Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item BIOLOGICAL AND FUNCTIONAL CHANGES IN SUPRASPINATUS MUSCLE AFTER ROTATOR CUFF TEAR(2017) Valencia, Ana Patricia; Spangenburg, Espen E; Hagberg, James M; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rotator cuff (RTC) tears impair upper limb mobility and affect 20% of the adult population. Unfortunately, surgical repair of major RTC tears often fails to restore shoulder function and has a high risk of re-tear. RTC tears induce irreversible, degenerative changes to the muscle that may hinder the recovery of shoulder function. Currently, very few studies have comprehensively assessed RTC muscle function, thus, little is known about which markers may be able predict changes in function after RTC tear. In this dissertation, I present three studies designed to systemically determine the impact of a RTC tear on contractile function of the supraspinatus (SS), the muscle most commonly affected in the RTC. In study #1 I developed a novel method to test in vivo SS contractile function using animal species common to RTC research. In study #2, I found that the SS exhibited a 30% loss in force prior to onset of muscle atrophy after acute RTC tear using the rat model. The initial loss of force was associated with a decrease in the size and continuity of the neuromuscular junction (NMJ). The SS muscle was also more susceptible to injury, which was associated with a reduction in collagen packing density. Therefore, SS size is not the strongest predictor of force output with acute RTC tears. In addition, the increased susceptibility to injury could compound the dysfunction already apparent in the SS muscle after RTC tear. In study #3, I found that the rabbit model experienced a 40% loss of force after 6 weeks of RTC tear that persisted at 12 weeks. Using a number of different in vivo and ex vivo imaging approaches I found the degree of fatty infiltration (FI) to be the strongest predictor of muscle force production after RTC tear. Surprisingly, the data suggested that muscle atrophy only explained the loss in force in torn muscles when little to no FI was present. Therefore, FI is a prognostic marker for muscle weakness after RTC tear, and can help clinicians predict the force generating capacity of the SS for surgery and rehabilitation decision-making. Results from both studies found that SS contractile function was significantly impaired after RTC tear, and identified measureable markers beyond muscle atrophy that were associated with the loss in muscle force that may act as potential therapeutic targets to improve functional outcomes after RTC tear.Item Association between increased hepatic lipid storage and impaired hepatic mitochondrial function in ovariectomized mice(2012) Valencia, Ana Patricia; Spangenburg, Espen E; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Reduced ovarian function is associated with development of the metabolic syndrome (MetS). Increased risk for MetS is strongly linked to hepatic metabolic dysfunction. However, at this time few studies have examined metabolic function of hepatic tissue under conditions of reduced ovarian function. The purpose of this study was to determine if ovariectomy (OVX) impaired hepatic mitochondrial function and its potential association with sirtuin (SIRT) function. Female C57BL/6 mice were divided into two groups (SHAM, OVX). Hepatic mitochondrial function was measured by assessing oxygen consumption, reactive oxygen species (ROS) production, and mitochondrial protein content. In addition, mitochondrial acetylation status and SIRT protein content was determined. The OVX group exhibited increased ROS production compared to the SHAM group. However, no differences were detected in oxygen consumption, mitochondrial protein content, acetylation status, or total SIRT content between groups. The data shows that ovariectomy increases mitochondrial ROS production, which suggests a novel mechanism to consider.