Mutated Human SOD1 Causes Dysfunction of Oxidative Phosphorylation in Mitochondria of Transgenic Mice

Abstract

A growing body of evidence suggests that impaired mitochondrial energy production and increased oxidative radical damage to the mitochondria could be causally involved in motor neuron death in amyotrophic lateral sclerosis (ALS) and in familial ALS associated with mutations of Cu,Zn superoxide dismutase (SOD1). For example, morphologically abnormal mitochondria and impaired mitochondrial histoenzymatic respiratory chain activities have been described in motor neurons of patients with sporadic ALS. To investigate further the role of mitochondrial alterations in the pathogenesis of ALS, we studied mitochondria from transgenic mice expressing wild type and G93A mutated hSOD1. We found that a significant proportion of enzymatically active SOD1 was localized in the intermembrane space of mitochondria. Mitochondrial respiration, electron transfer chain, and ATP synthesis were severely defective in G93A mice at the time of onset of the disease. We also found evidence of oxidative damage to mitochondrial proteins and lipids. On the other hand, presymptomatic G93A transgenic mice and mice expressing the wild type form of hSOD1 did not show significant mitochondrial abnormalities. Our findings suggest that G93A-mutated hSOD1 in mitochondria may cause mitochondrial defects, which contribute to precipitating the neurodegenerative process in motor neurons.Amyotrophic lateral sclerosis (ALS) 1 is a devastating neurodegenerative disease affecting spinal cord and cortical motor neurons. The onset of the disease is generally in the 4th and 5th decade, and it progresses over an average of 5 years leading to progressive paralysis and premature death (1). Although the majority of the cases are sporadic and due to unknown causes, about 5-10% are familial (FALS), of which ϳ25% are associated with mutations in the Cu,Zn superoxide dismutase gene (SOD1) (2-6). The symptoms and pathology of FALS patients resemble those of patients with the sporadic form of ALS, suggesting that the mechanisms of neurodegeneration share common pathways. Since the initial report (7) of mutant SOD1, more than 90 different mutations of the SOD1 gene have been found in FALS patients. Because these mutations do not always affect the dismutase activity (8, 9), a toxic gain of function of the mutated protein has been postulated, possibly causing enhanced reactive oxygen species generation (10).In the motor neurons of transgenic mice expressing the G93A-mutated SOD1 (11), among other pathological features is the presence of membrane-bound vacuoles deriving from mitochondrial degeneration. In these mice, the onset of the paralysis is immediately preceded by an increase in degenerating mitochondria (12), suggesting that mitochondrial alterations might represent a triggering factor in precipitating the degeneration of motor neurons. A decrease of mitochondrial membrane potential and disturbed mitochondrial calcium homeostasis have also been reported (13) in cultured primary motor neurons from G93A mice. Reduced respiratory chain activities were found in the spinal c...

“Preconditioning” with latrepirdine, an adenosine 5′-monophosphate-activated protein kinase activator, delays amyotrophic lateral sclerosis progression in SOD1G93A mice

“…This build up of mutant protein is suggested to impair mitochondrial function (Song et al 2013, Israelson et al 2010, Pasinelli et al 2004. In line with these findings, mitochondria had a metabolic switch from oxidative phosphorylation to glycolysis in transgenic SOD1 G93A mice, NSC34 cells (motor neuron-like cell line) and fibroblasts transfected with mutant SOD1 compared to controls (Mattiazzi et al 2002, Richardson et al 2013, Allen et al 2013. Glucose utilization and ATP levels have been shown to be significantly reduced in corticospinal and bulbospinal motor tracts and the motor cortex of SOD1 G93A prior to pathologic changes (Browne et al 2006).…”

Mitochondrial dysfunction in familial amyotrophic lateral sclerosis

“…For example, ATP generation was markedly decreased in neuronal cells of mutant SOD1 G93A mice (Browne et al 2006;Mattiazzi et al 2002). Cytosolic ATP levels were significantly reduced in neuroblastoma cells expressing mutant SOD1 G37R (Coussee et al 2011) and decreased more rapidly and to a greater extent in rotenonetreated SOD1 G93A neuronal cells .…”

“…Transgenic mouse models of ALS expressing mutant human SOD1 support human studies showing increased oxidative damage to mitochondrial proteins, lipids and DNA (reviewed in Barber and Shaw 2010). This has been explained by excessive dismutase activity of mutant SOD1 (Goldsteins et al 2008;Wiedau-Pazos et al 1996), increased levels of ROS produced by mitochondria following inhibition of complex I (Kruman et al 1999;Mattiazzi et al 2002;Murphy 2009;Zimmerman et al 2007), or increased NADPH oxidase (NOX) activity through mutant SOD1 interacting with Rac1, a NOX regulator (reviewed in Boillee and Cleveland 2008). It should be noted, however, that recent data indicate that overexpression of mutant SOD1 G93A in yeast cells actually provided increased protection against respiration-derived ROS (Kloppel et al 2010).…”

“…Changes in the activity of the different complexes of the electron transport chain have been described in tissues obtained from ALS patients, and in cell and animal disease models. Although some of these studies have produced mixed and somewhat contradictory results, the most consistent abnormality in mitochondrial respiratory function has been associated with reduced complex I and IV activity (Browne et al 1998;Kirkinezos et al 2005;Mattiazzi et al 2002;Menzies et al 2002;Rizzardini et al 2006;Son et al 2008). In motor neurons of mutant SOD1 G93A mice a reduction in activity of complex I was observed before disease onset and progressing to inhibition of complex IV at later stages (Jung et al 2002).…”

Sirt1/PGC-1

“…Les symptômes et la progression de la pathologie chez les patients atteints d'une mutation du gène SOD1 sont similaires à ceux des patients atteints de la forme sporadique, ce qui suggère l'existence de points communs entre les mécanismes de ces deux formes de la SAL. SOD1 présente une localisation cytosolique mais également mitochondriale [2] et, de façon inté-ressante, les patients atteints de la forme sporadique présentent des anomalies morphologiques au niveau des mitochondries des axones proximaux et de la moelle épinière [3]. Un déficit d'activité des complexes I et IV de la chaîne respiratoire mitochondriale a également été rapporté [4].…”