Emerin Represses STAT3 Signaling through Nuclear Membrane-Based Spatial Control

Emerin is the inner nuclear membrane protein involved in maintaining the mechanical integrity of the nuclear membrane. Mutations in EMD encoding emerin cause Emery–Dreifuss muscular dystrophy (EDMD). Evidence is accumulating that emerin regulation of specific gene expression is associated with this disease, but the exact function of emerin has not been fully elucidated. Here, we show that emerin downregulates Signal transducer and activators of transcription 3 (STAT3) signaling, activated exclusively by Janus kinase (JAK). Deletion mutation experiments show that the lamin-binding domain of emerin is essential for the inhibition of STAT3 signaling. Emerin interacts directly and co-localizes with STAT3 in the nuclear membrane. Emerin knockdown induces STAT3 target genes Bcl2 and Survivin to increase cell survival signals and suppress hydrogen peroxide-induced cell death in HeLa cells. Specifically, downregulation of BAF or lamin A/C increases STAT3 signaling, suggesting that correct-localized emerin, by assembling with BAF and lamin A/C, acts as an intrinsic inhibitor against STAT3 signaling. In C2C12 cells, emerin knockdown induces STAT3 target gene, Pax7, and activated abnormal myoblast proliferation associated with muscle wasting in skeletal muscle homeostasis. Our results indicate that emerin downregulates STAT3 signaling by inducing retention of STAT3 and delaying STAT3 signaling in the nuclear membrane. This mechanism provides clues to the etiology of emerin-related muscular dystrophy and may be a new therapeutic target for treatment.

The role of Nrf2 in acute and chronic muscle injury

The nuclear factor erythroid 2-related factor 2 (Nrf2) is considered as a master cytoprotective factor regulating the expression of genes encoding anti-oxidant, anti-inflammatory, and detoxifying proteins. The role of Nrf2 in the pathophysiology of skeletal muscles has been evaluated in different experimental models, however, due to inconsistent data, we aimed to investigate how Nrf2 transcriptional deficiency (Nrf2tKO) affects muscle functions both in an acute and chronic injury. The acute muscle damage was induced in mice of two genotypes-WT and Nrf2tKO mice by cardiotoxin (CTX) injection. To investigate the role of Nrf2 in chronic muscle pathology, mdx mice that share genetic, biochemical, and histopathological features with Duchenne muscular dystrophy (DMD) were crossed with mice lacking transcriptionally active Nrf2 and double knockouts (mdx/Nrf2tKO) were generated. To worsen the dystrophic phenotype, the analysis of disease pathology was also performed in aggravated conditions, by applying a long-term treadmill test. We have observed slightly increased muscle damage in Nrf2tKO mice after CTX injection. Nevertheless, transcriptional ablation of Nrf2 in mdx mice did not significantly aggravate the most deleterious, pathological hallmarks of DMD related to degeneration, inflammation, fibrotic scar formation, angiogenesis, and the number and proliferation of satellite cells in non-exercised conditions. On the other hand, upon chronic exercises, the degeneration and inflammatory infiltration of the gastrocnemius muscle, but not the diaphragm, turned to be increased in Nrf2tKOmdx in comparison to mdx mice. In conclusion, the lack of transcriptionally active Nrf2 influences moderately muscle pathology in acute CTX-induced muscle injury and chronic DMD mouse model, without affecting muscle functionality. Hence, in general, we demonstrated that the deficiency of Nrf2 transcriptional activity has no profound impact on muscle pathology in various models of muscle injury.

A new patient-derived iPSC model for dystroglycanopathies validates a compound that increases glycosylation of α-dystroglycan

Dystroglycan, an extracellular matrix receptor, has essential functions in various tissues. Loss of α-dystroglycan-laminin interaction due to defective glycosylation of α-dystroglycan underlies a group of congenital muscular dystrophies often associated with brain malformations, referred to as dystroglycanopathies. The lack of isogenic human dystroglycanopathy cell models has limited our ability to test potential drugs in a human- and neural-specific context. Here, we generated induced pluripotent stem cells (iPSCs) from a severe dystroglycanopathy patient with homozygous FKRP (fukutin-related protein gene) mutation. We showed that CRISPR/Cas9-mediated gene correction of FKRP restored glycosylation of α-dystroglycan in iPSC-derived cortical neurons, whereas targeted gene mutation of FKRP in wild-type cells disrupted this glycosylation. In parallel, we screened 31,954 small molecule compounds using a mouse myoblast line for increased glycosylation of α-dystroglycan. Using human FKRP-iPSC-derived neural cells for hit validation, we demonstrated that compound 4-(4-bromophenyl)-6-ethylsulfanyl-2-oxo-3,4-dihydro-1H-pyridine-5-carbonitrile (4BPPNit) significantly augmented glycosylation of α-dystroglycan, in part through upregulation of LARGE1 glycosyltransferase gene expression. Together, isogenic human iPSC-derived cells represent a valuable platform for facilitating dystroglycanopathy drug discovery and therapeutic development.

Blockade of TRPV2 is a Novel Therapy for Cardiomyopathy in Muscular Dystrophy

Muscular dystrophy and dilated cardiomyopathy are intractable diseases and their treatment options are very limited. Transient receptor potential cation channel subfamily V, member 2 (TRPV2), is a stretch-sensitive Ca²⁺-permeable channel that causes sustained intracellular Ca²⁺ increase in muscular cells, which is a pathophysiological feature of degenerative muscular disease. Recent reports have clarified that TRPV2 is concentrated and activated in the sarcolemma of cardiomyocytes/myocytes during cardiomyopathy/heart failure and muscular dystrophy. Furthermore, these reports showed that inactivation of TRPV2 ameliorates muscle dysgenesis to improve cardiac function and survival prognosis. Although TRPV2 is a potential therapeutic target for cardiomyopathy, there were no TRPV2 inhibitors available until recently. In this review, we introduce our recent findings and discuss the current progress in the development of TRPV2 inhibitors and their therapeutic applications for cardiomyopathy associated with muscular dystrophy.

[Selenium deficiency in an organic extensive water buffalo farm]

This case report presents investigations of muscle problems in three male water buffaloes (1-2 years) kept extensively (loose housing, pasture). The bulls were presented because of listlessness and increased lying periods. They displayed difficulties to stand up, a stilted gait, and tremor in the legs. The determination of the selenium concentration by the measurement of glutathione peroxidase activity in whole blood samples (EDTA) demonstrated selenium deficiency in all three buffaloes. This confirmed the tentative diagnosis of nutritive myodystrophy due to selenium deficiency. Following a single injection of 1500 mg all-rac-alpha-tocopherol acetate and 11 mg sodium selenite, the bulls recovered clinically. The whole blood samples taken subsequently from seven adult water buffaloes on the farm showed selenium deficiency in all animals. Consequently, slow-release multi-trace element boluses were administered once orally - as far as possible - to all adult animals of the herd. After 1 year, a good to very good selenium supply was observed in all these buffaloes, except for one cow, in which bolus application had failed.

Muscle Stem Cells: A Model System for Adult Stem Cell Biology

Skeletal muscle stem cells, originally termed satellite cells for their position adjacent to differentiated muscle fibers, are absolutely required for the process of skeletal muscle repair and regeneration. In the last decade, satellite cells have become one of the most studied adult stem cell systems and have emerged as a standard model not only in the field of stem cell-driven tissue regeneration but also in stem cell dysfunction and aging. Here, we provide background in the field and discuss recent advances in our understanding of muscle stem cell function and dysfunction, particularly in the case of aging, and the potential involvement of muscle stem cells in genetic diseases such as the muscular dystrophies.

Mouse models of fukutin-related protein mutations show a wide range of disease phenotypes

Dystroglycanopathies are characterized by a reduction in the glycosylation of alpha-dystroglycan (α-DG). A common cause for this subset of muscular dystrophies is mutations in the gene of fukutin-related protein (FKRP). FKRP mutations have been associated with a wide spectrum of clinical severity from severe Walker-Warburg syndrome and muscle-eye-brain disease with brain and eye defects to mild limb-girdle muscular dystrophy 2I with myopathy only. To examine the affects of FKRP mutations on the severity of the disease, we have generated homozygous and compound heterozygous mouse models with human mutations in the murine FKRP gene. P448Lneo+ and E310delneo+ mutations result in severe dystrophic and embryonic lethal phenotypes, respectively. P448Lneo+/E310delneo+ compound heterozygotes exhibit brain defects and severe muscular dystrophies with near absence of α-DG glycosylation. Removal of the Neo(r) cassette from the P448Lneo+ homozygous mice eliminates overt brain and eye defects, and reduces severity of dystrophic phenotypes. Furthermore, introduction of the common L276I mutation to generate transgenic L276Ineo+ homozygous and L276Ineo+/P448Lneo+ and L276Ineo+/E310delneo+ compound heterozygotes results in mice displaying milder dystrophies with reduced α-DG glycosylation and no apparent brain defects. Limited sampling and variation in functionally glycosylated α-DG levels between and within muscles may explain the difficulties in correlating FKRP expression levels with phenotype in clinics. The nature of individual mutations, expression levels and status of muscle differentiation all contribute to the phenotypic manifestation. These mutant FKRP mice are useful models for the study of disease mechanism(s) and experimental therapies.

Muscular dystrophies

Muscular dystrophies are a heterogeneous group of inherited disorders that share similar clinical features and dystrophic changes on muscle biopsy. An improved understanding of their molecular bases has led to more accurate definitions of the clinical features associated with known subtypes. Knowledge of disease-specific complications, implementation of anticipatory care, and medical advances have changed the standard of care, with an overall improvement in the clinical course, survival, and quality of life of affected people. A better understanding of the mechanisms underlying the molecular pathogenesis of several disorders and the availability of preclinical models are leading to several new experimental approaches, some of which are already in clinical trials. In this Seminar, we provide a comprehensive review that integrates clinical manifestations, molecular pathogenesis, diagnostic strategy, and therapeutic developments.

Laminopathies and lamin-associated signaling pathways

Laminopathies are genetic diseases due to mutations or altered post-translational processing of nuclear envelope/lamina proteins. The majority of laminopathies are caused by mutations in the LMNA gene, encoding lamin A/C, but manifest as diverse pathologies including muscular dystrophy, lipodystrophy, neuropathy, and progeroid syndromes. Lamin-binding proteins implicated in laminopathies include lamin B2, nuclear envelope proteins such as emerin, MAN1, LBR, and nesprins, the nuclear matrix protein matrin 3, the lamina-associated polypeptide, LAP2alpha and the transcriptional regulator FHL1. Thus, the altered functionality of a nuclear proteins network appears to be involved in the onset of laminopathic diseases. The functional interplay among different proteins involved in this network implies signaling partners. The signaling effectors may either modify nuclear envelope proteins and their binding properties, or use nuclear envelope/lamina proteins as platforms to regulate signal transduction. In this review, both aspects of lamin-linked signaling are presented and the major pathways so far implicated in laminopathies are summarized.

Laminopathies and the long strange trip from basic cell biology to therapy

The main function of the nuclear lamina, an intermediate filament meshwork lying primarily beneath the inner nuclear membrane, is to provide structural scaffolding for the cell nucleus. However, the lamina also serves other functions, such as having a role in chromatin organization, connecting the nucleus to the cytoplasm, gene transcription, and mitosis. In somatic cells, the main protein constituents of the nuclear lamina are lamins A, C, B1, and B2. Interest in the nuclear lamins increased dramatically in recent years with the realization that mutations in LMNA, the gene encoding lamins A and C, cause a panoply of human diseases ("laminopathies"), including muscular dystrophy, cardiomyopathy, partial lipodystrophy, and progeroid syndromes. Here, we review the laminopathies and the long strange trip from basic cell biology to therapeutic approaches for these diseases.

Joint hypermobility as a distinctive feature in the differential diagnosis of myopathies

Congenital and adult-onset inherited myopathies represent a wide spectrum of syndromes. Classification is based upon clinical features and biochemical and genetic defects. Joint hypermobility is one of the distinctive clinical features that has often been underrecognized so far. We therefore present an overview of myopathies associated with joint hypermobility: Ullrich congenital muscular dystrophy, Bethlem myopathy, congenital muscular dystrophy with joint hyperlaxity, multi-minicore disease, central core disease, and limb girdle muscular dystrophy 2E with joint hyperlaxity and contractures. We shortly discuss a second group of disorders characterised by both muscular features and joint hypermobility: the inherited disorders of connective tissue Ehlers-Danlos syndrome and Marfan syndrome. Furthermore, we will briefly discuss the extent and pattern of joint hypermobility in these myopathies and connective tissue disorders and propose two grading scales commonly used to score the severity of joint hypermobility. We will conclude focusing on the various molecules involved in these disorders and on their role and interactions in muscle and tendon, with a view to further elucidate the pathophysiology of combined hypermobility and myopathy. Hopefully, this review will contribute to enhanced recognition of joint hypermobility and thus be of aid in differential diagnosis.

Mechanisms of disease: congenital muscular dystrophies-glycosylation takes center stage

Recent studies have defined a group of muscular dystrophies, now termed the dystroglycanopathies, as novel disorders of glycosylation. These conditions include Walker-Warburg syndrome, muscle-eye-brain disease, Fukuyama-type congenital muscular dystrophy, congenital muscular dystrophy types 1C and 1D, and limb-girdle muscular dystrophy type 2I. Although clinical findings can be highly variable, dystroglycanopathies are all characterized by cortical malformations and ocular defects at the more severe end of the clinical spectrum, in addition to muscular dystrophy. All of these disorders are defined by the underglycosylation of alpha-dystroglycan. Defective glycosylation of dystroglycan severs the link between this important cell adhesion molecule and the extracellular matrix, thereby contributing to cellular pathology. Recent experiments indicate that glycosylation might not only define forms of muscular dystrophy but also provide an avenue to the development of therapies for these disorders.

Protein-bound 4-hydroxy-2-nonenal: an endogenous triggering antigen of antI-DNA response

Several lines of evidence indicate that the nonenzymatic oxidative modification of proteins and the subsequent accumulation of the modified proteins have been found in cells during aging and oxidative stress and in various pathological states, including premature diseases, muscular dystrophy, rheumatoid arthritis, and atherosclerosis. Our previous work suggested the existence of molecular mimicry between antibodies raised against hydroxy-2-nonenal (HNE)-modified protein and anti-DNA autoantibodies, a serologic hallmark of systemic lupus erythematosus (SLE). In the present study, we investigated the possible involvement of HNE-modified proteins as the endogenous source of the anti-DNA antibodies. Accumulation of the antigen recognized by the antibody against the HNE-modified protein was observed in the nucleus of almost all of the epidermal cells from patients with autoimmune diseases, including SLE. The SLE patients also showed significantly higher serum levels of the anti-HNE titer than healthy individuals. To determine if a specific anti-DNA response could be initiated by the HNE-derived epitopes, we immunized BALB/c mice with the HNE-modified protein and observed a progressive increase in the anti-DNA response. Moreover, we generated the monoclonal antibodies, showing recognition specificity toward DNA, and found that they can bind to two structurally distinct antigens (i.e. the native DNA and protein-bound 4-oxo-2-nonenal). The findings in this study provide evidence to suspect an etiologic role for lipid peroxidation in autoimmune diseases.

Modeling human muscle disease in zebrafish

Zebrafish reproduce in large quantities, grow rapidly, and are transparent early in development. For these reasons, zebrafish have been used extensively to model vertebrate development and disease. Like mammals, zebrafish express dystrophin and many of its associated proteins early in development and these proteins have been shown to be vital for zebrafish muscle stability. In dystrophin-null zebrafish, muscle degeneration becomes apparent as early as 3 days post-fertilization (dpf) making the zebrafish an excellent organism for large-scale screens to identify other genes involved in the disease process or drugs capable of correcting the disease phenotype. Being transparent, developing zebrafish are also an ideal experimental model for monitoring the fate of labeled transplanted cells. Although zebrafish dystrophy models are not meant to replace existing mammalian models of disease, experiments requiring large numbers of animals may be best performed in zebrafish. Results garnered from using this model could lead to a better understanding of the pathogenesis of the muscular dystrophies and the development of future therapies.

Mitochondrial dysfunction in the pathogenesis of Ullrich congenital muscular dystrophy and prospective therapy with cyclosporins

Ullrich congenital muscular dystrophy is a severe genetically and clinically heterogeneous muscle disorder linked to collagen VI deficiency. The pathogenesis of the disease is unknown. To assess the potential role of mitochondrial dysfunction in the onset of muscle fiber death in this form of dystrophy, we studied biopsies and myoblast cultures obtained from patients with different genetic defects of collagen VI and variable clinical presentations of the disease. We identified a latent mitochondrial dysfunction in myoblasts from patients with Ullrich congenital muscular dystrophy that matched an increased occurrence of spontaneous apoptosis. Unlike those in myoblasts from healthy donors, mitochondria in cells from patients depolarized upon addition of oligomycin and displayed ultrastructural alterations that were worsened by treatment with oligomycin. The increased apoptosis, the ultrastructural defects, and the anomalous response to oligomycin could be normalized by Ca(2+) chelators, by plating cells on collagen VI, and by treatment with cyclosporin A or with the specific cyclophilin inhibitor methylAla(3)ethylVal(4)-cyclosporin, which does not affect calcineurin activity. Here we demonstrate that mitochondrial dysfunction plays an important role in muscle cell wasting in Ullrich congenital muscular dystrophy. This study represents an essential step toward a pharmacological therapy of Ullrich congenital muscular dystrophy with cyclosporin A and methylAla(3)ethylVal(4) cyclosporin.

Molecular mechanism of rigid spine with muscular dystrophy type 1 caused by novel mutations of selenoprotein N gene

Mutations of selenoprotein N, 1 gene (SEPN1) cause rigid spine with muscular dystrophy type 1 (RSMD1), multiminicore disease, and desmin-related myopathy. We found two novel SEPN1 mutations in two Japanese patients with RSMD1. To clarify the pathomechanism of RSMD1, we performed immunohistochemical studies using a newly developed antibody for selenoprotein N. Selenoprotein N was diffusely distributed in the cytoplasm of the control muscle, but was reduced and irregularly expressed in the cytoplasm of a patient with RSMD1. The expression pattern was very similar to that of calnexin, a transmembrane protein of the endoplasmic reticulum. Selenoprotein N seems to be an endoplasmic reticulum glycoprotein, and loss of this protein leads to disturbance of muscular function. One of the families had the SEPN1 homozygous mutation in the initiation codon 1_2 ins T in exon 1 and showed truncated protein expression. The other had a homozygous 20-base duplication mutation at 80 (80_99dup, frameshift at R27) which, in theory, should generate many nonsense mutations including TGA. These nonsense mutations are premature translation termination codons and they degrade immediately by the process of nonsense-mediated decay (NMD). However, truncated selenoprotein N was also expressed. A possible mechanism behind this observation is that SEPN1 mRNAs may be resistant to NMD. We report on the possible molecular mechanism behind these mutations in SEPN1. Our study clarifies molecular mechanisms of this muscular disorder.

Laminin alpha1 chain mediated reduction of laminin alpha2 chain deficient muscular dystrophy involves integrin alpha7beta1 and dystroglycan

Transgenically introduced laminin (LN) alpha1 chain prevents muscular dystrophy in LNalpha2 chain deficient mice. We now report increased integrin alpha7Bbeta1D synthesis in dystrophic LNalpha2 chain deficient muscle. Yet, immunofluorescence demonstrated a reduced expression of integrin alpha7B subunit at the sarcolemma. Transgenic expression of LNalpha1 chain reconstituted integrin alpha7B at the sarcolemma. Expression of alpha- and beta-dystroglycan is enhanced in LNalpha2 chain deficient muscle and normalized by transgenic expression of LNalpha1 chain. We suggest that LNalpha1 chain in part ameliorates the development of LNalpha2 chain deficient muscular dystrophy by retaining the binding sites for integrin alpha7Bbeta1D and alpha-dystroglycan, respectively.

Defect in glycosylation that causes muscular dystrophy

Muscular dystrophies are a diverse group of inherited disorders characterized by progressive muscle weakness and wasting. The dystrophin-glycoprotein complex is composed of alpha-, beta-dystroglycan (DG), dystrophin and some other molecules. alpha- and beta-DG stabilize the sarcolemma by acting as an axis through which the extracellular matrix is tightly linked to the cytoskeleton. The relative molecular weights of alpha-DG differ in different tissues as a result of differential glycosylation. New findings indicate that disrupted glycosylation of alpha-DG results in a loss of ligand binding, giving rise to both progressive muscle degeneration and abnormal neuronal migration in the brain. This article discusses methods, including purification of alpha-DG and glycosyltransferase assays involved in alpha-DG glycosylation.

Actin-organising properties of the muscular dystrophy protein myotilin

Myotilin is a sarcomeric Z-disc protein that binds F-actin directly and bundles actin filaments, although it does not contain a conventional actin-binding domain. Expression of mutant myotilin leads to sarcomeric alterations in the dominantly inherited limb-girdle muscular dystrophy 1A and in myofibrillar myopathy/desmin-related myopathy. Together, with previous in vitro studies, this indicates that myotilin has an important function in the assembly and maintenance of Z-discs. This study characterises further the interaction between myotilin and actin. Functionally important regions in myotilin were identified by actin pull-down and yeast two-hybrid assays and with a novel strategy that combines in vitro DNA transposition-based peptide insertion mutagenesis with phenotype analysis in yeast cells. The shortest fragment to bind actin was the second Ig domain together with a short C-terminal sequence. Concerted action of the first and second Ig domain was, however, necessary for the functional activity of myotilin, as verified by analysis of transposon mutants, actin binding and phenotypic effect in mammalian cells. Furthermore, the Ig domains flanked with N- and C-terminal regions were needed for actin-bundling, indicating that the mere actin-binding sequence was insufficient for the actin-regulating activity. None of the four known disease-associated mutations altered the actin-organising ability. These results, together with previous studies in titin and kettin, identify the Ig domain as an actin-binding unit.

Prenatal diagnosis in laminin α2 chain (merosin)-deficient congenital muscular dystrophy: A collective experience of five international centers

The congenital muscular dystrophies (CMD) are clinically and genetically heterogeneous. The merosin (laminin alpha2 chain) deficient form (MDC1A), is characterized clinically by neonatal hypotonia, delayed motor milestones and associated contractures. It is caused by deficiency in the basal lamina of muscle fibers of the alpha2 chain of laminins 2 and 4 (LAMA2 gene at 6q22-23). Laminin alpha2 chain is also expressed in fetal trophoblast, which provides a suitable tissue for prenatal diagnosis in families where the index case has total deficiency of the protein. This article reports the collective experience of five centers over the past 10 years in 114 prenatal diagnostic studies using either protein analysis of the chorionic villus (CV) of the trophoblast plus DNA molecular studies with markers flanking the 6q22-23 region and intragenic polymorphisms (n=58), or using only DNA (n=44) or only protein (n=12) approaches. Of the 102 fetuses studied by molecular genetics, 27 (26%) were predicted to be affected while 75 (74%) were considered as unaffected, with 52 (51%) being heterozygous, thus conforming closely to an autosomal recessive inheritance. In 18 of the 27 affected fetuses, the trophoblast was studied by immunocytochemistry and there was a total or only traces deficiency of the protein in CV basement membrane in all. In 10 cases material from the presumably affected fetus was available for analysis after termination of the pregnancy and immunohistochemical study confirmed the diagnosis in all of them. Prenatal studies of 'at risk' pregnancies in the five centers produced neither false negative (merosin-deficiency in CVs in a normal fetus), nor false positive (normal merosin expression in CVs and affected child), indicating the reliability of the technique, when all the necessary controls are done. Our experience suggests that protein and DNA analysis can be used either independently or combined, according to the facilities of each center, to provide accurate prenatal diagnosis of the MDC1A, and have an essential role in genetic counseling.

[Genes and their functional mechanisms in the pathogenesis of muscular dystrophy]

Muscular dystrophy (MD), a group of inherited disorders characterized by progressive skeletal muscle wasting and weakness, can be classified into several groups according to Mendelian inheritance patterns and clinical features. Many genes related to MD have been identified and cloned by genetic linkage analysis and positional cloning strategy. Our understanding of the molecular mechanisms giving rise to muscular dystrophy have made a progress by the functional analysis of proteins encoded by candidate genes for MD. This article reviews genes and their functional mechanisms in the pathogenesis of muscular dystrophy.

The nuclear lamina comes of age

Many nuclear proteins form lamin-dependent complexes, including LEM-domain proteins, nesprins and SUN-domain proteins. These complexes have roles in chromatin organization, gene regulation and signal transduction. Some link the nucleoskeleton to cytoskeletal structures, ensuring that the nucleus and centrosome assume appropriate intracellular positions. These complexes provide new insights into cell architecture, as well as a foundation for the understanding of the molecular mechanisms that underlie the human laminopathies - clinical disorders that range from Emery-Dreifuss muscular dystrophy to the accelerated ageing seen in Hutchinson-Gilford progeria syndrome.

Respiratory muscle fibres: specialisation and plasticity

Skeletal muscles are composed of fibres of different types, each type being identified by the isoform of myosin heavy chain which is expressed as slow 1, fast 2A, fast 2X, and fast 2B. Slow fibres are resistant to fatigue due to their highly oxidative metabolism whereas 2X and 2B fibres are easily fatiguable and fast 2A fibres exhibit intermediate fatigue resistance. Slow fibres and fast fibres are present in equal proportions in the adult human diaphragm while intercostal muscles contain a higher proportion of fast fibres. A small fibre size, abundance of capillaries, and a high aerobic oxidative enzyme activity are typical features of diaphragm fibres and give them the resistance to fatigue required by their continuous activity. Because of their fibre composition, intercostal muscles are less resistant to fatigue. The structural and functional characteristics of respiratory muscle fibres are not fixed, however, and can be modified in response to several physiological and pathological conditions such as training (adaptation to changes in respiratory load), adaptation to hypoxia, age related changes, and changes associated with respiratory diseases. The properties of respiratory muscle fibres can also be modified by pharmacological agents such as beta2 agonists and corticosteroids used for the treatment of respiratory diseases.

Sacral nerve stimulation for treatment of fecal incontinence in a patient with muscular dystrophy: report of a case

Fecal incontinence is a common condition that causes major impairment of social life. Sacral nerve stimulation is a promising treatment in idiopathic fecal incontinence when conventional treatments have failed. However, new indications for sacral nerve stimulation are emerging. The present case shows that sacral nerve stimulation for treatment of fecal incontinence may be justified in other diseases in which fecal incontinence is a major problem.

Disruption of muscle membrane and phenotype divergence in two novel mouse models of dysferlin deficiency

Limb girdle muscular dystrophy type 2B and Miyoshi myopathy are clinically distinct forms of muscular dystrophy that arise from defects in the dysferlin gene. Here, we report two novel lines of dysferlin-deficient mice obtained by (a) gene targeting and (b) identification of an inbred strain, A/J, bearing a retrotransposon insertion in the dysferlin gene. The mutations in these mice were located at the 3' and 5' ends of the dysferlin gene. Both lines of mice lacked dysferlin and developed a progressive muscular dystrophy with histopathological and ultrastructural features that closely resemble the human disease. Vital staining with Evans blue dye revealed loss of sarcolemmal integrity in both lines of mice, similar to that seen in mdx and caveolin-3 deficient mice. However, in contrast to the latter group of animals, the dysferlin-deficient mice have an intact dystrophin glycoprotein complex and normal levels of caveolin-3. Our findings indicate that muscle membrane disruption and myofiber degeneration in dysferlinopathy were directly mediated by the loss of dysferlin via a new pathogenic mechanism in muscular dystrophies. We also show that the mutation in the A/J mice arose between the late 1970s and the early 1980s, and had become fixed in the production breeding stocks. Therefore, all studies involving the A/J mice or mice derived from A/J, including recombinant inbred, recombinant congenic and chromosome substitution strains, should take into account the dysferlin defect in these strains. These new dysferlin-deficient mice should be useful for elucidating the pathogenic pathway in dysferlinopathy and for developing therapeutic strategies.

[Immunohistochemical studies of a variant of congenital muscular dystrophy]

Three Japanese patients from 2 families had a phenotype indistinguishable from that of Fukuyama-type congenital muscular dystrophy (FCMD). A full mutational analysis of the fukutin gene, however, revealed neither a 3 kb insertion (the Japanese founder mutation) nor a point mutation. A RT-PCR analysis of one of the patients revealed a normal expression of the fukutin transcript, suggesting that they have a new variant of CMD. An immunohistochemical analysis of the muscle of one case showed that the immunoreaction to alpha-dystroglycan (DG) was barely detectable on the surface membranes of muscle fibers. Immunoreactions to beta-DG, dystrophin, laminin alpha-2 chain and sarcoglycan were normal. These findings raise the possibility that the abnormality of alpha-DG is integral to the pathology seen in this variant of CMD. Analysis of POMGnT1 gene, which is causative of muscle-eye-brain disease, revealed no mutation in this case.

[Calpain and pathology in view of structure-function relationships]

Calpain, a Ca(2+)-requiring cytoplasmic cysteine protease, plays indispensable roles in various cellular functions such as signal transduction, cell growth and differentiation, apoptosis, necrosis, and so on. Although most of the detailed physiological functions of calpains have not yet been elucidated, the importance of calpain is obvious from the increasing numbers of papers describing relationships between human disease states (such as Alzheimer's disease, cataract, and muscular dystrophies) and malfunction of calpain. One of the recent remarkable topics of calpain is that a single nucleotide polymorphism of CAPN10, the gene for calpain 10, is related to type 2 diabetes. However, physiological functions of calpain 10 and its relation to diabetes are still unclear. Among 14 human calpain genes, mutations in CAPN3, the gene for p94/calpain 3a and Lp82/calpain 3b, are the only example that genetically connects the calpain gene and human disease, in this case, limb-girdle muscular dystrophy type 2A (LGMD2A). p94 has unique characteristics such as apparent Ca(2+)-independent activation and very rapid autolytic activity, which are dependent on p94-specific regions, NS, IS1, and IS2. Based on the 3D structures of micro - and m-calpain, molecular functions of p94 in relation to LGMD2A are discussed, with the hope of providing us with some clues to understand calpain functions and its relationships to human diseases.

The origin of dystrophin-glycoprotein complex(DGC)-related muscular dystrophies: the need for protection against an ancestral pathogen?

Because of its crucial role during the early stages of morphogenesis, no genetic defects associated to dystroglycan have been reported so far. Dystroglycan is an important member of the dystrophin-glycoprotein complex (DGC) and in several muscular dystrophies, depending on abnormalities of proteins belonging to or associated with the DGC, it is frequently observed a significant reduction of dystroglycan levels at the sarcolemma. Recently, it has been demonstrated that dystroglycan acts as a receptor for pathogens such as M. leprae and arenaviruses. It is well-known that mutated alleles causing diseases can be selected in order to confer an additional genetic advantage. Herein it is discussed the possibility that mutations leading to a certain number of muscular dystrophies might have been originally selected to indirectly gain a specific advantage: the absence or the lower levels of dystroglycan could have greatly reduced the risk of some ancestral lethal infections specifically directed against muscles.

Occipito-temporal polymicrogyria and subclinical muscular dystrophy

We report a two-year-old Caucasian boy who had neonatal seizures and was found to have bilateral occipito-temporal polymicrogyria on neonatal brain MRI. The child had no additional neurological abnormality other than the neonatal seizures, but serum CK was found to be elevated (5 - 7 times normal values) and the muscle biopsy showed evidence of early muscular dystrophy. Detailed protein and genetic studies did not allow the identification of a known form of muscular dystrophy. The boy has been followed regularly and he currently has mild global developmental delay but no clinical signs of muscle involvement. The association of polymicrogyria and muscular dystrophy is known to occur in Fukuyama and Walker Warburg muscular dystrophies, in muscle-eye-brain disease and in some patients with merosin deficient CMD. However the absence of weakness and of eye involvement, the normal expression of merosin and alpha dystroglycan and the pattern of brain involvement make it very unlikely that the child is affected by one of these forms. As the pattern of brain involvement and the muscle pathology is not typical of one of the forms of neuronal migration disorders secondary to a known gene defect, we suspect that the combination of muscle and brain involvement found in this child is not coincidental. Our findings suggest that serum CK should be determined in children with undiagnosed polymicrogyria, even in the absence of weakness. This may lead to an expansion of our understanding of muscle dystrophies and cortical dysplasias.

Zeta-sarcoglycan, a novel component of the sarcoglycan complex, is reduced in muscular dystrophy

The dystrophin glycoprotein complex (DGC) is found at the plasma membrane of muscle cells, where it provides a link between the cytoskeleton and the extracellular matrix. A subcomplex within the DGC, the sarcoglycan complex, associates with dystrophin and mediates muscle membrane stability. Mutations in sarcoglycan genes lead to muscular dystrophy and cardiomyopathy in both humans and mice. In invertebrates, there are three sarcoglycan genes, while in mammals there are additional sarcoglycan genes that probably arose from gene duplication events. We identified a novel mammalian sarcoglycan, zeta-sarcoglycan, that is highly related to gamma-sarcoglycan and delta-sarcoglycan. We generated a zeta-sarcoglycan-specific antibody and found that zeta-sarcoglycan associated with other members of the sarcoglycan complex at the plasma membrane. Additionally, zeta-sarcoglycan was reduced at the membrane in muscular dystrophy, consistent with a role in mediating membrane stability. zeta-Sarcoglycan was also found as a component of the vascular smooth muscle sarcoglycan complex. Together, these data demonstrate that zeta-sarcoglycan is an integral component of the sarcoglycan complex and, as such, is important in the pathogenesis of muscular dystrophy.

Muscular dystrophy into the new millennium

Since the identification of the gene for Duchenne muscular dystrophy and its protein product some 15 years ago, the basic defects in all the commoner forms of dystrophy have now been identified. It is thus possible, on the basis of this information, to make a precise diagnosis in an affected individual and to offer accurate genetic counselling and prenatal diagnosis. Now newer technologies are being applied to the investigation of these disorders. These include studies of single nucleotide polymorphisms, microarray analysis and expression profiling, the yeast two-hybrid assay, and proteomics. A great deal of new information is emerging in this way which will hopefully help us to understand the causes of inter-familial and intra-familial variation and particularly pathogenesis, a detailed understanding of which could be the first step in finding effective treatments.

Sarcoglycanopathies: a report of 25 cases

Twenty five patients with sarcoglycanopathies were studied prospectively. 21 of them had mild phenotype. Muscle involvement was more pronounced in adductor and flexor groups of muscles of the limbs, hip adductor muscles being the weakest. The selective and differential weakness between weak hip adductors and stronger hip abductors resulted in the hip abduction sign in 64% of cases. Distal muscle involvement in lower limbs was seen in 92% of cases, but was mild and late in the course of the disease. 44% patients had winging of scapulae. Immunocytochemistry showed multiple sarcoglycan deficiencies in 84% patients. Primary beta and delta sarcoglycanopathy was seen in the remaining 16% cases. Secondary dystrophin reduction was seen in 44% patients and correlated with beta sarcoglycan deficiency but not with functional disability.

Characterization of adiposity and metabolism in Lmna-deficient mice

Dunnigan's Familial Partial Lipodystrophy (FPLD) is an autosomal dominant disease characterized by regional fat loss and insulin resistance. FPLD is caused by mutations in the LMNA gene, which encodes intermediate filaments of the nuclear lamina. Different LMNA mutations cause Emery-Dreifuss muscular dystrophy and/or a dilated cardiomyopathy. It is not known how LMNA mutations cause any of the disease phenotypes. Here we measure physical and metabolic characteristics of Lmna-/- and +/- mice to determine their usefulness as models for FPLD. Lmna-/- mice, which die prematurely of muscular dystrophy, have little fat, but do not show the insulin resistance characteristic of FPLD. Lmna+/- mice, despite treatment with a high fat diet, do not have decreased fat stores or metabolic features of FPLD. We also show, in mice, that Lmna transcripts are expressed at high levels in muscle and adipose tissue, but do not vary by body region or sex. In conclusion, Lmna+/- and -/- mice do not mimic Dunnigan's FPLD, and differential expression of lamins A and C does not appear to contribute to sex- or tissue-specific LMNA phenotypes.

Myopathy with lobulated muscle fibers: evidence for heterogeneous etiology and clinical presentation

The clinico-pathological features of 17 patients displaying a myopathy with lobulated (trabeculated) fibers are reported. All these patients had a limb girdle phenotype and at least 20% of lobulated fibers in their muscle biopsies. There were ten females and seven males. The onset of symptoms ranged from 2 to 55 years (mean 24). The average age at the time of muscle biopsy was 39 (range 3-63). Interestingly, in six patients, high prevalence of lobulated fibers was observed at the second biopsy only, performed on average 11 years after the first or in another muscle. Six patients had a suggestively positive family history. Facial weakness was noted in two patients (genetic study confirmed FSH dystrophy). The course and the severity of weakness varied from one patient to another. Immunohistochemistry and Western blot analyses revealed one Duchenne carrier, one alpha-sarcoglycanopathy, no dysferlinopathy and four calpain deficiencies (including one patient with FSH dystrophy), but SSCP revealed mutation in the calpain gene in only one of the patients. These results show that (1) myopathies with lobulated fibers are clinically and genetically heterogeneous, (2) lack of calpain expression by Western blot analysis is not always associated with null mutation, (3) a molecular diagnosis is made in less than 40% of myopathy with lobulated fibers, (4) when observed, lobulated fibers are most prominent in proximal muscles and require time to appear.

[Recent advances in limb-girdle muscular dystrophy research]

In our laboratory, limb-girdle muscular dystrophy (LGMD) accounted for 20% of all patients with muscular dystrophy. To determine the incidence of various forms of LGMD phenotypes, we looked for mutations in the calpain 3 gene and, for deficiencies in dysferlin and sarcoglycan by immunohistochemical studies with specific antibodies on muscle biopsies from patients with probable autosomal recessive inheritance (LGMD2), which were mostly sporadic cases of LGMD. Fourteen of 276 (5%) patients examined had sarcoglycan complex deficiency (sarcoglycanopathy) and 21 of 80 (26%) had mutations in the calpain 3 gene. Although we have not performed gene analysis in all patients, 10 of 64 (15%) patients examined had no apparent immunoreactivity against the dysferlin antibody. Thus, approximately 46% of LGMD2 patients had the above 3 distinct disorders, but in 54% the causative defects remain unknown.

Role of nitric oxide in the pathogenesis of muscular dystrophies: a "two hit" hypothesis of the cause of muscle necrosis

Although the genetic and biochemical bases of many of the muscular dystrophies have been elucidated, the pathophysiological mechanisms leading to muscle cell death and degeneration remain elusive. Among the most well studied of the dystrophies are those due to defects in proteins that make up the dystrophin-glycoprotein complex (DGC). There has been much interest in the role of nitric oxide (NO(*)) in the pathogenesis of these diseases because the enzyme that synthesizes NO(*), nitric oxide synthase (NOS), is associated with the DGC. Recent studies of dystrophies related to DGC defects suggest that one mechanism of cellular injury is functional ischemia related to alterations in cellular NOS and disruption of a normal protective action of NO(*). This protective action is the prevention of local ischemia during contraction-induced increases in sympathetic vasoconstriction. However, the loss of this protection, alone, does not explain the subsequent muscle cell death and degeneration since mice lacking neuronal NOS (the predominant isoform expressed in muscle) do not develop a muscular dystrophy. Thus, there must be additional biochemical changes conferred upon the cells by these DGC defects, and these changes are discussed in terms of a proposed "two hit" hypothesis of the pathogenetic mechanisms that underlie the muscular dystrophies. According to this hypothesis, pathogenic defects in the DGC have at least two biochemical consequences: a reduction in NO(*)-mediated protection against ischemia, and an increase in cellular susceptibility to metabolic stress. Either one alone may be insufficient to lead to muscle cell death. However, in combination, the biochemical consequences are sufficient to cause muscle degeneration. The role of oxidative stress as a final common pathophysiologic pathway is discussed in terms of data showing that oxidative injury precedes pathologic changes and that muscle cells with defects in the DGC have an increased susceptibility to oxidant challenges. Accordingly, this "two hit" hypothesis may explain many of the complex spatial and temporal variations in disease expression that characterize the muscular dystrophies, such as grouped necrosis, a pre-necrotic phase of the disease, and selective muscle involvement.