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Tau and amyloid ? proteins distinctively associate to functional network changes in the aging brain.

ABSTRACT: INTRODUCTION:Misfolded tau and amyloid ? (A?) proteins progressively accumulate in the human brain, causing altered neuronal function and neurodegeneration. This study sought to investigate whether the wide spectrum of functional reorganization in aging brains of cognitively normal individuals relates to specific pathological patterns of tau and A? deposits. METHODS:We used functional connectivity neuroimaging and in vivo tau and A? positron emission tomography scans to study cortical spatial relationships between imaging modalities. RESULTS:We found that a negative association between tau and functional connectivity combined with a positive association between A? and functional connectivity is the most frequent cortical pattern among elderly subjects. Moreover, we found specific brain areas that interrelate hypoconnectivity and hyperconnectivity regions. DISCUSSION:Our findings have critical implications to understanding how the two main elements of Alzheimer's disease-related pathology affect the aging brain and how they cause alterations in large-scale neuronal circuits.

SUBMITTER: Sepulcre J

PROVIDER: S-EPMC5623176 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Tau and amyloid β proteins distinctively associate to functional network changes in the aging brain.

Sepulcre Jorge J Sabuncu Mert R MR Li Quanzheng Q El Fakhri Georges G Sperling Reisa R Johnson Keith A KA

Alzheimer's & dementia : the journal of the Alzheimer's Association 20170330 11

<h4>Introduction</h4>Misfolded tau and amyloid β (Aβ) proteins progressively accumulate in the human brain, causing altered neuronal function and neurodegeneration. This study sought to investigate whether the wide spectrum of functional reorganization in aging brains of cognitively normal individuals relates to specific pathological patterns of tau and Aβ deposits.<h4>Methods</h4>We used functional connectivity neuroimaging and in vivo tau and Aβ positron emission tomography scans to study cort ...[more]

PMID: 28366797

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Project description:Background: Integrity of functional brain networks is closely associated with maintained cognitive performance at old age. Consistently, both carrier status of Apolipoprotein E ε4 allele (APOE4), and age-related aggregation of Alzheimer's disease (AD) pathology result in altered brain network connectivity. The posterior cingulate and precuneus (PCP) is a node of particular interest due to its role in crucial memory processes. Moreover, the PCP is subject to the early aggregation of AD pathology. The current study aimed at characterizing brain network properties associated with unimpaired cognition in old aged adults. To determine the effects of age-related brain change and genetic risk for AD, pathological proteins β-amyloid and tau were measured by Positron-emission tomography (PET), PCP connectivity as a proxy of cognitive network integrity, and genetic risk by APOE4 carrier status. Methods: Fifty-seven cognitively unimpaired old-aged adults (MMSE = 29.20 ± 1.11; 73 ± 8.32 years) were administered 11C Pittsburgh Compound B and 18F Flutemetamol PET for assessing β-amyloid, and 18F AV-1451 PET for tau. Individual functional connectivity seed maps of the PCP were obtained by resting-state multiband BOLD functional MRI at 3-Tesla for increased temporal resolution. Voxelwise correlations between functional connectivity, β-amyloid- and tau-PET were explored by Biological Parametric Mapping (BPM). Results: Local β-amyloid was associated with increased connectivity in frontal and parietal regions of the brain. Tau was linked to increased connectivity in more spatially distributed clusters in frontal, parietal, occipital, temporal, and cerebellar regions. A positive interaction was observable for APOE4 carrier status and functional connectivity with brain regions characterized by increased local β-amyloid and tau tracer retention. Conclusions: Our data suggest an association between spatially differing connectivity systems and local β-amyloid, and tau aggregates in cognitively normal, old-aged adults, which is moderated by APOE4. Additional longitudinal studies may determine protective connectivity patterns associated with healthy aging trajectories of AD-pathology aggregation.

Project description:Current approaches to the early detection of Alzheimer's disease (AD) rely upon classifying individuals as "positive" or "negative" for biomarkers related to the core pathology of ?-amyloid (A?). However, the accumulation of A? begins slowly, years before biomarkers become abnormal. We used longitudinal [11C] Pittsburgh Compound B PET scanning and neuropsychological assessment to investigate the earliest changes in AD pathology and how it affects memory in cognitively normal older humans (N = 71; mean age 75 years; 35% male). We used [18F] AV-1451 PET scanning at the end of the observation period to measure subsequent tau deposition in a subset of our sample (N = 37). We found evidence for an inverted-U relationship between baseline A? levels and A? slope in asymptomatic older adults, suggesting a slowing of A? accumulation even in cognitively normal adults. In participants who were nominally amyloid negative, both the rate of amyloid accumulation and the baseline levels of A? predicted early tau deposition in cortical Braak regions associated with AD. Amyloid measures were only sensitive to memory decline as baseline levels of A? increased, suggesting that pathological accumulation occurs before impacting memory. These findings support the necessity of early intervention with amyloid-lowering therapies even in those who are amyloid negative.SIGNIFICANCE STATEMENT The progressive nature of Alzheimer's disease (AD) necessitates the earliest possible detection of pathological or cognitive change if disease progression is to be slowed. We examined cognitively normal older adults in whom AD pathology is starting to develop, with the goal of early detection of AD pathology or cognitive changes. We found amyloid measures to be sensitive early on in predicting subsequent early tau deposition. Further, it appears that rates of amyloid accumulation already begin to slow in preclinical AD, suggesting that it is a relatively late stage of AD progression. Thus, it is crucial to examine older adults early, before amyloid levels have saturated, to intervene to slow disease progression.

Project description:The emergence of longevity in the modern world has brought a sense of urgency to understanding age-related neurodegenerative diseases such as Alzheimer's disease. Unfortunately, there is a lack of consensus regarding the correlation between the pathological substrates of neurodegeneration and dementia status, particularly in the oldest-old. To better understand the pathological correlates of dementia in the oldest-old, we characterized the topographical spread and severity of amyloid-?, tau, TDP-43 and ?-synuclein pathologies in the 90+ Study, a prospective longitudinal population-based study of ageing and dementia. Neuropathological analysis with immunohistochemically labelled sections was carried out blind to clinical diagnosis on the first 108 participants of the 90+ Study who came to autopsy including participants with dementia (n = 66) and without dementia (n = 42). We used quantitative and/or semi-quantitative measures to assess the burden of amyloid-?, tau, TDP-43 and ?-synuclein pathologies as well as hippocampal sclerosis. Amyloid-? and tau were the predominant pathologies in the 90+ Study cohort and both amyloid-? area and tau area occupied measures were strongly associated with the presence of dementia, as was Braak staging but semi-quantitative plaque scores were not. Notably, TDP-43 pathology also correlated with dementia, while ?-synuclein distribution did not. In addition, hippocampal sclerosis was specific to participants with dementia and correlated with the presence of limbic TDP-43. In contrast to previous reports, we found that tau and amyloid-? continue to be robust pathological correlates of dementia, even in the oldest-old. While individuals with no dementia had limited hippocampal tau and neocortical amyloid-? pathology, dementia associated with an expansion in pathology, including increased neocortical tau and hippocampal amyloid-? plaques, more abundant neocortical amyloid-? deposition and hippocampal sclerosis with its attendant TDP-43 pathology.

Dataset Information

Tau and amyloid ? proteins distinctively associate to functional network changes in the aging brain.

Publications

Tau and amyloid β proteins distinctively associate to functional network changes in the aging brain.

Similar Datasets

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