Duchenne muscular dystrophy (DMD) is a fatal, x-linked disease that causes progressive muscle weakness and susceptibility to damage. DMD is caused by a lack of dystrophin, a large muscle protein that performs both structural and signaling functions. A promising treatment currently in clinical trials is microdystrophin gene therapy, which delivers a truncated version of dystrophin to muscle via a viral vector. Preclinical studies have established efficacy of microdystrophin to improve muscle quality and function. With clinical success of this treatment, patients affected by DMD could become more physically active. However, the effect of exercise on both dystrophic and gene therapy-treated muscles is unclear. Recently, we demonstrated that microdystrophin gene therapy with and without 21 weeks of voluntary wheel running (VWR) improved treadmill time to fatigue and in vivo plantarflexor torque output in young mdx mice, a mouse model of DMD. Although treated mice could run well, diaphragm force and power output were blunted by VWR. A subsequent study tested longevity of two different microdystrophin gene therapy constructs in combination with VWR. Versions of each construct are being tested in clinical trials. Construct 1 contained the nNOS-binding site found in full-length dystrophin, which localizes nNOS to the sarcolemma and reduces functional ischemia of exercising limb muscles, while construct 2 lacked the nNOS-binding site and was the same microdystrophin used in the previous study. Gene- therapy treated mice that were sedentary or performed 52 weeks of VWR demonstrated similar outcomes including increased plantarflexor torque and exceptional treadmill endurance capacity. However, ex vivo diaphragm and soleus force, as well as metabolic enzyme and mitochondrial respiration assays were differentially improved, revealing unique physiological adaptations to each microdystrophin construct. Together, the data demonstrated that response to exercise after gene therapy treatment was variable and dependent on age, microdystrophin construct, and muscle type. / Doctor of Philosophy / Duchenne muscular dystrophy (DMD) is a rare, fatal muscle disease that causes progressive muscle weakness and cardiorespiratory failure. Available treatments, such as corticosteroids, slow progression of the disease but do not address the underlying genetic cause. DMD is caused by a genetic mutation that results in the loss of the muscle protein dystrophin. Microdystrophin gene therapy aims to address the genetic cause of the disease by using a non-pathogenic virus to deliver microdystrophin, a small, functional version of dystrophin, to muscle. This gene therapy is in clinical trials, and, if it is successful, treated patients will likely want to engage in more physical activity than previously possible due to muscle weakness. However, the effects of physical activity on muscles treated with gene therapy are unclear. Therefore, we conducted two studies to test the effects of voluntary wheel running on microdystrophin gene therapy in the mdx mouse, a model of DMD. The first study demonstrated that voluntary wheel running was beneficial to whole-body muscle function in mice treated with microdystrophin gene therapy. However, adaptations to the gene therapy and voluntary wheel running were variable in individual muscles. In the second study, we tested two microdystrophin constructs, which each contain different structural components of full-length dystrophin. In addition, mice ran for 52 weeks, more than twice as long as the first study. The results of the second study found that adaptations in individual muscles depended on microdystrophin construct and activity level. Additionally, we confirmed that voluntary wheel running was beneficial to whole-body function of microdystrophin–treated muscles. Together, these studies demonstrated that adaptations of gene therapy-treated muscles were dependent on microdystrophin structure, activity level, and age.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110498 |
| Date | 08 June 2022 |
| Creators | Hamm, Shelby Elizabeth |
| Contributors | Human Nutrition, Foods and Exercise, Grange, Robert W., Mack, David L., Schmelz, Eva Maria, Craige, Siobhan |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nc-nd/4.0/ |
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