Project description:The platelet-derived growth-factor receptors alpha and beta (PDGFRα and PDGFRβ) mark fibroblasts and pericytes in skeletal muscle, respectively. While the role that these cells play in muscle growth has been evaluated, it was not known whether the receptors that mark these cells play a role in controlling transcriptional and functional changes during skeletal muscle hypertrophy. To evaluate this, we inhibited PDGFR signaling in mice subjected to a synergist ablation muscle growth procedure, and measured changes 3 and 10 days later. The results indicated that PDGF signaling was required for fiber hypertrophy and ECM production that occur during muscle growth.
Project description:The oncogenic transcription factor Myc stimulates many growth processes including cell cycle progression and ribosome biogenesis. Myc expression is low in adult skeletal muscle, but is upregulated upon growth stimuli. Furthermore, muscle fiber Myc overexpression recapitulates many aspects of growth-related gene expression, leading to the hypothesis that Myc mediates pro-growth responses to anabolic stimuli, such as exercise. Here, we tested this hypothesis by examining mouse models in which Myc was specifically eliminated or overexpressed in skeletal muscle fibers or muscle stem cells (MuSC). While muscle fiber Myc expression increased during muscle growth and Myc expression in MuSCs was required for successful muscle regeneration, muscle fiber Myc expression was dispensable for post-natal, mechanical overload or PKBα/Akt1-induced muscle growth in mice. Similarly, constitutive Myc expression did not promote skeletal muscle hypertrophy, but instead impaired muscle fiber structure and function within days. These data question the role of Myc in skeletal muscle growth.
Project description:The oncogenic transcription factor Myc stimulates many growth processes including cell cycle progression and ribosome biogenesis. Myc expression is low in adult skeletal muscle, but is upregulated upon growth stimuli. Furthermore, muscle fiber Myc overexpression recapitulates many aspects of growth-related gene expression, leading to the hypothesis that Myc mediates pro-growth responses to anabolic stimuli, such as exercise. Here, we tested this hypothesis by examining mouse models in which Myc was specifically eliminated or overexpressed in skeletal muscle fibers or muscle stem cells (MuSC). While muscle fiber Myc expression increased during muscle growth and Myc expression in MuSCs was required for successful muscle regeneration, muscle fiber Myc expression was dispensable for post-natal, mechanical overload or PKBα/Akt1-induced muscle growth in mice. Similarly, constitutive Myc expression did not promote skeletal muscle hypertrophy, but instead impaired muscle fiber structure and function within days. These data question the role of Myc in skeletal muscle growth.
Project description:The oncogenic transcription factor Myc stimulates many growth processes including cell cycle progression and ribosome biogenesis. Myc expression is low in adult skeletal muscle, but is upregulated upon growth stimuli. Furthermore, muscle fiber Myc overexpression recapitulates many aspects of growth-related gene expression, leading to the hypothesis that Myc mediates pro-growth responses to anabolic stimuli, such as exercise. Here, we tested this hypothesis by examining mouse models in which Myc was specifically eliminated or overexpressed in skeletal muscle fibers or muscle stem cells (MuSC). While muscle fiber Myc expression increased during muscle growth and Myc expression in MuSCs was required for successful muscle regeneration, muscle fiber Myc expression was dispensable for post-natal, mechanical overload or PKBα/Akt1-induced muscle growth in mice. Similarly, constitutive Myc expression did not promote skeletal muscle hypertrophy, but instead impaired muscle fiber structure and function within days. These data question the role of Myc in skeletal muscle growth.
Project description:The myogenic regulatory factor MRF4 is expressed at high levels in myofibers of adult skeletal muscle, but its function is unknown. Here we show that knockdown of MRF4 in adult muscle causes hypertrophy and prevents denervation-induced atrophy. This effect is accompanied by increased protein synthesis and the widespread activation of genes involved in muscle contraction, excitation-contraction coupling and energy metabolism, many of which are known targets of MEF2 transcription factors. Genes regulated by MEF2 represent the top-ranking gene set enriched after Mrf4 RNAi, and a MEF2 reporter is inhibited by co-transfected MRF4 and activated by Mrf4 RNAi. The role of MEF2 in mediating the effect of MRF4 knockdown is supported by the finding that Mrf4 RNAi-dependent increase in fiber size is prevented by dominant negative MEF2, while constitutively active MEF2 is able to induce myofiber hypertrophy. The nuclear localization of the MEF2 co-repressor HDAC4 is impaired by Mrf4 knockdown, suggesting that MRF4 acts by stabilizing a repressor complex that controls MEF2 activity. The demonstration that fiber size in adult skeletal muscle is controlled by the MRF4-MEF2 axis opens new perspectives in the search for therapeutic targets to prevent muscle wasting, in particular sarcopenia and cachexia. Adult innervated and denervated rat soleus muscles were transfected with shRNA to Mrf4 (M1) or to LacZ as a control. Muscles were dissected and examined after 7 days. For each group/condition we selected three different muscles (biological replicas).
Project description:The skeletal muscle growth and development is a very complicated but precisely regulated process with interwoven molecular mechanisms. Skeletal muscle is a very heterogeneous tissue that is made up of a large variety of functionally diverse fiber types. Muscle mass is therefore largely determined by the number and size of those fibres. These fibre characteristics are determined by hyperplasia before birth and by hypertrophy after. Around 65 dpc and three postnatal stages (newborn, 3 days; young, 60 days; and mature, 120 days) are key time points in swine skeletal muscle growth and development. We used microarrays to detail the global programme of gene expression underlying porcine skeletal muscle growth and development.
Project description:Melatonin has been reported to play crucial roles in regulating meat quality, improving reproductive properties and maintaining intestinal health in animal production, but whether it regulates skeletal muscle development in weaned piglet is rarely studied. This study was conducted to investigate the effects of melatonin on growth performance, skeletal muscle development and lipid metabolism in animals by intragastric administration of melatonin solution. Twelve 28-day-old DLY (Duroc × Landrace × Yorkshire) weaned piglets with similar body weight were randomly divided into two groups: control group and melatonin group. The results showed that melatonin supplementation for 23 days had no effect on growth performance, but significantly reduced serum glucose content (P<0.05). Remarkably, melatonin increased longissimus dorsi muscle (LDM) weight, eye muscle area and decreased the liver weight in weaned piglets (P<0.05). In addition, the cross-sectional area of muscle fibers was increased (P<0.05), while triglyceride (TG) levels were decreased in LDM and psoas major muscle (PMM) by melatonin treatment (P<0.05). Transcriptome sequencing showed melatonin induced the expression of genes related to skeletal muscle hypertrophy and fatty acid oxidation. Enrichment analysis indicated that melatonin regulated cholesterol metabolism, protein digestion and absorption and mitophagy signaling pathways in muscle. Gene set enrichment analysis (GSEA) also confirmed the effects of melatonin on skeletal muscle development and mitochondrial structure and function. Moreover, quantitative real-time polymerase chain reaction (qPCR) analysis revealed that melatonin supplementation elevated the gene expression of cell differentiation and muscle fiber development, including paired box 7 (PAX7), myogenin (MYOG), myosin heavy chain (MYHC) ⅡA and MYHC ⅡB (P<0.05), which was accompanied by increased insulin like growth factor 1 (IGF1) and insulin like growth factor binding protein 5 (IGFBP5) expression in LDM (P<0.05). Additionally, melatonin regulated lipid metabolism and activated mitochondrial function in muscle by increasing the mRNA abundance of cytochrome c oxidase subunit 6A (COX6A), COX5B and carnitine palmitoyltransferase 2 (CPT2) and decreasing the mRNA expression of peroxisome proliferator activated receptor gamma (PPARG), Acetyl-CoA carboxylase (ACC) and fatty acid binding protein 4 (FABP4) (P<0.05). Together, our results suggest that melatonin could promote skeletal muscle growth and muscle fiber hypertrophy, improve mitochondrial function and decrease fat deposition in muscle.
Project description:The myogenic regulatory factor MRF4 is expressed at high levels in myofibers of adult skeletal muscle, but its function is unknown. Here we show that knockdown of MRF4 in adult muscle causes hypertrophy and prevents denervation-induced atrophy. This effect is accompanied by increased protein synthesis and the widespread activation of genes involved in muscle contraction, excitation-contraction coupling and energy metabolism, many of which are known targets of MEF2 transcription factors. Genes regulated by MEF2 represent the top-ranking gene set enriched after Mrf4 RNAi, and a MEF2 reporter is inhibited by co-transfected MRF4 and activated by Mrf4 RNAi. The role of MEF2 in mediating the effect of MRF4 knockdown is supported by the finding that Mrf4 RNAi-dependent increase in fiber size is prevented by dominant negative MEF2, while constitutively active MEF2 is able to induce myofiber hypertrophy. The nuclear localization of the MEF2 co-repressor HDAC4 is impaired by Mrf4 knockdown, suggesting that MRF4 acts by stabilizing a repressor complex that controls MEF2 activity. The demonstration that fiber size in adult skeletal muscle is controlled by the MRF4-MEF2 axis opens new perspectives in the search for therapeutic targets to prevent muscle wasting, in particular sarcopenia and cachexia.
Project description:We have developed an inducible, skeletal muscle-specific mouse model of DM1 (CUG960) that expresses 960 CUG repeat-expressing animals (CUG960) in the context of human DMPK exons 11-15. CUG960 RNA-expressing mice induced at postnatal day 1, as well as adult-onset animals, show clear, measurable muscle wasting accompanied by severe histological defects including central myonuclei, reduced fiber cross-sectional area, increased percentage of oxidative myofibers, the presence of nuclear RNA foci that colocalize with Mbnl1 protein, and increased Celf1 protein in severely affected muscles. Importantly, muscle loss, histological abnormalities and RNA foci are reversible, demonstrating recovery upon removal of toxic RNA. RNA-seq and protein array analysis indicate that the balance between anabolic and catabolic pathways that normally regulate muscle mass may be disrupted by deregulation of platelet derived growth factor receptor beta signaling and the PI3K/AKT pathways, along with prolonged activation of AMP-activated protein kinase alpha signaling. Similar changes were detected in DM1 skeletal muscle compared with unaffected controls.
Project description:The skeletal muscle growth and development is a very complicated but precisely regulated process with interwoven molecular mechanisms. Skeletal muscle is a very heterogeneous tissue that is made up of a large variety of functionally diverse fiber types. Muscle mass is therefore largely determined by the number and size of those fibres. These fibre characteristics are determined by hyperplasia before birth and by hypertrophy after. Around 65 dpc and three postnatal stages (newborn, 3 days; young, 60 days; and mature, 120 days) are key time points in swine skeletal muscle growth and development. We used microarrays to detail the global programme of gene expression underlying porcine skeletal muscle growth and development. Porcine longissimus dorsi muscles were selected at four stages of development for RNA extraction and hybridization on Affymetrix microarrays. We sought to investigate the global gene expression patterns accompanying the skeletal muscle development. To that end, we selected longissimus dorsi muscles at four time-points: 65 days post coitus, 3 days, 60 days and 120 days afterbirth.