Browsing by Subject "Duchenne Muscular Dystrophy"
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Item Acute contraction-induced strength loss, muscle inexcitability and recovery after exercise in males with Duchenne muscular dystrophy(2020-11) Trost, JoyceannThis dissertation had three objectives with the overall goal to explore contraction-induced strength loss and recovery in males with Duchenne muscular dystrophy (DMD) specifically to: 1) evaluate a novel protocol, combining voluntary and evoked contractions to measure strength and excitability of wrist extensor muscles, for safety, feasibility, reliability and discriminant validity for males with DMD and aged-matched controls, 2) explore strength loss and muscle fiber inexcitability contribution to strength loss after submaximal isometric contractions in males with DMD, and. 3) determine the recovery of strength and muscle excitability immediately following contraction-induced force loss in males with DMD. Through the literature review, I discovered a need for a reliable and valid measurement protocol of muscle contractile function that could be used for DMD across all disease levels. Several measures for walking and upper extremity function are currently used to measure outcomes during clinical trials. However, none of the current measurements for DMD incorporate a way to quantitatively measure both voluntary and evoked strength along with muscle excitability over disease progression or in response to an intervention. The key to the assessment and protocol design needed to be feasibility and safety for boys and men with DMD at different stages of the disease process. I was able to design and evaluate a novel protocol, combining voluntary and evoked contractions to measure strength and excitability of wrist extensor muscles for safety, feasibility, reliability and discriminant validity between males with DMD and controls (Chapter 3). Wrist extensor muscle strength and excitability were assessed in males with DMD (N=10; mean 15.4 [SD 5.9] years) (Brooke 1-6) and age-matched healthy male controls (N=15; mean 15.5 [SD 5.0] years). Torque and EMG measurements were analyzed under maximum voluntary and stimulated conditions at two visits. I discovered that our protocol of multiple maximal voluntary contractions (MVC) and evoked twitch contractions was feasible and safe, with 96% of the participants able to complete the assessment protocol maintaining >93% strength both for DMD and controls (P≥0.074). Reliability was excellent for voluntary and evoked measurements. Torque, EMG and timing of twitch onset measurements discriminated between DMD and controls (P<0.001). This first part of the study demonstrated a useful protocol for measuring skeletal muscle function in clinical trials in males with DMD across various ages and disease levels. The second part of the study addressed in the context of a neuromuscular disease the concern of injury to dystrophic deficient skeletal muscle during and after repeated contractions (exercise) that result in acute strength loss. I knew that a feature of dystrophin-deficient skeletal muscle in the mdx mouse model was a hypersensitivity to strength loss from eccentric exercise due to fibers becoming unexcitable. I wanted to explore how this feature translated to humans lacking dystrophin. We hypothesized that there would be no difference in strength loss during exercise and that males with Duchenne muscular dystrophy (DMD) would have more significant impairment in muscle excitability corresponding with a loss of strength than age-matched controls (Chapter 4). Males with DMD and a group of age-matched controls performed a sub-maximal voluntary isometric wrist extensor exercise protocol until 55% of maximal voluntary contraction (MVC) could no longer be sustained. Voluntary and evoked force and EMG were accessed before, during, and after exercise. There was a significant interaction (time*group) (p<0.001) for MVC torque during exercise, suggesting that the two groups were different in how they reached muscle fatigue. No difference was measured between groups in MVC torque decrement at the time of exercise cessation (by design). Evoked twitch torque decrement was 34% for DMD and 36% for control with no group*time interaction observed (p=0.834). Muscle excitability contributed to the evoked torque variance in DMD (76%) and control (59%). The groups were not different in RMS EMG decrement (P=0.986) or M-wave decrement (P=0.911) during exercise, which does not support our hypothesis that the DMD groups had a more considerable decline in muscle excitability with fatigue during exercise. Lastly, the recovery of both strength and muscle excitability was explored and compared between groups. The DMD group recovered MVC baseline strength by 10 minutes post-exercise (P=0.530) and evoked torque by 5 minutes (P=0.266). In contrast, controls were still different from MVC and evoked torque baseline at 15 minutes after exercise (P<0.002). Strength loss from submaximal intermittent isometric exercise does not result in more significant impairment of muscle excitability is transient, and recovers faster in males with DMD than controls, suggesting a different mechanism of peripheral fatigue between the groups. The work contained in my dissertation begins to address the fear of exercise that has been a common concern for individuals with DMD and will contribute to knowledge of evidence-based exercise prescription in the future.Item Duchenne muscular dystrophy and extraocular muscle: a potential sparing mechanism with therapeutic implications.(2009-10) Kallestad, Kristen MarieThis project investigates the role of extraocular muscle (EOM) progenitor cells in sparing the muscles from pathology associated with Duchenne Muscular Dystrophy (DMD). Mouse models of muscular dystrophy and wild type mice were analyzed by flow cytometry and cell culture for the size, heterogeneity and functional characteristics of stem and satellite cell populations of EOM and limb muscles. EOM have a 5-fold increase in progenitor cells compared with limb muscles. Additionally, an enriched population of cells expressing the stem cell marker CD34 but no other typical stem or differentiation markers (Sca-1, CD45, CD31, pax-7, m-cadherin) exists in the EOM. We refer to this population as EOMCD34 cells. The EOMCD34 cells are present in developing muscle, but only maintained in adult EOM, surviving in very aged animals. The EOMCD34 cells are also present in EOM of DMD model animals, but not their limb muscles. EOMCD34 cells are resistant to apoptosis and proliferate in vivo. Finally, these cells are capable of forming myotubes in vitro. The EOMCD34 cells may represent a primitive stem cell population, which is capable of maintaining life-long pools of myogenic precursor cells. Since EOM continuously remodel throughout life, unlike other skeletal muscle, it is logical that the proliferative potential of their precursor cells is enhanced. Since one proposed mechanism of DMD muscle destruction is exhaustion of the reparative progenitor cells, the EOMCD34 cells might prove useful for myoblast transplant therapies for DMD.Item The Effects Of Beta2-Adrenergic Receptor Genotype On Cardiopulmonary And Body Composition Measures In Duchenne Muscular Dystrophy(2017-01) Kelley, EliObjective: Duchenne muscular dystrophy (DMD) is an inherited x-link disease caused by the deletion of the dystrophin gene. DMD is characterized by progressive muscle weakness and degeneration of skeletal, cardiac and respiratory muscles resulting in severe functional impairment. The beta-2 adrenergic receptor (ADRB2) plays a functional role in muscle size, strength and regeneration through regulation of multiple downstream mechanisms. Multiple polymorphisms of the ADRB2 have been identified as including a glycine (Gly) for arginine (Arg) substitution at amino acid 16. This polymorphism (Gly16) has been shown to have higher receptor density on lymphocytes, be more resistant to receptor down regulation, and have improved lung function. The objective of this study was to determine the influence, if any, of ADRB2 genotype on body composition and cardiopulmonary health outcomes in DMD. Methods: Nineteen patients were recruited through the University of Minnesota Fairview Clinic. DNA was collected via buccal swabs and analyzed for ADRB2 genotype. Medical records were then accessed to obtain retrospective data on age of loss of ambulation and start of corticosteroid treatment, DEXA, and cardiopulmonary measures when available. Results: There were no differences between genotype groups in age of loss of ambulation (AMB) or start of corticosteroid treatment (STER) (AMB = 11.3 ± 1.09, 12 ± 0.71, STER = 8.67 ± 3.68, 7.22 ± 2.23 for Arg and Gly respectively). Additionally, there were no differences between genotype groups in age, height, weight, BMI, or BSA (age = 11.9 ± 4.1, 11.3 ± 3.5, height = 140.8 ± 18.7, 143.1 ± 19.7, weight = 47.7 ± 22.8, 45.7 ± 19.3, BMI = 23.6 ± 18.6, 21.5 ± 5.5, and BSA = 1.3 ± 0.39, 1.3 ± 0.33 for Arg and Gly respectively). Further, there were no differences between genotype groups in L1-L4, TBD, LBM, or LBM/BSA (L1-L4 = 0.66 ± 0.13, 0.69 ± 0.09, TBD = 0.69 ± 0.12, 0.64 ± 0.01, LBM = 62.6 ± 16.1, 65.5 ± 17.1, and LBM/BSA = 56.1 ± 29.6, 65.5 ± 17.1 for Arg and Gly respectively). There was a statistically significant difference between genotype groups for FEFmax at the patients’ youngest age (FEFmax = 77.1 ± 14.1, 97.4 ± 16.9 for Arg and Gly respectively). There may also have been a clinically significant difference between genotype groups for FVC and FEV1 at the patients’ youngest age (FVC = 85.1 ± 18.5, 94.5 ± 15.7, and FEV1 = 84.7 ± 16.1, 99.1 ± 18.9 for Arg and Gly respectively). However, there were no differences between genotype groups for FEFmax, FVC, and FEV1 at the patients’ mid-point and oldest age nor were there differences for MEP and MIP at any age. Furthermore, there were no differences between genotype groups for any of the cardiac measures at any age. Discussion: These data suggest the ADRB2 may play a role in an improved functional pulmonary capacity but does not influence body composition or cardiac measures. This suggests early intervention with ADRB2 treatment may serve to preserve functional pulmonary capacity and health outcomes in DMD.Item Engineering functional muscle tissues and modeling muscular diseases using myogenic cells differentiated from human pluripotent stem cells or human fibroblasts(2019-09) Xu, BinThe advances in efficient generation of myogenic cells using human pluripotent stem cells (hPSCs) offer unlimited opportunities for translational applications, such as the study of muscle development and diseases, drug screening, and regenerative medicine. Functional muscle constructs tissue-engineered from these myogenic cells prove excellent tools for those applications. However, these myogenic cells are developmentally immature, and the protocol to derive them is time-consuming. In this thesis, we aim to model muscle diseases and to improve the maturity of muscles using hPSC-derived myogenic cells. We also develop transdifferentiation as an alternative method to obtain myogenic cells more quickly. We modeled Duchenne Muscular Dystrophy (DMD), a genetic disorder leading to muscle wasting and death. We fabricated nanogrooved substrate immobilized with muscle basement membrane mimicking materials and discovered that non-diseased and DMD muscles derived from hPSCs exhibit substantial differences in cell alignments on nanogrooved substrates when these substrates are functionalized with laminin. To improve the maturity of the muscles, we generated hPSC-derived muscle constructs in customized devices and discovered that addition of the endothelial growth medium-2 supplements in the first two weeks of differentiation leads to substantial increases in contractile forces. These constructs show wider myotubes and higher gene expression levels for skeletal muscle-specific myosin heavy chain isoforms, suggesting that a more mature differentiation stage of the cells. Those tissue-engineered constructs were also used to validate the screening of small molecules for enhancing the function and maturation during myogenic differentiation. We found a significant increase in contractile force generation when treated with a cocktail of four small molecules (SB431542, DAPT, Dexamethasone, and Forskolin). To explore an alternative approach to generating functional human muscles more quickly, we chose to transdifferentiate normal human dermal fibroblasts (NHDF) transduced with inducible MyoD. We demonstrated that myogenic transdifferentiation of NHDF could be enhanced by using small molecules CHIR99021 and DAPT when coupled with MyoD induction. We further proved that muscle constructs engineered from transdifferentiated NHDF can generate contractile forces in response to electrical stimuli after 2-week 3D culture. Temporal expression of MyoD in the first week boosts twitch and tetanic forces significantly, and small molecule (CHIR and DAPT) treatment could further improve force generation.Item Preclinical Models of Dystrophic Cardiomyopathy and Therapies for the Dystrophic Heart(2019-08) Meyers, TatyanaMuscular dystrophies are a diverse group of genetic diseases characterized by progressive muscle weakness and deterioration with wide variability in severity and affected muscle groups. Some of the more devastating muscular dystrophies result from the absence of components of the dystrophin-glycoprotein complex (DGC). Disruption of the DGC compromises sarcolemmal integrity in striated muscle, leading to increased myocyte injury and death. These forms of muscular dystrophy often feature both skeletal muscle wasting and marked cardiomyopathy. The most common of these muscular dystrophies is Duchenne muscular dystrophy (DMD), caused by mutations in the dystrophin gene that result in the loss of this large membrane-stabilizing protein. DMD features a childhood onset and leads to premature death at ages ranging from the teens into the 30’s, often from cardiorespiratory failure. DMD is an X-linked disorder, and is usually inherited from carrier mothers who also face a high risk of cardiomyopathy. Sarcoglycanopathies are a rarer group of autosomal recessive Limb Girdle muscular dystrophies (LGMD) that arise from mutations in the sarcoglycan genes, sometimes leading to an aggressive Duchenne-like disease course in patients of both sexes. The heterotetrameric sarcoglycan complex is a key component of the DGC, and its loss induces significant myocyte pathology that can trigger childhood disease onset and premature death. Muscles and hearts devoid of the sarcolgycan complex display hallmark dystrophic pathology, including muscle wasting, loss of ambulation, and a high incidence of lethal dilated cardiomyopathy. The work presented here is driven by efforts to quantify the susceptibility of dystrophic hearts to acute injury caused by increased cardiac workload, and to understand the contribution of angiotensin signaling to dystrophic heart injury. It describes the following key findings: 1) angiotensin receptor blockers (ARBs) can markedly reduce acute injury in dystrophin-null and sarcoglycan-null mouse hearts; 2) female mouse hearts lacking the sarcoglycan complex are significantly protected compared to male hearts, and do not derive the same benefit from ARBs; and 3) mosaic expression of dystrophin in the heart results in elevated vulnerability to injury that is modulated by factors besides dystrophin levels. This work suggests that angiotensin signaling plays an exaggerated role in dystrophic heart injury through mechanisms that may be sex-dependent, and that earlier and more consistent use of angiotensin-blocking therapies has the potential to limit dystrophic cardiomyopathy. Furthermore, it reveals that dystrophic hearts may continue to show significant vulnerability in the context of gene therapies that restore partial dystrophin expression.