In vitro evidence of propagation of superoxide dismutase-1 protein aggregation in canine degenerative myelopathy.

Canine degenerative myelopathy (DM) is a progressive and fatal neurodegenerative disorder that has been linked to mutations in the superoxide dismutase 1 (SOD1) gene. The accumulation of misfolded protein aggregates in spinal neurons and astrocytes is implicated as an important pathological process in DM; however, the mechanism of protein aggregate formation is largely unknown. In human neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), cell-to-cell propagation of disease-relevant proteins has been demonstrated. Therefore, in this study, propagation of aggregation-forming property of mutant SOD1 protein in DM in vitro was investigated. This study demonstrated that aggregates composed of canine wild type SOD1 protein were increased by co-transfection with canine mutant SOD1 (E40K SOD1), indicating intracellular propagation of SOD1 aggregates. Further, aggregated recombinant SOD1 proteins were released from the cells, taken up by other cells, and induced further aggregate formation of normally folded SOD1 proteins. These results suggest intercellular propagation of SOD1 aggregates. The hypothesis of cell-to-cell propagation of SOD1 aggregates proposed in this study may underly the progressive nature of DM pathology.

Accumulation and aggregate formation of mutant superoxide dismutase 1 in canine degenerative myelopathy.

Canine degenerative myelopathy (DM) is an adult-onset progressive neurodegenerative disorder that has recently been linked to mutations in the superoxide dismutase 1 (SOD1) gene. We generated a polyclonal antibody against canine SOD1 to further characterize the mutant SOD1 protein and its involvement in DM pathogenesis. This antibody (SYN3554) was highly specific to canine SOD1 and had the ability to reveal distinct cytoplasmic aggregates in cultured cells expressing canine mutant SOD1 and also in the spinal neurons of symptomatic homozygotes. A similar staining pattern was observed in asymptomatic homozygotes. SOD1 aggregates were not detected in the spinal neurons of heterozygotes; the accumulation of SOD1 was also detected in the reactive astrocytes of homozygotes and heterozygotes to a similar extent. Our results support the hypothesis that the cytoplasmic accumulation and aggregate formation of the mutant SOD1 protein, especially in astrocytes, are closely associated with the pathogenesis of DM. Therefore, this disease is regarded as a spontaneous large-animal model of SOD1-mediated amyotrophic lateral sclerosis in humans.

Gliomatosis cerebelli in a Saint Bernard dog.

A 6-year-old, neutered male Saint Bernard dog was presented with a 1-month history of ataxia, hypermetria and head tilt. High-field magnetic resonance imaging revealed a mass in the cerebellar vermis. During necropsy examination, a cream-coloured irregular area was observed in the cerebellar white matter. Microscopically, the mass comprised a diffuse neoplastic proliferation of spindle cells with oval pleomorphic nuclei in the white and grey matter of the cerebellum and pons and in the subpial area. Neoplastic infiltration was not found in the cerebrum. Immunohistochemistry revealed that the neoplastic cells were positive for vimentin and partially positive for glial fibrillary acidic protein. Based on these findings, the neoplastic lesion was diagnosed as gliomatosis cerebelli, without involvement of the cerebrum.