Comparative biochemistry of tau in progressive supranuclear palsy, corticobasal degeneration, FTDP-17 and Pick's disease

[Molecular neuropathology of Non-Alzheimer dementia]

The increasing life expectancy will cause an increasing share for neurodegenerative and dementing illnesses in the total cost for health care. New developments such as the discovery of TDP-43 as disease protein have opened new viewpoints on frontotemporal dementias, as well as its relation to amyotrophic lateral sclerosis. As pathologists and neuropathologists we are committed to contributing to the progress of clinical diagnosis, which often proves difficult, by standardized post-mortem diagnosis. The diagnostic responsibility will increase with the development of new specific therapeutics and knowledge of contraindications such as the use of neuroleptics in patients suffering from Lewy body dementia. The Reference Center for Neurodegenerative Diseases of the German Society of Neuropathology and Neuroanatomy and the German Brain Bank (Brain-Net) at the Institute for Neuropathology, Ludwig-Maximilians-University Munich, are available for diagnosis in difficult or complex cases.

The role of tau in neurodegeneration

Since the identification of tau as the main component of neurofibrillary tangles in Alzheimer's disease and related tauopathies, and the discovery that mutations in the tau gene cause frontotemporal dementia, much effort has been directed towards determining how the aggregation of tau into fibrillar inclusions causes neuronal death. As evidence emerges that tau-mediated neuronal death can occur even in the absence of tangle formation, a growing number of studies are focusing on understanding how abnormalities in tau (e.g. aberrant phosphorylation, glycosylation or truncation) confer toxicity. Though data obtained from experimental models of tauopathies strongly support the involvement of pathologically modified tau and tau aggregates in neurodegeneration, the exact neurotoxic species remain unclear, as do the mechanism(s) by which they cause neuronal death. Nonetheless, it is believed that tau-mediated neurodegeneration is likely to result from a combination of toxic gains of function as well as from the loss of normal tau function. To truly appreciate the detrimental consequences of aberrant tau function, a better understanding of all functions carried out by tau, including but not limited to the role of tau in microtubule assembly and stabilization, is required. This review will summarize what is currently known regarding the involvement of tau in the initiation and development of neurodegeneration in tauopathies, and will also highlight some of the remaining questions in need of further investigation.

Development of a sensitive ELISA for quantification of three- and four-repeat tau isoforms in tauopathies

Tau protein plays an important role in stabilising and assembling neuronal microtubules. Pathological changes in expression and aggregation of tau isoforms containing three (3R-tau) and four (4R-tau) microtubule-binding repeat domains are associated with several tauopathies. This paper describes novel sandwich ELISAs for quantification of 3R- and 4R-tau in brain. The assays are constructed using well-characterised isoform-specific antibodies (RD3 and RD4) as capture antibodies and an affinity-purified HRP-anti-tau peptide antibody and biotin-tyramide amplification for detection. For 3R-tau, we achieved a minimal detection limit in buffer of 460 pg mL(-1) and a recovery of 81.0% using 500 pg mL(-1) recombinant 3R-tau spiked in diluted brain homogenate. Mean intra- and inter-assay variation of the 3R-tau ELISA was 8.8 and 10.5%, respectively. For 4R-tau, the detection limit was 780 pg mL(-1) and the recovery of 5 ng mL(-1) spiked recombinant 4R-tau was 86.0% and the mean intra- and inter-assay variation was 10.4 and 15.6%, respectively. With these assays, we showed that in progressive supranuclear palsy (PSP) brains, 4R-tau is significantly increased in frontal cortex and caudate, the two regions that are usually associated with 4R-tau-dominant pathology. This increase was not observed in occipital lobe, a region that is spared of tau inclusions. No differences in 3R-tau levels were found between PSP and control brains in all regions tested. With this, we have for the first time developed ELISAs for quantification of 3R- and 4R-tau isoforms in pathological samples. These could prove useful in the pathological investigation and differential diagnosis of tauopathies.

An autopsy case of diffuse neurofibrillary tangles with calcification: early stage pathologic findings

A 66-year-old man with no medically remarkable past or family history gradually showed personality changes, memory disturbance, sleeplessness and abnormal behavior. Neurologic examination showed no focal signs and neither parkinsonism nor cerebellar ataxia was recognized. He died 4 years after the onset of dementia due to chronic renal failure. Neuropathologic examination revealed neuronal loss and gliosis in the temporal cortex, particularly in the subiculum, parahippocampal gyrus and entorhinal cortex, and insular cortex. NFTs were observed to be widespread in the cerebral cortex, especially the temporal cortex and brainstem, while senile plaques were not observed. Gallyas-Braak silver staining revealed the presence of numerous NFTs, glial inclusions and neuropil threads throughout the cerebral neocortex, limbic system, hippocampus and brainstem. The subiculum showed the most severe involvement; severe atrophy, severe neuron loss, and numerous ghost tangles (extracellular NFTs) were apparent. Although NFTs contained both monoclonal anti-3repeat-tau antibody (RD3) and RD4 immunoreactivity, this differed between the intracellular NFTs and ghost tangles. RD3 immunoreactivity was mainly observed in ghost tangles and neuropil threads, whereas RD4 immunoreactivity was mainly observed in intracellular NFTs and glial inclusions. Calcification was also found to be widespread in the cerebral cortex and white matter, basal ganglia, thalamus, cerebellar cortex, white matter and dentate nucleus. These characteristic neuropathologic findings lead to the pathologic diagnosis of diffuse neurofibrillary tangles with calcification (DNTC). It is argued that this patient showed early stage pathologic signs of DNTC due to a short disease duration, which may provide clues regarding the progression of this rare disease.

Differential incorporation of tau isoforms in Alzheimer's disease

There are 6 different isoforms of tau expressed in the adult human brain, and little information is available on the cellular distribution of the isoforms. Tau inclusions are found in neurons and occasionally glia in a variety of diseases. Previous studies conducted on brain homogenates suggested that tau isoforms might be differentially incorporated into inclusions. To further elucidate the complex issue of tau isoform composition in Alzheimer's disease (AD) and other neurodegenerative diseases, monoclonal antibodies that differentiate between tau containing residues encoded by exon 10 (4R tau) and tau lacking exon 10 residues (3R tau) were used in single and double labeling immunohistochemistry as well as biochemical analyses of tau isolated from AD and other neurodegenerative diseases. Immunohistochemical analysis of the hippocampus in 34 AD cases performed with these antibodies showed both 3R and 4R tau isoforms in tangles. While biochemical studies showed that both isoforms were present in insoluble tau aggregates in AD hippocampus and cortex, not all tangles appear to be labeled with the 3R and 4R tau specific monoclonal antibodies. Similar studies in progressive supranuclear palsy and Pick's disease confirmed that these diseases were characterized by incorporation of specific isoforms in fibrillar lesions, but lesions in neither disease were exclusively composed of 3R tau or 4R tau isoforms.

H1 tau haplotype-related genomic variation at 17q21.3 as an Asian heritage of the European Gypsy population

In this study, we examine the frequency of a 900 kb inversion at 17q21.3 in the Gypsy and Caucasian populations of Hungary, which may reflect the Asian origin of Gypsy populations. Of the two haplotypes (H1 and H2), H2 is thought to be exclusively of Caucasian origin, and its occurrence in other racial groups is likely to reflect admixture. In our sample, the H1 haplotype was significantly more frequent in the Gypsy population (89.8 vs 75.5%, P<0.001) and was in Hardy-Weinberg disequilibrium (P=0.017). The 17q21.3 region includes the gene of microtubule-associated protein tau, and this result might imply higher sensitivity to H1 haplotype-related multifactorial tauopathies among Gypsies.

Tau-based treatment strategies in neurodegenerative diseases

Neurofibrillary tangles are a characteristic hallmark of Alzheimer's and other neurodegenerative diseases, such as Pick's disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). These diseases are summarized as tauopathies, because neurofibrillary tangles are composed of intracellular aggregates of the microtubule-associated protein tau. The molecular mechanisms of tau-mediated neurotoxicity are not well understood; however, pathologic hyperphosphorylation and aggregation of tau play a central role in neurodegeneration and neuronal dysfunction. The present review, therefore, focuses on therapeutic approaches that aim to inhibit tau phosphorylation and aggregation or to dissolve preexisting tau aggregates. Further experimental therapy strategies include the enhancement of tau clearance by activation of proteolytic, proteasomal, or autophagosomal degradation pathways or anti-tau directed immunotherapy. Hyperphosphorylated tau does not bind microtubules, leading to microtubule instability and transport impairment. Pharmacological stabilization of microtubule networks might counteract this effect. In several tauopathies there is a shift toward four-repeat tau isoforms, and interference with the splicing machinery to decrease four-repeat splicing might be another therapeutic option.

Microglial activation in brain lesions with tau deposits: comparison of human tauopathies and tau transgenic mice TgTauP301L

The aim of this study is to clarify the relationship of microglia to phosphorylated tau accumulation and the characteristics of microglial activation in brain lesions of human tauopathies in comparison to mutant tau transgenic (TG) mice. We performed immunocytochemical analyses of brains from six patients with tauopathies, and 24 mice (18 TG mice expressing mutant tau P301L and six non-TG control mice, 11 to 27 months of age) using anti-tau antibodies and various microglial markers. In the tau TG, both semiquantitative severity ratings of microglial activation and an ultrastructural study were performed. In human tauopathies, Iba1- and major histocompatibility complex (MHC) class II-positive activated microglia increased in regions of phosphorylated tau (AT8) accumulation. The immunoreactivity of scavenger receptor class A (SRA) was present in some activated microglia, including phagocytic microglia in Alzheimer's disease (AD). Double-immunofluorescent analysis under a confocal microscope showed activated microglia at the vicinity of AT8-positive cells. Semiquantitative data of the TG and control mice indicated that the immunopositivity of AT8 was closely associated with the number of Iba1-positive microglia in the cortical area. Tau-associated microglia showed rare immunoreactivity for MHC class II antigen and SRA in the TG mice. Ultrastructurally, activated microglia with enlarged cytoplasm were located near neurons containing abnormal cytoskeletons. This comparative study of human tauopathies and tau TG mice indicated that microglial activation was closely related to phosphorylated tau accumulation, and that activated microglia of the TG mice may have the low expression of MHC class II and SRA compared with those of human tauopathies.

Alzheimer disease models and human neuropathology: similarities and differences

Animal models aim to replicate the symptoms, the lesions or the cause(s) of Alzheimer disease. Numerous mouse transgenic lines have now succeeded in partially reproducing its lesions: the extracellular deposits of Abeta peptide and the intracellular accumulation of tau protein. Mutated human APP transgenes result in the deposition of Abeta peptide, similar but not identical to the Abeta peptide of human senile plaque. Amyloid angiopathy is common. Besides the deposition of Abeta, axon dystrophy and alteration of dendrites have been observed. All of the mutations cause an increase in Abeta 42 levels, except for the Arctic mutation, which alters the Abeta sequence itself. Overexpressing wild-type APP alone (as in the murine models of human trisomy 21) causes no Abeta deposition in most mouse lines. Doubly (APP x mutated PS1) transgenic mice develop the lesions earlier. Transgenic mice in which BACE1 has been knocked out or overexpressed have been produced, as well as lines with altered expression of neprilysin, the main degrading enzyme of Abeta. The APP transgenic mice have raised new questions concerning the mechanisms of neuronal loss, the accumulation of Abeta in the cell body of the neurons, inflammation and gliosis, and the dendritic alterations. They have allowed some insight to be gained into the kinetics of the changes. The connection between the symptoms, the lesions and the increase in Abeta oligomers has been found to be difficult to unravel. Neurofibrillary tangles are only found in mouse lines that overexpress mutated tau or human tau on a murine tau -/- background. A triply transgenic model (mutated APP, PS1 and tau) recapitulates the alterations seen in AD but its physiological relevance may be discussed. A number of modulators of Abeta or of tau accumulation have been tested. A transgenic model may be analyzed at three levels at least (symptoms, lesions, cause of the disease), and a reading key is proposed to summarize this analysis.

Increase in the relative expression of tau with four microtubule binding repeat regions in frontotemporal lobar degeneration and progressive supranuclear palsy brains

Some cases of familial frontotemporal dementia (FTD) leading to frontotemporal lobar degeneration (FTLD) are caused by mutations in tau on chromosome 17 (FTDP-17). Certain mutations alter the ratio between four (4R tau) and three (3R tau) repeat tau isoforms whereas cases with progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) mainly have 4R tau brain pathology. We assessed tau mRNA and protein levels in frontal cortex from 15 sporadic FTLD, 21 PSP, 5 CBD, 15 Alzheimer's disease (AD) and 16 control brains. Moreover, we investigated the disease association and possible tau splicing effects of the tau H1 haplotype. Cases with FTLD and PSP had lower tau mRNA levels than control brains. When analyzing 4R tau and 3R tau mRNA separately, control subjects displayed a 4R tau/3R tau ratio of 0.48. Surprisingly, FTLD brains displayed a more elevated ratio (1.32) than PSP brains (1.12). Also, several FTLD and PSP cases had higher 4R tau/3R tau mRNA than FTDP-17 cases, included as reference tissues, and the ratio increase was seen regardless of underlying histopathology, i.e. both for tau-positive and tau-negative FTLD cases. Furthermore, total tau protein levels were slightly decreased in both FTLD and AD as compared to control subjects. Finally, we confirmed the association of tau H1 with PSP, but could not find any haplotype-related effect on tau exon 10 splicing. In conclusion, we demonstrated increased but largely variable 4R tau/3R tau mRNA ratios in FTLD and PSP cases, suggesting heterogeneous pathophysiological processes within these disorders.

The genetics of frontotemporal dementia

This article describes the remarkable progress that has been made over the past decade in identifying the genetic contribution to frontotemporal dementia. The clinical and neuropathologic features of frontotemporal dementia with parkinsonism linked to chromosome 17 and the nature of the mutations in the progranulin and microtubule-associated protein tau genes are emphasized.

The molecular genetics and neuropathology of frontotemporal lobar degeneration: recent developments

The past year has seen a number of significant advances in our understanding of the neuropathological and molecular genetic basis of frontotemporal lobar degeneration (FTLD). Whereas, in the past, most attention focused on FTLD associated with tau-based pathology and microtubule associated protein tau gene (MAPT) mutations, there has recently been greater attention paid to non-tau FTLD. FTLD with tau-negative, ubiquitinated inclusions (FTLD-U) is now recognized as the most common pathology associated with clinical FTLD. Mutations in the progranulin gene (PGRN) have been identified as the cause of FTLD-U linked to chromosome 17. A rapidly growing number of PGRN mutations have been identified, and to date, all appear to cause FTLD by reducing the amount of functional PGRN protein (haploinsufficiency). The neuropathology associated with each of the known non-MAPT FTLD genes and loci (PGRN, valosin-containing protein gene, CHMP2B and 9p), has been shown to be a specific subtype of FTLD-U. The ubiquitinated pathological protein in FTLD-U has been identified as TAR deoxyribonucleic acid-binding protein with M (r) 43 kDa (TDP-43). Immunohistochemical and biochemical studies of TDP-43 have helped to clarify the relationship between different sub-types of FTLD-U and related conditions. It is anticipated that these discoveries will facilitate the development of new diagnostic tests and therapeutics.

Neuropathologic diagnostic and nosologic criteria for frontotemporal lobar degeneration: consensus of the Consortium for Frontotemporal Lobar Degeneration

The aim of this study was to improve the neuropathologic recognition and provide criteria for the pathological diagnosis in the neurodegenerative diseases grouped as frontotemporal lobar degeneration (FTLD); revised criteria are proposed. Recent advances in molecular genetics, biochemistry, and neuropathology of FTLD prompted the Midwest Consortium for Frontotemporal Lobar Degeneration and experts at other centers to review and revise the existing neuropathologic diagnostic criteria for FTLD. The proposed criteria for FTLD are based on existing criteria, which include the tauopathies [FTLD with Pick bodies, corticobasal degeneration, progressive supranuclear palsy, sporadic multiple system tauopathy with dementia, argyrophilic grain disease, neurofibrillary tangle dementia, and FTD with microtubule-associated tau (MAPT) gene mutation, also called FTD with parkinsonism linked to chromosome 17 (FTDP-17)]. The proposed criteria take into account new disease entities and include the novel molecular pathology, TDP-43 proteinopathy, now recognized to be the most frequent histological finding in FTLD. TDP-43 is a major component of the pathologic inclusions of most sporadic and familial cases of FTLD with ubiquitin-positive, tau-negative inclusions (FTLD-U) with or without motor neuron disease (MND). Molecular genetic studies of familial cases of FTLD-U have shown that mutations in the progranulin (PGRN) gene are a major genetic cause of FTLD-U. Mutations in valosin-containing protein (VCP) gene are present in rare familial forms of FTD, and some families with FTD and/or MND have been linked to chromosome 9p, and both are types of FTLD-U. Thus, familial TDP-43 proteinopathy is associated with defects in multiple genes, and molecular genetics is required in these cases to correctly identify the causative gene defect. In addition to genetic heterogeneity amongst the TDP-43 proteinopathies, there is also neuropathologic heterogeneity and there is a close relationship between genotype and FTLD-U subtype. In addition to these recent significant advances in the neuropathology of FTLD-U, novel FTLD entities have been further characterized, including neuronal intermediate filament inclusion disease. The proposed criteria incorporate up-to-date neuropathology of FTLD in the light of recent immunohistochemical, biochemical, and genetic advances. These criteria will be of value to the practicing neuropathologist and provide a foundation for clinical, clinico-pathologic, mechanistic studies and in vivo models of pathogenesis of FTLD.

Neuropathologic diagnostic and nosologic criteria for frontotemporal lobar degeneration: consensus of the Consortium for Frontotemporal Lobar Degeneration

The aim of this study was to improve the neuropathologic recognition and provide criteria for the pathological diagnosis in the neurodegenerative diseases grouped as frontotemporal lobar degeneration (FTLD); revised criteria are proposed. Recent advances in molecular genetics, biochemistry, and neuropathology of FTLD prompted the Midwest Consortium for Frontotemporal Lobar Degeneration and experts at other centers to review and revise the existing neuropathologic diagnostic criteria for FTLD. The proposed criteria for FTLD are based on existing criteria, which include the tauopathies [FTLD with Pick bodies, corticobasal degeneration, progressive supranuclear palsy, sporadic multiple system tauopathy with dementia, argyrophilic grain disease, neurofibrillary tangle dementia, and FTD with microtubule-associated tau (MAPT) gene mutation, also called FTD with parkinsonism linked to chromosome 17 (FTDP-17)]. The proposed criteria take into account new disease entities and include the novel molecular pathology, TDP-43 proteinopathy, now recognized to be the most frequent histological finding in FTLD. TDP-43 is a major component of the pathologic inclusions of most sporadic and familial cases of FTLD with ubiquitin-positive, tau-negative inclusions (FTLD-U) with or without motor neuron disease (MND). Molecular genetic studies of familial cases of FTLD-U have shown that mutations in the progranulin (PGRN) gene are a major genetic cause of FTLD-U. Mutations in valosin-containing protein (VCP) gene are present in rare familial forms of FTD, and some families with FTD and/or MND have been linked to chromosome 9p, and both are types of FTLD-U. Thus, familial TDP-43 proteinopathy is associated with defects in multiple genes, and molecular genetics is required in these cases to correctly identify the causative gene defect. In addition to genetic heterogeneity amongst the TDP-43 proteinopathies, there is also neuropathologic heterogeneity and there is a close relationship between genotype and FTLD-U subtype. In addition to these recent significant advances in the neuropathology of FTLD-U, novel FTLD entities have been further characterized, including neuronal intermediate filament inclusion disease. The proposed criteria incorporate up-to-date neuropathology of FTLD in the light of recent immunohistochemical, biochemical, and genetic advances. These criteria will be of value to the practicing neuropathologist and provide a foundation for clinical, clinico-pathologic, mechanistic studies and in vivo models of pathogenesis of FTLD.

Frontotemporal lobar degeneration: current concepts in the light of recent advances

Work done over the past decade has led to a molecular understanding of frontotemporal lobar degeneration (FTLD), a deadly disease that afflicts patients in mid-life. It is a common cause of dementia, second only to Alzheimer's disease in the population below 65 years of age. Neuroanatomical and neurobiological substrates have been identified for the three major subtypes of FTLD and these discoveries have broadened the FTLD spectrum to include amyotrophic lateral sclerosis (ALS). Mutations in MAPT were found to cause frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), a familial disorder with filamentous tau inclusions in nerve cells and glial cells. FTDP-17 can result in clinical syndromes that closely resemble progressive supranuclear palsy, corticobasal degeneration and Pick's disease. More recently, mutations in three genes (VCP, CHMP2B and PGRN) have been found to cause FTLD with ubiquitin-positive, tau-negative neuronal inclusions (FTLD-U). They explain a large proportion of inherited FTLD-U. It remains to be seen whether dementia lacking distinctive histopathology (DLDH) constitutes a third disease category, as many of these cases are now being reclassified as FTLD-U. Recently, TAR DNA-binding protein-43 (TDP-43) has been identified as a key protein of the ubiquitin inclusions of FTLD-U and ALS. Thus, for familial forms of FTLD and related disorders, we now know the primary etiologies and accumulating proteins. These findings are pivotal for dissecting the pathways by which different etiologies lead to the varied clinicopathological presentations of FTLD.

Progressive supranuclear palsy: pathology and genetics

Progressive supranuclear palsy (PSP) is an atypical Parkinsonian disorder associated with progressive axial rigidity, vertical gaze palsy, dysarthria and dysphagia. Neuropathologically, the subthalamic nucleus and brainstem, especially the midbrain tectum and the superior cerebellar peduncle, show atrophy. The substantia nigra shows loss of pigment corresponding to nigrostriatal dopaminergic degeneration. Microscopic findings include neuronal loss, gliosis and neurofibrillary tangles in basal ganglia, diencephalon and brainstem. Characteristic tau pathology is also found in glia. The major genetic risk factor for sporadic PSP is a common variant in the gene encoding microtubule-associated protein tau (MAPT) and recent studies have suggested that this may result in the altered expression of specific tau protein isoforms. Imaging studies suggest that there may be sensitive and specific means to differentiate PSP from other parkinsonian disorders, but identification of a diagnostic biomarker is still elusive.

Novel conformation-sensitive antibodies specific to three- and four-repeat tau

Two types of tau isoform, three- and four-repeat tau, are found in neurofibrillary tangles--a pathological hallmark of tauopathies. Which isoform is deposited in the affected tissues depends on the tauopathy. To study how and which tau isoforms contribute to neuronal degeneration, we have developed and characterized two novel conformation-sensitive antibodies, T3R and T4R. Two closely related synthetic peptides, PGGGKVQIVYK and PGGGSVQIVYK, respectively, were designed as antigens. The isoform-specific residues, (305)K in three-repeat tau or (305)S in four-repeat tau, and the PHF6 motif (VQIVYK) were identified as critical sequences. Despite the high similarity of the antigens, there was no cross-reactivity between T3R and T4R. Furthermore, T3R and T4R showed reduced binding to the thioflavin-positive beta-structural form of their target. These features may enable these antibodies to act as novel indicators that allow us to observe and evaluate conformational changes in each distinct isoform of tau.

Expression of embryonic tau protein isoforms persist during adult neurogenesis in the hippocampus

Tau is a microtubule-associated protein with a developmentally regulated expression of multiple isoforms. The neonatal isoform is devoid of two amino terminal inserts and contains only three instead of four microtubule-binding repeats (0N/3R-tau). We investigated the temporal expression pattern of 0N-tau and 3R-tau in the rat hippocampus. After the decline of 0N- and 3R-tau immunoreactivity during the postnatal development both isoforms remain highly expressed in a few cells residing beneath the granule cell layer. Coexpression of the polysialylated neuronal cell adhesion molecule, doublecortin, and incorporated bromodeoxyuridine showed that these cells are proliferating progenitor cells. In contrast mature granule cells express the adult tau protein isoform containing one aminoterminal insert domain (1N-tau). Therefore a shift in tau isoform expression takes place during adult neurogenesis, which might be related to migration, differentiation, and integration in the granule cell layer. A model for studying shifts in tau isoform expression in a defined subset of neurons might help to understand the etiology of tauopathies, when isoform composition is crucial for neurodegeneration, as in Pick's disease or FTDP-17.

The MAPT H1c risk haplotype is associated with increased expression of tau and especially of 4 repeat containing transcripts

Previously we have shown that the H1c haplotype on the background of the H1 clade of haplotypes at the MAPT locus is associated with increased risk for progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and Alzheimer's disease (AD). Here we replicated the association with AD in an additional autopsy confirmed series. We show that this haplotype increases both the expression of total MAPT transcript as well as specifically increasing the proportion of 4 microtubule binding repeat containing transcripts. We discuss these findings both in terms of the problems facing the dissection of the etiologies of complex traits and the pathogenesis of the tauopathies.

Neurofibrillary tangle-predominant dementia: comparison with classical Alzheimer disease

Neurofibrillary tangle predominant dementia (NFTPD) is a subset of late onset dementia, clinically different from traditional "plaque and tangle" Alzheimer disease (AD): later onset, shorter duration, less severe cognitive impairment, and almost absence of ApoE epsilon4. Neuropathology reveals abundant allocortical neurofibrillary pathology with no or few isocortical tau lesions, absence of neuritic plaques, absence or scarcity of amyloid deposits, but neurofibrillary changes comprising both 3 and 4 repeat (3R and 4R) tau immunohistochemistry are not significantly different from those in classical AD. Comparing 51 autopsy cases of NFTPD with 244 classical AD subjects, the nosology of NFTPD and its differences from AD are discussed.

Tauopathies: A Distinct Class of Neurodegenerative Diseases

Neurodegenerative diseases are characterized by neuronal loss and intraneuronal accumulation of fibrillary materials, of which, neurofibrillary tangles (NFT) are the most common. Neurofibrillary tangles also occur in normal aging and contain the hyperphosphorylated microtubule-associated protein tau. A detailed presentation is made of the molecular bases of Alzheimer's disease (AD), postencephalitic parkinsonism, amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) of Guam, progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), Pick's disease, frontotemporal dementia (FTD), Down's syndrome, myotonic dystrophy (DM) and Niemann-Pick Type C (NPC) disease, which are considered to be common tauopathies. The unique human tau gene extends over 100 kb of the long arm of chromosome 17 and contains 16 exons. The human brain contains six tau isoforms that contain from 352 to 441 amino acids. To date, 34 pathogenic tau mutations have been described among 101 families affected by FTD with parkinsonism linked to chromosome 17 (FTDP-17). These mutations may involve alternative splicing of exon 10 that lead to changes in the proportion of 4-repeat- and 3-repeat-tau isoforms, or may modify tau interactions with microtubules. Tau aggregates differ in degree of phosphorylation and in content of tau isoforms. Five classes of tauopathies have been defined depending on the type of tau aggregates. The key event in tauopathies is the disorganization of the cytoskeleton, which is based on mutations/polymorphisms in the tau gene and lead to nerve cell degeneration. In this review, tauopathies as a distinct class of neurodegenerative diseases are discussed with emphasis on their molecular pathology and genetics.

Cellular tau pathology and immunohistochemical study of tau isoforms in sporadic tauopathies

Pathological inclusions in neurons and glial cells containing fibrillary aggregates of abnormally hyperphosphorylated tau protein are characteristic features in sporadic tauopathies. In the first part of this paper we outline the morphological features of some major sporadic tauopathies. In the second part, to better define the tau isoform composition, we report on the immunohistochemistry of tau isoforms in autopsied brains, including two cases with AD, two with diffuse neurofibrillary tangles with calcification, four with Pick's disease with Pick bodies (PiD), seven with progressive supranuclear palsy (PSP), six with corticobasal degeneration (CBD) and seven cases with argyrophilic grain disease. We used two monoclonal antibodies, RD3 and RD4, and a polyclonal antibody for exon 10 that effectively distinguish between three-repeat (3R) tau and four-repeat (4R) tau. Neuronal neurofibrillary tangles (NFT) in AD and diffuse neurofibrillary tangles with calcification contained both 3R-tau and 4R-tau. The Pick bodies were immunopositive for 3R-tau in two cases; however, in two other cases they were mainly immunopositive for 4R-tau. Thus, Pick bodies demonstrated heterogeneity. 3R-tau PiD contained 3R-tau glial inclusions, and 4R-tau PiD contained mainly 4R-tau glial inclusions. Glial inclusions were more abundant in 4R-tau PiD cases. In progressive supranuclear palsy and CBD, both neuronal and glial tau accumulation forming NFF, pretangles, tuft-shaped astrocytes, astrocytic plaques, coiled bodies and threads demonstrated 4R-tau in the cerebral cortices, although in the basal ganglia and brainstem neuronal and glial inclusions were occasionally immunopositive for 3R-tau in addition to 4R-tau. Argyrophilic grains (AG) were immunopositive for 4R-tau, although pretangles were weakly stained for 4R-tau. Thus the immunoreactivity for 4R-tau was different between AG and pretangles. Therefore, the isoform composition on immunohistochemical study showed heterogeneity in PiD, and was not uniform in the basal ganglia and brain stem in PSP and CBD. It is suggested that the isoform composition of sporadic tauopathies may have a spectrum in individual cases, and cellular isoform composition may differ in various brain regions.

Unexpected abundance of pathological tau in progressive supranuclear palsy white matter

OBJECTIVE

To investigate whether biochemical insoluble tau with 4 (4R) and/or 3 (3R) microtubule-binding repeats accumulate in white as well as gray matter in progressive supranuclear palsy (PSP), a neurodegenerative tauopathy.

METHODS

To assess tau pathology in PSP white matter, we combined Western blot (WB) and immunohistochemical methods to analyze 23 autopsy-confirmed PSP brains.

RESULTS

WBs showed an unexpected abundance of insoluble tau in white and gray matter of PSP brains, but biochemical tau pathology in white matter was not correlated with immunohistochemistry using the same panel of epitope-specific anti-tau antibodies used for WB. Despite heterogeneity in the representation of pathological 3R and 4R tau isoforms in cortical versus subcortical regions, biochemically detectable white matter tau pathology is a constant feature of PSP.

INTERPRETATION

These studies show additional similarities between PSP and corticobasal degeneration, but unlike corticobasal degeneration, more abundant white matter tau pathology in PSP is detectable by WB than by immunohistochemistry. The differential detection of abnormal tau by biochemistry versus microscopy in PSP may reflect distinct pathological mechanisms, and elucidation of these processes will augment efforts to develop better strategies for the diagnosis and treatment of PSP and related neurodegenerative tauopathies.

[Nosology of dementias: the neuropathologist's point of view]

The diagnosis of degenerative dementias heavily relies on the identification of neuronal or glial inclusions. Tauopathy is probably the largest group including Alzheimer and Pick disease, mutation of the tau gene, progressive supranuclear palsy, corticobasal degeneration, and argyrophilic grain disease. Lewy bodies, when numerous in the cerebral cortex, are usually associated with the cognitive deficit of Parkinson disease dementia or of dementia with Lewy bodies--both conditions being distinguished by clinical information. The inclusions of the dentate gyrus, only labeled by anti-ubiquitin antibodies, isolate a subgroup of fronto-temporal dementia (FTDu), sometimes familial and sometimes associated with amyotrophic lateral sclerosis. Mutations of the progranulin gene have been recently discovered among a significant proportion of these patients. Neuronal Intermediate Filament Inclusion Disease (NIFID) is a rare, apparently sporadic dementia, characterized by the presence of large inclusions in the cell body of many neurons. These inclusions react with antibodies directed against neurofilaments or against other intermediate filaments (such as alpha-internexin). The diagnostic value of some of these inclusions allowing the classification of the degenerative dementias has been discussed. The link between the inclusions and the pathogenetic mechanism is indeed probably variable. It should however be stressed that whenever their composition has been elucidated, the inclusions have given important clues to the pathogenesis of the disease in which they had been found.

No alteration in tau exon 10 alternative splicing in tangle-bearing neurons of the Alzheimer's disease brain

Defective splicing of tau mRNA, promoting a shift between tau isoforms with (4R tau) and without (3R tau) exon 10, is believed to be a pathological consequence of certain tau mutations causing frontotemporal dementia. By assessing protein and mRNA levels of 4R tau and 3R tau in 27 AD and 20 control temporal cortex, we investigated whether altered tau splicing is a feature also in Alzheimer's disease (AD). However, apart from an expected increase of sarcosyl-insoluble tau in AD, there were no significant differences between the groups. Next, by laser-capture microscopy and quantitative PCR, we separately analyzed CA1 hippocampal neurons with and without neurofibrillary pathology from six of the AD and seven of the control brains. No statistically significant differences in 4R tau/3R tau mRNA were found between the different subgroups. Moreover, we confirmed the absence of significant ratio differences in a second data set with laser-captured entorhinal cortex neurons from four AD and four control brains. Finally, the 4R tau/3R tau ratio in CA1 neurons was roughly half of the ratio in temporal cortex, indicating region-specific differences in tau mRNA splicing. In conclusion, this study indicated region-specific and possibly cell-type-specific tau splicing but did not lend any support to overt changes in alternative splicing of tau exon 10 being an underlying factor in AD pathogenesis.

The 2,6-disubstituted naphthalene derivative FDDNP labeling reliably predicts Congo red birefringence of protein deposits in brain sections of selected human neurodegenerative diseases

Deposition of conformationally altered proteins prominently characterizes pathogenesis and pathomorphology of a number of neurodegenerative disorders. 2-(1-{6-[(2-[F-18]fluoroethyl) (methyl)amino]-2-naphthyl} ethylidene) malononitrile ([F-18]FDDNP), a hydrophobic, viscosity-sensitive, solvent-sensitive, fluorescent imaging probe has been used with positron emission tomography to visualize brain pathology in the living brain of Alzheimer disease (AD) patients. Its non-radiofluorinated analog FDDNP was shown to label senile plaques and neurofibrillary tangles (NFTs) in brain tissue sections. This work aimed at evaluating FDDNP labeling of various protein deposits in fixed, paraffin-embedded brain tissue sections of selected neurodegenerative disorders: AD, cerebral amyloid angiopathy (CAA), transmissible spongiform encephalopathies, progressive supranuclear palsy (PSP), Pick disease (PiD), Parkinson disease, dementia with Lewy bodies, multiple system atrophy (MSA). Cerebral hypertensive vascular hyalinosis (HVH) was used as negative control. Significant agreement between amyloid histochemical properties and FDDNP labeling of the deposits was established. FDDNP labeling showed high positive predictive value for birefringence in senile plaques and NFTs in AD, prion plaques and amyloid deposits in CAA. No FDDNP labeled structures were observed in HVH, PSP, PiD or MSA tissue sections. Our findings may be of significant value for the detection of neuropathological aggregates with [F-18]FDDNP in some of these disorders in the living brain of human subjects.

The effects of APOE and tau gene variability on risk of frontotemporal dementia

Frontotemporal dementia (FTD) is a complex dementing syndrome whose genetic/non genetic risk factors are mostly unknown. Aim of the present work was to investigate whether APOE and/or tau gene variability does affect the risk of FTD. A sample of FTD cases (sporadic: n = 54; familial: n = 46, one subject per family) was collected in a genetically homogeneous population (Calabria, southern Italy) and analyzed in comparison with an age- and sex-matched control group (n = 180) extracted from the same population. Logistic regression analysis showed that APOE gene variability affects the probability of disease, with allele epsilon4 increasing (exp(beta1) = 2.68 with [1.51-4.76] 95% confidence interval; p = 0.001) and allele epsilon2 decreasing (exp(beta1) = 0.28 with [0.12-0.66] 95% confidence interval; p = 0.003) the risk of FTD. On the contrary, tau gene variability was ineffectual (exp(beta1) non significantly different from 1 for either H1 or H2 haplotypes), although a small effect was observed by the H1 haplotype in increasing the protective effect of the epsilon2 allele (p = 0.007).

Co-localization of beta-peptide and phosphorylated tau in astrocytes in a patient with corticobasal degeneration

The co-localization of amyloid beta (Abeta) and phosphorylated tau in astrocytes in a patient with corticobasal degeneration is described. At autopsy, the present case exhibited neuropathological findings compatible with those of corticobasal degeneration, including atrophy of the frontal and temporal lobes, neuronal loss and gliosis in the cortical and subcortical regions, and presence of cortical ballooned neurons and astrocytic plaques. Moreover, many senile plaques were found in the cerebral cortex. There were also clusters of Abeta-positive granules associated with astrocytic cytoplasm and processes in the subiculum and entorhinal cortex. In the entorhinal cortex, the Abeta-positive granules were occasionally co-localized with phosphorylated tau-positive fibrillary structures in the astrocytic cytoplasm. To our knowledge, this is the first demonstration of co-localization of Abeta and phosphorylated tau in astrocytes. This phenomenon implies that phagocytosis of Abeta coincides with production of phosphorylated tau in the same reactive astrocytes.

Hippocampal sclerosis dementia with tauopathy

In some elderly individuals with dementia, hippocampal sclerosis (HS) is the only remarkable autopsy finding. The cause of HS in this setting is puzzling, since known causes of HS such as seizures or global hypoxic-ischemic episodes are rarely present. We here describe a series of HS cases that have a widespread neuronal and/or glial tauopathy. Of 14 consecutive cases of HS, 12 had been clinically diagnosed with dementia and/or Alzheimer's disease (AD) while 2 were non-demented; 7 cases had also been clinically diagnosed with parkinsonism. In addition to HS, 6 cases also met pathologic diagnostic criteria for AD. Gallyas silver staining and immunohistochemistry with the AT8 antibody revealed a glial and/or neuronal tauopathy in 12 of 14 cases, with frequent positive neurons and/or glial cells in the neocortex, basal ganglia, thalamus and/or limbic regions; in addition, 8 of the 14 cases had argyrophilic grains. Screening for known tau mutations was negative in all cases. Western blots of sarkosyl-insoluble tau protein showed a mixture of 3- and 4-repeat forms. The results suggest that most cases of HS dementia are sporadic multisystem tauopathies; we suggest the term "hippocampal sclerosis dementia with tauopathy" (HSDT) for these.

Raised CSF phospho-tau concentrations in variant Creutzfeldt-Jakob disease: diagnostic and pathological implications

OBJECTIVE

To investigate whether phosphorylated tau protein (tau-pT181) is increased in variant Creutzfeldt-Jakob disease (vCJD) and if the tau-pT181/tau protein ratio is useful for distinguishing between patients with and without CJD.

METHODS

CSF tau protein and tau-pT181 were measured in 50 patients with sporadic CJD (sCJD), 51 patients with vCJD, 46 sCJD controls, and 37 vCJD controls, using Innotest hTau and Innotest P-Thr181, Innogenetics.

RESULTS

Concentrations of CSF tau protein were increased in sCJD (5120 v 367 pg/ml in controls, p < 0.001) and vCJD (952 v 106 pg/ml, p < 0.001); tau-pT181 was also raised in sCJD (61 v 35 pg/ml in controls, p = 0.002) and vCJD (114 v 33 pg/ml, p < 0.001). Median concentrations of tau-pT181 were higher in vCJD than in sCJD (p < 0.001). The tau-pT181/tau protein ratio was lower than in controls in both sCJD (12 v 128 (p < 0.001)) and vCJD (119 v 279 (p < 0.001)). Mean tau-pT181/tau protein ratio was 10-fold higher in vCJD than in sCJD. Raised CSF tau protein had the highest efficiency for distinguishing sCJD and vCJD from controls.

CONCLUSIONS

CSF tau-pT181 concentrations are raised in vCJD and are higher than in sCJD. Measurement of CSF tau-pT181/tau protein ratio does not improve the diagnostic efficiency of CSF tau protein alone for either vCJD or sCJD. The higher concentration of CSF tau-pT181 found in vCJD suggests that unexplained pathogenic factors influence the phosphorylation of tau protein in vCJD patients.

Progressive supranuclear palsy and corticobasal degeneration: lumping versus splitting

Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are both sporadic disorders with tau pathology. Criteria have been defined that in most instances allow for adequate diagnosis of the two disorders both clinically and neuropathologically; however, overlap is not uncommon. For example, patients with PSP may present with severe unilateral apraxia and supranuclear gaze palsy can occur in CBD. Pathological overlap also occurs and pathologically "mixed" cases are encountered. Common to both these two tauopathies is that isoforms of four-repeat tau due to splicing of exon 10 define the tau filamentous aggregates. This is in contrast to other tau disorders such as Pick's with three-repeat tau aggregates. Additional evidence for a causal link between PSP and CBD is the finding that both disorders are homozygous for the H1 tau haplotype. Furthermore, in some families with parkinsonism linked to defined mutations of the tau gene (FTDP-17), involved relatives have presented with PSP whereas others with the CBD phenotype. Although PSP and CBD frequently can be clearly separated clinically and pathologically, the degree of clinicopathological and genetic overlap is important and suggests that they represent different phenotypes of the same disorder, with differences occurring perhaps in relation to different genetic background. That PSP and CBD are distinct nosological entities occurring in patients with similar genetic predisposition cannot be ruled out.

Relationship between microtubule-binding repeats and morphology of neurofibrillary tangle in Alzheimer's disease

OBJECTIVE

The present study was performed to compare the distributions of three-repeat (3R) and four-repeat (4R) neurofibrillary tangles (NFT) with those of pretangles (p-NFT), intracellular NFT (i-NFT), and extracellular NFT (e-NFT) in the hippocampus of Alzheimer's disease brains.

METHODS

NFT labeling was performed using anti-tau antibodies: pSer262 for p-NFT, pSer422 for i-NFT, AT8 for e-NFT, RD3 for 3R, and RD4 for 4R tau, and Gallyas impregnation for the NFT population. RD4- and pSer422-positive NFT were detected predominantly in sectors from CA2 to CA4, while RD3- and pSer262-positive NFT were predominantly present in CA1, the entorhinal cortex, and the subiculum. The tau epitope recognized by pSer262 belongs to 4R tau but it showed a strong correlation with RD3- and AT8-positive NFT.

CONCLUSIONS

Sectors CA2-CA4 showed predominantly 4R-NFT containing the pSer422 epitope. pSer262 may detect the process of transformation from p-NFT to i-NFT, and e-NFT consisted predominantly of 3R tau.

Frontotemporal dementia, motor neuron disease and tauopathy: clinical and neuropathological study in a family

We report a familial disorder occurring in three patients that presented as frontotemporal dementia (FTD). A neuropathological study was performed in a 58-year-old patient, who developed FTD 2 years prior to the onset of motor neuron disease (MND), and died at age 62. Lesions indicative of associated MND were observed: neuronal loss in the anterior horns of the spinal cord, Bunina bodies, axonal spheroids, degeneration of the pyramidal tracts, and of FTD: decreased neuronal density and laminar microvacuolation of layers II and III in the frontal and temporal cortex. Ubiquitin-only-immunoreactive changes were found in the spinal cord and medulla, but were absent from the temporal and frontal cortex. There were also widespread deposits of various neuronal and glial inclusions containing abnormally phosphorylated tau protein, the Western blotting pattern of which was characterized by two major bands of 64 and 69 kDa. There were no abnormalities of the entire coding sequences of microtubule-associated protein tau (MAPT) and copper-zinc superoxide dismutase (SOD(1)) genes. Our results suggest that FTD associated with MND can be caused by a larger spectrum of neuropathological lesions than commonly accepted.

Neuropathologic, biochemical, and molecular characterization of the frontotemporal dementias

The frontotemporal dementias (FTDs) are a heterogeneous group of neurodegenerative disorders that are characterized clinically by dementia, personality changes, language impairment, and occasionally extrapyramidal movement disorders. Historically, the diagnosis and classification of FTDs has been fraught with difficulties, especially with regard to establishing a consensus on the neuropathologic diagnosis. Recently, an international group of scientists participated in a consensus conference to develop such neuropathologic criteria. They recommended a diagnostic classification scheme that incorporated a biochemical analysis of the insoluble tau isoform composition, as well as ubiquitin immunohistochemistry. The use and reliability of this classification system has yet to be examined. In this study, we evaluated 21 cases of FTD. Using traditional histochemical stains and tau protein and ubiquitin immunohistochemistry, we separated each case into one of the following categories: classic Pick disease (PiD; n = 7), corticobasal degeneration (CBD; n = 5), dementia lacking distinctive histopathologic features (DLDH; n = 4), progressive supranuclear palsy (PSP; n = 2), frontotemporal lobar degeneration with motor neuron disease or motor neuron disease-type inclusions (FTLD-MND/MNI; n = 2), and neurofibrillary tangle dementia (NFTD; n = 1). Additionally, we independently categorized each case by the insoluble tau isoform pattern, including 3R (n = 5), 4R (n = 7), 3R/4R (n = 3), and no insoluble tau (n = 6). As suggested by the proposed diagnostic scheme, we found that the insoluble tau isoform patterns correlated strongly with the independently derived histopathologic diagnoses (p < 0.001). The data show that cases containing predominantly 3R tau were classic PiD (100%). Cases with predominantly 4R tau were either CBD (71%) or PSP (29%). Cases with both 3R and 4R tau were either a combination of PiD and Alzheimer disease (67%) or NFTD (33%). Finally, cases with no insoluble tau were either DLDH (67%) or FTLD-MND/MNI (33%). To further characterize these cases, we also performed quantitative Western blots for soluble tau, APOE genotyping, and, in selected cases, tau gene sequencing. We show that soluble tau is reduced in DLDH and FTLD-MND/MNI and that APOE4 is overrepresented in PiD and DLDH. We also identified a new family with the R406W mutation and pathology consistent with NFTD. This study validates the recently proposed diagnostic criteria and forms a framework for further refinement of this classification scheme.

The nature of the parkinsonism-dementia complex and amyotrophic lateral sclerosis of Guam and magnesium deficiency

The parkinsonism-dementia complex (PDC) and amyotrophic lateral sclerosis (ALS) were the fatal neurological diseases, showing very high incidence during 1950-1970 and dramatic decrease after 1970 on Guam. Through the research, the present author insisted that; (1) NFTs in Guam ALS patients are merely a background feature widely dispersed in the population, (2) Guam ALS and PDC are basically different diseases, and (3) Guam ALS occurs initially as classic ALS. As pathogeneses of the diseases, intake of low calcium (Ca) and magnesium (Mg) and high aluminum water and of some plant excitatory neurotoxin has been speculated. To elucidate the pathogenesis, the author performed an experiment exposing rats to low Ca and/or Mg intake for two generations, so as to follow the actual way of human living on the island, since several generations live continuously in the same environment. The study indicates that continuous low Mg intake for two generations induces exclusive loss of dopaminergic neurons in in rats, and may support the Mg hypothesis in the pathogenesis of PDC of Guam.

Quantitative analysis of tau isoform transcripts in sporadic tauopathies

A number of neurodegenerative diseases, including Alzheimer's disease (AD), are characterized by intraneuronal accumulation of the tau protein. Some forms of FTDP-17 are caused by mutations in the tau gene affecting exon 10 splicing. Therefore, dysregulation of tau pre-mRNA splicing may be a contributing factor to sporadic tauopathies. To address this question, we devised a real-time RT-PCR strategy based on the use of a single fluorogenic probe to evaluate the ratio between tau isoforms containing or lacking exon 10 (4R/3R ratio) in post-mortem brain samples. We found a two- to six-fold increase in the 4R/3R ratio in cases of FTDP-17 linked to a splice site mutation, hence confirming the validity of the strategy. The difference in the 4R/3R ratio in the superior temporal and superior frontal gyri between AD and control brains was not statistically significant. Similarly, there was no significant difference in the 4R/3R ratio between Pick's disease cases and controls, indicating that the predominance of tau3R protein in PiD reflects post-translational modifications of specific isoforms. This study indicates that post-translational events are likely to be the main factors controlling tau isoform composition in sporadic tauopathies and highlights the benefit of quantitative RT-PCR in the assessment of splicing abnormalities in tauopathies.

Linkage disequilibrium fine mapping and haplotype association analysis of the tau gene in progressive supranuclear palsy and corticobasal degeneration

BACKGROUND

The haplotype H1 of the tau gene, MAPT, is highly associated with progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD).

OBJECTIVE

To investigate the pathogenic basis of this association.

METHODS

Detailed linkage disequilibrium and common haplotype structure of MAPT were examined in 27 CEPH trios using validated HapMap genotype data for 24 single nucleotide polymorphisms (SNPs) spanning MAPT.

RESULTS

Multiple variants of the H1 haplotype were resolved, reflecting a far greater diversity of MAPT than can be explained by the H1 and H2 clades alone. Based on this, six haplotype tagging SNPs (htSNPs) that capture 95% of the common haplotype diversity were used to genotype well characterised PSP and CBD case-control cohorts. In addition to strong association with PSP and CBD of individual SNPs, two common haplotypes derived from these htSNPs were identified that are highly associated with PSP: the sole H2 derived haplotype was underrepresented and one of the common H1 derived haplotypes was highly associated, with a similar trend observed in CBD. There were powerful and highly significant associations with PSP and CBD of haplotypes formed by three H1 specific SNPs. This made it possible to define a candidate region of at least approximately 56 kb, spanning sequences from upstream of MAPT exon 1 to intron 9. On the H1 haplotype background, these could harbour the pathogenic variants.

CONCLUSIONS

The findings support the pathological evidence that underlying variations in MAPT could contribute to disease pathogenesis by subtle effects on gene expression and/or splicing. They also form the basis for the investigation of the possible genetic role of MAPT in Parkinson's disease and other tauopathies, including Alzheimer's disease.

Characteristics of two distinct clinical phenotypes in pathologically proven progressive supranuclear palsy: Richardson's syndrome and PSP-parkinsonism

The clinical diagnosis of progressive supranuclear palsy (PSP) relies on the identification of characteristic signs and symptoms. A proportion of pathologically diagnosed cases do not develop these classic features, prove difficult to diagnose during life and are considered as atypical PSP. The aim of this study was to examine the apparent clinical dichotomy between typical and atypical PSP, and to compare the biochemical and genetic characteristics of these groups. In 103 consecutive cases of pathologically confirmed PSP, we have identified two clinical phenotypes by factor analysis which we have named Richardson's syndrome (RS) and PSP-parkinsonism (PSP-P). Cases of RS syndrome made up 54% of all cases, and were characterized by the early onset of postural instability and falls, supranuclear vertical gaze palsy and cognitive dysfunction. A second group of 33 (32%) were characterized by asymmetric onset, tremor, a moderate initial therapeutic response to levodopa and were frequently confused with Parkinson's disease (PSP-P). Fourteen cases (14%) could not be separated according to these criteria. In RS, two-thirds of cases were men, whereas the sex distribution in PSP-P was even. Disease duration in RS was significantly shorter (5.9 versus 9.1 years, P < 0.001) and age at death earlier (72.1 versus 75.5 years, P = 0.01) than in PSP-P. The isoform composition of insoluble tangle-tau isolated from the basal pons also differed significantly. In RS, the mean four-repeat:three-repeat tau ratio was 2.84 and in PSP-P it was 1.63 (P < 0.003). The effect of the H1,H1 PSP susceptibility genotype appeared stronger in RS than in PSP-P (odds ratio 13.2 versus 4.5). The difference in genotype frequencies between the clinical subgroups was not significant. There were no differences in apolipoprotein E genotypes. The classic clinical description of PSP, which includes supranuclear gaze palsy, early falls and dementia, does not adequately describe one-third of cases in this series of pathologically confirmed cases. We propose that PSP-P represents a second discrete clinical phenotype that needs to be clinically distinguished from classical PSP (RS). The different tau isoform deposition in the basal pons suggests that this may ultimately prove to be a discrete nosological entity.

Frontotemporal dementia with co-occurrence of astrocytic plaques and tufted astrocytes, and severe degeneration of the cerebral white matter: a variant of corticobasal degeneration?

We report two patients who exhibited frontotemporal dementia (FTD) with unusual neuropathological features. The ages of the patients at death were 65 and 67 years, the disease durations were 6 and 5 years, and the clinical diagnoses were Pick's disease and corticobasal degeneration (CBD), respectively. At autopsy, both cases exhibited neuropathological findings compatible with those of CBD, including atrophy of the frontal and parietal lobes, neuronal loss and gliosis in the cortical and subcortical regions, and presence of cortical ballooned neurons and astrocytic plaques (APs). In both cases, immunoblotting of insoluble tau exhibited the pattern of selective accumulation of four-repeat tau, a finding that is also compatible with CBD. However, severe degeneration was evident in the frontal and parietal white matter in both cases. Moreover, a striking finding was the widespread presence in the affected cortex of tufted astrocytes (TAs), which are characteristic of progressive supranuclear palsy (PSP). Neither co-occurrence of APs and TAs nor severe degeneration of the cerebral white matter is a feature of either CBD or PSP. No mutations were found in the tau gene in either case. In conclusion, the possibility that these two cases represent a new neuropathological phenotype of non-familial FTD rather than simply a variant of CBD cannot be completely excluded.

Transcriptional and conformational changes of the tau molecule in Alzheimer's disease

Mutations in the tau gene cause frontotemporal dementia with parkinsonism, presumably by affecting the balance between tau isoforms (with either three or four microtubule-binding repeats) or by impairing tau-tubulin binding. Although to date no mutations have been found for Alzheimer's disease, it is plausible that tangle pathology in this disorder is also driven by similar molecular modifications. Investigations of Alzheimer brain tissue with new technologies such as laser capture microscopy, quantitative PCR and fluorescence lifetime imaging will shed light on whether transcriptional or conformational alterations play a role in Alzheimer pathogenesis.

Characterization of paired helical filaments by scanning transmission electron microscopy

Paired helical filaments (PHFs) are abnormal twisted filaments composed of hyperphosphorylated tau protein. They are found in Alzheimer's disease and other neurodegenerative disorders designated as tauopathies. They are a major component of intracellular inclusions known as neurofibrillary tangles (NFTs). The objective of this review is to summarize various structural studies of PHFs in which using scanning transmission electron microscopy (STEM) has been particularly informative. STEM provides shape and mass per unit length measurements important for studying ultrastructural aspects of filaments. These include quantitative comparisons between dispersed and aggregated populations of PHFs as well as comparative studies of PHFs in Alzheimer's disease and other neurodegenerative disorders. Other approaches are also discussed if relevant or complementary to studies using STEM, e.g., application of a novel staining reagent, Nanovan. Our understanding of the PHF structure and the development of PHFs into NFTs is presented from a historical perspective. Others goals are to describe the biochemical and ultrastructural complexity of authentic PHFs, to assess similarities between authentic and synthetic PHFs, and to discuss recent advances in PHF modeling.

Synaptophysin immunoreactivity in Pick's disease: comparison with Alzheimer's disease and dementia with Lewy bodies

Frontotemporal lobe atrophy is a hallmark of Pick's disease (PiD), however, the underlying pathobiology of the neuronal losses is unknown. Synaptic losses have been described in Alzheimer's disease (AD) and correlate with the severity of dementia, however few studies of synaptic integrity have been done to determine whether synaptic loss also contributes to symptoms in non-AD dementias. To begin to assess synaptic integrity in other types of dementia, we examined the site of termination of the hippocampal perforant pathway, the major source of afferent tracts to the hippocampus. We determined immunoreactivity for the synaptic-terminal specific protein synaptophysin in the outer molecular layer of the hippocampal dentate gyrus (OMDG) in eight PiD, nine AD, nine dementia with Lewy bodies (DLB), and seven control cases. Quantitative data were obtained using an Image-Pro automated image analysis system. In AD and PiD, synaptophysin immunoreactivity was visibly reduced in the OMDG Densitometric analysis confirmed that there were statistically significant differences among groups in synaptophysin immunoreactivity when comparing the OMDG to the adjacent inner molecular layer of the hippocampal dentate gyrus (IMDG) (p = 0.002). These differences were present between PiD and both the control and DLB groups. The AD group also showed a reduction in synaptophysin immunoreactivity compared with DLB and control groups. In contrast, perforant pathway synaptic losses in DLB were minimal. Our data supports the hypothesis that focal synaptic losses occur in PiD and AD and may contribute to the cognitive deficits in both conditions.