Interaction of Wnt Signaling with BMP/Smad Signaling during the Transition from Cell Proliferation to Myogenic Differentiation in Mouse Myoblast-Derived Cells

Expression and regulation of Noggin4 gene in chicken ovarian follicles and its role in the proliferation and differentiation of granulosa cells

As a member of Noggin family, Noggin4 is reported to play an important role in the formation of head structure during the embryo development of Xenopus laevis and chicken. We previously detected an increase of Noggin4 transcript in the granulosa cells of chicken hierarchal follicles (Post-GCs) compared to pre-hierarchal follicles (Pre-GCs) by ONT transcriptome sequencing. To further clarify the role of Noggin4 in chicken follicle selection, in this study, we investigated its expression, regulation and function in follicles and granulosa cells. The mRNA expression of chicken Noggin4 exhibited dynamic changes during follicle development. It was significantly higher in the small yellow follicles than in the small white, F6, F5 and F4 follicles, and also increased in Post-GCs than in Pre-GCs. The Noggin4 mRNA could be stimulated by follicle stimulating hormone (FSH) and bone morphogenetic protein 4 (BMP4) in both Pre-GCs and Post-GCs. However, the estrogen and progesterone could exert opposing transcriptional regulations on Noggin 4 mRNA in both Pre- and Post-GCs. In chicken Post-GCs, knockdown of Noggin4 by siRNA reduced the mRNA expression of steroidogenic acute regulatory protein (STAR), cytochrome P450 family 11 subfamily A member 1 (CYP11A1), but increased that of Wnt family member 4 (Wnt4), while overexpression of Noggin4 significantly decreased the mRNA expression of Wnt4 but had no marked effects on that of STAR and CYP11A1. Moreover, Noggin4 significantly decreased the mRNA expression of BMP4 in both Pre-GCs and Post-GCs. Overexpression of Noggin4 inhibited the proliferation of both Pre-GCs and Post-GCs. These data collectively suggest an important role of Noggin4 in chicken follicle selection, especially on the proliferation of granulosa cells.

Activation of β-catenin in mesenchymal progenitors leads to muscle mass loss

Loss of muscle mass is a common manifestation of chronic disease. We find the canonical Wnt pathway to be activated in mesenchymal progenitors (MPs) from cancer-induced cachectic mouse muscle. Next, we induce β-catenin transcriptional activity in murine MPs. As a result, we observe expansion of MPs in the absence of tissue damage, as well as rapid loss of muscle mass. Because MPs are present throughout the organism, we use spatially restricted CRE activation and show that the induction of tissue-resident MP activation is sufficient to induce muscle atrophy. We further identify increased expression of stromal NOGGIN and ACTIVIN-A as key drivers of atrophic processes in myofibers, and we verify their expression by MPs in cachectic muscle. Finally, we show that blocking ACTIVIN-A rescues the mass loss phenotype triggered by β-catenin activation in MPs, confirming its key functional role and strengthening the rationale for targeting this pathway in chronic disease.

MicroRNAs as the Sentinels of Redox and Hypertrophic Signalling

Oxidative stress and inflammation are associated with skeletal muscle function decline with ageing or disease or inadequate exercise and/or poor diet. Paradoxically, reactive oxygen species and inflammatory cytokines are key for mounting the muscular and systemic adaptive responses to endurance and resistance exercise. Both ageing and lifestyle-related metabolic dysfunction are strongly linked to exercise redox and hypertrophic insensitivity. The adaptive inability and consequent exercise intolerance may discourage people from physical training resulting in a vicious cycle of under-exercising, energy surplus, chronic mitochondrial stress, accelerated functional decline and increased susceptibility to serious diseases. Skeletal muscles are malleable and dynamic organs, rewiring their metabolism depending on the metabolic or mechanical stress resulting in a specific phenotype. Endogenous RNA silencing molecules, microRNAs, are regulators of these metabolic/phenotypic shifts in skeletal muscles. Skeletal muscle microRNA profiles at baseline and in response to exercise have been observed to differ between adult and older people, as well as trained vs. sedentary individuals. Likewise, the circulating microRNA blueprint varies based on age and training status. Therefore, microRNAs emerge as key regulators of metabolic health/capacity and hormetic adaptability. In this narrative review, we summarise the literature exploring the links between microRNAs and skeletal muscle, as well as systemic adaptation to exercise. We expand a mathematical model of microRNA burst during adaptation to exercise through supporting data from the literature. We describe a potential link between the microRNA-dependent regulation of redox-signalling sensitivity and the ability to mount a hypertrophic response to exercise or nutritional cues. We propose a hypothetical model of endurance exercise-induced microRNA "memory cloud" responsible for establishing a landscape conducive to aerobic as well as anabolic adaptation. We suggest that regular aerobic exercise, complimented by a healthy diet, in addition to promoting mitochondrial health and hypertrophic/insulin sensitivity, may also suppress the glycolytic phenotype and mTOR signalling through miRNAs which in turn promote systemic metabolic health.

Transcriptional regulation of cyclophilin D by BMP/Smad signaling and its role in osteogenic differentiation

Cyclophilin D (CypD) promotes opening of the mitochondrial permeability transition pore (MPTP) which plays a key role in both cell physiology and pathology. It is, therefore, beneficial for cells to tightly regulate CypD and MPTP but little is known about such regulation. We have reported before that CypD is downregulated and MPTP deactivated during differentiation in various tissues. Herein, we identify BMP/Smad signaling, a major driver of differentiation, as a transcriptional regulator of the CypD gene, Ppif. Using osteogenic induction of mesenchymal lineage cells as a BMP/Smad activation-dependent differentiation model, we show that CypD is in fact transcriptionally repressed during this process. The importance of such CypD downregulation is evidenced by the negative effect of CypD 'rescue' via gain-of-function on osteogenesis both in vitro and in a mouse model. In sum, we characterized BMP/Smad signaling as a regulator of CypD expression and elucidated the role of CypD downregulation during cell differentiation.

FGF signaling promotes myoblast proliferation through activation of wingless signaling

Indirect flight muscles (IFMs) are the largest muscles in Drosophila and are made up of hundreds of myonuclei. The generation of these giant muscles requires a large pool of wing disc associated adult muscle precursors (AMPs), however the factors that control proliferation to form this myoblast pool are incompletely known. Here, we examine the role of fibroblast growth factor (FGF) signaling in the proliferation of wing disc associated myoblasts. We find that the components of FGF signaling are expressed in myoblasts and surrounding epithelial cells of the wing disc. Next, we show that attenuation of FGF signaling results in a diminished myoblast pool. This reduction in the pool size is due to decreased myoblast proliferation. By contrast, activating the FGF signaling pathway increases the myoblast pool size and restores the proliferative capacity of FGF knockdown flies. Finally, our results demonstrate that the FGF receptor Heartless acts through up-regulating β-catenin/Armadillo signaling to promote myoblast proliferation. Our studies identify a novel role for FGF signaling during IFM formation and uncover the mechanism through which FGF coordinates with Wingless signaling to promote myoblast proliferation.

Bu-M-P-ing Iron: How BMP Signaling Regulates Muscle Growth and Regeneration

The bone morphogenetic protein (BMP) pathway is best known for its role in promoting bone formation, however it has been shown to play important roles in both development and regeneration of many different tissues. Recent work has shown that the BMP proteins have a number of functions in skeletal muscle, from embryonic to postnatal development. Furthermore, complementary studies have recently demonstrated that specific components of the pathway are required for efficient muscle regeneration.

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.

Gene expression profiling reveals the plausible mechanisms underlying the antitumor and antimetastasis effects of Andrographis paniculata in esophageal cancer

Esophageal cancer (EC) is a seriously invasive malignancy with high mortality and poor prognosis. Metastasis of EC is the major cause of mortality. Our studies previously demonstrated that a herbal medicine Andrographis paniculata (AP) significantly suppressed EC growth and metastasis in vitro and in vivo. However, the underlying mechanisms responsible for these effects have not yet been systematically elucidated. In this context, gene expression profiling of AP-treated squamous EC cells (EC-109) was performed to reveal the regulatory mechanisms of AP in antitumor and antimetastasis signaling pathways using gene expression microarray analysis. Differentially expressed genes were identified by Affymetrix Gene Chip, followed by the real-time polymerase chain reaction validation. The results showed that the canonical pathways were significantly regulated by AP treatment, including multiple genes related to proliferation, apoptosis, intercellular adhesion, metastatic processes, and drug resistance, such as WNT, TGF-β, MAPK and ErbB signaling pathways, and ATP-binding cassette transporter subfamily members. This genomic study emerges candidate molecular targets and pathways to reveal the mechanisms involved in AP's effects, which provides scientific evidence to support the clinical application of AP in EC treatment.

Adenofection: A Method for Studying the Role of Molecular Chaperones in Cellular Morphodynamics by Depletion-Rescue Experiments

Cellular processes such as mitosis and cell differentiation are governed by changes in cell shape that largely rely on proper remodeling of the cell cytoskeletal structures. This involves the assembly-disassembly of higher-order macromolecular structures at a given time and location, a process that is particularly sensitive to perturbations caused by overexpression of proteins. Methods that can preserve protein homeostasis and maintain near-to-normal cellular morphology are highly desirable to determine the functional contribution of a protein of interest in a wide range of cellular processes. Transient depletion-rescue experiments based on RNA interference are powerful approaches to analyze protein functions and structural requirements. However, reintroduction of the target protein with minimum deviation from its physiological level is a real challenge. Here we describe a method termed adenofection that was developed to study the role of molecular chaperones and partners in the normal operation of dividing cells and the relationship with actin remodeling. HeLa cells were depleted of BAG3 with siRNA duplexes targeting the 3'UTR region. GFP-tagged BAG3 proteins were reintroduced simultaneously into >75% of the cells using recombinant adenoviruses coupled to transfection reagents. Adenofection enabled to express BAG3-GFP proteins at near physiological levels in HeLa cells depleted of BAG3, in the absence of a stress response. No effect was observed on the levels of endogenous Heat Shock Protein chaperones, the main stress-inducible regulators of protein homeostasis. Furthermore, by adding baculoviruses driving the expression of fluorescent markers at the time of cell transduction-transfection, we could dissect mitotic cell dynamics by time-lapse microscopic analyses with minimum perturbation of normal mitotic progression. Adenofection is applicable also to hard-to-infect mouse cells, and suitable for functional analyses of myoblast differentiation into myotubes. Thus adenofection provides a versatile method to perform structure-function analyses of proteins involved in sensitive biological processes that rely on higher-order cytoskeletal dynamics.

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.

Single-nucleus RNA-seq of differentiating human myoblasts reveals the extent of fate heterogeneity

Myoblasts are precursor skeletal muscle cells that differentiate into fused, multinucleated myotubes. Current single-cell microfluidic methods are not optimized for capturing very large, multinucleated cells such as myotubes. To circumvent the problem, we performed single-nucleus transcriptome analysis. Using immortalized human myoblasts, we performed RNA-seq analysis of single cells (scRNA-seq) and single nuclei (snRNA-seq) and found them comparable, with a distinct enrichment for long non-coding RNAs (lncRNAs) in snRNA-seq. We then compared snRNA-seq of myoblasts before and after differentiation. We observed the presence of mononucleated cells (MNCs) that remained unfused and analyzed separately from multi-nucleated myotubes. We found that while the transcriptome profiles of myoblast and myotube nuclei are relatively homogeneous, MNC nuclei exhibited significant heterogeneity, with the majority of them adopting a distinct mesenchymal state. Primary transcripts for microRNAs (miRNAs) that participate in skeletal muscle differentiation were among the most differentially expressed lncRNAs, which we validated using NanoString. Our study demonstrates that snRNA-seq provides reliable transcriptome quantification for cells that are otherwise not amenable to current single-cell platforms. Our results further indicate that snRNA-seq has unique advantage in capturing nucleus-enriched lncRNAs and miRNA precursors that are useful in mapping and monitoring differential miRNA expression during cellular differentiation.

Formation of the Embryonic Head in the Mouse: Attributes of a Gene Regulatory Network

The embryonic head is the first major body part to be constructed during embryogenesis. The allocation and the assembly of the progenitor tissues, which start at gastrulation, are accompanied by the spatiotemporal activity of transcription factors and signaling pathways that drives lineage specification, germ layer formation, and cell/tissue movement. The morphogenesis, regionalization, and patterning of the brain and craniofacial structures rely on the function of LIM-domain, homeodomain, and basic helix-loop-helix transcription factors. These factors constitute the central nodes of a gene regulatory network (GRN) which encompasses and intersects with signaling pathways involved with head formation. It is predicted that the functional output of this "head GRN" impacts on cellular function and cell-cell interactions that are essential for lineage differentiation and tissue modeling, which are key processes underpinning the formation of the head.

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

Background

Skeletal muscle differentiation is a multistep, complex pathway in which several important signaling molecules are involved. Recently, microRNAs (miRNAs), endogenous non-coding small RNAs that regulate mRNAs, have been proposed to be involved in skeletal muscle differentiation. In this study, we identified skeletal muscle differentiation-associated miRNAs by comparing miRNA expression profiles between C2C12 cells and Wnt4 over-expressing C2C12 cells (W4-08), which can spontaneously differentiate into myotubes.

Results

We identified miR-206, miR-133a, and miR-133b as up-regulated miRNAs and miR-487b, miR-3963 and miR-6412 as down-regulated miRNAs in differentiating cells. We focused on the down-regulated miRNAs because their functions were largely unknown. Transfection of mimics of these miRNAs into C2C12 cells resulted in significantly reduced expression of myogenic differentiation markers, including troponin T and myosin heavy chain fast type and slow type, but did not affect the expression of the myogenic transcription factors, MyoD and myogenin.

Conclusions

These miRNAs were characterized as new myogenic differentiation-associated miRNAs which may delay late myogenic differentiation or maturation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-015-0061-9) contains supplementary material, which is available to authorized users.

TGF-β/BMP signaling and other molecular events: regulation of osteoblastogenesis and bone formation

Transforming growth factor-beta (TGF-β)/bone morphogenetic protein (BMP) plays a fundamental role in the regulation of bone organogenesis through the activation of receptor serine/threonine kinases. Perturbations of TGF-β/BMP activity are almost invariably linked to a wide variety of clinical outcomes, i.e., skeletal, extra skeletal anomalies, autoimmune, cancer, and cardiovascular diseases. Phosphorylation of TGF-β (I/II) or BMP receptors activates intracellular downstream Smads, the transducer of TGF-β/BMP signals. This signaling is modulated by various factors and pathways, including transcription factor Runx2. The signaling network in skeletal development and bone formation is overwhelmingly complex and highly time and space specific. Additive, positive, negative, or synergistic effects are observed when TGF-β/BMP interacts with the pathways of MAPK, Wnt, Hedgehog (Hh), Notch, Akt/mTOR, and miRNA to regulate the effects of BMP-induced signaling in bone dynamics. Accumulating evidence indicates that Runx2 is the key integrator, whereas Hh is a possible modulator, miRNAs are regulators, and β-catenin is a mediator/regulator within the extensive intracellular network. This review focuses on the activation of BMP signaling and interaction with other regulatory components and pathways highlighting the molecular mechanisms regarding TGF-β/BMP function and regulation that could allow understanding the complexity of bone tissue dynamics.

CEP2 attenuates myoblast differentiation but does not affect proliferation

CEP2 (CDC42EP2) is a member of the CDC42 subfamily that belongs to the Rho family. The Rho family plays an important role in a variety of cellular processes including skeletal myogenesis. Here, we find the expression of CEP2 increased significantly during C2C12 myogenesis. Overexpression of CEP2 could attenuate myoblast differentiation, while knockdown of CEP2 by siRNA results in enhancing myogenesis. Furthermore, we demonstrate for the first time that CEP2 attenuates myoblast differentiation via suppression of muscle regulatory factors (MRFs) rather than influencing myoblast proliferation. These results indicate that CEP2 acts as a repressor during myogenesis, which provides new insights into the role of CEP2 in muscle development.

Wnt4/β-catenin signaling pathway modulates balloon-injured carotid artery restenosis via disheveled-1

BACKGROUND

Restenosis is a common adverse event of endovascular procedures and troubles cardiologists. However, the mechanism underlying restenosis is still not fully understood. To evaluate whether disheveled-1 (Dvl-1) is involved in the Wnt4/β-catenin signaling pathway to participate in the mechanisms of vascular restenosis.

METHODOLOGY

Rat model of balloon-injured carotid artery was established and atorvastatin was used to treat artery injury. Vascular smooth muscle cells (VSMC) were isolated from rats and cultured in DMEM exposed to AngII. Down-regulation and overexpression of Dvl-1 were conducted in cells to explore the role underlying its effects on VSMC proliferation and collagen expression. Adenovirus with overexpressing Dvl-1 was injected into rats to evaluate the role of Dvl-1 in artery injury rats.

RESULTS

The results in vivo found that Wnt4, Dvl-1 and β-catenin expression as well as collagen volume fraction (CVF) in injured artery were significantly increased. The results in vitro showed that Dvl-1 overexpression reversed the treatment effects of atorvastatin on VSMCs proliferation and collagen expression. It was also canceled by overexpressing Dvl-1 that the decrease of β-catenin protein treated with atorvastatin in cells exposed to AngII. In addition, treated artery injury rats with atorvastatin, the group with injection of Ad-Dvl-1 had higher levels of intima thickness, intimal/medial area ratio and CVF.

CONCLUSION

Dvl-1 was probably a key regulator in the pathway of wnt4/β-catenin to take part in the vascular restenosis partly, and Dvl-1 is a potential gene to anti- restenosis.

Vitamin D deficiency down-regulates Notch pathway contributing to skeletal muscle atrophy in old wistar rats

BACKGROUND

The diminished ability of aged muscle to self-repair is a factor behind sarcopenia and contributes to muscle atrophy. Muscle repair depends on satellite cells whose pool size is diminished with aging. A reduction in Notch pathway activity may explain the age-related decrease in satellite cell proliferation, as this pathway has been implicated in satellite cell self-renewal. Skeletal muscle is a target of vitamin D which modulates muscle cell proliferation and differentiation in vitro and stimulates muscle regeneration in vivo. Vitamin D status is positively correlated to muscle strength/function, and elderly populations develop a vitamin D deficiency. The aim of this study was to evaluate how vitamin D deficiency induces skeletal muscle atrophy in old rats through a reduction in Notch pathway activity and proliferation potential in muscle.

METHODS

15-month-old male rats were vitamin D-depleted or not (control) for 9 months (n = 10 per group). Rats were 24-month-old at the end of the experiment. Gene and/or protein expression of markers of proliferation, or modulating proliferation, and of Notch signalling pathway were studied in the tibialis anterior muscle by qPCR and western blot. An unpaired student's t-test was performed to test the effect of the experimental conditions.

RESULTS

Vitamin D depletion led to a drop in concentrations of plasma 25-hydroxyvitamin D in depleted rats compared to controls (-74%, p < 0.01). Tibialis anterior weight was decreased in D-depleted rats (-25%, p < 0.05). The D-depleted group showed -39%, -31% drops in expression of two markers known to modulate proliferation (Bmp4, Fgf-2 mRNA levels) and -56% drop in one marker of cell proliferation (PCNA protein expression) compared to controls (p < 0.05). Notch pathway activity was blunted in tibialis anterior of D-depleted rats compared to controls, seen as a down-regulation of cleaved Notch (-53%, p < 0.05) and its target Hes1 (-35%, p < 0.05).

CONCLUSIONS

A 9-month vitamin D depletion induced vitamin D deficiency in old rats. Vitamin D depletion induces skeletal muscle atrophy in old rats through a reduction in Notch pathway activity and proliferation potential. Vitamin D deficiency could aggravate the age-related decrease in muscle regeneration capacity.

Heparin microparticle effects on presentation and bioactivity of bone morphogenetic protein-2

Biomaterials capable of providing localized and sustained presentation of bioactive proteins are critical for effective therapeutic growth factor delivery. However, current biomaterial delivery vehicles commonly suffer from limitations that can result in low retention of growth factors at the site of interest or adversely affect growth factor bioactivity. Heparin, a highly sulfated glycosaminoglycan, is an attractive growth factor delivery vehicle due to its ability to reversibly bind positively charged proteins, provide sustained delivery, and maintain protein bioactivity. This study describes the fabrication and characterization of heparin methacrylamide (HMAm) microparticles for recombinant growth factor delivery. HMAm microparticles were shown to efficiently bind several heparin-binding growth factors (e.g. bone morphogenetic protein-2 (BMP-2), vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (FGF-2)), including a wide range of BMP-2 concentrations that exceeds the maximum binding capacity of other common growth factor delivery vehicles, such as gelatin. BMP-2 bioactivity was assessed on the basis of alkaline phosphatase (ALP) activity induced in skeletal myoblasts (C2C12). Microparticles loaded with BMP-2 stimulated comparable C2C12 ALP activity to soluble BMP-2 treatment, indicating that BMP-2-loaded microparticles retain bioactivity and potently elicit a functional cell response. In summary, our results suggest that heparin microparticles stably retain large amounts of bioactive BMP-2 for prolonged periods of time, and that presentation of BMP-2 via heparin microparticles can elicit cell responses comparable to soluble BMP-2 treatment. Consequently, heparin microparticles present an effective method of delivering and spatially retaining growth factors that could be used in a variety of systems to enable directed induction of cell fates and tissue regeneration.