A family of microRNAs encoded by myosin genes governs myosin expression and muscle performance. Dev Cell. 2009;17:662-673. [PMID: 19922871 DOI: 10.1016/j.devcel.2009.10.013]

Mechanisms and therapeutic potential of microRNAs in hypertension

Hypertension is the major risk factor for the development of stroke, coronary artery disease, heart failure and renal disease. The underlying cellular and molecular mechanisms of hypertension are complex and remain largely elusive. MicroRNAs (miRNAs) are short, noncoding RNA fragments of 22-26 nucleotides and regulate protein expression post-transcriptionally by targeting the 3'-untranslated region of mRNA. A growing body of recent research indicates that miRNAs are important in the pathogenesis of arterial hypertension. Herein, we summarize the current knowledge regarding the mechanisms of miRNAs in cardiovascular remodeling, focusing specifically on hypertension. We also review recent progress of the miRNA-based therapeutics including pharmacological and nonpharmacological therapies (such as exercise training) and their potential applications in the management of hypertension.

Polymorphisms and expression analysis of SOX-6 in relation to porcine growth, carcass, and meat quality traits

The aim of the study was to investigate single nucleotide polymorphisms (SNPs) and expression of SOX-6 to support its candidacy for growth, carcass, and meat quality traits in pigs. The first SNP, rs81358375, was associated with pH 45 min post mortem in loin (pH1L), the thickness of backfat and side fat, and carcass length in Pietrain (Pi) population, and related with backfat thickness and daily gain in Duroc × Pietrain F2 (DuPi) population. The other SNP, rs321666676, was associated with meat colour in Pi population. In DuPi population, the protein, not mRNA, level of SOX-6 in high pH1L pigs was significantly less abundant compared with low pH1L pigs, where microRNAs targeting SOX-6 were also differently regulated. This paper shows that SOX-6 could be a potential candidate gene for porcine growth, carcass, and meat quality traits based on genetic association and gene expression.

miR-487b, miR-3963 and miR-6412 delay myogenic differentiation in mouse myoblast-derived C2C12 cells

Background

Skeletal muscle differentiation is a multistep, complex pathway in which several important signaling molecules are involved. Recently, microRNAs (miRNAs), endogenous non-coding small RNAs that regulate mRNAs, have been proposed to be involved in skeletal muscle differentiation. In this study, we identified skeletal muscle differentiation-associated miRNAs by comparing miRNA expression profiles between C2C12 cells and Wnt4 over-expressing C2C12 cells (W4-08), which can spontaneously differentiate into myotubes.

Results

We identified miR-206, miR-133a, and miR-133b as up-regulated miRNAs and miR-487b, miR-3963 and miR-6412 as down-regulated miRNAs in differentiating cells. We focused on the down-regulated miRNAs because their functions were largely unknown. Transfection of mimics of these miRNAs into C2C12 cells resulted in significantly reduced expression of myogenic differentiation markers, including troponin T and myosin heavy chain fast type and slow type, but did not affect the expression of the myogenic transcription factors, MyoD and myogenin.

Conclusions

These miRNAs were characterized as new myogenic differentiation-associated miRNAs which may delay late myogenic differentiation or maturation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-015-0061-9) contains supplementary material, which is available to authorized users.

The miRNA Transcriptome Directly Reflects the Physiological and Biochemical Differences between Red, White, and Intermediate Muscle Fiber Types

MicroRNAs (miRNAs) are small non-coding RNAs that can regulate their target genes at the post-transcriptional level. Skeletal muscle comprises different fiber types that can be broadly classified as red, intermediate, and white. Recently, a set of miRNAs was found expressed in a fiber type-specific manner in red and white fiber types. However, an in-depth analysis of the miRNA transcriptome differences between all three fiber types has not been undertaken. Herein, we collected 15 porcine skeletal muscles from different anatomical locations, which were then clearly divided into red, white, and intermediate fiber type based on the ratios of myosin heavy chain isoforms. We further illustrated that three muscles, which typically represented each muscle fiber type (i.e., red: peroneal longus (PL), intermediate: psoas major muscle (PMM), white: longissimus dorsi muscle (LDM)), have distinct metabolic patterns of mitochondrial and glycolytic enzyme levels. Furthermore, we constructed small RNA libraries for PL, PMM, and LDM using a deep sequencing approach. Results showed that the differentially expressed miRNAs were mainly enriched in PL and played a vital role in myogenesis and energy metabolism. Overall, this comprehensive analysis will contribute to a better understanding of the miRNA regulatory mechanism that achieves the phenotypic diversity of skeletal muscles.

MicroRNA Transcriptome Profile Analysis in Porcine Muscle and the Effect of miR-143 on the MYH7 Gene and Protein

Porcine skeletal muscle fibres are classified based on their different physiological and biochemical properties. Muscle fibre phenotype is regulated by several independent signalling pathways, including the mitogen-activated protein kinase (MAPK), nuclear factor of activated T cells (NFAT), myocyte enhancer factor 2 (MEF2) and peroxisome proliferator-activated receptor (PPAR) signalling pathways. MicroRNAs are non-coding small RNAs that regulate many biological processes. However, their function in muscle fibre type regulation remains unclear. The aim of our study was to identify miRNAs that regulate muscle fibre type during porcine growth to help understand the miRNA regulation mechanism of fibre differentiation. We performed Solexa/Illumina deep sequencing for the microRNAome during 3 muscle growth stages (63, 98 and 161 d). In this study, 271 mature miRNAs and 243 pre-miRNAs were identified. We detected 472 novel miRNAs in the muscle samples. Among the mature miRNAs, there are 23 highest expression miRNAs (over 10,000 RPM), account for 85.3% of the total counts of mature miRNAs., including 10 (43.5%) muscle-related miRNAs (ssc-miR-133a-3p, ssc-miR-486, ssc-miR-1, ssc-miR-143-3p, ssc-miR-30a-5p, ssc-miR-181a, ssc-miR-148a-3p, ssc-miR-92a, ssc-miR-21, ssc-miR-126-5p). Particularly, both ssc-miR-1 and ssc-miR-133 belong to the MyomiRs, which control muscle myosin content, myofibre identity and muscle performance. The involvement of these miRNAs in muscle fibre phenotype provides new insight into the mechanism of muscle fibre regulation underlying muscle development. Furthermore, we performed cell transfection experiment. Overexpression/inhibition of ssc-miR-143-3p in porcine skeletal muscle satellite cell induced an/a increase/reduction of the slow muscle fibre gene and protein (MYH7), indicating that miR-143 activity regulated muscle fibre differentiate in skeletal muscle. And it regulate MYH7 through the HDAC4-MEF2 pathway.

microRNA-151-3p regulates slow muscle gene expression by targeting ATP2a2 in skeletal muscle cells

MicroRNAs (miRNAs) are a group of small noncoding RNAs that regulate the stability or translation of cognate mRNAs at the post-transcriptional level. Accumulating evidence indicates that miRNAs play important roles in many aspects of muscle function, including muscle growth and development, regeneration, contractility, and muscle fiber type plasticity. In the current study, we examined the function of miR-151-3p in myoblast proliferation and differentiation. Results show that overexpression of miR-151-3p not only upregulates myoblast proliferation, but also decreases slow muscle gene expression (such as MHC-β/slow and slow muscle troponin I) in both C2C12 myotubes and in primary cultures. Alternatively, inhibition of miR-151-3p by antisense RNA was found to upregulate MHC-β/slow expression, indicating that miR-151-3p plays a role in muscle fiber type determination. Further investigation into the underlying mechanisms revealed for the first time that miR-151-3p directly targets ATP2a2, a gene encoding for a slow skeletal and cardiac muscle specific Ca(2+) ATPase, SERCA2 thus downregulating slow muscle gene expression. Mechanisms by which the alteration in SERCA2 expression induces changes in other slow muscle gene expression levels needs to be defined in future research.

MiR-218 mediates tumorigenesis and metastasis: Perspectives and implications

MicroRNAs (miRNAs) are a class of small non-coding RNAs that negatively regulate gene expression at the post-transcriptional level. As a highly conserved miRNA across a variety of species, microRNA-218 (miR-218) was found to play pivotal roles in tumorigenesis and progression. A group of evidence has demonstrated that miR-218 acts as a tumor suppressor by targeting many oncogenes related to proliferation, apoptosis and invasion. In this review, we provide a complex overview of miR-218, including its regulatory mechanisms, known functions in cancer and future challenges as a potential therapeutic target in human cancers.

MicroRNA in pulmonary vascular disease

MicroRNA (miRNA) are short noncoding RNA that regulate gene expression by inhibiting translation or promoting degradation of target mRNA. miRNA are key regulators of a wide range of cellular processes and their discovery has revolutionized our understanding of gene regulatory networks. Pulmonary arterial hypertension (PAH) is a debilitating and fatal disease characterized by remodeling of pulmonary arteries and right heart failure. Factors including sustained pulmonary vasoconstriction, inflammation, and altered cellular signaling pathways drive disease through pulmonary artery endothelial dysfunction, smooth muscle cell proliferation, and the recruitment of circulating cells. miRNA have been shown to regulate many of the key drivers of pathology, yet the role of only a limited number of miRNA has been recognized in PAH. Investigation of the diverse regulatory functions of miRNA offers the potential to further understanding of the cellular pathology of PAH and to provide much needed diagnostic and therapeutic strategies. This review focuses on recent advances in the investigation of miRNA in PAH.

PPARs and ERRs: molecular mediators of mitochondrial metabolism

Since the revitalization of 'the Warburg effect', there has been great interest in mitochondrial oxidative metabolism, not only from the cancer perspective but also from the general biomedical science field. As the center of oxidative metabolism, mitochondria and their metabolic activity are tightly controlled to meet cellular energy requirements under different physiological conditions. One such mechanism is through the inducible transcriptional co-regulators PGC1α and NCOR1, which respond to various internal or external stimuli to modulate mitochondrial function. However, the activity of such co-regulators depends on their interaction with transcriptional factors that directly bind to and control downstream target genes. The nuclear receptors PPARs and ERRs have been shown to be key transcriptional factors in regulating mitochondrial oxidative metabolism and executing the inducible effects of PGC1α and NCOR1. In this review, we summarize recent gain-of-function and loss-of-function studies of PPARs and ERRs in metabolic tissues and discuss their unique roles in regulating different aspects of mitochondrial oxidative metabolism.

Non-coding RNA in control of gene regulatory programs in cardiac development and disease

Organogenesis of the vertebrate heart is a highly specialized process involving progressive specification and differentiation of distinct embryonic cardiac progenitor cell populations driven by specialized gene programming events. Likewise, the onset of pathologies in the adult heart, including cardiac hypertrophy, involves the reactivation of embryonic gene programs. In both cases, these intricate genomic events are temporally and spatially regulated by complex signaling networks and gene regulatory networks. Apart from well-established transcriptional mechanisms, increasing evidence indicates that gene programming in both the developing and the diseased myocardium are under epigenetic control by non-coding RNAs (ncRNAs). MicroRNAs regulate gene expression at the post-transcriptional level, and numerous studies have now established critical roles for this species of tiny RNAs in a broad range of aspects from cardiogenesis towards adult heart failure. Recent reports now also implicate the larger family of long non-coding RNAs (lncRNAs) in these processes as well. Here we discuss the involvement of these two ncRNA classes in proper cardiac development and hypertrophic disease processes of the adult myocardium. This article is part of a Special Issue entitled: Non-coding RNAs.

Unique patterns of transcript and miRNA expression in the South American strong voltage electric eel (Electrophorus electricus)

Background

With its unique ability to produce high-voltage electric discharges in excess of 600 volts, the South American strong voltage electric eel (Electrophorus electricus) has played an important role in the history of science. Remarkably little is understood about the molecular nature of its electric organs.

Results

We present an in-depth analysis of the genome of E. electricus, including the transcriptomes of eight mature tissues: brain, spinal cord, kidney, heart, skeletal muscle, Sachs’ electric organ, main electric organ, and Hunter’s electric organ. A gene set enrichment analysis based on gene ontology reveals enriched functions in all three electric organs related to transmembrane transport, androgen binding, and signaling. This study also represents the first analysis of miRNA in electric fish. It identified a number of miRNAs displaying electric organ-specific expression patterns, including one novel miRNA highly over-expressed in all three electric organs of E. electricus. All three electric organ tissues also express three conserved miRNAs that have been reported to inhibit muscle development in mammals, suggesting that miRNA-dependent regulation of gene expression might play an important role in specifying an electric organ identity from its muscle precursor. These miRNA data were supported using another complete miRNA profile from muscle and electric organ tissues of a second gymnotiform species.

Conclusions

Our work on the E. electricus genome and eight tissue-specific gene expression profiles will greatly facilitate future research on determining the coding and regulatory sequences that specify the function, development, and evolution of electric organs. Moreover, these data and future studies will be informed by the first comprehensive analysis of miRNA expression in an electric fish presented here.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1288-8) contains supplementary material, which is available to authorized users.

MicroRNA-499 expression distinctively correlates to target genes sox6 and rod1 profiles to resolve the skeletal muscle phenotype in Nile tilapia

A class of small non-coding RNAs, the microRNAs (miRNAs), has been shown to be essential for the regulation of specific cell pathways, including skeletal muscle development, maintenance and homeostasis in vertebrates. However, the relative contribution of miRNAs for determining the red and white muscle cell phenotypes is far from being fully comprehended. To better characterize the role of miRNA in skeletal muscle cell biology, we investigated muscle-specific miRNA (myomiR) signatures in Nile tilapia fish. Quantitative (RT-qPCR) and spatial (FISH) expression analyses revealed a highly differential expression (forty-four-fold) of miR-499 in red skeletal muscle compared to white skeletal muscle, whereas the remaining known myomiRs were equally expressed in both muscle cell types. Detailed examination of the miR-499 targets through bioinformatics led us to the sox6 and rod1 genes, which had low expression in red muscle cells according to RT-qPCR, FISH, and protein immunofluorescence profiling experiments. Interestingly, we verified that the high expression of miR-499 perfectly correlates with a low expression of sox6 and rod1 target genes, as verified by a distinctive predominance of mRNA destabilization and protein translational decay to these genes, respectively. Through a genome-wide comparative analysis of SOX6 and ROD1 protein domains and through an in silico gene regulatory network, we also demonstrate that both proteins are essentially similar in vertebrate genomes, suggesting their gene regulatory network may also be widely conserved. Overall, our data shed light on the potential regulation of targets by miR-499 associated with the slow-twitch muscle fiber type phenotype. Additionally the results provide novel insights into the evolutionary dynamics of miRNA and target genes enrolled in a putative constrained molecular pathway in the skeletal muscle cells of vertebrates.

Heterogeneous activation of a slow myosin gene in proliferating myoblasts and differentiated single myofibers

Each skeletal muscle contains a fixed ratio of fast and slow myofibers that are distributed in a stereotyped pattern to achieve a specific motor function. How myofibers are specified during development and regeneration is poorly understood. Here we address this question using transgenic reporter mice that indelibly mark the myofiber lineages based on activation of fast or slow myosin. Lineage tracing indicates that during development all muscles have activated the fast myosin gene Myl1, but not the slow myosin gene Myh7, which is activated in all slow but a subset of fast myofibers. Similarly, most nascent myofibers do not activate Myh7 during fast muscle regeneration, but the ratio and pattern of fast and slow myofibers are restored at the completion of regeneration. At the single myofiber level, most mature fast myofibers are heterogeneous in nuclear composition, manifested by mosaic activation of Myh7. Strikingly, Myh7 is activated in a subpopulation of proliferating myoblasts that co-express the myogenic progenitor marker Pax7. When induced to differentiate, the Myh7-activated myoblasts differentiate more readily than the non-activated myoblasts, and have a higher tendency, but not restricted, to become slow myotubes. Together, our data reveal significant nuclear heterogeneity within a single myofiber, and challenge the conventional view that myosin genes are only expressed after myogenic differentiation. These results provide novel insights into the regulation of muscle fiber type specification.

The biological functions of miRNAs: lessons from in vivo studies

Despite their clear importance as a class of regulatory molecules, pinpointing the relevance of individual miRNAs has been challenging. Studies querying miRNA functions by overexpressing or silencing specific miRNAs have yielded data that are often at odds with those collected from loss-of-functions models. In addition, knockout studies suggest that many conserved miRNAs are dispensable for animal development or viability. In this review, we discuss these observations in the context of our current knowledge of miRNA biology and review the evidence implicating miRNA-mediated gene regulation in the mechanisms that ensure biological robustness.

miRNA expression in control and FSHD fetal human muscle biopsies

Background

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal-dominant disorder and is one of the most common forms of muscular dystrophy. We have recently shown that some hallmarks of FSHD are already expressed in fetal FSHD biopsies, thus opening a new field of investigation for mechanisms leading to FSHD. As microRNAs (miRNAs) play an important role in myogenesis and muscle disorders, in this study we compared miRNAs expression levels during normal and FSHD muscle development.

Methods

Muscle biopsies were obtained from quadriceps of both healthy control and FSHD1 fetuses with ages ranging from 14 to 33 weeks of development. miRNA expression profiles were analyzed using TaqMan Human MicroRNA Arrays.

Results

During human skeletal muscle development, in control muscle biopsies we observed changes for 4 miRNAs potentially involved in secondary muscle fiber formation and 5 miRNAs potentially involved in fiber maturation. When we compared the miRNA profiles obtained from control and FSHD biopsies, we did not observe any differences in the muscle specific miRNAs. However, we identified 8 miRNAs exclusively expressed in FSHD1 samples (miR-330, miR-331-5p, miR-34a, miR-380-3p, miR-516b, miR-582-5p, miR-517* and miR-625) which could represent new biomarkers for this disease. Their putative targets are mainly involved in muscle development and morphogenesis. Interestingly, these FSHD1 specific miRNAs do not target the genes previously described to be involved in FSHD.

Conclusions

This work provides new candidate mechanisms potentially involved in the onset of FSHD pathology. Whether these FSHD specific miRNAs cause deregulations during fetal development, or protect against the appearance of the FSHD phenotype until the second decade of life still needs to be investigated.

miR-30 family microRNAs regulate myogenic differentiation and provide negative feedback on the microRNA pathway

microRNAs (miRNAs) are short non-coding RNAs that can mediate changes in gene expression and are required for the formation of skeletal muscle (myogenesis). With the goal of identifying novel miRNA biomarkers of muscle disease, we profiled miRNA expression using miRNA-seq in the gastrocnemius muscles of dystrophic mdx4cv mice. After identifying a down-regulation of the miR-30 family (miR-30a-5p, -30b, -30c, -30d and -30e) when compared to C57Bl/6 (WT) mice, we found that overexpression of miR-30 family miRNAs promotes differentiation, while inhibition restricts differentiation of myoblasts in vitro. Additionally, miR-30 family miRNAs are coordinately down-regulated during in vivo models of muscle injury (barium chloride injection) and muscle disuse atrophy (hindlimb suspension). Using bioinformatics tools and in vitro studies, we identified and validated Smarcd2, Snai2 and Tnrc6a as miR-30 family targets. Interestingly, we show that by targeting Tnrc6a, miR-30 family miRNAs negatively regulate the miRNA pathway and modulate both the activity of muscle-specific miR-206 and the levels of protein synthesis. These findings indicate that the miR-30 family may be an interesting biomarker of perturbed muscle homeostasis and muscle disease.

Influence of microRNA-related polymorphisms on clinical outcomes in coronary artery disease

Genetic variants in pre-microRNA (miRNA) genes or the 3'UTR of miRNA target genes could influence miRNA-mediated regulation of gene expression and thus contribute to the susceptibility and prognosis of human diseases. This study aimed to investigate the effect of 6 miRNA-related polymorphisms (miR-149 rs71428439, miR-146a rs2910164, miR-499 rs3746444, miR-423 rs6505162, miR-4513 rs2168518, and FABP2 rs11724758) on prognosis in 1004 patients with angiographic coronary artery disease (CAD). We found that miR-4513 rs2168518 was associated with blood pressure, triglycerides, total cholesterol, and fasting glucose levels, and risk of diabetes mellitus. miR-499 rs3746444 and miR-423 rs6505162 were associated with blood pressure and HDL levels, respectively. Both miR-4513 rs2168518 and miR-499 rs3746444 had significant impact on even-free survival. Furthermore, miR-4513 rs2168518 was associated with higher morality in CAD patients. In conclusion, miR-4513 rs2168518 and miR-499 rs3746444 might be potential biomarkers for the clinical prognosis of CAD.

Development of microRNA therapeutics is coming of age

MicroRNAs (miRNAs) play key regulatory roles in diverse biological processes and are frequently dysregulated in human diseases. Thus, miRNAs have emerged as a class of promising targets for therapeutic intervention. Here, we describe the current strategies for therapeutic modulation of miRNAs and provide an update on the development of miRNA-based therapeutics for the treatment of cancer, cardiovascular disease and hepatitis C virus (HCV) infection.

MiR-206, a key modulator of skeletal muscle development and disease

MicroRNAs (miRNAs) have recently emerged as fundamental post-transcriptional regulators inhibit gene expression linked to various biological processes. MiR-206 is one of the most studied and best characterized miRNA to date, which specifically expressed in skeletal muscle. In this review, we summarized the results of studies of miR-206 with emphasis on its function in skeletal muscle development. Importantly, dysregulation of miR-206 has been linked to many disorders in skeletal muscle such as Duchenne muscular dystrophy (DMD) and amyotrophic lateral sclerosis (ALS), and circulating miR-206 has highlighted its potential as a diagnose biomarker. In addition, a mutation in the 3' untranslated region (3'-UTR) of the myostatin gene in the Texel sheep creating a target site for the miR-206 and miR-1 leads to inhibition of myostatin expression, which likely to cause the muscular hypertrophy phenotype of this breed of sheep. Therefore, miR-206 may become novel target for ameliorating skeletal muscle-related disorders and optimization of muscle quantity of domestic animals.

Improved knee extensor strength with resistance training associates with muscle specific miRNAs in older adults

Regular exercise, particularly resistance training (RT), is the only therapy known to consistently improve muscle strength and quality (force per unit of mass) in older persons, but there is considerable variability in responsiveness to training. Identifying sensitive diagnostic biomarkers of responsiveness to RT may inform the design of a more efficient exercise regimen to improve muscle strength in older adults. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression. We quantified six muscle specific miRNAs (miR-1, -133a, -133b, -206, -208b and -499) in both muscle tissue and blood plasma, and their relationship with knee extensor strength in seven older (age=70.5 ± 2.5 years) adults before and after 5 months of RT. MiRNAs differentially responded to RT; muscle miR-133b decreased, while all plasma miRNAs tended to increase. Percent changes in knee extensor strength with RT showed strong positive correlations with percent changes in muscle miR-133a, -133b, and -206 and with percent changes in plasma and plasma/muscle miR-499 ratio. Baseline level of plasma or plasma/muscle miR-499 ratio further predicts muscle response to RT, while changes in muscle miR-133a, -133b, and -206 may correlate with muscle TNNT1 gene alternative splicing in response to RT. Our results indicate that RT alters muscle specific miRNAs in muscle and plasma, and that these changes account for some of the variation in strength responses to RT in older adults.

A micropeptide encoded by a putative long noncoding RNA regulates muscle performance

Functional micropeptides can be concealed within RNAs that appear to be noncoding. We discovered a conserved micropeptide, which we named myoregulin (MLN), encoded by a skeletal muscle-specific RNA annotated as a putative long noncoding RNA. MLN shares structural and functional similarity with phospholamban (PLN) and sarcolipin (SLN), which inhibit SERCA, the membrane pump that controls muscle relaxation by regulating Ca(2+) uptake into the sarcoplasmic reticulum (SR). MLN interacts directly with SERCA and impedes Ca(2+) uptake into the SR. In contrast to PLN and SLN, which are expressed in cardiac and slow skeletal muscle in mice, MLN is robustly expressed in all skeletal muscle. Genetic deletion of MLN in mice enhances Ca(2+) handling in skeletal muscle and improves exercise performance. These findings identify MLN as an important regulator of skeletal muscle physiology and highlight the possibility that additional micropeptides are encoded in the many RNAs currently annotated as noncoding.

MicroRNAs as therapeutic targets and biomarkers of cardiovascular disease

MicroRNAs play central roles in cardiovascular disease, and their therapeutic manipulation raises exciting opportunities as well as challenges in the path toward clinical development.

Expression of circulating microRNA-1 and microRNA-133 in pediatric patients with tachycardia

Paroxysmal or persistent tachycardia in pediatric patients is a common disease. Certain circulating microRNAs (miRNAs) have been associated with arrhythmia. The present study investigated miRNAs in the plasma of pediatric patients with tachycardia. Forty pediatric subjects were included retrospectively: 24 with recurrent sustained tachycardia [seven cases of ventricular tachycardia (VT) and 17 cases of supraventricular tachycardia (SVT)] and 16 healthy controls. Circulating miR-1 and miR-133 in the plasma were detected by fluorescent quantitative polymerase chain reaction. miR-1 levels were significantly decreased in the arrhythmia group compared with those in the controls (P=0.004) whilst miR-133 expression levels were not significantly different between the two groups (P=0.456). Both miR-1 and miR-133 levels showed significant differences between the SVT and VT groups (P=0.004 and P=0.046, respectively), and a significant decrease in miR-1 levels was observed in the SVT group as compared with the controls (P<0.001). No significant difference was observed in the expression levels of miR-133. By contrast, miR-133 levels were significantly increased in the VT group compared with those in the controls (P=0.024), whereas no statistically significant difference was observed in the expression levels of miR-1. Receiver operating characteristic curves showed that 1/miR-1 was significant for the evaluation of tachycardia. Additionally, miR-1 produced enhanced sensitivity and specificity for the evaluation of SVT compared with miR-133, whereas miR-133 was a better marker to assess VT. This study demonstrated that miRNAs may be appropriate markers for pediatric tachycardia; miR-1 levels were decreased in the arrhythmia group compared with those in the healthy controls. Furthermore, patients with SVT had lower miR-1 expression levels while those with VT had higher miR-133 expression levels.

Noncoding RNAs as epigenetic mediators of skeletal muscle regeneration

Skeletal muscle regeneration is a well-characterized biological process in which resident adult stem cells must undertake a series of cell-fate decisions to ensure efficient repair of the damaged muscle fibers while also maintaining the stem cell niche. Satellite cells, the main stem cell contributing to the repaired muscle fiber, are maintained in a quiescent state in healthy muscle. Upon injury, the satellite cells become activated, and proliferate to expand the muscle progenitor cell population before returning to the quiescent state or differentiating to become myofibers. Importantly, the determination of cell fate is controlled at the epigenetic level in response to environmental cues. In this review, we discuss our current understanding of the role played by noncoding RNAs (both miRNAs and long-noncoding RNAs) in the epigenetic control of muscle regeneration.

MiR-214 and N-ras regulatory loop suppresses rhabdomyosarcoma cell growth and xenograft tumorigenesis

Rhabdomyosarcoma (RMS) is a childhood malignant soft tissue cancer that is derived from myogenic progenitors trapped in a permanent mode of growth. Here, we report that miR-214 is markedly down-regulated in human RMS cell lines. Although not required for embryogenesis in mice, miR-214 suppresses mouse embryonic fibroblast (MEF) proliferation. When re-introduced into RD cells, a line of human embryonal RMS cells, miR-214 showed inhibition of tumor cell growth, induction of myogenic differentiation and apoptosis, as well as suppression of colony formation and xenograft tumorigenesis. We show that in the absence of miR-214, expression of proto-oncogene N-ras is markedly elevated in miR-214^−/− MEFs, and manipulations of miR-214 levels using microRNA mimics or inhibitor in RD cells reciprocally altered N-ras expression. We further demonstrate that forced expression of N-ras from a cDNA that lacks its 3'-untranslated region neutralized the pro-myogenic and anti-proliferative activities of miR-214. Finally, we show that N-ras is a conserved target of miR-214 in its suppression of xenograft tumor growth, and N-ras expression is up-regulated in xenograft tumor models as well as actual human RMS tissue sections. Taken together, these data indicate that miR-214 is a bona fide suppressor of human RMS tumorigensis.

microRNAs and Cardiovascular Remodeling

Heart failure (HF) is associated with significant morbidity and mortality attributable largely to structural changes in the heart and with associated cardiac dysfunction. Remodeling is defined as alteration of the mass, dimensions, or shape of the heart (termed cardiac or ventricular remodeling) and vessels (vascular remodeling) in response to hemodynamic load and/or cardiovascular injury in association with neurohormonal activation. Remodeling may be described as physiologic or pathologic; alternatively, remodeling may be classified as adaptive or maladaptive. The importance of remodeling as a pathogenic mechanism has been controversial because factors leading to remodeling as well as the remodeling itself may be major determinants of patients' prognosis. The basic mechanisms of cardiovascular remodeling, and especially the roles of microRNAs in HF progression and vascular diseases, will be reviewed here.

Application of microRNAs in diagnosis and treatment of cardiovascular disease

Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Innovative, more stringent diagnostic and prognostic biomarkers and effective treatment options are needed to lessen its burden. In recent years, microRNAs have emerged as master regulators of gene expression - they bind to complementary sequences within the mRNAs of their target genes and inhibit their expression by either mRNA degradation or translational repression. microRNAs have been implicated in all major cellular processes, including cell cycle, differentiation and metabolism. Their unique mode of action, fine-tuning gene expression rather than turning genes on/off, and their ability to simultaneously regulate multiple elements of relevant pathways makes them enticing potential biomarkers and therapeutic targets. Indeed, cardiovascular patients have specific patterns of circulating microRNA levels, often early in the disease process. This article provides a systematic overview of the role of microRNAs in the pathophysiology, diagnosis and treatment of CVD.

Regulation of skeletal muscle development and disease by microRNAs

The identification of microRNAs (miRNA) in vertebrates has uncovered new mechanisms regulating skeletal muscle development and disease. miRNAs are inhibitors and act by silencing specific mRNAs or by repressing protein translation. In many cases, miRNAs are involved in physiological or pathological stress, suggesting they function to exacerbate or protect the organism during stress or disease. Although many skeletal muscle diseases differ in clinical and pathological manifestations, they all have a common feature of dysregulation of miRNA expression. In particular, analysis of miRNA expression patterns in skeletal muscle diseases reveals miRNA signatures, showing many miRNAs are dysregulated during disease. Emerging identification of miRNA targets and involvement in genetic regulatory networks serve to reveal new regulatory pathways in skeletal muscle biology. This chapter features the findings pertaining to skeletal muscle miRNAs in skeletal muscle development and disease and highlights therapeutic applications of miRNA-based technology in diagnosis and treatment of skeletal muscle myopathies.

The role of microRNAs in skeletal muscle health and disease

Over the last decade non-coding RNAs have emerged as importance regulators of gene expression. In particular, microRNAs are a class of small RNAs of ∼ 22 nucleotides that repress gene expression through a post-transcriptional mechanism. MicroRNAs have been shown to be involved in a broader range of biological processes, both physiological and pathological, including myogenesis, adaptation to exercise and various myopathies. The purpose of this review is to provide a comprehensive summary of what is currently known about the role of microRNAs in skeletal muscle health and disease.

microRNA and Cardiac Regeneration

Heart diseases are a very common health problem in developed as well as developing countries. In particular, ischemic heart disease and heart failure represent a plague for the patients and for the society. Loss of cardiac tissue after myocardial infarction or dysfunctioning tissue in nonischemic cardiomyopathies may result in cardiac failure. Despite great advancements in the treatment of these diseases, there is a substantial unmet need for novel therapies, ideally addressing repair and regeneration of the damaged or lost myocardium. Along this line, cardiac cell based therapies have gained substantial attention. Three main approaches are currently under investigation: stem cell therapy with either embryonic or adult stem cells; generation of patient-specific induced pluripotent stem cells; stimulation of endogenous regeneration trough direct reprogramming of fibroblasts into cardiomyocytes, activation of resident cardiac stem cells or induction of native resident cardiomyocytes to reenter the cell cycle. All these strategies need to be optimized since their efficiency is low.It has recently become clear that cardiac signaling and transcriptional pathways are intimately intertwined with microRNA molecules which act as modulators of cardiac development, function, and disease. Moreover, miRNA also regulates stem cell differentiation. Here we describe how miRNA may circumvent hurdles that hamper the field of cardiac regeneration and stem cell therapy, and how miRNA may result as the most suitable solution for the damaged heart.

The Role of miR-378a in Metabolism, Angiogenesis, and Muscle Biology

MicroRNA-378a (miR-378a, previously known as miR-378) is one of the small noncoding RNA molecules able to regulate gene expression at posttranscriptional level. Its two mature strands, miR-378a-3p and miR-378a-5p, originate from the first intron of the peroxisome proliferator-activated receptor gamma, coactivator 1 beta (ppargc1b) gene encoding PGC-1β. Embedding in the sequence of this transcriptional regulator of oxidative energy metabolism implies involvement of miR-378a in metabolic pathways, mitochondrial energy homeostasis, and related biological processes such as muscle development, differentiation, and regeneration. On the other hand, modulating the expression of proangiogenic factors such as vascular endothelial growth factor, angiopoietin-1, or interleukin-8, influencing inflammatory reaction, and affecting tumor suppressors, such as SuFu and Fus-1, miR-378a is considered as a part of an angiogenic network in tumors. In the latter, miR-378a can evoke broader actions by enhancing cell survival, reducing apoptosis, and promoting cell migration and invasion. This review describes the current knowledge on miR-378a linking oxidative/lipid metabolism, muscle biology, and blood vessel formation.

Temporal analysis of reciprocal miRNA-mRNA expression patterns predicts regulatory networks during differentiation in human skeletal muscle cells

microRNAs (miRNAs) are short noncoding RNAs that regulate gene expression through posttranscriptional repression of target genes. miRNAs exert a fundamental level of control over many developmental processes, but their role in the differentiation and development of skeletal muscle from myogenic progenitor cells in humans remains incompletely understood. Using primary cultures established from human skeletal muscle satellite cells, we performed microarray profiling of miRNA expression during differentiation of myoblasts (day 0) into myotubes at 48 h intervals (day 2, 4, 6, 8, and 10). Based on a time-course analysis, we identified 44 miRNAs with altered expression [false discovery rate (FDR) < 5%, fold change > ±1.2] during differentiation, including the marked upregulation of the canonical myogenic miRNAs miR-1, miR-133a, miR-133b, and miR-206. Microarray profiling of mRNA expression at day 0, 4, and 10 identified 842 and 949 genes differentially expressed (FDR < 10%) at day 4 and 10, respectively. At day 10, 42% of altered transcripts demonstrated reciprocal expression patterns in relation to the directional change of their in silico predicted regulatory miRNAs based on analysis using Ingenuity Pathway Analysis microRNA Target Filter. Bioinformatic analysis predicted networks of regulation during differentiation including myomiRs miR-1/206 and miR-133a/b, miRNAs previously established in differentiation including miR-26 and miR-30, and novel miRNAs regulated during differentiation of human skeletal muscle cells such as miR-138-5p and miR-20a. These reciprocal expression patterns may represent new regulatory nodes in human skeletal muscle cell differentiation. This analysis serves as a reference point for future studies of human skeletal muscle differentiation and development in healthy and disease states.

Epitranscriptional regulation of cardiovascular development and disease

Development, homeostasis and responses to stress in the heart all depend on appropriate control of mRNA expression programmes, which may be enacted at the level of DNA sequence, DNA accessibility and RNA-mediated control of mRNA output. Diverse mechanisms underlie promoter-driven transcription of coding mRNAs and their translation into protein, and the ways in which sequence alteration of DNA can make an impact on these processes have been studied for some time. The field of epigenetics explores changes in DNA structure that influence its accessibility by transcriptional machinery, and we are continuing to develop our understanding of how these processes modify cardiac RNA production. In this topical review, we do not focus on how DNA sequence and methylation, and histone interactions, may alter its accessibility, but rather on newly described mechanisms by which some transcribed RNAs may alter initial transcription or downstream processing of other RNAs, involving both short non-coding RNAs (microRNAs) and long non-coding RNAs (lncRNAs). Here we present examples of how these two classes of non-coding RNAs mediate widespread effects on cardiac transcription and protein output in processes for which we use the broad term 'epitranscriptional regulation' and that are complementary to the DNA methylation and histone modification events studied by classical epigenetics.

A polymorphism in the porcine miR-208b is associated with microRNA biogenesis and expressions of SOX-6 and MYH7 with effects on muscle fibre characteristics and meat quality

MicroRNAs (miRNAs) encoded by the myosin heavy chain (MHC) genes are muscle-specific miRNAs (myomiRs) and regulate the expression of MHC isoforms in skeletal muscle. These miRNAs have been implicated in muscle fibre types and their characteristics by affecting the heterogeneity of myosin. In pigs, miR-208b and miR-499 are embedded in introns of MYH7 and MYH7b respectively. Here, we identified a novel single nucleotide polymorphism (SNP) in intron 30 of MYH7 by which porcine miR-208b is encoded. Based on the association study using a total of 487 pigs including Berkshire (n = 164), Landrace (n = 121) and Yorkshire (n = 202), the miR-208b SNP (g.17104G>A) had significant effects on the proportions of types I and IIb fibre numbers (P < 0.010) among muscle fibre characteristics and on drip loss (P = 0.012) in meat quality traits. Moreover, the SNP affected the processing of primary miR-208b into precursor miR-208b with a marginal trend towards significance (P = 0.053), thereby leading to significant changes in the levels of mature miR-208b (P = 0.009). These SNP-dependent changes in mature miR-208b levels were negatively correlated with the expression levels of its target gene, SOX-6 (P = 0.038), and positively associated with the expression levels of its host gene, MYH7 (P = 0.046). Taken together, our data suggest that the porcine miR-208b SNP differentially represses the expression of SOX-6 by regulating miRNA biogenesis, thereby affecting the expression of MYH7 and the traits of muscle fibre characteristics and meat quality.

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.

Impact of the genetic background on the composition of the chicken plasma MiRNome in response to a stress

Circulating extra-cellular microRNAs (miRNAs) have emerged as promising minimally invasive markers in human medicine. We evaluated miRNAs isolated from total plasma as biomarker candidates of a response to an abiotic stress (feed deprivation) in a livestock species. Two chicken lines selected for high (R+) and low (R-) residual feed intake were chosen as an experimental model because of their extreme divergence in feed intake and energy metabolism. Adult R+ and R- cocks were sampled after 16 hours of feed deprivation and again four hours after re-feeding. More than 292 million sequence reads were generated by small RNA-seq of total plasma RNA. A total of 649 mature miRNAs were identified; after quality filtering, 148 miRNAs were retained for further analyses. We identified 23 and 19 differentially abundant miRNAs between feeding conditions and between lines respectively, with only two miRNAs identified in both comparisons. We validated a panel of six differentially abundant miRNAs by RT-qPCR on a larger number of plasma samples and checked their response to feed deprivation in liver. Finally, we evaluated the conservation and tissue distribution of differentially abundant miRNAs in plasma across a variety of red jungle fowl tissues. We show that the chicken plasma miRNome reacts promptly to the alteration of the animal physiological condition driven by a feed deprivation stress. The plasma content of stress-responsive miRNAs is strongly influenced by the genetic background, with differences reflecting the phenotypic divergence acquired through long-term selection, as evidenced by the profiles of conserved miRNAs with a regulatory role in energy metabolism (gga-miR-204, gga-miR-let-7f-5p and gga-miR-122-5p). These results reinforce the emerging view in human medicine that even small genetic differences can have a considerable impact on the resolution of biomarker studies, and provide support for the emerging interest in miRNAs as potential novel and minimally invasive biomarkers for livestock species.

Circulating microRNAs in cardiovascular diseases: from biomarkers to therapeutic targets

microRNAs (miRNAs) are a class of conserved, short, non-coding RNAs that have important and potent capacities to regulate gene expression at the posttranscriptional level. In the past several years, the aberrant expressions of miRNAs in the cardiovascular system have been widely reported, and the crucial roles of some special miRNAs in heart development and pathophysiology of various cardiovascular diseases have been gradually recognized. Recently, it was discovered that miRNAs are presented in peripheral circulation abundantly and stably. This has raised the possibility of using circulating miRNAs as biomarkers for diseases. Furthermore, some studies demonstrated that circulating miRNAs may serve as novel extracellular communicators of cell-cell communication. These discoveries not only reveal the functions of circulating miRNAs in cardiovascular system but also inform the development of miRNAs therapeutic strategies. In this review, we discuss the potential roles of circulating miRNAs in a variety of cardiovascular diseases from biomarkers to therapeutic targets to clearly understand the roles of circulating miRNAs in cardiovascular system.

The emerging role of microRNAs in cardiovascular disease

Cardiovascular disease remains the most prevalent cause of human morbidity and mortality in ageing Western societies. Basic and translational scientific efforts have focused on the development and improvement of diagnostic and therapeutic strategies to limit the burden of associated diseases, such as stroke and myocardial infarction, and diabetes mellitus and arterial hypertension. Progress in molecular medicine and biology has unravelled a complex epigenetic and post-transcriptional gene-regulating machinery in humans which may limit disease development. An increasing number of attractive molecular strategies, which use the potential of modulating noncoding RNAs, have surfaced over the last decade. Currently, the most extensively studied gene-regulating RNA subspecies are microRNAs, which have been shown to adjust the translational output of coding transcripts by enforcing their degradation and inhibiting their translation into protein. Key findings indicate that microRNAs act as crucial regulators in the majority of human pathologies. Thus, recent research has focused on detecting and modulating microRNAs for therapeutic and biomarker purposes. This review focuses on main and repeated discoveries regarding the role and the therapeutic and biomarker feasibility of microRNAs during cardiovascular disease development and exacerbation.

Mechanisms modulating skeletal muscle phenotype

Mammalian skeletal muscles are composed of a variety of highly specialized fibers whose selective recruitment allows muscles to fulfill their diverse functional tasks. In addition, skeletal muscle fibers can change their structural and functional properties to perform new tasks or respond to new conditions. The adaptive changes of muscle fibers can occur in response to variations in the pattern of neural stimulation, loading conditions, availability of substrates, and hormonal signals. The new conditions can be detected by multiple sensors, from membrane receptors for hormones and cytokines, to metabolic sensors, which detect high-energy phosphate concentration, oxygen and oxygen free radicals, to calcium binding proteins, which sense variations in intracellular calcium induced by nerve activity, to load sensors located in the sarcomeric and sarcolemmal cytoskeleton. These sensors trigger cascades of signaling pathways which may ultimately lead to changes in fiber size and fiber type. Changes in fiber size reflect an imbalance in protein turnover with either protein accumulation, leading to muscle hypertrophy, or protein loss, with consequent muscle atrophy. Changes in fiber type reflect a reprogramming of gene transcription leading to a remodeling of fiber contractile properties (slow-fast transitions) or metabolic profile (glycolytic-oxidative transitions). While myonuclei are in postmitotic state, satellite cells represent a reserve of new nuclei and can be involved in the adaptive response.

Regulation of Cardiac Cell Fate by microRNAs: Implications for Heart Regeneration

microRNAs are post-transcriptional regulators of gene expression that have been shown to be central players in the establishment of cellular programs, often acting as switches that control the choice between proliferation and differentiation during development and in adult tissues. The heart develops from two small patches of cells in the mesoderm, the heart fields, which originate the different cardiac cell types, including cardiomyocytes, vascular smooth muscle and endothelial cells. These progenitors proliferate and differentiate to establish a highly connected three-dimensional structure, involving a robust succession of gene expression programs strongly influenced by microRNAs. Although the mammalian heart has conventionally been viewed as a post-mitotic organ, cardiac cells have recently been shown to display some regenerative potential, which is nonetheless insufficient to regenerate heart lesions, in contrast with other vertebrates like the zebrafish. Both the proliferation of adult cardiac stem cells and the ability of cardiomyocytes to re-enter the cell cycle have been proposed to sustain these regenerative processes. Here we review the role of microRNAs in the control of stem cell and cardiomyocyte dependent cardiac regeneration processes, and discuss potential applications for the treatment of cardiac injury.

Genetic networks governing heart development

Animal genomes contain a code for construction of the body plan from a fertilized egg. Understanding how genome information is deciphered to create the complex multilayered regulatory systems that drive organismal development, and which become altered in disease, is one of the greatest challenges in the biological sciences. The development of methods that effectively represent and communicate the complexity inherent in gene regulatory networks remains a major barrier. This review introduces the philosophy of systems biology and discusses recent progress in understanding the development of the heart at a systems biology level.

Hormone replacement therapy enhances IGF-1 signaling in skeletal muscle by diminishing miR-182 and miR-223 expressions: a study on postmenopausal monozygotic twin pairs

MiRNAs are fine-tuning modifiers of skeletal muscle regulation, but knowledge of their hormonal control is lacking. We used a co-twin case–control study design, that is, monozygotic postmenopausal twin pairs discordant for estrogen-based hormone replacement therapy (HRT) to explore estrogen-dependent skeletal muscle regulation via miRNAs. MiRNA profiles were determined from vastus lateralis muscle of nine healthy 54–62-years-old monozygotic female twin pairs discordant for HRT (median 7 years). MCF-7 cells, human myoblast cultures and mouse muscle experiments were used to confirm estrogen’s causal role on the expression of specific miRNAs, their target mRNAs and proteins and finally the activation of related signaling pathway. Of the 230 miRNAs expressed at detectable levels in muscle samples, qPCR confirmed significantly lower miR-182, miR-223 and miR-142-3p expressions in HRT using than in their nonusing co-twins. Insulin/IGF-1 signaling emerged one common pathway targeted by these miRNAs. IGF-1R and FOXO3A mRNA and protein were more abundantly expressed in muscle samples of HRT users than nonusers. In vitro assays confirmed effective targeting of miR-182 and miR-223 on IGF-1R and FOXO3A mRNA as well as a dose-dependent miR-182 and miR-223 down-regulations concomitantly with up-regulation of FOXO3A and IGF-1R expression. Novel finding is the postmenopausal HRT-reduced miRs-182, miR-223 and miR-142-3p expression in female skeletal muscle. The observed miRNA-mediated enhancement of the target genes’ IGF-1R and FOXO3A expression as well as the activation of insulin/IGF-1 pathway signaling via phosphorylation of AKT and mTOR is an important mechanism for positive estrogen impact on skeletal muscle of postmenopausal women.