Human Truncated Tau Protein Research Articles

Viral Delivery of Non-Mutated Human Truncated Tau to Neurons Recapitulates Key Features of Human Tauopathy in Wild-Type Mice.

Neuronal accumulation of hyperphosphorylated and truncated tau aggregates is one of the major defining factors and key drivers of neurodegeneration in Alzheimer's disease and other tauopathies. We developed an AAV-induced model of tauopathy mediated by human truncated tau protein without familial frontotemporal dementia-related mutations to study tau propagation and the functional consequences of tau pathology. We performed targeted transductions of the hippocampus or entorhinal cortex in adult mice followed by histological analysis to study the progression of hippocampal tau pathology and tau spreading. We performed behavioral analysis of mice with AAV-induced hippocampal tau pathology. AAV-induced hippocampal tau pathology was characterized by tau hyperphosphorylation (AT8 positivity), sarkosyl insolubility, and the presence of neurofibrillary tangles. AAV-induced tau pathology was associated with microgliosis and hypertrophic astrocytes in the absence of cognitive deficits. Additionally, the co-expression of mCherry fluorescent protein and human truncated tau enabled us to detect both local spreading of human tau and spreading from the entorhinal cortex to the synaptically connected dentate gyrus. Targeted delivery of AAV with truncated tau protein into subcortical and cortical structures of mammalian brains represents an efficient approach for creating temporally and spatially well-defined tau pathology suitable for in vivo studies of tau propagation and neuronal circuit deficits in Alzheimer's disease.

Changes of Cerebrospinal Fluid Peptides due to Tauopathy.

Alzheimer's disease (AD) and progressive supranuclear palsy are two common neurodegenerative tauopathies, and the most common cause of progressive brain dementia in elderly affecting more than 35 million people. The tauopathies are characterized by abnormal deposition of microtubule associated protein tau into intracellular neurofibrillary tangles composed mainly of the hyperphosphorylated form of the protein. The diagnosis of tauopathies is based on the presence of clinical features and pathological changes. Over the last decade, there has been an intensive search for novel biochemical markers for clinical diagnosis of AD and other tauopathies. In the present study, we used transgenic rat model for tauopathy expressing human truncated tau protein (aa 151-391/4R) to analyze the cerebrospinal fluid (CSF) peptidome using liquid chromatography - matrix assisted laser desorption/ionization mass spectrometry (LC-MALDI TOF/TOF). From 345 peptides, we identified a total of 175 proteins. Among them, 17 proteins were significantly altered in the CSF of transgenic rats. The following proteins were elevated in the CSF of transgenic rats when compared to the control animals: neurofilament light and medium chain, apolipoprotein E, gamma-synuclein, chromogranin A, reticulon-4, secretogranin-2, calsyntein-1 and -3, endothelin-3, neuroendocrine protein B72A, alpha-1-macroglobulin, and augurin. Interestingly most of the identified proteins were previously linked to AD and other tauopathies, indicating the significance of transgenic animals in biomarker validation.

Brainstem pathology induces peripheral changes correlating with hippocampal markers of Alzheimer's disease in animal model

Alzheimer's disease (AD) and related tauopathies are difficult to diagnose in early phase and their diseases modifying treatment is still missing. Epidemiological studies indicate relationships between AD and level of leptin in blood. However, the mechanistic link behind this association is not yet defined. Here, we investigated the link between selected metabolic parameters including leptin and pathogenic markers of neurodegeneration in a transgenic rat model of AD.Brains of transgenic rats expressing human truncated tau protein, whose primary sequence was designed according to AD‐core tau protein, were analysed in pre‐symptomatic and terminal phase of disease. The data were correlated with biochemical parameters such as glucose, insulin and lipids in plasma. We found that development of AD pathology leads to reduction of body weight accompanied with significant decrease in level of plasma leptin in transgenic animal model of sporadic AD. The plasma leptin inversely and significantly correlates with amount of hippocampal tau proteins hyperphosphorylated on several AD‐specific epitopes. Moreover, the strong inverse correlation between the load of neurofibrillary pathology and peripheral levels of leptin was observed.We provide a molecular evidence and experimental confirmation for association of circulating leptin and early stage of neurofibrillary degeneration in hippocampus, thus leptin could serve as a convenient peripheral biomarker, which can help to recognize an early phase of neurodegeneration.This study was supported by research grants:Slovak research and development agency APVV‐0677‐12 and VEGA 2/0147/16

Immunomodulation of Memory-Impairing Protein Tau in Alzheimer’s Disease

Background: Neurodegeneration induced by misfolded tau protein and neuroinflammation represent the major hallmarks of human tauopathies including Alzheimer’s disease (AD). While tau driven neurodegeneration significantly correlates with disease progression, inflammation is considered to be an important factor regulating the resistance or susceptibility to AD. The emerging evidence suggests that the genes related to immunity can influence neurodegeneration. Objective: In order to determine the role of MHC class II in the tau neurofibrillary cascade, we generated and used transgenic lines expressing human truncated tau protein in either spontaneously hypertensive rat (SHR) or Wistar-Kyoto rat (WKY) genetic background. Methods: Brains of WKY and SHR transgenic rats and their age-matched nontransgenic littermates were examined by immunohistochemistry and RT-PCR. Results: Our results clearly showed that genetic background determined the inflammatory pattern (MHC class II) induced by tau neurodegenerative cascade in the transgenic rats expressing human misfolded truncated tau. Conclusion: Using two transgenic rat lines with different immunogenetic backgrounds, expressing the same transgene, we conclude that genetic background is a potent modifier of the type of the immune response induced by tau neurodegeneration.

Genetic background modifies neurodegeneration and neuroinflammation driven by misfolded human tau protein in rat model of tauopathy: implication for immunomodulatory approach to Alzheimer's disease

BackgroundNumerous epidemiological studies demonstrate that genetic background modifies the onset and the progression of Alzheimer's disease and related neurodegenerative disorders. The efficacious influence of genetic background on the disease pathway of amyloid beta has been meticulously described in rodent models. Since the impact of genetic modifiers on the neurodegenerative and neuroinflammatory cascade induced by misfolded tau protein is yet to be elucidated, we have addressed the issue by using transgenic lines expressing the same human truncated tau protein in either spontaneously hypertensive rat (SHR) or Wistar-Kyoto (WKY) genetic background.MethodsBrains of WKY and SHR transgenic rats in the terminal stage of phenotype and their age-matched non-transgenic littermates were examined by means of immunohistochemistry and unbiased stereology. Basic measures of tau-induced neurodegeneration (load of neurofibrillary tangles) and neuroinflammation (number of Iba1-positive microglia, their activated morphology, and numbers of microglia immunoreactive for MHCII and astrocytes immunoreactive for GFAP) were quantified with an optical fractionator in brain areas affected by neurofibrillary pathology (pons, medulla oblongata). The stereological data were evaluated using two-way ANOVA and Student's t-test.ResultsTau neurodegeneration (neurofibrillary tangles (NFTs), axonopathy) and neuroinflammation (microgliosis, astrocytosis) appeared in both WKY and SHR transgenic rats. Although identical levels of transgene expression in both lines were present, terminally-staged WKY transgenic rats displayed significantly lower final NFT loads than their SHR transgenic counterparts. Interestingly, microglial responses showed a striking difference between transgenic lines. Only 1.6% of microglia in SHR transgenic rats expressed MHCII in spite of having a robust phagocytic phenotype, whereas in WKY transgenic rats, 23.2% of microglia expressed MHCII despite displaying a considerably lower extent of transformation into phagocytic phenotype.ConclusionsThese results show that the immune response represents a pivotal and genetically variable modifying factor that is able to influence vulnerability to neurodegeneration. Therefore, targeted immunomodulation could represent a prospective therapeutic approach to Alzheimer's disease.

CSF phospho-tau correlates with behavioural decline and brain insoluble phospho-tau levels in a rat model of tauopathy

The aim of the present study was to identify the relationship between progressive neurobehavioural decline and phospho-tau levels (p-tau(181)) in the cerebrospinal fluid (CSF) and the brain in transgenic rats expressing human truncated tau protein. Behavioural analyses, as quantified using the NeuroScale scoring method, revealed that the transgenic rats fell into two main groups based on the baseline behavioural functioning: (1) mild neurobehavioural impairment (MNI, score 3.3-26) and (2) severe neurobehavioural impairment (SNI, score 36-44). SNI transgenic rats showed a significant increase in brain sarkosyl insoluble p-tau(181) when compared to their MNI counterparts. In order to determine whether CSF phospho-tau reflects the behavioural decline and increase in sarkosyl insoluble tau in the brain, p-tau(181) was measured in the CSF in a longitudinal study. The study showed a significant increase in CSF p-tau(181) during the progression of the disease from MNI to SNI. Moreover, increased levels of p-tau(181) in CSF correlated with an increase in the sarkosyl insoluble p-tau(181) levels in the brain. The increase in the CSF level of p-tau(181) during progressive behavioural decline suggests that it may represent a useful surrogate biomarker for preclinical drug development and a potential surrogate endpoint for clinical trials of disease-modifying therapy for Alzheimer's disease and related human tauopathies.

Expression of a Truncated Human Tau Protein Induces Aqueous-Phase Free Radicals in a Rat Model of Tauopathy: Implications for Targeted Antioxidative Therapy

Oxidative stress has been implicated in the pathogenesis of many neurodegenerative diseases including Alzheimer's disease (AD). We investigated the effect of a truncated form of the human tau protein in the neurons of transgenic rats. Using electron paramagnetic resonance we observed significantly increased accumulation of ascorbyl free radicals in brains of transgenic animals (up to 1.5-fold increase; P < 0.01). Examination of an in vitro model of cultured rat corticohippocampal neurons revealed that even relatively low level expression of human truncated tau protein (equal to 50% of endogenous tau) induced oxidative stress that resulted in increased depolarization of mitochondria (approximately 1.2-fold above control, P < 0.01) and increases in reactive oxygen species (approximately 1.3-fold above control, P < 0.001). We show that mitochondrial damage-associated oxidative stress is an early event in neurodegeneration. Furthermore, using two common antioxidants (vitamin C and E), we were able significantly eliminate tau-induced elevation of reactive oxygen species. Interestingly, vitamin C was found to be selective in the scavenging activity, suggesting that expression of truncated tau protein preferentially leads to increases in aqueous phase oxidants and free radicals such as hydrogen peroxide and hydroxyl and superoxide radicals. Our results suggest that antioxidant strategies designed to treat AD should focus on elimination of aqueous phase oxidants and free radicals.

Memantine prevents sensitivity to excitotoxic cell death of rat cortical neurons expressing human truncated tau protein.

We have previously shown that human misfolded tau proteins strongly perturb mitochondrial transport and induce accumulation of free radicals in neurons. This interference is underlying cause of increased susceptibility to oxidative stress and could be linked to excitotoxic pathways. In order to understand integral mechanisms of misfolded tau driven neurodegeneration, we have investigated the role of human truncated tau protein, derived from Alzheimer's disease, in rat cortical neurons under the conditions of excitotoxic stress induced by glutamate. We found that primary neurons expressing truncated tau protein are highly susceptible to glutamate-induced cell death. Pre-treatment with memantine (N-methyl-D-aspartate receptor antagonist) significantly improved survival of rat neurons exposed to glutamate and its effect was associated with overall decrease of reactive oxygen species (ROS) in both transgenic and nontransgenic neurons. Interestingly, despite of this overall effect, memantine was not able to decrease misfolded tau-induced ROS level specifically in transgenic cells. Our data suggest that memantine does not interfere with specific pathological pathways induced by misfolded tau protein nevertheless is able to attenuate oxidative stress in neurons.

P1-100: Neuronal loss is age-related and is not linked to massive neurofibrillary degeneration induced by expression of human truncated Tau protein in transgenic animals

P1-100: Neuronal loss is age-related and is not linked to massive neurofibrillary degeneration induced by expression of human truncated Tau protein in transgenic animals

Neurodegeneration caused by expression of human truncated tau leads to progressive neurobehavioural impairment in transgenic rats

Human truncated tau protein is an active constituent of the neurofibrillary degeneration in sporadic Alzheimer's disease. We have shown that modified tau protein, when expressed as a transgene in rats, induced AD characteristic tau cascade consisting of tau hyperphosphorylation, formation of argyrophilic tangles and sarcosyl-insoluble tau complexes. These pathological changes led to the functional impairment characterized by a variety of neurobehavioural symptoms. In the present study we have focused on the behavioural alterations induced by transgenic expression of human truncated tau. Transgenic rats underwent a battery of behavioural tests involving cognitive- and sensorimotor-dependent tasks accompanied with neurological assessment at the age of 4.5, 6 and 9 months. Behavioural examination of these rats showed altered spatial navigation in Morris water maze resulting in less time spent in target quadrant ( p < 0.05) and fewer crossings over previous platform position ( p < 0.05) during probe trial. Spontaneous locomotor activity and anxiety in open field was not influenced by transgene expression. However beam walking test revealed that transgenic rats developed progressive sensorimotor disturbances related to the age of tested animals. The disturbances were most pronounced at the age of 9 months ( p < 0.01). Neurological alterations indicating impaired reflex responses were other added features of behavioural phenotype of this novel transgenic rat. These results allow us to suggest that neurodegeneration, caused by the non-mutated human truncated tau derived from sporadic human AD, result in the neuronal dysfunction consequently leading to the progressive neurobehavioural impairment.

Expression of a truncated tau protein induces oxidative stress in a rodent model of tauopathy

Truncation of tau protein and oxidative stress have been implicated as important pathogenetic events in tauopathies including Alzheimer's disease (AD). We have generated a transgenic rat model that expresses a human truncated tau protein analogous to a variant form derived from sporadic AD. We employed this model to investigate the relationship between tau protein truncation and oxidative stress. We have found that rat cortical neurons (derived from transgenic animals) that had been cultured in vitro for 16 days showed an increased accumulation of reactive oxygen species (up to 1.4-fold increase; P < 0.01) when compared to neurons derived from nontransgenic control animals. Transgene-expressing neurons treated with inducers of oxidative stress, such as glucose oxidase (GO) and buthionine sulfoximine (BSO), displayed dramatically reduced survival (31.4 +/- 3.3 and 24.9 +/- 3.6%, respectively; both P < 0.001) compared to neurons from control animals (79.9 +/- 7.1%, survival following treatment with GO and to 98.2 +/- 3.8%, survival following treatment with BSO). The number of mitochondria in processes of neurons from transgenic animals was decreased by about one-third from that present in neurons from control animals. The results reveal that expression of a human truncated variant form of tau protein leads to the accumulation of reactive oxygen species and sensitizes rat cortical neurons to cell death induced by oxidative stress. This indicates that truncation of tau may precede oxidative stress in the pathogenesis of neurodegenerative diseases such as AD and other tauopathies. These findings may have implications for therapeutic strategies aiming at prevention of neurofibrillary degeneration and cognitive decline, and identify potential new targets for drug development.

P3-326: Expression of human truncated tau protein in long term culture of rat hippocampal neurons derived from Axon transgenic AD rat model

Truncated and hyperphosphorylated tau protein is one of the most important molecular and histopathological hallmarks found in Alzheimer‘s disease. Mutual occurrence of both events – truncation and hyperphosphorylation – is essential for disease progression and therefore transgenic models expressing non–mutated truncated tau could be successfully employed for detailed analysis of molecular pathways leading to neurodegeneration. To investigate the role of human truncated tau in neurofibrillary degeneration in long term rat primary hippocampal neuronal cultures. All experiments were performed using long–term hippocampal neuronal cultures prepared from transgenic rats expressing truncated human AlzTau. Neurons were cultured in vitro for 6–84 days (DIV). Distribution of AlzTau within the cell body and neurites was analyzed by staining with anti–human tau mAb – HT7. Tau protein phosphorylation at epitope 199/202,205 was detected with AT8 mAb. Pictures of neurons were taken at constant exposure times using confocal microscope (Olympus–Fluoview). Expression of transgenic human AlzTau in hippocampal neurons was observed from 6DIV. Intraneuronal AlzTau was not evenly distributed within the cell body and neurites. In the time period of 6th – 37th DIV AlzTau was present exclusively in bigger (wider) processes. However, on 52nd DIV it emerged also in peripheral neurites of neurons. Alzheimer‘s tau expression (gene dose dependent) pattern was enhanced in homozygous animals. Neurons derived from these animals displayed AlzTau in all neurites already on 25th DIV. Embryonic tau protein phosphorylation was detected up to 6th DIV in both, wild type and transgenic cultures. Strikingly AT–8 phosphorylation in transgenic neurons persisted up to 84 DIV. Detailed analysis of aged AT8 positive neurons (84DIV) showed the presence of granular and filamentous tau protein structures, localized within the cell bodies, suggesting early stage of NFT maturation. We have shown the expression pattern and intraneuronal distribution of human truncated tau protein in transgenic hippocampal neurons. Transgenic neuronal primary cultures (6 – 84 DIV) strongly suggest that truncated tau induced phosphorylation and formation of altered tau that leads to assembly into filamentous and granular structures.

Truncated tau from sporadic Alzheimer’s disease suffices to drive neurofibrillary degeneration in vivo

Truncated tau protein is the characteristic feature of human sporadic Alzheimer’s disease. We have identified truncated tau proteins conformationally different from normal healthy tau. Subpopulations of these structurally different tau species promoted abnormal microtubule assembly in vitro suggesting toxic gain of function. To validate pathological activity in vivo we expressed active form of human truncated tau protein as transgene, in the rat brain. Its neuronal expression led to the development of the neurofibrillary degeneration of Alzheimer’s type. Furthermore, biochemical analysis of neurofibrillary changes revealed that massive sarcosyl insoluble tau complexes consisted of human Alzheimer’s tau and endogenous rat tau in ratio 1:1 including characteristic Alzheimer’s disease (AD)-specific proteins (A68). This work represents first insight into the possible causative role of truncated tau in AD neurofibrillary degeneration in vivo.