Oligodendrocyte loss during the disease course in a canine model of the lysosomal storage disease fucosidosis.

Hypomyelination is a poorly understood feature of many neurodegenerative lysosomal storage diseases including fucosidosis in children and animals. To gain insight into hypomyelination in fucosidosis, we investigated lysosomal storage, oligodendrocyte death, and axonal and neuron loss in central nervous system tissues of fucosidosis-affected dogs aged 3 weeks to 42 months using immunohistochemistry, electron microscopy and gene expression assays. Vacuole accumulation in fucosidosis oligodendrocytes commenced by 5 weeks age; all oligodendrocytes were affected by 16 weeks. Despite progressive vacuolation, mature oligodendrocyte loss by apoptosis (caspase-6 positive) in the corpus callosum and cerebellar white matter stabilized by 16 weeks with no further subsequent loss. Axonal neurofilament loss progressed, however, suggesting that disturbed axon-oligodendrocyte interactions are unlikely to be the primary cause of hypomyelination. A 67% decline in Purkinje cell layer oligodendrocyte numbers coincided with a 67% increase in caspase-6-positive Purkinje cells at 16 weeks suggesting that early oligodendrocyte loss contributes to Purkinje cell apoptosis. Fucosidosis hypomyelination appeared to follow normal spatiotemporal patterns of myelination with greater loss of oligodendrocytes and larger downregulation of CNP, MAL and PLP1 genes at 16 weeks in cerebellum vs. the frontal cortex. These studies suggest that survival of oligodendrocytes in fucosidosis is limited during active myelination although the mechanisms remain unknown.