Timing of Biomarker Changes in Sporadic Alzheimer's Disease in Estimated Years from Symptom Onset

OBJECTIVE

A clock relating amyloid positron emission tomography (PET) to time was used to estimate the timing of biomarker changes in sporadic Alzheimer disease (AD).

METHODS

Research participants were included who underwent cerebrospinal fluid (CSF) collection within 2 years of amyloid PET. The ages at amyloid onset and AD symptom onset were estimated for each individual. The timing of change for plasma, CSF, imaging, and cognitive measures was calculated by comparing restricted cubic splines of cross-sectional data from the amyloid PET positive and negative groups.

RESULTS

The amyloid PET positive sub-cohort (n = 118) had an average age of 70.4 ± 7.4 years (mean ± standard deviation) and 16% were cognitively impaired. The amyloid PET negative sub-cohort (n = 277) included individuals with low levels of amyloid plaque burden at all scans who were cognitively unimpaired at the time of the scans. Biomarker changes were detected 15-19 years before estimated symptom onset for CSF Aβ42/Aβ40, plasma Aβ42/Aβ40, CSF pT217/T217, and amyloid PET; 12-14 years before estimated symptom onset for plasma pT217/T217, CSF neurogranin, CSF SNAP-25, CSF sTREM2, plasma GFAP, and plasma NfL; and 7-9 years before estimated symptom onset for CSF pT205/T205, CSF YKL-40, hippocampal volumes, and cognitive measures.

INTERPRETATION

The use of an amyloid clock enabled visualization and analysis of biomarker changes as a function of estimated years from symptom onset in sporadic AD. This study demonstrates that estimated years from symptom onset based on an amyloid clock can be used as a continuous staging measure for sporadic AD and aligns with findings in autosomal dominant AD. ANN NEUROL 2024;95:951-965.

Highly accurate blood test for Alzheimer's disease is similar or superior to clinical cerebrospinal fluid tests

With the emergence of Alzheimer's disease (AD) disease-modifying therapies, identifying patients who could benefit from these treatments becomes critical. In this study, we evaluated whether a precise blood test could perform as well as established cerebrospinal fluid (CSF) tests in detecting amyloid-β (Aβ) plaques and tau tangles. Plasma %p-tau217 (ratio of phosporylated-tau217 to non-phosphorylated tau) was analyzed by mass spectrometry in the Swedish BioFINDER-2 cohort (n = 1,422) and the US Charles F. and Joanne Knight Alzheimer Disease Research Center (Knight ADRC) cohort (n = 337). Matched CSF samples were analyzed with clinically used and FDA-approved automated immunoassays for Aβ42/40 and p-tau181/Aβ42. The primary and secondary outcomes were detection of brain Aβ or tau pathology, respectively, using positron emission tomography (PET) imaging as the reference standard. Main analyses were focused on individuals with cognitive impairment (mild cognitive impairment and mild dementia), which is the target population for available disease-modifying treatments. Plasma %p-tau217 was clinically equivalent to FDA-approved CSF tests in classifying Aβ PET status, with an area under the curve (AUC) for both between 0.95 and 0.97. Plasma %p-tau217 was generally superior to CSF tests in classification of tau-PET with AUCs of 0.95-0.98. In cognitively impaired subcohorts (BioFINDER-2: n = 720; Knight ADRC: n = 50), plasma %p-tau217 had an accuracy, a positive predictive value and a negative predictive value of 89-90% for Aβ PET and 87-88% for tau PET status, which was clinically equivalent to CSF tests, further improving to 95% using a two-cutoffs approach. Blood plasma %p-tau217 demonstrated performance that was clinically equivalent or superior to clinically used FDA-approved CSF tests in the detection of AD pathology. Use of high-performance blood tests in clinical practice can improve access to accurate AD diagnosis and AD-specific treatments.

Disease staging of Alzheimer's disease using a CSF-based biomarker model

Biological staging of individuals with Alzheimer's disease (AD) may improve diagnostic and prognostic workup of dementia in clinical practice and the design of clinical trials. In this study, we used the Subtype and Stage Inference (SuStaIn) algorithm to establish a robust biological staging model for AD using cerebrospinal fluid (CSF) biomarkers. Our analysis involved 426 participants from BioFINDER-2 and was validated in 222 participants from the Knight Alzheimer Disease Research Center cohort. SuStaIn identified a singular biomarker sequence and revealed that five CSF biomarkers effectively constituted a reliable staging model (ordered: Aβ42/40, pT217/T217, pT205/T205, MTBR-tau243 and non-phosphorylated mid-region tau). The CSF stages (0-5) demonstrated a correlation with increased abnormalities in other AD-related biomarkers, such as Aβ-PET and tau-PET, and aligned with longitudinal biomarker changes reflective of AD progression. Higher CSF stages at baseline were associated with an elevated hazard ratio of clinical decline. This study highlights a common molecular pathway underlying AD pathophysiology across all patients, suggesting that a single CSF collection can accurately indicate the presence of AD pathologies and characterize the stage of disease progression. The proposed staging model has implications for enhancing diagnostic and prognostic assessments in both clinical practice and the design of clinical trials.

Comparison of cerebrospinal fluid, plasma and neuroimaging biomarker utility in Alzheimer's disease

Alzheimer's disease biomarkers are crucial to understanding disease pathophysiology, aiding accurate diagnosis and identifying target treatments. Although the number of biomarkers continues to grow, the relative utility and uniqueness of each is poorly understood as prior work has typically calculated serial pairwise relationships on only a handful of markers at a time. The present study assessed the cross-sectional relationships among 27 Alzheimer's disease biomarkers simultaneously and determined their ability to predict meaningful clinical outcomes using machine learning. Data were obtained from 527 community-dwelling volunteers enrolled in studies at the Charles F. and Joanne Knight Alzheimer Disease Research Center at Washington University in St Louis. We used hierarchical clustering to group 27 imaging, CSF and plasma measures of amyloid beta, tau [phosphorylated tau (p-tau), total tau t-tau)], neuronal injury and inflammation drawn from MRI, PET, mass-spectrometry assays and immunoassays. Neuropsychological and genetic measures were also included. Random forest-based feature selection identified the strongest predictors of amyloid PET positivity across the entire cohort. Models also predicted cognitive impairment across the entire cohort and in amyloid PET-positive individuals. Four clusters emerged reflecting: core Alzheimer's disease pathology (amyloid and tau), neurodegeneration, AT8 antibody-associated phosphorylated tau sites and neuronal dysfunction. In the entire cohort, CSF p-tau181/Aβ40lumi and Aβ42/Aβ40lumi and mass spectrometry measurements for CSF pT217/T217, pT111/T111, pT231/T231 were the strongest predictors of amyloid PET status. Given their ability to denote individuals on an Alzheimer's disease pathological trajectory, these same markers (CSF pT217/T217, pT111/T111, p-tau/Aβ40lumi and t-tau/Aβ40lumi) were largely the best predictors of worse cognition in the entire cohort. When restricting analyses to amyloid-positive individuals, the strongest predictors of impaired cognition were tau PET, CSF t-tau/Aβ40lumi, p-tau181/Aβ40lumi, CSF pT217/217 and pT205/T205. Non-specific CSF measures of neuronal dysfunction and inflammation were poor predictors of amyloid PET and cognitive status. The current work utilized machine learning to understand the interrelationship structure and utility of a large number of biomarkers. The results demonstrate that, although the number of biomarkers has rapidly expanded, many are interrelated and few strongly predict clinical outcomes. Examining the entire corpus of available biomarkers simultaneously provides a meaningful framework to understand Alzheimer's disease pathobiological change as well as insight into which biomarkers may be most useful in Alzheimer's disease clinical practice and trials.

Cerebrospinal fluid proteomics define the natural history of autosomal dominant Alzheimer's disease

Alzheimer's disease (AD) pathology develops many years before the onset of cognitive symptoms. Two pathological processes-aggregation of the amyloid-β (Aβ) peptide into plaques and the microtubule protein tau into neurofibrillary tangles (NFTs)-are hallmarks of the disease. However, other pathological brain processes are thought to be key disease mediators of Aβ plaque and NFT pathology. How these additional pathologies evolve over the course of the disease is currently unknown. Here we show that proteomic measurements in autosomal dominant AD cerebrospinal fluid (CSF) linked to brain protein coexpression can be used to characterize the evolution of AD pathology over a timescale spanning six decades. SMOC1 and SPON1 proteins associated with Aβ plaques were elevated in AD CSF nearly 30 years before the onset of symptoms, followed by changes in synaptic proteins, metabolic proteins, axonal proteins, inflammatory proteins and finally decreases in neurosecretory proteins. The proteome discriminated mutation carriers from noncarriers before symptom onset as well or better than Aβ and tau measures. Our results highlight the multifaceted landscape of AD pathophysiology and its temporal evolution. Such knowledge will be critical for developing precision therapeutic interventions and biomarkers for AD beyond those associated with Aβ and tau.

CSF MTBR-tau243 is a specific biomarker of tau tangle pathology in Alzheimer's disease

Aggregated insoluble tau is one of two defining features of Alzheimer's disease. Because clinical symptoms are strongly correlated with tau aggregates, drug development and clinical diagnosis need cost-effective and accessible specific fluid biomarkers of tau aggregates; however, recent studies suggest that the fluid biomarkers currently available cannot specifically track tau aggregates. We show that the microtubule-binding region (MTBR) of tau containing the residue 243 (MTBR-tau243) is a new cerebrospinal fluid (CSF) biomarker specific for insoluble tau aggregates and compared it to multiple other phosphorylated tau measures (p-tau181, p-tau205, p-tau217 and p-tau231) in two independent cohorts (BioFINDER-2, n = 448; and Knight Alzheimer Disease Research Center, n = 219). MTBR-tau243 was most strongly associated with tau-positron emission tomography (PET) and cognition, whereas showing the lowest association with amyloid-PET. In combination with p-tau205, MTBR-tau243 explained most of the total variance in tau-PET burden (0.58 ≤ R2 ≤ 0.75) and the performance in predicting cognitive measures (0.34 ≤ R2 ≤ 0.48) approached that of tau-PET (0.44 ≤ R2 ≤ 0.52). MTBR-tau243 levels longitudinally increased with insoluble tau aggregates, unlike CSF p-tau species. CSF MTBR-tau243 is a specific biomarker of tau aggregate pathology, which may be utilized in interventional trials and in the diagnosis of patients. Based on these findings, we propose to revise the A/T/(N) criteria to include MTBR-tau243 as representing insoluble tau aggregates ('T').

Novel CSF tau biomarkers can be used for disease staging of sporadic Alzheimer's disease

Biological staging of individuals with Alzheimer's disease (AD) may improve diagnostic and prognostic work-up of dementia in clinical practice and the design of clinical trials. Here, we created a staging model using the Subtype and Stage Inference (SuStaIn) algorithm by evaluating cerebrospinal fluid (CSF) amyloid-β (Aβ) and tau biomarkers in 426 participants from BioFINDER-2, that represent the entire spectrum of AD. The model composition and main analyses were replicated in 222 participants from the Knight ADRC cohort. SuStaIn revealed in the two cohorts that the data was best explained by a single biomarker sequence (one subtype), and that five CSF biomarkers (ordered: Aβ42/40, tau phosphorylation occupancies at the residues 217 and 205 [pT217/T217 and pT205/T205], microtubule-binding region of tau containing the residue 243 [MTBR-tau243], and total tau) were sufficient to create an accurate disease staging model. Increasing CSF stages (0-5) were associated with increased abnormality in other AD-related biomarkers, such as Aβ- and tau-PET, and aligned with different phases of longitudinal biomarker changes consistent with current models of AD progression. Higher CSF stages at baseline were associated with higher hazard ratio of clinical decline. Our findings indicate that a common pathophysiologic molecular pathway develops across all AD patients, and that a single CSF collection is sufficient to reliably indicate the presence of both AD pathologies and the degree and stage of disease progression.

Acute sleep loss decreases CSF-to-blood clearance of Alzheimer's disease biomarkers

INTRODUCTION

Sleep deprivation increases cerebrospinal fluid (CSF) amyloid beta (Aβ) and tau levels; however, sleep's effect on Aβ and tau in plasma is unknown.

METHODS

In a cross-over design, CSF Aβ and tau concentrations were measured in five cognitively normal individuals who had blood and CSF collected every 2 hours for 36 hours during sleep-deprived and normal sleep control conditions.

RESULTS

Aβ40, Aβ42, unphosphorylated tau threonine181 (T181), unphosphorylated tau threonine-217 (T217), and phosphorylated T181 (pT181) concentrations increased ∼35% to 55% in CSF and decreased ∼5% to 15% in plasma during sleep deprivation. CSF/plasma ratios of all Alzheimer's disease (AD) biomarkers increased during sleep deprivation while the CSF/plasma albumin ratio, a measure of blood-CSF barrier permeability, decreased. CSF and plasma Aβ42/40, pT181/T181, and pT181/Aβ42 ratios were stable longitudinally in both groups.

DISCUSSION

These findings show that sleep loss alters some plasma AD biomarkers by lowering brain clearance mechanisms and needs to be taken into account when interpreting individual plasma AD biomarkers but not ratios.

Change in Cerebrospinal Fluid Tau Microtubule Binding Region Detects Symptom Onset, Cognitive Decline, Tangles, and Atrophy in Dominantly Inherited Alzheimer's Disease

OBJECTIVE

Identifying cerebrospinal fluid measures of the microtubule binding region of tau (MTBR-tau) species that reflect tau aggregation could provide fluid biomarkers that track Alzheimer's disease related neurofibrillary tau pathological changes. We examined the cerebrospinal fluid (CSF) MTBR-tau species in dominantly inherited Alzheimer's disease (DIAD) mutation carriers to assess the association with Alzheimer's disease (AD) biomarkers and clinical symptoms.

METHODS

Cross-sectional and longitudinal CSF from 229 DIAD mutation carriers and 130 mutation non-carriers had sequential characterization of N-terminal/mid-domain phosphorylated tau (p-tau) followed by MTBR-tau species and tau positron emission tomography (tau PET), other soluble tau and amyloid biomarkers, comprehensive clinical and cognitive assessments, and brain magnetic resonance imaging of atrophy.

RESULTS

CSF MTBR-tau species located within the putative "border" region and one species corresponding to the "core" region of aggregates in neurofibrillary tangles (NFTs) increased during the presymptomatic stage and decreased during the symptomatic stage. The "border" MTBR-tau species were associated with amyloid pathology and CSF p-tau; whereas the "core" MTBR-tau species were associated stronger with tau PET and CSF measures of neurodegeneration. The ratio of the border to the core species provided a continuous measure of increasing amounts that tracked clinical progression and NFTs.

INTERPRETATION

Changes in CSF soluble MTBR-tau species preceded the onset of dementia, tau tangle increase, and atrophy in DIAD. The ratio of 4R-specific MTBR-tau (border) to the NFT (core) MTBR-tau species corresponds to the pathology of NFTs in DIAD and change with disease progression. The dynamics between different MTBR-tau species in the CSF may serve as a marker of tau-related disease progression and target engagement of anti-tau therapeutics. ANN NEUROL 2023;93:1158-1172.

CSF tau phosphorylation occupancies at T217 and T205 represent improved biomarkers of amyloid and tau pathology in Alzheimer's disease

Cerebrospinal fluid (CSF) amyloid-β peptide (Aβ)42/Aβ40 and the concentration of tau phosphorylated at site 181 (p-tau181) are well-established biomarkers of Alzheimer's disease (AD). The present study used mass spectrometry to measure concentrations of nine phosphorylated and five nonphosphorylated tau species and phosphorylation occupancies (percentage phosphorylated/nonphosphorylated) at ten sites. In the present study we show that, in 750 individuals with a median age of 71.2 years, CSF pT217/T217 predicted the presence of brain amyloid by positron emission tomography (PET) slightly better than Aβ42/Aβ40 (P = 0.02). Furthermore, for individuals with positive brain amyloid by PET (n = 263), CSF pT217/T217 was more strongly correlated with the amount of amyloid (Spearman's ρ = 0.69) than Aβ42/Aβ40 (ρ = -0.42, P < 0.0001). In two independent cohorts of participants with symptoms of AD dementia (n = 55 and n = 90), CSF pT217/T217 and pT205/T205 were better correlated with tau PET measures than CSF p-tau181 concentration. These findings suggest that CSF pT217/T217 and pT205/T205 represent improved CSF biomarkers of amyloid and tau pathology in AD.

Mitigating the Associations of Kidney Dysfunction With Blood Biomarkers of Alzheimer Disease by Using Phosphorylated Tau to Total Tau Ratios

Importance

Chronic kidney disease (CKD) has been associated with increased plasma concentrations of phosphorylated tau (p-tau) 217 and p-tau181, which potentially decreases their usefulness in the diagnostic workup of Alzheimer disease (AD).

Objective

To investigate associations of CKD with plasma ratios of p-tau217 and p-tau181 to the corresponding unphosphorylated peptides in AD.

Design, Setting, and Participants

This cross-sectional study included patients with mild cognitive impairment (cohort 1; enrollment in 2000-2005) and replication in cohort 2 from the Swedish BioFINDER-2 study, including both cognitively unimpaired individuals and those with cognitive impairment (enrollment in 2017-2022). All participants were from 2 memory clinics in Sweden and had plasma tau assessments and CKD status established within 6 months of plasma collection.

Exposures

P-tau217 and p-tau181, unphosphorylated peptides (Tau212-221 and Tau181-190), and the ratios (pT217/T217 and pT181/T181) as well as estimated glomerular filtration rate (eGFR) as an indicator of CKD.

Main Outcomes and Measures

Associations between plasma-soluble p-tau and CKD.

Results

A total of 141 participants from cohort 1 (mean [SD] age, 72.2 [7.7] years; 82 [58.2%] women) and 332 participants from cohort 2 (172 with cognitive impairment and 160 cognitively unimpaired individuals; mean [SD] age, 69.8 [9.4] years; 169 [50.9%] women) were included. Higher eGFR was associated with increased levels of plasma p-tau217, p-tau181, Tau212-221, and Tau181-190 in individuals with cognitive impairment (cohort 1: R range, -0.24 to -0.59; P < .004; cohort 2: R range, -0.18 to -0.53; P < .02) and cognitively unimpaired individuals (cohort 2: R range, -0.44 to -0.50; P < .001). However, eGFR did not correlate with the pT217/T217 ratio in patients with cognitive impairment (cohort 1: R, -0.11; P = .19; cohort 2: R, -0.02; P = .78), and the correlations with pT217/T217 ratio were significantly attenuated in cognitively unimpaired individuals (difference: R, -0.14 [95% CI, -0.22 to -0.007]; P = .001). For p-tau217 and pT217/T217, the mean fold increases in amyloid-β positive (Aβ+) compared with Aβ- groups ranged from 2.31 (95% CI, 1.86-2.77) to 4.61 (95% CI, 3.39-5.83) in participants with cognitive impairment and from 1.26 (95% CI, 0.98-1.55) to 1.27 (95% CI, 0.94-1.59) in cognitively unimpaired individuals and were clearly higher than the mean fold increases in those with CKD compared with those without CKD, ranging from 0.05 (95% CI, -0.28 to 0.38) to 0.72 (95% CI, 0.25-1.19) in participants with cognitive impairment and from 0.09 (95% CI, -0.08 to 0.26) to 0.36 (95% CI, 0.19-0.52) in cognitively unimpaired individuals.

Conclusions and Relevance

In this study, CKD was associated with increased plasma levels of soluble tau, but for p-tau217 the associations were considerably lower than the association with Aβ positivity. Importantly, the ratios, and especially pT217/T217, were less associated with CKD than p-tau forms alone and therefore are likely to more accurately reflect AD-related pathological changes.

Suvorexant acutely decreases tau phosphorylation and Aβ in the human CNS

OBJECTIVE

In Alzheimer's disease, hyperphosphorylated tau is associated with formation of insoluble paired helical filaments that aggregate as neurofibrillary tau tangles and are associated with neuronal loss and cognitive symptoms. Dual orexin receptor antagonists decrease soluble amyloid-β levels and amyloid plaques in mouse models over-expressing amyloid-β, but have not been reported to affect tau phosphorylation. In this randomized controlled trial, we tested the acute effect of suvorexant, a dual orexin receptor antagonist, on amyloid-β, tau, and phospho-tau.

METHODS

Thirty-eight cognitively unimpaired participants aged 45-65 years were randomized to placebo (N = 13), suvorexant 10 mg (N = 13), and suvorexant 20 mg (N = 12). Six milliliters of cerebrospinal fluid was collected via an indwelling lumbar catheter every 2 hours for 36 hours starting at 20:00. Participants received placebo or suvorexant at 21:00. All samples were processed and measured for multiple forms of amyloid-β, tau, and phospho-tau via immunoprecipitation and liquid chromatography-mass spectrometry.

RESULTS

The ratio of phosphorylated-tau-threonine-181 to unphosphorylated-tau-threonine-181, a measure of phosphorylation at this tau phosphosite, decreased ~10-15% in participants treated with suvorexant 20 mg compared to placebo. However, phosphorylation at tau-serine-202 and tau-threonine-217 were not decreased by suvorexant. Suvorexant decreased amyloid-β ~10-20% compared to placebo starting 5 hours after drug administration.

INTERPRETATION

In this study, suvorexant acutely decreased tau phosphorylation and amyloid-β concentrations in the central nervous system. Suvorexant is approved by the Food and Drug Administration to treatment insomnia and may have potential as a repurposed drug for the prevention of Alzheimer's disease, however future studies with chronic treatment are needed. This article is protected by copyright. All rights reserved.

CSF tau microtubule-binding region identifies pathological changes in primary tauopathies

Despite recent advances in fluid biomarker research in Alzheimer's disease (AD), there are no fluid biomarkers or imaging tracers with utility for diagnosis and/or theragnosis available for other tauopathies. Using immunoprecipitation and mass spectrometry, we show that 4 repeat (4R) isoform-specific tau species from microtubule-binding region (MTBR-tau275 and MTBR-tau282) increase in the brains of corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), frontotemporal lobar degeneration (FTLD)-MAPT and AD but decrease inversely in the cerebrospinal fluid (CSF) of CBD, FTLD-MAPT and AD compared to control and other FTLD-tau (for example, Pick's disease). CSF MTBR-tau measures are reproducible in repeated lumbar punctures and can be used to distinguish CBD from control (receiver operating characteristic area under the curve (AUC) = 0.889) and other FTLD-tau, such as PSP (AUC = 0.886). CSF MTBR-tau275 and MTBR-tau282 may represent the first affirmative biomarkers to aid in the diagnosis of primary tauopathies and facilitate clinical trial designs.

Head-to-head comparison of 10 plasma phospho-tau assays in prodromal Alzheimer’s disease

Plasma phospho-tau (p-tau) species have emerged as the most promising blood-based biomarkers of Alzheimer's disease. Here, we performed a head-to-head comparison of p-tau181, p-tau217 and p-tau231 measured using 10 assays to detect abnormal brain amyloid-β status and predict future progression to Alzheimer's dementia. The study included 135 patients with baseline diagnosis of mild cognitive impairment (mean age 72.4 years; 60.7% women) who were followed for an average of 4.9 years. Seventy-one participants had abnormal Aβ-status (i.e., abnormal CSF Aβ42/40) at baseline; and 45 of these Aβ-positive participants progressed to Alzheimer's dementia during follow-up. P-tau concentrations were determined in baseline plasma and CSF. P-tau217 and p-tau181 were both measured using immunoassays developed by Lilly Research Laboratories (Lilly) and mass spectrometry assays developed at Washington University (WashU). P-tau217 was also analysed using Simoa immunoassay developed by Janssen Research and Development (Janss). P-tau181 was measured using Simoa immunoassay from ADxNeurosciences (ADx), Lumipulse immunoassay from Fujirebio (Fuji) and Splex immunoassay from Mesoscale Discovery (Splex). Both p-tau181 and p-tau231 were quantified using Simoa immunoassay developed at the University of Gothenburg (UGOT). We found that the mass spectrometry-based p-tau217 (p-tau217WashU) exhibited significantly better performance than all other plasma p-tau biomarkers when detecting abnormal Aβ status (AUC = 0.947; pdiff &lt; 0.015) or progression to Alzheimer's dementia (AUC = 0.932; pdiff &lt; 0.027). Among immunoassays, p-tau217Lilly had the highest AUCs (0.886-0.889), which was not significantly different from the AUCs of p-tau217Janss, p-tau181ADx and p-tau181WashU (AUCrange, 0.835-0.872; pdiff &gt; 0.09), but higher compared with AUC of p-tau231UGOT, p-tau181Lilly, p-tau181UGOT, p-tau181Fuji, and p-tau181Splex (AUCrange, 0.642-0.813; pdiff ≤0.029). Correlations between plasma and CSF values were strongest for p-tau217WashU (R = 0.891) followed by p-tau217Lilly (R = 0.755; pdiff = 0.003 vs p-tau217WashU) and weak to moderate for the rest of the p-tau biomarkers (Rrange, 0.320-0.669). In conclusion, the findings suggest that among all tested plasma p-tau assays, mass spectrometry-based measures of p-tau217 perform best when identifying mild cognitive impairment patients with abnormal brain Aβ or those who will subsequently progress to Alzheimer's dementia. Several other assays (p-tau217Lilly, p-tau217Janss, p-tau181ADx, and p-tau181WashU) showed relatively high and consistent accuracy across both outcomes. The results further indicate that the highest performing assays have performance metrics that rival the gold standards of Aβ-PET and CSF. If further validated, our findings will have significant impacts in diagnosis, screening and treatment for Alzheimer's dementia in the future.

Recapitulation of endogenous 4R tau expression and formation of insoluble tau in directly reprogrammed human neurons

Tau is a microtubule-binding protein expressed in neurons, and the equal ratios between 4-repeat (4R) and 3-repeat (3R) isoforms are maintained in normal adult brain function. Dysregulation of 3R:4R ratio causes tauopathy, and human neurons that recapitulate tau isoforms in health and disease will provide a platform for elucidating pathogenic processes involving tau pathology. We carried out extensive characterizations of tau isoforms expressed in human neurons derived by microRNA-induced neuronal reprogramming of adult fibroblasts. Transcript and protein analyses showed that miR neurons expressed all six isoforms with the 3R:4R isoform ratio equivalent to that detected in human adult brains. Also, miR neurons derived from familial tauopathy patients with a 3R:4R ratio altering mutation showed increased 4R tau and the formation of insoluble tau with seeding activity. Our results collectively demonstrate the utility of miRNA-induced neuronal reprogramming to recapitulate endogenous tau regulation comparable with the adult brain in health and disease.

Association of BDNF Val66Met With Tau Hyperphosphorylation and Cognition in Dominantly Inherited Alzheimer Disease

IMPORTANCE

Allelic variation in the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism moderates increases in cerebrospinal fluid (CSF) levels of tau and phosphorylated tau 181 (p-tau181), measured using immunoassay, and cognitive decline in presymptomatic dominantly inherited Alzheimer disease (DIAD). Advances in mass spectrometry show that CSF tau phosphorylation occupancy at threonine 181 and 217 (p-tau181/tau181, p-tau217/tau217) increases with initial β-amyloid (Aβ) aggregation, while phosphorylation occupancy at threonine 205 (p-tau205/tau205) and level of total tau increase when brain atrophy and clinical symptoms become evident.

OBJECTIVE

To determine whether site-specific tau phosphorylation occupancy (ratio of phosphorylated to unphosphorylated tau) is associated with BDNF Val66Met in presymptomatic and symptomatic DIAD.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional cohort study included participants from the Dominantly Inherited Alzheimer Network (DIAN) and Aβ-positive cognitively normal older adults in the Alzheimer's Disease Neuroimaging Initiative (ADNI). Data were collected from 2009 through 2018 at multicenter clinical sites in the United States, United Kingdom, and Australia, with no follow-up. DIAN participants provided a CSF sample and completed clinical and cognitive assessments. Data analysis was conducted between March 2020 and March 2021.

MAIN OUTCOMES AND MEASURES

Mass spectrometry analysis was used to determine site-specific tau phosphorylation level; tau levels were also measured using immunoassay. Episodic memory and global cognitive composites were computed.

RESULTS

Of 374 study participants, 144 were mutation noncarriers, 156 were presymptomatic mutation carriers, and 74 were symptomatic carriers. Of the 527 participants in the network, 153 were excluded because their CSF sample, BDNF status, or both were unavailable. Also included were 125 Aβ-positive cognitively normal older adults in the ADNI. The mean (SD) age of DIAD participants was 38.7 (10.9) years; 43% were women. The mean (SD) age of participants with preclinical sporadic AD was 74.8 (5.6) years; 52% were women. In presymptomatic mutation carriers, compared with Val66 homozygotes, Met66 carriers showed significantly poorer episodic memory (d = 0.62; 95% CI, 0.28-0.95), lower hippocampal volume (d = 0.40; 95% CI, 0.09-0.71), and higher p-tau217/tau217 (d = 0.64; 95% CI, 0.30-0.97), p-tau181/tau181 (d = 0.65; 95% CI, 0.32-0.99), and mass spectrometry total tau (d = 0.43; 95% CI, 0.10-0.76). In symptomatic mutation carriers, Met66 carriers showed significantly poorer global cognition (d = 1.17; 95% CI, 0.65-1.66) and higher p-tau217/tau217 (d = 0.53; 95% CI, 0.05-1.01), mass spectrometry total tau (d = 0.78; 95% CI, 0.28-1.25), and p-tau205/tau205 (d = 0.97; 95% CI, 0.46-1.45), when compared with Val66 homozygotes. In preclinical sporadic AD, Met66 carriers showed poorer episodic memory (d = 0.39; 95% CI, 0.00-0.77) and higher total tau (d = 0.45; 95% CI, 0.07-0.84) and p-tau181 (d = 0.46; 95% CI, 0.07-0.85).

CONCLUSIONS AND RELEVANCE

In DIAD, clinical disease stage and BDNF Met66 were associated with cognitive impairment and levels of site-specific tau phosphorylation. This suggests that pharmacological strategies designed to increase neurotrophic support in the presymptomatic stages of AD may be beneficial.

Site-Specific Cerebrospinal Fluid Tau Hyperphosphorylation in Response to Alzheimer's Disease Brain Pathology: Not All Tau Phospho-Sites are Hyperphosphorylated

BACKGROUND

Understanding patterns of association between CSF phosphorylated tau (p-tau) species and clinical disease severity will aid Alzheimer's disease (AD) diagnosis and treatment.

OBJECTIVE

To evaluate changes in tau phosphorylation ratios to brain imaging (amyloid PET, [18F]GTP1 PET, and MRI) and cognition across clinical stages of AD in two different cohorts.

METHODS

A mass spectrometry (MS)-based method was used to evaluate the relationship between p-tau/tau phosphorylation ratios on 11 sites in CSF and AD pathology measured by tau PET ([18F]GTP1) and amyloid PET ([18F]florbetapir or [18F]florbetaben). Cohort A included cognitively normal-amyloid negative (n = 6) and positive (n = 5) individuals, and amyloid positive prodromal (n = 13), mild (n = 12), and moderate AD patients (n = 10); and Cohort B included amyloid positive prodromal (n = 24) and mild (n = 40) AD patients.

RESULTS

In this cross-sectional analysis, we identified clusters of phosphosites with different profiles of phosphorylation ratios across stages of disease. Eight of 11 investigated sites were hyperphosphorylated and associated with the SUVR measures from [18F]GTP1 and amyloid PET. Novel sites 111, 153, and 208 may be relevant biomarkers for AD diagnosis to complement tau hyperphosphorylation measures on previously established sites 181, 205, 217, and 231. Hypophosphorylation was detected on residues 175, 199, and 202, and was inversely associated with [18F]GTP1 and amyloid PET.

CONCLUSION

Hyperphosphorylated and hypophosphorylated forms of tau are associated with AD pathologies, and due to their different site-specific profiles, they may be used in combination to assist with staging of disease.

MAPT R406W increases tau T217 phosphorylation in absence of amyloid pathology

Objective

Tau hyperphosphorylation at threonine 217 (pT217) in cerebrospinal fluid (CSF) has recently been linked to early amyloidosis and could serve as a highly sensitive biomarker for Alzheimer’s disease (AD). However, it remains unclear whether other tauopathies induce pT217 modifications. To determine if pT217 modification is specific to AD, CSF pT217 was measured in AD and other tauopathies.

Methods

Using immunoprecipitation and mass spectrometry methods, we compared CSF T217 phosphorylation occupancy (pT217/T217) and amyloid‐beta (Aβ) 42/40 ratio in cognitively normal individuals and those with symptomatic AD, progressive supranuclear palsy, corticobasal syndrome, and sporadic and familial frontotemporal dementia.

Results

Individuals with AD had high CSF pT217/T217 and low Aβ42/40. In contrast, cognitively normal individuals and the majority of those with 4R tauopathies had low CSF pT217/T217 and normal Aβ 42/40. We identified a subgroup of individuals with increased CSF pT217/T217 and normal Aβ 42/40 ratio, most of whom were MAPT R406W mutation carriers. Diagnostic accuracies of CSF Aβ 42/40 and CSF pT217/T217, alone and in combination were compared. We show that CSF pT217/T217 × CSF Aβ 42/40 is a sensitive composite biomarker that can separate MAPT R406W carriers from cognitively normal individuals and those with other tauopathies.

Interpretation

MAPT R406W is a tau mutation that leads to 3R+4R tauopathy similar to AD, but without amyloid neuropathology. These findings suggest that change in CSF pT217/T217 ratio is not specific to AD and might reflect common downstream tau pathophysiology common to 3R+4R tauopathies.

CSF tau microtubule binding region identifies tau tangle and clinical stages of Alzheimer's disease

Tau is a microtubule associated protein in the brain that aggregates in Alzheimer's disease to form pathological tangles and neurites. Insoluble tau aggregates composed of the microtubule binding region (MTBR) of tau are highly associated with the cognitive and clinical symptoms of Alzheimer's disease. In contrast, levels of soluble forms of tau, such as CSF total tau and phosphorylated tau-181 and tau-217, increase prior to tau aggregation in Alzheimer's disease, but these biomarkers do not measure the MTBR of tau. Thus, how CSF MTBR-tau is altered in Alzheimer's disease remains unclear. In this study, we used sequential immunoprecipitation and chemical extraction methods followed by mass spectrometry to analyse MTBR-tau species in Alzheimer's disease and control CSF. We quantified MTBR-tau-specific regions in the CSF and identified that species containing the region beginning at residue 243 were the most highly correlated with tau PET and cognitive measures. This finding suggests that CSF level of tau species containing the upstream region of MTBR may reflect changes in tau pathology that occur in Alzheimer's disease and could serve as biomarkers to stage Alzheimer's disease and track the development of tau-directed therapeutics.

Blood plasma phosphorylated-tau isoforms track CNS change in Alzheimer's disease

Highly sensitive and specific plasma biomarkers for Alzheimer’s disease (AD) have the potential to improve diagnostic accuracy in the clinic and facilitate research studies including enrollment in prevention and treatment trials. We recently reported CSF tau hyperphosphorylation, especially on T217, is an accurate predictor of β-amyloidosis at asymptomatic and symptomatic stages. In the current study, we determine by mass spectrometry the potential utility of plasma p-tau isoforms to detect AD pathology and investigate CSF and plasma tau isoforms’ profile relationships. Plasma tau was truncated as previously described in CSF. CSF and plasma measures of p-tau-217 and p-tau-181 were correlated. No correlation was found between CSF and plasma on total-tau levels and pS202 measures. We found p-tau-217 and p-tau-181 were highly specific for amyloid plaque pathology in the discovery cohort (n = 36, AUROC = 0.99 and 0.98 respectively). In the validation cohort (n = 92), p-tau-217 measures were still specific to amyloid status (AUROC = 0.92), and p-tau-181 measures were less specific (AUROC = 0.75).

Neurofilaments: neurobiological foundations for biomarker applications

Interest in neurofilaments has risen sharply in recent years with recognition of their potential as biomarkers of brain injury or neurodegeneration in CSF and blood. This is in the context of a growing appreciation for the complexity of the neurobiology of neurofilaments, new recognition of specialized roles for neurofilaments in synapses and a developing understanding of mechanisms responsible for their turnover. Here we will review the neurobiology of neurofilament proteins, describing current understanding of their structure and function, including recently discovered evidence for their roles in synapses. We will explore emerging understanding of the mechanisms of neurofilament degradation and clearance and review new methods for future elucidation of the kinetics of their turnover in humans. Primary roles of neurofilaments in the pathogenesis of human diseases will be described. With this background, we then will review critically evidence supporting use of neurofilament concentration measures as biomarkers of neuronal injury or degeneration. Finally, we will reflect on major challenges for studies of the neurobiology of intermediate filaments with specific attention to identifying what needs to be learned for more precise use and confident interpretation of neurofilament measures as biomarkers of neurodegeneration.

Regional correlation of biochemical measures of amyloid and tau phosphorylation in the brain

Alzheimer’s disease (AD) neuropathologic change is characterized by amyloid plaques and neurofibrillary tangles (NFTs) that consist of aggregated amyloid beta (Abeta) and hyperphosphorylated tau proteins (p-tau), respectively. Although the global relationship between Abeta and p-tau has been studied for decades, it is still unclear whether a regional correlation exists between Abeta and p-tau in the human brain. Recent studies in cerebrospinal fluid (CSF) have suggested that tau phosphorylation at specific sites such as T217 is modified at an early stage of AD when amyloid plaques become detectable. We applied biochemical and mass spectrometry methods in human brain samples with and without Abeta plaque pathology to measure site-specific phosphorylation occupancies in soluble and insoluble tau. Our quantitative results identified multiple residues specifically hyper-phosphorylated in AD, including at sites T111, T153, S184 (or S185), T205, S208, T217, S262, and S285 in brain soluble tau. In contrast, the most enriched phosphorylated residues in brain insoluble tau were T111, S113, T153, T181, S199, S202, T205, T217, T231, S262, and S396. Tau phosphorylation occupancies in the insoluble fraction were relatively constant across brain regions, suggesting that tau has a consistent phosphorylation pattern once it has aggregated into NFTs. We did not find regional association between Abeta42 and insoluble tau. However, the phosphorylation profile of soluble tau in AD brain was highly correlated to that in AD CSF, which was analyzed in a previous study. We also found a higher regional association between total Abeta42 and soluble tau phosphorylation occupancy at residues T111, T153 and T217 in the brain. This study provides insights into regional interactions between amyloidosis and specific tau phosphorylated residues in the human brain and may explain the specific increases of tau species phosphorylation observed in AD CSF.

Cerebrospinal fluid phospho-tau T217 outperforms T181 as a biomarker for the differential diagnosis of Alzheimer's disease and PET amyloid-positive patient identification

BACKGROUND

Cerebrospinal fluid biomarker profiles characterized by decreased amyloid-beta peptide levels and increased total and phosphorylated tau levels at threonine 181 (pT181) are currently used to discriminate between Alzheimer's disease and other neurodegenerative diseases. However, these changes are not entirely specific to Alzheimer's disease, and it is noteworthy that other phosphorylated isoforms of tau, possibly more specific for the disease process, have been described in the brain parenchyma of patients. The precise detection of these isoforms in biological fluids remains however a challenge.

METHODS

In the present study, we used the latest quantitative mass spectrometry approach, which achieves a sensitive detection in cerebrospinal fluid biomarker of two phosphorylated tau isoforms, pT181 and pT217, and first analyzed a cohort of probable Alzheimer's disease patients and patients with other neurological disorders, including tauopathies, and a set of cognitively normal controls. We then checked the validity of our results on a second cohort comprising cognitively normal individuals and patients with mild cognitive impairments and AD stratified in terms of their amyloid status based on PiB-PET imaging methods.

RESULTS

In the first cohort, pT217 but not pT181 differentiated between Alzheimer's disease patients and those with other neurodegenerative diseases and control subjects much more specificity and sensitivity than pT181. T217 phosphorylation was increased by 6.0-fold in patients with Alzheimer's disease whereas T181 phosphorylation was only increased by 1.3-fold, when compared with control subjects. These results were confirmed in the case of a second cohort, in which the pT217 cerebrospinal fluid levels marked out amyloid-positive patients with a sensitivity and a specificity of more than 90% (AUC 0.961; CI 0.874 to 0.995). The pT217 concentrations were also highly correlated with the PiB-PET values (correlation coefficient 0.72; P < 0.001).

CONCLUSIONS

Increased cerebrospinal fluid pT217 levels, more than those of pT181, are highly specific biomarkers for detecting both the preclinical and advanced forms of Alzheimer's disease. This finding should greatly improve the diagnosis of Alzheimer's disease, along with the correlations found to exist between pT217 levels and PiB-PET data. It also suggests that pT217 is a promising potential target for therapeutic applications and that a link exists between amyloid and tau pathology.

A soluble phosphorylated tau signature links tau, amyloid and the evolution of stages of dominantly inherited Alzheimer's disease

Development of tau-based therapies for Alzheimer's disease requires an understanding of the timing of disease-related changes in tau. We quantified the phosphorylation state at multiple sites of the tau protein in cerebrospinal fluid markers across four decades of disease progression in dominantly inherited Alzheimer's disease. We identified a pattern of tau staging where site-specific phosphorylation changes occur at different periods of disease progression and follow distinct trajectories over time. These tau phosphorylation state changes are uniquely associated with structural, metabolic, neurodegenerative and clinical markers of disease, and some (p-tau217 and p-tau181) begin with the initial increases in aggregate amyloid-β as early as two decades before the development of aggregated tau pathology. Others (p-tau205 and t-tau) increase with atrophy and hypometabolism closer to symptom onset. These findings provide insights into the pathways linking tau, amyloid-β and neurodegeneration, and may facilitate clinical trials of tau-based treatments.

Sleep Deprivation Affects Tau Phosphorylation in Human Cerebrospinal Fluid

Tau hyperphosphorylation is an early step in tau-mediated neurodegeneration and is associated with intracellular aggregation of tau as neurofibrillary tangles, neuronal and synaptic loss, and eventual cognitive dysfunction in Alzheimer disease. Sleep loss increases the cerebrospinal fluid concentration of amyloid-β and tau. Using mass spectrometry, we measured tau and phosphorylated tau concentrations in serial samples of cerebrospinal fluid collected from participants who were sleep-deprived, treated with sodium oxybate, or allowed to sleep normally. We found that sleep loss affected phosphorylated tau differently depending on the modified site. These findings suggest a mechanism for sleep loss to increase risk of Alzheimer disease. ANN NEUROL 2020;87:700-709.

Tau Kinetics in Neurons and the Human Central Nervous System

We developed stable isotope labeling and mass spectrometry approaches to measure the kinetics of multiple isoforms and fragments of tau in the human central nervous system (CNS) and in human induced pluripotent stem cell (iPSC)-derived neurons. Newly synthesized tau is truncated and released from human neurons in 3 days. Although most tau proteins have similar turnover, 4R tau isoforms and phosphorylated forms of tau exhibit faster turnover rates, suggesting unique processing of these forms that may have independent biological activities. The half-life of tau in control human iPSC-derived neurons is 6.74 ± 0.45 days and in human CNS is 23 ± 6.4 days. In cognitively normal and Alzheimer's disease participants, the production rate of tau positively correlates with the amount of amyloid plaques, indicating a biological link between amyloid plaques and tau physiology.

SILK studies - capturing the turnover of proteins linked to neurodegenerative diseases

Alzheimer disease (AD) is one of several neurodegenerative diseases characterized by dysregulation, misfolding and accumulation of specific proteins in the CNS. The stable isotope labelling kinetics (SILK) technique is based on generating amino acids labelled with naturally occurring stable (that is, nonradioactive) isotopes of carbon and/or nitrogen. These labelled amino acids can then be incorporated into proteins, enabling rates of protein production and clearance to be determined in vivo and in vitro without the use of radioactive or chemical labels. Over the past decade, SILK studies have been used to determine the turnover of key pathogenic proteins amyloid-β (Aβ), tau and superoxide dismutase 1 (SOD1) in the cerebrospinal fluid of healthy individuals, patients with AD and those with other neurodegenerative diseases. These studies led to the identification of several factors that alter the production and/or clearance of these proteins, including age, sleep and disease-causing genetic mutations. SILK studies have also been used to measure Aβ turnover in blood and within brain tissue. SILK studies offer the potential to elucidate the mechanisms underlying various neurodegenerative disease mechanisms, including neuroinflammation and synaptic dysfunction, and to demonstrate target engagement of novel disease-modifying therapies.

Tau Phosphorylation Rates Measured by Mass Spectrometry Differ in the Intracellular Brain vs. Extracellular Cerebrospinal Fluid Compartments and Are Differentially Affected by Alzheimer's Disease

Tau protein aggregation into neurofibrillary tangles in the central nervous system contributes to the etiology of certain neurodegenerative disorders, including Alzheimer's disease (AD). Though the mechanism of tau destabilization is not fully understood yet, tau protein has been found to be hyperphosphorylated in tau aggregates. To investigate this further, we developed a highly sensitive and specific mass spectrometry (MS) method using parallel reaction monitoring (PRM) to identify tau phosphorylation sites. This method enables us to compare the abundance of phosphorylation sites in tau proteins in the brain and cerebrospinal fluid (CSF) in humans with and without AD. We detected 29 distinct phosphorylated tau (p-tau) sites in full-length tau from soluble human brain lysate and 12 sites on truncated tau in CSF, mainly in the mid-domain. Brain soluble tau phosphorylation sites are localized on three domains including a proline-rich mid-domain, the C-terminus, and a cluster on the N-terminal projection domain not previously characterized. Some phosphorylation sites increased in CSF, while others decreased compared to brain. Notably, phosphorylation on T205 and S208, recognized by AT8 antibody defining Braak stages of brain tau aggregation, were not detected in normal brain soluble tau but were found in the CSF. Comparison of the p-tau rates from the brain and the CSF indicated that the abundance of phosphorylated sites varied in a site-specific manner. CSF tau proteins from non-AD participants were significantly hyperphosphorylated on T111, T205, S208, T217 and T231. In AD CSF, hyperphosphorylation on these sites was exacerbated, and phosphorylation on T153 and T175 specifically were detected. This supports the hypothesis that tau hyperphosphorylation could be a physiological process amplified by AD pathology. Conversely, we found that S202 was hypophosphorylated in CSF and was not hyperphosphorylated in AD, demonstrating that p-tau isoforms could have different metabolisms depending on which sites are phosphorylated. These site-specific p-tau rates are independent of tau concentration and distinct of current CSF tau and p-tau assays measuring tau isoforms levels. Targeted MS multiplexing ability and high-throughput capacity lets us envision the use of these new p-tau measurements as promising biomarkers for AD diagnosis and tracking therapeutic responses.

Differential Mass Spectrometry Profiles of Tau Protein in the Cerebrospinal Fluid of Patients with Alzheimer's Disease, Progressive Supranuclear Palsy, and Dementia with Lewy Bodies

Microtubule-associated Tau proteins are major actors in neurological disorders, the so-called tauopathies. In some of them, and specifically in Alzheimer's disease (AD), hyperphosphorylated forms of Tau aggregate into neurofibrillary tangles. Following and understanding the complexity of Tau's molecular profile with its multiple isoforms and post-translational modifications represent an important issue, and a major analytical challenge. Immunodetection methods are, in fact, limited by the number, specificity, sensitivity, and capturing property of the available antibodies. Mass spectrometry (MS) has recently allowed protein quantification in complex biological fluids using isotope-labeled recombinant standard for absolute quantification (PSAQ). To study Tau proteins, which are found at very low concentrations within the cerebrospinal fluid (CSF), we relied on an innovative two-step pre-fractionation strategy, which was not dependent on immuno-enrichment. We then developed a sensitive multiplex peptide detection capability using targeted high-resolution MS to quantify Tau-specific peptides covering its entire sequence. This approach was used on a clinical cohort of patients with AD, progressive supranuclear palsy (PSP), and dementia with Lewy body (DLB) and with control non-neurodegenerative disorders. We uncovered a common CSF Tau molecular profile characterized by a predominance of central core expression and 1N/3R isoform detection. While PSP and DLB tau profiles showed minimal changes, AD was characterized by a unique pattern with specific modifications of peptide distribution. Taken together these results provide important information on Tau biology for future therapeutic interventions, and improved molecular diagnosis of tauopathies.