Alzheimer disease with amygdala Lewy bodies: a distinct form of alpha-synucleinopathy

Protein coding of neurodegenerative dementias: the neuropathological basis of biomarker diagnostics

Neuropathological diagnosis of neurodegenerative dementias evolved by adapting the results of neuroanatomy, biochemistry, and cellular and molecular biology. Milestone findings of intra- and extracellular argyrophilic structures, visualizing protein deposition, initiated a protein-based classification. Widespread application of immunohistochemical and biochemical investigations revealed that (1) there are modifications of proteins intrinsic to disease (species that are phosphorylated, nitrated, oligomers, proteinase-resistant, with or without amyloid characteristics; cleavage products), (2) disease forms characterized by the accumulation of a single protein only are rather the exception than the rule, and (3) some modifications of proteins elude present neuropathological diagnostic procedures. In this review, we summarize how neuropathology, together with biochemistry, contributes to disease typing, by demonstrating a spectrum of disorders characterized by the deposition of various modifications of various proteins in various locations. Neuropathology may help to elucidate how brain pathologies alter the detectability of proteins in body fluids by upregulation of physiological forms or entrapment of different proteins. Modifications of at least the five most relevant proteins (amyloid-beta, prion protein, tau, alpha-synuclein, and TDP-43), aided by analysis of further "attracted" proteins, are pivotal to be evaluated simultaneously with different methods. This should complement the detection of biomarkers associated with pathogenetic processes, and also neuroimaging and genetic analysis, in order to obtain a highly personalized diagnostic profile. Defining clusters of patients based on the patterns of protein deposition and immunohistochemically or biochemically detectable modifications of proteins ("codes") may have higher prognostic predictive value, may be useful for monitoring therapy, and may open new avenues for research on pathogenesis.

Selective molecular alterations in the autophagy pathway in patients with Lewy body disease and in models of alpha-synucleinopathy

BACKGROUND

Lewy body disease is a heterogeneous group of neurodegenerative disorders characterized by alpha-synuclein accumulation that includes dementia with Lewy bodies (DLB) and Parkinson's Disease (PD). Recent evidence suggests that impairment of lysosomal pathways (i.e. autophagy) involved in alpha-synuclein clearance might play an important role. For this reason, we sought to examine the expression levels of members of the autophagy pathway in brains of patients with DLB and Alzheimer's Disease (AD) and in alpha-synuclein transgenic mice.

METHODOLOGY/PRINCIPAL FINDINGS

By immunoblot analysis, compared to controls and AD, in DLB cases levels of mTor were elevated and Atg7 were reduced. Levels of other components of the autophagy pathway such as Atg5, Atg10, Atg12 and Beclin-1 were not different in DLB compared to controls. In DLB brains, mTor was more abundant in neurons displaying alpha-synuclein accumulation. These neurons also showed abnormal expression of lysosomal markers such as LC3, and ultrastructural analysis revealed the presence of abundant and abnormal autophagosomes. Similar alterations were observed in the brains of alpha-synuclein transgenic mice. Intra-cerebral infusion of rapamycin, an inhibitor of mTor, or injection of a lentiviral vector expressing Atg7 resulted in reduced accumulation of alpha-synuclein in transgenic mice and amelioration of associated neurodegenerative alterations.

CONCLUSIONS/SIGNIFICANCE

This study supports the notion that defects in the autophagy pathway and more specifically in mTor and Atg7 are associated with neurodegeneration in DLB cases and alpha-synuclein transgenic models and supports the possibility that modulators of the autophagy pathway might have potential therapeutic effects.

Clinical, neuropathologic, and biochemical profile of the amyloid precursor protein I716F mutation

We report the clinical, pathologic, and biochemical characteristics of the recently described amyloid precursor protein (APP) I716F mutation. We present the clinical findings of individuals carrying the APP I716F mutation and the neuropathologic examination of the proband. The mutation was found in a patient with Alzheimer disease with onset at the age of 31 years and death at age 36 years and who had a positive family history of early-onset Alzheimer disease. Neuropathologic examination showed abundant diffuse amyloid plaques mainly composed of amyloid-beta42 and widespread neurofibrillary pathology. Lewy bodies were found in the amygdala. Chinese hamster ovary cells transfected with this mutation showed a marked increase in the amyloid-beta42/40 ratio and APP C-terminal fragments and a decrease in APP intracellular domain production, suggesting reduced APP proteolysis by gamma-secretase. Taken together, these findings indicate that the APP I716F mutation is associated with the youngest age of onset for this locus and strengthen the inverse association between amyloid-beta42/40 ratio and age of onset. The mutation leads to a protein that is poorly processed by gamma-secretase. This loss of function may be an additional mechanism by which some mutations around the gamma-secretase cleavage site lead to familial Alzheimer disease.

Formation and development of Lewy pathology: a critical update

Filamentous protein inclusions in neurons (Lewy bodies, LB) and dystrophic neurites containing pathologic alpha-synuclein (alpha Syn) are the morphologic hallmarks of sporadic Parkinson disease (PD) and dementia with Lewy bodies (DLB), but are also found in aged subjects and in a variety of neurogenerative disorders. They occur in the central, peripheral, and autonomic nervous system as an essential or coincident feature. Their formation runs through several phases from initial dust-like particles cross-linked with alpha Syn to aggregation of ubiquitinated dense filaments, formation of LBs, finally degradation and death of the afflicted neurons. Pathologic accumulation of alpha Syn/LBs proposed by Braak et al. (Neurobiol Aging 24:197-211, 2003), following a predictable sequence of lesions in six stages with ascending progression from medullary and olfactory nuclei to the cortex, has been considered to be linked to clinical dysfunctions. The consensus pathologic guidelines of DLB (Neurology 65:1863-1872, 2005), by semiquantitative scoring to alpha Syn pathology (LB density and distribution) in specific brain regions, distinguish three phenotypes (brainstem, transitional/limbic, and diffuse neocortical), and also consider concomitant Alzheimer-related pathology. alpha Syn pathology in the amygdala is often associated with Alzheimer disease. Although some retrospective clinico-pathologic studies have largely confirmed the Braak LB staging system, it shows neither correlation to the clinical severity and duration of parkinsonism nor to nigral alpha Syn burden and cell loss which significantly correlates with resulting striatal loss of dopamine, dopamine transporter and tyrosine hydroxylase, duration and severity of motor dysfunction. Between 6.3 and 43% of clinically manifested PD cases did not follow this pattern, and in 7-8.3% of those with alpha Syn-positive inclusions in midbrain and cortex the medullary nuclei were spared. On the other hand, 30-55% of elderly subjects with widespread Lewy pathology revealed no neuropsychiatric symptoms or were not classifiable. Therefore, detection and staging of Lewy pathology without assessment of neuronal loss in specific areas may not have clinical impact and its predictive validity is questionable. For demented patients, modified criteria for categorization of Lewy pathology were proposed. If robust correlations between clinical course and Lewy/alpha Syn pathology are to be confirmed by future studies, the currently used morphologic staging/classification systems should be revised accordingly.

Absence of alpha-synuclein pathology in postencephalitic parkinsonism

Postencephalitic parkinsonism (PEP), a chronic complication of encephalitis lethargica, is a tauopathy characterized by multisystem neuronal loss and gliosis with widespread neurofibrillary lesions composed of both 3- and 4-repeat (3R and 4R) tau isoforms. Previous immunohistochemical studies in a small number of PEP cases demonstrated absence of Lewy bodies as well as the lack of other alpha-synuclein pathology, classifying PEP as a "pure" tauopathy. Neuropathologic examination of 10 brains with clinico-pathologically verified PEP confirmed widespread neurodegeneration in subcortical and brainstem areas associated with multifocal neurofibrillary pathology comprising both 3R and 4R tau. Very rare beta-amyloid deposits were observed in two elderly patients, while Lewy bodies and neurites or any other alpha-synuclein deposits were completely absent. The causes and molecular background of total absence of alpha-synuclein pathology in PEP, in contrast to most other tauopathies, remain as unknown as the pathogenesis of PEP.

Neuropathology of non-Alzheimer degenerative disorders

Neurodegenerative diseases are characterized by selective and progressive loss of specific populations of neurons, which determines the clinical presentation. The same neuronal populations can be affected in a number of different disorders. Given that the clinical presentation reflects the particular population of neurons that are targets of the disease process, it is clear that for any given clinical syndrome, more than one neurodegenerative disease can account for the clinical syndrome. Because of this clinical ambiguity, for the purpose of this brief review neurodegenerative disorders are classified according to the underlying molecular pathology rather than their clinical presentation. The major neurodegenerative diseases can be classified into amyloidoses, tauopathies, alpha-synucleinopathies and TDP-43 proteinopathies.

Lewy body pathology in normal elderly subjects

Lewy bodies and Lewy neurites are the hallmark neuropathologic findings in Parkinson disease, Parkinson disease with dementia, dementia with Lewy bodies, and other alpha-synucleinopathies. They have also been described in the brains of normal older individuals and referred to as incidental Lewy body disease. The purpose of this study was to determine the prevalence of Lewy bodies and Lewy neurites (Lewy body pathology [LBP]) in 139 autopsies from our normal volunteer control group of the University of Kentucky Alzheimer's Disease Center. All subjects were followed longitudinally and were cognitively normal and without any type of movement disorder, neuropsychiatric features, or other CNS findings. The brains of 33 of 139 normal subjects contained LBP in various regions. The most common regions involved were the medulla (26%), amygdala (24%), pons (20%), and midbrain (20%). No mean statistical differences were found between those with and without LBP on any demographic or cognitive variable, Braak stage, or neurofibrillary tangle and neuritic plaque quantitation. An explanation for the high prevalence of LBP in our elderly, well-educated study group is not clear, although it does not seem to be related to aging or the presence of Alzheimer disease pathology. Overall, our findings support the concept that incidental Lewy body disease most likely represents preclinical or presymptomatic Parkinson disease, Parkinson disease with dementia, or dementia with Lewy bodies.

Classification and basic pathology of Alzheimer disease

The lesions of Alzheimer disease include accumulation of proteins, losses of neurons and synapses, and alterations related to reactive processes. Extracellular Abeta accumulation occurs in the parenchyma as diffuse, focal or stellate deposits. It may involve the vessel walls of arteries, veins and capillaries. The cases in which the capillary vessel walls are affected have a higher probability of having one or two apoepsilon 4 alleles. Parenchymal as well as vascular Abeta deposition follows a stepwise progression. Tau accumulation, probably the best histopathological correlate of the clinical symptoms, takes three aspects: in the cell body of the neuron as neurofibrillary tangle, in the dendrites as neuropil threads, and in the axons forming the senile plaque neuritic corona. The progression of tau pathology is stepwise and stereotyped from the entorhinal cortex, through the hippocampus, to the isocortex. The neuronal loss is heterogeneous and area-specific. Its mechanism is still discussed. The timing of the synaptic loss, probably linked to Abeta peptide itself, maybe as oligomers, is also controversial. Various clinico-pathological types of Alzheimer disease have been described, according to the type of the lesions (plaque only and tangle predominant), the type of onset (focal onset), the cause (genetic or sporadic) and the associated lesions (Lewy bodies, vascular lesions, hippocampal sclerosis, TDP-43 inclusions and argyrophilic grain disease).

Incidental Lewy body disease: do some cases represent a preclinical stage of dementia with Lewy bodies?

Lewy pathology occurs in 8-17% of neurologically normal people age >60, termed incidental Lewy body disease (iLBD). It is often assumed to represent preclinical Parkinson disease (PD). However, some iLBD cases have diffuse pathology inconsistent with preclinical PD. We analyzed iLBD cases (α-synuclein immunohistochemistry) using the Braak PD staging scheme and determined if some had a neuropathological pattern suggestive of preclinical dementia with Lewy bodies (DLB). Of the 235 brains examined, 34 had iLBD (14.5%) and all but one could be assigned a Braak PD stage. The distribution of α-synuclein pathology in the 33 cases fell into three patterns: (1) diffuse cortical and subcortical α-synuclein pathology; (2) no cortical α-synuclein pathology, but a caudal-to-rostral ascending pattern, primarily involving brainstem; and (3) intermediate between these two categories. Also, 6/33 cases failed to follow the pattern of contiguous spread proposed by Braak. These findings suggest dichotomy in the distribution of iLBD: some cases fit the Braak ascending scheme, conceptually consistent with preclinical PD, whereas others displayed prominent cortical involvement that might represent preclinical DLB.

Staging/typing of Lewy body related alpha-synuclein pathology: a study of the BrainNet Europe Consortium

When 22 members of the BrainNet Europe (BNE) consortium assessed 31 cases with alpha-synuclein (alphaS) immunoreactive (IR) pathology applying the consensus protocol described by McKeith and colleagues in 2005, the inter-observer agreement was 80%, being lowest in the limbic category (73%). When applying the staging protocol described by Braak and colleagues in 2003, agreement was only 65%, and in some cases as low as 36%. When modifications of these strategies, i.e., McKeith's protocol by Leverenz and colleagues from 2009, Braak's staging by Müller and colleagues from 2005 were applied then the agreement increased to 78 and 82%, respectively. In both of these modifications, a reduced number of anatomical regions/blocks are assessed and still in a substantial number of cases, the inter-observer agreement differed significantly. Over 80% agreement in both typing and staging of alphaS pathology could be achieved when applying a new protocol, jointly designed by the BNE consortium. The BNE-protocol assessing alphaS-IR lesions in nine blocks offered advantages over the previous modified protocols because the agreement between the 22 observers was over 80% in most cases. Furthermore, in the BNE-protocol, the alphaS pathology is assessed as being present or absent and thus the quality of staining and the assessment of the severity of alphaS-IR pathology do not alter the inter-observer agreement, contrary to other assessment strategies. To reach these high agreement rates an entity of amygdala-predominant category was incorporated. In conclusion, here we report a protocol for assessing alphaS pathology that can achieve a high inter-observer agreement for both the assignment to brainstem, limbic, neocortical and amygdala-predominant categories of synucleinopathy and the Braak stages.

Frontotemporal lobar degeneration and dementia with Lewy bodies: clinicopathological issues associated with antemortem diagnosis

Currently, the clinical diagnostic criteria of frontotemporal lobar degeneration (FTLD) and dementia with Lewy bodies (DLB) are well known to neurologists and psychiatrists. However, the accuracy of the clinical diagnosis of these diseases in autopsy series is not always adequate. For example, FTLD is a syndrome rather than a clinicopathological disease entity that is comprised of various pathological substrates, including Pick's disease, FTLD with microtubule-associated protein tau gene mutation, FTLD with tau-negative ubiquitin-positive inclusions (FTLD-U), FTLD-U with progranulin gene mutation, corticobasal degeneration, basophilic inclusion body disease, and neuronal intermediate filament inclusion disease. Whether these underlying pathologies can be identified clinically is one of the greatest interests in neuropathological research. The pathophysiological relationship between Lewy pathology and Alzheimer pathology in DLB is explored with interest because it may be associated with the accuracy of clinical diagnoses. For example, although Lewy pathology may progress from the brain stem nuclei to the cerebral cortex in Parkinson's disease, recent studies have demonstrated that the progression pattern in DLB is not always identical to that in Parkinson's disease. It is also considered that the progression pattern of Lewy pathology correlates with the evolution of clinical symptoms and that the progression pattern of Lewy pathology may be altered when Alzheimer pathology coexists. In the present paper, the clinicopathological features of two demented cases are presented, and some pathological issues associated with the clinical diagnosis of FTLD and DLB are discussed.

Unified staging system for Lewy body disorders: correlation with nigrostriatal degeneration, cognitive impairment and motor dysfunction

The two current major staging systems in use for Lewy body disorders fail to classify up to 50% of subjects. Both systems do not allow for large numbers of subjects who have Lewy-type alpha-synucleinopathy (LTS) confined to the olfactory bulb or who pass through a limbic-predominant pathway that at least initially bypasses the brainstem. The results of the current study, based on examination of a standard set of ten brain regions from 417 subjects stained immunohistochemically for alpha-synuclein, suggest a new staging system that, in this study, allows for the classification of all subjects with Lewy body disorders. The autopsied subjects included elderly subjects with Parkinson's disease, dementia with Lewy bodies, incidental Lewy body disease and Alzheimer's disease with Lewy bodies, as well as comparison groups without Lewy bodies. All subjects were classifiable into one of the following stages: I. Olfactory Bulb Only; IIa Brainstem Predominant; IIb Limbic Predominant; III Brainstem and Limbic; IV Neocortical. Progression of subjects through these stages was accompanied by a generally stepwise worsening in terms of striatal tyrosine hydroxylase concentration, substantia nigra pigmented neuron loss score, Mini Mental State Examination score and score on the Unified Parkinson's Disease Rating Scale Part 3. Additionally, there were significant correlations between these measures and LTS density scores. It is suggested that the proposed staging system would improve on its predecessors by allowing classification of a much greater proportion of cases.

Criteria for the neuropathological diagnosis of dementing disorders: routes out of the swamp?

There are several consensus criteria for both the clinical and neuropathological diagnosis of different types of dementias. The clinical diagnostic accuracy using revised research criteria and newly developed biomarkers (MRI, PET, CSF analysis, genetic markers) ranges from 65 to 96% (for Alzheimer disease) with a specificity of diagnostic criteria versus other dementias of 23-88%. Neuropathological assessment of dementing disorders using immunohistochemistry, molecular biologic and genetic methods can achieve a diagnosis/classification, based on the homogeneous definitions, harmonized inter-laboratory methods and standards for the assessment of nervous system lesions, in about 99%, without, however, being able to clarify the causes/etiology of most of these disorders. Further prospective and concerted clinicopathological studies using revised methodological and validated protocols and uniform techniques are required to establish the nature, distribution pattern and grades of lesions and; thus, to overcome the limitations of the current diagnostic framework. By data fusion this my allow their more uniform application and correlation with the clinical data in order to approach a diagnostic "gold standard", and to create generally accepted criteria for differentiating cognitive disorders from healthy brain aging. The detection of disease-specific pathologies will be indispensable to determinate the efficacy of new therapy options.

Modeling the association between 43 different clinical and pathological variables and the severity of cognitive impairment in a large autopsy cohort of elderly persons

We evaluated the association between mini-mental status examination (MMSE) scores proximal to death and the values of 43 different clinical and pathological parameters. Studies were performed using data from 334 elderly, longitudinally evaluated research subjects who had undergone autopsy and satisfied inclusion criteria from an initial study group of 501. Interindividual variance in MMSE scores was used as a surrogate for the severity of cognitive impairment linked to aging (CILA). A statistical linear regression-based model provided a framework for assessing the parameters with significant, direct impact on CILA severity. Strong association between CILA and Alzheimer's disease (AD) pathology, especially isocortical neurofibrillary tangles, was evident. The pattern of association between AD lesion densities with cognitive impairment severity was biologically informative, with neuritic plaques having more impact in relatively high-functioning individuals. Abundant isocortical Lewy bodies tended to be an additive pathology correlating with final MMSE scores approximately 10 points lower. In a subset of cases we found evidence for association between TDP-43-related pathology and CILA severity, independent of AD or hippocampal sclerosis. There was no support for independent association between CILA severity and most evaluated indices including diffuse plaques, argyrophilic grains, heart disease, education level, apolipoprotein E alleles or diabetes.

Early onset familial Alzheimer Disease with spastic paraparesis, dysarthria, and seizures and N135S mutation in PSEN1

OBJECTIVE

Early onset familial Alzheimer disease (EOFAD) can be caused by mutations in genes for amyloid precursor protein, presenilin 1 (PSEN1), or presenilin 2 (PSEN2). There is considerable phenotypic variability in EOFAD, including some patients with spastic paraparesis. The objective is to describe clinical and neuropathologic features of a family with a PSEN1 mutation that has been reported previously, without autopsy confirmation, in a single Greek family whose affected members presented with memory loss in their 30s, as well as variable limb spasticity and seizures.

METHODS

We prospectively evaluated 2 children (son and daughter) with EOFAD and reviewed medical records on their mother. Archival material from the autopsy of the mother was reviewed and postmortem studies were performed on the brain of the daughter.

RESULTS

All 3 individuals in this family had disease onset in their 30s, with cognitive deficits in multiple domains, including memory, language, and attention, as well as less common features such as spastic dysarthria, limb spasticity, and seizures. At autopsy both the mother and her daughter had pathologic findings of Alzheimer disease, and histologic evidence of corticospinal tract degeneration. Genetic studies revealed a mutation in PSEN1 leading to an asparagine to serine substitution at amino acid residue 135 (N135S) in presenilin 1.

CONCLUSIONS

This is the first description of neuropathologic findings in EOFAD owing to N135S PSEN1 mutation. The clinical phenotype was remarkable for spastic dysarthria, limb spasticity, and seizures, in addition to more typical features of EOFAD.

Is malfunction of the ubiquitin proteasome system the primary cause of alpha-synucleinopathies and other chronic human neurodegenerative disease?

Neuropathological investigations have identified major hallmarks of chronic neurodegenerative disease. These include protein aggregates called Lewy bodies in dementia with Lewy bodies and Parkinson's disease. Mutations in the alpha-synuclein gene have been found in familial disease and this has led to intense focused research in vitro and in transgenic animals to mimic and understand Parkinson's disease. A decade of transgenesis has lead to overexpression of wild type and mutated alpha-synuclein, but without faithful reproduction of human neuropathology and movement disorder. In particular, widespread regional neuronal cell death in the substantia nigra associated with human disease has not been described. The intraneuronal protein aggregates (inclusions) in all of the human chronic neurodegenerative diseases contain ubiquitylated proteins. There could be several reasons for the accumulation of ubiquitylated proteins, including malfunction of the ubiquitin proteasome system (UPS). This hypothesis has been genetically tested in mice by conditional deletion of a proteasomal regulatory ATPase gene. The consequences of gene ablation in the forebrain include extensive neuronal death and the production of Lewy-like bodies containing ubiquitylated proteins as in dementia with Lewy bodies. Gene deletion in catecholaminergic neurons, including in the substantia nigra, recapitulates the neuropathology of Parkinson's disease.

Progranulin gene mutation with an unusual clinical and neuropathologic presentation

Progranulin gene (PGRN) mutations cause frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U). Patients usually present with a frontotemporal dementia syndrome and have prominent atrophy and neuronal loss in frontal and temporal cortices and the striatum, with neuronal intranuclear and cytoplasmic inclusions. Clinical, neuropathological, and genetic studies are reported on an individual with PGRN mutation and her family members. We describe a patient with a PGRN c.26C>A mutation who presented with progressive stuttering dysarthria, oculomotor abnormalities, choreic buccolingual movements, and mild parkinsonism. Two other family members were affected, one with a behavioral variant frontotemporal dementia syndrome, the other with a diagnosis of probable Alzheimer's disease. At autopsy there was no neuronal loss in the cortex or medial temporal lobe structures, but there was striatal gliosis. Immunohistochemistry for ubiquitin and TDP-43 revealed neuronal cytoplasmic and intranuclear inclusions as well as neurites. This study further expands the clinical and pathological spectrum of PGRN mutations, and suggests the diagnosis could be missed in some individuals with atypical presentations.

Validation of the neuropathologic criteria of the third consortium for dementia with Lewy bodies for prospectively diagnosed cases

There is limited information on the validity of the pathologic criteria of the Third Consortium on Dementia with Lewy bodies (CDLB), and none are based on prospectively diagnosed cases. In this study, the core clinical features of dementia with Lewy bodies (DLB) and the suggestive clinical feature of rapid eye movement sleep behavior disorder were assessed using a battery of standardized clinical instruments in 76 patients with the clinical diagnosis of either DLB or Alzheimer disease. At autopsy, 29 patients had high-likelihood, 17 had intermediate-likelihood, and 6 had low-likelihood DLB pathology. The frequency of core clinical features and the accuracy of the clinical diagnosis of probable DLB were significantly greater in high-likelihood than in low-likelihood cases. This is consistent with the concept that the DLB clinical syndrome is directly related to Lewy body pathology and inversely related to Alzheimer pathology. Thus, the Third Consortium on DLB neuropathologic criteria scheme performed reasonably well and are useful for estimating the likelihood of the premortem DLB syndrome based on postmortem findings. In view of differences in the frequency of clinically probable DLB in cases with Braak neurofibrillary tangle stages V (90%) and VI (20%) and diffuse cortical Lewy bodies, a possible modification of the scheme is to consider cases with neurofibrillary tangle stage VI to be low-likelihood DLB.

Mechanisms of hybrid oligomer formation in the pathogenesis of combined Alzheimer's and Parkinson's diseases

Background

Misfolding and pathological aggregation of neuronal proteins has been proposed to play a critical role in the pathogenesis of neurodegenerative disorders. Alzheimer's disease (AD) and Parkinson's disease (PD) are frequent neurodegenerative diseases of the aging population. While progressive accumulation of amyloid β protein (Aβ) oligomers has been identified as one of the central toxic events in AD, accumulation of α-synuclein (α-syn) resulting in the formation of oligomers and protofibrils has been linked to PD and Lewy body Disease (LBD). We have recently shown that Aβ promotes α-syn aggregation and toxic conversion in vivo, suggesting that abnormal interactions between misfolded proteins might contribute to disease pathogenesis. However the molecular characteristics and consequences of these interactions are not completely clear.

Methodology/Principal Findings

In order to understand the molecular mechanisms involved in potential Aβ/α-syn interactions, immunoblot, molecular modeling, and in vitro studies with α-syn and Aβ were performed. We showed in vivo in the brains of patients with AD/PD and in transgenic mice, Aβ and α-synuclein co-immunoprecipitate and form complexes. Molecular modeling and simulations showed that Aβ binds α-syn monomers, homodimers, and trimers, forming hybrid ring-like pentamers. Interactions occurred between the N-terminus of Aβ and the N-terminus and C-terminus of α-syn. Interacting α-syn and Aβ dimers that dock on the membrane incorporated additional α-syn molecules, leading to the formation of more stable pentamers and hexamers that adopt a ring-like structure. Consistent with the simulations, under in vitro cell-free conditions, Aβ interacted with α-syn, forming hybrid pore-like oligomers. Moreover, cells expressing α-syn and treated with Aβ displayed increased current amplitudes and calcium influx consistent with the formation of cation channels.

Conclusion/Significance

These results support the contention that Aβ directly interacts with α-syn and stabilized the formation of hybrid nanopores that alter neuronal activity and might contribute to the mechanisms of neurodegeneration in AD and PD. The broader implications of such hybrid interactions might be important to the pathogenesis of other disorders of protein misfolding.

Temporal lobar predominance of TDP-43 neuronal cytoplasmic inclusions in Alzheimer disease

TAR DNA binding protein-43 (TDP-43) immunoreactive neuronal inclusions are detected in 20-30% of Alzheimer disease (AD) brains, but the distribution of this pathology has not been rigorously studied. In this report, we describe region-specific distribution and density of TDP-43 positive neuronal cytoplasmic inclusions (NCIs) in clinically demented individuals with high probability AD pathology, all with Braak neurofibrillary tangle stages of V or VI. Sections of hippocampus, amygdala, as well as temporal, frontal, and parietal neocortex, were analyzed with TDP-43 immunohistochemistry, and the density of NCIs was assessed using a semiquantitative scoring method. Of the 29 cases, six had TDP-43 positive NCIs in the amygdala only and seven had TDP-43 inclusions restricted to amygdala and hippocampus. In 16 cases, TDP-43 immunoreactivity was more widespread, affecting temporal, frontal or parietal neocortex. These findings indicate that medial temporal lobe limbic structures are vulnerable to TDP-43 pathology in advanced AD, and that the amygdala appears to be the most susceptible region. The distribution of the lesions in this cross-sectional analysis may suggest a progression of TDP-43 pathology in AD, with limbic structures in the medial temporal lobe affected first, followed by higher order association cortices.

Alzheimer disease: postmortem neuropathologic correlates of antemortem 1H MR spectroscopy metabolite measurements

PURPOSE

To determine the neuropathologic correlates of antemortem hydrogen 1 ((1)H) magnetic resonance (MR) spectroscopy metabolite measurements in subjects with Alzheimer disease (AD)-type pathology.

MATERIALS AND METHODS

This study was approved by the institutional review board and was compliant with HIPAA regulations. Informed consent was obtained from each subject. The authors identified 54 subjects who underwent antemortem (1)H MR spectroscopy and were clinically healthy or had AD-type pathology with low to high likelihood of AD according to National Institute on Aging-Reagan neuropathologic criteria at autopsy. They investigated the associations between (1)H MR spectroscopy metabolite measurements and Braak neurofibrillary tangle stage (Braak stage), neuritic plaque score, and AD likelihood, with adjustments for subject age, subject sex, and time between (1)H MR spectroscopy and death.

RESULTS

Decreases in N-acetylaspartate-to-creatine ratio, an index of neuronal integrity, and increases in myo-inositol-to-creatine ratio were associated with higher Braak stage, higher neuritic plaque score, and greater likelihood of AD. The N-acetylaspartate-to-myo-inositol ratio proved to be the strongest predictor of the pathologic likelihood of AD. The strongest association observed was that between N-acetylaspartate-to-myo-inositol ratio and Braak stage (R(N)(2) = 0.47, P < .001).

CONCLUSION

Antemortem (1)H MR spectroscopy metabolite changes correlated with AD-type pathology seen at autopsy. The study findings validated (1)H MR spectroscopy metabolite measurements against the neuropathologic criteria for AD, and when combined with prior longitudinal (1)H MR spectroscopy findings, indicate that these measurements could be used as biomarkers for disease progression in clinical trials.

Co-localization of tau and alpha-synuclein in the olfactory bulb in Alzheimer's disease with amygdala Lewy bodies

We recently reported that Alzheimer's disease (AD) with amygdala Lewy bodies (ALB) is a distinct form of alpha-synucleinopathy that occurs in advanced AD. In AD/ALB the alpha-synuclein pathology correlated with tau pathology, but not amyloid plaques, and there was often co-localization of tau and alpha-synuclein in the same neuron. Given the anatomical connectivity of the anterior olfactory nucleus and the amygdala, which receives axonal projections from the olfactory bulb, we hypothesized that there might be a relationship between tau and alpha-synuclein pathology in the olfactory bulb and the amygdala in AD. We screened for alpha-synuclein pathology in the olfactory bulb in AD with and without ALB, and investigated its relationship with tau pathology. In 38 of 41 (93%) AD/ALB cases and 4 of 21 (19%) AD cases without ALB (AD/non-ALB), alpha-synuclein pathology was detected in the olfactory bulb. Double immunolabeling at the light and electron microscopic levels revealed co-localization of tau and alpha-synuclein in the olfactory bulb neurons and neurites. The severity of tau pathology correlated with alpha-synuclein pathology in the olfactory bulb. In addition, alpha-synuclein pathology in the olfactory bulb correlated with alpha-synuclein pathology in amygdala. Tau pathology was greater in both the olfactory bulb and amygdala in AD/ALB than in AD/non-ALB, but there was no difference in tau pathology between the two groups in other brain regions assessed. The present study shows that in AD/ALB, the olfactory bulb is nearly equally vulnerable to tau and alpha-synuclein pathology as the amygdala and suggests that neurodegeneration in these two anatomical regions is linked.

A critical reappraisal of current staging of Lewy-related pathology in human brain

Sporadic Parkinson disease (sPD) or brainstem-predominant type of Lewy body (LB) disease, and dementia with Lewy bodies (DLB), the two most frequent alpha-synucleinopathies, are progressive multisystem neurodegenerative disorders with widespread occurrence of alpha-synuclein (AS) deposits in the central, peripheral, and autonomic nervous system. For both LB-related disorders, staging/classification systems based on semiquantitative assessment of the distribution and progression pattern of Lewy-related/AS pathology are used that are considered to be linked to clinical dysfunctions. In PD, a six-stage system (Braak) has been suggested to indicate a predictable sequence of lesions with ascending progression from medullary and olfactory nuclei to the cortex, the first two presymptomatic stages being related to incidental LB disease, stages 3 and 4 with motor symptoms, and the last two (cortical) stages may be frequently associated with cognitive impairment. DLB, according to consensus pathologic guidelines, by semiquantitative scoring of AS pathology (LB density and distribution) in specific brain regions, is distinguished into three phenotypes (brainstem, transitional/limbic, and diffuse neocortical), also considering concomitant Alzheimer-related pathology. Retrospective clinico-pathologic studies, although largely confirming the staging system, particularly for younger onset PD with long duration, have shown that between 6.3 and 43% of the cases did not follow the proposed caudo-rostral progression pattern of AS pathology. There was sparing of medullary nuclei in 7-8.3% of clinically manifested PD cases with AS inclusions in midbrain and cortex corresponding to Braak stages 4 and 5, whereas mild parkinsonian symptoms were already observed in stages 2 and 3. There is considerable clinical and pathologic overlap between PD (with or without dementia) and DLB, corresponding to Braak LB stages 5 and 6, both frequently associated with variable Alzheimer-type pathology. Dementia often does not correlate with progressed stages of LB pathology, but may also be related to concomitant Alzheimer lesions or mixed pathologies. There is no relationship between Braak LB stage and the clinical severity of PD, and the predictive validity of this concept is doubtful, since large unselected, retrospective autopsy series in 30-55% of elderly subjects with widespread AS/Lewy-related pathology (Braak stages 5 and 6) reported no definite neuropsychiatric symptoms, suggesting considerable cerebral compensatory mechanisms. Applying the original criteria to large dementia samples, 49% of positive cases were not classifiable. Therefore, modified criteria for the categorization of Lewy-related pathology were proposed for patients with a history of dementia. The causes and molecular basis of the not infrequent deviations from the current staging schemes of AS pathology in PD and DLB, its relation to the onset of classical parkinsonian symptoms and for the lack of definite clinical deficits despite widespread AS pathology in the nervous system remain to be elucidated.

Systematic appraisal using immunohistochemistry of brain pathology in aged and demented subjects

BACKGROUND/AIMS

Abnormal processing of hyperphosphorylated tau (HPtau), amyloid-beta (Abeta) and alpha-synuclein (alphaS) proteins is considered as causative with regard to the clinical symptoms in age-related neurodegenerative diseases.

METHODS

In this retrospective, postmortem study applying immunohistochemical methodology, we assessed Alzheimer's-disease (AD)-related HPtau and Abeta pathology in 178 subjects with alphaS pathology.

RESULTS

These pathologies were frequently seen concomitantly, i.e. HPtau in 83% and Abeta in 62% of the alphaS-positive cases. Furthermore, the striatum was frequently involved, particularly in subjects with cognitive impairment (65%). The predictive value of widespread HPtau pathology, i.e. stages V-VI, with respect to cognitive impairment was high, since all 18 subjects presenting with this stage were demented. In contrast, the predictive value of widespread alphaS pathology, i.e. stages 5-6 according to Braak's Parkinson disease staging, was debatable. Fifty-three percent of the subjects with widespread alphaS pathology and no or mild AD-related HPtau pathology were cognitively unimpaired. It is noteworthy that striatal Abeta pathology was more often seen in demented subjects independently of HPtau and/or alphaS status.

CONCLUSION

The causative pathology in subjects with clinically diagnosed dementia with Lewy bodies needs to be clarified in future studies.

Clinicopathological outline of dementia with Lewy bodies applying the revised criteria: the Hisayama study

To explore the validity of the criteria for dementia with Lewy bodies (DLB) revised in 2005, we examined community based consecutive autopsy cases. 10.3% of the non-demented subjects and 31.2% of the demented subjects showed the Lewy body pathology. Applying the revised pathological criteria to the 205 demented subjects, the types of LB pathology of 11 cases (5.4%) were brainstem-predominant, 24 cases (11.7%) were limbic type and 24 cases (11.7%) were diffuse neocortical type, although there were many subjects not to fit the criteria exactly. The prevalence of Lewy bodies (LBs) was almost same regardless of gender; however, the extent of the LB pathology among females was more severe than that in males. The likelihood of DLB being modified by concomitant Alzheimer's pathology was as follows: 27 cases (13.2%) showed low likelihood, 16 cases (7.8%) showed intermediate likelihood and 16 cases (7.8%) showed high likelihood. Since the numbers of clinical features of DLB were significantly higher in the pathological intermediate and high likelihood DLB groups than in the low likelihood DLB group or no LB group, both the intermediate and high likelihood groups of DLB should be considered as pathological DLB.

Applicability of current staging/categorization of alpha-synuclein pathology and their clinical relevance

In Parkinson’s disease (PD) and dementia with Lewy bodies (DLB) α-synuclein (αS) pathology is seen that displays a predictable topographic distribution. There are two staging/categorization systems, i.e. Braak’s and McKeith’s, currently in use for the assessment of αS pathology. The aim of these diagnostic strategies in pathology is, in addition to assess the stage/severity of pathology, to assess the probabilities of the related clinical symptomatology i.e. dementia and extrapyramidal symptoms (EPS). Herein, we assessed the applicability of these two staging/categorization systems and the frequency of dementia and EPS in a cohort of 226 αS-positive-subjects. These subject were selected from a large autopsy sample (n = 1,720), irrespective of the clinical presentation, based on the detection of αS-immunoreactivity (IR) in one of the most vulnerable nuclei; in the dorsal motor nucleus of vagus, substantia nigra and basal forebrain. The frequency of αS-IR lesions in this large cohort was 14% (248 out of 1,720). If applicable, each of the 226 subjects with all required material available was assigned a neuropathological stage/category of PD/DLB and finally the neuropathological data was analyzed in relation to dementia and EPS. 83% of subjects showed a distribution pattern of αS-IR that was compatible with the current staging/categorization systems. Around 55% of subjects with widespread αS pathology (Braak’s PD stages 5–6) lacked clinical signs of dementia or EPS. Similarly, in respect to those subjects that fulfilled the McKeith criteria for diffuse neocortical category and displaying only mild concomitant Alzheimer’s disease-related pathology, only 48% were demented and 54% displayed EPS. It is noteworthy that some subjects (17%) deviated from the suggested caudo-rostral propagation suggesting alternative routes of progression, perhaps due to concomitant diseases and genetic predisposition. In conclusion, our results do indeed confirm that current staging/categorization systems can readily be applied to most of the subjects with αS pathology. However, finding that around half of the subjects with abundant αS pathology remain neurologically intact is intriguing and raises the question whether we do assess the actual disease process.

Prevalence and impact of vascular and Alzheimer pathologies in Lewy body disease

Whereas the prevalence and impact of vascular pathology in Alzheimer diease (AD) are well established, the role of vascular and Alzheimer pathologies in the progression of neurodegeneration and cognitive impairment in Parkinson disease (PD) is under discussion. A retrospective clinico-pathologic study of 100 patients with autopsy proven PD (including 44 cases with dementia/PDD) and 20 cases of dementia with Lewy bodies (DLB) confirmed essential clinical (duration of illness, Mini-Mental State Examination/MMSE, age at death) and morphologic differences between these groups; Lewy body Braak scores and Alzheimer pathologies (neuritic Braak stage, cortical Abeta plaque load, and generalized cerebral amyloid angiopathy or CAA) were significantly higher/more severe in DLB and PDD than in PD without dementia. Duration of illness showed no association to any of the examined pathologic parameters, while there was a moderate association between LB scores and neuritic Braak stages, the latter significantly increasing with age. Significant association between cerebrovascular lesions and neuritic Braak stage was seen in PDD but not in PD subjects without dementia. These data suggest an influence of Alzheimer-related lesions on the progression of the neurodegenerative process and, in particular, on cognitive decline in both PDD and DLB. On the other hand, both these factors in PD and DLB appear to be largely independent from coexistent vascular pathology, except in cases with severe cerebrovascular lesions or those related to neuritic AD pathology. Assessment of ApoE genotype in a small number of cases showed no significant differences in the severity of Abeta plaque load and CAA except for much lower intensities in non-demented epsilon3/3 patients. Despite increasing evidence suggesting synergistic reactions between alpha-synuclein (alphaSyn), tau and Abeta-peptides, the major protein markers of both AD and Lewy body diseases, and of both vascular pathology and AD, the molecular background and pathophysiological impact of these pathologies on the progression of neurodegeneration and development of cognitive decline in PD await further elucidation.

Staging of neurofibrillary pathology in Alzheimer's disease: a study of the BrainNet Europe Consortium

It has been recognized that molecular classifications will form the basis for neuropathological diagnostic work in the future. Consequently, in order to reach a diagnosis of Alzheimer's disease (AD), the presence of hyperphosphorylated tau (HP‐tau) and β‐amyloid protein in brain tissue must be unequivocal. In addition, the stepwise progression of pathology needs to be assessed. This paper deals exclusively with the regional assessment of AD‐related HP‐tau pathology. The objective was to provide straightforward instructions to aid in the assessment of AD‐related immunohistochemically (IHC) detected HP‐tau pathology and to test the concordance of assessments made by 25 independent evaluators. The assessment of progression in 7‐µm‐thick sections was based on assessment of IHC labeled HP‐tau immunoreactive neuropil threads (NTs). Our results indicate that good agreement can be reached when the lesions are substantial, i.e., the lesions have reached isocortical structures (stage V–VI absolute agreement 91%), whereas when only mild subtle lesions were present the agreement was poorer (I–II absolute agreement 50%). Thus, in a research setting when the extent of lesions is mild, it is strongly recommended that the assessment of lesions should be carried out by at least two independent observers.

Neuropathological aspects of Alzheimer disease, Parkinson disease and frontotemporal dementia

BACKGROUND

Proteinopathies are a heterogenous group of neurodegenerative disorders, characterized by intra- and extracellular accumulation of abnormal filament proteins.

OBJECTIVE

To describe the neuropathology of specific forms of tauopathies and synucleinopathies, the overlap of morphologic features and molecular interactions.

METHODS

The study uses currently available morphologic criteria of different proteinopathies.

RESULTS

Alzheimer disease (AD) is featured by deposition of beta-amyloid peptides, phosphorylated tau protein (3- and 4-repeat tau) and frequent alpha-synuclein (aSyn) deposits. Lewy body diseases (LBD), such as sporadic Parkinson disease (PD) and dementia with Lewy bodies (DLB), show aSyn-positive deposits in neurons, neurites, glia, and presynaptic terminals, while frontotemporal dementias present tau-positive and tau-negative, ubiquitin- and TDP-43-positive neuronal and glial inclusions. The latter have also been observed in AD, PD, PD dementia and motor neuron disorders. Molecular interactions between major proteins, which may occur within the same brain in various distribution patterns, cause variable phenotypes and mixed pathologies, e.g. AD with aSyn pathology in the brainstem and amygdala, PD and DLB with AD lesions, and frontotemporal dementia with a mixture of various deposits, while others are featured by one principal pathology without other lesions (e.g. tangle-predominant type of dementia, pure PD, brainstem-predominant LBD).

CONCLUSION

Animal models and in vitro studies showing co-occurrence and mutual promotion of fibrillation of these proteins indicate their synergistic interactions in the pathogenesis of these disorders which, at least in part, are genetically influenced.

Empiric refinement of the pathologic assessment of Lewy-related pathology in the dementia patient

Lewy-related pathology (LRP) is a common pathologic finding at autopsy in dementia patients. Recently criteria for categorizing types of LRP in dementia patients were published, though these criteria have yet to be systematically applied to large dementia samples. We examined a large (n = 208) referral-based autopsy sample for LRP, and applied the published criteria for LRP categorization to these cases. We found almost half (49%) of LRP positive cases from this sample were not classifiable. However, modifying the published criteria by reducing the number of regions requiring examination, allowing more variability in LRP severity scores within specific brain regions, and adding an amygdala predominant category permitted classification of 97% of LRP positive cases from the referral-based sample. Application of the modified criteria to an unrelated community-based autopsy sample (n = 226) allowed classification of 96% of LRP positive cases. Modest modifications in the published criteria permit a significantly greater number of dementia cases with LRP to be classified. In addition, this modification allows for more limited sampling of brain regions for classification of LRP. We propose that these modified criteria for the categorization of LRP be utilized in patients with a history of dementia.

Limbic lobe microvacuolation is minimal in Alzheimer's disease in the absence of concurrent Lewy body disease

Microvacuolation is relatively common in the limbic lobe in Lewy body disease (LBD). Similar pathology has also been reported in Alzheimer's disease (AD). Almost all of the studies of microvacuolation in AD, however, antedated the routine application of sensitive immunohistochemical methods to detect Lewy bodies. This raises the possibility that microvacuolation previously reported in AD may have been due to unrecognized LB pathology. To explore this issue, alpha-synuclein immunohistochemistry was used to evaluate a consecutive series of AD as well as cases with mixed AD and LBD (AD/LBD). Independently, the degree of microvacuolation was graded in the entorhinal cortex and the amygdala of the same cases. The results showed that microvacuolation was more common and more severe in AD/LBD than in pure AD cases. In pure AD cases microvacuolation was related to senile plaque density, especially in the amygdala, where many of the neuropil vacuoles were around dense-cored, neuritic plaques. In contrast, in AD/LBD microvacuolation correlated with LB density in the entorhinal cortex and amygdala. These results suggest that microvacuolation has a different pathogenesis in AD and in AD/LBD. Moreover, when prominent microvacuolation is detected in AD, it is imperative to exclude concurrent LBD.

The dorsal motor nucleus of the vagus is not an obligatory trigger site of Parkinson's disease: a critical analysis of alpha-synuclein staging

AIMS

It has been proposed that alpha-synuclein (alpha Syn) pathology in Parkinson's disease (PD) spreads in a predictable caudo-rostral way with the earliest changes seen in the dorsal motor nucleus of the vagus nerve (DMV). However, the reliability of this stereotypical spread of alpha Syn pathology has been questioned. In addition, the comparative occurrence of alpha Syn pathology in the spinal cord and brain has not been closely studied.

METHODS

In order to address these issues, we have examined 71 cases of PD from the UK Parkinson's Disease Society Tissue Bank at Imperial College, London. The incidence and topographic distribution of alpha Syn pathology in several brain regions and the spinal cord were assessed.

RESULTS

The most affected regions were the substantia nigra (SN; in 100% of cases) followed by the Nucleus Basalis of Meynert (NBM) in 98.5%. Fifty-three per cent of cases showed a distribution pattern of alpha Syn compatible with a caudo-rostral spread of alpha Syn through the PD brain. However, 47% of the cases did not fit the predicted spread of alpha Syn pathology and in 7% the DMV was not affected even though alpha Syn inclusions were found in SN and cortical regions. We also observed a high incidence of alpha Syn in the spinal cord with concomitant affection of the DMV and in a few cases in the absence of DMV involvement.

CONCLUSIONS

Our results demonstrate a predominant involvement of the SN and NBM in PD but do not support the existence of a medullary induction site of alpha Syn pathology in all PD brains.

Parkinson's disease: a dual-hit hypothesis

Accumulating evidence suggests that sporadic Parkinson's disease has a long prodromal period during which several non-motor features develop, in particular, impairment of olfaction, vagal dysfunction and sleep disorder. Early sites of Lewy pathology are the olfactory bulb and enteric plexus of the stomach. We propose that a neurotropic pathogen, probably viral, enters the brain via two routes: (i) nasal, with anterograde progression into the temporal lobe; and (ii) gastric, secondary to swallowing of nasal secretions in saliva. These secretions might contain a neurotropic pathogen that, after penetration of the epithelial lining, could enter axons of the Meissner's plexus and, via transsynaptic transmission, reach the preganglionic parasympathetic motor neurones of the vagus nerve. This would allow retrograde transport into the medulla and, from here, into the pons and midbrain until the substantia nigra is reached and typical aspects of disease commence. Evidence for this theory from the perspective of olfactory and autonomic dysfunction is reviewed, and the possible routes of pathogenic invasion are considered. It is concluded that the most parsimonious explanation for the initial events of sporadic Parkinson's disease is pathogenic access to the brain through the stomach and nose - hence the term 'dual-hit'.

Rates of brain atrophy over time in autopsy-proven frontotemporal dementia and Alzheimer disease

Rates of brain loss have been shown to accelerate over time in early Alzheimer disease (AD); however the trajectory of change in frontotemporal lobar degeneration with ubiquitin immunoreactive-changes (FTLD-U) is unknown. This study compared the progression of atrophy over multiple MRI in subjects with autopsy-confirmed AD and FTLD-U. Nine subjects with autopsy-confirmed FTLD-U and nine with autopsy-confirmed AD were identified that had three or more serial MRI. The boundary-shift integral was used to calculate change over time in whole-brain and ventricular volume. A hierarchical regression model was used to estimate the slope of volume change in AD and FTLD-U over time and to estimate differences in the slopes across the subject groups. Whole-brain volume loss did not deviate from a linear rate over time in both AD and FTLD-U subjects, although this may be due to limited sample size. The FTLD-U subjects had a faster rate (23 ml/year) than the AD subjects (10 ml/year). The rate of ventricular expansion accelerated over time. At the point when each subject had a Clinical Dementia Rating Sum-of-Boxes score of 6, the annual rate was 7 ml/year in FTLD-U and 5 ml/year in AD. These rates of change increased by an estimated 1.66 ml/year in FTLD-U and 0.44 ml/year in AD, although these estimates were not significantly different between the two groups. The trajectories of brain and ventricular changes were similar in AD and FTLD-U suggesting that it is independent of pathology, although subjects with FTLD-U show a more rapidly progressive decline.

TDP-43 immunoreactivity in hippocampal sclerosis and Alzheimer's disease

OBJECTIVE

This study aimed to determine the frequency of frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD-U) in the setting of hippocampal sclerosis (HpScl) and Alzheimer's disease (AD) using immunohistochemistry for TAR DNA binding protein 43 (TDP-43), a putative marker for FTLD-U.

METHODS

Initially, 21 cases of HpScl associated with a variety of other pathological processes and 74 cases of AD were screened for FTLD-U with TDP-43 immunohistochemistry. A confirmation study was performed on 93 additional AD cases. Specificity of TDP-43 antibodies was assessed using double-immunolabeling confocal microscopy, immunoelectron microscopy, and biochemistry.

RESULTS

TDP-43 immunoreactivity was detected in 71% of HpScl and 23% of AD cases. Double immunostaining of AD cases for TDP-43 and phospho-tau showed that the TDP-43-immunoreactive inclusions were usually distinct from neurofibrillary tangles. At the ultrastructural level, TDP-43 immunoreactivity in AD was associated with granular and filamentous cytosolic material and only occasionally associated with tau filaments. Western blots of AD cases showed a band that migrated at a higher molecular weight than normal TDP-43 that was not present in AD cases without TDP-43 immunoreactivity.

INTERPRETATION

These results suggest that as many as 20% of AD cases and more than 70% of HpScl cases have pathology similar to that found in FTLD-U. Whether this represents concomitant FTLD-U or is analogous to colocalization of alpha-synuclein and tau in AD, reflecting a propensity for codeposition of abnormal protein conformers, remains to be determined.

TDP-43 in differential diagnosis of motor neuron disorders

Motor neuron disorders are clinically and pathologically heterogeneous. They can be classified into those that affect primarily upper motor neurons, lower motor neurons or both. The most common disorder to affect both upper and lower motor neurons is amyotrophic lateral sclerosis (ALS). Some forms of motor neuron disease (MND) affect primarily motor neurons in the spinal cord or brainstem, while others affect motor neurons at all levels of the neuraxis. A number of genetic loci have been identified for the various motor neuron disorders. Several of the MND genes encode for proteins important for cytoskeletal stability and axoplasmic transport. Despite these genetic advances, the relationship of the various motor neuron disorders to each other is unclear. Except for rare familial forms of ALS associated with mutations in superoxide dismutase type 1 (SOD1), which are associated with neuronal inclusions that contain SOD1, specific molecular or cellular markers that differentiate ALS from other motor neuron disorders have not been available. Recently, the TAR DNA binding protein 43 (TDP-43) has been shown to be present in neuronal inclusions in ALS, and it has been suggested that TDP-43 may be a specific marker for ALS. This pilot study aimed to determine the value of TDP-43 in the differential diagnosis of MND. Immunohistochemistry for TDP-43 was used to detect neuronal inclusions in the medulla of disorders affecting upper motor neurons, lower motor neurons or both. Medullary motor neuron pathology also was assessed in frontotemporal lobar degeneration (FTLD) that had no evidence of MND. TDP-43 immunoreactivity was detected in the hypoglossal nucleus in all cases of ALS, all cases of FTLD-MND and some of cases of primary lateral sclerosis (PLS). It was not detected in FTLD-PLS. Surprisingly, sparse TDP-43 immunoreactivity was detected in motor neurons in about 10% of FTLD that did not have clinical or pathologic features of MND. The results suggest that TDP-43 immunoreactivity is useful in differentiating FTLD-MND and ALS from other disorders associated with upper or lower motor neuron pathology. It also reveals subclinical MND in a subset of cases of FTLD without clinical or pathologic evidence of MND.

Analysis of the adrenal gland is useful for evaluating pathology of the peripheral autonomic nervous system in lewy body disease

Lewy body disease is defined as Lewy body-related neuronal degeneration involving the nigrostriatal system, limbic-neocortical system, and peripheral autonomic nervous system (PANS). We investigated whether the adrenal gland, which is evolutionarily related to sympathetic ganglia and is routinely examined in general autopsy, could be used to assess pathology of the PANS in Lewy body disease. Brains, spinal cords, and adrenal glands from 783 consecutive autopsy cases from a general geriatric hospital were examined immunohistochemically with antiphosphorylated alpha-synuclein antibodies and routine staining. Parkinson disease (PD) with dementia and dementia with Lewy bodies (DLB) were defined using 1996 Consensus Guidelines for DLB and the secondary Lewy body-related alpha-synucleinopathy or amygdala variants using previously established criteria. Lewy body-related alpha-synucleinopathy was found in 207 (26.4%) of 783 cases, with 1 case solely in the adrenal gland. In all 18 PD cases with or without dementia and in 33 of 38 DLB cases, the adrenal gland was involved, but it was spared in all cases of amygdala variants. Our results indicate that the adrenal gland can provide useful information for evaluation of the PANS in Lewy body disease.

Alpha-synuclein pathology in the olfactory pathways of dementia patients

Lewy-type pathology is a characteristic of a number of neurodegenerative disorders, including Parkinson's disease and dementia with Lewy bodies. Thus far, the definitive diagnosis of these dementias can only be confirmed at post-mortem. However, it is known that the loss of smell (anosmia) is an early symptom in patients who develop dementia, and the use of the smell test has been proposed as an early diagnostic procedure. The aim of this study was to understand further the extent of Lewy pathology in the olfactory system of patients with neurodegenerative disorders. Post-mortem tissue from 250 subjects was obtained from the OPTIMA brain bank. Five areas of the olfactory pathway were examined by immunolabelling for alpha-synuclein - a major component of Lewy pathology: the olfactory tract/bulb (n = 79), the anterior olfactory nucleus in the lateral olfactory gyrus (n = 193), the region of olfactory projection to the orbito-frontal cortex (n = 225), the hippocampus (n = 236) and the amygdala (n = 201). Results show that Lewy pathology affects different parts of the olfactory pathways differentially, suggesting a specific pattern of development of pathology. Clinical Parkinson's disease is most likely to be identified if the orbito-frontal cortex is affected, while the diagnosis is less likely if the pathology is restricted to the olfactory bulb or tract. These results suggest that pathology in the olfactory bulb and tract occurs prior to clinical signs of Parkinson's disease. Furthermore, the results presented here provide further evidence supporting the possible value of a smell test to aid the clinical diagnosis of neurodegenerative diseases.