Muscle fibro-adipogenic progenitors from a single-cell perspective: Focus on their "virtual" secretome.

Skeletal muscle is a highly plastic tissue composed of a number of heterogeneous cell populations that, by interacting and communicating with each other, participate to the muscle homeostasis, and orchestrate regeneration and repair in healthy and diseased conditions. Although muscle regeneration relies on the activity of muscle stem cells (MuSCs), many other cellular players such as inflammatory, vascular and tissue-resident mesenchymal cells participate and communicate with MuSCs to sustain the regenerative process. Among them, Fibro-Adipogenic Progenitors (FAPs), a muscle interstitial stromal population, are crucial actors during muscle homeostasis and regeneration, interacting with MuSCs and other cellular players and dynamically producing and remodelling the extra-cellular matrix.

Age-related alterations in muscle architecture are a signature of sarcopenia: the ultrasound sarcopenia index.

Background: The assessment of muscle mass is a key determinant of the diagnosis of sarcopenia. We introduce for the first time an ultrasound imaging method for diagnosing sarcopenia based on changes in muscle geometric proportions.

Methods: Vastus lateralis muscle fascicle length (Lf) and thickness (Tm) were measured at 35% distal femur length by ultrasonography in a population of 279 individuals classified as moderately active elderly (MAE), sedentary elderly (SE) (n = 109), mobility impaired elderly (MIE) (n = 43), and in adult young controls (YC) (n = 60).

Combined methods to evaluate human cells in muscle xenografts.

Xenotransplantation of human cells into immunodeficient mouse models is a very powerful tool and an essential step for the pre-clinical evaluation of therapeutic cell- and gene- based strategies. Here we describe an optimized protocol combining immunofluorescence and real-time quantitative PCR to both quantify and visualize the fate and localization of human myogenic cells after injection in regenerating muscles of immunodeficient mice. Whereas real-time quantitative PCR-based method provides an accurate quantification of human cells, it does not document their specific localization.

Improvement of Duchenne muscular dystrophy phenotype following obestatin treatment.

Background: This study was performed to test the therapeutic potential of obestatin, an autocrine anabolic factor regulating skeletal muscle repair, to ameliorate the Duchenne muscular dystrophy (DMD) phenotype.

Methods And Results: Using a multidisciplinary approach, we characterized the ageing-related preproghrelin/GPR39 expression patterns in tibialis anterior (TA) muscles of 4-, 8-, and 18-week-old mdx mice (n = 3/group) and established the effects of obestatin administration at this level in 8-week-old mdx mice (n = 5/group). The findings were extended to in vitro effects on human immortalized DMD myotubes.

HGF potentiates extracellular matrix-driven migration of human myoblasts: involvement of matrix metalloproteinases and MAPK/ERK pathway.

Background: The hepatocyte growth factor (HGF) is required for the activation of muscle progenitor cells called satellite cells (SC), plays a role in the migration of proliferating SC (myoblasts), and is present as a soluble factor during muscle regeneration, along with extracellular matrix (ECM) molecules. In this study, we aimed at determining whether HGF is able to interact with ECM proteins, particularly laminin 111 and fibronectin, and to modulate human myoblast migration.

Methods: We evaluated the expression of the HGF-receptor c-Met, laminin, and fibronectin receptors by immunoblotting, flow cytometry, or immunofluorescence and used Transwell assays to analyze myoblast migration on laminin 111 and fibronectin in the absence or presence of HGF.

Cellular Therapies for Muscular Dystrophies: Frustrations and Clinical Successes.

Cell-based therapy for muscular dystrophies was initiated in humans after promising results obtained in murine models. Early trials failed to show substantial clinical benefit, sending researchers back to the bench, which led to the discovery of many hurdles as well as many new venues to optimize this therapeutic strategy. In this review we summarize progress in preclinical cell therapy approaches, with a special emphasis on human cells potentially attractive for human clinical trials.

Role of Oxidized Protein Repair in Human Skeletal Muscle.

There is now increasing evidence that reactive oxygen species (ROS) are signalling molecules that regulate growth, differentiation, proliferation and apoptosis, at least in physiological concentration. However, when ROS levels overcome the capacity of cellular antioxidant systems, they damage cellular components such as nucleic acids, lipids and in particular proteins, inflicting alterations to cell structure and function. Oxidation of sulfur-containing aminoacids, like cysteine and methionine, within proteins, can be repaired by specific enzymatic systems.

Human Adipocytes Induce Inflammation and Atrophy in Muscle Cells During Obesity.

Inflammation and lipid accumulation are hallmarks of muscular pathologies resulting from metabolic diseases such as obesity and type 2 diabetes. During obesity, the hypertrophy of visceral adipose tissue (VAT) contributes to muscle dysfunction, particularly through the dysregulated production of adipokines. We have investigated the cross talk between human adipocytes and skeletal muscle cells to identify mechanisms linking adiposity and muscular dysfunctions.

Invited review: Stem cells and muscle diseases: advances in cell therapy strategies.

Despite considerable progress to increase our understanding of muscle genetics, pathophysiology, molecular and cellular partners involved in muscular dystrophies and muscle ageing, there is still a crucial need for effective treatments to counteract muscle degeneration and muscle wasting in such conditions. This review focuses on cell-based therapy for muscle diseases. We give an overview of the different parameters that have to be taken into account in such a therapeutic strategy, including the influence of muscle ageing, cell proliferation and migration capacities, as well as the translation of preclinical results in rodent into human clinical approaches.

Expression of myogenic regulatory factors and myo-endothelial remodeling in sporadic inclusion body myositis.

Muscle repair relies on coordinated activation and differentiation of satellite cells, a process that is unable to counterbalance progressive degeneration in sporadic inclusion body myositis (s-IBM). To explore features of myo regeneration, the expression of myogenic regulatory factors Pax7, MyoD and Myogenin and markers of regenerating fibers was analyzed by immunohistochemistry in s-IBM muscle compared with polymyositis, dermatomyositis, muscular dystrophy and age-matched controls. In addition, the capillary density and number of interstitial CD34(+) hematopoietic progenitor cells was determined by double-immunoflourescence staining.

Generation of isogenic D4Z4 contracted and noncontracted immortal muscle cell clones from a mosaic patient: a cellular model for FSHD.

In most cases facioscapulohumeral muscular dystrophy (FSHD) is caused by contraction of the D4Z4 repeat in the 4q subtelomere. This contraction is associated with local chromatin decondensation and derepression of the DUX4 retrogene. Its complex genetic and epigenetic cause and high clinical variability in disease severity complicate investigations on the pathogenic mechanism underlying FSHD.

Regenerative potential of human muscle stem cells in chronic inflammation.

Introduction: Chronic inflammation is a profound systemic modification of the cellular microenvironment which could affect survival, repair and maintenance of muscle stem cells. The aim of this study was to define the role of chronic inflammation on the regenerative potential of satellite cells in human muscle.

Methods: As a model for chronic inflammation, 11 patients suffering from rheumatoid arthritis (RA) were included together with 16 patients with osteoarthritis (OA) as controls.

Skeletal muscle telomere length in healthy, experienced, endurance runners.

Measuring the DNA telomere length of skeletal muscle in experienced endurance runners may contribute to our understanding of the effects of chronic exposure to endurance exercise on skeletal muscle. This study compared the minimum terminal restriction fragment (TRF) length in the vastus lateralis muscle of 18 experienced endurance runners (mean age: 42 +/- 7 years) to those of 19 sedentary individuals (mean age: 39 +/- 10 years). The runners had covered almost 50,000 km in training and racing over 15 years.

In vivo myogenic potential of human CD133+ muscle-derived stem cells: a quantitative study.

In recent years, numerous reports have identified in mouse different sources of myogenic cells distinct from satellite cells that exhibited a variable myogenic potential in vivo. Myogenic stem cells have also been described in humans, although their regenerative potential has rarely been quantified. In this study, we have investigated the myogenic potential of human muscle-derived cells based on the expression of the stem cell marker CD133 as compared to bona fide satellite cells already used in clinical trials.

Analysis of growth factor expression in affected and unaffected muscles of oculo-pharyngeal muscular dystrophy (OPMD) patients: a pilot study.

Oculo-pharyngeal muscular dystrophy (OPMD) is characterised by progressive eyelid drooping (ptosis) and difficulties with swallowing (dysphagia). In order to determine the role of growth factors, cytokines and chemokines in the physiopathology of muscle disease we have compared the level of expression of 174 factors in both the affected (cricopharyngeal) and non-affected (sternocleidomastoid) muscles of 8 OPMD patients by means of antibody arrays. Despite an important inter-individual variability the expression of sixty factors was found to be persistently different between affected and non-affected muscles.

Muscleblind-like proteins: similarities and differences in normal and myotonic dystrophy muscle.

In myotonic dystrophy, muscleblind-like protein 1 (MBNL1) protein binds specifically to expanded CUG or CCUG repeats, which accumulate as discrete nuclear foci, and this is thought to prevent its function in the regulation of alternative splicing of pre-mRNAs. There is strong evidence for the role of the MBNL1 gene in disease pathology, but the roles of two related genes, MBNL2 and MBNL3, are less clear. Using new monoclonal antibodies specific for each of the three gene products, we found that MBNL2 decreased during human fetal development and myoblast culture, while MBNL1 was unchanged.

Human myoblast engraftment is improved in laminin-enriched microenvironment.

Background: One major challenge in developing cell therapy for muscle diseases is to define the best condition for the recipient's muscle to niche donor cells. We have examined the efficiency of human myoblast transplantation in an immunodeficient animal model, after local irradiation, as well as the potential impact of laminin on myoblast behavior.

Methods: Human myoblasts were injected into preirradiated tibialis anterior muscles from immunodeficient mice.

Proteome analysis of differentiating human myoblasts by dialysis-assisted two-dimensional gel electrophoresis (DAGE).

In the present study, modifications in cytosolic expressed proteins during human myoblast differentiation were studied by dialysis-assisted 2-DE (DAGE, [1]). About 1000 spots were analysed on the 5th and 13th day of differentiation with a dynamic range of protein expression exceeding 1000-fold. During myogenic differentiation, the number of nonmatching spots as well as the extent of quantitative differences between matched spots significantly increased.

Drug-induced readthrough of premature stop codons leads to the stabilization of laminin alpha2 chain mRNA in CMD myotubes.

Background: The most common form of congenital muscular dystrophy is caused by a deficiency in the alpha2 chain of laminin-211, a protein of the extracellular matrix. A wide variety of mutations, including 20 to 30% of nonsense mutations, have been identified in the corresponding gene, LAMA2. A promising approach for the treatment of genetic disorders due to premature termination codons (PTCs) is the use of drugs to force stop codon readthrough.

Replicative aging down-regulates the myogenic regulatory factors in human myoblasts.

Background Information: Aging of human skeletal muscle results in a decline in muscle mass and force, and excessive turnover of muscle fibres, such as in muscular dystrophies, further increases this decline. Although it has been shown in rodents, by cross-age transplantation of whole muscles, that the environment plays an important role in this process, the implication of proliferating aging of the muscle progenitors has been poorly investigated, particularly in humans, since the regulation of cell proliferation differs between rodents and humans. The myogenic differentiation of human myoblasts is regulated by the muscle-specific regulatory factors.

Defective mRNA in myotonic dystrophy accumulates at the periphery of nuclear splicing speckles.

Nuclear speckles are storage sites for small nuclear RNPs (snRNPs) and other splicing factors. Current ideas about the role of speckles suggest that some pre-mRNAs are processed at the speckle periphery before being exported as mRNA. In myotonic dystrophy type 1 (DM1), the export of mutant DMPK mRNA is prevented by the presence of expanded CUG repeats that accumulate in nuclear foci.

Cellular senescence in human myoblasts is overcome by human telomerase reverse transcriptase and cyclin-dependent kinase 4: consequences in aging muscle and therapeutic strategies for muscular dystrophies.

Cultured human myoblasts fail to immortalize following the introduction of telomerase. The availability of an immortalization protocol for normal human myoblasts would allow one to isolate cellular models from various neuromuscular diseases, thus opening the possibility to develop and test novel therapeutic strategies. The parameters limiting the efficacy of myoblast transfer therapy (MTT) could be assessed in such models.

IL-13 mediates the recruitment of reserve cells for fusion during IGF-1-induced hypertrophy of human myotubes.

Insulin-like growth factor-1 (IGF-1) has been shown to induce skeletal muscle hypertrophy, to prevent the loss of muscle mass with ageing and to improve the muscle phenotype of dystrophic mice. We previously developed a model of IGF-1-induced hypertrophy of human myotubes, in which hypertrophy was not only characterized by an increase in myotube size and myosin content but also by an increased recruitment of reserve cells for fusion. Here, we describe a new mechanism of IGF-1-induced hypertrophy by demonstrating that IGF-1 signals exclusively to myotubes but not to reserve cells, leading, under the control of the transcription factor NFATc2, to the secretion of IL-13 that will secondly recruit reserve cells for differentiation and fusion.

Human muscle stem cells.

Stem cells are unspecialized cells that have been defined in many different ways but they have two important characteristics that distinguish them from other cells in the body. First, they can replenish their numbers for long periods through cell division. Second, after receiving certain chemical signals, they can produce, through asymmetric cell division, a progeny that can differentiate or transform into specialized cells with specific functions, such as heart, nerve or muscle.