Ginsenoside Rg1 attenuates β-amyloid generation via suppressing PPARγ-regulated BACE1 activity in N2a-APP695 cells

The level of beta-site APP-cleaving enzyme 1 (BACE1) has been documented to increase in the brains of patients with Alzheimer's disease, which has resulted in elevation of beta-amyloid (A beta) peptides. As a transcription factor binding site of the BACE1 promoter, peroxisome proliferator-activated receptor-gamma (PPAR gamma) response element regulates the activity of the BACE1 promoter activity, indicating that PPAR gamma may become a potential target for Alzheimer's disease treatment. Recent studies have demonstrated that ginsenoside Rg1 which is an effective component of extracts of ginseng can prevent memory loss and improve cognitive function in a variety of animal models. However, the underlying mechanism remains unclear. In the present study, we found that Rg1 decreased the levels of A beta(1-40) and A beta(1-42) secreted in N2a-APP695 cells. The expression levels of both BACE1 mRNA and protein as well as beta-CTFs, a cleavaged C-terminal fragment of APP by BACE1, were reduced in cells treated with Rg1. Moreover, Rg1 treatment led to a translocation of PPAR. from cytoplasm to nuclear. Intriguingly, Rg1, like pioglitazone (a PPAR gamma agonist), suppressed BACE1 activity in N2a-APP695 cells, while its effect on BACE1 activity was attenuated by GW9662 (a PPAR gamma antagonist). These results indicate that Rg1 may be a PPAR. agonist to enhance the binding of nuclear PPAR gamma to the BACE1 promoter, which may in turn inhibit the transcription and translation of BACE1, suppress the activity of BACE1, and ultimately attenuate A beta generation. Therefore, ginsenoside Rg1 may serve as a promising agent in modulating A beta-related pathology in Alzheimer's disease. (C) 2011 Elsevier B.V. All rights reserved.