Article

Recruitment of mitochondria into apoptotic signaling correlates with the presence of inclusions formed by amyotrophic lateral sclerosisassociated SOD1 mutations

Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia.
Journal of Neurochemistry (Impact Factor: 4.24). 12/2008; 108(3):578-90. DOI: 10.1111/j.1471-4159.2008.05799.x
Source: PubMed

ABSTRACT Mutations in Cu, Zn-superoxide dismutase 1 (SOD1) are associated with degeneration of motor neurons in the disease, familial amyotrophic lateral sclerosis. Intracellular protein inclusions containing mutant SOD1 (mSOD1) are associated with disease but it is unclear whether they are neuroprotective or cytotoxic. We report here that the formation of mSOD1 inclusions in a motor neuron-like cell line (NSC-34) strongly correlates with apoptosis via the mitochondrial death pathway. Applying confocal microscopic analyses, we observed changes in nuclear morphology and activation of caspase 3 specifically in cells expressing mSOD1 A4V or G85R inclusions. Furthermore, markers of mitochondrial apoptosis (activation and recruitment of Bax, and cytochrome c redistribution) were observed in 30% of cells bearing mSOD1 inclusions but not in cells expressing dispersed SOD1. In the presence of additional apoptotic challenges (staurosporine, etoposide, and hydrogen peroxide), cells bearing mSOD1 inclusions were susceptible to further apoptosis suggesting they were in a pro-apoptotic state, thus confirming that inclusions are linked to toxicity. Surprisingly, cells displaying dispersed SOD1 [both wildtype (WT) and mutant] were protected against apoptosis upstream of mitochondrial apoptotic signaling, induced by all agents tested. This protection against apoptosis was unrelated to SOD1 enzymatic activity because the G85R that lacks enzymatic function protected cells similarly to both WT SOD1 and A4V that possesses WT-like activity. These findings demonstrate new aspects of SOD1 in relation to cellular viability; specifically, mSOD1 can be either neuroprotective or cytotoxic depending on its aggregation state.

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    • "Similarly, VSVG-ts045 transport was inhibited in two different mSOD1 stable cell lines, and fragmentation of the Golgi was detected in mSOD1 D90A expressing cells (Figure S3), neither of which formed inclusions. These data therefore suggest that small soluble forms of SOD1 inhibit transport, and while linked to apoptosis (Soo et al. 2009), inclusions form after apoptosis has commenced. We demonstrated previously that SOD1 is secreted and that the secretion of mSOD1 is impaired relative to SOD1 WT (Turner et al. 2005). "
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    • "This line of thought is based on results showing that mutant SOD1 was important in neurons for disease initiation and in glia for disease progression in a mouse model of ALS (Boillee et al., 2006). Although the role of protein aggregation in disease pathology has not been clarified, SOD1 aggregates are certainly toxic to the neurons they accumulate in culture (Matsumoto et al., 2005; Soo et al., 2009). It is possible then that protein aggregation and inclusion formation are linked with the initiation event in ALS. "
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