Cu/Zn-superoxide dismutase and wild-type like fALS SOD1 mutants produce cytotoxic quantities of H2O2 via cysteine-dependent redox short-circuit

Abstract

The Cu/Zn−superoxide dismutase (SOD1) is a ubiquitous enzyme that catalyzes the dismutation of superoxide radicals to oxygen and hydrogen peroxide. In addition to this principal reaction, the enzyme is known to catalyze, with various efficiencies, several redox side-reactions using alternative substrates, including biological thiols, all involving the catalytic copper in the enzyme’s active-site, which is relatively surface exposed. The accessibility and reactivity of the catalytic copper is known to increase upon SOD1 misfolding, structural alterations caused by a mutation or environmental stresses. These competing side-reactions can lead to the formation of particularly toxic ROS, which have been proposed to contribute to oxidative damage in amyotrophic lateral sclerosis (ALS), a neurodegenerative disease that affects motor neurons. Here, we demonstrated that metal-saturated SOD1 WT (holo-SOD1 WT ) and a familial ALS (fALS) catalytically active SOD1 mutant, SOD1 G93A , are capable, under defined metabolic circumstances, to generate cytotoxic quantities of H 2 O 2 through cysteine (CSH)/glutathione (GSH) redox short-circuit. Such activity may drain GSH stores, therefore discharging cellular antioxidant potential. By analyzing the distribution of thiol compounds throughout the CNS, the location of potential hot-spots of ROS production can be deduced. These hot-spots may constitute the origin of oxidative damage to neurons in ALS.

Changes in the Activity and Concentration of Superoxide Dismutase Isoenzymes (Cu/Zn SOD, MnSOD) in the Blood of Healthy Subjects and Patients with Acute Pancreatitis

“…Two copper/zinc superoxide dismutases (Cu/Zn SOD): SOD1 within the cytosol, mitochondrial intermembrane space, nucleus, lysosomes and peroxisomes and SOD3 (EcSOD), which is the predominant antioxidant enzyme secreted into the extracellular space, were found [ 1 , 4 , 8 ]. In these isoenzymes, Zn 2+ ion plays a structural role, as it is required for efficient SOD folding and long-term stability, whereas Cu 2+ in active sites catalyzes O 2 •− dismutation by alternating between the reduced and oxidized states [ 9 ]. SOD1, in its homodimeric form, is a main intracellular isoenzyme of SODs.…”

Intersection between Redox Homeostasis and Autophagy: Valuable Insights into Neurodegeneration

“…Conversely, inhibition of SOD1 activity or treatment with antioxidants ameliorates the toxicity of motor neurons [ 76 , 79 ]. This increase in oxidative stress in cells caused SOD1 and TDP-43 protein aggregates, which are hallmarks of ALS [ 80 , 81 ]. As a result, the brain and motor neurons of patients with ALS as well as those of animal models of ALS exhibited increased levels of oxidized proteins, lipid peroxidation, and ROS, and decreased levels of antioxidants [ 82 , 83 , 84 , 85 , 86 , 87 ].…”

Emerging Evidence Highlighting the Importance of Redox Dysregulation in the Pathogenesis of Amyotrophic Lateral Sclerosis (ALS)

“…Treating cells with L-buthionine sulfoximine (BSO), an inhibitor that blocks the synthesis of GSH, renders neuronal SH-SY5Y cells expressing mutant valosin-containing protein (VCP) R487H more susceptible to oxidative stress (Hirano et al, 2015 ) and increases mutant SOD1 toxicity (Alvarez-Zaldiernas et al, 2016 ; Bakavayev et al, 2019 ). Furthermore, BSO induces the misfolding of mutant TDP-43 and mutant SOD1 (see “Protein Folding” section).…”

“…This is implicated in perturbing many cellular processes in both motor neurons and non-neuronal cells, including neuroinflammation (Bruijn et al, 2004 ; Wu et al, 2006 ; Marden et al, 2007 ). Also, both mutant and WT SOD1 produce cytotoxic levels of H 2 O 2 via a cysteine redox regulation system (Bakavayev et al, 2019 ). Also, SOD1 G93A mice show significantly increased protein carbonyl levels in the spinal cord, including elevated carbonylation of mutant SOD1, which has been linked to motor neuron degeneration (Poon et al, 2005 ).…”