Dementia of frontal type and dementias with subcortical gliosis

Entorhinal cortex astrocytic atrophy in human frontotemporal dementia

The pathophysiology of Fronto Temporal Dementia (FTD) remains poorly understood, specifically the role of astroglia. Our aim was to explore the hypothesis of astrocytic alterations as a component for FTD pathophysiology. We performed an in-depth tri-dimensional (3-D) anatomical and morphometric study of glial fibrillary acidic protein (GFAP)-positive and glutamine synthetase (GS)-positive astrocytes in the human entorhinal cortex (EC) of FTD patients. The studies at this level in the different types of human dementia are scarce. We observed a prominent astrocyte atrophy of GFAP-positive astrocytes and co-expressing GFAP/GS astrocytes, characterised by a decrease in area and volume, whilst minor changes in GS-positive astrocytes in FTD compared to non-dementia controls (ND) samples. This study evidences the importance of astrocyte atrophy and dysfunction in human EC. We hypothesise that FTD is not only a neuropathological disease, but also a gliopathological disease having a major relevance in the understanding the astrocyte role in FTD pathological processes and development.

Microglial burden, activation and dystrophy patterns in frontotemporal lobar degeneration

Background

Microglial dysfunction is implicated in frontotemporal lobar degeneration (FTLD). Although studies have reported excessive microglial activation or senescence (dystrophy) in Alzheimer’s disease (AD), few have explored this in FTLD. We examined regional patterns of microglial burden, activation and dystrophy in sporadic and genetic FTLD, sporadic AD and controls.

Methods

Immunohistochemistry was performed in frontal and temporal grey and white matter from 50 pathologically confirmed FTLD cases (31 sporadic, 19 genetic: 20 FTLD-tau, 26 FTLD-TDP, four FTLD-FUS), five AD cases and five controls, using markers to detect phagocytic (CD68-positive) and antigen-presenting (CR3/43-positive) microglia, and microglia in general (Iba1-positive). Microglial burden and activation (morphology) were assessed quantitatively for each microglial phenotype. Iba1-positive microglia were assessed semi-quantitatively for dystrophy severity and qualitatively for rod-shaped and hypertrophic morphology. Microglia were compared in each region between FTLD, AD and controls, and between different pathological subtypes of FTLD, including its main subtypes (FTLD-tau, FTLD-TDP, FTLD-FUS), and subtypes of FTLD-tau, FTLD-TDP and genetic FTLD. Microglia were also compared between grey and white matter within each lobe for each group.

Results

There was a higher burden of phagocytic and antigen-presenting microglia in FTLD and AD cases than controls, but activation was often not increased. Burden was generally higher in white matter than grey matter, but activation was greater in grey matter. However, microglia varied regionally according to FTLD subtype and disease mechanism. Dystrophy was more severe in FTLD and AD than controls, and more severe in white than grey matter, but this also varied regionally and was particularly extensive in FTLD due to progranulin (GRN) mutations. Presence of rod-shaped and hypertrophic microglia also varied by FTLD subtype.

Conclusions

This study demonstrates regionally variable microglial involvement in FTLD and links this to underlying disease mechanisms. This supports investigation of microglial dysfunction in disease models and consideration of anti-senescence therapies in clinical trials.

Cognitive Impairment in Amyotrophic Lateral Sclerosis: A Consideration for Occupational Performance

Traditionally, amyotrophic lateral sclerosis (ALS) has been viewed as a degenerative disease, selective to the motor system. Until recently, research into cognitive impairment in ALS was confined primarily to a small proportion of patients with overt and clinically evident frontotemporal dementia (ALS/FTD). However, evidence from contemporary neuropsychological analysis and functional imaging studies, as identified in this review, indicates that a significantly higher percentage of patients with ALS presents with milder cognitive impairment in frontotemporal function. These deficits are considered progressive in nature, with increasing disability. Disturbances within the supervisory attentional system or central executive are thought to be responsible.

It would appear that patients diagnosed with ALS may not be equally susceptible to developing cognitive deficits. The relationship between bulbar-onset ALS and increased cognitive decline is noteworthy. In ALS, the impact of cognitive disturbance on occupational performance must be considered in addition to physical disability.

Amyloid-β and Astrocytes Interplay in Amyloid-β Related Disorders

Amyloid-β (Aβ) pathology is known to promote chronic inflammatory responses in the brain. It was thought previously that Aβ is only associated with Alzheimer's disease and Down syndrome. However, studies have shown its involvement in many other neurological disorders. The role of astrocytes in handling the excess levels of Aβ has been highlighted in the literature. Astrocytes have a distinctive function in both neuronal support and protection, thus its involvement in Aβ pathological process may tip the balance toward chronic inflammation and neuronal death. In this review we describe the involvement of astrocytes in Aβ related disorders including Alzheimer's disease, Down syndrome, cerebral amyloid angiopathy, and frontotemporal dementia.

Glial fibrillar acidic protein in the cerebrospinal fluid of Alzheimer's disease, dementia with Lewy bodies, and frontotemporal lobar degeneration

Biomarkers in the cerebrospinal fluid (CSF) are currently regarded as indispensable indicators for accurate differential diagnosis of neurodegenerative disorders. Although high levels of astrocyte-secreted glial fibrillar acidic protein (GFAP) in the CSF of patients with Alzheimer's disease (AD) have been reported, the levels of GFAP in the CSF have not been fully investigated in other neurological disorders that cause dementia, such as dementia with Lewy bodies (DLB) and frontotemporal lobar degeneration (FTLD). In this study, we determined the levels of GFAP in the CSF of healthy control subjects and AD, DLB, and FTLD patients to address two questions: (i) Do the levels of GFAP differ among these disorders? and (ii) Can GFAP be used as a biomarker for the differential diagnosis of these neurodegenerative disorders? The levels of GFAP in AD, DLB, and FTLD patients were significantly higher than those in the healthy control subjects. Although the levels of GFAP were not significantly different between AD and DLB patients, a higher level of GFAP was observed in FTLD patients than in AD and DLB patients. It is concluded that representative neurological disorders causing dementia were associated with higher levels of GFAP in the CSF. We propose the following mechanism concerning the amount of glial fibrillar acidic protein (GFAP) in the cerebrospinal fluid (CSF) in Alzheimer's disease (AD), dementia with Lewy bodies (DLB), and frontotemporal lobar degeneration (FTLD). The increase in the release of GFAP into CSF is considered to reflect the sum of degeneration of astrocytes and astrocytosis. The sum of degeneration and astrocytosis or the GFAP release could be in the order of FTLD > DLB > AD > normal condition.

Heterogeneous imaging characteristics of JC virus granule cell neuronopathy (GCN): a case series and review of the literature

Granule cell neuronopathy (GCN) is a rare JC virus (JCV)-related disease in immunocompromised patients, characterized by lytic infection of the cerebellar granule cell layer. To enable early diagnosis and intervention, we identify features of GCN and describe possible aspects of disease heterogeneity. We report on two new cases of GCN in HIV-infected patients of whom we retrospectively assessed clinical and radiologic data. In addition, we carried out a literature search and review of clinical, radiologic and histopathologic findings of all published GCN cases. Including the two new cases reported here, a total of 18 GCN cases were included in this study. HIV infection, present in 12 of the cases, was the most common underlying condition, followed by monoclonal antibody treatment which was present in three cases. Cerebellar atrophy was detected in all except two cases. In 12 patients a heterogeneous distribution pattern of white matter changes in the cerebellum and brainstem was observed. Imaging findings in GCN are remarkably heterogeneous; exhibiting cerebellar atrophy, as well as white matter pathology, particularly in the adjacent infratentorial white matter. This suggests an overlap of GCN with other JCV-related diseases, such as progressive multifocal leukoencephalopathy.

Interaction of transactive response DNA binding protein 43 with nuclear factor κB in mild cognitive impairment with episodic memory deficits

INTRODUCTION

Transactive response DNA binding protein 43 (TDP-43) is detected in pathological inclusions in many cases of Alzheimer's disease (AD) and mild cognitive impairment (MCI), but its pathological role in AD and MCI remains unknown. Recently, TDP-43 was reported to contribute to pathogenesis in amyotrophic lateral sclerosis through its interaction with p65 nuclear factor κB (NF-κB) resulting in abnormal hyperactivation of this signaling pathway in motor neurons. Hence, we investigated the interaction of TDP-43 with p65 in the temporal cortex of subjects with a clinical diagnosis of MCI (n = 12) or AD (n = 12) as well as of age-matched controls with no cognitive impairment (NCI, n = 12).

RESULTS

Immunoprecipitation and immunofluorescence approaches revealed a robust interaction of TDP-43 with p65 in the nucleus of temporal lobe neurons in four individuals with MCI (named MCI-p). These MCI-p cases exhibited high expression levels of soluble TDP-43, p65, phosphorylated p65 and low expression levels of β-amyloid 40 when compared to AD or NCI cases. The analysis of cognitive performance tests showed that MCI-p individuals presented intermediate deficits of global cognition and episodic memory between those of AD cases and of NCI cases and MCI cases with no interaction of TDP-43 with p65.

CONCLUSIONS

From these results, we propose that enhanced NF-κB activation due to TDP-43 and p65 interaction may contribute to neuronal dysfunction in MCI individuals with episodic memory deficits. Accordingly, treatment with inhibitors of NF-κB activation may be considered for MCI individuals with episodic memory deficits.

Progranulin promotes neurite outgrowth and neuronal differentiation by regulating GSK-3β

Progranulin (PGRN) has recently emerged as a key player in a subset of frontotemporal dementias (FTD). Numerous mutations in the progranulin gene have been identified in patients with familial or sporadic frontotemporal lobar degeneration (FTLD). In order to understand the molecular mechanisms by which PGRN deficiency leads to FTLD, we examined activity of PGRN in mouse cortical and hippocampal neurons and in human neuroblastoma SH-SY5Y cells. Treatment of mouse neurons with PGRN protein resulted in an increase in neurite outgrowth, supporting the role of PGRN as a neurotrophic factor. PGRN treatment stimulated phosphorylation of glycogen synthase kinase-3 beta (GSK-3β) in cultured neurons. Knockdown of PGRN in SH-SY5Y cells impaired retinoic acid induced differentiation and reduced the level of phosphorylated GSK-3β. PGRN knockdown cells were also more sensitized to staurosporine-induced apoptosis. These results reveal an important role of PGRN in neurite outgrowth and involvement of GSK-3β in mediating PGRN activity. Identification of GSK-3β activation as a downstream event for PGRN signaling provides a mechanistic explanation for PGRN activity in the nervous system. Our work also suggest that loss of axonal growth stimulation during neural injury repair or deficits in axonal repair may contribute to neuronal damage or axonal loss in FTLD associated with PGRN mutations. Finally, our study suggests that modulating GSK-3β or similar signaling events may provide therapeutic benefits for FTLD cases associated with PGRN mutations.

Review: Recent progress in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a highly familial condition and is increasingly being recognized as an important form of dementia. The literature published on this disease is often difficult to collate due to the wide range in nomenclature used. Thankfully, consensus recommendations have now been published to address this issue and hopefully the community will adopt these as intended. Much progress has been made in our understanding of the clinical, pathological and genetic understanding of FTLD in recent years. Progranulin and TDP-43 have recently been identified as new important proteins involved in the pathophysiology of FTLD and this latter protein may have potential as a biomarker of this disease. However, much remains before we have a full picture of the genes that cause FTLD and the biological pathways in which they function. The purpose of this review is to summarize the current concepts and recent advances in our knowledge of this disease.

Quantitative proton magnetic resonance spectroscopy detects abnormalities in dorsolateral prefrontal cortex and motor cortex of patients with frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a neurodegenerative disease of the frontal and temporal neocortex. The single most common pathology underlying FTLD is neuronal degeneration with ubiquitin-positive but tau-negative inclusions consisting of Tar DNA binding proteins (TDP-43). Inclusions containing TDP-43 in neurons are also the most common pathology underlying motor neuron disease (MND). The present study tested the hypothesis that abnormal metabolite patterns within the dorsolateral prefrontal cortex (DLPFC) as well as the motor cortex (MC) may be observed in FTLD patients without motor disorders, using proton magnetic resonance spectroscopy ((1)H MRS). Twenty-six FTLD patients with cognitive damage and ten controls underwent multivoxel (1)H MRS. Absolute concentrations of N-acetyl aspartate (NAA), creatine (Cr), choline (Cho) and myo-inositol (mI) were measured from the DLPFC, the MC and the parietal cortex (PC, an internal control). Statistical analyses were performed for group differences between FTLD patients and controls. Comparisons were also made across brain regions (PC and DLPFC; PC and MC) within FTLD patients. Significant reductions in NAA and Cr along with increased Cho and mI were observed in the DLPFC of FTLD patients compared to controls. Significantly lower NAA and higher Cho were also observed in the MCs of patients as compared to controls. Within the FTLD patients, both the MC and the DLPFC exhibited significantly decreased NAA and elevated Cho compared to the PC. However, only the DLPFC had significantly lower Cr and higher mI. Abnormal metabolite pattern from the MC supports the hypothesis that FTLD and MND may be closely linked.

Neuropathologic features of frontotemporal lobar degeneration with ubiquitin-positive inclusions visualized with ubiquitin-binding protein p62 immunohistochemistry

Genetic, clinical, and neuropathologic heterogeneity have been observed in frontotemporal lobar degeneration with ubiquitin (Ubq)-positive inclusions (FTLD-U) and FTLD-U with motor neuron disease. Here, the distribution and morphologic features of neuronal and glial inclusions in the brains of 20 FTLD-U and 2 FTLD-U/motor neuron disease cases were assessed using immunohistochemistry for Ubq-binding protein p62. Eighteen cases displayed TAR DNA-binding protein 43-immunoreactive lesions and were classified as Types 3 (neuronal cytoplasmic inclusions and neurites; 72%), 2 (primarily neuronal cytoplasmic inclusions; 17%), or 1 (primarily neurites; 11%) FTLD-U. The distribution of p62-immunoreactivity varied considerably in each type. Of 4 unclassifiable cases, 2 displayed p62-immunoreactive lesions suggestive of FTLD-U with a mutation in the charged multivesicular body protein 2B gene; 1 suggested basophilic inclusion body disease, and 1 was of a type not previously described. By immunohistochemistry for Ubq-binding protein p62, the distribution of abnormalities was wider than expected; in approximately half of the cases, there were p62-positive but TAR DNA-binding protein 43-negative inclusions in the cerebellum, a region not previously considered to be affected. In other regions, TAR DNA-binding protein 43-, Ubq-, and Ubq-binding protein p62 labeling of inclusions was variable. Whether variations in inclusion morphologies, immunoreactivity, and topographic distribution are due to methodologic factors, different stages of inclusion and disease evolution, different disease entities or biologic modifications of the same disease are presently unclear.

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.

Progranulin and frontotemporal lobar degeneration

Frontotemporal lobar degeneration is the term used to describe the non-Alzheimer clinical syndromes of frontotemporal dementia, semantic dementia and progressive non-fluent aphasia, regardless of the underlying neuropathological features. Considerable progress has been made in recent years in our understanding of the aetiology of this disorder, notably the identification of mutations in tau and progranulin genes, both on chromosome 17q21. Mutations in tau appear to affect the ability of tau to bind microtubules and/or increase this protein's ability to form fibrils. In contrast, progranulin mutations cause haploinsufficiency leading to TDP-43 accumulation. These genes collectively account for 10-20% of FTLD. However, it is clear that much remains to be discovered before our knowledge of this heterogeneous condition is complete.

The complex aetiology of frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is now a widely recognised form of dementia. This heterogeneous disease has been of particular interest to geneticists due to its high rate of heritability with up to 40% of patients reporting a family history of the disease in at least one extra family member. There have been several chromosome loci linked to this disorder and three genes have already been identified. Remarkably, it has been recently demonstrated that 2 of these are only 1.7 Mb from one another on chromosome 17q21, these being tau and progranulin. The identification of these genes has contributed greatly to our understanding of the differing neuropathologies associated with FTLD. Furthermore, the discovery that TDP-43 is a component of the neuronal inclusions seen in the most common neuropathological subtype has also helped expand the biochemical pathways that are the focus of much FTLD research. Nevertheless, other genes causing FTLD remain to be identified and their biology elucidated before we have a complete understanding of the complex aetiology of this disease.

Establishing a pathological diagnosis in degenerative dementias

While clinicopathological studies have confirmed that Alzheimer's disease (AD) is the most common neurodegenerative cause of dementia, these same studies have also revealed that other degenerative pathologies account for a significant proportion of patients with cognitive decline. Because pathological assessment of non-Alzheimer neurodegenerative diseases now demands routine use of a costly panel of immunohistochemical techniques a scheme for staged examination of brain tissue has been developed. This scheme is weighted to initially screen out cases of Alzheimer's disease, dementia with Lewy bodies and vascular dementia using conventional staining methods and established diagnostic protocols, bringing in immunochemical techniques to discriminate between non-Alzheimer degenerative dementias. Diagnosis of pathologies causing the clinical syndrome of frontotemporal dementia can be ascertained using conventional staining supplemented by immunochemical detection of ubiquitin, tau protein and alpha beta crystallin. The diagnosis of prion disease is reliably confirmed by immunohistochemical detection of prion protein. This morphological assessment complements emerging genetic insights into many of these neurodegenerative diseases.

Neural substrates of cognitive and behavioral deficits in atypical Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive cognitive decline that typically affects first memory and later executive functions, language, and visuospatial skills. This sequence of cognitive deterioration is thought to reflect the progressive invasion of the cerebral cortex by the two major pathological hallmarks of AD, neurofibrillary tangles (NFT) and senile plaques (SP), as well as degree of neuronal and synaptic loss. In atypical AD, prominent and early deficits are found in language, motor abilities, frontal and executive capacities, or visuospatial skills. These atypical clinical features are associated with an unusual pattern of NFT or SP formation that predominantly involves cortical areas usually spared in the course of the degenerative process. In an attempt to classify this highly heterogeneous subgroup, the present article provides an overview of clinicopathological analyses in patients with atypical progression of AD symptomatology with special reference to the relationship between specific cognitive and behavioral deficits and hierarchical patterns of AD lesion distribution within the cerebral cortex. On the basis of these representative examples of a cortical circuit-based approach to explore the mechanisms giving rise to AD neuropsychological expression, we also critically discuss the possibility to develop a matrix linking clinical presentations to degeneration of forward and backward long corticocortical pathways in this disorder.

Microglia and inflammation-mediated neurodegeneration: multiple triggers with a common mechanism

Inflammation, a common denominator among the diverse list of neurodegenerative diseases, has recently been implicated as a critical mechanism responsible for the progressive nature of neurodegeneration. Microglia are the resident innate immune cells in the central nervous system and produce a barrage of factors (IL-1, TNFalpha, NO, PGE2, superoxide) that are toxic to neurons. Evidence supports that the unregulated activation of microglia in response to environmental toxins, endogenous proteins, and neuronal death results in the production of toxic factors that propagate neuronal injury. In the following review, we discuss the common thread of microglial activation across numerous neurodegenerative diseases, define current perceptions of how microglia are damaging neurons, and explain how the microglial response to neuronal damage results in a self-propelling cycle of neuron death.

Regional and cellular pathology in frontotemporal dementia: relationship to stage of disease in cases with and without Pick bodies

Frontotemporal dementia (FTD) is a prevalent neurodegenerative disease of heterogeneous histopathology. Neuropathological subtypes are identified on the basis of the presence or absence of tau- or ubiquitin-positive neuronal inclusions. Our recent work has established four disease stages that are independent of neuropathological subtype and reflect the clinical and degenerative progression observed in FTD. The variability in the extent of neuronal loss, astrogliosis, and microvacuolation are, therefore, more likely to reflect disease stage with potentially predictable differences between cases at early versus late disease stages. Understanding the variability in these parameters may assist in determining the importance of diverse disease subtypes in FTD. We examined 21 cases of sporadic, behavioural variant FTD and quantified the progression of histopathological change. The neuropathology of early disease was marked by severe astrogliosis of both the frontal and temporal cortices and neuronal loss, which was more evident in upper cortical layers of the frontal lobe. In late disease, neuronal loss was evident from both layer III and V in frontal and temporal cortices, and particularly the CA1 sector of the hippocampus. In addition, we compared the neuropathology of Pick's disease, dementia lacking distinctive histopathology and FTD with motor neuron disease, and found no difference in these pathological subtypes on the basis of neuronal loss, astrogliosis or microvacuolation. These results show that the earliest cellular changes in FTD occur in glia, and that disease stage rather than FTD subtype determines the pattern and extent of neuronal degeneration.

Frontotemporal lobar degeneration and ubiquitin immunohistochemistry

We set out to determine the frequency of the different pathologies underlying frontotemporal degeneration (FTD) in our brain bank series, by reviewing all cases of pathologically diagnosed FTD over the last 12 years. We identified and reviewed 29 cases of FTD and classified them using the most recent consensus criteria with further histological analysis of 6 initially unclassifiable cases. Detailed histological analysis of these 6 cases revealed variable numbers of ubiquitin-positive (tau and alpha-synuclein-negative) inclusions in 5 cases, consistent with the diagnosis of frontotemporal lobar degeneration with ubiquitin-only-immunoreactive neuronal changes (FTLD-U). As a consequence of the current re-evaluation, 18 (62%) of the 29 cases with FTD have underlying pathology consistent with FTLD-U. Therefore in our brain bank series of frontotemporal degeneration, most cases were non-tauopathies with FTLD-U accounting for 62% of all the diagnoses.

Neurofilament inclusion body disease: a new proteinopathy?

We describe four cases of a new clinicopathological entity presenting with either a frontotemporal dementia or corticobasal degeneration syndrome with a mean age of onset of 45 years (range 41-50) characterized pathologically by deposition of neurofilament proteins. All four patients had a rapidly progressive course and have become mute and non-ambulatory, and three have died after mean illness duration of only 3 years (range 2 1/2 -4). Both structural (MRI) and functional (PET and SPECT) imaging demonstrated frontal and temporal lobe and basal ganglia involvement. Gross neuropathological examination in the three deceased patients (the fourth patient, still alive, was diagnosed by brain biopsy) revealed changes affecting predominantly the frontal and temporal cortices, basal ganglia and brainstem. There was superficial linear spongiosis affecting the frontal lobes in all three autopsied patients, and severe caudate atrophy was noted in two of them and demonstrated on MRI in the living patient. On routine staining, there were numerous intracytoplasmic inclusions, which ranged from eosinophilic to basophilic. Some had a clearly defined basophilic margin, while others were granular with a hyaline core. With modified Bielschowsky silver technique, a small number of the inclusions were intensely stained. Inclusions were not labelled with other silver stains. Immuno histochemistry revealed that the inclusions were immunoreactive with antibodies to neurofilament heavy and light chain subunits and to ubiquitin, but not with antibodies to tau and alpha-synuclein. These neurofilament- and ubiquitin-positive inclusions were widespread, specific to neurons and occasionally intranuclear. The frequency and distribution of the inclusions and the silver and immunohistochemical profiles in these four cases is novel and has not been described in detail before. We propose the term neurofilament inclusion body disease for this entity.

Predictors of mortality in frontotemporal dementia: a retrospective study of the prognostic influence of pre-diagnostic features

OBJECTIVES

To find associations between predictors and survival in frontotemporal dementia (FTD).

METHODS

96 patients with FTD, here defined as Dementia in Pick's disease, were studied. The predictors included psychiatric/behavioural features, language impairment and neurological deficits present up to the time of diagnosis. The influence on mortality was studied by means of Cox regression analyses.

RESULTS

Most of the behavioural/psychiatric features were associated with longer survival. Among these features, anxiety and suicidal ideation were associated with a statistically significant decreased mortality. Semi-mutism/mutism and neurological deficits were associated with a statistically significant increased mortality. Analyses of the dementia-specific mortality strengthened the already significant results and revealed dysphagia as significantly related to increased mortality.

CONCLUSIONS

Two groups of predictors with different influence on survival were identified in FTD. Most behavioural/psychiatric features were associated with longer survival. These features may indicate a slower disease progress and a better preserved cerebral function. By contrast, semi-mutism/mutism, neurological deficits and dysphagia were associated with shorter survival, indicating an aggressive, degenerative process.

Neuronal loss in familial frontotemporal dementia with ubiquitin-positive, tau-negative inclusions

The neuronal density in the frontal, temporal, and parietal lobes was determined in nine cases of familial frontotemporal dementia with ubiquitin-positive, tau-negative inclusions (FTDU). The mean age at onset was 56.9 +/- 2.2 years and the duration of disease was 6.7 +/- 0.5 years. The mean age at death was 63.6 +/- 2.2 years. There was substantial loss (34%) of brain weight (877 +/- 73 g) in the familial cases in comparison with 10 normal aged controls (1326 +/- 50 g, P < 0.001). All of the familial FTDU cases showed atrophy of the frontal, temporal, and parietal lobes; neuronal loss; vacuolation in superficial laminae; reactive astrocytosis; and ubiquitin-positive, tau-negative intracytoplasmic and intranuclear inclusions and dystrophic neurites in varying sites and numbers. Neuronal loss was estimated in nine cases of familial FTDU and in 10 aged controls using a stereological probe, the optical "disector," and a computerized stereology system (CAST-Grid, Olympus, Denmark). There was a significant reduction in neuronal density in the frontal lobe (22.3 +/- 3.8 x 10(3)/mm(3)) of familial FTDU in comparison to aged controls (33.1 +/- 1.7 x 10(3) per mm(3), P < 0.05). An estimate of the relative numbers of neurons was calculated by multiplying the numerical density by the cortical thickness, which showed a striking loss of neurons of 56% in the frontal lobe, 52% loss in the temporal lobe, and a 49% loss in the parietal lobe of familial FTDU when compared to controls. This study shows that familial FTDU has profound focal neuronal loss in multiple association areas that relate to the clinical symptoms characteristic of the disease.

Patients with a novel neurofilamentopathy: dementia with neurofilament inclusions

We report a new disease, dementia with neurofilament inclusions, characterized clinically by early-onset dementia with frontal lobe signs, focal atrophy of the frontal and temporal lobes, and microscopically by the presence in many brain regions of intraneuronal, cytoplasmic, neurofilament inclusions. The neuronal inclusions are immunoreactive to all three molecular weight neurofilament subunits: heavy (NF-H), light, and medium subunits, including the phosphorylated and non-phosphorylated forms of NF-H. Prion protein and beta-amyloid deposits were absent. The inclusions do not contain tau or alpha-synuclein protein aggregates known to characterize many neurodegenerative disorders. In addition to delineating a new disease entity, the identification of intraneuronal, cytoplasmic, neurofilament inclusions extends the molecular classification of neurodegenerative diseases and implicates new mechanisms of neurodegeneration in diseases affecting the human brain.

The binding of 2-(4'-methylaminophenyl)benzothiazole to postmortem brain homogenates is dominated by the amyloid component

2-(4'-methylaminophenyl)benzothiazole (BTA-1) is an uncharged derivative of thioflavin-T that has high affinity for Abeta fibrils and shows very good brain entry and clearance. In this study, we asked whether BTA-1, at concentrations typical of those achieved during positron emission tomography (PET) studies, could specifically bind to amyloid deposits in the complex milieu of human brain or whether amyloid binding was overshadowed by nonspecific binding, found even in brains that did not contain amyloid deposits. We quantitatively assessed [3H]BTA-1 binding to crude homogenates of postmortem brain obtained from nine Alzheimer's disease (AD) subjects, eight controls, and six subjects with non-AD dementia. BTA-1 binding was >10-fold higher in AD brain, and the majority (94%) of the binding was specific (displaceable). High-affinity [3H]BTA-1 was observed only in AD brain gray matter and was not present in control brain gray matter, AD brain white matter, or cerebellum. The K(d) of [3H]BTA-1 for binding to AD brain (5.8 +/- 0.90 nm) was very similar to the K(d) for binding to synthetic Abeta fibrils. In addition, the K(i) of various BTA analogs for inhibition of [3H]BTA-1 binding to AD brain homogenates was very similar to their K(i) for inhibition of [3H]BTA-1 binding to synthetic Abeta fibrils. Nanomolar concentrations of [3H]BTA-1 did not appear to bind to neurofibrillary tangles. Finally, BTA-1 did not appear to bind significantly to common neuroreceptors or transporter sites. These data suggest that the binding of BTA-1 to AD brain is dominated by a specific interaction with Abeta amyloid deposits.

The binding of 2-(4'-methylaminophenyl)benzothiazole to postmortem brain homogenates is dominated by the amyloid component

2-(4'-methylaminophenyl)benzothiazole (BTA-1) is an uncharged derivative of thioflavin-T that has high affinity for Abeta fibrils and shows very good brain entry and clearance. In this study, we asked whether BTA-1, at concentrations typical of those achieved during positron emission tomography (PET) studies, could specifically bind to amyloid deposits in the complex milieu of human brain or whether amyloid binding was overshadowed by nonspecific binding, found even in brains that did not contain amyloid deposits. We quantitatively assessed [3H]BTA-1 binding to crude homogenates of postmortem brain obtained from nine Alzheimer's disease (AD) subjects, eight controls, and six subjects with non-AD dementia. BTA-1 binding was >10-fold higher in AD brain, and the majority (94%) of the binding was specific (displaceable). High-affinity [3H]BTA-1 was observed only in AD brain gray matter and was not present in control brain gray matter, AD brain white matter, or cerebellum. The K(d) of [3H]BTA-1 for binding to AD brain (5.8 +/- 0.90 nm) was very similar to the K(d) for binding to synthetic Abeta fibrils. In addition, the K(i) of various BTA analogs for inhibition of [3H]BTA-1 binding to AD brain homogenates was very similar to their K(i) for inhibition of [3H]BTA-1 binding to synthetic Abeta fibrils. Nanomolar concentrations of [3H]BTA-1 did not appear to bind to neurofibrillary tangles. Finally, BTA-1 did not appear to bind significantly to common neuroreceptors or transporter sites. These data suggest that the binding of BTA-1 to AD brain is dominated by a specific interaction with Abeta amyloid deposits.

Sporadic amyotrophic lateral sclerosis with circumscribed temporal atrophy: a report of an autopsy case without dementia and with ubiquitinated intraneuronal inclusions

This report concerns an autopsy case of amyotrophic lateral sclerosis (ALS) with circumscribed temporal atrophy. The patient was a Japanese woman without hereditary burden who was 71-year-old at the time of death. She developed dysarthria and gait disturbance at age 69, followed by dysphagia. A neurological examination about 1 year 11 months after the onset of the disease revealed absence of character change and of dementia. Neuroradiological examination disclosed circumscribed atrophy of the anterior part of the right temporal lobe. The patient died of respiratory failure 2 years after the disease onset. No respirator administration was performed throughout the clinical course. Macroscopically, neuropathological examination showed circumscribed atrophy of the right first temporal gyrus. Histologically, there was neuronal loss in the cerebral cortex, including the first temporal gyrus, the parahippocampal gyrus, subiculum, amygdala, substantia nigra, brain stem motor nuclei, and anterior horns of the spinal cord, in addition to loss of Betz cells, obvious degeneration of the pyramidal tracts, and the presence of Bunina bodies. Ubiquitin-immunoreactive intraneuronal inclusions were present in the hippocampal dentate granular cells, frontotemporal cortical layer II neurons, and motor neurons in the brain stem and spinal cord. Based on these clinicopathological findings and a review of the literature, we concluded that our case was atypical ALS without dementia, showing temporal lobe atrophy macroscopically, in addition to pathological hallmarks compatible with ALS with dementia. We also note the possibility that there is a forme fruste of ALS with dementia showing no overt dementia clinically.

Excitotoxic neurodegeneration induced by intranasal administration of kainic acid in C57BL/6 mice

Glutamate excitotoxicity plays a key role in inducing neuronal cell death in many neurological diseases. In mice, administration of kainic acid, an analogue of the excitotoxin glutamate, results in hippocampal cell death and seizures. Kainic-acid-induced seizures in mice provide a well-characterized model for studies of human neurodegenerative diseases. However, C57BL/6 mice, which are often used for genetic analyses and transgenic and knockout studies, are resistant to excitotoxicity induced by subcutaneous administration of kainic acid. In the present study, kainic acid administered by the intranasal route was shown to result in continuous tonic-clonic seizures in C57BL/6 mice. These seizures continued for 1-5 h and successfully induced selective lesions in area CA3 of the hippocampus. The survival rate was high even after mice experienced severe seizures. The hippocampal lesions were associated with a high level of cyclooxygenase-2 production as well as astrogliosis. Administration of kainic acid also altered behavioral responses, with mice showing a significant increase in locomotion and rearing activity as indicated by an open-field test. This animal model could provide a valuable tool for exploring the role of excitotoxicity in neuropathological conditions and should be further evaluated in gene-targeting studies of neurodegenerative diseases.

Ubiquitin and the molecular pathology of neurodegenerative diseases

Ubiquitin plays a central role in normal cellular function as well as in disease. It is possible to group ubiquitin-immunostained structures into several main groups, the most distinctive being the ubiquitin/intermediate filament/alphaB crystallin family of inclusions that seem to represent a general cellular response to abnormal proteins recently termed the aggresomal response. While ubiquitin immunohistochemistry is a very useful technique for detecting pathological changes and inclusion bodies in the nervous system this alone is not enough to classify inclusions, and a panel of antibodies is recommended to clarify any findings made by screening tissues with anti-ubiquitin. Several mechanistic possibilities now exist to explain the accumulation of ubiquitinated proteins in cells of the nervous system, understanding of which should lead to new therapeutic advances in the group of chronic neurodegenerative diseases.

Neurodegenerative tauopathies

The defining neuropathological characteristics of Alzheimer's disease are abundant filamentous tau lesions and deposits of fibrillar amyloid beta peptides. Prominent filamentous tau inclusions and brain degeneration in the absence of beta-amyloid deposits are also hallmarks of neurodegenerative tauopathies exemplified by sporadic corticobasal degeneration, progressive supranuclear palsy, and Pick's disease, as well as by hereditary frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). Because multiple tau gene mutations are pathogenic for FTDP-17 and tau polymorphisms appear to be genetic risk factors for sporadic progressive supranuclear palsy and corticobasal degeneration, tau abnormalities are linked directly to the etiology and pathogenesis of neurodegenerative disease. Indeed, emerging data support the hypothesis that different tau gene mutations are pathogenic because they impair tau functions, promote tau fibrillization, or perturb tau gene splicing, thereby leading to formation of biochemically and structurally distinct aggregates of tau. Nonetheless, different members of the same kindred often exhibit diverse FTDP-17 syndromes, which suggests that additional genetic or epigenetic factors influence the phenotypic manifestations of neurodegenerative tauopathies. Although these and other hypothetical mechanisms of neurodegenerative tauopathies remain to be tested and validated, transgenic models are increasingly available for this purpose, and they will accelerate discovery of more effective therapies for neurodegenerative tauopathies and related disorders, including Alzheimer's disease.

Frontal lobe dementia with abnormal cholesterol metabolism and heterozygous mutation in sterol 27-hydroxylase gene (CYP27)

Of the primary dementing disorders that cause frontotemporal dementia, the best-known is Pick disease. We report on a 44-year-old woman with progressive frontal lobe dementia and spastic paraplegia. Examination revealed increased serum levels of cholestanol with abnormal cholesterol metabolism and a heterozygous mutation of the sterol 27-hydroxylase gene (CYP27). Biochemical findings were compatible with cerebrotendinous xanthomatosis (CTX); however, the clinical manifestations were very dissimilar. To our knowledge, a symptomatic carrier of this mutation among CTX patients has not been reported. We speculate that the present patient has a previously undescribed neurodegenerative disease related to abnormal cholesterol metabolism with this heterozygous mutation.

Amyloid beta protein deposition in patients with frontotemporal lobar degeneration: relationship to age and apolipoprotein E genotype

Amyloid beta protein (Abeta) deposition was investigated in the frontal cortex of 54 autopsy cases of frontotemporal lobar degeneration (FTLD) using methenamine silver staining, and immunohistochemistry employing the monoclonal end-specific antibodies BC05 and BA27 to visualize deposits containing Abeta(42(43)) and Abeta(40), respectively. Abeta was detected in 14 (26%) patients, nearly always in the form of diffuse Abeta(42(43)) containing plaques though some cored, neuritic plaques with trace amounts of Abeta(40) were occasionally seen. The 14 patients showing Abeta deposits were significantly older at onset of illness than those 40 patients without Abeta. It was only possible to genotype 46/54 cases, 16 of whom bore at least one copy of the Apolipoprotein E (APOE) epsilon4 allele, giving an allele frequency of 20%. Possession of APOE epsilon4 allele was significantly associated with deposition of Abeta such that 10/16 epsilon4 allele bearers had Abeta deposits. Eight of these ten patients showed only mild to moderate amounts of Abeta, but in two patients, one homozygous and one heterozygous for epsilon4 allele, there was extensive neuritic plaque and neurofibrillary tangle formation. In contrast, only few non-epsilon4 allele bearers (4/30) showed minor Abeta deposits. When stratifying for APOE epsilon4 allele, both bearers and non-bearers of epsilon4 allele with Abeta deposits had a significantly later age at onset than their respective groups without Abeta deposits. We conclude that the likelihood of Abeta deposition, as a secondary and coincidental feature unrelated to the primary pathological process, within the brains of individuals with FTLD will be high if patients have a sufficiently late onset of illness or happen to be a bearer of the APOE epsilon4 allele. Indeed 9/14 patients with Abeta deposits studied here had an onset of illness after 55 years of age and bore APOE epsilon4 allele.

Astrocytes degenerate in frontotemporal dementia: possible relation to hypoperfusion

To understand the extent and specificity of astrocyte pathology in sporadic frontotemporal dementia (FTD), we examined several FTD cases for molecular and morphologic characteristics of astrocyte degeneration. We quantified reactive and degenerating astrocytes in sections of frontal, temporal, parietal, and occipital cortex identified using glial fibrillary acidic protein (GFAP) immunoreactivity, terminal deoxynucleotidyl transferase (TdT) labeling, and morphological characteristics and compared them with nondemented, age-matched control brains. Conventional and confocal microscopy revealed that a subpopulation of GFAP(+) astrocytes exhibited positive TdT labeling and beading of their processes in the frontal, temporal, and parietal cortices in 5 of 7 FTD cases that also exhibited gliosis. This morphology was reproduced in cultured astrocytes using ischemic insults. Degenerating astrocytes in FTD correlated inversely with cerebral blood flow as measured by single photon emission computed tomography (SPECT) analysis of (133)Xe inhalation (r = 0.55, p < 0.05). Furthermore, areas of significant astrogliosis corresponded to areas of SPECT hypoperfusion, suggesting that astrocytes may be affected by or perhaps have a causal role in the disturbances of cerebral perfusion in FTD.

Selective impairment of verb processing associated with pathological changes in Brodmann areas 44 and 45 in the motor neurone disease-dementia-aphasia syndrome

We report six patients with clinically diagnosed and electrophysiologically confirmed motor neurone disease (MND), in whom communication problems were an early and dominant feature. All patients developed a progressive non-fluent aphasia culminating in some cases in complete mutism. In five cases, formal testing revealed deficits in syntactic comprehension. Comprehension and production of verbs were consistently more affected those that of nouns and this effect remained stable upon subsequent testing, despite overall deterioration. The classical signs of MND, including wasting, fasciculations and severe bulbar symptoms, occurred over the following 6-12 months. The behavioural symptoms ranged from mild anosognosia to personality change implicating frontal-lobe dementia. In three cases, post-mortem examination has confirmed the clinical diagnosis of MND-dementia. In addition to the typical involvement of motor and premotor cortex, particularly pronounced pathological changes were observed in the Brodmann areas 44 (Broca's area) and 45. The finding of a selective impairment of verb/action processing in association with the dementia/aphasia syndrome of MND suggests that the neural substrate underlying verb representation is strongly connected to anterior cortical motor systems.

New insights into genetic and molecular mechanisms of brain degeneration in tauopathies

Abundant neurofibrillary lesions consisting of the microtubule associated protein tau and amyloid beta peptide deposits are the defining lesions of Alzheimer's disease. Prominent filamentous tau pathology and brain degeneration in the absence of extracellular amyloid deposition characterize a number of other neurodegenerative disorders (i.e. progressive supranuclear palsy, corticobasal degeneration, Pick's disease) collectively referred to as tauopathies. The discovery of multiple tau gene mutations that are pathogenic for hereditary frontotemporal dementia and parkinsonism linked to chromosome 17 in many kindreds, as well as the demonstration that tau polymorphisms are genetic risk factors for sporadic tauopathies, directly implicate tau abnormalities in the onset/progression of neurodegenerative disease. Different tau gene mutations may be pathogenic by impairing the functions of tau or by perturbing the splicing of the tau gene, thereby resulting in biochemically and structurally distinct tau aggregates. However, since specific polymorphisms and mutations in the tau gene lead to diverse phenotypes, it is plausible that additional genetic or epigenetic factors influence the clinical and pathological manifestations of both familial and sporadic tauopathies. Thus, efforts to develop animal models of tau-mediated neurodegeneration should provide further insights into the onset and progression of tauopathies as well as Alzheimer's disease, and they could accelerate research to discover more effective therapies for these disorders.

The nosology of dementia

The nosology of dementia has evolved from the simple distinctions between senility, degenerative dementia, and vascular insults that existed a few decades ago. The differentiation of normal cognitive aging from very mild dementia has sharpened considerably; however, appreciation of the heterogeneity of Alzheimer's disease (AD) and its clinical and pathologic overlap with other dementing disorders has blurred previous classification systems. Rather than viewing AD and vascular dementia, for example, as dichotomous entities, it may be more relevant to consider their additive or synergistic interactions producing dementia. Further elucidation of the nature and contribution of genetic factors in AD and related disorders will accelerate the use of genotype-phenotype correlations in dementia classification.

Volumetric study of lobar atrophy in Pick complex and Alzheimer's disease

BACKGROUND

Lobar atrophy is an important neuroimaging feature of Pick complex (PiC). However, differences in patterns of focal brain atrophy between PiC and Alzheimer's disease (AD), and among PiC subgroups, have not been studied quantitatively.

OBJECTIVE

To compare volumetric measures among primary progressive aphasia (PPA), frontotemporal dementia (FTD) and AD; to assess association between brain atrophy and cognition.

PATIENTS

Seventeen patients with PPA, 11 with FTD and 24 with probable AD were studied.

METHODS

We measured total and regional volume quantitatively using MRI and computerized volumetry. Contributing factors were controlled statistically or by adopting brain volume ratios. We investigated the classifying power of volumetry and correlated regional brain volume with cognitive and language test scores.

RESULTS

The ratio for fronto-temporo-central region was smaller on the left in PPA and on the right in FTD. AD and some PPA patients had smaller parietal lobes. The frontal ratios correctly classified 93% of PPA and FTD patients, but only 50% of the entire PiC and AD patients. Language-dependent examinations correlated with the left fronto-temporal volume.

CONCLUSIONS

Brain atrophy differs in PPA, FTD and AD, but there is some morphological overlap between PiC and AD in parietal volumes. Focal brain atrophy is most consistently associated with language impairments.

Brain-derived neurotrophic factor in patients with frontotemporal dementia

Brain-derived neurotrophic factor (BDNF) promotes survival and growth of various nerve cell populations during normal development and following different insults in the developing and adult brain. BDNF expression is reduced in Alzheimer disease, but little is known about BDNF expression in other types of dementia. Frontotemporal dementia (FTD) is a common cause of mental impairment in old age, which is characterized by neuron loss in the upper cortical layers mainly of the frontal and temporal cortex. BDNF protein expression has been examined by Western blotting and immunohistochemistry in the cerebral cortex of individuals affected by FTD. Examination of pathological samples (n = 8, mean age: 74.7 years; four men, four women) was conducted in parallel with corresponding samples from age-matched controls (n = 8; mean age: 72.6 years; three men, five women). Post-mortem delay was between 2 and 6 h. Preserved BDNF expression, as revealed by Western blotting, has been observed in the frontal and temporal cortices of patients with FTD. Furthermore, immunohistochemistry has disclosed maintained BDNF immunoreactivity in surviving neurons of the upper cellular layers, as well as in neurons of the inner cellular layers in FTD. These results show that FTD is not associated with a decay of BDNF in cortical neurons, and therefore, that BDNF is differentially regulated in diseases causing dementia.

Specific cognitive deficits in mild frontal variant frontotemporal dementia

Eight patients with relatively mild frontal variant frontotemporal dementia (fvFTD) were compared with age- and IQ-matched control volunteers on tests of executive and mnemonic function. Tests of pattern and spatial recognition memory, spatial span, spatial working memory, planning, visual discrimination learning/attentional set-shifting and decision-making were employed. Patients with fvFTD were found to have deficits in the visual discrimination learning paradigm specific to the reversal stages. Furthermore, in the decision-making paradigm, patients were found to show genuine risk-taking behaviour with increased deliberation times rather than merely impulsive behaviour. It was especially notable that these patients demonstrated virtually no deficits in other tests that have also been shown to be sensitive to frontal lobe dysfunction, such as the spatial working memory and planning tasks. These results are discussed in relation to the possible underlying neuropathology, the anatomical connectivity and the hypothesized heterogeneous functions of areas of the prefrontal cortex. In particular, given the nature of the cognitive deficits demonstrated by these patients, we postulate that, relatively early in the course of the disease, the ventromedial (or orbitofrontal) cortex is a major locus of dysfunction and that this may relate to the behavioural presentation of these patients clinically described in the individual case histories.