Involvement of iron ions in 6-hydroxydopamine-induced disruption of intracellular copper metabolism

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra. Recently, disorders in metabolism of metals, including copper (Cu) and iron (Fe), have been reported to be linked to the pathogenesis of PD. We previously demonstrated that 6-hydoroxydopamine (6-OHDA), a neurotoxin used for the production of PD model animals, decreases Atox1, a Cu chaperone, and ATP7A, a Cu transporter, and disrupts intracellular Cu metabolism in human neuroblastoma SH-SY5Y cells. However, the exact mechanisms remain unclear. Meanwhile, intracellular Fe modulates 6-OHDA-induced cellular responses. In this study, we investigated whether Fe participates in 6-OHDA-induced abnormality in Cu metabolism. 6-OHDA-induced reactive oxygen species (ROS) production and cellular injury were suppressed by Fe chelators, deferoxamine and 2,2'-bipyridyl (BIP). These chelators also restored 6-OHDA-induced degradation of Atox1 and ATP7A proteins and subsequent Cu accumulation, indicating that intracellular Fe is involved in the disruption of Cu homeostasis associated with 6-OHDA. Atox1 has redox-sensitive cysteine (Cys) residues in its Cu-binding site. The Cys residues of Atox1 were oxidized by 6-OHDA, and BIP suppressed their oxidation. Moreover, the replacement of Cys with histidine in the Cu-binding site conferred resistance to 6-OHDA-induced Atox1 degradation. These results suggest that oxidized modification of Atox1 by 6-OHDA is likely to accelerate its degradation. Thus, we conclude that Fe and Cu metabolisms are closely related to each other in the pathogenesis of PD.