No description available.

Typescript (Photocopy) / Copy of published paper co-authored by author, in back / Bibliography: leaves 209-228 / xiv, 232 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1989

It has been proposed that intermittent exercise can differentially affect mitochondrial responses to training, with training volume being more important than intensity for increasing skeletal muscle mitochondrial content and with intensity playing a greater role in mitochondrial respiration. To test this hypothesis, we examined markers of skeletal muscle mitochondrial content and respiration in response to two different interval training protocols performed using single-leg cycling, which permitted a within-subjects design. Ten healthy active adults [6 males / 4 females, 22±4 y, peak oxygen uptake (VO2peak) = 42±4 ml/kg/min] were recruited. Each leg was randomized to either a HIIT [4 × (5 min at 65% Wpeak and 2.5 min at 20% Wpeak)] or SIT [4 x (30-s “all-out” sprints and 4 min active recovery)] protocol and completed three exercise sessions/wk over 4 wk for a total of 12 exercise sessions/leg. The mean work performed during each session was 133±32 and 44±8.0 kJ for HIIT and SIT respectively, and the average workload during intervals was 95±25 W and 322±77 W for HIIT and SIT respectively. Citrate synthase (CS) maximal activity increased compared to baseline after training interventions, with the change being greater after SIT vs HIIT (42±25% vs 16±13%, interaction p=0.01). COXIV protein content and succinate-supported state 3 were unchanged. Single-leg VO2peak and time to exhaustion (TTE) increased to a similar extent in both HIIT and SIT (main effect of time, p<0.05). These data suggest that, in contrast to what has been proposed by others, training intensity is more important than volume for increasing mitochondrial content during short-term interval training in human skeletal muscle. / Thesis / Master of Science in Kinesiology / Mitochondria are an important component of cells that use oxygen to convert fuels such as sugars and fats into energy. One of the factors that determines the amount of mitochondria in skeletal muscle is physical activity. Aerobic exercise training can be performed over a range of intensities, from relatively easy to very hard, and in an intermittent or continuous manner. This thesis examined the effect of short-term, intermittent exercise training performed at two different intensities on the content of mitochondria in human skeletal muscle. It found that both high- intensity interval training (HIIT) and sprint interval training (SIT) increased mitochondrial content. The increase was greater after SIT compared to HIIT, even though the total “dose” or amount of exercise was lower in the former compared to the latter. These results suggest that intensity is an important determinant of skeletal muscle remodelling induced by intermittent exercise in humans.

No description available.

INTRODUCTION: Following damaging stimuli, skeletal muscle exhibits coordinated interplay between intra- and extra-cellular processes resulting in satellite cell (SC) recruitment. SCs are known to play a central role in muscle plasticity post-injury by differentiating into myoblasts (MBL) and fusing with damaged tissue to donate myonuclei. Yet, their role within skeletal muscle remodeling through paracrine signaling remains to be fully elucidated. Thus, the purpose of this project was two-fold: 1) develop an in vitro model of MBL intercellular communication following myotube damage and 2) to determine if MBL proximity alone is adequate for improving tissue repair and reducing cellular stress during recovery. METHODS: C2C12 myotubes were exposed to 1 hour of electrical pulse stimulation (EPS) with 15Hz pulse for 5s and 5Hz pulse for 5s, separated by a 5s break. Myotubes were then introduced to non-electrically stimulated (NS) MBL adhered to a porous cell insert to allow paracrine signaling and samples were collected at varying timepoints post-EPS. RESULTS: EPS induced Z line sarcomeric disorganization and creatine kinase release into the cell culture media, which was mitigated in MBL+ groups (p<0.05). A significant main effect of MBL exposure was observed in EPS myotubes where MBL+ myotubes had greater Hsp70 gene expression, calpain 3 protein and gene expression, and t-ACC, p-ACCSer79, t-ULK, p-ULKSer555 protein expression than MBL- myotubes when recovering from EPS (p<0.05). A main effect of time was observed where B-dystroglycan and p-mTORSer2448 protein expression decreased in the EPS myotubes, and myotube diameter only decreased in the MBL+ condition (p<0.05). CONCLUSION: MBL signaling to damaged myotubes is evident and may increase catabolic processes through upregulating contraction-mediated protease activity and autophagy, as well as increase ATP generation through oxidative phosphorylation during regeneration. / Thesis / Master of Science (MSc) / When muscle damage occurs, whether through rigorous exercise or physical trauma, the muscle relies on a specific group of stem cells to help repair itself. These stem cells, termed satellite cells, can migrate to specific sites of muscle damage, differentiate into myoblasts, and donate nuclei and genetic material to the injured muscle. This increase in nuclear content helps the muscle synthesize more protein to rebuild and regenerate and promotes muscle growth. However, when the satellite cell becomes dysfunctional, as seen in aging muscle and certain genetic conditions, the muscle struggles to repair itself in response to damage and cannot grow in response to exercise. Satellite cell biology has clearly defined the role of nuclear donation in muscle function, however very little is known about how this stem cell ‘talks’ to the muscle through signaling molecules. As such, this thesis elucidates the effect of myoblast signaling on electrically stimulated damaged immature muscle fibers, otherwise known as myotubes, by preventing myoblast-myotube physical interactions in cell culture experimentation. Interestingly, the data presented here demonstrate that myoblast exposure to damaged myotubes may increase muscle protein breakdown as myotube diameters are reduced in size acutely post-damage, likely resulting from the increase in protease and autophagy protein expression markers. Additionally, myoblast exposure to damaged myotubes may increase mitochondrial fatty acid oxidation to generate energy, which is the fuel of choice during muscle regeneration.

published_or_final_version / abstract / Pharmacology / Doctoral / Doctor of Philosophy

Hyperkalemic periodic paralysis is characterized by myotonic discharges followed by paralysis. Caused by a mutation in the gene encoding for NaV1.4 channel, patients do not experience symptoms during infancy, but the onset starts between 1-10 years of age. The symptoms severity then increases with age until adolescence. A large increase in gene expression marked by an increase in oxidative capacity of muscles has also been reported in HyperKPP. It is possible that the onset of symptoms is related solely to NaV1.4 channel content/activity reaching a critical level. It is also possible that the onset of some symptoms are due to defective NaV1.4, while other symptoms and the increase in severity with age are related to changes in membrane components as a result of changes in gene expression. To test these possibilities, the progression of paralysis and changes in fiber types were followed with age in HyperKPP mice in relation to changes in NaV1.4 content and activity. Changes in fiber types (index of changes in gene expression), started after the onset of paralysis was observed, which coincided with NaV1.4 channels reaching maximum expression. Therefore, the onset of symptoms was related to defective NaV1.4 channels.

Hyperkalemic periodic paralysis is characterized by myotonic discharges followed by paralysis. Caused by a mutation in the gene encoding for NaV1.4 channel, patients do not experience symptoms during infancy, but the onset starts between 1-10 years of age. The symptoms severity then increases with age until adolescence. A large increase in gene expression marked by an increase in oxidative capacity of muscles has also been reported in HyperKPP. It is possible that the onset of symptoms is related solely to NaV1.4 channel content/activity reaching a critical level. It is also possible that the onset of some symptoms are due to defective NaV1.4, while other symptoms and the increase in severity with age are related to changes in membrane components as a result of changes in gene expression. To test these possibilities, the progression of paralysis and changes in fiber types were followed with age in HyperKPP mice in relation to changes in NaV1.4 content and activity. Changes in fiber types (index of changes in gene expression), started after the onset of paralysis was observed, which coincided with NaV1.4 channels reaching maximum expression. Therefore, the onset of symptoms was related to defective NaV1.4 channels.

Hyperkalemic periodic paralysis is characterized by myotonic discharges followed by paralysis. Caused by a mutation in the gene encoding for NaV1.4 channel, patients do not experience symptoms during infancy, but the onset starts between 1-10 years of age. The symptoms severity then increases with age until adolescence. A large increase in gene expression marked by an increase in oxidative capacity of muscles has also been reported in HyperKPP. It is possible that the onset of symptoms is related solely to NaV1.4 channel content/activity reaching a critical level. It is also possible that the onset of some symptoms are due to defective NaV1.4, while other symptoms and the increase in severity with age are related to changes in membrane components as a result of changes in gene expression. To test these possibilities, the progression of paralysis and changes in fiber types were followed with age in HyperKPP mice in relation to changes in NaV1.4 content and activity. Changes in fiber types (index of changes in gene expression), started after the onset of paralysis was observed, which coincided with NaV1.4 channels reaching maximum expression. Therefore, the onset of symptoms was related to defective NaV1.4 channels.

Skeletal muscle functions as an endocrine organ. Exosomes, small vesicles containing mRNAs, miRNAs, and proteins, are secreted from muscle cells and facilitate cell-to-cell communication. Our recent work found greater exosome release from oxidative compared to glycolytic muscle. Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is a key driver of mitochondrial biogenesis, a characteristic of oxidative muscle. It was hypothesized that PGC1α regulates exosome biogenesis and secretion in skeletal muscle. The purpose of this study is to determine if PGC-1α regulates skeletal muscle exosome biogenesis and secretion. On day 4 of differentiation, human primary myotubes from vastus lateralis biopsies from lean donors (BMI < 25.0 kg/m2) were exposed to adenovirus encoding human PGC-1α or GFP control. On day 6 of differentiation, culture media was replaced with exosome-free media. On day 8, cells were collected for mRNA and protein analysis, and culture media was collected for exosome isolation. Overexpression of PGC-1α increases regulators of exosome biogenesis in the endosomal sorting complexes required for transport (ESCRT) pathway: Alix (CON: 1.0 ± 0.2 vs. PGC-1α: 7.6 ± 3.8), TSG-101 (CON: 1.0 ± 0.1 vs. PGC-1α: 7.3 ± 2.1), CD63 (CON: 1.0 ± 0.17 vs. PGC-1α: 3.7 ± 0.4), Clathrin (CON: 1.0 ± 0.2 vs. PGC-1α: 11.6 ± 2.5), and the secretion pathway: Rab27b (CON: 1.0 ± 0.3 vs. PGC-1α: 3.2 ± 0.3), STAM (CON: 1.0 ± 0.3 vs. PGC-1α: 7.3 ± 0.6), and VTA1 (CON: 1.0 ± 0.1 vs. PGC-1α: 7.3 ± 2.4). Exosome count and total extracellular vesicle count were not significantly different from control. Overexpression of PGC-1α increases gene 9 expression of regulators of exosome biogenesis and secretion in human primary myotubes. In the future, in vitro studies assessing exosomal content from PGC-1 OE cells as well as in vivo effects of PGC-1 OE on exosome production and release should be investigated to further understand the role PGC-1 plays in exosome secretion.