Hematopoietic cell transplantation provides an immune-tolerant platform for myoblast transplantation in dystrophic dogs

Decoding the Gene Regulatory Network of Muscle Stem Cells in Mouse Duchenne Muscular Dystrophy: Revelations from Single-Nuclei RNA Sequencing Analysis

The gene dystrophin is responsible for Duchenne muscular dystrophy (DMD), a grave X-linked recessive ailment that results in respiratory and cardiac failure. As the expression of dystrophin in muscle stem cells (MuSCs) is a topic of debate, there exists a limited understanding of its influence on the gene network of MuSCs. This study was conducted with the objective of investigating the effects of dystrophin on the regulatory network of genes in MuSCs. To comprehend the function of dystrophin in MuSCs from DMD, this investigation employed single-nuclei RNA sequencing (snRNA-seq) to appraise the transcriptomic profile of MuSCs obtained from the skeletal muscles of dystrophin mutant mice (DMDmut) and wild-type control mice. The study revealed that the dystrophin mutation caused the disruption of several long non-coding RNAs (lncRNAs), leading to the inhibition of MEG3 and NEAT1 and the upregulation of GM48099, GM19951, and GM15564. The Gene Ontology (GO) enrichment analysis of biological processes (BP) indicated that the dystrophin mutation activated the cell adhesion pathway in MuSCs, inhibited the circulatory system process, and affected the regulation of binding. The study also revealed that the metabolic pathway activity of MuSCs was altered. The metabolic activities of oxidative phosphorylation (OXPHOS) and glycolysis were elevated in MuSCs from DMDmut. In summary, this research offers novel insights into the disrupted gene regulatory program in MuSCs due to dystrophin mutation at the single-cell level.

Comparison of dystrophin expression following gene editing and gene replacement in an aged preclinical DMD animal model

Gene editing has shown promise for correcting or bypassing dystrophin mutations in Duchenne muscular dystrophy (DMD). However, preclinical studies have focused on young animals with limited muscle fibrosis and wasting, thereby favoring muscle transduction, myonuclear editing, and prevention of disease progression. Here, we explore muscle-specific dystrophin gene editing following intramuscular delivery of AAV6:CK8e-CRISPR/SaCas9 in 3- and 8-year-old dystrophic CXMD dogs and provide a qualitative comparison to AAV6:CK8e-micro-dystrophin gene replacement at 6 weeks post-treatment. Gene editing restored the dystrophin reading frame in ∼1.3% of genomes and in up to 4.0% of dystrophin transcripts following excision of a 105-kb mutation containing region spanning exons 6-8. However, resulting dystrophin expression levels and effects on muscle pathology were greater with the use of micro-dystrophin gene transfer. This study demonstrates that our muscle-specific multi-exon deletion strategy can correct a frequently mutated region of the dystrophin gene in an aged large animal DMD model, but underscores that further enhancements are required to reach efficiencies comparable to AAV micro-dystrophin. Our observations also indicate that treatment efficacy and state of muscle pathology at the time of intervention are linked, suggesting the need for additional methodological optimizations related to age and disease progression to achieve relevant clinical translation of CRISPR-based therapies to all DMD patients.

Developments and translational relevance for the canine haematopoietic cell transplantation preclinical model

The development of safe and reliable haematopoietic cell transplantation (HCT) protocols to treat human patients with malignant and non-malignant blood disorders was highly influenced by preclinical studies obtained in random-bred canines. The surmounted barriers included recognizing the crucial importance of histocompatibility matching, establishing long-term donor haematopoietic cell engraftment, preventing graft-vs-host disease and advancing effective conditioning and post-grafting immunosuppression protocols, all of which were evaluated in canines. Recent studies have applied the tolerance inducing potential of HCT to solid organ and vascularized composite tissue transplantation. Several advances in HCT and tolerance induction that were first developed in the canine preclinical model and subsequently applied to human patients are now being recruited into veterinary practice for the treatment of malignant and non-malignant disorders in companion dogs. Here, we review recent HCT advancements attained in the canine model during the past 15 years.

Hydrogel biomaterials and their therapeutic potential for muscle injuries and muscular dystrophies

Muscular diseases such as muscular dystrophies and muscle injuries constitute a large group of ailments that manifest as muscle weakness, atrophy or fibrosis. Although cell therapy is a promising treatment option, the delivery and retention of cells in the muscle is difficult and prevents sustained regeneration needed for adequate functional improvements. Various types of biomaterials with different physical and chemical properties have been developed to improve the delivery of cells and/or growth factors for treating muscle injuries. Hydrogels are a family of materials with distinct advantages for use as cell delivery systems in muscle injuries and ailments, including their mild processing conditions, their similarities to natural tissue extracellular matrix, and their ability to be delivered with less invasive approaches. Moreover, hydrogels can be made to completely degrade in the body, leaving behind their biological payload in a process that can enhance the therapeutic process. For these reasons, hydrogels have shown great potential as cell delivery matrices. This paper reviews a few of the hydrogel systems currently being applied together with cell therapy and/or growth factor delivery to promote the therapeutic repair of muscle injuries and muscle wasting diseases such as muscular dystrophies.

Generation and characterization of integration-free induced pluripotent stem cells from patients with autoimmune disease

Autoimmune diseases (AIDs), a heterogeneous group of immune-mediated disorders, are a major and growing health problem. Although AIDs are currently treated primarily with anti-inflammatory and immunosuppressive drugs, the use of stem cell transplantation in patients with AIDs is becoming increasingly common. However, stem cell transplantation therapy has limitations, including a shortage of available stem cells and immune rejection of cells from nonautologous sources. Induced pluripotent stem cell (iPSC) technology, which allows the generation of patient-specific pluripotent stem cells, could offer an alternative source for clinical applications of stem cell therapies in AID patients. We used nonintegrating oriP/EBNA-1-based episomal vectors to reprogram dermal fibroblasts from patients with AIDs such as ankylosing spondylitis (AS), Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE). The pluripotency and multilineage differentiation capacity of each patient-specific iPSC line was validated. The safety of these iPSCs for use in stem cell transplantation is indicated by the fact that all AID-specific iPSCs are integrated transgene free. Finally, all AID-specific iPSCs derived in this study could be differentiated into cells of hematopoietic and mesenchymal lineages in vitro as shown by flow cytometric analysis and induction of terminal differentiation potential. Our results demonstrate the successful generation of integration-free iPSCs from patients with AS, SS and SLE. These findings support the possibility of using iPSC technology in autologous and allogeneic cell replacement therapy for various AIDs, including AS, SS and SLE.

Amniotic fluid stem cells restore the muscle cell niche in a HSA-Cre, Smn(F7/F7) mouse model

Mutations in the survival of motor neuron gene (SMN1) are responsible for spinal muscular atrophy, a fatal neuromuscular disorder. Mice carrying a homozygous deletion of Smn exon 7 directed to skeletal muscle (HSA-Cre, Smn(F7/F7) mice) present clinical features of human muscular dystrophies for which new therapeutic approaches are highly warranted. Herein we demonstrate that tail vein transplantation of mouse amniotic fluid stem (AFS) cells enhances the muscle strength and improves the survival rate of the affected animals. Second, after cardiotoxin injury of the Tibialis Anterior, only AFS-transplanted mice efficiently regenerate. Most importantly, secondary transplants of satellite cells (SCs) derived from treated mice show that AFS cells integrate into the muscle stem cell compartment and have long-term muscle regeneration capacity indistinguishable from that of wild-type-derived SC. This is the first study demonstrating the functional and stable integration of AFS cells into the skeletal muscle, highlighting their value as cell source for the treatment of muscular dystrophies.

Activation of Notch signaling during ex vivo expansion maintains donor muscle cell engraftment

Transplantation of myogenic stem cells possesses great potential for long‐term repair of dystrophic muscle. However, a single donor muscle biopsy is unlikely to provide enough cells to effectively transplant the muscle mass of a patient affected by muscular dystrophy. Expansion of cells ex vivo using traditional culture techniques significantly reduces engraftment potential. We hypothesized that activation of Notch signaling during ex vivo expansion would maintain donor cell engraftment potential. In this study, we expanded freshly isolated canine muscle‐derived cells on tissue culture plates coated with Delta‐1^ext‐IgG to activate Notch signaling or with human IgG as a control. A model of canine‐to‐murine xenotransplantation was used to quantitatively compare canine muscle cell engraftment and determine whether engrafted donor cells could function as satellite cells in vivo. We show that Delta‐1^ext‐IgG inhibited differentiation of canine muscle‐derived cells and increased the level of genes normally expressed in myogenic precursors. Moreover, cells expanded on Delta‐1^ext‐IgG resulted in a significant increase in the number of donor‐derived fibers, as compared to cells expanded on human IgG, reaching engraftment levels similar to freshly isolated cells. Importantly, cells expanded on Delta‐1^ext‐IgG engrafted to the recipient satellite cell niche and contributed to further regeneration. A similar strategy of expanding human muscle‐derived cells on Notch ligand might facilitate engraftment and muscle regeneration for patients affected with muscular dystrophy. Stem Cells2012;30:2212–2220

Stem cell therapies for muscle disorders

PURPOSE OF REVIEW

This review focuses on stem cell-based therapies to treat skeletal muscle disorders, with a special emphasis on muscular dystrophies.

RECENT FINDINGS

We briefly review previous attempts at cell therapy by the use of donor myoblasts, explaining the likely reasons for the poor clinical results; we then describe the use of the same cells in current promising trials for localized treatments of different diseases of skeletal muscle. Moreover, we discuss important novel findings on muscle stem/progenitor cell biology and their promise for future clinical translation. Preclinical and clinical applications of novel myogenic stem/progenitor cells are also described.

SUMMARY

We summarize several ongoing clinical trials for different muscle disorders and the advances in the understanding of the biology of the myogenic progenitors used in such trials. On the basis of the currently available information, a prediction of developments in the field is proposed.

Inhibition of CD26/DPP-IV enhances donor muscle cell engraftment and stimulates sustained donor cell proliferation

BACKGROUND

Transplantation of myogenic stem cells possesses great potential for long-term repair of dystrophic muscle. In murine-to-murine transplantation experiments, CXCR4 expression marks a population of adult murine satellite cells with robust engraftment potential in mdx mice, and CXCR4-positive murine muscle-derived SP cells home more effectively to dystrophic muscle after intra-arterial delivery in mdx5cv mice. Together, these data suggest that CXCR4 plays an important role in donor cell engraftment. Therefore, we sought to translate these results to a clinically relevant canine-to-canine allogeneic transplant model for Duchenne muscular dystrophy (DMD) and determine if CXCR4 is important for donor cell engraftment.

METHODS

In this study, we used a canine-to-murine xenotransplantation model to quantitatively compare canine muscle cell engraftment, and test the most effective cell population and modulating factor in a canine model of DMD using allogeneic transplantation experiments.

RESULTS

We show that CXCR4 expressing cells are important for donor muscle cell engraftment, yet FACS sorted CXCR4-positive cells display decreased engraftment efficiency. However, diprotin A, a positive modulator of CXCR4-SDF-1 binding, significantly enhanced engraftment and stimulated sustained proliferation of donor cells in vivo. Furthermore, the canine-to-murine xenotransplantation model accurately predicted results in canine-to-canine muscle cell transplantation.

CONCLUSIONS

Therefore, these results establish the efficacy of diprotin A in stimulating muscle cell engraftment, and highlight the pre-clinical utility of a xenotransplantation model in assessing the relative efficacy of muscle stem cell populations.

Canine models of Duchenne muscular dystrophy and their use in therapeutic strategies

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder in which the loss of dystrophin causes progressive degeneration of skeletal and cardiac muscle. Potential therapies that carry substantial risk, such as gene- and cell-based approaches, must first be tested in animal models, notably the mdx mouse and several dystrophin-deficient breeds of dogs, including golden retriever muscular dystrophy (GRMD). Affected dogs have a more severe phenotype, in keeping with that of DMD, so may better predict disease pathogenesis and treatment efficacy. Various phenotypic tests have been developed to characterize disease progression in the GRMD model. These biomarkers range from measures of strength and joint contractures to magnetic resonance imaging. Some of these tests are routinely used in clinical veterinary practice, while others require specialized equipment and expertise. By comparing serial measurements from treated and untreated groups, one can document improvement or delayed progression of disease. Potential treatments for DMD may be broadly categorized as molecular, cellular, or pharmacologic. The GRMD model has increasingly been used to assess efficacy of a range of these therapies. A number of these studies have provided largely general proof-of-concept for the treatment under study. Others have demonstrated efficacy using the biomarkers discussed. Importantly, just as symptoms in DMD vary among patients, GRMD dogs display remarkable phenotypic variation. Though confounding statistical analysis in preclinical trials, this variation offers insight regarding the role that modifier genes play in disease pathogenesis. By correlating functional and mRNA profiling results, gene targets for therapy development can be identified.

Successful bone marrow transplantation in a patient with Diamond-Blackfan anemia with co-existing Duchenne muscular dystrophy: a case report

Introduction

Diamond-Blackfan anemia and Duchenne muscular dystrophy are two rare congenital anomalies. Both anomalies occurring in the same child is extremely rare. Allogeneic hematopoietic stem cell transplantation is a well-established therapy for Diamond-Blackfan anemia. However, in patients with Duchenne muscular dystrophy, stem cell therapy still remains experimental.

Case presentation

We report the case of a nine-year-old boy of north Indian descent with Diamond-Blackfan anemia and Duchenne muscular dystrophy who underwent successful allogeneic hematopoietic stem cell transplantation. He is transfusion-independent, and his Duchenne muscular dystrophy has shown no clinical deterioration over the past 45 months. His creatine phosphokinase levels have significantly decreased to 300 U/L from 14,000 U/L pre-transplant. The patient is 100% donor chimera in the hematopoietic system, and his muscle tissue has shown 8% to 10.4% cells of donor origin.

Conclusion

Our patient's Diamond-Blackfan anemia was cured by allogeneic hematopoietic stem cell transplantation. The interesting clinical observation of a possible benefit in Duchenne muscular dystrophy cannot be ruled out. However, further clinical follow-up with serial muscle biopsies and molecular studies are needed to establish this finding.

[The regulation of UTROPHIN expression by EN1]

To investigate possible factors up-regulating the expression of UTROPHIN, potential regulatory elements in the promoter of the human UTROPHIN was predicted by P-match software and verified by EMSA and ChIP. The mechanism of EN1 regulation of the human UTROPHIN expression was evaluated by RNA interference and real-time PCR analyses. Two potential EN1 binding sites in UTROPHIN promoter region were predicted by P-Match software but only the second site was verified to interact directly with EN1 by EMSA and ChIP. The results from RNA interference and real-time PCR showed that the mRNA level of UTROPHIN increased in HeLa cells after EN1 was knockdowned by siRNA. It indicated that EN1 might be a negative regulatory factor for UTROPHIN. Our study suggested that UTROPHIN might be a new target for DMD therapy.

Clinical use of immunosuppressants in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a degenerative disease primarily affecting voluntary muscles with secondary consequences on heart and breathing muscles. DMD is an X-linked recessive disease that results in the loss of dystrophin, a key muscle protein. Inflammation can play different roles in DMD; it can be a secondary response to muscle degeneration, a primary cause of degeneration, or can contribute to the disease progression. Several immunosuppressants have been used with the aim to reduce the inflammation associated with DMD. Most recently, myoblast transplantation has shown the possibility to restore the dystrophin lack in the DMD patient's muscle fibers and this evidence has emphasized the importance of the use of immunosuppressants and the necessity of studying them and their secondary effects. The aim of this review is to analyze the main immunosuppressants drugs starting from the mdx mice experiments and concluding with the most recent human clinical studies.

Chronic administration of membrane sealant prevents severe cardiac injury and ventricular dilatation in dystrophic dogs

Duchenne muscular dystrophy (DMD) is a fatal disease of striated muscle deterioration caused by lack of the cytoskeletal protein dystrophin. Dystrophin deficiency causes muscle membrane instability, skeletal muscle wasting, cardiomyopathy, and heart failure. Advances in palliative respiratory care have increased the incidence of heart disease in DMD patients, for which there is no cure or effective therapy. Here we have shown that chronic infusion of membrane-sealing poloxamer to severely affected dystrophic dogs reduced myocardial fibrosis, blocked increased serum cardiac troponin I (cTnI) and brain type natriuretic peptide (BNP), and fully prevented left-ventricular remodeling. Mechanistically, we observed a markedly greater primary defect of reduced cell compliance in dystrophic canine myocytes than in the mildly affected mdx mouse myocytes, and this was associated with a lack of utrophin upregulation in the dystrophic canine cardiac myocytes. Interestingly, after chronic poloxamer treatment, the poor compliance of isolated canine myocytes remained evident, but this could be restored to normal upon direct application of poloxamer. Collectively, these findings indicate that dystrophin and utrophin are critical to membrane stability-dependent cardiac myocyte mechanical compliance and that poloxamer confers a highly effective membrane-stabilizing chemical surrogate in dystrophin/utrophin deficiency. We propose that membrane sealant therapy is a potential treatment modality for DMD heart disease and possibly other disorders with membrane defect etiologies.

Characterization of canine embryonic stem cell lines derived from different niche microenvironments

Embryo-derived stem cells hold enormous potential for producing cell-based transplantation therapies, allowing high-throughput drug screening and delineating early embryonic development. However, potential clinical applications must first be tested for safety and efficacy in preclinical animal models. Due to physiological and genetic parity to humans, the domestic dog is widely used as a clinically relevant animal model for cardiovascular, neurodegenerative, orthopedic, and oncologic diseases. Therefore, we established numerous putative canine embryonic stem cell (cESC) lines by immunodissection of the inner cell mass (ICM), which we termed OVC.ID.1-23, and by explant outgrowths from whole canine blastocysts, named OVC.EX.1-16. All characterized lines were immunopositive for OCT4, SOX2, NANOG, SSEA-3, and SSEA-4; displayed high telomerase and alkaline phosphatase (ALP) activities; and were maintained in this state up to 37 passages ( approximately 160 days). Colonies from OVC.EX lines showed classic domed hESC-like morphology surrounded by a ring of fibroblast-like cells, whereas all OVC.ID lines exhibited a mixed cell colony of tightly packed cESCs surrounded by a GATA6+/CDX2- hypoblast-derived support layer. Spontaneous serum-only differentiation without feeder layers demonstrated a strong lineage selection associated with the colony niche type, and not the isolation method. Upon differentiation, cESC lines formed embryoid bodies (EB) comprised of cells representative of all germinal layers, and differentiated into cell types of each layer. Canine ESC lines such as these have the potential to identify differences between embryonic stem cell line derivations, and to develop or to test cell-based transplantation therapies in the dog before attempting human clinical trials.

Derivation and characterization of canine embryonic stem cell lines with in vitro and in vivo differentiation potential

Embryonic stem cells (ESCs) represent permanent cell lines that can be maintained in an undifferentiated state. In an environment that induces differentiation, they form derivatives of the three embryonic germ layers: mesoderm, ectoderm, and endoderm. These characteristics give ESCs great potential for both basic research and clinical applications in the areas of regenerative medicine and tissue engineering. The establishment of ESCs from large animals that model human diseases is of significant importance. We describe the derivation of permanent canine cell lines from preimplantation-stage embryos. Similar to human ESCs, canine ESCs expressed OCT3/4, NANOG, SOX2, SSEA-3, SSEA-4, TRA-1-60, TRA-1-81, and alkaline phosphatase, whereas they expressed very low levels of SSEA-1. They maintained a normal karyotype and morphology typical of undifferentiated ESCs after multiple in vitro passages and rounds of cryopreservation. Plating cells in the absence of a feeder layer, either in attachment or suspension culture, resulted in the formation of embryoid bodies and their differentiation to multiple cell types. In vivo, canine ESCs gave rise to teratomas comprising cell types of all three embryonic germ layers. These cells represent the first pluripotent canine ESC lines with both in vitro and in vivo differentiation potential and offer the exciting possibility of testing the efficacy and safety of ESC-based therapies in large animal models of human disease.

Gene therapy in large animal models of muscular dystrophy

The muscular dystrophies are a group of genetically and phenotypically heterogeneously inherited diseases characterized by progressive muscle wasting, which can lead to premature death in severe forms such as Duchenne muscular dystrophy (DMD). In many cases they are caused by the absence of proteins that are critical components of the dystrophin-glycoprotein complex, which links the cytoskeleton and the basal lamina. There is no effective treatment for these disorders at present, but several novel strategies for replacing or repairing the defective gene are in development, with early encouraging results from animal models. We review these strategies, which include the use of stem cells of different tissue origins, gene replacement therapies mediated by various viral vectors, and transcript repair treatments using exon skipping strategies. We comment on their advantages and on limitations that must be overcome before successful application to human patients. Our focus is on studies in a clinically relevant large canine model of DMD. Recent advances in the field suggest that effective therapies for muscular dystrophies are on the horizon. Because of the complex nature of these diseases, it may be necessary to combine multiple approaches to achieve a successful treatment.

The value of mammalian models for duchenne muscular dystrophy in developing therapeutic strategies

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy. There is no effective treatment and patients typically die in approximately the third decade. DMD is an X-linked recessive disease caused by mutations in the dystrophin gene. There are three mammalian models of DMD that have been used to understand better the pathogenesis of disease and develop therapeutic strategies. The mdx mouse is the most widely used model of DMD that displays some features of muscle degeneration, but the pathogenesis of disease is comparatively mild. The severity of disease in mice lacking both dystrophin and utrophin is similar to DMD, but one has to account for the discrete functions of utrophin. Canine X-linked muscular dystrophy (cxmd) is the best representation of DMD, but the phenotype of the most widely used golden retriever (GRMD) model is variable, making functional endpoints difficult to ascertain. Although each mammalian model has its limitations, together they have been essential for the development of several treatment strategies for DMD that target dystrophin replacement, disease progression, and muscle regeneration.