Saburo Yagishita

Distinct isoforms of tau aggregated in neurons and glial cells in brains of patients with Pick's disease, corticobasal degeneration and progressive supranuclear palsy

Abstract. We investigated isoform composition of aggregated tau protein in brains with Picks disease (PiD), corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) by immunoblot analysis of sarkosyl-insoluble fractions of brain homogenates. We also examined the adjacent brain tissues immunohistochemically with a rabbit antibody, Ex10, which specifically recognizes exon 10 of tau. The Ex10 recognizes tau isoforms with four microtubule-binding repeats (4Rtau) but not those with three microtubule-binding repeats (3Rtau). Sarkosyl-insoluble tau from the brains of patients with CBD and PSP consisted of 4Rtau. Insoluble tau from the PiD brains contained both 3Rtau and 4Rtau, where 3Rtau predominated over 4Rtau. In brain tissues of CBD and PSP, Ex10 immunostained all neuronal and glial tau-positive structures. They included pre-tangles, astrocytic plaques, tuft-shaped astrocytes, and oligodendroglial coiled bodies. In PiD brains, astrocytic inclusions were also positive for 4Rtau. However, the majority of, if not all, Pick bodies and oligodendroglial tau inclusions were negative for 4Rtau. Such results suggest that, in neurons and oligodendroglia, tau isoforms involved in the pathological processes differ between CBD/PSP and PiD, and are thus disease specific. This contrasts with the astrocytic tau isoforms that accumulate similarly in all three disorders.

Astrocytic plaques and tufts of abnormal fibers do not coexist in corticobasal degeneration and progressive supranuclear palsy

Abstract Corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) are characterized by their unique clinical features and neuronal pathology. Although astrocytic plaques and tufts of abnormal fibers have been suggested to be specific histopathologic markers, recent studies have revealed significant clinicopathologic overlap between CBD and PSP. Based on the distinctive camera lucida profile of astrocytic inclusions on Gallyas-Braak silver staining, we found that astrocytic plaques and tufts of abnormal fibers did not coexist in the same patient among 30 cases of clinically diagnosed CBD, PSP and atypical Parkinson’s disease. Using Tau immunohistochemistry it was difficult to verify the absence of tufts of abnormal fibers. A morphometric analysis revealed that the two groups classified by the presence or absence of astrocytic plaques and tufts of abnormal fibers exhibited significant differences in the density of ballooned neurons and neurofibrillary tangles and degeneration of the subcortical nuclei. Assessment using the NINDS neuropathologic criteria revealed that the cases with astrocytic plaques and tufts of abnormal fibers closely correspond to CBD and typical PSP, respectively. In addition, the cases lacking either of these two astrocytic inclusions had atypical PSP according to the NINDS criteria, and were associated with novel tau-positive astrocytes (spiny astrocytes). We thus conclude that astrocytic plaques and tufts of abnormal fibers are highly characteristic structures for CBD and typical PSP, respectively. We emphasize the importance of strict differentiation between different astrocytic inclusions not only for diagnosis, but also for further studies for elucidation of their role in the disease mechanisms of CBD and PSP.

Neuronal intranuclear inclusions in spinocerebellar ataxia type 2: triple-labeling immunofluorescent study

Spinocerebellar ataxia type 2 (SCA2) is associated with an expansion of CAG/polyglutamine-repeat of a gene of unknown function. We performed an immunohistochemical study to identify the immunolocalization of the disease protein ataxin-2 in normal and SCA2 patients. Although normal and expanded ataxin-2 were ubiquitously localized to the cytoplasm of neurons, ubiquitinated intranuclear inclusions were observed selectively in 1-2% of neurons of affected brain regions except the cerebellum. Triple-labeling immunofluorescence revealed that ataxin-2, expanded polyglutamine and ubiquitin were colocalized to these neuronal intranuclear inclusions (NIs), indicating that SCA2 shares morphological characteristics common to other neurological disorders associated with an expansion of CAG/polyglutamine-repeat. Lack of NIs in the cerebellar lesion, however, suggests the discrepancy between formation of NIs and neuronal degeneration in SCA2.

Identification of amino‐terminally cleaved tau fragments that distinguish progressive supranuclear palsy from corticobasal degeneration

Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are neurodegenerative diseases that are characterized by intracytoplasmic aggregates of hyperphosphorylated tau with four microtubule‐binding repeats. Although PSP and CBD have distinctive pathological features, no biochemical difference in aggregated tau has been identified. In this study, we examined the brains of eight patients with PSP, six patients with CBD, and one atypical case with pathological features of both CBD and PSP. On immunoblots of sarkosyl‐insoluble brain extracts, a 33kDa band predominated in the low molecular weight tau fragments in PSP, whereas two closely related bands of approximately 37kDa predominated in CBD. Immunoblots of the atypical case showed both the 33kDa band and the 37kDa doublet. Protein sequencing and immunochemical analyses showed that the 33kDa band and the 37kDa doublet consisted of the carboxyl half of tau with different amino termini. These results suggest that, despite the identical composition of tau isoforms, different proteolytic processing of abnormal tau takes place in these two diseases. Such a biochemical divergence may be related to the neuropathological features of these diseases.

The distribution and dynamic density of oligodendroglial cytoplasmic inclusions (GCIs) in multiple system atrophy: a correlation between the density of GCIs and the degree of involvement of striatonigral and olivopontocerebellar systems

Abstract The distribution and dynamic density of oligodendroglial cytoplasmic inclusions (GCIs) were studied based on 30 cases of multiple system atrophy (MSA), including striatonigral degeneration (SND), olivopontocerebellar atrophy (OPCA) and Shy-Drager syndrome. GCIs were widely spread throughout the central nervous system, including the striatonigral and olivopontocerebellar systems. Inclusion-bearing cells appeared to be oligodendrocytes which usually had larger and lighter nuclei than those of normal-looking oligodendrocytes. The distribution of GCIs was similar in all cases, irrespective of the degrees of OPCA and SND, but the frequency of GCIs varied from case to case. We classified all the cases into two categories based on the degree of neuropathological changes of SND (mild and severe) and, independently, into three groups based on that of OPCA (minimal, moderate, and severe), i.e., a total of six groups. An association between the frequency of GCIs and the severity of the lesions was obtained. For example, many GCIs exist in the cerebellar white matter in the cases in which OPCA was not histologically confirmed. More GCIs were seen in the cases with moderate OPCA. In the cases with severe OPCA, GCIs were rarer and smaller, in proportion to the devastation of fibers; no GCIs were seen in the cases with more severe OPCA. The incidence of GCIs showed a positive correlation to the severity of OPCA but not that of SND in the corticopontine tracts, of both OPCA and SND in the pyramidal tracts, and of SND but not of OPCA in the pencil fibers of the putamen. It is suggested that GCIs may represent either a change synchronous with neuronal degeneration or a phenomenon preceding neuronal changes, especially in the cerebellar white matter. Thus, they may represent the early changes in MSA and may be a useful neuropathological hallmark for diagnosis of MSA, even in cases with minimal OPCA and SND.

Non-expanded polyglutamine proteins in intranuclear inclusions of hereditary ataxias--triple-labeling immunofluorescence study.

Abstract. Neuronal intranuclear inclusions (NIIs) found in CAG/polyglutamine-expansion disorders contain both expanded polyglutamine and the gene product without the CAG repeat. The gene product containing expanded polyglutamine has, therefore, been considered to be a major component of NIIs. In this immunohistochemical study, we showed recruitment of ataxin-2, ataxin-3 and TATA box binding protein (TBP) into NIIs of the pontine neurons of spinocerebellar ataxia type (SCA) 1, SCA2, SCA3 and dentatorubral-pallidoluysian atrophy brains. Triple-labeling immunofluorescence demonstrated colocalization of ataxin-2 and ataxin-3 in NIIs containing expanded polyglutamine, irrespective of the disease examined. These in vivo findings indicate that polyglutamine proteins recruited into NIIs are not restricted to their expanded form. Among these proteins, recruitment of ataxin-2 was least frequent in every case examined, suggesting that the rate of recruitment partly depends on the protein transported into NIIs. Because other proteins lacking polyglutamine motif were not detected in NIIs, it is suggested that the presence of polyglutamine is a prerequisite for these proteins to be recruited into nucleus and to form NIIs. Interaction between expanded and non-expanded polyglutamine may play roles during these processes.

Argyrophilic glial intracytoplasmic inclusions in multiple system atrophy: immunocytochemical and ultrastructural study

SummaryArgyrophilic intracytoplasmic inclusions in oligodendrocytes (AGCIs) were seen in all of 15 cases of multiple system atrophy (MSA), and none in other neurodegenerative diseases, including 9 cases of Menzel-type olivopontocerebellar atrophy and 4 cases of Josephs disease. The inclusions were widespread, not only in the olivopontocerebellar and striatonigral systems but also among fibers connecting their affecting lesions of MSA. Immunohistochemically, they were closely associated with tau, tubulins and microtubuleassociated protein 5. Ultrastructurally, they consisted of 30-to 50-nm filaments (not tubules) and electron-dense granules, in varying proportions, and their formation is discussed. The specific occurrence of AGCIs could be a key to approach the pathogenesis of MSA.

Clear cell ependymoma. A histological variant with diagnostic implications.

Four cystic brain tumours, one from the frontal lobe, one in the third ventricle and two in the cerebellum, were studied histologically including immunostaining and electron microscopy. Anatomically, all the tumours were located within or adjacent to the ventricular system. By light microscopy, the tumours had a largely honeycomb pattern and were made up of clear cells. Some of the clear cells showed positive for GFAP. Leu 7, Factor VIII and NSE were negative. Electron microscopy of the areas with clear cells revealed densely packed polyhedral cells with clear cytoplasm. They had well developed intercellular junctions, microvilli and some cilia which confirmed their ependymal derivation. Perivascular pseudorosettes or papillary features were only seen in limited areas, where GFAP was strongly positive in the tumour cell processes. As these tumours mimic oligodendroglioma and cerebellar haemangioblastoma, they are called as “clear cell ependymoma” to obviate such errors in diagnosis.

Paradoxical absence of nuclear inclusion in cerebellar Purkinje cells of hereditary ataxias linked to CAG expansion

Degeneration of cerebellar cortex is one of the principal features of hereditary ataxias linked to expansion of CAG repeat. In an attempt to clarify possible correlation between neuronal depletion and neuronal intranuclear inclusions, both triggered by the pathological expansion of CAG repeat, cerebellar sections from SCA1, SCA2, SCA3, and DRPLA cases were immunostained with anti-ubiquitin or anti-expanded polyglutamine antibody (1C2) and were screened for the presence of neuronal intranuclear inclusions. Although the degree of cerebellar degeneration varied greatly, cerebellar Purkinje cells were uniformly characterised by the absence of neuronal intranuclear inclusion. Complete absence of neuronal intranuclear inclusion in Purkinje cells is apparently paradoxical and hardly explained if neuronal intranuclear inclusion formation is positively correlated to a mechanism accelerating neuronal death. It may, otherwise, suggest an intrinsic link between neuronal intranuclear inclusion formation and neurodegeneration in opposite directions in human Purkinje cells, more or less affected in these CAG repeat disorders.

Oligodendroglioma-like Cells (Clear Cells) in Ependymoma

SummaryA brain tumor of a 22-year-old man was composed mostly of round cells with perinuclear halos (clear cells), forming clusters intersected by small blood vessels. In some areas, the tumor cells showed perivascular arrangement and epithelial pattern. Phosphotungstic-acid hematoxylin stain and immunoper-oxidase stain for glial fibrillary acidic protein (GFAP) technique failed to stain the clear cells. Electron microscopy of the clear cells revealed them to be classical ependymoma cells with well developed intercellular junctions, microvilli and cilia. As no reporters in the past showed the evidence to clarify the nature of the clear cells, this case is considered a good example to support the viewpoint that the clear cells (oligodendroglioma-like cells) commonly observed in ependymomas are in reality ependymoma cells. It is stressed that the diagnosis of “mixed glioma” or “oligoependymoma” should be made with sufficient caution despite the recent advances of GFAP technique.