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Background: Muscle stem cell transplantation is a possible treatment for muscular dystrophy. In addition to the intrinsic properties of the stem cells, the local and systemic environment plays an important role in determining the fate of the grafted cells. We therefore investigated the effect of modulating the host muscle environment in different ways (irradiation or cryoinjury or a combination of irradiation and cryoinjury) in two immunodeficient mouse strains (mdx nude and recombinase-activating gene (Rag)2-/γ chain-/C5-) on the regenerative capacity of two types of human skeletal muscle-derived stem cell (pericytes and CD133+ cells). Methods: Human skeletal muscle-derived pericytes or CD133+ cells were transplanted into muscles of either mdx nude or recombinase-activating gene (Rag)2-/γ chain-/C5- host mice. Host muscles were modulated prior to donor cell transplantation by either irradiation, or cryoinjury, or a combination of irradiation and cryoinjury. Muscles were analysed four weeks after transplantation, by staining transverse cryostat sections of grafted muscles with antibodies to human lamin A/C, human spectrin, laminin and Pax 7. The number of nuclei and muscle fibres of donor origin and the number of satellite cells of both host and donor origin were quantified. Results: Within both host strains transplanted intra-muscularly with both donor cell types, there were significantly more nuclei and muscle fibres of donor origin in host muscles that had been modulated by cryoinjury, or irradiation+cryoinjury, than by irradiation alone. Irradiation has no additive effects in further enhancing the transplantation efficiency than cryodamage. Donor pericytes did not give rise to satellite cells. However, using CD133+ cells as donor cells, there were significantly more nuclei, muscle fibres, as well as satellite cells of donor origin in Rag2-/γ chain-/C5- mice than mdx nude mice, when the muscles were injured by either cryodamage or irradiation+cryodamage. Conclusions: Rag2-/γ chain-/C5- mice are a better recipient mouse strain than mdx nude mice for human muscle stem cell transplantation. Cryodamage of host muscle is the most effective method to enhance the transplantation efficiency of human skeletal muscle stem cells. This study highlights the importance of modulating the muscle environment in preclinical studies to optimise the efficacy of transplanted stem cells. [ABSTRACT FROM AUTHOR]

There is currently no cure for muscular dystrophies, although several promising strategies are in basic and clinical research. One such strategy is cell transplantation with satellite cells (or their myoblast progeny) to repair damaged muscle and provide dystrophin protein with the aim of preventing subsequent myofibre degeneration and repopulating the stem cell niche for future use. The present review aims to cover recent advances in satellite cell/myoblast therapy and to discuss the challenges that remain for it to become a realistic therapy. [ABSTRACT FROM AUTHOR]

Skeletal muscle has a remarkable capability of regeneration following injury. Satellite cells, the principal muscle stem cells, are responsible for this process. However, this regenerative capacity is reduced in muscular dystrophies or in old age: in both these situations, there is a net loss of muscle fibres. Promoting skeletal muscle muscle hypertrophy could therefore have potential applications for treating muscular dystrophies or sarcopenia. Here, we observed that muscles of dystrophic mdx nude host mice that had been acutely injured by myotoxin and grafted with a single myofibre derived from a normal donor mouse exhibited increased muscle area. Transplantation experiments revealed that the hypertrophic effect is mediated by the grafted fibre and does not require either an imposed injury to the host muscle, or the contribution of donor cells to the host muscle. These results suggest the presence of a crucial cross-talk between the donor fibre and the host muscle environment. [ABSTRACT FROM AUTHOR]

The dystrophin-associated glycoprotein complex (DGC) is found at the muscle fiber sarcolemma and forms an essential structural link between the basal lamina and internal cytoskeleton. In a set of muscular dystrophies known as the dystroglycanopathies, hypoglycosylation of the DGC component α-dystroglycan results in reduced binding to basal lamina components, a loss in structural stability, and repeated cycles of muscle fiber degeneration and regeneration. The satellite cells are the key stem cells responsible for muscle repair and reside between the basal lamina and sarcolemma. In this study, we aimed to determine whether pathological changes associated with the dystroglycanopathies affect satellite cell function. In the Largemyd mouse dystroglycanopathy model, satellite cells are present in significantly greater numbers but display reduced proliferation on their native muscle fibers in vitro, compared with wild type. However, when removed from their fiber, proliferation in culture is restored to that of wild type. Immunohistochemical analysis of Largemyd muscle reveals alterations to the basal lamina and interstitium, including marked disorganization of laminin, upregulation of fibronectin and collagens. Proliferation and differentiation of wild-type satellite cells is impaired when cultured on substrates such as collagen and fibronectin, compared with laminins. When engrafted into irradiated tibialis anterior muscles of mdx-nude mice, wild-type satellite cells expanded on laminin contribute significantly more to muscle regeneration than those expanded on fibronectin. These results suggest that defects in α-dystroglycan glycosylation are associated with an alteration in the satellite cell niche, and that regenerative potential in the dystroglycanopathies may be perturbed. S TEM C ells 2012;30:2330-2341 [ABSTRACT FROM AUTHOR]

A new conditionally immortal satellite cell-derived cell-line, H2K 2B4, was generated from the H2Kb-tsA58 immortomouse. Under permissive conditions H2K 2B4 cells terminally differentiate in vitro to form uniform myotubes with a myogenic protein profile comparable with freshly isolated satellite cells. Following engraftment into immunodeficient dystrophindeficient mice, H2K 2B4 cells regenerated host muscle with donor derived myofibres that persisted for at least 24 weeks, without forming tumours. These cells were readily transfectable using both retrovirus and the non-viral transfection methods and importantly upon transplantation, were able to reconstitute the satellite cell niche with functional donor derived satellite cells. Finally using the Class II DNA transposon, Sleeping Beauty, we successfully integrated a reporter plasmid into the genome of H2K 2B4 cells without hindering the myogenic differentiation. Overall, these data suggest that H2K 2B4 cells represent a readily transfectable stable cell-line in which to investigate future stem cell based therapies for muscle disease. [ABSTRACT FROM AUTHOR]

LMNA encodes both lamin A and C: major components of the nuclear lamina. Mutations in LMNA underlie a range of tissuespecific degenerative diseases, including those that affect skeletal muscle, such as autosomal-Emery-Dreifuss muscular dystrophy (A-EDMD) and limb girdle muscular dystrophy 1B. Here, we examine the morphology and transcriptional activity of myonuclei, the structure of the myotendinous junction and the muscle contraction dynamics in the lmna-null mouse model of A-EDMD. We found that there were fewer myonuclei in lmna-null mice, of which ∼50% had morphological abnormalities. Assaying transcriptional activity by examining acetylated histone H3 and PABPN1 levels indicated that there was a lack of coordinated transcription between myonuclei lacking lamin A/C. Myonuclei with abnormal morphology and transcriptional activity were distributed along the length of the myofibre, but accumulated at the myotendinous junction. Indeed, in addition to the presence of abnormal myonuclei, the structure of the myotendinous junction was perturbed, with disorganised sarcomeres and reduced interdigitation with the tendon, together with lipid and collagen deposition. Functionally, muscle contraction became severely affected within weeks of birth, with specific force generation dropping as low as ∼65% and ∼27% of control values in the extensor digitorum longus and soleus muscles respectively. These observations illustrate the importance of lamin A/C for correct myonuclear function, which likely acts synergistically with myotendinous junction disorganisation in the development of A-EDMD, and the consequential reduction in force generation and muscle wasting. [ABSTRACT FROM AUTHOR]

Abstract: Skeletal muscle is maintained and repaired by resident stem cells called muscle satellite cells, but there is a gradual failure of this process during the progressive skeletal muscle weakness and wasting that characterises muscular dystrophies. The pathogenic mutation causes muscle wasting, but in conditions including Duchenne muscular dystrophy, the mutant gene is not expressed in satellite cells, and so muscle maintenance/repair is not directly affected. The chronic muscle wasting, however, produces an increasingly hostile micro-environment in dystrophic muscle. This probably combines with excessive satellite cell use to eventually culminate in an indirect failure of satellite cell-mediated myofibre repair. By contrast, in disorders such as Emery–Dreifuss muscular dystrophy, the pathogenic mutation not only instigates muscle wasting, but could also directly compromise satellite cell function, leading to less effective muscle homeostasis. This may again combine with excessive use and a hostile environment to further compromise satellite cell performance. Whichever the mechanism, the ultimate consequence of perturbed satellite cell activity is a chronic failure of myofibre maintenance in dystrophic muscle. Here, we review whether the pathogenic mutation can directly contribute to satellite cell dysfunction in a number of muscular dystrophies. [ABSTRACT FROM AUTHOR]

Cell therapy for degenerative muscle diseases such as the muscular dystrophies requires a source of cells with the capacity to participate in the formation of new muscle fibers. We investigated the myogenic potential of human fetal mesenchymal stem cells (hfMSCs) using a variety of stimuli. The use of 5-azacytidine or steroids did not produce skeletal muscle differentiation, whereas myoblast-conditioned medium resulted in only 1%–2% of hfMSCs undergoing muscle differentiation. However, in the presence of galectin-1, 66.1% ± 5.7% of hfMSCs, but not adult bone marrow-derived mesenchymal stem cells, assumed a muscle phenotype, forming long, multinucleated fibers expressing both desmin and sarcomeric myosin via activation of muscle regulatory factors. Continuous exposure to galectin-1 resulted in more efficient muscle differentiation than pulsed exposure (62.3% vs. 39.1%; p < .001). When transplanted into regenerating murine muscle, galectin-1-exposed hfMSCs formed fourfold more human muscle fibers than nonstimulated hfMSCs (p = .008), with similar results obtained in a scid/mdx dystrophic mouse model. These data suggest that hfMSCs readily undergo muscle differentiation in response to galectin-1 through a stepwise progression similar to that which occurs during embryonic myogenesis. The high degree of myogenic conversion achieved by this method has relevance for the development of therapies for muscular dystrophies. [ABSTRACT FROM AUTHOR]

Demonstrates that culture of myoblasts or skeletal muscle fiber precursors which are transplanted into muscles of dystrophic mice contain subpopulations that can self-renew and generate myogenic cells. Stem cell-like properties or capacity of the subpopulations to differentiate which contribute to regeneration in the postnatal host muscle.

Abstract: Stem cell therapy holds promise for treating muscle diseases. Although satellite cells regenerate skeletal muscle, they only have a local effect after intra-muscular transplantation. Alternative cell types, more easily obtainable and systemically-deliverable, were therefore sought. Human synovial stem cells (hSSCs) have been reported to regenerate muscle fibres and reconstitute the satellite cell pool. We therefore determined if these cells are able to regenerate skeletal muscle after intra-muscular injection into cryodamaged muscles of Rag2-/γ chain-/C5-mice. We found that hSSCs possess only limited capacity to undergo myogenic differentiation in vitro or to contribute to muscle regeneration in vivo. However, this is enhanced by over-expression of human MyoD1. Interestingly, hSSCs express extracellular matrix components laminin α2 and collagen VI within grafted muscles. Therefore, despite their limited capacity to regenerate skeletal muscle, hSSCs could play a role in treating muscular dystrophies secondary to defects in extracellular matrix proteins. [Copyright &y& Elsevier]