Morphological aspects of superoxide dismutase-1 mutation in amyotrophic lateral sclerosis and its transgenic mouse model

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that primarily involves the motor neuron system. Recent investigations have obtained evidence that mutations in the gene for superoxide dismutase-1 (SOD1) are detected in a subset of familial ALS patients, and that mutant SOD 1-expressing transgenic mice develop ALS-like clinicopathological features. Several in vitro studies suggest that SOD 1-mutated ALS is caused by a newly acquired neurotoxicity of mutant SOD 1, but not by reduced enzyme activity. From the viewpoint of morphology, we analyzed the immunolocalization of SOD1 and some other substances in spinal cords from familial ALS patients with SOD1 Ala⁴→Val mutation. The spinal cords of the ALS patients demonstrated the characteristic neuronal hyaline inclusions (NHIs) immunoreactive with antibodies to ubiquitin and phosphorylated neurofilament protein (NFP) in the lower motor neurons and cordlike swollen axons. The NHIs contained the epitopes of SOD1 and Nε-carboxymethyllysine (CML), one of the major advanced glycation endproducts (AGE), whereas there was no focal accumulation of SOD1 and CML in control individuals. Immunoelectron microscopy depicted the SOD1 and CML determinants on the granule-associated thick linear structures that mainly compose the NHIs. We also performed a similar study on mice carrying a transgene for Gly⁹³→Ala mutant SOD1. The spinal cords of the transgenic mice were characterized by the appearance of NHIs resembling those of familial ALS and by vacuolar degeneration. The mouse NHIs were immunoreactive for ubiquitin, phophorylated NFP, SOD1 and CML. Our findings of the coexistence of SOD1 and AGE in both the human and mouse NHIs indicate that certain substances are implicated in glycoxidation in the presence of oxidative stress originating from mutant SOD1 and finally deposited in the NHIs, suggesting a pathogenic role of the oxidative processes in motor neuron degeneration in vivo.