Search

The generation of myogenic progenitors from iPSCs (iMPs) with therapeutic potential for in vivo tissue regeneration has long been a goal in the skeletal muscle community. Today, protocols enable the production of potent, albeit immature, iMPs that resemble Pax7+ adult muscle stem cells. While muscular dystrophies are often the primary therapeutic target for these cells, an underexplored application is their use in treating traumatic muscle injuries. Notably absent from recent reviews on iMPs is the concept of engineering these cells to perform functions post-transplantation that non-transgenic cells cannot. Here, we highlight protocols to enhance the generation, purification, and maturation of iMPs, and introduce the idea of engineering these cells to perform functions beyond their normal capacities, envisioning novel therapeutic applications. [ABSTRACT FROM AUTHOR]

The generation of myogenic progenitors from iPSCs (iMPs) with therapeutic potential for in vivo tissue regeneration has long been a goal in the skeletal muscle community. Today, protocols enable the production of potent, albeit immature, iMPs that resemble Pax7+ adult muscle stem cells. While muscular dystrophies are often the primary therapeutic target for these cells, an underexplored application is their use in treating traumatic muscle injuries. Notably absent from recent reviews on iMPs is the concept of engineering these cells to perform functions post-transplantation that non-transgenic cells cannot. Here, we highlight protocols to enhance the generation, purification, and maturation of iMPs, and introduce the idea of engineering these cells to perform functions beyond their normal capacities, envisioning novel therapeutic applications.

Abstract Background Muscle is severely affected by ischemia/reperfusion injury (IRI). Quiescent satellite cells differentiating into myogenic progenitor cells (MPC) possess a remarkable regenerative potential. We herein established a model of local application of MPC in murine hindlimb ischemia/reperfusion to study cell engraftment and differentiation required for muscle regeneration. Methods A clamping model of murine (C57b/6 J) hindlimb ischemia was established to induce IRI in skeletal muscle. After 2 h (h) warm ischemic time (WIT) and reperfusion, reporter protein expressing MPC (TdTomato or Luci-GFP, 1 × 106 cells) obtained from isolated satellite cells were injected intramuscularly. Surface marker expression and differentiation potential of MPC were analyzed in vitro by flow cytometry and differentiation assay. In vivo bioluminescence imaging and histopathologic evaluation of biopsies were performed to quantify cell fate, engraftment and regeneration. Results 2h WIT induced severe IRI on muscle, and muscle fiber regeneration as per histopathology within 14 days after injury. Bioluminescence in vivo imaging demonstrated reporter protein signals of MPC in 2h WIT animals and controls over the study period (75 days). Bioluminescence signals were detected at the injection site and increased over time. TdTomato expressing MPC and myofibers were visible in host tissue on postoperative days 2 and 14, respectively, suggesting that injected MPC differentiated into muscle fibers. Higher reporter protein signals were found after 2h WIT compared to controls without ischemia, indicative for enhanced growth and/or engraftment of MPC injected into IRI-affected muscle antagonizing muscle damage caused by IRI. Conclusion WIT-induced IRI in muscle requests increased numbers of injected MPC to engraft and persist, suggesting a possible rational for cell therapy to antagonize IRI. Further investigations are needed to evaluate the regenerative capacity and therapeutic advantage of MPC in the setting of ischemic limb injury.

Abstract It is still unclear if immune responses will compromise the large‐scale utilization of human induced pluripotent stem cells (hiPSCs)‐derived cell therapies. To answer this question, we used humanized mouse models generated by the adoptive transfer of peripheral blood mononuclear cells or the cotransplantation of hematopoietic stem cells and human thymic tissue. Using these mice, we evaluated the engraftment in skeletal muscle of myoblasts derived either directly from a muscle biopsy or differentiated from hiPSCs or fibroblasts. Our results showed that while allogeneic grafts were mostly rejected and highly infiltrated with human T cells, engraftment of autologous cells was tolerated. We also observed that hiPSC‐derived myogenic progenitor cells (MPCs) are not targeted by autologous T cells and natural killer cells in vitro. These findings suggest that the reprogramming and differentiation procedures we used are not immunogenic and that hiPSC‐derived MPCs will be tolerated in the presence of a competent human immune system.

Abstract Background Degeneration of smooth muscles in sphincters can cause debilitating diseases such as fecal incontinence. Skeletal muscle-derived cells have been effectively used in clinics for the regeneration of the skeletal muscle sphincters, such as the external anal or urinary sphincter. However, little is known about the in vitro smooth muscle differentiation potential and in vivo regenerative potential of skeletal muscle-derived cells. Methods Myogenic progenitor cells (MPC) were isolated from the skeletal muscle and analyzed by flow cytometry and in vitro differentiation assays. The differentiation of MPC to smooth muscle cells (MPC-SMC) was evaluated by immunofluorescence, flow cytometry, patch-clamp, collagen contraction, and microarray gene expression analysis. In vivo engraftment of MPC-SMC was monitored by transplanting reporter protein-expressing cells into the pyloric sphincter of immunodeficient mice. Results MPC derived from human skeletal muscle expressed mesenchymal surface markers and exhibit skeletal myogenic differentiation potential in vitro. In contrast, they lack hematopoietic surface marker, as well as adipogenic, osteogenic, and chondrogenic differentiation potential in vitro. Cultivation of MPC in smooth muscle differentiation medium significantly increases the fraction of alpha smooth muscle actin (aSMA) and smoothelin-positive cells, while leaving the number of desmin-positive cells unchanged. Smooth muscle-differentiated MPC (MPC-SMC) exhibit increased expression of smooth muscle-related genes, significantly enhanced numbers of CD146- and CD49a-positive cells, and in vitro contractility and express functional Cav and Kv channels. MPC to MPC-SMC differentiation was also accompanied by a reduction in their skeletal muscle differentiation potential. Upon removal of the smooth muscle differentiation medium, a major fraction of MPC-SMC remained positive for aSMA, suggesting the definitive acquisition of their phenotype. Transplantation of murine MPC-SMC into the mouse pyloric sphincter revealed engraftment of MPC-SMC based on aSMA protein expression within the host smooth muscle tissue. Conclusions Our work confirms the ability of MPC to give rise to smooth muscle cells (MPC-SMC) with a well-defined and stable phenotype. Moreover, the engraftment of in vitro-differentiated murine MPC-SMC into the pyloric sphincter in vivo underscores the potential of this cell population as a novel cell therapeutic treatment for smooth muscle regeneration of sphincters.

Mitochondrial remodeling through fusion and fission is crucial for progenitor cell differentiation but its role in myogenesis is poorly understood. Here, we characterized the function of mitofusin 2 (Mfn2), a mitochondrial outer membrane protein critical for mitochondrial fusion, in muscle progenitor cells (myoblasts). Mfn2 expression is upregulated during myoblast differentiation in vitro and muscle regeneration in vivo. Targeted deletion of Mfn2 gene in myoblasts (Mfn2MKO) increases oxygen‐consumption rates (OCR) associated with the maximal respiration and spare respiratory capacity, and increased levels of reactive oxygen species (ROS). Skeletal muscles of Mfn2MKO mice exhibit robust mitochondrial swelling with normal mitochondrial DNA content. Additionally, mitochondria isolated from Mfn2MKO muscles have reduced OCR at basal state and for complex I respiration, associated with decreased levels of complex I proteins NDUFB8 (NADH ubiquinone oxidoreductase subunit B8) and NDUFS3 (NADH ubiquinone oxidoreductase subunit S3). However, Mfn2MKO has no obvious effects on myoblast differentiation, muscle development and function, and muscle regeneration. These results demonstrate a novel role of Mfn2 in regulating mitochondrial complex I protein abundance and respiratory functions in myogenic progenitors and myofibers. [ABSTRACT FROM AUTHOR]

Background: Muscle is severely affected by ischemia/reperfusion injury (IRI). Quiescent satellite cells differentiating into myogenic progenitor cells (MPC) possess a remarkable regenerative potential. We herein established a model of local application of MPC in murine hindlimb ischemia/reperfusion to study cell engraftment and differentiation required for muscle regeneration. Methods: A clamping model of murine (C57b/6 J) hindlimb ischemia was established to induce IRI in skeletal muscle. After 2 h (h) warm ischemic time (WIT) and reperfusion, reporter protein expressing MPC (TdTomato or Luci-GFP, 1 × 106 cells) obtained from isolated satellite cells were injected intramuscularly. Surface marker expression and differentiation potential of MPC were analyzed in vitro by flow cytometry and differentiation assay. In vivo bioluminescence imaging and histopathologic evaluation of biopsies were performed to quantify cell fate, engraftment and regeneration. Results: 2h WIT induced severe IRI on muscle, and muscle fiber regeneration as per histopathology within 14 days after injury. Bioluminescence in vivo imaging demonstrated reporter protein signals of MPC in 2h WIT animals and controls over the study period (75 days). Bioluminescence signals were detected at the injection site and increased over time. TdTomato expressing MPC and myofibers were visible in host tissue on postoperative days 2 and 14, respectively, suggesting that injected MPC differentiated into muscle fibers. Higher reporter protein signals were found after 2h WIT compared to controls without ischemia, indicative for enhanced growth and/or engraftment of MPC injected into IRI-affected muscle antagonizing muscle damage caused by IRI. Conclusion: WIT-induced IRI in muscle requests increased numbers of injected MPC to engraft and persist, suggesting a possible rational for cell therapy to antagonize IRI. Further investigations are needed to evaluate the regenerative capacity and therapeutic advantage of MPC in the setting of ischemic limb injury. [ABSTRACT FROM AUTHOR]

Background: Degeneration of smooth muscles in sphincters can cause debilitating diseases such as fecal incontinence. Skeletal muscle-derived cells have been effectively used in clinics for the regeneration of the skeletal muscle sphincters, such as the external anal or urinary sphincter. However, little is known about the in vitro smooth muscle differentiation potential and in vivo regenerative potential of skeletal muscle-derived cells. Methods: Myogenic progenitor cells (MPC) were isolated from the skeletal muscle and analyzed by flow cytometry and in vitro differentiation assays. The differentiation of MPC to smooth muscle cells (MPC-SMC) was evaluated by immunofluorescence, flow cytometry, patch-clamp, collagen contraction, and microarray gene expression analysis. In vivo engraftment of MPC-SMC was monitored by transplanting reporter protein-expressing cells into the pyloric sphincter of immunodeficient mice. Results: MPC derived from human skeletal muscle expressed mesenchymal surface markers and exhibit skeletal myogenic differentiation potential in vitro. In contrast, they lack hematopoietic surface marker, as well as adipogenic, osteogenic, and chondrogenic differentiation potential in vitro. Cultivation of MPC in smooth muscle differentiation medium significantly increases the fraction of alpha smooth muscle actin (aSMA) and smoothelin-positive cells, while leaving the number of desmin-positive cells unchanged. Smooth muscle-differentiated MPC (MPC-SMC) exhibit increased expression of smooth muscle-related genes, significantly enhanced numbers of CD146- and CD49a-positive cells, and in vitro contractility and express functional Cav and Kv channels. MPC to MPC-SMC differentiation was also accompanied by a reduction in their skeletal muscle differentiation potential. Upon removal of the smooth muscle differentiation medium, a major fraction of MPC-SMC remained positive for aSMA, suggesting the definitive acquisition of their phenotype. Transplantation of murine MPC-SMC into the mouse pyloric sphincter revealed engraftment of MPC-SMC based on aSMA protein expression within the host smooth muscle tissue. Conclusions: Our work confirms the ability of MPC to give rise to smooth muscle cells (MPC-SMC) with a well-defined and stable phenotype. Moreover, the engraftment of in vitro-differentiated murine MPC-SMC into the pyloric sphincter in vivo underscores the potential of this cell population as a novel cell therapeutic treatment for smooth muscle regeneration of sphincters. [ABSTRACT FROM AUTHOR]

Blunted muscle hypertrophy and impaired regeneration with aging have been partly attributed to satellite cell (SC) dysfunction. However, true muscle regeneration has not yet been studied in elderly individuals. To investigate this, muscle injury was induced by 200 electrically stimulated (ES) eccentric contractions of the vastus lateralis (VL) of one leg in seven young (20‐31 years) and 19 elderly men (60‐73 years). This was followed by 13 weeks of resistance training (RT) for both legs to investigate the capacity for hypertrophy. Muscle biopsies were collected Pre‐ and Post‐RT, and 9 days after ES, for immunohistochemistry and RT‐PCR. Hypertrophy was assessed by MRI, DEXA, and immunohistochemistry. Overall, surprisingly comparable responses were observed between the young and elderly. Nine days after ES, Pax7+ SC number had doubled (P <.05), alongside necrosis and substantial changes in expression of genes related to matrix, myogenesis, and innervation (P <.05). Post‐RT, VL cross‐sectional area had increased in both legs (~15%, P <.05) and SCs/type II fiber had increased ~2‐4 times more with ES+RT vs RT alone (P <.001). Together these novel findings demonstrate "youthful" regeneration and hypertrophy responses in human elderly muscle. Furthermore, boosting SC availability in healthy elderly men does not enhance the subsequent muscle hypertrophy response to RT. [ABSTRACT FROM AUTHOR]

Progressive cardiomyocyte loss in Duchenne muscular dystrophy (DMD) leads to cardiac fibrosis, cardiomyopathy, and eventually heart failure. In the present study, we observed that myogenic progenitor cells (MPC) carry mRNA for the dystrophin gene. We tested whether cardiac function can be improved in DMD by allograft transplantation of MPC-derived exosomes (MPC-Exo) into the heart to restore dystrophin protein expression. Exo from C2C12 cells (an MPC cell line) or vehicle were delivered locally into the hearts of MDX mice. After 2 days of treatment, we observed that MPC-Exo restored dystrophin expression in the hearts of MDX mice, which correlated with improved myocardial function in dystrophin-deficient MDX mouse hearts. In conclusion, this study demonstrated that allogeneic WT-MPC-Exo transplantation transiently restored dystrophin gene expression and improved cardiac function in MDX mice, suggesting that allogenic exosomal delivery may serve as an alternative treatment for cardiomyopathy of DMD. [ABSTRACT FROM AUTHOR]

Accumulating evidence indicates that the circadian clock, a transcriptional/translational feedback circuit that generates ~24-hour oscillations in behavior and physiology, is a key temporal regulatory mechanism involved in many important aspects of muscle physiology. Given the clock as an evolutionarily-conserved time-keeping mechanism that synchronizes internal physiology to environmental cues, locomotor activities initiated by skeletal muscle enable entrainment to the light-dark cycles on earth, thus ensuring organismal survival and fitness. Despite the current understanding of the role of molecular clock in preventing age-related sarcopenia, investigations into the underlying molecular pathways that transmit clock signals to the maintenance of skeletal muscle growth and function are only emerging. In the current review, the importance of the muscle clock in maintaining muscle mass during development, repair and aging, together with its contribution to muscle metabolism, will be discussed. Based on our current understandings of how tissue-intrinsic muscle clock functions in the key aspects muscle physiology, interventions targeting the myogenic-modulatory activities of the clock circuit may offer new avenues for prevention and treatment of muscular diseases. Studies of mechanisms underlying circadian clock function and regulation in skeletal muscle warrant continued efforts.

Duchenne muscular dystrophy (DMD) is a lethal muscle wasting disease caused by a lack of dystrophin, which eventually leads to apoptosis of muscle cells and impaired muscle contractility. Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR associated protein 9 (CRISPR/Cas9) gene editing of induced pluripotent stem cells (IPSC) offers the potential to correct the DMD gene defect and create healthy IPSC for autologous cell transplantation without causing immune activation. However, IPSC carry a risk of tumor formation, which can potentially be mitigated by differentiation of IPSC into myogenic progenitor cells (MPC). We hypothesize that precise genetic editing in IPSC using CRISPR-Cas9 technology, coupled with MPC differentiation and autologous transplantation, can lead to safe and effective muscle repair. With future research, our hypothesis may provide an optimal autologous stem cell-based approach to treat the dystrophic pathology and improve the quality of life for patients with DMD. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this study was to demonstrate a method of isolating myogenic progenitor cells from human placenta chorionic villi and to confirm the myogenic characteristics of the isolated cells. Methods Cells were isolated from chorionic villi of a second trimester male placenta via a combined enzymatic digestion and explant culture. A morphologically distinct subpopulation of elongated and multinucleated cells was identified. This subpopulation was manually passaged from the explant culture, expanded, and analyzed by fluorescence in situ hybridization (FISH) assay, immunocytochemistry, and flow cytometry. Myogenic characteristics including alignment and fusion were tested by growing these cells on aligned polylactic acid microfibrous scaffold in a fusion media composed of 2% horse serum in Dulbecco's modified Eagle medium/high glucose. Results The expanded subpopulation was uniformly positive for integrin α-7. Presence of Y-chromosome by FISH analysis confirmed chorionic villus origin rather than maternal cell contamination. Isolated cells grew, aligned, and fused on the microfibrous scaffold, and they expressed myogenin, desmin, and MHC confirming their myogenic identity. Conclusion Myogenic progenitor cells can be isolated from human chorionic villi. This opens the possibility for translational and clinical applications using autologous myogenic cells for possible engraftment in treatment of chest and abdominal wall defects. [ABSTRACT FROM AUTHOR]

Background: The stiffness of the myogenic stem cell microenvironment markedly influences the ability to regenerate tissue. We studied the effect of damaged myofibers on myogenic progenitor cell (MPC) proliferation and determined whether the structural integrity of the microenvironment contributes to phenotypic changes. Methods: Individual myofibers were isolated and cultured for 6 days. During this period, the cytoskeleton of myofibers and transcription factors regulating MPC differentiation were characterized by immunostaining. Atomic Force Microscopy (AFM) was performed to measure stiffness of cultured myofibers. Healthy and damaged myofibers, and their associated MPCs, were studied in skeletal muscle from dystrophic and tenotomy mouse models. MPCs were cultured on stiffness-tunable substrates, and their phenotypes were assessed by immunostaining of myogenic transcription factors. Results: We showed that individual myofibers tend to shrink or collapse when cultured ex vivo starting from day 1 and that this is associated with a marked increase in the number of proliferative MPCs (Pax7+MyoD+). The myofibers collapsed due to a loss of viability as shown by Evans blue dye uptake and the disorganization of their cytoskeletons. Interestingly, collapsed myofibers in mdx skeletal muscles were similar to damaged myofibers in that they lose their viability, have a disorganized cytoskeleton (actin and α-actinin), and display local MPC (MyoD+) proliferation at their periphery. In a tenotomy model that causes loss of muscle tension, the cytoskeletal disorganization of myofibers also correlated with the activation/proliferation of MPCs. A deeper analysis of collapsed myofibers revealed that they produce trophic factors that influence MPC proliferation. In addition, collapsed myofibers expressed several genes related to the basal lamina. Immunostaining revealed the presence of fibronectin in the basal lamina and the cytoplasm of damaged myofibers. Lastly, using atomic force microscopy (AFM), we showed that collapsed myofibers exhibit greater stiffness than intact myofibers. Growing MPCs on a 2-kPa polyacrylamide-based substrate, exempt of additional microenvironmental cues, recapitulated proliferation and reduced spontaneous differentiation compared to growth on a 0.5-kPa substrate. Conclusions: Our results support the notion that collapsed or damaged myofibers increase the structural stiffness of the satellite cell microenvironment, which in addition to other cues such as trophic factors and changes in extracellular matrix composition, promotes the proliferation and maintenance of MPCs, required for myofiber repair. [ABSTRACT FROM AUTHOR]

Background and Aims: Fecal incontinence (FI) improvement following injection of autologous skeletal muscle-derived cells has been previously suggested. This study aimed to test the efficacy and safety of said cells through a multicenter, placebo-controlled study, to determine an appropriate cell dose, and to delineate the target patient population that can most benefit from cell therapy., Methods: Patients experiencing FI for at least 6 months were randomized to receive a cell-free medium or low or high dose of cells. All patients received pelvic floor electrical stimulation before and after treatment. Incontinence episode frequency (IEF), FI quality of life, FI burden assessed on a visual analog scale, Wexner score, and parameters reflecting anorectal physiological function were all assessed for up to 12 months., Results: Cell therapy improved IEF, FI quality of life, and FI burden, reaching a preset level of statistical significance in IEF change compared with the control treatment. Post hoc exploratory analyses indicated that patients with limited FI duration and high IEF at baseline are most responsive to cells. Effects prevailed or increased in the high cell count group from 6 to 12 months but plateaued or diminished in the low cell count and control groups. Most physiological parameters remained unaltered. No unexpected adverse events were observed., Conclusions: Injection of a high dose of autologous skeletal muscle-derived cells followed by electrical stimulation significantly improved FI, particularly in patients with limited FI duration and high IEF at baseline, and could become a valuable tool for treatment of FI, subject to confirmatory phase 3 trial(s). (ClinicalTrialRegister.eu; EudraCT Number: 2010-021463-32)., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Craniofacial and trunk skeletal muscles are evolutionarily distinct and derive from cranial and somitic mesoderm, respectively. Different regulatory hierarchies act upstream of myogenic regulatory factors in cranial and somitic mesoderm, but the same core regulatory network – MyoD, Myf5 and Mrf4 – executes the myogenic differentiation program. Notch signaling controls self-renewal of myogenic progenitors as well as satellite cell homing during formation of trunk muscle, but its role in craniofacial muscles has been little investigated. We show here that the pool of myogenic progenitor cells in craniofacial muscle of Dll1 LacZ/Ki mutant mice is depleted in early fetal development, which is accompanied by a major deficit in muscle growth. At the expense of progenitor cells, supernumerary differentiating myoblasts appear transiently and these express MyoD. The progenitor pool in craniofacial muscle of Dll1 LacZ/Ki mutants is largely rescued by an additional mutation of MyoD . We conclude from this that Notch exerts its decisive role in craniofacial myogenesis by repression of MyoD. This function is similar to the one previously observed in trunk myogenesis, and is thus conserved in cranial and trunk muscle. However, in cranial mesoderm-derived progenitors, Notch signaling is not required for Pax7 expression and impinges little on the homing of satellite cells. Thus, Dll1 functions in satellite cell homing and Pax7 expression diverge in cranial- and somite-derived muscle. [ABSTRACT FROM AUTHOR]

Finding an effective method to regenerate muscle is a growing issue in the orthopedic field. Platelet-rich plasma (PRP) has recently been considered for therapeutic use due to its capacity to induce proliferation of myogenic progenitor cells (MPCs). Adipose-derived stem cells (ASCs) and its extract are regarded as a promising treatment for various disorders within the orthopedic field but their therapeutic relevance in the muscle regeneration is poorly investigated. In this study, rabbit MPCs were cultured from the supraspinatus of rabbit and characterized by myogenic markers. To investigate the paracrine effect of ASCs on MPCs, coculture experiments were performed. In order to see the anabolic effect of ASC-extracts (ASC-ex) in MPCs, cell proliferation assays were performed and compared with the PRP-added condition. Coculture experiment showed ASCs had an anabolic paracrine effect on proliferation of MPCs. PRP had a positive effect on proliferation of MPCs when compared to the control (100 ± 7.4% vs 195.2 ± 19.2%, p < 0.001); however, ASC-ex promoted greater proliferation than the PRP condition (467.3 ± 38.7%, p < 0.001 compared with PRP). Similarly, in C2C12 cells, PRP showed an increased rate when compared to the control (100 ± 5.9% vs 205.1 ± 45.4%, p < 0.001), and treatment of ASC-ex showed dramatic increase in proliferation (335.9 ± 37.8%, p < 0.001 compared with PRP). ASC-ex had positive effect on expanding MPCs of rabbit and myoblast cell line, and its capacity to induce proliferation was notably stronger than that of PRP. In conclusion, the study suggests that rabbit ASC-ex have stronger proliferative effect on MPCs than rabbit PRP. Thus, ASC-ex could be a therapeutic candidate for muscle regeneration by activation of endogenous MPCs. [ABSTRACT FROM AUTHOR]

Our aim in the current study was to determine the necessity of satellite cells for long-term muscle growth and maintenance. We utilized a transgenic Pax7-DTA mouse model, allowing for the conditional depletion of > 90% of satellite cells with tamoxifen treatment. Synergist ablation surgery, where removal of synergist muscles places functional overload on the plantaris, was used to stimulate robust hypertrophy. Following 8 wk of overload, satellite celldepleted muscle demonstrated an accumulation of extracellular matrix (ECM) and fibroblast expansion that resulted in reduced specific force of the plantaris. Although the early growth response was normal, an attenuation of hypertrophy measured by both muscle wet weight and fiber cross-sectional area occurred in satellite cell-depleted muscle. Isolated primary myogenic progenitor cells (MPCs) negatively regulated fibroblast ECM mRNA expression in vitro, suggesting a novel role for activated satellite cells/MPCs in muscle adaptation. These results provide evidence that satellite cells regulate the muscle environment during growth.--Fry, C. S., Lee, J. D., Jackson, J. R., Kirby, T. J., Stasko, S. A., Liu, H., Dupont-Versteegden, E. E., McCarthy, J. J., Peterson, C. A. Regulation of the muscle fiber microenvironment by activated satellite cells during hypertrophy. [ABSTRACT FROM AUTHOR]

The addition of aerobic exercise (AE) to a resistance exercise (RE) program (concurrent exercise, CE) can interfere with maximum muscle fiber growth achieved with RE. Further, CE appears to markedly affect the growth of myosin heavy chain (MHC) I, but not MHC IIa fibers. The mechanism responsible for this "interference" is unclear. Satellite cell (SC) responsiveness to exercise appears to influence muscle adaptation but has not yet been examined following acute concurrent exercise. Thus, we assessed the fiber-type-specific SC response to RE, AE, and CE exercise. Eight college-aged males completed the following two exercise trials: the RE trial, which consisted of unilateral leg extensions and presses (4 sets ⩾ 10 repetitions: 75% 1 repetition maximum, RM), and the AE/CE trial, which included an identical RE protocol with the opposite leg, immediately followed by subjects cycling for 90 min (60% Wmax). Muscle biopsies were obtained from the vastus lateralis before and 4 days after each session. Samples were cross-sectioned, stained with antibodies against NCAM, Ki-67, and MHC I, counterstained with DAPI, and analyzed for SC density (SC per fiber), SC activation, and fiber type. SC density increased to a greater extent following RE (38 ± 10%), compared with CE (-6 ± 8%). Similarly, MHC I muscle fiber SC density displayed a greater increase following RE (46 ± 14%), compared with AE (-7 ± 17%) and CE (-8 ± 8%). Our data indicate that the SC response to RE is blunted when immediately followed by AE, at least in MHC I muscle fibers, and possibly MHC II fibers. This suggests that the physiological environment evoked by AE might attenuate the eventual addition of myonuclei important for maximum muscle fiber growth and consequent force-producing capacity. [ABSTRACT FROM AUTHOR]

The emergence of selective cell transplantation and tissue engineering has opened up new alternatives for the treatment of heart failure. These involve the use of stem and progenitor cells, as well as new biodegradable polymer scaffolds. The last two decades have seen a dramatic increase in our knowledge of how to fabricate a wide array of tissues, including cardiovascular structures. This article reviews current trends in selective cell transplantation and tissue engineering, and summarises recent achievements and remaining questions in constructing functional cardiac tissue. [ABSTRACT FROM AUTHOR]

For decades now, cell transplantation has been considered a possible therapeutic strategy for muscular dystrophy, but failures have largely outnumbered success or at least encouraging outcomes. In this review we will briefly recall the history of cell transplantation, discuss the peculiar features of skeletal muscle, and dystrophic skeletal muscle in particular, that make the procedure complicated and inefficient. As there are many recent and exhaustive reviews on the various myogenic cell types that have been or will be transplanted, we will only briefly describe them and refer the reader to these reviews. Finally, we will discuss possible strategies to overcome the hurdles that prevent biological efficacy and hence clinical success. [ABSTRACT FROM AUTHOR]

The physiological process of muscle regeneration is quite limited due to low satellite cell quantity and also the inability to regenerate and reconstruct niche tissue. The purpose of the study was to examine whether a graphene oxide scaffold is able to stimulate myogenic progenitor cell proliferation and the endocrine functions of differentiating cells, and therefore, their active participation in the construction of muscle tissue. Studies were carried out using mesenchymal cells taken from 6-day-old chicken embryos and human umbilical vein endothelial cells (HUVEC) were used to assess angiogenesis. The graphene scaffold was readily colonized by myogenic progenitor cells and the cells dissected from heart, brain, eye, and blood vessels did not avoid the scaffold. The scaffold strongly induced myogenic progenitor cell signaling pathways and simultaneously activated proangiogenic signaling pathways via exocrine vascular endothelial growth factor (VEGF) secretion. The present study revealed that the graphene oxide (GO) scaffold initiates the processes of muscle cell differentiation due to mechanical interaction with myogenic progenitor cell. [ABSTRACT FROM AUTHOR]

Background: Myogenic progenitor cells (activated satellite cells) are able to express both HGF and its receptor cMet. After muscle injury, HGF-Met stimulation promotes activation and primary division of satellite cells. MAGIC-F1 (Met-Activating Genetically Improved Chimeric Factor-1) is an engineered protein that contains two human Met-binding domains that promotes muscle hypertrophy. MAGIC-F1 protects myogenic precursors against apoptosis and increases their fusion ability enhancing muscle differentiation. Hemizygous and homozygous Magic-F1 transgenic mice displayed constitutive muscle hypertrophy., Methods: Here we describe microarray analysis on Magic-F1 myogenic progenitor cells showing an altered gene signatures on muscular hypertrophy and angiogenesis compared to wild-type cells. In addition, we performed a functional analysis on Magic-F1+/+ transgenic mice versus controls using treadmill test., Results: We demonstrated that Magic-F1+/+ mice display an increase in muscle mass and cross-sectional area leading to an improvement in running performance. Moreover, the presence of MAGIC-F1 affected positively the vascular network, increasing the vessel number in fast twitch fibers. Finally, the gene expression profile analysis of Magic-F1+/+ satellite cells evidenced transcriptomic changes in genes involved in the control of muscle growth, development and vascularisation., Conclusion: We showed that MAGIC-F1-induced muscle hypertrophy affects positively vascular network, increasing vessel number in fast twitch fibers. This was due to unique features of mammalian skeletal muscle and its remarkable ability to adapt promptly to different physiological demands by modulating the gene expression profile in myogenic progenitors., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

Skeletal muscle regeneration requires coordination between dynamic cellular populations and tissue microenvironments. Macrophages, recruited via CCR2, are essential for regeneration; however, the contribution of macrophages and the role of CCR2 on nonhematopoietic cells has not been defined. In addition, aging and sex interactions in regeneration and sarcopenia are unclear. Muscle regeneration was measured in young (3-6 mo), middle (11-15 mo), old (24-32 mo) male and female CCR2 -/- mice. Whereas age-related muscle atrophy/sarcopenia was present, regenerated myofiber cross-sectional area (CSA) in CCR2 -/- mice was comparably impaired across all ages and sexes, with increased adipocyte area compared with wild-type (WT) mice. CCR2 -/- mice myofibers achieved approximately one third of baseline CSA even 84 d after injury. Regenerated CSA and clearance of necrotic tissue were dependent on bone marrow-derived cellular expression of CCR2. Myogenic progenitor cells isolated from WT and CCR2 -/- mice exhibited comparable proliferation and differentiation capacity. The most striking cellular anomaly in injured muscle of CCR2 -/- mice was markedly decreased macrophages, with a predominance of Ly6C - anti-inflammatory monocytes/macrophages. Ablation of proinflammatory TLR signaling did not affect muscle regeneration or resolution of necrosis. Of interest, many proinflammatory, proangiogenic, and chemotactic cytokines were markedly elevated in injured muscle of CCR2 -/- relative to WT mice despite impairments in macrophage recruitment. Collectively, these results suggest that CCR2 on bone marrow-derived cells, likely macrophages, were essential to muscle regeneration independent of TLR signaling, aging, and sex. Decreased proinflammatory monocytes/macrophages actually promoted a proinflammatory microenvironment, which suggests that inflammaging was present in young CCR2 -/- mice., (© Society for Leukocyte Biology.)