Welcome to the AD/PD™ 2022 Interactive Program
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ASSOCIATION OF PLASMA P-TAU231, P-TAU181 AND GFAP WITH BETA-AMYLOID AND COGNITIVE PERFORMANCE IN HEALTHY ELDERLY APOE Ε4 CARRIERS
Abstract
Aims
Plasma p-tau231, p-tau181 and glial fibrillary acidic protein (GFAP) are biomarkers of Alzheimer’s disease pathology known to increase early in Alzheimer’s continuum. We investigated differences in plasma p-tau231, p-tau181 and GFAP concentrations, and their association with beta-amyloid deposition and cognitive performance in healthy volunteers with and without increased genetic risk for sporadic Alzheimer’s disease.
Methods
Cognitively unimpaired participants (N=60), aged 60-75-years, with either APOE ε4/ε4 (N=19), APOE ε4/ε3 (N=21) or APOE ε3/ε3 genotype (N=20) underwent amyloid positron emission tomography with 11C-PiB, blood sampling and cognitive assessment with the API preclinical cognitive composite. Plasma biomarkers were measured with Single molecule array (Simoa) technology. 11C-PiB uptake was quantified as standardized uptake value ratio (SUVR) to cerebellar cortex. Amyloid positivity was defined as SUVR >1.5 in cortical composite volume-of-interest.
Results
Plasma p-tau231 and p-tau181 showed significant differences between cognitively unimpaired APOE groups (p=0.027 and p=0.042, 1-way ANOVA). A similar trend was observed for plasma GFAP (p=0.08). After post-hoc multiple comparisons, significantly higher p-tau231 concentration was present in APOE ε4/ε4 compared with APOE ε3/ε3 (p=0.025). All plasma biomarkers were associated with amyloid deposition in composite volume-of-interest (rs=0.31-0.40, p<0.018 for all), however, voxel-wise analysis revealed slightly different spatial patterns for p-tau markers and GFAP (Figure 1). In the whole cohort, only higher plasma GFAP concentration was associated with lower cognitive composite score (rs=-0.36, p=0.0047).
Conclusions
Plasma p-tau231 and p-tau181 were increased in healthy APOE ε4 carriers and associated with 11C-PiB binding with different spatial pattern than plasma GFAP.
THE CROSS-SECTIONAL AND LONGITUDINAL ASSOCIATION OF PLASMA P-TAU181, P-TAU217 AND P-TAU231 WITH ALZHEIMER’S DISEASE PHENOTYPES
Abstract
Aims
Plasma biomarkers, namely phosphorylated tau (p-tau), have proven to be highly valuable to identify Alzheimer’s disease (AD) pathology in presence of cognitive decline. In addition, both p-tau181 and p-tau217 have been shown to be effective in categorizing those who are at high-risk for AD. Recently, p-tau231 has also been shown to be an accurate measure of AD pathology and postulated to be elevated earlier in the AD continuum. This is the first description of plasma p-tau231 in the BioFINDER cohort(s) and compares the cross-sectional and longitudinal association of three plasma p-tau biomarkers with AD phenotypes.
Methods
In both BioFINDER-1 and BioFINDER-2 cohorts, plasma p-tau181 and plasma p-tau231 were quantified by single molecular arrays (Simoa) developed at the University of Gothenburg, Sweden. Plasma p-tau217 was quantified by the Meso Scale Discovery (MSD) by Eli Lily. Aβ status was quantified by both CSF Aβ42/Aβ40 or Aβ-PET.
Results
In BioFINDER-2, plasma p-tau231 was elevated in Aβ+ individuals compared to Aβ– (AUC=0.85) and a stepwise increase of p-tau231 was observed throughout the AD continuum. At dementia stages, however, plasma p-tau217 exhibited the largest fold-changes between Aβ+ and Aβ– groups. In the preclinical stage, both p-tau231 and p-tau217 outperformed p-tau181 to indicate Aβ+ (DeLong, P<0.01) and both biomarkers were equally suitable (AUC=0.74–76) to identify the earliest Aβ accumulators (CSF+/PET-).
Conclusions
P-tau231 has high accuracy to determine AD pathology. However, in considering other p-tau biomarkers, it performs best preclinically to identify earliest Aβ accumulators. Further analysis will present the longitudinal trajectories of plasma p-tau181, p-tau217 and p-tau231 in BioFINDER-1.
CSF GFAP IS ASSOCIATED WITH BRAIN AMYLOID-BETA WHILE CSF YLK-40 IS ASSOCIATED WITH BRAIN TAU IN ALZHEIMER’S DISEASE
Abstract
Aims
To test the association between amyloid-β (Aβ) and tau pathologies with fluid glial fibrillary acidic protein (GFAP) and chitinase-3-like protein 1 (YKL-40) across the Alzheimer’s disease (AD) spectrum.
Methods
We assessed 77 cognitively unimpaired and 48 cognitively impaired (30 mild cognitive impairment and 18 AD dementia) participants (age > 50 years) from the McGill TRIAD cohort. Individuals had available positron emission tomography (PET; [18F]AZD4694 for Aβ and [18F]MK6240 for tau tangles) and magnetic resonance imaging, as well as cerebrospinal fluid (CSF) astrocyte GFAP and YKL-40 markers. Cognition was assessed with the Mini-Mental State Examination.
Results
Voxel-wise linear regression revealed that higher GFAP levels but not YKL-40 levels were associated with increased Aβ-PET load in typical AD brain regions independently of tau pathology (Figure 1). On the other hand, higher YKL-40 levels but not GFAP levels were positively associated with tau-PET uptake in brain regions of early and late tau tangle accumulation independently of Aβ pathology (Figure 2). Structural equations models demonstrated that GFAP mediates the association between Aβ and hippocampal atrophy, while YKL-40 mediates the association between tau and hippocampal atrophy.
Conclusions
We showed for the first time in living individuals that two of the most important astrocyte reactivity markers, GFAP and YKL-40, are differentially associated with AD pathological hallmarks. While GFAP better represents Aβ pathology, YKL-40 better represents tau pathology. Our findings support that understanding the role of the different astrocyte phenotypes in the development of AD may shed light on the complex link between brain proteinopathies and downstream disease progression.
WHOLE-BLOOD RNA SEQUENCING DETECTS CHANGES IN THE PERIPHERAL BLOOD TRANSCRIPTOME IN PRECLINICAL ALZHEIMER’S DISEASE
Abstract
Aims
We investigate longitudinal changes in peripheral blood gene expression to better understand molecular changes in preclinical Alzheimer’s disease (AD).
Methods
RNA was extracted and sequenced from whole-blood for 63 cognitively healthy Flemish Prevent AD Cohort KU Leuven (F-PACK) participants (70 (56-80) years) at baseline and follow-up (interval: 4.6 (3.4-8.59) years). Participants also received amyloid-PET and structural MRI at both timepoints. We performed differential gene expression analysis to identify changes in expression of single genes, based on APOE4 status (present/absent) and amyloid rate of change. Results were significant when meeting FDR<0.05 and log fold change (LFC)±1.
Results
There were 121 differentially expressed genes (DEGs) at follow-up compared to baseline in APOE4 carriers. Top differentially expressed genes (DEGs) included GP1BA (FDR=0.003, LFC=-2.70) and RPL17 (FDR=0.003, LFC=2.13). Over-representation analysis revealed DEGs were particularly enriched for gene ontology terms related to structural constituents of ribosomes and endoplasmic reticulum function. No significant DEGs were observed in APOE4 non-carriers between baseline and follow-up. There was only one gene, ZFAT, that was differentially expressed at baseline with respect to amyloid rate of change (FDR=0.002, LFC=20.2). However, the significance appears to be driven by one individual with a particularly high accumulation rate, Figure 1A. Significance is lost when this individual is removed (FDR=0.99, Figure 1B).
Conclusions
Early peripheral blood-related RNA expression changes occur in relation to AD genetic risk factors (APOE4), as well as early brain amyloid changes. These results may aid in targeting genes or pathways for biomarker development or finding druggable targets for AD.
ASSESSMENT OF ALZHEIMER DISEASE RELATED PLASMA BIOMARKER PHOSPHORYLATED TAU 181 IN INDIVIDUALS OF DIVERSE ANCESTRAL BACKGROUNDS
Abstract
Aims
Plasma proteins, like phosphorylated threonine 181 of Tau (pTau181), as biomarkers for differential diagnosis and preclinical detection of Alzheimer disease (AD), is well supported. However, these observations are nearly exclusively from individuals of non-Hispanic European ancestry. Given differences in risk for across populations, generalizability of these findings is not assured. This study explores plasma pTau181 in discriminating clinically diagnosed AD from cognitively intact, age-matched controls in ancestrally diverse African American and Puerto Rican cohorts.
Methods
We measured pTau181 in 583 African American individuals (157 AD, 426 controls), 632 Puerto Rican individuals (341 AD, 291 controls), and 48 autopsy-confirmed cases of European ancestry. Plasma was isolated from EDTA blood tubes and assayed using the pTau181 AdvantageV2 Simoa chemistry. Samples were randomized, measurements performed in duplicate, and non-parametric Kruskal-Wallis tests used to detect differences in pTau181 concentration.
Results
Mean pTau levels in cases was higher than controls in African Americans (2.71±1.63pg/mL vs 1.36±1.06pg/mL, pcorr=9.5x10-27) and Puerto Ricans (2.55±1.28pg/mL vs 1.63±0.92pg/mL, pcorr=1.1x10-26). The pTau levels in the European ancestry autopsy confirmed cases (3.66±2.69pg/mL) were significantly higher than observed in the African American (pcorr=0.03) or Puerto Rican (pcorr=0.007) cases.
Conclusions
This study suggests that pTau181 biomarker findings are generalizable, though there is a suggestion that plasma of autopsy confirmed AD cases carries a higher concentration than individuals with only clinical diagnosis. Analysis of other biomarkers in these diverse cohorts is currently underway. Ultimately, combining genomic and biomarker data in diverse individuals will increase understanding of genetic risk and refine clinical diagnoses in individuals of diverse ancestries.
CSF PROTEOME PROFILING REVEALS NOVEL BIOMARKERS FOR SPECIFIC DIAGNOSIS OF DEMENTIA WITH LEWY BODIES
Abstract
Aims
Specific diagnosis of dementia with Lewy bodies (DLB) remains challenging and biomarkers discriminating DLB from Alzheimer’s disease (AD) are highly needed. We aimed to identify the specific cerebrospinal fluid (CSF) proteomic changes that underlie DLB and identify translatable diagnostic biomarkers.
Methods
Proximity ligation-based multiplex immunoassays were used to measure 665 proteins in 534 CSF samples from patients with Dementia with Lewy bodies (n=109), AD-dementia (n=235) and cognitively-unimpaired controls (n=190).
Results
Nested linear models identified 97 CSF proteins dysregulated in DLB compared to controls (p<0.05). After comparison with the AD CSF proteome, we observed 52 of these proteins (54%) especially associated to DLB (e.g.DDC, GH, FCER2, MMP1), while 15 proteins (16%) showed opposite changes to those detected in AD patients (CRH, MMP3). The strongest dysregulated DLB protein was L-amino acid decarboxylase (DDC; >1.5 fold-change vs.CN or AD; q<1E-16), an enzyme involved in dopamine biosynthesis. DDC could optimally discriminate DLB from controls and AD patients (AUC: 0.91 and 0.81 respectively). Using penalized generalized linear modelling we identified a panel of 7-CSF markers including DDC that could discriminate DLB from AD patients with even higher accuracy (AUC: 0.93), which has been successfully translated into customized multiplex assays.
Conclusions
We unveil CSF changes specifically related to DLB pathophysiology and identified a panel of 7-CSF markers associated to specific aspects of DLB or AD pathophysiology able to discriminate these dementia types with high accuracy. Multiplex custom assays containing these markers are currently been clinically validated in independent cohorts for its potential use in diagnostic settings or clinical trials.
IDENTIFICATION OF A NOVEL PROTEOMIC BIOMARKER IN PARKINSON’S DISEASE: DISCOVERY AND REPLICATION IN BLOOD, BRAIN AND CSF
Abstract
Aims
Biomarkers to aid diagnosis and understand progression of Parkinson’s Disease (PD) are vital for targeting treatment in the early phases of disease. Here, we aim to discover a multi-protein panel representative of PD and make mechanistic inferences from protein expression profiles with the broader objective of finding novel biomarkers.
Methods
We used aptamer-based technology (SomaLogic®) to measure proteins in 1599 serum samples, 85 CSF samples and 37 brain tissue samples collected from two observational longitudinal cohorts (Oxford Parkinson’s Disease Centre and Tracking Parkinson’s) and the PD Brain Bank respectively. Random forest machine learning was performed to discover new proteins related to disease status. Differential regulation analysis and pathway analysis was performed to identify functional and mechanistic disease associations.
Results
We have generated multi-protein expression signatures containing potential novel biomarkers. The diagnostic classifier signature was tested across modalities (CSF AUC = 0.74, p-value 0.0009; brain AUC = 0.75, p-value = 0.006). In the validation dataset we showed the same classifiers were significantly related to disease status (p-values < 0.001). Differential expression analysis and Weighted Gene Correlation Network Analysis (WGCNA) highlighted key proteins and pathways with known relationships to PD. Of note are proteins from the complement and coagulation cascades suggesting a disease relationship to immune response.
Conclusions
The combined analytical approaches in a relatively large number of samples, across tissue types and with replication as well as validation provides mechanistic insights into disease as well as nominating a protein signature that might be a starting point for further biomarker evaluation.
LRRK2 AND RAB DETECTION IN BIOFLUIDS AS POTENTIAL BIOMARKER FOR PD
Abstract
Aims
Levels of expression or of phosphorylation of leucine-rich repeat kinase 2 (LRRK2) have the potential for use as disease or pharmacodynamic biomarkers. LRRK2 phosphorylation levels at the S910-S935-S955-S973 phosphosites are reduced for most disease mutant forms of LRRK2, while for phospho-S1292, phospho-Rab8 and phospho-Rab10, levels are increased for most mutants. Also, all of these 5 sites are rapidly dephosphorylated upon LRRK2 inhibitor treatment, considered potential therapeutics. The main objective of this study is therefore to characterize detection of leucine-rich repeat kinase 2 (LRRK2) in human and rat urine.
Methods
With urine collected from test individuals as well as rats, we have applied an ultracentrifugation based fractionation protocol to isolate exosome-enriched fractions. We used western blot with antibodies directed against LRRK2, LRRK2 phosphorylation sites as well as Rab8 and Rab10 total and phosphorylated proteins in order to measure these LRRK2 and Rab epitopes in urine.
Results
We confirm the presence of LRRK2 and Rab8/10 in human urinary exosomes, including total LRRK2 as well phosphorylated forms of LRRK2 pS910, pS935, pS955, pS973, pS1292 and phosphorylated Rab8 and Rab10. We also confirm LRRK2 and Rab expression in rodent urinary exosomes. We will aslo present work currently ongoing to assess changes in total-LRRK2 as well as pS935-LRRK2, pS1292-LRRK2, phospho-Rab8 and phospho-Rab10 in PD patient groups relative to controls.
Conclusions
This study assesses LRRK2 and Rabs as a disease and pharmacodynamic marker in human urine samples and our current analysis shows LRRK2 and Rab epitopes modified in patient groups.