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

The Severity of Muscle Performance Deterioration in Sarcopenia Correlates With Circulating Muscle Tissue-Specific miRNAs

Sarcopenia is defined as an age-associated loss of skeletal muscle function and muscle mass and is common in older adults. Sarcopenia as a disease is currently of interest not only to orthopedists and surgeons but also to internists, endocrinologists, rheumatologists, cardiologists, diabetologists, gynaecologists, geriatricians and paediatricians. In cooperation with the 5th Internal Medicine Clinic, we, as a unit of clinical research, aimed to describe a sarcopenic specific miRNA expression profile for disease diagnostics and classification of the severity of muscle performance deterioration. This study included a total of 80 patients (age 55-86 years) hospitalized at the V. Internal medicine clinic of LFUK and UNB with different severity of muscle performance deterioration. The study participants were evaluated and classified according to short physical performance battery score (SPPB). In this study, we investigated the role of circulating miRNAs in sarcopenia in the elderly. We hypothesized that sarcopenia effects the expression of muscle tissue-specific miRNAs (MyomiRNAs), which could be potentially reflected in the blood plasma miRNA expression profile. The expression of specific circulating miRNAs in patients with different muscle performances was analyzed. Patients’ blood plasma was evaluated for the expression of myomiRNAs: miRNA-29a, miRNA-29b, miRNA-1, miRNA-133a, miRNA-133b, miRNA-206, miRNA-208b and miRNA-499, and the data were correlated with diagnostic indicators of the disease. We showed a specific sarcopenia miRNA profile that could be considered a possible biomarker for the disease. Patients with low muscle performance showed increased miRNA-1, miRNA-29a and miRNA-29b expression and decreased for the miRNA-206, miRNA-133a, miRNA-133b, miRNA-208b and miRNA-499 expression. We show that the severity of muscle performance deterioration in sarcopenia correlates with specific miRNA expression. We also propose the profile of miRNAs expression in blood plasma as a specific biomarker for sarcopenia diagnostics. Future clinical studies will be necessary to eventually naturally have to elucidate the underlined molecular mechanism responsible for specific miRNAs expression in sarcopenia pathology and progression of the disease.

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 epigenetic landscape of exercise in cardiac health and disease

With the rising incidence of cardiovascular diseases, the concomitant mortality and morbidity impose huge burdens on quality of life and societal costs. It is generally accepted that physical inactivity is one of the major risk factors for cardiac disease and that exercise benefits the heart in both physiological and pathologic conditions. However, the molecular mechanisms governing the cardioprotective effects exerted by exercise remain incompletely understood. Most recently, an increasing number of studies indicate the involvement of epigenetic modifications in the promotion of cardiac health and prevention of cardiac disease. Exercise and other lifestyle factors extensively induce epigenetic modifications, including DNA/RNA methylation, histone post-translational modifications, and non-coding RNAs in multiple tissues, which may contribute to their positive effects in human health and diseases. In addition, several studies have shown that maternal or paternal exercise prevents age-associated or high-fat diet-induced metabolic dysfunction in the offspring, reinforcing the importance of epigenetics in mediating the beneficial effects of exercise. It has been shown that exercise can directly modify cardiac epigenetics to promote cardiac health and protect the heart against various pathological processes, or it can modify epigenetics in other tissues, which reduces the risk of cardiac disease and affords cardioprotection through exerkines. An in-depth understanding of the epigenetic landscape of cardioprotective response to exercise will provide new therapeutic targets for cardiac diseases. This review, therefore, aimed to acquaint the cardiac community with the rapidly advancing and evolving field of exercise and epigenetics.

The Severity of Muscle Performance Deterioration in Sarcopenia Correlates With Circulating Muscle Tissue-Specific miRNAs

Sarcopenia is defined as an age-associated loss of skeletal muscle function and muscle mass and is common in older adults. Sarcopenia as a disease is currently of interest not only to orthopedists and surgeons but also to internists, endocrinologists, rheumatologists, cardiologists, diabetologists, gynaecologists, geriatricians and paediatricians. In cooperation with the 5th Internal Medicine Clinic, we, as a unit of clinical research, aimed to describe a sarcopenic specific miRNA expression profile for disease diagnostics and classification of the severity of muscle performance deterioration. This study included a total of 80 patients (age 55-86 years) hospitalized at the V. Internal medicine clinic of LFUK and UNB with different severity of muscle performance deterioration. The study participants were evaluated and classified according to short physical performance battery score (SPPB). In this study, we investigated the role of circulating miRNAs in sarcopenia in the elderly. We hypothesized that sarcopenia effects the expression of muscle tissue-specific miRNAs (MyomiRNAs), which could be potentially reflected in the blood plasma miRNA expression profile. The expression of specific circulating miRNAs in patients with different muscle performances was analyzed. Patients' blood plasma was evaluated for the expression of myomiRNAs: miRNA-29a, miRNA-29b, miRNA-1, miRNA-133a, miRNA-133b, miRNA-206, miRNA-208b and miRNA-499, and the data were correlated with diagnostic indicators of the disease. We showed a specific sarcopenia miRNA profile that could be considered a possible biomarker for the disease. Patients with low muscle performance showed increased miRNA-1, miRNA-29a and miRNA-29b expression and decreased for the miRNA-206, miRNA-133a, miRNA-133b, miRNA-208b and miRNA-499 expression. We show that the severity of muscle performance deterioration in sarcopenia correlates with specific miRNA expression. We also propose the profile of miRNAs expression in blood plasma as a specific biomarker for sarcopenia diagnostics. Future clinical studies will be necessary to eventually naturally have to elucidate the underlined molecular mechanism responsible for specific miRNAs expression in sarcopenia pathology and progression of the disease.

Construction of a Porcine Skeletal Muscle-Specific Promoter by Inducing the Seed Region of miR-208a

Transgenic promoter systems are of great interest for their potential use in gene therapy or production due to their high activity, long term, and cell specificity. Here, in order to obtain promoters with high activity and expressed specifically in skeletal muscle, the MYOD1, MYF5, and MCK were selected as the candidate genes. The truncated promoters were amplified and their activity was verified through dual-luciferase reporter gene test. We used genetic engineering techniques to improve promoter activity by tandemly linking enhancers and promoters or two promoters. Furthermore, synthetic promoter was the most active when two eMCK enhancers and pMCK promoter were cascaded. To improve the tissue specificity of the promoter, the seed region of translational repressor miR-208a was inserted into the downstream of the promoter (pGL3-2eMCK-pMCK-T208-mCherry-EGFP). The results showed that the expression level of target genes decreased significantly (P < 0.05) in myocardium rather than in skeletal muscle. The results of in vivo transfection indicated that tandem transcriptional regulatory elements can increase promoter activity in mice. This work laid the foundation for future research on genetically modified pigs.

Analysis of inflammation-related microRNA expression in patients with ankylosing spondylitis

Ankylosing spondylitis (AS) is a complex genetic disease characterized by axial skeletal inflammation. Available scientific evidence suggests that a relationship may exist between miRNA expression levels and the pathogenesis of AS. This study investigated the clinical diagnostic value of miR-146a, miR-15a, miR-20a, miR-125a-3p, miR-125a-5p, miR-125b-5p, miR-148a, miR-149a, miR-499, and miR-155a in AS. A total of 44 AS patients and 56 healthy controls (HCs) were included in the study. MiRNA expression levels were detected using fluorescence quantitative PCR (qPCR). Results showed that the expression levels of miR-146a, miR-125a-3p, miR-125a-5p, miR-125b-5p, and miR-155a decreased, whereas miR-499a expression increased significantly in AS patients compared to that in the controls. Logistic regression analysis with receiver operating characteristic (ROC) curves showed that combined miR-146a/miR-125a-5p/miR-125b-5p/miR-499a/miR-155a (area under curve [AUC] = 0.824, 95% confidence interval [CI] = 0.727-0.921) had high sensitivity and specificity for AS diagnosis. C-reactive protein (CRP) levels were positively correlated with the expression of miR-125a-5p (r_s = 0.438, p = 0.005) and miR-155a (r_s = 0.414, p = 0.006), which indicates that miR-125a-5p and miR-155a can perhaps aggravate AS-induced inflammation. Our findings suggest the association of miR-125a-5p and miR-155a with disease activity in AS patients. Furthermore, miR-146a, miR-125a-5p, miR-125b-5p, miR-499a, and miR-155a could have potential diagnostic value in AS.

Therapeutic Implications of miRNAs for Muscle-Wasting Conditions

MicroRNAs (miRNAs) are small, non-coding RNA molecules that are mainly involved in translational repression by binding to specific messenger RNAs. Recently, miRNAs have emerged as biomarkers, relevant for a multitude of pathophysiological conditions, and cells can selectively sort miRNAs into extracellular vesicles for paracrine and endocrine effects. In the overall context of muscle-wasting conditions, a multitude of miRNAs has been implied as being responsible for the typical dysregulation of anabolic and catabolic pathways. In general, chronic muscle disorders are associated with the main characteristic of a substantial loss in muscle mass. Muscular dystrophies (MDs) are a group of genetic diseases that cause muscle weakness and degeneration. Typically, MDs are caused by mutations in those genes responsible for upholding the integrity of muscle structure and function. Recently, the dysregulation of miRNA levels in such pathological conditions has been reported. This revelation is imperative for both MDs and other muscle-wasting conditions, such as sarcopenia and cancer cachexia. The expression levels of miRNAs have immense potential for use as potential diagnostic, prognostic and therapeutic biomarkers. Understanding the role of miRNAs in muscle-wasting conditions may lead to the development of novel strategies for the improvement of patient management.

NcRNAs in Vascular and Valvular Intercellular Communication

Non-coding RNAs have been shown to be important biomarkers and mediators of many different disease entities, including cardiovascular (CV) diseases like atherosclerosis, aneurysms, and valvulopathies. Growing evidence suggests a central role of ncRNAs as regulators of different pathological pathways involved in endothelial dysfunction, cardiovascular inflammation, cell differentiation, and calcification. This review will discuss the role of protein-bound and extracellular vesicular-bound ncRNAs as biomarkers of vascular and valvular diseases, their role as intercellular communicators, and regulators of disease pathways and also highlights possible treatment strategies.

MicroRNAs based regulation of cytokine regulating immune expressed genes and their transcription factors in COVID-19

Background

Coronavirus disease 2019 is characterized by the elevation of a broad spectrum of inflammatory mediators associated with poor disease outcomes. We aimed at an in-silico analysis of regulatory microRNA and their transcription factors (TF) for these inflammatory genes that may help to devise potential therapeutic strategies in the future.

Methods

The cytokine regulating immune-expressed genes (CRIEG) were sorted from literature and the GEO microarray dataset. Their co-differentially expressed miRNA and transcription factors were predicted from publicly available databases. Enrichment analysis was done through mienturnet, MiEAA, Gene Ontology, and pathways predicted by KEGG and Reactome pathways. Finally, the functional and regulatory features were analyzed and visualized through Cytoscape.

Results

Sixteen CRIEG were observed to have a significant protein-protein interaction network. The ontological analysis revealed significantly enriched pathways for biological processes, molecular functions, and cellular components. The search performed in the miRNA database yielded ten miRNAs that are significantly involved in regulating these genes and their transcription factors.

Conclusion

An in-silico representation of a network involving miRNAs, CRIEGs, and TF, which take part in the inflammatory response in COVID-19, has been elucidated. Thus, these regulatory factors may have potentially critical roles in the inflammatory response in COVID-19 and may be explored further to develop targeted therapeutic strategies and mechanistic validation.

Analysis of potential regulatory LncRNAs and CircRNAs in the oxidative myofiber and glycolytic myofiber of chickens

SART and PMM are mainly composed of oxidative myofibers and glycolytic myofibers, respectively, and myofiber types profoundly influence postnatal muscle growth and meat quality. SART and PMM are composed of lncRNAs and circRNAs that participate in myofiber type regulation. To elucidate the regulatory mechanism of myofiber type, lncRNA and circRNA sequencing was used to systematically compare the transcriptomes of the SART and PMM of Chinese female Qingyuan partridge chickens at their marketing age. The luminance value (L*), redness value (a*), average diameter, cross-sectional area, and density difference between the PMM and SART were significant (p < 0.05). ATPase staining results showed that PMMs were all darkly stained and belonged to the glycolytic type, and the proportion of oxidative myofibers in SART was 81.7%. A total of 5 420 lncRNAs were identified, of which 365 were differentially expressed in the SART compared with the PMM (p < 0.05). The cis-regulatory analysis identified target genes that were enriched for specific GO terms and KEGG pathways (p < 0.05), including striated muscle cell differentiation, regulation of cell proliferation, regulation of muscle cell differentiation, myoblast differentiation, regulation of myoblast differentiation, and MAPK signaling pathway. Pathways and coexpression network analyses suggested that XR_003077811.1, XR_003072304.1, XR_001465942.2, XR_001465741.2, XR_001470487.1, XR_003077673.1 and XR_003074785.1 played important roles in regulating oxidative myofibers by TBX3, QKI, MYBPC1, CALM2, and PPARGC1A expression. A total of 10 487 circRNAs were identified, of which 305 circRNAs were differentially expressed in the SART compared with the PMM (p < 0.05). Functional enrichment analysis showed that differentially expressed circRNAs were involved in host gene expression and were enriched in the AMPK, calcium signaling pathway, FoxO signaling pathway, p53 signaling pathway, and cellular senescence. Novel_circ_004282 and novel_circ_002121 played important roles in regulating oxidative myofibers by PPP3CA and NFATC1 expression. Using lncRNA-miRNA/circRNA-miRNA integrated analysis, we identified many candidate interaction networks that might affect muscle fiber performance. Important lncRNA-miRNA-mRNA networks, such as lncRNA-XR_003074785.1/miR-193-3p/PPARGC1A, regulate oxidative myofibers. This study reveals that lncXR_003077811.1, lncXR_003072304.1, lncXR_001465942.2, lncXR_001465741.2, lncXR_001470487.1, lncXR_003077673.1, XR_003074785.1, novel_circ_004282 and novel_circ_002121 might regulate oxidative myofibers. The lncRNA-XR_003074785.1/miR-193-3p/PPARGC1A pathway might regulate oxidative myofibers. All these findings provide rich resources for further in-depth research on the regulatory mechanism of lncRNAs and circRNAs in myofibers.

A multiplexed ion-exchange membrane-based miRNA (MIX·miR) detection platform for rapid diagnosis of myocardial infarction

Micro RNAs (miRNAs) have shown great potential as rapid and discriminating biomarkers for acute myocardial infarction (AMI) diagnosis. We have developed a multiplexed ion-exchange membrane-based miRNA (MIX·miR) preconcentration/sensing amplification-free platform for quantifying in parallel a panel of miRNAs, including miR-1, miR-208b, and miR-499, from the same plasma samples from: 1) reference subjects with no evident coronary artery disease (NCAD); 2) subjects with stable coronary artery disease (CAD); and 3) subjects experiencing ST-elevation myocardial infarction (STEMI) prior to (STEMI-pre) and following (STEMI-PCI) percutaneous coronary intervention. The picomolar limit of detection from raw plasma and 3-decade dynamic range of MIX·miR permits detection of the miRNA panel in untreated samples from disease patients and its precise standard curve, provided by large 0.1 to 1 V signals and eliminates individual sensor calibration. The use of molecular concentration feature reduces the assay time to less than 30 minutes and increases the detection sensitivity by bringing all targets close to the sensors. miR-1 was low for NCAD patients but more than one order of magnitude above the normal value for all samples from three categories (CAD, STEMI-pre, and STEMI-PCI) of patients with CAD. In fact, miR-1 expression levels of stable CAD, STEMI-pre and STEMI-PCI are each more than 10-fold higher than the previous class, in that order, well above the 95% confidence level of MIX·miR. Its overexpression estimate is significantly higher than the PCR benchmark. This suggests that, in contrast to protein biomarkers of myocardial injury, miR-1 appears to differentiate ischemia from both reperfusion injury and non-AMI CAD patients. The battery-operated MIX·miR can be a portable and low-cost AMI diagnostic device, particularly useful in settings where cardiac catheterization is not readily available to determine the status of coronary reperfusion.

Regulation of the Expression of the Myosin Heavy Chain (MYH) Gene myh14 in Zebrafish Development

The human sarcomeric myosin heavy chain gene MYH14 contains an intronic microRNA, miR-499. Our previous studies demonstrated divergent genomic organization and expression patterns of myh14/miR-499 among teleosts; however, the regulatory mechanism is partly known. In this study, we report the regulation of myh14 expression in zebrafish, Danio rerio. Zebrafish myh14 has three paralogs, myh14-1, myh14-2, and myh14-3. Detailed promoter analysis suggested that a 5710-bp 5'-flanking region of myh14-1 and a 5641-bp region of myh14-3 contain a necessary regulatory region to recapitulate specific expression during embryonic development. The 5'-flanking region of zebrafish myh14-1 and its torafugu ortholog shared two distal and a single proximal conserved region. The two distal conserved regions had no effect on zebrafish myh14-1 expression, in contrast to torafugu expression, suggesting an alternative regulatory mechanism among the myh14 orthologs. Comparison among the 5'-flanking regions of the myh14 paralogs revealed two conserved regions. Deletion of these conserved regions significantly reduced the promoter activity of myh14-3 but had no effect on myh14-1, indicating different cis-regulatory mechanisms of myh14 paralogs. Loss of function of miR-499 resulted in a marked reduction in slow muscle fibers in embryonic development. Our study identified different cis-regulatory mechanisms controlling the expression of myh14/miR-499 and an indispensable role of miR-499 in muscle fiber-type specification in zebrafish.

In vitro CSC-derived cardiomyocytes exhibit the typical microRNA-mRNA blueprint of endogenous cardiomyocytes

miRNAs modulate cardiomyocyte specification by targeting mRNAs of cell cycle regulators and acting in cardiac muscle lineage gene regulatory loops. It is unknown if or to-what-extent these miRNA/mRNA networks are operative during cardiomyocyte differentiation of adult cardiac stem/progenitor cells (CSCs). Clonally-derived mouse CSCs differentiated into contracting cardiomyocytes in vitro (iCMs). Comparison of "CSCs vs. iCMs" mRNome and microRNome showed a balanced up-regulation of CM-related mRNAs together with a down-regulation of cell cycle and DNA replication mRNAs. The down-regulation of cell cycle genes and the up-regulation of the mature myofilament genes in iCMs reached intermediate levels between those of fetal and neonatal cardiomyocytes. Cardiomyo-miRs were up-regulated in iCMs. The specific networks of miRNA/mRNAs operative in iCMs closely resembled those of adult CMs (aCMs). miR-1 and miR-499 enhanced myogenic commitment toward terminal differentiation of iCMs. In conclusions, CSC specification/differentiation into contracting iCMs follows known cardiomyo-MiR-dependent developmental cardiomyocyte differentiation trajectories and iCMs transcriptome/miRNome resembles that of CMs.

MyoData: An expression knowledgebase at single cell/nucleus level for the discovery of coding-noncoding RNA functional interactions in skeletal muscle

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Regulation of gene expression through non-coding RNAs at single myofiber and nucleus resolution.

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Reinterpretation of KEGG pathways with microRNA and long non-coding RNA activities.

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miR-149, -214, and let-7e alter mitochondrial shape.

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The long non-coding RNA Pvt1 is a sponge for miR-27a.

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miR-208b regulates Sox6; miR-214 regulates both Sox6 and Slc16a3.

Non-coding RNAs represent the largest part of transcribed mammalian genomes and prevalently exert regulatory functions. Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) can modulate the activity of each other. Skeletal muscle is the most abundant tissue in mammals. It is composed of different cell types with myofibers that represent the smallest complete contractile system. Considering that lncRNAs and miRNAs are more cell type-specific than coding RNAs, to understand their function it is imperative to evaluate their expression and action within single myofibers. In this database, we collected gene expression data for coding and non-coding genes in single myofibers and used them to produce interaction networks based on expression correlations. Since biological pathways are more informative than networks based on gene expression correlation, to understand how altered genes participate in the studied phenotype, we integrated KEGG pathways with miRNAs and lncRNAs. The database also integrates single nucleus gene expression data on skeletal muscle in different patho-physiological conditions. We demonstrated that these networks can serve as a framework from which to dissect new miRNA and lncRNA functions to experimentally validate. Some interactions included in the database have been previously experimentally validated using high throughput methods. These can be the basis for further functional studies. Using database information, we demonstrate the involvement of miR-149, -214 and let-7e in mitochondria shaping; the ability of the lncRNA Pvt1 to mitigate the action of miR-27a via sponging; and the regulatory activity of miR-214 on Sox6 and Slc16a3. The MyoData is available at https://myodata.bio.unipd.it.

Non-Coding RNAs in COVID-19: Emerging Insights and Current Questions

The highly infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged as the causative agent of coronavirus disease 2019 (COVID-19) in late 2019, igniting an unprecedented pandemic. A mechanistic picture characterising the acute immunopathological disease in severe COVID-19 is developing. Non-coding RNAs (ncRNAs) constitute the transcribed but un-translated portion of the genome and, until recent decades, have been undiscovered or overlooked. A growing body of research continues to demonstrate their interconnected involvement in the immune response to SARS-CoV-2 and COVID-19 development by regulating several of its pathological hallmarks: cytokine storm syndrome, haemostatic alterations, immune cell recruitment, and vascular dysregulation. There is also keen interest in exploring the possibility of host-virus RNA-RNA and RNA-RBP interactions. Here, we discuss and evaluate evidence demonstrating the involvement of short and long ncRNAs in COVID-19 and use this information to propose hypotheses for future mechanistic and clinical studies.

Acetoacetate promotes muscle cell proliferation via the miR-133b/SRF axis through the Mek-Erk-MEF2 pathway

Acetoacetate (AA) is an important ketone body that is used as an oxidative fuel to supply energy for the cellular activities of various tissues, including the brain and skeletal muscle. We recently revealed a new signaling role for AA by showing that it promotes muscle cell proliferation in vitro, enhances muscle regeneration in vivo, and ameliorates the dystrophic muscle phenotype of Mdx mice. In this study, we provide new molecular insight into this function of AA. We show that AA promotes C2C12 cell proliferation by transcriptionally upregulating the expression of muscle-specific miR-133b, which in turn stimulates muscle cell proliferation by targeting serum response factor. Furthermore, we show that the AA-induced upregulation of miR-133b is transcriptionally mediated by MEF2 via the Mek-Erk1/2 signaling pathway. Mechanistically, our findings provide further convincing evidence that AA acts as signaling metabolite to actively regulate various cellular activities in mammalian cells.

Nonproductive Splicing Prevents Expression of MYH7b Protein in the Mammalian Heart

Background

Although the roles of alpha‐myosin heavy chain (α‐MyHC) and beta‐myosin heavy chain (β‐MyHC) proteins in cardiac contractility have long been appreciated, the biological contribution of another closely related sarcomeric myosin family member, MYH7b (myosin heavy chain 7b), has become a matter of debate. In mammals, MYH7b mRNA is transcribed but undergoes non‐productive alternative splicing that prevents protein expression in a tissue‐specific manner, including in the heart. However, several studies have recently linked MYH7b variants to different cardiomyopathies or have reported MYH7b protein expression in mammalian hearts.

Methods and Results

By analyzing mammalian cardiac transcriptome and proteome data, we show that the vast majority of MYH7b RNA is subject to exon skipping and cannot be translated into a functional myosin molecule. Notably, we discovered a lag in the removal of introns flanking the alternatively spliced exon, which could retain the non‐coding RNA in the nucleus. This process could play a significant role in controlling MYH7b expression as well as the activity of other cardiac genes. Consistent with the negligible level of full‐length protein coding mRNA, no MYH7b protein expression was detected in adult mouse, rat, and human hearts by Western blot analysis. Furthermore, proteome surveys including quantitative mass spectrometry analyses revealed only traces of cardiac MYH7b protein and even then, only in a subset of individual samples.

Conclusions

The comprehensive analysis presented here suggests that previous studies showing cardiac MYH7b protein expression were likely attributable to antibody cross‐reactivity. More importantly, our data predict that the MYH7b disease‐associated variants may operate through the alternately spliced RNA itself.

Emerging roles of microRNA-208a in cardiology and reverse cardio-oncology

Cardiovascular diseases (CVDs) and cancer, which are the leading causes of mortality globally, have been viewed as two distinct diseases. However, the fact that cancer and CVDs may coincide has been noted by cardiologists when taking care of patients with CVDs caused by cancer chemotherapy; this entity is designated cardio-oncology. More recently, patients with CVDs have also been found to have increased risk of cancers, termed reverse cardio-oncology. Although reverse cardio-oncology has been highlighted as an important disease state in recent studies, how the diseased heart affects cancer and the potential mediators of the crosstalk between CVDs and cancer are largely unknown. Here, we focus on the roles of cardiac-specific microRNA-208a (miR-208a) in cardiac and cancer biology and explore its essential roles in reverse cardio-oncology. Accumulating evidence has shown that within the heart, increased miR-208a promotes myocardial injury, arrhythmia, cardiac remodeling, and dysfunction and that secreted miR-208a in the circulation may have novel roles in promoting tumor proliferation and invasion. This review, therefore, provides insights into the novel roles of miR-208a in reverse cardio-oncology and strategies to prevent secondary carcinogenesis in patients with early- or late-stage heart failure.

Promising Role of Growth Hormone-Boosting Peptide in Regulating the Expression of Muscle-Specific Genes and Related MicroRNAs in Broiler Chickens

Appropriate skeletal muscle development in poultry is positively related to increasing its meat production. Synthetic peptides with growth hormone-boosting properties can intensify the effects of endogenous growth hormones. However, their effects on the mRNA and miRNA expression profiles that control muscle development post-hatching in broiler chicks is unclear. Thus, we evaluated the possible effects of synthetic growth hormone-boosting peptide (GHBP) inclusion on a chicken's growth rate, skeletal muscle development-related genes and myomiRs, serum biochemical parameters, and myofiber characteristics. A total of 400 one-day-old broiler chicks were divided into four groups supplied with GHBP at the levels of 0, 100, 200 and 300 μg/kg for 7 days post-hatching. The results showed that the highest levels of serum IGF-1 and GH at d 20 and d 38 post-hatching were found in the 200 μg/kg GHBP group. Targeted gene expression analysis in skeletal muscle revealed that the GHBP effect was more prominent at d 20 post-hatching. The maximum muscle development in the 200 μg/kg GHBP group was fostered by the upregulation of IGF-1, mTOR, myoD, and myogenin and the downregulation of myostatin and the Pax-3 and -7 genes compared to the control group. In parallel, muscle-specific myomiR analysis described upregulation of miR-27b and miR-499 and down-regulation of miR-1a, miR-133a, miR-133b, and miR-206 in both the 200 and 300 μg/kg GHBP groups. This was reflected in the weight gain of birds, which was increased by 17.3 and 11.2% in the 200 and 300 μg/kg GHBP groups, respectively, when compared with the control group. Moreover, the maximum improvement in the feed conversion ratio was achieved in the 200 μg/kg GHBP group. The myogenic effects of GHBP were also confirmed via studying myofiber characteristics, wherein the largest myofiber sizes and areas were achieved in the 200 μg/kg GHBP group. Overall, our findings indicated that administration of 200 μg/kg GHBP for broiler chicks could accelerate their muscle development by positively regulating muscle-specific mRNA and myomiR expression and reinforcing myofiber growth.

Muscle-derived exosomes encapsulate myomiRs and are involved in local skeletal muscle tissue communication

Exosomes are extracellular vesicles that are released from most cell types encapsulating specific molecular cargo. Exosomes serve as mediators of cell-to-cell and tissue-to-tissue communications under normal and pathological conditions. It has been shown that exosomes carrying muscle-specific miRNAs, myomiRs, are secreted from skeletal muscle cells in vitro and are elevated in the blood of muscle disease patients. The aim of this study was to investigate the secretion of exosomes encapsulating the four myomiRs from skeletal muscle tissues and to assess their role in inter-tissue communication between neighboring skeletal muscles in vivo. We demonstrate, for the first time, that isolated, intact skeletal muscle tissues secrete exosomes encapsulating the four myomiRs, miR-1, miR-133a, miR-133b, and miR-206. Notably, we show that the sorting of the four myomiRs within exosomes varies between skeletal muscles of different muscle fiber-type composition. miR-133a and miR-133b downregulation in TA muscles caused a reduction of their levels in neighboring skeletal muscles and in serum exosomes. In conclusion, our results reveal that skeletal muscle-derived exosomes encapsulate the four myomiRs, some of which enter the blood, while a portion is used for the local communication between proximal muscle tissues. These findings provide important evidence regarding novel pathways implicated in skeletal muscle function.

miR-208b Reduces the Expression of Kcnj5 in a Cardiomyocyte Cell Line

MicroRNAs (miRs) contribute to different aspects of cardiovascular pathology, among them cardiac hypertrophy and atrial fibrillation. Cardiac miR expression was analyzed in a mouse model with structural and electrical remodeling. Next-generation sequencing revealed that miR-208b-3p was ~25-fold upregulated. Therefore, the aim of our study was to evaluate the impact of miR-208b on cardiac protein expression. First, an undirected approach comparing whole RNA sequencing data to miR-walk 2.0 miR-208b 3'-UTR targets revealed 58 potential targets of miR-208b being regulated. We were able to show that miR-208b mimics bind to the 3' untranslated region (UTR) of voltage-gated calcium channel subunit alpha1 C and Kcnj5, two predicted targets of miR-208b. Additionally, we demonstrated that miR-208b mimics reduce GIRK1/4 channel-dependent thallium ion flux in HL-1 cells. In a second undirected approach we performed mass spectrometry to identify the potential targets of miR-208b. We identified 40 potential targets by comparison to miR-walk 2.0 3'-UTR, 5'-UTR and CDS targets. Among those targets, Rock2 and Ran were upregulated in Western blots of HL-1 cells by miR-208b mimics. In summary, miR-208b targets the mRNAs of proteins involved in the generation of cardiac excitation and propagation, as well as of proteins involved in RNA translocation (Ran) and cardiac hypertrophic response (Rock2).

Hypoxic Signaling in Skeletal Muscle Maintenance and Regeneration: A Systematic Review

In skeletal muscle tissue, oxygen (O₂) plays a pivotal role in both metabolism and the regulation of several intercellular pathways, which can modify proliferation, differentiation and survival of cells within the myogenic lineage. The concentration of oxygen in muscle tissue is reduced during embryogenesis and pathological conditions. Myogenic progenitor cells, namely satellite cells, are necessary for muscular regeneration in adults and are localized in a hypoxic microenvironment under the basal lamina, suggesting that the O₂ level could affect their function. This review presents the effects of reduced oxygen levels (hypoxia) on satellite cell survival, myoblast regeneration and differentiation in vertebrates. Further investigations and understanding of the pathways involved in adult muscle regeneration during hypoxic conditions are maybe clinically relevant to seek for novel drug treatments for patients with severe muscle damage. We especially outlined the effect of hypoxia-inducible factor 1-alpha (HIF1A), the most studied transcriptional regulator of cellular and developmental response to hypoxia, whose investigation has recently been awarded with the Nobel price.

Epigenetic Regulation of Autophagy in Cardiovascular Pathobiology

Cardiovascular diseases (CVDs) are the number one cause of debilitation and mortality worldwide, with a need for cost-effective therapeutics. Autophagy is a highly conserved catabolic recycling pathway triggered by various intra- or extracellular stimuli to play an essential role in development and pathologies, including CVDs. Accordingly, there is great interest in identifying mechanisms that govern autophagic regulation. Autophagic regulation is very complex and multifactorial that includes epigenetic pathways, such as histone modifications to regulate autophagy-related gene expression, decapping-associated mRNA degradation, microRNAs, and long non-coding RNAs; pathways are also known to play roles in CVDs. Molecular understanding of epigenetic-based pathways involved in autophagy and CVDs not only will enhance the understanding of CVDs, but may also provide novel therapeutic targets and biomarkers for CVDs.

MyomiRs and their multifaceted regulatory roles in muscle homeostasis and amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by loss of both upper and lower motor neurons (MNs). The main clinical features of ALS are motor function impairment, progressive muscle weakness, muscle atrophy and, ultimately, paralysis. Intrinsic skeletal muscle deterioration plays a crucial role in the disease and contributes to ALS progression. Currently, there are no effective treatments for ALS, highlighting the need to obtain a deeper understanding of the molecular events underlying degeneration of both MNs and muscle tissue, with the aim of developing successful therapies. Muscle tissue is enriched in a group of microRNAs called myomiRs, which are effective regulators of muscle homeostasis, plasticity and myogenesis in both physiological and pathological conditions. After providing an overview of ALS pathophysiology, with a focus on the role of skeletal muscle, we review the current literature on myomiR network dysregulation as a contributing factor to myogenic perturbations and muscle atrophy in ALS. We argue that, in view of their critical regulatory function at the interface between MNs and skeletal muscle fiber, myomiRs are worthy of further investigation as potential molecular targets of therapeutic strategies to improve ALS symptoms and counteract disease progression.

Circulating microRNAs after a 24-h ultramarathon run in relation to muscle damage markers in elite athletes

Ultra-endurance sports are growing in popularity but can be associated with adverse health effects, such as exercise-induced muscle damage (EIMD), which can lead to exertional rhabdomyolysis. Circulating microRNAs (miRNAs) may be useful to approach the degree of EIMD. We aimed to (1) investigate the relevance of circulating miRNAs as biomarkers of muscle damage and (2) examine the acute response of skeletal/cardiac muscle and kidney biomarkers to a 24-h run in elite athletes. Eleven elite athletes participated in the 24-h run World Championships. Counter-movement jump (CMJ), creatine kinase (CK), myoglobin (Mb), creatinine (Cr), high-sensitive cardiac troponin T (hs-cTnT), and muscle-specific miRNA (myomiR) levels were measured before, immediately after, and 24 and 48h after the race. CMJ height was reduced immediately after the race (-84.0 ± 25.2%, p < 0.001) and remained low at 24 h (-43.6 ± 20.4%, p = 0.002). We observed high CK activity (53 239 ± 63 608 U/L, p < 0.001) immediately after the race, and it remained elevated 24h after (p < 0.01). Circulating myomiR levels (miR-1-3p, miR-133a-3p, miR-133b, miR-208a-3p, miR-208b-3p, and miR-499a-5p) were elevated immediately after the 24-h run (fold changes: 18-124,723, p<0.001) and significantly (p < 0.05) correlated or tended to significantly (p < 0.07) correlate with the reduction in CMJ height at 24 h. We found no significant correlation between CMJ height loss at 24 h and CK (p = 0.23) or Mb (p = 0.41) values. All elite ultramarathon runners included in our study were diagnosed with exertional rhabdomyolysis after the 24-h ultramarathon race. MyomiR levels may be useful to approach the degree of muscle damage.

miRNA in cardiac development and regeneration

Ischemic heart disease is one of the main causes of morbidity and mortality in the world. In adult mammalian hearts, most cardiomyocytes are terminally differentiated and have extremely limited capacity of proliferation, making it impossible to regenerate the heart after injuries such as myocardial infarction. MicroRNAs (miRNAs), a class of non-coding single-stranded RNA, which are involved in mRNA silencing and the regulation of post-transcriptional gene expression, have been shown to play a crucial role in cardiac development and cardiomyocyte proliferation. Muscle specific miRNAs such as miR-1 are key regulators of cardiomyocyte maturation and growth, while miR-199-3p and other miRNAs display potent activity to induce proliferation of cardiomyocytes. Given their small size and relative pleiotropic effects, miRNAs have gained significant attraction as promising therapeutic targets or tools in cardiac regeneration. Increasing number of studies demonstrated that overexpression or inhibition of specific miRNAs could induce cardiomyocyte proliferation and cardiac regeneration. Some common targets of pro-proliferation miRNAs, such as the Hippo-Yap signaling pathway, were identified in multiple species, highlighting the power of miRNAs as probes to dissect core regulators of biological processes. A number of miRNAs have been shown to improve heart function after myocardial infarction in mice, and one trial in swine also demonstrated promising outcomes. However, technical difficulties, especially in delivery methods, and adverse effects, such as uncontrolled proliferation, remain. In this review, we summarize the recent progress in miRNA research in cardiac development and regeneration, examine the mechanisms of miRNA regulating cardiomyocyte proliferation, and discuss its potential as a new strategy for cardiac regeneration therapy.

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.

The Role of GSK-3β in the Regulation of Protein Turnover, Myosin Phenotype, and Oxidative Capacity in Skeletal Muscle under Disuse Conditions

Skeletal muscles, being one of the most abundant tissues in the body, are involved in many vital processes, such as locomotion, posture maintenance, respiration, glucose homeostasis, etc. Hence, the maintenance of skeletal muscle mass is crucial for overall health, prevention of various diseases, and contributes to an individual’s quality of life. Prolonged muscle inactivity/disuse (due to limb immobilization, mechanical ventilation, bedrest, spaceflight) represents one of the typical causes, leading to the loss of muscle mass and function. This disuse-induced muscle loss primarily results from repressed protein synthesis and increased proteolysis. Further, prolonged disuse results in slow-to-fast fiber-type transition, mitochondrial dysfunction and reduced oxidative capacity. Glycogen synthase kinase 3β (GSK-3β) is a key enzyme standing at the crossroads of various signaling pathways regulating a wide range of cellular processes. This review discusses various important roles of GSK-3β in the regulation of protein turnover, myosin phenotype, and oxidative capacity in skeletal muscles under disuse/unloading conditions and subsequent recovery. According to its vital functions, GSK-3β may represent a perspective therapeutic target in the treatment of muscle wasting induced by chronic disuse, aging, and a number of diseases.

Small-RNA Sequencing Reveals Altered Skeletal Muscle microRNAs and snoRNAs Signatures in Weanling Male Offspring from Mouse Dams Fed a Low Protein Diet during Lactation

Maternal diet during gestation and lactation affects the development of skeletal muscles in offspring and determines muscle health in later life. In this paper, we describe the association between maternal low protein diet-induced changes in offspring skeletal muscle and the differential expression (DE) of small non-coding RNAs (sncRNAs). We used a mouse model of maternal protein restriction, where dams were fed either a normal (N, 20%) or a low protein (L, 8%) diet during gestation and newborns were cross-fostered to N or L lactating dams, resulting in the generation of NN, NL and LN offspring groups. Total body and tibialis anterior (TA) weights were decreased in weanling NL male offspring but were not different in the LN group, as compared to NN. However, histological evaluation of TA muscle revealed reduced muscle fibre size in both groups at weaning. Small RNA-sequencing demonstrated DE of multiple miRs, snoRNAs and snRNAs. Bioinformatic analyses of miRs-15a, -34a, -122 and -199a, in combination with known myomiRs, confirmed their implication in key muscle-specific biological processes. This is the first comprehensive report for the DE of sncRNAs in nutrition-associated programming of skeletal muscle development, highlighting the need for further research to unravel the detailed molecular mechanisms.

The Impact of microRNAs in Renin-Angiotensin-System-Induced Cardiac Remodelling

Current knowledge on the renin-angiotensin system (RAS) indicates its central role in the pathogenesis of cardiovascular remodelling via both hemodynamic alterations and direct growth and the proliferation effects of angiotensin II or aldosterone resulting in the hypertrophy of cardiomyocytes, the proliferation of fibroblasts, and inflammatory immune cell activation. The noncoding regulatory microRNAs has recently emerged as a completely novel approach to the study of the RAS. A growing number of microRNAs serve as mediators and/or regulators of RAS-induced cardiac remodelling by directly targeting RAS enzymes, receptors, signalling molecules, or inhibitors of signalling pathways. Specifically, microRNAs that directly modulate pro-hypertrophic, pro-fibrotic and pro-inflammatory signalling initiated by angiotensin II receptor type 1 (AT1R) stimulation are of particular relevance in mediating the cardiovascular effects of the RAS. The aim of this review is to summarize the current knowledge in the field that is still in the early stage of preclinical investigation with occasionally conflicting reports. Understanding the big picture of microRNAs not only aids in the improved understanding of cardiac response to injury but also leads to better therapeutic strategies utilizing microRNAs as biomarkers, therapeutic agents and pharmacological targets.

Adipocyte, Immune Cells, and miRNA Crosstalk: A Novel Regulator of Metabolic Dysfunction and Obesity

Obesity is characterized as a complex and multifactorial excess accretion of adipose tissue (AT) accompanied with alterations in the immune response that affects virtually all age and socioeconomic groups around the globe. The abnormal accumulation of AT leads to several metabolic diseases, including nonalcoholic fatty liver disorder (NAFLD), low-grade inflammation, type 2 diabetes mellitus (T2DM), cardiovascular disorders (CVDs), and cancer. AT is an endocrine organ composed of adipocytes and immune cells, including B-Cells, T-cells and macrophages. These immune cells secrete various cytokines and chemokines and crosstalk with adipokines to maintain metabolic homeostasis and low-grade chronic inflammation. A novel form of adipokines, microRNA (miRs), is expressed in many developing peripheral tissues, including ATs, T-cells, and macrophages, and modulates the immune response. miRs are essential for insulin resistance, maintaining the tumor microenvironment, and obesity-associated inflammation (OAI). The abnormal regulation of AT, T-cells, and macrophage miRs may change the function of different organs including the pancreas, heart, liver, and skeletal muscle. Since obesity and inflammation are closely associated, the dysregulated expression of miRs in inflammatory adipocytes, T-cells, and macrophages suggest the importance of miRs in OAI. Therefore, in this review article, we have elaborated the role of miRs as epigenetic regulators affecting adipocyte differentiation, immune response, AT browning, adipogenesis, lipid metabolism, insulin resistance (IR), glucose homeostasis, obesity, and metabolic disorders. Further, we will discuss a set of altered miRs as novel biomarkers for metabolic disease progression and therapeutic targets for obesity.

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).

miRNA interplay: mechanisms and consequences in cancer

Canonically, microRNAs (miRNAs) control mRNA expression. However, studies have shown that miRNAs are also capable of targeting non-coding RNAs, including long non-coding RNAs and miRNAs. The latter, termed a miRNA:miRNA interaction, is a form of self-regulation. In this Review, we discuss the three main modes of miRNA:miRNA regulation: direct, indirect and global interactions, and their implications in cancer biology. We also discuss the cell-type-specific nature of miRNA:miRNA interactions, current experimental approaches and bioinformatic techniques, and how these strategies are not sufficient for the identification of novel miRNA:miRNA interactions. The self-regulation of miRNAs and their impact on gene regulation has yet to be fully understood. Investigating this hidden world of miRNA self-regulation will assist in discovering novel regulatory mechanisms associated with disease pathways.

Parsing the microRNA genetics basis regulating skeletal muscle fiber types and meat quality traits in pigs

Muscle fibers are closely related to human diseases and livestock meat quality. However, the genetics basis of microRNAs (miRNAs) in regulating muscle fibers is not completely understood. In this study, we constructed the whole genome-wide miRNA expression profiles of porcine fast-twitch muscle [biceps femoris (Bf)] and slow-twitch muscle [soleus (Sol)], and identified hundreds of miRNAs, including four skeletal muscle-highly expressed miRNAs, ssc-miR-378, ssc-let-7f, ssc-miR-26a, and ssc-miR-27b-3p. Moreover, we identified 63 differentially expressed (DE) miRNAs between biceps femoris vs. soleus, which are the key candidate miRNAs regulating the skeletal muscle fiber types. In addition, we found that the expression of DE ssc-miR-499-5p was significantly correlated to the expression of Myoglobin (r = 0.6872, P < 0.0001) and Myosin heavy chain 7 (MYH7; r = 0.5408, P = 0.0020), and pH_45 min (r = 0.3806, P = 0.0380) and glucose content (r = -0.4382, P = 0.0154); while the expression of DE ssc-miR-499-3p was significantly correlated to the expression of Myoglobin (r = 0.5340, P = 0.0024) and pH_45 min (r = 0.4857, P = 0.0065). Taken together, our data established a sound foundation for further studies on the regulatory mechanisms of miRNAs in skeletal muscle fiber conversion and meat quality traits in livestock, and could provide a genetic explanation of the role of miRNAs in human muscular diseases.

MicroRNA-129-5p inhibits C2C12 myogenesis and represses slow fiber gene expression in vitro

The miR-129 family is widely reported as tumor repressors, although their roles in skeletal muscle have not been fully investigated. Here, the function and mechanism of miR-129-5p in skeletal muscle, a member of the miR-129 family, were explored using C2C12 cell line. Our study showed that miR-129-5p was widely detected in mouse tissues, with the highest expression in skeletal muscle. Gain- and loss-of-function study showed that miR-129-5p could negatively regulate myogenic differentiation, indicated by reduced ratio of MyHC-positive myofibers and repressed expression of myogenic genes, such as MyoD, MyoG, and MyHC. Furthermore, miR-129-5p was more enriched in fast extensor digitorum longus (EDL) than in slow soleus (SOL). Enhanced miR-129-5p could significantly reduce the expression of mitochondrial cox family, together with that of MyHC I, and knockdown of miR-129-5p conversely increased the expression of cox genes and MyHC I. Mechanistically, miR-129-5p directly targeted the 3'-UTR of Mef2a, which was suppressed by miR-129-5p agomir at both mRNA and protein levels in C2C12 cells. Moreover, overexpression of Mef2a could rescue the inhibitory effects of miR-129-5p on the expression of myogenic factors and MyHC I. Collectively, our data revealed that miR-129-5p is a negative regulator of myogenic differentiation and slow fiber gene expression, thus affecting body metabolic homeostasis.

AMPK-dependent and -independent coordination of mitochondrial function and muscle fiber type by FNIP1

Mitochondria are essential for maintaining skeletal muscle metabolic homeostasis during adaptive response to a myriad of physiologic or pathophysiological stresses. The mechanisms by which mitochondrial function and contractile fiber type are concordantly regulated to ensure muscle function remain poorly understood. Evidence is emerging that the Folliculin interacting protein 1 (Fnip1) is involved in skeletal muscle fiber type specification, function, and disease. In this study, Fnip1 was specifically expressed in skeletal muscle in Fnip1-transgenic (Fnip1^Tg) mice. Fnip1^Tg mice were crossed with Fnip1-knockout (Fnip1^KO) mice to generate Fnip1^TgKO mice expressing Fnip1 only in skeletal muscle but not in other tissues. Our results indicate that, in addition to the known role in type I fiber program, FNIP1 exerts control upon muscle mitochondrial oxidative program through AMPK signaling. Indeed, basal levels of FNIP1 are sufficient to inhibit AMPK but not mTORC1 activity in skeletal muscle cells. Gain-of-function and loss-of-function strategies in mice, together with assessment of primary muscle cells, demonstrated that skeletal muscle mitochondrial program is suppressed via the inhibitory actions of FNIP1 on AMPK. Surprisingly, the FNIP1 actions on type I fiber program is independent of AMPK and its downstream PGC-1α. These studies provide a vital framework for understanding the intrinsic role of FNIP1 as a crucial factor in the concerted regulation of mitochondrial function and muscle fiber type that determine muscle fitness.

Mitochondria provide an essential source of energy to drive cellular processes and the function of mitochondria is particularly important in skeletal muscle, a metabolically demanding tissue that depends critically on mitochondria, accounting for ~40% of total body mass. In this study, we discovered an essential function of adaptor protein FNIP1 in the coordinated regulation of the mitochondrial and structural programs controlling muscle fitness. Using both gain-of-function and loss-of-function strategies in mice and muscle cells, we provide clear genetic data that demonstrate FNIP1-dependent signaling is crucial for muscle mitochondrial remodeling as well as type I muscle fiber specification. We also uncover that FNIP1 exerts control upon muscle mitochondrial program through AMPK but not mTORC1 signaling. Furthermore, we demonstrate that FNIP1 acts independently of PGC-1α to regulate fiber type specification. Hence, our study emphasizes FNIP1 as a dominant factor that coordinates mitochondrial and muscle fiber type programs that govern muscle fitness.

The Impact of Melatonin and NLRP3 Inflammasome on the Expression of microRNAs in Aged Muscle

Muscular aging is a complex process and underlying physiological mechanisms are not fully clear. In recent years, the participation of the NF-kB pathway and the NLRP3 inflammasome in the chronic inflammation process that accompanies the skeletal muscle's aging has been confirmed. microRNAs (miRs) form part of a gene regulatory machinery, and they control numerous biological processes including inflammatory pathways. In this work, we studied the expression of four miRs; three of them are considered as inflammatory-related miRs (miR-21, miR-146a, and miR-223), and miR-483, which is related to the regulation of melatonin synthesis, among other targets. To investigate the changes of miRs expression in muscle along aging, the impact of inflammation, and the role of melatonin in aged skeletal muscle, we used the gastrocnemius muscle of wild type (WT) and NLRP3-knockout (NLRP3^-) mice of 3, 12, and 24 months-old, with and without melatonin supplementation. The expression of miRs and pro-caspase-1, caspase-3, pro-IL-1β, bax, bcl-2, and p53, was investigated by qRT-PCR analysis. Histological examination of the gastrocnemius muscle was also done. The results showed that age increased the expression of miR-21 (p < 0.01), miR-146a, and miR-223 (p < 0.05, for both miRs) in WT mice, whereas the 24-months-old mutant mice revealed decline of miR-21 and miR-223 (p < 0.05), compared to WT age. The lack of NLRP3 inflammasome also improved the skeletal muscle fibers arrangement and reduced the collagen deposits compared with WT muscle during aging. For the first time, we showed that melatonin significantly reduced the expression of miR-21, miR-146a, and miR-223 (p < 0.05 for all ones, and p < 0.01 for miR-21 at 24 months old) in aged WT mice, increased miR-223 in NLRP3^- mice (p < 0.05), and induced miR-483 expression in both mice strains, this increase being significant at 24 months of age.

Purine-rich element binding protein B attenuates the coactivator function of myocardin by a novel molecular mechanism of smooth muscle gene repression

Myocardin is a potent transcriptional coactivator protein, which functions as the master regulator of vascular smooth muscle cell differentiation. The cofactor activity of myocardin is mediated by its physical interaction with serum response factor, a ubiquitously expressed transactivator that binds to CArG boxes in genes encoding smooth muscle-restricted proteins. Purine-rich element binding protein B (Purβ) represses the transcription of the smooth muscle α-actin gene (Acta2) in fibroblasts and smooth muscle cells by interacting with single-stranded DNA sequences flanking two 5' CArG boxes in the Acta2 promoter. In this study, the ability of Purβ to modulate the cofactor activity of myocardin was investigated using a combination of cellular and biochemical approaches. Results of smooth muscle gene promoter-reporter assays indicated that Purβ specifically inhibits the coactivator function of myocardin in a manner requiring the presence of all three single-stranded DNA binding domains in the Purβ homodimer. DNA binding analyses demonstrated that Purβ interacts with CArG-containing DNA elements with a much lower affinity compared to other purine-rich target sequences present in the Acta2 promoter. Co-immunoprecipitation and DNA pull-down assays revealed that Purβ associates with myocardin and serum response factor when free or bound to duplex DNA containing one or more CArG boxes. Functional analysis of engineered Purβ point mutants identified several amino acid residues essential for suppression of myocardin activity. Collectively, these findings suggest an inhibitory mechanism involving direct protein-protein interaction between the homodimeric Purβ repressor and the myocardin-serum response factor-CArG complex.

microRNA-mRNA Profile of Skeletal Muscle Differentiation and Relevance to Congenital Myotonic Dystrophy

microRNAs (miRNAs) regulate messenger RNA (mRNA) abundance and translation during key developmental processes including muscle differentiation. Assessment of miRNA targets can provide insight into muscle biology and gene expression profiles altered by disease. mRNA and miRNA libraries were generated from C2C12 myoblasts during differentiation, and predicted miRNA targets were identified based on presence of miRNA binding sites and reciprocal expression. Seventeen miRNAs were differentially expressed at all time intervals (comparing days 0, 2, and 5) of differentiation. mRNA targets of differentially expressed miRNAs were enriched for functions related to calcium signaling and sarcomere formation. To evaluate this relationship in a disease state, we evaluated the miRNAs differentially expressed in human congenital myotonic dystrophy (CMD) myoblasts and compared with normal control. Seventy-four miRNAs were differentially expressed during healthy human myocyte maturation, of which only 12 were also up- or downregulated in CMD patient cells. The 62 miRNAs that were only differentially expressed in healthy cells were compared with differentiating C2C12 cells. Eighteen of the 62 were conserved in mouse and up- or down-regulated during mouse myoblast differentiation, and their C2C12 targets were enriched for functions related to muscle differentiation and contraction.

Circulating cardiovascular microRNAs in critically ill COVID-19 patients

AIMS

Coronavirus disease 2019 (COVID-19) is a still growing pandemic, causing many deaths and socio-economic damage. Elevated expression of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry receptor angiotensin-converting enzyme 2 on cardiac cells of patients with heart diseases may be related to cardiovascular burden. We have thus analysed cardiovascular and inflammatory microRNAs (miRs), sensitive markers of cardiovascular damage, in critically ill, ventilated patients with COVID-19 or influenza-associated acute respiratory distress syndrome (Influenza-ARDS) admitted to the intensive care unit and healthy controls.

METHODS AND RESULTS

Circulating miRs (miR-21, miR-126, miR-155, miR-208a, and miR-499) were analysed in a discovery cohort consisting of patients with mechanically-ventilated COVID-19 (n = 18) and healthy controls (n = 15). A validation study was performed in an independent cohort of mechanically-ventilated COVID-19 patients (n = 20), Influenza-ARDS patients (n = 13) and healthy controls (n = 32). In both cohorts, RNA was isolated from serum and cardiovascular disease/inflammatory-relevant miR concentrations were measured by miR-specific TaqMan PCR analyses. In both the discovery and the validation cohort, serum concentration of miR-21, miR-155, miR-208a and miR-499 were significantly increased in COVID-19 patients compared to healthy controls. Calculating the area under the curve using receiver operating characteristic analysis miR-155, miR-208a and miR-499 showed a clear distinction between COVID-19 and Influenza-ARDS patients.

CONCLUSION

In this exploratory study, inflammation and cardiac myocyte-specific miRs were upregulated in critically ill COVID-19 patients. Importantly, miR profiles were able to differentiate between severely ill, mechanically-ventilated Influenza-ARDS and COVID-19 patients, indicating a rather specific response and cardiac involvement of COVID-19.

Centennial Review: Metabolic microRNA - shifting gears in the regulation of metabolic pathways in poultry

Over 20 yr ago, a small noncoding class of RNA termed microRNA (miRNA) that was able to recognize sequences in mRNAs and inhibit their translation was discovered in Caenorhabditis elegans. In the intervening years, miRNA have been discovered in most eukaryotes and are now known to regulate the majority of protein-coding genes. It has been discovered that disruption of miRNA function often leads to the development of pathological conditions. One physiological system under extensive miRNA-mediated regulation is metabolism. Metabolism is one of the most dynamic of biological networks within multiple organs, including the liver, muscle, and adipose tissue, working in concert to respond to ever-changing nutritional cues and energy demands. Therefore, it is not surprising that miRNA regulate virtually all aspects of eukaryotic metabolism and have been linked to metabolic disorders, such as obesity, fatty liver diseases, and diabetes, just to name a few. Chickens, and birds in general, face their own unique metabolic challenges, particularly after hatching, when their metabolism must completely transform from using lipid-rich yolk to carbohydrate-rich feed as fuel in a very short period of time. Furthermore, commercial poultry breeds have undergone extensive selection over the last century for more desirable production traits, which has resulted in numerous metabolic consequences. Here, we review the current knowledge of miRNA-mediated regulation of metabolic development and function in chickens.

A comparative analysis of heart microRNAs in vertebrates brings novel insights into the evolution of genetic regulatory networks

BACKGROUND

During vertebrate evolution, the heart has undergone remarkable changes that lead to morphophysiological differences in the fully formed heart of these species, such as chamber septation, heart rate frequency, blood pressure, and cardiac output volume. Despite these differences, the heart developmental process is guided by a core gene set conserved across vertebrates. Nonetheless, the regulatory mechanisms controlling the expression of genes involved in heart development and maintenance are largely uncharted. MicroRNAs (miRNAs) have been described as important regulatory elements in several biological processes, including heart biology. These small RNA molecules are broadly conserved in sequence and genomic context in metazoans. Mutations may occur in miRNAs and/or genes that contribute to the establishment of distinct repertoires of miRNA-target interactions, thereby favoring the differential control of gene expression and, consequently, the origin of novel phenotypes. In fact, several studies showed that miRNAs are integrated into genetic regulatory networks (GRNs) governing specific developmental programs and diseases. However, studies integrating miRNAs in vertebrate heart GRNs under an evolutionary perspective are still scarce.

RESULTS

We comprehensively examined and compared the heart miRNome of 20 species representatives of the five major vertebrate groups. We found 54 miRNA families with conserved expression and a variable number of miRNA families with group-specific expression in fishes, amphibians, reptiles, birds, and mammals. We also detected that conserved miRNAs present higher expression levels and a higher number of targets, whereas the group-specific miRNAs present lower expression levels and few targets.

CONCLUSIONS

Both the conserved and group-specific miRNAs can be considered modulators orchestrating the core and peripheral genes of heart GRNs of vertebrates, which can be related to the morphophysiological differences and similarities existing in the heart of distinct vertebrate groups. We propose a hypothesis to explain evolutionary differences in the putative functional roles of miRNAs in the heart GRNs analyzed. Furthermore, we present new insights into the molecular mechanisms that could be helping modulate the diversity of morphophysiology in the heart organ of vertebrate species.

Cyclic stretching boosts microRNA-499 to regulate Bcl-2 via microRNA-208a in atrial fibroblasts

MicroRNAs that modulate transcription can regulate other microRNAs and are also up-regulated under pathological stress. MicroRNA-499 (miR-499), microRNA-208a (miR-208a) and B-cell lymphoma 2 (Bcl-2) play roles in cardiovascular diseases, such as direct reprogramming of cardiac fibroblast into cardiomyocyte and cardiomyocyte apoptosis. Whether miR208a, miR499 and Bcl-2 were critical regulators in cardiac fibroblast apoptosis under mechanical stretching conditions in human cardiac fibroblasts-adult atrial (HCF-aa) was investigated. Using negative pressure, HCF-aa grown on a flexible membrane base were cyclically stretched to 20% of their maximum elongation. In adult rats, an aortocaval shunt was used to create an in vivo model of volume overload. MiR208a was up-regulated early by stretching and returned to normal levels with longer stretching cycles, whereas the expression of miR499 and Bcl-2 was up-regulated by longer stretching times. Pre-treatment with antagomir-499 reversed the miR-208a down-regulation, whereas Bcl-2 expression could be suppressed by miR-208a overexpression. In the HCF-aa under stretching for 1 h, miR-499 overexpression decreased pri-miR-208a luciferase activity; this inhibition of pri-miR-208a luciferase activity with stretching was reversed when the miR-499-5p binding site in pri-miR-208a was mutated. The addition of antagomir-208a reversed the Bcl-2-3'UTR suppression from stretching for 1 h. Flow cytometric analysis revealed that pre-treatment with miR-499 or antagomir-208a inhibited cellular apoptosis in stretched HCF-aa. In hearts with volume overload, miR-499 overexpression inhibited myocardial miR-208a expression, whereas Bcl-2 expression could be suppressed by the addition of miR-208a. In conclusion, miR-208a mediated the regulation of miR-499 on Bcl-2 expression in stretched HCF-aa and hearts with volume overload.

Histone methyltransferase MLL4 controls myofiber identity and muscle performance through MEF2 interaction

Skeletal muscle depends on the precise orchestration of contractile and metabolic gene expression programs to direct fiber-type specification and to ensure muscle performance. Exactly how such fiber type-specific patterns of gene expression are established and maintained remains unclear, however. Here, we demonstrate that histone monomethyl transferase MLL4 (KMT2D), an enhancer regulator enriched in slow myofibers, plays a critical role in controlling muscle fiber identity as well as muscle performance. Skeletal muscle-specific ablation of MLL4 in mice resulted in downregulation of the slow oxidative myofiber gene program, decreased numbers of type I myofibers, and diminished mitochondrial respiration, which caused reductions in muscle fatty acid utilization and endurance capacity during exercise. Genome-wide ChIP-Seq and mRNA-Seq analyses revealed that MLL4 directly binds to enhancers and functions as a coactivator of the myocyte enhancer factor 2 (MEF2) to activate transcription of slow oxidative myofiber genes. Importantly, we also found that the MLL4 regulatory circuit is associated with muscle fiber-type remodeling in humans. Thus, our results uncover a pivotal role for MLL4 in specifying structural and metabolic identities of myofibers that govern muscle performance. These findings provide therapeutic opportunities for enhancing muscle fitness to combat a variety of metabolic and muscular diseases.

Plantar Mechanical Stimulation Maintains Slow Myosin Expression in Disused Rat Soleus Muscle via NO-Dependent Signaling

It was observed that gravitational unloading during space missions and simulated microgravity in ground-based studies leads to both transformation of slow-twitch muscle fibers into fast-twitch fibers and to the elimination of support afferentation, leading to the "switching-off" of postural muscle motor units electrical activity. In recent years, plantar mechanical stimulation (PMS) has been found to maintain the neuromuscular activity of the hindlimb muscles. Nitric oxide (NO) was shown to be one of the mediators of muscle fiber activity, which can also promote slow-type myosin expression. We hypothesized that applying PMS during rat hindlimb unloading would lead to NO production upregulation and prevention of the unloading-induced slow-to-fast fiber-type shift in rat soleus muscles. To test this hypothesis, Wistar rats were hindlimb suspended and subjected to daily PMS, and one group of PMS-subjected animals was also treated with nitric oxide synthase inhibitor (L-NAME). We discovered that PMS led to sustained NO level in soleus muscles of the suspended animals, and NOS inhibitor administration blocked this effect, as well as the positive effects of PMS on myosin I and IIa mRNA transcription and slow-to-fast fiber-type ratio during rat hindlimb unloading. The results of the study indicate that NOS activity is necessary for the PMS-mediated prevention of slow-to-fast fiber-type shift and myosin I and IIa mRNA transcription decreases during rat hindlimb unloading.

Functional Non-coding RNA During Embryonic Myogenesis and Postnatal Muscle Development and Disease

Skeletal muscle is a highly heterogeneous tissue that plays a crucial role in mammalian metabolism and motion maintenance. Myogenesis is a complex biological process that includes embryonic and postnatal development, which is regulated by specific signaling pathways and transcription factors. Various non-coding RNAs (ncRNAs) account for the majority of total RNA in cells and have an important regulatory role in myogenesis. In this review, we introduced the research progress in miRNAs, circRNAs, and lncRNAs related to embryonic and postnatal muscle development. We mainly focused on ncRNAs that regulate myoblast proliferation, differentiation, and postnatal muscle development through multiple mechanisms. Finally, challenges and future perspectives related to the identification and verification of functional ncRNAs are discussed. The identification and elucidation of ncRNAs related to myogenesis will enrich the myogenic regulatory network, and the effective application of ncRNAs will enhance the function of skeletal muscle.

Cardiac-specific microRNA-125b deficiency induces perinatal death and cardiac hypertrophy

MicroRNA-125b, the first microRNA to be identified, is known to promote cardiomyocyte maturation from embryonic stem cells; however, its physiological role remains unclear. To investigate the role of miR-125b in cardiovascular biology, cardiac-specific miR-125b-1 knockout mice were generated. We found that cardiac-specific miR-125b-1 knockout mice displayed half the miR-125b expression of control mice resulting in a 60% perinatal death rate. However, the surviving mice developed hearts with cardiac hypertrophy. The cardiomyocytes in both neonatal and adult mice displayed abnormal mitochondrial morphology. In the deficient neonatal hearts, there was an increase in mitochondrial DNA, but total ATP production was reduced. In addition, both the respiratory complex proteins in mitochondria and mitochondrial transcription machinery were impaired. Mechanistically, using transcriptome and proteome analysis, we found that many proteins involved in fatty acid metabolism were significantly downregulated in miR-125b knockout mice which resulted in reduced fatty acid metabolism. Importantly, many of these proteins are expressed in the mitochondria. We conclude that miR-125b deficiency causes a high mortality rate in neonates and cardiac hypertrophy in adult mice. The dysregulation of fatty acid metabolism may be responsible for the cardiac defect in the miR-125b deficient mice.

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.

Thyroid Hormones Interaction With Immune Response, Inflammation and Non-thyroidal Illness Syndrome

The interdependence between thyroid hormones (THs), namely, thyroxine and triiodothyronine, and immune system is nowadays well-recognized, although not yet fully explored. Synthesis, conversion to a bioactive form, and release of THs in the circulation are events tightly supervised by the hypothalamic-pituitary-thyroid (HPT) axis. Newly synthesized THs induce leukocyte proliferation, migration, release of cytokines, and antibody production, triggering an immune response against either sterile or microbial insults. However, chronic patho-physiological alterations of the immune system, such as infection and inflammation, affect HPT axis and, as a direct consequence, THs mechanism of action. Herein, we revise the bidirectional crosstalk between THs and immune cells, required for the proper immune system feedback response among diverse circumstances. Available circulating THs do traffic in two distinct ways depending on the metabolic condition. Mechanistically, internalized THs form a stable complex with their specific receptors, which, upon direct or indirect binding to DNA, triggers a genomic response by activating transcriptional factors, such as those belonging to the Wnt/β-catenin pathway. Alternatively, THs engage integrin αvβ3 receptor on cell membrane and trigger a non-genomic response, which can also signal to the nucleus. In addition, we highlight THs-dependent inflammasome complex modulation and describe new crucial pathways involved in microRNA regulation by THs, in physiological and patho-physiological conditions, which modify the HPT axis and THs performances. Finally, we focus on the non-thyroidal illness syndrome in which the HPT axis is altered and, in turn, affects circulating levels of active THs as reported in viral infections, particularly in immunocompromised patients infected with human immunodeficiency virus.