TF and Parkinson disease: In various PD animal and cellular models and brain tissues of PD patients, iron regulation-related protein expression is dysregulated, and iron, Tf, and TfR2 levels are high in dopaminergic neurons.[49] It was found that overexpression of TfR2 resulted in the uptake and targeting of extracellular Tf-bound iron to mitochondria, while TfR2 deficiency was shown to inhibit iron overload and degeneration of dopaminergic neurons.[50] Therefore, excessive iron accumulation in mitochondria via the Tf/TfR2 system may be a critical factor in the progression of PD.