Mass and functional capacity of regenerating muscle is enhanced by myoblast transfer

Changes in Mass and Performance in Rabbit Muscles after Muscle Damage with or without Transplantation of Primary Satellite Cells

Changes in morphology, metabolism, myosin heavy chain gene expression, and functional performances in damaged rabbit muscles with or without transplantation of primary satellite cells were investigated. For this purpose, we damaged bilaterally the fast muscle tibialis anterior (TA) with either 1.5 or 2.6 ml cardiotoxin 10–5 M injections. Primary cultures of satellite cells were autotransplanted unilaterally 5 days after muscle degeneration. Two months postoperation, the masses of damaged TAs, with or without transplantation, were significantly larger than those of the controls. Furthermore, damaged transplanted muscles weighed significantly more than damaged muscles only. The increase in muscle mass was essentially due to increased fiber size. These results were independent of the quantity of cardiotoxin injected into the muscles. Maximal forces were similar in control and 2.6 ml damaged TAs with or without satellite cell transfer. In contrast, 1.5 ml damaged TAs showed a significant decrease in maximal forces that reached the level of controls after transplantation of satellite cells. Fatigue resistance was similar in control and 1.5 ml damaged TAs independently of satellite cell transfer. Fatigue index was significantly higher in 2.6 ml damaged muscles with or without cell transplantation. These changes could be explained in part by muscle metabolism, which shifted towards oxidative activities, and by gene expression of myosin heavy chain isoforms, which presented an increase in type IIa and a decrease in type I and IIb in all damaged muscles with or without cell transfer. Under our experimental conditions, these results show that muscle damage rather than satellite cell transplantation changes muscle metabolism, myosin heavy chain isoform gene expression, and, to a lesser extent, muscle contractile properties. In contrast, muscle weight and fiber size are increased both by muscle damage and by satellite cell transfer.

Development of Approaches to Improve the Healing following Muscle Contusion

Muscle injuries are a challenging problem in traumatology, and the most frequent occurrence in sports medicine. Muscle contusions are among the most common muscle injuries. Although this injury is capable of healing, an incomplete functional recovery often occurs, depending on the severity of the blunt trauma. We have developed an animal model of muscle contusion in mice (high energy blunt trauma) and characterized the muscle's ability to heal following this injury using histology and immunohistochemistry to determine the level of muscle regeneration and the development of scar tissue. We have observed a massive muscle regeneration occurring in the first 2 wk postinjury that is subsequently followed by the development of muscle fibrosis. Based on these observations, we propose that the enhancement of muscle growth and regeneration, as well as the prevention of fibrotic development, could be used as approach(es) to improve the healing of muscle injuries. In fact, we have identified three growth factors (bFGF, IGF-1, and NGF) capable of enhancing myoblast proliferation and differentiation in vitro and improving the healing of the injured muscle in vivo. Furthermore, the ability of adenovirus to mediate direct and ex vivo gene transfer of β-galactosidase into the injured site opens possibilities of delivering an efficient and persistent expression of these growth factors in the injured muscle. These studies should help in the development of strategies to promote efficient muscle healing with complete functional recovery following muscle contusion. © 1998 Elsevier Science Inc.

Syngeneic Myoblast Transplantation Improves Muscle Function in a Murine Model of X-Linked Myotubular Myopathy

X-linked myotubular myopathy (XLMTM) is an isogenic muscle disease characterized by progressive wasting of skeletal muscle, weakness, and premature death of affected male offspring. Recently, the XLMTM gene knock-in mouse, Mtm1 p.R69C, was found to have a similar phenotype as the Mtm1 gene mutation in humans (e.g., central nucleation of small myofibers, attenuated muscle strength, and motor unit potentials). Using this rodent model, we investigated whether syngeneic cell therapy could mitigate muscle weakness. Donor skeletal muscle-derived myoblasts were isolated from C57BL6 wild-type (WT) and Mtm1 p.R69C (KI) mice for transplantation into the gastrocnemius muscle of recipient KI mice. Initial experiments demonstrated that donor skeletal muscle-derived myoblasts from WT and KI mice remained in the gastrocnemius muscle of the recipient KI mouse for up to 4 weeks posttransplantation. KI mice receiving syngeneic skeletal muscle-derived myoblasts displayed an increase in skeletal muscle mass, augmented force generation, and increased nerve-evoked skeletal muscle action potential amplitude. Taken together, these results support our hypothesis that syngeneic cell therapy may potentially be used to ameliorate muscle weakness and delay the progression of XLMTM, as application expands to other muscles.

In vitro development and characterization of a tissue-engineered conduit resembling esophageal wall using human and pig skeletal myoblast, oral epithelial cells, and biologic scaffolds

INTRODUCTION

Tissue engineering represents a promising approach for esophageal replacement, considering the complexity and drawbacks of conventional techniques.

AIM

To create the components necessary to reconstruct in vitro or in vivo an esophageal wall, we analyzed the feasibility and the optimal conditions of human and pig skeletal myoblast (HSM and PSM) and porcine oral epithelial cell (OEC) culture on biologic scaffolds.

MATERIALS AND METHODS

PSM and HSM were isolated from striated muscle and porcine OECs were extracted from oral mucosa biopsies. Myoblasts were seeded on an acellular scaffold issue from porcine small intestinal submucosa (SIS) and OEC on decellularized human amniotic membrane (HAM). Seeding conditions (cell concentrations [0.5×10(6) versus 10(6) cells/cm(2)] and culture periods [7, 14 and 21 days]), were analyzed using the methyl thiazoltetrazolium assay, quantitative PCR, flow cytometry, and immunohistochemistry.

RESULTS

Phenotypic stability was observed after cellular expansion for PSM and HSM (85% and 97% CD56-positive cells, respectively), and OECs (90% AE1/AE3- positive cells). After PSM and HSM seeding, quantities of viable cells were similar whatever the initial cell concentration used and remained stable at all time points. During cell culture on SIS, a decrease of CD56-positive cells was observed (76% and 76% by D7, 56% and 70% by D14, 28% and 60% by D21, for PSM and HSM, respectively). Multilayered surface of α-actin smooth muscle and Desmine-positive cells organized in bundles was seen as soon as D7, with no evidence of cell within the SIS. Myoblasts fusion was observed at D21. Pax3 and Pax7 expression was downregulated and MyoD expression upregulated, at D14.OEC proliferation was observed on HAM with both cell concentrations from D7 to D21. The cell metabolism activity was more important on matrix seeded by 10(6) cells/cm(2). With 0.5×10(6) OEC/cm(2), a single layer of pancytokeratin-positive cells was seen at D7, which became pluristratified by D14, while when 10(6) OEC/cm(2) were used, a pluristratified epithelial structure was seen as soon as D7. Proliferative cells (Proliferating Cell Nuclear Antigen staining) were mainly located at the basal layer.

CONCLUSION

In this model, the optimal conditions of cell seeding in terms of cell concentration and culture duration were 0.5×10(6) myoblasts/cm(2) and 10(6) OEC/cm(2), and 7 days.

Restricted Myogenic Potential of Mesenchymal Stromal Cells Isolated from Umbilical Cord

Nonhematopoietic cord blood cells and mesenchymal cells of umbilical cord Wharton's jelly have been shown to be able to differentiate into various cell types. Thus, as they are readily available and do not raise any ethical issues, these cells are considered to be a potential source of material that can be used in regenerative medicine. In our previous study, we tested the potential of whole mononucleated fraction of human umbilical cord blood cells and showed that they are able to participate in the regeneration of injured mouse skeletal muscle. In the current study, we focused at the umbilical cord mesenchymal stromal cells isolated from Wharton's jelly. We documented that limited fraction of these cells express markers of pluripotent and myogenic cells. Moreover, they are able to undergo myogenic differentiation in vitro, as proved by coculture with C2C12 myoblasts. They also colonize injured skeletal muscle and, with low frequency, participate in the formation of new muscle fibers. Pretreatment of Wharton's jelly mesenchymal stromal cells with SDF-1 has no impact on their incorporation into regenerating muscle fibers but significantly increased muscle mass. As a result, transplantation of mesenchymal stromal cells enhances the skeletal muscle regeneration.

Discrepancies between the fate of myoblast xenograft in mouse leg muscle and NMR label persistency after loading with Gd-DTPA or SPIOs

1H-NMR (nuclear magnetic resonance) imaging is regularly proposed to non-invasively monitor cell therapy protocols. Prior to transplantation, cells must be loaded with an NMR contrast agent (CA). Most studies performed so far make use of superparamagnetic iron oxide particles (SPIOs), mainly for favorable detection sensitivity. However, in the case of labeled cell death, SPIO recapture by inflammatory cells might introduce severe bias. We investigated whether NMR signal changes induced by preloading with SPIOs or the low molecular weight gadolinium (Gd)-DTPA accurately monitored the outcome of transplanted cells in a murine model of acute immunologic rejection. CA-loaded human myoblasts were grafted in the tibialis anterior of C57BL/6 mice. NMR imaging was repeated regularly until 3 months post-transplantation. Label outcome was evaluated by the size of the labeled area and its relative contrast to surrounding tissue. In parallel, immunohistochemistry assessed the presence of human cells. Data analysis revealed that CA-induced signal changes did not strictly reflect the graft status. Gd-DTPA label disappeared rapidly yet with a 2-week delay compared with immunohistochemical evaluation. More problematically, SPIO label was still visible after 3 months, grossly overestimating cell survival (<1 week). SPIOs should be used with extreme caution to evaluate the presence of grafted cells in vivo and could hardly be recommended for the long-term monitoring of cell transplantation protocols.

Transurethral ultrasonography-guided injection of adult autologous stem cells versus transurethral endoscopic injection of collagen in treatment of urinary incontinence

In the last years preclinical studies have paved the way for the use of adult muscle derived stem cells for reconstruction of the lower urinary tract. Between September 2002 and October 2004, 42 women and 21 men suffering from urinary stress incontinence (age 36-84 years) were recruited and subsequently treated with transurethral ultrasonography-guided injections of autologous myoblasts and fibroblasts obtained from skeletal muscle biopsies. The fibroblasts were injected into the urethral submucosa, while the myoblasts were implanted into the rhabdosphincter. In parallel, 7 men and 21 women (age 39-83 years) also diagnosed with urinary stress incontinence were treated with standard transurethral endoscopic injections of collagen. Patients were randomly assigned to both groups. After a follow-up of 12 months incontinence was cured in 39 women and 11 men after injection of autologous myoblasts and fibroblasts. Mean quality of life score (51.38 preoperatively, 104.06 postoperatively), thickness of urethra and rhabdosphincter (2.103 mm preoperatively, 3.303 mm postoperatively) as well as contractility of the rhabdosphincter (0.56 mm preoperatively, 1.462 mm postoperatively) were improved postoperatively. Only in two patients treated with injections of collagen incontinence was cured. The present clinical results demonstrate that, in contrast to injections of collagen, urinary incontinence can be treated effectively with ultrasonography-guided injections of autologous myo- and fibroblasts.

Autologous myoblasts and fibroblasts versus collagen for treatment of stress urinary incontinence in women: a randomised controlled trial

BACKGROUND

Preclinical studies have suggested that transurethral injections of autologous myoblasts can aid in regeneration of the rhabdosphincter, and fibroblasts in reconstruction of the urethral submucosa. We aimed to compare the effectiveness and tolerability of ultrasonography-guided injections of autologous cells with those of endoscopic injections of collagen for stress incontinence.

METHODS

Between 2002 and 2004, we recruited 63 eligible women with urinary stress incontinence. 42 of these women were randomly assigned to receive transurethral ultrasonography-guided injections of autologous myoblasts and fibroblasts, and 21 to receive conventional endoscopic injections of collagen. The first primary outcome measure was an incontinence score (range 0-6) based on a 24-hour voiding diary, a 24-hour pad test, and a patient questionnaire. The other primary outcome measures were contractility of the rhabdosphincter and thickness of both the urethra and rhabdosphincter. Analysis was by intention to treat. This trial is registered with Controlled-Trials.com, number CCT-NAPN-16630.

FINDINGS

At 12-months' follow-up, 38 of the 42 women injected with autologous cells were completely continent, compared with two of the 21 patients given conventional treatment with collagen. The median incontinence score decreased from a baseline of 6.0 (IQR 6.0-6.0; where 6 represents complete incontinence), to 0 (0-0) for patients treated with autologous cells, and 6.0 (3.5-6.0) for patients treated with collagen (p<0.0001). Ultrasonographic measurements showed that the mean thickness of the rhabdosphincter increased from a baseline of 2.13 mm (SD 0.39) for all patients to 3.38 mm (0.26) for patients treated with autologous cells and 2.32 mm (0.44) for patients treated with collagen (p<0.0001). Contractility of the rhabdosphincter increased from a baseline of 0.58 mm (SD 0.32) to 1.56 mm (0.28) for patients treated with autologous cells and 0.67 mm (0.51) for controls (p<0.0001). The change in the thickness of the urethra after treatment was not significantly different between treatment groups. No adverse effects were recorded in any of the 63 patients.

INTERPRETATION

Long-term postoperative results and data from multicentre trials with larger numbers of patients are needed to assess whether injection of autologous cells into the rhabdosphincter and the urethra could become a standard treatment for urinary incontinence.

Short- or long-term effects of adult myoblast transfer on properties of reinnervated skeletal muscles

Skeletal muscle demonstrates a force deficit after repair of injured peripheral nerves. Data from the literature indicate that myoblast transfer enhances recovery of muscle function. Thus, we tested the hypothesis that transfer of adult myoblasts improves the properties of reinnervated rabbit tibialis anterior (TA) muscles in both the short term (4 months) and long term (14 months). Two months after transection and immediate suture of the common peroneal nerve, TA muscles were made to degenerate by cardiotoxin injection and then transplanted with adult myoblasts cultured for 13 days. Under these conditions, muscles studied at 4 months were heavier, contained larger fibers, and developed a significantly higher maximal force than muscles that had only been denervated-reinnervated. In the long term, although muscles made to degenerate were heavier and developed a significantly higher maximal force than denervated-reinnervated muscles, myoblast transfer failed to improve these parameters. However, the overall characteristics of long-term operated muscles tended clearly to approach those of the controls. Taken together, these results may have significant implications in certain orthopedic contexts, particularly after immediate or delayed muscle reinnervation.

Autologous Bone Marrow-Derived Cells Enhance Muscle Strength Following Skeletal Muscle Crush Injury in Rats

Insufficient post-traumatic skeletal muscle regeneration with consecutive functional deficiency continues to be a serious problem in orthopedic and trauma surgery. Transplantation of autologous muscle precursor cells has shown encouraging results in muscle trauma treatment but is associated with significant donor site morbidity. In contrast to this, bone marrow-derived (BMD) cells can be obtained without any functional deficit by puncture. The goal of this study was to examine whether regular muscle regeneration can be improved by local application of autologous BMD cells in a rat model of blunt skeletal muscle trauma. One week after standardized open blunt crush injury to the left soleus muscle, 10(6) autologous BMD cells were injected into the traumatized muscle of male Sprague Dawley rats. Rats of the control group received saline solution as treatment. Three weeks after application, the fast twitch and tetanic contraction capacity of the soleus muscles was measured bilaterally by stimulating the sciatic nerves. Contraction forces of injured soleus muscles in control animals recovered to 39 +/- 10% (tetanic) and 59 +/- 12% (fast twitch) of the contralateral noninjured soleus muscles (p < 0.001). In contrast, autologous BMD cell injection significantly restored contractile forces to 53 +/- 8% (tetanic) and 72 +/- 13% (fast twitch) compared to those observed in contralateral noninjured soleus muscles. Thus, muscle function was significantly increased by BMD cell treatment (tetanic, p = 0.014; fast twitch, p = 0.05). In conclusion, autologous BMD cell grafting leads to an increase in contraction force, 14% in tetanic and 13% in fast twitch stimulation, demonstrating its potential to improve functional outcome after skeletal muscle crush injury.

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.

Transplantation of primary satellite cells improves properties of reinnervated skeletal muscles

Skeletal muscle demonstrates a force deficit after repair of injured peripheral nerves. We tested the hypothesis that transplantation of satellite cells into reinnervated rabbit tibialis anterior (TA) muscles improves their properties. Adult rabbits underwent transection and immediate suture of the common peroneal nerve. In order to provide an environment favorable for cell transplantation, TA were then made to degenerate by cardiotoxin injection, either immediately or after a 2-month delay, which is sufficient for muscle reinnervation. In both cases, the injured TA were transplanted with cultured satellite cells 5 days after induction of muscle degeneration. When cells were transferred immediately after nerve repair, drastic morphological and functional muscle alterations were observed. However, when the muscles were allowed to become reinnervated before cell transplantation, muscles were heavier and developed a significantly higher maximal force compared to denervated-reinnervated muscles. Thus, application of the cell therapy protocol improved properties of denervated muscles only when they were allowed to become innervated. These results, which represent the application of cell therapy to improve force recovery of reinnervated muscles, will be of significant interest in certain clinical contexts, particularly after immediate or delayed muscle reinnervation.

Myotoxic phospholipases A2 and the regeneration of skeletal muscles

The review explains why the myotoxic phospholipases A2 and cardiotoxins are such important tools in the study of the regeneration and maturation of mammalian skeletal muscle. The role of satellite cells as precursors of cell-based regeneration is discussed and recent controversies on the origin of myogenic cells involved in the regeneration of mature skeletal muscle are addressed. This is followed by discussions of sarcomere reconstruction, myosin and sarcoplasmic reticulum ATPase expression, the electrophysiological properties of regenerating muscle, and the reconstruction of the neuromuscular junction. The emphasis throughout is on the plastic changes of major structural and functional proteins that occur during regeneration, and on other influences that determine the final outcome of regenerative activity such as innervation, thyroid status, mechanical work and the functional integrity of the microcirculation. The review closes with a discussion of some of the factors--such as active regeneration--that influence the success of gene-based therapies applied to inherited muscle disease.

Restoration of functional motor units in a rat model of sphincter injury by muscle precursor cell autografts1

BACKGROUND

Urinary incontinence is a debilitating condition that affects primarily elderly individuals. One major mechanism results from chronic denervation of the striated urethral sphincter with associated fibrosis. The authors investigated the fate of muscle precursor cells (MPC) injected into a model of striated urethral sphincter injury that reproduces the histopathologic changes of sphincter insufficiency.

METHODS

The striated urethral sphincter of older male rats was damaged by electrocoagulation. MPC were isolated from limb myofiber explants, infected with an adenovirus carrying the transgene encoding beta-galactosidase, and injected into the sphincter of the same animal 37 days after injury. Animals were killed 5 and 30 days after injection for assessment of sphincter function and the formation of motor units.

RESULTS

Electrocoagulation resulted in an irreversible destruction of both sphincteric myofibers and nerve endings, with a functional incapacity of the damaged sphincter to sustain an increase in bladder pressure; atrophy and fibrosis developed after 1 month. Injection of MPC resulted in the formation of beta-galactosidase-expressing myotubes in the sphincter that persisted beyond 30 days. The regenerated myotubes carried acetylcholine receptors associated with a nerve ending and were thus considered to form anatomic motor units. Urodynamic studies confirmed the restoration of 41% of sphincter function 1 month after MPC injection.

CONCLUSIONS

The authors showed that MPC isolated from limb muscles of an older animal can recapitulate a myogenic program when injected into an irreversibly injured sphincter. The maturation of MPC activates nerve regeneration and restores functional motor units.

Effect of injecting primary myoblasts versus putative muscle-derived stem cells on mass and force generation in mdx mice

It is well established that the injection of normal myoblasts or of muscle-derived stem cells (MDSCs) into the muscle of dystrophin-deficient mdx mice results in the incorporation of a number of donor myoblasts into the host muscle. However, the effect of the injected exogenous cells on mdx muscle mass and functional capacity has not been evaluated. This study evaluates the mass and functional capacity of the extensor digitorum longus (EDL) muscles of adult, male mdx mice that received intramuscular injections of primary myoblasts or of MDSCs (isolated by a preplating technique; Qu, Z., Balkir, L., van Deutekom, J.C., Robbins, P.D., Pruchnic, R., and Huard, J., J. Cell Biol. 1998;142:1257-1267) derived from normal mice. Evaluations were made 9 weeks after cell transplantation. Uninjected mdx EDL muscles have a mass 50% greater than that of age-matched C57BL/10J (normal) EDL muscles. Injections of either primary myoblasts or MDSCs have no effect on the mass of mdx EDL muscles. EDL muscles of mdx mice generate 43% more absolute twitch tension and 43% less specific tetanic tension then do EDL muscles of C57BL/10J mice. However, the absolute tetanic and specific twitch tension of mdx and C57BL/10J EDL muscles are similar. Injection of either primary myoblasts or MDSCs has no effect on the absolute or specific twitch and tetanic tensions of mdx muscle. Approximately 25% of the myofibers in mdx EDL muscles that received primary myoblasts react positively with antibody to dystrophin. There is no significant difference in the number of dystrophin-positive myofibers when MDSCs are injected. Regardless of the source of donor cells, dystrophin is limited to short distances (60-900 microm) along the length of the myofibers. This may, in part, explain the failure of cellular therapy to alter the contractile properties of murine dystrophic muscle.

Muscle precursor cell autografting in a murine model of urethral sphincter injury

OBJECTIVE

To determine whether muscle precursor cells (MPCs) harvested from limb skeletal muscle can enhance the regeneration process of the striated urethral sphincter after injury.

MATERIAL AND METHODS

Striated urethral sphincters of male mice were injured by an injection of a myotoxic substance (notexin). In the experimental group, 2 days after injury, MPCs were enzymatically harvested from striated muscles of the lower limbs and labelled with PKH 26, then immediately re-injected into the injured urethral sphincter of the same animal. In the control group, saline buffer was injected instead of MPCs. Animals were killed 7 days or 1 month after injury and the sphincters removed for histological study (the presence of PKH 26-labelled myofibres, measurement of myofibre diameter and total number of myofibres).

RESULTS

MPC autografting accelerated sphincter muscle repair, as shown by a higher myofibre diameter (P = 0.03) and number (P = 0.01) in the experimental group than in the controls at 7 days. One month after their injection MPCs were still detectable in the regenerating sphincters and participated in the formation of new myofibres.

CONCLUSION

This study provides the experimental basis for a new therapeutic approach to urethral sphincter insufficiency after surgical or obstetrical injury, based on MPC autografting.

Enhancement of adult muscle regeneration by primary myoblast transplantation

Extensor digitorum longus muscles (EDL) of SCID mice were induced to undergo degeneration-regeneration subsequent to orthotopic, whole-muscle transplantation. Two days after transplantation some of these muscles received injections of primary myoblasts derived from EDL muscles of transgenic mice, which express nuclear localizing beta-galactosidase under the control of the myosin light-chain 3F promoter and enhancer. Nine weeks after transplantation, regenerated muscles that received exogenous myoblasts were compared to similarly transplanted muscles that received no further treatment and to unoperated EDL muscles in order to determine the effect of myoblast transfer on muscle regeneration. Many myofibers containing donor derived myonuclei could be identified in the regenerated muscles that had received exogenous myoblasts. The mass of the muscles subjected to transplantation only was significantly less (31% less) than that of unoperated muscles. The addition of exogenous myoblasts to the regenerating EDL resulted in a muscle mass similar to that of unoperated muscles. The absolute twitch and tetanic tensions and specific twitch and tetanic tensions of transplant-only muscles were 28%, 36%, 32%, and 41%, respectively, of those of unoperated muscles. Myoblast transfer increased the absolute twitch and tetanic tensions of the regenerated muscles by 65% and 74%, respectively, and their specific twitch and tetanic tensions were increased by 41% and 48%, respectively. These data suggest a possible role for the addition of exogenous, primary myoblasts in the treatment of traumatized and/or diseased muscles that are characterized by myofiber loss.

Myoblast transplantation in whole muscle of nonhuman primates

The goal of the present study was to determine the feasibility, success, and toxicity of myoblast transplantation (MT) in the whole muscle of primates. Allogenic myoblasts transduced with the beta-galactosidase (beta-Gal) gene were transplanted in the whole Biceps brachii of 5 monkeys immunosuppressed with FK506. Myoblast injections were spaced at every 1 to 1.5 mm in 7 muscles, as well as at every 5 mm in 2 muscles. Myoblasts were resuspended in HBSS, notexin 1 microg/ml or notexin 5 microg/ml. Depending on the number of beta-Gal labeled myoblasts and the injection protocol, biopsies of transplanted muscles exhibited 7% to 74% beta-Gal+ fibers 1 month after MT. Beta-Gal+ fibers were present in muscle biopsies made 3, 8, and 12 months after MT. Myoglobinuria and hyperkalemia, the risk factors after extensive muscle damage and notexin toxicity, were not observed. The withdrawal of immunosuppression led to histological evidences of cellular rejection of the graft. We concluded that MT can be successfully performed in large primate muscles without toxicity due to muscle damage. An effective immunosuppression allowed the maintenance of beta-Gal+ fibers up to 1 year after MT. These results suggest parameters that may allow effective MT in humans.

Progress in myoblast transplantation: a potential treatment of dystrophies

Myoblast transplantation (MT) consists of injecting normal or genetically modified myogenic cells into muscles, where they are expected to fuse and form mature fibers. As an experimental approach to treat severe genetic muscle diseases, MT was tested in dystrophic patients at the beginning of the 1990s. Although these early clinical trials were unsuccessful, MT has progressed through the research on animal models. Many factors that may condition the success of MT were identified in the last years. The present review updates our knowledge on MT and describes the different problems that have limited its success. Factors that were first underestimated, like the specific immune response after MT, are presently well characterized. Destruction of the hybrid fibers by activated T-lymphocytes and production of antibodies against the transplanted myoblasts take place after MT and are responsible for the graft rejection. The choice of the immunosuppression seems to be very important, and FK506 is the best agent known to allow the best results after MT. Under FK506 immunosuppression, very efficient MT were obtained both in mice and monkeys. Moreover, in dystrophic mice it was demonstrated that MT ameliorates some phenotypical characteristics of the disease. The improvement of the survival of the transplanted cells and the increase of their migration into the injected tissue are presently under investigation. Some of the present research is directed also to bypass the immunosuppression by using the patient's own cells for MT. In this sense, efforts are conducted to introduce the normal gene into the patient's myoblasts before MT and to improve the ability of these cells to proliferate in vitro. Micros. Res. Tech. 48:213-222, 2000.

Insulin-like growth factor (IGF)-binding protein-related protein-1: an autocrine/paracrine factor that inhibits skeletal myoblast differentiation but permits proliferation in response to IGF

Skeletal myogenic cells respond to the insulin-like growth factors (IGF-I and IGF-II) by differentiating or proliferating, which are mutually exclusive pathways. What determines which of these responses to IGF skeletal myoblast undergo is unclear. IGF-binding protein-related protein 1 (IGFBP-rP1) is a secreted protein with close homology to the IGF-binding proteins (IGFBPs) in the N-terminal region. IGFBP-rP1, previously called mac25 and IGFBP-7, is highly expressed in C2 skeletal myoblasts during the proliferative phase, but is down-regulated during myoblast differentiation. To determine the role of IGFBP-rP1 in myogenesis, IGFBP-rP1 was overexpressed in C2 myoblasts using a retroviral vector. Western blots indicated that the resulting C2-rP1 myoblasts secreted approximately 27-fold higher levels of IGFBP-rP1 than control C2-LX myoblasts that were transduced with a control vector (LXSN). Compared with C2-LX myoblasts, the differentiation responses of C2-rP1 myoblasts to IGF-I, IGF-II, insulin, and des(1-3)IGF-I were significantly reduced (P < 0.05). However, proliferation responses of C2-rP1 and C2-LX myoblasts to these same factors were not significantly different. Exposure of control C2-LX myoblasts to factors secreted by C2-rP1 myoblasts using a transwell coculture system reduced C2-LX myoblast differentiation significantly (P < 0.05). Experiments with the mitogen-activated protein kinase (MAPK) kinase inhibitor PD098059 suggested that IGFBP-rP1 inhibits a MAPK-dependent differentiation pathway. In confirmation of this idea, levels of phosphorylated extracellular signal-regulated kinase-2 (a MAPK) were reduced in C2-rP1 myoblasts compared with those in C2-LX myoblasts. These findings indicate that IGFBP-rP1 may function as an autocrine/paracrine factor that specifies the proliferative response to the IGFs in myogenesis.

Hepatocyte growth factor affects satellite cell activation and differentiation in regenerating skeletal muscle

Hepatocyte growth factor (HGF) is the only known growth factor that activates quiescent satellite cells in skeletal muscle. We hypothesized that local delivery of HGF may enhance regeneration after trauma by increasing the number of myoblasts available for restoring normal tissue architecture. Injection of HGF into muscle at the time of injury increases myoblast number but does not enhance tissue repair as determined using quantitative histological analyses. Rather, depending on the dose and the timing of HGF administration relative to the injury, regeneration can be inhibited. The greatest inhibitory effect is observed when HGF is administered on the day of injury and continued for 3 days, corresponding to the time when satellite cell activation, proliferation, and early differentiation normally occur. To establish a mechanism for this inhibition, we show that HGF can act directly on primary muscle cells to block differentiation. These results demonstrate that 1) exogenous HGF synergizes with factors in damaged muscle to increase myoblast number, 2) regeneration is not regulated solely by myoblast number, and 3) HGF inhibits muscle differentiation both in vitro and in vivo.

Systemic administration of the NF-kappaB inhibitor curcumin stimulates muscle regeneration after traumatic injury

Skeletal muscle is often the site of tissue injury due to trauma, disease, developmental defects or surgery. Yet, to date, no effective treatment is available to stimulate the repair of skeletal muscle. We show that the kinetics and extent of muscle regeneration in vivo after trauma are greatly enhanced following systemic administration of curcumin, a pharmacological inhibitor of the transcription factor NF-kappaB. Biochemical and histological analyses indicate an effect of curcumin after only 4 days of daily intraperitoneal injection compared with controls that require >2 wk to restore normal tissue architecture. Curcumin can act directly on cultured muscle precursor cells to stimulate both cell proliferation and differentiation under appropriate conditions. Other pharmacological and genetic inhibitors of NF-kappaB also stimulate muscle differentiation in vitro. Inhibition of NF-kappaB-mediated transcription was confirmed using reporter gene assays. We conclude that NF-kappaB exerts a role in regulating myogenesis and that modulation of NF-kappaB activity within muscle tissue is beneficial for muscle repair. The striking effects of curcumin on myogenesis suggest therapeutic applications for treating muscle injuries.

Successful myoblast transplantation in primates depends on appropriate cell delivery and induction of regeneration in the host muscle

Myoblast transplantation (MT) may be a potential treatment for severe recessive hereditary myopathies. The limited results of MT in clinical trials led us to improve this technique in monkeys, an animal model phylogenetically similar to humans. Three Macaca mulata monkeys were used as donors and six as receivers for MT. Myoblasts were grown in culture from muscle biopsies of adult monkeys and infected with a retroviral vector encoding the LacZ gene. Different numbers of cells (i.e., 4 x 10(6), 8 x 10(6), and 24 x 10(6) cells) were transplanted into different muscles and 8 x 10(6) cells (resuspended in a notexin solution) were injected in one muscle of four monkeys. For these transplantations, the cell suspension (in a volume of about 100 microl) was injected at 35 sites less than 1 mm apart. Two other monkeys received 100 x 10(6) myoblasts resuspended in 1 ml of HBSS or 1 ml of notexin. For these two monkeys, the myoblasts were injected at 200-250 sites within a small portion of the muscle. All monkeys were immunosuppressed with daily injections of FK506. Four weeks after MT, the transplanted muscle portions were biopsied and the presence of beta-galactosidase-positive (beta-Gal+) muscle fibers was investigated. The number of beta-Gal+ fibers was 822 +/- 150 (site grafted with 4 x 10(6) cells), 1253 +/- 515 (8 x 10(6) cells), 1084 +/- 278 (24 x 10(6)), and 2852 +/- 1211 (notexin). In the monkeys grafted with 100 x 10(6) myoblasts, the number of beta-Gal+ fibers was 4850 (site without notexin) and 9600 (site with notexin). We demonstrated that a precise mechanical distribution of myoblasts into the tissue improves substantially MT in primates. The presence of notexin with the transplanted cells further increased the success of their transplantation. These are the best results obtained either with MT or gene therapy in primates and they encourage the possibility to human MT trials.