PDF(Pubmed)
Abstract：
β-Amyloid peptide (Aβ) 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 γ (PPARγ), is able to proteolyze Aβ. One of the members of the MAPK family, ERK, is able to mediate the phosphorylation of PPARγ 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 Aβ production. The present study was designed to investigate whether ginsenoside Rg1 is able to affect the regulation of PPARγ based on the expression of its target gene, IDE, and whether it is able to promote Aβ degradation via inhibition of the ERK/PPARγ phosphorylation pathway. In the present study, primary cultured rat hippocampal neurons were treated with Aβ1-42, 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 Aβ1-42 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 PPARγ, and finally, western blotting was used to detect the phosphorylation of PPARγ at Ser112 and IDE expression. The results demonstrated that ginsenoside Rg1 or PD98059 were able to inhibit primary cultured hippocampal neuron apoptosis induced by Aβ1-42 treatment, reduce the levels of intra- and extraneuronal Aβ1-42 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 PPARγ, inhibition of phosphorylation of PPARγ 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/PPARγ phosphorylation pathway, which led to an increase in IDE expression, the promotion of Aβ degradation and the decrease of neuronal apoptosis. These results could provide a theoretical basis for the clinical application of ginsenoside Rg1 in AD.
摘要：
脑内β-淀粉样肽(Aβ)沉积是阿尔茨海默病(AD)的重要病理改变。胰岛素降解酶(IDE),受过氧化物酶体增殖物激活受体γ（PPARγ）转录调节，能够蛋白水解Aβ。MAPK家族的成员之一,ERK,能够介导PPARγ在Ser112上的磷酸化，从而抑制其转录活性。人参皂苷Rg1是天然药物人参中的活性成分之一，对Aβ的产生具有抑制作用。本研究旨在研究人参皂苷Rg1是否能够根据其靶基因的表达来影响PPARγ的调节。IDE,以及是否能够通过抑制ERK/PPARγ磷酸化途径促进Aβ降解。在本研究中,用Aβ1-42，人参皂苷Rg1和ERK抑制剂PD98059处理原代培养的大鼠海马神经元，随后用TUNEL染色检测神经元凋亡水平。随后采用ELISA检测细胞内和细胞外Aβ1-42水平，免疫荧光染色和免疫印迹检测ERK从细胞质到细胞核的易位,免疫荧光双重染色检测ERK和PPARγ的共表达,最后，免疫印迹法检测PPARγ在Ser112和IDE表达的磷酸化。结果表明，人参皂苷Rg1或PD98059能够抑制Aβ1-42诱导的原代培养海马神经元凋亡，降低神经元内和神经元外Aβ1-42的水平，并抑制ERK从细胞质到细胞核的易位。此外，人参皂苷Rg1或PD98059的给药导致减弱的ERK和PPARγ的共表达，ERK介导的Ser112处PPARγ磷酸化的抑制和IDE表达的增加。此外,发现PD98059抑制ERK后用人参皂苷Rg1治疗的效果比单独使用PD98059时更明显。总之,人参皂苷Rg1通过抑制ERK/PPARγ磷酸化通路对AD发挥神经保护作用,这导致了IDE表达式的增加，促进Aβ降解和减少神经元凋亡。本研究结果可为人参皂苷Rg1在AD中的临床应用提供理论依据。
