Small Molecule Amyloid-ß Protein Precursor Processing Modulators Lower Amyloid-ß Peptide Levels via cKit Signaling.

ABSTRACT

Alzheimer's disease (AD) is characterized by the accumulation of neurotoxic amyloid-ß (Aß) peptides consisting of 39-43 amino acids, proteolytically derived fragments of the amyloid-ß protein precursor (AßPP), and the accumulation of the hyperphosphorylated microtubule-associated protein tau. Inhibiting Aß production may reduce neurodegeneration and cognitive dysfunction associated with AD. We have previously used an AßPP-firefly luciferase enzyme complementation assay to conduct a high throughput screen of a compound library for inhibitors of AßPP dimerization, and identified a compound that reduces Aß levels. In the present study, we have identified an analog, compound Y10, which also reduced Aß. Initial kinase profiling assays identified the receptor tyrosine kinase cKit as a putative Y10 target. To elucidate the precise mechanism involved, AßPP phosphorylation was examined by IP-western blotting. We found that Y10 inhibits cKit phosphorylation and increases AßPP phosphorylation mainly on tyrosine residue Y743, according to AßPP751 numbering. A known cKit inhibitor and siRNA specific to cKit were also found to increase AßPP phosphorylation and lower Aß levels. We also investigated a cKit downstream signaling molecule, the Shp2 phosphatase, and found that known Shp2 inhibitors and siRNA specific to Shp2 also increase AßPP phosphorylation, suggesting that the cKit signaling pathway is also involved in AßPP phosphorylation and Aß production. We further found that inhibitors of both cKit and Shp2 enhance AßPP surface localization. Thus, regulation of AßPP phosphorylation by small molecules should be considered as a novel therapeutic intervention for AD.