There is a growing recognition that noncoding RNAs (ncRNA) play an important role in the regulation of gene expression. A class of small (19–22 nt) ncRNAs, known as microRNAs (miRs), have received ...

Evidence of MyomiR network regulation of β-myosin heavy chain gene expression during skeletal muscle atrophy

Essential amino acids (EAA) stimulate muscle protein synthesis in humans. However, little is known about whether microRNAs (miRNA) and genes associated with muscle growth are expressed differently following EAA ingestion. Our purpose in this experiment was to determine whether miRNA and growth-related mRNA expressed in skeletal muscle are up- or downregulated in humans following the ingestion of EAA. We hypothesized that EAA would alter miRNA expression in skeletal muscle as well as select growth-related genes. Muscle biopsies were obtained from the vastus lateralis of 7 young adult participants (3 male, 4 female) before and 3 h after ingesting 10 g of EAA. Muscle samples were analyzed for muscle miRNA (miR-499, -208b, -23a, -1, -133a, and -206) and muscle-growth related genes [MyoD1, myogenin, myostatin, myocyte enhancer factor C (MEF2C), follistatin-like-1 (FSTL1), histone deacytylase 4, and serum response factor mRNA] before and after EAA ingestion using real-time PCR. Following EAA ingestion, miR-499, -208b, -23a, -1, and pri-miR-206 expression increased (P < 0.05). The muscle-growth genes MyoD1 and FSTL1 mRNA expression increased (P < 0.05), and myostatin and MEF2C mRNA were downregulated following EAA ingestion (P < 0.05). We conclude that miRNA and growth-related genes expressed in skeletal muscle are rapidly altered within hours following EAA ingestion. Further work is needed to determine whether these miRNA are post-transcriptional regulators of growth-related genes following an anabolic stimulus.

Essential Amino Acids Increase MicroRNA-499, -208b, and -23a and Downregulate Myostatin and Myocyte Enhancer Factor 2C mRNA Expression in Human Skeletal Muscle

Pulmonary hypertension (PH) is occult, with no distinctive clinical manifestations and a poor prognosis. Pulmonary vascular remodelling is an important pathological feature in which pulmonary artery smooth muscle cells (PASMCs) phenotypic switching plays a crucial role. MicroRNAs (miRNAs) are a class of evolutionarily highly conserved single-stranded small noncoding RNAs. An increasing number of studies have shown that miRNAs play an important role in the occurrence and development of PH by regulating PASMCs phenotypic switching, which is expected to be a potential target for the prevention and treatment of PH. miRNAs such as miR-221, miR-15b, miR-96, miR-24, miR-23a, miR-9, miR-214, and miR-20a can promote PASMCs phenotypic switching, while such as miR-21, miR-132, miR-449, miR-206, miR-124, miR-30c, miR-140, and the miR-17~92 cluster can inhibit it. The article reviews the research progress on growth factor-related miRNAs and hypoxia-related miRNAs that mediate PASMCs phenotypic switching in PH.

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An Overview of miRNAs Involved in PASMC Phenotypic Switching in Pulmonary Hypertension.

In the recent years, microRNAs (miRNAs) have been discovered to play a very important role in biological processes such as development, differentiation, and apoptosis. The miRNA expression levels in cells are associated with diverse diseases including cancers. MiRNA inhibitors have been widely employed for studying the functions and targets of miRNAs by transfecting the inhibitors into cells. The concentrations of miRNA inhibitors used for such studies can vary depending on the types of miRNAs being tested, the cell lines under study, and the analysis methods. Therefore, in order to obtain accurate results, appropriate amounts of miRNA inhibitors have to be used in the experiments. Apart from amounts, the evaluation of inhibitors may also have to be conducted for functional studies. Here we developed capillary electrophoresis with laser-induced fluorescence (CE-LIF) method for evaluating miRNA inhibitor and for optimizing miRNA inhibitor concentrations, in the A549 lung cancer cell line. The target miRNAs, miRNA-23a and miRNA-24 are biomarker candidates in lung cancer cell lines. Our results showed that miRNA-23a and miRNA-24 were effectively inhibited upon transfection with 20 nM miRNA inhibitors using CE-LIF method. Furthermore, these results demonstrated the potential of CE for fast, specific, sensitive and specific analyses for the evaluation and determination of the optimal concentration of miRNA inhibitors for functional studies.

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Analysis of miRNA inhibitors Efficacy using Capillary Electrophoresis with Laser-Induced Fluorescence

Evaluating alterations in circulating microRNA (c-miRNA) expression may provide deeper insight into the role of exercise in the attenuation of the negative effects of aging on musculoskeletal health. Currently, there are sparse data on c-miRNA responses to acute exercise in postmenopausal women. The purpose of this study was to characterize the effects of acute bouts of resistance exercise and whole-body vibration on expression of selected c-miRNAs in postmenopausal women aged 65-76 years (n=10). We also examined relationships between c-miRNAs and muscle strength and bone characteristics. This randomized crossover design study compared c-miRNA responses to a bout of resistance exercise (RE) (3 sets 10 reps 70% 1 repetition maximum (1RM), 5 exercises) and a bout of whole-body vibration (WBV) (5 sets 1 min bouts 20Hz 3.38mm peak to peak displacement, Vibraflex vibration platform). DXA was used to measure body composition and areal bone mineral density (aBMD) of the total body, AP lumbar spine, and dual proximal femur. pQCT was used to measure tibia bone characteristics (4%, 38%, 66% sites). Blood samples were collected before exercise (Pre), immediately-post (IP), 60 minutes post (60P), 24 hours (24H), and 48 hours (48H) after exercise to measure serum miR-21-5p, -23a-3p, -133a-3p, -148a-3p (qPCR) and TRAP5b (ELISA). There was a significant modality × time interaction for c-miR-21-5p expression (p=0.019), which decreased from 60P to 24H after WBV only. TRAP5b serum concentrations significantly increased IP then decreased below Pre at 24H for both WBV and RE (p<0.01). Absolute changes in TRAP5b were negatively correlated with c-miR-21-5p fold changes (r= -0.642 to -0.724, p<0.05) for both exercise modalities. There were significant negative correlations between baseline c-miRNAs and bone status variables (r= -0.639 to -0.877, p<0.05). Our findings suggest that whole-body vibration is a sufficient mechanical stimulus for altering c-miR-21-5p expression, whereas a high intensity resistance exercise protocol did not elicit any c-miRNA responses in postmenopausal women. Increases in the bone resorption marker, TRAP5b, were associated with greater downregulation of c-miR-21-5p expression.

/pdf/circulating-microrna-responses-to-acute-whole-body-vibration-1owddvay.pdf

Circulating microRNA responses to acute whole-body vibration and resistance exercise in postmenopausal women

Muscle atrophy occurs in many pathological states and results primarily from accelerated protein degradation by the ubiquitin-proteasome pathway. We used dexamethasone to induce muscle wasting and investigated the role of a microRNA (miRNA) in the control of muscle-specific E3 ubiquitin ligase MAFbx/atrogin-1. Here we show that miR-23a suppresses MAFbx/atrogin-1 translation by binding to 3'UTR of the mRNA. Furthermore, ectopic expression of miR-23a is sufficient to protect myocytes from atrophy in vitro and in vivo in response to dexamethasone treatment, and heat stress-induced miR-23a protects muscle from dexamethasone-induced muscle atrophy. Our surprising discovery of the physiological role of miR-23a in preventing the atrophy program should lay the basis not only for further understanding of the mechanisms of muscle wasting in diverse diseases, but also for developing novel therapies for these debilitating conditions.

Takashi Ushida

Papers

Stress responsive miR-23a attenuates skeletal muscle atrophy by targeting MAFbx /atrogin-1

Functions of miR-23−27−24 cluster miRNAs in skeletal muscle plasticity