Immunohistochemical Study of Mitochondrial Ferritin in the Midbrain of Patients with Progressive Supranuclear Palsy

Mitochondrial ferritin (FtMt) is a novel ferritin that is localized in the mitochondria. FtMt expression is low in the liver and spleen, and high in the heart, testis, and brain. We previously detected FtMt in dopaminergic neurons in the substantia nigra pars compacta (SNc) in human and monkey midbrains. We investigated the localization and expression of FtMt in the midbrain of patients with progressive supranuclear palsy (PSP) and controls using a monoclonal antibody (C65-2) against human FtMt. FtMt immunoreactivity was weakly detected in neuromelanin-containing neurons in the SNc and ventral tegmental area (VTA) of control cases compared with PSP, which exhibited a remarkable increase in FtMt immunoreactivity. Preincubation of C65-2 with the immunizing FtMt peptide significantly reduced the staining, indicating the specificity of C65-2. Several puncta were observed outside the neurons of PSP, in contrast with the control cases. Double immunofluorescence histochemistry for FtMt and tyrosine hydroxylase (TH), glial fibrillary acidic protein, and Iba1 showed localization of FtMt in dopaminergic neurons, microglia, and astrocytes in PSP. Furthermore, FtMt immunoreactivity was detected in a few TH-negative neurons. In the SNc and VTA, FtMt immunoreactivity colocalized with phosphorylated tau immunoreactivity. Our results indicate that FtMt is involved in the pathology of PSP. Clarifying the involvement of FtMt in PSP is of great interest.