Stem cell based therapies to treat muscular dystrophy

CD133(+) cells isolated from various sources and their role in future clinical perspectives

BACKGROUND

CD133 is a member of a novel family of cell surface glycoproteins. Initially, the expression of CD133 antigen was seen only in the hematopoietic derived CD34(+) stem cells. At present, CD133 expression is demonstrated in undifferentiated epithelium, different types of tumors and myogenic cells. CD133(+) neurosphere cells isolated from brain are able to differentiate into both neurons and glial cells. These data suggested that CD133 could be a specific marker for various stem and progenitor cell populations.

OBJECTIVES

The main goal would be to describe the role for CD133 as a marker of stem cells able to engraft and differentiate, to form functional non-hematopoietic adult lineages and contribute to disease amelioration via tissue regeneration.

RESULTS/CONCLUSION

In conclusion, since the rise of CD133 antigen as a suitable stem cell marker, the possible use of CD133(+) stem cells in therapeutic applications has opened a new promising field in the treatment of degenerating diseases. The human circulating cells expressing the CD133 antigen behave as a stem cell population capable of commitment to hematopoietic, endothelial and myogenic lineages. CD133 cell therapy may represent a promising treatment for many diseases.

Stem cell therapies to treat muscular dystrophy: progress to date

Muscular dystrophies are heritable, heterogeneous neuromuscular disorders and include Duchenne and Becker muscular dystrophies (DMD and BMD, respectively). DMD patients exhibit progressive muscle weakness and atrophy followed by exhaustion of muscular regenerative capacity, fibrosis, and eventually disruption of the muscle tissue architecture. In-frame mutations in the dystrophin gene lead to expression of a partially functional protein, resulting in the milder BMD. No effective therapies are available at present. Cell-based therapies have been attempted in an effort to promote muscle regeneration, with the hope that the host cells would repopulate the muscle and improve muscle function and pathology. Injection of adult myoblasts has led to the development of new muscle fibers, but several limitations have been identified, such as poor cell survival and limited migratory ability. As an alternative to myoblasts, stem cells were considered preferable for therapeutic applications because of their capacity for self-renewal and differentiation potential. In recent years, encouraging results have been obtained with adult stem cells to treat human diseases such as leukemia, Parkinson's disease, stroke, and muscular dystrophies. Embryonic stem cells (ESCs) can be derived from mammalian embryos in the blastocyst stage, and because they can differentiate into a wide range of specialized cells, they hold potential for use in treating almost all human diseases. Several ongoing studies focus on this possibility, evaluating differentiation of specific cell lines from human ESCs (hESCs) as well as the potential tumorigenicity of hESCs. The most important limitation with using hESCs is that it requires destruction of human blastocysts or embryos. Conversely, adult stem cells have been identified in various tissues, where they serve to maintain, generate, and replace terminally differentiated cells within their specific tissue as the need arises for cell turnover or from tissue injury. Moreover, these cells can participate in regeneration of more than just their specific tissue type. Here we describe multiple types of muscle- and fetal-derived myogenic stem cells, their characterization, and their possible use in treating muscular dystrophies such as DMD and BMD. We also emphasize that the most promising possibility for the management and therapy of DMD and BMD is a combination of different approaches, such as gene and stem cell therapy.

Regulatory factors and cell populations involved in skeletal muscle regeneration

Skeletal muscle regeneration is a complex process, which is not yet completely understood. Satellite cells, the skeletal muscle stem cells, become activated after trauma, proliferate, and migrate to the site of injury. Depending on the severity of the myotrauma, activated satellite cells form new multinucleated myofibers or fuse to damaged myofibers. The specific microenvironment of the satellite cells, the niche, controls their behavior. The niche contains several components that maintain satellite cells quiescence until they are activated. In addition, a great diversity of stimulatory and inhibitory growth factors such as IGF-1 and TGF-beta1 regulate their activity. Donor-derived satellite cells are able to improve muscle regeneration, but their migration through the muscle tissue and across endothelial layers is limited. Less than 1% of their progeny, the myoblasts, survive the first days upon intra-muscular injection. However, a range of other multipotent muscle- and non-muscle-derived stem cells are involved in skeletal muscle regeneration. These stem cells can occupy the satellite cell niche and show great potential for the treatment of skeletal muscle injuries and diseases. The aim of this review is to discuss the niche factors, growth factors, and other stem cells, which are involved in skeletal muscle regeneration. Knowledge about the factors regulating satellite cell activity and skeletal muscle regeneration can be used to improve the treatment of muscle injuries and diseases.

Use of Encapsulated Stem Cells to Overcome the Bottleneck of Cell Availability for Cell Therapy Approaches

Nowadays cell-based therapy is rarely in clinical practice because of the limited availability of appropriate cells. To apply cells therapeutically, they must not cause any immune response wherefore mainly autologous cells have been used up to now. The amount of vital cells in patients is limited, and under certain circumstances in highly degenerated tissues no vital cells are left. Moreover, the extraction of these cells is connected with additional surgery; also the expansion in vitro is difficult. Other approaches avoid these problems by using allo-or even xenogenic cells. These cells are more stable concerning their therapeutic behavior and can be produced in stock. To prevent an immune response caused by these cells, cell encapsulation (e.g. with alginate) can be performed. Certain studies showed that encapsulated allo- and xenogenic cells achieve promising results in treatment of several diseases. For such cell therapy approaches, stem cells, particularly mesenchymal stem cells, are an interesting cell source. This review deals on the one hand with the use of encapsulated cells, especially stem cells, in cell therapy and on the other hand with bioreactor systems for the expansion and differentiation of mesenchymal stem cells in reproducible and sufficient amounts for potential clinical use.

Repairing skeletal muscle: regenerative potential of skeletal muscle stem cells

Skeletal muscle damaged by injury or by degenerative diseases such as muscular dystrophy is able to regenerate new muscle fibers. Regeneration mainly depends upon satellite cells, myogenic progenitors localized between the basal lamina and the muscle fiber membrane. However, other cell types outside the basal lamina, such as pericytes, also have myogenic potency. Here, we discuss the main properties of satellite cells and other myogenic progenitors as well as recent efforts to obtain myogenic cells from pluripotent stem cells for patient-tailored cell therapy. Clinical trials utilizing these cells to treat muscular dystrophies, heart failure, and stress urinary incontinence are also briefly outlined.

Cell based therapy for Duchenne muscular dystrophy

Mutations in the dystrophin gene cause an X-linked genetic disorder: Duchenne muscular dystrophy (DMD). Stem cell therapy is an attractive method to treat DMD because a small number of cells are required to obtain a therapeutic effect. Here, we discussed about multiple types of myogenic stem cells and their possible use to treat DMD. The identification of a stem cell population providing efficient muscle regeneration is critical for the progression of cell therapy for DMD. We speculated that the most promising possibility for the treatment of DMD is a combination of different approaches, such as gene and stem cell therapy.

Mesenchymal stem cells: emerging therapy for Duchenne muscular dystrophy

Multipotent cells that can give rise to bone, cartilage, fat, connective tissue, and skeletal and cardiac muscle are termed mesenchymal stem cells. These cells were first identified in the bone marrow, distinct from blood-forming stem cells. Based on the embryologic derivation, availability, and various pro-regenerative characteristics, research exploring their use in cell therapy shows great promise for patients with degenerative muscle diseases and a number of other conditions. In this review, the authors explore the potential for mesenchymal stem cell therapy in the emerging field of regenerative medicine with a focus on treatment for Duchenne muscular dystrophy.

Sarcoglycanopathies: molecular pathogenesis and therapeutic prospects

Sarcoglycanopathies are a group of autosomal recessive muscle-wasting disorders caused by genetic defects in one of four cell membrane glycoproteins, alpha-, beta-, gamma- or delta-sarcoglycan. These four sarcoglycans form a subcomplex that is closely linked to the major dystrophin-associated protein complex, which is essential for membrane integrity during muscle contraction and provides a scaffold for important signalling molecules. Proper assembly, trafficking and targeting of the sarcoglycan complex is of vital importance, and mutations that severely perturb tetramer formation and localisation result in sarcoglycanopathy. Gene defects in one sarcoglycan cause the absence or reduced concentration of the other subunits. Most genetic defects generate mutated proteins that are degraded through the cell's quality control system; however, in many cases, conformational modifications do not affect the function of the protein, yet it is recognised as misfolded and prematurely degraded. Recent evidence shows that misfolded sarcoglycans could be rescued to the cell membrane by assisting their maturation along the ER secretory pathway. This review summarises the etiopathogenesis of sarcoglycanopathies and highlights the quality control machinery as a potential pharmacological target for therapy of these genetic disorders.

Genetic control of wayward pluripotent stem cells and their progeny after transplantation

The proliferative capacity of pluripotent stem cells and their progeny brings a unique aspect to therapeutics, in that once a transplant is initiated the therapist no longer has control of the therapy. In the context of the recent FDA approval of a human ESC trial and report of a neuronal-stem-cell-derived tumor in a human trial, strategies need to be developed to control wayward pluripotent stem cells. Here, we focus on one approach: direct genetic modification of the cells prior to transplantation with genes that can prevent the adverse events and/or eliminate the transplanted cells and their progeny.

Non-canonical role for the TRAIL receptor DR5/FADD/caspase pathway in the regulation of MyoD expression and skeletal myoblast differentiation

We report herein that the TRAIL receptor DR5/FADD/caspase pathway plays a role in skeletal myoblast differentiation through modulation of the expression of the muscle regulatory transcription factor MyoD. Specifically, treatment with the selective caspase 3 inhibitor DEVD-fmk or the selective caspase 8 inhibitor IETD-fmk in growth media (GM), prior to culture in differentiation media (DM), inhibited differentiation. Further, this treatment resulted in decreased levels of MyoD message and protein. We next explored a role for the TRAIL receptor DR5/FADD pathway. We found that expression of either dominant negative (dn) FADD or dominant negative (dn) DR5 also resulted in decreased levels of MyoD mRNA and protein and blocked differentiation. This decreased level of MyoD mRNA was not a consequence of altered stability. Treatment with TSA, an inhibitor of histone deacetylases (HDACs), allowed MyoD expression in myoblasts expressing dnDR5. Finally, acetylation of histones associated with the distal regulatory region (DRR) enhancer of MyoD was decreased in myoblasts expressing dnDR5. Thus, our data suggests a non-canonical role for the TRAIL receptor/FADD pathway in the regulation of MyoD expression and skeletal myoblast differentiation.

Oral health considerations in muscular dystrophies

Muscular dystrophies (MD) are a heterogeneous group of inherited neuromuscular disorders characterized by muscle necrosis and progressive muscle weakness. It is important for oral healthcare providers to be familiar with MD as special considerations are necessary to provide appropriate and safe dental care for these medically complex patients. This article briefly reviews the more common types of MD, namely, Duchenne MD, Becker MD, Emery-Dreifuss MD, facioscapulo-humeral MD, limb-girdle MD, oculopharyngeal MD, and myotonic dystrophy. Aspects of their epidemiology, pathophysiology, clinical presentation, diagnosis, and medical management as well as oral health considerations are discussed.

Effective rescue of dystrophin improves cardiac function in dystrophin-deficient mice by a modified morpholino oligomer

Antisense oligonucleotide-mediated exon skipping is able to correct out-of-frame mutations in Duchenne muscular dystrophy and restore truncated yet functional dystrophins. However, its application is limited by low potency and inefficiency in systemic delivery, especially failure to restore dystrophin in heart. Here, we conjugate a phosphorodiamidate morpholino oligomer with a designed cell-penetrating peptide (PPMO) targeting a mutated dystrophin exon. Systemic delivery of the novel PPMO restores dystrophin to almost normal levels in the cardiac and skeletal muscles in dystrophic mdx mouse. This leads to increase in muscle strength and prevents cardiac pump failure induced by dobutamine stress in vivo. Muscle pathology and function continue to improve during the 12-week course of biweekly treatment, with significant reduction in levels of serum creatine kinase. The high degree of potency of the oligomer in targeting all muscles and the lack of detectable toxicity and immune response support the feasibility of testing the novel oligomer in treating Duchenne muscular dystrophy patients.

Bone marrow side population cells are enriched for progenitors capable of myogenic differentiation

Although the contribution of bone marrow-derived cells to regenerating skeletal muscle has been repeatedly documented, there remains considerable debate as to whether this incorporation is exclusively a result of inflammatory cell fusion to regenerating myofibers or whether certain populations of bone marrow-derived cells have the capacity to differentiate into muscle. The present study uses a dual-marker approach in which GFP(+) cells were intravenously transplanted into lethally irradiated beta-galactosidase(+) recipients to allow for simple determination of donor and host contribution to the muscle. FACS analysis of cardiotoxin-damaged muscle revealed that CD45(+) bone-marrow side-population (SP) cells, a group enriched in hematopoietic stem cells, can give rise to CD45(-)/Sca-1(+)/desmin(+) cells capable of myogenic differentiation. Moreover, after immunohistochemical examination of the muscles of both SP- and whole bone marrow-transplanted animals, we noted the presence of myofibers composed only of bone marrow-derived cells. Our findings suggest that a subpopulation of bone marrow SP cells contains precursor cells whose progeny have the potential to differentiate towards a muscle lineage and are capable of de novo myogenesis following transplantation and initiation of muscle repair via chemical damage.

The emerging biology of satellite cells and their therapeutic potential

Adult skeletal muscle contains an abundant and highly accessible population of muscle stem and progenitor cells called satellite cells. The primary function of satellite cells is to mediate postnatal muscle growth and repair. Owing to their availability and remarkable capacity to regenerate damaged muscle, satellite cells and their descendent myoblasts have been considered as powerful candidates for cell-based therapies to treat muscular dystrophies and other neuromuscular diseases. However, regenerative medicine in muscle repair requires a thorough understanding of, and the ability to manipulate, the molecular mechanisms that control the proliferation, self-renewal and myogenic differentiation of satellite cells. Here, we review the latest advances in our current understanding of the quiescence, activation, proliferation and self-renewal of satellite cells and the challenges in the development of satellite cell-based regenerative medicine.

Novel application of flow cytometry: determination of muscle fiber types and protein levels in whole murine skeletal muscles and heart

Conventional methods for measuring proteins within muscle samples such as immunohistochemistry and western blot analysis can be time consuming, labor intensive and subject to sampling errors. We have developed flow cytometry techniques to detect proteins in whole murine heart and skeletal muscle. Flow cytometry and immunohistochemistry were performed on quadriceps and soleus muscles from male C57BL/6J, BALB/c, CBA and mdx mice. Proteins including actins, myosins, tropomyosin and alpha-actinin were detected via single staining flow cytometric analysis. This correlated with immunohistochemistry using the same antibodies. Muscle fiber types could be determined by dual labeled flow cytometry for skeletal muscle actin and different myosins. This showed similar results to immunohistochemistry for I, IIA and IIB myosins. Flow cytometry of heart samples from C57BL/6J and BALB/c mice dual labeled with cardiac and skeletal muscle actin antibodies demonstrated the known increase in skeletal actin protein in BALB/c hearts. The membrane-associated proteins alpha-sarcoglycan and dystrophin could be detected in C57BL/6J mice, but were decreased or absent in mdx mice. With the ability to label whole muscle samples simultaneously with multiple antibodies, flow cytometry may have advantages over conventional methods for certain applications, including assessing the efficacy of potential therapies for muscle diseases.

Activated beta-catenin induces myogenesis and inhibits adipogenesis in BM-derived mesenchymal stromal cells

BACKGROUND

Mesenchymal stromal cells (MSC) have been thought to be attractive candidates for the treatment of degenerative muscle diseases. However, little is known about the molecular mechanisms governing the myogenic differentiation in MSC. As the Wnt signaling pathway has been associated with myogenesis in embryogenesis and post-natal muscle regeneration, we hypothesized that the Wnt signaling pathway may be involved in governing the myogenic differentiation in MSC.

METHODS

Primary MSC were isolated from Sprague-Dawley rats and expanded in proliferation medium. The rMSC were transfected with a constitutively active hbeta-catenin (S37A) plasmid or control vector by Lipofectamine followed by G418 selection. The transfected rMSC were grown to 80% confluence and then cultured in myogenic or adipogenic differentiation medium. Cells were characterized by light microscopy, immunofluorescence and RT-PCR at different time points after myogenic or adipogenic introduction.

RESULTS

Ectopic expression of activated beta-catenin located primarily in the nucleus and activated transcription in rMSC. Overexpression of stabilized beta-catenin induced 27.1 +/- 3.91% rMSC forming long multinucleated cells expressing MyoD, myogenin, desmin and myosin heavy chain (MHC) via evoking the expression of skeletal muscle-specific transcription factors. In addition, overexpression of activated beta-catenin inhibited the adipogenic differentiation in rMSC through down-regulated expressions of C/EBPalpha and PPARgamma.

DISCUSSION

To our knowledge, this is the first evidence that activated beta-catenin can induce myogenic differentiation in rMSC. The ability of stabilized beta-catenin to induce myogenic differentiation in rMSC may allow for its therapeutic application.

New therapies for Duchenne muscular dystrophy: challenges, prospects and clinical trials

Muscular dystrophies primarily affect skeletal muscle. Mutations in a large number of genes, mainly encoding cytoskeletal proteins, cause different forms of dystrophy that compromise patient mobility and quality of life, and in the most severe cases lead to complete paralysis and premature death. Although muscular dystrophies still lack an effective therapy, several novel strategies are entering or are ready to enter clinical trials. Here we review the main experimental strategies, namely drug, gene and cell therapies, outlining their goals and limitations. We also provide an update of ongoing or planned clinical trials based on these strategies.

Wnt3a signaling promotes proliferation, myogenic differentiation, and migration of rat bone marrow mesenchymal stem cells

AIM

To investigate the effects of the wingless-related MMTV integration site 3A (Wnt3a) signaling on the proliferation, migration, and the myogenic and adipogenic differentiation of rat bone marrow mesenchymal stem cells (rMSC).

METHODS

Primary MSC were isolated and cultured from Sprague-Dawley rats and characterized by flow cytometry. Mouse L cells were transfected with Wnt3a cDNA, and conditioned media containing active Wnt3a proteins were prepared. Cell proliferation was evaluated by cell count and 5-bromodeoxyuridine incorporation assay. The migration of rMSC was performed by using a transwell migration and wound healing assay. The myogenic and adipogenic differentiation in rMSC were examined by light microscopy, immunofluorescence, and RT-PCR at different time points after myogenic or adipogenic introduction.

RESULTS

Wnt3a signaling induced beta-catenin nuclear translocation and activated the Wnt pathway in rMSC. In the presence of Wnt3a, rMSC proliferated more rapidly than the control cells, keeping their differentiation potential. Moreover, Wnt3a signaling induced 2.62% and 3.76% of rMSC-expressed desmin and myosin heavy chain after being cultured in myogenic medium. The myogenic differentiation genes, including Pax7, MyoD, Myf5, Myf4, and myogenin, were activated after Wnt3a treatment. On the other hand, Wnt3a inhibited the adipogenic differentiation in rMSC through the downregulated expression of CCAAT/enhancer-binding protein alpha (C/EBPalpha) and peroxisome proliferator-activated receptor gamma (PPARgamma). Furthermore, Wnt3a promoted the migration capacity of rMSC.

CONCLUSION

The results indicate that Wnt3a signaling can induce myogenic differentiation in rMSC. Wnt3a signaling is also involved in the regulation of the proliferation and migration of rMSC. These results could provide a rational foundation for cell-based tissue repair in humans.

Activating muscle stem cells: therapeutic potential in muscle diseases

PURPOSE OF REVIEW

The satellite cell is the principal muscle stem cell. Recent research, however, has highlighted new stem cell sources that, once activated in the muscle tissue, can participate in muscle regeneration. This article reviews the state of research on stem cell populations that have potential for treatment of muscular dystrophies.

RECENT FINDINGS

Despite recent findings about the stem cell character of satellite cells and their in-vivo myogenic potential, limitations related to muscle precursor cell transfer therapy have encouraged the investigation of stem cell sources other than satellite cells. Current research is focused on identifying the best stem cell in the endothelial compartment, which is able to be systemically delivered to reach all the muscles and to contribute to widespread muscle regeneration within these muscles.

SUMMARY

Current results highlight many possible stem cell sources for stem cell therapy of muscle diseases, and work is ongoing to identify the most effective candidate that is able to robustly regenerate muscle tissue and to functionally repopulate the muscle stem cell compartment.

Dissociated flexor digitorum brevis myofiber culture system—A more mature muscle culture system

Considerable knowledge regarding skeletal muscle physiology and disease has been gleaned from cultured myoblastic cell lines or isolated primary myoblasts. Such muscle cultures can be induced to differentiate into multinucleated myotubes that become striated. However they in general do not fully mature and therefore do not model mature muscle. Contrastingly, fresh and cultured dissociated adult mouse flexor digitorum brevis (FDB) myofibers have been studied for many years. We aimed to investigate the possibility of using the FDB myofiber culture system for drug screening and thus long-term cultures of enzymatically dissociated FDB myofibers were established in 96-well plates. Ca2+ handling experiments were used to investigate the functional state of the myofibers. Imaging of intracellular Ca2+ during electric field stimulation revealed that calcium handling was maintained throughout the culture period of at least 8 days. Western blot and immunostaining analysis showed that the FDB cultures maintained expression of mature proteins throughout the culture period, including alpha-sarcoglycan, dystrophin, fast myosin heavy chain and skeletal muscle alpha-actin. The high levels of the fetal proteins cardiac alpha-actin and utrophin, seen in cultured C2C12 myotubes, were absent in the FDB cultures. The expression of developmentally mature proteins and the absence of fetal proteins, in addition to the maintenance of normal calcium handling, highlights the FDB culture system as a more mature and perhaps more relevant culture system for the study of adult skeletal muscle function. Moreover, it may be a useful system for screening therapeutic agents for the treatment of skeletal muscle disorders.