PINK1/Parkin-mediated mitophagy is involved in NaAsO2-induced apoptosis of human hepatic cells through activation of ERK signaling

Mitochondrial dysfunction has been demonstrated as one key event in arsenic-induced hepatic cell damage though the exact molecular target remains unknown. Here we examined NaAsO2-induced mitochondrial damage in the L-02 cell led to mitochondrial depolarization and cytochrome c release, mitophagy, apoptosis in a dose response manner. Mitophagy was measured by analysis of PINK1, Parkin, LC3-II and p62 protein. Apoptosis was assessed by measuring Annexin V. Using the mitophagy inhibitor cyclosporine A (CsA) or ERK inhibitor (PD98059), the balance between mitophagy and apoptosis were further explored. When CsA was used prior to cell exposure to NaAsO2, it was found that the levels of mitophagy were decreased as expected and apoptosis was increased in response. CsA alone had no effect on the apoptosis rate. When the ERK signaling inhibitor PD98059 was used, there was a similar result that mitophagy was reduced though in contrast with CsA the apoptosis rate was also decreased compared with NaAsO2 alone. This result, along with the increased levels of ERK measured here in response to NaAsO2, indicates that ERK activation is a second key molecular response to NaAsO2 through the activation of both apoptosis and mitophagy. Thus the results with CsA indicate that the likely key biological event in NaAsO2 toxicity is at the level of the mitochondria leading to cytochrome c release and apoptosis. Mitophagy is increased in response to a secondary effect of NaAsO2 on ERK signaling that activates both mitophagy and apoptosis. The activation of mitophagy allows the cell to avoid some apoptosis. When ERK signaling is inhibited by PD98059 both the levels of apoptosis and mitophagy are decreased compared with the response produced by NaAsO2 alone in comparison to the inhibition of mitophagy by CsA that reduced mitophagy but dramatically increased apoptosis in response.