Therapeutic Benefits to SOD1 Silencing by way of AAV:miRNA Infection in ALS

Summary of:

Dirren, E., Aebischer, J., Rochat, C., Towne, C., Schneider, B. L., & Aebischer, P. (2015). SOD1 silencing in motoneurons or glia rescues neuromuscular function in ALS mice. Annals of Clinical and Translational Neurology. 

Brandon Goldson and Jessica Snyder

What is ALS?:

Also known as Lou Gehrig’s disease,  ALS (Amyotrophic lateral sclerosis ) is a fatal and incurable disorder primarily characterized by rapid progressive degeneration of motor neurons in the brain and spinal cord. This degeneration of the motor neurons leads to immobility, paralysis and eventually death 3-5yrs after diagnosis. About 5,000 people are diagnosed with an estimated 30,000 people living with ALS in the United States each year. Though ALS occurs in the world with no racial or socioeconomic boundaries, risk factors include age, sex and genetics. Regarding genetics, 10% of the people suffering from ALS display an inherited form of the disease. Within that population, 20% present a mutation in the gene encoding superoxide dismutase 1(SOD1).



What is the Known Pathophysiology of ALS and SOD1?:

Over 160 mutations of SOD1 have been found to cause ALS. These mutations cause an increase in toxicity and a degeneration of motor neurons in the brain and spinal cord.

 

What is the Hypothesis?

MiR Sod1 and MiR -b SOD1 effectively silence SOD1 (g93A) activity in mice expressing the human mutated gene. This silencing improves function and delays degeneration and symptoms associated with ALS in mice.

 

What is the Experimental Design

The effect of a miRNA designed to silence the SOD1 gene was tested both in cell culture and a mice model.  Both models contained a SOD1 gene mutation.  After the silencing effect was confirmed in vitro,  the researchers tested the efficacy of two treatments in SOD1 transgenic mice.  The first treatment was AAV6:miR SOD1 and the second was a combination of AAV6:miR SOD1 and AAV9:miR SOD1.  In all but the final experiment, the mice were given the treatment soon after birth.

 

The effect of the treatment in the mouse model was tested in the following ways:

  • examine whether or not the AAV is localized in correct cells (motor neurons and astrocytes are test in the spinal cord)
  • Observe SOD1 expression with and without the AAV miR treatment
  • motor function test of mice with & without treatment (swimming latency test and rotarod test)
  • test of proteins contained within muscle sample
  • staining of spinal tissue to see motor neurons status (intact or not)  as well as the viability of neuromuscular junctions
  • muscle fiber thickness to evaluate whether or not muscle atrophy was lessened
  • Finally, adult transgenic SOD1 mice were given the treatment and evaluated for viability, motor function and the state of neuronal cells in the spinal cord.

What are the Key Results?:

1: Suppressing of SOD1 in astrocytes and motor neurons : Figure 1

  • Quantification of human SOD1 levels relative to miR control confirms that human SOD1 expression is significantly reduced in cells overexpressing miR SOD1 and miR-b SOD1.

2: Delays Disease Progression and Improved Disease Outcome in the following ways

 

  • Increase in intact spinal motor neurons:  Figure 4
    • NMJ function was rescued to 90% as compared to control G93ASOD1 mic
  • Rescues Neuromuscular junctions: Figure 4
    • As compared to WT and PBS-injected G93ASOD1 mice, significant preservation of motoneuron integrity at all levels of the spinal cord was observed in AAV6:miR SOD1 and AAV6 + AAV9:miR SOD1 groups.
  • Increase in muscle fiber diameter (rescues muscle atrophy): Figure 5
    • Hematoxylin and eosin staining of gastrocnemius muscle sections displayed maintenance of muscle integrity with respect to AAV9:miR SOD1 mice compared to control transgenic mice.

 

 

What is the Broader context?

These results show promise for the treatment of familial ALS.  The maintenance of motor neurons and NMJ is key to attenuating disease symptoms and improving quality of life in ALS patients. Full or partial rescue of neuromuscular function following neonatal and adult ICV infection of AAV-miR SODI may establish the therapeutic silencing approach as an effective treatment for ALS. Furthermore,  this paper confirms that SOD1 silencing in specific cell types such as motor neurons and astrocytes is crucial to this therapeutic targeting. Additionally AAV based therapeutic targeting may be used to alter other genes related to ALS prevalence.

 

P.S.  Helpful YouTube Videos about the Nervous System Below!

12 thoughts on “Therapeutic Benefits to SOD1 Silencing by way of AAV:miRNA Infection in ALS”

  1. I find this article and your summary fascinating, especially in the context of different types of cells affected by ALS. I am interested in how the researchers tested the delivery of SOD1 to motor-neurons or astrocytes, and found an improvement in the disease outcome. I am also curious as to how the treatment differs in the two cell types, specifically since the suppression of SOD1 preserved innervation while the motor-neurons were only partially projected.

  2. I am curious about the animal model used for this study. In human patients, 160 different mutations in the SOD1 gene have been identified. Do all of these mutations have essentially the same phenotype? If not, how does the phenotype of the transgenic model model compare? It would be interesting to understand more about the specific toxic effects of the various mutations in both humans and animal models.

  3. This article shows interesting promise for the treatment of one form of ALS. However, it was pretty unsatisfying to read that this paper focuses on the mutation in the gene encoding SOD1, which only accounts for 2% of ALS occurrence. Obviously, connections can be made to relate these findings to other forms of ALS, but this statistic really surprised me in showing just how much is unknown about ALS.

  4. Although the paper illustrates some interesting and conclusive results, I am not convinced as to how this would work as a treatment in humans. The authors state that the mice experienced various side-effects (with unknown causes) such as ataxia, infections, and sudden death. Additionally, when the authors discuss the effects on muscle cells, they mention that some mice actually have increased muscle size. Is it possible that there are steroidal implications with this treatment?

  5. While the researchers on this project were successful in their analysis of SOD1-related cases of ALS, due to the fact that these mutations only comprise 2% of all ALS cases, it begs the question as to whether or not these findings translate to larger pool.
    Their AAV treatment seems to be an effective treatment, but I wonder if it can be applied to other genes, like C9orf72, which cause a large number of the familial ALS cases.
    Also, I’m curious if any of their findings help shed light on the processes which cause ALS that are not genetic as this comprises nearly 90% of all cases.

  6. In the discussion, the authors reiterate key differences in the neuroprotective effects between the two vectors at the lumbar level following IT injection of adult mice. They found that SOD1 silencing in motoneurons was more neuroprotective than astrocyte-specific SOD1 silencing. What is thought to account for this discrepancy?

  7. I found it interesting that the results of this article showed that silencing SOD1 had such a large impact on the prevention of the disease. However, I am unsure how easy treatment in humans would be. Would injection into the spinal cord be necessary or could a drug be developed? In addition, what effect does silencing SOD1 have on other cells in the body besides motoneurons and astrocytes?

  8. I think it is interesting that several of our papers this year have utilized miRNA silencing! As far as this paper goes, one thing that I wish they had discussed a little more were the side effects seen in some miR SOD1 mice. I am curious as to whether these complications were due to a downstream or unintended effect of the miRNA, or if there was some sort of inflammatory damage caused by the genotype or presence of a viral vector, etc. In their conclusion, the authors suggest another possibility, that the effects seen are caused by a genetic defect that this genotype of mouse does not typically survive to experience. However, I feel that this is an area that deserves further investigation, particularly if the knockdown of SOD1 or an associated protein is the cause.

  9. This paper gives a glimpse at how complex ALS is as a disorder. While the SOD1 mutation only accounts for 2% of the known cases, I think through investigating its function and the cell type that benefits most from therapeutics, there are gains made through their findings. I find their use of AAV9-shRNA as a therapeutic treatment to be fascinating, and wonder how exactly this works in the process of targeting specific locations. Along those lines, I would be interested to see this move into human treatments. While this research is certainly helpful in coming closer to a therapeutic regiment for certain patients, I am not convinced that it is the most worthwhile ALS research in terms of benefiting a large number of patients diagnosed with ALS.

  10. Nice comments, everyone!

    I am unsatisfied with the background information on SOD1 in the introduction section of this paper. All it states is that mutations in SOD1 result in gain of toxicity and that mutant SOD1 “can perturb a number of cellular functions” with only 1 reference to this statement. This language is too vague. What is the molecular mechanism responsible for the effects of SOD1 mutation?

  11. This paper gives really clear immunostaining that I could see what is going on with their immunostaining. I like their figures. I like how the paper goes further with injecting SOD1 (therapies). However, I was confused how they can suggest there was improved muscle response in treated animals compared to PBS-injected mice by looking at figure 6B. Instead of analyzing what they had from data, in the result section, I feel like they should just state what they had especially in figure 6D. and I wish they could just mention or label where they got the information on NMJs (from Figure 6H) in the result section. In addition, wouldn’t figure 5 is supporting ideas of the paper have rather than the main key figure?

  12. I would like to further understand the effects of SOD1 in all forms of ALS. If it is known that with the isolation of SOD1 mutations there is an increased toxicity and degeneration of motor neurons in the CNS how can researchers relate this to those other 90% without a hereditary version of ALS. Could age and unknown exposure to environmental cause mutations in the gene or the way in which it is replicated? I am very curious to further expand upon the role of SOD1 in those ALS cases that have not been deemed hereditary. Along with any findings on this could treatment or therapy be overlapped? Or could we gain a better detection or prevention method of this degeneration and toxicity among motor neurons in the CNS.

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