Neuronal and glial tau-positive inclusions in diverse neurologic diseases share common phosphorylation characteristics

Low clinical sensitivity and unexpectedly high incidence for neuropathologically diagnosed progressive supranuclear palsy

The objective of this study was to determine the prevalence, incidence, and clinical diagnostic accuracy for neuropathologically diagnosed progressive supranuclear palsy (PSP) with data from a longitudinal clinicopathological study using Rainwater criteria to define neuropathological PSP. Of 954 autopsy cases, 101 met Rainwater criteria for the neuropathologic diagnosis of PSP. Of these, 87 were termed clinicopathological PSP as they also had either dementia or parkinsonism or both. The prevalence of clinicopathologically defined PSP subjects in the entire autopsy dataset was 9.1%, while the incidence rate was estimated at 780 per 100 000 persons per year, roughly 50-fold greater than most previous clinically determined PSP incidence estimates. A clinical diagnosis of PSP was 99.6% specific but only 9.2% sensitive based on first examination, and 99.3% specific and 20.7% sensitive based on the final clinical exam. Of the clinicopathologically defined PSP cases, 35/87 (∼40%) had no form of parkinsonism at first assessment, while this decreased to 18/83 (21.7%) at final assessment. Our study confirms a high specificity but low sensitivity for the clinical diagnosis of PSP. The low clinical sensitivity for PSP is likely primarily responsible for previous underestimates of the PSP population incidence rate.

Populations of Tau Conformers Drive Prion-like Strain Effects in Alzheimer's Disease and Related Dementias

Recent findings of diverse populations of prion-like conformers of misfolded tau protein expand the prion concept to Alzheimer's disease (AD) and monogenic frontotemporal lobar degeneration (FTLD)-MAPT P301L, and suggest that distinct strains of misfolded proteins drive the phenotypes and progression rates in many neurodegenerative diseases. Notable progress in the previous decades has generated many lines of proof arguing that yeast, fungal, and mammalian prions determine heritable as well as infectious traits. The extraordinary phenotypic diversity of human prion diseases arises from structurally distinct prion strains that target, at different progression speeds, variable brain structures and cells. Although human prion research presents beneficial lessons and methods to study the mechanism of strain diversity of protein-only pathogens, the fundamental molecular mechanism by which tau conformers are formed and replicate in diverse tauopathies is still poorly understood. In this review, we summarize up to date advances in identification of diverse tau conformers through biophysical and cellular experimental paradigms, and the impact of heterogeneity of pathological tau strains on personalized structure- and strain-specific therapeutic approaches in major tauopathies.

Structures of tau and α-synuclein filaments from brains of patients with neurodegenerative diseases

Intracellular accumulations and aggregates of abnormal protein, consisting of amyloid-like fibrils, are common neuropathological features of many neurodegenerative diseases. The distributions and spreading of these pathological proteins are closely correlated with clinical symptoms and progression. Recent evidence supports the idea that template-mediated amplification of amyloid-like fibrils and intracellular propagation of fibril seeds are the main mechanisms by which pathological features spread along the neural circuits in the brain. Here, we review recent developments in the structural analysis of amyloid-like fibrils from brains of patients with various types of tauopathy and alpha-synucleinopathy, focusing on cryo-electron microscopy and mass analysis, and we discuss their relevance to the mechanisms of template-mediated amplification and intracellular propagation.

Rainwater Charitable Foundation criteria for the neuropathologic diagnosis of progressive supranuclear palsy

Neuropathologic criteria for progressive supranuclear palsy (PSP) proposed by a National Institute of Neurological Disorders and Stroke (NINDS) working group were published in 1994 and based on the presence of neurofibrillary tangles in basal ganglia and brainstem. These criteria did not stipulate detection methods or incorporate glial tau pathology. In this study, a group of 14 expert neuropathologists scored digital slides from 10 brain regions stained with hematoxylin and eosin (H&E) and phosphorylated tau (AT8) immunohistochemistry. The cases included 15 typical and atypical PSP cases and 10 other tauopathies. Blinded to clinical and neuropathological information, raters provided a categorical diagnosis (PSP or not-PSP) based upon provisional criteria that required neurofibrillary tangles or pretangles in two of three regions (substantia nigra, subthalamic nucleus, globus pallidus) and tufted astrocytes in one of two regions (peri-Rolandic cortices, putamen). The criteria showed high sensitivity (0.97) and specificity (0.91), as well as almost perfect inter-rater reliability for diagnosing PSP and differentiating it from other tauopathies (Fleiss kappa 0.826). Most cases (17/25) had 100% agreement across all 14 raters. The Rainwater Charitable Foundation criteria for the neuropathologic diagnosis of PSP feature a simplified diagnostic algorithm based on phosphorylated tau immunohistochemistry and incorporate tufted astrocytes as an essential diagnostic feature.

Neurodegenerative proteinopathies associated with neuroinfections

Infectious agents, including viruses and bacteria, are proposed to be involved in the pathogenesis of Alzheimer’s disease (AD). According to this hypothesis, these agents have capacity to evade the host immune system leading to chronic infection, inflammation, and subsequent deposition of Aβ and phosphorylated-tau in the brain. Co-existing proteinopathies and age-related pathologies are common in AD and the brains of elderly individuals, but whether these are also related to neuroinfections remain to be established. This study determined the prevalence and distribution of neurodegenerative proteinopathies in patients with infection-induced acute or chronic inflammation associated with herpes simplex virus (HSV) encephalitis (n = 13) and neurosyphilis (n = 23). The mean age at death in HSV patients was 53 ± 12 years (range 24–65 years) and survival was 9 days–6 years following initial infection. The mean age at death and survival in neurosyphilis patients was 60 ± 15 years (range 36–86 years) and 1–5 years, respectively. Neuronal tau-immunoreactivity and neurites were observed in 8 HSV patients and 19 neurosyphilis patients, and in approximately half of these, this was found in regions associated with inflammation and expanding beyond regions expected from the Braak stage of neurofibrillary degeneration. Five neurosyphilis patients had cortical ageing-related tau astrogliopathy. Aβ-plaques were found in 4 HSV patients and 11 neurosyphilis patients. Lewy bodies were observed in one HSV patient and two neurosyphilis patients. TDP-43 pathology was absent. These observations provide insights into deposition of neurodegenerative proteins in neuroinfections, which might have implications for COVID-19 patients with chronic and/or post-infectious neurological symptoms and encephalitis.

Comparison of Common and Disease-Specific Post-translational Modifications of Pathological Tau Associated With a Wide Range of Tauopathies

Tauopathies are the most common type of neurodegenerative proteinopathy, being characterized by cytoplasmic aggregates of hyperphosphorylated tau protein. The formation and morphologies of these tau inclusions, the distribution of the lesions and related metabolic changes in cytoplasm differ among different tauopathies. The aim of this study was to examine whether there are differences in the post-translational modifications (PTMs) in the pathological tau proteins. We analyzed sarkosyl-insoluble pathological tau proteins prepared from brains of patients with Alzheimer's disease, Pick's disease, progressive supranuclear palsy, corticobasal degeneration, globular glial tauopathy, and frontotemporal dementia and parkinsonisms linked to chromosome 17 with tau inclusions using liquid chromatography mass spectrometry. In pathological tau proteins associated with a wide range of tauopathies, 170 PTMs in total were identified including new PTMs. Among them, common PTMs were localized in the N- and C-terminal flanking regions of the microtubule binding repeats and PTMs, which were considered to be disease-specific, were found in microtubule binding repeats forming filament core. These suggested that the differences in PTMs reflected the differences in tau filament core structures in each disease.

Distribution of tau hyperphosphorylation in canine dementia resembles early Alzheimer's disease and other tauopathies

Some aged community dogs acquire a degenerative syndrome termed Canine Cognitive Dysfunction (CCD) that resembles human dementia because of Alzheimer’s Disease (AD), with comparable cognitive and behavioral deficits. Dogs also have similar neuroanatomy, share our domestic environment and develop amyloid‐β plaques, making them likely a valuable ecological model of AD. However, prior investigations have demonstrated a lack of neurofibrillary tau pathology in aged dogs, an important hallmark of AD, though elevated phosphorylated tau (p‐tau) at the Serine 396 (S396) epitope has been reported in CCD. Here using enhanced immunohistochemical methods, we investigated p‐tau in six CCD brains and six controls using the AT8 antibody (later stage neurofibrillary pathology), and an antibody against S396 p‐tau (earlier stage tau dysfunction). For the first time, we systematically assessed the Papez circuit and regions associated with Braak staging and found that all CCD dogs displayed elevated S396 p‐tau labeling throughout the circuit. The limbic thalamus was particularly implicated, with a similar labeling pattern to that reported for AD neurofibrillary pathology, especially the anterior nuclei, while the hippocampus exhibited dysfunction confined to synaptic layers and efferent pathways. The cingulate and temporal lobes displayed significantly greater tauopathy than the frontal and occipital cortices, also reflective of early Braak staging patterns in AD. Immunofluorescence confirmed that S396 was accumulating within neuronal axons, somata and oligodendrocytes. We also observed AT8 labeling in one CCD brain, near the transentorhinal cortex in layer II neurons, one of the first regions to be affected in AD. Together, these data demonstrate a concordance in regional distribution of tauopathy between CCD and AD, most evident in the limbic thalamus, an important step in further validating CCD as a translational model for human AD and understanding early AD pathogenic mechanisms.

Dale Schenk One Year Anniversary: Fighting to Preserve the Memories

It has been a year since we lost Dale Schenk on September 30, 2016. Dale's visionary work resulted in the remarkable discovery in 1999 that an experimental amyloid-β (Aβ) vaccine reduced the neurodegeneration in a transgenic model of Alzheimer's disease (AD). Following Dale's seminal work, several active and passive immunotherapies have since been developed and tested in the clinic for AD, Parkinson's disease (PD), and other neurodegenerative disorders. Here we provide a brief overview of the current state of development of immunotherapy for AD, PD, and other neurodegenerative disorders in the context of this anniversary. The next steps in the development of immunotherapies will require combinatorial approaches mixing antibodies against various targets (e.g., Aβ, α-syn, Tau, and TDP43) with small molecules that block toxicity, aggregation, inflammation, and promote cell survival.

Reconsideration of Amyloid Hypothesis and Tau Hypothesis in Alzheimer's Disease

The so-called amyloid hypothesis, that the accumulation and deposition of oligomeric or fibrillar amyloid β (Aβ) peptide is the primary cause of Alzheimer's disease (AD), has been the mainstream concept underlying AD research for over 20 years. However, all attempts to develop Aβ-targeting drugs to treat AD have ended in failure. Here, we review recent findings indicating that the main factor underlying the development and progression of AD is tau, not Aβ, and we describe the deficiencies of the amyloid hypothesis that have supported the emergence of this idea.

Exposure of the Amino Terminus of Tau Is a Pathological Event in Multiple Tauopathies

Pathological changes to the tau protein, including conformational changes and aggregation, are major hallmarks of a group of neurodegenerative disorders known as tauopathies. Among the conformational changes are alterations involving the extreme amino terminus of the protein, known as the phosphatase-activating domain (PAD). Aberrant PAD exposure induces a signaling cascade that leads to disruption of axonal transport, a critical function for neuronal survival. Conformational display of PAD is an early marker of pathological tau in Alzheimer disease (AD), but its role in other tauopathies has yet to be firmly established. We used a relatively novel N-terminal, conformation-sensitive antibody, TNT2, to determine whether misfolding in the amino terminus (ie, PAD exposure) occurs in non-AD tauopathies. We found that TNT2 specifically labeled pathological tau in post-mortem human brain tissue from Pick disease, progressive supranuclear palsy, corticobasal degeneration, and chronic traumatic encephalopathy, but did not label nonpathological, parenchymal tau. Tau13, another N-terminal antibody, was not sensitive to pathological N-terminal conformations. Tau13 did not readily distinguish between normal (ie, parenchymal tau) and pathological tau species and showed a range of effectiveness at identifying tau pathologies in the non-AD tauopathies. These findings demonstrate that the conformational display of the PAD in tau represents a common pathological event in many tauopathies.

Tau downregulates BDNF expression in animal and cellular models of Alzheimer's disease

In Alzheimer's disease, soluble tau accumulates and deposits as neurofibrillary tangles (NFTs). However, a precise toxic mechanism of tau is not well understood. We hypothesized that overexpression of wild-type tau downregulates brain-derived neurotrophic factor (BDNF), a neurotrophic peptide essential for learning and memory. Two transgenic mouse models of human tau expression and human tau (hTau40)-transfected human neuroblastoma (SH-SY5Y) cells were used to examine the effect of excess or pathologically modified wild-type human tau on BDNF expression. Both transgenic mouse models, with or without NFTs, as well as hTau40-SH-SY5Y cells significantly downregulated BDNF messenger RNA compared with controls. Similarly, transgenic mice overexpressing amyloid-β (Aβ) significantly downregulated BDNF expression. However, when crossed with tau knockout mice, the resulting animals exhibited BDNF levels that were not statistically different from wild-type mice. These results demonstrate that excess or pathologically modified wild-type human tau downregulates BDNF and that neither a mutation in tau nor the presence of NFTs is required for toxicity. Moreover, our findings suggest that tau at least partially mediates Aβ-induced BDNF downregulation. Therefore, Alzheimer's disease treatments targeting Aβ alone may not be effective without considering the impact of tau pathology on neurotrophic pathways.

Molecular Mechanisms in the Pathogenesis of Alzheimer's disease and Tauopathies-Prion-Like Seeded Aggregation and Phosphorylation

Neurofibrillary tau pathology (tangles and threads) and extracellular amyloid-β (Aβ) pathology are defining features of Alzheimer’s disease. For 25 years, most research has focused on the amyloid hypothesis of AD pathogenesis and progression. But, because of failures in clinical trials of Aβ-targeted therapies and the new concept of prion-like propagation of intracellular abnormal proteins, tau has come back into the spotlight as a candidate therapeutic target in AD. Tau pathologies are found in a range of neurodegenerative disorders, but extensive analyses of pathological tau in diseased brains has demonstrated that the abnormal tau protein in each disease is structurally distinct, supporting the idea that progression of the diverse but characteristic tau pathologies occurs through prion-like seed-dependent aggregation. Therefore, intervention in the conversion of normal tau to abnormal forms and in cell-to-cell transmission of tau may be the key to development of disease-modifying therapies for AD and other dementing disorders.

Immunotherapeutic Approaches Targeting Amyloid-β, α-Synuclein, and Tau for the Treatment of Neurodegenerative Disorders

Disease-modifying alternatives are sorely needed for the treatment of neurodegenerative disorders, a group of diseases that afflict approximately 50 million Americans annually. Immunotherapy is one of the most developed approaches in this direction. Vaccination against amyloid-β, α-synuclein, or tau has been extensively explored, specially as the discovery that these proteins may propagate cell-to-cell and be accessible to antibodies when embedded into the plasma membrane or in the extracellular space. Likewise, the use of passive immunization approaches with specific antibodies against abnormal conformations of these proteins has also yielded promising results. The clinical development of immunotherapies for Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia, dementia with Lewy bodies, and other neurodegenerative disorders is a field in constant evolution. Results to date suggest that immunotherapy is a promising therapeutic approach for neurodegenerative diseases that progress with the accumulation and prion-like propagation of toxic protein aggregates. Here we provide an overview of the most novel and relevant immunotherapeutic advances targeting amyloid-β in Alzheimer’s disease, α-synuclein in Alzheimer’s disease and Parkinson’s disease, and tau in Alzheimer’s disease and frontotemporal dementia.

Impaired APP activity and altered Tau splicing in embryonic stem cell-derived astrocytes obtained from an APPsw transgenic minipig

Animal models of familial juvenile onset of Alzheimer's disease (AD) often fail to produce diverse pathological features of the disease by modification of single gene mutations that are responsible for the disease. They can hence be poor models for testing and development of novel drugs. Here, we analyze in vitro-produced stem cells and their derivatives from a large mammalian model of the disease created by overexpression of a single mutant human gene (APPsw). We produced hemizygous and homozygous radial glial-like cells following culture and differentiation of embryonic stem cells (ESCs) isolated from embryos obtained from mated hemizygous minipigs. These cells were confirmed to co-express varying neural markers, including NES, GFAP and BLBP, typical of type one radial glial cells (RGs) from the subgranular zone. These cells had altered expression of CCND1 and NOTCH1 and decreased expression of several ribosomal RNA genes. We found that these cells were able to differentiate into astrocytes upon directed differentiation. The astrocytes produced had decreased α- and β-secretase activity, increased γ-secretase activity and altered splicing of tau. This indicates novel aspects of early onset mechanisms related to cell renewal and function in familial AD astrocytes. These outcomes also highlight that radial glia could be a potentially useful population of cells for drug discovery, and that altered APP expression and altered tau phosphorylation can be detected in an in vitro model of the disease. Finally, it might be possible to use large mammal models to model familial AD by insertion of only a single mutation.

Summary: Insight into astrocyte and radial glia pathology in an in vitro culture system derived from the APPsw pig.

Immunotherapy for neurodegenerative diseases: focus on α-synucleinopathies

Immunotherapy is currently being intensively explored as much-needed disease-modifying treatment for neurodegenerative diseases. While Alzheimer's disease (AD) has been the focus of numerous immunotherapeutic studies, less attention has been paid to Parkinson's disease (PD) and other neurodegenerative disorders. The reason for this difference is that the amyloid beta (Aβ) protein in AD is a secreted molecule that circulates in the blood and is readably recognized by antibodies. In contrast, α-synuclein (α-syn), tau, huntingtin and other proteins involved in neurodegenerative diseases have been considered to be exclusively of intracellular nature. However, the recent discovery that toxic oligomeric versions of α-syn and tau accumulate in the membrane and can be excreted to the extracellular environment has provided a rationale for the development of immunotherapeutic approaches for PD, dementia with Lewy bodies, frontotemporal dementia, and other neurodegenerative disorders characterized by the abnormal accumulation of these proteins. Active immunization, passive immunization, and T cell-mediated cellular immunotherapeutic approaches have been developed targeting Aβ, α-syn and tau. Most advanced studies, including results from phase III clinical trials for passive immunization in AD, have been recently reported. Results suggest that immunotherapy might be a promising therapeutic approach for neurodegenerative diseases that progress with the accumulation and propagation of toxic protein aggregates. In this manuscript we provide an overview on immunotherapeutic advances for neurodegenerative disorders, with special emphasis on α-synucleinopathies.

CSF T-Tau/Aβ42 predicts white matter microstructure in healthy adults at risk for Alzheimer's disease

Cerebrospinal fluid (CSF) biomarkers T-Tau and Aβ(42) are linked with Alzheimer's disease (AD), yet little is known about the relationship between CSF biomarkers and structural brain alteration in healthy adults. In this study we examined the extent to which AD biomarkers measured in CSF predict brain microstructure indexed by diffusion tensor imaging (DTI) and volume indexed by T1-weighted imaging. Forty-three middle-aged adults with parental family history of AD received baseline lumbar puncture and MRI approximately 3.5 years later. Voxel-wise image analysis methods were used to test whether baseline CSF Aβ(42), total tau (T-Tau), phosphorylated tau (P-Tau) and neurofilament light protein predicted brain microstructure as indexed by DTI and gray matter volume indexed by T1-weighted imaging. T-Tau and T-Tau/Aβ(42) were widely correlated with indices of brain microstructure (mean, axial, and radial diffusivity), notably in white matter regions adjacent to gray matter structures affected in the earliest stages of AD. None of the CSF biomarkers were related to gray matter volume. Elevated P-Tau and P-Tau/Aβ(42) levels were associated with lower recognition performance on the Rey Auditory Verbal Learning Test. Overall, the results suggest that CSF biomarkers are related to brain microstructure in healthy adults with elevated risk of developing AD. Furthermore, the results clearly suggest that early pathological changes in AD can be detected with DTI and occur not only in cortex, but also in white matter.

RETRACTED: Wild type and P301L mutant Tau promote neuro-inflammation and α-Synuclein accumulation in lentiviral gene delivery models

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Concerns about the article were raised on PubPeer [https://pubpeer.com/publications/DA4525FDCD8F7FEA2E4ACC9EC9322F] namely that in the western blots there are similarities between Fig. 1D and 1E, Fig. 2B duplicates Fig. 3E, Fig. 4L duplicates Fig. 5A and Fig. 4A partly duplicates Fig. 4F, and Figure 2D is the same as Figure 1B in Algarzae, N., Hebron, M., Miessau, M., Moussa, C.E.H., 2012. Parkin prevents cortical atrophy and Ab-induced alterations of brain metabolism: 13C NMR and magnetic resonance imaging studies in AD models. Neuroscience 225, 22-34. The corresponding author was not able to provide the raw data, and therefore requested to retract the article. Authors Charbel E.-H. Moussa, G. William Rebeck and Alexander M. Herman agreed to this retraction, Preeti J. Khandelwal and Sonya B. Dumanis are no longer in science and could not be contacted.

The cell cycle regulator phosphorylated retinoblastoma protein is associated with tau pathology in several tauopathies

Retinoblastoma protein (pRb) is a ubiquitous 928-amino acid cell cycle regulatory molecule with diverse biologic activities. One critical function of pRb is the control of the G1-to-S phase checkpoint of the cell cycle. In the hypophosphorylated state, pRb suppresses the activity of E2F transcription factors thereby inhibiting transcription of cell cycle-promoting genes. On phosphorylation, primarily by cyclin-dependent kinases, phosphorylated pRb dissociates from E2F and permits cell cycle progression. We previously found phosphorylated pRb to be intimately associated with hyperphosphorylated tau-containing neurofibrillary tangles of Alzheimer disease (AD), the pathogenesis of which is believed to involve dysregulation of the cell cycle and marked neuronal death. Here, we used immunohistochemistry to investigate the presence of phosphorylated pRb in other distinct neurodegenerative diseases that share the common characteristic of hyperphosphorylated tau pathology and neuronal loss with AD.We found colocalized labeling of tau pathology and phosphorylated pRb in Pick disease and progressive supranuclear palsy (3 cases each), neurodegeneration with brain iron accumulation type 1 (2 cases), and Parkinson-amyotrophic lateral sclerosis of Guam, subacute sclerosing panencephalitis, frontotemporal dementia and Parkinsonism linked to chromosome 17, and dementia pugilistica (1 case each). These observations further implicate aberrant neuronal cell cycle progression in neurodegenerative diseases, particularly tauopathies, and suggest a novel target for therapeutic intervention.

Neuropathology of Alzheimer's disease

Alois Alzheimer first pointed out that the disease which would later bear his name has a distinct and recognizable neuropathological substrate. Since then, much has been added to our understanding of the pathological lesions associated with the condition. The 2 primary cardinal lesions associated with Alzheimer's disease are the neurofibrillary tangle and the senile plaque. The neurofibrillary tangle consists of abnormal accumulations of abnormally phosphorylated tau within the perikaryal cytoplasm of certain neurons. The senile plaque consists of a central core of beta-amyloid, a 4-kD peptide, surrounded by abnormally configured neuronal processes or neurites. Other neuropathological lesions are encountered in cases of Alzheimer's disease, but the disease is defined and recognized by these 2 cardinal lesions. Other lesions include poorly understood changes such as granulovacuolar degeneration and eosinophilic rodlike bodies (Hirano bodies). The loss of synaptic components is a change that clearly has a significant impact on cognitive function and represents another important morphological alteration. It is important to recognize that distinguishing between Alzheimer's disease, especially in its early stages, and normal aging may be very difficult, particularly if one is examining the brains of patients who died at an advanced old age. It is also noted that instances of pure forms of Alzheimer's disease, in the absence of other coexistent brain disease processes, such as infarctions or Parkinson's disease-related lesions, are relatively uncommon, and this must be taken into account by researchers who employ postmortem brain tissues for research.

The Relationship between Parkin and Protein Aggregation in Neurodegenerative Diseases

The most prominent changes in neurodegenerative diseases are protein accumulation and inclusion formation. Several neurodegenerative diseases, including Alzheimer's, the Synucleinopathies and Tauopathies share several overlapping clinical symptoms manifest in Parkinsonism, cognitive decline and dementia. As degeneration progresses in the disease process, clinical symptoms suggest convergent pathological pathways. Biochemically, protein cleavage, ubiquitination and phosphorylation seem to play fundamental roles in protein aggregation, inclusion formation and inflammatory responses. In the following we provide a synopsis of the current knowledge about protein accumulation and astrogliosis as a common denominator in neurodegenerative diseases, and we propose insights into protein degradation and anti-inflammation. We review the E3-ubiquitin ligase and other possible functions of parkin as a suppressant of inflammatory signs and a strategy to clear amyloid proteins in neurodegenerative diseases.

Beta-amyloid overload does not directly correlate with SAPK/JNK activation and tau protein phosphorylation in the cerebellar cortex of Ts65Dn mice

It is known that in the nervous tissue beta-amyloid overproduction and its extracellular or intracellular deposition can activate mitogen-activated protein kinases involved in tau protein phosphorylation. Hyperphosphorylated tau is not more able to bind neuron microtubules, leading to their disassembly and axon degeneration. We have previously described that at 10 months of age in the cerebellum of Ts65Dn mice, which are partially trisomic for the chromosome 16 and are considered a valuable model for Down syndrome, Purkinje cells undergo axon degeneration. Taking into consideration that Ts65Dn mice carry three copies of the gene encoding for the amyloid precursor protein, to characterize potential signaling events triggering the degenerative phenomenon, specific antibodies were used to examine the role of beta-amyloid overload in the activation of the stress activated kinase/c-jun N-terminal kinase (SAPK/JNK) and tau protein phosphorylation in the cerebellar cortex of 12-month-old Ts65Dn mice. We found small extracellular deposits of beta-amyloid at the borderline between the granule cell layer and the white matter, i.e., in the vicinity of the area where calbindin immunostaining of Purkinje cell axons revealed clusters of newly formed terminals of injured axons. Moreover, intracellular deposits were present in the somata of Purkinje cells. The level of activation of SAPK/JNK was greatly increased. The activation occurred in the "pinceaux" made by basket interneuron axons at the axon hillock of Purkinje cells. Antibody directed against tau protein phosphorylated at Ser-396/Ser-404 revealed positive NG2 cells and Bergman fibers in the molecular layer and oligodendrocytes in the white matter. Data indicate that beta-amyloid extracellular deposits could have exerted a local cytotoxic effect, leading to Purkinje cell axon degeneration. The activation of SAPK/JNK in basket cell "pinceaux" may be a consequence of altered functionality of Purkinje cells and may represent an attempt of basket cells of synaptic remodeling. Moreover, the findings for tau protein phosphorylation suggest that Ts65Dn mice are affected by a cerebellar glial tauopathy.

Drosophila melanogaster as a model organism of brain diseases

Drosophila melanogaster has been utilized to model human brain diseases. In most of these invertebrate transgenic models, some aspects of human disease are reproduced. Although investigation of rodent models has been of significant impact, invertebrate models offer a wide variety of experimental tools that can potentially address some of the outstanding questions underlying neurological disease. This review considers what has been gleaned from invertebrate models of neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, metabolic diseases such as Leigh disease, Niemann-Pick disease and ceroid lipofuscinoses, tumor syndromes such as neurofibromatosis and tuberous sclerosis, epilepsy as well as CNS injury. It is to be expected that genetic tools in Drosophila will reveal new pathways and interactions, which hopefully will result in molecular based therapy approaches.

Protein aggregation in the brain: the molecular basis for Alzheimer's and Parkinson's diseases

Developing effective treatments for neurodegenerative diseases is one of the greatest medical challenges of the 21st century. Although many of these clinical entities have been recognized for more than a hundred years, it is only during the past twenty years that the molecular events that precipitate disease have begun to be understood. Protein aggregation is a common feature of many neurodegenerative diseases, and it is assumed that the aggregation process plays a central role in pathogenesis. In this process, one molecule (monomer) of a soluble protein interacts with other monomers of the same protein to form dimers, oligomers, and polymers. Conformation changes in three-dimensional structure of the protein, especially the formation of beta-strands, often accompany the process. Eventually, as the size of the aggregates increases, they may precipitate as insoluble amyloid fibrils, in which the structure is stabilized by the beta-strands interacting within a beta-sheet. In this review, we discuss this theme as it relates to the two most common neurodegenerative conditions-Alzheimer's and Parkinson's diseases.

Widespread spinal cord involvement in progressive supranuclear palsy

We describe the histopathologic features of spinal cord lesions in 10 cases of progressive supranuclear palsy (PSP) and review the literature. Histologic examination revealed atrophy with myelin pallor in the anterior funiculus and anterolateral funiculus in the cervical and thoracic segments in eight of the 10 cases, whereas the posterior funiculus was well preserved. The degrees of atrophy of the anterior funiculus and the anterolateral funiculus correlated with that of the tegmentum of the medulla oblongata. Myelin pallor of the lateral corticospinal tract was observed in two of the 10 cases. Microscopic observation of the spinal white matter, particularly the cervical segment, revealed a few to several neuropil threads, particularly in the white matter surrounding the anterior horn after Gallyas-Braak (GB) staining or AT-8 tau immunostaining. However, the posterior funiculus was completely preserved from the presence of argyrophilic or tau-positive structures. In the spinal gray matter, widespread distribution of neurons with cytoplasmic inclusions and neuropil threads was observed, particularly in the medial division of the anterior horn and intermediate gray matter, especially in the cervical segment. Globose-type neurofibrillary tangles and pretangles were found. The distribution of GB- or AT-8 tau-positive small neurons and neuropil threads resembled that of the spinal interneurons. In conclusion, the spinal cord, especially the cervical segment, is constantly involved in the pathologic process of PSP. We speculate that spinal interneurons and their neuronal processes, particularly in the medial division of the anterior horn and intermediate gray matter of the cervical segment, are most severely damaged in the PSP spinal cord.

Induction of cellular stress and chaperone activation in organotypic slice cultures of hippocampus

Neurodegenerative diseases are often associated with the occurrence of misfolded proteins preceding neuronal cell death. Accumulation of misfolded proteins in the endoplasmic reticulum induces ER stress, which in consequence enhances chaperone expression to restore protein homeostasis. Here we used organotypic hippocampal slice cultures to analyze the time course of chaperone expression and neuronal death after induction of ER stress by tunicamycin treatment. Shortly after explantation many cells stain positive for Fluoro Jade B demonstrating neuronal cell death. While in control cultures the number of Fluoro Jade B labeled cells remarkably decrease over the total period of cultivation, neuronal death remains elevated in ER-stressed slice cultures. Caspase-3 staining revealed that neuronal death is primarily due to apoptosis in tunicamycin-treated slice cultures. The chaperone GRP78/BiP is expressed at low levels in control sections. Its expression is largely restricted to hippocampal neurons. Tunicamycin treatment resulted in upregulation of GRP78/BiP in the neuronal cells. Double-immunolabeling for GFAP shows a concomitant de novo expression of GRP78/BiP in astrocytes. The astrocytic GRP78/BiP upregulation might reflect an early, neuroprotective response. The increase of GRP78/BiP in neurons and astrocytes show successful induction of the ER stress response. The hippocampal slice cultures are, thus, a useful tool to examine the process of neurodegeneration and to investigate neuroprotective devices in an ER stress paradigm.

Argyrophilic thorny astrocyte clusters in association with Alzheimer's disease pathology in possible primary progressive aphasia

Although most cases of primary progressive aphasia (PPA) have one of the varieties of frontotemporal lobar degeneration (FTLD) as their pathological substrate, a subset shows Alzheimer's disease (AD) pathology. We report that all eight cases in our clinic diagnosed as possible PPA, on account of the presence of episodic memory difficulties in addition to severe language impairment at the onset of disease, showed AD pathology. Neither focal accentuation of AD pathology nor vascular lesions in language-related areas was observed. Seven of these eight patients showed large argyrophilic thorny astrocyte clusters (ATAC) in the fronto-temporo-parietal cortex and subcortical white matter. The intensely tau immunoreactive astrocytes in ATAC were morphologically similar to the perivascular, subpial, and subependymal astrocytes in elderly brains, but ATAC differ from the latter by the cortical and subcortical location, widespread distribution outside the medial temporal lobe, and intense argyrophilia. The location of ATAC was related to neither local variations in the load of AD pathology, nor the myelin density of white matter. ATAC were not seen in a comparison group of six cases of AD without a prominent aphasia syndrome. Because of the similarity of astrocytes in ATAC to those seen independently of AD pathology in several subtypes of FTLD and two reported cases of PPA we hypothesize that they are a marker of a pathological process concurrent with AD, and related to the focality of the clinical presentation.

Alzheimer's neuroborreliosis with trans-synaptic spread of infection and neurofibrillary tangles derived from intraneuronal spirochetes

In the realm of dementia, it is astonishing to note that neurofibrillary tangles (NFT) are microscopically identical in a childhood illness (SSPE) and in a dementia of late adult life (Alzheimer's disease). The words "Alzheimer-type" NFT in peer reviewed scientific articles written by acknowledged experts underscore the striking similarities in "tangles" in two different diseases. Subacute Sclerosing Panencephalitis (SSPE) is caused by infection with atypical measles virus. Alzheimer's disease has no known cause. There is little controversy in suggesting that all of the Tangles in SSPE infected neurons are produced by slow viral type variant of Measles infection. But the mere suggestion that infection might be a cause of Alzheimer's disease confounds the establishment. If a good case is to be made for infection in Alzheimer's disease, an excellent nerve cell infection model is needed. Monkeys have provided a very reasonable model. Recently, a primate neuroborreliosis brain infection model demonstrated that Borrelia injected into the skin of monkeys resulted in the appearance of Borrelia transcriptomes in brain neurons. If Borrelia can travel from skin to brain in the monkey, then why not look at human Alzheimer's tissues to see if the DNA of Borrelia is present in the human brain? The molecular detection tools perfected in animal neuroborreliosis studies have been applied to human Alzheimer's disease brain tissues. Seven of ten cases of Alzheimer's disease from McLean Hospital Brain Bank of Harvard University yielded positive signals for infectious DNA in a small pilot study. Alzheimer's diseased neurons analyzed with DNA probes, produced little "dots" of positive staining. Granulovacuolar bodies in Alzheimer's diseased neurons (little dots in a bubble), are one of the expected microscopic profiles of Alzheimer's disease. "Little dots" inside nerve cells are also signatures of viral infectious agents inside of nerve cells. So with the assistance of the microscope and the tools of molecular biology, a new model of infection emerges as a cause of "Alzheimer's-type" neurofibrillary tangles. Here I hypothesize that it is chronic infection of human neurons in Alzheimer's disease that produces neurofibrillary tangles by a pathway similar to the chronic SSPE infection tangle pathway. In addition, transmission of infection from nerve to nerve is proposed to explain the evolution of Alzheimer's disease. Herein is offered a new view for the origins and for the progression of diseased nerves with tangle formations in Alzheimer's disease based on infection.

Predicting Alzheimer dementia in mild cognitive impairment patients. Are biomarkers useful?

A correct clinical diagnosis in the early stage of Alzheimer disease is not only of importance given the current available treatment with acetylcholine esterase inhibitors, but would be the basis for disease-modifying therapy slowing down or arresting the degenerative process. Moreover, in the last years, several efforts have been made to determine if a patient with mild cognitive impairment has incipient Alzheimer disease, i.e. will progress to Alzheimer disease with dementia, or have a benign form of mild cognitive impairment. In this review, the recent published reports regarding progress in early and preclinical Alzheimer disease diagnosis are discussed and the role of peripheral and cerebrospinal fluid biomarkers highlighted. Approaches combining panels of different biomarkers show promise for discovering profiles that are characteristic of Alzheimer disease, even in the pre-symptomatic stage. More work is needed but available novel perspectives offered by recent introduced technologies shed some lights in identifying incipient Alzheimer disease in mild cognitive impairment subjects.

Corticobasal ganglionic degeneration and progressive supranuclear palsy presenting with cognitive decline

Corticobasal ganglionic degeneration (CBGD) and progressive supranuclear palsy (PSP) were originally described in the sixties as predominantly motor syndromes. Over the years, the detailed study of additional cases of CBGD has shown that it is a distinctive histological entity which can often present as dementia or aphasia. Although some pathological features of CBGD overlap with those of other forms of non-Alzheimer non-Lewy body dementia, the distribution and relative number of these abnormalities and the distinctive pattern of tau immunodeposits allows the distinction of CBGD from Pick's disease and fronto-temporal dementia. In contrast, PSP only rarely presents with prominent dementia or behavioral changes. In these unusual PSP cases, care must be taken to exclude the diagnoses of CBGD and familial tangle-only dementia.

Dementia with grains (argyrophilic grain disease)

Dementia with grains, also referred to as argyrophilic grain disease, is a morphological condition in elderly individuals histologically characterised by the widespread occurrence of minute, spindle or comma-shaped argyrophilic, tau-immunoreactive structures distinct from neuropil threads that are predominantly located in the hippocampus and related limbic areas including the amygdala. They are suggested to arise mainly in dendrites of neurons showing accumulation of hyperphosphorylated tau proteins (pretangle stage) but not necessarily forming paired helical filaments. Argyrophilic grains are associated with argyrophilic, tau-positive oligodendroglial inclusions ("coiled bodies") in the white matter, while astroglia are not affected. Argyrophilic grain disease is considered to be a progressive disorder that may or may not be associated with dementia, the grains occasionally being the only morphologic substrates of cognitive decline. They often occur in combination with neuritic Alzheimer-type lesions (many corresponding to "limbic" Braak stages III and IV) or other neurodegenerative disorders, such as progressive supranuclear palsy, corticobasal degeneration, or Pick's disease. The prevalence and pathogenesis of this condition, its clinicopathologic correlations and nosological position among tau-pathology related disorders await further elucidation.

Pick's disease: a modern approach

Pick's disease is a rare dementing disorder that is sometimes familial. The cardinal features are circumscribed cortical atrophy most often affecting the frontal and temporal poles and argyrophilic, round intraneuronal inclusions (Pick bodies). Clinical manifestations reflect the distribution of cortical degeneration, and personality deterioration and memory deficits are often more severe than visuospatial and apraxic disorders that are common in Alzheimer's disease, but clinical overlap with other non-Alzheimer degenerative disorders is increasingly recognized. Neuronal loss and degeneration are usually maximal in the limbic system, including hippocampus, entorhinal cortex and amygdala. Numerous Pick bodies are often present in the dentate fascia of the hippocampus. Less specific features include leukoencephalopathy and ballooned cortical neurons (Pick cells). Glial reaction is often pronounced in affected cerebral gray and white matter. Tau-immunoreactive glial inclusions are a recently recognized finding in Pick's disease, and neuritic changes have also recently been described. Variable involvement of the deep gray matter and the brainstem is typical, with a predilection for the monoaminergic nuclei and nuclei of the pontine base. Neurochemical studies demonstrate deficits in intrinsic cortical neurotransmitter systems (e.g., somatostatin), but inconsistent loss of transmitters in systems projecting to the cortex (e.g., cholinergic neurons of the basal nucleus). Biochemical and immunocytochemical studies have demonstrated that abnormal tau proteins are the major structural components of Pick bodies. A specific tau protein immunoblotting pattern different from that seen in Alzheimer's disease and certain other disorders has been suggested in some studies. A specific molecular marker and a genetic locus for familial cases are not known.

Tau-positive glial inclusions in progressive supranuclear palsy, corticobasal degeneration and Pick's disease

The presence of tau-positive glial inclusions has been recently found a consistent feature in the brains of patients with progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and Pick's disease (PiD). These inclusions are classified based on cellular origin as tau-positive astrocytes, presumably either fibrillary or protoplasmic, coiled bodies and glial threads. Immunohistochemically, their major structural component is abnormal tau proteins, similar to those found in Alzheimer's disease. Nevertheless, their morphology, including ultrastructural profile, has been suggested to be distinctive for each disease. The profile and extent of particular glial inclusions correlate well with disease phenotype. Highly characteristic correlations include tufts of abnormal fibers in PSP, astrocytic plaques and dense glial threads in CBD and ramified astrocytes and small Pick body-like inclusions in PiD. The significance of the inclusions in disease pathogenesis and their biochemical characteristics remain to be clarified. Nevertheless, these distinctive glial lesions most likely reflect fundamental alterations in isoform composition of tau as well as its specific cellular and regional expression in sporadic tauopathies.

Widespread spinal cord involvement in corticobasal degeneration

We examined spinal cord lesions in eight patients with a pathological diagnosis of corticobasal degeneration (CBD). Using Gallyas-Braak (G-B) staining or AT-8 tau immunostaining, a few neuropil threads were identified in the white matter of the CBD spinal cords, mainly in the anterior funiculus, whereas the posterior funiculus was well preserved without threads. In the gray matter of the CBD spinal cords, particularly in the intermediate gray matter, there were widespread neuropil threads and neuronal inclusions. Large motor neurons in the anterior horn, neurons in the intermediolateral column, and Clarke's column were relatively well preserved from neuronal loss and gliosis. Neuronal inclusions were of the globose type, suggestive of neurofibrillary tangles (NFTs), or showed diffuse granular accumulations of cytoplasmic tau, suggestive of pretangles. No typical NFTs, recognized by Bodian silver staining, were identified. The distribution of neuropil threads and G-B- or AT-8 tau-positive small neurons resembled that of interneurons. No astrocytic plaques were present in any of the CBD spinal cords, and only a few coiled bodies were seen. Neuropil threads in the white and gray matter and neuronal inclusions in the gray matter were prominent in cervical segments, and their density decreased caudally. We suggest that the presence of neuropil threads, particularly in the cervical intermediate gray matter, and the presence of neuronal inclusions, particularly in cervical interneurons, is an essential pathological feature of CBD.

Tuft-shaped astrocytes in Lewy body disease

We investigated the occurrence and distribution of tuft-shaped astrocytes (TuSAs) in 60 brains from patients with Lewy body disease (LBD), which were clinically diagnosed as Parkinson's disease (PD) or dementia with Lewy bodies (DLB), and 85 brains from control subjects. TuSAs have been documented as a neuropathological hallmark of progressive supranuclear palsy (PSP). We found phosphorylated tau (p-tau)-positive and alpha-synuclein-negative TuSAs in 10 of 60 patients with LBD and 3 of 85 control cases. TuSAs were mainly located within the precentral and premotor gyri of the frontal lobe cortex. There were only few TuSAs, but the distribution pattern and morphological and immunohistological features were similar to that in PSP. Furthermore, other p-tau positive structures, including aggregates in neurons, coiled-like glial cells and threads showed a similar distribution to those in PSP; mainly in the hippocampus, striatum, subthalamic nucleus, precentral and premotor gyri, brainstem nucleus, and dentate nucleus. In these cases, however, neuronal loss and gliosis were not seen in the regions involved in PSP, such as the subthalamic nucleus, pallidum, inferior olivary, cerebellar dentate nuclei, and periaqueductal gray matter. Clinical features were indistinguishable between the LBD with and without TuSAs. The appearance of TuSAs was not related to the frequency of Lewy bodies, neurofibrillary tangles, and senile plaques, but was significantly more pronounced with advancing age in both LBD and controls. These findings suggest that in a subgroup of elderly individual cases, especially associated with LB pathology, the glial and neuronal p-tau accumulation is increased and has a distributional pattern similar to PSP.

TAU mutations are not a predominant cause of frontotemporal dementia in Canadian patients

OBJECTIVE

Frontotemporal dementia is a neurodegenerative disease affecting mostly the frontal and/or temporal lobes, with neuronal loss and intraneuronal and/or intraglial inclusions composed of hyperphosphorylated microtubule-associated protein tau and ubiquitin. Missense and splice site mutations in the TAU gene have been identified in approximately 15% of all frontotemporal dementia cases. In this study, we evaluated the involvement of mutations in the TAU gene in development of frontotemporal dementia phenotype in patients of French or English Canadian origins.

METHODS

Fourteen patients with frontotemporal dementia phenotype and 98 normal controls were recruited for the study. The TAU gene was screened by sequencing and denaturing high performance liquid chromatography.

RESULTS

No mutations, except some new polymorphisms, were detected in the TAU gene of these patients. One polymorphism, however, may play a role in pathogenesis.

CONCLUSION

Our results agree with previous work suggesting that mutations in this gene are not a frequent cause of the frontotemporal dementia phenotype in Canadian patients.

Comparative distribution of tau phosphorylated at Ser262 in pre-tangles and tangles

The Phospho-Ser(262) epitope of phosphorylated tau, which accumulates in tangles in Alzheimer's disease (AD) brains, has been shown to have a strong disruptive effect on microtubules. Using antibodies which specifically recognize the Phospho-Ser(262) of tau, we compared the presence of this epitope in normal appearing neurons (pre-tangles) and tangles, with the presence of Phospho-Ser(199/202) (AT-8) and Phospho-Ser(396/404) (PHF-1) epitopes. All antibodies visualized lightly or darkly stained pre-tangles, neurons with immunoreactive clumps, intracellular and extracellular tangles. Pre-tangles were more abundant in control cases which showed some pathology, when compared with AD brains. Immunoreactivity for Phospho-Ser(262) was preferentially present in intracellular and extracellular tangles and was found in a significantly smaller number of pre-tangles when compared with the other epitopes. These results indicate the presence of various epitopes of Phospho-Tau in a substantial number of pre-tangles which may represent an early marker of tangle formation. The differential distribution of various epitopes suggests that the presence of the Phospho-Ser(262) epitope of tau either accelerates the transition form pre-tangle to tangle, or appears later than the other epitopes in the process of tangle formation.

Tau and axonopathy in neurodegenerative disorders

The microtubule (MT)-associated protein (MAP) tau in neurons has been implicated as a significant factor in the axonal growth, development of neuronal polarity, and the maintenance of MT dynamics. Tau is localized to the axon, and is known to promote MT assembly and to stabilize axonal MTs. These functions of tau are primarily regulated by the activities of protein kinases and phosphatases. In Alzheimer's disease and other neurodegenerative disorders, abundant filamentous tau inclusions are found to be major neuropathological characteristics of these diseases. Both somato-dendritic and axonal tau lesions appear to be closely associated with axonal disruption. Furthermore, recent discoveries of pathogenic mutations on the tau gene suggest that abnormalities of tau alone are causative of neurodegeneration. Finally, analyses of transgenic mice that express human tau proteins have enabled in vivo quantitative assessments of axonal functions and have provided information about mechanistic relationships between pathological alteration of tau and axonal degeneration.

Office of Rare Diseases neuropathologic criteria for corticobasal degeneration

A working group supported by the Office of Rare Diseases of the National Institutes of Health formulated neuropathologic criteria for corticobasal degeneration (CBD) that were subsequently validated by an independent group of neuropathologists. The criteria do not require a specific clinical phenotype, since CBD can have diverse clinical presentations, such as progressive asymmetrical rigidity and apraxia, progressive aphasia, or frontal lobe dementia. Cortical atrophy, ballooned neurons, and degeneration of the substantia nigra have been emphasized in previous descriptions and are present in CBD, but the present criteria emphasize tau-immunoreactive lesions in neurons, glia, and cell processes in the neuropathologic diagnosis of CBD. The minimal pathologic features for CBD are cortical and striatal tau-positive neuronal and glial lesions, especially astrocytic plaques and thread-like lesions in both white matter and gray matter, along with neuronal loss in focal cortical regions and in the substantia nigra. The methods required to make this diagnosis include histologic stains to assess neuronal loss, spongiosis and ballooned neurons, and a method to detect tau-positive neuronal and glial lesions. Use of either the Gallyas silver staining method or immunostains with sensitive tau antibodies is acceptable. In cases where ballooned neurons are sparse or difficult to detect, immunostaining for phospho-neurofilament or alpha-B-crystallin may prove helpful. Methods to assess Alzheimer-type pathology and Lewy body pathology are necessary to rule out other causes of dementia and Parkinsonism. Using these criteria provides good differentiation of CBD from other tauopathies, except frontotemporal dementia and Parkinsonism linked to chromosome 17, where additional clinical or molecular genetic information is required to make an accurate diagnosis.

Transgenic mouse model of tauopathies with glial pathology and nervous system degeneration

Frontotemporal dementias (FTDs), including corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP), are neurodegenerative tauopathies characterized by widespread CNS neuronal and glial tau pathologies, but there are no tau transgenic (Tg) mice that model neurodegeneration with glia tau lesions. Thus, we generated Tg mice overexpressing human tau in neurons and glia. No neuronal tau aggregates were detected, but old mice developed Thioflavin S- and Gallyas-positive glial tau pathology resembling CBD astrocytic plaques. Tau-immunoreactive and Gallyas-positive oligodendroglial coiled bodies (similar to CBD and PSP), glial degeneration, and motor deficits were associated with age-dependent accumulations of insoluble hyperphosphorylated human tau and tau immunopositive filaments in degenerating glial cells. Thus, tau-positive glial lesions similar to human FTDs occur in these Tg mice, and these pathologies are linked to glial and axonal degeneration.

alpha-Synuclein is phosphorylated in synucleinopathy lesions

The deposition of the abundant presynaptic brain protein alpha-synuclein as fibrillary aggregates in neurons or glial cells is a hallmark lesion in a subset of neurodegenerative disorders. These disorders include Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy, collectively referred to as synucleinopathies. Importantly, the identification of missense mutations in the alpha-synuclein gene in some pedigrees of familial PD has strongly implicated alpha-synuclein in the pathogenesis of PD and other synucleinopathies. However, specific post-translational modifications that underlie the aggregation of alpha-synuclein in affected brains have not, as yet, been identified. Here, we show by mass spectrometry analysis and studies with an antibody that specifically recognizes phospho-Ser 129 of alpha-synuclein, that this residue is selectively and extensively phosphorylated in synucleinopathy lesions. Furthermore, phosphorylation of alpha-synuclein at Ser 129 promoted fibril formation in vitro. These results highlight the importance of phosphorylation of filamentous proteins in the pathogenesis of neurodegenerative disorders.

Morphological and biochemical correlations of abnormal tau filaments in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is characterized by specific filamentous tau inclusions present in 3 types of cells including oligodendrocytes (coiled bodies), astrocytes (tufted astrocytes), and neurons (neurofibrillary tangles; NFTs). To correlate the morphological features and biochemical composition of tau in the inclusions, we examined tau filament-enriched fractions isolated from selected brain regions. Frontal and cerebellar white matter manifested a predominance of coiled bodies. The isolated fractions contained straight, 14-nm-wide filaments of relatively smooth appearance. Caudate nucleus and motor cortex with numerous tufted astrocytes contained mostly straight, but irregular, 22-nm-wide filaments with jagged contours. Perirhinal cortex and hippocampus, rich in NFTs, contained 22-nm-wide filaments that were twisted at 80-nm intervals. Among the regions, those with tufted astrocytes showed the most heterogeneity in the ultrastructure of filaments. In all regions, isolated filaments were immunolabeled with PHF-1, Tau 46, and AT8. Fractions from all regions showed 2 PHF-1 immunoreactive bands of 64 and 68 kDa, while an additional band of 60 kDa was detected in NFT-enriched regions. All fractions, in varying extents, showed Tau-1-immunoreactive bands between 45-64 kDa. The results indicate that the 3 types of PSP tau inclusions vary in the ultrastructure although with some overlapping features. Neuronal and glial inclusions also vary in the biochemical profile of tau protein. These differences may depend on the metabolism of tau in the diseased oligodendrocytes, astrocytes, and neurons.

Microglial activation parallels system degeneration in progressive supranuclear palsy and corticobasal degeneration

The role of microglia in progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) is unknown. To address this issue we examined 10 cases of PSP, 5 cases of CBD, and 4 normal controls. Microglial and tau burdens were determined with image analysis on brain sections that had been immunostained with monoclonal antibodies to HLA-DR and phospho-tau. We found that microglial activation was greater in PSP and CBD than normal controls, and that the microglial burden correlated with the tau burden in most areas. There were distinct patterns of microglial activation and tau pathology in PSP and CBD, with PSP showing more pathology in infratentorial structures and CBD showing more pathology in supratentorial structures. These results support the notion that PSP and CBD are distinct clinicopathologic entities. Microglial activation was not well correlated with tau pathology in the brainstem of PSP, which suggests that brainstem pathology in PSP is not exclusively due to tau pathology. While the results do not necessarily support a direct causal link between microglial activation and neurodegeneration in PSP or CBD, they nevertheless suggest that microglia play a role in disease pathogenesis.

Neuropathology of Alzheimer's disease and related disorders

Neuropathologic studies have done much to define the range of disorders that may underlie dementia. By far, the most important disease entity is Alzheimer's disease, with its characteristic neurofibrillary tangles and senile plaques. The neuropathologic distinction between Alzheimer's disease, particularly in its early stages, and normal aging is a subject of intense interest, attracting considerable current research activity. The neuropathologic substrate of other entities that may lead to dementia is extensive and, in the absence of biologic markers for most of these disorders, postmortem examination remains the only definitive method for establishing a diagnosis.

Cerebellar involvement in Pick's disease: affliction of mossy fibers, monodendritic brush cells, and dentate projection neurons

Pick's disease chiefly is characterized by progressive degeneration of specific telencephalic cortical areas and associated subcortical nuclei. Components of the cerebellum also are affected. Immunoreactions for abnormally hyperphosphorylated tau protein, indicating the development of cytoskeletal anomalies in a few susceptible neuroectodermal cell types, permit visualization and identification of the pathology. Initially, accumulations of nonargyrophilic material appear in the perikarya and cellular processes of susceptible nerve cells. In some neuronal types, the abnormal deposits are transformed into more condensed inclusions, so-called Pick bodies in perikarya and Pick neurites in cellular processes, some of which become argyrophilic in the course of the disease. This study employs silver techniques and immunoreactions to draw attention to Pick's disease-associated lesions in the cerebellar cortex and cerebellar nuclei. Immunoreactive rosettes, which correspond to the terminal synaptic boutons of mossy fibers, frequently are encountered in the cerebellar granule cell layer. Some cases of Pick's disease also exhibit afflicted monodendritic brush cells in this layer. Single immunopositive Purkinje cells occasionally are seen as well. The brunt of the alterations is borne by cerebellar subdivisions receiving dense input from the telencephalic cortex through the pontocerebellar pathway (neocerebellum). The dentate nucleus shows immunoreactive axons with numerous varicose thickenings which remain confined to the reaches of this band-like nuclear gray and probably represent collaterals of altered mossy fibers. A large number of the dentate projection cells also contain the abnormal material in the perikarya, as well as in all of the neuronal processes. Many of these cells develop spherical nonargyrophilic condensations of this material. Output of the neocerebellum is conveyed to extended territories of the telencephalic cortex via the dentate nucleus and thalamus. Therefore, all of the cerebellar territories which receive major input from and generate output chiefly to the telencephalic cortex (pontocerebellum or neocerebellum) are notably afflicted in Pick's disease. Other subdivisions with preponderant input from the spinal cord and/or other noncortical sources remain intact or else are only minimally involved. It is concluded that the pattern of cerebellar involvement reflects Pick's disease-associated neocortical destruction.

Neuropathologic differentiation of progressive supranuclear palsy and corticobasal degeneration

Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are usually sporadic multi-system degenerations associated with filamentous tau inclusions in neurons and glia. As such they can be considered sporadic tauopathies in contrast to familial tauopathies linked to mutations in the tau gene. Mutations have not been found in the tau gene in either PSP or CBD. The clinical syndromes and neuroimaging of typical cases of PSP and CBD are distinct; however, atypical cases are described that have overlapping clinical and pathologic features. Both PSP and CBD have similar biochemical alterations in the tau protein, with the abnormal tau protein containing predominantly four-repeat tau. While there is overlap in the pathology in PSP and CBD, there are sufficient differences to continue the present day trend to consider these separate disorders. Several important pathologic features differentiate PSP from CBD. Ballooned neurons are frequent and nearly a sine qua non for CBD, but they are found in PSP at a frequency similar to that of other neurodegenerative diseases, such as Alzheimer's disease. Astrocytic lesions are different, with tufted astrocytes found in motor cortex and striatum in PSP and astrocytic plaques in focal atrophic cortices in CBD. The most characteristic neuronal tau pathology in CBD is wispy, fine filamentous inclusions within neuronal cell bodies, while affected neurons in PSP have compact, dense filamentous aggregates characteristic of globose neurofibrillary tangles. Thread-like processes in gray and white matter are much more numerous and widespread in CBD than in PSP. The brunt of the pathology in CBD is in the cerebrum, while the basal ganglia, diencephalon and brainstem are the targets of PSP. Further clinicopathologic studies will refine our understanding of these disorders and open the possibility that common etiologic factors may be identified for these unusual sporadic tauopathies.

Genetic classification of primary neurodegenerative disease

Review During the past 10 years (the "decade of the brain"), some of the genetic causes of many of the primary neurodegenerative diseases, which include Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, prion disease, and many ataxic syndromes, have been found. These breakthroughs mean that for many of these diseases we now know the initiating trigger as well as the final outcome. These diseases have many pathological mechanisms in common, and there may be relatively few pathways to neuronal death seen in these disorders. Thus, treatment strategies developed for a particular disease may be found to have efficacy in more than one disorder.