Targeting reverse electron transport preserves mitochondrial function and prevents dopaminergic neurodegeneration in Parkinson’s disease

Mitochondrial dysfunction, redox imbalance, and excessive reactive oxygen species (ROS) generation are key pathological hallmarks of Parkinson’s disease (PD). The origin of these defects and their contribution to dopaminergic neurodegeneration remain unclear. Mitochondrial reverse electron transport (RET) reduces NAD + /NADH ratio and generates excess ROS. Here we show that RET is activated in the MPTP model of PD. We investigated the neuroprotective effects of CPT, a specific RET inhibitor, in the mouse MPTP/MPP⁺ model using co-treatment and post-treatment regimes. CPT markedly attenuated mitochondrial dysfunction by restoring the NAD⁺/NADH redox balance, reducing ROS accumulation, and preserving ATP production. These mitochondrial improvements were associated with significant recovery of motor function and preservation of dopaminergic neurons in the nigrostriatal pathway. Mechanistically, MPTP-induced NAD⁺ depletion led to PARP1 upregulation, downregulation of SIRT1 and SIRT3, impaired autophagy, and accumulation of phosphorylated alpha-synuclein (α-Syn). CPT reversed these effects. CPT also significantly reduced microglial and astrocytic activation and suppressed NLRP3 inflammasome signaling, thereby limiting neuroinflammation and downstream apoptotic pathways. At the mitochondrial level, CPT stabilized complex I architecture by restoring proper subunit interactions and preserving respiratory supercomplex assembly. Inhibition of NAD⁺ synthesis or SIRT3 signaling partially abolished the protective effects of CPT in BV-2 microglial cells, confirming the essential roles of NAD + /NAD redox balance and the NAD⁺-Sirtuin axis. Overall, these findings identify RET inhibition as an effective strategy of maintaining mitochondrial redox homeostasis that protects dopaminergic neurons by suppressing oxidative stress, maintaining NAD + /NADH ratio and Sirtuin signaling, and reducing neuroinflammation. RET inhibitors such as CPT therefore represent potential therapeutic candidates for PD.