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      A novel high-throughput immunofluorescence analysis method for quantifying dystrophin intensity in entire transverse sections of Duchenne muscular dystrophy muscle biopsy samples

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          Abstract

          Clinical trials using strategies aimed at inducing dystrophin expression in Duchenne muscular dystrophy (DMD) are underway or at advanced planning stage, including splice switching antisense oligonucleotides (AON), drugs to induce read-through of nonsense mutations and viral mediated gene therapy. In all these strategies, different dystrophin proteins, often internally deleted, are produced, similar to those found in patients with the milder DMD allelic variant, Becker muscular dystrophy (BMD). The primary biological endpoint of these trials is to induce functional dystrophin expression. A reliable and reproducible method for quantification of dystrophin protein expression at the sarcolemma is crucial to monitor the biochemical outcome of such treatments. We developed a new high throughput semi quantitative fluorescent immunofluorescence method for quantifying dystrophin expression in transverse sections of skeletal muscle. This technique is completely operator independent as it based on an automated scanning system and an image processing script developed with Definiens software. We applied this new acquisition-analysis method to quantify dystrophin and sarcolemma-related proteins using paediatric control muscles from cases without a neuromuscular disorder as well as DMD and BMD samples. The image analysis script was instructed to recognize myofibres immunostained for spectrin or laminin while dystrophin was quantified in each identified myofibre (from 2,000 to over 20,000 fibres, depending on the size of the biopsy). We were able to simultaneously extrapolate relevant parameters such as mean sarcolemmal dystrophin, mean spectrin and laminin intensity, fibre area and diameter. In this way we assessed dystrophin production in each muscle fibre in samples of DMD, BMD and controls. This new method allows the unbiased quantification of dystrophin in every myofibre within a transverse muscle section and will be of help for translational research projects as a biological outcome in clinical trials in DMD and BMD.

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          Dystrophin protects the sarcolemma from stresses developed during muscle contraction.

          The protein dystrophin, normally found on the cytoplasmic surface of skeletal muscle cell membranes, is absent in patients with Duchenne muscular dystrophy as well as mdx (X-linked muscular dystrophy) mice. Although its primary structure has been determined, the precise functional role of dystrophin remains the subject of speculation. In the present study, we demonstrate that dystrophin-deficient muscle fibers of the mdx mouse exhibit an increased susceptibility to contraction-induced sarcolemmal rupture. The level of sarcolemmal damage is directly correlated with the magnitude of mechanical stress placed upon the membrane during contraction rather than the number of activations of the muscle. These findings strongly support the proposition that the primary function of dystrophin is to provide mechanical reinforcement to the sarcolemma and thereby protect it from the membrane stresses developed during muscle contraction. Furthermore, the methodology used in this study should prove useful in assessing the efficacy of dystrophin gene therapy in the mdx mouse.
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            Therapy for Duchenne muscular dystrophy: renewed optimism from genetic approaches.

            Duchenne muscular dystrophy (DMD) is a devastating progressive disease for which there is currently no effective treatment except palliative therapy. There are several promising genetic approaches, including viral delivery of the missing dystrophin gene, read-through of translation stop codons, exon skipping to restore the reading frame and increased expression of the compensatory utrophin gene. The lessons learned from these approaches will be applicable to many other disorders.
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              How much dystrophin is enough: the physiological consequences of different levels of dystrophin in the mdx mouse.

              Splice modulation therapy has shown great clinical promise in Duchenne muscular dystrophy, resulting in the production of dystrophin protein. Despite this, the relationship between restoring dystrophin to established dystrophic muscle and its ability to induce clinically relevant changes in muscle function is poorly understood. In order to robustly evaluate functional improvement, we used in situ protocols in the mdx mouse to measure muscle strength and resistance to eccentric contraction-induced damage. Here, we modelled the treatment of muscle with pre-existing dystrophic pathology using antisense oligonucleotides conjugated to a cell-penetrating peptide. We reveal that 15% homogeneous dystrophin expression is sufficient to protect against eccentric contraction-induced injury. In addition, we demonstrate a >40% increase in specific isometric force following repeated administrations. Strikingly, we show that changes in muscle strength are proportional to dystrophin expression levels. These data define the dystrophin restoration levels required to slow down or prevent disease progression and improve overall muscle function once a dystrophic environment has been established in the mdx mouse model.
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Project administrationRole: ValidationRole: Writing – original draft
                Role: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: SoftwareRole: ValidationRole: Writing – review & editing
                Role: ConceptualizationRole: Formal analysisRole: ValidationRole: Writing – original draft
                Role: InvestigationRole: MethodologyRole: Writing – review & editing
                Role: InvestigationRole: MethodologyRole: Writing – review & editing
                Role: MethodologyRole: Writing – review & editing
                Role: ConceptualizationRole: InvestigationRole: MethodologyRole: SupervisionRole: Writing – review & editing
                Role: ConceptualizationRole: InvestigationRole: MethodologyRole: SupervisionRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: Funding acquisitionRole: InvestigationRole: MethodologyRole: SupervisionRole: ValidationRole: Writing – original draft
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: Funding acquisitionRole: InvestigationRole: MethodologyRole: SupervisionRole: ValidationRole: Writing – original draft
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                26 March 2018
                2018
                : 13
                : 3
                : e0194540
                Affiliations
                [1 ] Dubowitz Neuromuscular Centre, Molecular Neurosciences Section, Developmental Neuroscience Programme, UCL Great Ormond Street Institute of Child Health, London, United Kingdom
                [2 ] Department of Neurodegenerative Diseases, UCL Institute of Neurology, London, United Kingdom
                [3 ] Division of Neuropathology, UCL Institute of Neurology, National Hospital for Neurology and Neurosurgery, UCLH NHS Foundation Trust, London, United Kingdom
                [4 ] Department of Orthopaedics, Great Ormond Street Hospital, London, United Kingdom
                [5 ] The Royal National Orthopaedic Hospital, Stanmore, United Kingdom
                [6 ] Wolfson Centre for Inherited Neuromuscular Diseases, RJAH Orthopaedic Hospital, Oswestry, United Kingdom
                [7 ] NIHR Great Ormond Street Hospital Biomedical Research Centre, London, United Kingdom
                University of Minnesota Medical Center, UNITED STATES
                Author notes

                Competing Interests: VS was partially sponsored by Sarepta Therapeutics. FM has served on scientific advisory boards for Roche; Summit Therapeutics; Italfarmaco; Pfizer and Sarepta Therapeutics. He serves on the editorial board of Neuromuscular Disorders and Neuropediatrics. His institution (UCL) receives research support from the European Union, the Medical Research Council, the Wellcome Trust, the Association Francaise Contre les Myopathies (AFM), the Muscular Dystrophy Campaign, the Great Ormond Street Hospital (GOSH) Biomedical Research Centre, Genethon and National Institutes of Health (NIH). His institutions (UCL and GOSH) receive funding for clinical trials from Prosensa/Biomarin, the British Heat Foundation, Summit Therapeutics, Roche, ISIS, Pfizer, Sarepta and the European Community. CAS serves on the advisor board of Audentes. She serves on the editorial board of Neuromuscular Disorders and Neuropathology Applied Neurobiology. This does not alter the authors’ adherence to PLOS ONE policies on sharing data and materials.

                Author information
                http://orcid.org/0000-0003-2499-9560
                Article
                PONE-D-17-28868
                10.1371/journal.pone.0194540
                5868811
                29579078
                5f3c2d5d-3527-4fff-ab6a-04044c575a20
                © 2018 Sardone et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 3 August 2017
                : 5 March 2018
                Page count
                Figures: 9, Tables: 4, Pages: 21
                Funding
                Funded by: funder-id http://dx.doi.org/10.13039/100011199, FP7 Ideas: European Research Council;
                Award ID: HEALTH-F4-2012-30537
                Award Recipient :
                Funded by: SAREPTA THERAPEUTICS
                Award Recipient :
                This work was funded by a European Union Framework Project 7 grant SKIP-NMD (No. HEALTH-F4-2012-30537) and by Sarepta Therapeutics (both awarded to FM). VS was supported by the EU grant SKIP-NMD (No. HEALTH-F4-2012-30537) and by Sarepta Therapeutics. FM is supported by the National Institute for Health Research Biomedical Research Centre at Great Ormond Street Hospital for Children NHS Foundation Trust and University College London. JEM is supported by Great Ormond Street Hospital Children’s Charity. We gratefully acknowledge the support of the National Institute for Health Research Biomedical Research Centre at Great Ormond Street Hospital for Children NHS Foundation Trust and University College London and for their support of the Centre for Neuromuscular Disease Bank. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. This research was supported by the NIHR Great Ormond Street Hospital Biomedical Research Centre. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health.
                Categories
                Research Article
                Biology and Life Sciences
                Biochemistry
                Proteins
                Cytoskeletal Proteins
                Dystrophin
                Medicine and Health Sciences
                Neurology
                Muscular Dystrophies
                Duchenne Muscular Dystrophy
                Medicine and Health Sciences
                Clinical Genetics
                X-Linked Traits
                Duchenne Muscular Dystrophy
                Biology and Life Sciences
                Genetics
                Heredity
                Genetic Linkage
                Sex Linkage
                X-Linked Traits
                Duchenne Muscular Dystrophy
                Biology and Life Sciences
                Biochemistry
                Proteins
                Cytoskeletal Proteins
                Spectrins
                Medicine and Health Sciences
                Surgical and Invasive Medical Procedures
                Biopsy
                Biology and Life Sciences
                Cell Biology
                Cellular Types
                Animal Cells
                Muscle Cells
                Sarcolemmas
                Biology and Life Sciences
                Anatomy
                Biological Tissue
                Muscle Tissue
                Muscle Cells
                Sarcolemmas
                Medicine and Health Sciences
                Anatomy
                Biological Tissue
                Muscle Tissue
                Muscle Cells
                Sarcolemmas
                Medicine and Health Sciences
                Pediatrics
                Biology and Life Sciences
                Biochemistry
                Proteins
                Muscle Proteins
                Biology and Life Sciences
                Cell Biology
                Cellular Types
                Animal Cells
                Muscle Fibers
                Biology and Life Sciences
                Anatomy
                Musculoskeletal System
                Muscles
                Muscle Fibers
                Medicine and Health Sciences
                Anatomy
                Musculoskeletal System
                Muscles
                Muscle Fibers
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                All relevant data are within the paper.

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