Dystrophin insufficiency causes selective muscle histopathology and loss of dystrophin-glycoprotein complex assembly in pig skeletal muscle

Diversity of mutations in the dystrophin gene and details of muscular lesions in porcine dystrophinopathies

During meat inspections in pigs, dystrophinopathies are among the muscle lesions targeted for disposal. In this study, the authors examined the lesions and the distribution of dystrophin expression in 25 pigs with dystrophinopathy. In addition, complementary deoxyribonucleic acid (cDNA) sequencing and western blotting were performed in 6 of the 25 cases, all of which were characterized by degeneration, necrosis, and fat replacement of muscle fibers. Comparing the results of immunohistochemistry with anti-dystrophin antibodies that recognized at different sites in the protein, the authors noted that the loss of dystrophin expression was most pronounced in the C-terminus-recognizing antibody (19/25 cases). The authors detected 5 missense mutations and 3 types of shortened transcripts generated by the skipping of exons in the cDNA, which were associated with the pathogenesis. One missense mutation had been reported previously, whereas the remaining mutations identified had not been previously documented in pigs. In the cases with shortened transcripts, normal-sized transcripts were detected together with the defective transcripts, suggesting that these mutations were caused by splicing abnormalities. In addition, they were in-frame mutations, all of which have similar pathogeneses of Becker muscular dystrophy in humans. These cases were 6 months of age and exhibited macroscopic discoloration, fatty replacement, and muscle degeneration, suggesting that the effect of these mutations on skeletal muscle was significant.

Dystrophin (DMD) Missense Variant in Cats with Becker-Type Muscular Dystrophy

Muscular dystrophy due to dystrophin deficiency in humans is phenotypically divided into a severe Duchenne and milder Becker type. Dystrophin deficiency has also been described in a few animal species, and few DMD gene variants have been identified in animals. Here, we characterize the clinical, histopathological, and molecular genetic aspects of a family of Maine Coon crossbred cats with clinically mild and slowly progressive muscular dystrophy. Two young adult male littermate cats exhibited abnormal gait and muscular hypertrophy with macroglossia. Serum creatine kinase activities were highly increased. Histopathologically, dystrophic skeletal muscle exhibited marked structural changes including atrophic, hypertrophic, and necrotic muscle fibers. Immunohistochemistry showed irregularly reduced expression of dystrophin but the staining of other muscle proteins such as β- and γ-sarcoglycans as well as desmin was also diminished. Whole genome sequencing of one affected cat and genotyping of the littermate found both to be hemizygous mutant at a single DMD missense variant (c.4186C>T). No other protein-changing variants in candidate genes for muscular dystrophy were detected. In addition, one clinically healthy male littermate was hemizygous wildtype, while the queen and one female littermate were clinically healthy, but heterozygous. The predicted amino acid exchange (p.His1396Tyr) resides in a conserved central rod spectrin domain of dystrophin. Various protein modeling programs did not predict major disruption of the dystrophin protein by this substitution, but the altered charge of the region may still affect protein function. This study represents the first genotype-to-phenotype correlation of Becker-type dystrophin deficiency in companion animals.

A Nonsense Variant in the DMD Gene Causes X-Linked Muscular Dystrophy in the Maine Coon Cat

(1) Feline dystrophin-deficient muscular dystrophy (ddMD) is a fatal disease characterized by progressive weakness and degeneration of skeletal muscles and is caused by variants in the DMD gene. To date, only two feline causal variants have been identified. This study reports two cases of male Maine coon siblings that presented with muscular hypertrophy, growth retardation, weight loss, and vomiting. (2) Both cats were clinically examined and histopathology and immunofluorescent staining of the affected muscle was performed. DMD mRNA was sequenced to identify putative causal variants. (3) Both cats showed a significant increase in serum creatine kinase activity. Electromyography and histopathological examination of the muscle samples revealed abnormalities consistent with a dystrophic phenotype. Immunohistochemical testing revealed the absence of dystrophin, confirming the diagnosis of dystrophin-deficient muscular dystrophy. mRNA sequencing revealed a nonsense variant in exon 11 of the feline DMD gene, NC_058386.1 (XM_045050794.1): c.1180C > T (p.(Arg394*)), which results in the loss of the majority of the dystrophin protein. Perfect X-linked segregation of the variant was established in the pedigree. (4) ddMD was described for the first time in the Maine coon and the c.1180C>T variant was confirmed as the causal variant.

Macroglossia in a pig diagnosed as Becker muscular dystrophy due to dystrophin pseudoexon insertion derived from intron 26

We report a case of Becker muscular dystrophy in a 6-month-old, mixed-breed, castrated male pig detected with macroglossia at a meat inspection center. The pig presented a severely enlarged tongue extending outside its mouth. The tongue was firm and pale with discolored muscles. Histologically, there was severe fibrosis, fatty replacement, and myofiber necrosis, degeneration, and regeneration. Immunofluorescence showed focal and severely weak labeling for dystrophin at the sarcolemma of myocytes in the tongue. Analysis of dystrophin mRNA showed a 62 base pair insertion between exons 26 and 27. The insertion was derived from intron 26. Based on these findings, we diagnosed the case as Becker muscular dystrophy—the first known muscular dystrophy case induced by pseudoexon insertion in animals.

Muscular dystrophy: Experimental animal models and therapeutic approaches (Review)

The muscular dystrophies are a heterogeneous group of genetically inherited diseases characterized by muscle weakness and progressive wasting, which can cause premature death in severe forms. Although >30 years have passed since the identification of the first protein involved in a type of muscular dystrophy, there is no effective treatment for these disabling disorders. In the last decade, several novel therapeutic approaches have been developed and investigated as promising therapeutic approaches aimed to ameliorate the dystrophic phenotype either by restoring dystrophin expression or by compensating for dystrophin deficiency. Concurrently, with the development of therapeutic approaches, in addition to naturally occurring animal models, a wide range of genetically engineered animal models has been generated. The use of animals as models of muscular dystrophies has greatly improved the understanding of the pathogenicity of these diseases and has proven useful in gene therapy studies. In this review, we summarize these latest innovative therapeutic approaches to muscular dystrophies and the usefulness of the various most common experimental animal models.

Investigation of the Efficacy of a Postbiotic Yeast Cell Wall-Based Blend on Newly-Weaned Pigs under a Dietary Challenge of Multiple Mycotoxins with Emphasis on Deoxynivalenol

Pigs are highly susceptible to mycotoxins. This study investigated the effects of a postbiotic yeast cell wall-based blend (PYCW; Nicholasville, KY, USA) on growth and health of newly-weaned pigs under dietary challenge of multiple mycotoxins. Forty-eight newly-weaned pigs (21 d old) were individually allotted to four dietary treatments, based on a three phase-feeding, in a randomized complete block design (sex; initial BW) with two factors for 36 d. Two factors were dietary mycotoxins (deoxynivalenol: 2000 μg/kg supplemented in three phases; and aflatoxin: 200 μg/kg supplemented only in phase 3) and PYCW (0.2%). Growth performance (weekly), blood serum (d 34), and jejunal mucosa immune and oxidative stress markers (d 36) data were analyzed using MIXED procedure of SAS. Mycotoxins reduced (p < 0.05) average daily feed intake (ADFI) and average daily gain (ADG) during the entire period whereas PYCW did not affect growth performance. Mycotoxins reduced (p < 0.05) serum protein, albumin, creatinine, and alanine aminotransferase whereas PYCW decreased (p < 0.05) serum creatine phosphokinase. Neither mycotoxins nor PYCW affected pro-inflammatory cytokines and oxidative damage markers in the jejunal mucosa. No interaction was observed indicating that PYCW improved hepatic enzymes regardless of mycotoxin challenge. In conclusion, deoxynivalenol (2000 μg/kg, for 7 to 25 kg body weight) and aflatoxin B1 (200 μg/kg, for 16 to 25 kg body weight) impaired growth performance and nutrient digestibility of newly-weaned pigs, whereas PYCW could partially improve health of pigs regardless of mycotoxin challenge.

Mouse models of two missense mutations in actin-binding domain 1 of dystrophin associated with Duchenne or Becker muscular dystrophy

Missense mutations in the dystrophin protein can cause Duchenne muscular dystrophy (DMD) or Becker muscular dystrophy (BMD) through an undefined pathomechanism. In vitro studies suggest that missense mutations in the N-terminal actin-binding domain (ABD1) cause protein instability, and cultured myoblast studies reveal decreased expression levels that can be restored to wild-type with proteasome inhibitors. To further elucidate the pathophysiology of missense dystrophin in vivo, we generated two transgenic mdx mouse lines expressing L54R or L172H mutant dystrophin, which correspond to missense mutations identified in human patients with DMD or BMD, respectively. Our biochemical, histologic and physiologic analysis of the L54R and L172H mice show decreased levels of dystrophin which are proportional to the phenotypic severity. Proteasome inhibitors were ineffective in both the L54R and L172H mice, yet mice homozygous for the L172H transgene were able to express even higher levels of dystrophin which caused further improvements in muscle histology and physiology. Given that missense dystrophin is likely being degraded by the proteasome but whole body proteasome inhibition was not possible, we screened for ubiquitin-conjugating enzymes involved in targeting dystrophin to the proteasome. A myoblast cell line expressing L54R mutant dystrophin was screened with an siRNA library targeting E1, E2 and E3 ligases which identified Amn1, FBXO33, Zfand5 and Trim75. Our study establishes new mouse models of dystrophinopathy and identifies candidate E3 ligases that may specifically regulate dystrophin protein turnover in vivo.

Current Translational Research and Murine Models For Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder characterized by progressive muscle degeneration. Mutations in the DMD gene result in the absence of dystrophin, a protein required for muscle strength and stability. Currently, there is no cure for DMD. Since murine models are relatively easy to genetically manipulate, cost effective, and easily reproducible due to their short generation time, they have helped to elucidate the pathobiology of dystrophin deficiency and to assess therapies for treating DMD. Recently, several murine models have been developed by our group and others to be more representative of the human DMD mutation types and phenotypes. For instance, mdx mice on a DBA/2 genetic background, developed by Fukada et al., have lower regenerative capacity and exhibit very severe phenotype. Cmah-deficient mdx mice display an accelerated disease onset and severe cardiac phenotype due to differences in glycosylation between humans and mice. Other novel murine models include mdx52, which harbors a deletion mutation in exon 52, a hot spot region in humans, and dystrophin/utrophin double-deficient (dko), which displays a severe dystrophic phenotype due the absence of utrophin, a dystrophin homolog. This paper reviews the pathological manifestations and recent therapeutic developments in murine models of DMD such as standard mdx (C57BL/10), mdx on C57BL/6 background (C57BL/6-mdx), mdx52, dystrophin/utrophin double-deficient (dko), mdxβgeo, Dmd-null, humanized DMD (hDMD), mdx on DBA/2 background (DBA/2-mdx), Cmah-mdx, and mdx/mTRKO murine models.

Duchenne muscular dystrophy: an updated review of common available therapies

BACKGROUND AND PURPOSE

Duchenne muscular dystrophy (DMD) is a lethal progressive pediatric muscle disorder and genetically inherited as an X-linked disease that caused by mutations in the dystrophin gene. DMD leads to progressive muscle weakness, degeneration, and wasting; finally, follows with the premature demise in affected individuals due to respiratory and/or cardiac failure typically by age of 30. For decades, scientists tried massively to find an effective therapy method, but there is no absolute cure currently for patients with DMD, nevertheless, recent advanced progressions on the treatment of DMD will be hopeful in the future. Several promising gene therapies are currently under investigation. These include gene replacement, exon skipping, suppression of stop codons. More recently, a promising gene editing tool referred to as CRISPR/Cas9 offers exciting perspectives for restoring dystrophin expression in patients with DMD. This review intents to briefly describe these methods and comment on their advances. Since DMD is a genetic disorder, it should be treated by replacing the deficient DMD copy with a functional one. However, there are different types of mutations in this gene, so such therapeutic approaches are highly mutation specific and thus are personalized. Therefore, DMD has arisen as a model of genetic disorder for understanding and overcoming of the challenges of developing personalized genetic medicines, consequently, the lessons learned from these approaches will be applicable to many other disorders.

CONCLUSIONS

This review provides an update on the recent gene therapies for DMD that aim to compensate for dystrophin deficiency and the related clinical trials.

Transcriptome analysis reveals long intergenic non-coding RNAs involved in skeletal muscle growth and development in pig

Long intergenic non-coding RNAs (lincRNAs) play essential roles in numerous biological processes and are widely studied. The skeletal muscle is an important tissue that plays an essential role in individual movement ability. However, lincRNAs in pig skeletal muscles are largely undiscovered and their biological functions remain elusive. In this study, we assembled transcriptomes using RNA-seq data published in previous studies of our laboratory group and identified 323 lincRNAs in porcine leg muscle. We found that these lincRNAs have shorter transcript length, fewer exons and lower expression level than protein-coding genes. Gene ontology and pathway analyses indicated that many potential target genes (PTGs) of lincRNAs were involved in skeletal-muscle-related processes, such as muscle contraction and muscle system process. Combined our previous studies, we found a potential regulatory mechanism in which the promoter methylation of lincRNAs can negatively regulate lincRNA expression and then positively regulate PTG expression, which can finally result in abnormal phenotypes of cloned piglets through a certain unknown pathway. This work detailed a number of lincRNAs and their target genes involved in skeletal muscle growth and development and can facilitate future studies on their roles in skeletal muscle growth and development.

Oral quercetin administration transiently protects respiratory function in dystrophin-deficient mice

KEY POINT

PGC-1α pathway activation has been shown to decrease disease severity and can be driven by quercetin. Oral quercetin supplementation protected respiratory function for 4-6 months during a 12 month dosing regimen. This transient protection was probably due to a failure to sustain elevated SIRT1 activity and downstream PGC-1α signalling. Quercetin supplementation may be a beneficial treatment as part of a cocktail provided continued SIRT1 activity elevation is achieved.

ABSTRACT

Duchenne muscular dystrophy (DMD) impacts 1 : 3500 boys and leads to muscle dysfunction culminating in death due to respiratory or cardiac failure. There is an urgent need for effective therapies with the potential for immediate application for this patient population. Quercetin, a flavonoid with an outstanding safety profile, may provide therapeutic relief to DMD patients as the wait for additional therapies continues. This study evaluated the capacity of orally administered quercetin (0.2%) in 2 month old mdx mice to improve respiratory function and end-point functional and histological outcomes in the diaphragm following 12 months of treatment. Respiratory function was protected for the first 4-6 months of treatment but appeared to become insensitive to quercetin thereafter. Consistent with this, end-point functional measures were decreased and histopathological measures were more severe in dystrophic muscle compared to C57 and similar between control-fed and quercetin-fed mdx mice. To better understand the transient nature of improved respiratory function, we measured PGC-1α pathway activity, which is suggested to be up-regulated by quercetin supplementation. This pathway was largely suppressed in dystrophic muscle compared to healthy muscle, and at the 14 month time point dietary quercetin enrichment did not increase expression of downstream effectors. These data support the efficacy of quercetin as an intervention for DMD in skeletal muscle, and also indicate the development of age-dependent quercetin insensitivity when continued supplementation fails to drive the PGC-1α pathway. Continued study is needed to determine if this is related to disease severity, age or other factors.

Molecular characterization and expression patterns of emerin (EMD) gene in skeletal muscle between Meishan and Large White pigs

The emerin protein is a nuclear membrane protein and has important functions in muscle development, regeneration, and cell signal transduction. However, knowledge regarding emerin in the domestic animal is limited. In this study, we cloned and characterized the pig emerin (EMD) gene. Semi-quantitative RT-PCR analysis revealed that the EMD gene was expressed at the highest level in the heart and fat at 120d. However, the fetal skeletal muscles displayed a greater abundance of EMD mRNA than that in skeletal muscles at postnatal development stages. In addition, the expression level of EMD at 60 day was significantly higher (p<0.05) in Meishan than Large White pigs. Pig EMD protein displayed the sarcolemma and perinuclear distribution in skeletal muscle sections, and there was no distribution change of EMD in skeletal muscle sections between Large White and Meishan pigs. These studies provide useful information for further research on the functions of pig EMD gene in skeletal muscle.

Porcine models of muscular dystrophy

Duchenne muscular dystrophy is a progressive, fatal, X-linked disease caused by a failure to accumulate the cytoskeletal protein dystrophin. This disease has been studied using a variety of animal models including fish, mice, rats, and dogs. While these models have contributed substantially to our mechanistic understanding of the disease and disease progression, limitations inherent to each model have slowed the clinical advancement of therapies, which necessitates the development of novel large-animal models. Several porcine dystrophin-deficient models have been identified, although disease severity may be so severe as to limit their potential contributions to the field. We have recently identified and completed the initial characterization of a natural porcine model of dystrophin insufficiency. Muscles from these animals display characteristic focal necrosis concomitant with decreased abundance and localization of dystrophin-glycoprotein complex components. These pigs recapitulate many of the cardinal features of muscular dystrophy, have elevated serum creatine kinase activity, and preliminarily appear to display altered locomotion. They also suffer from sudden death preceded by EKG abnormalities. Pig dystrophinopathy models could allow refinement of dosing strategies in human-sized animals in preparation for clinical trials. From an animal handling perspective, these pigs can generally be treated normally, with the understanding that acute stress can lead to sudden death. In summary, the ability to create genetically modified pig models and the serendipitous discovery of genetic disease in the swine industry has resulted in the emergence of new animal tools to facilitate the critical objective of improving the quality and length of life for boys afflicted with such a devastating disease.

Current Progress in Therapeutic Gene Editing for Monogenic Diseases

Programmable nucleases allow defined alterations in the genome with ease-of-use, efficiency, and specificity. Their availability has led to accurate and widespread genome engineering, with multiple applications in basic research, biotechnology, and therapy. With regard to human gene therapy, nuclease-based gene editing has facilitated development of a broad range of therapeutic strategies based on both nonhomologous end joining and homology-dependent repair. This review discusses current progress in nuclease-based therapeutic applications for a subset of inherited monogenic diseases including cystic fibrosis, Duchenne muscular dystrophy, diseases of the bone marrow, and hemophilia and highlights associated challenges and future prospects.

Animal models of Duchenne muscular dystrophy: from basic mechanisms to gene therapy

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disorder. It is caused by loss-of-function mutations in the dystrophin gene. Currently, there is no cure. A highly promising therapeutic strategy is to replace or repair the defective dystrophin gene by gene therapy. Numerous animal models of DMD have been developed over the last 30 years, ranging from invertebrate to large mammalian models. mdx mice are the most commonly employed models in DMD research and have been used to lay the groundwork for DMD gene therapy. After ~30 years of development, the field has reached the stage at which the results in mdx mice can be validated and scaled-up in symptomatic large animals. The canine DMD (cDMD) model will be excellent for these studies. In this article, we review the animal models for DMD, the pros and cons of each model system, and the history and progress of preclinical DMD gene therapy research in the animal models. We also discuss the current and emerging challenges in this field and ways to address these challenges using animal models, in particular cDMD dogs.

Dystrophin-deficient large animal models: translational research and exon skipping

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder caused by mutations in the dystrophin gene. Affecting approximately 1 in 3,600-9337 boys, DMD patients exhibit progressive muscle degeneration leading to fatality as a result of heart or respiratory failure. Despite the severity and prevalence of the disease, there is no cure available. While murine models have been successfully used in illustrating the mechanisms of DMD, their utility in DMD research is limited due to their mild disease phenotypes such as lack of severe skeletal muscle and cardiac symptoms. To address the discrepancy between the severity of disease displayed by murine models and human DMD patients, dystrophin-deficient dog models with a splice site mutation in intron 6 were established. Examples of these are Golden Retriever muscular dystrophy and beagle-based Canine X-linked muscular dystrophy. These large animal models are widely employed in therapeutic DMD research due to their close resemblance to the severity of human patient symptoms. Recently, genetically tailored porcine models of DMD with deleted exon 52 were developed by our group and others, and can potentially act as a new large animal model. While therapeutic outcomes derived from these large animal models can be more reliably extrapolated to DMD patients, a comprehensive understanding of these models is still needed. This paper will discuss recent progress and future directions of DMD studies with large animal models such as canine and porcine models.

Pharmacologic management of Duchenne muscular dystrophy: target identification and preclinical trials

Duchenne muscular dystrophy (DMD) is an X-linked human disorder in which absence of the protein dystrophin causes degeneration of skeletal and cardiac muscle. For the sake of treatment development, over and above definitive genetic and cell-based therapies, there is considerable interest in drugs that target downstream disease mechanisms. Drug candidates have typically been chosen based on the nature of pathologic lesions and presumed underlying mechanisms and then tested in animal models. Mammalian dystrophinopathies have been characterized in mice (mdx mouse) and dogs (golden retriever muscular dystrophy [GRMD]). Despite promising results in the mdx mouse, some therapies have not shown efficacy in DMD. Although the GRMD model offers a higher hurdle for translation, dogs have primarily been used to test genetic and cellular therapies where there is greater risk. Failed translation of animal studies to DMD raises questions about the propriety of methods and models used to identify drug targets and test efficacy of pharmacologic intervention. The mdx mouse and GRMD dog are genetically homologous to DMD but not necessarily analogous. Subcellular species differences are undoubtedly magnified at the whole-body level in clinical trials. This problem is compounded by disparate cultures in clinical trials and preclinical studies, pointing to a need for greater rigor and transparency in animal experiments. Molecular assays such as mRNA arrays and genome-wide association studies allow identification of genetic drug targets more closely tied to disease pathogenesis. Genes in which polymorphisms have been directly linked to DMD disease progression, as with osteopontin, are particularly attractive targets.

Inhibition of autoimmune Chagas-like heart disease by bone marrow transplantation

BACKGROUND

Infection with the protozoan Trypanosoma cruzi manifests in mammals as Chagas heart disease. The treatment available for chagasic cardiomyopathy is unsatisfactory.

METHODS/PRINCIPAL FINDINGS

To study the disease pathology and its inhibition, we employed a syngeneic chicken model refractory to T. cruzi in which chickens hatched from T. cruzi inoculated eggs retained parasite kDNA (1.4 kb) minicircles. Southern blotting with EcoRI genomic DNA digests revealed main 18 and 20 kb bands by hybridization with a radiolabeled minicircle sequence. Breeding these chickens generated kDNA-mutated F1, F2, and F3 progeny. A targeted-primer TAIL-PCR (tpTAIL-PCR) technique was employed to detect the kDNA integrations. Histocompatible reporter heart grafts were used to detect ongoing inflammatory cardiomyopathy in kDNA-mutated chickens. Fluorochromes were used to label bone marrow CD3+, CD28+, and CD45+ precursors of the thymus-dependent CD8α+ and CD8β+ effector cells that expressed TCRγδ, vβ1 and vβ2 receptors, which infiltrated the adult hearts and the reporter heart grafts.

CONCLUSIONS/SIGNIFICANCE

Genome modifications in kDNA-mutated chickens can be associated with disruption of immune tolerance to compatible heart grafts and with rejection of the adult host's heart and reporter graft, as well as tissue destruction by effector lymphocytes. Autoimmune heart rejection was largely observed in chickens with kDNA mutations in retrotransposons and in coding genes with roles in cell structure, metabolism, growth, and differentiation. Moreover, killing the sick kDNA-mutated bone marrow cells with cytostatic and anti-folate drugs and transplanting healthy marrow cells inhibited heart rejection. We report here for the first time that healthy bone marrow cells inhibited heart pathology in kDNA+ chickens and thus prevented the genetically driven clinical manifestations of the disease.

Characterization of dystrophin deficient rats: a new model for Duchenne muscular dystrophy

A few animal models of Duchenne muscular dystrophy (DMD) are available, large ones such as pigs or dogs being expensive and difficult to handle. Mdx (X-linked muscular dystrophy) mice only partially mimic the human disease, with limited chronic muscular lesions and muscle weakness. Their small size also imposes limitations on analyses. A rat model could represent a useful alternative since rats are small animals but 10 times bigger than mice and could better reflect the lesions and functional abnormalities observed in DMD patients. Two lines of Dmd mutated-rats (Dmdmdx) were generated using TALENs targeting exon 23. Muscles of animals of both lines showed undetectable levels of dystrophin by western blot and less than 5% of dystrophin positive fibers by immunohistochemistry. At 3 months, limb and diaphragm muscles from Dmdmdx rats displayed severe necrosis and regeneration. At 7 months, these muscles also showed severe fibrosis and some adipose tissue infiltration. Dmdmdx rats showed significant reduction in muscle strength and a decrease in spontaneous motor activity. Furthermore, heart morphology was indicative of dilated cardiomyopathy associated histologically with necrotic and fibrotic changes. Echocardiography showed significant concentric remodeling and alteration of diastolic function. In conclusion, Dmdmdx rats represent a new faithful small animal model of DMD.

A sensitive, reproducible and objective immunofluorescence analysis method of dystrophin in individual fibers in samples from patients with duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is characterized by the absence or reduced levels of dystrophin expression on the inner surface of the sarcolemmal membrane of muscle fibers. Clinical development of therapeutic approaches aiming to increase dystrophin levels requires sensitive and reproducible measurement of differences in dystrophin expression in muscle biopsies of treated patients with DMD. This, however, poses a technical challenge due to intra- and inter-donor variance in the occurrence of revertant fibers and low trace dystrophin expression throughout the biopsies. We have developed an immunofluorescence and semi-automated image analysis method that measures the sarcolemmal dystrophin intensity per individual fiber for the entire fiber population in a muscle biopsy. Cross-sections of muscle co-stained for dystrophin and spectrin have been imaged by confocal microscopy, and image analysis was performed using Definiens software. Dystrophin intensity has been measured in the sarcolemmal mask of spectrin for each individual muscle fiber and multiple membrane intensity parameters (mean, maximum, quantiles per fiber) were calculated. A histogram can depict the distribution of dystrophin intensities for the fiber population in the biopsy. This method was tested by measuring dystrophin in DMD, Becker muscular dystrophy, and healthy muscle samples. Analysis of duplicate or quadruplicate sections of DMD biopsies on the same or multiple days, by different operators, or using different antibodies, was shown to be objective and reproducible (inter-assay precision, CV 2-17% and intra-assay precision, CV 2-10%). Moreover, the method was sufficiently sensitive to detect consistently small differences in dystrophin between two biopsies from a patient with DMD before and after treatment with an investigational compound.

Development of rabbit monoclonal antibodies for detection of alpha-dystroglycan in normal and dystrophic tissue

Alpha-dystroglycan requires a rare O-mannose glycan modification to form its binding epitope for extracellular matrix proteins such as laminin. This functional glycan is disrupted in a cohort of muscular dystrophies, the secondary dystroglycanopathies, and is abnormal in some metastatic cancers. The most commonly used reagent for detection of alpha-dystroglycan is mouse monoclonal antibody IIH6, but it requires the functional O-mannose structure for recognition. Therefore, the ability to detect alpha-dystroglycan protein in disease states where it lacks the full O-mannose glycan has been limited. To overcome this hurdle, rabbit monoclonal antibodies against the alpha-dystroglycan C-terminus were generated. The new antibodies, named 5–2, 29–5, and 45–3, detect alpha-dystroglycan from mouse, rat and pig skeletal muscle by Western blot and immunofluorescence. In a mouse model of fukutin-deficient dystroglycanopathy, all antibodies detected low molecular weight alpha-dystroglycan in disease samples demonstrating a loss of functional glycosylation. Alternately, in a porcine model of Becker muscular dystrophy, relative abundance of alpha-dystroglycan was decreased, consistent with a reduction in expression of the dystrophin-glycoprotein complex in affected muscle. Therefore, these new rabbit monoclonal antibodies are suitable reagents for alpha-dystroglycan core protein detection and will enhance dystroglycan-related studies.