Tau Tg Mice Research Articles

E2511, a novel small compound TrkA biased positive allosteric modulator, reinnervates cholinergic neuron and activates cholinergic functions in non‐clinical studies

AbstractBackgroundCholinergic innervation is particularly vulnerable in many neurodegenerative diseases associated with cognitive dysfunction, and loss of cholinergic neurons in Alzheimer’s disease (AD) is pathogenic event observed from early stage correlated with cognitive impairment. Nerve growth factor (NGF) plays a major role in the maintenance and function of cholinergic neurons, and a decrease in trophic signalling by NGF‐Tropomyosin receptor kinase A (TrkA) contributes to cholinergic neurodegeneration and cognitive decline during the course of AD. The activation of NGF‐induced trophic signal could be a promising therapy for the neurodegenerative diseases including AD, reinnervating and maintaining cholinergic neurons to functional status. E2511 was identified as a novel small compound TrkA biased positive allosteric modulator that can enhance specific trophic signal of NGF signal without induction of NGF‐like adverse effect via direct binding to TrkA in primary neuron culture and animal model. We present evidence that E2511 induced functional restoration of cholinergic neuron in animal model and rats.MethodThe trophic effect of E2511 on cholinergic neurons was assessed by biochemical studies such as western blotting and immunohistochemistry in human Tau P301S transgenic mice (Tau tg mice) following once‐daily oral administrations of E2511 for 3 months. E2511 TrkA downstream trophic effects on acetylcholine (ACh) were evaluated in cerebrospinal fluid (CSF) collected from cisterna magna in normal SD rats treated with once‐daily oral E2511 for 14 days, using an original LCMS method.ResultChronic administration of E2511 demonstrated reinnervative effects on cholinergic presynapses as well as a correlation with improvement of the number of cholinergic neurons in Tau tg mice. In SD rats, CSF ACh increased in a dose‐dependent manner at exposures associated with cholinergic reinnervation, with changes also correlating with increases in choline acetyltransferase mRNA level. These results suggest that CSF ACh may be a useful marker to establish the E2511 effective dose in humans.ConclusionE2511 functionally reinnervates cholinergic neuronal network in the Tau tg mice. CSF ACh increased in a dose‐related manner in SD rats. CSF ACh may be used as a pharmacodynamic marker to establish the dose showing the reinnervative effect of E2511 in clinical studies.

Monoclonal antibody Y01 prevents tauopathy progression induced by lysine 280-acetylated tau in cell and mouse models.

The spatiotemporal pattern of the spread of pathologically modified tau through brain regions in Alzheimer's disease (AD) can be explained by prion-like cell-to-cell seeding and propagation of misfolded tau aggregates. Hence, to develop targeted therapeutic antibodies, it is important to identify the seeding- and propagation-competent tau species. The hexapeptide 275VQIINK280 of tau is a critical region for tau aggregation, and K280 is acetylated in various tauopathies, including AD. However, the mechanism that links tau acetylated on lysine 280 (tau-acK280) to subsequent progression to neurodegenerative disease remains unclear. Here, we demonstrate that tau-acK280 is critical for tau propagation processes including secretion, aggregation, and seeding. We developed an antibody, Y01, that specifically targets tau-acK280 and solved the crystal structure of Y01 in complex with an acK280 peptide. The structure confirmed that Y01 directly recognizes acK280 and the surrounding residues. Strikingly, upon interaction with acetylated tau aggregates, Y01 prevented tauopathy progression and increased neuronal viability in neuron cultures and in tau-Tg mice through antibody-mediated neutralization and phagocytosis, respectively. Based on our observations that tau-acK280 is a core species involved in seeding and propagation activities, the Y01 antibody that specifically recognizes acK280 represents a promising therapeutic candidate for AD and other neurodegenerative diseases associated with tauopathy.

PS-B05-10: DIABETES MELLITUS AGGRAVATES BEHAVIORAL DEFICIT AND INCREASES SITE-SPECIFIC PHOSPHORYLATION OF TAU PROTEIN IN ALZHEIMER'S DISEASE MOUSE MODEL

Objective: Numerous epidemiological studies have demonstrated that vascular risk factors including diabetes mellitus (DM) increase the risk of developing Alzheimer's disease (AD). However, the mechanisms underlying the pathological relationship between DM and AD remain largely unknown. Tau is a microtubule-associated protein that is predominantly expressed in the axons of neurons. More than 80 residues of tau can be potentially phosphorylated. Accumulation of hyperphosphorylated tau protein plays a role in neurodegeneration and cognitive impairment in patients with AD. Here, we developed a unique diabetic AD mouse model and analyzed behavioral phenotypes and biochemical changes occurring in the brain to investigate the impact of DM on tau pathology. Design and method: Tau-tg and WT mice were fed with either normal chow diet (NCD; 12% kcal fat, n = 9) or high-fat diet (HFD; 60% kcal fat, n = 10) from the age of one and a half to nine months. Metabolic parameters and behavioral phenotypes were assessed at eight months of age. Mice were then sacrificed at nine months of age and brains were analyzed histologically and biochemically. A quantitative proteomic analysis of protein phosphorylation was performed using brain extracts of tau-tg mice. Results: Tau-tg mice fed with HFD (HFD tau-tg) showed severe obesity and hyperinsulinemia compared with tau-tg mice fed with NCD (NCD tau-tg) (p < 0.01), with slight elevation of plasma glucose levels. HFD tau-tg showed exacerbation of motor impairments and decrement of habituation to novel environment. Histological analysis showed a significant decrease in the number of neurons in HFD tau-tg compared to NCD tau-tg. The amount of aggregated form of phospho-tau (Ser396) was increased in HFD tau-tg brain. Comprehensive phosphoproteomic analysis identified 11 phosphosites of tau significantly hyperphosphorylated in the brain of HFD tau-tg (p < 0.05). Conclusions: These results suggest that diabetic conditions such as obesity and hyperinsulinemia with minimal hyperglycemia exacerbate behavioral deficits in AD via hyperphosphorylation of tau protein. We identified specific phosphosites of tau involved in pathological relationship between DM and AD.

E2511, a novel small compound TrkA allosteric modulator, induces a specific trophic signaling via direct binding to TrkA, and can reverse the loss of choline acetyltransferase (ChAT) positive neurons in transgenic models of AD

AbstractBackgroundLoss of cholinergic neurons in Alzheimer’s disease (AD) is an early pathogenic event correlated with cognitive impairment. Nerve growth factor (NGF) plays a major role in the maintenance and function of cholinergic neurons. Decrease in NGF‐Tropomyosin receptor kinase A (TrkA) induced trophic signaling contributes to cholinergic neurodegeneration and cognitive decline during the course of AD. The activation of the trophic signaling could be a promising therapy for AD, reinnervating basal forebrain cholinergic neurons. We provide evidence that our novel small compound E2511 is TrkA allosteric modulator showing an increase in specific trophic signaling via direct binding to TrkA.MethodE2511 was characterized in several in vitro assays such as NMR assay for detecting binding to TrkA and biochemical studies for evaluating the phosphorylation level of TrkA in each site using rat primary septal neurons. The in vivo effects of the compound on TrkA signaling were investigated in human Tau P301S transgenic mice (Tau tg mice) by biochemical studies such as western blot analysis, while assessing whether the compound induces hyperalgesia in behaviour studies and pain‐related signaling in normal and pain model rats. Moreover, the trophic effect of the compound on cholinergic neurons was investigated in Tau tg mice.ResultE2511 enhanced phosphorylation level of TrkA in the presence of NGF via direct binding to TrkA in rat primary neurons, and phosphorylation level of each site of TrkA induced by the compound was different from that of NGF. In vivo experiments demonstrated that oral administration of E2511 elevated trophic signaling in the septum, while induction of hyperalgesia was not detected. Furthermore, chronic administration of E2511 reversed the loss of ChAT‐positive cells in Tau tg mice by therapeutic treatment.ConclusionE2511 enhances specific trophic signaling by altering TrkA signaling as specific allosteric modulator via direct binding to TrkA, and E2511 shows the reinnervative effect on cholinergic neurons through activation of TrkA signaling without induction of NGF‐like adverse effect.

Exposure to 3-Nitropropionic Acid Mitochondrial Toxin Induces Tau Pathology in Tangle-Mouse Model and in Wild Type-Mice.

Oxidative stress, particularly of mitochondrial origin, plays an important role in the pathogenesis of neurodegenerative disorders, including Alzheimer’s disease (AD) and other tauopathies. Controversies regarding the responses of tau phosphorylation state to various stimuli causing oxidative stress have been reported. Here we investigated the effect of 3-nitropropionic acid (3NP), a mitochondrial toxin which induces oxidative stress, on the tangle-pathology in our previously generated double mutant (E257T/P301S, DM) -Tau-tg mice and in WT-mice. We detected an increase in tangle pathology in the hippocampus and cortex of the DM-Tau-tg mice following exposure of the mice to the toxin, as well as generation of tangles in WT-mice. This increase was accompanied with alterations in the level of the glycogen synthase kinase 3β (GSK3β), the kinase which phosphorylates the tau protein, and in the phosphorylation state of this kinase. A response of microglial cells was noticed. These results point to the involvement of mitochondrial dysfunction in the development of the tangle-pathology and may suggest that interfering with mitochondrial dysfunction may have an anti-tangle therapeutic potential.

The sterol regulatory element-binding protein 2 is dysregulated by tau alterations in Alzheimer disease.

Disturbed neuronal cholesterol homeostasis has been observed in Alzheimer disease (AD) and contributes to the pathogenesis of AD. As the master switch of cholesterol biosynthesis, the sterol regulatory element-binding protein 2 (SREBP-2) translocates to the nucleus after cleavage/activation, but its expression and activation have not been studied in AD which is the focus of the current study. We found both a significant decrease in the nuclear translocation of N-terminal SREBP-2 accompanied by a significant accumulation of C-terminal SREBP-2 in NFT-containing pyramidal neurons in AD. N-terminal- SREBP-2 is also found in dystrophic neurites around plaques in AD brain. Western blot confirmed a significantly reduced nuclear translocation of mature SREBP-2 (mSREBP-2) in AD brain. Interestingly, reduced nuclear mSREBP-2 was only found in animal models of tauopathies such as 3XTg AD mice and P301L Tau Tg mice but not in CRND8 APP transgenic mice, suggesting that tau alterations likely are involved in the changes of mSREBP-2 distribution and activation in AD. Altogether, our study demonstrated disturbed SREBP-2 signaling in AD and related models, and proved for the first time that tau alterations contribute to disturbed cholesterol homeostasis in AD likely through modulation of nuclear mSREBP-2 translocation.

Deregulation of neuronal miRNAs induced by amyloid-\u03b2 or TAU pathology

BackgroundDespite diverging levels of amyloid-β (Aβ) and TAU pathology, different mouse models, as well as sporadic AD patients show predictable patterns of episodic memory loss. MicroRNA (miRNA) deregulation is well established in AD brain but it is unclear whether Aβ or TAU pathology drives those alterations and whether miRNA changes contribute to cognitive decline.MethodsmiRNAseq was performed on cognitively intact (4 months) and impaired (10 months) male APPtg (APPswe/PS1L166P) and TAUtg (THY-Tau22) mice and their wild-type littermates (APPwt and TAUwt). We analyzed the hippocampi of 12 mice per experimental group (n = 96 in total), and employed a 2-way linear model to extract differentially expressed miRNAs. Results were confirmed by qPCR in a separate cohort of 4 M and 10 M APPtg and APPwt mice (n = 7–9 per group) and in human sporadic AD and non-demented control brain. Fluorescent in situ hybridization identified their cellular expression. Functional annotation of predicted targets was performed using GO enrichment. Behavior of wild-type mice was assessed after intracerebroventricular infusion of miRNA mimics.ResultsSix miRNAs (miR-10a-5p, miR-142a-5p, miR-146a-5p, miR-155-5p, miR-211-5p, miR-455-5p) are commonly upregulated between APPtg and TAUtg mice, and four of these (miR-142a-5p, miR-146a-5p, miR-155-5p and miR-455-5p) are altered in AD patients. All 6 miRNAs are strongly enriched in neurons. Upregulating these miRNAs in wild-type mice is however not causing AD-related cognitive disturbances.ConclusionDiverging AD-related neuropathologies induce common disturbances in the expression of neuronal miRNAs. 4 of these miRNAs are also upregulated in AD patients. Therefore these 4 miRNAs (miR-142a-5p, miR-146a-5p, miR-155-5p and miR-455-5p) appear part of a core pathological process in AD patients and APPtg and TAUtg mice. They are however not causing cognitive disturbances in wild-type mice. As some of these miRNA target AD relevant proteins, they may be, in contrast, part of a protective response in AD.

Anti-Tau Monoclonal Antibodies Derived from Soluble and Filamentous Tau Show Diverse Functional Properties in vitro and in vivo.

The tau spreading hypothesis provides rationale for passive immunization with an anti-tau monoclonal antibody to block seeding by extracellular tau aggregates as a disease-modifying strategy for the treatment of Alzheimer's disease (AD) and potentially other tauopathies. As the biochemical and biophysical properties of the tau species responsible for the spatio-temporal sequences of seeding events are poorly defined, it is not yet clear which epitope is preferred for obtaining optimal therapeutic efficacy. Our internal tau antibody collection has been generated by immunizations with different tau species: aggregated- and non-aggregated tau and human postmortem AD brain-derived tau fibrils. In this communication, we describe and characterize a set of these anti-tau antibodies for their biochemical and biophysical properties, including binding, tissue staining by immunohistochemistry, and epitope. The antibodies bound to different domains of the tau protein and some were demonstrated to be isoform-selective (PT18 and hTau56) or phospho-selective (PT84). Evaluation of the antibodies in cellular- and in vivo seeding assays revealed clear differences in maximal efficacy. Limited proteolysis experiments support the hypothesis that some epitopes are more exposed than others in the tau seeds. Moreover, antibody efficacy seems to depend on the structural properties of fibrils purified from tau Tg mice- and postmortem human AD brain.

ANTI-INFLAMMATORY EFFECT OF TSPO LIGAND IN MOUSE MODEL OF TAUOPATHY

The mitochondrial translocator protein (TSPO) is a sensitive marker of neuroinflammation, becoming markedly upregulated in activated astrocytes and microglia surrounding pathological lesions in the Alzheimer‘s brain. TSPO has also been identified as a potential therapeutic target, with pleiotropic anti-inflammatory and neuroprotective benefits of TSPO ligands described in multiple models of injury and neurodegenerative disease. Recently, we have demonstrated that the well characterized TSPO ligand, Ro5–4864, reduces beta amyloid accumulation and inflammation in a transgenic mouse model of beta-amyloidosis. Here, we evaluate the potential therapeutic effects of Ro5–4864 in a transgenic mouse model of tauopathy. The effects of the TSPO ligand, Ro5–4864, were examined on AD-related neuropathy and behavioral impairment in the rTg4510 transgenic model of tauopathy (tauTg). Inflammation and tau pathogenesis were assessed in vivo by [18F]FEBMP-PET for TSPO and [11C]PBB-3-PET for tau deposits respectively, and neuronal loss was measured in living mice by volumetric MRI. In vivo findings were confirmed by immunohistochemistry of brain sections from scanned mice. Learning and memory performance was assessed in the Y-maze and anxiety-related behavior was assessed in the elevated plus maze. Ro5–4864 improved functional outcomes and attenuated markers of inflammation in TauTg mice, in the absence of any benefit on tau pathogenesis or neuronal loss. These findings suggest that TSPO is a promising target for the development of immunomodulatory strategies for the management of AD.

Neurodegeneration Enhances the Development of Arthritis.

The prevalence of neurodegenerative disease and arthritis increases with age. Despite both processes being associated with immune activation and inflammation, little is known about the mechanistic interactions between neurodegenerative disease and arthritis. In this article, we show that tau-transgenic (tau-tg) mice that develop neurodegenerative disease characterized by deposition of tau tangles in the brain are highly susceptible to developing arthritis. Already at steady-state conditions, tau-tg mice exhibit peripheral immune activation that is manifested by higher numbers of granulocytes, plasmablasts, and inflammatory Ly6Chi CCR2+ monocytes, as well as increased levels of proinflammatory cytokines, such as TNF-α and IL-17. Upon induction of collagen-induced arthritis (CIA), tau-tg mice displayed an increased incidence and an earlier onset of CIA that was associated with a more pronounced inflammatory cytokine response. Furthermore, induction of CIA led to significantly elevated numbers of Iba-1-expressing cells in the brain, indicative of microglia activation, and the formation of anti-tau Abs in tau-tg mice. These changes were accompanied by the resolution of tau tangles and significantly decreased neurodegenerative pathology. In summary, these data show that neurodegenerative disease enhances the development of arthritis. In addition, arthritis, once induced, triggers innate immune responses in the brain, leading to resolution of neurodegenerative changes.

Cerebrolysin™ efficacy in a transgenic model of tauopathy: role in regulation of mitochondrial structure.

BackgroundAlzheimer’s Disease (AD) and Fronto temporal lobar dementia (FTLD) are common causes of dementia in the aging population for which limited therapeutical options are available. These disorders are associated with Tau accumulation. We have previously shown that CerebrolysinTM (CBL), a neuropeptide mixture with neurotrophic effects, ameliorates the behavioral deficits and neuropathological alterations in amyloid precursor protein (APP) transgenic (tg) mouse model of AD by reducing hyper-phosphorylated Tau. CBL has been tested in clinical trials for AD, however it’s potential beneficial effects in FTLD are unknown. For this purpose we sought to investigate the effects of CBL in a tg model of tauopathy. Accordingly, double tg mice expressing mutant Tau under the mThy-1 promoter and GSK3β (to enhance Tau phosphorylation) were treated with CBL and evaluated neuropathologically.ResultsCompared to single Tau tg mice the Tau/GSK3β double tg model displayed elevated levels of Tau phosphorylation and neurodegeneration in the hippocampus. CBL treatment reduced the levels of Tau phosphorylation in the dentate gyrus and the degeneration of pyramidal neurons in the temporal cortex and hippocampus of the Tau/GSK3β double tg mice. Interestingly, the Tau/GSK3β double tg mice also displayed elevated levels of Dynamin-related protein-1 (Drp-1), a protein that hydrolyzes GTP and is required for mitochondrial division. Ultrastructural analysis of the mitochondria in the Tau/GSK3β double tg mice demonstrated increased numbers and fragmentation of mitochondria in comparison to non-tg mice. CBL treatment normalized levels of Drp-1 and restored mitochondrial structure.ConclusionsThese results suggest that the ability of CBL to ameliorate neurodegenerative pathology in the tauopathy model may involve reducing accumulation of hyper-phosphorylated Tau and reducing alterations in mitochondrial biogenesis associated with Tau.

APOMORPHINE THERAPY FOR NEURONAL INSULIN RESISTANCE IN ALZHEIMER'S MICE

detected by immunoprecipitation and double-labeling immunofluorescence. Results: As oligomer, PrP c, Fyn, NMDA receptor, GSK3s, and phosphorylated tau were detected in lipid rafts of doubleTg mice. As oligomer-PrP c complex accumulated in lipid rafts. According with As oligomer accumulation, fyn, phosphorylated NMDA receptor, phosphorylated tau, and GSK3s increased in lipid rafts of double Tg mice compared to that of single tau Tg mice. Conclusions: These findings suggest that As oligomer-PrP c complex may induce Fyn, and phosphorylation of both NMDA receptor and tau in lipid rafts leading to neurodegeneration.

Neurofibrillary tangle formation by introducing wild-type human tau into APP transgenic mice

Senile plaques comprised of Aβ aggregates and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau filaments are the hallmarks of Alzheimer's disease (AD). A number of amyloid precursor protein (APP) transgenic (Tg) mice harboring APP mutations have been generated as animal models of AD. These mice successfully display amyloid plaque formation and subsequent tau hyperphosphorylation, but seldom induce NFT formations. We have demonstrated that the APPOSK-Tg mice, which possess the E693Δ (Osaka) mutation in APP and thereby accumulate Aβ oligomers without plaques, exhibit tau hyperphosphorylation at 8 months, but not NFT formation even at 24 months. We assumed that APP-Tg mice, including ours, failed to form NFTs because NFT formation requires human tau. To test this hypothesis, we crossbred APPOSK-Tg mice with tau-Tg mice (tau264), which express low levels of 3-repeat and 4-repeat wild-type human tau without any pathology. The resultant double Tg mice displayed tau hyperphosphorylation at 6 months and NFT formation at 18 months in the absence of tau mutations. Importantly, these NFTs contained both 3-repeat and 4-repeat human tau, similar to those in AD. Furthermore, the double Tg mice exhibited Aβ oligomer accumulation, synapse loss, and memory impairment at 6 months and neuronal loss at 18 months, all of which appeared earlier than in the parent APPOSK-Tg mice. These results suggest that Aβ and human tau synergistically interact to accelerate each other's pathology, that the presence of human tau is critical for NFT formation, and that Aβ oligomers can induce NFTs in the absence of amyloid plaques.

Accelerated Tau Aggregation, Apoptosis and Neurological Dysfunction Caused by Chronic Oral Administration of Aluminum in a Mouse Model of Tauopathies

To clarify whether long-term oral ingestion of aluminum (Al) can increase tau aggregation in mammals, we examined the effects of oral Al administration on tau accumulation, apoptosis in the central nervous system (CNS) and motor function using tau transgenic (Tg) mice that show very slowly progressive tau accumulation. Al-treated tau Tg mice had almost twice as many tau-positive inclusions in the spinal cord as tau Tg mice without Al treatment at 12 months of age, a difference that reached statistical significance, and the development of pretangle-like tau aggregates in the brain was also significantly advanced from 9 months. Al exposure did not induce any tau pathology in wild-type (WT) mice. Apoptosis was observed in the hippocampus in Al-treated tau Tg mice, but was virtually absent in the other experimental groups. Motor function as assessed by the tail suspension test was most severely impaired in Al-treated tau Tg mice. Given our results, chronic oral ingestion of Al may more strongly promote tau aggregation, apoptosis and neurological dysfunction if individuals already had a pathological process causing tau aggregation. These findings may also implicate chronic Al neurotoxicity in humans, who frequently have had mild tau pathology from a young age.

Tau-focused therapy and tau transmission: Implications for Alzheimer’s Disease and related tauopathies

Tau pathology is characteristic of Alzheimer’s disease (AD) and related tauopathies including Parkinson’s disease (PD) wherein a significant percentage of PD patients who develop dementia harbor AD-like tau pathology. Tau pathology is characterized by insoluble filamentous aggregates of hyperphosphorylated tau in CNS neurons known as neurofibrillary tangles (NFTs) and neuropil threads (NTs). NFTs and NTs are implicated in mechanisms of neurodegeneration through gains of toxic functions or losses of normal tau functions. Hyperphosphorylation and decreased solubility of tau leads to a loss of the ability of tau to bind to and stabilize microtubules (MTs) which impairs axonal transport and results in neuronal dysfunction and degeneration. This presentation describes the use of MT stabilizing drugs to counteract the loss of tau function and prevent/ameliorate tau mediated neurodegeneration in a transgenic (Tg) mouse model of an AD-like neurodegenerative tauopathy. Briefly, proof of concept prevention and intervention studies of the brain-penetrant MT-stabilizing agent epothilone D (EpoD) are described in young (prevention) and aged (intervention) P301S mutant tau Tg mice (PS 19 mice) with little (young PS 19 mice) or abundant tau pathology and behavioral impairments (aged PS19 mice). In the prevention and intervention studies, EpoD treatment reduced axonal dystrophy and increased axonal MT density which led to improved neuronal integrity and cognitive performance. EpoD treatment also improved fast axonal transport in the aged PS19 Tg mice. Unexpectedly, aged PS19 mice treated with EpoD showed a marked reduction in forebrain tau pathology and increased hippocampal neuronal integrity. There were no dose-limiting side effects in the EpoD treated young and aged PS19 mice. These studies support the view that EpoD and other brain-penetrant MT-stabilizing drugs offset the loss of tau function in neurodegenerative tauopathies and therefore are potential therapeutics for the treatment of AD and related tauopathies. Finally, a new seeded transmission model of tauopathy is presented using injections of preformed tau fibrils into the brains of PS19 mice which presents new opportunities to assess the efficacy of MT stabilizers and other potential passive immunization therapies for AD and related tauopathies. Supported by grants from the NINDS/NIA.

Brain-penetrant microtubule-stabilizing compounds as potential therapeutic agents for tauopathies

Neurons within the brains of those with AD (Alzheimer's disease) and related neurodegenerative disorders, collectively termed 'tauopathies', contain fibrillar inclusions composed of hyperphosphorylated tau protein. Tau is normally enriched in axons, where it binds and stabilizes MTs (microtubules). Tau hyperphosphorylation and aggregation probably result in reduced MT binding that could affect axonal transport and neuronal function. A possible therapeutic strategy to overcome a loss of tau function in tauopathies is administration of MT-stabilizing agents, such as those used in the treatment of cancer. However, these drugs elicit severe side effects, and most existing MT-stabilizing compounds have poor BBB (blood-brain barrier) permeability, which renders them unsuitable for tauopathy treatment. We identified EpoD (epothilone D) as a brain-penetrant MT-stabilizing agent with preferred pharmacokinetic and pharmacodynamic properties. EpoD was evaluated for its ability to compensate for tau loss-of-function in an established Tg (transgenic) mouse model, using both preventative and interventional dosing paradigms. EpoD at doses much lower than previously used in human cancer patients caused improved axonal MT density and decreased axonal dystrophy in the tau Tg mice, leading to an alleviation of cognitive deficits. Moreover, EpoD reduced the extent of tau pathology in aged tau Tg mice. Importantly, no adverse side effects were observed in the EpoD-treated mice. These results suggest that EpoD might be a viable drug candidate for the treatment of AD and related tauopathies.

Reduced secretagogin expression in the hippocampus of P301L tau transgenic mice

Neuropathological features in Alzheimer's Disease (AD) include the presence of hyperphosphorylated forms of the microtubule-associated tau protein (tau) in hippocampal neurones. Numerous studies indicate a neuroprotective effect of calcium-binding proteins (Ca2+ binding proteins) in neurodegenerative diseases (e.g., AD). Secretagogin is a newly described Ca2+ binding protein that is produced by pyramidal neurones of the human hippocampus. Recently, secretagogin expressing hippocampal neurones were demonstrated to resist tau-induced pathology in AD in contrast to the majority of neighbouring neurones. This suggested a neuroprotective effect of secretagogin in hippocampal neurones. Here, we investigated secretagogin expression in wild type (wt) mice as well as in hemizygous and homozygous P301L tau transgenic (tg) mice, which show pronounced and widespread tau pathology in hippocampal neurones. Secretagogin expression was analyzed at the immunohistochemical and biochemical levels in brains of age-matched wt and hemi- and homozygous tau tg mice. In wt mice hippocampal secretagogin-immunoreactive neurones were invariably detected, while immunoreactivity was much lower (P < 0.001) in tau tg mice. Of note, hippocampal secretagogin immunoreactivity was absent in 62.5% of homozygous tau tg mice. In line with this finding, Western blot analysis demonstrated a significant reduction in protein expression levels of secretagogin in homozygous tau tg compared to wt mice. Our results suggest that increased levels of tau negatively influence secretagogin expression in the hippocampus of tau tg mice.

Aggregation of Detergent-insoluble Tau Is Involved in Neuronal Loss but Not in Synaptic Loss

Neurofibrillary tangles (NFTs), which consist of highly phosphorylated tau, are hallmarks of neurodegenerative diseases including Alzheimer disease (AD). In neurodegenerative diseases, neuronal dysfunction due to neuronal loss and synaptic loss accompanies NFT formation, suggesting that a process associated with NFT formation may be involved in neuronal dysfunction. To clarify the relationship between the tau aggregation process and synapse and neuronal loss, we compared two lines of mice expressing human tau with or without an aggregation-prone P301L mutation. P301L tau transgenic (Tg) mice exhibited neuronal loss and produced sarcosyl-insoluble tau in old age but did not exhibit synaptic loss and memory impairment. By contrast, wild-type tau Tg mice neither exhibited neuronal loss nor produced sarcosyl-insoluble tau but did exhibit synaptic loss and memory impairment. Moreover, P301L tau was less phosphorylated than wild-type tau, suggesting that the tau phosphorylation state is involved in synaptic loss, whereas the tau aggregation state is involved in neuronal loss. Finally, increasing concentrations of insoluble tau aggregates leads to the formation of fibrillar tau, which causes NFTs to form.

3R tau expression modifies behavior in transgenic mice

Tauopathy is a group of disorders characterized by the accumulation of hyperphosphorylated tau protein in the brain, resulting in dementia. Here, tau-related behavior was evaluated in a mouse model with brain overexpression of the shortest human tau isoform (0N3R). Two groups of animals [tau-transgenic (tau-tg) and control littermates] were tested for learning and memory at 1 and 7 months. In the Morris water maze, all mice learned the task at 1 month of age and did not learn at 7 months. In contrast, at 7 months, the tau-tg animals demonstrated better retention of the passive avoidance response compared with their control littermates, which did not learn. In the open field test, no differences were measured between transgenic and nontransgenic young mice, but significantly higher locomotion was observed in the 7-month-old tau-tg mice compared with controls. Behavior during the elevated plus maze test was the same at 1 month, but at 7 months increased entrance to the different arms was observed in the tau-tg group. Tau expression and phosphorylation levels were analyzed at 8 months. In the subcortical brain region associated with passive avoidance behavior, the tau-tg mice demonstrated increased brain tau expression coupled with reduced relative phosphorylation. In contrast, increased tau expression and phosphorylation were measured in the cerebral cortex of the tau-tg mice. In conclusion, 7-8-month-old tau-tg mice overexpressing nonmutated 0N3R human tau isoform demonstrated enhanced behavior in the passive avoidance test, paralleled by relative tau hypophosphorylation in the subcortical brain region.

Amyloid precursor protein cytoplasmic domain with phospho-Thr668 accumulates in Alzheimer’s disease and its transgenic models: a role to mediate interaction of Aβ and tau

Abnormal accumulation of Abeta and tau in senile plaques (SP) and neurofibrillary tangles (NFTs) is a key event in Alzheimer's disease (AD). Here, we show that T668-phosphorylated cytoplasmic domain of APP (pT668-ACD) accumulates Abeta and tau in AD and its transgenic models. Anti-pT668 immunostaining of AD brain sections with hydrated autoclave enhancement identified SP neurites and NFTs in which pT668-ACD colocalizes with tau. We produced and examined transgenic (Tg) mice that overexpress human APP695, harboring the double Swedish/London mutation, and develop age-dependently Abeta plaques in the brain. All Abeta plaques contain co-accumulations of pT668-ACD, but co-accumulation of tau appears in only a fraction of Abeta plaques in older animals. We also examined the established tau Tg mice that overexpress the smallest human brain tau isoform and develop neuronal accumulations of tau in older animals. Examination of the old tau Tg mice showed that neuronal cells affected by tau accumulation induce co-accumulation of pT668-ACD. We speculate that in AD brains, extracellular Abeta deposition is accompanied by intracellular accumulation of pT668-ACD, followed by tau accumulation in the SP with dystrophic neurites and that neuronal cells affected by tau accumulation induce co-accumulation of pT668-ACD in NFTs. Thus, pT668-ACD is likely to mediate pathological interaction between Abeta and tau.