The Effect of SOD1 Mutation on Cellular Bioenergetic Profile and Viability in Response to Oxidative Stress and Influence of Mutation-Type

Abstract

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the progressive degeneration of motor neurons. Substantial evidence implicates oxidative stress and mitochondrial dysfunction as early events in disease progression. Our aim was to ascertain whether mutation of the SOD1 protein increases metabolic functional susceptibility to oxidative stress. Here we used a motor neuron-like cell line (NSC34) stably transfected with various human mutant SOD1 transgenes (G93A, G37R, H48Q) to investigate the impact of oxidative stress on cell viability and metabolic function within intact cells. NSC34 cells expressing mutant SOD1 showed a dose dependent reduction in cell viability when exposed to oxidative stress induced by hydrogen peroxide, with variation between mutations. The G93A transfectants showed greater cell death and LDH release compared to cells transfected with the other SOD1 mutations, and H48Q showed an accelerated decline at later time points. Differences in mitochondrial bioenergetics, including mitochondrial respiration, coupling efficiency and proton leak, were identified between the mutations, consistent with the differences observed in viability. NSC34 cells expressing G93A SOD1 displayed reduced coupled respiration and mitochondrial membrane potential compared to controls. Furthermore, the G93A mutation had significantly increased metabolic susceptibility to oxidative stress, with hydrogen peroxide increasing ROS production, reducing both cellular oxygen consumption and glycolytic flux in the cell. This study highlights bioenergetic defects within a cellular model of ALS and suggests that oxidative stress is not only detrimental to oxygen consumption but also glycolytic flux, which could lead to an energy deficit in the cell.

“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).…”

Hypoxia causes autophagic stress and derangement of metabolic adaptation in a cell model of amyotrophic lateral sclerosis

“…Earlier studies in normoxic conditions with NSC-34 cell lines stably expressing high/low levels of human mutant SOD1 transgenes and cultured with/without the addition of oxidants highlighted alterations to metabolic markers, including some of those examined in this study (Mali and Zisapels 2008;Mali and Zisapel 2010;D'Alessandro et al 2011;Richardson et al 2013). Reduced O 2 concentration is also a stimulus causing enhanced ROS formation; these results as a whole suggest that oxidative stress causes significant metabolic derangements and this occurs when cells express either a high level of mutant SOD1 or a low level but are exposed to oxidants.…”

“…The role of mitochondrial adaptation to low O 2 in ALS has been poorly investigated, although mitochondria are known to be involved in the disease pathogenesis in patients and mutant SOD1 mice mainly through mitochondrial dysfunction, generation of free radicals, and impairment of calcium handling (Duffy et al 2011;Richardson et al 2013;Robberecht and Philips 2013).…”

Superoxide dismutase 1 is positively selected to minimize protein aggregation in great apes

“…Thus protein misfolding may not represent a distinct toxic molecular mode of interaction as generally assumed but perhaps rather the systemic loss of available cellular energy caused by increased protein turnover [101]. This would explain metabolic features of neurological diseases [111] such as the persistent hyper-metabolism of ALS patients [112] and the link between proteasome inhibition and toxicity of ALS-related SOD1 mutants [109], and it indicates why protein misfolding diseases are primarily neurological, since neurons need energy to maintain ion gradients for signaling [35].…”