Localization and characterization of dystrophin in muscle biopsy specimens from Duchenne muscular dystrophy and various neuromuscular disorders

Electrophysiologic and cardiovascular manifestations of Duchenne and Becker muscular dystrophies

There have been significant advances in the diagnosis and management of the hereditary muscular disorders Duchenne and Becker muscular dystrophy (DMD and BMD). Cardiac electrophysiologic and cardiovascular involvement has long been important in the surveillance, care, and prognosis of patients with both BMD and DMD and is the leading cause of mortality in patients with DMD. With improved long-term prognosis, rhythm disorders and progressive cardiomyopathy with resultant heart failure are increasingly common. This review aimed to provide an overview to electrophysiologists and cardiologists of the cardiac electrophysiologic phenotypes and genetics of BMD and DMD and to highlight the recent discoveries that have advanced clinical course and management. A systematic review was performed of the diagnosis and management of DMD and BMD. The Cochrane Library, PubMed, MEDLINE, Europe PubMed Central, AMED, and Embase databases were accessed for available evidence. The research reported in this paper adhered to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Evidence from randomized controlled trials and studies cited in expert consensus and practice guidelines are examined. Advanced imaging techniques and a spectrum of rhythm disorders associated with the progressive cardiomyopathy are presented. Early initiation of heart failure therapies, the role of cardiac implantable devices, and novel gene therapies approved for use with the potential to alter the disease course are discussed. When profound cardiac and cardiac electrophysiologic involvement is diagnosed and treated earlier, outcomes for DMD and BMD patients may be improved.

Becker muscular dystrophy-like myopathy regarded as so-called "fatty muscular dystrophy" in a pig: a case report and its diagnostic method

We describe a case of human Becker muscular dystrophy (BMD)-like myopathy that was characterized by the declined stainability of dystrophin at sarcolemma in a pig and the immunostaining for dystrophin on the formalin-fixed, paraffin-embedded (FFPE) tissue. The present case was found in a meat inspection center. The pig looked appeared healthy at the ante-mortem inspection. Muscular abnormalities were detected after carcass dressing as pale, discolored skeletal muscles with prominent fat infiltrations and considered so-called “fatty muscular dystrophy”. Microscopic examination revealed following characteristics: diffused fat infiltration into the skeletal muscle and degeneration and regeneration of the remaining skeletal muscle fibers. Any lesions that were suspected of neurogenic atrophy, traumatic muscular degeneration, glycogen storage disease or other porcine muscular disorders were not observed. The immunostaining for dystrophin was conducted and confirmed to be applicable on FFPE porcine muscular tissues and revealed diminished stainability of dystrophin at the sarcolemma in the present case. Based on the histological observations and immunostaining results, the present case was diagnosed with BMD-like myopathy associated with dystrophin abnormality in a pig. Although the genetic properties were not clear, the present BMD-like myopathy implied the occurrence of dystrophinopathy in pigs. To the best of our knowledge, this is the first report of a natural case of myopathy associated with dystrophin abnormalities in a pig.

Cell-lineage regulated myogenesis for dystrophin replacement: a novel therapeutic approach for treatment of muscular dystrophy

Duchenne muscular dystrophy (DMD) is characterized in skeletal muscle by cycles of myofiber necrosis and regeneration leading to loss of muscle fibers and replacement with fibrotic connective and adipose tissue. The ongoing activation and recruitment of muscle satellite cells for myofiber regeneration results in loss of regenerative capacity in part due to proliferative senescence. We explored a method whereby new myoblasts could be generated in dystrophic muscles by transplantation of primary fibroblasts engineered to express a micro-dystrophin/enhanced green fluorescent protein (muDys/eGFP) fusion gene together with a tamoxifen-inducible form of the myogenic regulator MyoD [MyoD-ER(T)]. Fibroblasts isolated from mdx(4cv) mice, a mouse model for DMD, were efficiently transduced with lentiviral vectors expressing muDys/eGFP and MyoD-ER(T) and underwent myogenic conversion when exposed to tamoxifen. These cells could also be induced to differentiate into muDys/eGFP-expressing myocytes and myotubes. Transplantation of transduced mdx(4cv) fibroblasts into mdx(4cv) muscles enabled tamoxifen-dependent regeneration of myofibers that express muDys. This lineage control method therefore allows replenishment of myogenic stem cells using autologous fibroblasts carrying an exogenous dystrophin gene. This strategy carries several potential advantages over conventional myoblast transplantation methods including: (i) the relative simplicity of culturing fibroblasts compared with myoblasts, (ii) a readily available cell source and ease of expansion and (iii) the ability to induce MyoD gene expression in vivo via administration of a medication. Our study provides a proof of concept for a novel gene/stem cell therapy technique and opens another potential therapeutic approach for degenerative muscle disorders.

Altered mRNA splicing of dystrophin in type 1 myotonic dystrophy

Myotonic dystrophy type1 (DM1) is a multisystemic disorder caused by a CTG repeat expansion in the DMPK gene. Aberrant mRNA splicing of several genes has been reported to contribute to some of the symptoms, including myotonia and insulin resistance, but the cause of muscle wasting is unknown. Dystrophin is a cytoskeletal protein that is required for structural stability and signaling at the sarcolemma and has several spliced isoforms. We investigated the alternative splicing of dystrophin in skeletal and cardiac muscle of DM1 patients by using reverse transcriptase-polymerase chain reaction and found that dystrophin isoforms lacking exon 71 or 78, which is suggested to encode an important region for protein binding and hydrophobicity, were significantly increased. We suggest that the aberrantly spliced dystrophin is responsible for the muscle wasting in DM1.

Variable histomorphology of muscle in congenital muscular dystrophy

Congenital muscular dystrophy (CMD) is a relatively uncommon disease with a controversial nosological status. That collagen synthesis could be the primary abnormality has been suggested earlier (Fidzianska et al., 1982). Amongst eighteen cases of CMD diagnosed during the past twelve years, muscle biopsy in three cases revealed prominence of myofibre necrosis and phagocytosis, and serum CPK was markedly elevated suggesting a rapidly progressive form. In twelve cases, marked increase in endomysial collagen, pronounced fallout of myofibres and significant fibre diameter variation was seen. This was associated with myonecrosis and regenerative activity of mild degree resembling the classical form of CMD. In the remaining three cases, polyfocal, polyphasic necrosis was noticed. Fibre splitting was more frequently observed, better delineated in the enzyme histochemical preparations, affecting both fibre types, while endomysial fibrofatty tissue was only moderately increased. The histomorphology in the latter group resembled that of limb girdle dystrophy. Ultrastructural findings in all the eighteen cases correlated well with light microscopic observations. lmmunohistochemical studies done on three of the eighteen cases showed normal localization of dystrophin protein. Such variable histomorphology, revealing a spectrum of myopathic features, suggests that the primary change in CMD is likely to be in the myofibre rather than in collagen synthesis.

Dystrophin is not a specific component of the cardiac costamere

Dystrophin is a key component of the subsarcolemmal skeleton of muscle cells, and lack of dystrophin is the direct cause of Duchenne muscular dystrophy. In skeletal muscle, dystrophin is reported to be localized specifically at costameres, transversely oriented riblike subsarcolemmal plaques that mechanically couple the contractile apparatus to the extracellular matrix. Costameres are characteristically rich in vinculin and are prominent in cardiac as well as skeletal muscle. To define the precise spatial relationship between dystrophin in relation to the costamere in cardiac muscle, we applied high-resolution single- and double-immunolabeling techniques, under a range of preparative conditions, with visualization of vinculin (as a costamere marker) and dystrophin by confocal microscopy and by the freeze-fracture cytochemical technique, fracture label. Immunoconfocal visualization revealed dystrophin as a continuous uniform layer at the cytoplasmic surface of the peripheral plasma membrane of the rat cardiac myocyte at both costameric and noncostameric regions. The pattern of labeling was reproducible with three different antibodies and was independent of time and antibody concentration. Platinum/carbon replicas and thin sections of fracture-label specimens permitted high-resolution visualization of the distribution of dystrophin in plane views of the freeze-fractured plasma membrane and in relation to the sarcomeric banding patterns of the underlying myofibrils. These results confirmed no preferential association of dystrophin with costameres or with any region of the sarcomeres of underlying myofibrils in rat cardiac tissue. We conclude that in contrast to skeletal muscle, dystrophin in cardiac muscle is not exclusively a component of the costamere.

Subcellular distribution of dystrophin in isolated adult and neonatal cardiac myocytes

The subcellular localization of dystrophin was examined in adult rabbit and rat cardiac myocytes with immunofluorescence and at higher resolution with immunogold. The aim was to resolve the conflicting reports on the presence of dystrophin in the transverse tubules (T tubules) of cardiac muscle and to determine its distribution in neonatal myocytes before and during the development of the T tubules. Dystrophin was localized to the peripheral sarcolemma and the T-tubular membrane and was absent from the intercalated disk membranes. In addition, dystrophin localization was followed with immunofluorescence in developing rabbit myocytes at 4 days, 1 wk, and 1 mo after birth. At 4 days of age, T tubules are absent and dystrophin was localized only in the peripheral sarcolemma. Dystrophin was present in the developing T tubules at 1 wk and 1 mo. These results imply that dystrophin is expressed in the T tubules as soon as they develop and confirm the different distribution of dystrophin in the T tubules of cardiac and skeletal muscle.

PCR and immunoblot analyses of dystrophin in Becker muscular dystrophy

The dystrophin gene was examined by PCR analysis in 30 Japanese patients with Becker muscular dystrophy (BMD). Fifteen PCR of these patients had exon deletion, generally, less than three exons. Muscle biopsies were also performed in 20 BMD patients (10 with sequence deletions, and 10 without detectable sequence deletions) in order to correlate PCR findings with immunoblot and immunostaining data. A patchy, heterogeneous membrane immunostaining pattern of reduced intensity was found, irrespective of the presence or absence of deletions. Immunoblotting studies demonstrated dystrophin of low molecular mass and quantity in BMD patients with deletion mutations, while a low quantity of dystrophin with an apparent wild type molecular mass was observed in nearly half the BMD patients without detectable deletions. However, these dystrophins were also found to have slightly abnormal molecular masses when the standard electrophoresis time was prolonged. This suggests that immunoblots and PCR data correlate well in patients with BMD. Additionally, it is suggested that immunoblot assays can detect abnormalities in dystrophin in the absence of detectable PCR deletions.

Dystrophin and dystrophin-related protein in the brains of normal and mdx mice

To clarify the localization and characterization of dystrophin and dystrophin-related protein (DRP) in the brains of normal and mdx mice, we carried out immunostaining and immunoblotting studies using four region-specific antidystrophin and anti-DRP antibodies. With immunostaining, punctate immunoreactivity of dystrophin was seen along the cell bodies and dendrites of the cerebral cortical neurons in the normal mice. By contrast, dystrophin was not detected at all in the brains of mdx mice. Immunoreactivity of DRP was observed in the vascular walls, pia mater, and choroid plexus of both normal and mdx brains, but not in the neuronal cells. The possible compensatory increase of DRP as seen in the skeletal muscles of mdx mice was not noted in the brains. The immunoblot findings were very consistent with those of immunostain. Although further studies of brain-type dystrophin are necessary, it seems unlikely that DRP participates in any physiological function of the neuronal cells.

Localisation and characterisation of dystrophin in the central nervous system of controls and patients with Duchenne muscular dystrophy

The aim was to localise and characterise dystrophin in various human tissues, especially in the CNS. Immunoblotting and immunostaining studies were carried out with eight region-specific dystrophin antibodies. In necropsy tissue from controls, dystrophin was noted as a doublet in immunoblots of striated muscle, and as a single band in those of smooth muscle and the CNS. With immunostaining, punctate immunoreactivity was seen on the cell bodies and dendrites of the cerebral cortical neurons and cerebellar Purkinje cells. By contrast, dystrophin was not detected in any tissues, including the cerebrum and cerebellum, of patients with Duchenne muscular dystrophy who had an intellectual disturbance.

Dystrophin and dystrophin-related protein in the central nervous system of normal controls and Duchenne muscular dystrophy

To clarify the localization and characterization of dystrophin and dystrophin-related protein (DRP) in the human central nervous system (CNS), we carried out immunoblotting and immunostaining studies using three region-specific anti-dystrophin and one anti-DRP antibodies. With immunostaining, punctuate immuno-reactivity of dystrophin was seen along the cell bodies and dendrites of the cerebral cortical neurons and cerebellar Purkinje cells in the normal controls autopsied. By contrast, dystrophin was not detected at all in the CNS of Duchenne muscular dystrophy (DMD) patients with intellectual disturbance. Immunoreactivity of DRP was observed in the vascular walls of both normal and DMD brains, but not in the neuronal cells. Compensatory increase of DRP was not noted in DMD brains. This study suggests that in DMD the brain-type dystrophin originally present in neurons is absent and may be related to the intellectual disturbance.

Lung and respiratory muscle function in limb girdle muscular dystrophy

BACKGROUND

Pulmonary involvement is frequently observed in patients with limb girdle muscular dystrophy and occurs early in the disease. The aim of this study was to establish the prevalence of pulmonary dysfunction; the type of dysfunction; and any correlation between patient age, disease duration, or limb weakness and lung or respiratory muscle dysfunction.

METHODS

Twenty patients with strictly delineated limb girdle muscular dystrophy and 20 healthy controls were evaluated. Full inspiration chest radiographs were obtained. Standard lung and respiratory muscle function tests were performed and the data were statistically analysed.

RESULTS

The mean age of the patients was 40.6 years, the mean disease duration was 18.9 years, and the mean average muscle score (a numerical expression of limb weakness) was 5.73 out of 10. Chest radiography showed unilateral paresis of the diaphragm in three patients. Increased residual volumes, with either increased or decreased total lung capacity, correlated inversely with disease duration. Respiratory muscle weakness was common but mild. Expiratory muscle function was more impaired than inspiratory muscle function and correlated positively with expiratory reserve volume.

CONCLUSIONS

Respiratory muscle strength is commonly impaired in limb girdle muscle dystrophy. A dissociation of the limb and mild respiratory muscle involvement is observed; wheelchair restriction does not predict worsening of pulmonary function, and patient age, disease duration, or degree of limb weakness do not predict pulmonary morbidity. The diaphragm is not disproportionately affected by the dystrophic process compared with limb muscles.

Size and localization of dystrophin molecule: immunoelectron microscopic and freeze etching studies of muscle plasma membranes of murine skeletal myofibers

The ultrastructure and mode of existence of the dystrophin molecule and its relations to actin filaments were examined in murine skeletal myofibers. Electron microscopy of freeze-etched replicas of gold-labelled dystrophin molecules in quick-freeze, deep-etch, rotary-shadow preparations revealed rod-like structures 108.2 +/- 16.3 nm long and 3.1 +/- 1.5 nm thick. Some dystrophin molecules appeared to link their ends to form anastomosing networks; others were separate from each other. The dystrophin molecules were parallel or nearly parallel to the inner surface of the muscle plasma membrane. Double immuno-labelling transmission electron microscopy using N- and C-terminal dystrophin antibodies showed that the group mean distances of the N- and C-terminal signals from the muscle plasma membrane were 52.7 +/- 8.1 nm and 45.9 +/- 11.3 nm, respectively, which were not significantly different. Histograms of the distribution of the N- and C-terminal distances from the muscle plasma membrane had similar patterns with peaks 10-20 nm from the membrane. This was consistent with the findings of the mode of existence of dystrophin molecules seen in freeze-etched replicas. Finally, the dystrophin molecules were linked with the most peripheral sarcoplasmic actin like filaments, end to side as well as end to end.

Congenital muscular dystrophy. A study on the variability of morphological changes and dystrophin distribution in muscle biopsies

Histomorphological and histochemical variability was studied in muscle specimens from 30 patients with congenital muscular dystrophy (CMD). We found involvement of the central nervous system in 8 patients (Fukuyama CMD, F-CMD), involvement of the brain and the eyes in 5 patients (muscle, eye and brain disease, MEB-D) and hypodense white matter on the CT scans of 2 patients with (sub)normal intelligence (occidental-type cerebromuscular dystrophy, O-CMD). No morphological hallmarks were found to differentiate these subgroups. Only fat cell infiltration was found to be increased with increasing age in 'pure' CMD (pure-CMD). The morphological data did not appear to be correlated with the clinical severity or type of dystrophy (pure-CMD, F-CMD, MEB-D and O-CMD). Immunohistochemistry with dystrophin, vimentin and desmin antibodies in 14 patients (6 pure-CMD, 5 F-CMD, 2 MEB-D and 1 O-CMD) showed a normal expression pattern.

The cardiomyopathy of Duchenne's muscular dystrophy and the function of dystrophin

Duchenne's muscular dystrophy (DMD) is a common X-linked neuromuscular disease which predominantly affects skeletal and cardiac muscle. The absence of dystrophin, the metabolic defect that causes DMD, leads to a peculiar cardiomyopathy which initially affects the posterior wall of the left ventricle. We review evidence that dystrophin deficient myocytes become dystrophic in order of increasing axial stress upon the myocyte. Thus, dystrophin's function may be that of physically reinforcing the sarcolemma against the axial forces exerted upon the myocyte.

Dystrophin-glycoprotein complex and laminin colocalize to the sarcolemma and transverse tubules of cardiac muscle

The expression and subcellular distribution of the dystrophin-glycoprotein complex and laminin were examined in cardiac muscle by immunoblot and immunofluorescence analysis of rabbit and sheep papillary muscle. The five dystrophin-associated proteins (DAPs), 156-DAG, 59-DAP, 50-DAG, 43-DAG, and 35-DAG, were identified in rabbit ventricular muscle and found to codistribute with dystrophin in both papillary myofibers and Purkinje fibers. The DAPs and dystrophin codistributed not only in the free surface sarcolemma but also in interior regions of the myofibers where T tubules are present. Neither the DAPs nor dystrophin were detected in intercalated discs, a specialized region of cardiac sarcolemma where neighboring myocardial cells are physically joined by cell-cell junctions. Similarly, in bundles of Purkinje fibers, which lack T tubules, DAPs and dystrophin were also found to codistribute at the free surface sarcolemma but were not detected either in the region of surface sarcolemma closely apposed to a neighboring Purkinje fiber or in interior regions of these myofibers. Comparison between the distribution of the dystrophin-glycoprotein complex and laminin showed that laminin codistributes with the components of this complex in both papillary myofibers and Purkinje fibers. These results are consistent with previous findings demonstrating that the extracellularly exposed 156-DAG (dystroglycan) of the skeletal muscle dystrophin-glycoprotein complex binds laminin, a component of the basement membrane. Although we demonstrate that DAPs, dystrophin, and laminin colocalize to the sarcolemma in rabbit and sheep papillary myofibers as they do in skeletal myofibers, the most striking difference between the subcellular distribution of these proteins in cardiac and skeletal muscle is that the dystrophin-glycoprotein complex and laminin also localize to regions of the fibers where T tubules are distributed in cardiac but not in skeletal muscle. These results imply that the protein composition and thus possibly some functions of T tubules in cardiac muscle are distinct from those of skeletal muscle.

Transfer versus lengthening of the posterior tibial tendon in Duchenne's muscular dystrophy

Transfer of the posterior tibialis tendon to the dorsum of the foot was compared with lengthening of this tendon in 15 patients with Duchenne's muscular dystrophy. Patients undergoing tendon transfer (N = 9) had a longer operating time and two perioperative complications, but retained plantigrade posture of their feet even after walking ceased. By contrast, lengthening of the posterior tibialis tendon (N = 6) was associated with a recurrent equinovarus foot deformity that frequently interfered with shoe wear. Although transfer of the posterior tibialis is out of phase and technically more demanding, the unique prolongation of posterior tibialis strength in Duchenne's muscular dystrophy makes this operation a better option for these patients.

The dystrophin-related protein, utrophin, is expressed on the sarcolemma of regenerating human skeletal muscle fibres in dystrophies and inflammatory myopathies

Utrophin is the 400 kDa protein product of an autosomal homologue (DMDL) of the dystrophin gene. In normal skeletal muscle, utrophin is expressed in vascular smooth muscle, endothelium and nerves but not in mature muscle fibres except at the neuromuscular junction. We have examined the expression of utrophin in a wide range of human skeletal muscle diseases using monoclonal antibodies against three C-terminal epitopes. Utrophin is consistently expressed in all basophilic, regenerating fibres irrespective of the underlying disease or expression of dystrophin. It is also found in regenerating fibres from a normal volunteer. In Duchenne and Becker dystrophies, as well as in dermatomyositis, sarcolemmal staining for utrophin is also seen in larger fibres which are not obviously regenerating. These studies do not support the idea that utrophin occupies membrane attachment sites only when dystrophin is absent or reduced, but would be consistent with utrophin expression as part of an activated foetal programme during regeneration.

Changes in muscle plasma membranes in young mice with X chromosome-linked muscular dystrophy: a freeze-fracture study

The structure of the muscle plasma membrane of tibialis anterior muscles of X chromosome-linked muscular dystrophy (mdx) mice was studied by the freeze-fracture technique at 3, 7 and 14 days after birth. The ultrastructural features of the freeze-fracture replicas of the muscle plasma membrane alterations in young mdx mice showed a decrease of orthogonal array, orthogonal array subunit particle and intramembranous particle densities on the protoplasmic face. The results are consistent with the previous studies which have shown that the orthogonal arrays are significantly decreased in number in muscle plasma membranes of adult mdx mice and in those of Duchenne dystrophy. However, the immature mdx mouse membranes at 3 days after birth contained as many orthogonal arrays as controls and did not show a statistically significant decrease (P greater than 0.1 by the Wilcoxon rank-sum test). Moreover, the orthogonal arrays were also numerous in young mdx mouse muscle plasma membranes at 7 and 14 days after birth, although the density was less than that of the control mice (P less than 0.01 by the Wilcoxon rank-sum test). These changes in young mdx mouse plasma membranes may precede the later muscle fibre degeneration in this mouse dystrophy and may provide us with an additional clue to the mechanism why mdx mice scarcely show any disability despite the absence of dystrophyn.

An injury model myopathy mimicking dystrophy: implications regarding the function of dystrophin

The pathogenesis of dystrophin deficient myopathies remains unknown. Rat and human muscles subjected to severe injury following repeated eccentric muscle actions demonstrate histopathological alterations which mimic a dystrophic process. Immunofluorescent histochemical examination of these injured muscles demonstrates a separation of proteoglycans of the basal lamina from the muscle plasma membrane, the identical histopathological alteration observed in Duchenne muscular dystrophy. These findings are consistent with the hypothesis that dystrophin is essential for maintenance of the structural integrity of the sarcolemma.

Dystrophin: localization and presumed function

To determine the localization and functional significance of dystrophin, we studied various tissues from almost the entire body of control and mdx mice, and control rats, using polyclonal antibodies against dystrophin. We observed a dystrophin reaction in synaptic regions such as neuromuscular junctions, the equatorial region of intrafusal muscle fibers, the outer plexiform layer of the retina, the myoepithelial cell layer of salivary and sweat glands, tactile nerve endings, and neurons in the brain. These dystrophin-positive regions reportedly contain actin filaments as a common characteristic, which is compatible with the dystrophin cDNA sequence. Dystrophin was absent in these regions in mdx mice. These results suggest that dystrophin plays an important physiological and/or structural role in cell motility as a trigger for propagating contractile force in, for example, the conduction system, with some relationship between actin filaments.

Immunofluorescence dystrophin study in Duchenne dystrophy through the concomitant use of two antibodies directed against the carboxy-terminal and the amino-terminal region of the protein

Dystrophin immunohistochemical studies in muscle from Duchenne patients (DMD) have shown a population of fibers with partial labelling. In order to determine whether this is related to a cross reaction or to the presence of dystrophin. 22 DMD patients were studied immunohistochemically, through the concomitant use of antibodies from the N-terminal and the C-terminal regions of the protein. In 2, the reaction was negative while in 2 others 17 and 25% of fibers were positive with both antibodies. In the remainder, a population of partially stained fibers was seen: 11 were positive with both antibodies and in 7 only with the N-terminal one. Apparently, there is no correlation between the proportion of positive fibers and clinical progression, or the presence and pattern of DNA deletions in the central part of the gene. These observations led us to suggest that some truncated protein, intermediate synthesis or degradation products of dystrophin are present in muscle from Duchenne patients.