Yoshitaka Tatebayashi

Tau filament formation and associative memory deficit in aged mice expressing mutant (R406W) human tau

The R406W tau mutation found in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) causes a hereditary tauopathy clinically resembling Alzheimers disease. Expression of modest levels of the longest human tau isoform with this mutation under the control of the α-calcium–calmodulin-dependent kinase-II promoter in transgenic (Tg) mice resulted in the development of congophilic hyperphosphorylated tau inclusions in forebrain neurons. These inclusions appeared as early as 18 months of age. As with human cases, tau inclusions were composed of both mutant and endogenous wild-type tau, and were associated with microtubule disruption and flame-shaped transformations of the affected neurons. Straight tau filaments were recovered from Sarkosyl-insoluble fractions from only the aged Tg brains. Behaviorally, aged Tg mice had associative memory impairment without obvious sensorimotor deficits. Therefore, these mice that exhibit a phenotype mimicking R406W FTDP-17 provide an animal model for investigating the adverse properties associated with this mutation, which might potentially recapitulate some etiological events in Alzheimers disease.

Alterations in Glucose Metabolism Induce Hypothermia Leading to Tau Hyperphosphorylation through Differential Inhibition of Kinase and Phosphatase Activities: Implications for Alzheimer's Disease

Alzheimers disease (AD) brains contain neurofibrillary tangles (NFTs) composed of abnormally hyperphosphorylated tau protein. Regional reductions in cerebral glucose metabolism correlating to NFT densities have been reported in AD brains. Assuming that reduced glucose metabolism might cause abnormal tau hyperphosphorylation, we induced in vivo alterations of glucose metabolism in mice by starvation or intraperitoneal injections of either insulin or deoxyglucose. We found that the treatments led to abnormal tau hyperphosphorylation with patterns resembling those in early AD brains and also resulted in hypothermia. Surprisingly, tau hyperphosphorylation could be traced down to a differential effect of low temperatures on kinase and phosphatase activities. These data indicate that abnormal tau hyperphosphorylation is associated with altered glucose metabolism through hypothermia. Our results imply that serine-threonine protein phosphatase 2A plays a major role in regulating tau phosphorylation in the adult brain and provide in vivo evidence for its crucial role in abnormal tau hyperphosphorylation in AD.

Failure of neuronal maturation in Alzheimer disease dentate gyrus.

The dentate gyrus, an important anatomic structure of the hippocampal formation, is one of the major areas in which neurogenesis takes place in the adult mammalian brain. Neurogenesis in the dentate gyrus is thought to play an important role in hippocampus-dependent learning and memory. Neurogenesis has been reported to be increased in the dentate gyrus of patients with Alzheimer disease, but it is not known whether the newly generated neurons differentiate into mature neurons. In this study, the expression of the mature neuronal marker high molecular weight microtubule-associated protein (MAP) isoforms MAP2a and b was found to be dramatically decreased in Alzheimer disease dentate gyrus, as determined by immunohistochemistry and in situ hybridization. The total MAP2, including expression of the immature neuronal marker, the MAP2c isoform, was less affected. These findings suggest that newly generated neurons in Alzheimer disease dentate gyrus do not become mature neurons, although neuroproliferation is increased.

Insulin Dysfunction Induces In Vivo Tau Hyperphosphorylation through Distinct Mechanisms

Hyperphosphorylated tau is the major component of paired helical filaments in neurofibrillary tangles found in Alzheimers disease (AD) brains, and tau hyperphosphorylation is thought to be a critical event in the pathogenesis of the disease. The large majority of AD cases is late onset and sporadic in origin, with aging as the most important risk factor. Insulin resistance, impaired glucose tolerance, and diabetes mellitus (DM) are other common syndromes in the elderly also strongly age dependent, and there is evidence supporting a link between insulin dysfunction and AD. To investigate the possibility that insulin dysfunction might promote tau pathology, we induced insulin deficiency and caused DM in mice with streptozotocin (STZ). A mild hyperphosphorylation of tau could be detected 10, 20, and 30 d after STZ injection, and a massive hyperphosphorylation of tau was observed after 40 d. The robust hyperphosphorylation of tau was localized in the axons and neuropil, and prevented tau binding to microtubules. Neither mild nor massive tau phosphorylation induced tau aggregation. Body temperature of the STZ-treated mice did not differ from control animals during 30 d, but dropped significantly thereafter. No change in β-amyloid (Aβ) precursor protein (APP), APP C-terminal fragments, or Aβ levels were observed in STZ-treated mice; however, cellular protein phosphatase 2A activity was significantly decreased. Together, these data indicate that insulin dysfunction induced abnormal tau hyperphosphorylation through two distinct mechanisms: one was consequent to hypothermia; the other was temperature-independent, inherent to insulin depletion, and probably caused by inhibition of phosphatase activity.

The dentate gyrus neurogenesis: a therapeutic target for Alzheimer's disease

Abstract. Neurogenesis persists in the aged human dentate gyrus but its role and regulation in pathological conditions such as Alzheimers disease (AD), where the neurotrophic environment is changed, are poorly understood. In this study we investigated the effect of changes in the neurotrophic environment on neurogenesis in cultured rat hippocampal progenitors and in normal adult rats as models. In hippocampal progenitor cells from adult rats, fibroblast growth factor-2 (FGF-2) dose-dependently decreased microtubule-associated protein 2 and increased tau levels, indicating an FGF-2-induced dendrite to axon polarity shift. Cerebrolysin, a neurotrophic drug which has been shown to improve cognition and mood of AD patients, was found to increase neuron-like differentiated adult rat hippocampal progenitors in culture both by reducing apoptosis and by counteracting the FGF-2-induced polarity shift. Intraperitoneal administration of Cerebrolysin enhanced dentate gyrus neurogenesis and maze performance of 8- to 12-month-old female rats. These studies suggest that AD pathogenesis might involve an abnormally elevated FGF-2-associated dysregulation of dentate gyrus neurogenesis, especially neuronal polarity and that the neurogenesis pathology is a promising therapeutic target for this disease.

Role of tau phosphorylation by glycogen synthase kinase-3β in the regulation of organelle transport

Anterograde organelle transport is known to be inhibited by overexpression of the microtubule-associated protein tau in cultured cells. However, the molecular mechanism regulating this function of tau protein has not previously been understood. We found that in PC12 cells treated with NGF or fibroblast growth factor-2, glycogen synthase kinase-3β and tau were upregulated simultaneously from around day 2 of differentiation, with increasing glycogen synthase kinase-3-mediated tau phosphorylation. This phosphorylation did not alter taus ability to bind to microtubules but appeared to be required for the maintenance of the anterograde organelle transport in differentiated cells. Lithium, alsterpaullone or valproate, three independent glycogen synthase kinase-3 inhibitors, but not butyrolactone 1, an inhibitor of cyclin-dependent protein kinases, induced mitochondrial clustering in association with tau dephosphorylation. In CHO cells transfected with human tau441, mitochondrial clustering was found in cells in which tau was unphosphorylated. These findings raise the possibility that the phosphorylation of tau by glycogen synthase kinase-3 might be involved in the regulation of organelle transport.

Formation of Tau Inclusions in Knock-in Mice with Familial Alzheimer Disease (FAD) Mutation of Presenilin 1 (PS1)

Mutations in the presenilin 1 (PS1) gene are responsible for the early onset of familial Alzheimer disease (FAD). Accumulating evidence shows that PS1 is involved in γ-secretase activity and that FAD-associated mutations of PS1 commonly accelerate Aβ1–42 production, which causes Alzheimer disease (AD). Recent studies suggest, however, that PS1 is involved not only in Aβ production but also in other processes that lead to neurodegeneration. To better understand the causes of neurodegeneration linked to the PS1 mutation, we analyzed the development of tau pathology, another key feature of AD, in PS1 knock-in mice. Hippocampal samples taken from FAD mutant (I213T) PS1 knock-in mice contained hyperphosphorylated tau that reacted with various phosphodependent tau antibodies and with Alz50, which recognizes the conformational change of PHF tau. Some neurons exhibited Congo red birefringence and Thioflavin T reactivity, both of which are histological criteria for neurofibrillary tangles (NFTs). Biochemical analysis of the samples revealed SDS-insoluble tau, which under electron microscopy examination, resembled tau fibrils. These results indicate that our mutant PS1 knock-in mice exhibited NFT-like tau pathology in the absence of Aβ deposition, suggesting that PS1 mutations contribute to the onset of AD not only by enhancing Aβ1–42 production but by also accelerating the formation and accumulation of filamentous tau.

A novel, rapid, quantitative cell-counting method reveals oligodendroglial reduction in the frontopolar cortex in major depressive disorder

A novel, rapid, quantitative cell-counting method reveals oligodendroglial reduction in the frontopolar cortex in major depressive disorder

A novel, rapid, cell-counting method for unfixed frozen brains comprehensively quantifies at least four neural cell populations

A novel, rapid, cell-counting method for unfixed frozen brains comprehensively quantifies at least four neural cell populations

c-jun N-terminal kinase hyperphosphorylates R406W tau at the PHF-1 site during mitosis

Tauopathies such as Alzheimer disease (AD) probably involve a type of phosphorylation imbalance causing the accumulation of abnormally hyperphosphorylated tau in neurons and/or glias. Investigation of R406W tau mutation may provide insight into such abnormal tau hyperphosphorylation, since this mutation causes AD‐like dementia and tauopathy in humans and because it has the unique ability to reduce tau phosphorylation in vitro and in cultured cells. Here we show that R406W mutation primarily disrupts tau phosphorylation at Ser404, a priming phosphorylation site of glycogen synthase kinase‐3β (GSK‐3β), thereby reducing subsequent GSK‐3β‐mediated phosphorylation at the PHF‐1 site (mostly Ser396). In contrast, c‐jun N‐terminal kinase (JNK) as activated in the mitotic phase directly hyperphosphorylates R406W tau at the PHF‐1 site. This was confirmed by PHF‐1 hyperphosphorylation of R406W tau in mitotic cells, its association with cytoplasmic JNK activation, and its inhibition by a JNK inhibitor, SP600125. These data unveil the unknown mechanisms of physiological tau phosphorylation at the PHF‐1 site and suggest that cytoplasmic JNK activation may play an important role in the abnormal tau hyperphosphorylation associated with R406W tau mutation and in AD.