Mutual interaction of neurons and astrocytes derived from iPSCs with APP V717L mutation developed the astrocytic phenotypes of Alzheimer's disease.

BACKGROUND: The development of induced pluripotent stem cells (iPSCs) technology has enabled human cellular disease modeling for inaccessible cell types, such as neural cells in the brain. However, many of the iPSC-derived disease models established to date typically involve only a single cell type. These monoculture models are inadequate for accurately simulating the brain environment, where multiple cell types interact. The limited cell type diversity in monoculture models hinders the accurate recapitulation of disease phenotypes resulting from interactions between different cell types. Therefore, our goal was to create cell models that include multiple interacting cell types to better recapitulate disease phenotypes. METHODS: To establish a co-culture model of neurons and astrocytes, we individually induced neurons and astrocytes from the same iPSCs using our novel differentiation methods, and then co-cultured them. We evaluated the effects of co-culture on neurons and astrocytes using immunocytochemistry, immuno-electron microscopy, and Ca2+ imaging. We also developed a co-culture model using iPSCs from a patient with familial Alzheimer's disease (AD) patient (APP V717L mutation) to investigate whether this model would manifest disease phenotypes not seen in the monoculture models. RESULTS: The co-culture of the neurons and astrocytes increased the branching of astrocyte processes, the number of GFAP-positive cells, neuronal activities, the number of synapses, and the density of presynaptic vesicles. In addition, immuno-electron microscopy confirmed the formation of a tripartite synaptic structure in the co-culture model, and inhibition of glutamate transporters increased neuronal activity. Compared to the co-culture model of the control iPSCs, the co-culture model of familial AD developed astrogliosis-like phenotype, which was not observed in the monoculture model of astrocytes. CONCLUSIONS: Co-culture of iPSC-derived neurons and astrocytes enhanced the morphological changes mimicking the in vivo condition of both cell types. The formation of the functional tripartite synaptic structures in the co-culture model suggested the mutual interaction between the cells. Furthermore, the co-culture model with the APP V717L mutation expressed in neurons exhibited an astrocytic phenotype reminiscent of AD brain pathology. These results suggest that our co-culture model is a valuable tool for disease modeling of neurodegenerative diseases.

Estradiol enhanced neuronal plasticity and ameliorated astrogliosis in human iPSC-derived neural models.

Introduction: 17ß-Estradiol (E2) is a sex hormone that has been previously demonstrated to have neurotherapeutic effects on animal models of Alzheimer's disease (AD). However, clinical trials on E2 replacement therapy for preventing AD onset yielded inconsistent results. Therefore, it is imperative to clarify the therapeutic effects of E2 on human cells. In this study, we utilized induced pluripotent stem cells (iPSCs) derived from multiple AD donors to explore the therapeutic effects of E2 on the in vitro model of human cells. Methods: We conducted a systematic review and meta-analysis using a random-effects model of the previously reported AD clinical trials to summarize the effects of E2 replacement therapy on AD prevention. Subsequently, we induced iPSCs from the donors of the healthy control (1210B2 line (female) and 201B7 line (female)), the familial AD (APP V717L line (female) and APP KM670/671NL line (female)), and the sporadic AD (UCSD-SAD3.7 line (APOE ε3/ε3) (male), UCSD-SAD7D line (APOE ε3/ε4) (male), and TMGH-1 line (APOE ε3/ε3) (female)), then differentiated to neurons. In addition to the mono-culture model of the neurons, we also examined the effects of E2 on the co-culture model of neurons and astrocytes. Results: The meta-analysis of the clinical trials concluded that E2 replacement therapy reduced the risk of AD onset (OR, 0.69; 95 % confidence interval [CI], 0.53-0.91; I2 = 82 %). Neural models from the iPSCs of AD donors showed an increase in secreted amyloid-beta (Aß) levels in the mono-culture model and an astrogliosis-like phenotype in the co-culture model. E2 treatment to the neuronal models derived from the iPSCs enhanced neuronal activity and increased neurite complexity. Furthermore, E2 treatment of the co-culture model ameliorated the astrogliosis-like phenotype. However, in contrast to the previous reports using mouse models, E2 treatment did not change AD pathogenesis, including Aß secretion and phosphorylated tau (pTau) accumulation. Conclusion: E2 treatment of the human cellular model did not impact Aß secretion and pTau accumulation, but promoted neuronal plasticity and alleviated the astrogliosis-like phenotype. The limited effects of E2 may give a clue for the mixed results of E2 clinical trials.

Urine-derived cells from the aged donor for the 2D/3D modeling of neural cells via iPSCs.

Human neural cell models derived from induced pluripotent stem cells (iPSCs) have been widely accepted to model various neurodegenerative diseases such as Alzheimer's disease (AD) in vitro. Although the most common sources of iPSCs are fibroblasts and peripheral blood mononuclear cells, the collection of these cells is invasive. To reduce the donor's burden, we propose the use of urine-derived cells (UDCs), which can be obtained non-invasively from a urine sample. However, the collection of UDCs from elderly donors suffering from age-related diseases such as AD has not been reported, and it is unknown whether these UDCs from the donor aged over 80 years old can be converted into iPSCs and differentiated into neural cells. In this study, we reported a case of using the UDCs from the urine sample of an 89-year-old AD patient, and the UDCs were successfully reprogrammed into iPSCs and differentiated into neural cells in four different ways: (i) the dual SMAD inhibition with small-molecules via the neural progenitor precursor stage, (ii) the rapid induction method using transient expression of Ngn2 and microRNAs without going through the neural progenitor stage, (iii) the cortical brain organoids for 3D culture, and (iv) the human astrocytes. The accumulation of phosphorylated Tau proteins, which is a pathological hallmark of AD, was examined in the neuronal models generated from the UDCs of the aged donor. The application of this cell source will broaden the target population for disease modeling using iPS technology.

Establishment of KEIOi005-A iPSC line from urine-derived cells (UDCs) of a mild Alzheimer's disease (AD) donor with multiple risk SNPs for sporadic Alzheimer's disease (sAD).

Sporadic Alzheimer's disease (sAD) is a neurodegenerative disease that has the highest prevalence among patients with dementia. The genetic risk factors for sAD are comprised of many single nucleotide polymorphisms (SNPs), as indicated by genome-wide association studies. Herein, we generated the KEIOi005-A-induced pluripotent stem cell (iPSC) line from urine-derived cells (UDCs) of a mild Alzheimer's disease (AD) patient with multiple sAD risk SNPs comprising T > C heterozygous APOE ε3/ε4 (rs429358), A > G heterozygous BIN1 (rs744373), and T > G homozygous MS4A6A (rs610932). The established iPSC line demonstrates normal stemness and pluripotency and can be used for in vitro disease modeling of AD.

Utilization of Human Induced Pluripotent Stem Cells-Derived In vitro Models for the Future Study of Sex Differences in Alzheimer's Disease.

Alzheimer's disease (AD) is an aging-dependent neurodegenerative disease that impairs cognitive function. Although the main pathologies of AD are the aggregation of amyloid-beta (Aß) and phosphorylated Tau protein, the mechanisms that lead to these pathologies and their effects are believed to be heterogeneous among patients. Many epidemiological studies have suggested that sex is involved in disease prevalence and progression. The reduction of sex hormones contributes to the pathogenesis of AD, especially in females, suggesting that the supplementation of sex hormones could be a therapeutic intervention for AD. However, interventional studies have revealed that hormone therapy is beneficial under limited conditions in certain populations with specific administration methods. Thus, this suggests the importance of identifying crucial factors that determine hormonal effects in patients with AD. Based on these factors, it is necessary to decide which patients will receive the intervention before starting it. However, the long observational period and many uncontrollable environmental factors in clinical trials made it difficult to identify such factors, except for the APOE ε4 allele. Induced pluripotent stem cells (iPSCs) derived from patients can differentiate into neurons and recapitulate some aspects of AD pathogenesis. This in vitro model allows us to control non-cell autonomous factors, including the amount of Aß aggregates and sex hormones. Hence, iPSCs provide opportunities to investigate sex-dependent pathogenesis and predict a suitable population for clinical trials of hormone treatment.

Integrated Collection of Stem Cell Bank Data, a Data Portal for Standardized Stem Cell Information.

The past decade has witnessed an extremely rapid increase in the number of newly established stem cell lines. However, due to the lack of a standardized format, data exchange among stem cell line resources has been challenging, and no system can search all stem cell lines across resources worldwide. To solve this problem, we have developed the Integrated Collection of Stem Cell Bank data (ICSCB) (http://icscb.stemcellinformatics.org/), the largest database search portal for stem cell line information, based on the standardized data items and terms of the MIACARM framework. Currently, ICSCB can retrieve >16,000 cell lines from four major data resources in Europe, Japan, and the United States. ICSCB is automatically updated to provide the latest cell line information, and its integrative search helps users collect cell line information for over 1,000 diseases, including many rare diseases worldwide, which has been a formidable task, thereby distinguishing itself from other database search portals.

Pathological Progression Induced by the Frontotemporal Dementia-Associated R406W Tau Mutation in Patient-Derived iPSCs.

Mutations in the microtubule-associated protein tau (MAPT) gene are known to cause familial frontotemporal dementia (FTD). The R406W tau mutation is a unique missense mutation whose patients have been reported to exhibit Alzheimer's disease (AD)-like phenotypes rather than the more typical FTD phenotypes. In this study, we established patient-derived induced pluripotent stem cell (iPSC) models to investigate the disease pathology induced by the R406W mutation. We generated iPSCs from patients and established isogenic lines using CRISPR/Cas9. The iPSCs were induced into cerebral organoids, which were dissociated into cortical neurons with high purity. In this neuronal culture, the mutant tau protein exhibited reduced phosphorylation levels and was increasingly fragmented by calpain. Furthermore, the mutant tau protein was mislocalized and the axons of the patient-derived neurons displayed morphological and functional abnormalities, which were rescued by microtubule stabilization. The findings of our study provide mechanistic insight into tau pathology and a potential for therapeutic intervention.

Methylene Blue Inhibits Formation of Tau Fibrils but not of Granular Tau Oligomers: A Plausible Key to Understanding Failure of a Clinical Trial for Alzheimer's Disease.

Alzheimer's disease pathology is characterized by extracellular deposits of amyloid-ß (Aß) and intracellular inclusions of hyperphosphorylated tau. Although genetic studies of familial Alzheimer's disease suggest a causal link between Aß and disease symptoms, the failure of various Aß-targeted strategies to slow or halt disease progression has led to consideration of the idea that inhibition of tau aggregation might be a more promising therapeutic approach. Methylene blue (MB), which inhibits tau aggregation and rescue memory deficits in a mouse model of tauopathy, however, lacked efficacy in a recent Phase III clinical trial. In order to gain insight into this failure, the present study was designed to examine the mechanism through which MB inhibits tau aggregation. We found that MB inhibits heparin-induced tau aggregation in vitro, as measured by thioflavin T fluorescence. Further, MB reduced the amount of tau in precipitants recovered after ultracentrifugation of the aggregation mixture. Atomic force microscopy revealed that MB reduces the number of tau fibrils but increases the number of granular tau oligomers. The latter result was confirmed by sucrose gradient centrifugation: MB treatment was associated with higher levels of granular tau oligomers (fraction 3) and lower levels of tau fibrils (fractions 5 and 6). We previously demonstrated that the formation of granular tau oligomers, rather than tau fibrils, is essential for neuronal death. Thus, the fact that MB actions are limited to inhibition of tau fibril formation provides a mechanistic explanation for the poor performance of MB in the recent Phase III clinical trial.

Tau Oligomers.

The accumulation of tau filaments in neurons is a pathological hallmark of various neurodegenerative diseases, including Alzheimer's disease. However, it is not the filamentous aggregates themselves, but non-filamentous tau species, tau oligomer, that is thought to be the culprit in tau-mediated neurodegeneration. The definition of and methodology for isolating tau oligomers vary among researchers. Here we describe how tau oligomers are identified, summarize the differences of tau oligomers among research groups, and discuss their hypothesized functions.

Frontotemporal dementia with Parkinsonism linked to chromosome-17 mutations enhance tau oligomer formation.

The P301 L mutation in tau, a microtubule-associated protein, causes frontotemporal dementia with Parkinsonism linked to chromosome-17 (FTDP-17) that is accompanied by formation of filamentous polymers of tau. The mutation reduces the binding capability of microtubules and enhances tau filament formation. However, it is unclear whether the P301 L mutation increases the formation of the intermediates of tau filaments that are suggested to be a toxic species of tau. To determine the amount and structure of the intermediates harboring with the P301L mutation, we purified recombinant versions of wild-type, P301L, and 4 other mutants (i.e., P301S, P301T, V337M, and R406W) tau proteins and analyzed the heparin-induced aggregation of those tau constructs. We found that all of the FTDP-17 mutants increased levels of the intermediate tau oligomers. The sizes were determined by atomic force microscopy and laser light scattering. The V337M and R406W oligomers were similar in size to the wild-type, but the P301L, P301T, and P301S mutants formed smaller oligomers. In a P301L transgenic mouse model, we found tau aggregates that were similar in size to the recombinant tau oligomer. These results indicate that FTDP-17 mutations contribute to the pathogenesis via the increased formation of tau oligomers.

Neuronal levels and sequence of tau modulate the power of brain rhythms.

Neural network dysfunction may contribute to functional decline and disease progression in neurodegenerative disorders. Diverse lines of evidence suggest that neuronal accumulation of tau promotes network dysfunction and cognitive decline. The A152T-variant of human tau (hTau-A152T) increases the risk of Alzheimer's disease (AD) and several other tauopathies. When overexpressed in neurons of transgenic mice, it causes age-dependent neuronal loss and cognitive decline, as well as non-convulsive epileptic activity, which is also seen in patients with AD. Using intracranial EEG recordings with electrodes implanted over the parietal cortex, we demonstrate that hTau-A152T increases the power of brain oscillations in the 0.5-6 Hz range more than wildtype human tau in transgenic lines with comparable levels of human tau protein in brain, and that genetic ablation of endogenous tau in Mapt-/- mice decreases the power of these oscillations as compared to wildtype controls. Suppression of hTau-A152T production in doxycycline-regulatable transgenic mice reversed their abnormal network activity. Treatment of hTau-A152T mice with the antiepileptic drug levetiracetam also rapidly and persistently reversed their brain dysrhythmia and network hypersynchrony. These findings suggest that both the level and the sequence of tau modulate the power of specific brain oscillations. The potential of EEG spectral changes as a biomarker deserves to be explored in clinical trials of tau-lowering therapeutics. Our results also suggest that levetiracetam treatment is able to counteract tau-dependent neural network dysfunction. Tau reduction and levetiracetam treatment may be of benefit in AD and other conditions associated with brain dysrhythmias and network hypersynchrony.

Tau Phosphorylation-Much More than a Biomarker.

Lasagna-Reeves et al. (2016) demonstrate that preventing the kinase Nuak1 from phosphorylating the microtubule-associated protein tau reduces the level of potentially pathogenic tau species in brain, a novel therapeutic strategy that could help counteract Alzheimer's disease and several other neurological disorders.

Expression of A152T human tau causes age-dependent neuronal dysfunction and loss in transgenic mice.

A152T-variant human tau (hTau-A152T) increases risk for tauopathies, including Alzheimer's disease. Comparing mice with regulatable expression of hTau-A152T or wild-type hTau (hTau-WT), we find age-dependent neuronal loss, cognitive impairments, and spontaneous nonconvulsive epileptiform activity primarily in hTau-A152T mice. However, overexpression of either hTau species enhances neuronal responses to electrical stimulation of synaptic inputs and to an epileptogenic chemical. hTau-A152T mice have higher hTau protein/mRNA ratios in brain, suggesting that A152T increases production or decreases clearance of hTau protein. Despite their functional abnormalities, aging hTau-A152T mice show no evidence for accumulation of insoluble tau aggregates, suggesting that their dysfunctions are caused by soluble tau. In human amyloid precursor protein (hAPP) transgenic mice, co-expression of hTau-A152T enhances risk of early death and epileptic activity, suggesting copathogenic interactions between hTau-A152T and amyloid-ß peptides or other hAPP metabolites. Thus, the A152T substitution may augment risk for neurodegenerative diseases by increasing hTau protein levels, promoting network hyperexcitability, and synergizing with the adverse effects of other pathogenic factors.

Toxic tau oligomer formation blocked by capping of cysteine residues with 1,2-dihydroxybenzene groups.

Neurofibrillary tangles, composed of hyperphosphorylated tau fibrils, are a pathological hallmark of Alzheimer's disease; the neurofibrillary tangle load correlates strongly with clinical progression of the disease. A growing body of evidence indicates that tau oligomer formation precedes the appearance of neurofibrillary tangles and contributes to neuronal loss. Here we show that tau oligomer formation can be inhibited by compounds whose chemical backbone includes 1,2-dihydroxybenzene. Specifically, we demonstrate that 1,2-dihydroxybenzene-containing compounds bind to and cap cysteine residues of tau and prevent its aggregation by hindering interactions between tau molecules. Further, we show that orally administered DL-isoproterenol, an adrenergic receptor agonist whose skeleton includes 1,2-dihydroxybenzene and which penetrates the brain, reduces the levels of detergent-insoluble tau, neuronal loss and reverses neurofibrillary tangle-associated brain dysfunction. Thus, compounds that target the cysteine residues of tau may prove useful in halting the progression of Alzheimer's disease and other tauopathies.

Tau post-translational modifications in wild-type and human amyloid precursor protein transgenic mice.

The microtubule-associated protein tau has been implicated in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative disorders. Reducing tau levels ameliorates AD-related synaptic, network, and behavioral abnormalities in transgenic mice expressing human amyloid precursor protein (hAPP). We used mass spectrometry to characterize the post-translational modification of endogenous tau isolated from wild-type and hAPP mice. We identified seven types of tau modifications at 63 sites in wild-type mice. Wild-type and hAPP mice had similar modifications, supporting the hypothesis that neuronal dysfunction in hAPP mice is enabled by physiological forms of tau. Our findings provide clear evidence for acetylation and ubiquitination of the same lysine residues; some sites were also targeted by lysine methylation. Our findings refute the hypothesis of extensive O-linked N-acetylglucosamine (O-GlcNAc) modification of endogenous tau. The complex post-translational modification of physiological tau suggests that tau is regulated by diverse mechanisms.

Human P301L-mutant tau expression in mouse entorhinal-hippocampal network causes tau aggregation and presynaptic pathology but no cognitive deficits.

Accumulation of hyperphosphorylated tau in the entorhinal cortex (EC) is one of the earliest pathological hallmarks in patients with Alzheimer's disease (AD). It can occur before significant Aß deposition and appears to "spread" into anatomically connected brain regions. To determine whether this early-stage pathology is sufficient to cause disease progression and cognitive decline in experimental models, we overexpressed mutant human tau (hTauP301L) predominantly in layer II/III neurons of the mouse EC. Cognitive functions remained normal in mice at 4, 8, 12 and 16 months of age, despite early and extensive tau accumulation in the EC. Perforant path (PP) axon terminals within the dentate gyrus (DG) contained abnormal conformations of tau even in young EC-hTau mice, and phosphorylated tau increased with age in both the EC and PP. In old mice, ultrastructural alterations in presynaptic terminals were observed at PP-to-granule cell synapses. Phosphorylated tau was more abundant in presynaptic than postsynaptic elements. Human and pathological tau was also detected within hippocampal neurons of this mouse model. Thus, hTauP301L accumulation predominantly in the EC and related presynaptic pathology in hippocampal circuits was not sufficient to cause robust cognitive deficits within the age range analyzed here.

Adaptive responses to alloxan-induced mild oxidative stress ameliorate certain tauopathy phenotypes.

Oxidative stress is considered to promote aging and age-related disorders such as tauopathy. Although recent reports suggest that oxidative stress under certain conditions possesses anti-aging properties, no such conditions have been reported to ameliorate protein-misfolding diseases. Here, we used neuronal and murine models that overexpress human tau to demonstrate that mild oxidative stress generated by alloxan suppresses several phenotypes of tauopathy. Alloxan treatment reduced HSP90 levels and promoted proteasomal degradation of tau, c-Jun N-amino terminal kinase, and histone deacetylase (HDAC) 6. Moreover, reduced soluble tau (phosphorylated tau) levels suppressed the formation of insoluble tau in tau transgenic mice, while reduced HDAC6 levels contributed to microtubule stability by increasing tubulin acetylation. Age-dependent decreases in HDAC2 and phospho-tau levels correlated with spatial memory enhancement in alloxan-injected tau mice. These results suggest that mild oxidative stress, through adaptive stress responses, operates counteractively against some of the tauopathy phenotypes.

The many faces of tau.

While the microtubule-binding capacity of the protein tau has been known for many years, new functions of tau in signaling and cytoskeletal organization have recently emerged. In this review, we highlight these functions and the potential roles of tau in neurodegenerative disease. We also discuss the therapeutic potential of drugs targeting various aspects of tau biology.

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.

A traditional medicinal herb Paeonia suffruticosa and its active constituent 1,2,3,4,6-penta-O-galloyl-beta-D-glucopyranose have potent anti-aggregation effects on Alzheimer's amyloid beta proteins in vitro and in vivo.

The deposition of amyloid beta (Abeta) protein is a consistent pathological hallmark of Alzheimer's disease (AD) brains; therefore, inhibition of Abeta fibril formation and destabilization of pre-formed Abeta fibrils is an attractive therapeutic and preventive strategy in the development of disease-modifying drugs for AD. This study demonstrated that Paeonia suffruticosa, a traditional medicinal herb, not only inhibited fibril formation of both Abeta(1-40) and Abeta(1-42) but it also destabilized pre-formed Abeta fibrils in a concentration-dependent manner. Memory function was examined using the passive-avoidance task followed by measurement of Abeta burden in the brains of Tg2576 transgenic mice. The herb improved long-term memory impairment in the transgenic mice and inhibited the accumulation of Abeta in the brain. Three-dimensional HPLC analysis revealed that a water extract of the herb contained several different chemical compounds including 1,2,3,4,6-penta-O-galloyl-beta-D-glucopyranose (PGG). No obvious adverse/toxic were found following treatment with PGG. As was observed with Paeonia suffruticosa, PGG alone inhibited Abeta fibril formation and destabilized pre-formed Abeta fibrils in vitro and in vivo. Our results suggest that both Paeonia suffruticosa and its active constituent PGG have strong inhibitory effects on formation of Abeta fibrils in vitro and in vivo. PGG is likely to be a safe and promising lead compound in the development of disease-modifying drugs to prevent and/or cure AD.