APOE and astrocytoma (excluding glioblastoma): To analyze the physiological function of ApoE and its relationship with SphK2/S1P signaling in astrocytes, we established SphK2 stably overexpressing cells based on human astrocytoma U87 cell line (U87-SphK2 cells), which have the most common genotype of ApoE, ε3/ε3 (26).