Ginsenoside Rf inhibits human tau proteotoxicity and causes specific LncRNA, miRNA and mRNA expression changes in Caenorhabditis elegans model of tauopathy.

Under pathological conditions, human tau (htau) hyperphosphorylation promotes formation of proteotoxic intracellular amyloid aggregates that may underlie neurodegenerative diseases known as tauopathies, prompting researchers to develop treatments that inhibit htau aggregation as a promising therapeutic strategy. Ginsenosides, the main active constituents of Panax ginseng C. A. Meyer (ginseng), appear to inhibit tau aggregation and disassociation in tauopathy models, although their active components and molecular mechanisms are unknown. Here, we used a novel Caenorhabditis elegans (C. elegans) tauopathy model to identify ginsenoside monomers which may repress htau proteotoxicity. Our findings indicated that ginsenoside Rf prevented tau aggregation and reversed abnormal tau aggregation-induced phenotypes and alleviated neurodegeneration in worms. Notably, deep RNA-seq analysis of ginsenoside Rf-treated and untreated worms with tauopathy revealed that ginsenoside Rf altered expression levels of 24 up- and 36 down-regulated lncRNA transcripts, 32 up- and 22 down-regulated miRNAs and 65 up- and 30 down-regulated mRNA transcripts. Based on GO and KEGG pathway annotation analyses, identified mRNAs, miRNAs and lncRNAs-associated gene targets were functionally related to neuron-related terms (e.g., neuron development, axon and motor neuron axon guidance) and longevity regulating pathways. Importantly, RT-qRCR results suggested that 6 miRNAs (miR-786, miR-2208b, miR-34, miR-241, miR-247 and miR-4805), 8 lncRNAs (MSTRG.20812.2, MSTRG.22617.2, MSTRG.28210.13, MSTRG.5728.12, MSTRG.29708.1, MSTRG.3342.25, MSTRG.3342.31 and MSTRG.8841.8) and 7 mRNAs (nas-33, math-28, T14B4.19, col-17, rol-6, sqt-1 and irg-4) were potential targets of ginsenoside Rf inhibition of tauopathy. These results partially explain mechanisms underlying ginsenoside Rf-associated alleviation of htau proteotoxicity and will guide future strategies to discover potential therapeutic targets for preventing and alleviating tauopathies.

Neurotherapeutic effect of Hyptis spp. leaf extracts in Caenorhabditis elegans models of tauopathy and polyglutamine disease: Role of the glutathione redox cycle.

Hyptis suaveolens (HS), Hyptis pectinata (HP) and Hyptis marrubioides (HM) are plants used in folk medicine for treatment of several diseases. Here, we tested the in vivo antioxidant and neuroprotective potential of methanolic extracts from these plants, containing several rosmarinic acid derivatives and isoquercetin. In C. elegans, HS, HP and HM leaf extracts enhanced the antioxidant responses through the induction of specific antioxidant enzymes and demonstrated neurotherapeutic potential in transgenic models of genetically determined human neurodegenerative diseases - Frontotemporal dementia with parkinsonism linked to chromosome 17 and Machado-Joseph disease. Chronic treatment of disease models with HS, HP and HM leaf extracts improved the animals' motor function and increased their tolerance to an oxidative insult. The restorative effect of HM extract in motor performance of both disease models required the presence of glutathione reductase (gsr-1), an enzyme that assures the glutathione redox cycle, highlighting the role of this pathway and unveiling a common candidate therapeutic target for these diseases. Our findings strengthen the relevance of plant-derived bioactive compound discovery for neurodegenerative disorders that remain without effective treatment.

Cornel Iridoid Glycoside Suppresses Hyperactivity Phenotype in rTg4510 Mice through Reducing Tau Pathology and Improving Synaptic Dysfunction.

rTg4510 mice are transgenic mice expressing P301L mutant tau and have been developed as an animal model of tauopathies including Alzheimer's disease (AD). Besides cognitive impairments, rTg4510 mice also show abnormal hyperactivity behavior. Cornel iridoid glycoside (CIG) is an active ingredient extracted from Cornus officinalis, a traditional Chinese herb. The purpose of the present study was to investigate the effects of CIG on the emotional disorders such as hyperactivity, and related mechanisms. The emotional hyperactivity was detected by locomotor activity test and Y maze test. Immunofluorescent and immunohistochemical analyses were conducted to measure neuron loss and phosphorylated tau. Western blotting was used to detect the expression of related proteins. The results showed that intragastric administration of CIG for 3 months decreased the hyperactivity phenotype, prevented neuronal loss, reduced tau hyperphosphorylation and aggregation in the amygdala of rTg4510 mice. Meanwhile, CIG alleviated the synaptic dysfunction by increasing the expression of N-methyl-D-aspartate receptors (NMDARs) subunits GluN1 and GluN2A and αamino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) subunits GluA1 and GluA2, and increased the level of phosphorylated Ca2+/calmodulin dependent protein kinase II α (p-CaMK IIα) in the brain of rTg4510 mice. In conclusion, CIG may have potential to treat the emotional disorders in tauopathies such as AD through reducing tau pathology and improving synaptic dysfunction.

Microglia drive APOE-dependent neurodegeneration in a tauopathy mouse model.

Chronic activation of brain innate immunity is a prominent feature of Alzheimer's disease (AD) and primary tauopathies. However, to what degree innate immunity contributes to neurodegeneration as compared with pathological protein-induced neurotoxicity, and the requirement of a particular glial cell type in neurodegeneration, are still unclear. Here we demonstrate that microglia-mediated damage, rather than pathological tau-induced direct neurotoxicity, is the leading force driving neurodegeneration in a tauopathy mouse model. Importantly, the progression of ptau pathology is also driven by microglia. In addition, we found that APOE, the strongest genetic risk factor for AD, regulates neurodegeneration predominantly by modulating microglial activation, although a minor role of apoE in regulating ptau and insoluble tau formation independent of its immunomodulatory function was also identified. Our results suggest that therapeutic strategies targeting microglia may represent an effective approach to prevent disease progression in the setting of tauopathy.

Screening of a neuronal cell model of tau pathology for therapeutic compounds.

We have developed a cell-based phenotypic automated high-content screening approach for N2a cells expressing the pro-aggregant repeat domain of tau protein (tauRDΔK), which allows analysis of a chemogenomic library of 1649 compounds for their effect on the inhibition or stimulation of intracellular tau aggregation. We identified several inhibitors and stimulators of aggregation and achieved a screening reproducibility >85% for all data. We identified 18 potential inhibitors (= 1.1% of the library) and 10 stimulators (= 0.6% of the library) of tau aggregation in this cell model of tau pathology. The results provide insights into the regulation of cellular tau aggregation and the pathways involved in this process (e.g., involving signaling via p38 mitogen-activated protein kinase, histone deacetylases, vascular endothelial growth factor, rho/ROCK). For example, inhibitors of protein kinases (e.g., p38) can reduce tau aggregation, whereas inhibitors of deacetylases (histone deacetylases) can enhance aggregation. These observations are compatible with reports that phosphorylated or acetylated tau promotes pathology.

MicroRNA-132 provides neuroprotection for tauopathies via multiple signaling pathways.

MicroRNAs (miRNA) regulate fundamental biological processes, including neuronal plasticity, stress response, and survival. Here, we describe a neuroprotective function of miR-132, the miRNA most significantly downregulated in neurons in Alzheimer's disease. We demonstrate that miR-132 protects primary mouse and human wild-type neurons and more vulnerable Tau-mutant neurons against amyloid ß-peptide (Aß) and glutamate excitotoxicity. It lowers the levels of total, phosphorylated, acetylated, and cleaved forms of Tau implicated in tauopathies, promotes neurite elongation and branching, and reduces neuronal death. Similarly, miR-132 attenuates PHF-Tau pathology and neurodegeneration, and enhances long-term potentiation in the P301S Tau transgenic mice. The neuroprotective effects are mediated by direct regulation of the Tau modifiers acetyltransferase EP300, kinase GSK3ß, RNA-binding protein Rbfox1, and proteases Calpain 2 and Caspases 3/7. These data suggest miR-132 as a master regulator of neuronal health and indicate that miR-132 supplementation could be of therapeutic benefit for the treatment of Tau-associated neurodegenerative disorders.

Zinc Exacerbates Tau Pathology in a Tau Mouse Model.

Hyperphosphorylated tau protein is a key pathology in Alzheimer's disease (AD), frontotemporal dementia, chronic traumatic encephalopathy, and Parkinson's disease. The essential trace element zinc exacerbates tauopathy in vitro as well as in a Drosophila model of AD. However, the interaction has never been assessed behaviorally or biochemically in mammals. Zinc supplementation is prevalent in society, finding use as a treatment for macular degeneration and cataracts, and is also taken as an immune system booster with high levels appearing in multivitamins marketed toward the elderly. Using a transgenic mouse model that contains the human gene for tau protein (P301L), we assessed the effects of excess chronic zinc supplementation on tau pathology. Behavioral tests included nest building, circadian rhythm, Morris Water Maze, fear conditioning, and open field. Biochemically, total tau and Ser396 phosphorylation were assessed using western blot. Number of tangles were assessed by Thioflavin-S and free zinc levels were assessed by Zinpyr-1. Tau mice demonstrated behavioral deficits compared to control mice. Zinc supplementation exacerbated tauopathic deficits in circadian rhythm, nesting behavior, and Morris Water Maze. Biochemically, zinc-supplemented tau mice showed increased phosphorylation at pSer396. Zinc supplementation in tau mice also increased tangle numbers in the hippocampus while decreasing free-zinc levels, demonstrating that tangles were sequestering zinc. These results show that zinc intensified the deficits in behavior and biochemistry caused by tau.

α-Lipoic acid improves abnormal behavior by mitigation of oxidative stress, inflammation, ferroptosis, and tauopathy in P301S Tau transgenic mice.

Alzheimer's disease (AD) is the most common neurodegenerative disease and is characterized by neurofibrillary tangles (NFTs) composed of Tau protein. α-Lipoic acid (LA) has been found to stabilize the cognitive function of AD patients, and animal study findings have confirmed its anti-amyloidogenic properties. However, the underlying mechanisms remain unclear, especially with respect to the ability of LA to control Tau pathology and neuronal damage. Here, we found that LA supplementation effectively inhibited the hyperphosphorylation of Tau at several AD-related sites, accompanied by reduced cognitive decline in P301S Tau transgenic mice. Furthermore, we found that LA not only inhibited the activity of calpain1, which has been associated with tauopathy development and neurodegeneration via modulating the activity of several kinases, but also significantly decreased the calcium content of brain tissue in LA-treated mice. Next, we screened for various modes of neural cell death in the brain tissue of LA-treated mice. We found that caspase-dependent apoptosis was potently inhibited, whereas autophagy did not show significant changes after LA supplementation. Interestingly, Tau-induced iron overload, lipid peroxidation, and inflammation, which are involved in ferroptosis, were significantly blocked by LA administration. These results provide compelling evidence that LA plays a role in inhibiting Tau hyperphosphorylation and neuronal loss, including ferroptosis, through several pathways, suggesting that LA may be a potential therapy for tauopathies.

Astrocytes in mouse models of tauopathies acquire early deficits and lose neurosupportive functions.

Microtubule-associated protein tau aggregates constitute the characteristic neuropathological features of several neurodegenerative diseases grouped under the name of tauopathies. It is now clear that the process of tau aggregation is associated with neurodegeneration. Several transgenic tau mouse models have been developed where tau progressively aggregates, causing neuronal death. Previously we have shown that transplantation of astrocytes in P301S tau transgenic mice rescues cortical neuron death, implying that the endogenous astrocytes are deficient in survival support. We now show that the gliosis markers Glial fibrillary acidic protein (GFAP) and S100 calcium-binding protein B (S100ß) are elevated in brains from P301S tau mice compared to control C57Bl/6 mice whereas the expression of proteins involved in glutamine/glutamate metabolism are reduced, pointing to a functional deficit. To test whether astrocytes from P301S mice are intrinsically deficient, we co-cultured astrocytes and neurons from control and P301S mice. Significantly more C57-derived and P301S-derived neurons survived when cells were cultured with C57-derived astrocytes or astrocyte conditioned medium (C57ACM) than with P301S-derived astrocytes or astrocyte conditioned medium (P301SACM), or ACM from P301L tau mice, where the transgene is also specifically expressed in neurons. The astrocytic alterations developed in mice during the first postnatal week of life. In addition, P301SACM significantly decreased presynaptic (synaptophysin, SNP) and postsynaptic (postsynaptic density protein 95, PSD95) protein expression in cortical neuron cultures whereas C57ACM enhanced these markers. Since thrombospondin 1 (TSP-1) is a major survival and synaptogenic factor, we examined whether TSP-1 is deficient in P301S mouse brains and ACM. Significantly less TSP-1 was expressed in the brains of P301S tau mice or produced by P301S-derived astrocytes, whereas supplementation of P301SACM with TSP-1 increased its neurosupportive capacity. Our results demonstrate that P301S-derived astrocytes acquire an early functional deficiency that may explain in part the loss of cortical neurons in the P301S tau mice.

Development of a Scalable, High-Throughput-Compatible Assay to Detect Tau Aggregates Using iPSC-Derived Cortical Neurons Maintained in a Three-Dimensional Culture Format.

Tau aggregation is the pathological hallmark that best correlates with the progression of Alzheimer's disease (AD). The presence of neurofibrillary tangles (NFTs), formed of hyperphosphorylated tau, leads to neuronal dysfunction and loss, and is directly associated with the cognitive decline observed in AD patients. The limited success in targeting ß-amyloid pathologies has reinforced the hypothesis of blocking tau phosphorylation, aggregation, and/or spreading as alternative therapeutic entry points to treat AD. Identification of novel therapies requires disease-relevant and scalable assays capable of reproducing key features of the pathology in an in vitro setting. Here we use induced pluripotent stem cells (iPSCs) as a virtually unlimited source of human cortical neurons to develop a robust and scalable tau aggregation model compatible with high-throughput screening (HTS). We downscaled cell culture conditions to 384-well plate format and used Matrigel to introduce an extra physical protection against cell detachment that reduces shearing stress and better recapitulates pathological conditions. We complemented the assay with AlphaLISA technology for the detection of tau aggregates in a high-throughput-compatible format. The assay is reproducible across users and works with different commercially available iPSC lines, representing a highly translational tool for the identification of novel treatments against tauopathies, including AD.

Curcumin improves tau-induced neuronal dysfunction of nematodes.

Tau is a key protein in the pathogenesis of various neurodegenerative diseases, which are categorized as tauopathies. Because the extent of tau pathologies is closely linked to that of neuronal loss and the clinical symptoms in Alzheimer's disease, anti-tau therapeutics, if any, could be beneficial to a broad spectrum of tauopathies. To learn more about tauopathy, we developed a novel transgenic nematode (Caenorhabditis elegans) model that expresses either wild-type or R406W tau in all the neurons. The wild-type tau-expressing worms exhibited uncoordinated movement (Unc) and neuritic abnormalities. Tau accumulated in abnormal neurites that lost microtubules. Similar abnormalities were found in the worms that expressed low levels of R406W-tau but were not in those expressing comparative levels of wild-type tau. Biochemical studies revealed that tau is aberrantly phosphorylated but forms no detergent-insoluble aggregates. Drug screening performed in these worms identified curcumin, a major phytochemical compound in turmeric, as a compound that reduces not only Unc but also the neuritic abnormalities in both wild-type and R406W tau-expressing worms. Our observations suggest that microtubule stabilization mediates the antitoxicity effect of curcumin. Curcumin is also effective in the worms expressing tau fragment, although it does not prevent the formation of tau-fragment dimers. These data indicate that curcumin improves the tau-induced neuronal dysfunction that is independent of insoluble aggregates of tau.

Binding of the PET radiotracer [¹8F]BF227 does not reflect the presence of alpha-synuclein aggregates in transgenic mice.

Alpha-synuclein (α-syn) aggregation is a neuropathological hallmark of many neurodegenerative diseases, collectively termed synucleinopathies. There is currently no pre-mortem diagnosis tool for these diseases. Although some compounds have been described as potential ligands for α-syn aggregates, no specific PET radiotracer of aggregated α-syn is currently available. Recently, [(18)F]BF227 has been proposed as an α-syn PET radiotracer in the absence of other specific candidates. We proposed here, for the first time, to use this radiotracer in an accelerated mouse model of synucleinopathy presenting α-syn depositions in brainstem and thalamus. Our in vivo and in vitro studies showed that [(18)F]BF227 does not bind to α-syn aggregates. These results highlight the fact that [(18)F]BF227 PET has no suitable characteristics for monitoring this experimental synucleinopathy, justifying the need to develop alternative α-syn PET radiotracers.

Plant-based vaccines for Alzheimer's disease: an overview.

Plants are considered advantageous platforms for biomanufacturing recombinant vaccines. This constitutes a field of intensive research and some plant-derived vaccines are expected to be marketed in the near future. In particular, plant-based production of immunogens targeting molecules with implications on the pathology of Alzheimer's has been explored over the last decade. These efforts involve targeting amyloid beta and ß-secretase with several immunogen configurations that have been evaluated in test animals. The results of these developments are analyzed in this review. Perspectives on the topic are identified, such as exploring additional antigen configurations and adjuvants in order to improve immunization schemes, characterizing in detail the elicited immune responses, and immunological considerations in the achievement of therapeutic humoral responses via mucosal immunization. Safety concerns related to these therapies will also be discussed.

Tau pathology is present in vivo and develops in vitro in sensory neurons from human P301S tau transgenic mice: a system for screening drugs against tauopathies.

Intracellular tau aggregates are the neuropathological hallmark of several neurodegenerative diseases, including Alzheimer's disease, progressive supranuclear palsy, and cases of frontotemporal dementia, but the link between these aggregates and neurodegeneration remains unclear. Neuronal models recapitulating the main features of tau pathology are necessary to investigate the molecular mechanisms of tau malfunction, but current models show little and inconsistent spontaneous tau aggregation. We show that dorsal root ganglion (DRG) neurons in transgenic mice expressing human P301S tau (P301S-htau) develop tau pathology similar to that found in brain and spinal cord and a significant reduction in mechanosensation occurs before detectable fibrillar tau formation. DRG neuronal cultures established from adult P301S-htau mice at different ages retained the pattern of aberrant tau found in vivo. Moreover, htau became progressively hyperphosphorylated over 2 months in vitro beginning with nonsymptomatic neurons, while hyperphosphorylated P301S-htau-positive neurons from 5-month-old mice cultured for 2 months died preferentially. P301S-htau-positive neurons grew aberrant axons, including spheroids, typically found in human tauopathies. Neurons cultured at advanced stages of tau pathology showed a 60% decrease in the fraction of moving mitochondria. SEG28019, a novel O-GlcNAcase inhibitor, reduced steady-state pSer396/pSer404 phosphorylation over 7 weeks in a significant proportion of DRG neurons showing for the first time the possible beneficial effect of prolonged dosing of O-GlcNAcase inhibitor in vitro. Our system is unique in that fibrillar tau forms without external manipulation and provides an important new tool for understanding the mechanisms of tau dysfunction and for screening of compounds for treatment of tauopathies.

Dopamine D2 receptor antagonism suppresses tau aggregation and neurotoxicity.

BACKGROUND: Tauopathies, including Alzheimer's disease and frontotemporal dementia, are diseases characterized by the formation of pathological tau protein aggregates in the brain and progressive neurodegeneration. Presently no effective disease-modifying treatments exist for tauopathies. METHODS: To identify drugs targeting tau neurotoxicity, we have used a Caenorhabditis elegans model of tauopathy to screen a drug library containing 1120 compounds approved for human use for the ability to suppress tau-induced behavioral effects. RESULTS: One compound, the typical antipsychotic azaperone, improved the motility of tau transgenic worms, reduced levels of insoluble tau, and was protective against neurodegeneration. We found that azaperone reduces insoluble tau in a human cell culture model of tau aggregation and that other antipsychotic drugs (flupenthixol, perphenazine, and zotepine) also ameliorate the effects of tau expression in both models. CONCLUSIONS: Reduction of dopamine signaling through the dopamine D2 receptor with the use of gene knockouts in Caenorhabditis elegans or RNA interference knockdown in human cell culture has similar protective effects against tau toxicity. These results suggest dopamine D2 receptor antagonism holds promise as a potential neuroprotective strategy for targeting tau aggregation and neurotoxicity.

D-NAP prophylactic treatment in the SOD mutant mouse model of amyotrophic lateral sclerosis: review of discovery and treatment of tauopathy.

Davunetide (NAP) is a leading drug candidate being tested against tauopathy. Davunetide is an eight-amino-acid peptide fragment derived by structure-activity studies from activity-dependent neuroprotective protein, activity-dependent neuroprotective protein (ADNP). ADNP is essential for brain formation. ADNP haploinsufficiency in mice results in tauopathy and cognitive deficits ameliorated by davunetide treatment. This article summarizes in brief recent reviews about NAP protection against tauopathy including the all D-amino acid analogue-D-NAP (AL-408). D-NAP was discovered to have similar neuroprotective functions to NAP in vitro. Here, D-NAP was tested as prophylactic as well as therapeutic treatment for amytrophic lateral sclerosis (ALS) in the widely used TgN(SOD1-G93A)1Gur transgenic mouse model. Results showed D-NAP-associated prophylactic protection, thus daily treatment starting from day 2 of age resulted in a prolonged life course in the D-NAP-treated mice, which was coupled to a significant decrease in tau hyperphosphorylation. These studies correlate protection against tau hyperphosphorylation and longevity in a severe model of ALS-like motor impairment and early mortality. NAP is a first-in-class drug candidate/investigation compound providing neuroprotection coupled to inhibition of tau pathology. D-NAP (AL-408) is a pipeline product.

Hyperdynamic microtubules, cognitive deficits, and pathology are improved in tau transgenic mice with low doses of the microtubule-stabilizing agent BMS-241027.

Tau is a microtubule (MT)-stabilizing protein that is altered in Alzheimer's disease (AD) and other tauopathies. It is hypothesized that the hyperphosphorylated, conformationally altered, and multimeric forms of tau lead to a disruption of MT stability; however, direct evidence is lacking in vivo. In this study, an in vivo stable isotope-mass spectrometric technique was used to measure the turnover, or dynamicity, of MTs in brains of living animals. We demonstrated an age-dependent increase in MT dynamics in two different tau transgenic mouse models, 3xTg and rTg4510. MT hyperdynamicity was dependent on tau expression, since a reduction of transgene expression with doxycycline reversed the MT changes. Treatment of rTg4510 mice with the epothilone, BMS-241027, also restored MT dynamics to baseline levels. In addition, MT stabilization with BMS-241027 had beneficial effects on Morris water maze deficits, tau pathology, and neurodegeneration. Interestingly, pathological and functional benefits of BMS-241027 were observed at doses that only partially reversed MT hyperdynamicity. Together, these data suggest that tau-mediated loss of MT stability may contribute to disease progression and that very low doses of BMS-241027 may be useful in the treatment of AD and other tauopathies.

Dietary supplementation with S-adenosyl methionine delayed amyloid-ß and tau pathology in 3xTg-AD mice.

S-adenosyl methionine (SAM) contributes to multiple pathways in neuronal homeostasis, several of which are compromised in age-related neurodegeneration and Alzheimer's disease. Dietary supplementation of transgenic mice with SAM maintained acetylcholine levels, cognitive performance, oxidative buffering capacity, and phosphatase activity, and reduced aggression, calcium influx, endogenous PS-1 expression, γ-secretase activity, and levels of amyloid-ß (Aß) and phospho-tau. Herein, we examined whether or not SAM could delay neuropathology in 3xTg-AD mice, which harbor mutant genes for human AßPP, PS-1 and tau. Mice received a standard AIN-76 diet with or without SAM (100 mg/kg diet) for 1 month commencing at 10 months of age or for 3 months commencing at 12.5 months of age; mice were sacrificed and examined for Aß and tau neuropathology at 11 and 15.5 months of age, respectively. SAM supplementation reduced hippocampal intracellular AßPP/Aß and phospho-tau immunoreactivity to a similar extent at both sampling intervals. Supplementation reduced the number of extracellular Aß deposits by 80% (p < 0.01) at 11 months of age after 1 month of treatment but only by 24% (p < 0.34) at 15.5 months of age after 3 months of treatment. As anticipated, neurofibrillary tangles were not observed in mice at these young ages; however, supplementation reduced levels of phospho-tau and caspase-cleaved tau within Sarkosyl-insoluble preparations in mice at 15.5 months of age. These limited analyses indicate that SAM can modulate the time course of AD neuropathology, and support further long-term analyses.

N-phenylamine derivatives as aggregation inhibitors in cell models of tauopathy.

Cell models of tauopathy were generated in order to study mechanisms of neurodegeneration involving abnormal changes of tau. They are based on neuroblastoma cell lines (N2a) that inducibly express different forms of the repeat domain of tau (tau(RD)), e.g. the 4-repeat domain of tau with the wild-type sequence, the repeat domain with the DeltaK280 mutation ("pro-aggregation mutant"), or the repeat domain with DeltaK280 and two proline point mutations ("anti-aggregation mutant"). The data indicate that the aggregation of tau(RD) is toxic, and that aggregation and toxicity can be prevented by low molecular weight compounds, notably compounds based on the N-phenylamine core. Thus the cell models are suitable for developing aggregation inhibitor drugs.