Browsing by Author "Mack, David L."

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    Physiological adaptations in mdx mice treated with microdystrophin gene therapy and endurance exercise
    Hamm, Shelby Elizabeth (Virginia Tech, 2022-06-08)
    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.
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    Potential adaptive signaling pathways in the diaphragm of mdx mice treated with micro-dystrophin combined with voluntary running
    McQueen, Lucas Flynn (Virginia Tech, 2022-02-16)
    Hamm et al., 2021 reported that voluntary wheel running (R) was complementary to micro-dystrophin gene therapy (GT) in mdx mice, a model of Duchenne muscular dystrophy (DMD). After 21 weeks of running, time to fatigue on a treadmill for the mdxRGT mice was increased 1.8-fold compared to mdxGT mice (no run) and ~5-fold compared to mdx mice (no micro-dystrophin, no run). Fatigue times for mdxRGT were similar to wild type runners (WTR), while mdxGT and WT (no run) were also similar. The diaphragm is an important muscle for endurance exercise. Remarkably, diaphragm power in mdxRGT was depressed compared to mdxGT, suggesting a negative impact of running on GT. To explore mechanisms to explain this decrease, transcriptome profiles for each of the study groups were assessed. RNASeq data revealed differentially expressed genes (DEGs) from groupwise comparisons. Transcripts identified using the Jackson Labs' Gene Expression Database and extensive literature review were organized into a master signaling pathway composed of two sub-pathways: muscle regeneration and fast-slow fiber type shift. Both sub-pathways were hypothesized to explain the improved treadmill performance despite decreased diaphragm power in mdxRGT as potential adaptive mechanisms. Analysis revealed that GT alone (mdxGT) rescued transcriptome expression to WT values in the mdx phenotype more than GT and running combined (mdxRGT). This outcome indicates that, at the 26-week timepoint of sacrifice, the signaling of the transcripts in the muscle regeneration and fast-slow fiber type shift sub-pathways was likely not responsible for the observed improved running performance of mdxRGT compared to mdx.
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    Systemic AAV8-Mediated Gene Therapy Drives Whole-Body Correction of Myotubular Myopathy in Dogs
    Mack, David L.; Poulard, Karine; Goddard, Melissa A.; Latoumerie, Virginie; Snyder, Jessica M.; Grange, Robert W.; Elverman, Matthew R.; Denard, Jerome; Veron, Philippe; Buscara, Laurine; Le Bec, Christine; Hogrel, Jean-Yves; Brezovec, Annie G.; Meng, Hui; Yang, Lin; Liu, Fujun; O'Callaghan, Michael; Gopal, Nikhil; Kelly, Valerie E.; Smith, Barbara K.; Strande, Jennifer L.; Mavilio, Fulvio; Beggs, Alan H.; Mingozzi, Federico; Lawlor, Michael W.; Buj-Bello, Ana; Childers, Martin K. (2017-04-05)
    X-linked myotubular myopathy (XLMTM) results from MTM1 gene mutations and myotubularin deficiency. Most XLMTM patients develop severe muscle weakness leading to respiratory failure and death, typically within 2 years of age. Our objective was to evaluate the efficacy and safety of systemic gene therapy in the p.N155K canine model of XLMTM by performing a dose escalation study. A recombinant adeno-associated virus serotype 8 (rAAV8) vector expressing canine myotubularin (cMTM1) under the muscle-speCific desmin promoter (rAAV8-cMTM1) was administered by simple peripheral venous infusion in XLMTM dogs at 10 weeks of age, when signs of the disease are already present. A comprehensive analysis of survival, limb strength, gait, respiratory function, neurological assessment, histology, vector biodistribution, transgene expression, and immune response was performed over a 9-month study period. Results indicate that systemic gene therapy was well tolerated, prolonged lifespan, and corrected the skeletal musculature throughout the body in a dose-dependent manner, defining an efficacious dose in this large-animal model of the disease. These results support the development of gene therapy clinical trials for XLMTM.
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    Voluntary wheel running complements microdystrophin gene therapy to improve muscle function in mdx mice
    Hamm, Shelby E.; Fathalikhani, Daniel D.; Bukovec, Katherine E.; Addington, Adele K.; Zhang, Haiyan; Perry, Justin B.; McMillan, Ryan P.; Lawlor, Michael W.; Prom, Mariah J.; Vanden Avond, Mark A.; Kumar, Suresh N.; Coleman, Kirsten E.; Dupont, J.B.; Mack, David L.; Brown, David A.; Morris, Carl A.; Gonzalez, J. Patrick; Grange, Robert W. (Cell Press, 2021-02-25)
    We tested the hypothesis that voluntary wheel running would complement microdystrophin gene therapy to improve muscle function in young mdx mice, a model of Duchenne muscular dystrophy. mdx mice injected with a single dose of AAV9- CK8-microdystrophin or vehicle at age 7 weeks were assigned to three groups: mdxRGT (run, gene therapy), mdxGT (no run, gene therapy), or mdx (no run, no gene therapy). Wildtype (WT) mice were assigned to WTR (run) and WT (no run) groups.WTRandmdxRGTperformed voluntary wheel running for 21 weeks; remaining groups were cage active. Robust expression of microdystrophin occurred in heart and limb muscles of treated mice. mdxRGT versus mdxGT mice showed increased microdystrophin in quadriceps but decreased levels in diaphragm. mdx final treadmill fatigue time was depressed compared to all groups, improved in mdxGT, and highest in mdxRGT. Both weekly running distance (km) and final treadmill fatigue time for mdxRGT and WTR were similar. Remarkably, mdxRGT diaphragm power was only rescued to 60% of WT, suggesting a negative impact of running. However, potential changes in fiber type distribution in mdxRGT diaphragms could indicate an adaptation to trade power for endurance. Post-treatment in vivo maximal plantar flexor torque relative to baseline values was greater for mdxGT and mdxRGT versus all other groups. Mitochondrial respiration rates from red quadriceps fibers were significantly improved in mdxGTanimals, but the greatest bioenergetic benefit was observed in the mdxRGT group. Additional assessments revealed partial to full functional restoration in mdxGT and mdxRGT muscles relative to WT. These data demonstrate that voluntary wheel running combined with microdystrophin gene therapy in young mdx mice improved whole-body performance, affected muscle function differentially, mitigated energetic deficits, but also revealed some detrimental effects of exercise. With microdystrophin gene therapy currently in clinical trials, these data may help us understand the potential impact of exercise in treated patients.