Apolipoprotein E ε4 homozygosity exacerbates retinal and cerebral microvascular dysfunction in Alzheimer's disease: A mediation analysis of vascular contributions to cognitive decline

Abstract

INTRODUCTION: Apolipoprotein E (APOE) ε4 is the strongest genetic risk factor for Alzheimer's disease (AD), with homozygous carriers (ε4/ε4) experiencing accelerated cognitive decline. While its role in amyloid and tau pathology is established, its impact on retinal and cerebral microvasculature remains underexplored. METHODS: A total of 107 AD (46 non-carriers, 42 heterozygotes, 19 homozygotes) underwent optical coherence tomography angiography (OCTA) to assess retinal microvasculature and magnetic resonance imaging (MRI) -derived peak width of skeletonized mean diffusivity (PSMD) to evaluate cerebral small vessel disease. Plasma biomarkers (Aβ42, p-tau217, glial fibrillary acidic protein [GFAP], neurofilament light chain [NfL]) and cognitive scores were also analyzed. RESULTS: Homozygous APOE ε4 carriers exhibited the most severe reduction in retinal microvascular density and higher PSMD (p < 0.001). Superficial retinal vessels and PSMD partially mediated APOE ε4's association with cognitive impairment. DISCUSSION: APOE ε4 homozygosity exacerbates retinal and cerebral microvascular dysfunction, which partially mediates cognitive impairment in AD. Highlights: Apolipoprotein E (APOE) ε4 homozygosity is associated with the most severe reductions in retinal microvascular densities and elevated cerebral small vessel disease (peak width of skeletonized mean diffusivity [PSMD]) in Alzheimer's disease (AD). Vascular dysfunction (retinal and cerebral) correlates with lower Aβ42, higher p-tau217/Aβ42, and worse cognitive scores (Mini-Mental State Examination [MMSE], Montreal Cognitive Assessment [MoCA]). Mediation analysis reveals that retinal (superficial vascular complex [SVC]) and cerebral (PSMD) microvascular changes partially explain the link between APOE ε4 and cognitive decline. Findings highlight vascular pathways as potential therapeutic targets in APOE ε4 carriers to mitigate cognitive impairment.