyP40 ameliorated silver-positive and oligomeric tau species in a mouse model of tau accumulation, preserving neuronal health and cognition. Nuclear magnetic resonance (NMR) revealed that CyP40 interacts with tau at sites rich in proline residues. CyP40 was also able to interact with and disaggregate other aggregating proteins that contain prolines. Moreover, CyP40 lacking PPIase activity prevented its capacity for disaggregation in vitro. Finally, we describe a unique structural property of CyP40 that may permit disaggregation to occur in an energy-independent manner. This study identifies a novel human protein disaggregase and, for the first time, demonstrates its capacity to dissolve intracellular amyloids.

Concepts: Alzheimer's disease, Protein, Nuclear magnetic resonance, Prion, Amyloid, Quaternary structure, Beta sheet, Tau protein

25

Chronic traumatic encephalopathy (CTE) is a tauopathy associated with prior exposure to repetitive head impacts, such as those incurred through American football and other collision sports. Diagnosis is made through neuropathological examination. Many of the clinical features of CTE are common in the general population, with and without a history of head impact exposure, making clinical diagnosis difficult. As is now common in the diagnosis of other neurodegenerative disorders, such as Alzheimer’s disease, there is a need for methods to diagnose CTE during life through objective biomarkers.

Concepts: Alzheimer's disease, Greek loanwords, Neurology, Neurodegenerative disorders, Dementia, Tau protein, Tauopathy, Proteopathy

25

Neuronal inclusions of hyperphosphorylated and aggregated tau protein are a pathological hallmark of several neurodegenerative tauopathies, including Alzheimer’s disease (AD). The hypothesis of tau transmission in AD has emerged from histopathological studies of the spatial and temporal progression of tau pathology in postmortem patient brains. Increasing evidence in cellular and animal models supports the phenomenon of intercellular spreading of tau. However, the molecular and cellular mechanisms of pathogenic tau transmission remain unknown. The studies described herein investigate tau pathology propagation using human neurons derived from induced pluripotent stem cells. Neurons were seeded with full-length human tau monomers and oligomers and chronic effects on neuronal viability and function were examined over time. Tau oligomer-treated neurons exhibited an increase in aggregated and phosphorylated pathological tau. These effects were associated with neurite retraction, loss of synapses, aberrant calcium homeostasis, and imbalanced neurotransmitter release. In contrast, tau monomer treatment did not produce any measureable changes. This work supports the hypothesis that tau oligomers are toxic species that can drive the spread of tau pathology and neurodegeneration.

Concepts: Alzheimer's disease, Neuron, Pathology, Stem cell, Cell biology, Action potential, Acetylcholine, Tau protein