Cell-type and Amyloid Precursor Protein-type Specific Inhibition of Aβ Release by Bafilomycin A1, a Selective Inhibitor of Vacuolar ATPases (∗)

Treatment of human 293 cells transfected with amyloid precursor protein (APP)K595N,M596L (the “Swedish” mutation) with a specific inhibitor of the vacuolar H+-ATPases, bafilomycin A1 (baf A), leads to a potent inhibition of the release of the Aβ peptide. This is accompanied by a selective inhibition of β-secretase activity. Surprisingly, baf A did not inhibit the production of Aβ from either wild-type APP (WT APP) or from APPV717I (the “Hardy” mutation), expressed in the same cell type. In contrast, the robust production of Aβ from a human neuroglioma-derived cell line (HS683) transfected with WT APP, or from primary human mixed brain cultures (HMBC) expressing genomic WT APP, were also effectively inhibited by baf A. The inhibition of Aβ production from the HMBC was also accompanied by the inhibition of β-s-APP release. No inhibition of α-s-APP release was seen in any of the cell types tested. These results indicate that intracellular acidic processes are rate-limiting for β-secretase cleavage and Aβ production from SW APP, but not WT APP, in the peripheral 293 cell line. Furthermore, such acidic processes also play a rate-limiting role in Aβ release from human central nervous system-derived cells, including HMBC. Differential trafficking of the SW APP into an acidic compartment conducive to β-secretase cleavage and Aβ release could be one explanation for the increased production of Aβ observed on expression of this mutation.