Physiology - Research Publications

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    Phosphoproteomics reveals conserved exercise-stimulated signaling and AMPK regulation of store-operated calcium entry
    Nelson, ME ; Parker, BL ; Burchfield, JG ; Hoffman, NJ ; Needham, EJ ; Cooke, KC ; Naim, T ; Sylow, L ; Ling, NXY ; Francis, D ; Norris, DM ; Chaudhuri, R ; Oakhill, JS ; Richter, EA ; Lynch, GS ; Stockli, J ; James, DE (WILEY, 2019-08-05)
    Exercise stimulates cellular and physiological adaptations that are associated with widespread health benefits. To uncover conserved protein phosphorylation events underlying this adaptive response, we performed mass spectrometry-based phosphoproteomic analyses of skeletal muscle from two widely used rodent models: treadmill running in mice and in situ muscle contraction in rats. We overlaid these phosphoproteomic signatures with cycling in humans to identify common cross-species phosphosite responses, as well as unique model-specific regulation. We identified > 22,000 phosphosites, revealing orthologous protein phosphorylation and overlapping signaling pathways regulated by exercise. This included two conserved phosphosites on stromal interaction molecule 1 (STIM1), which we validate as AMPK substrates. Furthermore, we demonstrate that AMPK-mediated phosphorylation of STIM1 negatively regulates store-operated calcium entry, and this is beneficial for exercise in Drosophila. This integrated cross-species resource of exercise-regulated signaling in human, mouse, and rat skeletal muscle has uncovered conserved networks and unraveled crosstalk between AMPK and intracellular calcium flux.
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    Deletion of Skeletal Muscle SOCS3 Prevents Insulin Resistance in Obesity
    Jorgensen, SB ; O'Neill, HM ; Sylow, L ; Honeyman, J ; Hewitt, KA ; Palanivel, R ; Fullerton, MD ; Oberg, L ; Balendran, A ; Galic, S ; van der Poel, C ; Trounce, IA ; Lynch, GS ; Schertzer, JD ; Steinberg, GR (AMER DIABETES ASSOC, 2013-01-01)
    Obesity is associated with chronic low-grade inflammation that contributes to defects in energy metabolism and insulin resistance. Suppressor of cytokine signaling (SOCS)-3 expression is increased in skeletal muscle of obese humans. SOCS3 inhibits leptin signaling in the hypothalamus and insulin signal transduction in adipose tissue and the liver. Skeletal muscle is an important tissue for controlling energy expenditure and whole-body insulin sensitivity; however, the physiological importance of SOCS3 in this tissue has not been examined. Therefore, we generated mice that had SOCS3 specifically deleted in skeletal muscle (SOCS MKO). The SOCS3 MKO mice had normal muscle development, body mass, adiposity, appetite, and energy expenditure compared with wild-type (WT) littermates. Despite similar degrees of obesity when fed a high-fat diet, SOCS3 MKO mice were protected against the development of hyperinsulinemia and insulin resistance because of enhanced skeletal muscle insulin receptor substrate 1 (IRS1) and Akt phosphorylation that resulted in increased skeletal muscle glucose uptake. These data indicate that skeletal muscle SOCS3 does not play a critical role in regulating muscle development or energy expenditure, but it is an important contributing factor for inhibiting insulin sensitivity in obesity. Therapies aimed at inhibiting SOCS3 in skeletal muscle may be effective in reversing obesity-related glucose intolerance and insulin resistance.
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    G-CSF does not influence C2C12 myogenesis despite receptor expression in healthy and dystrophic skeletal muscle (vol 5, 170, 2014)
    Wright, CR ; Brown, EL ; Della-Gatta, PA ; Ward, AC ; Lynch, GS ; Russell, AP (FRONTIERS MEDIA SA, 2017-10-30)
    [This corrects the article on p. 170 in vol. 5, PMID: 24822049.].
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    Deletion of suppressor of cytokine signaling 3 (SOCS3) in muscle stem cells does not alter muscle regeneration in mice after injury
    Swiderski, K ; Caldow, MK ; Naim, T ; Trieu, J ; Chee, A ; Koopman, R ; Lynch, GS ; Alway, SE (PUBLIC LIBRARY SCIENCE, 2019-02-27)
    Muscles of older animals are more susceptible to injury and regenerate poorly, in part due to a persistent inflammatory response. The janus kinase (Jak)/signal transducer and activator of transcription (Stat) pathway mediates inflammatory signaling and is tightly regulated by the suppressor of cytokine signaling (SOCS) proteins, especially SOCS3. SOCS3 expression is altered in the muscle of aged animals and may contribute to the persistent inflammation and impaired regeneration. To test this hypothesis, we performed myotoxic injuries on mice with a tamoxifen-inducible deletion of SOCS3 specifically within the muscle stem cell compartment. Muscle stem cell-specific SOCS3 deletion reduced muscle mass at 14 days post-injury (-14%, P < 0.01), altered the myogenic transcriptional program, and reduced myogenic fusion based on the number of centrally-located nuclei per muscle fiber. Despite the delay in myogenesis, muscles with a muscle stem cell-specific deletion of SOCS3 were still able to regenerate after a single bout or multiple bouts of myotoxic injury. A reduction in SOCS3 expression in muscle stem cells is unlikely to be responsible for the incomplete muscle repair in aged animals.
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    The Microenvironment Is a Critical Regulator of Muscle Stem Cell Activation and Proliferation
    Nguyen, JH ; Chung, JD ; Lynch, GS ; Ryall, JG (FRONTIERS MEDIA SA, 2019-10-29)
    Skeletal muscle has a remarkable capacity to regenerate following injury, a property conferred by a resident population of muscle stem cells (MuSCs). In response to injury, MuSCs must double their cellular content to divide, a process requiring significant new biomass in the form of nucleotides, phospholipids, and amino acids. This new biomass is derived from a series of intracellular metabolic cycles and alternative routing of carbon. In this review, we examine the link between metabolism and skeletal muscle regeneration with particular emphasis on the role of the cellular microenvironment in supporting the production of new biomass and MuSC proliferation.
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    Glycine administration attenuates progression of dystrophic pathology in prednisolone-treated dystrophin/utrophin null mice
    Ham, DJ ; Gardner, A ; Kennedy, TL ; Trieu, J ; Naim, T ; Chee, A ; Alves, FM ; Caldow, MK ; Lynch, GS ; Koopman, R (NATURE PUBLISHING GROUP, 2019-09-10)
    Duchenne muscular dystrophy (DMD) is an X-linked genetic disease characterized by progressive muscle wasting and weakness and premature death. Glucocorticoids (e.g. prednisolone) remain the only drugs with a favorable impact on DMD patients, but not without side effects. We have demonstrated that glycine preserves muscle in various wasting models. Since glycine effectively suppresses the activity of pro-inflammatory macrophages, we investigated the potential of glycine treatment to ameliorate the dystrophic pathology. Dystrophic mdx and dystrophin-utrophin null (dko) mice were treated with glycine or L-alanine (amino acid control) for up to 15 weeks and voluntary running distance (a quality of life marker and strong correlate of lifespan in dko mice) and muscle morphology were assessed. Glycine increased voluntary running distance in mdx mice by 90% (P < 0.05) after 2 weeks and by 60% (P < 0.01) in dko mice co-treated with prednisolone over an 8 week treatment period. Glycine treatment attenuated fibrotic deposition in the diaphragm by 28% (P < 0.05) after 10 weeks in mdx mice and by 22% (P < 0.02) after 14 weeks in dko mice. Glycine treatment augmented the prednisolone-induced reduction in fibrosis in diaphragm muscles of dko mice (23%, P < 0.05) after 8 weeks. Our findings provide strong evidence that glycine supplementation may be a safe, simple and effective adjuvant for improving the efficacy of prednisolone treatment and improving the quality of life for DMD patients.
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    Glycine Protects Muscle Cells From Wasting in vitro via mTORC1 Signaling
    Caldow, MK ; Ham, DJ ; Trieu, J ; Chung, JD ; Lynch, GS ; Koopman, R (FRONTIERS MEDIA SA, 2019-11-13)
    Glycine supplementation can protect skeletal muscles of mice from cancer-induced wasting, but the mechanisms underlying this protection are not well-understood. The aim of this study was to determine whether exogenous glycine directly protects skeletal muscle cells from wasting. C2C12 muscle cells were exposed to non-inflammatory catabolic stimuli via two models: serum withdrawal (SF) for 48 h; or incubation in HEPES buffered saline (HBS) for up to 5 h. Cells were supplemented with glycine or equimolar concentrations of L-alanine. SF- and HBS-treated myotubes (with or without L-alanine) were ~20% and ~30% smaller than control myotubes. Glycine-treated myotubes were up to 20% larger (P < 0.01) compared to cells treated with L-alanine in both models of muscle cell atrophy. The mTORC1 inhibitor rapamycin prevented the glycine-stimulated protection of myotube diameter, and glycine-stimulated S6 phosphorylation, suggesting that mTORC1 signaling may be necessary for glycine's protective effects in vitro. Increasing glycine availability may be beneficial for muscle wasting conditions associated with inadequate nutrient intake.
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    Using AAV vectors expressing the beta 2-adrenoceptor or associated G alpha proteins to modulate skeletal muscle mass and muscle fibre size
    Hagg, A ; Colgan, TD ; Thomson, RE ; Qian, H ; Lynch, GS ; Gregorevic, P (NATURE PUBLISHING GROUP, 2016-03-14)
    Anabolic β2-adrenoceptor (β2-AR) agonists have been proposed as therapeutics for treating muscle wasting but concerns regarding possible off-target effects have hampered their use. We investigated whether β2-AR-mediated signalling could be modulated in skeletal muscle via gene delivery to the target tissue, thereby avoiding the risks of β2-AR agonists. In mice, intramuscular administration of a recombinant adeno-associated virus-based vector (rAAV vector) expressing the β2-AR increased muscle mass by >20% within 4 weeks. This hypertrophic response was comparable to that of 4 weeks' treatment with the β2-AR agonist formoterol, and was not ablated by mTOR inhibition. Increasing expression of inhibitory (Gαi2) and stimulatory (GαsL) G-protein subunits produced minor atrophic and hypertrophic changes in muscle mass, respectively. Furthermore, Gαi2 over-expression prevented AAV:β2-AR mediated hypertrophy. Introduction of the non-muscle Gαs isoform, GαsXL elicited hypertrophy comparable to that achieved by AAV:β2-AR. Moreover, GαsXL gene delivery was found to be capable of inducing hypertrophy in the muscles of mice lacking functional β1- and β2-ARs. These findings demonstrate that gene therapy-based interventions targeting the β2-AR pathway can promote skeletal muscle hypertrophy independent of ligand administration, and highlight novel methods for potentially modulating muscle mass in settings of disease.
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    Muscle-specific deletion of SOCS3 does not reduce the anabolic response to leucine in a mouse model of acute inflammation
    Caldow, MK ; Ham, DJ ; Chee, A ; Trieu, J ; Naim, T ; Stapleton, DI ; Swiderski, K ; Lynch, GS ; Koopman, R (ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2017-08-01)
    Excessive inflammation reduces skeletal muscle protein synthesis leading to wasting and weakness. The janus kinase/signal transducers and activators of transcription-3 (JAK/STAT3) pathway is important for the regulation of inflammatory signaling. As such, suppressor of cytokine signaling-3 (SOCS3), the negative regulator of JAK/STAT signaling, is thought to be important in the control of muscle homeostasis. We hypothesized that muscle-specific deletion of SOCS3 would impair the anabolic response to leucine during an inflammatory insult. Twelve week old (n=8 per group) SOCS3 muscle-specific knockout mice (SOCS3-MKO) and littermate controls (WT) were injected with lipopolysaccharide (LPS, 1mg/kg) or saline and were studied during fasted conditions or after receiving 0.5g/kg leucine 3h after the injection of LPS. Markers of inflammation, anabolic signaling, and protein synthesis were measured 4h after LPS injection. LPS injection robustly increased mRNA expression of inflammatory molecules (Socs3, Socs1, Il-6, Ccl2, Tnfα and Cd68). In muscles from SOCS3-MKO mice, the Socs3 mRNA response to LPS was significantly blunted (∼6-fold) while STAT3 Tyr705 phosphorylation was exacerbated (18-fold). Leucine administration increased protein synthesis in both WT (∼1.6-fold) and SOCS3-MKO mice (∼1.5-fold) compared to basal levels. LPS administration blunted this effect, but there were no differences between WT and SOCS3-MKO mice. Muscle-specific SOCS3 deletion did not alter the response of AKT, mTOR, S6 or 4EBP1 under any treatment conditions. Therefore, SOCS3 does not appear to mediate the early inflammatory or leucine-induced changes in protein synthesis in skeletal muscle.
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    Dietary meat and protection against sarcopenia
    Lynch, GS ; Koopman, R (ELSEVIER SCI LTD, 2018-10-01)
    Sarcopenia describes the age-related loss of skeletal muscle mass and associated muscle weakness. Sarcopenia is a major global health problem given that the number and proportion of older people in the population is escalating worldwide and represent the fastest growing segment of society. The loss of muscle mass compromises physical capacity, increases susceptibility to falls, and impacts on an individual's functional independence and quality of life. Tackling sarcopenia sensibly and effectively will identify strategies that will enable older adults to age well and age productively. The underlying causes of sarcopenia are complex and multifactorial and will likely require combinatorial therapies to address its symptoms. Nutrition, particularly protein intake, is a more easily modifiable factor, especially when combined with structured (resistance) exercise programs. The relative success of protein feeding strategies for sarcopenia, is limited by a so-called anabolic resistance in older people. Meat contains essential amino acids and nutritive compounds of high quality, and even a moderate intake can increase muscle protein synthesis in older men and women. However, health risks have been identified with the consumption of different meats, with high intake of processed meats increasing the risk for cardiovascular disease and different cancers. Risks for fresh white and red meat are considerably less and modest consumption is encouraged as part of a healthy eating plan for many older adults to ensure adequate protein intake. Other nutritive strategies of relevance for sarcopenia involve fortifying the nutrient value of different meats. Studies on muscle cells and animal models of muscle wasting, have identified the therapeutic potential of the amino acid, glycine, to reduce inflammation, attenuate muscle atrophy, and re-sensitize muscle to anabolic stimuli. Glycine supplementation or feeding animal products with a high glycine content (e.g. gelatin), could represent simple and effective nutritional strategies as part of a suite of therapies to attenuate sarcopenia.