Association of plasma glial fibrillary acidic protein and APOE-ε4 with Alzheimer's disease.

Both Apolipoprotein E-ε4 (APOE-ε4) and astrocytic activation, as measured by glial fibrillary acidic protein (GFAP), play critical roles in Alzheimer's disease (AD). However, the influence of astrocytic activation on the relationship between APOE-ε4 and AD pathologies remains unclear. This study investigates the interrelationships among astrocytic activation, APOE-ε4, and AD pathophysiology in 529 participants who underwent plasma biomarker measurements, APOE genotyping, and cognitive testing. Additionally, 277, 284, and 104 underwent structural magnetic resonance imaging (MRI), amyloid-β (Aβ) positron emission tomography (PET), and tau PET, respectively. The associations of plasma GFAP, APOE-ε4, and AD-related biomarkers, as well as whether plasma GFAP mediates APOE-ε4-related effects on AD, were investigated. Higher plasma GFAP and APOE-ε4 were independently associated with more severe Aβ and tau aggregation, as well as cognitive decline. Mediation analyses showed a significant indirect effect of APOE-ε4 on plasma p-tau biomarkers (21.1%-24.9%), Aβ PET (16.4%), and cognition (19.6%), while the indirect effect on tau PET was trend-level (29.1%, pFDR = 0.051). These findings highlight the central role of astrocytic activation in AD pathogenesis and underscore plasma GFAP as a promising biomarker for risk stratification and therapeutic targeting.