Perfluoroalkyl acid exposure induces protective mitochondrial and endoplasmic reticulum autophagy in lung cells

Abstract

Wide application of perfluoroalkyl acids (PFAAs) has raised great concerns on their side-effects on human health. PFAAs have been shown to accumulate mainly in the liver and cause hepatotoxicity. However, PFAAs can also deposit in lung tissues through air-borne particles and cause serious pulmonary toxicity. But the underlying mechanisms are still largely unknown. Autophagy is a type of programmed cell death parallel to necrosis and apoptosis, and may be involved in the lung toxicity of PFAAs. In this study, lung cancer cells, A549, were employed as the model to investigate the effects of three PFAAs with different carbon chain lengths on cell autophagy. Through Western blot analysis on LC3-I/II ratio of cells exposed to non-cytotoxic concentration (200 µM) and cytotoxic concentration (350 µM), we found concentration-dependent increase of autophagosomes in cells, which was further confirmed by TEM examination on ultra-thin section of cells and fluorescence imaging on autophagosomes in live cells. The abundance of p62 increased with the PFAAs concentration indicating the blockage of autophagy flux. Furthermore, we identified the mitochondrial autophagy (mitophagy) and endoplasmic reticulum autophagy (ER-phagy) morphologically as the major types of autophagy, suggesting the disruption on mitochondria and ERs. These organelle damages were confirmed by the overgeneration of ROS, hyperpolarization of mitochondrial membrane potential, as well as the up-regulation of ER-stress-related proteins, ATF4 and p-IRE1. Further analysis on the signaling pathways showed that PFAAs activated the MAPK pathways and inhibited the PI3K/Akt pathway, with potencies following the order of PFDA > PFNA > PFOA. Anti-oxidant (NAC) treatment did not rescue cells from death, indicating that oxidative stress is not the reason of cytotoxicity. Inhibition of autophagy by Atg5 siRNA and chloroquine even increased the toxicity of PFAAs, suggesting that PFAAs-autophagy was induced as the secondary effects of organelle damages and played a protective role during cell death.

Perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), and perfluorononanoic acid (PFNA) increase triglyceride levels and decrease cholesterogenic gene expression in human HepaRG liver cells

“…Activation of these pathways has also been reported to be induced by saturated fatty acids in human liver cells, possibly playing a role in the induction of non-alcoholic fatty liver disease (NAFLD) (Cao et al 2012 ). Previously, it has been demonstrated that PFOA induces ER stress and UPR in HepG2 liver cells (Yan et al 2015 ) and ER-stress-related autophagy in A549 lung cells (Xin et al 2018 ).…”

Hydroxychloroquine Potentiates Apoptosis Induced by PPARα Antagonist in 786-O Clear Cell Renal Cell Carcinoma Cells Associated with Inhibiting Autophagy

“…It was observed that cotreatment of the pancreatic cells with gambogic acid and chloroquine lowered the cell viability to a greater extent and that the level of ROS was accentuated since the scavenging of the damaged mitochondria was inhibited [65]. In lung cells, perfluoroalkyl acid can decrease cell viability and induce autophagy by engulfing the damaged endoplasmic reticulum and avoiding excessive endoplasmic 10 PPAR Research reticulum stress [66]. On the other hand, energy can be generated via autophagy in the cells under stress.…”

Exosomal cargos modulate autophagy in recipient cells via different signaling pathways

“…Recently, Xue et al reported that Mitofusin2 was capable of inducing autophagy flux in pancreatic cancer cells via inhibiting the PI3K/AKT/ mTOR pathway [114]. In a similar vein, it was demonstrated that treatment of lung cells with Perfluoroalkyl acid caused autophagy flux through suppressing the PI3K/AKT pathway [114]. Recent experiments indicated that the exosomes of MSCs have the potential to control autophagy through PI3K/AKT/mTOR pathway.…”

“…PI3K/ AKT/mTOR axis facilities growth and metabolism events of mammalians [113]. Recently, Xue et al reported that Mitofusin2 was capable of inducing autophagy flux in pancreatic cancer cells via inhibiting the PI3K/AKT/ mTOR pathway [114]. In a similar vein, it was demonstrated that treatment of lung cells with Perfluoroalkyl acid caused autophagy flux through suppressing the PI3K/AKT pathway [114].…”

“…Red color for Akt/mTOR signaling pathway, Blue color for Toll-like receptor-ligand signal pathway, Light purple color for AMPK/mTOR signal pathway mRNA levels of STAT3 in human intrahepatic biliary epithelial cells, which resulted in autophagy activation [122]. A growing body of evidence has demonstrated the interaction between autophagy and apoptosis [114]. In this scenario, there is evidence that Bcl-2, an anti-apoptotic molecule, interacts with Beclin-1, which may result in inducing autophagy [123] (Fig.…”