Abstract
APOE is the greatest genetic risk factor for late-onset Alzheimer's disease (AD). In humans, APOE has three isoforms: APOE2 (E2), APOE3 (E3), and APOE4 (E4); E4 increases AD risk, while E3 is neutral and E2 decreases risk. In the brain, APOE is predominantly produced by astrocytes, where it binds lipids to form HDL-like particles, and plays a central role in lipid homeostasis, Aβ clearance, and neuroimmune modulation. Its lipidation state is critical for function, with E4 being poorly lipidated compared to E2 and E3, contributing to the pathogenic effects of E4 while also offering a potential therapeutic target. We have previously demonstrated that the HDL-mimetic peptide 4F increases APOE secretion and lipidation in wild-type mouse astrocytes and counteracts the inhibitory effects of Aβ42. Here, we assessed the ability of 4F to mitigate E4-associated dysfunction using primary astrocytes from humanized E3 and E4 knock-in mice and isogenic human iPSC-derived astrocytes and cerebral organoids. Results showed that 4F enhanced APOE secretion and lipidation in both cellular and organoid models in the absence or presence of aggregated Aβ42. Compared to E3 astrocytes, E4 astrocytes were prone to Aβ42-induced inhibition of APOE secretion and lipidation and increased accumulation of lipid droplets. 4F treatment ameliorated the inhibitory effects of Aβ42 and reduced lipid droplet accumulation. These findings support the therapeutic potential of HDL-mimetic peptides for E4-associated dysfunction in AD.