The potential role of misfolded wild-type SOD1 protein in sporadic amyotrophic lateral sclerosis (ALS): a review of the evidence

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterised by the selective loss of motor neurons in the motor cortex, brainstem and spinal cord. In 1993, the first ALS-linked gene mutations were identified in the Cu,Zn superoxide dismutase (SOD1) gene, which account for approximately 20 % of familial ALS cases. The mechanism of toxicity in this subset of patients is thought to arise from a gain-of-toxic function from the protein's propensity to misfold and aggregate into cytoplasmic inclusions. Immunohistochemical studies have shown that misfolded wildtype SOD1 (wtSOD1) is also detected in the motor neurons and glial cells of ALS patients without SOD1 mutations. It is proposed that disrupted, or aberrant, post-translational modifications cause wtSOD1 to adopt a toxic conformation similar to that of the mutant protein. Subsequent mechanistic studies have shown that this misfolded wtSOD1 can disrupt cellular function and lead to motor neuron death through pathways similar to those observed in mutant SOD1-ALS. Given the limited neuroprotective treatments currently available that can effectively slow or reverse disease progression, targeting a pathogenic mechanism that features in both familial and sporadic ALS cases represents a promising therapeutic approach for a broader patient population. This review examines the growing body of evidence that supports or challenges the role of misfolded wtSOD1 in the pathophysiology of sporadic ALS and explores the potential implications of this mechanism in disease progression. Understanding how misfolded wtSOD1 contributes to disease pathogenesis provides new opportunities for developing more widely available treatments for this devastating disease.