Enhancement of adult muscle regeneration by primary myoblast transplantation

Muscle Precursor Cells Enhance Functional Muscle Recovery and Show Synergistic Effects With Postinjury Treadmill Exercise in a Muscle Injury Model in Rats

BACKGROUND

Skeletal muscle injuries represent a major concern in sports medicine. Cell therapy has emerged as a promising therapeutic strategy for muscle injuries, although the preclinical data are still inconclusive and the potential clinical use of cell therapy has not yet been established.

PURPOSE

To evaluate the effects of muscle precursor cells (MPCs) on muscle healing in a small animal model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 27 rats were used in the study. MPCs were isolated from rat (n = 3) medial gastrocnemius muscles and expanded in primary culture. Skeletal muscle injury was induced in 24 rats, and the animals were assigned to 3 groups. At 36 hours after injury, animals received treatment based on a single ultrasound-guided MPC (10⁵ cells) injection (Cells group) or MPC injection in combination with 2 weeks of daily exercise training (Cells+Exercise group). Animals receiving intramuscular vehicle injection were used as controls (Vehicle group). Muscle force was determined 2 weeks after muscle injury, and muscles were collected for histological and immunofluorescence evaluation.

RESULTS

Red fluorescence-labeled MPCs were successfully transplanted in the site of the injury by ultrasound-guided injection and were localized in the injured area after 2 weeks. Transplanted MPCs participated in the formation of regenerating muscle fibers as corroborated by the co-localization of red fluorescence with developmental myosin heavy chain (dMHC)-positive myofibers by immunofluorescence analysis. A strong beneficial effect on muscle force recovery was detected in the Cells and Cells+Exercise groups (102.6% ± 4.0% and 101.5% ± 8.5% of maximum tetanus force of the injured vs healthy contralateral muscle, respectively) compared with the Vehicle group (78.2% ± 5.1%). Both Cells and Cells+Exercise treatments stimulated the growth of newly formed regenerating muscles fibers, as determined by the increase in myofiber cross-sectional area (612.3 ± 21.4 µm² and 686.0 ± 11.6 µm², respectively) compared with the Vehicle group (247.5 ± 10.7 µm²), which was accompanied by a significant reduction of intramuscular fibrosis in Cells and Cells+Exercise treated animals (24.2% ± 1.3% and 26.0% ± 1.9% of collagen type I deposition, respectively) with respect to control animals (40.9% ± 4.1% in the Vehicle group). MPC treatment induced a robust acceleration of the muscle healing process as demonstrated by the decreased number of dMHC-positive regenerating myofibers (enhanced replacement of developmental myosin isoform by mature myosin isoforms) (4.3% ± 2.6% and 4.1% ± 1.5% in the Cells and Cells+Exercise groups, respectively) compared with the Vehicle group (14.8% ± 13.9%).

CONCLUSION

Single intramuscular administration of MPCs improved histological outcome and force recovery of the injured skeletal muscle in a rat injury model that imitates sports-related muscle injuries. Cell therapy showed a synergistic effect when combined with an early active rehabilitation protocol in rats, which suggests that a combination of treatments can generate novel therapeutic strategies for the treatment of human skeletal muscle injuries.

CLINICAL RELEVANCE

Our study demonstrates the strong beneficial effect of MPC transplant and the synergistic effect when the cell therapy is combined with an early active rehabilitation protocol for muscle recovery in rats; this finding opens new avenues for the development of effective therapeutic strategies for muscle healing and clinical trials in athletes undergoing MPC transplant and rehabilitation protocols.

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.

Use of Repeating Dispensers to Increase the Efficiency of the Intramuscular Myogenic Cell Injection Procedure

Intramuscular myoblast transplantation in humans and nonhuman primates requires precise repetitive cell injections very close to each other. Performed with syringes operated manually throughout large regions, this procedure takes a lot of time, becoming tiring and thus imprecise. We tested two repetitive dispensers with Hamilton syringes as cell injection devices to facilitate this procedure. Monkeys received intramuscular allotransplantations of β-galactosidase-labeled myoblasts, using either a monosyringe or a multisyringe repeating dispenser. The monosyringe repeating dispenser allowed performing cell injections faster and easier than with a manually operated syringe. The multisyringe dispenser accelerated the procedure still more, but it was not ergonomic. Biopsies of the myoblast-injected sites 1 month later showed abundant β-galactosidase-positive myofibers, with the same density and morphological pattern observed following myoblast transplantation with a syringe operated manually. We recommend the monosyringe repeating dispenser for myoblast transplantation in skeletal muscles and maybe in the heart.

Dose-response relationship of mesenchymal stem cell transplantation and functional regeneration after severe skeletal muscle injury in rats

Various therapeutic strategies that aim to influence clinical outcome after severe skeletal muscle trauma have been considered. One such method, the local transplantation of stem cells, has been shown to improve tissue regeneration. The number of cells required for successful regeneration, however, remains unclear. The aim of this study was therefore to examine the correlation between the number of transplanted bone marrow-derived mesenchymal stem cells (MSCs) and the resulting muscle function. One week after inducing an open crush trauma in 34 female Sprague Dawley rats, increasing quantities of autologous MSCs (0.1 x 10(6), 1 x 10(6), 2.5 x 10(6), and 10 x 10(6) cells) or saline solution (control group) were transplanted into the left soleus muscle of the rat hind limb. At 4 weeks posttrauma, the outcome was assessed by measuring muscle contraction forces following an indirect fast twitch and tetanic stimulation. A logarithmic dose-response relationship was observed for both maximum twitch and tetanic contraction forces (R(2) = 0.9 for fast twitch [p = 0.004]; R(2) = 0.87 [p = 0.002] for tetanic contraction). The transplantation of 10 x 10(6) cells resulted in the most pronounced improvement of muscle force. MSC therapy represents a promising new tool for the treatment of skeletal muscle trauma that shows potential for aiding in the prevention of severe functional deficiencies. The logarithmic dose-response relationship demonstrates the association between the number of transplanted cells and the resulting muscle forces, as well as the amount of MSCs required for promoting muscular 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.

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.

Stammzelltherapie der Harninkontinenz

Experimental and clinical studies investigated whether urinary incontinence can be effectively treated with transurethral ultrasound-guided injections of autologous myoblasts and fibroblasts.This new therapy was performed in eight female pigs. It could be shown that the injected cells survived well and that new muscle tissue was formed. Next, 42 patients (29 women, 13 men) suffering from urinary stress incontinence were treated. The fibroblasts were mixed with a small amount of collagen as carrier material and injected into the urethral submucosa to treat atrophies of the mucosa. The myoblasts were directly injected into the rhabdosphincter to reconstruct the muscle and to heal morphological and functional defects. In 35 patients urinary incontinence could be completely cured. In seven patients who had undergone multiple surgical procedures and radiotherapy urinary incontinence improved. No side effects or complications were encountered postoperatively. The experimental as well as the clinical data clearly demonstrate that urinary incontinence can be treated effectively with autologous stem cells. The present data support the conclusion that this new therapeutic concept may represent a very promising treatment modality in the future.

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.

An evaluation of leukaemia inhibitory factor as a potential therapeutic agent in the treatment of muscle disease

The exogenous delivery of growth factors and cytokines is a potential therapeutic strategy to alleviate the degenerative effects of primary inherited myopathies such as Duchenne muscular dystrophy. The mdx mouse diaphragm is a model for examining the progressive degeneration of dystrophic muscle. We have delivered leukaemia inhibitory factor to the mdx diaphragm using slow release alginate gels. Previous studies have reported an improvement in the histology of mdx diaphragms after delivery of leukaemia inhibitory factor in a similar manner, but little attention has been paid to the mechanism by which leukaemia inhibitory factor acts. We have used autoradiography to examine cell proliferation, Evans Blue Dye to examine myofibre damage, and morphometric analysis to examine histology in leukaemia-inhibitory-factor-treated diaphragms and compared them with untreated mdx and normal C57Bl10/ScSn diaphragms. Autoradiography showed that although myoblast proliferation was significantly increased in leukaemia inhibitory factor-treated mdx diaphragms, leukaemia inhibitory factor did not reduce myofibre damage and no histological improvement was observed. The data presented here, while demonstrating a role for leukaemia inhibitory factor in myoblast proliferation, do not support a strong and consistent benefit of leukaemia inhibitory factor on dystrophic muscle in vivo as a means of alleviating the effects of chronic dystrophic muscle degeneration.

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.

Morphometric and dynamic studies of bone changes in hyperthyroidism

Bone biopsies were performed after tetracycline double-labelling by transfixing the right iliac crest in forty hyperthyroid patients. The bone changes in cortical and trabecular bone were determined by simple measurement and point counting on decalcified and undecalcified stained sections. A slight decrease in the amount of cancellous bone was found. The mean cortical width was normal. The amount of osteoid and the length of the osteoid seams were increased, whereas the mean width of osteoid seams was decreased. The cortical osteoclastic activity and porosity were markedly increased. The trabecular osteoclasic activity was moderately increased and the mean size of periosteocytic lacunae was slightly increased. The calcification rate in cancellous bone was increased as were the active calcification surfaces (tetracycline-labelled). The osteoclastic activity in cortical bone was positively correlated to the free thyroxine index and to the urinary calcium and phosphorus excretion. The findings indicate that the bone changes in hyperthyroidism are specific and that thyroid hormone(s) stimulates both bone formation and resorption followed by increased porosity in cortical bone and by mobilization of bone mineral.