Neurofibrillary pathology of Alzheimer's disease and other tauopathies

Application of neurotrophic factor-secreting cells (astrocyte - Like cells) in the in-vitro Alzheimer's disease-like pathology on the human neuroblastoma cells

This study investigated physical proximity and paracrine activity of neurotrophic factor-secreting cells (NTF-SCs) on beta-amyloid treated cells. Mesenchymal stem cells (MSCs) - to-NTF-SCs (Astrocyte -like cells) trans-differentiation was confirmed using immunofluorescence staining of GFAP. BDNF and NGF levels were measured by ELISA. To mimic AD-like condition, SH-SY5Y cells were exposed to 10 μM Aβ1-42. SH-SY5Y cells were allocated into Control; and Aβ1-42-treated cells. Treated cells were further classified into three subgroups including Aβ1-42 cells, Aβ1-42 cells + NTF-SCs (CM) and Aβ1-42 cells + NTF-SCs co-culture. Cell viability was measured by MTT assay. Anti-inflammatory and anti-tau hyperphosphorylation effects of NTF-SCs were assessed via monitoring TNF-α and hyperphosphorylated Tau protein expression level respectively. To explore the impact of NTF-SCs on synaptogenesis and synaptic functionality, real-time PCR assay was performed to measure the expression of synapsine 1, homer 1 and ZIF268. The level of synaptophysin was monitored via immunofluorescence staining. Data showed MSCs potential in trans-differentiating toward NTF-SCs indicated with enhanced GFAP expression (p < 0.05). ELISA assay confirmed the superiority of NTF-SCs in releasing NGF and BDNF compared to the MSCs (p < 0.05). Aβ significantly induced SH-SY5Y cells death while juxtacrine and paracrine activity of NTF-SCs significantly blunted these conditions (p < 0.05). Trans-differentiated cells had potential to reduce Tau hyperphosphorylation and TNF-α level after treatment with Aβ through juxtacrine and paracrine mechanisms (p < 0.05). Moreover, NTF-SCs significantly increased the expression rate of synapsin 1, homer 1 and zif 268 genes in Aβ-treated cells compared to matched-control group coincided with induction of synaptophysin at the protein level(p < 0.05). NTF-SCs reversed AD-like neuropathological alterations in SH-SY5Y cells via paracrine and juxtacrine mechanisms.

Impact of the Hereditary P301L Mutation on the Correlated Conformational Dynamics of Human Tau Protein Revealed by the Paramagnetic Relaxation Enhancement NMR Experiments

Tau forms intracellular insoluble aggregates as a neuropathological hallmark of Alzheimer’s disease. Tau is largely unstructured, which complicates the characterization of the tau aggregation process. Recent studies have demonstrated that tau samples two distinct conformational ensembles, each of which contains the soluble and aggregation-prone states of tau. A shift to populate the aggregation-prone ensemble may promote tau fibrillization. However, the mechanism of this ensemble transition remains elusive. In this study, we explored the conformational dynamics of a tau fragment by using paramagnetic relaxation enhancement (PRE) and interference (PRI) NMR experiments. The PRE correlation map showed that tau is composed of segments consisting of residues in correlated motions. Intriguingly, residues forming the β-structures in the heparin-induced tau filament coincide with residues in these segments, suggesting that each segment behaves as a structural unit in fibrillization. PRI data demonstrated that the P301L mutation exclusively alters the transiently formed tau structures by changing the short- and long-range correlated motions among residues. The transient conformations of P301L tau expose the amyloid motif PHF6 to promote tau self-aggregation. We propose the correlated motions among residues within tau determine the population sizes of the conformational ensembles, and perturbing the correlated motions populates the aggregation-prone form.

Superior Synaptogenic Effect of Electrospun PLGA-PEG Nanofibers Versus PLGA Nanofibers on Human Neural SH-SY5Y Cells in a Three-Dimensional Culture System

Synapses are touted as the main structural and functional components of neural cells within in the nervous system, providing tissue connectivity and integration via the formation of perineuronal nets. In the present study, we evaluated the synaptogenic activity of electrospun PLGA and PLGA-PEG nanofibers on human SH-SY5Y cells after 14 days in vitro. Electrospun PLGA and PLGA-PEG nanofibers were fabricated and physicochemical properties were examined using the HNMR technique. The cells were classified into three random groups, i.e., control (laminin-coated surface), PLGA, and PLGA-PEG. Scaffolds' features, cell morphology, attachment, and alignment were monitored by SEM imaging. We performed MTT assay to measure cell survival rate. To evaluate neurite formation and axonal outgrowth, cells were stained with an antibody against β-tubulin III using immunofluorescence imaging. Antibodies against synapsin-1 and synaptophysin were used to explore the impact of PLGA and PLGA-PEG scaffolds on synaptogenesis and functional activity of synapses. According to SEM analysis, the PLGA-PEG scaffold had less thick nanofibers compared with the PLGA scaffold. Cell attachment, expansion, neurite outgrowth, and orientation were promoted in the PLGA-PEG group in comparison with the PLGA substrate (p < 0.05). MTT assay revealed that both scaffolds did not exert any neurotoxic effects on cell viability. Notably, PLGA-PEG surface increased cell viability compared to PLGA by time (p < 0.05). Immunofluorescence staining indicated an increased β-tubulin III level in the PLGA-PEG group days coincided with axonal outgrowth and immature neuron marker after seven compared with the PLGA and control groups (p < 0.05). Based on our data, both synaptogenesis and functional connectivity were induced in cells plated on the PLGA-PEG surface that coincide with the increase of synapsin-1 and synaptophysin in comparsion with the PLGA and control groups (p < 0.05). Taken together, our results imply that the PLGA-PEG nanofibers could provide the desirable microenvironment to develop perineuronal net formation, contributing to efficient synaptogenesis and neuron-to-neuron crosstalk.

Modulation of tau protein aggregation using 'Trojan' sequences

BACKGROUND

The abnormal assembly of tau into neurofibrillary tangles has been associated with over 30 debilitating disorders known as tauopathies. Tauopathies affect millions of people worldwide, yet no clinically approved solution for tau aggregation is currently available.

METHODS

We employed a structure-based design approach to make a series of short peptide-based perturbants (Trojans), that can interact with the core hydrophobic fragment of tau protein. Through a combination of various biophysical methods, serum stability, toxicity, and blood-brain barrier translocation assays, we have assessed the efficacy of these designed peptides to intervene the aggregation of tau protein fragment.

RESULTS

Our observations suggest that Trojan peptides could modulate the aggregation of the Ac-VQIVYK-NH₂ peptide by either accelerating or arresting its self-assembly and reduce the neurotoxicity of the fibrils formed. The designed perturbant peptides showed three essential pre-requisites such as negligible cytotoxicity, high proteolytic stability in serum, and an ability to cross human blood-brain barrier (BBB). Furthermore, the Trojans could disassemble the pre-formed fibrillar assemblies.

CONCLUSIONS

These designed Trojan peptides can serve as a potential therapeutic option for tauopathies, modulating post as well as pre-aggregation leading to the diseases condition.

GENERAL SIGNIFICANCE

Tauopathies are a group of over 20 progressive neurodegenerative disorders that affect millions of people worldwide. The available therapies of tau-linked neurodegenerative syndromes are limited and mostly symptomatic and therefore there is an urgent need for a cost-effective treatment option. We are presenting a series of structure-based, de novo designed, short peptides that can potentially modulate tau protein aggregation.

Quercetin promotes learning and memory performance concomitantly with neural stem/progenitor cell proliferation and neurogenesis in the adult rat dentate gyrus

The decline in neurogenesis is a very critical problem in Alzheimer disease. Different biological activities have been reported for medicinal application of quercetin. Herein, we investigated the neurogenesis potential of quercetin in a rat model of Alzheimer's disease induced by amyloid-beta injection. Rats were randomly divided into Control, Alzheimer + Saline and Alzheimer + Quercetin groups. Following the administration of Amyloid-beta, rats in the Alzheimer + Quercetin group received 40 mg/kg/day quercetin orally for one month. Our data demonstrated amyloid-β injection could impair learning and memory processing in rats indicated by passive avoidance test evaluation. We noted that one-month quercetin treatment alleviated the detrimental effects of amyloid-β on spatial learning and memory parameters using Morris water maze analysis. Quercetin was found to increase the number of proliferating neural stem/progenitor cells. Notably, quercetin increased the number of DCX-expressing cells, indicating the active dynamic growth of neural progenitor cells in the dentate gyrus of the hippocampus. We further observed that the quercetin improved the number of BrdU/NeuN positive cells contributed to enhanced adult neurogenesis. Based on our results, quercetin had the potential to promote the expression of BDNF, NGF, CREB, and EGR-1 genes involved in regulating neurogenesis. These data suggest that quercetin can play a valuable role in alleviating Alzheimer's disease symptoms by enhancing adult neurogenesis mechanism.

Therapeutic effect of Rho kinase inhibitor FSD-C10 in a mouse model of Alzheimer's disease

Fasudil, a Rho kinase (ROCK) inhibitor, effectively inhibits disease severity in a mouse model of Alzheimer's disease (AD). However, given its significant limitations, including a relatively narrow safety window and poor oral bioavailability, Fasudil is not suitable for long-term use. Thus, screening for ROCK inhibitor(s) that are more efficient, safer, can be used orally and suitable for long-term use in the treatment of neurodegenerative disorders is required. The main purpose of the present study is to explore whether FSD-C10, a novel ROCK inhibitor, has therapeutic potential in amyloid precursor protein/presenilin-1 transgenic (APP/PS1 Tg) mice, and to determine possible mechanisms of its action. The results showed that FSD-C10 effectively improved learning and memory impairment, accompanied by reduced expression of amyloid-β 1-42 (Aβ_1-42), Tau protein phosphorylation (P-tau) and β-site APP-cleaving enzyme in the hippocampus and cortex area of brain. In addition, FSD-C10 administration boosted the expression of synapse-associated proteins, such as postynaptic density protein 95, synaptophsin, α-amino 3-hydroxy-5-methyl-4-isoxa-zolep-propionate receptor and neurotrophic factors, e,g., brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor. Taken together, our results demonstrate that FSD-C10 has therapeutic potential in the AD mouse model, possibly through inhibiting the formation of Aβ_1-42 and P-tau, and promoting the generation of synapse-associated proteins and neurotrophic factors.

Hyperforin attenuates aluminum-induced Aβ production and Tau phosphorylation via regulating Akt/GSK-3β signaling pathway in PC12 cells

Aluminum (Al) is a neurotoxicant and cause β-amyloid (Aβ) peptides aggregation and tau hyperphosphorylation. Hyperforin (HF) is one of the major active constituents of the extracts of St. John's Wort (Hypericum perforatum), can treat Alzheimer's disease (AD) and other diseases involving peptide accumulation and cognition impairment. To determine the effects of HF on Al-induced Aβ formation and tau hyperphosphorylation, PC12 cells were cultured and treated with Al-malt (500μM) and/or HF (1μM). The results showed that HF treatment significantly attenuated Al-malt-induced Aβ_1-42 production by reducing the expressions of APP, BACE1 and PS1, while increasing the expressions of sAPPα, ADAM9/10/17, and tau phosphorylation in PC12 cells. In addition, HF treatment also increased phosphorylation of AKT (Ser473) and inhibited GSK-3β activity by increasing phosphorylation of GSK-3β (Ser9). These results indicated that HF may exert the protection via regulating the AKT/GSK-3β signaling to reduce Aβ production and tau phosphorylation in PC12 cells. Furthermore, these results could lead a possible therapeutics for the management of Al neurotoxicity.

Molecular Signaling Pathways Behind the Biological Effects of Salvia Species Diterpenes in Neuropharmacology and Cardiology

The genus Salvia, from the Lamiaceae family, has diverse biological properties that are primarily attributable to their diterpene contents. There is no comprehensive review on the molecular signaling pathways of these active components. In this review, we investigated the molecular targets of bioactive Salvia diterpenes responsible for the treatment of nervous and cardiovascular diseases. The effects on different pathways, including apoptosis signaling, oxidative stress phenomena, the accumulation of amyloid beta plaques, and tau phosphorylation, have all been considered to be mechanisms of the anti-Alzheimer properties of Salvia diterpenes. Additionally, effects on the benzodiazepine and kappa opioid receptors and neuroprotective effects are noted as neuropharmacological properties of Salvia diterpenes, including tanshinone IIA, salvinorin A, cryptotanshinone, and miltirone. Tanshinone IIA, as the primary diterpene of Salvia miltiorrhiza, has beneficial activities in heart diseases because of its ability to scavenge free radicals and its effects on transcription factors, such as nuclear transcription factor-kappa B (NF-κB) and the mitogen-activated protein kinases (MAPKs). Additionally, tanshinone IIA has also been proposed to have cardioprotective properties including antiarrhythmic activities and effects on myocardial infarction. With respect to the potential therapeutic effects of Salvia diterpenes, comprehensive clinical trials are warranted to evaluate these valuable molecules as lead compounds. Copyright © 2016 John Wiley & Sons, Ltd.

A Simple Model to Study Tau Pathology

Tau proteins play a role in the stabilization of microtubules, but in pathological conditions, tauopathies, tau is modified by phosphorylation and can aggregate into aberrant aggregates. These aggregates could be toxic to cells, and different cell models have been used to test for compounds that might prevent these tau modifications. Here, we have used a cell model involving the overexpression of human tau in human embryonic kidney 293 cells. In human embryonic kidney 293 cells expressing tau in a stable manner, we have been able to replicate the phosphorylation of intracellular tau. This intracellular tau increases its own level of phosphorylation and aggregates, likely due to the regulatory effect of some growth factors on specific tau kinases such as GSK3. In these conditions, a change in secreted tau was observed. Reversal of phosphorylation and aggregation of tau was found by the use of lithium, a GSK3 inhibitor. Thus, we propose this as a simple cell model to study tau pathology in nonneuronal cells due to their viability and ease to work with.

Propagation of Neuronal Damage to Embryonic Grafts Transplanted in the Hippocampus of Murine Models of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia, characterized by the presence of two principal hallmarks-amyloid plaques and neurofibrillary tangles. The primary cause of the majority of AD cases is not known. Likewise, the mechanisms underlying the propagation of the pathology from affected tissue to neighboring healthy neurons are largely unknown, but knowledge about them could be helpful to design strategies aimed at halting the progression of the disease. To throw light on the mechanisms of propagation of neuronal damage to healthy tissue, wild-type (WT) hippocampal solid tissue chunks derived from green fluorescent protein (GFP)-positive embryos were grafted into the hippocampus of 6-month-old WT and 3xTg-AD mice, a triple-transgenic mouse model that exhibits both amyloid-beta (Aβ) and tau protein pathology. The histological and morphological alterations of the grafted tissues were assessed 3 months post-transplantation. Tissues grafted in 3xTg-AD hosts, compared to those grafted in WT recipients, presented a significant decrease in neurite outgrowth (35.4%) and dendritic spine density (41.3%), mainly due to a reduction of stubby and thin-shaped spines. Moreover, some cells of the tissue transplanted in 3xTg-AD hosts accumulated intracellular amyloid peptide deposits similar to the cells of the host. Furthermore, the immunohistochemical examination of reactive astrocytes and microglia revealed the presence of more inflammation in the grafted tissues hosted in 3xTg-AD compared to WT recipients. These results show a propagation of neuronal damage to initially healthy embryonic grafts, validating this methodology for future studies on the mechanisms of the progression of AD pathology to surrounding regions.

Genetics of Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative syndrome that is clinically characterized by progressive postural instability, supranuclear gaze palsy, parkinsonism and cognitive decline. Pathologically, diagnosis of PSP is based on characteristic features, such as neurofibrillary tangles, neutrophil threads, tau-positive astrocytes and their processes in basal ganglia and brainstem, and the accumulation of 4 repeat tau protein. PSP is generally recognized as a sporadic disorder; however, understanding of genetic background of PSP has been expanding rapidly. Here we review relevant publications to outline the genetics of PSP. Although only small number of familial PSP cases have been reported, the recognition of familial PSP has been increasing. In some familial cases of clinically probable PSP, PSP pathologies were confirmed based on NINDS neuropathological diagnostic criteria. Several mutations in MAPT, the gene that causes a form of familial frontotemporal lobar degeneration with tauopathy, have been identified in both sporadic and familial PSP cases. The H1 haplotype of MAPT is a risk haplotype for PSP, and within H1, a sub-haplotype (H1c) is associated with PSP. A recent genome-wide association study on autopsyproven PSP revealed additional PSP risk alleles in STX6 and EIF2AK3. Several heredodegenerative parkinsonian disorders are referred to as PSP-look-alikes because their clinical phenotype, but not their pathology, mimics PSP. Due to the fast development of genomics and bioinformatics, more genetic factors related to PSP are expected to be discovered. Undoubtedly, these studies will provide a better understanding of the pathogenesis of PSP and clues for developing therapeutic strategies.

A physically-modified saline suppresses neuronal apoptosis, attenuates tau phosphorylation and protects memory in an animal model of Alzheimer's disease

Alzheimer's disease (AD), the leading cause of dementia in the aging population, is characterized by the presence of neuritic plaques, neurofibrillary tangles and extensive neuronal apoptosis. Neuritic plaques are mainly composed of aggregates of amyloid-β (Aβ) protein while neurofibrillary tangles are composed of the hyperphosphorylated tau protein. Despite intense investigations, no effective therapy is currently available to halt the progression of this disease. Here, we have undertaken a novel approach to attenuate apoptosis and tau phosphorylation in cultured neuronal cells and in a transgenic animal model of AD. RNS60 is a 0.9% saline solution containing oxygenated nanobubbles that is generated by subjecting normal saline to Taylor-Couette-Poiseuille (TCP) flow under elevated oxygen pressure. In our experiments, fibrillar Aβ1-42, but not the reverse peptide Aβ42-1, induced apoptosis and cell death in human SHSY5Y neuronal cells. RNS60, but not NS (normal saline), RNS10.3 (TCP-modified saline without excess oxygen) or PNS60 (saline containing excess oxygen without TCP modification), attenuated Aβ(1–42)-induced cell death. RNS60 inhibited neuronal cell death via activation of the type 1A phosphatidylinositol-3 (PI-3) kinase – Akt – BAD pathway. Furthermore, RNS60 also decreased Aβ(1–42)-induced tau phosphorylation via (PI-3 kinase – Akt)-mediated inhibition of GSK-3β. Similarly, RNS60 treatment suppressed neuronal apoptosis, attenuated Tau phosphorylation, inhibited glial activation, and reduced the burden of Aβ in the hippocampus and protected memory and learning in 5XFAD transgenic mouse model of AD. Therefore, RNS60 may be a promising pharmaceutical candidate in halting or delaying the progression of AD.

Are tau aggregates toxic or protective in tauopathies?

Aggregation of highly phosphorylated tau into aggregated forms such as filaments and neurofibrillary tangles is one of the defining pathological hallmarks of Alzheimer's disease and other tauopathies. Hence therapeutic strategies have focused on inhibition of tau phosphorylation or disruption of aggregation. However, animal models imply that tau-mediated dysfunction and toxicity do not require aggregation but instead are caused by soluble hyper-phosphorylated tau. Over the years, our findings from a Drosophila model of tauopathy have reinforced this. We have shown that highly phosphorylated wild-type human tau causes behavioral deficits resulting from synaptic dysfunction, axonal transport disruption, and cytoskeletal destabilization in vivo. These deficits are evident in the absence of neuronal death or filament/tangle formation. Unsurprisingly, both pharmacological and genetic inhibition of GSK-3β rescue these tau phenotypes. However, GSK-3β inhibition also unexpectedly increases tau protein levels, and produces insoluble granular tau oligomers. As well as underlining the growing consensus that tau toxicity is mediated by a highly phosphorylated soluble tau species, our findings further show that not all insoluble tau aggregates are toxic. Some tau aggregates, in particular tau oligomers, are non-toxic, and may even be protective against tau toxicity in vivo. This has serious implications for emerging therapeutic strategies to dissolve tau aggregates, which might be ineffective or even counter-productive. In light of this, it is imperative to identify the key toxic tau species and to understand how it mediates dysfunction and degeneration so that the effective disease-modifying therapies can be developed.

Alzheimer's disease pathologic cascades: who comes first, what drives what

This review discusses known and speculated relationships between Alzheimer's disease (AD) biochemical, molecular, and histologic phenomena. In the AD brain, various pathologies including neuritic plaques, neurofibrillary tangles, synaptic loss, oxidative stress, cell cycle re-entry, and mitochondrial changes have all been described. In an attempt to explain what exactly goes wrong in the AD brain various investigators have proposed different heuristic and hierarchical schemes. It is important to accurately define the AD pathology hierarchy because treatments targeting the true apex of its pathologic cascade arguably have the best chance of preventing, mitigating, or even curing this disease.

Role of Rab GTPases in membrane traffic and cell physiology

Intracellular membrane traffic defines a complex network of pathways that connects many of the membrane-bound organelles of eukaryotic cells. Although each pathway is governed by its own set of factors, they all contain Rab GTPases that serve as master regulators. In this review, we discuss how Rabs can regulate virtually all steps of membrane traffic from the formation of the transport vesicle at the donor membrane to its fusion at the target membrane. Some of the many regulatory functions performed by Rabs include interacting with diverse effector proteins that select cargo, promoting vesicle movement, and verifying the correct site of fusion. We describe cascade mechanisms that may define directionality in traffic and ensure that different Rabs do not overlap in the pathways that they regulate. Throughout this review we highlight how Rab dysfunction leads to a variety of disease states ranging from infectious diseases to cancer.

Implication of phosphatidylinositol-3 kinase/Akt/glycogen synthase kinase-3β pathway in ginsenoside Rb1's attenuation of beta-amyloid-induced neurotoxicity and tau phosphorylation

Ginseng has long been used to alleviate many ailments, particularly those associated with aging and memory deterioration. In the present study we aimed to investigate the neuroprotective effects of ginsenoside Rb1, against Aβ(1-42) toxicity in cultured cortical neurons and also the potential involvement of PI3K/Akt/GSK-3β signal pathway. Cortical neurons were pre-treated with ginsenoside Rb1 (20, 40, 100 μM) or LiCl (1, 5, 10 mM) for 24 h, and then were co-treated with 20 μM Aβ(1-42) for 12 h. In some experiments to evaluate the mechanism of Rb1 action, a PI3K inhibitor (LY294002 10 μM) was co-administered with Rb1 for the 24-h pretreatment. We revealed that Rb1 significantly attenuated Aβ(1-42)-induced neurotoxicity and tau hyperphosphorylation at multiple AD-related sites in a dose-dependent manner. Simultaneously, it increased the levels of phospho-Ser(473)-Akt and down-regulated GSK-3β activity by PI3K activation. The neuroprotective effects of Rb1 against Aβ(1-42)-induced neurotoxicity and tau hyperphosphorylation were blocked by LY294002 (10 μM), a PI3K inhibitor. In addition, Rb1 reversed the Aβ(1-42)-induced decrease in phosphorylation cyclic AMP response element binding (CREB) protein, which could also be blocked by the PI3K inhibitor. All these findings suggest that Rb1 may represent a potential treatment strategy for Alzheimer's disease.

Polymorphisms in genes involved in vincristine pharmacokinetics or pharmacodynamics are not related to impaired motor performance in children with leukemia

INTRODUCTION

Impaired motor performance in children who completed treatment for acute lymphoblastic leukemia (ALL) may be related to polymorphisms of the metabolising gene CYP3A5 or vincristine toxicity related genes MDR-1 and MAPT.

METHODS

Motor performance was measured with the Movement Assessment Battery for Children (movement-ABC). DNA, from mononuclear blood cells was genotyped for CYP3A5, MDR-1 and MAPT polymorphisms.

RESULTS

Motor performance was not significantly affected by CYP3A5*3/*3 and CYP3A5*1*3 genotypes, MDR-1 polymorphisms or MAPT haplotype.

CONCLUSION

Our data did not show that CYP3A5, MDR-1 or MAPT polymorphisms are linked to impaired motor performance in children after treatment for ALL.

Conformational changes and cleavage; are these responsible for the tau aggregation in Alzheimer’s disease?

In the past, post-translational modifications of tau protein, such as phosphorylation, cleavage and conformational changes, have long been implicated in the pathogenesis of Alzheimer’s disease. Unfortunately, the accurate role and relationship between these pathological modifications during tau aggregation remains under extensive study. We had proposed a chronological model of tau pathological processing during Alzheimer´s disease, in which phosphorylation and cleavage could lead to conformational changes causing aggregation and therefore, cell toxicity. We discuss this issue and review in vitro and in situ evidence that supports the relevance of tau modifications that cause its pathological conformations and toxic aggregation. Thus, we offer a brief discussion regarding conformational change and cleavage as future clinical targets.

Alzheimer's Disease, Diagnosis and the Need for Biomarkers

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of aging that presents with memory loss, disorientation, confusion and a reduction in cognitive ability. Although a definite diagnosis of the disorder can only be made post-mortem by histopathological analysis, a number of methods are currently available for the in vivo assessment of AD including psycho-metric tests and neuro-imaging. However, these clinical assessments are relatively nonspecific and imaging is very costly. Genetic testing can be performed if familial AD is suspected, although such cases represent a very small minority of total AD cases. Apolipoprotein E genotype provides a measure for analysing the risk of developing AD, but does not act as an absolute predictive biomarker for AD. Therefore there is a need for an accurate, universal, specific and cost-effective biomarker to facilitate not only ante-mortem diagnosis of AD, but also to allow progression of the disease and response to therapy to be monitored. This is the ultimate goal that our group is pursuing through the pan-European AddNeuroMed project.

Clinical-pathologic study of biomarkers in FTDP-17 (PPND family with N279K tau mutation)

The objective of this clinical-pathologic study was to identify biomarkers for a pallidopontonigral degeneration (PPND) kindred of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) harboring the N279K tau mutation. Five affected subjects, one at-risk who later became symptomatic, and one at-risk asymptomatic mutation carrier, had abnormal (18)fluorodeoxyglucose PET demonstrating asymmetric temporal lobe hypometabolism. All except the asymptomatic mutation carrier had abnormal brain MRI. Parkinsonism, myoclonus, anosmia, insomnia, speech, and autonomic dysfunction were identified. Autopsy of six affected subjects showed frontotemporal degeneration with extensive tauopathy. Further studies of FTDP-17 patients are needed to replicate these findings.

Is aging part of Alzheimer's disease, or is Alzheimer's disease part of aging?

For 70 years after Alois Alzheimer described a disorder of tangle-and-plaque dementia, Alzheimer's disease was a condition of the relatively young. Definitions of Alzheimer's disease (AD) have, however, changed over the past 30 years and under the revised view AD has truly become an age-related disease. Most now diagnosed with AD are elderly and would not have been diagnosed with AD as originally conceived. Accordingly, younger patients that qualify for a diagnosis of AD under both original and current Alzheimer's disease constructs now represent an exceptionally small percentage of the diagnosed population. The question of whether pathogenesis of the "early" and "late" onset cases is similar enough to qualify as a single disease was previously raised although not conclusively settled. Interestingly, debate on this issue has not kept pace with advancing knowledge about the molecular, biochemical and clinical underpinnings of tangle-and-plaque dementias. Since the question of whether both forms of AD share a common pathogenesis could profoundly impact diagnostic and treatment development efforts, it seems worthwhile to revisit this debate.

Polymerization of hyperphosphorylated tau into filaments eliminates its inhibitory activity

Accumulation of abnormally hyperphosphorylated tau (P-tau) in the form of tangles of paired helical filaments and/or straight filaments is one of the hallmarks of Alzheimer's disease (AD) and other tauopathies. P-tau is also found unpolymerized in AD. Although the cognitive decline is known to correlate with the degree of neurofibrillary pathology, whether the formation of filaments or the preceding abnormal hyperphosphorylation of tau is the inhibitory entity that leads to neurodegeneration has been elusive. We have previously shown that cytosolic abnormally hyperphosphorylated tau in AD brain (AD P-tau) sequesters normal tau (N-tau), microtubule-associated protein (MAP) 1, and MAP2, which results in the inhibition of microtubule assembly and disruption of microtubules. Here, we show that polymerization of AD P-tau into filaments inhibits its ability to bind N-tau and as well as the ability to inhibit the assembly of tubulin into microtubules in vitro and in the regenerating microtubule system from cultured cells. Like AD P-tau, the in vitro abnormally hyperphosphorylated recombinant brain N-tau binds N-tau and loses this binding activity on polymerization into filaments. Dissociation of the hyperphosphorylated N-tau filaments by ultrasonication restores its ability to bind N-tau. These findings suggest that the nonfibrillized P-tau is most likely the responsible entity for the disruption of microtubules in neurons in AD. The efforts in finding a therapeutic intervention for tau-induced neurodegeneration need to be directed either to prevent the abnormal hyperphosphorylation of this protein or to neutralize its binding to normal MAPs, rather than to prevent its aggregation into filaments.

PTEN levels in Alzheimer's disease medial temporal cortex

Phosphatase and tensin homologue deleted from chromosome 10 (PTEN) is a dual (protein tyrosine and lipid) phosphatase one of the functions of which is to dephosphorylate phosphatidylinositol 3,4,5-trisphosphate to phosphatidylinositol-3,4-biphosphate thereby inhibiting phosphoinositide-dependent kinase activation of the cell survival kinase Akt. Akt activity is up regulated in Alzheimer's disease (AD) brain in parallel to the progression of neurofibrillary pathology. The present study determined whether altered expression of PTEN occurs in Alzheimer's disease brain. Western immunoblotting revealed no significant changes of PTEN protein levels in nuclear and membrane fractions of medial temporal cortex from a series of Alzheimer's disease and control cases. Similarly, no changes in PTEN protein levels, as determined by dot-blotting, were seen in temporal cortex homogenates from a separate series of Alzheimer's disease and control brains. A small but significant decrease in the levels of Ser(380) p-PTEN was seen in homogenates of Alzheimer's disease temporal cortex. Immunohistochemistry revealed PTEN immunoreactivity in a number of brain structures including neurons, capillaries and structures resembling oligodendrocytes and astrocytes. The majority of temporal cortex pyramidal neurons (93-100%) were PTEN immunopositive. The Alzheimer's disease cases had significantly lower numbers of total ( approximately 12% loss, P<0.02) and PTEN immunopositive ( approximately 15% loss, P<0.01) pyramidal neurons as compared to the control cases.

Glutamate induces rapid loss of axonal neurofilament proteins from cortical neurons in vitro

One of the primary hallmarks of glutamate excitotoxicity is degradation of the neuronal cytoskeleton. Using a tissue culture approach, we have investigated the relationship between excitotoxicity and cytoskeletal degradation within axons, with particular reference to the axon specific neurofilament proteins. Neurofilaments were rapidly lost from axons over a 24-h period in response to excitotoxic insult (as observed by immunocytochemistry and western blotting), while other axonal cytoskeletal markers (such as betaIII-tubulin) remained intact. Treatment with kainic acid and NMDA, or complementary experiments using the pharmacological glutamate receptors blockers CNQX (kainate/AMPA receptor antagonist) and MK-801 (NMDA receptor antagonist), demonstrated that neurofilament degeneration was mediated primarily by NMDA receptor activity. This work suggests that excitotoxicity triggers a progressive pathway of cytoskeletal degeneration within axons, initially characterised by the loss of neurofilament proteins.

Precursor form of brain-derived neurotrophic factor and mature brain-derived neurotrophic factor are decreased in the pre-clinical stages of Alzheimer's disease

Brain-derived neurotrophic factor (BDNF) is critical for the function and survival of neurons that degenerate in the late stage of Alzheimer's disease (AD). There are two forms of BDNF, the BDNF precursor (proBDNF) and mature BDNF, in human brain. Previous studies have shown that BDNF mRNA and protein, including proBDNF, are dramatically decreased in end-stage AD brain. To determine whether this BDNF decrease is an early or late event during the progression of cognitive decline, we used western blotting to measure the relative amounts of BDNF proteins in the parietal cortex of subjects clinically classified with no cognitive impairment (NCI), mild cognitive impairment (MCI) or mild to moderate AD. We found that the amount of proBDNF decreased 21 and 30% in MCI and AD groups, respectively, as compared with NCI, consistent with our previous results of a 40% decrease in end-stage AD. Mature BDNF was reduced 34 and 62% in MCI and AD groups, respectively. Thus, the decrease in mature BDNF and proBDNF precedes the decline in choline acetyltransferase activity which occurs later in AD. Both proBDNF and mature BDNF levels were positively correlated with cognitive measures such as the Global Cognitive Score and the Mini Mental State Examination score. These results demonstrate that the reduction of both forms of BDNF occurs early in the course of AD and correlates with loss of cognitive function, suggesting that proBDNF and BDNF play a role in synaptic loss and cellular dysfunction underlying cognitive impairment in AD.

Tau protein aggregation in the frontal and entorhinal cortices as a function of aging

OBJECTIVES

The abnormal accumulation of tau protein is increasingly recognized as the neuropathological hallmark of a number of dementing illness in which frontotemporal lobar degeneration occurs. In this paper we examined the age-dependant deposition of tau protein in the frontal and entorhinal neocortices.

METHODS

We examined autopsy records from 1997 to 2002 and selected 87 cases (10 in each decade from 0 to 79 years of age, 7 in 80-89 decade) with no history of dementia or other neurodegenerative diseases, and for which neurodegenerative diseases were excluded neuropathologically. Archival paraffin-embedded frontal and entorhinal cortices were examined by both Gallyas-Braak silver staining and a panel of antibodies recognizing tau protein accumulation.

RESULTS

Tau neuronal aggregates were observed in both frontal and entorhinal cortices in the third decade. While the frontal neuronal tau aggregates remained infrequent in the remaining decades, the number and extent ofneuronal tau aggregates in the entorhinal cortex increased such that by the 7th decade the majority of cases showed extensive tau aggregate formation. The most consistent morphological observation was of dense, perikaryal neuronal tau-immunoreactive aggregates, similar to the total tau distribution, firstly presenting in cortical layers II and III and subsequently involving in layers IV-VI. Neuropil threads became maximal in the 9th decade in both frontal and entorhinal cortices. Astrocytic tau accumulation was first observed in both frontal and entorhinal cortices in the 6th decade, predominantly in layer I and subcortical white matter, and increased in number with aging. Extraneuronal tau reactive aggregates and coiled bodies were rarely observed in the entorhinal cortex, and when present, were scattered through layer II to VI.

CONCLUSIONS

We have observed an age-dependant pattern of neuronal, extraneuronal and glial tau protein accumulation in the entorhinal cortex in individuals without neurodegenerative diseases. In contrast, tau protein aggregation is infrequently observed in the frontal cortex as a function of aging.

Cyclin-dependent kinase inhibitors attenuate protein hyperphosphorylation, cytoskeletal lesion formation, and motor defects in Niemann-Pick Type C mice

Dysregulation of cyclin-dependent kinases (cdks) and cytoskeletal protein hyperphosphorylation characterizes a subset of human neurodegenerative diseases, including Alzheimer's disease, amyotrophic lateral sclerosis, and Niemann-Pick Type C (NPC). It is thought that these cytoskeletal changes lead eventually to development of hallmark cytoskeletal lesions such as neurofibrillary tangles and axonal spheroids. Although many studies support an involvement of cdks in these neurodegenerative cascades, it is not known whether cdk activity is essential. The naturally occurring npc-1 mutant mouse mimics human NPC, in displaying activation of cdk5, mitotic cdc2, and cdk4, with concomitant cytoskeletal pathology and neurodegeneration. We availed of this model and specific pharmacological inhibitors of cdk activity, to determine whether cdks are necessary for NPC neuropathology. The inhibitors were infused intracerebroventricularly for a 2-week period, initiated at a pathologically incipient stage. While an inactive stereoisomer, iso-olomoucine, was ineffective, two potent inhibitors, roscovitine and olomoucine, attenuated significantly the hyperphosphorylation of neurofilament, tau, and mitotic proteins, reduced the number of spheroids, modulated Purkinje neuron death, and ameliorated motor defects in npc mice. These results suggest that cdk activity is required for neuropathology and subsequent motor impairment in NPC. Studies aimed at knocking down individual cdks in these mice will help identify the specific cdk(s) that are essential, and delineate their precise roles in the neurodegenerative process.

PAR-1 Kinase Plays an Initiator Role in a Temporally Ordered Phosphorylation Process that Confers Tau Toxicity in Drosophila

Multisite hyperphosphorylation of tau has been implicated in the pathogenesis of neurodegenerative diseases including Alzheimer's disease (AD). However, the phosphorylation events critical for tau toxicity and mechanisms regulating these events are largely unknown. Here we show that Drosophila PAR-1 kinase initiates tau toxicity by triggering a temporally ordered phosphorylation process. PAR-1 directly phosphorylates tau at S262 and S356. This phosphorylation event is a prerequisite for the action of downstream kinases, including glycogen synthase kinase 3 (GSK-3) and cyclin-dependent kinase-5 (Cdk5), to phosphorylate several other sites and generate disease-associated phospho-epitopes. The initiator role of PAR-1 is further underscored by the fact that mutating PAR-1 phosphorylation sites causes a much greater reduction of overall tau phosphorylation and toxicity than mutating S202, one of the downstream sites whose phosphorylation depends on prior PAR-1 action. These findings begin to differentiate the effects of various phosphorylation events on tau toxicity and provide potential therapeutic targets.

Akt/PKB kinase phosphorylates separately Thr212 and Ser214 of tau protein in vitro

Microtubule-associated protein tau contains a consensus motif for protein kinase B/Akt (Akt), which plays an essential role in anti-apoptotic signaling. The motif encompasses the AT100 double phospho-epitope (Thr212/Ser214), a specific marker for Alzheimer's disease (AD) and other neurodegenerations, raising the possibility that it could be generated by Akt. We studied Akt-dependent phosphorylation of tau protein in vitro. We found that Akt phosphorylated both Thr212 and Ser214 in the longest and shortest tau isoforms as determined using phospho site-specific antibodies against tau. Akt did not phosphorylate other tau epitopes, including Tau-1, AT8, AT180, 12E8 and PHF-1. The Akt-phosphorylated tau retained its initial electrophoretic mobility. Immunoprecipitation studies with phospho-specific Thr212 and Ser214 antibodies revealed that only one of the two sites is phosphorylated per single tau molecule, resulting in tau immunonegative for AT100. Mixed kinase studies showed that prior Ser214 phosphorylation by Akt blocked protein kinase A but not GSK3beta activity. On the other hand, GSK3beta selectively blocked Ser214 phosphorylation, which was prevented by lithium. The results suggest that Akt may be involved in AD-specific phosphorylation of tau at the AT100 epitope in conjunction with other kinases. Our data suggest that phosphorylation of tau by Akt may play specific role(s) in Akt-mediated anti-apoptotic signaling, particularly relevant to AD and other neurodegenerations.

The role of tau (MAPT) in frontotemporal dementia and related tauopathies

Tau is a multifunctional protein that was originally identified as a microtubule-associated protein. In patients diagnosed with frontotemporal dementia and parkinsonism linked to chromosome 17, mutations in the gene encoding tau (MAPT) have been identified that disrupt the normal binding of tau to tubulin resulting in pathological deposits of hyperphosphorylated tau. Abnormal filamentous tau deposits have been reported as a pathological characteristic in several other neurodegenerative diseases, including frontotemporal dementia, Pick Disease, Alzheimer disease, argyrophilic grain disease, progressive supranuclear palsy, and corticobasal degeneration. In the last five years, extensive research has identified 34 different pathogenic MAPT mutations in 101 families worldwide. In vitro, cell-free and transfected cell studies have provided valuable information on tau dysfunction and transgenic mice carrying human MAPT mutations are being generated to study the influence of MAPT mutations in vivo. This mutation update describes the considerable differences in clinical and pathological presentation of patients with MAPT mutations and summarizes the effect of the different mutations on tau functioning. In addition, the role of tau as a genetic susceptibility factor is discussed, together with the genetic evidence for additional causal genes for tau-positive as well as tau-negative dementia.

Structure, stability, and aggregation of paired helical filaments from tau protein and FTDP-17 mutants probed by tryptophan scanning mutagenesis

By using tryptophan scanning mutagenesis, we observed the kinetics and structure of the polymerization of tau into paired helical filaments (PHFs) independently of exogenous reporter dyes. The fluorescence exhibits pronounced blue shifts due to burial of the residue inside PHFs, depending on Trp position. The effect is greatest near the center of the repeat domain, showing that the packing is tightest near the beta-structure inducing hexapeptide motifs. The tryptophan response allows measurement of PHF stability made by different tau isoforms and mutants. Unexpectedly, the stability of PHFs is quite low (denaturation half-points approximately 1.0 m GdnHCl), implying that incipient aggregation should be reversible and that the observed high stability of Alzheimer PHFs is due to other factors. The stability increases with the number of repeats and with tau mutants promoting beta-structure, arguing for a gain of toxic function in frontotemporal dementias. Fluorescence resonance energy transfer (FRET) was used to analyze the distances of Tyr(310) to tryptophans in different positions. The degree of FRET in the soluble protein was position-dependent, with highest signals within the second and third repeats but low or no signals further away. In PHFs most mutants showed FRET, indicating that tight packing results from assembly of tau into PHFs.

Tau aggregation in the hippocampal formation: an ageing or a pathological process?

Tauopathy is a concept to describe different genetic or metabolic dysfunctions of tau proteins that generate most of the known dementing disorders. Tauopathy is a degenerating process that also affects the entorhinal formation, and then the hippocampal formation in ageing. In Alzheimer's disease (AD), a disease due to APP dysfunction, a similar tauopathy process in observed in neocortical areas, well correlated to cognitive impairment. One important gap of knowledge is the relationship between tauopathy in the hippocampal formation, ageing, AD, and cognitive impairment. Here we show that the multidisciplinary analysis of numerous brains from non-demented and demented patients suggests the following observations: tauopathy of the hippocampal formation in humans is age-related but not an age-dependent process, also independent of AD, but amplified by APP dysfunctions. Tauopathy in the entorhinal and hippocampal formation could be another type of pathological dysfunction of tau proteins, and a therapeutic target to delay AD. Relevant animal models are desperately needed to address this issue.

Intracellular A-beta amyloid, a sign for worse things to come?

In this review the authors discuss the possible neuropathological role of intracellular amyloid-beta accumulation in Alzheimer's disease (AD) pathology. There is abundant evidence that at early stages of the disease, prior to A-beta amyloid plaque formation, A-beta peptides accumulate intraneuronally in the cerebral cortex and the hippocampus. The experimental evidence would indicate that intracellular amyloid-beta could originate both by intracellular biosynthesis and also from the uptake of amyloidogenic peptides from the extracellular milieu. Herein the aspects of the possible impact of intracellular amyloid-beta in human AD pathology are discussed, as well as recent observations from a rat transgenic model with a phenotype of intracellular accumulation of A-beta fragments in neurons of the hippocampus and cortex, without plaque formation. In this model, the intracellular amyloid-beta phenotype is accompanied by increased MAPK/ERK activity and tau hyperphosphorylation. Finally, the authors discuss the hypothesis that, prior to plaque formation, intracellular A-beta accumulation induces biochemical and pathological changes in the brain at the cellular level priming neurons to further cytotoxic attack of extracellular amyloidogenic peptides.

Mutations of tau protein in frontotemporal dementia promote aggregation of paired helical filaments by enhancing local beta-structure

The microtubule-associated protein tau is a natively unfolded protein in solution, yet it is able to polymerize into the ordered paired helical filaments (PHF) of Alzheimer's disease. In the splice isoforms lacking exon 10, this process is facilitated by the formation of beta-structure around the hexapeptide motif PHF6 ((306)VQIVYK(311)) encoded by exon 11. We have investigated the structural requirements for PHF polymerization in the context of adult tau isoforms containing four repeats (including exon 10). In addition to the PHF6 motif there exists a related PHF6* motif ((275)VQIINK(280)) in the repeat encoded by the alternatively spliced exon 10. We show that this PHF6* motif also promotes aggregation by the formation of beta-structure and that there is a cross-talk between the two hexapeptide motifs during PHF aggregation. We also show that two of the tau mutations found in hereditary frontotemporal dementias, DeltaK280 and P301L, have a much stronger tendency for PHF aggregation which correlates with their high propensity for beta-structure around the hexapeptide motifs.

JNK activation is associated with intracellular beta-amyloid accumulation

c-Jun has been implicated in the pathogenesis of Alzheimer's disease (AD), but the upstream cascade leading to c-Jun activation in AD is not known. Activation of c-Jun N-terminal kinase (JNK) is obviously a candidate for the upstream event. We tested this possibility focusing on PS1-linked AD. First, we observed that JNK is actually activated in cerebral neurons of PS1-linked AD patients, using immunohistochemistry and Western blot analyses with anti-activated JNK antibodies. We analyzed the relationship between beta-amyloid (beta A) and JNK activation by using aged transgenic mice overexpressing mutant (M146L) PS1 and human AD brains. The mice showed no neuronal loss but a very few diffuse beta A deposits, corresponding to the early stage of PS1-linked AD brain. Some neurons were reactive for anti-beta A antibodies in the cerebral cortex. Interestingly, JNK activation was observed in neurons showing intracellular beta A immunoreactivity in transgenic mice. Association between intracellular beta A and JNK activation was confirmed in cortical neurons of sporadic and PS1-linked AD patients. Furthermore, introduction of beta A peptides into the primary culture cortical neurons induced JNK activation and cell death. Collectively, these results suggested that intracellular beta A accumulation might trigger JNK activation leading to neuronal death.

Increased Protein Tyrosine Phosphorylation in Apoptotic Neural Cell Death Due to Microtubule Perturbations

The microtubule-perturbing drugs colchicine and taxol have been found to induce apoptosis in a CNS neuronal cell line. Apoptosis in drug-treated rat B103 neuroblastoma cells was evident in characteristic morphological changes, internucleosomal DNA fragmentation, and loss of nuclear content. Since colchicine and taxol have opposite actions on microtubule integrity, disruption of the active turnover of the microtubule network appears to be a crucial step for apoptosis to occur. It has been suggested that the basis for apoptosis by these drugs derives from their known block of the cell cycle at G₂/M, but this does not appear the sole reason as both colchicine and taxol were able to evoke high levels of apoptosis in cells differentiated by Bt₂cAMP or serum withdrawal. Further tests of cellular consequences of microtubule perturbation revealed a specific impact on signal transduction involving protein tyrosine phosphorylation. Immunoprecipitation with antibodies against tyrosine phosphorylated proteins showed a striking increase in the phosphorylation of a Triton-insoluble ~90 kDa protein, roughly concurrent with the onset of internucleosomal DNA fragmentation. Cycloheximide and genistein significantly reduced cell death and blocked appearance of the ~90 kDa tyrosine phosphorylated protein. Data suggest the hypothesis that signal transduction leading to apoptosis can be triggered by anomalous microtubule turnover and that the mechanism involves tyrosine phosphorylation of a ~90 kDa Triton-resistant protein.

Induction of Alzheimer-specific Tau epitope AT100 in apoptotic human fetal astrocytes

In Alzheimer's and other neurodegenerative diseases, hyperphosphorylated tau accumulates in affected neuronal and glial cells in the form of paired helical filaments (PHFs). This tau binds antibody AT100, which recognizes the double phosphorylation site (Thr212/Ser214) that is not present in normal biopsy tau. In primary cultures, highly enriched (>98%) in astrocytes of human fetal brain, three polypeptides of 52, 64, and 70 kD showed immunoreactivity with tau antibodies against non-phosphorylated epitopes, accounting for 88, 12, and <1%, respectively, of the total reactivity. All three polypeptides were phosphorylated at the PHF-1 epitope but not at the epitopes Tau-1, 12E8, AT8, and AT100. Treatment of cultures with okadaic acid resulted in apoptosis characterized by the blebbing of the plasma membrane, condensation of nuclear chromatin, and fragmentation of the nucleus. This treatment also resulted in a 3- to 5-fold increase in the content of both tau protein and phosphorylation. The increases were observed in all phosphorylation sites examined, and included the AT100 site. The AT100 site has been proposed to be generated by protein kinase B/Akt and Cdc2. Since okadaic acid can induce an AD-like hyperphosphorylated state of normal tau in primary cultures of human brain cells, a simple cellular model is available permitting study of self-aggregation of tau and phosphorylation events characteristic of neurodegeneration.

Alzheimer-like neurodegeneration in aged antinerve growth factor transgenic mice

Neurotrophin nerve growth factor (NGF) has been suggested to be involved in age-related neurodegenerative diseases, but no transgenic model is currently available to study this concept. We have obtained transgenic mice expressing a neutralizing anti-NGF recombinant antibody, in which the levels of antibodies are three orders of magnitude higher in adult than in newborn mice [F.R., S. C. , A.C., E. Di Daniel, J. Franzot, S. Gonfloni, G. Rossi, N. B. & A. C. (2000) J. Neurosci., 20, 2589-2601]. In this paper, we analyze the phenotype of aged anti-NGF transgenic mice and demonstrate that these mice acquire an age-dependent neurodegenerative pathology including amyloid plaques, insoluble and hyperphosphorylated tau, and neurofibrillary tangles in cortical and hippocampal neurons. Aged anti-NGF mice also display extensive neuronal loss throughout the cortex, cholinergic deficit in the basal forebrain, and behavioral deficits. The overall picture is strikingly reminiscent of human Alzheimer's disease. Aged anti-NGF mice represent, to our knowledge, the most comprehensive animal model for this severe neurodegenerative disease. Also, these results demonstrate that, in mice, a deficit in the signaling and/or transport of NGF leads to neurodegeneration.

Aberrant splicing of tau pre-mRNA caused by intronic mutations associated with the inherited dementia frontotemporal dementia with parkinsonism linked to chromosome 17

Frontotemporal dementia accounts for a significant fraction of dementia cases. Frontotemporal dementia with parkinsonism linked to chromosome 17 is associated with either exonic or intronic mutations in the tau gene. This highlights the involvement of aberrant pre-mRNA splicing in the pathogenesis of neurodegenerative disorders. Little is known about the molecular mechanisms of the splicing defects underlying these diseases. To establish a model system for studying the role of pre-mRNA splicing in neurodegenerative diseases, we have constructed a tau minigene that reproduces tau alternative splicing in both cultured cells and in vitro biochemical assays. We demonstrate that mutations in a nonconserved intronic region of the human tau gene lead to increased splicing between exon 10 and exon 11. Systematic biochemical analyses indicate the importance of U1 snRNP and, to a lesser extent, U6 snRNP in differentially recognizing wild-type versus intron mutant tau pre-mRNAs. Gel mobility shift assays with purified U1 snRNP and oligonucleotide-directed RNase H cleavage experiments support the idea that the intronic mutations destabilize a stem-loop structure that sequesters the 5' splice site downstream of exon 10 in tau pre-mRNA, leading to increases in U1 snRNP binding and in splicing between exon 10 and exon 11. Thus, mutations in nonconserved intronic regions that increase rather than decrease alternative splicing can be an important pathogenic mechanism for the development of human diseases.

Filamentous tau pathology in nerve cells, astrocytes, and oligodendrocytes of aged baboons

Intracellular filamentous inclusions containing abnormally phosphorylated tau protein are hallmarks of several human neurodegenerative disorders. This study reveals tau-positive cytoskeletal abnormalities in neurons and glial cells of aged baboons. The brains of four baboons (Papio hamadryas, 20-30 yr of age) were examined using the Gallyas silver technique for neurofibrillary changes and phosphorylation-dependent anti-tau antibodies (AT8, AT100, AT270, PHF-1, TG-3). Conspicuous changes were noted in two animals, 26 and 30 yr of age. In both animals, a combination of neuronal and glial cytoskeletal pathology was seen preferentially affecting limbic brain areas, including the hippocampal formation. In the 30-yr-old animal, numerous tau-positive inclusions were seen in the granule cells of the fascia dentata. These cells even exhibited an accumulation of argyrophilic neurofibrillary tangles. The glial changes affected both astrocytes and oligodendrocytes. Tau-positive astrocytes were seen in perivascular, subpial, and subependymal locations. Tau-positive oligodendrocytes preferentially occurred in limbic fiber tracts including the entorhinal perforant path. Ultrastructurally, tau-positive straight filaments (10-14 nm) in both neurons and glial cells were revealed by anti-tau immunoelectron microscopy. This study thus indicates the potential usefulness of aged baboons for experimental investigation of neuronal and glial filamentous tau pathology. This nonhuman primate species may provide valuable information pertinent to the broad spectrum of human tauopathies.