Triptolide Inhibited Cytotoxicity of Differentiated PC12 Cells Induced by Amyloid-Beta(25–35) via the Autophagy Pathway

Evidence shows that an abnormal deposition of amyloid beta-peptide(25–35) (Aβ(25–35)) was the primary cause of the pathogenesis of Alzheimer’s disease (AD). And the elimination of Aβ(25–35) is considered an important target for the treatment of AD. Triptolide (TP), isolated from Tripterygium wilfordii Hook.f. (TWHF), has been shown to possess a broad spectrum of biological profiles, including neurotrophic and neuroprotective effects. In our study investigating the effect and potential mechanism of triptolide on cytotoxicity of differentiated rat pheochromocytoma cell line (the PC12 cell line is often used as a neuronal developmental model) induced by Amyloid-Beta(25–35) (Aβ(25–35)), we used 3-(4, 5-dimethylthiazol-2-yl)-2, 5- diphenyltetrazolium bromide (MTT) assay, flow cytometry, Western blot, and acridine orange staining to detect whether triptolide could inhibit Aβ(25–35)–induced cell apoptosis. We focused on the potential role of the autophagy pathway in Aβ(25–35)-treated differentiated PC12 cells. Our experiments show that cell viability is significantly decreased, and the apoptosis increased in Aβ(25–35)-treated differentiated PC12 cells. Meanwhile, Aβ(25–35) treatment increased the expression of microtubule-associated protein light chain 3 II (LC3 II), which indicates an activation of autophagy. However, triptolide could protect differentiated PC12 cells against Aβ(25–35)-induced cytotoxicity and attenuate Aβ(25–35)-induced differentiated PC12 cell apoptosis. Triptolide could also suppress the level of autophagy. In order to assess the effect of autophagy on the protective effects of triptolide in differentiated PC12 cells treated with Aβ(25–35), we used 3-Methyladenine (3-MA, an autophagy inhibitor) and rapamycin (an autophagy activator). MTT assay showed that 3-MA elevated cell viability compared with the Aβ(25–35)-treated group and rapamycin inhibits the protection of triptolide. These results suggest that triptolide will repair the neurological damage in AD caused by deposition of Aβ(25–35) via the autophagy pathway, all of which may provide an exciting view of the potential application of triptolide or TWHF as a future research for AD.