Disruption of mitochondrial membrane integrity induced by amyloid aggregates arising from variants of SOD1

Amyotrophic lateral sclerosis (ALS) is a fatal progressive neurodegenerative disorder selectively affecting motor neurons; 90% of the total cases are sporadic, but 2% are associated with mutations in the gene coding for copper–zinc superoxide dismutase (SOD1). The causes of motor neuron death in ALS are poorly understood in general, but for SOD1-linked familial ALS (fALS), aberrant oligomerization of SOD1 mutant proteins has been strongly implicated. A growing body of evidence suggests that fALS-causing mutations destabilize the native structure of SOD1, leading to aberrant protein interactions for aggregation. In this work, we show that wild-type human SOD1 and two of its mutants (D101N, G72S) form amyloid like fibrils under destabilizing condition (in the presence of KSCN 0.2 M and DTT 50 mM) at 37 °C, pH 7.4. The formation of the aggregates was monitored by their ability to enhance the fluorescence of Thioflavin T (ThT) and their morphology was assessed by transmission electron microscopy (TEM). Furthermore, interaction of SOD1 aggregates with mitochondrial membrane of rat brain, as an in vitro biological model, with the aim of gaining an insight into possible mechanism of cytotoxicity at the membrane level was verified. Release of mitochondrial enzyme, malate dehydrogenase (MDH), upon exposure to SOD1 aggregates demonstrates that these aggregates could affect membrane permeability.