MiR-351 transiently increases during muscle regeneration and promotes progenitor cell proliferation and survival upon differentiation

miRNAs in Heart Development and Disease

Cardiovascular diseases (CVD) are a group of disorders that affect the heart and blood vessels. They include conditions such as myocardial infarction, coronary artery disease, heart failure, arrhythmia, and congenital heart defects. CVDs are the leading cause of death worldwide. Therefore, new medical interventions that aim to prevent, treat, or manage CVDs are of prime importance. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the posttranscriptional level and play important roles in various biological processes, including cardiac development, function, and disease. Moreover, miRNAs can also act as biomarkers and therapeutic targets. In order to identify and characterize miRNAs and their target genes, scientists take advantage of computational tools such as bioinformatic algorithms, which can also assist in analyzing miRNA expression profiles, functions, and interactions in different cardiac conditions. Indeed, the combination of miRNA research and bioinformatic algorithms has opened new avenues for understanding and treating CVDs. In this review, we summarize the current knowledge on the roles of miRNAs in cardiac development and CVDs, discuss the challenges and opportunities, and provide some examples of recent bioinformatics for miRNA research in cardiovascular biology and medicine.

Arntl deficiency in myeloid cells reduces neutrophil recruitment and delays skeletal muscle repair

After a muscle injury, a process comprising inflammation, repair, and regeneration must occur in a time-sensitive manner for skeletal muscle to be adequately repaired and regenerated. This complex process is assumed to be controlled by various myeloid cell types, including monocytes and macrophages, though the mechanism is not fully understood. Aryl hydrocarbon receptor nuclear translocator-like (Arntl or Bmal1) is a transcription factor that controls the circadian rhythm and has been implicated in regulating myeloid cell functions. In the present study, we generated myeloid cell-specific Arntl conditional knockout (cKO) mice to assess the role of Arntl expressed in myeloid cell populations during the repair process after muscle injury. Myeloid cell-specific Arntl deletion impaired muscle regeneration after cardiotoxin injection. Flow cytometric analyses revealed that, in cKO mice, the numbers of infiltrating neutrophils and Ly6C^hi monocytes within the injured site were reduced on days 1 and 2, respectively, after muscle injury. Moreover, neutrophil migration and the numbers of circulating monocytes were significantly reduced in cKO mice, which suggests these effects may account, at least in part, for the impaired regeneration. These findings suggest that Arntl, expressed in the myeloid lineage regulates neutrophil and monocyte recruitment and is therefore required for skeletal muscle regeneration.

Skeletal Muscle Regeneration in Cardiotoxin-Induced Muscle Injury Models

Skeletal muscle injuries occur frequently in daily life and exercise. Understanding the mechanisms of regeneration is critical for accelerating the repair and regeneration of muscle. Therefore, this article reviews knowledge on the mechanisms of skeletal muscle regeneration after cardiotoxin-induced injury. The process of regeneration is similar in different mouse strains and is inhibited by aging, obesity, and diabetes. Exercise, microcurrent electrical neuromuscular stimulation, and mechanical loading improve regeneration. The mechanisms of regeneration are complex and strain-dependent, and changes in functional proteins involved in the processes of necrotic fiber debris clearance, M1 to M2 macrophage conversion, SC activation, myoblast proliferation, differentiation and fusion, and fibrosis and calcification influence the final outcome of the regenerative activity.

Epigenetic Alterations in Sports-Related Injuries

It is a well-known fact that physical activity benefits people of all age groups. However, highly intensive training, maladaptation, improper equipment, and lack of sufficient rest lead to contusions and sports-related injuries. From the perspectives of sports professionals and those performing regular–amateur sports activities, it is important to maintain proper levels of training, without encountering frequent injuries. The bodily responses to physical stress and intensive physical activity are detected on many levels. Epigenetic modifications, including DNA methylation, histone protein methylation, acetylation, and miRNA expression occur in response to environmental changes and play fundamental roles in the regulation of cellular activities. In the current review, we summarise the available knowledge on epigenetic alterations present in tissues and organs (e.g., muscles, the brain, tendons, and bones) as a consequence of sports-related injuries. Epigenetic mechanism observations have the potential to become useful tools in sports medicine, as predictors of approaching pathophysiological alterations and injury biomarkers that have already taken place.

Decreased miR-497-5p Suppresses IL-6 Induced Atrophy in Muscle Cells

Interleukin-6 (IL-6) is a pro-inflammatory cytokine associated with skeletal muscle wasting in cancer cachexia. The control of gene expression by microRNAs (miRNAs) in muscle wasting involves the regulation of thousands of target transcripts. However, the miRNA-target networks associated with IL6-induced muscle atrophy remain to be characterized. Here, we show that IL-6 promotes the atrophy of C2C12 myotubes and changes the expression of 20 miRNAs (5 up-regulated and 15 down-regulated). Gene Ontology analysis of predicted miRNAs targets revealed post-transcriptional regulation of genes involved in cell differentiation, apoptosis, migration, and catabolic processes. Next, we performed a meta-analysis of miRNA-published data that identified miR-497-5p, a down-regulated miRNAs induced by IL-6, also down-regulated in other muscle-wasting conditions. We used miR-497-5p mimics and inhibitors to explore the function of miR-497-5p in C2C12 myoblasts and myotubes. We found that miR-497-5p can regulate the expression of the cell cycle genes CcnD2 and CcnE1 without affecting the rate of myoblast cellular proliferation. Notably, miR-497-5p mimics induced myotube atrophy and reduced Insr expression. Treatment with miR-497-5p inhibitors did not change the diameter of the myotubes but increased the expression of its target genes Insr and Igf1r. These genes are known to regulate skeletal muscle regeneration and hypertrophy via insulin-like growth factor pathway and were up-regulated in cachectic muscle samples. Our miRNA-regulated network analysis revealed a potential role for miR-497-5p during IL6-induced muscle cell atrophy and suggests that miR-497-5p is likely involved in a compensatory mechanism of muscle atrophy in response to IL-6.

Influence of microRNAs and exosomes in muscle health and diseases

microRNAs are short, (18-22 nt) non-coding RNAs involved in important cellular processes due to their ability to regulate gene expression at the post-transcriptional level. Exosomes are small (50-200 nm) extracellular vesicles, naturally secreted from a variety of living cells and are believed to mediate cell-cell communication through multiple mechanisms, including uptake in destination cells. Circulating microRNAs and exosome-derived microRNAs can have key roles in regulating muscle cell development and differentiation. Several microRNAs are highly expressed in muscle and their regulation is important for myocyte homeostasis. Changes in muscle associated microRNA expression are associated with muscular diseases including muscular dystrophies, inflammatory myopathies, and congenital myopathies. In this review, we aim to highlight the biology of microRNAs and exosomes as well as their roles in muscle health and diseases. We also discuss the potential crosstalk between skeletal and cardiac muscle through exosomes and their contents.

MicroRNA-223-3p promotes skeletal muscle regeneration by regulating inflammation in mice

After injury, the coordinated balance of pro- and anti-inflammatory factors in the microenvironment contribute to skeletal muscle regeneration. However, the underlying molecular mechanisms regulating this balance remain incompletely understood. In this study, we examined the roles of microRNAs (miRNAs) in inflammation and muscle regeneration. miRNA-Seq transcriptome analysis of mouse skeletal muscle revealed that miR-223-3p is upregulated in the early stage of muscle regeneration after injury. miR-223-3p knockout resulted in increased inflammation, impaired muscle regeneration, and increased interstitial fibrosis. Mechanistically, we found that myeloid-derived miR-223-3p suppresses the target gene interleukin-6 (Il6), associated with the maintenance of the proinflammatory macrophage phenotype during injury. Administration of IL-6-neutralizing antibody in miR-223-3p-knockout muscle could rescue the impaired regeneration ability and reduce the fibrosis. Together, our results reveal that miR-223-3p improves muscle regeneration by regulating inflammation, indicating that miRNAs can participate in skeletal muscle regeneration by controlling the balance of pro- and anti-inflammatory factors in the skeletal muscle microenvironment.

MicroRNAs facilitate skeletal muscle maintenance and metabolic suppression in hibernating brown bears

Hibernating brown bears, Ursus arctos, undergo extended periods of inactivity and yet these large hibernators are resilient to muscle disuse atrophy. Physiological characteristics associated with atrophy resistance in bear muscle have been examined (e.g., muscle mechanics, neural activity) but roles for molecular signaling/regulatory mechanisms in the resistance to muscle wasting in bears still require investigation. Using quantitative reverse transcription PCR (RT-qPCR), the present study characterized the responses of 36 microRNAs linked with development, metabolism, and regeneration of skeletal muscle, in the vastus lateralis of brown bears comparing winter hibernating and summer active animals. Relative levels of mRNA of selected genes (mef2a, pax7, id2, prkaa1, and mstn) implicated upstream and downstream of the microRNAs were examined. Results indicated that hibernation elicited a myogenic microRNA, or "myomiR", response via MEF2A-mediated signaling. Upregulation of MEF2A-controlled miR-1 and miR-206 and respective downregulation of pax7 and id2 mRNA are suggestive of responses that promote skeletal muscle maintenance. Increased levels of metabolic microRNAs, such as miR-27, miR-29, and miR-33, may facilitate metabolic suppression during hibernation via mechanisms that decrease glucose uptake and fatty acid oxidation. This study identified myomiR-mediated mechanisms for the promotion of muscle regeneration, suppression of ubiquitin ligases, and resistance to muscle atrophy during hibernation mediated by observed increases in miR-206, miR-221, miR-31, miR-23a, and miR-29b. This was further supported by the downregulation of myomiRs associated with a muscle injury and inflammation (miR-199a and miR-223) during hibernation. The present study provides evidence of myomiR-mediated signaling pathways that are activated during hibernation to maintain skeletal muscle functionality in brown bears.

Direct interaction analysis of microRNA-351-5p and nuclear scaffold lamin B1 mRNA by the cell-free in vitro mRNA/miRNA binding evaluation system

We previously demonstrated that miR-351-5p regulates nuclear scaffold lamin B1 expression and mediates the anticancer floxuridine-induced necrosis shift to apoptosis in mammalian tumor cells. Notably, it is unknown whether lamin B1 mRNA is a direct target of miR-351-5p. Here, we show that miR-351-5p interacts with a lamin B1 mRNA partial sequence by using the cell-free in vitro miRNA and mRNA binding evaluation system. In addition, the interaction of miR-351-5p/lamin B1 mRNA was suppressed by an miR-351-5p inhibitor. Our findings are important in exploring the functions of miRNAs in cellular processes, including cell death.

Clinical value of non-coding RNAs in cardiovascular, pulmonary, and muscle diseases

Although a majority of the mammalian genome is transcribed to RNA, mounting evidence indicates that only a minor proportion of these transcriptional products are actually translated into proteins. Since the discovery of the first non-coding RNA (ncRNA) in the 1980s, the field has gone on to recognize ncRNAs as important molecular regulators of RNA activity and protein function, knowledge of which has stimulated the expansion of a scientific field that quests to understand the role of ncRNAs in cellular physiology, tissue homeostasis, and human disease. Although our knowledge of these molecules has significantly improved over the years, we have limited understanding of their precise functions, protein interacting partners, and tissue-specific activities. Adding to this complexity, it remains unknown exactly how many ncRNAs there are in existence. The increased use of high-throughput transcriptomics techniques has rapidly expanded the list of ncRNAs, which now includes classical ncRNAs (e.g., ribosomal RNAs and transfer RNAs), microRNAs, and long ncRNAs. In addition, splicing by-products of protein-coding genes and ncRNAs, so-called circular RNAs, are now being investigated. Because there is substantial heterogeneity in the functions of ncRNAs, we have summarized the present state of knowledge regarding the functions of ncRNAs in heart, lungs, and skeletal muscle. This review highlights the pathophysiologic relevance of these ncRNAs in the context of human cardiovascular, pulmonary, and muscle diseases.

MicroRNA-351-5p mediates skeletal myogenesis by directly targeting lactamase-β and is regulated by lnc-mg

Skeletal muscle is an important and complex organ with a variety of functions in humans and animals. Skeletal myogenesis is a multistep and complex process, and increasing evidence suggests that microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) play critical roles in skeletal myogenesis. In this study the expression of miR-351-5p is dynamically regulated during skeletal myogenesis in vitro and in vivo. Cell-counting kit-8, qRT-PCR, and EdU immunofluorescence analysis showed that miR-351-5p overexpression promoted the proliferation and inhibited the differentiation of C2C12 myoblast, whereas inhibition of miR-351-5p had the opposite effect. In addition, miR-351-5p mediated the regulation of muscle fiber type transition in vivo. In vitro, loss of miR-351-5p in muscle tissues promoted muscle hypertrophy and increased slow-twitch fibers in the gastrocnemius muscles of mice. Luciferase reporter assay and functional analyses demonstrated that lactamase β ( LACTB) is a direct target of miR-351-5p involved in the regulation of skeletal myogenesis. Expression levels of a myogenesis-associated lncRNA ( lnc-mg) correlated negatively with miR-351-5p and positively with LACTB during C2C12 myoblast proliferation and differentiation. Further analyses showed that lnc-mg acted as a molecular sponge for miR-351-5p, demonstrating its involvement in the negative regulation of LACTB by miR-351-5p during skeletal myogenesis. These findings indicate that miRNA-351-5p functions in skeletal myogenesis by targeting LACTB and is regulated by lnc-mg, supporting the role of the competing endogenous RNA network in skeletal myogenesis.-Du, J., Zhang, P., Zhao, X., He, J., Xu, Y., Zou, Q., Luo, J., Shen, L., Gu, H., Tang, Q., Li, M., Jiang, Y., Tang, G., Bai, L., Li, X., Wang, J., Zhang, S., Zhu, L. MicroRNA-351-5p mediates skeletal myogenesis by directly targeting lactamase β and is regulated by lnc-mg.

Upregulation of microRNA-351 exerts protective effects during sepsis by ameliorating skeletal muscle wasting through the Tead-4-mediated blockade of the Hippo signaling pathway

Sepsis-induced skeletal muscle wasting may lead to various severe clinical consequences. Understanding molecular mechanisms of the regulation of the loss of skeletal muscle mass in septic patients remains a significant clinical challenge. The current study was conducted to establish septic mice models to explore the relationship between microRNA (miR)-351 and the transcription element apical (TEA) domain transcription factor (Tead)-4 gene and to investigate its effects on the skeletal muscle through mediating the Hippo signaling pathway in mice with acute sepsis. A total of 60 mice were collected to establish mouse models of acute sepsis. The positive expression rate of Tead-4 and the apoptotic index (AI) were measured. A dual-luciferase reporter gene assay was conducted to verify the targeting relationship between miR-351 and Tead-4. Furthermore, the muscle fiber diameter (MFD) and area (MFA) and the content of 3-methylhistidine (3-MH) and tyrosine (Tyr) were assessed. The expression levels of miR-351, p38-MAPK, Yes-associated protein, Tead-4, B-cell lymphoma X protein (Bax), and Caspase-3 were determined with quantitative RT-PCR and Western blot analysis. Finally, cell viability, apoptosis, and levels of inflammatory factors, including IL-1β, IL-6, IGF-1, TNF-α, and monocyte chemoattractant protein-1 were detected by 3-(4,5-dimethylthiazol-2- yl)-2,5-diphenyltetrazolium bromide assay, flow cytometry, and ELISA. Initially, Tead-4 protein expression was higher in skeletal muscle tissues of mice with acute sepsis. Tead-4 was identified to negatively regulate miR-351. Upregulation of miR-351 increased MFA and MFD, muscle weight water content, Bcl-2 expression levels, and cell viability. Up-regulation of miR-351 reduced AI; 3-MH and Tyr content; positive expression of Tead-4 protein; the expression levels of p38-MAPK, Yap, Tead-4, Bax, and Caspase-3; apoptosis; and inflammatory responses. The current study demonstrated that up-regulation of miR-351 inhibits the degradation of skeletal muscle protein and the atrophy of skeletal muscle in mice with acute sepsis by targeting Tead-4 through suppression of the Hippo signaling pathway. Thus, miR-351 overexpression may be a future therapeutic strategy for acute sepsis.-Zhang, L.-N., Tian, H., Zhou, X.-L., Tian, S.-C., Zhang, X.-H., Wu, T.-J. Upregulation of microRNA-351 exerts protective effects during sepsis by ameliorating skeletal muscle wasting through the Tead-4-mediated blockade of the Hippo signaling pathway.

MiRNA-221 from tissue may predict the prognosis of patients with osteosarcoma

This study was aimed to investigate the relationship between miR-221 expression and prognosis in patients with osteosarcoma.miR-221 expression in 69 osteosarcoma specimens and corresponding noncancer tissues were characterized by quantitative reverse transcription polymerase chain reaction. The associations of miR-221 expression with clinicopathologic factors and prognosis in patients with osteosarcoma were statistically analyzed.miR-221 expression in patients with osteosarcoma was significantly higher than in the corresponding noncancer tissues (P < .01). miR-221 overexpression was significantly associated with tumor stage, metastatic status, and response to chemotherapy pretreatment. Cox regression analysis revealed that miR-221expression, metastasis, and response to chemotherapy were independent prognostic indicators for osteosarcoma.miR-221 upregulation may predict clinical outcomes in patients with osteosarcoma.

Effects of microRNAs on skeletal muscle development

MicroRNAs (miRNAs) are small (about 22 nucleotides) noncoding RNAs, which were highly conserved among mammals. They have ushered in a new era in molecular biology over twenty years. They can negatively regulate gene expression at the posttranscriptional level through the principle of complementary base pairing with the 3' untranslated region (UTR) of their target mRNAs and induce their degradation. They involve in tissue morphogenesis, cellular processes like apoptosis, and major signaling pathways. Previous studies have promoted our understanding that miRNAs play an important role in myogenesis and have a big impact on muscle mass, muscle fiber type and muscle diseases. Many researchers have provided evidence of the involvement of muscle-specific and enriched miRNAs in the individual stages of skeletal muscle development as well as of their significant influence on muscle metabolism during quiescence, proliferation, differentiation and regeneration. Here, we focus on the microRNAs that related to the development of skeletal muscle. For example, some microRNAs are upregulated in differentiated skeletal muscle and can promote differentiation, like, miR-1, miR-24, miR-26a, miR-181 and miR-206. However, some microRNAs highly expressed in proliferating myoblasts, downregulated in differentiated and could inhibit differentiation, like MiR-221 and miR-222. Some others not only promote skeletal muscle proliferation, but also promote differentiation, like miR-214. Studying the miRNAs' regulatory mechanisms in skeletal development will help us know more about the knowledge of miRNAs in muscle developmental biology and make us learn more about involved signal pathway.

Long noncoding RNAs and their roles in skeletal muscle fate determination

Myogenic fate determination is important in skeletal muscle development, growth and repair. A variety of factors regulate myogenic cell determination via transcriptional and non-transcriptional mechanisms. Amongst these factors, long noncoding RNAs (lncRNAs) have gained considerable attention for their important roles in regulating myogenic differentiation and function. Many classes of lncRNAs have been discovered; various lncRNAs have been implicated in the regulation of myogenic cell fate determination and are the subject of this brief review.

The miR-125 family is an important regulator of the expression and maintenance of maternal effect genes during preimplantational embryo development

Previously, we reported that Sebox is a new maternal effect gene (MEG) that is required for early embryo development beyond the two-cell (2C) stage because this gene orchestrates the expression of important genes for zygotic genome activation (ZGA). However, regulators of Sebox expression remain unknown. Therefore, the objectives of the present study were to use bioinformatics tools to identify such regulatory microRNAs (miRNAs) and to determine the effects of the identified miRNAs on Sebox expression. Using computational algorithms, we identified a motif within the 3′UTR of Sebox mRNA that is specific to the seed region of the miR-125 family, which includes miR-125a-5p, miR-125b-5p and miR-351-5p. During our search for miRNAs, we found that the Lin28a 3′UTR also contains the same binding motif for the seed region of the miR-125 family. In addition, we confirmed that Lin28a also plays a role as a MEG and affects ZGA at the 2C stage, without affecting oocyte maturation or fertilization. Thus, we provide the first report indicating that the miR-125 family plays a crucial role in regulating MEGs related to the 2C block and in regulating ZGA through methods such as affecting Sebox and Lin28a in oocytes and embryos.

MiR-351 negatively regulates osteoblast differentiation of MSCs induced by (+)-cholesten-3-one through targeting VDR

Our previous reports indicated that (+)-cholesten-3-one induces osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs) by activating vitamin D receptor (VDR). However, whether and how miRNAs modulate osteogenic differentiation induced by (+)-cholesten-3-one have not been explored. In this study, miRNA array profiling and further validation by quantitative real-time PCR revealed that miR-351 was downregulated during (+)-cholesten-3-one-induced osteogenic differentiation of MSCs. Overexpression of miR-351 by miR-351 precursor transfection markedly inhibited the expression of osteoblast-specific genes, such as alkaline phosphatase (ALP), collagen type II, osteopontin (OPN), and runt-related transcription factor 2 (RUNX2), which consequently decreased a number of calcium mineralized nodules. Inhibition of miR-351 function by anti-miR-351 promoted expression of osteoblast-specific genes. Our results suggest that miR-351 is a negative regulator of osteoblast differentiation of MSCs induced by (+)-cholesten-3-one. Target prediction analysis tools and experimental validation by luciferase 3'UTR reporter assay identified VDR as a direct target of miR-351. miR-351 inhibited the expression of the VDR, which played a critical role in the control of osteogenic differentiation of MSCs. Importantly, overexpression of VDR significantly abolished the inhibitory effect of miR-351 on (+)-cholesten-3-one induced osteogenic differentiation. Taken together, our results demonstrate that miR-351 negatively regulates osteoblast differentiation of MSCs induced by (+)-cholesten-3-one through targeting VDR. These findings provid evidence that miR-351 can bea possible therapeutic target for bone repair and regeneration.

Characterization of extracellular vesicles derived from cardiac cells in an in vitro model of preconditioning

Preconditioning is a promising technique to protect the heart from ischaemia-reperfusion injury. In this context, the crosstalk between different cardiac cell types and especially the exchange of cardioprotective mediators has come into the focus of current research. Recently, extracellular vesicles (EVs), nano-sized structures, emerged as possible communication mediators. They are taken up by recipient cells and can alter gene expression or activate intracellular signal cascades. It has been shown that all cardiac cell types are able to secrete EVs, but so far the influence of an in vitro preconditioning stimulus on EV concentration and composition has not been investigated. Therefore, we stimulated primary cardiac myocytes and fibroblasts from neonatal rats, as well as H9c2 cells, with two known in vitro preconditioning stimuli: hypoxia or isoflurane. EVs were isolated from cell culture supernatants 48 h after stimulation by differential centrifugation and size exclusion chromatography. They were characterized by transmission electron microscopy, tunable resistive pulse sensing, miRNA array and Western blot analysis. The detected EVs had the typical cup-shaped morphology and a size of about 150 nm. No significant differences in EV concentration were observed between the different groups. The protein and miRNA load was affected by in vitro preconditioning with isoflurane or hypoxia. EV markers like Alix, CD63, flotillin-1 and especially heat shock protein 70 were significantly up-regulated by the treatments. Several miRNAs like miR-92b-3p, miR-761 and miR-101a-5p were also significantly affected. A migration assay confirmed the physiological benefit of these EVs. Taken together, our findings show that a model of in vitro preconditioning of cardiac cells does not influence EV concentration but strongly regulates the EV cargo and affects migration. This might indicate a role for EV-mediated communication in isoflurane- and hypoxia-induced in vitro preconditioning.

Non-coding RNAs in skeletal muscle regeneration

Following injury, skeletal muscles can regenerate from muscle specific stem cells, called satellite cells. Quiescent in uninjured muscles, satellite cells become activated, proliferate and differentiate into myotubes. Muscle regeneration occurs following distinct main overlapping phases, including inflammation, regeneration and maturation of the regenerated myofibers. Each step of muscle regeneration is orchestrated through complex signaling networks and gene regulatory networks, leading to the expression of specific set of genes in each concerned cell type. Apart from the well-established transcriptional mechanisms involving the myogenic regulatory factors of the MyoD family, increasing data indicate that each step of muscle regeneration is controlled by a wide range of non-coding RNAs. In this review, we discuss the role of two classes of non-coding RNAs (microRNAs and long non-coding RNAs) in the inflammatory, regeneration and maturation steps of muscle regeneration.

MicroRNA expression patterns in post-natal mouse skeletal muscle development

Background

MiRNAs are essential regulators of skeletal muscle development and homeostasis. To date, the role and regulation of miRNAs in myogenesis have been mostly studied in tissue culture and during embryogenesis. However, little information relating to miRNA regulation during early post-natal skeletal muscle growth in mammals is available. Using a high-throughput miRNA qPCR-based array, followed by stringent statistical and bioinformatics analysis, we describe the expression pattern and putative role of 768 miRNAs in the quadriceps muscle of mice aged 2 days, 2 weeks, 4 weeks and 12 weeks.

Results

Forty-six percent of all measured miRNAs were expressed in mouse quadriceps muscle during the first 12 weeks of life. We report unprecedented changes in miRNA expression levels over time. The expression of a majority of miRNAs significantly decreased with post-natal muscle maturation in vivo. MiRNA clustering identified 2 subsets of miRNAs that are potentially involved in cell proliferation and differentiation, mainly via the regulation of non-muscle specific targets.

Conclusion

Collective miRNA expression in mouse quadriceps muscle is subjected to substantial levels of regulation during the first 12 weeks of age. This study identified a new suite of highly conserved miRNAs that are predicted to influence early muscle development. As such it provides novel knowledge pertaining to post-natal myogenesis and muscle regeneration in mammals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3399-2) contains supplementary material, which is available to authorized users.

MicroRNA-351 inhibits denervation-induced muscle atrophy by targeting TRAF6

MicroRNAs (miRs) have been observed to be involved in the modulation of various physiopathological processes. However, the impacts of miRNAs on muscle atrophy have not been fully investigated. In the present study, the results demonstrated that miR-351 was differentially expressed in the tibialis anterior (TA) muscle at various times following sciatic nerve transection, and the time-dependent expression profile of miR-351 was inversely correlated with that of tumor necrosis factor receptor-associated factor 6 (TRAF6) at the mRNA and protein levels. The dual luciferase reporter assay indicated that miR-351 was able to significantly downregulate the expression levels of TRAF6 by directly targeting the 3'-untranslated region of TRAF6. Overexpression of miR-351 inhibited a significant decrease in the wet weight ratio or cross-sectional area of the TA muscle following sciatic nerve transection. Western blot analysis indicated that the protein expression levels of TRAF6, muscle ring-finger protein 1 (MuRF1) and muscle atrophy F-box (MAFBx) in denervated TA muscles were suppressed by overexpression of miR-351. These results demonstrate that miR-351 inhibits denervation-induced atrophy of TA muscles following sciatic nerve transection at least partially through negative regulation of TRAF6 as well as MuRF1 and MAFBx, the two downstream signaling molecules of TRAF6.

From Nutrient to MicroRNA: a Novel Insight into Cell Signaling Involved in Skeletal Muscle Development and Disease

Skeletal muscle is a remarkably complicated organ comprising many different cell types, and it plays an important role in lifelong metabolic health. Nutrients, as an external regulator, potently regulate skeletal muscle development through various internal regulatory factors, such as mammalian target of rapamycin (mTOR) and microRNAs (miRNAs). As a nutrient sensor, mTOR, integrates nutrient availability to regulate myogenesis and directly or indirectly influences microRNA expression. MiRNAs, a class of small non-coding RNAs mediating gene silencing, are implicated in myogenesis and muscle-related diseases. Meanwhile, growing evidence has emerged supporting the notion that the expression of myogenic miRNAs could be regulated by nutrients in an epigenetic mechanism. Therefore, this review presents a novel insight into the cell signaling network underlying nutrient-mTOR-miRNA pathway regulation of skeletal myogenesis and summarizes the epigenetic modifications in myogenic differentiation, which will provide valuable information for potential therapeutic intervention.

Absence of CCR2 results in an inflammaging environment in young mice with age-independent impairments in muscle regeneration

Skeletal muscle regeneration requires coordination between dynamic cellular populations and tissue microenvironments. Macrophages, recruited via CCR2, are essential for regeneration; however, the contribution of macrophages and the role of CCR2 on nonhematopoietic cells has not been defined. In addition, aging and sex interactions in regeneration and sarcopenia are unclear. Muscle regeneration was measured in young (3-6 mo), middle (11-15 mo), old (24-32 mo) male and female CCR2^-/- mice. Whereas age-related muscle atrophy/sarcopenia was present, regenerated myofiber cross-sectional area (CSA) in CCR2^-/- mice was comparably impaired across all ages and sexes, with increased adipocyte area compared with wild-type (WT) mice. CCR2^-/- mice myofibers achieved approximately one third of baseline CSA even 84 d after injury. Regenerated CSA and clearance of necrotic tissue were dependent on bone marrow-derived cellular expression of CCR2. Myogenic progenitor cells isolated from WT and CCR2^-/- mice exhibited comparable proliferation and differentiation capacity. The most striking cellular anomaly in injured muscle of CCR2^-/- mice was markedly decreased macrophages, with a predominance of Ly6C^- anti-inflammatory monocytes/macrophages. Ablation of proinflammatory TLR signaling did not affect muscle regeneration or resolution of necrosis. Of interest, many proinflammatory, proangiogenic, and chemotactic cytokines were markedly elevated in injured muscle of CCR2^-/- relative to WT mice despite impairments in macrophage recruitment. Collectively, these results suggest that CCR2 on bone marrow-derived cells, likely macrophages, were essential to muscle regeneration independent of TLR signaling, aging, and sex. Decreased proinflammatory monocytes/macrophages actually promoted a proinflammatory microenvironment, which suggests that inflammaging was present in young CCR2^-/- mice.

MicroRNA-351 Regulates Two-Types of Cell Death, Necrosis and Apoptosis, Induced by 5-fluoro-2'-deoxyuridine

Cell-death can be necrosis and apoptosis. We are investigating the mechanisms regulating the cell death that occurs on treatment of mouse cancer cell-line FM3A with antitumor 5-fluoro-2'-deoxyuridine (FUdR): necrosis occurs for the original clone F28-7, and apoptosis for its variant F28-7-A. Here we report that a microRNA (miR-351) regulates the cell death pattern. The miR-351 is expressed strongly in F28-7-A but only weakly in F28-7. Induction of a higher expression of miR-351 in F28-7 by transfecting an miRNA mimic into F28-7 resulted in a change of the death mode; necrosis to apoptosis. Furthermore, transfection of an miR-351 inhibitor into F28-7-A resulted in the morphology change, apoptosis to necrosis, in this death-by-FUdR. Possible mechanism involving lamin B1 in this miR-351's regulatory action is discussed.

Uvrag targeting by Mir125a and Mir351 modulates autophagy associated with Ewsr1 deficiency

The EWSR1 (EWS RNA-binding protein 1/Ewing Sarcoma Break Point Region 1) gene encodes a RNA/DNA binding protein that is ubiquitously expressed and involved in various cellular processes. EWSR1 deficiency leads to impairment of development and accelerated senescence but the mechanism is not known. Herein, we found that EWSR1 modulates the Uvrag (UV radiation resistance associated) gene at the post-transcription level. Interestingly, EWSR1 deficiency led to the activation of the DROSHA-mediated microprocessor complex and increased the level of Mir125a and Mir351, which directly target Uvrag. Moreover, the Mir125a- and Mir351-mediated reduction of Uvrag was associated with the inhibition of autophagy that was confirmed in ewsr1 knockout (KO) MEFs and ewsr1 KO mice. Taken together, our data indicate that EWSR1 is involved in the post-transcriptional regulation of Uvrag via a miRNA-dependent pathway, resulting in the deregulation of autophagy inhibition. The mechanism of Uvrag and autophagy regulation by EWSR1 provides new insights into the role of EWSR1 deficiency-related cellular dysfunction.

Mmu-miR-351 attenuates the survival of cardiac arterial endothelial cells through targeting STAT3 in the atherosclerotic mice

The signal transducer and activator of transcription 3 (STAT3) signaling pathway was involved in regulation of endothelial cell survival/apoptosis and was regarded as a target for prevention of atherosclerosis or other cardiovascular diseases. Factors, regulating STAT3 expression and activity, have aroused a wide range of interest, such as miRNAs or transcription factors. The aim of this study is to explore the role of miR-351, a miRNA found not long before, in the regulation of STAT3 expression and endothelial cell survival in the model mice with atherosclerosis (AS). Expression of miR-351 in the serum and cardiac arterial endothelial cells of the WT mice and AS mice was detected. Real-time qPCR analysis showed that miR-351 was upregulated in the serum and endothelial cells of the AS mice, displaying an opposite expression pattern with STAT3. To explore the role and mechanism of miR-351 in the endothelial cell survival, the miR-351 mimic was transfected in to the endothelial cells. MTT and Trypan Blue assays showed miR-351 attenuated the survival of endothelial cells. Our results of the TargetScan output and the 3'UTR luciferase reporter assay indicated that STAT3 was target of miR-351. Additionally, miR-351 resisted the elevation of STAT3 protein level and promotion of endothelial cell survival caused by SD19. Finally, our in vitro angiogenesis assay revealed that miR-351 suppressed angiogenesis and resisted the promotion of angiogenesis caused by SD19. In conclusion, miR-351 was upregulated in the atherosclerotic mice. MiR-351 can attenuate the survival of endothelial cells and suppress angiogenesis through targeting STAT3 in vitro.

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.

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 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.

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.

Identifying microRNAs involved in aging of the lateral wall of the cochlear duct

Age-related hearing loss is a progressive sensorineural hearing loss that occurs during aging. Degeneration of the organ of Corti and atrophy of the lateral wall of the cochlear duct (or scala media) in the inner ear are the two primary causes. MicroRNAs (miRNAs), a class of short non-coding RNAs that regulate the expression of mRNA/protein targets, are important regulators of cellular senescence and aging. We examined miRNA gene expression profiles in the lateral wall of two mouse strains, along with exploration of the potential targets of those miRNAs that showed dynamic expression during aging. We show that 95 and 60 miRNAs exhibited differential expression in C57 and CBA mice during aging, respectively. A majority of downregulated miRNAs are known to regulate pathways of cell proliferation and differentiation, while all upregulated miRNAs are known regulators in the pro-apoptotic pathways. By using apoptosis-related gene array and bioinformatic approaches to predict miRNA targets, we identify candidate miRNA-regulated genes that regulate apoptosis pathways in the lateral wall of C57 and CBA mice during aging.

Preparation of primary myogenic precursor cell/myoblast cultures from basal vertebrate lineages

Due to the inherent difficulty and time involved with studying the myogenic program in vivo, primary culture systems derived from the resident adult stem cells of skeletal muscle, the myogenic precursor cells (MPCs), have proven indispensible to our understanding of mammalian skeletal muscle development and growth. Particularly among the basal taxa of Vertebrata, however, data are limited describing the molecular mechanisms controlling the self-renewal, proliferation, and differentiation of MPCs. Of particular interest are potential mechanisms that underlie the ability of basal vertebrates to undergo considerable postlarval skeletal myofiber hyperplasia (i.e. teleost fish) and full regeneration following appendage loss (i.e. urodele amphibians). Additionally, the use of cultured myoblasts could aid in the understanding of regeneration and the recapitulation of the myogenic program and the differences between them. To this end, we describe in detail a robust and efficient protocol (and variations therein) for isolating and maintaining MPCs and their progeny, myoblasts and immature myotubes, in cell culture as a platform for understanding the evolution of the myogenic program, beginning with the more basal vertebrates. Capitalizing on the model organism status of the zebrafish (Danio rerio), we report on the application of this protocol to small fishes of the cyprinid clade Danioninae. In tandem, this protocol can be utilized to realize a broader comparative approach by isolating MPCs from the Mexican axolotl (Ambystoma mexicanum) and even laboratory rodents. This protocol is now widely used in studying myogenesis in several fish species, including rainbow trout, salmon, and sea bream(1-4).

miR-223: An inflammatory oncomiR enters the cardiovascular field

MicroRNAs (miRNAs) are small, noncoding RNAs of 18-22 nucleotides in length that regulate post-transcriptional expression by base-pairing with target mRNAs. It is now clearly established that miRNAs are involved in most of the cell's physiopathological processes (including carcinogenesis and metabolic disorders). This review focuses on miR-223, which was first described as a modulator of hematopoietic lineage differentiation. We outline the role of miR-223 deregulation in several types of cancers and highlight its inclusion in a newly identified and fast-growing family of miRNAs called oncomiRs. We then look at miR-223's emerging role in inflammatory and metabolic disorders, with a particular focus on muscle diseases, type II diabetes, atherosclerosis and vascular calcification. miR-223 is one of the growing number of RNA biomarkers of various human metabolic diseases and is thus of special interest to both researchers and clinicians in the cardiovascular field.

Prognostic role of microRNA-221 in various human malignant neoplasms: a meta-analysis of 20 related studies

Background

MicroRNA-221 (miR-221) has been shown to play an important role in cancer prognosis. In order to evaluate the predictive value of miR-221, we compiled the evidence from 20 eligible studies to perform a meta-analysis.

Design

All of relevant studies were identified by searching PubMed, Embase, and Web of Science, and were assessed by further quality evaluation. Pooled hazard ratios (HRs) with 95% confidence intervals (CIs) of total and stratified analyses, for overall survival (OS) and recurrence-free survival (RFS), were calculated to investigate the association between high miR-221 expression and cancer prognosis.

Results

We found that high miR-221 expression can predict a poor OS in malignant tumors (pooled HR = 1.55, P = 0.017) but has no significant association with RFS (pooled HR = 1.02, P = 0.942). Further in stratified analyses, high miR-221 expression was significantly associated with a poor OS in Asians (pooled HR = 2.04, P = 0.010) or serum/ plasma subgroup (pooled HR = 2.28, P<0.001), and even showed significantly poor OS (pooled HR = 1.80, P<0.001) and RFS (pooled HR = 2.43, P = 0.010) in hepatocellular carcinoma (HCC) subgroup, but was correlated to a favorable RFS in prostate cancer subgroup (pooled HR = 0.51, P = 0.004).

Conclusions

Our findings demonstrate that miR-221 is more suitable to predict cancer prognosis in Asians, and it is a promising prognostic biomarker for HCC. The detection of miR-221 in serum or plasma samples may make it become an effective method for monitoring patients' prognosis and assessing therapeutic efficacy in the future.

Role of microRNA-27a in myoblast differentiation

MicroRNAs (miRNAs) are a class of endogenous non-coding RNAs that are critically involved in roles in various aspects of skeletal myogenesis. microRNA miR-27a promotes myoblast proliferation by targeting myostatin, a critical inhibitor of skeletal muscle development, but its mode of action in myoblast differentiation remains unclear. We have found that expression of miR-27a and myostatin were upregulated and downregulated, respectively, during myoblast differentiation. Overexpression of miR-27a increased the number of myosin heavy chain (MHC)-positive cells and upregulated mRNA and protein of MyoD and myogenin. These findings indicate that miR-27a plays a role in enhancing myoblast differentiation.

Integrative analysis of porcine microRNAome during skeletal muscle development

Pig is an important agricultural animal for meat production and provides a valuable model for many human diseases. Functional studies have demonstrated that microRNAs (miRNAs) play critical roles in almost all aspects of skeletal muscle development and disease pathogenesis. To investigate the miRNAs involved in regulating different periods of skeletal muscle development, we herein performed a comprehensive research for porcine microRNAome (miRNAome) during 10 skeletal muscle developmental stages including 35, 49, 63, 77, 91 dpc (days post coitum) and 2, 28, 90, 120, 180 dpn (days postnatal) using Solexa sequencing technology. Our results extend the repertoire of pig miRNAome to 247 known miRNAs processed from 210 pre-miRNAs and 297 candidate novel miRNAs through comparison with known miRNAs in the miRBase. Expression analysis of the 15 most abundant miRNAs in every library indicated that functional miRNAome may be smaller and tend to be highly expressed. A series of muscle-related miRNAs summarized in our study present different patterns between myofibers formation phase and muscle maturation phase, providing valuable reference for investigation of functional miRNAs during skeletal muscle development. Analysis of temporal profiles of miRNA expression identifies 18 novel candidate myogenic miRNAs in pig, which might provide new insight into regulation mechanism mediated by miRNAs underlying muscle development.

MicroRNAs in skeletal muscle biology and exercise adaptation

MicroRNAs (miRNAs) have emerged as important players in the regulation of gene expression, being involved in most biological processes examined to date. The proposal that miRNAs are primarily involved in the stress response of the cell makes miRNAs ideally suited to mediate the response of skeletal muscle to changes in contractile activity. Although the field is still in its infancy, the studies presented in this review highlight the promise that miRNAs will have an important role in mediating the response and adaptation of skeletal muscle to various modes of exercise. The roles of miRNAs in satellite cell biology, muscle regeneration, and various myopathies are also discussed.

Species-specific microRNA regulation influences phenotypic variability: perspectives on species-specific microRNA regulation

Phenotypic divergence among animal species may be due in part to species-specific (SS) regulation of gene expression by small, non-coding regulatory RNAs termed "microRNAs". This phenomenon can be modulated by several variables. First, microRNA genes vary by their level of conservation, many of them being SS, or unique to a particular evolutionary lineage. Second, microRNA expression levels vary spatially and temporally in different species. Lastly, while microRNAs bind the 3'UTR of target genes in order to silence their expression, the binding sites themselves are often non-conserved. The variability of the miRNA-target paradigm between different species is thus multifactorial, and this paradigm has only just started to gain attention from researchers in various fields. Here we present and discuss recent findings regarding the characteristics and implications of SS microRNA regulation.

MicroRNA in myogenesis and muscle atrophy

PURPOSE OF REVIEW

To understand the impact of microRNA on myogenesis and muscle wasting in order to provide valuable information for clinical investigation.

RECENT FINDINGS

Muscle wasting increases the risk of morbidity/mortality in primary muscle diseases, secondary muscle disorders and elderly population. Muscle mass is controlled by several different signalling pathways. Insulin-like growth factor/PI3K/Akt is a positive signalling pathway, as it increases muscle mass by increasing protein synthesis and decreasing protein degradation. This pathway is directly and/or indirectly downregulated by miR-1, miR-133, miR-206 or miR-125b, and upregulated by miR-23a or miR-486. Myostatin and the transforming growth factor-β signalling pathway are negative regulators that cause muscle wasting. An increase of miR-27 reduces myostatin and increases muscle cell proliferation. Muscle regeneration capacity also plays a significant role in the regulation of muscle mass. This review comprehensively describes the effect of microRNA on myoblasts proliferation and differentiation, and summarizes the varied influences of microRNA on different muscle atrophy.

SUMMARY

Growing evidence indicates that microRNAs significantly impact muscle growth, regeneration and metabolism. MicroRNAs have a great potential to become diagnostic and/or prognostic markers, therapeutic agents and therapeutic targets.