(-)-Epigallocatechin-3-Gallate Ameliorates Learning and Memory Deficits by Adjusting the Balance of TrkA/p75NTR Signaling in APP/PS1 Transgenic Mice

Alzheimer's disease (AD) is pathologically characterized by deposition of beta-amyloid (A beta) peptides, which closely correlates with the balance of nerve growth factor (NGF)-related TrkA/p75(NTR) signaling. (-)-Epigallocatechin-3- gallate (EGCG) is used for prevention and treatment of many neurodegenerative diseases, including AD. However, whether the neuroprotective effects of EGCG treatment were via modulating the balance of TrkA/p75(NTR) signaling was still unknown. In this study, we found that EGCG treatment (2 mg . kg(-1) . day(-1)) dramatically ameliorated the cognitive impairments, reduced the overexpressions of A beta(1-40) and amyloid precursor protein (APP), and inhibited the neuronal apoptosis in the APP/PS1 mice. Interestingly, the EGCG treatment enhanced the relative expression level of NGF by increasing the NGF/proNGF ratio in the APP/PS1 mice. Moreover, after EGCG treatment, TrkA signaling was activated by increasing the phosphorylation of TrkA following the increased phosphorylation of c-Raf, ERK1/2, and cAMP response element-binding protein (CREB), simultaneously the p75(NTR) signaling was significantly inhibited by decreasing the p75(ICD) expression, JNK2 phosphorylation, and cleaved-caspase 3 expression, so that the A beta deposits and neuronal apoptosis in the hippocampus were inhibited.