APOE genotype and astrocyte activity collectively influence AD biomarkers and Aβ burden.

BACKGROUND: The apolipoprotein E ε4 (APOE ε4), a well-established genetic risk factor for Alzheimer's disease (AD), is deeply involved in amyloid-β (Aβ) and tau pathology. Blood-based biomarkers (BBMs), including Aβ42/40, phosphorylated tau (p-tau181), glial fibrillary acidic protein (GFAP) and neurofilament light (NfL), offer accessible proxies of AD pathology. Reactive astrocytes, indicated by elevated GFAP, are increasingly recognized as key players in AD progression. However, how astrocyte reactivity interacts with APOE genotype to shape BBMs and Aβ deposition remains unclear. METHODS: We included 283 participants across the cognitive spectrum including cognitively unimpaired (CU), mild cognitive impairment (MCI), and all-cause dementia (ACD) from Guangzhou health aging and dementia cohort. Primary outcome measures were plasma biomarkers (Aβ42/40 ratio, p-tau181, GFAP, and NfL) and amyloid PET standardized uptake value ratio (SUVR). Participants were stratified by APOE ε4 carrier status and astrocyte activation. Group comparisons, correlation analyses, and sensitivity analyses were performed. RESULTS: Stage-dependent APOE effects were observed: while modulating Aβ42/40 ratios in both CU and MCI, APOE influenced p-Tau181 only in MCI, exclusively under Ast-. SUVR was significantly higher in APOE ε4 + group at MCI stage, particularly in Ast- cases. Intriguingly, p-Tau/Aβ42 showed strong SUVR correlations across all subgroups except APOE ε4- Ast- group. DISCUSSION: Our findings indicate that astrocyte reactivity is associated with differences in how APOE ε4 relates to both peripheral BBMs and central Aβ deposition, supporting an interplay between genetic risk and neuroinflammatory states in AD pathogenesis.