title: Electron tomography of degenerating neurons in mice with abnormal regulation of iron metabolism.
abstract: Previous studies have shown that IRP1(+/-) IRP2(-/-) knockout mice develop progressive neurodegenerative symptoms similar to those observed in human movement disorders such as Parkinson's disease. Histological investigations using optical microscopy show that these IRP knockout mice display accumulation of ferritin in axonal tracts in the brain, suggesting a possible role for excess ferritin in mediating axonal degeneration. Direct observation of the 3D distribution of ferritin by electron tomography indicates that ferritin amounts are increased by 3- to 4-fold in selected regions of the brain, and structural damage is observed within the axon as evidenced by the loss of the internal network of filaments, and the invaginations of neighboring oligodendrocyte membranes into the axonal medium. While optical microscopic investigations suggest that there is a large increase in ferritin in the presumptive axonal regions of the IRP knockout mice, electron tomographic studies reveal that most of the excess ferritin is localized to double-walled vesicular compartments which are present in the interior of the axon and appear to represent invaginations of the oligodendrocyte cells into the axon. The amount of ferritin observed in the axonal space of the knockout mice is at least 10-fold less than the amount of ferritin observed in wild-type mouse axons. The surprising conclusion from our analysis, therefore, is that despite the overall increase in ferritin levels in the knockout mouse brain, ferritin is absent from axons of degenerating neurons, suggesting that trafficking is compromised in early stages of this type of neuronal degeneration.
authors.affiliation: Laboratory of Cell Biology, National Cancer Institute, NIH, Bethesda, MD 20817, USA.
authors.forename: Peijun
authors.initials: P
authors.lastname: Zhang
authors.forename: William
authors.initials: W
authors.lastname: Land
authors.forename: Stanton
authors.initials: S
authors.lastname: Lee
authors.forename: Jemma
authors.initials: J
authors.lastname: Juliani
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lefman
authors.forename: Sophia R
authors.initials: SR
authors.lastname: Smith
authors.forename: David
authors.initials: D
authors.lastname: Germain
authors.forename: Martin
authors.initials: M
authors.lastname: Kessel
authors.forename: Richard
authors.initials: R
authors.lastname: Leapman
authors.forename: Tracey A
authors.initials: TA
authors.lastname: Rouault
authors.forename: Sriram
authors.initials: S
authors.lastname: Subramaniam
mesh_terms: D000818:Animals; D001369:Axons / Q000737:chemistry / Q000473:pathology; D001921:Brain / Q000473:pathology; D001928:Brain Diseases, Metabolic / Q000473:pathology*; D005293:Ferritins / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009410:Nerve Degeneration / Q000209:etiology* / Q000473:pathology; D009474:Neurons / Q000473:pathology*; D009836:Oligodendroglia; D021381:Protein Transport; D014018:Tissue Distribution; D014057:Tomography, X-Ray Computed
chemical_list: D005293:Ferritins; D007501:Iron