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An unresolved question for the understanding of Alzheimer’s disease (AD) pathophysiology is why a significant percentage of amyloid-β (Aβ)-positive cognitively unimpaired (CU) individuals do not develop detectable downstream tau pathology and, consequently, clinical deterioration. In vitro evidence suggests that reactive astrocytes unleash Aβ effects in pathological tau phosphorylation. Here, in a biomarker study across three cohorts (n = 1,016), we tested whether astrocyte reactivity modulates the association of Aβ with tau phosphorylation in CU individuals. We found that Aβ was associated with increased plasma phosphorylated tau only in individuals positive for astrocyte reactivity (Ast+). Cross-sectional and longitudinal tau–positron emission tomography analyses revealed an AD-like pattern of tau tangle accumulation as a function of Aβ only in CU Ast+ individuals. Our findings suggest astrocyte reactivity as an important upstream event linking Aβ with initial tau pathology, which may have implications for the biological definition of preclinical AD and for selecting CU individuals for clinical trials.

Animal studies suggest that the apolipoprotein E ε4 ( APOE ε4) allele is a culprit of early microglial activation in Alzheimer’s disease (AD). Here, we tested the association between APOE ε4 status and microglial activation in living individuals across the aging and AD spectrum. We studied 118 individuals with positron emission tomography for amyloid-β (Aβ; [ 18 F]AZD4694), tau ([ 18 F]MK6240), and microglial activation ([ 11 C]PBR28). We found that APOE ε4 carriers presented increased microglial activation relative to noncarriers in early Braak stage regions within the medial temporal cortex accounting for Aβ and tau deposition. Furthermore, microglial activation mediated the Aβ-independent effects of APOE ε4 on tau accumulation, which was further associated with neurodegeneration and clinical impairment. The physiological distribution of APOE mRNA expression predicted the patterns of APOE ε4-related microglial activation in our population, suggesting that APOE gene expression may regulate the local vulnerability to neuroinflammation. Our results support that the APOE ε4 genotype exerts Aβ-independent effects on AD pathogenesis by activating microglia in brain regions associated with early tau deposition.

Gold-standard diagnosis of Alzheimer’s disease (AD) relies on histopathological staging systems. Using the topographical information from [18F]MK6240 tau positron-emission tomography (PET), we applied the Braak tau staging system to 324 living individuals. We used PET-based Braak stage to model the trajectories of amyloid-β, phosphorylated tau (pTau) in cerebrospinal fluid (pTau181, pTau217, pTau231 and pTau235) and plasma (pTau181 and pTau231), neurodegeneration and cognitive symptoms. We identified nonlinear AD biomarker trajectories corresponding to the spatial extent of tau-PET, with modest biomarker changes detectable by Braak stage II and significant changes occurring at stages III–IV, followed by plateaus. Early Braak stages were associated with isolated memory impairment, whereas Braak stages V–VI were incompatible with normal cognition. In 159 individuals with follow-up tau-PET, progression beyond stage III took place uniquely in the presence of amyloid-β positivity. Our findings support PET-based Braak staging as a framework to model the natural history of AD and monitor AD severity in living humans.

An unresolved question for the understanding of Alzheimer’s disease (AD) pathophysiology is why a significant percentage of amyloid β (Aβ)-positive cognitively unimpaired (CU) individuals do not develop detectable downstream tau pathology and, consequently, clinical deterioration. In vitro evidence suggests that reactive astrocytes are key to unleashing Aβ effects in pathological tau phosphorylation. In a large study (n=1,016) across three cohorts, we tested whether astrocyte reactivity modulates the association of Aβ with plasma tau phosphorylation in CU people. We found that Aβ pathology was associated with increased plasma phosphorylated tau levels only in individuals positive for astrocyte reactivity (Ast+). Cross-sectional and longitudinal tau-PET analysis revealed that tau tangles accumulated as a function of Aβ burden only in CU Ast+ individuals with a topographic distribution compatible with early AD. Our findings suggest that increased astrocyte reactivity is an important upstream event linking Aβ burden with initial tau pathology which might have implications for the biological definition of preclinical AD and for selecting individuals for early preventive clinical trials.

ImportanceThe recent proliferation of phosphorylated tau (p-tau) biomarkers has raised questions about their preferential association with the hallmark pathologies of Alzheimer disease (AD): amyloid-β plaques and tau neurofibrillary tangles.ObjectiveTo determine whether cerebrospinal fluid (CSF) and plasma p-tau biomarkers preferentially reflect cerebral β-amyloidosis or neurofibrillary tangle aggregation measured with positron emission tomography (PET).Design, Setting, and ParticipantsThis was a cross-sectional study of 2 observational cohorts: the Translational Biomarkers in Aging and Dementia (TRIAD) study, with data collected between October 2017 and August 2021, and the Alzheimer’s Disease Neuroimaging Initiative (ADNI), with data collected between September 2015 and November 2019. TRIAD was a single-center study, and ADNI was a multicenter study. Two independent subsamples were derived from TRIAD. The first TRIAD subsample comprised individuals assessed with CSF p-tau (p-tau181, p-tau217, p-tau231, p-tau235), [18F]AZD4694 amyloid PET, and [18F]MK6240 tau PET. The second TRIAD subsample included individuals assessed with plasma p-tau (p-tau181, p-tau217, p-tau231), [18F]AZD4694 amyloid PET, and [18F]MK6240 tau PET. An independent cohort from ADNI comprised individuals assessed with CSF p-tau181, [18F]florbetapir PET, and [18F]flortaucipir PET. Participants were included based on the availability of p-tau and PET biomarker assessments collected within 9 months of each other. Exclusion criteria were a history of head trauma or magnetic resonance imaging/PET safety contraindications. No participants who met eligibility criteria were excluded.ExposuresAmyloid PET, tau PET, and CSF and plasma assessments of p-tau measured with single molecule array (Simoa) assay or enzyme-linked immunosorbent assay.Main Outcomes and MeasuresAssociations between p-tau biomarkers with amyloid PET and tau PET.ResultsA total of 609 participants (mean [SD] age, 66.9 [13.6] years; 347 female [57%]; 262 male [43%]) were included in the study. For all 4 phosphorylation sites assessed in CSF, p-tau was significantly more closely associated with amyloid-PET values than tau-PET values (p-tau181 difference, 13%; 95% CI, 3%-22%; P = .006; p-tau217 difference, 11%; 95% CI, 3%-20%; P = .003; p-tau231 difference, 15%; 95% CI, 5%-22%; P 235 difference, 9%; 95% CI, 1%-19%; P = .02) . These results were replicated with plasma p-tau181 (difference, 11%; 95% CI, 1%-22%; P = .02), p-tau217 (difference, 9%; 95% CI, 1%-19%; P = .02), p-tau231 (difference, 13%; 95% CI, 3%-24%; P = .009), and CSF p-tau181 (difference, 9%; 95% CI, 1%-21%; P = .02) in independent cohorts.Conclusions and RelevanceResults of this cross-sectional study of 2 observational cohorts suggest that the p-tau abnormality as an early event in AD pathogenesis was associated with amyloid-β accumulation and highlights the need for careful interpretation of p-tau biomarkers in the context of the amyloid/tau/neurodegeneration, or A/T/(N), framework.

The mechanisms by which the apolipoprotein E ε4 (APOEε4) allele influences Alzheimer’s disease (AD) pathophysiological progression are poorly understood. Here, we tested the association of APOEε4 carriership and amyloid-β (Aβ) burden with longitudinal tau pathology progression. We studied 104 individuals across the aging and AD spectrum who underwent clinical assessments, APOE genotyping, magnetic resonance imaging, positron emission tomography (PET) for Aβ ([18F]AZD4694) and tau ([18F]MK-6240) at baseline, as well as a follow-up tau-PET scan (mean follow-up, 2.4 years). We further assessed longitudinal changes in tau phosphorylation (plasma phosphorylated tau at threonine 217 [p-tau217+]), brain atrophy (gray matter density), and clinical function (clinical dementia rating scale sum of boxes). We found that APOEε4 carriership potentiates Aβ effects on longitudinal tau tangle accumulation over two years. The APOEε4-potentiated Aβ effects on tangles were mediated by longitudinal plasma p-tau217+ increase. This longitudinal tau accumulation as measured by PET was accompanied by brain atrophy and clinical decline. Our results support a model in which the APOEε4 allele plays a key role in Aβ downstream effects on the aggregation of phosphorylated tau in the form of neurofibrillary tangles in the living human brain.

A classical early sign of typical Alzheimer’s disease is memory decline, which has been linked to the aggregation of tau in the medial temporal lobe. Verbal delayed free recall and recognition tests have consistently probed useful to detect early memory decline, and there is substantial debate on how performance, particularly in recognition tests, is differentially affected through health and disease in older adults. Using in vivo PET-Braak staging, we investigated delayed recall and recognition memory dysfunction across the Alzheimer’s disease spectrum. Our cross-sectional study included 144 cognitively unimpaired elderly, 39 amyloid-β+ individuals with mild cognitive impairment and 29 amyloid-β+ Alzheimer’s disease patients from the Translational Biomarkers in Aging and Dementia cohort, who underwent [18F]MK6240 tau and [18F]AZD4694 amyloid PET imaging, structural MRI and memory assessments. We applied non-parametric comparisons, correlation analyses, regression models and voxel-wise analyses. In comparison with PET-Braak Stage 0, we found that reduced, but not clinically significant, delayed recall starts at PET-Braak Stage II (adjusted P < 0.0015), and that recognition (adjusted P = 0.011) displayed a significant decline starting at PET-Braak Stage IV. While performance in both delayed recall and recognition related to tau in nearly the same cortical areas, further analyses showed that delayed recall rendered stronger associations in areas of early tau accumulation, whereas recognition displayed stronger correlations in mostly posterior neocortical regions. Our results support the notion that delayed recall and recognition deficits are predominantly associated with tau load in allocortical and neocortical areas, respectively. Overall, delayed recall seems to be more dependent on the integrity of anterior medial temporal lobe structures, while recognition appears to be more affected by tau accumulation in cortices beyond medial temporal regions.

Alzheimer’s disease can be detected in living people using in vivo biomarkers of amyloid-β and tau, even in the absence of cognitive impairment during the preclinical phase. [18F]-MK-6420 is a high-affinity PET tracer that quantifies tau neurofibrillary tangles, but its ability to predict cognitive changes associated with early Alzheimer’s disease symptoms, such as memory decline, is unclear. Here, we assess the prognostic accuracy of baseline [18F]-MK-6420 tau-PET for predicting longitudinal memory decline in asymptomatic elderly individuals. In a longitudinal observational study, we evaluated a cohort of cognitively normal elderly participants (n = 111) from the translational biomarkers in ageing and dementia study (data collected between October 2017 and July 2020, with a follow-up period of 12 months). All participants underwent tau-PET with [18F]-MK-6420 and amyloid-β PET with [18F]-AZD-4694. The exclusion criteria included the presence of head trauma, stroke or other neurological disorders. There were 111 eligible participants selected based on the availability of amyloid-β PET, tau-PET, MRI and APOEɛ4 genotyping. Among these participants, the mean standard deviation age was 70.1 (8.6) years; 20 (18%) were tau-PET-positive and 71 of 111 (63.9%) were women. A significant association between the baseline Braak Stages I–II [18F]-MK-6240 standardized uptake value ratio positivity and change in composite memory score were observed at the 12-month follow-up, after correcting for age, sex and years of education [logical memory and Rey Auditory Verbal Learning Test, standardized beta = −0.52 (−0.82–0.21), P < 0.001, for dichotomized tau-PET and −1.22 (−1.84−(−0.61)], P < 0.0001, for continuous tau-PET]. Moderate cognitive decline was observed for A + T + over the follow-up period, whereas no significant change was observed for A−T+, A + T- and A-T-, although it should be noted that the A−T + group was small. Our results indicate that baseline tau neurofibrillary tangle pathology is associated with longitudinal changes in memory function, supporting the use of [18F]-MK-6420 PET to predict the likelihood of asymptomatic elderly individuals experiencing future memory decline. Overall, [18F]-MK-6420 PET is a promising tool for predicting memory decline in older adults without cognitive impairment at baseline. This is of critical relevance as the field is shifting towards a biological model of Alzheimer’s disease defined by the aggregation of pathologic tau. Therefore, early detection of tau pathology using [18F]-MK-6420 PET provides us with hope that living patients with Alzheimer’s disease may be diagnosed during the preclinical phase before it is too late.

Introduction The Epworth Sleepiness Scale (ESS) is commonly used to assess excessive daytime sleepiness, but its accuracy is limited. In this study, we aim to compare the ESS with the Observation-based Diurnal Sleepiness Inventory (ODSI), a subjective measure of sleepiness that has been validated using the ESS in older adults, to objective measures of sleepiness obtained through the Psychomotor Vigilance Task (PVT). Despite being validated with the ESS, the ODSI has not yet been tested with objective measures of sleepiness. By comparing subjective measures of sleepiness (ODSI and ESS) to objective measures (PVT), we aim to expand the usage of ODSI to other populations. Methods 91 persons with newly diagnosed obstructive sleep apnea and not yet treated on continuous positive airway pressure (CPAP) were administered the ESS, ODSI, and PVT sleepiness tests, and the results were analyzed for correlations using linear regression. The average age was 50.48 ± 12.74, the mean body mass index (BMI) was 35.9 ± 9.3, the mean apnea hypopnea index was 30.9 ± 23.7, and 53.5% were male. The ESS and ODSI scores were run against PVT lapses and transformed average reaction time, which are the two primary outcomes of PVT. Results PVT lapses were significantly different between sleepy and non-sleepy individuals as defined by both ESS and ODSI categorization. Both the ODSI and the ESS were significantly correlated to the transformed average reaction time. The second question on the ODSI was also significantly correlated to PVT lapses as well as the transformed average reaction time. Conclusion The ODSI and ESS correlated well with objective measures of sleepiness through the PVT. The ODSI is a suitable measure of sleepiness appropriate for usage in middle-aged adults with obstructive sleep apnea. Support (if any) R00NR014675-05 (PI: Pak)

The burden imposed by the COVID-19 pandemic deferentially interferes with the outcomes of clinical trials of aging and dementia. We examined the impact of the lockdown on cognitive impairment due to Alzheimer’s Disease (AD), anxiety, and COVID-19-related stress in participants from the Translational Biomarkers In Aging and Dementia (TRIAD) cohort using neuropsychiatric assessments, tau and amyloid PET. We found that, before the lockdown, anxiety was higher in cognitively impaired individuals (CI) and positively associated with brain tau load. However, during the lockdown, anxiety increased only in the cognitively unimpaired (CU) and was positively associated with COVID-19 related stress. Interestingly, we found that in patients, tau load was anti-correlated with higher anxiety during lockdown. Our findings contribute to a framework for interpreting the effects of the pandemic on neuropsychiatric symptoms among clinical trial participants. Collectively, our results suggest that caregivers are more vulnerable to external stressors than patients.

Microglial activation is an early phenomenon in Alzheimer’s disease (AD) that may occur prior to and independently of amyloid-β (Aβ) aggregation. Recent studies in transgenic animal models suggest that the apolipoprotein E ε4 (APOEε4) allele may be a culprit of early microglial activation in AD. However, it is unclear whether the APOEε4 genotype is associated with microglial reactivity in the living human brain. Here, we tested whether APOEε4 carriership is associated with microglial activation in individuals across the aging and AD spectrum. We studied 118 individuals who had positron emission tomography (PET) for Aβ ([18F]AZD4694), tau ([18F]MK6240), and microglial activation ([11C]PBR28), as well as clinical, genetic, and magnetic resonance imaging data. We found that APOEε4 carriership was associated with increased microglial activation mainly in early Braak-staging regions within the medial temporal cortex, and this effect of APOEε4 was independent of Aβ and tau deposition. Furthermore, microglial activation mediated the Aβ-independent effects of APOEε4 on downstream tau accumulation, neurodegeneration, and clinical impairment. Interestingly, the physiological distribution of APOE mRNA expression, obtained from the Allen Human Atlas, predicted the patterns of APOEε4-related microglial activation in our population, suggesting that the deleterious effects of APOEε4 occur at the level of gene expression. These results support a model in which the APOEε4 has Aβ-independent effects on AD pathogenesis by activating microglia in brain regions associated with early tau deposition. Our findings provide a rationale for the development of novel AD therapies targeting the interplay between ApoE and neuroinflammation.

IntroductionPlasma amyloid-β (Aβ), phosphorylated tau (p-tau), and glial fibrillar acid protein (GFAP) can identify Alzheimer’s disease (AD) pathophysiology with high accuracy. However, comparing their performance in the same individuals remains under-explored.MethodsWe compared the predictive performance of plasma Aβ42/40, p-tau(at threonine 181 and 231), neurofilament light (NfL), and GFAP to identify Aβ- and tau-PET positivity in 138 cognitive unimpaired (CU) and 87 cognitive impaired (CI) individuals.ResultsIn CU, plasma p-tau231 had the best performance to identify both Aβ- and tau-PET positivity. In CI, plasma GFAP showed the best predictive accuracy to identify both Aβ and tau-PET positivity.DiscussionOur results support plasma p-tau231 as a marker of early AD pathology and, that GFAP best identifies both PET Aβ and tau abnormalities in the brain of CI individuals. These findings highlight that the performance of blood-based protein biomarkers to identify the presence of AD pathophysiology is disease-stage dependent.

Astrocytes can adopt multiple molecular phenotypes in the brain of Alzheimer’s disease (AD) patients. Here, we studied the associations of cerebrospinal fluid (CSF) glial fibrillary acidic protein (GFAP) and chitinase-3-like protein 1 (YKL-40) levels with brain amyloid-β (Aβ) and tau pathologies. We assessed 121 individuals across the aging and AD clinical spectrum with positron emission tomography (PET) brain imaging for Aβ ([18F]AZD4694) and tau ([18F]MK-6240), as well as CSF GFAP and YKL-40 measures. We observed that higher CSF GFAP levels were associated with elevated Aβ-PET but not tau-PET load. By contrast, higher CSF YKL-40 levels were associated with elevated tau-PET but not Aβ-PET burden. Structural equation modeling revealed that CSF GFAP and YKL-40 mediate the effects of Aβ and tau, respectively, on hippocampal atrophy, which was further associated with cognitive impairment. Our results suggest the existence of distinct astrocyte biomarker signatures in response to brain Aβ and tau accumulation, which may contribute to our understanding of the complex link between reactive astrogliosis heterogeneity and AD progression.

Funder: Helmholts International BigBrain Analytics & Learning Laboratory, Neurotransmitter receptors support the propagation of signals in the human brain. How receptor systems are situated within macro-scale neuroanatomy and how they shape emergent function remain poorly understood, and there exists no comprehensive atlas of receptors. Here we collate positron emission tomography data from more than 1,200 healthy individuals to construct a whole-brain three-dimensional normative atlas of 19 receptors and transporters across nine different neurotransmitter systems. We found that receptor profiles align with structural connectivity and mediate function, including neurophysiological oscillatory dynamics and resting-state hemodynamic functional connectivity. Using the Neurosynth cognitive atlas, we uncovered a topographic gradient of overlapping receptor distributions that separates extrinsic and intrinsic psychological processes. Finally, we found both expected and novel associations between receptor distributions and cortical abnormality patterns across 13 disorders. We replicated all findings in an independently collected autoradiography dataset. This work demonstrates how chemoarchitecture shapes brain structure and function, providing a new direction for studying multi-scale brain organization., For the Cambridge authors (Coles, Fryer & Aigbirhio): This work was funded by an MRC PET Neuroscience programme grant (Training and Novel Probes Programme in PET Neurochemistry - MR/K02308X/1) and by an MRC Developmental Pathway Funding Scheme grant (MR/L013215/1). This research in Cambridge was supported by the NIHR Cambridge Biomedical Research Centre (BRC-1215-20014). The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care. JPC was supported by a British Journal of Anaesthesia/Royal College of Anaesthetists grant from the National Institute of Academic Anaesthesia.

This study aimed to investigate the potential of quantitative radiomic data extracted from conventional MR images in discriminating IDH-mutant grade 4 astrocytomas from IDH-wild-type glioblastomas (GBMs). A cohort of 57 treatment-naïve patients with IDH-mutant grade 4 astrocytomas (n = 23) and IDH-wild-type GBMs (n = 34) underwent anatomical imaging on a 3T MR system with standard parameters. Post-contrast T1-weighted and T2-FLAIR images were co-registered. A semi-automatic segmentation approach was used to generate regions of interest (ROIs) from different tissue components of neoplasms. A total of 1050 radiomic features were extracted from each image. The data were split randomly into training and testing sets. A deep learning-based data augmentation method (CTGAN) was implemented to synthesize 200 datasets from the training sets. A total of 18 classifiers were used to distinguish two genotypes of grade 4 astrocytomas. From generated data using 80% training set, the best discriminatory power was obtained from core tumor regions overlaid on post-contrast T1 using the K-best feature selection algorithm and a Gaussian naïve Bayes classifier (AUC = 0.93, accuracy = 0.92, sensitivity = 1, specificity = 0.86, PR_AUC = 0.92). Similarly, high diagnostic performances were obtained from original and generated data using 50% and 30% training sets. Our findings suggest that conventional MR imaging-based radiomic features combined with machine/deep learning methods may be valuable in discriminating IDH-mutant grade 4 astrocytomas from IDH-wild-type GBMs.