MIR-206 regulates connexin43 expression during skeletal muscle development

Novel Circular RNA CircSLC2A13 Regulates Chicken Muscle Development by Sponging MiR-34a-3p

The skeletal muscle is the major muscle tissue in animals, and its production is subject to a complex and strict regulation. The proliferation and differentiation of myoblasts are important factors determining chicken muscle development. Circular RNAs (circRNAs) are endogenous RNAs that are widely present in various tissues of organisms. Recent studies have shown that circRNA plays key roles in the development of skeletal muscles. The solute carrier (SLC) family functions in the transport of metabolites such as amino acids, glucose, nucleotides, and essential nutrients and is widely involved in various basic physiological metabolic processes within the body. In this study, we have cloned a novel chicken circular RNA circSLC2A13 generated from the solute carrier family 2 member 13 gene (SLC2A13). Also, circSLC2A1 was confirmed by sequencing verification, RNase R treatment, and reverse transcription analysis. Currently, our results show that circSLC2A13 promoted the proliferation and differentiation of chicken myoblasts. The double luciferase reporter system revealed that circSLC2A13 regulated the proliferation and differentiation of myoblasts by competitive binding with miR-34a-3p. In addition, results indicated that circSLC2A13 acts as a miR-34a-3p sponge to relieve its inhibitory effect on the target SMAD3 gene. In summary, this study found that chicken circSLC2A13 can bind to miR-34a-3p and weaken its inhibitory effect on the SMAD family member 3 gene (SMAD3), thereby promoting the proliferation and differentiation of myoblasts. This study laid foundations for broiler industry and muscle development research.

IFRD2, a target of miR-2400, regulates myogenic differentiation of bovine skeletal muscle satellite cells via decreased phosphorylation of ERK1/2 proteins

The proliferation and differentiation of skeletal muscle satellite cells is a complex physiological process involving various transcription factors and small RNA molecules. This study aimed to understand the regulatory mechanisms underlying these processes, focusing on interferon-related development factor 2 (IFRD2) as a target gene of miRNA-2400 in bovine skeletal MuSCs (MuSCs). IFRD2 was identified as a target gene of miRNA-2400 involved in regulating the proliferation and differentiation of bovine skeletal MuSCs. Our results indicate that miR-2400 can target binding the 3'UTR of IFRD2 and inhibit its translation. mRNA and protein expression levels of IFRD2 increased significantly with increasing days of differentiation. Moreover, overexpression of the IFRD2 gene inhibited proliferation and promoted differentiation of bovine MuSCs. Conversely, the knockdown of the gene had the opposite effect. Overexpression of IFRD2 resulted in the inhibition of ERK1/2 phosphorylation levels in bovine MuSCs, which in turn promoted differentiation. In summary, IFRD2, as a target gene of miR-2400, crucially affects bovine skeletal muscle proliferation and differentiation by precisely regulating ERK1/2 phosphorylation.

Whole-transcriptome analysis of longissimus dorsi muscle in cattle-yaks reveals the regulatory functions of ADAMTS6 gene in myoblasts

Cattle-yak, which is the hybrid F1 generation of cattle and yak, demonstrates better production performance compared to yak. However, there is limited research on the molecular mechanisms responsible for the muscle development of cattle-yak. To address this knowledge gap, a comprehensive transcriptomic survey of the longissimus dorsi muscle in cattle-yak was conducted. Three transcript types, namely lncRNAs, miRNAs, and circRNAs, along with protein-coding genes were characterized at two developmental stages (6 m, 18 m) of cattle-yak. The results revealed significant enrichment of these transcripts into pathways related to myoblast differentiation and muscle development signaling. Additionally, the study identified the TCONS00024465/circHIPK3-bta-miR-499-ADAMTS6 regulatory network, which may play a crucial role in the muscle development of cattle-yak by combining the transcriptome data of yak and constructing the ceRNA co-expression network. HEK 293 T cells were used to validate that TCONS00024465 and circHIPK3 are located upstream of bta-miR-499, and can competitively bind to bta-miR-499 as ceRNA. The study also verified that ADAMTS6 regulates skeletal muscle development by inhibiting myoblast proliferation, promoting myoblast differentiation, and positively regulating the apoptosis of myoblasts. Taken together, this study provides new insights into the advantages of cattle-yak production performance and offers a molecular basis for further research on muscle development.

Role of miRNA in Cardiovascular Diseases in Children-Systematic Review

The number of children suffering from cardiovascular diseases (CVDs) is rising globally. Therefore, there is an urgent need to acquire a better understanding of the genetic factors and molecular mechanisms related to the pathogenesis of CVDs in order to develop new prevention and treatment strategies for the future. MicroRNAs (miRNAs) constitute a class of small non-coding RNA fragments that range from 17 to 25 nucleotides in length and play an essential role in regulating gene expression, controlling an abundance of biological aspects of cell life, such as proliferation, differentiation, and apoptosis, thus affecting immune response, stem cell growth, ageing and haematopoiesis. In recent years, the concept of miRNAs as diagnostic markers allowing discrimination between healthy individuals and those affected by CVDs entered the purview of academic debate. In this review, we aimed to systematise available information regarding miRNAs associated with arrhythmias, cardiomyopathies, myocarditis and congenital heart diseases in children. We focused on the targeted genes and metabolic pathways influenced by those particular miRNAs, and finally, tried to determine the future of miRNAs as novel biomarkers of CVD.

The roles of miRNAs in adult skeletal muscle satellite cells

Satellite cells are bona fide muscle stem cells that are indispensable for successful post-natal muscle growth and regeneration after severe injury. These cells also participate in adult muscle adaptation in several capacities. MicroRNAs (miRNAs) are post-transcriptional regulators of mRNA that are implicated in several aspects of stem cell function. There is evidence to suggest that miRNAs affect satellite cell behavior in vivo during development and myogenic progenitor behavior in vitro, but the role of miRNAs in adult skeletal muscle satellite cells is less studied. In this review, we provide evidence for how miRNAs control satellite cell function with emphasis on satellite cells of adult skeletal muscle in vivo. We first outline how miRNAs are indispensable for satellite cell viability and control the phases of myogenesis. Next, we discuss the interplay between miRNAs and myogenic cell redox status, senescence, and communication to other muscle-resident cells during muscle adaptation. Results from recent satellite cell miRNA profiling studies are also summarized. In vitro experiments in primary myogenic cells and cell lines have been invaluable for exploring the influence of miRNAs, but we identify a need for novel genetic tools to further interrogate how miRNAs control satellite cell behavior in adult skeletal muscle in vivo.

Use of AgomiR and AntagomiR technologies to alter satellite cell proliferation in vitro, miRNA expression, and muscle fiber hypertrophy in intrauterine growth-restricted lambs

Introduction: microRNAs (miRNAs) are small non-coding RNAs that work at the posttranscriptional level to repress gene expression. Several miRNAs are preferentially expressed in skeletal muscle and participate in myogenesis. This research was conducted to alter endogenous miRNA expression in skeletal muscle to promote muscle hypertrophy. Methods: Two experiments were conducted using mimic/agomiR or antagomir technologies to alter miRNA expression and examine changes in myoblast proliferation in vitro (experiment 1) and muscle hypertrophy in vivo (experiment 2). In vitro experiments found that antagomiR-22-3p and mimic-127 increased myoblast proliferation compared to other miRNA treatments or controls. These miRNA treatments, antagomiR-22-3p (ANT22) and agomiR-127 (AGO127), were then used for intramuscular injections in longissimus muscle. Results and discussion: The use of antagomiR or mimic/agomiR treatments down-regulated or up-regulated, respectively, miRNA expression for that miRNA of interest. Expression of predicted target KIF3B mRNA for miR-127 was up-regulated and ACVR2a mRNA was up-regulated for miR-22-3p. ANT22 injection also up-regulated the major regulator of protein synthesis (mTOR). Proteomic analyses identified 11 proteins for AGO127 and 9 proteins for ANT22 that were differentially expressed. Muscle fiber type and cross-sectional area were altered for ANT22 treatments to transition fibers to a more oxidative state. The use of agomiR and antagomir technologies allows us to alter miRNA expression in vitro and in vivo to enhance myoblast proliferation and alter muscle fiber hypertrophy in IUGR lambs during early postnatal growth.

Skeletal Muscle Atrophy Induced by Diabetes Is Mediated by Non-Selective Channels and Prevented by Boldine

Individuals with diabetes mellitus present a skeletal muscle myopathy characterized by atrophy. However, the mechanism underlying this muscular alteration remains elusive, which makes it difficult to design a rational treatment that could avoid the negative consequences in muscles due to diabetes. In the present work, the atrophy of skeletal myofibers from streptozotocin-induced diabetic rats was prevented with boldine, suggesting that non-selective channels inhibited by this alkaloid are involved in this process, as has previously shown for other muscular pathologies. Accordingly, we found a relevant increase in sarcolemma permeability of skeletal myofibers of diabetic animals in vivo and in vitro due to de novo expression of functional connexin hemichannels (Cx HCs) containing connexins (Cxs) 39, 43, and 45. These cells also expressed P2X7 receptors, and their inhibition in vitro drastically reduced sarcolemma permeability, suggesting their participation in the activation of Cx HCs. Notably, sarcolemma permeability of skeletal myofibers was prevented by boldine treatment that blocks Cx43 and Cx45 HCs, and now we demonstrated that it also blocks P2X7 receptors. In addition, the skeletal muscle alterations described above were not observed in diabetic mice with myofibers deficient in Cx43/Cx45 expression. Moreover, murine myofibers cultured for 24 h in high glucose presented a drastic increase in sarcolemma permeability and levels of NLRP3, a molecular member of the inflammasome, a response that was also prevented by boldine, suggesting that, in addition to the systemic inflammatory response found in diabetes, high glucose can promote the expression of functional Cx HCs and activation of the inflammasome in skeletal myofibers. Therefore, Cx43 and Cx45 HCs play a critical role in myofiber degeneration, and boldine could be considered a potential therapeutic agent to treat muscular complications due to diabetes.

Bta-miR-206 and a Novel lncRNA-lncA2B1 Promote Myogenesis of Skeletal Muscle Satellite Cells via Common Binding Protein HNRNPA2B1

Skeletal muscle satellite cells (MuSCs) can proliferate, differentiate, and self-renew, and can also participate in muscle formation and muscle injury repair. Long noncoding RNAs (lncRNAs) can play an important role with the RNA binding protein and microRNAs (miRNAs) to regulate the myogenesis of bovine MuSCs, however, its molecular mechanism is still being explored. In this study, differentially expressed 301 lncRNAs were identified during the myogenic differentiation of cells based on an in vitro model of induced differentiation of bovine MuSCs using RNA sequencing (RNA-seq). Based on the ability of miR-206 to regulate myogenic cell differentiation, a new kind of lncRNA-lncA2B1 without protein-coding ability was found, which is expressed in the nucleus and cytoplasm. Subsequently, lncA2B1 inhibited cell proliferation by downregulating the expression of the proliferation marker Pax7 and promoted myogenic differentiation by upregulating the expression of the differentiation marker MyHC, whose regulatory function is closely related to miR-206. By RNA pulldown/LC-MS experiments, heterogeneous ribonucleoprotein A2/B1 (HNRNPA2B1), and DExH-Box Helicase 9 (DHX9) were identified as common binding proteins of lncA2B1 and miR-206. Overexpression of lncA2B1 and miR-206 significantly upregulated the expression level of HNRNPA2B1. Downregulation of HNRNPA2B1 expression significantly decreased the expression level of the differentiation marker MyHC, which indicates that miR-206 and lncA2B1 regulate myogenic differentiation of bovine MuSCs by acting on HNRNPA2B1. This study screened and identified a novel lncRNA-lncA2B1, which functions with miR-206 to regulate myogenesis via the common binding proteins HNRNPA2B1. The results of this study provide a new way to explore the molecular mechanisms by which lncRNAs and miRNAs regulate muscle growth and development.

Upregulation of Sarcolemmal Hemichannels and Inflammatory Transcripts with Neuromuscular Junction Instability during Lower Limb Unloading in Humans

Human skeletal muscle atrophy and a disproportionate force loss occur within a few days of unloading in space and on Earth, but the underlying mechanisms are not fully understood. Disruption of neuromuscular junction homeostasis has been proposed as one of the possible causes. Here, we investigated the potential mechanisms involved in this neuromuscular disruption induced by a 10-day unilateral lower limb suspension (ULLS) in humans. Specifically, we investigated hemichannels’ upregulation, neuromuscular junction and axonal damage, neurotrophins’ receptor downregulation and inflammatory transcriptional signatures. Biomarkers were evaluated at local and systemic levels. At the sarcolemmal level, changes were found to be associated with an increased expression of connexin 43 and pannexin-1. Upregulation of the inflammatory transcripts revealed by deep transcriptomics was found after 10 days of ULLS. The destabilisation of the neuromuscular junction was not accompanied by changes in the secretion of the brain-derived neurotrophic factor and neurotrophin-4, while their receptor, BDNF/NT growth factors receptor (TrkB), decreased. Furthermore, at 5 days of ULLS, there was already a significant upregulation of the serum neurofilament light chain concentration, an established clinical biomarker of axonal injury. At 10 days of ULLS, other biomarkers of early denervation processes appeared. Hence, short periods of muscle unloading induce sarcolemmal hemichannels upregulation, inflammatory transcripts upregulation, neuromuscular junction instability and axonal damage.

Nuclear Factor Erythroid 2-Related Factor 2 and Its Targets in Skeletal Muscle Repair and Regeneration

Significance: Skeletal muscles have a robust regenerative capacity in response to acute and chronic injuries. Muscle repair and redox homeostasis are intimately linked; increased generation of reactive oxygen species leads to cellular dysfunction and contributes to muscle wasting and progression of muscle diseases. In exemplary muscle disease, Duchenne muscular dystrophy (DMD), caused by mutations in the DMD gene that encodes the muscle structural protein dystrophin, the regeneration machinery is severely compromised, while oxidative stress contributes to the progression of the disease. The nuclear factor erythroid 2-related factor 2 (NRF2) and its target genes, including heme oxygenase-1 (HO-1), provide protective mechanisms against oxidative insults. Recent Advances: Relevant advances have been evolving in recent years in understanding the mechanisms by which NRF2 regulates processes that contribute to effective muscle regeneration. To this end, pathways related to muscle satellite cell differentiation, oxidative stress, mitochondrial metabolism, inflammation, fibrosis, and angiogenesis have been studied. The regulatory role of NRF2 in skeletal muscle ferroptosis has been also suggested. Animal studies have shown that NRF2 pathway activation can stop or reverse skeletal muscle pathology, especially when endogenous stress defence mechanisms are imbalanced. Critical Issues: Despite the growing recognition of NRF2 as a factor that regulates various aspects of muscle regeneration, the mechanistic impact on muscle pathology in various models of muscle injury remains imprecise. Future Directions: Further studies are necessary to fully uncover the role of NRF2 in muscle regeneration, both in physiological and pathological conditions, and to investigate the possibilities for development of new therapeutic modalities. Antioxid. Redox Signal. 38, 619-642.

Loss of neuromuscular junction integrity and muscle atrophy in skeletal muscle disuse

Physical inactivity (PI) is a major risk factor of chronic diseases. A major aspect of PI is loss of muscle mass and strength. The latter phenomenon significantly impacts daily life and represent a major issue for global health. Understandably, skeletal muscle itself has been the major focus of studies aimed at understanding the mechanisms underlying loss of mass and strength. Relatively lesser attention has been given to the contribution of alterations in somatomotor control, despite the fact that these changes can start very early and can occur at multiple levels, from the cortex down to the neuromuscular junction (NMJ). It is well known that exposure to chronic inactivity or immobilization causes a disproportionate loss of force compared to muscle mass, i.e. a loss of specific or intrinsic whole muscle force. The latter phenomenon may be partially explained by the loss of specific force of individual muscle fibres, but several other players are very likely to contribute to such detrimental phenomenon. Irrespective of the length of the disuse period, the loss of force is, in fact, more than two-fold greater than that of muscle size. It is very likely that somatomotor alterations may contribute to this loss in intrinsic muscle force. Here we review evidence that alterations of one component of somatomotor control, namely the neuromuscular junction, occur in disuse. We also discuss some of the novel players in NMJ stability (e.g., homer, bassoon, pannexin) and the importance of new established and emerging molecular markers of neurodegenerative processes in humans such as agrin, neural-cell adhesion molecule and light-chain neurofilaments.

Gap Junctions and Ageing

Gap junctions, comprising connexin proteins, create conduits directly coupling the cytoplasms of adjacent cells. Expressed in essentially all tissues, dynamic gap junction structures enable the exchange of small molecules including ions and second messengers, and are central to maintenance of homeostasis and synchronized excitability. With such diverse and critical roles throughout the body, it is unsurprising that alterations to gap junction and/or connexin expression and function underlie a broad array of age-related pathologies. From neurological dysfunction to cardiac arrhythmia and bone loss, it is hard to identify a human disease state that does not involve reduced, or in some cases inappropriate, intercellular communication to affect organ function. With a complex life cycle encompassing several key regulatory steps, pathological gap junction remodeling during ageing can arise from alterations in gene expression, translation, intracellular trafficking, and posttranslational modification of connexins. Connexin proteins are now known to "moonlight" and perform a variety of non-junctional functions in the cell, independent of gap junctions. Furthermore, connexin "hemichannels" on the cell surface can communicate with the extracellular space without ever coupling to an adjacent cell to form a gap junction channel. This chapter will focus primarily on gap junctions in ageing, but such non-junctional connexin functions will be referred to where appropriate and the full spectrum of connexin biology should be noted as potentially causative/contributing to some findings in connexin knockout animals, for example.

NRF2 Regulates Viability, Proliferation, Resistance to Oxidative Stress, and Differentiation of Murine Myoblasts and Muscle Satellite Cells

Increased oxidative stress can slow down the regeneration of skeletal muscle and affect the activity of muscle satellite cells (mSCs). Therefore, we evaluated the role of the NRF2 transcription factor (encoded by the Nfe2l2 gene), the main regulator of the antioxidant response, in muscle cell biology. We used (i) an immortalized murine myoblast cell line (C2C12) with stable overexpression of NRF2 and (ii) primary mSCs isolated from wild-type and Nfe2l2 (transcriptionally)-deficient mice (Nfe2l2^tKO). NRF2 promoted myoblast proliferation and viability under oxidative stress conditions and decreased the production of reactive oxygen species. Furthermore, NRF2 overexpression inhibited C2C12 cell differentiation by down-regulating the expression of myogenic regulatory factors (MRFs) and muscle-specific microRNAs. We also showed that NRF2 is indispensable for the viability of mSCs since the lack of its transcriptional activity caused high mortality of cells cultured in vitro under normoxic conditions. Concomitantly, Nfe2l2^tKO mSCs grown and differentiated under hypoxic conditions were viable and much more differentiated compared to cells isolated from wild-type mice. Taken together, NRF2 significantly influences the properties of myoblasts and muscle satellite cells. This effect might be modulated by the muscle microenvironment.

The role of muscle-specific MicroRNAs in patients with chronic obstructive pulmonary disease and skeletal muscle dysfunction

Skeletal muscle dysfunction is a systematic manifestation of chronic obstructive pulmonary disease (COPD), which is manifested through the changes in the respiratory and peripheral muscle fiber types, reducing muscle strength and endurance, and muscle atrophy. Muscle dysfunction limits the daily mobility, negatively affects the quality of life, and may increase the patient’s risk of mortality. MicroRNAs (miRNAs) as the regulators of gene expression, plays an important role in modulating skeletal muscle dysfunction in COPD by regulating skeletal muscle development (proliferation, differentiation), protein synthesis and degradation, inflammatory response, and metabolism. In particular, muscle-specific miRNAs (myomiRs) may play an important role in this process, although the different expression levels of myomiRs in COPD and skeletal muscle dysfunction and the mechanisms underlying their role remain unclear. In this paper, we review the differential expression of the myomiRs in COPD to identify myomiRs that play a role in skeletal muscle dysfunction in COPD. We further explore their possible mechanisms and action in order to provide new ideas for the prevention and treatment of the skeletal muscle dysfunction in COPD.

Connexins and Glucose Metabolism in Cancer

Connexins are a family of transmembrane proteins that regulate diverse cellular functions. Originally characterized for their ability to mediate direct intercellular communication through the formation of highly regulated membrane channels, their functions have been extended to the exchange of molecules with the extracellular environment, and the ability to modulate numerous channel-independent effects on processes such as motility and survival. Notably, connexins have been implicated in cancer biology for their context-dependent roles that can both promote or suppress cancer cell function. Moreover, connexins are able to mediate many aspects of cellular metabolism including the intercellular coupling of nutrients and signaling molecules. During cancer progression, changes to substrate utilization occur to support energy production and biomass accumulation. This results in metabolic plasticity that promotes cell survival and proliferation, and can impact therapeutic resistance. Significant progress has been made in our understanding of connexin and cancer biology, however, delineating the roles these multi-faceted proteins play in metabolic adaptation of cancer cells is just beginning. Glucose represents a major carbon substrate for energy production, nucleotide synthesis, carbohydrate modifications and generation of biosynthetic intermediates. While cancer cells often exhibit a dependence on glycolytic metabolism for survival, cellular reprogramming of metabolic pathways is common when blood perfusion is limited in growing tumors. These metabolic changes drive aggressive phenotypes through the acquisition of functional traits. Connections between glucose metabolism and connexin function in cancer cells and the surrounding stroma are now apparent, however much remains to be discovered regarding these relationships. This review discusses the existing evidence in this area and highlights directions for continued investigation.

LncRNA SENCR overexpression attenuated the proliferation, migration and phenotypic switching of vascular smooth muscle cells in aortic dissection via the miR-206/myocardin axis

BACKGROUND AND AIMS

Smooth muscle and endothelial cell-enriched migration/differentiation-associated lncRNA (SENCR) has been reported to be associated with some cardiovascular diseases; however, its function and exact molecular mechanism in aortic dissection (AD) remain undefined. Thus, we investigated the effects of SENCR on AD and its potential mechanisms.

METHODS AND RESULTS

SENCR expression in aortic media specimens from AD patients was detected by quantitative real-time PCR (qPCR). The roles of SENCR in vascular smooth muscle cell (VMSC) proliferation and migration as well as in the regulation of contractile phenotype genes were studied using CCK-8, wound healing, Transwell, qPCR and Western blot assays. Dual-luciferase reporter assays were performed to identify the regulatory correlation between SENCR, miR-206 and myocardin. Furthermore, mouse AD models were constructed with ApoE^-/- mice, and the effect of upregulated SENCR on phenotypic switching in the AD model was detected using hematoxylin and eosin (H&E) staining and immunohistochemistry (IHC) assays. SENCR overexpression inhibited VSMC proliferation, migration and synthetic phenotype-related gene expression; decreased miR-206 expression; increased myocardin expression; and suppressed rupture of the aortic media in mice. SENCR knockdown had the opposite effects. Our results further suggested that miR-206 upregulation could reverse the inhibitory roles of SENCR upregulation and that myocardin upregulation could restore the function of SENCR upregulation in VSMCs. Dual-luciferase reporter assays confirmed that SENCR regulated miR-206, which directly targeted myocardin in VSMCs.

CONCLUSION

SENCR overexpression suppressed VMSC proliferation and migration, maintained the contractile phenotype and suppressed aortic dilatation via the miR-206/myocardin axis.

Pleomorphic adenoma gene 1 (PLAG1) promotes proliferation and inhibits apoptosis of bovine primary myoblasts through the PI3K-Akt signaling pathway

Pleomorphic adenoma gene 1 (PLAG1) is a transcription factor involved in various cellular processes in organismal growth and development. However, its role in muscle function is unclear. This work investigated the roles of PLAG1 in muscle development and explored its regulatory mechanisms. The PLAG1 was proved to promote the proliferation of bovine primary myoblasts using the cell counting kit 8 (CCK-8) assay (P < 0.001), 5-ethynyl-2'-deoxyuridine (EdU) proliferation assay (P = 0.005), quantitative real-time polymerase chain reaction (qRT-PCR) (P = 0.028), western blot, and flow cytometry (P < 0.05), and to inhibit apoptosis of bovine primary myoblasts using qRT-PCR (P = 0.038), western blot, and flow cytometry (P < 0.001). Chromatin immunoprecipitation sequencing (ChIP-seq) and western blot showed PLAG1 upregulated phosphorylated (p)-PI3K, PI3K, p-Akt, Akt, Cyclin D1, and CDK2 and inhibited the expression of p21 and p27 to enhance myoblast proliferation, and increased expression of Bcl-2, and Bcl-xL to inhibit apoptosis. Additionally, PLAG1 was identified as a target of miR-1 using dual-luciferase assay (P < 0.001), qRT-PCR (P < 0.001), and western blot. Furthermore, miR-1 might be a potential mediator of the positive feedback regulation relationship between PLAG1 and the PI3K-Akt signaling pathway.

Circular RNA ACTA1 Acts as a Sponge for miR-199a-5p and miR-433 to Regulate Bovine Myoblast Development through the MAP3K11/MAP2K7/JNK Pathway

Circular RNAs (circRNAs) are a special class of noncoding RNA molecules that regulate many different biological processes. Myogenesis, a complex process, is primarily regulated by myogenic regulatory factors (MRFs) and various noncoding RNAs. However, the functions and regulatory mechanisms of circRNAs in myoblast development are unclear. In this study, we analyzed circRNA sequencing data of bovine myocyte tissues and identified circACTA1. Functional assays showed that circACTA1 could inhibit bovine myocyte proliferation and promote cell apoptosis and cytodifferentiation. In addition, circACTA1 could promote muscle repair in vivo. Mechanistically, luciferase assay and RNA immunoprecipitation were used to examine the interaction between circACTA1, miR-199a-5p, miR-433, and the target genes MAP3K11 and MAPK8. Meanwhile, we found that miR-199a-5p and miR-433 could suppress the expression of MAP3K11 and MAPK8, respectively. However, circACTA1 could mitigate this effect and activate the JNK signaling pathway. In conclusion, our results suggest that circACTA1 regulates the multiplication, apoptosis, and cytodifferentiation of bovine myocytes by competitively combining with miR-199a-5p and miR-433 to activate the mitogen-activated protein kinase kinase kinase 11 (MAP3K11)/mitogen-activated protein kinase kinase 7 (MAP2K7)/JNK signaling pathway.

miRNA transcriptome and myofiber characteristics of lamb skeletal muscle during hypertrophic growth1

Postnatal muscle growth is achieved through hypertrophy of the muscle fibers and is impacted by the activity of satellite cells, the quiescent muscle stem cell. Several miRNAs are preferentially expressed in skeletal muscle and could provide a mechanism for increasing muscle hypertrophy through satellite cell proliferation and/or differentiation. The objectives of this study were to: 1) Characterize the miRNA transcriptome of the longissimus thoracis et lumborum muscle at several developmental timepoints [gestational d 85 (PN1), 110 (PN2), 133 (PN3), postnatal d 42 (PW1), 65 (PW2), 243 (MAT)] during muscle hypertrophy in lambs, and 2) examine miR-29a, identified in sequencing to be differentially regulated across development, loss of function on satellite cell proliferation and differentiation. Muscle fiber characteristics showed drastic increases (p < 0.0001) in fiber size and alterations in muscle fiber type occur during pre and postnatal development. miRNA sequencing comparisons were performed in developmental order (PN1 vs. PN2, PN2 vs. PN3, PN3 vs. PW1, PW1 vs. PW2, PW2 vs. MAT). There were 184 differentially expressed (P _adj < 0.05) miRNA, 142 unique miRNA, from all 5 comparisons made. The transitional stage (PN3 vs. PW1) had the largest number (115) of differentially expressed miRNA. Inhibition of miR-29a in satellite cell culture increased (p < 0.05) cell proliferation and differentiation capacity. Characterization of the miRNA transcriptome provides valuable insights into the miRNA involved in muscle fiber hypertrophy and the potential importance of the transitional period.

Circular RNA circUSP13 sponges miR-29c to promote differentiation and inhibit apoptosis of goat myoblasts by targeting IGF1

Circular RNAs (circRNAs) are an indispensable element of post-transcriptional gene regulation, influencing a variety of biological processes including myogenic differentiation; however, little is known about the function of circRNA in goat myogenic differentiation. Using RNA-sequencing data from our laboratory, we explored the influences of circUSP13, as a candidate circRNA, on myoblast differentiation since its expression is higher in myoblasts of lamb (first day of age) than that of the fetus (75th day of pregnancy). In in vitro experiments, circUSP13 significantly promoted differentiation and inhibited apoptosis in goat primary myoblasts. Mechanistically, circUSP13 localized with miR-29c in the cytoplasm of goat myoblasts to regulate IGF1 expression. We further demonstrated that circUSP13 sponges miR-29c, promoting IGF1 expression that upregulated the expression of MyoG and MyHC. Thus, our results identified circUSP13 as a molecular marker for breeding programs of mutton production, as well as the circUSP13-miR-29c-IGF1 axis as a potential therapeutic target for combating muscle wasting.

Age-Related Exosomal and Endogenous Expression Patterns of miR-1, miR-133a, miR-133b, and miR-206 in Skeletal Muscles

Skeletal muscle growth and maintenance depend on two tightly regulated processes, myogenesis and muscle regeneration. Both processes involve a series of crucial regulatory molecules including muscle-specific microRNAs, known as myomiRs. We recently showed that four myomiRs, miR-1, miR-133a, miR-133b, and miR-206, are encapsulated within muscle-derived exosomes and participate in local skeletal muscle communication. Although these four myomiRs have been extensively studied for their function in muscles, no information exists regarding their endogenous and exosomal levels across age. Here we aimed to identify any age-related changes in the endogenous and muscle-derived exosomal myomiR levels during acute skeletal muscle growth. The four endogenous and muscle-derived myomiRs were investigated in five skeletal muscles (extensor digitorum longus, soleus, tibialis anterior, gastrocnemius, and quadriceps) of 2-week–1-year-old wild-type male mice. The expression of miR-1, miR-133a, and miR-133b was found to increase rapidly until adolescence in all skeletal muscles, whereas during adulthood it remained relatively stable. By contrast, endogenous miR-206 levels were observed to decrease with age in all muscles, except for soleus. Differential expression of the four myomiRs is also inversely reflected on the production of two protein targets; serum response factor and connexin 43. Muscle-derived exosomal miR-1, miR-133a, and miR-133b levels were found to increase until the early adolescence, before reaching a plateau phase. Soleus was found to be the only skeletal muscle to release exosomes enriched in miR-206. In this study, we showed for the first time an in-depth longitudinal analysis of the endogenous and exosomal levels of the four myomiRs during skeletal muscle development. We showed that the endogenous expression and extracellular secretion of the four myomiRs are associated to the function and size of skeletal muscles as the mice age. Overall, our findings provide new insights for the myomiRs’ significant role in the first year of life in mice.

The role of connexins in breast cancer: from misregulated cell communication to aberrant intracellular signaling

In spite of clinical advancements and improved diagnostic techniques, breast cancers are the leading cause of cancer-associated deaths in women worldwide. Although 70% of early breast cancers can be cured, there are no efficient therapies against metastatic breast cancers. Several factors including connexins and gap junctions play roles in breast tumorigenesis. Connexins are critical for cellular processes as a linkage between connexin mutations and hereditary disorders demonstrated their importance for tissue homeostasis. Further, alterations in their expression, localization and channel activities were observed in many cancers including breast cancer. Both channel-dependent and independent functions of connexins were reported in initiation and progression of cancers. Unlike initial reports suggesting tumor suppressor functions, connexins and gap junctions have stage, context and isoform dependent effects in breast cancers similar to other cancers. In this review, we tried to describe the current understanding of connexins in tumorigenesis specifically in breast cancers.

MicroRNAs as monitoring markers for right-sided heart failure and congestive hepatopathy

The last decades showed a worrying increase in the evolution of cardiovascular diseases towards different stages of heart failure (HF), as a stigma of the western lifestyle. MicroRNAs (miRNAs), non-coding RNAs, which are approximately 22-nucleotide long, were shown to regulate gene expression at the post-transcriptional level and play a role in the pathogenesis and progression of HF. miRNAs research is of high interest nowadays, as these molecules display mechanisms of action that can influence the course of evolution of common chronic diseases, including HF. The potential of post-transcriptional regulation by miRNAs concerning the diagnosis, management, and therapy for HF represents a new promising approach in the accurate assessment of cardiovascular diseases. This review aims to assess the current knowledge of miRNAs in cardiovascular diseases, especially right-sided heart failure and hepatomegaly. Moreover, attention is focused on their role as potential molecular biomarkers and more promising aspects involving miRNAs as future therapeutic targets in the pathophysiology of HF.

The mechanism by which noncoding RNAs regulate muscle wasting in cancer cachexia

Cancer cachexia (CC) is a complex metabolic syndrome that accelerates muscle wasting and affects up to 80% of patients with cancer; however, timely diagnostic methods and effective cures are lacking. Although a considerable number of studies have focused on the mechanism of CC-induced muscle atrophy, few novel therapies have been applied in the last decade. In recent years, noncoding RNAs (ncRNAs) have attracted great attention as many differentially expressed ncRNAs in cancer cachectic muscles have been reported to participate in the inhibition of myogenesis and activation of proteolysis. In addition, extracellular vesicles (EVs), which function as ncRNA carriers in intercellular communication, are closely involved in changing ncRNA expression profiles in muscle and promoting the development of muscle wasting; thus, EV-related ncRNAs may represent potential therapeutic targets. This review comprehensively describes the process of ncRNA transmission through EVs and summarizes the pathways and targets of ncRNAs that lead to CC-induced muscle atrophy.

MiRNAs and Muscle Regeneration: Therapeutic Targets in Duchenne Muscular Dystrophy

microRNAs (miRNAs) are small non-coding RNAs required for the post-transcriptional control of gene expression. MicroRNAs play a critical role in modulating muscle regeneration and stem cell behavior. Muscle regeneration is affected in muscular dystrophies, and a critical point for the development of effective strategies for treating muscle disorders is optimizing approaches to target muscle stem cells in order to increase the ability to regenerate lost tissue. Within this framework, miRNAs are emerging as implicated in muscle stem cell response in neuromuscular disorders and new methodologies to regulate the expression of key microRNAs are coming up. In this review, we summarize recent advances highlighting the potential of miRNAs to be used in conjunction with gene replacement therapies, in order to improve muscle regeneration in the context of Duchenne Muscular Dystrophy (DMD).

Mycobacterial infection-induced miR-206 inhibits protective neutrophil recruitment via the CXCL12/CXCR4 signalling axis

Pathogenic mycobacteria actively dysregulate protective host immune signalling pathways during infection to drive the formation of permissive granuloma microenvironments. Dynamic regulation of host microRNA (miRNA) expression is a conserved feature of mycobacterial infections across host-pathogen pairings. Here we examine the role of miR-206 in the zebrafish model of Mycobacterium marinum infection, which allows investigation of the early stages of granuloma formation. We find miR-206 is upregulated following infection by pathogenic M. marinum and that antagomir-mediated knockdown of miR-206 is protective against infection. We observed striking upregulation of cxcl12a and cxcr4b in infected miR-206 knockdown zebrafish embryos and live imaging revealed enhanced recruitment of neutrophils to sites of infection. We used CRISPR/Cas9-mediated knockdown of cxcl12a and cxcr4b expression and AMD3100 inhibition of Cxcr4 to show that the enhanced neutrophil response and reduced bacterial burden caused by miR-206 knockdown was dependent on the Cxcl12/Cxcr4 signalling axis. Together, our data illustrate a pathway through which pathogenic mycobacteria induce host miR-206 expression to suppress Cxcl12/Cxcr4 signalling and prevent protective neutrophil recruitment to granulomas.

Circular RNA circ_0057558 Controls Prostate Cancer Cell Proliferation Through Regulating miR-206/USP33/c-Myc Axis

We previously reported the elevated expression of circ_0057558 in prostate cancer tissues and cell lines. Here, we aimed to determine the biological function of circ_0057558 in prostate cancer. In the current study, circ_0057558 knockdown in prostate cancer cells significantly repressed cell proliferation and colony formation, but promoted cell arrest and enhanced the sensitivity to docetaxel. Bioinformatics analysis prediction and RNA-pull down assay identified miR-206 as the potential binding miRNA of circ_0057558. A negative correlation was observed between the expression of miR-206 and circ_0057558 in prostate cancer tissues. miR-206 mimics rescued the function of circ_0057558 overexpression on prostate cancer cells. Further, the bioinformatics analysis and luciferase assay suggested that miR-206 may target ubiquitin-specific peptidase 33 (USP33). USP33 mRNA expression has negative correlation with miR-206 expression and positive correlation with circ_0057558 expression in prostate cancer tissues. USP33 overexpression partially blocked the effects of miR-206 mimics on prostate cell proliferation. USP33 could bind and deubiquitinate c-Myc. Increased c-Myc protein by circ_0057558 overexpression was partially reversed by miR-206 mimics. The proliferation inhibition activity of MYC inhibitor 361 (MYCi361) was more prominent in primary prostate cancer cells and patient-derived xenograft (PDX) model with higher level of circ_0057558. Collectively, circ_0057558 gives an impetus to cell proliferation and cell cycle control in prostate cancer cell lines by sponging miR-206 and positively regulating the transcription of the miR-206 target gene USP33.

The Role of miRNA-7 in the Biology of Cancer and Modulation of Drug Resistance

MicroRNAs (miRNAs, miRs) are small non-coding RNA (ncRNA) molecules capable of regulating post-transcriptional gene expression. Imbalances in the miRNA network have been associated with the development of many pathological conditions and diseases, including cancer. Recently, miRNAs have also been linked to the phenomenon of multidrug resistance (MDR). MiR-7 is one of the extensively studied miRNAs and its role in cancer progression and MDR modulation has been highlighted. MiR-7 is engaged in multiple cellular pathways and acts as a tumor suppressor in the majority of human neoplasia. Its depletion limits the effectiveness of anti-cancer therapies, while its restoration sensitizes cells to the administered drugs. Therefore, miR-7 might be considered as a potential adjuvant agent, which can increase the efficiency of standard chemotherapeutics.

Deciphering the miRNA transcriptome of breast muscle from the embryonic to post-hatching periods in chickens

Background

miRNAs play critical roles in growth and development. Various studies of chicken muscle development have focused on identifying miRNAs that are important for embryo or adult muscle development. However, little is known about the role of miRNAs in the whole muscle development process from embryonic to post-hatching periods. Here, we present a comprehensive investigation of miRNA transcriptomes at 12-day embryo (E12), E17, and day 1 (D1), D14, D56 and D98 post-hatching stages.

Results

We identified 337 differentially expressed miRNAs (DE-miRNAs) during muscle development. A Short Time-Series Expression Miner analysis identified two significantly different expression profiles. Profile 4 with downregulated pattern contained 106 DE-miRNAs, while profile 21 with upregulated pattern contained 44 DE-miRNAs. The DE-miRNAs with the upregulated pattern mainly played regulatory roles in cellular turnover, such as pyrimidine metabolism, DNA replication, and cell cycle, whereas DE-miRNAs with the downregulated pattern directly or indirectly contributed to protein turnover metabolism such as glycolysis/gluconeogenesis, pyruvate metabolism and biosynthesis of amino acids.

Conclusions

The main functional miRNAs during chicken muscle development differ between embryonic and post-hatching stages. miRNAs with an upregulated pattern were mainly involved in cellular turnover, while miRNAs with a downregulated pattern mainly played a regulatory role in protein turnover metabolism. These findings enrich information about the regulatory mechanisms involved in muscle development at the miRNA expression level, and provide several candidates for future studies concerning miRNA-target function in regulation of chicken muscle development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07374-y.

MiR-455-5p monitors myotube morphogenesis by targeting mylip

As a posttranscriptional regulatory factor, microRNA (miRNA) plays an important role in the formation of myotubes. However, little is known about the mechanism of miRNA regulating myotube morphogenesis. Here, we aimed to characterize the function of miR-455-5p in myotube morphogenesis by inducing differentiation in C2C12 myoblasts containing murine Mylip fragments with the miR-455-5p target sequence. We found that miR-455-5p overexpression promoted the differentiation and hypertrophy of myotubes, while miR-455-5p inhibition led to the failure of myotube differentiation and formation of short myotubes. Furthermore, we demonstrated that miR-455-5p directly targeted the Mylip 3'-untranslated region, which plays a key role in monitoring myotube morphogenesis. Interestingly, the expression and function of Mylip were opposite to those of miR-455-5p during myogenesis. Our data uncovered novel miR-455-5p targets and established a functional link between Mylip and myotube morphogenesis. Understanding the involvement of Mylip in myotube morphogenesis provides insight into the function of the gene regulatory network.

Post-Transcriptional Regulation in Skeletal Muscle Development, Repair, and Disease

Skeletal muscle formation is a complex process that requires tight spatiotemporal control of key myogenic factors. Emerging evidence suggests that RNA processing is crucial for the regulation of these factors, and that multiple post-transcriptional regulatory pathways work dependently and independently of one another to enable precise control of transcripts throughout muscle development and repair. Moreover, disruption of these pathways is implicated in neuromuscular disease, and the recent development of RNA-mediated therapies shows enormous promise in the treatment of these disorders. We discuss the overlapping post-transcriptional regulatory pathways that mediate muscle development, how these pathways are disrupted in neuromuscular disorders, and advances in RNA-mediated therapies that present a novel approach to the treatment of these diseases.

Role of microRNAs in myogenesis and their effects on meat quality in pig - A review

The demand for food is increasing day by day because of the increasing global population. Therefore, meat, the easiest and largely available source of protein, needs to be produced in large amounts with good quality. The pork industry is a significant shareholder in fulfilling the global meat demands. Notably, myogenesis- development of muscles during embryogenesis- is a complex mechanism which culminates in meat production. But the molecular mechanisms which govern the myogenesis are less known. The involvement of miRNAs in myogenesis and meat quality, which depends on factors such as myofiber composition and intramuscular fat contents which determine the meat color, flavor, juiciness, and water holding capacity, are being extrapolated to increase both the quantity and quality of pork. Various kinds of microRNAs (miRNAs), miR-1, miR-21, miR22, miR-27, miR-34, miR-127, miR-133, miR-143, miR-155, miR-199, miR-206, miR-208, miR-378, and miR-432 play important roles in pig skeletal muscle development. Further, the quality of meat also depends upon myofiber which is developed through the expression of different kinds of miRNAs at different stages. This review will focus on the mechanism of myogenesis, the role of miRNAs in myogenesis, and meat quality with a focus on the pig.

MiR-543 regulates myoblast proliferation and differentiation of C2C12 cells by targeting KLF6

MicroRNA-543 (miR-543) has been found to play a suppressive role in various human cancers in many studies, whereas the specific functions of miR-543 in muscle development remain poorly understood. Here, we found that the expression of miR-543 was high in skeletal muscle and increased during the differentiation of C2C12 cells. Overexpression of miR-543 repressed C2C12 cell proliferation and promoted differentiation, while knockdown of miR-543 expression produced the opposite results. During myogenesis, we predicted and verified that Krüppel-like factor 6 (KLF6), a suppressor of multiple tumor cells, was a target gene of miR-543. Then, miR-543 was found to specifically target KLF6 and repress its expression. Besides this, knockdown of KLF6 promoted the differentiation but inhibited the proliferation of C2C12 cells. Si-KLF6 can rescue the influence of miR-543 inhibitor on C2C12 cell differentiation. Our results indicate a new regulatory mechanism of miR-543 on KLF6 expression and suggest the possibility of using the miR-543/KLF6 pathway as a potential target for studying myogenesis.

Tiny Regulators of Massive Tissue: MicroRNAs in Skeletal Muscle Development, Myopathies, and Cancer Cachexia

Skeletal muscles are the largest tissues in our body and the physiological function of muscle is essential to every aspect of life. The regulation of development, homeostasis, and metabolism is critical for the proper functioning of skeletal muscle. Consequently, understanding the processes involved in the regulation of myogenesis is of great interest. Non-coding RNAs especially microRNAs (miRNAs) are important regulators of gene expression and function. MiRNAs are small (~22 nucleotides long) noncoding RNAs known to negatively regulate target gene expression post-transcriptionally and are abundantly expressed in skeletal muscle. Gain- and loss-of function studies have revealed important roles of this class of small molecules in muscle biology and disease. In this review, we summarize the latest research that explores the role of miRNAs in skeletal muscle development, gene expression, and function as well as in muscle disorders like sarcopenia and Duchenne muscular dystrophy (DMD). Continuing with the theme of the current review series, we also briefly discuss the role of miRNAs in cancer cachexia.

MiR-2014-5p and miR-1231-5p regulate muscle growth of Larimichthys crocea by targeting MSTN gene

MicroRNAs (miRNAs) play an important role in regulating gene expression, and myostatin (MSTN) has been widely recognized as a key gene for muscle growth and development. Through high-throughput sequencing to study the effects of starvation on miRNA transcriptomes in Larimichthys crocea muscle tissue, we found that the expression of miR-2014, miR-1231 and miR-1470 were significantly different between fasting and normal feeding Larimichthys crocea. Bioinformatics analysis predicted that miR-2014, miR-1231 and miR-1470 target MSTN mRNA 3'UTR. To verify the accuracy of predictions, we constructed double luciferase plasmids containing MSTN 3'UTR and confirmed that miR-2014-5p and miR-1231-5p can inhibit MSTN expression by targeting MSTN 3'UTR using double luciferase experiments, while miR-1470 is not involved in regulation. Subsequent site-directed mutation experiments reflected the specificity of the target sequence. In addition, quantitative PCR experiments revealed that miR-2014-5p and miR-1231-5p may participate in the regulation of MSTN expression in fasting and refeeding period, respectively. These results implied that miRNA may take part in muscle growth regulation during starvation. It provides some insights into the molecular regulation mechanism of MSTN in response to starvation stress in fish.

Chikungunya virus replication in skeletal muscle cells is required for disease development

Chikungunya virus (CHIKV) is an arbovirus capable of causing a severe and often debilitating rheumatic syndrome in humans. CHIKV replicates in a wide variety of cell types in mammals, which has made attributing pathologic outcomes to replication at specific sites difficult. To assess the contribution of CHIKV replication in skeletal muscle cells to pathogenesis, we engineered a CHIKV strain exhibiting restricted replication in these cells via incorporation of target sequences for skeletal muscle cell-specific miR-206. This virus, which we term SKE, displayed diminished replication in skeletal muscle cells in a mouse model of CHIKV disease. Mice infected with SKE developed less severe disease signs, including diminished swelling in the inoculated foot and less necrosis and inflammation in the interosseous muscles. SKE infection was associated with diminished infiltration of T cells into the interosseous muscle as well as decreased production of Il1b, Il6, Ip10, and Tnfa transcripts. Importantly, blockade of the IL-6 receptor led to diminished swelling of a control CHIKV strain capable of replication in skeletal muscle, reducing swelling to levels observed in mice infected with SKE. These data implicate replication in skeletal muscle cells and release of IL-6 as important mediators of CHIKV disease.

Targeting gap junctional intercellular communication by hepatocarcinogenic compounds

Gap junctions in liver, as in other organs, play a critical role in tissue homeostasis. Inherently, these cellular constituents are major targets for systemic toxicity and diseases, including cancer. This review provides an overview of chemicals that compromise liver gap junctions, in particular biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. The focus in this review is placed upon the mechanistic scenarios that underlie these adverse effects. Further, the potential use of gap junctional activity as an in vitro biomarker to identify non-genotoxic hepatocarcinogenic chemicals is discussed.

MicroRNA-127-3p regulates myoblast proliferation by targeting Sept7

OBJECTIVE

MicroRNAs (miRNAs) are highly conserved, endogenous small RNAs that regulate gene expression at the post-transcriptional level. miR-127 plays an essential role in myogenic differentiation in vivo and in vitro. However, it is not clear whether miR-127-3p affects myogenic cell proliferation.

METHODS

The detailed function of miR-127-3p in proliferative C2C12 cell lines and further identified its regulatory mechanism by qRT-PCR, western blot, flow cytometry analysis and luciferase reporter assay.

RESULTS

Overexpression of miR-127-3p significantly inhibited proliferation of C2C12 cells and vice versa. Sept7 was a target gene of miR-127-3p using dual-luciferase reporter assay, qRT-PCR, and western blotting. The RNA interference analysis, in which Sept7 was downregulated, showed that Sept7 significantly promoted the proliferation of C2C12 cells. Besides, the expression level of Sept7 was detected analysis in muscle cells and tissues.

CONCLUSIONS

These findings reveal that miR-127-3p regulates myoblast proliferation by targeting Sept7.

Myofibers deficient in connexins 43 and 45 expression protect mice from skeletal muscle and systemic dysfunction promoted by a dysferlin mutation

Dysferlinopathy is a genetic human disease caused by mutations in the gene that encodes the dysferlin protein (DYSF). Dysferlin is believed to play a relevant role in cell membrane repair. However, in dysferlin-deficient (blAJ) mice (a model of dysferlinopathies) the recovery of the membrane resealing function by means of the expression of a mini-dysferlin does not arrest progressive muscular damage, suggesting the participation of other unknown pathogenic mechanisms. Here, we show that proteins called connexins 39, 43 and 45 (Cx39, Cx43 and Cx45, respectively) are expressed by blAJ myofibers and form functional hemichannels (Cx HCs) in the sarcolemma. At rest, Cx HCs increased the sarcolemma permeability to small molecules and the intracellular Ca²⁺ signal. In addition, skeletal muscles of blAJ mice showed lipid accumulation and lack of dysferlin immunoreactivity. As sign of extensive damage and atrophy, muscles of blAJ mice presented elevated numbers of myofibers with internal nuclei, increased number of myofibers with reduced cross-sectional area and elevated creatine kinase activity in serum. In agreement with the extense muscle damage, mice also showed significantly low motor performance. We generated blAJ mice with myofibers deficient in Cx43 and Cx45 expression and found that all above muscle and systemic alterations were absent, indicating that these two Cxs play a critical role in a novel pathogenic mechanism of dysfernolophaties, which is discussed herein. Therefore, Cx HCs could constitute an attractive target for pharmacologic treatment of dyferlinopathies.

miR-206 family is important for mitochondrial and muscle function, but not essential for myogenesis in vitro

miR-206, miR-1a-1, and miR-1a-2 are induced during differentiation of skeletal myoblasts and promote myogenesis in vitro. miR-206 is required for skeletal muscle regeneration in vivo. Although this miRNA family is hypothesized to play an essential role in differentiation, a triple knock-out (tKO) of the three genes has not been done to test this hypothesis. We report that tKO C2C12 myoblasts generated using CRISPR/Cas9 method differentiate despite the expected derepression of the miRNA targets. Surprisingly, their mitochondrial function is diminished. tKO mice demonstrate partial embryonic lethality, most likely due to the role of miR-1a in cardiac muscle differentiation. Two tKO mice survive and grow normally to adulthood with smaller myofiber diameter, diminished physical performance, and an increase in PAX7 positive satellite cells. Thus, unlike other miRNAs important in other differentiation pathways, the miR-206 family is not absolutely essential for myogenesis and is instead a modulator of optimal differentiation of skeletal myoblasts.

miR-206 knockout shows it is critical for myogenesis and directly regulates newly identified target mRNAs

The muscle specific miRNA, miR-206, is important for the process of myogenesis; however, studying the function of miR-206 in muscle development and differentiation still proves challenging because the complement of mRNA targets it regulates remains undefined. In addition, miR-206 shares close sequence similarity to miR-1, another muscle specific miRNA, making it hard to study the impact of miR-206 alone in cell culture models. Here we used CRISPR/Cas9 technology to knockout miR-206 in C2C12 muscle cells. We show that knocking out miR-206 significantly impairs and delays differentiation and myotube formation, revealing that miR-206 alone is important for myogenesis. In addition, we use an experimental affinity purification technique to identify new mRNA targets of miR-206 in C2C12 cells. We identified over one hundred mRNAs as putative miR-206 targets. Functional experiments on six of these targets indicate that Adam19, Bgn, Cbx5, Smarce1, and Spg20 are direct miR-206 targets in C2C12 cells. Our data show a unique and important role for miR-206 in myogenesis.

Active acetylcholine receptors prevent the atrophy of skeletal muscles and favor reinnervation

Denervation of skeletal muscles induces severe muscle atrophy, which is preceded by cellular alterations such as increased plasma membrane permeability, reduced resting membrane potential and accelerated protein catabolism. The factors that induce these changes remain unknown. Conversely, functional recovery following denervation depends on successful reinnervation. Here, we show that activation of nicotinic acetylcholine receptors (nAChRs) by quantal release of acetylcholine (ACh) from motoneurons is sufficient to prevent changes induced by denervation. Using in vitro assays, ACh and non-hydrolysable ACh analogs repressed the expression of connexin43 and connexin45 hemichannels, which promote muscle atrophy. In co-culture studies, connexin43/45 hemichannel knockout or knockdown increased innervation of muscle fibers by dorsal root ganglion neurons. Our results show that ACh released by motoneurons exerts a hitherto unknown function independent of myofiber contraction. nAChRs and connexin hemichannels are potential molecular targets for therapeutic intervention in a variety of pathological conditions with reduced synaptic neuromuscular transmission.

Denervation of muscle fibres induces muscle atrophy, via mechanisms that remain unclear. Here, the authors show that binding of acetylcoline to its receptor at the neuromuscular junction represses the expression of connexins 43 and 45, which promote atrophy, and is sufficient to prevent denervation-induced loss of myofibre mass.

Deciphering the miRNA transcriptome of Rongchang pig longissimus dorsi at weaning and slaughter time points

MicroRNA (miRNA) is essential for the process of gene posttranscriptional regulation in skeletal muscle of many species, such as mice, cattle and so on. However, a little number of miRNAs have been reported in the muscle development of Chinese native pig breeds. In this study, the longissimus dorsi transcripts of Chinese native Rongchang pig at weaning and slaughter time points were analysed for miRNA-seq. The results showed that 19 novel and 186 known miRNAs involved in the Rongchang pig skeletal muscle development were identified. Based on these findings, we further confirmed that porcine miR-127, miR-299 and miR-432-5p were obviously down-expressed in adult pig (287 days of age), while miR-7134-3p and 664-5p were significantly up-expressed in weaning pig (35 days of age). In other words, these miRNAs could be the potential molecular markers and play vital roles in the muscle development process. Moreover, we found miR-127 could inhibit the proliferation and myogenesis of porcine satellite cells in longissimus dorsi muscle. Our findings will provide deep insight into miRNA function for pork quality research with Chinese indigenous pig breeds.

Circulating MicroRNAs in Duchenne Muscular Dystrophy

OBJECTIVE

The diagnosis of Duchenne Muscular Dystrophy (DMD) currently depends on non-specific measures such as Creatine kinase (CK) levels. MicroRNAs (miRNAs) are a class of small, endogenous RNAs of 21-25 nucleotides, that are important regulators for numerous physiological and pathological processes. The aim of the current study is to assess the potential of miRNAs as non-invasive biomarker for the diagnosis of DMD and for identifying carriers.

PATIENTS AND METHODS

Thirty healthy subjects and 29 families with one member diagnosed with DMD were enrolled in the study. Peripheral blood samples were collected from all subjects where microRNAs were extracted from plasma followed by the quantification of miR-499, miR-103a-3p, miR-103a-5p, miR-206, miR-208a, miR-223 and miR-191-5p. MLPA and NGS were carried out as a gold standard technique to identify the mutations in the participants.

RESULTS

Our data revealed that miR-499 was significantly upregulated in all DMD patients, and true carriers (mothers), while 78 % of potential carriers (sisters) exhibited high levels of this miRNA. Similarly, miR-103a-3p showed an increase in the patients' families although to a lesser extent. On the other hand, miR-206 and miR-191-5p were significantly downregulated in the majority of the DMD patients and the tested female family members. MicroRNA miR-103a-5p and miR-208a followed a comparable trend in patients and mothers.

CONCLUSIONS

Ourresults suggest that the plasma levels of miRNAs have the capability to diagnose DMD patients and more importantly, miRNAs can be used to identify female carriers.

MicroRNA-206 regulates cell proliferation by targeting G6PD in skeletal muscle

Skeletal muscle is a major component of body mass and plays a central role in the control of whole-body metabolism in humans and animals. Therefore, elucidation of the underlying mechanisms of skeletal growth and development are expected to lead to the discovery of novel genes and pathways related to muscle disease. miR-206, a skeletal muscle-specific microRNA, plays a crucial role in myogenesis; however, miR-206 is known to function in myogenic differentiation, whether or not it affects muscle cells' proliferation, and the underlying mechanisms are unknown. In this study, we investigated the effect of miR-206 on muscle cell proliferation and differentiation, as well as its effect on myofiber type conversion using mouse C2C12 myoblasts. The results showed that overexpression of miR-206 inhibited cell proliferation and promoted muscle cell differentiation, but it did not affect myofiber type conversion. Intriguingly, we found that overexpression of miR-206 suppressed muscle cell proliferation and induced cell cycle arrest in G₀/G₁ phase by inhibiting the glucose-6-phosphate dehydrogenase (G6PD) gene. Taken together, we demonstrated that the miR-206-G6PD pathway suppresses muscle cell proliferation, and these findings may facilitate the treatment of muscle diseases.-Jiang, A., Dong, C., Li, B., Zhang, Z., Chen, Y., Ning, C., Wu, W., Liu, H. MicroRNA-206 regulates cell proliferation by targeting G6PD in skeletal muscle.

Long non-coding RNA MALAT1 functions as miR-1 sponge to regulate Connexin 43-mediated ossification of the posterior longitudinal ligament

Ossification of the posterior longitudinal ligament (OPLL) is the major cause for several deteriorate bone and joint diseases. Its development is a highly organized dynamic process as modulated by various physiological and pathophysiological factors. Both long non-coding RNAs (lncRNAs) and small non-coding RNAs (miRNAs) have been postulated to involve into almost all the biological conditions. Here, we applied high through-put transcriptome screening to unveil lncRNAs highly regulated under OPLL condition. siRNA assay in combination with western blot and quantitative PCR deciphered the lncRNA and miRNA functions in OPLL and their underlying mechanism. Here we identified an lncRNA, named Metastasis Associated Lung Adenocarcinoma Transcript 1 (MALAT1) engaged into the development of OPLL by indirectly targeting Connexin 43 (Cx43) gene. As previously reported, Cx43 is one of the main proteins contributing to OPLL partially through enhancing inflammatory signaling. On top of that, we provided another regulatory layer that MALAT1 served as the upstream effector governing the transcription of Cx43 gene. Perturbation of MALAT1 significantly inhibited Cx43 expression, inflammation, and osteogenesis. Mechanistically, in silico analysis and experimental validation both confirmed that microRNA-1 (miR-1) was the mediator connecting MALAT1-Cx43 axis: overexpression of miR-1 diminished Cx43 expression and OPLL process; meanwhile, MALAT1 acted as miR-1 sponge to inhibit its suppressive transcription effect on downstream ossification related genes. Knock-down of MALAT1 released sequestered miR-1, which repressed Cx43 expression and associated OPLL. Likewise, induced OPLL caused by overexpression of MALAT1 can be ameliorated by enhanced miR-1 function, knock-down of Cx43 or inhibition of inflammation. More importantly, further validation using patient ligament samples from non-OPLL and OPLL individuals identified MALAT1-miR-1-Cx43 regulatory axis. Collectively, we found a novel mechanism through lncRNA-miRNA interaction that provides more insights into understanding the development of OPLL.

Expression patterns of regulatory lncRNAs and miRNAs in muscular atrophy models induced by starvation in vitro and in vivo

Starvation or severe deprivation of nutrients, which is commonly seen in surgical patients, can result in catabolic changes in skeletal muscles, such as muscle atrophy. Therefore, it is important to elucidate the underlying molecular regulatory mechanisms during skeletal muscle atrophy. In the present study, muscular atrophy was induced by starvation and the results demonstrated that myosin heavy chain was decreased, whereas muscle RING finger protein 1 and atrogin-1 were increased, both in vitro and in vivo. The impact of starvation on the expression patterns of long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) was next determined. The expression patterns of miR-23a, miR-206 and miR-27b in the starved mice exhibited similar trends as those in starved C2C12 cells in vitro, whereas the expression patterns of six other miRNAs (miR-18a, miR-133a, miR-133b, miR-186, miR-1a and miR-29b) differed between the in vivo and the in vitro starvation models. The present study indicated that in vitro expression of the selected miRNAs was not completely consistent with that in vivo. By contrast, lncRNAs showed excellent consistency in their expression patterns in both the in vitro and in vivo starvation models; six of the lncRNAs (Atrolnc-1, long intergenic non-protein coding RNA of muscle differentiation 1, Myolinc, lncRNA myogenic differentiation 1, Dum and muscle anabolic regulator 1) were significantly elevated in starved tissues and cells, while lnc-mg was significantly decreased, compared with the control groups. Thus, lncRNAs involved in muscle atrophy have the potential to be developed as diagnostic tools.

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.

miR-1, miR-499 and miR-208 are sensitive markers to diagnose sudden death due to early acute myocardial infarction

MicroRNAs (miRNAs) are strongly up-regulated under pathological stress and in a wide range of diseases. In recent years, miRNAs are under investigation for their potential use as biomarkers in cardiovascular diseases. We investigate whether specific cardio-miRNAs are overexpressed in heart samples from subjects deceased for acute myocardial infarction (AMI) or sudden cardiac death (SCD), and whether miRNA could help differentiate between them. Forty four cases of death due to cardiovascular disease were selected, respectively, 19 cases categorized as AMI and 25 as SCD. Eighteen cases of traumatic death without pathological cardiac involvement were selected as control. Immunohistochemical investigation was performed for CD15, IL-15, Cx43, MCP-1, tryptase, troponin C and troponin I. Reverse transcription and quantitative real-time PCR were performed for miR-1, miR-133, miR-208 and miR-499. In AMI group, stronger immunoreaction for the CD15, IL-15 and MCP-1 antibodies was detectable compared with SCD and control. Cx43 showed a negative reaction with respect to the other groups. Real-time PCR results showed a down-regulation of all miRNAs in the AMI group compared with SCD and control. The selected miRNAs presented high accuracy in discriminating SCD from AMI (miR-1 and miR-499) and AMI from control (miR-208) representing a potential aid for both clinicians and pathologists for differential diagnosis.