Mutant SOD1 causes motor neuron disease independent of copper chaperone-mediated copper loading

Copper-mediated oxidative damage is proposed to play a critical role in the pathogenesis of Cu/Zn superoxide dismutase (SOD1)-linked familial amyotrophic lateral sclerosis (FALS). We tested this hypothesis by ablating the gene encoding the copper chaperone for SOD1 (CCS) in a series of FALS-linked SOD1 mutant mice. Metabolic ⁶⁴Cu labeling in SOD1-mutant mice lacking the CCS showed that the incorporation of copper into mutant SOD1 was significantly diminished in the absence of CCS. Motor neurons in CCS^−/− mice showed increased rate of death after facial nerve axotomy, a response documented for SOD1^−/− mice. Thus, CCS is necessary for the efficient incorporation of copper into SOD1 in motor neurons. Although the absence of CCS led to a significant reduction in the amount of copper-loaded mutant SOD1, however, it did not modify the onset and progression of motor neuron disease in SOD1-mutant mice. Hence, CCS-dependent copper loading of mutant SOD1 plays no role in the pathogenesis of motor neuron disease in these mouse models.