Inhibition of autophagy enhances cadmium-induced apoptosis in duck renal tubular epithelial cells

Abstract

Increasing evidence indicates autophagy and apoptosis are involved in the toxicity mechanism of heavy metals. Our previous studies showed that cadmium (Cd) could induce autophagy and apoptosis in duck kidneys in vivo, nevertheless, the interaction between them has yet to be elucidated. Herein, the cells were either treated with 3CdSO4·8H2O (0, 1.25, 2.5, 5.0 μM Cd) or/and 3-methyladenine (3-MA) (2.5 μM) for 12 h and the indictors related autophagy and apoptosis were detected to assess the correlation between autophagy and apoptosis induced by Cd in duck renal tubular epithelial cells. The results demonstrated that Cd exposure notably elevated intracellular and extracellular Cd contents, the number of autophagosomes and LC3 puncta, up-regulated LC3A, LC3B, Beclin-1, Atg5 mRNA levels, and Beclin-1 and LC3II/LC3I protein levels, down-regulated mTOR, p62 and Dynein mRNA levels and p62 protein level. Additionally, autophagy inhibitor 3-MA decreased Beclin-1, LC3II/LC3I protein levels and increased p62 protein level. Moreover, co-treatment with Cd and 3-MA could notably elevate Caspase-3, Cyt C, Bax, and Bak-1 mRNA levels, Caspase-3 and cleaved Caspase-3 protein levels, and cell apoptotic rate as well as cell damage, decreased mitochondrial membrane potential (MMP), Bcl-2 mRNA level and the ratio of Bcl-2 to Bax compared to treatment with Cd alone. Overall, these results indicate Cd exposure can induce autophagy in duck renal tubular epithelial cells, and inhibition of autophagy might aggravate Cd-induced apoptosis through mitochondria-mediated pathway.