Chapter 9 - Organic Pollutant Perfluorooctane Sulfonate–Induced Lysosomal Membrane Permeabilization Blocks Autophagy Flux in Human Hepatoma Cells

Abstract

Perfluorooctane sulfonate (PFOS) is an emerging persistent organic pollutant widely distributed in the environment, wildlife, and human. In our studies, as observed under the transmission electron microscope, PFOS increased autophagosome numbers in HepG2 cells. It was confirmed by elevated LC3-II levels in Western blot analysis. PFOS increased P62 level and chloroquine failed to further increase the expression of LC3-II after PFOS treatment, indicating that the accumulation of autophagosome was due to impaired degradation rather than increased formation. With acridine orange staining, we found that PFOS caused lysosomal membrane permeabilization (LMP). In our studies, autophagosome formation inhibitor 3-methyladenine protected cells against PFOS toxicity. Autophagy stimulator rapamycin further decreased cell viability and increased LDH release. Cathepsin inhibitor did not influence cell viability of PFOS-treated HepG2 cells significantly. These results supported the notion that autophagic cell death contributed to PFOS-induced hepatotoxicity. In summary, the data of this study revealed that PFOS induced LMP and consequent blockage of autophagy flux, leading to an excessive accumulation of the autophagosomes and turning autophagy into a destructive process eventually. These findings will provide clues for effective prevention and treatment of PFOS-induced hepatic disease.