Age-dependent impairment of memory and neurofibrillary tangle formation and clearance in a mouse model of tauopathy.

Insoluble, fibrillar intraneuronal accumulation of the tau protein termed neurofibrillary tangles (NFTs), are characteristic hallmarks of Alzheimer's disease (AD). They play a significant role in the behavioral phenotypes of AD. Certain mice (rTg4510) constitutively express mutant human tau until transgene expression is inactivated by the administration of doxycycline (DOX). The present study aimed to determine the timing of the onset of memory impairment in rTg4510 mice and define the relationship between the extent of memory deficit and the duration of NFT overexpression. In 6-month-old (young) rTg4510 mice, both spatial memory and object recognition memory were impaired. These impairments were prevented by pre-treatment with DOX for 2 months. In parallel, the expression of NFTs decreased in the DOX-treated group. Ten-month-old (aged) rTg4510 mice showed severe impairments in memory performance. Pretreatment with DOX did not prevent these impairments. Increasing levels of NFTs were observed in aged rTg4510 mice. DOX treatment did not prevent tau pathology in aged rTg4510 mice. Expression of the autophagy markers LC3A and LC3B increased in rTg4510 mice, along with an increase in NFT formation. These results suggest that the clearance mechanisms of NFTs are impaired at 10 months of age.

Paucity of Entorhinal Cortex Pathology of the Alzheimer's Type in SuperAgers with Superior Memory Performance.

Advancing age is typically associated with declining memory capacity and increased risk of Alzheimer's disease (AD). Markers of AD such as amyloid plaques (AP) and neurofibrillary tangles (NFTs) are commonly found in the brains of cognitively average elderly but in more limited distribution than in those at the mild cognitive impairment and dementia stages of AD. Cognitive SuperAgers are individuals over age 80 who show superior memory capacity, at a level consistent with individuals 20-30 years their junior. Using a stereological approach, the current study quantitated the presence of AD markers in the memory-associated entorhinal cortex (ERC) of seven SuperAgers compared with six age-matched cognitively average normal control individuals. Amyloid plaques and NFTs were visualized using Thioflavin-S histofluorescence, 6E10, and PHF-1 immunohistochemistry. Unbiased stereological analysis revealed significantly more NFTs in ERC in cognitively average normal controls compared with SuperAgers (P < 0.05) by a difference of ~3-fold. There were no significant differences in plaque density. To highlight relative magnitude, cases with typical amnestic dementia of AD showed nearly 100 times more entorhinal NFTs than SuperAgers. The results suggest that resistance to age-related neurofibrillary degeneration in the ERC may be one factor contributing to preserved memory in SuperAgers.

Microglial activation correlates in vivo with both tau and amyloid in Alzheimer's disease.

Alzheimer's disease is characterized by the histopathological presence of amyloid-ß plaques and tau-containing neurofibrillary tangles. Microglial activation is also a recognized pathological component. The relationship between microglial activation and protein aggregation is still debated. We investigated the relationship between amyloid plaques, tau tangles and activated microglia using PET imaging. Fifty-one subjects (19 healthy controls, 16 mild cognitive impairment and 16 Alzheimer's disease subjects) participated in the study. All subjects had neuropsychometric testing, MRI, amyloid (18F-flutemetamol), and microglial (11C-PBR28) PET. All subjects with mild cognitive impairment and Alzheimer's disease and eight of the controls had tau (18F-AV1451) PET. 11C-PBR28 PET was analysed using Logan graphical analysis with an arterial plasma input function, while 18F-flutemetamol and 18F-AV1451 PET were analysed as target:cerebellar ratios to create parametric standardized uptake value ratio maps. Biological parametric mapping in the Statistical Parametric Mapping platform was used to examine correlations between uptake of tracers at a voxel-level. There were significant widespread clusters of positive correlation between levels of microglial activation and tau aggregation in both the mild cognitive impairment (amyloid-positive and amyloid-negative) and Alzheimer's disease subjects. The correlations were stronger in Alzheimer's disease than in mild cognitive impairment, suggesting that these pathologies increase together as disease progresses. Levels of microglial activation and amyloid deposition were also correlated, although in a different spatial distribution; correlations were stronger in mild cognitive impairment than Alzheimer's subjects, in line with a plateauing of amyloid load with disease progression. Clusters of positive correlations between microglial activation and protein aggregation often targeted similar areas of association cortex, indicating that all three processes are present in specific vulnerable brain areas. For the first time using PET imaging, we show that microglial activation can correlate with both tau aggregation and amyloid deposition. This confirms the complex relationship between these processes. These results suggest that preventative treatment for Alzheimer's disease should target all three processes.

Degradation or aggregation: the ramifications of post-translational modifications on tau.

Tau protein is encoded in the microtubule-associated protein tau (MAPT) gene and contributes to the stability of microtubules in axons. Despite of its basic isoelectric point and high solubility, tau is often found in intraneuronal filamentous inclusions such as paired helical filaments (PHFs), which are the primary constituent of neurofibrillary tangles (NFTs). This pathological feature is the nosological entity termed "tauopathies" which notably include Alzheimer's disease (AD). A proteinaceous signature of all tauopathies is hyperphosphorylation of the accumulated tau, which has been extensively studied as a major pharmacological target for AD therapy. However, in addition to phosphorylation events, tau undergoes a number of diverse posttranslational modifications (PTMs) which appear to be controlled by complex crosstalk. It remains to be elucidated which of the PTMs or their combinations have pro-aggregation or anti-aggregation properties. In this review, we outline the consequences of and communications between several key PTMs of tau, such as acetylation, phosphorylation, and ubiquitination, focusing on their roles in aggregation and degradation. We place emphasis on the structure of tau protofilaments from the human AD brain, which may be good targets to modulate etiological PTMs which cause tau aggregation. [BMB Reports 2018; 51(6): 265-273].

The Involvement of Post-Translational Modifications in Alzheimer's Disease.

BACKGROUND: Alzheimer's disease (AD) is a neurodegenerative disorder recognized as the most common cause of chronic dementia among the ageing population. AD is histopathologically characterized by progressive loss of neurons and deposits of insoluble proteins, primarily composed of amyloid-ß pelaques and neurofibrillary tangles (NFTs). METHODS: Several molecular processes contribute to the formation of AD cellular hallmarks. Among them, post-translational modifications (PTMs) represent an attractive mechanism underlying the formation of covalent bonds between chemical groups/peptides to target proteins, which ultimately result modified in their function. Most of the proteins related to AD undergo PTMs. Several recent studies show that AD-related proteins like APP, Aß, tau, BACE1 undergo post-translational modifications. The effect of PTMs contributes to the normal function of cells, although aberrant protein modification, which may depend on many factors, can drive the onset or support the development of AD. RESULTS: Here we will discuss the effect of several PTMs on the functionality of AD-related proteins potentially contributing to the development of AD pathology. CONCLUSION: We will consider the role of Ubiquitination, Phosphorylation, SUMOylation, Acetylation and Nitrosylation on specific AD-related proteins and, more interestingly, the possible interactions that may occur between such different PTMs.

Variations in Acetylcholinesterase Activity within Human Cortical Pyramidal Neurons Across Age and Cognitive Trajectories.

We described an extensive network of cortical pyramidal neurons in the human brain with abundant acetylcholinesterase (AChE) activity. Emergence of these neurons during childhood/adolescence, attainment of highest density in early adulthood, and virtual absence in other species led us to hypothesize involvement of AChE within these neurons in higher cortical functions. The current study quantified the density and staining intensity of these neurons using histochemical procedures. Few faintly stained AChE-positive cortical pyramidal neurons were observed in children/adolescents. These neurons attained their highest density and staining intensity in young adulthood. Compared with the young adult group, brains of cognitively normal elderly displayed no significant change in numerical density but a significant decrease in staining intensity of AChE-positive cortical pyramidal neurons. Brains of elderly above age 80 with unusually preserved memory performance (SuperAgers) showed significantly lower staining intensity and density of these neurons when compared with same-age peers. Conceivably, low levels of AChE activity could enhance the impact of acetylcholine on pyramidal neurons to counterbalance other involutional factors that mediate the decline of memory capacity during average aging. We cannot yet tell if elderly with superior memory capacity have constitutively low neuronal AChE levels or if this feature reflects adaptive neuroplasticity.

Tau and neurodegenerative disease: the story so far.

In 1975, tau protein was isolated as a microtubule-associated factor from the porcine brain. In the previous year, a paired helical filament (PHF) protein had been identified in neurofibrillary tangles in the brains of individuals with Alzheimer disease (AD), but it was not until 1986 that the PHF protein and tau were discovered to be one and the same. In the AD brain, tau was found to be abnormally hyperphosphorylated, and it inhibited rather than promoted in vitro microtubule assembly. Almost 80 disease-causing exonic missense and intronic silent mutations in the tau gene have been found in familial cases of frontotemporal dementia but, to date, no such mutation has been found in AD. The first phase I clinical trial of an active tau immunization vaccine in patients with AD was recently completed. Assays for tau levels in cerebrospinal fluid and plasma are now available, and tau radiotracers for PET are under development. In this article, we provide an overview of the pivotal discoveries in the tau research field over the past 40 years. We also review the current status of the field, including disease mechanisms and therapeutic approaches.

Vulnerability of calbindin, calretinin and parvalbumin in a transgenic/knock-in APPswe/PS1dE9 mouse model of Alzheimer disease together with disruption of hippocampal neurogenesis.

The pathogenesis of Alzheimer disease (AD) is characterized by accumulation of ß-amyloid protein in the brain (in both soluble and insoluble forms) and by the presence of intracellular neurofibrillary tangles (NFTs), leading to neurotoxicity. The exact mechanisms whereby Aß triggers brain alterations are unclear. However, accumulating evidence suggests that a deregulation of Ca(2+) signaling may play a major role in disease progression. Calcium-buffering proteins, including calbindin-D28K (CB), calretinin (CR) and parvalbumin (PV), may offer neuroprotection by maintaining calcium homeostasis. Although marked reductions in these proteins have been observed in the brains of mice and humans with AD, their contribution to AD pathology remains unclear. The aim of the present study was to analyze distribution patterns of CB(+,) CR(+) and PV(+) interneurons in different areas of the hippocampus, a brain region that is severely affected in AD. A transgenic knock-in APPswe/PS1dE9 mouse model of familial AD was used. The data were obtained from the brains of 3- and 12-month-old animals. These ages roughly correspond to an early mature adult (prior to clinical manifestations) and a late middle-age (clinical symptoms readily detectable) phase in human AD patients. Immunostaining revealed increases in CB and PV immunoreactivity (IR) in the hippocampus of 3-month-old transgenic mice, compared to wild-type animals. Possibly, these proteins are upregulated in an attempt to control cellular homeostasis and synaptic plasticity. However, the pattern of CB-IR was reversed in 12-month-old animals, potentially indicating a loss of cellular capacity to respond to pathophysiological processes. In addition, at this age, a noticeable increase in PV-IR was observed, suggesting the presence of hippocampal network hyperactivity in older AD-like mice. Our results indicate that CaBP(+) neuronal subpopulations play a role in adult neurogenesis and in AD pathology, particularly at early disease stages, suggesting that these neurons may serve as potential predictors of future AD in non-demented individuals.

Senescence may mediate conversion of tau phosphorylation-induced apoptotic escape to neurodegeneration.

Neurodegeneration is the characteristic pathology in the brains of Alzheimer's disease (AD). However, the nature and molecular mechanism leading to the degeneration are not clarified. Given that only the neurons filled with neurofibrillary tangles survive to the end stage of the disease and the major component of the tangles is the hyperphosphorylated tau proteins, it is conceivable that tau hyperphosphorylation must play a crucial role in AD neurodegeneration. We have demonstrated that tau hyperphosphorylation renders the cells more resistant to the acute apoptosis. The molecular mechanisms involve substrate competition of tau and ß-catenin for glycogen synthase kinase 3ß (GSK-3ß); activation of Akt; preservation of Bcl-2 and suppression of Bax, cytosolic cytochrome-c, and caspase-3 activity; and upregulation of unfolded protein response (UPR), i.e., up-regulating phosphorylation of PERK, eIF2 and IRE1 with an increased cleavage of ATF6 and ATF4. On the other hand, tau hyperphosphorylation promotes its intracellular accumulation and disrupts axonal transport; hyperphosphorylated tau also impairs cholinergic function and inhibits proteasome activity. These findings indicate that tau hyperphosphorylation and its intracellular accumulation play dual role in the evolution of AD. We speculate that transient tau phosphorylation helps cells abort from an acute apoptosis, while persistent tau hyperphosphorylation/accumulation may trigger cell senescence that eventually causes a chronic neurodegeneration. Therefore, the nature of "AD neurodegeneration" may represent a new type of tau-regulated chronic neuron death; and the stage of cell senescence may provide a broad window for the intervention of AD.

Distinct chronology of neuronal cell cycle re-entry and tau pathology in the 3xTg-AD mouse model and Alzheimer's disease patients.

Cell cycle re-entry in Alzheimer's disease (AD) has emerged as an important pathological mechanism in the progression of the disease. This appearance of cell cycle related proteins has been linked to tau pathology in AD, but the causal and temporal relationship between the two is not completely clear. In this study, we found that hyperphosphorylated retinoblastoma protein (ppRb), a key regulator for G1/S transition, is correlated with a late marker for hyperphosphorylation of tau but not with other early markers for tau alteration in the 3xTg-AD mouse model. However, in AD brains, ppRb can colocalize with both early and later markers for tau alterations, and can often be found singly in many degenerating neurons, indicating the distinct development of pathology between the 3xTg-AD mouse model and human AD patients. The conclusions of this study are two-fold. First, our findings clearly demonstrate the pathological link between the aberrant cell cycle re-entry and tau pathology. Second, the chronological pattern of cell cycle re-entry with tau pathology in the 3xTg-AD mouse is different compared to AD patients suggesting the distinct pathogenic mechanism between the animal AD model and human AD patients.

Deciphering the mechanism underlying late-onset Alzheimer disease.

Despite tremendous investments in understanding the complex molecular mechanisms underlying Alzheimer disease (AD), recent clinical trials have failed to show efficacy. A potential problem underlying these failures is the assumption that the molecular mechanism mediating the genetically determined form of the disease is identical to the one resulting in late-onset AD. Here, we integrate experimental evidence outside the 'spotlight' of the genetic drivers of amyloid-ß (Aß) generation published during the past two decades, and present a mechanistic explanation for the pathophysiological changes that characterize late-onset AD. We propose that chronic inflammatory conditions cause dysregulation of mechanisms to clear misfolded or damaged neuronal proteins that accumulate with age, and concomitantly lead to tau-associated impairments of axonal integrity and transport. Such changes have several neuropathological consequences: focal accumulation of mitochondria, resulting in metabolic impairments; induction of axonal swelling and leakage, followed by destabilization of synaptic contacts; deposition of amyloid precursor protein in swollen neurites, and generation of aggregation-prone peptides; further tau hyperphosphorylation, ultimately resulting in neurofibrillary tangle formation and neuronal death. The proposed sequence of events provides a link between Aß and tau-related neuropathology, and underscores the concept that degenerating neurites represent a cause rather than a consequence of Aß accumulation in late-onset AD.

Molecular approaches to the treatment, prophylaxis, and diagnosis of Alzheimer's disease: tangle formation, amyloid-ß, and microglia in Alzheimer's disease.

Pathological hallmarks of Alzheimer's disease (AD) include senile plaques, neurofibrillary tangles (NFTs), synaptic loss, and neurodegeneration. Senile plaques are composed of amyloid-ß (Aß) and are surrounded by microglia, a primary immune effector cell in the central nervous system. NFTs are formed by the intraneuronal accumulation of hyperphosphorylated tau, and progressive synaptic and neuronal losses closely correlate with cognitive deficits in AD. Studies on responsible genes of familial AD and temporal patterns of pathological changes in brains of patients with Down's syndrome (Trisomy 21), who invariably develop neuropathology of AD, have suggested that Aß accumulation is a primary event that influences other AD pathologies. Although details of the interaction between AD pathologies remain unclear, experimental evidences to discuss this issue have been accumulated. In this paper, we review and discuss recent findings that link the AD pathologies to each other. Further studies on the interaction between pathologies induced in AD brain may contribute to provide deep insight into the pathogenesis of AD and to develop novel therapeutic, prophylactic, and early diagnostic strategies for AD.

Neuropathological alterations in Alzheimer disease.

The neuropathological hallmarks of Alzheimer disease (AD) include "positive" lesions such as amyloid plaques and cerebral amyloid angiopathy, neurofibrillary tangles, and glial responses, and "negative" lesions such as neuronal and synaptic loss. Despite their inherently cross-sectional nature, postmortem studies have enabled the staging of the progression of both amyloid and tangle pathologies, and, consequently, the development of diagnostic criteria that are now used worldwide. In addition, clinicopathological correlation studies have been crucial to generate hypotheses about the pathophysiology of the disease, by establishing that there is a continuum between "normal" aging and AD dementia, and that the amyloid plaque build-up occurs primarily before the onset of cognitive deficits, while neurofibrillary tangles, neuron loss, and particularly synaptic loss, parallel the progression of cognitive decline. Importantly, these cross-sectional neuropathological data have been largely validated by longitudinal in vivo studies using modern imaging biomarkers such as amyloid PET and volumetric MRI.

[Significance of tau in the development of Alzheimer's disease].

Based on the amyloid hypothesis, studies on for Alzheimer disease (AD) therapy mostly focus on elimination of beta-amyloid. However, results of recent studies on amyloid immunotherapy suggest that it may not be sufficient to target only beta-amyloid for AD therapy. Neurofibrillary tangles (NFTs), which contain hyperphosphorylated tau are the other pathological hallmark of AD; clinical progression of NFTs is from the entorhinal cortex to the limbic cortex, and neocortex. In a brain region showing NFTs, synapse loss and neuronal loss were observed; this suggests the possibility that NFT formation is involved in brain dysfunction because of synapse loss and neuronal loss. In the process of NFT formation, tau formed different aggregation species- tau oligomers, granules, and fibrils. From the analysis of different human tau-expressing mouse lines, soluble hyperphosphorylated tau, including the tau oligomer, was found to be involved in synapse loss; and granular tau formation was also found to be involved in neuronal loss. Therefore, inhibition of tau aggregation and tau phosphorylation is expected to prevent synapse loss and neuron loss, which may halt progressive dementia in AD.

Alzheimer's disease neurofibrillary degeneration: pivotal and multifactorial.

Independent of the aetiology, AD (Alzheimer's disease) neurofibrillary degeneration of abnormally hyperphosphorylated tau, a hallmark of AD and related tauopathies, is apparently required for the clinical expression of the disease and hence is a major therapeutic target for drug development. However, AD is multifactorial and heterogeneous and probably involves several different aetiopathogenic mechanisms. On the basis of CSF (cerebrospinal fluid) levels of Abeta(1-42) (where Abeta is amyloid beta-peptide), tau and ubiquitin, five different subgroups, each with its own clinical profile, have been identified. A successful development of rational therapeutic disease-modifying drugs for AD will require understanding of the different aetiopathogenic mechanisms involved and stratification of AD patients by different disease subgroups in clinical trials. We have identified a novel aetiopathogenic mechanism of AD which is initiated by the cleavage of SET, also known as inhibitor-2 (I(2)(PP2A)) of PP2A (protein phosphatase 2A) at Asn(175) into N-terminal (I(2NTF)) and C-terminal (I(2CTF)) halves and their translocation from the neuronal nucleus to the cytoplasm. AAV1 (adeno-associated virus 1)-induced expression of I(2CTF) in rat brain induces inhibition of PP2A activity, abnormal hyperphosphorylation of tau, neurodegeneration and cognitive impairment in rats. Restoration of PP2A activity by inhibition of the cleavage of I(2)(PP2A)/SET offers a promising therapeutic opportunity in AD with this aetiopathogenic mechanism.

Structural and functional changes in tau mutant mice neurons are not linked to the presence of NFTs.

In the rTg4510 mouse model, expression of the mutant human tau variant P301L leads to development of neurofibrillary tangles (NFTs), neuronal death, and memory impairment, reminiscent of the pathology observed in human tauopathies. In the present study, we examined the effects of mutant tau expression on the electrophysiology and morphology of individual neurons using whole-cell patch-clamp recordings and biocytin filling of pyramidal cells in cortical slices prepared from rTg4510 (TG) and wild-type (WT) littermate mice. Among the TG cells, 42% contained a clear Thioflavin-S positive inclusion in the soma and were categorized as NFT positive (NFT+), while 58% had no discernable inclusion and were categorized as NFT negative (NFT-). The resting membrane potential (V(r)) was significantly depolarized (+8 mV) in TG cells, and as a consequence, evoked repetitive action potential (AP) firing rates were also significantly increased. Further, single APs were significantly shorter in duration in TG cells and the depolarizing voltage deflection or "sag" evoked by hyperpolarization was significantly greater in amplitude. In addition to these functional electrophysiological changes, TG cells exhibited significant morphological alterations, including loss or significant atrophy of the apical tuft, reduced dendritic complexity and length, and reduced spine density. Importantly, NFT- and NFT+ TG cells were indistinguishable with regard to both morphological and electrophysiological properties. Our observations show that expression of mutated tau results in significant structural and functional changes in neurons, but that these changes occur independent of mature NFT formation.

Does Alzheimer's disease begin in the brainstem?

Although substantial evidence indicates that the progression of pathological changes of the neuronal cytoskeleton is crucial in determining the severity of dementia in Alzheimer's disease (AD), the exact causes and evolution of these changes, the initial site at which they begin, and the neuronal susceptibility levels for their development are poorly understood. The current clinical criteria for diagnosis of AD are focused mostly on cognitive deficits produced by dysfunction of hippocampal and high-order neocortical areas, whereas noncognitive, behavioural and psychological symptoms of dementia such as disturbances in mood, emotion, appetite, and wake-sleep cycle, confusion, agitation and depression have been less considered. The early occurrence of these symptoms suggests brainstem involvement, and more specifically of the serotonergic nuclei. In spite of the fact that the Braak and Braak staging system and National Institutes of Aging - Reagan Institute (NIA-RI) criteria do not include their evaluation, several recent reports drew attention to the possibility of selective and early involvement of raphe nuclei, particularly the dorsal raphe nucleus (DRN), in the pathogenesis of AD. Based on these findings of differential susceptibility and anatomical connectivity, a novel pathogenetic scheme of AD progression was proposed. Although the precise mechanisms of neurofibrillary degeneration still await elucidation, we speculated that cumulative oxidative damage may be the main cause of DRN alterations, as the age is the main risk factor for sporadic AD. Within such a framework, beta-amyloid production is considered only as one of the factors (although a significant one in familial cases) that promotes molecular series of events underlying AD-related neuropathological changes.

Tangle-bearing neurons survive despite disruption of membrane integrity in a mouse model of tauopathy.

Neurofibrillary tangles (NFTs) are associated with neuronal loss and correlate with cognitive impairment in Alzheimer disease, but how NFTs relate to neuronal death is not clear. We studied cell death in Tg4510 mice that reversibly express P301L mutant human tau and accumulate NFTs using in vivo multiphoton imaging of neurofibrillary pathology, propidium iodide (PI) incorporation into cells, caspase activation, and DNA labeling. We first observed that in live mice, a minority of neurons were labeled with the caspase probe or with PI fluorescence. These markers of cell stress were localized in the same cells and appeared specifically within NFT-bearing neurons. Contrary to expectations, the PI-stained neurons did not die during a day of observation; the presence of Hoechst-positive nuclei in them on the subsequent day indicated that the NFT-associated membrane disruption, as suggested by PI staining, and caspase activation do not lead to immediate death of neurons in this tauopathy model. This unique combination of in vivo multiphoton imaging with markers of cell death and pathological alteration is a powerful tool for investigating neuronal damage associated with neurofibrillary pathology.

Neurofibrillary and neurodegenerative pathology in APP-transgenic mice injected with AAV2-mutant TAU: neuroprotective effects of Cerebrolysin.

Alzheimer's disease (AD) continues to be the most common cause of cognitive and motor alterations in the aging population. Accumulation of amyloid beta (Abeta)-protein oligomers and the microtubule associated protein-TAU might be responsible for the neurological damage. We have previously shown that Cerebrolysin (CBL) reduces the synaptic and behavioral deficits in amyloid precursor protein (APP) transgenic (tg) mice by decreasing APP phosphorylation via modulation of glycogen synthase kinase-3beta (GSK3beta) and cyclin-dependent kinase-5 (CDK5) activity. These kinases also regulate TAU phosphorylation and are involved in promoting neurofibrillary pathology. In order to investigate the neuroprotective effects of CBL on TAU pathology, a new model for neurofibrillary alterations was developed using somatic gene transfer with adeno-associated virus (AAV2)-mutant (mut) TAU (P301L). The Thy1-APP tg mice (3 m/o) received bilateral injections of AAV2-mutTAU or AAV2-GFP, into the hippocampus. After 3 months, compared to non-tg controls, in APP tg mice intra-hippocampal injections with AAV2-mutTAU resulted in localized increased accumulation of phosphorylated TAU and neurodegeneration. Compared with vehicle controls, treatment with CBL in APP tg injected with AAV2-mutTAU resulted in a significant decrease in the levels of TAU phosphorylation at critical sites dependent on GSK3beta and CDK5 activity. This was accompanied by amelioration of the neurodegenerative alterations in the hippocampus. This study supports the concept that the neuroprotective effects of CBL may involve the reduction of TAU phosphorylation by regulating kinase activity.