ALS-linked misfolded SOD1 species have divergent impacts on mitochondria.

Sarah Pickles,Sabrina Semmler,Neil R Cashman,Nathalie Arbour,Laurine Legroux,Helen R Broom,Elizabeth Meiering,Christine Vande Velde,Laurie Destroismaisons

doi:10.1186/s40478-016-0313-8

Abstract

Approximately 20 % of familial Amyotrophic Lateral Sclerosis (ALS) is caused by mutations in superoxide dismutase (SOD1), which leads to misfolding of the SOD1 protein, resulting in a toxic gain of function. Several conformation-restricted antibodies have been generated that specifically recognize misfolded SOD1 protein, and have been used as therapeutics in pre-clinical models. Misfolded SOD1 selectively associates with spinal cord mitochondria in SOD1 rodent models. Using the SOD1G93A rat model, we find that SOD1 conformational specific antibodies AMF7-63 and DSE2-3H1 labeled a fibrillar network concentrated in the anterior horn; while A5C3, B8H10, C4F6 and D3H5 labeled motor neurons as well as puncta in the neuropil. There is a time-dependent accumulation of misfolded SOD1 at the surface of spinal cord mitochondria with AMF7-63-labeled mitochondria having increased volume in contrast to a mitochondrial subset labeled with B8H10. In spinal cord homogenates and isolated mitochondria, AMF7-63, DSE2-3H1 and B8H10 detect misfolded SOD1 aggregates. SOD1 that lacks its metal cofactors has an increased affinity for naïve mitochondria and misfolded SOD1 antibodies B8H10 and DSE2-3H1 readily detect demetalated mutant and wild-type SOD1. Together, these data suggest that multiple non-native species of misfolded SOD1 may exist, some of which are associated with mitochondrial damage. Conformational antibodies are invaluable tools to identify and characterize the variation in misfolded SOD1 species with regards to biochemical characteristics and toxicity. This information is highly relevant to the further development of these reagents as therapeutics.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-016-0313-8) contains supplementary material, which is available to authorized users.

Highlights

The defining feature of the neurodegenerative disease Amyotrophic Lateral Sclerosis (ALS) is the loss of motor neurons in the cortex, brain stem and spinal cord [1]
Misfolded Superoxide Dismutase 1 (SOD1) specific antibodies DSE2-3H1 and AMF763 detect fibrils in the spinal cord of SOD1G93A rats To evaluate whether multiple antibodies targeted to non-native/misfolded conformations of SOD1 yielded a universal localization under similar conditions, lumbar sections of symptomatic SOD1G93A rat spinal cords were labeled with a panel of misfolded SOD1 specific antibodies
Immunohistochemistry for misfolded SOD1 in SOD1G93A lumbar spinal cords. a Lumbar sections of a symptomatic SOD1G93A rat were stained with misfolded SOD1 specific antibody A5C3 and co-labeled with choline acetyltransferase (ChAT)

Summary

Introduction

The defining feature of the neurodegenerative disease Amyotrophic Lateral Sclerosis (ALS) is the loss of motor neurons in the cortex, brain stem and spinal cord [1]. Pickles et al Acta Neuropathologica Communications (2016) 4:43 adopts a non-native conformation induced either by mutation, loss of its zinc cofactor, and/or oxidation. While many of these were developed with the intent to be potential therapeutics, these reagents have become valuable tools with which to track the toxic forms of SOD1. In preclinical research using mutant SOD1 animals, it is appreciated that reducing misfolded SOD1 levels via immunization significantly increases survival [8, 17]. This provides additional support that misfolded SOD1 lies at the root of SOD1-mediated ALS [8, 17]

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