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Evaluating protein crosslinking as a therapeutic strategy to stabilize SOD1 variants in a mouse model of familial ALS

ABSTRACT: Mutations in the gene encoding Cu-Zn superoxide dismutase 1 (SOD1) cause a subset of familial amyotrophic lateral sclerosis (fALS) cases. A shared effect of these mutations is that SOD1, which is normally a stable dimer, dissociates into toxic monomers that seed toxic aggregates. Considerable research effort has been devoted to developing compounds that stabilize the dimer of fALS SOD1 variants, but unfortunately, this has not yet resulted in a treatment. We hypothesized that cyclic thiosulfinate cross-linkers, which selectively target a rare, two cysteine-containing motif, can stabilize fALS-causing SOD1 variants in vivo. We created a library of chemically diverse cyclic thiosulfinates and determined structure-cross-linking-activity relationships. A pre-lead compound, “S-XL6,” was selected based upon its cross-linking rate and drug-like properties. Co-crystallographic structure clearly establishes the binding of S-XL6 at Cys 111 bridging the monomers and stabilizing the SOD1 dimer. Biophysical studies reveal that the degree of stabilization afforded by S-XL6 (up to 24 °C) is unprecedented for fALS, and to our knowledge, for any protein target of any kinetic stabilizer. Gene silencing and protein degrading therapeutic approaches require careful dose titration to balance the benefit of diminished fALS SOD1 expression with the toxic loss-of enzymatic function. We show that S-XL6 does not share this liability because it rescues the activity of fALS SOD1 variants. No pharmacological agent has been proven to bind to SOD1 in vivo. Here, using a fALS mouse model, we demonstrate oral bioavailability; rapid engagement of SOD1G93A by S-XL6 that increases SOD1G93A’s in vivo half-life; and that S-XL6 crosses the blood-brain barrier. S-XL6 demonstrated a degree of selectivity by avoiding off-target binding to plasma proteins. Taken together, our results indicate that cyclic thiosulfinate-mediated SOD1 stabilization should receive further attention as a potential therapeutic approach for fALS.

INSTRUMENT(S): 6220 Time-of-Flight LC/MS

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Blood Cell, Blood

DISEASE(S): Amyotrophic Lateral Sclerosis Type 1

SUBMITTER: Md Amin Hossain

LAB HEAD: Jeffrey N. Agar

PROVIDER: PXD047030 | Pride | 2023-12-17

REPOSITORIES: Pride

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Project description:Missense mutations in the gene for the ubiquitously expressed superoxide dismutase-1 (SOD1) are one of the causes of familial amyotrophic lateral sclerosis (ALS), the most common adult onset motor neuron disease in humans killing selectively large motor neurons. Mice and rats overexpressing mutant SOD1 develop an adult onset neurodegenerative disease with hindlimb-paralysis and subsequent death similar to the human condition. In order to analyze the effects of mutant SOD1 expression onto the most affected cell-type in ALS, a small subpopulation of spinal cord cells, we propose to use laser microdissection to isolate mouse lumbar motor neurons and to assess the changes onto the mRNA expression profile using Affymetrix GeneChips compared to control animals. While two studies applying a genomic approach on the ALS mouse models used the entire spinal cord, contributions of changes to motor neurons were masked by the inflammatory effects of mutant SOD1 and the much larger population of non-motor neuronal cells. What is therefore needed is a cell-type specific expression profile that could reveal dysregulations in the transcriptome of the affected motor neurons. In order to find and analyze disease relevant gene expression profile changes in the mutant vs. the wildtype overexpressing SOD1 mice, we propose to use two different mutant SOD1 lines. Both lines develop the same ALS-like motor neuron disease, however, line 1 (with a G37R mutation) retains the full activity of the SOD1 enzyme while line 2 (with a G85R mutation) has almost no SOD1 enzymatic activity. We believe that by using these two most extreme variants of ALS-inducing mutant SOD1 forms, candidate genes that will be similarly dysregulated in both mutant lines will have great potential to be a disease relevant hit. We will collect from both mutant SOD1 mouse lines lumbar motor neurons from three presymptomatic timepoints, equally distributed during their adult life and before obvious hindlimb-weakness or paralysis signs and compare them to two control lines, negative littermates and wildtype SOD1 overexpressing mice. Furthermore, to determine if their are already mutant SOD1-induced changes since the formation of the affected cells, we will also isolate embryonic spinal cord motor neurons and compare them between mutant SOD1 and wildtype SOD1 overexpressing animals. Both, mice deleted in wildtype SOD1 and mice overexpressing mutant human SOD1 clearly established that the toxic property of mutant SOD1 is based upon a gain-of-toxic function phenomenon rather than a loss-of-function effect, since the SOD1 knock-out mice are overall normal. Furthermore, mice overexpressing wildtype SOD1 are healthy and serve as ideal control animals. Therefore, one of the most important question in ALS is to determine what slowly acting mechanism, or build-up of toxic products is responsible for ultimately killing more than 50-70% of the large lumbar spinal cord motor neurons. We hypothezise that the toxic property of mutant SOD1 must already induce changes onto the transcriptome of the most at-risk cell-type, the large lumbar spinal cord motor neuron, very early on in the presymptomatic phase of the disease course, when the animal is still without any paralysis signs and moving normally around the cage. We will choose 3 timepoints before phenotypic disease-onset that is at 22 weeks for the SOD1G37R line (L42) and at 11 months for the SOD1G85R line (L148). The timepoints are 8, 15 and 18 weeks for SOD1G37R line and 4, 7.5 and 9 months for the SOD1G85R line all compared to age-matched control animals (wildtype SOD1 overexpressing mice (L76) for the SOD1G37R line (high mutant SOD1 levels) and negative littermates for the SOD1G85R line (low mutant SOD1 levels)). Using the Leica lasermicrodissection system on fresh frozen spinal cord sections, we process a single spinal cord sample in 3 days resulting in approximately 4000 ventral horn motor neurons collected from 150 consecutive 20 um sections of the most affected lumbar spinal cord region (L4-L6). To visualize the motor neurons, we have established a fast Nissel-staining protocol that is optimized for speed to preserve the integrity of the RNA. Before lasermicrodissection slides containing 5 spinal cord sections are dessicated for 1 hour and samples are collected directly into RNA-preserving lysis-buffer. Using Stratagene's NanoPrep RNA-extraction columns a yield of around 150 ng of total RNA was obtained (Ribogreen-quantification), that is enough for both the 2-round linear RNA amplification and for future candidate confirmation studies using real-time PCR analysis. We are using the Affymetrix Two-Cycle 3'-Amplification Kit, starting with 100 ng of total RNA and will hybridize on Affymetrix Mouse 430 2.0 GeneChips. Embryonic motor neurons are isolated from e14 mutant SOD1G93A overexpressing rat embryos and compared to wildtype SOD1 overexpressing embryos using a metrazimide gradient followed by a p75-antibody purification in combination with magnetic beads. Cells from one litter of embryos were directly collected into lysis-buffer, yielding at least 200-500 ng of total RNA, enough for one Rat 230 2.0 GeneChip (2-round amplification using 100 ng total RNA). Keywords: time-course

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Evaluating protein crosslinking as a therapeutic strategy to stabilize SOD1 variants in a mouse model of familial ALS

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