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Short Communication |
Proteins in Argyrophilic Grain Disease, Alzheimers Disease, and Picks Disease




From the Department of Pathology and Laboratory Medicine,* Center for Neurodegenerative Disease Research, and the Department of Clinical Neuroanatomy,
J. W. Goethe University, Frankfurt, Germany; the Department of Neurology,
and the Institute of Aging,
University of Pennsylvania, Philadelphia, Pennsylvania
| Abstract |
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-positive lesions known as argyrophilic grains located predominantly in limbic brain regions in the absence of other diagnostic neuropathologies, the biochemical correlates of argyrophilic grains in gray and white matter have not been reported. Thus, we analyzed insoluble (pathological)
proteins in five argyrophilic grain disease brains in comparison with those seen in Alzheimers disease and Picks disease. Analyses of separately dissected gray and white matter samples from various cortical regions revealed that pathological
in argyrophilic grain disease was confined primarily to mediotemporal neocortical gray and adjacent white matter, and also to the allocortex, amygdala, and hippocampus. The amounts of sarcosyl-insoluble
in all five cases were substantially lower than in Alzheimers disease and Picks disease, but the amounts of sarcosyl-insoluble
in white matter were higher or comparable to that detected in gray matter from the same region, which distinguishes argyrophilic grain disease from Alzheimers disease. The banding patterns of
isoforms in argyrophilic grain disease varied: in three cases they were similar to Alzheimers disease, but in two other cases, 4 microtubule binding repeat (4R)
predominated, which distinguishes argyrophilic grain disease from classical Picks disease. The differences between these three diseases were re-enforced by the predominance of straight
filaments from argyrophilic grain disease brains. Thus, we conclude that argyrophilic grain disease is a distinct tauopathy characterized by prominent accumulation of argyrophilic grains in limbic brain regions in association with the characteristic
biochemical and ultrastructural profile reported here.
antibodies similarly to filamentous
inclusions in AD9,10
and other tauopathies.11
The presence of argyrophilic glial cytoplasmic inclusions in AGD and the presence of AGs in other neurodegenerative disorders, including Picks disease (PiD), progressive supranuclear palsy,12,13
corticobasal degeneration, multiple system atrophy,14,15
and motoneuron disease15-17
suggests that AGs may co-occur with other pathologies.16,18
Nonetheless, in a small percentage of dementia patients (usually older than 65 years of age), AGs are the overwhelmingly predominant neuropathological lesions, thereby suggesting that AGD is a distinct neurodegenerative disorder.5,16,19
However, the mechanism(s) underlying the formation of AGs is poorly understood, and biochemical analyses of the abnormal
proteins gray and white matter of this tauopathy have not been reported.
Thus, we characterized pathological
biochemically in frozen brain tissue from five AGD cases and compared the brain region-specific distribution of
pathology and biochemical
profile in AGD with those seen in AD and PiD.
| Materials and Methods |
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Frozen brain samples from five patients with neuropathologically diagnosed AGD, two with AD, and two with PiD were obtained through the German Brain Bank Brain-Net (Munich Institute for Neuropathology) (cases 1 to 4) and The Center for Neurodegenerative Disease Research, University of Pennsylvania (cases 5 to 9). Demographic data and other information on these cases are summarized in Table 1
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Fresh autopsy-derived brain tissue was fixed in neutral buffered formalin, paraffin-embedded, cut into 6-µm sections and processed as described elsewhere.20 Additionally, frozen tissue from the area adjacent to the regions used for biochemical analysis was fixed in neutral buffered formalin and processed similarly to fresh-fixed material. Phosphorylation-dependent monoclonal antibodies (mAbs) PHF1 (1:500, a gift from Dr. P. Davies) were used for neuropathological evaluation.
Biochemical and Western Blot Analysis
Biochemical analyses of
proteins in different brain regions were performed in five AGD cases and in one AD case using cortical gray and underlying white matter that were separately dissected and processed as described previously.20-23
Frozen brain samples from frontal, occipital, temporal, parietal, occipital lobes, and cerebellum were used for the regional analysis of
pathology. Also, tissue from the hippocampus, amygdala, and entorhinal allocortex was analyzed in cases 1, 3, and 4. Sarcosyl-insoluble
samples were prepared, and the
isoform profiles therein were examined after enzymatic dephosphorylation using Escherichia coli alkaline phosphatase (Sigma Chemical Co., St. Louis, MO) as described22-24
and were resolved on 7.5% sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Six recombinant human brain
isoforms were used as a standard for the Western blot studies including quantitative analysis of
isoforms using a mixture of phosphorylation-independent
mAb, Tau14 (1:3000; N-terminal) and Tau46 (1:1000; C-terminal). Mouse 125I-IgG was used as a secondary detection antibody.22,23
Final data were presented as a ratio 4R:3R (Table 1)
.
Electron Microscopy of Isolated Filaments
Dispersed
filaments were prepared from separately dissected temporal cortical gray and white matter (case 2), adsorbed on carbon-coated 400-mesh grids, and stained with 0.4% uranyl acetate as described.11,25
Electron photomicrographs were taken at a nominal magnification of x120,000. Immunoelectron microscopy was performed on similar samples and probed with phosphorylation-dependent antibodies to
(PHF1, 1:10). Goat anti-mouse antibodies conjugated to colloidal gold (10-nm diameter, 1:20; Amersham) were used as a secondary antibody. Negative staining with 1% uranyl acetate in 100% methanol was performed and grids were examined with a JEM1010 electron microscope at 80 kV.
Sequential Extraction of
Proteins
Selected brain areas were used for the sequential extraction of
proteins using buffers with increasing abilities to solubilize proteins. Each extraction step was repeated two times, samples were spun at 45 K for 30 minutes at 4°C, supernatants were collected and subjected to Western blot analysis. The following sequential series of solubilizing buffers with a mixture of protease inhibitors were used for extraction:11
1) buffer A (0.75 mol/L NaCl, 50 mmol/L Tris buffer, pH 7.4, 2 mmol/L ethylenediaminetetraacetic acid; 2) 1% Triton in buffer A; 3) RIPA buffer (0.1% SDS, 1% Nonidet P-40, 0.5% sodium deoxycholate, 2 mmol/L ethylenediaminetetraacetic acid, 150 mmol/L NaCl, 50 mmol/L Tris buffer, pH 8.0); 4) 2% SDS; 5) 70% formic acid. Because of differences in the amount of extraction buffer used in each step, protein concentrations were adjusted in samples prepared under similar conditions.
| Results |
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Immunocytochemical Findings
Neuropathological evaluation of five AGD cases revealed a variable distribution and abundance of AGs in selected brain areas. The highest density of AGs was found throughout CA1 of the hippocampus and in the amygdala, as well as in mediotemporal and entorhinal deep cortical areas and white matter (Figure 1)
. Coiled bodies were also notably present in deep cortical layers and white matter. Mild AD pathology (eg, sparse tangles and neuropil threads) was present in all cases, thereby supporting the observations by others that AGs frequently occur with a low abundance of other
lesions in AGD, and that cases of AGD with AGs in the complete absence of other brain lesions are very rare.10,16,19
The distribution and the intensity of neuritic changes corresponded to Braak stages I to III.2
Senile plaques were unremarkable in all AGD cases in densities resembling plaque distribution found in nondemented elderly controls rather than those in AD.
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Proteins
To analyze the distribution of pathological
in AGD and to assess the
isoform composition in this tauopathy, we conducted brain region-specific analysis of sarcosyl-insoluble
proteins in multiple brain regions in separately dissected gray and white matter samples. The amount of sarcosyl-insoluble
was variable between the cases and different brain regions (Figure 2A)
. Pathological
in cases 1, 4, and 5 was confined primarily to the temporal lobe in both gray and white matter, whereas frontal, parietal, and occipital regions had relatively sparse of pathology. Interestingly, although the
pathology in cases 2 and 3 was mild overall, it was restricted predominantly to the white matter. As expected, based on immunohistochemical analysis of the adjacent tissue, the amount of sarcosyl-insoluble
in the amygdala, entorhinal allocortex, and hippocampus was substantially higher than in other cortical areas (cases 3 and 4). Insoluble
proteins in low quantities also were detected in brain regions where sparse tangles and occasional treads, but not AGs, were found by neuropathological examination. The distribution and amount of sarcosyl-insoluble
in all AGD cases were notably different from AD. Whereas in AGD pathological
was detected only in selected brain regions, abundant sarcosyl-insoluble
was present in gray matter of all cortical areas in AD cases.
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isoforms were comprised of a mixture of 3R- and 4R-
in all five AGD cases similar to AD (Figure 2A)
ratio is
1,22
a preponderance of 4R-
isoforms (4R-0N and 4R-1N) in the mediotemporal and entorhinal regions was evident in cases 3 (4R:3R = 1.2:1), 4 (2.2:1), and 5 (1.9:1).
Electron Microscopy of Isolated
Filaments
The electron microscopy of tissue sections from AGD brains described by others1,5,10,18
revealed that AGs consist of 9- to 19-nm straight
filaments. To further characterize pathological
in AGD, we isolated dispersed
filaments from sarcosyl-insoluble fractions of the separately dissected temporal gray and white matter samples that were used for the biochemical studies of case 2 (Figure 2B)
. In these preparations straight
filaments were predominant structures (width,
9 to 22 nm), but paired helical filament (PHF)-like structures similar to those found in AD also were detected in low quantities only in the gray matter. The phosphorylation-dependent mAb PHF1 decorated the entire length of filaments isolated from both gray and white matter. A subset of PHF1-negative thin straight filaments (width,
9 to 10 nm) was also detected in the preparation from the white matter thereby suggesting heterogeneity of filaments in AGD.
Sequential Extraction of
Proteins
Sarcosyl-insoluble
proteins represent a substantial fraction of the total extractable
pool and are commonly used to characterize the distribution of
pathology throughout the brain.11,23
To further characterize pathological
proteins in AGD and to compare it with AD and PiD, we conducted studies of a wide spectrum of
proteins ranging from soluble to very insoluble species using a graded sequential series of buffers containing detergents or acids with an increasing ability to solublize proteins. To ensure the completeness of extraction, each step was repeated twice. The amounts of soluble
extracted from separately dissected samples of gray and white matter with 0.75 of mol/L NaCl (buffer A) and 1% Triton X-100 were comparable in different cases (Figure 3)
. The more insoluble
proteins (ie, those extracted with RIPA buffer) were detected only in two PiD cases, but these species were below the level of detection by Western blot methods in AD and AGD. Further extractions of samples with 2% SDS and 70% formic acid recovered the most highly insoluble
proteins in variable amounts. Although the amount of SDS-soluble
in all five AGD cases was variable and substantially lower than in AD and PiD, formic acid extracts contained comparable amounts of insoluble
in all cases. Interestingly, in three (cases 2 to 5) of five AGD brains, highly insoluble
species were detected in the formic acid extracts, and in cases 2 and 4, high-molecular weight
-immunopositive aggregates were evident in the upper portion of the gels (arrows) consistent with a pool of formic acid resistant or insoluble
. Also, a banding pattern of
proteins in SDS-soluble fractions of AD brains was represented by a typical triplet of 69-, 64-, and 60-kd bands similar to a sarcosyl-insoluble
pattern, whereas in PiD and AGD only two bands of 69 and 64 kd were evident in both SDS and formic acid extracts.
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| Discussion |
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-positive AGs within the limbic system of elderly demented individuals,2,5,6,26
biochemical analysis of
proteins has been reported only recently in several AGD cases.27
Analysis of
proteins in five AGD brains reported here determined the pathological
profiles in this tauopathy. Brain region-specific analyses of sarcosyl-insoluble fractions from separately dissected gray and white matter samples from various cortical regions revealed that pathological
in AGD was confined primarily to mediotemporal cortical gray and adjacent white matter, and also to entorhinal cortex, amygdala, and hippocampus.
The amounts of sarcosyl-insoluble
in all five AGD cases were substantially lower than those in AD and PiD. The abundance of
-positive AGs usually correlates with advancing age and disease severity,2,28
and there is some evidence that AGs can occur without other neurodegenerative changes or neuropsychological impairments.16,19
In our study we found no obvious correlation between the amount of
pathology and progression of dementia in all AGD cases. Interestingly, the most severe burden of AGs in our AGD cases was found in a 54-year-old patient (case 5) with clinical symptoms of frontotemporal dementia with motor neuron disease. Although the overall
pathology in AGD was lower than in AD and PiD, the amount of sarcosyl-insoluble
in AGD white matter was higher or comparable to that detected in gray matter from the same region. This distinguishes AGD from AD (wherein there is little or no white matter
pathology), and these data support the notion that
-positive glial inclusions are major neuropathological lesions in AGD subcortical white matter.
Notably, similar to AGD, white matter
lesions also distinguish PiD, progressive supranuclear palsy, and corticalbasal degeneration from AD.11,29-31
Although the banding patterns of
isoforms in AGD varied, in some cases they were similar to AD, whereas in other cases or brain regions, 4R-0N and 4R-1N
isoforms were overrepresented.
Ultrastructural analyses of
filaments have been widely used to characterize
lesions in tauopathies such as FTDP-17,23,32-35
progressive supranuclear palsy, corticalbasal degeneration,36,37
and PiD.11,38-40
Isolated dispersed
filaments from the AGD brain described here were straight with only occasional PHF-like structures present. Moreover, we used a sequential extraction approach24
to analyze the profile of abnormal
proteins in AGD, and showed that there was no significant difference between the banding pattern of normal
in soluble fractions among cases, although the amount of
protein was variable as described in other tauopathies.20
Although the amount of SDS-extractable
from gray and white matter was low in AGD, the amount of highly insoluble
species in formic acid extracts of four of five AGD cases was comparable to that in AD and PiD cases. Interestingly, variable amounts of high-molecular weight
-positive aggregates were evident in formic acid fractions mostly in the white matter samples from three AGD cases, and this is in concordance with our observation that sarcosyl-insoluble
was also found predominantly in the white matter of different brain regions. The differential
solubility reported for the first time in this study of AGD might provide additional information for understanding the mechanisms that lead to the formation of heterogeneous
inclusions in different tauopathies, but further studies are needed to elucidate the role of abnormal
and AGs in the pathogenesis of AGD.
| Acknowledgements |
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| Footnotes |
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Supported by the National Institute on Aging (grants AG17586 to V. M.-Y. L. and AG 10124 to J. Q. T.).
V. Y.-M. L. is the John H. Ware, III, Professor of Alzheimers Disease Research at the University of Pennsylvania.
Accepted for publication July 23, 2002.
| References |
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