Impairment of mitochondrial anti-oxidant defence in SOD1-related motor neuron injury and amelioration by ebselen

Abstract

There is now compelling evidence of mitochondrial dysfunction in motor neuron disease (MND), but the molecular basis of these abnormalities is unknown. It is also unclear whether the observed mitochondrial dysfunction plays a central role in disease pathogenesis, and if so, whether its amelioration might present therapeutic opportunities. We adopted a candidate generation approach using proteomics to screen for changes in mitochondrial protein expression in a well-validated cell-culture model of superoxide dismutase 1 (SOD1) related familial MND (fMND). Changed proteins were identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy. Protein candidates included apoptotic regulators, anti-oxidants and components of the electron transport chain. Confirmatory Western blotting was performed, and validated protein expression changes were further investigated. Peroxiredoxin 3 (Prx3), a mitochondrial thioredoxin-dependent hydroperoxidase, is downregulated in the presence of mutant SOD1 in both our cell-culture model and in the spinal cord mitochondria of mutant SOD1 transgenic mice. We confirm the expression of Prx3 within the mitochondria of spinal motor neurons in mouse and humans by immunohistochemistry. Using quantitative real-time PCR (Q-PCR), we show that Prx3 is also downregulated in spinal motor neurons from patients with both sporadic (sMND) and SOD1-related fMND. In a disease characterized by oxidative stress, this represents a potentially important deficit in mitochondrial anti-oxidant defence. Recent evidence suggests that oxidative stress from aberrant copper chemistry may not play a major part in the pathogenesis of SOD1-related fMND. From the results of this study we propose disruption of mitochondrial anti-oxidant defence as an alternative mechanism whereby mutant SOD1 may generate oxidative stress within motor neurons. We further demonstrate that ebselen, an anti-oxidant drug already safely used in human studies and that acts as a Prx mimic, is able to ameliorate the toxicity of mutant SOD1 in our cell-culture model. We conclude by showing that ebselen is capable of inducing transcription of the anti-oxidant response element (ARE) and postulate that ebselen may act both by the transcriptional upregulation of anti-oxidant proteins, and directly as an anti-oxidant in its own right.

Rotaviral Enterotoxin Nonstructural Protein 4 Targets Mitochondria for Activation of Apoptosis during Infection

“…For protein extraction, the pellets were resuspended in buffer containing 7 M urea, 2 M thiourea, 4% CHAPS, 120 mM dithiothreitol (DTT), 2% ampholytes, pH 3-10, and 40 mM Tris-HCl and further incubated in ice for 30 min. Pure mitochondrial fractions from SA11-infected (8 h) cells were isolated by ultracentrifugation using iodixanol as described previously (20). Endoplasmic reticulum fractions and mitochondrial fractions were isolated from SA11-infected (8 h) cells by ultracentrifugation using sucrose gradient as described previously (21).…”

Mitochondrial Thiols in the Regulation of Cell Death Pathways

“…Conversely, Prx3 knockdown leads to increased mitochondrial oxidant production and protein carbonyl content, altered mitochondrial morphology, and renders cells susceptible to apoptosis (19, 44, 60, 101, 120). Prx3 levels are found significantly lower in brains of Alzheimer's disease patients (91) and deficiency in Prx3 is also associated with amyotrophic lateral sclerosis (ALS), Parkinson's disease, and Down syndrome (94,192), thus emphasizing the significance of mitochondrial Prx in neurodegenerative disorders. Mitochondrial Prx5, a 17 kDa atypical 2-Cys Prx (157), is less effective than Prx3 in reducing H 2 O 2 but has a higher reactivity towards ONOO - (173).…”

KLP6: a newly identified kinesin that regulates the morphology and transport of mitochondria in neuronal cells

“…The resultant supernatant was then centrifuged at 100,000 g for 60 minutes to separate the high-speed supernatant and high-speed pellet fractions. To prepare a mitochondria-enriched fraction, the low-speed pellet fraction was subjected to flotation using a 0, 20, 25 and 36% discontinuous gradient of OptiPrep (Axis-Shield) as described previously (Wood-Allum et al, 2006). After ultracentrifugation at 100,000 g for 4 hours, the proteins that migrated to the interface between the 20 and 25% OptiPrep solutions were collected as a mitochondriaenriched (Mt) fraction.…”