Aβ peptide secretion is reduced by Radix Polygalae-induced autophagy via activation of the AMPK/mTOR pathway

Radix Polygalae is a traditional Chinese medicine that has been used as a sedative and to improve memory for a number of years. The impact of Radix Polygalae in patients with Alzheimer's disease has been investigated. However the mechanisms underlying its effects remain unclear. In the current study, the toxicity of various doses (100, 40, 20, 10, 5 and 0 μg/ml) of Radix Polygalae was measured in the human neuroblastoma cell line (SH-SY5Y) using an MTT assay. Changes in amyloid β (Aβ) levels in the supernatant of Chinese hamster ovary (CHO) cells overexpressing β-amyloid pro-protein (APP) and BACE1 (CHO-APP/BACE1), were detected using an ELISA assay. In order to confirm that the Aβ reduction was associated with autophagy, the autophagy marker protein, light chain 3 (LC3), was measured by western blot analysis and autophagosomes were assessed using MDC staining. In addition, the mechanism underlying the autophagy induced by Radix Polygalae was analyzed using western blotting to measure the protein expression of mammalian target of rapamycin (mTOR), p70s6k, Raptor, protein kinase B and adenosine monophosphate-activated protein kinase (AMPK), in addition to the phosphorylated forms of these proteins. The results demonstrated no significant toxicity of Radix Polygalae in SH-SY5Y cells, at a dose of 100 μg/ml. The secretion of Aβ was markedly reduced following treatment with Radix Polygalae, and this reduction occurred in a dose-dependent manner. The autophagy levels were shown to be enhanced in the drug treatment group, using fluorescence microscopy. In addition, levels of LC3II/LC3I, the marker protein of autophagy, were also increased. The results of the current study suggest that Radix Polygalae may aid in the elimination of the Aβ peptide, via the induction of autophagy, by the AMPK/mTOR signaling pathway. These results may provide a basis for further kin vivo investigation.