Biomedical subjects

C R Harrington

Publications and source records attributed to C R Harrington.

42 records · Page 3Linked to original sources

PubMedDate not supplied

Examination of phosphorylated tau protein as a PHF-precursor at early stage Alzheimer's disease.

Hyperphosphorylated tau protein which can be isolated on the basis of insolubility in 1% sarkosyl (A68-tau fraction) is thought to represent a precursor pool for PHF assembly, associated histologically with neuritic pathology, which feeds into a more resistant tangle-associated PHF pool via cross-linking and proteolysis. We examined these predictions at the earliest detectable stages of neurofibrillary pathology. We report that there is no evidence that neuritic pathology represents an early pathologic stage, no evidence of an association between neuritic pathology and phosphorylated tau, no evidence of selective accumulation of phosphorylated tau at early stages of pathology, and no evidence for a precursor/product relationship between phosphorylated tau and PHFs during progression of pathology. We conclude that altered phosphorylation is a secondary process affecting 5% of PHFs and does not explain PHF assembly in 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↗