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Neurotoxicology. 2004 Sep;25(5):779-92.

Overexpression of metallothionein protects cultured motor neurons against oxidative stress, but not mutant Cu/Zn-superoxide dismutase toxicity.

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Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Que. H3A 2B4, Canada.


Mutations in Cu/Zn-superoxide dismutase 1 (SOD1) are responsible for a familial form of amyotrophic lateral sclerosis (FALS). It has been proposed that oxidative stress and abnormal metal homeostasis contribute to death of motor neurons in this disease. Also, inability of motor neurons to upregulate protective proteins under stress may contribute to their preferential vulnerability to toxicity. Metallothioneins (MT) are low molecular weight, metal-binding proteins with established antioxidant capabilities. This study investigated the ability of motor neurons to upregulate MT isoforms in response to expression of mutant SOD1(G93A) or exposure to other neurotoxicants, and the ability of MT-I gene transfer to protect motor neurons from these stresses. MT isoform-I and -II were expressed constitutively in astrocytes and other non-neuronal cells of dissociated spinal cord cultures, but not in motor neurons. MT-I/II was upregulated in astrocytes, but not motor neurons, following treatment with ZnCl(2) or excitotoxic concentrations of glutamate. MT-III expression was restricted to neurons and was unaffected by treatment with ZnCl(2), paraquat, or glutamate. Overexpression of MT-I in motor neurons by gene transfer reduced the toxicity of ZnCl(2) and paraquat, but failed to protect them against glutamate or SOD1(G93A). These data are evidence against metal-catalyzed, oxidative stress being the primary mechanisms of toxicity conferred by disease-causing mutations in SOD1.

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