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 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.
Project description:The size of skeletal muscles, like that of all cells, is precisely regulated by intracellular signaling networks that determine the balance between overall rates of protein synthesis and degradation. Muscle fiber growth and protein synthesis are stimulated by the IGF1/Akt/mTOR pathway, and muscle wasting, as occurs with disuse, denervation, fasting, and various systemic diseases (e.g. cancer, sepsis) results from excessive protein breakdown in muscle and induction of a set of atrophy-related genes by the FoxO transcription factors. Here we show that the transcription factor JunB is also a major regulator of growth and atrophy of adult (post mitotic) muscle cells. We found that in atrophying myotubes, JunB protein was excluded from the nucleus and that decreasing JunB expression by RNAi in muscles of adults reduced fiber size. Furthermore, in normal muscles of adult mice JunB over-expression increased fiber diameter dramatically (up to 40% in 7 days), and stimulated protein synthesis, but unlike IGF-1 or insulin, JunB did not activate the Akt/mTOR pathway. Importantly, when JunB was transfected into denervated muscles to maintain its level high, fiber atrophy was prevented, and the induction of the critical atrophy-associated ubiquitin-ligases, atrogin-1 and MuRF-1, was greatly reduced. JunB inhibited their induction by impairing FoxO3 binding to their promoters and thus reduced the stimulation of protein breakdown by FoxO3. Thus JunB is important, not only in dividing populations, but also in mature skeletal muscle where it is required for the maintenance of muscle size and can induce rapid hypertrophy and block atrophy.
Project description:In cell biology, ribosomal RNA (rRNA) 2'O-methyl (2'-O-Me) is the most prevalent post-transcriptional chemical modification contributing to ribosome heterogeneity. The modification involves a family of small nucleolar RNAs (snoRNAs) and is specified by box C/D snoRNAs (SNORDs). Given the importance of ribosome biogenesis for skeletal muscle growth, we asked if rRNA 2'-O-Me in nascent ribosomes synthesized in response to a growth stimulus is an unrecognized mode of ribosome heterogeneity in muscle. To determine the pattern and dynamics of 2'-O-Me rRNA, we used a sequencing-based profiling method called RiboMeth-seq. We applied this method to tissue-derived rRNA of skeletal muscle and rRNA specifically from the muscle fiber using an inducible myofiber-specific RiboTag mouse in sedentary and mechanically overloaded conditions. These analyses were complemented by myonuclear-specific small RNA sequencing to profile SNORDs and link the rRNA epitranscriptome to known regulatory elements generated within the muscle fiber. We demonstrate for the first time that mechanical overload of skeletal muscle 1) induces decreased 2'-O-Me at a subset of skeletal muscle rRNAand 2) alters the SNORD profile in isolated myonuclei. These findings point to a transient diversification of the ribosome pool via 2'-O-Me during growth and adaptation in skeletal muscle. These findings suggest changes in ribosome heterogeneity at the 2'-O-Me level during muscle hypertrophy and lay the foundation for studies investigating the functional implications of these newly identified "growth-induced" ribosomes.
Project description:Skeletal muscle atrophy is a serious and highly prevalent condition that remains poorly understood at the molecular level. Previous work found that skeletal muscle atrophy involves an increase in skeletal muscle Gadd45a expression, which is necessary and sufficient for skeletal muscle fiber atrophy. However, the direct mechanism by which Gadd45a promotes skeletal muscle atrophy was unknown. To address this question, we biochemically isolated skeletal muscle fiber proteins that associate with Gadd45a as it induces skeletal muscle atrophy in living mice. We found that Gadd45a interacts with multiple proteins in skeletal muscle fibers, including, most prominently, the MAP kinase kinase kinase MEKK4. Furthermore, by forming a complex with MEKK4 in skeletal muscle fibers, Gadd45a increases MEKK4 protein kinase activity, which is sufficient to induce skeletal muscle fiber atrophy and required for Gadd45a-mediated skeletal muscle fiber atrophy. Together, these results identify a direct biochemical mechanism by which Gadd45a induces skeletal muscle atrophy and provide new insight into way that skeletal muscle atrophy occurs at the molecular level.