Pathophysiology of duchenne muscular dystrophy: current hypotheses

Alpha-dystrobrevin-1 recruits alpha-catulin to the alpha1D-adrenergic receptor/dystrophin-associated protein complex signalosome

α(1D)-Adrenergic receptors (ARs) are key regulators of cardiovascular system function that increase blood pressure and promote vascular remodeling. Unfortunately, little information exists about the signaling pathways used by this important G protein-coupled receptor (GPCR). We recently discovered that α(1D)-ARs form a "signalosome" with multiple members of the dystrophin-associated protein complex (DAPC) to become functionally expressed at the plasma membrane and bind ligands. However, the molecular mechanism by which the DAPC imparts functionality to the α(1D)-AR signalosome remains a mystery. To test the hypothesis that previously unidentified molecules are recruited to the α(1D)-AR signalosome, we performed an extensive proteomic analysis on each member of the DAPC. Bioinformatic analysis of our proteomic data sets detected a common interacting protein of relatively unknown function, α-catulin. Coimmunoprecipitation and blot overlay assays indicate that α-catulin is directly recruited to the α(1D)-AR signalosome by the C-terminal domain of α-dystrobrevin-1 and not the closely related splice variant α-dystrobrevin-2. Proteomic and biochemical analysis revealed that α-catulin supersensitizes α(1D)-AR functional responses by recruiting effector molecules to the signalosome. Taken together, our study implicates α-catulin as a unique regulator of GPCR signaling and represents a unique expansion of the intricate and continually evolving array of GPCR signaling networks.

Leupeptin-based inhibitors do not improve the mdx phenotype

Calpain activation has been implicated in the disease pathology of Duchenne muscular dystrophy. Inhibition of calpain has been proposed as a promising therapeutic target, which could lessen the protein degradation and prevent progressive fibrosis. At the same time, there are conflicting reports as to whether elevation of calpastatin, an endogenous calpain inhibitor, alters pathology. We compared the effects of pharmacological calpain inhibition in the mdx mouse using leupeptin and a proprietary compound (C101) that linked the inhibitory portion of leupeptin to carnitine (to increase uptake into muscle). Administration of C101 for 4 wk did not improve muscle histology, function, or serum creatine kinase levels in mdx mice. Mdx mice injected daily with leupeptin (36 mg/kg) for 6 mo also failed to show improved muscle function, histology, or creatine kinase levels. Biochemical analysis revealed that leupeptin administration caused an increase in m-calpain autolysis and proteasome activity, yet calpastatin levels were similar between treated and untreated mdx mice. These data demonstrate that pharmacological inhibition of calpain is not a promising intervention for the treatment of Duchenne muscular dystrophy due to the ability of skeletal muscle to counter calpain inhibitors by increasing multiple degradative pathways.

A muscle resident cell population promotes fibrosis in hindlimb skeletal muscles of mdx mice through the Wnt canonical pathway

Previous work has pointed to a role for the Wnt canonical pathway in fibrosis formation in aged skeletal muscles. In the present study, we studied the dystrophic mdx mouse, which displays skeletal muscle fibrosis. Our results indicated that the muscle resident stromal cell (mrSC) population in the muscles of dystrophic mice is higher than in the muscles of age-matched wild-type mice. Wnt3a promoted the proliferation of and collagen expression by cultured mrSCs but arrested the growth of and collagen expression by cultured myoblasts. Injections of Wnt3A in the tibialis anterior muscles of adult wild-type mice significantly enhanced the mrSC population and collagen deposition compared with the contralateral muscles. Conversely, an injection of the Wnt antagonist Dickkof protein (DKK1) into the skeletal muscles of mdx mice significantly reduced collagen deposition. These results suggested that the Wnt canonical pathway expands the population of mrSCs and stimulates their production of collagen as observed during aging and in various myopathies.

Can inhalation agents be used in the presence of a child with myopathy?

PURPOSE OF REVIEW

Anaesthesia for a child with a muscle disease is always challenging because there is a risk of malignant hyperthermia, rhabdomyolysis or hypermetabolic reaction if a halogenated agent is used. Ongoing progress in genetics helps in clarifying the link between malignant hyperthermia (a calcium channelopathy) and muscle diseases.

RECENT FINDINGS

We provide a summary of the most recent clinical, pathophysiological and genetic information on those risks when the diagnosis is known or suspected preoperatively. Some simple clues are also given to help make a decision in the presence of an infant or child with hypotonia or motor delay but no diagnosis.

SUMMARY

Only a few muscle diseases are really associated with a risk of malignant hyperthermia. The risk of rhabdomyolysis is more difficult to clarify and a multicentric database would be useful to evaluate the risk/benefit ratio of all anaesthetic drugs in patients with muscle diseases.

Age-related differences in lower-limb muscle cross-sectional area and torque production in boys with Duchenne muscular dystrophy

OBJECTIVE

To examine the relationship between lower-extremity muscle cross-sectional area, muscle strength, specific torque, and age in ambulatory boys with Duchenne muscular dystrophy (DMD) compared with controls.

DESIGN

Observational cross-sectional study.

SETTING

University research setting.

PARTICIPANTS

Volunteer sample of boys with DMD (n=22) and healthy control boys (n=10), ages 5 through 14 years.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Maximal muscle cross-sectional area (CSA(max)) assessed by magnetic resonance imaging of quadriceps, plantarflexors (PFs) and dorsiflexors (DFs), peak isometric torque from dynamometry, and timed functional tests.

RESULTS

The average CSA(max) of the triceps surae muscle group was approximately 60% higher in boys with DMD compared with controls (39.1+/-13.6 cm(2) vs 24.5+/-9.3 cm(2); P=.002), while the tibialis anterior muscle showed age-appropriate increases in CSA(max). The increase in quadriceps CSA(max) was also distinctly different in boys with DMD compared with controls. Specific torque (ie, peak torque/CSA(max)) was impaired in all 3 muscles groups, with the knee extensor (KE) and PF muscles showing 4-fold, and the DF muscles 2-fold, higher values in controls compared with boys with DMD. Large age-related gains in specific torque were observed in all 3 muscle groups of control subjects, which were absent in ambulatory boys with DMD. Correlations were observed between performance on functional tasks and quadriceps and PF torque production (r=-.45 to -.57, P<.05), but not with DF strength.

CONCLUSIONS

Age-related changes in muscle cross-sectional area and specific torque production in lower-extremity muscles showed distinctly different patterns in the KE, PF, and DF muscles of boys with DMD compared with controls.

Transcriptomic analysis of dystrophin RNAi knockdown reveals a central role for dystrophin in muscle differentiation and contractile apparatus organization

BACKGROUND

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disorder caused by mutations in the dystrophin gene. DMD has a complex and as yet incompletely defined molecular pathophysiology hindering development of effective ameliorative approaches. Transcriptomic studies so far conducted on dystrophic cells and tissues suffer from non-specific changes and background noise due to heterogeneous comparisons and secondary pathologies. A study design in which a perfectly matched control cell population is used as reference for transcriptomic studies will give a much more specific insight into the effects of dystrophin deficiency and DMD pathophysiology.

RESULTS

Using RNA interference (RNAi) to knock down dystrophin in myotubes from C57BL10 mice, we created a homogenous model to study the transcriptome of dystrophin-deficient myotubes. We noted significant differences in the global gene expression pattern between these myotubes and their matched control cultures. In particular, categorical analyses of the dysregulated genes demonstrated significant enrichment of molecules associated with the components of muscle cell contractile unit, ion channels, metabolic pathways and kinases. Additionally, some of the dysregulated genes could potentially explain conditions and endophenotypes associated with dystrophin deficiency, such as dysregulation of calcium homeostasis (Pvalb and Casq1), or cardiomyopathy (Obscurin, Tcap). In addition to be validated by qPCR, our data gains another level of validity by affirmatively reproducing several independent studies conducted previously at genes and/or protein levels in vivo and in vitro.

CONCLUSION

Our results suggest that in striated muscles, dystrophin is involved in orchestrating proper development and organization of myofibers as contractile units, depicting a novel pathophysiology for DMD where the absence of dystrophin results in maldeveloped myofibers prone to physical stress and damage. Therefore, it becomes apparent that any gene therapy approaches for DMD should target early stages in muscle development to attain a maximum clinical benefit. With a clear and specific definition of the transcriptome of dystrophin deficiency, manipulation of identified dysregulated molecules downstream of dystrophin may lead to novel ameliorative approaches for DMD.

Proteomic Profiling of the Dystrophin-Deficient MDX Heart Reveals Drastically Altered Levels of Key Metabolic and Contractile Proteins

Although Duchenne muscular dystrophy is primarily classified as a neuromuscular disease, cardiac complications play an important role in the course of this X-linked inherited disorder. The pathobiochemical steps causing a progressive decline in the dystrophic heart are not well understood. We therefore carried out a fluorescence difference in-gel electrophoretic analysis of 9-month-old dystrophin-deficient versus age-matched normal heart, using the established MDX mouse model of muscular dystrophy-related cardiomyopathy. Out of 2,509 detectable protein spots, 79 2D-spots showed a drastic differential expression pattern, with the concentration of 3 proteins being increased, including nucleoside diphosphate kinase and lamin-A/C, and of 26 protein species being decreased, including ATP synthase, fatty acid binding-protein, isocitrate dehydrogenase, NADH dehydrogenase, porin, peroxiredoxin, adenylate kinase, tropomyosin, actin, and myosin light chains. Hence, the lack of cardiac dystrophin appears to trigger a generally perturbed protein expression pattern in the MDX heart, affecting especially energy metabolism and contractile proteins.

Dystrophin: more than just the sum of its parts

Dystrophin is one of a number of large cytoskeleton associated proteins that connect between various cytoskeletal elements and often are tethered to the membrane through other transmembrane protein complexes. These cytolinker proteins often provide structure and support to the cells where they are expressed, and mutations in genes encoding these proteins frequently gives rise to disease. Dystrophin is no exception in any of these respects, providing connections between a transmembrane complex known as the dystrophin-glycoprotein complex and the underlying cytoskeleton. The most established connection and possibly the most important is that to F-actin, but more recently evidence has been forthcoming of connections to membrane phospholipids, intermediate filaments and microtubules. Moreover it is becoming increasingly clear that the multiple spectrin-like repeats in the centre of the molecule, that had hitherto been thought to be largely redundant, harbour binding activities that have a significant impact on dystrophin functionality. This functionality is particularly apparent when assessed by the ability to rescue the dystrophic phenotype in mdx mice. This review will focus on the relatively neglected but functionally vital coiled-coil region of dystrophin, highlighting the structural relationships and interactions of the coiled-coil region and providing new insights into the functional role of this region.

Specific anchoring modes of two distinct dystrophin rod sub-domains interacting in phospholipid Langmuir films studied by atomic force microscopy and PM-IRRAS

Dystrophin rod repeats 1-3 sub-domain binds to acidic phosphatidylserine in a small vesicle binding assay, while the repeats 20-24 sub-domain does not. In the present work, we studied the adsorption behaviour of both sub-domains at the air/liquid interface and at the air/lipid interface in a Langmuir trough in order to highlight differences in interfacial properties. The adsorption behaviour of the two proteins at the air/liquid interface shows that they display surface activity while maintaining their alpha-helical secondary structure as shown by PM-IRRAS. Strikingly, R20-24 needs to be highly hydrated even at the interface, while this is not the case for R1-3, indicating that the surface activity is dramatically higher for R1-3 than R20-24. Surface-pressure measurements, atomic force microscopy and PM-IRRAS are used in a Langmuir experiment with DOPC-DOPS monolayers at two different surface pressures, 20 mN/m and 30 mN/m. At the lower surface pressure, the proteins are adsorbed at the lipid film interface while maintaining its alpha-helical structure. After an increase of the surface pressure, R1-3 subsequently produces a stable film, while R20-24 induces a reorganization of the lipid film with a subsequent decrease of the surface pressure close to the initial value. AFM and PM-IRRAS show that R1-3 is present in high amounts at the interface, being arranged in clusters representing 3.3% of the surface at low pressure. By contrast, R20-24 is present at the interface in small amounts bound only by a few electrostatic residues to the lipid film while the major part of the molecule remains floating in the sub-phase. Then for R1-3, the electrostatic interaction between the proteins and the film is enhanced by hydrophobic interactions. At higher surface pressure, the number of protein clusters increases and becomes closer in both cases implying the electrostatic character of the binding. These results indicate that even if the repeats exhibit large structural similarities, their interfacial properties are highly contrasted by their differential anchor mode in the membrane. Our work provides strong support for distinct physiological roles for the spectrin-like repeats and may partly explain the effects of therapeutic replacement of dystrophin deficiency by minidystrophins.

Use of Evans blue dye to compare limb muscles in exercised young and old mdx mice

Evans blue dye (EBD) is used to mark damaged and permeable muscle fibers in mouse models of muscular dystrophy and as an endpoint in therapeutic trials. We counted EBD-positive muscle fibers and extracted EBD from muscles sampled throughout the hindlimbs in young adult and old mdx mice to determine if the natural variability in morphology would allow measurement of a functional improvement in one limb compared to the contralateral limb. Following one bout of rotarod or treadmill exercise that greatly increased serum creatine kinase levels, the number of EBD(+) muscle fibers in 12-19-month-old mdx mice increased 3-fold, EBD in the muscles increased, and, importantly, contralateral pairs of muscles contained similar amounts of EBD. In contrast, the intra- and interlimb amounts of EBD in 2-7-month-old mdx mice were much too variable. A therapeutic effect can more readily be measured in old mdx mice. These results will be useful in the design of therapy protocols using the mdx mouse.

Melatonin treatment normalizes plasma pro-inflammatory cytokines and nitrosative/oxidative stress in patients suffering from Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), a lethal disorder characterized by dystrophin absence, courses with chronic inflammation, sarcolemmal damage, and skeletal muscle degeneration. Among the multiple pathogenic mechanisms proposed for DMD, oxidative stress and inflammation are directly involved in the dystrophic process. Unfortunately, there is no current treatment for DMD, and the inflammatory process is an important target for therapies. Based on the antioxidant and anti-inflammatory properties of melatonin, we investigated whether melatonin treatment may reduce the dystrophic process. Ten DMD patients aged 12.8 +/- 0.98 yr, were treated with melatonin (60 mg at 21:00 hr plus 10 mg at 09:00 hr), and plasma levels of lipid peroxidation (LPO), nitrites (NO(x)), interleukin (IL)-1beta, IL-2, IL-6, tumor necrosis factor-alpha, interferon-gamma, and plasma markers of muscle injury, were determined at 3, 6 and 9 months of treatment. Healthy age- and sex-matched subjects were used as controls. The results show a significant increase in LPO, NO(x), and cytokine levels in plasma of DMD patients compared with controls. Melatonin administration reduced these values to control levels at 3 months of treatment, decreasing further 9 months later. In parallel, melatonin also reduced plasma levels of creatine kinase (CK; 50%), lactate dehydrogenase (28%), aspartate aminotransferase (28%), alanine aminotransferase (20%), and myoglobin (13%). These findings strongly support the conclusion that melatonin administration significantly reduced the hyperoxidative and inflammatory process in DMD patients, reducing the muscle degenerative process.

Dystrophin isoform induction in vivo by antisense-mediated alternative splicing

Antisense oligomer-induced manipulation of dystrophin pre-mRNA processing can remove exons carrying mutations, or exclude exons flanking frameshifting mutations, and restore dystrophin expression in dystrophinopathy models and in Duchenne muscular dystrophy (DMD) patients. Splice intervention can also be used to manipulate the normal dystrophin pre-mRNA processing and ablate dystrophin expression in wild-type mice, with signs of pathology being induced in selected muscles within 4 weeks of commencing treatment. The disruption of normal dystrophin pre-mRNA processing to alter the reading frame can be very efficient and offers an alternative mechanism to RNA silencing for gene suppression. In addition, it is possible to remove in-frame exon blocks from the DMD gene transcript and induce specific dystrophin isoforms that retain partial functionality, without having to generate transgenic animal models. Specific exon removal to yield in-frame dystrophin transcripts will facilitate mapping of functional protein domains, based upon exon boundaries, and will be particularly relevant where there is either limited, or conflicting information as to the consequences of in-frame dystrophin exon deletions on the clinical severity and progression of the dystrophinopathy.

Therapeutic potential of proteasome inhibition in Duchenne and Becker muscular dystrophies

Duchenne muscular dystrophy (DMD) and its milder allelic variant, Becker muscular dystrophy (BMD), result from mutations of the dystrophin gene and lead to progressive muscle deterioration. Enhanced activation of proteasomal degradation underlies critical steps in the pathogenesis of the DMD/BMD dystrophic process. Previously, we demonstrated that treatment with the proteasome inhibitor MG-132 rescues the cell membrane localization of dystrophin and the dystrophin glycoprotein complex in mdx mice, a natural genetic mouse model of DMD. The current work aims to thoroughly define the therapeutic potential in dystrophinopathies of Velcade, a drug that selectively blocks the ubiquitin-proteasome pathway. Velcade is particularly intriguing since it has been approved for the treatment of multiple myeloma. Therefore, its side effects in humans have been explored. Velcade effects were analyzed through two independent methodological approaches. First, we administered the drug systemically in mdx mice over a 2-week period. In this system, Velcade restores the membrane expression of dystrophin and dystrophin glycoprotein complex members and improves the dystrophic phenotype. In a second approach, we treated with the compound explants from muscle biopsies of DMD or BMD patients. We show that the inhibition of the proteasome pathway up-regulates dystrophin, alpha-sarcoglycan, and beta-dystroglycan protein levels in explants from BMD patients, whereas it increases the proteins of the dystrophin glycoprotein complex in DMD cases.

Left ventricular T2 distribution in Duchenne muscular dystrophy

BACKGROUND

Although previous studies have helped define the natural history of Duchenne muscular dystrophy (DMD)-associated cardiomyopathy, the myocardial pathobiology associated with functional impairment in DMD is not yet known.The objective of this study was to assess the distribution of transverse relaxation time (T2) in the left ventricle (LV) of DMD patients, and to determine the association of myocardial T2 heterogeneity to the severity of cardiac dysfunction. DMD patients (n = 26) and normal control subjects (n = 13) were studied by cardiovascular magnetic resonance (CMR). DMD subject data was stratified based on subject age and LV ejection fraction (EF) into the following groups: A (<12 years old, n = 12); B (>or=12 years old, EF or=12 years old, EF = 55%, n = 6). Controls were also stratified by age into Groups N1 (<12 years, n = 6) and N2 (>12 years, n = 5). LV mid-slice circumferential myocardial strain (epsilon cc) was calculated using tagged CMR imaging. T2 maps of the LV were generated for all subjects using a black blood dual spin echo method at two echo times. The full width at half maximum (FWHM) was calculated from a histogram of LV T2 distribution constructed for each subject.

RESULTS

In DMD subject groups, FWHM of the T2 histogram rose progressively with age and decreasing EF (Group A FWHM= 25.3 +/- 3.8 ms; Group B FWHM= 30.9 +/- 5.3 ms; Group C FWHM= 33.0 +/- 6.4 ms). Further, FWHM was significantly higher in those with reduced circumferential strain (|epsilon cc| 12% (Group A). Group A FWHM was not different from the two normal groups (N1 FWHM = 25.3 +/- 3.5 ms; N2 FWHM= 24.0 +/- 7.3 ms).

CONCLUSION

Reduced EF and epsilon cc correlates well with increased T2 heterogeneity quantified by FWHM, indicating that subclinical functional impairments could be associated with pre-existing abnormalities in tissue structure in young DMD patients.

Alterações fisiológicas e metabólicas em indivíduo com distrofia muscular de Duchenne durante tratamento fisioterapêutico: um estudo de caso

INTRODUÇÃO: A Distrofia Muscular de Duchenne (DMD) caracteriza-se por uma perda progressiva da força muscular. O tratamento fisioterapêutico tem fundamental importância na manutenção da qualidade de vida desses pacientes. Contudo, existe grande dificuldade em graduar o grau de cansaço e o limite de exigência da musculatura durante o tratamento. Adicionalmente, não existe na literatura descrição sobre alterações fisiológicas e metabólicas durante uma atividade de esforço nessa população específica. OBJETIVOS: O presente trabalho teve como objetivos avaliar as alterações fisiológicas e metabólicas em indivíduo com DMD durante um programa de fisioterapia, relacionando-as com a percepção subjetiva de esforço (PSE). METODOLOGIA: Este estudo foi realizado na Clínica de Prevenção e Reabilitação Física da Universidade do Estado de Santa Catarina (UDESC). O sujeito do estudo foi um paciente com DMD (sexo masculino, 17 anos). Foram coletados dados de concentrações plasmáticas de lactato e glicose, frequência cardíaca e frequência respiratória, pressão arterial e percepção de esforço segundo a escala de PSE CR10 de Borg. Os dados foram coletados aos 0, 15, 30 e 45 minutos de atendimento fisioterapêutico. A sessão de fisioterapia foi dividida em 3 etapas com atividade de intensidade e exigência muscular crescentes. Foram realizados 6 atendimentos. RESULTADOS: Os resultados demonstraram PSE crescente durante a sessão de fisioterapia. Foi verificada uma relação linear entre as variáveis metabólicas e a PSE. Já as variáveis fisiológicas não demonstraram relação proporcional com a PSE. CONCLUSÃO: Sugere-se que a PSE é uma forma simples de monitoramento do cansaço de pacientes com DMD, durante o tratamento fisioterapêutico.

Making fast-twitch dystrophic muscles bigger protects them from contraction injury and attenuates the dystrophic pathology

The lack of functional dystrophin protein in Duchenne muscular dystrophy (DMD) renders muscle fibers highly fragile and susceptible to damage during contractions. Contraction-mediated injury is a major contributor to the progressive degeneration and etiology of muscle wasting in DMD. The prevailing understanding is that large fibers are highly susceptible to contraction damage and are affected preferentially, whereas smaller fibers are relatively spared in DMD. We tested the hypothesis that a pharmacological treatment that caused myofiber hypertrophy would increase the susceptibility of muscles from dystrophin-deficient mdx mice to contraction-induced injury, and thus aggravate the dystrophic pathology. The beta-agonist formoterol (100 microg/kg per day, i.p.) was administered to mdx mice for 28 days. Formoterol increased muscle mass, fiber cross-sectional area, and maximum force producing capacity by 30%, 23%, and 21%, respectively, in fast-twitch tibialis anterior muscles of mdx mice. Myofiber hypertrophy and increased maximum force producing capacity were also observed in the predominantly slow-twitch soleus muscles of mdx mice. Our original hypothesis was rejected since tibialis anterior muscles from formoterol-treated mdx mice had lower cumulative force deficits, indicating that they were less susceptible to contraction-induced injury. Formoterol treatment did not affect injury susceptibility in soleus muscles. These findings indicate that making dystrophic muscles bigger protects them from contraction damage and does not aggravate the dystrophic pathophysiology. These novel results further support the contention that anabolic agents have therapeutic potential for muscle wasting conditions including DMD.

In vivo analyzes of dystroglycan function during somitogenesis in Xenopus laevis

Dystroglycan (Dg) is a cell adhesion receptor for laminin that has been reported to play a role in skeletal muscle cell stability, cytoskeletal organization, cell polarity, and signaling. Here we show that Dg is expressed at both the notochord/somite and the intersomitic boundaries, where laminin and fibronectin are accumulated during somitogenesis. Inhibition of Dg function with morpholino antisense oligonucleotides or a dominant negative mutant results in the normal segmentation of the presomitic mesoderm but affects the number, the size, and the integrity of somites. Depletion of Dg disrupts proliferation and alignment of myoblasts without affecting XMyoD and XMRF4 expression. It also leads to defects in laminin deposition at the intersomitic junctions, whereas expression of integrin beta1 subunits and fibronectin assembly occur normally. Our results show that Dg is critical for both proliferation and elongation of somitic cells and that the Dg-cytoplasmic domain is required for the laminin assembly at the intersomitic boundaries. Developmental Dynamics 238:1332-1345, 2009. (c) 2008 Wiley-Liss, Inc.

SLIMMER (FHL1B/KyoT3) interacts with the proapoptotic protein Siva-1 (CD27BP) and delays skeletal myoblast apoptosis

The fhl1 gene encoding four-and-a-half LIM protein-1 (FHL1) and its spliced isoform, SLIMMER, is mutated in reducing body myopathy, X-linked myopathy with postural muscle atrophy, scapuloperoneal myopathy, and rigid spine syndrome. In this study we have identified a novel function for SLIMMER in delaying skeletal muscle apoptosis via an interaction with the proapoptotic protein Siva-1. Siva-1 was identified as a SLIMMER-specific-interacting protein using yeast two-hybrid screening, direct-binding studies, and glutathione S-transferase pulldown analysis of murine skeletal muscle lysates. In C2C12 skeletal myoblasts, SLIMMER and Siva co-localized in the nucleus; however, both proteins exhibited redistribution to the cytoplasm following the differentiation of mononucleated myoblasts to multinucleated myotubes. In sections of mature skeletal muscle from wild type mice, SLIMMER and Siva-1 co-localized at the Z-line. SLIMMER and Siva-1 were also enriched in Pax-7-positive satellite cells, muscle stem cells that facilitate repair and regeneration. Significantly, SLIMMER delayed Siva-1-dependent apoptosis in C2C12 myoblasts. In skeletal muscle sections from the mdx mouse model of Duchenne muscular dystrophy, SLIMMER and Siva-1 co-localized in the nucleus of apoptotic myofibers. Therefore, SLIMMER may protect skeletal muscle from apoptosis.

Imatinib mesylate ameliorates the dystrophic phenotype in exercised mdx mice

Myofiber degeneration, inflammation, and fibrosis are remarkable features of Duchenne muscular dystrophy. We hypothesized that the administration of imatinib mesylate, an inhibitor of tyrosine kinase and TGF-beta pro-fibrogenic activity, could improve the muscular conditions in mdx mice. Four-week old mdx mice were treated and exercised for 6 weeks. Gastrocnemius and diaphragm histopathology, strength, creatine kinase, and cytokine levels were evaluated. The treated group presented increased muscular strength and decreased CK levels, injured myofibers, and inflammatory infiltrates. Pro-inflammatory cytokines and TGF-beta were also reduced, while IL-10 was increased, suggesting an immunomodulatory effect of imatinib, which can ameliorate the dystrophic phenotype in mdx mice.

Mitochondrial abnormalities, energy deficit and oxidative stress are features of calpain 3 deficiency in skeletal muscle

Mutations in the non-lysosomal cysteine protease calpain-3 cause autosomal recessive limb girdle muscular dystrophy. Pathological mechanisms occurring in this disease have not yet been elucidated. Here, we report both morphological and biochemical evidence of mitochondrial abnormalities in calpain-3 knockout (C3KO) muscles, including irregular ultrastructure and distribution of mitochondria. The morphological abnormalities in C3KO muscles are associated with reduced in vivo mitochondrial ATP production as measured by (31)P magnetic resonance spectroscopy. Mitochondrial abnormalities in C3KO muscles also correlate with the presence of oxidative stress; increased protein modification by oxygen free radicals and an elevated concentration of the anti-oxidative enzyme Mn-superoxide dismutase were observed in C3KO muscles. Previously we identified a number of mitochondrial proteins involved in beta-oxidation of fatty acids as potential substrates for calpain-3. In order to determine if the mitochondrial abnormalities resulted from the loss of direct regulation of mitochondrial proteins by calpain-3, we validated the potential substrates that were identified in previous proteomic studies. This analysis showed that the beta-oxidation enzyme, VLCAD, is cleaved by calpain-3 in vitro, but we were not able to confirm that VLCAD is an in vivo substrate for calpain-3. However, the activity of VLCAD was decreased in C3KO mitochondrial fractions compared with wild type, a finding that likely reflects a general mitochondrial dysfunction. Taken together, these data suggest that mitochondrial abnormalities leading to oxidative stress and energy deficit are important pathological features of calpainopathy and possibly represent secondary effects of the absence of calpain-3.

Skeletal muscle as a paradigm for regenerative biology and medicine

Tissue development and regeneration share common features, since modules of regulatory pathways and transcription factors that are crucial for prenatal development are redeployed for tissue reconstruction after trauma. Regenerative medicine has therefore gained important insights through the study of developmental and regenerative biology. Moreover, diverse experimental models have been used to investigate the regeneration process in different tissues and organs. Paradoxically, little is known regarding the relative contribution of stem cells with respect to the supporting tissue during tissue regeneration. Particular attention will be given to mouse models using distinct injury paradigms to investigate the regenerative biology of skeletal muscle. An understanding of the response of stem and parenchymal cells is crucial for the development of clinical strategies to combat the normal decline in tissue performance during aging or its reconstitution after trauma and during disease. This review addresses these issues, focusing on muscle regeneration and how different factors, including genes, cells and the environment, impinge on this process.

Protein O-mannosylation: conserved from bacteria to humans

Protein O-mannosylation is an essential modification in fungi and animals. Different from most other types of O-glycosylation, protein O-mannosylation is initiated in the endoplasmic reticulum by the transfer of mannose from dolichol monophosphate-activated mannose to serine and threonine residues of secretory proteins. In recent years, it has emerged that even bacteria are capable of O-mannosylation and that the biosynthetic pathway of O-mannosyl glycans is conserved between pro- and eukaryotes. In this review, we summarize the observations that have opened up the field and highlight characteristics of O-mannosylation in the different domains/kingdoms of life.

Proteomic profiling of antisense-induced exon skipping reveals reversal of pathobiochemical abnormalities in dystrophic mdx diaphragm

The disintegration of the dystrophin-glycoprotein complex represents the initial pathobiochemical insult in Duchenne muscular dystrophy. However, secondary changes in signalling, energy metabolism and ion homeostasis are probably the main factors that eventually cause progressive muscle wasting. Thus, for the proper evaluation of novel therapeutic approaches, it is essential to analyse the reversal of both primary and secondary abnormalities in treated muscles. Antisense oligomer-mediated exon skipping promises functional restoration of the primary deficiency in dystrophin. In this study, an established phosphorodiamidate morpholino oligomer coupled to a cell-penetrating peptide was employed for the specific removal of exon 23 in the mutated mouse dystrophin gene transcript. Using DIGE analysis, we could show the reversal of secondary pathobiochemical abnormalities in the dystrophic diaphragm following exon-23 skipping. In analogy to the restoration of dystrophin, beta-dystroglycan and neuronal nitric oxide synthase, the muscular dystrophy-associated differential expression of calsequestrin, adenylate kinase, aldolase, mitochondrial creatine kinase and cvHsp was reversed in treated muscle fibres. Hence, the re-establishment of Dp427 coded by the transcript missing exon 23 has counter-acted dystrophic alterations in Ca2+-handling, nucleotide metabolism, bioenergetic pathways and cellular stress response. This clearly establishes the exon-skipping approach as a realistic treatment strategy for diminishing diverse downstream alterations in dystrophinopathy.

Airway clearance in Duchenne muscular dystrophy

This is a summary of the presentation on airway clearance in neuromuscular disorders presented as part of the program on airway clearance in Duchenne muscular dystrophy at the 30th annual Carrell-Krusen Neuromuscular Symposium on February 20, 2008.

Mapping of the lipid-binding and stability properties of the central rod domain of human dystrophin

Dystrophin is a cytoskeletal protein that confers resistance to the sarcolemma against the stress of contraction-relaxation cycles by interacting with cytoskeletal and membrane partners. Apart from several proteins, membrane phospholipids are a partner of the central rod domain made up of 24 spectrin-like repeats, separated into sub-domains by four hinges. We previously showed that repeats 1 to 3 bind to membrane anionic phospholipids, while repeats 20 to 24 are not able to do so. We focus here on the phospholipid-binding properties of the major part of the central rod domain, namely, the sub-domain delineated by hinges 2 and 3 comprising 16 repeats ranging from repeat 4 to 19 (R4-19). We designed and produced multirepeat proteins comprising three to five repeats and report their lipid-binding properties as well as their thermal stabilities. When these proteins are mixed with liposomes including the anionic lipid phosphatidylserine, they form stable protein-vesicle complexes as determined by gel-filtration chromatography. The absence of an anionic lipid precludes the formation of such complexes. Spectroscopic analyses by circular dichroism and tryptophan fluorescence show that, while the alpha-helical secondary structures are not modified by the binding, protein trans conformation leads to the movement of tryptophan residues into more hydrophobic environments. In addition, the decrease in the molar ellipticity ratio at 222/208 nm as observed by circular dichroism indicates that lipid binding reduces the inter-helical interactions of multirepeat proteins, thus suggesting partly "opened" coiled-coil structures. Combining these results with data from our previous studies, we propose a new model of the dystrophin molecule lying along the membrane bilayer, in which the two sub-domains R1-3 and R4-19 interact with lipids and F-actin, while the distal sub-domain R20-24 does not exhibit any interaction. These lipid-binding domains should thus maintain a structural link between cytoskeletal actin and sarcolemma via the membrane phospholipids.

Identifying set-wise differential co-expression in gene expression microarray data

Background

Previous differential coexpression analyses focused on identification of differentially coexpressed gene pairs, revealing many insightful biological hypotheses. However, this method could not detect coexpression relationships between pairs of gene sets. Considering the success of many set-wise analysis methods for microarray data, a coexpression analysis based on gene sets may elucidate underlying biological processes provoked by the conditional changes. Here, we propose a differentially coexpressed gene sets (dCoxS) algorithm that identifies the differentially coexpressed gene set pairs between conditions.

Results

dCoxS is a two-step analysis method. In each condition, dCoxS measures the interaction score (IS), which represents the expression similarity between two gene sets using Renyi relative entropy. When estimating the relative entropy, multivariate kernel density estimation was used to model gene-gene correlation structure. Statistical tests for the conditional difference between the ISs determined the significance of differential coexpression of the gene set pair. Simulation studies supported that the IS is a representative measure of similarity between gene expression matrices. Single gene coexpression analysis of two publicly available microarray datasets detected no significant results. However, the dCoxS analysis of the datasets revealed differentially coexpressed gene set pairs related to the biological conditions of the datasets.

Conclusion

dCoxS identified differentially coexpressed gene set pairs not found by single gene analysis. The results indicate that set-wise differential coexpression analysis is useful for understanding biological processes induced by conditional changes.

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

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

The decrease of expression of ryanodine receptor sub-type 2 is reversed by gentamycin sulphate in vascular myocytes from mdx mice

The mdx mouse, a model of the human Duchenne muscular dystrophy, displays impaired contractile function in skeletal, cardiac and smooth muscles. We explored the possibility that ryanodine receptor (RYR) expression could be altered in vascular muscle. The three RYR sub-types were expressed in portal vein myocytes. As observed through mRNA and protein levels, RYR2 expression was strongly decreased in mdx myocytes, whereas RYR3 and RYR1 expression were unaltered. The use of antisense oligonucleotide directed against RYR sub-types indicated that caffeine-induced Ca²⁺ response and Ca²⁺ spark frequency depended on RYR2 and RYR1. In mdx mice, caffeine-induced Ca²⁺ responses were decreased in both amplitude and maximal rate of rise, and the frequency of Ca²⁺ sparks was also strongly decreased. The gentamycin treatment was able to increase both the expression of RYR2 and the caffeine-induced Ca²⁺ response to the same level as that observed in wild-type mice. Taken together, these results confirm that both RYR1 and RYR2 are required for vascular Ca²⁺ signalling and indicate that inhibition of RYR2 expression may account for the decreased Ca²⁺ release from the SR in mdx vascular myocytes. Finally, we suggest that gentamycin can restore the Ca²⁺ signalling in smooth muscle from mdx mice by increasing RYR2 and dystrophin expression. These results may help explain the reduced efficacy of contraction in vascular myocytes of mdx mice and Duchenne muscular dystrophy–afflicted patients. Gentamycin treatment could be a good therapeutic tool to restore the vascular function.

Does satellite cell dysfunction contribute to disease progression in Emery–Dreifuss muscular dystrophy?

Muscular dystrophies comprise at least 34 conditions, characterized by progressive skeletal muscle weakness and degeneration. The loci affected include mutations in both muscle-specific genes and genes that are more widely expressed such as LMNA and EMD, responsible for EDMD (Emery–Dreifuss muscular dystrophy). LMNA encodes A-type lamins, whereas EMD encodes emerin, both located in the nuclear envelope. Mutation or loss of A-type lamins or emerin in the terminally differentiated myonuclei of muscle fibres results in muscle damage. Importantly, since LMNA and EMD are also expressed by the resident skeletal muscle stem cells, the satellite cells, the mutations that cause muscle damage may also directly compromise the regenerative response. Thus EDMD is different from dystrophic conditions such as Duchenne muscular dystrophy, where the mutated gene is only expressed in the muscle fibres. In this brief review, we examine the evidence that myoblasts carrying EDMD-causing mutations are compromised, and discuss the possibility that such dysfunction results in reduced efficiency of muscle regeneration, so actively contributes to disease progression.

Degeneration of dystrophic or injured skeletal muscles induces high expression of Galectin-1

Muscle degenerative diseases such as Duchenne Muscular Dystrophy are incurable and treatment options are still restrained. Understanding the mechanisms and factors responsible for muscle degeneration and regeneration will facilitate the development of novel therapeutics. Several recent studies have demonstrated that Galectin-1 (Gal-1), a carbohydrate-binding protein, induces myoblast differentiation and fusion in vitro, suggesting a potential role for this mammalian lectin in muscle regenerative processes in vivo. However, the expression and localization of Gal-1 in vivo during muscle injury and repair are unclear. We report the expression and localization of Gal-1 during degenerative-regenerative processes in vivo using two models of muscular dystrophy and muscle injury. Gal-1 expression increased significantly during muscle degeneration in the murine mdx and in the canine Golden Retriever Muscular Dystrophy animal models. Compulsory exercise of mdx mouse, which intensifies degeneration, also resulted in sustained Gal-1 levels. Furthermore, muscle injury of wild-type C57BL/6 mice, induced by BaCl(2) treatment, also resulted in a marked increase in Gal-1 levels. Increased Gal-1 levels appeared to localize both inside and outside the muscle fibers with significant extracellular Gal-1 colocalized with infiltrating CD45(+) leukocytes. By contrast, regenerating muscle tissue showed a marked decrease in Gal-1 to baseline levels. These results demonstrate significant regulation of Gal-1 expression in vivo and suggest a potential role for Gal-1 in muscle homeostasis and repair.

Ultrastructural definition of apoptosis in heart failure

Cardiac myocytes die through apoptosis, oncosis, and autophagy. Apoptosis affects single cells and is morphologically characterized by nuclear fragmentation with generation of apoptotic bodies that can be seen either within dying cells or free in the interstitial spaces. Dead myocytes are removed by macrophages through phagocytosis without triggering inflammation. The circulating markers of myocyte necrosis are not increased by apoptosis. The morphologic changes of the induction and early execution phases are seen at electron microscopy while late fragmentation is visible on both light and electron microscopy. Immunoelectron microscopy provides combined functional and structural information showing cytochrome c immuno-labelling release from mitochondria, TUNEL labelling of apoptotic nuclei, annexin V translocation in the outer plasma cell layer. Oncosis is characterized by specific morphologic features that may coexist with apoptosis, especially in ischemic myocardium. Autophagy is a defense process that is associated with significant myocardial damage and necrosis when removal of the lysosomal content is impaired. Morphological features of apoptosis, oncosis, and autophagocytosis may coexist at the same time. Although dead myocytes showing characteristics of autophagy and apoptosis are rarely observed in human decompensated hearts, autophagic vacuoles, and early apoptotic changes may be seen more often in morphologically viable myocytes. Such features may occur in failing hearts of both ischemic and non-ischemic etiology. The shared mode of cardiac myocyte death in failing human hearts of different etiologies suggests that preservation of myocyte integrity may be possible by similar therapeutic strategies.

Prevention of muscle fibrosis and improvement in muscle performance in the mdx mouse by halofuginone

Fibrosis is a known feature of dystrophic muscles, particularly the diaphragm, in the mdx mouse. In this study we evaluated the effect of halofuginone, a collagen synthesis inhibitor, on collagen synthesis in various muscles of young wild-type (C57/BL/6J) and mdx mice. Halofuginone prevented the age-dependent increase in collagen synthesis in the diaphragms of mdx with no effect on wild-type mice (n = 5 for each time point). This was associated with a decrease in the degenerated areas and number of central nuclei. Halofuginone also inhibited collagen synthesis in cardiac muscle. Moreover, enhanced motor coordination, balance and improved cardiac muscle function were observed implying reduced muscle injury. Halofuginone inhibited Smad3 phosphorylation downstream of TGFbeta in the diaphragm and cardiac muscles, in C2 cell line and in primary mouse myoblast cultures representing various muscular dystrophies. We suggest that via its effect on Smad3 phosphorylation, halofuginone inhibits muscle fibrosis and improves cardiac and skeletal muscle functions in mdx mice.

Destabilization of the dystrophin-glycoprotein complex without functional deficits in alpha-dystrobrevin null muscle

α-Dystrobrevin is a component of the dystrophin-glycoprotein complex (DGC) and is thought to have both structural and signaling roles in skeletal muscle. Mice deficient for α-dystrobrevin (adbn^−/−) exhibit extensive myofiber degeneration and neuromuscular junction abnormalities. However, the biochemical stability of the DGC and the functional performance of adbn^−/− muscle have not been characterized. Here we show that the biochemical association between dystrophin and β-dystroglycan is compromised in adbn^−/− skeletal muscle, suggesting that α-dystrobrevin plays a structural role in stabilizing the DGC. However, despite muscle cell death and DGC destabilization, costamere organization and physiological performance is normal in adbn^−/− skeletal muscle. Our results demonstrate that myofiber degeneration alone does not cause functional deficits and suggests that more complex pathological factors contribute to the development of muscle weakness in muscular dystrophy.

Literature-aided meta-analysis of microarray data: a compendium study on muscle development and disease

Background

Comparative analysis of expression microarray studies is difficult due to the large influence of technical factors on experimental outcome. Still, the identified differentially expressed genes may hint at the same biological processes. However, manually curated assignment of genes to biological processes, such as pursued by the Gene Ontology (GO) consortium, is incomplete and limited. We hypothesised that automatic association of genes with biological processes through thesaurus-controlled mining of Medline abstracts would be more effective. Therefore, we developed a novel algorithm (LAMA: Literature-Aided Meta-Analysis) to quantify the similarity between transcriptomics studies. We evaluated our algorithm on a large compendium of 102 microarray studies published in the field of muscle development and disease, and compared it to similarity measures based on gene overlap and over-representation of biological processes assigned by GO.

Results

While the overlap in both genes and overrepresented GO-terms was poor, LAMA retrieved many more biologically meaningful links between studies, with substantially lower influence of technical factors. LAMA correctly grouped muscular dystrophy, regeneration and myositis studies, and linked patient and corresponding mouse model studies. LAMA also retrieves the connecting biological concepts. Among other new discoveries, we associated cullin proteins, a class of ubiquitinylation proteins, with genes down-regulated during muscle regeneration, whereas ubiquitinylation was previously reported to be activated during the inverse process: muscle atrophy.

Conclusion

Our literature-based association analysis is capable of finding hidden common biological denominators in microarray studies, and circumvents the need for raw data analysis or curated gene annotation databases.

L-arginine decreases inflammation and modulates the nuclear factor-kappaB/matrix metalloproteinase cascade in mdx muscle fibers

Duchenne muscular dystrophy (DMD) is a lethal, X-linked disorder associated with dystrophin deficiency that results in chronic inflammation, sarcolemma damage, and severe skeletal muscle degeneration. Recently, the use of L-arginine, the substrate of nitric oxide synthase (nNOS), has been proposed as a pharmacological treatment to attenuate the dystrophic pattern of DMD. However, little is known about signaling events that occur in dystrophic muscle with l-arginine treatment. Considering the implication of inflammation in dystrophic processes, we asked whether L-arginine inhibits inflammatory signaling cascades. We demonstrate that L-arginine decreases inflammation and enhances muscle regeneration in the mdx mouse model. Classic stimulatory signals, such as proinflammatory cytokines interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha, are significantly decreased in mdx mouse muscle, resulting in lower nuclear factor (NF)-kappaB levels and activity. NF-kappaB serves as a pivotal transcription factor with multiple levels of regulation; previous studies have shown perturbation of NF-kappaB signaling in both mdx and DMD muscle. Moreover, L-arginine decreases the activity of metalloproteinase (MMP)-2 and MMP-9, which are transcriptionally activated by NF-kappaB. We show that the inhibitory effect of L-arginine on the NF-kappaB/MMP cascade reduces beta-dystroglycan cleavage and translocates utrophin and nNOS throughout the sarcolemma. Collectively, our results clarify the molecular events by which L-arginine promotes muscle membrane integrity in dystrophic muscle and suggest that NF-kappaB-related signaling cascades could be potential therapeutic targets for DMD management.

Early regional myocardial dysfunction in young patients with Duchenne muscular dystrophy

BACKGROUND

In young patients (aged <12 years) with Duchenne muscular dystrophy (DMD), cardiac systolic function is generally described to be within the normal range. Recent studies have suggested the presence of subclinical dysfunction in these young patients using cardiac magnetic resonance imaging, tissue Doppler measurements, and myocardial velocity gradients. The aim of this study was to further assess regional myocardial function in a young group of patients with DMD using myocardial velocity and deformation imaging.

METHODS

Thirty-two patients with DMD (mean age, 7.9 years; range, 3-12 years) and 29 age-matched normal controls were studied with echocardiography. Standard echocardiographic measurements of left ventricular (LV) systolic and diastolic function were performed. Myocardial velocity and deformation data, including peak systolic and early and late diastolic myocardial velocities, peak systolic strain rate (SR), and peak systolic strain (epsilon), were calculated in the radial direction in the inferolateral LV wall and in the longitudinal direction in the interventricular septum, the LV anterolateral wall, and the right ventricular (RV) free wall.

RESULTS

Higher heart rates and increased LV end-systolic dimensions were seen in patients with DMD compared with controls. Significant decreases in radial and longitudinal peak systolic SR, peak systolic epsilon, and peak systolic and early diastolic myocardial velocities were found in the LV inferolateral and anterolateral walls in patients with DMD. No significant differences in longitudinal function could be found in the interventricular septum or in the RV free wall.

CONCLUSION

In young patients with DMD who have global normal systolic function, reductions in systolic deformation parameters as well as reduced early diastolic myocardial velocities can be detected in the anterolateral and inferolateral LV walls. The prognostic significance of these findings warrants further longitudinal follow-up.

Functional resolution of fibrosis in mdx mouse dystrophic heart and skeletal muscle by halofuginone

The effect of halofuginone (Halo) on established fibrosis in older mdx dystrophic muscle was investigated. Mice (8 to 9 mo) treated with Halo (or saline in controls) for 5, 10, or 12 wk were assessed weekly for grip strength and voluntary running. Echocardiography was performed at 0, 5, and 10 wk. Respiratory function and exercise-induced muscle damage were tested. Heart, quadriceps, diaphragm, and tibialis anterior muscles were collected to study fibrosis, collagen I and III expression, collagen content using a novel collagenase-digestion method, and cell proliferation. Hepatocyte growth factor and α-smooth muscle actin proteins were assayed in quadriceps. Halo decreased fibrosis (diaphragm and quadriceps), collagen I and III expression, collagen protein, and smooth muscle actin content after 10 wk treatment. Muscle-cell proliferation increased at 5 wk, and hepatocyte growth factor increased by 10 wk treatment. Halo markedly improved both cardiac and respiratory function and reduced damage and improved recovery from exercise. The overall impact of established dystrophy and dysfunction in cardiac and skeletal muscles was reduced by Halo treatment. Marked improvements in vital-organ functions implicate Halo as a strong candidate drug to reduce morbidity and mortality in Duchenne muscular dystrophy.

Stressed out: the skeletal muscle ryanodine receptor as a target of stress

Over the past century, understanding the mechanisms underlying muscle fatigue and weakness has been the focus of much investigation. However, the dominant theory in the field, that lactic acidosis causes muscle fatigue, is unlikely to tell the whole story. Recently, dysregulation of sarcoplasmic reticulum (SR) Ca(2+) release has been associated with impaired muscle function induced by a wide range of stressors, from dystrophy to heart failure to muscle fatigue. Here, we address current understandings of the altered regulation of SR Ca(2+) release during chronic stress, focusing on the role of the SR Ca(2+) release channel known as the type 1 ryanodine receptor.

Atelocollagen-mediated local and systemic applications of myostatin-targeting siRNA increase skeletal muscle mass

RNA interference (RNAi) offers a novel therapeutic strategy based on the highly specific and efficient silencing of a target gene. Since it relies on small interfering RNAs (siRNAs), a major issue is the delivery of therapeutically active siRNAs into the target tissue/target cells in vivo. For safety reasons, strategies based on vector delivery may be of only limited clinical use. The more desirable approach is to directly apply active siRNAs in vivo. Here, we report the effectiveness of in vivo siRNA delivery into skeletal muscles of normal or diseased mice through nanoparticle formation of chemically unmodified siRNAs with atelocollagen (ATCOL). ATCOL-mediated local application of siRNA targeting myostatin, a negative regulator of skeletal muscle growth, in mouse skeletal muscles or intravenously, caused a marked increase in the muscle mass within a few weeks after application. These results imply that ATCOL-mediated application of siRNAs is a powerful tool for future therapeutic use for diseases including muscular atrophy.

Glucocorticoid corticosteroids for Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy of childhood. This incurable disease is characterised by muscle wasting and loss of walking ability leading to complete wheelchair dependence by 13 years of age. Prolongation of walking is one of the major aims of treatment.

OBJECTIVES

The aim of this review was to assess whether glucocorticoid corticosteroids stabilize or improve muscle strength and walking in boys with DMD.

SEARCH STRATEGY

This is an update of the Cochrane systematic review first published in 2004 (Manzur 2004). We searched the Cochrane Neuromuscular Disease Group Trials Register (August 2006) using the term 'Duchenne muscular dystrophy'. We also searched MEDLINE (January 1966 to July 2007), EMBASE (January 1980 to August 2006), CINAHL and LILACS (January 1982 to August 2006). We wrote to authors of published studies and other experts in this disease to help identify other trials, checked the references in the identified trials and hand searched the abstracts of relevant journals.

SELECTION CRITERIA

Types of studies: randomised or quasi-randomised trials.

TYPES OF PARTICIPANTS

all patients with a definite diagnosis of Duchenne muscular dystrophy. Types of interventions: glucocorticoids such as prednisone, prednisolone, deflazacort or others, with a minimum treatment period of three months.

PRIMARY OUTCOME MEASURE

prolongation of walking (independent walking without long leg calipers).

SECONDARY OUTCOME MEASURES

strength outcome measures, manual muscle strength testing using Medical Research Council strength scores, functional outcome measures and adverse events.

DATA COLLECTION AND ANALYSIS

We identified six randomised controlled trials that met the inclusion criteria for our review, and one of these (Beenakker 2005) is a new addition to this update, as it was published subsequent to our first review (Manzur 2004). Two review authors independently selected the trials for the review and assessed methodological quality. Data extraction and inputting were double-checked.

PRIMARY OUTCOME MEASURE

data from one small study used prolongation of walking as an outcome measure and did not show significant benefit.

SECONDARY OUTCOME MEASURES

The meta-analysis of the results from four randomised controlled trials with altogether 249 participants showed that glucocorticoid corticosteroids improved muscle strength and function over six months. Improvements were seen in time taken to rise from the floor (Gowers' time), nine metres walking time, four-stair climbing time, ability to lift weights, leg function grade and forced vital capacity. One randomised controlled trial with altogether 28 participants showed that glucocorticoid corticosteroids stabilize muscle strength and function for up to two years. The most effective prednisolone regime appears to be 0.75 mg/kg/day, given in a daily dose regime. Not enough data were available to compare efficacy of prednisone with deflazacort. Adverse effects: Excessive weight gain, behavioural abnormalities, cushingoid appearance and excessive hair growth were all more common with glucocorticoid corticosteroids than placebo. Long-term adverse effects of glucocorticoid therapy could not be evaluated because of the short-term duration of the randomised studies.Non-randomised studies: A number of non-randomised studies with important efficacy and adverse effects data are tabulated and discussed.

AUTHORS' CONCLUSIONS

There is evidence from randomised controlled studies that glucocorticoid corticosteroid therapy in Duchenne muscular dystrophy improves muscle strength and function in the short-term (six months to two years). The most effective prednisolone regime appears to be 0.75 mg/kg/day, given daily. In the short term, adverse effects were significantly more common but not clinically severe. Long-term benefits and hazards of glucocorticoid treatment cannot be evaluated from the currently published randomised studies. Non-randomised studies support the conclusions of functional benefits but also identify clinically significant adverse effects of long-term treatment. These benefits and adverse effects have implications for future research studies and clinical practice.

Dystroglycan and protein O-mannosyltransferases 1 and 2 are required to maintain integrity of Drosophila larval muscles

In vertebrates, mutations in Protein O-mannosyltransferase1 (POMT1) or POMT2 are associated with muscular dystrophy due to a requirement for O-linked mannose glycans on the Dystroglycan (Dg) protein. In this study we examine larval body wall muscles of Drosophila mutant for Dg, or RNA interference knockdown for Dg and find defects in muscle attachment, altered muscle contraction, and a change in muscle membrane resistance. To determine if POMTs are required for Dg function in Drosophila, we examine larvae mutant for genes encoding POMT1 or POMT2. Larvae mutant for either POMT, or doubly mutant for both, show muscle attachment and muscle contraction phenotypes identical to those associated with reduced Dg function, consistent with a requirement for O-linked mannose on Drosophila Dg. Together these data establish a central role for Dg in maintaining integrity in Drosophila larval muscles and demonstrate the importance of glycosylation to Dg function in Drosophila. This study opens the possibility of using Drosophila to investigate muscular dystrophy.

Deletion of integrin-linked kinase from skeletal muscles of mice resembles muscular dystrophy due to alpha 7 beta 1-integrin deficiency

Integrin-linked kinase (Ilk) is a serine/threonine kinase and an adaptor protein that links integrins to the actin cytoskeleton and to a number of signaling pathways involved in integrin action. We hypothesized that Ilk may act as an important effector of integrins in skeletal muscle, where these receptors provide a critical link between the sarcolemma and the extracellular matrix. Using the cre/lox system, we deleted Ilk from skeletal muscles of mice. The resulting mutants developed a progressive muscular dystrophy with multiple degenerating and regenerating muscle fibers, increased central nuclei, and endomysial fibrosis. These defects were widespread but were most severe near myofascial junctions where Ilk mutants showed displacement of focal adhesion-related proteins, including vinculin, paxillin, focal adhesion kinase, dystrophin, and the alpha 7 beta 1D-integrin subunits. Distal ends of mutant muscle fibers appeared irregular, and there was restructuring of the actin cytoskeleton. These findings resemble those seen in humans and mice lacking the alpha 7-integrin subunit and suggest that Ilk may act as a cytoplasmic effector of alpha 7 beta1-integrin in the pathogenesis of these deficiencies.