title: Ultrastructural study of aggregates in the spinal cord of transgenic mice with a G93A mutant SOD1 gene.
abstract: The ultrastructural features of SOD1-positive aggregates were determined to clarify whether these aggregates are associated with the pathogenesis of SOD1 mutant mice. We examined the spinal cord of transgenic mice expressing a G93A mutant human SOD1 gene with fewer copies (gene copy 10). At the early presymptomatic stage (age 24 weeks), SOD1- and ubiquitin-positive granular, linear, or round deposits were found occasionally in the neuropil of the anterior horns. Ultrastructurally, small filamentous aggregates were observed occasionally in the neuronal processes including the axons in the anterior horns. At the late presymptomatic stage (28 weeks), SOD1- and ubiquitin-positive deposits and Lewy body-like inclusions (LIs) were frequently demonstrated in the neuronal processes including cord-like swollen axons and in some remaining anterior horn neurons. Ultrastructurally, larger filamentous aggregates were frequent, predominating in the neuronal processes of the anterior horns including the proximal axons, but were rare in the somata and dendrites. The aggregates usually consisted of interwoven intermediate filaments (about 10-15 nm in diameter) and frequently contained electron-dense cores in the center resembling LIs. Occasionally the aggregates consisted mainly of granular, amorphous, or vesicular substance, showing fewer filamentous structures. At the symptomatic stages (32 and 35 weeks), LIs were frequently demonstrated within the neuronal processes in the anterior horns, particularly in the cord-like swollen axons. Many more prominent SOD1- and ubiquitin-positive deposits were observed over the whole white matter columns and in the gray matter of the anterior and posterior horns than at the previous stage. Ultrastructurally, aggregates frequently contained electron-dense cores, and were frequently observed in cord-like swollen axons consisting of accumulated neurofilaments. A high level of human SOD1-and ubiquitin-immunogold labeling was present in small to large aggregates even at the presymptomatic stages, and the aggregates increased in size and frequency with time. Compactly packed filaments and electron-dense cores of aggregates showed SOD1-and ubiquitin-immunogold labeling more prominently than in loosely packed filaments. These findings suggest that the accumulation of SOD1-positive aggregates in the neuronal processes, predominantly in the axons, constitutes an important determinant of neurotoxicity and the pathogenesis of this animal model, probably causing impairment of axonal transport by the sequestration of mutant SOD1 protein within aggregates, or in part by physically blocking the axonal transport.
authors.affiliation: Department of Neurology, Tokyo Women's Medical University, 8-1 Kawada-cho, Shinjuku-ku, 162-8666, Tokyo, Japan. ssasaki@nij.twmu.ac.jp
authors.forename: Shoichi
authors.initials: S
authors.lastname: Sasaki
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Warita
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Murakami
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Shibata
authors.forename: Takashi
authors.initials: T
authors.lastname: Komori
authors.forename: Koji
authors.initials: K
authors.lastname: Abe
authors.forename: Makio
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Makoto
authors.initials: M
authors.lastname: Iwata
mesh_terms: D000367:Age Factors; D000818:Animals; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D046529:Microscopy, Electron, Transmission / Q000379:methods; D016253:Microscopy, Immunoelectron / Q000379:methods; D016900:Neurofilament Proteins / Q000378:metabolism; D019581:Neuropil / Q000473:pathology / Q000648:ultrastructure; D013116:Spinal Cord / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure*; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D016900:Neurofilament Proteins; D025801:Ubiquitin; C109415:SOD1 G93A protein; D013482:Superoxide Dismutase