APOE4 Reshapes Brain Blood Vessel Lipids in Alzheimer's Disease

Alzheimer's disease is not purely a neuronal disorder — the cerebrovascular system plays a critical and underappreciated role. Cerebral amyloid angiopathy (CAA), defined by amyloid-β deposits in leptomeningeal and cortical arteries, affects over 90% of AD patients. APOE ε4, the strongest genetic risk factor for late-onset AD, is also tied to cerebrovascular dysfunction and impaired lipid transport. Yet how APOE genotype specifically shapes the lipid landscape of brain blood vessels had never been systematically characterized — until now.

To address this gap, investigators isolated cerebral vessels from the middle temporal cortex of 89 pathologically confirmed AD brains (Mayo Clinic Brain Bank), spanning five APOE genotypes: ε2/ε3 (N=9), ε2/ε4 (N=14), ε3/ε3 (N=21), ε3/ε4 (N=23), and ε4/ε4 (N=22). All cases were non-Hispanic White, age >60, Thal phase ≥III, and Braak stage ≥IV. Non-targeted lipidomics detected 10 major lipid classes, with phosphatidylcholine (PC) and phosphatidylethanolamine (PE) as the most abundant species. Cohort groups were matched for age, sex, and CAA scores, and no significant differences in these variables were found across genotypes.

Several key findings emerged. First, total acyl-carnitine (CAR) levels showed a positive association with age (p=0.0008), suggesting age-related shifts in fatty acid oxidation within cerebrovascular tissue. Specific CAR subclasses were additionally influenced by APOE ε4 dosage. Second, APOE ε4 was independently associated with higher PE levels (p=0.049) and lower sphingomyelin (SM) levels (p=0.028) in cerebral vessels — a pattern distinct from what has been reported in brain parenchyma. Third, cerebrovascular Aβ40 and Aβ42 concentrations correlated with sphingolipid levels, including SM (p=0.0079) and ceramide (CER) (p=0.024), suggesting that amyloid deposition in vessel walls disrupts or is driven by sphingolipid metabolism. Fourth, weighted correlation network analysis linked total tau and phosphorylated tau to lipid clusters enriched in PE plasmalogens and lysoglycerophospholipids — lipids known for antioxidant and membrane-protective functions that are consistently reduced in AD parenchyma.

These findings carry important mechanistic implications. PE plasmalogens serve as endogenous antioxidants and structural membrane components; their depletion in cerebrovascular tissue associated with tau pathology suggests a shared vulnerability between neuronal and vascular compartments. The APOE ε4-driven reduction in SM may compromise membrane raft integrity and signaling in vascular mural cells (smooth muscle cells and pericytes), potentially contributing to impaired Aβ clearance along perivascular pathways. The elevation of PE alongside SM reduction under APOE ε4 may reflect compensatory remodeling or a primary defect in lipid flipping and efflux.

Caveats include the cross-sectional, postmortem design, which precludes causal inference. The sample is exclusively non-Hispanic White, limiting generalizability. The relatively small subgroup sizes, especially for ε2/ε3 (N=9), reduce statistical power for some comparisons. Comorbid neuropathologies were present in some cases, potentially confounding lipid profiles. Nonetheless, this study represents the most comprehensive cerebrovascular lipidomic characterization in human AD to date, opening avenues for vascular lipid-targeted diagnostics and therapeutics.