Molecular dissection of ALS-associated toxicity of SOD1 in transgenic mice using an exon-fusion approach

Mutations in Cu,Zn superoxide dismutase (SOD1) are associated with amyotrophic lateral sclerosis (ALS). Among more than 100 ALS-associated SOD1 mutations, premature termination codon (PTC) mutations exclusively occur in exon 5, the last exon of SOD1. The molecular basis of ALS-associated toxicity of the mutant SOD1 is not fully understood. Here, we show that nonsense-mediated mRNA decay (NMD) underlies clearance of mutant mRNA with a PTC in the non-terminal exons. To further define the crucial ALS-associated SOD1 fragments, we designed and tested an exon-fusion approach using an artificial transgene SOD1T116X that harbors a PTC in exon 4. We found that the SOD1T116X transgene with a fused exon could escape NMD in cellular models. We generated a transgenic mouse model that overexpresses SOD1T116X. This mouse model developed ALS-like phenotype and pathology. Thus, our data have demonstrated that a ‘mini-SOD1’ of only 115 amino acids is sufficient to cause ALS. This is the smallest ALS-causing SOD1 molecule currently defined. This proof of principle result suggests that the exon-fusion approach may have potential not only to further define a shorter ALS-associated SOD1 fragment, thus providing a molecular target for designing rational therapy, but also to dissect toxicities of other proteins encoded by genes of multiple exons through a ‘gain of function’ mechanism

The SOD1-mediated ALS phenotype shows a decoupling between age of symptom onset and disease duration

Superoxide dismutase (SOD1) gene variants may cause amyotrophic lateral sclerosis, some of which are associated with a distinct phenotype. Most studies assess limited variants or sample sizes. In this international, retrospective observational study, we compare phenotypic and demographic characteristics between people with SOD1-ALS and people with ALS and no recorded SOD1 variant. We investigate which variants are associated with age at symptom onset and time from onset to death or censoring using Cox proportional-hazards regression. The SOD1-ALS dataset reports age of onset for 1122 and disease duration for 883 people; the comparator population includes 10,214 and 9010 people respectively. Eight variants are associated with younger age of onset and distinct survival trajectories; a further eight associated with younger onset only and one with distinct survival only. Here we show that onset and survival are decoupled in SOD1-ALS. Future research should characterise rarer variants and molecular mechanisms causing the observed variability

ACTH (Acthar Gel) Reduces Toxic SOD1 Protein Linked to Amyotrophic Lateral Sclerosis in Transgenic Mice: A Novel Observation.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with a complex etiology and pathology that makes the development of new therapies difficult. ACTH has neurotrophic and myotrophic effects, but has not been tested in an ALS mouse model. The G93A-SOD1 mouse model of ALS was used to test the ability of this drug to delay ALS-like symptoms. We showed that within a specific dose range, ACTH significantly postponed the disease onset and paralysis in the mouse model. To our surprise and of greater significance is that ACTH significantly reduced the levels of soluble SOD1 in the spinal cord and CNS tissues of G93A-SOD1 treated mice as well as cultured fibroblasts

Therapeutic effects of ACTH on ALS-like symptoms in G93A-SOD1 mice.

<p>Proportion of onset (A), paralysis (B), and survival (C). Kaplan Meier was used to plot the survival curves.</p

Effect of ACTH on SOD1 protein expression in different parts of the central nervous system.

<p>SOD1 was measured in the corresponding tissue lysates by ELISA and then normalized to GAPDH activity. Ctl: the nontreated animals, SC, spinal cord, CB: cerebellum, BS: brain stem, CX: cortex. n = 6 for the non-treated mice, n = 4 for treated animals. Mice treated with ACTH showed decreased expression of SOD1 protein in spinal cord and selected brain tissues.</p

Experimental treatment arms for the study.

<p>Experimental treatment arms for the study.</p

Rotarod statistics.

<p>Rotarod statistics.</p

ACTH has variable dose-dependent effects on changes in the weight of G93A-SOD1 transgenic mice.

<p>Panel A shows the fractional weight change of males, while l B shows the change in female mice over the time course of treatment. Error bars are the standard deviation for each point. Bars are not visible when they are smaller than the size of the symbol.</p