Higher plasma YKL‐40 was associated with greater white matter hyperintensity (WMH), whereas higher plasma GFAP was related to increased 18F‐florbetapir (FBP) standardized uptake value ratio (SUVR) and higher plasma p‐tau217 was associated with reduced MTL cortical thickness and hippocampal volume.
Abstract
Abstract INTRODUCTION Upstream neuroinflammation plays an important role in Alzheimer's disease (AD) but remains poorly understood. We tested whether two distinct neuroinflammatory markers are associated with cerebrovascular burden and amyloid beta (Aβ), and downstream, with plasma phosphorylated tau (p‐tau217), medial temporal lobe (MTL) cortical and hippocampal atrophy, and memory deficits.
Methods
Cognitively unimpaired older adults without dementia or mild cognitive impairment were recruited from a community sample (Biomarker Exploration in Aging, Cognition, and Neurodegeneration; [BEACoN]; N = 126). We used structural equation modeling to test whether plasma chitinase‐3‐like protein 1 (YKL‐40) and glial fibrillary acidic protein (GFAP) contribute to distinct pathways.
Results
Higher plasma YKL‐40 was associated with greater white matter hyperintensity (WMH), whereas higher plasma GFAP was related to increased 18F‐florbetapir (FBP) standardized uptake value ratio (SUVR). Higher plasma GFAP, WMH, and FBP SUVR were independently associated with increased p‐tau217. Plasma p‐tau217 was associated with reduced MTL cortical thickness and hippocampal volume. Reduced hippocampal volume was related to worse memory.
Discussion
Future work can further investigate these neuroinflammatory pathways as potential therapeutic targets for AD.
BACKGROUND AND OBJECTIVES
Plasma glial fibrillary acidic protein (GFAP), a marker of astrocyte reactivity, is elevated across multiple neurodegenerative conditions, including Alzheimer disease. However, its role in neurodegeneration and cognitive decline driven by cerebrovascular pathology, independent of β-amyloid (Aβ) copathology, remains poorly characterized. We investigated whether plasma GFAP is associated with medial temporal atrophy and cognition across a spectrum of cerebrovascular burden in Aβ-negative cognitively impaired individuals.
METHODS
In this cross-sectional multicenter study, Aβ PET-negative cognitively impaired participants were recruited from South Korean memory clinics. Plasma GFAP was measured using ultrasensitive Simoa assays. White matter hyperintensity burden was graded using the Fazekas scale and stratified into low (LVP: Fazekas 1) and high (HVP: Fazekas 2-3) cerebrovascular burden groups. Medial temporal gray matter density was assessed using voxel-based morphometry, and hippocampal and amygdalar volumes were derived from T1-weighted MRI adjusted for intracranial volume. Linear regression, interaction, and bootstrap mediation models were used to assess associations among GFAP, brain structure, and cognition.
RESULTS
A total of 324 participants were included (LVP n = 203; HVP n = 121; median age 73 years [interquartile range 66-78]; 67.9% female). Compared with LVP, HVP participants were older (75 vs 71 years; p < 0.0001), had lower Mini-Mental State Examination (MMSE) scores (22.7 vs 24.5; p = 0.005), and higher plasma GFAP (136.7 vs 112.1 pg/mL; p = 0.001). Higher GFAP was associated with lower medial temporal gray matter density in HVP (β = -0.311; p = 0.001) but not LVP (β = -0.012; p = 0.858), with a significant GFAP-vascular burden interaction (β = -0.309; p = 0.008). In HVP, higher GFAP was associated with smaller hippocampal (β = -0.179; p = 0.044) and amygdalar volumes (β = -0.169; p = 0.049) and lower MMSE (β = -0.194; p = 0.039). Medial temporal atrophy statistically explained the GFAP-MMSE association (indirect β = -0.071, 95% CI -0.140 to -0.010; p = 0.016). Vascular comorbidities (diabetes, dyslipidemia, hypertension) did not modify the GFAP-cognition association.
DISCUSSION
In Aβ-negative cognitively impaired individuals with high cerebrovascular burden, elevated plasma GFAP is associated with medial temporal atrophy and cognitive decline, suggesting GFAP may capture astrocyte-reactivity relevant to vascular cognitive impairment beyond amyloid pathology. These cross-sectional findings require confirmation in longitudinal and ethnically diverse cohorts.
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In cognitively unimpaired older adults, elevated blood p-tau217 was linked to faster shrinkage in AD-specific brain regions, whereas NfL and GFAP were associated with more widespread atrophy, with NfL also associated with accelerated WMH accumulation.
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Structural brain changes during the earliest asymptomatic stages of Alzheimer’s disease (AD) remain poorly understood. Previous research in preclinical AD shows heterogeneous findings, reporting both subtle neuronal loss and paradoxical increases in grey matter (GM) volume. This study applies an extensive cerebrospinal fluid (CSF) biomarker panel to better understand the biological processes underlying longitudinal GM changes in cognitively unimpaired (CU) adults, spanning the amyloid/tau (AT) continuum.
We analysed data from 627 CU individuals from three longitudinal cohorts (ALFA+, Wisconsin ADRC, WRAP), with repeated MRI (3.5 ± 0.9 years) and baseline CSF biomarkers from the NeuroToolKit panel (Roche Diagnostics). Using non-negative matrix factorization, we decomposed the CSF biomarker levels into six latent components, reflecting amyloid-β (Aβ) pathology, tau-related pathophysiology with synaptic injury, neuroaxonal injury, microglial reactivity, astrocytic reactivity, and cytokine signalling. We tested associations between component weights and voxel-wise longitudinal GM volume changes using single-component and a joint-all components model. Analyses were performed across the full sample and stratified by AT status. Associations with longitudinal cognitive performance (PACC) were assessed using linear mixed-effects models.
The Aβ pathology component was the strongest and most widespread predictor of longitudinal GM atrophy, predominantly in temporal and frontal regions, also when controlling for tau pathophysiology, neuroaxonal injury, or neuroinflammatory components. Higher Aβ pathology scores were also associated with cognitive decline. The component capturing tau-related pathophysiology and synaptic injury initially associated with GM loss but lost significance after accounting for other biomarker components. In contrast, components reflecting microglial reactivity, astrocytic reactivity, and cytokine signalling were associated with longitudinal GM volume increases, with effects varying by AT stage.
In this large longitudinal sample of asymptomatic individuals, the Aβ-dominant biomarker component showed the strongest association with longitudinal GM atrophy and cognitive decline, beyond the effects of tau pathophysiology and neuroaxonal injury. While glial and inflammatory processes may contribute to transient GM increases in preclinical AD. A better understanding of these dynamic relationships between structural brain changes and various biological pathways at the earliest stages of AD is crucial to inform the development of interventions before irreversible neurodegeneration occurs.
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