Ginsenoside Rg1 promotes -amyloid peptide degradation through inhibition of the ERK/PPAR phosphorylation pathway in an Alzheimer's disease neuronal model

beta-Amyloid peptide (A beta) deposition in the brain is an important pathological change in Alzheimer's disease (AD). Insulin-degrading enzyme (IDE), which is regulated transcriptionally by peroxisome proliferator-activated receptor gamma (PPAR gamma), is able to proteolyze A beta. One of the members of the MAPK family, ERK, is able to mediate the phosphorylation of PPAR gamma at Ser112, thereby inhibiting its transcriptional activity. Ginsenoside Rg1 is one of the active ingredients in the natural medicine ginseng and has inhibitory effects on A beta production. The present study was designed to investigate whether ginsenoside Rg1 is able to affect the regulation of PPAR gamma based on the expression of its target gene, IDE, and whether it is able to promote A beta degradation via inhibition of the ERK/PPAR gamma phosphorylation pathway. In the present study, primary cultured rat hippocampal neurons were treated with A beta 1-42, ginsenoside Rg1 and the ERK inhibitor PD98059, and subsequently TUNEL staining was used to detect the level of neuronal apoptosis. ELISA was subsequently employed to detect the intra- and extracellular A beta 1-42 levels, immunofluorescence staining and western blotting were used to detect the translocation of ERK from the cytoplasm to the nucleus, immunofluorescence double staining was used to detect the co-expression of ERK and PPAR gamma, and finally, western blotting was used to detect the phosphorylation of PPAR gamma at Ser112 and IDE expression. The results demonstrated that ginsenoside Rg1 or PD98059 were able to inhibit primary cultured hippocampal neuron apoptosis induced by A beta 1-42 treatment, reduce the levels of intra- and extraneuronal A beta 1-42 and inhibit the translocation of ERK from the cytoplasm to the nucleus. Furthermore, administration of ginsenoside Rg1 or PD98059 resulted in attenuated co-expression of ERK and PPAR gamma, inhibition of phosphorylation of PPAR gamma at Ser112 mediated by ERK and an increase in IDE expression. In addition, the effects when PD98059 to inhibit ERK followed by treatment with ginsenoside Rg1 were found to be more pronounced than those when using PD98059 alone. In conclusion, ginsenoside Rg1 was demonstrated to exert neuroprotective effects on AD via inhibition of the ERK/PPAR gamma phosphorylation pathway, which led to an increase in IDE expression, the promotion of A beta degradation and the decrease of neuronal apoptosis. These results could provide a theoretical basis for the clinical application of ginsenoside Rg1 in AD.