Overexpression of TEAD-1 in transgenic mouse striated muscles produces a slower skeletal muscle contractile phenotype

Crosstalk among canonical Wnt and Hippo pathway members in skeletal muscle and at the neuromuscular junction

Skeletal muscles are essential for locomotion, posture, and metabolic regulation. To understand physiological processes, exercise adaptation, and muscle-related disorders, it is critical to understand the molecular pathways that underlie skeletal muscle function. The process of muscle contraction, orchestrated by a complex interplay of molecular events, is at the core of skeletal muscle function. Muscle contraction is initiated by an action potential and neuromuscular transmission requiring a neuromuscular junction. Within muscle fibers, calcium ions play a critical role in mediating the interaction between actin and myosin filaments that generate force. Regulation of calcium release from the sarcoplasmic reticulum plays a key role in excitation-contraction coupling. The development and growth of skeletal muscle are regulated by a network of molecular pathways collectively known as myogenesis. Myogenic regulators coordinate the differentiation of myoblasts into mature muscle fibers. Signaling pathways regulate muscle protein synthesis and hypertrophy in response to mechanical stimuli and nutrient availability. Several muscle-related diseases, including congenital myasthenic disorders, sarcopenia, muscular dystrophies, and metabolic myopathies, are underpinned by dysregulated molecular pathways in skeletal muscle. Therapeutic interventions aimed at preserving muscle mass and function, enhancing regeneration, and improving metabolic health hold promise by targeting specific molecular pathways. Other molecular signaling pathways in skeletal muscle include the canonical Wnt signaling pathway, a critical regulator of myogenesis, muscle regeneration, and metabolic function, and the Hippo signaling pathway. In recent years, more details have been uncovered about the role of these two pathways during myogenesis and in developing and adult skeletal muscle fibers, and at the neuromuscular junction. In fact, research in the last few years now suggests that these two signaling pathways are interconnected and that they jointly control physiological and pathophysiological processes in muscle fibers. In this review, we will summarize and discuss the data on these two pathways, focusing on their concerted action next to their contribution to skeletal muscle biology. However, an in-depth discussion of the non-canonical Wnt pathway, the fibro/adipogenic precursors, or the mechanosensory aspects of these pathways is not the focus of this review.

Methylome-proteome integration after late-life voluntary exercise training reveals regulation and target information for improved skeletal muscle health

Exercise is a potent stimulus for combatting skeletal muscle ageing. To study the effects of exercise on muscle in a preclinical setting, we developed a combined endurance-resistance training stimulus for mice called progressive weighted wheel running (PoWeR). PoWeR improves molecular, biochemical, cellular and functional characteristics of skeletal muscle and promotes aspects of partial epigenetic reprogramming when performed late in life (22-24 months of age). In this investigation, we leveraged pan-mammalian DNA methylome arrays and tandem mass-spectrometry proteomics in skeletal muscle to provide detailed information on late-life PoWeR adaptations in female mice relative to age-matched sedentary controls (n = 7-10 per group). Differential CpG methylation at conserved promoter sites was related to transcriptional regulation genes as well as Nr4a3, Hes1 and Hox genes after PoWeR. Using a holistic method of -omics integration called binding and expression target analysis (BETA), methylome changes were associated with upregulated proteins related to global and mitochondrial translation after PoWeR (P = 0.03). Specifically, BETA implicated methylation control of ribosomal, mitoribosomal, and mitochondrial complex I protein abundance after training. DNA methylation may also influence LACTB, MIB1 and UBR4 protein induction with exercise - all are mechanistically linked to muscle health. Computational cistrome analysis predicted several transcription factors including MYC as regulators of the exercise trained methylome-proteome landscape, corroborating prior late-life PoWeR transcriptome data. Correlating the proteome to muscle mass and fatigue resistance revealed positive relationships with VPS13A and NPL levels, respectively. Our findings expose differential epigenetic and proteomic adaptations associated with translational regulation after PoWeR that could influence skeletal muscle mass and function in aged mice. KEY POINTS: Late-life combined endurance-resistance exercise training from 22-24 months of age in mice is shown to improve molecular, biochemical, cellular and in vivo functional characteristics of skeletal muscle and promote aspects of partial epigenetic reprogramming and epigenetic age mitigation. Integration of DNA CpG 36k methylation arrays using conserved sites (which also contain methylation ageing clock sites) with exploratory proteomics in skeletal muscle extends our prior work and reveals coordinated and widespread regulation of ribosomal, translation initiation, mitochondrial ribosomal (mitoribosomal) and complex I proteins after combined voluntary exercise training in a sizeable cohort of female mice (n = 7-10 per group and analysis). Multi-omics integration predicted epigenetic regulation of serine β-lactamase-like protein (LACTB - linked to tumour resistance in muscle), mind bomb 1 (MIB1 - linked to satellite cell and type 2 fibre maintenance) and ubiquitin protein ligase E3 component N-recognin 4 (UBR4 - linked to muscle protein quality control) after training. Computational cistrome analysis identified MYC as a regulator of the late-life training proteome, in agreement with prior transcriptional analyses. Vacuolar protein sorting 13 homolog A (VPS13A) was positively correlated to muscle mass, and the glycoprotein/glycolipid associated sialylation enzyme N-acetylneuraminate pyruvate lyase (NPL) was associated to in vivo muscle fatigue resistance.

VGLL3 confers slow-twitch muscle differentiation via PGC-1α expression in C2C12 myocytes

Vestigial-like family member 3 (VGLL3) is a cofactor for the TEA-domain transcription factor (TEAD) family. Although VGLL3 influences myogenic differentiation, its involvement in slow- and fast-twitch fiber specification remains unknown. In this study, we established a cell line stably overexpressing VGLL3 and analyzed effects of VGLL3 on the myogenic differentiation of murine myoblast C2C12 cells. We found that VGLL3 expression promotes slow-twitch muscle differentiation. Mechanistically, VGLL3 expression induced the expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a master transcriptional regulator of slow-twitch muscle development. We also found that VGLL3 proteins are degraded by the proteasome, which causes switching of TEAD cofactors from VGLL3 to Yes-associated protein (YAP) and transcriptional coactivator with a PDZ-binding motif (TAZ). These results suggest that the balance between the two kinds of TEAD cofactors VGLL3 and YAP/TAZ controls muscle fiber-type specification.

Developmental, physiologic and phylogenetic perspectives on the expression and regulation of myosin heavy chains in mammalian skeletal muscles

The kinetics of myosin controls the speed and power of muscle contraction. Mammalian skeletal muscles express twelve kinetically different myosin heavy chain (MyHC) genes which provides a wide range of muscle speeds to meet different functional demands. Myogenic progenitors from diverse craniofacial and somitic mesoderm specify muscle allotypes with different repertoires for MyHC expression. This review provides a brief synopsis on the historical and current views on how cell lineage, neural impulse patterns, and thyroid hormone influence MyHC gene expression in muscles of the limb allotype during development and in adult life and the molecular mechanisms thereof. During somitic myogenesis, embryonic and foetal myoblast lineages form slow and fast primary and secondary myotube ontotypes which respond differently to postnatal neural and thyroidal influences to generate fully differentiated fibre phenotypes. Fibres of a given phenotype may arise from myotubes of different ontotypes which retain their capacity to respond differently to neural and thyroidal influences during postnatal life. This gives muscles physiological plasticity to adapt to fluctuations in thyroid hormone levels and patterns of use. The kinetics of MyHC isoforms vary inversely with animal body mass. Fast 2b fibres are specifically absent in muscles involved in elastic energy saving in hopping marsupials and generally absent in large eutherian mammals. Changes in MyHC expression are viewed in the context of the physiology of the whole animal. The roles of myoblast lineage and thyroid hormone in regulating MyHC gene expression are phylogenetically the most ancient while that of neural impulse patterns the most recent.

The Molecular Mechanism of the TEAD1 Gene and miR-410-5p Affect Embryonic Skeletal Muscle Development: A miRNA-Mediated ceRNA Network Analysis

Muscle development is a complex biological process involving an intricate network of multiple factor interactions. Through the analysis of transcriptome data and molecular biology confirmation, this study aims to reveal the molecular mechanism underlying sheep embryonic skeletal muscle development. The RNA sequencing of embryos was conducted, and microRNA (miRNA)-mediated competitive endogenous RNA (ceRNA) networks were constructed. qRT-PCR, siRNA knockdown, CCK-8 assay, scratch assay, and dual luciferase assay were used to carry out gene function identification. Through the analysis of the ceRNA networks, three miRNAs (miR-493-3p, miR-3959-3p, and miR-410-5p) and three genes (TEAD1, ZBTB34, and POGLUT1) were identified. The qRT-PCR of the DE-miRNAs and genes in the muscle tissues of sheep showed that the expression levels of the TEAD1 gene and miR-410-5p were correlated with the growth rate. The knockdown of the TEAD1 gene by siRNA could significantly inhibit the proliferation of sheep primary embryonic myoblasts, and the expression levels of SLC1A5, FoxO3, MyoD, and Pax7 were significantly downregulated. The targeting relationship between miR-410-5p and the TEAD1 gene was validated by a dual luciferase assay, and miR-410-5p can significantly downregulate the expression of TEAD1 in sheep primary embryonic myoblasts. We proved the regulatory relationship between miR-410-5p and the TEAD1 gene, which was related to the proliferation of sheep embryonic myoblasts. The results provide a reference and molecular basis for understanding the molecular mechanism of embryonic muscle development.

Analysis of the effect of zoledronic acid on gene differences in rat jaw

BACKGROUND

With the widespread use of bisphosphonates, there are more and more complications about bisphosphonates, bisphosphonate-related osteonecrosis of the jaw is one.In the past ten years, there have been many studies on the mechanism of bisphosphonate associated jaw necrosis.

OBJECTIVE

To investigate the influence and analysis of zoledronic acid on gene differences in rat jaw.

METHODS

Six Sprague-Dawley female rats were randomly divided into control group (n = 3) and experimental group (n = 3). The experimental group received zoledronic acid injection for 12 weeks (dose of 0.2 mg / kg, 3 times a week).Control groups were injected with normal saline for 12 weeks. All rats were subjected to left mandibular first molar extraction 12 weeks later.After 8 weeks of tooth extraction, all rats were sacrificed and the mandible was removed.RNA-seq was used to analyze differential gene changes in all mandibles. Bioinformatics analysis of differential genes.

RESULTS

Compared with the two rat groups, there were 2,830 different genes, including 1,001 upregulated genes and 1,829 down-regulated genes. Gene Ontology analysis revealed that the upregulated genes were mainly associated with immune-related pathways. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that Hedgehog signaling pathway, Notch signaling pathway and Hippo signaling pathway were associated with upregulated genes. After the Gene Set Enrichment Analysis, the Gene Ontology analysis showed that 2559 / 6588 gene sets are upregulated in phenotype experimental group,and 342 gene sets with p <0.05. The Kyoto Encyclopedia of Genes and Genomes analysis revealed that 95 / 316 gene sets are upregulated in phenotype experimental group, and four gene sets(Notch pathway, other types of O-glycan biosynthesis, ovarian steridogenesis and Hippo pathway) with p <0.05.

CONCLUSIONS

Changes in differential genes are mainly related to immune-related processes and pathways, and pathways related to bone metabolism. The up-regulation of some genes can promote the progress of Bisphosphonate-related osteonecrosis of the jaw.

The Functional Role of Long Non-Coding RNA in Myogenesis and Skeletal Muscle Atrophy

Skeletal muscle is a pivotal organ in humans that maintains locomotion and homeostasis. Muscle atrophy caused by sarcopenia and cachexia, which results in reduced muscle mass and impaired skeletal muscle function, is a serious health condition that decreases life longevity in humans. Recent studies have revealed the molecular mechanisms by which long non-coding RNAs (lncRNAs) regulate skeletal muscle mass and function through transcriptional regulation, fiber-type switching, and skeletal muscle cell proliferation. In addition, lncRNAs function as natural inhibitors of microRNAs and induce muscle hypertrophy or atrophy. Intriguingly, muscle atrophy modifies the expression of thousands of lncRNAs. Therefore, although their exact functions have not yet been fully elucidated, various novel lncRNAs associated with muscle atrophy have been identified. Here, we comprehensively review recent knowledge on the regulatory roles of lncRNAs in skeletal muscle atrophy. In addition, we discuss the issues and possibilities of targeting lncRNAs as a treatment for skeletal muscle atrophy and muscle wasting disorders in humans.

A Tead1-Apelin axis directs paracrine communication from myogenic to endothelial cells in skeletal muscle

Apelin (Apln) is a myokine that regulates skeletal muscle plasticity and metabolism and declines during aging. Through a yeast one-hybrid transcription factor binding screen, we identified the TEA domain transcription factor 1 (Tead1) as a novel regulator of the Apln promoter. Single-cell analysis of regenerating muscle revealed that the apelin receptor (Aplnr) is enriched in endothelial cells, whereas Tead1 is enriched in myogenic cells. Knock-down of Tead1 stimulates Apln secretion from muscle cells in vitro and myofiber-specific overexpression of Tead1 suppresses Apln secretion in vivo. Apln secretion via Tead1 knock-down in muscle cells stimulates endothelial cell expansion via endothelial Aplnr. In vivo, Apln peptide supplementation enhances endothelial cell expansion while Tead1 muscle overexpression delays endothelial remodeling following muscle injury. Our work describes a novel paracrine crosstalk in which Apln secretion is controlled by Tead1 in myogenic cells and influences endothelial remodeling during muscle repair.

Comparative analyses of copy number variations between swamp and river buffalo

Domestic buffalo is an important livestock in the tropical and sub-tropical region, including two types: swamp and river buffalo. The swamp buffalo is mainly used as draft animal, while the river buffalo is raised for milk production. In this study, based on the new high-quality buffalo reference genome UOA_WB_1, we firstly investigated the copy number variants in buffalo using whole-genome Illumina sequencing. A total of 3,734 CNV regions (CNVRs) were detected in 106 buffalo population with a total length of 23,429,066 bp, corresponding to ∼ 0.88% of the water buffalo genome (UOA_WB_1). Our results revealed a clear population differentiation in CNV between swamp and river buffalo. In addition, a total of 667 highly differentiated CNVRs (covering 886 genes) were detected between river and swamp buffalo population. We detected a set of CNVR-overlapping genes associated with exercise, immunity, nerve, and milk trait which exhibited different copy numbers between swamp and river buffalo population. This study provides valuable genome variation resources for buffalo and would contribute to understanding the genetic differences between swamp and river buffalo.

The exercise-induced long noncoding RNA CYTOR promotes fast-twitch myogenesis in aging

[Figure: see text].

Six1 promotes skeletal muscle thyroid hormone response through regulation of the MCT10 transporter

BACKGROUND

The Six1 transcription factor is implicated in controlling the development of several tissue types, notably skeletal muscle. Six1 also contributes to muscle metabolism and its activity is associated with the fast-twitch, glycolytic phenotype. Six1 regulates the expression of certain genes of the fast muscle program by directly stimulating their transcription or indirectly acting through a long non-coding RNA. We hypothesized that additional mechanisms of action of Six1 might be at play.

METHODS

A combined analysis of gene expression profiling and genome-wide location analysis data was performed. Results were validated using in vivo RNA interference loss-of-function assays followed by measurement of gene expression by RT-PCR and transcriptional reporter assays.

RESULTS

The Slc16a10 gene, encoding the thyroid hormone transmembrane transporter MCT10, was identified as a gene with a transcriptional enhancer directly bound by Six1 and requiring Six1 activity for full expression in adult mouse tibialis anterior, a predominantly fast-twitch muscle. Of the various thyroid hormone transporters, MCT10 mRNA was found to be the most abundant in skeletal muscle, and to have a stronger expression in fast-twitch compared to slow-twitch muscle groups. Loss-of-function of MCT10 in the tibialis anterior recapitulated the effect of Six1 on the expression of fast-twitch muscle genes and led to lower activity of a thyroid hormone receptor-dependent reporter gene.

CONCLUSIONS

These results shed light on the molecular mechanisms controlling the tissue expression profile of MCT10 and identify modulation of the thyroid hormone signaling pathway as an additional mechanism by which Six1 influences skeletal muscle metabolism.

TEAD family transcription factors in development and disease

The balance between stem cell potency and lineage specification entails the integration of both extrinsic and intrinsic cues, which ultimately influence gene expression through the activity of transcription factors. One example of this is provided by the Hippo signalling pathway, which plays a central role in regulating organ size during development. Hippo pathway activity is mediated by the transcriptional co-factors Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), which interact with TEA domain (TEAD) proteins to regulate gene expression. Although the roles of YAP and TAZ have been intensively studied, the roles played by TEAD proteins are less well understood. Recent studies have begun to address this, revealing that TEADs regulate the balance between progenitor self-renewal and differentiation throughout various stages of development. Furthermore, it is becoming apparent that TEAD proteins interact with other co-factors that influence stem cell biology. This Primer provides an overview of the role of TEAD proteins during development, focusing on their role in Hippo signalling as well as within other developmental, homeostatic and disease contexts.

Tissue-Engineered Skeletal Muscle Models to Study Muscle Function, Plasticity, and Disease

Skeletal muscle possesses remarkable plasticity that permits functional adaptations to a wide range of signals such as motor input, exercise, and disease. Small animal models have been pivotal in elucidating the molecular mechanisms regulating skeletal muscle adaptation and plasticity. However, these small animal models fail to accurately model human muscle disease resulting in poor clinical success of therapies. Here, we review the potential of in vitro three-dimensional tissue-engineered skeletal muscle models to study muscle function, plasticity, and disease. First, we discuss the generation and function of in vitro skeletal muscle models. We then discuss the genetic, neural, and hormonal factors regulating skeletal muscle fiber-type in vivo and the ability of current in vitro models to study muscle fiber-type regulation. We also evaluate the potential of these systems to be utilized in a patient-specific manner to accurately model and gain novel insights into diseases such as Duchenne muscular dystrophy (DMD) and volumetric muscle loss. We conclude with a discussion on future developments required for tissue-engineered skeletal muscle models to become more mature, biomimetic, and widely utilized for studying muscle physiology, disease, and clinical use.

Molecular Signaling Pathways and Essential Metabolic Elements in Bone Remodeling: An Implication of Therapeutic Targets for Bone Diseases

Bone is one of the dynamic tissues in the human body that undergoes continuous remodelling through subsequent actions of bone cells, osteoclasts, and osteoblasts. Several signal transduction pathways are involved in the transition of mesenchymal stem cells into osteoblasts. These primarily include Runx2, ATF4, Wnt signaling and sympathetic signalling. The differentiation of osteoclasts is controlled by M-CSF, RANKL, and costimulatory signalling. It is well known that bone remodelling is regulated through receptor activator of nuclear factor-kappa B ligand followed by binding to RANK, which eventually induces the differentiation of osteoclasts. The resorbing osteoclasts secrete TRAP, cathepsin K, MMP-9 and gelatinase to digest the proteinaceous matrix of type I collagen and form a saucer-shaped lacuna along with resorption tunnels in the trabecular bone. Osteoblasts secrete a soluble decoy receptor, osteoprotegerin that prevents the binding of RANK/RANKL and thus moderating osteoclastogenesis. Moreover, bone homeostasis is also regulated by several growth factors like, cytokines, calciotropic hormones, parathyroid hormone and sex steroids. The current review presents a correlation of the probable molecular targets underlying the regulation of bone mass and the role of essential metabolic elements in bone remodelling. Targeting these signaling pathways may help to design newer therapies for treating bone diseases.

The role of MAP-kinase p38 in the m. soleus slow myosin mRNA transcription regulation during short-term functional unloading

The unloading of postural muscles leads to the changes in myosins heavy chains isoforms (MyHCs) mRNAs transcription pattern, that cause severe alterations of muscle functioning. Several transcription factors such as NFATc1 and TEAD1 upregulate slow MyHC mRNA transcription, and p38 MAP kinase can phosphorylate NFAT and TEAD1, causing their inactivation. However, the role p38 MAP kinase plays in MyHCs mRNAs transcription regulation in postural soleus muscle during unloading remains unclear. We aimed to investigate whether pharmacological inhibition of p38 MAPK during rat soleus unloading would prevent the unloading-induced slow-type MyHC mRNA transcription decrease by affecting calcineurin/NFATc1 or TEAD1 signaling. Male Wistar rats were randomly assigned to three groups: cage control (C), 3-day hindlimb suspended group (3HS) and 3-day hindlimb suspended group with the daily oral supplementation of 10 mg/kg p38 MAPK inhibitor VX-745 (3HS + VX-745). 3 days of hindlimb suspension caused the significant decreases of slow MyHC and slow-tonic myh7b mRNAs transcription as well as the decrease of NFATc1-dependent MCIP1.4 mRNA transcription in rat soleus muscles compared to the cage control. P38 MAP-kinase inhibition during hindlimb suspension completely prevented slow MyHC mRNA content decrease and partially prevented slow-tonic myh7b and MCIP1.4 mRNAs transcription decreases compared to the 3HS group. We also observed NFATc1 and TEAD1 myonuclear contents increases in the 3HS + VX-745 group compared to both 3HS and C groups (p < 0.05). Therefore, we found that p38 inhibition counteracts the unloading-induced slow MyHC mRNA transcription downregulation and leads to the activation of calcineurin/NFAT signaling cascade in unloaded rat soleus muscles.

Genome-wide meta-analysis of variant-by-diuretic interactions as modulators of lipid traits in persons of European and African ancestry

Hypertension (HTN) is a significant risk factor for cardiovascular morbidity and mortality. Metabolic abnormalities, including adverse cholesterol and triglycerides (TG) profiles, are frequent comorbid findings with HTN and contribute to cardiovascular disease. Diuretics, which are used to treat HTN and heart failure, have been associated with worsening of fasting lipid concentrations. Genome-wide meta-analyses with 39,710 European-ancestry (EA) individuals and 9925 African-ancestry (AA) individuals were performed to identify genetic variants that modify the effect of loop or thiazide diuretic use on blood lipid concentrations. Both longitudinal and cross sectional data were used to compute cohort-specific interaction results, which were then combined through meta-analysis in each ancestry. These ancestry-specific results were further combined through trans-ancestry meta-analysis. Analysis of EA data identified two genome-wide significant (p < 5 × 10-8) loci with single nucleotide variant (SNV)-loop diuretic interaction on TG concentrations (including COL11A1). Analysis of AA data identified one genome-wide significant locus adjacent to BMP2 with SNV-loop diuretic interaction on TG concentrations. Trans-ancestry analysis strengthened evidence of association for SNV-loop diuretic interaction at two loci (KIAA1217 and BAALC). There were few significant SNV-thiazide diuretic interaction associations on TG concentrations and for either diuretic on cholesterol concentrations. Several promising loci were identified that may implicate biologic pathways that contribute to adverse metabolic side effects from diuretic therapy.

MicroRNA-mRNA Co-sequencing Identifies Transcriptional and Post-transcriptional Regulatory Networks Underlying Muscle Wasting in Cancer Cachexia

Cancer cachexia is a metabolic syndrome with alterations in gene regulatory networks that consequently lead to skeletal muscle wasting. Integrating microRNAs-mRNAs omics profiles offers an opportunity to understand transcriptional and post-transcriptional regulatory networks underlying muscle wasting. Here, we used RNA sequencing to simultaneously integrate and explore microRNAs and mRNAs expression profiles in the tibialis anterior (TA) muscles of the Lewis Lung Carcinoma (LLC) model of cancer cachexia. We found 1,008 mRNAs and 18 microRNAs differentially expressed in cachectic mice compared with controls. Although our transcriptomic analysis demonstrated a high heterogeneity in mRNA profiles of cachectic mice, we identified a reduced number of differentially expressed genes that were uniformly regulated within cachectic muscles. This set of uniformly regulated genes is associated with the extracellular matrix (ECM), proteolysis, and inflammatory response. We also used transcriptomic data to perform enrichment analysis of transcriptional factor binding sites in promoter sequences, which revealed activation of the atrophy-related transcription factors NF-κB, Stat3, AP-1, and FoxO. Furthermore, the integration of mRNA and microRNA expression profiles identified post-transcriptional regulation by microRNAs of genes involved in ECM organization, cell migration, transcription factors binding, ion transport, and the FoxO signaling pathway. Our integrative analysis of microRNA-mRNA co-profiles comprehensively characterized regulatory relationships of molecular pathways and revealed microRNAs targeting ECM-associated genes in cancer cachexia.

Understanding divergent domestication traits from the whole-genome sequencing of swamp- and river-buffalo populations

Domesticated buffaloes have been integral to rice-paddy agro-ecosystems for millennia, yet relatively little is known about the buffalo genomics. Here, we sequenced and assembled reference genomes for both swamp and river buffaloes and we re-sequenced 230 individuals (132 swamp buffaloes and 98 river buffaloes) sampled from across Asia and Europe. Beyond the many actionable insights that our study revealed about the domestication, basic physiology and breeding of buffalo, we made the striking discovery that the divergent domestication traits between swamp and river buffaloes can be explained with recent selections of genes on social behavior, digestion metabolism, strengths and milk production.

β-Hydroxy-β-methylbutyrate-Induced Upregulation of miR-199a-3p Contributes to Slow-To-Fast Muscle Fiber Type Conversion in Mice and C2C12 Cells

The influence of β-hydroxy-β-methylbutyrate (HMB) on proliferation and differentiation of myogenic cells has been well-studied. However, the role of HMB in myofiber specification and potential mechanisms is largely unknown. Thus, the objective of this research was to explore the role of HMB supplementation in myofiber specification. Results showed that HMB treatment significantly increased the fast MyHC protein level (mice: 1.59 ± 0.08, P < 0.01; C2C12: 2.26 ± 0.11, P < 0.001), decreased the slow MyHC protein level (mice: 0.76 ± 0.05, P < 0.05; C2C12: 0.52 ± 0.02, P < 0.001), and increased the miR-199a-3p level (mice: 4.93 ± 0.37, P < 0.001; C2C12: 11.25 ± 0.57, P < 0.001). Besides, we also observed that HMB promoted the activity of glycolysis-related enzymes and reduced the activities of oxidation-related enzymes in mice and C2C12 cells. Overexpression of miR-199a-3p downregulated the slow MyHC protein level (0.71 ± 0.02, P < 0.01) and upregulated the fast MyHC protein level (2.13 ± 0.09, P < 0.001), while repression of miR-199a-3p exhibited the opposite effect. Target identification results verified that miR-199a-3p targets the 3'UTR of the TEA domain family member 1 (TEAD1) to cause its post-transcriptional inhibition (0.41 ± 0.07, P < 0.01). Knockdown of TEAD1 exhibited a similar effect with miR-199a-3p on myofiber specification. Moreover, suppression of miR-199a-3p blocked slow-to-fast myofiber type transition induced by HMB. Together, our finding revealed that miR-199-3p is induced by HMB and contributes to the action of HMB on slow-to-fast myofiber type conversion via targeting TEAD1.

Dynamic enhancers control skeletal muscle identity and reprogramming

Skeletal muscles consist of fibers of differing metabolic activities and contractility, which become remodeled in response to chronic exercise, but the epigenomic basis for muscle identity and adaptation remains poorly understood. Here, we used chromatin immunoprecipitation sequencing of dimethylated histone 3 lysine 4 and acetylated histone 3 lysine 27 as well as transposase-accessible chromatin profiling to dissect cis-regulatory networks across muscle groups. We demonstrate that in vivo enhancers specify muscles in accordance with myofiber composition, show little resemblance to cultured myotube enhancers, and identify glycolytic and oxidative muscle-specific regulators. Moreover, we find that voluntary wheel running and muscle-specific peroxisome proliferator-activated receptor gamma coactivator-1 alpha (Pgc1a) transgenic (mTg) overexpression, which stimulate endurance performance in mice, result in markedly different changes to the epigenome. Exercise predominantly leads to enhancer hypoacetylation, whereas mTg causes hyperacetylation at different sites. Integrative analysis of regulatory regions and gene expression revealed that exercise and mTg are each associated with myocyte enhancer factor (MEF) 2 and estrogen-related receptor (ERR) signaling and transcription of genes promoting oxidative metabolism. However, exercise was additionally associated with regulation by retinoid X receptor (RXR), jun proto-oncogene (JUN), sine oculis homeobox factor (SIX), and other factors. Overall, our work defines the unique enhancer repertoires of skeletal muscles in vivo and reveals that divergent exercise-induced or PGC1α-driven epigenomic programs direct partially convergent transcriptional networks.

Transcriptional cofactor Vgll2 is required for functional adaptations of skeletal muscle induced by chronic overload

Skeletal muscle is composed of heterogeneous populations of myofibers classified as slow- and fast-twitch fibers. Myofiber size and composition are drastically changed in response to physiological demands. We previously showed that transcriptional cofactor vestigial-like (Vgll) 2 is a pivotal regulator of slow muscle gene programming under sedentary conditions. However, whether Vgll2 is required for skeletal muscle adaptations after chronic overload is unclear. Therefore, we investigated the role of Vgll2 in chronic overload-inducing skeletal muscle adaptations using synergist ablation (SA) on plantaris. We found that Vgll2 is an essential regulator of the switch towards a slow-contractile phenotype and oxidative metabolism during chronic overload. Mice lacking Vgll2 exhibited limited fiber type transition and downregulation of genes related to lactate metabolism and their regulator peroxisome proliferator-activated receptor gamma coactivator 1α1, after SA, was augmented in Vgll2-deficient mice compared with in wild-type mice. Mechanistically, increased muscle usage elevated Vgll2 levels and promoted the interaction between Vgll2 and its transcription partners such as TEA domain1 (TEAD1), MEF2c, and NFATc1. Calcium ionophore treatment promoted nuclear translocation of Vgll2 and increased TEAD-dependent MYH7 promotor activity in a Vgll2-dependent manner. Taken together, these data demonstrate that Vgll2 plays an important role for functional adaptation of skeletal muscle to chronic overload.

VGLL3 operates via TEAD1, TEAD3 and TEAD4 to influence myogenesis in skeletal muscle

VGLL proteins are transcriptional co-factors that bind TEAD family transcription factors to regulate events ranging from wing development in fly, to muscle fibre composition and immune function in mice. Here, we characterise Vgll3 in skeletal muscle. We found that mouse Vgll3 was expressed at low levels in healthy muscle but that its levels increased during hypertrophy or regeneration; in humans, VGLL3 was highly expressed in tissues from patients with various muscle diseases, such as in dystrophic muscle and alveolar rhabdomyosarcoma. Interaction proteomics revealed that VGLL3 bound TEAD1, TEAD3 and TEAD4 in myoblasts and/or myotubes. However, there was no interaction with proteins from major regulatory systems such as the Hippo kinase cascade, unlike what is found for the TEAD co-factors YAP (encoded by YAP1) and TAZ (encoded by WWTR1). Vgll3 overexpression reduced the activity of the Hippo negative-feedback loop, affecting expression of muscle-regulating genes including Myf5, Pitx2 and Pitx3, and genes encoding certain Wnts and IGFBPs. VGLL3 mainly repressed gene expression, regulating similar genes to those regulated by YAP and TAZ. siRNA-mediated Vgll3 knockdown suppressed myoblast proliferation, whereas Vgll3 overexpression strongly promoted myogenic differentiation. However, skeletal muscle was overtly normal in Vgll3-null mice, presumably due to feedback signalling and/or redundancy. This work identifies VGLL3 as a transcriptional co-factor operating with the Hippo signal transduction network to control myogenesis.

Summary: VGLL3 interacts with TEAD transcription factors to direct expression of crucial muscle regulatory genes and contribute to the control of skeletal myogenesis.

Network modules uncover mechanisms of skeletal muscle dysfunction in COPD patients

Background

Chronic obstructive pulmonary disease (COPD) patients often show skeletal muscle dysfunction that has a prominent negative impact on prognosis. The study aims to further explore underlying mechanisms of skeletal muscle dysfunction as a characteristic systemic effect of COPD, potentially modifiable with preventive interventions (i.e. muscle training). The research analyzes network module associated pathways and evaluates the findings using independent measurements.

Methods

We characterized the transcriptionally active network modules of interacting proteins in the vastus lateralis of COPD patients (n = 15, FEV₁ 46 ± 12% pred, age 68 ± 7 years) and healthy sedentary controls (n = 12, age 65 ± 9  years), at rest and after an 8-week endurance training program. Network modules were functionally evaluated using experimental data derived from the same study groups.

Results

At baseline, we identified four COPD specific network modules indicating abnormalities in creatinine metabolism, calcium homeostasis, oxidative stress and inflammatory responses, showing statistically significant associations with exercise capacity (VO₂ peak, Watts peak, BODE index and blood lactate levels) (P < 0.05 each), but not with lung function (FEV₁). Training-induced network modules displayed marked differences between COPD and controls. Healthy subjects specific training adaptations were significantly associated with cell bioenergetics (P < 0.05) which, in turn, showed strong relationships with training-induced plasma metabolomic changes; whereas, effects of training in COPD were constrained to muscle remodeling.

Conclusion

In summary, altered muscle bioenergetics appears as the most striking finding, potentially driving other abnormal skeletal muscle responses.

Trial registration The study was based on a retrospectively registered trial (May 2017), ClinicalTrials.gov identifier: NCT03169270

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1405-y) contains supplementary material, which is available to authorized users.

The emerging role of Hippo signaling pathway in regulating osteoclast formation

A delicate balance between osteoblastic bone formation and osteoclastic bone resorption is crucial for bone homeostasis. This process is regulated by the Hippo signaling pathway including key regulatory molecules RASSF2, NF2, MST1/2, SAV1, LATS1/2, MOB1, YAP, and TAZ. It is well established that the Hippo signaling pathway plays an important part in regulating osteoblast differentiation, but its role in osteoclast formation and activation remains poorly understood. In this review, we discuss the emerging role of Hippo-signaling pathway in osteoclast formation and bone homeostasis. It is revealed that specific molecules of the Hippo-signaling pathway take part in a stage specific regulation in pre-osteoclast proliferation, osteoclast differentiation and osteoclast apoptosis and survival. Upon activation, MST and LAST, transcriptional co-activators YAP and TAZ bind to the members of the TEA domain (TEAD) family transcription factors, and influence osteoclast differentiation via regulating the expression of downstream target genes such as connective tissue growth factor (CTGF/CCN2) and cysteine-rich protein 61 (CYR61/CCN1). In addition, through interacting or cross talking with RANKL-mediated signaling cascades including NF-κB, MAPKs, AP1, and NFATc1, Hippo-signaling molecules such as YAP/TAZ/TEAD complex, RASSF2, MST2, and Ajuba could also potentially modulate osteoclast differentiation and function. Elucidating the roles of the Hippo-signaling pathway in osteoclast development and specific molecules involved is important for understanding the mechanism of bone homeostasis and diseases.

Vestigial-like 2 contributes to normal muscle fiber type distribution in mice

Skeletal muscle is composed of heterogeneous populations of myofibers that are classified as slow- and fast-twitch fibers. The muscle fiber-type is regulated in a coordinated fashion by multiple genes, including transcriptional factors and microRNAs (miRNAs). However, players involved in this regulation are not fully elucidated. One of the members of the Vestigial-like factors, Vgll2, is thought to play a pivotal role in TEA domain (TEAD) transcription factor-mediated muscle-specific gene expression because of its restricted expression in skeletal muscles of adult mice. Here, we generated Vgll2 null mice and investigated Vgll2 function in adult skeletal muscles. These mice presented an increased number of fast-twitch type IIb fibers and exhibited a down-regulation of slow type I myosin heavy chain (MyHC) gene, Myh7, which resulted in exercise intolerance. In accordance with the decrease in Myh7, down-regulation of miR-208b, encoded within Myh7 gene and up-regulation of targets of miR-208b, Sox6, Sp3, and Purβ, were observed in Vgll2 deficient mice. Moreover, we detected the physical interaction between Vgll2 and TEAD1/4 in neonatal skeletal muscles. These results suggest that Vgll2 may be both directly and indirectly involved in the programing of slow muscle fibers through the formation of the Vgll2-TEAD complex.

Metabolic control of myofibers: promising therapeutic target for obesity and type 2 diabetes

Mammalian skeletal muscles are composed of two major fibre types (I and II) that differ in terms of size, metabolism and contractile properties. In general, slow-twitch type I fibres are rich in mitochondria and have a greater insulin sensitivity than fast-twitch type II skeletal muscles. Although not widely appreciated, a forced induction of the slow skeletal muscle phenotype may inhibit the progress of obesity and diabetes. This potentially forms the basis for targeting slow/oxidative myofibers in the treatment of obesity. In this context, a better understanding of the molecular basis of fibre-type specification and plasticity may help to identify potential therapeutic targets for obesity and diabetes.

Myofiber-specific TEAD1 overexpression drives satellite cell hyperplasia and counters pathological effects of dystrophin deficiency

When unperturbed, somatic stem cells are poised to affect immediate tissue restoration upon trauma. Yet, little is known regarding the mechanistic basis controlling initial and homeostatic ‘scaling’ of stem cell pool sizes relative to their target tissues for effective regeneration. Here, we show that TEAD1-expressing skeletal muscle of transgenic mice features a dramatic hyperplasia of muscle stem cells (i.e. satellite cells, SCs) but surprisingly without affecting muscle tissue size. Super-numeral SCs attain a ‘normal’ quiescent state, accelerate regeneration, and maintain regenerative capacity over several injury-induced regeneration bouts. In dystrophic muscle, the TEAD1 transgene also ameliorated the pathology. We further demonstrate that hyperplastic SCs accumulate non-cell-autonomously via signal(s) from the TEAD1-expressing myofiber, suggesting that myofiber-specific TEAD1 overexpression activates a physiological signaling pathway(s) that determines initial and homeostatic SC pool size. We propose that TEAD1 and its downstream effectors are medically relevant targets for enhancing muscle regeneration and ameliorating muscle pathology.

DOI:http://dx.doi.org/10.7554/eLife.15461.001

Skeletal muscles are primarily composed of cells called muscle fibers, which attach to bones via tendons. These muscle fibers contract to help move the body. Muscle also contains a population of muscle stem cells that repair injured tissue. Normally, in adult skeletal muscle, these stems cells are in a resting state. However, upon injury, the stem cells become activated, divide to increase in number and then develop into new muscle fibers to replace those that were damaged. The balance between the number of stem cells and the size of the muscle must be tightly regulated to ensure that there are enough stem cells to fully regenerate the tissue after injury. However, little is known about how tissues keep their number of stem cells in proportion with their overall size.

Previous attempts to make mice with more muscle stem cells invariably also created mice with larger muscles overall. This raised the question: is it possible to increase the numbers of stem cells without changing the size of the muscle?

Now, Southard, Kim et al. show it is possible and report that mice engineered to overproduce a protein called Tead1 in their muscle fibers have up to 6-times more stem cells yet normally sized muscles. Tead1 is a transcription factor that controls the activity of a number of genes as part of a major signaling pathway.

The stem cells in mice that overproduce Tead1 began to increase in number two weeks after the mice were born because they went through additional rounds of cell division before they entered the resting state. Further experiments then showed that having more stem cells meant that the muscles were repaired more quickly after an injury. Additionally, when mice with extra Tead1 had a mutation that normally leads to muscle wasting, experiments showed that the progression of the disease was stunted.

Southard, Kim et al. also show that the muscle fibers that are directly attached to the muscle stem cells are needed for the stem cells to increase in number in the Tead1-overexpressing mice. Together these findings suggest that a signal from the muscle fiber to its stem cells regulates the size of the stem cell population in the tissue. The next challenge is to uncover the molecule (or molecules) that signals from the muscle fiber to the stem cells and to gain deeper insight into how the Tead1 protein can counteract the effects of a muscle wasting disease.

DOI:http://dx.doi.org/10.7554/eLife.15461.002

Wnt/β-catenin signaling via Axin2 is required for myogenesis and, together with YAP/Taz and Tead1, active in IIa/IIx muscle fibers

Canonical Wnt/β-catenin signaling plays an important role in myogenic differentiation, but its physiological role in muscle fibers remains elusive. Here, we studied activation of Wnt/β-catenin signaling in adult muscle fibers and muscle stem cells in an Axin2 reporter mouse. Axin2 is a negative regulator and a target of Wnt/β-catenin signaling. In adult muscle fibers, Wnt/β-catenin signaling is only detectable in a subset of fast fibers that have a significantly smaller diameter than other fast fibers. In the same fibers, immunofluorescence staining for YAP/Taz and Tead1 was detected. Wnt/β-catenin signaling was absent in quiescent and activated satellite cells. Upon injury, Wnt/β-catenin signaling was detected in muscle fibers with centrally located nuclei. During differentiation of myoblasts expression of Axin2, but not of Axin1, increased together with Tead1 target gene expression. Furthermore, absence of Axin1 and Axin2 interfered with myoblast proliferation and myotube formation, respectively. Treatment with the canonical Wnt3a ligand also inhibited myotube formation. Wnt3a activated TOPflash and Tead1 reporter activity, whereas neither reporter was activated in the presence of Dkk1, an inhibitor of canonical Wnt signaling. We propose that Axin2-dependent Wnt/β-catenin signaling is involved in myotube formation and, together with YAP/Taz/Tead1, associated with reduced muscle fiber diameter of a subset of fast fibers.

The Hippo signal transduction network for exercise physiologists

The ubiquitous transcriptional coactivators Yap (gene symbol Yap1) and Taz (gene symbol Wwtr1) regulate gene expression mainly by coactivating the Tead transcription factors. Being at the center of the Hippo signaling network, Yap and Taz are regulated by the Hippo kinase cassette and additionally by a plethora of exercise-associated signals and signaling modules. These include mechanotransduction, the AKT-mTORC1 network, the SMAD transcription factors, hypoxia, glucose homeostasis, AMPK, adrenaline/epinephrine and angiotensin II through G protein-coupled receptors, and IL-6. Consequently, exercise should alter Hippo signaling in several organs to mediate at least some aspects of the organ-specific adaptations to exercise. Indeed, Tead1 overexpression in muscle fibers has been shown to promote a fast-to-slow fiber type switch, whereas Yap in muscle fibers and cardiomyocytes promotes skeletal muscle hypertrophy and cardiomyocyte adaptations, respectively. Finally, genome-wide association studies in humans have linked the Hippo pathway members LATS2, TEAD1, YAP1, VGLL2, VGLL3, and VGLL4 to body height, which is a key factor in sports.

YAP-Mediated Mechanotransduction in Skeletal Muscle

Skeletal muscle is not only translating chemical energy into mechanical work, it is also a highly adaptive and regenerative tissue whose architecture and functionality is determined by its mechanical and physical environment. Processing intra- and extracellular mechanical signaling cues contributes to the regulation of cell growth, survival, migration and differentiation. Yes-associated Protein (YAP), a transcriptional coactivator downstream of the Hippo pathway and its paralog, the transcriptional co-activator with PDZ-binding motif (TAZ), were recently found to play a key role in mechanotransduction in various tissues including skeletal muscle. Furthermore, YAP/TAZ modulate myogenesis and muscle regeneration and abnormal YAP activity has been reported in muscular dystrophy and rhabdomyosarcoma. Here, we summarize the current knowledge of mechanosensing and -signaling in striated muscle. We highlight the role of YAP signaling and discuss the different routes and hypotheses of its regulation in the context of mechanotransduction.

HDAC4-myogenin axis as an important marker of HD-related skeletal muscle atrophy

Skeletal muscle remodelling and contractile dysfunction occur through both acute and chronic disease processes. These include the accumulation of insoluble aggregates of misfolded amyloid proteins that is a pathological feature of Huntington’s disease (HD). While HD has been described primarily as a neurological disease, HD patients’ exhibit pronounced skeletal muscle atrophy. Given that huntingtin is a ubiquitously expressed protein, skeletal muscle fibres may be at risk of a cell autonomous HD-related dysfunction. However the mechanism leading to skeletal muscle abnormalities in the clinical and pre-clinical HD settings remains unknown. To unravel this mechanism, we employed the R6/2 transgenic and HdhQ150 knock-in mouse models of HD. We found that symptomatic animals developed a progressive impairment of the contractile characteristics of the hind limb muscles tibialis anterior (TA) and extensor digitorum longus (EDL), accompanied by a significant loss of motor units in the EDL. In symptomatic animals, these pronounced functional changes were accompanied by an aberrant deregulation of contractile protein transcripts and their up-stream transcriptional regulators. In addition, HD mouse models develop a significant reduction in muscle force, possibly as a result of a deterioration in energy metabolism and decreased oxidation that is accompanied by the re-expression of the HDAC4-DACH2-myogenin axis. These results show that muscle dysfunction is a key pathological feature of HD.

Huntington’s disease (HD) is a neurodegenerative disorder in which the mutation results in an extra-long tract of glutamines that causes the huntingtin protein to aggregate. It is characterized by neurological symptoms and brain pathology, which is associated with nuclear and cytoplasmic protein aggregates and with transcriptional deregulation. Despite the fact that HD has been recognized principally as a neurological disease, there are multiple studies indicating that peripheral pathologies including cardiac dysfunction and skeletal muscle atrophy, contribute to the overall progression of HD. To unravel the cause of the skeletal muscle dysfunction, we applied a wide range of molecular and physiological methods to the analysis of two well established genetic mouse models of this disease. We found that symptomatic animals developed muscle dysfunction characterised by a change in the contractile characteristics of fast twitch muscles and a decrease in twitch and tetanic force of hindlimb muscles. In addition, there is a significant decrease in the number of motor units innervating the EDL muscle, and this motor unit loss progresses during the course of the disease. These changes were accompanied by the re-expression of contractile transcripts and markers of muscle denervation such as the HDAC4-Dach2-myogenin axis, as well as the apparent deterioration in energy metabolism and decreased oxidation. Therefore, we conclude, that the HD-related skeletal muscle atrophy is accompanied by progressive loss of functional motor units.

Gene coexpression networks reveal key drivers of phenotypic divergence in porcine muscle

Background

Domestication of the wild pig has led to obese and lean phenotype breeds, and evolutionary genome research has sought to identify the regulatory mechanisms underlying this phenotypic diversity. However, revealing the molecular mechanisms underlying muscle phenotype variation based on differentially expressed genes has proved to be difficult. To characterize the mechanisms regulating muscle phenotype variation under artificial selection, we aimed to provide an integrated view of genome organization by weighted gene coexpression network analysis.

Results

Our analysis was based on 20 publicly available next-generation sequencing datasets of lean and obese pig muscle generated from 10 developmental stages. The evolution of the constructed coexpression modules was examined using the genome resequencing data of 37 domestic pigs and 11 wild boars. Our results showed the regulation of muscle development might be more complex than had been previously acknowledged, and is regulated by the coordinated action of muscle, nerve and immunity related genes. Breed-specific modules that regulated muscle phenotype divergence were identified, and hundreds of hub genes with major roles in muscle development were determined to be responsible for key functional distinctions between breeds. Our evolutionary analysis showed that the role of changes in the coding sequence under positive selection in muscle phenotype divergence was minor.

Conclusions

Muscle phenotype divergence was found to be regulated by the divergence of coexpression network modules under artificial selection, and not by changes in the coding sequence of genes. Our results present multiple lines of evidence suggesting links between modules and muscle phenotypes, and provide insights into the molecular bases of genome organization in muscle development and phenotype variation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1238-5) contains supplementary material, which is available to authorized users.

Thyroid hormone regulates muscle fiber type conversion via miR-133a1

Thyroid hormone promotes slow-to-fast muscle fiber type conversion by inducing miR-133a1 and thereby repressing the expression of the slow muscle determinant TEAD1.

It is known that thyroid hormone (TH) is a major determinant of muscle fiber composition, but the molecular mechanism by which it does so remains unclear. Here, we demonstrated that miR-133a1 is a direct target gene of TH in muscle. Intriguingly, miR-133a, which is enriched in fast-twitch muscle, regulates slow-to-fast muscle fiber type conversion by targeting TEA domain family member 1 (TEAD1), a key regulator of slow muscle gene expression. Inhibition of miR-133a in vivo abrogated TH action on muscle fiber type conversion. Moreover, TEAD1 overexpression antagonized the effect of miR-133a as well as TH on muscle fiber type switch. Additionally, we demonstrate that TH negatively regulates the transcription of myosin heavy chain I indirectly via miR-133a/TEAD1. Collectively, we propose that TH inhibits the slow muscle phenotype through a novel epigenetic mechanism involving repression of TEAD1 expression via targeting by miR-133a1. This identification of a TH-regulated microRNA therefore sheds new light on how TH achieves its diverse biological activities.

The Hippo signal transduction network in skeletal and cardiac muscle

The discovery of the Hippo pathway can be traced back to two areas of research. Genetic screens in fruit flies led to the identification of the Hippo pathway kinases and scaffolding proteins that function together to suppress cell proliferation and tumor growth. Independent research, often in the context of muscle biology, described Tead (TEA domain) transcription factors, which bind CATTCC DNA motifs to regulate gene expression. These two research areas were joined by the finding that the Hippo pathway regulates the activity of Tead transcription factors mainly through phosphorylation of the transcriptional coactivators Yap and Taz, which bind to and activate Teads. Additionally, many other signal transduction proteins crosstalk to members of the Hippo pathway forming a Hippo signal transduction network. We discuss evidence that the Hippo signal transduction network plays important roles in myogenesis, regeneration, muscular dystrophy, and rhabdomyosarcoma in skeletal muscle, as well as in myogenesis, organ size control, and regeneration of the heart. Understanding the role of Hippo kinases in skeletal and heart muscle physiology could have important implications for translational research.

Maximum shortening velocity of lymphatic muscle approaches that of striated muscle

Lymphatic muscle (LM) is widely considered to be a type of vascular smooth muscle, even though LM cells uniquely express contractile proteins from both smooth muscle and cardiac muscle. We tested the hypothesis that LM exhibits an unloaded maximum shortening velocity (Vmax) intermediate between that of smooth muscle and cardiac muscle. Single lymphatic vessels were dissected from the rat mesentery, mounted in a servo-controlled wire myograph, and subjected to isotonic quick release protocols during spontaneous or agonist-evoked contractions. After maximal activation, isotonic quick releases were performed at both the peak and plateau phases of contraction. Vmax was 0.48 ± 0.04 lengths (L)/s at the peak: 2.3 times higher than that of mesenteric arteries and 11.4 times higher than mesenteric veins. In cannulated, pressurized lymphatic vessels, shortening velocity was determined from the maximal rate of constriction [rate of change in internal diameter (-dD/dt)] during spontaneous contractions at optimal preload and minimal afterload; peak -dD/dt exceeded that obtained during any of the isotonic quick release protocols (2.14 ± 0.30 L/s). Peak -dD/dt declined with pressure elevation or activation using substance P. Thus, isotonic methods yielded Vmax values for LM in the mid to high end (0.48 L/s) of those the recorded for phasic smooth muscle (0.05-0.5 L/s), whereas isobaric measurements yielded values (>2.0 L/s) that overlapped the midrange of values for cardiac muscle (0.6-3.3 L/s). Our results challenge the dogma that LM is classical vascular smooth muscle, and its unusually high Vmax is consistent with the expression of cardiac muscle contractile proteins in the lymphatic vessel wall.

Overexpression of Six1 gene suppresses proliferation and enhances expression of fast-type muscle genes in C2C12 myoblasts

Sine oculis homeobox 1 (Six1) homeodomain transcription factor is implicated in the genesis of muscle fiber type diversity, but its regulatory mechanisms on the formation of muscle fiber type are still poorly understood. To elucidate the biological roles of Six1 gene in muscle fiber formation, we established C2C12 cell line overexpressing Six1 and determined the effects of forced Six1 expression on muscle-specific genes expression, cell proliferation, and cell cycles. Our results indicated that Six1 overexpression could significantly promote the expression of fast-type muscle genes Atp2a1, Srl, and Mylpf. Furthermore, Six1 overexpressing C2C12 cells displayed a relative lower proliferative potential, and cell cycle analysis showed that Six1 exerted its role in cell cycle primarily through the regulation of G1/S and G2/M phases. In conclusion, Six1 plays an essential role in modulation of the fast-twitch muscle fiber phenotype through up-regulating fast-type muscle genes expression, and it could suppress the proliferation of muscle cells.

Constitutive expression of Yes-associated protein (Yap) in adult skeletal muscle fibres induces muscle atrophy and myopathy

The aim of this study was to investigate the function of the Hippo pathway member Yes-associated protein (Yap, gene name Yap1) in skeletal muscle fibres in vivo. Specifically we bred an inducible, skeletal muscle fibre-specific knock-in mouse model (MCK-tTA-hYAP1 S127A) to test whether the over expression of constitutively active Yap (hYAP1 S127A) is sufficient to drive muscle hypertrophy or stimulate changes in fibre type composition. Unexpectedly, after 5–7 weeks of constitutive hYAP1 S127A over expression, mice suddenly and rapidly lost 20–25% body weight and suffered from gait impairments and kyphosis. Skeletal muscles atrophied by 34–40% and the muscle fibre cross sectional area decreased by ≈40% when compared to control mice. Histological analysis revealed evidence of skeletal muscle degeneration and regeneration, necrotic fibres and a NADH-TR staining resembling centronuclear myopathy. In agreement with the histology, mRNA expression of markers of regenerative myogenesis (embryonic myosin heavy chain, Myf5, myogenin, Pax7) and muscle protein degradation (atrogin-1, MuRF1) were significantly elevated in muscles from transgenic mice versus control. No significant changes in fibre type composition were detected using ATPase staining. The phenotype was largely reversible, as a cessation of hYAP1 S127A expression rescued body and muscle weight, restored muscle morphology and prevented further pathological progression. To conclude, high Yap activity in muscle fibres does not induce fibre hypertrophy nor fibre type changes but instead results in a reversible atrophy and deterioration.

The role of transcription enhancer factors in cardiovascular biology

The transcriptional enhancer factor (TEF) multigene family is primarily functional in muscle-specific genes through binding to MCAT elements that activate or repress transcription of many genes in response to physiological and pathological stimuli. Among the TEF family, TEF-1, RTEF-1, and DTEF-1 are critical regulators of cardiac and smooth muscle-specific genes during cardiovascular development and cardiac disorders including cardiac hypertrophy. Emerging evidence suggests that in addition to functioning as muscle-specific transcription factors, members of the TEF family may be key mediators of gene expression induced by hypoxia in endothelial cells by virtue of its multidomain organization, potential for post-translational modifications, and interactions with numerous transcription factors, which represent a cell-selective control mediator of nuclear signaling. We review the recent literature demonstrating the involvement of the TEF family of transcription factors in the regulation of differential gene expression in cardiovascular physiology and pathology.

The skeletal muscle Wnt pathway may modulate insulin resistance and muscle development in a diet-induced obese rat model

The Wnt signaling pathway is involved in lipid metabolism and obesity development. Skeletal muscle, a pivotal tissue for metabolism, is regulated by the Wnt signaling. However, little is known of this pathway's involvement in insulin sensitivity and myogenesis in animals. The current study focused on the potential role of Wnt signaling in insulin sensitivity and myogenic events and its further impact on intramuscular fat accumulation. Obesity resistant (OR) and obesity prone (OP) rats were fed a high-fat (HF, 45% kcal fat) diet for 13 weeks. Body weight and circulating triglyceride (TG) were measured and gastrocnemius muscle was collected for analysis of gene expression and protein amount. OP rats had higher body weight and blood TG than OR, and our study demonstrated that the skeletal muscle of OR and OP rats had different levels of β-catenin, which also corresponded to the expression of Wnt downstream genes. The expression of insulin receptor substrate (IRS) was significantly lower in OP than OR skeletal muscle, as was the protein amount of phosphorylated Akt, myocyte enhancer factor-2 (MEF2), and GLUT4. Expression of Myogenic regulatory factor (Myf) 5 and Myf3 (MyoD) were decreased significantly in OP skeletal muscle when compared to OR. Additionally, intramuscular fat was higher in OP than in OR rats. Thus, we propose that the differential Wnt signaling in the skeletal muscle of OR and OP rats is highly likely associated with the differences in insulin sensitivity and myogenic capability in these two strains.

Regulation of an antisense RNA with the transition of neonatal to IIb myosin heavy chain during postnatal development and hypothyroidism in rat skeletal muscle

Postnatal development of fast skeletal muscle is characterized by a transition in expression of myosin heavy chain (MHC) isoforms, from primarily neonatal MHC at birth to primarily IIb MHC in adults, in a tightly coordinated manner. These isoforms are encoded by distinct genes, which are separated by ∼17 kb on rat chromosome 10. The neonatal-to-IIb MHC transition is inhibited by a hypothyroid state. We examined RNA products [mRNA, pre-mRNA, and natural antisense transcript (NAT)] of developmental and adult-expressed MHC genes (embryonic, neonatal, I, IIa, IIx, and IIb) at 2, 10, 20, and 40 days after birth in normal and thyroid-deficient rat neonates treated with propylthiouracil. We found that a long noncoding antisense-oriented RNA transcript, termed bII NAT, is transcribed from a site within the IIb-Neo intergenic region and across most of the IIb MHC gene. NATs have previously been shown to mediate transcriptional repression of sense-oriented counterparts. The bII NAT is transcriptionally regulated during postnatal development and in response to hypothyroidism. Evidence for a regulatory mechanism is suggested by an inverse relationship between IIb MHC and bII NAT in normal and hypothyroid-treated muscle. Neonatal MHC transcription is coordinately expressed with bII NAT. A comparative phylogenetic analysis also suggests that bII NAT-mediated regulation has been a conserved trait of placental mammals for most of the eutherian evolutionary history. The evidence in support of the regulatory model implicates long noncoding antisense RNA as a mechanism to coordinate the transition between neonatal and IIb MHC during postnatal development.

Differentiation and fiber type-specific activity of a muscle creatine kinase intronic enhancer

BACKGROUND

Hundreds of genes, including muscle creatine kinase (MCK), are differentially expressed in fast- and slow-twitch muscle fibers, but the fiber type-specific regulatory mechanisms are not well understood.

RESULTS

Modulatory region 1 (MR1) is a 1-kb regulatory region within MCK intron 1 that is highly active in terminally differentiating skeletal myocytes in vitro. A MCK small intronic enhancer (MCK-SIE) containing a paired E-box/myocyte enhancer factor 2 (MEF2) regulatory motif resides within MR1. The SIE's transcriptional activity equals that of the extensively characterized 206-bp MCK 5'-enhancer, but the MCK-SIE is flanked by regions that can repress its activity via the individual and combined effects of about 15 different but highly conserved 9- to 24-bp sequences. ChIP and ChIP-Seq analyses indicate that the SIE and the MCK 5'-enhancer are occupied by MyoD, myogenin and MEF2. Many other E-boxes located within or immediately adjacent to intron 1 are not occupied by MyoD or myogenin. Transgenic analysis of a 6.5-kb MCK genomic fragment containing the 5'-enhancer and proximal promoter plus the 3.2-kb intron 1, with and without MR1, indicates that MR1 is critical for MCK expression in slow- and intermediate-twitch muscle fibers (types I and IIa, respectively), but is not required for expression in fast-twitch muscle fibers (types IIb and IId).

CONCLUSIONS

In this study, we discovered that MR1 is critical for MCK expression in slow- and intermediate-twitch muscle fibers and that MR1's positive transcriptional activity depends on a paired E-box MEF2 site motif within a SIE. This is the first study to delineate the DNA controls for MCK expression in different skeletal muscle fiber types.

Analysis of the single-nucleotide polymorphism in the 5'UTR and part of intron I of the sheep MSTN gene

The myostatin (MSTN) gene region encompassing the 5'UTR and part of intron I was sequenced in animals of two herds of Latvian Darkhead sheep to extend data on the ovine MSTN gene polymorphism and to provide information useful for local breed conservation. Two and four polymorphic loci were revealed in the 5'UTR and intron I. Four and five local haplotypes were constructed, respectively. The genotyping data obtained and that previously reported for the same genomic region were combined in one dataset for the haplotype analysis. Recombination events were detected between loci (c.-40, c.-37) in the 5'UTR and (c.373+18, c.373+101) and (c.373+101, c.373+241) in intron I. Single-nucleotide polymorphisms at c.373+249 and c.373+323 appear to be involved in the strong linkage (p < 0.01). Linkage blocks (c.373+241, c.373+243) and (c.373+241, c.373+259) were revealed at nominal (p < 0.05) level of probability. Haplotype-specific patterns of the transcription factor binding sites predicted in silico were constructed to evaluate a putative functional significance of the particular alleles and haplotypes. A nucleotide at c.373+18 was shown to influence the pre-mRNA secondary structure. DNA curvature predicted in silico for allele c.373+101C was proven experimentally. A possible impact of the particular polymorphisms on the transcription and/or splicing efficiency is discussed.

IRF2BP2 is a skeletal and cardiac muscle-enriched ischemia-inducible activator of VEGFA expression

We sought to identify an essential component of the TEAD4/VGLL4 transcription factor complex that controls vascular endothelial growth factor A (VEGFA) expression in muscle. A yeast 2-hybrid screen was used to clone a novel component of the TEAD4 complex from a human heart cDNA library. We identified interferon response factor 2 binding protein 2 (IRF2BP2) and confirmed its presence in the TEAD4/VGLL4 complex in vivo by coimmunoprecipitation and mammalian 2-hybrid assays. Coexpression of IRF2BP2 with TEAD4/VGLL4 or TEAD1 alone potently activated, whereas knockdown of IRF2BP2 reduced, VEGFA expression in C(2)C(12) muscle cells. Thus, IRF2BP2 is required to activate VEGFA expression. In mouse embryos, IRF2BP2 was ubiquitously expressed but became progressively enriched in the fetal heart, skeletal muscles, and lung. Northern blot analysis revealed high levels of IRF2BP2 mRNA in adult human heart and skeletal muscles, but immunoblot analysis showed low levels of IRF2BP2 protein in skeletal muscle, indicating post-transcriptional regulation of IRF2BP2 expression. IRF2BP2 protein levels are markedly increased by ischemia in skeletal and cardiac muscle compared to normoxic controls. IRF2BP2 is a novel ischemia-induced coactivator of VEGFA expression that may contribute to revascularization of ischemic cardiac and skeletal muscles.

Fine-mapping of muscle weight QTL in LG/J and SM/J intercrosses

Genetic variation plays a substantial role in variation in strength, but the underlying mechanisms remain poorly understood. The objective of the present study was to examine the mechanisms underlying variation in muscle mass, a predictor of strength, between LG/J and SM/J strains, which are the inbred progeny of mice selected, respectively, for high and low body weight. We measured weight of five hindlimb muscles in LG/J and SM/J males and females, in F(1) and F(2) intercrosses, and in an advanced intercross (AI), F(34), between the two. F(2) mice were genotyped using 162 SNPs throughout the genome; F(34) mice were genotyped at 3,015 SNPs. A twofold difference in muscle mass between the LG/J and SM/J mouse strains was observed. Integrated genome-wide association analysis in the combined population of F(2) and AI identified 22 quantitative trait loci (QTL; genome-wide P < 0.05) affecting muscle weight on Chr 2 (2 QTL), 4, 5, 6 (7 QTL), 7 (4 QTL), 8 (4 QTL), and 11 (3 QTL). The LG/J allele conferred greater muscle weight in all cases. The 1.5-LOD QTL support intervals ranged between 0.3 and 13.4 Mb (median 3.7 Mb) restricting the list of candidates to between 5 and 97 genes. Selection for body weight segregated the alleles affecting skeletal muscle, the most abundant tissue in the body. Combination of analyses in an F(2) and AI was an effective strategy to detect and refine the QTL in a genome-wide manner. The achieved resolution facilitates further elucidation of the underlying genetic mechanisms affecting muscle mass.

TEAD-1 overexpression in the mouse heart promotes an age-dependent heart dysfunction

TEA domain transcription factor-1 (TEAD-1) is essential for proper heart development and is implicated in cardiac specific gene expression and the hypertrophic response of primary cardiomyocytes to hormonal and mechanical stimuli, and its activity increases in the pressure-overloaded hypertrophied rat heart. To investigate whether TEAD-1 is an in vivo modulator of cardiac specific gene expression and hypertrophy, we developed transgenic mice expressing hemagglutinin-tagged TEAD-1 under the control of the muscle creatine kinase promoter. We show that a sustained increase in TEAD-1 protein leads to an age-dependent dysfunction. Magnetic resonance imaging revealed decreases in cardiac output, stroke volume, ejection fraction, and fractional shortening. Isolated TEAD-1 hearts revealed decreased left ventricular power output that correlated with increased betaMyHC protein. Histological analysis showed altered alignment of cardiomyocytes, septal wall thickening, and fibrosis, although electrocardiography displayed a left axis shift of mean electrical axis. Transcripts representing most members of the fetal heart gene program remained elevated from fetal to adult life. Western blot analyses revealed decreases in p-phospholamban, SERCA2a, p-CX43, p-GSK-3alpha/beta, nuclear beta-catenin, GATA4, NFATc3/c4, and increased NCX1, nuclear DYKR1A, and Pur alpha/beta protein. TEAD-1 mice did not display cardiac hypertrophy. TEAD-1 mice do not tolerate stress as they die over a 4-day period after surgical induction of pressure overload. These data provide the first in vivo evidence that increased TEAD-1 can induce characteristics of cardiac remodeling associated with cardiomyopathy and heart failure.

Acute molecular response of mouse hindlimb muscles to chronic stimulation

Stimulation of the mouse hindlimb via the sciatic nerve was performed for a 4-h period to investigate acute muscle gene activation in a model of muscle phenotype conversion. Initial force production (1.6 +/- 0.1 g/g body wt) declined 45% within 10 min and was maintained for the remainder of the experiment. Force returned to initial levels upon study completion. An immediate-early growth response was present in the extensor digitorum longus (EDL) muscle (FOS, JUN, activating transcription factor 3, and musculoaponeurotic fibrosarcoma oncogene) with a similar but attenuated pattern in the soleus muscle. Transcript profiles showed decreased fast fiber-specific mRNA (myosin heavy chains 2A and 2B, fast troponins T(3) and I, alpha-tropomyosin, muscle creatine kinase, and parvalbumin) and increased slow transcripts (myosin heavy chain-1beta/slow, troponin C slow, and tropomyosin 3y) in the EDL versus soleus muscles. Histological analysis of the EDL revealed glycogen depletion without inflammatory cell infiltration in stimulated versus control muscles, whereas ultrastructural analysis showed no evidence of myofiber damage after stimulation. Multiple fiber type-specific transcription factors (tea domain family member 1, nuclear factor of activated T cells 1, peroxisome proliferator-activated receptor-gamma coactivator-1alpha and -beta, circadian locomotor output cycles kaput, and hypoxia-inducible factor-1alpha) increased in the EDL along with transcription factors characteristic of embryogenesis (Kruppel-like factor 4; SRY box containing 17; transcription factor 15; PBX/knotted 1 homeobox 1; and embryonic lethal, abnormal vision). No established in vivo satellite cell markers or genes activated in our parallel experiments of satellite cell proliferation in vitro (cyclins A(2), B(2), C, and E(1) and MyoD) were differentially increased in the stimulated muscles. These results indicated that the molecular onset of fast to slow phenotype conversion occurred in the EDL within 4 h of stimulation without injury or satellite cell recruitment. This conversion was associated with the expression of phenotype-specific transcription factors from resident fiber myonuclei, including the activation of nascent developmental transcriptional programs.