MicroRNA-499-5p regulates skeletal myofiber specification via NFATc1/MEF2C pathway and Thrap1/MEF2C axis

MicroRNA-542-3p targets Pten to inhibit the myoblasts proliferation but suppresses myogenic differentiation independent of targeted Pten

BACKGROUND

Non-coding RNA is a key epigenetic regulation factor during skeletal muscle development and postnatal growth, and miR-542-3p was reported to be conserved and highly expressed in the skeletal muscle among different species. However, its exact functions in the proliferation of muscle stem cells and myogenesis remain to be determined.

METHODS

Transfection of proliferative and differentiated C2C12 cells used miR-542-3p mimic and inhibitor. RT-qPCR, EdU staining, immunofluorescence staining, cell counting kit 8 (CCK-8), and Western blot were used to evaluate the proliferation and myogenic differentiation caused by miR-542-3p. The dual luciferase reporter analysis and rescued experiment of the target gene were used to reveal the molecular mechanism.

RESULTS

The data shows overexpression of miR-542-3p downregulation of mRNA and protein levels of proliferation marker genes, reduction of EdU+ cells, and cellular vitality. Additionally, knocking it down promoted the aforementioned phenotypes. For differentiation, the miR-542-3p gain-of-function reduced both mRNA and protein levels of myogenic genes, including MYOG, MYOD1, et al. Furthermore, immunofluorescence staining immunized by MYHC antibody showed that the myotube number, fluorescence intensity, differentiation index, and myotube fusion index all decreased in the miR-542-3p mimic group, compared with the control group. Conversely, these phenotypes exhibited an increased trend in the miR-542-3p inhibitor group. Mechanistically, phosphatase and tensin homolog (Pten) was identified as the bona fide target gene of miR-542-3p by dual luciferase reporter gene assay, si-Pten combined with miR-542-3p inhibitor treatments totally rescued the promotion of proliferation by loss-function of miR-542-3p.

CONCLUSIONS

This study indicates that miR-542-3p inhibits the proliferation and differentiation of myoblast and Pten is a dependent target gene of miR-542-3p in myoblast proliferation, but not in differentiation.

Low myoglobin concentration in skeletal muscle of elite cyclists is associated with low mRNA expression levels

Myoglobin is essential for oxygen transport to the muscle fibers. However, measurements of myoglobin (Mb) protein concentrations within individual human muscle fibers are scarce. Recent observations have revealed surprisingly low Mb concentrations in elite cyclists, however it remains unclear whether this relates to Mb translation, transcription and/or myonuclear content. The aim was to compare Mb concentration, Mb messenger RNA (mRNA) expression levels and myonuclear content within muscle fibers of these elite cyclists with those of physically-active controls. Muscle biopsies were obtained from m. vastus lateralis in 29 cyclists and 20 physically-active subjects. Mb concentration was determined by peroxidase staining for both type I and type II fibers, Mb mRNA expression level was determined by quantitative PCR and myonuclear domain size (MDS) was obtained by immunofluorescence staining. Average Mb concentrations (mean ± SD: 0.38 ± 0.04 mM vs. 0.48 ± 0.19 mM; P = 0.014) and Mb mRNA expression levels (0.067 ± 0.019 vs. 0.088 ± 0.027; P = 0.002) were lower in cyclists compared to controls. In contrast, MDS and total RNA per mg muscle were not different between groups. Interestingly, in cyclists compared to controls, Mb concentration was only lower for type I fibers (P < 0.001), but not for type II fibers (P > 0.05). In conclusion, the lower Mb concentration in muscle fibers of elite cyclists is partly explained by lower Mb mRNA expression levels per myonucleus and not by a lower myonuclear content. It remains to be determined whether cyclists may benefit from strategies that upregulate Mb mRNA expression levels, particularly in type I fibers, to enhance their oxygen supply.

The spatiotemporal matching pattern of Ezrin/Periaxin involved in myoblast differentiation and fusion and Charcot-Marie-Tooth disease-associated muscle atrophy

BACKGROUND

Clinically, Charcot-Marie-Tooth disease (CMT)-associated muscle atrophy still lacks effective treatment. Deletion and mutation of L-periaxin can be involved in CMT type 4F (CMT4F) by destroying the myelin sheath form, which may be related to the inhibitory role of Ezrin in the self-association of L-periaxin. However, it is still unknown whether L-periaxin and Ezrin are independently or interactively involved in the process of muscle atrophy by affecting the function of muscle satellite cells.

METHOD

A gastrocnemius muscle atrophy model was prepared to mimic CMT4F and its associated muscle atrophy by mechanical clamping of the peroneal nerve. Differentiating C2C12 myoblast cells were treated with adenovirus-mediated overexpression or knockdown of Ezrin. Then, overexpression of L-periaxin and NFATc1/c2 or knockdown of L-periaxin and NFATc3/c4 mediated by adenovirus vectors were used to confirm their role in Ezrin-mediated myoblast differentiation, myotube formation and gastrocnemius muscle repair in a peroneal nerve injury model. RNA-seq, real-time PCR, immunofluorescence staining and Western blot were used in the above observation.

RESULTS

For the first time, instantaneous L-periaxin expression was highest on the 6th day, while Ezrin expression peaked on the 4th day during myoblast differentiation/fusion in vitro. In vivo transduction of adenovirus vectors carrying Ezrin, but not Periaxin, into the gastrocnemius muscle in a peroneal nerve injury model increased the numbers of muscle myosin heavy chain (MyHC) I and II type myofibers, reducing muscle atrophy and fibrosis. Local muscle injection of overexpressed Ezrin combined with incubation of knockdown L-periaxin within the injured peroneal nerve or injection of knockdown L-periaxin into peroneal nerve-injured gastrocnemius muscle not only increased the number of muscle fibers but also recovered their size to a relatively normal level in vivo. Overexpression of Ezrin promoted myoblast differentiation/fusion, inducing increased MyHC-I⁺ and MyHC-II + muscle fiber specialization, and the specific effects could be enhanced by the addition of adenovirus vectors for knockdown of L-periaxin by shRNA. Overexpression of L-periaxin did not alter the inhibitory effects on myoblast differentiation and fusion mediated by knockdown of Ezrin by shRNA in vitro but decreased myotube length and size. Mechanistically, overexpressing Ezrin did not alter protein kinase A gamma catalytic subunit (PKA-γ cat), protein kinase A I alpha regulatory subunit (PKA reg Iα) or PKA reg Iβ levels but increased PKA-α cat and PKA reg II α levels, leading to a decreased ratio of PKA reg I/II. The PKA inhibitor H-89 remarkably abolished the effects of overexpressing-Ezrin on increased myoblast differentiation/fusion. In contrast, knockdown of Ezrin by shRNA significantly delayed myoblast differentiation/fusion accompanied by an increased PKA reg I/II ratio, and the inhibitory effects could be eliminated by the PKA reg activator N6-Bz-cAMP. Meanwhile, overexpressing Ezrin enhanced type I muscle fiber specialization, accompanied by an increase in NFATc2/c3 levels and a decrease in NFATc1 levels. Furthermore, overexpressing NFATc2 or knocking down NFATc3 reversed the inhibitory effects of Ezrin knockdown on myoblast differentiation/fusion.

CONCLUSIONS

The spatiotemporal pattern of Ezrin/Periaxin expression was involved in the control of myoblast differentiation/fusion, myotube length and size, and myofiber specialization, which was related to the activated PKA-NFAT-MEF2C signaling pathway, providing a novel L-Periaxin/Ezrin joint strategy for the treatment of muscle atrophy induced by nerve injury, especially in CMT4F.

Continuous exposure to isoprenaline reduced myotube size by delaying myoblast differentiation and fusion through the NFAT-MEF2C signaling pathway

We aimed to explore whether superfluous sympathetic activity affects myoblast differentiation, fusion, and myofiber types using a continuous single-dose isoprenaline exposure model in vitro and to further confirm the role of distinct NFATs in ISO-mediated effects. Compared with delivery of single and interval single, continuous single-dose ISO most obviously diminished myotube size while postponing myoblast differentiation/fusion in a time- and dose-dependent pattern, accompanied by an apparent decrease in nuclear NFATc1/c2 levels and a slight increase in nuclear NFATc3/c4 levels. Overexpression of NFATc1 or NFATc2, particularly NFATc1, markedly abolished the inhibitory effects of ISO on myoblast differentiation/fusion, myotube size and Myh7 expression, which was attributed to a remarkable increase in the nuclear NFATc1/c2 levels and a reduction in the nuclear NFATc4 levels and the associated increase in the numbers of MyoG and MEF2C positive nuclei within more than 3 nuclei myotubes, especially in MEF2C. Moreover, knockdown of NFATc3 by shRNA did not alter the inhibitory effect of ISO on myoblast differentiation/fusion or myotube size but partially recovered the expression of Myh7, which was related to the slightly increased nuclear levels of NFATc1/c2, MyoG and MEF2C. Knockdown of NFATc4 by shRNA prominently increased the number of MyHC +, MyoG or MEF2C + myoblast cells with 1 ~ 2 nuclei, causing fewer numbers and smaller myotube sizes. However, NFATc4 knockdown further deteriorated the effects of ISO on myoblast fusion and myotube size, with more than 5 nuclei and Myh1/2/4 expression, which was associated with a decrease in nuclear NFATc2/c3 levels. Therefore, ISO inhibited myoblast differentiation/fusion and myotube size through the NFAT-MyoG-MEF2C signaling pathway.

Metformin Attenuates Slow-to-Fast Fiber Shift and Proteolysis Markers Increase in Rat Soleus after 7 Days of Rat Hindlimb Unloading

Muscle unloading leads to signaling alterations that cause muscle atrophy and weakness. The cellular energy sensor AMPK can regulate myofiber-type shift, calcium-dependent signaling and ubiquitin-proteasome system markers. We hypothesized that the prevention of p-AMPK downregulation during the first week of muscle unloading would impede atrophy development and the slow-to-fast shift of soleus muscle fibers, and the aim of the study was to test this hypothesis. Thirty-two male Wistar rats were randomly assigned to four groups: placebo control (C), control rats treated with metformin (C + M), 7 days of hindlimb suspension (HS) + placebo (7HS), and 7 days of HS + metformin administration (7HS + M). In the soleus of the 7HS rats, we detected a slow-to-fast fiber-type shift as well as a significant downregulation of MEF-2D and p300 in the nuclei. In the 7HS group, we also found decreases in p-ACC (AMPK target) protein level and in the expression of E3 ubiquitin ligases and p-CaMK II protein level vs. the C group. The 7-day metformin treatment for soleus muscle unloading (1) prevented slow-to-fast fiber-type shift; (2) counteracted changes in the p-ACC protein level; (3) hindered changes in the nuclear protein level of the slow myosin expression activators MEF-2D and p300, but did not affect NFATc1 signaling; and (4) attenuated the unloading-induced upregulation of MuRF-1, atrogin-1, ubiquitin and myostatin mRNA expression, but did not prevent soleus muscle atrophy. Thus, metformin treatment during muscle disuse could be useful to prevent the decrease in the percentage of slow-type fatigue-resistant muscle fibers.

Effects of dietary dihydromyricetin supplementation on intestinal barrier and humoral immunity in growing-finishing pigs

In this study, we investigated the effect of dietary dihydromyricetin (DHM) supplementation on intestinal barrier and humoral immunity in growing-finishing pigs. The data showed that dietary DHM supplementation improved jejunal barrier function by upregulating the protein expressions of Occludin and Claudin-1 and the mRNA levels of MUC1 and MUC2. Dietary DHM supplementation increased the amylase, lipase, sucrase and maltase activities and the mRNA expression of nutrient transporter (SGLT1, GLUT2, PepT1) in the jejunum mucosa. Dietary DHM supplementation significantly reduced the E. coli population in the cecum and colon and increased the Lactobacillus population in the cecum. In addition, dietary DHM supplementation increased the contents of butyric acid and valeric acid in cecum and colon. In serum, dietary DHM supplementation reduced interleukin-1β (IL-1β) content and increased interleukin-10 (IL-10), Immunoglobulin M (IgM) and Immunoglobulin A (IgA) contents (p < 0.05). In addition, compared with the control group, dietary DHM supplementation improved secretory immunoglobulin A (sIgA) and interleukin-10 (IL-10) contents and down-regulated TNF-α protein expression in jejunum mucosa (p < 0.05). Together, this study demonstrated that dietary DHM supplementation improved intestinal barrier function, digestion and absorption capacity and immune function in growing-finishing pigs.

CircRNAs Related to Breast Muscle Development and Their Interaction Regulatory Network in Gushi Chicken

Circular RNAs (circRNAs) play a significant regulatory role during skeletal muscle development. To identify circRNAs during postnatal skeletal muscle development in chickens, we constructed 12 cDNA libraries from breast muscle tissues of Chinese Gushi chickens at 6, 14, 22, and 30 weeks and performed RNA sequencing. In total, 2112 circRNAs were identified, and among them 79.92% were derived from exons. CircRNAs are distributed on all chromosomes of chickens, especially chromosomes 1-9 and Z. Bioinformatics analysis showed that each circRNA had an average of 38 miRNA binding sites, 61.32% of which have internal ribosomal entry site (IRES) elements. Furthermore, in total 543 differentially expressed circRNAs (DE-circRNAs) were identified. Functional enrichment analysis revealed that DE-circRNAs source genes are engaged in biological processes and muscle development-related pathways; for example, cell differentiation, sarcomere, and myofibril formation, mTOR signaling pathway, and TGF-β signaling pathway, etc. We also established a competitive endogenous RNA (ceRNA) regulatory network associated with skeletal muscle development. The results in this report indicate that circRNAs can mediate the development of chicken skeletal muscle by means of a complex ceRNA network among circRNAs, miRNAs, genes, and pathways. The findings of this study might help increase the number of known circRNAs in skeletal muscle tissue and offer a worthwhile resource to further investigate the function of circRNAs in chicken skeletal muscle development.

Transcriptome sequencing analysis of the role of miR-499-5p and SOX6 in chicken skeletal myofiber specification

MicroRNAs (miRNAs) might play critical roles in skeletal myofiber specification. In a previous study, we found that chicken miR-499-5p is specifically expressed in slow-twitch muscle and that its potential target gene is SOX6. In this study, we performed RNA sequencing to investigate the effects of SOX6 and miR-499-5p on the modulation and regulation of chicken muscle fiber type and its regulatory mechanism. The expression levels of miR-499-5p and SOX6 demonstrated opposing trends in different skeletal muscles and were associated with muscle fiber type composition. Differential expression analysis revealed that miR-499-5p overexpression led to significant changes in the expression of 297 genes in chicken primary myoblasts (CPMs). Myofiber type-related genes, including MYH7B and CSRP3, showed expression patterns similar to those in slow-twitch muscle. According to functional enrichment analysis, differentially expressed genes were mostly associated with muscle development and muscle fiber-related processes. SOX6 was identified as the target gene of miR-499-5p in CPM using target gene mining and luciferase reporter assays. SOX6 knockdown resulted in upregulation of the slow myosin genes and downregulation of fast myosin genes. Furthermore, protein-protein interaction network analysis revealed that MYH7B and RUNX2 may be the direct targets of SOX6. These results indicated that chicken miR-499-5p may promote slow-twitch muscle fiber formation by repressing SOX6 expression. Our study provides a dataset that can be used as a reference for animal meat quality and human muscle disease studies.

Sustained injection of miR-499-5p alters the gastrocnemius muscle metabolome in broiler chickens

To investigate the effects of miR-499-5p on muscle metabolism in broiler chickens, eight broiler chicks were assigned to the control group and eight to the treatment group, and then we monitored the effects using metabolomics. Chicks were fed basal diets without or with miR-499-5p delivery. Gastrocnemius muscle samples were collected and analyzed by ultrahigh-performance liquid chromatography–tandem mass spectrometry. The results showed that miR-499-5p injection altered the concentrations of a variety of metabolites in the gastrocnemius muscle. Thereby, a total of 46 metabolites were identified at higher (P<0.05) concentrations and 30 metabolites were identified at lower (P<0.05) concentrations in the treatment group compared with the control group. These metabolites were primarily involved with the regulation of lipid and carbohydrate metabolism. Further metabolic pathway analysis revealed that fructose and mannose metabolism, galactose metabolism, inositol phosphate metabolism, and terpenoid backbone biosynthesis were the most critical pathway which may partially interpret the effects of miR-499-5p. To our knowledge, this research is the first report of metabolic signatures and related metabolic pathways in the skeletal muscle for miR-499-5p injection and provides new insight into the effect of miRNA on growth performance.

Dihydromyricetin Enhances Intestinal Antioxidant Capacity of Growing-Finishing Pigs by Activating ERK/Nrf2/HO-1 Signaling Pathway

Oxidative stress is one of the main factors affecting animal health and reducing performance. The small intestine is the primary site of free-radical attacks. Dihydromyricetin (DHM) is a flavonoid compound with antioxidant, anti-inflammatory, and other biological activities, which is mainly extracted from Rattan tea. However, the effects of DHM on the intestinal antioxidant function of growing-finishing pigs and related mechanisms remain unclear. The aim of this study was to investigate the effect of dietary DHM supplementation on the intestinal antioxidant capacity of growing-finishing pigs and its mechanism. Our results show that dietary 0.03% DHM increased the activities of the total antioxidant capacity (T-AOC), catalase (CAT), and glutathione peroxidase (GSH-Px), decreased malondialdehyde (MDA) level, and upregulated protein expressions of HO-1, NQO1, nuclear Nrf2, and phospho-ERK (p-ERK) in the jejunum of growing-finishing pigs. Again, we found that 20 μmol/mL and 40 μmol/mL DHM treatment significantly upregulated the protein expression of HO-1 and promoted the nuclear translocation of Nrf2 and ERK phosphorylation in IPCE-J2 cells. ERK inhibitor PD98059 eliminated the DHM-induced upregulation of p-ERK, nuclear Nrf2, and HO-1. Our findings provided the first evidence that DHM enhanced the intestinal antioxidant capacity of growing-finishing pigs by activating the ERK/Nrf2/HO-1 signaling pathway.

miRNAs as markers for the development of individualized training regimens: A pilot study

Small, non‐coding RNAs (microRNAs) have been shown to regulate gene expression in response to exercise in various tissues and organs, thus possibly coordinating their adaptive response. Thus, it is likely that differential microRNA expression might be one of the factors that are responsible for different training responses of different individuals. Consequently, determining microRNA patterns might be a promising approach toward the development of individualized training strategies. However, little is known on (1) microRNA patterns and their regulation by different exercise regimens and (2) possible correlations between these patterns and individual training adaptation. Here, we present microarray data on skeletal muscle microRNA patterns in six young, female subjects before and after six weeks of either moderate‐intensity continuous or high‐intensity interval training on a bicycle ergometer. Our data show that n = 36 different microRNA species were regulated more than twofold in this cohort (n = 28 upregulated and n = 8 downregulated). In addition, we correlated baseline microRNA patterns with individual changes in VO₂max and identified some specific microRNAs that might be promising candidates for further testing and evaluation in the future, which might eventually lead to the establishment of microRNA marker panels that will allow individual recommendations for specific exercise regimens.

Post-Transcriptional Regulation of Molecular Determinants during Cardiogenesis

Cardiovascular development is initiated soon after gastrulation as bilateral precardiac mesoderm is progressively symmetrically determined at both sides of the developing embryo. The precardiac mesoderm subsequently fused at the embryonic midline constituting an embryonic linear heart tube. As development progress, the embryonic heart displays the first sign of left-right asymmetric morphology by the invariably rightward looping of the initial heart tube and prospective embryonic ventricular and atrial chambers emerged. As cardiac development progresses, the atrial and ventricular chambers enlarged and distinct left and right compartments emerge as consequence of the formation of the interatrial and interventricular septa, respectively. The last steps of cardiac morphogenesis are represented by the completion of atrial and ventricular septation, resulting in the configuration of a double circuitry with distinct systemic and pulmonary chambers, each of them with distinct inlets and outlets connections. Over the last decade, our understanding of the contribution of multiple growth factor signaling cascades such as Tgf-beta, Bmp and Wnt signaling as well as of transcriptional regulators to cardiac morphogenesis have greatly enlarged. Recently, a novel layer of complexity has emerged with the discovery of non-coding RNAs, particularly microRNAs and lncRNAs. Herein, we provide a state-of-the-art review of the contribution of non-coding RNAs during cardiac development. microRNAs and lncRNAs have been reported to functional modulate all stages of cardiac morphogenesis, spanning from lateral plate mesoderm formation to outflow tract septation, by modulating major growth factor signaling pathways as well as those transcriptional regulators involved in cardiac development.

MicroRNAs in obesity, sarcopenia, and commonalities for sarcopenic obesity: a systematic review

Sarcopenic obesity is a distinct condition of sarcopenia in the context of obesity, with the cumulative health risks of both phenotypes. Differential expression of microRNAs (miRNAs) has been reported separately in people with obesity and sarcopenia and may play a role in the pathogenesis of sarcopenic obesity. However, this has not been explored to date. This study aimed to identify differentially expressed miRNAs reported in serum, plasma, and skeletal muscle of people with obesity and sarcopenia and whether there are any commonalities between these conditions. We performed a systematic review on Embase and MEDLINE (PROSPERO, CRD42020224486) for differentially expressed miRNAs (fold change >1.5 or P-value <0.05) in (i) sarcopenia or frailty and (ii) obesity or metabolic syndrome. The functions and targets of miRNAs commonly changed in both conditions, in the same direction, were searched using PubMed. Following deduplication, 247 obesity and 42 sarcopenia studies were identified for full-text screening. Screening identified 36 obesity and 6 sarcopenia studies for final inclusion. A total of 351 miRNAs were identified in obesity and 157 in sarcopenia. Fifty-five miRNAs were identified in both obesity and sarcopenia-by sample type, 48 were found in plasma and one each in serum and skeletal muscle. Twenty-four miRNAs were identified from 10 of the included studies as commonly changed in the same direction (22 in plasma and one each in serum and skeletal muscle) in obesity and sarcopenia. The majority of miRNA-validated targets identified in the literature search were members of the phosphoinositide 3-kinase/protein kinase B and transforming growth factor-β signalling pathways. The most common targets identified were insulin-like growth factor 1 (miR-424-5p, miR-483-3p, and miR-18b-5p) and members of the SMAD family (miR-483-3p, miR-92a-3p, and miR-424-5p). The majority of commonly changed miRNAs were involved in protein homeostasis, mitochondrial dynamics, determination of muscle fibre type, insulin resistance, and adipogenesis. Twenty-four miRNAs were identified as commonly dysregulated in obesity and sarcopenia with functions and targets implicated in the pathogenesis of sarcopenic obesity. Given the adverse health outcomes associated with sarcopenic obesity, understanding the pathogenesis underlying this phenotype has the potential to lead to effective screening, monitoring, or treatment strategies. Further research is now required to confirm whether these miRNAs are differentially expressed in older adults with sarcopenic obesity.

Effects of dietary grape seed proanthocyanidin extract supplementation on meat quality, muscle fiber characteristics and antioxidant capacity of finishing pigs

The aim of this study was to investigate effects of dietary grape seed proanthocyanidin extract (GSPE) supplementation on meat quality, muscle fiber characteristics and antioxidant capacity of finishing pigs. The data showed GSPE increased pH24 h, redness, crude protein content and decreased shear force, drip loss48 h, lactate content and glycolytic potential in longissimus dorsi (LD) muscle, accompanied by increased contents of total polyunsaturated fatty acid (PUFA), n-3 PUFA, and the ratio of PUFA to saturated fatty acid. GSPE promoted MyHC I mRNA and slow MyHC protein expression, and increased slow-twitch fiber percentage. The activities of total antioxidant capacity, total superoxide dismutase, catalase and glutathione peroxidase in LD muscle were increased by GSPE while malondialdehyde content was decreased. Together, this study demonstrated that dietary GSPE supplementation can effectively improve the color, water-holding capacity, tenderness and nutritional value of pork, and increase slow-twitch fiber percentage and antioxidant capacity of finishing pigs.

Effects of Various Muscle Disuse States and Countermeasures on Muscle Molecular Signaling

Skeletal muscle is capable of changing its structural parameters, metabolic rate and functional characteristics within a wide range when adapting to various loading regimens and states of the organism. Prolonged muscle inactivation leads to serious negative consequences that affect the quality of life and work capacity of people. This review examines various conditions that lead to decreased levels of muscle loading and activity and describes the key molecular mechanisms of muscle responses to these conditions. It also details the theoretical foundations of various methods preventing adverse muscle changes caused by decreased motor activity and describes these methods. A number of recent studies presented in this review make it possible to determine the molecular basis of the countermeasure methods used in rehabilitation and space medicine for many years, as well as to identify promising new approaches to rehabilitation and to form a holistic understanding of the mechanisms of gravity force control over the muscular system.

Non-coding RNA basis of muscle atrophy

Muscle atrophy is a common complication of many chronic diseases including heart failure, cancer cachexia, aging, etc. Unhealthy habits and usage of hormones such as dexamethasone can also lead to muscle atrophy. However, the underlying mechanisms of muscle atrophy are not completely understood. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long ncRNAs (lncRNAs), and circular RNAs (circRNAs), play vital roles in muscle atrophy. This review mainly discusses the regulation of ncRNAs in muscle atrophy induced by various factors such as heart failure, cancer cachexia, aging, chronic obstructive pulmonary disease (COPD), peripheral nerve injury (PNI), chronic kidney disease (CKD), unhealthy habits, and usage of hormones; highlights the findings of ncRNAs as common regulators in multiple types of muscle atrophy; and summarizes current therapies and underlying mechanisms for muscle atrophy. This review will deepen the understanding of skeletal muscle biology and provide new strategies and insights into gene therapy for muscle atrophy.

Suppression of MALAT1 alleviates neurocyte apoptosis and reactive oxygen species production through the miR-499-5p/SOX6 axis in subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH), a common devastating cerebrovascular accident, is a great threat to human health and life. Exploration of the potential therapeutic target of SAH is urgently needed. Previous studies showed that long noncoding RNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) promotes cell apoptosis in various diseases, while its role in SAH remains unclear. In our study, we established a mouse model of SAH and used the oxyhemoglobin (OxyHb) to induce neuronal injury in vitro. Interestingly, MALAT1 was found upregulated in brain tissues of SAH mice and OxyHb-stimulated neurons. In addition, knockdown of MALAT1 attenuated apoptosis and decreased reactive oxygen species (ROS) production in OxyHb-stimulated neurons. Mechanistically, we demonstrated that MALAT1 bound with miR-499-5p. Furthermore, our findings indicated that miR-499-5p bound to SOX6 3' untranslated region (UTR) and negatively regulated SOX6 mRNA and protein levels. Rescue assays suggested that SOX6 overexpression counteracted the effects of MALAT1 knockdown on neurocyte apoptosis, and ROS production in OxyHb-stimulated neurons. The in vivo assays indicated that knockdown of MALAT1 improved brain injury of SAH mice. Our study demonstrates that silencing of MALAT1 alleviates neurocyte apoptosis and reduces ROS production through the miR-499-5p/SOX6 axis after SAH injury.

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.

Procyanidin B2 induces porcine skeletal slow-twitch myofiber gene expression by AMP-activated protein kinase signaling pathway

In this study, our aim is to investigate the effect of dimer procyanidin B2 [epicatechin-(4β-8)-epicatechin] (PB2) on porcine skeletal myofiber gene expression in vitro. Our data showed PB2 promoted the protein expression of slow myosin heavy chain (MyHC) in porcine myotubes, concomitant with the increases in mRNA levels of MyHC I, MyHC IIa and Tnni1. We also found PB2 activated AMPK signaling in porcine myotubes. NRF1 and CaMKKβ that are two important upstream factors of AMPK, and Sirt1 and PGC-1α that are two major downstream factors of AMPK, were also up-regulated by PB2. The mechanism study showed the effect of PB2 on slow-twitch myofiber gene expression was abolished by AMPK inhibitor compound C or by AMPKα1 siRNA. Together, we found PB2 induced porcine skeletal slow-twitch myofiber gene expression by AMPK signaling pathway.

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.

Potential roles of mediator Complex Subunit 13 in Cardiac Diseases

Mediator complex subunit 13 (MED13, previously known as THRAP1 and TRAP240) is a subunit of the cyclin-dependent kinase 8 (CDK8) kinase module in the eukaryotic mediator complex. MED13 has been known to play critical roles in cell cycle, development, and growth. The purpose of this review is to comprehensively discuss its newly identified potential roles in myocardial energy metabolism and non-metabolic cardiovascular diseases. Evidence indicates that cardiac MED13 mainly participates in the regulation of nuclear receptor signaling, which drives the transcription of genes involved in modulating cardiac and systemic energy homeostasis. MED13 is also associated with several pathological conditions, such as metabolic syndrome and thyroid disease-associated heart failure. Therefore, MED13 constitutes a potential therapeutic target for the regulation of metabolic disorders and other cardiovascular diseases.

MicroRNA-499-5p targets SIRT1 to aggravate lipopolysaccharide-induced acute lung injury

Acute lung injury (ALI) is a life-threatening disease without effective and specific therapeutic strategies except the life-supporting treatments. Inflammation and oxidative stress are essential for the progression of ALI. MicroRNA-499-5p (miR-499-5p) has multiple pathophysiological actions; however, its function and mechanisms in ALI remain elusive. Mice were intravenously injected with miR-499-5p agomir, antagomir or the negative controls for 3 consecutive days and then received a single intratracheal injection of lipopolysaccharide (LPS, 5 mg/kg) to generate ALI model. Twenty four hours prior to LPS injection, EX-527 (1 mg/kg) was applied to inhibit SIRT1 activity. We identified a significant upregulation of miR-499-5p in LPS-treated lung tissues. miR-499-5p antagomir prevented, while miR-499-5p agomir promoted inflammation, oxidative stress and ALI in LPS-treated mice. Further studies indicated that miR-499-5p directly bound to the 3'-untranslated region of Sirtuin 1 (Sirt1) and decreased its protein level. SIRT1 inhibition blocked miR-499-5p antagomir-mediated pulmonary protection against LPS injury. miR-499-5p targets SIRT1 to aggravate LPS-induced ALI and it is a promising therapeutic target for the treatment of ALI.

NO-Dependent Mechanisms of Myosin Heavy Chain Transcription Regulation in Rat Soleus Muscle After 7-Days Hindlimb Unloading

It is known that nitric oxide (NO) may affect myosin heavy chain (MyHC) isoform mRNA transcription in skeletal muscles. The content of NO in soleus muscles decreases during rat hindlimb unloading as well as slow MyHC mRNA transcription. We aimed to detect which signaling pathways are involved in NO-dependent prevention of hindlimb-suspension (HS)-induced changes in MyHCs’ expression pattern. Male Wistar rats were divided into four groups: cage control group (C), hindlimb suspended for 7 days (7HS), hindlimb suspended for 7 days with L-arginine administration (7HS+A) (500 mg/kg body mass), and hindlimb suspended for 7 days with both L-arginine (500 mg/kg) and NO-synthase inhibitor L-NAME administration (50 mg/kg) (7HS+A+N). L-arginine treatment during 7 days of rat HS prevented HS-induced NO content decrease and slow MyHC mRNA transcription decrease and attenuated fast MyHC IIb mRNA transcription increase; it also prevented NFATc1 nuclear content decrease, calsarcin-2 expression increase, and GSK-3β Ser 9 phosphorylation decrease. Moreover, L-arginine administration prevented the HS-induced myh7b and PGC1α mRNAs content decreases and slow-type genes repressor SOX6 mRNA transcription increase. All these slow fiber-type protective effects of L-arginine were blocked in HS+A+N group, indicating that these effects were NO-dependent. Thus, NO decrease prevention during HS restores calcineurin/NFATc1 and myh7b/SOX6 signaling.

miRNA-mRNA network regulation in the skeletal muscle fiber phenotype of chickens revealed by integrated analysis of miRNAome and transcriptome

Skeletal muscle fibers are primarily categorized into oxidative and glycolytic fibers, and the ratios of different myofiber types are important factors in determining livestock meat quality. However, the molecular mechanism for determining muscle fiber types in chickens was hardly understood. In this study, we used RNA sequencing to systematically compare mRNA and microRNA transcriptomes of the oxidative muscle sartorius (SART) and glycolytic muscle pectoralis major (PMM) of Chinese Qingyuan partridge chickens. Among the 44,705 identified mRNAs in the two types of muscles, 3,457 exhibited significantly different expression patterns, including 2,364 up-regulated and 1,093 down-regulated mRNAs in the SART. A total of 698 chicken miRNAs were identified, including 189 novel miRNAs, among which 67 differentially expressed miRNAs containing 42 up-regulated and 25 down-regulated miRNAs in the SART were identified. Furthermore, function enrichment showed that the differentially expressed mRNAs and miRNAs were involved in energy metabolism, muscle contraction, and calcium, peroxisome proliferator-activated receptor (PPAR), insulin and adipocytokine signaling. Using miRNA-mRNA integrated analysis, we identified several candidate miRNA-gene pairs that might affect muscle fiber performance, viz, gga-miR-499-5p/SOX6 and gga-miR-196-5p/CALM1, which were supported by target validation using the dual-luciferase reporter system. This study revealed a mass of candidate genes and miRNAs involved in muscle fiber type determination, which might help understand the molecular mechanism underlying meat quality traits in chickens.

Profiling and Functional Analysis of Circular RNAs in Porcine Fast and Slow Muscles

The different skeletal muscle fiber types exhibit distinctively different physiological and metabolic properties, and have been linked to both human metabolic diseases and meat quality traits in livestock. Circular RNAs (circRNAs) are a new class of endogenous RNA regulating gene expression, but regulatory mechanisms of skeletal muscle fibers involved in circRNAs remain poorly understood. Here, we constructed circRNA expression profiles of three fast-twitch biceps femoris (Bf) and three slow-twitch soleus (Sol) muscles in pigs using RNA-seq and identified 16,342 distinct circRNA candidates. Notably, 242 differentially expressed (DE) circRNAs between Bf and Sol muscles were identified, including 105 upregulated and 137 downregulated circRNAs, and are thus potential candidates for the regulation of skeletal muscle fiber conversion. Moreover, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of host genes of DE circRNAs revealed that host genes were mainly involved in skeletal muscle fiber-related GO terms (e.g., muscle contraction, contractile fiber part, and Z disk) and skeletal muscle fiber-related signaling pathways (e.g., AMPK and cGMP-PKG). We also constructed co-expression networks of DE circRNA-miRNA-mRNA using previously acquired high-throughput sequencing mRNA and miRNA data, from which 112 circRNA-miRNA and 95 miRNA-mRNA interactions were identified. Multiple circRNAs essentially serve as a sponge for miR-499-5p, which is preferentially expressed in slow-twitch muscle and reduces the severity of Duchenne muscular dystrophy (DMD). Taken together, a series of novel candidate circRNAs involved in the growth and development of porcine skeletal muscle was identified. Furthermore, they provide a comprehensive circRNA resource for further in-depth research on the regulatory mechanisms of circRNA in the formation of skeletal muscle fiber, and may provide insights into human skeletal muscle diseases.

miR-22-3p regulates muscle fiber-type conversion through inhibiting AMPK/SIRT1/PGC-1α pathway

MicroRNAs (miRNAs) are a class of conserved non-coding RNAs that are widely regarded as important regulators in a variety of biological processes. Increasing evidence has revealed that skeletal muscle fiber-type conversion is regulated by miRNAs, but the molecular mechanism is still not fully understood. In this study, we confirmed the role of miR-22-3p on skeletal muscle fiber-type conversion and investigated its potential mechanism in C2C12 myotubes. Here, we found that the miR-22-3p mimics inhibited the expressions of myosin heavy chain I (MyHC I), MyHC IIa and promoted the expression of MyHC IIb, while miR-22-3p inhibitor got inverse results. miR-22-3p mimics also downregulated phosphorylated AMPK, SIRT1 and PGC-1ɑ protein levels, which control the expression of oxidative fiber-related genes. Furthermore, Compound C (AMPK inhibitor) eliminated the effect of miR-22-3p inhibitor on MyHC I, MyHC IIa and MyHC IIb expressions. However, AICAR (AMPK activator) also abolished the effect of miR-22-3p mimics on MyHC I, MyHC IIa and MyHC IIb expressions. Collectively, our results suggest that miR-22-3p regulates skeletal muscle fiber-type conversion through inhibiting AMPK/SIRT1/PGC-1ɑ signaling pathway.

Procyanidin B2 Promotes Skeletal Slow-Twitch Myofiber Gene Expression through the AMPK Signaling Pathway in C2C12 Myotubes

Dimer procyanidin B2 [epicatechin-(4β-8)-epicatechin] (PB2) has attracted a lot of interest in nutrition and medicine because of its significant health-promoting abilities. However, the function of PB2 on different types of skeletal myofiber is still unclear. Here, we have found that PB2 significantly increased protein expression of the slow myosin heavy chain (MyHC) and decreased fast MyHC protein in C2C12 myotubes, accompanied by upregulation of mRNA expression of MyHC I, MyHC IIa, and Tnni1 and downregulation of MyHC IIx and MyHC IIb. We have also found that PB2 enhanced the activities of malate dehydrogenase and succinic dehydrogenase and reduced lactate dehydrogenase activity. PB2 promoted phosphorylation of AMPK and significantly increased mRNA expression of AMPKα1. The upstream factors of AMPK, such as phospho-LKB1, NRF1, and CaMKKβ, and the downstream factors of AMPK, including Sirt1 and PGC-1α, were also increased by PB2. Specific suppression of AMPK signaling by AMPKα1 siRNA or by AMPK inhibitor compound C significantly attenuated the PB2-induced upregulation of phospho-AMPK, PGC-1α, and slow MyHC and downregulation of fast MyHC. Our findings suggested that PB2 promotes skeletal slow-twitch myofiber gene expression through the AMPK signaling pathway in C2C12 myotubes.

Geniposide Improves Glucose Homeostasis via Regulating FoxO1/PDK4 in Skeletal Muscle

It is well-known that imbalance state of glucose metabolism triggers many metabolic diseases and glucose uptake in skeletal muscle accounts for 90% of body weight. Geniposide is one of the major natural bioactive constituents of gardenia fruit, and the regulation of geniposide on glucose metabolism in skeletal muscle has not yet been investigated. Here, on the basis of microarray analysis, we discovered that geinposide decreased pyruvate dehydrogenase kinase 4 (PDK4) expression in skeletal muscle of mice and subsequently found that geniposide inhibited the expressions of forkhead box O1 (FoxO1), PDK4, and phosphorylated pyruvate dehydrogenase in vitro and in vivo. Moreover, geniposide promoted a switch of slow-to-fast myofiber type and glucose utilization, suggesting that geniposide improved glucose homeostasis. In addition, mechanistic studies revealed that geniposide played above roles by regulating FoxO1/PDK4, which controlled fuel selection via pyruvate dehydrogenase. Meanwhile, effects of geniposide mentioned above could be reversed by FoxO1 overexpression. Together, these results establish that geniposide confers controls on fuel usage and glucose homeostasis through FoxO1/PDK4 in skeletal muscle.