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-Synuclein Pathology in Amygdala of Parkinsonism-Dementia Complex Patients of Guam

From the Center for Neurodegenerative Disease Research and Department of Pathology and Laboratory Medicine,*University of Pennsylvania, Philadelphia, Pennsylvania; and the Departments of Pathology and Psychiatry,
Mt. Sinai School of Medicine, New York, New York
| Abstract |
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-synuclein positive pathology, primarily in the amygdala. We further characterized the tau and
-synuclein pathology in the amygdala of a large series of 30 Chamorros using immunohistochemical and biochemical techniques. Tau pathology was readily detected in both affected and unaffected Chamorros. In contrast,
-synuclein pathology was detected in 37% of patients with PDC but not detected in Chamorros without PDC or AD. The
-synuclein aggregates often co-localized within neurons harboring neurofibrillary tangles suggesting a possible interaction between the two proteins. Tau and
-synuclein pathology within the amygdala is biochemically similar to that observed in AD and synucleinopathies, respectively. Thus, the amygdala may be selectively vulnerable to developing both tau and
-synuclein pathology or tau pathology may predispose it to synuclein aggregation. Furthermore, in PDC, tau and
-synuclein pathology occurs independent of ß-amyloid deposition in amygdala thereby implicating the aggregation of these molecules in the severe neurodegeneration frequently observed in this location.
-Synuclein, a small, highly conserved pre-synaptic protein, is the major constituent of Lewy bodies (LBs) and Lewy neurites as well as the glial cytoplasmic inclusions of multiple system atrophy.18
More recently,
-synuclein positive pathology was identified, primarily in the amygdala, in a variety of disorders with extensive tau pathology including familial AD,19
Downs syndrome with AD,20
neurodegeneration with brain iron accumulation,21-23
as well as up to 60 to 70% of sporadic AD.24,25
In Guamanian PDC patients, LBs have been reported in the substantia nigra8
and, more recently,
-synuclein positive pathology was identified in the amygdala.26
In this study, we further characterized the tau and
-synuclein pathology in the amygdala of a large series of 30 Chamorros patients using both immunohistochemical and biochemical techniques.
| Materials and Methods |
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Amygdala from 30 Chamorros were used in this study. The age, gender, and pathological diagnosis of these patients are given in Table 1
. These included 13 patients with PDC, 3 patients with pre-clinical or early PDC, and 6 patients with PDC plus additional neurological disorder(s) (PDC+) including one patient with PDC/ALS and one patient with early PDC/ALS. The distinction between PDC, PDC/ALS, and ALS is based largely on clinical criteria, ie, the presence of dementia and parkinsonism (PDC), amyotrophy (ALS), or both (ALS/PDC), because spinal cords are not available in the majority of cases. Pre-clinical PDC refers to cases that show widespread tau pathology in the absence of a clinical history of dementia while early PDC refers to similar patients but with mild neurological dysfunction that is insufficient for a clinical diagnosis of PDC. In addition, 3 patients without neurological disease and 5 control patients with a neurological disorder other than PDC were also available.
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The tissues were fixed in 10% formalin, paraffin-embedded, and cut into 6-µm-thick sections. For thioflavin-S staining, rehydrated sections were immersed in 0.05% KMNO4 in phosphate-buffered saline (PBS) for 20 minutes and differentiated in 0.2% K2S2O5/0.2% oxalic acid in PBS. Subsequently, the slides were immersed in 1% thioflavin-S in the dark for 3 minutes and further differentiated in 50% ethanol in PBS, rinsed, and mounted. Immunohistochemistry was performed as previously described using the ABC method (Vectastain ABC kit, Vector Laboratories, Burlingame, CA) and 3,3'-diaminobenzidine (DAB) as chromogen.6,27
The following primary antibodies were used: monoclonal antibodies (mAb) Syn202 (1:20,000) and Syn303 (1:500) to
-synuclein and oxidized
-synuclein, respectively;28,29
mAb to tau included AT8 (1:1000),30,31
PHF1 (1:1000), the generous gift of Peter Davies (Albert Einstein College of Medicine, New York, NY),32
12E8 (1:500),33
T14 (1:3000) and T46 (1:1000);34
polyclonal antiserum 17026 (1:10,000) to recombinant tau,35
and a polyclonal antiserum to glial fibrillary acidic protein (GFAP; 1:10,000) was purchased from Dako Corp. (Carpinteria, CA). Tau and
-synuclein pathology was assessed semiquantitatively as absent (-), mild, (1+) moderate (2+) or marked (3+) based on the number of tau or
-synuclein-positive inclusions in the area of highest density. For tau immunostaining, mild (1+),
2 inclusions/10x field; moderate (2+), 2 to 10 inclusions/10x field; and marked (3+)
, 10 inclusions/10x field. For
-synuclein, mild, 1 inclusion/10x field; moderate, 2 to 4 inclusions/10x field; and marked, > 4 inclusions/10x field (Figure 2)
. Double-labeling immunofluorescence studies were performed by incubating sections with the antibodies PHF1 and GFAP. Following extensive washes, sections were labeled using Alexa Fluor 488 and 594 conjugated secondary antibodies (Molecular Probes, Eugene, OR) and coverslipped with Vectashield-DAPI-mounting medium (Vector Laboratories). Sections containing
-synuclein-positive LBs were double-stained with Congo red,36
dehydrated and coverslipped with Cytoseal (Stephens Scientific, Kalamazoo, MI). The sections were viewed in a Nikon FXA microscope equipped with bright-field and fluorescence light sources. The Congo red fluorescence was observed using a Texas red filter set. From the double-stained preparations both bright-field and fluorescent images were obtained from the same field using a Coolsnap camera (BioVision Technologies, Exton, PA). For publication the Congo red image was converted to black and white, brightened, and superimposed onto the bright-field image of the DAB stain in Adobe Photoshop (Adobe Systems Incorporated, San Jose, CA). The images were printed on a Fuji Pictography 3000 printer (Fuji Photo Film Co., Ltd., Tokyo, Japan).
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-Synuclein Protein Extraction
Fresh, frozen brain tissue from the amygdala of seven Guam PDC patients were used for biochemical analysis. In addition, brain tissue from non-Chamorro normal and LB variant of AD patients was obtained through the University of Pennsylvania Alzheimers Disease Center. Heat-stable soluble tau and
-synuclein proteins were extracted as described previously.37
Insoluble tau and
-synuclein proteins were extracted as described.19,38
Briefly, the insoluble pellets were homogenized in 1 mol/L sucrose in RAB buffer (0.1 mol/L morpholineethane sulfonic acid, 1 mmol/L EGTA, 0.5 mmol/L MgSO4, pH 7.0) and centrifuged at 50,000 x g to remove myelin. The resulting pellets were extracted with 1 ml/g RIPA buffer (50 mmol/L Tris, 150 mmol/L NaCl, 1% NP40, 5 mmol/L EDTA, 0.5% sodium deoxycholate, and 0.1% SDS, pH 8.0) and centrifuged at 50,000 x g to generate RIPA-soluble samples. The RIPA-insoluble fractions were subsequently extracted with 1 ml/g 70% formic acid and disrupted with sonication. Formic acid was evaporated in an Automatic Environmental SpeedVac system (Savant Instruments, Holbrook, NY). The dried pellets were resuspended in 1 ml/g sample buffer and centrifuged at 50,000 x g for 30 minutes. Where indicated, tau was dephosphorylated by dialyzing a sample of the soluble or insoluble fraction into 50 mmol/L Tris, 0.2 mmol/L EDTA (pH 8.0) and treatment with Escherichia coli alkaline phosphatase (Sigma, St. Louis, MO) at 67°C for 1 hour. For Western blot analysis, nitrocellulose replicas were prepared from 7.5% or 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) slab gels containing either the soluble, RIPA-soluble or insoluble protein samples and probed with antibodies for tau or
-synuclein as indicated. For all Western blots, 10 µl of heat-stable soluble, RIPA-soluble or -insoluble fractions was used corresponding to 10 mg of the extracted amygdala. mAb were detected with horseradish peroxidase-conjugated anti-mouse IgG (Santa Cruz Biotechnologies). Immunoreactive proteins were revealed used the ECL chemiluminescence (NEN Life Science, Boston, MA) and/or DAB detection systems.
| Results |
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-synuclein-positive LBs and neurites was identified in the amygdala (Table 1
-Synuclein positive pathology was not identified in the amygdala of any of the Chamorro patients with ALS, preclinical PDC, or control Chamorro patients with the exception of one AD patient who showed a low density of
-synuclein pathology (Figure 2
-synuclein pathology, the NFTs were frequently seen as wisps of fibrillar tau immunoreactivity at the periphery of the LB (Figure 3)
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-synuclein pathology, we performed Western blot analysis of both soluble and insoluble (formic acid extractable) fractions from the amygdala of Guam PDC patients. Fresh, frozen tissue from the amygdala of the hemispheres contralateral to those used for immunohistochemical analysis was available from 7 of the 19 patients with the pathological diagnosis of PDC or PDC+, including 3 of the patients with
-synuclein positive pathology detected by immunohistochemistry. In sequential extractions with both RIPA buffer (1% NP40/0.1% SDS) and 70% formic acid, insoluble tau was composed of four major protein bands ranging from 60- to 72-kd (Figure 4A)
-synuclein revealed formic acid extractable, high molecular weight, insoluble aggregates similar to that observed in LBVAD in two of the three Chamorro patients with
-synuclein pathology detected by immunohistochemistry (Figure 4C)
-synuclein pathology as well as the non-Chamorro normal control brain lacked the high molecular weight aggregates of
-synuclein. As with tau, the relative quantity of insoluble, aggregated
-synuclein was highly variable. Moreover, both affected and control brains demonstrated abundant soluble synuclein protein (Figure 4C)
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| Discussion |
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-synuclein pathology in 5 of 13 PDC patients primarily within the amygdala. In the present study, we found
-synuclein pathology in the form of both LBs and Lewy neurites in the amygdala of 37% of PDC and PDC+ Chamorro patients. LBs were not detected in the amygdala in any of the patients with ALS and only 1 of 8 Guamanian control patients, ranging in age from 41 to 86 years. This Chamorro was an 86-year-old female diagnosed with AD. In contrast, similar to previous reports, tau pathology was found in six of these control Chamorros.15,40
Thus, unlike NFTs, LBs do not occur in older Chamorros without PDC or other synucleinopathies. Furthermore, it is argued that PDC and ALS of Guam are distinct disease entities, rather than a single disorder with different clinical and pathological features.2
The absence of
-synuclein pathology in all of the patients with ALS might support the two-disease hypothesis. However, the limited number of cases with ALS and the identification of synuclein pathology in only a subset of PDC patients preclude this conclusion until additional cases are analyzed.
-Synuclein pathology has been identified primarily in the amygdala in several disorders with prominent tau pathology including sporadic AD,24,25
familial AD,19
Downs syndrome with AD,20
and neurodegeneration with brain iron accumulation.21-23
While there are rare reports of coexistent Parkinsons disease/dementia with LBs and tau disorders such as progressive supranuclear palsy and corticobasal degeneration,41-45
Guam PDC represents the first example of a primary tauopathy with synuclein aggregation in a large subset of patients. In all of these disorders with both
-synuclein and tau pathology there is often co-localization of the aggregates within at least a subset of neurons in the amygdala.23,26,46-49
It is unclear whether the coexistence of both pathologies within the same neuron represents a chance event in a highly affected brain region or if tau and synuclein interact to promote their mutual aggregation. However, the selective vulnerability of the neurons within the amygdala to develop both LBs and NFTs probably plays a mechanistic role in the severe neurodegeneration often observed in the amygdala. The reason for the convergence of tau and
-synuclein pathology in the neurons of the amygdala remains largely unknown. One recent report suggests an interaction between these two molecules whereby
-synuclein binds directly to tau and stimulates the phosphorylation of tau by protein kinase A.50
The authors proposed that by modulating the phosphorylation state of tau, this kinase affects the stability of axonal microtubules, but it is unclear how this would lead to the aggregation of both tau and
-synuclein.
The neurofibrillary pathology in Guam ALS/PDC is composed of insoluble, hyperphosphorylated tau that is similar biochemically and ultrastructurally to what is observed in AD.5,6
In this study, we also characterized tau and
-synuclein pathology biochemically. We detected a pattern of insoluble tau similar to that of AD in the amygdalas of Guam PDC patients which was composed of all six tau isoforms and was hyperphosphorylated and heavily aggregated. In addition, in the brains of 2 of 3 patients with
-synuclein pathology detected by immunohistochemistry, we observed aggregated
-synuclein similar to that observed in LBVAD and other synucleinopathies.19,51
It is unclear why case 21 which showed evidence of
-synuclein pathology by immunohistochemistry did not show biochemical evidence of insoluble aggregated synuclein. However, the amygdala tissue obtained for the biochemical analysis was procured from the hemisphere contralateral to that used for immunohistochemical analysis and it is not known whether there was
-synuclein pathology in this hemisphere. Furthermore, similar to tau, the amount of insoluble
-synuclein detected is highly variable and may simply be below the level of detection of the Western blot.
Despite the similarities of both the biochemical and immunohistochemical characteristics of tau and
-synuclein to that observed in AD and LBVAD, in Guam PDC, both proteins aggregate independent of ß-amyloid suggesting a common disease mechanism in all of these disorders. However, a recent study in transgenic mice suggests that Aß deposits may augment LB formation.52
This notwithstanding, it is clear that further studies are needed to elucidate mechanisms of aggregation of these molecules and facilitate an understanding of their role in the neurodegenerative process.
| Acknowledgements |
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| Footnotes |
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Supported by National Institute of Health postdoctoral training grant T32 AG00255 (to M.S.F.) and by grants from the National Institute of Aging of the National Institutes of Health, the Dana Foundation, and the Alzheimers Association.
V.M.-Y.L. is the John H. Ware third Chair of Alzheimers disease research at the University of Pennsylvania.
Accepted for publication February 4, 2002.
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