Figure 4. ApoE is essential for efficient degradation of Aβ.

(A) Loss of ApoE resulted in intracellular accumulation of Aβ. Primary microglia from wild type or Apoe −/− mice were treated with 2 µg/ml Aβ₄₂ for 24 hours. The lysates were subjected to SDS-PAGE and Western blotted for ABCA1, ApoE, Aβ and β-tubulin as a loading control. Blots shown are representative of three independent experiments. (B) Intracellular Aβ levels were quantified using ELISA for Aβ₄₂ and normalized to total protein. The data represent the outcome of 5 independent experiments (**P<0.01). (C) Exogenous ApoE rescued the Aβ degrading deficiency in Apoe −/− microglia. Primary microglia from Apoe −/− mice were incubated with 2 µg/ml Aβ₄₂ in the absence or presence of 1 µg/ml ApoE for an additional 24 hours. Intracellular Aβ₄₂ levels were quantified using ELISA and the data normalized to total protein (***P<0.001). (D) ApoE is required for LXR-mediated effect on Aβ degradation. Primary microglia from Apoe −/− mice were pretreated with DMSO or 1 µM GW3965 for 18 hours. The cells were then incubated with 2 µg/ml Aβ₄₂ for an additional 24 hours. Intracellular Aβ₄₂ levels were quantified using ELISA and data normalized to total protein. (E) Native ApoE particles enhanced Aβ degradation in an isoform-dependent manner. Primary microglia from ApoE −/− mice were treated with 2 µg/ml Aβ₄₂ in the absence or the presence of 200 ng/ml purified ApoE-containing native HDL particles isolated from immortalized astrocytes expressing the human ApoE isoforms for 24 hours. The levels of remaining intracellular Aβ were quantified using ELISA for Aβ₄₂. The data represent the outcome of 4 independent experiments (**P<0.01; ***P<0.001; #P<0.05).