Complex II inhibition suppresses RSL3-induced ferroptosis by restoring mitochondrial bioenergetics

The mitochondrial electron transport chain (ETC) serves as the main site of cellular energy production and a major source of reactive oxygen species (ROS) generation, which can contribute to the lipid peroxidation associated with ferroptosis. However, the critical roles of mitochondria in ferroptosis are still being debated, and the consequences for cell survival vary depending on different ferroptosis inducers or mitochondrial modulators. In the neuroblastoma clonal cells SH-SY5Y, we demonstrated that inhibition of mitochondrial Complex II by 2-thenoyltrifluoroacetone (TTFA) markedly suppressed RSL3-induced ferroptotic lipid peroxidation and cell death. RSL3, a known inhibitor of glutathione peroxidase 4 (GPX4), significantly increased the mitochondrial membrane potential and superoxide production while reducing ATP-linked oxygen consumption. Co-treatment with TTFA effectively attenuated RSL3-induced mitochondrial hyperpolarization, lowered mitochondrial ROS generation, and restored respiratory activities - particularly enhanced ATP-linked oxygen consumption and reduced proton leak. Consistently, TTFA restored ATP production suppressed by RSL3. In contrast, inhibition of Complex I by rotenone did not suppress superoxide production and lipid peroxidation induced by RSL3, although it provided some protection against RSL3-mediated cytotoxicity. These findings suggest that inhibition of Complex II confers protection against ferroptosis by maintaining mitochondrial redox balance and protecting mitochondrial energy metabolism. In addition, our results uncover a novel mitochondrial mechanism underlying RSL3-induced oxidative stress and ferroptosis that can be modulated through targeted regulation of the ETC.