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]

Slit-miR-218-Robo axis regulates retinal neovascularization

miR-218 is an important intronic microRNA (miRNA or miR) which is known to regulate angiogenesis in tumors. The present study aimed to investigate the effects of miR-218, as well as its host genes, Slit2 and Slit3, on oxygen-induced retinal neovascularization (RNV) and to explore the associated mechanisms of action. For this purpose, a mouse model of oxygen-induced retinopathy (OIR) was established. The expression levels of miR-218-1 and miR-218-2, as well as those of their host genes, Slit2 and Slit3, were determined by RT-qPCR. Fluorescein angiography was performed on the retinas of the mice with OIR, and RNV was quantified by H&E staining in order to evaluate the effect of pCDH-CMV-miR-218 intravitreal injection on RNV in the mouse model of OIR. Roundabout, axon guidance receptor, homolog 1 (Robo1) expression was detected in mouse retinal vascular endothelial cells expressing high or low levels of miR-218 and in retinal tissues from mice with OIR by western blot analysis. Cell migration was evaluated by a scratch wound assay. We noted that in the mice with OIR, the expression level of miR-218 was significantly downregulated. We also noted that Robo1 expression was suppressed by miR-218. Furthermore, in the mice with OIR, the expression level of miR-218 was significantly downregulated, and that of miR-218-1 and its host gene, Slit2, was concomitantly downregulated as well. The restoration of miR-218 inhibited retinal angiogenesis by targeting Robo1. Taken together, our findings suggest that the Slit2-miR-218-Robo1 axis contributes to the inhibition of retinal angiogenesis and that miR-218 may be a new therapeutic target for preventing RNV.

Exercise-Induced Skeletal Muscle Adaptations Alter the Activity of Adipose Progenitor Cells

Exercise decreases adiposity and improves metabolic health; however, the physiological and molecular underpinnings of these phenomena remain unknown. Here, we investigate the effect of endurance training on adipose progenitor lineage commitment. Using mice with genetically labeled adipose progenitors, we show that these cells react to exercise by decreasing their proliferation and differentiation potential. Analyses of mouse models that mimic the skeletal muscle adaptation to exercise indicate that muscle, in a non-autonomous manner, regulates adipose progenitor homeostasis, highlighting a role for muscle-derived secreted factors. These findings support a humoral link between skeletal muscle and adipose progenitors and indicate that manipulation of adipose stem cell function may help address obesity and diabetes.

Role of miRNAs and alternative mRNA 3'-end cleavage and polyadenylation of their mRNA targets in cardiomyocyte hypertrophy

miRNAs play critical roles in heart disease. In addition to differential miRNA expression, miRNA-mediated control is also affected by variable miRNA processing or alternative 3'-end cleavage and polyadenylation (APA) of their mRNA targets. To what extent these phenomena play a role in the heart remains unclear. We sought to explore miRNA processing and mRNA APA in cardiomyocytes, and whether these change during cardiac hypertrophy. Thoracic aortic constriction (TAC) was performed to induce hypertrophy in C57BL/6J mice. RNA extracted from cardiomyocytes of sham-treated, pre-hypertrophic (2 days post-TAC), and hypertrophic (7 days post-TAC) mice was subjected to small RNA- and poly(A)-test sequencing (PAT-Seq). Differential expression analysis matched expectations; nevertheless we identified ~400 mRNAs and hundreds of noncoding RNA loci as altered with hypertrophy for the first time. Although multiple processing variants were observed for many miRNAs, there was little change in their relative proportions during hypertrophy. PAT-Seq mapped ~48,000 mRNA 3'-ends, identifying novel 3' untranslated regions (3'UTRs) for over 7000 genes. Importantly, hypertrophy was associated with marked changes in APA with a net shift from distal to more proximal mRNA 3'-ends, which is predicted to decrease overall miRNA repression strength. We independently validated several examples of 3'UTR proportion change and showed that alternative 3'UTRs associate with differences in mRNA translation. Our work suggests that APA contributes to altered gene expression with the development of cardiomyocyte hypertrophy and provides a rich resource for a systems-level understanding of miRNA-mediated regulation in physiological and pathological states of the heart.

Epigenetic and lncRNA regulation of cardiac pathophysiology

Our developmental studies provide an insight into the pathogenesis of heart failure in adults. These studies reveal a mechanistic link between fetal cardiomyocytes and pathologically stressed adult cardiomyocytes at the level of chromatin regulation. In embryos, chromatin-regulating factors within the cardiomyocytes respond to developmental signals to program cardiac gene expression to promote cell proliferation and inhibit premature cell differentiation. In the neonatal period, the activity of these developmental chromatin regulators is quickly turned off in cardiomyocytes, coinciding with the cessation of cell proliferation and advance in cell differentiation toward adult maturity. When the mature hearts are pathologically stressed, those chromatin regulators essential for cardiomyocyte development in embryos are reactivated, triggering gene reprogramming to a fetal-like state and pathological cardiac hypertrophy. Furthermore, in the study of chromatin regulation and cardiac gene expression, we identified a long noncoding RNA that interacts with chromatin remodeling factor to regulate the cardiac response to environmental changes. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

Circulating miRNAs as Biomarkers of Acute Muscle Damage in Rats

Skeletal muscle damage is an often-occurring event. Diagnosis using the classic blood marker creatine kinase sometimes yields unsatisfactory results due to great interindividual variability. Therefore, the identification of reliable biomarkers is important. Our aim was to detect and characterize circulating miRNAs in plasma in response to acute notexin-induced muscle damage in rats. Real-time quantitative RT-PCR profiling led to the identification of miRNAs that were highly increased in plasma in response to notexin injection into several muscles, namely miR-1-3p, -133a-3p, -133b-3p, -206-3p, -208b-3p, and -499-5p, as well as miR-378a-3p and miR-434-3p. Peak values of miRNAs appeared 12 hours after injury, and were contained both in the vesicular and nonvesicular fractions of plasma. Receiver operating characteristic curve analysis showed that circulating miRNAs could accurately discriminate between damaged and nondamaged tissues. Furthermore, we tested the robustness of expression profiles in slow- and fast-type fibers. Upon inducing damage in slow- or fast-type muscle, we found that the damaged-muscle phenotype had a very limited impact on the miRNA response. Similarly, the circulating miRNAs selected were not affected by hemolysis or platelets, two pre-analytical factors known to affect plasma miRNA profiles. Taken together, our results show that circulating muscle-specific miRNAs, miR-378a-3p and miR-434-3p, are robust and promising biomarkers of acute muscle damage in rats.

A genome-wide association study of congenital cardiovascular left-sided lesions shows association with a locus on chromosome 20

Congenital heart defects involving left-sided lesions (LSLs) are relatively common birth defects with substantial morbidity and mortality. Previous studies have suggested a high heritability with a complex genetic architecture, such that only a few LSL loci have been identified. We performed a genome-wide case-control association study to address the role of common variants using a discovery cohort of 778 cases and 2756 controls. We identified a genome-wide significant association mapping to a 200 kb region on chromosome 20q11 [P= 1.72 × 10^-8 for rs3746446; imputed Single Nucleotide Polymorphism (SNP) rs6088703 P= 3.01 × 10^-9, odds ratio (OR)= 1.6 for both]. This result was supported by transmission disequilibrium analyses using a subset of 541 case families (lowest P in region= 4.51 × 10^-5, OR= 1.5). Replication in a cohort of 367 LSL cases and 5159 controls showed nominal association (P= 0.03 for rs3746446) resulting in P= 9.49 × 10^-9 for rs3746446 upon meta-analysis of the combined cohorts. In addition, a group of seven SNPs on chromosome 1q21.3 met threshold for suggestive association (lowest P= 9.35 × 10^-7 for rs12045807). Both regions include genes involved in cardiac development-MYH7B/miR499A on chromosome 20 and CTSK, CTSS and ARNT on chromosome 1. Genome-wide heritability analysis using case-control genotyped SNPs suggested that the mean heritability of LSLs attributable to common variants is moderately high ([Formula: see text] range= 0.26-0.34) and consistent with previous assertions. These results provide evidence for the role of common variation in LSLs, proffer new genes as potential biological candidates, and give further insight to the complex genetic architecture of congenital heart disease.

Epigenetic response to environmental stress: Assembly of BRG1-G9a/GLP-DNMT3 repressive chromatin complex on Myh6 promoter in pathologically stressed hearts

Chromatin structure is determined by nucleosome positioning, histone modifications, and DNA methylation. How chromatin modifications are coordinately altered under pathological conditions remains elusive. Here we describe a stress-activated mechanism of concerted chromatin modification in the heart. In mice, pathological stress activates cardiomyocytes to express Brg1 (nucleosome-remodeling factor), G9a/Glp (histone methyltransferase), and Dnmt3 (DNA methyltransferase). Once activated, Brg1 recruits G9a and then Dnmt3 to sequentially assemble repressive chromatin-marked by H3K9 and CpG methylation-on a key molecular motor gene (Myh6), thereby silencing Myh6 and impairing cardiac contraction. Disruption of Brg1, G9a or Dnmt3 erases repressive chromatin marks and de-represses Myh6, reducing stress-induced cardiac dysfunction. In human hypertrophic hearts, BRG1-G9a/GLP-DNMT3 complex is also activated; its level correlates with H3K9/CpG methylation, Myh6 repression, and cardiomyopathy. Our studies demonstrate a new mechanism of chromatin assembly in stressed hearts and novel therapeutic targets for restoring Myh6 and ventricular function. The stress-induced Brg1-G9a-Dnmt3 interactions and sequence of repressive chromatin assembly on Myh6 illustrates a molecular mechanism by which the heart epigenetically responds to environmental signals. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

MicroRNA deep sequencing reveals chamber-specific miR-208 family expression patterns in the human heart

BACKGROUND

Heart chamber-specific mRNA expression patterns have been extensively studied, and dynamic changes have been reported in many cardiovascular diseases. MicroRNAs (miRNAs) are also important regulators of normal cardiac development and functions that generally suppress gene expression at the posttranscriptional level. Recent focus has been placed on circulating miRNAs as potential biomarkers for cardiac disorders. However, miRNA expression levels in human normal hearts have not been thoroughly studied, and chamber-specific miRNA expression signatures in particular remain unclear.

METHODS AND RESULTS

We performed miRNA deep sequencing on human paired left atria (LA) and ventricles (LV) under normal physiologic conditions. Among 438 miRNAs, miR-1 was the most abundant in both chambers, representing 21% of the miRNAs in LA and 26% in LV. A total of 25 miRNAs were differentially expressed between LA and LV; 14 were upregulated in LA, and 11 were highly expressed in LV. Notably, the miR-208 family in particular showed prominent chamber specificity; miR-208a-3p and miR-208a-5p were abundant in LA, whereas miR-208b-3p and miR-208b-5p were preferentially expressed in LV. Subsequent real-time polymerase chain reaction analysis validated the predominant expression of miR-208a in LA and miR-208b in LV.

CONCLUSIONS

Human atrial and ventricular tissues display characteristic miRNA expression signatures under physiological conditions. Notably, miR-208a and miR-208b show significant chamber-specificity as do their host genes, α-MHC and β-MHC, which are mainly expressed in the atria and ventricles, respectively. These findings might also serve to enhance our understanding of cardiac miRNAs and various heart diseases.

The functional consequences of age-related changes in microRNA expression in skeletal muscle

A common characteristic of ageing is disrupted homeostasis between growth and atrophy of skeletal muscle resulting in loss of muscle mass and function, which is associated with sarcopenia. Sarcopenia is related to impaired balance, increased falls and decline in quality of life of older people. Ageing-related transcriptome and proteome changes in skeletal muscle have been characterised, however the molecular mechanisms underlying sarcopenia are still not fully understood. microRNAs are novel regulators of gene expression known to modulate skeletal muscle development and homeostasis. Expression of numerous microRNAs is disrupted in skeletal muscle with age however, the functional consequences of this are not yet understood. Given that a single microRNA can simultaneously affect multiple signalling pathways, microRNAs are potent modulators of pathophysiological changes occurring during ageing. Here we use microRNA and transcript expression profiling together with microRNA functional assays to show that disrupted microRNA:target interactions play an important role in maintaining muscle homeostasis. We identified miR-181a as a regulator of the sirtuin1 (Sirt1) gene expression in skeletal muscle and show that the expression of miR-181a and its target gene is disrupted in skeletal muscle from old mice. Moreover, we show that miR-181a:Sirt1 interactions regulate myotube size. Our results demonstrate that disrupted microRNA:target interactions are likely related to the pathophysiological changes occurring in skeletal muscle during ageing.

Micromanaging cardiac regeneration: Targeted delivery of microRNAs for cardiac repair and regeneration

The loss of cardiomyocytes during injury and disease can result in heart failure and sudden death, while the adult heart has a limited capacity for endogenous regeneration and repair. Current stem cell-based regenerative medicine approaches modestly improve cardiomyocyte survival, but offer neglectable cardiomyogenesis. This has prompted the need for methodological developments that crease de novo cardiomyocytes. Current insights in cardiac development on the processes and regulatory mechanisms in embryonic cardiomyocyte differentiation provide a basis to therapeutically induce these pathways to generate new cardiomyocytes. Here, we discuss the current knowledge on embryonic cardiomyocyte differentiation and the implementation of this knowledge in state-of-the-art protocols to the direct reprogramming of cardiac fibroblasts into de novo cardiomyocytes in vitro and in vivo with an emphasis on microRNA-mediated reprogramming. Additionally, we discuss current advances on state-of-the-art targeted drug delivery systems that can be employed to deliver these microRNAs to the damaged cardiac tissue. Together, the advances in our understanding of cardiac development, recent advances in microRNA-based therapeutics, and innovative drug delivery systems, highlight exciting opportunities for effective therapies for myocardial infarction and heart failure.

Mechanical Stretch Inhibits MicroRNA499 via p53 to Regulate Calcineurin-A Expression in Rat Cardiomyocytes

BACKGROUND

MicroRNAs play an important role in cardiac remodeling. MicroRNA 499 (miR499) is highly enriched in cardiomyocytes and targets the gene for Calcineurin A (CnA), which is associated with mitochondrial fission and apoptosis. The mechanism regulating miR499 in stretched cardiomyocytes and in volume overloaded heart is unclear. We sought to investigate the mechanism regulating miR499 and CnA in stretched cardiomyocytes and in volume overload-induced heart failure.

METHODS & RESULTS

Rat cardiomyocytes grown on a flexible membrane base were stretched via vacuum to 20% of maximum elongation at 60 cycles/min. An in vivo model of volume overload with aorta-caval shunt in adult rats was used to study miR499 expression. Mechanical stretch downregulated miR499 expression, and enhanced the expression of CnA protein and mRNA after 12 hours of stretch. Expression of CnA and calcineurin activity was suppressed with miR499 overexpression; whereas, expression of dephosphorylated dynamin-related protein 1 (Drp1) was suppressed with miR499 overexpression and CnA siRNA. Adding p53 siRNA reversed the downregulation of miR499 when stretched. A gel shift assay and promoter-activity assay demonstrated that stretch increased p53 DNA binding activity but decreased miR499 promoter activity. When the miR499 promoter p53-binding site was mutated, the inhibition of miR499 promoter activity with stretch was reversed. The in vivo aorta-caval shunt also showed downregulated myocardial miR499 and overexpression of miR499 suppressed CnA and cellular apoptosis.

CONCLUSION

The miR499-controlled apoptotic pathway involving CnA and Drp1 in stretched cardiomyocytes may be regulated by p53 through the transcriptional regulation of miR499.

MicroRNA Signature and Cardiovascular Dysfunction

The worldwide increase in the prevalence of obesity and type 2 diabetes and the associated elevated risk of cardiovascular disease (CVD) has emphasized the need to seek new therapeutic targets to offset the negative impact on human health outcomes. In this regards, microRNAs (miRNAs), a class of small noncoding RNAs that mediate posttranscriptional gene silencing, have received considerable interest. miRNAs repress gene expression by their ability to pair with target sequences in the 3' untranslated region of the messenger RNA. miRNAs play a crucial role in the biogenesis and function of the cardiovascular system and are implicated as dynamic regulators of cardiac and vascular signaling and pathophysiology. Numerous miRNAs have been identified as novel biomarkers and potential therapeutic targets for CVD. In this review, we discuss the contribution of miRNAs to the regulation of CVD, their role in macrovascular/microvascular (dys)function, their potential as important biomarkers for the early detection of CVD, and, finally, as therapeutic targets.

Dynamical Expression of MicroRNA-127-3p in Proliferating and Differentiating C2C12 Cells

MicroRNAs (miRNAs) are highly conserved, short non-coding RNAs that regulate gene expression at the posttranscriptional level. Although many miRNAs are identified in muscles and muscle cells, their individual roles are still not fully understood. In the present study, we investigated a muscle highly-expressed miRNA, miR-127-3p, in C2C12 myoblasts and tissues of goats with different muscle phenotypes (Boer vs Wushan black goats). Our results demonstrated that i) miR-127-3p was extensively expressed in tissues of goats; ii) miR-127-3p was higher expressed in muscle, spleen, heart, and skin in the muscular goats (Boer goats) than the control (Wushan black goats). Then we further characterized the dynamical expression of miR-127-3p, MyoD, MyoG, Myf5, Mef2c, and Myosin in the proliferating and differentiating C2C12 myoblasts at day of 0, 1, 3, 5, and 7 in culture mediums. Especially, we found that miR-127-3p was significantly higher expressed in the proliferating than differentiating cells. Our findings suggest that miR-127-3p probably plays roles in the proliferation and differentiation of myoblasts, which further underlies regulation of muscle phenotype in goats.

MicroRNA-29a in Adult Muscle Stem Cells Controls Skeletal Muscle Regeneration During Injury and Exercise Downstream of Fibroblast Growth Factor-2

The expansion of myogenic progenitors (MPs) in the adult muscle stem cell niche is critical for the regeneration of skeletal muscle. Activation of quiescent MPs depends on the dismantling of the basement membrane and increased access to growth factors such as fibroblast growth factor-2 (FGF2). Here, we demonstrate using microRNA (miRNA) profiling in mouse and human myoblasts that the capacity of FGF2 to stimulate myoblast proliferation is mediated by miR-29a. FGF2 induces miR-29a expression and inhibition of miR-29a using pharmacological or genetic deletion decreases myoblast proliferation. Next generation RNA sequencing from miR-29a knockout myoblasts (Pax7(CE/+) ; miR-29a(flox/flox) ) identified members of the basement membrane as the most abundant miR-29a targets. Using gain- and loss-of-function experiments, we confirm that miR-29a coordinately regulates Fbn1, Lamc1, Nid2, Col4a1, Hspg2 and Sparc in myoblasts in vitro and in MPs in vivo. Induction of FGF2 and miR-29a and downregulation of its target genes precedes muscle regeneration during cardiotoxin (CTX)-induced muscle injury. Importantly, MP-specific tamoxifen-induced deletion of miR-29a in adult skeletal muscle decreased the proliferation and formation of newly formed myofibers during both CTX-induced muscle injury and after a single bout of eccentric exercise. Our results identify a novel miRNA-based checkpoint of the basement membrane in the adult muscle stem cell niche. Strategies targeting miR-29a might provide useful clinical approaches to maintain muscle mass in disease states such as ageing that involve aberrant FGF2 signaling.

Role of the Thyroid System in the Dynamic Complex Network of Cardioprotection

Cardioprotection is a common goal of new therapeutic strategies in patients with coronary artery disease and/or left ventricular dysfunction. Myocardial damage following ischaemia/reperfusion injury lead to left ventricular adverse remodelling through many mechanisms arising from different cell types in different myocardial districts, namely the border and remote zone. Cardioprotection must face this complex, dynamic network of cooperating units. In this scenario, thyroid hormones can represent an effective therapeutic strategy due to the numerous actions and regulating mechanisms carried out at the level of the myocytes, interstitium and the vasculature, as well as to the activation of different pro-survival intracellular pathways involved in cardioprotection.

The role of microRNAs in cardiac development and regenerative capacity

The mammalian heart has long been considered to be a postmitotic organ. It was thought that, in the postnatal period, the heart underwent a transition from hyperplasic growth (more cells) to hypertrophic growth (larger cells) due to the conversion of cardiomyocytes from a proliferative state to one of terminal differentiation. This hypothesis was gradually disproven, as data were published showing that the myocardium is a more dynamic tissue in which cardiomyocyte karyokinesis and cytokinesis produce new cells, leading to the hyperplasic regeneration of some of the muscle mass lost in various pathological processes. microRNAs have been shown to be critical regulators of cardiomyocyte differentiation and proliferation and may offer the novel opportunity of regenerative hyperplasic therapy. Here we summarize the relevant processes and recent progress regarding the functions of specific microRNAs in cardiac development and regeneration.

MicroRNA-208a Dysregulates Apoptosis Genes Expression and Promotes Cardiomyocyte Apoptosis during Ischemia and Its Silencing Improves Cardiac Function after Myocardial Infarction

Aims. miR-208a is associated with adverse outcomes in several cardiac pathologies known to have increased apoptosis, including myocardial infarction (MI). We investigated if miR-208a has proapoptotic effects on ischemic cardiomyocytes and if its silencing has therapeutic benefits in MI. Methods and Results. The effect of miR-208a on apoptosis during ischemia was studied in cultured neonatal mice myocytes transfected with agomir or antagomir. Differential gene expression was assessed using microarrays. MI was induced in male C57BL/6 mice randomly assigned to antagomir (n = 6) or control group (n = 7), while sham group (n = 7) had sham operation done. Antagomir group received miR208a antagomir, while control and sham group mice received vehicle only. At 7 and 28 days, echocardiography was done and thereafter hearts were harvested for analysis of apoptosis by TUNEL method, fibrosis using Masson's trichrome, and hypertrophy using hematoxylin and eosin. miR-208a altered apoptosis genes expression and increased apoptosis in ischemic cardiomyocytes. Therapeutic inhibition of miR-208a decreased cardiac fibrosis, hypertrophy, and apoptosis and significantly improved cardiac function 28 days after MI. Conclusion. miR-208a alters apoptosis genes expression and promotes apoptosis in ischemic cardiomyocytes, and its silencing attenuates apoptosis, fibrosis, and hypertrophy after MI, with significant improvement in cardiac function.

MicroRNA-208b progressively declines after spinal cord injury in humans and is inversely related to myostatin expression

The effects of long-term physical inactivity on the expression of microRNAs involved in the regulation of skeletal muscle mass in humans are largely unknown. MicroRNAs are short, noncoding RNAs that fine-tune target expression through mRNA degradation or by inhibiting protein translation. Intronic to the slow, type I, muscle fiber type genes MYH7 and MYH7b, microRNA-208b and microRNA-499-5p are thought to fine-tune the expression of genes important for muscle growth, such as myostatin. Spinal cord injured humans are characterized by both skeletal muscle atrophy and transformation toward fast-twitch, type II fibers. We determined the expression of microRNA-208b, microRNA-499-5p, and myostatin in human skeletal muscle after complete cervical spinal cord injury. We also determined whether these microRNAs altered myostatin expression in rodent skeletal muscle. A progressive decline in skeletal muscle microRNA-208b and microRNA-499-5p expression occurred in humans during the first year after spinal cord injury and with long-standing spinal cord injury. Expression of myostatin was inversely correlated with microRNA-208b and microRNA-499-5p in human skeletal muscle after spinal cord injury. Overexpression of microRNA-208b in intact mouse skeletal muscle decreased myostatin expression, whereas microRNA-499-5p was without effect. In conclusion, we provide evidence for an inverse relationship between expression of microRNA-208b and its previously validated target myostatin in humans with severe skeletal muscle atrophy. Moreover, we provide direct evidence that microRNA-208b overexpression decreases myostatin gene expression in intact rodent muscle. Our results implicate that microRNA-208b modulates myostatin expression and this may play a role in the regulation of skeletal muscle mass following spinal cord injury.

Identification of General and Heart-Specific miRNAs in Sheep (Ovis aries)

MicroRNAs (miRNAs or miRs) are small regulatory RNAs crucial for modulation of signaling pathways in multiple organs. While the link between miRNAs and heart disease has grown more readily apparent over the past three years, these data are primarily limited to small animal models or cell-based systems. Here, we performed a high-throughput RNA sequencing (RNAseq) analysis of left ventricle and other tissue from a pre-clinical ovine model. We identified 172 novel miRNA precursors encoding a total of 264 mature miRNAs. Notably, 84 precursors were detected in both the left ventricle and other tissues. However, 10 precursors, encoding 11 mature sequences, were specific to the left ventricle. Moreover, the total 168 novel miRNA precursors included 22 non-conserved ovine-specific sequences. Our data identify and characterize novel miRNAs in the left ventricle of sheep, providing fundamental new information for our understanding of protein regulation in heart and other tissues.

Association between microRNA-499 polymorphism and gastric cancer risk in Chinese population

Single-nucleotide polymorphisms in microRNAs are related to the occurrence, development and prognosis of cancer. The aim of the present study is to investigate the possible influence of the miR-499(rs3746444) polymorphism on the risk of gastric cancer in Chinese population. A total of 363 GC patients and 969 cancer-free controls were enrolled in this study. The genotypes were obtained using MassARRAY method. The results showed that, compared with T allele, C allele was associated with a significantly increased risk of GC (OR=1.491, 95% CI=1.155-1.923, P=0.002). Moreover, a significantly increased risk of GC in subjects with the TC genotype was observed (adjusted OR of 1.559, 95% CI=1.148-2.117, P=0.004), compared with the wide type TT. We also found that basically dominant model (TT vs. TC+CC) was suitable for the association between rs6513497 and the risk of GC (OR=1.568, 95% CI=1.173-2.097, P=0.002). However, the same association was also shown in males and females. Meanwhile, rs3746444 was associated with the tumor size of GC patients. The present study indicated that miR-499 rs3746444 might contribute to GC risk and this SNP could be developed as a biomarker for GC prediction.

De novo assembly and characterization of tissue-specific transcriptome in the endangered golden mahseer, Tor putitora

The golden mahseer (Tor putitora) graces most of the Himalayan Rivers of India and neighboring South Asian countries. Despite its several importance as a research model, as food, and in sport fishing, knowledge on transcriptome database is nil. Therefore, it was targeted to develop reference transcriptome databases of the species using next-generation sequencing. In the present study, 100,540,130 high-quality paired-end reads were obtained from six cDNA libraries of spleen, liver, gill, kidney, muscle, and brain with 28.4 GB data using Illumina paired-end sequencing technology. Tissue-specific transcriptomes as well as complete transcriptome assembly were analyzed for concise representation of the study. In brief, the de novo assembly of individual tissue resulted in an average of 31,829 (18,512–46,348) contigs per sample, while combined transcriptome comprised 77,907 unique transcript fragments (unigenes) assembled from reads of six tissues. Approximately 75,407 (96.8%) unigenes could be annotated according to their homology matches in the nr, SwisseProt, GO, or KEGG databases. Comparative analysis showed that 84% of the unigenes have significant similarity to zebra fish RefSeq proteins. Tissue-specific-dominated genes were also identified to hypothesize their localization and expression in individual tissue. In addition, 2485 simple sequence repeats (SSRs) were detected from 77,907 transcripts in the combined transcriptome of the golden mahseer. This study has generated organ-specific transcriptome profiles, which will be helpful to understand the local adaptation, genome evolution, and also future functional studies on immune system of the golden mahseer.

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Organ specific and concatenated transcriptome of 6 organs of golden mahseer was generated using illumina sequencing.

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A total of 100,540,130 high-quality paired-ends reads with 28.4 GB data that assembled into 77,907 contigs were obtained.

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Contigs were annotated using GO and KEGG pathway and organ-specific few genes were identified.

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Thirty four usable SSR markers were extracted from 2485 identified.

Cardiac Disease Status Dictates Functional mRNA Targeting Profiles of Individual MicroRNAs

BACKGROUND

MicroRNAs are key players in cardiac stress responses, but the mRNAs, whose abundance and translational potential are primarily affected by changes in cardiac microRNAs, are not well defined. Stimulus-induced, large-scale alterations in the cardiac transcriptome, together with consideration of the law of mass action, further suggest that the mRNAs most substantively targeted by individual microRNAs will vary between unstressed and stressed conditions. To test the hypothesis that microRNA target profiles differ in health and disease, we traced the fate of empirically determined miR-133a and miR-378 targets in mouse hearts undergoing pressure overload hypertrophy.

METHODS AND RESULTS

Ago2 immunoprecipitation with RNA sequencing (RNA-induced silencing complex sequencing) was used for unbiased definition of microRNA-dependent and microRNA-independent alterations occurring among ≈13 000 mRNAs in response to transverse aortic constriction (TAC). Of 37 direct targets of miR-133a defined in unstressed hearts (fold change ≥25%, false discovery rate <0.02), only 4 (11%) continued to be targeted by miR-133a during TAC, whereas for miR-378 direct targets, 3 of 32 targets (9%) were maintained during TAC. Similarly, only 16% (for miR-133a) and 53% (for miR-378) of hundreds of indirectly affected mRNAs underwent comparable regulation, demonstrating that the effect of TAC on microRNA direct target selection resulted in widespread alterations of signaling function. Numerous microRNA-mediated regulatory events occurring exclusively during pressure overload revealed signaling networks that may be responsive to the endogenous decreases in miR-133a during TAC.

CONCLUSIONS

Pressure overload-mediated changes in overall cardiac RNA content alter microRNA targeting profiles, reinforcing the need to define microRNA targets in tissue-, cell-, and status-specific contexts.

Differential microRNA Expression in Fast- and Slow-Twitch Skeletal Muscle of Piaractus mesopotamicus during Growth

Pacu (Piaractus mesopotamicus) is a Brazilian fish with a high economic value in pisciculture due to its rusticity and fast growth. Postnatal growth of skeletal muscle in fish occurs by hyperplasia and/or hypertrophy, processes that are dependent on the proliferation and differentiation of myoblasts. A class of small noncoding RNAs, known as microRNAs (miRNAs), represses the expression of target mRNAs, and many studies have demonstrated that miR-1, miR-133, miR-206 and miR-499 regulate different processes in skeletal muscle through the mRNA silencing of hdac4 (histone deacetylase 4), srf (serum response factor), pax7 (paired box 7) and sox6 ((sex determining region Y)-box 6), respectively. The aim of our work was to evaluate the expression of these miRNAs and their putative target mRNAs in fast- and slow-twitch skeletal muscle of pacu during growth. We used pacus in three different development stages: larval (aged 30 days), juvenile (aged 90 days and 150 days) and adult (aged 2 years). To complement our study, we also performed a pacu myoblast cell culture, which allowed us to investigate miRNA expression in the progression from myoblast proliferation to differentiation. Our results revealed an inverse correlation between the expression of the miRNAs and their target mRNAs, and there was evidence that miR-1 and miR-206 may regulate the differentiation of myoblasts, whereas miR-133 may regulate the proliferation of these cells. miR-499 was highly expressed in slow-twitch muscle, which suggests its involvement in the specification of the slow phenotype in muscle fibers. The expression of these miRNAs exhibited variations between different development stages and between distinct muscle twitch phenotypes. This work provides the first identification of miRNA expression profiles in pacu skeletal muscle and suggests an important role of these molecules in muscle growth and in the maintenance of the muscle phenotype.

microRNAs: Modulators of the underlying pathophysiology of sarcopenia?

Skeletal muscle homeostasis depends on an intricate balance between muscle hypertrophy, atrophy and regeneration. As we age, maintenance of muscle homeostasis is perturbed, resulting in a loss of muscle mass and function, termed sarcopenia. Individuals with sarcopenia exhibit impaired balance, increased falls (leading to subsequent injury) and an overall decline in quality of life. The mechanisms mediating sarcopenia are still not fully understood but clarity in our understanding of the precise pathophysiological changes occurring during skeletal muscle ageing has improved dramatically. Advances in transcriptomics has highlighted significant deregulation in skeletal muscle gene expression with ageing, suggesting epigenetic alterations may play a crucial and potentially causative role in the skeletal muscle ageing process. microRNAs (miRNAs, miRs), novel regulators of gene expression, can modulate many processes in skeletal muscle, including myogenesis, tissue regeneration and cellular programming. Expression of numerous evolutionary conserved miRNAs is disrupted in skeletal muscle with age. Given that a single miRNA can simultaneously affect the functionality of multiple signaling pathways, miRNAs are potent modulators of pathophysiological changes. miRNA-based interventions provide a promising new therapeutic strategy against alterations in muscle homeostasis. The aim of this review is two-fold; firstly to outline the latest understanding of the pathophysiological alterations impacting the deregulation of skeletal muscle mass and function with ageing, and secondly, to highlight the mounting evidence for a role of miRNAs in modulating muscle mass, and the need to explore their specific role in sarcopenia.

Regulation of cardiac miR-208a, an inducer of obesity, by rapamycin and nebivolol

OBJECTIVE

Resistance to obesity is observed in rodents and humans treated with rapamycin (Rap) or nebivolol (Neb). Because cardiac miR-208a promotes obesity, this study tested whether the modes of actions of Rap and Neb involve inhibition of miR-208a.

METHODS

Mouse cardiomyocyte HL-1 cells and Zucker obese (ZO) rats were used to investigate regulation of cardiac miR-208a.

RESULTS

Angiotensin II (Ang II) increased miR-208a expression in HL-1 cells. Pretreatment with an AT1 receptor (AT1R) antagonist, losartan (1 μM), antagonized this effect, whereas a phospholipase C inhibitor, U73122 (10 μM), and an NADPH oxidase inhibitor, apocynin (0.5 mM), did not. Ang II-induced increase in miR-208a was suppressed by Rap (10 nM), an inhibitor of nutrient sensor kinase mTORC1, and Neb (1 μM), a 3rd generation β-blocker that suppressed bioavailable AT1R binding of (125) I-Ang II. Thus, suppression of AT1R expression by Neb, inhibition of AT1R activation by losartan, and inhibition of AT1R-induced activation of mTORC1 by Rap attenuated the Ang II-induced increase in miR-208a. In ZO rats, Rap treatment (750 μg kg(-1)  day(-1) ; 12 weeks) reduced obesity despite similar food intake, suppressed cardiac miR-208a, and increased cardiac MED13, a suppresser of obesity.

CONCLUSIONS

Rap and Neb suppressed cardiac miR-208a. Suppression of miR-208a and increase in MED13 correlated with attenuated weight gain despite leptin resistance.

Transdifferentiation via transcription factors or microRNAs: Current status and perspective

Transdifferentiation as a new approach for obtaining the ideal cells for transplantation has gradually become a hot research topic. Compared with the induced pluripotent stem cells technique, transdifferentiation may have better efficiency and safety. Although the mechanism of transdifferentiation is still unknown, many studies have achieved transformation of one cell type to another through transcription factors or microRNA. The current major strategy for transdifferentiation is via transcription factors; however, there are some safety issues with the use of transcription factors. In contrast, microRNA as a novel tool for inducing transdifferentiation through post-transcriptional regulation may be more safe and efficient. In addition, the present transdifferentiation strategies involve obtaining the terminal cell directly, so the amount of cells produced may not be sufficient and they may have low capacity for cell immigration and integration. Therefore, an indirect transdifferentiation strategy for producing unipotent cells is ideal as it can preserve the proliferation capacity and differentiation pathway.

Influence of statins on distinct circulating microRNAs during prolonged aerobic exercise

Statins exacerbate exercise-induced skeletal muscle injury. Muscle-specific microRNAs (myomiRs) increase in plasma after prolonged exercise, but the patterns of myomiRs release after statin-associated muscle injury have not been examined. We examined the relationships between statin exposure, in vitro and in vivo muscle contraction, and expression of candidate circulating myomiRs. We measured plasma levels of myomiRs, circulating microRNA-1 (c-miR-1), c-miR-133a, c-miR-206, and c-miR-499-5p from 28 statin-using and 28 nonstatin-using runners before (PRE), immediately after (FINISH), and 24 h after they ran a 42-km footrace (the 2011 Boston marathon) (POST-24). To examine these cellular-regulation myomiRs, we used contracting mouse C2C12 myotubes in culture with and without statin exposure to compare intracellular and extracellular expression of these molecules. In marathoners, c-miR-1, c-miR-133a, and c-miR-206 increased at FINISH, returned to baseline at POST-24, and were unaffected by statin use. In contrast, c-miR-499-5p was unchanged at FINISH but increased at POST-24 among statin users compared with PRE and runners who did not take statins. In cultured C2C12 myotubes, extracellular c-miR-1, c-miR-133a, and c-miR-206 were significantly increased by muscle contraction regardless of statin use. In contrast, extracellular miR-499-5p was unaffected by either isolated statin exposure or isolated carbachol exposure but it was increased when muscle contraction was combined with statin exposure. In summary, we found that statin-potentiated muscle injury during exercise is accompanied by augmented extracellular release of miR-499-5p. Thus c-miR-499-5p may serve as a biomarker of statin-potentiated muscle damage.

Expression Change of miR-214 and miR-135 during Muscle Differentiation

Objective

MicroRNAs (miRNAs) are a class of small non-coding RNAs that play pivotal roles in many biological processes such as regulating skeletal muscle development where alterations in miRNA expression are reported during myogenesis. In this study, we aimed to investigate the impact of predicted miRNAs and their target genes on the myoblast to myocyte differentiation process.

Materials and Methods

This experimental study was conducted on the C2C12 cell line. Using a bioinformatics approach, miR-214 and miR-135 were selected according to their targets as potential factors in myoblast to myocyte differentiation induced by 3% horse serum. Immunocytochemistry (ICC) was undertaken to confirm the differentiation process and quantitative real-time polymerase chain reaction (PCR) to determine the expression level of miRNAs and their targets.

Results

During myoblast to myocyte differentiation, miR-214 was significantly down- regulated while miRNA-135, Irs2, Akt2 and Insr were overexpressed during the process.

Conclusion

miR-214 and miR-135 are potential regulators of myogenesis and are involved in skeletal muscle development through regulating the IRS/PI3K pathway.

Harnessing the microRNA pathway for cardiac regeneration

Mounting evidence over the last few years has indicated that the rate of cardiomyocyte proliferation, and thus the extent of cardiac renewal, is under the control of the microRNA network. Several microRNAs (e.g. miR-1) regulate expansion of the cardiomyocyte pool and its terminal differentiation during the embryonic life; some not only promote cardiomyocyte proliferation but also their de-differentiation towards an embryonic cell phenotype (e.g. the miR-302/367 cluster); a few others are involved in the repression of cardiomyocyte proliferation occurring suddenly after birth (e.g. the miR-15 family); others again are not physiologically involved in the regulation of cardiomyocyte turnover, but nevertheless are able to promote cardiomyocyte proliferation and cardiac regeneration when delivered exogenously (e.g. miR-199a-3p). With a few exceptions, the molecular mechanisms underlying the pro-proliferative effect of these microRNAs, most of which appear to act at the level of already differentiated cardiomyocytes, remain to be thoroughly elucidated. The possibility of harnessing the miRNA network to achieve cardiac regeneration paves the way to exciting therapeutic applications. This could be achieved by either administering miRNA mimics or inhibitors, or transducing the heart with viral vectors expressing miRNA-encoding genes.

Circulating MicroRNA and Long Noncoding RNA as Biomarkers of Cardiovascular Diseases

Although >85% of the human genome is transcribed, only <2% is transcribed into protein-coding RNA (messenger RNA, mRNA). Many thousands of noncoding RNAs are transcribed and recognized as functional RNAs with diverse sizes, structures, and biological functions. Based on size, noncoding RNA can be generally divided into two subgroups: short noncoding RNA (<200 nucleotides including microRNA or miRNA) and long noncoding RNA (lncRNA, >200 nucleotides). It is now clear that these RNAs fulfil critical roles as transcriptional and post-transcriptional regulators and as guides of chromatin-modifying complexes. Although not translated into protein, noncoding RNAs can regulate cardiac function through diverse mechanisms and their dysregulation is increasingly linked with cardiovascular pathophysiology. Furthermore, a series of recent studies have discovered that noncoding RNAs can be found in the bloodstream and some species are remarkably stable. This has raised the possibility that such noncoding RNAs may be measured in body fluids and serve as novel diagnostic biomarkers. Here, we summarize the current knowledge of noncoding RNAs' function and biomarker potential in cardiac diseases, concentrating mainly on circulating miRNAs and lncRNAs. J. Cell. Physiol. 231: 751-755, 2016. © 2015 Wiley Periodicals, Inc.

Grazing Affects Exosomal Circulating MicroRNAs in Cattle

Circulating microRNAs (c-miRNAs) are associated with physiological adaptation to acute and chronic aerobic exercise in humans. To investigate the potential effect of grazing movement on miRNA circulation in cattle, here we profiled miRNA expression in centrifugally prepared exosomes from the plasma of both grazing and housed Japanese Shorthorn cattle. Microarray analysis of the c-miRNAs resulted in detection of a total of 231 bovine exosomal miRNAs in the plasma, with a constant expression level of let-7g across the duration and cattle groups. Expression of muscle-specific miRNAs such as miR-1, miR-133a, miR-206, miR-208a/b, and miR-499 were undetectable, suggesting the mildness of grazing movement as exercise. According to validation by quantitative RT-PCR, the circulating miR-150 level in the grazing cattle normalized by the endogenous let-7g level was down-regulated after 2 and 4 months of grazing (P < 0.05), and then its levels in housed and grazing cattle equalized when the grazing cattle were returned to a housed situation. Likewise, the levels of miR-19b, miR-148a, miR-221, miR-223, miR-320a, miR-361, and miR-486 were temporarily lowered in the cattle at 1 and/or 2 month of grazing compared to those of the housed cattle (P < 0.05). In contrast, the miR-451 level was up-regulated in the grazing cattle at 2 months of grazing (P = 0.044). The elevation of miR-451 level in the plasma was coincident with that in the biceps femoris muscle of the grazing cattle (P = 0.008), which suggests the secretion or intake of miR-451 between skeletal muscle cells and circulation during grazing. These results revealed that exosomal c-miRNAs in cattle were affected by grazing, suggesting their usefulness as molecular grazing markers and functions in physiological adaptation of grazing cattle associated with endocytosis, focal adhesion, axon guidance, and a variety of intracellular signaling, as predicted by bioinformatic analysis.

Myostatin: expanding horizons

Myostatin is a secreted growth and differentiation factor that belongs to the TGF-β superfamily. Myostatin is predominantly synthesized and expressed in skeletal muscle and thus exerts a huge impact on muscle growth and function. In keeping with its negative role in myogenesis, myostatin expression is tightly regulated at several levels including epigenetic, transcriptional, post-transcriptional, and post-translational. New revelations regarding myostatin regulation also offer mechanisms that could be exploited for developing myostatin antagonists. Increasingly, it is becoming clearer that besides its conventional role in muscle, myostatin plays a critical role in metabolism. Hence, molecular mechanisms by which myostatin regulates several key metabolic processes need to be further explored.

Aerobic exercise training promotes physiological cardiac remodeling involving a set of microRNAs

Left ventricular (LV) hypertrophy is an important physiological compensatory mechanism in response to chronic increase in hemodynamic overload. There are two different forms of LV hypertrophy, one physiological and another pathological. Aerobic exercise induces beneficial physiological LV remodeling. The molecular/cellular mechanisms for this effect are not totally known, and here we review various mechanisms including the role of microRNA (miRNA). Studies in the heart, have identified antihypertrophic miRNA-1, -133, -26, -9, -98, -29, -378, and -145 and prohypertrophic miRNA-143, -103, -130a, -146a, -21, -210, -221, -222, -27a/b, -199a/b, -208, -195, -499, -34a/b/c, -497, -23a, and -15a/b. Four miRNAs are recognized as cardiac-specific: miRNA-1, -133a/b, -208a/b, and -499 and called myomiRs. In our studies we have shown that miRNAs respond to swimming aerobic exercise by 1) decreasing cardiac fibrosis through miRNA-29 increasing and inhibiting collagen, 2) increasing angiogenesis through miRNA-126 by inhibiting negative regulators of the VEGF pathway, and 3) modulating the renin-angiotensin system through the miRNAs-27a/b and -143. Exercise training also increases cardiomyocyte growth and survival by swimming-regulated miRNA-1, -21, -27a/b, -29a/c, -30e, -99b, -100, -124, -126, -133a/b, -143, -144, -145, -208a, and -222 and running-regulated miRNA-1, -26, -27a, -133, -143, -150, and -222, which influence genes associated with the heart remodeling and angiogenesis. We conclude that there is a potential role of these miRNAs in promoting cardioprotective effects on physiological growth.

Hypertrophic and antihypertrophic microRNA levels in peripheral blood mononuclear cells and their relationship to left ventricular hypertrophy in patients with essential hypertension

MicroRNAs regulate several aspects of physiological and pathologic cardiac hypertrophy, and they represent promising therapeutic targets in cardiovascular disease. We assessed the expression levels of the microRNAs miR-1, miR-133a, miR-26b, miR-208b, miR-499, and miR-21, in 102 patients with essential hypertension and 30 healthy individuals. All patients underwent two-dimensional echocardiography. MicroRNA expression levels in peripheral blood mononuclear cells were quantified by real-time reverse transcription polymerase chain reaction. Hypertensive patients showed significantly lower miR-133a (5.06 ± 0.50 vs. 13.20 ± 2.15, P < .001) and miR-26b (6.76 ± 0.53 vs. 9.36 ± 1.40, P = .037) and higher miR-1 (25.99 ± 3.07 vs. 12.28 ± 2.06, P = .019), miR-208b (22.29 ± 2.96 vs. 8.73 ± 1.59, P = .016), miR-499 (10.06 ± 1.05 vs. 5.70 ± 0.91, P = .033), and miR-21 (2.75 ± 0.15 vs. 1.82 ± 0.20, P = .002) expression levels compared with healthy controls. In hypertensive patients, we observed significant negative correlations of miR-1 (r = -0.374, P < .001) and miR-133a (r = -0.431, P < .001) and significant positive correlations of miR-26b (r = 0.302, P = .002), miR-208b (r = 0.426, P < .001), miR-499 (r = 0.433, P < .001) and miR-21 (r = 0.498, P < .001) expression levels with left ventricular mass index. Our data reveal that miR-1, miR-133a, miR-26b, miR-208b, miR-499, and miR-21 show distinct expression profiles in hypertensive patients relative to healthy individuals and they are associated with clinical indices of left ventricular hypertrophy in hypertensive patients. Thus, they may be related to heart hypertrophy in hypertensive patients and are possibly candidate therapeutic targets in hypertensive heart disease.

cAMP induces hypertrophy and alters DNA methylation in HL-1 cardiomyocytes

cAMP is a highly regulated secondary messenger involved in many biological processes. Chronic activation of the cAMP pathway by catecholamines results in cardiac hypertrophy and fibrosis; however, the mechanism by which elevated cAMP leads to cardiomyopathy is not fully understood. To address this issue, we increased intracellular cAMP levels in HL-1 cardiomyocytes, a cell line derived from adult mouse atrium, using either the stable cAMP analog N(6),2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP) or phosphodiesterase (PDE) inhibitors caffeine and theophylline. Elevated cAMP levels increased cell size and altered expression levels of cardiac genes and micro-RNAs associated with hypertrophic cardiomyopathy (HCM), including Myh6, Myh7, Myh7b, Tnni3, Anp, Bnp, Gata4, Mef2c, Mef2d, Nfatc1, miR208a, and miR208b. In addition, DBcAMP altered the expression of DNA methyltransferases (Dnmts) and Tet methylcytosine dioxygenases (Tets), enzymes that regulate genomic DNA methylation levels. Changes in expression of DNA methylation genes induced by elevated cAMP led to increased global DNA methylation in HL-1 cells. In contrast, inhibition of DNMT activity with 5-azacytidine treatment decreased global DNA methylation levels and blocked the increased expression of several HCM genes (Myh7, Gata4, Mef2c, Nfatc1, Myh7b, Tnni3, and Bnp) observed with DBcAMP treatment. These results demonstrate that cAMP induces cardiomyocyte hypertrophy and altered HCM gene expression in vitro and that DNA methylation patterns mediate the upregulation of HCM genes induced by cAMP. These data identify a previously unknown mechanism by which elevated levels of cAMP lead to increased expression of genes associated with cardiomyocyte hypertrophy.

MicroRNAs and Cardiac Regeneration

The human heart has a limited capacity to regenerate lost or damaged cardiomyocytes after cardiac insult. Instead, myocardial injury is characterized by extensive cardiac remodeling by fibroblasts, resulting in the eventual deterioration of cardiac structure and function. Cardiac function would be improved if these fibroblasts could be converted into cardiomyocytes. MicroRNAs (miRNAs), small noncoding RNAs that promote mRNA degradation and inhibit mRNA translation, have been shown to be important in cardiac development. Using this information, various researchers have used miRNAs to promote the formation of cardiomyocytes through several approaches. Several miRNAs acting in combination promote the direct conversion of cardiac fibroblasts into cardiomyocytes. Moreover, several miRNAs have been identified that aid the formation of inducible pluripotent stem cells and miRNAs also induce these cells to adopt a cardiac fate. MiRNAs have also been implicated in resident cardiac progenitor cell differentiation. In this review, we discuss the current literature as it pertains to these processes, as well as discussing the therapeutic implications of these findings.

Noncoding RNAs, Emerging Regulators of Skeletal Muscle Development and Diseases

A healthy and independent life requires skeletal muscles to maintain optimal function throughout the lifespan, which is in turn dependent on efficient activation of processes that regulate muscle development, homeostasis, and metabolism. Thus, identifying mechanisms that modulate these processes is of crucial priority. Noncoding RNAs (ncRNAs), including microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), have emerged as a class of previously unrecognized transcripts whose importance in a wide range of biological processes and human disease is only starting to be appreciated. In this review, we summarize the roles of recently identified miRNAs and lncRNAs during skeletal muscle development and pathophysiology. We also discuss several molecular mechanisms of these noncoding RNAs. Undoubtedly, further systematic understanding of these noncoding RNAs' functions and mechanisms will not only greatly expand our knowledge of basic skeletal muscle biology, but also significantly facilitate the development of therapies for various muscle diseases, such as muscular dystrophies, cachexia, and sarcopenia.

The miR-199-dynamin regulatory axis controls receptor-mediated endocytosis

Small non-coding RNAs (microRNAs) are important regulators of gene expression that modulate many physiological processes; however, their role in regulating intracellular transport remains largely unknown. Intriguingly, we found that the dynamin (DNM) genes, a GTPase family of proteins responsible for endocytosis in eukaryotic cells, encode the conserved miR-199a and miR-199b family of miRNAs within their intronic sequences. Here, we demonstrate that miR-199a and miR-199b regulate endocytic transport by controlling the expression of important mediators of endocytosis such as clathrin heavy chain (CLTC), Rab5A, low-density lipoprotein receptor (LDLR) and caveolin-1 (Cav-1). Importantly, miR-199a-5p and miR-199b-5p overexpression markedly inhibits CLTC, Rab5A, LDLR and Cav-1 expression, thus preventing receptor-mediated endocytosis in human cell lines (Huh7 and HeLa). Of note, miR-199a-5p inhibition increases target gene expression and receptor-mediated endocytosis. Taken together, our work identifies a new mechanism by which microRNAs regulate intracellular trafficking. In particular, we demonstrate that the DNM, miR-199a-5p and miR-199b-5p genes act as a bifunctional locus that regulates endocytosis, thus adding an unexpected layer of complexity in the regulation of intracellular trafficking.

Oxidative Modification of miR-184 Enables It to Target Bcl-xL and Bcl-w

MicroRNAs (miRNAs) are small non-coding RNAs, and they bind to complementary sequences in the three prime untranslated regions (3' UTRs) of target mRNA transcripts, thereby inhibiting mRNA translation or promoting mRNA degradation. Excessive reactive oxygen species (ROS) can cause cell-damaging effects through oxidative modification of macromolecules leading to their inappropriate functions. Such oxidative modification is related to cancers, aging, and neurodegenerative and cardiovascular diseases. Here we report that miRNAs can be oxidatively modified by ROS. We identified that miR-184 upon oxidative modification associates with the 3' UTRs of Bcl-xL and Bcl-w that are not its native targets. The mismatch of oxidized miR-184 with Bcl-xL and Bcl-w is involved in the initiation of apoptosis in the study with rat heart cell line H9c2 and mouse models. Our results reveal a model of ROS in regulating cellular events by oxidatively modifying miRNA.

The mesmiRizing complexity of microRNAs for striated muscle tissue engineering

microRNAs (miRs) are small non-protein-coding RNAs, able to post-transcriptionally regulate many genes and exert pleiotropic effects. Alteration of miR levels in tissues and in the circulation has been associated with various pathological and regenerative conditions. In this regard, tissue engineering of cardiac and skeletal muscles is a fascinating context for harnessing the complexity of miR-based circuitries and signals. In this review, we will focus on miR-driven regulation of cardiac and skeletal myogenic routes in homeostatic and challenging states. Furthermore, we will survey the intriguing perspective of exosomal and circulating miRs as novel paracrine players, potentially useful for current and future approaches of regenerative medicine for the striated muscles.

Trbp regulates heart function through microRNA-mediated Sox6 repression

Cardiomyopathy is associated with altered expression of genes encoding contractile proteins. Here we show that Trbp (Tarbp2), an RNA-binding protein, is required for normal heart function. Cardiac-specific inactivation in mice of Trbp (Trbp(cKO)) caused progressive cardiomyopathy and lethal heart failure. Loss of Trbp function resulted in upregulation of Sox6, repression of genes encoding normal cardiac slow-twitch myofiber proteins and pathologically increased expression of genes encoding skeletal fast-twitch myofiber proteins. Remarkably, knockdown of Sox6 fully rescued the Trbp-mutant phenotype, whereas mice overexpressing Sox6 phenocopied Trbp(cKO) mice. Trbp inactivation was mechanistically linked to Sox6 upregulation through altered processing of miR-208a, which is a direct inhibitor of Sox6. Transgenic overexpression of Mir208a sufficiently repressed Sox6, restored the balance in gene expression for fast- and slow-twitch myofiber proteins, and rescued cardiac function in Trbp(cKO) mice. Together, our studies identify a new Trbp-mediated microRNA-processing mechanism in the regulation of a linear genetic cascade essential for normal heart function.

Effects of Dietary Energy Sources on Post Mortem Glycolysis, Meat Quality and Muscle Fibre Type Transformation of Finishing Pigs

Dietary energy source can influence muscle glycogen storage at slaughter. However, few studies have demonstrated whether the diet-induced change of muscle glycogen is achieved by the transformation of muscle fibre type. This study investigated the effects of dietary energy sources on meat quality, post mortem glycolysis and muscle fibre type transformation of finishing pigs. Seventy-two barrows with an average body weight of 65.0 ± 2.0 kg were selected and were allotted to three iso-energetic and iso-nitrogenous diets A, B or C, and each treatment consisted of three replicates (pens) of eight pigs each. Diet A contained 44.1% starch, 5.9% crude fat and 12.6% neutral detergent fiber (NDF); diet B contained 37.6% starch, 9.5% crude fat and 15.4% NDF; and diet C contained 30.9% starch, 14.3% crude fat and 17.8% NDF. The duration of the experiment was 28 days. After feed withdrawal 12 h, 24 pigs (eight per treatment) were slaughtered, samples from M. longissimus lumborum (LL) were collected for subsequent analysis. The results showed that pigs fed diet C had lesser average daily gain, average daily feed intake and back fat depth than those fed diet A (P<0.05). Diet C increased pH_45min (P<0.05) and decreased drip loss (P<0.05) in LL muscles compared with diet A. Meat from pigs fed diet A showed increased contents of lactate and greater glycolytic potential (GP) compared with those fed diet C (P<0.05). Greater mRNA expression of myosin heavy-chain (MyHC)-I and IIa and lesser expression of MyHC-IIx and IIb (P<0.05) in LL muscles were found in pigs fed diet C, than in pigs fed diet A. In addition, pigs fed diet C resulted in downregulation of miR23a and upregulation of miR409 and miR208b (P<0.05), associated with conserved changes of their corresponding targets. These findings indicated that diets containing low starch and high fibre were beneficial in reducing muscle glycolysis, improving meat quality of finishing pigs. This reduction of GP may be partially associated with the improvement of oxidative fibre composition in LL muscle, and the change in myofibre type may be correlated with the change in the miRNA expression.

Grazing-induced changes in muscle microRNA-206 and -208b expression in association with myogenic gene expression in cattle

To investigate the roles of microRNAs (miRNAs) in muscle type conversion, the effects of 4 months of grazing on the expression levels of miRNAs and mRNAs associated with skeletal muscle development were analyzed by quantitative RT-PCR using the Biceps femoris muscle of Japanese Shorthorn cattle. After 4 months of grazing, the expression of muscle fiber type-associated miR-208b was higher in the grazed cattle than in the housed. In concordance with the pattern in miR-208b expression, the expression of MyoD, a myogenic regulatory factor associated with the shifting of muscle property to the fast type, was lower in the grazed cattle after 4 months of grazing than in the housed cattle. In addition, the expression of MyHC-2x (a fast type) was higher in the housed cattle than in the grazed, after 4 months of grazing. During the grazing period, miR-206 expression decreased in the housed cattle, whereas expression in the grazed cattle did not change, but rather remained higher than that of the housed cattle even at 3 months after the grazing ended. These miRNAs including miR-206 persisting with muscles of grazed cattle may be associated with regulation of muscle gene expression during skeletal muscle adaptation to grazing.

An overview of microRNAs

The discovery of the first microRNA (miRNA) over 20 years ago has ushered in a new era in molecular biology. There are now over 2000 miRNAs that have been discovered in humans and it is believed that they collectively regulate one third of the genes in the genome. miRNAs have been linked to many human diseases and are being pursued as clinical diagnostics and as therapeutic targets. This review presents an overview of the miRNA pathway, including biogenesis routes, biological roles, and clinical approaches.