Strategies for stabilizing superoxide dismutase (SOD1), the protein destabilized in the most common form of familial amyotrophic lateral sclerosis

Abstract

Amyotrophic lateral sclerosis (ALS) is a disorder characterized by the death of both upper and lower motor neurons and by 3-to 5-yr median survival postdiagnosis. The only US Food and Drug Administration-approved drug for the treatment of ALS, Riluzole, has at best, moderate effect on patient survival and quality of life; therefore innovative approaches are needed to combat neurodegenerative disease. Some familial forms of ALS (fALS) have been linked to mutations in the Cu/Zn superoxide dismutase (SOD1). The dominant inheritance of mutant SOD1 and lack of symptoms in knockout mice suggest a "gain of toxic function" as opposed to a loss of function. A prevailing hypothesis for the mechanism of the toxicity of fALS-SOD1 variants, or the gain of toxic function, involves dimer destabilization and dissociation as an early step in SOD1 aggregation. Therefore, stabilizing the SOD1 dimer, thus preventing aggregation, is a potential therapeutic strategy. Here, we report a strategy in which we chemically cross-link the SOD1 dimer using two adjacent cysteine residues on each respective monomer (Cys111). Stabilization, measured as an increase in melting temperature, of ∼20°C and ∼45°C was observed for two mutants, G93A and G85R, respectively. This stabilization is the largest for SOD1, and to the best of our knowledge, for any disease-related protein. In addition, chemical cross-linking conferred activity upon G85R, an otherwise inactive mutant. These results demonstrate that targeting these cysteine residues is an important new strategy for development of ALS therapies.mass spectrometry | thiol-disulfide I nnovative approaches are needed to combat neurodegenerative disease, among the most serious of which is amyotrophic lateral sclerosis (ALS), a disorder characterized by the death of both upper and lower motor neurons and by 3-to -5-yr median survival postdiagnosis. The only US Food and Drug Administrationapproved drug for the treatment of ALS, Riluzole, has at best, moderate effect on patient survival and quality of life (1-3). Although the causes of sporadic neurodegenerative diseases remain a mystery, mutations causing familial forms of many of these diseases (e.g., Alzheimer's, Parkinson, and ALS) are known. For example, mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) are responsible for ∼20% of the familial ALS cases (fALS) and 2% of all ALS (4, 5). Two such mutations are G93A, which maintains wild-type-like enzymatic activity, and the metal-deficient G85R, which is essentially inactive. Posttranslational modifications of proteins involved in familial diseases have been invoked in the etiology of the corresponding sporadic diseases, for example, alpha-synuclein (6) and Parkin (7) modification in Parkinson, Abeta (8) and tau (9) modification in Alzheimer's, and TDP43 (10) and SOD1 (11-14) modification in ALS. The hope, therefore, is that strategies for treating familial diseases may translate to at least a subset of sporadic diseases.Both dominant inheritance of mutant SOD1 (15) and lack of symptoms i...

Post-Translational Modification by Cysteine Protects Cu/Zn-Superoxide Dismutase from Oxidative Damage

“…Dimer destabilization of SOD1 has been implicated in disease progression for amyotrophic lateral sclerosis (ALS) 15, 33–36 . Oxygen-modified cysteine residues are negatively charged 37 and if both Cys 111 are oxidized there would be a columbic impetus for destabilizing the SOD1 dimer.…”

Nonnative SOD1 trimer is toxic to motor neurons in a model of amyotrophic lateral sclerosis

“…Knowledge of the structures of these species would not only allow for definitive testing of their toxicity but could potentially lead to an understanding of disease mechanism and therapeutic strategies against diseases for which no cure or effective treatment exists (22). By their nature, however, these oligomers are only metastable, and therefore difficult to isolate.…”

Proteostasis and Movement Disorders: Parkinson's Disease and Amyotrophic Lateral Sclerosis

“…How should one stabilize the native, benign fold of SOD1? Strategies involving cross-linking (Ray et al 2004;Auclair et al 2010) and ligand binding (Ray et al 2005) have all showed promise of stabilizing the dimer in vitro. None has been tried in vivo yet.…”