Recombinant sialylated ApoE2 suppresses ApoE4 and sex-specifically strengthens brain metabolism and cognition in ApoE4 mice.

Human APOE4 is the strongest genetic risk factor for late-onset Alzheimer's disease (AD), whereas the relatively rare APOE2 confers exceptional protection. This study examines whether recombinant ApoE2 protein can therapeutically leverage this genetic advantage to strengthen aging brains at risk for AD. We produced recombinant human ApoE2 (rhApoE2) using the FreeStyle 293-F system, yielding rhApoE2 with extensive sialylation that closely resembles its natural form in the human brain. In ApoE4-knockin mouse primary neurons, exposure to rhApoE2 induced significant increases in hexokinase 2 expression and decreases in endogenous ApoE4 protein levels. rhApoE2 also protected ApoE4 neurons from oligomeric amyloid-β toxicity and oxidative stress. We further developed a cadherin-derived peptide (ADTC5) that transiently increases paracellular porosity of the blood-brain barrier, enabling safe, non-invasive delivery of rhApoE2 into the mouse brain. When co-administered with ADTC5, weekly intravenous doses of rhApoE2 for 4-8 weeks in middle-aged and aged ApoE4 mice enhanced synaptosomal glycolytic and exocytotic activities, promoted cortical lipid metabolic dynamics and DHA utilization, and improved learning and memory, with sex differences observed in some outcomes. These findings offer preliminary evidence supporting the therapeutic potential of human brain-like rhApoE2 sialoprotein, which enhances metabolic robustness and cognitive strength in aging ApoE4 brains, possibly modulated by sex.