Functional consequences of familial ALS‐associated SOD1L84F in neuronal and muscle cells

Abstract Amyotrophic lateral sclerosis is a fatal neurodegenerative disorder characterized by progressive skeletal muscle denervation and loss of motor neurons that results in muscle atrophy and eventual death due to respiratory failure. Previously, we identified a novel SOD1 L84F variation in a familial ALS case. In this study, we examined the functional consequences of SOD1 L84F overexpression in the mouse motor neuron cell line (NSC‐34). The cells expressing SOD1 L84F showed increased oxidative stress and increased cell death. Interestingly, SOD1 L84F destabilized the native dimer and formed high molecular weight SDS‐resistant protein aggregates. Furthermore, SOD1 L84F also decreased the percentage of differentiated cells and significantly reduced neurite length. A plethora of evidence suggested active involvement of skeletal muscle in disease initiation and progression. We observed differential processing of the mutant SOD1 and perturbations of cellular machinery in NSC‐34 and muscle cell line C2C12. Unlike neuronal cells, mutant protein failed to accumulate in muscle cells probably due to the activated autophagy, as evidenced by increased LC3‐II and reduced p62. Further, SOD1 L84F altered mitochondrial dynamics only in NSC‐34. In addition, microarray analysis also revealed huge variations in differentially expressed genes between NSC‐34 and C2C12. Interestingly, SOD1 L84F hampered the endogenous FUS autoregulatory mechanism in NSC‐34 by downregulating retention of introns 6 and 7 resulting in a two‐fold upregulation of FUS. No such changes were observed in C2C12. Our findings strongly suggest the differential processing and response towards the mutant SOD1 in neuronal and muscle cell lines.