Céline Heraud

Lithium Treatment Arrests the Development of Neurofibrillary Tangles in Mutant Tau Transgenic Mice with Advanced Neurofibrillary Pathology

Neurofibrillary tangles (NFTs) made of phosphorylated tau proteins are a key lesion of Alzheimers disease and other neurodegenerative diseases, and previous studies have indicated that lithium can decrease tau phosphorylation in tau transgenic models. In this study, we have reassessed the effectiveness of treatment per os with lithium on the prevention, the arrest, or the reversal of NFT development in a tau transgenic line (Tg30tau) developing severe neurofibrillary pathology in the brain and the spinal cord. Wild-type and Tgtau30 mice were treated per os with lithium carbonate or with natrium carbonate by chronic chow feeding for 8 months starting at the age of 3 months (to test for a preventive effect on NFT formation) or by oral gavage for 1 month starting at the age of 9 months (after development of NFTs). In mice treated by oral gavage, a decrease of tau phosphorylation and of Sarkosyl-insoluble aggregated tau was observed in the brain and in the spinal cord. The density of NFTs identified by Gallyas staining in the hippocampus and in the spinal cord was also significantly reduced and was similar to that observed at the beginning of the lithium treatment. In these animals, the level of brain beta-catenin was increased probably as a result of its stabilization by glycogen synthase kinase-3beta inhibition. Despite this inhibitory effect of lithium on NFT development, the motor and working memory deficits were not significantly rescued in these aged animals. Chronic chow feeding with lithium did not alter the development of NFT. Nevertheless, this study indicates that even a relatively short-term per os treatment leading to high blood concentration of lithium is effective in arresting the formation of NFTs in the hippocampus and the spinal cord of a tau transgenic model.

Lack of Tau Proteins Rescues Neuronal Cell Death and Decreases Amyloidogenic Processing of APP in APP/PS1 Mice.

Lack of tau expression has been reported to protect against excitotoxicity and to prevent memory deficits in mice expressing mutant amyloid precursor protein (APP) identified in familial Alzheimer disease. In APP mice, mutant presenilin 1 (PS1) enhances generation of Aβ42 and inhibits cell survival pathways. It is unknown whether the deficient phenotype induced by concomitant expression of mutant PS1 is rescued by absence of tau. In this study, we have analyzed the effect of tau deletion in mice expressing mutant APP and PS1. Although APP/PS1/tau(+/+) mice had a reduced survival, developed spatial memory deficits at 6 months and motor impairments at 12 months, these deficits were rescued in APP/PS1/tau(-/-) mice. Neuronal loss and synaptic loss in APP/PS1/tau(+/+) mice were rescued in the APP/PS1/tau(-/-) mice. The amyloid plaque burden was decreased by roughly 50% in the cortex and the spinal cord of the APP/PS1/tau(-/-) mice. The levels of soluble and insoluble Aβ40 and Aβ42, and the Aβ42/Aβ40 ratio were reduced in APP/PS1/tau(-/-) mice. Levels of phosphorylated APP, of β-C-terminal fragments (CTFs), and of β-secretase 1 (BACE1) were also reduced, suggesting that β-secretase cleavage of APP was reduced in APP/PS1/tau(-/-) mice. Our results indicate that tau deletion had a protective effect against amyloid induced toxicity even in the presence of mutant PS1 and reduced the production of Aβ.

Accelerated human mutant tau aggregation by knocking out murine tau in a transgenic mouse model.

Many models of human tauopathies have been generated in mice by expression of a human mutant tau with maintained expression of mouse endogenous tau. Because murine tau might interfere with the toxic effects of human mutant tau, we generated a model in which a pathogenic human tau protein is expressed in the absence of wild-type tau protein, with the aim of facilitating the study of the pathogenic role of the mutant tau and to reproduce more faithfully a human tauopathy. The Tg30 line is a tau transgenic mouse model overexpressing human 1N4R double-mutant tau (P301S and G272V) that develops Alzheimers disease-like neurofibrillary tangles in an age-dependent manner. By crossing Tg30 mice with mice invalidated for their endogenous tau gene, we obtained Tg30xtau(-/-) mice that express only exogenous human double-mutant 1N4R tau. Although Tg30xtau(-/-) mice express less tau protein compared with Tg30, they exhibit signs of decreased survival, increased proportion of sarkosyl-insoluble tau in the brain and in the spinal cord, increased number of Gallyas-positive neurofibrillary tangles in the hippocampus, increased number of inclusions in the spinal cord, and a more severe motor phenotype. Deletion of murine tau accelerated tau aggregation during aging of this mutant tau transgenic model, suggesting that murine tau could interfere with the development of tau pathology in transgenic models of human tauopathies.

Increased misfolding and truncation of tau in APP/PS1/tau transgenic mice compared to mutant tau mice.

Neurofibrillary degeneration in transgenic models of tauopathies has been observed to be enhanced when these models are crossed with transgenic models developing an Aβ pathology. The mechanisms leading to this enhanced tau pathology are not well understood. We have performed a detailed analysis of tau misprocessing in a new transgenic mouse model combining APP, PS1 and tau mutations (5xFAD×Tg30 mice) by comparison with littermates expressing only a FTD mutant tau (Tg30 mice). These 5xFAD×Tg30 mice showed a more severe deficient motor phenotype than Tg30 mice and developed with age a dramatically accelerated NFT load in the brain compared to Tg30 mice. Insoluble tau in 5xFAD×Tg30 mice compared to insoluble tau in Tg30 mice showed increased phosphorylation, enhanced misfolding and truncation changes mimicking more closely the post-translational changes characteristic of PHF-tau in Alzheimers disease. Endogenous wild-type mouse tau was recruited at much higher levels in insoluble tau in 5xFAD×Tg30 than in Tg30 mice. Extracellular amyloid load, Aβ40 and Aβ42, β-CTFs and β-CTF phosphorylation levels were lower in 5xFAD×Tg30 mice than in 5xFAD mice. Despite this reduction of Aβ, a significant hippocampal neuronal loss was observed in 5xFAD×Tg30 but not in 5xFAD mice indicating its closer association with increased tau pathology. This 5xFAD×Tg30 model thus mimics more faithfully tau pathology and neuronal loss observed in AD and suggests that additional post-translational changes in tau and self-recruitment of endogenous tau drive the enhanced tau pathology developing in the presence of Aβ pathology.

Rapamycin Ester Analog CCI-779/Temsirolimus Alleviates Tau Pathology and Improves Motor Deficit in Mutant Tau Transgenic Mice

Neurofibrillary tangles are intracellular inclusions made of tau protein that accumulates in neurons in Alzheimers disease (AD) and in other tauopathies. We have investigated the ability of the rapamycin ester CCI-779/Temsilorimus, a mTOR inhibitor with better stability and pharmacological properties compared to rapamycin, to interfere with the development of a motor phenotype and tau pathology in a mutant tau mouse model developing neurofibrillary tangles, by stimulation of mTOR dependent macroautophagy. Mutant tau mice (Tg30) were treated with CCI-779 before onset of motor signs for 7 months (from 5 to 12 months of age) or after the onset of motor signs for 2 months (from 10 to 12 months of age). End-point motor deficits were 50% lower in the group of Tg30 mice treated for 7 months. Inhibition of mTOR signaling and stimulation of macroautophagy in the brain of CCI-779 treated Tg30 mice was suggested by decreased phosphorylation of mTOR downstream signaling molecules p70S6 kinase and Akt and increased level of the autophagy markers Rab7 and LC3-II. CCI-779 treatment decreased the brain levels of Sarkosyl-insoluble tau and phosphotau inTg30 mice both after 2 months or 7 months of treatment. The density of neurofibrillary tangles was significantly decreased when treatment was started prior onset of motor signs. These results indicate that stimulation of mTOR dependent autophagy by CCI-779 compound is efficient to counteract the accumulation of abnormal tau when administered early or late in a tauopathy model and to improve a motor deficit when started before onset of motor signs.

Levels of kinesin light chain and dynein intermediate chain are reduced in the frontal cortex in Alzheimer's disease: implications for axoplasmic transport.

Fast anterograde and retrograde axoplasmic transports in neurons rely on the activity of molecular motors and are critical for maintenance of neuronal and synaptic functions. Disturbances of axoplasmic transport have been identified in Alzheimer’s disease and in animal models of this disease, but their mechanisms are not well understood. In this study we have investigated the distribution and the level of expression of kinesin light chains (KLCs) (responsible for binding of cargos during anterograde transport) and of dynein intermediate chain (DIC) (a component of the dynein complex during retrograde transport) in frontal cortex and cerebellar cortex of control subjects and Alzheimer’s disease patients. By immunoblotting, we found a significant decrease in the levels of expression of KLC1 and 2 and DIC in the frontal cortex, but not in the cerebellar cortex, of Alzheimer’s disease patients. A significant decrease in the levels of synaptophysin and of tubulin-β3 proteins, two neuronal markers, was also observed. KLC1 and DIC immunoreactivities did not co-localize with neurofibrillary tangles. The mean mRNA levels of KLC1, 2 and DIC were not significantly different between controls and AD patients. In SH-SY5Y neural cells, GSK-3β phosphorylated KLC1, a change associated to decreased association of KLC1 with its cargoes. Increased levels of active GSK-3β and of phosphorylated KLC1 were also observed in AD frontal cortex. We suggest that reduction of KLCs and DIC proteins in AD cortex results from both reduced expression and neuronal loss, and that these reductions and GSK-3β-mediated phosphorylation of KLC1 contribute to disturbances of axoplasmic flows and synaptic integrity in Alzheimer’s disease.

Deletion of murine tau gene increases tau aggregation in a human mutant tau transgenic mouse model.

We have reported previously a tau transgenic mouse model (Tg30tau) overexpressing human 4R1N double-mutant tau (P301S and G272V) and that develops AD (Alzheimers disease)-like NFTs (neurofibrillary tangles) in an age-dependent manner. Since murine tau might interfere with the toxic effects of human mutant tau, we set out to analyse the phenotype of our Tg30tau model in the absence of endogenous murine tau with the aim to reproduce more faithfully a model of human tauopathy. By crossing the Tg30tau line with TauKO (tau-knockout) mice, we have obtained a new mouse line called Tg30xTauKO that expresses only exogenous human double-mutant 4R1N tau. Whereas Tg30xTauKO mice express fewer tau proteins compared with Tg30tau, they exhibit augmented sarkosyl-insoluble tau in the brain and an increased number of Gallyas-positive NFTs in the hippocampus. Taken together, exclusion of murine tau causes accelerated tau aggregation during aging of this mutant tau transgenic model.

Vaccination with Sarkosyl insoluble PHF-tau decrease neurofibrillary tangles formation in aged tau transgenic mouse model: a pilot study.

Active immunization using tau phospho-peptides in tauopathy mouse models has been observed to reduce tau pathology, especially when given prior to the onset of pathology. Since tau aggregates in these models and in human tauopathies are composed of full-length tau with many post-translational modifications, and are composed of several tau isoforms in many of them, pathological tau proteins bearing all these post-translational modifications might prove to be optimal tau conformers to use as immunogens, especially in models with advanced tau pathology. To this aim, we immunized aged wild-type and mutant tau mice with preparations containing human paired helical filaments (PHF) emulsified in Alum-adjuvant. This immunization protocol with fibrillar PHF-tau was well tolerated and did not induce an inflammatory reaction in the brain or adverse effect in these aged mice. Mice immunized with four repeated injections developed anti-PHF-tau antibodies with rising titers that labeled human neurofibrillary tangles in situ. Immunized mutant tau mice had a lower density of hippocampal Gallyas-positive neurons. Brain levels of Sarkosyl-insoluble tau were also reduced in immunized mice. These results indicate that an immunization protocol using fibrillar PHF-tau proteins is an efficient and tolerated approach to reduce tau pathology in an aged tauopathy animal model.

Modulation of tau pathology in tau transgenic models.

NFTs (neurofibrillary tangles) in Alzheimers disease and in tauopathies are hallmark neuropathological lesions whose relationship with neuronal dysfunction, neuronal death and with other lesions [such as Abeta (amyloid beta-peptide) pathology] are still imperfectly understood. Many transgenic mice overexpressing wild-type or mutant tau proteins have been generated to investigate the physiopathology of tauopathies. Most of the mice overexpressing wild-type tau do not develop NFTs, but can develop a severe axonopathy, whereas overexpression of mutant tau leads to NFT formation, synaptic loss and neuronal death in several models. The association between neuronal death and NFTs has, however, been challenged in some models showing a dissociation between tau aggregation and tau toxicity. Cross-breeding of mice developing NFTs with mice developing Abeta deposits increases NFT pathology, highlighting the relationship between tau and amyloid pathology. On the other hand, tau expression seems to be necessary for expression of a pathological phenotype associated with amyloid pathology. These findings suggest that there is a bilateral cross-talk between Abeta and tau pathology. These observations are discussed by the presentation of some relevant models developed recently.

Identification of feline panleukopenia virus proteins expressed in Purkinje cell nuclei of cats with cerebellar hypoplasia.

Parvoviruses depend on initiation of host cell division for their replication. Undefined parvoviral proteins have been detected in Purkinje cells of the cerebellum after experimental feline panleukopenia virus (FPV) infection of neonatal kittens and in naturally occurring cases of feline cerebellar hypoplasia. In this study, a parvoviral protein in the nucleus of Purkinje cells of kittens with cerebellar hypoplasia was shown by immunoprecipitation to be the FPV viral capsid protein VP2. In PCR-confirmed, FPV-associated feline cerebellar hypoplasia, expression of the FPV VP2 protein was demonstrated by immunohistochemistry in Purkinje cell nuclei in 4/10 cases and expression of the FPV non-structural protein NS1 was demonstrated in Purkinje cell nuclei in 5/10 cases. Increased nuclear ERK1 expression was observed in several Purkinje cells in 1/10 kittens. No expression of the G1 and S mitotic phase marker proliferating cell nuclear antigen (PCNA) was evident in Purkinje cell nuclei. These results support the hypothesis that FPV is able to proceed far into its replication cycle in post-mitotic Purkinje cells.