Absence of dystrophin alters the passive properties of the extensor digitorum longus muscle in mice

Dystrophin is a cytoskeletal protein not directly participating the myosin-actin contractile apparatus in muscle. The loss of dystrophin leads to Duchenne muscular dystrophy. It is well-established that contractility is reduced in dystrophin-null muscle. Surprisingly, little is known about the influences of dystrophin-deficiency on the passive properties of muscle. We hypothesize that the loss of dystrophin alters the passive properties of the skeletal muscle. To test this hypothesis, we examined the passive properties of the extensor digitorum longus (EDL) muscle from normal BL10 and dystrophin-null mdx mice

In vivo genome editing improves muscle function in a mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating disease affecting about 1 out of 5000 male births and caused by mutations in the dystrophin gene. Genome editing has the potential to restore expression of a modified dystrophin gene from the native locus to modulate disease progression. In this study, adeno-associated virus was used to deliver the CRISPR/Cas9 system to the mdx mouse model of DMD to remove the mutated exon 23 from the dystrophin gene. This includes local and systemic delivery to adult mice and systemic delivery to neonatal mice. Exon 23 deletion by CRISPR/Cas9 resulted in expression of the modified dystrophin gene, partial recovery of functional dystrophin protein in skeletal myofibers and cardiac muscle, improvement of muscle biochemistry, and significant enhancement of muscle force. This work establishes CRISPR/Cas9-based genome editing as a potential therapy to treat DMD

Ectopic Catalase Expression in Mitochondria by Adeno-Associated Virus Enhances Exercise Performance in Mice

Oxidative stress is thought to compromise muscle contractility. However, administration of generic antioxidants has failed to convincingly improve performance during exhaustive exercise. One possible explanation may relate to the inability of the supplemented antioxidants to effectively eliminate excessive free radicals at the site of generation. Here, we tested whether delivering catalase to the mitochondria, a site of free radical production in contracting muscle, could improve treadmill performance in C57Bl/6 mice. Recombinant adeno-associated virus serotype-9 (AV.RSV.MCAT) was generated to express a mitochondria-targeted catalase gene. AV.RSV.MCAT was delivered to newborn C57Bl/6 mouse circulation at the dose of 1012 vector genome particles per mouse. Three months later, we observed a ∼2 to 10-fold increase of catalase protein and activity in skeletal muscle and the heart. Subcellular fractionation western blot and double immunofluorescence staining confirmed ectopic catalase expression in the mitochondria. Compared with untreated control mice, absolute running distance and body weight normalized running distance were significantly improved in AV.RSV.MCAT infected mice during exhaustive treadmill running. Interestingly, ex vivo contractility of the extensor digitorum longus muscle was not altered. Taken together, we have demonstrated that forced catalase expression in the mitochondria enhances exercise performance. Our result provides a framework for further elucidating the underlying mechanism. It also raises the hope of applying similar strategies to remove excessive, pathogenic free radicals in certain muscle diseases (such as Duchenne muscular dystrophy) and ameliorate muscle disease

Gene replacement restores the contractile and passive properties of skeletal muscle in murine models of Duchenne muscular dystrophy

Title from PDF of title page (University of Missouri--Columbia, viewed on March 11, 2013).The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Dissertation advisor: Professor Dongsheng DuanIncludes bibliographical references.Ph. D. University of Missouri-Columbia 2012."December 2012"[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Duchenne muscular dystrophy (DMD) is a lethal disease caused by the loss of the dystrophin protein. Loss of mobility is a key clinical presentation in DMD. It is believed that deterioration in the mechanical properties (contractile and passive properties) of skeletal muscle contribute to reduction in mobility. These two sets of properties are inseparable aspects of muscle function. To improve mobility of patients, both contractile and passive properties must be restored. Gene therapy holds great promise for treating DMD. Restoration of dystrophin expression using gene replacement strategies has improved histopathology and increased muscle force in mouse models of DMD. However, it is not yet known if gene replacement can also ameliorate defects of the passive properties. To address this concern, I performed comprehensive studies that provided new information on the passive properties changes in skeletal muscles of murine models of DMD, and have also offered new insights on how gene replacement may help improve the passive muscle properties in DMD. Furthermore, these studies provided support to further develop mini- and micro-dystrophin gene therapy to improve loss of mobility in DMD patients.Includes bibliographical reference

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

The FVB Background Does Not Dramatically Alter the Dystrophic Phenotype of Mdx Mice

The mdx mouse is the most frequently used animal model for Duchenne muscular dystrophy (DMD), a fatal muscle disease caused by the loss of dystrophin. Mdx mice are naturally occurring dystrophin-null mice on the C57BL/10 (BL10) background. We crossed black mdx to the white FVB background and generated mdx/FVB mice. Compared to that of age- and sex-matched FVB mice, mdx/FVB mice showed characteristic limb muscle pathology similar to that of original mdx mice. Further, the forelimb grip strength and limb muscle (tibialis anterior and extensor digitorum longus) specific force of mdx/FVB mice were significantly lower than that of wild type FVB mice. Consistent with what has been reported in original mdx mice, mdx/FVB mice also showed increased susceptibility to eccentric contraction-induced force loss and elevated serum creatine kinase. Our results suggest that the FVB background does not dramatically alter the dystrophic phenotype of mdx mice