MicroRNA-23a has minimal effect on endurance exercise-induced adaptation of mouse skeletal muscle

Skeletal muscles contain several subtypes of myofibers that differ in contractile and metabolic properties. Transcriptional control of fiber-type specification and adaptation has been intensively investigated over the past several decades. Recently, microRNA (miRNA)-mediated posttranscriptional gene regulation has attracted increasing attention. MiR-23a targets key molecules regulating contractile and metabolic properties of skeletal muscle, such as myosin heavy-chains and peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC-1α). In the present study, we analyzed the skeletal muscle phenotype of miR-23a transgenic (miR-23a Tg) mice to explore whether forced expression of miR-23a affects markers of mitochondrial content, muscle fiber composition, and muscle adaptations induced by 4 weeks of voluntary wheel running. When compared with wild-type mice, protein markers of mitochondrial content, including PGC-1α, and cytochrome c oxidase complex IV (COX IV), were significantly decreased in the slow soleus muscle, but not the fast plantaris muscle of miR-23a Tg mice. There was a decrease in type IId/x fibers only in the soleus muscle of the Tg mice. Following 4 weeks of voluntary wheel running, there was no difference in the endurance exercise capacity as well as in several muscle adaptive responses including an increase in muscle mass, capillary density, or the protein content of myosin heavy-chain IIa, PGC-1α, COX IV, and cytochrome c. These results show that miR-23a targets PGC-1α and regulates basal metabolic properties of slow but not fast twitch muscles. Elevated levels of miR-23a did not impact on whole body endurance capacity or exercise-induced muscle adaptations in the fast plantaris muscle.

Identification of MicroRNAs linked to regulators of muscle protein synthesis and regeneration in young and old skeletal muscle

Over the course of ageing there is a natural and progressive loss of skeletal muscle mass. The onset and progression of age-related muscle wasting is associated with an attenuated activation of Akt-mTOR signalling and muscle protein synthesis in response to anabolic stimuli such as resistance exercise. MicroRNAs (miRNAs) are novel and important post-transcriptional regulators of numerous cellular processes. The role of miRNAs in the regulation of muscle protein synthesis following resistance exercise is poorly understood. This study investigated the changes in skeletal muscle miRNA expression following an acute bout of resistance exercise in young and old subjects with a focus on the miRNA species predicted to target Akt-mTOR signalling.

MicroRNAs: biogenesis, roles for carcinogenesis and as potential biomarkers for cancer diagnosis and prognosis

MicroRNAs (miRNAs) are short non-coding RNAs of 20-24 nucleotides that play important roles in carcinogenesis. Accordingly, miRNAs control numerous cancer-relevant biological events such as cell proliferation, cell cycle control, metabolism and apoptosis. In this review, we summarize the current knowledge and concepts concerning the biogenesis of miRNAs, miRNA roles in cancer and their potential as biomarkers for cancer diagnosis and prognosis including the regulation of key cancer-related pathways, such as cell cycle control and miRNA dysregulation. Moreover, microRNA molecules are already receiving the attention of world researchers as therapeutic targets and agents. Therefore, in-depth knowledge of microRNAs has the potential not only to identify their roles in cancer, but also to exploit them as potential biomarkers for cancer diagnosis and identify therapeutic targets for new drug discovery.

MicroRNAs in skeletal muscle and their regulation with exercise, ageing, and disease

Skeletal muscle makes up approximately 40% of the total body mass, providing structural support and enabling the body to maintain posture, to control motor movements and to store energy. It therefore plays a vital role in whole body metabolism. Skeletal muscle displays remarkable plasticity and is able to alter its size, structure and function in response to various stimuli; an essential quality for healthy living across the lifespan. Exercise is an important stimulator of extracellular and intracellular stress signals that promote positive adaptations in skeletal muscle. These adaptations are controlled by changes in gene transcription and protein translation, with many of these molecules identified as potential therapeutic targets to pharmacologically improve muscle quality in patient groups too ill to exercise. MicroRNAs (miRNAs) are recently identified regulators of numerous gene networks and pathways and mainly exert their effect by binding to their target messenger RNAs (mRNAs), resulting in mRNA degradation or preventing protein translation. The role of exercise as a regulatory stimulus of skeletal muscle miRNAs is now starting to be investigated. This review highlights our current understanding of the regulation of skeletal muscle miRNAs with exercise and disease as well as how they may control skeletal muscle health.

Blocking the maturation of OncomiRNAs using pri-miRNA-17∼92 aptamer in retinoblastoma

The miR-17∼92. or oncomiR-1, cluster encodes oncogenic microRNAs (miRNAs), and it also promotes retinoblastoma (RB) tumor formation. Antagomir and miRNA mimics based approaches are widely tried against oncogenic and tumor suppressive miRNAs. Other methods for targeting cancer related miRNAs are still under development. In the current study, we focused on the pri-miRNA-17∼92 aptamer (pri-apt), which can potentially replace the mix of five antagomirs by one aptamer that function to abrogate the maturation of miR-17, miR-18a, and miR-19b (P<0.05) for targeting RB. We used RB cell lines WERI-Rb1 and Y79 as an in vitro model. Cellular changes upon transfecting the pri-apt led to S-phase arrest in WERI-Rb1 cells and onset of apoptosis in both Y79 and WERI-Rb1 cell lines. There was increased cytotoxicity as measured by lactate dehydrogenase activity in pri-apt treated Y79 cells (P<0.05), and significant inhibition of cell proliferation was observed in both of the cell lines. Thus we showed the antiproliferative property of pri-apt in RB cell lines, which can be readily modified by developing appropriate vectors for the delivery of the aptamer specifically to cancer cells.

Exercise, skeletal muscle and circulating microRNAs

Regular exercise stimulates numerous structural, metabolic, and morphological adaptations in skeletal muscle. These adaptations are vital to maintain human health over the life span. Exercise is therefore seen as a primary intervention to reduce the risk of chronic disease. Advances in molecular biology, biochemistry, and bioinformatics, combined with exercise physiology, have identified many key signaling pathways as well as transcriptional and translational processes responsible for exercise-induced adaptations. Noncoding RNAs, and specifically microRNAs (miRNAs), constitute a new regulatory component that may play a role in these adaptations. The short single-stranded miRNA sequences bind to the 3' untranslated region of specific messenger RNAs (mRNAs) on the basis of sequence homology. This results in the degradation of the target mRNA or the inhibition of protein translation causing repression of the corresponding protein. While tissue specificity or enrichment of certain miRNAs makes them ideal targets to manipulate and understand tissue development, function, health, and disease, other miRNAs are ubiquitously expressed; however, it is uncertain whether their mRNA/protein targets are conserved across different tissues. miRNAs are stable in plasma and serum and their altered circulating expression levels in disease conditions may provide important biomarker information. The emerging research into the role that miRNAs play in exercise-induced adaptations has predominantly focused on the miRNA species that are regulated in skeletal muscle or in circulation. This chapter provides an overview of these current research findings, highlights the strengths and weaknesses identified to date, and suggests where the exercise-miRNA field may move into the future.

Finding motifs in miRNA sequences

Recently, the emergence of non-coding miRNA has attracted biology and computer researchers. miRNA plays an important role in regulation of genes. Finding motifs in RNA is one of important topics. In our work, we attempt to find motifs in mature miRNA from combinations ranging from two to ten nucleotides. Interestingly, we have found several motifs only appear in mature miRNA but not appear in other regions of primary miRNA sequences taken from latest miRNA datasets. The findings of our investigation may help in the building model to predict all possible miRNAs in genomes

Viral RNA silencing suppressors (RSS) : novel strategy of viruses to ablate the host RNA interference (RNAi) defense system

Pathogenic viruses have developed a molecular defense arsenal for their survival by counteracting the host anti-viral system known as RNA interference (RNAi). Cellular RNAi, in addition to regulating gene expression through microRNAs, also serves as a barrier against invasive foreign nucleic acids. RNAi is conserved across the biological species, including plants, animals and invertebrates. Viruses in turn, have evolved mechanisms that can counteract this anti-viral defense of the host. Recent studies of mammalian viruses exhibiting RNA silencing suppressor (RSS) activity have further advanced our understanding of RNAi in terms of host–virus interactions. Viral proteins and non-coding viral RNAs can inhibit the RNAi (miRNA/siRNA) pathway through different mechanisms. Mammalian viruses having dsRNA-binding regions and GW/WG motifs appear to have a high chance of conferring RSS activity. Although, RSSs of plant and invertebrate viruses have been well characterized, mammalian viral RSSs still need in-depth investigations to present the concrete evidences supporting their RNAi ablation characteristics. The information presented in this review together with any perspective research should help to predict and identify the RSS activity-endowed new viral proteins that could be the potential targets for designing novel anti-viral therapeutics.

MicroRNA in human cancer and chronic inflammatory diseases

MicroRNAs (miRNAs) are the non-coding RNAs that act as post-translational regulators to their complimentary messenger RNAs (mRNA). Due to their specific gene silencing property, miRNAs have been implicated in a number of cellular and developmental processes. Also, it has been proposed that a particular set of miRNA spectrum is expressed only in a particular type of tissue. Many interesting findings related to the differential expression of miRNAs in various human diseases including several types of cancers, neurodegenerative diseases and metabolic diseases have been reported. Deregulation of miRNA expression in different types of human diseases and the roles various miRNAs play as tumour suppressors as well as oncogenes, suggest their contribution to cancer and/or in other disease development. These findings have possible implications in the development of diagnostics and/or therapeutics in human malignancies. In this review, we discuss various miRNAs that are differentially expressed in human chronic inflammatory diseases, neurodegenerative diseases, cancer and the further prospective development of miRNA based diagnostics and therapeutics.

Regulation of miRNAs in human skeletal muscle following acute endurance exercise and short-term endurance training

The identification of microRNAs (miRNAs) has established new mechanisms that control skeletal muscle adaptation to exercise. The present study investigated the mRNA regulation of components of the miRNA biogenesis pathway (Drosha, Dicer and Exportin-5), muscle enriched miRNAs, (miR-1, -133a, -133b and -206), and several miRNAs dysregulated in muscle myopathies (miR-9, -23, -29, -31 and -181). Measurements were made in muscle biopsies from nine healthy untrained males at rest, 3 h following an acute bout of moderate-intensity endurance cycling and following 10 days of endurance training. Bioinformatics analysis was used to predict potential miRNA targets. In the 3 h period following the acute exercise bout, Drosha, Dicer and Exportin-5, as well as miR-1, -133a, -133-b and -181a were all increased. In contrast miR-9, -23a, -23b and -31 were decreased. Short-term training increased miR-1 and -29b, while miR-31 remained decreased. Negative correlations were observed between miR-9 and HDAC4 protein (r=-0.71; P= 0.04), miR-31 and HDAC4 protein (r =-0.87; P= 0.026) and miR-31 and NRF1 protein (r =-0.77; P= 0.01) 3 h following exercise. miR-31 binding to the HDAC4 and NRF1 3′ untranslated region (UTR) reduced luciferase reporter activity. Exercise rapidly and transiently regulates several miRNA species in muscle. Several of these miRNAs may be involved in the regulation of skeletal muscle regeneration, gene transcription and mitochondrial biogenesis. Identifying endurance exercise-mediated stress signals regulating skeletal muscle miRNAs, as well as validating their targets and regulatory pathways post exercise, will advance our understanding of their potential role/s in human health

Visualising single molecules of HIV-1 and miRNA nucleic acids

Background
The scarcity of certain nucleic acid species and the small size of target sequences such as miRNA, impose a significant barrier to subcellular visualization and present a major challenge to cell biologists. Here, we offer a generic and highly sensitive visualization approach (oligo fluorescent in situ hybridization, O-FISH) that can be used to detect such nucleic acids using a single-oligonucleotide probe of 19–26 nucleotides in length.

Results
We used O-FISH to visualize miR146a in human and avian cells. Furthermore, we reveal the sensitivity of O-FISH detection by using a HIV-1 model system to show that as little as 1–2 copies of nucleic acids can be detected in a single cell. We were able to discern newly synthesized viral cDNA and, moreover, observed that certain HIV RNA sequences are only transiently available for O-FISH detection.

Conclusions
Taken together, these results suggest that the O-FISH method can potentially be used for in situ probing of, as few as, 1–2 copies of nucleic acid and, additionally, to visualize small RNA such as miRNA. We further propose that the O-FISH method could be extended to understand viral function by probing newly transcribed viral intermediates; and discern the localisation of nucleic acids of interest. Additionally, interrogating the conformation and structure of a particular nucleic acid in situ might also be possible, based on the accessibility of a target sequence.