Unsaturated Fatty Acids Induce Cytotoxic Aggregate Formation of Amyotrophic Lateral Sclerosis-linked Superoxide Dismutase 1 Mutants

Abstract

Formation of misfolded protein aggregates is a remarkable hallmark of various neurodegenerative diseases including Alzheimer disease, Parkinson disease, Huntington disease, prion encephalopathies, and amyotrophic lateral sclerosis (ALS). Superoxide dismutase 1 (SOD1) immunoreactive inclusions have been found in the spinal cord of ALS animal models and patients, implicating the close involvement of SOD1 aggregates in ALS pathogenesis. Here we examined the molecular mechanism of aggregate formation of ALS-related SOD1 mutants in vitro. We found that long-chain unsaturated fatty acids (FAs) promoted aggregate formation of SOD1 mutants in both dose-and time-dependent manners. Metal-deficient SOD1s, wild-type, and mutants were highly oligomerized compared with holo-SOD1s by incubation in the presence of unsaturated FAs. Oligomerization of SOD1 is closely associated with its structural instability. Heat-treated holo-SOD1 mutants were readily oligomerized by the addition of unsaturated FAs, whereas wild-type SOD1 was not. The monounsaturated FA, oleic acid, directly bound to SOD1 and was characterized by a solid-phase FA binding assay using oleate-Sepharose. The FA binding characteristics were closely correlated with the oligomerization propensity of SOD1 proteins, which indicates that FA binding may change SOD1 conformation in a way that favors the formation of aggregates. High molecular mass aggregates of SOD1 induced by FAs have a granular morphology and show significant cytotoxicity. These findings suggest that SOD1 mutants gain FA binding abilities based on their structural instability and form cytotoxic granular aggregates. Amyotrophic lateral sclerosis (ALS)1 is a progressive and fatal neurodegenerative disorder that mainly affects motor neurons in the brain stem and spinal cord. Approximately 10% of ALS patients are familial cases, with autosomal dominant inheritance. More than 90 different mutations in the gene coding for superoxide dismutase 1 (SOD1) have been identified in about 20% of familial ALS (FALS) families (1, 2). Although the molecular mechanisms of selective motor neuron degeneration by SOD1 mutants in FALS remain largely unknown, common pathological features of conformational diseases, as evidenced by SOD1 immunoreactive inclusions, are found in the spinal cord of ALS patients and in the SOD1 mutant FALS mouse model (3-8). The characteristics of FALS resemble those of many other neurodegenerative diseases in which a causative protein undergoes a conformational rearrangement, which endows it with a tendency to aggregate and form deposits within affected tissues.SOD1 is a 32-kDa homodimeric enzyme that decreases the intracellular concentration of superoxide radicals by catalyzing their dismutation to O 2 and H 2 O 2 . ALS-linked mutations of SOD1 are distributed throughout the primary and tertiary structures, and most mutations appear unrelated to the dismutase activity. Many biochemical and biophysical studies have reported that SOD1 mutants are structurally unstable compared with wild-type forms (...

Omega-3 fatty acids differentially modulate enzymatic anti-oxidant systems in skeletal muscle cells

“…Furthermore, there is evidence that these products may alter the action of SOD1 through the formation of protein aggregation (Kim et al 2005). In our study, SOD1 activity was decreased after DHA treatment with no modification of its expression.…”

Metabolismo, oxidação e implicações biológicas do ácido docosahexaenoico em doenças neurodegenerativas

“…104 Sabe-se que 20% dos casos familiares desta doença são causados por mutações no gene que codifica a enzima antioxidante citosólica, Cu, Zn superóxido dismutase (SOD1). 102,105,106 A enzima Cu, Zn superóxido dismutase (SOD1) é uma metaloproteína homodimérica de 32 KDa, citosólicas, tendo um Cu 2+ e um Zn + . Mais de 190 mutações já são descritas, no entanto, os mecanismos moleculares da degeneração seletiva dos neurônios motores por SOD1 mutante em ELAf ainda são desconhecidos.…”

“…A mutação resulta em um ganho de função tóxica, que alguns estudos sugerem poder estar relacionada ao efeito pró-oxidante da mutante SOD1 104 e /ou à formação de agregados citotóxicos de SOD1. [104][105][106] Os eventos estruturais que levam à formação de oligômeros de alto peso molecular de SOD1 ainda são incertos. 102,106 Alguns estudos sugerem que esses oligômeros seriam formados a partir de pontes dissulfeto entre os resíduos de cisteína livre presente na estrutura do dímero SOD1 (6 e Cys Cys 111).…”

“…[104][105][106] Os eventos estruturais que levam à formação de oligômeros de alto peso molecular de SOD1 ainda são incertos. 102,106 Alguns estudos sugerem que esses oligômeros seriam formados a partir de pontes dissulfeto entre os resíduos de cisteína livre presente na estrutura do dímero SOD1 (6 e Cys Cys 111). 102 Estudo realizado por Kim e colaboradores mostrou que há indução da agregação de SOD1 na presença de ácidos graxos poli-insaturados.…”

“…Esses agregados de alta massa molecular têm uma morfologia granular e apresentam citotoxicidade significativa. 106 Elevados níveis de adutos de HHE-histidina também foram encontrados na medula espinhal de pacientes com ALS. 107 O HHE é um aldeído formado a partir da oxidação não enzimática do DHA e a detecção deste aduto indica que este ácido graxo é um alvo importante de oxidação na doença.…”