Biomarker development for the tau therapeutic landscape

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. 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. 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. 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.

BackgroundHyperphosphorylated tau isoforms (p‐tau) in cerebrospinal fluid (CSF) and plasma represent promising measures to monitor Alzheimer disease (AD) pathological changes. Brain amyloid deposition precedes tau aggregation and associated clinical decline by two decades. Several CSF and plasma p‐tau isoforms have been described as potential surrogates for tau Positron Emission Tomography (PET) imaging, but p‐tau isoforms have a strong association with amyloid PET, and increase without tau pathology. In this study, we investigated the relationship between multiple CSF p‐tau isoforms and brain imaging measures in the Knight ADRC cohort.MethodWe analyzed 10 p‐tau isoforms by mass spectrometry in 1932 CSF samples (1173 participants). Associated data includes 1250 amyloid PET and 442 tau PET scans, as well as CSF Aβ42/Aβ40 by immunoassay for all samples. We measured phosphorylation occupancies (ptau/tau) at T111, T153, T175, T181, S199, S202, T205, S208, T217 and T231, together with corresponding p‐tau and tau concentrations. We compared the accuracy of CSF p‐tau isoforms in predicting amyloid PET and tau PET status stratified according to amyloid PET, tau PET and/or Clinical Dementia Rating (CDR) status.ResultsPT217/T217 best‐predicted abnormal amyloid PET (AUROC=0.980) or CSF Aβ42/Aβ40 (AUC=0.954). PT217/T217 predicted brain amyloidosis in asymptomatic and symptomatic participants with similar accuracy (AUC=0.979 and 0.986 respectively) and was correlated with amyloid PET centiloid and CSF Aβ42/Aβ40 (Spearman R=0.73 and ‐0.76, p<0.0001). Notably, the correlation between pT217/T217 and amyloid PET centiloid was higher in amyloid PET(+)/tau PET(‐) compared to amyloid PET(+)/tau‐PET(+) (R=0.77, p<0.0001 versus 0.16, p=0.007). PT205/T205 and pT217/T217 better predicted tau PET positivity in amyloid PET(+)positive participants (AUC=0.908 and 0.866). These markers were also associated with tau PET signal in tau PET(+) participants (R=0.53 and 0.55 p<0.0001). Other p‐tau isoforms also predicted amyloidosis, except for T175, S199, S202 and T205. Only pT205/T205 and pT217/T217 were correlated with tau‐PET in tau PET(+) participants.ConclusionThese results suggest that tau hyperphosphorylation, notably at T217, is more strongly associated with brain amyloid burden than tau deposition in tau PET(‐) individuals. After tau PET becomes positive, p‐tau217 and p‐tau205 are correlated with tau burden. Soluble p‐tau are markers of both amyloid and tau aggregation in the AD brain.

Gold nanoparticle-based immuno-PCR for detection of tau protein in cerebrospinal fluid

Tau Pathology Generated by Overexpression of Tau

Increasing evidence points to soluble assemblies of aggregating proteins as a major mediator of neuronal and synaptic dysfunction. In Alzheimer disease (AD), soluble amyloid-beta (Abeta) appears to be a key factor in inducing synaptic and cognitive abnormalities. Here we report the novel finding that soluble tau also plays a role in the cognitive decline in the presence of concomitant Abeta pathology. We describe improved cognitive function following a reduction in both soluble Abeta and tau levels after active or passive immunization in advanced aged 3xTg-AD mice that contain both amyloid plaques and neurofibrillary tangles (NFTs). Notably, reducing soluble Abeta alone did not improve the cognitive phenotype in mice with plaques and NFTs. Our results show that Abeta immunotherapy reduces soluble tau and ameliorates behavioral deficit in old transgenic mice.

Alzheimer's disease (AD) is a progressive neurological disorder that gradually impairs all cognitive functions. The diagnosis typically requires a combination of cognitive assessments, neuroimaging techniques, and biomarker analysis. In healthy neurons, Tau protein stabilizes microtubules, which are vital for maintaining the structure and proper functioning of nerve cells. However, elevated levels of Tau in cerebrospinal or other body fluids can be related to the progression of Alzheimer's disease. This study introduces an optical technique that employs a dual label‐free and fluorescence operation mode to detect Tau protein in both standard running buffer and cerebrospinal fluid. This innovative method enables label‐free analysis of the bio‐conjugation process on biochips used for resolved fluorescence‐based Tau detection. This work successfully demonstrates Tau protein detection in both matrixes, achieving an outstanding limit of detection of 2.4 pM in cerebrospinal fluid. Moreover, the analysis of the dose‐response curve allows to estimate the dissociation constant (KD = 18 nM) for Tau interactions, yielding values that are in excellent agreement with existing literature using other techniques. These aspects highlight the added value of this technique, providing a valuable tool for investigating Alzheimer's‐related biomarkers, as demonstrated in this study with Tau protein.

A Population-based Study of tau Protein and Ubiquitin in Cerebrospinal Fluid in 85-year-olds: Relation to Severity of Dementia and Cerebral Atrophy, but not to the Apolipoprotein E4 Allele

BackgroundGosuranemab is a humanized monoclonal antibody that is hypothesized to neutralize extracellular tau and prevent the trans‐neuronal propagation of tau pathology across the brain. The TANGO study is an ongoing randomized, placebo‐controlled, global Phase 2 study evaluating safety and clinical efficacy of gosuranemab in individuals diagnosed with mild cognitive impairment (MCI) due to Alzheimer’s disease (AD) or mild AD dementia. The TANGO study included two biomarker sub‐studies: cerebrospinal fluid (CSF) sub‐study and Tau positron emission tomography (PET) sub‐study; the baseline characteristics of the Tau PET sub‐study are described below.MethodTANGO enrolled 654 individuals aged 50‐80 years, diagnosed with MCI or mild AD, who were amyloid positive as assessed by amyloid PET or CSF testing. Approximately 350 patients enrolled in the longitudinal 18F‐MK‐6240 Tau PET sub‐study. Randomization was stratified by biomarker sub‐study participation among other factors. Baseline standardized uptake value ratio (SUVR) was measured in composite brain regions of interest (ROIs) corresponding to Braak I‐II, Braak III‐IV, and Braak V‐VI regions using superior‐eroded cerebellum as the reference region. Tau extent (percentage of supra‐threshold voxels within an ROI relative to reference region), an exploratory measure of the spatial extent of 18F‐MK‐6240 binding, was also investigated.ResultThe baseline demographics of the Tau PET sub‐study population were consistent with the overall TANGO study population including clinical stage (MCI vs. mild AD), age, gender, APOE4, and clinical scores. At baseline, average SUVR (±SD) was 1.92±0.6 in Braak I‐II, 1.90±0.7 in Braak III‐IV and 1.75±0.8 in Braak V‐VI composite ROIs. The Braak composite SUVRs were positively associated with disease stage (i.e. higher SUVR with increasing disease severity). Exploratory analyses of extent were supportive of the SUVR results.ConclusionAt study baseline, tau SUVR was highest in Braak I‐II, followed by Braak III‐IV, then Braak V‐VI. Cross‐sectionally, higher tau PET SUVR was associated with increasing disease severity and worse clinical scores, as expected. The TANGO Tau PET sub‐study will aid our understanding of gosuranemab’s effect on tau pathology and further inform on the value of tau PET in clinical trials.

E2814 is a human IgG1 antibody that binds to microtubule binding region of tau (MTBR-tau), a critical domain for the seeding and spreading of tau pathology in Alzheimer's Disease (AD). It is being developed for the treatment of AD by stopping tau propagation and slowing the associated cognitive decline. E2814 has been evaluated in healthy and Dominantly Inherited Alzheimer's Disease (DIAD) participants for safety, pharmacokinetics (PK), and cerebrospinal fluid (CSF) target engagement. Seventy-two healthy participants were enrolled in single and multiple ascending dose cohorts of Study 001 (NCT04231513) and received randomized, double-blind, placebo-controlled treatment of E2814. Intravenous infusion of single and multiple doses (once every 4 weeks for three times) were administered. In Study 103 (NCT04971733), 7 DIAD participants with confirmed mutations and mild to moderate cognitive impairment were enrolled and received open-label treatment of E2814. Four sequential doses were evaluated as intravenous infusion every 4 weeks. Serum and CSF PK, and CSF target engagement (by analyzing both bound and unbound MTBR-tau299 and MTBR-tau354 [containing the epitopes of E2814]) were measured in both healthy and DIAD participants, as well as safety assessments. CSF MTBR-tau243 recapitulating AD tau pathology was also measured in DIAD participants using methods previously described (Horie et al., J Prev Alz Dis 2022). E2814 was safe and well-tolerated over a wide dose range. No infusion-related reactions or other clinically significant safety signals were observed with single or repeated dose administration for up to 15 months. E2814 showed a dose-related increase in serum and CSF exposure with CSF-to-serum ratio of ∼0.2%, comparable between healthy and DIAD participants. CSF target engagement was demonstrated by concentration-related and sustained MTBR-tau299 and MTBR-tau354 binding in healthy and DIAD participants. More importantly, E2814 elicited a rapid and robust reduction on MTBR-tau243, a neurofibrillary tangle-specific biomarker, in DIAD participants. E2814 demonstrated promising safety, PK and CSF target engagement profile in DIAD participants, and showed evidence of downstream effects on tangle-specific biomarker MTBR-tau243. Data supports further evaluation in the ongoing Ph2/3 DIAN-TU Tau NexGen Platform Study in DIAD (NCT05269394) and future exploration in sporadic AD.

Background: Alzheimer’s disease (AD) is the most common type of dementia, with progressive onset of clinical symptoms. The main pathological hallmarks are brain deposits of extracellular amyloid beta plaques and intracellular neurofibrillary tangles (NFT). Cerebrospinal fluid reflects pathological changes in the brain; amyloid beta 1-42 is a marker of amyloid plaques, while total and phosphorylated tau are markers of NFT formation. Additional biomarkers associated with disease pathogenesis are needed, for better prognosis, more specific diagnosis, prediction of disease severity and progression and for improved patient classification in clinical trials. The aim of the present study was to evaluate brain-specific proteins as potential biomarkers of progression of AD. Methods: Overall, 30 candidate proteins were quantified in cerebrospinal fluid (CSF) samples from patients with mild cognitive impairment (MCI) and mild, moderate and severe AD dementia (n=101) using mass spectrometry-based selected reaction monitoring assays. ELISA was used for neuronal pentraxin receptor-1 (NPTXR) confirmation. Results: The best discrimination between MCI and more advanced AD stages (moderate and severe dementia) was observed for protein NPTXR (area under the curve, AUC=0.799). A statistically different abundance of this protein was observed between the two groups, with severe AD patients having progressively lower levels (p<0.05). ELISA confirmed lower levels in AD, in a separate cohort that included controls, MCI and AD patients. Conclusions: We conclude that NPTXR protein in CSF is a novel potential biomarker of AD progression and could have important utility in assessing treatment success in clinical trials.

INTRODUCTIONTau PET informs Alzheimer's disease (AD) staging but is limited by cost and access. Plasma phosphorylated‐to‐nonphosphorylated tau217 ratio (pTau217R) predicts amyloid and tau positron emission tomography (PET), while cerebrospinal fluid (CSF) MTBR‐tau243 (tryptic form) and its endogenous form (eMTBR‐tau243) reflect tau pathology. We evaluated whether combining them improves tau PET prediction in amyloid‐positive early AD.METHODSIn the phase III lecanemab trial, plasma pTau217R was available for 242 participants, CSF markers for 80, and both for 57. Tau PET used [18F]MK6240. Stochastic gradient boosting models included demographics and apolipoprotein E (APOE) ε4, with performance assessed via repeated cross‐validation.RESULTSPlasma pTau217R matched CSF eMTBR‐tau243 and outperformed MTBR‐tau243. Combining pTau217R with either CSF marker improved prediction (R2 to 0.74; AUROC to 0.94) and could reduce PET use by 58%–80% for prescreening at 10% false negatives.DISCUSSIONPlasma pTau217R plus CSF eMTBR‐tau243 predict regional tau burden and may reduce reliance on tau PET in early AD trials.CLINICALTRIALS.GOV IDENTIFIERSNCT03887455 (ClarityAD)HighlightsCombining plasma pTau217R and CSF eMTBR‑tau243 improves tau PET prediction.The model predicts regional tau PET SUVRs with high accuracy across key regions.Single‐marker models show pTau217R and eMTBR‐tau243 outperform MTBR‐tau243.PET‑sparing triage reduces scan burden by up to 80% at 10% false negatives.Stochastic gradient boosting enables region‐specific tau PET prediction in one unified model.

Neurofibrillary tangles associated with Alzheimer's disease are composed mainly of paired helical filaments that are formed by the aggregation of abnormally phosphorylated microtubule-associated protein tau. 14-3-3, a highly conserved protein family that exists as seven isoforms and regulates diverse cellular processes is present in neurofibrillary tangles (Layfield, R., Fergusson, J., Aitken, A., Lowe, J., Landon, M., Mayer, R. J. (1996) Neurosci. Lett. 209, 57-60). The role of 14-3-3 in Alzheimer's disease pathogenesis is not known. In this study, we found that the 14-3-3zeta isoform is associated with tau in brain extract and profoundly stimulates cAMP-dependent protein kinase catalyzed in vitro phosphorylation on Ser(262)/Ser(356) located within the microtubule-binding region of tau. 14-3-3zeta binds to both phosphorylated and nonphosphorylated tau, and the binding site is located within the microtubule-binding region of tau. From brain extract, 14-3-3zeta co-purifies with microtubules, and tubulin blocks 14-3-3zeta-tau binding. Among four 14-3-3 isoforms tested, beta and zeta but not gamma and epsilon associate with tau. Our data suggest that 14-3-3zeta is a tau protein effector and may be involved in the abnormal tau phosphorylation occurring during Alzheimer's disease ontogeny.

INTRODUCTIONAlzheimer's disease (AD) shows clinical and molecular heterogeneity shaped by demographic and genetic factors.METHODSTo resolve this heterogeneity, we performed a network‐based proteomic analysis of cerebrospinal fluid (CSF) from 431 individuals, including 111 African Americans, to identify protein co‐expression modules and define AD subtypes.RESULTSTen co‐expression modules reflecting diverse pathways and cell types were identified, many linked to demographics and AD biomarkers. One subtype, enriched in African Americans and males, showed low CSF tau, elevated plasma proteins, and reduced synaptic proteins, features consistent with blood–brain barrier (BBB) dysfunction. This subtype also showed the highest levels of thrombin activity, capable of cleaving tau. Introducing plasma into CSF ex vivo recapitulated the BBB subtype signature, supporting a causal role for plasma proteases in tau and synaptic protein depletion.CONCLUSIONThese findings link BBB dysfunction and plasma proteases to CSF tau loss and highlight the need for diversity in AD‐biomarker research.HighlightsRace and sex correlate with key AD proteomic network modules.We identify six proteomic subtypes with distinct demographic and AD biomarker profiles.Subtype 3 demonstrates an A+/T− phenotype and a profile suggestive of BBB dysfunction.Low CSF tau and neuronal proteins may stem from infiltrating plasma protease cleavage.Plasma spike‐in experiments show decreased endogenous CSF tau and neuronal proteins.

Progressive accumulation of tau neurofibrillary tangles in the brain is a defining pathologic feature of Alzheimer's disease (AD). Tau pathology exhibits a predictable spatiotemporal spreading pattern, but the underlying mechanisms of this spread are poorly understood. Although AD is conventionally considered a disease of the gray matter, it is also associated with pronounced and progressive deterioration of the white matter (WM). A link between abnormal tau and WM degeneration is suggested by findings from both animal and postmortem studies, but few studies demonstrated their interplay in vivo. Recent advances in diffusion magnetic resonance imaging and the availability of tau positron emission tomography (PET) have made it possible to evaluate the association of tau and WM degeneration (tau-WM) in vivo. In this study, we explored the spatial pattern of tau-WM associations across the whole brain to evaluate the hypothesis that tau deposition is associated with WM microstructural alterations not only in isolated tracts, but in continuous structural connections in a stereotypic pattern. Sixty-two participants, including 22 cognitively normal subjects, 22 individuals with subjective cognitive decline, and 18 with mild cognitive impairment were included in the study. WM characteristics were inferred by classic diffusion tensor imaging (DTI) and a complementary diffusion compartment model – neurite orientation dispersion and density imaging (NODDI) that provides a proxy for axonal density. A data-driven iterative searching (DDIS) approach, coupled with whole-brain graph theory analyses, was developed to continuously track tau-WM association patterns. Without applying prior knowledge of the tau spread, we observed a distinct spatial pattern that resembled the typical propagation of tau pathology in AD. Such association pattern was not observed between diffusion and amyloid-β PET signal. Tau-related WM degeneration is characterized by an increase in the mean diffusivity (with a dominant change in the radial direction) and a decrease in the intra-axonal volume fraction. These findings suggest that cortical tau deposition (as measured in tau PET) is associated with a lower axonal packing density and greater diffusion freedom. In conclusion, our in vivo findings using a data-driven method on cross-sectional data underline the important role of WM alterations in the AD pathological cascade with an association pattern similar to the postmortem Braak staging of AD. Future studies will focus on longitudinal analyses to provide in vivo evidence of tau pathology spreads along neuroanatomically connected brain areas.

BackgroundThe pathological hallmarks of Alzheimer's disease (AD) include the amyloid-β (Aβ) plaques and phosphorylated tau (p-tau) forming neurofibrillary tangles. Understanding the pathophysiological cascade related to Aβ and tau process is crucial.ObjectiveTo investigate the impact of Aβ positron emission tomography (PET) and cerebrospinal fluid (CSF) p-tau on tau pathology and cognitive decline in AD.MethodsWe analyzed 319 older individuals from the Alzheimer's Disease Neuroimaging Initiative (ADNI) who underwent Aβ (18F-florbetapir or 18F-florbetaben) and tau (18F-flortaucipir) PET scans, along with CSF and cognitive assessments. Aβ positivity (A+) was determined by global standardized uptake value ratio thresholds of ≥1.11 for 18F-florbetapir or ≥1.08 for 18F-florbetaben, while p-tau positivity (T+) was defined as CSF p-tau181 levels ≥23 pg/ml. Linear mixed regression models were used to assess the effects of PET Aβ and CSF p-tau181 levels on tau accumulation in predefined Braak regions and cognitive function over time.ResultsOur results revealed significant differences in PET tau pathology and cognitive decline between A + and A- individuals. We observed that interactions between Aβ and p-tau proteins were associated with tau accumulation and cognitive decline. Additionally, A-/T + individuals exhibited higher levels of tau accumulation in all Braak regions compared to A-/T- counterparts, suggesting a potential independent role of p-tau in tau pathology in the absence of Aβ.ConclusionsOur findings suggest that Aβ positivity and elevated CSF p-tau181 levels were associated with tau accumulation and cognitive decline, highlighting the relevance of soluble p-tau as a potential biomarker for further investigation.