Progressive behavioral and cognitive decline in Drosophila harboring AD-associated APOE4 variants

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder, and its incidence is rising rapidly with population aging. Pathologically, AD is characterized by the accumulation of amyloid-beta (Abeta) plaques and hyperphosphorylated Tau neurofibrillary tangles. Human genomic studies have identified numerous risk alleles, with the APOE4 variant representing the strongest and most common genetic risk factor, present in approximately 75 percent of AD patients. However, APOE4 is neither necessary nor sufficient to cause disease, suggesting that additional genetic and environmental factors contribute to AD pathogenesis. Emerging evidence highlights a central role for oxidized lipid metabolism in AD. Disruption of lipid metabolism leads to lipid accumulation, reactive oxygen species (ROS) toxicity, and neurodegeneration, suggesting that oxidative stress may be a critical factor in enhancing AD susceptibility. To systematically investigate APOE function in vivo, we tested humanized Drosophila expressing the human APOE3 or APOE4 variants in place of the Drosophila ortholog Glial Lazarillo (GLaz). The lifespan of APOE3 and APOE4 flies does not differ under standard housing conditions, but the lifespan of APOE4 flies is significantly reduced when exposed to the ROS-promoting drug rotenone, supporting a multi-hit model of disease pathogenesis. APOE4 flies exposed to rotenone exhibit several AD-associated phenotypes, including age-related memory loss and chemosensory deficits, supporting the use of this model to investigate AD pathogenesis. Furthermore, progressive AD-associated phenotypes are also observed in APOE4 flies maintained on an obesogenic diet, suggesting that enhanced disease susceptibility is not specific to rotenone-induced stress but reflects a broader vulnerability to metabolic challenges. Together, these findings establish a scalable model to dissect APOE-dependent mechanisms and identify therapeutic targets in AD.