Novel therapies for Duchenne muscular dystrophy

Cell Therapy Strategies on Duchenne Muscular Dystrophy: A Systematic Review of Clinical Applications

Duchenne Muscular Dystrophy (DMD) is an inherited genetic disorder characterized by progressive degeneration of muscle tissue, leading to functional disability and premature death. Despite extensive research efforts, the discovery of a cure for DMD continues to be elusive, emphasizing the need to investigate novel treatment approaches. Cellular therapies have emerged as prospective approaches to address the underlying pathophysiology of DMD. This review provides an examination of the present situation regarding cell-based therapies, including CD133 + cells, muscle precursor cells, mesoangioblasts, bone marrow-derived mononuclear cells, mesenchymal stem cells, cardiosphere-derived cells, and dystrophin-expressing chimeric cells. A total of 12 studies were found eligible to be included as they were completed cell therapy clinical trials, clinical applications, or case reports with quantitative results. The evaluation encompassed an examination of limitations and potential advancements in this particular area of research, along with an assessment of the safety and effectiveness of cell-based therapies in the context of DMD. In general, the available data indicates that diverse cell therapy approaches may present a new, safe, and efficacious treatment modality for patients diagnosed with DMD. However, further studies are required to comprehensively understand the most advantageous treatment approach and therapeutic capacity.

TBX1 regulates myogenic differentiation by activating the TGFβ-Smad2/3 pathway in myoblasts

TBX1 is systematically conserved in the T-box transcription factor family and regulates craniofacial muscle development during various stages of myogenesis, including commitment, proliferation, terminal differentiation, and survival. However, the role and mechanism by which TBX1 regulates the myogenic development of myoblasts remains unclear. In our study, we overexpressed TBX1 in mouse C2C12 myoblasts using a lentivirus method. We found that TBX1 inhibited cell proliferation and muscle differentiation, which had no effect on apoptosis. During myogenic differentiation, we also found that TBX1 overexpressing cells regulate myogenic differentiation by upregulating the expression levels of Smad2 and Smad3 and downregulating the expression level of MEF2C. After treatment with a specific inhibitor of Smad3 (SIS3), the myogenic differentiation of wild-type and TBX1 overexpressing cells increased. Thus, TBX1 may regulate myoblast muscle differentiation by enhancing the expression of Smad2 and Smad3. TBX1 may be a therapeutic target for muscular dystrophy.

The impact of sex differences on genomic research

Sex and gender differences affect all dimensions of human health ranging from the biological basis of disease to therapeutic access, choice and response. Genomics research has long ignored the role of sex differences as potential modulators and the concept is gaining more attention only recently. In the present review we summarize the current knowledge of the impact of sex differences on genomic and epigenomic research, the potential interaction of genomics and gender and the role of these differences in disease etiopathogenesis. Sex differences can emerge from differences in the sex chromosomes themselves, from their interaction with the genome and from the influence of hormones on genomic processes. The impact of these processes on the incidence of autoimmune and oncologic disease is well documented. The growing field of systems biology, which aims at integrating information from different networks of the human body, could also greatly benefit from this approach. In the present review we summarize the current knowledge and provide recommendations for the future performance of sex-sensitive genomics research.

Wet-Spun Trojan Horse Cell Constructs for Engineering Muscle

Engineering of 3D regenerative skeletal muscle tissue constructs (skMTCs) using hydrogels containing muscle precursor cells (MPCs) is of potential benefit for repairing Volumetric Muscle Loss (VML) arising from trauma (e.g., road/industrial accident, war injury) or for restoration of functional muscle mass in disease (e.g., Muscular Dystrophy, muscle atrophy). Additive Biofabrication (AdBiofab) technologies make possible fabrication of 3D regenerative skMTCs that can be tailored to specific delivery requirements of VML or functional muscle restoration. Whilst 3D printing is useful for printing constructs of many tissue types, the necessity of a balanced compromise between cell type, required construct size and material/fabrication process cyto-compatibility can make the choice of 3D printing a secondary alternative to other biofabrication methods such as wet-spinning. Alternatively, wet-spinning is more amenable to formation of fibers rather than (small) layered 3D-Printed constructs. This study describes the fabrication of biosynthetic alginate fibers containing MPCs and their use for delivery of dystrophin-expressing cells to dystrophic muscle in the mdx mouse model of Duchenne Muscular Dystrophy (DMD) compared to poly(DL-lactic-co-glycolic acid) copolymer (PLA:PLGA) topically-seeded with myoblasts. In addition, this study introduces a novel method by which to create 3D layered wet-spun alginate skMTCs for bulk mass delivery of MPCs to VML lesions. As such, this work introduces the concept of "Trojan Horse" Fiber MTCs (TH-fMTCs) and 3d Mesh-MTCs (TH-mMTCs) for delivery of regenerative MPCs to diseased and damaged muscle, respectively.

The Use of Tricyclo-DNA Oligomers for the Treatment of Genetic Disorders

Antisense Oligonucleotides (ASOs) represent very attractive therapeutic compounds for the treatment of numerous diseases. The antisense field has remarkably progressed over the last few years with the approval of the first antisense drugs and with promising developments of more potent and nuclease resistant chemistries. Despite these recent clinical successes and advances in chemistry and design, effective delivery of ASOs to their target tissues remains a major issue. This review will describe the latest advances obtained with the tricyclo-DNA (tcDNA) chemistry which displays unique pharmacological properties and unprecedented uptake in many tissues after systemic administration. We will examine the variety of therapeutic approaches using both fully modified tcDNA-ASOs and gapmers, including splice switching applications, correction of aberrant splicing, steric blocking strategies and targeted gene knock-down mediated by RNase H recruitment. We will then discuss the merits and potential liabilities of the tcDNA chemistry in the context of ASO drug development.

Effectiveness of diffusion tensor imaging in assessing disease severity in Duchenne muscular dystrophy: preliminary study

BACKGROUND

There is currently a lack of suitable objective endpoints to measure disease progression in Duchenne muscular dystrophy (DMD). Emerging research suggests that diffusion tensor imaging (DTI) has potential as an outcome measure for the evaluation of skeletal muscle injury.

OBJECTIVE

The objective of this study was to evaluate the potential of DTI as quantitative magnetic resonance imaging (MRI) markers of disease severity in DMD.

MATERIALS AND METHODS

Thirteen consecutive boys (8.9 years ± 3.0 years) with DMD were evaluated using DTI. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were compared with clinical outcome measures of manual muscle testing and MRI determinations of muscle fat fraction (MFF) in the right lower extremity.

RESULTS

Both MRI measures of FA and ADC strongly correlated with age and muscle strength. Values for FA positively correlated with age and negatively correlated with muscle strength (r = 0.78 and -0.96; both P ≤ 0.002) while measures of ADC negatively correlated age, but positively correlated with muscle strength (r = -0.87 and 0.83; both P ≤ 0.0004). Additionally, ADC and FA strongly correlated with MFF (r = -0.891 and 0.894, respectively; both P ≤ 0.0001). Mean MMF was negatively correlated with muscle strength (r = -0.89, P = 0.0001).

CONCLUSION

DTI measures of muscle structure strongly correlated with muscle strength and adiposity in boys with DMD in this pilot study, although these markers may be more reflective of fat replacement rather than muscle damage in later stages of the disease. Further studies in presymptomatic younger children are needed to assess the ability of DTI to detect early changes in DMD.

SNP and INDEL detection in a QTL region on chicken chromosome 2 associated with muscle deposition

Genetic improvement is important for the poultry industry, contributing to increased efficiency of meat production and quality. Because breast muscle is the most valuable part of the chicken carcass, knowledge of polymorphisms influencing this trait can help breeding programs. Therefore, the complete genome of 18 chickens from two different experimental lines (broiler and layer) from EMBRAPA was sequenced, and SNPs and INDELs were detected in a QTL region for breast muscle deposition on chicken chromosome 2 between microsatellite markers MCW0185 and MCW0264 (105,849-112,649 kb). Initially, 94,674 unique SNPs and 10,448 unique INDELs were identified in the target region. After quality filtration, 77% of the SNPs (85,765) and 60% of the INDELs (7828) were retained. The studied region contains 66 genes, and functional annotation of the filtered variants identified 517 SNPs and three INDELs in exonic regions. Of these, 357 SNPs were classified as synonymous, 153 as non-synonymous, three as stopgain, four INDELs as frameshift and three INDELs as non-frameshift. These exonic mutations were identified in 37 of the 66 genes from the target region, three of which are related to muscle development (DTNA, RB1CC1 and MOS). Fifteen non-tolerated SNPs were detected in several genes (MEP1B, PRKDC, NSMAF, TRAPPC8, SDR16C5, CHD7, ST18 and RB1CC1). These loss-of-function and exonic variants present in genes related to muscle development can be considered candidate variants for further studies in chickens. Further association studies should be performed with these candidate mutations as should validation in commercial populations to allow a better explanation of QTL effects.

Andrographolide attenuates skeletal muscle dystrophy in mdx mice and increases efficiency of cell therapy by reducing fibrosis

Background

Duchenne muscular dystrophy (DMD) is characterized by the absence of the cytoskeletal protein dystrophin, muscle wasting, increased transforming growth factor type beta (TGF-β) signaling, and fibrosis. At the present time, the only clinically validated treatments for DMD are glucocorticoids. These drugs prolong muscle strength and ambulation of patients for a short term only and have severe adverse effects. Andrographolide, a bicyclic diterpenoid lactone, has traditionally been used for the treatment of colds, fever, laryngitis, and other infections with no or minimal side effects. We determined whether andrographolide treatment of mdx mice, an animal model for DMD, affects muscle damage, physiology, fibrosis, and efficiency of cell therapy.

Methods

mdx mice were treated with andrographolide for three months and skeletal muscle histology, creatine kinase activity, and permeability of muscle fibers were evaluated. Fibrosis and TGF-β signaling were evaluated by indirect immunofluorescence and Western blot analyses. Muscle strength was determined in isolated skeletal muscles and by a running test. Efficiency of cell therapy was determined by grafting isolated skeletal muscle satellite cells onto the tibialis anterior of mdx mice.

Results

mdx mice treated with andrographolide exhibited less severe muscular dystrophy than untreated dystrophic mice. They performed better in an exercise endurance test and had improved muscle strength in isolated muscles, reduced skeletal muscle impairment, diminished fibrosis and a significant reduction in TGF-β signaling. Moreover, andrographolide treatment of mdx mice improved grafting efficiency upon intramuscular injection of dystrophin-positive satellite cells.

Conclusions

These results suggest that andrographolide could be used to improve quality of life in individuals with DMD.

Exploration of lipid metabolism in relation with plasma membrane properties of Duchenne muscular dystrophy cells: influence of L-carnitine

Duchenne muscular dystrophy (DMD) arises as a consequence of mutations in the dystrophin gene. Dystrophin is a membrane-spanning protein that connects the cytoskeleton and the basal lamina. The most distinctive features of DMD are a progressive muscular dystrophy, a myofiber degeneration with fibrosis and metabolic alterations such as fatty infiltration, however, little is known on lipid metabolism changes arising in Duchenne patient cells. Our goal was to identify metabolic changes occurring in Duchenne patient cells especially in terms of L-carnitine homeostasis, fatty acid metabolism both at the mitochondrial and peroxisomal level and the consequences on the membrane structure and function. In this paper, we compared the structural and functional characteristics of DMD patient and control cells. Using radiolabeled L-carnitine, we found, in patient muscle cells, a marked decrease in the uptake and the intracellular level of L-carnitine. Associated with this change, a decrease in the mitochondrial metabolism can be seen from the analysis of mRNA encoding for mitochondrial proteins. Probably, associated with these changes in fatty acid metabolism, alterations in the lipid composition of the cells were identified: with an increase in poly unsaturated fatty acids and a decrease in medium chain fatty acids, mono unsaturated fatty acids and in cholesterol contents. Functionally, the membrane of cells lacking dystrophin appeared to be less fluid, as determined at 37°C by fluorescence anisotropy. These changes may, at least in part, be responsible for changes in the phospholipids and cholesterol profile in cell membranes and ultimately may reduce the fluidity of the membrane. A supplementation with L-carnitine partly restored the fatty acid profile by increasing saturated fatty acid content and decreasing the amounts of MUFA, PUFA, VLCFA. L-carnitine supplementation also restored muscle membrane fluidity. This suggests that regulating lipid metabolism in DMD cells may improve the function of cells lacking dystrophin.

Marking the tempo for myogenesis: Pax7 and the regulation of muscle stem cell fate decisions

Post-natal growth and regeneration of skeletal muscle is highly dependent on a population of resident myogenic precursors known as satellite cells. Transcription factors from the Pax gene family, Pax3 and Pax7, are critical for satellite cell biogenesis, survival and potentially self-renewal; however, the underlying molecular mechanisms remain unsolved. This is particularly true in the case of Pax7, which appears to regulate myogenesis at multiple levels. Accordingly, recent data have highlighted the importance of a functional relationship between Pax7 and the MyoD family of muscle regulatory transcription factors during normal muscle formation and disease. Here we will critically review key findings suggesting that Pax7 may play a dual role by promoting resident muscle progenitors to commit to the skeletal muscle lineage while preventing terminal differentiation, thus keeping muscle progenitors poised to differentiate upon environmental cues. In addition, potential regulatory mechanisms for the control of Pax7 activity will be proposed.

Relationships of thigh muscle contractile and non-contractile tissue with function, strength, and age in boys with Duchenne muscular dystrophy

The purpose of this study was to assess the contractile and non-contractile content in thigh muscles of patients with Duchenne muscular dystrophy (DMD) and determine the relationship with functional abilities. Magnetic resonance images of the thigh were acquired in 28 boys with DMD and 10 unaffected boys. Muscle strength, timed functional tests, and the Brookes Lower Extremity scale were also assessed. Non-contractile content in the DMD group was significantly greater than in the control group for six muscles, including rectus femoris, biceps femoris-long head and adductor magnus. Non-contractile content in the total thigh musculature assessed by MRI correlated with the Brookes scale (r(s)=0.75) and supine-up test (r(s)=0.68), as well as other functional measures. An age-related specific torque increase was observed in the control group (r(s)=0.96), but not the DMD (r(s)=0.06). These findings demonstrate that MRI measures of contractile and non-contractile content can provide important information about disease progression in DMD.

Delay in diagnosis of muscle disorders depends on the subspecialty of the initially consulted physician

Background

New therapeutic strategies in muscular dystrophies will make a difference in prognosis only if they are begun early in the course of the disease. Therefore, we investigated factors that influence the time to diagnosis in muscle dystrophy patients.

Methods

A sample of 101 patients (mean age 49 years; range 19-80; 44% women) with diagnosed muscle dystrophies from neurological practices and the neuromuscular specialty clinic in Berlin, Germany, was invited to participate. Time from first consultation to diagnosis, subspecialty of physician, and sociodemographic data were assessed with self-report questionnaires. The association between time to diagnosis and potential predictors (subspecialty of initially consulted physician, diagnoses, gender, and age at onset) was modeled with linear regression analysis.

Results

The mean time span between first health-care contact and diagnosis was 4.3 years (median 1). The diagnostic delay was significantly longer if patients were initially seen by a non-neurological specialist compared to a general practitioner (5.2 vs. 3.5 years, p = 0.047). Other factors that were independently associated with diagnostic delay were female gender and inherited muscle disease.

Conclusion

Action to improve clinical awareness of muscle diseases in non-neurological specialists is needed.

Targeted gene therapy for the treatment of heart failure

Chronic heart failure is one of the leading causes of morbidity and mortality in Western countries and is a major financial burden to the health care system. Pharmacologic treatment and implanting devices are the predominant therapeutic approaches. They improve survival and have offered significant improvement in patient quality of life, but they fall short of producing an authentic remedy. Cardiac gene therapy, the introduction of genetic material to the heart, offers great promise in filling this void. In-depth knowledge of the underlying mechanisms of heart failure is, obviously, a prerequisite to achieve this aim. Extensive research in the past decades, supported by numerous methodological breakthroughs, such as transgenic animal model development, has led to a better understanding of the cardiovascular diseases and, inadvertently, to the identification of several candidate genes. Of the genes that can be targeted for gene transfer, calcium cycling proteins are prominent, as abnormalities in calcium handling are key determinants of heart failure. A major impediment, however, has been the development of a safe, yet efficient, delivery system. Nonviral vectors have been used extensively in clinical trials, but they fail to produce significant gene expression. Viral vectors, especially adenoviral, on the other hand, can produce high levels of expression, at the expense of safety. Adeno-associated viral vectors have emerged in recent years as promising myocardial gene delivery vehicles. They can sustain gene expression at a therapeutic level and maintain it over extended periods of time, even for years, and, most important, without a safety risk.

Identification of a novel muscle targeting peptide in mdx mice

Exon-skipping oligonucleotides are a well-researched therapeutic strategy for Duchenne's muscular dystrophy (DMD). Despite remarkable successes in animal models with intramuscular and intravenous delivery of unmodified oligonucleotides, the ability to specifically target both normal and dystrophic muscle with a simple peptide ligand could decrease the therapeutic dose required and reduce the potential for toxicity. Thus, 3 rounds of in vivo phage display utilizing a 12-mer peptide library were performed with mdx mice and a peptide motif with potential for targeting to muscle but not liver was identified. This motif was shown to have enhanced binding affinity to C2C12 myoblasts over a scrambled control peptide and in vivo application of a fluorescein-labeled peptide containing the identified motif resulted in increased specificity for the heart and quadriceps muscle after tail-vein administration in C57BL/6 mice. This work has many potential applications for oligonucleotide or drug delivery to muscle for myopathies.

NO more muscle fatigue

NOS is a key enzyme in the production of NO, a molecule that directly regulates vasorelaxation and blood supply. Diverse forms of muscle disease have been clinically associated with unusual fatigue after exercise. The localization of neuronal NOS (nNOS) at the plasma membrane of muscle has recently been shown to prevent muscle fatigue after exercise. In this issue of the JCI, Lai et al. show that dystrophin--the structural protein missing in individuals with Duchenne muscular dystrophy--anchors nNOS to the sarcolemma through a direct interaction with dystrophin spectrin-like repeats 16 and 17 (see the related article, doi:10.1172/JCI36612). Furthermore, in another recently reported study of mouse models of muscular dystrophy, phosphodiesterase 5A inhibitors were used to treat the downstream ischemia that is associated with nNOS mislocalization. Collectively, these findings significantly advance our understanding of exercise-induced muscle fatigue and its role in muscle disease.

Clinical heterogeneity of duchenne muscular dystrophy (DMD): definition of sub-phenotypes and predictive criteria by long-term follow-up

Background

To explore clinical heterogeneity of Duchenne muscular dystrophy (DMD), viewed as a major obstacle to the interpretation of therapeutic trials

Methodology/Principal Findings

A retrospective single institution long-term follow-up study was carried out in DMD patients with both complete lack of muscle dystrophin and genotyping. An exploratory series (series 1) was used to assess phenotypic heterogeneity and to identify early criteria predicting future outcome; it included 75 consecutive steroid-free patients, longitudinally evaluated for motor, respiratory, cardiac and cognitive functions (median follow-up: 10.5 yrs). A validation series (series 2) was used to test robustness of the selected predictive criteria; it included 34 more routinely evaluated patients (age>12 yrs). Multivariate analysis of series 1 classified 70/75 patients into 4 clusters with distinctive intellectual and motor outcomes: A (early infantile DMD, 20%): severe intellectual and motor outcomes; B (classical DMD, 28%): intermediate intellectual and poor motor outcome; C (moderate pure motor DMD, 22%): normal intelligence and delayed motor impairment; and D (severe pure motor DMD, 30%): normal intelligence and poor motor outcome. Group A patients had the most severe respiratory and cardiac involvement. Frequency of mutations upstream to exon 30 increased from group A to D, but genotype/phenotype correlations were restricted to cognition (IQ>71: OR 7.7, 95%CI 1.6–20.4, p<0.003). Diagnostic accuracy tests showed that combination of “clinical onset <2 yrs” with “mental retardation” reliably assigned patients to group A (sensitivity 0.93, specificity 0.98). Combination of “lower limb MMT score>6 at 8 yrs” with “normal or borderline mental status” reliably assigned patients to group C (sensitivity: 1, specificity: 0.94). These criteria were also predictive of “early infantile DMD” and “moderate pure motor DMD” in series 2.

Conclusions/Significance

DMD can be divided into 4 sub-phenotypes differing by severity of muscle and brain dysfunction. Simple early criteria can be used to include patients with similar outcomes in future therapeutic trials.

A novel functional assessment of the differentiation of micropatterned muscle cells

Duchenne muscular dystrophy (DMD) is a lethal disease characterized by rapid, progressive atrophy of muscle tissues. Timely screening of therapeutic interventions is necessary for the development of effective treatment approaches for DMD. We have developed an in vitro model using a combination of micropatterning of C2C12 skeletal muscle cells and cell traction force microscopy (CTFM). In this model, C2C12 cells were micropatterned on a highly elongated adhesive island such that the cells assumed a shape typical of a myotube. During differentiation, these cells gradually fused together and began expressing dystrophin, a structural protein of myotubes, meanwhile, their contractile forces, represented by cell traction forces, continually increased until the myotubes reached maturation. In addition, the high-degree alignment of cells favored myotube differentiation and dystrophin expression. Since the fundamental structural unit of muscle tissue is myofiber, which is responsible for muscle contraction, such a technology that can directly quantify the contractile forces of the myotube, a precursor of myofiber, may constitute a fast and efficient screening approach for DMD therapies.

Gentamicin treatment in exercised mdx mice: Identification of dystrophin-sensitive pathways and evaluation of efficacy in work-loaded dystrophic muscle

Aminoglycosides force read through of premature stop codon mutations and introduce new mutation-specific gene-corrective strategies in Duchenne muscular dystrophy. A chronic treatment with gentamicin (32 mg/kg/daily i.p., 8-12 weeks) was performed in exercised mdx mice with the dual aim to clarify the dependence on dystrophin of the functional, biochemical and histological alterations present in dystrophic muscle and to verify the long term efficiency of small molecule gene-corrective strategies in work-loaded dystrophic muscle. The treatment counteracted the exercise-induced impairment of in vivo forelimb strength after 6-8 weeks. We observed an increase in dystrophin expression level in all the fibers, although lower than that observed in normal fibers, and found a concomitant recovery of aquaporin-4 at sarcolemma. A significant reduction in centronucleated fibers, in the area of necrosis and in the percentage of nuclear factor-kB-positive nuclei was observed in gastrocnemious muscle of treated animals. Plasma creatine kinase was reduced by 70%. Ex vivo, gentamicin restored membrane ionic conductance in mdx diaphragm and limb muscle fibers. No effects were observed on the altered calcium homeostasis and sarcolemmal calcium permeability, detected by electrophysiological and microspectrofluorimetric approaches. Thus, the maintenance of a partial level of dystrophin is sufficient to reinforce sarcolemmal stability, reducing leakiness, inflammation and fiber damage, while correction of altered calcium homeostasis needs greater expression of dystrophin or direct interventions on the channels involved.

Cell delivery mechanisms for tissue repair

Many cell populations, derived from both adult tissues and embryonic stem cells, show promise for the treatment of a variety of diseases. Although the major effort in stem cell therapies in the past has been identifying potentially therapeutic cells, it is now clear that developing systems to deliver these cells and promote their efficient engraftment will provide an equally challenging task. More sophisticated pretransplantation manipulations and material carriers may dramatically improve the survival, engraftment, and fate control of transplanted stem cells and their ultimate clinical utility.

Myostatin blockade improves function but not histopathology in a murine model of limb-girdle muscular dystrophy 2C

Myostatin is a negative regulator of skeletal muscle growth. Myostatin mutations and pharmacological strategies increase muscle mass in vivo, suggesting that myostatin blockade may prove useful in diseases characterized by muscle wasting, such as the muscular dystrophies. We subjected the gamma-sarcoglycan-deficient (Sgcg(-/-)) mouse model of limb-girdle muscular dystrophy (LGMD) 2C to antibody-mediated myostatin blockade in vivo. Myostatin inhibition led to increased fiber size, muscle mass, and absolute force. However, no clear improvement in muscle histopathology was evident, demonstrating discordance between physiological and histological improvement. These results and previous studies on the dyw/dyw mouse model of congenital muscular dystrophy and in the late-stage delta-sarcoglycan-deficient (Sgcd(-/-)) mouse model of LGMD2F document disease-specific limitations to therapeutic strategies based on myostatin blockade in the more severe mouse models of different muscular dystrophies.

Three-point technique of fat quantification of muscle tissue as a marker of disease progression in Duchenne muscular dystrophy: preliminary study

OBJECTIVE

Clinical trials involving patients with Duchenne muscular dystrophy are hindered by the lack of suitable objective end points. The purpose of this study was to examine whether muscle lipid infiltration measured with the three-point Dixon MRI technique has value as a marker of disease severity.

SUBJECTS AND METHODS

Disease severity in nine boys (mean age, 8.6 +/- 2.7 years) with Duchenne muscular dystrophy was determined with the functional ability scale of Brooke and associates. Functional scores were compared with strength measurements obtained by manual testing of muscles of the lower extremities, knee extensor strength measured with an isokinetic dynamometer, and muscle fat percentage in the quadriceps and hamstrings determined with the three-point Dixon MRI technique.

RESULTS

MRI measurements of fat infiltration had stronger correlation (p < 0.05) with functional grade than did measurements obtained with manual muscle testing (p = 0.07) or quantitative strength measured with the isokinetic dynamometer (p = 0.54). Muscle fat percentage did not correlate with strength measurements from manual or dynamometer muscle testing but increased with age in subjects with Duchenne muscular dystrophy.

CONCLUSION

Muscle adiposity values obtained with three-point Dixon MRI are accurate in assessment of disease severity in patients with Duchenne muscular dystrophy. Because they are not influenced by patient effort or examiner variability, these measurements are more objective and reproducible than measurements of muscle strength.

Enhanced effect of microdystrophin gene transfection by HSV-VP22 mediated intercellular protein transport

Background

Duchenne musclar dystrophy (DMD) is an X-linked recessive disease caused by mutations of dystrophin gene, there is no effective treatment for this disorder at present. Plasmid-mediated gene therapy is a promising therapeutical approach for the treatment of DMD. One of the major issues with plasmid-mediated gene therapy for DMD is poor transfection efficiency and distribution. The herpes simplex virus protein VP22 has the capacity to spread from a primary transduced cell to surrounding cells and improve the outcome of gene transfer. To improve the efficiency of plasmid-mediated gene therapy and investigate the utility of the intercellular trafficking properties of VP22-linked protein for the treatment for DMD, expression vectors for C-terminal versions of VP22-microdystrophin fusion protein was constructed and the VP22-mediated shuttle effect was evaluated both in vitro and in vivo.

Results

Our results clearly demonstrate that the VP22-microdystrophin fusion protein could transport into C2C12 cells from 3T3 cells, moreover, the VP22-microdystrophin fusion protein enhanced greatly the amount of microdystrophin that accumulated following microdystrophin gene transfer in both transfected 3T3 cells and in the muscles of dystrophin-deficient (mdx) mice.

Conclusion

These results highlight the efficiency of the VP22-mediated intercellular protein delivery for potential therapy of DMD and suggested that protein transduction may be a potential and versatile tool to enhance the effects of gene delivery for somatic gene therapy of DMD.

PGC-1alpha regulates the neuromuscular junction program and ameliorates Duchenne muscular dystrophy

The coactivator PGC-1alpha mediates key responses of skeletal muscle to motor nerve activity. We show here that neuregulin-stimulated phosphorylation of PGC-1alpha and GA-binding protein (GABP) allows recruitment of PGC-1alpha to the GABP complex and enhances transcription of a broad neuromuscular junction gene program. Since a subset of genes controlled by PGC-1alpha and GABP is dysregulated in Duchenne muscular dystrophy (DMD), we examined the effects of transgenic PGC-1alpha in muscle of mdx mice. These animals show improvement in parameters characteristic of DMD, including muscle histology, running performance, and plasma creatine kinase levels. Thus, control of PGC-1alpha levels in skeletal muscle could represent a novel avenue to prevent or treat DMD.

BM stem cell transplantation rescues pathophysiologic features of aged dystrophic mdx muscle

BACKGROUND

The value of transplantation of BM stem cells in aged (12-month-old) mdx was evaluated because it is thought to be a more ideal model for studying the praxiology of Duchenne muscular dystrophy (DMD). The possible mechanisms of stem cell differentiation were then discussed.

METHODS

BM was isolated from 8-10-week-old male C57 BL/10 mice. After injecting BM cells into 12-month-old female mdx mice through the tail vein, the expression of dystrophin and MyoD was detected at different time points by immunofluorescence staining, RT-PCR and Western blot.

RESULTS

The C57 male mice donor-specific and Y-chromosome-specific sequence could be detected in all female aged mdx mice, implying the success of the transplantation. Expression of dystrophin and MyoD was detected and increased over time.

DISCUSSION

BM cells were recruited to the muscle and partially restored specific pathophysiologic features of the dystrophic muscle in aged mdx mice. Muscle differentiation of BM cells recapitulated embryonic myogenesis.

Well-devised quantification analysis for duplication mutation of Duchenne muscular dystrophy aimed at preimplantation genetic diagnosis

PURPOSE

Preimplantation genetic diagnosis (PGD) has been performed for deletion and point mutation type of Duchenne muscular dystrophy (DMD). Our aim was to develop a PGD technique, not yet established, to directly detect duplication mutation instead of substitute diagnosis similar to gender determination.

METHODS

Our method is based on comparative quantification using conventional duplex PCR, real-time PCR and gender determination. We evaluated this method in single lymphocytes from a duplication type of DMD patient and a normal male.

RESULTS

There was a significant difference in the mean values of the ratios (the mutation locus/a normal reference): mean value +/- SE was 1.84 +/- 0.15 in the duplication patient, and 1.00 +/- 0.09 in the normal male (p < 0.001).

CONCLUSION

It is suggested that our comparative quantification method could be a new option in PGD for carriers with duplication mutation who wish to have an unaffected son.

Multiexon skipping leading to an artificial DMD protein lacking amino acids from exons 45 through 55 could rescue up to 63% of patients with Duchenne muscular dystrophy

Approximately two-thirds of Duchenne muscular dystrophy (DMD) patients show intragenic deletions ranging from one to several exons of the DMD gene and leading to a premature stop codon. Other deletions that maintain the translational reading frame of the gene result in the milder Becker muscular dystrophy (BMD) form of the disease. Thus the opportunity to transform a DMD phenotype into a BMD phenotype appeared as a new treatment strategy with the development of antisense oligonucleotides technology, which is able to induce an exon skipping at the pre-mRNA level in order to restore an open reading frame. Because the DMD gene contains 79 exons, thousands of potential transcripts could be produced by exon skipping and should be investigated. The conventional approach considers skipping of a single exon. Here we report the comparison of single- and multiple-exon skipping strategies based on bioinformatic analysis. By using the Universal Mutation Database (UMD)-DMD, we predict that an optimal multiexon skipping leading to the del45-55 artificial dystrophin (c.6439_8217del) could transform the DMD phenotype into the asymptomatic or mild BMD phenotype. This multiple-exon skipping could theoretically rescue up to 63% of DMD patients with a deletion, while the optimal monoskipping of exon 51 would rescue only 16% of patients.

Therapeutics in duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a fatal disorder affecting approximately 1 in 3,500 live born males, characterized by progressive muscle weakness. Several different strategies are being investigated in developing a cure for this disorder. Until a cure is found, therapeutic and supportive care is essential in preventing complications and improving the afflicted child's quality of life. Currently, corticosteroids are the only class of drug that has been extensively studied in this condition, with controversy existing over the use of these drugs, especially in light of the multiple side effects that may occur. The use of nutritional supplements has expanded in recent years as researchers improve our abilities to use gene and stem cell therapies, which will hopefully lead to a cure soon. This article discusses the importance of therapeutic interventions in children with DMD, the current debate over the use of corticosteroids to treat this disease, the growing use of natural supplements as a new means of treating these boys and provides an update on the current state of gene and stem cell therapies.

Intravenous infusion of an antisense oligonucleotide results in exon skipping in muscle dystrophin mRNA of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease that is characterized by muscle dystrophin deficiency. We report that intravenous (IV) infusion of an antisense oligonucleotide created an in-frame dystrophin mRNA from an out-of-frame DMD mutation (via exon skipping) which led to muscle dystrophin expression. A 10-year-old DMD patient possessing an out-of-frame, exon 20 deletion of the dystrophin gene received a 0.5 mg/kg IV infusion of an antisense 31-mer phosphorothioate oligonucleotide against the splicing enhancer sequence of exon 19. This antisense construct was administered at one-week intervals for 4 wk. No side effects attributable to infusion were observed. Exon 19 skipping appeared in a portion of the dystrophin mRNA in peripheral lymphocytes after the infusion. In a muscle biopsy one week after the final infusion, the novel in-frame mRNA lacking both exons 19 and 20 was identified and found to represent approximately 6% of the total reverse transcription PCR product. Dystrophin was identified histochemically in the sarcolemma of muscle cells after oligonucleotide treatment. These findings demonstrate that phosphorothioate oligonucleotides may be administered safely to children with DMD, and that a simple IV infusion is an effective delivery mechanism for oligonucleotides that lead to exon skipping in DMD skeletal muscles.

Mini-dystrophin efficiently incorporates into the dystrophin protein complex in living cells

Dystrophin is a critical muscle cell structural protein which when deficient results in Duchenne muscular dystrophy. Recently miniature versions of the dystrophin gene have been constructed that ameliorate the pathology in mouse models. To characterize mini-dystrophin's incorporation into the dystrophin protein complex in living cells, two fusion proteins were constructed where mini-dystrophin is fused to the N- or C-terminus of an enhanced green fluorescent protein reporter gene. Both fusion proteins correctly localize at the plasma membrane in vitro and in vivo. Live cell microscopy establishes that mini-dystrophin translocates directly to the PM of differentiating muscle cells, within 4 h of expression. Latrunculin A treatment, actin and beta-dystroglycan binding domain deletion constructs, and co-immunoprecipitation assays demonstrate that mini-dystrophin is firmly anchored to the sarcolemma primarily through its connections to beta-dystroglycan, mimicking effects seen with wild type dystrophin. Furthermore, point mutations made within the putative beta-dystroglycan anchoring ZZ domain of mini-dystrophin result in an ablation of beta-dystroglycan binding and a nuclear translocation of the protein. These results demonstrate that mini-dystrophin is efficiently bound and incorporated into the dystrophin protein complex, via beta-dystroglycan in living cells, similarly to the full length dystrophin protein.

The GTPase RhoA increases utrophin expression and stability, as well as its localization at the plasma membrane

The Rho family of small GTPases are signalling molecules involved in cytoskeleton remodelling and gene transcription. Their activities are important for many cellular processes, including myogenesis. In particular, RhoA positively regulates skeletal-muscle differentiation. We report in the present study that the active form of RhoA increases the expression of utrophin, the autosomal homologue of dystrophin in the mouse C2C12 and rat L8 myoblastic cell lines. Even though this RhoA-dependent utrophin increase is higher in proliferating myoblasts, it is maintained during myogenic differentiation. This occurs via two mechanisms: (i) transcriptional activation of the utrophin promoter A and (ii) post-translational stabilization of utrophin. In addition, RhoA increases plasma-membrane localization of utrophin. Thus RhoA activation up-regulates utrophin levels and enhances its localization at the plasma membrane.

UMD (Universal Mutation Database): 2005 update

With the completion of the Human Genome Project, our vision of human genetic diseases has changed. The cloning of new disease-causing genes can now be performed in silico, and thousands of mutations are being identified in diagnostic and research laboratories yearly. Knowledge about these mutations and their association with clinical and biological data is essential for clinicians, geneticists, and researchers. To collect and analyze these data, we developed a generic software called Universal Mutation Databases (UMD) to create locus-specific databases. Here we report the new release (September 2004) of this freely available tool (www.umd.be), which allows the creation of LSDBs for virtually any gene and includes a large set of new analysis tools. We have implemented new features to integrate noncoding sequences, clinical data, pictures, monoclonal antibodies, and polymorphic markers (SNPs). Today the UMD retains all specifically designed tools to analyze mutations at the molecular level, as well as new sets of routines to search for genotype-phenotype correlations. We also created specific tools for infrequent mutations such as gross deletions and duplications, and deep intronic mutations. A large set of dedicated tools are now available for intronic mutations, including methods to calculate the consensus values (CVs) of potential splice sites and to search for exonic splicing enhancer (ESE) motifs. In addition, we have created specific routines to help researchers design new therapeutic strategies, such as exon skipping, aminoglycoside read-through of stop codons, or monoclonal antibody selection and epitope scanning for gene therapy.

The interface of genomic technologies and nursing

PURPOSES

(a) to summarize views of the interface of technology, genomic technology, and nursing; (b) provide an overview of current and emerging genomic technologies; (c) present clinical exemplars of uses of genomic technology in two disease conditions; and (d) list genomic-focused nursing research on genomic technologies.

ORGANIZING FRAMEWORK

A discussion of genomic technology in the context of nurses' views of technology, the importance of genomic technology for nurses, linking the central dogma of molecular biology to state-of-the-art tests and assays, and nurses' current use of technologies.

CONCLUSIONS

Human genome discoveries will continue to be an integral part of disease prevention, diagnosis, treatment, and management. These discoveries also have the potential for being integrated into nursing science. Genomic technologies are becoming a driving force in patient management, so that nurses will be unable to provide quality care without knowledge of the types of genomic technologies, the rationale for their use, and the possible sequelae that can result from genetic diagnosis or treatment. Many nurses already are using genomic technologies to conduct genomic-focused nursing research. The biobehavioral nature of much of this research further indicates the important contributions of nurses in genomics.

In vivo fusion of circulating fluorescent cells with dystrophin-deficient myofibers results in extensive sarcoplasmic fluorescence expression but limited dystrophin sarcolemmal expression

To investigate the therapeutic potential of bone marrow transplantation in Duchenne muscular dystrophy, green fluorescent protein-positive (GFP+) bone marrow cells were transplanted into irradiated wild-type and dystrophin-deficient mdx mice. Tibialis anterior muscles showed fivefold to sixfold more GFP+ mononucleated cells and threefold to fourfold more GFP+ myofibers in mdx than in wild-type mice. In contrast, dystrophin expression in mdx mice remained within the level of nontransplanted mdx mice, and co-expression with GFP was rare. Longitudinal sections of 5000 myofibers showed 160 GFP+ fibers, including 9 that co-expressed dystrophin. GFP was always visualized as full-length sarcoplasmic fluorescence that exceeded the span of sample length (up to 1500 microm), whereas dystrophin expression was restricted to 11 to 28% of this length. Dystrophin expression span was much shorter in GFP+ fibers (116 +/- 46 microm) than in revertant fibers (654 +/- 409 microm). These data suggest that soluble GFP diffuses far from the fusion site with a pre-existing dystrophin(-) myofiber whereas dystrophin remains mainly expressed close to the site of fusion. Because restoration of dystrophin in whole muscle fiber length is required to expect functional improvement and clinical benefits for Duchenne muscular dystrophy, future applications of cell therapies to neuromuscular disorders could be more appropriately envisaged for replacement of defective soluble sarcoplasmic proteins.

Myostatin propeptide‐mediated amelioration of dystrophic pathophysiology

Mutations in myostatin (GDF8) cause marked increases in muscle mass, suggesting that this transforming growth factor-beta (TGF-beta) superfamily member negatively regulates muscle growth. Myostatin blockade therefore offers a strategy for reversing muscle wasting in Duchenne's muscular dystrophy (DMD) without resorting to genetic manipulation. Here, we demonstrate that pharmacological blockade using a myostatin propeptide stabilized by fusion to IgG-Fc improved pathophysiology of the mdx mouse model of DMD. Functional benefits evidenced by specific force improvement, exceeded those reported previously using myostatin antibody-mediated blockade. More importantly, use of a propeptide blockade strategy obviates possibilities of anti-idiotypic responses that could potentially limit the effectiveness of antibody-mediated myostatin blockade strategies over time. This study provides a novel pharmacological strategy for treatment of diseases associated with muscle wasting such as DMD and since it uses an endogenous inhibitor of myostatin should help circumvent technical hurdles and toxicity associated with conventional gene or cell based therapies.

Subproteomics analysis of Ca+-binding proteins demonstrates decreased calsequestrin expression in dystrophic mouse skeletal muscle

Duchenne muscular dystrophy represents one of the most common hereditary diseases. Abnormal ion handling is believed to render dystrophin-deficient muscle fibres more susceptible to necrosis. Although a reduced Ca(2+) buffering capacity has been shown to exist in the dystrophic sarcoplasmic reticulum, surprisingly no changes in the abundance of the main luminal Ca(2+) reservoir protein calsequestrin have been observed in microsomal preparations. To address this unexpected finding and eliminate potential technical artefacts of subcellular fractionation protocols, we employed a comparative subproteomics approach with total mouse skeletal muscle extracts. Immunoblotting, mass spectrometry and labelling of the entire muscle protein complement with the cationic carbocyanine dye 'Stains-All' was performed in order to evaluate the fate of major Ca(2+)-binding proteins in dystrophin-deficient skeletal muscle fibres. In contrast to a relatively comparable expression pattern of the main protein population in normal vs. dystrophic fibres, our analysis showed that the expression of key Ca(2+)-binding proteins of the luminal sarcoplasmic reticulum is drastically reduced. This included the main terminal cisternae constituent, calsequestrin, and the previously implicated Ca(2+)-shuttle element, sarcalumenin. In contrast, the 'Stains-All'-positive protein spot, representing the cytosolic Ca(2+)-binding component, calmodulin, was not changed in dystrophin-deficient fibres. The reduced 2D 'Stains-All' pattern of luminal Ca(2+)-binding proteins in mdx preparations supports the calcium hypothesis of muscular dystrophy. The previously described impaired Ca(2+) buffering capacity of the dystrophic sarcoplasmic reticulum is probably caused by a reduction in luminal Ca(2+)-binding proteins, including calsequestrin.

Processing, characterisation and biocompatibility of iron-phosphate glass fibres for tissue engineering

Iron-phosphate glass fibres based on the CaO-Na2O-Fe2O3-P2O5 system have been processed and characterised via thermal, XRPD, dissolution rates, diameter and biocompatibility studies. The compositions investigated were fixed at 50mol% P2O5, and the CaO content was varied between 30, 35 and 40mol%. The Fe2O3 was added in low amounts from 1-5mol%, substituting it for the Na2O mol%. The number of Tc (crystallisation temperature) peaks detected from the thermal analysis traces only showed correlation with XRPD analysis, for five out of the 15 compositions investigated. It has been suggested that either the crystalline phases had very similar Tc temperatures or that the other phase(s) were present in very small quantities. There was a good match seen with number of Tm (melting temperature) peaks picked up from the DTA traces, with the number of phases identified from XRPD analysis. The main phases identified from XRPD were NaCa(PO3)3, CaP2O6 and NaFeP2O7. Using network connectivity (NC), predictions on Qn species present within the compositions investigated were made. The predicted species (metaphosphates) matched with phases identified from XRPD analysis. A decrease in dissolution rates for the bulk glass and glass fibres was seen with an increase in CaO mol%, along with an increase in Fe2O3 mol%. An increase in fibre dissolution rates was seen with a decrease in diameter size. The biocompatibility studies were conducted using a conditionally immortal muscle precursor cell line derived from the H-2Kb-tsA58 immortomouse. It was found that iron-phosphate glass fibres containing 4-5mol% Fe2O3 was sufficient for cell attachment and differentiation. It was seen that myotubes formed along the axis of the fibres (which was indicative of differentiation). The biocompatibility of these compositions was attributed to the enhanced chemical durability of the glass fibres.

STRETCH-ACTIVATED CHANNELS IN STRETCH-INDUCED MUSCLE DAMAGE: ROLE IN MUSCULAR DYSTROPHY

1. Stretch-induced muscle injury results in the damage that causes reduced force and increased membrane permeability. This muscle damage is caused, in part, by ionic entry through stretch-activated channels and blocking these channels with Gd3+ or streptomycin reduces the force deficit associated with damage. 2. Dystrophin-deficient muscles are more susceptible to stretch-induced muscle injury and the recovery from injury can be incomplete. We have found that Na+ entry associated with stretch-induced injury is enhanced in dystrophin-deficient muscles and that blockers of stretch-activated channels are capable of preventing ionic entry and reducing muscle damage. 3. A model is presented that proposes links between stretch-induced injury, opening of stretch-activated channels, increased levels of intracellular ions and various forms of muscle damage. Although changes in Na+ accompany stretch-induced muscle injury, we believe that changes in Ca2+ probably have a more central role in the damage process.

The molecular era of myology

This review covers, in general terms, the salient features and impact of molecular myology under the following headings: its role in providing clues for the understanding of molecular etiology and pathogenesis of genetic myopathies, its contribution to the modernization and rationalization of the classification of muscle diseases, providing means of precise diagnosis and prevention of myopathies, development of radically new cell and gene therapies, and determination of future research directions. Myology appears to be among the medical disciplines that have benefited a great deal from molecular science. This remarkable progress will hopefully translate into effective treatment capabilities in the near future.