Understanding the regulatory mechanisms controlling utrophin A expression at the sarcolemma of dystrophic muscles will facilitate the development of therapeutic strategies to ameliorate the pathophysiological features of Duchenne Muscular Dystrophy (DMD). The main goal of this study was to characterize the regulation of utrophin A IRES activity using a transgenic mouse model expressing the utrophin A 5’UTR bicistronic reporter and to identify trans-acting factors that could mediate IRES activity and endogenous expression of utrophin A. We found that utrophin A IRES activity is specifically expressed in skeletal muscles. Moreover, we identified eEF1A2 as a muscle-specific trans-acting factor that can interact with utrophin A and mediate IRES-dependent translation of utrophin A. Finally, we showed that eEF1A2 mediates endogenous utrophin A expression and localization in skeletal muscle. Identifying pharmacological compounds that would specifically target eEF1A2 and increase endogenous levels of utrophin A expression could serve as a drug-based therapy to treat DMD.

Since a significantly greater percentage of body weight is supported by the non-paretic limb following stroke, a greater amount of fatigue may be present during daily activities. This may affect the ability of these individuals to maintain a stable upright posture. The presence of falls following a stroke has been attributed in part to this asymmetrical stance post-stroke. Therefore the purpose of this study was to assess the effect of quadriceps muscle fatigue on bi-pedal posture in individuals who had a stroke and an age-matched control group. Although individuals after stroke displayed greater postural sway under the paretic limb than the non-paretic limb or control subjects, results of this study show that sustaining an isometric knee extension of the non-paretic limb induces changes in postural control for individuals after stroke, but that these changes do not markedly differ from those of healthy age-matched controls.

The Na+-K+-ATPase (pump) is a transmembrane, multi-subunit (α and β) protein that is expressed in all cells, and particularly in skeletal muscle cells. In one cycle, it pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell at the expense of 1 ATP molecule. This enzyme is responsible for maintaining muscle cell excitability. This is of particular importance during contractile activity, when the flux of Na+ and K+ across the cell membrane is high. The activity of the Na+-K+-ATPase is highly regulated and very responsive to hormonal stimuli. Previous research has shown that 20-30 min insulin exposure in vivo induces the translocation of pumps from intracellular stores to the plasma membrane. However, no study has examined the catalytic properties of this enzyme in response to short insulin exposures. The objective of this study was to investigate the response of the Na+-K+-ATPase to short insulin incubation in vitro in muscles of different fibre type. It was hypothesized that the short insulin treatment would result in an increase in pump activity, not only through translocation but also increased intrinsic activity. Using an in vitro model, rat soleus (Sol), red gastrocnemius (RG), and white gastrocnemius (WG) muscle homogenates were incubated at 37°C for 5 min with and without 75μM insulin (Ins). Next, in order to separate mechanisms of translocation and intrinsic activation, the plasma (SLP) and endosomal (EN) membranes were separated through a fractionation procedure. This allowed the investigation of insulin-induced increases in intrinsic activity in SLP and EN fractions of Na+-K+-ATPase; SLP and EN (non-treated) membranes were incubated at 37°C for 5 min with and without 75μM insulin. Lastly, muscle homogenates were insulin-treated for 5 min at 37°C with 625μM insulin prior to fractionation. These SLP and EN fractions (insulin-treated) were then incubated at 37°C for 5 min with and without 75μM insulin. Na+-K+-ATPase maximal activity (Vmax, mmol•mg prot-1•h-1) and km (substrate affinity), α2 content, and tyrosine phosphorylation (Tyr-P) were probed. It was found that insulin increased Vmax (P<0.05) in Sol and RG, but not WG, homogenates (Con vs Ins, Sol=221±17 vs 256±21; RG=190±14 vs 256±18; WG=104±4.6 vs 99±1.8). In non-treated fractions, insulin increased Vmax (P<0.05) in Sol and RG SLP fractions (Con vs Ins, Sol=1710±186 vs 1970±231; RG=1476±128 vs 1655±139). A main effect, Con<Ins (P<0.05) was observed in non-treated WG SLP. Insulin also increased Vmax in non-treated RG EN (Con vs Ins, 246±38 vs 304±43). In insulin-treated fractions, insulin increased Vmax¬ in RG SLP only (Con vs Ins, 1145±119 vs 1426±150). Increased Vmax was not observed in insulin-treated fractions when compared to non-treated fractions. No evidence of translocation or increased Tyr-P was detected with insulin treatment via α2 Western blotting. Short insulin exposure induced increases in Na+-K+-ATPase activity, and these increases were due to stimulation of intrinsic activity and not due to translocation.

Research has uncovered an essential role of proper abdominal muscle function in ensuring the health and integrity of the lumbar spine. The anatomical arrangement of the abdominal musculature (rectus abdominis, external oblique, internal oblique, transverse abdominis) and intervening connective tissues is unique in the human body. Despite the hypothesized importance and uniqueness of the abdominal muscles, very little research has been directed to understanding their role from a neuro-mechanical standpoint. Thus, this thesis was designed to study the neuro-activation and mechanical characteristics of the abdominal musculature and connective tissues, with a specific focus on torso stiffening mechanisms. Several experiments were performed and unified around this theme. The first study explored the fundamental relationship between EMG muscle activation recordings and the moments generated by the trunk musculature. This study was novel in that investigation of the abdominal musculature was augmented with consideration of antagonist muscle co-activation. The main finding was that the EMG-moment relationships were quite similar in both the abdominal and extensor muscle groups; however, the form of this relationship differed from that often reported in the literature. Specifically, consideration of antagonist muscle moments linearized the EMG-moment relationship of the agonist muscle groups. Once this activation-moment relationship had been established, the next line of questioning explored the association between torso muscle activation, driven through the abdominals, and torso stiffness. Two studies addressed this issue: the first examined the intrinsic resistance of the torso to bending in the flexion, extension, and lateral bend directions, while varying the levels of torso muscle activation; the second examined the response of the trunk to perturbations while varying the levels of torso muscle activation under the presence of limited reflexes. The first of these two studies demonstrated a rise in trunk stiffness as muscle activation increased over the lower 40% of range of motion. At greater ranges of motion in flexion and lateral bend the trunk appeared to become less stiff as the musculature contracted to higher levels. The latter study revealed substantial spinal displacements in response to trunk perturbations, indicating that in the absence of reflex activity, the stiffness produced by muscular contraction may be inadequate to stiffen the torso to prevent damage to spinal tissues. The fourth study was designed to enable in-vivo observation of abdominal muscle and connective tissue deformation using ultrasound imaging. During relatively simple abdominal contractions, the oblique aponeurosis demonstrated surprising deformation patterns that often exhibited the characteristic of a negative Poisson’s ratio. This was hypothesized to be facilitated by the composite laminate arrangement of the abdominal wall, whereby the loose connective tissues separating layers of collagen fibres may allow for separation of adjacent layers, giving the appearance of structural volume expansion. Further, a lateral displacement of the rectus abdominis muscle was noted in a majority of contractions, highlighting the dominance of the laterally oriented forces generated by the oblique muscles. The final study questioned, at a basic level, the nature of the anatomical arrangement of the abdominal muscle-connective tissue network. Examining the contraction of the rat abdominal wall uncovered the transfer of muscularly generated force and stiffness through the connective tissues binding the layered muscles. This suggests a functionality of the abdominal wall as a composite laminate structure, allowing substantial multi-directional stiffness to be generated and transmitted around the torso, thereby enhancing the ability to effectively stabilize the spine.

Results: Age of gymnasts was positively associated with BMD at all measured sites (p <0.001; r=0.62-0.68). Weight was positively associated with BMD at all measured sites (p <0.001; r=0.82-0.90). Lean body mass was positively associated with BMD at all measured sites (p <0.001; r=0.74-0.87). Body fat percentage was positively associated with BMD at all measured sites (p <0.001-p=0.01; r=0.39-0.54). However, calcium intake was not significantly associated with any of the BMD sites. Sunlight exposure and indirect estimates of vitamin D were not significantly associated with any of the BMD sites; all r-values indicated a weak positive association with BMD. Of the gymnasts who had experienced menses (n=15), those with regular menstrual periods (n=8) had significantly higher BMD values at the arm, leg, trunk, rib, and spine, and total body than those who did not have regular menstrual periods (n=7). There was no significant difference in BMD for gymnasts who had regular periods at the pelvis. A regression analysis was performed. The predictors total BMD values from the regression equation were the following: regular menses, height, weight, percent kilocalorie requirement consumed from predicted kilocalorie needs, calcium intake with supplements, lean body mass, hourly deficits >300 kilocalories from predicted kilocalorie needs, and hourly surpluses >300 kilocalories from predicted kilocalorie needs.

The Na+-K+-ATPase (pump) is a transmembrane, multi-subunit (α and β) protein that is expressed in all cells, and particularly in skeletal muscle cells. In one cycle, it pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell at the expense of 1 ATP molecule. This enzyme is responsible for maintaining muscle cell excitability. This is of particular importance during contractile activity, when the flux of Na+ and K+ across the cell membrane is high. The activity of the Na+-K+-ATPase is highly regulated and very responsive to hormonal stimuli. Previous research has shown that 20-30 min insulin exposure in vivo induces the translocation of pumps from intracellular stores to the plasma membrane. However, no study has examined the catalytic properties of this enzyme in response to short insulin exposures. The objective of this study was to investigate the response of the Na+-K+-ATPase to short insulin incubation in vitro in muscles of different fibre type. It was hypothesized that the short insulin treatment would result in an increase in pump activity, not only through translocation but also increased intrinsic activity. Using an in vitro model, rat soleus (Sol), red gastrocnemius (RG), and white gastrocnemius (WG) muscle homogenates were incubated at 37°C for 5 min with and without 75μM insulin (Ins). Next, in order to separate mechanisms of translocation and intrinsic activation, the plasma (SLP) and endosomal (EN) membranes were separated through a fractionation procedure. This allowed the investigation of insulin-induced increases in intrinsic activity in SLP and EN fractions of Na+-K+-ATPase; SLP and EN (non-treated) membranes were incubated at 37°C for 5 min with and without 75μM insulin. Lastly, muscle homogenates were insulin-treated for 5 min at 37°C with 625μM insulin prior to fractionation. These SLP and EN fractions (insulin-treated) were then incubated at 37°C for 5 min with and without 75μM insulin. Na+-K+-ATPase maximal activity (Vmax, mmol•mg prot-1•h-1) and km (substrate affinity), α2 content, and tyrosine phosphorylation (Tyr-P) were probed. It was found that insulin increased Vmax (P<0.05) in Sol and RG, but not WG, homogenates (Con vs Ins, Sol=221±17 vs 256±21; RG=190±14 vs 256±18; WG=104±4.6 vs 99±1.8). In non-treated fractions, insulin increased Vmax (P<0.05) in Sol and RG SLP fractions (Con vs Ins, Sol=1710±186 vs 1970±231; RG=1476±128 vs 1655±139). A main effect, Con<Ins (P<0.05) was observed in non-treated WG SLP. Insulin also increased Vmax in non-treated RG EN (Con vs Ins, 246±38 vs 304±43). In insulin-treated fractions, insulin increased Vmax¬ in RG SLP only (Con vs Ins, 1145±119 vs 1426±150). Increased Vmax was not observed in insulin-treated fractions when compared to non-treated fractions. No evidence of translocation or increased Tyr-P was detected with insulin treatment via α2 Western blotting. Short insulin exposure induced increases in Na+-K+-ATPase activity, and these increases were due to stimulation of intrinsic activity and not due to translocation.

Research has uncovered an essential role of proper abdominal muscle function in ensuring the health and integrity of the lumbar spine. The anatomical arrangement of the abdominal musculature (rectus abdominis, external oblique, internal oblique, transverse abdominis) and intervening connective tissues is unique in the human body. Despite the hypothesized importance and uniqueness of the abdominal muscles, very little research has been directed to understanding their role from a neuro-mechanical standpoint. Thus, this thesis was designed to study the neuro-activation and mechanical characteristics of the abdominal musculature and connective tissues, with a specific focus on torso stiffening mechanisms. Several experiments were performed and unified around this theme. The first study explored the fundamental relationship between EMG muscle activation recordings and the moments generated by the trunk musculature. This study was novel in that investigation of the abdominal musculature was augmented with consideration of antagonist muscle co-activation. The main finding was that the EMG-moment relationships were quite similar in both the abdominal and extensor muscle groups; however, the form of this relationship differed from that often reported in the literature. Specifically, consideration of antagonist muscle moments linearized the EMG-moment relationship of the agonist muscle groups. Once this activation-moment relationship had been established, the next line of questioning explored the association between torso muscle activation, driven through the abdominals, and torso stiffness. Two studies addressed this issue: the first examined the intrinsic resistance of the torso to bending in the flexion, extension, and lateral bend directions, while varying the levels of torso muscle activation; the second examined the response of the trunk to perturbations while varying the levels of torso muscle activation under the presence of limited reflexes. The first of these two studies demonstrated a rise in trunk stiffness as muscle activation increased over the lower 40% of range of motion. At greater ranges of motion in flexion and lateral bend the trunk appeared to become less stiff as the musculature contracted to higher levels. The latter study revealed substantial spinal displacements in response to trunk perturbations, indicating that in the absence of reflex activity, the stiffness produced by muscular contraction may be inadequate to stiffen the torso to prevent damage to spinal tissues. The fourth study was designed to enable in-vivo observation of abdominal muscle and connective tissue deformation using ultrasound imaging. During relatively simple abdominal contractions, the oblique aponeurosis demonstrated surprising deformation patterns that often exhibited the characteristic of a negative Poisson’s ratio. This was hypothesized to be facilitated by the composite laminate arrangement of the abdominal wall, whereby the loose connective tissues separating layers of collagen fibres may allow for separation of adjacent layers, giving the appearance of structural volume expansion. Further, a lateral displacement of the rectus abdominis muscle was noted in a majority of contractions, highlighting the dominance of the laterally oriented forces generated by the oblique muscles. The final study questioned, at a basic level, the nature of the anatomical arrangement of the abdominal muscle-connective tissue network. Examining the contraction of the rat abdominal wall uncovered the transfer of muscularly generated force and stiffness through the connective tissues binding the layered muscles. This suggests a functionality of the abdominal wall as a composite laminate structure, allowing substantial multi-directional stiffness to be generated and transmitted around the torso, thereby enhancing the ability to effectively stabilize the spine.

Altered apoptotic signaling in skeletal muscle has been observed in a number of disease states associated with skeletal muscle atrophy. Therefore, understanding the mechanisms that lead to increased skeletal muscle apoptosis may help to prevent the atrophy associated with various diseases. Apoptosis repressor with caspase recruitment domain (ARC) is a potent anti-apoptotic protein that is able to inhibit apoptosis mediated by both the death-receptor and mitochondrial pathways. In addition, ARC has a unique distribution pattern and is highly expressed in terminally differentiated tissue such as skeletal muscle. To characterize the role of ARC in skeletal muscle morphology and apoptosis, soleus and plantaris muscles of 18 week-old ARC-deficient mice were excised and compared to those of age-matched wild-type littermates. While no differences were seen in muscle weights between genotypes, in the ARC KO animals, the cross-sectional area (CSA) of the soleus was smaller, while the CSA of the plantaris was larger. With respect to fiber type distribution, both muscles demonstrated a shift towards a faster myosin heavy chain expression pattern. For example, soleus muscles of ARC KO animals had significantly less type I fibers and more IIa fibers, while plantaris muscles had significantly less type IIa fibers, and more IIb fibers. In ARC KO animals, type I and IIa fibers were significantly smaller in the soleus, while type IIb fibers were larger in the plantaris. DNA fragmentation (a hallmark of apoptosis) was increased in the soleus, but not plantaris muscles of ARC KO animals. Surprisingly, activity of the proteolytic enzymes caspase-2, -3, -8, and -9, as well as calpains, was not different in either soleus or plantaris muscles. To determine whether a lack of ARC protein affects apoptotic signaling in skeletal muscle, the total expression of pro- and anti-apoptotic proteins were also assessed. In the soleus, no changes were observed in whole tissue AIF, cytochrome c, EndoG, and Smac. In the plantaris, there was no change in total muscle AIF; however, there were trends towards decreased cytochrome c, and increased Smac, as well as a significant decrease in EndoG ARC KO animals. No changes were observed in Bcl-2 and XIAP in the soleus; however, there were significant reductions in FLIP(s) and HSP70 content. In the plantaris, no changes were observed in anti-apoptotic protein content. Subcellular fractionation of red quadriceps for ARC KO mice revealed an increased Bax:Bcl-2 ratio in the isolated mitochondrial fractions. Furthermore, in cytosolic fractions of red quadriceps, AIF protein content was significantly increased in ARC KO animals. Conversely, no changes in apoptotic-related protein content were observed in any fractions from white quadriceps between groups. In agreement with these findings, isolated mitochondria from ARC-deficient animals were more susceptible to calcium induced swelling, as well as membrane potential loss compared to controls. Taken together, these results suggest that in slow-oxidative skeletal muscle of ARC-deficient mice there is increased apoptosis due to caspase-independent, mitochondrial-mediated apoptotic signaling. Furthermore, this study is the first to show ARC plays an important role in skeletal muscle morphology, as ARC KO mice have an altered skeletal muscle phenotype and morphology.

The somatosensory system has been implicated in the compensatory response of the nervous system to postural perturbations in humans and cats. The approach elicited - dubbed the Force Constraint Strategy - through a possible combined action of proprioceptive and cutaneous feedback, determines, and adjusts for, horizontal disturbances in various directions of a supporting surface. To understand the mechanisms underlying this strategy, we asked whether the response patterns of muscle proprioceptors correspond to those of electromyographic recordings (EMG) in the aforementioned Force Constraint experiments. The mechanical properties of the musculoskeletal system may also play a role in the restoration of stability. Thus, we also hypothesize that a proximal muscle would be relatively tightly tuned spatially whereas the distal muscle would exhibit a more diffuse spatial response distribution. To this end we selected the medial gastrocnemius (MG) and biceps femoris (BF) muscles to serve as our proximal and distal models respectively. Cats anesthetized using pentobarbital were set in a stereotaxic frame with the right leg positioned on a servo-controlled platform. The platform was shifted horizontally in 16 different directions according to a ramp-and-hold waveform. Intra-axonal recordings of activity from Ia afferents of BF and MG muscles were taken. Results indicate that the strategy makes use of information from the muscle proprioceptors. However, there is no differential response in tuning breadth with respect to muscle architecture. By characterizing the role of muscle proprioceptors in the mediation of corrective responses to perturbations of balance and stability, the results from this experiment can be used to verify biomechanical models, as well as further elucidate the underlying mechanisms of motor control.

Thesis (M.Sc.)--York University, 2006. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR29615