The Immediate Early Response of Proliferating Myoblasts to One Bout of Electrical Stimulation

The maintenance of muscle mass is important across the lifespan. The activation of satellite cells, followed by their proliferation and subsequent differentiation is important in this maintenance. Cell cycle arrest must precede differentiation, and preservation of the molecular networks involved within the regenerative process are necessary. Electrical stimulation is a common method of altering activity within a cell, and is known to alter the phenotype of myogenic cells. This thesis looks at the immediate effects of electrical stimulation on proliferating C2C12 myoblasts, in order to determine what induces the long term reductions in cell number associated with electrical stimulation. The results indicate that stimulation alters intracellular processes within these cells, promoting cell cycle arrest and autophagy-mediated cellular remodelling, explaining the long term reduction in cell number associated with stimulation. The research conducted is important in our understanding of muscle regeneration and muscle health

The Impact of Aging, Exercise and Muscle Disuse on Skeletal Muscle Autophagy, Mitophagy and Lysosome Biogenesis

Inactivity and age-related sarcopenia similarly lead to a loss of muscle mass and function. This has largely been attributed to deficits in the synthesis of proteins and organelles, yet the processes that govern the clearance of such constituents remain unexplored. The maintenance of the latter is integral, as damaged proteins/organelles perpetuate functional impairments within the tissue. The autophagy-lysosome system (ALS), which entails the selective tagging of damaged proteins and organelles, followed by their digestion in the lysosomes, is one such method. When confined to the mitochondria, the energy producing organelles, this process is termed mitophagy. Our work is focused on the regulation of intracellular degradation through the ALS, in both disuse and aging models, with implications for mitochondrial and tissue health. To examine the dynamic effects of muscle disuse, we unilaterally denervated the hindlimb muscle of rats for 1, 3 or 7 days. Our results indicate that autophagy and mitophagy flux are biphasic, being upregulated in the early time points (i.e., 1 and 3 days) and downregulated at the latter time point. Increases in lysosomal protein levels were promoted by the upregulation and nuclear activation of the transcriptional regulator of lysosomal protein synthesis (Tfeb). Utilizing electron microscopy, we measured an increase in vacuolar inclusions, indicative of lysosomal dysfunction with prolonged denervation. In aged muscle we similarly report elevations in ALS components and higher nuclear TFEB versus young mice. Uniquely, female mice had a greater abundance of ALS-related proteins and indices of autophagosomal turnover. This indicates that biological sex influences the capacity for autophagy. Paradoxically, catabolic events are also transiently upregulated in response to exercise, serving to "prune" the tissue's faulty parts, including the mitochondria. Thus, we subjected young and aged mice to exhaustive exercise. Young male mice were able to activate autophagy and lysosome biogenesis to a greater extent than female counterparts. This effect was blunted in aged mouse muscle, independent of sex. We have uncovered how autophagy and mitophagy are differentially regulated in denervated and aged muscle. Further, we were able to show that biological sex influences the regulation of the autophagy-lysosome system in young, aged, and exercised muscle

Impact of Aging and Exercise on Mitochondrial Quality Control in Skeletal Muscle

Mitochondria are characterized by its pivotal roles in managing energy production, reactive oxygen species, and calcium, whose aging-related structural and functional deteriorations are observed in aging muscle. Although it is still unclear how aging alters mitochondrial quality and quantity in skeletal muscle, dysregulation of mitochondrial biogenesis and dynamic controls has been suggested as key players for that. In this paper, we summarize current understandings on how aging regulates muscle mitochondrial biogenesis, while focusing on transcriptional regulations including PGC-1α, AMPK, p53, mtDNA, and Tfam. Further, we review current findings on the muscle mitochondrial dynamic systems in aging muscle: fusion/fission, autophagy/mitophagy, and protein import. Next, we also discuss how endurance and resistance exercises impact on the mitochondrial quality controls in aging muscle, suggesting possible effective exercise strategies to improve/maintain mitochondrial health

3-(1-Methyl-3-imidazolio)propane­sulfonate: a precursor to a Brønsted acid ionic liquid

The title compound, C7H12N2O3S, is a zwitterion precursor to a Brønsted acid ionic liquid with potential as an acid catalyst. The C—N—C—C torsion angle of 100.05 (8)° allows the positively charged imidazolium head group and the negatively charged sulfonate group to inter­act with neighboring zwitterions, forming a C—H⋯O hydrogen-bonding network; the shortest among these inter­actions is 2.9512 (9) Å. The C—H⋯O inter­actions can be described by graph-set notation as two R 2 2(16) and one R 2 2(5) hydrogen-bonded rings

The Role of p53 in Determining Mitochondrial Adaptations to Endurance Training in Skeletal Muscle

Abstract p53 plays an important role in regulating mitochondrial homeostasis. However, it is unknown whether p53 is required for the physiological and mitochondrial adaptations with exercise training. Furthermore, it is also unknown whether impairments in the absence of p53 are a result of its loss in skeletal muscle, or a secondary effect due to its deletion in alternative tissues. Thus, we investigated the role of p53 in regulating mitochondria both basally, and under the influence of exercise, by subjecting C57Bl/6J whole-body (WB) and muscle-specific p53 knockout (mKO) mice to a 6-week training program. Our results confirm that p53 is important for regulating mitochondrial content and function, as well as proteins within the autophagy and apoptosis pathways. Despite an increased proportion of phosphorylated p53 (Ser15) in the mitochondria, p53 is not required for training-induced adaptations in exercise capacity or mitochondrial content and function. In comparing mouse models, similar directional alterations were observed in basal and exercise-induced signaling modifications in WB and mKO mice, however the magnitude of change was less pronounced in the mKO mice. Our data suggest that p53 is required for basal mitochondrial maintenance in skeletal muscle, but is not required for the adaptive responses to exercise training

Optic atrophy 1 mediates muscle differentiation by promoting a metabolic switch via the supercomplex assembly factor SCAF1

Summary: Myogenic differentiation is integral for the regeneration of skeletal muscle following tissue damage. Though high-energy post-mitotic muscle relies predominantly on mitochondrial respiration, the importance of mitochondrial remodeling in enabling muscle differentiation and the players involved are not fully known. Here we show that the mitochondrial fusion protein OPA1 is essential for muscle differentiation. Our study demonstrates that OPA1 loss or inhibition, through genetic and pharmacological means, abolishes in vivo muscle regeneration and in vitro myotube formation. We show that both the inhibition and genetic deletion of OPA1 prevent the early onset metabolic switch required to drive myoblast differentiation. In addition, we observe an OPA1-dependent upregulation of the supercomplex assembly factor, SCAF1, at the onset of differentiation. Importantly, preventing the upregulation of SCAF1, through OPA1 loss or siRNA-mediated SCAF1 knockdown, impairs metabolic reprogramming and muscle differentiation. These findings reveal the integral role of OPA1 and mitochondrial reprogramming at the onset of myogenic differentiation

Relationship between Mitochondrial Quality Control Markers, Lower Extremity Tissue Composition, and Physical Performance in Physically Inactive Older Adults

Altered mitochondrial quality and function in muscle may be involved in age-related physical function decline. The role played by the autophagy–lysosome system, a major component of mitochondrial quality control (MQC), is incompletely understood. This study was undertaken to obtain initial indications on the relationship between autophagy, mitophagy, and lysosomal markers in muscle and measures of physical performance and lower extremity tissue composition in young and older adults. Twenty-three participants were enrolled, nine young (mean age: 24.3 ± 4.3 years) and 14 older adults (mean age: 77.9 ± 6.3 years). Lower extremity tissue composition was quantified volumetrically by magnetic resonance imaging and a tissue composition index was calculated as the ratio between muscle and intermuscular adipose tissue volume. Physical performance in older participants was assessed via the Short Physical Performance Battery (SPPB). Protein levels of the autophagy marker p62, the mitophagy mediator BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3), the lysosomal markers transcription factor EB, vacuolar-type ATPase, and lysosomal-associated membrane protein 1 were measured by Western immunoblotting in vastus lateralis muscle biopsies. Older adults had smaller muscle volume and lower tissue composition index than young participants. The protein content of p62 and BNIP3 was higher in older adults. A negative correlation was detected between p62 and BNIP3 and the tissue composition index. p62 and BNIP3 were also related to the performance on the 5-time sit-to-stand test of the SPPB. Our results suggest that an altered expression of markers of the autophagy/mitophagy–lysosomal system is related to deterioration of lower extremity tissue composition and muscle dysfunction. Additional studies are needed to clarify the role of defective MQC in human muscle aging and identify novel biological targets for drug development