Recruitment of mitochondria into apoptotic signaling correlates with the presence of inclusions formed by amyotrophic lateral sclerosis-associated SOD1 mutations.
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.
Full-textDOI: · Available from: Phillip Nagley, Dec 06, 2014
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ABSTRACT: Bioenergetic abnormalities and metabolic dysfunctionoccur in amyotrophic lateral sclerosis (ALS) patients and genetic mouse models. However, whether metabolic dysfunction occurs earlyin ALS pathophysiology linked to different ALS genes remains unclear.Here, we investigatedAMP-activated protein kinase (AMPK) activation, which is a key enzyme induced by energy depletion and metabolic stress, inneuronal cells and mouse models expressing mutantsuperoxide dismutase 1 (SOD1)or TAR DNA binding protein 43 (TDP-43) linked to ALS.AMPKphosphorylation was sharply increased in spinal cords of transgenic SOD1G93A mice at disease onset and accumulated incytoplasmic granules in motor neurons, but not in pre-symptomatic mice. AMPK phosphorylation also occurred in peripheraltissues, liver and kidney, in SOD1G93A mice at disease onset, demonstrating that AMPK activation occurs late and is not restricted to motor neurons. Conversely, AMPK activity was drastically diminished in spinal cords and brains of presymptomatic and symptomatictransgenic TDP-43A315T mice and motor neuronal cells expressing different TDP-43 mutants. We show that mutant TDP-43 induction of the AMPK phosphatase,protein phosphatase 2A (PP2A), is associated with AMPK inactivation in these ALS models. Furthermore, PP2A inhibition by okadaic acid reversed AMPK inactivation by mutant TDP-43 in neuronal cells. Our results suggest that mutant SOD1 and TDP-43 exert contrasting effects on AMPK activation which may reflect key differences in energy metabolism and neurodegeneration in spinal cords of SOD1G93A and TDP-43A315T mice. While AMPK activation in motor neurons correlateswith progressionin mutant SOD1-mediated disease, AMPK inactivation mediated by PP2Ais associated withmutant TDP-43-linked ALS.PLoS ONE 03/2014; 9(3):e90449. DOI:10.1371/journal.pone.0090449 · 3.53 Impact Factor
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ABSTRACT: Amyotrophic lateral sclerosis (ALS), the most common adult-onset motor neuron disorder, is fatal for most patients less than 3 years from when the first symptoms appear. The aetiologies for sporadic and most familial forms of ALS are unknown, but genetic factors are increasingly recognized as causal in a subset of patients. Studies of disease physiology suggest roles for oxidative stress, glutamate-mediated excitotoxicity or protein aggregation; how these pathways interact in the complex pathophysiology of ALS awaits elucidation. Cellular models are being used to examine disease mechanisms. Recent advances include the availability of expanded cell types, from neuronal or glial cell culture to motoneuron-astrocyte co-culture genetically or environmentally modified. Cell culture experiments confirmed the central role of glial cells in ALS. The recent adaptation of induced pluripotent stem cells (iPSC) for ALS modeling could allow a broader perspective and is expected to generate new hypotheses, related particularly to mechanisms underlying genetic factors. Cellular models have provided meaningful advances in the understanding of ALS, but, to date, complete characterization of in vitro models is only partially described. Consensus on methodological approaches, strategies for validation and techniques that allow rapid adaptation to new genetic or environmental influences is needed. In this article, we review the principal cellular models being employed in ALS and highlight their contribution to the understanding of disease mechanisms. We conclude with recommendations on means to enhance the robustness and generalizability of the different concepts for experimental ALS.Molecular Neurobiology 11/2013; DOI:10.1007/s12035-013-8573-9 · 5.29 Impact Factor
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ABSTRACT: Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by the selective death of upper and lower motor neurons which ultimately leads to paralysis and ultimately death. Pathological changes in ALS are closely associated with pronounced and progressive changes in mitochondrial morphology, bioenergetics and calcium homeostasis. Converging evidence suggests that impaired mitochondrial function could be pivotal in the rapid neurodegeneration of this condition. In this review, we provide an update of recent advances in understanding mitochondrial biology in the pathogenesis of ALS and highlight the therapeutic value of pharmacologically targeting mitochondrial biology to slow disease progression.Linked ArticlesThis article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue-8British Journal of Pharmacology 04/2014; 171(8). DOI:10.1111/bph.12476 · 4.99 Impact Factor