Up-regulation of divalent metal transporter 1 is involved in 1-methyl-4-phenylpyridinium (MPP⁺)-induced apoptosis in MES23.5 cells

Apoptosis has been identified as one of the important mechanisms involved in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Our previous study showed increased iron levels in the substantia nigra as well as loss of dopaminergic neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced PD mouse models. 1-Methyl-4-phenylpyridinium (MPP⁺) is commonly used to establish a cellular model of PD. Although intracellular iron plays a crucial role in MPP⁺-induced apoptosis, the molecular mechanism linking increased iron and MPP⁺-induced neurodegeneration is largely unknown. In the present study, we investigate the involvement of divalent metal transporter 1 (DMT1) that accounts for the ferrous iron transport in MPP⁺-treated MES23.5 cells. In the treated cells, a significant influx of ferrous iron was observed. This resulted in a decreased mitochondrial membrane potential. Additionally, an elevated level of ROS production and activation of caspase-3 were also detected, as well as the subsequent cell apoptosis. These effects could be fully abolished by iron chelator desferal (DFO). Increased DMT1 (-IRE) expression but not DMT1 (+IRE) accounted for the increased iron influx. However, there were no changes for iron regulatory protein 1 (IRP1), despite decreased expression of IRP2. Iron itself had no effect on IRP1 and IRP2 expression. Our data suggest that although DMT1 mRNA contains an iron responsive element, its expression is not totally controlled by this. MPP⁺ could up-regulate the expression of DMT1 (-IRE) in an IRE/IRP-independent manner. Our findings also show that MPP⁺-induced apoptosis in MES23.5 cells involves DMT1-dependent iron influx and mitochondria dysfunction.