Zinc oxide nanoparticles harness autophagy to induce cell death in lung epithelial cells

Abstract

Although zinc oxide nanoparticles (ZnONPs) are widely used, they have raised concerns of toxicity in humans. Previous studies have indicated that reactive oxygen species (ROS) and autophagy are involved in the cytotoxicity of ZnONPs, but the regulatory mechanisms between autophagy and ROS remain to be elucidated. Herein, we comprehensively investigated the regulatory mechanism of autophagy and the link between autophagy and ROS in ZnONPs-treated lung epithelial cells. We demonstrated that ZnONPs could induce autophagy, and this process could enhance the dissolution of ZnONPs in lysosomes to release zinc ions. Sequentially, zinc ions released from ZnONPs were able to damage not only lysosomes, leading to impaired autophagic flux, but also mitochondria. Impaired autophagic flux resulted in the accumulation of damaged mitochondria, which could generate excessive ROS to cause cell death. We further demonstrated that the inhibition of autophagy by either pharmacological inhibitors or small interfering RNA (siRNA)-mediated knockdown of Beclin-1 and AMP-activated protein kinase could ameliorate ZnONPs-induced cell death. Moreover, we found that lysosomal-associated membrane protein 1/2 (LAMP-1/2), which were the most abundant highly glycosylated protein in late endosomes/lysosomes, exhibited aberrant expression pattern upon treatment with ZnONPs. Intriguingly, LAMP-2 knockdown, but not LAMP-1 knockdown, could exacerbate the ROS generation and cell death induced by ZnONPs treatment. Meanwhile, LAMP-2 overexpression alleviated ZnONPs-induced cell death, suggesting that LAMP-2 was linked to this toxic phenotype induced by ZnONPs. Our results indicate that autophagic dysfunction could contribute to excessive ROS generation upon treatment with ZnONPs in lung epithelial cells, suggesting that modulating the autophagy process would minimize ZnONPs-associated toxicity.

Mechanically induced autophagy is associated with ATP metabolism and cellular viability in osteocytes in vitro

“…To monitor the autophagic flux in the MLO-Y4 cells, a western blotting assay of endogenous LC3 and p62 proteins was performed as described previously [21] . The cells were collected and then washed with cold PBS and lysed with cold RIPA lysis solution (Santa Cruz Biotechnology, Santa Cruz, CA).…”

The Advancing of Zinc Oxide Nanoparticles for Biomedical Applications

“…Previous studies have indicated that ROS and autophagy are involved in the cytotoxicity of ZnO NPs, but the regulatory mechanisms between autophagy and ROS remain to be elucidated. Zhang et al investigated the regulatory mechanism of autophagy and the link between autophagy and ROS in ZnO NPs-treated lung epithelial cells [ 65 ]. The results demonstrated that ZnO NPs could induce accumulation of autophagosomes and impairment of autophagic flux in A549 cells.…”

In vitro comparative cytotoxicity study of aminated polystyrene, zinc oxide and silver nanoparticles on a cervical cancer cell line

“…ZnO NPs are initially recognized by the phagocytes, which further ingest them into the phagosomes, which are then acidified by phagosomes/lysosomes fusion (Cho et al 2011). The resultant dissolution of the ZnO NPs to its ions in the acidic micro-environment inside phagosomes/lysosomes causes lysosomal destabilization and subsequent cell death, which is regarded as the most accepted pathway for ZnO NPs induced toxicity (Pokhrel et al 2009, Cho et al 2011, Zhang et al 2017. ZnO NPs interaction with immune system due to their accumulation in spleen and lymph nodes has been shown in a mice in vivo model (Senapati et al 2017), where ZnO NPs have also been found to induce the release of inflammatory cytokines and causing an imbalance of Th-1/Th-2 cells (Senapati et al 2017).…”