SERCA2a gene transfer improves electrocardiographic performance in aged mdx mice

<p>Abstract</p> <p>Background</p> <p>Cardiomyocyte calcium overloading has been implicated in the pathogenesis of Duchenne muscular dystrophy (DMD) heart disease. The cardiac isoform of sarcoplasmic reticulum calcium ATPase (SERCA2a) plays a major role in removing cytosolic calcium during heart muscle relaxation. Here, we tested the hypothesis that SERCA2a over-expression may mitigate electrocardiography (ECG) abnormalities in old female mdx mice, a murine model of DMD cardiomyopathy.</p> <p>Methods</p> <p>1 × 10¹²viral genome particles/mouse of adeno-associated virus serotype-9 (AAV-9) SERCA2a vector was delivered to 12-m-old female mdx mice (N = 5) via a single bolus tail vein injection. AAV transduction and the ECG profile were examined eight months later.</p> <p>Results</p> <p>The vector genome was detected in the hearts of all AAV-injected mdx mice. Immunofluorescence staining and western blot confirmed SERCA2a over-expression in the mdx heart. Untreated mdx mice showed characteristic tachycardia, PR interval reduction and QT interval prolongation. AAV-9 SERCA2a treatment corrected these ECG abnormalities.</p> <p>Conclusions</p> <p>Our results suggest that AAV SERCA2a therapy may hold great promise in treating dystrophin-deficient heart disease.</p

Gene therapy for Duchenne muscular dystrophy heart disease requires treating both heart and skeletal muscle

Abstract only availableDuchenne muscular dystrophy (DMD) is a lethal muscle wasting disease caused by mutations in the dystrophin gene. Affected children are wheelchair bound by the age of ten and die in their mid-twenties from respiratory and/or cardiac failure. Gene therapy represents a promising avenue for curing DMD. While significant progress has been made for treatment of skeletal muscle disease, few studies have investigated the potential of gene therapy to treat heart disease. A cure for DMD requires rescuing both skeletal and heart muscles. Gene therapy aims to deliver a functional copy of the dystrophin gene to affected muscle cells. However, the dystrophin gene is the largest gene in the body and cannot be effectively delivered with any currently available methods. This led researchers to develop abbreviated versions of the dystrophin gene. The most promising of these genes is a 7 kb mini-dystrophin gene which can completely restore skeletal muscle in the mdx mouse model of DMD. The potential of the mini-dystrophin gene for treating heart disease is uncertain. Cardiac specific mini-dystrophin gene expression improved but did not normalize heart function. To investigate whether the incomplete cardiac rescue is due to skeletal muscle disease, we generated double transgenic male mdx mice which expressed the mini-dystrophin gene in both heart and skeletal muscle. We performed comprehensive skeletal and cardiac muscle testing at 6 months of age. Restoration of skeletal muscle function was confirmed by the grip strength assay. Next, we performed an uphill treadmill assay to gauge overall cardiac performance. Double transgenic mice ran significantly farther than cardiac transgenic mice. Finally, we performed electrocardiographic (ECG) analysis to examine the function of the cardiac conduction system. ECG analysis revealed an improved heart rate for double transgenic mice when compared to heart-only transgenic mice. Taken together, these results support a role for skeletal muscle disease in modulating heart function. Furthermore, these findings highlight the importance of tailoring gene therapy approaches to treat both the heart and skeletal muscle.Life Sciences Undergraduate Research Opportunity Progra

An intronic LINE-1 element insertion in the dystrophin gene aborts dystrophin expression and results in Duchenne-like muscular dystrophy in the corgi breed

Duchenne muscular dystrophy (DMD) is a dystrophin-deficient lethal muscle disease. To date, the catastrophic muscle wasting phenotype has only been seen in dystrophin-deficient humans and dogs. While Duchenne-like symptoms have been observed in more than a dozen dog breeds, the mutation is often not known and research colonies are rarely established. Here we report an independent canine DMD model originally derived from the Pembroke Welsh corgi breed. The affected dogs presented clinical signs of muscular dystrophy. Immunostaining revealed the absence of dystrophin and up-regulation of utrophin. Histopathologic examination showed variable fiber size, central nucleation, calcification, fibrosis, neutrophil and macrophage infiltration and cardiac focal vacuolar degeneration. Carrier dogs also displayed mild myopathy. The mutation was identified as a long interspersed repetitive element-1 (LINE-1) insertion in intron 13 which introduced a new exon containing an in-frame stop codon. Similar mutations have been seen in human patients. A colony was generated by crossing carrier females with normal males. Affected puppies had a normal birth weight but they experienced a striking growth delay in the first 5 days. In summary, the new corgi DMD model offers an excellent opportunity to study DMD pathogenesis and to develop novel therapies