Autophagy Alleviates Melamine-Induced Cell Death in PC12 Cells Via Decreasing ROS Level

Since melamine was illegally added to raw milk for increasing the apparent protein content, such a scandal has not been quite blown out. Previous studies showed that melamine induced apoptosis and oxidative damage in both in vivo and in vitro experiments. It is well known that autophagy is closely related to oxidative stress. In the present study, we examined whether autophagy played an important role in protecting PC12 cells, which were damaged by melamine. Immunofluorescence assay showed that melamine enhanced the number of punctuate dot, indicating the increase of autophagosomes. Western blot assay presented that melamine significantly elevated the expression level of autophagy markers including LC3-II/LC3-I ratio, beclin-1, and Atg 7. Rapamycin further enhanced the effect, whereas 3-methyadenine (3-MA) inhibited it. MTT assay exhibited that rapamycin significantly enhanced the cell viability (P < 0.01), while 3-MA considerably reduced it in melamine-treated PC12 cells (P < 0.01). Furthermore, flow cytometry assay showed that rapamycin considerably reduced the reactive oxygen species (ROS) level of the cells (P < 0.01), but 3-MA increased the generation of ROS (P < 0.01). Additionally, the superoxide dismutase (SOD) activity was notably increased by rapamycin in melamine-treated PC12 cells (P < 0.01), while the activity of which was prominently decreased by 3-MA (P < 0.01). Malondialdehyde (MDA) assay showed that rapamycin remarkably decreased the MDA level of the cells (P < 0.05), while 3-MA increased it (P < 0.01). Consequently, this study demonstrated that autophagy protected PC12 cells from melamine-induced cell death via inhibiting the excessive generation of ROS. Regulating autophagy may become a new targeted therapy to relieve the damage induced by melamine.