Isolation and Characterization of Mesoangioblasts from Facioscapulohumeral Muscular Dystrophy Muscle Biopsies

The use of umbilical cord-derived mesenchymal stem cells in patients with muscular dystrophies: Results from compassionate use in real-life settings

Muscular dystrophies are genetically determined progressive diseases with no cause‐related treatment and limited supportive treatment. Although stem cells cannot resolve the underlying genetic conditions, their wide‐ranging therapeutic properties may ameliorate the consequences of the involved mutations (oxidative stress, inflammation, mitochondrial dysfunction, necrosis). In this study, we administered advanced therapy medicinal product containing umbilical cord‐derived mesenchymal stem cells (UC‐MSCs) to 22 patients with muscular dystrophies. Patients received one to five intravenous and/or intrathecal injections per treatment course in up to two courses every 2 months. Four standard doses of 10, 20, 30, or 40 × 10⁶ UC‐MSCs per injection were used; the approximate dose per kilogram was 1 × 10⁶ UC‐MSCs. Muscle strength was measured with a set of CQ Dynamometer computerized force meters (CQ Elektronik System, Czernica, Poland). Statistical analysis of muscle strength in the whole group showed significant improvement in the right upper limb (+4.0 N); left hip straightening (+4.5 N) and adduction (+0.5 N); right hip straightening (+1.0 N), bending (+7.5 N), and adduction (+2.5 N); right knee straightening (+8.5 N); left shoulder revocation (+13.0 N), straightening (+5.5 N), and bending (+6.5 N); right shoulder adduction (+3.0 N), revocation (+10.5 N), and bending (+5 N); and right elbow straightening (+9.5 N); all these differences were statistically significant. In six patients (27.3%) these changes led to improvement in gait analysis or movement scale result. Only one patient experienced transient headache and lower back pain after the last administration. In conclusion, UC‐MSC therapy may be considered as a therapeutic option for these patients.

Stem cell therapy for muscular dystrophies

Muscular dystrophies are a heterogeneous group of genetic diseases, characterized by progressive degeneration of skeletal and cardiac muscle. Despite the intense investigation of different therapeutic options, a definitive treatment has not been developed for this debilitating class of pathologies. Cell-based therapies in muscular dystrophies have been pursued experimentally for the last three decades. Several cell types with different characteristics and tissues of origin, including myogenic stem and progenitor cells, stromal cells, and pluripotent stem cells, have been investigated over the years and have recently entered in the clinical arena with mixed results. In this Review, we do a roundup of the past attempts and describe the updated status of cell-based therapies aimed at counteracting the skeletal and cardiac myopathy present in dystrophic patients. We present current challenges, summarize recent progress, and make recommendations for future research and clinical trials.

Proteomics of Muscle Microdialysates Identifies Potential Circulating Biomarkers in Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is caused by a complex epigenetic mechanism finally leading to the misexpression of DUX4 in skeletal muscle. Detecting DUX4 and quantifying disease progression in FSHD is extremely challenging, thus increasing the need for surrogate biomarkers. We applied a shotgun proteomic approach with two different setups to analyze the protein repertoire of interstitial fluids obtained from 20 muscles in different disease stages classified by magnetic resonance imaging (MRI) and serum samples from 10 FSHD patients. A total of 1156 proteins were identified in the microdialysates by data independent acquisition, 130 of which only found in muscles in active disease stage. Proteomic profiles were able to distinguish FSHD patients from controls. Two innate immunity mediators (S100-A8 and A9) and Dermcidin were upregulated in muscles with active disease and selectively present in the sera of FSHD patients. Structural muscle and plasminogen pathway proteins were downregulated. Together with the upstream inhibition of myogenic factors, this suggests defective muscle regeneration and increased fibrosis in early/active FSHD. Our MRI targeted exploratory approach confirmed that inflammatory response has a prominent role, together with impaired muscle regeneration, before clear muscle wasting occurs. We also identified three proteins as tissue and possibly circulating biomarkers in FSHD.

Biomedical applications of muscle-derived stem cells: from bench to bedside

INTRODUCTION

Skeletal muscle-derived stem cells (Sk-MDSCs) are considered promising sources of adult stem cell therapy. Skeletal muscle comprises approximately 40-50% of the total body mass with marked potential for postnatal adaptive response, such as muscle hypertrophy, hyperplasia, atrophy, and regenerative capacity. This strongly suggests that skeletal muscle contains various stem/progenitor cells related to muscle-nerve-vascular tissues, which would support the above postnatal events even in adulthood.

AREA COVERED

The focus of this review is the therapeutic potential of the Sk-MDSCs as an adult stem cell autograft. For this purpose, the validity of cell isolation and purification, tissue reconstitution capacity in vivo after transplantation, comparison of the results of basic mouse and preclinical human studies, potential problematic and beneficial aspects, and effective usage have been discussed following the history of clinical applications.

EXPERT OPINION

Although the clinical application of Sk-MDSCs began as a therapy for the systemic disease of Duchenne muscular dystrophy, here, through the unique local injection method, therapy for severely damaged peripheral nerves, particularly the long-gap nerve transection, has been introduced. The beneficial aspects of the use of Sk-MDSCs as the source of local tissue transplantation therapy have also been discussed.

Intrinsic Myogenic Potential of Skeletal Muscle-Derived Pericytes from Patients with Myotonic Dystrophy Type 1

Pericytes are multipotent, vessel-associated progenitors that exhibit high proliferative capacity, can cross the blood-muscle barrier, and have the ability to home to muscle tissue and contribute to myogenesis. Consequently, pericyte-based therapies hold great promise for muscular dystrophies. A complex multi-system disorder exhibiting muscular dystrophy for which pericytes might be a valuable cell source is myotonic dystrophy type 1 (DM1). DM1 is caused by an unstable (CTG)n repeat in the DMPK gene and characterized by skeletal muscle weakness, muscle wasting, and myotonia. We have successfully isolated alkaline phosphatase-positive pericytes from skeletal muscle of DM1 patients and a transgenic mouse model. Intranuclear (CUG)n RNA foci, a pathogenic DM1 hallmark, were identified in human and mouse pericytes. Notably, pericytes from DM1 patients maintained similar growth parameters and innate myogenic characteristics in vitro compared to cells from unaffected controls. Our in vitro results thus demonstrate the potential of pericytes to ameliorate muscle features in DM1 in a therapeutic setting.

Skeletal muscle cell transplantation: models and methods

Xenografts of skeletal muscle are used to study muscle repair and regeneration, mechanisms of muscular dystrophies, and potential cell therapies for musculoskeletal disorders. Typically, xenografting involves using an immunodeficient host that is pre-injured to create a niche for human cell engraftment. Cell type and method of delivery to muscle depend on the specific application, but can include myoblasts, satellite cells, induced pluripotent stem cells, mesangioblasts, immortalized muscle precursor cells, and other multipotent cell lines delivered locally or systemically. Some studies follow cell engraftment with interventions to enhance cell proliferation, migration, and differentiation into mature muscle fibers. Recently, several advances in xenografting human-derived muscle cells have been applied to study and treat Duchenne muscular dystrophy and Facioscapulohumeral muscular dystrophy. Here, we review the vast array of techniques available to aid researchers in designing future experiments aimed at creating robust muscle xenografts in rodent hosts.

The effect of type 2 diabetes mellitus and obesity on muscle progenitor cell function

In addition to its primary function to provide movement and maintain posture, the skeletal muscle plays important roles in energy and glucose metabolism. In healthy humans, skeletal muscle is the major site for postprandial glucose uptake and impairment of this process contributes to the pathogenesis of type 2 diabetes mellitus (T2DM). A key component to the maintenance of skeletal muscle integrity and plasticity is the presence of muscle progenitor cells, including satellite cells, fibroadipogenic progenitors, and some interstitial progenitor cells associated with vessels (myo-endothelial cells, pericytes, and mesoangioblasts). In this review, we aim to discuss the emerging concepts related to these progenitor cells, focusing on the identification and characterization of distinct progenitor cell populations, and the impact of obesity and T2DM on these cells. The recent advances in stem cell therapies by targeting diabetic and obese muscle are also discussed.

DUX4-induced constitutive DNA damage and oxidative stress contribute to aberrant differentiation of myoblasts from FSHD patients

Facioscapulohumeral dystrophy (FSHD) is one of the three most common muscular dystrophies in the Western world, however, its etiology remains only partially understood. Here, we provide evidence of constitutive DNA damage in in vitro cultured myoblasts isolated from FSHD patients and demonstrate oxidative DNA damage implication in the differentiation of these cells into phenotypically-aberrant myotubes. Double homeobox 4 (DUX4), the major actor in FSHD pathology induced DNA damage accumulation when overexpressed in normal human myoblasts, and RNAi-mediated DUX4 inhibition reduced the level of DNA damage in FSHD myoblasts. Addition of tempol, a powerful antioxidant, to the culture medium of proliferating DUX4-transfected myoblasts and FSHD myoblasts reduced the level of DNA damage, suggesting that DNA alterations are mainly due to oxidative stress. Antioxidant treatment during the myogenic differentiation of FSHD myoblasts significantly reduced morphological defects in myotube formation. We propose that the induction of DNA damage is a novel function of the DUX4 protein affecting myogenic differentiation of FSHD myoblasts.

The potential of stem cells in the treatment of cardiovascular diseases

Although the adult mammalian heart was once believed to be a post-mitotic organ without any capacity for regeneration, recent findings have challenged this dogma. A modified view assigns to the mammalian heart a measurable capacity for regeneration throughout life. The ultimate goals of the cardiac regeneration field have been pursued by multiple strategies, including understanding the developmental biology of cardiomyocytes and cardiac stem and progenitor cells, applying chemical genetics, and engineering biomaterials and delivery methods that facilitate cell transplantation. Successful stimulation of endogenous regenerative capacity in injured adult mammalian hearts can benefit from studies of natural cardiac regeneration.

Facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by a typical and asymmetric pattern of muscle involvement and disease progression. Two forms of FSHD, FSHD1 and FSHD2, have been identified displaying identical clinical phenotype but different genetic and epigenetic basis. Autosomal dominant FSHD1 (95% of patients) is characterized by chromatin relaxation induced by pathogenic contraction of a macrosatellite repeat called D4Z4 located on the 4q subtelomere (FSHD1 patients harbor 1 to 10 D4Z4 repeated units). Chromatin relaxation is associated with inappropriate expression of DUX4, a retrogene, which in muscles induces apoptosis and inflammation. Consistent with this hypothesis, individuals carrying zero repeat on chromosome 4 do not develop FSHD1. Not all D4Z4 contracted alleles cause FSHD. Distal to the last D4Z4 unit, a polymorphic site with two allelic variants has been identified: 4qA and 4qB. 4qA is in cis with a functional polyadenylation consensus site. Only contractions on 4qA alleles are pathogenic because the DUX4 transcript is polyadenylated and translated into stable protein. FSHD2 is instead a digenic disease. Chromatin relaxation of the D4Z4 locus is caused by heterozygous mutations in the SMCHD1 gene encoding a protein essential for chromatin condensation. These patients also harbor at least one 4qA allele in order to express stable DUX4 transcripts. FSHD1 and FSHD2 may have an additive effect: patients harboring D4Z4 contraction and SMCHD1 mutations display a more severe clinical phenotype than with either defect alone. Knowledge of the complex genetic and epigenetic defects causing these diseases is essential in view of designing novel therapeutic strategies. This article is part of a Special Issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis.

Cancer-related genes in the transcription signature of facioscapulohumeral dystrophy myoblasts and myotubes

Muscular dystrophy is a condition potentially predisposing for cancer; however, currently, only Myotonic dystrophy patients are known to have a higher risk of cancer. Here, we have searched for a link between facioscapulohumeral dystrophy (FSHD) and cancer by comparing published transcriptome signatures of FSHD and various malignant tumours and have found a significant enrichment of cancer-related genes among the genes differentially expressed in FSHD. The analysis has shown that gene expression profiles of FSHD myoblasts and myotubes resemble that of Ewing's sarcoma more than that of other cancer types tested. This is the first study demonstrating a similarity between FSHD and cancer cell expression profiles, a finding that might indicate the existence of a common step in the pathogenesis of these two diseases.

Muscle regeneration and inflammation in patients with facioscapulohumeral muscular dystrophy

BACKGROUND AND OBJECTIVES

The aim of this study was to investigate whether inflammation and regeneration are prominent in mildly affected muscles of patients with facioscapulohumeral muscular dystrophy type 1A (FSHD1A). Inflammation in muscle has been suggested by MRI studies in patients with FSHD1A.

METHODS

We analysed immunohistological and histological stains of muscle biopsies from 24 patients with FSHD1A, using 10 patients with Becker muscular dystrophy (BMD) for comparison.

RESULTS

Internalized nuclei were more prevalent in BMD (23.7 ± 10.8%) vs FSHD1A (6.3 ± 6.8%; P < 0.001), indicating more past regenerating fibres in BMD. Recently regenerating fibres, expressing neonatal myosin heavy chain and vimentin, did not differ significantly between patients with FSHD1A (1.1 ± 2.9%) and patients with BMD (1.8 ± 1.9%). Regeneration was not correlated with the number of KpnI restriction fragment repeats, an FSHD1A-defining genotype property within the D4Z4 locus, or overall disease severity in patients with FSHD1A. Macrophages were more prevalent in FSHD1A (0.50 ± 0.63 per mm(2) ) vs BMD (0.07 ± 0.07 per mm(2) ), whereas inflammatory T cells were equally infrequent.

CONCLUSIONS

Macrophages were more prevalent in patients with FSHD1A and could be an important pathogenic mechanism for the initiation of the dystrophic process. Furthermore, regeneration was unrelated to genotype and disease severity in FSHD1A.

miR-411 is up-regulated in FSHD myoblasts and suppresses myogenic factors

BACKGROUND

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant muscle disorder, which is linked to the contraction of the D4Z4 array at chromosome 4q35. Recent studies suggest that this shortening of the D4Z4 array leads to aberrant expression of double homeobox protein 4 (DUX4) and causes FSHD. In addition, misregulation of microRNAs (miRNAs) has been reported in muscular dystrophies including FSHD. In this study, we identified a miRNA that is differentially expressed in FSHD myoblasts and investigated its function.

METHODS

To identify misregulated miRNAs and their potential targets in FSHD myoblasts, we performed expression profiling of both miRNA and mRNA using TaqMan Human MicroRNA Arrays and Affymetrix Human Genome U133A plus 2.0 microarrays, respectively. In addition, we over-expressed miR-411 in C₂C₁₂ cells to determine the effect of miR-411 on myogenic markers.

RESULTS

Using miRNA and mRNA expression profiling, we identified 8 miRNAs and 1,502 transcripts that were differentially expressed in FSHD myoblasts during cell proliferation. One of the 8 differentially expressed miRNAs, miR-411, was validated by quantitative RT-PCR in both primary (2.1 fold, p<0.01) and immortalized (2.7 fold, p<0.01) myoblasts. In situ hybridization showed cytoplasmic localization of miR-411 in FSHD myoblasts. By analyzing both miRNA and mRNA data using Partek Genomics Suite, we identified 4 mRNAs potentially regulated by miR-411 including YY1 associated factor 2 (YAF2). The down-regulation of YAF2 in immortalized myoblasts was validated by immunoblotting (-3.7 fold, p<0.01). C₂C₁₂ cells were transfected with miR-411 to determine whether miR-411 affects YAF2 expression in myoblasts. The results showed that over-expression of miR-411 reduced YAF2 mRNA expression. In addition, expression of myogenic markers including Myod, myogenin, and myosin heavy chain 1 (Myh1) were suppressed by miR-411.

CONCLUSIONS

The study demonstrated that miR-411 was differentially expressed in FSHD myoblasts and may play a role in regulating myogenesis.

Rbfox1 downregulation and altered calpain 3 splicing by FRG1 in a mouse model of Facioscapulohumeral muscular dystrophy (FSHD)

Facioscapulohumeral muscular dystrophy (FSHD) is a common muscle disease whose molecular pathogenesis remains largely unknown. Over-expression of FSHD region gene 1 (FRG1) in mice, frogs, and worms perturbs muscle development and causes FSHD-like phenotypes. FRG1 has been implicated in splicing, and we asked how splicing might be involved in FSHD by conducting a genome-wide analysis in FRG1 mice. We find that splicing perturbations parallel the responses of different muscles to FRG1 over-expression and disease progression. Interestingly, binding sites for the Rbfox family of splicing factors are over-represented in a subset of FRG1-affected splicing events. Rbfox1 knockdown, over-expression, and RNA-IP confirm that these are direct Rbfox1 targets. We find that FRG1 is associated to the Rbfox1 RNA and decreases its stability. Consistent with this, Rbfox1 expression is down-regulated in mice and cells over-expressing FRG1 as well as in FSHD patients. Among the genes affected is Calpain 3, which is mutated in limb girdle muscular dystrophy, a disease phenotypically similar to FSHD. In FRG1 mice and FSHD patients, the Calpain 3 isoform lacking exon 6 (Capn3 E6-) is increased. Finally, Rbfox1 knockdown and over-expression of Capn3 E6- inhibit muscle differentiation. Collectively, our results suggest that a component of FSHD pathogenesis may arise by over-expression of FRG1, reducing Rbfox1 levels and leading to aberrant expression of an altered Calpain 3 protein through dysregulated splicing.

Human skeletal muscle cells with a slow adhesion rate after isolation and an enhanced stress resistance improve function of ischemic hearts

Identification of cells that are endowed with maximum potency could be critical for the clinical success of cell-based therapies. We investigated whether cells with an enhanced efficacy for cardiac cell therapy could be enriched from adult human skeletal muscle on the basis of their adhesion properties to tissue culture flasks following tissue dissociation. Cells that adhered slowly displayed greater myogenic purity and more readily differentiated into myotubes in vitro than rapidly adhering cells (RACs). The slowly adhering cell (SAC) population also survived better than the RAC population in kinetic in vitro assays that simulate conditions of oxidative and inflammatory stress. When evaluated for the treatment of a myocardial infarction (MI), intramyocardial injection of the SACs more effectively improved echocardiographic indexes of left ventricular (LV) remodeling and contractility than the transplantation of the RACs. Immunohistological analysis revealed that hearts injected with SACs displayed a reduction in myocardial fibrosis and an increase in infarct vascularization, donor cell proliferation, and endogenous cardiomyocyte survival and proliferation in comparison with the RAC-treated hearts. In conclusion, these results suggest that adult human skeletal muscle-derived cells are inherently heterogeneous with regard to their efficacy for enhancing cardiac function after cardiac implantation, with SACs outperforming RACs.

Retinal vascular disease and the pathogenesis of facioscapulohumeral muscular dystrophy. A signalling message from Wnt?

The peripheral retinal vascular abnormality which accompanies FSHD belongs morphologically and clinically to a class of developmental 'retinal hypovasculopathies' caused by abnormalities of 'Wnt' signalling, which controls retinal angiogenesis. Wnt signalling is also fundamental to myogenesis. This paper integrates modern concepts of myogenic cell signalling and of transcription factor expression and control with data from the classic early ophthalmic and myology embryology literature. Together, they support an hypothesis that abnormalities of Wnt signalling, which activates myogenic programs and transcription factors in myoblasts and satellite cells, leads to defective muscle regeneration in FSHD. The selective vulnerability of different FSHD muscles (notably facial muscle, from the second branchial arch) might reflect patterns of transcription factor redundancies. This hypothesis has implications for FSHD research through study of transcription factors patterning in normal human muscles, and for autologous cell transplantation.

Contribution of human muscle-derived cells to skeletal muscle regeneration in dystrophic host mice

BACKGROUND

Stem cell transplantation is a promising potential therapy for muscular dystrophies, but for this purpose, the cells need to be systemically-deliverable, give rise to many muscle fibres and functionally reconstitute the satellite cell niche in the majority of the patient's skeletal muscles. Human skeletal muscle-derived pericytes have been shown to form muscle fibres after intra-arterial transplantation in dystrophin-deficient host mice. Our aim was to replicate and extend these promising findings.

METHODOLOGY/PRINCIPAL FINDINGS

Isolation and maintenance of human muscle derived cells (mdcs) was performed as published for human pericytes. Mdscs were characterized by immunostaining, flow cytometry and RT-PCR; also, their ability to differentiate into myotubes in vitro and into muscle fibres in vivo was assayed. Despite minor differences between human mdcs and pericytes, mdscs contributed to muscle regeneration after intra-muscular injection in mdx nu/nu mice, the CD56+ sub-population being especially myogenic. However, in contrast to human pericytes delivered intra-arterially in mdx SCID hosts, mdscs did not contribute to muscle regeneration after systemic delivery in mdx nu/nu hosts.

CONCLUSIONS/SIGNIFICANCE

Our data complement and extend previous findings on human skeletal muscle-derived stem cells, and clearly indicate that further work is necessary to prepare pure cell populations from skeletal muscle that maintain their phenotype in culture and make a robust contribution to skeletal muscle regeneration after systemic delivery in dystrophic mouse models. Small differences in protocols, animal models or outcome measurements may be the reason for differences between our findings and previous data, but nonetheless underline the need for more detailed studies on muscle-derived stem cells and independent replication of results before use of such cells in clinical trials.

Mesoangioblasts from facioscapulohumeral muscular dystrophy display in vivo a variable myogenic ability predictable by their in vitro behavior

Facioscapulohumeral muscular dystrophy (FSHD) is the third most frequent inherited myopathy. We previously demonstrated that mesoangioblasts can be efficiently isolated from FSHD muscles, although their differentiation ability into skeletal muscle was variably impaired. This correlates with overall disease severity and degree of histopathologic abnormalities, since mesoangioblasts from morphologically normal muscles did not show any myogenic differentiation block. The aim of our present study was to verify whether mesoangioblasts from differentially affected FSHD muscles reproduce in vivo the same differentiation ability shown in vitro by studying their capability to form new muscle fibers during muscle regeneration of experimentally damaged muscles. We show that a diverse ability of FSHD mesoangioblasts to engraft and differentiate into skeletal muscle of SCID mice is strictly related to the characteristics of the muscle of origin, closely replicating in vivo what was previously observed in vitro. Moreover, we demonstrate that mesoangioblasts obtained from severely affected muscles scarcely integrate into muscle fibers, remaining mainly localized in the connective tissue. This suggests a defective migration in response to chemoattractants released by damaged fibers, as indicated by cell migration assays in response to HMGB1 and very low levels of RAGE expression, along with a decreased ability to fuse or to appropriately trigger the myogenic program. Our study indicates that FSHD mesoangioblasts from unaffected muscles can be used as selective treatment to halt muscle degeneration in severely affected muscles, and suggests that pharmacological and molecular interventions aimed to ameliorate homing and engraftment of transplanted autologous mesoangioblasts may open the way to cell therapy for FSHD patients, without requiring immunosuppression or genetic correction in vitro.

Redox remodeling: a candidate regulator of HMGB1 function in injured skeletal muscle

High-mobility group box-1 (HMGB1) is a prototypical endogenous signal that links tissue necrosis and wound healing. Extracellular HMGB1 has apparently contrasting biological actions: it sustains inflammation (with the possible establishment of autoimmunity or of self-maintaining tissue damage) while activating and recruiting stem cells, which foster tissue repair. However, little is known about the role environmental cues play in the extracellular functions of HMGB1. The skeletal muscle is an optimal tissue model to help us unravel these underlying molecular events. Here, sterile injury triggers a potent inflammatory response that includes infiltration by inflammatory leukocytes and the parallel activation, proliferation, and fusion of muscle-specific stem cells. Recent data suggest that the regulation of environmental redox is critical for the bioactivity of HMGB1, which is extremely sensitive to oxidation. Moreover, data suggest a potential role for infiltrating alternatively activated macrophages to influence the outcome of inflammatory responses to sterile skeletal muscle necrosis.

Vessel-associated stem cells from skeletal muscle: From biology to future uses in cell therapy

Over the last years, the existence of different stem cells with myogenic potential has been widely investigated. Besides the classical skeletal muscle progenitors represented by satellite cells, numerous multipotent and embryologically unrelated progenitors with a potential role in muscle differentiation and repair have been identified. In order to conceive a therapeutic approach for degenerative muscle disorders, it is of primary importance to identify an ideal stem cell endowed with all the features for a possible use in vivo. Among all emerging populations, vessel-associated stem cells are a novel and promising class of multipotent progenitors of mesodermal origin and with high myogenic potential which seem to best fit all the requirements for a possible cell therapy. In vitro and in vivostudies have already tested the effectiveness and safety of vessel-associated stem cells in animal models. This leads to the concrete possibility in the future to start pilot human clinical trials, hopefully opening the way to a turning point in the treatment of genetic and acquired muscle disorders.

Myoblasts from affected and non-affected FSHD muscles exhibit morphological differentiation defects

Facioscapulohumeral dystrophy (FSHD) is a muscular hereditary disease with a prevalence of 1 in 20,000 caused by a partial deletion of a subtelomeric repeat array on chromosome 4q. However, very little is known about the pathogenesis as well as the molecular and biochemical changes linked to the progressive muscle degeneration observed in these patients. Several studies have investigated possible pathophysiological pathways in FSHD myoblasts and mature muscle cells but some of these reports were apparently in contradiction. The discrepancy between these studies may be explained by differences between the sources of myoblasts. Therefore, we decided to thoroughly analyze affected and unaffected muscles from patients with FSHD in terms of vulnerability to oxidative stress, differentiation capacity and morphological abnormalities. We have established a panel of primary myoblast cell cultures from patients affected with FSHD and matched healthy individuals. Our results show that primary myoblasts are more susceptible to an induced oxidative stress than control myoblasts. Moreover, we demonstrate that both types of FSHD primary myoblasts differentiate into multi-nucleated myotubes, which present morphological abnormalities. Whereas control myoblasts fuse to form branched myotubes with aligned nuclei, FSHD myoblasts fuse to form either thin and branched myotubes with aligned nuclei or large myotubes with random nuclei distribution. In conclusion, we postulate that these abnormalities could be responsible for muscle weakness in patients with FSHD and provide an important marker for FSHD myoblasts.

Analysis of allele-specific RNA transcription in FSHD by RNA-DNA FISH in single myonuclei

Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is likely caused by epigenetic alterations in chromatin involving contraction of the D4Z4 repeat array near the telomere of chromosome 4q. The precise mechanism by which deletions of D4Z4 influence gene expression in FSHD is not yet resolved. Regulatory models include a cis effect on proximal gene transcription (position effect), DNA looping, non-coding RNA, nuclear localization and trans-effects. To directly test whether deletions of D4Z4 affect gene expression in cis, nascent RNA was examined in single myonuclei so that transcription from each allele could be measured independently. FSHD and control myotubes (differentiated myoblasts) were subjected to sequential RNA-DNA FISH. A total of 16 genes in the FSHD region (FRG2, TUBB4Q, FRG1, FAT1, F11, KLKB1, CYP4V2, TLR3, SORBS2, PDLIM3 (ALP), LRP2BP, ING2, SNX25, SLC25A4 (ANT1), HELT and IRF2) were examined for interallelic variation in RNA expression within individual myonuclei. Sequential DNA hybridization with a unique 4q35 chromosome probe was then applied to confirm the localization of nascent RNA to 4q. A D4Z4 probe, labeled with a third fluorochrome, distinguished between the deleted and normal allele in FSHD nuclei. Our data do not support an FSHD model in which contracted D4Z4 arrays induce altered transcription in cis from 4q35 genes, even for those genes (FRG1, FRG2 and SLC25A4 (ANT1)) for which such an effect has been proposed.

Biphasic myopathic phenotype of mouse DUX, an ORF within conserved FSHD-related repeats

Facioscapulohumeral muscular dystrophy (FSHD) is caused by contractions of D4Z4 repeats at 4q35.2 thought to induce misregulation of nearby genes, one of which, DUX4, is actually localized within each repeat. A conserved ORF (mDUX), embedded within D4Z4-like repeats, encoding a double-homeodomain protein, was recently identified on mouse chromosome 10. We show here that high level mDUX expression induces myoblast death, while low non-toxic levels block myogenic differentiation by down-regulating MyoD and Myf5. Toxicity and MyoD/Myf5 expression changes were competitively reversed by overexpression of Pax3 or Pax7, implying mechanistic similarities with the anti-myogenic activity of human DUX4. We tested the effect of mDUX expression on Xenopus development, and found that global overexpression led to abnormalities in gastrulation. When targeted unilaterally into blastomeres fated to become tail muscle in 16-cell embryos, mDUX caused markedly reduced tail myogenesis on the injected side. These novel cell and animal models highlight the myopathic nature of sequences within the FSHD-related repeat array.

The origin, molecular regulation and therapeutic potential of myogenic stem cell populations

Satellite cells, originating in the embryonic dermamyotome, reside beneath the myofibre of mature adult skeletal muscle and constitute the tissue-specific stem cell population. Recent advances following the identification of markers for these cells (including Pax7, Myf5, c-Met and CD34) (CD, cluster of differentiation; c-Met, mesenchymal epithelial transition factor) have led to a greater understanding of the role played by satellite cells in the regeneration of new skeletal muscle during growth and following injury. In response to muscle damage, satellite cells harbour the ability both to form myogenic precursors and to self-renew to repopulate the stem cell niche following myofibre damage. More recently, other stem cell populations including bone marrow stem cells, skeletal muscle side population cells and mesoangioblasts have also been shown to have myogenic potential in culture, and to be able to form skeletal muscle myofibres in vivo and engraft into the satellite cell niche. These cell types, along with satellite cells, have shown potential when used as a therapy for skeletal muscle wasting disorders where the intrinsic stem cell population is genetically unable to repair non-functioning muscle tissue. Accurate understanding of the mechanisms controlling satellite cell lineage progression and self-renewal as well as the recruitment of other stem cell types towards the myogenic lineage is crucial if we are to exploit the power of these cells in combating myopathic conditions. Here we highlight the origin, molecular regulation and therapeutic potential of all the major cell types capable of undergoing myogenic differentiation and discuss their potential therapeutic application.

FSHD region gene 1 (FRG1) is crucial for angiogenesis linking FRG1 to facioscapulohumeral muscular dystrophy-associated vasculopathy

The genetic lesion that is diagnostic for facioscapulohumeral muscular dystrophy (FSHD) results in an epigenetic misregulation of gene expression, which ultimately leads to the disease pathology. FRG1 (FSHD region gene 1) is a leading candidate for a gene whose misexpression might lead to FSHD. Because FSHD pathology is most prominent in the musculature, most research and therapy efforts focus on muscle cells. Previously, using Xenopus development as a model, we showed that altering frg1 expression levels systemically leads to aberrant muscle development, illustrating the potential for aberrant FRG1 levels to disrupt the musculature. However, 50-75% of FSHD patients also exhibit retinal vasculopathy and FSHD muscles have increased levels of vascular- and endothelial-related FRG1 transcripts, illustrating an underlying vascular component to the disease. To date, no FSHD candidate gene has been proposed to affect the vasculature. Here, we focus on a role for FRG1 expression in the vasculature. We found that endogenous frg1 is expressed in both the developing and adult vasculature in Xenopus. Furthermore, expression of FRG1 was found to be essential for the development of the vasculature, as a knockdown of FRG1 resulted in decreased angiogenesis and reduced expression of the angiogenic regulator DAB2. Conversely, tadpoles subjected to frg1 overexpression displayed the pro-angiogenic phenotypes of increased blood vessel branching and dilation of blood vessels, and developed edemas, suggesting that their circulation was disrupted. Thus, the systemic upregulation of the FRG1 protein shows the potential for acquiring a disrupted vascular phenotype, providing the first link between a FSHD candidate gene and the vascular component of FSHD pathology. Overall, in conjunction with our previous analysis, we show that FRG1 overexpression is capable of disrupting both the musculature and vasculature, recapitulating the two most prominent features of FSHD.

Inflammatory and alternatively activated human macrophages attract vessel-associated stem cells, relying on separate HMGB1- and MMP-9-dependent pathways

Inflammatory macrophages recruited at the site of damaged muscles progressively acquire an alternative activation profile. Inflammatory (M1) and alternatively activated (M2) macrophages exert various and even opposite functions. M1 cells amplify tissue damage, and M2 cells dispose of necrotic fibers and deliver survival signals to myogenic precursors, finally supporting healing. A critical step in muscle healing is the recruitment of myogenic stem cells, including vessel-associated stem cells (mesoangioblasts), which have been demonstrated to home to damaged skeletal muscle selectively and preferentially. Little information is available about the signals involved and the role played by infiltrating macrophages. Here, we report that the polarization of macrophages dramatically skews the secretion of high mobility group box 1 (HMGB1), TNF-alpha, vascular endothelial growth factor, and metalloproteinase 9 (MMP-9), molecules involved in the regulation of cell diapedesis and migration. All polarized macrophage populations were strikingly effective at inducing mesoangioblast migration. By means of specific inhibitors, we verified that the recruitment of mesoangioblasts requires the secretion of HMGB1 and TNF-alpha by M1 cells and of MMP-9 by M2 cells. Together, these data demonstrate a feature, unrecognized previously, of macrophages: their ability to attract stem cells, which is conserved throughout their polarization. Moreover, they open the possibility of novel strategies, aimed at interfering selectively with signals that recruit blood-derived stem cells toward pro- or anti-inflammatory macrophages.

Facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD), a dominantly inherited disorder, is the third most common dystrophy after Duchenne and myotonic muscular dystrophy. No known effective treatments exist for FSHD. The lack of an understanding of the underlying pathophysiology remains an obstacle in the development of targeted therapeutic interventions. The genetic defect is a loss of a critical number of a repetitive element (D4Z4) in the 4q subtelomeric region. The loss of the repeats results in specific changes in chromatin structure, although neither the molecular nor the cellular consequences of this change are known. Nevertheless, these epigenetic changes in chromatin structure offer a potential therapeutic target. This review discusses current management strategies in FSHD as well as potential therapeutic interventions to slow down or reverse the progressive muscle atrophy and weakness.

Facioscapulohumeral dystrophy: case report and discussion

Facioscapulohumeral dystrophy (FSHD) is often cited as the third most common form of muscular dystrophy. Therefore, it should be considered in patients with complaints of progressive weakness. We present the case of a man with facial, truncal, and leg weakness that initially sought medical attention for lower back pain. Electrodiagnostic testing revealed findings in the trapezius, serratus anterior, biceps, triceps, pectoralis major, tibialis anterior, and gastrocnemius muscles consistent with a myopathic disorder. Subsequent genetic testing identified a FSHD allele size consistent with a FSHD deletion mutation. Therefore, confirming the diagnosis of FSHD. Unfortunately, no effective treatments currently exist for FSHD. However, supportive measures involving physical therapy and the use of orthotics may aid in improving function and mobility.