The extracellular matrix dimension of skeletal muscle development

Effects of long-term feeding of rapeseed meal on skeletal muscle transcriptome, production efficiency and meat quality traits in Norwegian Landrace growing-finishing pigs

This study was performed to investigate the effects of dietary inclusion of 20% rapeseed meal (RSM) as an alternative to soybean meal (SBM) in a three-month feeding experiment with growing finishing pigs. Dietary alteration affected growth performance, several carcass traits and transcriptional responses in the skeletal muscle, but did not affect measured meat quality traits. In general, pigs fed the RSM test diet exhibited reduced growth performance compared to pigs on SBM control diet. Significant transcriptional changes in the skeletal muscle of growing pigs fed RSM diet were likely the consequence of an increased amount of fiber and higher polyunsaturated fatty acids, and presence of bioactive phytochemicals, such as glucosinolates. RNAseq pipeline using Tophat2-Cuffdiff identified 57 upregulated and 63 downregulated genes in RSM compared to SBM pigs. Significantly enriched among downregulated pathways was p53-mediated signalling involved in cellular proliferation, while activation of negative growth regulators (IER5, KLF10, BTG2, KLF11, RETREG1, PRUNE2) in RSM fed pigs provided further evidence for reduced proliferation and increased cellular death, in accordance with the observed reduction in performance traits. Upregulation of well-known metabolic controllers (PDK4, UCP3, ESRRG and ESRRB), involved in energy homeostasis (glucose and lipid metabolism, and mitochondrial function), suggested less available energy and nutrients in RSM pigs. Furthermore, several genes supported more pronounced proteolysis (ABTB1, OTUD1, PADI2, SPP1) and reduced protein synthesis (THBS1, HSF4, AP1S2) in RSM muscle tissue. In parallel, higher levels of NR4A3, PDK4 and FGF21, and a drop in adropin, ELOVL6 and CIDEC/FSP27 indicated increased lipolysis and fatty acid oxidation, reflective of lower dressing percentage. Finally, pigs exposed to RSM showed greater expression level of genes responsive to oxidative stress, indicated by upregulation of GPX1, GPX2, and TXNIP.

Dermatopontin in Skeletal Muscle Extracellular Matrix Regulates Myogenesis

Dermatopontin (DPT) is an extensively distributed non-collagenous component of the extracellular matrix predominantly found in the dermis of the skin, and consequently expressed in several tissues. In this study, we explored the role of DPT in myogenesis and perceived that it enhances the cell adhesion, reduces the cell proliferation and promotes the myoblast differentiation in C2C12 cells. Our results reveal an inhibitory effect with fibronectin (FN) in myoblast differentiation. We also observed that DPT and fibromodulin (FMOD) regulate positively to each other and promote myogenic differentiation. We further predicted the 3D structure of DPT, which is as yet unknown, and validated it using state-of-the-art in silico tools. Furthermore, we explored the in-silico protein-protein interaction between DPT-FMOD, DPT-FN, and FMOD-FN, and perceived that the interaction between FMOD-FN is more robust than DPT-FMOD and DPT-FN. Taken together, our findings have determined the role of DPT at different stages of the myogenic process.

Loss of miR-451a enhances SPARC production during myogenesis

MicroRNAs (miRNAs) are small noncoding RNAs that critically regulate gene expression. Their abundance and function have been linked to a range of physiologic and pathologic processes. In aged monkey muscle, miR-451a and miR-144-3p were far more abundant than in young monkey muscle. This observation led us to hypothesize that miR-451a and miR-144-3p may influence muscle homeostasis. To test if these conserved microRNAs were implicated in myogenesis, we investigated their function in the mouse myoblast line C2C12. The levels of both microRNAs declined with myogenesis; however, only overexpression of miR-451a, but not miR-144-3p, robustly impeded C2C12 differentiation, suggesting an inhibitory role for miR-451a in myogenesis. Further investigation of the regulatory influence of miR-451a identified as one of the major targets Sparc mRNA, which encodes a secreted protein acidic and rich in cysteine (SPARC) that functions in wound healing and cellular differentiation. In mouse myoblasts, miR-451a suppressed Sparc mRNA translation. Together, our findings indicate that miR-451a is downregulated in differentiated myoblasts and suggest that it decreases C2C12 differentiation at least in part by suppressing SPARC biosynthesis.

Syndecan-4 influences mammalian myoblast proliferation by modulating myostatin signalling and G1/S transition

Myostatin, a TGF‐β superfamily member, is a negative regulator of muscle growth. Here we describe how myostatin activity is regulated by syndecan‐4, a ubiquitous transmembrane heparan sulfate proteoglycan. During muscle regeneration the levels of both syndecan‐4 and promyostatin decline gradually after a sharp increase, concurrently with the release of mature myostatin. Promyostatin and syndecan‐4 co‐immunoprecipitate, and the interaction is heparinase‐sensitive. ShRNA‐mediated silencing of syndecan‐4 reduces C2C12 myoblast proliferation via blocking the progression from G1‐ to S‐phase of the cell cycle, which is accompanied by elevated levels of myostatin and p21(Waf1/Cip1), and decreases in cyclin E and cyclin D1 expression. Our results suggest that syndecan‐4 functions as a reservoir for promyostatin regulating the local bioavailability of mature myostatin.

4D imaging reveals stage dependent random and directed cell motion during somite morphogenesis

Somites are paired embryonic segments that form in a regular sequence from unsegmented mesoderm during vertebrate development. Although transient structures they are of fundamental importance as they generate cell lineages of the musculoskeletal system in the trunk such as cartilage, tendon, bone, endothelial cells and skeletal muscle. Surprisingly, very little is known about cellular dynamics underlying the morphological transitions during somite differentiation. Here, we address this by examining cellular rearrangements and morphogenesis in differentiating somites using live multi-photon imaging of transgenic chick embryos, where all cells express a membrane-bound GFP. We specifically focussed on the dynamic cellular changes in two principle regions within the somite, the medial and lateral domains, to investigate extensive morphological transformations. Furthermore, by using quantitative analysis and cell tracking, we capture for the first time a directed movement of dermomyotomal progenitor cells towards the rostro-medial domain of the dermomyotome, where skeletal muscle formation initiates.

In Vitro Tissue-Engineered Skeletal Muscle Models for Studying Muscle Physiology and Disease

Healthy skeletal muscle possesses the extraordinary ability to regenerate in response to small-scale injuries; however, this self-repair capacity becomes overwhelmed with aging, genetic myopathies, and large muscle loss. The failure of small animal models to accurately replicate human muscle disease, injury and to predict clinically-relevant drug responses has driven the development of high fidelity in vitro skeletal muscle models. Herein, the progress made and challenges ahead in engineering biomimetic human skeletal muscle tissues that can recapitulate muscle development, genetic diseases, regeneration, and drug response is discussed. Bioengineering approaches used to improve engineered muscle structure and function as well as the functionality of satellite cells to allow modeling muscle regeneration in vitro are also highlighted. Next, a historical overview on the generation of skeletal muscle cells and tissues from human pluripotent stem cells, and a discussion on the potential of these approaches to model and treat genetic diseases such as Duchenne muscular dystrophy, is provided. Finally, the need to integrate multiorgan microphysiological systems to generate improved drug discovery technologies with the potential to complement or supersede current preclinical animal models of muscle disease is described.

Comparison between Collagen and Lidocaine Intramuscular Injections in Terms of Their Efficiency in Decreasing Myofascial Pain within Masseter Muscles: A Randomized, Single-Blind Controlled Trial

Background and Objective

A novel option for myofascial pain (MFP) management and muscle regeneration is intramuscular collagen injections. The aim of the study was to evaluate the efficiency of intramuscular injections of collagen and lidocaine in decreasing MFP within masseter muscles.

Methods

Myofascial pain within masseter muscles was diagnosed on the basis of the Diagnostic Criteria for Temporomandibular Disorders (II.1.A. 2 and 3). A total of 43 patients with diagnosed MFP within masseter muscles were enrolled to the study (17 male and 26 female, 40 ± 3.8 years old) and randomly divided into three groups. The first group received injections using 2 ml of collagen MD Muscle (Guna), the second group received 2 ml of 2% lidocaine without a vasoconstrictor, and the third group 2 ml of saline as a control (0.9% NaCl). All patients received repeated injections at one-week intervals (days 0 and 7). The visual analogue scale was used to determine pain intensity changes during each follow-up visit (days 0, 7, and 14) in each group. The masseter muscle activity was measured on each visit (days 0, 7, and 14) with surface electromyography (sEMG) (Neurobit Optima 4, Neurobit Systems).

Results

We found that sEMG masseter muscle activity was significantly decreased in Group I (59.2%), less in Group II (39.3%), and least in Group III (14%). Pain intensity reduction was 53.75% in Group I, 25% in Group II, and 20.1% in Group III.

Conclusions

The study confirmed that intramuscular injection of collagen is a more efficient method for reducing myofascial pain within masseter muscles than intramuscular injection of lidocaine.

Regulation of skeletal myotube formation and alignment by nanotopographically controlled cell-secreted extracellular matrix

Skeletal muscle has a well-organized tissue structure comprised of aligned myofibers and an encasing extracellular matrix (ECM) sheath or lamina, within which reside satellite cells. We hypothesize that the organization of skeletal muscle tissues in culture can affect both the structure of the deposited ECM and the differentiation potential of developing myotubes. Furthermore, we posit that cellular and ECM cues can be a strong determinant of myoblast fusion and morphology in 3D tissue culture environments. To test these, we utilized a thermoresponsive nanofabricated substratum to engineer anisotropic sheets of myoblasts which could then be transferred and stacked into multilayered tissues. Within such engineered tissues, we found that myoblasts rapidly sense topography and deposit structurally organized ECM proteins. Furthermore, the initial tissue structure was found to exert significant control over myoblast fusion and eventual myotube organization. These results highlight the importance of ECM structure on myoblast fusion and organization, and provide insights into substrate-mediated control of myotube formation in the development of novel, more effective, engineered skeletal muscle tissues. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1543-1551, 2018.

Genome-wide strategies identify downstream target genes of chick connective tissue-associated transcription factors

Connective tissues support organs and play crucial roles in development, homeostasis and fibrosis, yet our understanding of their formation is still limited. To gain insight into the molecular mechanisms of connective tissue specification, we selected five zinc-finger transcription factors - OSR1, OSR2, EGR1, KLF2 and KLF4 - based on their expression patterns and/or known involvement in connective tissue subtype differentiation. RNA-seq and ChIP-seq profiling of chick limb micromass cultures revealed a set of common genes regulated by all five transcription factors, which we describe as a connective tissue core expression set. This common core was enriched with genes associated with axon guidance and myofibroblast signature, including fibrosis-related genes. In addition, each transcription factor regulated a specific set of signalling molecules and extracellular matrix components. This suggests a concept whereby local molecular niches can be created by the expression of specific transcription factors impinging on the specification of local microenvironments. The regulatory network established here identifies common and distinct molecular signatures of limb connective tissue subtypes, provides novel insight into the signalling pathways governing connective tissue specification, and serves as a resource for connective tissue development.

Odd skipped-related 1 identifies a population of embryonic fibro-adipogenic progenitors regulating myogenesis during limb development

Fibro-adipogenic progenitors (FAPs) are an interstitial cell population in adult skeletal muscle that support muscle regeneration. During development, interstitial muscle connective tissue (MCT) cells support proper muscle patterning, however the underlying molecular mechanisms are not well understood and it remains unclear whether adult FAPs and embryonic MCT cells share a common lineage. We show here that mouse embryonic limb MCT cells expressing the transcription factor Osr1, differentiate into fibrogenic and adipogenic cells in vivo and in vitro defining an embryonic FAP-like population. Genetic lineage tracing shows that developmental Osr1⁺ cells give rise to a subset of adult FAPs. Loss of Osr1 function leads to a reduction of myogenic progenitor proliferation and survival resulting in limb muscle patterning defects. Transcriptome and functional analyses reveal that Osr1⁺ cells provide a critical pro-myogenic niche via the production of MCT specific extracellular matrix components and secreted signaling factors.

Fibro-adipogenic progenitors (FAPs) form part of interstitial muscle connective tissue (MCT) in adults but the origin of this non-myogenic lineage is unclear. Here, the authors show that Odd skipped related 1 (Osr1) in mice marks embryonic MCT, giving rise to FAPs, and loss of Osr1 in the limb causes muscle defects.

Impaired fetal muscle development and JAK-STAT activation mark disease onset and progression in a mouse model for merosin-deficient congenital muscular dystrophy

Merosin-deficient congenital muscular dystrophy type 1A (MDC1A) is a dramatic neuromuscular disease in which crippling muscle weakness is evident from birth. Here, we use the dyW mouse model for human MDC1A to trace the onset of the disease during development in utero. We find that myotomal and primary myogenesis proceed normally in homozygous dyW-/- embryos. Fetal dyW-/- muscles display the same number of myofibers as wildtype (WT) muscles, but by E18.5 dyW-/- muscles are significantly smaller and muscle size is not recovered post-natally. These results suggest that fetal dyW-/- myofibers fail to grow at the same rate as WT myofibers. Consistent with this hypothesis between E17.5 and E18.5 dyW-/- muscles display a dramatic drop in the number of Pax7- and myogenin-positive cells relative to WT muscles, suggesting that dyW-/- muscles fail to generate enough muscle cells to sustain fetal myofiber growth. Gene expression analysis of dyW-/- E17.5 muscles identified a significant increase in the expression of the JAK-STAT target gene Pim1 and muscles from 2-day and 3-week old dyW-/- mice demonstrate a dramatic increase in pSTAT3 relative to WT muscles. Interestingly, myotubes lacking integrin α7β1, a laminin-receptor, also show a significant increase in pSTAT3 levels compared with WT myotubes, indicating that α7β1 can act as a negative regulator of STAT3 activity. Our data reveal for the first time that dyW-/- mice exhibit a myogenesis defect already in utero. We propose that overactivation of JAK-STAT signaling is part of the mechanism underlying disease onset and progression in dyW-/- mice.

Global misregulation of genes largely uncoupled to DNA methylome epimutations characterizes a congenital overgrowth syndrome

Assisted reproductive therapies (ART) have become increasingly common worldwide and numerous retrospective studies have indicated that ART-conceived children are more likely to develop the overgrowth syndrome Beckwith-Wiedemann (BWS). In bovine, the use of ART can induce a similar overgrowth condition, which is referred to as large offspring syndrome (LOS). Both BWS and LOS involve misregulation of imprinted genes. However, it remains unknown whether molecular alterations at non-imprinted loci contribute to these syndromes. Here we examined the transcriptome of skeletal muscle, liver, kidney, and brain of control and LOS bovine fetuses and found that different tissues within LOS fetuses have perturbations of distinct gene pathways. Notably, in skeletal muscle, multiple pathways involved in myoblast proliferation and fusion into myotubes are misregulated in LOS fetuses. Further, characterization of the DNA methylome of skeletal muscle demonstrates numerous local methylation differences between LOS and controls; however, only a small percent of differentially expressed genes (DEGs), including the imprinted gene IGF2R, could be associated with the neighboring differentially methylated regions. In summary, we not only show that misregulation of non-imprinted genes and loss-of-imprinting characterize the ART-induced overgrowth syndrome but also demonstrate that most of the DEGs is not directly associated with DNA methylome epimutations.

Laminin mimetic peptide nanofibers regenerate acute muscle defect

Skeletal muscle cells are terminally differentiated and require the activation of muscle progenitor (satellite) cells for their regeneration. There is a clinical need for faster and more efficient treatment methods for acute muscle injuries, and the stimulation of satellite cell proliferation is promising in this context. In this study, we designed and synthesized a laminin-mimetic bioactive peptide (LM/E-PA) system that is capable of accelerating satellite cell activation by emulating the structure and function of laminin, a major protein of the basal membrane of the skeletal muscle. The LM/E-PA nanofibers enhance myogenic differentiation in vitro and the clinical relevance of the laminin-mimetic bioactive scaffold system was demonstrated further by assessing its effect on the regeneration of acute muscle injury in a rat model. Laminin mimetic peptide nanofibers significantly promoted satellite cell activation in skeletal muscle and accelerated myofibrillar regeneration following acute muscle injury. In addition, the LM/E-PA scaffold treatment significantly reduced the time required for the structural and functional repair of skeletal muscle. This study represents one of the first examples of molecular- and tissue-level regeneration of skeletal muscle facilitated by bioactive peptide nanofibers following acute muscle injury.

SIGNIFICANCE STATEMENT

Sports, heavy lifting and other strength-intensive tasks are ubiquitous in modern life and likely to cause acute skeletal muscle injury. Speeding up regeneration of skeletal muscle injuries would not only shorten the duration of recovery for the patient, but also support the general health and functionality of the repaired muscle tissue. In this work, we designed and synthesized a laminin-mimetic nanosystem to enhance muscle regeneration. We tested its activity in a rat tibialis anterior muscle by injecting the bioactive nanosystem. The evaluation of the regeneration and differentiation capacity of skeletal muscle suggested that the laminin-mimetic nanosystem enhances skeletal muscle regeneration and provides a suitable platform that is highly promising for the regeneration of acute muscle injuries. This work demonstrates for the first time that laminin-mimetic self-assembled peptide nanosystems facilitate myogenic differentiation in vivo without the need for additional treatment.

ECM-Related Myopathies and Muscular Dystrophies: Pros and Cons of Protein Therapies

Extracellular matrix (ECM) myopathies and muscular dystrophies are a group of genetic diseases caused by mutations in genes encoding proteins that provide critical links between muscle cells and the extracellular matrix. These include structural proteins of the ECM, muscle cell receptors, enzymes, and intracellular proteins. Loss of adhesion within the myomatrix results in progressive muscle weakness. For many ECM muscular dystrophies, symptoms can occur any time after birth and often result in reduced life expectancy. There are no cures for the ECM-related muscular dystrophies and treatment options are limited to palliative care. Several therapeutic approaches have been explored to treat muscular dystrophies including gene therapy, gene editing, exon skipping, embryonic, and adult stem cell therapy, targeting genetic modifiers, modulating inflammatory responses, or preventing muscle degeneration. Recently, protein therapies that replace components of the defective myomatrix or enhance muscle and/or extracellular matrix integrity and function have been explored. Preclinical studies for many of these biologics have been promising in animal models of these muscle diseases. This review aims to summarize the ECM muscular dystrophies for which protein therapies are being developed and discuss the exciting potential and possible limitations of this approach for treating this family of devastating genetic muscle diseases. © 2017 American Physiological Society. Compr Physiol 7:1519-1536, 2017.

Quaking RNA-Binding Proteins Control Early Myofibril Formation by Modulating Tropomyosin

Skeletal muscle contraction is mediated by myofibrils, complex multi-molecular scaffolds structured into repeated units, the sarcomeres. Myofibril structure and function have been extensively studied, but the molecular processes regulating its formation within the differentiating muscle cell remain largely unknown. Here we show in zebrafish that genetic interference with the Quaking RNA-binding proteins disrupts the initial steps of myofibril assembly without affecting early muscle differentiation. Using RNA sequencing, we demonstrate that Quaking is required for accumulation of the muscle-specific tropomyosin-3 transcript, tpm3.12. Further functional analyses reveal that Tpm3.12 mediates Quaking control of myofibril formation. Moreover, we identified a Quaking-binding site in the 3' UTR of tpm3.12 transcript, which is required in vivo for tpm3.12 accumulation and myofibril formation. Our work uncovers a Quaking/Tpm3 pathway controlling de novo myofibril assembly. This unexpected developmental role for Tpm3 could be at the origin of muscle defects observed in human congenital myopathies associated with tpm3 mutation.

R1ρ dispersion and sodium imaging in human calf muscle

PURPOSE

To evaluate the magnitude of chemical exchange effects and R_1ρ dispersion in muscle and their relationship to tissue sodium levels with aging.

METHODS

Seven healthy volunteers (aged 24 to 87years, median age 47) underwent MRI to assess tissue sodium levels and water T_1ρ values at different spin-locking frequencies in calf muscles. T_1ρ values at each locking field were computed based on a three-parameter mono-exponential model to fit signals obtained at different locking times, and R_1ρ (=1/T_1ρ) rates were compared at different locking fields. In particular, the dispersion of R_1ρ (ΔR_1ρ=R_1ρ(0Hz)-R_1ρ(500Hz)) was examined as a function of subject age. Muscle sodium content was calculated by comparing signal intensities between tissues and reference standards within the same image. The variations of ΔR_1ρ with age and sodium were analyzed by linear regression.

RESULTS

T_1ρ values and sodium content both increased with age. R_1ρ dispersion also increased with age and showed a strong linear correlation (correlation coefficient r=0.98, P=0.000578) with sodium content.

CONCLUSION

ΔR_1ρ reports on the contribution of labile protons such as hydroxyls which may be associated with macromolecule accumulation in the extracellular matrix (ECM). An increase of sodium signal suggests an enlarged ECM volume fraction and/or an increase in sodium concentration, which occurs during normal aging. The strong correlation between ΔR_1ρ and sodium is likely the consequence of increased ECM and density of total charged sites within the matrix from molecules such as collagens and proteoglycans. The results from this study show the potential use of R_1ρ dispersion and sodium imaging in the assessment of pathological changes in muscle such as fibrosis.

Dysregulation of nuclear receptor COUP-TFII impairs skeletal muscle development

Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) has been shown to inhibit myogenesis and skeletal muscle metabolism in vitro. However, its precise role and in vivo function in muscle development has yet to be clearly defined. COUP-TFII protein expression level is high in undifferentiated progenitors and gradually declines during differentiation, raising an important question of whether downregulation of COUP-TFII expression is required for proper muscle cell differentiation. In this study, we generated a mouse model ectopically expressing COUP-TFII in myogenic precursors to maintain COUP-TFII activity during myogenesis and found that elevated COUP-TFII activity resulted in inefficient skeletal muscle development. Using in vitro cell culture and in vivo mouse models, we showed that COUP-TFII hinders myogenic development by repressing myoblast fusion. Mechanistically, the inefficient muscle cell fusion correlates well with the transcriptional repression of Npnt, Itgb1D and Cav3, genes important for cell-cell fusion. We further demonstrated that COUP-TFII also reduces the activation of focal adhesion kinase (FAK), an integrin downstream regulator which is essential for fusion process. Collectively, our studies highlight the importance of down-regulation of COUP-TFII signaling to allow for the induction of factors crucial for myoblast fusion.

Binding of the chemokine CXCL12α to its natural extracellular matrix ligand heparan sulfate enables myoblast adhesion and facilitates cell motility

The chemokine CXCL12α is a potent chemoattractant that guides the migration of muscle precursor cells (myoblasts) during myogenesis and muscle regeneration. To study how the molecular presentation of chemokines influences myoblast adhesion and motility, we designed multifunctional biomimetic surfaces as a tuneable signalling platform that enabled the response of myoblasts to selected extracellular cues to be studied in a well-defined environment. Using this platform, we demonstrate that CXCL12α, when presented by its natural extracellular matrix ligand heparan sulfate (HS), enables the adhesion and spreading of myoblasts and facilitates their active migration. In contrast, myoblasts also adhered and spread on CXCL12α that was quasi-irreversibly surface-bound in the absence of HS, but were essentially immotile. Moreover, co-presentation of the cyclic RGD peptide as integrin ligand along with HS-bound CXCL12α led to enhanced spreading and motility, in a way that indicates cooperation between CXCR4 (the CXCL12α receptor) and integrins (the RGD receptors). Our findings reveal the critical role of HS in CXCL12α induced myoblast adhesion and migration. The biomimetic surfaces developed here hold promise for mechanistic studies of cellular responses to different presentations of biomolecules. They may be broadly applicable for dissecting the signalling pathways underlying receptor cross-talks, and thus may guide the development of novel biomaterials that promote highly specific cellular responses.

Cell Density and Joint microRNA-133a and microRNA-696 Inhibition Enhance Differentiation and Contractile Function of Engineered Human Skeletal Muscle Tissues

To utilize three-dimensional (3D) engineered human skeletal muscle tissue for translational studies and in vitro studies of drug toxicity, there is a need to promote differentiation and functional behavior. In this study, we identified conditions to promote contraction of engineered human skeletal muscle bundles and examined the effects of transient inhibition of microRNAs (miRs) on myogenic differentiation and function of two-dimensional (2D) and 3D cultures of human myotubes. In 2D cultures, simultaneously inhibiting both miR-133a, which promotes myoblast proliferation, and miR-696, which represses oxidative metabolism, resulted in an increase in sarcomeric α-actinin protein and the metabolic coactivator PGC-1α protein compared to transfection with a scrambled miR sequence (negative control). Although PGC-1α was elevated following joint inhibition of miRs 133a and 696, there was no difference in myosin heavy chain (MHC) protein isoforms. 3D engineered human skeletal muscle myobundles seeded with 5 × 10(6) human skeletal myoblasts (HSkM)/mL and cultured for 2 weeks after onset of differentiation consistently did not contract when stimulated electrically, whereas those seeded with myoblasts at 10 × 10(6) HSkM/mL or higher did contract. When HSkM were transfected with both anti-miRs and seeded into fibrin hydrogels and cultured for 2 weeks under static conditions, twitch and tetanic specific forces after electrical stimulation were greater than for myobundles prepared with HSkM transfected with scrambled sequences. Immunofluorescence and Western blots of 3D myobundles indicate that anti-miR-133a or anti-miR-696 treatment led to modest increases in slow MHC, but no consistent increase in fast MHC. Similar to results in 2D, only myobundles prepared with myoblasts treated with anti-miR-133a and anti-miR-696 produced an increase in PGC-1α mRNA. PGC-1α targets were differentially affected by the treatment. HIF-2α mRNA showed an expression pattern similar to that of PGC-1α mRNA, but COXII mRNA levels were not affected by the anti-miRs. Overall, joint inhibition of miR-133a and miR-696 accelerated differentiation, elevated the metabolic coactivator PGC-1α, and increased the contractile force in 3D engineered human skeletal muscle bundles.

Axial and limb muscle development: dialogue with the neighbourhood

Skeletal muscles are part of the musculoskeletal system which also includes nerves, tendons, connective tissue, bones and blood vessels. Here we review the development of axial and limb muscles in amniotes within the context of their surrounding tissues in vivo. We highlight the reciprocal dialogue mediated by signalling factors between cells of these adjacent tissues and developing muscles and also demonstrate its importance from the onset of muscle cell differentiation well into foetal development. Early embryonic tissues secrete factors which are important regulators of myogenesis. However, later muscle development relies on other tissue collaborators, such as developing nerves and connective tissue, which are in turn influenced by the developing muscles themselves. We conclude that skeletal muscle development in vivo is a compelling example of the importance of reciprocal interactions between developing tissues for the complete and coordinated development of a functional system.

Tmem2 regulates cell-matrix interactions that are essential for muscle fiber attachment

Skeletal muscle morphogenesis depends upon interactions between developing muscle fibers and the extracellular matrix (ECM) that anchors fibers to the myotendinous junction (MTJ). The pathways that organize the ECM and regulate its engagement by cell-matrix adhesion complexes (CMACs) are therefore essential for muscle integrity. Here, we demonstrate the impact of transmembrane protein 2 (tmem2) on cell-matrix interactions during muscle morphogenesis in zebrafish. Maternal-zygotic tmem2 mutants (MZtmem2) exhibit muscle fiber detachment, in association with impaired laminin organization and ineffective fibronectin degradation at the MTJ. Similarly, disorganized laminin and fibronectin surround MZtmem2 cardiomyocytes, which could account for their hindered movement during cardiac morphogenesis. In addition to ECM defects, MZtmem2 mutants display hypoglycosylation of α-dystroglycan within the CMAC, which could contribute to the observed fiber detachment. Expression of the Tmem2 ectodomain can rescue aspects of the MZtmem2 phenotype, consistent with a possible extracellular function of Tmem2. Together, our results suggest that Tmem2 regulates cell-matrix interactions by affecting both ECM organization and CMAC activity. These findings evoke possible connections between the functions of Tmem2 and the etiologies of congenital muscular dystrophies, particularly dystroglycanopathies.

Development of the ventral body wall in the human embryo

Migratory failure of somitic cells is the commonest explanation for ventral body wall defects. However, the embryo increases ~ 25-fold in volume in the period that the ventral body wall forms, so that differential growth may, instead, account for the observed changes in topography. Human embryos between 4 and 10 weeks of development were studied, using amira reconstruction and cinema 4D remodeling software for visualization. Initially, vertebrae and ribs had formed medially, and primordia of sternum and hypaxial flank muscle primordium laterally in the body wall at Carnegie Stage (CS)15 (5.5 weeks). The next week, ribs and muscle primordium expanded in ventrolateral direction only. At CS18 (6.5 weeks), separate intercostal and abdominal wall muscles differentiated, and ribs, sterna, and muscles began to expand ventromedially and caudally, with the bilateral sternal bars fusing in the midline after CS20 (7 weeks) and the rectus muscles reaching the umbilicus at CS23 (8 weeks). The near-constant absolute distance between both rectus muscles and approximately fivefold decline of this distance relative to body circumference between 6 and 10 weeks identified dorsoventral growth in the dorsal body wall as determinant of the 'closure' of the ventral body wall. Concomitant with the straightening of the embryonic body axis after the 6th week, the abdominal muscles expanded ventrally and caudally to form the infraumbilical body wall. Our data, therefore, show that the ventral body wall is formed by differential dorsoventral growth in the dorsal part of the body.

Construction and myogenic differentiation of 3D myoblast tissues fabricated by fibronectin-gelatin nanofilm coating

In this study, we used a recently developed approach of coating the cells with fibronectin-gelatin nanofilms to build 3D skeletal muscle tissue models. We constructed the microtissues from C2C12 myoblasts and subsequently differentiated them to form muscle-like tissue. The thickness of the constructs could be successfully controlled by altering the number of seeded cells. We were able to build up to ∼76 μm thick 3D constructs that formed multinucleated myotubes. We also found that Rho-kinase inhibitor Y27632 improved myotube formation in thick constructs. Our approach makes it possible to rapidly form 3D muscle tissues and is promising for the in vitro construction of physiologically relevant human skeletal muscle tissue models.

Impaired primary mouse myotube formation on crosslinked type I collagen films is enhanced by laminin and entactin

In skeletal muscle, the stem cell niche is important for controlling the quiescent, proliferation and differentiation states of satellite cells, which are key for skeletal muscle regeneration after wounding. It has been shown that type I collagen, often used as 3D-scaffolds for regenerative medicine purposes, impairs myoblast differentiation. This is most likely due to the absence of specific extracellular matrix proteins providing attachment sites for myoblasts and/or myotubes. In this study we investigated the differentiation capacity of primary murine myoblasts on type I collagen films either untreated or modified with elastin, laminin, type IV collagen, laminin/entactin complex, combinations thereof, and Matrigel as a positive control. Additionally, increased reactive oxygen species (ROS) and ROCK signaling might also be involved. To measure ROS levels with live-cell microscopy, fibronectin-coated glass coverslips were additionally coated with type I collagen and Matrigel onto which myoblasts were differentiated. On type I collagen-coated coverslips, myotube formation was impaired while ROS levels were increased. However, anti-oxidant treatment did not enhance myotube formation. ROCK inhibition, which generally improve cellular attachment to uncoated surfaces or type I collagen, enhanced myoblast attachment to type I collagen-coated coverslips and -films, but slightly enhanced myotube formation. Only modification of type I collagen films by Matrigel and a combination of laminin/entactin significantly improved myotube formation. Our results indicate that type I collagen scaffolds can be modified by satellite cell niche factors of which specifically laminin and entactin enhanced myotube formation. This offers a promising approach for regenerative medicine purposes to heal skeletal muscle wounds.

STATEMENT OF SIGNIFICANCE

In this manuscript we show for the first time that impaired myotube formation on type I collagen scaffolds can be completely restored by modification with laminin and entactin, two extracellular proteins from the satellite cell niche. This offers a promising approach for regenerative medicine approaches to heal skeletal muscle wounds.

Exploring transcriptomic diversity in muscle revealed that cellular signaling pathways mainly differentiate five Western porcine breeds

Background

Among transcriptomic studies, those comparing species or populations can increase our understanding of the impact of the evolutionary forces on the differentiation of populations. A particular situation is the one of short evolution time with breeds of a domesticated species that underwent strong selective pressures. In this study, the gene expression diversity across five pig breeds has been explored in muscle. Samples came from: 24 Duroc, 33 Landrace, 41 Large White dam line, 10 Large White sire line and 39 Piétrain. From these animals, 147 muscle samples obtained at slaughter were analyzed using the porcine Agilent 44 K v1 microarray.

Results

A total of 12,358 genes were identified as expressed in muscle after normalization and 1,703 genes were declared differential for at least one breed (FDR < 0.001). The functional analysis highlighted that gene expression diversity is mainly linked to cellular signaling pathways such as the PI3K (phosphoinositide 3-kinase) pathway. The PI3K pathway is known to be involved in the control of development of the skeletal muscle mass by affecting extracellular matrix - receptor interactions, regulation of actin cytoskeleton pathways and some metabolic functions. This study also highlighted 228 spots (171 unique genes) that differentiate the breeds from each other. A common subgroup of 15 genes selected by three statistical methods was able to differentiate Duroc, Large White and Piétrain breeds.

Conclusions

This study on transcriptomic differentiation across Western pig breeds highlighted a global picture: mainly signaling pathways were affected. This result is consistent with the selection objective of increasing muscle mass. These transcriptional changes may indicate selection pressure or simply breed differences which may be driven by human selection. Further work aiming at comparing genetic and transcriptomic diversities would further increase our understanding of the consequences of human impact on livestock species.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2259-9) contains supplementary material, which is available to authorized users.

Whole transcriptome analysis reveals a role for OGG1-initiated DNA repair signaling in airway remodeling

Reactive oxygen species (ROS) generated by environmental exposures, and endogenously as by-products of respiration, oxidatively modify biomolecules including DNA. Accumulation of ROS-induced DNA damage has been implicated in various diseases that involve inflammatory processes, and efficient DNA repair is considered critical in preventing such diseases. One of the most abundant DNA base lesions is 7,8-dihydro-8-oxoguanine (8-oxoG), which is repaired by the 8-oxoguanine DNA glycosylase 1 (OGG1)-initiated base-excision repair (OGG1-BER) pathway. Recent studies have shown that the OGG1-BER by-product 8-oxoG base forms a complex with cytosolic OGG1, activating small GTPases and downstream cell signaling in cultured cells and lungs. This implies that persistent OGG1-BER could result in signaling leading to histological changes in airways. To test this, we mimicked OGG1-BER by repeatedly challenging airways with its repair product 8-oxoG base. Gene expression was analyzed by RNA sequencing (RNA-Seq) and qRT-PCR, and datasets were evaluated by gene ontology and statistical tools. RNA-Seq analysis identified 3252 differentially expressed transcripts (2435 up- and 817 downregulated, ≥ 3-fold change). Among the upregulated transcripts, 2080 mRNAs were identified whose encoded protein products were involved in modulation of the actin family cytoskeleton, extracellular matrix, cell adhesion, cadherin, and cell junctions, affecting biological processes such as tissue development, cell-to-cell adhesion, cell communication, and the immune system. These data are supported by histological observations showing epithelial alterations, subepithelial fibrosis, and collagen deposits in the lungs. These data imply that continuous challenge by the environment and consequent OGG1-BER-driven signaling trigger gene expression consistent with airway remodeling.

The central role of muscle stem cells in regenerative failure with aging

Skeletal muscle mass, function, and repair capacity all progressively decline with aging, restricting mobility, voluntary function, and quality of life. Skeletal muscle repair is facilitated by a population of dedicated muscle stem cells (MuSCs), also known as satellite cells, that reside in anatomically defined niches within muscle tissues. In adult tissues, MuSCs are retained in a quiescent state until they are primed to regenerate damaged muscle through cycles of self-renewal divisions. With aging, muscle tissue homeostasis is progressively disrupted and the ability of MuSCs to repair injured muscle markedly declines. Until recently, this decline has been largely attributed to extrinsic age-related alterations in the microenvironment to which MuSCs are exposed. However, as highlighted in this Perspective, recent reports show that MuSCs also progressively undergo cell-intrinsic alterations that profoundly affect stem cell regenerative function with aging. A more comprehensive understanding of the interplay of stem cell-intrinsic and extrinsic factors will set the stage for improving cell therapies capable of restoring tissue homeostasis and enhancing muscle repair in the aged.

In vitro myogenesis induced by human recombinant elastin-like proteins

Mammalian adult skeletal muscle has a limited ability to regenerate after injury, usage or trauma. A promising strategy for successful regenerative technology is the engineering of bio interfaces that mimic the characteristics of the extracellular matrix. Human elastin-like polypeptides (HELPs) have been synthesized as biomimetic materials that maintain some peculiar properties of the native protein. We developed a novel Human Elastin Like Polypeptide obtained by fusing the elastin-like backbone to a domain present in the α2 chain of type IV collagen, containing two RGD motives. We employed this peptide as adhesion substrate for C2C12 myoblasts and compared its effects to those induced by two other polypeptides of the HELP series. Myoblast adhered to all HELPs coatings, where they assumed morphology and cytoarchitecture that depended on the polypeptide structure. Adhesion to HELPs stimulated at a different extent cell proliferation and differentiation, the expression of Myosin Heavy Chain and the fusion of aligned fibers into multinucleated myotubes. Adhesion substrates significantly altered myotubes stiffness, measured by Atomic Force Microscopy, and differently affected the cells Ca(2+) handling capacity and the maturation of excitation-contraction coupling machinery, evaluated by Ca(2+) imaging. Overall, our findings indicate that the properties of HELP biopolymers can be exploited for dissecting the molecular connections underlying myogenic differentiation and for designing novel substrates for skeletal muscle regeneration.

Extracellular matrix regulation in the muscle satellite cell niche

Increasing evidence points to extracellular matrix (ECM) components playing integral roles in regulating the muscle satellite cell (SC) niche. Even small alterations to the niche ECM can have profound effects on SC localization, activation, self-renewal, proliferation and differentiation. This review will focus on the ECM components that comprise the niche, how they are modulated in health and disease and how these changes are thought to affect SC function. Particular emphasis will be placed on the pathological niche and interventions that aim to restore healthy structure and function, as a better understanding of the interplay between the SC and its environment will drive more targeted and effective therapies.

Hanging on for the ride: adhesion to the extracellular matrix mediates cellular responses in skeletal muscle morphogenesis and disease

Skeletal muscle specification and morphogenesis during early development are critical for normal physiology. In addition to mediating locomotion, skeletal muscle is a secretory organ that contributes to metabolic homeostasis. Muscle is a highly adaptable tissue, as evidenced by the ability to increase muscle cell size and/or number in response to weight bearing exercise. Conversely, muscle wasting can occur during aging (sarcopenia), cancer (cancer cachexia), extended hospital stays (disuse atrophy), and in many genetic diseases collectively known as the muscular dystrophies and myopathies. It is therefore of great interest to understand the cellular and molecular mechanisms that mediate skeletal muscle development and adaptation. Muscle morphogenesis transforms short muscle precursor cells into long, multinucleate myotubes that anchor to tendons via the myotendinous junction. This process requires carefully orchestrated interactions between cells and their extracellular matrix microenvironment. These interactions are dynamic, allowing muscle cells to sense biophysical, structural, organizational, and/or signaling changes within their microenvironment and respond appropriately. In many musculoskeletal diseases, these cell adhesion interactions are disrupted to such a degree that normal cellular adaptive responses are not sufficient to compensate for accumulating damage. Thus, one major focus of current research is to identify the cell adhesion mechanisms that drive muscle morphogenesis, with the hope that understanding how muscle cell adhesion promotes the intrinsic adaptability of muscle tissue during development may provide insight into potential therapeutic approaches for muscle diseases. Our objectives in this review are to highlight recent studies suggesting conserved roles for cell-extracellular matrix adhesion in vertebrate muscle morphogenesis and cellular adaptive responses in animal models of muscle diseases.

Extracellular deposition of matrilin-2 controls the timing of the myogenic program during muscle regeneration

Here, we identify a role for the matrilin-2 (Matn2) extracellular matrix protein in controlling the early stages of myogenic differentiation. We observed Matn2 deposition around proliferating, differentiating and fusing myoblasts in culture and during muscle regeneration in vivo. Silencing of Matn2 delayed the expression of the Cdk inhibitor p21 and of the myogenic genes Nfix, MyoD and Myog, explaining the retarded cell cycle exit and myoblast differentiation. Rescue of Matn2 expression restored differentiation and the expression of p21 and of the myogenic genes. TGF-β1 inhibited myogenic differentiation at least in part by repressing Matn2 expression, which inhibited the onset of a positive-feedback loop whereby Matn2 and Nfix activate the expression of one another and activate myoblast differentiation. In vivo, myoblast cell cycle arrest and muscle regeneration was delayed in Matn2(-/-) relative to wild-type mice. The expression levels of Trf3 and myogenic genes were robustly reduced in Matn2(-/-) fetal limbs and in differentiating primary myoblast cultures, establishing Matn2 as a key modulator of the regulatory cascade that initiates terminal myogenic differentiation. Our data thus identify Matn2 as a crucial component of a genetic switch that modulates the onset of tissue repair.

Thrombospondin-4 controls matrix assembly during development and repair of myotendinous junctions

Tendons are extracellular matrix (ECM)-rich structures that mediate muscle attachments with the skeleton, but surprisingly little is known about molecular mechanisms of attachment. Individual myofibers and tenocytes in Drosophila interact through integrin (Itg) ligands such as Thrombospondin (Tsp), while vertebrate muscles attach to complex ECM fibrils embedded with tenocytes. We show for the first time that a vertebrate thrombospondin, Tsp4b, is essential for muscle attachment and ECM assembly at myotendinous junctions (MTJs). Tsp4b depletion in zebrafish causes muscle detachment upon contraction due to defects in laminin localization and reduced Itg signaling at MTJs. Mutation of its oligomerization domain renders Tsp4b unable to rescue these defects, demonstrating that pentamerization is required for ECM assembly. Furthermore, injected human TSP4 localizes to zebrafish MTJs and rescues muscle detachment and ECM assembly in Tsp4b-deficient embryos. Thus Tsp4 functions as an ECM scaffold at MTJs, with potential therapeutic uses in tendon strengthening and repair.

DOI:http://dx.doi.org/10.7554/eLife.02372.001

Tendons, the tough connective tissues that link muscles to bones, are essential for lifting, running and other movements in animals. A matrix of proteins, called the extracellular matrix, connects the cells in a tendon, giving it the strength it needs to prevent muscles from detaching from bones during strenuous activities.

To achieve this strength, extracellular matrix proteins bind to one another and to receptors on the muscle cell surface that are linked to its internal scaffolding, thereby organizing other proteins into a structure called a myotendinous junction. However, despite the essential roles of tendons, scientists do not fully understand how this organization occurs, or how it can go awry.

Subramanian and Schilling screened zebrafish for genes that are essential for proper muscle attachment, and zeroed in on a gene encoding a protein called Thrombospondin-4b (Tsp4b). A similar protein helps to connect muscle and tendon cells in fruit flies. Without Tsp4b, zebrafish are able to form connections between muscles and tendons, but the muscles detach easily during movement. This weakened connection is caused by disorganization of the proteins in the extracellular matrix, which results in reduced signaling from the muscle cell receptors.

When a human form of this protein was injected into zebrafish embryos lacking Tsp4b, it settled into the junctions between muscle and tendon cells. The human protein repaired the detached muscles and restored the proper organization of the matrix. This improved the strength of the muscle-tendon attachment in the treated fish embryos, suggesting that similar injections could also help to strengthen and repair muscles and tendons in people.

DOI:http://dx.doi.org/10.7554/eLife.02372.002

The effect of delivering the chemokine SDF-1α in a matrix-bound manner on myogenesis

Several chemokines are important in muscle myogenesis and in the recruitment of muscle precursors during muscle regeneration. Among these, the SDF-1α chemokine (CXCL12) is a potent chemoattractant known to be involved in muscle repair. SDF-1α was loaded in polyelectrolyte multilayer films made of poly(L-lysine) and hyaluronan to be delivered locally to myoblast cells in a matrix-bound manner. The adsorbed amounts of SDF-1α were tuned over a large range from 100 ng/cm(2) to 5 μg/cm(2), depending on the initial concentration of SDF-1α in solution, its pH, and on the film crosslinking extent. Matrix-bound SDF-1α induced a striking increase in myoblast spreading, which was revealed when it was delivered from weakly crosslinked films. It also significantly enhanced cell migration in a dose-dependent manner, which again depended on its presentation by the biopolymeric film. The low-crosslinked film was the most efficient in boosting cell migration. Furthermore, matrix-bound SDF-1α also increased the expression of myogenic markers but the fusion index decreased in a dose-dependent manner with the adsorbed amount of SDF-1α. At high adsorbed amounts of SDF-1α, a large number of Troponin T-positive cells had only one nucleus. Overall, this work reveals the importance of the presentation mode of SDF-1α to emphasize its effect on myogenic processes. These films may be further used to provide insight into the role of SDF-1α presented by a biomaterial in physiological or pathological processes.

Biofunctional hydrogels for skeletal muscle constructs

Hydrogel scaffolds encapsulating C2C12 mouse skeletal muscle cells have been engineered as in vitro constructs towards regenerative medicine therapies for the enhancement and inducement of functional skeletal muscle formation. Previous work has largely involved two-dimensional (2D) muscle strips, naturally occurring hydrogels and incomplete examination of the effects of the scaffold and/or biological functionalization on myogenic differentiation in a controllable manner. The goal of this study was to identify key properties in functionalized poly(ethylene glycol) (PEG)-maleimide (MAL) synthetic hydrogels that promote cell attachment, proliferation and differentiation for the formation of multinucleated myotubes and functional skeletal muscle tissue constructs. Significant differences in myoblast viability were observed as a function of cell seeding density, polymer weight percentage and bioadhesive ligands. The identified optimized conditions for cell survival, required for myotube development, were carried over for differentiation assays. PEG hydrogels (5% weight/volume), functionalized with 2.0 mm RGD adhesive peptide and crosslinked with protease-cleavable peptides, incubated for 3 days before supplementation with 2% horse serum, significantly increased expression of differentiated skeletal muscle markers by 50%; 17% more multinucleated cells and a 40% increase in the number of nuclei/differentiated cell compared to other conditions. Functionality of cell-laden hydrogels was demonstrated by a 20% decrease in the extruded length of the hydrogel when stimulated with a contractile agent, compared to 7% for a saline control. This study provided strategies to engineer a three-dimensional (3D) microenvironment, using synthetic hydrogels to promote the development of differentiated muscle tissue from skeletal muscle progenitor cells to form contractile units. Copyright © 2014 John Wiley & Sons, Ltd.

Functional pathways altered after silencing Pnpla6 (the codifying gene of neuropathy target esterase) in mouse embryonic stem cells under differentiation

Neuropathy target esterase (NTE) is involved in several disorders in adult organisms and embryos. A relationship between NTE and nervous system integrity and maintenance in adult systems has been suggested. NTE-related motor neuron disease is associated with the expression of a mutant form of NTE and the inhibition and further modification of NTE by organophosphorus compounds is the trigger of a delayed neurodegenerative neuropathy. Homozygotic NTE knockout mice embryos are not viable, while heterozygotic NTE knockout mice embryos yields mice with neurological disorders, which suggest that this protein plays a critical role in embryonic development. The present study used D3 mouse embryonic stem cells with the aim of gaining mechanistic insights on the role of Pnpla6 (NTE gene encoding) in the developmental process. D3 cells were silenced by lipofectamine transfection with a specific interference RNA for Pnpla6. Silencing Pnpla6 in D3 monolayer cultures reduced NTE enzymatic activity to 50% 20 h post-treatment, while the maximum loss of Pnpla6 expression reached 80% 48 h postsilencing. Pnpla6 was silenced in embryoid bodies and 545 genes were differentially expressed regarding the control 96 h after silencing, which revealed alterations in multiple genetic pathways, such as cell motion and cell migration, vesicle regulation, and cell adhesion. These findings also allow considering that these altered pathways would impair the formation of respiratory, neural, and vascular tubes causing the deficiencies observed in the in vivo development of nervous and vascular systems. Our findings, therefore, support the previous observations made in vivo concerning lack of viability of mice embryos not expressing NTE and help to understand the biology of several neurological and developmental disorders in which NTE is involved.

Mid-long term effect of non-ablative high radiofrequency therapy on the rabbit dermal extracellular matrix

This study quantitatively investigated the postoperative effects of radiofrequency (RF) application on the normal dermal extracellular matrix (ECM) of in vivo rabbits. Postoperative effects were evaluated by histology and atomic force microscopy analysis of dermal tissues treated using three RF energy levels (10 ~ 30 W) and either a single- or multiple-pass procedure. Progressive changes in the morphology of rabbit dermal ECMs were investigated over a 30-day postoperartive period. All RF-treated groups, except for the low energy group (10 W), displayed more prominent inflammatory responses compared to the control. This inflammatory reaction was more prominent a day after application. Dermal tissues 30 days after RF application exhibited prominent myofibroblast activity associated with ECM contractile activity during wound healing in addition to chronic inflammation. A decrease in the morphology of dermal ECMs after RF application continued until seven days postoperatively. The ECM diameter increased to near baseline at 30 days postoperatively. Low energy and multi-pass applications resulted in greater collagen fibril contraction and recovery at the ultra-structural level at 30 days postoperatively than did a single high energy application.

Internal-specific morphological analysis of sciatic nerve fibers in a radiofrequency-induced animal neuropathic pain model

This study investigated the reversible effects of pulsed radiofrequency (PRF) treatment at 42 °C on the ultrastructural and biological changes in nerve and collagen fibers in the progression of neuropathic pain after rat sciatic nerve injury. Assessments of morphological changes in the extracellular matrices by atomic force microscopy and hematoxylin-eosin, Masson's trichrome and picrosirius-red staining as well as the expressions of two fibril-forming collagens, types-I and -III, and two inflammatory cytokines, TNF-α and IL-6, were evaluated on day 30 after RF exposure. There were four groups for different RF thermal treatments: no treatment, no current, PRF, and continuous RF (CRF). An RF procedure similar to that used in human clinical trials was used in this study. The CRF treatment at 82 °C led to neural and collagen damage by the permanent blockage of sensory nociceptors. The PRF treatment led to excellent performance and high expandability compared to CRF, with effects including slight damage and swelling of myelinated axons, a slightly decreased amount of collagen fibers, swelling of collagen fibril diameters, decreased immunoreactivity of collagen types-I and -III, presence of newly synthesized collagen, and recovery of inflammatory protein immunoreactivity. These evidence-based findings suggest that PRF-based pain relief is responsible for the temporary blockage of nerve signals as well as the preferential destruction of pain-related principal sensory fibers like the Aδ and C fibers. This suggestion can be supported by the interaction between the PRF-induced electromagnetic field and cell membranes; therefore, PRF treatment provides pain relief while allowing retention of some tactile sensation.

The combination of glycosaminoglycans and fibrous proteins improves cell proliferation and early differentiation of bovine primary skeletal muscle cells

Primary muscle cell model systems from farm animals are widely used to acquire knowledge about muscle development, muscle pathologies, overweight issues and tissue regeneration. The morphological properties of a bovine primary muscle cell model system, in addition to cell proliferation and differentiation features, were characterized using immunocytochemistry, western blotting and real-time PCR. We observed a reorganization of the Golgi complex in differentiated cells. The Golgi complex transformed to a highly fragmented network of small stacks of cisternae positioned throughout the myotubes as well as around the nucleus. Different extracellular matrix (ECM) components were used as surface coatings in order to improve cell culture conditions. Our experiments demonstrated improved proliferation and early differentiation for cells grown on surface coatings containing a mixture of both glycosaminoglycans (GAGs) and fibrous proteins. We suggest that GAGs and fibrous proteins mixed together into a composite biomaterial can mimic a natural ECM, and this could improve myogenesis for in vitro cell cultures.

The time course effects of electroacupuncture on promoting skeletal muscle regeneration and inhibiting excessive fibrosis after contusion in rabbits

The aim of this study was to investigate the longitudinal effects of electroacupuncture (EA) on Zusanli (ST36) and Ashi acupoints in promoting skeletal muscle regeneration and inhibiting excessive fibrosis after contusion in rabbits. Sixty rabbits were randomly divided into four groups: normal, contusion, EA, and recombinant human insulin-like growth factor-I (rhIGF-I). An acute skeletal muscle contusion was produced on the right gastrocnemius (GM) by an instrument-based drop-mass technique. EA was performed for 15 minutes every two days with 0.4 mA (2 Hz), and GM injections were executed with rhIGF-I (0.25 mL once a week). Rabbits treated with EA had a higher T-SOD and T-AOC serum activities and lower MDA serum level, the blood perfusion of which was also significantly higher. In the EA group, the diameter of the myofibril was uniform and the arrangement was regular, contrary to the contusion group. The number and diameter of regenerative myofibers and MHC expression were increased in the EA group. EA treatment significantly decreased fibrosis formation and reduced both GDF-8 and p-Smad2/3 expressions in injured muscle. Our data indicate that EA may promote myofiber regeneration and reduce excessive fibrosis by improving blood flow and antioxidant capacities. Additionally, EA may regulate signaling factor expression after contusion.

Optimizing the structure and contractility of engineered skeletal muscle thin films

An experimental system was developed to tissue engineer skeletal muscle thin films with well-defined tissue architecture and to quantify the effect on contractility. Using the C2C12 cell line, the authors tested whether tailoring the width and spacing of micropatterned fibronectin lines can be used to increase myoblast differentiation into functional myotubes and maximize uniaxial alignment within a 2-D sheet. Using a combination of image analysis and the muscular thin film contractility assay, it was demonstrated that a fibronectin line width of 100μm and line spacing of 20μm is able to maximize the formation of anisotropic, engineered skeletal muscle with consistent contractile properties at the millimeter length scale. The engineered skeletal muscle exhibited a positive force-frequency relationship, could achieve tetanus and produced a normalized peak twitch stress of 9.4±4.6kPa at 1Hz stimulation. These results establish that micropatterning technologies can be used to control skeletal muscle differentiation and tissue architecture and, in combination with the muscular thin film contractility, assay can be used to probe structure-function relationships. More broadly, an experimental platform is provided with the potential to examine how a range of microenvironmental cues such as extracellular matrix protein composition, micropattern geometries and substrate mechanics affect skeletal muscle myogenesis and contractility.

Effect of RGD functionalization and stiffness modulation of polyelectrolyte multilayer films on muscle cell differentiation

Skeletal muscle tissue engineering holds promise for the replacement of muscle damaged by injury and for the treatment of muscle diseases. Although arginylglycylaspartic acid (RGD) substrates have been widely explored in tissue engineering, there have been no studies aimed at investigating the combined effects of RGD nanoscale presentation and matrix stiffness on myogenesis. In the present work we use polyelectrolyte multilayer films made of poly(L-lysine) (PLL) and poly(L-glutamic) acid (PGA) as substrates of tunable stiffness that can be functionalized by a RGD adhesive peptide to investigate important events in myogenesis, including adhesion, migration, proliferation and differentiation. C2C12 myoblasts were used as cellular models. RGD presentation on soft films and increasing film stiffness could both induce cell adhesion, but the integrins involved in adhesion were different in the case of soft and stiff films. Soft films with RGD peptide appeared to be the most appropriate substrate for myogenic differentiation, while the stiff PLL/PGA films induced significant cell migration and proliferation and inhibited myogenic differentiation. ROCK kinase was found to be involved in the myoblast response to the different films. Indeed, its inhibition was sufficient to rescue differentiation on stiff films, but no significant changes were observed on stiff films with the RGD peptide. These results suggest that different signaling pathways may be activated depending on the mechanical and biochemical properties of multilayer films. This study emphasizes the advantage of soft PLL/PGA films presenting the RGD peptide in terms of myogenic differentiation. This soft RGD-presenting film may be further used as a coating of various polymeric scaffolds for muscle tissue engineering.

In vitro colonization of the muscle extracellular matrix components by Escherichia coli O157:H7: the influence of growth medium, temperature and pH on initial adhesion and induction of biofilm formation by collagens I and III

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 are responsible for repeated food-poisoning cases often caused by contaminated burgers. EHEC infection is predominantly a pediatric illness, which can lead to life-threatening diseases. Ruminants are the main natural reservoir for EHEC and food contamination almost always originates from faecal contamination. In beef meat products, primary bacterial contamination occurs at the dehiding stage of slaughtering. The extracellular matrix (ECM) is the most exposed part of the skeletal muscles in beef carcasses. Investigating the adhesion to the main muscle fibrous ECM proteins, insoluble fibronectin, collagen I, III and IV, laminin-α2 and elastin, results demonstrated that the preceding growth conditions had a great influence on subsequent bacterial attachment. In the tested experimental conditions, maximal adhesion to fibril-forming collagens I or III occurred at 25°C and pH 7. Once initially adhered, exposure to lower temperatures, as applied to meat during cutting and storage, or acidification, as in the course of post-mortem physiological modifications of muscle, had no effect on detachment, except at pHu. In addition, dense biofilm formation occurred on immobilized collagen I or III and was induced in growth medium supplemented with collagen I in solution. From this first comprehensive investigation of EHEC adhesion to ECM proteins with respect to muscle biology and meat processing, new research directions for the development of innovative practices to minimize the risk of meat contamination are further discussed.

The myotomal basement membrane: insight into laminin-111 function and its control by Sonic hedgehog signaling

The importance of laminin-containing basement membranes (BM) for adult muscle function is well established, in particular due to the severe phenotype of congenital muscular dystrophies in patients with mutations disrupting the BM-muscle cell interaction. Developing muscles in the embryo are also dependent on an intact BM. However, the processes controlled by BM-muscle cell interactions in the embryo are only beginning to be elucidated. In this review, we focus on the myotomal BM to illustrate the critical role of laminin-111 in BM assembly and function at the surface of embryonic muscle cells. The myotomal BM provides also an interesting paradigm to study the complex interplay between laminins-containing BM and growth factor-mediated signaling and activity.

Secondary muscle pathology and metabolic dysregulation in adults with cerebral palsy

Cerebral palsy (CP) is caused by an insult to or malformation of the developing brain which affects motor control centers and causes alterations in growth, development, and overall health throughout the life span. In addition to the disruption in development caused by the primary neurological insult, CP is associated with exaggerated sedentary behaviors and a hallmark accelerated progression of muscle pathology compared with typically developing children and adults. Factors such as excess adipose tissue deposition and altered partitioning, insulin resistance, and chronic inflammation may increase the severity of muscle pathology throughout adulthood and lead to cardiometabolic disease risk and/or early mortality. We describe a model of exaggerated health risk represented in adults with CP and discuss the mechanisms and secondary consequences associated with chronic sedentary behavior, obesity, aging, and muscle spasticity. Moreover, we highlight novel evidence that implicates aberrant inflammation in CP as a potential mechanism linking both metabolic and cognitive dysregulation in a cyclical pattern.