Browsing by Subject "skeletal muscle"

Now showing 1 - 4 of 4
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    Body Composition Assessment and Protein Recommendations In Clinical Populations
    (2020-03) Price, Kathleen
    Malnutrition, sarcopenia, cachexia, and frailty are terms that rely on muscle assessment, and they all have ongoing refinement in their definition and diagnostic criteria as well as significant clinical overlap. Uncertainties in how best to assess muscle objectively have led to subjectivity in their diagnoses, leading to confusion and misuse of these terms throughout the literature. Additionally, protein recommendations in the hospital which serve as the foundation for nutrition intervention to prevent or treat muscle loss are based on nitrogen balance studies that are non-specific and have known limitations. The clinical Registered Dietitian Nutritionist (RDN) is well-positioned to diagnose, track, and treat muscle wasting disorders in clinical populations, and improvement in both the assessment of muscle as well as protein recommendations to prevent or treat muscle loss will advance the clinical utility of RDN. A detailed look at the history of malnutrition in the medical literature indicates that body composition has long been known to be of critical importance to its diagnosis, and current efforts are underway to utilize body composition technologies to assess muscle in acute care settings. Computed tomography data can indicate best-treatment methods for individuals as well as those who would benefit from targeted nutrition intervention, and this dissertation discusses its utility for predicting outcomes in chronic pancreatitis patients undergoing a total pancreatectomy with islet autotransplantation and heart failure patients undergoing a heart transplant. Finally, this dissertation demonstrates that a multi-step feeding protocol of stable isotope amino acids is feasible to characterize whole body protein kinetics over a single study day to ultimately improve protein recommendations in patients with head and neck cancer. Ultimately, loss of muscle is known to worsen clinical outcomes and increase cost, and advancements in both muscle assessment using body composition technologies and protein recommendations using stable isotope amino acid tracers to prevent or treat muscle loss will improve the ability of the clinical RDN to positively impact patient prognosis.
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    Engineering functional muscle tissues and modeling muscular diseases using myogenic cells differentiated from human pluripotent stem cells or human fibroblasts
    (2019-09) Xu, Bin
    The 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.
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    Estrogen Deficiency-Induced Phosphoproteomic Alterations In Skeletal Muscle Of Female Mice
    (2022-08) Peyton, Mina
    Dynapenia, the age-related loss of muscle strength without the loss of muscle mass, significantly impacts the physical function and overall quality of life in older adults, thereby decreasing their health span. Skeletal muscle strength loss has been shown to occur earlier and is greater in aging females than males. Furthermore, clinical and preclinical studies have measured associations between skeletal muscle strength loss and the age at which circulating estrogen begins to decline in females. Despite copious years of skeletal muscle research, the molecular mechanisms underlying muscle strength loss in aging females remain poorly understood. Age-related protein phosphorylation changes have been reported in skeletal muscle of males, and protein phosphorylation alterations have been shown in cardiac muscle across age and sex. However, the extent and magnitude of these changes in the skeletal muscle phosphoproteome of females in response to estrogen deficiency have yet to be determined. This dissertation aims to further our molecular understanding of how estrogen deficiency impacts skeletal muscle function (i.e., the force-generating capacity of muscle) in females by investigating the skeletal muscle phosphoproteome using high-throughput mass spectrometry coupled with bioinformatic analyses and computational modeling. First, using an ovariectomy model, we determined the physiological remodeling of the skeletal muscle phosphoproteome associated with estrogen deficiency. Next, due to the controversies related to using an ovariectomy model to implicate estrogen-related changes in aging females and because the primary function of skeletal muscle is contraction (i.e., molecular force generation), we sought to discern estrogen deficiency-associated protein phosphorylation alterations in contracted skeletal muscle via evoked electrical stimulations in ovariectomized and natural aging ovarian-senescent female mice compared to their respective controls. Examining the phosphoproteomic alterations in resting, non-contracted, and contracted skeletal muscle of estrogen-deficient females, we identified novel phosphosites, candidate kinases and phosphatases, as well as illuminated key pathways that are sensitive to estrogen levels that may contribute to the loss of skeletal muscle strength. This dissertation provides new avenues for further research and novel targets for the development of therapeutics and interventions to mitigate the loss of skeletal muscle strength in females.
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    Satellite cell maintenance and strength recovery after injury: the impact of estradiol signaling
    (2021-12) Larson, Alexie
    My dissertation work established a crucial role for estradiol (E2) in the recovery of muscle strength after injuries and maintenance of the satellite cell population under homeostatic conditions (Chapters 3 & 4). I demonstrated that E2 deficiency impairs the adaptive potential of skeletal muscle after repeated injuries, indicated by blunted muscle mass and strength, and that the reduction in satellite cell number with E2 deficiency likely contributes to this impairment (Chapter 3). With the ovariectomy mouse model and a transgenic female mouse model that specifically ablated ER⍺ in satellite cells, I demonstrated that E2 is the hormone that drives the loss of satellite cells as opposed to any other ovarian hormone, and that the loss of E2 or its receptor for only 14 d impairs satellite cell maintenance (Chapter 4). Mechanistically, I showed that impaired satellite cell maintenance caused by E2 deficiency involves altered satellite cell cycle progression, kinetics, proliferation, and differentiation (Chapter 4). The work of my dissertation highlights a novel mechanism for E2 in maintaining the satellite cell population in female mice through appropriate satellite cell cycle progression. My findings, accompanied by future studies that identify E2-sensitive molecular pathways in satellite cells, are instrumental for developing effective therapies to preserve efficient skeletal muscle regeneration and improve overall skeletal muscle health of post-menopausal women.