Quercetin reduces eIF2α phosphorylation by GADD34 induction

The production of amyloid beta (A beta) in the brain from Ab precursor protein (APP) through gamma-secretase is important for the pathogenesis of Alzheimer's disease (AD). Our previous studies have demonstrated that autophagy impairment and endoplasmic reticulum stress increase presenilin 1 expression and enhance gamma-secretase activity through the phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2 alpha) and the translation of activating transcription factor 4 (ATF4). However, the inhibitory molecules for gamma-secretase are largely unknown. Here, we demonstrate that the levels of ATF4 expression are increased in the brain of APP23 AD model mice; furthermore, these levels enhanced in the brain of APP23 mice crossed with obese and diabetic db/db (Lepr(db/db)) mice. A polyhydroxylated flavonoid, quercetin, suppressed presenilin 1 expression and Ab secretion in autophagy-impaired cells by the induction of growth arrest and DNA damaged-inducible gene (GADD) 34, which mediates eIF2 alpha dephosphorylation, leading to decreased ATF4 expression. GADD34 induction was observed in the brain of wild-type mice, and APP23 mice fed quercetin in their diet. After the long-term feeding of quercetin, deterioration in memory assessed by freezing behavior was delayed in APP23 mice. These results indicate that quercetin may reduce eIF2 alpha phosphorylation and ATF4 expression through GADD34 induction in the brain, leading to the improvement of memory in aged mice and the delay of deterioration in memory at the early stage of AD in AD model mice. (C) 2015 Elsevier Inc. All rights reserved.