Partial GSK3 knockdown improves muscle performance in mdx mice: investigating the cellular mechanisms

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disease caused by an X-linked mutation to the dystrophin gene that primarily affects boys. The absence of functional dystrophin protein leads to muscle wasting and weakness that progressively worsens over time with affected boys typically being wheelchair-bound by their teenage years, living a shortened lifespan of 30-40 years. Today, most treatment plans are focused on improving quality of life and preserving muscle strength for as long as possible, with glucocorticoids being the current standard of care. While effective in delaying the loss of ambulation, the side effects associated with these medications often lead to drug discontinuation. Our lab has recently shown that knocking down the enzyme glycogen synthase kinase 3 (GSK3) improved muscle strength and fatigue resistance in a preclinical model for DMD, the mdx mouse. However, the exact cellular mechanisms leading to these benefits remain unknown and is the purpose of the present thesis. To this end, male muscle-specific GSK3 knockdown mice (C57BL/6J background) were bred with female homozygous D2 mdx mice to produce 1) mdx mice with partial (30-40%) muscle-specific GSK3 knockdown (mdx/GSK3KD) and 2) mdx mice with GSK3 intact (flox control). To determine how GSK3 knockdown improves muscle strength and endurance, muscle glycogen content, fibre type composition, calcium handling, histopathology, and oxidative stress was assessed in extensor digitorum longus muscle at 4-6 weeks and 10-14 weeks of age, with glycogen content also being measured in the soleus as well. RNASeq analysis was conducted in gastrocnemius muscles obtained from mdx and mdx/GSK3KD mice. We saw an increase in glycogen content in both the EDL and soleus, an increase in the proportion of oxidative fibre types, along with a reduction in histopathology, and oxidative stress in the mdx/GSK3KD mice, with no change to maximal SERCA activity. RNASeq analysis corroborated findings of lowered fibrosis with significant downregulated genes associated with the extracellular matrix and collagen-containing extracellular matrix gene ontology pathways. In conclusion, this thesis provided a deeper understanding of the mechanisms leading to the improvement in muscle health in mdx/GSK3KD mice, adding further evidence in support of targeting GSK3 for DMD.

Name thesis:degree_name

M.Sc. Applied Health Sciences

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Faculty of Applied Health Sciences

Department dc:contributor.department

Applied Health Sciences Program

Grantor dc:publisher

Brock University

Year dc:date.issued

2025

Author dc:creator

• Marais,Amélie Annie Thérèsa

Advisor dc:contributor.advisor

• Fajardo, Val Andrew

• MEDICINE::Physiology and pharmacology::Physiology::Laboratory animal science
• NATURAL SCIENCES::Biology::Organism biology::Animal physiology
• MEDICINE::Morphology, cell biology, pathology::Morphology::Histology

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-nd/4.0/

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/10464/19590

OAI identifier oai:identifier

oai:brocku.scholaris.ca:10464/19590