Human Molecular Genetics Advance Access originally published online on May 15, 2007
Human Molecular Genetics 2007 16(13):1604-1618; doi:10.1093/hmg/ddm110
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Mutation of SOD1 in ALS: a gain of a loss of function
1 Institute of Endocrinology, Center of Excellence on Neurodegenerative Diseases, 2 Department of Biomolecular Sciences and Biotechnologies, 3 Department of Food Science and Microbiology, Division of Human Nutrition, University of Milan, Milan, Italy, 4 Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy and 5 InterUniversity Center on Neurodegenerative Diseases of the Universities of Milan, Florence, Rome, Italy
* To whom correspondence should be addressed at:, Institute of Endocrinology, Center of Excellence on Neurodegenerative Diseases, University of Milan, via Balzaretti 9, 20133 Milan, Italy. Tel: +39 250318215; Fax: +39 250318204; Email: angelo.poletti{at}unimi.it or angelo.poletti{at}libero.it
Received October 6, 2006; Accepted April 25, 2007
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease caused by motoneuron loss. Some familial cases (fALS) are linked to mutations of superoxide dismutase type-1 (SOD1), an antioxidant enzyme whose activity is preserved in most mutant forms. Owing to the similarities in sporadic and fALS forms, mutant SOD1 animal and cellular models are a useful tool to study the disease. In transgenic mice expressing either wild-type (wt) human SOD1 or mutant G93A-SOD1, we found that wtSOD1 was present in cytoplasm and in nuclei of motoneurons, whereas mutant SOD1 was mainly cytoplasmic. Similar results were obtained in immortalized motoneurons (NSC34 cells) expressing either wtSOD1 or G93A-SOD1. Analyzing the proteasome activity, responsible for misfolded protein clearance, in the two subcellular compartments, we found proteasome impairment only in the cytoplasm. The effect of G93A-SOD1 exclusion from nuclei was then analyzed after oxidative stress. Cells expressing G93A-SOD1 showed a higher DNA damage compared with those expressing wtSOD1, possibly because of a loss of nuclear protection. The toxicity of mutant SOD1 might, therefore, arise from an initial misfolding (gain of function) reducing nuclear protection from the active enzyme (loss of function in the nuclei), a process that may be involved in ALS pathogenesis.