Increased hydroxyl radical production and apoptosis in PC12 neuron cells expressing the gain-of-function mutant G93A SOD1 gene.

Mutations of the SOD1 gene (formerly known as Cu,Zn-SOD) are frequently associated with the familial form of amyotrophic lateral sclerosis (ALS). The G93A mutation of SOD1 with substitution of Gly to Ala at residue 93 results in gain of a peroxidative function. Here we report that transfection of PC12 neuron precursor cells with the G93A mutation of SOD1 results in increased production of hydroxyl radicals (*OH) and an enhanced rate of cell death by apoptosis. Notably, PC12 cells transfected with the H63C/G93A mutant of SOD1 with a mutation in the catalytic site that converts histidine at position 63 to cysteine showed a dramatically reduced production of *OH and rate of death by apoptosis. Thus the gain of function of the mutant G93A SOD1 can be reduced by an active site mutation. These results provide additional genetic evidence for the hypothesis that the increased *OH production and induced cytotoxicity in neuron cells expressing the mutant G93A SOD1 results from the gain of peroxidative function by the enzyme's catalytic site.