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Differential degradation of [35S]methionine polypeptides in Duchenne muscular dystrophy skin fibroblasts in vitro.

Rates of protein turnover have been measured in three normal and three Duchenne muscular dystrophy (DMD) skin fibroblast cell lines. Cell populations were analyzed at identical states with regard to cell number, state of topoinhibition, and cumulative population doublings (CPD). Net protein synthesis measured by the incorporation of [35S]methionine in an 18-hr pulse was reduced by an average of 34%; degradation of total cellular protein measured after an 18-hr pulse with [35S]methionine and a 24-hr chase was enhanced by an average of 50% in DMD fibroblasts. Two-dimensional gel electrophoresis analyses revealed that the breakdown of the majority of [35S]methionine polypeptides was markedly increased in DMD fibroblasts. Quantitative determinations of the differential degradation rates of 10 selected proteins in the tropomyosin region of two-dimensional gels were undertaken by scintillation counting and computer analyses. In three series of experiments, the degradation of the 10 proteins in DMD fibroblasts was enhanced by individual polypeptides between 12.0% and 151.2% as measured by scintillation counting or between 0.8% and 128% as determined by computer analyses.

Autoradiography↗

A 71-kilodalton protein is a major product of the Duchenne muscular dystrophy gene in brain and other nonmuscle tissues.

The known Duchenne muscular dystrophy (DMD) gene products, the muscle- and brain-type dystrophin isoforms, are 427-kDa proteins translated from 14-kilobase (kb) mRNAs. Recently we described a 6.5-kb mRNA that also is transcribed from the DMD gene. Cloning and in vitro transcription and translation of the entire coding region show that the 6.5-kb mRNA encodes a 70.8-kDa protein that is a major product of the DMD gene. It contains the C-terminal and the cysteine-rich domains of dystrophin, seven additional amino acids at the N terminus, and some modifications formed by alternative splicing in the C-terminal domain. It lacks the entire large domain of spectrin-like repeats and the actin-binding N-terminal domain of dystrophin. This protein is the major DMD gene product in brain and other nonmuscle tissues but is undetectable in skeletal muscle extracts.

Amino Acid Sequence↗

A second promoter provides an alternative target for therapeutic up-regulation of utrophin in Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is an inherited muscle-wasting disease caused by the absence of a muscle cytoskeletal protein, dystrophin. We have previously shown that utrophin, the autosomal homologue of dystrophin, is able to compensate for the absence of dystrophin in a mouse model of DMD; we have therefore undertaken a detailed study of the transcriptional regulation of utrophin to identify means of effecting its up-regulation in DMD muscle. We have previously isolated a promoter element lying within the CpG island at the 5' end of the gene and have shown it to be synaptically regulated in vivo. In this paper, we show that there is an alternative promoter lying within the large second intron of the utrophin gene, 50 kb 3' to exon 2. The promoter is highly regulated and drives transcription of a widely expressed unique first exon that splices into a common full-length mRNA at exon 3. The two utrophin promoters are independently regulated, and we predict that they respond to discrete sets of cellular signals. These findings significantly contribute to understanding the molecular physiology of utrophin expression and are important because the promoter reported here provides an alternative target for transcriptional activation of utrophin in DMD muscle. This promoter does not contain synaptic regulatory elements and might, therefore, be a more suitable target for pharmacological manipulation than the previously described promoter.

Amino Acid Sequence↗

Adult life with Duchenne muscular dystrophy: observations among an emerging and unforeseen patient population.

The knowledge of adult life with Duchenne muscular dystrophy (DMD) is sparse. The purpose of this study was to review existing information and describe body functional, social participatory and quality of life profiles of the ordinary adult Danish DMD patient. Sixty-five study subjects aged 18-42 years were included in a cross-sectional survey based on data from a semi-structured questionnaire comprising 197 items. The ordinary adult DMD patient states his quality of life as excellent; he is worried neither about his disease nor about the future. His assessment of income, hours of personal assistance, housing, years spent in school and ability to participate in desired activities are positive. Despite heavy immobilization, he is still capable of functioning in a variety of activities that are associated with normal life. He lacks qualifying education and he is in painful need of a love life. The frequency of pains is surprisingly high; nearly 40% has pains daily. The nature, magnitude, consequence and possible cure of these reported pains must be scrutinized. Parents and professionals, paediatricians not the least, must anticipate in all measures taken that the DMD boy grows up to manhood and will need competences for adult social life in all respects.

Adolescent↗

UK physicians' attitudes and practices in long-term non-invasive ventilation of Duchenne Muscular Dystrophy.

Previous studies have shown that long-term non-invasive ventilation (NIV) is not always routinely offered by all physicians in Duchenne Muscular Dystrophy (DMD), despite evidence that this treatment improves quality of life and survival. This study examined UK physicians' practices related to respiratory follow-up and DMD ventilation. A mailed questionnaire was used. Thirty-eight of the 59 (64%) UK physicians identified via the Muscular Dystrophy Campaign (MDC) responded. Eighty-one per cent of respondents felt ethically obliged to discuss NIV with families while 13% believed that NIV results in poor quality of life. Forty-seven per cent of physicians discuss in-depth the use of NIV when the patient is in respiratory failure. Eighty-four ventilated DMD patients in the respondents' practice use NIV (via Bi-Pap Nasal mask). Nearly 66% of physicians do not consider the public cost to be an impediment to offering NIV, despite significant problems with resources' allocation in their area. While the majority of UK physicians have comparable attitudes and practices regarding NIV, the questionnaire highlighted that not all specialists were aware of the existence of consensus guidelines regarding respiratory monitoring. In addition, different practices of disclosure of life-prolonging ventilation options were used by different physicians. Seventy-one per cent of physicians wished for national consensus guidelines for different DMD age groups.

Adult↗

The Xq22 inversion breakpoint interrupted a novel Ras-like GTPase gene in a patient with Duchenne muscular dystrophy and profound mental retardation.

A male patient with profound mental retardation, athetosis, nystagmus, and severe congenital hypotonia (Duchenne muscular dystrophy [DMD]) was previously shown to carry a pericentric inversion of the X chromosome, 46,Y,inv(X)(p21.2q22.2). His mother carried this inversion on one X allele. The patient's condition was originally misdiagnosed as cerebral palsy, and only later was it diagnosed as DMD. Because the DMD gene is located at Xp21.2, which is one breakpoint of the inv(X), and because its defects are rarely associated with severe mental retardation, the other clinical features of this patient were deemed likely to be associated with the opposite breakpoint at Xq22. Our precise molecular-cytogenetic characterization of both breakpoints revealed three catastrophic genetic events that had probably influenced neuromuscular and cognitive development: deletion of part of the DMD gene at Xp21.2, duplication of the human proteolipid protein gene (PLP) at Xq22.2, and disruption of a novel gene. The latter sequence, showing a high degree of homology to the Sec4 gene of yeast, encoded a putative small guanine-protein, Ras-like GTPase that we have termed "RLGP." Immunocytochemistry located RLGP at mitochondria. We speculate that disruption of RLGP was responsible for the patient's profound mental retardation.

Adolescent↗

Antisense-induced multiexon skipping for Duchenne muscular dystrophy makes more sense.

Dystrophin deficiency, which leads to severe and progressive muscle degeneration in patients with Duchenne muscular dystrophy (DMD), is caused by frameshifting mutations in the dystrophin gene. A relatively new therapeutic strategy is based on antisense oligonucleotides (AONs) that induce the specific skipping of a single exon, such that the reading frame is restored. This allows the synthesis of a largely functional dystrophin, associated with a milder Becker muscular dystrophy phenotype. We have previously successfully targeted 20 different DMD exons that would, theoretically, be beneficial for >75% of all patients. To further enlarge this proportion, we here studied the feasibility of double and multiexon skipping. Using a combination of AONs, double skipping of exon 43 and 44 was induced, and dystrophin synthesis was restored in myotubes from one patient affected by a nonsense mutation in exon 43. For another patient, with an exon 46-50 deletion, the therapeutic double skipping of exon 45 and 51 was achieved. Remarkably, in control myotubes, the latter combination of AONs caused the skipping of the entire stretch of exons from 45 through 51. This in-frame multiexon skipping would be therapeutic for a series of patients carrying different DMD-causing mutations. In fact, we here demonstrate its feasibility in myotubes from a patient with an exon 48-50 deletion. The application of multiexon skipping may provide a more uniform methodology for a larger group of patients with DMD.

Base Sequence↗

Dystrophin expression in muscle following gene transfer with a fully deleted ("gutted") adenovirus is markedly improved by trans-acting adenoviral gene products.

Helper-dependent adenoviruses (HDAd) are Ad vectors lacking all or most viral genes. They hold great promise for gene therapy of diseases such as Duchenne muscular dystrophy (DMD), because they are less immunogenic than E1/E3-deleted Ad (first-generation Ad or FGAd) and can carry the full-length (Fl) dystrophin (dys) cDNA (12 kb). We have compared the transgene expression of a HDAd (HDAdCMVDysFl) and a FGAd (FGAdCMV-dys) in cell culture (HeLa, C2C12 myotubes) and in the muscle of mdx mice (the mouse model for DMD). Both vectors encoded dystrophin regulated by the same cytomegalovirus (CMV) promoter. We demonstrate that the amount of dystrophin expressed was significantly higher after gene transfer with FGAdCMV-dys compared to HDAdCMVDysFl both in vitro and in vivo. However, gene transfer with HDAdCMVDysFl in the presence of a FGAd resulted in a significant increase of dystrophin expression indicating that gene products synthesized by the FGAd increase, in trans, the amount of dystrophin produced. This enhancement occurred in cell culture and after gene transfer in the muscle of mdx mice and dystrophic golden retriever (GRMD) dogs, another animal model for DMD. The E4 region of Ad is required for the enhancement, because no increase of dystrophin expression from HDAdCMVDysFl was observed in the presence of an E1/E4-deleted Ad in vitro and in vivo. The characterization of these enhancing gene products followed by their inclusion into an HDAd may be required to produce sufficient dystrophin to mitigate the pathology of DMD by HDAd-mediated gene transfer.

Adenoviridae↗

Interleukin 6 induces overexpression of the sarcolemmal utrophin in neonatal mdx skeletal muscle.

Duchenne muscular dystrophy (DMD) is an X-linked lethal disorder caused by a defect in the DMD gene, which encodes the cytoskeletal protein dystrophin. Utrophin is an autosomal homolog of the DMD gene product dystrophin, and augmented expression of endogenous utrophin is expected to provide an alternative therapeutic approach to DMD. We previously reported that an immune response against a beta-galactosidase-expressing adenovirus vector, AxCALacZ, resulted in an accumulation of endogenous utrophin on the extrasynaptic sarcolemma in dystrophin-deficient mdx mice. To determine which cytokine is involved in the regulation of utrophin expression, we directly injected several cytokines separately into neonatal mdx muscles and tested whether the expression of utrophin is increased on the sarcolemma. Importantly, among the cytokines tested, solely interleukin 6 (IL-6) successfully increased expression of utrophin. Moreover, the increase in utrophin mRNA was detected in recombinant IL-6-injected mdx muscles by quantitative real-time reverse transcriptase-polymerase chain reaction. Further, IL-6 expression was elevated in AxCALacZ-infected mdx muscle at an early stage, and anti-IL-6 receptor (IL-6R) antibody treatment blocked enhanced utrophin expression in AxCALacZ-infected mdx muscle. We should point out, however, that overexpression of utrophin due to recombinant IL-6 treatment lasted only 1 week. In addition, expression of utrophin was not evident in normal C57BL/10 neonatal muscles injected with IL-6. Taken together, these results suggest that IL-6 can induce overexpression of utrophin on the extrasynaptic sarcolemma but requires preexisting factors in neonatal mdx muscle to fully regulate utrophin expression.

Adenoviridae↗

Adenovirus-mediated utrophin gene transfer mitigates the dystrophic phenotype of mdx mouse muscles.

Utrophin is a close homolog of dystrophin, the protein whose mutations cause Duchenne muscular dystrophy (DMD). Utrophin is present at low levels in normal and dystrophic muscle, whereas dystrophin is largely absent in DMD. In such cases, the replacement of dystrophin using a utrophin gene transfer strategy could be more advantageous because utrophin would not be a neoantigen. To establish if adenovirus (AV)-mediated utrophin gene transfer is a possible option for the treatment of DMD, an AV vector expressing a shortened version of utrophin (AdCMV-Utr) was constructed. The effect of utrophin overexpression was investigated following intramuscular injection of this AV into mdx mice, the mouse model of DMD. When the tibialis anterior (TA) muscles of 3- to 5-day-old animals were injected with 5 microl of AdCMV-Utr (7.0 x 10(11) virus/ml), an average of 32% of fibers were transduced and the transduction level remained stable for at least 60 days. The presence of utrophin restored the normal histochemical pattern of the dystrophin-associated protein complex at the cell surface and resulted in a reduction in the number of centrally nucleated fibers. The transduced fibers were largely impermeable to the tracer dye Evans blue, suggesting that utrophin protects the surface membrane from breakage. In vitro measurements of the force decline in response to high-stress eccentric contractions demonstrated that the muscles overexpressing utrophin were more resistant to mechanical stress-induced injury. Taken together, these data indicate that AV-mediated utrophin gene transfer can correct various aspects of the dystrophic phenotype. However, a progressive reduction in the number of transduced fibers was observed when the TA muscles of 30- to 45-day-old mice were injected with 25 microl of AdCMV-Utr. This reduction coincides with a humoral response to the AV and transgene, which consists of a hybrid mouse-human cDNA.

Adenoviridae↗

Neonatal screening for Duchenne muscular dystrophy: a novel semiquantitative application of the bioluminescence test for creatine kinase in a pilot national program in Cyprus.

The objectives of this study were to evaluate a novel semiquantitative application of the bioluminescence test for screening newborns for Duchenne muscular dystrophy (DMD) and to use this technique in a pilot national program. The study was performed on the island of Cyprus, which provides ideal conditions for maximizing the prevention rate due to the small size of the country, the well-defined population, and the high degree of awareness of the public concerning genetic diseases. Guthrie spots were obtained through the national screening center for phenylketonuria and congenital hypothyroidism. The bioluminescence method for measuring creatine kinase (CK) in dried blood spots was adapted for use in a semiquantitative way. During the first 6 years of the program (1992-1997), we screened 30,014 samples and found 43 with initially high CK values. We were able to obtain repeat specimens in 35 cases. Of the repeat samples, 30 were found to have normal activity, giving a false-positive rate of 0.10%. Five boys had persistent CK elevations and were confirmed to be DMD or Becker (BMD) cases by DNA analysis and/or dystrophin analysis. The semiquantitative application of the bioluminescence assay of CK that we have introduced has proved to be a fast and reliable method for screening large numbers of samples for DMD. It has a low rate of false positives, which compares favorably with that of other DMD screening programs. Although it is early to evaluate its impact fully, the program seems to be bringing about the anticipated benefits to affected families.

Creatine Kinase↗

Improved molecular diagnosis of dystrophin gene mutations using the multiplex ligation-dependent probe amplification method.

Mutation detection in the DMD gene defective in Duchenne (DMD) and Becker muscular dystrophies (BMD) is complicated by the presence of 79 exons. The majority of recognized mutations are, however, copy number changes of individual exons, which traditionally have been identified by three common multiplex polymerase chain reaction (PCR) assays and/or Southern blotting. Here we report the use of the newly developed quantitative assay multiplex ligation-dependent probe amplification (MLPA) to determine the copy number of each of the 79 DMD exons in 182 males and 14 carrier females referred to our diagnostic facility on the clinical suspicion of DMD or BMD. The MLPA method confirmed all previously recognized mutations and identified an additional 28, including four point mutations. Also, the assay reliably identified 7 carrier females, which are usually not easily recognized. In our hands the method is highly reproducible, easy to handle, and has increased our mutation pick-up rate by a total of 33%.

DNA Mutational Analysis↗

Recombinant truncated dystrophin minigenes: construction, expression, and adenoviral delivery.

Duchenne muscular dystrophy (DMD) is a lethal genetic disorder for which there is currently no effective treatment. Although clinical application of adenoviral vector-mediated gene transfer has not been fully developed, it shows promise for the treatment of DMD. One significant problem posed by adenoviral vector-mediated gene transfer for DMD is that currently available adenoviral vectors cannot accommodate the entire 14-kb dystrophin cDNA. To address this problem, we selectively deleted regions of the murine dystrophin cDNA to produce truncated constructs. We created three constructs, each with an in-frame deletion of a segment (3.0, 4.4, and 5.7 kb) of the spectrin-like repeat region of dystrophin. As an additional modification, we removed the majority of the 3' untranslated region of the cDNA in expression vectors encoding some of these truncated constructs. Comparative quantitative expression studies after transfection into COS and C2C12 mouse muscle cells demonstrate variations in the level of expression with different deletions in the spectrin-like repeat region. Furthermore, deletion of the 3' untranslated region was tested for one recombinant construct and resulted in a reduction in the level of expression in both cell culture systems. Toward the ultimate goal of gene transfer therapy for DMD, we created an adenoviral vector from one of our truncated constructs. Using this vector, we demonstrated truncated dystrophin expression in vitro in primary mdx (dystrophin-deficient) muscle cells and in vivo in mdx mouse muscle. In vivo, recombinant dystrophin was properly localized to the muscle membrane.

Adenoviridae↗

Perspective on Adeno-Associated Virus Capsid Modification for Duchenne Muscular Dystrophy Gene Therapy.

Duchenne muscular dystrophy (DMD) is a X-linked, progressive childhood myopathy caused by mutations in the dystrophin gene, one of the largest genes in the genome. It is characterized by skeletal and cardiac muscle degeneration and dysfunction leading to cardiac and/or respiratory failure. Adeno-associated virus (AAV) is a highly promising gene therapy vector. AAV gene therapy has resulted in unprecedented clinical success for treating several inherited diseases. However, AAV gene therapy for DMD remains a significant challenge. Hurdles for AAV-mediated DMD gene therapy include the difficulty to package the full-length dystrophin coding sequence in an AAV vector, the necessity for whole-body gene delivery, the immune response to dystrophin and AAV capsid, and the species-specific barriers to translate from animal models to human patients. Capsid engineering aims at improving viral vector properties by rational design and/or forced evolution. In this review, we discuss how to use the state-of-the-art AAV capsid engineering technologies to overcome hurdles in AAV-based DMD gene therapy.

Animals↗

Oral glutamine and amino acid supplementation inhibit whole-body protein degradation in children with Duchenne muscular dystrophy.

BACKGROUND: Glutamine has been shown to acutely decrease whole-body protein degradation in Duchenne muscular dystrophy (DMD). OBJECTIVE: To improve nutritional support in DMD, we tested whether oral supplementation with glutamine for 10 d decreased whole-body protein degradation significantly more than did an isonitrogenous amino acid control mixture. DESIGN: Twenty-six boys with DMD were included in this randomized, double-blind parallel study; they received an oral supplement of either glutamine (0.5 g . kg(-1) . d(-1)) or an isonitrogenous, nonspecific amino acid mixture (0.8 g . kg(-1) . d(-1)) for 10 d. The subjects in each group were not clinically different at entry. Leucine and glutamine metabolisms were estimated in the postabsorptive state by using a primed continuous intravenous infusion of [1-(13)C]leucine and [2-(15)N]glutamine before and 10 d after supplementation. RESULTS: A significant effect of time was observed on estimates of whole-body protein degradation. A significant (P < 0.05) decrease in the rate of leucine appearance (an index of whole-body protein degradation) was observed after both glutamine and isonitrogenous amino acid supplementation [x +/-SEM: 136 +/- 9 to 124 +/- 6 micromol . kg fat-free mass (FFM)(-1) . h(-1) for glutamine and 136 +/- 6 to 131 +/- 8 micromol . kg FFM(-1) . h(-1) for amino acids]. A significant (P < 0.05) decrease in endogenous glutamine due to protein breakdown was also observed (91 +/- 6 to 83 +/- 4 micromol . kg FFM(-1) . h(-1) for glutamine and 91 +/- 4 to 88 +/- 5 micromol . kg FFM(-1) . h(-1) for amino acids). The decrease in the estimates of whole-body protein degradation did not differ significantly between the 2 supplemental groups. CONCLUSION: Oral glutamine or amino acid supplementation over 10 d equally inhibits whole-body protein degradation in DMD.

Administration, Oral↗

Clinical concepts of Duchenne muscular dystrophy. The impact of molecular genetics.

Molecular genetics has transformed clinical concepts of Duchenne muscular dystrophy (DMD) in several different ways. (1) The disease can now be defined as a myopathy due to mutation at Xp21, a specific locus on the short arm of the X chromosome. (2) As a consequence of that discovery, any myopathy due to mutation at Xp21 should be a variant of DMD and should affect the same gene product. Moreover, any myopathy due to mutation at a location other than Xp21 should affect some other gene product. (3) For these reasons, DNA analysis is now needed for clinical diagnosis of muscle disease. (4) Xp21 myopathies may be mild or severe, may occur in females even though X-linked, and may be manifest only by high serum levels of creatine kinase. (5) Mental retardation is not consistently related to diseases that are encoded at Xp21. The association of mental retardation with DMD may be due to mutation in a separate gene near that for DMD. Concepts may soon be altered again as we learn about the affected gene product (dystrophin) and its role in these diseases.

Adult↗

Cytotoxic mechanisms in inflammatory myopathies. Co-expression of Fas and protective Bcl-2 in muscle fibres and inflammatory cells.

Expression of the Fas 'death receptor', Fas (CD95/APO-1) renders cells susceptible to programmed cell death ('apoptosis'), whereas Bcl-2 protects cells from apoptosis. Using fluorescence immunohistochemistry, we analysed Fas and Bcl-2 expression in muscle from five patients with polymyositis (PM), four patients with inclusion body myositis (IBM), three patients with dermatomyositis (DM), three patients with Duchenne muscular dystrophy (DMD) and three nonmyopathic controls. Fas (CD95) and Bcl-2 were not detected in control muscle, but expressed in muscle fibres and inflammatory cells in PM, IBM, DM and DMD. The proportion of Fas+ muscle fibres ranged from < 1 to 50%, and was higher in PM and IBM than in DM and DMD. On average, the Fas+ muscle fibres were smaller (median diameter, 10 microns; range, 7-32 microns) than the Fas- fibres (median, 36 microns; range, 10-60 microns). Less than 10% of the Fas+ muscle fibres co-expressed the regeneration marker CD56 (neural cell adhesion molecule N-CAM). In PM and IBM, the proportion of Fas+ muscle fibres was higher among fibres invaded or contacted by T cells than among fibres not contacted by T cells (P < 0.01). The proportion of Fas+ fibres co-expressing Bcl-2 was 76 +/- 16% in PM, 100% in IBM and 63 +/- 23% in DM. Fas and Bcl-2 expression was also noted in inflammatory cells in PM, IBM, DM and DMD. Using the terminal deoxytransferase-catalysed DNA nick end labelling technique for detection of nuclear DNA fragmentation, none of myonuclei, and < 0.1% of inflammatory cell nuclei, showed signs of apoptosis. Our results suggest that, although Fas expression confers susceptibility to Fas-mediated apoptosis, Fas-expressing muscle fibres and inflammatory cells are protected by the anti-apoptotic protein Bcl-2.

Adolescent↗

A method for fate mapping the foci of lethal and behavioral mutants in Drosophila melanogaster.

A new method of mosaic fate mapping, called focusing, is introduced. Its advantages are that it allows a mapping, on the blastoderm surface, of the site of action of functions defined by either pre-adult lethal or behavioral mutations. Moreover, it does not require that the mosaics used be 50% of one genotype and 50% of the other. Methods for quantitative evaluation of the results of focusing, and a comparison of this method with others, are discussed.--Focusing is applied to the analysis of a new mutant, doomed (symbol: dmd), a distally located X-linked recessive in D. melanogaster, that causes the deaths of males and females around the time of eclosion. The dmd phenotype among eclosing flies is first seen as the loss of thoracic motor coordination and as ether sensitivity. Fate mapping by the method of focusing places the site of action of the dmd+ function in the same region of the map as that of the thoracic neural ganglia primordia, but not that of muscle, suggesting the possibility that the effect of dmd is on a thoracic neural function rather than a muscular one.

Animals↗