Suppression of amyloid-β production by 24S-hydroxycholesterol via inhibition of intracellular amyloid precursor protein trafficking.

Cholesterol can be converted to 24S-hydroxycholesterol (24SOHC) by neuronal cholesterol 24-hydroxylase. In mouse models of Alzheimer's disease (AD), increasing 24SOHC levels reduced AD pathology. However, mechanisms underlying the effects of 24SOHC on amyloid-β (Aβ) production have remained unclear. Here we report that 24SOHC treatment reduces Aβ production and increases endoplasmic reticulum (ER)-resident immature amyloid precursor protein (APP) levels in human neuroblastoma SH-SY5Y cells and CHO cells stably expressing human APP. Treatment with 1-10 μM 24SOHC (equivalent to the concentrations detected in human brain homogenates) diminished Aβ production (IC50=4.6 μM for Aβ40) without affecting secretase activities. To evaluate the intracellular APP transport, we established an in vitro vesicle formation assay. We found that APP budding via COPII vesicles was diminished by 70% in 24SOHC-treated cells. The proteomics and immunoblotting analysis revealed that 24SOHC induced the expression of glucose-regulated protein 78 (GRP78), an ER chaperone, through unfolded protein response pathways, and enhanced the formation of the APP/GRP78 complex. Knockdown of GRP78 diminished the inhibitory effects of 24SOHC on Aβ production. These results suggest that 24SOHC down-regulates APP trafficking via enhancement of the complex formation of APP with up-regulated GRP78 in the ER, resulting in suppression of Aβ production.