SOD1 aggregation in ALS mice shows simplistic test tube behavior

Abstract

A longstanding challenge in studies of neurodegenerative disease has been that the pathologic protein aggregates in live tissue are not amenable to structural and kinetic analysis by conventional methods. The situation is put in focus by the current progress in demarcating protein aggregation in vitro, exposing new mechanistic details that are now calling for quantitative in vivo comparison. In this study, we bridge this gap by presenting a direct comparison of the aggregation kinetics of the ALS-associated protein superoxide dismutase 1 (SOD1) in vitro and in transgenic mice. The results based on tissue sampling by quantitative antibody assays show that the SOD1 fibrillation kinetics in vitro mirror with remarkable accuracy the spinal cord aggregate buildup and disease progression in transgenic mice. This similarity between in vitro and in vivo data suggests that, despite the complexity of live tissue, SOD1 aggregation follows robust and simplistic rules, providing new mechanistic insights into the ALS pathology and organism-level manifestation of protein aggregation phenomena in general.superoxide dismutase 1 | aggregation | transgenic mice | aggregation kinetics

Thermodynamics of protein destabilization in live cells

“…15 N-labeled protein was delivered into the cytosol of mammalian cells by electroporation (SI Materials and Methods) and after recovery and washing, the treated cells were gently packed in an NMR tube (SI Materials and Methods). Intracellular SOD1 barrel concentrations were 20-30 μM, matching those in transgenic ALS mice (34,35), and substantially higher than the 1-to 5-μM endogenous concentration of SOD1 in mammalian cells (36). Controls of efficiency and yield of internalization are described in SI Controls and Fig.…”

Susceptibility of Mutant SOD1 to Form a Destabilized Monomer Predicts Cellular Aggregation and Toxicity but Not In vitro Aggregation Propensity

“…The concepts of aggregate strains and prion-like seeding have recently become prominent within the study of neurodegenerative disease, especially relating to ALS (Grad et al, 2014; Bergh et al, 2015; Lang et al, 2015; Bidhendi et al, 2016). Owing to the fact that spinal cord material from SOD1 G37R mice were unable to propagate disease in SOD1 G85R mice while SOD1 G93A material was (Ayers et al, 2014), we next performed an experiment to elucidate if this unfolded species could template onto other preformed SOD1 aggregates.…”

“…Recent work has emphasized the role that different aggregation pathways, leading to the formation of different aggregate strains, may play in the role of amyotrophic lateral sclerosis (Bergh et al, 2015; Lang et al, 2015; Bidhendi et al, 2016). Using binary epitope mapping, Bergh et al (2015) determined that mice overexpressing human SOD1 D90A developed SOD1 aggregates that were found to be competing strains termed strain A and B.…”

How Do Gyrating Beads Accelerate Amyloid Fibrillization?

“…A complete set of physical and chemical rules by which a gyrating bead affects the rate of amyloid formation—i.e., a set that includes hydrophobic, omniphobic, and electrostatic effects; contact mechanics; shear force; and mass—does not exist. For example, will a Teflon bead of 3.2 mm diameter (used in some studies of SOD1 fibrillization ( 13 )) accelerate fibrillization more or less than a Teflon bead of 2.4 mm diameter (used in other studies ( 24 )), and could these differences explain the disparity in reported rates? In microplate-based assays that commonly employ discontinuous gyration (e.g., gyration for 15 s followed by a 15-s pause), will the momentum of a gyrating bead cause a heavier bead to continue orbiting the well longer than a bead of lower mass?…”