Hypertrophic signalling in human skeletal muscle

Ý-lactoglobulin enriched whey protein isolate, but not carbohydrate, increased growth signalling in human skeletal muscle when consumed in conjunction with resistance exercise. Ageing did not impair the anabolic signalling response; however this response was attenuated after training. These findings help identify strategies to prevent, or delay the onset of sarcopenia.

AHI1 and NDRG2 function in skeletal muscle and the development of type 2 diabetes

In this study, AHI1 and NDRG2 gene function in the insulin signalling pathways regulating skeletal muscle homeostasis was investigated. Findings implicate AHI1 in the regulation of insulin-stimulated glucose transport and the development of insulin resistance, whilst associating NDRG2 with the regulation of myoblast proliferation and differentiation; possible via interactions with PICK1 and arfaptin2.

Enhanced proliferation of human skeletal muscle precursor cells derived from elderly donors cultured in estimated physiological (5%) oxygen

Human skeletal muscle precursor cells (myoblasts) have significant therapeutic potential and are a valuable research tool to study muscle cell biology. Oxygen is a critical factor in the successful culture of myoblasts with low (1–6%) oxygen culture conditions enhancing the proliferation, differentiation, and/or viability of mouse, rat, and bovine myoblasts. The specific effects of low oxygen depend on the myoblast source and oxygen concentration; however, variable oxygen conditions have not been tested in the culture of human myoblasts. In this study, muscle precursor cells were isolated from vastus lateralis muscle biopsies and myoblast cultures were established in 5% oxygen, before being divided into physiological (5%) or standard (20%) oxygen conditions for experimental analysis. Five percent oxygen increased proliferating myoblast numbers, and since low oxygen had no significant effect on myoblast viability, this increase in cell number was attributed to enhanced proliferation. The proportion of cells in the S (DNA synthesis) phase of the cell cycle was increased by 50%, and p21^Cip1 gene and protein expression was decreased in 5 versus 20% oxygen. Unlike in rodent and bovine myoblasts, the increase in myoD, myogenin, creatine kinase, and myosin heavy chain IIa gene expression during differentiation was similar in 5 and 20% oxygen; as was myotube hypertrophy. These data indicate for the first time that low oxygen culture conditions stimulate proliferation, whilst maintaining (but not enhancing) the viability and the differentiation potential of human primary myoblasts and should be considered as optimum conditions for exvivo expansion of these cells.

Mitrochondrial target discovery in diabetic skeletal muscle

This study identified the protein PARL (Presenilin-associated rhomboid like) as a potential mediator of the mitochondrial abnormalities that are observed in diabetic skeletal muscle. This was demonstrated by analysing PARL expression in an animal model of type 2 diabetes and by investigating the biological effects of genetic variation in the human PARL gene.

Investigation of JAK/STAT signaling in human skeletal muscle

Understanding muscle adaptation and repair is vital for preserving muscle loss with aging. Analysis of the inflammatory-responsive signalling pathway, JAK/STAT was performed. After intense exercise, the STAT3 pathway is highly activated, potentially by the pro-inflammatory regulator IL-6. This pathway is suppressed in older individuals, possible leading to altered inflammatory regulation.

Glycogen-protein associations in human skeletal muscle

The collective findings of this dissertation demonstrated little effect of exercise on the absolute or relative expression of glycogen regulatory proteins associated with a glycogen enriched fraction in human skeletal muscle. However the findings of this thesis help inform methodological approaches to future investigations into glycogen-protein associations.

CoQ10 conveys protection from oxidative stress in plasma but not skeletal muscle

Coenzyme Q10 (CoQ10) is commonly consumed as an antiaging supplement at doses of 30–210 mg/day. The aim of the study was to determine if CoQ10 alters markers of antioxidant status, oxidative damage, and gene expression in aging skeletal muscle. Female guinea pigs aged 26 months were supplemented for 6 weeks with CoQ10 at a human equivalent dose of 10 mg/kg/day. Body weight, plasma CoQ10 concentration, and WBC DNA abasic sites were measured at weeks 0, 2, 4, and 6 of the supplementation period. At the end of supplementation, concentrations of skeletal muscle CoQ10, glutathione, malondialdehyde, protein carbonyls, DNA abasic sites, activities of catalase and glutathione peroxidase, and the gene expression of cyctochrome c oxidase subunits were measured. Dietary supplementation with CoQ10 elevated plasma CoQ10 levels (pre 73 ± 3 nmol/L, post 581 ± 15 nmol/L, P < 0.05) and decreased abasic sites in WBC DNA (pre 16.8 ± 0.5 Ap/100000 bp, post 9.7 ± 0.4 Ap/100000 bp, P < 0.05). In contrast, all of the measures made in skeletal muscle were not different between groups (P > 0.05). These results indicate that dietary supplementation with CoQ10 at a dose of 10 mg/kg/day may be capable of increasing antioxidant protection and reducing oxidative damage in the plasma, but may have no effect in skeletal muscle.

Regulation of skeletal muscle oxidative capacity and insulin signaling by the Mitochondrial Rhomboid Protease PARL

Type 2 diabetes mellitus (T2DM) and aging are characterized by insulin resistance and impaired mitochondrial energetics. In lower organisms, remodeling by the protease pcp1 (PARL ortholog) maintains the function and lifecycle of mitochondria. We examined whether variation in PARL protein content is associated with mitochondrial abnormalities and insulin resistance. PARL mRNA and mitochondrial mass were both reduced in elderly subjects and in subjects with T2DM. Muscle knockdown of PARL in mice resulted in malformed mitochondrial cristae, lower mitochondrial content, decreased PGC1α protein levels, and impaired insulin signaling. Suppression of PARL protein in healthy myotubes lowered mitochondrial mass and insulin-stimulated glycogen synthesis and increased reactive oxygen species production. We propose that lower PARL expression may contribute to the mitochondrial abnormalities seen in aging and T2DM.

TGF-Ý signalling in human skeletal muscle regeneration and diabetes

The TGF-Ý superfamily comprises a large group of proteins with many effects on muscle growth and maturation. The molecular regulation of skeletal muscle regeneration and metabolism in response to prominent superfamily members, myostatin and TGF-Ý1, were analysed, demonstrating the importance of this pathway in controlling how muscles grow and are regulated.

Fatigue depresses maximal in vitro skeletal muscle Na+-K+-ATPase activity in untrained and trained individuals

This study investigated whether fatiguing dynamic exercise depresses maximal in vitro Na+-K+-ATPase activity and whether any depression is attenuated with chronic training. Eight untrained (UT), eight resistance-trained (RT), and eight endurance-trained (ET) subjects performed a quadriceps fatigue test, comprising 50 maximal isokinetic contractions (180°/s, 0.5 Hz). Muscle biopsies (vastus lateralis) were taken before and immediately after exercise and were analyzed for maximal in vitro Na+-K+-ATPase (K+-stimulated 3-O-methylfluoroscein phosphatase) activity. Resting samples were analyzed for [3H]ouabain binding site content, which was 16.6 and 18.3% higher (P < 0.05) in ET than RT and UT, respectively (UT 311 ± 41, RT 302 ± 52, ET 357 ± 29 pmol/g wet wt). 3-O-methylfluoroscein phosphatase activity was depressed at fatigue by −13.8 ± 4.1% (P < 0.05), with no differences between groups (UT −13 ± 4, RT −9 ± 6, ET −22 ± 6%). During incremental exercise, ET had a lower ratio of rise in plasma K+ concentration to work than UT (P < 0.05) and tended (P = 0.09) to be lower than RT (UT 18.5 ± 2.3, RT 16.2 ± 2.2, ET 11.8 ± 0.4 nmol · l−1 · J−1). In conclusion, maximal in vitro Na+-K+-ATPase activity was depressed with fatigue, regardless of training state, suggesting that this may be an important determinant of fatigue.