Mitophagy is involved in chromium (VI)-induced mitochondria damage in DF-1 cells

Cr (VI), which is a common heavy metal pollutant with strong oxidizing property, exists widely in nature. Organisms can be exposed to Cr (VI) through various means. Cr (VI) causes mitochondrial dysfunction after being absorbed by cells. Whether Cr (VI) induces the selective autophagic degradation of mitochondria, which is a biological process called mitophagy, remains unclear. Mitophagy not only recycles intracellularly damaged mitochondria to compensate for nutrient deprivation but also is involved in mitochondria quality control. Thus, this study investigated whether Cr (VI) could induce mitophagy in DF-1 cells. Carbonyl cyanide m-chlorophenylhydrazone, which is a mitochondrial-uncoupling reagent that induces mitophagy, was used. DF-1 cells were incubated with different doses of Cr (VI) for varying durations. The autophagy-related proteins LC3-II and p62 levels decreased after 6 h of Cr (VI) treatment but recovered within 24 h. The mitochondrial membrane potential, which is an indicator of mitochondrial damage, was detected by flow cytometry. We found that different durations of Cr (VI) treatment induced mitochondrial mass decrease and depolarization. Furthermore, the expression of the protein translocase of outer mitochondrial membrane 20 (TOMM20), which is a mitochondrial outer membrane protein, was decreased significantly in the presence of Cr (VI). Our findings indicate that Cr (VI) may contribute to the mitochondrial morphology and function damage and may therefore lead to the autophagic clearance of mitochondria.