From genetics to pathology: tau and alpha-synuclein assemblies in neurodegenerative diseases

An updated review on animal models to study attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a neuropsychiatric disorder affecting both children and adolescents. Individuals with ADHD experience heterogeneous problems, such as difficulty in attention, behavioral hyperactivity, and impulsivity. Recent studies have shown that complex genetic factors play a role in attention-deficit hyperactivity disorders. Animal models with clear hereditary traits are crucial for studying the molecular, biological, and brain circuit mechanisms underlying ADHD. Owing to their well-managed genetic origins and the relative simplicity with which the function of neuronal circuits is clearly established, models of mice can help learn the mechanisms involved in ADHD. Therefore, in this review, we highlighting the important genetic animal models that can be used to study ADHD.

Extracellular Vesicle-Based Therapeutics in Neurological Disorders

Neurological diseases remain some of the major causes of death and disability in the world. Few types of drugs and insufficient delivery across the blood-brain barrier limit the treatment of neurological disorders. The past two decades have seen the rapid development of extracellular vesicle-based therapeutics in many fields. As the physiological and pathophysiological roles of extracellular vesicles are recognized in neurological diseases, they have become promising therapeutics and targets for therapeutic interventions. Moreover, advanced nanomedicine technologies have explored the potential of extracellular vesicles as drug delivery systems in neurological diseases. In this review, we discussed the preclinical strategies for extracellular vesicle-based therapeutics in neurological disorders and the struggles involved in their clinical application.

α-synuclein abnormalities trigger focal tau pathology, spreading to various brain areas in Parkinson disease

Parkinson disease (PD) is the second most common neurodegenerative disorder, whose prevalence is 2~3% in the population over 65. α-Synuclein aggregation is the major pathological hallmark of PD. However, recent studies have demonstrated enhancing evidence of tau pathology in PD. Despite extensive considerations, thus far, the actual spreading mechanism of neurodegeneration has remained elusive in a PD brain. This study aimed to further investigate the development of α-synuclein and tau pathology. We employed various PD models, including cultured neurons treated with either 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or with recombinant α-synuclein. Also, we studied dopaminergic neurons of cytokine Interferon-β knock-out. Moreover, we examined rats treated with 6-hydroxydopamine, Rhesus monkeys administrated with MPTP neurotoxin, and finally, human post-mortem brains. We found the α-synuclein phosphorylation triggers tau pathogenicity. Also, we observed more widespread phosphorylated tau than α-synuclein with prion-like nature in various brain areas. We optionally removed P-tau or P-α-synuclein from cytokine interferon-β knock out with respective monoclonal antibodies. We found that tau immunotherapy suppressed neurodegeneration more than α-synuclein elimination. Our findings indicate that the pathogenic tau could be one of the leading causes of comprehensive neurodegeneration triggered by PD. Thus, we can propose an efficient therapeutic target to fight the devastating disorder.

Fragmentation of the Golgi complex of dopaminergic neurons in human substantia nigra: New cytopathological findings in Parkinson's disease

Fragmentation of the Golgi ribbon is a common feature of Parkinson´s disease and other neurodegenerative diseases. This alteration could be the consequence of the anterograde and retrograde transport imbalance, α-synuclein aggregates, and/or cytoskeleton alterations. Most information on this process has been obtained from cellular and animal experimental models, and as such, there is little information available on human tissue. If the information on human tissue was available, it may help to understand the cytopathological mechanisms of this disease. In the present study, we analyzed the morphological characteristics of the Golgi complex of dopaminergic neurons in human samples of substantia nigra of control and Parkinson's disease patients. We measured the expression levels of putative molecules involved in Golgi fragmentation, including α-synuclein, tubulin, and Golgi-associated regulatory and structural proteins. We show that, as a consequence of the disease, the Golgi complex is fragmented into small stacks without vesiculation. We found that only a limited number of regulatory proteins are altered. Rab1, a small GTPase regulating endoplasmic reticulum-to-Golgi transport, is the most dramatically affected, being highly overexpressed in the surviving neurons. We found that the SNARE protein syntaxin 5 forms extracellular aggregates resembling the amyloid plaques characteristic of Alzheimer's disease. These findings may help to understand the cytopathology of Parkinson's disease.

α-Synuclein conformational strains spread, seed and target neuronal cells differentially after injection into the olfactory bulb

Alpha-synuclein inclusions, the hallmarks of synucleinopathies, are suggested to spread along neuronal connections in a stereotypical pattern in the brains of patients. Ample evidence now supports that pathological forms of alpha-synuclein propagate in cell culture models and in vivo in a prion-like manner. However, it is still not known why the same pathological protein targets different cell populations, propagates with different kinetics and leads to a variety of diseases (synucleinopathies) with distinct clinical features. The aggregation of the protein alpha-synuclein yields different conformational polymorphs called strains. These strains exhibit distinct biochemical, physical and structural features they are able to imprint to newly recruited alpha-synuclein. This had led to the view that the clinical heterogeneity observed in synucleinopathies might be due to distinct pathological alpha-synuclein strains.To investigate the pathological effects of alpha-synuclein strains in vivo, we injected five different pure strains we generated de novo (fibrils, ribbons, fibrils-65, fibrils-91, fibrils-110) into the olfactory bulb of wild-type female mice. We demonstrate that they seed and propagate pathology throughout the olfactory network within the brain to different extents. We show strain-dependent inclusions formation in neurites or cell bodies. We detect thioflavin S-positive inclusions indicating the presence of mature amyloid aggregates.In conclusion, alpha-synuclein strains seed the aggregation of their cellular counterparts to different extents and spread differentially within the central nervous system yielding distinct propagation patterns. We provide here the proof-of-concept that the conformation adopted by alpha-synuclein assemblies determines their ability to amplify and propagate in the brain in vivo. Our observations support the view that alpha-synuclein polymorphs may underlie different propagation patterns within human brains.

Sorting out release, uptake and processing of alpha-synuclein during prion-like spread of pathology

Parkinson's disease is a progressive neurological disorder that is characterized by the formation of intracellular protein inclusion bodies composed primarily of a misfolded and aggregated form of the protein α-synuclein. There is growing evidence that supports the prion-like hypothesis of α-synuclein progression. This hypothesis postulates that α-synuclein is a prion-like pathological agent and is responsible for the progression of Parkinson pathology in the brain. Potential misfolding or aggregation of α-synuclein that might occur in the peripheral nervous system as a result of some insult, environmental or genetic (or more likely a combination of both) that might spread into the midbrain, eventually causing degeneration of the neurons in the substantia nigra. As the disease progresses further, it is likely that α-synuclein pathology continues to spread throughout the brain, including the cortex, leading to deterioration of cognition and higher brain functions. While it is unknown why α-synuclein initially misfolds and aggregates, a great deal has been learned about how the cell handles aberrant α-synuclein assemblies. In this review, we focus on these mechanisms and discuss them in an attempt to define the role that they might play in the propagation of misfolded α-synuclein from cell-to-cell. The prion-like hypothesis of α-synuclein pathology suggests a method for the transmission of misfolded α-synuclein from one neuron to another. This hypothesis postulates that misfolded α-synuclein becomes aggregation prone and when released and taken up by neighboring cells, seeds further misfolding and aggregation. In this review we examine the cellular mechanisms that are involved in the processing of α-synuclein and how these may contribute to the prion-like propagation of α-synuclein pathology. This article is part of a special issue on Parkinson disease.

How neuroinflammation contributes to neurodegeneration

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and frontotemporal lobar dementia are among the most pressing problems of developed societies with aging populations. Neurons carry out essential functions such as signal transmission and network integration in the central nervous system and are the main targets of neurodegenerative disease. In this Review, I address how the neuron's environment also contributes to neurodegeneration. Maintaining an optimal milieu for neuronal function rests with supportive cells termed glia and the blood-brain barrier. Accumulating evidence suggests that neurodegeneration occurs in part because the environment is affected during disease in a cascade of processes collectively termed neuroinflammation. These observations indicate that therapies targeting glial cells might provide benefit for those afflicted by neurodegenerative disorders.

Telomere shortening leads to an acceleration of synucleinopathy and impaired microglia response in a genetic mouse model

Parkinson’s disease is one of the most common neurodegenerative disorders of the elderly and ageing hence described to be a major risk factor. Telomere shortening as a result of the inability to fully replicate the ends of linear chromosomes is one of the hallmarks of ageing. The role of telomere dysfunction in neurological diseases and the ageing brain is not clarified and there is an ongoing discussion whether telomere shortening is linked to Parkinson’s disease. Here we studied a mouse model of Parkinson’s disease (Thy-1 [A30P] α-synuclein transgenic mouse model) in the background of telomere shortening (Terc knockout mouse model). α-synuclein transgenic mice with short telomeres (αSYN^tg/tg G3Terc^-/-) developed an accelerated disease with significantly decreased survival. This accelerated phenotype of mice with short telomeres was characterized by a declined motor performance and an increased formation of α-synuclein aggregates. Immunohistochemical analysis and mRNA expression studies revealed that the disease end-stage brain stem microglia showed an impaired response in αSYN^tg/tg G3Terc^-/- microglia animals. These results provide the first experimental data that telomere shortening accelerates α-synuclein pathology that is linked to limited microglia function in the brainstem.

The interrelationship of proteasome impairment and oligomeric intermediates in neurodegeneration

Various neurodegenerative diseases are characterized by the accumulation of amyloidogenic proteins such as tau, α-synuclein, and amyloid-β. Prior to the formation of these stable aggregates, intermediate species of the respective proteins-oligomers-appear. Recently acquired data have shown that oligomers may be the most toxic and pathologically significant to neurodegenerative diseases such as Alzheimer's and Parkinson's. The covalent modification of these oligomers may be critically important for biological processes in disease. Ubiquitin and small ubiquitin-like modifiers are the commonly used tags for degradation. While the modification of large amyloid aggregates by ubiquitination is well established, very little is known about the role ubiquitin may play in oligomer processing and the importance of the more recently discovered sumoylation. Many proteins involved in neurodegeneration have been found to be sumoylated, notably tau protein in brains afflicted with Alzheimer's. This evidence suggests that while the cell may not have difficulty recognizing dangerous proteins, in brains afflicted with neurodegenerative disease, the proteasome may be unable to properly digest the tagged proteins. This would allow toxic aggregates to develop, leading to even more proteasome impairment in a snowball effect that could explain the exponential progression in most neurodegenerative diseases. A better understanding of the covalent modifications of oligomers could have a huge impact on the development of therapeutics for neurodegenerative diseases. This review will focus on the proteolysis of tau and other amyloidogenic proteins induced by covalent modification, and recent findings suggesting a relationship between tau oligomers and sumoylation.

Different molecular pathologies result in similar spatial patterns of cellular inclusions in neurodegenerative disease: a comparative study of eight disorders

Recent research suggests cell-to-cell transfer of pathogenic proteins such as tau and α-synuclein may play a role in neurodegeneration. Pathogenic spread along neural pathways may give rise to specific spatial patterns of the neuronal cytoplasmic inclusions (NCI) characteristic of these disorders. Hence, the spatial patterns of NCI were compared in four tauopathies, viz., Alzheimer's disease, Pick's disease, corticobasal degeneration, and progressive supranuclear palsy, two synucleinopathies, viz., dementia with Lewy bodies and multiple system atrophy, the 'fused in sarcoma' (FUS)-immunoreactive inclusions in neuronal intermediate filament inclusion disease, and the transactive response DNA-binding protein (TDP-43)-immunoreactive inclusions in frontotemporal lobar degeneration, a TDP-43 proteinopathy (FTLD-TDP). Regardless of molecular group or morphology, NCI were most frequently aggregated into clusters, the clusters being regularly distributed parallel to the pia mater. In a significant proportion of regions, the regularly distributed clusters were in the size range 400-800 μm, approximating to the dimension of cell columns associated with the cortico-cortical pathways. The data suggest that cortical NCI in different disorders exhibit a similar spatial pattern in the cortex consistent with pathogenic spread along anatomical pathways. Hence, treatments designed to protect the cortex from neurodegeneration may be applicable across several different disorders.

Neuromelanin enhances the toxicity of α-synuclein in SK-N-SH cells

The key pathological feature of Parkinson's disease (PD) is selective degeneration of the neuromelanin (NM)-pigmented dopaminergic neurons in the substantia nigra (SN). NM, like other risk factors, such as oxidative stress (OS) and α-synuclein (α-syn), is involved in the pathogenesis of PD. But whether or not NM synergizes with α-syn or OS in the pathogenesis of PD remains unexplored. In the present study, we examined the effects of NM on cellular viability, apoptosis and free radical production in α-syn over-expressing human neuroblastoma cell line (SK-N-SH) in the presence or absence of the oxidizer Fenton's Reagent (FR). We showed that NM synergized with FR in suppressing cell viability, and in inducing apoptosis and hydroxyl radical production in all SK-N-SH cell lines. α-Syn over-expressing cells exhibited more pronounced effect, especially the A53T mutation. Our findings suggest that NM synergizes with both OS and α-syn in conferring dopaminergic vulnerability, adding to our understanding of the pathogenesis of PD.

Spatial patterns of TDP-43 neuronal cytoplasmic inclusions (NCI) in fifteen cases of frontotemporal lobar degeneration with TDP-43 proteinopathy (FTLD-TDP)

Neuronal cytoplasmic inclusions (NCI) immunoreactive for transactive response DNA-binding protein (TDP-43) are the pathological hallmark of frontotemporal lobar degeneration with TDP-43 proteinopathy (FTLD-TDP). We studied the spatial patterns of the TDP-43 immunoreactive NCI in the frontal and temporal cortex of 15 cases of FTLD-TDP. The NCI were distributed parallel to the tissue boundary predominantly in regular clusters 50-400 μm in diameter. In five cortical areas, the size of the clusters approximated to the cells of the cortico-cortical pathways. In most regions, cluster size was smaller than 400 μm. There were no significant differences in spatial patterns between familial and sporadic cases. Cluster size of the NCI was not correlated with disease duration, brain weight, Braak stage, or disease subtype. The spatial pattern of the NCI was similar to that of neuronal inclusions in other neurodegenerative diseases and may reflect a common pattern of degeneration involving the cortico-cortical projections.

Conserved core of amyloid fibrils of wild type and A30P mutant α-synuclein

The major component of neural inclusions that are the pathological hallmark of Parkinson's disease are amyloid fibrils of the protein α-synuclein (aS). Here we investigated if the disease-related mutation A30P not only modulates the kinetics of aS aggregation, but also alters the structure of amyloid fibrils. To this end we optimized the method of quenched hydrogen/deuterium exchange coupled to NMR spectroscopy and performed two-dimensional proton-detected high-resolution magic angle spinning experiments. The combined data indicate that the A30P mutation does not cause changes in the number, location and overall arrangement of β-strands in amyloid fibrils of aS. At the same time, several residues within the fibrillar core retain nano-second dynamics. We conclude that the increased pathogenicity related to the familial A30P mutation is unlikely to be caused by a mutation-induced change in the conformation of aS aggregates.

A morphometric study of the spatial patterns of TDP-43 immunoreactive neuronal inclusions in frontotemporal lobar degeneration (FTLD) with progranulin (GRN) mutation

Mutations of the progranulin (GRN) gene are a major cause of familial frontotemporal lobar degeneration with transactive response (TAR) DNA-binding protein of 43 kDa (TDP-43) proteinopathy (FTLD-TDP). We studied the spatial patterns of TDP-43 immunoreactive neuronal cytoplasmic inclusions (NCI) and neuronal intranuclear inclusions (NII) in histological sections of the frontal and temporal lobe in eight cases of FTLD-TDP with GRN mutation using morphometric methods and spatial pattern analysis. In neocortical regions, the NCI were clustered and the clusters were regularly distributed parallel to the pia mater; 58% of regions analysed exhibiting this pattern. The NII were present in regularly distributed clusters in 35% of regions but also randomly distributed in many areas. In neocortical regions, the sizes of the regular clusters of NCI and NII were 400-800 μm, approximating to the size of the modular columns of the cortico-cortical projections, in 31% and 36% of regions respectively. The NCI and NII also exhibited regularly spaced clustering in sectors CA1/2 of the hippocampus and in the dentate gyrus. The clusters of NCI and NII were not spatially correlated. The data suggest degeneration of the cortico-cortical and cortico-hippocampal pathways in FTLD-TDP with GRN mutation, the NCI and NII affecting different clusters of neurons.

Prion-like mechanisms in neurodegenerative diseases

Many non-infectious neurodegenerative diseases are associated with the accumulation of fibrillar proteins. These diseases all exhibit features that are reminiscent of those of prionopathies, including phenotypic diversity and the propagation of pathology. Furthermore, emerging studies of amyloid-beta, alpha-synuclein and tau--proteins implicated in common neurodegenerative diseases--suggest that they share key biophysical and biochemical characteristics with prions. Propagation of protein misfolding in these diseases may therefore occur through mechanisms similar to those that underlie prion pathogenesis. If this hypothesis is verified in vivo, it will suggest new therapeutic strategies to block propagation of protein misfolding throughout the brain.

The expanding realm of prion phenomena in neurodegenerative disease

The aggregation of a soluble protein into insoluble, beta-sheet rich amyloid fibrils is a defining characteristic of many neurodegenerative diseases, including prion disorders. The prion protein has so far been considered unique because of its infectious nature. Recent investigations, however, suggest that other amyloid-forming proteins associated with much more common diseases, such as tau, alpha-synuclein, amyloid beta and polyglutamine proteins, while not infectious in the classical sense, share certain essential properties with prions that may explain phenotypic diversity, and patterns of spread within the nervous system. We suggest a common mechanism of pathogenesis of myriad sporadic and inherited neurodegenerative diseases based on templated conformational change.

What determines the molecular composition of abnormal protein aggregates in neurodegenerative disease?

Abnormal protein aggregates, in the form of either extracellular plaques or intracellular inclusions, are an important pathological feature of the majority of neurodegenerative disorders. The major molecular constituents of these lesions, viz., beta-amyloid (Abeta), tau, and alpha-synuclein, have played a defining role in the diagnosis and classification of disease and in studies of pathogenesis. The molecular composition of a protein aggregate, however, is often complex and could be the direct or indirect consequence of a pathogenic gene mutation, be the result of cell degeneration, or reflect the acquisition of new substances by diffusion and molecular binding to existing proteins. This review examines the molecular composition of the major protein aggregates found in the neurodegenerative diseases including the Abeta and prion protein (PrP) plaques found in Alzheimer's disease (AD) and prion disease, respectively, and the cellular inclusions found in the tauopathies and synucleinopathies. The data suggest that the molecular constituents of a protein aggregate do not directly cause cell death but are largely the consequence of cell degeneration or are acquired during the disease process. These findings are discussed in relation to diagnosis and to studies of to disease pathogenesis.

Rates of cerebral atrophy differ in different degenerative pathologies

Neurodegenerative disorders are pathologically characterized by the deposition of abnormal proteins in the brain. It is likely that future treatment trials will target the underlying protein biochemistry and it is therefore increasingly important to be able to distinguish between different pathologies during life. The aim of this study was to determine whether rates of brain atrophy differ in neurodegenerative dementias that vary by pathological diagnoses and characteristic protein biochemistry. Fifty-six autopsied subjects were identified with a clinical diagnosis of dementia and two serial head MRI. Subjects were subdivided based on pathological diagnoses into Alzheimer's disease, dementia with Lewy bodies (DLB), mixed Alzheimer's disease/DLB, frontotemporal lobar degeneration with ubiquitin-only-immunoreactive changes (FTLD-U), corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). Twenty-five controls were matched by age, gender and scan interval, to the study cohort. The boundary-shift integral was used to calculate change over time in whole brain (BBSI) and ventricular volume (VBSI). All BSI results were annualized by adjusting for scan interval. The rates of whole brain atrophy and ventricular expansion were significantly increased compared to controls in the Alzheimer's disease, mixed Alzheimer's disease/DLB, FTLD-U, CBD and PSP groups. However, atrophy rates in the DLB group were not significantly different from control rates of atrophy. The largest rates of atrophy were observed in the CBD group which had a BBSI of 2.3% and VBSI of 16.2%. The CBD group had significantly greater rates of BBSI and VBSI than the DLB, mixed Alzheimer's disease/DLB, Alzheimer's disease and PSP groups, with a similar trend observed when compared to the FTLD-U group. The FTLD-U group showed the next largest rates with a BBSI of 1.7% and VBSI of 9.6% which were both significantly greater than the DLB group. There was no significant difference in the rates of atrophy between the Alzheimer's disease, mixed Alzheimer's disease/DLB and PSP groups, which all showed similar rates of atrophy; BBSI of 1.1, 1.3 and 1.0% and VBSI of 8.3, 7.2 and 10.9%, respectively. Rates of atrophy therefore differ according to the pathological diagnoses and underlying protein biochemistry. While rates are unlikely to be useful in differentiating Alzheimer's disease from cases with mixed Alzheimer's disease/DLB pathology, they demonstrate important pathophysiological differences between DLB and those with mixed Alzheimer's disease/DLB and Alzheimer's disease pathology, and between those with CBD and PSP pathology.

Dopamine Affects the Stability, Hydration, and Packing of Protofibrils and Fibrils of the Wild Type and Variants of α-Synuclein†

Parkinson's disease (PD) is characterized by the presence of cytoplasmic inclusions composed of alpha-synuclein (alpha-syn) in dopaminergic neurons. This suggests a pivotal role of dopamine (DA) on PD development. Here, we show that DA modulates differently the stability of protofibrils (PF) and fibrils (F) composed of wild type or variants of alpha-syn (A30P and A53T) as probed by high hydrostatic pressure (HHP). While in the absence of DA, all alpha-syn PF exhibited identical stability, in its presence, the variant-composed PF acquired a greater stability (DAPFwt < DAPFA30P = DAPFA53T), implying that they would last longer, which could shed light onto why these mutations are so aggressive. When alpha-syn was incubated for long times (18 days) in the presence of DA, we observed the formation of F by electronic microscopy, suggesting that the PF trapped in the presence of DA in short times can evolve into F. The stability of F was also altered by DA. DAFwt was more labile than Fwt, indicating that the former would be more susceptible to breakage. PFA30P and DAPFA30P, when added to mesencephalic and cortical neurons in culture, decreased the number and length of neurites and increased the number of apoptotic cells. Surprisingly, these toxic effects of PFA30P and DAPFA30P were practically abolished with HHP treatment, which was able to break the PF into smaller aggregates, as seen by atomic force microscopy. These results suggest that strategies aimed at breaking and/or clearing these aggregates is promising in alleviating the symptoms of PD.

Cytosine beta-D-arabinofuranoside used as a paradigm modifier to increase production of tau aggregates in a cellular model of tauopathy

Intraneuronal deposition of filamentous tau is a hallmark of Alzheimer's disease (AD) and related tauopathies. We developed previously a cellular model recapitulating such tau anomaly and demonstrated therein consistent production of 70-kD tau. Importantly, the 70-kD species appears to derive from tau fragments with carboxy-terminal truncation and is larger than intact tau in size, suggesting the oligomeric nature in its assembly from tau. To generate the 70-kD tau in sufficient quantity for its characterization at the molecular level, we explored and demonstrated herein that cytosine beta-D-arabinofuranoside is a useful paradigm modifier to increase production of the 70-kD tau. Such oligomeric tau was enriched thereafter by immunoprecipitation to remove tau species with intact carboxy-terminus. Two-dimensional gel electrophoresis revealed that the 70-kD tau has an isoelectric point of 5.8-6.0. Future elucidation of key aggregates will provide valuable insights into the natural history of neurofibrillary degeneration and identify novel targets to develop therapeutic interventions.

Spatial patterns of the pathological changes in neuronal intermediate filament inclusion disease (NIFID): an α-internexin immunohistochemical study

Neuronal intermediate filament inclusion disease (NIFID) is characterized by alpha-internexin positive neuronal cytoplasmic inclusions (NCI), swollen achromatic neurons (SN), neuronal loss, and gliosis. This study tested: 1) whether the spatial patterns of the lesions was topographically organized in areas of the frontal and temporal lobe and 2) whether a spatial relationship exists between the NCI and SN. The NCI were distributed in regular clusters and in a quarter of these areas, the clusters were 400-800 microm in diameter approximating to the size of the cells of origin of the cortico-cortical pathways. Variations in the density of the NCI were positively correlated with the SN. Hence, cortical degeneration in NIFID appears to be topographically organized and may affect the cortico-cortical projections, the clusters of NCI and SN developing within the same vertical columns of cells.

Current strategies for the treatment of Alzheimer’s disease and other tauopathies

The pathological hallmarks of Alzheimer's disease (AD) include abnormal intra- and extraneuronal tau and amyloid accumulation, respectively, accompanied by gliosis, oxidative stress and neuron loss. The discovery of mutations within the tau gene itself that cause clinical dementia (i.e., fronto-temporal dementia with Parkinsonism linked to chromosome 17 [FTDP17]) demonstrated that disruption of normal tau function independent of amyloidogenesis was sufficient to cause neuronal loss and clinical dementia. These studies demonstrate the need for therapeutics that either decrease the total pool of tau or selectively reduce aberrant forms of tau (i.e., hyperphosphorylated, misfolded etc.). To this point, therapeutic development for tauopathies, including AD, have primarily focused on either the phosphorylation of tau, as it is a downstream target for many kinases and signalling cascades, or inhibition of tau aggregation. Recent developments, however, suggest that pharmacological targeting of other mechanisms may hold therapeutic promise for the treatment of tauopathies.

Topography of alpha-internexin-positive neuronal aggregates in 10 patients with neuronal intermediate filament inclusion disease

Abnormal neuronal intermediate filament (IF) inclusions immunopositive for the type IV IF alpha-internexin have been identified as the pathological hallmark of neuronal intermediate filament inclusion disease (NIFID). We studied the topography of these inclusions in the frontal and temporal lobe in 68 areas from 10 cases of NIFID. In the cerebral cortex, CA sectors of the hippocampus, and dentate gyrus granule cell layer, the inclusions were distributed mainly in regularly distributed clusters, 50-800 microm in diameter. In seven cortical areas, there was a more complex pattern in which the clusters of inclusions were aggregated into larger super clusters. In 11 cortical areas, the size of the clusters approximated to those of the cells of origin of the cortico-cortical pathways but in the majority of the remaining areas, cluster size was smaller than 400 microm. The topography of the lesions suggests that there is degeneration of the cortico-cortical projections in NIFID with the formation of alpha-internexin-positive aggregates within vertical columns of cells. Initially, only a subset of cells within a vertical column develops inclusions but as the disease progresses, the whole of the column becomes affected. The corticostriate projection appears to have little effect on the cortical topography of the inclusions.

Pharmacologic reductions of total tau levels; implications for the role of microtubule dynamics in regulating tau expression

The microtubule-associated protein tau (MAPT) is a pathological component of several neurodegenerative diseases and clinical dementias. Here, we have investigated the effects of a series of commercially available FDA-approved compounds and natural products on total tau protein levels using a cell-based approach that allows for the rapid and efficient measurement of changes in protein expression.

Convergence of heat shock protein 90 with ubiquitin in filamentous alpha-synuclein inclusions of alpha-synucleinopathies

Heat shock proteins (Hsps) facilitate refolding of denatured polypeptides, but there is limited understanding about their roles in neurodegenerative diseases characterized by misfolded proteins. Because Parkinson's disease (PD), dementia with Lewy bodies, and multiple system atrophy are alpha-synucleinopathies characterized by filamentous alpha-synuclein (alpha-syn) inclusions, we assessed which Hsps might be implicated in these disorders by examining human brain samples, transgenic mouse models, and cell culture systems. Light and electron microscopic multiple-label immunohistochemistry showed Hsp90 was the predominant Hsp examined that co-localized with alpha-syn in Lewy bodies, Lewy neurites, and glial cell inclusions and that Hsp90 co-localized with alpha-syn filaments of Lewy bodies in PD. Hsp90 levels were most predominantly increased in PD brains, which correlated with increased levels of insoluble alpha-syn. These alterations in Hsp90 were recapitulated in a transgenic mouse model of PD-like alpha-syn pathologies. Cell culture studies also revealed that alpha-syn co-immunoprecipitated preferentially with Hsp90 and Hsc70 relative to other Hsps, and exposure of cells to proteasome inhibitors resulted in increased levels of Hsp90. These data implicate predominantly Hsp90 in the formation of alpha-syn inclusions in PD and related alpha-synucleinopathies.

Spatial patterns of the pathological changes in the temporal lobe of patients with neuronal intermediate filament inclusion disease

Neuronal intermediate filament inclusion disease (NIFID) is a new neurodegenerative disease characterized histologically by the presence of neuronal cytoplasmic inclusions (NI) immunopositive for intermediate filament proteins, neuronal loss, swollen achromatic neurons (SN), and gliosis. We studied the spatial patterns of these pathological changes parallel to the pia mater in gyri of the temporal lobe in four cases of NIFID. Both the NI and SN occurred in clusters that were regularly distributed parallel to the pia mater, the cluster sizes of the SN being significantly greater than those of the NI. In a significant proportion of areas studied, there was a spatial correlation between the clusters of NI and those of the SN and with the density of the surviving neurons. In addition, the clusters of surviving neurons were negatively correlated (out of phase) with the clusters of glial cell nuclei. The pattern of clustering of these histological features suggests that there is degeneration of the cortico-cortical projections in NIFID leading to the formation of NI and SN within the same vertical columns of cells. The glial cell reaction may be a response to the loss of neurons rather than to the appearance of the NI or SN.

The cytoskeleton in neurodegenerative diseases

Abundant abnormal aggregates of cytoskeletal proteins are neuropathological signatures of many neurodegenerative diseases that are broadly classified by filamentous aggregates of neuronal intermediate filament (IF) proteins, or by inclusions containing the microtubule-associated protein (MAP) tau. The discovery of mutations in neuronal IF and tau genes firmly establishes the importance of neuronal IF proteins and tau in the pathogenesis of neurodegenerative diseases. Multiple IF gene mutations are pathogenic for Charcot-Marie-Tooth (CMT) disease and amyotrophic lateral sclerosis (ALS)--in addition to those in the copper/zinc superoxide dismutase-1 (SOD1) gene. Tau gene mutations are pathogenic for frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), and tau polymorphisms are genetic risk factors for sporadic progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). Thus, IF and tau abnormalities are linked directly to the aetiology and pathogenesis of neurodegenerative diseases. In vitro and transgenic animal models are being used to demonstrate that different mutations impair protein function, promote tau fibrilization, or perturb tau gene splicing, leading to aberrant and distinct tau aggregates. For recognition of these disorders at neuropathological examination, immunohistochemistry is needed, and this may be combined with biochemistry and molecular genetics to properly determine the nosology of a particular case. As reviewed here, the identification of molecular genetic defects and biochemical alterations in cytoskeletal proteins of human neurodegenerative diseases has facilitated experimental studies and will promote the development of assays of molecules which inhibit abnormal neuronal IF and tau protein inclusions.

Cerebrospinal fluid analysis differentiates multiple system atrophy from Parkinson's disease

We investigated whether cerebrospinal fluid (CSF) analysis discriminates between idiopathic Parkinson's disease (PD; n = 35) and multiple system atrophy (MSA; n = 30). The median CSF concentration of the neurotransmitter metabolites 5-hydroxyindolacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) was reduced significantly (49-70%) in MSA compared to PD. In contrast, several brain-specific proteins (tau, neuron-specific enolase, myelin basic protein) were elevated (130-230%) in MSA compared with those in PD. A combination of CSF tau and MHPG discriminated PD from MSA (adjusted odds ratios: tau, 27.2; MHPG, 0.14). Our data suggest that the more progressive and widespread neurodegenerative nature of MSA, as compared with PD, is reflected in the composition of CSF. We propose that CSF analysis may become part of the diagnostic work-up of patients with parkinsonian syndromes.

alpha-Internexin aggregates are abundant in neuronal intermediate filament inclusion disease (NIFID) but rare in other neurodegenerative diseases

Abnormal neuronal aggregates of alpha-internexin and the three neurofilament (NF) subunits, NF-L, NF-M, and NF-H have recently been identified as the pathological hallmarks of neuronal intermediate filament (IF) inclusion disease (NIFID), a novel neurological disease of early onset with a variable clinical phenotype including frontotemporal dementia, pyramidal and extrapyramidal signs. alpha-Internexin, a class IV IF protein, a major component of inclusions in NIFID, has not previously been identified as a component of the pathological protein aggregates of any other neurodegenerative disease. Therefore, to determine the specificity of this protein, alpha-internexin immunohistochemistry was undertaken on cases of NIFID, non-tau frontotemporal dementias, motor neuron disease, alpha-synucleinopathies, tauopathies, and normal aged control brains. Our results indicate that class IV IF proteins are present within the pleomorphic inclusions of all cases of NIFID. Small subsets of abnormal neuronal inclusions in Alzheimer's disease, Lewy body diseases, and motor neuron disease also contain epitopes of alpha-internexin. Thus, alpha-internexin is a major component of the neuronal inclusions in NIFID and a relatively minor component of inclusions in other neurodegenerative diseases. The discovery of alpha-internexin in neuronal cytoplasmic inclusions implicates novel mechanisms of pathogenesis in NIFID and other neurological diseases with pathological filamentous neuronal inclusions.

No evidence for tau duplications in frontal temporal dementia families showing genetic linkage to the tau locus in which tau mutations have not been found

Given the remarkable similarities between the genetics of tau diseases and the genetics of alpha-synuclein diseases, and given the fact that we have recently found a triplication of the alpha-synuclein locus in a family in which we had shown linkage to the alpha-synuclein locus, we determined to test whether some of the several families with autosomal dominant frontal temporal dementia which show genetic linkage to the tau locus but in which tau mutations have not been found could be caused by similar structural mutations. We did not find any such mutations.

alpha-internexin is present in the pathological inclusions of neuronal intermediate filament inclusion disease

Neuronal intermediate filament (IF) inclusion disease (NIFID) is a novel neurological disease of early onset with a variable clinical phenotype including frontotemporal dementia, pyramidal, and extrapyramidal signs. Pathologically, in affected areas, there is neuronal loss, astrocytosis, and neuronal intracytoplasmic aggregates of abnormal neuronal IFs that contain neither tau nor alpha-synuclein. Thus, to characterize the neuronal IF protein profile of inclusions in NIFID, immunohistochemistry (IHC) was performed on 10 cases of NIFID, four normal aged controls (NL), and two cases of Alzheimer's disease (AD) using a panel of anti-neuronal IF proteins. Immunoelectron microscopy was performed on selected cases and frozen tissue from the frontal lobe of four cases was used for biochemical studies including sequential extractions and Western blotting. Based on these studies, we report here for the first time that alpha-internexin, a neuronal IF protein, is present within the inclusions of NIFID as are all three neurofilament subunits: heavy, medium, and light. Thus, all class IV neuronal IF proteins are present within the pathological inclusions of this disease. Biochemistry revealed that IF aggregates were soluble in sodium dodecyl sulfate (SDS) and no post-translational modification was detected when compared with Alzheimer's disease or aged control brains. Hence, we conclude that NIFID is characterized by the pathological cytoplasmic aggregation of all class IV neuronal IF proteins in brain. The discovery of alpha-internexin in the cytoplasmic inclusions implicates novel mechanisms of pathogenesis in NIFID and other neurological diseases with pathological accumulations of IFs.

Post mortem sampling of the brain and other tissues in neurodegenerative disease

The importance of the autopsy in neurodegenerative disease is often not appreciated. Yet clinical diagnosis of neurodegenerative disease is relatively inaccurate, many neurodegenerative diseases are inherited or are associated with specific genetic risk factors, and several non-transmissible neurodegenerative diseases may be confused clinically with prion diseases. In all these cases, the autopsy is the only practical way in which brain tissue can be obtained for diagnosis. The pathologist should ensure that consent by the next-of-kin to post mortem examination is based on clear information as to the nature, scope and limitations of the autopsy, and that any constraints on retaining brain and other tissues are documented. The autopsy should be preceded by a careful review of the clinical notes and ante mortem studies, and consideration of the possible and likely pathological processes. This may suggest the need to retain fixed or frozen samples of cerebrospinal fluid, skeletal muscle, peripheral nerve and other tissues in addition to brain and spinal cord. Ideally, the brain should be fixed intact for 2-3 weeks before it is sliced and blocks are taken. If the period of fixation is limited to a few days only, it is best to slice the brain whilst it is fresh and to allow the diagnostically relevant slices to fix flat; after about 3 days the fixed slices can be sliced further, examined macroscopically and sampled. Even if consent is limited to the retention of only a few tissue samples for histology, a reasonably confident diagnosis can still usually be made, provided that the sampling is careful and systematic. The selection of blocks or brain and spinal cord for histology should be based on internationally accepted guidelines for the pathological diagnosis of different types of neurodegenerative disease, where such guidelines are available. Illustrations are provided to indicate which regions of the brain are critical to establishing a diagnosis in the main categories of neurodegenerative disease. When difficulties arise in the pathological diagnosis of neurodegenerative disease, inadequate post mortem sampling or rapid processing of poorly fixed brain tissue is usually to blame.

Research on the brain

Sponsored by the Movement Disorder Society, the 3rd International Workshop on Dementia with Lewy Bodies and Parkinson's Disease Dementia was held on 17 to 20 September 2003 in Newcastle upon Tyne, United Kingdom. This meeting report summarizes findings presented at this meeting. The presentations focused on clinicopathological correlations, therapy, genetics, and basic science research.

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.

Parkinson's syndrome associated with neurofibrillary degeneration and tau pathologic findings

Several distinct clinical syndromes presenting with parkinsonism have been associated with subcortical neurofibrillary degeneration and the abnormal accumulation of hyperphosphorylated tau protein in the brain. Mutations of tau have been linked with a small number of autosomal dominantly inherited families who present with frontolimbic cognitive deficits, behavioural disorders, and Parkinson's syndrome. Some of the sporadic disorders (progressive supranuclear palsy [PSP] and corticobasal degeneration) have been referred to by molecular pathologists as primary tauopathies, implicating abnormalities of tau in their pathogenesis. We have identified a sporadic parkinsonian syndrome characterised by bradykinesia, a variable response to levodopa, and a mean duration of disease of 9 years, which resembles bodig (Parkinson's-dementia of Guam), and histologically has close similarities with both PSP and postencephalitic parkinsonism. Further characterisation of these cases frequently confused with Parkinson's disease may broaden the clinical spectrum of parkinsonian disorders linked with neurofibrillary tangle formation.

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.

Where does parkinson disease pathology begin in the brain?

The substantia nigra is not the induction site in the brain of the neurodegenerative process underlying Parkinson disease (PD). Instead, the results of this semi-quantitative study of 30 autopsy cases with incidental Lewy body pathology indicate that PD in the brain commences with the formation of the very first immunoreactive Lewy neurites and Lewy bodies in non-catecholaminergic neurons of the dorsal glossopharyngeus-vagus complex, in projection neurons of the intermediate reticular zone, and in specific nerve cell types of the gain setting system (coeruleus-subcoeruleus complex, caudal raphe nuclei, gigantocellular reticular nucleus), olfactory bulb, olfactory tract, and/or anterior olfactory nucleus in the absence of nigral involvement. The topographical parcellation of the nuclear grays described here is based upon known architectonic analyses of the human brainstem and takes into consideration the pigmentation properties of a few highly susceptible nerve cell types involved in PD. In this sample and in all 58 age- and gender-matched controls, Lewy bodies and Lewy neurites do not occur in any of the known prosencephalic predilection sites (i.e. hippocampal formation, temporal mesocortex, proneocortical cingulate areas, amygdala, basal nucleus of Meynert, interstitial nucleus of the diagonal band of Broca, hypothalamic tuberomamillary nucleus).