Myoblast Cultures Research Articles

Dynamic Profiling of Protein Mole Synthesis Rates during C2C12 Myoblast Differentiation.

Mole (MSR) and fractional (FSR) synthesis rates of proteins during C2C12 myoblast differentiation are investigated. Myoblast cultures supplemented with D2 O during 0-24 h or 72-96 h of differentiation are analyzed by LC-MS/MS to calculate protein FSR and MSR after samples are spiked with yeast alcohol dehydrogenase (ADH1). Profiling of 153 proteins detected 70 significant (p ≤ 0.05, FDR ≤ 1%) differences in abundance between cell states. Early differentiation is enriched by clusters of ribosomal and heat shock proteins, whereas later differentiation is associated with actin filament binding. The median (first-third quartile) FSR (%/h) during early differentiation 4.1 (2.7-5.3) is approximately twofold greater than later differentiation 1.7 (1.0-2.2), equating to MSR of 0.64 (0.38-1.2) and 0.28 (0.1-0.5) fmolh-1 µg-1 total protein, respectively. MSR corresponds more closely with abundance data and highlights proteins associated with glycolytic processes and intermediate filament protein binding that are not evident among FSR data. Similarly, MSR during early differentiation accounts for 78% of the variation in protein abundance during later differentiation, whereas FSR accounts for 4%. Conclusively, the interpretation of protein synthesis data differs when reported in mole or fractional terms, which has consequences when studying the allocation of cellular resources.

Mesenchymal Stromal Cell-Derived Extracellular Vesicles: Their Features and Impact on Fibrosis and Myogenesis in Vitro

Extracellular vesicles (EVs) and, particularly, exosomes are becoming a promising material for “cell-free therapy” of many pathologic conditions. In the recent years therapeutic effects of mesenchymal stromal cells (MSCs) have been attributed to their secretory factors, including EVs. In this study we aim to investigate how EVs produced by MSCs of different tissue origin can influence myogenesis and fibrosis–the main processes that accompany skeletal muscle regeneration. Bone marrow, adipose tissue, intact muscle, and injured muscle-derived rat MSCs were obtained and cultured according to standard protocols. EVs were obtained by ultracentrifugation from the MSC-conditioned medium of cell passages 2 and 3. The effects of EVs were estimated on the in vitro models of myogenesis and fibrosis. Samples of isolated EVs contained nano-sized vesicles that carried some exosomal markers. Promyogenic microRNA were found in EVs from bone marrow and muscle MSCs. We found that MSC-derived EVs from all sources significantly increased the number of newly formed myotubes in myoblast culture in vitro and also reduced the number and size of fibrotic nodules in muscle fibroblast culture in vitro. Our results suggest that MSC-derived EVs indeed possess antifibrotic and promyogenic potentials. However, the role of microRNA in these processes is yet to be determined, and the effect of EVs on skeletal muscle regeneration is yet to be tested in vivo.

Advanced Simultaneous Isolation, Culture, and Identification of Myoblasts and Fibroblasts From Sternocleidomastoid Muscle of Congenital Muscular Torticollis.

Congenital muscular torticollis (CMT) is a common pediatric disease caused by contracture of sternocleidomastoid muscle (SCM) that leads to neck stiffness and deformity. Based on the adhesion characteristics of different cells in affected SCM of CMT, myoblasts and fibroblasts can be isolated simultaneously by advanced culture conditions. Our study aimed to explore and optimize the isolation, culture, and identification of myoblasts and fibroblasts in SCM of CMT. Myoblasts and fibroblasts were separated by combined digestion with trypsin and collagenase. With this improved method, the morphology of isolated myoblasts and fibroblasts was observed under the microscope, the cell growth curve was drawn, and the purity of myoblasts and fibroblasts was determined by immunofluorescence. The method allowed to satisfactorily culture myoblasts and fibroblasts. The cells could stably grow and be passaged, provided they were at least 80% confluent. Immunofluorescence of myoblasts and fibroblasts showed high rate of positive staining, and cell count showed excellent growth state. Moreover, according to the growth curve, fibroblasts grew at a higher rate than myoblasts. The isolated myoblasts and fibroblasts have high purity, intact structure, and relatively high vitality. This method can be used to establish a cell model with myoblasts and fibroblasts, which can be applied to investigate etiology of CMT or mechanisms of drug action.

Effect of treatment with conditioned media derived from C2C12 myotube on adipogenesis and lipolysis in 3T3-L1 adipocytes.

Regular exercise is an effective strategy that is used to prevent and treat obesity as well as type 2 diabetes. Exercise-induced myokine secretion is considered a mechanism that coordinates communication between muscles and other organs. In order to examine the possibility of novel communications from muscle to adipose tissue mediated by myokines, we treated 3T3-L1 adipocytes with C2C12 myotube electrical pulse stimulation-conditioned media (EPS-CM), using a C2C12 myotube contraction system stimulated by an electrical pulse. Continuous treatment with myotube EPS-CM promoted adipogenesis of 3T3-L1 pre-adipocytes via the upregulation of the peroxisome proliferator-activated receptor-gamma (PPARγ) 2 and PPARγ-regulated gene expression. Furthermore, our results revealed that myotube EPS-CM induces lipolysis and secretion of adiponectin in mature adipocytes. EPS-CM obtained from a C2C12 myoblast culture did not induce such changes in these genes, suggesting that contraction-induced myokine(s) secretion occurs particularly in differentiated myotubes. Thus, contraction-induced secretion of myokine(s) promotes adipogenesis and lipid metabolism in 3T3-L1 adipocytes. These findings suggest the possibility that skeletal muscle communicates to adipose tissues during exercise, probably by the intermediary of unidentified myokines.

Formation of Aberrant Myotubes by Myoblasts Lacking Myosin VI Is Associated with Alterations in the Cytoskeleton Organization, Myoblast Adhesion and Fusion.

We have previously postulated that unconventional myosin VI (MVI) could be involved in myoblast differentiation. Here, we addressed the mechanism(s) of its involvement using primary myoblast culture derived from the hindlimb muscles of Snell’s waltzer mice, the natural MVI knockouts (MVI-KO). We observed that MVI-KO myotubes were formed faster than control heterozygous myoblasts (MVI-WT), with a three-fold increase in the number of myosac-like myotubes with centrally positioned nuclei. There were also changes in the levels of the myogenic transcription factors Pax7, MyoD and myogenin. This was accompanied by changes in the actin cytoskeleton and adhesive structure organization. We observed significant decreases in the levels of proteins involved in focal contact formation, such as talin and focal adhesion kinase (FAK). Interestingly, the levels of proteins involved in intercellular communication, M-cadherin and drebrin, were also affected. Furthermore, time-dependent alterations in the levels of the key proteins for myoblast membrane fusion, myomaker and myomerger, without effect on their cellular localization, were observed. Our data indicate that in the absence of MVI, the mechanisms controlling cytoskeleton organization, as well as myoblast adhesion and fusion, are dysregulated, leading to the formation of aberrant myotubes.

In vitro assay for the efficacy assessment of AAV vectors expressing microdystrophin

AAV-delivered microdystrophin genes hold great promise for Duchenne muscular dystrophy (DMD) treatment. It is anticipated that the optimization of engineered dystrophin genes will be required to increase the efficacy and reduce the immunogenicity of transgenic proteins. An in vitro system is required for the efficacy testing of genetically engineered dystrophin genes. We report here on the proof of concept for an in vitro assay based on the assessment of sarcolemma damage after repetitively applied electrical stimuli. The primary cell culture of myoblasts was established from wild-type C57BL/10ScSnJ and dystrophin-deficient mdx mice. The preparation parameters and the differentiation of contractile myotubes were optimized. DAPI and TO-PRO-3 dyes were used to assess myotubular membrane permeability in response to electrical pulse stimulation (EPS). Myotubes derived from mdx mice exhibited a greater increase in membrane damage, as assessed by TO-PRO-3-measured permeability after EPS, than was exhibited by the healthy control myotubes. AAV-DJ particles carrying the microdystrophin gene were used to transduce mdx-derived differentiated myotubes. Microdystrophin delivery ameliorated the disease phenotype and reduced the EPS-induced membrane damage to a level comparable to that of the healthy controls. Thus, the in vitro system was shown to be capable of supporting studies on DMD gene therapy.

Effect of Tahiti lime (Citrus latifolia) juice on the Production of the PGF2\u03b1/PGE2 and Pro-Inflammatory Cytokines involved in Menstruation

Tahiti lemon juice (Citrus latifolia) (TLJ), as a natural source of flavonoids, has been used as an alternative to anti-inflammatory drugs for the treatment of dysmenorrhea and menstrual excessive bleeding, often associated with an imbalance of the prostaglandins (PG) levels. However, despite the positive effects, the mechanisms that rule menstruation control are still unknown. Therefore, the objectives were to characterize the TLJ and analyze its effect on the production of PGF2α, PGE2 and pro-inflammatory cytokines involved inmenstruation. Flavonoids from TLJ were discriminated by UPLC-DAD-MS/MS (Qq-TOF) and the effects of TLJ were studied in vitro by quantification of the contraction of myoblasts in culture and PGF2α and PGE2 productions. Further, the systemic and menstrual fluid levels of PGF2α, PGE2, IL-1β, TNF-α, IL-6, AK1B1 and AK1C3 enzymes produced by women during the menstrual period were compared after exposition or not to TLJ or meloxicam. The results showed that TLJ induces an increase in the contraction of myoblasts and the PGF2α supernatant level. Regarding in vivo analysis, a higher concentration of PGF2α and an unaltered PGE2 level was also found in the menstrual blood of women treated with TLJ, in contrast with a lower level of PGE2 and PGF2α observed in the meloxicam group. Concerning cytokines, only menstrual TNF-α levels decrease after treatment with TLJ or meloxicam. In conclusion, TLJ may favor the control of menstruation events via a PGF2α mediated muscle contractile response.

Multiple Effects of Mechanical Stretch on Myogenic Progenitor Cells.

Mechanically stretched skeletal muscle undergoes dramatic shifts in structure, mass, and function. In vitro tensile strain models have demonstrated that myogenic progenitor cells, including satellite cells and myoblasts, are highly mechanosensitive cells, and respond to mechanical strain in a wide variety of aspects. However, the experimental results from different researchers and laboratories are not always in support of each other. Moreover, some specific molecules or signaling pathways were reported to play distinct roles in stretched myogenic cells, according to the statements of different studies. The purpose of this review is to integrate the researches conducting in vitro culture of satellite cells or myoblasts and exploring their mechanoresponses using in vitro stretching apparatus. These responses will be categorized into several groups, such as activation, proliferation, myogenic differentiation, cellular damage or apoptosis, properties of plasma membrane, transdifferentiation, reorientation, etc. In addition, detailed experimental designs like culturing conditions and straining regimens will be displayed and compared, to interpret some contradictory statements in different studies. Furthermore, the currently known interconnections among some mechanosensitive pathways will be pictured to give a better understanding about the complex regulations of myogenic cell responses to mechanical stretch. Hopefully, by summarizing the published studies about mechanoresponses of myogenic progenitor cells, future directions, and perspectives would be made clearer to researchers in this field.

Triazine-cored polymeric vectors for antisense oligonucleotide delivery in vitro and in vivo

BackgroundThe polymer-based drug/gene delivery is promising for the treatment of inherent or acquire disease, because of the polymer’s structural flexibility, larger capacity for therapeutic agent, low host immunogenicity and less cost. Antisense therapy is an approach to fighting genetic disorders or infections using antisense oligonucleotides (AOs). Unfortunately, the naked AOs showed low therapeutic efficacy in vivo and in clinical trial due to their poor cellular uptake and fast clearance in bloodstream. In this study, a series of triazine-cored amphiphilic polymers (TAPs) were investigated for their potential to enhance delivery of AOs, 2′-O-methyl phosphorothioate RNA (2′-OMePS) and phosphorodiamidate morpholino oligomer (PMO) both in vitro and in vivo.ResultsTAPs significantly enhanced AO-induced exon-skipping in a GFP reporter-based myoblast and myotube culture system, and observed cytotoxicity of the TAPs were lower than Endoporter, Lipofectamine-2000 or PEI 25K. Application of optimized formulations of TAPs with AO targeted to dystrophin exon 23 demonstrated a significant increase in exon-skipping efficiency in dystrophic mdx mice. The best ones for PMO and 2′-OMePS delivery have reached to 11-, 15-fold compared with the AO only in mdx mice, respectively.ConclusionThe study of triazine-cored amphiphilic polymers for AO delivery in vitro and in mdx mice indicated that the carrier’s performances are related to the molecular size, compositions and hydrophilic-lipophilic balance (HLB) of the polymers, as well as the AO’s structure. Improved exon-skipping efficiency of AOs observed in vitro and in mdx mice accompanied with low cytotoxicity demonstrated TAP polymers are potentials as safe and effective delivery carrier for gene/drug delivery.

Novel Fluorescent Mitochondria-Targeted Probe MitoCLox Reports Lipid Peroxidation in Response to Oxidative Stress In Vivo.

A new mitochondria-targeted probe MitoCLox was designed as a starting compound for a series of probes sensitive to cardiolipin (CL) peroxidation. Fluorescence microscopy reported selective accumulation of MitoCLox in mitochondria of diverse living cell cultures and its oxidation under stress conditions, particularly those known to cause a selective cardiolipin oxidation. Ratiometric fluorescence measurements using flow cytometry showed a remarkable dependence of the MitoCLox dynamic range on the oxidation of the sample. Specifically, MitoCLox oxidation was induced by low doses of hydrogen peroxide or organic hydroperoxide. The mitochondria-targeted antioxidant 10-(6′-plastoquinonyl)decyltriphenyl-phosphonium (SkQ1), which was shown earlier to selectively protect cardiolipin from oxidation, prevented hydrogen peroxide-induced MitoCLox oxidation in the cells. Concurrent tracing of MitoCLox oxidation and membrane potential changes in response to hydrogen peroxide addition showed that the oxidation of MitoCLox started without a delay and was complete during the first hour, whereas the membrane potential started to decay after 40 minutes of incubation. Hence, MitoCLox could be used for splitting the cell response to oxidative stress into separate steps. Application of MitoCLox revealed heterogeneity of the mitochondrial population; in living endothelial cells, a fraction of small, rounded mitochondria with an increased level of lipid peroxidation were detected near the nucleus. In addition, the MitoCLox staining revealed a specific fraction of cells with an increased level of oxidized lipids also in the culture of human myoblasts. The fraction of such cells increased in high-density cultures. These specific conditions correspond to the initiation of spontaneous myogenesis in vitro, which indicates that oxidation may precede the onset of myogenic differentiation. These data point to a possible participation of oxidized CL in cell signalling and differentiation.

Decellularized extracellular matrices derived from cultured cells at stepwise myogenic stages for the regulation of myotube formation

The regulation of stem cell differentiation is key for muscle tissue engineering and regenerative medicine. To this end, various substrates mimicking the native extracellular matrix (ECM) have been developed with consideration of the mechanical, topological, and biochemical properties. However, mimicking the biochemical properties of the native ECM is difficult due to its compositional complexity. To develop substrates that mimic the native ECM and its biochemical properties, decellularization is typically used. Here, substrates mimicking the native ECM at each myogenic stage are prepared as stepwise myogenesis-mimicking matrices via the in vitro myogenic culture of C2C12 myoblasts and decellularization. Cells adhered to the stepwise myogenesis-mimicking matrices at similar levels. However, the matrices derived from cells at the myogenic early stage suppressed cell growth and promoted myogenesis. This promotion of myogenesis was potentially due to the suppression of the activation of endogenous BMP signaling following the suppression of the expression of the myogenic-inhibitory factors, Id2 and Id3. Our stepwise myogenesis-mimicking matrices will be suitable ECM models for basic biological research and myogenesis of stem cells. Further, these matrices will provide insights that improve the efficacy of decellularized ECM for muscle repair.

Isolation, Culture, and Differentiation of Primary Myoblasts Derived from Muscle Satellite Cells

The skeletal muscle is key for body mobility and motor performance, but aging and diseases often lead to progressive loss of muscle mass due to wasting or degeneration of muscle cells. Muscle satellite cells (MuSCs) represent a population of tissue stem cells residing in the skeletal muscles and are responsible for homeostatic maintenance and regeneration of skeletal muscles. Growth, injury, and degenerative signals activate MuSCs, which then proliferate (proliferating MuSCs are called myoblasts), differentiate and fuse with existing multinuclear muscle cells (myofibers) to mediate muscle growth and repair. Here, we describe a protocol for isolating MuSCs from skeletal muscles of mice for in vitro analysis. In addition, we provide a detailed protocol on how to culture and differentiate primary myoblasts into myotubes and an immunofluorescent staining procedure to characterize the cells. These methods are essential for modeling regenerative myogenesis in vitro to understand the dynamics, function and molecular regulation of MuSCs.

Myopalladin promotes muscle growth through modulation of the serum response factor pathway.

BackgroundMyopalladin (MYPN) is a striated muscle‐specific, immunoglobulin‐containing protein located in the Z‐line and I‐band of the sarcomere as well as the nucleus. Heterozygous MYPN gene mutations are associated with hypertrophic, dilated, and restrictive cardiomyopathy, and homozygous loss‐of‐function truncating mutations have recently been identified in patients with cap myopathy, nemaline myopathy, and congenital myopathy with hanging big toe.MethodsConstitutive MYPN knockout (MKO) mice were generated, and the role of MYPN in skeletal muscle was studied through molecular, cellular, biochemical, structural, biomechanical, and physiological studies in vivo and in vitro.ResultsMKO mice were 13% smaller compared with wild‐type controls and exhibited a 48% reduction in myofibre cross‐sectional area (CSA) and significantly increased fibre number. Similarly, reduced myotube width was observed in MKO primary myoblast cultures. Biomechanical studies showed reduced isometric force and power output in MKO mice as a result of the reduced CSA, whereas the force developed by each myosin molecular motor was unaffected. While the performance by treadmill running was similar in MKO and wild‐type mice, MKO mice showed progressively decreased exercise capability, Z‐line damage, and signs of muscle regeneration following consecutive days of downhill running. Additionally, MKO muscle exhibited progressive Z‐line widening starting from 8 months of age. RNA‐sequencing analysis revealed down‐regulation of serum response factor (SRF)‐target genes in muscles from postnatal MKO mice, important for muscle growth and differentiation. The SRF pathway is regulated by actin dynamics as binding of globular actin to the SRF‐cofactor myocardin‐related transcription factor A (MRTF‐A) prevents its translocation to the nucleus where it binds and activates SRF. MYPN was found to bind and bundle filamentous actin as well as interact with MRTF‐A. In particular, while MYPN reduced actin polymerization, it strongly inhibited actin depolymerization and consequently increased MRTF‐A‐mediated activation of SRF signalling in myogenic cells. Reduced myotube width in MKO primary myoblast cultures was rescued by transduction with constitutive active SRF, demonstrating that MYPN promotes skeletal muscle growth through activation of the SRF pathway.ConclusionsMyopalladin plays a critical role in the control of skeletal muscle growth through its effect on actin dynamics and consequently the SRF pathway. In addition, MYPN is important for the maintenance of Z‐line integrity during exercise and aging. These results suggest that muscle weakness in patients with biallelic MYPN mutations may be associated with reduced myofibre CSA and SRF signalling and that the disease phenotype may be aggravated by exercise.

The effects of myokines on osteoclasts and osteoblasts

Recently, muscle has received much attention as an endocrine organ regulating other biological targets, including the pancreas, liver, and adipose tissue. Although there is a possibility that muscle-secreting factors biochemically affect bone metabolism in a paracrine manner, the net effects of myokines on the biology of osteoclasts and osteoblasts, particularly on bone mass in vivo, have not yet been thoroughly investigated. Therefore, we performed in vitro as well as animal experiments using conditioned media (CM) collected from C2C12 myoblast and myotube cultures to better understand the interactions between muscle and bone. Compared with non-CM (i.e., control) and myoblast CM, myotube CM markedly inhibited in vitro bone resorption through the suppression of osteoclast differentiation and resorptive activity of individual osteoclasts. Consistently, the expressions of osteoclast differentiation markers, such as tartrate-resistant acid phosphatase (Trap) and calcitonin receptor (Ctr), decreased with myotube CM. Myotube CM significantly stimulated preosteoblast viability and migration and reduced apoptosis, thereby resulting in an increase in calvaria bone formation. Importantly, systemic treatment with myotube CM for 4 weeks increased bone per tissue volume by 30.7% and 19.6% compared with control and myoblast CM, respectively. These results support the hypothesis that muscle plays beneficial roles in bone health via secretion of anabolic factors, in addition to mechanical stimuli, and importantly indicate that muscle-derived factors can be potential therapeutic targets against metabolic bone diseases.

Interactions of Organosilanes with Fibrinogen and Their Influence on Muscle Cell Proliferation in 3D Fibrin Hydrogels.

Silanization of biomacromolecules has emerged as a fruitful approach to prepare hybrid biohydrogels. However, very little is known about interactions between organosilanes and biopolymers in solution. Here we focused on fibrin, a protein of interest in the biomedical field, whose self-assembly process and resulting gel structure are highly sensitive to experimental conditions. Three main silanes were selected to decipher the relative influence of the silanol groups and organic functions. Whereas no protein denaturation was observed, silanes bearing hydrophobic groups had a surfactant-like behavior and could improve the dispersion of fibrinogen molecules, impacting gel formation kinetics and rheological properties. 3D cultures of myoblasts evidenced that organosilanes could promote or impede cell proliferation, suggesting interactions of silanols with fibrin. These results demonstrate that the two sides of the coin of organosilane reactivity are relevant at different stages of fibrin gel formation and must be considered for future development of hybrid biomaterials.

Chlorella vulgaris Modulates Genes and Muscle-Specific microRNAs Expression to Promote Myoblast Differentiation in Culture.

Background Loss of skeletal muscle mass, strength, and function due to gradual decline in the regeneration of skeletal muscle fibers was observed with advancing age. This condition is known as sarcopenia. Myogenic regulatory factors (MRFs) are essential in muscle regeneration as its activation leads to the differentiation of myoblasts to myofibers. Chlorella vulgaris is a coccoid green eukaryotic microalga that contains highly nutritious substances and has been reported for its pharmaceutical effects. The aim of this study was to determine the effect of C. vulgaris on the regulation of MRFs and myomiRs expression in young and senescent myoblasts during differentiation in vitro. Methods Human skeletal muscle myoblast (HSMM) cells were cultured and serial passaging was carried out to obtain young and senescent cells. The cells were then treated with C. vulgaris followed by differentiation induction. The expression of Pax7, MyoD1, Myf5, MEF2C, IGF1R, MYOG, TNNT1, PTEN, and MYH2 genes and miR-133b, miR-206, and miR-486 was determined in untreated and C. vulgaris-treated myoblasts on Days 0, 1, 3, 5, and 7 of differentiation. Results The expression of Pax7, MyoD1, Myf5, MEF2C, IGF1R, MYOG, TNNT1, and PTEN in control senescent myoblasts was significantly decreased on Day 0 of differentiation (p<0.05). Treatment with C. vulgaris upregulated Pax7, Myf5, MEF2C, IGF1R, MYOG, and PTEN in senescent myoblasts (p<0.05) and upregulated Pax7 and MYOG in young myoblasts (p<0.05). The expression of MyoD1 and Myf5 in young myoblasts however was significantly decreased on Day 0 of differentiation (p<0.05). During differentiation, the expression of these genes was increased with C. vulgaris treatment. Further analysis on myomiRs expression showed that miR-133b, miR-206, and miR-486 were significantly downregulated in senescent myoblasts on Day 0 of differentiation which was upregulated by C. vulgaris treatment (p<0.05). During differentiation, the expression of miR-133b and miR-206 was significantly increased with C. vulgaris treatment in both young and senescent myoblasts (p<0.05). However, no significant change was observed on the expression of miR-486 with C. vulgaris treatment. Conclusions C. vulgaris demonstrated the modulatory effects on the expression of MRFs and myomiRs during proliferation and differentiation of myoblasts in culture. These findings may indicate the beneficial effect of C. vulgaris in muscle regeneration during ageing thus may prevent sarcopenia in the elderly.

Myostatin Upregulation in Patients in the Chronic Phase of Severe Burn Injury Leads to Muscle Cell Catabolism

Background: Burn injury leads to a hypercatabolic response and ultimately muscle wasting with drastic implications for recovery of bodily functions, patient’s quality of life (QoL), and long-term survival. Several treatment options target the body’s initial stress response, but pharmacological approaches to specifically address muscle protein metabolism have only been poorly investigated. Objective: The aim of this study was to assess the role of myostatin and follistatin in burn injury and its possible implications in muscle wasting syndrome. Methods: We harvested serum from male patients within 48 h and again 9–12 months after severe burn injury (>20% of total body surface area). By means of myoblast cultures, immunohistochemistry, immunoblotting, and scratch assay, the role of myostatin and its implications in post-burn muscle metabolism and myoblast proliferation and differentiation was analyzed. Results: We were able to show increased proliferative and myogenic capacity, decreased myostatin, decreased SMAD 2/3, and elevated follistatin concentrations in human skeletal myoblast cultures with serum conditioned medium of patients in the acute phase of burn injury and conversely a reversed situation in patients in the chronic phase of burn injury. Thus, there is a biphasic response to burn trauma, initiated by an anabolic state and followed by long-term hypercatabolism. Conclusion: We conclude that the myostatin signaling pathway plays an important regulative role in burn-associated muscle wasting and that blockade of myostatin could prove to be a valuable treatment approach improving the rehabilitation process, QoL, and long-term survival after severe burn injury.

Citrulline stimulates muscle protein synthesis, by reallocating ATP consumption to muscle protein synthesis.

BackgroundAnimal studies and clinical data support the interest of citrulline as a promising therapeutic for sarcopenia. Citrulline is known to stimulate muscle protein synthesis, but how it affects energy metabolism to support the highly energy‐dependent protein synthesis machinery is poorly understood.MethodsHere, we used myotubes derived from primary culture of mouse myoblasts to study the effect of citrulline on both energy metabolism and protein synthesis under different limiting conditions.ResultsWhen serum/amino acid deficiency or energy stress (mild uncoupling) were applied, citrulline stimulated muscle protein synthesis by +22% and +11%, respectively. Importantly, this increase was not associated with enhanced energy status (ATP/ADP ratio) or mitochondrial respiration. We further analysed the share of mitochondrial respiration and thus of generated ATP allocated to different metabolic pathways by using specific inhibitors. Our results indicate that addition of citrulline allocated an increased share of mitochondrially generated ATP to the protein synthesis machinery under conditions of both serum/amino acid deficiency (+28%) and energy stress (+21%). This reallocation was not because of reduced ATP supply to DNA synthesis or activities of sodium and calcium cycling ion pumps.ConclusionsUnder certain stress conditions, citrulline increases muscle protein synthesis by specifically reallocating mitochondrial fuel to the protein synthesis machinery. Because ATP/ADP ratios and thus Gibbs free energy of ATP hydrolysis remained globally constant, this reallocation may be linked to decreased activation energies of one or several ATP (and GTP)‐consuming reactions involved in muscle protein synthesis.

Optimising the biocompatibility of 3D printed photopolymer constructs in vitro and in vivo

3D printing is a rapid and accessible fabrication technology that engenders creative custom design solutions for cell scaffolds, perfusion systems and cell culture systems for tissue engineering. Critical to its success is the biocompatibility of the materials used, which should allow long-term tissue culture without affecting cell viability or inducing an inflammatory response for in vitro and in vivo applications. Polyjet 3D printers offer arguably the highest resolution with the fewest design constraints of any commercially available 3D printing systems. Although widely used for rapid-prototyping of medical devices and 3D anatomical modelling, polyjet printing has not been adopted by the tissue engineering field, largely due to the cytotoxicity of leachates from the printed parts. Biocompatibility in the context of cell culture is not commonly addressed for polyjet materials, as they tend to be optimised for their ability to fabricate complex structures. In order to study the potential issues surrounding the leaching of toxins, we prepared cell culture substrates using the commercially available MED610 photopolymer. The substrates were cleaned using either the manufacturer-specified ‘biocompatible’ washing procedures, or a novel protocol incorporating a sonication in isopropanol and water step. We then compared the effectiveness of these both in vitro and in vivo. Using primary mouse myoblast cultures, the manufacturer’s protocol led to inconsistent and poorer cell viability when compared to the sonication protocol (p = 0.0002 at 48 h after indirect exposure). Subdermal implantation of MED610 into nude rats demonstrated a significant foreign body response with a greater number of giant cells (p = 0.0161) and foreign bodies (p = 0.0368) when compared to the sonication protocol, which was comparable to the control (sham) groups. These results present an improved, cytocompatible cleaning protocol of printable photopolymers to facilitate creative 3D-printed custom designs for cell culture systems for both in vitro and in vivo tissue engineering applications.

Altered myogenesis and premature senescence underlie human TRIM32-related myopathy

TRIM32 is a E3 ubiquitin -ligase containing RING, B-box, coiled-coil and six C-terminal NHL domains. Mutations involving NHL and coiled-coil domains result in a pure myopathy (LGMD2H/STM) while the only described mutation in the B-box domain is associated with a multisystemic disorder without myopathy (Bardet-Biedl syndrome type11), suggesting that these domains are involved in distinct processes. Knock-out (T32KO) and knock-in mice carrying the c.1465G > A (p.D489N) involving the NHL domain (T32KI) show alterations in muscle regrowth after atrophy and satellite cells senescence. Here, we present phenotypical description and functional characterization of mutations in the RING, coiled-coil and NHL domains of TRIM32 causing a muscle dystrophy. Reduced levels of TRIM32 protein was observed in all patient muscle studied, regardless of the type of mutation (missense, single amino acid deletion, and frameshift) or the mutated domain. The affected patients presented with variable phenotypes but predominantly proximal weakness. Two patients had symptoms of both muscular dystrophy and Bardet-Biedl syndrome. The muscle magnetic resonance imaging (MRI) pattern is highly variable among patients and families. Primary myoblast culture from these patients demonstrated common findings consistent with reduced proliferation and differentiation, diminished satellite cell pool, accelerated senescence of muscle, and signs of autophagy activation.