Reactive Oxygen Species Generation Drives Iron Accumulation by Rotenone-Mediated Inhibition of Mitochondrial Complex I in Dopaminergic Neurons

Iron is an essential element that plays a critical role in mitochondrial bioenergetics, yet its excess is cytotoxic and contributes to the development of neurodegenerative diseases such as Parkinson’s disease (PD). Impaired Complex I (CI) activity, which can be caused by exposure to the environmental toxin rotenone, is implicated in PD. The mechanistic underpinnings connecting iron dyshomeostasis to cytotoxicity remain unclear, which creates challenges towards preventing neuronal cell death in PD. We hypothesized that CI inhibition is sufficient to disrupt cellular iron homeostasis via reactive oxygen species (ROS) generation. Using SH-SY5Y cells differentiated into dopaminergic neurons, we show that rotenone-induced CI inhibition increases ROS, promotes oxidative stress and cytotoxicity, and drives a redistribution of labile iron. Specifically, mitochondrial and total cellular iron levels increase, while cytosolic labile iron is reduced. Antioxidant treatment blocks both ROS production and iron accumulation, suggesting that ROS is critical for iron maldistribution in our system. Conversely, iron chelation suppresses ROS propagation, suggesting a positive feedback loop in which iron further amplifies oxidative stress. Our data are consistent with a greater sensitivity of mitochondrial [4Fe-4S]-containing proteins relative to the [2Fe-2S] proteins examined, potentially contributing to mitochondrial iron retention. Together, these findings establish a mechanistic link between mitochondrial dysfunction and iron dyshomeostasis and offer insights into how environmental CI inhibitors contribute to the pathogenesis of PD. More broadly, this work may have relevance to sporadic PD and other genetic or age-related disorders associated with iron accumulation and mitochondrial diseases such as Leigh Syndrome.