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C M Wischik

Publications and source records attributed to C M Wischik.

51 records · Page 3Linked to original sources
PubMed1988

Isolation of a fragment of tau derived from the core of the paired helical filament of Alzheimer disease.

A substantially enriched preparation of Alzheimer paired helical filaments (PHFs) has been used as a starting point for biochemical studies. Pronase treatment, which strips off adhering proteins, leaves a resistant core that is structurally intact. This has been used to raise a monoclonal antibody that decorates the filament core. The antibody has been used to follow the extraction of two peptide fragments (9.5 and 12 kDa) by immunoblotting. The link between the PHF as a morphological entity and these peptides has been established independently by photoaffinity labeling with a chemical ligand to the PHF core. Sequence analysis of these peptides was used to design oligonucleotide probes for cloning a cognate cDNA, which leads to its identification as human microtubule-associated tau protein. The sequencing of the 9.5- and 12-kDa peptides shows they are derived from a conserved region of tau containing three repeating segments. Since these fragments have been copurified with the Pronase-resistant core and are only released by subsequent steps, the corresponding part of the tau molecule must be tightly bound in the PHF core.

Alzheimer Disease↗
PubMed1988

Structural characterization of the core of the paired helical filament of Alzheimer disease.

The paired helical filament, the principal constituent of the neurofibrillary tangles characteristic of Alzheimer disease, is shown to consist of two structurally distinct parts. An external fuzzy region can be removed by Pronase treatment to leave a Pronase-resistant morphologically recognizable core. Scanning transmission electron microscopy gives an estimate for the mass per unit length as 79 kDa.nm-1 before Pronase treatment and 65 kDa.nm-1 after treatment. The fuzzy region carries all the epitopes recognized by two different antisera against microtubule-associated protein tau. By contrast, a monoclonal antibody (mAb) we have raised to paired helical filament cores (mAb 423) decorates Pronase-treated filaments much more strongly than it does untreated ones. We have shown in previous papers that the epitope recognized by mAb 423 is carried by a central 9.5-kDa fragment of tau protein, which therefore forms part of the Pronase-resistant core structure. The remainder of the tau protein incorporated into the filaments must contribute part, if not all, of the fuzzy region. The mass per unit length measurements imply that the three-domain structural subunit of the core that we visualized previously by image reconstruction has a molecular mass of approximately equal to 100 kDa.

Alzheimer Disease↗
PubMed1985

Image reconstruction of the Alzheimer paired helical filament.

The paired helical filament (PHF) is the principal constituent of the neurofibrillary tangles that occur in the brain in senile dementias of the Alzheimer type. We have previously shown from fragmentation patterns of isolated PHFs that they consist of a regularly repeating subunit, which is axially compact and not an extended fibrous molecule or protofilament. Here we present diffraction patterns of PHFs and an objective reconstruction of the cross-sectional density of the PHF computed from the diffraction patterns. We demonstrate the presence of an axial periodicity (3 nm) in PHFs. These results establish conclusively that the PHF is made up of a double helical stack of transversely oriented subunits, each of which has three domains, and precludes purely descriptive models based on helical rearrangements of preformed cytoskeletal polymers or protofilaments. The structure is of the type that might arise by the de novo assembly of a single structural subunit, which appears to be produced in considerable abundance in those neurons where tangles form.

Alzheimer Disease↗
PubMed1985

Subunit structure of paired helical filaments in Alzheimer's disease.

The neurofibrillary tangles that occur in the brain in cases of senile dementia of the Alzheimer type contain a distinctive type of filament, the paired helical filament (PHF). We have developed a method for isolating the tangles postmortem in sufficient yield for structural study of PHFs by electron microscopy of negatively stained and shadowed preparations. This material shows the characteristic helical structure seen in sectioned embedded material. In addition, two striking fragmentation patterns are observed. (a) Some filaments show sharp transverse breaks at apparently random positions along the filament. (b) In a few PHFs one strand is missing for a variable length, whereas the other appears to maintain its structural integrity. The shadowed specimens show the PHF to be wound in a left-handed manner. These observations indicate that the PHF consists of subunits of very limited axial extent arranged along two left-handed helical strands. The visualization of the substructure within the PHFs is rather variable and a model building approach has therefore been adopted, which has allowed the main features seen in the images to be interpreted. The subunit appears to have at least two domains in a radial direction and an axial extent of less than 5 nm. The whole structure can best be described as a twisted ribbon and indeed alkali treatment does untwist PHFs to give flat ribbons. The nature of the proposed model makes it most unlikely that the PHF is formed by a simple collapse of normal cytoskeletal elements, such as neurofilaments.

Aged↗
PubMed1983

Cell organization in the stroma of the rat uterus. II. Responses to progesterone in the ovariectomised rat.

The organisation and activity of cells in the uterine stroma of ovariectomised rats have been studied over the 24 hours following an injection of progesterone. Autoradiographically, the rate of incorporation of [3H]lysine falls 1 hour after progesterone, rising progressively at 3 and 7 hours to levels higher than in control animals. A gradient of grain density is evident at 1, 3 and 7 hours, higher in regions adjacent to luminal epithelium than near the muscularis. No such gradient appears relative to glandular epithelium. Morphometric studies show that the array of stromal cells 24 hours after progesterone is similar to that in control rats, except that cells near the luminal epithelium are larger in the former group. At intermediate times, changes in cell size and spacing occur throughout the stroma in patterns that vary with distance from luminal epithelium. The organisation and activity of cells in the uterine stroma change in response to progesterone in a manner conditioned by their position in the uterus, in particular by their distance from luminal epithelium.

Animals↗
PubMedDate not supplied

Quantitative analysis of tau protein in paired helical filament preparations: implications for the role of tau protein phosphorylation in PHF assembly in Alzheimer's disease.

In Alzheimer's disease, there is a major redistribution of the tau protein pool from soluble to PHF-bound forms. PHF-bound tau can be distinguished from normal tau by acid reversible occlusion of a generic tau epitope in the tandem repeat region and characteristic sedimentation in the if-II protocol developed in this laboratory. We show that 85% of tau bound in the PHF-like configuration can be recovered in the if-II PHF-fraction. Less than 1% of this material was phosphorylated at the mAb AT8 site in aged clinical controls or in cases with minimal or mild dementia. Of tau phosphorylated at the mAb AT8 site, only 12% was found to co-sediment with PHFs. These low levels could not be explained by postmortem dephosphorylation. As more than 95% of PHF-tau is not phosphorylated, even at early stages of pathology, it is misleading to use the terms "PHF-tau" and "phosphorylated tau" as though they were synonymous, particularly as this implies a pathogenetic role which phosphorylation need not have.

Alzheimer Disease↗
PubMedDate not supplied

Normal densities of 5-HT3 receptor recognition sites in Alzheimer's disease.

The present studies investigate the possible difference in 5-HT3 receptor recognition site density in amygdaloid and hippocampal homogenates from patients with Alzheimer's disease compared with age-matched controls. The 5-HT3 receptor recognition site radioligand [3H]-(S)-zacopride identified a comparable density of specific sites (defined by granisetron 10.0 microM) in tissues obtained from patients with Alzheimer's disease as compared to age-matched controls (amygdala, Bmax 41 +/- 4 and 43 +/- 9; hippocampus, Bmax 59 +/- 9 and 51 +/- 9 fmol mg-3 protein; tissue from Alzheimer's disease patients and age-matched controls, respectively, mean +/- s.e.m., n = 7-8). These results suggest that the density of 5-HT3 receptor recognition sites labelled by [3H]-(S)-zacopride are not altered in the amygdala and hippocampus of patients with Alzheimer's disease.

Aged↗
PubMedDate not supplied

Presence of the apolipoprotein E type epsilon 4 allele is not associated with neurofibrillary pathology or biochemical changes to tau protein.

Alzheimer's disease (AD) represents a heterogeneous disorder, and several factors have been associated with its development. The presence of the apolipoprotein E type (APOE) epsilon 4 allele has been proposed as a risk factor for AD, but how it influences the development of the characteristic hallmarks of the disease remains unknown. In the present study, the neuropathological changes and levels of both core PHF-tau and normal tau protein in 4 neocortical areas, cerebellum and medial temporal cortex were determined in 18 AD cases. The extent of these changes was compared between 10 cases possessing an epsilon 4 allele and 8 cases without. These two groups were indistinguishable in terms of neurofibrillary pathology, whereas cases with an epsilon 4 allele had more diffuse plaques, particularly in the temporal neocortex. Biochemically, there was no difference in the levels of PHF-tau protein between the two groups. These data indicate that APOE epsilon 4 allele may influence deposition of diffuse amyloid, but altered tau protein processing, which underlies the development of the neurofibrillary pathology in AD, is not influenced by this allele.

Aged↗
PubMedDate not supplied

Senile dementia of Lewy body type and Alzheimer type are biochemically distinct in terms of paired helical filaments and hyperphosphorylated tau protein.

We have used biochemical assays to examine cingulate and occipital cortices from age-matched cases of Alzheimer's disease (AD; n = 12), senile dementia of the Lewy body type (SDLT; n = 13), Parkinson's disease (PD; 5 non-demented cases and 7 cognitively impaired cases) and controls (n = 11) for paired helical filaments (PHFs), phosphorylated and normal tau protein and beta/A4-protein. Whereas cingulate cortex is characterised by relatively high densities of cortical Lewy bodies in the SDLT cases and lower numbers in PD, these inclusion bodies were absent in the cingulate cortex from AD and control cases. Protease-resistant PHFs and hyperphosphorylated tau protein were found in AD and, at low levels, in a minority of SDLT cases. Qualitatively, both of these preparations were indistinguishable in SDLT from those found in AD but levels of both parameters in SDLT were less than 5% of those in AD. SDLT, PD and control groups did not differ from each other in terms of the quantity of protease-resistant PHFs or the level of hyperphosphorylated tau. Furthermore, PHF accumulation did not distinguish between PD cases with or without dementia. The levels of normal tau protein did not differ between the four groups. beta/A4 protein levels did not distinguish between PD and control groups, between AD and SDLT groups, or between SDLT and control groups for either cingulate or occipital cortices. Thus extensive accumulation of PHFs in either neurofibrillary tangles or dystrophic neurites is not a feature of either SDLT or PD. Our findings provide molecular support for the neuropathological and clinical separation of SDLT as a form of dementia that is distinct from AD.

Aged↗
PubMedDate not supplied

Alterations in tau protein metabolism during normal aging.

It is unknown whether aging and Alzheimer's disease (AD) are on the same continuum, or whether they are qualitatively distinct. Tau protein has been identified as a major constituent of paired helical filaments (PHFs) and AD is characterised by a major redistribution of the normal tau protein pool into PHFs. Little is known about the changes in tau protein distribution that occur in the course of normal aging. We have examined PHF-bound and normal tau fractions in frontal, temporal, parietal and occipital neocortex, cerebellum, hippocampus and entorhinal cortex in 15 cognitively unimpaired individuals aged 19-88 years at death. Insoluble tau protein in the PHF fraction did not increase with aging in any brain region, despite the appearance of neurofibrillary pathology at low density in the more elderly cases. By contrast, normal tau protein decreased with aging (r = 0.32, p < 0.001), with an average loss of 14% of soluble tau per decade after the age of 20 years. This was unrelated either to neurofibrillary or beta-amyloid pathology. Frontal grey matter and hippocampus were most vulnerable to age-related tau loss, decreasing by as much as 90% in the older subgroup. These findings contrast with those we have previously reported in AD, where the redistribution of tau protein into the PHF-bound fraction was highly correlated with the extent of neurofibrillary pathology, and suggest that the mechanisms of tau loss in aging and AD are distinct. Age-related tau loss may underlie the neuropsychological impairments seen in the non-demented elderly.

Adult↗
PubMedDate not supplied

Apolipoprotein E genotype in the prediction of cognitive decline and dementia in a prospectively studied elderly population.

An increased apolipoprotein E (ApoE) type epsilon 4 allele frequency is associated with both sporadic and familial late-onset Alzheimer's disease (AD). The age of onset of disease in patients homozygous for the epsilon 4 allele appears to be decreased by approximately 15 years compared with E2/3 individuals. In order to assess the influence of this allele on both dementia and cognitive decline in the elderly we have determined the ApoE genotype of 150 individuals over the age of 75 years who have taken part in a longitudinal study. Homozygosity for the epsilon 4 allele was rare. Of the 2 homozygotes, 1 was severely demented but the other did not receive a clinical diagnosis of dementia. The latter individual did demonstrate marked cognitive decline over a 28-month period. There was a consistent association between the presence of an epsilon 4 allele and both the clinical diagnosis of dementia and cognitive decline. These findings confirm a genetic heterogeneity in late-onset sporadic AD and prompt caution in the use of ApoE genotype to predict an elderly individual's susceptibility to either dementia or cognitive decline.

Aged↗
PubMedDate not supplied

Changes in a CSF antigen associated with dementia.

An 85-kDa antigen was detected in cerebrospinal fluid (CSF) using a monoclonal antibody, 11.57, raised against a fraction of paired helical filaments extracted from Alzheimer's disease (AD) brain tissues. The antigen is a thermostable protein that is unrelated either to tau or amyloid beta-protein precursor. Its level was measured in lumbar and post-mortem CSF samples and found to be decreased significantly in patients with dementia as compared with non-demented controls. There was no difference in its level between patients with AD and those with non-Alzheimer type dementia. In AD, however, there was a significant relationship between disease progression and the amount of the 85-kDa antigen.

Adolescent↗