miR-487b, miR-3963 and miR-6412 delay myogenic differentiation in mouse myoblast-derived C2C12 cells

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.

MicroRNA-24-3p promotes skeletal muscle differentiation and regeneration by regulating HMGA1

Numerous studies have established the critical roles of microRNAs in regulating post-transcriptional gene expression in diverse biological processes. Here, we report on the role and mechanism of miR-24-3p in skeletal muscle differentiation and regeneration. miR-24-3p promotes myoblast differentiation and skeletal muscle regeneration by directly targeting high mobility group AT-hook 1 (HMGA1) and regulating it and its direct downstream target, the inhibitor of differentiation 3 (ID3). miR-24-3p knockdown in neonatal mice increases PAX7-positive proliferating muscle stem cells (MuSCs) by derepressing Hmga1 and Id3. Similarly, inhibition of miR-24-3p in the tibialis anterior muscle prevents Hmga1 and Id3 downregulation and impairs regeneration. These findings provide evidence that the miR-24-3p/HMGA1/ID3 axis is required for MuSC differentiation and skeletal muscle regeneration in vivo.

MondoA Is Required for Normal Myogenesis and Regulation of the Skeletal Muscle Glycogen Content in Mice

BACKGROUND

Skeletal muscle is the largest tissue in the human body, and it plays a major role in exerting force and maintaining metabolism homeostasis. The role of muscle transcription factors in the regulation of metabolism is not fully understood. MondoA is a glucose-sensing transcription factor that is highly expressed in skeletal muscle. Previous studies suggest that MondoA can influence systemic metabolism homeostasis. However, the function of MondoA in the skeletal muscle remains unclear.

METHODS

We generated muscle-specific MondoA knockout (MAKO) mice and analyzed the skeletal muscle morphology and glycogen content. Along with skeletal muscle from MAKO mice, C2C12 myocytes transfected with small interfering RNA against MondoA were also used to investigate the role and potential mechanism of MondoA in the development and glycogen metabolism of skeletal muscle.

RESULTS

MAKO caused muscle fiber atrophy, reduced the proportion of type II fibers compared to type I fibers, and increased the muscle glycogen level. MondoA knockdown inhibited myoblast proliferation, migration, and differentiation by inhibiting the phosphatase and tensin homolog (PTEN)/phosphoinositide 3-kinase (PI3K)/Akt pathway. Further mechanistic experiments revealed that the increased muscle glycogen in MAKO mice was caused by thioredoxin-interacting protein (TXNIP) downregulation, which led to upregulation of glucose transporter 4 (GLUT4), potentially increasing glucose uptake.

CONCLUSION

MondoA appears to mediate mouse myofiber development, and MondoA decreases the muscle glycogen level. The findings indicate the potential function of MondoA in skeletal muscle, linking the glucose-related transcription factor to myogenesis and skeletal myofiber glycogen metabolism.

New perspective on the regulation of acetylcholinesterase via the aryl hydrocarbon receptor

Acetylcholinesterase (AChE, EC 3.1.1.7) plays important roles in cholinergic neurotransmission and has been widely recognized as a biomarker for monitoring pollution by organophosphate (OP) and carbamate pesticides. Dioxin is an emerging environmental AChE disruptor and is a typical persistent organic pollutant with multiple toxic effects on the nervous system. Growing evidence has shown that there is a significant link between dioxin exposure and neurodegenerative diseases and neurodevelopmental disorders, most of which involve AChE and cholinergic dysfunctions. Therefore, an in-depth understanding of the effects of dioxin on AChE and the related mechanisms of action might help to shed light on the molecular bases of dioxin impacts on the nervous system. In the past decade, the effects of dioxins on AChE have been revealed in cultured cells of different origins and in rodent animal models. Unlike OP and carbamate pesticides, dioxin-induced AChE disturbance is not due to direct inhibition of enzymatic activity; instead, dioxin causes alterations of AChE expression in certain models. As a widely accepted mechanism for most dioxin effects, the aryl hydrocarbon receptor (AhR)-dependent pathway has become a research focus in studies on the mechanism of action of dioxin-induced AChE dysregulation. In this mini-review, the effects of dioxin on AChE and the diverse roles of the AhR pathway in AChE regulation are summarized. Additionally, the involvement of AhR in AChE regulation during different neurodevelopmental processes is discussed. These AhR-related findings might also provide new insight into AChE regulation triggered by diverse xenobiotics capable of interacting with AhR.

DKK3 knockdown confers negative effects on the malignant potency of head and neck squamous cell carcinoma cells via the PI3K/Akt and MAPK signaling pathways

Dickkopf‑related protein 3 (DKK3), which is a member of the Dickkopf WNT signaling pathway inhibitor family, is considered to be a tumor suppressor, due to its reduced expression in cancer cells and its ability to induce apoptosis when overexpressed by adenovirus. However, our previous study demonstrated alternative functions for DKK3 in head and neck squamous cell carcinoma (HNSCC). Our study reported that DKK3 expression was predominantly upregulated in HNSCC cell lines and tissue samples, and its expression was significantly correlated with poor prognosis. Furthermore, DKK3 overexpression in HNSCC cells significantly increased cancer cell proliferation, migration, invasion and in vivo tumor growth. These data have led to the hypothesis that DKK3 may exert oncogenic functions and may increase the malignant properties of HNSCC. The present study established a stable DKK3 knockdown cell line (HSC‑3 shDKK3) using lentivirus‑mediated short hairpin RNA, and assessed its effects on cancer cell behavior using MTT, migration and invasion assays. In addition, its effects on in vivo tumor growth were assessed using a xenograft model. Furthermore, the molecular mechanisms underlying the effects of DKK3 knockdown were investigated by microarray analysis, pathway analysis and western blotting. Compared with control cells, HSC‑3 shDKK3 cells exhibited significantly reduced proliferation, migration and invasion, and formed significantly smaller tumor masses when subcutaneously transplanted into nude mice. In addition, in HSC‑3 shDKK3 cells, the expression levels of phosphorylated (p)‑protein kinase B (Akt) (Ser473), p‑phosphoinositide 3‑kinase (PI3K) p85 (Tyr467), p‑PI3K p55 (Try199), p‑3‑phosphoinositide‑dependent protein kinase‑1 (PDK1) (Ser241) and total p38 mitogen‑activated protein kinase (MAPK) were reduced. Furthermore, phosphorylation of mechanistic target of rapamycin (mTOR) (Ser2448) was slightly decreased in HSC‑3 shDKK3 cells, which may be due to the increased expression of DEP domain‑containing mTOR‑interacting protein. Conversely, DKK3 overexpression in HSC‑3 shDKK3 cells rescued cellular proliferation, migration and invasion. With regards to expression levels, p‑PI3K and p‑PDK1 expression was not altered, whereas mTOR and p‑p38 MAPK expression was elevated. These data supported the hypothesis and indicated that DKK3 may contribute to the malignant phenotype of HNSCC cells via the PI3K/Akt/mTOR and MAPK signaling pathways.

MiR-139 promotes differentiation of bovine skeletal muscle-derived satellite cells by regulating DHFR gene expression

MicroRNAs play an important regulatory role in the proliferation and differentiation of skeletal muscle-derived satellite cells (MDSCs). In particular, miR-139 can inhibit tumor cell proliferation and invasion, and its expression is down-regulated during C2C12 myoblast differentiation. The aim of this study was thus to examine the effect and potential mechanism of miR-139 in bovine MDSCs. The expression of miR-139 was found to be significantly increased during bovine MDSC differentiation by stem-loop reverse transcription-polymerase chain reaction amplification. Statistical analysis of the myotube fusion rate was done through immunofluorescence detection of desmin, and western blotting was used to measure the change in protein expression of the muscle differentiation marker genes MYOG and MYH3. The results showed that the miR-139 mimic could enhance the differentiation of bovine MDSCs, whereas the inhibitor had the opposite effect. By using the dual-luciferase reporter system, miR-139 was found to target the 3'-untranslated region of the dihydrofolate reductase (DHFR) gene and regulate its expression. In addition, the expression of miR-139 was found to be regulated by its host gene phosphodiesterase 2A (PDE2A) via inhibition of the latter by CRISPR interference (CRISPRi). Overall, our findings indicate that miR-139 plays an important role in regulating the differentiation of bovine MDSCs.

A newly identified lncRNA MAR1 acts as a miR-487b sponge to promote skeletal muscle differentiation and regeneration

BACKGROUND

Skeletal muscle atrophy induced by either aging (sarcopenia) or mechanical unloading is associated with serious health consequences. Long non-coding RNAs (lncRNAs) are implicated as important regulators in numerous physiological and pathological processes.

METHODS

Microarray analysis was performed to identify the differentially expressed lncRNAs in skeletal muscle between adult and aged mice. The most decreased lncRNA in aged skeletal muscle was identified. The C2C12 mouse myoblast cells were used to assess the biological function of the lncRNA in vitro. The target microRNA of lncRNA and the target protein of microRNA were predicted by bioinformatics analysis and validated in vitro. Furthermore, the biology function of the lncRNA in vivo was investigated by local overexpression or knockdown the lncRNA in skeletal muscle. The therapeutic effect of the lncRNA overexpression in age-related or mechanical unloading-induced muscle atrophy was also evaluated.

RESULTS

We identified a novel lncRNA (muscle anabolic regulator 1, MAR1) which was highly expressed in mice skeletal muscle and positively correlated with muscle differentiation and growth in vitro and in vivo. We predicted and validated that microRNA-487b (miR-487b) was a direct target of MAR1. We also predicted and validated that Wnt5a, an important regulator during myogenesis, was a target of miR-487b in C2C12 cells. Our findings further demonstrated that enforced MAR1 expression in myoblasts led to derepression of Wnt5a. Moreover, MAR1 promoted skeletal muscle mass/strength and Wnt5a protein level in mice. Enforced MAR1 expression in mice attenuated muscle atrophy induced by either aging or unloading.

CONCLUSIONS

The newly identified lncRNA MAR1 acts as a miR-487b sponge to regulate Wnt5a protein, resulting in promoting muscle differentiation and regeneration. MAR1 could be a novel therapeutic target for treating muscle atrophy induced by either aging or mechanical unloading.

Effects of microRNAs on skeletal muscle development

MicroRNAs (miRNAs) are small (about 22 nucleotides) noncoding RNAs, which were highly conserved among mammals. They have ushered in a new era in molecular biology over twenty years. They can negatively regulate gene expression at the posttranscriptional level through the principle of complementary base pairing with the 3' untranslated region (UTR) of their target mRNAs and induce their degradation. They involve in tissue morphogenesis, cellular processes like apoptosis, and major signaling pathways. Previous studies have promoted our understanding that miRNAs play an important role in myogenesis and have a big impact on muscle mass, muscle fiber type and muscle diseases. Many researchers have provided evidence of the involvement of muscle-specific and enriched miRNAs in the individual stages of skeletal muscle development as well as of their significant influence on muscle metabolism during quiescence, proliferation, differentiation and regeneration. Here, we focus on the microRNAs that related to the development of skeletal muscle. For example, some microRNAs are upregulated in differentiated skeletal muscle and can promote differentiation, like, miR-1, miR-24, miR-26a, miR-181 and miR-206. However, some microRNAs highly expressed in proliferating myoblasts, downregulated in differentiated and could inhibit differentiation, like MiR-221 and miR-222. Some others not only promote skeletal muscle proliferation, but also promote differentiation, like miR-214. Studying the miRNAs' regulatory mechanisms in skeletal development will help us know more about the knowledge of miRNAs in muscle developmental biology and make us learn more about involved signal pathway.

Involvement of miR-140-3p in Wnt3a and TGFβ3 signaling pathways during osteoblast differentiation in MC3T3-E1 cells

The Wnt/β-catenin signaling and TGFβ signaling pathways play a key role in osteoblast differentiation. The miRNAs play important roles in regulating gene expression at the post-transcriptional level through fine-tuning of protein-encoding gene expression. However, involvement of miRNAs is not established for Wnt3a and TGFβ signaling pathways in osteoblast differentiation. Here, we examined the role of miRNAs expressed differentially after Wnt3a expression during osteoblast differentiation. Over-expression of the Wnt3a gene increased ALP transcription, but decreased Col1, Runx2, and OCN transcription in osteoblastic MC3T3-E1 cells. Expression profiling and quantitative PCR for miRNAs showed that miR-140-3p decreased in Wnt3a-over-expressing osteoblastic cells. Wnt3a over-expression increased TGFβ3 expression, whereas transfection of the miR-140-3p mimic into MC3T3-E1 cells significantly inhibited TGFβ3 expression. Luciferase assay for the TGFβ3 transcript showed that TGFβ3 was a direct target of miR-140-3p. miR-140-3p mimic transfection resulted in significantly increased OCN transcription, but did not affect ALP, Col1, and Runx2 transcription in MC3T3-E1 cells. rTGFβ3 treatment decreased OCN transcription in MC3T3-E1 cells. These results suggest that the miR-140-3p is involved in osteoblast differentiation as a critical regulatory factor between Wnt3a and TGFβ3 signaling pathways.

Distinct transcriptomic changes in E14.5 mouse skeletal muscle lacking RYR1 or Cav1.1 converge at E18.5

In skeletal muscle the coordinated actions of two mechanically coupled Ca2+ channels-the 1,4-dihydropyridine receptor (Cav1.1) and the type 1 ryanodine receptor (RYR1)-underlie the molecular mechanism of rapid cytosolic [Ca2+] increase leading to contraction. While both [Ca2+]i and contractile activity have been implicated in the regulation of myogenesis, less is known about potential specific roles of Cav1.1 and RYR1 in skeletal muscle development. In this study, we analyzed the histology and the transcriptomic changes occurring at E14.5 -the end of primary myogenesis and around the onset of intrauterine limb movement, and at E18.5 -the end of secondary myogenesis, in WT, RYR1-/-, and Cav1.1-/- murine limb skeletal muscle. At E14.5 the muscle histology of both mutants exhibited initial alterations, which became much more severe at E18.5. Immunohistological analysis also revealed higher levels of activated caspase-3 in the Cav1.1-/- muscles at E14.5, indicating an increase in apoptosis. With WT littermates as controls, microarray analyses identified 61 and 97 differentially regulated genes (DEGs) at E14.5, and 493 and 1047 DEGs at E18.5, in RYR1-/- and Cav1.1-/- samples, respectively. Gene enrichment analysis detected no overlap in the affected biological processes and pathways in the two mutants at E14.5, whereas at E18.5 there was a significant overlap of DEGs in both mutants, affecting predominantly processes linked to muscle contraction. Moreover, the E18.5 vs. E14.5 comparison revealed multiple genotype-specific DEGs involved in contraction, cell cycle and miRNA-mediated signaling in WT, neuronal and bone development in RYR1-/-, and lipid metabolism in Cav1.1-/- samples. Taken together, our study reveals discrete changes in the global transcriptome occurring in limb skeletal muscle from E14.5 to E18.5 in WT, RYR1-/- and Cav1.1-/- mice. Our results suggest distinct functional roles for RYR1 and Cav1.1 in skeletal primary and secondary myogenesis.

Predicted effects of observed changes in the mRNA and microRNA transcriptome of lung neutrophils during S. pneumoniae pneumonia in mice

The complex role of neutrophils in modulating the inflammatory response is increasingly appreciated. Our studies profiled the expression of mRNAs and microRNAs (miRs) in lung neutrophils in mice during S. pneumoniae pneumonia and performed in depth in silico analyses. Lung neutrophils were isolated 24 hours after intratracheal instillation of PBS or S. pneumoniae, and differentially expressed (DE) mRNAs and miRs were identified. Lung neutrophils from mice with S. pneumoniae pneumonia contained 4127 DE mRNAs, 36% of which were upregulated at least 2-fold. During pneumonia, lung neutrophils increase expression of pattern recognition receptors, receptors for inflammatory mediators, transcription factors including NF-κB and AP-1, Nrf2 targets, cytokines, chemokines and other inflammatory mediators. Interestingly, neutrophils responded to Type I interferons, whereas they both produced and responded to Type II interferon. Expression of regulators of the inflammatory and immune response was verified at the mRNA and protein level. Of approximately 1100 miRs queried, 31 increased and 67 decreased more than 2-fold in neutrophils from S. pneumoniae pneumonia. Network analyses of potential DE miR-target DE mRNA interactions revealed candidate key regulatory miRs. Thus, S. pneumoniae modulates mRNA and miR expression by lung neutrophils, increasing their ability to respond and facilitating host defense.

DKK3 Overexpression Increases the Malignant Properties of Head and Neck Squamous Cell Carcinoma Cells

DKK3, a member of the dickkopf Wnt signaling pathway inhibitor family, is believed to be a tumor suppressor because of its reduced expression in cancer cells. However, our previous studies have revealed that DKK3 expression is predominantly observed in head and neck/oral squamous cell carcinoma (HNSCC/OSCC). Interestingly, HNSCC/OSCC patients with DKK3 expression showed a high rate of metastasis and poorer survival, and siRNA-mediated knockdown of DKK3 in HNSCC-derived cancer cell lines resulted in reduced cellular migration and invasion. From these data, it was hypothesized that DKK3 might exert an oncogenic function specific to HNSCC. In the present research, the DKK3 overexpression model was established, and its influences were investigated, together with molecular mechanism studies. The DKK3 expression profile in cancer cell lines was investigated, including HNSCC/OSCC, esophageal, gastric, colorectal, pancreatic, prostatic, and lung cancers. DKK3 overexpression was performed in HNSCC-derived cells by transfection of expression plasmid. The effects of DKK3 overexpression were assessed on cellular proliferation, migration, invasion, and in vivo tumor growth. The molecular mechanism of DKK3 overexpression was investigated by Western blotting and microarray analysis. DKK3 overexpression significantly elevated cellular proliferation, migration, and invasion, as well as increased mRNA expression of cyclin D1 and c-myc. However, reporter assays did not show TCF/LEF activation, suggesting that the increased malignant property of cancer cells was not driven by the Wnt/β-catenin pathway. For the investigation of the pathways/molecules in DKK3-mediated signals, the Western blot analyses revealed that phosphorylation of Akt (S473) and c-Jun (Ser63) was elevated. The application of a PI3K kinase inhibitor, LY294002, on HSC-3 DKK3 cells significantly decreased tumor cell proliferation, migration, and invasion. From these results, we demonstrated that DKK3 might contribute to cellular proliferation, invasion, migration, and tumor cell survival in HNSCC cells through a mechanism other than the canonical Wnt signaling pathway, which might be attributed to PI3K–Akt signaling.

Genome-wide identification of novel ovarian-predominant miRNAs: new insights from the medaka (Oryzias latipes)

MicroRNAs (miRNAs) are small, highly conserved non-coding RNAs that play important roles in the regulation of many physiological processes. However, the role of miRNAs in vertebrate oocyte formation (i.e., oogenesis) remains poorly investigated. To gain new insights into the roles of miRNAs in oogenesis, we searched for ovarian-predominant miRNAs. Using a microarray displaying 3,800 distinct miRNAs originating from different vertebrate species, we identified 66 miRNAs that are expressed predominantly in the ovary. Of the miRNAs exhibiting the highest overabundance in the ovary, 20 were selected for further analysis. Using a combination of QPCR and in silico analyses, we identified 8 novel miRNAs that are predominantly expressed in the ovary, including 2 miRNAs (miR-4785 and miR-6352) that exhibit strict ovarian expression. Of these 8 miRNAs, 7 were previously uncharacterized in fish. The strict ovarian expression of miR-4785 and miR-6352 suggests an important role in oogenesis and/or early development, possibly involving a maternal effect. Together, these results indicate that, similar to protein-coding genes, a significant number of ovarian-predominant miRNA genes are found in fish.

Lrrc75b is a novel negative regulator of C2C12 myogenic differentiation

Many transcription factors and signaling molecules involved in the guidance of myogenic differentiation have been investigated in previous studies. However, the precise molecular mechanisms of myogenic differentiation remain largely unknown. In the present study, by performing a meta-analysis of C2C12 myogenic differentiation microarray data, we found that leucine-rich repeat-containing 75B (Lrrc75b), also known as AI646023, a molecule of unknown biological function, was downregulated during C2C12 myogenic differentiation. The knockdown of Lrrc75b using specific siRNA in C2C12 myoblasts markedly enhanced the expression of muscle-specific myogenin and increased myoblast fusion and the myotube diameter. By contrast, the adenovirus-mediated overexpression of Lrrc75b in C2C12 cells markedly inhibited myoblast differentiation accompanied by a decrease in myogenin expression. In addition, the phosphorylation of extracellular signal-regulated kinase 1/2 (Erk1/2) was suppressed in the cells in which Lrrc75b was silenced. Taken together, our results demonstrate that Lrrc75b is a novel suppressor of C2C12 myogenic differentiation by modulating myogenin and Erk1/2 signaling.

MicroRNA-17-92 regulates myoblast proliferation and differentiation by targeting the ENH1/Id1 signaling axis

Myogenesis is an important biological process that occurs during both skeletal muscle regeneration and postnatal growth. Growing evidence points to the critical role of microRNAs (miRNAs) in myogenesis. Our analysis of miRNA expression patterns reveal that miRNAs of miR-17-92 cluster are dramatically downregulated in C2C12 cells after myogenesis stimulation, are strongly induced in mouse skeletal muscle after injury and decrease steadily thereafter and are downregulated with age in skeletal muscle during mouse and porcine postnatal growth. However, their roles in muscle developmental processes remain elusive. We show that the miR-17-92 cluster promotes mouse myoblast proliferation but inhibits myotube formation. miR-17, -20a and -92a target the actin-associated protein enigma homolog 1 (ENH1). The silencing of ENH1 increased the nuclear accumulation of the inhibitor of differentiation 1 (Id1) and represses myogenic differentiation. Furthermore, the injection of adenovirus expressing miR-20a into the tibialia anterior muscle downregulates ENH1 and delays regeneration. In addition, the downregulation of miR-17-92 during myogenesis is transcriptionally regulated by E2F1. Overall, our results reveal a E2F1/miR-17-92/ENH1/Id1 regulatory axis during myogenesis.