FOXO3 promoted mitophagy via nuclear retention induced by manganese chloride in SH-SY5Y cells

To evaluate the role of FOXO3 during the process of mitophagy induced by manganese chloride (MnCl2), mitochondrial dysfunction and mitophagy were detected before and after FOXO3 was knocked down in SH-SY5Y cells.Transmission electron microscopy (TEM), flow cytometry, confocal microscopy and a western blot were used to detect mitochondrial ultrastructure and autophagy, Ca2+ levels, mitochondrial reactive oxygen species (ROS) and the mitochondrial membrane potential (MMP), autophagosomes and mitophagy marker proteins (p62, LC3-II/LC3-I, Beclin-1, PINK1 and P-parkin), respectively.After SH-SY5Y cells were exposed to MnCl2, the levels of cytoplasmic Ca2+ and mitochondrial ROS increased but the mitochondrial MMP decreased significantly compared to the control in a dose- and time-dependent manner (p < 0.05), which indicated that MnCl2 can lead to mitochondrial dysfunction. Under TEM, mitophagy and autolysosomes were observed. The WB results also showed that mitophagy marker proteins including LC3-II/LC3-I, Beclin-1, PINK1 and P-parkin except for p62 increased in a dose- and time-dependent manner, accompanied by FOXO3 nuclear retention, which indicated that MnCl2 can lead to mitophagy and FOXO3 nuclear translocation may be involved in this process. After FOXO3 was knocked down, the inverse results of mitophagy and the levels of mitochondrial ROS decreasing were observed, which showed that FOXO3 silencing could inhibit mitophagy and mitochondrial dysfunction induced by MnCl2.Our results indicated that Mn could induce mitophagy by enhancing FOXO3 nuclear retention, which might promote mitophagy induced by MnCl2.