Extracorporeal circulation as a new experimental pathway for myoblast implantation in mdx mice

Myoblast Therapy: From Bench to Bedside

Myoblasts are defined as stem cells containing skeletal muscle cell precursors. A decade of experimental work has revealed many properties of myoblasts, including the stability of resulting hybrid myofibers without immune suppression, the persistence of transgene expression, and the lack of tumorigenicity. Early phase clinical trials also showed that myoblast-based therapy is a promising approach for many intractable clinical conditions, including both muscle-related and non-muscle-related diseases. The potential application of myoblast therapy may be in the treatment of genetic muscle diseases, cardiomyocyte damaged heart diseases, and urinary incontinence. This review will provide an overview of myoblast biology, along with discussion of the potential application in clinical medicine. In addition, problems in current myoblast therapy and possible future improvements will be addressed.

Skeletal muscle satellite cell migration to injured tissue measured with 111In-oxine and high-resolution SPECT imaging

The delivery of adult skeletal muscle stem cells, called satellite cells, to several injured muscles via the circulation would be useful, however, an improved understanding of cell fate and biodistribution following their delivery is important for this goal to be achieved. The objective of this study was to evaluate the ability of systemically delivered satellite cells to home to injured skeletal muscle using single-photon emission computed tomography (SPECT) imaging of (111)In-labeled satellite cells. Satellite cells labeled with (111)In-oxine and green fluorescent protein (GFP) were injected intravenously after bupivicaine-induced injury to the tibialis anterior muscle. Animals were imaged with a high-resolution SPECT system called FastSPECT II for up to 7 days after transplantation. In vivo FastSPECT II imaging demonstrated a three to five-fold greater number of transplanted satellite cells in bupivicaine-injured muscle as compared to un-injured muscle after transplantation; a finding that was verified through autoradiograph analysis and quantification of GFP expression. Satellite cells also accumulated in other organs including the lung, liver, and spleen, as determined by biodistribution measurements. These data support the ability of satellite cells to home to injured muscle and support the use of SPECT and autoradiograph imaging techniques to track systemically transplanted (111)In labeled satellite cells in vivo, and suggest their homing may be improved by reducing their entrapment in filter organs.

Evaluation of Sca-1 and c-Kit As Selective Markers for Muscle Remodelling by Nonhemopoietic Bone Marrow Cells

Bone marrow (BM)-derived cells (BMCs) have demonstrated a myogenic tissue remodeling capacity. However, because the myoremodeling is limited to approximately 1%-3% of recipient muscle fibers in vivo, there is disagreement regarding the clinical relevance of BM for therapeutic application in myodegenerative conditions. This study sought to determine whether rare selectable cell surface markers (in particular, c-Kit) could be used to identify a BMC population with enhanced myoremodeling capacity. Dystrophic mdx muscle remodeling has been achieved using BMCs sorted by expression of stem cell antigen-1 (Sca-1). The inference that Sca-1 is also a selectable marker associated with myoremodeling capacity by muscle-derived cells prompted this study of relative myoremodeling contributions from BMCs (compared with muscle cells) on the basis of expression or absence of Sca-1. We show that myoremodeling activity does not differ in cells sorted solely on the basis of Sca-1 from either muscle or BM. In addition, further fractionation of BM to a more mesenchymal-like cell population with lineage markers and CD45 subsequently revealed a stronger selectability of myoremodeling capacity with c-Kit/Sca-1 (p < .005) than with Sca-1 alone. These results suggest that c-Kit may provide a useful selectable marker that facilitates selection of cells with an augmented myoremodeling capacity derived from BM and possibly from other nonmuscle tissues. In turn, this may provide a new methodology for rapid isolation of myoremodeling capacities from muscle and nonmuscle tissues. Disclosure of potential conflicts of interest is found at the end of this article.

Human umbilical cord blood cells differentiate into muscle in sjl muscular dystrophy mice

Limb girdle muscular dystrophy type 2B form (LGMD-2B) and Miyoshi myopathy (MM) are both caused by mutations in the dysferlin (dysf) gene. In this study, we used dysferlin-deficient sjl mice as a mouse model to study cell therapy for LGMD-2B and MM. A single-blind study evaluated the therapeutic potential of human umbilical cord blood (HUCB) as a source of myogenic progenitor stem cells. Three groups of donor cells were used: unfractionated mononuclear HUCB cells, HUCB subfractionated to enrich for cells that were negative for lineage surface markers (LIN(-)) and substantially enriched for the CD34 surface marker (CD34(+)), and irradiated control spleen cells. We administrated 1 x 10(6) donor cells to each animal intravenously and euthanized them at different time points (1-12 weeks) after transplantation. All animals were immunosuppressed (FK506 and leflunomide) from the day before the injection until the time of euthanasia. Immunohistochemical analyses documented that a small number of human cells from the whole HUCB and LIN(-)CD34(+/-)-enriched HUCB subgroups engraft in the recipient muscle to express both dysferlin and human-specific dystrophin at 12 weeks after transplantation. We conclude that myogenic progenitor cells are present in the HUCB, that they can disseminate into muscle after intravenous administration, and that they are capable of myogenic differentiation in host muscle.

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.

Chemotactic factors enhance myogenic cell migration across an endothelial monolayer

Recent reports revealed that myogenic progenitors, derived from either bone marrow or muscle can migrate into muscle tissue and participate in myofiber regeneration, when injected in the peripheral circulation. This observation might open a new strategy for the treatment of muscular dystrophies. The signals involved in myoblast recruitment from circulation are at present poorly understood. To investigate myoblast migration we used a transwell assay in which murine myoblasts and myogenic cell lines were seeded on microporous membrane covered by an endothelial monolayer and chemotactic factors were added in the lower chamber. We demonstrated that myoblasts are able to cross the endothelium and that this process can be modulated. In particular among tested factors, we observed a gradient of chemotactic activity as follows: HGF >> RANTES > PDGF-A > PDGF-B > FGF >> TNF-alpha > IFN-gamma > EGF. Endothelial and myoblast expression of Pax3 (a transcription factor expressed by embryonic migrating myogenic cells) and cytokine transcripts (TNF-alpha, IFN-gamma) was also monitored either at the basal level and after transmigration. We observed increased Pax3 expression after interaction of C2C12 myoblasts with endothelial cells. We consider that any new report elucidating the molecular signals involved in myoblast migration may be useful toward the development of systemic cellular-mediated gene therapy of muscle diseases.

Life and death of a cardiac myocyte: principles of cellular biology

If the future of extracorporeal circulation is to include approaches to enhance localized or widespread distribution of cells, and/or gene transfer for augmentation of cardiac function, it is imperative that we gain an increased understanding of the mechanisms that define the cardiac myocyte phenotype. The purpose of this paper is to review the natural history of the cardiac myocyte. A variety of signals determine the cellular processes that characterize birth, growth, differentiation and death of cardiomyocytes. Examined here are primary aspects of the molecular genetics of growth and development, including signal transduction, protein phosphorylation, the cell division cycle, and transcriptional activation. This review is intended to be an update on insights into molecular aspects of the cell, with emphasis on gene expression during cardiac myogenesis and a discussion of its relevance to the field of extracorporeal circulation. In addition, the current status of research in myogenesis is presented.

Intracellular delivery of a Tat-eGFP fusion protein into muscle cells

The Tat protein from HIV-1, when fused with heterologous proteins or peptides, can traverse biological membranes in a process called "protein transduction," delivering its cargo into cells. A Tat-eGFP fusion protein was purified from bacteria to study the transduction kinetics of Tat fusion proteins into cultured myoblasts and in the muscle tissue. Correctly folded Tat-eGFP reaches a maximum intracellular level in nearly 30 min, while its endogenous fluorescence is first detected only after 14 h. The nuclear localization signal from the basic domain of Tat was not sufficient to confer nuclear localization to Tat-eGFP, suggesting that the nuclear import pathway used by the exogenously added Tat-eGFP might be sensitive to the folding state of eGFP. In mice, the direct delivery to the muscle tissue using subcutaneous injections or the intra-arterial pathway led to few positive fibers in the muscle periphery or surrounding the blood vessels. Muscles injected with Tat-eGFP showed intense labeling of the extracellular matrix (ECM), suggesting that, although Tat fusion proteins can transduce muscle fibers, their binding by components of the ECM surrounding myofibers could interfere with the intracellular transduction process.