Genome-wide CRISPR screen reveals that Wnt signaling regulates lipid accumulation in APOE4 oligodendrocytes.

APOE4 is the strongest genetic risk factor for late-onset Alzheimer's disease, yet the cellular mechanisms linking APOE variants to disease risk remain unclear. We previously found that APOE4 expression causes lipid droplet accumulation in oligodendrocytes, reducing myelination, but the underlying mechanisms were unknown. Using a genome-wide CRISPR screen and assay for transposase-accessible chromatin (ATAC) sequencing in human-induced pluripotent stem cell (iPSC)-derived oligodendrocytes, we identified decreased Wnt signaling and overactive glycogen synthase kinase-3 beta (GSK3B) as key regulators of lipid-droplet accumulation. Genetic and pharmacological inhibition of GSK3B reduced lipid droplets in APOE4 oligodendrocytes and increased myelination in three-dimensional iPSC-derived brain organoids. Pharmacological GSK3B inhibition also reduced lipid droplets and improved myelination in APOE4;PS19 tau transgenic mice. Together, these findings establish a mechanistic framework linking Wnt/GSK3B signaling to APOE4-driven disruptions in oligodendrocyte lipid metabolism and myelination, pointing to GSK3B as a potential therapeutic target for APOE4-associated Alzheimer's disease.