Bibenzyl compound 20c protects against endoplasmic reticulum stress in tunicamycin-treated PC12 cells in vitro

Aim: Accumulation of alpha-synuclein (alpha-syn) in the brain is a characteristic of Parkinson's disease (PD). In this study, we investigated whether treatment with tunicamycin, an endoplasmic reticulum (ER) stress inducer, led to the accumulation of alpha-syn in PC12 cells, and where alpha-syn protein was accumulated, and finally, whether bibenzyl compound 20c, a novel compound isolated from Gastrodia elata (Tian ma), could alleviate the accumulation of alpha-syn and ER stress activation in tunicamycin-treated PC12 cells. Methods: PC12 cells were treated with tunicamycin for different time (6 h, 12 h, 24 h, 48 h). Cell viability was determined by a MTT assay. Subcellular fractions of ER and mitochondria were extracted with the Tissue Endoplasmic reticulum Isolation Kit. The levels of alpha-syn protein and ER-stress-associated downstream chaperones were detected using Western blots and immunofluorescence. Results: Treatment of PC12 cells with tunicamycin (0.5-10 mu g/mL) dose-dependently increased the accumulation of alpha-syn monomer (19 kDa) and oligomer (55 kDa), and decreased the cell viability. Accumulation of the two forms of alpha-syn was observed in both the ER and mitochondria with increasing treatment time. Co-treatment with 20c (10(-5) mol/L) significantly increased the viability of tunicamycin-treated cells, reduced the level of alpha-syn protein and suppressed ER stress activation in the cells, evidenced by the reductions in phosphorylation of eIF2 alpha and expression of spliced ATF6 and XBP1. Conclusion: Tunicamycin treatment caused accumulation of alpha-syn monomer and oligomer in PC12 cells. Bibenzyl compound 20c reduces the accumulation of alpha-syn and inhibits the activation of ER stress, which protected PC12 cells against the toxicity induced by tunicamycin.