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

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.

Prionoids in amyotrophic lateral sclerosis

“… 168 In contrast with other prion-like pathogenic proteins found in Alzheimer’s disease or Parkinson’s disease, no evidence of an ALS pathology supported by wildtype human SOD1 spread have been revealed. 169 Indeed, recent work reveals that transgenic mice overexpressing wildtype SOD1 appear to be resistant to misfolded mutant SOD1 seeds. 169 Together, these results show that mutant SOD1 aggregates can transmit and propagate ALS-like dysfunctions when they reach the CNS.…”

“… 169 Indeed, recent work reveals that transgenic mice overexpressing wildtype SOD1 appear to be resistant to misfolded mutant SOD1 seeds. 169 Together, these results show that mutant SOD1 aggregates can transmit and propagate ALS-like dysfunctions when they reach the CNS.…”

Multiple Factors Influence the Incubation Period of ALS Prion-like Transmission in SOD1 Transgenic Mice

“…The method used for sciatic nerve injections has been described in detail previously [ 13 , 22 ], with the following modification. To reduce postoperative pain, after the injection site was shaved and sterilized, the site was injected subcutaneously with 100 ul of a 0.05% solution of bupivacaine.…”

“…We have extensively used a version of G85R-SOD1 mice in which the human protein is fused in frame to yellow fluorescent protein (YFP) [ 21 ]. Mice that are heterozygous for the transgene do not develop paralysis until after 18 months of age [ 21 , 22 ], whereas newborn mice injected with preparations containing misfolded SOD1 conformers develop paralysis in less than 3 months [ 18 , 22 ]. Additionally, we observed that injecting fibrilized recombinant human SOD1 can induce early-onset paralysis in G85R-SOD1:YFP mice [ 14 , 23 ].…”

“…An important consideration in the prion-like propagation of misfolded SOD1 is the interaction of the seeding ALS conformer with the SOD1 expressed by the host. Mice that express the G85R variant of human SOD1 are highly permissive hosts, whereas mice that express wild-type SOD1, or mice that express ALS variants that are biochemically similar to wild-type SOD1, show little or no propagation of ALS conformers [ 14 , 18 , 22 ]. Because of these limitations in host susceptibility, we refrain from referring to propagating SOD1 as an ALS prion, in favor of the term ALS conformer.…”