Muscling through the microRNA world

The Function and Regulation Mechanism of Non-Coding RNAs in Muscle Development

Animal skeletal muscle growth is regulated by a complex molecular network including some non-coding RNAs (ncRNAs). In this paper, we review the non-coding RNAs related to the growth and development of common animal skeletal muscles, aiming to provide a reference for the in-depth study of the role of ncRNAs in the development of animal skeletal muscles, and to provide new ideas for the improvement of animal production performance.

Downregulation of miR-1-3p expression inhibits the hypertrophy and mineralization of chondrocytes in DDH

BACKGROUND

Developmental dysplasia of the hip (DDH) is a highly prevalent hip disease among children. However, its pathogenesis remains unclear. MicroRNAs (miRNA) are important regulators of cartilage development. In a previous study, high-throughput miRNA sequencing of tissue samples from an animal model of DDH showed a low level of miR-1-3p in the cartilage of the acetabular roof (ARC), but its role in DDH pathogenesis was not addressed. Therefore, our aim here was to investigate the effects of miR-1-3p in the ARC.

METHODS

The diagnosis of acetabular dysplasia was confirmed with X-ray examination, while imaging and HE staining were conducted to further evaluate the ARC thickness in each animal model. FISH was employed to verify miR-1-3p expression in the ARC and chondrocytes. The miR-1-3p target genes were predicted by a bioinformatics database. A dual-luciferase reporter assay was used to confirm the targeting relationship between miR-1-3p and SOX9. The gene expression of miR-1-3p, SOX9, RUNX2 and collagen type X was evaluated by qPCR analysis. The protein expression of SOX9, RUNX2 and collagen type X was detected by western blot analysis. The levels of SOX9, RUNX2, and collagen type X in the ARC were further assessed via immunohistochemistry analysis. Finally, Alizarin Red S staining was used to observe the mineralized nodules produced by the chondrocytes.

RESULTS

We observed low expression of miR-1-3p in the ARC of animals with DDH. SOX9 is a miR-1-3p target gene. Using miR-1-3p silencing technology in vitro, we demonstrated significantly reduced chondrocyte-generated mineralized nodules compared to those of the control. We also confirmed that with miR-1-3p silencing, SOX9 expression was upregulated, whereas the expression of genes associated with endochondral osteogenesis such as RUNX2 and collagen type X was downregulated. To confirm the involvement of miR-1-3p silencing in abnormal ossification through SOX9, we also performed a rescue experiment in which SOX9 silencing restored the low expression of RUNX2 and collagen type X produced by downregulated miR-1-3p expression. Finally, the elevated SOX9 levels and reduced RUNX2 and collagen type X levels in the ARC of rabbits with DDH were also verified using immunohistochemistry, RT-PCR, and western blots.

CONCLUSION

The relatively low expression of miR-1-3p in the ARC may be the cause of abnormal endochondral ossification in the acetabular roof of animals with DDH.

Age-Related Alterations at Neuromuscular Junction: Role of Oxidative Stress and Epigenetic Modifications

With advancing aging, a decline in physical abilities occurs, leading to reduced mobility and loss of independence. Although many factors contribute to the physio-pathological effects of aging, an important event seems to be related to the compromised integrity of the neuromuscular system, which connects the brain and skeletal muscles via motoneurons and the neuromuscular junctions (NMJs). NMJs undergo severe functional, morphological, and molecular alterations during aging and ultimately degenerate. The effect of this decline is an inexorable decrease in skeletal muscle mass and strength, a condition generally known as sarcopenia. Moreover, several studies have highlighted how the age-related alteration of reactive oxygen species (ROS) homeostasis can contribute to changes in the neuromuscular junction morphology and stability, leading to the reduction in fiber number and innervation. Increasing evidence supports the involvement of epigenetic modifications in age-dependent alterations of the NMJ. In particular, DNA methylation, histone modifications, and miRNA-dependent gene expression represent the major epigenetic mechanisms that play a crucial role in NMJ remodeling. It is established that environmental and lifestyle factors, such as physical exercise and nutrition that are susceptible to change during aging, can modulate epigenetic phenomena and attenuate the age-related NMJs changes. This review aims to highlight the recent epigenetic findings related to the NMJ dysregulation during aging and the role of physical activity and nutrition as possible interventions to attenuate or delay the age-related decline in the neuromuscular system.

miR-378a influences vascularization in skeletal muscles

AIMS

MicroRNA-378a, highly expressed in skeletal muscles, was demonstrated to affect myoblasts differentiation and to promote tumour angiogenesis. We hypothesized that miR-378a could play a pro-angiogenic role in skeletal muscle and may be involved in regeneration after ischaemic injury in mice.

METHODS AND RESULTS

Silencing of miR-378a in murine C2C12 myoblasts did not affect differentiation but impaired their secretory angiogenic potential towards endothelial cells. miR-378a knockout (miR-378a-/-) in mice resulted in a decreased number of CD31-positive blood vessels and arterioles in gastrocnemius muscle. In addition, diminished endothelial sprouting from miR-378a-/- aortic rings was shown. Interestingly, although fibroblast growth factor 1 (Fgf1) expression was decreased in miR-378a-/- muscles, this growth factor did not mediate the angiogenic effects exerted by miR-378a. In vivo, miR-378a knockout did not affect the revascularization of the ischaemic muscles in both normo- and hyperglycaemic mice subjected to femoral artery ligation (FAL). No difference in regenerating muscle fibres was detected between miR-378a-/- and miR-378+/+ mice. miR-378a expression temporarily declined in ischaemic skeletal muscles of miR-378+/+ mice already on Day 3 after FAL. At the same time, in the plasma, the level of miR-378a-3p was enhanced. Similar elevation of miR-378a-3p was reported in the plasma of patients with intermittent claudication in comparison to healthy donors. Local adeno-associated viral vectors-based miR-378a overexpression was enough to improve the revascularization of the ischaemic limb of wild-type mice on Day 7 after FAL, what was not reported after systemic delivery of vectors. In addition, the number of infiltrating CD45+ cells and macrophages (CD45+ CD11b+ F4/80+ Ly6G-) was higher in the ischaemic muscles of miR-378a-/- mice, suggesting an anti-inflammatory action of miR-378a.

CONCLUSIONS

Data indicate miR-378a role in the pro-angiogenic effect of myoblasts and vascularization of skeletal muscle. After the ischaemic insult, the anti-angiogenic effect of miR-378a deficiency might be compensated by enhanced inflammation.

The functional analysis of transiently upregulated miR-101 suggests a "braking" regulatory mechanism during myogenesis

Skeletal muscle differentiation is a highly coordinated process that involves many cellular signaling pathways and microRNAs (miRNAs). A group of muscle-specific miRNAs has been reported to promote myogenesis by suppressing key signaling pathways for cell growth. However, the functional role and regulatory mechanism of most non-muscle-specific miRNAs with stage-specific changes during differentiation are largely unclear. Here, we describe the functional characterization of miR-101a/b, a pair of non-muscle-specific miRNAs that show the largest change among a group of transiently upregulated miRNAs during myogenesis in C2C12 cells. The overexpression of miR-101a/b inhibits myoblast differentiation by suppressing the p38/MAPK, Interferon Gamma, and Wnt pathways and enhancing the C/EBP pathway. Mef2a, a key protein in the p38/MAPK pathway, was identified as a direct target of miR-101a/b. Interestingly, we found that the long non-coding RNA (lncRNA) Malat1, which promotes muscle differentiation, interacts with miR-101a/b, and this interaction competes with Mef2a mRNA to relieve the inhibition of the p38/MAPK pathway during myogenesis. These results uncovered a "braking" role in differentiation of transiently upregulated miRNAs and provided new insights into the competing endogenous RNA (ceRNA) regulatory mechanism in myoblast differentiation and myogenesis.

Nutrition and microRNAs: Novel Insights to Fight Sarcopenia

Sarcopenia is a progressive age-related loss of skeletal muscle mass and strength, which may result in increased physical frailty and a higher risk of adverse events. Low-grade systemic inflammation, loss of muscle protein homeostasis, mitochondrial dysfunction, and reduced number and function of satellite cells seem to be the key points for the induction of muscle wasting, contributing to the pathophysiological mechanisms of sarcopenia. While a range of genetic, hormonal, and environmental factors has been reported to contribute to the onset of sarcopenia, dietary interventions targeting protein or antioxidant intake may have a positive effect in increasing muscle mass and strength, regulating protein homeostasis, oxidative reaction, and cell autophagy, thus providing a cellular lifespan extension. MicroRNAs (miRNAs) are endogenous small non-coding RNAs, which control gene expression in different tissues. In skeletal muscle, a range of miRNAs, named myomiRNAs, are involved in many physiological processes, such as growth, development, and maintenance of muscle mass and function. This review aims to present and to discuss some of the most relevant molecular mechanisms related to the pathophysiological effect of sarcopenia. Besides, we explored the role of nutrition as a possible way to counteract the loss of muscle mass and function associated with ageing, with special attention paid to nutrient-dependent miRNAs regulation. This review will provide important information to better understand sarcopenia and, thus, to facilitate research and therapeutic strategies to counteract the pathophysiological effect of ageing.

MicroRNA‑23a‑5p mediates the proliferation and differentiation of C2C12 myoblasts

Skeletal myogenesis is a highly ordered and complex biological process that is mediated by numerous regulatory factors. In previous studies, it has been demonstrated that microRNAs (miRs) and long non-coding RNAs (lncRNAs) serve key roles in skeletal myogenesis. The present study showed that the expression levels of miR-23a-5p showed a dynamic change from decrease to increase during C2C12 myoblast proliferation and differentiation. Functional analysis using 5-ethynyl-2′-deoxyuridine proliferation and Cell Counting Kit-8 detection assays indicated that overexpression of miR-23a-5p significantly promoted C2C12 myoblast proliferation compared with the negative control. In addition, in C2C12 myoblasts transfected with miR-23a-5p mimics, increased expression levels of regulators associated with cell proliferation (Cyclin E, CCND1 and Cyclin B) were observed compared with the negative control. By contrast, overexpression of miR-23a-5p decreased the expression levels of specific-myogenesis factors (MyoD, MyoG and Myf5) and decreased C2C12 myoblast differentiation. Luciferase activity assays indicated that miR-23a-5p suppressed the luciferase activity of lncDum. Further analysis demonstrated that miR-23a-5p not only showed an opposite expression level pattern compared with lncDum, which was first increased and then decreased, but also had an opposite effect on the proliferation and differentiation of C2C12 myoblasts compared with lncDum which inhibited cell proliferation and promoted cell differentiation. Taken together, these results indicated that miR-23a-5p may mediate the proliferation and differentiation of C2C12 myoblasts, which may be involved in lncDum regulation.

MiR-1-3p regulates the differentiation of mesenchymal stem cells to prevent osteoporosis by targeting secreted frizzled-related protein 1

Osteoporosis (OP) is a systemic skeletal disorder with the characteristics of bone mass reduction and microarchitecture deterioration, resulting in bone fragility and increased fracture risk. A reduction in the osteoblast-differentiation of bone marrow mesenchymal stem cells (BMSCs) is considered as a basic pathogenesis of osteoporosis. miRNAs play a substantial role in the development and differentiation of BMSCs. In the present study, we found that miR-1-3p was significantly downregulated in the bones of Chinese osteoporotic patients (n = 29). Secreted frizzled-related protein 1 (SFRP1) was predicted as a target gene of miR-1-3p via the TargetScan and PicTar softwares and validated by dual-luciferase reporter assays. The findings revealed that the expression of SFRP1 was inversely correlated with miR-1-3p in osteoporotic patients. We induced mouse MSCs (mMSCs) to osteogenesis or adipogenesis and found that miR-1-3p was upregulated during osteogenesis but downregulated during adipogenesis. The overexpression of miR-1-3p stimulated osteogenesis and inhibited adipogenesis of mMSCs. In addition, ovariectomized (OVX) mice were tested and the function of miR-1-3p in vivo was explored. Immunohistochemistry and histomorphometric assays showed that in vivo inhibition of miR-1-3p increased the expression level of SFRP1 and reduced bone formation and bone mass. Furthermore, tartrate-resistant acid phosphatase (TRAP) staining indicated that the in vivo suppression of miR-1-3p promoted osteoclast activity, suggesting that miR-1-3p may influence bone mass by regulating bone resorption. It can be concluded that miR-1-3p plays a pivotal role in the pathogenesis of osteoporosis via targeting SFRP1 and may be a potential therapeutic target for osteoporosis.

Long-Term Exercise Alters the Profiles of Circulating Micro-RNAs in the Plasma of Young Women

Objective: The objective of this paper was to study the effects of long-term exercise on circulating microRNAs (miRNAs) in human plasma.

Methods: Whole blood was collected from 10 female elite athletes with at least 5 years of training experience in a Synchronized Swimming Group (S group) and 15 female college students without regular exercise training (C group). Plasma miRNAs were then isolated, sequenced, and semi-quantified by the second-generation sequencing technology, and the results were analyzed by bioinformatics methods.

Results: We found 380 differentially expressed miRNAs in the S group compared with the C group, among which 238 miRNAs were upregulated and 142 were downregulated. The top five abundant miRNAs in the 380 miRNAs of the S group are hsa-miR-451a, hsa-miR-486, hsa-miR-21-5p, hsa-miR-423-5p, and hsa-let-7b-5p. Muscle-specific/enriched miRNAs were not significantly different, except for miR-206 and miR-486. According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, a large proportion of the differentially expressed miRNAs are targeted in cancer-related pathways, including proteoglycans in cancer and miRNAs in cancer and basal cell carcinoma. As the levels of circulating miRNAs (ci-miRNAs) are commonly known to be significantly deregulated in cancer patients, we further compared the levels of some well-studied miRNAs in different types of cancer patients with those in the S group and found that long-term exercise regulates the level of ci-miRNAs in an opposite direction to those in cancer patients.

Conclusion: Long-term exercise significantly alters the profiles of plasma miRNAs in healthy young women. It may reduce the risk of certain types of cancers by regulating plasma miRNA levels.

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

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

Childhood Obesity Risk in Relationship to Perilipin 1 (PLIN1) Gene Regulation by Circulating microRNAs

Childhood obesity is a growing public health burden in many countries. The lipid perilipin 1 (PLIN1) gene is involved in regulation of lipolysis, and thus represents a viable candidate mechanism for obesity genetics research in children. In addition, the regulation of candidate gene expression by circulating microRNAs (miRNAs) offers a new research venue for diagnostic innovation. We report new findings on associations among circulating miRNAs, regulation of the PLIN1 gene, and susceptibility to childhood obesity. In a sample of 135 unrelated subjects, 35 children with obesity (between ages 3 and 13) and 100 healthy controls (between ages 4 and 16), we examined the expression levels of four candidate miRNAs (hsa-miR-4777-3p, hsa-miR-642b-3p, hsa-miR-3671-1, and hsa-miR-551b-2) targeting the PLIN1 as measured by real-time polymerase chain reaction in whole blood samples. We found that the full genetic model, including the four candidate miRNAs and the PLIN1 gene, explained a statistically significant 12.7% of the variance in childhood obesity risk (p = 0.0034). The four miRNAs together explained 10.1% of the risk (p = 0.008). The percentage of variation in childhood obesity risk explained by hsa-miR-642b-3p and age was 19%. In accordance with biological polarity of the observed association, for example, hsa-miR-642b-3p was upregulated, while the PLIN1 expression decreased in obese participants compared to healthy controls. To the best of our knowledge, this is the first clinical association study of these candidate miRNAs targeting the PLIN1 in childhood obesity. These data offer new molecular leads for future clinical biomarker and diagnostic discovery for childhood obesity.

Butyrate promotes slow-twitch myofiber formation and mitochondrial biogenesis in finishing pigs via inducing specific microRNAs and PGC-1α expression1

The present study aimed to investigate the influence of dietary butyrate supplementation on muscle fiber-type composition and mitochondrial biogenesis of finishing pigs, and the underlying mechanisms. Thirty-two LY (Landrace × Yorkshire) growing pigs with BW of 64.9 ± 5.7 kg were randomly allotted to either control (basal diet) or butyrate diets (0.3% butyrate sodium). Compared with the control group, diet supplemented with butyrate tended to increase average daily gain (P < 0.10). Pigs fed butyrate diet had higher intramuscular fat content, marbling score and pH24 h, and lower shear force and L*24 h in longissimus thoracis (LT) muscle than that fed control diet (P < 0.05). Interestingly, supplemented with butyrate increased (P < 0.05) the mRNA level of myosin heavy chain I (MyHC-I) and the percentage of slow-fibers, and decreased (P < 0.05) the mRNA level of MyHC-IIb in LT muscle. Meanwhile, pigs in butyrate group had an increase in mitochondrial DNA (mtDNA) copy number and the mRNA levels of mtDNA-encoded genes (P < 0.05). Moreover, feeding butyrate diet increased PGC-1α (PPAR γ coactivator 1α) level, decreased miR-133a-3p level and increased its target gene level (TEAD1, TEA domain transcription factor 1), increased miR-208b and miR-499-5p levels and decreased their target genes levels (Sp3 and Sox6, specificity protein 3 and SRY-box containing gene 6; P < 0.05) in the LT muscle. Collectively, these findings suggested that butyrate promoted slow-twitch myofiber formation and mitochondrial biogenesis, and the molecular mechanism may be via upgrading specific microRNAs and PGC-1α expression, finally improving meat quality.

Analysis of potential roles of combinatorial microRNA regulation in occurrence of valvular heart disease with atrial fibrillation based on computational evidences

Background

Atrial fibrillation (AF) is the most common arrhythmia. Patients with valvular heart disease (VHD) frequently have AF. Growing evidence demonstrates that a specifically altered pattern of microRNA (miRNA) expression is related to valvular heart disease with atrial fibrillation (AF-VHD) processes. However, the combinatorial regulation by multiple miRNAs in inducing AF-VHD remains largely unknown.

Methods

The work identified AF-VHD-specific miRNAs and their combinations through mapping miRNA expression profile into differential co-expression network. The expressions of some dysregulated miRNAs were measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The regulations of signaling pathways by the combinatorial miRNAs were predicted by enrichment analysis tools.

Results

Thirty-two differentially expressed (DE) miRNAs were identified to be AF-VHD-specific, some of which were new findings. These miRNAs interacted to form 5 combinations. qRT-PCR confirmed the different expression of several identified miRNAs, which illustrated the reliability and biomarker potentials of 32 dysregulation miRNAs. The biological characteristics of combinatorial miRNAs related to AF-VHD were highlighted. Twelve signaling pathways regulated by combinatorial miRNAs were predicted to be possibly associated with AF-VHD.

Conclusions

The AF-VHD-related signaling pathways regulated by combinatorial miRNAs may play an important role in the occurrence of AF-VHD. The work brings new insights into biomarkers and miRNA combination regulation mechanism in AF-VHD as well as further biological experiments.

Correlation of myomir-206 and proinflammatory cytokines (IL-16 and IL-17) in patients with rheumatoid arthritis

Introduction

Rheumatoid arthritis (RA) is a persistent autoimmune disease in which the activity of proinflammatory cytokines and the imbalance, related to the inflammatory process, between elements of bone tissue remodeling such as osteoclasts and osteoblasts play a key role in development of erosions and bone destruction. MicroRNAs are important regulators of skeletal remodeling and are involved in RA pathogenesis. Myomir-206 (miR-206) is unrivalled among the myomirRs, where it is expressed in skeletal muscle and either absent or minimally expressed in other tissues

Material and methods

This study was designed to analyze the miR-206 expression pattern in peripheral blood mononuclear cells (PBMCs) using quantitative real time polymerase chain reaction and its correlation with IL-16/IL-17 proinflammatory cytokines in two groups – 20 healthy individuals and 30 patients with RA.

Results

Elevated expression of miR-206 was observed in RA patients compared with healthy controls (p < 0.001). A significant increase in both IL-17 and IL-16 serum levels was found in the RA group (p < 0.01 and p < 0.05; respectively) compared to the control group. miR-206 expression level and IL-17 production were directly positively correlated (r = 0.491; p < 0.01). ROC analysis of miR-206 showed a cutoff value of 2.7 with 70% sensitivity, 85% specificity, and the area under the curve was 0.802 (p < 0.001) with the 95% confidence interval from 0. 676 to 0.927

Conclusions

Taken together, our results indicate the importance of miR-206 expression in patients with RA, as a potential new biomarker that affects bone loss/deformity and its collaborative role with proinflammatory cytokines such as IL-16 and IL-17 in RA bone metabolism. Particular interest should be given to further research to determine the contribution of expression of miR-206 in RA pathogenesis

Micro(RNA)-managing muscle wasting

Progressive skeletal muscle wasting is a natural consequence of aging and is common in chronic and acute diseases. Loss of skeletal muscle mass and function (strength) often leads to frailty, decreased independence, and increased risk of hospitalization. Despite progress made in our understanding of the mechanisms underlying muscle wasting, there is still no treatment available, with exercise training and dietary supplementation improving, but not restoring, muscle mass and/or function. There has been slow progress in developing novel therapies for muscle wasting, either during aging or disease, partially due to the complex nature of processes underlying muscle loss. The mechanisms of muscle wasting are multifactorial, with a combination of factors underlying age- and disease-related functional muscle decline. These factors include well-characterized changes in muscle such as changes in protein turnover and more recently described mechanisms such as autophagy or satellite cell senescence. Advances in transcriptomics and other high-throughput approaches have highlighted significant deregulation of skeletal muscle gene and protein levels during aging and disease. These changes are regulated at different levels, including posttranscriptional gene expression regulation by microRNAs. microRNAs, potent regulators of gene expression, modulate many processes in muscle, and microRNA-based interventions have been recently suggested as a promising new therapeutic strategy against alterations in muscle homeostasis. Here, we review recent developments in understanding the aging-associated mechanisms of muscle wasting and explore potential microRNA-based therapeutic avenues.

MiR-139 promotes differentiation of bovine skeletal muscle-derived satellite cells by regulating DHFR gene expression

MicroRNAs play an important regulatory role in the proliferation and differentiation of skeletal muscle-derived satellite cells (MDSCs). In particular, miR-139 can inhibit tumor cell proliferation and invasion, and its expression is down-regulated during C2C12 myoblast differentiation. The aim of this study was thus to examine the effect and potential mechanism of miR-139 in bovine MDSCs. The expression of miR-139 was found to be significantly increased during bovine MDSC differentiation by stem-loop reverse transcription-polymerase chain reaction amplification. Statistical analysis of the myotube fusion rate was done through immunofluorescence detection of desmin, and western blotting was used to measure the change in protein expression of the muscle differentiation marker genes MYOG and MYH3. The results showed that the miR-139 mimic could enhance the differentiation of bovine MDSCs, whereas the inhibitor had the opposite effect. By using the dual-luciferase reporter system, miR-139 was found to target the 3'-untranslated region of the dihydrofolate reductase (DHFR) gene and regulate its expression. In addition, the expression of miR-139 was found to be regulated by its host gene phosphodiesterase 2A (PDE2A) via inhibition of the latter by CRISPR interference (CRISPRi). Overall, our findings indicate that miR-139 plays an important role in regulating the differentiation of bovine MDSCs.

Influence of physical exercise on microRNAs in skeletal muscle regeneration, aging and diseases

Skeletal muscle is a dynamic tissue with remarkable plasticity and its growth and regeneration are highly organized, with the activation of specific transcription factors, proliferative pathways and cytokines. The decline of skeletal muscle tissue with age, is one of the most important causes of functional loss of independence in older adults. Maintaining skeletal muscle function throughout the lifespan is a prerequisite for good health and independent living.

Physical activity represents one of the most effective preventive agents for muscle decay in aging.

Several studies have underlined the importance of microRNAs (miRNAs) in the control of myogenesis and of skeletal muscle regeneration and function.

In this review, we reported an overview and recent advances about the role of miRNAs expressed in the skeletal muscle, miRNAs regulation by exercise in skeletal muscle, the consequences of different physical exercise training modalities in the skeletal muscle miRNA profile, their regulation under pathological conditions and the role of miRNAs in age-related muscle wasting.

Specific miRNAs appear to be involved in response to different types of exercise and therefore to play an important role in muscle fiber identity and myofiber gene expression in adults and elder population.

Understanding the roles and regulation of skeletal muscle miRNAs during muscle regeneration may result in new therapeutic approaches in aging or diseases with impaired muscle function or re-growth.

Expression analysis of selected classes of circulating exosomal miRNAs in soccer players as an indicator of adaptation to physical activity

Recently studies have shown that, depending on the type of training and its duration, the expression levels of selected circulating myomiRNAs (c-miR-27a,b, c-miR-29a,b,c, c-miR-133a) differ and correlate with the physiological indicators of adaptation to physical activity. To analyse the expression of selected classes of miRNAs in soccer players during different periods of their training cycle. The study involved 22 soccer players aged 17-18 years. The multi-stage 20-m shuttle run test was used to estimate VO2 max among the soccer players. Samples serum were collected at baseline (time point I), after one week (time point II), and after 2 months of training (time point III). The analysis of the relative quantification (RQ) level of three exosomal myomiRNAs, c-miRNA-27b, c-miR-29a, and c-miR-133, was performed by quantitative polymerase chain reaction (qPCR) at three time points - before the training, after 1 week of training and after the completion of two months of competition season training. The expression analysis showed low expression levels (according to references) of all evaluated myomiRNAs before the training cycle. Analysis performed after a week of the training cycle and after completion of the entire training cycle showed elevated expression of all tested myomiRNAs. Statistical analysis revealed significant differences between the first and the second time point in soccer players for c-miR-27b and c-miR-29a; between the first and the third time point for c-miR-27b and c-miR-29a; and between the second and the third time point for c-miR-27b. Statistical analysis showed a positive correlation between the levels of c-miR-29a and VO2 max. Two months of training affected the expression of c-miR-27b and miR-29a in soccer players. The increased expression of c-miR-27b and c-miR-29 with training could indicate their probable role in the adaptation process that takes place in the muscular system. Possibly, the expression of c-miR-29a will be found to be involved in cardiorespiratory fitness in future research.

Proteomic and microRNA Transcriptome Analysis revealed the microRNA-SmyD1 network regulation in Skeletal Muscle Fibers performance of Chinese perch

Fish myotomes are comprised of anatomically segregated fast and slow muscle fibers that possess different metabolic and contractile properties. Although the expression profile properties in fast and slow muscle fibers had been investigated at the mRNA levels, a comprehensive analysis at proteomic and microRNA transcriptomic levels is limited. In the present study, we first systematically compared the proteomic and microRNA transcriptome of the slow and fast muscles of Chinese perch (Siniperca chuatsi). Total of 2102 proteins were identified in muscle tissues. Among them, 99 proteins were differentially up-regulated and 400 were down-regulated in the fast muscle compared with slow muscle. MiRNA microarrays revealed that 199 miRNAs identified in the two types of muscle fibers. Compared with the fast muscle, the 32 miRNAs was up-regulated and 27 down-regulated in the slow muscle. Specifically, expression of miR-103 and miR-144 was negatively correlated with SmyD1a and SmyD1b expression in fast and slow muscles, respectively. The luciferase reporter assay further verified that the miR-103 and miR-144 directly regulated the SmyD1a and SmyD1b expression by targeting their 3′-UTR. The constructed miRNA-SmyD1 interaction network might play an important role in controlling the development and performance of different muscle fiber types in Chinese perch.

Extracellular Vesicles Released by Oxidatively Injured or Intact C2C12 Myotubes Promote Distinct Responses Converging toward Myogenesis

Myogenic differentiation is triggered, among other situations, in response to muscle damage for regenerative purposes. It has been shown that during myogenic differentiation, myotubes release extracellular vesicles (EVs) which participate in the signalling pattern of the microenvironment. Here we investigated whether EVs released by myotubes exposed or not to mild oxidative stress modulate the behaviour of targeted differentiating myoblasts and macrophages to promote myogenesis. We found that EVs released by oxidatively challenged myotubes (H₂O₂-EVs) are characterized by an increased loading of nucleic acids, mainly DNA. In addition, incubation of myoblasts with H₂O₂-EVs resulted in a significant decrease of myotube diameter, myogenin mRNA levels and myosin heavy chain expression along with an upregulation of proliferating cell nuclear antigen: these effects collectively lead to an increase of recipient myoblast proliferation. Notably, the EVs from untreated myotubes induced an opposite trend in myoblasts, that is, a slight pro-differentiation effect. Finally, H₂O₂-EVs were capable of eliciting an increased interleukin 6 mRNA expression in RAW264.7 macrophages. Notably, this is the first demonstration that myotubes communicate with surrounding macrophages via EV release. Collectively, the data reported herein suggest that myotubes, depending on their conditions, release EVs carrying differential signals which could contribute to finely and coherently orchestrate the muscle regeneration process.

Stem Cell-Derived Exosomes, Autophagy, Extracellular Matrix Turnover, and miRNAs in Cardiac Regeneration during Stem Cell Therapy

Stem cell therapy (SCT) raises the hope for cardiac regeneration in ischemic hearts. However, underlying molecular mechanisms for repair of dead myocardium by SCT in the ischemic heart is poorly understood. Growing evidences suggest that cardiac matrix stiffness and differential expressions of miRNAs play a crucial role in stem cell survival and differentiation. However, their roles on transplanted stem cells, for myocardial repair of the ischemic heart, remain unclear. Transplanted stem cells may act in an autocrine and/or paracrine manner to regenerate the dead myocardium. Paracrine mediators such as stem cell-derived exosomes are emerging as a novel therapeutic strategy to overcome some of the limitations of SCT. These exosomes carry microRNAs (miRNAs) that may regulate stem cell differentiation into a specific lineage. MicroRNAs may also contribute to stiffness of surrounding matrix by regulating extracellular matrix (ECM) turnover. The survival of transplanted stem cell depends on its autophagic process that maintains cellular homeostasis. Therefore, exosomes, miRNAs, extracellular matrix turnover, and autophagy may have an integral role in improving the efficacy of SCT. This review elaborates the specific roles of these regulatory components on cardiac regeneration in the ischemic heart during SCT.

miR-101-1 expression pattern in Qinchuan cattle and its role in the regulation of cell differentiation

MiRNAs have emerged as key regulators of skeletal muscle development, but the knowledge of miRNAs in the molecular network of muscle development remains poorly understood. In this study, we designed to examine the biological function of bovine-miR-101-1. The bovine miR-101-1 was detected in the skeletal muscle of fetal, calf and adult cattle. Its abundance was significantly higher in the skeletal muscle of calf cattle than that in fetal and adult cattle. In the course of C2C12 myoblast differentiation, the expression of miR-101-1 gradually increased. Transfected the exogenous miR-101-1 into the C2C12 myoblast could decrease myotube formation, and the mRNA expression levels of the myogenic marker genes MyOD, MyOG and MyHC were up-regulated. The protein level of MyOD, MyOG and MyHC were also up-regulated. Through TargetScan to predict the target gene of bovine miR-101-1, and the dual luciferase system was used for target gene verification. The results show that amyloid precursor protein (APP) is the target gene of miR-101-1. Therefore, our results shed light on miR-101-1 in the regulation of the skeletal muscle development.

MicroRNA-133 mediates cardiac diseases: Mechanisms and clinical implications

MicroRNAs (miRNAs) belong to the family of small non-coding RNAs that mediate gene expression by post-transcriptional regulation. Increasing evidence have demonstrated that miR-133 is enriched in muscle tissues and myogenic cells, and its aberrant expression could induce the occurrence and development of cardiac disorders, such as cardiac hypertrophy, heart failure, etc. In this review, we summarized the regulatory roles of miR-133 in cardiac disorders and the underlying mechanisms, which suggest that miR-133 may be a potential diagnostic and therapeutic tool for cardiac disorders.

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.

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.

COMPUTATIONAL EVIDENCE FROM TWO CORRELATED DATA SOURCES AT DIFFERENT MOLECULAR LEVELS FOR AF-VHD-SPECIFIC MICRORNA SIGNATURE

The important roles of microRNAs (miRNAs) in the pathological process of the cardiovascular system have been recognized. However, identification of miRNAs related to valvular heart disease with atrial fibrillation (AF-VHD) has been difficult and very slow because of complex pathological mechanism of AF-VHD. Analysis of microarray expression profiles provides the possibility to rapid prediction of disease-regulating miRNAs and can lay a theoretical foundation for further experimental studies. A computational method is proposed to predict AF-VHD-specific miRNAs by combining miRNA and gene expression data, which are strongly correlated. Using the proposed method, a 45-miRNA AF-VHD-specific signature is predicted. Compared with other related results, 15 of 45 miRNAs are the same and the rest 30 miRNAs are different. Our analysis shows that 11 of 30 new miRNAs are associated with the diseases inducing AF-VHD and the remaining 19 miRNAs have good combinational discrimination power. Therefore, the AF-VHD signature we have predicted is confirmed to be reliable and specific. In a word, this study proposes an effective computational strategy in prediction of disease-regulating miRNAs and finds some AF-VHD-specific miRNAs, which provides new insight into the further experimental study and molecular mechanism leading to the development of AF-VHD.

Impaired exercise tolerance, mitochondrial biogenesis, and muscle fiber maintenance in miR-133a-deficient mice

Exercise promotes multiple beneficial effects on muscle function, including induction of mitochondrial biogenesis. miR-133a is a muscle-enriched microRNA that regulates muscle development and function. The role of miR-133a in exercise tolerance has not been fully elucidated. In the current study, mice that were deficient in miR-133a demonstrated low maximal exercise capacity and low resting metabolic rate. Transcription of the mitochondrial biogenesis regulators peroxisome proliferator-activated receptor-γ coactivator 1-α, peroxisome proliferator-activated receptor-γ coactivator 1-β, nuclear respiratory factor-1, and transcription factor A, mitochondrial were lower in miR-133a-deficient muscle, which was consistent with lower mitochondrial mass and impaired exercise capacity. Six weeks of endurance exercise training increased the transcriptional level of miR-133a and stimulated mitochondrial biogenesis in wild-type mice, but failed to improve mitochondrial function in miR-133a-deficient mice. Further mechanistic analysis showed an increase in the miR-133a potential target, IGF-1 receptor, along with hyperactivation of Akt signaling, in miR-133a-deficient mice, which was consistent with lower transcription of the mitochondrial biogenesis regulators. These findings indicate an essential role of miR-133a in skeletal muscle mitochondrial biogenesis, exercise tolerance, and response to exercise training.-Nie, Y., Sato, Y., Wang, C., Yue, F., Kuang, S., Gavin, T. P. Impaired exercise tolerance, mitochondrial biogenesis, and muscle fiber maintenance in miR-133a-deficient mice.

Regulation of human adipogenesis by miR125b-5p

MicroRNAs (miRNAs) are non-coding RNAs that regulate target gene expression at the post-transcriptional level and are supposed to be implicated in the control of adipogenesis. We aimed to identify miRNAs which are involved in the regulation of human adipogenesis and searched for their molecular targets. Applying microarray-analysis we identified miR125b-5p as upregulated during human adipocyte differentiation, although its role during adipogenesis is unknown. We identified and characterized the matrix metalloproteinase 11 (MMP11) as a direct target of miR125b-5p by showing that miR125b-5p overexpression significantly reduces MMP11 luciferase activity and mutation of any single binding site was sufficient to abolish the miR125b-5p mediated inhibition of luciferase activity. MMP11 overexpression decreased fat accumulation, indicating that MMP11 acts as an anti-adipogenic regulator. In contrast, overexpression of miR125b-5p itself reduced adipogenesis. In summary, we identified miR125b-5p as upregulated during human adipogenesis indicating that miR125b-5p may serve as a regulator of human adipocyte differentiation. We further show that miR125b-5p downregulates the anti-adipogenic MMP11, but directly inhibits adipogenesis itself. Taken together, these data implicate that miR125b-5p can affect human adipogenesis via MMP11 and probably additional targets.

MicroRNA-Regulated Proinflammatory Cytokines in Sarcopenia

Sarcopenia has been defined as the aging-related disease with the declined mass, strength, and function of skeletal muscle, which is the major cause of frailty and falls in elders. The activation of inflammatory signal pathways due to diseases and aging is suggested to reveal the critical impact on sarcopenia. Several proinflammatory cytokines, especially interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), play crucial roles in modulation of inflammatory signaling pathway during the aging-related loss of skeletal muscle. MicroRNAs (miRNAs) have emerged as the important regulators for the mass and functional maintenance of skeletal muscle through regulating gene expression of proinflammatory cytokines. In this paper, we have systematically discussed regulatory mechanisms of miRNAs for the expression and secretion of inflammatory cytokines during sarcopenia, which will provide some novel targets and therapeutic strategies for controlling aging-related atrophy of skeletal muscle and corresponding chronic inflammatory diseases.

Non-coding RNAs in muscle differentiation and musculoskeletal disease

RNA is likely to be the most rediscovered macromolecule in biology. Periodically, new non-canonical functions have been ascribed to RNA, such as the ability to act as a catalytic molecule or to work independently from its coding capacity. Recent annotations show that more than half of the transcriptome encodes for RNA molecules lacking coding activity. Here we illustrate how these transcripts affect skeletal muscle differentiation and related disorders. We discuss the most recent scientific discoveries that have led to the identification of the molecular circuitries that are controlled by RNA during the differentiation process and that, when deregulated, lead to pathogenic events. These findings will provide insights that can aid in the development of new therapeutic interventions for muscle diseases.

Developmental regulation and evolution of muscle-specific microRNAs

MicroRNAs (miRs) are a group of small RNAs that play a major role in post-transcriptional regulation of gene expression. In animals, many of the miRs are expressed in a conserved spatiotemporal manner. Muscle tissues, the major cellular systems involved in the locomotion and physiological functions of animals, have been one of the main sites for verification of miR targets and analysis of their developmental functions. During the determination and differentiation of muscle cells, numerous miRs bind to and repress target mRNAs in a highly specific but redundant manner. Interspecific comparisons of the sequences and expression of miRs have suggested that miR regulation became increasingly important during the course of vertebrate evolution. However, the detailed molecular interactions that have led to the highly complex morphological structures still await investigation. In this review, we will summarize the recent findings on the functional and developmental characteristics of miRs that have played major roles in vertebrate myogenesis, and discuss how the evolution of miRs is related to the morphological complexity of the vertebrates.

Analysis of MicroRNA Expression Profiles in Weaned Pig Skeletal Muscle after Lipopolysaccharide Challenge

MicroRNAs (miRNAs) constitute a class of non-coding RNAs that play a crucial regulatory role in skeletal muscle development and disease. Several acute inflammation conditions including sepsis and cancer are characterized by a loss of skeletal muscle due primarily to excessive muscle catabolism. As a well-known inducer of acute inflammation, a lipopolysaccharide (LPS) challenge can cause serious skeletal muscle wasting. However, knowledge of the role of miRNAs in the course of inflammatory muscle catabolism is still very limited. In this study, RNA extracted from the skeletal muscle of pigs injected with LPS or saline was subjected to small RNA deep sequencing. We identified 304 conserved and 114 novel candidate miRNAs in the pig. Of these, four were significantly increased in the LPS-challenged samples and five were decreased. The expression of five miRNAs (ssc-miR-146a-5p, ssc-miR-221-5p, ssc-miR-148b-3p, ssc-miR-215 and ssc-miR-192) were selected for validation by quantitative polymerase chain reaction (qPCR), which found that ssc-miR-146a-5p and ssc-miR-221-5p were significantly upregulated in LPS-challenged pig skeletal muscle. Moreover, we treated mouse C2C12 myotubes with 1000 ng/mL LPS as an acute inflammation cell model. Expression of TNF-α, IL-6, muscle atrophy F-box (MAFbx) and muscle RING finger 1 (MuRF1) mRNA was strongly induced by LPS. Importantly, miR-146a-5p and miR-221-5p also showed markedly increased expression in LPS-treated C2C12 myotubes, suggesting the two miRNAs may be involved in muscle catabolism systems in response to acute inflammation caused by a LPS challenge. To our knowledge, this study is the first to examine miRNA expression profiles in weaned pig skeletal muscle challenged with LPS, and furthers our understanding of miRNA function in the regulation of inflammatory muscle catabolism.

Genome-wide Mechanosensitive MicroRNA (MechanomiR) Screen Uncovers Dysregulation of Their Regulatory Networks in the mdm Mouse Model of Muscular Dystrophy

Muscular dystrophies (MDs) are a heterogeneous group of genetic and neuromuscular disorders, which result in severe loss of motor ability and skeletal muscle mass and function. Aberrant mechanotransduction and dysregulated-microRNA pathways are often associated with the progression of MD. Here, we hypothesized that dysregulation of mechanosensitive microRNAs (mechanomiRs) in dystrophic skeletal muscle plays a major role in the progression of MD. To test our hypothesis, we performed a genome-wide expression profile of anisotropically regulated mechanomiRs and bioinformatically analyzed their target gene networks. We assessed their functional roles in the advancement of MD using diaphragm muscles from mdm (MD with myositis) mice, an animal model of human tibial MD (titinopathy), and their wild-type littermates. We were able to show that ex vivo anisotropic mechanical stretch significantly alters the miRNA expression profile in diaphragm muscles from WT and mdm mice; as a result, some of the genes associated with MDs are dysregulated in mdm mice due to differential regulation of a distinct set of mechanomiRs. Interestingly, we found a contrasting expression pattern of the highly expressed let-7 family mechanomiRs, let-7e-5p and miR-98-5p, and their target genes associated with the extracellular matrix and TGF-β pathways, respectively, between WT and mdm mice. Gain- and loss-of-function analysis of let-7e-5p in myocytes isolated from the diaphragms of WT and mdm mice confirmed Col1a1, Col1a2, Col3a1, Col24a1, Col27a1, Itga1, Itga4, Scd1, and Thbs1 as target genes of let-7e-5p. Furthermore, we found that miR-98 negatively regulates myoblast differentiation. Our study therefore introduces additional biological players in the regulation of skeletal muscle structure and myogenesis that may contribute to unexplained disorders of MD.

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.

Altered expression of hyperpolarization-activated cyclic nucleotide-gated channels and microRNA-1 and -133 in patients with age-associated atrial fibrillation

Hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels mediate pacemaker currents in the atrium. The microRNA (miR) families miR-1 and miR-133 regulate the expression of multiple genes involved in myocardial function, including HCN channels. It was hypothesized that age‑dependent changes in HCN2, HCN4, miR‑1 and miR‑133 expression may contribute to age‑associated atrial fibrillation, and therefore the correlation between expression levels, among adult (≤65 years) and aged patients (≥65 years), and sinus rhythm was determined. Right atrial appendage samples were collected from 60 patients undergoing coronary artery bypass grafting. Reverse transcription-quantitative polymerase chain reaction (PCR) and western blot analyses were performed in order to determine target RNA and protein expression levels. Compared with aged patients with sinus rhythm, aged patients with atrial fibrillation exhibited significantly higher HCN2 and HCN4 channel mRNA and protein expression levels (P<0.05), but significantly lower expression levels of miR‑1 and miR‑133 (P<0.05). In addition, aged patients with sinus rhythm exhibited significantly higher expression levels of HCN2 and HCN4 channel mRNA and protein (P<0.05), but significantly lower expression levels of miR‑1 and ‑133 (P<0.05), compared with those of adult patients with sinus rhythm. Expression levels of HCN2 and HCN4 increased with age, and a greater increase was identified in patients with age‑associated atrial fibrillation compared with that in those with aged sinus rhythm. These electrophysiological changes may contribute to the induction of ectopic premature beats that trigger atrial fibrillation.

Functions of miR-1 and miR-133a during the postnatal development of masseter and gastrocnemius muscles

The present study investigated the function of miR-1 and miR-133a during the postnatal development of mouse skeletal muscles. The amounts of miR-1 and miR-133a were measured in mouse masseter and gastrocnemius muscles between 1 and 12 weeks after birth with real-time polymerase chain reaction and those of HDACs, MEF2, MyoD family, MCK, SRF, and Cyclin D1 were measured at 2 and 12 weeks with Western blotting. In both the masseter and gastrocnemius muscles, the amount of miR-1 increased between 1 and 12 weeks, whereas the amount of HADC4 decreased between 2 and 12 weeks. In the masseter muscle, those of MEF2, MyoD, Myogenin, and MCK increased between 2 and 12 weeks, whereas, in the gastrocnemius muscle, only those of MRF4 and MCK increased. The extent of these changes in the masseter muscle was greater than that in the gastrocnemius muscle. The amounts of miR-133a, SRF, and Cyclin D1 did not change significantly in the masseter muscle between 1 and 12 weeks after birth. By contrast, in the gastrocnemius muscle, the amounts of miR-133a and Cyclin D1 increased, whereas that of SRF decreased. Our findings suggest that the regulatory pathway of miR-1 via HDAC4 and MEF2 plays a more prominent role during postnatal development in the masseter muscle than in the gastrocnemius muscle, whereas that of miR-133a via SRF plays a more prominent role in the gastrocnemius muscle than in the masseter muscle.

MicroRNA signature in response to nutrient restriction and re-feeding in fast skeletal muscle of grass carp (Ctenopharyngodon idella)

The grass carp (Ctenopharyngodon idella) is one of the most important cultivated fish species in China. Mounting evidences suggests that microRNAs (miRNAs) may be key regulators of skeletal muscle among the grass carp, but the knowledge of the identity of myogenic miRNAs and role of miRNAs during skeletal muscle anabolic state remains limited. In the present study, we choose 8 miRNAs previously reported to act as muscle growth-related miRNAs for fasting-refeeding research. We investigated postprandial changes in the expression of 8 miRNAs following a single satiating meal in grass carp juveniles who had been fasting for one week and found that 7 miRNAs were sharply up-regulated within 1 or 3 h after refeeding, suggesting that they may be promising candidate miRNAs involved in a fast-response signaling system that regulates fish skeletal muscle growth.

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

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

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

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

Next-generation sequencing analysis of miRNA expression in control and FSHD myogenesis

Emerging evidence has demonstrated that miRNA sequences can regulate skeletal myogenesis by controlling the process of myoblast proliferation and differentiation. However, at present a deep analysis of miRNA expression in control and FSHD myoblasts during differentiation has not yet been derived. To close this gap, we used a next-generation sequencing (NGS) approach applied to in vitro myogenesis. Furthermore, to minimize sample genetic heterogeneity and muscle-type specific patterns of gene expression, miRNA profiling from NGS data was filtered with FC≥4 (log₂FC≥2) and p-value<0.05, and its validation was derived by qRT-PCR on myoblasts from seven muscle districts. In particular, control myogenesis showed the modulation of 38 miRNAs, the majority of which (34 out 38) were up-regulated, including myomiRs (miR-1, -133a, -133b and -206). Approximately one third of the modulated miRNAs were not previously reported to be involved in muscle differentiation, and interestingly some of these (i.e. miR-874, -1290, -95 and -146a) were previously shown to regulate cell proliferation and differentiation. FSHD myogenesis evidenced a reduced number of modulated miRNAs than healthy muscle cells. The two processes shared nine miRNAs, including myomiRs, although with FC values lower in FSHD than in control cells. In addition, FSHD cells showed the modulation of six miRNAs (miR-1268, -1268b, -1908, 4258, -4508- and -4516) not evidenced in control cells and that therefore could be considered FSHD-specific, likewise three novel miRNAs that seem to be specifically expressed in FSHD myotubes. These data further clarify the impact of miRNA regulation during control myogenesis and strongly suggest that a complex dysregulation of miRNA expression characterizes FSHD, impairing two important features of myogenesis: cell cycle and muscle development. The derived miRNA profiling could represent a novel molecular signature for FSHD that includes diagnostic biomarkers and possibly therapeutic targets.

miRNA transcriptome of hypertrophic skeletal muscle with overexpressed myostatin propeptide

MicroRNAs (miRNAs) play an imperative role in cell proliferation, differentiation, and cell metabolism through regulation of gene expression. Skeletal muscle hypertrophy that results from myostatin depression by its propeptide provides an interesting model to understand how miRNA transcriptome is involved in myostatin-based fiber hypertrophy. This study employed Solexa deep sequencing followed by Q-PCR methods to analyze miRNA transcriptome of skeletal muscle of myostatin propeptide transgenic mice in comparison with their littermate controls. A total of 461 mature known and 69 novel miRNAs were reported from this study. Fifty-seven miRNAs were expressed differentially between transgenic and littermate controls, of which most abundant miRNAs, miR-133a and 378a, were significantly differentially expressed. Expression profiling was validated on 8 known and 2 novel miRNAs. The miRNA targets prediction and pathway analysis showed that FST, SMAD3, TGFBR1, and AcvR1a genes play a vital role in skeletal muscle hypertrophy in the myostatin propeptide transgenic mice. It is predicted that miR-101 targeted to TGFBR1 and SMAD3, miR-425 to TGFBR2 and FST, and miR-199a to AcvR2a and TGF-β genes. In conclusion, the study offers initial miRNA profiling and methodology of miRNA targets prediction for myostatin-based hypertrophy. These differentially expressed miRNAs are proposed as candidate miRNAs for skeletal muscle hypertrophy.

The Basis of Muscle Regeneration

Muscle regeneration recapitulates many aspects of embryonic myogenesis and is an important homeostatic process of the adult skeletal muscle, which, after development, retains the capacity to regenerate in response to appropriate stimuli, activating the muscle compartment of stem cells, namely, satellite cells, as well as other precursor cells. Moreover, significant evidence suggests that while stem cells represent an important determinant for tissue regeneration, a “qualified” environment is necessary to guarantee and achieve functional results. It is therefore plausible that the loss of control over these cell fate decisions could lead to a pathological transdifferentiation, leading to pathologic defects in the regenerative process. This review provides an overview about the general aspects of muscle development and discusses the cellular and molecular aspects that characterize the five interrelated and time-dependent phases of muscle regeneration, namely, degeneration, inflammation, regeneration, remodeling, and maturation/functional repair.

Mega roles of microRNAs in regulation of skeletal muscle health and disease

Skeletal muscle is a dynamic tissue with remarkable plasticity. Skeletal muscle growth and regeneration are highly organized processes thus it is not surprising that a high degree of complexity exists in the regulation of these processes. Recent discovery of non-coding microRNAs (miRNAs) has prompted extensive research in understanding the roles of these molecules in skeletal muscle. Research so far shows that miRNAs play a very significant role at every aspect of muscle biology. Besides muscle growth, development, and regeneration miRNAs are also involved in the pathology of muscle diseases and metabolism. In this review, recent advancements in miRNA function during myogenesis, exercise, atrophy, aging, and dystrophy are discussed.

miR-182 attenuates atrophy-related gene expression by targeting FoxO3 in skeletal muscle

Skeletal muscle atrophy occurs in response to a variety of conditions including chronic kidney disease, diabetes, cancer, and elevated glucocorticoids. MicroRNAs (miR) may play a role in the wasting process. Activation of the forkhead box O3 (FoxO3) transcription factor causes skeletal muscle atrophy in patients, animals, and cultured cells by increasing the expression of components of the ubiquitin-proteasome and autophagy-lysosome proteolytic systems. To identify microRNAs that potentially modulate the atrophy process, an in silico target analysis was performed and miR-182 was predicted to target FoxO3 mRNA. Using a combination of immunoblot analysis, quantitative real-time RT-PCR, and FoxO3 3'-UTR luciferase reporter genes, miR-182 was confirmed to regulate FoxO3 expression in C2C12 myotubes. Transfection of miR-182 into muscle cells decreased FoxO3 mRNA 30% and FoxO3 protein 67% (P < 0.05) and also prevented a glucocorticoid-induced upregulation of multiple FoxO3 gene targets including MAFbx/atrogin-1, autophagy-related protein 12 (ATG12), cathepsin L, and microtubule-associated protein light chain 3 (LC3). Treatment of C2C12 myotubes with dexamethasone (Dex) (1 μM, 6 h) to induce muscle atrophy decreased miR-182 expression by 63% (P < 0.05). Similarly, miR-182 was decreased 44% (P < 0.05) in the gastrocnemius muscle of rats injected with streptozotocin to induce diabetes compared with controls. Finally, miR-182 was present in exosomes isolated from the media of C2C12 myotubes and Dex increased its abundance. These data identify miR-182 as an important regulator of FoxO3 expression that participates in the control of atrophy-inducing genes during catabolic diseases.

Identification and profiling of microRNAs and their target genes from developing caprine skeletal Muscle

Goat is an important agricultural animal for meat production. Functional studies have demonstrated that microRNAs (miRNAs) regulate gene expression at the post-transcriptional level and play an important role in various biological processes. Although studies on miRNAs expression profiles have been performed in various animals, relatively limited information about goat muscle miRNAs has been reported. To investigate the miRNAs involved in regulating different periods of skeletal muscle development, we herein performed a comprehensive research for expression profiles of caprine miRNAs during two developmental stages of skeletal muscles: fetal stage and six month-old stage. As a result, 15,627,457 and 15,593,721 clean reads were obtained from the fetal goat library (FC) and the six month old goat library (SMC), respectively. 464 known miRNAs and 83 novel miRNA candidates were identified. Furthermore, by comparing the miRNA profile, 336 differentially expressed miRNAs were identified and then the potential targets of the differentially expressed miRNAs were predicted. To understand the regulatory network of miRNAs during muscle development, the mRNA expression profiles for the two development stages were characterized and 7322 differentially expressed genes (DEGs) were identified. Then the potential targets of miRNAs were compared to the DEGs, the intersection of the two gene sets were screened out and called differentially expressed targets (DE-targets), which were involved in 231 pathways. Ten of the 231 pathways that have smallest P-value were shown as network figures. Based on the analysis of pathways and networks, we found that miR-424-5p and miR-29a might have important regulatory effect on muscle development, which needed to be further studied. This study provided the first global view of the miRNAs in caprine muscle tissues. Our results help elucidation of complex regulatory networks between miRNAs and mRNAs and for the study of muscle development.