Successive injections in mdx mice of myoblasts grown with bFGF

Stem cells migration during skeletal muscle regeneration - the role of Sdf-1/Cxcr4 and Sdf-1/Cxcr7 axis

The skeletal muscle regeneration occurs due to the presence of tissue specific stem cells - satellite cells. These cells, localized between sarcolemma and basal lamina, are bound to muscle fibers and remain quiescent until their activation upon muscle injury. Due to pathological conditions, such as extensive injury or dystrophy, skeletal muscle regeneration is diminished. Among the therapies aiming to ameliorate skeletal muscle diseases are transplantations of the stem cells. In our previous studies we showed that Sdf-1 (stromal derived factor −1) increased migration of stem cells and their fusion with myoblasts in vitro. Importantly, we identified that Sdf-1 caused an increase in the expression of tetraspanin CD9 - adhesion protein involved in myoblasts fusion. In the current study we aimed to uncover the details of molecular mechanism of Sdf-1 action. We focused at the Sdf-1 receptors - Cxcr4 and Cxcr7, as well as signaling pathways induced by these molecules in primary myoblasts, as well as various stem cells - mesenchymal stem cells and embryonic stem cells, i.e. the cells of different migration and myogenic potential. We showed that Sdf-1 altered actin organization via FAK (focal adhesion kinase), Cdc42 (cell division control protein 42), and Rac-1 (Ras-Related C3 Botulinum Toxin Substrate 1). Moreover, we showed that Sdf-1 modified the transcription profile of genes encoding factors engaged in cells adhesion and migration. As the result, cells such as primary myoblasts or embryonic stem cells, became characterized by more effective migration when transplanted into regenerating muscle.

Promotion of muscle regeneration by myoblast transplantation combined with the controlled and sustained release of bFGFcpr

Although myoblast transplantation is an attractive method for muscle regeneration, its efficiency remains limited. The efficacy of myoblast transplantation in combination with the controlled and sustained delivery of basic fibroblast growth factor (bFGF) was investigated. Defects of thigh muscle in Sprague-Dawley (SD) rats were created, and GFP-positive myoblasts were subsequently transplanted. The rats were divided into three groups. In control group 1 (C1) only myoblasts were transplanted, while in control group 2 (C2) myoblasts were introduced along with empty gelatin hydrogel microspheres. In the experimental group (Ex), myoblasts were transplanted along with bFGF incorporated into gelatin hydrogel microspheres. Four weeks after transplantation, GFP-positive myoblasts were found to be integrated into the recipient muscle and to contribute to muscle fibre regeneration in all groups. A significantly higher expression level of GFP in the Ex group demonstrated that the survival rate of transplanted myoblasts in Ex was remarkably improved compared with that in C1 and C2. Furthermore, myofibre regeneration, characterized by centralization of the nuclei, was markedly accelerated in Ex. The expression level of CD31 in Ex was higher than that in both C1 and C2, but the differences were not statistically significant. A significantly higher expression level of Myogenin and a lower expression level of MyoD1 were both observed in Ex after 4 weeks, suggesting the promotion of differentiation to myotubes. Our findings suggest that the controlled and sustained release of bFGF from gelatin hydrogel microspheres improves the survival rate of transplanted myoblasts and promotes muscle regeneration by facilitating myogenesis rather than angiogenesis.

Growth Factor Coinjection Improves the Migration Potential of Monkey Myogenic Precursors without Affecting Cell Transplantation Success

Duchenne muscular dystrophy (DMD) is an inherited disease and a main target of myogenic cell transplantation (MT). After the failure of the first clinical trials with DMD patients, the poor migration of transplanted cells has been suspected to be a major problem for a more effective clinical application of MT. Previous investigations suggested that the quantity and dispersion of myofibers containing donor cell nuclei might be improved by increasing the migration of the transplanted cells outside the injection sites. Because the coinjection of motogenic factors with human myoblasts enhanced their intramuscular migration following MT in SCID mice, the present study aimed to investigate whether this approach was appropriate to increase MT success in muscles of nonhuman primates. In vitro studies indicated that IGF-1 or bFGF increased components of proteolytic systems involved in myoblast migration. In vitro and in vivo experiments also demonstrated that coinjection of bFGF or IGF-1 was able to improve monkey myogenic cell migration and invasion. Sixty hours after MT in skeletal muscle tissue, the migration distances reached by monkey myoblasts increased by nearly twofold when one of the growth factors was coinjected with the cells. However, long-term observations in adult monkeys suggest that promigratory treatments are not intrinsically sufficient to improve the success of MT. Even if short-term observations reveal that grafted cells are not always trapped inside the injection site and in spite of the fact that both factors enhanced transplanted cell migration, myofibers including grafted cell nuclei were still restrained to the injection trajectory without notable difference in their amount or their dispersion. The incapacity of transplanted cells to fuse with undamaged myofibers, which are located outside the injection sites, is a priority problem to solve in order to improve transplantation success and reduce the number of injections required for the treatment of DMD patients.

Regulating activation of transplanted cells controls tissue regeneration

Current approaches to tissue regeneration are limited by the death of most transplanted cells and/or resultant poor integration of transplanted cells with host tissue. We hypothesized that transplanting progenitor cells within synthetic microenvironments that maintain viability, prevent terminal differentiation, and promote outward migration would significantly enhance their repopulation and regeneration of damaged host tissue. This hypothesis was addressed in the context of muscle regeneration by transplanting satellite cells to muscle laceration sites on a delivery vehicle releasing factors that induce cell activation and migration (hepatocyte growth factor and fibroblast growth factor 2) or transplantation on materials lacking factor release. Controls included direct cell injection into muscle, the implantation of blank scaffolds, and scaffolds releasing factors without cells. Injected cells demonstrated a limited repopulation of damaged muscle and led to a slight improvement in muscle regeneration, as expected. Delivery of cells on scaffolds that did not promote migration resulted in no improvement in muscle regeneration. Strikingly, delivery of cells on scaffolds that promoted myoblast activation and migration led to extensive repopulation of host muscle tissue and increased the regeneration of muscle fibers at the wound and the mass of the injured muscle. This previously undescribed strategy for cell transplantation significantly enhances muscle regeneration from transplanted cells and may be broadly applicable to the various tissues and organ systems in which provision and instruction of a cell population competent to participate in regeneration may be clinically useful.

Normal growth and regenerating ability of myoblasts from unaffected muscles of facioscapulohumeral muscular dystrophy patients

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disease characterized by a typical regional distribution, featuring composed patterns of clinically affected and unaffected muscles. No treatment is available for this condition, in which the pathophysiological mechanism is still unknown. Autologous transfer of myoblasts from unaffected to affected territories could be considered as a potential strategy to delay or stop muscle degeneration. To evaluate the feasibility of this concept, we explored and compared the growth and differentiation characteristics of myoblasts prepared from phenotypically unaffected muscles of five FSHD patients and 10 control donors. According to a clinically approved procedure, 10(9) cells of a high degree of purity were obtained within 16-23 days. More than 80% of these cells were myoblasts, as demonstrated by labeling of the muscle markers CD56 and desmin. FSHD myoblasts presented a doubling time equivalent to that of control cells; they kept high proliferation ability and did not show early telomere shortening. In vitro, these cells were able to differentiate and to express muscle-specific antigens. In vivo, they participated to muscle structures when injected into immunodeficient mice. These data suggest that myoblasts expanded from unaffected FSHD muscles may be suitable tools in view of autologous cell transplantation clinical trials.

Human muscle precursor cell regeneration in the mouse host is enhanced by growth factors

The aim of this study was to optimize human muscle formation in vivo from implanted human muscle precursor cells. We transplanted donor muscle precursor cells (MPCs) prepared from postnatal or fetal human muscle into immunodeficient host mice and showed that irradiation of host muscle significantly enhanced muscle formation by donor cells. The amount of donor muscle formed in cryodamaged host muscle was increased by exposure of donor cells to growth factors before their implantation into injured host muscle. Insulin-like growth factor type I (IGF-I) significantly increased the amount of muscle formed by postnatal human muscle cells, but not by fetal human MPCs. However, treatment of fetal muscle cells with IGF-I, in combination with basic fibroblast growth factor and plasmin, significantly increased the amount of donor muscle formed. In vivo, human MPCs formed mosaic human-mouse muscle fibers, in which each human myonucleus was associated with a zone of human sarcolemmal protein spectrin.

GROWTH FACTORS IMPROVE THE IN VIVO MIGRATION OF HUMAN SKELETAL MYOBLASTS BY MODULATING THEIR ENDOGENOUS PROTEOLYTIC ACTIVITY

BACKGROUND

A main technological problem related to the clinical application of myoblast transplantation is the poor migration of transplanted cells. In this study, we investigated a new physiologic approach that consists of coinjecting motogenic factors insulin growth factor (IGF)-1 or basic fibroblast growth factor (bFGF) to enhance the migration of human skeletal myoblasts. Among the different ways by which those factors can induce the cell migration processes, we investigated their capacity to enhance cell endogenous proteolytic activity that will help transplanted cells to migrate through the extracellular matrix.

METHODS

In vitro, myoblasts were coincubated with bFGF or IGF-1. Growth factors effects on cell migration were evaluated using invasion chambers, and their effects on proteolytic systems were evaluated by zymography, Western blot, and reverse transcription polymerase chain reaction. In vivo, myoblasts were coinjected with growth factors and the intramuscular migration capacity was assessed using the microtube technique.

RESULTS

In vitro, the presence of IGF-1 or bFGF significantly enhanced the expression of the gelatinase matrix metalloproteinase-9 and focalized the fibrinolytic system activity at the cell membrane. In vitro and in vivo, both bFGF and IGF-1 showed strong chemokinetic potentials and improved the migration of human myoblasts. Moreover, the implication some proteinases in the in vivo enhanced migration was confirmed using specific inhibitors (BB94 or amiloride).

CONCLUSIONS

These results suggest that IGF-1 or bFGF coinjection with human myoblasts increased their proteolytic activities and consequently their migratory capacity. This study may help to develop approaches that will reduce the number of injection sites for the treatment of Duchenne muscular dystrophy patients.

Therapeutic Strategies for Duchenne and Becker Dystrophies

Duchenne muscular dystrophy (DMD), a severe X-linked genetic disease affecting one in 3500 boys, is the most common myopathy in children. DMD is due to a lack of dystrophin, a submembrane protein of the cytoskeleton, which leads to the progressive degeneration of skeletal, cardiac, and smooth muscle tissue. A milder form of the disease, Becker muscular dystrophy (BMD), is characterized by the presence of a semifunctional truncated dystrophin, or reduced levels of full-length dystrophin. DMD is the focus of three different supportive or therapeutic approaches: gene therapy, cell therapy, and drug therapy. Here we consider these approaches in terms of three potential goals: improvement of dystrophic phenotype, expression of dystrophin, and overexpression of utrophin. Utrophin exhibits 80% homology with dystrophin and is able to perform similar functions. Pharmacological strategies designed to overexpress utrophin appear promising and may circumvent many obstacles to gene and cell-based therapies.

Tumor necrosis factor-alpha (TNF-alpha) stimulates chemotactic response in mouse myogenic cells

Migration of transplanted myogenic cells occurs during both embryogenesis and regeneration of skeletal muscles and is important for successful myoblast transplantation, but little is known about factors that promote chemotaxis of these cells. Tumor necrosis factor-alpha (TNF-alpha) is known to induce chemotactic effect on several cell types. In this study, we investigated its influence on the in vitro and in vivo motility of C2C12 and primary myoblasts. In the in vitro test performed in the blind-well Boyden chambers, we showed that TNF-alpha (50-400 U/ml) significantly enhanced the ability of myogenic cells to migrate. The dose-response curve for this factor was bell shaped, with maximum activity in the 200 U/ml range. In the in vivo test, intramuscular administration of TNF-alpha was performed by an Alzet pump connected to a perforated polyethylene microtube inserted in the tibialis anterior (TA) of CD1 mice. In these experiments, myoblasts were injected under the muscle epimysium. The recipient mice were immunosuppressed with FK506. Our results showed that, 5 days after myoblast transplantation, cells migrated further in the muscles infused with TNF-alpha than in the muscles not exposed to TNF-alpha. TNF-alpha not only has a chemotactic activity but may also modify cell migration via its action on matrix metalloproteinase (MMP) expression. The proteolytic activities of the MMPs secreted in the muscles were thus also assessed by gelatin zymography. The results showed an increased of MMP-2 and MMP-9 transcripts in the TNF-alpha-infused muscles injected with myogenic cells. Myoblast migration during transplantation may be enhanced by overlapping gradients of several effector molecules such as TNF-alpha, interferon-gamma (INF-gamma), and interleukins, released at the site of muscle injury. We propose that TNF-alpha may promote myoblast migration directly through chemotactic activity and indirectly by enhancing MMP activity at the site of muscle injury.

Efficacy of myoblast transplantation in nonhuman primates following simple intramuscular cell injections: toward defining strategies applicable to humans

Nonhuman primates were used to define myoblast transplantation strategies applicable to humans. Nevertheless, previous experiments were based on the use of myotoxins concomitant with the myoblast injections. Since myotoxins must be avoided for clinical applications, we analyzed the efficacy of simple myoblast injections (i.e., myoblasts resuspended only in saline) into monkey muscles. We also evaluated different FK506 dosages (in combination or not with mycophenolate mofetil) for immunosuppression. Allogeneic myoblasts transduced with the beta-galactosidase (beta-Gal) gene were implanted in the muscles of 19 monkeys by injections placed 1 to 2 mm from each other. A biopsy was performed at the implanted sites 1 month later, and histologically studied for demonstration of beta-Gal+ myofibers, lymphocyte infiltration, and CD8+ cells. The presence of antibodies against the donor myoblasts and the blood levels of FK506 were analyzed. Our results show that: (1) If myoblast injections are sufficiently close to each other, high percentages of hybrid myofibers can be obtained following myoblast transplantation in primates (25 to 67% with an interinjection distance of 1 mm). (2) Efficient immunosuppression can be reached by increasing FK506 dosages, but also by combining this drug with mycophenolate mofetil, a combination that reduces toxic effects. The present results represent a step towards a better designing of myoblast transplantation strategies in humans.

Absence of MyoD increases donor myoblast migration into host muscle

Donor myoblast migration is a major limiting factor in the success of myoblast transfer therapy, a potential treatment for Duchenne muscular dystrophy. A possible strategy to promote the migration of donor myoblasts into host muscle is to enhance their proliferation and delay their fusion, two properties that are major characteristics of myoblasts in regenerating skeletal muscle in MyoD null (-/-) mice. Here we investigate whether the migration of MyoD (-/-) donor myoblasts into host muscle is enhanced in vivo. Sliced muscle grafts from male MyoD (-/-) or normal control (Balb/c) mice were transplanted into the muscles of female normal (Balb/c) host mice. Muscles were sampled at 1, 3, and 12 weeks after grafting, and the fate of male donor myoblasts within female host muscles determined by in situ hybridization with the mouse Y-chromosome-specific Y-1 probe. MyoD (-/-) donor myoblasts migrated into host muscle continuously over 1, 3, and 12 weeks after grafting, in contrast with Balb/c donor myoblasts, whose overall numbers and migratory distances did not increase significantly after 1 week. These results strongly support a role for elevated donor myoblast proliferation and/or their delayed fusion in enhancing migration into host muscle in vivo, and endorse the use of either genetically engineered donor myoblasts, or the administration of exogenous myoblast mitogens to improve donor myoblast migration in myoblast transfer therapy.

Leukemia inhibitory factor enhances regeneration in skeletal muscles after myoblast transplantation

Cell-based therapies, such as myoblast transfer therapy, are likely to become an integral part of any approach to treat myopathies such as Duchenne muscular dystrophy. Previous studies have shown that an increased level of regeneration in the host muscle enhances incorporation of donor myoblasts. Leukemia inhibitory factor (LIF) increases the number of dystrophic fibers expressing dystrophin after myoblast transplantation and enhances regeneration in injured and diseased muscle. Morphometric analysis was used to investigate whether an increased level of regeneration is induced by LIF after myoblast transplantation. We found that, in muscles treated with LIF, the number of fibers undergoing regeneration was increased. The increased incorporation of donor myoblasts and thus dystrophin expression induced by LIF may be due, at least in part, to an increased level of regeneration of dystrophic muscle.

Problems and solutions in myoblast transfer therapy

Duchenne muscular dystrophy is a severe X-linked neuromuscular disease that affects approximately 1/3500 live male births in every human population, and is caused by a mutation in the gene that encodes the muscle protein dystrophin. The characterization and cloning of the dystrophin gene in 1987 was a major breakthrough and it was considered that simple replacement of the dystrophin gene would ameliorate the severe and progressive skeletal muscle wasting characteristic of Duchenne muscular dystrophy. After 20 years, attempts at replacing the dystrophin gene either experimentally or clinically have met with little success, but there have been many significant advances in understanding the factors that limit the delivery of a normal dystrophin gene into dystrophic host muscle. This review addresses the host immune response and donor myoblast changes underlying some of the major problems associated with myoblast-mediated dystrophin replacement, presents potential solutions, and outlines other novel therapeutic approaches.

In vivo targeted repair of a point mutation in the canine dystrophin gene by a chimeric RNA/DNA oligonucleotide

In the canine model of Duchenne muscular dystrophy in golden retrievers (GRMD), a point mutation within the splice acceptor site of intron 6 leads to deletion of exon 7 from the dystrophin mRNA, and the consequent frameshift causes early termination of translation. We have designed a DNA and RNA chimeric oligonucleotide to induce host cell mismatch repair mechanisms and correct the chromosomal mutation to wild type. Direct skeletal muscle injection of the chimeric oligonucleotide into the cranial tibialis compartment of a six-week-old affected male dog, and subsequent analysis of biopsy and necropsy samples, demonstrated in vivo repair of the GRMD mutation that was sustained for 48 weeks. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of exons 5-10 demonstrated increasing levels of exon 7 inclusion with time. An isolated exon 7-specific dystrophin antibody confirmed synthesis of normal-sized dystrophin product and positive localization to the sarcolemma. Chromosomal repair in muscle tissue was confirmed by restriction fragment length polymorphism (RFLP)-PCR and sequencing the PCR product. This work provides evidence for the long-term repair of a specific dystrophin point mutation in muscle of a live animal using a chimeric oligonucleotide.

Immunobiology and the future of myoblast transfer therapy

Myoblast transfer therapy (MTT) is a cell-mediated gene transfer method aimed at the restoration of normal dystrophin expression in Duchenne muscular dystrophy (DMD). Initial clinical MTT trials were conducted amid much controversy, as they were based on very few animal studies. Unfortunately, the trials were of little therapeutic benefit. As a result, there has been a renaissance of interest in experimental studies in animal models. In MTT, myoblasts are obtained by muscle biopsy from normal, i.e., dystrophin-positive, donors, expanded in culture, and injected directly into the muscles of dystrophic recipients. The major requirement for successful MTT is the survival of injected donor myoblasts in the host environment. However, a vast majority of donor cells fail to survive for more than 1 h after injection, and very few last beyond the first week. This review on the immunological aspects of MTT focuses in particular on the roles of specific components of the host immune response, the effects of tissue culture on donor cells, and strategies under development to circumvent the problem of donor myoblast death after injection in vivo.

Intramuscular grafts of myoblasts genetically modified to secrete glial cell line-derived neurotrophic factor prevent motoneuron loss and disease progression in a mouse model of familial amyotrophic lateral sclerosis

Effects of ex vivo GDNF gene delivery on the degeneration of motoneurons were studied in the G1H transgenic mouse model of familial ALS carrying a human superoxide dismutase (SOD1) with a Gly93Ala mutation (Gurney et al., 1994). Retroviral vectors were made to produce human GDNF or E. coli beta-galactosidase (beta-Gal) by transient transfection of the Phoenix cell line and used to infect primary mouse myoblasts. In 6-week-old G1H mice, 50,000 myoblasts per muscle were injected bilaterally into two hindlimb muscles. Untreated G1H and wild-type mice served as additional controls. At 17 weeks of age, 1 week before sacrifice, these muscles were injected with fluorogold (FG) to retrogradely label spinal motoneurons that maintained axonal projections to the muscles. There were significantly more large FG-labeled alpha motoneurons at 18 weeks in GDNF-treated G1H mice than in untreated and beta-Gal-treated G1H mice. A morphometric study of motoneuron size distribution showed that GDNF shifted the size distribution of motoneurons toward larger cells compared with control G1H mice, although the average size and number of large motoneurons in GDNF-treated mice were less than that in wild-type mice. GDNF also prolonged the onset of disease, delayed the deterioration of performance in tests of motor behavior, and slowed muscle atrophy. Quantitative, real-time RT-PCR and PCR showed persistence of transgene mRNA and DNA in muscle for up to 12 weeks postgrafting. These observations demonstrate that ex vivo GDNF gene therapy in a mouse model of FALS promotes the survival of functional motoneurons, suggesting that a similar approach might delay the progression of neurodegeneration in ALS.

Myoblast transplantations lead to the expression of the laminin alpha 2 chain in normal and dystrophic (dy/dy) mouse muscles

Laminin-2 is part of the basement membrane of the skeletal muscle fibers. The laminin alpha 2 chain is absent or drastically reduced in a subgroup of congenital muscular dystrophy patients, and in the severely affected dystrophic dy/dy mouse. We previously reported that heterogeneous primary mouse muscle cell cultures conferred laminin alpha 2 chain expression in dy/dy mice muscles upon cell transplantation. In the present study we investigated whether pure myoblast cell lines were able to confer laminin alpha 2 chain expression in vivo. We observed that: (1) xeno-transplantation of non-immortalized human myoblast in SCID mouse muscles allows human laminin alpha 2 chain expression; (2) allotransplantation of the permanent G8 mouse myoblast cell line in dy/dy muscles allows the expression of the murine laminin alpha 2 chain; and (3) allo-transplantation of the D7 dystrophic dy/dy cell line allows the formation of new and hybrid muscle fibers in dy/dy muscle in the absence of laminin alpha 2 chain expression. We conclude that normal myoblasts are able to restore the expression of an extracellular skeletal muscle protein and that the absence of laminin-2 does not prevent transplanted muscle cells from participating in the formation of myofibers. Myoblasts are, therefore, attractive tools for further exploration of gene complementation strategies in the animal models of congenital muscular dystrophy.

Prior culture with concanavalin A increases intramuscular migration of transplanted myoblast

The effect was studied of pretreatment with concanavalin A (ConA) of primary myoblast cultures on their migration when transplanted into muscles. As donors, transgenic CD1 mice in which the beta-galactosidase gene is under the control of a CMV promoter (CMVLacZ.9) were used. The myoblasts were grown with 20 microg/mL ConA during the 2 days before injecting them in the right tibialis anterior (TA) muscles of BALB/c mice and mdx mice. As a control, myoblasts from the same primary cultures were grown without ConA and injected in the left TA muscles. The host muscles were not previously irradiated or damaged by notexin injection. The recipient mice were immunosuppressed with FK506. Four days after myoblast transplantation, the area occupied by donor cells was significantly greater (more than threefold) following culture with ConA than without ConA. This result indicates that culture of myoblasts with ConA permits them to migrate farther following their transplantation in host muscles not previously damaged by notexin injection or irradiation. This suggests that pretreatment with ConA may be helpful for myoblast transplantation in humans. The mechanism of this effect still remains to be investigated.