Multimodal Synchrotron Radiation Microscopy of Intact Astrocytes from the hSOD1 G93A Rat Model of Amyotrophic Lateral Sclerosis

Abstract

© 2018 American Chemical Society. Amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease, is the most common adult onset neurodegenerative disorder affecting motor neurons. Disruptions in metal ion homeostasis have been described in association with ALS, but the pathological mechanisms are still poorly understood. One of the familial ALS cases is caused by mutations in the metallo-enzyme copper-zinc superoxide dismutase (SOD1). In this study, we employed orthogonal cellular synchrotron radiation based spectro-microscopies to investigate the astrocytes of an ALS animal model: the rat hSOD1 G93A that overexpresses human mutated SOD1, which is known to increase the susceptibility of the SOD1 protein to form insoluble intracellular aggregates. Specifically, we applied soft X-ray transmission tomography and hard X-ray fluorescence microscopy in situ, Fourier transform infrared spectro-microscopy to detect and analyze aggregates, as well as to determine the alterations in the cellular ultrastructure and the elemental and the organic composition of ALS model astrocytes with respect to the control astrocytes isolated from nontransgenic littermates (NTg). The present study demonstrates that large aggregates in the form of multivesicular inclusions form exclusively in the ALS model astrocytes and not in the NTg counterpart. Furthermore, the number of mitochondria, the cellular copper concentration, and the amount of antiparallel β-sheet structures were significantly changed within the cells of the ALS model as well as the lipid localization and composition. Also, our data indicate that choline was decreased in the ALS model astrocytes, which could explain their higher sensitivity to oxidative stress that we observed. These results show that the hG93A SOD1 mutation causes metabolic and ultrastructural cellular changes and point to a link between an increased copper concentration and aggregation: the most probable that the aggregation of G93A hSOD1 may perturb its binding to Cu, thus directly or indirectly affecting Cu homeostasis.