Variation in the vulnerability of mice expressing human superoxide dismutase 1 to prion-like seeding: a study of the influence of primary amino acid sequence

Jacob I Ayers,Zhijuan Chen,John Beckman,David R Borchelt,Kristy Dillon,Alma K Moreno-Romero,Guilian Xu,Qing Lu,Ahmad Galaleldeen,Diana L Zamora

doi:10.1186/s40478-021-01191-w

Abstract

Misfolded forms of superoxide dismutase 1 (SOD1) with mutations associated with familial amyotrophic lateral sclerosis (fALS) exhibit prion characteristics, including the ability to act as seeds to accelerate motor neuron disease in mouse models. A key feature of infectious prion seeding is that the efficiency of transmission is governed by the primary sequence of prion protein (PrP). Isologous seeding, where the sequence of the PrP in the seed matches that of the host, is generally much more efficient than when there is a sequence mis-match. Here, we used paradigms in which mutant SOD1 seeding homogenates were injected intraspinally in newborn mice or into the sciatic nerve of adult mice, to assess the influence of SOD1 primary sequence on seeding efficiency. We observed a spectrum of seeding efficiencies depending upon both the SOD1 expressed by mice injected with seeds and the origin of the seed preparations. Mice expressing WT human SOD1 or the disease variant G37R were resistant to isologous seeding. Mice expressing G93A SOD1 were also largely resistant to isologous seeding, with limited success in one line of mice that express at low levels. By contrast, mice expressing human G85R-SOD1 were highly susceptible to isologous seeding but resistant to heterologous seeding by homogenates from paralyzed mice over-expressing mouse SOD1-G86R. In other seeding experiments with G85R SOD1:YFP mice, we observed that homogenates from paralyzed animals expressing the H46R or G37R variants of human SOD1 were less effective than seeds prepared from mice expressing the human G93A variant. These sequence mis-match effects were less pronounced when we used purified recombinant SOD1 that had been fibrilized in vitro as the seeding preparation. Collectively, our findings demonstrate diversity in the abilities of ALS variants of SOD1 to initiate or sustain prion-like propagation of misfolded conformations that produce motor neuron disease.

Highlights

Amyotrophic lateral sclerosis (ALS) can present clinically as focal weakness in a limb, hand, or foot that progressively worsens before weakness spreads alongAyers et al acta neuropathol commun (2021) 9:92 no obvious family history; up to 25% of patients have a family history of disease with a subset of these classified as familial based on the inheritance of rare genetic variants [2]
We have demonstrated previously that intraspinal injection of spinal homogenates from paralyzed mutant superoxide dismutase 1 (SOD1) mice into newborn G85R-SOD1:YFP mice accelerates the onset of paralysis and intraspinal SOD1 inclusion pathology [15, 17]
We have previously demonstrated that paralysis in G85R-SOD1:YFP mice is not induced by injection of PBS or spinal tissue homogenates from various types of controls (Additional file 2: Table S1) [17]

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) can present clinically as focal weakness in a limb, hand, or foot that progressively worsens before weakness spreads alongAyers et al acta neuropathol commun (2021) 9:92 no obvious family history; up to 25% of patients have a family history of disease with a subset of these classified as familial based on the inheritance of rare genetic variants [2]. Though the effects of most of these mutations on enzymatic function have not been characterized, studies of a random subset of mutations have shown that many disease-associated mutants of SOD1 retain high enzymatic activity [3]. These mutants have been classified as wild-type-like (WT-like) mutants. Work from multiple laboratories including ours has demonstrated that mutations associated with ALS cause conformational changes in SOD1 that induce the protein to misfold and self-associate into insoluble aggregates and pathological inclusions (reviewed in [4]). Studies in cell culture models have established the potential for misfolded WT SOD1 to propagate between cells, leading to the hypothesis that prion-like propagation of misfolded WT SOD1 could be involved in the progressive spread of weakness in sporadic ALS patients [6, 14]

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Conclusion